High-Brightness Blue Light-Emitting Diodes Enabled by a Directly Grown Graphene Buffer Layer.

PubMed

Chen, Zhaolong; Zhang, Xiang; Dou, Zhipeng; Wei, Tongbo; Liu, Zhiqiang; Qi, Yue; Ci, Haina; Wang, Yunyu; Li, Yang; Chang, Hongliang; Yan, Jianchang; Yang, Shenyuan; Zhang, Yanfeng; Wang, Junxi; Gao, Peng; Li, Jinmin; Liu, Zhongfan

2018-06-08

Single-crystalline GaN-based light-emitting diodes (LEDs) with high efficiency and long lifetime are the most promising solid-state lighting source compared with conventional incandescent and fluorescent lamps. However, the lattice and thermal mismatch between GaN and sapphire substrate always induces high stress and high density of dislocations and thus degrades the performance of LEDs. Here, the growth of high-quality GaN with low stress and a low density of dislocations on graphene (Gr) buffered sapphire substrate is reported for high-brightness blue LEDs. Gr films are directly grown on sapphire substrate to avoid the tedious transfer process and GaN is grown by metal-organic chemical vapor deposition (MOCVD). The introduced Gr buffer layer greatly releases biaxial stress and reduces the density of dislocations in GaN film and In x Ga 1- x N/GaN multiple quantum well structures. The as-fabricated LED devices therefore deliver much higher light output power compared to that on a bare sapphire substrate, which even outperforms the mature process derived counterpart. The GaN growth on Gr buffered sapphire only requires one-step growth, which largely shortens the MOCVD growth time. This facile strategy may pave a new way for applications of Gr films and bring several disruptive technologies for epitaxial growth of GaN film and its applications in high-brightness LEDs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer

PubMed Central

Muhammed, M. M.; Roldan, M. A.; Yamashita, Y.; Sahonta, S.-L.; Ajia, I. A.; Iizuka, K.; Kuramata, A.; Humphreys, C. J.; Roqan, I. S.

2016-01-01

We demonstrate the high structural and optical properties of InxGa1−xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 107 cm−2) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1−xN epilayers can be achieved with high optical quality of InxGa1−xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design. PMID:27412372

High-quality III-nitride films on conductive, transparent (2̅01)-oriented β-Ga2O3 using a GaN buffer layer.

PubMed

Muhammed, M M; Roldan, M A; Yamashita, Y; Sahonta, S-L; Ajia, I A; Iizuka, K; Kuramata, A; Humphreys, C J; Roqan, I S

2016-07-14

We demonstrate the high structural and optical properties of InxGa1-xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 10(7) cm(-2)) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1-xN epilayers can be achieved with high optical quality of InxGa1-xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design.

Effect of ZnO seed layer on the morphology and optical properties of ZnO nanorods grown on GaN buffer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nandi, R., E-mail: rajunandi@iitb.ac.in; Mohan, S., E-mail: rajunandi@iitb.ac.in; Major, S. S.

2014-04-24

ZnO nanorods were grown by chemical bath deposition on sputtered, polycrystalline GaN buffer layers with and without ZnO seed layer. Scanning electron microscopy and X-ray diffraction show that the ZnO nanorods on GaN buffer layers are not vertically well aligned. Photoluminescence spectrum of ZnO nanorods grown on GaN buffer layer, however exhibits a much stronger near-band-edge emission and negligible defect emission, compared to the nanorods grown on ZnO buffer layer. These features are attributed to gallium incorporation at the ZnO-GaN interface. The introduction of a thin (25 nm) ZnO seed layer on GaN buffer layer significantly improves the morphology andmore » vertical alignment of ZnO-NRs without sacrificing the high optical quality of ZnO nanorods on GaN buffer layer. The presence of a thick (200 nm) ZnO seed layer completely masks the effect of the underlying GaN buffer layer on the morphology and optical properties of nanorods.« less

Selectively Enhanced UV-A Photoresponsivity of a GaN MSM UV Photodetector with a Step-Graded AlxGa1-xN Buffer Layer.

PubMed

Lee, Chang-Ju; Won, Chul-Ho; Lee, Jung-Hee; Hahm, Sung-Ho; Park, Hongsik

2017-07-21

The UV-to-visible rejection ratio is one of the important figure of merits of GaN-based UV photodetectors. For cost-effectiveness and large-scale fabrication of GaN devices, we tried to grow a GaN epitaxial layer on silicon substrate with complicated buffer layers for a stress-release. It is known that the structure of the buffer layers affects the performance of devices fabricated on the GaN epitaxial layers. In this study, we show that the design of a buffer layer structure can make effect on the UV-to-visible rejection ratio of GaN UV photodetectors. The GaN photodetector fabricated on GaN-on-silicon substrate with a step-graded Al x Ga -x N buffer layer has a highly-selective photoresponse at 365-nm wavelength. The UV-to-visible rejection ratio of the GaN UV photodetector with the step-graded Al x Ga 1-x N buffer layer was an order-of-magnitude higher than that of a photodetector with a conventional GaN/AlN multi buffer layer. The maximum photoresponsivity was as high as 5 × 10 - ² A/W. This result implies that the design of buffer layer is important for photoresponse characteristics of GaN UV photodetectors as well as the crystal quality of the GaN epitaxial layers.

Non-polar a-plane ZnO films grown on r-Al2O3 substrates using GaN buffer layers

NASA Astrophysics Data System (ADS)

Xu, C. X.; Chen, W.; Pan, X. H.; Chen, S. S.; Ye, Z. Z.; Huang, J. Y.

2016-09-01

In this work, GaN buffer layer has been used to grow non-polar a-plane ZnO films by laser-assisted and plasma-assisted molecular beam epitaxy. The thickness of GaN buffer layer ranges from ∼3 to 12 nm. The GaN buffer thickness effect on the properties of a-plane ZnO thin films is carefully investigated. The results show that the surface morphology, crystal quality and optical properties of a-plane ZnO films are strongly correlated with the thickness of GaN buffer layer. It was found that with 6 nm GaN buffer layer, a-plane ZnO films display the best crystal quality with X-ray diffraction rocking curve full-width at half-maximum of only 161 arcsec for the (101) reflection.

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate

PubMed Central

2013-01-01

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques. PMID:23448090

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate.

PubMed

Wei, Xianqi; Zhao, Ranran; Shao, Minghui; Xu, Xijin; Huang, Jinzhao

2013-02-28

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zni and Vo is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques.

Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

PubMed

Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

2016-06-08

The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.

Selective-area catalyst-free MBE growth of GaN nanowires using a patterned oxide layer.

PubMed

Schumann, T; Gotschke, T; Limbach, F; Stoica, T; Calarco, R

2011-03-04

GaN nanowires (NWs) were grown selectively in holes of a patterned silicon oxide mask, by rf-plasma-assisted molecular beam epitaxy (PAMBE), without any metal catalyst. The oxide was deposited on a thin AlN buffer layer previously grown on a Si(111) substrate. Regular arrays of holes in the oxide layer were obtained using standard e-beam lithography. The selectivity of growth has been studied varying the substrate temperature, gallium beam equivalent pressure and patterning layout. Adjusting the growth parameters, GaN NWs can be selectively grown in the holes of the patterned oxide with complete suppression of the parasitic growth in between the holes. The occupation probability of a hole with a single or multiple NWs depends strongly on its diameter. The selectively grown GaN NWs have one common crystallographic orientation with respect to the Si(111) substrate via the AlN buffer layer, as proven by x-ray diffraction (XRD) measurements. Based on the experimental data, we present a schematic model of the GaN NW formation in which a GaN pedestal is initially grown in the hole.

MOCVD growth and study of thin films of indium nitride

NASA Astrophysics Data System (ADS)

Jain, Abhishek

This thesis is focused on a study of MOCVD growth of InN with the goal of providing new information on the effects of growth conditions and buffer/substrate materials on InN film properties. Initial studies, using both (111) Si and (0001) sapphire substrates, identified an optimum growth temperature window of 540--560°C for the formation of stable InN films. When attempting to grow InN films on sapphire with thicknesses greater than approximately 150 nanometers using an AlN buffer layer, the InN films were observed to delaminate from the buffer/substrate at growth temperature. The combined effect of compressive stress due to high lattice mismatch between InN and AlN (˜14%) and tensile stress due to grain coalescence along with the relatively weak bond strength of InN compared to GaN and AlN, is believed to cause the InN film to crack along the interface and delaminate. To further investigate the effect of the buffer layer on InN growth, studies were carried out using GaN films grown on sapphire as the growth template. Recent MBE results had indicated a significant difference in the thermal stability and growth mode of In-polar and N-polar InN, with improved properties reported for N-polar material grown on N-polar GaN. MOCVD growth of N-polar GaN is very difficult; consequently, all of the results reported in the literature for InN growth on GaN were likely carried out on Ga-polar material resulting in films with a high surface roughness. By utilizing N-polar and Ga-polar GaN films, it was possible to produce N-polar and In-polar InN films by MOCVD, as determined by convergent beam electron diffraction (CBED) analysis. Furthermore, the polarity was found to dramatically alter the surface roughness and growth mode of the InN films with enhanced lateral growth and reduced surface roughness obtained for N-polar InN. A qualitative model was proposed to explain the different growth mechanisms observed for In-polar and N-polar InN. In spite of the improvements in surface morphology obtained with growth of N-polar InN, delamination at the InN/GaN interface was still observed in these films, and was also present in In-polar InN samples. Attempts were made to further reduce the lattice mismatch and improve the adhesion between InN and GaN by using a compositionally graded InGaN buffer layer. The fabrication of InGaN over its entire composition range is challenging since the optimal growth parameters window for InGaN varies with composition and film quality is strongly dependent on temperature and precursor flow rates. The structural properties of the InN films grown on the graded InGaN layers were comparable to films grown directly on GaN, however, the film adhesion was significantly improved with no evidence of interfacial cracks between the InN and GaN. These preliminary results indicate that graded InGaN layers can be used to improve the adhesion of InN on both Ga-polar and N-polar GaN, however, further work is needed to develop graded InGaN buffer layers or constant composition InGaN interlayers with improved structural properties for InN growth. (Abstract shortened by UMI.)

Buffer transport mechanisms in intentionally carbon doped GaN heterojunction field effect transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uren, Michael J.; Cäsar, Markus; Kuball, Martin

2014-06-30

Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer layers in a carbon doped GaN power heterojunction field effect transistor. Carbon doped GaN and multiple layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C doped layer is shown to occur by hole conduction in the valence band withmore » activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.« less

Integration of (208) oriented epitaxial Hf-doped Bi4Ti3O12 with (0002) GaN using SrTiO3/TiO2 buffer layer

NASA Astrophysics Data System (ADS)

Luo, W. B.; Zhu, J.; Li, Y. R.; Wang, X. P.; Zhang, Y.

2009-05-01

Hf-doped Bi4Ti3O12 (BTH) ferroelectric films with excellent electrical properties were epitaxially integrated with GaN semiconductor using (111) SrTiO3 (STO)/rutile (200) TiO2 as buffer layer. The STO/TiO2 buffer layer was deposited by laser molecular beam epitaxy. The structural characteristics of the buffer layer were in situ and ex situ characterized by reflective high energy electron diffraction, x-ray diffraction (XRD), and high resolution transmission microscopy. The overlaying SrRuO3 (SRO) and BTH films were then deposited by pulsed laser deposition. XRD spectra, including θ-2θ and Φ scans, show that the (208) BTH films were epitaxially grown on GaN, and the BTH films inherit the in-plane twin-domain of STO buffer layer. Electrical measurements demonstrate that the non-c axis BTH films possess a large remnant polarization (2Pr=45 μC/cm2), excellent fatigue endurance (10.2% degradation after 1.1×1010 switching cycles), and a low leakage current density (1.94×10-7 A/cm2 at an electric field of 200 kV/cm). These results reveal that the (208) BTH films with favorable electrical performance could be epitaxially grown on GaN template using STO/TiO2 buffer layer.

Growth Optimization of Metal-polar III-Nitride High-electron-mobility Transistor Structures by Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Kaun, Stephen William

GaN-based high-electron-mobility transistors (HEMTs) will play an important role in the next generation of high-frequency amplifiers and power-switching devices. Since parasitic conduction (leakage) through the GaN buffer layer and (Al,Ga,In)N barrier reduces the efficiency of operation, HEMT performance hinges on the epitaxial quality of these layers. Increasing the sheet charge density and mobility of the two-dimensional electron gas (2DEG) is also essential for reducing the channel resistance and improving output. The growth conditions applied in plasma-assisted molecular beam epitaxy (PAMBE) and ammonia-based molecular beam epitaxy (NH3-MBE) that result in high-quality metal-polar HEMT structures are described. The effects of threading dislocations on the gate leakage and channel conductivity of AlGaN/GaN HEMTs were studied in detail. For this purpose, a series of HEMT structures were grown on GaN templates with threading dislocation densities (TDDs) that spanned three orders of magnitude. There was a clear trend of reduced gate leakage with reduced TDD for HEMTs grown by Ga-rich PAMBE; however, a reduction in TDD also entailed an increase in buffer leakage. By reducing the unintentionally doped (UID) GaN buffer thickness and including an AlGaN back barrier, a HEMT regrown by Ga-rich PAMBE on low-TDD free-standing (FS) GaN (~5 x 107 cm-2 TDD) yielded a three-terminal breakdown voltage greater than 50 V and a power output (power-added efficiency) of 6.7 W/mm (50 %) at 4 GHz with a 40 V drain bias. High TDD was then shown to severely degrade the 2DEG mobility of AlxGa1-xN/GaN (x = 0.24, 0.12, 0.06) and AlGaN/AlN/GaN heterostructures grown by Ga-rich PAMBE. By regrowing on low-TDD FS GaN and including a 2.5 nm AlN interlayer, an Al0.24Ga0.76N/AlN/GaN heterostructure achieved a room temperature (RT) 2DEG sheet resistance of 169 Ω/□. As evidenced by atom probe tomography, the AlN interlayer grown by Ga-rich PAMBE was pure with abrupt interfaces. The pure AlN interlayer greatly reduced alloy-related scattering. When AlGaN/AlN/GaN heterostructures were grown by NH3-MBE at 820 °C, the 2DEG sheet density was lower than expected. These AlN interlayers were shown to have a significant concentration of Ga impurities by atom probe tomography. The source of these impurities was most likely the decomposition of the underlying GaN layers, as reduction of the growth temperature below 750 °C yielded a much lower concentration of Ga impurities. Flux optimization and application of an In surfactant was necessary to reduce the interface roughness in AlGaN/AlN/GaN heterostructures grown by NH3-MBE at low temperature, yielding sheet resistances below 300 Ω/□. The growth of InAlN/(GaN)/(AlN)/GaN heterostructures with lattice-matched In0.17Al0.83N barriers by N-rich PAMBE is also described. Through flux optimization, the columnar microstructure previously observed in N-rich PAMBE-grown InAlN layers was eliminated. By including a 3 nm AlN interlayer and 2 nm GaN interlayer, an In0.17Al0.83N/GaN/AlN/GaN heterostructure regrown on low-TDD FS GaN achieved an exceptionally low RT 2DEG sheet resistance of 145 Ω/□.

Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bagnall, Kevin R.; Wang, Evelyn N.

2016-06-01

Micro-Raman thermography is one of the most popular techniques for measuring local temperature rise in gallium nitride (GaN) high electron mobility transistors with high spatial and temporal resolution. However, accurate temperature measurements based on changes in the Stokes peak positions of the GaN epitaxial layers require properly accounting for the stress and/or strain induced by the inverse piezoelectric effect. It is common practice to use the pinched OFF state as the unpowered reference for temperature measurements because the vertical electric field in the GaN buffer that induces inverse piezoelectric stress/strain is relatively independent of the gate bias. Although this approach has yielded temperature measurements that agree with those derived from the Stokes/anti-Stokes ratio and thermal models, there has been significant difficulty in quantifying the mechanical state of the GaN buffer in the pinched OFF state from changes in the Raman spectra. In this paper, we review the experimental technique of micro-Raman thermography and derive expressions for the detailed dependence of the Raman peak positions on strain, stress, and electric field components in wurtzite GaN. We also use a combination of semiconductor device modeling and electro-mechanical modeling to predict the stress and strain induced by the inverse piezoelectric effect. Based on the insights gained from our electro-mechanical model and the best values of material properties in the literature, we analyze changes in the E2 high and A1 (LO) Raman peaks and demonstrate that there are major quantitative discrepancies between measured and modeled values of inverse piezoelectric stress and strain. We examine many of the hypotheses offered in the literature for these discrepancies but conclude that none of them satisfactorily resolves these discrepancies. Further research is needed to determine whether the electric field components could be affecting the phonon frequencies apart from the inverse piezoelectric effect in wurtzite GaN, which has been predicted theoretically in zinc blende gallium arsenide (GaAs).

Long wavelength emitting GaInN quantum wells on metamorphic GaInN buffer layers with enlarged in-plane lattice parameter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Däubler, J., E-mail: juergen.daeubler@iaf.fraunhofer.de; Passow, T.; Aidam, R.

Metamorphic (i.e., linear composition graded) GaInN buffer layers with an increased in-plane lattice parameter, grown by plasma-assisted molecular beam epitaxy, were used as templates for metal organic vapor phase epitaxy (MOVPE) grown GaInN/GaInN quantum wells (QWs), emitting in the green to red spectral region. A composition pulling effect was observed allowing considerable higher growth temperatures for the QWs for a given In composition. The internal quantum efficiency (IQE) of the QWs was determined by temperature and excitation power density dependent photoluminescence (PL) spectroscopy. An increase in IQE by a factor of two was found for green emitting QWs grown onmore » metamorphic GaInN buffer compared to reference samples grown on standard GaN buffer layers. The ratio of room temperature to low temperature intensity PL of the red emitting QWs were found to be comparable to the PL efficiency of green emitting QWs, both grown on metamorphic GaInN buffers. The excitation density and well width dependence of the IQE indicate a reduction of the quantum confined Stark effect upon growth on GaInN buffer layers with increased in-plane lattice parameter.« less

High-Quality GaN Epilayers Achieved by Facet-Controlled Epitaxial Lateral Overgrowth on Sputtered AlN/PSS Templates.

PubMed

He, Chenguang; Zhao, Wei; Zhang, Kang; He, Longfei; Wu, Hualong; Liu, Ningyang; Zhang, Shan; Liu, Xiaoyan; Chen, Zhitao

2017-12-13

It is widely believed that the lack of high-quality GaN wafers severely hinders the progress in GaN-based devices, especially for defect-sensitive devices. Here, low-cost AlN buffer layers were sputtered on cone-shaped patterned sapphire substrates (PSSs) to obtain high-quality GaN epilayers. Without any mask or regrowth, facet-controlled epitaxial lateral overgrowth was realized by metal-organic chemical vapor deposition. The uniform coating of the sputtered AlN buffer layer and the optimized multiple modulation guaranteed high growth selectivity and uniformity of the GaN epilayer. As a result, an extremely smooth surface was achieved with an average roughness of 0.17 nm over 3 × 3 μm 2 . It was found that the sputtered AlN buffer layer could significantly suppress dislocations on the cones. Moreover, the optimized three-dimensional growth process could effectively promote dislocation bending. Therefore, the threading dislocation density (TDD) of the GaN epilayer was reduced to 4.6 × 10 7 cm -2 , which is about an order of magnitude lower than the case of two-step GaN on the PSS. In addition, contamination and crack in the light-emitting diode fabricated on the obtained GaN were also effectively suppressed by using the sputtered AlN buffer layer. All of these advantages led to a high output power of 116 mW at 500 mA with an emission wavelength of 375 nm. This simple, yet effective growth technique is believed to have great application prospects in high-performance TDD-sensitive optoelectronic and electronic devices.

A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD.

PubMed

Wang, Wenliang; Wang, Haiyan; Yang, Weijia; Zhu, Yunnong; Li, Guoqiang

2016-04-22

High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first, and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality, and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates.

Study on GaN buffer leakage current in AlGaN/GaN high electron mobility transistor structures grown by ammonia-molecular beam epitaxy on 100-mm Si(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ravikiran, L.; Radhakrishnan, K., E-mail: ERADHA@e.ntu.edu.sg; Ng, G. I.

2015-06-28

The effect of carbon doping on the structural and electrical properties of GaN buffer layer of AlGaN/GaN high electron mobility transistor (HEMT) structures has been studied. In the undoped HEMT structures, oxygen was identified as the dominant impurity using secondary ion mass spectroscopy and photoluminescence (PL) measurements. In addition, a notable parallel conduction channel was identified in the GaN buffer at the interface. The AlGaN/GaN HEMT structures with carbon doped GaN buffer using a CBr{sub 4} beam equivalent pressure of 1.86 × 10{sup −7} mTorr showed a reduction in the buffer leakage current by two orders of magnitude. Carbon doped GaN buffersmore » also exhibited a slight increase in the crystalline tilt with some pits on the growth surface. PL and Raman measurements indicated only a partial compensation of donor states with carbon acceptors. However, AlGaN/GaN HEMT structures with carbon doped GaN buffer with 200 nm thick undoped GaN near the channel exhibited good 2DEG characteristics.« less

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy.

PubMed

Bagnall, Kevin R; Moore, Elizabeth A; Badescu, Stefan C; Zhang, Lenan; Wang, Evelyn N

2017-11-01

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E 2 (high), A 1 longitudinal optical (LO), and E 2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bagnall, Kevin R.; Moore, Elizabeth A.; Badescu, Stefan C.; Zhang, Lenan; Wang, Evelyn N.

2017-11-01

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E2 (high), A1 longitudinal optical (LO), and E2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

DOE PAGES

Ahn, Shihyun; Zhu, Weidi; Dong, Chen; ...

2015-04-21

Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 10 9 and 5 × 10 8 cm ₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, theremore » was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

AlGaN/GaN High Electron Mobility Transistor Grown and Fabricated on ZrTi Metallic Alloy Buffer Layers

DOE PAGES

Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

2017-09-26

AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated for structures grown on ZrTi metallic alloy buffer layers, which provided lattice matching of the in-plane lattice parameter (“a-parameter”) to hexagonal GaN. The quality of the GaN buffer layer and HEMT structure were confirmed with X-ray 2θ and rocking scans as well as cross-section transmission electron microscopy (TEM) images. The X-ray 2θ scans showed full widths at half maximum (FWHM) of 0.06°, 0.05° and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM of the lower section of the HEMT structure containing the GaN buffer layer andmore » the AlN/ZrTi/AlN stack on the Si substrate showed that it was important to grow AlN on the top of ZrTi prior to growing the GaN buffer layer. Finally, the estimated threading dislocation (TD) density in the GaN channel layer of the HEMT structure was in the 10 8 cm -2 range.« less

The effects of GaN nanocolumn arrays and thin SixNy buffer layers on the morphology of GaN layers grown by plasma-assisted molecular beam epitaxy on Si(111) substrates

NASA Astrophysics Data System (ADS)

Shubina, K. Yu; Pirogov, E. V.; Mizerov, A. M.; Nikitina, E. V.; Bouravleuv, A. D.

2018-03-01

The effects of GaN nanocolumn arrays and a thin SixNy layer, used as buffer layers, on the morphology of GaN epitaxial layers are investigated. Two types of samples with different buffer layers were synthesized by PA-MBE. The morphology of the samples was characterized by SEM. The crystalline quality of the samples was assessed by XRD. The possibility of synthesis of continuous crystalline GaN layers on Si(111) substrates without the addition of other materials such as aluminum nitride was demonstrated.

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics.

PubMed

Mánuel, J M; Jiménez, J J; Morales, F M; Lacroix, B; Santos, A J; García, R; Blanco, E; Domínguez, M; Ramírez, M; Beltrán, A M; Alexandrov, D; Tot, J; Dubreuil, R; Videkov, V; Andreev, S; Tzaneva, B; Bartsch, H; Breiling, J; Pezoldt, J; Fischer, M; Müller, J

2018-05-02

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

Contributed Review: Experimental characterization of inverse piezoelectric strain in GaN HEMTs via micro-Raman spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagnall, Kevin R.; Wang, Evelyn N.

2016-06-15

Micro-Raman thermography is one of the most popular techniques for measuring local temperature rise in gallium nitride (GaN) high electron mobility transistors with high spatial and temporal resolution. However, accurate temperature measurements based on changes in the Stokes peak positions of the GaN epitaxial layers require properly accounting for the stress and/or strain induced by the inverse piezoelectric effect. It is common practice to use the pinched OFF state as the unpowered reference for temperature measurements because the vertical electric field in the GaN buffer that induces inverse piezoelectric stress/strain is relatively independent of the gate bias. Although this approachmore » has yielded temperature measurements that agree with those derived from the Stokes/anti-Stokes ratio and thermal models, there has been significant difficulty in quantifying the mechanical state of the GaN buffer in the pinched OFF state from changes in the Raman spectra. In this paper, we review the experimental technique of micro-Raman thermography and derive expressions for the detailed dependence of the Raman peak positions on strain, stress, and electric field components in wurtzite GaN. We also use a combination of semiconductor device modeling and electro-mechanical modeling to predict the stress and strain induced by the inverse piezoelectric effect. Based on the insights gained from our electro-mechanical model and the best values of material properties in the literature, we analyze changes in the E{sub 2} high and A{sub 1} (LO) Raman peaks and demonstrate that there are major quantitative discrepancies between measured and modeled values of inverse piezoelectric stress and strain. We examine many of the hypotheses offered in the literature for these discrepancies but conclude that none of them satisfactorily resolves these discrepancies. Further research is needed to determine whether the electric field components could be affecting the phonon frequencies apart from the inverse piezoelectric effect in wurtzite GaN, which has been predicted theoretically in zinc blende gallium arsenide (GaAs).« less

Formation of gallium nitride templates and freestanding substrates by hydride vapor phase epitaxy for homoepitaxial growth of III-nitride devices

NASA Astrophysics Data System (ADS)

Williams, Adrian Daniel

Gallium nitride (GaN) is a direct wide band gap semiconductor currently under heavy development worldwide due to interest in its applications in ultra-violet optoelectronics, power electronics, devices operating in harsh environments (high temperature or corrorsive), etc. While a number of devices have been demonstrated with this material and its related alloys, the unavailability of GaN substrates is seen as one of the current major bottlenecks to both material quality and device performance. This dissertation is concerned with the synthesis of high quality GaN substrates by the hydride vapor phase epitaxy method (HVPE). In this work, the flow of growth precursors in a home-built HVPE reactor was modeled by the Navier-Stokes equation and solved by finite element analysis to promote uniformity of GaN on 2'' sapphire substrates. Kinetics of growth was studied and various regimes of growth were identified to establish a methodology for HVPE GaN growth, independent of reactor geometry. GaN templates as well as bulk substrates were fabricated in this work. Realization of freestanding GaN substrates was achieved through discovery of a natural stress-induced method of separating bulk GaN from sapphire via mechanical failure of a low-temperature GaN buffer layer. Such a process eliminates the need for pre- or post-processing of sapphire substrates, as is currently the standard. Stress in GaN-on-sapphire is discussed, with the dominant contributor identified as thermal stress due to thermal expansion coefficient mismatch between the two materials. This thermal stress is analyzed using Stoney's equation and conditions for crack-free growth of thick GaN substrates were identified. An etch-back process for planarizing GaN templates was also developed and successfully applied to rough GaN templates. The planarization of GaN has been mainly addressed by chemo-mechanical polishing (CMP) methods in the literature, with notable shortcomings including the inability to effectively planarize gallium-polar GaN, the preferred growth plane for devices. The process developed in this work bypasses the constraints of CMP, allowing for the planarization of all surfaces of GaN irrespective of crystal orientation. The GaN samples grown for this dissertation were studied by various techniques to characterize their structural, optical, and electrical properties.

Growth of crack-free GaN films on Si(111) substrate by using Al-rich AlN buffer layer

NASA Astrophysics Data System (ADS)

Lu, Yuan; Cong, Guangwei; Liu, Xianglin; Lu, Da-Cheng; Zhu, Qinsheng; Wang, Xiaohui; Wu, Jiejun; Wang, Zhanguo

2004-11-01

GaN epilayers were grown on Si(111) substrate by metalorganic chemical vapor deposition. By using the Al-rich AlN buffer which contains Al beyond stoichiometry, crack-free GaN epilayers with 1 μm thickness were obtained. Through x-ray diffraction (XRD) and secondary ion mass spectroscopy analyses, it was found that a lot of Al atoms have diffused into the under part of the GaN epilayer from the Al-rich AlN buffer, which results in the formation of an AlxGa1-xN layer at least with 300 nm thickness in the 1 μm thick GaN epilayer. The Al fraction x was estimated by XRD to be about 2.5%. X-ray photoelectron spectroscopy depth analysis was also applied to investigate the stoichiometry in the Al-rich buffer before GaN growth. It is suggested that the underlayer AlxGa1-xN originated from Al diffusion probably provides a compressive stress to the upper part of the GaN epilayer, which counterbalances a part of tensile stress in the GaN epilayer during cooling down and consequently reduces the cracks of the film effectively. The method using the Al diffusion effect to form a thick AlGaN layer is really feasible to achieve the crack-free GaN films and obtain a high crystal quality simultaneously.

Surface morphology of Al0.3Ga0.7N/Al2O3-high electron mobility transistor structure.

PubMed

Cörekçi, S; Usanmaz, D; Tekeli, Z; Cakmak, M; Ozçelik, S; Ozbay, E

2008-02-01

We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.

Enzymatic glucose detection using ZnO nanorods on the gate region of AlGaN /GaN high electron mobility transistors

NASA Astrophysics Data System (ADS)

Kang, B. S.; Wang, H. T.; Ren, F.; Pearton, S. J.; Morey, T. E.; Dennis, D. M.; Johnson, J. W.; Rajagopal, P.; Roberts, J. C.; Piner, E. L.; Linthicum, K. J.

2007-12-01

ZnO nanorod-gated AlGaN /GaN high electron mobility transistors (HEMTs) are demonstrated for the detection of glucose. A ZnO nanorod array was selectively grown on the gate area using low temperature hydrothermal decomposition to immobilize glucose oxidase (GOx). The one-dimensional ZnO nanorods provide a large effective surface area with high surface-to-volume ratio and provide a favorable environment for the immobilization of GOx. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when target glucose in a buffer with a pH value of 7.4 was added to the GOx immobilized on the ZnO nanorod surface. We could detect a wide range of concentrations from 0.5nMto125μM. The sensor exhibited a linear range from 0.5nMto14.5μM and an experiment limit of detection of 0.5nM. This demonstrates the possibility of using AlGaN /GaN HEMTs for noninvasive exhaled breath condensate based glucose detection of diabetic application.

Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, X.; Nilsson, D.; Danielsson, Ö.

2015-12-28

The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement showsmore » a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.« less

Ohmic contacts to n-GaN formed by ion-implanted Si into p-GaN

NASA Astrophysics Data System (ADS)

Bao, Xichang; Xu, Jintong; Zhang, Wenjing; Wang, Ling; Chu, Kaihui; Li, Chao; Li, Xiangyang

2009-07-01

In this paper, we report the ohmic contact to n-GaN fabricated by implanting silicon into Mg-doped GaN using an alloy of Ti/Al/Ti/Au metallization. The used materials were grown on (001) sapphire substrates by metal-organic chemical-vapor deposition (MOCVD). The layer structure was comprised of a GaN buffer layer and followed by a 2 μm thickness Mg-doped GaN (Na=5×1017cm-3) and then double silicon implantation was performed in order to convert p-type GaN into n-type GaN films. The as-implanted samples were then thermal annealed at 1150 °C for 5 min in N2 ambient. The carrier concentration and Hall mobility were 3.13×1018 cm3 and 112 cm2/ (VÂ.s) measured by Hall method. Multilayer electrode of Ti (50 nm)/Al (50 nm)/Ti (30 nm)/Au (30 nm) was deposited on n-GaN using an electron-beam evaporation and contacts were formed by a N2 annealing technique ranging from 600 to 900 °C. After annealing lower than 700 °C, the contacts exhibited a rectifying behavior and became ohmic contact only after high temperature processes (>=700 °C). Specific contact resistance was as low as 9.58×10-4 ΩÂ.cm2 after annealing at 800 °C for 60 seconds. While annealing temperature is higher than 800 °C, the specific contact resistance becomes worse. This phenomenon is caused by the surface morphology degradation.

AlGaN/GaN HEMTs regrown by MBE on epi-ready semi-insulating GaN-on-sapphire with inhibited interface contamination

NASA Astrophysics Data System (ADS)

Cordier, Y.; Azize, M.; Baron, N.; Chenot, S.; Tottereau, O.; Massies, J.

2007-11-01

In this work, we show that, by carefully designing the subsurface Fe doping profile in SI-GaN templates grown by MOVPE and by optimizing the MBE regrowth conditions, a highly resistive GaN buffer can be achieved on these epi-ready GaN-on-sapphire templates without any addition of acceptors during the regrowth. As a result, high-quality high electron mobility transistors can be fabricated. Furthermore, we report on the excellent properties of two-dimensional electron gas and device performances with electron mobility greater than 2000 cm 2/V s at room temperature and off-state buffer leakage currents as low as 5 μA/mm at 100 V.

Room-temperature continuous-wave electrically injected InGaN-based laser directly grown on Si

NASA Astrophysics Data System (ADS)

Sun, Yi; Zhou, Kun; Sun, Qian; Liu, Jianping; Feng, Meixin; Li, Zengcheng; Zhou, Yu; Zhang, Liqun; Li, Deyao; Zhang, Shuming; Ikeda, Masao; Liu, Sheng; Yang, Hui

2016-09-01

Silicon photonics would greatly benefit from efficient, visible on-chip light sources that are electrically driven at room temperature. To fully utilize the benefits of large-scale, low-cost manufacturing foundries, it is highly desirable to grow direct bandgap III-V semiconductor lasers directly on Si. Here, we report the demonstration of a blue-violet (413 nm) InGaN-based laser diode grown directly on Si that operates under continuous-wave current injection at room temperature, with a threshold current density of 4.7 kA cm-2. The heteroepitaxial growth of GaN on Si is confronted with a large mismatch in both the lattice constant and the coefficient of thermal expansion, often resulting in a high density of defects and even microcrack networks. By inserting an Al-composition step-graded AlN/AlGaN multilayer buffer between the Si and GaN, we have not only successfully eliminated crack formation, but also effectively reduced the dislocation density. The result is the realization of a blue-violet InGaN-based laser on Si.

Growth and characterizations of various GaN nanostructures on C-plane sapphire using laser MBE

NASA Astrophysics Data System (ADS)

Ch., Ramesh; Tyagi, P.; Maurya, K. K.; Kumar, M. Senthil; Kushvaha, S. S.

2017-05-01

We have grown various GaN nanostructures such as three-dimensional islands, nanowalls and nanocolumns on c-plane sapphire substrates using laser assisted molecular beam epitaxy (LMBE) system. The shape of the GaN nanostructures was controlled by using different nucleation surfaces such as bare and nitridated sapphire with GaN or AlN buffer layers. The structural and surface morphological properties of grown GaN nanostructures were characterized by ex-situ high resolution x-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. The symmetric x-ray rocking curve along GaN (0002) plane shows that the GaN grown on pre-nitridated sapphire with GaN or AlN buffer layer possesses good crystalline quality compared to sapphire without nitridation. The Raman spectroscopy measurements revealed the wurtzite phase for all the GaN nanostructures grown on c-sapphire.

Compositionally graded relaxed AlGaN buffers on semipolar GaN for mid-ultraviolet emission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, Erin C.; Wu Feng; Haeger, Daniel A.

In this Letter, we report on the growth and properties of relaxed, compositionally graded Al{sub x}Ga{sub 1-x}N buffer layers on freestanding semipolar (2021) GaN substrates. Continuous and step compositional grades with Al concentrations up to x = 0.61 have been achieved, with emission wavelengths in the mid-ultraviolet region as low as 265 nm. Coherency stresses were relaxed progressively throughout the grades by misfit dislocation generation via primary (basal) slip and secondary (non-basal) slip systems. Threading dislocation densities in the final layers of the grades were less than 10{sup 6}/cm{sup 2} as confirmed by plan-view transmission electron microscopy and cathodoluminescence studies.

Compositionally graded relaxed AlGaN buffers on semipolar GaN for mid-ultraviolet emission

NASA Astrophysics Data System (ADS)

Young, Erin C.; Wu, Feng; Romanov, Alexey E.; Haeger, Daniel A.; Nakamura, Shuji; Denbaars, Steven P.; Cohen, Daniel A.; Speck, James S.

2012-10-01

In this Letter, we report on the growth and properties of relaxed, compositionally graded AlxGa1 - xN buffer layers on freestanding semipolar (202¯1) GaN substrates. Continuous and step compositional grades with Al concentrations up to x = 0.61 have been achieved, with emission wavelengths in the mid-ultraviolet region as low as 265 nm. Coherency stresses were relaxed progressively throughout the grades by misfit dislocation generation via primary (basal) slip and secondary (non-basal) slip systems. Threading dislocation densities in the final layers of the grades were less than 106/cm2 as confirmed by plan-view transmission electron microscopy and cathodoluminescence studies.

Impact of varying buffer thickness generated strain and threading dislocations on the formation of plasma assisted MBE grown ultra-thin AlGaN/GaN heterostructure on silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chowdhury, Subhra, E-mail: subhra1109@gmail.com; Biswas, Dhrubes; Department of E and E C E, Indian Institute of Technology Kharagpur, Kharagpur 721302

2015-05-15

Plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructures on Si(111) substrate with three buffer thickness (600 nm/400 nm/200 nm) have been reported. An unique growth process has been developed that supports lower temperature epitaxy of GaN buffer which minimizes thermally generated tensile strain through appropriate nitridation and AlN initiated epitaxy for achieving high quality GaN buffer which supports such ultra-thin heterostructures in the range of 10-15Å. It is followed by investigations of role of buffer thickness on formation of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructure, in terms of stress-strain and threading dislocation (TD). Structural characterization were performedmore » by High-Resolution X-Ray Diffraction (HRXRD), room-temperature Photoluminescence (RT-PL), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Analysis revealed increasing biaxial tensile stress of 0.6918 ± 0.04, 1.1084, 1.1814 GPa in heterostructures with decreasing buffer thickness of 600, 400, 200 nm respectively which are summed up with residual tensile strain causing red-shift in RT-PL peak. Also, increasing buffer thickness drastically reduced TD density from the order 10{sup 10} cm{sup −2} to 10{sup 8} cm{sup −2}. Surface morphology through AFM leads to decrease of pits and root mean square value with increasing buffer thickness which are resulted due to reduction of combined effect of strain and TDs.« less

GaN Micromechanical Resonators with Meshed Metal Bottom Electrode.

PubMed

Ansari, Azadeh; Liu, Che-Yu; Lin, Chien-Chung; Kuo, Hao-Chung; Ku, Pei-Cheng; Rais-Zadeh, Mina

2015-03-17

This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO₂) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient ( d 33 ) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF₂) etch and therefore eliminating the need for backside lithography and etching.

Investigation on the compensation effect of residual carbon impurities in low temperature grown Mg doped GaN films

NASA Astrophysics Data System (ADS)

Yang, J.; Zhao, D. G.; Jiang, D. S.; Chen, P.; Liu, Z. S.; Le, L. C.; Li, X. J.; He, X. G.; Liu, J. P.; Zhang, S. M.; Wang, H.; Zhu, J. J.; Yang, H.

2014-04-01

The influence of unintentionally doped carbon impurities on electrical resistivity and yellow luminescence (YL) of low-temperature (LT) grown Mg doped GaN films is investigated. It is found that the resistivity of Mg doped GaN films are closely related to the residual carbon impurity concentration, which may be attributed to the compensation effect of carbon impurities. The carbon impurity may preferentially form deep donor complex CN-ON resulting from its relatively low formation energy. This complex is an effective compensate center for MgGa acceptors as well as inducing YL in photoluminescence spectra. Thus, the low resistivity LT grown p-type GaN films can be obtained only when the residual carbon impurity concentration is sufficiently low, which can explain why LT P-GaN films with lower resistivity were obtained more easily when relatively higher pressure, temperature, or NH3/TMGa flow rate ratio were used in the LT grown Mg doped GaN films reported in earlier reports.

Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun

Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 10 8 cm –2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (f T) of 8.9 GHz and a maximum frequency of oscillation (f max) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

DOE PAGES

Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

2016-09-21

Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 10 8 cm –2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (f T) of 8.9 GHz and a maximum frequency of oscillation (f max) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

New PLAD apparatus and fabrication of epitaxial films and junctions of functional materials: SiC, GaN, ZnO, diamond and GMR layers

NASA Astrophysics Data System (ADS)

Muto, Hachizo; Kusumori, Takeshi; Nakamura, Toshiyuki; Asano, Takashi; Hori, Takahiro

2006-04-01

We have developed a new pulsed laser ablation-deposition (PLAD) apparatus and techniques for fabricating films of high-temperature or functional materials, including two short-wavelength lasers: (a) a YAG 5th harmonic (213 nm) and (b) Raman-shifted lasers containing vacuum ultraviolet light; also involved are (c) a high-temperature heater with a maximum temperature of 1350 °C, (d) dual-target simultaneous ablation mechanics, and (e) hybrid PLAD using a pico-second YAG laser combined with (c) and/or (d). Using the high-T heater, hetero-epitaxial films of 3C-, 2H- and 4H-SiC have been prepared on sapphire-c. In situ p-doping for GaN epitaxial films is achieved by simultaneous ablation of GaN and Mg targets by (d) during film growth. Junctions such as pGaN (Mg-doped)-film/n-SiC(0 0 0 1) substrate and pGaN/n-Si(1 1 1) show good diode characteristics. Epitaxial films with a diamond lattice can be grown on the sapphire-c plane by hybrid PLAD (e) with a high-T heater using a 6H-SiC target. High quality epitaxial films of ZnO are grown by PLAD by introducing a low-temperature self-buffer layer; magnetization of ferromagnetic materials is enforced by overlaying on a ferromagnetic lattice plane of an anti-ferromagnetic material, showing the value of the layer-overlaying method in improving quality. The short-wavelength lasers are useful in reducing surface particles on functional films, including superconductors.

Gallium nitride microcavities formed by photoenhanced wet oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, L.-H.; Lu, C.-Y.; Wu, W.-H.

We report the formation of gallium nitride (GaN) microcavities by manipulating a photoenhanced oxidation rate difference between the polar and nonpolar crystallographic planes of GaN. When immersed in a buffered acetic (CH{sub 3}COOH) electrolyte of pH{approx}6.2 at room temperature, it is shown that the photo-oxidation can proceed at a rate that is one order of magnitude slower on the nonpolar plane of {l_brace}1100{r_brace}{sub GaN} than on the polar plane of {l_brace}0001{r_brace}{sub GaN} due to the reduced surface field action. Gallium nitride microcavities bounded by optically smooth {l_brace}1100{r_brace} and {l_brace}1103{r_brace} facets can thus be preferentially formed on the c-plane sapphire substratemore » after dissolving the oxide layer. The optical properties of these GaN hexagonal cavities reveal characteristic peaks of whispering gallery modes in resonance with the GaN band edge emission spectrum. A typical cavity Q factor of 10{sup 3} is observed in these GaN microcavities due to a reduced optical scattering loss in the wet chemical reaction process.« less

Pt-decorated GaN nanowires with significant improvement in H2 gas-sensing performance at room temperature.

PubMed

Abdullah, Q N; Yam, F K; Hassan, Z; Bououdina, M

2015-12-15

Superior sensitivity towards H2 gas was successfully achieved with Pt-decorated GaN nanowires (NWs) gas sensor. GaN NWs were fabricated via chemical vapor deposition (CVD) route. Morphology (field emission scanning electron microscopy and transmission electron microscopy) and crystal structure (high resolution X-ray diffraction) characterizations of the as-synthesized nanostructures demonstrated the formation of GaN NWs having a wurtzite structure, zigzaged shape and an average diameter of 30-166nm. The Pt-decorated GaN NWs sensor shows a high response of 250-2650% upon exposure to H2 gas concentration from 7 to 1000ppm respectively at room temperature (RT), and then increases to about 650-4100% when increasing the operating temperature up to 75°C. The gas-sensing measurements indicated that the Pt-decorated GaN NWs based sensor exhibited efficient detection of H2 at low concentration with excellent sensitivity, repeatability, and free hysteresis phenomena over a period of time of 100min. The large surface-to-volume ratio of GaN NWs and the catalytic activity of Pt metal are the most influential factors leading to the enhancement of H2 gas-sensing performances through the improvement of the interaction between the target molecules (H2) and the sensing NWs surface. The attractive low-cost, low power consumption and high-performance of the resultant decorated GaN NWs gas sensor assure their uppermost potential for H2 gas sensor working at low operating temperature. Copyright © 2015 Elsevier Inc. All rights reserved.

Characterizations of GaN film growth by ECR plasma chemical vapor deposition

NASA Astrophysics Data System (ADS)

Fu, Silie; Chen, Junfang; Zhang, Hongbin; Guo, Chaofen; Li, Wei; Zhao, Wenfen

2009-06-01

The electron cyclotron resonance plasma-enhanced metalorganic chemical vapor deposition technology (ECR-MOPECVD) is adopted to grow GaN films on (0 0 0 1) α-Al2O3 substrate. The gas sources are pure N2 and trimethylgallium (TMG). Optical emission spectroscopy (OES) and thermodynamic analysis of GaN growth are applied to understand the GaN growth process. The OES of ECR plasma shows that TMG is significantly dissociated in ECR plasma. Reactants N and Ga in the plasma, obtained easily under the self-heating condition, are essential for the GaN growth. They contribute to the realization of GaN film growth at a relatively low temperature. The thermodynamic study shows that the driving force for the GaN growth is high when N2:TMG>1. Furthermore, higher N2:TMG flow ratio makes the GaN growth easier. Finally, X-ray diffraction, photoluminescence, and atomic force microscope are applied to investigate crystal quality, morphology, and roughness of the GaN films. The results demonstrate that the ECR-MOPECVD technology is favorable for depositing GaN films at low temperatures.

Structural and optical studies of GaN pn-junction with AlN buffer layer grown on Si (111) by RF plasma enhanced MBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yusoff, Mohd Zaki Mohd; Hassan, Zainuriah; Woei, Chin Che

2012-06-29

GaN pn-junction grown on silicon substrates have been the focus in a number of recent reports and further effort is still necessary to improve its crystalline quality for practical applications. GaN has the high n-type background carrier concentration resulting from native defects commonly thought to be nitrogen vacancies. In this work, we present the growth of pn-junction of GaN on Si (111) substrate using RF plasma-enhanced molecular beam epitaxy (MBE). Both of the layers show uniformity with an average thickness of 0.709 {mu}m and 0.095 {mu}m for GaN and AlN layers, respectively. The XRD spectra indicate that no sign ofmore » cubic phase of GaN are found, so it is confirmed that the sample possessed hexagonal structure. It was found that all the allowed Raman optical phonon modes of GaN, i.e. the E2 (low), E1 (high) and A1 (LO) are clearly visible.« less

Self-organization of dislocation-free, high-density, vertically aligned GaN nanocolumns involving InGaN quantum wells on graphene/SiO2 covered with a thin AlN buffer layer.

PubMed

Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

2016-02-05

We demonstrated the self-organization of high-density GaN nanocolumns on multilayer graphene (MLG)/SiO2 covered with a thin AlN buffer layer by RF-plasma-assisted molecular beam epitaxy. MLG/SiO2 substrates were prepared by the transfer of CVD graphene onto thermally oxidized SiO2/Si [100] substrates. Employing the MLG with an AlN buffer layer enabled the self-organization of high-density and vertically aligned nanocolumns. Transmission electron microscopy observation revealed that no threading dislocations, stacking faults, or twinning defects were included in the self-organized nanocolumns. The photoluminescence (PL) peak intensities of the self-organized GaN nanocolumns were 2.0-2.6 times higher than those of a GaN substrate grown by hydride vapor phase epitaxy. Moreover, no yellow luminescence or ZB-phase GaN emission was observed from the nanocolumns. An InGaN/GaN MQW and p-type GaN were integrated into GaN nanocolumns grown on MLG, displaying a single-peak PL emission at a wavelength of 533 nm. Thus, high-density nitride p-i-n nanocolumns were fabricated on SiO2/Si using the transferred MLG interlayer, indicating the possibility of developing visible nanocolumn LEDs on graphene/SiO2.

Ultraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szyszka, A., E-mail: szyszka@ihp-microelectronics.com, E-mail: adam.szyszka@pwr.wroc.pl; Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw; Lupina, L.

2014-08-28

Based on a novel double step oxide buffer heterostructure approach for GaN integration on Si, we present an optimized Metal-Semiconductor-Metal (MSM)-based Ultraviolet (UV) GaN photodetector system with integrated short-period (oxide/Si) Distributed Bragg Reflector (DBR) and leakage suppressing Metal-Oxide-Semiconductor (MOS) electrode contacts. In terms of structural properties, it is demonstrated by in-situ reflection high energy electron diffraction and transmission electron microscopy-energy dispersive x-ray studies that the DBR heterostructure layers grow with high thickness homogeneity and sharp interface structures sufficient for UV applications; only minor Si diffusion into the Y{sub 2}O{sub 3} films is detected under the applied thermal growth budget. Asmore » revealed by comparative high resolution x-ray diffraction studies on GaN/oxide buffer/Si systems with and without DBR systems, the final GaN layer structure quality is not significantly influenced by the growth of the integrated DBR heterostructure. In terms of optoelectronic properties, it is demonstrated that—with respect to the basic GaN/oxide/Si system without DBR—the insertion of (a) the DBR heterostructures and (b) dark current suppressing MOS contacts enhances the photoresponsivity below the GaN band-gap related UV cut-off energy by almost up to two orders of magnitude. Given the in-situ oxide passivation capability of grown GaN surfaces and the one order of magnitude lower number of superlattice layers in case of higher refractive index contrast (oxide/Si) systems with respect to classical III-N DBR superlattices, virtual GaN substrates on Si via functional oxide buffer systems are thus a promising robust approach for future GaN-based UV detector technologies.« less

Study of 3D-growth conditions for selective area MOVPE of high aspect ratio GaN fins with non-polar vertical sidewalls

NASA Astrophysics Data System (ADS)

Hartmann, Jana; Steib, Frederik; Zhou, Hao; Ledig, Johannes; Nicolai, Lars; Fündling, Sönke; Schimpke, Tilman; Avramescu, Adrian; Varghese, Tansen; Trampert, Achim; Straßburg, Martin; Lugauer, Hans-Jürgen; Wehmann, Hergo-Heinrich; Waag, Andreas

2017-10-01

GaN fins are 3D architectures elongated in one direction parallel to the substrate surface. They have the geometry of walls with a large height to width ratio as well as small footprints. When appropriate symmetry directions of the GaN buffer are used, the sidewalls are formed by non-polar {1 1 -2 0} planes, making the fins particularly suitable for many device applications like LEDs, FETs, lasers, sensors or waveguides. The influence of growth parameters like temperature, pressure, V/III ratio and total precursor flow on the fin structures is analyzed. Based on these results, a 2-temperature-step-growth was developed, leading to fins with smooth side and top facets, fast vertical growth rates and good homogeneity along their length as well as over different mask patterns. For the core-shell growth of fin LED heterostructures, the 2-temperature-step-growth shows much smoother sidewalls and less crystal defects in the InGaN QW and p-GaN shell compared to structures with cores grown in just one step. Electroluminescence spectra of the 2-temperature-step-grown fin LED are demonstrated.

Stress related aspects of GaN technology physics

NASA Astrophysics Data System (ADS)

Suhir, Ephraim

2015-03-01

Simple, easy-to-use and physically meaningful analytical models have been developed for the assessment of the combined effect of the lattice and thermal mismatch on the induced stresses in an elongated bi-material assembly, as well as on the thermal mismatch on the thermal stresses in a tri-material assembly, in which the lattice mismatched stresses are eliminated in one way or another. This could be done, e.g., by using a polished or an etched substrate. The analysis is carried out in application to Gallium Nitride (GaN)-Silicon Carbide (SiC) and GaN-diamond (C) filmsubstrate assemblies. The calculated data are obtained, assuming that no annealing or other stress reduction means is applied. The data agree reasonably well with the reported (available) in-situ measurements. The most important conclusion from the computed data is that even if a reasonably good lattice match takes place (as, e.g., in the case of a GaN film fabricated on a SiC substrate, when the mismatch strain is only about 3%) and, in addition, the temperature change (from the fabrication/growth temperature to the operation temperature) is significant (as high as 1000 °C), the thermal stresses are still considerably lower than the lattice-mismatch stresses. Although there are structural and technological means for further reduction of the lattice-mismatch stresses (e.g., by high temperature annealing or by providing one or more buffering layers, or by using patterned or porous substrates), there is still a strong incentive to eliminate completely the lattice mismatch stresses. This seems to be indeed possible, if polished or otherwise flattened (e.g., chemically etched) substrates and sputter deposited GaN film is employed. In such a case only thermal stresses remain, but even these could be reduced, if necessary, by using compliant buffering layers, including layers of variable compliance, or by introducing variable compliance into the properly engineered substrate. In any event, it is expected that strong adhesion could be achieved by using an appropriate fabrication technology, so that no GaN film cracking would be possible, if the film is in tension, or delamination buckling could occur if the film is in compression. The developed models can be used to assess the possibilities and opportunities associated with GaN materials technology.

Group-III nitride based high electron mobility transistor (HEMT) with barrier/spacer layer

DOEpatents

Chavarkar, Prashant; Smorchkova, Ioulia P.; Keller, Stacia; Mishra, Umesh; Walukiewicz, Wladyslaw; Wu, Yifeng

2005-02-01

A Group III nitride based high electron mobility transistors (HEMT) is disclosed that provides improved high frequency performance. One embodiment of the HEMT comprises a GaN buffer layer, with an Al.sub.y Ga.sub.1-y N (y=1 or y 1) layer on the GaN buffer layer. An Al.sub.x Ga.sub.1-x N (0.ltoreq.x.ltoreq.0.5) barrier layer on to the Al.sub.y Ga.sub.1-y N layer, opposite the GaN buffer layer, Al.sub.y Ga.sub.1-y N layer having a higher Al concentration than that of the Al.sub.x Ga.sub.1-x N barrier layer. A preferred Al.sub.y Ga.sub.1-y N layer has y=1 or y.about.1 and a preferred Al.sub.x Ga.sub.1-x N barrier layer has 0.ltoreq.x.ltoreq.0.5. A 2DEG forms at the interface between the GaN buffer layer and the Al.sub.y Ga.sub.1-y N layer. Respective source, drain and gate contacts are formed on the Al.sub.x Ga.sub.1-x N barrier layer. The HEMT can also comprising a substrate adjacent to the buffer layer, opposite the Al.sub.y Ga.sub.1-y N layer and a nucleation layer between the Al.sub.x Ga.sub.1-x N buffer layer and the substrate.

Investigation of buffer traps in AlGaN/GaN-on-Si devices by thermally stimulated current spectroscopy and back-gating measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shu; Zhou, Chunhua; Jiang, Qimeng

2014-01-06

Thermally stimulated current (TSC) spectroscopy and high-voltage back-gating measurement are utilized to study GaN buffer traps specific to AlGaN/GaN lateral heterojunction structures grown on a low-resistivity Si substrate. Three dominating deep-level traps in GaN buffer with activation energies of ΔE{sub T1} ∼ 0.54 eV, ΔE{sub T2} ∼ 0.65 eV, and ΔE{sub T3} ∼ 0.75 eV are extracted from TSC spectroscopy in a vertical GaN-on-Si structure. High back-gate bias applied to the Si substrate could influence the drain current in an AlGaN/GaN-on-Si high-electron-mobility transistor in a way that cannot be explained with a simple field-effect model. By correlating the trap states identified in TSC with the back-gating measurement results, itmore » is proposed that the ionization/deionization of both donor and acceptor traps are responsible for the generation of buffer space charges, which impose additional modulation to the 2DEG channel.« less

III-nitride integration on ferroelectric materials of lithium niobate by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Namkoong, Gon; Lee, Kyoung-Keun; Madison, Shannon M.; Henderson, Walter; Ralph, Stephen E.; Doolittle, W. Alan

2005-10-01

Integration of III-nitride electrical devices on the ferroelectric material lithium niobate (LiNbO3) has been demonstrated. As a ferroelectric material, lithium niobate has a polarization which may provide excellent control of the polarity of III-nitrides. However, while high temperature, 1000°C, thermal treatments produce atomically smooth surfaces, improving adhesion of GaN epitaxial layers on lithium niobate, repolarization of the substrate in local domains occurs. These effects result in multi domains of mixed polarization in LiNbO3, producing inversion domains in subsequent GaN epilayers. However, it is found that AlN buffer layers suppress inversion domains of III-nitrides. Therefore, two-dimensional electron gases in AlGaN /GaN heterojunction structures are obtained. Herein, the demonstration of the monolithic integration of high power devices with ferroelectric materials presents possibilities to control LiNbO3 modulators on compact optoelectronic/electronic chips.

Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

NASA Astrophysics Data System (ADS)

Dixit, Ripudaman; Tyagi, Prashant; Kushvaha, Sunil Singh; Chockalingam, Sreekumar; Yadav, Brajesh Singh; Sharma, Nita Dilawar; Kumar, M. Senthil

2017-04-01

We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500-700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20-30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique.

High hole mobility p-type GaN with low residual hydrogen concentration prepared by pulsed sputtering

NASA Astrophysics Data System (ADS)

Arakawa, Yasuaki; Ueno, Kohei; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

2016-08-01

We have grown Mg-doped GaN films with low residual hydrogen concentration using a low-temperature pulsed sputtering deposition (PSD) process. The growth system is inherently hydrogen-free, allowing us to obtain high-purity Mg-doped GaN films with residual hydrogen concentrations below 5 × 1016 cm-3, which is the detection limit of secondary ion mass spectroscopy. In the Mg profile, no memory effect or serious dopant diffusion was detected. The as-deposited Mg-doped GaN films showed clear p-type conductivity at room temperature (RT) without thermal activation. The GaN film doped with a low concentration of Mg (7.9 × 1017 cm-3) deposited by PSD showed hole mobilities of 34 and 62 cm2 V-1 s-1 at RT and 175 K, respectively, which are as high as those of films grown by a state-of-the-art metal-organic chemical vapor deposition apparatus. These results indicate that PSD is a powerful tool for the fabrication of GaN-based vertical power devices.

Study on high breakdown voltage GaN-based vertical field effect transistor with interfacial charge engineering for power applications

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Liu, Dong; Liu, Yong; Bai, Zhiyuan; Jiang, Zhiguang; Liu, Yang; Yu, Qi

2017-11-01

A high voltage GaN-based vertical field effect transistor with interfacial charge engineering (GaN ICE-VFET) is proposed and its breakdown mechanism is presented. This vertical FET features oxide trenches which show a fixed negative charge at the oxide/GaN interface. In the off-state, firstly, the trench oxide layer acts as a field plate; secondly, the n-GaN buffer layer is inverted along the oxide/GaN interface and thus a vertical hole layer is formed, which acts as a virtual p-pillar and laterally depletes the n-buffer pillar. Both of them modulate electric field distribution in the device and significantly increase the breakdown voltage (BV). Compared with a conventional GaN vertical FET, the BV of GaN ICE-VFET is increased from 1148 V to 4153 V with the same buffer thickness of 20 μm. Furthermore, the proposed device achieves a great improvement in the tradeoff between BV and on-resistance; and its figure of merit even exceeds the GaN one-dimensional limit.

Infrared Reflectance Analysis of Epitaxial n-Type Doped GaN Layers Grown on Sapphire.

PubMed

Tsykaniuk, Bogdan I; Nikolenko, Andrii S; Strelchuk, Viktor V; Naseka, Viktor M; Mazur, Yuriy I; Ware, Morgan E; DeCuir, Eric A; Sadovyi, Bogdan; Weyher, Jan L; Jakiela, Rafal; Salamo, Gregory J; Belyaev, Alexander E

2017-12-01

Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n + /n 0 /n + -GaN structure grown on GaN buffer with GaN-template/sapphire substrate. Analysis of the investigated structure by photo-etching, SEM, and SIMS methods showed the existence of the additional layer with the drastic difference in Si and O doping levels and located between the epitaxial GaN buffer and template. Simulation of the experimental reflectivity spectra was performed in a wide frequency range. It is shown that the modeling of IR reflectance spectrum using 2 × 2 transfer matrix method and including into analysis the additional layer make it possible to obtain the best fitting of the experimental spectrum, which follows in the evaluation of GaN layer thicknesses which are in good agreement with the SEM and SIMS data. Spectral dependence of plasmon-LO-phonon coupled modes for each GaN layer is obtained from the spectral dependence of dielectric of Si doping impurity, which is attributed to compensation effects by the acceptor states.

The fabrication of white light-emitting diodes using the n-ZnO/NiO/p-GaN heterojunction with enhanced luminescence.

PubMed

Abbasi, Mazhar Ali; Ibupoto, Zafar Hussain; Hussain, Mushtaque; Nur, Omer; Willander, Magnus

2013-07-13

Cheap and efficient white light-emitting diodes (LEDs) are of great interest due to the energy crisis all over the world. Herein, we have developed heterojunction LEDs based on the well-aligned ZnO nanorods and nanotubes on the p-type GaN with the insertion of the NiO buffer layer that showed enhancement in the light emission. Scanning electron microscopy have well demonstrated the arrays of the ZnO nanorods and the proper etching into the nanotubes. X-ray diffraction study describes the wurtzite crystal structure array of ZnO nanorods with the involvement of GaN at the (002) peak. The cathodoluminescence spectra represent strong and broad visible emission peaks compared to the UV emission and a weak peak at 425 nm which is originated from GaN. Electroluminescence study has shown highly improved luminescence response for the LEDs fabricated with NiO buffer layer compared to that without NiO layer. Introducing a sandwich-thin layer of NiO between the n-type ZnO and the p-type GaN will possibly block the injection of electrons from the ZnO to the GaN. Moreover, the presence of NiO buffer layer might create the confinement effect.

Novel approach for III-N on Si (111) templates fabrication by low-temperature PA MBE using porous Si layer

NASA Astrophysics Data System (ADS)

Zolotukhin, D.; Seredin, P.; Lenshin, A.; Goloshchapov, D.; Mizerov, A.

2017-11-01

We report on successful growth of GaN nanorods by low-temperature plasma-assisted molecular beam epitaxy on a Si(111) substrate with and without preformed thin porous Si layer (por-Si). The deposited GaN initially forms islands which act as a seed for the wires. Porous structure of the por-Si layer helps to control nucleation islands sizes and achieve homogeneous distribution of the nanorods diameters. In addition 850 nm-thick crack-free GaN layer was formed on Si(111) substrate with preformed por-Si layer.

Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

NASA Astrophysics Data System (ADS)

Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

2016-10-01

Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si.

PubMed

Tanaka, Atsunori; Choi, Woojin; Chen, Renjie; Dayeh, Shadi A

2017-10-01

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain-relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN-on-Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack-free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10 7 cm -2 achieved to date in GaN-on-Si is demonstrated. With these advances, the first vertical GaN metal-insulator-semiconductor field-effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost-effective high power device paradigm on an Si CMOS platform are demonstrated. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation.

PubMed

Hwang, Jih-Shang; Liu, Tai-Yan; Chattopadhyay, Surjit; Hsu, Geng-Ming; Basilio, Antonio M; Chen, Han-Wei; Hsu, Yu-Kuei; Tu, Wen-Hsun; Lin, Yan-Gu; Chen, Kuei-Hsien; Li, Chien-Cheng; Wang, Sheng-Bo; Chen, Hsin-Yi; Chen, Li-Chyong

2013-02-08

Enhanced photoelectrochemical (PEC) performances of Ga(2)O(3) and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga(2)O(3) and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga(2)O(3) NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga(2)O(3). These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga(2)O(3) NWs, or by incorporation of indium to form InGaN NWs.

Hafnium nitride buffer layers for growth of GaN on silicon

DOEpatents

Armitage, Robert D.; Weber, Eicke R.

2005-08-16

Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

Interface science of virtual GaN substrates on Si(111) via Sc2O3/Y2O3 buffers: Experiment and theory

NASA Astrophysics Data System (ADS)

Tarnawska, L.; Dabrowski, J.; Grzela, T.; Lehmann, M.; Niermann, T.; Paszkiewicz, R.; Storck, P.; Schroeder, T.

2013-06-01

The final film quality of GaN on foreign substrates is known to crucially depend on the initial GaN interface and nucleation characteristics. To shed light on these characteristics of recently pioneered virtual, hexagonal GaN(0001) substrates on Si(111) via step graded Sc2O3(111)/Y2O3(111) buffers, a complex GaN(0001)/Sc2O3(111) interface structure model and the initial nucleation scenario is derived from a combined experimental (reflection high energy electron diffraction and X-ray photoelectron spectroscopy) and theoretical ab initio study. It is shown that the GaN/Sc2O3 interface chemistry is determined by a N-Ga-O-Sc atomic arrangement leading to N-polar GaN films. However, the atomic GaN(0001)/Sc2O3(111) interface configuration is complex and local perturbations might be at the origin of Ga-polar inversion domains in the mainly N-polar GaN films. The initial growth of GaN on Sc2O3 is characterized by an ultrathin N-Ga-O-Sc wetting layer which carries tensile strain and relaxes with increasing thickness. Further GaN deposition results in the formation of 3D islands which fully relax before island coalescence occurs. The implications of the GaN/Sc2O3 interface configuration, the 3D nucleation growth mode, and the coalescence process of misaligned islands are discussed with respect to the defect characteristics (inversion domains, cubic inclusions, threading dislocations) of the final GaN layer.

Impurity distribution and microstructure of Ga-doped ZnO films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kvit, A. V.; Yankovich, A. B.; Avrutin, V.; Liu, H.; Izyumskaya, N.; Özgür, Ü.; Morkoç, H.; Voyles, P. M.

2012-12-01

We report microstructural characterization of heavily Ga-doped ZnO (GZO) thin films on GaN and sapphire by aberration-corrected scanning transmission electron microscopy. Growth under oxygen-rich and metal-rich growth conditions leads to changes in the GZO polarity and different extended defects. For GZO layers on sapphire, the primary extended defects are voids, inversion domain boundaries, and low-angle grain boundaries. Ga doping of ZnO grown under metal-rich conditions causes a switch from pure oxygen polarity to mixed oxygen and zinc polarity in small domains. Electron energy loss spectroscopy and energy dispersive spectroscopy spectrum imaging show that Ga is homogeneous, but other residual impurities tend to accumulate at the GZO surface and at extended defects. GZO grown on GaN on c-plane sapphire has Zn polarity and no voids. There are misfit dislocations at the interfaces between GZO and an undoped ZnO buffer layer and at the buffer/GaN interface. Low-angle grain boundaries are the only threading microstructural defects. The potential effects of different extended defects and impurity distributions on free carrier scattering are discussed.

Characterization of vertical GaN p-n diodes and junction field-effect transistors on bulk GaN down to cryogenic temperatures

NASA Astrophysics Data System (ADS)

Kizilyalli, I. C.; Aktas, O.

2015-12-01

There is great interest in wide-bandgap semiconductor devices and most recently in vertical GaN structures for power electronic applications such as power supplies, solar inverters and motor drives. In this paper the temperature-dependent electrical behavior of vertical GaN p-n diodes and vertical junction field-effect transistors fabricated on bulk GaN substrates of low defect density (104 to 106 cm-2) is described. Homoepitaxial MOCVD growth of GaN on its native substrate and the ability to control the doping in the drift layers in GaN have allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations as low as 1 × 1015 cm-3. This parameter range is suitable for applications requiring breakdown voltages of 1.2 kV to 5 kV. Mg, which is used as a p-type dopant in GaN, is a relatively deep acceptor (E A ≈ 0.18 eV) and susceptible to freeze-out at temperatures below 200 K. The loss of holes in p-GaN has a deleterious effect on p-n junction behavior, p-GaN contacts and channel control in junction field-effect transistors at temperatures below 200 K. Impact ionization-based avalanche breakdown (BV > 1200 V) in GaN p-n junctions is characterized between 77 K and 423 K for the first time. At higher temperatures the p-n junction breakdown voltage improves due to increased phonon scattering. A positive temperature coefficient in the breakdown voltage is demonstrated down to 77 K; however, the device breakdown characteristics are not as abrupt at temperatures below 200 K. On the other hand, contact resistance to p-GaN is reduced dramatically above room temperature, improving the overall device performance in GaN p-n diodes in all cases except where the n-type drift region resistance dominates the total forward resistance. In this case, the electron mobility can be deconvolved and is found to decrease with T -3/2, consistent with a phonon scattering model. Also, normally-on vertical junction field-effect transistors with BV = 1000 V and drain currents of 4 A are fabricated and characterized over the same temperature range. It is demonstrated that vertical GaN devices (diodes and transistors) utilizing p-n junctions are suitable for most practical applications including automotive ones (210 K < T < 423 K). While devices are functional at cryogenic temperatures (77 K) there may be some limitations to their performance due the freeze-out of Mg acceptors.

Resistivity control of unintentionally doped GaN films

NASA Astrophysics Data System (ADS)

Grzegorczyk, A. P.; Macht, L.; Hageman, P. R.; Rudzinski, M.; Larsen, P. K.

2005-05-01

GaN epilayers were grown on sapphire substrates via low temperature GaN and AlN nucleation layers (NL) by metalorganic chemical vapor phase epitaxy (MOCVD). The morphology of the individual NLs strongly depends on the carrier gas used during the growth and recrystallization and this is the key factor for control of the resistivity of the GaN layer grown on it. The GaN nucleation layer grown in presence of N2 has a higher density of islands with a statistically smaller diameter than the samples grown in H2 atmosphere. The NL grown in N2 enables the growth GaN with a sheet resistivity higher than 3×104 cm as opposed to a 0.5 cm value obtained for the NL grown in H2. Introduction of an additional intermediate (IL) low temperature (GaN or AlN) nucleation layer changes the GaN epilayer resistivity to about 50 cm, regardless of the carrier gas used during the growth of the IL. Defect selective etching demonstrated that control of the type and density of the dislocations in GaN enables the growth of highly resistive layers without any intentional acceptor doping (Mg, Zn). It will be demonstrated that by changing the ratio of edge type to screw dislocations the resistivity of the layer can be changed by a few orders of magnitude.

Formation of definite GaN p-n junction by Mg-ion implantation to n--GaN epitaxial layers grown on a high-quality free-standing GaN substrate

NASA Astrophysics Data System (ADS)

Oikawa, Takuya; Saijo, Yusuke; Kato, Shigeki; Mishima, Tomoyoshi; Nakamura, Tohru

2015-12-01

P-type conversion of n--GaN by Mg-ion implantation was successfully performed using high quality GaN epitaxial layers grown on free-standing low-dislocation-density GaN substrates. These samples showed low-temperature PL spectra quite similar to those observed from Mg-doped MOVPE-grown p-type GaN, consisting of Mg related donor-acceptor pair (DAP) and acceptor bound exciton (ABE) emission. P-n diodes fabricated by the Mg-ion implantation showed clear rectifying I-V characteristics and UV and blue light emissions were observed at forward biased conditions for the first time.

Undoped p-type GaN1-xSbx alloys: Effects of annealing

NASA Astrophysics Data System (ADS)

Segercrantz, N.; Baumgartner, Y.; Ting, M.; Yu, K. M.; Mao, S. S.; Sarney, W. L.; Svensson, S. P.; Walukiewicz, W.

2016-12-01

We report p-type behavior for undoped GaN1-xSbx alloys with x ≥ 0.06 grown by molecular beam epitaxy at low temperatures (≤400 °C). Rapid thermal annealing of the GaN1-xSbx films at temperatures >400 °C is shown to generate hole concentrations greater than 1019 cm-3, an order of magnitude higher than typical p-type GaN achieved by Mg doping. The p-type conductivity is attributed to a large upward shift of the valence band edge resulting from the band anticrossing interaction between localized Sb levels and extended states of the host matrix.

A Rapid Method for Deposition of Sn-Doped GaN Thin Films on Glass and Polyethylene Terephthalate Substrates

NASA Astrophysics Data System (ADS)

Pat, Suat; Özen, Soner; Korkmaz, Şadan

2018-01-01

We report the influence of Sn doping on microstructure, surface, and optical properties of GaN thin films deposited on glass and polyethylene terephthalate (PET) substrate. Sn-doped GaN thin films have been deposited by thermionic vacuum arc (TVA) at low temperature. TVA is a rapid deposition technology for thin film growth. Surface and optical properties of the thin films were presented. Grain size, height distribution, roughness values were determined. Grain sizes were calculated as 20 nm and 13 nm for glass and PET substrates, respectively. Nano crystalline forms were shown by field emission scanning electron microscopy. Optical band gap values were determined by optical methods and photoluminescence measurement. The optical band gap values of Sn doped GaN on glass and PET were determined to be approximately ˜3.40 eV and ˜3.47 eV, respectively. As a result, TVA is a rapid and low temperature deposition technology for the Sn doped GaN deposited on glass and PET substrate.

Optical properties of Mg doped p-type GaN nanowires

NASA Astrophysics Data System (ADS)

Patsha, Avinash; Pandian, Ramanathaswamy; Dhara, S.; Tyagi, A. K.

2015-06-01

Mg doped p-type GaN nanowires are grown using chemical vapor deposition technique in vapor-liquid-solid (VLS) process. Morphological and structural studies confirm the VLS growth process of nanowires and wurtzite phase of GaN. We report the optical properties of Mg doped p-type GaN nanowires. Low temperature photoluminescence studies on as-grown and post-growth annealed samples reveal the successful incorporation of Mg dopants. The as-grwon and annealed samples show passivation and activation of Mg dopants, respectively, in GaN nanowires.

Growth kinetics for temperature-controlled atomic layer deposition of GaN using trimethylgallium and remote-plasma-excited NH3

NASA Astrophysics Data System (ADS)

Pansila, P.; Kanomata, K.; Miura, M.; Ahmmad, B.; Kubota, S.; Hirose, F.

2015-12-01

Fundamental surface reactions in the atomic layer deposition of GaN with trimethylgallium (TMG) and plasma-excited NH3 are investigated by multiple-internal-reflection infrared absorption spectroscopy (MIR-IRAS) at surface temperatures varying from room temperature (RT) to 400 °C. It is found that TMG is saturated at RT on GaN surfaces when the TMG exposure exceeds 8 × 104 Langmuir (L), where 1 L corresponds to 1.33 × 10-4 Pa s (or 1.0 × 10-6 Torr s), and its saturation density reaches the maximum value at RT. Nitridation with the plasma-excited NH3 on the TMG-saturated GaN surface is investigated by X-ray photoelectron spectroscopy (XPS). The nitridation becomes effective at surface temperatures in excess of 100 °C. The reaction models of TMG adsorption and nitridation on the GaN surface are proposed in this paper. Based on the surface analysis, a temperature-controlled ALD process consisting of RT-TMG adsorption and nitridation at 115 °C is examined, where the growth per cycle of 0.045 nm/cycle is confirmed. XPS analysis indicates that all N atoms are bonded as GaN. Atomic force microscopy indicates an average roughness of 0.23 nm. We discuss the reaction mechanism of GaN ALD in the low-temperature region at around 115 °C with TMG and plasma-excited NH3.

Growth optimization toward low angle incidence microchannel epitaxy of GaN using ammonia-based metal-organic molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lin, Chia-Hung; Abe, Ryota; Uchiyama, Shota; Maruyama, Takahiro; Naritsuka, Shigeya

2012-08-01

Growth optimization toward low angle incidence microchannel epitaxy (LAIMCE) of GaN was accomplished using ammonia-based metal-organic molecular beam epitaxy (NH3-based MOMBE). Firstly, the [NH3]/[trimethylgallium (TMG)] ratio (R) dependence of selective GaN growth was studied. The growth temperature was set at 860 °C while R was varied from 5 to 200 with precursors being supplied parallel to the openings cut in the SiO2 mask. The selectivity of the growth was superior for all R, because TMG and NH3 preferably decompose on the GaN film. The formation of {112¯0}GaN or {112¯2}GaN sidewalls and (0001)GaN surface were observed by the change in R. The intersurface diffusion of Ga adatoms was also changed by a change in R. Ga adatoms migrate from the sidewalls to the top at R lower than 50, whereas the migration weakened with R greater than 100. Secondly, LAIMCE was optimized by changing the growth temperature. Consequently, 6 μm wide lateral overgrowth in the direction of precursor incidence was achieved with no pit after etching by H3PO4, which was six times wider than that in the opposite direction.

GaN microring waveguide resonators bonded to silicon substrate by a two-step polymer process.

PubMed

Hashida, Ryohei; Sasaki, Takashi; Hane, Kazuhiro

2018-03-20

Using a polymer bonding technique, GaN microring waveguide resonators were fabricated on a Si substrate for future hybrid integration of GaN and Si photonic devices. The designed GaN microring consisted of a rib waveguide having a core of 510 nm in thickness, 1000 nm in width, and a clad of 240 nm in thickness. A GaN crystalline layer of 1000 nm in thickness was grown on a Si(111) substrate by metal organic chemical vapor deposition using a buffer layer of 300 nm in thickness for the compensation of lattice constant mismatch between GaN and Si crystals. The GaN/Si wafer was bonded to a Si(100) wafer by a two-step polymer process to prevent it from trapping air bubbles. The bonded GaN layer was thinned from the backside by a fast atom beam etching to remove the buffer layer and to generate the rib waveguides. The transmission characteristics of the GaN microring waveguide resonators were measured. The losses of the straight waveguides were measured to be 4.0±1.7  dB/mm around a wavelength of 1.55 μm. The microring radii ranged from 30 to 60 μm, where the measured free-spectral ranges varied from 2.58 to 5.30 nm. The quality factors of the microring waveguide resonators were from 1710 to 2820.

Elimination of trench defects and V-pits from InGaN/GaN structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smalc-Koziorowska, Julita; Grzanka, Ewa; Czernecki, Robert

2015-03-09

The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defectsmore » were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits.« less

Atomic layer epitaxy of GaN over sapphire using switched metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Khan, M. A.; Skogman, R. A.; van Hove, J. M.; Olson, D. T.; Kuznia, J. N.

1992-03-01

In this letter the first switched atomic layer epitaxy (SALE) of single crystal GaN over basal plane sapphire substrates is reported. A low pressure metalorganic chemical vapor deposition (LPMOCVD) system was used for the epilayer depositions. In contrast to conventional LPMOCVD requiring temperatures higher than 700 C, the SALE process resulted in single crystal insulating GaN layers at growth temperatures ranging from 900 to 450 C. The band-edge transmission and the photoluminescence of the films from the SALE process were comparable to the best LPMOCVD films. As best as is known this is the first report of insulating GaN films which show excellent band-edge photoluminescence.

Atomic layer epitaxy of GaN over sapphire using switched metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Asif Khan, M.; Skogman, R. A.; Van Hove, J. M.; Olson, D. T.; Kuznia, J. N.

1992-03-01

In this letter we report the first switched atomic layer epitaxy (SALE) of single crystal GaN over basal plane sapphire substrates. A low pressure metalorganic chemical vapor deposition (LPMOCVD) system was used for the epilayer depositions. In contrast to conventional LPMOCVD requiring temperatures higher than 700 °C, the SALE process resulted in single crystal insulating GaN layers at growth temperatures ranging from 900 to 450 °C. The band-edge transmission and the photoluminescence of the films from the SALE process were comparable to the best LPMOCVD films. To the best of our knowledge this is the first report of insulating GaN films which show excellent band-edge photoluminescence.

Effect of strain on gallium nitride and gallium indium arsenide nitride growth and doping

NASA Astrophysics Data System (ADS)

G. S., Sudhir

GaN and the related (Al,In)N materials are currently used in manufacturing optoelectronic and electronic devices. However, the efficiency of these devices is limited due to lack of high structural quality and of low resistive p-type GaN. The GaN thin films are under strain during growth due to the large lattice mismatch, thermal expansion difference, and low growth temperature. Developing a better understanding of the effect of strain on the properties of thin films is important in furthering our knowledge of thin film growth affecting the performance of III-nitride based devices. Pulsed laser deposition was used to grow thin films of AlN and GaN on sapphire substrates. It is shown that the structure and surface morphology of layers are controlled by the nitrogen partial pressure during the growth. Through these nitrogen pressure related effects, thin films with microstructure ranging from crystalline to amorphous can be produced. A minimal surface root mean square roughness of 0.7 nm for amorphous AlN is obtained which compares well with the substrate roughness of 0.5 nm. Incorporation of impurities changes the lattice constants of thin films of GaN deposited on basal plane sapphire by molecular beam epitaxy. Both Mg (1017 cm-3) and Zn (3 x 10 20 cm-3) doping were found to expand the c lattice parameter by +0.38 x 10-2 and +0.62 x 10 -2, respectively. Oxygen up to concentrations 9 x 10 21 cm-3 is shown to replace nitrogen in GaN thin films reducing the c parameter only by a small amount. Incorporation of Si leads to a large decrease of the c parameter, which can not be attributed to the different size of Ga and Si. It is suggested that doping alters the film stoichiometry by a predicted Fermi level dependence of defect formation energies and thereby, lattice parameters and stress. A proper buffer layer design is shown to increase the incorporation of Mg by two orders of magnitude Finally, the balance of lattice parameter change caused by dopant and native point defects with strain contributed by growth condition leads to high mobility p-type GaN thin films. Incorporation of N in thin films of GaAsN and GaInAsN on GaAs was studied by molecular beam epitaxy. X-ray diffraction results indicated that the amount of N in GaAs increased with the power to plasma source and the slower growth rate, but was not affected by the growth temperature. Photoluminescence (PL) results showed a drastic narrowing of the bandgap with increased N incorporation. High pressure measurements showed the pressure coefficient of the absorption edge of 4 mum thick GaInAsN layer to be unusually small (51 meV/GPa). Also, the temperature-induced shift of the edge is reduced by 50% compared to that of GaAs. Based on the results of the detailed materials characterization, optimized p-GaAs/i-GaInAsN/n-GaAs structures were grown for I mum photo-detectors. The device characteristics of the prototype devices are presented.

Advanced Technologies for Heterodyne Radio Astronomy Instrumentation - Part1 By A. Pavolotsky, and Advanced Technologies for Heterodyne Radio Astronomy Instrumentation - Part2 By V. Desmaris

NASA Astrophysics Data System (ADS)

Desmaris, Vincent

2018-01-01

We present the advanced micro/nano technological engineering at the atomic level producing state-of-the-art epitaxial NbN thin-films on GaN buffer layers. Furthermore, we report the outstanding performance of the hot electron bolometers fabricated on epitaxial NbN thin films on GaN buffer layers. Finally we present advanced passive devices such as waveguide hybrids, IF hybrids and combiners for the realization of heterodyne THz receivers.

Epitaxial GaN layers formed on langasite substrates by the plasma-assisted MBE method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lobanov, D. N., E-mail: dima@ipmras.ru; Novikov, A. V.; Yunin, P. A.

2016-11-15

In this publication, the results of development of the technology of the epitaxial growth of GaN on single-crystal langasite substrates La{sub 3}Ga{sub 5}SiO{sub 14} (0001) by the plasma-assisted molecular-beam epitaxy (PA MBE) method are reported. An investigation of the effect of the growth temperature at the initial stage of deposition on the crystal quality and morphology of the obtained GaN layer is performed. It is demonstrated that the optimal temperature for deposition of the initial GaN layer onto the langasite substrate is about ~520°C. A decrease in the growth temperature to this value allows the suppression of oxygen diffusion frommore » langasite into the growing layer and a decrease in the dislocation density in the main GaN layer upon its subsequent high-temperature deposition (~700°C). Further lowering of the growth temperature of the nucleation layer leads to sharp degradation of the GaN/LGS layer crystal quality. As a result of the performed research, an epitaxial GaN/LGS layer with a dislocation density of ~10{sup 11} cm{sup –2} and low surface roughness (<2 nm) is obtained.« less

Microstructural study of Mg-doped p-type GaN: Correlation between high-resolution electron microscopy and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Tsen, S.-C. Y.; Smith, David J.; Tsen, K. T.; Kim, W.; Morkoç, H.

1997-12-01

A series of Mg-doped GaN films (˜1-1.3 μm) grown by reactive molecular beam epitaxy at substrate temperatures of 750 and 800 °C has been studied by high-resolution electron microscopy (HREM) and Raman spectroscopy. Stacking defects parallel to the substrate surface were observed in samples grown on sapphire substrates at 750 °C with AlN buffer layers (60-70 nm) at low Mg concentration. A transition region with mixed zinc-blende cubic (c) and wurtzite hexagonal (h) phases having the relative orientations of (111)c//(00.1)h and (11¯0)c//(10.0)h was observed for increased Mg concentration. The top surfaces of highly doped samples were rough and assumed a completely zinc-blende phase with some inclined stacking faults. Samples grown with a Mg cell temperature of 350 °C and high doping levels were highly disordered with many small crystals having inclined stacking faults, microtwins, and defective wurtzite and zinc-blende phases. Correlation between HREM and Raman scattering results points towards the presence of compressive lattice distortion along the growth direction which might be attributable to structural defects. The films grown at 800 °C had better quality with less observable defects and less yellow luminescence than samples grown at 750 °C.

Different annealing temperature suitable for different Mg doped P-GaN

NASA Astrophysics Data System (ADS)

Liu, S. T.; Yang, J.; Zhao, D. G.; Jiang, D. S.; Liang, F.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Li, X.; Liu, W.; Zhang, L. Q.; Long, H.; Li, M.

2017-04-01

In this work, epitaxial GaN with different Mg doping concentration annealed at different temperature is investigated. Through Hall and PL spectra measurement we found that when Mg doping concentration is different, different annealing temperature is needed for obtaining the best p-type conduction of GaN, and this difference comes from the different influence of annealing on compensated donors. For ultra-heavily Mg doped sample, the process of Mg related donors transferring to non-radiative recombination centers is dominated, so the performance of P-GaN deteriorates with temperature increase. But for low Mg doped sample, the process of Mg related donors transfer to non-raditive recombination is weak compare to the Mg acceptor activation, so along the annealing temperature increase the performance GaN gets better.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novikov, S. V.; Ting, M.; Yu, K. M.

In this paper we report our study on n-type Te doping of amorphous GaN 1-xAs x layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN 1-xAs x layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN 1-xAs x layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN 1-xAs x layers hasmore » been determined.« less

The origin of the residual conductivity of GaN films on ferroelectric materials

NASA Astrophysics Data System (ADS)

Lee, Kyoung-Keun; Cai, Zhuhua; Ziemer, Katherine; Doolittle, William Alan

2009-08-01

In this paper, the origin of the conductivity of GaN films grown on ferroelectric materials was investigated using XPS, AES, and XRD analysis tools. Depth profiles confirmed the existence of impurities in the GaN film originating from the substrates. Bonding energy analysis from XPS and AES verified that oxygen impurities from the substrates were the dominant origin of the conductivity of the GaN film. Furthermore, Ga-rich GaN films have a greater chance of enhancing diffusion of lithium oxide from the substrates, resulting in more substrate phase separation and a wider inter-mixed region confirmed by XRD. Therefore, the direct GaN film growth on ferroelectric materials causes impurity diffusion from the substrates, resulting in highly conductive GaN films. Future work needs to develop non-conductive buffer layers for impurity suppression in order to obtain highly resistive GaN films.

Electron spin relaxation in two polymorphic structures of GaN

NASA Astrophysics Data System (ADS)

Kang, Nam Lyong

2015-03-01

The relaxation process of electron spin in systems of electrons interacting with piezoelectric deformation phonons that are mediated through spin-orbit interactions was interpreted from a microscopic point of view using the formula for the electron spin relaxation times derived by a projection-reduction method. The electron spin relaxation times in two polymorphic structures of GaN were calculated. The piezoelectric material constant for the wurtzite structure obtained by a comparison with a previously reported experimental result was {{P}pe}=1.5 × {{10}29} eV {{m}-1}. The temperature and magnetic field dependence of the relaxation times for both wurtzite and zinc-blende structures were similar, but the relaxation times in zinc-blende GaN were smaller and decreased more rapidly with increasing temperature and magnetic field than that in wurtzite GaN. This study also showed that the electron spin relaxation for wurtzite GaN at low density could be explained by the Elliot-Yafet process but not for zinc-blende GaN in the metallic regime.

Tellurium n-type doping of highly mismatched amorphous GaN 1-xAs x alloys in plasma-assisted molecular beam epitaxy

DOE PAGES

Novikov, S. V.; Ting, M.; Yu, K. M.; ...

2014-10-01

In this paper we report our study on n-type Te doping of amorphous GaN 1-xAs x layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN 1-xAs x layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN 1-xAs x layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN 1-xAs x layers hasmore » been determined.« less

High thermal stability of abrupt SiO2/GaN interface with low interface state density

NASA Astrophysics Data System (ADS)

Truyen, Nguyen Xuan; Taoka, Noriyuki; Ohta, Akio; Makihara, Katsunori; Yamada, Hisashi; Takahashi, Tokio; Ikeda, Mitsuhisa; Shimizu, Mitsuaki; Miyazaki, Seiichi

2018-04-01

The effects of postdeposition annealing (PDA) on the interface properties of a SiO2/GaN structure formed by remote oxygen plasma-enhanced chemical vapor deposition (RP-CVD) were systematically investigated. X-ray photoelectron spectroscopy clarified that PDA in the temperature range from 600 to 800 °C has almost no effects on the chemical bonding features at the SiO2/GaN interface, and that positive charges exist at the interface, the density of which can be reduced by PDA at 800 °C. The capacitance-voltage (C-V) and current density-SiO2 electric field characteristics of the GaN MOS capacitors also confirmed the reduction in interface state density (D it) and the improvement in the breakdown property of the SiO2 film after PDA at 800 °C. Consequently, a high thermal stability of the SiO2/GaN structure with a low fixed charge density and a low D it formed by RP-CVD was demonstrated. This is quite informative for realizing highly robust GaN power devices.

Zero lattice mismatch and twin-free single crystalline ScN buffer layers for GaN growth on silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lupina, L.; Zoellner, M. H.; Dietrich, B.

2015-11-16

We report the growth of thin ScN layers deposited by plasma-assisted molecular beam epitaxy on Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3}/Si(111) substrates. Using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we find that ScN films grown at 600 °C are single crystalline, twin-free with rock-salt crystal structure, and exhibit a direct optical band gap of 2.2 eV. A high degree of crystalline perfection and a very good lattice matching between ScN and GaN (misfit < 0.1%) makes the ScN/Sc{sub 2}O{sub 3}/Y{sub 2}O{sub 3} buffer system a very promising template for the growth of high quality GaN layers on silicon.

Effect of substrate nitridation temperature on the persistent photoconductivity of unintentionally-doped GaN layer grown by PAMBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prakash, Nisha, E-mail: prakasnisha@gmail.com; Barvat, Arun; Anand, Kritika

2016-05-23

The surface roughness and defect density of GaN epitaxial layers grown on c-plane sapphire substrate are investigated and found to be dependent on nitridation temperature. GaN epitaxial layers grown after nitridation of sapphire at 200°C have a higher defect density and higher surface roughness compared to the GaN layers grown at 646°C nitridation as confirmed by atomic force microscopy (AFM). The persistent photoconductivity (PPC) was observed in both samples and it was found to be decreasing with decreasing temperature in the range 150-300°C due to long carrier lifetime and high electron mobility at low temperature. The photoresponse of the GaNmore » films grown in this study exhibit improved PPC due to their better surface morphology at 646°C nitrided sample. The point defects or extended microstructure defects limits the photocarrier lifetime and electron mobility at 200°C nitrided sample.« less

Nitride Semiconductors for Ultraviolet Detection

DTIC Science & Technology

1992-12-01

intrinsic n- and p-type doped GaN, (4) deposition of monocrystalline GaN via atomic layer epitaxy, (5) the initial conduct of studies regarding the ion...crystalline quality of the films; it indicated that all the films for x ranging from I to 0 to be monocrystalline . The Al/Ga composition ratios in the...shown in Figure 1. An analysis of these RHEED patterns indicated that both the AIN buffer layer and the GaN film are monocrystalline films. The RHEED

As-Grown Gallium Nitride Nanowire Electromechanical Resonators

NASA Astrophysics Data System (ADS)

Montague, Joshua R.

Technological development in recent years has led to a ubiquity of micro- and nano-scale electromechanical devices. Sensors for monitoring temperature, pressure, mass, etc., are now found in nearly all electronic devices at both the industrial and consumer levels. As has been true for integrated circuit electronics, these electromechanical devices have continued to be scaled down in size. For many nanometer-scale structures with large surface-to-volume ratio, dissipation (energy loss) becomes prohibitively large causing a decreasing sensitivity with decreasing sensor size. In this work, gallium nitride (GaN) nanowires are investigated as singly-clamped (cantilever) mechanical resonators with typical mechanical quality factors, Q (equal to the ratio of resonance frequency to peak full-width-at-half-maximum-power) and resonance frequencies, respectively, at or above 30,000, and near 1 MHz. These Q values---in vacuum at room temperature---indicate very low levels of dissipation; they are essentially the same as those for bulk quartz crystal resonators that form the basis of simple clocks and mass sensors. The GaN nanowires have lengths and diameters, respectively, of approximately 15 micrometers and hundreds of nanometers. As-grown GaN nanowire Q values are larger than other similarly-sized, bottom-up, cantilever resonators and this property makes them very attractive for use as resonant sensors. We demonstrate the capability of detecting sub-monolayer levels of atomic layer deposited (ALD) films, and the robust nature of the GaN nanowires structure that allows for their 'reuse' after removal of such layers. In addition to electron microscope-based measurement techniques, we demonstrate the successful capacitive detection of a single nanowire using microwave homodyne reflectometry. This technique is then extended to allow for simultaneous measurements of large ensembles of GaN nanowires on a single sample, providing statistical information about the distribution of individual nanowire properties. We observe nanowire-to-nanowire variations in the temperature dependence of GaN nanowire resonance frequency and in the observed mechanical dissipation. We also use this ensemble measurement technique to demonstrate unique, very low-loss resonance behavior at low temperatures. The low dissipation (and corresponding large Q values) observed in as-grown GaN nanowires also provides a unique opportunity for studying fundamental energy loss mechanisms in nano-scale objects. With estimated mass sensitivities on the level of zeptograms (10-21 g) in a one second averaging time, GaN nanowires may be a significant addition to the field of resonant sensors and worthy of future research and device integration.

Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

NASA Astrophysics Data System (ADS)

Yang, Liu; Changchun, Chai; Chunlei, Shi; Qingyang, Fan; Yuqian, Liu

2016-12-01

Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2 × 1016 to 5 × 1019 cm-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices. Project supported by the National Basic Research Program of China (No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (No. 2015-0214.XY.K).

MBE growth and optical properties of GaN layers on SiC/Si(111) hybrid substrate

NASA Astrophysics Data System (ADS)

Reznik, R. R.; Kotlyar, K. P.; Soshnikov, I. P.; Kukushkin, S. A.; Osipov, A. V.; Nikitina, E. V.; Cirlin, G. E.

2017-11-01

The fundamental possibility of the growth of GaN layers by molecular-beam epitaxy on a silicon substrate with nanoscale buffer layer of silicon carbide without any AlN layers has been demonstrated for the first time. Morphological properties of the resulting system have been studied.

Design of high breakdown voltage GaN vertical HFETs with p-GaN buried buffer layers for power switching applications

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Liu, Dong; Zhao, Ziqi; Bai, Zhiyuan; Li, Liang; Mo, Jianghui; Yu, Qi

2015-07-01

To achieve a high breakdown voltage, a GaN vertical heterostructure field effect transistor with p-GaN buried layers (PBL-VHFET) is proposed in this paper. The breakdown voltage of this GaN-based PBL-VHFET could be improved significantly by the optimizing thickness of p-GaN buried layers and doping concentration in PBL. When the GaN buffer layer thickness is 15 μm, the thickness, length and p-doping concentration of PBL are 0.3 μm, 2.7 μm, and 3 × 1017 cm-3, respectively. Simulation results show that the breakdown voltage and on-resistance of the device with two p-GaN buried layers are 3022 V and 3.13 mΩ cm2, respectively. The average breakdown electric field would reach as high as 201.5 V/μm. Compared with the typical GaN vertical heterostructure FETs without PBL, both of breakdown voltage and average breakdown electric field of device are increased more than 50%.

Backward diodes using heavily Mg-doped GaN growth by ammonia molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Okumura, Hironori; Martin, Denis; Malinverni, Marco; Grandjean, Nicolas

2016-02-01

We grew heavily Mg-doped GaN using ammonia molecular-beam epitaxy. The use of low growth temperature (740 °C) allows decreasing the incorporation of donor-like defects (<3 × 1017 cm-3) responsible for p-type doping compensation. As a result, a net acceptor concentration of 7 × 1019 cm-3 was achieved, and the hole concentration measured by Hall effect was as high as 2 × 1019 cm-3 at room temperature. Using such a high Mg doping level, we fabricated GaN backward diodes without polarization-assisted tunneling. The backward diodes exhibited a tunneling-current density of 225 A/cm2 at a reverse bias of -1 V at room temperature.

Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

NASA Astrophysics Data System (ADS)

Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

2008-12-01

Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

Fine structure of the red luminescence band in undoped GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reshchikov, M. A., E-mail: mreshchi@vcu.edu; Usikov, A.; Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics, 49 Kronverkskiy Ave., 197101 Saint Petersburg

2014-01-20

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RLmore » band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.« less

The investigation of stress in freestanding GaN crystals grown from Si substrates by HVPE.

PubMed

Lee, Moonsang; Mikulik, Dmitry; Yang, Mino; Park, Sungsoo

2017-08-17

We investigate the stress evolution of 400 µm-thick freestanding GaN crystals grown from Si substrates by hydride vapour phase epitaxy (HVPE) and the in situ removal of Si substrates. The stress generated in growing GaN can be tuned by varying the thickness of the MOCVD AlGaN/AlN buffer layers. Micro Raman analysis shows the presence of slight tensile stress in the freestanding GaN crystals and no stress accumulation in HVPE GaN layers during the growth. Additionally, it is demonstrated that the residual tensile stress in HVPE GaN is caused only by elastic stress arising from the crystal quality difference between Ga- and N-face GaN. TEM analysis revealed that the dislocations in freestanding GaN crystals have high inclination angles that are attributed to the stress relaxation of the crystals. We believe that the understanding and characterization on the structural properties of the freestanding GaN crystals will help us to use these crystals for high-performance opto-electronic devices.

Charge movement in a GaN-based hetero-structure field effect transistor structure with carbon doped buffer under applied substrate bias

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pooth, Alexander, E-mail: a.pooth@bristol.ac.uk; IQE; Uren, Michael J.

2015-12-07

Charge trapping and transport in the carbon doped GaN buffer of a GaN-based hetero-structure field effect transistor (HFET) has been investigated under both positive and negative substrate bias. Clear evidence of redistribution of charges in the carbon doped region by thermally generated holes is seen, with electron injection and capture observed during positive bias. Excellent agreement is found with simulations. It is shown that these effects are intrinsic to the carbon doped GaN and need to be controlled to provide reliable and efficient GaN-based power HFETs.

Method of growing GaN films with a low density of structural defects using an interlayer

DOEpatents

Bourret-Courchesne, Edith D.

2003-01-01

A dramatic reduction of the dislocation density in GaN was obtained by insertion of a single thin interlayer grown at an intermediate temperature (IT-IL) after the growth of an initial grown at high temperature. A description of the growth process is presented with characterization results aimed at understanding the mechanisms of reduction in dislocation density. A large percentage of the threading dislocations present in the first GaN epilayer are found to bend near the interlayer and do not propagate into the top layer which grows at higher temperature in a lateral growth mode. TEM studies show that the mechanisms of dislocation reduction are similar to those described for the epitaxial lateral overgrowth process, however a notable difference is the absence of coalescence boundaries.

Growth Temperature Dependence of Morphology of GaN Single Crystals in the Na-Li-Ca Flux Method

NASA Astrophysics Data System (ADS)

Wu, Xi; Hao, Hangfei; Li, Zhenrong; Fan, Shiji; Xu, Zhuo

2018-02-01

In this paper, the effect of growth temperature on the morphology and transparency of the GaN crystals obtained by the Li-Ca-added Na Flux method was studied. Addition of Li-Ca was attempted to control the growth habit and further improve transparency of GaN crystals. The samples with wurtzite structure of GaN were confirmed by the x-ray powder diffraction analysis. GaN single crystal with maximum size of about 6 mm was grown at 750°C. As the growth temperature was increased from 700°C to 850°C, the morphology of the crystals changed from pyramid to prism, and their surfaces became smooth. It was found that high growth temperature was beneficial to obtain a transparent crystal, but the evaporation of sodium would suppress its further growth. The E 2 (high) mode in the Raman spectra was at 568 cm-1, and the full-width at half-maximum values of this peak for the crystals obtained at 700°C, 750°C, 800°C, and 850°C were 7.5 cm-1, 10.3 cm-1, 4.4 cm-1, and 4.0 cm-1, respectively. It indicates that all the crystals are stress free and the transparent crystal grown at high temperature has high structural quality or low impurity concentrations.

Study on the structural, optical, and electrical properties of the yellow light-emitting diode grown on free-standing (0001) GaN substrate

NASA Astrophysics Data System (ADS)

Deng, Gaoqiang; Zhang, Yuantao; Yu, Ye; Yan, Long; Li, Pengchong; Han, Xu; Chen, Liang; Zhao, Degang; Du, Guotong

2018-04-01

In this paper, GaN-based yellow light-emitting diodes (LEDs) were homoepitaxially grown on free-standing (0001) GaN substrates by metal-organic chemical vapor deposition. X-ray diffraction (XRD), photoluminescence (PL), and electroluminescence (EL) measurements were conducted to investigate the structural, optical, and electrical properties of the yellow LED. The XRD measurement results showed that the InGaN/GaN multiple quantum wells (MQWs) in the LED structure have good periodicity because the distinct MQWs related higher order satellite peaks can be clearly observed from the profile of 2θ-ω XRD scan. The low temperature (10 K) and room temperature PL measurement results yield an internal quantum efficiency of 16% for the yellow LED. The EL spectra of the yellow LED present well Gaussian distribution with relatively low linewidth (47-55 nm), indicating the homogeneous In-content in the InGaN quantum well layers in the yellow LED structure. It is believed that this work will aid in the future development of GaN on GaN LEDs with long emission wavelength.

Ion channeling studies on mixed phases formed in metalorganic chemical vapor deposition grown Mg-doped GaN on Al2O3(0001)

NASA Astrophysics Data System (ADS)

Sundaravel, B.; Luo, E. Z.; Xu, J. B.; Wilson, I. H.; Fong, W. K.; Wang, L. S.; Surya, C.

2000-01-01

Rutherford backscattering spectrometry and ion channeling were used to determine the relative quantities of wurtzite and zinc-blende phases in metalorganic chemical vapor deposition grown Mg-doped GaN(0001) on an Al2O3(0001) substrate with a GaN buffer layer. Offnormal axial channeling scans were used. High-resolution x-ray diffraction measurements also confirmed the presence of mixed phases. The in-plane orientation was found to be GaN[11¯0]‖GaN[112¯0]‖Al2O3[112¯0]. The effects of rapid thermal annealing on the relative phase content, thickness and crystalline quality of the GaN epilayer were also studied.

GaN grown on nano-patterned sapphire substrates

NASA Astrophysics Data System (ADS)

Jing, Kong; Meixin, Feng; Jin, Cai; Hui, Wang; Huaibing, Wang; Hui, Yang

2015-04-01

High-quality gallium nitride (GaN) film was grown on nano-patterned sapphire substrates (NPSS) and investigated using XRD and SEM. It was found that the optimum thickness of the GaN buffer layer on the NPSS is 15 nm, which is thinner than that on micro-patterned sapphire substrates (MPSS). An interesting phenomenon was observed for GaN film grown on NPSS:GaN mainly grows on the trench regions and little grows on the sidewalls of the patterns at the initial growth stage, which is dramatically different from GaN grown on MPSS. In addition, the electrical and optical properties of LEDs grown on NPSS were characterized. Project supported by the Suzhou Nanojoin Photonics Co., Ltd and the High-Tech Achievements Transformation of Jiangsu Province, China (No.BA2012010).

Role of low-temperature AlGaN interlayers in thick GaN on silicon by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Fritze, S.; Drechsel, P.; Stauss, P.; Rode, P.; Markurt, T.; Schulz, T.; Albrecht, M.; Bläsing, J.; Dadgar, A.; Krost, A.

2012-06-01

Thin AlGaN interlayers have been grown into a thick GaN stack on Si substrates to compensate tensile thermal stress and significantly improve the structural perfection of the GaN. In particular, thicker interlayers reduce the density in a-type dislocations as concluded from x-ray diffraction (XRD) measurements. Beyond an interlayer thickness of 28 nm plastic substrate deformation occurs. For a thick GaN stack, the first two interlayers serve as strain engineering layers to obtain a crack-free GaN structure, while a third strongly reduces the XRD ω-(0002)-FWHM. The vertical strain and quality profile determined by several XRD methods demonstrates the individual impact of each interlayer.

III-nitride core–shell nanorod array on quartz substrates

PubMed Central

Bae, Si-Young; Min, Jung-Wook; Hwang, Hyeong-Yong; Lekhal, Kaddour; Lee, Ho-Jun; Jho, Young-Dahl; Lee, Dong-Seon; Lee, Yong-Tak; Ikarashi, Nobuyuki; Honda, Yoshio; Amano, Hiroshi

2017-01-01

We report the fabrication of near-vertically elongated GaN nanorods on quartz substrates. To control the preferred orientation and length of individual GaN nanorods, we combined molecular beam epitaxy (MBE) with pulsed-mode metal–organic chemical vapor deposition (MOCVD). The MBE-grown buffer layer was composed of GaN nanograins exhibiting an ordered surface and preferred orientation along the surface normal direction. Position-controlled growth of the GaN nanorods was achieved by selective-area growth using MOCVD. Simultaneously, the GaN nanorods were elongated by the pulsed-mode growth. The microstructural and optical properties of both GaN nanorods and InGaN/GaN core–shell nanorods were then investigated. The nanorods were highly crystalline and the core–shell structures exhibited optical emission properties, indicating the feasibility of fabricating III-nitride nano-optoelectronic devices on amorphous substrates. PMID:28345641

High Temperature Heterojunction Bipolar Transistors

DTIC Science & Technology

1994-04-15

Furthermore, p-type doping has only recently been announced in GaN,󈧒 and p-type conductivity had to be induced by irradiating Mg-doped GaN with a low ...confinement of the electron gas by a potential barrier should not be a problem even for low In concentrations. Although InN is not lattice matched to GaN...epitaxy.3 The films were grown by the reaction of Ga vapor with ECR-activated nitrogen . This study found that at low microwave power levels

Study on GaN nanostructures: Growth and the suppression of the yellow emission

NASA Astrophysics Data System (ADS)

Wang, Ting; Chen, Fei; Ji, Xiaohong; Zhang, Qinyuan

2018-07-01

GaN nanostructures were synthesized via a simple chemical vapor deposition using Ga2O3 and NH3 as precursors. Structural and morphological properties were systematically characterized by field emission scanning electron microscopy, X-ray diffractometer, transmission electron microscopy, and Raman spectroscopy. The configuration of GaN nanostructures was found to be strongly dependent on the growth temperature and the NH3 flow rate. Photoluminescence analysis revealed that all the fabricated GaN NSs exhibited a strong ultra-violet emission (∼364 nm), and the yellow emission of GaN nanorods can be suppressed at appropriate III/V ratio. The suppression of the yellow emission was attributed to the low density of surface or the VGa defect. The work demonstrates that the GaN nanostructures have potential applications in the optoelectronic and nanoelectronic devices.

From GaN to ZnGa(2)O(4) through a low-temperature process: nanotube and heterostructure arrays.

PubMed

Lu, Ming-Yen; Zhou, Xiang; Chiu, Cheng-Yao; Crawford, Samuel; Gradečak, Silvija

2014-01-22

We demonstrate a method to synthesize GaN-ZnGa2O4 core-shell nanowire and ZnGa2O4 nanotube arrays by a low-temperature hydrothermal process using GaN nanowires as templates. Transmission electron microscopy and X-ray photoelectron spectroscopy results show that a ZnGa2O4 shell forms on the surface of GaN nanowires and that the shell thickness is controlled by the time of the hydrothermal process and thus the concentration of Zn ions in the solution. Furthermore, ZnGa2O4 nanotube arrays were obtained by depleting the GaN core from GaN-ZnGa2O4 core-shell nanowire arrays during the reaction and subsequent etching with HCl. The GaN-ZnGa2O4 core-shell nanowires exhibit photoluminescence peaks centered at 2.60 and 2.90 eV attributed to the ZnGa2O4 shell, as well as peaks centered at 3.35 and 3.50 eV corresponding to the GaN core. We also demonstrate the synthesis of GaN-ZnGa2O4 heterojunction nanowires by a selective formation process as a simple route toward development of heterojunction nanodevices for optoelectronic applications.

Epitaxial growth of GaN by radical-enhanced metalorganic chemical vapor deposition (REMOCVD) in the downflow of a very high frequency (VHF) N2/H2 excited plasma - effect of TMG flow rate and VHF power

NASA Astrophysics Data System (ADS)

Lu, Yi; Kondo, Hiroki; Ishikawa, Kenji; Oda, Osamu; Takeda, Keigo; Sekine, Makoto; Amano, Hiroshi; Hori, Masaru

2014-04-01

Gallium nitride (GaN) films have been grown by using our newly developed Radical-Enhanced Metalorganic Chemical Vapor Deposition (REMOCVD) system. This system has three features: (1) application of very high frequency (60 MHz) power in order to increase the plasma density, (2) introduction of H2 gas together with N2 gas in the plasma discharge region to generate not only nitrogen radicals but also active NHx molecules, and (3) radical supply under remote plasma arrangement with suppression of charged ions and photons by employing a Faraday cage. Using this new system, we have studied the effect of the trimethylgallium (TMG) source flow rate and of the plasma generation power on the GaN crystal quality by using scanning electron microscopy (SEM) and double crystal X-ray diffraction (XRD). We found that this REMOCVD allowed the growth of epitaxial GaN films of the wurtzite structure of (0001) orientation on sapphire substrates with a high growth rate of 0.42 μm/h at a low temperature of 800 °C. The present REMOCVD is a promising method for GaN growth at relatively low temperature and without using costly ammonia gas.

Effect of SiC buffer layer on GaN growth on Si via PA-MBE

NASA Astrophysics Data System (ADS)

Kukushkin, S. A.; Mizerov, A. M.; Osipov, A. V.; Redkov, A. V.; Telyatnik, R. S.; Timoshnev, S. N.

2017-11-01

The study is devoted to comparison of GaN thin films grown on SiC/Si substrates made by the method of atoms substitution with the films grown directly on Si substrates. The growth was performed in a single process via plasma assisted molecular beam epitaxy. The samples were studied via optical microscopy, Raman spectroscopy, ellipsometry, and a comparison of their characteristics was made. Using chemical etching in KOH, the polarity of GaN films grown on SiC/Si and Si substrates was determined.

GaN growth via HVPE on SiC/Si substrates: growth mechanisms

NASA Astrophysics Data System (ADS)

Sharofidinov, Sh Sh; Redkov, A. V.; Osipov, A. V.; Kukushkin, S. A.

2017-11-01

The article focuses on the study of GaN thin film growth via chloride epitaxy on SiC/Si hybrid substrate. SiC buffer layer was grown by a method of substitution of atoms, which allows one to reduce impact of mechanical stress therein on subsequent growth of III-nitride films. It is shown, that change in GaN growth conditions leads to change in its growth mechanism. Three mechanisms: epitaxial, spiral and stepwise growth are considered and mechanical stresses are estimated via Raman spectroscopy.

Proximity Effects of Beryllium-Doped GaN Buffer Layers on the Electronic Properties of Epitaxial AlGaN/GaN Heterostructures

DTIC Science & Technology

2010-05-17

arranged by Prof. A. Zaslavsky Keywords: Gallium nitride High electron mobility transistor Molecular beam epitaxy Homoepitaxy Doping a b s t r a c t AlGaN...GaN/Be:GaN heterostructures have been grown by rf-plasma molecular beam epitaxy on free- standing semi-insulating GaN substrates, employing...hydride vapor phase epitaxy (HVPE) grown GaN sub- strates has enabled the growth by molecular beam epitaxy (MBE) of AlGaN/GaNHEMTswith significantly

Low-temperature preparation of GaN-SiO2 interfaces with low defect density. II. Remote plasma-assisted oxidation of GaN and nitrogen incorporation

NASA Astrophysics Data System (ADS)

Bae, Choelhwyi; Lucovsky, Gerald

2004-11-01

Low-temperature remote plasma-assisted oxidation and nitridation processes for interface formation and passivation have been extended from Si and SiC to GaN. The initial oxidation kinetics and chemical composition of thin interfacial oxide were determined from analysis of on-line Auger electron spectroscopy features associated with Ga, N, and O. The plasma-assisted oxidation process is self-limiting with power-law kinetics similar to those for the plasma-assisted oxidation of Si and SiC. Oxidation using O2/He plasma forms nearly pure GaOx, and oxidation using 1% N2O in N2 forms GaOxNy with small nitrogen content, ~4-7 at. %. The interface and dielectric layer quality was investigated using fabricated GaN metal-oxide-semiconductor capacitors. The lowest density of interface states was achieved with a two-step plasma-assisted oxidation and nitridation process before SiO2 deposition.

Ambient-temperature diffusion and gettering of Pt atoms in GaN with surface defect region under 60Co gamma or MeV electron irradiation

NASA Astrophysics Data System (ADS)

Hou, Ruixiang; Li, Lei; Fang, Xin; Xie, Ziang; Li, Shuti; Song, Weidong; Huang, Rong; Zhang, Jicai; Huang, Zengli; Li, Qiangjie; Xu, Wanjing; Fu, Engang; Qin, G. G.

2018-01-01

Generally, the diffusion and gettering of impurities in GaN needs high temperature. Calculated with the ambient-temperature extrapolation value of the high temperature diffusivity of Pt atoms in GaN reported in literature, the time required for Pt atoms diffusing 1 nm in GaN at ambient temperature is about 19 years. Therefore, the ambient-temperature diffusion and gettering of Pt atoms in GaN can hardly be observed. In this work, the ambient-temperature diffusion and gettering of Pt atoms in GaN is reported for the first time. It is demonstrated by use of secondary ion mass spectroscopy that in the condition of introducing a defect region on the GaN film surface by plasma, and subsequently, irradiated by 60Co gamma-ray or 3 MeV electrons, the ambient-temperature diffusion and gettering of Pt atoms in GaN can be detected. It is more obvious with larger irradiation dose and higher plasma power. With a similar surface defect region, the ambient-temperature diffusion and gettering of Pt atoms in GaN stimulated by 3 MeV electron irradiation is more marked than that stimulated by gamma irradiation. The physical mechanism of ambient-temperature diffusion and gettering of Pt atoms in a GaN film with a surface defect region stimulated by gamma or MeV electron irradiation is discussed.

Individual electron and hole localization in submonolayer InN quantum sheets embedded in GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feix, F., E-mail: feix@pdi-berlin.de; Flissikowski, T.; Chèze, C.

2016-07-25

We investigate sub-monolayer InN quantum sheets embedded in GaN(0001) by temperature-dependent photoluminescence spectroscopy under both continuous-wave and pulsed excitation. Both the peak energy and the linewidth of the emission band associated with the quantum sheets exhibit an anomalous dependence on temperature indicative of carrier localization. Photoluminescence transients reveal a power law decay at low temperatures reflecting that the recombining electrons and holes occupy spatially separate, individual potential minima reminiscent of conventional (In,Ga)N(0001) quantum wells exhibiting the characteristic disorder of a random alloy. At elevated temperatures, carrier delocalization sets in and is accompanied by a thermally activated quenching of the emission.more » We ascribe the strong nonradiative recombination to extended states in the GaN barriers and confirm our assumption by a simple rate-equation model.« less

Spectroscopic Ellipsometry Measurements of Wurtzite Gallium Nitride Surfaces as a Function of Buffered Oxide Etch Substrate Submersion

NASA Astrophysics Data System (ADS)

Szwejkowski, Chester; Constantin, Costel; Duda, John; Hopkins, Patrick; Optical Studies of GaN interfaces Collaboration

2013-03-01

Gallium nitride (GaN) is considered the most important semiconductor after the discovery of silicon. Understanding the optical properties of GaN surfaces is imperative in determining the utility and applicability of this class of materials to devices. In this work, we present preliminary results of spectroscopic ellipsometry measurements as a function of surface root mean square (RMS). We used commercially available 5mm x 5mm, one side polished GaN (3-7 μm)/Sapphire (430 μm) substrates that have a wurtzite crystal structure and they are slightly n-type doped. The GaN substrates were cleaned with Acetone (20 min)/Isopropanol(20 min)/DI water (20 min) before they were submerged into Buffered Oxide Etch (BOE) for 10s - 60s steps. This BOE treatment produced RMS values of 1-30 nm as measured with an atomic force microscope. Preliminary qualitative ellipsometric measurements show that the complex refractive index and the complex dielectric function decrease with an increase of RMS. More measurements need to be done in order to provide explicit quantitative results. This work was supported by the 4-VA Collaborative effort between James Madison University and University of Virginia.

Effects of GaN interlayer on the transport properties of lattice-matched AlInN/AlN/GaN heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, F.; Gao, K. H., E-mail: khgao@tju.edu.cn; Li, Z. Q.

2015-04-21

We study the effects of GaN interlayer on the transport properties of two-dimensional electron gases confined in lattice-matched AlInN/AlN/GaN heterostructures. It is found that the Hall mobility is evidently enhanced when an additional ultrathin GaN interlayer is introduced between AlInN and AlN layers. The enhancement of the Hall mobility is especially remarkable at low temperature. The high Hall mobility results in a low sheet resistance of 23 Ω/◻ at 2 K. Meanwhile, Shubnikov-de Haas oscillations (SdH) are also remarkably enhanced due to the existence of GaN interlayer. The enhancement of the SdH oscillations is related to the larger quantum mobility μ{sub q}more » owing to the suppression of the interface roughness, alloy disorder, and ionized impurity scatterings by the GaN interlayer.« less

Adsorption and desorption of hydrogen at nonpolar GaN (1 1 ¯ 00 ) surfaces: Kinetics and impact on surface vibrational and electronic properties

NASA Astrophysics Data System (ADS)

Lymperakis, L.; Neugebauer, J.; Himmerlich, M.; Krischok, S.; Rink, M.; Kröger, J.; Polyakov, V. M.

2017-05-01

The adsorption of hydrogen at nonpolar GaN (1 1 ¯00 ) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the GaN (1 1 ¯00 ) surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga-N surface dimer buckling. The signatures of the Ga-H and N-H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean GaN (1 1 ¯00 ) surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion.

Photoluminescence enhancement from GaN by beryllium doping

NASA Astrophysics Data System (ADS)

García-Gutiérrez, R.; Ramos-Carrazco, A.; Berman-Mendoza, D.; Hirata, G. A.; Contreras, O. E.; Barboza-Flores, M.

2016-10-01

High quality Be-doped (Be = 0.19 at.%) GaN powder has been grown by reacting high purity Ga diluted alloys (Be-Ga) with ultra high purity ammonia in a horizontal quartz tube reactor at 1200 °C. An initial low-temperature treatment to dissolve ammonia into the Ga melt produced GaN powders with 100% reaction efficiency. Doping was achieved by dissolving beryllium into the gallium metal. The powders synthesized by this method regularly consist of two particle size distributions: large hollow columns with lengths between 5 and 10 μm and small platelets in a range of diameters among 1 and 3 μm. The GaN:Be powders present a high quality polycrystalline profile with preferential growth on the [10 1 bar 1] plane, observed by means of X-ray diffraction. The three characteristics growth planes of the GaN crystalline phase were found by using high resolution TEM microscopy. The optical enhancing of the emission in the GaN powder is attributed to defects created with the beryllium doping. The room temperature photoluminescence emission spectra of GaN:Be powders, revealed the presence of beryllium on a shoulder peak at 3.39 eV and an unusual Y6 emission at 3.32eV related to surface donor-acceptor pairs. Also, a donor-acceptor-pair transition at 3.17 eV and a phonon replica transition at 3.1 eV were observed at low temperature (10 K). The well-known yellow luminescence band coming from defects was observed in both spectra at room and low temperature. Cathodoluminescence emission from GaN:Be powders presents two main peaks associated with an ultraviolet band emission and the yellow emission known from defects. To study the trapping levels related with the defects formed in the GaN:Be, thermoluminescence glow curves were obtained using UV and β radiation in the range of 50 and 150 °C.

Microstructural response of InGaN to swift heavy ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, L. M.; Jiang, W.; Fadanelli, R. C.

2016-12-01

A monocrystalline In0.18Ga0.82N film of ~275 nm in thickness grown on a GaN/Al 2O 3 substrate was irradiated with 290 MeV 238U 32+ ions to a fluence of 1.2 x 12 cm -2 at room temperature. The irradiated sample was characterized using helium ion microscopy (HIM), Rutherford backscattering spectrometry under ion-channeling conditions (RBS/C), and high-resolution x-ray diffraction (HRXRD). The irradiation leads to formation of ion tracks throughout the thin In 0.18Ga 0.82N film and the 3.0 µm thick GaN buffer layer. The mean diameter of the tracks in In 0.18Ga 0.82N is ~9 nm, as determined by HIM examination. Combinationmore » of the HIM and RBS/C data suggests that the material in the track is likely to be highly disordered or fully amorphized, in contrast to a crystalline structure within the ion track in GaN. Lattice relaxation in In0.18Ga0.82N and a distribution of d-spacing of the (0002) planes in GaN with lattice expansion are observed after irradiation.« less

GdN nanoisland-based GaN tunnel junctions.

PubMed

Krishnamoorthy, Sriram; Kent, Thomas F; Yang, Jing; Park, Pil Sung; Myers, Roberto C; Rajan, Siddharth

2013-06-12

Tunnel junctions could have a great impact on gallium nitride and aluminum nitride-based devices such as light-emitting diodes and lasers by overcoming critical challenges related to hole injection and p-contacts. This paper demonstrates the use of GdN nanoislands to enhance interband tunneling and hole injection into GaN p-n junctions by several orders of magnitude, resulting in low tunnel junction specific resistivity (1.3 × 10(-3) Ω-cm(2)) compared to the previous results in wide band gap semiconductors. Tunnel injection of holes was confirmed by low-temperature operation of GaN p-n junction with a tunneling contact layer, and strong electroluminescence down to 20 K. The low tunnel junction resistance combined with low optical absorption loss in GdN is very promising for incorporation in GaN-based light emitters.

Selective Area Sublimation: A Simple Top-down Route for GaN-Based Nanowire Fabrication.

PubMed

Damilano, B; Vézian, S; Brault, J; Alloing, B; Massies, J

2016-03-09

Post-growth in situ partial SiNx masking of GaN-based epitaxial layers grown in a molecular beam epitaxy reactor is used to get GaN selective area sublimation (SAS) by high temperature annealing. Using this top-down approach, nanowires (NWs) with nanometer scale diameter are obtained from GaN and InxGa1-xN/GaN quantum well epitaxial structures. After GaN regrowth on InxGa1-xN/GaN NWs resulting from SAS, InxGa1-xN quantum disks (QDisks) with nanometer sizes in the three dimensions are formed. Low temperature microphotoluminescence experiments demonstrate QDisk multilines photon emission around 3 eV with individual line widths of 1-2 meV.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calabrese, Gabriele, E-mail: calabrese@pdi-berlin.de; Corfdir, Pierre; Gao, Guanhui

We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pavemore » the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.« less

Structural, Electrical and Optical Properties of Sputtered-Grown InN Films on ZnO Buffered Silicon, Bulk GaN, Quartz and Sapphire Substrates

NASA Astrophysics Data System (ADS)

Bashir, Umar; Hassan, Zainuriah; Ahmed, Naser M.; Afzal, Naveed

2018-05-01

Indium nitride (InN) films were grown on Si (111), bulk GaN, quartz and sapphire substrates by radio frequency magnetron sputtering. Prior to the film deposition, a zinc oxide (ZnO) buffer layer was deposited on all the substrates. The x-ray diffraction patterns of InN films on ZnO-buffered substrates indicated c-plane-oriented films whereas the Raman spectroscopy results indicated A1 (LO) and E2 (high) modes of InN on all the substrates. The crystalline quality of InN was found to be better on sapphire and quartz than on the other substrates. The surface roughness of InN was studied using an atomic force microscope. The results indicated higher surface roughness of the film on sapphire as compared to the others; however, roughness of the film was lower than 8 nm on all the substrates. The electrical properties indicated higher electron mobility of InN (20.20 cm2/Vs) on bulk GaN than on the other substrates. The optical band gap of InN film was more than 2 eV in all the cases and was attributed to high carrier concentration in the film.

Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

NASA Astrophysics Data System (ADS)

Ueno, Kohei; Fudetani, Taiga; Arakawa, Yasuaki; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

2017-12-01

We report a systematic investigation of the transport properties of highly degenerate electrons in Ge-doped and Si-doped GaN epilayers prepared using the pulsed sputtering deposition (PSD) technique. Secondary-ion mass spectrometry and Hall-effect measurements revealed that the doping efficiency of PSD n-type GaN is close to unity at electron concentrations as high as 5.1 × 1020 cm-3. A record low resistivity for n-type GaN of 0.16 mΩ cm was achieved with an electron mobility of 100 cm2 V-1 s-1 at a carrier concentration of 3.9 × 1020 cm-3. We explain this unusually high electron mobility of PSD n-type GaN within the framework of conventional scattering theory by modifying a parameter related to nonparabolicity of the conduction band. The Ge-doped GaN films show a slightly lower electron mobility compared with Si-doped films with the same carrier concentrations, which is likely a consequence of the formation of a small number of compensation centers. The excellent electrical properties presented in this letter clearly demonstrate the striking advantages of the low-temperature PSD technique for growing high-quality and highly conductive n-type GaN.

Substrate impact on the low-temperature growth of GaN thin films by plasma-assisted atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kizir, Seda; Haider, Ali; Biyikli, Necmi, E-mail: biyikli@unam.bilkent.edu.tr

2016-07-15

Gallium nitride (GaN) thin films were grown on Si (100), Si (111), and c-plane sapphire substrates at 200 °C via hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD) using GaEt{sub 3} and N{sub 2}/H{sub 2} plasma as group-III and V precursors, respectively. The main aim of the study was to investigate the impact of substrate on the material properties of low-temperature ALD-grown GaN layers. Structural, chemical, and optical characterizations were carried out in order to evaluate and compare film quality of GaN on different substrates. X-ray reflectivity measurements showed film density values of 5.70, 5.74, and 5.54 g/cm{sup 3} for GaN grown on Simore » (100), Si (111), and sapphire, respectively. Grazing incidence x-ray diffraction measurements exhibited hexagonal wurtzite structure in all HCPA-ALD grown GaN samples. However, dominant diffraction peak for GaN films grown on Si and sapphire substrates were detected differently as (002) and (103), respectively. X-ray diffraction gonio scans measured from GaN grown on c-plane sapphire primarily showed (002) orientation. All samples exhibited similar refractive index values (∼2.17 at 632 nm) with 2–3 at. % of oxygen impurity existing within the bulk of the films. The grain size was calculated as ∼9–10 nm for GaN grown on Si (100) and Si (111) samples while it was ∼5 nm for GaN/sapphire sample. Root-mean-square surface roughness values found as 0.68, 0.76, and 1.83 nm for GaN deposited on Si (100), Si (111), and sapphire, respectively. Another significant difference observed between the samples was the film growth per cycle: GaN/sapphire sample showed a considerable higher thickness value when compared with GaN/Si samples, which might be attributed to a possibly more-efficient nitridation and faster nucleation of sapphire surface.« less

Effect of growth pressure on the morphology evolution and doping characteristics in nonpolar a-plane GaN

NASA Astrophysics Data System (ADS)

Song, Keun Man; Kim, Jong Min; Kang, Bong Kyun; Shin, Chan Soo; Ko, Chul Gi; Kong, Bo Hyun; Cho, Hyung Koun; Yoon, Dae Ho; Kim, Hogyoung; Hwang, Sung Min

2012-02-01

Nonpolar a-plane GaN layers grown on r-plane sapphire substrates were examined by using a two-step growth process. The higher initial growth pressure for the nucleation layer resulted in the improved crystalline quality with lower density of both threading dislocations and basal stacking faults. This was attributed to the higher degree of initial roughening and recovery time via a growth mode transition from three-dimensional (3D) to quasi two-dimensional (2D) lateral growth. Using Hall-effect measurements, the overgrown Si doped GaN layers grown with higher initial growth pressure were found to have higher mobility. The scattering mechanism due to the dislocations was dominant especially at low temperature (<200 K) for the lower initial growth pressure, which was insignificant for the higher initial growth pressure. The temperature-dependent Hall-effect measurements for the Mg doped GaN with a higher initial growth pressure yielded the activation energy and the acceptor concentration to be 128 meV and 1.2 × 1019 cm-3, respectively, corresponding to about 3.6% of activation at room temperature. Two-step growth scheme with a higher initial growth pressure is suggested as a potential method to improve the performance of nonpolar a-plane GaN based devices.

Mocvd Growth of Group-III Nitrides on Silicon Carbide: From Thin Films to Atomically Thin Layers

NASA Astrophysics Data System (ADS)

Al Balushi, Zakaria Y.

Group-III nitride semiconductors (AlN, GaN, InN and their alloys) are considered one of the most important class of materials for electronic and optoelectronic devices. This is not limited to the blue light-emitting diode (LED) used for efficient solid-state lighting, but other applications as well, such as solar cells, radar and a variety of high frequency power electronics, which are all prime examples of the technological importance of nitride based wide bandgap semiconductors in our daily lives. The goal of this dissertation work was to explore and establish new growth schemes to improve the structural and optical properties of thick to atomically thin films of group-III nitrides grown by metalorganic chemical vapor deposition (MOCVD) on SiC substrates for future novel devices. The first research focus of this dissertation was on the growth of indium gallium nitride (InGaN). This wide bandgap semiconductor has attracted much research attention as an active layer in LEDs and recently as an absorber material for solar cells. InGaN has superior material properties for solar cells due to its wavelength absorption tunability that nearly covers the entire solar spectrum. This can be achieved by controlling the indium content in thick grown material. Thick InGaN films are also of interest as strain reducing based layers for deep-green and red light emitters. The growth of thick films of InGaN is, however, hindered by several combined problems. This includes poor incorporation of indium in alloys, high density of structural and morphological defects, as well as challenges associated with the segregation of indium in thick films. Overcoming some of these material challenges is essential in order integrate thick InGaN films into future optoelectronics. Therefore, this dissertation research investigated the growth mechanism of InGaN layers grown in the N-polar direction by MOCVD as a route to improve the structural and optical properties of thick InGaN films. The growth of N-polar InGaN by MOCVD is challenging. These challenges arise from the lack of available native substrates suitable for N-polar film growth. As a result, InGaN layers are conventionally grown in the III-polar direction (i.e. III-polar InGaN) and typically grow under considerable amounts of stress on III-polar GaN base layers. While the structure-property relations of thin III-polar InGaN layers have been widely studied in quantum well structures, insight into the growth of thick films and N-polar InGaN layers have been limited. Therefore, this dissertation research compared the growth of both thick III-polar and N-polar InGaN films grown on optimized GaN base layers. III-polar InGaN films were rough and exhibited a high density of V-pits, while the growth of thick N-polar InGaN films showed improved structural quality and low surface roughness. The results of this dissertation work thereby provide an alternative route to the fabrication of thick InGaN films for potential use in solar cells as well as strain reducing schemes for deep-green and red light emitters. Moreover, this dissertation investigated stress relaxation in thick N-polar films using in situ reflectivity and curvature measurements. The results showed that stress relaxation in N-polar InGaN significantly differed from III-polar InGaN due to the absence of V-pits and it was hypothesized that plastic relaxation in N-polar InGaN could occur by dislocation glide, which typically is kinetically limited at such low growth temperatures required for InGaN. The second part of this dissertation research work focused on buffer free growth of GaN directly on SiC and on epitaxial graphene produced on SiC for potential vertical devices. The studies presented in this dissertation work on the growth of GaN directly on SiC compared the stress evolution of GaN films grown with and without an AlN buffer layer. Films grown directly on SiC showed reduced threading dislocation densities and improved surface roughness when compared to the growth of GaN on an AlN buffer layer. The dislocations in the GaN films grown di

Thermal buffering performance of composite phase change materials applied in low-temperature protective garments

NASA Astrophysics Data System (ADS)

Yang, Kai; Jiao, Mingli; Yu, Yuanyuan; Zhu, Xueying; Liu, Rangtong; Cao, Jian

2017-07-01

Phase change material (PCM) is increasingly being applied in the manufacturing of functional thermo-regulated textiles and garments. This paper investigated the thermal buffering performance of different composite PCMs which are suitable for the application in functional low-temperature protective garments. First, according to the criteria selecting PCM for functional textiles/garments, three kinds of pure PCM were selected as samples, which were n-hexadecane, n-octadecane and n-eicosane. To get the adjustable phase change temperature range and higher phase change enthalpy, three kinds of composite PCM were prepared using the above pure PCM. To evaluate the thermal buffering performance of different composite PCM samples, the simulated low-temperature experiments were performed in the climate chamber, and the skin temperature variation curves in three different low temperature conditions were obtained. Finally composite PCM samples’ thermal buffering time, thermal buffering capacity and thermal buffering efficiency were calculated. Results show that the comprehensive thermal buffering performance of n-octadecane and n-eicosane composite PCM is the best.

Temperature dependent growth of GaN nanowires using CVD technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Mukesh, E-mail: mukeshjihrnp@gmail.com; Singh, R.; Kumar, Vikram

2016-05-23

Growth of GaN nanowires have been carried out on sapphire substrates with Au as a catalyst using chemical vapour deposition technique. GaN nanowires growth have been studied with the experimental parameter as growth temperature. Diameter of grown GaN nanowires are in the range of 50 nm to 100 nm while the nanowire length depends on growth temperature. Morphology of the GaN nanowires have been studied by scanning electron microscopy. Crystalline nature has been observed by XRD patterns. Optical properties of grown GaN nanowires have been investigated by photoluminescence spectra.

Effect of the nand p-type Si(100) substrates with a SiC buffer layer on the growth mechanism and structure of epitaxial layers of semipolar AlN and GaN

NASA Astrophysics Data System (ADS)

Bessolov, V. N.; Grashchenko, A. S.; Konenkova, E. V.; Myasoedov, A. V.; Osipov, A. V.; Red'kov, A. V.; Rodin, S. N.; Rubets, V. P.; Kukushkin, S. A.

2015-10-01

A new effect of the n-and p-type doping of the Si(100) substrate with a SiC film on the growth mechanism and structure of AlN and GaN epitaxial layers has been revealed. It has been experimentally shown that the mechanism of AlN and GaN layer growth on the surface of a SiC layer synthesized by substituting atoms on n- and p-Si substrates is fundamentally different. It has been found that semipolar AlN and GaN layers on the SiC/Si(100) surface grow in the epitaxial and polycrystalline structures on p-Si and n-Si substrates, respectively. A new method for synthesizing epitaxial semipolar AlN and GaN layers by chloride-hydride epitaxy on silicon substrates has been proposed.

Yi-gan san restores behavioral alterations and a decrease of brain glutathione level in a mouse model of schizophrenia.

PubMed

Makinodan, Manabu; Yamauchi, Takahira; Tatsumi, Kouko; Okuda, Hiroaki; Noriyama, Yoshinobu; Sadamatsu, Miyuki; Kishimoto, Toshifumi; Wanaka, Akio

2009-01-01

The traditional Chinese herbal medicine yi-gan san has been used to cure neuropsychological disorders. Schizophrenia can be one of the target diseases of yi-gan san. We aimed at evaluating the possible use of yi-gan san in improving the schizophrenic symptoms of an animal model. Yi-gan san or distilled water was administered to mice born from pregnant mice injected with polyinosinic-polycytidilic acid or phosphate buffered saline. The former is a model of schizophrenia based on the epidemiological data that maternal infection leads to psychotic disorders including schizophrenia in the offspring. Prepulse inhibition and sensitivity to methamphetamine in open field tests were analyzed and the total glutathione content of whole brains was measured. Yi-gan san reversed the decrease in prepulse inhibition, hypersensitivity to methamphetamine and cognitive deficits found in the model mice to the level of control mice. Total glutathione content in whole brains was reduced in the model mice but was restored to normal levels by yi-gan san treatment. These results suggest that yi-gan san may have ameliorating effects on the pathological symptoms of schizophrenia.

Effect of annealing time and NH3 flow on GaN films deposited on amorphous SiO2 by MOCVD

NASA Astrophysics Data System (ADS)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Xu, Bingshe

2018-05-01

GaN polycrystalline films were successfully grown on amorphous SiO2 by metal-organic chemical vapour deposition to fabricate transferable devices using inorganic films. Field-emission scanning electron microscopy images show that by prolonging the annealing time, re-evaporation is enhanced, which reduced the uniformity of the nucleation layer and GaN films. X-ray diffraction patterns indicate that the decomposition rate of the nucleation layer increases when the annealing flow rate of NH3 is 500 sccm, which makes the unstable plane and amorphous domains decompose rapidly, thereby improving the crystallinity of the GaN films. Photoluminescence spectra also indicate the presence of fewer defects when the annealing flow rate of NH3 is 500 sccm. The excellent crystal structure of the GaN films grown under optimized conditions was revealed by transmission electron microscopy analysis. More importantly, the crystal structure and orientation of GaN grown on SiO2 are the same as that of GaN grown on conventional sapphire substrate when a buffer layer is used. This work can aid in the development of transferable devices using GaN films.

Synthesis and impurity doping of GaN powders by the two-stage vapor-phase method for phosphor applications

NASA Astrophysics Data System (ADS)

Hara, K.; Okuyama, E.; Yonemura, A.; Uchida, T.; Okamoto, N.

2006-09-01

The analysis of particle formation and the doping of luminescent impurities during the two-stage vapor-phase synthesis of GaN powder were carried. GaN particles were grown very fast during the second stage of this method, and the increment in particle size was larger for higher reaction temperature in the region between 800 and 1000 °C. The analysis on the behaviour of particle growth based on the reaction kinetics suggested that the growth almost finishes in a few seconds with an extremely high rate at the early stage at 1000 °C, whereas the growth lasts with relatively low rates for a time longer than the actual growth duration for the case of lower temperature synthesis. GaN powders doped with various impurity atoms were synthesized by supplying impurity sources with GaCl during the second stage. The samples doped with Zn, Mg and Tb showed emissions characteristic for each doped impurity.

In-situ transport and microstructural evolution in GaN Schottky diodes and epilayers exposed to swift heavy ion irradiation

NASA Astrophysics Data System (ADS)

Kumar, Ashish; Singh, R.; Kumar, Parmod; Singh, Udai B.; Asokan, K.; Karaseov, Platon A.; Titov, Andrei I.; Kanjilal, D.

2018-04-01

A systematic investigation of radiation hardness of Schottky barrier diodes and GaN epitaxial layers is carried out by employing in-situ electrical resistivity and cross sectional transmission electron microscopy (XTEM) microstructure measurements. The change in the current transport mechanism of Au/n-GaN Schottky barrier diodes due to irradiation is reported. The role of irradiation temperature and ion type was also investigated. Creation of damage is studied in low and medium electron energy loss regimes by selecting different ions, Ag (200 MeV) and O (100 MeV) at various fluences at two irradiation temperatures (80 K and 300 K). GaN resistivity increases up to 6 orders of magnitude under heavy Ag ions. Light O ion irradiation has a much lower influence on sheet resistance. The presence of isolated defect clusters in irradiated GaN epilayers is evident in XTEM investigation which is explained on the basis of the thermal spike model.

Optical spectroscopy of bulk GaN crystals grown from a Na-Ga melt

NASA Astrophysics Data System (ADS)

Skromme, B. J.; Palle, K. C.; Poweleit, C. D.; Yamane, H.; Aoki, M.; DiSalvo, F. J.

2002-11-01

Colorless transparent platelet and prismatic GaN crystals up to 3-4 mm, grown from a Na-Ga melt (0.6-0.7 mol fraction of Na) at temperatures of 700-800 °C in a modest (5 MPa) pressure of N2, are characterized using Raman scattering, room and low temperature photoluminescence, and reflectance. They exhibit sharp free and bound exciton luminescence features (down to 0.22 meV full width at half maximum), including multiple excited states. Residual Mg and Zn acceptors and a 33.6 meV donor (possibly ON) are identified. Raman spectra suggest free carrier concentrations down to the low to mid 1016 cm-3 range.

Non-equilibrium GaNAs Alloys with Band Gap Ranging from 0.8-3.4 eV

DTIC Science & Technology

2010-01-01

isova- lent atoms substitute more electronegative host atoms as occurs in the dilute N-rich GaN1-xAsx alloys. In this case due to the substantial...6]. In this study low temperature MBE (LT-MBE) has been employed to overcome the mis- cibility gap in the GaN1-xAsx, allowing the synthesis of GaN1...600 °C. The same active N flux with the total N beam equivalent pressure ( BEP ) ~1.5 10-5 Torr and the same deposition time (2hr) were used for the

Spoof plasmon waveguide enabled ultrathin room temperature THz GaN quantum cascade laser: a feasibility study.

PubMed

Sun, Greg; Khurgin, Jacob B; Tsai, Din Ping

2013-11-18

We propose and study the feasibility of a THz GaN/AlGaN quantum cascade laser (QCL) consisting of only five periods with confinement provided by a spoof surface plasmon (SSP) waveguide for room temperature operation. The QCL design takes advantages of the large optical phonon energy and the ultrafast phonon scattering in GaN that allow for engineering favorable laser state lifetimes. Our analysis has shown that the waveguide loss is sufficiently low for the QCL to reach its threshold at the injection current density around 6 kA/cm2 at room temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ruikang; Hu, Run, E-mail: hurun@hust.edu.cn, E-mail: luoxb@hust.edu.cn; Luo, Xiaobing, E-mail: hurun@hust.edu.cn, E-mail: luoxb@hust.edu.cn

In this study, we developed a first-principle-based full-dispersion Monte Carlo simulation method to study the anisotropic phonon transport in wurtzite GaN thin film. The input data of thermal properties in MC simulations were calculated based on the first-principle method. The anisotropy of thermal conductivity in bulk wurtzite GaN is found to be strengthened by isotopic scatterings and reduced temperature, and the anisotropy reaches 40.08% for natural bulk GaN at 100 K. With the GaN thin film thickness decreasing, the anisotropy of the out-of-plane thermal conductivity is heavily reduced due to both the ballistic transport and the less importance of the low-frequencymore » phonons with anisotropic group velocities. On the contrary, it is observed that the in-plane thermal conductivity anisotropy of the GaN thin film is strengthened by reducing the film thickness. And the anisotropy reaches 35.63% when the natural GaN thin film thickness reduces to 50 nm at 300 K with the degree of specularity being zero. The anisotropy is also improved by increasing the surface roughness of the GaN thin film.« less

Increase the threshold voltage of high voltage GaN transistors by low temperature atomic hydrogen treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erofeev, E. V., E-mail: erofeev@micran.ru; Fedin, I. V.; Kutkov, I. V.

High-electron-mobility transistors (HEMTs) based on AlGaN/GaN epitaxial heterostructures are a promising element base for the fabrication of high voltage electronic devices of the next generation. This is caused by both the high mobility of charge carriers in the transistor channel and the high electric strength of the material, which makes it possible to attain high breakdown voltages. For use in high-power switches, normally off-mode GaN transistors operating under enhancement conditions are required. To fabricate normally off GaN transistors, one most frequently uses a subgate region based on magnesium-doped p-GaN. However, optimization of the p-GaN epitaxial-layer thickness and the doping levelmore » makes it possible to attain a threshold voltage of GaN transistors close to V{sub th} = +2 V. In this study, it is shown that the use of low temperature treatment in an atomic hydrogen flow for the p-GaN-based subgate region before the deposition of gate-metallization layers makes it possible to increase the transistor threshold voltage to V{sub th} = +3.5 V. The effects under observation can be caused by the formation of a dipole layer on the p-GaN surface induced by the effect of atomic hydrogen. The heat treatment of hydrogen-treated GaN transistors in a nitrogen environment at a temperature of T = 250°C for 12 h reveals no degradation of the transistor’s electrical parameters, which can be caused by the formation of a thermally stable dipole layer at the metal/p-GaN interface as a result of hydrogenation.« less

High-electron-mobility GaN grown on free-standing GaN templates by ammonia-based molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kyle, Erin C. H., E-mail: erinkyle@umail.ucsb.edu; Kaun, Stephen W.; Burke, Peter G.

2014-05-21

The dependence of electron mobility on growth conditions and threading dislocation density (TDD) was studied for n{sup −}-GaN layers grown by ammonia-based molecular beam epitaxy. Electron mobility was found to strongly depend on TDD, growth temperature, and Si-doping concentration. Temperature-dependent Hall data were fit to established transport and charge-balance equations. Dislocation scattering was analyzed over a wide range of TDDs (∼2 × 10{sup 6} cm{sup −2} to ∼2 × 10{sup 10} cm{sup −2}) on GaN films grown under similar conditions. A correlation between TDD and fitted acceptor states was observed, corresponding to an acceptor state for almost every c lattice translation along each threading dislocation. Optimizedmore » GaN growth on free-standing GaN templates with a low TDD (∼2 × 10{sup 6} cm{sup −2}) resulted in electron mobilities of 1265 cm{sup 2}/Vs at 296 K and 3327 cm{sup 2}/Vs at 113 K.« less

A Compact Two-Stage 120 W GaN High Power Amplifier for SweepSAR Radar Systems

NASA Technical Reports Server (NTRS)

Thrivikraman, Tushar; Horst, Stephen; Price, Douglas; Hoffman, James; Veilleux, Louise

2014-01-01

This work presents the design and measured results of a fully integrated switched power two-stage GaN HEMT high-power amplifier (HPA) achieving 60% power-added efficiency at over 120Woutput power. This high-efficiency GaN HEMT HPA is an enabling technology for L-band SweepSAR interferometric instruments that enable frequent repeat intervals and high-resolution imagery. The L-band HPA was designed using space-qualified state-of-the-art GaN HEMT technology. The amplifier exhibits over 34 dB of power gain at 51 dBm of output power across an 80 MHz bandwidth. The HPA is divided into two stages, an 8 W driver stage and 120 W output stage. The amplifier is designed for pulsed operation, with a high-speed DC drain switch operating at the pulsed-repetition interval and settles within 200 ns. In addition to the electrical design, a thermally optimized package was designed, that allows for direct thermal radiation to maintain low-junction temperatures for the GaN parts maximizing long-term reliability. Lastly, real radar waveforms are characterized and analysis of amplitude and phase stability over temperature demonstrate ultra-stable operation over temperature using integrated bias compensation circuitry allowing less than 0.2 dB amplitude variation and 2 deg phase variation over a 70 C range.

Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

NASA Astrophysics Data System (ADS)

Zhang, Z.; Cardwell, D.; Sasikumar, A.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Arehart, A. R.; Ringel, S. A.

2016-04-01

The impact of proton irradiation on the threshold voltage (VT) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of VT was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 1014 cm-2. Silvaco Atlas simulations of VT shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different VT dependences on proton irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed VT shifts. The proton irradiation induced VT shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.

Study of Electrical Contacts and Devices in Advanced Semiconductors

NASA Technical Reports Server (NTRS)

Hall, H. P.; Das, K.; Alterovitz, Samuel (Technical Monitor)

2001-01-01

Research conducted at Tuskegee University concentrates on electrical contacts to GaN films and their characterization with the objective of understanding contact formation and realizing low-resistance metal contacts. Contact properties are known to be strongly related to surface preparation. It appears that the as-received material had a thin oxide film on the surface of the GaN film. Various cleaning treatments were employed in order to render the surface contamination free and removal of the oxide film. Metal films were then deposited by e-beam evaporation. Electrical characteristics of these contacts indicated that the optimal treatment was an organic solvent cleaning followed by etching in buffered oxide solution. Contacts established with Al were observed to be ohmic in nature, whereas Au, Cr, Ti, and Pt exhibit rectifying contacts. Platinum contacts were almost ideal as shown by an ideality factor of 1.02.

Microstructure and Optical Properties of Nonpolar m-Plane GaN Films Grown on m-Plane Sapphire by Hydride Vapor Phase Epitaxy

NASA Astrophysics Data System (ADS)

Wei, Tongbo; Duan, Ruifei; Wang, Junxi; Li, Jinmin; Huo, Ziqiang; Yang, Jiankun; Zeng, Yiping

2008-05-01

Thick nonpolar (1010) GaN layers were grown on m-plane sapphire substrates by hydride vapor phase epitaxy (HVPE) using magnetron sputtered ZnO buffers, while semipolar (1013) GaN layers were obtained by the conventional two-step growth method using the same substrate. The in-plane anisotropic structural characteristics and stress distribution of the epilayers were revealed by high resolution X-ray diffraction and polarized Raman scattering measurements. Atomic force microscopy (AFM) images revealed that the striated surface morphologies correlated with the basal plane stacking faults for both (1010) and (1013) GaN films. The m-plane GaN surface showed many triangular-shaped pits aligning uniformly with the tips pointing to the c-axis after etching in boiled KOH, whereas the oblique hillocks appeared on the semipolar epilayers. In addition, the dominant emission at 3.42 eV in m-plane GaN films displayed a red shift with respect to that in semipolar epilayers, maybe owing to the different strain states present in the two epitaxial layers.

Plasma-assisted MBE growth kinetics and characterization studies of wide bandgap III-V epitaxial materials

NASA Astrophysics Data System (ADS)

O'Steen, Mark Lee

2000-10-01

Scope and method of study. The purpose of this research was to understand the physics of RF plasma-assisted molecular beam epitaxial growth of GaN epitaxial films and InGaN/GaN superlattice structures grown on Al2O3 (0001) substrates. The techniques used to characterize the RF-MBE grown samples include in situ reflection high energy electron diffraction (RHEED) and optical pyrometry, and ex situ spatially-resolved high resolution X-ray diffraction, spatially-resolved reflectance spectroscopy, atomic force microscopy, and low-temperature photoluminescence (PL) spectroscopy. Findings and conclusions. RF plasma-assisted molecular beam epitaxy (RF-MBE) has been used to grow GaN epitaxial films and InGaN/GaN superlattice structures. The most important growth parameters in the growth of GaN epitaxial films were identified as the substrate temperature, incident N*/Ga flux ratio, and GaN growth rate. The effect of these growth parameters on GaN growth and quality of GaN epitaxial films is discussed. Additionally, an interpretation of the effects of growth conditions on the underlying microscopic growth processes occurring is presented. All of the observed GaN growth results may be understood in terms of these microscopic growth processes. InGaN/GaN superlattice samples are grown to identify and quantitatively access the InGaN growth phenomenology. It is inferred that InN requires a higher N*/III flux ratio than does GaN for stoichiometric growth. At substrate temperatures below 590°C, the In composition of the superlattice samples is nominally constant. However, in the narrow temperature range 590--670°C, the In composition decreases by more than an order-or-magnitude at the lowest N*/III flux ratio of this study. Additionally, the incident N*/III flux ratio is found to strongly influence the In composition as well. Nearly an order-of-magnitude increase in In composition is observed despite only a 20% increase in the N*/III flux ratio at the highest temperature of this study. RHEED and PL measurements support the assessment of the In reduction mechanism as thermally-activated surface-segregation and surface-desorption of In. Implications of these results for device growth are discussed.

Optimization of GaN Nanorod Growth Conditions for Coalescence Overgrowth

DTIC Science & Technology

2016-02-04

GaN core and QW deposition, an NR LED array can be implemented by covering the NRs with a transparent conductor . It has been demonstrated that the...with a transparent conductor . It has been demonstrated that the optical and electrical performances of an NR LED array can be comparable to those of a...a process of buffered oxide etching for removing this SiNx layer on the sidewalls is required before sidewall QW deposition. Nevertheless, the

Ion implantation damage, annealing and dopant activation in epitaxial gallium nitride

NASA Astrophysics Data System (ADS)

Suvkhanov, Agajan

2001-07-01

Successful n- and p-doping of GaN is an extremely important technological problem. More recently, ion implantation has been used to achieve both n- and p-type GaN. The ion implantation process is accompanied by the presence of radiation defects as the result of the ion-solid interactions. The temperatures (above 1000°C) required for recovery of the implantation induced damage and dopant activation strongly affect the GaN's surface integrity due to the significant nitrogen vapor pressure. Preservation of the surface integrity of GaN during high temperature post-implantation annealing is one of the key issues in the fabrication of GaN-based light-emitting devices. The radiation damage build-up in the implanted GaN layers has been investigated as a function of ion dose and the substrate's temperature. Results of measurements of structural damage by the Rutherford backscattering/Channeling (RBS/C) and the spectroscopic ellipsometry (SE) techniques have demonstrated the complex nature of the damage build-up. Analysis of GaN implanted at high temperature has demonstrated the presence of competing processes of layer-by-layer damage build-up and defect annihilation. Using a capping layer and annealing in a sealed quartz capsule filled with dry nitrogen can preserve the integrity of the GaN's surface. In this work the ion-implanted GaN samples were capped with 40 run MOCVD (Metal Organic Chemical Vapor Deposition) grown AlN film prior to annealing. The results of this work showed the advantage of high-temperature annealing of implanted GaN in a quartz capsule with nitrogen ambient, as compared with annealing in argon and nitrogen gas flow. Partial to complete decomposition of the AlN cap and underlying GaN has been observed by RBS/C and SEM (Scanning electron microscopy) for the samples annealed in flowing argon, as well as for the samples processed in flowing nitrogen. Encapsulation with nitrogen overpressure prevented the decomposition of the AlN capping film and the GaN crystal, and made it possible to achieve optical activation of the implanted Mg + and Si+ ions. PL measurements at 16 K of GaN samples implanted with Mg+ and annealed in a capsule showed three relatively strong peaks at 211, 303, and 395 meV from the band-edge emission. The relative intensity of the "yellow" band emission (i.e. defect band) was several times lower in the case of annealing in a sealed capsule as compared to that of open anneals in flowing argon or nitrogen. A separate set of specially-grown GaN samples was used for low temperature (1.8 K) PL analysis of the activation properties of Mg+-implanted and Mg+/P+-implanted samples. The samples were annealed in Rapid thermal processor (RTP) at 1300°C for 10 s with AlON encapsulation in flowing N2. The Mg+ implants showed good optical activation, producing a dose-correlated acceptor bound exciton peak with 12.2 meV localization energy, and donor-to-acceptor and band-to-acceptor peaks at 3.270 and 3.284 eV, respectively. The spectroscopic Mg acceptor binding energy was found to be 224 meV. A broad peak at 2.35 eV is attributed to implantation-induced defects stable in p-type material.

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

NASA Astrophysics Data System (ADS)

Hsiao, F.-M.; Schnedler, M.; Portz, V.; Huang, Y.-C.; Huang, B.-C.; Shih, M.-C.; Chang, C.-W.; Tu, L.-W.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.; Chiu, Y.-P.

2017-01-01

We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

Preparation of Graphene-Modified Acupuncture Needle and Its Application in Detecting Neurotransmitters

PubMed Central

Tang, Lina; Du, Danxin; Yang, Fan; Liang, Zhong; Ning, Yong; Wang, Hua; Zhang, Guo-Jun

2015-01-01

We report a unique nanosensing platform by combining modern nanotechnology with traditional acupuncture needle to prepare graphene-modified acupuncture needle (G-AN), and using it for sensitive detection of neurotransmitters via electrochemistry. An electrochemical deposition method was employed to deposit Au nanoparticles (AuNPs) on the tip surface of the traditional acupuncture needle, while the other part of the needle was coated with insulation paste. Subsequently, the G-AN was obtained by cyclic voltammetry reduction of a graphene oxide solution on the surface of the AuNPs. To investigate the sensing property of the G-AN, pH dependence was measured by recording the open circuit potential in the various pH buffer solutions ranging from 2.0 to 10.0. What’s more, the G-AN was further used for detection of dopamine (DA) with a limit of detection of 0.24 μM. This novel G-AN exhibited a good sensitivity and selectivity, and could realize direct detection of DA in human serum. PMID:26112773

RBS/Channeling Studies of Swift Heavy Ion Irradiated GaN Layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sathish, N.; Dhamodaran, S.; Pathak, A. P.

2009-03-10

Epitaxial GaN layers grown by MOCVD on c-plane sapphire substrates were irradiated with 150 MeV Ag ions at a fluence of 5x10{sup 12} ions/cm{sup 2}. Samples used in this study are 2 {mu}m thick GaN layers, with and without a thin AlN cap-layer. Energy dependent RBS/Channeling measurements have been carried out on both irradiated and unirradiated samples for defects characterization. Observed results are compared and correlated with previous HRXRD, AFM and optical studies. The {chi}{sub min} values for unirradiated samples show very high value and the calculated defect densities are of the order of 10{sup 10} cm{sup -2} as expectedmore » in these samples. Effects of irradiation on these samples are different as initial samples had different defect densities. Epitaxial reconstruction of GaN buffer layer has been attributed to the observed changes, which are generally grown to reduce the strain between GaN and Sapphire.« less

Ultrathin silicon oxynitride layer on GaN for dangling-bond-free GaN/insulator interface.

PubMed

Nishio, Kengo; Yayama, Tomoe; Miyazaki, Takehide; Taoka, Noriyuki; Shimizu, Mitsuaki

2018-01-23

Despite the scientific and technological importance of removing interface dangling bonds, even an ideal model of a dangling-bond-free interface between GaN and an insulator has not been known. The formation of an atomically thin ordered buffer layer between crystalline GaN and amorphous SiO 2 would be a key to synthesize a dangling-bond-free GaN/SiO 2 interface. Here, we predict that a silicon oxynitride (Si 4 O 5 N 3 ) layer can epitaxially grow on a GaN(0001) surface without creating dangling bonds at the interface. Our ab initio calculations show that the GaN/Si 4 O 5 N 3 structure is more stable than silicon-oxide-terminated GaN(0001) surfaces. The electronic properties of the GaN/Si 4 O 5 N 3 structure can be tuned by modifying the chemical components near the interface. We also propose a possible approach to experimentally synthesize the GaN/Si 4 O 5 N 3 structure.

Preparation of Graphene-Modified Acupuncture Needle and Its Application in Detecting Neurotransmitters

NASA Astrophysics Data System (ADS)

Tang, Lina; Du, Danxin; Yang, Fan; Liang, Zhong; Ning, Yong; Wang, Hua; Zhang, Guo-Jun

2015-06-01

We report a unique nanosensing platform by combining modern nanotechnology with traditional acupuncture needle to prepare graphene-modified acupuncture needle (G-AN), and using it for sensitive detection of neurotransmitters via electrochemistry. An electrochemical deposition method was employed to deposit Au nanoparticles (AuNPs) on the tip surface of the traditional acupuncture needle, while the other part of the needle was coated with insulation paste. Subsequently, the G-AN was obtained by cyclic voltammetry reduction of a graphene oxide solution on the surface of the AuNPs. To investigate the sensing property of the G-AN, pH dependence was measured by recording the open circuit potential in the various pH buffer solutions ranging from 2.0 to 10.0. What’s more, the G-AN was further used for detection of dopamine (DA) with a limit of detection of 0.24 μM. This novel G-AN exhibited a good sensitivity and selectivity, and could realize direct detection of DA in human serum.

Mechanisms of Loss in Internal Quantum Efficiency in III-Nitride-based Blue-and Green-Light Emitting Diodes

NASA Astrophysics Data System (ADS)

Huang, Li

The overarching goals of the research conducted for this dissertation have been to understand the scientific reasons for the losses in the internal quantum efficiency (IQE) in Group III-nitride-based blue and especially green light-emitting diodes (LEDs) containing a multi-quantum well (MQW) active region and to simultaneously develop LED epitaxial structures to ameliorate these losses. The p-type AlGaN EBL was determined to be both mandatory and effective in the prevention of electron overflow from the MQW region into the p-type cladding layer and the resultant lowering of the IQE. The overflow phenomenon was partially due to the low concentration (˜ 5 x 1017 cm-3) and mobility (˜ 10 cm2/(V•s)) of the holes injected into the active region. Electroluminescence (EL) studies of LEDs without an EBL revealed a dominant emission from donor-acceptor pair recombination in the p-type GaN layer. The incorporation of a 90 nm compositionally graded In0-0.1 Ga1-0.9N buffer layer between each MQW and n-GaN cladding layer grown on an Al/SiC substrate resulted in an increase in the luminescence intensity and a blue-shift in the emission wavelength, as observed in photoluminescence (PL) spectra. The graded InGaN buffer layer reduced the stress and thus the piezoelectric field across the MQW; this improved the electron/hole overlap that, in turn, resulted in an enhanced radiative recombination rate and an increase in efficiency. A direct correlation was observed between an increase in the IQE measured in temperature-dependent PL (TDPL) and an increase in the roughness of all the upper InGaN QW/GaN barrier interfaces, as determined using cross-sectional transmission electron microscopy of the MQW. These results agreed in general with the average surface roughness values of the pit-free region on the top GaN barrier determined via atomic force microscopy and the average roughness values of all the interfaces in the MQW calculated from the FWHM of the emission peak in the PL spectra acquired at 10 K for LED structures grown on both SiC and GaN substrates. This improvement occurred as a result of carrier localization at the rougher interfaces that, in turn, resulted in shorter carrier lifetimes and faster decay rates, as determined using time-resolved PL. The peak current densities determined from the curves of external quantum efficiency as a function of current density calculated from EL spectra acquired from a set of LEDs having 3 QWs, 5 QWs, and 6 QWs were 63 A/cm2, 78 A/cm2 and 78 A/cm2, respectively. These data indicated that the minority carrier (holes) in our powered devices penetrated into at least the 4th QW from the top p-type cladding layer. The peak emission from these LEDs occurred at 522 nm. The hole density decreased with distance away from the top p-type layer. Finally, a new process route was developed in this research for the epitaxial deposition of GaN(0001) thin films on chemo-mechanically polished GaN(0001) substrates. The latter possessed threading dislocations (TDs) having a density of the order of 5 x 107 cm-2, predominantly edge in character and oriented along [0001]. Step-flow-controlled growth of the films was achieved; thus, no additional TDs were generated at the film/substrate interface. The density of V-defects in InGaN films and in subsequently grown MQWs containing In0.26Ga0.74N wells grown on the GaN substrates was also reduced to within an order of 107 cm -2. The density of the latter defects was determined to be a function of both the density of the TDs and the growth temperature when the latter was > 900 °C. (Abstract shortened by UMI.)

Fabrication of full-color GaN-based light-emitting diodes on nearly lattice-matched flexible metal foils.

PubMed

Kim, Hyeryun; Ohta, Jitsuo; Ueno, Kohei; Kobayashi, Atsushi; Morita, Mari; Tokumoto, Yuki; Fujioka, Hiroshi

2017-05-18

GaN-based light-emitting diodes (LEDs) have been widely accepted as highly efficient solid-state light sources capable of replacing conventional incandescent and fluorescent lamps. However, their applications are limited to small devices because their fabrication process is expensive as it involves epitaxial growth of GaN by metal-organic chemical vapor deposition (MOCVD) on single crystalline sapphire wafers. If a low-cost epitaxial growth process such as sputtering on a metal foil can be used, it will be possible to fabricate large-area and flexible GaN-based light-emitting displays. Here we report preparation of GaN films on nearly lattice-matched flexible Hf foils using pulsed sputtering deposition (PSD) and demonstrate feasibility of fabricating full-color GaN-based LEDs. It was found that introduction of low-temperature (LT) grown layers suppressed the interfacial reaction between GaN and Hf, allowing the growth of high-quality GaN films on Hf foils. We fabricated blue, green, and red LEDs on Hf foils and confirmed their normal operation. The present results indicate that GaN films on Hf foils have potential applications in fabrication of future large-area flexible GaN-based optoelectronics.

Defect reduction of SiNx embedded m-plane GaN grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Woo, Seohwi; Kim, Minho; So, Byeongchan; Yoo, Geunho; Jang, Jongjin; Lee, Kyuseung; Nam, Okhyun

2014-12-01

Nonpolar (1 0 -1 0) m-plane GaN has been grown on m-plane sapphire substrates by hydride vapor phase epitaxy (HVPE). We studied the defect reduction of m-GaN with embedded SiNx interlayers deposited by ex-situ metal organic chemical vapor deposition (MOCVD). The full-width at half-maximum values of the X-ray rocking curves for m-GaN with embedded SiNx along [1 1 -2 0]GaN and [0 0 0 1]GaN were reduced to 528 and 1427 arcs, respectively, as compared with the respective values of 947 and 3170 arcs, of m-GaN without SiNx. Cross-section transmission electron microscopy revealed that the basal stacking fault density was decreased by approximately one order to 5×104 cm-1 due to the defect blocking of the embedded SiNx. As a result, the near band edge emission intensities of the room-temperature and low-temperature photoluminescence showed approximately two-fold and four-fold improvement, respectively.

Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bairamis, A.; Zervos, Ch.; Georgakilas, A., E-mail: alexandr@physics.uoc.gr

2014-09-15

AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10{sup 12} to 2.1 × 10{sup 13} cm{sup −2} as themore » AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10{sup 13} cm{sup −2} on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm{sup 2}/Vs for a density of 1.3 × 10{sup 13} cm{sup −2}. The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.« less

In-situ wafer bowing measurements of GaN grown on Si (111) substrate by reflectivity mapping in metal organic chemical vapor deposition system

NASA Astrophysics Data System (ADS)

Yang, Yi-Bin; Liu, Ming-Gang; Chen, Wei-Jie; Han, Xiao-Biao; Chen, Jie; Lin, Xiu-Qi; Lin, Jia-Li; Luo, Hui; Liao, Qiang; Zang, Wen-Jie; Chen, Yin-Song; Qiu, Yun-Ling; Wu, Zhi-Sheng; Liu, Yang; Zhang, Bai-Jun

2015-09-01

In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2″ Thomas Swan close coupled showerhead metal organic chemical vapor deposition (MOCVD) system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses (tensile and compressive) during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, GaN grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded AlGaN buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method. Project supported by the National Natural Science Foundation of China (Grant Nos. 61274039 and 51177175), the National Basic Research Program of China (Grant No. 2011CB301903), the Ph.D. Programs Foundation of Ministry of Education of China (Grant No. 20110171110021), the International Science and Technology Collaboration Program of China (Grant No. 2012DFG52260), the International Science and Technology Collaboration Program of Guangdong Province, China (Grant No. 2013B051000041), the Science and Technology Plan of Guangdong Province, China (Grant No. 2013B010401013), the National High Technology Research and Development Program of China (Grant No. 2014AA032606), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics, China (Grant No. IOSKL2014KF17).

Growth of blue GaN LED structures on 150-mm Si(1 1 1)

NASA Astrophysics Data System (ADS)

Dadgar, A.; Hums, C.; Diez, A.; Bläsing, J.; Krost, A.

2006-12-01

Up to 5.4-μm thick GaN on Si light emitting diode (LED) structures were grown by metalorganic chemical vapor phase epitaxy (MOVPE) on 150 mm Si(1 1 1) substrates. In-situ curvature measurements enable monitoring of stress development during growth and the influence of interlayers on strain balancing after cooling. In X-ray diffraction (XRD) ω-scans the GaN (0 0 0 2) reflection is about 380 arcsec and in θ-2 θ measurements the InGaN/GaN MQW interference peaks are well resolved indicating the high quality of the grown structure. In comparison to the growth on 2-in sapphire the wafer curvature after growth is low (>50 m) for the growth on Si and also during MQW growth at low temperatures a homogeneous wafer temperature can be achieved. The standard deviation of the wavelength over the whole 150-mm test wafer (5-mm edge exclusion) is <3.5 nm and reflects the three different heater zones of the MOVPE system used.

A study of the red-shift of a neutral donor bound exciton in GaN nanorods by hydrogenation

NASA Astrophysics Data System (ADS)

Park, Byung-Guon; Lee, Sang-Tae; Reddeppa, Maddaka; Kim, Moon-Deock; Oh, Jae-Eung; Lee, Sang-Kwon

2017-09-01

In this paper we account for the physics behind the exciton peak shift in GaN nanorods (NRs) due to hydrogenation. GaN NRs were selectively grown on a patterned Ti/Si(111) substrate using plasma-assisted molecular beam epitaxy, and the effect of hydrogenation on their optical properties was investigated in detail using low-temperature photoluminescence measurements. Due to hydrogenation, the emissions corresponding to the donor-acceptor pair and yellow luminescence in GaN NRs were strongly suppressed, while the emission corresponding to the neutral to donor bound exciton (D0X) exhibited red-shift. Thermal annealing of hydrogenated GaN NRs demonstrated the recovery of the D0X and deep level emission. To determine the nature of the D0X peak shift due to hydrogenation, comparative studies were carried out on various diameters of GaN NRs, which can be controlled by different growth conditions and wet-etching times. Our experimental results reveal that the D0X shift depends on the diameter of the GaN NRs after hydrogenation. The results clearly demonstrate that the hydrogenation leads to band bending of GaN NRs as compensated by hydrogen ions, which causes a red-shift in the D0X emission.

A study of the red-shift of a neutral donor bound exciton in GaN nanorods by hydrogenation.

PubMed

Park, Byung-Guon; Lee, Sang-Tae; Reddeppa, Maddaka; Kim, Moon-Deock; Oh, Jae-Eung; Lee, Sang-Kwon

2017-09-08

In this paper we account for the physics behind the exciton peak shift in GaN nanorods (NRs) due to hydrogenation. GaN NRs were selectively grown on a patterned Ti/Si(111) substrate using plasma-assisted molecular beam epitaxy, and the effect of hydrogenation on their optical properties was investigated in detail using low-temperature photoluminescence measurements. Due to hydrogenation, the emissions corresponding to the donor-acceptor pair and yellow luminescence in GaN NRs were strongly suppressed, while the emission corresponding to the neutral to donor bound exciton (D 0 X) exhibited red-shift. Thermal annealing of hydrogenated GaN NRs demonstrated the recovery of the D 0 X and deep level emission. To determine the nature of the D 0 X peak shift due to hydrogenation, comparative studies were carried out on various diameters of GaN NRs, which can be controlled by different growth conditions and wet-etching times. Our experimental results reveal that the D 0 X shift depends on the diameter of the GaN NRs after hydrogenation. The results clearly demonstrate that the hydrogenation leads to band bending of GaN NRs as compensated by hydrogen ions, which causes a red-shift in the D 0 X emission.

Growth kinetics and characterizations of gallium nitride thin films by remote PECVD

NASA Technical Reports Server (NTRS)

Choi, S. W.; Bachmann, K. J.; Lucovsky, G.

1993-01-01

Thin films of GaN have been deposited at relatively low growth temperatures by remote plasma-enhanced chemical-vapor deposition (RPECVD), using a plasma excited NH3, and trimethylgallium (TMG), injected downstream from the plasma. The activation energy for GaN growth has been tentatively assigned to the dissociation of NH groups as the primary N-atom precursors in the surface reaction with adsorbed TMG, or TMG fragments. At high He flow rates, an abrupt increase in the growth rate is observed and corresponds to a change in the reaction mechanism attributed to the formation of atomic N. XRD reveals an increased tendency to ordered growth in the (0001) direction with increasing growth temperature, He flow rate, and RF plasma power. IR spectra show the fundamental lattice mode of GaN at 530 cm without evidence for vibrational modes of hydrocarbon groups.

Uniformity of dc and rf performance of MBE-grown AlGaN/GaN HEMTS on HVPE-grown buffers

NASA Astrophysics Data System (ADS)

Gillespie, J. K.; Fitch, R. C.; Moser, N.; Jenkins, T.; Sewell, J.; Via, D.; Crespo, A.; Dabiran, A. M.; Chow, P. P.; Osinsky, A.; Mastro, M. A.; Tsvetkov, D.; Soukhoveev, V.; Usikov, A.; Dmitriev, V.; Luo, B.; Pearton, S. J.; Ren, F.

2003-10-01

AlGaN/GaN high electron mobility transistors (HEMTs) were grown by molecular beam epitaxy (MBE) on 2 in. diameter GaN buffer layers grown by hydride vapor epitaxy (HVPE) on sapphire substrates. HEMTs with 1 μm gate length displayed excellent dc and rf performance uniformity with up to 258 separate devices measured for each parameter. The drain-source saturation current was 561 mA with a standard deviation of 1.9% over the 2 in. diameter, with a corresponding transconductance of 118 ± 3.9 mS/mm. The threshold voltage was -5.3 ± 0.07 V. The rf performance uniformity was equally good, with an fT of 8.6 ± 0.8 GHz and fmax of 12.8 ± 2.5 GHz. The results show the excellent uniformity of the MBE technique for producing AlGaN/GaN HEMTs and also the ability of HVPE to provide high quality buffers at low cost.

P-type doping of GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wong, Raechelle Kimberly

2000-04-01

After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C.more » The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover.« less

CO2 detection using polyethylenimine/starch functionalized AlGaN /GaN high electron mobility transistors

NASA Astrophysics Data System (ADS)

Chang, C. Y.; Kang, B. S.; Wang, H. T.; Ren, F.; Wang, Y. L.; Pearton, S. J.; Dennis, D. M.; Johnson, J. W.; Rajagopal, P.; Roberts, J. C.; Piner, E. L.; Linthicum, K. J.

2008-06-01

AlGaN /GaN high electron mobility transistors (HEMTs) functionalized with polyethylenimine/starch were used for detecting CO2 with a wide dynamic range of 0.9%-50% balanced with nitrogen at temperatures from 46to220°C. Higher detection sensitivity to CO2 gas was achieved at higher testing temperatures. At a fixed source-drain bias voltage of 0.5V, drain-source current of the functionalized HEMTs showed a sublinear correlation upon exposure to different CO2 concentrations at low temperature. The superlinear relationship was at high temperature. The sensor exhibited a reversible behavior and a repeatable current change of 32 and 47μA with the introduction of 28.57% and 37.5% CO2 at 108°C, respectively.

Growth temperature optimization of GaAs-based In0.83Ga0.17As on InxAl1-xAs buffers

NASA Astrophysics Data System (ADS)

Chen, X. Y.; Gu, Y.; Zhang, Y. G.; Ma, Y. J.; Du, B.; Zhang, J.; Ji, W. Y.; Shi, Y. H.; Zhu, Y.

2018-04-01

Improved quality of gas source molecular beam epitaxy grown In0.83Ga0.17As layer on GaAs substrate was achieved by adopting a two-step InxAl1-xAs metamorphic buffer at different temperatures. With a high-temperature In0.83Al0.17As template following a low-temperature composition continuously graded InxAl1-xAs (x = 0.05-0.86) buffer, better structural, optical and electrical properties of succeeding In0.83Ga0.17As were confirmed by atomic force microscopy, photoluminescence and Hall-effect measurements. Cross-sectional transmission electron microscopy revealed significant effect of the two-step temperature grown InAlAs buffer layers on the inhibition of threading dislocations due to the deposition of high density nuclei on GaAs substrate at the low growth temperature. The limited reduction for the dark current of GaAs-based In0.83Ga0.17As photodetectors on the two-step temperature grown InxAl1-xAs buffer layers was ascribed to the contribution of impurities caused by the low growth temperature of InAlAs buffers.

Spatial identification of traps in AlGaN/GaN heterostructures by the combination of lateral and vertical electrical stress measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Anqi; Yang, Xuelin, E-mail: xlyang@pku.edu.cn; Cheng, Jianpeng

2016-01-25

We present a methodology and the corresponding experimental results to identify the exact location of the traps that induce hot electron trapping in AlGaN/GaN heterostructures grown on Si substrates. The methodology is based on a combination of lateral and vertical electrical stress measurements employing three ohmic terminals on the test sample structure with different GaN buffer designs. By monitoring the evolution of the lateral current during lateral as well as vertical stress application, we investigate the trapping/detrapping behaviors of the hot electrons and identify that the traps correlated with current degradation are in fact located in the GaN buffer layers.more » The trap activation energies (0.38–0.39 eV and 0.57–0.59 eV) extracted from either lateral or vertical stress measurements are in good agreement with each other, also confirming the identification. By further comparing the trapping behaviors in two samples with different growth conditions of an unintentionally doped GaN layer, we conclude that the traps are most likely in the unintentionally doped GaN layer but of different origins. It is suggested that the 0.38–0.39 eV trap is related to residual carbon incorporation while the 0.57–0.59 eV trap is correlated with native defects or complexes.« less

Red Light Emitting Schottky Diodes on p-TYPE GaN/AlN/Si(111) Substrate

NASA Astrophysics Data System (ADS)

Chuah, L. S.; Hassan, Z.; Abu Hassan, H.

High quality GaN layers doped with Mg were grown on Si(111) substrates using high temperature AlN as buffer layer by radio-frequency molecular beam epitaxy. From the Hall measurements, fairly uniform high hole concentration as high as (4-5) × 1020 cm-3 throughout the GaN was achieved. The fabrication of the device is very simple. Nickel ohmic contacts and Schottky contacts using indium were fabricated on Mg-doped p-GaN films. The light emission has been obtained from these thin film electroluminescent devices. Thin film electroluminescent devices were operated under direct current bias. Schottky and ohmic contacts used as cathode and anode were employed in these investigations. Alternatively, two Schottky contacts could be probed as cathode and anode. Thin film electroluminescent devices were able to emit light. However, electrical and optical differences could be observed from the two different probing methods. The red light color could be observed when the potential between the electrodes was increased gradually under forward bias of 8 V at room temperature. Electrical properties of these thin film electroluminescent devices were characterized by current-voltage (I-V) system, the heights of barriers determined from the I-V measurements were found to be related to the electroluminescence.

Advances in Hydrogen, Carbon Dioxide, and Hydrocarbon Gas Sensor Technology Using GaN and ZnO-Based Devices

PubMed Central

Anderson, Travis; Ren, Fan; Pearton, Stephen; Kang, Byoung Sam; Wang, Hung-Ta; Chang, Chih-Yang; Lin, Jenshan

2009-01-01

In this paper, we review our recent results in developing gas sensors for hydrogen using various device structures, including ZnO nanowires and GaN High Electron Mobility Transistors (HEMTs). ZnO nanowires are particularly interesting because they have a large surface area to volume ratio, which will improve sensitivity, and because they operate at low current levels, will have low power requirements in a sensor module. GaN-based devices offer the advantage of the HEMT structure, high temperature operation, and simple integration with existing fabrication technology and sensing systems. Improvements in sensitivity, recoverability, and reliability are presented. Also reported are demonstrations of detection of other gases, including CO2 and C2H4 using functionalized GaN HEMTs. This is critical for the development of lab-on-a-chip type systems and can provide a significant advance towards a market-ready sensor application. PMID:22408548

Epitaxial Growth of GaN Films by Pulse-Mode Hot-Mesh Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Komae, Yasuaki; Yasui, Kanji; Suemitsu, Maki; Endoh, Tetsuo; Ito, Takashi; Nakazawa, Hideki; Narita, Yuzuru; Takata, Masasuke; Akahane, Tadashi

2009-07-01

Intermittent gas supplies for hot-mesh chemical vapor deposition (CVD) for the epitaxial growth of gallium nitride (GaN) films were investigated to improve film crystallinity and optical properties. The GaN films were deposited on SiC/Si(111) substrates using an alternating-source gas supply or an intermittent supply of source gases such as ammonia (NH3) and trimethylgallium (TMG) in hot-mesh CVD after deposition of an aluminum nitride (AlN) buffer layer. The AlN layer was deposited using NH3 and trimethylaluminum (TMA) on a SiC layer grown by carbonization of a Si substrate using propane (C3H8). GaN films were grown on the AlN layer by a reaction between NHx radicals generated on a ruthenium (Ru)-coated tungsten (W) mesh and TMG molecules. After testing various gas supply modes, GaN films with good crystallinity and surface morphology were obtained using an intermittent supply of TMG and a continuous supply of NH3 gas. An optimal interval for the TMG gas supply was also obtained for the apparatus employed.

A Hybrid Multi-gate Model of a Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) Device Incorporating GaN-substrate Thermal Boundary Resistance

DTIC Science & Technology

2012-10-01

right by a pitch (P) and subsequently summed to provide a multi-gate superimposed temperature distribution ( TMG (x)). An example is shown in figure...temperature rise over the coolant, or the difference between the centerline multi gate junction temperature on the upper surface ( TMG ,GaN(0)) of the GaN...TC coolant temperature (°C) TCP(x) cold plate temperature distribution (°C) TGaN(x,y) temperature distribution within GaN (°C) TMG (x) multiple gate

Improved performance of GaN based light emitting diodes with ex-situ sputtered AlN nucleation layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Shuo-Wei; Epistar Corporation, Hsinchu 300, Taiwan; Li, Heng

The crystal quality, electrical and optical properties of GaN based light emitting diodes (LEDs) with ex-situ sputtered physical vapor deposition (PVD) aluminum nitride (AlN) nucleation layers were investigated. It was found that the crystal quality in terms of defect density and x-ray diffraction linewidth was greatly improved in comparison to LEDs with in-situ low temperature GaN nucleation layer. The light output power was 3.7% increased and the reverse bias voltage of leakage current was twice on LEDs with ex-situ PVD AlN nucleation layers. However, larger compressive strain was discovered in LEDs with ex-situ PVD AlN nucleation layers. The study showsmore » the potential and constrain in applying ex-situ PVD AlN nucleation layers to fabricate high quality GaN crystals in various optoelectronics.« less

Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, J.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.

2015-02-07

The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, andmore » therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.« less

Deep traps in n-type GaN epilayers grown by plasma assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamyczek, P.; Placzek-Popko, E.; Zielony, E.

2014-01-14

In this study, we present the results of investigations on Schottky Au-GaN diodes by means of conventional DLTS and Laplace DLTS methods within the temperature range of 77 K–350 K. Undoped GaN layers were grown using the plasma-assisted molecular beam epitaxy technique on commercial GaN/sapphire templates. The quality of the epilayers was studied by micro-Raman spectroscopy (μ-RS) which proved the hexagonal phase and good crystallinity of GaN epilayers as well as a slight strain. The photoluminescence spectrum confirmed a high crystal quality by intense excitonic emission but it also exhibited a blue emission band of low intensity. DLTS signal spectra revealed themore » presence of four majority traps: two high-temperature and two low-temperature peaks. Using the Laplace DLTS method and Arrhenius plots, the apparent activation energy and capture cross sections were obtained. For two high-temperature majority traps, they were equal to E{sub 1} = 0.65 eV, σ{sub 1} = 8.2 × 10{sup −16} cm{sup 2} and E{sub 2} = 0.58 eV, σ{sub 2} = 2.6 × 10{sup −15} cm{sup 2} whereas for the two low-temperature majority traps they were equal to E{sub 3} = 0.18 eV, σ{sub 3} = 9.7 × 10{sup −18} cm{sup 2} and E{sub 4} = 0.13 eV, σ{sub 4} = 9.2 × 10{sup −18} cm{sup 2}. The possible origin of the traps is discussed and the results are compared with data reported elsewhere.« less

Annealing of gallium nitride under high-N 2 pressure

NASA Astrophysics Data System (ADS)

Porowski, S.; Jun, J.; Krukowski, S.; Grzegory, I.; Leszczynski, M.; Suski, T.; Teisseyre, H.; Foxon, C. T.; Korakakis, D.

1999-04-01

GaN is the key material for blue and ultraviolet optoelectronics. It is a strongly bonded wurztite structure semiconductor with the direct energy gap 3.5 eV. Due to strong bonding, the diffusion processes require high temperatures, above 1300 K. However at this temperature range at ambient pressure, GaN becomes unstable and dissociates into Ga and N 2. Therefore high pressure of N 2 is required to study the diffusion and other annealing related processes. We studied annealing of bulk GaN nitride single crystals grown under high pressure and also annealing of homo- and heteroepitaxial GaN layers grown by MOCVD technique. Annealing at temperatures above 1300 K influences strongly the structural and optical properties of GaN crystals and layers. At this temperature diffusion of the Mg and Zn acceptors have been observed. In spite of very interesting experimental observations the understanding of microscopic mechanisms of these processes is limited.

Growth of semiconducting GaN hollow spheres and nanotubes with very thin shells via a controllable liquid gallium-gas interface chemical reaction.

PubMed

Yin, Long-Wei; Bando, Yoshio; Li, Mu-Sen; Golberg, Dmitri

2005-11-01

An in situ liquid gallium-gas interface chemical reaction route has been developed to synthesize semiconducting hollow GaN nanospheres with very small shell size by carefully controlling the synthesis temperature and the ammonia reaction gas partial pressure. In this process the gallium droplet does not act as a catalyst but rather as a reactant and a template for the formation of hollow GaN structures. The diameter of the synthesized hollow GaN spheres is typically 20-25 nm and the shell thickness is 3.5-4.5 nm. The GaN nanotubes obtained at higher synthesis temperatures have a length of several hundreds of nanometers and a wall thickness of 3.5-5.0 nm. Both the hollow GaN spheres and nanotubes are polycrystalline and are composed of very fine GaN nanocrystalline particles with a diameter of 3.0-3.5 nm. The room-temperature photoluminescence (PL) spectra for the synthesized hollow GaN spheres and nanotubes, which have a narrow size distribution, display a sharp, blue-shifted band-edge emission peak at 3.52 eV (352 nm) due to quantum size effects.

Wide-bandgap III-Nitride based Second Harmonic Generation

DTIC Science & Technology

2014-10-02

fabrication process for a GaN LPS. Fig. 1: 3-step Fabrication process of a GaN based lateral polar structure. ( a ) Growth of a 20 nm AlN buffer layer...etching of the LT-AlN stripes. This results are shown in Fig. 2 ( a ) and (b). Fig. 2: AFM images of KOH ( a ) and RIE (b) patterned templates for lateral ...was varied between 0.6 - 1.0. FIG. 3: Growth process of AlGaN based Lateral Polar Structures. ( a ) RIE patterning. (b) Growth of HT- AlN. (c

Synthesis and characterizations of nanoscale single crystal GaN grown by ion assisted gas source MBE

NASA Astrophysics Data System (ADS)

Cui, Bentao; Cohen, P. I.

2004-03-01

Nanoscale patterns could be induced by ion bombardment [1, 2]. In this study, an in-situ real time light scattering technique, combined with Reflection High Energy Electron Diffraction (RHEED), were used to study the surface morphology evolution during the ion beam assisted growth of GaN in a gas source MBE system. Ga was provided by a thermal effusion cell. Ammonia was used as the nitrogen source. A hot-filament Kaufman ion source was used to supply sub-KeV ion beams. Sapphire and MOCVD GaN templates were used as the substrates. A custom-designed Desorption Mass Spectrometer (DMS) was used to calibrate the growth temperature and determine the growth rate. Before growing GaN, the sapphire substrates were pretreated in an ion flux and then annealed for cleaning. The sapphire surface was then nitrided in ammonia at 1100K for about 10 min. After nitridation, a thin GaN buffer layer was prepared by a sequence of adsorption and annealing steps. During the growth, the short-range surface morphology and film quality were monitored in situ by RHEED. In a real-time way, the long-range surface morphology was monitored in-situ by light scattering technique. Photodiode array detector and CCD camera were used to record the reflected light scattering intensity and spectra profile respectively. Periodical patterns, such as ripple, have been observed during ion bombardment on GaN with or without growth. A linear theory (from Bradley and Harper 1988 [3]) has been modified to explain the dependence of ripple wavelength on ion species and ion energy. Partially supported by the National Science Foundation and the Air Force Office of Scientific Research. [1]. J. Erlebacher, M. J. Aziz, E. Chason, M. B. Sinclair, and J. A. Floro, Phys. Rev. Lett. 82, 2330 (1998); J. Erlebacher, M. J. Aziz, E. Chason, M. B. Sinclair, and J. A. Floro, Phys. Rev. Lett. 84, 5800 (2000). [2]. S. Facsko, T. Dekorsy, C. Koerdt, C. Trappe, H. Kurz, A. Vogt et al.. Science 285, 1551 (1999). [3]. R. M. Bradley and J. M. E. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988).

Growth of GaN micro/nanolaser arrays by chemical vapor deposition.

PubMed

Liu, Haitao; Zhang, Hanlu; Dong, Lin; Zhang, Yingjiu; Pan, Caofeng

2016-09-02

Optically pumped ultraviolet lasing at room temperature based on GaN microwire arrays with Fabry-Perot cavities is demonstrated. GaN microwires have been grown perpendicularly on c-GaN/sapphire substrates through simple catalyst-free chemical vapor deposition. The GaN microwires are [0001] oriented single-crystal structures with hexagonal cross sections, each with a diameter of ∼1 μm and a length of ∼15 μm. A possible growth mechanism of the vertical GaN microwire arrays is proposed. Furthermore, we report room-temperature lasing in optically pumped GaN microwire arrays based on the Fabry-Perot cavity. Photoluminescence spectra exhibit lasing typically at 372 nm with an excitation threshold of 410 kW cm(-2). The result indicates that these aligned GaN microwire arrays may offer promising prospects for ultraviolet-emitting micro/nanodevices.

Hexagonal Nanopyramidal Prisms of Nearly Intrinsic InN on Patterned GaN Nanowire Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golam Sarwar, A. T. M.; Leung, Benjamin; Wang, George T.

By using multiple growth steps that separate the nucleation and growth processes, we show that nearly intrinsic InN single nanocrystals of high optical quality can be formed on patterned GaN nanowire arrays by molecular beam epitaxy. The InN nanostructures form into well-defined hexagonal prisms with pyramidal tops. Micro-photoluminescence (μ-PL) is carried out at low temperature (LT: 28.2 K) and room temperature (RT: 285 K) to gauge the relative material quality of the InN nanostructures. Nanopyramidal prisms grown using a three-step growth method are found to show superior quantum efficiency. In conclusion, excitation and temperature dependent μ-PL demonstrates the very highmore » quality and nearly intrinsic nature of the ordered InN nanostructure arrays.« less

Hexagonal Nanopyramidal Prisms of Nearly Intrinsic InN on Patterned GaN Nanowire Arrays

DOE PAGES

Golam Sarwar, A. T. M.; Leung, Benjamin; Wang, George T.; ...

2018-01-04

By using multiple growth steps that separate the nucleation and growth processes, we show that nearly intrinsic InN single nanocrystals of high optical quality can be formed on patterned GaN nanowire arrays by molecular beam epitaxy. The InN nanostructures form into well-defined hexagonal prisms with pyramidal tops. Micro-photoluminescence (μ-PL) is carried out at low temperature (LT: 28.2 K) and room temperature (RT: 285 K) to gauge the relative material quality of the InN nanostructures. Nanopyramidal prisms grown using a three-step growth method are found to show superior quantum efficiency. In conclusion, excitation and temperature dependent μ-PL demonstrates the very highmore » quality and nearly intrinsic nature of the ordered InN nanostructure arrays.« less

Negligible carrier freeze-out facilitated by impurity band conduction in highly p-type GaN

NASA Astrophysics Data System (ADS)

Gunning, Brendan; Lowder, Jonathan; Moseley, Michael; Alan Doolittle, W.

2012-08-01

Highly p-type GaN films with hole concentrations exceeding 6 × 1019 cm-3 grown by metal-modulated epitaxy are electrically characterized. Temperature-dependent Hall effect measurements at cryogenic temperatures reveal minimal carrier freeze-out in highly doped samples, while less heavily doped samples exhibited high resistivity and donor-compensated conductivity as is traditionally observed. Effective activation energies as low as 43 meV were extracted, and a maximum Mg activation efficiency of 52% was found. In addition, the effective activation energy was found to be negatively correlated to the hole concentration. These results indicate the onset of the Mott-Insulator transition leading to impurity band conduction.

Diffusion and Stability of Hydrogen in Mg-Doped GaN: A Density Functional Study

NASA Astrophysics Data System (ADS)

Park, Ji-Sang; Chang, Kee Joo

2012-06-01

Using hybrid functional calculations, we study the diffusion and thermal stability of hydrogen in Mg-doped GaN. Compared with the generalized gradient approximation, we obtain a higher activation barrier for dissociating a Mg-H complex, which is attributed to the increase in the binding energy of Mg-H. Kinetic Monte Carlo simulations yield the annealing temperature of around 800 °C for activating Mg acceptors, close to the measured values. The results provide an insight to understanding the annealing effect such that the annealing temperature generally increases with the Mg-H concentration, and the retrapping of H is partly responsible for the low doping efficiencies at high Mg concentrations.

Enhancement of indium incorporation to InGaN MQWs on AlN/GaN periodic multilayers

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Hafiz, Shopan; Das, Saikat; Izyumskaya, Natalia; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

2016-02-01

The effect of compressive strain in buffer layer on strain relaxation and indium incorporation in InGaN multi-quantum wells (MQWs) is studied for two sets of samples grown side by side on both relaxed GaN layers and strained 10-pairs of AlN/GaN periodic multilayers. The 14-nm AlN layers were utilized in both multilayers, while GaN thickness was 4.5 and 2.5 nm in the first and the second set, respectively. The obtained results for the InGaN active layers on relaxed GaN and AlN/GaN periodic multilayers indicate enhanced indium incorporation for more relaxed InGaN active layers providing a variety of emission colors from purple to green.

Determination of axial and lateral exciton diffusion length in GaN by electron energy dependent cathodoluminescence

NASA Astrophysics Data System (ADS)

Hocker, Matthias; Maier, Pascal; Jerg, Lisa; Tischer, Ingo; Neusser, Gregor; Kranz, Christine; Pristovsek, Markus; Humphreys, Colin J.; Leute, Robert A. R.; Heinz, Dominik; Rettig, Oliver; Scholz, Ferdinand; Thonke, Klaus

2016-08-01

We demonstrate the application of low-temperature cathodoluminescence (CL) with high lateral, depth, and spectral resolution to determine both the lateral (i.e., perpendicular to the incident primary electron beam) and axial (i.e., parallel to the electron beam) diffusion length of excitons in semiconductor materials. The lateral diffusion length in GaN is investigated by the decrease of the GaN-related luminescence signal when approaching an interface to Ga(In)N based quantum well stripes. The axial diffusion length in GaN is evaluated from a comparison of the results of depth-resolved CL spectroscopy (DRCLS) measurements with predictions from Monte Carlo simulations on the size and shape of the excitation volume. The lateral diffusion length was found to be (95 ± 40) nm for nominally undoped GaN, and the axial exciton diffusion length was determined to be (150 ± 25) nm. The application of the DRCLS method is also presented on a semipolar (11 2 ¯ 2 ) sample, resulting in a value of (70 ± 10) nm in p-type GaN.

Growth and characterization of GaN nanostructures under various ammoniating time with fabricated Schottky gas sensor based on Si substrate

NASA Astrophysics Data System (ADS)

Abdullah, Q. N.; Ahmed, A. R.; Ali, A. M.; Yam, F. K.; Hassan, Z.; Bououdina, M.; Almessiere, M. A.

2018-05-01

This paper presents the investigation of the influence of the ammoniating time of GaN nanowires (NWs) on the crystalline structure, surface morphology, and optical characteristics. Morphological analysis indicates the growth of good quality and high density of NWs with diameters around 50 nm and lengths up to tens of microns after ammoniating for 30 min. Structural analysis shows that GaN NWs have a typical hexagonal wurtzite crystal structure. Raman spectroscopy confirms the formation of GaN compound with the presence of compressive stress. Photoluminescence (PL) measurements revealed two band emissions, an UV and a broad visible emission. Hydrogen sensor was subsequently fabricated by depositing Pt Schottky contact onto GaN NWs film. The sensor response was measured at various H2 concentrations ranged from 200 up to 1200 ppm at room temperature. It was found that the response increases significantly for low H2 concentration (200-300 ppm) to reach about 50% then increases smoothly to reach 60% at 1200 ppm. The as-fabricated sensor possesses higher performances as compared to similar devices reported in the literature.

Zero-phonon line and fine structure of the yellow luminescence band in GaN

NASA Astrophysics Data System (ADS)

Reshchikov, M. A.; McNamara, J. D.; Zhang, F.; Monavarian, M.; Usikov, A.; Helava, H.; Makarov, Yu.; Morkoç, H.

2016-07-01

The yellow luminescence band was studied in undoped and Si-doped GaN samples by steady-state and time-resolved photoluminescence. At low temperature (18 K), the zero-phonon line (ZPL) for the yellow band is observed at 2.57 eV and attributed to electron transitions from a shallow donor to a deep-level defect. At higher temperatures, the ZPL at 2.59 eV emerges, which is attributed to electron transitions from the conduction band to the same defect. In addition to the ZPL, a set of phonon replicas is observed, which is caused by the emission of phonons with energies of 39.5 meV and 91.5 meV. The defect is called the YL1 center. The possible identity of the YL1 center is discussed. The results indicate that the same defect is responsible for the strong YL1 band in undoped and Si-doped GaN samples.

Native defect-assisted enhanced response to CH4 near room temperature by Al0.07Ga0.93N nanowires.

PubMed

Parida, Santanu; Das, A; Prasad, Arun K; Ghatak, Jay; Dhara, Sandip

2018-06-26

Gas sensors at low operating temperature with high sensitivity require group III nitrides owing to their high chemical and thermal stabilities. For the first time, Al0.07Ga0.93N nanowires (NWs) have been utilized in CH4 sensing, and it has been demonstrated that they exhibit an improved response compared to GaN NWs at the low operating temperature of 50 °C. Al0.07Ga0.93N NWs have been synthesized via the ion beam mixing process using inert gas ion irradiation on the bilayer of Al/GaN NWs. The sensing mechanism is explained with the help of native defects present in the system. The number of shallow acceptors created by Ga vacancies (VGa) is found to be higher in Al0.07Ga0.93N NWs than in as-grown GaN NWs. The role of the O antisite defect (ON) for the formation of shallow VGa is inferred from photoluminescence spectroscopic analysis. These native defects strongly influence the gas sensing behaviour, which results in enhanced and low-temperature CH4 sensing.

Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chao; Cai, Yuefei; Liu, Zhaojun

2015-05-04

We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrownmore » n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme.« less

On the solubility of gallium nitride in supercritical ammonia-sodium solutions

NASA Astrophysics Data System (ADS)

Griffiths, Steven; Pimputkar, Siddha; Speck, James S.; Nakamura, Shuji

2016-12-01

Due to the disparity between observed gallium nitride (GaN) growth under conditions for which literature reports normal solubility, GaN solubility in supercritical NH3-Na containing solutions was re-evaluated. Isothermal gravimetric experiments on polycrystalline GaN were performed in the temperature range (T =415-650 °C) for which retrograde growth of GaN routinely occurs (P ≈ 200 MPa, molar NH3:Na fill ratio =20:1). Two previously-unreported error contributions to the gravimetric determination of GaN solubility were identified: Ga-alloying of exposed Ni-containing components, and the presence of a dense, Ga-absorbing Na-rich, second phase under these conditions. Due to the inability to measure Ga-alloying of the exposed autoclave wall for each experiment, considerable scatter was introduced in the refined GaN solubility curve. No clear dependence of GaN solubility on temperature was resolvable, while most solubility values were determined to be within a band of 0.03-0.10 mol% GaN, normalized by fill NH3.

Microstructures and growth mechanisms of GaN films epitaxially grown on AlN/Si hetero-structures by pulsed laser deposition at different temperatures.

PubMed

Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Zhou, Shizhong; Li, Guoqiang

2015-11-13

2 inch-diameter GaN films with homogeneous thickness distribution have been grown on AlN/Si(111) hetero-structures by pulsed laser deposition (PLD) with laser rastering technique. The surface morphology, crystalline quality, and interfacial property of as-grown GaN films are characterized in detail. By optimizing the laser rastering program, the ~300 nm-thick GaN films grown at 750 °C show a root-mean-square (RMS) thickness inhomogeneity of 3.0%, very smooth surface with a RMS surface roughness of 3.0 nm, full-width at half-maximums (FWHMs) for GaN(0002) and GaN(102) X-ray rocking curves of 0.7° and 0.8°, respectively, and sharp and abrupt AlN/GaN hetero-interfaces. With the increase in the growth temperature from 550 to 850 °C, the surface morphology, crystalline quality, and interfacial property of as-grown ~300 nm-thick GaN films are gradually improved at first and then decreased. Based on the characterizations, the corresponding growth mechanisms of GaN films grown on AlN/Si hetero-structures by PLD with various growth temperatures are hence proposed. This work would be beneficial to understanding the further insight of the GaN films grown on Si(111) substrates by PLD for the application of GaN-based devices.

Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth.

PubMed

Utsumi, Wataru; Saitoh, Hiroyuki; Kaneko, Hiroshi; Watanuki, Tetsu; Aoki, Katsutoshi; Shimomura, Osamu

2003-11-01

The synthesis of large single crystals of GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue-light-emitting diodes and lasers. Although high-quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N(2) at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melting of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred at about 2,220 degrees C, and decreasing the temperature allowed the GaN melt to crystallize to the original structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.

Local electronic and optical behavior of ELO a-plane GaN

NASA Astrophysics Data System (ADS)

Baski, A. A.; Moore, J. C.; Ozgur, U.; Kasliwal, V.; Ni, X.; Morkoc, H.

2007-03-01

Conductive atomic force microscopy (CAFM) and near-field optical microscopy (NSOM) were used to study a-plane GaN films grown via epitaxial lateral overgrowth (ELO). The ELO films were prepared by metal organic chemical vapor deposition on a patterned SiO2 layer with 4-μm wide windows, which was deposited on a GaN template grown on r-plane sapphire. The window regions of the coalesced ELO films appear as depressions with a high density of surface pits. At reverse bias below 12 V, very low uniform conduction (2 pA) is seen in the window regions. Above 20 V, a lower-quality sample shows localized sites inside the window regions with significant leakage, indicating a correlation between the presence of surface pits and leakage sites. Room temperature NSOM studies also suggest a greater density of surface terminated dislocations in the window regions, while wing regions explicitly show enhanced optical quality of the overgrown GaN. The combination of CAFM and NSOM data therefore indicates a correlation between the presence of surface pits, localized reverse-bias current leakage, and low PL intensity in the window regions.

Phase degradation in BxGa1-xN films grown at low temperature by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Gunning, Brendan P.; Moseley, Michael W.; Koleske, Daniel D.; Allerman, Andrew A.; Lee, Stephen R.

2017-04-01

Using metalorganic vapor phase epitaxy, a comprehensive study of BxGa1-xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750-900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to 7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stacking faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at 362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. Only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.

Correlation of proton irradiation induced threshold voltage shifts to deep level traps in AlGaN/GaN heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Z.; Cardwell, D.; Sasikumar, A.

2016-04-28

The impact of proton irradiation on the threshold voltage (V{sub T}) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of V{sub T} was found to increase monotonically as a function of 1.8 MeV proton fluence in a sub-linear manner reaching 0.63 V at a fluence of 1 × 10{sup 14} cm{sup −2}. Silvaco Atlas simulations of V{sub T} shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different V{sub T} dependences on protonmore » irradiation, confirming that deep, acceptor-like defects in the GaN buffer are primarily responsible for the observed V{sub T} shifts. The proton irradiation induced V{sub T} shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation.« less

ZnO nanorod arrays and direct wire bonding on GaN surfaces for rapid fabrication of antireflective, high-temperature ultraviolet sensors

NASA Astrophysics Data System (ADS)

So, Hongyun; Senesky, Debbie G.

2016-11-01

Rapid, cost-effective, and simple fabrication/packaging of microscale gallium nitride (GaN) ultraviolet (UV) sensors are demonstrated using zinc oxide nanorod arrays (ZnO NRAs) as an antireflective layer and direct bonding of aluminum wires to the GaN surface. The presence of the ZnO NRAs on the GaN surface significantly reduced the reflectance to less than 1% in the UV and 4% in the visible light region. As a result, the devices fabricated with ZnO NRAs and mechanically stable aluminum bonding wires (pull strength of 3-5 gf) showed higher sensitivity (136.3% at room temperature and 148.2% increase at 250 °C) when compared with devices with bare (uncoated) GaN surfaces. In addition, the devices demonstrated reliable operation at high temperatures up to 300 °C, supporting the feasibility of simple and cost-effective UV sensors operating with higher sensitivity in high-temperature conditions, such as in combustion, downhole, and space exploration applications.

Strain relaxation of thin Si{sub 0.6}Ge{sub 0.4} grown with low-temperature buffers by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, M.; Hansson, G. V.; Ni, W.-X.

A double-low-temperature-buffer variable-temperature growth scheme was studied for fabrication of strain-relaxed thin Si{sub 0.6}Ge{sub 0.4} layer on Si(001) by using molecular beam epitaxy (MBE), with particular focuses on the influence of growth temperature of individual low-temperature-buffer layers on the relaxation process and final structural qualities. The low-temperature buffers consisted of a 40 nm Si layer grown at an optimized temperature of {approx}400 deg. C, followed by a 20 nm Si{sub 0.6}Ge{sub 0.4} layer grown at temperatures ranging from 50 to 550 deg. C. A significant relaxation increase together with a surface roughness decrease both by a factor of {approx}2, accompaniedmore » with the cross-hatch/cross-hatch-free surface morphology transition, took place for the sample containing a low-temperature Si{sub 0.6}Ge{sub 0.4} layer that was grown at {approx}200 deg. C. This dramatic change was explained by the association with a certain onset stage of the ordered/disordered growth transition during the low-temperature MBE, where the high density of misfit dislocation segments generated near surface cusps largely facilitated the strain relaxation of the top Si{sub 0.6}Ge{sub 0.4} layer.« less

GaN: From three- to two-dimensional single-layer crystal and its multilayer van der Waals solids

NASA Astrophysics Data System (ADS)

Onen, A.; Kecik, D.; Durgun, E.; Ciraci, S.

2016-02-01

Three-dimensional (3D) GaN is a III-V compound semiconductor with potential optoelectronic applications. In this paper, starting from 3D GaN in wurtzite and zinc-blende structures, we investigated the mechanical, electronic, and optical properties of the 2D single-layer honeycomb structure of GaN (g -GaN ) and its bilayer, trilayer, and multilayer van der Waals solids using density-functional theory. Based on high-temperature ab initio molecular-dynamics calculations, we first showed that g -GaN can remain stable at high temperature. Then we performed a comparative study to reveal how the physical properties vary with dimensionality. While 3D GaN is a direct-band-gap semiconductor, g -GaN in two dimensions has a relatively wider indirect band gap. Moreover, 2D g -GaN displays a higher Poisson ratio and slightly less charge transfer from cation to anion. In two dimensions, the optical-absorption spectra of 3D crystalline phases are modified dramatically, and their absorption onset energy is blueshifted. We also showed that the physical properties predicted for freestanding g -GaN are preserved when g -GaN is grown on metallic as well as semiconducting substrates. In particular, 3D layered blue phosphorus, being nearly lattice-matched to g -GaN , is found to be an excellent substrate for growing g -GaN . Bilayer, trilayer, and van der Waals crystals can be constructed by a special stacking sequence of g -GaN , and they can display electronic and optical properties that can be controlled by the number of g -GaN layers. In particular, their fundamental band gap decreases and changes from indirect to direct with an increasing number of g -GaN layers.

Microstructures and growth mechanisms of GaN films epitaxially grown on AlN/Si hetero-structures by pulsed laser deposition at different temperatures

PubMed Central

Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Zhou, Shizhong; Li, Guoqiang

2015-01-01

2 inch-diameter GaN films with homogeneous thickness distribution have been grown on AlN/Si(111) hetero-structures by pulsed laser deposition (PLD) with laser rastering technique. The surface morphology, crystalline quality, and interfacial property of as-grown GaN films are characterized in detail. By optimizing the laser rastering program, the ~300 nm-thick GaN films grown at 750 °C show a root-mean-square (RMS) thickness inhomogeneity of 3.0%, very smooth surface with a RMS surface roughness of 3.0 nm, full-width at half-maximums (FWHMs) for GaN(0002) and GaN(102) X-ray rocking curves of 0.7° and 0.8°, respectively, and sharp and abrupt AlN/GaN hetero-interfaces. With the increase in the growth temperature from 550 to 850 °C, the surface morphology, crystalline quality, and interfacial property of as-grown ~300 nm-thick GaN films are gradually improved at first and then decreased. Based on the characterizations, the corresponding growth mechanisms of GaN films grown on AlN/Si hetero-structures by PLD with various growth temperatures are hence proposed. This work would be beneficial to understanding the further insight of the GaN films grown on Si(111) substrates by PLD for the application of GaN-based devices. PMID:26563573

Energy band structure and electrical properties of Ga-oxide/GaN interface formed by remote oxygen plasma

NASA Astrophysics Data System (ADS)

Yamamoto, Taishi; Taoka, Noriyuki; Ohta, Akio; Truyen, Nguyen Xuan; Yamada, Hisashi; Takahashi, Tokio; Ikeda, Mitsuhisa; Makihara, Katsunori; Nakatsuka, Osamu; Shimizu, Mitsuaki; Miyazaki, Seiichi

2018-06-01

The energy band structure of a Ga-oxide/GaN structure formed by remote oxygen plasma exposure and the electrical interface properties of the GaN metal–oxide–semiconductor (MOS) capacitors with the SiO2/Ga-oxide/GaN structures with postdeposition annealing (PDA) at various temperatures have been investigated. Reflection high-energy electron diffraction and X-ray photoelectron spectroscopy clarified that the formed Ga-oxide layer is neither a single nor polycrystalline phase with high crystallinity. We found that the energy band offsets at the conduction band minimum and at the valence band maximum between the Ga-oxide layer and the GaN surface were 0.4 and 1.2 ± 0.2 eV, respectively. Furthermore, capacitance–voltage (C–V) characteristics revealed that the interface trap density (D it) is lower than the evaluation limit of Terman method without depending on the PDA temperatures, and that the SiO2/Ga-oxide stack can work as a protection layer to maintain the low D it, avoiding the significant decomposition of GaN at the high PDA temperature of 800 °C.

Mg incorporation in GaN grown by plasma-assisted molecular beam epitaxy at high temperatures

NASA Astrophysics Data System (ADS)

Yang, W. C.; Lee, P. Y.; Tseng, H. Y.; Lin, C. W.; Tseng, Y. T.; Cheng, K. Y.

2016-04-01

The influence of growth conditions on the incorporation and activation of Mg in GaN grown by plasma-assisted molecular beam epitaxy at high growth temperature (>700 °C) is presented. It is found that the highest Mg incorporation with optimized electrical properties is highly sensitive both to the Mg/Ga flux ratio and III/V flux ratio. A maximum Mg activation of ~5% can be achieved at a growth temperature of 750 °C. The lowest resistivity achieved is 0.56 Ω-cm which is associated with a high hole mobility of 6.42 cm2/V-s and a moderately high hole concentration of 1.7×1018 cm-3. Although the highest hole concentration achieved in a sample grown under a low III/V flux ratio and a high Mg/Ga flux ratio reaches 7.5×1018 cm-3, the mobility is suffered due to the formation of defects by the excess Mg. In addition, we show that modulated beam growth methods do not enhance Mg incorporation at high growth temperature in contrast to those grown at a low temperature of 500 °C (Appl. Phys. Lett. 93, 172112, Namkoong et al., 2008 [19]).

Optimal activation condition of nonpolar a-plane p-type GaN layers grown on r-plane sapphire substrates by MOCVD

NASA Astrophysics Data System (ADS)

Son, Ji-Su; Hyeon Baik, Kwang; Gon Seo, Yong; Song, Hooyoung; Hoon Kim, Ji; Hwang, Sung-Min; Kim, Tae-Geun

2011-07-01

The optimal conditions of p-type activation for nonpolar a-plane (1 1 -2 0) p-type GaN films on r-plane (1 -1 0 2) sapphire substrates with various off-axis orientations have been investigated. Secondary ion mass spectrometry (SIMS) measurements show that Mg doping concentrations of 6.58×10 19 cm -3 were maintained in GaN during epitaxial growth. The samples were activated at various temperatures and periods of time in air, oxygen (O 2) and nitrogen (N 2) gas ambient by conventional furnace annealing (CFA) and rapid thermal annealing (RTA). The activation of nonpolar a-plane p-type GaN was successful in similar annealing times and temperatures when compared with polar c-plane p-type GaN. However, activation ambient of nonpolar a-plane p-type GaN was clearly different, where a-plane p-type GaN was effectively activated in air ambient. Photoluminescence shows that the optical properties of Mg-doped a-plane GaN samples are enhanced when activated in air ambient.

Synthesis and Raman scattering of GaN nanorings, nanoribbons and nanowires

NASA Astrophysics Data System (ADS)

Li, Z. J.; Chen, X. L.; Li, H. J.; Tu, Q. Y.; Yang, Z.; Xu, Y. P.; Hu, B. Q.

Low-dimensional GaN materials, including nanorings, nanoribbons and smooth nanowires have been synthesized by reacting gallium and ammonia using Ag particles as a catalyst on the substrate of MgO single crystals. They were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). EDX, XRD indicated that the low-dimensional nanomaterials were wurtzite GaN. New features are found in Raman scatterings for these low-dimensional GaN materials, which are different from the previous observations of GaN materials.

Development of III-nitride semiconductors by molecular beam epitaxy and cluster beam epitaxy and fabrication of LEDs based on indium gallium nitride MQWs

NASA Astrophysics Data System (ADS)

Chen, Tai-Chou Papo

The family of III-Nitrides (the binaries InN, GaN, AIN, and their alloys) is one of the most important classes of semiconductor materials. Of the three, Indium Nitride (InN) and Aluminum Nitride (AIN) have been investigated much less than Gallium Nitride (GaN). However, both of these materials are important for optoelectronic infrared and ultraviolet devices. In particular, since InN was found recently to be a narrow gap semiconductor (Eg=0.7eV), its development should extend the applications of nitride semiconductors to the spectral region appropriate to fiber optics communication and photovoltaic applications. Similarly, the development of AIN should lead to deep UV light emitting diodes (LEDs). The first part of this work addresses the evaluation of structural, optical and transport properties of InN films grown by two different deposition methods. In one method, active nitrogen was produced in the form of nitrogen radicals by a radio frequency (RF) plasma-assisted source. In an alternative method, active nitrogen was produced in the form of clusters containing approximately 2000 nitrogen molecules. These clusters were produced by adiabatic expansion from high stagnation pressure through a narrow nozzle into vacuum. The clusters were singly or doubly ionized with positive charge by electron impact and accelerated up to approximately 20 to 25 KV prior to their disintegration on the substrate. Due to the high local temperature produced during the impact of clusters with the substrate, this method is suitable for the deposition of InN at very low temperatures. The films are auto-doped n-type with carrier concentrations varying from 3 x 1018 to 1020 cm-3 and the electron effective mass of these films was determined to be 0.09m0. The majority of the AIN films was grown by the cluster beam epitaxy method and was doped n- and p- type by incorporating silicon (Si) and magnesium (Mg) during the film deposition. All films were grown under Al-rich conditions at relatively high temperatures (800˜1050°C) in order to increase the solubility of nitrogen into the free Al on the surface of the growing film. The films were found to have smooth surface morphology with narrow on-axis X-ray diffraction (XRD) rocking curves and relatively broad off-axis XRD rocking curves attributed to the lack of a buffer layer during the film growth. The device aspect of this work involves the material formation and the device fabrication of Indium Gallium Nitride (InGaN) based LEDs on textured GaN templates produced spontaneously by either hydride vapor phase epitaxy (HVPE) or using a method of natural lithography and reactive ion etching. This part of the work includes the film deposition and characterization of InGaNJGaN quantum wells on smooth and textured GaN template.

Mechanism of nucleation and growth of catalyst-free self-organized GaN columns by MOVPE

NASA Astrophysics Data System (ADS)

Wang, Xue; Li, Shunfeng; Fündling, Sönke; Wehmann, Hergo-H.; Strassburg, Martin; Lugauer, Hans-Jürgen; Steegmüller, Ulrich; Waag, Andreas

2013-05-01

The growth mechanism of catalyst-free self-organized GaN nuclei and three-dimensional columns on sapphire by metal organic vapour phase epitaxy (MOVPE) is investigated. Temperature- and time-dependent growth is performed. The growth behaviour can be characterized by two different kinetic regimes: mass-transport-limited growth and thermodynamically limited growth. The sum of activation energies for thermodynamic barrier of nucleation and for surface diffusion/mass-transport limitation, i.e. Whet +Ed, is 0.57 eV in the ‘low’-temperature region and 2.43 eV in the ‘high’-temperature region. GaN columns grown under the same conditions have very comparable height, which is not dependent on their diameter or the distance to other columns. Therefore, the growth rate is presumably limited by the incorporation rate on the top surface of columns. The height and diameter at the top of the GaN columns increase linearly with time and no height limit is observed. The GaN columns can reach more than 40 µm in height. Moreover, the investigated GaN columns are Ga-polar.

Thermal etching rate of GaN during MOCVD growth interruption in hydrogen and ammonia ambient determined by AlGaN/GaN superlattice structures

NASA Astrophysics Data System (ADS)

Zhang, Feng; Ikeda, Masao; Zhang, Shuming; Liu, Jianping; Tian, Aiqin; Wen, Pengyan; Cheng, Yang; Yang, Hui

2017-10-01

Thermal etching effect of GaN during growth interruption in the metalorganic chemical vapor deposition reactor was investigated in this paper. The thermal etching rate was determined by growing a series of AlGaN/GaN superlattice structures with fixed GaN growth temperature at 735 °C and various AlGaN growth temperature changing from 900 °C to 1007 °C. It was observed that the GaN layer was etched off during the growth interruption when the growth temperature ramped up to AlGaN growth temperature. The etching thickness was determined by high resolution X-ray diffractometer and the etching rate was deduced accordingly. An activation energy of 2.53 eV was obtained for the thermal etching process.

Influence of ammonia flow rate for improving properties of polycrystalline GaN

NASA Astrophysics Data System (ADS)

Ariff, A.; Ahmad, M. A.; Hassan, Z.; Zainal, N.

2018-06-01

Post-annealing treatment in ammonia ambient is widely accepted for GaN material, but less works have been done to investigate the influence of the ammonia (NH3) flow rate for reducing the N-deficiency as well as improving the quality of the material. In this work, we investigated the influence of NH3 flow rate at 1, 2, 3, and 4 slm in improving properties of a ∼1 μm thick polycrystalline GaN layer. Our simulation work suggested that the uniformity of temperature and pressure gradient of the NH3 gas did not lead to the reduction of N-deficiency of the polycrystalline GaN layer. Instead, it was found that the mitigation of the N-deficiency was strongly influenced by the fluid velocity of the NH3 gas, which had passed over the layer. Either at lower or higher fluid velocity, the chance for the active N atoms to incorporate into the GaN lattice structure was low. Therefore, the N-deficiency on the polycrystalline GaN layer could not be minimized under these conditions. As measured by EDX, the N atoms incorporation was the most effective when the NH3 flow rate at 3 slm, suggesting the flow rate significantly improved the N-deficiency of the polycrystalline GaN layer. Furthermore, it favored the formation of larger hexagonal faceted grains, with the smallest FWHM of XRD peaks from the GaN diffractions in (10 1 bar 0), (0002) and (10 1 bar 1) orientations, while allowing the polycrystalline GaN layer to show sharp and intense emissions peak of NBE in a PL spectrum.

Morphological evolution and characterization of GaN pyramid arrays fabricated by photo-assisted chemical etching

NASA Astrophysics Data System (ADS)

Zhang, Shiying; Xiu, Xiangqian; Xu, Qingjun; Li, Yuewen; Hua, Xuemei; Chen, Peng; Xie, Zili; Liu, Bin; Zhou, Yugang; Han, Ping; Zhang, Rong; Zheng, Youdou

2016-12-01

GaN pyramid arrays have been successfully synthesized by selective photo-assisted chemical etching in a K2S2O8/KOH solution. A detailed analysis of time evolution of surface morphology has been conducted, which describes an etching process of GaN pyramids. Room temperature cathodoluminescence images indicate that these pyramids are composed of crystalline GaN surrounding dislocations, which is caused by the greater recombination rate of electrons and holes at dislocation than that of crystalline GaN. The Raman results show a stress relaxation in GaN pyramids compared with unetched GaN. The optical property of both unetched GaN and GaN pyramids has been studied by photoluminescence. The formation mechanism and feature of GaN pyramids are also rationally explained.

Radiation Damage Formation And Annealing In Mg-Implanted GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whelan, Sean; Kelly, Michael J.; Yan, John

2005-06-30

We have implanted GaN with Mg ions over an energy range of 200keV to 1MeV at substrate temperatures of -150 (cold) and +300 deg. C (hot). The radiation damage formation in GaN was increased for cold implants when compared to samples implanted at elevated temperatures. The increase in damage formation is due to a reduction in the dynamic defect annealing during ion irradiation. The dopant stopping in the solid also depends upon the implant temperature. For a fixed implant energy and dose, Mg ions have a shorter range in GaN for cold implants when compared to hot implants which ismore » caused by the increase in scattering centres (disorder)« less

Propagation of misfit dislocations from buffer/Si interface into Si

DOEpatents

Liliental-Weber, Zuzanna [El Sobrante, CA; Maltez, Rogerio Luis [Porto Alegre, BR; Morkoc, Hadis [Richmond, VA; Xie, Jinqiao [Raleigh, VA

2011-08-30

Misfit dislocations are redirected from the buffer/Si interface and propagated to the Si substrate due to the formation of bubbles in the substrate. The buffer layer growth process is generally a thermal process that also accomplishes annealing of the Si substrate so that bubbles of the implanted ion species are formed in the Si at an appropriate distance from the buffer/Si interface so that the bubbles will not migrate to the Si surface during annealing, but are close enough to the interface so that a strain field around the bubbles will be sensed by dislocations at the buffer/Si interface and dislocations are attracted by the strain field caused by the bubbles and move into the Si substrate instead of into the buffer epi-layer. Fabrication of improved integrated devices based on GaN and Si, such as continuous wave (CW) lasers and light emitting diodes, at reduced cost is thereby enabled.

Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koleske, Daniel David; Lee, Stephen Roger; Lemp, Thomas Kerr

2009-07-01

With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growth-enabled reductions in dislocation density would be highly prized. GaN nucleation layers (NLs)more » are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density. In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5 x 10{sup 8} cm{sup -2} using our standard delay recovery growth technique to 1 x 10{sup 8} cm{sup -2} using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined using optical reflectance and the nucleation density was determined using atomic force microscopy (AFM) and Nomarski microscopy. Dislocation density was measured using X-ray diffraction and AFM after coating the surface with silicon nitride to delineate all dislocation types. The program milestone of producing GaN films with dislocation densities of 1 x 10{sup 8} cm{sup -2} was met by silicon nitride treatment of annealed sapphire followed by the multiple deposition of a low density of GaN nuclei followed by high temperature GaN growth. Details of this growth process and the underlying science are presented in this final report along with problems encountered in this research and recommendations for future work.« less

Microstructural response of InGaN to swift heavy ion irradiation

NASA Astrophysics Data System (ADS)

Zhang, L. M.; Jiang, W.; Fadanelli, R. C.; Ai, W. S.; Peng, J. X.; Wang, T. S.; Zhang, C. H.

2016-12-01

A monocrystalline In0.18Ga0.82N film of ∼275 nm in thickness grown on a GaN/Al2O3 substrate was irradiated with 290 MeV 238U32+ ions to a fluence of 1.2 × 1012 cm-2 at room temperature. The irradiated sample was characterized using helium ion microscopy (HIM), Rutherford backscattering spectrometry under ion-channeling conditions (RBS/C), and high-resolution X-ray diffraction (HRXRD). The irradiation leads to formation of ion tracks throughout the thin In0.18Ga0.82N film and the 3.0 μm thick GaN buffer layer. The mean diameter of the tracks in In0.18Ga0.82N is ∼9 nm, as determined by HIM examination. Combination of the HIM and RBS/C data suggests that the In0.18Ga0.82N material in the track is likely to be highly disordered or fully amorphized. The irradiation induced lattice relaxation in In0.18Ga0.82N and a distribution of d-spacing of the (0 0 0 2) planes in GaN with lattice expansion are observed by HRXRD.

Characterisation of defects in p-GaN by admittance spectroscopy

NASA Astrophysics Data System (ADS)

Elsherif, O. S.; Vernon-Parry, K. D.; Evans-Freeman, J. H.; Airey, R. J.; Kappers, M.; Humphreys, C. J.

2012-08-01

Mg-doped GaN films have been grown on (0 0 0 1) sapphire using metal organic vapour phase epitaxy. Use of different buffer layer strategies caused the threading dislocation density (TDD) in the GaN to be either approximately 2×109 cm-2 or 1×1010 cm-2. Frequency-dependent capacitance and conductance measurements at temperatures up to 450 K have been used to study the electronic states associated with the Mg doping, and to determine how these are affected by the TDD. Admittance spectroscopy of the films finds a single impurity-related acceptor level with an activation energy of 160±10 meV for [Mg] of about 1×1019 cm-3, and 120±10 eV as the Mg precursor flux decreased. This level is thought to be associated with the Mg acceptor state. The TDD has no discernible effect on the trap detected by admittance spectroscopy. We compare these results with cathodoluminescence measurements reported in the literature, which reveal that most threading dislocations are non-radiative recombination centres, and discuss possible reasons why our admittance spectroscopy have not detected electrically active defects associated with threading dislocations.

Increased p-type conductivity through use of an indium surfactant in the growth of Mg-doped GaN

NASA Astrophysics Data System (ADS)

Kyle, Erin C. H.; Kaun, Stephen W.; Young, Erin C.; Speck, James S.

2015-06-01

We have examined the effect of an indium surfactant on the growth of p-type GaN by ammonia-based molecular beam epitaxy. p-type GaN was grown at temperatures ranging from 700 to 780 °C with and without an indium surfactant. The Mg concentration in all films in this study was 4.5-6 × 1019 cm-3 as measured by secondary ion mass spectroscopy. All p-type GaN films grown with an indium surfactant had higher p-type conductivities and higher hole concentrations than similar films grown without an indium surfactant. The lowest p-type GaN room temperature resistivity was 0.59 Ω-cm, and the highest room temperature carrier concentration was 1.6 × 1018 cm-3. Fits of the temperature-dependent carrier concentration data showed a one to two order of magnitude lower unintentional compensating defect concentration in samples grown with the indium surfactant. Samples grown at higher temperature had a lower active acceptor concentration. Improvements in band-edge luminescence were seen by cathodoluminescence for samples grown with the indium surfactant, confirming the trends seen in the Hall data.

Phonon conduction in GaN-diamond composite substrates

NASA Astrophysics Data System (ADS)

Cho, Jungwan; Francis, Daniel; Altman, David H.; Asheghi, Mehdi; Goodson, Kenneth E.

2017-02-01

The integration of strongly contrasting materials can enable performance benefits for semiconductor devices. One example is composite substrates of gallium nitride (GaN) and diamond, which promise dramatically improved conduction cooling of high-power GaN transistors. Here, we examine phonon conduction in GaN-diamond composite substrates fabricated using a GaN epilayer transfer process through transmission electron microscopy, measurements using time-domain thermoreflectance, and semiclassical transport theory for phonons interacting with interfaces and defects. Thermoreflectance amplitude and ratio signals are analyzed at multiple modulation frequencies to simultaneously extract the thermal conductivity of GaN layers and the thermal boundary resistance across GaN-diamond interfaces at room temperature. Uncertainties in the measurement of these two properties are estimated considering those of parameters, including the thickness of a topmost metal transducer layer, given as an input to a multilayer thermal model, as well as those associated with simultaneously fitting the two properties. The volume resistance of an intermediate, disordered SiN layer between the GaN and diamond, as well as a presence of near-interfacial defects in the GaN and diamond, dominates the measured GaN-diamond thermal boundary resistances as low as 17 m2 K GW-1. The GaN thermal conductivity data are consistent with the semiclassical phonon thermal conductivity integral model that accounts for the size effect as well as phonon scattering on point defects at concentrations near 3 × 1018 cm-3.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhi, Ting; Tao, Tao; Liu, Bin, E-mail: bliu@nju.edu.cn, E-mail: rzhang@nju.edu.cn

Through investigating the temperature dependent current-voltage (T-I-V) properties of GaN based blue and green LEDs in this study, we propose an asymmetric tunneling model to understand the leakage current below turn-on voltage (V < 3.2 V): At the forward bias within 1.5 V ∼ 2.1 V (region 1), the leakage current is main attributed to electrons tunneling from the conduction band of n-type GaN layer to the valence band of p-type GaN layer via defect states in space-charge region (SCR); While, at the forward bias within 2 V ∼ 2.4 V (region 2), heavy holes tunneling gradually becomes dominant atmore » low temperature (T < 200K) as long as they can overcome the energy barrier height. The tunneling barrier for heavy holes is estimated to be lower than that for electrons, indicating the heavy holes might only tunnel to the defect states. This asymmetric tunneling model shows a novel carrier transport process, which provides better understanding of the leakage characteristics and is vital for future device improvements.« less

Dislocation blocking by AlGaN hot electron injecting layer in the epitaxial growth of GaN terahertz Gunn diode

NASA Astrophysics Data System (ADS)

Li, Liang; Yang, Lin'an; Zhang, Jincheng; Hao, Yue

2013-09-01

This paper reports an efficient method to improve the crystal quality of GaN Gunn diode with AlGaN hot electron injecting layer (HEI). An evident reduction of screw dislocation and edge dislocation densities is achieved by the strain management and the enhanced lateral growth in high temperature grown AlGaN HEI layer. Compared with the top hot electron injecting layer (THEI) structure, the bottom hot electron injecting layer (BHEI) structure enhances the crystal quality of transit region due to the growth sequence modulation of HEI layer. A high Hall mobility of 2934 cm2/Vs at 77 K, a nearly flat downtrend of Hall mobility at the temperature ranging from 300 to 573 K, a low intensity of ratio of yellow luminescence band to band edge emission, a narrow band edge emission line-width, and a smooth surface morphology are observed for the BHEI structural epitaxy of Gunn diode, which indicates that AlGaN BHEI structure is a promising candidate for fabrication of GaN Gunn diodes in terahertz regime.

Polarization of stacking fault related luminescence in GaN nanorods

NASA Astrophysics Data System (ADS)

Pozina, G.; Forsberg, M.; Serban, E. A.; Hsiao, C.-L.; Junaid, M.; Birch, J.; Kaliteevski, M. A.

2017-01-01

Linear polarization properties of light emission are presented for GaN nanorods (NRs) grown along [0001] direction on Si(111) substrates by direct-current magnetron sputter epitaxy. The near band gap photoluminescence (PL) measured at low temperature for a single NR demonstrated an excitonic line at ˜3.48 eV and the stacking faults (SFs) related transition at ˜3.43 eV. The SF related emission is linear polarized in direction perpendicular to the NR growth axis in contrast to a non-polarized excitonic PL. The results are explained in the frame of the model describing basal plane SFs as polymorphic heterostructure of type II, where anisotropy of chemical bonds at the interfaces between zinc blende and wurtzite GaN subjected to in-built electric field is responsible for linear polarization parallel to the interface planes.

TOPICAL REVIEW: The doping process and dopant characteristics of GaN

NASA Astrophysics Data System (ADS)

Sheu, J. K.; Chi, G. C.

2002-06-01

The characteristic effects of doping with impurities such as Si, Ge, Se, O, Mg, Be, and Zn on the electrical and optical properties of GaN-based materials are reviewed. In addition, the roles of unintentionally introduced impurities, such as C, H, and O, and grown-in defects, such as vacancy and antisite point defects, are also discussed. The doping process during epitaxial growth of GaN, AlGaN, InGaN, and their superlattice structures is described. Doping using the diffusion process and ion implantation techniques is also discussed. A p-n junction formed by Si implantation into p-type GaN is successfully fabricated. The results on crystal structure, electrical resistivity, carrier mobility, and optical spectra obtained by means of x-rays, low-temperature Hall measurements, and photoluminescence are also discussed.

Cathodoluminescence of stacking fault bound excitons for local probing of the exciton diffusion length in single GaN nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nogues, Gilles, E-mail: gilles.nogues@neel.cnrs.fr; Den Hertog, Martien; Inst. NEEL, CNRS, F-38042 Grenoble

We perform correlated studies of individual GaN nanowires in scanning electron microscopy combined to low temperature cathodoluminescence, microphotoluminescence, and scanning transmission electron microscopy. We show that some nanowires exhibit well localized regions emitting light at the energy of a stacking fault bound exciton (3.42 eV) and are able to observe the presence of a single stacking fault in these regions. Precise measurements of the cathodoluminescence signal in the vicinity of the stacking fault give access to the exciton diffusion length near this location.

Phase degradation in B xGa 1–xN films grown at low temperature by metalorganic vapor phase epitaxy

DOE PAGES

Gunning, Brendan P.; Moseley, Michael W.; Koleske, Daniel D.; ...

2016-11-01

Using metalorganic vapor phase epitaxy, a comprehensive study of B xGa 1-xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750–900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to ~7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stackingmore » faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at ~362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. As a result, only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.« less

Phase degradation in B xGa 1–xN films grown at low temperature by metalorganic vapor phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunning, Brendan P.; Moseley, Michael W.; Koleske, Daniel D.

Using metalorganic vapor phase epitaxy, a comprehensive study of B xGa 1-xN growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750–900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to ~7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stackingmore » faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at ~362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. As a result, only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.« less

Thermal quenching effect of an infrared deep level in Mg-doped p-type GaN films

NASA Astrophysics Data System (ADS)

Kim, Keunjoo; Chung, Sang Jo

2002-03-01

The thermal quenching of an infrared deep level of 1.2-1.5 eV has been investigated on Mg-doped p-type GaN films, using one- and two-step annealing processes and photocurrent measurements. The deep level appeared in the one-step annealing process at a relatively high temperature of 900 °C, but disappeared in the two-step annealing process with a low-temperature step and a subsequent high-temperature step. The persistent photocurrent was residual in the sample including the deep level, while it was terminated in the sample without the deep level. This indicates that the deep level is a neutral hole center located above a quasi-Fermi level, estimated with an energy of EpF=0.1-0.15 eV above the valence band at a hole carrier concentration of 2.0-2.5×1017/cm3.

Structural and optical properties of semi-polar (11-22) InGaN/GaN green light-emitting diode structure

NASA Astrophysics Data System (ADS)

Zhao, Guijuan; Wang, Lianshan; Li, Huijie; Meng, Yulin; Li, Fangzheng; Yang, Shaoyan; Wang, Zhanguo

2018-01-01

Semi-polar (11-22) InGaN multiple quantum well (MQW) green light-emitting diode (LED) structures have been realized by metal-organic chemical vapor deposition on an m-plane sapphire substrate. By introducing double GaN buffer layers, we improve the crystal quality of semi-polar (11-22) GaN significantly. The vertical alignment of the diffraction peaks in the (11-22) X-ray reciprocal space mapping indicates the fully strained MQW on the GaN layer. The photoluminescence spectra of the LED structure show stronger emission intensity along the [1-100] InGaN/GaN direction. The electroluminescence emission of the LED structure is very broad with peaks around 550 nm and 510 nm at the 100 mA current injection for samples A and B, respectively, and exhibits a significant blue-shift with increasing drive current.

Mg doping of GaN by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lieten, R. R.; Motsnyi, V.; Zhang, L.; Cheng, K.; Leys, M.; Degroote, S.; Buchowicz, G.; Dubon, O.; Borghs, G.

2011-04-01

We present a systematic study on the influence of growth conditions on the incorporation and activation of Mg in GaN layers grown by plasma-assisted molecular beam epitaxy. We show that high quality p-type GaN layers can be obtained on GaN-on-silicon templates. The Mg incorporation and the electrical properties have been investigated as a function of growth temperature, Ga : N flux ratio and Mg : Ga flux ratio. It was found that the incorporation of Mg and the electrical properties are highly sensitive to the Ga : N flux ratio. The highest hole mobility and lowest resistivity were achieved for slightly Ga-rich conditions. In addition to an optimal Ga : N ratio, an optimum Mg : Ga flux ratio was also observed at around 1%. We observed a clear Mg flux window for p-type doping of GaN : 0.31% < Mg : Ga < 5.0%. A lowest resistivity of 0.98 Ω cm was obtained for optimized growth conditions. The p-type GaN layer then showed a hole concentration of 4.3 × 1017 cm-3 and a mobility of 15 cm2 V-1 s-1. Temperature-dependent Hall effect measurements indicate an acceptor depth in these samples of 100 meV for a hole concentration of 5.5 × 1017 cm-3. The corresponding Mg concentration is 5 × 1019 cm-3, indicating approximately 1% activation at room temperature. In addition to continuous growth of Mg-doped GaN layers we also investigated different modulated growth procedures. We show that a modulated growth procedure has only limited influence on Mg doping at a growth temperature of 800 °C or higher. This result is thus in contrast to previously reported GaN : Mg doping at much lower growth temperatures of 500 °C.

Surface oxidation of GaN(0001): Nitrogen plasma-assisted cleaning for ultrahigh vacuum applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gangopadhyay, Subhashis; Schmidt, Thomas, E-mail: tschmidt@ifp.uni-bremen.de; Kruse, Carsten

The cleaning of metal-organic vapor-phase epitaxial GaN(0001) template layers grown on sapphire has been investigated. Different procedures, performed under ultrahigh vacuum conditions, including degassing and exposure to active nitrogen from a radio frequency nitrogen plasma source have been compared. For this purpose, x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and scanning tunneling microscopy have been employed in order to assess chemical as well as structural and morphological surface properties. Initial degassing at 600 °C under ultrahigh vacuum conditions only partially eliminates the surface contaminants. In contrast to plasma assisted nitrogen cleaning at temperatures as low as 300 °C, active-nitrogen exposure at temperaturesmore » as high as 700 °C removes the majority of oxide species from the surface. However, extended high-temperature active-nitrogen cleaning leads to severe surface roughening. Optimum results regarding both the removal of surface oxides as well as the surface structural and morphological quality have been achieved for a combination of initial low-temperature plasma-assisted cleaning, followed by a rapid nitrogen plasma-assisted cleaning at high temperature.« less

Suppression of the self-heating effect in GaN HEMT by few-layer graphene heat spreading elements

NASA Astrophysics Data System (ADS)

Volcheck, V. S.; Stempitsky, V. R.

2017-11-01

Self-heating has an adverse effect on characteristics of gallium nitride (GaN) high electron mobility transistors (HEMTs). Various solutions to the problem have been proposed, however, a temperature rise due to dissipated electrical power still hinders the production of high power and high speed GaN devices. In this paper, thermal management of GaN HEMT via few-layer graphene (FLG) heat spreading elements is investigated. It is shown that integration of the FLG elements on top of the device structure considerably reduces the maximum temperature and improves the DC and small signal AC performance.

Smart Materials for Electromagnetic and Optical Applications

NASA Astrophysics Data System (ADS)

Ramesh, Prashanth

The research presented in this dissertation focuses on the development of solid-state materials that have the ability to sense, act, think and communicate. Two broad classes of materials, namely ferroelectrics and wideband gap semiconductors were investigated for this purpose. Ferroelectrics possess coupled electromechanical behavior which makes them sensitive to mechanical strains and fluctuations in ambient temperature. Use of ferroelectrics in antenna structures, especially those subject to mechanical and thermal loads, requires knowledge of the phenomenological relationship between the ferroelectric properties of interest (especially dielectric permittivity) and the external physical variables, viz. electric field(s), mechanical strains and temperature. To this end, a phenomenological model of ferroelectric materials based on the Devonshire thermodynamic theory was developed. This model was then used to obtain a relationship expressing the dependence of the dielectric permittivity on the mechanical strain, applied electric field and ambient temperature. The relationship is shown to compare well with published experimental data and other related models in literature. A model relating ferroelectric loss tangent to the applied electric field and temperature is also discussed. Subsequently, relationships expressing the dependence of antenna operating frequency and radiation efficiency on those external physical quantities are described. These relationships demonstrate the tunability of load-bearing antenna structures that integrate ferroelectrics when they are subjected to mechanical and thermal loads. In order to address the inability of ferroelectrics to integrate microelectronic devices, a feature needed in a material capable of sensing, acting, thinking and communicating, the material Gallium Nitride (GaN) is pursued next. There is an increasing utilization of GaN in the area of microelectronics due to the advantages it offers over other semiconductors. This dissertation demonstrates GaN as a candidate material well suited for novel microelectromechanical systems. The potential of GaN for MEMS is demonstrated via the design, analysis, fabrication, testing and characterization of an optical microswitch device actuated by piezoelectric and electrostrictive means. The piezoelectric and electrostrictive properties of GaN and its differences from common piezoelectrics are discussed before elaborating on the device configuration used to implement the microswitch device. Next, the development of two recent fabrication technologies, Photoelectrochemical etch and Bias-enabled Dark Electrochemical etch, used to realize the 3-dimensional device structure in GaN are described in detail. Finally, an ultra-low-cost, laser-based, non-contact approach to test and characterize the microswitch device is described, followed by the device testing results.

Dependence of N-polar GaN rod morphology on growth parameters during selective area growth by MOVPE

NASA Astrophysics Data System (ADS)

Li, Shunfeng; Wang, Xue; Mohajerani, Matin Sadat; Fündling, Sönke; Erenburg, Milena; Wei, Jiandong; Wehmann, Hergo-Heinrich; Waag, Andreas; Mandl, Martin; Bergbauer, Werner; Strassburg, Martin

2013-02-01

Selective area growth of GaN rods by metalorganic vapor phase epitaxy has attracted great interest due to its novel applications in optoelectronic and photonics. In this work, we will present the dependence of GaN rod morphology on various growth parameters i.e. growth temperature, H2/N2 carrier gas concentration, V/III ratio, total carrier gas flow and reactor pressure. It is found that higher growth temperature helps to increase the aspect ratio of the rods, but reduces the height homogeneity. Furthermore, H2/N2 carrier gas concentration is found to be a critical factor to obtain vertical rod growth. Pure nitrogen carrier gas leads to irregular growth of GaN structure, while an increase of hydrogen carrier gas results in vertical GaN rod growth. Higher hydrogen carrier gas concentration also reduces the diameter and enhances the aspect of the GaN rods. Besides, increase of V/III ratio causes reduction of the aspect ratio of N-polar GaN rods, which could be explained by the relatively lower growth rate on (000-1) N-polar top surface when supplying more ammonia. In addition, an increase of the total carrier gas flow leads to a decrease in the diameter and the average volume of GaN rods. These phenomena are tentatively explained by the change of partial pressure of the source materials and boundary layer thickness in the reactor. Finally, it is shown that the average volume of the N-polar GaN rods keeps a similar value for a reactor pressure PR of 66 and 125 mbar, while an incomplete filling of the pattern opening is observed with PR of 250 mbar. Room temperature photoluminescence spectrum of the rods is also briefly discussed.

The metalorganic chemical vapor deposition of III-V nitrides for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Grudowski, Paul Alexander

Nitride-based light-emitting diodes (LEDs) and laser diodes are important for large-area LED displays, flat-panel displays, traffic signals, and optical data storage, due to their characteristic ultraviolet and visible light emission. However, much of the research and development addressing material related problems is recent. The room-temperature continuous wave (CW) operation of nitride-based laser diodes remains a major milestone because the material quality requirements for these devices are extremely high. This study investigates nitride material development by the metalorganic chemical vapor deposition (MOCVD) and characterization of GaN, AlGaN, and InGaN, and by qualifying these materials with fabricated devices. The ultimate goal was to develop a working laser diode. The nitride epitaxial films were characterized by 300K Hall effect, x-ray diffraction (XRD), photoluminescence (PL), cathodoluminescence (CL), secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). GaN grown heteroepitaxially on (0001) sapphire substrates was first optimized. A low-temperature GaN nucleation layer was developed that gave subsequent high-temperature GaN layers with low background carrier concentrations (n < 1×10sp{17}\\ cmsp{-3}). Intentional p-type hole concentrations up to 2× 10sp{18} cmsp{-3} and n-type electron concentrations up to 1× 10sp{19} cmsp{-3} were achieved at 300K with magnesium and silicon, respectively. The ternary alloy Insb{x}Gasb{1-x}N was grown with indium compositions up to x = 0.25. These films exhibited strong and narrow 300K PL bandedge peaks. Multiple-quantum-well structures with Insb{0.13}Gasb{0.87}N wells and Insb{0.03}Gasb{0.97}N barriers were grown and gave enhanced PL intensity compared to single InGaN layers. Modulation-doped MQW's produced enhanced PL intensity compared to uniformly-doped MQW's. 300K photopumping experiments produced stimulated emission from a five-period MQW. Light-emitting device structures comprised of InGaN MQW active regions and p-type and n-type GaN contact layers and AlGaN confinement layers were grown and fabricated. LED's showed bright emission at a wavelength of 400 nm. While optically pumped lasers were demonstrated, no injection lasing action was achieved in these devices. GaN grown by selective area lateral epitaxial overgrowth (SALEO) has reduced dislocation defect density and, therefore, may prove to be a promising substrate for nearly defect-free device structures. Plan-view and cross-sectional CL was used to compare spatial inhomogeneities in the bandedge luminescence.

Surfactant effect of gallium during molecular-beam epitaxy of GaN on AlN (0001)

NASA Astrophysics Data System (ADS)

Mula, Guido; Adelmann, C.; Moehl, S.; Oullier, J.; Daudin, B.

2001-11-01

We study the adsorption of Ga on (0001) GaN surfaces by reflection high-energy electron diffraction. It is shown that a dynamically stable Ga bilayer can be formed on the GaN surface for appropriate Ga fluxes and substrate temperatures. The influence of the presence of this Ga film on the growth mode of GaN on AlN(0001) by plasma-assisted molecular-beam epitaxy is studied. It is demonstrated that under nearly stoichiometric and N-rich conditions, the GaN layer relaxes elastically during the first stages of epitaxy. At high temperatures the growth follows a Stranski-Krastanov mode, whereas at lower temperatures kinetically formed flat platelets are observed. Under Ga-rich conditions-where a Ga bilayer is rapidly formed due to excess Ga accumulating on the surface-the growth follows a Frank-van der Merwe layer-by-layer mode at any growth temperature and no initial elastic relaxation occurs. Hence, it is concluded that excess Ga acts as a surfactant, effectively suppressing both Stranski-Krastanov islanding and platelet formation. It is further demonstrated that the Stranski-Krastanov transition is in competition with elastic relaxation by platelets, and it is only observed when relaxation by platelets is inefficient. As a result, a growth mode phase diagram is outlined for the growth of GaN on AlN(0001).

Metalorganic chemical vapor deposition of gallium nitride on sacrificial substrates

NASA Astrophysics Data System (ADS)

Fenwick, William Edward

GaN-based light emitting diodes (LEDs) face several challenges if the technology is to continue to make a significant impact in general illumination, and on technology that has become known as solid state lighting (SSL). Two of the most pressing challenges for the continued penetration of SSL into traditional lighting applications are efficacy and total lumens from the device, and their related cost. The development of alternative substrate technologies is a promising avenue toward addressing both of these challenges, as both GaN-based device technology and the associated metalorganic chemical vapor deposition (MOCVD) technology are already relatively mature technologies with a well-understood cost base. Zinc oxide (ZnO) and silicon (Si) are among the most promising alternative substrates for GaN epitaxy. These substrates offer the ability to access both higher efficacy and lumen devices (ZnO) at a much reduced cost. This work focuses on the development of MOCVD growth processes to yield high quality GaN-based materials and devices on both ZnO and Si. ZnO is a promising substrate for growth of low defect-density GaN because of its similar lattice constant and thermal expansion coefficient. The major hurdles for GaN growth on ZnO are the instability of the substrate in a hydrogen atmosphere, which is typical of nitride growth conditions, and the inter-diffusion of zinc and oxygen from the substrate into the GaN-based epitaxial layer. A process was developed for the MOCVD growth of GaN and InxGa 1-xN on ZnO that attempted to address these issues. The structural and optical properties of these films were studied using various techniques. X-ray diffraction (XRD) showed the growth of wurtzite GaN on ZnO, and room-temperature photoluminescence (RT-PL) showed near band-edge luminescence from the GaN and InxGa1-xN layers. However, high zinc and oxygen concentrations due to interdiffusion near the ZnO substrate remained an issue; therefore, the diffusion of zinc and oxygen into the subsequent GaN layer was studied in more detail. Several approaches were investigated---for example, transition layers such as Al2O3 and Al xGa1-xN/GaN---to minimize diffusion of these impurities into the GaN layer. Silicon, due to its prevalence, is the most promising material for the development of an inexpensive, large-area substrate technology. The challenge in MOCVD growth of GaN on Si is the tensile strain induced by the lattice and thermal mismatch between GaN and Si and the formation of anti-phase boundaries. Typical approaches to solve these problems involve complicated and multiple buffer layer structures, which lead to relatively slow growth rates. In this work, a thin atomic layer deposition (ALD)-grown Al2O3 interlayer was employed to relieve strain and increase material quality while also simplifying the growth process. While some residual strain was still observed in the GaN material by XRD and PL, the use of this oxide interlayer leads to an improvement in thin film quality as seen by a reduction in both crack density (<1 mm-2) on ALD-Al2O3/Si) and screw dislocation density (from 3x109cm-2 on bare Si to 2x108cm-2 on ALD-Al 2O3/Si) in the GaN films. A side-by-side comparison of GaN-based multiple quantum well LEDs grown on sapphire and on Al2O3/Si shows similar performance characteristic for both device structures. A redshift in peak emission wavelength was also observed on silicon compared to sapphire, and this is attributed to higher indium content due to the slight tensile strain in the layers on silicon. IQE of the devices on silicon is ˜32% as measured by LT-PL, compared to ˜37% on sapphire, but this difference can be assigned to the difference in indium compositions. These results show a great promise toward an inexpensive, large-area, silicon-based substrate technology for MOCVD growth of the next generation of GaN-based optoelectronic devices for SSL and other applications.

Carrier concentration dependence of donor activation energy in n-type GaN epilayers grown on Si (1 1 1) by plasma-assisted MBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Mahesh; Central Research Laboratory, Bharat Electronics, Bangalore 560 013; Bhat, Thirumaleshwara N.

Highlights: ► The n-type GaN layers were grown by plasma-assisted molecular beam epitaxy. ► The optical characteristics of a donor level in Si-doped GaN were studied. ► Activation energy of a Si-related donor was estimated from temperature dependent PL measurements. ► PL peak positions, FWHM of PL and activation energies are found to be proportional to the cube root of carrier density. ► The involvement of donor levels is supported by the temperature-dependent electron concentration measurements. -- Abstract: The n-type GaN layers were grown by plasma-assisted MBE and either intentionally doped with Si or unintentionally doped. The optical characteristics ofmore » a donor level in Si-doped, GaN were studied in terms of photoluminescence (PL) spectroscopy as a function of electron concentration. Temperature dependent PL measurements allowed us to estimate the activation energy of a Si-related donor from temperature-induced decay of PL intensity. PL peak positions, full width at half maximum of PL and activation energies are found to be proportional to the cube root of carrier density. The involvement of donor levels is supported by the temperature-dependent electron concentration measurements.« less

Temperature-Dependent Electrical Properties and Carrier Transport Mechanisms of TMAH-Treated Ni/Au/Al2O3/GaN MIS Diode

NASA Astrophysics Data System (ADS)

Reddy, M. Siva Pratap; Puneetha, Peddathimula; Reddy, V. Rajagopal; Lee, Jung-Hee; Jeong, Seong-Hoon; Park, Chinho

2016-11-01

The temperature-dependent electrical properties and carrier transport mechanisms of tetramethylammonium hydroxide (TMAH)-treated Ni/Au/Al2O3/GaN metal-insulator-semiconductor (MIS) diodes have been investigated by current-voltage ( I- V) and capacitance-voltage ( C- V) measurements. The experimental results reveal that the barrier height ( I- V) increases whereas the ideality factor decreases with increasing temperature. The TMAH-treated Ni/Au/Al2O3/GaN MIS diode showed nonideal behaviors which indicate the presence of a nonuniform distribution of interface states ( N SS) and effect of series resistance ( R S). The obtained R S and N SS were found to decrease with increasing temperature. Furthermore, it was found that different transport mechanisms dominated in the TMAH-treated Ni/Au/Al2O3/GaN MIS diode. At 150 K to 250 K, Poole-Frenkel emission (PFE) was found to be responsible for the reverse leakage, while Schottky emission (SE) was the dominant mechanism at high electric fields in the temperature range from 300 K to 400 K. Feasible energy band diagrams and possible carrier transport mechanisms for the TMAH-treated Ni/Au/Al2O3/GaN MIS diode are discussed based on PFE and SE.

Increased p-type conductivity through use of an indium surfactant in the growth of Mg-doped GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kyle, Erin C. H., E-mail: erinkyle@engineering.ucsb.edu; Kaun, Stephen W.; Young, Erin C.

2015-06-01

We have examined the effect of an indium surfactant on the growth of p-type GaN by ammonia-based molecular beam epitaxy. p-type GaN was grown at temperatures ranging from 700 to 780 °C with and without an indium surfactant. The Mg concentration in all films in this study was 4.5–6 × 10{sup 19} cm{sup −3} as measured by secondary ion mass spectroscopy. All p-type GaN films grown with an indium surfactant had higher p-type conductivities and higher hole concentrations than similar films grown without an indium surfactant. The lowest p-type GaN room temperature resistivity was 0.59 Ω-cm, and the highest room temperature carrier concentration wasmore » 1.6 × 10{sup 18} cm{sup −3}. Fits of the temperature-dependent carrier concentration data showed a one to two order of magnitude lower unintentional compensating defect concentration in samples grown with the indium surfactant. Samples grown at higher temperature had a lower active acceptor concentration. Improvements in band-edge luminescence were seen by cathodoluminescence for samples grown with the indium surfactant, confirming the trends seen in the Hall data.« less

Near band gap luminescence in hybrid organic-inorganic structures based on sputtered GaN nanorods.

PubMed

Forsberg, Mathias; Serban, Elena Alexandra; Hsiao, Ching-Lien; Junaid, Muhammad; Birch, Jens; Pozina, Galia

2017-04-26

Novel hybrid organic-inorganic nanostructures fabricated to utilize non-radiative resonant energy transfer mechanism are considered to be extremely attractive for a variety of light emitters for down converting of ultaviolet light and for photovoltaic applications since they can be much more efficient compared to devices grown with common design. Organic-inorganic hybrid structures based on green polyfluorene (F8BT) and GaN (0001) nanorods grown by magnetron sputtering on Si (111) substrates are studied. In such nanorods, stacking faults can form periodic polymorphic quantum wells characterized by bright luminescence. In difference to GaN exciton emission, the recombination rate for the stacking fault related emission increases in the presence of polyfluorene film, which can be understood in terms of Förster interaction mechanism. From comparison of dynamic properties of the stacking fault related luminescence in the hybrid structures and in the bare GaN nanorods, the pumping efficiency of non-radiative resonant energy transfer in hybrids was estimated to be as high as 35% at low temperatures.

Vertical GaN power diodes with a bilayer edge termination

DOE PAGES

Dickerson, Jeramy R.; Allerman, Andrew A.; Bryant, Benjamin N.; ...

2015-12-07

Vertical GaN power diodes with a bilayer edge termination (ET) are demonstrated. The GaN p-n junction is formed on a low threading dislocation defect density (10 4 - 10 5 cm -2) GaN substrate, and has a 15-μm-thick n-type drift layer with a free carrier concentration of 5 × 10 15 cm -3. The ET structure is formed by N implantation into the p+-GaN epilayer just outside the p-type contact to create compensating defects. The implant defect profile may be approximated by a bilayer structure consisting of a fully compensated layer near the surface, followed by a 90% compensated (p)more » layer near the n-type drift region. These devices exhibit avalanche breakdown as high as 2.6 kV at room temperature. In addition simulations show that the ET created by implantation is an effective way to laterally distribute the electric field over a large area. This increases the voltage at which impact ionization occurs and leads to the observed higher breakdown voltages.« less

Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerr, A. J.; Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093; Chagarov, E.

2014-09-14

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al{sub 2}O{sub 3} gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge.more » These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001)« less

Optimization of ion-atomic beam source for deposition of GaN ultrathin films.

PubMed

Mach, Jindřich; Šamořil, Tomáš; Kolíbal, Miroslav; Zlámal, Jakub; Voborny, Stanislav; Bartošík, Miroslav; Šikola, Tomáš

2014-08-01

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Observation and discussion of avalanche electroluminescence in GaN p-n diodes offering a breakdown electric field of 3 MV cm‑1

NASA Astrophysics Data System (ADS)

Mandal, S.; Kanathila, M. B.; Pynn, C. D.; Li, W.; Gao, J.; Margalith, T.; Laurent, M. A.; Chowdhury, S.

2018-06-01

We report on the first observation of avalanche electroluminescence resulting from band-to-band recombination (BTBR) of electron hole pairs at the breakdown limit of Gallium Nitride p-n diodes grown homo-epitaxially on single crystalline GaN substrates. The diodes demonstrated a near ideal breakdown electric field of 3 MV cm‑1 with electroluminescence (EL) demonstrating sharp peaks of emission energies near and at the band gap of GaN. The high critical electric field, near the material limit of GaN, was achieved by generating a smooth curved mesa edge with low plasma damage, using etch engineering without any use of field termination. The superior material quality was critical for such a near-ideal performance. An electric field of 3 MV cm‑1 recorded at the breakdown resulted in impact ionization, confirmed by a positive temperature dependence of the breakdown voltage. The spectral data provided evidence of BTBR of electron hole pairs that were generated by avalanche carrier multiplication in the depletion region.

Zero-internal fields in nonpolar InGaN/GaN multi-quantum wells grown by the multi-buffer layer technique.

PubMed

Song, Hooyoung; Kim, Jin Soak; Kim, Eun Kyu; Seo, Yong Gon; Hwang, Sung-Min

2010-04-02

The potential of nonpolar a-plane InGaN/GaN multi-quantum wells (MQWs), which are free from a strong piezoelectric field, was demonstrated. An a-GaN template grown on an r-plane sapphire substrate by the multi-buffer layer technique showed high structural quality with an omega full width at half maximum value along the c-axis of 418 arcsec obtained from high-resolution x-ray diffraction analysis. From barrier analysis by deep level transient spectroscopy, it appeared that a-plane InGaN/GaN MQWs can solve the efficiency droop problem as they have a lower electron capture barrier than the c-plane sample. The peak shift of the temperature-dependent photoluminescence signal for the nonpolar InGaN/GaN MQWs was well fitted by Varshni's empirical equation with zero-internal fields. A high photoluminescence efficiency of 0.27 from this sample also showed that nonpolar MQWs can be the key factor to solve the efficiency limitation in conventional c-plane GaN based light emitting diodes.

Bulk Group-III Nitride Crystal Growth in Supercritical Ammonia-Sodium Solutions

NASA Astrophysics Data System (ADS)

Griffiths, Steven Herbert

Gallium nitride (GaN) and its alloys with indium nitride (InGaN) and aluminum nitride (AlGaN), collectively referred to as Group-III Nitride semiconductors, have enabled white solid-state lighting (SSL) sources and power electronic devices. While these technologies have already made a lasting, positive impact on society, improvements in design and efficiency are anticipated by shifting from heteroepitaxial growth on foreign substrates (such as sapphire, Si, SiC, etc.) to homoepitaxial growth on native, bulk GaN substrates. Bulk GaN has not supplanted foreign substrate materials due to the extreme conditions required to achieve a stoichiometric GaN melt (temperatures and pressures in excess of 2200°C and 6 GPa, respectively). The only method used to produce bulk GaN on an industrial scale is hydride vapor phase epitaxy (HVPE), but the high cost of gaseous precursors and relatively poor crystal quality have limited the adoption of this technology. A solution growth technique known as the ammonothermal method has attracted interest from academia and industry alike for its ability to produce bulk GaN boules of exceedingly high crystal quality. The ammonothermal method employs supercritical ammonia (NH3) solutions to dissolve, transport, and crystallize GaN. However, ammonothermal growth pressures are still relatively high (˜200 MPa), which has thus far prevented the acquisition of fundamental crystal growth knowledge needed to efficiently (i.e. through data-driven approaches) advance the field. This dissertation focused on addressing the gaps in the literature through two studies employing in situ fluid temperature analysis. The first study focused on identifying the solubility of GaN in supercritical NH3-Na solutions. The design and utilization of in situ and ex situ monitoring equipment enabled the first reports of the two-phase nature of supercritical NH3-Na solutions, and of Ga-alloying of Ni-containing autoclave components. The effects of these error sources on the gravimetric determination of GaN solubility were explored in detail. The second study was aimed at correlating autoclave dissolution and growth zone fluid temperatures with bulk GaN crystal growth kinetics, crystal quality, and impurity incorporation. The insights resulting from this analysis include the identification of the barrier between mass transport and surface integration-limited GaN growth regimes, GaN crystal shape evolution with fluid temperature, the sensitivity of (0001)-orientation crystal quality with fluid temperature, and impurity-specific incorporation activated from the dissolution and growth zones of the autoclave. The results of the aforementioned studies motivated a paradigm-shift in ammonothermal growth. To address this need, a fundamentally different crystal growth approach involving isothermal solutions and tailor-made Group-III alloy source materials was developed/demonstrated. This growth method enabled impurity incorporation reduction compared to traditional ammonothermal GaN growth, and the realization of bulk, ternary Group-III Nitride crystals.

Photoluminescence and positron annihilation studies on Mg-doped nitrogen-polarity semipolar (101xAF1xAF) GaN heteroepitaxial layers grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Onuma, T.; Uedono, A.; Asamizu, H.; Sato, H.; Kaeding, J. F.; Iza, M.; DenBaars, S. P.; Nakamura, S.; Chichibu, S. F.

2010-03-01

The influences of enhanced stacking fault (SF) formation, which is peculiar to nitrogen-(N-) polarity growth and lattice-mismatched semipolar heteroepitaxy, on the electrical properties of (101¯1¯) Mg-doped GaN (GaN:Mg) epilayers were investigated. Although the residual donor concentration was higher than (0001) GaN because of N-polar growth, comparatively low Mg doping (3×1019 cm-3) gave a hole concentration approximately 1.5×1018 cm-3, which was an order of magnitude higher than (0001) GaN:Mg. As the acceptor ionization energy estimated from low temperature photoluminescence was quite similar for (101¯1¯) and (0001) GaN:Mg, the high Mg activation seems to result with the aid of high density SFs. Because the Doppler broadening S parameter for the positron annihilation measurement, which reflects the concentration or size of negatively charged cation vacancies, of (101¯1¯) GaN:Mg was smaller than (0001) case, (101¯1¯) orientation is well suited to Mg-doping.

Highly mismatched GaN1-x Sb x alloys: synthesis, structure and electronic properties

NASA Astrophysics Data System (ADS)

Yu, K. M.; Sarney, W. L.; Novikov, S. V.; Segercrantz, N.; Ting, M.; Shaw, M.; Svensson, S. P.; Martin, R. W.; Walukiewicz, W.; Foxon, C. T.

2016-08-01

Highly mismatched alloys (HMAs) is a class of semiconductor alloys whose constituents are distinctly different in terms of size, ionicity and/or electronegativity. Electronic properties of the alloys deviate significantly from an interpolation scheme based on small deviations from the virtual crystal approximation. Most of the HMAs were only studied in a dilute composition limit. Recent advances in understanding of the semiconductor synthesis processes allowed growth of thin films of HMAs under non-equilibrium conditions. Thus reducing the growth temperature allowed synthesis of group III-N-V HMAs over almost the entire composition range. This paper focuses on the GaN x Sb1-x HMA which has been suggested as a potential material for solar water dissociation devices. Here we review our recent work on the synthesis, structural and optical characterization of GaN1-x Sb x HMA. Theoretical modeling studies on its electronic structure based on the band anticrossing (BAC) model are also reviewed. In particular we discuss the effects of growth temperature, Ga flux and Sb flux on the incorporation of Sb, film microstructure and optical properties of the alloys. Results obtained from two separate MBE growths are directly compared. Our work demonstrates that a large range of direct bandgap energies from 3.4 eV to below 1.0 eV can be achieved for this alloy grown at low temperature. We show that the electronic band structure of GaN1-x Sb x HMA over the entire composition range is well described by a modified BAC model which includes the dependence of the host matrix band edges as well as the BAC model coupling parameters on composition. We emphasize that the modified BAC model of the electronic band structure developed for the full composition of GaN x Sb1-x is general and is applicable to any HMA.

High-quality GaN epitaxially grown on Si substrate with serpentine channels

NASA Astrophysics Data System (ADS)

Wei, Tiantian; Zong, Hua; Jiang, Shengxiang; Yang, Yue; Liao, Hui; Xie, Yahong; Wang, Wenjie; Li, Junze; Tang, Jun; Hu, Xiaodong

2018-06-01

A novel serpentine-channeled mask was introduced to Si substrate for low-dislocation GaN epitaxial growth and the fully coalesced GaN film on the masked Si substrate was achieved for the first time. Compared with the epitaxial lateral overgrowth (ELOG) growth method, this innovative mask only requires one-step epitaxial growth of GaN which has only one high-dislocation region per mask opening. This new growth method can effectively reduce dislocation density, thus improving the quality of GaN significantly. High-quality GaN with low dislocation density ∼2.4 × 107 cm-2 was obtained, which accounted for about eighty percent of the GaN film in area. This innovative technique is promising for the growth of high-quality GaN templates and the subsequent fabrication of high-performance GaN-based devices like transistors, laser diodes (LDs), and light-emitting diodes (LEDs) on Si substrate.

Local electronic and optical behaviors of a-plane GaN grown via epitaxial lateral overgrowth

NASA Astrophysics Data System (ADS)

Moore, J. C.; Kasliwal, V.; Baski, A. A.; Ni, X.; Özgür, Ü.; Morkoç, H.

2007-01-01

Conductive atomic force microscopy and near-field optical microscopy (NSOM) were used to study the morphology, conduction, and optical properties of a-plane GaN films grown via epitaxial lateral overgrowth (ELO) by metal organic chemical vapor deposition. The AFM images for the coalesced ELO films show undulations, where the window regions appear as depressions with a high density of surface pits. At reverse bias below 12V, very low uniform conduction (2pA) is seen in the window regions. Above 20V, a lower-quality sample shows localized sites inside the window regions with significant leakage, indicating a correlation between the presence of surface pits and leakage sites. Room temperature NSOM studies explicitly showed enhanced optical quality in the wing regions of the overgrown GaN due to a reduced density of dislocations, with the wings and the windows clearly discernible from near-field photoluminescence mapping.

High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Meng; Zhao, Yuning; Yan, Xiaodong

2015-12-07

Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm{sup 2} is obtained with reverse bias voltage up to −20 V. With a 400 nm thick n-drift region, an on-resistance of 0.23 mΩ cm{sup 2} is achieved, with a breakdown voltage corresponding to a peak electric field of ∼3.1 MV/cm in GaN. Single-crystal GaN substrates with very low dislocation densities enable the low leakage current and the high breakdown field in the diodes, showing significant potential for MBE growth to attain near-intrinsic performance when the density of dislocations is low.

Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template

NASA Astrophysics Data System (ADS)

Gogova, D.; Kasic, A.; Larsson, H.; Hemmingsson, C.; Monemar, B.; Tuomisto, F.; Saarinen, K.; Dobos, L.; Pécz, B.; Gibart, P.; Beaumont, B.

2004-07-01

Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy (HVPE) growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-μm-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ˜2.5×107 cm-2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8×1015 cm-3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 (3.4712) eV and 3.4721 (3.4718) eV for the Ga- (N-) polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E1(TO) phonon mode position measured at 558.52 cm-1 (Ga face) by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications.

Study of the Ohmic Contact Mechanism of Oxidized Ni/Au Contact to p-GaN

NASA Astrophysics Data System (ADS)

Roesler, Erika; Chengyu, Hu; Zhang, Guoyi

2004-03-01

In the semiconductor industry, GaN is important for blue Laser Diodes (LDs) and Light Emitting Diodes (LEDs). In order to maximize efficiency for optoelectronic devices that utilize GaN products, a low contact resistance and an ohmic contact are needed. Previously, the contact resistance has been found to be as low as 10-4 Ohms cm^2. The aim of this research project was to investigate the influence of different annealing conditions for the contact resistance; analyze the microstructure of the electrodes; find the relationship between the microstructure, annealing conditions, and contact resistance; and then explain the mechanism. The sample was grown in a MOCVD system and had a mesa structure. It was activated with Mg-H 800 C for 20 minutes to become a p-type GaN semiconductor. The sample underwent four different annealing conditions. The first condition varied the temperature in constant Oxygen ambient; the second varied the temperature in air; the third varied the percentage of Oxygen with Nitrogen in constant temperature; and the fourth varied the time annealed under Oxygen ambient. The third condition has never previously been tested. We found definite minimums of the contact resistivity (using the TLM method) in the first condition and second conditions at 500 C. The third condition had the best results with a mix of 50% Oxygen and 50the fourth condition had the best results at 5 minutes. Once the effects of the microstructure are analyzed for the sample at each condition, a better understanding of the physical mechanisms to yield the contact resistance will be known.

Selective-area growth of GaN nanocolumns on Si(111) substrates for application to nanocolumn emitters with systematic analysis of dislocation filtering effect of nanocolumns

NASA Astrophysics Data System (ADS)

Kishino, Katsumi; Ishizawa, Shunsuke

2015-06-01

The growth of highly uniform arrays of GaN nanocolumns with diameters from 122 to 430 nm on Si (111) substrates was demonstrated. The employment of GaN film templates with flat surfaces (root mean square surface roughness of 0.84 nm), which were obtained using an AlN/GaN superlattice (SL) buffer on Si, contributed to the high-quality selective-area growth of nanocolumns using a thin Ti mask of 5 nm thickness by rf-plasma-assisted molecular beam epitaxy. Although the GaN template included a large number of dislocations (dislocation density ˜1011 cm-2), the dislocation filtering effect of nanocolumns was enhanced with decreasing nanocolumn diameters (D). Systematic transmission electron microscopy (TEM) observation enabled us to explain the dependence of the dislocation propagation behavior in nanocolumns on the nanocolumn diameter for the first time. Plan-view TEM analysis was performed for nanocolumns with D = 120-324 nm by slicing the nanocolumns horizontally at a height of ˜300 nm above their bottoms and dislocation propagation through the nanocolumns was analyzed by the cross-sectional TEM observation of nanocolumns with D ˜ 200 nm. It was clarified that dislocations were effectively filtered in the bottom 300 nm region of the nanocolumns, the dislocation density of the nanocolumns decreased with decreasing D, and for narrow nanocolumns with D < 200 nm, dislocation-free crystals were obtained in the upper part of the nanocolumns. The dramatic improvement in the emission properties of GaN nanocolumns observed with decreasing diameter is discussed in relation to the decreased dislocation density. The laser action of InGaN/GaN-based nanocolumn arrays with a nanocolumn diameter of 170 nm and a period of 200 nm on Si under optical excitation was obtained with an emission wavelength of 407 nm. We also fabricated red-emitting InGaN-based nanocolumn light-emitting diodes on Si that operated at a wavelength of 652 nm, demonstrating vertical conduction through the AlN/GaN SL buffer to the Si substrate.

Multicycle rapid thermal annealing technique and its application for the electrical activation of Mg implanted in GaN

NASA Astrophysics Data System (ADS)

Feigelson, B. N.; Anderson, T. J.; Abraham, M.; Freitas, J. A.; Hite, J. K.; Eddy, C. R.; Kub, F. J.

2012-07-01

No reliable results were reported up-to-date on electrical activation of Mg implanted GaN without co-doping with other ions. The main reason of the poor ion-implanted activation in GaN is lack of the adequate GaN annealing technique. We have developed a new approach, Multicycle Rapid Thermal Annealing to overcome this limitation and enable longer annealing times at high temperature. We have applied this new technique to Mg-implanted GaN, and demonstrated p-type conductivity.

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires.

PubMed

Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T; Martinez, Julio A

2016-01-08

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

NASA Astrophysics Data System (ADS)

Greenlee, Jordan D.; Feigelson, Boris N.; Anderson, Travis J.; Tadjer, Marko J.; Hite, Jennifer K.; Mastro, Michael A.; Eddy, Charles R.; Hobart, Karl D.; Kub, Francis J.

2014-08-01

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N2 overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at half maximums of the E2 and A1 (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.

Low Temperature Locally-Controlled Growth of Wide Bandgap Nitride and Diamond Films via Plasmon Resonance-Excited Kinetic Processes

DTIC Science & Technology

2015-06-18

Ga2O3  film  grown  on  gold/Si  substrate.   Since  then,  we  have  worked  on  TEM  imaging  of  the  1:8:4  GaN...rate   of   1Hz,   which   we   previously   reported   to   result   in   a   mixed   composition   of   GaN/ Ga2O3 ...indicates  a   GaN/ Ga2O3  layer  <  10  nm  thick.  However,  energy

Mg doping of GaN grown by plasma-assisted molecular beam epitaxy under nitrogen-rich conditions

NASA Astrophysics Data System (ADS)

Zhang, Meng; Bhattacharya, Pallab; Guo, Wei; Banerjee, Animesh

2010-03-01

Acceptor doping of GaN with Mg during plasma-assisted molecular beam epitaxy, under N-rich conditions and a relatively high growth temperature of 740 °C, was investigated. The p-doping level steadily increases with increasing Mg flux. The highest doping level achieved, determined from Hall measurements, is 2.1×1018 cm-3. The corresponding doping efficiency and hole mobility are ˜4.9% and 3.7 cm2/V s at room temperature. Cross-sectional transmission electron microscopy and photoluminescence measurements confirm good crystalline and optical quality of the Mg-doped layers. An InGaN/GaN quantum dot light emitting diode (λpeak=529 nm) with p-GaN contact layers grown under N-rich condition exhibits a low series resistance of 9.8 Ω.

Discussion of enthalpy, entropy and free energy of formation of GaN

NASA Astrophysics Data System (ADS)

Jacob, K. T.; Rajitha, G.

2009-07-01

Presented in this letter is a critical discussion of a recent paper on experimental investigation of the enthalpy, entropy and free energy of formation of gallium nitride (GaN) published in this journal [T.J. Peshek, J.C. Angus, K. Kash, J. Cryst. Growth 311 (2008) 185-189]. It is shown that the experimental technique employed detects neither the equilibrium partial pressure of N 2 corresponding to the equilibrium between Ga and GaN at fixed temperatures nor the equilibrium temperature at constant pressure of N 2. The results of Peshek et al. are discussed in the light of other information on the Gibbs energy of formation available in the literature. Entropy of GaN is derived from heat-capacity measurements. Based on a critical analysis of all thermodynamic information now available, a set of optimized parameters is identified and a table of thermodynamic data for GaN developed from 298.15 to 1400 K.

Miscut dependent surface evolution in the process of N-polar GaN(000 1 bar) growth under N-rich condition

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.; Turski, Henryk; Sawicka, Marta; Skierbiszewski, Czesław

2017-01-01

The evolution of surface morphology during the growth of N-polar (000 1 bar) GaN under N-rich conditions is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2° and 4°. The results are compared with experimentally observed surface morphologies of (000 1 bar) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000 1 bar) surface where both types of atoms, nitrogen and gallium, attach to the surface and diffuse independently shows that at relatively high rates of the step flow (miscut angle < 2 °) the low mobility of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4°), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions crystal growth is realized by the process of two-dimensional island nucleation and coalescence. Larger crystal miscut, lower growth rate or higher temperature results in similar effect of the surface smoothening. We show that the surface also smoothens for the growth conditions with very high N-excess. In the presence of large number of nitrogen atoms the mobility of gallium atoms changes locally thus providing easier coalescence of separated island.

Efficient broad color luminescence from InGaN/GaN single quantum-well nanocolumn crystals on Si (111) substrate

NASA Astrophysics Data System (ADS)

Zhang, Wei; Zhang, Xuehua; Wang, Yongjin; Hu, Fangren

2017-10-01

Nanocolumn InGaN/GaN single quantum well crystals were deposited on Si (111) substrate with nitrified Ga dots as buffer layer. Transmission electron microscopy image shows the crystals' diameter of 100-130 nm and length of about 900 nm. Nanoscale spatial phase separation of cubic and hexagonal GaN was observed by selective area electron diffraction on the quantum well layer. Raman spectrum of the quantum well crystals proved that the crystals were fully relaxed. Room temperature photoluminescence from 450 to 750 nm and full width at half maximum of about 420 meV indicate broad color luminescence covering blue, green, yellow and red emission, which is helpful for the fabrication of tunable optoelectronic devices and colorful light emitting diodes.

Investigation on Surface Polarization of Al2O3-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray Photoelectron Spectroscopy.

PubMed

Duan, Tian Li; Pan, Ji Sheng; Wang, Ning; Cheng, Kai; Yu, Hong Yu

2017-08-17

The surface polarization of Ga-face gallium nitride (GaN) (2 nm)/AlGaN (22 nm)/GaN channel (150 nm)/buffer/Si with Al 2 O 3 capping layer is investigated by angle-resolved X-ray photoelectron spectroscopy (ARXPS). It is found that the energy band varies from upward bending to downward bending in the interface region, which is believed to be corresponding to the polarization variation. An interfacial layer is formed between top GaN and Al 2 O 3 due to the occurrence of Ga-N bond break and Ga-O bond forming during Al 2 O 3 deposition via the atomic layer deposition (ALD). This interfacial layer is believed to eliminate the GaN polarization, thus reducing the polarization-induced negative charges. Furthermore, this interfacial layer plays a key role for the introduction of the positive charges which lead the energy band downward. Finally, a N 2 annealing at 400 °C is observed to enhance the interfacial layer growth thus increasing the density of positive charges.

Substrate temperature influence on the properties of GaN thin films grown by hollow-cathode plasma-assisted atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alevli, Mustafa, E-mail: mustafaalevli@marmara.edu.tr; Gungor, Neşe; Haider, Ali

2016-01-15

Gallium nitride films were grown by hollow cathode plasma-assisted atomic layer deposition using triethylgallium and N{sub 2}/H{sub 2} plasma. An optimized recipe for GaN film was developed, and the effect of substrate temperature was studied in both self-limiting growth window and thermal decomposition-limited growth region. With increased substrate temperature, film crystallinity improved, and the optical band edge decreased from 3.60 to 3.52 eV. The refractive index and reflectivity in Reststrahlen band increased with the substrate temperature. Compressive strain is observed for both samples, and the surface roughness is observed to increase with the substrate temperature. Despite these temperature dependent material properties,more » the chemical composition, E{sub 1}(TO), phonon position, and crystalline phases present in the GaN film were relatively independent from growth temperature.« less

Study of the structure of 3D-ordered macroporous GaN-ZnS:Mn nanocomposite films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurdyukov, D. A., E-mail: kurd@gvg.ioffe.ru; Shishkin, I. I.; Grudinkin, S. A.

A film-type 3D-ordered macroporous GaN-ZnS:Mn nanocomposite with the structure of an inverted opal is fabricated. Structural studies of the nanocomposite are performed, and it is shown that GaN and ZnS:Mn introduced into the pores of the silica opal are nanocrystallites misoriented with respect to each other. It is shown that the nanocomposite is a structurally perfect 3D photonic crystal. The efficiency of using a buffer of GaN crystallites to preclude interaction between the surface of the spherical a-SiO{sub 2} particles forming the opal matrix and chemically active substances introduced into the pores is demonstrated.

Thermal stability of implanted dopants in GaN

NASA Astrophysics Data System (ADS)

Wilson, R. G.; Pearton, S. J.; Abernathy, C. R.; Zavada, J. M.

1995-04-01

Results are reported of measurements of depth profiles and stability against redistribution with annealing up to 800 or 900 °C, for implanted Be, C, Mg, Si, S, Zn, Ge, and Se as dopants in GaN. The results confirm the high-temperature stability of dopants in this material up to temperatures that vary from 600 to 900 °C. S redistributes for temperatures above 600 °C, and Zn and Se, for temperatures above 800 °C. All of the other elements are stable to 900 °C. These results indicate that direct implantation of dopants rather than masked diffusion will probably be necessary to define selective area doping of III-V nitride device structures based on these results for GaN.

Non-Ideal Properties of Gallium Nitride Based Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Shan, Qifeng

The spectacular development of gallium nitride (GaN) based light-emitting diodes (LEDs) in recent years foreshadows a new era for lighting. There are still several non-ideal properties of GaN based LEDs that hinder their widespread applications. This dissertation studies these non-ideal properties including the large reverse leakage current, large subthreshold forward leakage current, an undesired parasitic cyan luminescence and high-concentration deep levels in GaInN blue LEDs. This dissertation also studies the thermal properties of GaInN LEDs. Chapter 1 gives a brief introduction of non-ideal properties of GaN based LEDs. The leakage current of GaN based LEDs, defects in epitaxially grown GaN devices, and doping problems of p-type GaN materials are discussed. The transient junction temperature measurement technique for GaN based LEDs is introduced. The leakage current of an LED includes the subthreshold forward leakage current and the reverse leakage current. The leakage current of GaN based LEDs affects the reliability, electrostatic discharge resilience, and sub-threshold power consumption. In Chapter 2, the reverse leakage current of a GaInN LED is analyzed by temperaturedependent current-voltage measurements. At low temperature, the reverse leakage current is attributed to the variable-range-hopping conduction. At high temperature, the reverse leakage current is attributed to a thermally-assisted multi-step tunneling. The thermal activation energies (95 meV ~ 162 meV), extracted from the Arrhenius plot for the reverse current in the high-temperature range, indicate a thermally activated tunneling process. Additional room-temperature capacitance-voltage (C-V) measurements are performed to obtain information on the depletion width and doping concentration of the LED. The average internal electric field is estimated by the C-V measurements. The strong internal electric field enhances the thermal emission of electrons in the thermally-assisted multi-step tunneling process. Another problem of GaInN blue LEDs is the undesired parasitic cyan emission band. The undesired parasitic emission band strongly influence the electrical and optical properties of GaInN blue LEDs including the subthreshold forward leakage current and the color purity of the emission. In Chapter 3 , GaInN blue LEDs emitting at 445 nm with a parasitic cyan (blue-green) emission band (480 nm), which dominates the emission spectrum at low injection current, are analyzed. Photoluminescence using resonant optical excitation shows that the cyan emission originates from the active region of the LED. The current- and excitation-density-dependent blue-to-cyan intensity ratio reveals that the cyan emission is due to a transition from the conduction band to a Mg acceptor having diffused into the last-grown quantum well of the active region. The Mg in the active region provides an additional carrier-transport path, and therefore can explain the high subthreshold forward leakage current that is measured in these LEDs. Deep levels in GaN-based materials strongly affect the electrical and optical properties of GaN-based LEDs. Chapter 4 describes the basic principle and the setup of a deep-level transient spectroscopy (DLTS) measurement system. This DLTS system is used to determine the concentration and thermal activation energy of deep levels in the depletion region of the GaInN LED. Two types of hole traps in the n-type side of the depletion region are observed in the DLTS measurement. The thermal activation energies of these two types of hole traps are compared with the results reported in literature. The hole trap associated with the major DLTS peak with a thermal activation energy of 0.80 eV is presumably related to the “yellow luminescence band”. Self-heating of LEDs is an important issue that affects the efficiency and reliability. In Chapter 5, the thermal properties, including thermal time constants, of GaN LEDs are analyzed. The transient-junction-temperature behavior of unpackaged LED chips is described by a single time constant, which is the product of a thermal resistance Rth and a thermal capacitance Cth. Furthermore, a multistage RthCth thermal model for packaged LEDs is developed. The transient response of the junction temperature of LEDs after the power is switched on or switched off can be described by a multi-exponential function. Each time constant of this function is approximately the product of a thermal resistance, Rth, and a thermal capacitance, Cth. The transient junction temperature after the power is switched off is measured for a high-power flip-chip LED by the forward-voltage method. A two-stage RthCth model is used to analyze the thermal properties of the packaged LED. Two time constants, 2.72 ms and 18.7 ms are extracted from the junction temperature decay measurement and attributed to the thermal time constant of the LED GaN / sapphire chip and LED Si submount, respectively.

Systematic study on dynamic atomic layer epitaxy of InN on/in +c-GaN matrix and fabrication of fine-structure InN/GaN quantum wells: Role of high growth temperature

NASA Astrophysics Data System (ADS)

Yoshikawa, Akihiko; Kusakabe, Kazuhide; Hashimoto, Naoki; Hwang, Eun-Sook; Imai, Daichi; Itoi, Takaomi

2016-12-01

The growth kinetics and properties of nominally 1-ML (monolayer)-thick InN wells on/in +c-GaN matrix fabricated using dynamic atomic layer epitaxy (D-ALEp) by plasma-assisted molecular beam epitaxy were systematically studied, with particular attention given to the effects of growth temperature. Attention was also given to how and where the ˜1-ML-thick InN layers were frozen or embedded on/in the +c-GaN matrix. The D-ALEp of InN on GaN was a two-stage process; in the 1st stage, an "In+N" bilayer/monolayer was formed on the GaN surface, while in the 2nd, this was capped by a GaN barrier layer. Each process was monitored in-situ using spectroscopic ellipsometry. The target growth temperature was above 620 °C and much higher than the upper critical epitaxy temperature of InN (˜500 °C). The "In+N" bilayer/monolayer tended to be an incommensurate phase, and the growth of InN layers was possible only when they were capped with a GaN layer. The InN layers could be coherently inserted into the GaN matrix under self-organizing and self-limiting epitaxy modes. The growth temperature was the most dominant growth parameter on both the growth process and the structure of the InN layers. Reflecting the inherent growth behavior of D-ALEp grown InN on/in +c-GaN at high growth temperature, the embedded InN layers in the GaN matrix were basically not full-ML in coverage, and the thickness of sheet-island-like InN layers was essentially either 1-ML or 2-ML. It was found that these InN layers tended to be frozen at the step edges on the GaN and around screw-type threading dislocations. The InN wells formed type-I band line-up heterostructures with GaN barriers, with exciton localization energies of about 300 and 500 meV at 15 K for the 1-ML and 2-ML InN wells, respectively.

Multiferroic GaN nanofilms grown within Na-4 mica channels

NASA Astrophysics Data System (ADS)

Bhattacharya, Santanu; Datta, A.; Chakravorty, D.

2010-03-01

Gallium nitride nanofilms grown within nanochannels of Na-4 mica structure, exhibit ferromagnetism even at room temperature due to the presence of gallium vacancies at the surfaces of the nanofilms. These nanofilms also show a ferroelectric behavior at room temperature ascribed to a small distortion in the crystal structure of GaN due to its growth within the Na-4 mica nanochannels. A colossal increase in 338% in dielectric constant was observed for an applied magnetic field of 26 kOe. The magnetoelectric effect is ascribed to magnetostriction of magnetic GaN phase.

Advantages of InGaN/GaN multiple quantum wells with two-step grown low temperature GaN cap layers

NASA Astrophysics Data System (ADS)

Zhu, Yadan; Lu, Taiping; Zhou, Xiaorun; Zhao, Guangzhou; Dong, Hailiang; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

2017-11-01

Two-step grown low temperature GaN cap layers (LT-cap) are employed to improve the optical and structural properties of InGaN/GaN multiple quantum wells (MQWs). The first LT-cap layer is grown in nitrogen atmosphere, while a small hydrogen flow is added to the carrier gas during the growth of the second LT-cap layer. High-resolution X-ray diffraction results indicate that the two-step growth method can improve the interface quality of MQWs. Room temperature photoluminescence (PL) tests show about two-fold enhancement in integrated PL intensity, only 25 meV blue-shift in peak energy and almost unchanged line width. On the basis of temperature-dependent PL characteristics analysis, it is concluded that the first and the second LT-cap layer play a different role during the growth of MQWs. The first LT-cap layer acts as a protective layer, which protects quantum well from serious indium loss and interface roughening resulting from the hydrogen over-etching. The hydrogen gas employed in the second LT-cap layer is in favor of reducing defect density and indium segregation. Consequently, interface/surface and optical properties are improved by adopting the two-step growth method.

Aqueous synthesis of zinc oxide films for GaN optoelectronic devices

NASA Astrophysics Data System (ADS)

Reading, Arthur H.

GaN-based LEDs have generally made use of ITO transparent contacts as current-spreading layers for uniform current injection. However, the high raw material and processing costs of ITO layers have generated interest in potentially cheaper alternatives. In this work, zinc oxide transparent layers were fabricated by a low-cost, low-temperature aqueous epitaxial growth method at 90°C for use as transparent contacts to GaN LEDs on c-plane sapphire, and on semipolar bulk GaN substrates. Low-voltage operation was achieved for c-plane devices, with voltages below 3.8V for 1mm2 broad-area LEDs at a current density of 30A/cm 2. Blue-green LEDs on 202¯1¯-plane GaN also showed low voltage operation below 3.5V at 30A/cm2. Ohmic contact resistivity of 1:8 x 10-2Ocm2 was measured for films on (202¯1) p-GaN templates. Ga-doped films had electrical conductivities as high as 660S/cm after annealing at 300°C. Optical characterization revealed optical absorption coefficients in the 50--200cm -1 range for visible light, allowing thick films with sheet resistances below 10O/□ to be grown while minimizing absorption of the emitted light. Accurate and reproducible etch-free patterning of the ZnO films was achieved using templated growths with SiOx hard masks. A roughening method is described which was found to increase peak LED efficiencies by 13% on c-plane patterned sapphire (PSS) substrates. In addition, ZnO films were successfully employed as laser-cladding layers for blue (202¯1) lasers, with a threshold current density of 8.8kA/cm 2.

Macrodefect-free, large, and thick GaN bulk crystals for high-quality 2–6 in. GaN substrates by hydride vapor phase epitaxy with hardness control

NASA Astrophysics Data System (ADS)

Fujikura, Hajime; Konno, Taichiro; Suzuki, Takayuki; Kitamura, Toshio; Fujimoto, Tetsuji; Yoshida, Takehiro

2018-06-01

On the basis of a novel crystal hardness control, we successfully realized macrodefect-free, large (2–6 in.) and thick +c-oriented GaN bulk crystals by hydride vapor phase epitaxy. Without the hardness control, the introduction of macrodefects including inversion domains and/or basal-plane dislocations seemed to be indispensable to avoid crystal fracture in GaN growth with millimeter thickness. However, the presence of these macrodefects tended to limit the applicability of the GaN substrate to practical devices. The present technology markedly increased the GaN crystal hardness from below 20 to 22 GPa, thus increasing the available growth thickness from below 1 mm to over 6 mm even without macrodefect introduction. The 2 and 4 in. GaN wafers fabricated from these crystals had extremely low dislocation densities in the low- to mid-105 cm‑2 range and low off-angle variations (2 in.: <0.1° 4 in.: ∼0.2°). The realization of such high-quality 6 in. wafers is also expected.

Polarization-Engineered Ga-Face GaN-Based Heterostructures for Normally-Off Heterostructure Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Kim, Hyeongnam; Nath, Digbijoy; Rajan, Siddharth; Lu, Wu

2013-01-01

Polarization-engineered Ga-face GaN-based heterostructures with a GaN cap layer and an AlGaN/ p-GaN back barrier have been designed for normally-off field-effect transistors (FETs). The simulation results show that an unintentionally doped GaN cap and p-GaN layer in the buffer primarily deplete electrons in the channel and the Al0.2Ga0.8N back barrier helps to pinch off the channel. Experimentally, we have demonstrated a normally-off GaN-based field-effect transistor on the designed GaN cap/Al0.3Ga0.7N/GaN channel/Al0.2Ga0.8N/ p-GaN/GaN heterostructure. A positive threshold voltage of 0.2 V and maximum transconductance of 2.6 mS/mm were achieved for 80- μm-long gate devices. The device fabrication process does not require a dry etching process for gate recessing, while highly selective etching of the GaN cap against a very thin Al0.3GaN0.7N top barrier has to be performed to create a two-dimensional electron gas for both the ohmic and access regions. A self-aligned, selective etch of the GaN cap in the access region is introduced, using the gate metal as an etch mask. The absence of gate recess etching is promising for uniform and repeatable threshold voltage control in normally-off AlGaN/GaN heterostructure FETs for power switching applications.

Growth condition dependence of unintentional oxygen incorporation in epitaxial GaN

PubMed Central

Schubert, Felix; Wirth, Steffen; Zimmermann, Friederike; Heitmann, Johannes; Mikolajick, Thomas; Schmult, Stefan

2016-01-01

Abstract Growth conditions have a tremendous impact on the unintentional background impurity concentration in gallium nitride (GaN) synthesized by molecular beam epitaxy and its resulting chemical and physical properties. In particular for oxygen identified as the dominant background impurity we demonstrate that under optimized growth stoichiometry the growth temperature is the key parameter to control its incorporation and that an increase by 55 °C leads to an oxygen reduction by one order of magnitude. Quantitatively this reduction and the resulting optical and electrical properties are analyzed by secondary ion mass spectroscopy, photoluminescence, capacitance versus voltage measurements, low temperature magneto-transport and parasitic current paths in lateral transistor test structures based on two-dimensional electron gases. At a growth temperature of 665 °C the residual charge carrier concentration is decreased to below 1015 cm−3, resulting in insulating behavior and thus making the material suitable for beyond state-of-the-art device applications. PMID:27877874

Optical Probing of Low-Pressure Solution Grown GaN Crystal Properties

DTIC Science & Technology

2010-04-01

observed in Mg and Si doped epitaxial films deposited by MBE and MOCVD on freestanding GaN HVPE substrates [23–25]. Considering the purity of the precursors...bands with similar energy positions here reported, a dominant deeper acceptor impurity has been assigned to Zn , a well known deep acceptor in GaN . Room...00-00-2010 to 00-00-2010 4. TITLE AND SUBTITLE Optical probing of low-pressure solution grown GaN crystal properties 5a. CONTRACT NUMBER 5b

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenlee, Jordan D., E-mail: jordan.greenlee.ctr@nrl.navy.mil; Feigelson, Boris N.; Anderson, Travis J.

2014-08-14

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N{sub 2} overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at halfmore » maximums of the E{sub 2} and A{sub 1} (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.« less

Effect of thermal interaction between bulk GaN substrates and corral sapphire on blue light emission InGaN/GaN multi-quantum wells by MOCVD

NASA Astrophysics Data System (ADS)

Sivanathan, P. C.; Shuhaimi, Ahmad; Hamza, Hebal; Kowsz, Stacy J.; Abdul Khudus, Muhammad I. M.; Li, Hongjian; Allif, Kamarul

2018-07-01

The InGaN/GaN multi-quantum wells, growth on bulk GaN substrate were studied for blue light emission. Growth temperature plays a key role determining the peak wavelength of a quantum well. The study was carried out by growing quantum wells, MQWs on the whole sapphire at 716 °C and observed peak wavelength at 463 nm. While the bulk GaN substrate with sapphire corral grown at 703 °C and observed a blueshift at 433 nm peak wavelength. These results contradict that of typical observation of wavelength emission inversely proportional to the growth temperature. On the other hand, the growth of GaN-sapphire and GaN-silicon at similar conditions emits 435 nm and 450 nm respectively. The heat interaction of bulk GaN substrates surrounded by the sapphire corral exhibits different growth conditions in multi-quantum wells when compared to that of a whole sapphire substrate (absence of bulk GaN). The predicated surface temperature of bulk GaN substrate is 10 °C-15 °C of more than the corral sapphire. This observation may link to the difference in the thermal distribution of the growth surface corresponding to the different thermal conductivity ratio. The photoluminescence and computational techniques were used to understand in-depth of the heat interaction.

Self-Aligned ALD AlOx T-gate Insulator for Gate Leakage Current Suppression in SiNx-Passivated AlGaN/GaN HEMTs

DTIC Science & Technology

2010-01-01

Heterostructure epitaxial material growth was performed by RF plasma-assisted molecular - beam epitaxy (MBE) on a 2-in. semi- insulating 4H SiC wafer. From... beam epitaxy of beryllium-doped GaN buffer layers for AlGaN/GaN HEMTs . J Cryst Growth 2003;251:481–6. [25] Storm DF, Katzer DS, Binari SC, Glaser ER...Shanabrook BV, Roussos JA. Reduction of buffer layer conduction near plasma-assisted molecular - beam epitaxy grown GaN/AlN interfaces by beryllium

Controlling the optical properties of monocrystalline 3C-SiC heteroepitaxially grown on silicon at low temperatures

NASA Astrophysics Data System (ADS)

Colston, Gerard; Myronov, Maksym

2017-11-01

Cubic silicon carbide (3C-SiC) offers an alternative wide bandgap semiconductor to conventional materials such as hexagonal silicon carbide (4H-SiC) or gallium nitride (GaN) for the detection of UV light and can offer a closely lattice matched virtual substrate for subsequent GaN heteroepitaxy. As 3C-SiC can be heteroepitaxially grown on silicon (Si) substrates its optical properties can be manipulated by controlling the thickness and doping concentrations. The optical properties of 3C-SiC epilayers have been characterized by measuring the transmission of light through suspended membranes. Decreasing the thickness of the 3C-SiC epilayers is shown to shift the absorbance edge to lower wavelengths, a result of the indirect bandgap nature of silicon carbide. This property, among others, can be exploited to fabricate very low-cost, tuneable 3C-SiC based UV photodetectors. This study investigates the effect of thickness and doping concentration on the optical properties of 3C-SiC epilayers grown at low temperatures by a standard Si based growth process. The results demonstrate the potential photonic applications of 3C-SiC and its heterogeneous integration into the Si industry.

Depth Profiles of Mg, Si, and Zn Implants in GaN by Trace Element Accelerator Mass Spectrometry

NASA Astrophysics Data System (ADS)

Ravi Prasad, G. V.; Pelicon, P.; Mitchell, L. J.; McDaniel, F. D.

2003-08-01

GaN is one of the most promising electronic materials for applications requiring high-power, high frequencies, or high-temperatures as well as opto-electronics in the blue to ultraviolet spectral region. We have recently measured depth profiles of Mg, Si, and Zn implants in GaN substrates by the TEAMS particle counting method for both matrix and trace elements, using a gas ionization chamber. Trace Element Accelerator Mass Spectrometry (TEAMS) is a combination of Secondary Ion Mass Spectrometry (SIMS) and Accelerator Mass Spectrometry (AMS) to measure trace elements at ppb levels. Negative ions from a SIMS like source are injected into a tandem accelerator. Molecular interferences inherent with the SIMS method are eliminated in the TEAMS method. Negative ion currents are extremely low with GaN as neither gallium nor nitrogen readily forms negative ions making the depth profile measurements more difficult. The energies of the measured ions are in the range of 4-8 MeV. A careful selection of mass/charge ratios of the detected ions combined with energy-loss behavior of the ions in the ionization chamber eliminated molecular interferences.

Selective formation of GaN-based nanorod heterostructures on soda-lime glass substrates by a local heating method.

PubMed

Hong, Young Joon; Kim, Yong-Jin; Jeon, Jong-Myeong; Kim, Miyoung; Choi, Jun Hee; Baik, Chan Wook; Kim, Sun Il; Park, Sung Soo; Kim, Jong Min; Yi, Gyu-Chul

2011-05-20

We report on the fabrication of high-quality GaN on soda-lime glass substrates, heretofore precluded by both the intolerance of soda-lime glass to the high temperatures required for III-nitride growth and the lack of an epitaxial relationship with amorphous glass. The difficulties were circumvented by heteroepitaxial coating of GaN on ZnO nanorods via a local microheating method. Metal-organic chemical vapor deposition of ZnO nanorods and GaN layers using the microheater arrays produced high-quality GaN/ZnO coaxial nanorod heterostructures at only the desired regions on the soda-lime glass substrates. High-resolution transmission electron microscopy examination of the coaxial nanorod heterostructures indicated the formation of an abrupt, semicoherent interface. Photoluminescence and cathodoluminescence spectroscopy was also applied to confirm the high optical quality of the coaxial nanorod heterostructures. Mg-doped GaN/ZnO coaxial nanorod heterostructure arrays, whose GaN shell layers were grown with various different magnesocene flow rates, were further investigated by using photoluminescence spectroscopy for the p-type doping characteristics. The suggested method for fabrication of III-nitrides on glass substrates signifies potentials for low-cost and large-size optoelectronic device applications.

Ionic liquid gating on atomic layer deposition passivated GaN: Ultra-high electron density induced high drain current and low contact resistance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Hong; Du, Yuchen; Ye, Peide D., E-mail: yep@purdue.edu

2016-05-16

Herein, we report on achieving ultra-high electron density (exceeding 10{sup 14 }cm{sup −2}) in a GaN bulk material device by ionic liquid gating, through the application of atomic layer deposition (ALD) of Al{sub 2}O{sub 3} to passivate the GaN surface. Output characteristics demonstrate a maximum drain current of 1.47 A/mm, the highest reported among all bulk GaN field-effect transistors, with an on/off ratio of 10{sup 5} at room temperature. An ultra-high electron density exceeding 10{sup 14 }cm{sup −2} accumulated at the surface is confirmed via Hall-effect measurement and transfer length measurement. In addition to the ultra-high electron density, we also observe a reductionmore » of the contact resistance due to the narrowing of the Schottky barrier width on the contacts. Taking advantage of the ALD surface passivation and ionic liquid gating technique, this work provides a route to study the field-effect and carrier transport properties of conventional semiconductors in unprecedented ultra-high charge density regions.« less

Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Erdong; Li, Qiming; Swartzentruber, Brian

2015-11-25

The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN coremore » of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. As a result, selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.« less

Comparison of gate and drain current detection of hydrogen at room temperature with AlGaN /GaN high electron mobility transistors

NASA Astrophysics Data System (ADS)

Wang, Hung-Ta; Kang, B. S.; Ren, F.; Fitch, R. C.; Gillespie, J. K.; Moser, N.; Jessen, G.; Jenkins, T.; Dettmer, R.; Via, D.; Crespo, A.; Gila, B. P.; Abernathy, C. R.; Pearton, S. J.

2005-10-01

Pt-gated AlGaN /GaN high electron mobility transistors can be used as room-temperature hydrogen gas sensors at hydrogen concentrations as low as 100ppm. A comparison of the changes in drain and gate current-voltage (I-V) characteristics with the introduction of 500ppm H2 into the measurement ambient shows that monitoring the change in drain-source current provides a wider gate voltage operation range for maximum detection sensitivity and higher total current change than measuring the change in gate current. However, over a narrow gate voltage range, the relative sensitivity of detection by monitoring the gate current changes is up to an order of magnitude larger than that of drain-source current changes. In both cases, the changes are fully reversible in <2-3min at 25°C upon removal of the hydrogen from the ambient.

Room temperature exciton-polariton resonant reflection and suppressed absorption in periodic systems of InGaN quantum wells

NASA Astrophysics Data System (ADS)

Bolshakov, A. S.; Chaldyshev, V. V.; Zavarin, E. E.; Sakharov, A. V.; Lundin, W. V.; Tsatsulnikov, A. F.; Yagovkina, M. A.

2017-04-01

We studied the optical properties of periodic InGaN/GaN multiple quantum well systems with different numbers of periods. A resonant increase in the optical reflection and simultaneous suppression of the optical absorption have been revealed experimentally at room temperature when the Bragg and exciton resonances were tuned to each other. Numerical modeling with a single set of parameters gave a quantitatively accurate fit of the experimental reflection and transmission spectra in a wide wavelength range and various angles of the light incidence. The model included both exciton resonance and non-resonant band-to-band transitions in the InGaN quantum wells, as well as Rayleigh light scattering in the GaN buffer layer. The analysis also involved x-ray diffraction and photoluminescence data. It allowed us to determine the key parameters of the structure. In particular, the radiative broadening of the InGaN QW excitons was evaluated as 0.20 ± 0.02 meV.

NH3-free growth of GaN nanostructure on n-Si (1 1 1) substrate using a conventional thermal evaporation technique

NASA Astrophysics Data System (ADS)

Saron, K. M. A.; Hashim, M. R.; Farrukh, M. A.

2012-06-01

We have investigated the influence of carrier gas on grown gallium nitride (GaN) epitaxial layers deposited on n-Si (1 1 1) by a physical vapour deposition (PVD) via thermal evaporation of GaN powder at 1150 °C. The GaN nanostructures were grown at a temperature of 1050 °C for 60 min under various gases (N2, H2 mixed with N2, and Ar2) with absence of NH3. The morphology, structure, and optical properties (SEM) images showed that the morphology of GaN displayed various shapes of nanostructured depending on the type of carrier gas. X-ray diffraction (XRD) pattern showed that the GaN polycrystalline reveals a wurtzite-hexagonal structure with [0 0 1] crystal orientation. Raman spectra exhibited a red shift in peaks of E2 (high) as a result of tensile stress. Photoluminescence (PL) measurements showed two band emissions aside from the UV emission. The ultraviolet band gap of GaN nanostructure displayed a red shift as compared with the bulk GaN; this might be attributed to an increase in the defect and stress present in the GaN nanostructure. In addition, the observed blue and green-yellow emissions indicated defects due to the N vacancy and C impurity of the supplied gas. These results clearly indicated that the carrier gas, similar to the growth temperature, is one of the important parameters to control the quality of thermal evaporation (TE)-GaN epilayers.

Method to grow group III-nitrides on copper using passivation layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Qiming; Wang, George T; Figiel, Jeffrey T

Group III-nitride epilayers can be grown directly on copper substrates using intermediate passivation layers. For example, single crystalline c-plane GaN can be grown on Cu (110) substrates with MOCVD. The growth relies on a low temperature AlN passivation layer to isolate any alloying reaction between Ga and Cu.

Hydrogen effects on the electroluminescence of n-ZnO nanorod/p-GaN film heterojunction light-emitting diodes.

PubMed

Fang, Fang; Zhao, Dongxu; Li, Binghui; Zhang, Zhenzhong; Shen, Dezhen

2010-07-07

Through a facile low-temperature solution process, vertically n-type ZnO nanorod arrays were grown on a GaN film to form a n-ZnO nanorod/p-GaN film heterojunction. A study of the electroluminescence (EL) characteristics of the heterojunction in air and in air with 2000 ppm hydrogen revealed the sensitivity of such a device to the surrounding atmosphere. The additional hydrogen shallow donors increased the effective electron concentration in ZnO nanorods and the EL recombination zone changed from the ZnO nanorods to the GaN film, which can be identified visually from the color change.

Investigation on thermodynamics of ion-slicing of GaN and heterogeneously integrating high-quality GaN films on CMOS compatible Si(100) substrates.

PubMed

Huang, Kai; Jia, Qi; You, Tiangui; Zhang, Runchun; Lin, Jiajie; Zhang, Shibin; Zhou, Min; Zhang, Bo; Yu, Wenjie; Ou, Xin; Wang, Xi

2017-11-08

Die-to-wafer heterogeneous integration of single-crystalline GaN film with CMOS compatible Si(100) substrate using the ion-cutting technique has been demonstrated. The thermodynamics of GaN surface blistering is in-situ investigated via a thermal-stage optical microscopy, which indicates that the large activation energy (2.5 eV) and low H ions utilization ratio (~6%) might result in the extremely high H fluence required for the ion-slicing of GaN. The crystalline quality, surface topography and the microstructure of the GaN films are characterized in detail. The full width at half maximum (FWHM) for GaN (002) X-ray rocking curves is as low as 163 arcsec, corresponding to a density of threading dislocation of 5 × 10 7  cm -2 . Different evolution of the implantation-induced damage was observed and a relationship between the damage evolution and implantation-induced damage is demonstrated. This work would be beneficial to understand the mechanism of ion-slicing of GaN and to provide a platform for the hybrid integration of GaN devices with standard Si CMOS process.

Improved properties of barium strontium titanate thin films grown on copper foils by pulsed laser deposition using a self-buffered layer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, S.; Ma, B.; Narayanan, M.

2012-01-01

Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} (BST) films were deposited by pulsed laser deposition on copper foils with low-temperature self-buffered layers. The deposition conditions included a low oxygen partial pressure and a temperature of 700 C to crystallize the films without the formation of secondary phases and substrate oxidation. The results from x-ray diffraction and scanning electron microscopy indicated that the microstructure of the BST films strongly depended on the growth temperature. The use of the self-buffered layer improved the dielectric properties of the deposited BST films. The leakage current density of the BST films on the copper foil was 4.4 xmore » 10{sup -9} A cm{sup -2} and 3.3 x 10{sup -6} A cm{sup -2} with and without the self-buffered layer, respectively. The ferroelectric hysteresis loop for the BST thin film with buffer layer was slim, in contrast to the distorted loop observed for the film without the buffer layer. The permittivity (7 0 0) and dielectric loss tangent (0.013) of the BST film on the copper foil with self-buffered layer at room temperature were comparable to those of the film on metal and single-crystal substrates.« less

Synthesis of galium nitride thin films using sol-gel dip coating method

NASA Astrophysics Data System (ADS)

Hamid, Maizatul Akmam Ab; Ng, Sha Shiong

2017-12-01

In this research, gallium nitride (GaN) thin film were grown on silicon (Si) substrate by a low-cost sol-gel dip coating deposition method. The GaN precursor solution was prepared using gallium (III) nitrate hydrate powder, ethanol and diethanolamine as a starting material, solvent and surfactant respectively. The structural, morphological and optical characteristics of the deposited GaN thin film were investigated. Field-emission scanning electron microscopy observations showed that crack free and dense grains GaN thin films were formed. Energy dispersive X-ray analysis confirmed that the oxygen content in the deposited films was low. X-ray diffraction results revealed that deposited GaN thin films have hexagonal wurtzite structure.

High quality Ge epilayer on Si (1 0 0) with an ultrathin Si1-x Ge x /Si buffer layer by RPCVD

NASA Astrophysics Data System (ADS)

Chen, Da; Guo, Qinglei; Zhang, Nan; Xu, Anli; Wang, Bei; Li, Ya; Wang, Gang

2017-07-01

The authors report a method to grow high quality strain-relaxed Ge epilayer on a combination of low temperature Ge seed layer and Si1-x Ge x /Si superlattice buffer layer by reduced pressure chemical vapor deposition system without any subsequent annealing treatment. Prior to the growth of high quality Ge epilayer, an ultrathin Si1-x Ge x /Si superlattice buffer layer with the thickness of 50 nm and a 460 nm Ge seed layer were deposited successively at low temperature. Then an 840 nm Ge epilayer was grown at high deposition rate with the surface root-mean-square roughness of 0.707 nm and threading dislocation density of 2.5  ×  106 cm-2, respectively. Detailed investigations of the influence of ultrathin low-temperature Si1-x Ge x /Si superlattice buffer layer on the quality of Ge epilayer were performed, which indicates that the crystalline quality of Ge epilayer can be significantly improved by enhancing the Ge concentration of Si1-x Ge x /Si superlattice buffer layer.

Defect-related photoluminescence in Mg-doped GaN nanostructures

NASA Astrophysics Data System (ADS)

Reshchikov, M. A.; Shahedipour-Sandvik, F.; Messer, B. J.; Jindal, V.; Tripathi, N.; Tungare, M.

2009-12-01

Thin film of GaN:Mg, pyramidal GaN:Mg on GaN, sapphire and AlN substrates were grown in a MOCVD system under same growth conditions and at the same time. In samples with Mg-doped GaN pyramids on GaN:Si template a strong ultraviolet (UVL) band with few phonon replicas dominated at low temperature and was attributed to transitions from shallow donors to shallow Mg acceptor. In samples grown on sapphire and AlN substrates the UVL band appeared as a structureless band with the maximum at about 3.25 eV. There is a possibility that the structureless UVL band and the UVL band with phonon structure have different origin. In addition to the UVL band, the blue luminescence (BL) band peaking at 2.9 eV was observed in samples representing GaN:Mg pyramids on GaN:Si substrate. It is preliminary attributed to transitions from shallow donors to Zn acceptor in GaN:Si substrate.

Synthesis of GaN by high-pressure ammonolysis of gallium triiodide

NASA Astrophysics Data System (ADS)

Purdy, Andrew P.; Case, Sean; Muratore, Nicole

2003-05-01

The ammonothermal conversion of GaI 3 to both cubic (zinc-blende) and hexagonal GaN was explored in detail. Gallium triiodide, anhydrous NH 3, and in some cases CuI or LiI co-mineralizers, were sealed in quartz tubes and heated in a pressurized autoclave from 300°C to 515°C. At hot-zone temperatures above 430°C, a deposit of mostly c-GaN collects in the upper portion of the tube, and deposits of phase-pure c-GaN were reliably produced on a 50-60 mg scale when CuI co-mineralizer was added. Crystal morphologies of these microcrystalline c-GaN products are highly dependent on growth conditions and range from triangular prisms to triangular plates, dendritic crystals, and irregular particles. Hexagonal GaN products were either in the form of microrods or micron sized prisms. Nanorods, of presumably h-GaN, also formed in some reactions in low yields, intermixed with microcrystalline c-GaN products.

Development of high temperature stable Ohmic and Schottky contacts on n-gallium nitride

NASA Astrophysics Data System (ADS)

Khanna, Rohit

In this work the effort was made to towards develop and investigate high temperature stable Ohmic and Schottky contacts for n type GaN. Various borides and refractory materials were incorporated in metallization scheme to best attain the desired effect of minimal degradation of contacts when placed at high temperatures. This work focuses on achieving a contact scheme using different borides which include two Tungsten Borides (namely W2B, W2B 5), Titanium Boride (TiB2), Chromium Boride (CrB2) and Zirconium Boride (ZrB2). Further a high temperature metal namely Iridium (Ir) was evaluated as a potential contact to n-GaN, as part of continuing improved device technology development. The main goal of this project was to investigate the most promising boride-based contact metallurgies on GaN, and finally to fabricate a High Electron Mobility Transistor (HEMT) and compare its reliability to a HEMT using present technology contact. Ohmic contacts were fabricated on n GaN using borides in the metallization scheme of Ti/Al/boride/Ti/Au. The characterization of the contacts was done using current-voltage measurements, scanning electron microscopy (SEM) and Auger Electron Spectroscopy (AES) measurements. The contacts formed gave specific contact resistance of the order of 10-5 to 10-6 Ohm-cm2. A minimum contact resistance of 1.5x10-6 O.cm 2 was achieved for the TiB2 based scheme at an annealing temperature of 850-900°C, which was comparable to a regular ohmic contact of Ti/Al/Ni/Au on n GaN. When some of borides contacts were placed on a hot plate or in hot oven for temperature ranging from 200°C to 350°C, the regular metallization contacts degraded before than borides ones. Even with a certain amount of intermixing of the metallization scheme the boride contacts showed minimal roughening and smoother morphology, which, in terms of edge acuity, is crucial for very small gate devices. Schottky contacts were also fabricated and characterized using all the five boride compounds. The barrier height obtained on n GaN was ˜0-5-0.6 eV which was low compared to those obtained by Pt or Ni. This barrier height is too low for use as a gate contact and they can only have limited use, perhaps, in gas sensors where large leakage current can be tolerated in exchange for better thermal reliability. AlGaN/GaN High Electron Mobility Transistors (HEMTs) were fabricated with Ti/Al/TiB2/Ti/Au source/drain ohmic contacts and a variety of gate metal schemes (Pt/Au, Ni/Au, Pt/TiB2/Au or Ni/TiB 2/Au) and were subjected to long-term annealing at 350°C. By comparison with companion devices with conventional Ti/Al/Pt/Au ohmic contacts and Pt/Au gate contacts, the HEMTs with boride-based ohmic metal and either Pt/Au, Ni/Au or Ni/TiB2/Au gate metal showed superior stability of both source-drain current and transconductance after 25 days aging at 350°C. The need for sputter deposition of the borides causes' problem in achieving significantly lower specific contact resistance than with conventional schemes deposited using e-beam evaporation. The borides also seem to be, in general, good getters for oxygen leading to sheet resistivity issues. Ir/Au Schottky contacts and Ti/Al/Ir/Au ohmic contacts on n-type GaN were investigated as a function of annealing temperature and compared to their more common Ni-based counterparts. The Ir/Au ohmic contacts on n-type GaN with n˜1017 cm-3 exhibited barrier heights of 0.55 eV after annealing at 700°C and displayed less intermixing of the contact metals compared to Ni/Au. A minimum specific contact resistance of 1.6 x 10-6 O.cm2 was obtained for the ohmic contacts on n-type GaN with n˜1018 cm-3 after annealing at 900°C. The measurement temperature dependence of contact resistance was similar for both Ti/Al/Ir/Au and Ti/Al/Ni/Au, suggesting the same transport mechanism was present in both types of contacts. The Ir-based ohmic contacts displayed superior thermal aging characteristics at 350°C. Auger Electron Spectroscopy showed that Ir is a superior diffusion barrier at these moderate temperatures than Ni.

Photophysics of GaN single-photon emitters in the visible spectral range

NASA Astrophysics Data System (ADS)

Berhane, Amanuel M.; Jeong, Kwang-Yong; Bradac, Carlo; Walsh, Michael; Englund, Dirk; Toth, Milos; Aharonovich, Igor

2018-04-01

In this work, we present a detailed photophysical analysis of recently discovered, optically stable single-photon emitters (SPEs) in gallium nitride (GaN). Temperature-resolved photoluminescence measurements reveal that the emission lines at 4 K are three orders of magnitude broader than the transform-limited width expected from excited-state lifetime measurements. The broadening is ascribed to ultrafast spectral diffusion. The photophysical study on several emitters at room temperature (RT) reveals an average brightness of (427 ±215 )kCounts /s . Finally, polarization measurements from 14 emitters are used to determine visibility as well as dipole orientation of defect systems within the GaN crystal. Our results underpin some of the fundamental properties of SPEs in GaN both at cryogenic and RT, and define the benchmark for future work in GaN-based single-photon technologies.

Performance Analysis of GaN Capping Layer Thickness on GaN/AlGaN/GaN High Electron Mobility Transistors.

PubMed

Sharma, N; Periasamy, C; Chaturvedi, N

2018-07-01

In this paper, we present an investigation of the impact of GaN capping layer and AlGaN layer thickness on the two-dimensional (2D)-electron mobility and the carrier concentration which was formed close to the AlGaN/GaN buffer layer for Al0.25Ga0.75N/GaN and GaN/Al0.25Ga0.75N/GaN heterostructures deposited on sapphire substrates. The results of our analysis clearly indicate that expanding the GaN capping layer thickness from 1 nm to 100 nm prompts an increment in the electron concentration at hetero interface. As consequence of which drain current was additionally increments with GaN cap layer thicknesses, and eventually saturates at approximately 1.85 A/mm for capping layer thickness greater than 40 nm. Interestingly, for the same structure, the 2D-electron mobility, decrease monotonically with GaN capping layer thickness, and saturate at approximately 830 cm2/Vs for capping layer thickness greater than 50 nm. A device with a GaN cap layer didn't exhibit gate leakage current. Furthermore, it was observed that the carrier concentration was first decrease 1.03 × 1019/cm3 to 6.65 × 1018/cm3 with AlGaN Layer thickness from 5 to 10 nm and after that it increases with the AlGaN layer thickness from 10 to 30 nm. The same trend was followed for electric field distributions. Electron mobility decreases monotonically with AlGaN layer thickness. Highest electron mobility 1354 cm2/Vs were recorded for the AlGaN layer thickness of 5 nm. Results obtained are in good agreement with published experimental data.

Temperature dependence on plasma-induced damage and chemical reactions in GaN etching processes using chlorine plasma

NASA Astrophysics Data System (ADS)

Liu, Zecheng; Ishikawa, Kenji; Imamura, Masato; Tsutsumi, Takayoshi; Kondo, Hiroki; Oda, Osamu; Sekine, Makoto; Hori, Masaru

2018-06-01

Plasma-induced damage (PID) on GaN was optimally reduced by high-temperature chlorine plasma etching. Energetic ion bombardments primarily induced PID involving stoichiometry, surface roughness, and photoluminescence (PL) degradation. Chemical reactions under ultraviolet (UV) irradiation and chlorine radical exposure at temperatures higher than 400 °C can be controlled by taking into account the synergism of simultaneous photon and radical irradiations to effectively reduce PID.

Photoemission stability of negative electron affinity GaN photocathode

NASA Astrophysics Data System (ADS)

Zhang, Junju; Wang, Xiaohui; Yang, Wenzheng; Tang, Weidong; Fu, Xiaoqian; Li, Biao; Chang, Benkang

2012-11-01

The stability for reflection-mode GaN photocathode has been investigated by monitoring the photocurrent and the spectral response at room temperature. We watch that the photocurrent of the cathode decays with time in the vacuum system, and compare the spectral response curves after activation and after degradation. The photocurrent decay mechanism for reflection-mode NEA GaN photocathode was studied by the surface model ?GaN (Mg) :Cs ?:O-Cs. The reduction of the effective dipole quantity, which is caused by harmful gases, is the key factor of the photocurrent reduction.

Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology

PubMed Central

Li, Ying-Chang; Chang, Liann-Be; Chen, Hou-Jen; Yen, Chia-Yi; Pan, Ke-Wei; Huang, Bohr-Ran; Kuo, Wen-Yu; Chow, Lee; Zhou, Dan; Popko, Ewa

2017-01-01

Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot and reported LED’s color rendering index (CRI) are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL) and electroluminescence (EL) spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI) of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications. PMID:28772792

Influences of growth parameters on the reaction pathway during GaN synthesis

NASA Astrophysics Data System (ADS)

Zhang, Zhi; Liu, Zhongyi; Fang, Haisheng

2018-01-01

Gallium nitride (GaN) film growth is a complicated physical and chemical process including fluid flow, heat transfer, species transport and chemical reaction. Study of the reaction mechanism, i.e., the reaction pathway, is important for optimizing the growth process in the actual manufacture. In the paper, the growth pathway of GaN in a closed-coupled showerhead metal-organic chemical vapor deposition (CCS-MOCVD) reactor is investigated in detail using computational fluid dynamics (CFD). Influences of the process parameters, such as the chamber pressure, the inlet temperature, the susceptor temperature and the pre-exponential factor, on the reaction pathway are examined. The results show that increases of the chamber pressure or the inlet temperature, as well as reductions of the susceptor temperature or the pre-exponential factor lead to the adduct route dominating the growth. The deposition rate contributed by the decomposition route, however, can be enhanced dramatically by increasing the inlet temperature, the susceptor temperature and the pre-exponential factor.

Integration of PLZT and BST family oxides with GaN[Lead Lanthanum Zirconate Titanate, Barium Strontium Titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osinsky, A.V.; Fuflyigin, V.N.; Wang, F.

2000-07-01

Recent advances in the processing of complex-oxide materials has allowed the authors to monolithically grow ferroelectrics of lead lanthanum zirconate titanate (PLZT) and barium strontium titanate (BST) systems on a GaN/sapphire structure. High quality films of PLZT and BST were grown on GaN/c-Al{sub 2}O{sub 3} in a thickness range of 0.3--5 {micro}m by a sol-gel technique. Field-induced birefringence, as large as 0.02, was measured from a PLZT layer grown on a buffered GaN/sapphire structure. UV illumination was found to result in more symmetrical electrooptic hysteresis loop. BST films on GaN demonstrated a low frequency dielectric constant of up to 800more » with leakage current density as low as 5.5 {center_dot} 10{sup {minus}8} A/cm{sup 2}.« less

Bright Room-Temperature Single-Photon Emission from Defects in Gallium Nitride.

PubMed

Berhane, Amanuel M; Jeong, Kwang-Yong; Bodrog, Zoltán; Fiedler, Saskia; Schröder, Tim; Triviño, Noelia Vico; Palacios, Tomás; Gali, Adam; Toth, Milos; Englund, Dirk; Aharonovich, Igor

2017-03-01

Room-temperature quantum emitters in gallium nitride (GaN) are reported. The emitters originate from cubic inclusions in hexagonal lattice and exhibit narrowband luminescence in the red spectral range. The sources are found in different GaN substrates, and therefore are promising for scalable quantum technologies. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of gallium nitride nanostructures by nitridation of electrochemically deposited gallium oxide on silicon substrate.

PubMed

Ghazali, Norizzawati Mohd; Yasui, Kanji; Hashim, Abdul Manaf

2014-01-01

Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically deposited gallium oxide (Ga2O3) through the utilization of a so-called ammoniating process. Ga2O3 nanostructures were firstly deposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15 A/cm(2) using a mixture of Ga2O3, HCl, NH4OH and H2O for 2 h. Then, the deposited Ga2O3 sample was ammoniated in a horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridation of Ga2O3 nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was kept up to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peaks correspond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga2O3 structure was detected, suggesting a complete transformation of Ga2O3 to GaN. Thus, temperature seems to be a key parameter in a nitridation process where the deoxidization rate of Ga2O3 to generate gaseous Ga2O increase with temperature. The growth mechanism for the transformation of Ga2O3 to GaN was proposed and discussed. It was found that a complete transformation can not be realized without a complete deoxidization of Ga2O3. A significant change of morphological structures takes place after a complete transformation of Ga2O3 to GaN where the original nanorod structures of Ga2O3 diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to be promising in producing high-quality h-GaN nanostructures on Si.

Synthesis of gallium nitride nanostructures by nitridation of electrochemically deposited gallium oxide on silicon substrate

PubMed Central

2014-01-01

Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically deposited gallium oxide (Ga2O3) through the utilization of a so-called ammoniating process. Ga2O3 nanostructures were firstly deposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15 A/cm2 using a mixture of Ga2O3, HCl, NH4OH and H2O for 2 h. Then, the deposited Ga2O3 sample was ammoniated in a horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridation of Ga2O3 nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was kept up to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peaks correspond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga2O3 structure was detected, suggesting a complete transformation of Ga2O3 to GaN. Thus, temperature seems to be a key parameter in a nitridation process where the deoxidization rate of Ga2O3 to generate gaseous Ga2O increase with temperature. The growth mechanism for the transformation of Ga2O3 to GaN was proposed and discussed. It was found that a complete transformation can not be realized without a complete deoxidization of Ga2O3. A significant change of morphological structures takes place after a complete transformation of Ga2O3 to GaN where the original nanorod structures of Ga2O3 diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to be promising in producing high-quality h-GaN nanostructures on Si. PMID:25593562

One-step fabrication of porous GaN crystal membrane and its application in energy storage

NASA Astrophysics Data System (ADS)

Zhang, Lei; Wang, Shouzhi; Shao, Yongliang; Wu, Yongzhong; Sun, Changlong; Huo, Qin; Zhang, Baoguo; Hu, Haixiao; Hao, Xiaopeng

2017-03-01

Single-crystal gallium nitride (GaN) membranes have great potential for a variety of applications. However, fabrication of single-crystalline GaN membranes remains a challenge owing to its chemical inertness and mechanical hardness. This study prepares large-area, free-standing, and single-crystalline porous GaN membranes using a one-step high-temperature annealing technique for the first time. A promising separation model is proposed through a comprehensive study that combines thermodynamic theories analysis and experiments. Porous GaN crystal membrane is processed into supercapacitors, which exhibit stable cycling life, high-rate capability, and ultrahigh power density, to complete proof-of-concept demonstration of new energy storage application. Our results contribute to the study of GaN crystal membranes into a new stage related to the elelctrochemical energy storage application.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolat, S., E-mail: bolat@ee.bilkent.edu.tr, E-mail: aokyay@ee.bilkent.edu.tr; Tekcan, B.; UNAM, National Nanotechnology Research Center, Bilkent University, Ankara 06800

We report GaN thin film transistors (TFT) with a thermal budget below 250 °C. GaN thin films are grown at 200 °C by hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD). HCPA-ALD-based GaN thin films are found to have a polycrystalline wurtzite structure with an average crystallite size of 9.3 nm. TFTs with bottom gate configuration are fabricated with HCPA-ALD grown GaN channel layers. Fabricated TFTs exhibit n-type field effect characteristics. N-channel GaN TFTs demonstrated on-to-off ratios (I{sub ON}/I{sub OFF}) of 10{sup 3} and sub-threshold swing of 3.3 V/decade. The entire TFT device fabrication process temperature is below 250 °C, which is the lowest process temperaturemore » reported for GaN based transistors, so far.« less

Effects of radiation and temperature on gallium nitride (GaN) metal-semiconductor-metal ultraviolet photodetectors

NASA Astrophysics Data System (ADS)

Chiamori, Heather C.; Angadi, Chetan; Suria, Ateeq; Shankar, Ashwin; Hou, Minmin; Bhattacharya, Sharmila; Senesky, Debbie G.

2014-06-01

The development of radiation-hardened, temperature-tolerant materials, sensors and electronics will enable lightweight space sub-systems (reduced packaging requirements) with increased operation lifetimes in extreme harsh environments such as those encountered during space exploration. Gallium nitride (GaN) is a ceramic, semiconductor material stable within high-radiation, high-temperature and chemically corrosive environments due to its wide bandgap (3.4 eV). These material properties can be leveraged for ultraviolet (UV) wavelength photodetection. In this paper, current results of GaN metal-semiconductor-metal (MSM) UV photodetectors behavior after irradiation up to 50 krad and temperatures of 15°C to 150°C is presented. These initial results indicate that GaN-based sensors can provide robust operation within extreme harsh environments. Future directions for GaN-based photodetector technology for down-hole, automotive and space exploration applications are also discussed.

Room-Temperature Synthesis of GaN Driven by Kinetic Energy beyond the Limit of Thermodynamics.

PubMed

Imaoka, Takane; Okada, Takeru; Samukawa, Seiji; Yamamoto, Kimihisa

2017-12-06

The nitridation reaction is significantly important to utilize the unique properties of nitrides and nitrogen-doped materials. However, nitridation generally requires a high temperature or highly reactive reagents (often explosive) because the energies of N-N bond cleavage and nitrogen anion formation (N 3- ) are very high. We demonstrate the first room-temperature synthesis of GaN directly from GaCl 3 by nanoscale atom exchange reaction. Nonequilibrium nitrogen molecules with very high translational energy were used as a chemically stable and safe nitrogen source. The irradiation of molecular nitrogen to the desired reaction area successfully provided a gallium nitride (GaN) nanosheet that exhibited a typical photoluminescence spectrum. Because this process retains the target substrate room temperature and does not involve any photon nor charged ion, it allows damage-less synthesis of the semiconducting metal nitrides, even directly on plastic substrates such as polyethylene terephthalate (PET).

Detection of deep-level defects and reduced carrier concentration in Mg-ion-implanted GaN before high-temperature annealing

NASA Astrophysics Data System (ADS)

Akazawa, Masamichi; Yokota, Naoshige; Uetake, Kei

2018-02-01

We report experimental results for the detection of deep-level defects in GaN after Mg ion implantation before high-temperature annealing. The n-type GaN samples were grown on GaN free-standing substrates by metalorganic vapor phase epitaxy. Mg ions were implanted at 50 keV with a small dosage of 1.5×1011 cm-2, which did not change the conduction type of the n-GaN. By depositing Al2O3 and a Ni/Au electrode onto the implanted n-GaN, metal-oxide-semiconductor (MOS) diodes were fabricated and tested. The measured capacitance-voltage (C-V) characteristics showed a particular behavior with a plateau region and a region with an anomalously steep slope. Fitting to the experimental C-V curves by simulation showed the existence of deep-level defects and a reduction of the carrier concentration near the GaN surface. By annealing at 800oC, the density of the deep-level defects was reduced and the carrier concentration partially recovered.

Orbitally driven low thermal conductivity of monolayer gallium nitride (GaN) with planar honeycomb structure: a comparative study.

PubMed

Qin, Zhenzhen; Qin, Guangzhao; Zuo, Xu; Xiong, Zhihua; Hu, Ming

2017-03-23

Two-dimensional (2D) materials with graphene as a representative have been intensively studied for a long time. Recently, monolayer gallium nitride (ML GaN) with honeycomb structure was successfully fabricated in experiments, generating enormous research interest for its promising applications in nano- and opto-electronics. Considering all these applications are inevitably involved with thermal transport, systematic investigation of the phonon transport properties of 2D GaN is in demand. In this paper, by solving the Boltzmann transport equation (BTE) based on first-principles calculations, we performed a comprehensive study of the phonon transport properties of ML GaN, with detailed comparison to bulk GaN, 2D graphene, silicene and ML BN with similar honeycomb structure. Considering the similar planar structure of ML GaN to graphene, it is quite intriguing to find that the thermal conductivity (κ) of ML GaN (14.93 W mK -1 ) is more than two orders of magnitude lower than that of graphene and is even lower than that of silicene with a buckled structure. Systematic analysis is performed based on the study of the contribution from phonon branches, comparison among the mode level phonon group velocity and lifetime, the detailed process and channels of phonon-phonon scattering, and phonon anharmonicity with potential energy well. We found that, different from graphene and ML BN, the phonon-phonon scattering selection rule in 2D GaN is slightly broken by the lowered symmetry due to the large difference in the atomic radius and mass between Ga and N atoms. Further deep insight is gained from the electronic structure. Resulting from the special sp orbital hybridization mediated by the Ga-d orbital in ML GaN, the strongly polarized Ga-N bond, localized charge density, and its inhomogeneous distribution induce large phonon anharmonicity and lead to the intrinsic low κ of ML GaN. The orbitally driven low κ of ML GaN unraveled in this work would make 2D GaN prospective for applications in energy conversion such as thermoelectrics. Our study offers fundamental understanding of phonon transport in ML GaN within the framework of BTE and further electronic structure, which will enrich the studies of nanoscale phonon transport in 2D materials and shed light on further studies.

Investigation of HCl-based surface treatment for GaN devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okada, Hiroshi, E-mail: okada@ee.tut.ac.jp; Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580; Shinohara, Masatohi

2016-02-01

Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H{sub 2}O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treatedmore » samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication.« less

Influence of Ga vacancies, Mn and O impurities on the ferromagnetic properties of GaN micro- and nanostructures

NASA Astrophysics Data System (ADS)

Guzmán, G.; Escudero, R.; Silva, R.; Herrera, M.

2018-04-01

We present a study of the influence of gallium vacancy (VGa) point defects on the ferromagnetic properties of GaN:Mn and GaN:Mn,O micro- and nanostructures. Results demonstrate that the generation of these point defects enhances the ferromagnetic signal of GaN:Mn microstructures, while incorporation of oxygen as an impurity inhibits this property. XPS measurements revealed that Mn impurities in ferromagnetic GaN:Mn samples mainly exhibit a valence state of 2+. Cathodoluminescence (CL) spectra from Mn-doped GaN samples displayed emissions centered at about 1.97 eV, attributed to transitions between the 4T1-6A1 states of the Mn2+ d orbitals, and emissions centered at 2.45 and 2.9 eV, associated with the presence of VGa. CL measurements also revealed a blue shift of the GaN band-edge emission generated by the expansion of the wurtzite lattice due to Mn incorporation, which was confirmed by XRD measurements. These latter measurements also revealed an amorphization of GaN:Mn due to the incorporation of oxygen as impurities. The GaN:Mn samples were synthesized by thermal evaporation of GaN and MnCO3 powders onto Ni0.8Cr0.2/Si(100) in a horizontal furnace operated at low vacuum. The residual air inside the system was used as a source of oxygen during the synthesis of Mn and O co-doped GaN nanostructures. Mn and O impurities were incorporated into the nanostructures at different concentrations by varying the growth temperature. Energy Dispersive Spectroscopy, XRD, and XPS measurements confirmed that the obtained samples predominantly consisted of GaN.

Passivation and activation of Mg acceptors in heavily doped GaN

NASA Astrophysics Data System (ADS)

Zvanut, M. E.; Uprety, Y.; Dashdorj, J.; Moseley, M.; Alan Doolittle, W.

2011-08-01

Electron paramagnetic resonance measurements are used to monitor the passivation and activation of the Mg-related acceptor in GaN doped with different concentrations of Mg, up to 2 × 1020 cm-3. Samples were annealed in either forming gas (H2:N2) or pure N2 between 200 and 900 °C. As expected, the Mg-related EPR signal is reduced by at least a factor of ten during the forming gas treatment; while the pure N2 environment revives the signal. However, the study also shows that reactions between Mg and hydrogen occur at a temperature as low as 525 °C in the 1020 cm-3 Mg doped samples; while in more lightly doped samples, temperatures greater than 700 °C are required to observe changes in the Mg signal intensity. While the observations support the model in which a hydrogen atom ionizes at the Mg impurity and the remaining proton bonds at a near neighbor, the different temperature dependence suggests that hydrogen diffusion is affected by the increased Mg concentration.

Growth of high-quality InGaN/GaN LED structures on (1 1 1) Si substrates with internal quantum efficiency exceeding 50%

NASA Astrophysics Data System (ADS)

Lee, JaeWon; Tak, Youngjo; Kim, Jun-Youn; Hong, Hyun-Gi; Chae, Suhee; Min, Bokki; Jeong, Hyungsu; Yoo, Jinwoo; Kim, Jong-Ryeol; Park, Youngsoo

2011-01-01

GaN-based light-emitting-diodes (LEDs) on (1 1 1) Si substrates with internal quantum efficiency (IQE) exceeding 50% have been successfully grown by metal organic vapor phase epitaxy (MOVPE). 3.5 μm thick crack-free GaN epitaxial layers were grown on the Si substrates by the re-growth method on patterned templates. Series of step-graded Al xGa 1- xN epitaxial layers were used as the buffer layers to compensate thermal tensile stresses produced during the post-growth cooling process as well as to reduce the density of threading dislocations (TDs) generated due to the lattice mismatches between III-nitride layers and the silicon substrates. The light-emitting region consisted of 1.8 μm thick n-GaN, 3 periods of InGaN/GaN superlattice, InGaN/GaN multiple quantum wells (MQWs) designed for a peak wavelength of about 455 nm, an electron blocking layer (EBL), and p-GaN. The full-widths at half-maximum (FWHM) of (0 0 0 2) and (1 0 -1 2) ω-rocking curves of the GaN epitaxial layers were 410 and 560 arcsec, respectively. Cross-sectional transmission electron microscopy (TEM) investigation revealed that the propagation of the threading dislocations was mostly limited to the interface between the last Al xGa 1- xN buffer and n-GaN layers. The density of the threading dislocations induced pits of n-GaN, as estimated by atomic force microscopy (AFM), was about 5.5×10 8 cm -2. Temperature dependent photoluminescence (PL) measurements with a relative intensity integration method were carried out to estimate the internal quantum efficiency (IQE) of the light-emitting structures grown on Si, which reached up to 55%.

Influence of different aspect ratios on the structural and electrical properties of GaN thin films grown on nanoscale-patterned sapphire substrates

NASA Astrophysics Data System (ADS)

Lee, Fang-Wei; Ke, Wen-Cheng; Cheng, Chun-Hong; Liao, Bo-Wei; Chen, Wei-Kuo

2016-07-01

This study presents GaN thin films grown on nanoscale-patterned sapphire substrates (NPSSs) with different aspect ratios (ARs) using a homemade metal-organic chemical vapor deposition system. The anodic aluminum oxide (AAO) technique is used to prepare the dry etching mask. The cross-sectional view of the scanning electron microscope image shows that voids exist between the interface of the GaN thin film and the high-AR (i.e. ∼2) NPSS. In contrast, patterns on the low-AR (∼0.7) NPSS are filled full of GaN. The formation of voids on the high-AR NPSS is believed to be due to the enhancement of the lateral growth in the initial growth stage, and the quick-merging GaN thin film blocks the precursors from continuing to supply the bottom of the pattern. The atomic force microscopy images of GaN on bare sapphire show a layer-by-layer surface morphology, which becomes a step-flow surface morphology for GaN on a high-AR NPSS. The edge-type threading dislocation density can be reduced from 7.1 × 108 cm-2 for GaN on bare sapphire to 4.9 × 108 cm-2 for GaN on a high-AR NPSS. In addition, the carrier mobility increases from 85 cm2/Vs for GaN on bare sapphire to 199 cm2/Vs for GaN on a high-AR NPSS. However, the increased screw-type threading dislocation density for GaN on a low-AR NPSS is due to the competition of lateral growth on the flat-top patterns and vertical growth on the bottom of the patterns that causes the material quality of the GaN thin film to degenerate. Thus, the experimental results indicate that the AR of the particular patterning of a NPSS plays a crucial role in achieving GaN thin film with a high crystalline quality.

Luminescent N-polar (In,Ga)N/GaN quantum wells achieved by plasma-assisted molecular beam epitaxy at temperatures exceeding 700 °C

NASA Astrophysics Data System (ADS)

Chèze, C.; Feix, F.; Lähnemann, J.; Flissikowski, T.; Kryśko, M.; Wolny, P.; Turski, H.; Skierbiszewski, C.; Brandt, O.

2018-01-01

Previously, we found that N-polar (In,Ga)N/GaN quantum wells prepared on freestanding GaN substrates by plasma-assisted molecular beam epitaxy at conventional growth temperatures of about 650 °C do not exhibit any detectable luminescence even at 10 K. In the present work, we investigate (In,Ga)N/GaN quantum wells grown on Ga- and N-polar GaN substrates at a constant temperature of 730 °C . This exceptionally high temperature results in a vanishing In incorporation for the Ga-polar sample. In contrast, quantum wells with an In content of 20% and abrupt interfaces are formed on N-polar GaN. Moreover, these quantum wells exhibit a spatially uniform green luminescence band up to room temperature, but the intensity of this band is observed to strongly quench with temperature. Temperature-dependent photoluminescence transients show that this thermal quenching is related to a high density of nonradiative Shockley-Read-Hall centers with large capture coefficients for electrons and holes.

Low noise buffer amplifiers and buffered phase comparators for precise time and frequency measurement and distribution

NASA Technical Reports Server (NTRS)

Eichinger, R. A.; Dachel, P.; Miller, W. H.; Ingold, J. S.

1982-01-01

Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients.

Large electron capture-cross-section of the major nonradiative recombination centers in Mg-doped GaN epilayers grown on a GaN substrate

NASA Astrophysics Data System (ADS)

Chichibu, S. F.; Shima, K.; Kojima, K.; Takashima, S.; Edo, M.; Ueno, K.; Ishibashi, S.; Uedono, A.

2018-05-01

Complementary time-resolved photoluminescence and positron annihilation measurements were carried out at room temperature on Mg-doped p-type GaN homoepitaxial films for identifying the origin and estimating the electron capture-cross-section ( σ n ) of the major nonradiative recombination centers (NRCs). To eliminate any influence by threading dislocations, free-standing GaN substrates were used. In Mg-doped p-type GaN, defect complexes composed of a Ga-vacancy (VGa) and multiple N-vacancies (VNs), namely, VGa(VN)2 [or even VGa(VN)3], are identified as the major intrinsic NRCs. Different from the case of 4H-SiC, atomic structures of intrinsic NRCs in p-type and n-type GaN are different: VGaVN divacancies are the major NRCs in n-type GaN. The σ n value approximately the middle of 10-13 cm2 is obtained for VGa(VN)n, which is larger than the hole capture-cross-section (σp = 7 × 10-14 cm2) of VGaVN in n-type GaN. Combined with larger thermal velocity of an electron, minority carrier lifetime in Mg-doped GaN becomes much shorter than that of n-type GaN.

Design of high breakdown voltage vertical GaN p-n diodes with high-K/low-K compound dielectric structure for power electronics applications

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Li, Zhenchao; Liu, Dong; Bai, Zhiyuan; Liu, Yang; Yu, Qi

2017-11-01

In this work, a vertical GaN p-n diode with a high-K/low-K compound dielectric structure (GaN CD-VGD) is proposed and designed to achieve a record high breakdown voltage (BV) with a low specific on-resistance (Ron,sp). By introducing compound dielectric structure, the electric field near the p-n junction interface is suppressed due to the effects of high-K passivation layer, and a new electric field peak is induced into the n-type drift region, because of a discontinuity of electrical field at the interface of high-K and low-K layer. Therefore the distribution of electric field in GaN p-n diode becomes more uniform and an enhancement of breakdown voltage can be achieved. Numerical simulations demonstrate that GaN CD-VGD with a BV of 10650 V and a Ron,sp of 14.3 mΩ cm2, resulting in a record high figure-of-merit of 8 GW/cm2.

Design of Low Inductance Switching Power Cell for GaN HEMT Based Inverter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gurpinar, Emre; Iannuzzo, Francesco; Yang, Yongheng

Here in this paper, an ultra-low inductance power cell is designed for a three-Level Active Neutral Point Clamped (3LANPC) based on 650 V gallium nitride (GaN) HEMT devices. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which mainly contribute to voltage overshoots and increase of switching losses, are discussed. The ultra-low inductance power cell design based on a fourlayer Printed Circuit Board (PCB) with the aim to maximize the switching performance of GaN HEMTs is explained. The design of gate drivers for the GaN HEMT devicesmore » is presented. Parasitic inductance and resistance of the proposed design are extracted with finite element analysis and discussed. Common mode behaviours based on the SPICE model of the converter are analyzed. Experimental results on the designed 3L-ANPC with the output power of up to 1 kW are presented, which verifies the performance of the proposed design in terms of ultra-low inductance.« less

First-principles and thermodynamic analysis of trimethylgallium (TMG) decomposition during MOVPE growth of GaN

NASA Astrophysics Data System (ADS)

Sekiguchi, K.; Shirakawa, H.; Yamamoto, Y.; Araidai, M.; Kangawa, Y.; Kakimoto, K.; Shiraishi, K.

2017-06-01

We analyzed the decomposition mechanisms of trimethylgallium (TMG) used for the gallium source of GaN fabrication based on first-principles calculations and thermodynamic analysis. We considered two conditions. One condition is under the total pressure of 1 atm and the other one is under metal organic vapor phase epitaxy (MOVPE) growth of GaN. Our calculated results show that H2 is indispensable for TMG decomposition under both conditions. In GaN MOVPE, TMG with H2 spontaneously decomposes into Ga(CH3) and Ga(CH3) decomposes into Ga atom gas when temperature is higher than 440 K. From these calculations, we confirmed that TMG surely becomes Ga atom gas near the GaN substrate surfaces.

Surface potential barrier in m-plane GaN studied by contactless electroreflectance

NASA Astrophysics Data System (ADS)

Janicki, Lukasz; Misiewicz, Jan; Cywiński, Grzegorz; Sawicka, Marta; Skierbiszewski, Czeslaw; Kudrawiec, Robert

2016-02-01

Contactless electroreflectance (CER) is used to study the surface potential barrier in m-plane GaN UN+ [GaN (d = 20,30,50,70 nm)/GaN:Si] structures grown by using molecular beam epitaxy. Clear bandgap-related transitions followed by Franz-Keldysh oscillations (FKO) have been observed in the CER spectra of all samples at room temperature. The built-in electric fields in the undoped cap layers have been determined from the FKO period. From the built-in electric field and the undoped GaN layer thickness, the Fermi level location at the air-exposed m-plane GaN surface has been estimated as 0.42 ± 0.05 eV below the conduction band.

High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

McSkimming, Brian M., E-mail: mcskimming@engineering.ucsb.edu; Speck, James S.; Chaix, Catherine

2015-09-15

In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions,more » the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.« less

High-voltage vertical GaN Schottky diode enabled by low-carbon metal-organic chemical vapor deposition growth

NASA Astrophysics Data System (ADS)

Cao, Y.; Chu, R.; Li, R.; Chen, M.; Chang, R.; Hughes, B.

2016-02-01

Vertical GaN Schottky barrier diode (SBD) structures were grown by metal-organic chemical vapor deposition on free-standing GaN substrates. The carbon doping effect on SBD performance was studied by adjusting the growth conditions and spanning the carbon doping concentration between ≤3 × 1015 cm-3 and 3 × 1019 cm-3. Using the optimized growth conditions that resulted in the lowest carbon incorporation, a vertical GaN SBD with a 6-μm drift layer was fabricated. A low turn-on voltage of 0.77 V with a breakdown voltage over 800 V was obtained from the device.

Characterization of remote O2-plasma-enhanced CVD SiO2/GaN(0001) structure using photoemission measurements

NASA Astrophysics Data System (ADS)

Truyen, Nguyen Xuan; Ohta, Akio; Makihara, Katsunori; Ikeda, Mitsuhisa; Miyazaki, Seiichi

2018-01-01

The control of chemical composition and bonding features at a SiO2/GaN interface is a key to realizing high-performance GaN power devices. In this study, an ∼5.2-nm-thick SiO2 film has been deposited on an epitaxial GaN(0001) surface by remote O2-plasma-enhanced chemical vapor deposition (O2-RPCVD) using SiH4 and Ar/O2 mixture gases at a substrate temperature of 500 °C. The depth profile of chemical structures and electronic defects of the O2-RPCVD SiO2/GaN structures has been evaluated from a combination of SiO2 thinning examined by X-ray photoelectron spectroscopy (XPS) and the total photoelectron yield spectroscopy (PYS) measurements. As a highlight, we found that O2-RPCVD is effective for fabricating an abrupt SiO2/GaN interface.

First results for custom-built low-temperature (4.2 K) scanning tunneling microscope/molecular beam epitaxy and pulsed laser epitaxy system designed for spin-polarized measurements

NASA Astrophysics Data System (ADS)

Foley, Andrew; Alam, Khan; Lin, Wenzhi; Wang, Kangkang; Chinchore, Abhijit; Corbett, Joseph; Savage, Alan; Chen, Tianjiao; Shi, Meng; Pak, Jeongihm; Smith, Arthur

2014-03-01

A custom low-temperature (4.2 K) scanning tunneling microscope system has been developed which is combined directly with a custom molecular beam epitaxy facility (and also including pulsed laser epitaxy) for the purpose of studying surface nanomagnetism of complex spintronic materials down to the atomic scale. For purposes of carrying out spin-polarized STM measurements, the microscope is built into a split-coil, 4.5 Tesla superconducting magnet system where the magnetic field can be applied normal to the sample surface; since, as a result, the microscope does not include eddy current damping, vibration isolation is achieved using a unique combination of two stages of pneumatic isolators along with an acoustical noise shield, in addition to the use of a highly stable as well as modular `Pan'-style STM design with a high Q factor. First 4.2 K results reveal, with clear atomic resolution, various reconstructions on wurtzite GaN c-plane surfaces grown by MBE, including the c(6x12) on N-polar GaN(0001). Details of the system design and functionality will be presented.

Effect of same-temperature GaN cap layer on the InGaN/GaN multiquantum well of green light-emitting diode on silicon substrate.

PubMed

Zheng, Changda; Wang, Li; Mo, Chunlan; Fang, Wenqing; Jiang, Fengyi

2013-01-01

GaN green LED was grown on Si (111) substrate by MOCVD. To enhance the quality of InGaN/GaN MQWs, same-temperature (ST) GaN protection layers with different thickness of 8 Å, 15 Å, and 30 Å were induced after the InGaN quantum wells (QWs) layer. Results show that a relative thicker cap layer is benefit to get InGaN QWs with higher In percent at fixed well temperature and obtain better QW/QB interface. As the cap thickness increases, the indium distribution becomes homogeneous as verified by fluorescence microscope (FLM). The interface of MQWs turns to be abrupt from XRD analysis. The intensity of photoluminescence (PL) spectrum is increased and the FWHM becomes narrow.

Electronic Band Structure Tuning of Highly-Mismatched-Alloys for Energy Conversion Applications

NASA Astrophysics Data System (ADS)

Ting, Min

Highly-mismatched alloys: ZnO1-xTe x and GaN1-xSb x are discussed within the context of finding the suitable material for a cost-effective Si-based tandem solar cell (SBTSC). SBTSC is an attractive concept for breaking through the energy conversion efficiency theoretical limit of a single junction solar cell. Combining with a material of 1.8 eV band gap, SBTSC can theoretically achieve energy conversion efficiency > 45%. ZnO and GaN are wide band gap semiconductors. Alloying Te in ZnO and alloying Sb in GaN result in large band gap reduction to < 2 eV from 3.3 eV and 3.4 eV respectively. The band gap reduction is majorly achieved by the upward shift of valence band (VB). Incorporating Te in ZnO modifies the VB of ZnO through the valence-band anticrossing (VBAC) interaction between localized Te states and ZnO VB delocalized states, which forms a Te-derived VB at 1 eV above the host VB. Similar band structure modification is resulted from alloying Sb in GaN. Zn1-xTex and GaN 1-xSbx thin films are synthesized across the whole composition range by pulsed laser deposition (PLD) and low temperature molecular beam epitaxy (LT-MBE) respectively. The electronic band edges of these alloys are measured by synchrotron X-ray absorption, emission, and the X-ray photoelectron spectroscopies. Modeling the optical absorption coefficient with the band anticrossing (BAC) model revealed that the Te and Sb defect levels to be at 0.99 eV and 1.2 eV above the VB of ZnO and GaN respectively. Electrically, Zn1-xTex is readily n-type conductive and GaN1-xSbx is strongly p-type conductive. A heterojunction device of p-type GaN 0.93Sb0.07 with n-type ZnO0.77Te0.93 upper cell (band gap at 1.8 eV) on Si bottom cell is proposed as a promising SBTSC device.

Electrical, structural and surface morphological properties of thermally stable low-resistance W/Ti/Au multilayer ohmic contacts to n-type GaN

NASA Astrophysics Data System (ADS)

Jyothi, I.; Reddy, V. Rajagopal

2010-10-01

A W/Ti/Au multilayer scheme has been fabricated for achieving thermally stable low-resistance ohmic contact to n-type GaN (4.0 × 10 18 cm -3). It is shown that the as-deposited W/Ti/Au contact exhibits near linear I- V behaviour. However, annealing at temperature below 800 °C the contacts exhibit non-linear behaviour. After annealing at a temperature in excess of 850 °C, the W/Ti/Au contact showed ohmic behaviour. The W/Ti/Au contact produced specific contact resistance as low as 6.7 × 10 -6 Ω cm 2 after annealing at 900 °C for 1 min in a N 2 ambient. It is noted that the specific contact resistance decreases with increase in annealing temperature. It is also noted that annealing the contacts at 900 °C for 30 min causes insignificant degradation of the electrical and thermal properties. It is further shown that the overall surface morphology of the W/Ti/Au stayed fairly smooth even after annealing at 900 °C. The W/Ti/Au ohmic contact showed good edge sharpness after annealing at 900 °C for 30 min. Based on the Auger electron spectroscopy and glancing angle X-ray diffraction results, possible explanation for the annealing dependence of the specific contact resistance of the W/Ti/Au contacts are described and discussed.

Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations.

PubMed

Lee, H-P; Perozek, J; Rosario, L D; Bayram, C

2016-11-21

AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {Al x Ga 1-x N}/AlN, (b) Thin-GaN/3 × {Al x Ga 1-x N}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm 2 /V∙s) and 2DEG carrier concentration (>1.0 × 10 13  cm -2 ) on Si(111) substrates.

Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

PubMed Central

Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

2016-01-01

AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1−xN}/AlN, (b) Thin-GaN/3 × {AlxGa1−xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V∙s) and 2DEG carrier concentration (>1.0 × 1013 cm−2) on Si(111) substrates. PMID:27869222

Preparation and Optoelectronic Characteristics of ZnO/CuO-Cu2O Complex Inverse Heterostructure with GaP Buffer for Solar Cell Applications

PubMed Central

Hsu, Chih-Hung; Chen, Lung-Chien; Lin, Yi-Feng

2013-01-01

This study reports the optoelectronic characteristics of ZnO/GaP buffer/CuO-Cu2O complex (COC) inverse heterostructure for solar cell applications. The GaP and COC layers were used as buffer and absorber in the cell structure, respectively. An energy gap widening effect and CuO whiskers were observed as the copper (Cu) layer was exerted under heat treatment for oxidation at 500 °C for 10 min, and arose from the center of the Cu2O rods. For preparation of the 30 nm-thick GaP buffer by sputtering from GaP target, as the nitrogen gas flow rate increased from 0 to 2 sccm, the transmittance edge of the spectra demonstrated a blueshift form 2.24 to 3.25 eV. Therefore, the layer can be either GaP, GaNP, or GaN by changing the flow rate of nitrogen gas. PMID:28788341

Defect formation in MeV H+ implanted GaN and 4H-SiC investigated by cross-sectional Raman spectroscopy

NASA Astrophysics Data System (ADS)

Huang, Kai; Jia, Qi; You, Tiangui; Zhang, Shibin; Lin, Jiajie; Zhang, Runchun; Zhou, Min; Yu, Wenjie; Zhang, Bo; Ou, Xin; Wang, Xi

2017-09-01

Cross-sectional Raman spectroscopy is used to characterize the defect formation and the defect recovery in MeV H+ implanted bulk GaN and 4H-SiC in the high energy MeV ion-cut process. The Raman intensity decreases but the forbidden modes are activated at the damage region, and the intensity decrease is proportional to the damage level. The Raman spectrum is quite sensitive to detect the damage recovery after annealing. The main peak intensity increases and the forbidden mode disappears in both annealed GaN and 4H-SiC samples. The Raman spectra of GaN samples annealed at different temperatures suggest that higher annealing temperature is more efficient for damage recovery. While, the Raman spectra of SiC indicate that higher implantation temperature results in heavier lattice damage and other polytype clusters might be generated by high annealing temperature in the annealed SiC samples. The cross-sectional Raman spectroscopy is a straightforward method to characterize lattice damage and damage recovery in high energy ion-cut process. It can serve as a fast supplementary measurement technique to Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and transmission electron microscope (TEM) for the defect characterizations.

Ion Beam Assisted Deposition of Thin Epitaxial GaN Films.

PubMed

Rauschenbach, Bernd; Lotnyk, Andriy; Neumann, Lena; Poppitz, David; Gerlach, Jürgen W

2017-06-23

The assistance of thin film deposition with low-energy ion bombardment influences their final properties significantly. Especially, the application of so-called hyperthermal ions (energy <100 eV) is capable to modify the characteristics of the growing film without generating a large number of irradiation induced defects. The nitrogen ion beam assisted molecular beam epitaxy (ion energy <25 eV) is used to deposit GaN thin films on (0001)-oriented 6H-SiC substrates at 700 °C. The films are studied in situ by reflection high energy electron diffraction, ex situ by X-ray diffraction, scanning tunnelling microscopy, and high-resolution transmission electron microscopy. It is demonstrated that the film growth mode can be controlled by varying the ion to atom ratio, where 2D films are characterized by a smooth topography, a high crystalline quality, low biaxial stress, and low defect density. Typical structural defects in the GaN thin films were identified as basal plane stacking faults, low-angle grain boundaries forming between w-GaN and z-GaN and twin boundaries. The misfit strain between the GaN thin films and substrates is relieved by the generation of edge dislocations in the first and second monolayers of GaN thin films and of misfit interfacial dislocations. It can be demonstrated that the low-energy nitrogen ion assisted molecular beam epitaxy is a technique to produce thin GaN films of high crystalline quality.

The Influence of Phonons and Phonon Decay on the Optical Properties of GaN

NASA Astrophysics Data System (ADS)

Song, D. Y.; Basavaraj, M.; Nikishin, S. A.; Holtz, M.; Soukhoveev, V.; Usikov, A.; Dmitriev, V.

2006-03-01

The temperature dependences of vibrational and optical properties of high-quality GaN are studied using Raman and photoluminescence (PL) spectroscopies in the range 20 to 325 K. The Raman-active A1(LO) phonon has temperature dependence described well by combined two- and three-phonon decay. The temperature dependences of E2^2 phonon are almost entirely dominated by the thermal expansion, and the contribution of three-phonon decay process is very small throughout interested temperature range. The shallow neutral donor-bound exciton (D^0,X) and two free excitons (XA and XB) are observed at low temperatrue PL spectra. Also seen are two A1(LO) phonon sidebands (PSBs), originating from the XB free exciton, with the characteristic asymmetry attributed to interactions between discrete and continuum states. Analysis of the band-edge excitons reveals that energy gap shrinkage and exciton linewidths are completely described based on electron-phonon interactions with phonon properties consistent with the Raman analysis. First and second PSBs have temperature dependence associated with the A1(LO) phonon. The shift, broadening, and asymmetry of the PSBs are explained by Segall-Mahan theory adding the decay mechanism of A1(LO) phonon and the exciton broadening from electron-phonon interactions. Work at Texas Tech University supported by National Science Foundation grant ECS-0323640.

Growth kinetics and island evolution during double-pulsed molecular beam epitaxy of InN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, A.; Hein, C.; Bremers, H.

The kinetic processes of InN growth using alternating source fluxes with sub-monolayer In pulses in plasma-assisted molecular beam epitaxy have been investigated. Growth at various temperatures reveals the existence of two growth regimes. While growth at low temperatures is solely governed by surface diffusion, a combination of decomposition, desorption, and diffusion becomes decisive at growth temperatures of 470 °C and above. At this critical temperature, the surface morphology changes from a grainy structure to a structure made of huge islands. The formation of those islands is attributed to the development of an indium adlayer, which can be observed via reflection highmore » energy electron diffraction monitoring. Based on the growth experiments conducted at temperatures below T{sub Growth} = 470 °C, an activation energy for diffusion of 0.54 ± 0.02 eV has been determined from the decreasing InN island density. A comparison between growth on metalorganic vapor phase epitaxy GaN templates and pseudo bulk GaN indicates that step edges and dislocations are favorable nucleation sites. Based on the results, we developed a growth model, which describes the main mechanisms of the growth.« less

Diffusion of Mg dopant in metal-organic vapor-phase epitaxy grown GaN and AlxGa1-xN

NASA Astrophysics Data System (ADS)

Köhler, K.; Gutt, R.; Wiegert, J.; Kirste, L.

2013-02-01

Diffusion of the p-type dopant Mg in GaN and AlxGa1-xN which is accompanied by segregation and affected by transient effects in metal-organic vapor-phase epitaxy reactors is investigated. We have grown 110 nm thick Mg doped GaN and Al0.1Ga0.9N layers on top of undoped GaN and Al0.1Ga0.9N layers, respectively, in a temperature range between 925 °C and 1050 °C where we placed special emphasis on the lower temperature limit without diffusion to allow separation of Mg transients, diffusion, and segregation. Hereby, AlxGa1-xN layers enable monitoring of the resolution limit by secondary ion mass spectrometry analyses for the respective samples; therefore, thin AlxGa1-xN marker layers are incorporated in the thick GaN layers. We found an upper limit of 1.25 × 1019 cm-3 for diffusing Mg atoms in both sample types. Owing to the marked influence of Mg segregation in Al0.1Ga0.9N, diffusion is only seen by using a GaN cap on top of the Al0.1Ga0.9N layer sequence. Diffusion in Al0.1Ga0.9N is shown to be increased by about 25%-30% compared to GaN. Post growth annealing experiments under conditions equivalent to those used for growth of the Mg doped samples showed negligible diffusion. Comparing the results to well established findings on other doped III-V compounds, diffusion is explained by an interstitial-substitutional mechanism with a diffusion coefficient, which is concentration dependent. Analysis of the temperature dependent diffusivity revealed an activation energy of 5.0 eV for GaN:Mg and 5.2 eV for Al0.1Ga0.9N:Mg.

Electron mobility of self-assembled and dislocation free InN nanorods grown on GaN nano wall network template

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tangi, Malleswararao; De, Arpan; Ghatak, Jay

2016-05-28

A kinetically controlled two-step growth process for the formation of an array of dislocation free high mobility InN nanorods (NRs) on GaN nanowall network (NWN) by Molecular Beam Epitaxy is demonstrated here. The epitaxial GaN NWN is formed on c-sapphire under nitrogen rich conditions, and then changing the source from Ga to In at appropriate substrate temperature yields the nucleation of a self assembled spontaneous m-plane side faceted-InN NR. By HRTEM, the NRs are shown to be dislocation-free and have a low band gap value of 0.65 eV. Hall measurements are carried out on a single InN NR along with J-Vmore » measurements that yield mobility values as high as ≈4453 cm{sup 2}/V s and the carrier concentration of ≈1.1 × 10{sup 17} cm{sup −3}, which are unprecedented in the literature for comparable InN NR diameters.« less

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations

NASA Astrophysics Data System (ADS)

Horita, Masahiro; Takashima, Shinya; Tanaka, Ryo; Matsuyama, Hideaki; Ueno, Katsunori; Edo, Masaharu; Suda, Jun

2016-05-01

Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm-3 (lightly doped) to 3.8 × 1019 cm-3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of the p-GaN was 4 × 106 cm-2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 160 to 450 K. A low compensation ratio of less than 1% was revealed. We also obtained the depth of the Mg acceptor level of 235 meV considering the lowering effect by the Coulomb potential of ionized acceptors. The hole mobilities of 33 cm2 V-1 s-1 at 300 K and 72 cm2 V-1 s-1 at 200 K were observed in lightly doped p-GaN.

p-Type Doping of GaN Nanowires Characterized by Photoelectrochemical Measurements.

PubMed

Kamimura, Jumpei; Bogdanoff, Peter; Ramsteiner, Manfred; Corfdir, Pierre; Feix, Felix; Geelhaar, Lutz; Riechert, Henning

2017-03-08

GaN nanowires (NWs) doped with Mg as a p-type impurity were grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. In a systematic series of experiments, the amount of Mg supplied during NW growth was varied. The incorporation of Mg into the NWs was confirmed by the observation of donor-acceptor pairs and acceptor-bound excitons in low-temperature photoluminescence spectroscopy. Quantitative information about the Mg concentrations was deduced from Raman scattering by local vibrational modes related to Mg. In order to study the type and density of charge carriers present in the NWs, we employed two photoelectrochemical techniques, open-circuit potential and Mott-Schottky measurements. Both methods showed the expected transition from n-type to p-type conductivity with increasing Mg doping level, and the latter characterization technique allowed us to quantify the charge carrier concentration. Beyond the quantitative information obtained for Mg doping of GaN NWs, our systematic and comprehensive investigation demonstrates the benefit of photoelectrochemical methods for the analysis of doping in semiconductor NWs in general.

Contributions from gallium vacancies and carbon-related defects to the ``yellow luminescence'' in GaN

NASA Astrophysics Data System (ADS)

Armitage, R.; Hong, William; Yang, Qing; Feick, H.; Gebauer, J.; Weber, E. R.; Hautakangas, S.; Saarinen, K.

2003-05-01

Carbon-doped GaN layers grown by molecular-beam epitaxy are studied with photoluminescence and positron annihilation spectroscopy. Semi-insulating layers doped with >1018 cm-3 carbon show a strong luminescence band centered at ˜2.2 eV (yellow luminescence). The absolute intensity of the 2.2 eV band is compared with the gallium vacancy concentration determined by positron annihilation spectroscopy. The results indicate that a high concentration of gallium vacancies is not necessary for yellow luminescence and that there is in fact a causal relationship between carbon and the 2.2 eV band. Markedly different deep-level ionization energies are found for the high-temperature quenching of the 2.2 eV photoluminescence in carbon-doped and reference samples. We propose that while the model of Neugebauer and Van de Walle [Appl. Phys. Lett. 69, 503 (1996)] applies for GaN of low carbon concentration, a different yellow luminescence mechanism is involved when the interstitial carbon concentration is comparable to or exceeds the gallium vacancy concentration.

High-resolution mid-infrared spectroscopy of buffer-gas-cooled methyltrioxorhenium molecules

NASA Astrophysics Data System (ADS)

Tokunaga, S. K.; Hendricks, R. J.; Tarbutt, M. R.; Darquié, B.

2017-05-01

We demonstrate cryogenic buffer-gas cooling of gas-phase methyltrioxorhenium (MTO). This molecule is closely related to chiral organometallic molecules where the parity-violating energy differences between enantiomers is measurable. The molecules are produced with a rotational temperature of approximately 6 K by laser ablation of an MTO pellet inside a cryogenic helium buffer gas cell. Facilitated by the low temperature, we demonstrate absorption spectroscopy of the 10.2 μm antisymmetric Re=O stretching mode of MTO with a resolution of 8 MHz and a frequency accuracy of 30 MHz. We partially resolve the hyperfine structure and measure the nuclear quadrupole coupling of the excited vibrational state. Our ability to produce dense samples of complex molecules of this type at low temperatures represents a key step towards a precision measurement of parity violation in a chiral species.

Change in equilibrium position of misfit dislocations at the GaN/sapphire interface by Si-ion implantation into sapphire—I. Microstructural characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Sung Bo, E-mail: bolee@snu.ac.kr; Han, Heung Nam, E-mail: hnhan@snu.ac.kr; Lee, Dong Nyung

Much research has been done to reduce dislocation densities for the growth of GaN on sapphire, but has paid little attention to the elastic behavior at the GaN/sapphire interface. In this study, we have examined effects of the addition of Si to a sapphire substrate on its elastic property and on the growth of GaN deposit. Si atoms are added to a c-plane sapphire substrate by ion implantation. The ion implantation results in scratches on the surface, and concomitantly, inhomogeneous distribution of Si. The scratch regions contain a higher concentration of Si than other regions of the sapphire substrate surface,more » high-temperature GaN being poorly grown there. However, high-temperature GaN is normally grown in the other regions. The GaN overlayer in the normally-grown regions is observed to have a lower TD density than the deposit on the bare sapphire substrate (with no Si accommodated). As compared with the film on an untreated, bare sapphire, the cathodoluminescence defect density decreases by 60 % for the GaN layer normally deposited on the Si-ion implanted sapphire. As confirmed by a strain mapping technique by transmission electron microscopy (geometric phase analysis), the addition of Si in the normally deposited regions forms a surface layer in the sapphire elastically more compliant than the GaN overlayer. The results suggest that the layer can largely absorb the misfit strain at the interface, which produces the overlayer with a lower defect density. Our results highlight a direct correlation between threading-dislocation density in GaN deposits and the elastic behavior at the GaN/sapphire interface, opening up a new pathway to reduce threading-dislocation density in GaN deposits.« less

The Effect of Growth Environment on the Morphological and Extended Defect Evolution in GaN Grown by Metalorganic Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Fini, P.; Wu, X.; Tarsa, E.; Golan, Y.; Srikant, V.; Keller, S.; Denbaars, S.; Speck, J.

1998-08-01

The evolution of morphology and associated extended defects in GaN thin films grown on sapphire by metalorganic chemical vapor deposition (MOCVD) are shown to depend strongly on the growth environment. For the commonly used two-step growth process, a change in growth parameter such as reactor pressure influences the initial high temperature (HT) GaN growth mechanism. By means of transmission electron microscopy (TEM), atomic force microscopy (AFM), and high resolution X-ray diffraction (HRXRD) measurements, it is shown that the initial density of HT islands on the nucleation layer (NL) and subsequently the threading dislocation density in the HT GaN film may be directly controlled by tailoring the initial HT GaN growth conditions.

Droplet heteroepitaxy of zinc-blende vs. wurtzite GaN quantum dots

NASA Astrophysics Data System (ADS)

Reese, C.; Jeon, S.; Hill, T.; Jones, C.; Shusterman, S.; Yacoby, Y.; Clarke, R.; Deng, H.; Goldman, Rs

We have developed a GaN droplet heteroepitaxy process based upon plasma-assisted molecular-beam epitaxy. Using various surface treatments and Ga deposition parameters, we have demonstrated polycrystalline, zinc-blende (ZB), and wurtzite (WZ) GaN quantum dots (QDs) on Si(001), r-Al2O3, Si(111), and c-GaN substrates. For the polar substrates (i.e. Si(111) and c-GaN), high-resolution transmission electron microscopy and coherent Bragg rod analysis reveals the formation of coherent WZ GaN QDs with nitridation-temperature-dependent sizes and densities. For the non-polar substrates (i.e. Si(001) and r-Al2O3) , QDs with strong near-band photoluminescence emission are observed and ZB GaN QD growth on Si(001) is demonstrated for the first time.

Hysteretic photochromic switching of Eu-Mg defects in GaN links the shallow transient and deep ground states of the Mg acceptor.

PubMed

Singh, A K; O'Donnell, K P; Edwards, P R; Lorenz, K; Kappers, M J; Boćkowski, M

2017-02-03

Although p-type activation of GaN by Mg underpins a mature commercial technology, the nature of the Mg acceptor in GaN is still controversial. Here, we use implanted Eu as a 'spectator ion' to probe the lattice location of Mg in doubly doped GaN(Mg):Eu. Photoluminescence spectroscopy of this material exemplifies hysteretic photochromic switching (HPS) between two configurations, Eu0 and Eu1(Mg), of the same Eu-Mg defect, with a hyperbolic time dependence on 'switchdown' from Eu0 to Eu1(Mg). The sample temperature and the incident light intensity at 355 nm tune the characteristic switching time over several orders of magnitude, from less than a second at 12.5 K, ~100 mW/cm 2 to (an estimated) several hours at 50 K, 1 mW/cm 2 . Linking the distinct Eu-Mg defect configurations with the shallow transient and deep ground states of the Mg acceptor in the Lany-Zunger model, we determine the energy barrier between the states to be 27.7(4) meV, in good agreement with the predictions of theory. The experimental results further suggest that at low temperatures holes in deep ground states are localized on N atoms axially bonded to Mg acceptors.

Engineering future light emitting diodes and photovoltaics with inexpensive materials: Integrating ZnO and Si into GaN-based devices

NASA Astrophysics Data System (ADS)

Bayram, C.; Shiu, K. T.; Zhu, Y.; Cheng, C. W.; Sadana, D. K.; Teherani, F. H.; Rogers, D. J.; Sandana, V. E.; Bove, P.; Zhang, Y.; Gautier, S.; Cho, C.-Y.; Cicek, E.; Vashaei, Z.; McClintock, R.; Razeghi, M.

2013-03-01

Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our results suggest that groove structures are very promising for controlled local epitaxy of cubic phase GaN. Overall, it is concluded that there are significant opportunities for cost reduction in novel hybrid diodes based on ZnO-InGaN-Si hybridization.

Growth diagram of N-face GaN (0001{sup ¯}) grown at high rate by plasma-assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okumura, Hironori, E-mail: okumura@engineering.ucsb.edu; McSkimming, Brian M.; Speck, James S.

2014-01-06

N-face GaN was grown on free-standing GaN (0001{sup ¯}) substrates at a growth rate of 1.5 μm/h using plasma-assisted molecular beam epitaxy. Difference in growth rate between (0001{sup ¯}) and (0001) oriented GaN depends on nitrogen plasma power, and the (0001{sup ¯}) oriented GaN had only 70% of the growth rate of the (0001) oriented GaN at 300 W. Unintentional impurity concentrations of silicon, carbon, and oxygen were 2 × 10{sup 15}, 2 × 10{sup 16}, and 7 × 10{sup 16} cm{sup −3}, respectively. A growth diagram was constructed that shows the dependence of the growth modes on the difference in the Ga and active nitrogen flux, Φ{sub Ga} − Φ{submore » N*}, and the growth temperature. At high Φ{sub Ga} − Φ{sub N*} (Φ{sub Ga} ≫ Φ{sub N*}), two-dimensional (step-flow and layer-by-layer) growth modes were realized. High growth temperature (780 °C) expanded the growth window of the two-dimensional growth modes, achieving a surface with rms roughness of 0.48 nm without Ga droplets.« less

Electronic structure of ytterbium-implanted GaN at ambient and high pressure: experimental and crystal field studies.

PubMed

Kaminska, A; Ma, C-G; Brik, M G; Kozanecki, A; Boćkowski, M; Alves, E; Suchocki, A

2012-03-07

The results of high-pressure low-temperature optical measurements in a diamond-anvil cell of bulk gallium nitride crystals implanted with ytterbium are reported in combination with crystal field calculations of the Yb(3+) energy levels. Crystal field analysis of splitting of the (2)F(7/2) and (2)F(5/2) states has been performed, with the aim of assigning all features of the experimental luminescence spectra. A thorough analysis of the pressure behavior of the Yb(3+) luminescence lines in GaN allowed the determination of the ambient-pressure positions and pressure dependence of the Yb(3+) energy levels in the trigonal crystal field as well as the pressure-induced changes of the spin-orbit coupling coefficient.

Stability diagrams for the surface patterns of GaN(0001bar) as a function of Schwoebel barrier height

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.

2017-01-01

Height and type of Schwoebel barriers (direct or inverse) decides about the character of the surface instability. Different surface morphologies are presented. Step bunches, double steps, meanders, mounds and irregular patterns emerge at the surface as a result of step (Schwoebel) barriers at some temperature or miscut values. The study was carried out on the two-component kinetic Monte Carlo (kMC) model of GaN(0001bar) surface grown in nitrogen rich conditions. Diffusion of gallium adatoms over N-polar surface is slow and nitrogen adatoms are almost immobile. We show that in such conditions surfaces remain smooth when gallium adatoms diffuse in the presence of low inverse Schwoebel barrier. It is illustrated by adequate stability diagrams for surface morphologies.

Deep-level traps in lightly Si-doped n-GaN on free-standing m-oriented GaN substrates

NASA Astrophysics Data System (ADS)

Yamada, H.; Chonan, H.; Takahashi, T.; Yamada, T.; Shimizu, M.

2018-04-01

In this study, we investigated the deep-level traps in Si-doped GaN epitaxial layers by metal-organic chemical vapor deposition on c-oriented and m-oriented free-standing GaN substrates. The c-oriented and m-oriented epitaxial layers, grown at a temperature of 1000 °C and V/III ratio of 1000, contained carbon atomic concentrations of 1.7×1016 and 4.0×1015 cm-3, respectively. A hole trap was observed at about 0.89 eV above the valence band maximum by minority carrier transient spectroscopy. The trap concentrations in the c-oriented and m-oriented GaN epitaxial layers were consistent with the carbon atomic concentrations from secondary ion mass spectroscopy and the yellow luminescence intensity at 2.21 eV from photoluminescence. The trap concentrations in the m-oriented GaN epitaxial layers were lower than those in the c-oriented GaN. Two electron traps, 0.24 and 0.61 eV below the conduction band (EC) minimum, were observed in the c-oriented GaN epitaxial layer. In contrast, the m-oriented GaN epitaxial layer was free from the electron trap at EC - 0.24 eV, and the trap concentration at EC - 0.61 eV in the m-oriented GaN epitaxial layer was lower than that in the c-oriented GaN epitaxial layer. The m-oriented GaN epitaxial layer exhibited fewer hole and electron traps compared to the c-oriented GaN epitaxial layers.

Comprehensive dynamic on-resistance assessments in GaN-on-Si MIS-HEMTs for power switching applications

NASA Astrophysics Data System (ADS)

Chou, Po-Chien; Hsieh, Ting-En; Cheng, Stone; del Alamo, Jesús A.; Chang, Edward Yi

2018-05-01

This study comprehensively analyzed the reliability of trapping and hot-electron effects responsible for the dynamic on-resistance (Ron) of GaN-based metal–insulator–semiconductor high electron mobility transistors. Specifically, this study performed the following analyses. First, we developed the on-the-fly Ron measurement to analyze the effects of traps during stress. With this technique, the faster one (with a pulse period of 20 ms) can characterize the degradation; the transient behavior could be monitored accurately by such short measurement pulse. Then, dynamic Ron transients were investigated under different bias conditions, including combined off state stress conditions, back-gating stress conditions, and semi-on stress conditions, in separate investigations of surface- and buffer-, and hot-electron-related trapping effects. Finally, the experiments showed that the Ron increase in semi-on state is significantly correlated with the high drain voltage and relatively high current levels (compared with the off-state current), involving the injection of greater amount of hot electrons from the channel into the AlGaN/insulator interface and the GaN buffer. These findings provide a path for device engineering to clarify the possible origins for electron traps and to accelerate the development of emerging GaN technologies.

Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Hsu, Chih-Wei; Forsberg, Urban

2015-02-28

Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon andmore » oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.« less

Selective heteroepitaxy on deeply grooved substrate: A route to low cost semipolar GaN platforms of bulk quality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tendille, Florian, E-mail: florian.tendille@crhea.cnrs.fr; Vennéguès, Philippe; De Mierry, Philippe

2016-08-22

Semipolar GaN crystal stripes larger than 100 μm with dislocation densities below 5 × 10{sup 6} cm{sup −2} are achieved using a low cost fabrication process. An original sapphire patterning procedure is proposed, enabling selective growth of semipolar oriented GaN stripes while confining the defects to specific areas. Radiative and non-radiative crystalline defects are investigated by cathodoluminescence and can be correlated to the development of crystal microstructure during the growth process. A dislocation reduction mechanism, supported by transmission electron microscopy, is proposed. This method represents a step forward toward low-cost quasi-bulk semipolar GaN epitaxial platforms with an excellent structural quality which will allowmore » for even more efficient III-nitride based devices.« less

Polariton Bose–Einstein condensate at room temperature in an Al(Ga)N nanowire–dielectric microcavity with a spatial potential trap

PubMed Central

Das, Ayan; Bhattacharya, Pallab; Heo, Junseok; Banerjee, Animesh; Guo, Wei

2013-01-01

A spatial potential trap is formed in a 6.0-μm Al(Ga)N nanowire by varying the Al composition along its length during epitaxial growth. The polariton emission characteristics of a dielectric microcavity with the single nanowire embedded in-plane have been studied at room temperature. Excitation is provided at the Al(Ga)N end of the nanowire, and polariton emission is observed from the lowest bandgap GaN region within the potential trap. Comparison of the results with those measured in an identical microcavity with a uniform GaN nanowire and having an identical exciton–photon detuning suggests evaporative cooling of the polaritons as they are transported into the trap in the Al(Ga)N nanowire. Measurement of the spectral characteristics of the polariton emission, their momentum distribution, first-order spatial coherence, and time-resolved measurements of polariton cooling provides strong evidence of the formation of a near-equilibrium Bose–Einstein condensate in the GaN region of the nanowire at room temperature. In contrast, the condensate formed in the uniform GaN nanowire–dielectric microcavity without the spatial potential trap is only in self-equilibrium. PMID:23382183

Growth, Structural, Electronic, and Magnetic Characterization of GaN, CrN, Fe Islands on CrN, and Fe/CrN Bilayer Thin Films

NASA Astrophysics Data System (ADS)

Alam, Khan

As a part of my Ph.D research, initially I was involved in construction and calibration of an ultra-high vacuum thin film facility, and later on I studied structural, electronic, and magnetic properties of GaN, CrN, Fe/CrN bilayers, and Fe islands on CrN thin films. All of these films were grown by molecular beam epitaxy and characterized with a variety of state-of-the-art techniques including variable temperature reflection high energy electron diffraction, low temperature scanning tunneling microscopy and spectroscopy, variable temperature vibrating sample magnetometry, variable temperature neutron diffraction and reflectometry, variable temperature x-ray diffraction, x-ray reflectometry, Rutherford backscattering, Auger electron spectroscopy, and cross-sectional tunneling electron microscopy. The experimental results are furthermore understood by comparing with numerical calculations using generalized gradient approximation, local density approximation with Hubbard correction, Refl1D, and data analysis and visual environment program. In my first research project, I studied Ga gas adatoms on GaN surfaces. We discovered frozen-out gallium gas adatoms on atomically smooth c(6x12) GaN(0001¯) surface using low temperature scanning tunneling microscopy. We identified adsorption sites of the Ga adatoms on c(6x12) reconstructed surface. Their bonding is determined by measuring low unoccupied molecular orbital level. Absorption sites of the Ga gas adatoms on centered 6x12 are identified, and their asymmetric absorption on the chiral domains is investigated. In second project, I investigated magneto-structural phase transition in chromium nitride (CrN) thin films. The CrN thin films are grown by molecular beam epitaxy. Structural and magnetic transition are studied using variable temperature reflection high energy electron diffraction and variable temperature neutron diffraction. We observed a structural phase transition at the surface at 277+/-2 K, and a sharp, first-order magnetic phase transition from paramagnetic (room temperature) to antiferromagnetic (low temperature) at 280+/-3 K. Our experiments suggest that the structural transition in CrN thin films occur in out-of-plane direction, and epitaxial constraints suppress the in-plane transition; therefore, the low temperature crystal structure of CrN is tetragonal. This new model explains our structural and magnetic data at low temperatures, but it is different than the previously published orthorhombic model. In third project, I studied exchange bias and exchange spring effect in MBE grown Fe/CrN bilayer thin films. We grew Fe/CrN bilayer thin films on MgO(001) substrate by molecular beam epitaxy, and studied them using variable temperature vibrating sample magnetometry, polarized neutron reflectometry, x-ray reflectivity, and cross-sectional transmission electron microscopy. We observed exchange bias and exchange spring effect in all bilayer thin films. We studied the relationship of exchange bias, blocking temperature, and coercivity with Fe and CrN layers thicknesses. We used polarized neutron beam reflectometry to see if spins at Fe/CrN interface are pinned. We found a thin ferromagnetically ordered CrN layer at the interface. In my final project, I studied growth of submonolayer Fe islands on CrN thin films. These films are prepared in two stages: first, a CrN layer is grown by MBE and then a submonolayer Fe is deposited at room temperature from a carefully degassed e-beam evaporator. The films are studied at liquid helium temperature using low temperature scanning tunneling microscopy and spectroscopy. Islands are seen in STM images, after the Fe deposition, at the edges as well as at the center of atomically flat CrN terraces. However, numerical calculations performed by our collaborator Ponce-P'erez from Benem'erita Universidad Aut'onoma de Puebla show that the Fe islands are energetically unstable on the surface. The Fe atoms substitute Cr atoms in the surface layer and the Cr atoms comes out and form islands. In order to find out elemental composition of the islands, we attempted to map local density of state by measuring differential conductance spectra as a function of bias voltage using LT-STS. We observed three characteristically different spectra; one in the CrN substrate and two in the islands. The CrN substrate curve has a "U" shape near Fermi level and a peak at ≈ 105 mV. The islands spectra show Kondo-like resonances at Fermi level; some islands produce a peak whereas others produce a dip the dI/dV curves near Fermi level. Further investigations are needed to determine the origin of the peak and dip in the island curves, as well as to find the composition of the islands.

Neutral and charged gallium clusters: structures, physical properties and implications for the melting features

NASA Astrophysics Data System (ADS)

Núñez, Sara; López, José M.; Aguado, Andrés

2012-09-01

We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims.We report the putative Global Minimum (GM) structures and electronic properties of GaN+, GaN and GaN- clusters with N = 13-37 atoms, obtained from first-principles density functional theory structural optimizations. The calculations include spin polarization and employ an exchange-correlation functional which accounts for van der Waals dispersion interactions (vdW-DFT). We find a wide diversity of structural motifs within the located GM, including decahedral, polyicosahedral, polytetrahedral and layered structures. The GM structures are also extremely sensitive to the number of electrons in the cluster, so that the structures of neutral and charged clusters differ for most sizes. The main magic numbers (clusters with an enhanced stability) are identified and interpreted in terms of electronic and geometric shell closings. The theoretical results are consistent with experimental abundance mass spectra of GaN+ and with photoelectron spectra of GaN-. The size dependence of the latent heats of melting, the shape of the heat capacity peaks, and the temperature dependence of the collision cross-sections, all measured for GaN+ clusters, are properly interpreted in terms of the calculated cohesive energies, spectra of configurational excitations, and cluster shapes, respectively. The transition from ``non-melter'' to ``magic-melter'' behaviour, experimentally observed between Ga30+ and Ga31+, is traced back to a strong geometry change. Finally, the higher-than-bulk melting temperatures of gallium clusters are correlated with a more typically metallic behaviour of the clusters as compared to the bulk, contrary to previous theoretical claims. Electronic supplementary information (ESI) available: Atomic coordinates (in xyz format and Å units) and point group symmetries for the global minimum structures reported in this paper. See DOI: 10.1039/c2nr31222k

Efficient room temperature hydrogen sensor based on UV-activated ZnO nano-network

NASA Astrophysics Data System (ADS)

Kumar, Mohit; Kumar, Rahul; Rajamani, Saravanan; Ranwa, Sapana; Fanetti, Mattia; Valant, Matjaz; Kumar, Mahesh

2017-09-01

Room temperature hydrogen sensors were fabricated from Au embedded ZnO nano-networks using a 30 mW GaN ultraviolet LED. The Au-decorated ZnO nano-networks were deposited on a SiO2/Si substrate by a chemical vapour deposition process. X-ray diffraction (XRD) spectrum analysis revealed a hexagonal wurtzite structure of ZnO and presence of Au. The ZnO nanoparticles were interconnected, forming nano-network structures. Au nanoparticles were uniformly distributed on ZnO surfaces, as confirmed by FESEM imaging. Interdigitated electrodes (IDEs) were fabricated on the ZnO nano-networks using optical lithography. Sensor performances were measured with and without UV illumination, at room temperate, with concentrations of hydrogen varying from 5 ppm to 1%. The sensor response was found to be ˜21.5% under UV illumination and 0% without UV at room temperature for low hydrogen concentration of 5 ppm. The UV-photoactivated mode enhanced the adsorption of photo-induced O- and O2- ions, and the d-band electron transition from the Au nanoparticles to ZnO—which increased the chemisorbed reaction between hydrogen and oxygen. The sensor response was also measured at 150 °C (without UV illumination) and found to be ˜18% at 5 ppm. Energy efficient low cost hydrogen sensors can be designed and fabricated with the combination of GaN UV LEDs and ZnO nanostructures.

Heat resistive dielectric multi-layer micro-mirror array in epitaxial lateral overgrowth gallium nitride.

PubMed

Huang, Chen-Yang; Ku, Hao-Min; Liao, Wei-Tsai; Chao, Chu-Li; Tsay, Jenq-Dar; Chao, Shiuh

2009-03-30

Ta2O5 / SiO2 dielectric multi-layer micro-mirror array (MMA) with 3mm mirror size and 6mm array period was fabricated on c-plane sapphire substrate. The MMA was subjected to 1200 degrees C high temperature annealing and remained intact with high reflectance in contrast to the continuous multi-layer for which the layers have undergone severe damage by 1200 degrees C annealing. Epitaxial lateral overgrowth (ELO) of gallium nitride (GaN) was applied to the MMA that was deposited on both sapphire and sapphire with 2:56 mm GaN template. The MMA was fully embedded in the ELO GaN and remained intact. The result implies that our MMA is compatible to the high temperature growth environment of GaN and the MMA could be incorporated into the structure of the micro-LED array as a one to one micro backlight reflector, or as the patterned structure on the large area LED for controlling the output light.

Propagation of THz acoustic wave packets in GaN at room temperature

NASA Astrophysics Data System (ADS)

Maznev, A. A.; Hung, T.-C.; Yao, Y.-T.; Chou, T.-H.; Gandhi, J. S.; Lindsay, L.; Shin, H. D.; Stokes, D. W.; Forrest, R. L.; Bensaoula, A.; Sun, C.-K.; Nelson, K. A.

2018-02-01

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1-1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as high as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.

Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolat, Sami, E-mail: bolat@ee.bilkent.edu.tr; Tekcan, Burak; Ozgit-Akgun, Cagla

2015-01-15

Electronic and optoelectronic devices, namely, thin film transistors (TFTs) and metal–semiconductor–metal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N{sub 2}/H{sub 2} PA-ALD based GaN channels aremore » observed to have improved stability and transfer characteristics with respect to NH{sub 3} PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N{sub 2}:H{sub 2} ambient.« less

Determination of the electron-capture coefficients and the concentration of free electrons in GaN from time-resolved photoluminescence

PubMed Central

Reshchikov, M. A.; McNamara, J. D.; Toporkov, M.; Avrutin, V.; Morkoç, H.; Usikov, A.; Helava, H.; Makarov, Yu.

2016-01-01

Point defects in high-purity GaN layers grown by hydride vapor phase epitaxy are studied by steady-state and time-resolved photoluminescence (PL). The electron-capture coefficients for defects responsible for the dominant defect-related PL bands in this material are found. The capture coefficients for all the defects, except for the green luminescence (GL1) band, are independent of temperature. The electron-capture coefficient for the GL1 band significantly changes with temperature because the GL1 band is caused by an internal transition in the related defect, involving an excited state acting as a giant trap for electrons. By using the determined electron-capture coefficients, the concentration of free electrons can be found at different temperatures by a contactless method. A new classification system is suggested for defect-related PL bands in undoped GaN. PMID:27901025

Anharmonic phonon decay in cubic GaN

NASA Astrophysics Data System (ADS)

Cuscó, R.; Domènech-Amador, N.; Novikov, S.; Foxon, C. T.; Artús, L.

2015-08-01

We present a Raman-scattering study of optical phonons in zinc-blende (cubic) GaN for temperatures ranging from 80 to 750 K. The experiments were performed on high-quality, cubic GaN films grown by molecular-beam epitaxy on GaAs (001) substrates. The observed temperature dependence of the optical phonon frequencies and linewidths is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional-theory calculations. The longitudinal-optical (LO) mode relaxation is found to occur via asymmetric decay into acoustic phonons, with an appreciable contribution of higher-order processes. The transverse-optical mode linewidth shows a weak temperature dependence and its frequency downshift is primarily determined by the lattice thermal expansion. The LO phonon lifetime is derived from the observed Raman linewidth and an excellent agreement with previous theoretical predictions is found.

Effect of Same-Temperature GaN Cap Layer on the InGaN/GaN Multiquantum Well of Green Light-Emitting Diode on Silicon Substrate

PubMed Central

Zheng, Changda; Wang, Li; Mo, Chunlan; Fang, Wenqing; Jiang, Fengyi

2013-01-01

GaN green LED was grown on Si (111) substrate by MOCVD. To enhance the quality of InGaN/GaN MQWs, same-temperature (ST) GaN protection layers with different thickness of 8 Å, 15 Å, and 30 Å were induced after the InGaN quantum wells (QWs) layer. Results show that a relative thicker cap layer is benefit to get InGaN QWs with higher In percent at fixed well temperature and obtain better QW/QB interface. As the cap thickness increases, the indium distribution becomes homogeneous as verified by fluorescence microscope (FLM). The interface of MQWs turns to be abrupt from XRD analysis. The intensity of photoluminescence (PL) spectrum is increased and the FWHM becomes narrow. PMID:24369453

Vacancy-type defects in Al2O3/GaN structure probed by monoenergetic positron beams

NASA Astrophysics Data System (ADS)

Uedono, Akira; Nabatame, Toshihide; Egger, Werner; Koschine, Tönjes; Hugenschmidt, Christoph; Dickmann, Marcel; Sumiya, Masatomo; Ishibashi, Shoji

2018-04-01

Defects in the Al2O3(25 nm)/GaN structure were probed by using monoenergetic positron beams. Al2O3 films were deposited on GaN by atomic layer deposition at 300 °C. Temperature treatment above 800 °C leads to the introduction of vacancy-type defects in GaN due to outdiffusion of atoms from GaN into Al2O3. The width of the damaged region was determined to be 40-50 nm from the Al2O3/GaN interface, and some of the vacancies were identified to act as electron trapping centers. In the Al2O3 film before and after annealing treatment at 300-900 °C, open spaces with three different sizes were found to coexist. The density of medium-sized open spaces started to decrease above 800 °C, which was associated with the interaction between GaN and Al2O3. Effects of the electron trapping/detrapping processes of interface states on the flat band voltage and the defects in GaN were also discussed.

Near single-crystalline, high-carrier-mobility silicon thin film on a polycrystalline/amorphous substrate

DOEpatents

Findikoglu, Alp T [Los Alamos, NM; Jia, Quanxi [Los Alamos, NM; Arendt, Paul N [Los Alamos, NM; Matias, Vladimir [Santa Fe, NM; Choi, Woong [Los Alamos, NM

2009-10-27

A template article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material; is provided, together with a semiconductor article including a base substrate including: (i) a base material selected from the group consisting of polycrystalline substrates and amorphous substrates, and (ii) at least one layer of a differing material upon the surface of the base material; and, a buffer material layer upon the base substrate, the buffer material layer characterized by: (a) low chemical reactivity with the base substrate, (b) stability at temperatures up to at least about 800.degree. C. under low vacuum conditions, and (c) a lattice crystal structure adapted for subsequent deposition of a semiconductor material, and, a top-layer of semiconductor material upon the buffer material layer.

Injection Laser Using Rare Earth Doped GaN Thin Films for Visible and Infrared Applications

DTIC Science & Technology

2010-05-01

system is used to measure the conductivity of GaN thin films in Nanolab. Undoped GaN thin films are usually n-type conductive with the electron ...being investigated for potential applications in optical communication and displays, due to the wide and direct energy bandgap of GaN resulting in low...enhancement on Eu3+ PL intensity. The electrical properties of GaN:RE thin films were changed from high resistive to

Low loss GaN waveguides at the visible spectral wavelengths for integrated photonics applications.

PubMed

Chen, Hong; Fu, Houqiang; Huang, Xuanqi; Zhang, Xiaodong; Yang, Tsung-Han; Montes, Jossue A; Baranowski, Izak; Zhao, Yuji

2017-12-11

We perform comprehensive studies on the fundamental loss mechanisms in III-nitride waveguides in the visible spectral region. Theoretical analysis shows that free carrier loss dominates for GaN under low photon power injection. When optical power increases, the two photon absorption loss becomes important and eventually dominates when photon energy above half-bandgap of GaN. When the dimensions of the waveguides reduce, the sidewall scattering loss will start to dominate. To verify the theoretical results, a high performance GaN-on-sapphire waveguide was fabricated and characterized. Experimental results are consistent with the theoretical findings, showing that under high power injection the optical loss changed significantly for GaN waveguides. A low optical loss ~2 dB/cm was achieved on the GaN waveguide, which is the lowest value ever reported for the visible spectral range. The results and fabrication processes developed in this work pave the way for the development of III-nitride integrated photonics in the visible and potentially ultraviolet spectral range for nonlinear optics and quantum photonics applications.

Nanoscale morphology and optical property evolution of Pt nanostructures on GaN (0 0 0 1) by the systematic control of annealing temperature and duration with various Pt thickness

NASA Astrophysics Data System (ADS)

Kunwar, Sundar; Pandey, Puran; Sui, Mao; Zhang, Quanzhen; Li, Ming-Yu; Lee, Jihoon

2017-06-01

By the controlled fabrication of Pt nanostructures, various surface morphology dependent electronic, catalytic and optical properties can be exploited for a wide range of applications. In this paper, the evolution of Pt nanostructures on GaN (0 0 0 1) by the solid-state dewetting of Pt thin films is investigated. Controlling the annealing temperature, time and film thickness allows us to fabricate distinct size, density and configurations of Pt nanostructures. For 10 nm Pt thickness, tiny voids and Pt hillocks up to 550 °C, extensive void expansion and Pt nanostructure evolution between 600 °C-750 °C and finally Pt nanostructures assisted nanoholes penetration on GaN surface above 800 °C are demonstrated. Furthermore, comparatively elongated Pt nanostructures and NHs are resulted with 20 nm Pt thickness and voids growth and connected Pt nanostructure are formed by annealing duration control. The transformation of Pt films to nanostructures is governed by the surface diffusion, Rayleigh instability, Volmer-Weber growth and energy minimization mechanism whereas NHs penetration is commenced by the decomposition of GaN, Pt-Ga alloying and nitrogen desorption at high temperature. In addition, the optical characteristic of Pt nanostructures on GaN (0 0 0 1) by reflectance, photoluminescence (PL) and Raman spectroscopy demonstrate the surface morphology dependent spectral response.

Epitaxy of Polar Oxides and Semiconductors

NASA Astrophysics Data System (ADS)

Shelton, Christopher Tyrel

Integrating polar oxide materials with wide-bandgap nitride semiconductors offers the possibility of a tunable 2D carrier gas (2DCG) - provided defect densities are low and interfaces are abrupt. This dissertation investigates a portion of the synthesis science necessary to produce a "semiconductor-grade" interface between these highly dissimilar materials. A significant portion of this work is aligned with efforts to engineer a step-free GaN substrate to produce single in-plane oriented rocksalt oxide films. Initially, we explore the homoepitaxial MOCVD growth conditions necessary to produce highquality GaN films on ammonothermally grown substrates. Ammono substrates are only recently available for purchase and are the market leader in low-dislocation density material. Their novelty requires development of an understanding of morphology trade-offs in processing space. This includes preservation of the epi-polished surface in aggressive MOCVD environments and an understanding of the kinetic barriers affecting growth morphologies. Based on several factors, it was determined that GaN exhibits an 'uphill' diffusion bias that may likely be ascribed to a positive Ehrlich-Schwoebel (ES) barrier. This barrier should have a stabilizing effect against step-bunching but, for many growth conditions, regular step bunching was observed. One possible explanation for the step-bunching instability is the presence of impurities. Experimentally, conditions which incorporate more carbon into GaN homoepitaxial layers are correlated with step-bunching while conditions that suppress carbon produce bilayer stepped morphologies. These observations lead us to the conclusion that GaN homoepitaxial morphology is a competition between impurity induced step-bunching and a stabilizing diffusion bias due to a positive ES barrier. Application of the aforementioned homoepitaxial growth techniques to discrete substrate regions using selected- and confined area epitaxy (SAE,CAE) produces some remarkable surface morphologies. This work represents the first effort to extend SAE and CAE to true bulk single-crystal GaN substrates. By carefully controlling supersaturation during growth it is possible to prepare confined areas with a range of step densities, including surfaces that are entirely step-free. Single terrace GaN mesas up to 100 m in size have been observed, however the potential exists, due to the extremely low dislocation density of the substrate, to further extend the dimensions of these regions. Step-free GaN templates are ideal substrates for rocksalt heteroepitaxy and solve a long-standing challenge related to the integration of cubic and hexagonal materials. It has been previously observed that the origin of the two in-plane orientations in rocksalts grown on III-nitrides is a consequence of the stepped GaN surface. By using a substrate that is effectively step-free across a 100 m region, it is possible to prepare a rocksalt // GaN film with a single in-plane orientation. Heterojunctions of this type are disclination defect free and highly crystalline. The ability to locally prepare a single orientation rocksalt film, coupled with commensurate 2D layer-by-layer growth techniques, allows growth, for the first time, of a truly 'semiconductor-grade' oxide-nitride interface. To study the transport properties of oxide-nitride heterostructures, a series of experiments on standard GaN // sapphire template layers were conducted. Devices that allowed contact to the buried oxide-nitride interface were prepared and characterized using low-temperature Hall measurements. Although a high mobility 2DEG was not observed in these samples, a conduction path at the lattice matched Mg0.52Ca0.48O // GaN interface did appear. If confirmed, this finding could represent the first evidence for interfacial polar coupling between an oxide and a nitride. Overcoming the significant symmetry, chemistry and bonding environment barriers to forming a structurally perfect oxide-nitride interface has required many innovations and the development of several new technologies. It is encouraging, however, that a path around such challenging obstacles exists. We believe the techniques and findings presented in this work are general to many systems, offering hope for a future 'materials functionality' based integration strategy. (Abstract shortened by ProQuest.).

Hydrothermal growth and luminescent properties of nonpolar a-plane (11 2 - 0) ZnCdO films for light-emitting diodes

NASA Astrophysics Data System (ADS)

Baik, Kwang Hyeon; Kim, Jimin; Jang, Soohwan

2018-03-01

Nonpolar a-plane ZnCdO films have been obtained on a-plane GaN using a simple low-cost hydrothermal growth method at the low temperature of 80 °C. The morphological, structural, optical, and electrical properties of a-plane ZnCdO films with various Cd contents have been investigated and compared. The photoluminescence peak of the a-plane Zn0.957Cd 0.043O film, was observed to be centered at 429 nm at 25 °C. We demonstrated a heterostructure light-emitting diode (LED) using nonpolar n-type Zn0.957Cd0.043O/p-type GaN films. The rectifying behavior of the current-voltage characteristics was observed with a turn-on voltage of 5 V. The electroluminescence of the LED showed emission peaks including 430 nm, which indicates the near-band-edge emission of a-plane Zn0.957Cd0.043O at 25 °C.

Large-k exciton dynamics in GaN epilayers: Nonthermal and thermal regimes

NASA Astrophysics Data System (ADS)

Vinattieri, Anna; Bogani, Franco; Cavigli, Lucia; Manzi, Donatella; Gurioli, Massimo; Feltin, Eric; Carlin, Jean-François; Martin, Denis; Butté, Raphaël; Grandjean, Nicolas

2013-02-01

We present a detailed investigation performed at low temperature (T<50 K) concerning the exciton dynamics in GaN epilayers grown on c-plane sapphire substrates, focusing on the exciton formation and the transition from the nonthermal to the thermal regime. The time-resolved kinetics of longitudinal-optical-phonon replicas is used to address the energy relaxation in the excitonic band. From picosecond time-resolved spectra, we bring evidence for a long lasting nonthermal excitonic distribution, which accounts for the first 50 ps. Such a behavior is confirmed in different experimental conditions when both nonresonant and resonant excitations are used. At low excitation power density, the exciton formation and their subsequent thermalization are dominated by impurity scattering rather than by acoustic phonon scattering. The estimate of the average energy of the excitons as a function of delay after the excitation pulse provides information on the relaxation time, which describes the evolution of the exciton population to the thermal regime.

Asparagine deamidation dependence on buffer type, pH, and temperature.

PubMed

Pace, Amanda L; Wong, Rita L; Zhang, Yonghua Taylor; Kao, Yung-Hsiang; Wang, Y John

2013-06-01

The deamidation of asparagine into aspartate and isoaspartate moieties is a major pathway for the chemical degradation of monoclonal antibodies (mAbs). It can affect the shelf life of a therapeutic antibody that is not formulated or stored appropriately. A new approach to detect deamidation using ion exchange chromatography was developed that separates papain-digested mAbs into Fc and Fab fragments. From this, deamidation rates of each fragment can be calculated. To generate kinetic parameters useful in setting shelf life, buffers prepared at room temperature and then placed at the appropriate stability temperatures. Solution pH was not adjusted to the same at different temperatures. Deamidation rate at 40°C was faster in acidic buffers than in basic buffers. However, this trend is reversed at 5°C, attributed to the change in hydroxide ion concentration influenced by buffer and temperature. The apparent activation energy was higher for rates generated in an acidic buffer than in a basic buffer. The rate-pH profile for mAb1 can be deconvoluted to Fc and Fab. The Fc deamidation showed a V-shaped profile: deamidation of PENNY peptide is responsible for the rate at high-pH, whereas deamidation of a new site, Asn323, may be responsible for the rate at low-pH. The profile for Fab is a straight line without curvature. Copyright © 2013 Wiley Periodicals, Inc.

Site-controlled GaN nanocolumns with InGaN insertions grown by MBE

NASA Astrophysics Data System (ADS)

Nechaev, D. V.; Semenov, A. N.; Koshelev, O. A.; Jmerik, V. N.; Davydov, V. Yu; Smirnov, A. N.; Pozina, G.; Shubina, T. V.; Ivanov, S. V.

2017-11-01

The site-controlled plasma-assisted molecular beam epitaxy (PA MBE) has been developed to fabricate the regular array of GaN nanocolumns (NCs) with InGaN insertions on micro-cone patterned sapphire substrates (μ-CPSSs). Two-stage growth of GaN NCs, including a nucleation layer grown at metal-rich conditions and high temperature GaN growth in strong N-rich condition, has been developed to achieve the selective growth of the NCs. Microcathodoluminescence measurements have demonstrated pronounced emission from the InGaN insertions in 450-600 nm spectral range. The optically isolated NCs can be used as effective nano-emitters operating in the visible range.

Correlation of doping, structure, and carrier dynamics in a single GaN nanorod

NASA Astrophysics Data System (ADS)

Zhou, Xiang; Lu, Ming-Yen; Lu, Yu-Jung; Gwo, Shangjr; Gradečak, Silvija

2013-06-01

We report the nanoscale optical investigation of a single GaN p-n junction nanorod by cathodoluminescence (CL) in a scanning transmission electron microscope. CL emission characteristic of dopant-related transitions was correlated to doping and structural defect in the nanorod, and used to determine p-n junction position and minority carrier diffusion lengths of 650 nm and 165 nm for electrons and holes, respectively. Temperature-dependent CL study reveals an activation energy of 19 meV for non-radiative recombination in Mg-doped GaN nanorods. These results directly correlate doping, structure, carrier dynamics, and optical properties of GaN nanostructure, and provide insights for device design and fabrication.

The photocatalytic properties of hollow (GaN)1-x(ZnO)x composite nanofibers synthesized by electrospinning

NASA Astrophysics Data System (ADS)

Wang, Ding; Zhang, Minglu; Zhuang, Huaijuan; Chen, Xu; Wang, Xianying; Zheng, Xuejun; Yang, Junhe

2017-02-01

(GaN)1-x(ZnO)x composite nanofibers with hollow structure were prepared by initial electrospinning, and the subsequent calcination and nitridation. The structure and morphology characteristics of samples were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The characterization results showed the phase transition from ZnGa2O4 to (GaN)1-x(ZnO)x solid-solution under ammonia atmosphere. The preparation conditions were explored and the optimum nitridation temperature and holding time are 750 °C and 2 h, respectively. The photocatalytic properties of (GaN)1-x(ZnO)x with different Ga:Zn atomic ratios were investigated by degrading Rhodamine B under the visible light irradiation. The photocatalytic activity sequence is (GaN)1-x(ZnO)x (Ga:Zn = 1:2) > (GaN)1-x(ZnO)x (Ga:Zn = 1:3) > ZnO nanofibers > (GaN)1-x(ZnO)x (Ga:Zn = 1:4) > (GaN)1-x(ZnO)x (Ga:Zn = 1:1). The photocatalytic mechanism of the (GaN)1-x(ZnO)x hollow nanofibers was further studied by UV-vis diffuse reflectance spectra. The excellent photocatalytic performance of (GaN)1-x(ZnO)x hollow nanofibers was attributed to the narrow band gap and high surface area of porous nanofibers with hollow structure.

Free and bound excitons in thin wurtzite GaN layers on sapphire

NASA Astrophysics Data System (ADS)

Merz, C.; Kunzer, M.; Kaufmann, U.; Akasaki, I.; Amano, H.

1996-05-01

Free and bound excitons have been studied by photoluminescence in thin (0268-1242/11/5/010/img8) wurtzite-undoped GaN, n-type GaN:Si as well as p-type GaN:Mg and GaN:Zn layers grown by metal-organic chemical vapour phase deposition (MOCVD). An accurate value for the free A exciton binding energy and an estimate for the isotropically averaged hole mass of the uppermost 0268-1242/11/5/010/img9 valence band are deduced from the data on undoped samples. The acceptor-doped samples reveal recombination lines which are attributed to excitons bound to 0268-1242/11/5/010/img10 and 0268-1242/11/5/010/img11 respectively. These lines are spectrally clearly separated and the exciton localization energies are in line with Haynes' rule. Whenever a comparison is possible, it is found that the exciton lines in these thin MOCVD layers are ultraviolet-shifted by 20 to 25 meV as compared to quasi-bulk (0268-1242/11/5/010/img12) samples. This effect is interpreted in terms of the compressive hydrostatic stress component which thin GaN layers experience when grown on sapphire with an AlN buffer layer.

Systematic Study on the Self-Assembled Hexagonal Au Voids, Nano-Clusters and Nanoparticles on GaN (0001).

PubMed

Pandey, Puran; Sui, Mao; Li, Ming-Yu; Zhang, Quanzhen; Kim, Eun-Soo; Lee, Jihoon

2015-01-01

Au nano-clusters and nanoparticles (NPs) have been widely utilized in various electronic, optoelectronic, and bio-medical applications due to their great potentials. The size, density and configuration of Au NPs play a vital role in the performance of these devices. In this paper, we present a systematic study on the self-assembled hexagonal Au voids, nano-clusters and NPs fabricated on GaN (0001) by the variation of annealing temperature and deposition amount. At relatively low annealing temperatures between 400 and 600°C, the fabrication of hexagonal shaped Au voids and Au nano-clusters are observed and discussed based on the diffusion limited aggregation model. The size and density of voids and nano-clusters can systematically be controlled. The self-assembled Au NPs are fabricated at comparatively high temperatures from 650 to 800°C based on the Volmer-Weber growth model and also the size and density can be tuned accordingly. The results are symmetrically analyzed and discussed in conjunction with the diffusion theory and thermodynamics by utilizing AFM and SEM images, EDS maps and spectra, FFT power spectra, cross-sectional line-profiles and size and density plots.

Systematic Study on the Self-Assembled Hexagonal Au Voids, Nano-Clusters and Nanoparticles on GaN (0001)

PubMed Central

Pandey, Puran; Sui, Mao; Li, Ming-Yu; Zhang, Quanzhen; Kim, Eun-Soo; Lee, Jihoon

2015-01-01

Au nano-clusters and nanoparticles (NPs) have been widely utilized in various electronic, optoelectronic, and bio-medical applications due to their great potentials. The size, density and configuration of Au NPs play a vital role in the performance of these devices. In this paper, we present a systematic study on the self-assembled hexagonal Au voids, nano-clusters and NPs fabricated on GaN (0001) by the variation of annealing temperature and deposition amount. At relatively low annealing temperatures between 400 and 600°C, the fabrication of hexagonal shaped Au voids and Au nano-clusters are observed and discussed based on the diffusion limited aggregation model. The size and density of voids and nano-clusters can systematically be controlled. The self-assembled Au NPs are fabricated at comparatively high temperatures from 650 to 800°C based on the Volmer-Weber growth model and also the size and density can be tuned accordingly. The results are symmetrically analyzed and discussed in conjunction with the diffusion theory and thermodynamics by utilizing AFM and SEM images, EDS maps and spectra, FFT power spectra, cross-sectional line-profiles and size and density plots. PMID:26285135

Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.

PubMed

Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil

2017-12-13

Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.

Photoluminescence of Zn-implanted GaN

NASA Technical Reports Server (NTRS)

Pankove, J. I.; Hutchby, J. A.

1974-01-01

The photoluminescence spectrum of Zn-implanted GaN peaks at 2.87 eV at room temperature. The emission efficiency decreases linearly with the logarithm of the Zn concentration in the range from 1 x 10 to the 18th to 20 x 10 to the 18th Zn/cu cm.

Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

PubMed

Buckeridge, J; Catlow, C R A; Scanlon, D O; Keal, T W; Sherwood, P; Miskufova, M; Walsh, A; Woodley, S M; Sokol, A A

2015-01-09

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Determination of the Nitrogen Vacancy as a Shallow Compensating Center in GaN Doped with Divalent Metals

NASA Astrophysics Data System (ADS)

Buckeridge, J.; Catlow, C. R. A.; Scanlon, D. O.; Keal, T. W.; Sherwood, P.; Miskufova, M.; Walsh, A.; Woodley, S. M.; Sokol, A. A.

2015-01-01

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p -type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Temperature-dependent electrical characteristics and carrier transport mechanism of p-Cu2ZnSnS4/n-GaN heterojunctions

NASA Astrophysics Data System (ADS)

Niteesh Reddy, Varra; Reddy, M. Siva Pratap; Gunasekhar, K. R.; Lee, Jung-Hee

2018-04-01

This work explores the temperature-dependent electrical characteristics and carrier transport mechanism of Au/p-Cu2ZnSnS4/n-type GaN heterojunction (HJ) diodes with a CZTS interlayer. The electrical characteristics were examined by current-voltage-temperature, turn-on voltage-temperature and series resistance-temperature in the high-temperature range of 300-420 K. It is observed that an exponential decrease in the series resistance ( R S) and increase in the ideality factor ( n) and barrier height ( ϕ b) with increase in temperature. The thermal coefficient ( K j) is determined to be - 1.3 mV K-1 at ≥ 300 K. The effective ϕ b is determined to be 1.21 eV. This obtained barrier height is consistent with the theoretical one. The characteristic temperature ( T 0) resulting from the Cheung's functions [d V/d(ln I) vs. I and H( I) vs. I], is seen that there is good agreement between the T 0 values from both Cheung's functions. The relevant carrier transport mechanisms of Au/p-CZTS/n-type GaN HJ are explained based on the thermally decreased energy band gap of n-type GaN layers, thermally activated deep donors and increased further activated shallow donors.

High-Temperature Growth of GaN and Al x Ga1- x N via Ammonia-Based Metalorganic Molecular-Beam Epitaxy

NASA Astrophysics Data System (ADS)

Billingsley, Daniel; Henderson, Walter; Doolittle, W. Alan

2010-05-01

The effect of high-temperature growth on the crystalline quality and surface morphology of GaN and Al x Ga1- x N grown by ammonia-based metalorganic molecular-beam epitaxy (NH3-MOMBE) has been investigated as a means of producing atomically smooth films suitable for device structures. The effects of V/III ratio on the growth rate and surface morphology are described herein. The crystalline quality of both GaN and AlGaN was found to mimic that of the GaN templates, with (002) x-ray diffraction (XRD) full-widths at half- maximum (FWHMs) of ~350 arcsec. Nitrogen-rich growth conditions have been found to provide optimal surface morphologies with a root-mean-square (RMS) roughness of ~0.8 nm, yet excessive N-rich environments have been found to reduce the growth rate and result in the formation of faceted surface pitting. AlGaN exhibits a decreased growth rate, as compared with GaN, due to increased N recombination as a result of the increased pyrolysis of NH3 in the presence of Al. AlGaN films grown directly on GaN templates exhibited Pendellösung x-ray fringes, indicating an abrupt interface and a planar AlGaN film. AlGaN films grown for this study resulted in an optimal RMS roughness of ~0.85 nm with visible atomic steps.

Alignment control and atomically-scaled heteroepitaxial interface study of GaN nanowires.

PubMed

Liu, Qingyun; Liu, Baodan; Yang, Wenjin; Yang, Bing; Zhang, Xinglai; Labbé, Christophe; Portier, Xavier; An, Vladimir; Jiang, Xin

2017-04-20

Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH 3 flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001) GaN ∥(0001) sapphire and (101[combining macron]0) GaN ∥(112[combining macron]0) sapphire . Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of "type I" stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.

Inverted bulk-heterojunction organic solar cells with the transfer-printed anodes and low-temperature-processed ultrathin buffer layers

NASA Astrophysics Data System (ADS)

Itoh, Eiji; Sakai, Shota; Fukuda, Katsutoshi

2018-03-01

We studied the effects of a hole buffer layer [molybdenum oxide (MoO3) and natural copper oxide layer] and a low-temperature-processed electron buffer layer on the performance of inverted bulk-heterojunction organic solar cells in a device consisting of indium-tin oxide (ITO)/poly(ethylene imine) (PEI)/titanium oxide nanosheet (TiO-NS)/poly(3-hexylthiopnehe) (P3HT):phenyl-C61-butyric acid methylester (PCBM)/oxide/anode (Ag or Cu). The insertion of ultrathin TiO-NS (˜1 nm) and oxide hole buffer layers improved the open circuit voltage V OC, fill factor, and rectification properties owing to the effective hole blocking and electron transport properties of ultrathin TiO-NS, and to the enhanced work function difference between TiO-NS and the oxide hole buffer layer. The insertion of the TiO-NS contributed to the reduction in the potential barrier at the ITO/PEI/TiO-NS/active layer interface for electrons, and the insertion of the oxide hole buffer layer contributed to the reduction in the potential barrier for holes. The marked increase in the capacitance under positive biasing in the capacitance-voltage characteristics revealed that the combination of TiO-NS and MoO3 buffer layers contributes to the selective transport of electrons and holes, and blocks counter carriers at the active layer/oxide interface. The natural oxide layer of the copper electrode also acts as a hole buffer layer owing to the increase in the work function of the Cu surface in the inverted cells. The performance of the cell with evaporated MoO3 and Cu layers that were transfer-printed to the active layer was almost comparable to that of the cell with MoO3 and Ag layers directly evaporated onto the active layer. We also demonstrated comparable device performance in the cell with all-printed MoO3 and low-temperature-processed silver nanoparticles as an anode.

1.55 µm emission from a single III-nitride top-down and site-controlled nanowire quantum disk

NASA Astrophysics Data System (ADS)

Chen, Qiming; Yan, Changling; Qu, Yi

2017-07-01

InN/InGaN single quantum well (SQW) was fabricated on 100 nm GaN buffer layer which was deposited on GaN template by plasma assisted molecular beam epitaxy (PA-MBE). The In composition and the surface morphology were measured by x-ray diffusion (XRD) and atom force microscope (AFM), respectively. Afterwards, the sample was fabricated into site-controlled nanowires arrays by hot-embossing nano-imprint lithography (HE-NIL) and ultraviolet nanoimprint lithography (UV-NIL). The nanowires were uniform along the c-axis and aligned periodically as presented by scanning electron microscope (SEM). The single nanowire showed disk-in-a-wire structure by high angle annular dark field (HAADF) and an In-rich or Ga deficient region was observed by energy dispersive x-ray spectrum (EDXS). The optical properties of the SQW film and single nanowire were measured using micro photoluminescence (µ-PL) spectroscopy. The stimulating light wavelength was 632.8 nm which was emitted from a He-Ne laser and the detector was a liquid nitrogen cooled InGaAs detector. A blue peak shift from the film material to the nanowire was observed. This was due to the quantum confinement Stark Effect. More importantly, the 1.55 µm emission was given from the single disk-in-a-wire structure at room temperature. We believe the arrays of such nanowires may be useful for quantum communication in the future.

Effect of 60Co γ-irradiation on the nature of electronic transport in heavily doped n-type GaN based Schottky photodetectors

NASA Astrophysics Data System (ADS)

Chatterjee, Abhishek; Khamari, Shailesh K.; Porwal, S.; Kher, S.; Sharma, T. K.

2018-04-01

GaN Schottky photodetectors are fabricated on heavily doped n-type GaN epitaxial layers grown by the hydride vapour phase epitaxy technique. The effect of 60Co γ-radiation on the electronic transport in GaN epilayers and Schottky detectors is studied. In contrast to earlier observations, a steady rise in the carrier concentration with increasing irradiation dose is clearly seen. By considering a two layer model, the contribution of interfacial dislocations in carrier transport is isolated from that of the bulk layer for both the pristine and irradiated samples. The bulk carrier concentration is fitted by using the charge balance equation which indicates that no new electrically active defects are generated by γ-radiation even at 500 kGy dose. The irradiation induced rise in the bulk carrier concentration is attributed to the activation of native Si impurities that are already present in an electrically inert form in the pristine sample. Further, the rise in interfacial contribution in the carrier concentration is governed by the enhanced rate of formation of nitrogen vacancies by irradiation, which leads to a larger diffusion of oxygen impurities. A large value of the characteristic tunnelling energy for both the pristine and irradiated Au/Ni/GaN Schottky devices confirms that the dislocation-assisted tunnelling dominates the low temperature current transport even after irradiation. The advantage of higher displacement energy and larger bandgap of GaN as compared to GaAs is evident from the change in leakage current after irradiation. Further, a fast recovery of the photoresponse of GaN photodetectors after irradiation signifies their compatibility to operate in high radiation zones. The results presented here are found to be crucial in understanding the interaction of 60Co γ-irradiation with n+-GaN epilayers.

The controlled growth of GaN microrods on Si(111) substrates by MOCVD

NASA Astrophysics Data System (ADS)

Foltynski, Bartosz; Garro, Nuria; Vallo, Martin; Finken, Matthias; Giesen, Christoph; Kalisch, Holger; Vescan, Andrei; Cantarero, Andrés; Heuken, Michael

2015-03-01

In this paper, a selective area growth (SAG) approach for growing GaN microrods on patterned SiNx/Si(111) substrates by metal-organic chemical vapor deposition (MOCVD) is studied. The surface morphology, optical and structural properties of vertical GaN microrods terminated by pyramidal shaped facets (six { 10 1 bar 1} planes) were characterized using scanning electron microscopy (SEM), room temperature photoluminescence (PL) and Raman spectroscopy, respectively. Measurements revealed high-quality GaN microcolumns grown with silane support. Characterized structures were grown nearly strain-free (central frequency of Raman peak of 567±1 cm-1) with crystal quality comparable to bulk crystals (FWHM=4.2±1 cm-1). Such GaN microrods might be used as a next-generation device concept for solid-state lighting (SSL) applications by realizing core-shell InGaN/GaN multi-quantum wells (MQWs) on the n-GaN rod base.

The residual C concentration control for low temperature growth p-type GaN

NASA Astrophysics Data System (ADS)

Liu, Shuang-Tao; Zhao, De-Gang; Yang, Jing; Jiang, De-Sheng; Liang, Feng; Chen, Ping; Zhu, Jian-Jun; Liu, Zong-Shun; Li, Xiang; Liu, Wei; Xing, Yao; Zhang, Li-Qun

2017-09-01

Not Available Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFB0401801 and 2016YFB0400803), the National Natural Science Foundation of China (Grant Nos. 61674138, 61674139, 61604145, 61574135, 61574134, 61474142, 61474110, 61377020, and 61376089), the Science Challenge Project (Grant No. JCKY2016212A503), and Beijing Municipal Science and Technology Project (Grant No. Z161100002116037).

Gas Source Molecular Beam Epitaxial Growth of GaN

DTIC Science & Technology

1992-11-25

identify by block number) FIELW GROUP SUB-GROUP 19. ABSTRACT (Continue on reverse if necessary and Identify by block number) Aluminum gallium nitride (AlGaN...AND TASK OBJECTIVES Aluminum gallium nitride (AIGaN) has long been recognized as a promising radiation hard optoelectronic material. AIGaN has a wide...Efficient, pure, low temperature sources for the gas source molecular beam epitaxial (GSMBE) growth of aluminum gallium nitride will essentially

Operation of a New Half-Bridge Gate Driver for Enhancement - Mode GaN FETs, Type LM5113, Over a Wide Temperature Range

NASA Technical Reports Server (NTRS)

Patterson, Richard; Hammoud, Ahmad

2011-01-01

A new commercial-off-the-shelf (COTS) gate driver designed to drive both the high-side and the low-side enhancement-mode GaN FETs, National Semiconductor's type LM5113, was evaluated for operation at temperatures beyond its recommended specified limits of -40 C to +125 C. The effects of limited thermal cycling under the extended test temperature, which ranged from -194 C to +150 C, on the operation of this chip as well as restart capability at the extreme cryogenic and hot temperatures were also investigated. The driver circuit was able to maintain good operation throughout the entire test regime between -194 C and +150 C without undergoing any major changes in its outputs signals and characteristics. The limited thermal cycling performed on the device also had no effect on its performance, and the driver chip was able to successfully restart at each of the extreme temperatures of -194 C and +150 C. The plastic packaging of this device was also not affected by either the short extreme temperature exposure or the limited thermal cycling. These preliminary results indicate that this new commercial-off-the-shelf (COTS) halfbridge eGaN FET driver integrated circuit has the potential for use in space exploration missions under extreme temperature environments. Further testing is planned under long-term cycling to assess the reliability of these parts and to determine their suitability for extended use in the harsh environments of space.

Thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap semiconductors SiC, GaN, and ZnO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Zheng; Lü, Tie-Yu; Wang, Hui-Qiong

We have investigated the thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap(n-type) semiconductors SiC, GaN, and ZnO based on first-principles calculations and Boltzmann transport theory. Our results show that the thermoelectric performance increases from 3C to 6H, 4H, and 2H structures with an increase of hexagonality for SiC. However, for GaN and ZnO, their power factors show a very weak dependence on the polytype. Detailed analysis of the thermoelectric properties with respect to temperature and carrier concentration of 4H-SiC, 2H-GaN, and 2H-ZnO shows that the figure of merit of these three compounds increases with temperature,more » indicating the promising potential applications of these thermoelectric materials at high temperature. The significant difference of the polytype-dependent thermoelectric properties among SiC, GaN, and ZnO might be related to the competition between covalency and ionicity in these semiconductors. Our calculations may provide a new way to enhance the thermoelectric properties of wide-band-gap semiconductors through atomic structure design, especially hexagonality design for SiC.« less

Titanium induced polarity inversion in ordered (In,Ga)N/GaN nanocolumns.

PubMed

Kong, X; Li, H; Albert, S; Bengoechea-Encabo, A; Sanchez-Garcia, M A; Calleja, E; Draxl, C; Trampert, A

2016-02-12

We report on the formation of polarity inversion in ordered (In,Ga)N/GaN nanocolumns grown on a Ti-masked GaN-buffered sapphire substrate by plasma assisted molecular beam epitaxy. High-resolution transmission electron microscopy and electron energy-loss spectroscopy reveal a stacking fault-like planar defect at the homoepitaxial GaN interface due to Ti incorporation, triggering the generation of N-polar domains in Ga-polar nanocolumns. Density functional theory calculations are applied to clarify the atomic configurations of a Ti monolayer occupation on the GaN (0002) plane and to prove the inversion effect. The polarity inversion leads to an enhanced indium incorporation in the subsequent (In,Ga)N segment of the nanocolumn. This study provides a deeper understanding of the effects of Ti mask in the well-controlled selective area growth of (In,Ga)N/GaN nanocolumns.

Curvature evolution of 200 mm diameter GaN-on-insulator wafer fabricated through metalorganic chemical vapor deposition and bonding

NASA Astrophysics Data System (ADS)

Zhang, Li; Lee, Kwang Hong; Kadir, Abdul; Wang, Yue; Lee, Kenneth E.; Tan, Chuan Seng; Chua, Soo Jin; Fitzgerald, Eugene A.

2018-05-01

Crack-free 200 mm diameter N-polar GaN-on-insulator (GaN-OI) wafers are demonstrated by the transfer of metalorganic chemical vapor deposition (MOCVD)-grown Ga-polar GaN layers from Si(111) wafers onto SiO2/Si(100) wafers. The wafer curvature of the GaN-OI wafers after the removal of the original Si(111) substrate is correlated with the wafer curvature of the starting GaN-on-Si wafers and the voids on the GaN-on-Si surface that evolve into cracks on the GaN-OI wafers. In crack-free GaN-OI wafers, the wafer curvature during the removal of the AlN nucleation layer, AlGaN strain-compensation buffer layers and GaN layers is correlated with the residual stress distribution within individual layers in the GaN-OI wafer.

p-type zinc-blende GaN on GaAs substrates

NASA Astrophysics Data System (ADS)

Lin, M. E.; Xue, G.; Zhou, G. L.; Greene, J. E.; Morkoç, H.

1993-08-01

We report p-type cubic GaN. The Mg-doped layers were grown on vicinal (100) GaAs substrates by plasma-enhanced molecular beam epitaxy. Thermally sublimed Mg was, with N2 carrier gas, fed into an electron-cyclotron resonance source. p-type zinc-blende-structure GaN films were achieved with hole mobilities as high as 39 cm2/V s at room temperature. The cubic nature of the films were confirmed by x-ray diffractometry. The depth profile of Mg was investigated by secondary ions mass spectroscopy.

Characteristics of n-GaN after ICP etching

NASA Astrophysics Data System (ADS)

Han, Yanjun; Xue, Song; Guo, Wenping; Hao, Zhi-Biao; Sun, Changzheng; Luo, Yi

2002-09-01

In this work, a systematic study on the plasma-induced damage on n-type GaN by inductively coupled plasma (ICP) etching is presented. After n-contact metal formation and annealing, electrical property is evaluated by the I-V characteristics. Room temperature photoluminescence (PL) measurement of etched GaN surfaces is performed to investigate the etching damage on the optical properties of n-type GaN. Investigation of the effect of additive gas RF chuck power on these characteristics has also been carried out. The better etching conditions have been obtained based on these results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moutanabbir, O.; Scholz, R.; Goesele, U.

We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut conditions. By using transmission electron microscopy, we found that the damage band in as-implanted GaN is decorated with a high density of nanobubbles of approx1-2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains vacancy clusters and voids. In addition to vacancy clusters, the presence of V{sub Ga}, V{sub Ga}-H{sub 2}, and V{sub Ga}V{sub N} complexes was evidenced by pulsed low-energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes weremore » also investigated. As a general trend, a growth in open-volume defects is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450 deg. C, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Since the formation of positronium is not possible in a dense semiconductor, our finding demonstrates the presence of sufficiently large open-volume defects in this temperature range. Based on the Tao-Eldrup model, the average lattice opening during thermal annealing was quantified. We found that a void diameter of 0.4 nm is induced by annealing at 600 deg. C. The role of these complexes in the subsurface microcracking is discussed.« less

Gallium nitride photocathodes for imaging photon counters

NASA Astrophysics Data System (ADS)

Siegmund, Oswald H. W.; Hull, Jeffrey S.; Tremsin, Anton S.; McPhate, Jason B.; Dabiran, Amir M.

2010-07-01

Gallium nitride opaque and semitransparent photocathodes provide high ultraviolet quantum efficiencies from 100 nm to a long wavelength cutoff at ~380 nm. P (Mg) doped GaN photocathode layers ~100 nm thick with a barrier layer of AlN (22 nm) on sapphire substrates also have low out of band response, and are highly robust. Opaque GaN photocathodes are relatively easy to optimize, and consistently provide high quantum efficiency (70% at 120 nm) provided the surface cleaning and activation (Cs) processes are well established. We have used two dimensional photon counting imaging microchannel plate detectors, with an active area of 25 mm diameter, to investigate the imaging characteristics of semitransparent GaN photocathodes. These can be produced with high (20%) efficiency, but the thickness and conductivity of the GaN must be carefully optimized. High spatial resolution of ~50 μm with low intrinsic background (~7 events sec-1 cm-2) and good image uniformity have been achieved. Selectively patterned deposited GaN photocathodes have also been used to allow quick diagnostics of optimization parameters. GaN photocathodes of both types show great promise for future detector applications in ultraviolet Astrophysical instruments.

Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

NASA Astrophysics Data System (ADS)

Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

2017-01-01

GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

P-type surface effects for thickness variation of 2um and 4um of n-type layer in GaN LED

NASA Astrophysics Data System (ADS)

Halim, N. S. A. Abdul; Wahid, M. H. A.; Hambali, N. A. M. Ahmad; Rashid, S.; Ramli, M. M.; Shahimin, M. M.

2017-09-01

The internal quantum efficiency of III-Nitrides group, GaN light-emitting diode (LED) has been considerably limited due to the insufficient hole injection and this is caused by the lack of performance p-type doping and low hole mobility. The low hole mobility makes the hole less energetic, thus reduced the performance operation of GaN LED itself. The internal quantum efficiency of GaN-based LED with surface roughness (texture) can be changed by texture size, density, and thickness of GaN film or by the combined effects of surface shape and thickness of GaN film. Besides, due to lack of p-type GaN, attempts to look forward the potential of GaN LED relied on the thickness of n-type layer and surface shape of p-type GaN layer. This work investigates the characteristics of GaN LED with undoped n-GaN layer of different thickness and the surface shape of p-type layer. The LEDs performance is significantly altered by modifying the thickness and shape. Enhancement of n-GaN layer has led to the annihilation of electrical conductivity of the chip. Different surface geometry governs the emission rate extensively. Internal quantum efficiency is also predominantly affected by the geometry of n-GaN layer which subjected to the current spreading. It is recorded that the IQE droop can be minimized by varying the thickness of the active layer without amplifying the forward voltage. Optimum forward voltage (I-V), total emission rate relationship with the injected current and internal quantum efficiency (IQE) for 2,4 µm on four different surfaces of p-type layer are also reported in this paper.

Propagation of THz acoustic wave packets in GaN at room temperature

DOE PAGES

Maznev, A. A.; Hung, T.-C.; Yao, Y.-T.; ...

2018-02-05

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1–1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as highmore » as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.« less

Propagation of THz acoustic wave packets in GaN at room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maznev, A. A.; Hung, T.-C.; Yao, Y.-T.

We use femtosecond laser pulses to generate coherent longitudinal acoustic phonons at frequencies of 1–1.4 THz and study their propagation in GaN-based structures at room temperature. Two InGaN-GaN multiple-quantum-well (MQW) structures separated by a 2.3 μm-thick GaN spacer are used to simultaneously generate phonon wave packets with a central frequency determined by the period of the MQW and detect them after passing through the spacer. The measurements provide lower bounds for phonon lifetimes in GaN, which are still significantly lower than those from first principles predictions. The material Q-factor at 1 THz is found to be at least as highmore » as 900. The measurements also demonstrate a partial specular reflection from the free surface of GaN at 1.4 THz. This work shows the potential of laser-based methods for THz range phonon spectroscopy and the promise for extending the viable frequency range of GaN-based acousto-electronic devices.« less

Origin of the Electroluminescence from Annealed-ZnO/GaN Heterojunction Light-Emitting Diodes.

PubMed

Hsu, Kai-Chiang; Hsiao, Wei-Hua; Lee, Ching-Ting; Chen, Yan-Ting; Liu, Day-Shan

2015-11-16

This paper addressed the effect of post-annealed treatment on the electroluminescence (EL) of an n -ZnO/ p -GaN heterojunction light-emitting diode (LED). The bluish light emitted from the 450 °C-annealed LED became reddish as the LED annealed at a temperature of 800 °C under vacuum atmosphere. The origins of the light emission for these LEDs annealed at various temperatures were studied using measurements of electrical property, photoluminescence, and Auger electron spectroscopy (AES) depth profiles. A blue-violet emission located at 430 nm was associated with intrinsic transitions between the bandgap of n -ZnO and p -GaN, the green-yellow emission at 550 nm mainly originating from the deep-level transitions of native defects in the n -ZnO and p -GaN surfaces, and the red emission at 610 nm emerging from the Ga-O interlayer due to interdiffusion at the n -ZnO/ p -GaN interface. The above-mentioned emissions also supported the EL spectra of LEDs annealed at 700 °C under air, nitrogen, and oxygen atmospheres, respectively.

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals.

PubMed

Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

2017-12-12

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson's ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson's ratios at planes (100) and (111) are isotropic, while the Poisson's ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol -1 K -1 , respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of states in the orbital hybridization between Ga and N atoms of wurtzite GaN are much higher, indicating more electrons participate in forming Ga-N ionic bonds in the wurtzite GaN.

Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

PubMed Central

Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

2017-01-01

For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of states in the orbital hybridization between Ga and N atoms of wurtzite GaN are much higher, indicating more electrons participate in forming Ga-N ionic bonds in the wurtzite GaN. PMID:29231902

In situ chemical functionalization of gallium nitride with phosphonic acid derivatives during etching.

PubMed

Wilkins, Stewart J; Greenough, Michelle; Arellano, Consuelo; Paskova, Tania; Ivanisevic, Albena

2014-03-04

In situ functionalization of polar (c plane) and nonpolar (a plane) gallium nitride (GaN) was performed by adding (3-bromopropyl) phosphonic acid or propyl phosphonic acid to a phosphoric acid etch. The target was to modulate the emission properties and oxide formation of GaN, which was explored through surface characterization with atomic force microscopy, X-ray photoelectron spectroscopy, photoluminescence (PL), inductively coupled plasma-mass spectrometry, and water contact angle. The use of (3-bromopropyl) phosphonic acid and propyl phosphonic acid in phosphoric acid demonstrated lower amounts of gallium oxide formation and greater hydrophobicity for both sample sets, while also improving PL emission of polar GaN samples. In addition to crystal orientation, growth-related factors such as defect density in bulk GaN versus thin GaN films residing on sapphire substrates were investigated as well as their responses to in situ functionalization. Thin nonpolar GaN layers were the most sensitive to etching treatments due in part to higher defect densities (stacking faults and threading dislocations), which accounts for large surface depressions. High-quality GaN (both free-standing bulk polar and bulk nonpolar) demonstrated increased sensitivity to oxide formation. Room-temperature PL stands out as an excellent technique to identify nonradiative recombination as observed in the spectra of heteroepitaxially grown GaN samples. The chemical methods applied to tune optical and physical properties of GaN provide a quantitative framework for future novel chemical and biochemical sensor development.

Nano-scaled Pt/Ag/Ni/Au contacts on p-type GaN for low contact resistance and high reflectivity.

PubMed

Kwon, Y W; Ju, I C; Kim, S K; Choi, Y S; Kim, M H; Yoo, S H; Kang, D H; Sung, H K; Shin, K; Ko, C G

2011-07-01

We synthesized the vertical-structured LED (VLED) using nano-scaled Pt between p-type GaN and Ag-based reflector. The metallization scheme on p-type GaN for high reflectance and low was the nano-scaled Pt/Ag/Ni/Au. Nano-scaled Pt (5 A) on Ag/Ni/Au exhibited reasonably high reflectance of 86.2% at the wavelength of 460 nm due to high transmittance of light through nano-scaled Pt (5 A) onto Ag layer. Ohmic behavior of contact metal, Pt/Ag/Ni/Au, to p-type GaN was achieved using surface treatments of p-type GaN prior to the deposition of contact metals and the specific contact resistance was observed with decreasing Pt thickness of 5 A, resulting in 1.5 x 10(-4) ohms cm2. Forward voltages of Pt (5 A)/Ag/Ni contact to p-type GaN showed 4.19 V with the current injection of 350 mA. Output voltages with various thickness of Pt showed the highest value at the smallest thickness of Pt due to its high transmittance of light onto Ag, leading to high reflectance. Our results propose that nano-scaled Pt/Ag/Ni could act as a promising contact metal to p-type GaN for improving the performance of VLEDs.

Growth of hierarchical GaN nanowires for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Raj, Rishabh; Vignesh, Veeramuthu; Ra, Yong-Ho; Nirmala, Rajkumar; Lee, Cheul-Ro; Navamathavan, Rangaswamy

2017-01-01

Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers, and nanofluidic biochemical sensors. We report on the growth of hierarchical GaN nanowires (NWs) by dynamically adjusting the growth parameters using the pulsed flow metal-organic chemical vapor deposition technique. We carried out two step growth processes to grow hierarchical GaN NWs. In the first step, the GaN NWs were grown at 950°C, and in the second, we suitably decreased the growth temperature to 630°C and 710°C to grow the hierarchical structures. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and cathodoluminescence measurements. These kinds of hierarchical GaN NWs are promising for allowing flat band quantum structures that are shown to improve the efficiency of LEDs.

Deep level transient spectroscopy signatures of majority traps in GaN p-n diodes grown by metal-organic vapor-phase epitaxy technique on GaN substrates

NASA Astrophysics Data System (ADS)

PŁaczek-Popko, E.; Trzmiel, J.; Zielony, E.; Grzanka, S.; Czernecki, R.; Suski, T.

2009-12-01

In this study, we present the results of investigation on p-n GaN diodes by means of deep level transient spectroscopy (DLTS) within the temperature range of 77-350 K. Si-doped GaN layers were grown by metal-organic vapor-phase epitaxy technique (MOVPE) on the free-standing GaN substrates. Subsequently Mg-doped GaN layers were grown. To perform DLTS measurements Ni/Au contacts to p-type material and Ti/Au contacts to n-type material were processed. DLTS signal spectra revealed the presence of two majority traps of activation energies obtained from Arrhenius plots equal to E1=0.22 eV and E2=0.65 eV. In present work we show that the trap E1 is linked with the extended defects whereas the trap E2 is the point defect related. Its capture cross section is thermally activated with energy barrier for capture equal to 0.2 eV.

Gradual tilting of crystallographic orientation and configuration of dislocations in GaN selectively grown by vapour phase epitaxy methods

PubMed

Kuwan; Tsukamoto; Taki; Horibuchi; Oki; Kawaguchi; Shibata; Sawaki; Hiramatsu

2000-01-01

Cross-sectional transmission electron microscope (TEM) observation was performed for selectively grown gallium nitride (GaN) in order to examine the dependence of GaN microstructure on the growth conditions. The GaN films were grown by hydride vapour phase epitaxy (HVPE) or metalorganic vapour phase epitaxy (MOVPE) on GaN covered with a patterned mask. Thin foil specimens for TEM observation were prepared with focused ion beam (FIB) machining apparatus. It was demonstrated that the c-axis of GaN grown over the terrace of the mask tilts towards the centre of the terrace when the GaN is grown in a carrier gas of N2. The wider terrace results in a larger tilting angle if other growth conditions are identical. The tilting is attributed to 'horizontal dislocations' (HDs) generated during the overgrowth of GaN on the mask terrace. The HDs in HVPE-GaN have a semi-loop shape and are tangled with one another, while those in MOVPE-GaN are straight and lined up to form low-angle grain boundaries.

Anharmonic Damping of Terahertz Acoustic Waves in a Network Glass and Its Effect on the Density of Vibrational States

NASA Astrophysics Data System (ADS)

Baldi, G.; Giordano, V. M.; Ruta, B.; Dal Maschio, R.; Fontana, A.; Monaco, G.

2014-03-01

We report the observation, by means of high-resolution inelastic x-ray scattering, of an unusually large temperature dependence of the sound attenuation of a network glass at terahertz frequency, an unprecedentedly observed phenomenon. The anharmonicity can be ascribed to the interaction between the propagating acoustic wave and the bath of thermal vibrations. At low temperatures the sound attenuation follows a Rayleigh-Gans scattering law. As the temperature is increased the anharmonic process sets in, resulting in an almost quadratic frequency dependence of the damping in the entire frequency range. We show that the temperature variation of the sound damping accounts quantitatively for the temperature dependence of the density of vibrational states.

Low-temperature hermetic sealing of optical fiber components

DOEpatents

Kramer, D.P.

1996-10-22

A method for manufacturing low-temperature hermetically sealed optical fiber components is provided. The method comprises the steps of: inserting an optical fiber into a housing, the optical fiber having a glass core, a glass cladding and a protective buffer layer disposed around the core and cladding; heating the housing to a predetermined temperature, the predetermined temperature being below a melting point for the protective buffer layer and above a melting point of a solder; placing the solder in communication with the heated housing to allow the solder to form an eutectic and thereby fill a gap between the interior of the housing and the optical fiber; and cooling the housing to allow the solder to form a hermetic compression seal between the housing and the optical fiber. 5 figs.

Low-temperature hermetic sealing of optical fiber components

DOEpatents

Kramer, Daniel P.

1996-10-22

A method for manufacturing low-temperature hermetically sealed optical fi components is provided. The method comprises the steps of: inserting an optical fiber into a housing, the optical fiber having a glass core, a glass cladding and a protective buffer layer disposed around the core and cladding; heating the housing to a predetermined temperature, the predetermined temperature being below a melting point for the protective buffer layer and above a melting point of a solder; placing the solder in communication with the heated housing to allow the solder to form an eutectic and thereby fill a gap between the interior of the housing and the optical fiber; and cooling the housing to allow the solder to form a hermetic compression seal between the housing and the optical fiber.

Experimental evidence of Ga-vacancy induced room temperature ferromagnetic behavior in GaN films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roul, Basanta; Kumar, Mahesh; Central Research Laboratory, Bharat Electronics, Bangalore 560013

We have grown Ga deficient GaN epitaxial films on (0001) sapphire substrate by plasma-assisted molecular beam epitaxy and report the experimental evidence of room temperature ferromagnetic behavior. The observed yellow emission peak in room temperature photoluminescence spectra and the peak positioning at 300 cm{sup -1} in Raman spectra confirms the existence of Ga vacancies. The x-ray photoelectron spectroscopic measurements further confirmed the formation of Ga vacancies; since the N/Ga is found to be >1. The ferromagnetism is believed to originate from the polarization of the unpaired 2p electrons of N surrounding the Ga vacancy.

Synthesis and excellent field emission properties of three-dimensional branched GaN nanowire homostructures

NASA Astrophysics Data System (ADS)

Li, Enling; Sun, Lihe; Cui, Zhen; Ma, Deming; Shi, Wei; Wang, Xiaolin

2016-10-01

Three-dimensional branched GaN nanowire homostructures have been synthesized on the Si substrate via a two-step approach by chemical vapor deposition. Structural characterization reveals that the single crystal GaN nanowire trunks have hexagonal wurtzite characteristics and grow along the [0001] direction, while the homoepitaxial single crystal branches grow in a radial direction from the six-sided surfaces of the trunks. The field emission measurements demonstrate that the branched GaN nanowire homostructures have excellent field emission properties, with low turn-on field at 2.35 V/μm, a high field enhancement factor of 2938, and long emission current stability. This indicates that the present branched GaN nanowire homostructures will become valuable for practical field emission applications.

High Quality, Low Cost Bulk Gallium Nitride Substrates Grown by the Electrochemical Solution Growth Method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seacrist, Michael

The objective of this project was to develop the Electrochemical Solution Growth (ESG) method conceived / patented at Sandia National Laboratory into a commercially viable bulk gallium nitride (GaN) growth process that can be scaled to low cost, high quality, and large area GaN wafer substrate manufacturing. The goal was to advance the ESG growth technology by demonstrating rotating seed growth at the lab scale and then transitioning process to prototype commercial system, while validating the GaN material and electronic / optical device quality. The desired outcome of the project is a prototype commercial process for US-based manufacturing of highmore » quality, large area, and lower cost GaN substrates that can drive widespread deployment of energy efficient GaN-based power electronic and optical devices. In year 1 of the project (Sept 2012 – Dec 2013) the overall objective was to demonstrate crystalline GaN growth > 100um on a GaN seed crystal. The development plan included tasks to demonstrate and implement a method for purifying reagent grade salts, develop the reactor 1 process for rotating seed Electrochemical Solution Growth (ESG) of GaN, grow and characterize ESG GaN films, develop a fluid flow and reaction chemistry model for GaN film growth, and design / build an improved growth reactor capable of scaling to 50mm seed diameter. The first year’s project objectives were met in some task areas including salt purification, film characterization, modeling, and reactor 2 design / fabrication. However, the key project objective of the growth of a crystalline GaN film on the seed template was not achieved. Amorphous film growth on the order of a few tenths of a micron has been detected with a film composition including Ga and N, plus several other impurities originating from the process solution and hardware. The presence of these impurities, particularly the oxygen, has inhibited the demonstration of crystalline GaN film growth on the seed template. However, the presence of both Ga and N at the growth surface indicates that the reactor hardware physics is all functioning properly; achieving film growth is a matter of controlling the chemistry at the interface. The impurities originating from the hardware are expected to be straightforward to eliminate. Activities were defined for an extension of budget period 1 to eliminate the undesired impurities originating from the reactor hardware and interfering with crystalline GaN film growth. The budget period 1 extension was negotiated during the 1st half of 2014. The budget period 1 extension spanned approximately from August 2014 to August 2015. The project objective for this extension period was to demonstrate at least 0.5um crystalline GaN film on a GaN seed in the lab scale reactor. The focus of the budget 1 extension period from August 2014 to August 2015 was to eliminate oxygen contamination interference with GaN film growth. The team procured the highest purity lowest oxygen salt for testing. Low oxygen crucible materials such as silicon carbide were installed and evaluated in the laboratory reactor. Growth experiments were performed with high purity salt, high purity hardware, and optimized oxide removal from the seed surface. Experiments were characterized with methods including UV inspection, profilometry, x-ray diffraction (XRD) to determine crystalline structure, optical and scanning electron microscopy, photoluminescence, x-ray photon spectroscopy (XPS), transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). Despite successfully integrating the low oxygen materials in the laboratory reactor, the goal of depositing 0.5um of crystalline GaN on the MOCVD GaN seed was not met. Very thin (ca. 10nm) cubic phase GaN deposition was observed on the hexagonal MOCVD GaN seeds. But there was a competing etching reaction which was also observed and thought to be related to the presence of metallic lithium, a byproduct of the LiCl-KCl salt used as the process medium. The etching reaction could potentially be addressed by alternate salts not containing lithium, but would necessitate starting all over on the reactor and process design. Further, controlling the reaction of Ga and N in the bulk salt to favor deposition on the seed has proved to be very difficult and unlikely to be solved within the scope of this project in a manner consistent with the original objective for wafer or crystal scale thickness for GaN deposition on a GaN seed. Upon completion of the budget 1 extension period in August 2015 the project partners and DOE agreed to stop work on the project.« less

Development of Mid-infrared GeSn Light Emitting Diodes on a Silicon Substrate

DTIC Science & Technology

2015-04-22

Materials, Heterostrucuture Semiconductor, Light Emitting Devices, Molecular Beam Epitaxy 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT...LED) structure. Optimization of traditional and hetero- P-i-N structures designed and grown on Ge-buffer Si (001) wafers using molecular beam epitaxy ...designed structures were grown on Ge-buffer Si (001) wafers using molecular beam epitaxy (MBE) with the low-temperature growth technique. (The Ge-buffer

Spin injection in epitaxial MnGa(111)/GaN(0001) heterostructures

NASA Astrophysics Data System (ADS)

Zube, Christian; Malindretos, Joerg; Watschke, Lars; Zamani, Reza R.; Disterheft, David; Ulbrich, Rainer G.; Rizzi, Angela; Iza, Michael; Keller, Stacia; DenBaars, Steven P.

2018-01-01

Ferromagnetic MnGa(111) layers were grown on GaN(0001) by molecular beam epitaxy. MnGa/GaN Schottky diodes with a doping level of around n = 7 × 1018 cm-3 were fabricated to achieve single step tunneling across the metal/semiconductor junction. Below the GaN layer, a thin InGaN quantum well served as optical spin detector ("spin-LED"). For electron spin injection from MnGa into GaN and subsequent spin transport through a 45 nm (70 nm) thick GaN layer, we observe a circular polarization of 0.3% (0.2%) in the electroluminescence at 80 K. Interface mixing, spin polarization losses during electrical transport in the GaN layer, and spin relaxation in the InGaN quantum well are discussed in relation with the low value of the optically detected spin polarization.

Polarity Control of Heteroepitaxial GaN Nanowires on Diamond.

PubMed

Hetzl, Martin; Kraut, Max; Hoffmann, Theresa; Stutzmann, Martin

2017-06-14

Group III-nitride materials such as GaN nanowires are characterized by a spontaneous polarization within the crystal. The sign of the resulting sheet charge at the top and bottom facet of a GaN nanowire is determined by the orientation of the wurtzite bilayer of the different atomic species, called N and Ga polarity. We investigate the polarity distribution of heteroepitaxial GaN nanowires on different substrates and demonstrate polarity control of GaN nanowires on diamond. Kelvin Probe Force Microscopy is used to determine the polarity of individual selective area-grown and self-assembled nanowires over a large scale. At standard growth conditions, mixed polarity occurs for selective GaN nanowires on various substrates, namely on silicon, on sapphire and on diamond. To obtain control over the growth orientation on diamond, the substrate surface is modified by nitrogen and oxygen plasma exposure prior to growth, and the growth parameters are adjusted simultaneously. We find that the surface chemistry and the substrate temperature are the decisive factors for obtaining control of up to 93% for both polarity types, whereas the growth mode, namely selective area or self-assembled growth, does not influence the polarity distribution significantly. The experimental results are discussed by a model based on the interfacial bonds between the GaN nanowires, the termination layer, and the substrate.

Protein brownian rotation at the glass transition temperature of a freeze-concentrated buffer probed by superparamagnetic nanoparticles.

PubMed

Eloi, J-C; Okuda, M; Jones, S E Ward; Schwarzacher, W

2013-06-18

For applications from food science to the freeze-thawing of proteins it is important to understand the often complex freezing behavior of solutions of biomolecules. Here we use a magnetic method to monitor the Brownian rotation of a quasi-spherical cage-shaped protein, apoferritin, approaching the glass transition Tg in a freeze-concentrated buffer (Tris-HCl). The protein incorporates a synthetic magnetic nanoparticle (Co-doped Fe3O4 (magnetite)). We use the magnetic signal from the nanoparticles to monitor the protein orientation. As T decreases toward Tg of the buffer solution the protein's rotational relaxation time increases exponentially, taking values in the range from a few seconds up to thousands of seconds, i.e., orders of magnitude greater than usually accessed, e.g., by NMR. The longest relaxation times measured correspond to estimated viscosities >2 MPa s. As well as being a means to study low-temperature, high-viscosity environments, our method provides evidence that, for the cooling protocol used, the following applies: 1), the concentration of the freeze-concentrated buffer at Tg is independent of its initial concentration; 2), little protein adsorption takes place at the interface between ice and buffer; and 3), the protein is free to rotate even at temperatures as low as 207 K. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

A New Selective Area Lateral Epitaxy Approach for Depositing a-Plane GaN over r-Plane Sapphire

NASA Astrophysics Data System (ADS)

Chen, Changqing; Zhang, Jianping; Yang, Jinwei; Adivarahan, Vinod; Rai, Shiva; Wu, Shuai; Wang, Hongmei; Sun, Wenhong; Su, Ming; Gong, Zheng; Kuokstis, Edmundas; Gaevski, Mikhail; Khan, Muhammad Asif

2003-07-01

We report a new epitaxy procedure for growing extremely low defect density a-plane GaN films over r-plane sapphire. By combining selective area growth through a SiO2 mask opening to produce high height to width aspect ratio a-plane GaN pillars and lateral epitaxy from their c-plane facets, we obtained fully coalesced a-plane GaN films. The excellent structural, optical and electrical characteristics of these selective area lateral epitaxy (SALE) deposited films make them ideal for high efficiency III-N electronic and optoelectronic devices.

Amphoteric Be in GaN: Experimental Evidence for Switching between Substitutional and Interstitial Lattice Sites

NASA Astrophysics Data System (ADS)

Tuomisto, Filip; Prozheeva, Vera; Makkonen, Ilja; Myers, Thomas H.; Bockowski, Michal; Teisseyre, Henryk

2017-11-01

We show that Be exhibits amphoteric behavior in GaN, involving switching between substitutional and interstitial positions in the lattice. This behavior is observed through the dominance of BeGa in the positron annihilation signals in Be-doped GaN, while the emergence of VGa at high temperatures is a consequence of the Be impurities being driven to interstitial positions. The similarity of this behavior to that found for Na and Li in ZnO suggests that this could be a universal property of light dopants substituting for heavy cations in compound semiconductors.

Amphoteric Be in GaN: Experimental Evidence for Switching between Substitutional and Interstitial Lattice Sites.

PubMed

Tuomisto, Filip; Prozheeva, Vera; Makkonen, Ilja; Myers, Thomas H; Bockowski, Michal; Teisseyre, Henryk

2017-11-10

We show that Be exhibits amphoteric behavior in GaN, involving switching between substitutional and interstitial positions in the lattice. This behavior is observed through the dominance of Be_{Ga} in the positron annihilation signals in Be-doped GaN, while the emergence of V_{Ga} at high temperatures is a consequence of the Be impurities being driven to interstitial positions. The similarity of this behavior to that found for Na and Li in ZnO suggests that this could be a universal property of light dopants substituting for heavy cations in compound semiconductors.

Growth of wide-bandgap nitride semiconductors by MBE

NASA Astrophysics Data System (ADS)

Moustakas, T. D.

2002-08-01

This paper reviews progress in the heteroepitaxial growth of Ill-Nitride semiconductors. The growth of wurtzite and zinc-blende allotropic forms of GaN on various substrates with hexagonal and cubic symmetry respectively were discussed. In particular we addressed the growth on the various faces of sapphire, 6H-SiC and (001) Si. It has been shown that the kinetics of growth by plasma-MBE or ammonia-MBE are different. Specifically, in plasma-assisted MBE smooth films are obtained under group-III rich conditions of growth. On the other hand in ammonia-MBE smooth films are obtained under nitrogen rich conditions of growth. High quality films were obtained on 6H-SiC without the employment of any buffer. The various nucleation steps used to improve the two dimensional growth as well as to control the film polarity were discussed. The n- and p-doping of GaN were addressed. The concept of increasing the solubility of Mg in GaN by simultaneously bombarding the surface of the growing film with a flux of electrons (co-doping GaN with Mg and electrons) was discussed. The influence of the strength of Al-N, Ga-N and In-N bonds on the kinetics of growth of nitride alloys was pointed out. Specifically, it was shown that in both the nitrogen-rich and group-III rich growth regimes, the incorporation probability of aluminum is unity for the investigated temperature range of 750-800° C. On the other hand the incorporation probability of gallium is constant but less than unity only in the nitrogen-rich regime of growth. In the group-III regime the incorporation probability of gallium decreases monotonically with the total group-III flux, due to the competition with aluminum for the available active nitrogen. Alloy phenomena such as phase separation and atomic ordering and the influence of these phenomena to the optical properties were addressed. InGaN alloys are thermodynamically unstable against phase separation. At compositions above 30% they tend to undergo partial phase separation. Furthermore, InGaN alloys were found to undergo 1x1 monolayer cation ordering. AlGaN alloys do not show evidence of phase separation but they were found to undergo multiple type of superlattice ordering. Under nitrogen-rich growth conditions they show one monolayer periodicity, while under group-III rich growth it was found that the structure is a superposition of a seven monolayer and twelve monolayer superlattices. Finally, the growth of heterostructures and MQWs and the use of the MBE method for the fabrication of optical, electronic and electromechanical devices were discussed.

Structures and optical properties of \\text{H}_{2}^{+} -implanted GaN epi-layers

NASA Astrophysics Data System (ADS)

Li, B. S.; Wang, Z. G.

2015-06-01

The implantation damage build-up and optical properties of GaN epitaxial films under \\text{H}2+ ion implantation have been investigated by a combination of Rutherford backscattering in channeling geometry, Raman spectroscopy, UV-visible spectroscopy and transmission electron microscopy. GaN epitaxial films were implanted with 134 keV \\text{H}2+ ions to doses ranging from 3.75   ×   1016 to 1.75   ×   1017 \\text{H}2+  cm-2 at room temperature or the same dose of 1.5   ×   1017 \\text{H}2+  cm-2 at room temperature, 573 and 723 K. The dependence of lattice disorder induced by \\text{H}2+ -implantation on the ion dose can be divided into a three-step damage process. A strong influence of the H concentration on the defect accumulation is discussed. The decrease in relative Ga disorder induced by \\text{H}2+ -implantation is linear with increasing implantation temperature. The absorption coefficient of GaN epitaxial films increases with increasing ion dose, leading to the decrease in Raman scattering spectra of Ga-N vibration. With increasing implantation doses up to 5   ×   1016 \\text{H}2+  cm-2, nanoscale hydrogen bubbles are observed in the H deposition peak region. Interstitial-type dislocation loops are observed in the damaged layer located near the damage peak region, and the geometry of the dislocation loops produced by H implantation is analyzed. The surface layer is almost free of lattice disorder induced by \\text{H}2+ -implantation.

A Microstructural Comparison of the Initial Growth of AIN and GaN Layers on Basal Plane Sapphire and SiC Substrates by Low Pressure Metalorganic Chemical Vapor Depositon

NASA Technical Reports Server (NTRS)

George, T.; Pike, W. T.; Khan, M. A.; Kuznia, J. N.; Chang-Chien, P.

1994-01-01

The initial growth by low pressure metalorganic chemical vapor deposition and subsequent thermal annealing of AIN and GaN epitaxial layers on SiC and sapphire substrates is examined using high resolution transmission electron microscopy and atomic force microscopy.

Low-Angle-Incidence Microchannel Epitaxy of a-Plane GaN Grown by Ammonia-Based Metal-Organic Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Lin, Chia-Hung; Uchiyama, Shota; Maruyama, Takahiro; Naritsuka, Shigeya

2012-04-01

Low-angle-incidence microchannel epitaxy (LAIMCE) of a-plane GaN was performed using ammonia-based metal-organic molecular beam epitaxy to obtain wide and thin lateral overgrowth over a SiO2 mask. Trimethylgallium (TMG) was supplied perpendicular to the openings cut in the mask with a low incident angle of 5° relative to the substrate plane. The [NH3]/[TMG] ratio (R) dependence of GaN LAIMCE was optimized by varying R from 5 to 30. A wide lateral overgrowth of 3.7 µm with a dislocation density below the transmission electron microscope detection limit was obtained at R=15 for a thickness of 520 nm.

Dynamic atomic layer epitaxy of InN on/in +c-GaN matrix: Effect of “In+N” coverage and capping timing by GaN layer on effective InN thickness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoshikawa, Akihiko, E-mail: yoshi@faculty.chiba-u.jp; Graduate School of Engineering, Kogakuin University, Hachioji, Tokyo 192-0015; Kusakabe, Kazuhide

2016-01-11

The growth front in the self-organizing and self-limiting epitaxy of ∼1 monolayer (ML)-thick InN wells on/in +c-GaN matrix by molecular beam epitaxy (MBE) has been studied in detail, with special attention given to the behavior and role of the N atoms. The growth temperatures of interest are above 600 °C, far higher than the typical upper critical temperature of 500 °C in MBE. It was confirmed that 2 ML-thick InN wells can be frozen/inserted in GaN matrix at 620 °C, but it was found that N atoms at the growth front tend to selectively re-evaporate more quickly than In atoms at temperatures highermore » than 650 °C. As a result, the effective thickness of inserted InN wells in the GaN matrix at 660–670 °C were basically 1 ML or sub-ML, even though they were capped by a GaN barrier at the time of 2 ML “In+N” coverage. Furthermore, it was found that the N atoms located below In atoms in the dynamic atomic layer epitaxy growth front had remarkably weaker bonding to the +c-GaN surface.« less

Thermal quenching of the yellow luminescence in GaN

NASA Astrophysics Data System (ADS)

Reshchikov, M. A.; Albarakati, N. M.; Monavarian, M.; Avrutin, V.; Morkoç, H.

2018-04-01

We observed varying thermal quenching behavior of the yellow luminescence band near 2.2 eV in different GaN samples. In spite of the different behavior, the yellow band in all the samples is caused by the same defect—the YL1 center. In conductive n-type GaN, the YL1 band quenches with exponential law, and the Arrhenius plot reveals an ionization energy of ˜0.9 eV for the YL1 center. In semi-insulating GaN, an abrupt and tunable quenching of the YL1 band is observed, where the apparent activation energy in the Arrhenius plot is not related to the ionization energy of the defect. In this case, the ionization energy can be found by analyzing the shift of the characteristic temperature of PL quenching with excitation intensity. We conclude that only one defect, namely, the YL1 center, is responsible for the yellow band in undoped and doped GaN samples grown by different techniques.

Selective area growth of N-polar GaN nanorods by plasma-assisted MBE on micro-cone-patterned c-sapphire substrates

NASA Astrophysics Data System (ADS)

Jmerik, V. N.; Kuznetsova, N. V.; Nechaev, D. V.; Shubina, T. V.; Kirilenko, D. A.; Troshkov, S. I.; Davydov, V. Yu.; Smirnov, A. N.; Ivanov, S. V.

2017-11-01

The site-controlled selective area growth of N-polar GaN nanorods (NR) was developed by plasma-assisted MBE (PA MBE) on micro-cone-patterned sapphire substrates (μ-CPSS) by using a two-stage growth process. A GaN nucleation layer grown by migration enhanced epitaxy provides the best selectivity for nucleation of NRs on the apexes of 3.5-μm-diameter cones, whereas the subsequent growth of 1-μm-high NRs with a constant diameter of about 100 nm proceeds by standard high-temperature PA MBE at nitrogen-rich conditions. These results are explained by anisotropy of the surface energy for GaN of different polarity and crystal orientation. The InGaN single quantum wells inserted in the GaN NRs grown on the μ-CPSS demonstrate photoluminescence at 510 nm with a spatially periodic variation of its intensity with a period of ∼6 μm equal to that of the substrate patterning profile.

Dc and ac electrical response of MOCVD grown GaN in p-i-n structure, assessed through I-V and admittance measurement

NASA Astrophysics Data System (ADS)

Ayarcı Kuruoğlu, Neslihan; Özdemir, Orhan; Bozkurt, Kutsal; Sundaram, Suresh; Salvestrini, Jean-Paul; Ougazzaden, Abdallah; Gaimard, Quentin; Belahsene, Sofiane; Merghem, Kamel; Ramdane, Abderrahim

2017-12-01

The electrical response of gallium nitride (GaN), produced through metal-organic chemical vapor deposition in a p-i-n structure was investigated through temperature-dependent current-voltage (I-V) and admittance measurement. The I-V curves showed double diode behavior together with several distinct regions in which trap-assisted tunnelling current has been identified at low and moderate forward/reverse direction and space charge limited current (SCLC) at large forward/reverse bias. The value of extracted energy (˜200 meV in forward and  ˜70 meV in reverse direction) marked the tunnelling entity as electron and heavy hole in the present structure. These values were also obtained in space charge limited regime and considered as minority carriers which might originate the experimentally observed negative capacitance issue at low frequencies over the junction under both forward and reverse bias directions. Analytically derived expression for the admittance in the revised versions of SCLC model was also applied to explain the inductance effect, yielding good fits to the experimentally measured admittance data.

Low-Temperature Preparation of Tungsten Oxide Anode Buffer Layer via Ultrasonic Spray Pyrolysis Method for Large-Area Organic Solar Cells.

PubMed

Ji, Ran; Zheng, Ding; Zhou, Chang; Cheng, Jiang; Yu, Junsheng; Li, Lu

2017-07-18

Tungsten oxide (WO₃) is prepared by a low-temperature ultrasonic spray pyrolysis method in air atmosphere, and it is used as an anode buffer layer (ABL) for organic solar cells (OSCs). The properties of the WO₃ transition metal oxide material as well as the mechanism of ultrasonic spray pyrolysis processes are investigated. The results show that the ultrasonic spray pyrolysized WO₃ ABL exhibits low roughness, matched energy level, and high conductivity, which results in high charge transport efficiency and suppressive recombination in OSCs. As a result, compared to the OSCs based on vacuum thermal evaporated WO₃, a higher power conversion efficiency of 3.63% is reached with low-temperature ultrasonic spray pyrolysized WO₃ ABL. Furthermore, the mostly spray-coated OSCs with large area was fabricated, which has a power conversion efficiency of ~1%. This work significantly enhances our understanding of the preparation and application of low temperature-processed WO₃, and highlights the potential of large area, all spray coated OSCs for sustainable commercial fabrication.

Low-Temperature Preparation of Tungsten Oxide Anode Buffer Layer via Ultrasonic Spray Pyrolysis Method for Large-Area Organic Solar Cells

PubMed Central

Ji, Ran; Zheng, Ding; Zhou, Chang; Cheng, Jiang; Yu, Junsheng; Li, Lu

2017-01-01

Tungsten oxide (WO3) is prepared by a low-temperature ultrasonic spray pyrolysis method in air atmosphere, and it is used as an anode buffer layer (ABL) for organic solar cells (OSCs). The properties of the WO3 transition metal oxide material as well as the mechanism of ultrasonic spray pyrolysis processes are investigated. The results show that the ultrasonic spray pyrolysized WO3 ABL exhibits low roughness, matched energy level, and high conductivity, which results in high charge transport efficiency and suppressive recombination in OSCs. As a result, compared to the OSCs based on vacuum thermal evaporated WO3, a higher power conversion efficiency of 3.63% is reached with low-temperature ultrasonic spray pyrolysized WO3 ABL. Furthermore, the mostly spray-coated OSCs with large area was fabricated, which has a power conversion efficiency of ~1%. This work significantly enhances our understanding of the preparation and application of low temperature-processed WO3, and highlights the potential of large area, all spray coated OSCs for sustainable commercial fabrication. PMID:28773177

GaN nanophosphors for white-light applications

NASA Astrophysics Data System (ADS)

Kumar, Mirgender; Singh, V. P.; Dubey, Sarvesh; Suh, Youngsuk; Park, Si-Hyun

2018-01-01

GaN nanoparticles (NPs) were synthesized by carbothermal reduction combined with nitridation, using Ga2O3 powder and graphitic carbon nitride (g-C3N4) as precursors. Characterization of the NPs was performed by X-ray diffraction, scanning electron microscopy, and room-temperature photoluminescence measurements. X-ray photoelectron spectroscopy was also performed to detect the chemical states of the different species. A universal yellow luminescence (YL) band was observed from complexes of Ga vacancies with O anti-sites and of O anti-sites with C. Further increments in the C content were observed with continued growth and induced an additional blue luminescence (BL) band. Tuning of the YL and BL bands resulted in white-light emission under certain experimental conditions, thus offering a new way of employing GaN nanophosphors for solid-state white lighting. Calculations of the correlated color temperature and color-quality scale parameters confirmed the utility of the experimental process for different applications.

Probing exciton density of states through phonon-assisted emission in GaN epilayers: A and B exciton contributions

NASA Astrophysics Data System (ADS)

Cavigli, Lucia; Gabrieli, Riccardo; Gurioli, Massimo; Bogani, Franco; Feltin, Eric; Carlin, Jean-François; Butté, Raphaël; Grandjean, Nicolas; Vinattieri, Anna

2010-09-01

A detailed experimental investigation of the phonon-assisted emission in a high-quality c -plane GaN epilayer is presented up to 200 K. By performing photoluminescence and reflectivity measurements, we find important etaloning effects in the phonon-replica spectra, which have to be corrected before addressing the lineshape analysis. Direct experimental evidence for free exciton thermalization is found for the whole temperature range investigated. A close comparison with existing models for phonon replicas originating from a thermalized free exciton distribution shows that the simplified and commonly adopted description of the exciton-phonon interaction with a single excitonic band leads to a large discrepancy with experimental data. Only the consideration of the complex nature of the excitonic band in GaN, including A and B exciton contributions, allows accounting for the temperature dependence of the peak energy, intensity, and lineshape of the phonon replicas.

Process for growing epitaxial gallium nitride and composite wafers

DOEpatents

Weber, Eicke R.; Subramanya, Sudhir G.; Kim, Yihwan; Kruger, Joachim

2003-05-13

A novel growth procedure to grow epitaxial Group III metal nitride thin films on lattice-mismatched substrates is proposed. Demonstrated are the quality improvement of epitaxial GaN layers using a pure metallic Ga buffer layer on c-plane sapphire substrate. X-ray rocking curve results indicate that the layers had excellent structural properties. The electron Hall mobility increases to an outstandingly high value of .mu.>400 cm.sup.2 /Vs for an electron background concentration of 4.times.10.sup.17 cm.sup.-3.

Pure AlN layers in metal-polar AlGaN/AlN/GaN and AlN/GaN heterostructures grown by low-temperature ammonia-based molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kaun, Stephen W.; Mazumder, Baishakhi; Fireman, Micha N.; Kyle, Erin C. H.; Mishra, Umesh K.; Speck, James S.

2015-05-01

When grown at a high temperature (820 °C) by ammonia-based molecular beam epitaxy (NH3-MBE), the AlN layers of metal-polar AlGaN/AlN/GaN heterostructures had a high GaN mole fraction (∼0.15), as identified by atom probe tomography in a previous study (Mazumder et al 2013 Appl. Phys. Lett. 102 111603). In the study presented here, growth at low temperature (<740 °C) by NH3-MBE yielded metal-polar AlN layers that were essentially pure at the alloy level. The improved purity of the AlN layers grown at low temperature was correlated to a dramatic increase in the sheet density of the two-dimensional electron gas (2DEG) at the AlN/GaN heterointerface. Through application of an In surfactant, metal-polar AlN(3.5 nm)/GaN and AlGaN/AlN(2.5 nm)/GaN heterostructures grown at low temperature yielded low 2DEG sheet resistances of 177 and 285 Ω/□, respectively.

4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication.

PubMed

Lee, Changmin; Zhang, Chong; Cantore, Michael; Farrell, Robert M; Oh, Sang Ho; Margalith, Tal; Speck, James S; Nakamura, Shuji; Bowers, John E; DenBaars, Steven P

2015-06-15

We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.

Isotype InGaN/GaN heterobarrier diodes by ammonia molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fireman, Micha N.; Browne, David A.; Speck, James S.

The design of isotype InGaN/GaN heterobarrier diode structures grown by ammonia molecular beam epitaxy is presented. On the (0001) Ga-polar plane, a structure consisting of a surface n{sup +} GaN contact layer, followed by a thin InGaN layer, followed by a thick unintentionally doped (UID) GaN layer, and atop a buried n{sup +} GaN contact layer induces a large conduction band barrier via a depleted UID GaN layer. Suppression of reverse and subthreshold current in such isotype barrier devices under applied bias depends on the quality of this composite layer polarization. Sample series were grown under fixed InGaN growth conditionsmore » that varied either the UID GaN NH{sub 3} flow rate or the UID GaN thickness, and under fixed UID GaN growth conditions that varied InGaN growth conditions. Decreases in subthreshold current and reverse bias current were measured for thicker UID GaN layers and increasing InGaN growth rates. Temperature-dependent analysis indicated that although extracted barrier heights were lower than those predicted by 1D Schrödinger Poisson simulations (0.9 eV–1.4 eV for In compositions from 10% to 15%), optimized growth conditions increased the extracted barrier height from ∼11% to nearly 85% of the simulated values. Potential subthreshold mechanisms are discussed, along with those growth factors which might affect their prevalence.« less

A Study of Photoluminiscence and UV-Vis in Enhanced GaN Nanofibers

NASA Astrophysics Data System (ADS)

Robles-Garcia, Joshua; Melendez-Zambrana, Anamaris; Ramos, Idalia

2014-03-01

The photoluminiscence (PL) and UV-Vis properties of Gallium Nitride (GaN) nanofibers were investigated for samples fabricated with a precursor solution containing Gallium Nitrate Hydrate, Cellulose Acetate, and Urea in the solvents Dimethylacetamide (DMA) and Acetone. GaN is a wide bandgap (3.4 eV) semiconductor that can be used in a variety of applications including solid-state lighting, high power, and high frequency devices. In previous work, we produced polycrystalline GaN nanofibers with wurtzite structure, using the electrospinning method and a thermal treatment in nitrogen and ammonia at 1000C. In this research we study the addition of urea to the precursor solution to enhance the crystallinity of the fibers at lower sintering temperatures. The molar ratios of urea added to the precursor range from 0 to 1.7 M. After electrospinning the fibers were sintered in Nitrogen at 450C for 3 hours and then, under ammonia gas flow at 900C for 5 hours. X-Ray Diffraction (XRD), UV-Vis spectroscopy, and PL measurements at room temperature were used to study the structural and optical properties of the fibers during the sintering process. This work was sponsored by UPRH PREM (NSF-DMR-0934195).

Substitutional and interstitial oxygen in wurtzite GaN

NASA Astrophysics Data System (ADS)

Wright, A. F.

2005-11-01

Density-functional theory was used to compute energy-minimum configurations and formation energies of substitutional and interstitial oxygen (O) in wurtzite GaN. The results indicate that O substituted at a N site (ON) acts as a single donor with the ionized state (ON+1) being the most stable O state in p-type GaN. In n-type GaN, interstitial O (OI) is predicted to be a double acceptor and O substituted at a Ga site (OGa) is predicted to be a triple acceptor. The formation energies of these two species are comparable to that of ON in n-type GaN and, as such, they should form and compensate the ON donors. The extent of compensation was estimated for both Ga-rich and N-rich conditions with a total O concentration of 1017cm-3. Ga-rich conditions yielded negligible compensation and an ON concentration in excess of 9.9×1016cm-3. N-rich conditions yielded a 25% lower ON concentration, due to the increased stability of OI and OGa relative to ON, and moderate compensation. These findings are consistent with experimental results indicating that O acts as a donor in GaN(O). Complexes of ON with the Mg acceptor and OI with the Si donor were examined. Binding energies for charge-conserving reactions were ⩾0.5eV, indicating that these complexes can exist in equilibrium at room temperature. Complexes of ON with the Ga vacancy in n-type GaN were also examined and their binding energies were 1.2 and 1.4eV, indicating that appreciable concentrations can exist in equilibrium even at elevated temperatures.

Thermal characterization of gallium nitride p-i-n diodes

NASA Astrophysics Data System (ADS)

Dallas, J.; Pavlidis, G.; Chatterjee, B.; Lundh, J. S.; Ji, M.; Kim, J.; Kao, T.; Detchprohm, T.; Dupuis, R. D.; Shen, S.; Graham, S.; Choi, S.

2018-02-01

In this study, various thermal characterization techniques and multi-physics modeling were applied to understand the thermal characteristics of GaN vertical and quasi-vertical power diodes. Optical thermography techniques typically used for lateral GaN device temperature assessment including infrared thermography, thermoreflectance thermal imaging, and Raman thermometry were applied to GaN p-i-n diodes to determine if each technique is capable of providing insight into the thermal characteristics of vertical devices. Of these techniques, thermoreflectance thermal imaging and nanoparticle assisted Raman thermometry proved to yield accurate results and are the preferred methods of thermal characterization of vertical GaN diodes. Along with this, steady state and transient thermoreflectance measurements were performed on vertical and quasi-vertical GaN p-i-n diodes employing GaN and Sapphire substrates, respectively. Electro-thermal modeling was performed to validate measurement results and to demonstrate the effect of current crowding on the thermal response of quasi-vertical diodes. In terms of mitigating the self-heating effect, both the steady state and transient measurements demonstrated the superiority of the tested GaN-on-GaN vertical diode compared to the tested GaN-on-Sapphire quasi-vertical structure.

Highly-efficient GaN-based light-emitting diode wafers on La0.3Sr1.7AlTaO6 substrates

PubMed Central

Wang, Wenliang; Yang, Weijia; Gao, Fangliang; Lin, Yunhao; Li, Guoqiang

2015-01-01

Highly-efficient GaN-based light-emitting diode (LED) wafers have been grown on La0.3Sr1.7AlTaO6 (LSAT) substrates by radio-frequency molecular beam epitaxy (RF-MBE) with optimized growth conditions. The structural properties, surface morphologies, and optoelectronic properties of as-prepared GaN-based LED wafers on LSAT substrates have been characterized in detail. The characterizations have revealed that the full-width at half-maximums (FWHMs) for X-ray rocking curves of GaN(0002) and GaN(10-12) are 190.1 and 210.2 arcsec, respectively, indicating that high crystalline quality GaN films have been obtained. The scanning electron microscopy and atomic force microscopy measurements have shown the very smooth p-GaN surface with the surface root-mean-square (RMS) roughness of 1.3 nm. The measurements of low-temperature and room-temperature photoluminescence help to calculate the internal quantum efficiency of 79.0%. The as-grown GaN-based LED wafers have been made into LED chips with the size of 300 × 300 μm2 by the standard process. The forward voltage, the light output power and the external quantum efficiency for LED chips are 19.6 W, 2.78 V, and 40.2%, respectively, at a current of 20 mA. These results reveal the high optoelectronic properties of GaN-based LEDs on LSAT substrates. This work brings up a broad future application of GaN-based devices. PMID:25799042

The management of stress in MOCVD-grown InGaN/GaN LED multilayer structures on Si(1 1 1) substrates

NASA Astrophysics Data System (ADS)

Jiang, Quanzhong; Allsopp, Duncan W. E.; Bowen, Chris R.; Wang, Wang N.

2013-09-01

The tensile stress in light-emitting diode (LED)-on-Si(1 1 1) multilayer structures must be reduced so that it does not compromise the multiple quantum well emission wavelength uniformity and structural stability. In this paper it is shown for non-optimized LED structures grown on Si(1 1 1) substrates that both emission wavelength uniformity and structural stability can be achieved within the same growth process. In order to gain a deeper understanding of the stress distribution within such a structure, cross-sectional Raman and photo-luminescence spectroscopy techniques were developed. It is observed that for a Si:GaN layer grown on a low-temperature (LT) AlN intermediate layer there is a decrease in compressive stress with increasing Si:GaN layer thickness during MOCVD growth which leads to a high level of tensile stress in the upper part of the layer. This may lead to the development of cracks during cooling to room temperature. Such a phenomenon may be associated with annihilation of defects such as dislocations. Therefore, a reduction of dislocation intensity should take place at the early stage of GaN growth on an AlN or AlGaN layer in order to reduce a build up of tensile stress with thickness. Furthermore, it is also shown that a prolonged three dimensional GaN island growth on a LT AlN interlayer for the reduction of dislocations may result in a reduction in the compressive stress in the resulting GaN layer.

Structural investigations of GaN grown by low-pressure chemical vapor deposition on 6H{endash}SiC and Al{sub 2}O{sub 3} from GaCl{sub 3} and NH{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koynov, S.; Topf, M.; Fischer, S.

1997-08-01

GaN films grown on (0001) 6H{endash}SiC and (0001) Al{sub 2}O{sub 3} substrates using low-pressure chemical vapor deposition with GaCl{sub 3} and NH{sub 3} as precursors are comparatively explored by optical, scanning tunneling, and transmission electron microscopy. Independent of the substrate material used, the surface of the GaN layers is covered by hexagonally shaped islands. For GaN on 6H{endash}SiC, the islands are larger in diameter ({approx}50 {mu}m) and rather uniformly distributed. An atomically flat interface is observed for GaN on Al{sub 2}O{sub 3} in contrast to GaN grown on 6H{endash}SiC, where the interface is characterized by large steps. For both substrates,more » faceted holes (named as pinholes) are observed in near-surface regions of the GaN layers occurring with a density of about 7{times}10{sup 8} cm{sup {minus}2}. No unequivocal correlation between the density of pinholes and the density of threading dislocations ({approx}1.6{times}10{sup 10} cm{sup {minus}2} for GaN/Al{sub 2}O{sub 3} and {approx}4{times}10{sup 9} cm{sup {minus}2} for GaN/6H{endash}SiC) can be found. Rather, different types of defects are identified to be correlated with the pinholes, implying a dislocation-independent mechanism for the pinhole formation. Despite the small lattice mismatch between GaN and 6H{endash}SiC, the pronounced original surface roughness of this substrate material is believed to account for both the marked interfacial roughness and the still existing high density of threading dislocations. {copyright} {ital 1997 American Institute of Physics.}« less

Effect of screw threading dislocations and inverse domain boundaries in GaN on the shape of reciprocal-space maps.

PubMed

Barchuk, Mykhailo; Motylenko, Mykhaylo; Lukin, Gleb; Pätzold, Olf; Rafaja, David

2017-04-01

The microstructure of polar GaN layers, grown by upgraded high-temperature vapour phase epitaxy on [001]-oriented sapphire substrates, was studied by means of high-resolution X-ray diffraction and transmission electron microscopy. Systematic differences between reciprocal-space maps measured by X-ray diffraction and those which were simulated for different densities of threading dislocations revealed that threading dislocations are not the only microstructure defect in these GaN layers. Conventional dark-field transmission electron microscopy and convergent-beam electron diffraction detected vertical inversion domains as an additional microstructure feature. On a series of polar GaN layers with different proportions of threading dislocations and inversion domain boundaries, this contribution illustrates the capability and limitations of coplanar reciprocal-space mapping by X-ray diffraction to distinguish between these microstructure features.

Process dependency on threshold voltage of GaN MOSFET on AlGaN/GaN heterostructure

NASA Astrophysics Data System (ADS)

Wang, Qingpeng; Jiang, Ying; Miyashita, Takahiro; Motoyama, Shin-ichi; Li, Liuan; Wang, Dejun; Ohno, Yasuo; Ao, Jin-Ping

2014-09-01

GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with recessed gate on AlGaN/GaN heterostructure are reported in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. Negative threshold voltages were commonly observed in all devices. To investigate the reasons of the negative threshold voltages, different oxide thickness, etching gas and bias power of inductively-coupled plasma (ICP) system were utilized in the fabrication process of the GaN MOSFETs. It is found that positive charges of around 1 × 1012 q/cm2 exist near the interface at the just threshold condition in both silane- and tetraethylorthosilicate (TEOS)-based devices. It is also found that the threshold voltages do not obviously change with the different etching gas (SiCl4, BCl3 and two-step etching of SiCl4/Cl2) at the same ICP bias power level (20-25 W) and will become deeper when higher bias power is used in the dry recess process which may be related to the much serious ion bombardment damage. Furthermore, X-ray photoelectron spectroscopy (XPS) experiments were done to investigate the surface conditions. It is found that N 1s peaks become lower with higher bias power of the dry etching process. Also, silicon contamination was found and could be removed by HNO3/HF solution. It indicates that the nitrogen vacancies are mainly responsible for the negative threshold voltages rather than the silicon contamination. It demonstrates that optimization of the ICP recess conditions and improvement of the surface condition are still necessary to realize enhancement-mode GaN MOSFETs on AlGaN/GaN heterostructure.

Electrophoretic mobilities of erythrocytes in various buffers

NASA Technical Reports Server (NTRS)

Plank, L. D.; Kunze, M. E.; Todd, P. W.

1985-01-01

The calibration of space flight equipment depends on a source of standard test particles, this test particle of choice is the fixed erythrocyte. Erythrocytes from different species have different electrophoretic mobilities. Electrophoretic mobility depends upon zeta potential, which, in turn depends upon ionic strength. Zeta potential decreases with increasing ionic strength, so cells have high electrophoretic mobility in space electrophoresis buffers than in typical physiological buffers. The electrophoretic mobilities of fixed human, rat, and rabbit erythrocytes in 0.145 M salt and buffers of varying ionic strength, temperature, and composition, to assess the effects of some of the unique combinations used in space buffers were characterized. Several effects were assessed: glycerol or DMSO (dimethylsulfoxide) were considered for use as cryoprotectants. The effect of these substances on erythrocyte electrophoretic mobility was examined. The choice of buffer depended upon cell mobility. Primary experiments with kidney cells established the choice of buffer and cryoprotectant. A nonstandard temperature of EPM in the suitable buffer was determined. A loss of ionic strength control occurs in the course of preparing columns for flight, the effects of small increases in ionic strength over the expected low values need to be evaluated.

Influence of the heterostructure design on the optical properties of GaN and Al0.1Ga0.9N quantum dots for ultraviolet emission

NASA Astrophysics Data System (ADS)

Matta, S.; Brault, J.; Ngo, T. H.; Damilano, B.; Korytov, M.; Vennéguès, P.; Nemoz, M.; Massies, J.; Leroux, M.; Gil, B.

2017-08-01

The optical properties of AlyGa1-yN quantum dots (QDs), with y = 0 or y = 0.1, in an AlxGa1-xN matrix are studied. The influence of the QD layer design is investigated pointing out the correlations between the QD structural and optical properties. In a first part, the role of the epitaxial strain in the dot self-assembling process is studied by fabricating GaN QD layers on different AlxGa1-xN layers with 0.5 ≤ x ≤ 0.7. Photoluminescence (PL) measurements show the main influence of the increase of the internal electric field (Fint) on the QD optical response inducing a strong red shift in the emission energy as x increases. Time resolved combined with temperature dependent PL measurements enabled the estimation of the QD internal quantum efficiencies at low temperature showing values around 50%. In addition, a PL integrated intensity ratio up to 74% is shown, between 300 and 9 K. In the second part, the design of Al0.1Ga0.9N QDs was investigated, by varying the Al0.1Ga0.9N amount deposited. An increase of the transition energy (from 3.65 eV up to 3.83 eV) is obtained while decreasing the deposited amount. Calculations of the ground state transition energies as a function of the Al0.1Ga0.9N dot height give a value of Fint around 2.0 ± 0.5 MV/cm. Therefore, the propensity of Al0.1Ga0.9N dots to emit at much higher energies than GaN dots (a PL shift of ˜1 eV using a low excitation power) is seen as the consequence of the reduced Fint together with their smaller sizes.

On the luminescence of freshly introduced a-screw dislocations in low-resistance GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medvedev, O. S., E-mail: o.s.medvedev@spbu.ru; Vyvenko, O. F.; Bondarenko, A. S.

2015-09-15

Using scanning electron microscopy in the cathodoluminescence mode, it is shown that straight segments of a-screw dislocations introduced by plastic deformation at room temperature into unintentionally doped low-resistance gallium nitride luminesce in the spectral range 3.1–3.2 eV at 70 K. The spectral composition of dislocation luminescence shows a fine doublet structure with a component width of ∼15 meV and splitting of ∼30 meV, accompanied by LO-phonon replicas. Luminescent screw dislocations move upon exposure to an electron beam and at low temperatures, but retain immobility for a long time without external excitation. Optical transitions involving the quantum-well states of a stackingmore » fault in a split-dislocation core are considered to be the most probable mechanism of the observed phenomenon.« less

Distortion Properties of GaN Switches at High-Temperatures

NASA Astrophysics Data System (ADS)

Kameche, Mohamed

2006-08-01

The origins of HEMT distortion in passive control applications as SPST switch are presented in this paper. Also, this paper describes the change of the AlGaN/GaN HEMT switch distortion properties (second-and third distortion intercept points) over a wide range of temperature. The results indicate that the change in second-and third-order distortion intercept points is smaller (about 2dBm) over a wide range of temperature from -50 to +300°C. A comparison of the GaN-based HEMT switch with InP-and GaAs-HEMT switches shows that the GaN technology generates lower distortion than its InP and GaAs technologies counterpart.

Low p-type contact resistance by field-emission tunneling in highly Mg-doped GaN

NASA Astrophysics Data System (ADS)

Okumura, Hironori; Martin, Denis; Grandjean, Nicolas

2016-12-01

Mg-doped GaN with a net acceptor concentration (NA-ND) in the high 1019 cm-3 range was grown using ammonia molecular-beam epitaxy. Electrical properties of NiO contact on this heavily doped p-type GaN were investigated. A potential-barrier height of 0.24 eV was extracted from the relationship between NA-ND and the specific contact resistivity (ρc). We found that there is an optimum NA-ND value of 5 × 1019 cm-3 for which ρc is as low as 2 × 10-5 Ω cm2. This low ρc is ascribed to hole tunneling through the potential barrier at the NiO/p+-GaN interface, which is well accounted for by the field-emission model.

Improvement in performance and reliability with CF4 plasma pretreatment on the buffer oxide layer for low-temperature polysilicon thin-film transistor

NASA Astrophysics Data System (ADS)

Fan, Ching-Lin; Lin, Yi-Yan; Yang, Chun-Chieh

2012-03-01

This study applies CF4 plasma pretreatment to a buffer oxide layer to improve the performance of low-temperature polysilicon thin-film transistors (LTPS TFTs). Results show that the fluorine atoms piled up at the interface between the bulk channel and buffer oxide layer and accumulated in the bulk channel. The reduction of the trap states density by fluorine passivation can improve the electrical characteristics of the LTPS TFTs. It is found that the threshold voltage reduced from 4.32 to 3.03 V and the field-effect mobility increased from 29.71 to 45.65 cm2 V-1 S-1. In addition, the on current degradation and threshold voltage shift after stressing were significantly improved about 31% and 70%, respectively. We believe that the proposed CF4 plasma pretreatment on the buffer oxide layer can passivate the trap states and avoid the plasma induced damage on the polysilicon channel surface, resulting in the improvement in performance and reliability for LTPS-TFT mass production application on AMOLED displays with critical reliability requirement.

Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Xingsheng, E-mail: xsxu@semi.ac.cn

For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreasedmore » with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.« less

Wafer-scale Fabrication of Non-Polar Mesoporous GaN Distributed Bragg Reflectors via Electrochemical Porosification.

PubMed

Zhu, Tongtong; Liu, Yingjun; Ding, Tao; Fu, Wai Yuen; Jarman, John; Ren, Christopher Xiang; Kumar, R Vasant; Oliver, Rachel A

2017-03-27

Distributed Bragg reflectors (DBRs) are essential components for the development of optoelectronic devices. For many device applications, it is highly desirable to achieve not only high reflectivity and low absorption, but also good conductivity to allow effective electrical injection of charges. Here, we demonstrate the wafer-scale fabrication of highly reflective and conductive non-polar gallium nitride (GaN) DBRs, consisting of perfectly lattice-matched non-polar (11-20) GaN and mesoporous GaN layers that are obtained by a facile one-step electrochemical etching method without any extra processing steps. The GaN/mesoporous GaN DBRs exhibit high peak reflectivities (>96%) across the entire visible spectrum and wide spectral stop-band widths (full-width at half-maximum >80 nm), while preserving the material quality and showing good electrical conductivity. Such mesoporous GaN DBRs thus provide a promising and scalable platform for high performance GaN-based optoelectronic, photonic, and quantum photonic devices.

Gallium nitride vertical power devices on foreign substrates: a review and outlook

NASA Astrophysics Data System (ADS)

Zhang, Yuhao; Dadgar, Armin; Palacios, Tomás

2018-07-01

Vertical gallium nitride (GaN) power devices have attracted increased attention due to their superior high-voltage and high-current capacity as well as easier thermal management than lateral GaN high electron mobility transistors. Vertical GaN devices are promising candidates for next-generation power electronics in electric vehicles, data centers, smart grids and renewable energy process. The use of low-cost foreign substrates such as silicon (Si) substrates, instead of the expensive free-standing GaN substrates, could greatly trim material cost and enable large-diameter wafer processing while maintaining high device performance. This review illustrates recent progress in material epitaxy, device design, device physics and processing technologies for the development of vertical GaN power devices on low-cost foreign substrates. Although the device technologies are still at the early stage of development, state-of-the-art vertical GaN-on-Si power diodes have already shown superior Baliga’s figure of merit than commercial SiC and Si power devices at the voltage classes beyond 600 V. Furthermore, we unveil the design space of vertical GaN power devices on native and different foreign substrates, from the analysis of the impact of dislocation and defects on device performance. We conclude by identifying the application space, current challenges and exciting research opportunities in this very dynamic research field.

Temperature dependence of electrical characteristics of Pt/GaN Schottky diode fabricated by UHV e-beam evaporation.

PubMed

Kumar, Ashish; Arafin, Shamsul; Amann, Markus Christian; Singh, Rajendra

2013-11-15

Temperature-dependent electrical characterization of Pt/n-GaN Schottky barrier diodes prepared by ultra high vacuum evaporation has been done. Analysis has been made to determine the origin of the anomalous temperature dependence of the Schottky barrier height, the ideality factor, and the Richardson constant calculated from the I-V-T characteristics. Variable-temperature Hall effect measurements have been carried out to understand charge transport at low temperature. The modified activation energy plot from the barrier inhomogeneity model has given the value of 32.2 A/(cm2 K2) for the Richardson constant A** in the temperature range 200 to 380 K which is close to the known value of 26.4A/(cm2 K2) for n-type GaN.

Strained layer relaxation effect on current crowding and efficiency improvement of GaN based LED

NASA Astrophysics Data System (ADS)

Aurongzeb, Deeder

2012-02-01

Efficiency droop effect of GaN based LED at high power and high temperature is addressed by several groups based on career delocalization and photon recycling effect(radiative recombination). We extend the previous droop models to optical loss parameters. We correlate stained layer relaxation at high temperature and high current density to carrier delocalization. We propose a third order model and show that Shockley-Hall-Read and Auger recombination effect is not enough to account for the efficiency loss. Several strained layer modification scheme is proposed based on the model.

Recombination-related properties of a-screw dislocations in GaN: A combined CL, EBIC, TEM study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medvedev, O. S., E-mail: o.s.medvedev@spbu.ru; Mikhailovskii, V. Yu.; IRC for Nanotechnology, Research Park, St.-Petersburg State University

2016-06-17

Cathodoluminescence (CL), electron beam current (EBIC) and transmission electron microscopy (TEM) techniques have been applied to investigate recombination properties and structure of freshly introduced dislocations in low-ohmic GaN crystals. It was confirmed that the only a-screw dislocations exhibited an intense characteristic dislocation-related luminescence (DRL) which persisted up to room temperature and was red-shifted by about 0.3 eV with respect to the band gap energy not only in HVPE but also in MOCVD grown samples. EBIC contrast of the dislocations was found to be temperature independent indicating that the dislocation-related recombination level is situated below 200 meV with respect of conductionmore » band minimum. With the increasing of the magnification of the dislocation TEM cross-sectional images they were found to disappear, probably, due to the recombination enhanced dislocation glide (REDG) under electron beam exposure which was immediately observed in CL investigations on a large scale. The stacking fault ribbon in the core of dissociated a-screw dislocation which form a quantum well for electrons was proposed to play an important role both in DRL spectrum formation and in REDG.« less

Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

NASA Astrophysics Data System (ADS)

Li, M.; Whelan, M. J.; Wang, G.; White, S. M.

2012-12-01

The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO4 from Ca2+ and HPO42- when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC0) vary from 0.014 mg l-1 to 0.061 mg l-1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC0 and linear sorption coefficients (K) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC0 and K increase with increasing temperature, indicating a higher P buffering capacity at high temperatures.

Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

NASA Astrophysics Data System (ADS)

Li, M.; Whelan, M. J.; Wang, G. Q.; White, S. M.

2013-05-01

The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus (P) behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO4 from Ca2+ and HPO42- when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC0) vary from 0.014 mg L-1 to 0.061 mg L-1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC0 and linear sorption coefficients (K) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC0 and K increase with increasing temperature, indicating a higher P buffering capacity at high temperatures.

Production of cold beams of ND{sub 3} with variable rotational state distributions by electrostatic extraction of He and Ne buffer-gas-cooled beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Twyman, Kathryn S.; Bell, Martin T.; Heazlewood, Brianna R.

2014-07-14

The measurement of the rotational state distribution of a velocity-selected, buffer-gas-cooled beam of ND{sub 3} is described. In an apparatus recently constructed to study cold ion-molecule collisions, the ND{sub 3} beam is extracted from a cryogenically cooled buffer-gas cell using a 2.15 m long electrostatic quadrupole guide with three 90° bends. (2+1) resonance enhanced multiphoton ionization spectra of molecules exiting the guide show that beams of ND{sub 3} can be produced with rotational state populations corresponding to approximately T{sub rot} = 9–18 K, achieved through manipulation of the temperature of the buffer-gas cell (operated at 6 K or 17 K),more » the identity of the buffer gas (He or Ne), or the relative densities of the buffer gas and ND{sub 3}. The translational temperature of the guided ND{sub 3} is found to be similar in a 6 K helium and 17 K neon buffer-gas cell (peak kinetic energies of 6.92(0.13) K and 5.90(0.01) K, respectively). The characterization of this cold-molecule source provides an opportunity for the first experimental investigations into the rotational dependence of reaction cross sections in low temperature collisions.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Cheng-Cheng; Wang, Ru-Zhi, E-mail: wrz@bjut.edu.cn; Zhu, Man-Kang

GaN nanofilms (NFs) with different structures are grown on SiC substrates by pulsed laser deposition under different conditions. The synthesized GaN NFs are studied by X-ray diffraction, field-emission (FE) scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The GaN NFs are composed of diversified GaN nanoparticles with a diameter of 9–38 nm, thickness of 10–50 nm, and roughness of 0.22–13.03 nm. FE from the GaN NFs is structure dependent, which is explained by stress changing the band gap of the NFs. By structure modulation, the turn-on field of GaN NFs can be as low as 0.66 V/μm at a current density ofmore » 1 μA/cm{sup 2}, with a current density of up to 1.1 mA/cm{sup 2} at a field of 4.18 V/μm. Fowler-Nordheim curves of some samples contain multiple straight lines, which originate from the structural change and diversification of GaN nanoparticles under an applied field. Overall, our results suggest that GaN NFs with excellent FE properties can be prepared on SiC substrates, which provides a new route to fabricate high-efficiency FE nanodevices.« less

Crystallographic tilt and in-plane anisotropies of an a-plane InGaN/GaN layered structure grown by MOCVD on r-plane sapphire using a ZnO buffer

NASA Astrophysics Data System (ADS)

Liu, H. F.; Liu, W.; Guo, S.; Chi, D. Z.

2016-03-01

High-resolution x-ray diffraction (HRXRD) was used to investigate the crystallographic tilts and structural anisotropies in epitaxial nonpolar a-plane InGaN/GaN grown by metal-organic chemical vapor deposition on r-plane sapphire using a ZnO buffer. The substrate had an unintentional miscut of 0.14° towards its [-4 2 2 3] axis. However, HRXRD revealed a tilt of 0.26° (0.20°) between the ZnO (GaN) (11-20) and the Al2O3 (1-102) atomic planes, with the (11-20) axis of ZnO (GaN) tilted towards its c-axis, which has a difference of 163° in azimuth from that of the substrate’s miscut. Excess broadenings in the GaN/ZnO (11-20) rocking curves (RCs) were observed along its c-axis. Specific analyses revealed that partial dislocations and anisotropic in-plane strains, rather than surface-related effects, wafer curvature or stacking faults, are the dominant factors for the structural anisotropy. The orientation of the partial dislocations is most likely affected by the miscut of the substrate, e.g. via tilting of the misfit dislocation gliding planes created during island coalescences. Their Burgers vector components in the growth direction, in turn, gave rise to crystallographic tilts in the same direction as that of the excess RC-broadenings.

A Comparative Study of AlGaN and InGaN Back-Barriers in Ultrathin-Barrier AlN/GaN Heterostructures

NASA Astrophysics Data System (ADS)

All Abbas, J. M.; Atmaca, G.; Narin, P.; Kutlu, E.; Sarikavak-Lisesivdin, B.; Lisesivdin, S. B.

2017-08-01

Investigations of the effects of back-barrier introduction on the two-dimensional electron gas (2DEG) of ultrathin-barrier AlN/GaN heterostructures with AlGaN and InGaN back-barriers are carried out using self-consistent solutions of 1-dimensional Schrödinger-Poisson equations. Inserted AlGaN and InGaN back-barriers are used to provide a good 2DEG confinement thanks to raising the conduction band edge of GaN buffer with respect to GaN channel layer. Therefore, in this paper the influence of these back-barrier layers on sheet carrier density, 2DEG confinement, and mobility are systematically and comparatively investigated. As a result of calculations, although sheet carrier density is found to decrease with InGaN back-barrier layer, it is not changed with AlGaN back-barrier layer for suggested optimise heterostructures. Obtained results can give some insights for further experimental studies.

Multibias and thermal behavior of microwave GaN and GaAs based HEMTs

NASA Astrophysics Data System (ADS)

Alim, Mohammad A.; Rezazadeh, Ali A.; Gaquiere, Christophe

2016-12-01

Multibias and thermal characterizations on 0.25 μm × (2 × 100) μm AlGaN/GaN/SiC HEMT and 0.5 μm × (2 × 100) μm AlGaAs/InGaAs pseudomorphic HEMT have carried out for the first time. Two competitive device technologies are investigated with the variations of bias and temperature in order to afford a detailed realization of their potentialities. The main finding includes the self heating effect in the GaN device, zero temperature coefficient points at the drain current and transconductance in the GaAs device. The thermal resistance RTH of 7.1, 8.2 and 9.4 °C mm/W for the GaN device was estimated at 25, 75 and 150 °C respectively which are consistent with those found in the open literature. The temperature trend of the threshold voltage VT, Schottky barrier height ϕb, sheet charge densities of two dimensional electron gas ns, and capacitance under the gate Cg are exactly opposite in the two devices; whereas the knee voltage Vk, on resistance Ron, and series resistance Rseries are shows similar trend. The multi-bias and thermal behavior of the output current Ids, output conductance gds, transconductance gm, cut-off frequency ft, maximum frequency fmax, effective velocity of electron, veff and field dependent mobility, μ demonstrates a great potential of GaN device. These results provide some valuable insights for technology of preference for future and current applications.

The origins and properties of intrinsic nonradiative recombination centers in wide bandgap GaN and AlGaN

NASA Astrophysics Data System (ADS)

Chichibu, S. F.; Uedono, A.; Kojima, K.; Ikeda, H.; Fujito, K.; Takashima, S.; Edo, M.; Ueno, K.; Ishibashi, S.

2018-04-01

The nonradiative lifetime (τNR) of the near-band-edge emission in various quality GaN samples is compared with the results of positron annihilation measurement, in order to identify the origin and to determine the capture-cross-section of the major intrinsic nonradiative recombination centers (NRCs). The room-temperature τNR of various n-type GaN samples increased with decreasing the concentration of divacancies composed of a Ga vacancy (VGa) and a N vacancy (VN), namely, VGaVN. The τNR value also increased with increasing the diffusion length of positrons, which is almost proportional to the inverse third root of the gross concentration of all point defects. The results indicate that major intrinsic NRC in n-type GaN is VGaVN. From the relationship between its concentration and τNR, its hole capture-cross-section is estimated to be about 7 × 10-14 cm2. Different from the case of 4H-SiC, the major NRCs in p-type and n-type GaN are different: the major NRCs in Mg-doped p-type GaN epilayers are assigned to multiple vacancies containing a VGa and two (or three) VNs, namely, VGa(VN)n (n = 2 or 3). The ion-implanted Mg-doped GaN films are found to contain larger size vacancy complexes such as (VGa)3(VN)3. In analogy with GaN, major NRCs in Al0.6Ga0.4N alloys are assigned to vacancy complexes containing an Al vacancy or a VGa.

N-polar InGaN-based LEDs fabricated on sapphire via pulsed sputtering

NASA Astrophysics Data System (ADS)

Ueno, Kohei; Kishikawa, Eiji; Ohta, Jitsuo; Fujioka, Hiroshi

2017-02-01

High-quality N-polar GaN epitaxial films with an atomically flat surface were grown on sapphire (0001) via pulsed sputtering deposition, and their structural and electrical properties were investigated. The crystalline quality of N-polar GaN improves with increasing film thickness and the full width at half maximum values of the x-ray rocking curves for 0002 and 101 ¯ 2 diffraction were 313 and 394 arcsec, respectively, at the film thickness of 6 μ m . Repeatable p-type doping in N-polar GaN films was achieved using Mg dopant, and their hole concentration and mobility can be controlled in the range of 8 × 1016-2 × 1018 cm-3 and 2-9 cm2V-1s-1, respectively. The activation energy of Mg in N-polar GaN based on a temperature-dependent Hall measurement was estimated to be 161 meV, which is comparable to that of the Ga-polar GaN. Based on these results, we demonstrated the fabrication of N-polar InGaN-based light emitting diodes with the long wavelength up to 609 nm.

Enhancement of surface migration by Mg doping in the metalorganic vapor phase epitaxy of N-polar (000\\bar{1}) GaN/sapphire

NASA Astrophysics Data System (ADS)

Tanikawa, Tomoyuki; Shojiki, Kanako; Aisaka, Takashi; Kimura, Takeshi; Kuboya, Shigeyuki; Hanada, Takashi; Katayama, Ryuji; Matsuoka, Takashi

2014-01-01

With respect to N-polar (000\\bar{1}) GaN grown on a sapphire substrate, the effects of Mg doping on the surface morphology, and the optical, and electrical properties are precisely investigated. By doping Mg, hillocks observed on the surface of (000\\bar{1}) GaN can be suppressed, while step bunching becomes severe. The atomic terrace width is extended with increasing Mg/Ga precursor ratio. Mg doping can promote the surface migration of Ga adatoms on a GaN surface during growth. In the case of heavily Mg-doped GaN, atomic steps become wavy. From photoluminescence spectra, the dominant transition was found to change from near-band-edge transition to donor-acceptor-pair transition. Hall-effect measurement shows p-type conduction at room temperature for a sample grown with the Mg/Ga precursor ratio of 4.5 × 10-3. The activation energy is 143 meV, which is comparable to that of Mg in the conventional Ga-polar (0001) GaN.

Substrate misorientation induced strong increase in the hole concentration in Mg doped GaN grown by metalorganic vapor phase epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suski, T.; Litwin-Staszewska, E.; Piotrzkowski, R.

We demonstrate that relatively small GaN substrate misorientation can strongly change hole carrier concentration in Mg doped GaN layers grown by metalorganic vapor phase epitaxy. In this work intentionally misoriented GaN substrates (up to 2 deg. with respect to ideal <0001> plane) were employed. An increase in the hole carrier concentration to the level above 10{sup 18} cm{sup -3} and a decrease in GaN:Mg resistivity below 1 {omega} cm were achieved. Using secondary ion mass spectroscopy we found that Mg incorporation does not change with varying misorientation angle. This finding suggests that the compensation rate, i.e., a decrease in unintentionalmore » donor density, is responsible for the observed increase in the hole concentration. Analysis of the temperature dependence of electrical transport confirms this interpretation.« less

Pyramidal defects in highly Mg-doped GaN: atomic structure and influence on optoelectronic properties

NASA Astrophysics Data System (ADS)

Leroux, M.; Vennéguès, P.; Dalmasso, S.; de Mierry, P.; Lorenzini, P.; Damilano, B.; Beaumont, B.; Gibart, P.; Massies, J.

2004-07-01

A detailed transmission electron microscopy study is performed on the pyramidal inversion domains that appear in highly Mg-doped GaN grown by metalorganics vapor phase epitaxy or by the high-pressure, high-temperature method. From a comparison between high resolution images of the inversion domain boundaries and simulations using different atomic models, we conclude that both basal and inclined domain boundaries are likely formed of a monomolecular layer of the definite compound Mg{3}N{2}. We show that, due to their high concentration, the formation of these defects may account for auto-compensation in Mg-doped GaN. We also show that the local band bending induced by the polarity inversion due to these defects can be at the origin of the blue luminescence of highly Mg-doped GaN, always observed when nanometric pyramidal inversion domains are also present.

Luminescence studies of laser MBE grown GaN on ZnO nanostructures

NASA Astrophysics Data System (ADS)

Dewan, Sheetal; Tomar, Monika; Kapoor, Ashok K.; Tandon, R. P.; Gupta, Vinay

2017-08-01

GaN films have been successfully fabricated using Laser Molecular Beam Epitaxy (LMBE) technique on bare c-plane sapphire substrate and ZnO nanostructures (NS) decorated Si (100) substrates. The ZnO nanostructures were grown on Si (100) substrate using high pressure assisted Pulsed laser deposition technique in inert gas ambience. Discrete nanostructured morphology of ZnO was obtained using the PLD growth on Si substrates. Photoluminescence studies performed on the prepared GaN/Sapphire and GaN/ZnO-NS/Si systems, revealed a significant PL enhancement in case of GaN/ZnO-NS/Si system compared to the former. The hexagonal nucleation sites provided by the ZnO nanostructures strategically enhanced the emission of GaN film grown by Laser MBE Technique at relatively lower temperature of 700°C. The obtained results are attractive for the realization of highly luminescent GaN films on Si substrate for photonic devices.

Investigation of layered structure SAW devices fabricated using low temperature grown AlN thin film on GaN/sapphire.

PubMed

Lin, Hui-Feng; Wu, Chun-Te; Chien, Wei-Cheng; Chen, Sheng-Wen; Kao, Hui-Ling; Chyi, Jen-Inn; Chen, Jyh-Shin

2005-05-01

Epitaxial AlN films have been grown on GaN/sapphire using helicon sputtering at 300 degrees C. The surface acoustic wave (SAW) filters fabricated on AlN/GaN/sapphire exhibit more superior characteristics than those made on GaN/sapphire. This composite structure of AlN on GaN may bring about the development of high-frequency components, which integrate and use their semiconducting, optoelectronic, and piezoelectric properties.

Ultraviolet light-absorbing and emitting diodes consisting of a p-type transparent-semiconducting NiO film deposited on an n-type GaN homoepitaxial layer

NASA Astrophysics Data System (ADS)

Nakai, Hiroshi; Sugiyama, Mutsumi; Chichibu, Shigefusa F.

2017-05-01

Gallium nitride (GaN) and related (Al,Ga,In)N alloys provide practical benefits in the production of light-emitting diodes (LEDs) and laser diodes operating in ultraviolet (UV) to green wavelength regions. However, obtaining low resistivity p-type AlN or AlGaN of large bandgap energies (Eg) is a critical issue in fabricating UV and deep UV-LEDs. NiO is a promising candidate for useful p-type transparent-semiconducting films because its Eg is 4.0 eV and it can be doped into p-type conductivity of sufficiently low resistivity. By using these technologies, heterogeneous junction diodes consisting of a p-type transparent-semiconducting polycrystalline NiO film on an n-type single crystalline GaN epilayer on a low threading-dislocation density, free-standing GaN substrate were fabricated. The NiO film was deposited by using the conventional RF-sputtering method, and the GaN homoepitaxial layer was grown by metalorganic vapor phase epitaxy. They exhibited a significant photovoltaic effect under UV light and also exhibited an electroluminescence peak at 3.26 eV under forward-biased conditions. From the conduction and valence band (EV) discontinuities, the NiO/GaN heterointerface is assigned to form a staggered-type (TYPE-II) band alignment with the EV of NiO higher by 2.0 eV than that of GaN. A rectifying property that is consistent with the proposed band diagram was observed in the current-voltage characteristics. These results indicate that polycrystalline NiO functions as a hole-extracting and injecting layer of UV optoelectronic devices.

Atomic layer deposition TiO 2-Al 2O 3 stack: An improved gate dielectric on Ga-polar GaN metal oxide semiconductor capacitors

DOE PAGES

Wei, Daming; Edgar, James H.; Briggs, Dayrl P.; ...

2014-10-15

This research focuses on the benefits and properties of TiO 2-Al 2O 3 nano-stack thin films deposited on Ga 2O 3/GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. This combination of materials achieved a high dielectric constant, a low leakage current, and a low interface trap density. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15 nm thick and contained 5.1 nm TiO 2, 7.1 nm Al 2O 3 and 2 nm Ga 2O 3 as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectronmore » spectroscopy (XPS) depth profile, was negligible for GaN pretreated by thermal oxidation in O 2 for 30 minutes at 850°C. The RMS roughness slightly increased after thermal oxidation and remained the same after ALD of the nano-stack, as determined by atomic force microscopy. The dielectric constant of TiO 2-Al 2O 3 on Ga2O3/GaN was increased to 12.5 compared to that of pure Al 2O 3 (8~9) on GaN. In addition, the nano-stack's capacitance-voltage (C-V) hysteresis was small, with a total trap density of 8.74 × 10 11 cm -2. The gate leakage current density (J=2.81× 10 -8 A/cm 2) was low at +1 V gate bias. These results demonstrate the promising potential of plasma ALD deposited TiO 2/Al 2O 3 for serving as the gate oxide on Ga 2O 3/GaN based MOS devices.« less

Atomic layer deposition TiO 2-Al 2O 3 stack: An improved gate dielectric on Ga-polar GaN metal oxide semiconductor capacitors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Daming; Edgar, James H.; Briggs, Dayrl P.

This research focuses on the benefits and properties of TiO 2-Al 2O 3 nano-stack thin films deposited on Ga 2O 3/GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. This combination of materials achieved a high dielectric constant, a low leakage current, and a low interface trap density. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15 nm thick and contained 5.1 nm TiO 2, 7.1 nm Al 2O 3 and 2 nm Ga 2O 3 as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectronmore » spectroscopy (XPS) depth profile, was negligible for GaN pretreated by thermal oxidation in O 2 for 30 minutes at 850°C. The RMS roughness slightly increased after thermal oxidation and remained the same after ALD of the nano-stack, as determined by atomic force microscopy. The dielectric constant of TiO 2-Al 2O 3 on Ga2O3/GaN was increased to 12.5 compared to that of pure Al 2O 3 (8~9) on GaN. In addition, the nano-stack's capacitance-voltage (C-V) hysteresis was small, with a total trap density of 8.74 × 10 11 cm -2. The gate leakage current density (J=2.81× 10 -8 A/cm 2) was low at +1 V gate bias. These results demonstrate the promising potential of plasma ALD deposited TiO 2/Al 2O 3 for serving as the gate oxide on Ga 2O 3/GaN based MOS devices.« less

Atomic Resolution in Situ Imaging of a Double-Bilayer Multistep Growth Mode in Gallium Nitride Nanowires

DOE PAGES

Gamalski, A. D.; Tersoff, J.; Stach, E. A.

2016-04-13

We study the growth of GaN nanowires from liquid Au–Ga catalysts using environmental transmission electron microscopy. GaN wires grow in either (11¯20) or (11¯00) directions, by the addition of {11¯00} double bilayers via step flow with multiple steps. Step-train growth is not typically seen with liquid catalysts, and we suggest that it results from low step mobility related to the unusual double-height step structure. Finally, the results here illustrate the surprising dynamics of catalytic GaN wire growth at the nanoscale and highlight striking differences between the growth of GaN and other III–V semiconductor nanowires.

Controlled growth of heteroepitaxial zinc oxide nanostructures on gallium nitride.

PubMed

Kong, Bo Hyun; Kim, Dong Chan; Mohanta, Sanjay Kumar; Han, Won Suk; Cho, Hyung Koun; Hong, Chang-Hee; Kim, Hyung Gu

2009-07-01

ZnO epitaxial layers were grown on GaN underlying films by metalorganic chemical vapor deposition at various temperatures. An increase in growth temperature led to morphological changes from a smooth film with hexagonal-shaped surface pits to honeycomb-like nanostructures with deep hollow, and additionally resulted in a decrease in dislocation density in the interfacial layers. The reduced dislocation density at the higher growth temperature was attributed to an increase in the size of the critical nucleus and the low nucleation density at the initial stage. The shifts in the peak positions in the X-ray diffraction and photoluminescence were also observed in the samples grown at different temperatures, and were caused by the variation of residual strains after the complete coalescence of the nuclei.

Synthesis of p-type GaN nanowires.

PubMed

Kim, Sung Wook; Park, Youn Ho; Kim, Ilsoo; Park, Tae-Eon; Kwon, Byoung Wook; Choi, Won Kook; Choi, Heon-Jin

2013-09-21

GaN has been utilized in optoelectronics for two decades. However, p-type doping still remains crucial for realization of high performance GaN optoelectronics. Though Mg has been used as a p-dopant, its efficiency is low due to the formation of Mg-H complexes and/or structural defects in the course of doping. As a potential alternative p-type dopant, Cu has been recognized as an acceptor impurity for GaN. Herein, we report the fabrication of Cu-doped GaN nanowires (Cu:GaN NWs) and their p-type characteristics. The NWs were grown vertically via a vapor-liquid-solid (VLS) mechanism using a Au/Ni catalyst. Electrical characterization using a nanowire-field effect transistor (NW-FET) showed that the NWs exhibited n-type characteristics. However, with further annealing, the NWs showed p-type characteristics. A homo-junction structure (consisting of annealed Cu:GaN NW/n-type GaN thin film) exhibited p-n junction characteristics. A hybrid organic light emitting diode (OLED) employing the annealed Cu:GaN NWs as a hole injection layer (HIL) also demonstrated current injected luminescence. These results suggest that Cu can be used as a p-type dopant for GaN NWs.