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Sample records for cubic gan grown

  1. Doping of MBE grown cubic GaN on 3C-SiC (001) by CBr{sub 4}

    SciTech Connect

    Zado, A.; Tschumak, E.; Lischka, K.; As, D. J.; Gerlach, J. W.

    2010-11-01

    We report on carbon doping of cubic GaN by CBr{sub 4} using plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. The samples consist of a 70 nm thick GaN buffer followed by a 550 nm thick GaN:C layer. Carbon doping is realized with a home-made carbon tetrabromide sublimation source. The CBr{sub 4} beam equivalent pressure was established by a needle valve and was varied between 2x10{sup -9} mbar and 6x10{sup -6} mbar. The growth was controlled by in-situ reflection high energy electron diffraction. The incorporated carbon concentration is obtained from secondary ion mass spectroscopy. Capacitance voltage characteristics were measured using metal-insulator-semiconductor structures. Capacitance voltage measurements on nominally undoped cubic GaN showed n-type conductivity with N{sub D}-N{sub A} = 1x10{sup 17} cm{sup -3}. With increasing CBr{sub 4} flux the conductivity type changes to p-type and for the highest CBr{sub 4} flux N{sub A}-N{sub D} = 4{center_dot}5x10{sup 18} cm{sup -3} was obtained.

  2. Optical spectroscopy of cubic GaN in nanowires

    NASA Astrophysics Data System (ADS)

    Renard, J.; Tourbot, G.; Sam-Giao, D.; Bougerol, C.; Daudin, B.; Gayral, B.

    2010-08-01

    We show that highly homogeneous cubic GaN can be grown by plasma-assisted molecular beam epitaxy on wurtzite GaN nanowires. The line width of the donor bound exciton is below 3 meV and can reach 1.6 meV in the best parts of the studied sample. This allows to perform a detailed spectroscopy of cubic GaN, and, in particular, to determine the precise spectral positions of the donor bound exciton, the fundamental free exciton and the split-off exciton in a photoluminescence experiment.

  3. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  4. Optical properties and temperature dependence of the interband transitions of cubic and hexagonal GaN

    NASA Astrophysics Data System (ADS)

    Logothetidis, S.; Petalas, J.; Cardona, M.; Moustakas, T. D.

    1994-12-01

    The optical properties of cubic and hexagonal GaN thin films, grown by electron-cyclotron resonance microwave plasma-assisted molecular-beam epitaxy on silicon and sapphire substrates, respectively, have been studied at photon energies up to 25 eV with conventional and synchrotron-radiation spectroscopic ellipsometry. The fundamental gaps of the two polytypes are located at different energies, namely at 3.25 and 3.43 eV for cubic and hexagonal GaN. Analysis of the dielectric function of the two phases in the region 4.5-9.5 eV with appropriate models yields the energy location and broadening of the observed critical points. These critical points are assigned to specific points in the zinc-blende and wurtzite Brillouin zones, respectively, making use of the latest published band-structure studies and a comparison is made between the corresponding results for GaN, GaAs, and GaP. Measurements in the temperature range from 80 to 650 K provide the temperature dependence of these parameters. The features observed in the reflectivity spectra of hexagonal GaN are discussed in relation to other works. Kramers-Kronig analysis of the reflectivity between 0 and 33 eV of the hexagonal polytype verifies the existence of a broad feature centered at 14 eV. Finally, average properties, such as the effective ir dielectric constant and the effective number of valence electrons per atom are calculated for the two polytypes and compared to GaAs and GaP.

  5. Electron spin dynamics in cubic GaN

    NASA Astrophysics Data System (ADS)

    Buß, J. H.; Schupp, T.; As, D. J.; Brandt, O.; Hägele, D.; Rudolph, J.

    2016-12-01

    The electron spin dynamics in cubic GaN is comprehensively investigated by time-resolved magneto-optical Kerr-rotation spectroscopy over a wide range of temperatures, magnetic fields, and doping densities. The spin dynamics is found to be governed by the interplay of spin relaxation of localized electrons and Dyakonov-Perel relaxation of delocalized electrons. Localized electrons significantly contribute to spin relaxation up to room temperature at moderate doping levels, while Dyakonov-Perel relaxation dominates for high temperatures or degenerate doping levels. Quantitative agreement to Dyakonov-Perel theory requires a larger value of the spin-splitting constant than theoretically predicted. Possible reasons for this discrepancy are discussed, including the role of charged dislocations.

  6. Strain dependent electron spin dynamics in bulk cubic GaN

    SciTech Connect

    Schaefer, A.; Buß, J. H.; Hägele, D.; Rudolph, J.; Schupp, T.; Zado, A.; As, D. J.

    2015-03-07

    The electron spin dynamics under variable uniaxial strain is investigated in bulk cubic GaN by time-resolved magneto-optical Kerr-rotation spectroscopy. Spin relaxation is found to be approximately independent of the applied strain, in complete agreement with estimates for Dyakonov-Perel spin relaxation. Our findings clearly exclude strain-induced relaxation as an effective mechanism for spin relaxation in cubic GaN.

  7. Zinc-blende (Cubic) GaN and AlGaN Layers, Structures and Bulk Crystals by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Novikov, Sergei V.; Zainal, Norzaini; Akimov, Andrey V.; Staddon, Chris R.; Foxon, C. Thomas; Kent, Anthony J.

    2010-11-01

    We have studied the growth of zinc-blende GaN and AlGaN layers, structures and bulk crystals by molecular beam epitaxy (MBE). We have developed a process for growth by MBE of free-standing cubic GaN layers. Undoped thick cubic GaN films were grown on semi-insulating GaAs (001) substrates by a modified plasma-assisted molecular beam epitaxy (PA-MBE) method and were removed from the GaAs substrate after the growth. The resulting free-standing GaN wafers with thicknesses in the 30-100 μm range may be used as substrates for further epitaxy of cubic GaN-based structures and devices. We have developed procedures to cleave the wafers into 10×10 mm2 square substrates and to polish them to produce epi-ready surfaces. The first GaN/InGaN LEDs on our zinc-blende GaN substrates have been demonstrated by our collaborators at Sharp Laboratories of Europe.

  8. Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

    SciTech Connect

    Choudhary, B. S.; Singh, A.; Tyagi, P. K.; Tanwar, S.; Kumar, M. Senthil; Kushvaha, S. S.

    2016-04-13

    We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.

  9. Magnesium diffusion profile in GaN grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Benzarti, Z.; Halidou, I.; Bougrioua, Z.; Boufaden, T.; El Jani, B.

    2008-07-01

    The diffusion of magnesium has been studied in GaN layers grown on sapphire substrate by atmospheric pressure metalorganic vapor-phase-epitaxy (MOVPE) in a "home-made" reactor. Secondary Ion Mass Spectroscopy (SIMS) was used to visualise the Mg profiles in two kinds of multi-sublayer GaN structures. One structure was grown with a variable flow of Ga precursor (TMG) and the second one with a variable growth temperature. In both cases, the Mg dopant precursor (Cp 2Mg) flow was kept constant. Using the second Fick's law to fit the experimental SIMS data, we have deduced an increasing then a saturating Mg diffusion coefficient versus the Mg concentration. Mg incorporation was found to get higher for lower growth rate, i.e. when TMG flow is reduced. Furthermore, based on the temperature-related behaviour we have found that the activation energy for Mg diffusion coefficient in GaN was 1.9 eV. It is suggested that Mg diffuses via substitutional sites.

  10. Epitaxially-Grown GaN Junction Field Effect Transistors

    SciTech Connect

    Baca, A.G.; Chang, P.C.; Denbaars, S.P.; Lester, L.F.; Mishra, U.K.; Shul, R.J.; Willison, C.G.; Zhang, L.; Zolper, J.C.

    1999-05-19

    Junction field effect transistors (JFET) are fabricated on a GaN epitaxial structure grown by metal organic chemical vapor deposition (MOCVD). The DC and microwave characteristics of the device are presented. A junction breakdown voltage of 56 V is obtained corresponding to the theoretical limit of the breakdown field in GaN for the doping levels used. A maximum extrinsic transconductance (gm) of 48 mS/mm and a maximum source-drain current of 270 mA/mm are achieved on a 0.8 µ m gate JFET device at VGS= 1 V and VDS=15 V. The intrinsic transconductance, calculated from the measured gm and the source series resistance, is 81 mS/mm. The fT and fmax for these devices are 6 GHz and 12 GHz, respectively. These JFETs exhibit a significant current reduction after a high drain bias is applied, which is attributed to a partially depleted channel caused by trapped hot-electrons in the semi-insulating GaN buffer layer. A theoretical model describing the current collapse is described, and an estimate for the length of the trapped electron region is given.

  11. Inversion domains in GaN grown on sapphire

    SciTech Connect

    Romano, L.T.; Northrup, J.E.; OKeefe, M.A.

    1996-10-01

    Planar defects observed in GaN films grown on (0001) sapphire have been identified as inversion domain boundaries (IDBs) by a combination of high resolution transmission electron microscopy, multiple dark field imaging, and convergent beam electron diffraction techniques. Films grown by molecular beam epitaxy (MBE), metalorganic vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE) were investigated and all were found to contain IDBs. The IDBs in the MBE and HVPE films extended from the interface to the film surface and formed columnar domains that ranged in width from 3 to 20 nm in the MBE films and up to 100 nm in the HVPE films. For the films investigated, the MBE films had the highest density, and the MOCVD films had the lowest density of IDBs. The nucleation of inversion domains (IDs) may result from step-related inhomogeneities of the GaN/sapphire interface. {copyright} {ital 1996 American Institute of Physics.}

  12. Orthodox etching of HVPE-grown GaN

    SciTech Connect

    Weyher, J.L.; Lazar, S.; Macht, L.; Liliental-Weber, Z.; Molnar,R.J.; Muller, S.; Nowak, G.; Grzegory, I.

    2006-08-10

    Orthodox etching of HVPE-grown GaN in molten eutectic of KOH + NaOH (E etch) and in hot sulfuric and phosphoric acids (HH etch) is discussed in detail. Three size grades of pits are formed by the preferential E etching at the outcrops of threading dislocations on the Ga-polar surface of GaN. Using transmission electron microscopy (TEM) as the calibration tool it is shown that the largest pits are formed on screw, intermediate on mixed and the smallest on edge dislocations. This sequence of size does not follow the sequence of the Burgers values (and thus the magnitude of the elastic energy) of corresponding dislocations. This discrepancy is explained taking into account the effect of decoration of dislocations, the degree of which is expected to be different depending on the lattice deformation around the dislocations, i.e. on the edge component of the Burgers vector. It is argued that the large scatter of optimal etching temperatures required for revealing all three types of dislocations in HVPE-grown samples from different sources also depends upon the energetic status of dislocations. The role of kinetics for reliability of etching in both etches is discussed and the way of optimization of the etching parameters is shown.

  13. DLTS study of n-type GaN grown by MOCVD on GaN substrates

    NASA Astrophysics Data System (ADS)

    Tokuda, Y.; Matsuoka, Y.; Ueda, H.; Ishiguro, O.; Soejima, N.; Kachi, T.

    2006-10-01

    Electron traps in n-type GaN layers grown homoepitaxially by MOCVD on free-standing GaN substrates have been characterized using DLTS for vertical Schottky diodes. Two free-standing HVPE GaN substrates (A and B), obtained from two different sources, are used. The Si-doped GaN layers with the thickness of 5 μm are grown on an area of 0.9×0.9 cm 2 of substrate A and on an area of 1×1 cm 2 of substrate B. Two traps labeled B1 (Ec-0.23 eV) and B2 (Ec-0.58 eV) are observed with trap B2 dominant in GaN on both substrates. There exist no dislocation-related traps which have been previously observed in MOCVD GaN on sapphire. This might be correlated to the reduction in dislocation density due to the homoepitaxial growth. However, it is found that there is a large variation, more than an order of magnitude, in trap B2 concentration and that the B2 spatial distributions are different between the two substrates used.

  14. Study of isolated cubic GaN quantum dots by low-temperature cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Garayt, J. P.; Gérard, J. M.; Enjalbert, F.; Ferlazzo, L.; Founta, S.; Martinez-Guerrero, E.; Rol, F.; Araujo, D.; Cox, R.; Daudin, B.; Gayral, B.; Si Dang, Le; Mariette, H.

    2005-02-01

    We report single dot spectroscopy of cubic GaN/AlN self-assembled quantum dots. Typical linewidths of the zero-phonon line between 2 and 8 meV are observed and interpreted in terms of charge fluctuations around a given quantum dot. The phonon sideband contribution in this emission, even at low temperature, reveals the importance of the acoustic phonon broadening mechanism which controls the exciton dephasing and may impose the real limits to the optical properties of GaN single QDs emission.

  15. LEDs on HVPE grown GaN substrates: Influence of macroscopic surface features

    NASA Astrophysics Data System (ADS)

    Rahman, SK. S.; Leute, R. A. R.; Wang, J.; Meisch, T.; Klein, M.; Scholz, F.; Koyama, K.; Ishii, M.; Takeda, H.

    2014-07-01

    We demonstrate the strong influence of GaN substrate surface morphology on optical properties and performance of light emitting devices grown on freestanding GaN. As-grown freestanding HVPE GaN substrates show excellent AFM RMS and XRD FWHM values over the whole area, but distinctive features were observed on the surface, such as macro-pits, hillocks and facets extending over several millimeters. Electroluminescence measurements reveal a strong correlation of the performance and peak emission wavelength of LEDs with each of these observed surface features. This results in multiple peaks and non-uniform optical output power for LEDs on as-grown freestanding GaN substrates. Removal of these surface features by chemical mechanical polishing results in highly uniform peak wavelength and improved output power over the whole wafer area.

  16. Incorporation of indium on cubic GaN epitaxially induced on a nanofaceted Si(001) substrate by phase transition

    NASA Astrophysics Data System (ADS)

    Lee, S. C.; Youngblood, N.; Jiang, Y. B.; Peterson, E. J.; Stark, C. J. M.; Detchprohm, T.; Wetzel, C.; Brueck, S. R. J.

    2015-12-01

    The incorporation of In on the non-polar, piezoelectric-free (001) facet of cubic (c-) GaN epitaxially grown over a Si(001) substrate by metal-organic vapor phase epitaxy is reported. Relying on a hexagonal (h-) to c-phase transformation during epitaxy on an 800 nm-wide, Si(111)-faceted v-groove patterned into the substrate, the GaN epilayer at cross sectional view retains a triangular c-phase inside a chevron-shaped h-phase that results in a top surface bounded by a (001) facet parallel to Si(001) at the center and ( 1 1 ¯ 01 ) facets at both edges. A stack of five, ˜3 nm-thick, InxGa1-xN/GaN quantum wells (QWs) was deposited on the double-phased top surface. The c-phase region up to the QWs keeps extremely small misfit (˜0.002) to the fully relaxed h-GaN underneath it and is in tensile stress implying undefected by the h-c phase interface. The In incorporation on a strained non-polar (001) of c-GaN is comparable with that on totally relaxed semi-polar ( 1 1 ¯ 01 ) of h-GaN without noticeable adatom migration across the phase boundary, and sufficient to provide the room-temperature green emission at 496 nm from the c-InxGa1-xN/GaN QWs on Si(001) in photoluminescence.

  17. Depth dependence of defect density and stress in GaN grown on SiC

    SciTech Connect

    Faleev, N.; Temkin, H.; Ahmad, I.; Holtz, M.; Melnik, Yu.

    2005-12-15

    We report high resolution x-ray diffraction studies of the relaxation of elastic strain in GaN grown on SiC(0001). The GaN layers were grown with thickness ranging from 0.29 to 30 {mu}m. High level of residual elastic strain was found in thin (0.29 to 0.73 {mu}m thick) GaN layers. This correlates with low density of threading screw dislocations of 1-2x10{sup 7} cm{sup -2}, observed in a surface layer formed over a defective nucleation layer. Stress was found to be very close to what is expected from thermal expansion mismatch between the GaN and SiC. A model based on generation and diffusion of point defects accounts for these observations.

  18. 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.

  19. Evolution of deep centers in GaN grown by hydride vapor phaseepitaxy

    SciTech Connect

    Fang, Z.-Q.; Look, D.C.; Jasinski, J.; Benamara, M.; Liliental-Weber, Z.; Molnar, R.J.

    2001-04-18

    Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

  20. High-quality GaN nanowires grown on Si and porous silicon by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Shekari, L.; Ramizy, A.; Omar, K.; Hassan, H. Abu; Hassan, Z.

    2012-12-01

    Nanowires (NWs) of GaN thin films were prepared on as-grown Si (1 1 1) and porous silicon (PS) substrates using thermal evaporation method. The film growth produced high-quality wurtzite GaN NWs. The size, morphology, and nanostructures of the crystals were investigated through scanning electron microscopy, high-resolution X-ray diffraction and photoluminescence spectroscopy. The NWs grown on porous silicon were thinner, longer and denser compared with those on as-grown Si. The energy band gap of the NWs grown on PS was larger than that of NWs on as-grown Si. This is due to the greater quantum confinement effects of the crystalline structure of the NWs grown on PS.

  1. Strong photoluminescence emission from GaN grown on amorphous silica substrates by gas source MBE

    NASA Astrophysics Data System (ADS)

    Iwata, K.; Asahi, H.; Asami, K.; Kuroiwa, R.; Gonda, S.

    1998-06-01

    GaN layers are grown on amorphous fused silica glass substrates by gas source MBE using an ion removed electron cyclotron resonance (ECR) radical cell. Reflection high-energy electron diffraction (RHEED) and X-ray diffraction measurements reveal that they are polycrystalline. However, they show a strong photoluminescence emission peak without deep level emission. The emission peak is red-shifted by about 150 meV from that of the excitonic emission peak of GaN grown on a sapphire substrate and has wide spectral half-width (˜250 meV at 77 K). The peak is not corresponding to the donor-acceptor pair (DAP) emission but is excitonic from the excitation power and temperature dependence of PL spectrum. These optical properties indicate that GaN layers grown on a glass substrate are promising for fabrication of large area and low cost light emitting devices and solar cells.

  2. Uniform GaN thin films grown on (100) silicon by remote plasma atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Shih, Huan-Yu; Lin, Ming-Chih; Chen, Liang-Yih; Chen, Miin-Jang

    2015-01-01

    The growth of uniform gallium nitride (GaN) thin films was reported on (100) Si substrate by remote plasma atomic layer deposition (RP-ALD) using triethylgallium (TEG) and NH3 as the precursors. The self-limiting growth of GaN was manifested by the saturation of the deposition rate with the doses of TEG and NH3. The increase in the growth temperature leads to the rise of nitrogen content and improved crystallinity of GaN thin films, from amorphous at a low deposition temperature of 200 °C to polycrystalline hexagonal structures at a high growth temperature of 500 °C. No melting-back etching was observed at the GaN/Si interface. The excellent uniformity and almost atomic flat surface of the GaN thin films also infer the surface control mode of the GaN thin films grown by the RP-ALD technique. The GaN thin films grown by RP-ALD will be further applied in the light-emitting diodes and high electron mobility transistors on (100) Si substrate.

  3. Multi-wavelength emitting InGan/GaN quantum well grown on V-shaped gan(1101) microfacet.

    PubMed

    Kang, Eun-Sil; Ju, Jin-Woo; Kim, Jin Soo; Ahn, Haeng-Keun; Lee, June Key; Kim, Jin Hyeok; Shin, Dong-Chan; Lee, In-Hwan

    2007-11-01

    InGaN/GaN multiple quantum wells (MQWs) were successfully grown on the inclined GaN(1101) microfacets. Conventional photolithography and subsequent growth of GaN were employed to generate the V-shaped microfacets along (1120) direction. The well-developed microfacets observed by scanning electron microscopy and the clear transmission electron microscope interfacial images indicated that the MQW was successfully grown on the GaN microfacets. Interestingly, cathodoluminescence (CL) spectra measured on the microfacets showed a continuous change in the luminescence peak positions. The CL peaks were shifted to a longer wavelength from 420 nm to 440 nm as the probing points were changed along upward direction. This could be attributed to the nonuniform distribution of the In composition and/or the wavefunction overlapping between adjacent wells. Present works thus propose a novel route to fabricate a monolithic white light emitting diode without phosphors by growing the InGaN/GaN MQWs on (1101) facet.

  4. Growth of bulk GaN by HVPE on pressure grown seeds

    NASA Astrophysics Data System (ADS)

    Grzegory, I.; Łucznik, B.; Boćkowski, M.; Pastuszka, B.; Kryśko, M.; Kamler, G.; Nowak, G.; Porowski, S.

    2006-02-01

    Growth of GaN under pressure from solution in gallium results in almost dislocation free plate-like crystals but with size limited to app. 1-2 cm (lateral) and 100 μm (thickness) or up to about 1cm long needles. Deposition of GaN by HVPE on the pressure grown seeds allows stable crystallization (in terms of flatness of the crystallization front and uniformity of the new grown material) at a rate of about 100 μm/h on both types of seed crystals. However, in the thick GaN crystals grown on almost dislocation free plate-like substrates quite a high number of dislocations appears if the crystal thickness exceeds certain critical value. Since the critical thickness for defect generation is of the order of 100 μm, almost dislocation free layers (density below 10 4 cm -2) thinner than 100 μm can be grown. The most obvious further step is removing the substrate and continuation of the HVPE deposition on the free standing low dislocation density layer of sub-critical thickness. The pressure grown substrates were removed by mechanical polishing or conductivity sensitive electrochemical etching (for strongly n-type substrates). Then the HVPE low dislocation density GaN 1platelets were used as substrates for the growth of a few mm thick bulk GaN crystals. The crystals were characterized by defect selective etching of both polar (0001) and non-polar (10 -10) surfaces to check presence and distribution of structural defects. The X-ray measurements allowed concluding about character of strain and deformation in high pressure GaN-HVPE GaN system.

  5. Critical issues for homoepitaxial GaN growth by molecular beam epitaxy on hydride vapor-phase epitaxy-grown GaN substrates

    NASA Astrophysics Data System (ADS)

    Storm, D. F.; Hardy, M. T.; Katzer, D. S.; Nepal, N.; Downey, B. P.; Meyer, D. J.; McConkie, Thomas O.; Zhou, Lin; Smith, David J.

    2016-12-01

    While the heteroepitaxial growth of gallium nitride-based materials and devices on substrates such as SiC, sapphire, and Si has been well-documented, the lack of a cost-effective source of bulk GaN crystals has hindered similar progress on homoepitaxy. Nevertheless, freestanding GaN wafers are becoming more widely available, and there is great interest in growing GaN films and devices on bulk GaN substrates, in order to take advantage of the greatly reduced density of threading dislocations, particularly for vertical devices. However, homoepitaxial GaN growth is far from a trivial task due to the reactivity and different chemical sensitivities of N-polar (000_1) and Ga-polar (0001) GaN surfaces, which can affect the microstructure and concentrations of impurities in homoepitaxial GaN layers. In order to achieve high quality, high purity homoepitaxial GaN, it is necessary to investigate the effect of the ex situ wet chemical clean, the use of in situ cleaning procedures, the sensitivity of the GaN surface to thermal decomposition, and the effect of growth temperature. We review the current understanding of these issues with a focus on homoepitaxial growth of GaN by molecular beam epitaxy (MBE) on c-plane surfaces of freestanding GaN substrates grown by hydride vapor phase epitaxy (HVPE), as HVPE-grown substrates are most widely available. We demonstrate methods for obtaining homoepitaxial GaN layers by plasma-assisted MBE in which no additional threading dislocations are generated from the regrowth interface and impurity concentrations are greatly reduced.

  6. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AIN and InN

    DTIC Science & Technology

    1992-12-01

    AD-A258 804 Final Technical Report Ii Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent...Technical 6/1/86-12/31/92 4. TITLE AND SUBTITLE Growth, Nitrogen Vacancy Reduction and 5. FUNDING NUMBERS Solid Solution Formation in Cubic GaN Thin...According to the structural and chemical analyses, there is no reason to believe that a homogeneous solid solution close to this composition had

  7. Growth, nitrogen vacancy reduction and solid solution formation in cubic GaN thin films and the subsequent fabrication of superlattice structures using AIN and InN

    NASA Astrophysics Data System (ADS)

    Davis, Robert F.

    1992-02-01

    An atomic layer epitaxy deposition system configured for the growth of thin films of the III-V nitrides of Al, Ga and In has been designed, constructed and commissioned. The system allows the introduction of up to 16 gases without mixing. Self-terminating growth of crystalline GaN films has been achieved on single crystal wafers of (0001) alpha(6H)-SiC. Results of analyses via Auger spectroscopy, electron microscopy and electron diffraction are described. Deposition of AlN and GaN via gas-source MBE was also continued during this period. The principal emphasis concerned the initial stages of growth of both compounds on the substrates of (00001) alpha(6H)-SiC and (0001) sapphire, as determined using X-ray photoelectron spectroscopy. An initial layer of silicon nitride formed on the surface of SiC prior to the deposition of either nitride. The deposition of GaN on sapphire followed the Stranski-Krastanov mode of nucleation and growth, while on SiC, characteristics of three-dimensional growth were evident. By contrast, AlN grew initially in a layer-by-layer mode. Deposition of GaN on vicinal (100) Beta-SiC during UV irradiation resulted in the formation of a new 4H polytype of this material. Deposition of BN via gas-source MBE on Cu(110) resulted in nanocrystalline cBN; films grown on (111) Cu resulted in h-BN (graphitic phase). Similar studies using Si(100) substrates also resulted in the occurrence of cBN. The occurrence of the cubic polytype was enhanced while that of h-BN was discouraged with the use of the UV light at 400-500 C.

  8. Thermal Boundary Resistance between GaN and Cubic Ice and THz Acoustic Attenuation Spectrum of Cubic Ice from Complex Acoustic Impedance Measurements.

    PubMed

    Mante, Pierre-Adrien; Chen, Chien-Cheng; Wen, Yu-Chieh; Sheu, Jinn-Kong; Sun, Chi-Kuang

    2013-11-27

    A phonon nanoscopy method, based on the picosecond ultrasonics technique, capable of studying the complex acoustic reflection coefficient at frequency up to 1 THz is proposed and demonstrated. By measuring the reflection coefficient at the same surface location at the interface between GaN and air, and between GaN and the material to characterize, we get access to the THz amplitude and phase spectra of the acoustic phonon reflection. The retrieval of both these pieces of information then allows the calculation of the attenuation in a wide range of frequency and gives new insight into the Kapitza anomaly. This method is then applied to cubic ice, and the measurements of the elastic properties, the phonon anharmonic decay spectrum up to 1 THz, as well as the measurements of the thermal phonon lifetime at 150 K are all achieved.

  9. X-ray detection with zinc-blende (cubic) GaN Schottky diodes

    PubMed Central

    Gohil, T.; Whale, J.; Lioliou, G.; Novikov, S. V.; Foxon, C. T.; Kent, A. J.; Barnett, A. M.

    2016-01-01

    The room temperature X-ray responses as functions of time of two n type cubic GaN Schottky diodes (200 μm and 400 μm diameters) are reported. The current densities as functions of time for both diodes showed fast turn-on transients and increases in current density when illuminated with X-ray photons of energy up to 35 keV. The diodes were also electrically characterized: capacitance, implied depletion width and dark current measurements as functions of applied bias at room temperature are presented. At −5 V reverse bias, the capacitances of the diodes were measured to be (84.05 ± 0.01) pF and (121.67 ± 0.02) pF, respectively. At −5 V reverse bias, the dark current densities of the diodes were measured to be (347.2 ± 0.4) mA cm−2 and (189.0 ± 0.2) mA cm−2, respectively. The Schottky barrier heights of the devices (0.52 ± 0.07) eV and (0.63 ± 0.09) eV, respectively, were extracted from the forward dark current characteristics. PMID:27403806

  10. Characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Lo, Ikai; Pang, Wen-Yuan; Hsu, Yu-Chi; Hsieh, Chia-Ho; Shih, Cheng-Hung; Chou, Mitch M. C.; Chen, Wen-Yen; Hsu, Tzu-Min; Hsu, Gary Z. L.

    2013-06-15

    The characterization of GaN microstructures grown by plasma-assisted molecular beam epitaxy on LiAlO{sub 2} substrate was studied by cathodoluminescence and photoluminescence measurements. We demonstrated that the cathodoluminescence from oblique semi-polar surfaces of mushroom-shaped GaN was much brighter than that from top polar surface due to the reduction of polarization field on the oblique semi-polar surfaces. It implies that the oblique semi-polar surface is superior for the light-emitting surface of wurtzite nano-devices.

  11. Multilayer porous structures of HVPE and MOCVD grown GaN for photonic applications

    NASA Astrophysics Data System (ADS)

    Braniste, T.; Ciers, Joachim; Monaico, Ed.; Martin, D.; Carlin, J.-F.; Ursaki, V. V.; Sergentu, V. V.; Tiginyanu, I. M.; Grandjean, N.

    2017-02-01

    In this paper we report on a comparative study of electrochemical processes for the preparation of multilayer porous structures in hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor phase deposition (MOCVD) grown GaN. It was found that in HVPE-grown GaN, multilayer porous structures are obtained due to self-organization processes leading to a fine modulation of doping during the crystal growth. However, these processes are not totally under control. Multilayer porous structures with a controlled design have been produced by optimizing the technological process of electrochemical etching in MOCVD-grown samples, consisting of five pairs of thin layers with alternating-doping profiles. The samples have been characterized by SEM imaging, photoluminescence spectroscopy, and micro-reflectivity measurements, accompanied by transfer matrix analysis and simulations by a method developed for the calculation of optical reflection spectra. We demonstrate the applicability of the produced structures for the design of Bragg reflectors.

  12. Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature

    NASA Astrophysics Data System (ADS)

    Koblmüller, G.; Reurings, F.; Tuomisto, F.; Speck, J. S.

    2010-11-01

    The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ˜780-790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth (0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N˜1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ˜1016 cm-3 for all films attribute further to the significant benefits of the high-temperature growth regime.

  13. Optical and structural characterisation of epitaxial nanoporous GaN grown by CVD.

    PubMed

    Mena, Josué; Carvajal, Joan J; Martínez, Oscar; Jiménez, Juan; Zubialevich, Vitaly Z; Parbrook, Peter J; Diaz, Francesc; Aguiló, Magdalena

    2017-09-15

    In this paper we study the optical properties of nanoporous gallium nitride (GaN) epitaxial layers grown by chemical vapour deposition on non-porous GaN substrates, using photoluminescence, cathodoluminescence, and resonant Raman scattering, and correlate them with the structural characteristic of these films. We pay special attention to the analysis of the residual strain of the layers and the influence of the porosity in the light extraction. The nanoporous GaN epitaxial layers are under tensile strain, although the strain is progressively reduced as the deposition time and the thickness of the porous layer increases, becoming nearly strain free for a thickness of 1.7 μm. The analysis of the experimental data point to the existence of vacancy complexes as the main source of the tensile strain.

  14. Electrical characterization of ensemble of GaN nanowires grown by the molecular beam epitaxy technique

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K.

    2013-08-01

    High quality Schottky contacts are formed on GaN nanowires (NWs) structures grown by the molecular beam epitaxy technique on Si(111) substrate. The current-voltage characteristics show the rectification ratio of about 103 and the leakage current of about 10-4 A/cm2 at room temperature. From the capacitance-voltage measurements the free carrier concentration in GaN NWs is determined as about 1016 cm-3. Two deep levels (H200 and E280) are found in the structures containing GaN NWs. H200 is attributed to an extended defect located at the interface between the substrate and SiNx or near the sidewalls at the bottom of the NWs whereas E280 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  15. Optical and structural characterisation of epitaxial nanoporous GaN grown by CVD

    NASA Astrophysics Data System (ADS)

    Mena, Josué; Carvajal, Joan J.; Martínez, Oscar; Jiménez, Juan; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Diaz, Francesc; Aguiló, Magdalena

    2017-09-01

    In this paper we study the optical properties of nanoporous gallium nitride (GaN) epitaxial layers grown by chemical vapour deposition on non-porous GaN substrates, using photoluminescence, cathodoluminescence, and resonant Raman scattering, and correlate them with the structural characteristic of these films. We pay special attention to the analysis of the residual strain of the layers and the influence of the porosity in the light extraction. The nanoporous GaN epitaxial layers are under tensile strain, although the strain is progressively reduced as the deposition time and the thickness of the porous layer increases, becoming nearly strain free for a thickness of 1.7 μm. The analysis of the experimental data point to the existence of vacancy complexes as the main source of the tensile strain.

  16. Study of electrical properties of single GaN nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Mozharov, A. M.; Komissarenko, F. E.; Vasiliev, A. A.; Bolshakov, A. D.; Moiseev, E. I.; Mukhin, M. S.; Cirlin, G. E.; Mukhin, I. S.

    2016-08-01

    Electrical properties of single GaN nanowires grown by means of molecular beam epitaxy with N-plasma source were studied. Ohmic contacts connected to single n-type GaN wires were produced by the combination of electron beam lithography, metal vacuum evaporation and rapid thermal annealing technique. The optimal annealing temperature to produce ohmic contacts implemented in the form of Ti/Al/Ti/Au stack has been determined. By means of 2-terminal measurement wiring diagram the conductivity of single NW has been obtained for NWs with different growth parameters. The method of MESFET measurement circuit layout of single GaN nanowires (NWs) has been developed. In accordance with performed numerical calculation, free carriers' concentration and mobility of single NWs could be independently estimated using MESFET structure.

  17. The pyroelectric coefficient of free standing GaN grown by HVPE

    NASA Astrophysics Data System (ADS)

    Jachalke, Sven; Hofmann, Patrick; Leibiger, Gunnar; Habel, Frank S.; Mehner, Erik; Leisegang, Tilmann; Meyer, Dirk C.; Mikolajick, Thomas

    2016-10-01

    The present study reports on the temperature dependent pyroelectric coefficient of free-standing and strain-free gallium nitride (GaN) grown by hydride vapor phase epitaxy (HVPE). The Sharp-Garn method is applied to extract the pyroelectric coefficient from the electrical current response of the crystals subjected to a sinusoidal temperature excitation in a range of 0 °C to 160 °C. To avoid compensation of the pyroelectric response by an internal conductivity, insulating GaN crystals were used by applying C, Mn, and Fe doping during HVPE growth. The different pyroelectric coefficients observed at room temperature due to the doping correlate well with the change of the lattice parameter c. The obtained data are compared to previously published theoretical and experimental values of thin film GaN and discussed in terms of a strained lattice.

  18. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    SciTech Connect

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-15

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  19. Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

    NASA Astrophysics Data System (ADS)

    Kushvaha, S. S.; Kumar, M. Senthil; Maurya, K. K.; Dalai, M. K.; Sharma, Nita D.

    2013-09-01

    Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500-750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

  20. Improved crystalline quality of N-polar GaN epitaxial layers grown with reformed flow-rate-modulation technology

    NASA Astrophysics Data System (ADS)

    Zhang, Heng; Zhang, Xiong; Wang, Shuchang; Wang, Xiaolei; Zhao, Jianguo; Wu, Zili; Dai, Qian; Yang, Hongquan; Cui, Yiping

    2017-01-01

    A reformed flow-rate-modulation technology was developed for the metalorganic vapor phase epitaxy (MOVPE) growth of the N-polar GaN epitaxial layers. To improve the crystalline quality of the N-polar GaN epitaxial layers, a GaN nucleation layer was grown at relatively low temperature with carefully-controlled pulsed supply of Ga source and showed diverse morphology with atomic force microscope (AFM). Furthermore, the electrical and optical properties of the grown N-polar GaN epitaxial layers were investigated extensively by means of Hall effect, photoluminescence (PL), and X-ray rocking curve (XRC) measurements. The characterization results revealed that as compared with the N-polar GaN epitaxial layer grown over the conventional GaN nucleation layer which was deposited with continuous supply of both N and Ga sources, the electrical and optical properties of the N-polar GaN epitaxial layer grown with optimized supply of Ga source for the GaN nucleation layer were significantly improved.

  1. Fabrication of GaN Microporous Structure at a GaN/Sapphire Interface as the Template for Thick-Film GaN Separation Grown by HVPE

    NASA Astrophysics Data System (ADS)

    Chen, Jianli; Cheng, Hongjuan; Zhang, Song; Lan, Feifei; Qi, Chengjun; Xu, Yongkuan; Wang, Zaien; Li, Jing; Lai, Zhanping

    2016-10-01

    In this paper, a microporous structure at the GaN/sapphire interface has been obtained by an electrochemical etching method via a selective etching progress using an as-grown GaN/sapphire wafer grown by metal organic chemical vapor deposition. The as-prepared GaN interfacial microporous structure has been used as a template for the following growth of thick-film GaN crystal by hydride vapor phase epitaxy (HVPE), facilitating the fabrication of a free-standing GaN substrate detached from a sapphire substrate. The evolution of the interfacial microporous structure has been investigated by varying the etching voltages and time, and the formation mechanism of interfacial microporous structure has been discussed in detail as well. Appropriate interfacial microporous structure is beneficial for separating the thick GaN crystal grown by HVPE from sapphire during the cooling down process. The separation that occurred at the place of interfacial microporous can be attributed to the large thermal strain between GaN and sapphire. This work realized the fabrication of a free-standing GaN substrate with high crystal quality and nearly no residual strain.

  2. High electron mobility GaN grown under N-rich conditions by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Koblmueller, G.; Wu, F.; Mates, T.; Speck, J. S.; Fernandez-Garrido, S.; Calleja, E.

    2007-11-26

    An alternative approach is presented for the plasma-assisted molecular beam epitaxy of high-quality GaN. Under N-rich growth conditions, an unexpected layer-by-layer growth mode was found for a wide range of growth temperatures in the GaN thermal decomposition regime (>750 deg. C). Consequently, superior surface morphologies with roughness of less than 1 nm (rms) have been achieved. For lightly Si-doped GaN films, room-temperature electron mobilities exceeding 1100 cm{sup 2}/V s were measured, surpassing the commonly insulating nature of GaN grown under N-rich conditions at low temperature.

  3. Study of GaP single crystal layers grown on GaN by MOCVD

    SciTech Connect

    Li, Shuti; Liu, Chao; Ye, Guoguang; Xiao, Guowei; Zhou, Yugang; Su, Jun; Fan, Guanghan; Zhang, Yong; Liang, Fubo; Zheng, Shuwen

    2011-11-15

    Highlights: {yields} We investigated the growth of GaP layers on GaN by MOCVD. {yields} A single crystal GaP layer could be grown on GaN. {yields} The V/III ratio played an important role to improve GaP layer quality. {yields} The GaP:Mg layer with hole concentration of 4.2 x 10{sup 18} cm{sup -3} was obtained. -- Abstract: The performance of GaN based devices could possibly be improved by utilizing the good p-type properties of GaP layer and it provides the possibility of the integration of InAlGaN and AlGaInP materials to produce new devices, if high quality GaP compounds can be grown on III-nitride compounds. In this paper, the growth of GaP layers on GaN by metalorganic chemical vapor deposition (MOCVD) has been investigated. The results show that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature GaP growth. Using a 40 nm thick GaP buffer layer, a single crystal GaP layer, whose full-width at half-maximum of the (1 1 1) plane measured by double crystal X-ray diffraction is 580'', can be grown on GaN. The V/III ratio plays an important role in the GaP layer growth and an appropriate V/III ratio can improve the quality of GaP layer. The GaP:Mg layer with hole carrier concentration of 4.2 x 10{sup 18} cm{sup -3} has been obtained.

  4. Very strong photoluminescence emission from GaN grown on amorphous silica substrate by gas source MBE

    NASA Astrophysics Data System (ADS)

    Asahi, H.; Iwata, K.; Tampo, H.; Kuroiwa, R.; Hiroki, M.; Asami, K.; Nakamura, S.; Gonda, S.

    1999-05-01

    Polycrystalline GaN layers showing very strong photoluminescence (PL) intensities are successfully grown on amorphous fused silica (SiO 2) substrates by gas source molecular beam epitaxy (MBE) using an ion removed electron cyclotron resonance radical cell. The PL intensity is larger than that of undoped single crystalline GaN grown on sapphire by gas source MBE and is comparable to that of Si-doped single crystalline GaN grown on sapphire by metalorganic vapor-phase epitaxy at Nichia Chemical. The PL peak emission is considered to be excitonic. Undoped GaN layers grown on silica substrates exhibit n-type conduction and both n- and p-type conductions are achieved by impurity doping. These results open up the area of "Polycrystalline Semiconductor Photonics".

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

    SciTech Connect

    Prakash, Nisha Barvat, Arun; Anand, Kritika; Choursia, B.; Kushvaha, S. S.; Singh, V. N.; Pal, Prabir; Khanna, Suraj P.

    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 GaN 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.

  6. Nonpolar GaN grown on Si by hydride vapor phase epitaxy using anodized Al nanomask

    NASA Astrophysics Data System (ADS)

    Polyakov, A. Y.; Markov, A. V.; Mezhennyi, M. V.; Govorkov, A. V.; Pavlov, V. F.; Smirnov, N. B.; Donskov, A. A.; D'yakonov, L. I.; Kozlova, Y. P.; Malakhov, S. S.; Yugova, T. G.; Osinsky, V. I.; Gorokh, G. G.; Lyahova, N. N.; Mityukhlyaev, V. B.; Pearton, S. J.

    2009-01-01

    GaN growth by the hydride vapor phase technique on (100) Si substrates masked by porous Al anodic oxide is described. The masks were prepared by vacuum deposition of Al with subsequent anodic oxidation in dilute sorrel acid. The grown GaN layer is nonpolar, with (112¯0) a-orientation and a full width at half maximum of the (112¯0) reflection below 500 arc sec and showing small anisotropy. This result is comparable with the results obtained for a-GaN growth using selective epitaxy or advanced buffer growth routines. Microcathodoluminescence spectra of the grown films confirm a low density of stacking faults. Possible growth mechanisms are discussed.

  7. 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.

  8. Influence of GaN column diameter on structural properties for InGaN nanocolumns grown on top of GaN nanocolumns

    NASA Astrophysics Data System (ADS)

    Oto, Takao; Mizuno, Yutaro; Yanagihara, Ai; Miyagawa, Rin; Kano, Tatsuya; Yoshida, Jun; Sakakibara, Naoki; Kishino, Katsumi

    2016-11-01

    The influence of GaN column diameter DGaN on structural properties was systematically investigated for InGaN nanocolumns (NCs) grown on top of GaN NCs. We demonstrated a large critical layer thickness of above 400 nm for In0.3Ga0.7N/GaN NCs. The structural properties were changed at the boundary of DGaN=D0 (˜120 nm). Homogeneous InGaN NCs grew axially on the GaN NCs with DGaN≤D0, while InGaN-InGaN core-shell structures were spontaneously formed on the GaN NCs with DGaN>D0. These results can be explained by a growth system that minimizes the total strain energy of the NCs.

  9. Evaluation of GaN substrates grown in supercritical basic ammonia

    SciTech Connect

    Saito, Makoto; Yamada, Hisashi; Iso, Kenji; Sato, Hitoshi; Hirasawa, Hirohiko; Kamber, Derrick S.; Hashimoto, Tadao; Baars, Steven P. den; Speck, James S.; Nakamura, Shuji

    2009-02-02

    GaN crystals grown by the basic ammonothermal method were investigated for their use as substrates for device regrowth. X-ray diffraction analysis indicated that the substrates contained multiple grains while secondary ion mass spectroscopy (SIMS) revealed a high concentration of hydrogen, oxygen, and sodium. Despite these drawbacks, the emission from the light emitting diode structures grown by metal organic chemical vapor deposition on both the c-plane and m-plane epitaxial wafers was demonstrated. The SIMS depth profiles showed that the diffusion of the alkali metal from the substrate into the epitaxial film was small, especially in the m-direction.

  10. Far-infrared transmission in GaN, AlN, and AlGaN thin films grown by molecular beam epitaxy

    SciTech Connect

    Ibanez, J.; Hernandez, S.; Alarcon-Llado, E.; Cusco, R.; Artus, L.; Novikov, S. V.; Foxon, C. T.; Calleja, E.

    2008-08-01

    We present a far-infrared transmission study on group-III nitride thin films. Cubic GaN and AlN layers and c-oriented wurtzite GaN, AlN, and Al{sub x}Ga{sub 1-x}N (x<0.3) layers were grown by molecular beam epitaxy on GaAs and Si(111) substrates, respectively. The Berreman effect allows us to observe simultaneously the transverse optic and the longitudinal optic phonons of both the cubic and the hexagonal films as transmission minima in the infrared spectra acquired with obliquely incident radiation. We discuss our results in terms of the relevant electromagnetic theory of infrared transmission in cubic and wurtzite thin films. We compare the infrared results with visible Raman-scattering measurements. In the case of films with low scattering volumes and/or low Raman efficiencies and also when the Raman signal of the substrate material obscures the weaker peaks from the nitride films, we find that the Berreman technique is particularly useful to complement Raman spectroscopy.

  11. Cathodoluminescence of GaN nanorods and nanowires grown by thermal evaporation

    NASA Astrophysics Data System (ADS)

    Guzmán, G.; Herrera, M.

    2014-02-01

    GaN nanorods and nanowires have been grown by thermal evaporation of GaN on Au/Si (1 0 0) substrates. The nanorods recorded a surface decorated with numerous grains with an average size of about 100 nm. The nanowires grew onto the surface of the nanorods exhibiting multiple bends along them. TEM measurements revealed the formation of irregular porous and a polycrystalline structure in the nanowires with diameter higher than 100 nm, while the nanowires with lower diameter showed a tubular structure with wall thickness of 10 nm. The luminescence of the samples recorded three bands centered at about 2.1, 2.74, and 3.2 eV, attributed to the GaN yellow emission and to the blue and UV emissions of the β-Ga2O3, respectively. Ga-ion irradiation in samples revealed a decrease in the intensity of the β-Ga2O3 blue emission attributed to the elimination of gallium vacancies. A thermal annealing treatment at 800 °C in N2 atmosphere generated a quenching of the GaN yellow emission, due to the elimination of nitrogen vacancies.

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

    NASA Astrophysics Data System (ADS)

    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.

    2017-06-01

    Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n+/n0/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.

  13. Growth, nitrogen vacancy reduction, and solid solution formation in cubic GaN thin films and the subsequent fabrication of superlattice structures using AlN and InN

    NASA Astrophysics Data System (ADS)

    Davis, Robert F.; Ailey-Trent, K. S.; Kester, Daniel; Paisley, Michael J.; Perry, Bill

    1992-06-01

    Undoped GaN films have been deposited by gas-source MBE having essentially intrinsic electrical character. Acceptor-type behavior has been achieved with Mg doping. The electrical properties of these latter films were resistivity = 0.5 omega-cm, Hall mobility (holes = 10 sq cm/V-s and carrier concentration = 1(10)(exp 18) cu cm. Photo-assisted gas-source MBE growth of stoichiometric GaN was also achieved using a 500 W Hg lamp. Illumination and Ga cell temperature altered the texture of the polycrystalline GaN in unusual ways, changing the growth habit from (0001) is parallel to (100) to (0001) is parallel to (111) and back again. Thin films of cubic-BN (c-BN) were also deposited on various substrates via both gas-source MBE and electron beam MBE. The use of Si(100) substrates, the latter technique, and the characterization tools of RHEED, XPS, LEED, SEM, FTIR, and HRTEM resulted in the achievement of an initial amorphous BN layer followed by a layer of turbostratic BN and subsequently by a layer of cubic BN. Cubic BN films were also deposited on polycrystalline diamond films grown via CVD on Si(100). The effect of the bombarding species was examined. Finally, the plans for both a systematic investigation of the ion implantation and contact development and related characterization of AlN and GaN with n- and p-type dopants and the construction and employment of a UV luminescence facility is discussed.

  14. Effect of residual stress on the microstructure of GaN epitaxial films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    The stress-free GaN epitaxial films have been directly grown by pulsed laser deposition (PLD) at 850 °C, and the effect of different stress on the microstructure of as-grown GaN epitaxial films has been explored in detail. The as-grown stress-free GaN epitaxial films exhibit very smooth surface without any particles and grains, which is confirmed by the smallest surface root-mean-square roughness of 2.3 nm measured by atomic force microscopy. In addition, they also have relatively high crystalline quality, which is proved by the small full-width at half maximum values of GaN(0002) and GaN (10 1 bar 2) X-ray rocking curves as 0.27° and 0.68°, respectively. However, when the growth temperature is lower or higher than 850 °C, internal or thermal stress would be increased in as-grown GaN epitaxial films. To release the larger stress, a great number of dislocations are generated. Many irregular particulates, hexagonal GaN gains and pits are therefore produced on the films surface, and the crystalline quality is greatly reduced consequently. This work has demonstrated the direct growth of stress-free GaN epitaxial films with excellent surface morphology and high crystalline quality by PLD, and presented a comprehensive study on the origins and the effect of stress in GaN layer. It is instructional to achieve high-quality nitride films by PLD, and shows great potential and broad prospect for the further development of high-performance GaN-based devices.

  15. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AlN and InN

    DTIC Science & Technology

    1991-06-01

    p PTIC (AD-A238 521 Semi-Annual Letter Report Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the...SUBTITLE Growth, Nitrogen Vacancy Reduction and S. FUNDING NUMBERS solid Solution Formation in Cubic GaN Thin Films and the R&T:s40000lsrqO5 Subsequent

  16. GaN Quantum Dot Superlattices Grown by Molecular Beam Epitaxy at High Temperature

    SciTech Connect

    Xu,T.; Zhou, L.; Wang, Y.; Ozcan, A.; Ludwig, K.; Smith, D.; Moustakas, T.

    2007-01-01

    In this paper, we report the growth of GaN quantum dot superlattices (QDSLs) with AlN barriers on (0001) sapphire substrates by molecular beam epitaxy at relatively high temperature (770? C) using the modified Stranski-Krastanov growth mode. Observations with atomic force microscopy show that the height distribution of the dots depends strongly on the number of GaN monolayers (MLs) grown on the AlN barriers. Specifically, the height distribution consists of two Gaussian distributions (bimodal) for coverages of 3 or 4 ML, and becomes a single Gaussian distribution for 5 and 6 ML of coverage. Furthermore, the density of quantum dots increases with the degree of coverage and saturates at 2x1011?dots/cm2. An increase in the number of stacks in the superlattice structure with 4 ML coverage also leads to a more pronounced bimodal height distribution. Electron microscopy observations indicate that the GaN QDs are truncated pyramids faceted along the {l_brace}1math03{r_brace} planes and suggest that larger dots are associated with threading dislocations which presumably provide low-energy nucleation sites. Transmission electron microscopy studies also indicate that most of the larger dots are nucleated next to edge-type dislocations, while most of the smaller dots are located in dislocation-free regions. These GaN QDSLs were also studied by grazing-incidence small angle x-ray scattering and grazing-incidence x-ray diffraction methods. The average lateral deviation and the vertical correlation length between QD positions for two successive layers were determined to be 1.4?nm and 190?nm, respectively. A GaN QD growth model is proposed to explain the phenomenon.

  17. Spatial distribution of carrier concentration in un-doped GaN film grown on sapphire

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Chen, X. D.; Beling, C. D.; Fung, S.; Ling, C. C.

    2004-03-01

    The depth and lateral dependent carrier concentration of un-intentionally doped GaN film grown on sapphire substrate have been studied by temperature-dependent Hall effect measurement, confocal micro-Raman spectroscopy and capacitance-voltage (C-V) measurements. The depth-dependent free carrier concentration extracted from the depth-profiled Raman spectra confirms a non-uniform spatial distribution of free carriers in the GaN film with a highly conductive layer of 1 m thickness near the GaN/sapphire boundary. The temperature dependent Hall data have been analyzed using two-layer model to extract the carrier concentration in the GaN bulk film and in the parallel conduction channel adjacent to the GaN/sapphire boundary. The carrier concentrations of the two layers derived from the Raman technique and the Hall measurements agree with each other. The lateral-dependent carrier concentration of the 2-inch GaN epitaxial wafer has also been studied by micro-Raman spectroscopy and C-V measurements. The line-shape fitting of the Raman A1(LO) coupled modes taken from horizontal lateral-different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data are compared well with a lateral-dependent carrier concentration map of the wafer revealed by C-V measurements. The study in the article indicates that Raman spectroscopy of the LO phonon-plasmon mode can be used as a nondestructive and reliable, in situ diagnostic for GaN wafer production.

  18. Structural Defects in Laterally Overgrown GaN Layers Grown onNon-polar Substrates

    SciTech Connect

    Liliental-Weber, Z.; Ni, X.; Morkoc, H.

    2007-02-14

    Transmission electron microscopy was used to study defects in lateral epitaxial layers of GaN which were overgrown on a template of a-plane (11{und 2}0) GaN grown on (1{und 1}02) r-plane Al2O3. A high density of basal stacking faults is formed in these layers because the c-planes of wurtzite structure are arranged along the growth direction. Density of these faults is decreasing at least by two orders of magnitude lower in the wings compared to the seed areas. Prismatic stacking faults and threading dislocations are also observed, but their densities drastically decrease in the wings. The wings grow with opposite polarities and the Ga-wing width is at least 6 times larger than N-wing and coalescence is rather difficult. Some tilt and twist was detected using Large Angle Convergent Beam Electron Diffraction.

  19. High quality factor two dimensional GaN photonic crystal cavity membranes grown on silicon substrate

    NASA Astrophysics Data System (ADS)

    Vico Triviño, N.; Rossbach, G.; Dharanipathy, U.; Levrat, J.; Castiglia, A.; Carlin, J.-F.; Atlasov, K. A.; Butté, R.; Houdré, R.; Grandjean, N.

    2012-02-01

    We report on the achievement of freestanding GaN photonic crystal L7 nanocavities with embedded InGaN/GaN quantum wells grown by metal organic vapor phase epitaxy on Si (111). GaN was patterned by e-beam lithography, using a SiO2 layer as a hard mask, and usual dry etching techniques. The membrane was released by underetching the Si (111) substrate. Micro-photoluminescence measurements performed at low temperature exhibit a quality factor as high as 5200 at ˜420 nm, a value suitable to expand cavity quantum electrodynamics to the near UV and the visible range and to develop nanophotonic platforms for biofluorescence spectroscopy.

  20. Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates.

    PubMed

    Hwang, David; Yonkee, Benjamin P; Addin, Burhan Saif; Farrell, Robert M; Nakamura, Shuji; Speck, James S; DenBaars, Steven

    2016-10-03

    We demonstrate a thin-film flip-chip (TFFC) process for LEDs grown on freestanding c-plane GaN substrates. LEDs are transferred from a bulk GaN substrate to a sapphire submount via a photoelectrochemical (PEC) undercut etch. This PEC liftoff method allows for substrate reuse and exposes the N-face of the LEDs for additional roughening. The LEDs emitted at a wavelength of 432 nm with a turn on voltage of ~3 V. Etching the LEDs in heated KOH after transferring them to a sapphire submount increased the peak external quantum efficiency (EQE) by 42.5% from 9.9% (unintentionally roughened) to 14.1% (intentionally roughened).

  1. The depth-profiled carrier concentration and scattering mechanism in undoped GaN film grown on sapphire

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Chen, X. D.; Fung, S.; Beling, C. D.; Ling, C. C.; Wei, Z. F.; Xu, S. J.; Zhi, C. Y.

    2004-07-01

    Temperature-dependent Hall (TDH) measurements and confocal micro-Raman spectroscopy have been used to study the free carrier spatial distribution and scattering mechanism in unintentionally doped GaN film grown on the sapphire substrate with the method of metalorganic chemical vapor deposition. Both the TDH data and the depth-profiled Raman spectra agreed with the existence of a nonuniform spatial distribution of free carriers in the GaN film with a highly conductive layer of ˜1 μm thickness near the GaN sapphire boundary. With the consideration of this parallel conduction channel adjacent to GaN sapphire boundary, detailed analysis of the TDH mobility data suggests that a relatively high concentration of nitrogen vacancies exists and nitrogen vacancy scattering has an important influence on limiting the electron mobility in the bulk film of the present GaN sample.

  2. Surface morphology and optical properties of Eu3+ ions incorporated into N-polar GaN grown by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Fuji, Ryoken; Mitchell, Brandon; Koizumi, Atsushi; Inaba, Tomohiro; Fujiwara, Yasufumi

    2017-06-01

    N-polar GaN doped with Eu was grown by organometallic vapor phase epitaxy. Investigation of the surface morphology and photoluminescence properties indicated that Eu doping into N-polar GaN is more difficult than it is for Ga-polar GaN. The origin of this difficulty was also explored.

  3. Crystallographically tilted and partially strain relaxed GaN grown on inclined {111} facets etched on Si(100) substrate

    NASA Astrophysics Data System (ADS)

    Ansah Antwi, K. K.; Soh, C. B.; Wee, Q.; Tan, Rayson J. N.; Yang, P.; Tan, H. R.; Sun, L. F.; Shen, Z. X.; Chua, S. J.

    2013-12-01

    High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the {111} facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si{111} growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (IYL/INBE) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E2(high) optical phonon mode at 565.224 ± 0.001 cm-1 with a narrow full width at half maximum of 1.526 ± 0.002 cm-1 was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si{111} surface etched on Si(100).

  4. Crystallographically tilted and partially strain relaxed GaN grown on inclined (111) facets etched on Si(100) substrate

    SciTech Connect

    Ansah Antwi, K. K.; Soh, C. B.; Wee, Q.; Tan, Rayson J. N.; Tan, H. R.; Yang, P.; Sun, L. F.; Shen, Z. X.; Chua, S. J.

    2013-12-28

    High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the (111) facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si(111) growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (I{sub YL}/I{sub NBE}) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E{sub 2}(high) optical phonon mode at 565.224 ± 0.001 cm{sup −1} with a narrow full width at half maximum of 1.526 ± 0.002 cm{sup −1} was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si(111) surface etched on Si(100)

  5. Stress engineering in GaN structures grown on Si(111) substrates by SiN masking layer application

    SciTech Connect

    Szymański, Tomasz Wośko, Mateusz; Paszkiewicz, Bogdan; Paszkiewicz, Regina

    2015-07-15

    GaN layers without and with an in-situ SiN mask were grown by using metal organic vapor phase epitaxy for three different approaches used in GaN on silicon(111) growth, and the physical and optical properties of the GaN layers were studied. For each approach applied, GaN layers of 1.4 μm total thickness were grown, using silan SiH{sub 4} as Si source in order to grow Si{sub x}N{sub x} masking layer. The optical micrographs, scanning electron microscope images, and atomic force microscope images of the grown samples revealed cracks for samples without SiN mask, and micropits, which were characteristic for the samples grown with SiN mask. In situ reflectance signal traces were studied showing a decrease of layer coalescence time and higher degree of 3D growth mode for samples with SiN masking layer. Stress measurements were conducted by two methods—by recording micro-Raman spectra and ex-situ curvature radius measurement—additionally PLs spectra were obtained revealing blueshift of PL peak positions with increasing stress. The authors have shown that a SiN mask significantly improves physical and optical properties of GaN multilayer systems reducing stress in comparison to samples grown applying the same approaches but without SiN masking layer.

  6. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AIN and InN

    DTIC Science & Technology

    1992-02-01

    IK AD-A248 058 - - H Final Technical ReportI I Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the...structural and chemical analyses, there is no reason to believe that a homogeneous solid solution close to this composition had formed. Moreover

  7. Conductivity measurements on GaN grown by OMVPE and HVPE

    SciTech Connect

    Ben-Chorin, M.; Diener, J.; Meyer, B.K.; Drechsler, M.; Volm, D.; Amano, H.; Akasaki, I.; Detchprohm, T.; Hiramatsu, K.

    1996-11-01

    The authors report on conductance and cyclotron resonance (CR) experiments on GaN epitaxial films grown by the OMVPE and HVPE technique. From a precise determination of the electron effective mass the donor binding energy in the effective mass approximation (EMT) is calculated. The authors obtain 31.7 meV. The transport experiments on the HVPE films show that the conductance is thermally activated with an activation energy of 15 meV in contrast to the OMVPE films which showed temperature independent conductivity for temperatures between 4 and 100 K.

  8. Optical excitation of Er centers in GaN epilayers grown by MOCVD

    NASA Astrophysics Data System (ADS)

    George, D. K.; Hawkins, M. D.; Jiang, H. X.; Lin, J. Y.; Zavada, J. M.; Vinh, N. Q.

    2016-02-01

    In this paper we present results of photoluminescence (PL), photoluminescence excitation (PLE), and time resolved PL spectroscopy of the 4I13/2 → 4I15/2 transition in Er optical centers in GaN epilayers grown by metal-organic chemical vapor deposition. Under resonance excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, the PL and PLE spectra reveal an existence of two types of Er optical centers from isolated and the defect-related Er centers in GaN epilayers. These centers have different PL spectra, local defect environments, decay dynamics, and excitation cross-sections. The isolated Er optical center, which can be excited by either excitation mechanism, has the same decay dynamics, but possesses a much higher cross-section under band-to-band excitation. In contrast, the defect-related Er center can only be observed through band-to-band excitation but has the largest crosssection. Our results indicate pathways for efficient optical excitation of Er-doped GaN semiconductors.

  9. Microstructure of GaN films grown on Si(1 1 1) substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hu, G. Q.; Kong, X.; Wan, L.; Wang, Y. Q.; Duan, X. F.; Lu, Y.; Liu, X. L.

    2003-09-01

    We report the transmission electron microscopy (TEM) study of the microstructure of wurtzitic GaN films grown on Si(1 1 1) substrates with AlN buffer layers by metalorganic chemical vapor deposition (MOCVD) method. An amorphous layer was formed at the interface between Si and AlN when thick GaN film was grown. We propose the amorphous layer was induced by the large stress at the interface when thick GaN was grown. The In 0.1Ga 0.9N/GaN multiple quantum well (MQW) reduced the dislocation density by obstructing the mixed and screw dislocations from passing through the MQW. But no evident reduction of the edge dislocations by the MQW was observed. It was found that dislocations located at the boundaries of grains slightly in-plane misoriented have screw component. Inversion domain is also observed.

  10. GaN and AlGaN/GaN heterostructures grown on two dimensional BN templates

    NASA Astrophysics Data System (ADS)

    Snure, Michael; Siegel, Gene; Look, David C.; Paduano, Qing

    2017-04-01

    Two dimension materials, like BN and graphene, have been shown to be excellent templates for the growth and fabrication of freestanding III-nitride materials. In this paper we study the effects of BN morphology on GaN and AlGaN/GaN heterostructures grown on these templates. The crystallinity, transport, and optical properties of the GaN layer are examined and found to be well correlated to the BN template. The self-separation of GaN from the BN/sapphire template is also connected to morphology, resulting in freestanding GaN layers. Transport properties of Si doped GaN and AlGaN/GaN heterostructures were examined for different BN templates. The bulk GaN mobility was closely linked to the morphology of the BN template resulting in room temperature mobility from 395 to 520 cm2/Vs. The range in 3D mobility can be linked to increased dislocation densities in GaN grown on rougher BN templates. High 2DEG mobility ( 2000 cm2/Vs at 300 K) is achieved in AlGaN/GaN grown on atomically smooth BN templates, with a sheet electron density of 1×1013 cm-2, comparable to values obtained on conventional substrates. Samples grown on BN/sapphire showed mobilities (at 9 K) from 33000 cm2/Vs to 15200 cm2/Vs depending on BN roughness. The differences are associated with variations in AlGaN/GaN interface-roughness scattering and dislocation density due to the BN template morphology.

  11. Investigations about series resistance of MOVPE grown GaN laser structures

    NASA Astrophysics Data System (ADS)

    Scholz, F.; Moutchnik, G.; Dumitru, V.; Härle, R.; Schweizer, H.

    2003-02-01

    In order to reduce the total series resistance of an AlGaInN laser structure, we have exchanged the GaN:Mg contact layer normally covering a laser structure by GaInN:Mg and have investigated the influence of several growth conditions on its electrical properties. We found a significant decrease of the series resistance for a GaInN layer grown at 800°C with hydrogen as carrier gas which results, at lower current densities, in a voltage drop of at least 2 V compared to GaN contact layers. Our studies show that not only the changed growth conditions, but indeed the In content plays a major role for these improvements, although it is only about 2%. Laser structures grown on SiC wafers show minimum total differential resistivities below 1.5×10 -4 Ω cm 2.

  12. Studies of electrically and recombination active centers in undoped GaN grown by OMVPE

    SciTech Connect

    Polyakov, A.Y.; Shin, M.; Skowronski, M.; Greve, D.W.; Govorkov, A.V.; Smirnov, N.B.

    1997-12-31

    Deep centers were studied in GaN samples grown by organometallic vapor phase epitaxy (OMVPE). Electron traps 0.2 eV and 0.5 eV below conduction band edge and 0.25 eV and 0.5-0.85 eV above the valence band edge were detected by means of deep levels transient spectroscopy (DLTS), photoelectron relaxation spectroscopy (PERS) and thermally simulated current spectroscopy (TSC). The photoconductivity at low temperature is shown to be persistent and the magnitude of photosensitivity is dependent on the way the samples are grown. Microcathodoluminescence (MCL) and electron beam induced current (EBIC) measurements indicate that the density of deep recombination centers near the dislocation walls between the misoriented GaN domains is lower than inside the domains. Spatially resolved PERS measurements show that the concentration of the 0.85 eV level is higher in the low angle grain boundary regions that produce bright contrast in EBIC and MCL.

  13. Ultra-low resistance ohmic contacts to GaN with high Si doping concentrations grown by molecular beam epitaxy

    SciTech Connect

    Afroz Faria, Faiza; Guo Jia; Zhao Pei; Li Guowang; Kumar Kandaswamy, Prem; Wistey, Mark; Xing Huili; Jena, Debdeep

    2012-07-16

    Ti/Al/Ni/Au ohmic contacts were formed on heavily doped n{sup +} metal-polar GaN samples with various Si doping concentrations grown by molecular beam epitaxy. The contact resistivity (R{sub C}) and sheet resistance (R{sub sh}) as a function of corresponding GaN free carrier concentration (n) were measured. Very low R{sub C} values (<0.09 {Omega} mm) were obtained, with a minimum R{sub C} of 0.035 {Omega} mm on a sample with a room temperature carrier concentration of {approx}5 Multiplication-Sign 10{sup 19} cm{sup -3}. Based on the systematic study, the role of R{sub C} and R{sub sh} is discussed in the context of regrown n{sup +} GaN ohmic contacts for GaN based high electron mobility transistors.

  14. Maximizing cubic phase gallium nitride surface coverage on nano-patterned silicon (100)

    NASA Astrophysics Data System (ADS)

    Liu, R.; Bayram, C.

    2016-07-01

    Here we investigate the hexagonal-to-cubic phase transition in metalorganic-chemical-vapor-deposition-grown gallium nitride enabled via silicon (100) nano-patterning. Electron backscatter diffraction and depth-resolved cathodoluminescence experiments show complete cubic phase GaN surface coverage when GaN deposition thickness ( hc ), etch depth ( td ), and opening width ( p ) obey hc≈1.06 p -0.75 td ; in line with a geometrical model based on crystallography. Cubic GaN uniformity is studied via electron backscatter diffraction and cathodoluminescence measurements. Atomic force microscopy reveals a smooth cubic GaN surface. Phase-transition cubic GaN shows promising optical and structural quality for integrated photonic devices.

  15. Comparison between structural properties of bulk GaN grown under high N pressure and GaN grown by other methods

    SciTech Connect

    Liliental-Weber, Z.; Jasinski, J.; Washburn, J.

    2002-07-31

    In this paper defects formed in GaN grown by different methods are reviewed. Formation of particular defects are often related to the crystallographic direction in which the crystals grow. For bulk crystals the highest growth rates are observed for directions perpendicular to the c-axis. Threading dislocations and nanopipes along the c-axis are not formed in these crystals, but polarity of the growth direction plays a role concerning defects that are formed and surface roughness. For growth of homoepitaxial layers, where growth is forced to take place in the c-direction threading dislocations are formed and their density is related to the purity of constituents used for growth and to substrate surface inhomogeneities. In heteroepitaxial layers two other factors: lattice mismatch and thermal expansion mismatch are related to the formation of dislocations. Doping of crystals can also lead to formation of defects characteristic for a specific dopant. This type of defects tends to be growth method independent but can depend on growth polarity.

  16. 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.

  17. Semipolar (202̅1̅) GaN and InGaN Light-Emitting Diodes Grown on Sapphire.

    PubMed

    Song, Jie; Choi, Joowon; Xiong, Kanglin; Xie, Yujun; Cha, Judy J; Han, Jung

    2017-04-26

    We have demonstrated growing uniform and purely nitrogen polar semipolar (202̅1̅) GaN epilayers on 2 in. patterned sapphire substrates. The as-grown surface of (202̅1̅) GaN is composed of two stable facets: (101̅0) and (101̅1̅). A chemical mechanical polishing process was further used to planarize the surface with a final surface root-mean-square roughness of less than 1.5 nm over an area of 10 × 10 μm(2). InGaN light-emitting diodes were grown on a polished (202̅1̅) GaN/sapphire template with an electroluminescence emission at around 490 nm. Our work exhibits the potential to produce high-quality nitrogen-polar semipolar GaN templates and optoelectronic devices on large-area sapphire substrates with economical feasibility.

  18. Vacancy-type defects in bulk GaN grown by the Na-flux method probed using positron annihilation

    NASA Astrophysics Data System (ADS)

    Uedono, Akira; Imanishi, Masayuki; Imade, Mamoru; Yoshimura, Masashi; Ishibashi, Shoji; Sumiya, Masatomo; Mori, Yusuke

    2017-10-01

    Defects in bulk GaN grown by the Na-flux method have been studied using a positron annihilation technique. Pyramidal bulk samples showed striation and inhomogeneous color distributions. Measurements of the Doppler broadening spectra of the annihilation radiation and lifetime spectra of positrons revealed that the concentration of vacancy-type defects increased with decreasing transparency of the samples. The major defect species was identified as a Ga vacancy coupled with nitrogen vacancies. A correlation between the oxygen incorporation and the introduction of such vacancies was observed. For c-plane GaN grown by a coalescence growth method, the concentration of vacancy-type defects was close to or under the detection limit of positron annihilation technique (≤1015cm-3), suggesting that high-quality bulk GaN can be fabricated using this method.

  19. MBE and ALD grown High k Dielectrics Gate Stacks on GaN

    NASA Astrophysics Data System (ADS)

    Chang, Y. C.; Lee, K. Y.; Lee, W. C.; Lin, T. D.; Lee, Y. J.; Huang, M. L.; Hong, M.; Kwo, J.; Wang, Y. H.

    2007-03-01

    III-nitride compound semiconductors are attractive for high-temperature and high-power MOSFET applications due to their intrinsic properties of wide band gap, high breakdown field, and high saturation velocity under high fields. In this work GaN-based high k MOS diodes were fabricated using MBE-grown Ga2O3(Gd2O3), MBE-grown HfO2 and ALD-grown HfO2 as the gate dielectrics with dielectric constants of 14.7, 17.4 and 16.5, respectively. All MOS diodes exhibited low leakage (<10-6 A/cm^2 at Vfb+1) and well behaved capacitance-voltage curves with a low interfacial density of states of ˜10^11 cm-2eV-1. Energy-band diagrams of the MOS structures have been determined by extracting valance-band offset (δEV) from HR-XPS and with the bandgaps of the oxides. For example, the ALD-grown HfO2-GaN at the interfaces gave approximately δEC and δEV of 1.2 eV and 1.1 eV, respectively.

  20. TEM studies of laterally overgrown GaN layers grown on non-polarsubstrates

    SciTech Connect

    Liliental-Weber, Z.; Ni, X.; Morkoc, H.

    2006-01-05

    Transmission electron microscopy (TEM) was used to study pendeo-epitaxial GaN layers grown on polar and non-polar 4H SiC substrates. The structural quality of the overgrown layers was evaluated using a number of TEM methods. Growth of pendeo-epitaxial layers on polar substrates leads to better structural quality of the overgrown areas, however edge-on dislocations are found at the meeting fronts of two wings. Some misorientation between the 'seed' area and wing area was detected by Convergent Beam Electron Diffraction. Growth of pendeo-epitaxial layers on non-polar substrates is more difficult. Two wings on the opposite site of the seed area grow in two different polar directions with different growth rates. Most dislocations in a wing grown with Ga polarity are 10 times wider than wings grown with N-polarity making coalescence of these layers difficult. Most dislocations in a wing grown with Ga polarity bend in a direction parallel to the substrate, but some of them also propagate to the sample surface. Stacking faults formed on the c-plane and prismatic plane occasionally were found. Some misorientation between the wings and seed was detected using Large Angle Convergent Beam Diffraction.

  1. Electrical and structural properties of (Pd/Au) Schottky contact to as grown and rapid thermally annealed GaN grown by MBE

    SciTech Connect

    Nirwal, Varun Singh Singh, Joginder; Gautam, Khyati; Peta, Koteswara Rao

    2016-05-06

    We studied effect of thermally annealed GaN surface on the electrical and structural properties of (Pd/Au) Schottky contact to Ga-polar GaN grown by molecular beam epitaxy on Si substrate. Current voltage (I-V) measurement was used to study electrical properties while X-ray diffraction (XRD) measurement was used to study structural properties. The Schottky barrier height calculated using I-V characteristics was 0.59 eV for (Pd/Au) Schottky contact on as grown GaN, which increased to 0.73 eV for the Schottky contact fabricated on 700 °C annealed GaN film. The reverse bias leakage current at -1 V was also significantly reduced from 6.42×10{sup −5} A to 7.31×10{sup −7} A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of R{sub s} decreased from 373 Ω to 172 Ω after annealing. XRD results revealed the formation of gallide phases at the interface of (Pd/Au) and GaN for annealed sample, which could be the reason for improvement in the electrical properties of Schottky contact after annealing.

  2. Picosecond Acoustics in Single Quantum Wells of Cubic GaN /(Al ,Ga )N

    NASA Astrophysics Data System (ADS)

    Czerniuk, T.; Ehrlich, T.; Wecker, T.; As, D. J.; Yakovlev, D. R.; Akimov, A. V.; Bayer, M.

    2017-01-01

    A picosecond acoustic pulse is used to study the photoelastic interaction in single zinc-blende GaN /AlxGa1 -x N quantum wells. We use an optical time-resolved pump-probe setup and demonstrate that tuning the photon energy to the quantum well's lowest electron-hole transition makes the experiment sensitive to the quantum well only. Because of the small width, its temporal and spatial resolution allows us to track the few-picosecond-long transit of the acoustic pulse. We further deploy a model to analyze the unknown photoelastic coupling strength of the quantum well for different photon energies and find good agreement with the experiments.

  3. Thermoelectric Properties of MOVPE Grown AlInN, Lattice-Matched to GaN

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Tong, Hua; Liu, Guangyu; Herbsommer, Juan; Huang, Gensheng; Tansu, Nelson

    2010-03-01

    In this work, we investigate experimentally the growth and thermoelectric properties, i.e., thermal conductivity, Seebeck coefficient, and electrical conductivity, of n-type wurtzite high quality AlxIn1-xN, grown on GaN template on sapphire substrate by MOVPE, in-plane lattice-matched to GaN. The thermal conductivity is measured by 3φ method differential technique for thin films. The thermal conductivity value of Al0.83In0.17N is measured as 5.7 W/(mK). The Seebeck coefficient is calculated as the ratio of measured voltage difference and temperature difference when a temperature gradient is created in the sample. The absolute Seebeck coefficient value of Al0.83In0.17N is measured as 6.2x10-4 V/K. The sheet resistivity of lattice-matched Al0.83In0.17N is measured using Van der Pauw scheme and the electric conductivity is acquired accordingly to be 2.9x10^4 /(φ.m). The Z*T value of Al0.83In0.17N obtained is above 0.2 at room temperature. The results indicate AlInN based alloys are good candidates for thermoelectric devices.

  4. Nucleation mechanisms of self-induced GaN nanowires grown on an amorphous interlayer

    NASA Astrophysics Data System (ADS)

    Consonni, V.; Hanke, M.; Knelangen, M.; Geelhaar, L.; Trampert, A.; Riechert, H.

    2011-01-01

    The formation mechanisms of GaN nanowires grown on a SixNy amorphous interlayer within a self-induced approach by molecular beam epitaxy have been investigated by combining in situ reflection high-energy electron-diffraction measurements with ex situ high-resolution transmission electron microscopy imaging. It is found that GaN initially nucleates as spherical cap-shaped islands with a wetting angle of 42±7°. Subsequently, these islands coarsen and undergo a shape transition toward the nanowire morphology at an experimental critical radius of 5 nm. As the epitaxial constraint is very weak on an amorphous interlayer, the equivalent Laplace pressure due to the effects of surface stress has been taken into account. Analytical and finite-element method calculations show that the Laplace pressure results at the nanoscale dimensions in significant volume elastic strain in both spherical caps and nanowires. From thermodynamic considerations, it is revealed that the related strain energy density is slightly in favor of the shape transition toward the nanowire geometry owing to its higher ability to relieve the strain. Nevertheless, the anisotropy of surface energy is an even stronger driving force, since the nanowires are composed of c- and m-planes with very low surface energies. It is deduced that an energy barrier does exit for the shape transition and may be related to edge effects, resulting in a growth condition-dependent critical radius.

  5. Comparison of ultraviolet APDs grown on free-standing GaN and sapphire substrates

    NASA Astrophysics Data System (ADS)

    Cicek, Erdem; Vashaei, Zahra; Bayram, Can; McClintock, Ryan; Razeghi, Manijeh; Ulmer, Melville P.

    2010-08-01

    There is a need for semiconductor-based ultraviolet photodetectors to support avalanche gain in order to realize better performance andmore effective compete with existing technologies. Wide bandgap III-Nitride semiconductors are the promising material system for the development of avalanche photodiodes (APDs) that could be a viable alternative to current bulky UV detectors such as photomultiplier tubes. In this paper, we review the current state-of-the-art in IIINitride visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE.

  6. Microstructure of heteroepitaxial GaN grown on mesa-patterned 4H-SiC substrates

    NASA Astrophysics Data System (ADS)

    Bassim, N. D.; Twigg, M. E.; Eddy, C. R.; Henry, R. L.; Holm, R. T.; Culbertson, J. C.; Stahlbush, R. E.; Neudeck, P. G.; Trunek, A. J.; Powell, J. A.

    2004-06-01

    Cross-sectional transmission electron microscopy and atomic force microscopy have been used to study the microstructure of a thin heteroeptiaxial GaN film grown on (0001) 4H-SiC mesa surfaces with and without atomic scale steps. Analysis of a mesa that was completely free of atomic-scale surface steps prior to III -N film deposition showed that these GaN layers had a wide variation in island height (1-3μm ) and included the presence of pit-like defects on the film surface. This sample had a low dislocation density (5×108/cm2) as compared to conventionally grown samples on unpatterned (0001) on-axis 4H-SiC (2×109/cm2), coupled with a 3-5 times increase in grain size. A comparison of a GaN film on the step-free 4H-SiC mesa region with a GaN film on a stepped 4H-SiC mesa region on the same substrate showed that the presence of surface steps reduced the overall grain size of the film from 7-10μm to a grain size of about 2-3μm. Since the GaN films grow via a Volmer-Weber mechanism, a decrease in the number of heterogeneous nucleation sites may allow the growth of large GaN islands before coalescence, thus reducing the number of threading dislocations. These results are promising for the further development of unique, low-dislocation density active regions for GaN device structures on 4H-SiC.

  7. Annealing effect on threading dislocations in a GaN grown on Si substrate

    NASA Astrophysics Data System (ADS)

    Iwata, H.; Kobayashi, H.; Kamiya, T.; Kamei, R.; Saka, H.; Sawaki, N.; Irie, M.; Honda, Y.; Amano, H.

    2017-06-01

    Effect of rapid thermal annealing (RTA) on crystal defects in a GaN layer grown on a (111)Si substrate was investigated by photoluminescence (PL) and transmission electron microscopy (TEM) analyses. The PL spectra suggested that the density of gallium vacancy is not changed by the heat treatment up to 700 °C. In the TEM specimen, we had dislocation half loops generated by off-axis propagation of the threading dislocation. We found that the half-loop of c-type dislocation shrinks/moves by a repetitive RTA at 600-700 °C. In contrast, we could find no remarkable changes in the a-type or a+c-type dislocations.

  8. Near-ultraviolet micro-Raman study of diamond grown on GaN

    SciTech Connect

    Nazari, M. Hancock, B. L.; Anderson, J.; Savage, A.; Piner, E. L.; Holtz, M.; Graham, S.; Faili, F.; Oh, S.; Francis, D.; Twitchen, D.

    2016-01-18

    Ultraviolet (UV) micro-Raman measurements are reported of diamond grown on GaN using chemical vapor deposition. UV excitation permits simultaneous investigation of the diamond (D) and disordered carbon (DC) comprising the polycrystalline layer. From line scans of a cross-section along the diamond growth direction, the DC component of the diamond layer is found to be highest near the GaN-on-diamond interface and diminish with characteristic length scale of ∼3.5 μm. Transmission electron microscopy (TEM) of the diamond near the interface confirms the presence of DC. Combined micro-Raman and TEM are used to develop an optical method for estimating the DC volume fraction.

  9. Strain Relief Analysis of InN Quantum Dots Grown on GaN

    PubMed Central

    2007-01-01

    We present a study by transmission electron microscopy (TEM) of the strain state of individual InN quantum dots (QDs) grown on GaN substrates. Moiré fringe and high resolution TEM analyses showed that the QDs are almost fully relaxed due to the generation of a 60° misfit dislocation network at the InN/GaN interface. By applying the Geometric Phase Algorithm to plan-view high-resolution micrographs, we show that this network consists of three essentially non-interacting sets of misfit dislocations lying along the directions. Close to the edge of the QD, the dislocations curve to meet the surface and form a network of threading dislocations surrounding the system. PMID:21794190

  10. Morphology Control of Hot-Wall MOCVD Selective Area Grown Hexagonal GaN Pyramids

    NASA Astrophysics Data System (ADS)

    Lundskog, Anders; Forsberg, Urban; Holtz, Per Olof; Janzen, Erik

    2012-11-01

    Morphological variations of gallium polar (0001)-oriented hexagonal GaN pyramids grown by hot wall metal organic chemical vapor deposition under various growth conditions are investigated. The stability of the semipolar {1 (1) over bar 02} and nonpolar {1 (1) over bar 00} facets is particularly discussed. The presence of the {1 (1) over bar 02} facets near the apex of the pyramid was found to be controllable by tuning the absolute flow rate of ammonia during the growth Vertical nonpolar {1 (1) over bar 00} facets appeared in gallium rich conditions, which automatically were created when the growth time was prolonged beyond pyramid completion. The result was attributed to a gallium passivation of the {1 (1) over bar 00} surface.

  11. Realization of compressively strained GaN films grown on Si(110) substrates by inserting a thin AlN/GaN superlattice interlayer

    SciTech Connect

    Shen, X. Q.; Takahashi, T.; Kawashima, H.; Ide, T.; Shimizu, M.

    2012-07-16

    We investigate the strain properties of GaN films grown by plasma-assisted molecular beam epitaxy on Si(110) substrates. It is found that the strain of the GaN film can be converted from a tensile to a compressive state simply by inserting a thin AlN/GaN superlattice structure (SLs) within the GaN film. The GaN layers seperated by the SLs can have different strain states, which indicates that the SLs plays a key role in the strain modulation during the growth and the cooling down processes. Using this simple technique, we grow a crack-free GaN film exceeding 2-{mu}m-thick. The realization of the compressively strained GaN film makes it possible to grow thick GaN films without crack generation on Si substrates for optic and electronic device applications.

  12. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AlN and InN

    DTIC Science & Technology

    1992-06-01

    AD-A253 331 Semiannual Report Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication...Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using...34 substrates, such as using a graded AlxGal-xN solid solution as a buffer layer. E. Conclusion We have shown that in the use of our modified gas source MBE

  13. Hydride-vapor-phase epitaxial growth of highly pure GaN layers with smooth as-grown surfaces on freestanding GaN substrates

    NASA Astrophysics Data System (ADS)

    Fujikura, Hajime; Konno, Taichiro; Yoshida, Takehiro; Horikiri, Fumimasa

    2017-08-01

    Thick (20-30 µm) layers of highly pure GaN with device-quality smooth as-grown surfaces were prepared on freestanding GaN substrates by using our advanced hydride-vapor-phase epitaxy (HVPE) system. Removal of quartz parts from the HVPE system markedly reduced concentrations of residual impurities to below the limits of detection by secondary-ion mass spectrometry. Appropriate gas-flow management in the HVPE system realized device-quality, smooth, as-grown surfaces with an excellent uniformity of thickness. The undoped GaN layer showed insulating properties. By Si doping, the electron concentration could be controlled over a wide range, down to 2 × 1014 cm-3, with a maximum mobility of 1150 cm2·V-1·s-1. The concentration of residual deep levels in lightly Si-doped layers was in the 1014 cm-3 range or less throughout the entire 2-in. wafer surface. These achievements clearly demonstrate the potential of HVPE as a tool for epitaxial growth of power-device structures.

  14. As-grown deep-level defects in n-GaN grown by metal-organic chemical vapor deposition on freestanding GaN

    SciTech Connect

    Chen Shang; Ishikawa, Kenji; Hori, Masaru; Honda, Unhi; Shibata, Tatsunari; Matsumura, Toshiya; Tokuda, Yutaka; Ueda, Hiroyuki; Uesugi, Tsutomu; Kachi, Tetsu

    2012-09-01

    Traps of energy levels E{sub c}-0.26 and E{sub c}-0.61 eV have been identified as as-grown traps in n-GaN grown by metal-organic chemical vapor deposition by using deep level transient spectroscopy of the Schottky contacts fabricated by resistive evaporation. The additional traps of E{sub c}-0.13 and E{sub c}-0.65 eV have been observed in samples whose contacts are deposited by electron-beam evaporation. An increase in concentration of the E{sub c}-0.13 and E{sub c}-0.65 eV traps when approaching the interface between the contact and the GaN film supports our argument that these traps are induced by electron-beam irradiation. Conversely, the depth profiles of as-grown traps show different profiles between several samples with increased or uniform distribution in the near surface below 50 nm. Similar profiles are observed in GaN grown on a sapphire substrate. We conclude that the growth process causes these large concentrations of as-grown traps in the near-surface region. It is speculated that the finishing step in the growth process should be an essential issue in the investigation of the surface state of GaN.

  15. Strong coupling of light with A and B excitons in GaN microcavities grown on silicon

    SciTech Connect

    Sellers, I. R.; Semond, F.; Leroux, M.; Massies, J.; Disseix, P.; Henneghien, A-L.; Leymarie, J.; Vasson, A.

    2006-01-15

    We present experimental results demonstrating strong-light matter coupling at low and room temperature in bulk GaN microcavities with epitaxial (Al,Ga)N Bragg mirrors grown on silicon (111). At low temperature, the strong coupling of both the A and B excitonic features of GaN with the cavity mode is clearly resolved in the microcavity. At room temperature a Rabi energy of 50 meV is observed and well reproduced using transfer-matrix reflectivity calculations describing the interaction of both the A and B excitonic states with the photonic mode.

  16. GaN based LEDs with semipolar QWs employing embedded sub-micrometer sized selectively grown 3D structures

    NASA Astrophysics Data System (ADS)

    Leute, R. A. R.; Heinz, D.; Wang, J.; Lipski, F.; Meisch, T.; Thonke, K.; Thalmair, J.; Zweck, J.; Scholz, F.

    2013-05-01

    We present LED structures with embedded semipolar {101¯1} quantum wells based on 2-inch c-plane GaN templates grown on c-plane sapphire substrates. Using selective area epitaxy, we achieved periodic GaN stripe structures with triangular cross-section with dimensions of a few 100 nm on continuous areas of several cm2. These structures exhibit semipolar side facets on which GaInN quantum wells with reduced piezoelectric fields have been deposited. The small dimensions of these structures allow complete embedding by GaN cladding layers eventually resulting in a flat c-plane surface. Consequently, our approach allows conventional device processing to be applied. Structural, optical, and electrical characterization is presented and the influence of mask material and pattern on the performances of LED structures is investigated.

  17. Low-dislocation-density, nonplanar GaN templates for buried heterostructure lasers grown by lateral epitaxial overgrowth

    NASA Astrophysics Data System (ADS)

    Ren, Dawei; Zhou, Wei; Dapkus, P. Daniel

    2005-03-01

    We report here the formation of nonplanar GaN templates, which consist of low-dislocation-density, naturally grown GaN ridge mesas, as a mean to facilitate the fabrication of buried heterostructure lasers. Defect reduction is realized by introducing a two-step lateral epitaxial overgrowth procedure that utilizes dislocation bending in the formation of pyramidal mesas to eradicate the threading dislocations that originate from a planar buffer layer. Transmission electron microscopy and atomic force microscopy indicate a mesa top facet having low defect density (˜8×107cm-2), atomic flatness (˜0.29nm mean roughness). Our demonstration has opened the possibility of forming buried heterostructure lasers on nonplanar GaN templates.

  18. Some of structural and morphological optimization of GaN thin film on Si(100) substrate grown by RF sputter

    NASA Astrophysics Data System (ADS)

    Mantarcı, Asim; Kundakçı, Mutlu

    2017-04-01

    One of important material of III-nitrides can be said to be GaN with direct-wide band gap ( 3.4 eV) and many industrial devices such as solar cell, LED has been based on GaN thin film. In this research, we elaborately investigated growth of GaN thin film on Si(100) substrate by RF sputter technique and characterization of the film. We have successfully grown GaN thin film on Si substrate with hexagonal structure which has been confirmed by analysis of X-ray measurements. Also, we obtained structural properties of GaN film by (XRD) X-ray Diffraction measurements depending on different Argon, nitrogen and RF power values. During experiment, the value from 25sccm to 100sccm Argon gas value, the value from 0sccm to 4sccm Nitrogen gas value and from 50 watt to 125 watt RF power value has been applied. Among these values, we determined the best film in terms of crystalline structure of film. From AFM results, we attained and analyzed average roughness (Ra), maximum peak height (Rp), and maximum depth (Rv), average absolute slope of the profile (Δa)(°) of the fılms successfully. The film having the lowest roughness (Ra) has been achieved depending on different Argon, nitrogen and RF power values. Atomic Force Microscopy results confirmed that some of the films have homogeneous and uniform structure without any holes and crack; but others has voids referring impurities coming from growth process. To sum up, not only growing GaN thin film on Si substrate has been investigated, but also some of structural and morphological parameters' optimization has been studied, analyzed and the best film was determined in view of varied Argon, nitrogen and RF power values. For future direction, optimization of GaN thin film in detail can enable us to fabricate high quality film; therefore it will helps to improving device technology.

  19. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions

    NASA Astrophysics Data System (ADS)

    Aseev, P.; Gačević, Ž.; Torres-Pardo, A.; González-Calbet, J. M.; Calleja, E.

    2016-06-01

    Series of GaN nanowires (NW) with controlled diameters (160-500 nm) and heights (420-1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established.

  20. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions

    SciTech Connect

    Aseev, P. E-mail: gacevic@isom.upm.es; Gačević, Ž. E-mail: gacevic@isom.upm.es; Calleja, E.

    2016-06-20

    Series of GaN nanowires (NW) with controlled diameters (160–500 nm) and heights (420–1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established.

  1. Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy

    SciTech Connect

    Duc, Tran Thien; Pozina, Galia; Son, Nguyen Tien; Janzén, Erik; Hemmingsson, Carl; Ohshima, Takeshi

    2014-09-08

    Defects induced by electron irradiation in thick free-standing GaN layers grown by halide vapor phase epitaxy were studied by deep level transient spectroscopy. In as-grown materials, six electron traps, labeled D2 (E{sub C}–0.24 eV), D3 (E{sub C}–0.60 eV), D4 (E{sub C}–0.69 eV), D5 (E{sub C}–0.96 eV), D7 (E{sub C}–1.19 eV), and D8, were observed. After 2 MeV electron irradiation at a fluence of 1 × 10{sup 14 }cm{sup −2}, three deep electron traps, labeled D1 (E{sub C}–0.12 eV), D5I (E{sub C}–0.89 eV), and D6 (E{sub C}–1.14 eV), were detected. The trap D1 has previously been reported and considered as being related to the nitrogen vacancy. From the annealing behavior and a high introduction rate, the D5I and D6 centers are suggested to be related to primary intrinsic defects.

  2. Ultraviolet InGaN and GaN Single-Quantum-Well-Structure Light-Emitting Diodes Grown on Epitaxially Laterally Overgrown GaN Substrates

    NASA Astrophysics Data System (ADS)

    Mukai, Takashi; Nakamura, Shuji

    1999-10-01

    Ultraviolet (UV) InGaN and GaN single-quantum-well-structure light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. When the emission wavelength of UV InGaN LEDs was shorter than 380 nm, the external quantum efficiency (EQE) of the LED on ELOG was much higher than that on sapphire only under high-current operation. At low-current operation, both LEDs had the same EQE. When the active layer was GaN, EQE of the LED on sapphire was much lower than that on ELOG even under low-and high-current operations, due to the lack of localized energy states formed by alloy composition fluctuations. When the emission wavelengths were in the blue and green regions, EQE was almost the same between LEDs on both ELOG and sapphire due to a large number of deep localized energy states formed by large alloy composition fluctuations. The localized energy states are responsible for the high efficiency of InGaN-based LEDs in spite of a large number of dislocations.

  3. Characterization of mid-gap states in HVPE and MOVPE-grown n-type GaN

    NASA Astrophysics Data System (ADS)

    Hacke, P.; Okushi, H.; Kuroda, T.; Detchprohm, T.; Hiramatsu, K.; Sawaki, N.

    1998-06-01

    Optical-isothermal capacitance transient spectroscopy (O-ICTS) is used to characterize the mid-gap states in n-type GaN grown by hydride vapor phase epitaxy and metalorganic vapor phase epitaxy. Deep levels are resolved by the emission rate of carries in addition to the magnitude of the capacitance transient as a function of incident photon energy. The mid-gap region is dominated by a distribution of traps from which carriers photoionize to the conduction band in the range of about 1.5 to 2.5 eV; these traps are suspected of participating in the frequently observed yellow luminescence. The concentration of these mid-gap states are found to be lowest in thick HVPE-grown GaN films.

  4. Structure and morphology characters of GaN grown by ECR-MBE using hydrogen-nitrogen mixed gas plasma[Electron Cyclotron Resonance-Molecular Beam Epitaxy

    SciTech Connect

    Araki, Tsutomu; Chiba, Yasuo; Nanishi, Yasushi

    2000-07-01

    GaN growth by electron-cyclotron-resonance plasma-excited molecular beam epitaxy using hydrogen-nitrogen mixed gas plasma were carried out on GaN templates with a different polar-surface. Structure and surface morphology of the GaN layers were characterized using transmission electron microscopy. The GaN layer grown with hydrogen on N-polar template showed a relatively flat morphology including hillocks. Columnar domain existed in the center of the hillock, which might be attributed to the existence of tiny inversion domain with Ga-polarity. On the other hand, columnar structure was formed in the GaN layer grown with hydrogen on Ga-polar template.

  5. Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy

    SciTech Connect

    Wang, X. Q.; Sun, H. P.; Pan, X. Q.

    2010-10-11

    Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.

  6. Sub-230 nm deep-UV emission from GaN quantum disks in AlN grown by a modified Stranski-Krastanov mode

    NASA Astrophysics Data System (ADS)

    Islam, SM; Protasenko, Vladimir; Rouvimov, Sergei; (Grace Xing, Huili; Jena, Debdeep

    2016-05-01

    We report tunable deep-ultraviolet (DUV) emission over the 222-231 nm range from 1-2 monolayer (ML) GaN quantum disks (QDs) grown in an AlN matrix. The linewidth of the emission were as narrow as ˜10 nm at 5 K. The disks were grown in modified Stranski-Krastanov (mSK) mode. High resolution scanning transmission electron microscopy (STEM) images confirmed insertion of 1-2 MLs of GaN between 3 nm AlN barriers. The internal quantum efficiency was estimated from low temperature photoluminescence measurements for the disks, and compared with 1 and 2 ML GaN quantum wells/AlN barriers. The internal quantum efficiency (IQE) of the GaN QDs was found to be ˜35% for 222 nm emission, ˜200% higher than 1 ML GaN QWs.

  7. Deep Level Donor-like Centers in MOCVD-grown n-type GaN

    NASA Astrophysics Data System (ADS)

    Ahoujja, Mo; Yeo, Y. K.; Hengehold, R. L.; Johnstone, D. K.

    2002-03-01

    Defects in semiconductors are of high importance because they adversely affect device performance. For example, defects may act as carrier trap and generation centers which may lead to premature current leakage, and they may also act as non-radiative recombination centers that may reduce the quantum efficiency of electro-optical devices. Therefore understanding the dynamical properties of deep level defects is an important step toward improving device performance. In this work, deep level defects in GaN grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD) have been investigated using isothermal capacitance transient spectroscopy (ICTS) and current voltage temperature (IVT) measurements. ICTS analyses show that there are two deep levels of E3 and E4 with emission activation energies of 0.55 and 0.61 eV below the conduction band, respectively, at room temperature. The E4 trap center was found to be the most dominant defect having a larger cross section, smaller capture barrier, and higher concentration. The results from the I-V-T measurements show that this deep center is at about 0.54 eV below the conduction band, and decreases with increasing reverse bias voltage, indicating characteristics of a center with a donor nature. Further analyses of the trap filling dynamics reveal a coupled behavior nature between E3 and E4 traps.

  8. Enhanced Ferromagnetism in Nanoscale GaN:Mn Wires Grown on GaN Ridges.

    PubMed

    Cheng, Ji; Jiang, Shengxiang; Zhang, Yan; Yang, Zhijian; Wang, Cunda; Yu, Tongjun; Zhang, Guoyi

    2017-05-02

    The problem of weak magnetism has hindered the application of magnetic semiconductors since their invention, and on the other hand, the magnetic mechanism of GaN-based magnetic semiconductors has been the focus of long-standing debate. In this work, nanoscale GaN:Mn wires were grown on the top of GaN ridges by metalorganic chemical vapor deposition (MOCVD), and the superconducting quantum interference device (SQUID) magnetometer shows that its ferromagnetism is greatly enhanced. Secondary ion mass spectrometry (SIMS) and energy dispersive spectroscopy (EDS) reveal an obvious increase of Mn composition in the nanowire part, and transmission electron microscopy (TEM) and EDS mapping results further indicate the correlation between the abundant stacking faults (SFs) and high Mn doping. When further combined with the micro-Raman results, the magnetism in GaN:Mn might be related not only to Mn concentration, but also to some kinds of built-in defects introduced together with the Mn doping or the SFs.

  9. Enhanced Ferromagnetism in Nanoscale GaN:Mn Wires Grown on GaN Ridges

    PubMed Central

    Cheng, Ji; Jiang, Shengxiang; Zhang, Yan; Yang, Zhijian; Wang, Cunda; Yu, Tongjun; Zhang, Guoyi

    2017-01-01

    The problem of weak magnetism has hindered the application of magnetic semiconductors since their invention, and on the other hand, the magnetic mechanism of GaN-based magnetic semiconductors has been the focus of long-standing debate. In this work, nanoscale GaN:Mn wires were grown on the top of GaN ridges by metalorganic chemical vapor deposition (MOCVD), and the superconducting quantum interference device (SQUID) magnetometer shows that its ferromagnetism is greatly enhanced. Secondary ion mass spectrometry (SIMS) and energy dispersive spectroscopy (EDS) reveal an obvious increase of Mn composition in the nanowire part, and transmission electron microscopy (TEM) and EDS mapping results further indicate the correlation between the abundant stacking faults (SFs) and high Mn doping. When further combined with the micro-Raman results, the magnetism in GaN:Mn might be related not only to Mn concentration, but also to some kinds of built-in defects introduced together with the Mn doping or the SFs. PMID:28772843

  10. Optical properties of C-doped bulk GaN wafers grown by halide vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Khromov, S.; Hemmingsson, C.; Monemar, B.; Hultman, L.; Pozina, G.

    2014-12-01

    Freestanding bulk C-doped GaN wafers grown by halide vapor phase epitaxy are studied by optical spectroscopy and electron microscopy. Significant changes of the near band gap (NBG) emission as well as an enhancement of yellow luminescence have been found with increasing C doping from 5 × 1016 cm-3 to 6 × 1017 cm-3. Cathodoluminescence mapping reveals hexagonal domain structures (pits) with high oxygen concentrations formed during the growth. NBG emission within the pits even at high C concentration is dominated by a rather broad line at ˜3.47 eV typical for n-type GaN. In the area without pits, quenching of the donor bound exciton (DBE) spectrum at moderate C doping levels of 1-2 × 1017 cm-3 is observed along with the appearance of two acceptor bound exciton lines typical for Mg-doped GaN. The DBE ionization due to local electric fields in compensated GaN may explain the transformation of the NBG emission.

  11. Study of InN epitaxial films and nanorods grown on GaN template by RF-MOMBE

    PubMed Central

    2012-01-01

    This paper reports on high-quality InN materials prepared on a GaN template using radio-frequency metalorganic molecular beam epitaxy. We also discuss the structural and electro-optical properties of InN nanorods/films. The X-ray diffraction peaks of InN(0002) and InN(0004) were identified from their spectra, indicating that the (0001)-oriented hexagonal InN was epitaxially grown on the GaN template. Scanning electron microscopic images of the surface morphology revealed a two-dimensional growth at a rate of approximately 0.85 μm/h. Cross-sectional transmission electron microscopy images identified a sharp InN/GaN interface and a clear epitaxial orientation relationship of [0001]InN // [0001]GaN and ( 2¯110)InN // ( 2¯110)GaN. The optical properties of wurtzite InN nanorods were determined according to the photoluminescence, revealing a band gap of 0.77 eV. PMID:22908859

  12. Optical properties of C-doped bulk GaN wafers grown by halide vapor phase epitaxy

    SciTech Connect

    Khromov, S.; Hemmingsson, C.; Monemar, B.; Hultman, L.; Pozina, G.

    2014-12-14

    Freestanding bulk C-doped GaN wafers grown by halide vapor phase epitaxy are studied by optical spectroscopy and electron microscopy. Significant changes of the near band gap (NBG) emission as well as an enhancement of yellow luminescence have been found with increasing C doping from 5 × 10{sup 16} cm{sup −3} to 6 × 10{sup 17} cm{sup −3}. Cathodoluminescence mapping reveals hexagonal domain structures (pits) with high oxygen concentrations formed during the growth. NBG emission within the pits even at high C concentration is dominated by a rather broad line at ∼3.47 eV typical for n-type GaN. In the area without pits, quenching of the donor bound exciton (DBE) spectrum at moderate C doping levels of 1–2 × 10{sup 17} cm{sup −3} is observed along with the appearance of two acceptor bound exciton lines typical for Mg-doped GaN. The DBE ionization due to local electric fields in compensated GaN may explain the transformation of the NBG emission.

  13. III-nitride heterostructure field-effect transistors grown on semi-insulating GaN substrate without regrowth interface charge

    NASA Astrophysics Data System (ADS)

    Liu, J. P.; Ryou, J.-H.; Yoo, D.; Zhang, Y.; Limb, J.; Horne, C. A.; Shen, S.-C.; Dupuis, R. D.; Hanser, A. D.; Preble, E. A.; Evans, K. R.

    2008-03-01

    Charge is observed at the regrowth interface for heterostructure field-effect transistors (HFETs) grown on semi-insulating (SI) bulk GaN substrates, even with Fe doping in the regrown buffer layer for reduction of the interface charge. Ultraviolet photoenhanced chemical (PEC) etching is used to treat the surface of SI bulk GaN substrates. Employing optimized etching conditions, a very smooth surface is achieved for the bulk GaN substrate after the etching. The charge at the regrowth interface is eliminated for HFETs grown on etched SI GaN substrates. Secondary ion mass spectrometry measurements show that the Si impurity concentration at the regrowth interface for HFETs grown on etched SI GaN substrates is much lower than that for HFETs grown on unetched SI GaN substrates, which suggests that the charge-containing layer on the SI substrate is removed by PEC etching and that the effects of the reduced charge layer near the regrowth interface can be eliminated by Fe doping for HFETs grown on etched SI substrates.

  14. Polarity control of GaN grown on pulsed-laser-deposited AlN/GaN template by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Yoo, Jinyeop; Shojiki, Kanako; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Hanada, Takashi; Katayama, Ryuji; Matsuoka, Takashi

    2016-05-01

    We report on the polarity control of GaN regrown on pulsed-laser-deposition-grown N-polar AlN on a metalorganic-vapor-phase-epitaxy-grown Ga-polar GaN template. The polarity of the regrown GaN, which was confirmed using aqueous KOH solutions, can be inverted from that of AlN by inserting a low-temperature GaN (LT-GaN) buffer layer. We hypothetically ascribe the Ga-polarity selection of GaN on the LT-GaN buffer layer to the mixed polarity of LT-GaN grains and higher growth rate of the Ga-polar grain, which covers up the N-polar grain during the initial stage of the high-temperature growth. The X-ray rocking curve analysis revealed that the edge-dislocation density in the N-polar regrown GaN is 5 to 8 times smaller than that in the Ga-polar regrown GaN. N-polar GaN grows directly on N-polar AlN at higher temperatures. Therefore, nucleus islands grow larger than those of LT-GaN and the area fraction of coalescence boundaries between islands, where edge dislocations emerge, becomes smaller.

  15. 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

  16. Step-induced misorientation of GaN grown on r-plane sapphire

    SciTech Connect

    Smalc-Koziorowska, J.; Dimitrakopulos, G. P.; Sahonta, S.-L.; Komninou, Ph.; Tsiakatouras, G.; Georgakilas, A.

    2008-07-14

    In the growth of nonpolar (1120) a-plane GaN on r-plane (1102) sapphire by plasma-assisted molecular beam epitaxy, misoriented crystallites are observed close to the substrate. They have average diameter {approx}10 nm and are oriented with the (0001){sub GaN} plane approximately parallel to the (2113){sub sapph.} plane and [0110]{sub GaN} parallel [1101]{sub sapph.}. This semipolar orientation is promoted by a low misfit (2.4%) between (1011){sub GaN} and (1210){sub sapph.} planes. Its introduction, after nitridation treatment, is due to GaN nucleation on (2113){sub sapph.} step facets inclined at 26 deg. relative to the r-plane. Two variants are observed, leading to twinning when they abut inside the epilayer.

  17. 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.

  18. Multiple delta doping of single crystal cubic boron nitride films heteroepitaxially grown on (001)diamonds

    SciTech Connect

    Yin, H.; Ziemann, P.

    2014-06-23

    Phase pure cubic boron nitride (c-BN) films have been epitaxially grown on (001) diamond substrates at 900 °C. The n-type doping of c-BN epitaxial films relies on the sequential growth of nominally undoped (p-) and Si doped (n-) layers with well-controlled thickness (down to several nanometer range) in the concept of multiple delta doping. The existence of nominally undoped c-BN overgrowth separates the Si doped layers, preventing Si dopant segregation that was observed for continuously doped epitaxial c-BN films. This strategy allows doping of c-BN films can be scaled up to multiple numbers of doped layers through atomic level control of the interface in the future electronic devices. Enhanced electronic transport properties with higher hall mobility (10{sup 2} cm{sup 2}/V s) have been demonstrated at room temperature as compared to the normally continuously Si doped c-BN films.

  19. Multiple delta doping of single crystal cubic boron nitride films heteroepitaxially grown on (001)diamonds

    NASA Astrophysics Data System (ADS)

    Yin, H.; Ziemann, P.

    2014-06-01

    Phase pure cubic boron nitride (c-BN) films have been epitaxially grown on (001) diamond substrates at 900 °C. The n-type doping of c-BN epitaxial films relies on the sequential growth of nominally undoped (p-) and Si doped (n-) layers with well-controlled thickness (down to several nanometer range) in the concept of multiple delta doping. The existence of nominally undoped c-BN overgrowth separates the Si doped layers, preventing Si dopant segregation that was observed for continuously doped epitaxial c-BN films. This strategy allows doping of c-BN films can be scaled up to multiple numbers of doped layers through atomic level control of the interface in the future electronic devices. Enhanced electronic transport properties with higher hall mobility (102 cm2/V s) have been demonstrated at room temperature as compared to the normally continuously Si doped c-BN films.

  20. Deep traps in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Zhang, Z.; Hurni, C. A.; Arehart, A. R.; Yang, J.; Myers, R. C.; Speck, J. S.; Ringel, S. A.

    2012-01-01

    Deep level defects in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy were characterized using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) and compared with polar c-plane GaN that was grown simultaneously in the same growth run. Significant differences in both the levels present and their concentrations were observed upon comparison of both growth orientations. DLTS revealed electron traps with activation energies of 0.14 eV, 0.20 eV, and 0.66 eV in the m-plane material, with concentrations that were ˜10-50 × higher than traps of similar activation energies in the c-plane material. Likewise, DLOS measurements showed ˜20 × higher concentrations of both a CN acceptor-like state at EC - 3.26 eV, which correlates with a high background carbon concentration observed by secondary ion mass spectroscopy for the m-plane material [A. Armstrong, A. R. Arehart, B. Moran, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. A. Ringel, Appl. Phys. Lett. 84, 374 (2004)], and the VGa-related state level at EC - 2.49 eV, which is consistent with an enhanced yellow luminescence observed by photoluminescence. The findings suggest a strong impact of growth dynamics on the incorporation of impurities and electrically active native point defects as a function of GaN growth plane polarity.

  1. In Situ Oxidation of GaN Layer and Its Effect on Structural Properties of Ga2O3 Films Grown by Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Ngo, Trong Si; Le, Duc Duy; Tran, Duy Khanh; Song, Jung-Hoon; Hong, Soon-Ku

    2017-06-01

    Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [11\\overline{2} 0] Al2O3//[1\\overline{1} 00] AlN//[1\\overline{1} 00] GaN//[102] β-Ga2O3 and [1\\overline{1} 00] Al2O3//[11\\overline{2} 0] AlN//[11\\overline{2} 0] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (\\overline{2} 01) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

  2. In Situ Oxidation of GaN Layer and Its Effect on Structural Properties of Ga2O3 Films Grown by Plasma-Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Ngo, Trong Si; Le, Duc Duy; Tran, Duy Khanh; Song, Jung-Hoon; Hong, Soon-Ku

    2017-01-01

    Plasma-assisted molecular beam epitaxy (PAMBE) was used to grow Ga2O3 films on oxidized GaN layers on nitrided sapphire substrates. The GaN layer was grown by PAMBE, and the in situ oxidation of the GaN layer was achieved through exposure to oxygen plasma, which resulted in the formation of monoclinic β-Ga2O3. Crystalline monoclinic β-Ga2O3 films were grown on the GaN layers, with and without oxidation. The orientation relationships were [11overline{2} 0 ] Al2O3//[1overline{1} 00 ] AlN//[1overline{1} 00 ] GaN//[102] β-Ga2O3 and [1overline{1} 00 ] Al2O3//[11overline{2} 0 ] AlN//[11overline{2} 0 ] GaN//[010] β-Ga2O3. The grown β-Ga2O3 films were not single-crystalline but showed rotational domains along the growth direction with three variations, which resulted in six-fold rotational symmetry instead of two-fold rotational symmetry. The surface roughness of the grown β-Ga2O3 film was closely reflected to that of as-grown GaN and oxidized GaN. By analyzing the x-ray omega rocking curves for the on-axis (overline{2} 01 ) and off-axis (002) reflections, it was concluded that rotational domains dominantly affected the crystal quality of the β-Ga2O3 films.

  3. Polarization-resolved photoluminescence study of individual GaN nanowires grown by catalyst-free molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schlager, John B.; Sanford, Norman A.; Bertness, Kris A.; Barker, Joy M.; Roshko, Alexana; Blanchard, Paul T.

    2006-05-01

    Polarization- and temperature-dependent photoluminescence (PL) measurements were performed on individual GaN nanowires. These were grown by catalyst-free molecular beam epitaxy on Si(111) substrates, ultrasonically removed, and subsequently dispersed on sapphire substrates. The wires were typically 5-10μm in length, c-axis oriented, and 30-100nm in diameter. Single wires produced sufficient emission intensity to enable high signal-to-noise PL data. Polarized PL spectra differed for the σ and π polarization cases, illustrating the polarization anisotropy of the exciton emission associated with high-quality wurtzite GaN. This anisotropy in PL emission persisted even up to room temperature (4-296K). Additionally, the nanowire PL varied with excitation intensity and with (325nm) pump exposure time.

  4. Novel fully vertical GaN p-n diode on Si substrate grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Mase, Suguru; Urayama, Yuya; Hamada, Takeaki; Freedsman, Joseph J.; Egawa, Takashi

    2016-11-01

    We report novel GaN fully vertical p-n diode on Si grown by metalorganic chemical vapor deposition. The thick strained layer superlattice is effective in controlling a doping level of 1016 cm-3 in an n--GaN drift layer. The GaN p-n diode exhibits a differential on-resistance R on of 7.4 mΩ cm2, a turn-on voltage of 3.4 V, and a breakdown voltage V B of 288 V. The corresponding Baliga’s figure of merit (FOM) V\\text{B}2/R\\text{on} is 11.2 MW/cm2. A good FOM value for the GaN-on-Si vertical p-n diode is realized for a drift layer thickness of 1.5 µm without using substrate removal technology.

  5. Bending stability of GaN grown on a metallic flexible substrate by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Rodríguez, A. G.; Chávez-Veloz, S. G.; Compeán-García, V. D.; López-Luna, E.; Vidal, M. A.

    2017-08-01

    GaN thin films were grown on flexible metallic substrates by molecular beam epitaxy. MgO buffer layers were deposited by spin coating on Ni-Mo-Cr (Hastelloy C-276) alloy tapes that were used as substrates. The structural characterization of the GaN/MgO/hastelloy samples was performed by x-ray diffraction and Raman spectroscopy. The obtained nanometric films have the stable hexagonal phase (α-GaN) with an average crystallite size of 18 nm. The long and short range order of GaN decrease when the structure is bent. The most significant variations in the structural properties occur between 100 and 250 bending cycles.

  6. Study of carrier recombination transient characteristics in MOCVD grown GaN dependent on layer thickness

    SciTech Connect

    Gaubas, E. Čeponis, T.; Jasiunas, A.; Jelmakas, E.; Juršėnas, S.; Kadys, A.; Malinauskas, T.; Tekorius, A.; Vitta, P.

    2013-11-15

    The MOCVD grown GaN epi-layers of different thickness have been examined in order to clarify a role of surface recombination, to separate an impact of radiative and non-radiative recombination and disorder factors. The microwave probed –photoconductivity (MW-PC) and spectrally resolved photo-luminescence (PL) transients were simultaneously recorded under ultraviolet (UV) light 354 nm pulsed 500 ps excitation. The MW-PC transients exhibited the carrier decay components associated with carrier decay within micro-crystals and the disordered structure on the periphery areas surrounding crystalline columns. Three PL bands were resolved within PL spectrum, namely, the exciton ascribed UV-PL band edge for hν>3.3 eV, blue B-PL band for 2.5 < hν < 3.0 eV and yellow Y-PL band with hν < 2.4 eV. It has been obtained that intensity of UV-PL band increases with excitation density, while intensity of B-PL band is nearly invariant. However, intensity of the Y-PL increases with reduction of the excitation density. The Y-PL can be associated with trapping centers. A reduction of UV excitation density leads to a decrease of the relative amplitude of the asymptotic component within the MW-PC transients and to an increase of the amplitude as well as duration of the yellow spectral band (Y-PL) asymptotic component. Fractional index α with values 0.5 < α < 0.8 was evaluated for the stretched-exponent component which fits the experimental transients determined by the disordered structure ascribed to the periphery areas surrounding the crystalline columns.

  7. White emission from non-planar InGaN/GaN MQW LEDs grown on GaN template with truncated hexagonal pyramids.

    PubMed

    Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Lai, Wei-Chih; Sheu, Jinn-Kong

    2015-04-06

    Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

  8. Microstructures of GaN and In{sub x}Ga{sub 1-x}N films grown by MOCVD on free-standing GaN templates

    SciTech Connect

    Jasinski, J.; Liliental-Weber, Z.; Huang, D.; Reshchikov, M.A.; Yun, F.; Morkoc, H.; Sone, C.; Park, S.S.; Lee, K.Y.

    2002-04-30

    We summarize structural properties of thick HVPE GaN templates from the point of view of their application as substrates for growth of nitride layers. This is followed by the results of optical and structural studies, mostly transmission electron microscopy, of nitride layers grown by MOCVD on top of the HVPE substrates. The results indicate high structural quality of these layers with a low density of threading dislocations (in the range of 10{sup 6} cm{sup -2}). Convergent beam electron diffraction studies showed that the MOCVD GaN films have Ga-polarity, the same polarity as the HVPE GaN substrates. Structural studies of an InGaN layer grown on top of the MOCVD GaN film showed the presence of two layers, which differed in lattice parameter and composition. The upper layer, on the top of the structure had a c-lattice parameter about 2% larger than that of GaN and contained 10.3 {+-} 0.8% of In. Values measured for the thinner, intermediate layer adjacent to the GaN layer were about 2 .5 times lower.

  9. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  10. Triclinic deformation of InGaN layers grown on vicinal surface of GaN (00.1) substrates

    NASA Astrophysics Data System (ADS)

    Krysko, M.; Domagala, J. Z.; Czernecki, R.; Leszczynski, M.

    2013-09-01

    We report on a triclinic unit cell deformation of fully strained InGaN layers grown on vicinal GaN (00.1) substrates. The samples were examined using the high-resolution X-ray diffraction (HR XRD) using a set of asymmetrical reflections and one symmetrical reflection of 00.2. The substrate miscut induced triclinic deformation of the layer unit cells, breaking the hexagonal symmetry. The experimental results are compared with predictions of the theory of elasticity. We formulate equations for unit cell parameters of layers grown on substrates cut in any direction, based on the equations given by Romanov et al. [J. Appl. Phys. 100, 023522 (2006)]. Additionally, the paper provides a recipe of the XRD measurements necessary to establish unit cell parameters (useful for composition determination of ternary compounds) of the hexagonal mismatched layers grown on off-axis substrates.

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

    SciTech Connect

    Nandi, R. Mohan, S. Major, S. S.; Srinivasa, R. 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 and 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.

  12. Ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy on semipolar GaN (2021) substrates

    SciTech Connect

    Sawicka, M.; Grzanka, S.; Skierbiszewski, C.; Turski, H.; Muziol, G.; Krysko, M.; Grzanka, E.; Sochacki, T.; Siekacz, M.; Kucharski, R.

    2013-03-18

    Multi-quantum well (MQW) structures and light emitting diodes (LEDs) were grown on semipolar (2021) and polar (0001) GaN substrates by plasma-assisted molecular beam epitaxy. The In incorporation efficiency was found to be significantly lower for the semipolar plane as compared to the polar one. The semipolar MQWs exhibit a smooth surface morphology, abrupt interfaces, and a high photoluminescence intensity. The electroluminescence of semipolar (2021) and polar (0001) LEDs fabricated in the same growth run peaks at 387 and 462 nm, respectively. Semipolar LEDs with additional (Al,Ga)N cladding layers exhibit a higher optical output power but simultaneously a higher turn-on voltage.

  13. GaN nanorod light emitting diodes with suspended graphene transparent electrodes grown by rapid chemical vapor deposition

    SciTech Connect

    Xu, Kun; Xu, Chen Deng, Jun; Zhu, Yanxu; Guo, Weiling; Mao, Mingming; Xun, Meng; Chen, Maoxing; Zheng, Lei; Xie, Yiyang; Sun, Jie

    2013-11-25

    Ordered and dense GaN light emitting nanorods are studied with polycrystalline graphene grown by rapid chemical vapor deposition as suspended transparent electrodes. As the substitute of indium tin oxide, the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as-fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes. The suspended graphene remains electrically stable up to 300 °C in air. The graphene can be obtained at low cost and high efficiency, indicating its high potential in future applications.

  14. 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.

  15. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K.; Korona, K. P.

    2015-12-14

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 10{sup 2} and the leakage current of about 10{sup −4} A/cm{sup 2} at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ∼2 nm thick SiN{sub x} layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 10{sup 15 }cm{sup −3}. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiN{sub x} interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  16. Structural, electrical, and optical characterization of coalescent p-n GaN nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Korona, K. P.; Sobanska, M.; Klosek, K.

    2015-12-01

    The electrical, structural, and optical properties of coalescent p-n GaN nanowires (NWs) grown by molecular beam epitaxy on Si (111) substrate are investigated. From photoluminescence measurements the full width at half maximum of bound exciton peaks AX and DA is found as 1.3 and 1.2 meV, respectively. These values are lower than those reported previously in the literature. The current-voltage characteristics show the rectification ratio of about 102 and the leakage current of about 10-4 A/cm2 at room temperature. We demonstrate that the thermionic mechanism is not dominant in these samples and spatial inhomogeneties and tunneling processes through a ˜2 nm thick SiNx layer between GaN and Si could be responsible for deviation from the ideal diode behavior. The free carrier concentration in GaN NWs determined by capacitance-voltage measurements is about 4 × 1015 cm-3. Two deep levels (H190 and E250) are found in the structures. We attribute H190 to an extended defect located at the interface between the substrate and the SiNx interlayer or near the sidewalls at the bottom of the NWs, whereas E250 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

  17. Spontaneously grown GaN and AlGaN nanowires

    NASA Astrophysics Data System (ADS)

    Bertness, K. A.; Roshko, A.; Sanford, N. A.; Barker, J. M.; Davydov, A. V.

    2006-01-01

    We have identified crystal growth conditions in gas-source molecular beam epitaxy (MBE) that lead to spontaneous formation of GaN nanowires with high aspect ratio on Si (1 1 1) substrates. The nanowires were oriented along the GaN c-axis and normal to the substrate surface. Unlike in many other reports of GaN nanowire growth, no metal catalysts were used. Low growth rates at substrate temperatures near 820 °C were combined with high nitrogen flux (partially dissociated with RF plasma excitation) to form well-separated GaN wires with diameters from 50 to 250 nm in diameter and lengths ranging from 2 to 7 μm. The nanowires grew out of an irregular matrix layer containing deep faceted holes. X-ray diffraction indicated that the wires were fully relaxed and aligned to the silicon substrate. The growth morphology was strongly affected by the presence of Al and Be. The changes suggest that surface diffusion is a primary driving force in the growth of GaN nanowires with MBE.

  18. Growth parameter dependence of structural, electrical and magnetic properties in GaGdN layers grown on GaN(0001)

    NASA Astrophysics Data System (ADS)

    Sano, S.; Hasegawa, S.; Mitsuno, Y.; Higashi, K.; Ishimaru, M.; Sakurai, T.; Ohta, H.; Asahi, H.

    2013-09-01

    The growth parameter dependence of structural, electrical and magnetic properties in Gd-doped GaN layers grown by plasma-assisted molecular beam epitaxy has been investigated. The structural and magnetic properties of Gd-doped GaN films grown on GaN templates strongly depend on the MBE growth condition. While Gd-doped GaN grown under relatively high Ga fluxes consist of wurtzite GaGdN layers without Gd-related precipitates, Gd-incorporated GaN films grown under low Ga fluxes contain a lot of nanoparticles ranging from several nm to several tens nm in size. The samples with Gd-related nanoparticles exhibit hysteresis in the magnetization-magnetic field curves at 10 K. The separation between the field-cooled and zero-field-cooled magnetization-temperature curves is observed at around 30 K. This behavior is understood in terms of super-paramagnetism originating from the ferromagnetic nanoparticles observed in the cross-sectional transmission electron microscopy images.

  19. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AlN and InN

    DTIC Science & Technology

    1990-07-01

    that the BGaN film remained predominantly single crystal, but shows both a normal cubic [110] pattern and a second hexagonal pattern [0110]. By contrast...27 Transmission electron microscopy (iEM) was used (Hitachi H-800) to more closely examine the microstructural evolution of the BN/ BGaN /GaN epitaxial...area diffraction (SAD) also showed the BGaN layer to be a mixture of cubic and wurtzitic phases. This layer was heavily faulted. The latter phenomenon

  20. Photoconducting ultraviolet detectors based on GaN films grown by electron cyclotron resonance molecular beam epitaxy

    SciTech Connect

    Misra, M.; Shah, K.S.; Moustakas, T.D.; Vaudo, R.P.; Singh, R.

    1995-08-01

    We report for the first time, fabrication of photoconducting UV detectors made from GaN films grown by molecular beam epitaxy. Semi-instilating GaN films were grown by the method of electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (ECR-MBE). Photoconductive devices with interdigitated electrodes were fabricated and their photoconducting properties were investigated. In this paper we report on the performance of the detectors in terms of UV responsivity, gain-quantum efficiency product, spectral response and response time. We have measured responsivity of 125A/W and gain-quantum efficiency product of 600 at 254nm and 25V. The response time was measured to be on the order of 20ns for our detectors, corresponding to a bandwidth of 25Mhz. The spectral response showed a sharp long-wavelength cutoff at 365nm, and remained constant in the 200nm to 365nm range. The response of the detectors to low-energy x-rays was measured and found to be linear for x-rays with energies ranging from 60kVp to 90kVp.

  1. Microstructures of GaN Buffer Layers Grown on Si(111) Using Rapic Thermal Process Low-Pressure Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Peng, Chen; Bo, Shen; Jian-Min, Zhu; Zhi-Zhong, Chen; Yu-Gang, Zhou; Shi-Yong, Xie; Rong, Zhang; Ping, Han; Shu-Lin, Gu; You-Dou, Zheng; Shu-Sheng, Jiang; Duan, Feng; Z, Huang C.

    2000-03-01

    Microstructures of GaN buffer layers grown on Si (111) substrates using rapid thermal process low-pressure metalorganic chemical vapor deposition are investigated by an atomic force microscope (AFM) and a high-resolution transmission electron microscope (HRTEM). AFM images show that the islands appear in the GaN buffer layer after annealing at high temperature. Cross-sectional HRTEM micrographs of the buffer region of these samples indicate that there are bunched steps on the surface of the Si substrate and a lot of domains in GaN misorienting each other with small angles. The boundaries of those domains locate near the bunched steps, and the regions of the film on a terrace between steps have the same crystal orientation. An amorphous-like layer, about 3 nm thick, can also be observed between the GaN buffer layer and the Si substrate.

  2. 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.

  3. Structural, Optical and Electrical Properties of n-type GaN on Si (111) Grown by RF-plasma assisted Molecular Beam Epitaxy

    SciTech Connect

    Chin, C. W.; Hassan, Z.; Yam, F. K.

    2008-05-20

    In this paper, we present the study of the structural, optical and electrical of n-type GaN grown on silicon (111) by RF plasma-assisted molecular beam epitaxy (RF-MBE). X-ray diffraction (XRD) measurement reveals that the GaN was epitaxially grown on silicon. For the photoluminescence (PL) measurement, a sharp and intense peak at 364.5 nm indicates that the sample is of high optical quality. Hall effect measurement shows that the film has a carrier concentration of 3.28x10{sup 19} cm{sup -3}. The surface of the n-type GaN was smooth and no any cracks and pits.

  4. Dual-wavelength GaN-based LEDs grown on truncated hexagonal pyramids formed by selective-area regrowth on Si-implanted GaN templates.

    PubMed

    Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Wu, Ming-Jui; Lai, Wei-Chih; Sheu, Jinn-Kong

    2013-09-09

    GaN-based blue light-emitting diodes (LEDs) with micro truncated hexagonal pyramid (THP) array were grown on selective-area Si-implanted GaN (SIG) templates. The GaN epitaxial layer regrown on the SIG templates exhibited selective growth and subsequent lateral growth to form the THP array. The observed selective-area growth was attributed to the different crystal structures between the Si-implanted and implantation-free regions. Consequently, LEDs grown on the GaN THP array emitted broad electroluminescence spectra with multiple peaks. Spatially resolved cathodoluminescence revealed that the broad spectra originated from different areas within each THP. Transmission electron microscopy showed the GaN-based epitaxial layers, including InGaN/GaN multi-quantum wells regrown at different growth rates (or with different In content in the InGaN wells) between the semi-polar and c-face planes of each THP.

  5. Influence of Mg and In on defect formation in GaN; bulk and MOCVD grown samples

    SciTech Connect

    Liliental-Weber, Z.; Benamara, M.; Jasinski, J.; Swider, W.; Washburn, J.; Grzegory, I.; Porowski, S.; Bak-Misiuk, J.; Domagala, J.; Bedair, S.; Eiting, C.J.; Dupuis, R.D.

    2000-11-22

    Transmission electron microscopy studies were applied to study GaN crystals doped with Mg. Both: bulk GaN:Mg crystals grown by a high pressure and high temperature process and those grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. Structural dependence on growth polarity was observed in the bulk crystals. Spontaneous ordering (formation of polytypoids) was observed for growth in the N to Ga polar direction (N polarity). On the opposite site of the crystal (growth in the Ga to N polar direction) Mg-rich pyramidal defects with base on the basal planes and with walls inclined about 45O to these planes, empty inside (pinholes) were observed. A high concentration of these pyramidal defects was also observed in the MOCVD grown crystals. For samples grown with Mg delta doping planar defects were also observed especially at the early stages of growth followed by formation of pyramidal defects. TEM and x-ray studies of InxGa{sub 1{minus}x}N crystals for the range of 28-45% nominal In concentration shows formation of two sub-layers: strained and relaxed, with a much lower In concentration in the strained layer. Layers with the highest In concentration were fully relaxed.

  6. Interface roughness of double buffer layer of GaN film grown on Si(1 1 1) substrate using GIXR analysis

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Yamabe, N.; Ohachi, T.

    2011-03-01

    A double buffer layer (DBL), interface reaction epitaxy (IRE) AlN/β-Si3N4/Si, grown by an IRE of β-Si3N4 and AlN films on Si, was fabricated to improve the crystalline quality of successively grown 30 nm GaN on a 30 nm AlN buffer layer using plasma-assisted molecular beam epitaxy (PA-MBE). The DBL was first prepared by surface nitridation of Si and successively prepared by IRE between the deposited Al and N atoms in β-Si3N4. Both the AlN buffer layer on the DBL and GaN film on the AlN buffer layer were grown by activity-modulation migration enhanced epitaxy (AM-MEE). Hetero epitaxial grown films of GaN(30 nm)/AlN buffer(30 nm)/DBL/Si(1 1 1) were prepared for analysis using a three layer model of grazing incidence-angle X-ray reflectivity (GIXR), which consisted of three layers of GaN, AlN buffer and Si and of the three interfaces of the GaN surface, GaN/AlN buffer and AlN buffer/DBL/Si. The nitridation temperature dependence of the interface roughness of the DBL was measured to be 0.5 and 0.6 nm, for nitridation temperatures of 780 and 830 °C, respectively. The full width at half maximum (FWHM) of rocking curve GaN(0 0 0 2) measured by X-ray diffraction (XRD) for nitridation temperatures of 780 and 830 °C were 58.2 and 55.2 arcmin, respectively.

  7. Correlation between the residual stress and the density of threading dislocations in GaN layers grown by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Barchuk, M.; Röder, C.; Shashev, Y.; Lukin, G.; Motylenko, M.; Kortus, J.; Pätzold, O.; Rafaja, D.

    2014-01-01

    The correlation between the residual stress and the density of threading dislocations was investigated in polar GaN layers that were grown by using hydride vapor phase epitaxy (HVPE) on three different GaN templates. The first template type was GaN grown on sapphire by metal-organic vapor phase epitaxy. The second template type was a closed GaN nucleation layer grown on sapphire by HVPE. The third template type was a non-closed GaN nucleation layer grown by HVPE, which formed isolated pyramids on the sapphire surface. The residual stress was determined using the combination of micro-Raman spectroscopy and modified sin2 ψ method. The interplanar spacings needed for the sin2 ψ method were obtained from the reciprocal space maps that were measured using high-resolution X-ray diffraction. The density of threading dislocations was concluded from the broadening of the reciprocal lattice points that was measured using high-resolution X-ray diffraction as well. The fitting of the reciprocal space maps allowed the character of the threading dislocations to be described quantitatively in terms of the fractions of edge and screw dislocations. It was found that the threading dislocation density increases with increasing compressive residual stress. Furthermore, the dislocation density and the residual stress decrease with increasing thickness of the GaN layers. The edge component of the threading dislocations was dominant in all samples. Still, some differences in the character of the dislocations were observed for different templates.

  8. n{sup +}-GaN grown by ammonia molecular beam epitaxy: Application to regrown contacts

    SciTech Connect

    Lugani, L.; Malinverni, M.; Giraud, E.; Carlin, J.-F.; Grandjean, N.; Tirelli, S.; Marti, D.; Bolognesi, C. R.

    2014-11-17

    We report on the low-temperature growth of heavily Si-doped (>10{sup 20 }cm{sup −3}) n{sup +}-type GaN by N-rich ammonia molecular beam epitaxy (MBE) with very low bulk resistivity (<4 × 10{sup −4} Ω·cm). This is applied to the realization of regrown ohmic contacts on InAlN/GaN high electron mobility transistors. A low n{sup +}-GaN/2 dimensional electron gas contact resistivity of 0.11 Ω·mm is measured, provided an optimized surface preparation procedure, which is shown to be critical. This proves the great potentials of ammonia MBE for the realization of high performance electronic devices.

  9. Influence of edge-grown HVPE GaN on the structural quality of c-plane oriented HVPE-GaN grown on ammonothermal GaN substrates

    NASA Astrophysics Data System (ADS)

    Domagala, J. Z.; Smalc-Koziorowska, J.; Iwinska, M.; Sochacki, T.; Amilusik, M.; Lucznik, B.; Fijalkowski, M.; Kamler, G.; Grzegory, I.; Kucharski, R.; Zajac, M.; Bockowski, M.

    2016-12-01

    Study on the sources of stress in HVPE-GaN layer crystallized on 1-in. ammonothermally grown GaN seed is presented in this paper. Characterization by means of X-ray diffraction and transmission electron microscopy is performed. HVPE-GaN samples of high quality and those with visible quality deterioration are investigated on c-plane and m-plane cross-sections. Special attention is paid to HVPE material growing in semi-polar and non-polar directions on the edges of the seed and the growing layer. It is shown that this material generates significant stress leading to a structural deterioration of HVPE-GaN growing in the c-direction.

  10. Low defect large area semi-polar (112) GaN grown on patterned (113) silicon

    PubMed Central

    Pristovsek, Markus; Han, Yisong; Zhu, Tongtong; Frentrup, Martin; Kappers, Menno J; Humphreys, Colin J; Kozlowski, Grzegorz; Maaskant, Pleun; Corbett, Brian

    2015-01-01

    We report on the growth of semi-polar GaN (112) templates on patterned Si (113) substrates. Trenches were etched in Si (113) using KOH to expose Si {111} sidewalls. Subsequently an AlN layer to prevent meltback etching, an AlGaN layer for stress management, and finally two GaN layers were deposited. Total thicknesses up to 5 m were realised without cracks in the layer. Transmission electron microscopy showed that most dislocations propagate along [0001] direction and hence can be covered by overgrowth from the next trench. The defect densities were below and stacking fault densities less than 100 cm . These numbers are similar to reports on patterned r-plane sapphire. Typical X-ray full width at half maximum (FHWM) were 500” for the asymmetric (00.6) and 450” for the (11.2) reflection. These FHWMs were 50 % broader than reported for patterned r-plane sapphire which is attributed to different defect structures and total thicknesses. The surface roughness shows strong variation on templates. For the final surface roughness the roughness of the sidewalls of the GaN ridges at the time of coalescence are critical. PMID:26212392

  11. Study of carbon concentration in GaN grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Piao, Guanxi; Ikenaga, Kazutada; Yano, Yoshiki; Tokunaga, Hiroki; Mishima, Akira; Ban, Yuzaburo; Tabuchi, Toshiya; Matsumoto, Koh

    2016-12-01

    We investigated the C concentration in GaN as a function of the V/III ratio and growth rate for a p-n junction diode structure on a bulk GaN substrate by metalorganic chemical vapor deposition (MOCVD). The C concentration was independent of the growth rate for growth at atmospheric pressure. Moreover, the C concentration in GaN was 3.3×1015 cm-3 at a V/III ratio of 5000 with a growth rate of 2.3 μm/h and 4×1015 cm-3 at a V/III ratio of 3700 with a growth rate of 4.7 μm/h. Both of the major and minor carrier concentrations in the drift layers of a p-n junction structure were optimized at the reasonable growth rate in terms of the short growth time. The C impurity concentration was well controlled at a concentration on the order of 1015 cm-3.

  12. Enhanced performance of InGaN/GaN multiple-quantum-well light-emitting diodes grown on nanoporous GaN layers.

    PubMed

    Lee, Kwang Jae; Kim, Sang-Jo; Kim, Jae-Joon; Hwang, Kyungwook; Kim, Sung-Tae; Park, Seong-Ju

    2014-06-30

    We demonstrate the high efficiency of InGaN/GaN multiple quantum wells (MQWs) light-emitting diode (LED) grown on the electrochemically etched nanoporous (NP) GaN. The photoluminescence (PL) and Raman spectra show that the LEDs with NP GaN have a strong carrier localization effect resulting from the relaxed strain and reduced defect density in MQWs. Also, the finite-difference time-domain (FDTD) simulation shows that the light extraction efficiency (LEE) is increased by light scattering effect by nanopores. The output power of LED with NP GaN is increased up to 123.1% at 20 mA, compared to that of LED without NP GaN. The outstanding performance of LEDs with NP GaN is attributed to the increased internal quantum efficiency (IQE) by the carrier localization in the indium-rich clusters, low defect density in MQWs, and increased LEE owing to the light scattering in NP GaN.

  13. Effect of the Ammonia Flow on the Formation of Microstructure Defects in GaN Layers Grown by High-Temperature Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Barchuk, M.; Lukin, G.; Zimmermann, F.; Röder, C.; Motylenko, M.; Pätzold, O.; Heitmann, J.; Kortus, J.; Rafaja, D.

    2016-12-01

    High-temperature vapor phase epitaxy (HTVPE) is a physical vapor transport technology for a deposition of gallium nitride (GaN) layers. However, little is known about the influence of the deposition parameters on the microstructure of the layers. In order to fill this gap, the influence of the ammonia (NH3) flow applied during the HTVPE growth on the microstructure of the deposited GaN layers is investigated in this work. Although the HTVPE technology is intended to grow GaN layers on foreign substrates, the GaN layers under study were grown on GaN templates produced by metal organic vapor phase epitaxy in order to be able to separate the growth defects from the defects induced by the lattice misfit between the foreign substrate and the GaN layer. The microstructure of the layers is characterized by means of high-resolution x-ray diffraction (XRD), transmission electron microscopy and photoluminescence. In samples deposited at low ammonia flow, planar defects were detected, along which the nitrogen atoms are found to be substituted by impurity atoms. The interplay between these planar defects and the threading dislocations is discussed. A combination of XRD and micro-Raman spectroscopy reveals the presence of compressive residual stress in the samples.

  14. Effect of the Ammonia Flow on the Formation of Microstructure Defects in GaN Layers Grown by High-Temperature Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Barchuk, M.; Lukin, G.; Zimmermann, F.; Röder, C.; Motylenko, M.; Pätzold, O.; Heitmann, J.; Kortus, J.; Rafaja, D.

    2017-03-01

    High-temperature vapor phase epitaxy (HTVPE) is a physical vapor transport technology for a deposition of gallium nitride (GaN) layers. However, little is known about the influence of the deposition parameters on the microstructure of the layers. In order to fill this gap, the influence of the ammonia (NH3) flow applied during the HTVPE growth on the microstructure of the deposited GaN layers is investigated in this work. Although the HTVPE technology is intended to grow GaN layers on foreign substrates, the GaN layers under study were grown on GaN templates produced by metal organic vapor phase epitaxy in order to be able to separate the growth defects from the defects induced by the lattice misfit between the foreign substrate and the GaN layer. The microstructure of the layers is characterized by means of high-resolution x-ray diffraction (XRD), transmission electron microscopy and photoluminescence. In samples deposited at low ammonia flow, planar defects were detected, along which the nitrogen atoms are found to be substituted by impurity atoms. The interplay between these planar defects and the threading dislocations is discussed. A combination of XRD and micro-Raman spectroscopy reveals the presence of compressive residual stress in the samples.

  15. Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

    NASA Astrophysics Data System (ADS)

    Liu, Jianming; Liu, Xianlin; Li, Chengming; Wei, Hongyuan; Guo, Yan; Jiao, Chunmei; Li, Zhiwei; Xu, Xiaoqing; Song, Huaping; Yang, Shaoyan; Zhu, Qinsen; Wang, Zhanguo; Yang, Anli; Yang, Tieying; Wang, Huanhua

    2011-12-01

    Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate.

  16. Characterization of GaN nanowires grown on PSi, PZnO and PGaN on Si (111) substrates by thermal evaporation

    SciTech Connect

    Shekari, Leila; Hassan, Haslan Abu; Thahab, Sabah M.; Hassan, Zainuriah

    2012-06-20

    In this research, we used an easy and inexpensive method to synthesize highly crystalline GaN nanowires (NWs); on different substrates such as porous silicon (PSi), porous zinc oxide (PZnO) and porous gallium nitride (PGaN) on Si (111) wafer by thermal evaporation using commercial GaN powder without any catalyst. Micro structural studies by scanning electron microscopy and transmission electron microscope measurements reveal the role of different substrates in the morphology, nucleation and alignment of the GaN nanowires. The degree of alignment of the synthesized nanowires does not depend on the lattice mismatch between wires and their substrates. Further structural and optical characterizations were performed using high resolution X-ray diffraction and energy-dispersive X-ray spectroscopy. Results indicate that the nanowires are of single-crystal hexagonal GaN. The quality and density of grown GaN nanowires for different substrates are highly dependent on the lattice mismatch between the nanowires and their substrates and also on the size of the porosity of the substrates. Nanowires grown on PGaN have the best quality and highest density as compared to nanowires on other substrates. By using three kinds of porous substrates, we are able to study the increase in the alignment and density of the nanowires.

  17. Germanium doping of self-assembled GaN nanowires grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Schörmann, Jörg; Hille, Pascal; Schäfer, Markus; Müßener, Jan; Becker, Pascal; Klar, Peter J.; Hofmann, Detlev M.; Teubert, Jörg; Eickhoff, Martin; Kleine-Boymann, Matthias; Rohnke, Marcus; Mata, Maria de la; Arbiol, Jordi

    2013-09-14

    Germanium doping of GaN nanowires grown by plasma-assisted molecular beam epitaxy on Si(111) substrates is studied. Time of flight secondary ion mass spectrometry measurements reveal a constant Ge-concentration along the growth axis. A linear relationship between the applied Ge-flux and the resulting ensemble Ge-concentration with a maximum content of 3.3×10{sup 20} cm{sup −3} is extracted from energy dispersive X-ray spectroscopy measurements and confirmed by a systematic increase of the conductivity with Ge-concentration in single nanowire measurements. Photoluminescence analysis of nanowire ensembles and single nanowires reveals an exciton localization energy of 9.5 meV at the neutral Ge-donor. A Ge-related emission band at energies above 3.475 eV is found that is assigned to a Burstein-Moss shift of the excitonic emission.

  18. High quality InAlN single layers lattice-matched to GaN grown by molecular beam epitaxy

    SciTech Connect

    Gacevic, Z.; Fernandez-Garrido, S.; Calleja, E.; Estrade, S.

    2011-07-18

    We report on properties of high quality {approx}60 nm thick InAlN layers nearly in-plane lattice-matched to GaN, grown on c-plane GaN-on-sapphire templates by plasma-assisted molecular beam epitaxy. Excellent crystalline quality and low surface roughness are confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. High annular dark field observations reveal a periodic in-plane indium content variation (8 nm period), whereas optical measurements evidence certain residual absorption below the band-gap. The indium fluctuation is estimated to be {+-} 1.2% around the nominal 17% indium content via plasmon energy oscillations assessed by electron energy loss spectroscopy with sub-nanometric spatial resolution.

  19. GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tseng, H. Y.; Yang, W. C.; Lee, P. Y.; Lin, C. W.; Cheng, Kai-Yuan; Hsieh, K. C.; Cheng, K. Y.; Hsu, C.-H.

    2016-08-01

    GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

  20. Germanium doping of self-assembled GaN nanowires grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schörmann, Jörg; Hille, Pascal; Schäfer, Markus; Müßener, Jan; Becker, Pascal; Klar, Peter J.; Kleine-Boymann, Matthias; Rohnke, Marcus; de la Mata, Maria; Arbiol, Jordi; Hofmann, Detlev M.; Teubert, Jörg; Eickhoff, Martin

    2013-09-01

    Germanium doping of GaN nanowires grown by plasma-assisted molecular beam epitaxy on Si(111) substrates is studied. Time of flight secondary ion mass spectrometry measurements reveal a constant Ge-concentration along the growth axis. A linear relationship between the applied Ge-flux and the resulting ensemble Ge-concentration with a maximum content of 3.3×1020 cm-3 is extracted from energy dispersive X-ray spectroscopy measurements and confirmed by a systematic increase of the conductivity with Ge-concentration in single nanowire measurements. Photoluminescence analysis of nanowire ensembles and single nanowires reveals an exciton localization energy of 9.5 meV at the neutral Ge-donor. A Ge-related emission band at energies above 3.475 eV is found that is assigned to a Burstein-Moss shift of the excitonic emission.

  1. Raman mapping of hexagonal hillocks in N-polar GaN grown on c-plane sapphire

    NASA Astrophysics Data System (ADS)

    Jiang, Teng; Lin, Zhiyu; Zhang, Jincheng; Xu, Shengrui; Huang, Jun; Niu, Mutong; Gao, Xiaodong; Guo, Lixin; Hao, Yue

    2017-04-01

    A large amount of huge hexagonal hillocks were observed on the surface of N-polar GaN film grown on c-plane sapphire substrate by MOCVD. The distribution of residual stress and dislocation density in a typical hexagonal hillock was investigated by the mapping measurement of Micro-Raman and Cathodoluminescence (CL) spectroscopy. It is found that the residual stress at the top region of the hillock is much smaller than that of the sidewall region and the region around the hillock. Meanwhile, the CL images confirmed that the dislocation density around the hexagonal hillock is higher than the top region of the hillock. The bending and annihilation of the dislocations during the growth of the hexagonal hillock result in the relaxation of residual stress which should be responsible for the spatial variation of dislocation density and residual stress.

  2. GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Tseng, H. Y.; Yang, W. C.; Lee, P. Y.; Lin, C. W.; Cheng, Kai-Yuan; Hsieh, K. C.; Cheng, K. Y.; Hsu, C.-H.

    2016-08-22

    GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

  3. Ga-related defect in as-grown Zn-doped GaN: An optically detected magnetic resonance study

    NASA Astrophysics Data System (ADS)

    Hai, P. N.; Chen, W. M.; Buyanova, I. A.; Monemar, B.; Amano, H.; Akasaki, I.

    2000-10-01

    A detailed study of as-grown Zn-doped GaN employing optically detected magnetic resonance (ODMR) spectroscopy is presented. Besides the well-known ODMR spectra of an effective-mass-like donor and Zn acceptor, a positive ODMR signal of an S=12 paramagnetic center was observed when monitoring the dominating blue luminescence band peaking at 2.8 eV. The involvement of a single Ga nucleus in the defect center is revealed from the rather well-resolved hyperfine interactions involving the isotopes 71Ga (39.9%) and 69Ga (60.1%), both with nuclear spin I=32. The C3v symmetry, the hyperfine interaction and the defect formation suggest a Ga-related complex nature of this center.

  4. Controlled low Si doping and high breakdown voltages in GaN on sapphire grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Agarwal, Anchal; Gupta, Chirag; Enatsu, Yuuki; Keller, Stacia; Mishra, Umesh

    2016-12-01

    Controlled n-type doping down to 2 × 1015 cm-3 was achieved in GaN grown on sapphire by MOCVD by balancing the n-type Si doping with respect to the background carbon and oxygen levels. A dopant level of ˜1 × 1016 cm-3 displayed a very high mobility of 899 cm2 V-1 s-1. High electron mobility in the drift layer leads to a low on resistance and high current densities without compromising on any other properties of the device. Schottky diodes processed on these low n-type layers showed low R on values, while the p-n diodes display high reverse breakdown voltages in excess of 1000 V for 8 μm thick drift layers with a doping of 2 × 1015 cm-3.

  5. Low angle incidence microchannel epitaxy of GaN grown by ammonia-based metal-organic molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    GaN was grown by low angle incidence microchannel epitaxy (LAIMCE) using NH3-based metal-organic molecular beam epitaxy (NH3-based MOMBE). The growth mechanism was studied by varying the growth temperature and time. The effect of the incidence direction of precursors on lateral growth was also investigated by comparing the results obtained when precursors were supplied perpendicular and parallel to the openings in the mask. The thickness and width of lateral growth were largely influenced by the formation of a facet on the surface, which frequently terminates further growth. For example, a sample grown at 700 °C with a perpendicular supply of precursors stopped growing both vertically and laterally after a certain time despite continuous supply of the precursors. On the other hand, a sample grown at 820 °C with a parallel supply of precursors exhibited stable growth, and its width increased continuously with time. This is because inter-surface diffusion of adatoms occurred from the top to the sides, which enhanced the width of lateral growth. In contrast, low angle incidence supply of molecular beams perpendicular to the openings resulted in a Ga-rich condition on the side and formed the side facet, which terminated further LAIMCE growth.

  6. Effects of growth temperature on Mg-doped GaN grown by ammonia molecular beam epitaxy

    SciTech Connect

    Hurni, Christophe A.; Lang, Jordan R.; Burke, Peter G.; Speck, James S.

    2012-09-03

    The hole concentration p in Mg-doped GaN films grown by ammonia molecular beam epitaxy depends strongly on the growth temperature T{sub GR}. At T{sub GR}=760 Degree-Sign C, GaN:Mg films showed a hole concentration of p=1.2 Multiplication-Sign 10{sup 18} cm{sup -3} for [Mg]=4.5 Multiplication-Sign 10{sup 19} cm{sup -3}, while at T{sub GR}=840 Degree-Sign C, p=4.4 Multiplication-Sign 10{sup 16} cm{sup -3} for [Mg]=7 Multiplication-Sign 10{sup 19} cm{sup -3}. Post-growth annealing did not increase p. The sample grown at 760 Degree-Sign C exhibited a low resistivity of 0.7 {Omega}cm. The mobility for all the samples was around 3-7 cm{sup 2}/V s. Temperature-dependent Hall measurements and secondary ion mass spectroscopy suggest that the samples grown at T{sub GR}>760 Degree-Sign C are compensated by an intrinsic donor rather than hydrogen.

  7. The nature of catalyst particles and growth mechanisms of GaN nanowires grown by Ni-assisted metal-organic chemical vapor deposition.

    PubMed

    Weng, Xiaojun; Burke, Robert A; Redwing, Joan M

    2009-02-25

    The structure and chemistry of the catalyst particles that terminate GaN nanowires grown by Ni-assisted metal-organic chemical vapor deposition were investigated using a combination of electron diffraction, high-resolution transmission electron microscopy, and x-ray energy dispersive spectrometry. The crystal symmetry, lattice parameter, and chemical composition obtained reveal that the catalyst particles are Ni(3)Ga with an ordered L 1(2) structure. The results suggest that the catalyst is a solid particle during growth and therefore favor a vapor-solid-solid mechanism for the growth of GaN nanowires under these conditions.

  8. Influence of stress in GaN crystals grown by HVPE on MOCVD-GaN/6H-SiC substrate

    PubMed Central

    Zhang, Lei; Yu, Jiaoxian; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Shao, Yongliang; Zhang, Haodong; Tian, Yuan

    2014-01-01

    GaN crystals without cracks were successfully grown on a MOCVD-GaN/6H-SiC (MGS) substrate with a low V/III ratio of 20 at initial growth. With a high V/III ratio of 80 at initial growth, opaque GaN polycrystals were obtained. The structural analysis and optical characterization reveal that stress has a great influence on the growth of the epitaxial films. An atomic level model is used to explain these phenomena during crystal growth. It is found that atomic mobility is retarded by compressive stress and enhanced by tensile stress. PMID:24569601

  9. Influence of stress in GaN crystals grown by HVPE on MOCVD-GaN/6H-SiC substrate.

    PubMed

    Zhang, Lei; Yu, Jiaoxian; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Shao, Yongliang; Zhang, Haodong; Tian, Yuan

    2014-02-26

    GaN crystals without cracks were successfully grown on a MOCVD-GaN/6H-SiC (MGS) substrate with a low V/III ratio of 20 at initial growth. With a high V/III ratio of 80 at initial growth, opaque GaN polycrystals were obtained. The structural analysis and optical characterization reveal that stress has a great influence on the growth of the epitaxial films. An atomic level model is used to explain these phenomena during crystal growth. It is found that atomic mobility is retarded by compressive stress and enhanced by tensile stress.

  10. Effect of AlN buffer layer properties on the morphology and polarity of GaN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Brubaker, Matt D.; Rourke, Devin M.; Sanford, Norman A.; Bertness, Kris A.; Bright, Victor M.

    2011-09-01

    Low-temperature AlN buffer layers grown via plasma-assisted molecular beam epitaxy on Si (111) were found to significantly affect the subsequent growth morphology of GaN nanowires. The AlN buffer layers exhibited nanowire-like columnar protrusions, with their size, shape, and tilt determined by the AlN V/III flux ratio. GaN nanowires were frequently observed to adopt the structural characteristics of the underlying AlN columns, including the size and the degree of tilt. Piezoresponse force microscopy and polarity-sensitive etching indicate that the AlN films and the protruding columns have a mixed crystallographic polarity. Convergent beam electron diffraction indicates that GaN nanowires are Ga-polar, suggesting that Al-polar columns are nanowire nucleation sites for Ga-polar nanowires. GaN nanowires of low density could be grown on AlN buffers that were predominantly N-polar with isolated Al-polar columns, indicating a high growth rate for Ga-polar nanowires and suppressed growth of N-polar nanowires under typical growth conditions. AlN buffer layers grown under slightly N-rich conditions (V/III flux ratio = 1.0 to 1.3) were found to provide a favorable growth surface for low-density, coalescence-free nanowires.

  11. Investigation of Si and O Donor Impurities in Unintentionally Doped MBE-Grown GaN on SiC(0001) Substrate

    NASA Astrophysics Data System (ADS)

    Tingberg, Tobias; Ive, Tommy; Larsson, Anders

    2017-08-01

    We have investigated the unintentional n-type background doping in GaN(0001) layers grown on semi-insulating 4H-SiC(0001) substrate by plasma-assisted molecular beam epitaxy under Ga-rich conditions at growth temperatures from 780°C and 900°C. All layers exhibited very smooth surface morphology with monolayer steps as revealed by atomic force microscopy. Hall-effect measurements showed that the sample grown at 900°C had carrier concentration of 9.8 × 1017 cm-3 while the sample grown at 780°C had resistivity too high to obtain reliable measurements. Secondary-ion mass spectroscopy revealed O and Si concentrations of <1017 cm-3 in the sample grown at 900°C but >1017 cm-3 in the sample grown at 780°C. The trend for the atomic concentrations of O and Si, which are common donor impurities in GaN, was thus contrary to the trend of the carrier concentration. The full-width at half-maximum for x-ray rocking curves obtained across the GaN(0002) and GaN(10 \\bar{1} 5) reflections for the sample grown at 900°C was 62 arcsec and 587 arcsec, respectively. The half-width increased with decreasing growth temperature. The atomic concentrations of O and Si are too low to account for the unintentional background doping levels. A possible explanation proposed in early reports for the background doping is N-vacancies.

  12. Correlative analysis of the in situ changes of carrier decay and proton induced photoluminescence characteristics in chemical vapor deposition grown GaN

    SciTech Connect

    Gaubas, E. Ceponis, T.; Jasiunas, A.; Meskauskaite, D.; Pavlov, J.; Tekorius, A.; Vaitkus, J.; Kovalevskij, V.; Remeikis, V.

    2014-02-10

    In order to evaluate carrier densities created by 1.6 MeV protons and to trace radiation damage of the 2.5 μm thick GaN epi-layers grown by metalorganic chemical vapor deposition technique, a correlation between the photoconductivity transients and the steady-state photoluminescence spectra have been examined. Comparison of luminescence spectra induced by proton beam and by laser pulse enabled us to evaluate the efficiency of a single proton generation being of 1 × 10{sup 7} cm{sup −3} per 1.6 MeV proton and 40 carrier pairs per micrometer of layer depth. This result indicates that GaN layers can be an efficient material for detection of particle flows. It has been demonstrated that GaN material can also be a rather efficient scintillating material within several wavelength ranges.

  13. Substrate misorientation induced strong increase in the hole concentration in Mg doped GaN grown by metalorganic vapor phase epitaxy

    SciTech Connect

    Suski, T.; Litwin-Staszewska, E.; Piotrzkowski, R.; Krysko, M.; Nowak, G.; Franssen, G.; Dmowski, L. H.; Lucznik, B.

    2008-10-27

    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 unintentional donor density, is responsible for the observed increase in the hole concentration. Analysis of the temperature dependence of electrical transport confirms this interpretation.

  14. Characterization of Stress Relaxation, Dislocations and Crystallographic Tilt Via X-ray Microdiffraction in GaN (0001) Layers Grown by Maskless Pendeo-Epitaxy

    SciTech Connect

    Barabash, R.I.; Ice, G.E.; Liu, W.; Einfeldt, S.; Hommel, D.; Roskowski, A.M.; Davis, R.F.

    2010-06-25

    Intrinsic stresses due to lattice mismatch and high densities of threading dislocations and extrinsic stresses resulting from the mismatch in the coefficients of thermal expansion are present in almost all III-Nitride heterostructures. Stress relaxation in the GaN layers occurs in conventional and in pendeo-epitaxial films via the formation of additional misfit dislocations, domain boundaries, elastic strain and wing tilt. Polychromatic X-ray microdiffraction, high resolution monochromatic X-ray diffraction and finite element simulations have been used to determine the distribution of strain, dislocations, sub-boundaries and crystallographic wing tilt in uncoalesced and coalesced GaN layers grown by maskless pendeo-epitaxy. An important parameter was the width-to-height ratio of the etched columns of GaN from which the lateral growth of the wings occurred. The strain and tilt across the stripes increased with the width-to-height ratio. Tilt boundaries formed in the uncoalesced GaN layers at the column/wing interfaces for samples with a large ratio. Sharper tilt boundaries were observed at the interfaces formed by the coalescence of two laterally growing wings. The wings tilted upward during cooling to room temperature for both the uncoalesced and the coalesced GaN layers. It was determined that finite element simulations that account for extrinsic stress relaxation can explain the experimental results for uncoalesced GaN layers. Relaxation of both extrinsic and intrinsic stress components in the coalesced GaN layers contribute to the observed wing tilt and the formation of sub-boundaries.

  15. Characterization of Stress Relaxation, Dislocations and Crystallographic Tilt Via X-ray Microdiffraction in GaN (0001) Layers Grown by Maskless Pendeo-Epitaxy

    SciTech Connect

    Barabash, Rozaliya; Ice, Gene E; Liu, Wenjun; Einfeldt, S.; Hommel, D.; Roskowski, A. M.; Davis, R. F.

    2005-01-01

    Intrinsic stresses due to lattice mismatch and high densities of threading dislocations and extrinsic stresses resulting from the mismatch in the coefficients of thermal expansion are present in almost all III-Nitride heterostructures. Stress relaxation in the GaN layers occurs in conventional and in pendeo-epitaxial films via the formation of additional misfit dislocations, domain boundaries, elastic strain and wing tilt. Polychromatic X-ray microdiffraction, high resolution monochromatic X-ray diffraction and finite element simulations have been used to determine the distribution of strain, dislocations, sub-boundaries and crystallographic wing tilt in uncoalesced and coalesced GaN layers grown by maskless pendeo-epitaxy. An important parameter was the width-to-height ratio of the etched columns of GaN from which the lateral growth of the wings occurred. The strain and tilt across the stripes increased with the width-to-height ratio. Tilt boundaries formed in the uncoalesced GaN layers at the column/wing interfaces for samples with a large ratio. Sharper tilt boundaries were observed at the interfaces formed by the coalescence of two laterally growing wings. The wings tilted upward during cooling to room temperature for both the uncoalesced and the coalesced GaN layers. It was determined that finite element simulations that account for extrinsic stress relaxation can explain the experimental results for uncoalesced GaN layers. Relaxation of both extrinsic and intrinsic stress components in the coalesced GaN layers contribute to the observed wing tilt and the formation of sub-boundaries.

  16. Dislocations limited electronic transport in hydride vapour phase epitaxy grown GaN templates: A word of caution for the epitaxial growers

    SciTech Connect

    Chatterjee, Abhishek Khamari, Shailesh K.; Kumar, R.; Dixit, V. K.; Oak, S. M.; Sharma, T. K.

    2015-01-12

    GaN templates grown by hydride vapour phase epitaxy (HVPE) and metal organic vapour phase epitaxy (MOVPE) techniques are compared through electronic transport measurements. Carrier concentration measured by Hall technique is about two orders larger than the values estimated by capacitance voltage method for HVPE templates. It is learnt that there exists a critical thickness of HVPE templates below which the transport properties of epitaxial layers grown on top of them are going to be severely limited by the density of charged dislocations lying at layer-substrate interface. On the contrary MOVPE grown templates are found to be free from such limitations.

  17. Experimental phasing for structure determination using membrane-protein crystals grown by the lipid cubic phase method

    SciTech Connect

    Li, Dianfan; Pye, Valerie E.; Caffrey, Martin

    2015-01-01

    Very little information is available in the literature concerning the experimental heavy-atom phasing of membrane-protein structures where the crystals have been grown using the lipid cubic phase (in meso) method. In this paper, pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine labelling as applied to an integral membrane kinase crystallized in meso are described. An assay to assess cysteine accessibility for mercury labelling of membrane proteins is introduced. Despite the marked increase in the number of membrane-protein structures solved using crystals grown by the lipid cubic phase or in meso method, only ten have been determined by SAD/MAD. This is likely to be a consequence of the technical difficulties associated with handling proteins and crystals in the sticky and viscous hosting mesophase that is usually incubated in glass sandwich plates for the purposes of crystallization. Here, a four-year campaign aimed at phasing the in meso structure of the integral membrane diacylglycerol kinase (DgkA) from Escherichia coli is reported. Heavy-atom labelling of this small hydrophobic enzyme was attempted by pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine incorporation. Strategies and techniques for special handling are reported, as well as the typical results and the lessons learned for each of these approaches. In addition, an assay to assess the accessibility of cysteine residues in membrane proteins for mercury labelling is introduced. The various techniques and strategies described will provide a valuable reference for future experimental phasing of membrane proteins where crystals are grown by the lipid cubic phase method.

  18. Efficient reduction of defects in (1120) non-polar and (1122) semi-polar GaN grown on nanorod templates

    SciTech Connect

    Bai, J.; Gong, Y.; Xing, K.; Yu, X.; Wang, T.

    2013-03-11

    (1120) non-polar and (1122) semi-polar GaNs with a low defect density have been achieved by means of an overgrowth on nanorod templates, where a quick coalescence with a thickness even below 1 {mu}m occurs. On-axis and off-axis X-ray rocking curve measurements have shown a massive reduction in the linewidth for our overgrown GaN in comparison with standard GaN films grown on sapphire substrates. Transmission electron microscope observation demonstrates that the overgrowth on the nanorod templates takes advantage of an omni-directional growth around the sidewalls of the nanostructures. The dislocations redirect in basal planes during the overgrowth, leading to their annihilation and termination at voids formed due to a large lateral growth rate. In the non-polar GaN, the priority <0001> lateral growth from vertical sidewalls of nanorods allows basal plane stacking faults (BSFs) to be blocked in the nanorod gaps; while for semi-polar GaN, the propagation of BSFs starts to be impeded when the growth front is changed to be along inclined <0001> direction above the nanorods.

  19. Influence of High Nitrogen Flux on Crystal Quality of Plasma-Assisted MBE Grown GaN Layers Using Raman Spectroscopy: Part-II

    SciTech Connect

    Asghar, M.; Hussain, I.; Islah u din; Saleemi, F.

    2007-05-09

    We have investigated lattice properties of plasma assisted MBE grown hexagonal GaN layers at varying nitrogen and gallium fluxes using Raman spectroscopy. Room temperature Raman spectra of Ga-rich layers and stoichiometric GaN are similar showing excitation modes at 434 cm-1, 567 cm-1 and 729 cm-1 identified as residual laser line, E{sub 2}{sup H} and A1(LO) mode, respectively. Similarity of Ga-rich and stoichiometric GaN layers is interpreted as the indication of comparable crystal quality of both GaN layers. In contrast, Raman scattering associated with N-rich GaN samples mere exhibit a broad band of excitations in the range of 250-650cm-1 leaving out A1(LO) mode. This typical observation along with intensity distribution of the peaks, is correlated with rough surface, bad crystal quality and high concentration of defects. Based on atomic displacement scheme, the broad band is identified as Ga- vacancies.

  20. Influence of post-deposition annealing on interfacial properties between GaN and ZrO{sub 2} grown by atomic layer deposition

    SciTech Connect

    Ye, Gang; Wang, Hong Arulkumaran, Subramaniam; Ng, Geok Ing; Li, Yang; Ang, Kian Siong; Geok Ng, Serene Lay; Ji, Rong; Liu, Zhi Hong

    2014-10-13

    Influence of post-deposition annealing on interfacial properties related to the formation/annihilation of interfacial GaO{sub x} layer of ZrO{sub 2} grown by atomic layer deposition (ALD) on GaN is studied. ZrO{sub 2} films were annealed in N{sub 2} atmospheres in temperature range of 300 °C to 700 °C and analyzed by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that Ga-O bond to Ga-N bond area ratio decreases in the samples annealed at temperatures lower than 500 °C, which could be attributed to the thinning of GaO{sub x} layer associated with low surface defect states due to “clean up” effect of ALD-ZrO{sub 2} on GaN. However, further increase in annealing temperature results in deterioration of interface quality, which is evidenced by increase in Ga-O bond to Ga-N bond area ratio and the reduction of Ga-N binding energy.

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

    SciTech Connect

    Kamyczek, P.; Placzek-Popko, E.; Zielony, E.; Gumienny, Z.; Zytkiewicz, Z. R.

    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 the 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.

  2. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and Subsequent Fabrication of Superlattice Structures Using AlN and InN

    DTIC Science & Technology

    1990-12-01

    Laboratories, Inc. 3. Structural Analysis Reflection high-energy electron diffraction performed during growth indicated that the BGaN film remained...was used (Hitachi H-800) to more closely examine the microstructural evolution of the BN/ BGaN /GaN epitaxial films. Cross-section TEM specimens were... BGaN layer to be a mixture of cubic and wurtzitic phases. This layer was heavily faulted. The latter phenomenon is to be expected given the high

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

    SciTech Connect

    Kumar, Mahesh; Bhat, Thirumaleshwara N.; Roul, Basanta; Rajpalke, Mohana K.; Kalghatgi, A.T.; Krupanidhi, S.B.

    2012-06-15

    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 of 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.

  4. The effect of nucleation layer thickness on the structural evolution and crystal quality of bulk GaN grown by a two-step process on cone-patterned sapphire substrate

    NASA Astrophysics Data System (ADS)

    Shang, Lin; Zhai, Guangmei; Mei, Fuhong; Jia, Wei; Yu, Chunyan; Liu, Xuguang; Xu, Bingshe

    2016-05-01

    The role of nucleation layer thickness on the GaN crystal quality grown on cone-patterned sapphire substrate (PSS) was explored. The morphologies of epitaxial GaN at different growth stages were investigated by a series of growth interruption in detail. After 10- and 15-min three-dimensional growth, the nucleation sites are very important for the bulk GaN crystal quality. They have a close relationship with the nucleation layer thickness, as confirmed through the scanning electron microscope (SEM) analysis. Nucleation sites formed mainly on patterns are bad for bulk GaN crystal quality and nucleation sites formed mainly in the trenches of PSS mounds are good for bulk GaN crystal quality, as proved by X-ray diffraction analysis. Nucleation layer thickness can effectively control the nucleation sites and thus determine the crystal quality of bulk GaN.

  5. Experimental phasing for structure determination using membrane-protein crystals grown by the lipid cubic phase method

    PubMed Central

    Li, Dianfan; Pye, Valerie E.; Caffrey, Martin

    2015-01-01

    Despite the marked increase in the number of membrane-protein structures solved using crystals grown by the lipid cubic phase or in meso method, only ten have been determined by SAD/MAD. This is likely to be a consequence of the technical difficulties associated with handling proteins and crystals in the sticky and viscous hosting mesophase that is usually incubated in glass sandwich plates for the purposes of crystallization. Here, a four-year campaign aimed at phasing the in meso structure of the integral membrane diacylglycerol kinase (DgkA) from Escherichia coli is reported. Heavy-atom labelling of this small hydrophobic enzyme was attempted by pre-labelling, co-crystallization, soaking, site-specific mercury binding to genetically engineered single-cysteine mutants and selenomethionine incorporation. Strategies and techniques for special handling are reported, as well as the typical results and the lessons learned for each of these approaches. In addition, an assay to assess the accessibility of cysteine residues in membrane proteins for mercury labelling is introduced. The various techniques and strategies described will provide a valuable reference for future experimental phasing of membrane proteins where crystals are grown by the lipid cubic phase method. PMID:25615865

  6. m-plane GaN layers grown by rf-plasma assisted molecular beam epitaxy with varying Ga/N flux ratios on m-plane 4H-SiC substrates

    SciTech Connect

    Armitage, R.; Horita, M.; Suda, J.; Kimoto, T.

    2007-02-01

    A series of m-plane GaN layers with the Ga beam-equivalent pressure (BEP) as the only varied parameter was grown by rf-plasma assisted molecular beam epitaxy on m-plane 4H-SiC substrates using AlN buffer layers. The smoothest growth surfaces and most complete film coalescence were found for the highest Ga BEP corresponding to the Ga droplet accumulation regime. However, better structural quality as assessed by x-ray rocking curves was observed for growth at a lower Ga BEP value below the droplet limit. The variation of rocking curve widths for planes inclined with respect to the epilayer c axis followed a different trend with Ga BEP than those of reflections parallel to the c axis. The GaN layers were found to exhibit a large residual compressive strain along the a axis.

  7. Correlating exciton localization with compositional fluctuations in InGaN/GaN quantum wells grown on GaN planar surfaces and facets of GaN triangular prisms

    SciTech Connect

    Khatsevich, S.; Rich, D. H.; Zhang, X.; Dapkus, P. D.

    2007-11-01

    We have used spatially and temporally resolved cathodoluminescence (CL) to study the carrier recombination dynamics of InGaN quantum wells (QWs) grown on (0001)-oriented planar GaN and (1101)-oriented facets of GaN triangular prisms prepared by lateral epitaxial overgrowth in a metal-organic chemical vapor deposition system. The effects of In migration during growth on the resulting QW thickness and composition were examined. We employed a variable temperature time-resolved CL imaging approach that enables a spatial correlation between regions of enhanced exciton localization, luminescence efficiency, and radiative lifetime with the aim of distinguishing between excitons localized in In-rich quantum dots and those in the surrounding Ga-rich QW regions.

  8. Crystallographic Wet Chemical Etching of Semipolar GaN (11-22) Grown on m-Plane Sapphire Substrates.

    PubMed

    Kim, Jae-Kwan; Lee, Sung Nam; Song, Keun-Man; Yoon, Jae-Sik; Lee, Ji-Myon

    2015-07-01

    This paper reports the etch rates and etched surface morphology of semipolar GaN using a potassium hydroxide (KOH) solution. Semipolar (11-22) GaN could be etched easily using a KOH solution and the etch rate was higher than that of Ga-polar c-plane GaN (0001). The etch rate was anisotropic and the highest etch rate was measured to be approximately 116 nm/min for the (1011) plane and 62 nm/min for the (11-20) plane GaN using a 4 M KOH solution at 100 °C, resulting in specific surface features, such as inclined trigonal cells.

  9. Influence of growth rate on the carbon contamination and luminescence of GaN grown on silicon

    NASA Astrophysics Data System (ADS)

    Qinghua, Mao; Junlin, Liu; Xiaoming, Wu; Jianli, Zhang; Chuanbing, Xiong; Chunlan, Mo; Meng, Zhang; Fengyi, Jiang

    2015-09-01

    The unintentional carbon doping concentration of GaN films grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) depends strongly on the growth rate. The concentration of carbon is varied from 2.9 × 1017 to 5.7 × 1018 cm-3 when the growth rate increases from 2.0 to 7.2 μm/h, as detected by secondary ion mass spectroscopy. It is shown that the presence of N vacancies give rises to high carbon concentration. We show that a reduction of the carbon concentration by one order of magnitude compared to the regular sample with nearly same growth rate can be achieved by operating at an extremely high NH3 partial pressure during growth. The intensity ratios of yellow and blue luminescence to band edge luminescence in the samples are found to depend significantly on carbon concentration. The present results demonstrate direct and quantitative evidence that the carbon related defects are the origin of yellow and blue luminescence. Project supported by the Key Program of the National Natural Science Foundation of China (No. 61334001), the National Natural Science Foundation of China (No. 51072076), the National High Technology Research and Development Program of China (Nos. 2011AA03A101, 2012AA041002), the National Key Technology Research and Development Program of China (No. 2011BAE32B01), and the Fund for Less Developed Regions of the National Natural Science Foundation of China (No.11364034).

  10. 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.

  11. Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN

    PubMed Central

    2010-01-01

    Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO2 film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, ηextraction, was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period. PMID:21124627

  12. Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN.

    PubMed

    Soh, C B; Liu, W; Yong, A M; Chua, S J; Chow, S Y; Tripathy, S; Tan, R J N

    2010-08-01

    Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO(2) film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, η(extraction,) was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

  13. Impact of extended defects on optical properties of (1-101)GaN grown on patterned Si

    NASA Astrophysics Data System (ADS)

    Okur, S.; Izyumskaya, N.; Zhang, F.; Avrutin, V.; Metzner, S.; Karbaum, C.; Bertram, F.; Christen, J.; Morkoç, H.; Özgür, Ü.

    2014-03-01

    The optical quality of semipolar (1 101)GaN layers was explored by time- and polarization-resolved photoluminescence spectroscopy. High intensity bandedge emission was observed in +c-wing regions of the stripes as a result of better structural quality, while -c-wing regions were found to be of poorer optical quality due to basal plane and prismatic stacking faults (BSFs and PSFs) in addition to a high density of TDs. The high optical quality region formed on the +cwings was evidenced also from the much slower biexponential PL decays (0.22 ns and 1.70 ns) and an order of magnitude smaller amplitude ratio of the fast decay (nonradiative origin) to the slow decay component (radiative origin) compared to the -c-wing regions. In regard to defect-related emission, decay times for the BSF and PSF emission lines at 25 K (~ 0.80 ns and ~ 3.5 ns, respectively) were independent of the excitation density within the range employed (5 - 420 W/cm2), and much longer than that for the donor bound excitons (0.13 ns at 5 W/cm2 and 0.22 ns at 420 W/cm2). It was also found that the emission from BSFs had lower polarization degree (0.22) than that from donor bound excitons (0.35). The diminution of the polarization degree when photogenerated carriers recombine within the BSFs is another indication of the negative effects of stacking faults on the optical quality of the semipolar (1101)GaN. In addition, spatial distribution of defects in semipolar (1101)-oriented InGaN active region layers grown on stripe patterned Si substrates was investigated using near-field scanning optical microscopy. The optical quality of -c- wing regions was found to be worse compared to +c-wing regions due to the presence of higher density of stacking faults and threading dislocations. The emission from the +c-wings was very bright and relatively uniform across the sample, which is indicative of a homogeneous In distribution.

  14. Single-crystal cubic boron nitride thin films grown by ion-beam-assisted molecular beam epitaxy

    SciTech Connect

    Hirama, Kazuyuki Taniyasu, Yoshitaka; Karimoto, Shin-ichi; Krockenberger, Yoshiharu; Yamamoto, Hideki

    2014-03-03

    We investigated the formation of cubic boron nitride (c-BN) thin films on diamond (001) and (111) substrates by ion-beam-assisted molecular beam epitaxy (MBE). The metastable c-BN (sp{sup 3}-bonded BN) phase can be epitaxially grown as a result of the interplay between competitive phase formation and selective etching. We show that a proper adjustment of acceleration voltage for N{sub 2}{sup +} and Ar{sup +} ions is a key to selectively discriminate non-sp{sup 3} BN phases. At low acceleration voltage values, the sp{sup 2}-bonded BN is dominantly formed, while at high acceleration voltages, etching dominates irrespective of the bonding characteristics of BN.

  15. Highly-stable and low-state-density Al2O3/GaN interfaces using epitaxial n-GaN layers grown on free-standing GaN substrates

    NASA Astrophysics Data System (ADS)

    Kaneki, Shota; Ohira, Joji; Toiya, Shota; Yatabe, Zenji; Asubar, Joel T.; Hashizume, Tamotsu

    2016-10-01

    Interface characterization was carried out on Al2O3/GaN structures using epitaxial n-GaN layers grown on free-standing GaN substrates with relatively low dislocation density (<3 × 106 cm-2). The Al2O3 layer was prepared by atomic layer deposition. The as-deposited metal-oxide-semiconductor (MOS) sample showed a significant frequency dispersion and a bump-like feature in capacitance-voltage (C-V) curves at reverse bias, showing high-density interface states in the range of 1012 cm-1 eV-1. On the other hand, excellent C-V characteristics with negligible frequency dispersion were observed from the MOS sample after annealing under a reverse bias at 300 °C in air for 3 h. The reverse-bias-annealed sample showed state densities less than 1 × 1011 cm-1 eV-1 and small shifts of flat-band voltage. In addition, the C-V curve measured at 200 °C remained essentially similar compared with the room-temperature C-V curves. These results indicate that the present process realizes a stable Al2O3/GaN interface with low interface state densities.

  16. Vacancy-type defects in Mg-doped GaN grown by ammonia-based molecular beam epitaxy probed using a monoenergetic positron beam

    SciTech Connect

    Uedono, Akira; Malinverni, Marco; Martin, Denis; Grandjean, Nicolas; Okumura, Hironori; Ishibashi, Shoji

    2016-06-28

    Vacancy-type defects in Mg-doped GaN were probed using a monoenergetic positron beam. GaN films with a thickness of 0.5–0.7 μm were grown on GaN/sapphire templates using ammonia-based molecular beam epitaxy and characterized by measuring Doppler broadening spectra. Although no vacancies were detected in samples with a Mg concentration [Mg] below 7 × 10{sup 19 }cm{sup −3}, vacancy-type defects were introduced starting at above [Mg] = 1 × 10{sup 20 }cm{sup −3}. The major defect species was identified as a complex between Ga vacancy (V{sub Ga}) and multiple nitrogen vacancies (V{sub N}s). The introduction of vacancy complexes was found to correlate with a decrease in the net acceptor concentration, suggesting that the defect introduction is closely related to the carrier compensation. We also investigated Mg-doped GaN layers grown using In as the surfactant. The formation of vacancy complexes was suppressed in the subsurface region (≤80 nm). The observed depth distribution of defects was attributed to the thermal instability of the defects, which resulted in the introduction of vacancy complexes during the deposition process.

  17. Fe-doped semi-insulating GaN with solid Fe source grown on (110) Si substrates by NH3 molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Noh, Young Kyun; Lee, Sang Tae; Kim, Moon Deock; Oh, Jae Eung

    2017-02-01

    Iron doped GaN layers were grown on (110) Si substrates by ammonia molecular beam epitaxy (MBE) using solid elemental iron as a source. Specular films with concentrations up to 1×1020 cm-3, as determined by secondary ion mass spectroscopy, were grown, unlike a limited incorporation of Fe into GaN by metal-rich rf plasma MBE. The Fe concentration in the film showed an exponential dependence on the inverse of source temperature with an activation energy of 3.4 eV, which agrees well to the reported value for the sublimation of Fe. A 1.5 μm thick GaN film with a sheet resistance of 1 GΩ/sq. was obtained by compensating unintentional residual donors with a small Fe concentration of 1×1017 cm-3. X-ray diffraction rocking curves indicated high crystalline quality, very similar to an undoped film, showing that the Fe incorporation required to obtain the semi-insulating film properties did not affect the structural properties of the film. The low-temperature PL spectra of highly resistive and semi-insulating Fe:GaN in the range of 1017 1018 cm-3 show dominant exciton emissions and enhanced donor-acceptor-pair (DAP) emissions, implying that Fe ions contribute to the DAP transition between donor levels and Fe-related acceptor levels, possibly compensating the residual donors to achieve the semi-insulating electrical properties.

  18. Vacancy-type defects in Mg-doped GaN grown by ammonia-based molecular beam epitaxy probed using a monoenergetic positron beam

    NASA Astrophysics Data System (ADS)

    Uedono, Akira; Malinverni, Marco; Martin, Denis; Okumura, Hironori; Ishibashi, Shoji; Grandjean, Nicolas

    2016-06-01

    Vacancy-type defects in Mg-doped GaN were probed using a monoenergetic positron beam. GaN films with a thickness of 0.5-0.7 μm were grown on GaN/sapphire templates using ammonia-based molecular beam epitaxy and characterized by measuring Doppler broadening spectra. Although no vacancies were detected in samples with a Mg concentration [Mg] below 7 × 1019 cm-3, vacancy-type defects were introduced starting at above [Mg] = 1 × 1020 cm-3. The major defect species was identified as a complex between Ga vacancy (VGa) and multiple nitrogen vacancies (VNs). The introduction of vacancy complexes was found to correlate with a decrease in the net acceptor concentration, suggesting that the defect introduction is closely related to the carrier compensation. We also investigated Mg-doped GaN layers grown using In as the surfactant. The formation of vacancy complexes was suppressed in the subsurface region (≤80 nm). The observed depth distribution of defects was attributed to the thermal instability of the defects, which resulted in the introduction of vacancy complexes during the deposition process.

  19. Thermal characterization of polycrystalline diamond thin film heat spreaders grown on GaN HEMTs

    NASA Astrophysics Data System (ADS)

    Zhou, Yan; Ramaneti, Rajesh; Anaya, Julian; Korneychuk, Svetlana; Derluyn, Joff; Sun, Huarui; Pomeroy, James; Verbeeck, Johan; Haenen, Ken; Kuball, Martin

    2017-07-01

    Polycrystalline diamond (PCD) was grown onto high-k dielectric passivated AlGaN/GaN-on-Si high electron mobility transistor (HEMT) structures, with film thicknesses ranging from 155 to 1000 nm. Transient thermoreflectance results were combined with device thermal simulations to investigate the heat spreading benefit of the diamond layer. The observed thermal conductivity (κDia) of PCD films is one-to-two orders of magnitude lower than that of bulk PCD and exhibits a strong layer thickness dependence, which is attributed to the grain size evolution. The films exhibit a weak temperature dependence of κDia in the measured 25-225 °C range. Device simulation using the experimental κDia and thermal boundary resistance values predicts at best a 15% reduction in peak temperature when the source-drain opening of a passivated AlGaN/GaN-on-Si HEMT is overgrown with PCD.

  20. The interface analysis of GaN grown on 0° off 6H-SiC with an ultra-thin buffer layer

    NASA Astrophysics Data System (ADS)

    Sun, Zheng; Ohta, Akio; Miyazaki, Seiichi; Nagamatsu, Kentaro; Lee, Hojun; Olsson, Marc; Ye, Zheng; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-01-01

    Previously, we reported a growth method by metalorganic vapor phase epitaxy using a single two-dimensional growth step, resulting in 1.2-µm crack-free GaN directly grown on 6H-SiC substrate. The introduction of Al-treatment prior to the standard GaN growth step resulted in improved surface wetting of gallium on the SiC substrate. Transmission electron microscope and energy dispersive spectrometer analysis of the epitaxial interface to the SiC determined that an ultra-thin AlGaN interlayer had formed measuring around 2-3 nm. We expect our growth technique can be applied to the fabrication of GaN/SiC high frequency and high power devices.

  1. Local Strain, Defects and Crystallographic Tilt in GaN(0001) Layers Grown by Maskless Pendeo-epitaxy from X-ray Microdiffraction

    SciTech Connect

    Barabash, R.I.; Ice, G.E.; Liu, W.; Einfeldt, S.; Roskovski, A.M.; Davis, R.F.

    2010-07-13

    Polychromatic x-ray microdiffraction, high-resolution monochromatic x-ray diffraction, and finite element simulations have been used to determine the distribution of strain, defects, and crystallographic tilt in uncoalesced GaN layers grown by maskless pendeo-epitaxy. An important materials parameter was the width-to-height ratio of the etched columns of GaN from which occurred the lateral growth of the wings. Tilt boundaries formed at the column/wing interface for samples with a large ratio. Formation of the tilt boundary can be avoided by using smaller ratios. The strain and tilt across the stripe increased with the width-to-height ratio. The wings were tilted upward at room temperature.

  2. Preparation of Ag Schottky contacts on n-type GaN bulk crystals grown in nitrogen rich atmosphere by the hydride vapor phase epitaxy technique

    SciTech Connect

    Stübner, R. Kolkovsky, Vl.; Weber, J.; Leibiger, Gunnar; Habel, Frank

    2014-10-14

    Electrical properties of Schottky contacts on n-type GaN grown in nitrogen rich atmosphere with different N/Ga ratios by hydride vapor phase epitaxy were investigated. We show that tunneling of electrons from the conduction band of GaN to the metal is dominant in our samples. The quality of Schottky contacts does not only depend on surface preparation but also on the growth conditions of the crystals. Schottky contacts on these crystals show an increasing deterioration when higher N/Ga growth ratios are used. We correlate our results with the presence of negatively charged gallium vacancies in the samples. These charges compensate the positively charged donors and lead to a significant increase in series resistance.

  3. Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2¯01).

    PubMed

    Kollmannsberger, Sebastian L; Walenta, Constantin A; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

    2017-09-28

    In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga2O3(2¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

  4. Structural properties of free-standing 50 mm diameter GaN waferswith (101_0) orientation grown on LiAlO2

    SciTech Connect

    Jasinski, Jacek; Liliental-Weber, Zuzanna; Maruska, Herbert-Paul; Chai, Bruce H.; Hill, David W.; Chou, Mitch M.C.; Gallagher, John J.; Brown, Stephen

    2005-09-27

    (10{und 1}0) GaN wafers grown on (100) face of {gamma}-LiAlO{sub 2} were studied using transmission electron microscopy. Despite good lattice matching in this heteroepitaxial system, high densities of planar structural defects in the form of stacking faults on the basal plane and networks of boundaries located on prism planes inclined to the layer/substrate interface were present in these GaN layers. In addition, significant numbers of threading dislocations were observed. High-resolution electron microscopy indicates that stacking faults present on the basal plane in these layers are of low-energy intrinsic I1type. This is consistent with diffraction contrast experiments.

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

    SciTech Connect

    Alevli, Mustafa Gungor, Neşe; Haider, Ali; Kizir, Seda; Leghari, Shahid A.; Biyikli, Necmi

    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, the chemical composition, E{sub 1}(TO), phonon position, and crystalline phases present in the GaN film were relatively independent from growth temperature.

  6. Role of an ultra-thin AlN/GaN superlattice interlayer on the strain engineering of GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Shen, X. Q.; Takahashi, T.; Matsuhata, H.; Ide, T.; Shimizu, M.; Rong, X.; Chen, G.; Wang, X. Q.; Shen, B.

    2013-12-02

    We investigate the role of an ultra-thin AlN/GaN superlattice interlayer (SL-IL) on the strain engineering of the GaN films grown on Si(110) and Si(111) substrates by plasma-assisted molecular beam epitaxy. It is found that micro-cracks limitted only at the SL-IL position are naturally generated. These micro-cracks play an important role in relaxing the tensile strain caused by the difference of the coefficient of thermal expansion between GaN and Si and keeping the residual strain in the crack-free GaN epilayers resulted from the SL-IL during the growth. The mechanism understanding of the strain modulation by the SL-IL in the GaN epilayers grown on Si substrates makes it possible to design new heterostructures of III-nitrides for optic and electronic device applications.

  7. Low dislocation density InAlN/AlN/GaN heterostructures grown on GaN substrates and the effects on gate leakage characteristics

    NASA Astrophysics Data System (ADS)

    Kotani, Junji; Yamada, Atsushi; Ishiguro, Tetsuro; Tomabechi, Shuichi; Nakamura, Norikazu

    2016-04-01

    This paper reports on the electrical characterization of Ni/Au Schottky diodes fabricated on InAlN high-electron-mobility transistor (HEMT) structures grown on low dislocation density free-standing GaN substrates. InAlN HEMT structures were grown on sapphire and GaN substrates by metal-organic vapor phase epitaxy, and the effects of threading dislocation density on the leakage characteristics of Ni/Au Schottky diodes were investigated. Threading dislocation densities were determined to be 1.8 × 104 cm-2 and 1.2 × 109 cm-2 by the cathodoluminescence measurement for the HEMT structures grown on GaN and sapphire substrates, respectively. Leakage characteristics of Ni/Au Schottky diodes were compared between the two samples, and a reduction of the leakage current of about three to four orders of magnitude was observed in the forward bias region. For the high reverse bias region, however, no significant improvement was confirmed. We believe that the leakage current in the low bias region is governed by a dislocation-related Frenkel-Poole emission, and the leakage current in the high reverse bias region originates from field emission due to the large internal electric field in the InAlN barrier layer. Our results demonstrated that the reduction of dislocation density is effective in reducing leakage current in the low bias region. At the same time, it was also revealed that another approach will be needed, for instance, band modulation by impurity doping and insertion of insulating layers beneath the gate electrodes for a substantial reduction of the gate leakage current.

  8. Steady-State and Transient Photoconductivity in c-Axis GaN Nanowires Grown by Nitrogen-Plasma-Assisted Molecular Beam Epitaxy

    DTIC Science & Technology

    2010-02-01

    Steady-state and transient photoconductivity in c-axis GaN nanowires grown by nitrogen-plasma-assisted molecular beam epitaxy N. A. Sanford,1,a P. T...assisted molecular beam epitaxy primarily from two separate growth runs were examined. The results revealed carrier concentration in the range of 3–61016...cm−3 for one growth run, roughly 51014–11015 cm−3 for the second, and drift mobility in the range of 500–700 cm2 / V s for both. Nanowires were

  9. Strain in epitaxial Bi2Se3 grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

    NASA Astrophysics Data System (ADS)

    Li, Bin; Guo, Xin; Ho, Wingkin; Xie, Maohai

    2015-08-01

    Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi2Se3 has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi2Se3 by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi2Se3 grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van deer Waals interaction between Bi2Se3 quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi2Se3 deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi2Se3 during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi2Se3 is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.

  10. Steady-state and time-resolved photoluminescence from relaxed and strained GaN nanowires grown by catalyst-free molecular-beam epitaxy

    SciTech Connect

    Schlager, John B.; Bertness, Kris A.; Blanchard, Paul T.; Robins, Lawrence H.; Roshko, Alexana; Sanford, Norman A.

    2008-06-15

    We report steady-state and time-resolved photoluminescence (TRPL) measurements on individual GaN nanowires (6-20 {mu}m in length, 30-940 nm in diameter) grown by a nitrogen-plasma-assisted, catalyst-free molecular-beam epitaxy on Si(111) and dispersed onto fused quartz substrates. Induced tensile strain for nanowires bonded to fused silica and compressive strain for nanowires coated with atomic-layer-deposition alumina led to redshifts and blueshifts of the dominant steady-state PL emission peak, respectively. Unperturbed nanowires exhibited spectra associated with high-quality, strain-free material. The TRPL lifetimes, which were similar for both relaxed and strained nanowires of similar size, ranged from 200 ps to over 2 ns, compared well with those of low-defect bulk GaN, and depended linearly on nanowire diameter. The diameter-dependent lifetimes yielded a room-temperature surface recombination velocity S of 9x10{sup 3} cm/s for our silicon-doped GaN nanowires.

  11. Steady-state and time-resolved photoluminescence from relaxed and strained GaN nanowires grown by catalyst-free molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Schlager, John B.; Bertness, Kris A.; Blanchard, Paul T.; Robins, Lawrence H.; Roshko, Alexana; Sanford, Norman A.

    2008-06-01

    We report steady-state and time-resolved photoluminescence (TRPL) measurements on individual GaN nanowires (6-20 μm in length, 30-940 nm in diameter) grown by a nitrogen-plasma-assisted, catalyst-free molecular-beam epitaxy on Si(111) and dispersed onto fused quartz substrates. Induced tensile strain for nanowires bonded to fused silica and compressive strain for nanowires coated with atomic-layer-deposition alumina led to redshifts and blueshifts of the dominant steady-state PL emission peak, respectively. Unperturbed nanowires exhibited spectra associated with high-quality, strain-free material. The TRPL lifetimes, which were similar for both relaxed and strained nanowires of similar size, ranged from 200 ps to over 2 ns, compared well with those of low-defect bulk GaN, and depended linearly on nanowire diameter. The diameter-dependent lifetimes yielded a room-temperature surface recombination velocity S of 9×103 cm/s for our silicon-doped GaN nanowires.

  12. Structural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy

    SciTech Connect

    Lotsari, A.; Kehagias, Th.; Katsikini, M.; Arvanitidis, J.; Ves, S.; Komninou, Ph.; Dimitrakopulos, G. P.; Tsiakatouras, G.; Tsagaraki, K.; Georgakilas, A.; Christofilos, D.

    2014-06-07

    Heteroepitaxial non-polar III-Nitride layers may exhibit extensive anisotropy in the surface morphology and the epilayer microstructure along distinct in-plane directions. The structural anisotropy, evidenced by the “M”-shape dependence of the (112{sup ¯}0) x-ray rocking curve widths on the beam azimuth angle, was studied by combining transmission electron microscopy observations, Raman spectroscopy, high resolution x-ray diffraction, and atomic force microscopy in a-plane GaN epilayers grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). The structural anisotropic behavior was attributed quantitatively to the high dislocation densities, particularly the Frank-Shockley partial dislocations that delimit the I{sub 1} intrinsic basal stacking faults, and to the concomitant plastic strain relaxation. On the other hand, isotropic samples exhibited lower dislocation densities and a biaxial residual stress state. For PAMBE growth, the anisotropy was correlated to N-rich (or Ga-poor) conditions on the surface during growth, that result in formation of asymmetric a-plane GaN grains elongated along the c-axis. Such conditions enhance the anisotropy of gallium diffusion on the surface and reduce the GaN nucleation rate.

  13. Dynamics of thermalization in GaInN/GaN quantum wells grown on ammonothermal GaN

    SciTech Connect

    Binder, J.; Korona, K. P.; Wysmołek, A.; Kamińska, M.; Köhler, K.; Kirste, L.; Ambacher, O.; Zając, M.; Dwiliński, R.

    2013-12-14

    In this work, we present measurements of the dynamics of photoexcited carriers in GaInN/GaN quantum wells (QWs) grown on ammonothermal GaN, especially thermalization and recombination rates. Emission properties were measured by time-resolved photoluminescence (PL) and electroluminescence spectroscopy. Due to the use of high quality homoepitaxial material, we were able to obtain very valuable data on carrier thermalization. The temperature dependence of the QW energy observed in PL shows characteristic S-shape with a step of about 10 meV. Such a behavior (related to thermalization and localization at potential fluctuations) is often reported for QWs; but in our samples, the effect is smaller than in heteroepitaxial InGaN/GaN QWs due to lower potential fluctuation in our material. Absorption properties were studied by photocurrent spectroscopy measurements. A comparison of emission and absorption spectra revealed a shift in energy of about 60 meV. Contrary to PL, the QW energy observed in absorption decreases monotonically with temperature, which can be described by a Bose-like dependence E(T) = E(0) − λ/(exp(θ/T) − 1), with parameters λ = (0.11 ± 0.01) eV, θ = (355 ± 20) K, or by a Varshni dependence with coefficients α = (10 ± 3) × 10{sup −4} eV/K and β = (1500 ± 500) K. Taking into account absorption and emission, the fluctuation amplitude (according to Eliseev theory) was σ = 14 meV. The time resolved PL revealed that in a short period (<1 ns) after excitation, the PL peaks were broadened because of the thermal distribution of carriers. We interpreted this distribution in terms of quasi-temperature (T{sub q}) of the carriers. The initial T{sub q} was of the order of 500 K. The thermalization led to a fast decrease of T{sub q}. The obtained cooling time in the QW was τ{sub C} = 0.3 ns, which was faster than the observed recombination time τ{sub R} = 2.2 ns (at 4 K)

  14. Structural and optical characteristics of the hexagonal ZnO films grown on cubic MgO (001) substrates.

    PubMed

    Shen, Xiangqian; Zhou, Hua; Li, Yaping; Kang, Junyong; Zheng, Jin-Cheng; Ke, Shanming; Wang, Qingkang; Wang, Hui-Qiong

    2016-11-01

    In this Letter, we report on the structural and optical characteristics of ZnO films with a wurtzite structure grown on MgO (001) substrates with cubic structures. The ZnO films were prepared through the molecular beam epitaxy method, and growth orientation transformation from [0001] to [10-10] direction was observed with the change of growth temperature and thickness. The x-ray diffraction pole figures and in situ RHEED patterns demonstrated that the rotational relationship among grains within the ZnO films appeared in a typical two-fold rotation of about 30° for the [0001] growth orientation and four-fold rotation of about 30° or 60° for the [10-10] growth orientation, respectively. Last, we investigated their optical properties through measuring the transmission and photoluminescence spectra of the ZnO films, which showed the bulk-like bandgap feature of the ZnO films in spite of the existing growth orientation transformation.

  15. Optical Properties of Novel GaN 3D Structures Grown by Metal-Organic Chemical Vapor Deposition (MOCVD)

    NASA Astrophysics Data System (ADS)

    Sacilotti, Marco; Imhoff, Luc; Dumas, Colette; Viste, Pierre; Vial, Jean-Claude; Baldeck, Patrice; Colombier, Isabelle; Donatini, Fabrice

    2004-06-01

    Optical properties of novel micrometer-size Ga and GaN three-dimensional structures obtained by the metal-organic chemical vapour deposition (MOCVD) technique are presented in this letter. These structures are obtained as metallic three dimensions (3D) micrometer-size objects on an appropriate substrate by metalorganic (TMGa) pyrolisis and then GaN transformed on annealing under NH3 atmosphere at 650-750°C. These 3D GaN structures are analysed by optical means, using two-photon excitation (800 nm) and by UV Hg lamp fluorescent spectroscopy techniques, adapted to two-optical-microscopes apparatus. Very intense and blue/yellow light emission is observed from these 3D structures under 800 nm two-photon laser excitation and under UV Hg lamp excitation.

  16. Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (112{sup -}2) GaN templates

    SciTech Connect

    Niehle, M. Trampert, A.; Albert, S.; Bengoechea-Encabo, A.; Calleja, E.

    2015-03-01

    We present results of scanning transmission electron tomography on GaN/(In,Ga)N/GaN nanocolumns (NCs) that grew uniformly inclined towards the patterned, semi-polar GaN(112{sup -}2) substrate surface by molecular beam epitaxy. For the practical realization of the tomographic experiment, the nanocolumn axis has been aligned parallel to the rotation axis of the electron microscope goniometer. The tomographic reconstruction allows for the determination of the three-dimensional indium distribution inside the nanocolumns. This distribution is strongly interrelated with the nanocolumn morphology and faceting. The (In,Ga)N layer thickness and the indium concentration differ between crystallographically equivalent and non-equivalent facets. The largest thickness and the highest indium concentration are found at the nanocolumn apex parallel to the basal planes.

  17. Deep levels in as-grown and electron-irradiated n-type GaN studied by deep level transient spectroscopy and minority carrier transient spectroscopy

    SciTech Connect

    Duc, Tran Thien; Pozina, Galia; Son, Nguyen Tien; Kordina, Olof; Janzén, Erik; Hemmingsson, Carl; Ohshima, Takeshi

    2016-03-07

    Development of high performance GaN-based devices is strongly dependent on the possibility to control and understand defects in material. Important information about deep level defects is obtained by deep level transient spectroscopy and minority carrier transient spectroscopy on as-grown and electron irradiated n-type bulk GaN with low threading dislocation density produced by halide vapor phase epitaxy. One hole trap labelled H1 (E{sub V} + 0.34 eV) has been detected on as-grown GaN sample. After 2 MeV electron irradiation, the concentration of H1 increases and at fluences higher than 5 × 10{sup 14 }cm{sup −2}, a second hole trap labelled H2 is observed. Simultaneously, the concentration of two electron traps, labelled T1 (E{sub C} – 0.12 eV) and T2 (E{sub C} – 0.23 eV), increases. By studying the increase of the defect concentration versus electron irradiation fluence, the introduction rate of T1 and T2 using 2 MeV- electrons was determined to be 7 × 10{sup −3 }cm{sup −1} and 0.9 cm{sup −1}, respectively. Due to the low introduction rate of T1, it is suggested that the defect is associated with a complex. The high introduction rate of trap H1 and T2 suggests that the defects are associated with primary intrinsic defects or complexes. Some deep levels previously observed in irradiated GaN layers with higher threading dislocation densities are not detected in present investigation. It is therefore suggested that the absent traps may be related to primary defects segregated around dislocations.

  18. Partially polycrystalline GaN1- x As x alloys grown on GaAs in the middle composition range achieving a smaller band gap

    NASA Astrophysics Data System (ADS)

    Wu, Hong-Ming; Lin, Kuang-I.; Liu, Yu-Xuan; Lin, Hao-Hsiung; Cheng, Yung-Chen

    2017-08-01

    GaN1- x As x alloys have been successfully grown on (100) GaAs substrates over a wide composition range (0.15 < x < 0.98) by plasma-assisted molecular beam epitaxy. In the middle composition range, the weak and broad (111) diffraction peaks are observed in the X-ray diffraction patterns. These diffraction peaks most likely come from small crystalline grains within the amorphous matrix and are unlike the entirely amorphous GaNAs alloys grown on sapphire and Pyrex glass. A transmission electron microscopy micrograph of the GaN0.50As0.50 alloy also shows a weak periodic structure consisting of small polycrystalline grains. To study the band gap and the As-affected spin-orbit band to conduction-band minimum transition, photomodulated reflectance is utilized. The band gap energies range from 0.78 to 2.15 eV (3.4 eV for end-point compounds GaN). Finally, the original and modified band anticrossing (BAC) models for GaNAs alloys were thoroughly verified over the entire composition range. Remarkably, the band gap energies of the partially polycrystalline GaNAs alloys agree well with those obtained using the original BAC model in the middle composition range because the model has been developed for crystalline materials. These results improve the growth of highly mismatched GaNAs alloys with different substrates and should expedite studies of high-efficiency multijunction solar cells fabricated using such a single ternary alloy system.

  19. Strong light-matter coupling at room temperature in simple geometry GaN microcavities grown on silicon

    SciTech Connect

    Semond, F.; Sellers, I.R.; Natali, F.; Byrne, D.; Leroux, M.; Massies, J.; Ollier, N.; Leymarie, J.; Disseix, P.; Vasson, A.

    2005-07-11

    The reflectance spectra of simple design GaN-based microcavities have been studied in the 5 K-300 K range. The epitaxial structure consists of the silicon substrate and the stack of buffer layers as the back mirror, a GaN active layer, and a 100 A thick aluminium layer as the top mirror. Active layer thicknesses of {lambda}/2, {lambda}, or 3{lambda}/2 were investigated. The samples with GaN thicknesses {lambda}/2 and {lambda} display an anticrossing behavior between the cavity and exciton modes, with measured Rabi splittings of 47 and 60 meV, respectively, both at 5 K and room temperature.

  20. On the polarity of GaN micro- and nanowires epitaxially grown on sapphire (0001) and Si(111) substrates by metal organic vapor phase epitaxy and ammonia-molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Alloing, B.; Vézian, S.; Tottereau, O.; Vennéguès, P.; Beraudo, E.; Zuniga-Pérez, J.

    2011-01-01

    The polarity of GaN micro- and nanowires grown epitaxially by metal organic vapor phase epitaxy on sapphire substrates and by molecular-beam epitaxy, using ammonia as a nitrogen source, on sapphire and silicon substrates has been investigated. On Al2O3(0001), whatever the growth technique employed, the GaN wires show a mixture of Ga and N polarities. On Si(111), the wires grown by ammonia-molecular beam epitaxy are almost entirely Ga-polar (around 90%) and do not show inversion domains. These results can be understood in terms of the growth conditions employed during the nucleation stage.

  1. On the polarity of GaN micro- and nanowires epitaxially grown on sapphire (0001) and Si(111) substrates by metal organic vapor phase epitaxy and ammonia-molecular beam epitaxy

    SciTech Connect

    Alloing, B.; Vezian, S.; Tottereau, O.; Vennegues, P.; Beraudo, E.; Zuniga-Perez, J.

    2011-01-03

    The polarity of GaN micro- and nanowires grown epitaxially by metal organic vapor phase epitaxy on sapphire substrates and by molecular-beam epitaxy, using ammonia as a nitrogen source, on sapphire and silicon substrates has been investigated. On Al{sub 2}O{sub 3}(0001), whatever the growth technique employed, the GaN wires show a mixture of Ga and N polarities. On Si(111), the wires grown by ammonia-molecular beam epitaxy are almost entirely Ga-polar (around 90%) and do not show inversion domains. These results can be understood in terms of the growth conditions employed during the nucleation stage.

  2. TEM study of defect structure of GaN epitaxial films grown on GaN/Al2O3 substrates with buried column pattern

    NASA Astrophysics Data System (ADS)

    Mynbaeva, M. G.; Kremleva, A. V.; Kirilenko, D. A.; Sitnikova, A. A.; Pechnikov, A. I.; Mynbaev, K. D.; Nikolaev, V. I.; Bougrov, V. E.; Lipsanen, H.; Romanov, A. E.

    2016-07-01

    A TEM study of defect structure of GaN films grown by chloride vapor-phase epitaxy (HVPE) on GaN/Al2O3 substrates was performed. The substrates were fabricated by metal-organic chemical vapor deposition overgrowth of templates with buried column pattern. The results of TEM study showed that the character of the defect structure of HVPE-grown films was determined by the configuration of the column pattern in the substrate. By choosing the proper pattern, the reduction in the density of threading dislocations in the films by two orders of magnitude (in respect to the substrate material), down to the value of 107 cm-2, was achieved.

  3. Role of band potential roughness on the luminescence properties of InGaN quantum wells grown by MBE on bulk GaN substrates

    NASA Astrophysics Data System (ADS)

    Ž, A.

    Role of band potential roughness on luminescence decay time and stimulated emission in InGaN quantum wells (QWs) grown by rf plasma-assisted molecular beam epitaxy (MBE) on bulk GaN substrates was studied. A high-photoexcitation regime used ensured conditions similar to those in operating laser diodes. Standard deviation of the potential fluctuations in different thickness InGaN QWs was found to vary in the range of 13-22 meV as revealed by Monte Carlo simulation of localized exciton hopping. A negligible influence of this variation on the luminescence decay time (?700 ps) and stimulated emission threshold (?30 kW/cm2) was observed. We attribute this insensitivity to the low density of localized states (?1 × 1018 cm-3) estimated in our high-quality QWs grown by MBE, and therefore, assign extended states to be mainly responsible for the properties of highly-excited luminescence.

  4. Photoconduction efficiencies and dynamics in GaN nanowires grown by chemical vapor deposition and molecular beam epitaxy: A comparison study

    NASA Astrophysics Data System (ADS)

    Chen, R. S.; Tsai, H. Y.; Huang, Y. S.; Chen, Y. T.; Chen, L. C.; Chen, K. H.

    2012-09-01

    The normalized gains, which determines the intrinsic photoconduction (PC) efficiencies, have been defined and compared for the gallium nitride (GaN) nanowires (NWs) grown by chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). By excluding the contributions of experimental parameters and under the same light intensity, the CVD-grown GaN NWs exhibit the normalized gain which is near two orders of magnitude higher than that of the MBE-ones. The temperature-dependent time-resolved photocurrent measurement further indicates that the higher photoconduction efficiency in the CVD-GaN NWs is originated from the longer carrier lifetime induced by the higher barrier height (ϕB = 160 ± 30 mV) of surface band bending. In addition, the experimentally estimated barrier height at 20 ± 2 mV for the MBE-GaN NWs, which is much lower than the theoretical value, is inferred to be resulted from the lower density of charged surface states on the non-polar side walls.

  5. Strain in epitaxial Bi{sub 2}Se{sub 3} grown on GaN and graphene substrates: A reflection high-energy electron diffraction study

    SciTech Connect

    Li, Bin; Guo, Xin; Ho, Wingkin; Xie, Maohai

    2015-08-24

    Topological insulator (TI) has been one of the focus research themes in condensed matter physics in recent years. Due to the relatively large energy bandgap, Bi{sub 2}Se{sub 3} has been identified as one of the most promising three-dimensional TIs with application potentials. Epitaxial Bi{sub 2}Se{sub 3} by molecular-beam epitaxy has been reported by many groups using different substrates. A common feature is that Bi{sub 2}Se{sub 3} grows readily along the c-axis direction irrespective of the type and condition of the substrate. Because of the weak van der Waals interaction between Bi{sub 2}Se{sub 3} quintuple layers, the grown films are reported to be strain-free, taking the lattice constant of the bulk crystal. At the very initial stage of Bi{sub 2}Se{sub 3} deposition, however, strain may still exist depending on the substrate. Strain may bring some drastic effects to the properties of the TIs and so achieving strained TIs can be of great fundamental interests as well as practical relevance. In this work, we employ reflection high-energy electron diffraction to follow the lattice constant evolution of Bi{sub 2}Se{sub 3} during initial stage depositions on GaN and graphene, two very different substrates. We reveal that epitaxial Bi{sub 2}Se{sub 3} is tensile strained on GaN but strain-free on graphene. Strain relaxation on GaN is gradual.

  6. Phosphor-free white-light emitters using in-situ GaN nanostructures grown by metal organic chemical vapor deposition

    PubMed Central

    Min, Daehong; Park, Donghwy; Jang, Jongjin; Lee, Kyuseung; Nam, Okhyun

    2015-01-01

    Realization of phosphor-free white-light emitters is becoming an important milestone on the road to achieve high quality and reliability in high-power white-light-emitting diodes (LEDs). However, most of reported methods have not been applied to practical use because of their difficulties and complexity. In this study we demonstrated a novel and practical growth method for phosphor-free white-light emitters without any external processing, using only in-situ high-density GaN nanostructures that were formed by overgrowth on a silicon nitride (SiNx) interlayer deposited by metal organic chemical vapor deposition. The nano-sized facets produced variations in the InGaN thickness and the indium concentration when an InGaN/GaN double heterostructure was monolithically grown on them, leading to white-color light emission. It is important to note that the in-situ SiNx interlayer not only facilitated the GaN nano-facet structure, but also blocked the propagation of dislocations. PMID:26626890

  7. White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates

    NASA Astrophysics Data System (ADS)

    Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

    2017-06-01

    We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

  8. Strain management of AlGaN-based distributed Bragg reflectors with GaN interlayer grown by metalorganic chemical vapor deposition

    SciTech Connect

    Liu, Yuh-Shiuan; Kao, Tsung-Ting; Mehta, Karan; Jia, Xiao Jia; Shen, Shyh-Chiang; Yoder, P. Douglas; Detchprohm, Theeradetch; Dupuis, Russell D.; Wang, Shuo; Xie, Hongen; Ponce, Fernando A.

    2016-08-22

    We report the crack-free growth of a 45-pair Al{sub 0.30}Ga{sub 0.70}N/Al{sub 0.04}Ga{sub 0.96}N distributed Bragg reflector (DBR) on 2 in. diameter AlN/sapphire template by metalorganic chemical vapor deposition. To mitigate the cracking issue originating from the tensile strain of Al{sub 0.30}Ga{sub 0.70}N on GaN, an AlN template was employed in this work. On the other hand, strong compressive strain experienced by Al{sub 0.04}Ga{sub 0.96}N favors 3D island growth, which is undesired. We found that inserting an 11 nm thick GaN interlayer upon the completion of AlN template layer properly managed the strain such that the Al{sub 0.30}Ga{sub 0.70}N/Al{sub 0.04}Ga{sub 0.96}N DBR was able to be grown with an atomically smooth surface morphology. Smooth surfaces and sharp interfaces were observed throughout the structure using high-angle annular dark-field imaging in the STEM. The 45-pair AlGaN-based DBR provided a peak reflectivity of 95.4% at λ = 368 nm with a bandwidth of 15 nm.

  9. X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC

    NASA Astrophysics Data System (ADS)

    Sancho-Juan, O.; Cantarero, A.; Garro, N.; Cros, A.; Martínez-Criado, G.; Salomé, M.; Susini, J.; Olguín, D.; Dhar, S.

    2009-07-01

    By means of x-ray absorption near-edge structure (XANES) several Ga1-xMnxN (0.03GaN samples consisted of different epilayers grown by molecular beam epitaxy on [0001] SiC substrates. The low mismatch between GaN and SiC allows for a good quality and homogeneity of the material. The measurements were performed in fluorescence mode around both the Ga and Mn K edges. All samples studied present a similar Mn ionization state, very close to 2+, and tetrahedral coordination. In order to interpret the near-edge structure, we have performed ab initio calculations using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of a Mn bonding \\mathrm {t_{2}}\\uparrow band localized in the gap region, and the corresponding anti-bonding state \\mathrm {t_{2}}\\downarrow , which seem to be responsible for the double structure which appears at the pre-edge absorption region. The shoulders and main absorption peak of the XANES spectra are attributed to transitions from the Mn(1s) band to the conduction bands, which are partially dipole allowed because of the Mn(4p) contribution to these bands.

  10. Compositionally graded InGaN layers grown on vicinal N-face GaN substrates by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hestroffer, Karine; Lund, Cory; Koksaldi, Onur; Li, Haoran; Schmidt, Gordon; Trippel, Max; Veit, Peter; Bertram, Frank; Lu, Ning; Wang, Qingxiao; Christen, Jürgen; Kim, Moon J.; Mishra, Umesh K.; Keller, Stacia

    2017-05-01

    This work reports on compositionally graded (0 0 0 1 bar) N-polar InxGa1-xN layers. The InGaN grades with different final In compositions xf up to 0.25 were grown by plasma-assisted molecular beam epitaxy on vicinal GaN base layers with a miscut angle of 4° towards the m-direction. When increasing xf the surface morphology evolved from an interlacing finger structure, attributed to the Ehrlich-Schwöbel effect, towards fully strain-relaxed columnar features. Regardless of the crystal morphology and the strain state each graded sample exhibited a bright photoluminescence signal at room temperature spanning the whole visible range. Cross-sectional nanoscale cathodoluminescence evidenced a red-shift of the luminesced signal from 420 to 580 nm along the grade and also showed strong lateral emission inhomogeneities.

  11. Impact of barrier thickness on transistor performance in AlN/GaN high electron mobility transistors grown on free-standing GaN substrates

    SciTech Connect

    Deen, David A. Storm, David F.; Meyer, David J.; Bass, Robert; Binari, Steven C.; Gougousi, Theodosia; Evans, Keith R.

    2014-09-01

    A series of six ultrathin AlN/GaN heterostructures with varied AlN thicknesses from 1.5–6 nm have been grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. High electron mobility transistors (HEMTs) were fabricated from the set in order to assess the impact of barrier thickness and homo-epitaxial growth on transistor performance. Room temperature Hall characteristics revealed mobility of 1700 cm{sup 2}/V s and sheet resistance of 130 Ω/□ for a 3 nm thick barrier, ranking amongst the lowest room-temperature sheet resistance values reported for a polarization-doped single heterostructure in the III-Nitride family. DC and small signal HEMT electrical characteristics from submicron gate length HEMTs further elucidated the effect of the AlN barrier thickness on device performance.

  12. Impact of barrier thickness on transistor performance in AlN/GaN high electron mobility transistors grown on free-standing GaN substrates

    NASA Astrophysics Data System (ADS)

    Deen, David A.; Storm, David F.; Meyer, David J.; Bass, Robert; Binari, Steven C.; Gougousi, Theodosia; Evans, Keith R.

    2014-09-01

    A series of six ultrathin AlN/GaN heterostructures with varied AlN thicknesses from 1.5-6 nm have been grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. High electron mobility transistors (HEMTs) were fabricated from the set in order to assess the impact of barrier thickness and homo-epitaxial growth on transistor performance. Room temperature Hall characteristics revealed mobility of 1700 cm2/V s and sheet resistance of 130 Ω / □ for a 3 nm thick barrier, ranking amongst the lowest room-temperature sheet resistance values reported for a polarization-doped single heterostructure in the III-Nitride family. DC and small signal HEMT electrical characteristics from submicron gate length HEMTs further elucidated the effect of the AlN barrier thickness on device performance.

  13. Dual-polarity GaN micropillars grown by metalorganic vapour phase epitaxy: Cross-correlation between structural and optical properties

    SciTech Connect

    Coulon, P. M.; Mexis, M.; Teisseire, M.; Vennéguès, P.; Leroux, M.; Zuniga-Perez, J.; Jublot, M.

    2014-04-21

    Self-assembled catalyst-free GaN micropillars grown on (0001) sapphire substrates by metal organic vapor phase epitaxy are investigated. Transmission electron microscopy, as well as KOH etching, shows the systematic presence of two domains of opposite polarity within each single micropillar. The analysis of the initial growth stages indicates that such double polarity originates at the micropillar/substrate interface, i.e., during the micropillar nucleation, and it propagates along the micropillar. Furthermore, dislocations are also generated at the wire/substrate interface, but bend after several hundreds of nanometers. This leads to micropillars several tens of micrometers in length that are dislocation-free. Spatially resolved cathodoluminescence and microphotoluminescence show large differences in the optical properties of each polarity domain, suggesting unequal impurity/dopant/vacancy incorporation depending on the polarity.

  14. Influence of V/III growth flux ratio on trap states in m-plane GaN grown by ammonia-based molecular beam epitaxy

    SciTech Connect

    Zhang, Z.; Arehart, A. R.; Hurni, C. A.; Speck, J. S.; Ringel, S. A.

    2012-10-08

    Deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) were utilized to investigate the behavior of deep states in m-plane, n-type GaN grown by ammonia-based molecular beam epitaxy (NH{sub 3}-MBE) as a function of systematically varied V/III growth flux ratios. Levels were detected at E{sub C} - 0.14 eV, E{sub C} - 0.21 eV, E{sub C} - 0.26 eV, E{sub C} - 0.62 eV, E{sub C} - 0.67 eV, E{sub C} - 2.65 eV, and E{sub C} - 3.31 eV, with the concentrations of several traps exhibiting systematic dependencies on V/III ratio. The DLTS spectra are dominated by traps at E{sub C} - 0.14 eV and E{sub C} - 0.67 eV, whose concentrations decreased monotonically with increasing V/III ratio and decreasing oxygen impurity concentration, and by a trap at E{sub C} - 0.21 eV that revealed no dependence of its concentration on growth conditions, suggestive of different physical origins. Higher concentrations of deeper trap states detected by DLOS with activation energies of E{sub C} - 2.65 eV and E{sub C} - 3.31 eV in each sample did not display measureable sensitivity to the intentionally varied V/III ratio, necessitating further study on reducing these deep traps through growth optimization for maximizing material quality of NH{sub 3}-MBE grown m-plane GaN.

  15. Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. II. Sub-band-gap luminescence and electron irradiation effects

    SciTech Connect

    Robins, Lawrence H.; Bertness, Kris A.; Barker, Joy M.; Sanford, Norman A.; Schlager, John B.

    2007-06-01

    GaN nanowires with diameters of 50-250 nm, grown by catalyst-free molecular beam epitaxy, were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 to 297 K. Both as-grown samples and dispersions of the nanowires onto other substrates were examined. The properties of the near-band-edge PL and CL spectra were discussed in Part I of this study by [Robins et al. [L. H. Robins, K. A. Bertness, J. M. Barker, N. A. Sanford, and J. B. Schlager, J. Appl. Phys. 101,113505 (2007)]. Spectral features below the band gap, and the effect of extended electron irradiation on the CL, are discussed in Part II. The observed sub-band-gap PL and CL peaks are identified as phonon replicas of the free-exciton transitions, or excitons bound to structural defects or surface states. The defect-related peaks in the nanowires are correlated with luminescence lines previously reported in GaN films, denoted the Y lines [M. A. Reshchikov and H. Morkoc, J. Appl. Phys. 97, 061301 (2005)]. The CL was partially quenched by electron beam irradiation for an extended time; the quenching was stronger for the free and shallow-donor-bound exciton peaks than for the defect-related peaks. The quenching appeared to saturate at high irradiation dose (with final intensity {approx_equal}30% of initial intensity) and was reversible on thermal cycling to room temperature. The electron irradiation-induced quenching of the CL is ascribed to charge injection and trapping phenomena.

  16. Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. II. Sub-band-gap luminescence and electron irradiation effects

    NASA Astrophysics Data System (ADS)

    Robins, Lawrence H.; Bertness, Kris A.; Barker, Joy M.; Sanford, Norman A.; Schlager, John B.

    2007-06-01

    GaN nanowires with diameters of 50-250 nm, grown by catalyst-free molecular beam epitaxy, were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 to 297 K. Both as-grown samples and dispersions of the nanowires onto other substrates were examined. The properties of the near-band-edge PL and CL spectra were discussed in Part I of this study by [Robins et al. [L. H. Robins, K. A. Bertness, J. M. Barker, N. A. Sanford, and J. B. Schlager, J. Appl. Phys. 101,113505 (2007)]. Spectral features below the band gap, and the effect of extended electron irradiation on the CL, are discussed in Part II. The observed sub-band-gap PL and CL peaks are identified as phonon replicas of the free-exciton transitions, or excitons bound to structural defects or surface states. The defect-related peaks in the nanowires are correlated with luminescence lines previously reported in GaN films, denoted the Y lines [M. A. Reshchikov and H. Morkoc, J. Appl. Phys. 97, 061301 (2005)]. The CL was partially quenched by electron beam irradiation for an extended time; the quenching was stronger for the free and shallow-donor-bound exciton peaks than for the defect-related peaks. The quenching appeared to saturate at high irradiation dose (with final intensity ≈30% of initial intensity) and was reversible on thermal cycling to room temperature. The electron irradiation-induced quenching of the CL is ascribed to charge injection and trapping phenomena.

  17. Photoluminescence studies of band-edge transitions in GaN epitaxial layers grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chen, G. D.; Smith, M.; Lin, J. Y.; Jiang, H. X.; Salvador, A.; Sverdlov, B. N.; Botchkarv, A.; Morkoc, H.

    1996-03-01

    Continuous-wave and time-resolved photoluminescence spectroscopies have been employed to study the band-edge transitions in GaN epitaxial layers grown by plasma assisted molecular beam epitaxy. In addition to the neutral-donor-bound exciton transition (the I2 line), a transition line at about 83 meV below the band gap has been observed in an epitaxial layer grown under a lower plasma power or growth rate. This emission line has been assigned to the band-to-impurity transition resulting from the recombination between electrons bound to shallow donors and free holes D0, h+). Systematic studies of these optical transitions have been carried out under different temperatures and excitation intensities. The temperature variation of the spectral peak position of the D0, h+) emission line differs from the band gap variation with temperature, but is consistent with an existing theory for D0, h+) transitions. The dynamic processes of the D0, h+) transition have also been investigated and subnanosecond recombination lifetimes have been observed. The emission energy and the temperature dependencies of the recombination lifetime have been measured. These results have provided solid evidence for the assignment of the D0, h+) transition and show that the motions of the free holes which participated in this transition are more or less restricted in the plane of the epitaxial layer at temperatures below 140 K and that the thermal quenching of the emission intensity of this transition is due to the dissociation of neutral donors. Our results show that time-resolved photoluminescence spectroscopy can be of immense value in understanding the optical recombination dynamics in GaN.

  18. Role of sapphire nitridation temperature on GaN growth by plasma assisted molecular beam epitaxy: Part II. Interplay between chemistry and structure of layers

    NASA Astrophysics Data System (ADS)

    Losurdo, Maria; Capezzuto, Pio; Bruno, Giovanni; Namkoong, Gon; Doolittle, W. Alan; Brown, April S.

    2002-02-01

    The effect of sapphire nitridation temperature on the chemistry and microstructure of the sapphire substrate/GaN interface, nucleation layer, and of the GaN epilayers grown by rf plasma assisted molecular beam epitaxy is investigated. It is found that a sapphire nitridation temperature as low as 200 °C improves the structural and optical quality of GaN epilayers. This result can be explained by the chemistry of the sapphire nitridation process, which is discussed in the framework of a model considering the competitive formation of AlN and oxynitride (NO). In particular, at 200 °C, NO desorbs from the sapphire surface, yielding an homogeneous 6 Å AlN layer upon N2 plasma nitridation. This low temperature AlN template favors the nucleation of hexagonal GaN nuclei which coalesce completely resulting in a hexagonal GaN buffer layer that homogeneously covers the sapphire substrate. This condition promotes the growth of a high quality GaN epilayer. In contrast, high nitridation temperatures result in a mixed AlN/NO nitrided sapphire surface which induce a perturbed and more defected interface with the occurrence of cubic crystallites in the GaN buffer. A sapphire surface with random GaN islands is found upon annealing of the GaN buffer and this condition results in a low-quality GaN epilayer.

  19. Light-emitting diode based on mask- and catalyst-free grown N-polar GaN nanorods.

    PubMed

    Kunert, G; Freund, W; Aschenbrenner, T; Kruse, C; Figge, S; Schowalter, M; Rosenauer, A; Kalden, J; Sebald, K; Gutowski, J; Feneberg, M; Tischer, I; Fujan, K; Thonke, K; Hommel, D

    2011-07-01

    We report on the fabrication of a light-emitting diode based on GaN nanorods containing InGaN quantum wells. The unique system consists of tilted N-polar nanorods of high crystalline quality. Photoluminescence, electroluminescence, and spatially resolved cathodoluminescence investigations consistently show quantum well emission around 2.6 eV. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy measurements reveal a truncated shape of the quantum wells with In contents of (15 ± 5)%.

  20. Nucleation and coalescence effects on the density of self-induced GaN nanowires grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Consonni, V.; Knelangen, M.; Trampert, A.; Geelhaar, L.; Riechert, H.

    2011-02-01

    The evolution of the density of self-induced GaN nanowires as a function of the growth time, gallium rate, and growth temperature has been investigated by scanning and transmission electron microscopy. Nucleation and coalescence effects have been disentangled and quantified by distinguishing between single nanowires and nanowire clusters. Owing to the very specific nanowire nucleation mechanism involving a shape transition from spherical-cap-shaped islands, the nanowire density does not follow the standard island nucleation theory. Furthermore, the detrimental nanowire coalescence process can be significantly reduced by raising the growth temperature.

  1. High-quality Ga-rich AlGaN grown on trapezoidal patterned GaN template using super-short period AlN/GaN superlattices for rapid coalescence

    NASA Astrophysics Data System (ADS)

    Xiao, Ming; Zhang, Jincheng; Hao, Yue

    2017-04-01

    High quality crack-free Ga-rich Al26.1Ga73.9N film was grown on trapezoidal patterned GaN template (TPGT) by low-pressure metalorganic chemical vapor deposition. The super-short period AlN/GaN superlattices structure was used to grow AlGaN material instead of the direct growth method. We obtained large lateral to vertical growth rate ratio larger than 4.79. The growth rate of GaN layer was proved to be the decisive factor of the lateral to vertical growth rate ratio. Moreover, for AlGaN growth, we found that that the TPGT is more beneficial to suppression of crack and relaxation of biaxial tensile strain than planar GaN template. The obtained results demonstrate that, comparing with AlGaN grown on planar GaN template, the threading dislocation density in AlGaN grown on TPGT was reduced from 2×109 cm-2 to 2×108 cm-2.

  2. Electronic-grade GaN(0001)/Al{sub 2}O{sub 3}(0001) grown by reactive DC-magnetron sputter epitaxy using a liquid Ga target

    SciTech Connect

    Junaid, M.; Hsiao, C.-L.; Palisaitis, J.; Jensen, J.; Persson, P. O. A.; Hultman, L.; Birch, J.

    2011-04-04

    Electronic-grade GaN (0001) epilayers have been grown directly on Al{sub 2}O{sub 3} (0001) substrates by reactive direct-current-magnetron sputter epitaxy (MSE) using a liquid Ga sputtering target in an Ar/N{sub 2} atmosphere. The as-grown GaN epitaxial films exhibit low threading dislocation density on the order of {<=}10{sup 10} cm{sup -2} determined by transmission electron microscopy and modified Williamson-Hall plot. X-ray rocking curve shows narrow full-width at half maximum (FWHM) of 1054 arc sec of the 0002 reflection. A sharp 4 K photoluminescence peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. The high structural and optical qualities indicate that MSE-grown GaN epilayers can be used for fabricating high-performance devices without the need of any buffer layer.

  3. The determining factor of a preferred orientation of GaN domains grown on m-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Jue, Miyeon; Kim, Cheol-Woon; Kang, Seoung-Hun; Yoon, Hansub; Jang, Dongsoo; Kwon, Young-Kyun; Kim, Chinkyo

    2015-11-01

    Epitaxial lateral overgrowth in tandem with the first-principles calculation was employed to investigate the determining factor of a preferred orientation of GaN on SiO2-patterned m-plane sapphire substrates. We found that the (100)-orientation is favored over the (10)-orientation in the region with a small filling factor of SiO2, while the latter orientation becomes preferred in the region with a large filling factor. This result suggests that the effective concentration determines the preferred orientation of GaN: the (100)- and (10)-orientations preferred at their low and high concentrations, respectively. Our computational study revealed that at a low coverage of Ga and N atoms, the local atomic arrangement resembles that on the (10) surface, although the (100) surface is more stable at their full coverage. Such a (10)-like atomic configuration crosses over to the local structure resembling that on the (100) surface as the coverage increases. Based on results, we determined that high effective concentration of Ga and N sources expedites the growth of the (10)-orientation while keeping from transition to the (100)-orientation. At low effective concentration, on the other hand, there is a sufficient time for the added Ga and N sources to rearrange the initial (10)-like orientation to form the (100)-orientation.

  4. Study of Defects in GaN In Situ Doped with Eu3+ Ion Grown by OMVPE

    NASA Astrophysics Data System (ADS)

    Wang, Jingzhou; Koizumi, Atsushi; Fujiwara, Yasufumi; Jadwisienczak, Wojciech M.

    2016-04-01

    In this work, GaN epilayer in situ doped with Eu3+ ions was deposited on the top of an undoped n-GaN/LT-GaN/sapphire structure by organometallic vapor-phase epitaxy. A set of different ohmic and Schottky contacts on GaN:Eu3+ surface was fabricated by electron-beam evaporation for performing deep level transient spectroscopy (DLTS) measurement. The deep defect energy levels in GaN:Eu3+ epilayer were assessed by standard DLTS and high resolution Laplace DLTS (L-DLTS). Three dominant DLTS peaks were observed in the temperature range from 35 K to 400 K. The calculated activation energies of these defect energy levels were 0.108 ± 0.03 eV (Trap A), 0.287 ± 0.04 eV (Trap B) and 0.485 ± 0.06 eV (Trap C) below conduction band edge, respectively. High resolution L-DLTS conducted for the GaN:Eu3+ epilayer revealed at least four closely spaced defect energy levels associated with Trap B. It is proposed that these defect energy levels correspond to the selected optically active Eu3+ ion centers in GaN host previously identified by optical studies in this material (Fujiwara and Dierolf in Jpn J Appl Phys 53:05FA13, 2014).

  5. Understanding of surface pit formation mechanism of GaN grown in MOCVD based on local thermodynamic equilibrium assumption

    NASA Astrophysics Data System (ADS)

    Zhi-Yuan, Gao; Xiao-Wei, Xue; Jiang-Jiang, Li; Xun, Wang; Yan-Hui, Xing; Bi-Feng, Cui; De-Shu, Zou

    2016-06-01

    Frank’s theory describes that a screw dislocation will produce a pit on the surface, and has been evidenced in many material systems including GaN. However, the size of the pit calculated from the theory deviates significantly from experimental result. Through a careful observation of the variations of surface pits and local surface morphology with growing temperature and V/III ratio for c-plane GaN, we believe that Frank’s model is valid only in a small local surface area where thermodynamic equilibrium state can be assumed to stay the same. If the kinetic process is too vigorous or too slow to reach a balance, the local equilibrium range will be too small for the center and edge of the screw dislocation spiral to be kept in the same equilibrium state. When the curvature at the center of the dislocation core reaches the critical value 1/r 0, at the edge of the spiral, the accelerating rate of the curvature may not fall to zero, so the pit cannot reach a stationary shape and will keep enlarging under the control of minimization of surface energy to result in a large-sized surface pit. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204009 and 61204011) and the Beijing Municipal Natural Science Foundation, China (Grant No. 4142005).

  6. Analysis of reaction between c+a and -c+a dislocations in GaN layer grown on 4-inch Si(111) substrate with AlGaN/AlN strained layer superlattice by transmission electron microscopy

    SciTech Connect

    Sugawara, Yoshihiro; Ishikawa, Yukari; Watanabe, Arata; Miyoshi, Makoto; Egawa, Takashi

    2016-04-15

    The behavior of dislocations in a GaN layer grown on a 4-inch Si(111) substrate with an AlGaN/AlN strained layer superlattice using horizontal metal-organic chemical vapor deposition was observed by transmission electron microscopy. Cross-sectional observation indicated that a drastic decrease in the dislocation density occurred in the GaN layer. The reaction of a dislocation (b=1/3[-211-3]) and anothor dislocation (b =1/3[-2113]) to form one dislocation (b =2/3[-2110]) in the GaN layer was clarified by plan-view observation using weak-beam dark-field and large-angle convergent-beam diffraction methods.

  7. Strain states of AlN/GaN-stress mitigating layer and their effect on GaN buffer layer grown by ammonia molecular beam epitaxy on 100-mm Si(111)

    SciTech Connect

    Ravikiran, L.; Radhakrishnan, K.; Agrawal, M.; Dharmarasu, N.; Munawar Basha, S.

    2013-09-28

    The effect of strain states of AlN/GaN-stress mitigating layer (SML) on buried crack density and its subsequent influence on the residual stresses in GaN buffer layers grown using ammonia-molecular beam epitaxy on 100-mm Si(111) substrate has been investigated. Different stages involved in the formation of buried cracks, which are crack initialization, growth of relaxed AlN layer, and subsequent lateral over growth, are identified using in-situ curvature measurements. While the increase of GaN thickness in AlN/GaN-SML enhanced its compressive strain relaxation and resulted in reduced buried crack spacing, the variation of AlN thickness did not show any effect on the crack spacing. Moreover, the decrease in the crack spacing (or increase in the buried crack density) was found to reduce the residual compression in 1st and 2nd GaN layers of AlN/GaN-SML structure. The higher buried crack density relaxed the compressive strain in 1st GaN layer, which further reduced its ability to compensate the tensile stress generated during substrate cool down, and hence resulted in lower residual compressive stress in 2nd GaN layer.

  8. Strain states of AlN/GaN-stress mitigating layer and their effect on GaN buffer layer grown by ammonia molecular beam epitaxy on 100-mm Si(111)

    NASA Astrophysics Data System (ADS)

    Ravikiran, L.; Radhakrishnan, K.; Dharmarasu, N.; Agrawal, M.; Munawar Basha, S.

    2013-09-01

    The effect of strain states of AlN/GaN-stress mitigating layer (SML) on buried crack density and its subsequent influence on the residual stresses in GaN buffer layers grown using ammonia-molecular beam epitaxy on 100-mm Si(111) substrate has been investigated. Different stages involved in the formation of buried cracks, which are crack initialization, growth of relaxed AlN layer, and subsequent lateral over growth, are identified using in-situ curvature measurements. While the increase of GaN thickness in AlN/GaN-SML enhanced its compressive strain relaxation and resulted in reduced buried crack spacing, the variation of AlN thickness did not show any effect on the crack spacing. Moreover, the decrease in the crack spacing (or increase in the buried crack density) was found to reduce the residual compression in 1st and 2nd GaN layers of AlN/GaN-SML structure. The higher buried crack density relaxed the compressive strain in 1st GaN layer, which further reduced its ability to compensate the tensile stress generated during substrate cool down, and hence resulted in lower residual compressive stress in 2nd GaN layer.

  9. Relaxation and critical strain for maximum In incorporation in AlInGaN on GaN grown by metal organic vapour phase epitaxy

    SciTech Connect

    Reuters, Benjamin; Finken, M.; Wille, A.; Kalisch, H.; Vescan, A.; Hollaender, B.; Heuken, M.

    2012-11-01

    Quaternary AlInGaN layers were grown on conventional GaN buffer layers on sapphire by metal organic vapour phase epitaxy at different surface temperatures and different reactor pressures with constant precursor flow conditions. A wide range in compositions within 30-62% Al, 5-29% In, and 23-53% Ga was covered, which leads to different strain states from high tensile to high compressive. From high-resolution x-ray diffraction and Rutherford backscattering spectrometry, we determined the compositions, strain states, and crystal quality of the AlInGaN layers. Atomic force microscopy measurements were performed to characterize the surface morphology. A critical strain value for maximum In incorporation near the AlInGaN/GaN interface is presented. For compressively strained layers, In incorporation is limited at the interface as residual strain cannot exceed an empirical critical value of about 1.1%. Relaxation occurs at about 15 nm thickness accompanied by strong In pulling. Tensile strained layers can be grown pseudomorphically up to 70 nm at a strain state of 0.96%. A model for relaxation in compressively strained AlInGaN with virtual discrete sub-layers, which illustrates the gradually changing lattice constant during stress reduction is presented.

  10. Exciton emission of quasi-2D InGaN in GaN matrix grown by molecular beam epitaxy

    PubMed Central

    Ma, Dingyu; Rong, Xin; Zheng, Xiantong; Wang, Weiying; Wang, Ping; Schulz, Tobias; Albrecht, Martin; Metzner, Sebastian; Müller, Mathias; August, Olga; Bertram, Frank; Christen, Jürgen; Jin, Peng; Li, Mo; Zhang, Jian; Yang, Xuelin; Xu, Fujun; Qin, Zhixin; Ge, Weikun; Shen, Bo; Wang, Xinqiang

    2017-01-01

    We investigate the emission from confined excitons in the structure of a single-monolayer-thick quasi-two-dimensional (quasi-2D) InxGa1−xN layer inserted in GaN matrix. This quasi-2D InGaN layer was successfully achieved by molecular beam epitaxy (MBE), and an excellent in-plane uniformity in this layer was confirmed by cathodoluminescence mapping study. The carrier dynamics have also been investigated by time-resolved and excitation-power-dependent photoluminescence, proving that the recombination occurs via confined excitons within the ultrathin quasi-2D InGaN layer even at high temperature up to ~220 K due to the enhanced exciton binding energy. This work indicates that such structure affords an interesting opportunity for developing high-performance photonic devices. PMID:28417975

  11. Exciton emission of quasi-2D InGaN in GaN matrix grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ma, Dingyu; Rong, Xin; Zheng, Xiantong; Wang, Weiying; Wang, Ping; Schulz, Tobias; Albrecht, Martin; Metzner, Sebastian; Müller, Mathias; August, Olga; Bertram, Frank; Christen, Jürgen; Jin, Peng; Li, Mo; Zhang, Jian; Yang, Xuelin; Xu, Fujun; Qin, Zhixin; Ge, Weikun; Shen, Bo; Wang, Xinqiang

    2017-04-01

    We investigate the emission from confined excitons in the structure of a single-monolayer-thick quasi-two-dimensional (quasi-2D) InxGa1-xN layer inserted in GaN matrix. This quasi-2D InGaN layer was successfully achieved by molecular beam epitaxy (MBE), and an excellent in-plane uniformity in this layer was confirmed by cathodoluminescence mapping study. The carrier dynamics have also been investigated by time-resolved and excitation-power-dependent photoluminescence, proving that the recombination occurs via confined excitons within the ultrathin quasi-2D InGaN layer even at high temperature up to ~220 K due to the enhanced exciton binding energy. This work indicates that such structure affords an interesting opportunity for developing high-performance photonic devices.

  12. Strong potential profile fluctuations and effective localization process in InGaN/GaN multiple quantum wells grown on (10-1m) faceted surface GaN template

    SciTech Connect

    Haffouz, S.; Tang, H.; Bardwell, J. A.; Lefebvre, P.; Bretagnon, T.; Riemann, T.; Christen, J.

    2006-07-01

    Cathodoluminescence (CL) and time-resolved photoluminescence (TRPL) spectroscopy were used to investigate the relation between the surface morphology and emission efficiency in 10x InGaN(3 nm)/GaN(4 nm) quantum wells (QWs) deposited by plasma-assisted molecular beam epitaxy (MBE). For this study, two QWs with peak emission around 405 nm but grown on different surface morphologies have been investigated. A strong increase in the emission efficiency was observed in the QWs grown on (10-1m) faceted surface GaN template (m>2) as compared to those grown on an atomically smooth template. CL mapping and temperature-dependent PL studies revealed that the QWs grown on the faceted surface GaN epilayer exhibit much stronger in-plane indium content fluctuations and larger width PL peak in the temperature range of 8-300 K. We found that the use of (10-1m) faceted surface GaN template resulted in strong potential profile fluctuations (PPFs) inducing different localization centers at different energy levels. We found that the deeper the corresponding fluctuation of the energy level, the weaker the decrease of the PL intensity with increasing temperature, the higher the PL decay time ({tau}{sub PL}) in the whole temperature range and the slower the collapse of {tau}{sub PL}. Our results demonstrate that the use of (10-1m) faceted surface morphology GaN template is an amplifying process of the PPFs which favors a regime dominated by the recombination of localized carriers.

  13. Kinetics of self-induced nucleation and optical properties of GaN nanowires grown by plasma-assisted molecular beam epitaxy on amorphous Al{sub x}O{sub y}

    SciTech Connect

    Sobanska, M. Zytkiewicz, Z. R.; Klosek, K.; Tchutchulashvili, G.

    2015-11-14

    Nucleation kinetics of GaN nanowires (NWs) by molecular beam epitaxy on amorphous Al{sub x}O{sub y} buffers deposited at low temperature by atomic layer deposition is analyzed. We found that the growth processes on a-Al{sub x}O{sub y} are very similar to those observed on standard Si(111) substrates, although the presence of the buffer significantly enhances nucleation rate of GaN NWs, which we attribute to a microstructure of the buffer. The nucleation rate was studied vs. the growth temperature in the range of 720–790 °C, which allowed determination of nucleation energy of the NWs on a-Al{sub x}O{sub y} equal to 6 eV. This value is smaller than 10.2 eV we found under the same conditions on nitridized Si(111) substrates. Optical properties of GaN NWs on a-Al{sub x}O{sub y} are analyzed as a function of the growth temperature and compared with those on Si(111) substrates. A significant increase of photoluminescence intensity and much longer PL decay times, close to those on silicon substrates, are found for NWs grown at the highest temperature proving their high quality. The samples grown at high temperature have very narrow PL lines. This allowed observation that positions of donor-bound exciton PL line in the NWs grown on a-Al{sub x}O{sub y} are regularly lower than in samples grown directly on silicon suggesting that oxygen, instead of silicon, is the dominant donor. Moreover, PL spectra suggest that total concentration of donors in GaN NWs grown on a-Al{sub x}O{sub y} is lower than in those grown under similar conditions on bare Si. This shows that the a-Al{sub x}O{sub y} buffer efficiently acts as a barrier preventing uptake of silicon from the substrate to GaN.

  14. Influence of vicinal sapphire substrate on the properties of N-polar GaN films grown by metal-organic chemical vapor deposition

    SciTech Connect

    Lin, Zhiyu; Zhang, Jincheng Xu, Shengrui; Chen, Zhibin; Yang, Shuangyong; Tian, Kun; Hao, Yue; Su, Xujun; Shi, Xuefang

    2014-08-25

    The influence of vicinal sapphire substrates on the growth of N-polar GaN films by metal-organic chemical vapor deposition is investigated. Smooth GaN films without hexagonal surface feature are obtained on vicinal substrate. Transmission electron microscope results reveal that basal-plane stacking faults are formed in GaN on vicinal substrate, leading to a reduction in threading dislocation density. Furthermore, it has been found that there is a weaker yellow luminescence in GaN on vicinal substrate than that on (0001) substrate, which might be explained by the different trends of the carbon impurity incorporation.

  15. Transport and optical properties of c-axis oriented wedge shaped GaN nanowall network grown by molecular beam epitaxy

    SciTech Connect

    Bhasker, H. P.; Dhar, S.; Thakur, Varun; Kesaria, Manoj; Shivaprasad, S. M.

    2014-02-21

    The transport and optical properties of wedge-shaped nanowall network of GaN grown spontaneously on cplane sapphire substrate by Plasma-Assisted Molecular Beam Epitaxy (PAMBE) show interesting behavior. The electron mobility at room temperature in these samples is found to be orders of magnitude higher than that of a continuous film. Our study reveals a strong correlation between the mobility and the band gap in these nanowall network samples. However, it is seen that when the thickness of the tips of the walls increases to an extent such that more than 70% of the film area is covered, it behaves close to a flat sample. In the sample with lower surface coverage (≈40% and ≈60%), it was observed that the conductivity, mobility as well as the band gap increase with the decrease in the average tip width of the walls. Photoluminescence (PL) experiments show a strong and broad band edge emission with a large (as high as ≈ 90 meV) blue shift, compared to that of a continuous film, suggesting a confinement of carriers on the top edges of the nanowalls. The PL peak width remains wide at all temperatures suggesting the existence of a high density of tail states at the band edge, which is further supported by the photoconductivity result. The high conductivity and mobility observed in these samples is believed to be due to a “dissipation less” transport of carriers, which are localized at the top edges (edge states) of the nanowalls.

  16. Microstructural dependency of optical properties of m-plane InGaN multiple quantum wells grown on 2° misoriented bulk GaN substrates

    SciTech Connect

    Tang, Fengzai; Barnard, Jonathan S.; Zhu, Tongtong; Oehler, Fabrice; Kappers, Menno J.; Oliver, Rachel A.

    2015-08-24

    A non-polar m-plane structure consisting of five InGaN/GaN quantum wells (QWs) was grown on ammonothermal bulk GaN by metal-organic vapor phase epitaxy. Surface step bunches propagating through the QW stack were found to accommodate the 2° substrate miscut towards the -c direction. Both large steps with heights of a few tens of nanometres and small steps between one and a few atomic layers in height are observed, the former of which exhibit cathodoluminescence at longer wavelengths than the adjacent m-plane terraces. This is attributed to the formation of semi-polar facets at the steps on which the QWs are shown to be thicker and have higher Indium contents than those in the adjacent m-plane regions. Discrete basal-plane stacking faults (BSFs) were occasionally initiated from the QWs on the main m-plane terraces, but groups of BSFs were frequently observed to initiate from those on the large steps, probably related to the increased strain associated with the locally higher indium content and thickness.

  17. Phase transformation of molecular beam epitaxy-grown nanometer-thick Gd₂O₃ and Y₂O₃ on GaN.

    PubMed

    Chang, Wen-Hsin; Wu, Shao-Yun; Lee, Chih-Hsun; Lai, Te-Yang; Lee, Yi-Jun; Chang, Pen; Hsu, Chia-Hung; Huang, Tsung-Shiew; Kwo, J Raynien; Hong, Minghwei

    2013-02-01

    High quality nanometer-thick Gd₂O₃ and Y₂O₃ (rare-earth oxide, R₂O₃) films have been epitaxially grown on GaN (0001) substrate by molecular beam epitaxy (MBE). The R₂O₃ epi-layers exhibit remarkable thermal stability at 1100 °C, uniformity, and highly structural perfection. Structural investigation was carried out by in situ reflection high energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD) with synchrotron radiation. In the initial stage of epitaxial growth, the R₂O₃ layers have a hexagonal phase with the epitaxial relationship of R₂O₃ (0001)(H)<1120>(H)//GaN(0001)(H)<1120>(H). With the increase in R₂O₃ film thickness, the structure of the R₂O₃ films changes from single domain hexagonal phase to monoclinic phase with six different rotational domains, following the R₂O₃ (201)(M)[020](M)//GaN(0001)(H)<1120>(H) orientational relationship. The structural details and fingerprints of hexagonal and monoclinic phase Gd₂O₃ films have also been examined by using electron energy loss spectroscopy (EELS). Approximate 3-4 nm is the critical thickness for the structural phase transition depending on the composing rare earth element.

  18. Blue-violet InGaN laser diodes grown on bulk GaN substrates by plasma-assisted molecular-beam epitaxy

    SciTech Connect

    Skierbiszewski, C.; Wasilewski, Z.R.; Siekacz, M.; Feduniewicz, A.; Perlin, P.; Wisniewski, P.; Borysiuk, J.; Grzegory, I.; Leszczynski, M.; Suski, T.; Porowski, S.

    2005-01-03

    We report on the InGaN multiquantum laser diodes (LDs) made by rf plasma-assisted molecular beam epitaxy (PAMBE). The laser operation at 408 nm is demonstrated at room temperature with pulsed current injections using 50 ns pulses at 0.25% duty cycle. The threshold current density and voltage for the LDs with cleaved uncoated mirrors are 12 kA/cm{sup 2} (900 mA) and 9 V, respectively. High output power of 0.83 W is obtained during pulse operation at 3.6 A and 9.6 V bias with the slope efficiency of 0.35 W/A. The laser structures are deposited on the high-pressure-grown low dislocation bulk GaN substrates taking full advantage of the adlayer enhanced lateral diffusion channel for adatoms below the dynamic metallic cover. Our devices compare very favorably to the early laser diodes fabricated using the metalorganic vapor phase epitaxy technique, providing evidence that the relatively low growth temperatures used in this process pose no intrinsic limitations on the quality of the blue optoelectronic components that can be fabricated using PAMBE.

  19. Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

    SciTech Connect

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

    2015-01-12

    The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 10{sup 13 }cm{sup −2} and 3 × 10{sup 13 }cm{sup −2} fluences not only introduces a trap with an E{sub V} + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at E{sub V} + 0.48 eV, E{sub V} + 2.42 eV, E{sub V} + 3.00 eV, and E{sub V} + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment.

  20. Cubic nitride templates

    DOEpatents

    Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei

    2013-04-30

    A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.

  1. Raman spectroscopy based measurements of carrier concentration in n-type GaN nanowires grown by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Robins, L. H.; Horneber, E.; Sanford, N. A.; Bertness, K. A.; Brubaker, M. D.; Schlager, J. B.

    2016-09-01

    The carrier concentration in as-grown ensembles of n-type GaN nanowires was determined by Raman spectroscopy of the coupled longitudinal phonon-plasmon (LPP+) mode and modeling of the carrier concentration dependence of the LPP+ frequency. The Raman measurements and analyses enabled estimation of the carrier concentration in single-nanowire devices fabricated from the as-grown ensembles. The nanowires were grown by plasma-assisted molecular beam epitaxy in either of the two growth systems. Twelve samples were examined, of which 11 samples were Si-doped and one was undoped. The Raman-measured carrier concentrations in the Si-doped samples ranged from (5.28 ± 1.19) × 1016 cm-3 to (6.16 ± 0.35) × 1017 cm-3. For a subset of samples grown with varying Si cell temperature, from 1125 °C to 1175 °C, the carrier concentration was found to be an Arrhenius function of Si cell temperature, with activation energy of 6.281 ± 0.011 eV . Co-illumination by an above band gap UV laser (325 nm, excitation intensity = 0.7 W/cm2 or 4.5 W/cm2) induced small increases in carrier concentration, relative to illumination by the Raman excitation laser alone (633 nm, excitation intensity ≈100 kW/cm2). The lowest Si-doped sample showed the largest increase in carrier concentration, (6.3 ± 4.8) × 1015 cm-3 with UV excitation intensity of 0.7 W/cm2. These results imply that, even in the absence of UV illumination, surface depletion does not have a significant effect on the Raman carrier concentration measurements. Immersion in a high-dielectric-constant oil (ɛ = 2.24) caused downshifts of similar magnitude in the LPP+ frequencies of undoped and doped nanowires. This result implies that the LPP+ mode has bulk plasmon rather than surface plasmon character, because immersion in a high-dielectric-constant medium is predicted to cause a large decrease in the surface plasmon frequency, which would induce a larger LPP+ downshift in doped than undoped nanowires. A surface optical (SO) phonon

  2. Influences of group-III source preflow on the polarity, optical, and structural properties of GaN grown on nitridated sapphire substrates by metal-organic chemical vapor deposition

    SciTech Connect

    Li, Chengguo; Liu, Hongfei; Chua, Soo Jin

    2015-03-28

    We report the influences of group-III source preflow, which were introduced prior to the growth of the low temperature GaN on the polarity, photoluminescence (PL), and crystallographic properties of GaN epilayers grown on nitridated c-plane sapphire substrates by metal-organic chemical vapor deposition. By studying the surface morphology evolutions under chemical etching in KOH, we found that with increasing the trimethyl-gallium (TMGa) preflow duration (t), the polarity of the GaN film can be changed from a complete N-polarity to a mixture of N- and Ga-polarity and further to a complete Ga-polarity. PL and high-resolution X-ray diffraction studies revealed that the impurity incorporation and the edge- and screw-type threading dislocations are strongly polarity dependent. A further study at the optimized t (i.e., 30 s for TMGa) shows that the polarity inversion of GaN can be realized not only by TMGa preflow but also by trimethyl-aluminium preflow and by trimethyl-indium preflow. A two-monolayer model was employed to explain the polarity inversion mechanism.

  3. Nitrogen-Polar (0001¯) GaN Grown on c-Plane Sapphire with a High-Temperature AlN Buffer

    PubMed Central

    Song, Jie; Han, Jung

    2017-01-01

    We demonstrate growing nitrogen-polar (N-polar) GaN epilayer on c-plane sapphire using a thin AlN buffer layer by metalorganic chemical vapor deposition. We have studied the influence of the AlN buffer layer on the polarity, crystalline quality, and surface morphology of the GaN epilayer and found that the growth temperature of the AlN buffer layer played a critical role in the growth of the GaN epilayer. The low growth temperature of the AlN buffer results in gallium-polar GaN. Even a nitridation process has been conducted. High growth temperature for an AlN buffer layer is required to achieve pure N-polarity, high crystalline quality, and smooth surface morphology for a GaN epilayer. PMID:28772612

  4. Raman spectroscopic investigations of tetragonal to cubic transition in BaTiO{sub 3} films grown on LaAlO{sub 3} substrate

    SciTech Connect

    Kumar, Satish; Kumar, Dhirendra; Rathore, Ajay Kumar; Sathe, V. G.

    2016-05-23

    BaTiO{sub 3} [BTO] films have been grown on LaAlO{sub 3} (LAO) substrate using pulse laser deposition technique. The film is found highly oriented, possess 400 nm thickness and single phase in nature. However, the out-of-plane lattice parameter of the film obtained from the x-ray diffraction was found to be lower when compared to bulk compound indicating towards strain reversal. The Raman spectra recorded at room temperature showed that the film is tetragonal with C4v symmetry. Raman spectra collected at high temperatures for the film and the bulk compound showed that the tetragonal to cubic transition temperature in film is enhanced by 100 K.

  5. Transistors and tunnel diodes enabled by large-scale MoS2 nanosheets grown on GaN

    NASA Astrophysics Data System (ADS)

    San Yip, Pak; Zou, Xinbo; Cho, Wai Ching; Wu, Kam Lam; Lau, Kei May

    2017-07-01

    We report growth, fabrication, and device results of MoS2-based transistors and diodes implemented on a single 2D/3D material platform. The 2D/3D platform consists of a large-area MoS2 thin film grown on SiO2/p-GaN substrates. Atomic force microscopy, scanning electron microscopy, and Raman spectroscopy were used to characterize the thickness and quality of the as-grown MoS2 film, showing that the large-area MoS2 nanosheet has a smooth surface morphology constituted by small grains. Starting from the same material, both top-gated MoS2 field effect transistors and MoS2/SiO2/p-GaN heterojunction diodes were fabricated. The transistors exhibited a high on/off ratio of 105, a subthreshold swing of 74 mV dec-1, field effect mobility of 0.17 cm2 V-1 s-1, and distinctive current saturation characteristics. For the heterojunction diodes, current-rectifying characteristics were demonstrated with on-state current density of 29 A cm-2 and a current blocking property up to -25 V without breakdown. The reported transistors and diodes enabled by the same 2D/3D material stack present promising building blocks for constructing future nanoscale electronics.

  6. Structural and electrical properties of Pb(Zr ,Ti)O3 grown on (0001) GaN using a double PbTiO3/PbO bridge layer

    NASA Astrophysics Data System (ADS)

    Xiao, Bo; Gu, Xing; Izyumskaya, Natalia; Avrutin, Vitaliy; Xie, Jinqiao; Liu, Huiyong; Morkoç, Hadis

    2007-10-01

    Pb(Zr0.52Ti0.48)O3 films were deposited by rf magnetron sputtering on silicon-doped GaN(0001)/c-sapphire with a PbTiO3/PbO oxide bridge layer grown by molecular beam epitaxy. X-ray diffraction data showed the highly (111)-oriented perovskite phase in lead zirconate titanate (PZT) films with PbTiO3/PbO bridge layers, compared to the pyrochlore phase grown directly on GaN. The in-plane epitaxial relationships were found from x-ray pole figures to be PZT[112¯]‖GaN[11¯00] and PZT[11¯0]‖GaN[112¯0]. The polarization-electric field measurements revealed the ferroelectric behavior with remanent polarization of 30-40μC /cm2 and asymmetric hysteresis loops due to the depletion layer formed in GaN under reverse bias which resulted in a high negative coercive electric field (950kV/cm).

  7. Europium doping of zincblende GaN by ion implantation

    SciTech Connect

    Lorenz, K.; Franco, N.; Darakchieva, V.; Alves, E.; Roqan, I. S.; O'Donnell, K. P.; Trager-Cowan, C.; Martin, R. W.; As, D. J.; Panfilova, M.

    2009-06-01

    Eu was implanted into high quality cubic (zincblende) GaN (ZB-GaN) layers grown by molecular beam epitaxy. Detailed structural characterization before and after implantation was performed by x-ray diffraction (XRD) and Rutherford backscattering/channeling spectrometry. A low concentration (<10%) of wurtzite phase inclusions was observed by XRD analysis in as-grown samples with their (0001) planes aligned with the (111) planes of the cubic lattice. Implantation of Eu causes an expansion of the lattice parameter in the implanted region similar to that observed for the c-lattice parameter of wurtzite GaN (W-GaN). For ZB-GaN:Eu, a large fraction of Eu ions is found on a high symmetry interstitial site aligned with the <110> direction, while a Ga substitutional site is observed for W-GaN:Eu. The implantation damage in ZB-GaN:Eu could partly be removed by thermal annealing, but an increase in the wurtzite phase fraction was observed at the same time. Cathodoluminescence, photoluminescence (PL), and PL excitation spectroscopy revealed several emission lines which can be attributed to distinct Eu-related optical centers in ZB-GaN and W-GaN inclusions.

  8. Preparation and Characterization of Ni Spines Grown on the Surface of Cubic Boron Nitride Grains by Electroplating Method.

    PubMed

    Gui, Yanghai; Zhao, Jianbo; Chen, Jingbo; Jiang, Yuanli

    2016-03-04

    Cubic boron nitride (cBN) is widely applied in cutting and grinding tools. cBN grains plated by pure Ni and Ni/SiC composite were produced under the same conditions from an additive-free nickel Watts type bath. The processed electroplating products were characterized by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermoanalysis (TG-DTA). Due to the presence of SiC particles, there are some additional nodules on the surface of Ni/SiC plated cBN compared with the pure Ni plated cBN. The unique morphology of Ni/SiC plated cBN should attain greater retention force in resin bond. Moreover, the coating weight of cBN grains could be controlled by regulating the plating time. cBN grains with 60% coating weight possess the optimum grinding performance due to their roughest and spiniest surface. In addition, Ni spines plated cBN grains show good thermal stability when temperature is lower than 464 °C. Therefore, the plated cBN grains are more stable and suitable for making resin bond abrasive tools below 225 °C. Finally, the formation mechanism of electroplating products is also discussed.

  9. Preparation and Characterization of Ni Spines Grown on the Surface of Cubic Boron Nitride Grains by Electroplating Method

    PubMed Central

    Gui, Yanghai; Zhao, Jianbo; Chen, Jingbo; Jiang, Yuanli

    2016-01-01

    Cubic boron nitride (cBN) is widely applied in cutting and grinding tools. cBN grains plated by pure Ni and Ni/SiC composite were produced under the same conditions from an additive-free nickel Watts type bath. The processed electroplating products were characterized by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermoanalysis (TG-DTA). Due to the presence of SiC particles, there are some additional nodules on the surface of Ni/SiC plated cBN compared with the pure Ni plated cBN. The unique morphology of Ni/SiC plated cBN should attain greater retention force in resin bond. Moreover, the coating weight of cBN grains could be controlled by regulating the plating time. cBN grains with 60% coating weight possess the optimum grinding performance due to their roughest and spiniest surface. In addition, Ni spines plated cBN grains show good thermal stability when temperature is lower than 464 °C. Therefore, the plated cBN grains are more stable and suitable for making resin bond abrasive tools below 225 °C. Finally, the formation mechanism of electroplating products is also discussed. PMID:28773283

  10. Wafer-Size and Single-Crystal MoSe2 Atomically Thin Films Grown on GaN Substrate for Light Emission and Harvesting.

    PubMed

    Chen, Zuxin; Liu, Huiqiang; Chen, Xuechen; Chu, Guang; Chu, Sheng; Zhang, Hang

    2016-08-10

    Two-dimensional (2D) atomic-layered semiconductors are important for next-generation electronics and optoelectronics. Here, we designed the growth of an MoSe2 atomic layer on a lattice-matched GaN semiconductor substrate. The results demonstrated that the MoSe2 films were less than three atomic layers thick and were single crystalline of MoSe2 over the entire GaN substrate. The ultrathin MoSe2/GaN heterojunction diode demonstrated ∼850 nm light emission and could also be used in photovoltaic applications.

  11. Current conduction mechanism and electrical break-down in InN grown on GaN

    NASA Astrophysics Data System (ADS)

    Kuzmik, J.; Fleury, C.; Adikimenakis, A.; Gregušová, D.; Ťapajna, M.; Dobročka, E.; Haščík, Š.; Kučera, M.; Kúdela, R.; Androulidaki, M.; Pogany, D.; Georgakilas, A.

    2017-06-01

    Current conduction mechanism, including electron mobility, electron drift velocity (vd) and electrical break-down have been investigated in a 0.5 μm-thick (0001) InN layer grown by molecular-beam epitaxy on a GaN/sapphire template. Electron mobility (μ) of 1040 cm2/Vs and a free electron concentration (n) of 2.1 × 1018 cm-3 were measured at room temperature with only a limited change down to 20 K, suggesting scattering on dislocations and ionized impurities. Photoluminescence spectra and high-resolution X-ray diffraction correlated with the Hall experiment showing an emission peak at 0.69 eV, a full-width half-maximum of 30 meV, and a dislocation density Ndis ˜ 5.6 × 1010 cm-2. Current-voltage (I-V) characterization was done in a pulsed (10 ns-width) mode on InN resistors prepared by plasma processing and Ohmic contacts evaporation. Resistors with a different channel length ranging from 4 to 15.8 μm obeyed the Ohm law up to an electric field intensity Eknee ˜ 22 kV/cm, when vd ≥ 2.5 × 105 m/s. For higher E, I-V curves were nonlinear and evolved with time. Light emission with a photon energy > 0.7 eV has been observed already at modest Erad of ˜ 8.3 kV/cm and consequently, a trap-assisted interband tunneling was suggested to play a role. At Eknee ˜ 22 kV/cm, we assumed electron emission from traps, with a positive feed-back for the current enhancement. Catastrophic break-down appeared at E ˜ 25 kV/cm. Reduction of Ndis was suggested to fully exploit InN unique prospects for future high-frequency devices.

  12. Growth and optical properties of filamentary GaN nanocrystals grown on a hybrid SiC/Si(111) substrate by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    The potential to grow filamentary GaN nanocrystals by molecular beam epitaxy on a silicon substrate with a nanosized buffer layer of silicon carbide has been demonstrated. Morphological and optical properties of the obtained system have been studied. It has been shown that the intensity of the photoluminescence spectrum peak of such structures is higher than that of the best filamentary GaN nanocrystals without the buffer silicon carbide layer by a factor of more than two.

  13. Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tang, H.; Fang, Z. Q.; Rolfe, S.; Bardwell, J. A.; Raymond, S.

    2010-05-01

    Growth of unintentionally doped (UID) semi-insulating GaN on SiC and highly resistive GaN on sapphire using the ammonia molecular-beam epitaxy technique is reported. The semi-insulating UID GaN on SiC shows room temperature (RT) resistivity of 1011 Ω cm and well defined activation energy of 1.0 eV. The balance of compensation of unintentional donors and acceptors is such that the Fermi level is lowered to midgap, and controlled by a 1.0 eV deep level defect, which is thought to be related to the nitrogen antisite NGa, similar to the "EL2" center (arsenic antisite) in unintentionally doped semi-insulating GaAs. The highly resistive GaN on sapphire shows RT resistivity in range of 106-109 Ω cm and activation energy varying from 0.25 to 0.9 eV. In this case, the compensation of shallow donors is incomplete, and the Fermi level is controlled by levels shallower than the 1.0 eV deep centers. The growth mechanisms for the resistive UID GaN materials were investigated by experimental studies of the surface kinetics during growth. The required growth regime involves a moderate growth temperature range of 740-780 °C, and a high ammonia flux (beam equivalent pressure of 1×10-4 Torr), which ensures supersaturated coverage of surface adsorption sites with NHx radicals. Such highly nitrogen rich growth conditions lead to two-dimensional layer by layer growth and reduced oxygen incorporation.

  14. Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

    SciTech Connect

    Tang, H.; Rolfe, S.; Bardwell, J. A.; Raymond, S.; Fang, Z. Q.

    2010-05-15

    Growth of unintentionally doped (UID) semi-insulating GaN on SiC and highly resistive GaN on sapphire using the ammonia molecular-beam epitaxy technique is reported. The semi-insulating UID GaN on SiC shows room temperature (RT) resistivity of 10{sup 11} {Omega} cm and well defined activation energy of 1.0 eV. The balance of compensation of unintentional donors and acceptors is such that the Fermi level is lowered to midgap, and controlled by a 1.0 eV deep level defect, which is thought to be related to the nitrogen antisite N{sub Ga}, similar to the ''EL2'' center (arsenic antisite) in unintentionally doped semi-insulating GaAs. The highly resistive GaN on sapphire shows RT resistivity in range of 10{sup 6}-10{sup 9} {Omega} cm and activation energy varying from 0.25 to 0.9 eV. In this case, the compensation of shallow donors is incomplete, and the Fermi level is controlled by levels shallower than the 1.0 eV deep centers. The growth mechanisms for the resistive UID GaN materials were investigated by experimental studies of the surface kinetics during growth. The required growth regime involves a moderate growth temperature range of 740-780 deg. C, and a high ammonia flux (beam equivalent pressure of 1x10{sup -4} Torr), which ensures supersaturated coverage of surface adsorption sites with NH{sub x} radicals. Such highly nitrogen rich growth conditions lead to two-dimensional layer by layer growth and reduced oxygen incorporation.

  15. Observation of reaction between a-type dislocations in GaN layer grown on 4-in. Si(111) substrate with AlGaN/AlN strained layer superlattice after dislocation propagation

    NASA Astrophysics Data System (ADS)

    Sugawara, Yoshihiro; Ishikawa, Yukari; Watanabe, Arata; Miyoshi, Makoto; Egawa, Takashi

    2017-06-01

    Dislocation reaction in a GaN layer grown on 4-in. Si(111) with AlGaN/AlN strained layer superlattice was observed by transmission electron microscopy. The reaction between a dislocation (b=1/3[ 1 2 bar 10 ]) and another dislocation (b =1/3[ 11 2 bar 0 ]) to form a dislocation segment (b =1/3[ 2 1 bar 1 bar 0 ]) was demonstrated by plan-view observation using weak-beam dark-field and large-angle convergent-beam electron diffraction methods. Observed reaction occurred with dislocation motion after dislocation propagation with epitaxial growth.

  16. Effects of thickness ratio of InGaN to GaN in superlattice strain relief layer on the optoelectrical properties of InGaN-based green LEDs grown on Si substrates

    NASA Astrophysics Data System (ADS)

    Qi, Weijing; Zhang, Jianli; Mo, Chunlan; Wang, Xiaolan; Wu, Xiaoming; Quan, Zhijue; Wang, Guangxu; Pan, Shuan; Fang, Fang; Liu, Junlin; Jiang, Fengyi

    2017-08-01

    InGaN-based multiple quantum well (MQW) green light-emitting diodes with a InGaN/GaN superlattice as a strain relief layer (SSRL) were grown on Si(111) substrates by metal organic chemical vapor deposition. The influences of the thickness ratio of InGaN to GaN in SSRL on the optoelectrical properties have been investigated. Electrical measurements show that the sample with a higher thickness ratio has a lower series resistance. This is mainly ascribed to the improvement of carrier vertical transport due to the thinner GaN in SSRL. However, it is found that the leakage current increases with the thickness ratio from 1:1 to 2.5:1, which could be attributed to the larger density of small size V-pits forming at the first few QW pairs. Compared with the smaller thickness ratio, the sample with a higher thickness ratio of InGaN to GaN in SSRL is found to exhibit larger strain relaxation (about 33.7%), but the electroluminescence measurement exhibits inferior emission efficiency. Carrier leakage via the small V-pits and the rougher interface of MQW are believed to be responsible for the reduction of emission efficiency.

  17. Growth kinetics of AlN and GaN films grown by molecular beam epitaxy on R-plane sapphire substrates

    SciTech Connect

    Chandrasekaran, R.; Moustakas, T. D.; Ozcan, A. S.; Ludwig, K. F.; Zhou, L.; Smith, David J.

    2010-08-15

    This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its (1120) A-plane parallel to the (1102) R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having (1120) planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with (1126) planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut ({approx}0.5 deg. ) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects in the (1126) GaN films.

  18. Improved crystalline properties of laser molecular beam epitaxy grown SrTiO{sub 3} by rutile TiO{sub 2} layer on hexagonal GaN

    SciTech Connect

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

    2009-11-15

    Epitaxial SrTiO{sub 3} films were fabricated by laser molecular beam epitaxy on bare and TiO{sub 2} buffered GaN(0002), respectively. The whole deposition processes were in situ monitored by reflection high energy electron diffraction (RHEED). X-ray diffraction (XRD) was carried out to study the growth orientation and crystalline quality of STO films. The interfacial characters and epitaxial relationships were also investigated by high revolution transition electron microscope and selected area electron diffraction (SAED). According to the RHEED observation, the lowest epitaxy temperature of STO on TiO{sub 2} buffered GaN was decreased compared with the direct deposited one. The epitaxial relationship was (111)[110]STO//(0002)[1120]GaN in both cases as confirmed by RHEED, XRD, and SAED. The full width at half maximum of omega-scan and PHI-scan of STO on TiO{sub 2} buffered GaN was reduced compared with that deposited on bare GaN, indicating that epitaxial quality of STO film is improved by inserting TiO{sub 2} layer. In summary, the lattice mismatch was reduced by inserting rutile TiO{sub 2}. As a result, the crystalline temperature was reduced and enhanced epitaxial quality of STO thin film was obtained.

  19. Steady-state and transient photoconductivity in c-axis GaN nanowires grown by nitrogen-plasma-assisted molecular beam epitaxy

    SciTech Connect

    Sanford, N. A.; Blanchard, P. T.; Bertness, K. A.; Mansfield, L.; Schlager, J. B.; Sanders, A. W.; Roshko, A.; Burton, B. B.; George, S. M.

    2010-02-15

    Analysis of steady-state and transient photoconductivity measurements at room temperature performed on c-axis oriented GaN nanowires yielded estimates of free carrier concentration, drift mobility, surface band bending, and surface capture coefficient for electrons. Samples grown (unintentionally n-type) by nitrogen-plasma-assisted molecular beam epitaxy primarily from two separate growth runs were examined. The results revealed carrier concentration in the range of (3-6)x10{sup 16} cm{sup -3} for one growth run, roughly 5x10{sup 14}-1x10{sup 15} cm{sup -3} for the second, and drift mobility in the range of 500-700 cm{sup 2}/(V s) for both. Nanowires were dispersed onto insulating substrates and contacted forming single-wire, two-terminal structures with typical electrode gaps of {approx_equal}3-5 {mu}m. When biased at 1 V bias and illuminated at 360 nm (3.6 mW/cm{sup 2}) the thinner ({approx_equal}100 nm diameter) nanowires with the higher background doping showed an abrupt increase in photocurrent from 5 pA (noise level) to 0.1-1 {mu}A. Under the same conditions, thicker (151-320 nm) nanowires showed roughly ten times more photocurrent, with dark currents ranging from 2 nA to 1 {mu}A. With the light blocked, the dark current was restored in a few minutes for the thinner samples and an hour or more for the thicker ones. The samples with lower carrier concentration showed similar trends. Excitation in the 360-550 nm range produced substantially weaker photocurrent with comparable decay rates. Nanowire photoconductivity arises from a reduction in the depletion layer via photogenerated holes drifting to the surface and compensating ionized surface acceptors. Simulations yielded (dark) surface band bending in the vicinity of 0.2-0.3 V and capture coefficient in the range of 10{sup -23}-10{sup -19} cm{sup 2}. Atomic layer deposition (ALD) was used to conformally deposit {approx_equal}10 nm of Al{sub 2}O{sub 3} on several devices. Photoconductivity, persistent

  20. Steady-state and transient photoconductivity in c-axis GaN nanowires grown by nitrogen-plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sanford, N. A.; Blanchard, P. T.; Bertness, K. A.; Mansfield, L.; Schlager, J. B.; Sanders, A. W.; Roshko, A.; Burton, B. B.; George, S. M.

    2010-02-01

    Analysis of steady-state and transient photoconductivity measurements at room temperature performed on c-axis oriented GaN nanowires yielded estimates of free carrier concentration, drift mobility, surface band bending, and surface capture coefficient for electrons. Samples grown (unintentionally n-type) by nitrogen-plasma-assisted molecular beam epitaxy primarily from two separate growth runs were examined. The results revealed carrier concentration in the range of (3-6)×1016 cm-3 for one growth run, roughly 5×1014-1×1015 cm-3 for the second, and drift mobility in the range of 500-700 cm2/(V s) for both. Nanowires were dispersed onto insulating substrates and contacted forming single-wire, two-terminal structures with typical electrode gaps of ≈3-5 μm. When biased at 1 V bias and illuminated at 360 nm (3.6 mW/cm2) the thinner (≈100 nm diameter) nanowires with the higher background doping showed an abrupt increase in photocurrent from 5 pA (noise level) to 0.1-1 μA. Under the same conditions, thicker (151-320 nm) nanowires showed roughly ten times more photocurrent, with dark currents ranging from 2 nA to 1 μA. With the light blocked, the dark current was restored in a few minutes for the thinner samples and an hour or more for the thicker ones. The samples with lower carrier concentration showed similar trends. Excitation in the 360-550 nm range produced substantially weaker photocurrent with comparable decay rates. Nanowire photoconductivity arises from a reduction in the depletion layer via photogenerated holes drifting to the surface and compensating ionized surface acceptors. Simulations yielded (dark) surface band bending in the vicinity of 0.2-0.3 V and capture coefficient in the range of 10-23-10-19 cm2. Atomic layer deposition (ALD) was used to conformally deposit ≈10 nm of Al2O3 on several devices. Photoconductivity, persistent photoconductivity, and subgap photoconductivity of the coated nanowires were increased in all cases. TaN ALD coatings

  1. Improving the purity of GaN grown by the ammonothermal method with in-autoclave gas-phase acidic mineralizer synthesis

    NASA Astrophysics Data System (ADS)

    Tomida, D.; Chichibu, S. F.; Kagamitani, Y.; Bao, Q.; Hazu, K.; Simura, R.; Sugiyama, K.; Yokoyama, C.; Ishiguro, T.; Fukuda, T.

    2012-06-01

    In-autoclave synthesis of a gas-phase acidic mineralizer was investigated for high-purity GaN growth by the ammonothermal (AT) method. To reduce oxygen contamination of GaN from highly hygroscopic NH4Cl powder, purified NH3 and HCl gases were introduced sequentially fed into a Pt-lined autoclave to synthesize NH4Cl within the autoclave. The autoclave was pre-charged with GaN seed wafers and polycrystalline precursors, and carefully dehydrated under dynamic vacuum. Because of the decrease in oxygen concentration, the lattice parameter approached the intrinsic value. The Ga-polar layers exhibit a near-band-edge emission peak at room temperature.

  2. The compositional, structural, and magnetic properties of a Fe3O4/Ga2O3/GaN spin injecting hetero-structure grown by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Xu, Zhonghua; Huang, Shimin; Tang, Kun; Gu, Shulin; Zhu, Shunming; Ye, Jiandong; Xu, Mingxiang; Wang, Wei; Zheng, Youdou

    2016-12-01

    In this article, the authors have designed and fabricated a Fe3O4/Ga2O3/GaN spin injecting hetero-structure by metal-organic chemical vapor deposition. The compositional, structural, and magnetic properties of the hetero-structure have been characterized and discussed. From the characterizations, the hetero-structure has been successfully grown generally. However, due to the unintentional diffusion of Ga ions from Ga2O3/GaN layers, the most part of the nominal Fe3O4 layer is actually in the form of GaxFe3-xO4 with gradually decreased x values from the Fe3O4/Ga2O3 interface to the Fe3O4 surface. Post-annealing process can further aggravate the diffusion. Due to the similar ionic radius of Ga and Fe, the structural configuration of the GaxFe3-xO4 does not differ from that of pure Fe3O4. However, the ferromagnetism has been reduced with the incorporation of Ga into Fe3O4, which has been explained by the increased Yafet-Kittel angles in presence of considerable amount of Ga incorporation. A different behavior of the magnetoresistance has been found on the as-grown and annealed samples, which could be modelled and explained by the competition between the spin-dependent and spin-independent conduction channels. This work has provided detailed information on the interfacial properties of the Fe3O4/Ga2O3/GaN spin injecting hetero-structure, which is the solid basis for further improvement and application of the structure.

  3. Growth and coalescence control of inclined c-axis polar and semipolar GaN multilayer structures grown on Si(111), Si(112), and Si(115) by metalorganic vapor phase epitaxy

    SciTech Connect

    Szymański, Tomasz Wośko, Mateusz; Paszkiewicz, Bartłomiej; Paszkiewicz, Bogdan; Paszkiewicz, Regina

    2016-09-15

    Herein, silicon substrates in alternative orientations from the commonly used Si(111) were used to enable the growth of polar and semipolar GaN-based structures by the metalorganic vapor phase epitaxy method. Specifically, Si(112) and Si(115) substrates were used for the epitaxial growth of nitride multilayer structures, while the same layer schemes were also deposited on Si(111) for comparison purposes. Multiple approaches were studied to examine the influence of the seed layers and the growth process conditions upon the final properties of the GaN/Si(11x) templates. Scanning electron microscope images were acquired to examine the topography of the deposited samples. It was observed that the substrate orientation and the process conditions allow control to produce an isolated GaN block growth or a coalesced layer growth, resulting in inclined c-axis GaN structures under various forms. The angles of the GaN c-axis inclination were determined by x-ray diffraction measurements and compared with the results obtained from the analysis of the atomic force microscope (AFM) images. The AFM image analysis method to determine the structure tilt was found to be a viable method to estimate the c-axis inclination angles of the isolated blocks and the not-fully coalesced layers. The quality of the grown samples was characterized by the photoluminescence method conducted at a wide range of temperatures from 77 to 297 K, and was correlated with the sample degree of coalescence. Using the free-excitation peak positions plotted as a function of temperature, analytical Bose-Einstein model parameters were fitted to obtain further information about the grown structures.

  4. Investigation of AlN films grown by molecular beam epitaxy on vicinal Si(111) as templates for GaN quantum dots

    SciTech Connect

    Benaissa, M.; Vennegues, P.; Tottereau, O.; Nguyen, L.; Semond, F.

    2006-12-04

    The use of AlN epitaxial films deposited on vicinal Si(111) as templates for the growth of GaN quantum dots is investigated by transmission electron microscopy and atomic force microscopy. It is found that the substrate vicinality induces both a slight tilt of the AlN (0001) direction with respect to the [111] direction and a step bunching mechanism. As a consequence, a dislocation dragging behavior is observed giving rise to dislocation-free areas well suited for the nucleation of GaN quantum dots.

  5. Structural properties of Al-rich AlInN grown on c-plane GaN substrate by metal-organic chemical vapor deposition

    PubMed Central

    2014-01-01

    The attractive prospect for AlInN/GaN-based devices for high electron mobility transistors with advanced structure relies on high-quality AlInN epilayer. In this work, we demonstrate the growth of high-quality Al-rich AlInN films deposited on c-plane GaN substrate by metal-organic chemical vapor deposition. X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy show that the films lattice-matched with GaN can have a very smooth surface with good crystallinity and uniform distribution of Al and In in AlInN. PMID:25489282

  6. Elimination of columnar microstructure in N-face InAlN, lattice-matched to GaN, grown by plasma-assisted molecular beam epitaxy in the N-rich regime

    SciTech Connect

    Ahmadi, Elaheh; Wienecke, Steven; Keller, Stacia; Mishra, Umesh K.; Shivaraman, Ravi; Wu, Feng; Kaun, Stephen W.; Speck, James S.

    2014-02-17

    The microstructure of N-face InAlN layers, lattice-matched to GaN, was investigated by scanning transmission electron microscopy and atom probe tomography. These layers were grown by plasma-assisted molecular beam epitaxy (PAMBE) in the N-rich regime. Microstructural analysis shows an absence of the lateral composition modulation that was previously observed in InAlN films grown by PAMBE. A room temperature two-dimensional electron gas (2DEG) mobility of 1100 cm{sup 2}/V s and 2DEG sheet charge density of 1.9 × 10{sup 13} cm{sup −2} was measured for N-face GaN/AlN/GaN/InAlN high-electron-mobility transistors with lattice-matched InAlN back barriers.

  7. Epitaxial growth of GaAs and GaN by gas source molecular beam epitaxy using organic group V compounds

    NASA Astrophysics Data System (ADS)

    Okumura, H.; Yoshida, S.; Misawa, S.; Sakuma, E.

    1992-05-01

    GaAs and GaN epilayers were grown on GaAs substrates by gas source molecular beam epitaxy technique using triethylarsine (TEAs) and diethylarsine (DEAsH) as As sources, and dimethylhydrazine (DMHy) as an N source. It was found that GaAs grows layer by layer even when organic arsine molecular sources are used. Cubic GaN was found to grow epitaxially on sufficiently nitrided surfaces of GaAs (001) substrates, in contrast with the growth of hexagonal GaN on GaAs (111) surfaces. It was also found that nitridation of GaAs surfaces does not occur when DEAsH and DMHy beams are supplied onto the GaAs substrates, simultaneously. Thus, GaN/GaAs multilayers were obtained only by intermittent supply of a DEAsH beam.

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

    DTIC Science & Technology

    2010-05-17

    rf - plasma assisted MBE - grown homoepitaxial GaN has shown that oxygen, a shallow donor in GaN , is present at...properties of Al- GaN / GaN HEMTs grown by rf - MBE on native GaN substrates . 2. Experimental Seven AlGaN/ GaN heterostructures were grown by rf - plasma assisted... GaN /Be:GaN heterostructures have been grown by rf - plasma molecular beam epitaxy on free- standing semi-insulating

  9. Co-existence of harmonic generation and two-photon luminescence in selectively grown coaxial InGaN/GaN quantum wells on GaN pyramids

    NASA Astrophysics Data System (ADS)

    Butler, Sween; Fikry, Mohamed; Madel, Manfred; Thonke, Klaus; Neogi, Arup

    2015-02-01

    Nonlinear optical properties of coaxial InGaN/GaN multiple quantum well (MQWs) submicron hetero-structures were investigated using a tunable femtosecond laser at room temperature. Co-axial InGaN/GaN MQW hetero-structures were fabricated by depositing InGaN/GaN layers on the side walls of GaN submicron tubes on top of GaN micro-pyramids. Excitation and signal collection from a single micro-structure was achieved using multi-photon spectroscopy. Two photon excited photoluminescence (TPEL) was observed at around 390 nm independent of excitation wavelength. In addition to TPEL, observation of second harmonic signal of the excitation laser is also presented.

  10. 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.

  11. Growth and Characterization of Single Crystalline InN Grown on GaN by RF Sputtering for Robust Schottky Contacts

    NASA Astrophysics Data System (ADS)

    Harotoonian, Vache; Woodall, Jerry M.

    2016-12-01

    High-quality, single crystal wurtzite InN films were fabricated by radio-frequency magnetron reactive sputtering on GaN templates. The sputtered InN films in this study were about 100 nm thick. Atomic force microscopy analysis revealed the sputtered InN film had root-mean-square surface roughness of about 0.4 nm, which is comparable to the underlying GaN template. Coupled x-ray diffraction (XRD) measurements confirmed the (0001) preferred growth orientation and ω-rocking curve full-width-half-maximum (FWHM) = 0.85° for the symmetrical (0002) diffraction peak. The present InN film has the best crystal quality in terms of narrower FWHM of XRD rocking curve among reported sputtered InN thin films. In-plane and out-of-plane XRD measurements revealed a relaxed film. Room temperature Hall Effect measurements showed mobility of 110 cm2/V.s and electron concentration of 1-2 × 1020/cm3. The feasibility of utilizing a cost effective and productive method of sputtering to form robust Schottky contacts to GaN using InN, an immiscible and metallic-like semiconductor, was explored.

  12. The effect of AlN nucleation temperature on inverted pyramid defects in GaN layers grown on 200 mm silicon wafers

    NASA Astrophysics Data System (ADS)

    Charles, Matthew; Baines, Yannick; Bos, Sandra; Escoffier, René; Garnier, Gennie; Kanyandekwe, Joël; Lebreton, Julie; Vandendaele, William

    2017-04-01

    We have examined 200 mm GaN on silicon wafers, while varying the AlN nucleation temperature, and have found that higher temperatures result in a more convex bow on the wafers. In addition, by performing full wafer defect mapping, we have found that a higher nucleation temperature results in a higher density of inverted pyramid defects, which have previously been found to reduce the breakdown voltage of GaN on silicon layers. We have performed electrical measurements on a wafer with the lowest temperature AlN layer, which is still within our bow specification, and which therefore has the lowest density of inverted pyramid defects. This wafer showed the same leakage current density for both very small and very large test structures (2×10-3 and 18.7 mm2 respectively), with all but one of our large structures maintaining a breakdown voltage greater than 700 V. This is a very promising result for high yield of devices on 200 mm GaN on silicon wafers.

  13. Morphology evolution and emission properties of InGaN/GaN multiple quantum wells grown on GaN microfacets using crossover stripe patterns by selective area epitaxy

    NASA Astrophysics Data System (ADS)

    Wu, Zhenlong; Chen, Peng; Yang, Guofeng; Xu, Zhou; Xu, Feng; Jiang, Fulong; Zhang, Rong; Zheng, Youdou

    2015-03-01

    We investigate the morphological evolution of selective area epitaxy (SAE) GaN microfacets structures on crossover stripe patterns as a function of temperature, and the emission properties of semipolar InGaN/GaN multiple quantum wells (MQWs) grown on these microstructures with semipolar facets are also studied. The shapes of inner rings gradually change from nearly rectangular to hexagonal when the GaN growth temperature elevates, as a result of growth rates and surface stability varies with elevated temperatures. Three types of semipolar facets ({1 1 -2 2}, {2 1 -3 3} and {1 -1 0 1} facets) can be identified on the inner rings of these structures, which are verified by the emission properties of semipolar InGaN/GaN MQWs. The emission wavelengths of MQWs on these semipolar facets are ordered as {1 -1 0 1} > {2 1 -3 3} > {1 1 -2 2}, which is attributed to variations of growth rate and indium incorporation on different planes during InGaN growth. Furthermore, the indium composition of MQWs changes with the morphological evolution.

  14. Effects of Mg/Ga and V/III source ratios on hole concentration of N-polar (000\\bar{1}) p-type GaN grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Nonoda, Ryohei; Shojiki, Kanako; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Katayama, Ryuji; Matsuoka, Takashi

    2016-05-01

    The effects of growth conditions such as Mg/Ga and V/III ratios on the properties of N-polar (000\\bar{1}) p-type GaN grown by metalorganic vapor phase epitaxy were studied. Photoluminescence spectra from Mg-doped GaN depended on Mg/Ga and V/III ratios. For the lightly doped samples, the band-to-acceptor emission was observed at 3.3 eV and its relative intensity decreased with increasing V/III ratio. For the heavily doped samples, the donor-acceptor pair emission was observed at 2.8 eV and its peak intensity monotonically decreased with V/III ratio. The hole concentration was maximum for the Mg/Ga ratio. This is the same tendency as in group-III polar (0001) growth. The V/III ratio also reduced the hole concentration. The higher V/III ratio reduced the concentration of residual donors such as oxygen by substituting nitrogen atoms. The surface became rougher with increasing V/III ratio and the hillock density increased.

  15. Control of polarity of ZnO films grown by plasma-assisted molecular-beam epitaxy: Zn- and O-polar ZnO films on Ga-polar GaN templates

    NASA Astrophysics Data System (ADS)

    Hong, Soon-Ku; Hanada, Takashi; Ko, Hang-Ju; Chen, Yefan; Yao, Takafumi; Imai, Daisuke; Araki, Kiyoaki; Shinohara, Makoto

    2000-11-01

    We report on the growth of polarity-controlled ZnO films by plasma-assisted molecular-beam epitaxy. Different polar (Zn- and O-polar) ZnO films on unipolar (Ga-polar) GaN epilayers are selectively grown. Polarity of ZnO films is evaluated by coaxial impact collision ion scattering spectroscopy. Zn preexposure prior to ZnO growth results in Zn-polar ZnO films (Zn face), while O-plasma preexposure leads to the growth of O-polar ZnO films (O face). High-resolution transmission electron microscopy reveals the formation of an interface layer between ZnO and GaN epilayers in O-plasma preexposed samples, while no interface layer is observed in Zn preexposed samples. The interface layer is identified as single crystalline, monoclinic Ga2O3. We propose models for interface configurations at ZnO/GaN heterointerfaces, which can successfully explain the different polarities of the ZnO films.

  16. Mg-compensation effect in GaN buffer layer for AlGaN/GaN high-electron-mobility transistors grown on 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Ko, Kwangse; Lee, Kyeongjae; So, Byeongchan; Heo, Cheon; Lee, Kyungbae; Kwak, Taemyung; Han, Sang-Woo; Cha, Ho-Young; Nam, Okhyun

    2017-01-01

    The present study investigated the Mg doping effect in the gallium nitride (GaN) buffer layers (BLs) of AlGaN/GaN high-electron-mobility transistor (HEMT) structures grown on semi-insulating 4H-SiC substrates by metal organic chemical vapor deposition. When the Mg concentration was increased from 3 × 1017 to 8 × 1018 cm-3, the crystal quality slightly deteriorated, whereas electrical properties were significantly changed. The buffer leakage increased approximately 50 times from 0.77 to 39.2 nA at -50 V with the Mg doping concentration. The Mg-compensation effect and electron trapping effect were observed at Mg concentration of 3 × 1017 and 8 × 1018 cm-3, respectively, which were confirmed by an isolation leakage current test and low-temperature photoluminescence. When the BL was compensated, the two-dimensional electron gas (2DEG) mobility and sheet carrier concentration of the HEMTs were 1560 cm2 V-1 s-1 and 5.06 × 1012 cm-2, respectively. As a result, Mg-doped GaN BLs were demonstrated as a candidates of semi-insulating BLs for AlGaN/GaN HEMT.

  17. Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

    NASA Astrophysics Data System (ADS)

    Soh, C. B.; Hartono, H.; Chow, S. Y.; Chua, S. J.; Fitzgerald, E. A.

    2007-01-01

    Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20-50nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650to1015°C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.

  18. Origin of huge photoluminescence efficiency improvement in InGaN/GaN multiple quantum wells with low-temperature GaN cap layer grown in N2/H2 mixture gas

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    The nominal internal quantum efficiency of InGaN/GaN multiple quantum wells significantly increases from 5.6 to 26.8%, as a low-temperature GaN cap layer is grown in N2/H2 mixture gas. Meanwhile, the room-temperature photoluminescence (PL) peak energy shows a merely 73 meV blue shift. On the basis of temperature-dependent PL characteristics analysis, the huge improvement in PL efficiency arises mainly from the “etching effect” of hydrogen, which reduces the defect density and indium segregation at the upper well/barrier interface, and consequently contributes to the decrease in the number of nonradiative recombination centers and the enhancement of carrier localization.

  19. Self-regulated in-plane polarity of [11¯00]-oriented GaN domains coalesced from twins grown on a SiO2-patterned m-plane sapphire substrate

    NASA Astrophysics Data System (ADS)

    Lee, Hyemi; Jue, Miyeon; Yoon, Hansub; Lee, Sanghwa; Kim, Chinkyo

    2014-05-01

    In-plane polarity of [11¯00]-oriented GaN domains coalesced from twins grown on a SiO2-patterned m-plane sapphire substrate was observed to be self-regulated in such a way that basal faces of coalesced domains were mainly found to have the (0001¯) polarity only. This self-regulation behavior of in-plane polarity was explained by a computational simulation of plan-view surface morphology evolution during coalescence of twins. Based on a computational simulation, asymmetrically suppressed growth rates of twins near a SiO2 pattern were proposed to be responsible for the survival of the slower growing (0001¯) basal faces instead of the faster growing (0001) basal faces during coalescence of twins.

  20. Formation of I2-type basal-plane stacking faults in In0.25Ga0.75N multiple quantum wells grown on a ( 10 1 ¯ ) semipolar GaN template

    NASA Astrophysics Data System (ADS)

    Li, Yueliang; Qi, Haoyuan; Meisch, Tobias; Hocker, Matthias; Thonke, Klaus; Scholz, Ferdinand; Kaiser, Ute

    2017-01-01

    In this work, I2-type basal-plane stacking faults (BSFs) were observed in In0.25Ga0.75N multiple quantum wells (MQWs) grown on a ( 10 1 ¯1 ) semipolar GaN template by high-resolution transmission electron microscopy. The structure and formation mechanisms of the I2-type BSFs at the GaN-InGaN interface were investigated in detail. The formation of the I2-type BSFs contributes to lattice mismatch accommodation within the InGaN QWs. Their density varies in different regions of the sample due to the inhomogeneous distribution of the In content in the InGaN layer. The relationship between the In content in the InxGa1-xN layer and the I2-type BSFs is discussed.

  1. Control of ion content and nitrogen species using a mixed chemistry plasma for GaN grown at extremely high growth rates >9 μm/h by plasma-assisted molecular beam epitaxy

    SciTech Connect

    Gunning, Brendan P.; Clinton, Evan A.; Merola, Joseph J.; Doolittle, W. Alan; Bresnahan, Rich C.

    2015-10-21

    Utilizing a modified nitrogen plasma source, plasma assisted molecular beam epitaxy (PAMBE) has been used to achieve higher growth rates in GaN. A higher conductance aperture plate, combined with higher nitrogen flow and added pumping capacity, resulted in dramatically increased growth rates up to 8.4 μm/h using 34 sccm of N{sub 2} while still maintaining acceptably low operating pressure. It was further discovered that argon could be added to the plasma gas to enhance growth rates up to 9.8 μm/h, which was achieved using 20 sccm of N{sub 2} and 7.7 sccm Ar flows at 600 W radio frequency power, for which the standard deviation of thickness was just 2% over a full 2 in. diameter wafer. A remote Langmuir style probe employing the flux gauge was used to indirectly measure the relative ion content in the plasma. The use of argon dilution at low plasma pressures resulted in a dramatic reduction of the plasma ion current by more than half, while high plasma pressures suppressed ion content regardless of plasma gas chemistry. Moreover, different trends are apparent for the molecular and atomic nitrogen species generated by varying pressure and nitrogen composition in the plasma. Argon dilution resulted in nearly an order of magnitude achievable growth rate range from 1 μm/h to nearly 10 μm/h. Even for films grown at more than 6 μm/h, the surface morphology remained smooth showing clear atomic steps with root mean square roughness less than 1 nm. Due to the low vapor pressure of Si, Ge was explored as an alternative n-type dopant for high growth rate applications. Electron concentrations from 2.2 × 10{sup 16} to 3.8 × 10{sup 19} cm{sup −3} were achieved in GaN using Ge doping, and unintentionally doped GaN films exhibited low background electron concentrations of just 1–2 × 10{sup 15} cm{sup −3}. The highest growth rates resulted in macroscopic surface features due to Ga cell spitting, which is an engineering challenge still to be

  2. Molecular beam epitaxy as a method for the growth of free-standing bulk zinc-blende GaN and AlGaN crystals

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Staddon, C. R.; Foxon, C. T.; Luckert, F.; Edwards, P. R.; Martin, R. W.; Kent, A. J.

    2011-05-01

    We have studied the growth of zinc-blende GaN and AlxGa1-xN layers, structures and bulk crystals by molecular beam epitaxy (MBE). MBE is normally regarded as an epitaxial technique for growth of very thin layers with monolayer control of their thickness. However, we have used the MBE technique for bulk crystal growth and have produced GaN layers up to 100 μm in thickness. Thick, undoped, cubic GaN films were grown on semi-insulating GaAs (0 0 1) substrates by a modified plasma-assisted molecular beam epitaxy (PA-MBE) method and were removed from the GaAs substrate after the growth. The resulting free-standing GaN wafers may be used as substrates for further epitaxy of cubic GaN-based structures and devices. We have demonstrated that the PA-MBE process, we had developed, also allows us to achieve free-standing zinc-blende AlxGa1-xN wafers.

  3. Green cubic GaInN/GaN light-emitting diode on microstructured silicon (100)

    SciTech Connect

    Stark, Christoph J. M.; Detchprohm, Theeradetch; Wetzel, Christian; Lee, S. C.; Brueck, S. R. J.; Jiang, Y.-B.

    2013-12-02

    GaInN/GaN light-emitting diodes free of piezoelectric polarization were prepared on standard electronic-grade Si(100) substrates. Micro-stripes of GaN and GaInN/GaN quantum wells in the cubic crystal structure were grown on intersecting (111) planes of microscale V-grooved Si in metal-organic vapor phase epitaxy, covering over 50% of the wafer surface area. Crystal phases were identified in electron back-scattering diffraction. A cross-sectional analysis reveals a cubic structure virtually free of line defects. Electroluminescence over 20 to 100 μA is found fixed at 487 nm (peak), 516 nm (dominant). Such structures therefore should allow higher efficiency, wavelength-stable light emitters throughout the visible spectrum.

  4. Effect of Nitridation on the Regrowth Interface of AlGaN/GaN Structures Grown by Molecular Beam Epitaxy on GaN Templates

    NASA Astrophysics Data System (ADS)

    Wong, Yuen-Yee; Huang, Wei-Ching; Trinh, Hai-Dang; Yang, Tsung-Hsi; Chang, Jet-Rung; Chen, Micheal; Chang, Edward Yi

    2012-08-01

    AlGaN/GaN structures were regrown on GaN templates using plasma- assisted molecular beam epitaxy (PA-MBE). Prior to the regrowth, nitridation was performed using nitrogen plasma in the MBE chamber for different durations (0 min to 30 min). Direct-current measurements on high-electron-mobility transistor devices showed that good pinch-off characteristics and good interdevice isolation were achieved for samples prepared with a 30-min nitridation process. Current-voltage measurements on Schottky barrier diodes also revealed that, for samples prepared without nitridation, the reverse-bias gate leakage current was approximately two orders of magnitudes larger than that of samples prepared with a 30-min nitridation process. The improvement in the electrical properties is a result of contaminant removal at the regrowth interface which may be induced by the etching effect of nitridation.

  5. High quality and uniformity GaN grown on 150 mm Si substrate using in-situ NH3 pulse flow cleaning process

    NASA Astrophysics Data System (ADS)

    Ji, Panfeng; Yang, Xuelin; Feng, Yuxia; Cheng, Jianpeng; Zhang, Jie; Hu, Anqi; Song, Chunyan; Wu, Shan; Shen, Jianfei; Tang, Jun; Tao, Chun; Pan, Yaobo; Wang, Xinqiang; Shen, Bo

    2017-04-01

    By using in-situ NH3 pulse flow cleaning method, we have achieved the repeated growth of high quality and uniformity GaN and AlGaN/GaN high electron mobility transistors (HEMTs) on 150 mm Si substrate. The two dimensional electron gas (2DEG) mobility is 2200 cm2/Vs with an electron density of 7.3 × 1012 cm-2. The sheet resistance is 305 ± 4 Ω/□ with ±1.3% variation. The achievement is attributed to the fact that this method can significantly remove the Al, Ga, etc. metal droplets coating on the post growth flow flange and reactor wall which are difficult to clean by normal bake process under H2 ambient.

  6. The Peculiarities of Strain Relaxation in GaN/AlN Superlattices Grown on Vicinal GaN (0001) Substrate: Comparative XRD and AFM Study

    NASA Astrophysics Data System (ADS)

    Kuchuk, Andrian V.; Kryvyi, Serhii; Lytvyn, Petro M.; Li, Shibin; Kladko, Vasyl P.; Ware, Morgan E.; Mazur, Yuriy I.; Safryuk, Nadiia V.; Stanchu, Hryhorii V.; Belyaev, Alexander E.; Salamo, Gregory J.

    2016-05-01

    Superlattices (SLs) consisting of symmetric layers of GaN and AlN have been investigated. Detailed X-ray diffraction and reflectivity measurements demonstrate that the relaxation of built-up strain in the films generally increases with an increasing number of repetitions; however, an apparent relaxation for subcritical thickness SLs is explained through the accumulation of Nagai tilt at each interface of the SL. Additional atomic force microscopy measurements reveal surface pit densities which appear to correlate with the amount of residual strain in the films along with the appearance of cracks for SLs which have exceeded the critical thickness for plastic relaxation. These results indicate a total SL thickness beyond which growth may be limited for the formation of high-quality coherent crystal structures; however, they may indicate a growth window for the reduction of threading dislocations by controlled relaxation of the epilayers.

  7. 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.

  8. Nanostructured surface morphology of ZnO grown on p-type GaN and Si by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Hung, S. C.; Huang, P. J.; Chan, C. E.; Uen, W. Y.; Ren, F.; Pearton, S. J.; Yang, T. N.; Chiang, C. C.; Lan, S. M.; Chi, G. C.

    2008-12-01

    The surface morphology of ZnO grown on p-GaN templates and p-Si (1 1 1) substrates at various temperatures by metal organic chemical vapor deposition (MOCVD) in a vertical reactor at atmospheric pressure is reported. A low temperature ZnO buffer was deposited initially at 200 °C for 15 min as a nucleation layer. Epitaxial ZnO was grown at 500 °C, 550 °C, 600 °C for 40 min, respectively. Uniformly distributed and well-aligned ZnO nanorods with diameter in the range 80-120 nm and length ˜0.7 μm were observed for deposition on p-GaN template. By contrast, the morphology of ZnO epilayers grown on p-Si (1 1 1) transitioned from 2D to 3D with increasing growth temperature. X-ray diffraction (XRD) spectra showed all the ZnO epilayers had the hexagonal wurtzite structure but different preferred orientation. PL spectra showed only free-exciton emission at 378 nm (˜3.28 eV) with a full width at half maximum of 13 nm without defect-related green emission in the epitaxial ZnO grown at 550 °C and 600 °C. The epitaxial ZnO layers grown on p-GaN and p-Si at the same temperature have similar PL spectra. The PL measurement also exhibits strong exciton-related emission without defect peak, which showed that the ZnO nanostructures grown at 550 °C and 600 °C have good optical properties with excellent crystal quality.

  9. Surface Morphology Evolution Mechanisms of InGaN/GaN Multiple Quantum Wells with Mixture N2/H2-Grown GaN Barrier

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaorun; Lu, Taiping; Zhu, Yadan; Zhao, Guangzhou; Dong, Hailiang; Jia, Zhigang; Yang, Yongzhen; Chen, Yongkang; Xu, Bingshe

    2017-05-01

    Surface morphology evolution mechanisms of InGaN/GaN multiple quantum wells (MQWs) during GaN barrier growth with different hydrogen (H2) percentages have been systematically studied. Ga surface-diffusion rate, stress relaxation, and H2 etching effect are found to be the main affecting factors of the surface evolution. As the percentage of H2 increases from 0 to 6.25%, Ga surface-diffusion rate and the etch effect are gradually enhanced, which is beneficial to obtaining a smooth surface with low pits density. As the H2 proportion further increases, stress relaxation and H2 over- etching effect begin to be the dominant factors, which degrade surface quality. Furthermore, the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed. The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high-quality InGaN/GaN heterostructures.

  10. Surface Morphology Evolution Mechanisms of InGaN/GaN Multiple Quantum Wells with Mixture N2/H2-Grown GaN Barrier.

    PubMed

    Zhou, Xiaorun; Lu, Taiping; Zhu, Yadan; Zhao, Guangzhou; Dong, Hailiang; Jia, Zhigang; Yang, Yongzhen; Chen, Yongkang; Xu, Bingshe

    2017-12-01

    Surface morphology evolution mechanisms of InGaN/GaN multiple quantum wells (MQWs) during GaN barrier growth with different hydrogen (H2) percentages have been systematically studied. Ga surface-diffusion rate, stress relaxation, and H2 etching effect are found to be the main affecting factors of the surface evolution. As the percentage of H2 increases from 0 to 6.25%, Ga surface-diffusion rate and the etch effect are gradually enhanced, which is beneficial to obtaining a smooth surface with low pits density. As the H2 proportion further increases, stress relaxation and H2 over- etching effect begin to be the dominant factors, which degrade surface quality. Furthermore, the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed. The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high-quality InGaN/GaN heterostructures.

  11. Nanoair-bridged lateral overgrowth of GaN on ordered nanoporous GaN template

    NASA Astrophysics Data System (ADS)

    Wang, Y. D.; Zang, K. Y.; Chua, S. J.; Tripathy, S.; Chen, P.; Fonstad, C. G.

    2005-12-01

    We report the growth of high-quality GaN epilayers on an ordered nanoporous GaN template by metalorganic chemical vapor deposition. The nanopores in GaN template were created by inductively coupled plasma etching using anodic aluminum oxide film as an etch mask. The average pore diameter and interpore distance is about 65 and 110nm, respectively. Subsequent overgrowth of GaN first begins at the GaN crystallite surface between the pores, and then air-bridge-mediated lateral overgrowth leads to the formation of the continuous layer. Microphotoluminescence and micro-Raman measurements show improved optical properties and significant strain relaxation in the overgrown layer when compared to GaN layer of same thickness simultaneously grown on sapphire without any template. Similar to conventional epitaxial lateral overgrown GaN, such overgrown GaN on a nanopatterned surface would also serve as a template for the growth of ultraviolet-visible light-emitting III-nitride devices.

  12. GaN nanorods coated with pure BN

    NASA Astrophysics Data System (ADS)

    Han, Wei-Qiang; Zettl, A.

    2002-12-01

    We report a method to efficiently synthesize gallium nitride (GaN) nanorods coated with insulating boron nitride (BN) layers. The GaN core is crystalline (with either a cubic zincblende or hexagonal wurtzite structure) and has diameters ranging from 10 to 85 nm and lengths up to 60 μm. The outer encapsulating BN shells with typical thicknesses less than 5 nm extend fully over, and adhere well to, the entire nanorod surface.

  13. Behavior of temperature dependent electrical properties of Pd/Au Schottky contact to GaN grown on Si substrate by MBE

    NASA Astrophysics Data System (ADS)

    Singh Nirwal, Varun; Rao Peta, Koteswara

    2016-12-01

    We investigated the effect of temperature on the behavior of electrical properties of Pd/Au Schottky contact to GaN/Si (111) in the temperature range of 125-325 K in steps of 25 K using current-voltage (I-V) and capacitance-voltage (C-V) analysis. The Schottky barrier height (ϕ I-V ) and ideality factor is calculated using standard thermionic emission theory. The value of ϕ I-V was found to increase from 0.41 ± 0.002 eV to 0.79 ± 0.008 eV when temperature varied from 125 to 325 K. The ideality factor of diodes also decreased from 5.91 ± 0.01 to 1.03 ± 0.05 with increase in temperature. The series resistance (R s) is calculated using Cheung’s method and it is observed that the value of R s decreased from 74.40 ± 0.32 Ω to 58.59 ± 0.11 Ω when the temperature increased from 125 to 325 K. Barrier height (ϕ C-V ) and effective carrier concentration (Nd ) is also reported from C-V characteristics as a function of temperature and the value of ϕ C-V was found to decrease with increase in temperature. The behavior of barrier heights obtained from I-V and C-V characteristics is different due to difference in the nature of measurement techniques. The deviation of conventional Richardson’s constant from theoretical value of GaN is due to unusual behavior of temperature dependent electrical properties and barrier inhomogeneity. This is successfully explained by assuming the double Gaussian distribution of inhomogeneous barrier heights of Au/Pd/GaN/Si Schottky diode.

  14. Validity of Vegard’s rule for Al1-xInxN (0.08  <  x  <  0.28) thin films grown on GaN templates

    NASA Astrophysics Data System (ADS)

    Magalhães, S.; Franco, N.; Watson, I. M.; Martin, R. W.; O'Donnell, K. P.; Schenk, H. P. D.; Tang, F.; Sadler, T. C.; Kappers, M. J.; Oliver, R. A.; Monteiro, T.; Martin, T. L.; Bagot, P. A. J.; Moody, M. P.; Alves, E.; Lorenz, K.

    2017-05-01

    In this work, comparative x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements allow a comprehensive characterization of Al1-xInxN thin films grown on GaN. Within the limits of experimental accuracy, and in the compositional range 0.08  <  x  <  0.28, the lattice parameters of the alloys generally obey Vegard’s rule, varying linearly with the InN fraction. Results are also consistent with the small deviation from linear behaviour suggested by Darakchieva et al (2008 Appl. Phys. Lett. 93 261908). However, unintentional incorporation of Ga, revealed by atom probe tomography (APT) at levels below the detection limit for RBS, may also affect the lattice parameters. Furthermore, in certain samples the compositions determined by XRD and RBS differ significantly. This fact, which was interpreted in earlier publications as an indication of a deviation from Vegard’s rule, may rather be ascribed to the influence of defects or impurities on the lattice parameters of the alloy. The wide-ranging set of Al1-xInxN films studied allowed furthermore a detailed investigation of the composition leading to lattice-matching of Al1-xInxN/GaN bilayers.

  15. Structural defects in GaN revealed by Transmission Electron Microscopy

    DOE PAGES

    Liliental-Weber, Zuzanna

    2014-09-08

    This paper reviews the various types of structural defects observed by Transmission Electron Microscopy in GaN heteroepitaxial layers grown on foreign substrates and homoepitaxial layers grown on bulk GaN substrates. The structural perfection of these layers is compared to the platelet self-standing crystals grown by High Nitrogen Pressure Solution. Defects in undoped and Mg doped GaN are discussed. Lastly, some models explaining the formation of inversion domains in heavily Mg doped layers that are possible defects responsible for the difficulties of p-doping in GaN are also reviewed.

  16. Morphological and microstructural stability of N-polar InAlN thin films grown on free-standing GaN substrates by molecular beam epitaxy

    SciTech Connect

    Hardy, Matthew T. Storm, David F.; Downey, Brian P.; Katzer, D. Scott; Meyer, David J.; McConkie, Thomas O.; Smith, David J.; Nepal, Neeraj

    2016-03-15

    The sensitivity of the surface morphology and microstructure of N-polar-oriented InAlN to variations in composition, temperature, and layer thickness for thin films grown by plasma-assisted molecular beam epitaxy (PAMBE) has been investigated. Lateral compositional inhomogeneity is present in N-rich InAlN films grown at low temperature, and phase segregation is exacerbated with increasing InN fraction. A smooth, step-flow surface morphology and elimination of compositional inhomogeneity can be achieved at a growth temperature 50 °C above the onset of In evaporation (650 °C). A GaN/AlN/GaN/200-nm InAlN heterostructure had a sheet charge density of 1.7 × 10{sup 13 }cm{sup −2} and no degradation in mobility (1760 cm{sup 2}/V s) relative to 15-nm-thick InAlN layers. Demonstration of thick-barrier high-electron-mobility transistors with good direct-current characteristics shows that device quality, thick InAlN layers can be successfully grown by PAMBE.

  17. The effect of oxygen flow rate and radio frequency plasma power on cubic ZnMgO ultraviolet sensors grown by plasma-enhanced molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Casey Boutwell, R.; Wei, Ming; Schoenfeld, Winston V.

    2013-07-01

    Cubic Zn1-xMgxO thin films were produced by Plasma-Enhanced Molecular Beam Epitaxy. Oxygen flow rate and applied Radio-Frequency (RF) plasma power were varied to investigate the impact on film growth and optoelectronic device performance. Solar-blind and visible-blind detectors were fabricated with metal-semiconductor-metal interdigitated Ni/Mg/Au contacts and responsivity is compared under different growth conditions. Increasing oxygen flow rate and RF plasma power increased Zn incorporation in the film, which leads to phase segregation at relatively high Zn/Mg ratio. Responsivity as high as 61 A/W was measured in phase-segregated ZnMgO visible-blind detectors.

  18. Spectroscopic measurements of the surface stoichiometry of chemical vapor deposited GaN

    NASA Astrophysics Data System (ADS)

    Craft, H. S.; Rice, A. L.; Collazo, R.; Sitar, Z.; Maria, J.-P.

    2011-02-01

    We report on the surface stoichiometry of Ga-polar GaN films grown by metalorganic chemical vapor deposition as studied by x-ray photoelectron spectroscopy. GaN film surfaces are found to be Ga-rich, with Ga:N ratios ranging from 1.3:1 to 3.2:1. In vacuo ion-beam sputter/annealing studies show that these treatments drive the apparent Ga:N surface composition farther from unity, either through a decrease in surface contamination, oxidation of the surface, or both. Simple annealing experiments decrease the Ga:N ratio. The measured GaN ratio is correlated with the GaN growth time, suggesting that residual Ga precursor after growth interacts with the GaN surface as it cools.

  19. Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles.

    PubMed

    Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Cebotari, Serghei; Lux, Marco; Haverich, Axel; Hilfiker, Andres

    2016-01-01

    Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle-cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN.

  20. Optical properties of GaN pyramids

    SciTech Connect

    Zeng, K.C.; Lin, J.Y.; Jiang, H.X.; Yang, W.

    1999-03-01

    Picosecond time-resolved photoluminescence (PL) spectroscopy has been used to investigate the optical properties of GaN pyramids overgrown on hexagonal-patterned GaN(0001) epilayers on sapphire and silicon substrates with AlN buffer layers. We found that: (i) the release of the biaxial compressive strain in GaN pyramids on GaN/AlN/sapphire substrate led to a 7 meV redshift of the spectral peak position with respect to the strained GaN epilayer grown under identical conditions; (ii) in the GaN pyramids on GaN/AlN/sapphire substrate, strong band edge transitions with much narrower linewidths than those in the GaN epilayer have been observed, indicating the improved crystalline quality of the overgrown pyramids; (iii) PL spectra taken from different parts of the pyramids revealed that the top of the pyramid had the highest crystalline quality; and (iv) the presence of strong band-to-impurity transitions in the pyramids were primarily due to the incorporation of the oxygen and silicon impurities from the SiO{sub 2} mask. {copyright} {ital 1999 American Institute of Physics.}

  1. Growth of ZnO(0001) on GaN(0001)/4H-SiC buffer layers by plasma-assisted hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Adolph, David; Tingberg, Tobias; Ive, Tommy

    2015-09-01

    Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 °C and an O2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-half-maximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1 bar 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1×1019 cm-3 and a Hall mobility of 51 cm2/V s.

  2. Thickness measurement of semiconductor thin films by energy dispersive X-ray fluorescence benchtop instrumentation: Application to GaN epilayers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Queralt, I.; Ibañez, J.; Marguí, E.; Pujol, J.

    2010-07-01

    The importance of thin films in modern high technology products, such as semiconductors, requires fast and non-destructive analysis. A methodology to determine the thickness of single layers with benchtop energy dispersive X-ray fluorescence (EDXRF) instrumentation is described and tested following analytical validation criteria. The experimental work was carried out on gallium nitride thin films epitaxially grown on sapphire substrate. The results of samples with layers in the range from 400 to 1000 nm exhibit a good correlation with the layer thickness determined by optical reflectance. Spectral data obtained using thin layered samples indicate the possibility to precisely evaluate layer thickness from 5 nm, with a low relative standard deviation (RSD < 2%) of the results. In view of the limits of optical reflectance for very thin layer determination, EDXRF analysis offers the potential for the thickness determination of such kind of samples.

  3. Influences of residual oxygen impurities, cubic indium oxide grains and indium oxy-nitride alloy grains in hexagonal InN crystalline films grown on Si(111) substrates by electron cyclotron resonance plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yodo, T.; Nakamura, T.; Kouyama, T.; Harada, Y.

    2005-05-01

    We investigated the influences of residual oxygen (O) impurities, cubic indium oxide (-In2O3) grains and indium oxy-nitride (InON) alloy grains in 200 nm-thick hexagonal ()-InN crystalline films grown on Si(111) substrates by electron cyclotron resonance plasma-assisted molecular beam epitaxy. Although -In2O3 grains with wide band-gap energy were formed in In film by N2 annealing, they were not easily formed in N2-annealed InN films. Even if they were not detected in N2-annealed InN films, the as-grown films still contained residual O impurities with concentrations of less than 0.5% ([O]0.5%). Although [O]1% could be estimated by investigating In2O3 grains formed in N2-annealed InN films, [O]0.5% could not be measured by it. However, we found that they can be qualitatively measured by investigating In2O3 grains formed by H2 annealing with higher reactivity with InN and O2, using X-ray diffraction and PL spectroscopy. In this paper, we discuss the formation mechanism of InON alloy grains in InN films.

  4. A study of the optical and polarisation properties of InGaN/GaN multiple quantum wells grown on a-plane and m-plane GaN substrates

    PubMed Central

    Kundys, Dmytro; Sutherland, Danny; Davies, Matthew J.; Oehler, Fabrice; Griffiths, James; Dawson, Philip; Kappers, Menno J.; Humphreys, Colin J.; Schulz, Stefan; Tang, Fengzai; Oliver, Rachel A.

    2016-01-01

    Abstract We report on a comparative study of the low temperature emission and polarisation properties of InGaN/GaN quantum wells grown on nonpolar (112¯0) a-plane and (101¯0) m-plane free-standing bulk GaN substrates where the In content varied from 0.14 to 0.28 in the m-plane series and 0.08 to 0.21 for the a-plane series. The low temperature photoluminescence spectra from both sets of samples are broad with full width at half maximum height increasing from 81 to 330 meV as the In fraction increases. Photoluminescence excitation spectroscopy indicates that the recombination mainly involves strongly localised carriers. At 10 K the degree of linear polarisation of the a-plane samples is much smaller than of the m-plane counterparts and also varies across the spectrum. From polarisation-resolved photoluminescence excitation spectroscopy we measured the energy splitting between the lowest valence sub-bands to lie in the range of 23–54 meV for the a- and m-plane samples in which we could observe distinct exciton features. Thus the thermal occupation of a higher valence sub-band cannot be responsible for the reduction of the degree of linear polarisation at 10 K. Time-resolved spectroscopy indicates that in a-plane samples there is an extra emission component which is at least partly responsible for the reduction in the degree of linear polarisation. PMID:27933113

  5. Vacancy-type defects in In{sub x}Ga{sub 1−x}N grown on GaN templates probed using monoenergetic positron beams

    SciTech Connect

    Uedono, Akira; Watanabe, Tomohito; Kimura, Shogo; Zhang, Yang; Lozac'h, Mickael; Sang, Liwen; Sumiya, Masatomo; Ishibashi, Shoji; Oshima, Nagayasu; Suzuki, Ryoichi

    2013-11-14

    Native defects in In{sub x}Ga{sub 1−x}N layers grown by metalorganic chemical vapor deposition were studied using monoenergetic positron beams. Measurements of Doppler broadening spectra of the annihilation radiation and lifetime spectra of positrons for a 200-nm-thick In{sub 0.13}Ga{sub 0.87}N layer showed that vacancy-type defects were introduced by InN alloying, and the major species of such defects was identified as complexes between a cation vacancy and nitrogen vacancies. The presence of the defects correlated with lattice relaxation of the In{sub 0.13}Ga{sub 0.87}N layer and the increase in photon emissions from donor-acceptor-pair recombination. The species of native defects in In{sub 0.06}Ga{sub 0.94}N layers was the same but its concentration was decreased by decreasing the InN composition. With the layer thickness increased from 120 nm to 360 nm, a defect-rich region was introduced in the subsurface region (<160 nm), which can be associated with layer growth with the relaxation of compressive stress.

  6. Fabrication of a Lateral Polarity GaN MESFET: An Exploratory Study

    DTIC Science & Technology

    2007-06-27

    the sheet resistance between Ga- polar and mixed-polar GaN films. Highly resistive Ga-polar GaN is advantageous in optoelectronic and electronic device...re si st an ce [ M Ω /s q. ] 108642 2nd nitridation time [min] (b) Figure 5. Sheet resistance of GaN grown on AlN region for the first set of LT...AlN layers deposited for 4, 6, and 8 min. 2nd nitridation time after ex-situ process was kept at 950°C for 1 min. (b) Sheet resistance of GaN grown on

  7. Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Perillat-Merceroz, G.; Sam-Giao, D.; Durand, C.; Eymery, J.

    2010-10-01

    The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([0001¯]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff's plot points out the effect of surface polarity.

  8. 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)

    SciTech Connect

    Ravikiran, L.; Radhakrishnan, K. Ng, G. I.; Munawar Basha, S.; Dharmarasu, N.; Agrawal, M.; Manoj kumar, C. M.; Arulkumaran, S.

    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 buffers 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.

  9. CONDENSED MATTER: STRUCTURE, THERMAL AND MECHANICAL PROPERTIES: The effect of single AlGaN interlayer on the structural properties of GaN epilayers grown on Si (111) substrates

    NASA Astrophysics Data System (ADS)

    Wu, Yu-Xin; Zhu, Jian-Jun; Zhao, De-Gang; Liu, Zong-Shun; Jiang, De-Sheng; Zhang, Shu-Ming; Wang, Yu-Tian; Wang, Hui; Chen, Gui-Feng; Yang, Hui

    2009-10-01

    High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural properties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.

  10. High nitrogen pressure solution growth of GaN

    NASA Astrophysics Data System (ADS)

    Bockowski, Michal

    2014-10-01

    Results of GaN growth from gallium solution under high nitrogen pressure are presented. Basic of the high nitrogen pressure solution (HNPS) growth method is described. A new approach of seeded growth, multi-feed seed (MFS) configuration, is demonstrated. The use of two kinds of seeds: free-standing hydride vapor phase epitaxy GaN (HVPE-GaN) obtained from metal organic chemical vapor deposition (MOCVD)-GaN/sapphire templates and free-standing HVPE-GaN obtained from the ammonothermally grown GaN crystals, is shown. Depending on the seeds’ structural quality, the differences in the structural properties of pressure grown material are demonstrated and analyzed. The role and influence of impurities, like oxygen and magnesium, on GaN crystals grown from gallium solution in the MFS configuration is presented. The properties of differently doped GaN crystals are discussed. An application of the pressure grown GaN crystals as substrates for electronic and optoelectronic devices is reported.

  11. The impact of substrate nitridation temperature and buffer design and synthesis on the polarity of GaN epitaxial films

    NASA Astrophysics Data System (ADS)

    Namkoong, Gon; Alan Doolittle, W.; Brown, April S.; Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni

    2003-05-01

    The polarity of GaN epitaxial layers grown on GaN and AlN buffer layers was investigated and found to be dependent on nitridation temperature over the range of 200-700°C. When low temperature (LT), 500°C, GaN buffer layers are used, GaN epitaxial layers grown on 200°C nitrided sapphire have a higher density of N-polar inversion domains. However, a high density of dislocation pits was observed on GaN epitaxial layers based on AFM morphology when GaN epitaxial layers were grown on LT GaN buffer of 700°C nitrided sapphire substrate. With high temperature (HT), 850°C, AlN buffer layers, the density of N-polar inversion domains in GaN epitaxial layers depends on the thickness of AlN buffer layer. The structural quality of Ga-polar GaN epitaxial layer is dramatically improved when LT GaN and HT AlN buffer layers are combined with an optimized annealing time. The measured full-widths at half-maximum of (0 0 0 2) symmetric and (1 0 .4) asymmetric reflections are 68 and 246 arcsec, respectively, for 1.0 μm GaN epitaxial layers. The results presented here can be implemented to produce low dislocation density, single Ga-polar GaN epitaxial layers.

  12. Investigation of different mechanisms of GaN growth induced on AlN and GaN nucleation layers

    SciTech Connect

    Tasco, V.; Campa, A.; Tarantini, I.; Passaseo, A.; Gonzalez-Posada, F.; Munoz, E.; Redondo-Cubero, A.; Lorenz, K.; Franco, N.

    2009-03-15

    The evolution of GaN growth on AlN and GaN nucleation layers is compared through morphological and structural analyses, including ion beam analysis. By using AlN nucleation layer grown at high temperature, improved crystalline quality is exhibited by 300 nm thin GaN epilayers. GaN (002) x-ray rocking curve as narrow as 168 arc sec and atomic-step surface morphology characterize such a thin GaN film on AlN. Defects are strongly confined into the first 50 nm of growth, whereas a fast laterally coherent growth is observed when increasing thickness, as an effect of high temperature AlN surface morphology and Ga adatom dynamics over this template.

  13. New buffer layers for GaN on sapphire by atomic layer and molecular stream epitaxy

    SciTech Connect

    Piner, E.L.; He, Y.W.; Boutros, K.S.; McIntosh, F.G.; Roberts, J.C.; Bedair, S.M.; El-Masry, N.A.

    1996-11-01

    The current approach of depositing a low temperature then annealed AlN or GaN buffer for the growth of GaN on sapphire results in a high dislocation density. These dislocations thread through the GaN layer to the surface. Reducing their density either by growing thicker films or using a strained layer superlattice is ineffective. Two new approaches for AlN/GaN buffer layer growth for GaN on sapphire have been employed: Atomic Layer Epitaxy (ALE) and molecular Stream Epitaxy (MSE). ALE is distinguished by organo-metallic/ammonia separation while MSE is distinguished by cyclic annealing of the growing film. Both ALE and MSE enhance two dimensional growth of single crystal GaN on sapphire. The structural quality of epitaxial GaN grown on these buffer layers was studied by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The initial result for the ALE buffer shows an improved quality GaN film with lower defect densities. The MSE grown buffer layer closely resembles that of conventionally grown MOCVD buffer layers observed by others, with dislocations threading through the GaN epilayer. The effects of these buffer layers on the structural and optical properties of GaN grown on sapphire will be presented.

  14. Development of GaN photocathodes for UV detectors

    NASA Astrophysics Data System (ADS)

    Siegmund, O.; Vallerga, J.; McPhate, J.; Malloy, J.; Tremsin, A.; Martin, A.; Ulmer, M.; Wessels, B.

    2006-11-01

    We have made substantial progress in the development of GaN photocathodes, including crystalline and polycrystalline GaN and InGaN coatings grown by chemical vapor deposition or molecular beam epitaxy on sapphire substrates. GaN and InGaN photocathodes have been developed with efficiencies up to 70% and cutoffs at ˜380 nm with low out of band response, and high stability and longevity. Samples have been processed and tested at ultra high vacuum to establish cathode process parameters, and some have been integrated into sealed tubes for long-term evaluation.

  15. GaN film growth on LiNbO3 surfaces using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hoai Nam, Man; Goo, Son Chul; Deock Kim, Moon; Yang, Woochul

    2009-09-01

    GaN has been used for high power, high frequency electronic and optoelectronic devices such as light emitting diodes and laser diodes. Most of the GaN films grow on sapphire (0001) and silicon (111) substrates. In these work, we are trying to grow GaN films on lithium niobate (LiNbO3) substrates using molecular beam epitaxy (MBE). As a ferroelectric materials, LiNbO3 has a spontaneous polarization which may provide excellent control of polarity of GaN. The growth of GaN films on LiNbO3 has been performed after the LiNbO3 substrates was annealed in air at 1000°C for 2 hours. The annealed substrates allowed us to prepare atomically flat surfaces and improve adhesion of GaN on LiNbO3. The AlN buffer layer was deposited to get a smaller lattice mismatch with the GaN films. Compared with GaN films grown without a AlN layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The surface morphology of LiNbO3 substrates and the grown GaN films were characterized by atomic force microscopy (AFM), and the crystal structures were studied by X-ray diffraction (XRD).

  16. GaN growth on Si pillar arrays by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Won, Dongjin; Weng, Xiaojun; Yuwen, Yu A.; Ke, Yue; Kendrick, Chito; Shen, Haoting; Mayer, Theresa S.; Redwing, Joan M.

    2013-05-01

    GaN growth on high aspect ratio Si micro-pillar arrays prepared by deep reactive ion etching (DRIE) was investigated using Si(111), Si(110), Si(112), and Si(100) substrates. The sidewall roughness of the Si pillars resulting from DRIE was reduced by thermal annealing at 1100 °C in H2 for 5 min. Conformal AlN buffer layers were grown at 1100 °C on the pillars. In contrast, GaN films grown at 1100 °C were always faceted since GaN preferentially nucleated and grew on the Si{1 1¯ 0} and Si{1 1¯ 1} sidewall planes of the Si pillars. The preferential growth lead to unique symmetries for the independent GaN fins depending on pillar orientation. Lateral growth of the GaN fins at 1100 °C was enhanced with increasing V/III ratio up to 22710. However, the GaN fins did not coalesce seamlessly. A lower growth temperature of 800 °C gave rise to a conformal polycrystalline GaN shell. Post-annealing of the GaN shells at 1100 °C in H2 for 15 min after growth at 800 °C induced highly textured GaN films although the GaN films became partly faceted.

  17. Nearly 4-Inch-Diameter Free-Standing GaN Wafer Fabricated by Hydride Vapor Phase Epitaxy with Pit-Inducing Buffer Layer

    NASA Astrophysics Data System (ADS)

    Sato, Tadashige; Okano, Shinya; Goto, Takenari; Yao, Takafumi; Seto, Ritsu; Sato, Akira; Goto, Hideki

    2013-08-01

    A free-standing GaN wafer was fabricated by depositing a GaN buffer that induced the formation of pits (hereafter, pit-inducing GaN buffer) on a low-temperature-grown GaN buffer on the sapphire substrate. A high-temperature-grown GaN layer was grown on the pit-inducing GaN buffer that induced the formation of pits on the high-temperature-grown GaN layer. The pit-inducing buffer suppresses crack formation in the thick GaN film thereby releasing growth stress. Thermal stress in GaN on a sapphire system is also discussed on the basis of calculations utilizing a bilayer model. We have succeeded in the fabrication of a nearly 4-in.-diameter free-standing GaN thick wafer with a pit-inducing GaN buffer by one-stop hydride vapor phase epitaxy, which will lead to a low-cost fabrication of free-standing GaN wafers.

  18. Abnormal selective area growth of irregularly-shaped GaN structures on the apex of GaN pyramids and its application for wide spectral emission

    NASA Astrophysics Data System (ADS)

    Yu, Yeon Su; Lee, Jun Hyeong; Ahn, Hyung Soo; Yang, Min

    2014-12-01

    We report on the growth and the characterization of three-dimensional randomly-shaped InGaN/GaN structures selectively grown on the apex of GaN pyramids for the purpose of enlarging the emission spectral range. We found that the variations in the shape and the size of the three-dimensional GaN structures depend on the growth temperature and the surface area for selective growth under intentional turbulence in the gas stream. The selectively grown GaN structures grown at 1020 °C have irregular shape, while the samples grown at 1100 °C have rather uniform hexagonal pyramidal shapes. Irregularly shaped GaN structures were also obtained on the apex of GaN pyramids when the SiO2 mask was removed to 1/10 of the total height of the underlying GaN pyramid. When only 1/5 of the SiO2 mask was removed, however, the selectively grown GaN structures had similar hexagonal pyramidal shapes resembling those of the underlying GaN pyramids. The CL (Cathodoluminescence) spectra of the InGaN layers grown on the randomly shaped GaN structures showed a wide emission spectral range from 388 to 433 nm due to the non-uniform thickness and spatially inhomogeneous indium composition of the InGaN layers. This new selective growth method might have great potential for applications of non-phosphor white light emitting diodes (LEDs) with optimized growth conditions for InGaN active layers of high indium composition and with optimum process for fabrication of electrodes for electrical injection.

  19. GaN membrane MSM ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.

    2006-12-01

    GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) <111> oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

  20. Demonstration of flexible thin film transistors with GaN channels

    NASA Astrophysics Data System (ADS)

    Bolat, S.; Sisman, Z.; Okyay, A. K.

    2016-12-01

    We report on the thin film transistors (TFTs) with Gallium Nitride (GaN) channels directly fabricated on flexible substrates. GaN thin films are grown by hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) at 200 °C. TFTs exhibit 103 on-to-off current ratios and are shown to exhibit proper transistor saturation behavior in their output characteristics. Gate bias stress tests reveal that flexible GaN TFTs have extremely stable electrical characteristics. Overall fabrication thermal budget is below 200 °C, the lowest reported for the GaN based transistors so far.

  1. A growth diagram for plasma-assisted molecular beam epitaxy of GaN nanocolumns on Si(111)

    SciTech Connect

    Fernandez-Garrido, S.; Grandal, J.; Calleja, E.; Sanchez-Garcia, M. A.; Lopez-Romero, D.

    2009-12-15

    The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function of impinging Ga/N flux ratio and growth temperature (730-850 deg. C). Two different growth regimes were identified: compact and nanocolumnar. A growth diagram was established as a function of growth parameters, exhibiting the transition between growth regimes, and showing under which growth conditions GaN cannot be grown due to thermal decomposition and Ga desorption. Present results indicate that adatoms diffusion length and the actual Ga/N ratio on the growing surface are key factors to achieve nanocolumnar growth.

  2. Direct growth of freestanding GaN on C-face SiC by HVPE.

    PubMed

    Tian, Yuan; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Zhang, Lei; Dai, Yuanbin; Huo, Qin

    2015-06-02

    In this work, high quality GaN crystal was successfully grown on C-face 6H-SiC by HVPE using a two steps growth process. Due to the small interaction stress between the GaN and the SiC substrate, the GaN was self-separated from the SiC substrate even with a small thickness of about 100 μm. Moreover, the SiC substrate was excellent without damage after the whole process so that it can be repeatedly used in the GaN growth. Hot phosphoric acid etching (at 240 °C for 30 min) was employed to identify the polarity of the GaN layer. According to the etching results, the obtained layer was Ga-polar GaN. High-resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD) were done to characterize the quality of the freestanding GaN. The Raman measurements showed that the freestanding GaN film grown on the C-face 6H-SiC was stress-free. The optical properties of the freestanding GaN layer were determined by photoluminescence (PL) spectra.

  3. Direct growth of freestanding GaN on C-face SiC by HVPE

    PubMed Central

    Tian, Yuan; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Zhang, Lei; Dai, Yuanbin; Huo, Qin

    2015-01-01

    In this work, high quality GaN crystal was successfully grown on C-face 6H-SiC by HVPE using a two steps growth process. Due to the small interaction stress between the GaN and the SiC substrate, the GaN was self-separated from the SiC substrate even with a small thickness of about 100 μm. Moreover, the SiC substrate was excellent without damage after the whole process so that it can be repeatedly used in the GaN growth. Hot phosphoric acid etching (at 240 °C for 30 min) was employed to identify the polarity of the GaN layer. According to the etching results, the obtained layer was Ga-polar GaN. High-resolution X-ray diffraction (HRXRD) and electron backscatter diffraction (EBSD) were done to characterize the quality of the freestanding GaN. The Raman measurements showed that the freestanding GaN film grown on the C-face 6H-SiC was stress-free. The optical properties of the freestanding GaN layer were determined by photoluminescence (PL) spectra. PMID:26034939

  4. GaN Epitaxial Layer Grown with Conductive Al(x)Ga(1-x)N Buffer Layer on SiC Substrate Using Metal Organic Chemical Vapor Deposition.

    PubMed

    So, Byeongchan; Lee, Kyungbae; Lee, Kyungjae; Heo, Cheon; Pyeon, Jaedo; Ko, Kwangse; Jang, Jongjin; Nam, Okhyun

    2016-05-01

    This study investigated GaN epitaxial layer growth with a conductive Al(x)Ga(1-x)N buffer layer on n-type 4H-SiC by high-temperature metalorganic chemical vapor deposition (HT-MOCVD). The Al composition of the Al(x)Ga(1-x)N buffer was varied from 0% to 100%. In terms of the crystal quality of the GaN layer, 79% Al was the optimal composition of the Al(x)Ga(1-x)N buffer layer in our experiment. A vertical conductive structure was fabricated to measure the current voltage (I-V) characteristics as a function of Al composition, and the I-V curves showed that the resistance increased with increasing Al concentration of the Al(x)Ga(1-x)N buffer layer.

  5. GaN HEMTs

    NASA Astrophysics Data System (ADS)

    Anderson, Jonathan W.; Lee, Kyoung-Keun; Piner, Edwin L.

    2012-03-01

    Gallium nitride (GaN) has enormous potential for applications in high electron mobility transistors (HEMTs) used in RF and power devices. Intrinsic device properties such as high electron mobility, high breakdown voltage, very high current density, electron confinement in a narrow channel, and high electron velocity in the 2-dimensional electron gas of the HEMT structure are due in large part to the wide band gap of this novel semiconductor material system. This presentation discusses the properties of GaN that make it superior to other semiconductor materials, and outlines the research that will be undertaken in a new program at Texas State University to advance GaN HEMT technology. This program's aim is to further innovate the exceptional performance of GaN through improved material growth processes and epitaxial structure design.

  6. High-resistivity GaN buffer templates and their optimization for GaN-based HFETs

    NASA Astrophysics Data System (ADS)

    Hubbard, S. M.; Zhao, G.; Pavlidis, D.; Sutton, W.; Cho, E.

    2005-11-01

    High-resistance (HR) GaN templates for AlGaN/GaN heterojunction field effect transistor (HFET) applications were grown using organometallic vapor phase epitaxy. The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature and NL thickness. Using an annealing temperature of 1033 °C and NL thickness of 26 nm, GaN with sheet resistance of 10 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. Material characterization results show that the high-resistance GaN is achieved due to compensating acceptor levels that may be introduced through edge-type threading dislocations. Optimization of annealing temperature and NL thickness provided a means to maximize GaN sheet resistance without significantly degrading material quality. In situ laser reflectance was used to correlate the NL properties to sheet resistance and material quality, providing a figure of merit for expected sheet resistance. AlGaN/GaN HFET layers grown using HR GaN templates with R of 10 10 Ω/sq gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.

  7. Growth and characterization of GaN thin films on Si(111) substrates using SiC intermediate layer

    SciTech Connect

    Lim, K.Y.; Lee, K.J.; Park, C.I.; Kim, K.C.; Choi, S.C.; Lee, W.H.; Suh, E.K.; Yang, G.M.; Nahm, K.S.

    2000-07-01

    GaN films have been grown atop Si-terminated 3C-SiC intermediate layer on Si(111) substrates using low pressure metalorganic chemical vapor deposition (LP-MOCVD). The SiC intermediate layer was grown by chemical vapor deposition (CVD) using tetramethylsilane (TMS) as the single source precursor. The Si terminated SiC surface was obtained by immediately flow of SiH{sub 4} gas after growth of SiC film. LP-MOCVD growth of GaN on 3C-SiC/Si(111) was carried out with trimethylgallium (TMG) and NH{sub 3}. Single crystalline hexagonal GaN layers can be grown on Si terminated SiC intermediate layer using an AlN or GaN buffer layer. Compared with GaN layers grown using a GaN buffer layer, the crystal qualities of GaN films with AlN buffer layers are extremely improved. The GaN films were characterized by x-ray diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). Full width at half maximum (FWHM) of double crystal x-ray diffraction (DCXD) rocking curve for GaN (0002) on 3C-SiC/Si(111) was 890 arcsec. PL near band edge emission peak position and FWHM at room temperature are 3.38 eV and 79.35 meV, respectively.

  8. Vertical nonpolar growth templates for light emitting diodes formed with GaN nanosheets

    NASA Astrophysics Data System (ADS)

    Yeh, Ting-Wei; Lin, Yen-Ting; Ahn, Byungmin; Stewart, Lawrence S.; Daniel Dapkus, P.; Nutt, Steven R.

    2012-01-01

    We demonstrate that nonpolar m-plane surfaces can be generated on uniform GaN nanosheet arrays grown vertically from the (0001)-GaN bulk material. InGaN/GaN multiple quantum wells (MQWs) grown on the facets of these nanosheets are demonstrated by cross-sectional transmission electron microscopy. Owing to the high aspect ratio of the GaN nanosheet structure, the MQWs predominantly grow on nonpolar GaN planes. The results suggest that GaN nanosheets provide a conduction path for device fabrication and also a growth template to reduce the piezoelectric field inside the active region of InGaN-based light emitting diodes.

  9. Growth of thick GaN layers on laser-processed sapphire substrate by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Koyama, Koji; Aida, Hideo; Kim, Seong-Woo; Ikejiri, Kenjiro; Doi, Toshiro; Yamazaki, Tsutomu

    2014-10-01

    A 600 μm thick GaN layer was successfully grown by hydride vapor phase epitaxy by replacing the standard sapphire substrate with that processed by a focused laser beam within the substrate. The effects of the laser processing on the curvature and cracking of the GaN layer were investigated. Microscopic observations of the interior of the thick GaN layer revealed that the laser-processed substrate suppressed the generation of microcracks in the GaN layer. In addition, the laser processing was also found to reduce the change in the curvature during the GaN layer growth in comparison to that on the standard substrate. It is shown that the overlapping microcracks observed in the GaN layer on the standard sapphire substrate lead to serious cracking after thick GaN layer growth.

  10. Crystal field analysis of rare-earth ions energy levels in GaN

    NASA Astrophysics Data System (ADS)

    Stachowicz, M.; Kozanecki, A.; Ma, C.-G.; Brik, M. G.; Lin, J. Y.; Jiang, Hx; Zavada, J. M.

    2014-11-01

    Much effort has been put to achieve optoelectronic devices based on Er doped GaN, operating on the intra-4f-shell transitions of erbium. The key issue for good understanding of energy transfer mechanisms to Er and its luminescence properties is the position of Er3+ ions in the crystalline lattice of GaN. After doping, Er3+ ions are assumed to be placed in substitutional position for Ga3+ in GaN. Although Ga is positioned in high symmetry, tetrahedral [ErN4]9 - cluster, deviations from this after doping are impossible to avoid because of a large difference in ionic radii of Ga3+ (47 pm) and Er3+ (89 pm). In this work we report on crystal field analysis of Er ion energy levels in cubic and hexagonal GaN. It is shown that local symmetry of Er in cubic GaN is D2, whereas calculations reveal that in hexagonal GaN local symmetry is C3V. Some trends in crystal field parameters of trivalent lanthanides in hexagonal GaN are discussed.

  11. Mechanism of stress control for GaN growth on Si using AlN interlayers

    NASA Astrophysics Data System (ADS)

    Suzuki, Michihiro; Nakamura, Akihiro; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-04-01

    For the purpose of controlling the wafer bow of GaN-on-Si structure, in situ curvature transient during the growth of a GaN layer on an AlN interlayer was investigated systematically by estimating the compressive strain applied to the GaN layer with the progress of the layer growth. The compressive strain was dependent on the morphology of the GaN surface prior to the growth of the AlN interlayer. It was found that the transition sequence from GaN growth to AlN growth induces roughening of the GaN surface and both high NH3 partial pressure and the short transition time were effective for reducing the roughness of the GaN surface beneath the AlN interlayer. The improved transition sequence increased the compressive strain in GaN by a factor of 2.5. The AlN grown at the same temperature as that of GaN was beneficial in both better surface morphology and the reduction of the transition time between GaN growth and AlN growth. With this high-temperature AlN interlayer, its thickness is another important factor governing the compressive strain in GaN. To get AlN relaxed for applying the compressive strain to GaN, the AlN layer should be thicker but too thick layer after relaxation results in surface roughening, which in turn introduces defects to the overlying GaN layer and reduces the compressive strain by partial lattice relaxation of GaN.

  12. Smooth cubic commensurate oxides on gallium nitride

    SciTech Connect

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul; Biegalski, Michael D.; Christen, Hans M.

    2014-02-14

    Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  13. Smooth cubic commensurate oxides on gallium nitride

    NASA Astrophysics Data System (ADS)

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Biegalski, Michael D.; Christen, Hans M.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul

    2014-02-01

    Smooth, commensurate alloys of ⟨111⟩-oriented Mg0.52Ca0.48O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  14. Amphoteric arsenic in GaN

    SciTech Connect

    Wahl, U.; Correia, J. G.; Araujo, J. P.; Rita, E.; Soares, J. C.

    2007-04-30

    The authors have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive {sup 73}As. They give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As{sub Ga} 'antisites' are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called miscibility gap in ternary GaAs{sub 1-x}N{sub x} compounds, which cannot be grown with a single phase for values of x in the range of 0.1

  15. Nucleation and Growth of GaN on GaAs (001) Substrates

    SciTech Connect

    Drummond, Timothy J.; Hafich, Michael J.; Heller, Edwin J.; Lee, Stephen R.; Liliental-Weber, Zuzanna; Ruvimov, Sergei; Sullivan, John P.

    1999-05-03

    The nucleation of GaN thin films on GaAs is investigated for growth at 620 "C. An rf plasma cell is used to generate chemically active nitrogen from N2. An arsenic flux is used in the first eight monolayer of nitride growth to enhance nucleation of the cubic phase. Subsequent growth does not require an As flux to preserve the cubic phase. The nucleation of smooth interfaces and GaN films with low stacking fault densities is dependent upon relative concentrations of active nitrogen species in the plasma and on the nitrogen to gallium flux ratio.

  16. Investigation of structural and optical properties of GaN on flat and porous silicon

    NASA Astrophysics Data System (ADS)

    Abud, Saleh H.; Selman, Abbas M.; Hassan, Z.

    2016-09-01

    In this work, gallium nitride (GaN) layers were successfully grown on Flat-Si and porous silicon (PSi) using a radio frequency-magnetron sputtering system. Field emission scanning electron microscopy and atomic force microscopy images showed that the grown film on Flat-Si had smoother surface, even though there were some cracks on it. Furthermore, the X-ray diffraction measurements showed that the peak intensity of all the grown layers on PSi was higher than that of the grown layer on Flat-Si. Our detailed observation showed that PSi is a promising substrate to obtain GaN films.

  17. Biosensing operations based on whispering-gallery-mode optical cavities in single 1.0-µm diameter hexagonal GaN microdisks grown by radio-frequency plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Kouno, Tetsuya; Sakai, Masaru; Kishino, Katsumi; Hara, Kazuhiko

    2016-05-01

    Biosensing operations based on a whispering-gallery-mode optical cavity in a single hexagonal GaN microdisk of approximately 1.0 µm diameter were demonstrated here. The sharp resonant peak in the photoluminescence spectrum obtained from the microdisk in aqueous sucrose solution redshifts with a change in sucrose concentration. The results indicate that an extremely small microdisk could be used as an optical transducer for sensing sugar, namely, as a biosensor. Furthermore, we investigate the relationship between the diameter of the microdisk and the sensitivity of the biosensor.

  18. 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.

  19. Growth and Characterization of N-Polar GaN Films on Si(111) by Plasma Assisted Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Dasgupta, Sansaptak; Nidhi; Wu, Feng; Speck, James S.; Mishra, Umesh K.

    2012-11-01

    Smooth N-polar GaN films were epitaxially grown by plasma assisted molecular beam epitaxy (PAMBE) on on-axis p-Si(111). The structural quality of the as-grown GaN films was further improved by insertion of AlGaN/GaN superlattice structures, resulting in reduced threading dislocation density and also efficient stress management in the GaN film to mitigate crack formation. The structural quality of these films was comparable to N-polar GaN grown on C-SiC by MBE. Convergent beam electron diffraction (CBED) imaging and KOH etch studies were performed to confirm the N-polarity of the sample. Room temperature photoluminescence measurements revealed strong GaN band-edge emission.

  20. Terahertz study of m-plane GaN thin fims

    NASA Astrophysics Data System (ADS)

    Quadir, Shaham; Jang, Der-Jun; Lin, Ching-Liang; Lo, Ikai

    2014-03-01

    We investigate the optical properties of m-plane GaN thin films using the terahertz time domain spectroscopy. The m-plane GaN thin films were grown on γ-LiAlO2 substrates with buffer layers of low temperature grown GaN. The thin films were illuminated with terahertz radiation generated by a LT-GaAs antenna and the transmitted signal was detected by a ZnTe crystal. The polarization of the terahertz wave was chosen to be either parallel or perpendicular to the GaN [0001] direction. We compared the transmitted signals of the m-plane GaN thin films to that of the LAO substrate. The samples as well as the LAO substrate exhibited polarization dependence of absorption in terahertz spectrum. The carrier densities and the mobilities were derived from the transmittance of the THz wave using extended Drude model. We found, in all samples, both the carrier densities and mobilities along the GaN [0001] direction were smaller than those along the GaN [1120] direction due to the stripe formation along the GaN [1120].

  1. Growth of freestanding GaN using pillar-epitaxial lateral overgrowth from GaN nanocolumns

    NASA Astrophysics Data System (ADS)

    Bougrioua, Z.; Gibart, P.; Calleja, E.; Jahn, U.; Trampert, A.; Ristic, J.; Utrera, M.; Nataf, G.

    2007-12-01

    Dislocation-free and strain-free GaN nanopillars, grown on Si by molecular beam epitaxy, were used as nanoseeds for a new form of epitaxial lateral overgrowth (ELO) by metalorganic vapour phase epitaxy (MOVPE) until full coalescence. Such overgrown GaN films are almost relaxed and were used as templates for producing thick GaN layers by halide vapour phase epitaxy (HVPE). The final GaN film is easily separated from the starting Si substrate. This is henceforth a new technology to produce freestanding GaN. The GaN crystal quality was assessed by transmission electron microscopy (TEM), photo- and cathodoluminescence (PL, CL). It was seen that the pillar-ELO is produced from a limited number of nanopillars. Some dislocations and basal stacking faults are formed during the coalescence. However, those that propagate parallel to the substrate do not replicate in the top layer and it is expected that the thickened material present a reduced defect density.

  2. Anisotropic strain relaxation and the resulting degree of polarization by one- and two-step growth in nonpolar a-plane GaN grown on r-sapphire substrate

    SciTech Connect

    Feng, Shih-Wei Chen, Yu-Yu; Lai, Chih-Ming; Tu, Li-Wei; Han, Jung

    2013-12-21

    Anisotropic strain relaxation and the resulting degree of polarization of the electronic transition in nonpolar a-plane GaN using one- and two-step growth are studied. By using two-step growth, a slower coalescence and a longer roughening-recovery process lead to larger anisotropic strain relaxation, a less striated surface, and lower densities of basal stacking fault (BSF) and prismatic stacking fault (PSF). It is suggested that anisotropic in-plane strains, surface striation, and BSF and PSF densities in nonpolar a-GaN are consequences of the rate of coalescence, the period of roughening-recovery process, and the degree of anisotropic strain relaxation. In addition, the two-step growth mode can enhance the degree of polarization of the electronic transition. The simulation results of the k⋅p perturbation approach show that the oscillator strength and degree of polarization of the electronic transition strongly depend on the in-plane strains upon anisotropic in-plane strain relaxation. The research results provide important information for optimized growth of nonpolar III-nitrides. By using two-step growth and by fabricating the devices on the high-quality nonpolar free-standing GaN substrates, high-efficiency nonpolar a-plane InGaN LEDs can be realized. Nonpolar a-plane InGaN/GaN LEDs can exhibit a strongly polarized light to improve the contrast, glare, eye discomfort and eye strain, and efficiency in display application.

  3. Optical and field emission properties of layer-structure GaN nanowires

    SciTech Connect

    Cui, Zhen; Li, Enling; Shi, Wei; Ma, Deming

    2014-08-15

    Highlights: • The layer-structure GaN nanowires with hexagonal-shaped cross-sections are produced via a process based on the CVD method. • The diameter of the layer-structure GaN nanowire gradually decreases from ∼500 nm to ∼200 nm along the wire axis. • The layer-structure GaN nanowire film possesses good field emission property. - Abstract: A layer-structure gallium nitride (GaN) nanowires, grown on Pt-coated n-type Si (1 1 1) substrate, have been synthesized using chemical vapor deposition (CVD). The results show: (1) SEM indicates that the geometry structure is layer-structure. HRTEM indicates that GaN nanowire’s preferential growth direction is along [0 0 1] direction. (2) The room temperature PL emission spectrum of the layer-structure GaN nanowires has a peak at 375 nm, which proves that GaN nanowires have potential application in light-emitting nano-devices. (3) Field-emission measurements show that the layer-structure GaN nanowires film has a low turn-on field of 4.39 V/μm (at room temperature), which is sufficient for electron emission devices, field emission displays and vacuum nano-electronic devices. The growth mechanism for GaN nanowires has also been discussed briefly.

  4. Valence band offset of β-Ga2O3/wurtzite GaN heterostructure measured by X-ray photoelectron spectroscopy.

    PubMed

    Wei, Wei; Qin, Zhixin; Fan, Shunfei; Li, Zhiwei; Shi, Kai; Zhu, Qinsheng; Zhang, Guoyi

    2012-10-10

    A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV.

  5. Valence band offset of β-Ga2O3/wurtzite GaN heterostructure measured by X-ray photoelectron spectroscopy

    PubMed Central

    2012-01-01

    A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV. PMID:23046910

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

    PubMed Central

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

    2016-01-01

    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. PMID:27101930

  7. Novel high frequency devices with graphene and GaN

    NASA Astrophysics Data System (ADS)

    Zhao, Pei

    effective mass (NEM) region. The designed NEMO structures are grown by MBE on bulk GaN substrates. NDRs are observed in four NEMO samples under DC and pulsed measurements. The influence of traps and defects on NDRs is also discussed.

  8. Cubic and hexagonal gallium nitride/aluminum nitride superlattice structures for near-infrared detector applications

    NASA Astrophysics Data System (ADS)

    Decuir, Eric Anthony, Jr.

    Intersubband transitions and photoconductivity were observed for the first time in metastable GaN/AlN cubic superlattice structures. Further studies of intersubband transitions and photoconductivity in the well-studied stable hexagonal system were also presented herein. The main motivation prompting this study is linked to the polar nature of the hexagonal crystal structure system grown on c-plane sapphire substrates, which gives rise to the presence of large polarization fields (up to 10 MV/cm). Since these fields have been shown to complicate the design of intersubband transitions, a study of the nonpolar cubic phase, lacking these large built-in fields due to its symmetric nature, is presented in an effort to reduce the complexity of future device design. Structural characterization of GaN/AlN superlattices was performed using X-ray Diffraction, Atomic Force Microscopy, and Transmission Electron Microscopy. Optical and electrical characterization of intersubband absorption and photoconductivity in cubic and hexagonal GaN/AlN superlattices were recorded respectively using Fourier-transform spectroscopy in the temperature range of 77K--300K. An Electrochemical capacitance voltage technique was used to measure and confirm the three dimensional carrier concentrations in doped GaN layers since the presence of free carriers in the conduction is required for intersubband transitions. Reactive ion etching and e-beam evaporation was employed in the fabrication of mesa device structures with ohmic contacts. Theoretical calculations of the bound state energy levels in quantum well structures were made using a transfer matrix technique and then compared with experimental results.

  9. Ferromagnetism in undoped One-dimensional GaN Nanowires

    SciTech Connect

    Jeganathan, K. E-mail: jagan@physics.bdu.ac.in; Purushothaman, V.; Debnath, R.; Arumugam, S.

    2014-05-15

    We report an intrinsic ferromagnetism in vertical aligned GaN nanowires (NW) fabricated by molecular beam epitaxy without any external catalyst. The magnetization saturates at ∼0.75 × emu/gm with the applied field of 3000 Oe for the NWs grown under the low-Gallium flux of 2.4 × 10{sup −8} mbar. Despite a drop in saturation magnetization, narrow hysteresis loop remains intact regardless of Gallium flux. Magnetization in vertical standing GaN NWs is consistent with the spectral analysis of low-temperature photoluminescence pertaining to Ga-vacancies associated structural defects at the nanoscale.

  10. GaN surface states investigated by electrochemical studies

    NASA Astrophysics Data System (ADS)

    Winnerl, Andrea; Garrido, Jose A.; Stutzmann, Martin

    2017-03-01

    We present a systematic study of electrochemically active surface states on MOCVD-grown n-type GaN in aqueous electrolytes using cyclic voltammetry and impedance spectroscopy over a wide range of potentials and frequencies. In order to alter the surface states, the GaN samples are either etched or oxidized, and the influence of the surface treatment on the defect-mediated charge transfer to the electrolyte is investigated. Etching in HCl removes substoichiometric GaO x , and leads to a pronounced density of electrochemically active surface states. Oxidation effectively removes these surface states.

  11. Self-assembled GaN hexagonal micropyramid and microdisk

    SciTech Connect

    Lo Ikai; Hsieh, C.-H.; Hsu, Y.-C.; Pang, W.-Y.; Chou, M.-C.

    2009-02-09

    The self-assembled GaN hexagonal micropyramid and microdisk were grown on LiAlO{sub 2} by plasma-assisted molecular-beam epitaxy. It was found that the (0001) disk was established with the capture of N atoms by most-outside Ga atoms as the (1x1) surface was constructing, while the pyramid was obtained due to the missing of most-outside N atoms. The intensity of cathode luminescence excited from the microdisk was one order of amplitude greater than that from M-plane GaN.

  12. Laser Deposition of Cubic Boron Nitride on Electronic Materials.

    DTIC Science & Technology

    1991-08-12

    wurtzite or cubic structure of BN (see Figures 4 and 5). It is clear that the films grown via laser processing were amorphous rather than crystalline... cubic structure of BN can be obtained. It appears from our work and Dr. Doll’s work that excimer laser ablated species do not have sufficient energy

  13. GaN: Defect and Device Issues

    SciTech Connect

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.

    1998-11-09

    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  14. TEM characterization of GaN nanowires

    SciTech Connect

    Liliental-Weber, Zuzanna; Gao, Y.H.; Bando, Y.

    2002-02-21

    Transmission electron microscopy was applied to study GaN nanowires grown on carbon nanotube surfaces by chemical reaction between Ga{sub 2}O and NH{sub 3} gas in a conventional furnace. These wires grew in two crystallographic directions, <2{und 11}0> and <01{und 1}0> (fast growth directions of GaN), in the form of whiskers covered by small elongated GaN platelets. The morphology of these platelets is similar to that observed during the growth of single crystals from a Ga melt at high temperatures under high nitrogen pressure. It is thought that growth of nanowires in two different crystallographic directions and the arrangement of the platelets to the central whisker may be influenced by the presence of Ga{sub 2}O{sub 3} (based on the observation of the energy dispersive x-ray spectra), the interplanar spacings in the wire, and the presence of defects on the interface between the central part of the nanowire and the platelets surrounding it.

  15. Improvement of Crystalline Quality in GaN Films by Air-Bridged Lateral Epitaxial Growth

    NASA Astrophysics Data System (ADS)

    Kidoguchi, Isao; Ishibashi, Akihiko; Sugahara, Gaku; Tsujimura, Ayumu; Ban, Yuzaburoh

    2000-05-01

    Air-bridged lateral epitaxial growth (ABLEG), a new technique of lateral growth of GaN films, has been developed using low-pressure metalorganic vapor phase epitaxy. A previously grown 1-μm-thick GaN film is grooved along the < 1{\\bar 1}00 >\\textrm{GaN} direction, and the bottoms of the trenches and the sidewalls are covered with a silicon nitride mask. A free-standing GaN material is regrown from the exposed (0001) surface of the ridged GaN seed structure. Cross-sectional transmission electron microscopy analysis reveals that the dislocations originating from the underlying seed GaN extend straight in the < 0001 > direction and dislocations do not propagate into the wing region. The wing region also exhibits a smooth surface and the root mean square roughness is found to be 0.088 nm by atomic force microscopy measurement of the (0001) face of the wing region.

  16. Piecewise Cubic Interpolation Package

    SciTech Connect

    Fritsch, F. N.; LLNL,

    1982-04-23

    PCHIP (Piecewise Cubic Interpolation Package) is a set of subroutines for piecewise cubic Hermite interpolation of data. It features software to produce a monotone and "visually pleasing" interpolant to monotone data. Such an interpolant may be more reasonable than a cubic spline if the data contain both 'steep' and 'flat' sections. Interpolation of cumulative probability distribution functions is another application. In PCHIP, all piecewise cubic functions are represented in cubic Hermite form; that is, f(x) is determined by its values f(i) and derivatives d(i) at the breakpoints x(i), i=1(1)N. PCHIP contains three routines - PCHIM, PCHIC, and PCHSP to determine derivative values, six routines - CHFEV, PCHFE, CHFDV, PCHFD, PCHID, and PCHIA to evaluate, differentiate, or integrate the resulting cubic Hermite function, and one routine to check for monotonicity. A FORTRAN 77 version and SLATEC version of PCHIP are included.

  17. Desorption induced formation of negative nanowires in GaN

    NASA Astrophysics Data System (ADS)

    Kim, Bong-Joong; Stach, Eric A.

    2011-06-01

    We report in-situ transmission electron microscopy studies of the formation of negative nanowires created by thermal decomposition of single crystal GaN. During annealing, vertical negative nanowires are formed in [0 0 0 1] by preferential dissociation of GaN along the {1 0 1¯ 0} prism planes, while lateral negative nanowires grow in close-packed <1 0 1¯ 0> by the self-catalytic solid-liquid-vapor (SLV) mechanism. Our quantitative measurements show that the growth rates of the laterally grown negative nanowires are independent of the wire diameter, indicating that the rate-limiting step is the decomposition of GaN on the surface of the Ga droplets that catalyze their creation. These nanoscale features offer controllable templates for the creation and integration of a broad range of nanoscale materials systems, with potential applications in nanoscale fluidics.

  18. Transient atomic behavior and surface kinetics of GaN

    NASA Astrophysics Data System (ADS)

    Moseley, Michael; Billingsley, Daniel; Henderson, Walter; Trybus, Elaissa; Doolittle, W. Alan

    2009-07-01

    An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.

  19. Gallium kinetics on m-plane GaN

    NASA Astrophysics Data System (ADS)

    Lim, C. B.; Ajay, A.; Monroy, E.

    2017-07-01

    In this paper, we study the adsorption/desorption kinetics of gallium on (1-100) m-GaN during molecular-beam epitaxy on bulk substrates. We demonstrate the stabilization of a laterally contracted biatomic layer of Ga containing up to ≈2.5 times the (0001) surface atom density, on top of the GaN(1-100) surface. By assessing the surface morphology of m-GaN layers grown under different Ga/N flux ratios, we show that the presence of the Ga bilayer allows the growth of atomically smooth m-GaN without accumulation of Ga droplets and in conditions (substrate temperature and Ga/N ratio) that are compatible with the growth of c-GaN.

  20. Application of GaN for photoelectrolysis of water

    NASA Astrophysics Data System (ADS)

    Puzyk, M. V.; Usikov, A. S.; Kurin, S. Yu; Puzyk, A. M.; Fomichev, A. D.; Ermakov, I. A.; Kovalev, D. S.; Papchenko, B. P.; Helava, H.; Makarov, Yu N.

    2015-11-01

    GaN layers of n-type and p-type conductivity grown by HVPE on sapphire substrates were used as working electrodes for water electrolysis, photoelectrolysis and hydrogen gas generation. Specifically the water splitting process is discussed. Corrosion of the GaN materials is also considered. The hydrogen production rate under 365-nm UV LED irradiation of the GaN and external bias was 0.3 ml/(cm2*h) for an n-GaN photoanode (n∼8×1016 cm-3) in 1M Na2SO4 electrolyte and 1.2 ml/(cm2*h) for an n-GaN photoanode (n∼1×1017 cm-3) in 1M KOH electrolyte.

  1. Desorption Induced Formation of Negative Nanowires in GaN

    SciTech Connect

    Stach, E.A.; Kim, B.-J.

    2011-06-01

    We report in-situ transmission electron microscopy studies of the formation of negative nanowires created by thermal decomposition of single crystal GaN. During annealing, vertical negative nanowires are formed in [0 0 0 1] by preferential dissociation of GaN along the 1 0 {bar 1} 0 prism planes, while lateral negative nanowires grow in close-packed 1 0 {bar 1} 0 by the self-catalytic solid-liquid-vapor (SLV) mechanism. Our quantitative measurements show that the growth rates of the laterally grown negative nanowires are independent of the wire diameter, indicating that the rate-limiting step is the decomposition of GaN on the surface of the Ga droplets that catalyze their creation. These nanoscale features offer controllable templates for the creation and integration of a broad range of nanoscale materials systems, with potential applications in nanoscale fluidics.

  2. Effects of Al additives on growth of GaN polycrystals by the Na flux method

    NASA Astrophysics Data System (ADS)

    Imabayashi, Hiroki; Murakami, Kosuke; Matsuo, Daisuke; Honjo, Masatomo; Imanishi, Masayuki; Maruyama, Mihoko; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke

    2017-03-01

    In this study, we investigated the growth of GaN polycrystals using the Al-added Na flux method. We studied the effects of Al on accelerating the nucleation and purity of GaN polycrystals. The yields of GaN crystals grown in Al-added Na flux were dramatically increased from those in Al-free Na flux, and the polycrystals grown by the Al-added Na flux method were highly transparent. As observed in secondary ion mass spectroscopy measurements, the Al content of the polycrystals was below the detection limit of 3 × 1016 atoms/cm3. From these results, the Al-added Na flux method is found to be appropriate for fabricating a large amount of GaN polycrystals without deteriorating the crystal quality.

  3. GaN quantum dot polarity determination by X-ray photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Romanyuk, O.; Bartoš, I.; Brault, J.; Mierry, P. De; Paskova, T.; Jiříček, P.

    2016-12-01

    Growth of GaN quantum dots (QDs) on polar and semipolar GaN substrates is a promising technology for efficient nitride-based light emitting diodes (LED). The QDs crystal orientation typically repeats the polarity of the substrate. In case of non-polar or semipolar substrates, the polarity of QDs is not obvious. In this article, the polarity of GaN QDs and of underlying layers was investigated nondestructively by X-ray photoelectron diffraction (XPD). Polar and semipolar GaN/Al0.5Ga0.5N heterostructures were grown on the sapphire substrates with (0001) and (1 1 bar 00) orientations by molecular beam epitaxy (MBE). Polar angle dependence of N 1s core-level photoelectron intensities were measured from GaN QDs and compared with the corresponding experimental curves from free-standing GaN crystals. It is confirmed experimentally, that the crystalline orientation of polar (0001) GaN QDs follows the orientation of the (0001) sapphire substrate. In case of semipolar GaN QDs grown on (1 1 bar 00) sapphire substrate, the (11 2 bar 2) polarity of QDs was determined.

  4. Pulsed laser annealing of Be-implanted GaN

    SciTech Connect

    Wang, H.T.; Tan, L.S.; Chor, E.F.

    2005-11-01

    Postimplantation thermal processing of Be in molecular-beam-epitaxy-grown GaN by rapid thermal annealing (RTA) and pulsed laser annealing (PLA) was investigated. It has been found that the activation of Be dopants and the repair of implantation-induced defects in GaN films cannot be achieved efficiently by conventional RTA alone. On the other hand, good dopant activation and surface morphology and quality were obtained when the Be-implanted GaN film was annealed by PLA with a 248 nm KrF excimer laser. However, observations of off-resonant micro-Raman and high-resolution x-ray-diffraction spectra indicated that crystal defects and strain resulting from Be implantation were still existent after PLA, which probably degraded the carrier mobility and limited the activation efficiency to some extent. This can be attributed to the shallow penetration depth of the 248 nm laser in GaN, which only repaired the crystal defects in a thin near-surface layer, while the deeper defects were not annealed out well. This situation was significantly improved when the Be-implanted GaN was subjected to a combined process of PLA followed by RTA, which produced good activation of the dopants, good surface morphology, and repaired bulk and surface defects well.

  5. Pulsed laser annealing of Be-implanted GaN

    NASA Astrophysics Data System (ADS)

    Wang, H. T.; Tan, L. S.; Chor, E. F.

    2005-11-01

    Postimplantation thermal processing of Be in molecular-beam-epitaxy-grown GaN by rapid thermal annealing (RTA) and pulsed laser annealing (PLA) was investigated. It has been found that the activation of Be dopants and the repair of implantation-induced defects in GaN films cannot be achieved efficiently by conventional RTA alone. On the other hand, good dopant activation and surface morphology and quality were obtained when the Be-implanted GaN film was annealed by PLA with a 248 nm KrF excimer laser. However, observations of off-resonant micro-Raman and high-resolution x-ray-diffraction spectra indicated that crystal defects and strain resulting from Be implantation were still existent after PLA, which probably degraded the carrier mobility and limited the activation efficiency to some extent. This can be attributed to the shallow penetration depth of the 248 nm laser in GaN, which only repaired the crystal defects in a thin near-surface layer, while the deeper defects were not annealed out well. This situation was significantly improved when the Be-implanted GaN was subjected to a combined process of PLA followed by RTA, which produced good activation of the dopants, good surface morphology, and repaired bulk and surface defects well.

  6. Interfacial Structure and Chemistry of GaN on Ge(111)

    NASA Astrophysics Data System (ADS)

    Zhang, Siyuan; Zhang, Yucheng; Cui, Ying; Freysoldt, Christoph; Neugebauer, Jörg; Lieten, Ruben R.; Barnard, Jonathan S.; Humphreys, Colin J.

    2013-12-01

    The interface of GaN grown on Ge(111) by plasma-assisted molecular beam epitaxy is resolved by aberration corrected scanning transmission electron microscopy. A novel interfacial structure with a 5∶4 closely spaced atomic bilayer is observed that explains why the interface is flat, crystalline, and free of GeNx. Density functional theory based total energy calculations show that the interface bilayer contains Ge and Ga atoms, with no N atoms. The 5∶4 bilayer at the interface has a lower energy than a direct stacking of GaN on Ge(111) and enables the 5∶4 lattice-matching growth of GaN.

  7. Stress and Defect Control in GaN Using Low Temperature Interlayers

    SciTech Connect

    Akasaki, I.; Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S.; Iwaya, M.; Kashima, T.; Katsuragcawa, M.

    1998-12-04

    In organometallic vapor phase epitaxial growth of Gail on sapphire, the role of the low- temperature-deposited interlayers inserted between high-temperature-grown GaN layers was investigated by in situ stress measurement, X-ray diffraction, and transmission electron microscopy. Insertion of a series of low temperature GaN interlayers reduces the density of threading dislocations while simultaneously increasing the tensile stress during growth, ultimately resulting in cracking of the GaN film. Low temperature AIN interlayers were found to be effective in suppressing cracking by reducing tensile stress. The intedayer approach permits tailoring of the film stress to optimize film structure and properties.

  8. Opportunities and challenges in GaN metal organic chemical vapor deposition for electron devices

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koh; Yamaoka, Yuya; Ubukata, Akinori; Arimura, Tadanobu; Piao, Guanxi; Yano, Yoshiki; Tokunaga, Hiroki; Tabuchi, Toshiya

    2016-05-01

    The current situation and next challenge in GaN metal organic chemical vapor deposition (MOCVD) for electron devices of both GaN on Si and GaN on GaN are presented. We have examined the possibility of increasing the growth rate of GaN on 200-mm-diameter Si by using a multiwafer production MOCVD machine, in which the vapor phase parasitic reaction is well controlled. The impact of a high-growth-rate strained-layer-superlattice (SLS) buffer layer is presented in terms of material properties. An SLS growth rate of as high as 3.46 µm/h, which was 73% higher than the current optimum, was demonstrated. As a result, comparable material properties were obtained. Next, a typical result of GaN doped with Si of 1 × 1016 cm-3 grown at the growth rate of 3.7 µm/h is shown. For high-voltage application, we need a thick high-purity GaN drift layer with a low carbon concentration, of less than 1016 cm-3. It is shown that achieving a high growth rate by precise control of the vapor phase reaction is still challenge in GaN MOCVD.

  9. Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles

    PubMed Central

    Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Cebotari, Serghei; Lux, Marco; Haverich, Axel

    2016-01-01

    Summary Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle–cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN) semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO) nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN. PMID:27826507

  10. Growth of low-threading-dislocation-density GaN on graphene by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    He, Shunyu; Xu, Yu; Qi, Lin; Li, Zongyao; Cao, Bing; Wang, Chinhua; Zhang, Jicai; Wang, Jianfeng; Xu, Ke

    2017-03-01

    Recently, gallium nitride (GaN) films grown on graphene have been widely studied. Here, we have grown low-threading-dislocation-density GaN films on graphene by hydride vapor phase epitaxy (HVPE). The full widths at half maximum (FWHMs) of X-ray rocking curves (XRCs) of the GaN films were 276 and 350 arcsec at the 0002 and 10\\bar{1}2 reflections, respectively. This shows that the threading dislocation densities are on the order of magnitude of 108 cm‑2, which is consistent with the results of cathodoluminescence (CL).

  11. Growth and characterization of cubic and non-cubic Ge nanocrystals

    SciTech Connect

    Mukherjee, S.; Pradhan, A.; Bhunia, S.; Mukherjee, S.; Maitra, T.; Nayak, A.

    2016-05-06

    Germanium nanocrystals with tetragonal (ST-12) and diamond like cubic (Ge-I) phases have been selectively grown by controlling the ionization and electrostatic potential of Ge clusters in an ion cluster beam deposition system. Predominantly tetragonal nanocrystals were obtained when grown using neutral clusters. The percentage of cubic phase increased when grown by ionizing the clusters and accelerating them towards substrates by applying electrostatic bias in the range of 1.5 –2.5 kV. Raman spectroscopic measurement showed strong peak at 275 cm{sup −1} and 300 cm{sup −1} for tetragonal and cubic Ge nanocrystals, respectively. TEM measurements showed crystalline lattice fringes of both type of the nanocrystals. The selected area electron diffraction patterns showed (111) and (210) as the dominating lattice planes for tetragonal nanocrystals while the cubic phases had (111), (311) and (331) as the prominent lattice planes. The optical absorption edge redshifted from 1.75 to 1.55 eV as the percentage of the cubic phases increased in the NC composition in the composite film.

  12. Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Corrion, A. L.; Poblenz, C.; Wu, F.; Speck, J. S.

    2008-05-01

    The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH{sub 3}:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH{sub 3}:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of {approx}1.0 nm over 2x2 {mu}m{sup 2} atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 {mu}m/h were achieved. TD densities in the buffers as low as 3x10{sup 9} cm{sup -2} were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.

  13. Influence of Annealing Conditions on Dopant Antirotation of Si+ and Mg+ Implanted GaN

    SciTech Connect

    Suvkhanov, A.; Parikh, N.; Usov, I.; Hunn, J.D.; Withrow, S.; Thomson, D.; Herke, T.; Davis, R.F.; Krasnobaev, L.

    1999-10-12

    This report reflects the results of heat treatment under various conditions on as-grown and ion implanted GaN. The PL spectrums of as-grown GaN and GaN with 400 A AlN cap were almost identical. This fact allows one to use PL analysis without AlN stripping. As-grown GaN and ion implanted with Mg and Si crystals were annealed at 1300 C for 10 minutes in three different conditions: in flowing argon gas; in flowing ultra high purity nitrogen; and in a quartz capsule sealed with nitrogen gas. The results of PL, RBS, SEM and TEM analysis show an advantage of GaN high temperature annealing in quartz capsules with nitrogen ambient as compared to annealing in argon and nitrogen gas flow. Encapsulation with nitrogen over-pressure prevents the decomposition of the GaN crystal and the AlN capping film, and allows one to achieve optical activation of implanted Mg and Si after 1300 C annealing.

  14. Basic ammonothermal GaN growth in molybdenum capsules

    NASA Astrophysics Data System (ADS)

    Pimputkar, S.; Speck, J. S.; Nakamura, S.

    2016-12-01

    Single crystal, bulk gallium nitride (GaN) crystals were grown using the basic ammonothermal method in a high purity growth environment created using a non-hermetically sealed molybdenum (Mo) capsule and compared to growths performed in a similarly designed silver (Ag) capsule and capsule-free René 41 autoclave. Secondary ion mass spectrometry (SIMS) analysis revealed transition metal free (<1×1017 cm-3) GaN crystals. Anomalously low oxygen concentrations ((2-6)×1018 cm-3) were measured in a {0001} seeded crystal boule grown using a Mo capsule, despite higher source material oxygen concentrations ((1-5)×1019 cm-3) suggesting that molybdenum (or molybdenum nitrides) may act to getter oxygen under certain conditions. Total system pressure profiles from growth runs in a Mo capsule system were comparable to those without a capsule, with pressures peaking within 2 days and slowly decaying due to hydrogen diffusional losses. Measured Mo capsule GaN growth rates were comparable to un-optimized growth rates in capsule-free systems and appreciably slower than in Ag-capsule systems. Crystal quality replicated that of the GaN seed crystals for all capsule conditions, with high quality growth occurring on the (0001) Ga-face. Optical absorption and impurity concentration characterization suggests reduced concentrations of hydrogenated gallium vacancies (VGa-Hx).

  15. Features of molecular beam epitaxy of the GaN (0001) and GaN (0001-bar) layers with the use of different methods of activation of nitrogen

    SciTech Connect

    Mizerov, A. M. Jmerik, V. N.; Kaibyshev, V. K.; Komissarova, T. A.; Masalov, S. A.; Ivanov, S. V.

    2009-08-15

    The results of comparative studies of the growth kinetics of the GaN layers of different polarity during ammonia molecular beam epitaxy and plasma-assisted molecular beam epitaxy (PA MBE) of nitrogen with the use of sapphire substrates and GaN(0001-bar)/c-Al{sub 2}O{sub 3} templates grown by gas-phase epitaxy from metalorganic compounds are presented. The possibility is shown of obtaining the GaN layers with an atomically smooth surface during molecular beam epitaxy with plasma activation of nitrogen. For this purpose, it is suggested to carry out the growth in conditions enriched with metal near the mode of formation of the Ga drops at a temperature close to the decomposition temperature of GaN (TS {approx} 760 deg. C). The conclusion is made that an increase in the growth temperature positively affects the structural, optical, and electrical properties of the GaN (0001-bar) layers. A high quality of the GaN (0001) films grown by the PA MBE method at a low temperature of {approx}700 deg. C on the GaN/c-Al{sub 2}O{sub 3} templates is shown.

  16. Cubic topological Kondo insulators.

    PubMed

    Alexandrov, Victor; Dzero, Maxim; Coleman, Piers

    2013-11-27

    Current theories of Kondo insulators employ the interaction of conduction electrons with localized Kramers doublets originating from a tetragonal crystalline environment, yet all Kondo insulators are cubic. Here we develop a theory of cubic topological Kondo insulators involving the interaction of Γ(8) spin quartets with a conduction sea. The spin quartets greatly increase the potential for strong topological insulators, entirely eliminating the weak topological phases from the diagram. We show that the relevant topological behavior in cubic Kondo insulators can only reside at the lower symmetry X or M points in the Brillouin zone, leading to three Dirac cones with heavy quasiparticles.

  17. High internal quantum efficiency ultraviolet to green luminescence peaks from pseudomorphic m-plane Al{sub 1−x}In{sub x}N epilayers grown on a low defect density m-plane freestanding GaN substrate

    SciTech Connect

    Chichibu, S. F. Hazu, K.; Furusawa, K.; Ishikawa, Y.; Onuma, T.; Ohtomo, T.; Ikeda, H.; Fujito, K.

    2014-12-07

    Structural and optical qualities of half-a-μm-thick m-plane Al{sub 1−x}In{sub x}N epilayers grown by metalorganic vapor phase epitaxy were remarkably improved via coherent growth on a low defect density m-plane freestanding GaN substrate prepared by hydride vapor phase epitaxy. All the epilayers unexceptionally suffer from uniaxial or biaxial anisotropic in-plane stress. However, full-width at half-maximum values of the x-ray ω-rocking curves were nearly unchanged as the underlayer values being 80 ∼ 150 arc sec for (101{sup ¯}0) and (101{sup ¯}2) diffractions with both 〈0001〉 and 〈112{sup ¯}0〉 azimuths, as long as pseudomorphic structure was maintained. Such Al{sub 1−x}In{sub x}N epilayers commonly exhibited a broad but predominant luminescence peak in ultraviolet (x ≤ 0.14) to green (x = 0.30) wavelengths. Its equivalent value of the internal quantum efficiency at room temperature was as high as 67% for x = 0.14 and 44% for x = 0.30. Because its high-energy cutoff commonly converged with the bandgap energy, the emission peak is assigned to originate from the extended near-band-edge states with strong carrier localization.

  18. Vertically p-n-junctioned GaN nano-wire array diode fabricated on Si(111) using MOCVD.

    PubMed

    Park, Ji-Hyeon; Kim, Min-Hee; Kissinger, Suthan; Lee, Cheul-Ro

    2013-04-07

    We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 10(7) cm(-2). The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute).

  19. Accurate monotone cubic interpolation

    NASA Technical Reports Server (NTRS)

    Huynh, Hung T.

    1991-01-01

    Monotone piecewise cubic interpolants are simple and effective. They are generally third-order accurate, except near strict local extrema where accuracy degenerates to second-order due to the monotonicity constraint. Algorithms for piecewise cubic interpolants, which preserve monotonicity as well as uniform third and fourth-order accuracy are presented. The gain of accuracy is obtained by relaxing the monotonicity constraint in a geometric framework in which the median function plays a crucial role.

  20. Ultra High Temperature Rapid Thermal Annealing of GaN

    SciTech Connect

    Cao, X.A.; Fu, M.; Han, J.; Pearton, S.J.; Rieger, D.J.; Sekhar, J.A.; Shul, R.J.; Singh, R.K.; Wilson, R.G.; Zolper, J.C.

    1998-11-20

    All of the major acceptor (Mg, C, Be) and donor (Si, S, Se and Te) dopants have been implanted into GaN films grown on A1203 substrates. Annealing was performed at 1100- 1500 C, using AIN encapsulation. Activation percentages of >90Y0 were obtained for Si+ implantation annealed at 1400 C, while higher temperatures led to a decrease in both carrier concentration and electron mobility. No measurable redistribution of any of the implanted dopants was observed at 1450 C.

  1. Luminescence of GaN nanocolumns obtained by photon-assisted anodic etching

    NASA Astrophysics Data System (ADS)

    Tiginyanu, I. M.; Ursaki, V. V.; Zalamai, V. V.; Langa, S.; Hubbard, S.; Pavlidis, D.; Föll, H.

    2003-08-01

    GaN nanocolumns with transverse dimensions of about 50 nm were obtained by illumination-assisted anodic etching of epilayers grown by metalorganic chemical vapor deposition on sapphire substrates. The photoluminescence spectroscopy characterization shows that the as-grown bulk GaN layers suffer from compressive biaxial strain of 0.5 GPa. The majority of nanocolumns are fully relaxed from strain, and the room-temperature luminescence is free excitonic. The high quality of the columnar nanostructures evidenced by the enhanced intensity of the exciton luminescence and by the decrease of the yellow luminescence is explained by the peculiarities of the anodic etching processing.

  2. Study of the integrated growth of dielectric films on GaN semiconductor substrates.

    PubMed

    Li, Yanrong; Zhu, Jun; Luo, Wenbo

    2010-10-01

    Typical perovskite oxides SrTiO₃ (STO) and PbZr₀.₅₂Ti₀.₄₈O₃ (PZT) were fabricated on GaN semiconductor substrates by pulsed laser deposition. STO and PZT films were deposited on bare GaN, TiO₂, and MgO-buffered GaN. The effects of TiO₂ and MgO buffer-layers on the orientations and electric properties of the perovskite films were systematically studied. The crystalline properties were in situ monitored by reflective high energy electron diffraction and ex situ characterized by X-ray diffraction. It was found that the epitaxial temperature of STO and PZT was reduced by inserting a buffer layer. (111)-oriented films were obtained on bare and TiO₂-buffered GaN. However, the orientations of the perovskite films were changed to be (110) when deposited on MgO buffer layer. Furthermore, PZT films deposited on MgO- and TiO₂-buffered GaN show better electric performance compared with these films directly deposited on GaN. These results show that perovskite oxide could be epitaxially grown on GaN semiconductor substrates by inserting a proper buffer layer.

  3. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy.

    PubMed

    Zhong, Aihua; Hane, Kazuhiro

    2012-12-27

    GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/. The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining.

  4. Radiative defects in GaN nanocolumns: Correlation with growth conditions and sample morphology

    SciTech Connect

    Lefebvre, P.; Fernandez-Garrido, S.; Grandal, J.; Ristic, J.; Sanchez-Garcia, M.-A.; Calleja, E.

    2011-02-21

    Low-temperature photoluminescence is studied in detail in GaN nanocolumns (NCs) grown by plasma-assisted molecular beam epitaxy under various conditions (substrate temperature and impinging Ga/N flux ratio). The relative intensities of the different emission lines, in particular those related to structural defects, appear to be correlated with the growth conditions, and clearly linked to the NC sample morphology. We demonstrate, in particular, that all lines comprised between 3.10 and 3.42 eV rapidly lose intensity when the growth conditions are such that the NC coalescence is reduced. The well-known line around 3.45 eV, characteristic of GaN NC samples, shows, however, a behavior that is exactly the opposite of the other lines, namely, for growth conditions leading to reduced NC coalescence, this line tends to become more prominent, thus proving to be intrinsic to individual GaN NCs.

  5. 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.

  6. Controlled morphology of regular GaN microrod arrays by selective area growth with HVPE

    NASA Astrophysics Data System (ADS)

    Lekhal, Kaddour; Bae, Si-Young; Lee, Ho-Jun; Mitsunari, Tadashi; Tamura, Akira; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-08-01

    The selective area growth (SAG) of GaN was implemented on patterned GaN/sapphire templates by hydride vapor phase epitaxy (HVPE) to fabricate regular arrays of Ga-polar GaN microrods. The control of growth parameters such as H2/N2 carrier gas ratio, growth temperature, and absolute NH3/HCl gas flow resulted in changes in the growth morphology. In particular, for an optimized mixed-carrier gas ratio of H2 to N2, we achieved vertically well-aligned microrods. The topmost regions of the GaN microrods were terminated with pyramidal facets, indicating typical Ga polarity. The optical properties of the grown microrods were characterized by cathodoluminescence (CL) at a low temperature. This revealed that the GaN microrods had high crystal quality since they exhibited suppressed yellow luminescence as well as strong band edge emission.

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

    SciTech Connect

    Qi, Meng; Zhao, Yuning; Yan, Xiaodong; Li, Guowang; Verma, Jai; Fay, Patrick; Nomoto, Kazuki; Zhu, Mingda; Hu, Zongyang; Protasenko, Vladimir; Song, Bo; Xing, Huili Grace; Jena, Debdeep; Bader, Samuel

    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.

  8. Above room-temperature ferromagnetism of Mn delta-doped GaN nanorods

    SciTech Connect

    Lin, Y. T.; Wadekar, P. V.; Kao, H. S.; Chen, T. H.; Chen, Q. Y.; Tu, L. W.; Huang, H. C.; Ho, N. J.

    2014-02-10

    One-dimensional nitride based diluted magnetic semiconductors were grown by plasma-assisted molecular beam epitaxy. Delta-doping technique was adopted to dope GaN nanorods with Mn. The structural and magnetic properties were investigated. The GaMnN nanorods with a single crystalline structure and with Ga sites substituted by Mn atoms were verified by high-resolution x-ray diffraction and Raman scattering, respectively. Secondary phases were not observed by high-resolution x-ray diffraction and high-resolution transmission electron microscopy. In addition, the magnetic hysteresis curves show that the Mn delta-doped GaN nanorods are ferromagnetic above room temperature. The magnetization with magnetic field perpendicular to GaN c-axis saturates easier than the one with field parallel to GaN c-axis.

  9. Spectroscopic investigation of native defect induced electron-phonon coupling in GaN nanowires

    NASA Astrophysics Data System (ADS)

    Parida, Santanu; Patsha, Avinash; Bera, Santanu; Dhara, Sandip

    2017-07-01

    The integration of advanced optoelectronic properties in nanoscale devices of group III nitride can be realized by understanding the coupling of charge carriers with optical excitations in these nanostructures. The native defect induced electron-phonon coupling in GaN nanowires are reported using various spectroscopic studies. The GaN nanowires having different native defects are grown in an atmospheric pressure chemical vapor deposition technique. X-ray photoelectron spectroscopic analysis revealed the variation of Ga/N ratios in nanowires having possible native defects, with respect to their growth parameters. The analysis of the characteristic features of electron-phonon coupling in the Raman spectra show the variations in carrier density and mobility, with respect to the native defects in unintentionally doped GaN nanowires. The radiative recombination of donor acceptor pair transitions and the corresponding LO phonon replicas observed in photoluminescence studies further emphasize the role of native defects in electron-phonon coupling.

  10. Synthesis of GaN nanowires on gold-coated SiC substrates by novel pulsed electron deposition technique

    NASA Astrophysics Data System (ADS)

    Lei, M.; Yang, H.; Li, P. G.; Tang, W. H.

    2008-01-01

    A two-step approach for macro-synthesis of GaN nanowires was developed in this study. GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent dicyandiamide (C 2N 4H 4) and Ga 2O 3 as precursors. Subsequently, single-crystalline wurtzite GaN nanowires were grown on gold-coated 6H-SiC substrates via novel pulsed electron deposition (PED) technique using the as-prepared GaN nanoparticles as target, which provides a new route employing nanoparticles as precursors to fabricate GaN nanowires. It is found that pulsed electron ablation induced Ga and N plasma directly towards the gold-coated substrate to initialize the vapor-liquid-solid (VLS) growth processes. The morphological and structural properties were investigated in detail and Raman scattering spectrum of these nanowires presented some new features.

  11. Size-dependent shape and tilt transitions in In2O3 nanoislands grown on cubic Y-stabilized ZrO2(001) by molecular beam epitaxy.

    PubMed

    Zhang, Kelvin H L; Bourlange, Anne; Egdell, Russell G; Collins, Stephen P; Bean, Richard J; Robinson, Ian K; Cowley, Roger A

    2012-08-28

    The growth of In(2)O(3) on cubic Y-stabilized ZrO(2)(001) by molecular beam epitaxy leads to formation of nanoscale islands which may tilt relative to the substrate in order to help accommodate the 1.7% tensile mismatch between the epilayer and the substrate. High-resolution synchrotron-based X-ray diffraction has been used in combination with atomic force microscopy to probe the evolution in island morphology, orientation, and tilt with island size. Very small islands formed at low substrate coverage are highly strained but exhibit no tilt, while intermediate islands are tilted randomly in all directions, giving rise to distinctive doughnut-shaped structure in three-dimensional reciprocal space isosurfaces. The largest islands with lateral sizes on the order of 1 μm tilt away from the four equivalent in-plane <110> directions, giving three-dimensional scattering isosurfaces dominated by structure at the four corners of a square. Spatially resolved reciprocal space mapping using an X-ray beam with dimensions on the order of 1 μm suggests that the four-fold symmetry observed using a larger beam arises from averaging over an ensemble of islands, each with an individual tilt down one direction, rather than from the coexistence of differently tilted domains within a given island.

  12. Properties of H, O and C in GaN

    SciTech Connect

    Pearton, S.J.; Abernathy, C.R.; Lee, J.W.

    1996-04-01

    The electrical properties of the light ion impurities H, O and C in GaN have been examined in both as-grown and implanted material. H is found to efficiently passivate acceptors such as Mg, Ca and C. Reactivation occurs at {ge} 450 C and is enhanced by minority carrier injection. The hydrogen does not leave the GaN crystal until > 800 C, and its diffusivity is relatively high ({approximately} 10{sup {minus}11} cm{sup 2}/s) even at low temperatures (< 200 C) during injection by wet etching, boiling in water or plasma exposure. Oxygen shows a low donor activation efficiency when implanted into GaN, with an ionization level of 30--40 meV. It is essentially immobile up to 1,100 C. Carbon can produce low p-type levels (3 {times} 10{sup 17} cm{sup {minus}3}) in GaN during MOMBE, although there is some evidence it may also create n-type conduction in other nitrides.

  13. Electrochemical characterization of GaN surface states

    NASA Astrophysics Data System (ADS)

    Winnerl, Andrea; Garrido, Jose A.; Stutzmann, Martin

    2017-07-01

    In this work, we present a systematic study of the electrochemical properties of metal-organic chemical vapor deposition and hybrid vapor phase epitaxy grown n-type GaN in aqueous electrolytes. For this purpose, we perform cyclic voltammetry and impedance spectroscopy measurements over a wide range of potentials and frequencies, using a pure aqueous electrolyte and adding two different types of redox couples, as well as applying different surface treatments to the GaN electrodes. For Ga-polar GaN electrodes, the charge transfer to an electrolyte is dominated by surface states, which are not related to dislocations and are independent of the specific growth technique. These surface states can be modified by the surface treatment; they are generated by etching in HCl and are passivated by oxidation. Different surface defect states are present on N-polar GaN electrodes which do not significantly contribute to the charge transfer across the GaN/electrolyte interface.

  14. MOCVD growth of GaN on Si through novel substrate modification techniques

    NASA Astrophysics Data System (ADS)

    Gagnon, Jarod C.

    reduced by utilizing thinner buffer layers and increasing the implantation depth of N+ ions. Final studies were presented on a method of etching Si(001) substrates in order to fabricate trenches with Si{110} sidewalls. It was shown in these studies that GaN could be preferentially grown on Si{110} sidewalls such that GaN(0002)//Si{110}. The result was non-polar GaN "fins" which vertically overgrew Si(001) ridges. Further studies showed that high V/III, low temperature, and low pressure was required to promote the lateral growth of the GaN(0002) which was necessary to obtain a fully coalesced film.

  15. 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.

  16. Surface chemistry and electronic structure of nonpolar and polar GaN films

    NASA Astrophysics Data System (ADS)

    Mishra, Monu; Krishna, T. C. Shibin; Aggarwal, Neha; Gupta, Govind

    2015-08-01

    Photoemission and microscopic analysis of nonpolar (a-GaN/r-Sapphire) and polar (c-GaN/c-Sapphire) epitaxial gallium nitride (GaN) films grown via RF-Molecular Beam Epitaxy is reported. The effect of polarization on surface properties like surface states, electronic structure, chemical bonding and morphology has been investigated and correlated. It was observed that polarization lead to shifts in core level (CL) as well as valence band (VB) spectra. Angle dependent X-ray Photoelectron Spectroscopic analysis revealed higher surface oxide in polar GaN film compared to nonpolar GaN film. On varying the take off angle (TOA) from 0° to 60°, the Gasbnd O/Gasbnd N ratio varied from 0.11-0.23 for nonpolar and 0.17-0.36 for polar GaN film. The nonpolar film exhibited N-face polarity while Ga-face polarity was perceived in polar GaN film due to the inherent polarization effect. Polarization charge compensated surface states were observed on the polar GaN film and resulted in downward band bending. Ultraviolet photoelectron spectroscopic measurements revealed electron affinity and ionization energy of 3.4 ± 0.1 eV and 6.8 ± 0.1 eV for nonpolar GaN film and 3.8 ± 0.1 eV and 7.2 ± 0.1 eV for polar GaN film respectively. Field Emission Scanning Electron Microscopy measurements divulged smooth morphology with pits on polar GaN film. The nonpolar film on the other hand showed pyramidal structures having facets all over the surface.

  17. Annealing effects on polycrystalline GaN using nitrogen and ammonia ambients

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    This paper describes effects of using post-annealing treatment in different conditions on the properties of polycrystalline GaN layer grown on m-plane sapphire substrate by electron beam (e-beam) evaporator. Without annealing, GaN surface was found to have a low RMS roughness with agglomeration of GaN grains in a specific direction and the sample consisted of gallium oxide (Ga2O3) material. When the post-annealing treatment was carried out in N2 ambient at 650 °C, initial re-crystallization of the GaN grains was observed while the evidence of Ga2O3 almost disappeared. As the NH3 annealing was conducted at 950 °C, more effect of re-crystallization occurred but with less grains coalescence. Three dominant XRD peaks of GaN in (10 1 bar 0) , (0002) and (10 1 bar 1) orientations were evident. Near band edge (NBE) related emission in GaN was also observed. The significant improvement was attributed to simultaneous recrystallization and effective reduction of N deficiency density. The post-annealing in a mixture of N2 and NH3 ambient at 950 °C was also conducted, but has limited the effectiveness of the N atoms to incorporate on the GaN layer due to 'clouding' effect by the inert N2 gas. Further increase in the annealing temperature at 980 °C and 1100 °C, respectively caused severe deteriorations of the structural and optical properties of the GaN layer. Overall, this work demonstrated initial potential in improving polycrystalline GaN material in simple and inexpensive manner.

  18. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    NASA Astrophysics Data System (ADS)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  19. ''Cube-on-hexagon'' orientation relationship for Fe on GaN(0001): The missing link in bcc/hcp epitaxy

    SciTech Connect

    Gao Cunxu; Brandt, Oliver; Laehnemann, Jonas; Jahn, Uwe; Jenichen, Bernd; Schoenherr, Hans-Peter; Erwin, Steven C.

    2010-09-15

    We investigate, experimentally and theoretically, the epitaxy of body-centered-cubic Fe on hexagonal GaN. For growth on the Ga-polar GaN(0001) surface we find the well-known Pitsch-Schrader orientation relationship between Fe and GaN. On the N-polar GaN(0001) surface we observe coexistence between the familiar Burgers orientation and a new orientation in which the Fe(001) plane is parallel to GaN(0001). This 'cube-on-hexagon' orientation constitutes the high-symmetry link required for constructing a symmetry diagram for bcc/hcp systems in which all orientation relationships are connected by simple rotations.

  20. Cubic colloidal platinum nanoparticles

    SciTech Connect

    Ahmadi, T.S.; Wang, Z.L.; Henglein, A.; El-Sayed, M.A.

    1996-06-01

    Cubic platinum nanoparticles (4-18 nm) have been synthesized for the first time in solution by the controlled reduction of K{sub 2}PtCl{sub 4} with hydrogen gas in the presence of sodium polyacrylate as a capping material. The nanoparticles are found to have fcc structures, similar to the bulk metal with (100) facets.

  1. BF into cubic meters

    Treesearch

    Henry Spelter

    2002-01-01

    Noted forest products industry researcher and writer says the conversion factor traditionally used to convert logs measured in board feet to cubic meters has risen. In the U.S., most timber is measured in terms of board feet. The log scales currently in use to estimate lumber recovery from roundwood, however, were created in the 19th century according to sawmill...

  2. Growth optimization and characterization of GaN epilayers on multifaceted (111) surfaces etched on Si(100) substrates

    SciTech Connect

    Ansah-Antwi, KwaDwo Konadu Chua, Soo Jin; Soh, Chew Beng; Liu, Hongfei

    2015-11-15

    The four nearest Si(111) multifaceted sidewalls were exposed inside an array of 3 μm-wide square holes patterned on an Si(100) substrate, and this patterned Si(100) substrate was used as a substrate for the deposition of a gallium nitride (GaN) epilayer. Subsequently the effect that the growth pressure, the etched-hole profiles, and the etched-hole arrangement had upon the quality of the as-grown GaN was investigated. The coalescence of the as-grown GaN epilayer on the exposed Si(111) facets was observed to be enhanced with reduced growth pressure from 120 to 90 Torr. A larger Si(001) plane area at the bottom of the etched holes resulted in bidirectional GaN domains, which resulted in poor material quality. The bidirectional GaN domains were observed as two sets of six peaks via a high-resolution x-ray diffraction phi scan of the GaN(10-11) reflection. It was also shown that a triangular array of etched holes was more desirable than square arrays of etched holes for the growth high-quality and continuous GaN films.

  3. Zn-dopant dependent defect evolution in GaN nanowires

    NASA Astrophysics Data System (ADS)

    Yang, Bing; Liu, Baodan; Wang, Yujia; Zhuang, Hao; Liu, Qingyun; Yuan, Fang; Jiang, Xin

    2015-10-01

    Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101&cmb.macr;3), (101&cmb.macr;1) and (202&cmb.macr;1), as well as Type I stacking faults (...ABABC&cmb.b.line;BCB...), are observed in the nanowires. The increasing Zn doping level (<1 at%) induces the formation of screw dislocations featuring a predominant screw component along the radial direction of the GaN nanowires. At high Zn doping level (3-5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (...ABABAC&cmb.b.line;BA...) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires.Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a

  4. Utilisation of GaN and InGaN/GaN with nanoporous structures for water splitting

    SciTech Connect

    Benton, J.; Bai, J.; Wang, T.

    2014-12-01

    We report a cost-effective approach to the fabrication of GaN based nanoporous structure for applications in renewable hydrogen production. Photoelectrochemical etching in a KOH solution has been employed to fabricate both GaN and InGaN/GaN nanoporous structures with pore sizes ranging from 25 to 60 nm, obtained by controlling both etchant concentration and applied voltage. Compared to as-grown planar devices the nanoporous structures have exhibited a significant increase of photocurrent with a factor of up to four times. An incident photon conversion efficiency of up to 46% around the band edge of GaN has been achieved.

  5. Combined atomic force microscopy and scanning tunneling microscopy imaging of cross-sectioned GaN light-emitting diodes.

    PubMed

    Bender, J W; Salmon, M E; Russell, P E

    2003-01-01

    Cross-sectional scanning tunneling microscopy (STM) was combined with atomic force microscopy (AFM) over the same area to characterize a cross-sectioned GaN light emitting diode. Because GaN is typically grown on a non-native substrate and also forms a wurtzite crystal structure, a cryogenic cleaving technique was developed to generate smooth surfaces. The depletion region surrounding the p-n junction was clearly identified using STM. Furthermore, by imaging under multiple sample biases, distinctions between the n-doped and p-doped GaN could be made.

  6. Synthesis and characterization of GaN thin films deposited on different substrates using a low-cost electrochemical deposition technique

    SciTech Connect

    Al-Heuseen, K.; Hashim, M. R.

    2012-09-06

    Gallium nitride GaN thin films were deposited on three different substrates; Si (111), Si (100) and ITO coated glass using electrochemical deposition technique at 20 Degree-Sign C. A mixture of gallium nitrate, ammonium nitrate was used as electrolyte. The deposited films were investigated at room temperature by a series of material characterization techniques, namely; scanning electron microscopy (SEM), EDX and X-ray diffraction (XRD). SEM images and EDX results indicated that the growth of GaN films varies according to the substrates. XRD analyses showed the presence of hexagonal wurtzite and cubic zinc blende GaN phases with the crystallite size around 18-29 nm.

  7. Lattice-matched HfN buffer layers for epitaxy of GaN on Si

    SciTech Connect

    Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko; Sasaki, Katsutaka

    2002-05-08

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited 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 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  8. Understanding the pyramidal growth of GaN

    SciTech Connect

    Rouviere, J.L.; Arlery, M.; Bourret, A.

    1996-11-01

    By a combination of conventional, HREM and CBED TEM experiments the authors have studied wurtzite GaN layers grown by Metal-Organic Chemical Vapor Deposition (MOCVD) on (0001)Al{sub 2}O{sub 3}. They experimentally determine the structure of the macroscopic hexagonal pyramids that are visible at the surface of the layers when no optimized buffer is introduced. These pyramids look like hexagonal volcanoes with one hexagonal microscopic chimney (up to 75 nm wide) at their core. The crystal inside the chimney is a pure GaN crystal with a polarity opposed to the one of the neighboring material: the GaN layers grown on (0001)Al{sub 2}O{sub 3} are everywhere Ga-terminated except in the chimneys where they are N-terminated. Some of the N-terminated chimneys grow faster and form macroscopic hexagonal pyramids. Chimneys bounded by Inversion Domains Boundaries (IDBs) originate from steps at the surface of the substrate and may be suppressed by an adapted buffer layer.

  9. Pit assisted oxygen chemisorption on GaN surfaces.

    PubMed

    Mishra, Monu; Krishna T C, Shibin; Aggarwal, Neha; Kaur, Mandeep; Singh, Sandeep; Gupta, Govind

    2015-06-21

    A comprehensive analysis of oxygen chemisorption on epitaxial gallium nitride (GaN) films grown at different substrate temperatures via RF-molecular beam epitaxy was carried out. Photoemission (XPS and UPS) measurements were performed to investigate the nature of the surface oxide and corresponding changes in the electronic structure. It was observed that the growth of GaN films at lower temperatures leads to a lower amount of surface oxide and vice versa was observed for a higher temperature growth. The XPS core level (CL) and valence band maximum (VBM) positions shifted towards higher binding energies (BE) with oxide coverage and revealed a downward band bending. XPS valence band spectra were de-convoluted to understand the nature of the hybridization states. UPS analysis divulged higher values of electronic affinity and ionization energy for GaN films grown at a higher substrate temperature. The surface morphology and pit structure were probed via microscopic measurements (FESEM and AFM). FESEM and AFM analysis revealed that the film surface was covered with hexagonal pits, which played a significant role in oxygen chemisorption. The favourable energetics of the pits offered an ideal site for oxygen adsorption. Pit density and pit depth were observed to be important parameters that governed the surface oxide coverage. The contribution of surface oxide was increased with an increase in average pit density as well as pit depth.

  10. Growth of GaN films on PLD-deposited TaC substrates

    NASA Astrophysics Data System (ADS)

    Kirchner, K. W.; Derenge, M. A.; Zheleva, T. S.; Vispute, R. D.; Jones, K. A.

    2010-09-01

    GaN films were grown by metal organic chemical vapor deposition on TaC substrates that were created by pulsed laser deposition of TaC onto (0 0 0 1) SiC substrates at ˜1000 °C. This was done to determine if good quality TaC films could be grown, and if good quality GaN films could be grown on this closely lattice matched to GaN, conductive material. This was done by depositing the TaC on on-axis and 3° or 8° off-axis (0 0 0 1) SiC at temperatures ranging from 950 to 1200 °C, and examining them using X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The GaN films were grown on as-deposited TaC films, and films annealed at 1200, 1400, or 1600 °C, and examined using the same techniques. The TaC films were polycrystalline with a slight (1 1 1) texture, and the grains were ˜200 nm in diameter. Films grown on-axis were found to be of higher quality than those grown on off-axis substrates, but the latter could be improved to a comparable quality by annealing them at 1200-1600 °C for 30 min. TaC films deposited at temperatures above 1000 °C were found to react with the SiC. GaN films could be deposited onto the TaC when the surface was nitrided with NH 3 for 3 min at 1100 °C and the low temperature buffer layer was AlN. However, the GaN did not nucleate easily on the TaC film, and the crystallites did not have the desired (0 0 0 1) preferred orientation. They were ˜10 times larger than those typically seen in films grown on SiC or sapphire. Also the etch pit concentration in the GaN films grown on the TaC was more than 2 orders of magnitude less than it was for growth on the SiC.

  11. High-Q GaN nanowire resonators and oscillators

    SciTech Connect

    Tanner, S. M.; Gray, J. M.; Rogers, C. T.; Bertness, K. A.; Sanford, N. A.

    2007-11-12

    We report high mechanical quality factors Q for GaN nanowire cantilevers grown by molecular beam epitaxy. Nanowires with 30-500 nm diameters and 5-20 {mu}m lengths having resonance frequencies from 400 kHz to 2.8 MHz were measured. Q near room temperature and 10{sup -4} Pa ranged from 2700 to above 60 000 with most above 10 000. Positive feedback to a piezoelectric stack caused spontaneous nanowire oscillations with Q exceeding 10{sup 6}. Spontaneous oscillations also occurred with direct e-beam excitation of unintentionally doped nanowires. Doped nanowires showed no oscillations, consistent with oscillation arising via direct actuation of piezoelectric GaN.

  12. Study of Charge Carrier Transport in GaN Sensors.

    PubMed

    Gaubas, Eugenijus; Ceponis, Tomas; Kuokstis, Edmundas; Meskauskaite, Dovile; Pavlov, Jevgenij; Reklaitis, Ignas

    2016-04-18

    Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm²/Vs for electrons, and μh = 400 ± 80 cm²/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects.

  13. Study of Charge Carrier Transport in GaN Sensors

    PubMed Central

    Gaubas, Eugenijus; Ceponis, Tomas; Kuokstis, Edmundas; Meskauskaite, Dovile; Pavlov, Jevgenij; Reklaitis, Ignas

    2016-01-01

    Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm2/Vs for electrons, and μh = 400 ± 80 cm2/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects. PMID:28773418

  14. Why is Polonium simple cubic?

    NASA Astrophysics Data System (ADS)

    Roundy, David; Kraig, Robert E.; Cohen, Marvin L.

    2002-03-01

    Scientists have long pondered why the simple cubic structure is so rarely seen in nature. Only one element forms the simple cubic structure: polonium. There are `proofs' dating back to 1954 that the simple cubic lattice should be unstable. We will attempt to address the question of why polonium takes the simple cubic structure by means of ab initio calculations using the pseudopotential density functional method. We will discuss the electronic structure of polonium in relation to its crystal structure.

  15. Comparison of trimethylgallium and triethylgallium as “Ga” source materials for the growth of ultrathin GaN films on Si (100) substrates via hollow-cathode plasma-assisted atomic layer deposition

    SciTech Connect

    Alevli, Mustafa; Haider, Ali; Kizir, Seda; Leghari, Shahid A.; Biyikli, Necmi

    2016-01-15

    GaN films grown by hollow cathode plasma-assisted atomic layer deposition using trimethylgallium (TMG) and triethylgallium (TEG) as gallium precursors are compared. Optimized and saturated TMG/TEG pulse widths were used in order to study the effect of group-III precursors. The films were characterized by grazing incidence x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Refractive index follows the same trend of crystalline quality, mean grain, and crystallite sizes. GaN layers grown using TMG precursor exhibited improved structural and optical properties when compared to GaN films grown with TEG precursor.

  16. Layered transition metal dichalcogenides: promising near-lattice-matched substrates for GaN growth

    PubMed Central

    Gupta, Priti; Rahman, A. A.; Subramanian, Shruti; Gupta, Shalini; Thamizhavel, Arumugam; Orlova, Tatyana; Rouvimov, Sergei; Vishwanath, Suresh; Protasenko, Vladimir; Laskar, Masihhur R.; Xing, Huili Grace; Jena, Debdeep; Bhattacharya, Arnab

    2016-01-01

    Most III-nitride semiconductors are grown on non-lattice-matched substrates like sapphire or silicon due to the extreme difficulty of obtaining a native GaN substrate. We show that several layered transition-metal dichalcogenides are closely lattice-matched to GaN and report the growth of GaN on a range of such layered materials. We report detailed studies of the growth of GaN on mechanically-exfoliated flakes WS2 and MoS2 by metalorganic vapour phase epitaxy. Structural and optical characterization show that strain-free, single-crystal islands of GaN are obtained on the underlying chalcogenide flakes. We obtain strong near-band-edge emission from these layers, and analyse their temperature-dependent photoluminescence properties. We also report a proof-of-concept demonstration of large-area growth of GaN on CVD MoS2. Our results show that the transition-metal dichalcogenides can serve as novel near-lattice-matched substrates for nitride growth. PMID:27025461

  17. Low temperature homoepitaxy of GaN structures by Vapor Liquid Solid transport

    NASA Astrophysics Data System (ADS)

    Jaud, Alexandre; Auvray, Laurent; Kahouli, Abdelkarim; Abi-Tannous, Tony; Linas, Sébastien; Ferro, Gabriel; Brylinski, Christian

    2017-06-01

    Low temperature (500-800 °C) homoepitaxy of not intentionally doped GaN structures on GaN(0 0 0 1)/Si(1 1 1) seed has been investigated by Vapor-Liquid-Solid (VLS) approach. The growth sequence consists in the metalorganic chemical vapor deposition of a network of submicrometric liquid Ga droplets, followed by their nitridation under flowing ammonia diluted either in H2 or Ar. When nitridation is performed under Ar carrier gas, GaN growth is very difficult to control due to too high N supersaturation within the droplets, despite very low NH3 flows. Nucleation and growth at the droplets periphery are always favored and, in most cases, high growth rates induce a crust-like growth, forming hollow GaN gangues. The use of H2 as carrier gas is detrimental to GaN (seed and grown material) stability, for nitridation temperatures ≥700 °C. But, compared to Ar atmosphere, a pronounced decrease of N supersaturation is demonstrated, allowing a better control of the growth mode. This is probably a consequence of a lower thermal decomposition efficiency of NH3 at the droplets surface. Optimal growth conditions are found at relatively low temperature (600 °C) and NH3 flow (20 sccm) for which a network of well-separated and faceted epitaxial GaN dots or rings is obtained. The growth mechanisms allowing these results are discussed.

  18. Correlation between macroscopic transport parameters and microscopic electrical properties in GaN

    NASA Astrophysics Data System (ADS)

    Witte, H.; Krtschil, A.; Schrenk, E.; Fluegge, K.; Dadgar, A.; Krost, A.

    2005-02-01

    In GaN layers grown by metal-organic vapor phase epitaxy on sapphire substrates the temperature-dependent Hall (TDH) and photo-Hall-effect (PHE) measurements show essential differences between undoped and Si-doped GaN. In undoped GaN the maximum of the Hall mobility occurs at temperatures near 300K with a low value. In PHE, an illumination introduces an enhancement of the mobility and a decrease of the electron density. In contrast, in Si-doped GaN the maximum Hall mobility is higher by a factor of 10 and is observed at temperatures between 100 and 180K. The photoinduced changes in the mobility and electron density are only marginal. Intensity dependent PHE measurements suggest the existence of internal potential barriers caused by inhomogeneities in the undoped samples. These results are combined with the surface-potential roughness on a microscale, as determined by scanning surface-potential microscopy (SSPM). In SSPM the undoped layers show strong potential fluctuations while they are lower for the Si-doped GaN samples. A correlation among the rms roughness of the surface potential, the maximum Hall mobility in TDH, and the maximum changes of the photo-Hall mobility is observed. In undoped GaN the mobility seems to be determined by the scattering at inner potential barriers stemming from structural inhomogeneities.

  19. Thermal evolution of microstructure in ion-irradiated GaN

    SciTech Connect

    Bae, In-Tae; Jiang, Weilin; Wang, Chong M.; Weber, William J.; Zhang, Yanwen

    2009-04-20

    The thermal evolution of the microstructure created by irradiation of a GaN single crystal with 2 MeV Au2+ ions at 150 K is characterized following annealing at 973 K using transmission electron microscopy. In the as-irradiated sample characterized at 300 K, Ga nanocrystals with the diamond structure, which is an unstable configuration for Ga, are directly observed together with nitrogen bubbles in the irradiation-induced amorphous layer. Upon thermal annealing, the thickness of the amorphous layer decreases by ~13.1 %, and nano-beam electron diffraction analysis indicates no evidence for residual Ga nanocrystals, but instead reveals a mixture of hexagonal and cubic GaN phases in the annealed sample. Nitrogen molecules, captured in the as-irradiated bubbles, appear to debond and react with the Ga nanocrystals during the thermal annealing to form crystalline GaN. In addition, electron energy loss spectroscopy measurements reveal an atomic volume change of 18.9 % for the as-irradiated amorphous layer relative to the virgin single crystal GaN. This relative swelling of the damaged layer reduces to 7.7 % after thermal annealing. Partial recrystallization and structural relaxation of the GaN amorphous state are believed responsible for the volume change.

  20. 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.

  1. Ultrathin GaN quantum disk nanowire LEDs with sub-250 nm electroluminescence

    SciTech Connect

    Chisholm, Matthew F.; Golam Sarwar, A. T. M.; Myers, Roberto C.; Mays, Brelon J.; Duscher, Gerd J.

    2016-03-18

    By quantum confining GaN at monolayer thickness with AlN barriers inside of a nanowire, deep ultraviolet LEDs are demonstrated. Full three-dimensional strain dependent energy band simulations are carried out within multiple quantum disk (MQD) GaN/AlN nanowire superlattice heterostructures. It is found that, even within the same nanowire MQD, the emission energy of the ultrathin GaN QDs varies from disk to disk due to the changing strain distribution and polarization charge induced energy band bending along the axial nanowire direction. MQD heterostructures are grown by plasma-assisted molecular beam epitaxy to form self-assembled catalyst-free nanowires with 1 to 2 monolayer thick GaN insertions within an AlN matrix. Photoluminescence peaks are observed at 295 nm and 283 nm from the 2 ML and 1 ML thick MQD samples, respectively. Polarization-doped nanowire LEDs are grown incorporating 1 ML thick GaN MQD active regions from which we observe deep ultraviolet electroluminescence. As a result, the shortest LED wavelength peak observed is 240 nm and attributed to electron hole recombination within 1 ML thick GaN QDs.

  2. Ultrathin GaN quantum disk nanowire LEDs with sub-250 nm electroluminescence

    NASA Astrophysics Data System (ADS)

    Sarwar, A. T. M. Golam; May, Brelon J.; Chisholm, Matthew F.; Duscher, Gerd J.; Myers, Roberto C.

    2016-04-01

    By quantum confining GaN at monolayer thickness with AlN barriers inside of a nanowire, deep ultraviolet LEDs are demonstrated. Full three-dimensional strain dependent energy band simulations are carried out within multiple quantum disk (MQD) GaN/AlN nanowire superlattice heterostructures. It is found that, even within the same nanowire MQD, the emission energy of the ultrathin GaN QDs varies from disk to disk due to the changing strain distribution and polarization charge induced energy band bending along the axial nanowire direction. MQD heterostructures are grown by plasma-assisted molecular beam epitaxy to form self-assembled catalyst-free nanowires with 1 to 2 monolayer thick GaN insertions within an AlN matrix. Photoluminescence peaks are observed at 295 nm and 283 nm from the 2 ML and 1 ML thick MQD samples, respectively. Polarization-doped nanowire LEDs are grown incorporating 1 ML thick GaN MQD active regions from which we observe deep ultraviolet electroluminescence. The shortest LED wavelength peak observed is 240 nm and attributed to electron hole recombination within 1 ML thick GaN QDs.

  3. Ultrathin GaN quantum disk nanowire LEDs with sub-250 nm electroluminescence.

    PubMed

    Sarwar, A T M Golam; May, Brelon J; Chisholm, Matthew F; Duscher, Gerd J; Myers, Roberto C

    2016-04-21

    By quantum confining GaN at monolayer thickness with AlN barriers inside of a nanowire, deep ultraviolet LEDs are demonstrated. Full three-dimensional strain dependent energy band simulations are carried out within multiple quantum disk (MQD) GaN/AlN nanowire superlattice heterostructures. It is found that, even within the same nanowire MQD, the emission energy of the ultrathin GaN QDs varies from disk to disk due to the changing strain distribution and polarization charge induced energy band bending along the axial nanowire direction. MQD heterostructures are grown by plasma-assisted molecular beam epitaxy to form self-assembled catalyst-free nanowires with 1 to 2 monolayer thick GaN insertions within an AlN matrix. Photoluminescence peaks are observed at 295 nm and 283 nm from the 2 ML and 1 ML thick MQD samples, respectively. Polarization-doped nanowire LEDs are grown incorporating 1 ML thick GaN MQD active regions from which we observe deep ultraviolet electroluminescence. The shortest LED wavelength peak observed is 240 nm and attributed to electron hole recombination within 1 ML thick GaN QDs.

  4. Influence of growth temperature and temperature ramps on deep level defect incorporation in m-plane GaN

    SciTech Connect

    Armstrong, A. M.; Kelchner, K.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2013-12-02

    The dependence of deep level defect incorporation in m-plane GaN films grown by metal-organic chemical vapor deposition on bulk m-plane GaN substrates as a function of growth temperature (T{sub g}) and T{sub g} ramping method was investigated using deep level optical spectroscopy. Understanding the influence of T{sub g} on GaN deep level incorporation is important for InGaN/GaN multi-quantum well (MQW) light emitting diodes (LEDs) and laser diodes (LDs) because GaN quantum barrier (QB) layers are grown much colder than thin film GaN to accommodate InGaN QW growth. Deep level spectra of low T{sub g} (800 °C) GaN films grown under QB conditions were compared to deep level spectra of high T{sub g} (1150 °C) GaN. Reducing T{sub g}, increased the defect density significantly (>50×) through introduction of emergent deep level defects at 2.09 eV and 2.9 eV below the conduction band minimum. However, optimizing growth conditions during the temperature ramp when transitioning from high to low T{sub g} substantially reduced the density of these emergent deep levels by approximately 40%. The results suggest that it is important to consider the potential for non-radiative recombination in QBs of LED or LD active regions, and tailoring the transition from high T{sub g} GaN growth to active layer growth can mitigate such non-radiative channels.

  5. Container-Grown Longleaf Pine Seedling Quality

    Treesearch

    Mark J. Hainds; James P. Barnett

    2004-01-01

    This study examines the comparative hardiness of various classes or grades of container-grown longleaf pine (Pinus palustris Mill.) seedlings. Most container longleaf seedlings are grown in small ribbed containers averaging 5 to 7 cubic inches in volume and 3 to 6 inches in depth. Great variability is often exhibited in typical lots of container-...

  6. The effect of substrate on high-temperature annealing of GaN epilayers: Si versus sapphire

    SciTech Connect

    Pastor, D.; Cusco, R.; Artus, L.; Gonzalez-Diaz, G.; Iborra, E.; Jimenez, J.; Peiro, F.; Calleja, E.

    2006-08-15

    We have studied the effects of rapid thermal annealing at 1300 deg.C on GaN epilayers grown on AlN buffered Si(111) and on sapphire substrates. After annealing, the epilayers grown on Si display visible alterations with craterlike morphology scattered over the surface. The annealed GaN/Si layers were characterized by a range of experimental techniques: scanning electron microscopy, optical confocal imaging, energy dispersive x-ray microanalysis, Raman scattering, and cathodoluminescence. A substantial Si migration to the GaN epilayer was observed in the crater regions, where decomposition of GaN and formation of Si{sub 3}N{sub 4} crystallites as well as metallic Ga droplets and Si nanocrystals have occurred. The average diameter of the Si nanocrystals was estimated from Raman scattering to be around 3 nm. Such annealing effects, which are not observed in GaN grown on sapphire, are a significant issue for applications of GaN grown on Si(111) substrates when subsequent high-temperature processing is required.

  7. Characterization and density control of GaN nanodots on Si (111) by droplet epitaxy using plasma-assisted molecular beam epitaxy.

    PubMed

    Yu, Ing-Song; Chang, Chun-Pu; Yang, Chung-Pei; Lin, Chun-Ting; Ma, Yuan-Ron; Chen, Chun-Chi

    2014-01-01

    In this report, self-organized GaN nanodots have been grown on Si (111) by droplet epitaxy method, and their density can be controlled from 1.1 × 10(10) to 1.1 × 10(11) cm(-2) by various growth parameters, such as substrate temperatures for Ga droplet formation, the pre-nitridation treatment of Si substrate, the nitridation duration for GaN crystallization, and in situ annealing after GaN formation. Based on the characterization of in situ RHEED, we can observe the surface condition of Si and the formation of GaN nanodots on Si. The surface nitridaiton treatment at 600°C provides a-SiNx layer which makes higher density of GaN nanodots. Crystal GaN nanodots can be observed by the HRTEM. The surface composition of GaN nanodots can be analyzed by SPEM and μ-XPS with a synchrotron x-ray source. We can find GaN nanodots form by droplet epitaxy and then in situ annealing make higher-degree nitridation of GaN nanodots.

  8. Characterization and density control of GaN nanodots on Si (111) by droplet epitaxy using plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yu, Ing-Song; Chang, Chun-Pu; Yang, Chung-Pei; Lin, Chun-Ting; Ma, Yuan-Ron; Chen, Chun-Chi

    2014-12-01

    In this report, self-organized GaN nanodots have been grown on Si (111) by droplet epitaxy method, and their density can be controlled from 1.1 × 1010 to 1.1 × 1011 cm-2 by various growth parameters, such as substrate temperatures for Ga droplet formation, the pre-nitridation treatment of Si substrate, the nitridation duration for GaN crystallization, and in situ annealing after GaN formation. Based on the characterization of in situ RHEED, we can observe the surface condition of Si and the formation of GaN nanodots on Si. The surface nitridaiton treatment at 600°C provides a-SiNx layer which makes higher density of GaN nanodots. Crystal GaN nanodots can be observed by the HRTEM. The surface composition of GaN nanodots can be analyzed by SPEM and μ-XPS with a synchrotron x-ray source. We can find GaN nanodots form by droplet epitaxy and then in situ annealing make higher-degree nitridation of GaN nanodots.

  9. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    SciTech Connect

    McSkimming, Brian M. 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, 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.

  10. Influence of dopants on defect formation in GaN

    SciTech Connect

    Liliental-Weber, Z.; Jasinski, J.; Benamara, M.; Grzegory, I.; Porowski, S.; Lampert, D.J.H.; Eiting, C.J.; Dupuis R.D.

    2001-10-15

    Influence of p-dopants (Mg and Be) on the structure of GaN has been studied using Transmission Electron Microscopy (TEM). Bulk GaN:Mg and GaN:Be crystals grown by a high pressure and high temperature process and GaN:Mg grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. Structural dependence on growth polarity was observed in the bulk crystals. Spontaneous ordering in bulk GaN:Mg on c-plane (formation of Mg-rich planar defects with characteristics of inversion domains) was observed for growth in the N to Ga polar direction (N polarity). On the opposite site of the crystal (growth in the Ga to N polar direction) Mg-rich pyramidal defects empty inside (pinholes) were observed. Both these defects were also observed in MOCVD grown crystals. Pyramidal defects were also observed in the bulk GaN:Be crystals.

  11. Structural defects in bulk GaN

    NASA Astrophysics Data System (ADS)

    Liliental-Weber, Z.; dos Reis, R.; Mancuso, M.; Song, C. Y.; Grzegory, I.; Porowski, S.; Bockowski, M.

    2014-10-01

    Transmission Electron Microscopy (TEM) studies of undoped and Mg doped GaN layers grown on the HVPE substrates by High Nitrogen Pressure Solution (HNPS) with the multi-feed-seed (MFS) configuration are shown. The propagation of dislocations from the HVPE substrate to the layer is observed. Due to the interaction between these dislocations in the thick layers much lower density of these defects is observed in the upper part of the HNPS layers. Amorphous Ga precipitates with attached voids pointing toward the growth direction are observed in the undoped layer. This is similar to the presence of Ga precipitates in high-pressure platelets, however the shape of these precipitates is different. The Mg doped layers do not show Ga precipitates, but MgO rectangular precipitates are formed, decorating the dislocations. Results of TEM studies of HVPE layers grown on Ammonothermal substrates are also presented. These layers have superior crystal quality in comparison to the HNPS layers, as far as density of dislocation is concern. Occasionally some small inclusions can be found, but their chemical composition was not yet determined. It is expected that growth of the HNPS layers on these substrate will lead to large layer thickness obtained in a short time and with high crystal perfection needed in devices.

  12. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs

    PubMed Central

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-01-01

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors. PMID:26329829

  13. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

    PubMed

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-09-02

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

  14. High Quality, Low Cost Ammonothermal Bulk GaN Substrates

    SciTech Connect

    Ehrentraut, D; Pakalapati, RT; Kamber, DS; Jiang, WK; Pocius, DW; Downey, BC; McLaurin, M; D'Evelyn, MP

    2013-12-18

    Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5-3 mm. The highest growth rates are greater than 40 mu m/h and rates in the 10-30 mu m/h range are routinely observed for all orientations. These values are 5-100x larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20-100 arcsec and dislocation densities of 1 x 10(5)-5 x 10(6) cm(-2). Dislocation densities below 10(4) cm(-2) are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers. (C) 2013 The Japan Society of Applied Physics

  15. Surface-Effect-Induced Optical Bandgap Shrinkage in GaN Nanotubes.

    PubMed

    Park, Young S; Lee, Geunsik; Holmes, Mark J; Chan, Christopher C S; Reid, Benjamin P L; Alexander-Webber, Jack A; Nicholas, Robin J; Taylor, Robert A; Kim, Kwang S; Han, Sang W; Yang, Woochul; Jo, Y; Kim, J; Im, Hyunsik

    2015-07-08

    We investigate nontrivial surface effects on the optical properties of self-assembled crystalline GaN nanotubes grown on Si substrates. The excitonic emission is observed to redshift by ∼100 meV with respect to that of bulk GaN. We find that the conduction band edge is mainly dominated by surface atoms, and that a larger number of surface atoms for the tube is likely to increase the bandwidth, thus reducing the optical bandgap. The experimental findings can have important impacts in the understanding of the role of surfaces in nanostructured semiconductors with an enhanced surface/volume ratio.

  16. Eliminating stacking faults in semi-polar GaN by AlN interlayers

    SciTech Connect

    Dadgar, A.; Ravash, R.; Veit, P.; Schmidt, G.; Mueller, M.; Dempewolf, A.; Bertram, F.; Wieneke, M.; Christen, J.; Krost, A.

    2011-07-11

    We report on the elimination of stacking faults by the insertion of low-temperature AlN interlayers in nearly (1016) and (1104) oriented semi-polar GaN grown by metalorganic vapor phase epitaxy on Si(112) and Si(113), respectively. The elimination of these defects is visualized by cathodoluminescence (CL) as well as scanning transmission electron microscopy (STEM) and STEM-CL. A possible annihilation mechanism is discussed which leads to the conclusion that the elimination mechanism is most likely valid for all layers with (1101) surfaces, enabling heteroepitaxial semi- and non-polar GaN free from stacking faults.

  17. Determination of satellite valley position in GaN emitter from photoexcited field emission investigations

    NASA Astrophysics Data System (ADS)

    Semenenko, M.; Yilmazoglu, O.; Hartnagel, H. L.; Pavlidis, D.

    2011-01-01

    Argon plasma etched GaN field-emitter rods with nanometer-scale diameter were fabricated on GaN grown on an n+-GaN substrate. Their electron field emission properties were investigated both without and under illumination by using light sources with various wavelengths. The Fowler-Nordheim current-voltage characteristics of the cathodes show a change in slope for illuminated cathodes. The electron affinity difference ΔE between the different valleys in the conduction band has been ascertained and is in the range from 1.18 up to 1.21 eV.

  18. 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.

  19. 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.

  20. Low temperature thin film transistors with hollow cathode plasma-assisted atomic layer deposition based GaN channels

    SciTech Connect

    Bolat, S. E-mail: aokyay@ee.bilkent.edu.tr; Tekcan, B.; Ozgit-Akgun, C.; Biyikli, N.; Okyay, A. K. E-mail: aokyay@ee.bilkent.edu.tr

    2014-06-16

    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 temperature reported for GaN based transistors, so far.

  1. Fabrication of well-aligned ZnO nanorods by hydrothermal process using GaN epitaxial layer

    NASA Astrophysics Data System (ADS)

    Jang, Jae-Min; Yi, Sung-Hak; Choi, Seung-Kyu; Kim, Jung-A.; Jung, Woo-Gwang

    2007-02-01

    One dimensional (1-D) ZnO nanorod structure of hexagonal shape was fabricated on epitaxial GaN layer by hydrothermal method. The growth of GaN epitaxial layer was carried out in a two-flow horizontal MOCVD reactor maintained at a pressure of 200 torr. Firstly, a 25 nm thick GaN buffer layer was grown at 520 °C. Then 2~3μm thick GaN epilayer was deposited at 1070 °C. Trimethylgallium (TMG) and NH 3 were used as Ga and N source, and H II gas was used as carrier gas. After the deposition of GaN epilayer thin-film, single crystalline ZnO nanorod was fabricated in aqueous solution. XRD and FE-SEM results showed ZnO nanorod arrays were oriented highly along the (002) plane. The ZnO nanorod was analyzed to have good quality crystallization by FE-TEM. The SAED pattern has shown that ZnO nanorod was grown in the direction along (002)-plane. Photoluminescence (PL) has shown that the GaN-ZnO hetero-structure has shown ultra-violet lasing action at room temperature. Narrow and strong ultra-violet peak was observed in comparison with PL result from epitaxial GaN layer. The analysis results have proved that aqueous solution growth method developed in the present work can be a good application for optical electronic device.

  2. Radiation enhanced basal plane dislocation glide in GaN

    NASA Astrophysics Data System (ADS)

    Yakimov, Eugene B.; Vergeles, Pavel S.; Polyakov, Alexander Y.; Lee, In-Hwan; Pearton, Stephen J.

    2016-05-01

    A movement of basal plane segments of dislocations in GaN films grown by epitaxial lateral overgrowth under low energy electron beam irradiation (LEEBI) was studied by the electron beam induced current (EBIC) method. Only a small fraction of the basal plane dislocation segments were susceptible to irradiation and the movement was limited to relatively short distances. The effect is explained by the radiation enhanced dislocation glide (REDG) in the structure with strong pinning. A dislocation velocity under LEEBI with a beam current lower than 1 nA was estimated as about 10 nm/s. The results assuming the REDG for prismatic plane dislocations were presented.

  3. Field emission from quantum size GaN structures

    NASA Astrophysics Data System (ADS)

    Yilmazoglu, O.; Pavlidis, D.; Litvin, Yu. M.; Hubbard, S.; Tiginyanu, I. M.; Mutamba, K.; Hartnagel, H. L.; Litovchenko, V. G.; Evtukh, A.

    2003-12-01

    Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2×10 17 or 3×10 18 cm -3) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/μm and the appearance of quantum-size effect in the I- V curves.

  4. Surface studies of gallium nitride quantum dots grown using droplet epitaxy on bulk, native substrates

    NASA Astrophysics Data System (ADS)

    Jones, Christina; Jeon, Sunyeol; Goldman, Rachel; Yacoby, Yizhak; Clarke, Roy

    Gallium nitride (GaN) and its applications in light-emitting diodes play an integral part in efficient, solid-state lighting, as evidenced by its recognition in the 2014 Nobel prize in physics. In order to push this technology towards higher efficiency and reliability and lower cost, we must understand device growth on bulk GaN substrates, which have lower defect densities and strain than template GaN substrates grown on sapphire. In this work, we present our findings on the surface properties of GaN quantum dots (QDs) grown on commercial bulk GaN. QDs are grown using the droplet epitaxy method and analyzed using a surface X-ray diffraction technique called Coherent Bragg Rod Analysis (COBRA), which uses phase retrieval to reconstruct atomic positions near the substrate surface. While several QD growth conditions in our study produce dense QDs, COBRA reveals that only low nitridation temperatures result in GaN QDs that are coherent with the bulk GaN substrate. Results are supported with atomic force microscopy and high-resolution transmission electron microscopy.

  5. MgCaO Dry Etching on GaN

    NASA Astrophysics Data System (ADS)

    Hlad, M.; Ren, F.

    2005-11-01

    MgCaO films grown by rf plasma-assisted Molecular Beam Epitaxy and capped with Sc2O3 are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs) respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively Coupled Plasmas of CH4/H2/Ar produced etch rates only in the range 20-70 å/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (˜100 å/min) were obtained with Cl2/Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH4/H2/Ar plasma chemistry produced a selectivity of around 2 or etching the MgCaO with respect to GaN.

  6. Theoretical and Experiment Study of Cathodoluminescence of GaN

    NASA Astrophysics Data System (ADS)

    Ben Nasr, F.; Matoussi, A.; Salh, R.; Boufaden, T.; Guermazi, S.; Fitting, H.-J.; Eljani, B.; Fakhfakh, Z.

    2007-09-01

    In this work, we report the theoretical and experimental results of cathodoluminescence (CL) from GaN layers with thickness (1-3) micron grown at 800 °C by MOVPE on silicon substrate. The CL measurements were performed in a digital scanning electron microscope DSM 960 at room temperature. The CL spectra recorded at room temperature (RT) show the main UV peak at 3.42 eV of the fundamental transition and a broad yellow band at 2.2 eV attributed the intrinsic defects and extrinsic dopants and impurities. The simulation of the CL excitation and intensity is developed using consistent 2-D model based on the electron beam energy dissipation and taking into account the effects of carrier diffusion, internal absorption and the recombination processes in GaN. Then, we have investigated the evolution of the CL intensity from GaN as a function the electron beam energy in the range Eo = (5-20) keV. A comparative study between experimental and simulated CL spectra at room temperature is presented.

  7. Low-temperature growth of AlN and GaN by metal organic vapor phase epitaxy for polarization engineered water splitting photocathode

    NASA Astrophysics Data System (ADS)

    Nakamura, Akihiro; Suzuki, Michihiro; Fujii, Katsushi; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-04-01

    Crystal properties of low-temperature grown AlN (LT-AlN) combined with low temperature GaN (LT-GaN) grown by metal organic vapor phase epitaxy (MOVPE) were investigated to obtain a high quality GaN/AlN/GaN structure with a few-nm-thick AlN layer. LT-AlN suppresses unintentional Ga incorporation and can be pseudomorphically grown on GaN with a relatively smooth surface morphology. The lattice of LT-AlN coherent to GaN, however, was found to relax after reactor conditions were changed to grow the subsequent GaN layer at higher temperature. The top GaN layer grown on the relaxed LT-AlN, thus, exhibited a rough surface morphology and a threading dislocation density (TDD) higher than 109 cm-2 estimated from an X-ray diffraction measurement. An LT-GaN capping layer was found to be highly effective for avoiding such lattice relaxation of LT-AlN. The combination of LT-AlN and LT-GaN enables us to obtain a GaN/AlN/GaN junction with high Al content, a low TDD, and abrupt interfaces. As a result, introducing an LT-GaN layer improved the photoelectrochemical (PEC) property of a polarization engineered un-doped GaN/AlN/n-type GaN (u-GaN/AlN/n-GaN) photocathode for water splitting.

  8. Step-flow growth mode instability of N-polar GaN under N-excess

    SciTech Connect

    Chèze, C.

    2013-08-12

    GaN layers were grown on N-polar GaN substrates by plasma-assisted molecular beam epitaxy under different III/V ratios. Ga-rich conditions assure step-flow growth with atomically flat surface covered by doubly-bunched steps, as for Ga-polar GaN. Growth under N-excess however leads to an unstable step-flow morphology. Particularly, for substrates slightly miscut towards <1010>, interlacing fingers are covered by atomic steps pinned on both sides by small hexagonal pits. In contrast, a three-dimensional island morphology is observed on the Ga-polar equivalent sample. We attribute this result to lower diffusion barriers on N-polar compared to Ga-polar GaN under N-rich conditions.

  9. Spectroscopic study of semipolar (112{sup ¯}2)-HVPE GaN exhibiting high oxygen incorporation

    SciTech Connect

    Schustek, Philipp; Hocker, Matthias; Thonke, Klaus; Klein, Martin; Scholz, Ferdinand; Simon, Ulrich

    2014-10-28

    Spatially resolved luminescence and Raman spectroscopy investigations are applied to a series of (112{sup ¯}2)-GaN samples grown by hydride vapor phase epitaxy (HVPE) grown over an initial layer deposited by metal organic vapor phase epitaxy on patterned sapphire substrates. Whereas these two differently grown GaN layers are crystallographically homogeneous, they differ largely in their doping level due to high unintentional oxygen uptake in the HVPE layer. This high doping shows up in luminescence spectra, which can be explained by a free-electron recombination band for which an analytical model considering the Burstein-Moss shift, conduction band tailing, and the bandgap renormalization is included. Secondary ion mass spectrometry, Raman spectroscopy, and Hall measurements concordantly determine the electron density to be above 10{sup 19 }cm{sup −3}. In addition, the strain state is assessed by Raman spectroscopy and compared to a finite element analysis.

  10. 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

    2017-08-21

    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.

  11. Growth and characterizations of GaN micro-rods on graphene films for flexible light emitting diodes

    SciTech Connect

    Chung, Kunook; Beak, Hyeonjun; Tchoe, Youngbin; Oh, Hongseok; Yi, Gyu-Chul; Yoo, Hyobin; Kim, Miyoung

    2014-09-01

    We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto SiO{sub 2}/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metal–organic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance light-emitting diodes (LEDs), were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, In{sub x}Ga{sub 1–x}N/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation.

  12. Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

    NASA Astrophysics Data System (ADS)

    Calabrese, Gabriele; Corfdir, Pierre; Gao, Guanhui; Pfüller, Carsten; Trampert, Achim; Brandt, Oliver; Geelhaar, Lutz; Fernández-Garrido, Sergio

    2016-05-01

    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 pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.

  13. Development of semipolar (11-22) LEDs on GaN templates

    NASA Astrophysics Data System (ADS)

    Corbett, B.; Quan, Z.; Dinh, D. V.; Kozlowski, G.; O'Mahony, D.; Akhter, M.; Schulz, S.; Parbrook, P.; Maaskant, P.; Caliebe, M.; Hocker, M.; Thonke, K.; Scholz, F.; Pristovsek, M.; Han, Y.; Humphreys, C. J.; Brunner, F.; Weyers, M.; Meyer, T. M.; Lymperakis, L.

    2016-03-01

    We report on blue and green light-emitting-diodes (LEDs) grown on (11-22)-GaN templates. The templates were created by overgrowth on structured r-plane sapphire substrates. Low defect density, 100 mm diameter GaN templates were obtained by metal organic vapour phase epitaxy (VPE) and hydride VPE techniques. Chemical-mechanical polishing was used to obtain smooth surfaces for the subsequent growth of LED structures. Ohmic contacts to the p-type GaN were obtained despite the lower activated acceptor levels. The LEDs show excellent output power and fast carrier dynamics. Freestanding LEDs have been obtained by use of laser-lift-off. The work is the result of collaboration under the European Union funded ALIGHT project.

  14. Room-Temperature Transport of Indirect Excitons in (Al ,Ga )N /GaN Quantum Wells

    NASA Astrophysics Data System (ADS)

    Fedichkin, F.; Guillet, T.; Valvin, P.; Jouault, B.; Brimont, C.; Bretagnon, T.; Lahourcade, L.; Grandjean, N.; Lefebvre, P.; Vladimirova, M.

    2016-07-01

    We report on the exciton propagation in polar (Al ,Ga )N /GaN quantum wells over several micrometers and up to room temperature. The key ingredient to achieve this result is the crystalline quality of GaN quantum wells grown on GaN substrate that limits nonradiative recombination. From the comparison of the spatial and temporal dynamics of photoluminescence, we conclude that the propagation of excitons under continuous-wave excitation is assisted by efficient screening of the in-plane disorder. Modeling within drift-diffusion formalism corroborates this conclusion and suggests that exciton propagation is still limited by the exciton scattering on defects rather than by exciton-exciton scattering so that improving interface quality can boost exciton transport further. Our results pave the way towards room-temperature excitonic devices based on gate-controlled exciton transport in wide-band-gap polar heterostructures.

  15. Microstructure of GaN epitaxy on SiC using AlN buffer layers

    SciTech Connect

    Ponce, F.A.; Krusor, B.S.; Major, J.S. Jr.; Plano, W.E.; Welch, D.F.

    1995-07-17

    The crystalline structure of GaN epilayers on (0001) SiC substrates has been studied using x-ray diffraction and transmission microscopy. The films were grown by metalorganic chemical vapor deposition, using AlN buffer layers. X-ray diffraction measurements show negligible strain in the epilayer, and a long-range variation in orientation. Transmission electron lattice images show that the AlN buffer layer consists of small crystallites. The nature of the buffer layer and its interfaces with the substrate and the GaN film is discussed. The defect structure of the GaN film away from the substrate consists mostly of threading dislocations with a density of {similar_to}10{sup 9} cm{sup {minus}2}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  16. 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.

  17. Epitaxial Growth of GaN Nanowires with High Structural Perfection on a Metallic TiN Film.

    PubMed

    Wölz, M; Hauswald, C; Flissikowski, T; Gotschke, T; Fernández-Garrido, S; Brandt, O; Grahn, H T; Geelhaar, L; Riechert, H

    2015-06-10

    Vertical GaN nanowires are grown in a self-induced way on a sputtered Ti film by plasma-assisted molecular beam epitaxy. Both in situ electron diffraction and ex situ ellipsometry show that Ti is converted to TiN upon exposure of the surface to the N plasma. In addition, the ellipsometric data demonstrate this TiN film to be metallic. The diffraction data evidence that the GaN nanowires have a strict epitaxial relationship to this film. Photoluminescence spectroscopy of the GaN nanowires shows excitonic transitions virtually identical in spectral position, line width, and decay time to those of state-of-the-art GaN nanowires grown on Si. Therefore, the crystalline quality of the GaN nanowires grown on metallic TiN and on Si is equivalent. The freedom to employ metallic substrates for the epitaxial growth of semiconductor nanowires in high structural quality may enable novel applications that benefit from the associated high thermal and electrical conductivity as well as optical reflectivity.

  18. Analysis of reactor geometry and diluent gas flow effects on the metalorganic vapor phase epitaxy of AIN and GaN thin films on α(6H)-SiC substrates

    NASA Astrophysics Data System (ADS)

    Hanser, A. D.; Wolden, C. A.; Perry, W. G.; Zheleva, T.; Carlson, E. P.; Banks, A. D.; Therrien, R. J.; Davis, R. F.

    1998-04-01

    The influence of diluent gas on the metalorganic vapor phase epitaxy of AlN and GaN thin films has been investigated. A computational fluid dynamics model using the finite element method was employed to improve film uniformity and to analyze transport phenomena. The properties of AlN and GaN thin films grown on α(6H)-SiC(0001) substrates in H2 and N2 diluent gas environments were evaluated. Thin films of AlN grown in H2 and N2 had root mean square (rms) roughness values of 1.5 and 1.8 nm, respectively. The surface and defect microstructures of the GaN thin films, observed by scanning and transmission electron microscopy, respectively, were very similar for both diluents. Low temperature (12K) photoluminescence measurements of GaN films grown in N2 had peak intensities and full widths at half maximum equal to or better than those films grown in H2. A room temperature Hall mobility of 275 cm2/V·s was measured on 1 µm thick, Si-doped, n-type (1×1017 cm-3) GaN films grown in N2. Acceptor-type behavior of Mg-doped GaN films deposited in N2 was repeatably obtained without post-growth annealing, in contrast to similar films grown in H2. The GaN growth rates were ˜30% higher when H2 was used as the diluent. The measured differences in the growth rates of AlN and GaN films in H2 and N2 was attributed to the different transport properties of these mixtures, and agreed well with the computer model predictions. Nitrogen is shown to be a feasible alternative diluent to hydrogen for the growth of AlN and GaN thin films.

  19. Piezo-generator integrating a vertical array of GaN nanowires.

    PubMed

    Jamond, N; Chrétien, P; Houzé, F; Lu, L; Largeau, L; Maugain, O; Travers, L; Harmand, J C; Glas, F; Lefeuvre, E; Tchernycheva, M; Gogneau, N

    2016-08-12

    We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ∼12.7 mW cm(-3). This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

  20. Piezo-generator integrating a vertical array of GaN nanowires

    NASA Astrophysics Data System (ADS)

    Jamond, N.; Chrétien, P.; Houzé, F.; Lu, L.; Largeau, L.; Maugain, O.; Travers, L.; Harmand, J. C.; Glas, F.; Lefeuvre, E.; Tchernycheva, M.; Gogneau, N.

    2016-08-01

    We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ˜12.7 mW cm-3. This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

  1. Nanowire LEDs grown directly on flexible metal foil

    SciTech Connect

    May, Brelon J.; Sarwar, A. T. M. Golam; Myers, Roberto C.

    2016-04-04

    Using molecular beam epitaxy, self-assembled AlGaN nanowires are grown directly on Ta and Ti foils. Scanning electron microscopy shows that the nanowires are locally textured with the underlying metallic grains. Photoluminescence spectra of GaN nanowires grown on metal foils are comparable to GaN nanowires grown on single crystal Si wafers. Similarly, photoluminescence lifetimes do not vary significantly between these samples. Operational AlGaN light emitting diodes are grown directly on flexible Ta foil with an electroluminescence peak emission of ∼350 nm and a turn-on voltage of ∼5 V. These results pave the way for roll-to-roll manufacturing of solid state optoelectronics.

  2. Highly ordered catalyst-free and mask-free GaN nanorods on r-plane sapphire.

    PubMed

    Aschenbrenner, T; Kruse, C; Kunert, G; Figge, S; Sebald, K; Kalden, J; Voss, T; Gutowski, J; Hommel, D

    2009-02-18

    Self-organized and highly ordered GaN nanorods were grown without catalyst on r-plane sapphire using a combination of molecular beam epitaxy and metal-organic vapor-phase epitaxy. AlN nucleation centers for the nanorods were prepared by nitridation of the sapphire in a metal-organic vapor-phase epitaxy reactor, while the nanorods were grown by molecular beam epitaxy. A coalesced two-dimensional GaN layer was observed between the nanorods. The nanorods are inclined by 62 degrees towards the [Formula: see text]-directions of the a-plane GaN layer. The high degree of ordering and the structural perfection were confirmed by micro-photoluminescence measurements.

  3. GaN nanowires with pentagon shape cross-section by ammonia-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lin, Yong; Leung, Benjamin; Li, Qiming; Figiel, Jeffrey. J.; Wang, George T.

    2015-10-01

    Ammonia-based molecular beam epitaxy (NH3-MBE) was used to grow catalyst-assisted GaN nanowires on (1 1 bar 02) r-plane sapphire substrates. Dislocation free [ 11 2 bar 0 ] oriented nanowires are formed with pentagon shape cross-section, instead of the usual triangular shape facet configuration. Specifically, the cross-section is the result of the additional two nonpolar { 10 1 bar 0 } side facets, which appear due to a decrease in relative growth rate of the { 10 1 bar 0 } facets to the { 10 1 bar 1 } and { 10 1 bar 1 } facets under the growth regime in NH3-MBE. Compared to GaN nanowires grown by Ni-catalyzed metal-organic chemical vapor deposition, the NH3-MBE grown GaN nanowires show more than an order of magnitude increase in band-edge to yellow luminescence intensity ratio, as measured by cathodoluminescence, indicating improved microstructural and optical properties.

  4. Effect of flux composition ratio on the coalescence growth of GaN crystals by the Na-flux method

    NASA Astrophysics Data System (ADS)

    Honjo, Masatomo; Imanishi, Masayuki; Imabayashi, Hiroki; Nakamura, Kosuke; Murakami, Kosuke; Matsuo, Daisuke; Maruyama, Mihoko; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke

    2017-03-01

    Previously, we demonstrated that the Na-flux coalescence growth technique had high potential for the fabrication of large-diameter, high-quality GaN crystals. This present study investigates the relation between the flux composition (Ga/Na) and void formation in GaN crystals grown by this technique. It was found that void formation decreases with a decrease in the Ga composition of the flux and that stable coalescence with no voids at the GaN grain boundaries occurred for a Ga composition of 15 mol%. Band-edge emission peaks were clearly observed for a crystal grown at 15 mol% Ga composition, while other peaks were hardly observed.

  5. Dielectrics for GaN based MIS-diodes

    SciTech Connect

    Ren, F.; Abernathy, C.R.; MacKenzie, J.D.

    1998-02-01

    GaN MIS diodes were demonstrated utilizing AlN and Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) as insulators. A 345 {angstrom} of AlN was grown on the MOCVD grown n-GaN in a MOMBE system using trimethylamine alane as Al precursor and nitrogen generated from a wavemat ECR N2 plasma. For the Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) growth, a multi MBE chamber was used and a 195 {angstrom} oxide is E-beam evaporated from a single crystal source of Ga{sub 5}Gd{sub 3}O{sub 12}. The forward breakdown voltage of AlN and Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) diodes are 5V and 6V, respectively, which are significantly improved from {approximately} 1.2 V of schottky contact. From the C-V measurements, both kinds of diodes showed good charge modulation from accumulation to depletion at different frequencies. The insulator GaN interface roughness and the thickness of the insulator were measured with x-ray reflectivity.

  6. Optical and Structural Properties of Microcrystalline GaN on an Amorphous Substrate Prepared by a Combination of Molecular Beam Epitaxy and Metal-Organic Chemical Vapor Deposition

    SciTech Connect

    Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu; Park, Kwangwook; Kim, Ci-Hyun; Lee, Dong-Seon; Jho, Young-Dahl; Bae, Si-Young; Lee, Yong-Tak

    2016-05-01

    Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

  7. Direct growth of GaN on off-oriented SiC (0001) by molecular-beam epitaxy for GaN/SiC heterojunction bipolar transistor

    NASA Astrophysics Data System (ADS)

    Nakano, Y.; Suda, J.; Kimoto, T.

    2005-05-01

    Direct growth of GaN on misoriented 4H- and 6H-SiC (0001) Si-face substrates and electrical characteristics of n-GaN/p-SiC heterojunction mesa diodes are presented. GaN was grown by molecular-beam epitaxy (MBE) using elemental Ga and rf plasma-excited active nitrogen. SiC substrates misoriented 8° toward the [11-20] direction were used in this study. The surfaces of MBE-grown GaN layers have wavy features with peak-to-valley height of 30 nm. These features originated from the substrate misorientation. It was found that step bunching and large faceting along [01-10] and [10-10] directions occurred during the growth of GaN. Lowering the growth temperature suppresses large faceting, and results in reduction of the peak-to-valley height to 3 nm. However, the surface still has the same undulating features (on a smaller length scale). Mesa diodes were fabricated from the grown GaN layers. The correlation between the diode electrical characteristics and GaN growth conditions is discussed.

  8. Optical and structural properties of microcrystalline GaN on an amorphous substrate prepared by a combination of molecular beam epitaxy and metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Min, Jung-Wook; Hwang, Hyeong-Yong; Kang, Eun-Kyu; Park, Kwangwook; Kim, Ci-Hyun; Lee, Dong-Seon; Jho, Young-Dahl; Bae, Si-Young; Lee, Yong-Tak

    2016-05-01

    Microscale platelet-shaped GaN grains were grown on amorphous substrates by a combined epitaxial growth method of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). First, MBE GaN was grown on an amorphous substrate as a pre-orienting layer and its structural properties were investigated. Second, MOCVD grown GaN samples using the different growth techniques of planar and selective area growth (SAG) were comparatively investigated by transmission electron microscopy (TEM), cathodoluminescence (CL), and photoluminescence (PL). In MOCVD planar GaN, strong bound exciton peaks dominated despite the high density of the threading dislocations (TDs). In MOCVD SAG GaN, on the other hand, TDs were clearly reduced with bending, but basal stacking fault (BSF) PL peaks were observed at 3.42 eV. The combined epitaxial method not only provides a deep understanding of the growth behavior but also suggests an alternative approach for the growth of GaN on amorphous substances.

  9. Fine structure of the red luminescence band in undoped GaN

    SciTech Connect

    Reshchikov, M. A.; Usikov, A.; Helava, H.; Makarov, Yu.

    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 RL 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.

  10. Hierarchical growth of GaN nanowires for light emitting diode applications

    NASA Astrophysics Data System (ADS)

    Raj, Rishabh; Ra, Yong-Ho; Lee, Cheul-Ro; Obheroi, Sonika; Navamathavan, R.

    2016-02-01

    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. In this study, we report on the hierarchical growth of GaN nanowires (NWs) by dynamically adjusting the growth parameters using pulsed flow metalorganic chemical vapor deposition (MOCVD) technique. We carried out two step growth processes to grow hierarchical GaN NWs. At the first step the GaN NWs were grown at 950°C and in the second stage, we suitably decreased the growth temperature to 710°C to grow the hierarchical structures. The surface morphology, structural and optical characterization of the grown hierarchical GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and photoluminescence (PL) measurements, respectively. These kind of hierarchical NWs are promising to allow flat band quantum structures that are shown to improve the efficiency of light-emitting diodes.

  11. Ultrathin GaN quantum disk nanowire LEDs with sub-250 nm electroluminescence

    DOE PAGES

    Chisholm, Matthew F.; Golam Sarwar, A. T. M.; Myers, Roberto C.; ...

    2016-03-18

    By quantum confining GaN at monolayer thickness with AlN barriers inside of a nanowire, deep ultraviolet LEDs are demonstrated. Full three-dimensional strain dependent energy band simulations are carried out within multiple quantum disk (MQD) GaN/AlN nanowire superlattice heterostructures. It is found that, even within the same nanowire MQD, the emission energy of the ultrathin GaN QDs varies from disk to disk due to the changing strain distribution and polarization charge induced energy band bending along the axial nanowire direction. MQD heterostructures are grown by plasma-assisted molecular beam epitaxy to form self-assembled catalyst-free nanowires with 1 to 2 monolayer thick GaNmore » insertions within an AlN matrix. Photoluminescence peaks are observed at 295 nm and 283 nm from the 2 ML and 1 ML thick MQD samples, respectively. Polarization-doped nanowire LEDs are grown incorporating 1 ML thick GaN MQD active regions from which we observe deep ultraviolet electroluminescence. As a result, the shortest LED wavelength peak observed is 240 nm and attributed to electron hole recombination within 1 ML thick GaN QDs.« less

  12. 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.

  13. GaN Device Processing

    SciTech Connect

    Pearton, S.J.; Ren, F.; Zolper, J.C.; Shul, R.J.

    1998-01-01

    Recent progress in the development of dry and wet etching techniques, implant doping and isolation, thermal processing, gate insulator technology and high reliability contacts is reviewed. Etch selectivities up to 10 for InN over AlN are possible in Inductively Coupled Plasmas using a Cl2/Ar chemistry, but in general selectivities for each binary nitride relative to each other are low ({lt} OR = 2) BECAUSE OF THE HIGH ION ENERGIES NEEDED TO INITIATE ETCHING. IMPROVED N-TYPE OHMIC CONTACT RESISTANCES ARE OBTAINED BY SELECTIVE AREA SI+ IMPLANTATION FOLLOWED BY VERY HIGH TEMPERATURE ({gt}1300 deg C) anneals in which the thermal budget is minimized and AlN encapsulation prevents GaN surface decomposition. Implant isolation is effective in GaN, AlGaN and AlInN, but marginal in InGaN. Candidate gate insulators for GaN include AlN, AlON and Ga(Gd)O(x), but interface state densities are still to high to realize state-of-the-art MIS devices.

  14. Surfactant-Enabled Epitaxy of Smooth, Cubic Oxides on Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Paisley, Elizabeth Aldret

    Epitaxial integration of polar oxides with polar semiconductors presents the possibility of tunable 2D charge carriers at polar interfaces and integration of non-linear dielectric properties if defect densities are low and interfaces are smooth. Achieving this in materials with highly dissimilar structure and symmetry remains a serious challenge and requires a dramatically improved understanding of chemically and structurally dissimilar interfaces and their synthesis. Current efforts to achieve such devices are impeded by the fact that many polar oxides have a close-packed cubic substructure that requires the oxide to grow along the {111} direction, which is compatible with hexagonal (0002) GaN. Since the {111} direction is not the lowest energy face for these oxides, conventional methods used to synthesize these oxides usually allow the interface to compensate by forming facets resulting in defects, detrimental to the sustaining interface conductivity. This thesis demonstrates a new methodology developed to allow in situ stabilization of desired crystallographic habits where water vapor is utilized during growth to hydroxylate the oxide (111) surfaces, changing the equilibrium habit from cubic to octahedral, eliminating the (100)-faceting tendency. Bulk thermodynamic calculations show that a hydroxide termination can stabilize the (111)-face. Further, Ca(OH)2 (the structure likely to represent such termination) provides a low-energy surface with six-fold symmetry and atomic registry matching {111}-CaO and GaN. Additionally, the relative free energies of formation for CaO and Ca(OH)2 provide an adequate processing window to avoid competition between oxide and hydroxide deposition. This approach is demonstrated for three model systems of rocksalt oxides grown along a polar direction on GaN: MgO, CaO, and lattice-matched compositions: Mg0.52Ca0.48O. MBE growth of smooth (111) CaO is demonstrated using RHEED intensity vs. time oscillations that show layer

  15. Tri-halide vapor phase epitaxy of thick GaN using gaseous GaCl3 precursor

    NASA Astrophysics Data System (ADS)

    Murakami, Hisashi; Takekawa, Nao; Shiono, Anna; Thieu, Quang Tu; Togashi, Rie; Kumagai, Yoshinao; Matsumoto, Koh; Koukitu, Akinori

    2016-12-01

    Tri-halide vapor phase epitaxy (THVPE) of thick GaN using GaCl3 was investigated for fabricating low-cost, high-crystalline-quality GaN substrates instead of the conventional manufacturing method of GaCl-based hydride vapor phase epitaxy (HVPE). The growth rate and upper growth temperature limit of GaN using THVPE were found to be much higher than those obtained using conventional HVPE under the same growth conditions. Drastic reduction in the number of dark spots measured by cathodoluminescence at room temperature was observed for the high-temperature-grown GaN layer on the (000-1) GaN/sapphire template due to the enhancement of precursor migration on the growing surface. It was found that the incorporation of impurities such as O, C, and Cl can be reduced even on the N-polarity GaN by increasing the growth temperature. The possibility of enlargement of the crystal diameter by growing the N-polarity GaN layer using THVPE was also proposed.

  16. Localized tip enhanced Raman spectroscopic study of impurity incorporated single GaN nanowire in the sub-diffraction limit

    SciTech Connect

    Patsha, Avinash E-mail: dhara@igcar.gov.in; Dhara, Sandip; Tyagi, A. K.

    2015-09-21

    The localized effect of impurities in single GaN nanowires in the sub-diffraction limit is reported using the study of lattice vibrational modes in the evanescent field of Au nanoparticle assisted tip enhanced Raman spectroscopy (TERS). GaN nanowires with the O impurity and the Mg dopants were grown by the chemical vapor deposition technique in the catalyst assisted vapor-liquid-solid process. Symmetry allowed Raman modes of wurtzite GaN are observed for undoped and doped nanowires. Unusually very strong intensity of the non-zone center zone boundary mode is observed for the TERS studies of both the undoped and the Mg doped GaN single nanowires. Surface optical mode of A{sub 1} symmetry is also observed for both the undoped and the Mg doped GaN samples. A strong coupling of longitudinal optical (LO) phonons with free electrons, however, is reported only in the O rich single nanowires with the asymmetric A{sub 1}(LO) mode. Study of the local vibration mode shows the presence of Mg as dopant in the single GaN nanowires.

  17. GaN High Power Devices

    SciTech Connect

    PEARTON,S.J.; REN,F.; ZHANG,A.P.; DANG,G.; CAO,X.A.; LEE,K.P.; CHO,H.; GILA,B.P.; JOHNSON,J.W.; MONIER,C.; ABERNATHY,C.R.; HAN,JUNG; BACA,ALBERT G.; CHYI,J.-I.; LEE,C.-M.; NEE,T.-E.; CHUO,C.-C.; CHI,G.C.; CHU,S.N.G.

    2000-07-17

    A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers, GaN/AlGaN heterojunction bipolar transistors, GaN heterostructure and metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

  18. Compensation in epitaxial cubic SiC films

    NASA Technical Reports Server (NTRS)

    Segall, B.; Alterovitz, S. A.; Haugland, E. J.; Matus, L. G.

    1986-01-01

    Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC.

  19. Low dislocation GaN via defect-filtering, self-assembled SiO2-sphere layers.

    SciTech Connect

    Wang, George T.; Li, Qiming

    2009-09-01

    The III-nitride (AlGaInN) materials system forms the foundation for white solid-state lighting, the adoption of which could significantly reduce U.S. energy needs. While the growth of GaN-based devices relies on heteroepitaxy on foreign substrates, the heteroepitaxial layers possess a high density of dislocations due to poor lattice and thermal expansion match. These high dislocation densities have been correlated with reduced internal quantum efficiency and lifetimes for GaN-based LEDs. Here, we demonstrate an inexpensive method for dislocation reduction in GaN grown on sapphire and silicon substrates. This technique, which requires no lithographic patterning, GaN is selectively grown through self-assembled layers of silica microspheres which act to filter out dislocations. Using this method, the threading dislocation density for GaN on sapphire was reduced from 3.3 x 10{sup 9} cm{sup -2} to 4.0 x 10{sup 7} cm{sup -2}, and from the 10{sup 10} cm{sup -2} range to {approx}6.0 x 10{sup 7} cm{sup -2} for GaN on Si(111). This large reduction in dislocation density is attributed to a dislocation blocking and bending by the unique interface between GaN and silica microspheres.

  20. Surface state of GaN after rapid-thermal-annealing using AlN cap-layer

    NASA Astrophysics Data System (ADS)

    El-Zammar, G.; Khalfaoui, W.; Oheix, T.; Yvon, A.; Collard, E.; Cayrel, F.; Alquier, D.

    2015-11-01

    Critical issues need to be overcome to produce high performance Schottky diodes on gallium nitride (GaN). To activate dopant, high temperature thermal treatments are required but damage GaN surface where hexagonal pits appear and prevent any device processing. In this paper, we investigated the efficiency of cap-layers on GaN during thermal treatments to avoid degradation. Aluminum nitride (AlN) and silicon oxide (SiOx) were grown on GaN by direct current reactive magnetron sputtering and plasma-enhanced chemical vapor deposition, respectively. AlN growth parameters were studied to understand their effect on the grown layers and their protection efficiency. Focused ion beam was used to measure AlN layer thickness. Crystalline quality and exact composition were verified using X-ray diffraction and energy dispersive X-ray spectroscopy. Two types of rapid thermal annealing at high temperatures were investigated. Surface roughness and pits density were evaluated using atomic force microscopy and scanning electron microscopy. Cap-layers wet etching was processed in H3PO4 at 120 °C for AlN and in HF (10%) for SiOx. This work reveals effective protection of GaN during thermal treatments at temperatures as high as 1150 °C. Low surface roughness was obtained. Furthermore, no hexagonal pit was observed on the surface.