Science.gov

Sample records for high quality gan

  1. Growth of high quality GaN layer on carbon nanotube-graphene network structure as intermediate layer

    NASA Astrophysics Data System (ADS)

    Seo, Taeo Hoon; Park, Ah Hyun; Park, Sungchan; Kim, Myung Jong; Suh, Eun-Kyung

    2015-03-01

    In general, high-quality GaN layers are synthesized on low-temperature (LT) GaN buffer layer on a single crystal sapphire substrate. However, large differences in fundamental properties such as lattice constants and thermal expansion coefficients between GaN layer and sapphire substrate generate high density of threading dislocation (TD) that leads to deterioration of optical and structural properties. Graphene has been attracting much attention due to its excellent physical properties However, direct epitaxial growth of GaN film onto graphene layer on substrates is not easily accessible due to the lack of chemical reactivity on graphene which consisted of C-C bond of sp2 hexagonally arranged carbon atoms with no dangling bonds. In this work, an intermediate layer for the GaN growth on sapphire substrate was constructed by inserting carbon nanotubes and graphene hybrid structure (CGH) Optical and structural properties of GaN layer grown on CGH were compared with those of GaN layer directly grown on sapphire CNTs act as nucleation sites and play a crucial role in the growth of single crystal high-quality GaN on graphene layer. Also, graphene film acts as a mask for epitaxial lateral overgrowth of GaN layer, which can effectively reduce TD density. A grant from the Korea Institute of Science and Technology (KIST) institutional program.

  2. 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

  3. HVPE homoepitaxial growth of high quality bulk GaN using acid wet etching method and its mechanism analysis

    NASA Astrophysics Data System (ADS)

    Liu, Nanliu; Cheng, Yutian; Wu, Jiejun; Li, Xingbin; Yu, Tongjun; Xiong, Huan; Li, Wenhui; Chen, Jiao; Zhang, Guoyi

    2016-11-01

    In this paper, crack-free 2-inch bulk GaN wafer with the thickness up to 3 mm was obtained by HVPE homoepitaxy. A new method of acid wet etching was used to pre-treat GaN substrate before re-growth. The formation of the mesh-like subsurface crack and interface layer were found to be suppressed between the re-growth layer and as-grown GaN substrate. EDS and time varied contact angle measurement proved that chemical etching would decrease the oxygen related surface adsorption and increase atoms diffusion length during HVPE homoepitaxial growth. Moreover, Morphology, Low temperature photoluminescence measurements indicated a reduction in stress of wet etching treated as-grown GaN substrate due to etching effect on its N face. High quality bulk GaN with the dislocation density of 1×106 cm-2 was achieved by using wet etching and HVPE multiple re-growth. It would offer a simple method to obtain bulk GaN with thicker layer and high quality.

  4. 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.

  5. 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

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

    PubMed

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

    2016-04-22

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

  7. Grouped and Multistep Nanoheteroepitaxy: Toward High-Quality GaN on Quasi-Periodic Nano-Mask.

    PubMed

    Feng, Xiaohui; Yu, Tongjun; Wei, Yang; Ji, Cheng; Cheng, Yutian; Zong, Hua; Wang, Kun; Yang, Zhijian; Kang, Xiangning; Zhang, Guoyi; Fan, Shoushan

    2016-07-20

    A novel nanoheteroepitaxy method, namely, the grouped and multistep nanoheteroepitaxy (GM-NHE), is proposed to attain a high-quality gallium nitride (GaN) epilayer by metal-organic vapor phase epitaxy. This method combines the effects of sub-100 nm nucleation and multistep lateral growth by using a low-cost but unique carbon nanotube mask, which consists of nanoscale growth windows with a quasi-periodic 2D fill factor. It is found that GM-NHE can facilely reduce threading dislocation density (TDD) and modulate residual stress on foreign substrate without any regrowth. As a result, high-quality GaN epilayer is produced with homogeneously low TDD of 4.51 × 10(7) cm(-2) and 2D-modulated stress, and the performance of the subsequent 410 nm near-ultraviolet light-emitting diode is greatly boosted. In this way, with the facile fabrication of nanomask and the one-off epitaxy procedure, GaN epilayer is prominently improved with the assistance of nanotechnology, which demonstrates great application potential for high-efficiency TDD-sensitive optoelectronic and electronic devices. PMID:27351723

  8. Grouped and Multistep Nanoheteroepitaxy: Toward High-Quality GaN on Quasi-Periodic Nano-Mask.

    PubMed

    Feng, Xiaohui; Yu, Tongjun; Wei, Yang; Ji, Cheng; Cheng, Yutian; Zong, Hua; Wang, Kun; Yang, Zhijian; Kang, Xiangning; Zhang, Guoyi; Fan, Shoushan

    2016-07-20

    A novel nanoheteroepitaxy method, namely, the grouped and multistep nanoheteroepitaxy (GM-NHE), is proposed to attain a high-quality gallium nitride (GaN) epilayer by metal-organic vapor phase epitaxy. This method combines the effects of sub-100 nm nucleation and multistep lateral growth by using a low-cost but unique carbon nanotube mask, which consists of nanoscale growth windows with a quasi-periodic 2D fill factor. It is found that GM-NHE can facilely reduce threading dislocation density (TDD) and modulate residual stress on foreign substrate without any regrowth. As a result, high-quality GaN epilayer is produced with homogeneously low TDD of 4.51 × 10(7) cm(-2) and 2D-modulated stress, and the performance of the subsequent 410 nm near-ultraviolet light-emitting diode is greatly boosted. In this way, with the facile fabrication of nanomask and the one-off epitaxy procedure, GaN epilayer is prominently improved with the assistance of nanotechnology, which demonstrates great application potential for high-efficiency TDD-sensitive optoelectronic and electronic devices.

  9. GaN Electronics For High Power, High Temperature Applications

    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.; CHU,S.N.G.

    2000-06-12

    A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers. GaN/AlGaN heterojunction bipolar transistors and GaN metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

  10. Fabrication of high-quality \\{11\\bar{2}2\\} GaN substrates using the Na flux method

    NASA Astrophysics Data System (ADS)

    Maruyama, Mihoko; Nakamura, Koshi; Che, Songbek; Murakami, Kosuke; Takazawa, Hideo; Imanishi, Masayuki; Imade, Mamoru; Morita, Yukihiro; Mori, Yusuke

    2016-05-01

    Gallium nitride (GaN) substrates fabricated along the nonpolar and semipolar directions are the most promising materials for realizing optical and electronic devices with low power consumption. In this study, we carry out the Na flux growth on \\{ 11\\bar{2}2\\} -plane GaN templates grown heteroepitaxially on sapphires. The GaN crystals are grown at low supersaturation using the Na flux method with the dipping technique. The crystallinity of the grown GaN crystals is improved compared to that of the seed substrates. Then it improves further by lowering the supersaturation. Finally, we succeed in fabricating a 2-in. \\{ 11\\bar{2}2\\} -plane GaN single crystal with high transparency and crystallinity.

  11. 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.

  12. High-quality, 2-inch-diameter m-plane GaN substrates grown by hydride vapor phase epitaxy on acidic ammonothermal seeds

    NASA Astrophysics Data System (ADS)

    Tsukada, Yusuke; Enatsu, Yuuki; Kubo, Shuichi; Ikeda, Hirotaka; Kurihara, Kaori; Matsumoto, Hajime; Nagao, Satoru; Mikawa, Yutaka; Fujito, Kenji

    2016-05-01

    In this paper, we discusse the origin of basal-plane stacking faults (BSFs) generated in the homoepitaxial hydride vapor phase epitaxy (HVPE) growth of m-plane gallium nitride (GaN). We investigated the effects of seed quality, especially dislocation density, on BSF generation during homoepitaxy. The results clearly identify basal-plane dislocation in the seed as a cause of BSF generation. We realized high-quality m-plane GaN substrates with a 2-in. diameter using HVPE on low-dislocation-density m-plane seeds.

  13. High optical and structural quality of GaN epilayers grown on (2{sup ¯}01) β-Ga{sub 2}O{sub 3}

    SciTech Connect

    Muhammed, M. M.; Roqan, I. S.; Peres, M.; Franco, N.; Lorenz, K.; Yamashita, Y.; Morishima, Y.; Sato, S.; Kuramata, A.

    2014-07-28

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2{sup ¯}01) oriented β-Ga{sub 2}O{sub 3} has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2{sup ¯}01) oriented β-Ga{sub 2}O{sub 3} are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼10{sup 8 }cm{sup −2}. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2{sup ¯}01) β-Ga{sub 2}O{sub 3} with in-plane epitaxial orientation relationships between the β-Ga{sub 2}O{sub 3} and the GaN thin film defined by (010) β-Ga{sub 2}O{sub 3} || (112{sup ¯}0) GaN and (2{sup ¯}01) β-Ga{sub 2}O{sub 3} || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high.

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

    SciTech Connect

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; Kravchenko, I. I.; Zhang, Ming-Lan

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.

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

    DOE PAGES

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; et al

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersionmore » observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

  16. 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.

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

    PubMed

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

    2016-07-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    PubMed

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

    2016-01-01

    We demonstrate the high structural and optical properties of InxGa1-xN epilayers (0 ≤ x ≤ 23) grown on conductive and transparent (01)-oriented β-Ga2O3 substrates using a low-temperature GaN buffer layer rather than AlN buffer layer, which enhances the quality and stability of the crystals compared to those grown on (100)-oriented β-Ga2O3. Raman maps show that the 2″ wafer is relaxed and uniform. Transmission electron microscopy (TEM) reveals that the dislocation density reduces considerably (~4.8 × 10(7) cm(-2)) at the grain centers. High-resolution TEM analysis demonstrates that most dislocations emerge at an angle with respect to the c-axis, whereas dislocations of the opposite phase form a loop and annihilate each other. The dislocation behavior is due to irregular (01) β-Ga2O3 surface at the interface and distorted buffer layer, followed by relaxed GaN epilayer. Photoluminescence results confirm high optical quality and time-resolved spectroscopy shows that the recombination is governed by bound excitons. We find that a low root-mean-square average (≤1.5 nm) of InxGa1-xN epilayers can be achieved with high optical quality of InxGa1-xN epilayers. We reveal that (01)-oriented β-Ga2O3 substrate has a strong potential for use in large-scale high-quality vertical light emitting device design. PMID:27412372

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  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. High-resistance GaN epilayers with low dislocation density via growth mode modification

    NASA Astrophysics Data System (ADS)

    Xu, Z. Y.; Xu, F. J.; Wang, J. M.; Lu, L.; Yang, Z. J.; Wang, X. Q.; Shen, B.

    2016-09-01

    High-resistance GaN with low dislocation density adopting growth mode modification has been investigated by metalorganic chemical vapor deposition. The sheet resistance of the order of 1016 Ω/sq has been achieved at room temperature by diminishing the oxygen impurity level close to the substrate with an AlN blocking layer. Attributed to this method which offers more freedom to tailor the growth mode, a three-dimensional (3D) growth process is introduced by adjusting the growth pressure and temperature at the initial stage of the GaN epitaxy to improve the crystalline quality. The large 3D GaN grains formed during this period roughen the surface, and the following coalescence of the GaN grains causes threading dislocations bending, which finally remarkably reduces the dislocation density.

  4. Novel high frequency devices with graphene and GaN

    NASA Astrophysics Data System (ADS)

    Zhao, Pei

    This work focuses on exploring new materials and new device structures to develop novel devices that can operate at very high speed. In chapter 2, the high frequency performance limitations of graphene transistor with channel length less than 100 nm are explored. The simulated results predict that intrinsic cutoff frequency fT of graphene transistor can be close to 2 THz at 15 nm channel length. In chapter 3, we explored the possibility of developing a 2D materials based vertical tunneling device. An analytical model to calculate the channel potentials and current-voltage characteristics in a Symmetric tunneling Field-Effect-Transistor (SymFET) is presented. The symmetric resonant peak in SymFET is a good candidate for high-speed analog applications. Rest of the work focuses on Gallium Nitride (GaN), several novel device concepts based on GaN heterostructure have been proposed for high frequency and high power applications. In chapter 4, we compared the performance of GaN Schottky diodes on bulk GaN substrates and GaN-on-sapphire substrates. In addition, we also discussed the lateral GaN Schottky diode between metal/2DEGs. The advantage of lateral GaN Schottky diodes is the intrinsic cutoff frequency is in the THz range. In chapter 5, a GaN Heterostructure barrier diode (HBD) is designed using the polarization charge and band offset at the AlGaN/GaN heterojunction. The polarization charge at AlGaN/GaN interface behaves as a delta-doping which induces a barrier without any chemical doping. The IV characteristics can be explained by the barrier controlled thermionic emission current. GaN HBDs can be directly integrated with GaN HEMTs, and serve as frequency multipliers or mixers for RF applications. In chapter 6, a GaN based negative effective mass oscillator (NEMO) is proposed. The current in NEMO is estimated under the ballistic limits. Negative differential resistances (NDRs) can be observed with more than 50% of the injected electrons occupied the negative

  5. High Voltage GaN Schottky Rectifiers

    SciTech Connect

    CAO,X.A.; CHO,H.; CHU,S.N.G.; CHUO,C.-C.; CHYI,J.-I.; DANG,G.T.; HAN,JUNG; LEE,C.-M.; PEARTON,S.J.; REN,F.; WILSON,R.G.; ZHANG,A.P.

    1999-10-25

    Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V{sub RB}) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, R{sub ON}, was 6m{Omega}{center_dot} cm{sup 2} and 0.8{Omega}cm{sup 2}, respectively, producing figure-of-merit values for (V{sub RB}){sup 2}/R{sub ON} in the range 5-48 MW{center_dot}cm{sup -2}. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of this contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates. On-state voltages were 3.5V for the 550V diodes and {ge}15 for the 2kV diodes. Reverse recovery times were <0.2{micro}sec for devices switched from a forward current density of {approx}500A{center_dot}cm{sup -2} to a reverse bias of 100V.

  6. 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.

  7. O3-sourced atomic layer deposition of high quality Al2O3 gate dielectric for normally-off GaN metal-insulator-semiconductor high-electron-mobility transistors

    NASA Astrophysics Data System (ADS)

    Huang, Sen; Liu, Xinyu; Wei, Ke; Liu, Guoguo; Wang, Xinhua; Sun, Bing; Yang, Xuelin; Shen, Bo; Liu, Cheng; Liu, Shenghou; Hua, Mengyuan; Yang, Shu; Chen, Kevin J.

    2015-01-01

    High quality Al2O3 film grown by atomic layer deposition (ALD), with ozone (O3) as oxygen source, is demonstrated for fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Significant suppression of Al-O-H and Al-Al bonds in ALD-Al2O3 has been realized by substituting conventional H2O source with O3. A high dielectric breakdown E-field of 8.5 MV/cm and good TDDB behavior are achieved in a gate dielectric stack consisting of 13-nm O3-Al2O3 and 2-nm H2O-Al2O3 interfacial layer on recessed GaN. By using this 15-nm gate dielectric and a high-temperature gate-recess technique, the density of positive bulk/interface charges in normally-off AlGaN/GaN MIS-HEMTs is remarkably suppressed to as low as 0.9 × 1012 cm-2, contributing to the realization of normally-off operation with a high threshold voltage of +1.6 V and a low specific ON-resistance RON,sp of 0.49 mΩ cm2.

  8. High-Sensitivity GaN Microchemical Sensors

    NASA Technical Reports Server (NTRS)

    Son, Kyung-ah; Yang, Baohua; Liao, Anna; Moon, Jeongsun; Prokopuk, Nicholas

    2009-01-01

    Systematic studies have been performed on the sensitivity of GaN HEMT (high electron mobility transistor) sensors using various gate electrode designs and operational parameters. The results here show that a higher sensitivity can be achieved with a larger W/L ratio (W = gate width, L = gate length) at a given D (D = source-drain distance), and multi-finger gate electrodes offer a higher sensitivity than a one-finger gate electrode. In terms of operating conditions, sensor sensitivity is strongly dependent on transconductance of the sensor. The highest sensitivity can be achieved at the gate voltage where the slope of the transconductance curve is the largest. This work provides critical information about how the gate electrode of a GaN HEMT, which has been identified as the most sensitive among GaN microsensors, needs to be designed, and what operation parameters should be used for high sensitivity detection.

  9. Highly transparent ammonothermal bulk GaN substrates

    SciTech Connect

    Jiang, WK; Ehrentraut, D; Downey, BC; Kamber, DS; Pakalapati, RT; Do Yoo, H; D'Evelyn, MP

    2014-10-01

    A novel apparatus has been employed to grow ammonothermal (0001) gallium nitride (GaN) with diameters up to 2 in The crystals have been characterized by x-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), and optical spectroscopy. High crystallinity GaN with FWHM values about 20-50 arcsec and dislocation densities below 1 x 10(5) cm(-2) have been obtained. High optical transmission was achieved with an optical absorption coefficient below 1 cm(-1) at a wavelength of 450 nm. (C) 2014 Elsevier B.V. All rights reserved.

  10. O{sub 3}-sourced atomic layer deposition of high quality Al{sub 2}O{sub 3} gate dielectric for normally-off GaN metal-insulator-semiconductor high-electron-mobility transistors

    SciTech Connect

    Huang, Sen; Liu, Xinyu Wei, Ke; Liu, Guoguo; Wang, Xinhua; Sun, Bing; Yang, Xuelin; Shen, Bo; Liu, Cheng; Liu, Shenghou; Hua, Mengyuan; Yang, Shu; Chen, Kevin J.

    2015-01-19

    High quality Al{sub 2}O{sub 3} film grown by atomic layer deposition (ALD), with ozone (O{sub 3}) as oxygen source, is demonstrated for fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Significant suppression of Al–O–H and Al–Al bonds in ALD-Al{sub 2}O{sub 3} has been realized by substituting conventional H{sub 2}O source with O{sub 3}. A high dielectric breakdown E-field of 8.5 MV/cm and good TDDB behavior are achieved in a gate dielectric stack consisting of 13-nm O{sub 3}-Al{sub 2}O{sub 3} and 2-nm H{sub 2}O-Al{sub 2}O{sub 3} interfacial layer on recessed GaN. By using this 15-nm gate dielectric and a high-temperature gate-recess technique, the density of positive bulk/interface charges in normally-off AlGaN/GaN MIS-HEMTs is remarkably suppressed to as low as 0.9 × 10{sup 12 }cm{sup −2}, contributing to the realization of normally-off operation with a high threshold voltage of +1.6 V and a low specific ON-resistance R{sub ON,sp} of 0.49 mΩ cm{sup 2}.

  11. Fabrications and application of single crystalline GaN for high-performance deep UV photodetectors

    NASA Astrophysics Data System (ADS)

    Velazquez, R.; Aldalbahi, A.; Rivera, M.; Feng, P.

    2016-08-01

    High-quality single crystalline Gallium Nitride (GaN) semiconductor has been synthesized using molecule beam epitaxy (MBE) technique for development of high-performance deep ultraviolet (UV) photodetectors. Thickness of the films was estimated by using surface profile meter and scanning electron microscope. Electronic states and elemental composition of the films were obtained using Raman scattering spectroscopy. The orientation, crystal structure and phase purity of the films were examined using a Siemens x-ray diffractometer radiation. The surface microstructure was studied using high resolution scanning electron microscopy (SEM). Two types of metal pairs: Al-Al, Al-Cu or Cu-Cu were used for interdigital electrodes on GaN film in order to examine the Schottky properties of the GaN based photodetector. The characterizations of the fabricated prototype include the stability, responsivity, response and recovery times. Typical time dependent photoresponsivity by switching different UV light source on and off five times for each 240 seconds at a bias of 2V, respectively, have been obtained. The detector appears to be highly sensitive to various UV wavelengths of light with very stable baseline and repeatability. The obtained photoresponsivity was up to 354 mA/W at the bias 2V. Higher photoresponsivity could be obtained if higher bias was applied but it would unavoidably result in a higher dark current. Thermal effect on the fabricated GaN based prototype was discussed.

  12. Effect of initial growth on the quality of GaN on patterned sapphire substrate with ex situ physical vapor deposition AlN seed layer

    NASA Astrophysics Data System (ADS)

    Wang, Hongbo; Daigo, Yoshiaki; Seino, Takuya; Ishibashi, Sotaro; Sugiyama, Masakazu

    2016-10-01

    GaN epitaxy was explored on a cone-patterned sapphire substrate with an ex situ AlN seed layer prepared by physical vapor deposition (PVD). The effect of initial growth on the quality of the GaN epilayer was investigated using both ex situ PVD-AlN seed layers with various thicknesses and various deposition parameters such as temperature and reactor pressure in metal-organic vapor-phase epitaxy (MOVPE). It was found that the quality of GaN is insensitive to both the thickness of the ex situ PVD-AlN seed layer and the MOVPE growth conditions. A high-quality GaN film was realized, as indicated by room-temperature CL mapping (dark spot density of 1.6 × 108 cm-2), on a patterned sapphire substrate with a wide growth condition window by simply employing an ex situ PVD-AlN seed layer.

  13. High Efficiency m-plane LEDs on Low Defect Density Bulk GaN Substrates

    SciTech Connect

    David, Aurelien

    2012-10-15

    Solid-state lighting is a key technology for reduction of energy consumption in the US and worldwide. In principle, by replacing standard incandescent bulbs and other light sources with sources based on light-emitting diodes (LEDs), ultimate energy efficiency can be achieved. The efficiency of LEDs has improved tremendously over the past two decades, however further progress is required for solid- state lighting to reach its full potential. The ability of an LED at converting electricity to light is quantified by its internal quantum efficiency (IQE). The material of choice for visible LEDs is Gallium Nitride (GaN), which is at the basis of blue-emitting LEDs. A key factor limiting the performance of GaN LEDs is the so-called efficiency droop, whereby the IQE of the LED decreases significantly at high current density. Despite decades of research, efficiency droop remains a major issue. Since high-current operation is necessary for practical lighting applications, reducing droop is a major challenge for the scientific community and the LED industry. Our approach to solving the droop issue is the use of newly available low-defect-density bulk GaN non-polar substrates. In contrast to the standard foreign substrates (sapphire, silicon carbide, silicon) used in the industry, we have employed native bulk GaN substrates with very low defect density, thus ensuring exquisite material quality and high IQE. Whereas all commercial LEDs are grown along the c-plane crystal direction of GaN, we have used m-plane non-polar substrates; these drastically modify the physical properties of the LED and enable a reduction of droop. With this approach, we have demonstrated very high IQE performance and low droop. Our results focused on violet and blue LEDs. For these, we have demonstrated very high peak IQEs and current droops of 6% and 10% respectively (up to a high current density of 200A.cm-2). All these results were obtained under electrical operation. These high IQE and low droop

  14. Selective area growth of high-density GaN nanowire arrays on Si(111) using thin AlN seeding layers

    NASA Astrophysics Data System (ADS)

    Wu, C. H.; Lee, P. Y.; Chen, K. Y.; Tseng, Y. T.; Wang, Y. L.; Cheng, K. Y.

    2016-11-01

    Selective area growth (SAG) of high-density (2.5×109 cm-2) GaN nanowires (NWs) on Si(111) substrate by plasma-assisted molecular beam epitaxy is presented. The effects of morphology and thickness of the AlN seeding layer on the quality of SAG GaN NWs are investigated. A thin AlN seeding layer of 30 nm thick with a surface roughness of less than 0.5 nm is suitable for high quality SAG GaN NWs growth. High-density AlN nanopedestal arrays used as seeds for SAG GaN NWs are fabricated from thin AlN seeding layers using soft nanoimprint lithography. By adjusting the growth temperature and Ga/N flux ratio, hexagonal shaped SAG GaN NWs are realized. The quality of SAG GaN NWs is evaluated by low temperature photoluminescence (PL) measurements. Three major groups of PL peaks at 3.47, 3.45, and 3.41 eV are identified. The peak at 3.471 eV is related to the neutral donor-bound exciton emission, and the 3.41 eV broadband emission is attributed to stacking faults or structural defects. The 3.45 eV peak is identified as the emission due to exciton recombination at polar inversion domain boundaries of NWs.

  15. 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.

  16. Enhancement in the quality of GaN crystal grown on a thermal-treated silicon substrate

    NASA Astrophysics Data System (ADS)

    Chen, X. F.; Kato, T.; Sawaki, N.

    2002-04-01

    By using metalorganic vapor phase epitaxy, GaN layers are deposited on nominal Si(2 1 1) substrates that undergo different types of thermal treatment before the epitaxial growth. X-ray diffraction rocking curves and photoluminescence experimental results indicate that the crystal quality is improved significantly if the thermal treatment is composed of a high-temperature heating followed by a speedy cool-down process. It is observed that a high-temperature heat treatment alone on the substrates does not provide with measurable improvements in the GaN layers. In addition, atomic force microscopic images indicate that the easy glide system of Si{1 1 1} plane can be also a source of residual stresses built up in the GaN film. Consequently, a suitable pre-thermal treatment for use on a silicon substrate is suggested to prevent the GaN film from suffering any extra stress arising from the substrate during the post-growth cooling process.

  17. Materials physics and device development for improved efficiency of GaN HEMT high power amplifiers.

    SciTech Connect

    Kurtz, Steven Ross; Follstaedt, David Martin; Wright, Alan Francis; Baca, Albert G.; Briggs, Ronald D.; Provencio, Paula Polyak; Missert, Nancy A.; Allerman, Andrew Alan; Marsh, Phil F.; Koleske, Daniel David; Lee, Stephen Roger; Shul, Randy John; Seager, Carleton Hoover; Tigges, Christopher P.

    2005-12-01

    GaN-based microwave power amplifiers have been identified as critical components in Sandia's next generation micro-Synthetic-Aperture-Radar (SAR) operating at X-band and Ku-band (10-18 GHz). To miniaturize SAR, GaN-based amplifiers are necessary to replace bulky traveling wave tubes. Specifically, for micro-SAR development, highly reliable GaN high electron mobility transistors (HEMTs), which have delivered a factor of 10 times improvement in power performance compared to GaAs, need to be developed. Despite the great promise of GaN HEMTs, problems associated with nitride materials growth currently limit gain, linearity, power-added-efficiency, reproducibility, and reliability. These material quality issues are primarily due to heteroepitaxial growth of GaN on lattice mismatched substrates. Because SiC provides the best lattice match and thermal conductivity, SiC is currently the substrate of choice for GaN-based microwave amplifiers. Obviously for GaN-based HEMTs to fully realize their tremendous promise, several challenges related to GaN heteroepitaxy on SiC must be solved. For this LDRD, we conducted a concerted effort to resolve materials issues through in-depth research on GaN/AlGaN growth on SiC. Repeatable growth processes were developed which enabled basic studies of these device layers as well as full fabrication of microwave amplifiers. Detailed studies of the GaN and AlGaN growth of SiC were conducted and techniques to measure the structural and electrical properties of the layers were developed. Problems that limit device performance were investigated, including electron traps, dislocations, the quality of semi-insulating GaN, the GaN/AlGaN interface roughness, and surface pinning of the AlGaN gate. Surface charge was reduced by developing silicon nitride passivation. Constant feedback between material properties, physical understanding, and device performance enabled rapid progress which eventually led to the successful fabrication of state of the art

  18. Improvement of optical quality of semipolar (11 2 ¯ 2 ) GaN on m-plane sapphire by in-situ epitaxial lateral overgrowth

    NASA Astrophysics Data System (ADS)

    Monavarian, Morteza; Izyumskaya, Natalia; Müller, Marcus; Metzner, Sebastian; Veit, Peter; Can, Nuri; Das, Saikat; Özgür, Ümit; Bertram, Frank; Christen, Jürgen; Morkoç, Hadis; Avrutin, Vitaliy

    2016-04-01

    Among the major obstacles for development of non-polar and semipolar GaN structures on foreign substrates are stacking faults which deteriorate the structural and optical quality of the material. In this work, an in-situ SiNx nano-network has been employed to achieve high quality heteroepitaxial semipolar (11 2 ¯ 2 ) GaN on m-plane sapphire with reduced stacking fault density. This approach involves in-situ deposition of a porous SiNx interlayer on GaN that serves as a nano-mask for the subsequent growth, which starts in the nanometer-sized pores (window regions) and then progresses laterally as well, as in the case of conventional epitaxial lateral overgrowth (ELO). The inserted SiNx nano-mask effectively prevents the propagation of defects, such as dislocations and stacking faults, in the growth direction and thus reduces their density in the overgrown layers. The resulting semipolar (11 2 ¯ 2 ) GaN layers exhibit relatively smooth surface morphology and improved optical properties (PL intensity enhanced by a factor of 5 and carrier lifetimes by 35% to 85% compared to the reference semipolar (11 2 ¯ 2 ) GaN layer) which approach to those of the c-plane in-situ nano-ELO GaN reference and, therefore, holds promise for light emitting and detecting devices.

  19. High field effects of GaN HEMTs.

    SciTech Connect

    Barker, Joy; Shul, Randy John

    2004-09-01

    This report represents the completion of a Laboratory-Directed Research and Development (LDRD) program to develop and fabricate geometric test structures for the measurement of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue had to do with surface passivation. Test samples without a surface passivation, often failed at electric fields below 50 kV/cm, due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with varying lengths and widths (8x2, 10x3, 12x3, 12x4, 15x5, and 16x4 {micro}m) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 {Omega} environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the applied electric field was calculated and thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near to 2.5x10{sup 7} cm/s at 180 kV/cm and 3.1x10{sup 7} cm/s, at a field of 140 kV/cm, for the bulk GaN and AlGaN heterostructure samples, respectively. These experimental drift velocities mark the highest velocities measured in these materials to date and confirm

  20. Highly Uniform Characteristics of GaN Nanorods Grown on Si(111) by Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Ra, Yong-Ho; Navamathavan, Rangaswamy; Park, Ji-Hyeon; Song, Ki-Young; Lee, Young-Min; Kim, Dong-Wook; Jun, Baek Byung; Lee, Cheul-Ro

    2010-09-01

    Gallium nitride (GaN) nanorod (NR) arrays were grown on a gold-coated Si(111) substrate by metalorganic chemical vapor deposition (MOCVD). The synthesized single GaN NRs were characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and cathodoluminescence (CL) analysis. The HR-TEM images and selected area electron diffraction (SAED) patterns demonstrated that the GaN NRs were of high quality with a single-crystal wurtzite structure and free from defects. The GaN NRs were observed to have a uniform diameter ranging from 40 to 70 nm, length of up to 1 µm, and a sharp symmetrical pyramid-like tip at the top. The pyramid-like tip was attributed to the dissociation of nitrogen atoms by the cracking of ammonia (NH3) at the elevated growth temperature. Furthermore, there was no sign of any metal or alloy cluster at the end of the NRs. Thus, the growth of the GaN NRs does not occur by the typical vapor-liquid-solid (VLS) mechanism.

  1. Improved crystal quality of semipolar (10 1 bar 3) GaN on Si(001) substrates using AlN/GaN superlattice interlayer

    NASA Astrophysics Data System (ADS)

    Lee, Ho-Jun; Bae, Si-Young; Lekhal, Kaddour; Mitsunari, Tadashi; Tamura, Akira; Honda, Yoshio; Amano, Hiroshi

    2016-11-01

    The planar epitaxial growth of semipolar (10 1 bar 3) GaN on a Si(001) substrate was performed on a directionally sputtered AlN buffer layer. Three types of interlayers, i.e., single AlN, double AlN, and a stack of AlN/GaN layers were grown by metalorganic chemical vapor deposition (MOCVD) to achieve high quality GaN films. The results for the stack of AlN/GaN layers provide highest crystal quality and optical properties for GaN. Comparing the top (Ga face) and bottom (N face) surfaces of grown semipolar (10 1 bar 3) GaN confirms the defect density reduction that is due to the application of interlayers. Moreover, reduced inversion domain density on the bottom surface is attributed with the insertion of interlayers. Improving the quality of semipolar GaN on Si(001) substrates is expected to be useful for GaN/Si(001) integrated optoelectronics.

  2. Study of the structural quality of GaN epitaxial layers obtained by hydride vapor phase epitaxy using a low-temperature buffer layer

    NASA Astrophysics Data System (ADS)

    Belogorohov, I. A.; Donskov, A. A.; Knyazev, S. N.; Kozlova, Yu. P.; Pavlov, V. F.; Yugova, T. G.

    2015-11-01

    The structural quality and surface morphology of low-temperature (LT) buffer layers after deposition and high-temperature (HT) annealing and HT GaN layers grown on LT buffer layers by hydride vapor phase epitaxy have been investigated. The HCl flow rate through the Ga source varied from 0.3 to 2 L/h, and the carrier gas N2 flow rate was either 18 or 60 L/h. It is established that the structural quality of LT GaN buffer is determined to a great extent by the HCl and N2 flow rates; the best results are obtained at HCl and N2 flow rates of 0.3 and 18 L/h, respectively. These GaN layers are characterized by a mirror surface and a rocking curve half-width of 360". It is suggested that the layer structure is improved due to the increase in the lateral growth rate.

  3. Ammothermal Growth of Gan Substrates For Leds: High-Pressure Ammonothermal Process for Bulk Gallium Nitride Crystal Growth for Energy Efficient Commercially Competitive Lighting

    SciTech Connect

    2011-01-01

    Broad Funding Opportunity Announcement Project: The new GaN crystal growth method is adapted from that used to grow quartz crystals, which are very inexpensive and represent the second-largest market for single crystals for electronic applications (after silicon). More extreme conditions are required to grow GaN crystals and therefore a new type of chemical growth chamber was invented that is suitable for large-scale manufacturing. A new process was developed that grows GaN crystals at a rate that is more than double that of current processes. The new technology will enable GaN substrates with best-in-world quality at lowest-in-world prices, which in turn will enable new generations of white LEDs, lasers for full-color displays, and high-performance power electronics.

  4. GaN hexagonal pyramids formed by a photo-assisted chemical etching method

    NASA Astrophysics Data System (ADS)

    Zhang, Shi-Ying; Xiu, Xiang-Qian; Hua, Xue-Mei; Xie, Zi-Li; Liu, Bin; Chen, Peng; Han, Ping; Lu, Hai; Zhang, Rong; Zheng, You-Dou

    2014-05-01

    A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a convenient photo-assisted chemical (PAC) etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed analysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.

  5. High efficiency DC-DC converter using GaN transistors

    NASA Astrophysics Data System (ADS)

    Tómaş, Cosmin-Andrei; Grecu, Cristian; Pantazicǎ, Mihaela; Marghescu, Ion

    2015-02-01

    The paper presents a new high-efficiency power switching supply using the Gallium Nitride (GaN) technology. There are compared two solutions, the first using standard MOS transistors and the second using the new GaN transistor. The actual green technologies for obtaining the maximum energy and minimum losses have pushed the semiconductor industry into a continuous research regarding high power and high frequency devices, having uses in both digital communications and switching power supplies.

  6. Diffusion of oxygen in bulk GaN crystals at high temperature and at high pressure

    NASA Astrophysics Data System (ADS)

    Sadovyi, B.; Nikolenko, A.; Weyher, J. L.; Grzegory, I.; Dziecielewski, I.; Sarzynski, M.; Strelchuk, V.; Tsykaniuk, B.; Belyaev, O.; Petrusha, I.; Turkevich, V.; Kapustianyk, V.; Albrecht, M.; Porowski, S.

    2016-09-01

    Experimental studies of diffusion of oxygen in bulk wurtzite-type GaN crystals grown by Halide Vapor Phase Epitaxy (HVPE) are reported. Oxygen concentration profiles were studied in as-grown GaN crystals and also after annealing of crystals at temperatures up to 3400 K and pressures up to 9 GPa. Investigated crystals contained large conical defects i.e. pinholes of significantly higher oxygen concentration (NO=(2-4)×1019 cm-3) than that in the bulk matrix (NO<1×1017 cm-3). The pinholes were revealed by a photo-etching method in as-grown and annealed GaN samples. Confocal micro-Raman spectroscopy was applied to measure the profiles of free electron concentration, which directly corresponds to the concentration of oxygen impurity. Lateral scanning across the interfaces between pinholes and matrix in the as-grown HVPE GaN crystals showed sharp step-like carrier concentration profiles. Annealing at high temperature and high pressure resulted in the diffusion blurring of the profiles. Analysis of obtained data allowed for the first time for estimation of oxygen diffusion coefficients DO(T, P). The obtained values of DO(T, P) are anomalously small similarly to the values obtained by Harafuji et al. by molecular dynamic calculations for self-diffusion of nitrogen. Whereas oxygen and nitrogen are on the same sublattice it could explain the similarity of their diffusion coefficients.

  7. Piezotronic Effect in Polarity-Controlled GaN Nanowires.

    PubMed

    Zhao, Zhenfu; Pu, Xiong; Han, Changbao; Du, Chunhua; Li, Linxuan; Jiang, Chunyan; Hu, Weiguo; Wang, Zhong Lin

    2015-08-25

    Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Qi, Meng; Nomoto, Kazuki; Zhu, Mingda; Hu, Zongyang; Zhao, Yuning; Protasenko, Vladimir; Song, Bo; Yan, Xiaodong; Li, Guowang; Verma, Jai; Bader, Samuel; Fay, Patrick; Xing, Huili Grace; Jena, Debdeep

    2015-12-01

    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm2 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 cm2 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.

  10. High-resolution emission spectroscopy of random lasing in GaN films pumped by UV-pulsed laser

    NASA Astrophysics Data System (ADS)

    Cachoncinlle, C.; Millon, E.; Petit, A.

    2016-06-01

    We report on room temperature photoluminescence on GaN films grown by metal organic chemical vapor deposition (MOCVD). A NdYAG pulsed-laser at 266 nm illuminates the films. Two components, at 363 nm and 370 nm, are identified in the near band edge structure on the spectra. A laser threshold of 700±150 kW cm-2 is evidenced and corresponds to random lasing in the GaN film. A drastic narrowing of the spectral bandwidth from 5.2 to 1.8 nm is observed at 370 nm. High-resolution spectroscopy measurements show laser mode widths thinner than 50 pm leading to a high quality factor Q=7750. Low-resolution measurements show redshift from 370.0 to 373.1 nm for one component and from 363.1 nm to 363.9 nm for the other. Interpretation of this redshift is discussed.

  11. Effect of defects in oxide templates on Non-catalytic growth of GaN nanowires for high-efficiency light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Hwang, Sung Won; Choi, Suk-Ho

    2016-04-01

    Two kinds of oxide templates, one with and one without undercuts, are employed to study the effect of defects in oxide templates on non-catalytic growth of GaN nanowires (NWs). GaN NWs abnormally grown from the templates containing undercuts exhibit two types of patterns: earlystage growth of premature NWs and abnormally-overgrown (~2 μm) NWs. GaN NWs grown on perfectly-symmetric template patterns are highly crystalline and have high aspect ratios (2 ~ 5), and their tops are shaped as pyramids with semipolar facets, clearly indicating hexagonal symmetry. The internal quantum efficiency of the well-grown NWs is 10% larger than that of the deformed NWs, as estimated by using photoluminescence. These results suggest that our technique is an effective approach for growing large-area-patterned, vertically-aligned, hexagonal GaN NWs without catalysts, in strong contrast to catalytic vapor-liquid-solid growth, and that good formation of the oxide templates is crucial for the growth of high-quality GaN NWs.

  12. GaN High-Electron-Mobility Transistor with WN x /Cu Gate for High-Power Applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Li, Fang-Ming; Shi, Wang-Cheng; Huang, Yu-Xiang; Lan, Wei-Cheng; Chin, Ping-Chieh; Chang, Edward Yi

    2015-12-01

    A GaN high-electron-mobility transistor (HEMT) with WN x /Cu gate for high-power applications has been investigated. The direct-current (DC) characteristics of the device are comparable to those of conventional Ni/Au-gated GaN HEMTs. The results of high-voltage stress testing indicate that the device is stable after application of 200 V stress for 42 h. The WN x /Cu-gated GaN HEMT exhibited no obvious changes in the DC characteristics or Schottky barrier height before and after annealing at 250°C for 1 h. These results demonstrate that the WN x /Cu gate structure can be used in a GaN HEMT for high-power applications with good thermal stability.

  13. A high efficiency C-band internally-matched harmonic tuning GaN power amplifier

    NASA Astrophysics Data System (ADS)

    Lu, Y.; Zhao, B. C.; Zheng, J. X.; Zhang, H. S.; Zheng, X. F.; Ma, X. H.; Hao, Y.; Ma, P. J.

    2016-09-01

    In this paper, a high efficiency C-band gallium nitride (GaN) internally-matched power amplifier (PA) is presented. This amplifier consists of 2-chips of self-developed GaN high-electron mobility transistors (HEMTs) with 16 mm total gate width on SiC substrate. New harmonic manipulation circuits are induced both in the input and output matching networks for high efficiency matching at fundamental and 2nd-harmonic frequency, respectively. The developed amplifier has achieved 72.1% power added efficiency (PAE) with 107.4 W output power at 5 GHz. To the best of our knowledge, this amplifier exhibits the highest PAE in C-band GaN HEMT amplifiers with over 100 W output power. Additionally, 1000 hours' aging test reveals high reliability for practical applications.

  14. High voltage and high current density vertical GaN power diodes

    DOE PAGES

    Fischer, A. J.; Dickerson, J. R.; Armstrong, A. M.; Moseley, M. W.; Crawford, M. H.; King, M. P.; Allerman, A. A.; Kaplar, R. J.; van Heukelom, M. S.; Wierer, J. J.

    2016-01-01

    We report on the realization of a GaN high voltage vertical p-n diode operating at > 3.9 kV breakdown with a specific on-resistance < 0.9 mΩ.cm2. Diodes achieved a forward current of 1 A for on-wafer, DC measurements, corresponding to a current density > 1.4 kA/cm2. An effective critical electric field of 3.9 MV/cm was estimated for the devices from analysis of the forward and reverse current-voltage characteristics. Furthermore this suggests that the fundamental limit to the GaN critical electric field is significantly greater than previously believed.

  15. High voltage and high current density vertical GaN power diodes

    SciTech Connect

    Fischer, A. J.; Dickerson, J. R.; Armstrong, A. M.; Moseley, M. W.; Crawford, M. H.; King, M. P.; Allerman, A. A.; Kaplar, R. J.; van Heukelom, M. S.; Wierer, J. J.

    2016-01-01

    We report on the realization of a GaN high voltage vertical p-n diode operating at > 3.9 kV breakdown with a specific on-resistance < 0.9 mΩ.cm2. Diodes achieved a forward current of 1 A for on-wafer, DC measurements, corresponding to a current density > 1.4 kA/cm2. An effective critical electric field of 3.9 MV/cm was estimated for the devices from analysis of the forward and reverse current-voltage characteristics. Furthermore this suggests that the fundamental limit to the GaN critical electric field is significantly greater than previously believed.

  16. Electron Transport in a High Mobility Free-Standing GaN Substrate Grown by Hydride Vapor Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Farina, L.; Kurdak, C.; Yun, F.; Morkoc, H.; Rode, D. L.; Tsen, K. T.; Park, S. S.; Lee, K. Y.

    2001-03-01

    We studied electron transport properties in a high quality free-standing GaN grown by hydride vapor phase epitaxy. The GaN, with a thickness of more than 200 μm, was lifted off the sapphire substrate and mechanically polished. At room temperature the carrier density is 1.3x10^16cm-3 and the Hall mobility is 1200 cm^2/V-s, which is the highest reported electron mobility for GaN with a wurtzite structure. Transport properties are studied using a van der Pauw geometry in a temperature range of 20 to 300 K and in magnetic fields up to 8 Tesla. Electron mobility is found to increase at lower temperatures with a peak mobility of 7400 cm^2/V-s at 48 K. The carrier density decreases exponentially at temperatures below 80 K with an activation energy of 28 meV. The electron transport measurements were used to examine the contributions of different scattering mechanisms. Numerical solution of the Boltzmann transport equation was carried out, including non-parabolic conduction bands and wavefunction admixture, along with lattice scattering and ionized-impurity scattering. LO and TO phonon energies were determined by Raman spectroscopy.

  17. Prostate specific antigen detection using AlGaN /GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

    Antibody-functionalized Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect prostate specific antigen (PSA). The PSA antibody was anchored to the gate area through the formation of carboxylate succinimdyl ester bonds with immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when target PSA in a buffer at clinical concentrations was added to the antibody-immobilized surface. The authors could detect a wide range of concentrations from 10pg/mlto1μg/ml. The lowest detectable concentration was two orders of magnitude lower than the cutoff value of PSA measurements for clinical detection of prostate cancer. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN /GaN HEMTs for PSA screening.

  18. High-temperature molecular beam epitaxial growth of AlGaN/GaN on GaN templates with reduced interface impurity levels

    SciTech Connect

    Koblmueller, G.; Chu, R. M.; Raman, A.; Mishra, U. K.; Speck, J. S.

    2010-02-15

    We present combined in situ thermal cleaning and intentional doping strategies near the substrate regrowth interface to produce high-quality AlGaN/GaN high electron mobility transistors on semi-insulating (0001) GaN templates with low interfacial impurity concentrations and low buffer leakage. By exposing the GaN templates to an optimized thermal dissociation step in the plasma-assisted molecular beam epitaxy environment, oxygen, carbon, and, to lesser extent, Si impurities were effectively removed from the regrowth interface under preservation of good interface quality. Residual Si was further compensated by C-doped GaN via CBr{sub 4} to yield highly resistive GaN buffer layers. Improved N-rich growth conditions at high growth temperatures were then utilized for subsequent growth of the AlGaN/GaN device structure, yielding smooth surface morphologies and low residual oxygen concentration with large insensitivity to the (Al+Ga)N flux ratio. Room temperature electron mobilities of the two-dimensional electron gas at the AlGaN/GaN interface exceeded >1750 cm{sup 2}/V s and the dc drain current reached {approx}1.1 A/mm at a +1 V bias, demonstrating the effectiveness of the applied methods.

  19. Significant improvement of GaN crystal quality with ex-situ sputtered AlN nucleation layers

    NASA Astrophysics Data System (ADS)

    Chen, Shuo-Wei; Yang, Young; Wen, Wei-Chih; Li, Heng; Lu, Tien-Chang

    2016-03-01

    Ex-situ sputtered AlN nucleation layer has been demonstrated effective to significantly improve crystal quality and electrical properties of GaN epitaxy layers for GaN based Light-emitting diodes (LEDs). In this report, we have successfully reduced X-ray (102) FWHM from 240 to 110 arcsec, and (002) FWHM from 230 to 101 arcsec. In addition, reverse-bias voltage (Vr) increased around 20% with the sputtered AlN nucleation layer. Furthermore, output power of LEDs grown on sputtered AlN nucleation layer can be improved around 4.0% compared with LEDs which is with conventional GaN nucleation layer on pattern sapphire substrate (PSS).

  20. Selective heteroepitaxy on deeply grooved substrate: A route to low cost semipolar GaN platforms of bulk quality

    NASA Astrophysics Data System (ADS)

    Tendille, Florian; Martin, Denis; Vennéguès, Philippe; Grandjean, Nicolas; De Mierry, Philippe

    2016-08-01

    Semipolar GaN crystal stripes larger than 100 μm with dislocation densities below 5 × 106 cm-2 are achieved using a low cost fabrication process. An original sapphire patterning procedure is proposed, enabling selective growth of semipolar oriented GaN stripes while confining the defects to specific areas. Radiative and non-radiative crystalline defects are investigated by cathodoluminescence and can be correlated to the development of crystal microstructure during the growth process. A dislocation reduction mechanism, supported by transmission electron microscopy, is proposed. This method represents a step forward toward low-cost quasi-bulk semipolar GaN epitaxial platforms with an excellent structural quality which will allow for even more efficient III-nitride based devices.

  1. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Bajaj, Sanyam; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang; Reza, Shahed; Chumbes, Eduardo M.; Khurgin, Jacob; Rajan, Siddharth

    2015-10-01

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 107 cm/s at a low sheet charge density of 7.8 × 1011 cm-2. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  2. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    SciTech Connect

    Bajaj, Sanyam Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang; Reza, Shahed; Chumbes, Eduardo M.; Khurgin, Jacob; Rajan, Siddharth

    2015-10-12

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10{sup 7 }cm/s at a low sheet charge density of 7.8 × 10{sup 11 }cm{sup −2}. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  3. Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

    SciTech Connect

    Chen, Jr-Tai Hsu, Chih-Wei; Forsberg, Urban; Janzén, Erik

    2015-02-28

    Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

  4. Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

    NASA Astrophysics Data System (ADS)

    Chen-Tai, Jr.; Hsu, Chih-Wei; Forsberg, Urban; Janzén, Erik

    2015-02-01

    Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H2 atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ˜2000 cm2/V.s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ˜1 × 1020 cm-3 at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm2 SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

  5. Dielectric properties of highly resistive GaN crystals grown by ammonothermal method at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Krupka, Jerzy; Zajåc, Marcin; Kucharski, Robert; Gryglewski, Daniel

    2016-03-01

    Permittivity, the dielectric loss tangent and conductivity of semi-insulating Gallium Nitride crystals have been measured as functions of frequency from 10 GHz to 50 GHz and temperature from 295 to 560 K employing quasi TE0np mode dielectric resonator technique. Crystals were grown using ammonothermal method. Two kinds of doping were used to obtain high resistivity crystals; one with deep acceptors in form of transition metal ions, and the other with shallow Mg acceptors. The sample compensated with transition metal ions exhibited semi-insulating behavior in the whole temperature range. The sample doped with Mg acceptors remained semi-insulating up to 390 K. At temperatures exceeding 390 K the conductivity term in the total dielectric loss tangent of Mg compensated sample becomes dominant and it increases exponentially with activation energy of 1.14 eV. It has been proved that ammonothermal method with appropriate doping allows growth of high quality, temperature stable semi-insulating GaN crystals.

  6. Fabrication of high reflectivity nanoporous distributed Bragg reflectors by controlled electrochemical etching of GaN

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Min; Kang, Jin-Ho; Lee, June Key; Ryu, Sang-Wan

    2016-07-01

    The nanoporous medium is a valuable feature of optical devices because of its variable optical refractive index with porosity. One important application is in a GaN-based vertical cavity surface emitting laser having a distributed Bragg reflector (DBR) composed of alternating nanoporous and bulk GaNs. However, optimization of the fabrication process for high reflectivity DBRs having wellcontrolled high reflection bands has not been studied yet. We used electrochemical etching to study the fabrication process of a nanoporous GaN DBR and analyzed the relationship between the morphology and optical reflectivity. Several electrolytes were examined for the formation of the optimized nanoporous structure. A highly reflective DBRs having reflectivity of ~100% were obtained over a wide wavelength range of 450-750 nm. Porosification of semiconductors into nanoporous layers could provide a high reflectivity DBR due to controlled index-contrast, which would be advantages for the construction of a high-Q optical cavity.

  7. Fabrication of high reflectivity nanoporous distributed Bragg reflectors by controlled electrochemical etching of GaN

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Min; Kang, Jin-Ho; Lee, June Key; Ryu, Sang-Wan

    2016-09-01

    The nanoporous medium is a valuable feature of optical devices because of its variable optical refractive index with porosity. One important application is in a GaN-based vertical cavity surface emitting laser having a distributed Bragg reflector (DBR) composed of alternating nanoporous and bulk GaNs. However, optimization of the fabrication process for high reflectivity DBRs having wellcontrolled high reflection bands has not been studied yet. We used electrochemical etching to study the fabrication process of a nanoporous GaN DBR and analyzed the relationship between the morphology and optical reflectivity. Several electrolytes were examined for the formation of the optimized nanoporous structure. A highly reflective DBRs having reflectivity of ~100% were obtained over a wide wavelength range of 450-750 nm. Porosification of semiconductors into nanoporous layers could provide a high reflectivity DBR due to controlled index-contrast, which would be advantages for the construction of a high-Q optical cavity.

  8. GaN transistors on Si for switching and high-frequency applications

    NASA Astrophysics Data System (ADS)

    Ueda, Tetsuzo; Ishida, Masahiro; Tanaka, Tsuyoshi; Ueda, Daisuke

    2014-10-01

    In this paper, recent advances of GaN transistors on Si for switching and high-frequency applications are reviewed. Novel epitaxial structures including superlattice interlayers grown by metal organic chemical vapor deposition (MOCVD) relieve the strain and eliminate the cracks in the GaN over large-diameter Si substrates up to 8 in. As a new device structure for high-power switching application, Gate Injection Transistors (GITs) with a p-AlGaN gate over an AlGaN/GaN heterostructure successfully achieve normally-off operations maintaining high drain currents and low on-state resistances. Note that the GITs on Si are free from current collapse up to 600 V, by which the drain current would be markedly reduced after the application of high drain voltages. Highly efficient operations of an inverter and DC-DC converters are presented as promising applications of GITs for power switching. The high efficiencies in an inverter, a resonant LLC converter, and a point-of-load (POL) converter demonstrate the superior potential of the GaN transistors on Si. As for high-frequency transistors, AlGaN/GaN heterojuction field-effect transistors (HFETs) on Si designed specifically for microwave and millimeter-wave frequencies demonstrate a sufficiently high output power at these frequencies. Output powers of 203 W at 2.5 GHz and 10.7 W at 26.5 GHz are achieved by the fabricated GaN transistors. These devices for switching and high-frequency applications are very promising as future energy-efficient electronics because of their inherent low fabrication cost and superior device performance.

  9. Mg 2+-doped GaN nanoparticles as blue-light emitters: a method to avoid sintering at high temperatures.

    PubMed

    Mahalingam, Venkataramanan; Sudarsan, Vasanthakumaran; Munusamy, Prabhakaran; van Veggel, Frank C J M; Wang, Rui; Steckl, Andrew J; Raudsepp, Mati

    2008-01-01

    Bright blue-light emission at 410 nm is observed from Mg(2+)-doped GaN nanoparticles prepared by the nitridation of Ga(2)MgO(4) nanoparticles at 950 degrees C. The sintering of these nanoparticles during high-temperature nitridation was prevented by mixing the Ga(2)MgO(4) precursor nanoparticles with La(2)O(3) as an inert matrix before the nitridation process. The Mg(2+)-doped GaN nanoparticles were isolated from the matrix by etching with 10 % nitric acid. The Mg(2+)-doped GaN nanoparticles were characterized by photoluminescence, atomic force microscopy, X-ray diffraction, and IR analyses.

  10. Radar Waveform Pulse Analysis Measurement System for High-Power GaN Amplifiers

    NASA Technical Reports Server (NTRS)

    Thrivikraman, Tushar; Perkovic-Martin, Dragana; Jenabi, Masud; Hoffman, James

    2012-01-01

    This work presents a measurement system to characterize the pulsed response of high-power GaN amplifiers for use in space-based SAR platforms that require very strict amplitude and phase stability. The measurement system is able to record and analyze data on three different time scales: fast, slow, and long, which allows for greater detail of the mechanisms that impact amplitude and phase stability. The system is fully automated through MATLAB, which offers both instrument control capability and in-situ data processing. To validate this system, a high-power GaN HEMT amplifier operated in saturation was characterized. The fast time results show that variations to the amplitude and phase are correlated to DC supply transients, while long time characteristics are correlated to temperature changes.

  11. Spectroscopic study of semipolar ( 11 2 ¯ 2 ) -HVPE GaN exhibiting high oxygen incorporation

    NASA Astrophysics Data System (ADS)

    Schustek, Philipp; Hocker, Matthias; Klein, Martin; Simon, Ulrich; Scholz, Ferdinand; Thonke, Klaus

    2014-10-01

    Spatially resolved luminescence and Raman spectroscopy investigations are applied to a series of ( 11 2 ¯ 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 1019 cm-3. In addition, the strain state is assessed by Raman spectroscopy and compared to a finite element analysis.

  12. 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.

  13. Design and simulation of a novel GaN based resonant tunneling high electron mobility transistor on a silicon substrate

    NASA Astrophysics Data System (ADS)

    Chowdhury, Subhra; Chattaraj, Swarnabha; Biswas, Dhrubes

    2015-04-01

    For the first time, we have introduced a novel GaN based resonant tunneling high electron mobility transistor (RTHEMT) on a silicon substrate. A monolithically integrated GaN based inverted high electron mobility transistor (HEMT) and a resonant tunneling diode (RTD) are designed and simulated using the ATLAS simulator and MATLAB in this study. The 10% Al composition in the barrier layer of the GaN based RTD structure provides a peak-to-valley current ratio of 2.66 which controls the GaN based HEMT performance. Thus the results indicate an improvement in the current-voltage characteristics of the RTHEMT by controlling the gate voltage in this structure. The introduction of silicon as a substrate is a unique step taken by us for this type of RTHEMT structure.

  14. Basic Equations for the Modeling of Gallium Nitride (gan) High Electron Mobility Transistors (hemts)

    NASA Technical Reports Server (NTRS)

    Freeman, Jon C.

    2003-01-01

    Gallium nitride (GaN) is a most promising wide band-gap semiconductor for use in high-power microwave devices. It has functioned at 320 C, and higher values are well within theoretical limits. By combining four devices, 20 W has been developed at X-band. GaN High Electron Mobility Transistors (HEMTs) are unique in that the two-dimensional electron gas (2DEG) is supported not by intentional doping, but instead by polarization charge developed at the interface between the bulk GaN region and the AlGaN epitaxial layer. The polarization charge is composed of two parts: spontaneous and piezoelectric. This behavior is unlike other semiconductors, and for that reason, no commercially available modeling software exists. The theme of this document is to develop a self-consistent approach to developing the pertinent equations to be solved. A Space Act Agreement, "Effects in AlGaN/GaN HEMT Semiconductors" with Silvaco Data Systems to implement this approach into their existing software for III-V semiconductors, is in place (summer of 2002).

  15. In situ GaN decomposition analysis by quadrupole mass spectrometry and reflection high-energy electron diffraction

    SciTech Connect

    Fernandez-Garrido, S.; Calleja, E.; Koblmueller, G.; Speck, J. S.

    2008-08-01

    Thermal decomposition of wurtzite (0001)-oriented GaN was analyzed: in vacuum, under active N exposure, and during growth by rf plasma-assisted molecular beam epitaxy. The GaN decomposition rate was determined by measurements of the Ga desorption using in situ quadrupole mass spectrometry, which showed Arrhenius behavior with an apparent activation energy of 3.1 eV. Clear signatures of intensity oscillations during reflection high-energy electron diffraction measurements facilitated complementary evaluation of the decomposition rate and highlighted a layer-by-layer decomposition mode in vacuum. Exposure to active nitrogen, either under vacuum or during growth under N-rich growth conditions, strongly reduced the GaN losses due to GaN decomposition.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  17. P-type doping of GaN

    SciTech Connect

    Wong, R.K.

    2000-04-10

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

  18. 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.

  19. AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor

    NASA Astrophysics Data System (ADS)

    Bergsten, Johan; Li, Xun; Nilsson, Daniel; Danielsson, Örjan; Pedersen, Henrik; Janzén, Erik; Forsberg, Urban; Rorsman, Niklas

    2016-05-01

    AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using an alternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuning the growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growth conditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation and dispersion. Good isolation with OFF-state currents of 2 × 10-6 A/mm, breakdown fields of 70 V/µm, and low drain induced barrier lowering of 0.13 mV/V are found. Dispersive effects are examined using pulsed current-voltage measurements. Current collapse and knee walkout effects limit the maximum output power to 1.3 W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer a versatile approach to decrease dispersive effects in GaN HEMTs.

  20. Effects of the group V/III ratio and a gan inter-layer on the crystal quality of InN grown by using the hydride vapor-phase epitaxy method

    NASA Astrophysics Data System (ADS)

    Ha, Ju-Hyung; Wang, Juan; Lee, Won-Jae; Choi, Young-Jun; Lee, Hae-Yong; Kim, Jung-Gon; Harima, Hiroshi

    2015-03-01

    The hydride vapor-phase epitaxy (HVPE) method was used to deposit high-quality InN layers on GaN inter-layer/sapphire (0001) structures that had been fabricated by using either the HVPE method or the metal-organic chemical-phase deposition (MOCVD) method. The effects of the group V/III ratio and different GaN inter-layers on the crystal quality of the InN layers were systemically investigated. The InN layer grown at a low Group V/III ratio revealed a high crystal quality with a two-dimensional (2D) growth mode. Also, the 110.7-nm-thick InN layer grown by using HVPE on a GaN inter-layer/sapphire (0001) substrate structure that had been fabricated by using MOCVD had a high crystal quality, with the full width at half maximum (FWHM) of the InN X-ray diffraction (XRD) peak being about 844 arcsec, and a smooth surface with an atomic force microscopy (AFM) roughness of about 0.07 nm. On the other hand, the 145.7-nm-thick InN layer grown by using HVPE on a GaN inter-layer/sapphire (0001) substrate structure that had been fabricated by using the HVPE method had a lower crystal quality, a FWHM value for the InN (0002) peak of about 2772 arcsec, and a surface roughness of about 3.73 nm. In addition, the peak of the E2 (high) phonon mode for the 110.7-nm-thick InN layer grown by using HVPE on a GaN inter-layer/sapphire (0001) structure that had been fabricated by using MOCVD was detected at 491 cm -1 and had a FWHM of 9.9 cm-1. As a result, InN layers grown by using HVPE on GaN inter-layer/sapphire (0001) substrate structures fabricated by using MOCVD have a high crystal quality and a reduced Raman value, which agrees well with the results of the XRD analysis.

  1. Effect of nitridation surface treatment on silicon (1 1 1) substrate for the growth of high quality single-crystalline GaN hetero-epitaxy layer by MOCVD

    NASA Astrophysics Data System (ADS)

    Rahman, Mohd Nazri Abd.; Yusuf, Yusnizam; Mansor, Mazwan; Shuhaimi, Ahmad

    2016-01-01

    A single-crystalline with high quality of gallium nitride epilayers was grown on silicon (1 1 1) substrate by metal organic chemical vapor deposition. The process of nitridation surface treatment was accomplished on silicon (1 1 1) substrate by flowing the ammonia gaseous. Then, it was followed by a thin aluminum nitride nucleation layer, aluminum nitride/gallium nitride multi-layer and a thick gallium nitride epilayer. The influence of in situ nitridation surface treatment on the crystallinity quality of gallium nitride epilayers was studied by varying the nitridation times at 40, 220 and 400 s, respectively. It was shown that the nitridation times greatly affect the structural properties of the grown top gallium nitride epilayer on silicon (1 1 1) substrate. In the (0 0 0 2) and (1 0 1 bar 2) X-ray rocking curve analysis, a narrower value of full width at half-maximum has been obtained as the nitridation time increased. This is signifying the reduction of dislocation density in the gallium nitride epilayer. This result was supported by the value of bowing and root mean square roughness measured by surface profilometer and atomic force microscopy. Furthermore, a crack-free gallium nitride surface with an abrupt cross-sectional structure that observed using field effect scanning electron microscopy was also been obtained. The phi-scan curve of asymmetric gallium nitride proved the top gallium nitride epilayer exhibited a single-crystalline structure.

  2. 4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication.

    PubMed

    Lee, Changmin; Zhang, Chong; Cantore, Michael; Farrell, Robert M; Oh, Sang Ho; Margalith, Tal; Speck, James S; Nakamura, Shuji; Bowers, John E; DenBaars, Steven P

    2015-06-15

    We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.

  3. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    SciTech Connect

    Hodges, C. Pomeroy, J.; Kuball, M.

    2014-02-14

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  4. 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. PMID:19417425

  5. 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.

  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. 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

  8. 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.

  9. Threading dislocation-governed degradation in crystal quality of heteroepitaxial materials: The case of InAlN nearly lattice-matched to GaN

    NASA Astrophysics Data System (ADS)

    Chen, Z. T.; Fujita, K.; Ichikawa, J.; Egawa, T.

    2012-03-01

    The crystal qualities of InAlN nearly lattice-matched (LM) to GaN with different thicknesses have been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the crystal quality of InAlN starts to degrade when the InAlN thickness exceeds several hundred nanometers, forming a structure consisting of two sub-layers with one sub-layer coherent to GaN and the other being degraded. Moreover, the degradation was found to be governed by the threading dislocations (TDs) propagation from the underlying GaN layer, rather than by the misfit strain between InAlN and GaN. Based on TEM observations, the growth evolution of the two-sub-layer structure is proposed, which is different from those conventional mechanisms of crystal-quality degradation in heteroepitaxial material. The results of InAlN nearly LM to GaN are suggested to be helpful in understanding the growths of lattice-mismatched systems of other In-contained III-nitrides, including InGaN/GaN.

  10. High temperature electron spin dynamics in bulk cubic GaN: Nanosecond spin lifetimes far above room-temperature

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    The electron spin dynamics in n-doped bulk cubic GaN is investigated for very high temperatures from 293 K up to 500 K by time-resolved Kerr-rotation spectroscopy. We find extraordinarily long spin lifetimes exceeding 1 ns at 500 K. The temperature dependence of the spin relaxation time is in qualitative agreement with predictions of Dyakonov-Perel theory, while the absolute experimental times are an order of magnitude shorter than predicted. Possible reasons for this discrepancy are discussed, including the role of phase mixtures of hexagonal and cubic GaN as well as the impact of localized carriers.

  11. Nanoheteroepitaxial growth of GaN on Si nanopillar arrays

    NASA Astrophysics Data System (ADS)

    Hersee, S. D.; Sun, X. Y.; Wang, X.; Fairchild, M. N.; Liang, J.; Xu, J.

    2005-06-01

    Nanoheteroepitaxial growth of GaN by metal-organic chemical-vapor deposition on dense arrays of (111) Si nanopillars has been investigated. Scanning electron microscopy, cross-sectional transmission electron microscopy, and electron-diffraction analysis of 0.15-μm-thick GaN layers indicate single-crystal films. Most of the mismatch defects were in-plane stacking faults and the threading dislocation concentration was <108cm-2 at the interface and decreased away from the interface. High-resolution transmission electron microscopy indicated that grain-boundary defects could heal and were followed by high quality, single-crystal GaN. Facetted voids were also present at the GaN /Si interface and are believed to be an additional strain-energy reduction mechanism. The unusual defect behavior in these samples appears to be related to the high compliance of the nanopillar silicon substrate.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  13. Epitaxy of GaN Nanowires on Graphene.

    PubMed

    Kumaresan, Vishnuvarthan; Largeau, Ludovic; Madouri, Ali; Glas, Frank; Zhang, Hezhi; Oehler, Fabrice; Cavanna, Antonella; Babichev, Andrey; Travers, Laurent; Gogneau, Noelle; Tchernycheva, Maria; Harmand, Jean-Christophe

    2016-08-10

    Epitaxial growth of GaN nanowires on graphene is demonstrated using molecular beam epitaxy without any catalyst or intermediate layer. Growth is highly selective with respect to silica on which the graphene flakes, grown by chemical vapor deposition, are transferred. The nanowires grow vertically along their c-axis and we observe a unique epitaxial relationship with the ⟨21̅1̅0⟩ directions of the wurtzite GaN lattice parallel to the directions of the carbon zigzag chains. Remarkably, the nanowire density and height decrease with increasing number of graphene layers underneath. We attribute this effect to strain and we propose a model for the nanowire density variation. The GaN nanowires are defect-free and they present good optical properties. This demonstrates that graphene layers transferred on amorphous carrier substrates is a promising alternative to bulk crystalline substrates for the epitaxial growth of high quality GaN nanostructures.

  14. Epitaxy of GaN Nanowires on Graphene.

    PubMed

    Kumaresan, Vishnuvarthan; Largeau, Ludovic; Madouri, Ali; Glas, Frank; Zhang, Hezhi; Oehler, Fabrice; Cavanna, Antonella; Babichev, Andrey; Travers, Laurent; Gogneau, Noelle; Tchernycheva, Maria; Harmand, Jean-Christophe

    2016-08-10

    Epitaxial growth of GaN nanowires on graphene is demonstrated using molecular beam epitaxy without any catalyst or intermediate layer. Growth is highly selective with respect to silica on which the graphene flakes, grown by chemical vapor deposition, are transferred. The nanowires grow vertically along their c-axis and we observe a unique epitaxial relationship with the ⟨21̅1̅0⟩ directions of the wurtzite GaN lattice parallel to the directions of the carbon zigzag chains. Remarkably, the nanowire density and height decrease with increasing number of graphene layers underneath. We attribute this effect to strain and we propose a model for the nanowire density variation. The GaN nanowires are defect-free and they present good optical properties. This demonstrates that graphene layers transferred on amorphous carrier substrates is a promising alternative to bulk crystalline substrates for the epitaxial growth of high quality GaN nanostructures. PMID:27414518

  15. GaN grown on nano-patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  17. Development of patterned sapphire substrate and the application to the growth of non-polar and semi-polar GaN for light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Tadatomo, Kazuyuki; Okada, Narihito

    2011-03-01

    The light-emitting diodes (LEDs) with high external quantum efficiency (EQE) are usually fabricated on the patterned sapphire substrate (PSS). The PSS reduces the dislocation density in the GaN layer and enhances the light extraction efficiency (LEE) from the LED chip by scattering the light confined in GaN layer attributed to the critical angle between GaN (n=2.4) and sapphire substrate (n=1.7) (or air (n=1.0)). On the other hand, non-polar GaN and semipolar GaN are attracted much attention to eliminate the quantum confined Stark effect (QCSE). Recently, we have developed novel technology to grow non-polar or semi-polar GaN on the PSS with high quality and large diameter by metal-organic vapor phase epitaxy (MOVPE). For example, m-plane GaN grown on a-plane PSS and {112 (see manuscript)} plane GaN grown on r-plane PSS. The growth of c-plane GaN from the c-plane-like sidewall of the r-plane PSS results in {112 (see manuscript)} GaN on the r-plane PSS. The full widths at half maximum of X-ray rocking curves (FWHM-XRC) of the {112(see manuscript)} GaN along the azimuths parallel and perpendicular to the c-direction were 533 and 260 arcsec, respectively. Dislocation density of the GaN was approximately 2×108 cm-2. These non-polar and semi-polar GaN are expected to be suitable for novel GaN substrate or GaN template for LEDs.

  18. High-Density Plasma-Induced Etch Damage of GaN

    SciTech Connect

    Baca, A.G.; Han, J.; Lester, L.F.; Pearton, S.J.; Ren, F.; Shul, R.J.; Willison, C.G.; Zhang, L.; Zolper, J.C.

    1999-04-29

    Anisotropic, smooth etching of the group-III nitrides has been reported at relatively high rates in high-density plasma etch systems. However, such etch results are often obtained under high de-bias andlor high plasma flux conditions where plasma induced damage can be significant. Despite the fact that the group-III nitrides have higher bonding energies than more conventional III-V compounds, plasma-induced etch damage is still a concern. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or anisotropy which significantly limits critical dimensions and reduces the utility of the process for device applications requiring vertical etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in sheet resistance and contact resistance for n- and p-type GaN samples exposed to an Ar inductively coupled plasma (ICP). In general, plasma-induced damage was more sensitive to ion bombardment energies as compared to plasma flux. In addition, p-GaN was typically more sensitive to plasma-induced damage as compared to n-GaN.

  19. 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.

  20. Franz–Keldysh effect in n-type GaN Schottky barrier diode under high reverse bias voltage

    NASA Astrophysics Data System (ADS)

    Maeda, Takuya; Okada, Masaya; Ueno, Masaki; Yamamoto, Yoshiyuki; Horita, Masahiro; Suda, Jun

    2016-09-01

    The photocurrent of GaN vertical Schottky barrier diodes was investigated under sub-bandgap wavelength light irradiation. Under a low reverse bias voltage, the photocurrent is induced by internal photoemission, while under a high reverse bias voltage, the photocurrent increases significantly with the bias voltage. This is due to sub-bandgap optical absorption in a depletion region due to the Franz–Keldysh effect. The voltage and wavelength dependences of the photocurrent are successfully explained quantitatively.

  1. Transistors for Electric Motor Drives: High-Performance GaN HEMT Modules for Agile Power Electronics

    SciTech Connect

    2010-09-01

    ADEPT Project: Transphorm is developing transistors with gallium nitride (GaN) semiconductors that could be used to make cost-effective, high-performance power converters for a variety of applications, including electric motor drives which transmit power to a motor. A transistor acts like a switch, controlling the electrical energy that flows around an electrical circuit. Most transistors today use low-cost silicon semiconductors to conduct electrical energy, but silicon transistors don’t operate efficiently at high speeds and voltage levels. Transphorm is using GaN as a semiconductor material in its transistors because GaN performs better at higher voltages and frequencies, and it is more energy efficient than straight silicon. However, Transphorm is using inexpensive silicon as a base to help keep costs low. The company is also packaging its transistors with other electrical components that can operate quickly and efficiently at high power levels—increasing the overall efficiency of both the transistor and the entire motor drive.

  2. Highly mismatched GaN1‑x Sb x alloys: synthesis, structure and electronic properties

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  3. Coherent growth of GaGdN layers with high Gd concentration on GaN(0001)

    SciTech Connect

    Higashi, K.; Hasegawa, S.; Abe, D.; Mitsuno, Y.; Komori, S.; Ishimaru, M.; Asahi, H.; Ishikawa, F.

    2012-11-26

    We report on the coherent growth of GaGdN with high Gd concentration on a GaN template using radio-frequency plasma-assisted molecular beam epitaxy under elevated growth conditions. X-ray diffraction and cross-sectional transmission electron microscopy observations revealed that at a growth temperature of 700 {sup Degree-Sign }C or below, GaGdN layers are coherently grown on the GaN templates without segregation of the secondary phases. As the GdN mole fraction x was increased to 0.08, the c-axis lattice parameter in Ga{sub 1-x}Gd{sub x}N increased linearly. Increasing the growth temperature to 750 {sup Degree-Sign }C causes lattice relaxation in GaGdN. All GaGdN samples exhibited photoluminescence emissions near the band-edge, a blue luminescence band emission, and a green luminescence band emission. The origin of the green luminescence band emission is discussed in relation to the compressive strain existing in the GaGdN layers coherently grown on GaN.

  4. High-breakdown-voltage pn-junction diodes on GaN substrates

    NASA Astrophysics Data System (ADS)

    Yoshizumi, Yusuke; Hashimoto, Shin; Tanabe, Tatsuya; Kiyama, Makoto

    2007-01-01

    GaN pn-junction diodes have been grown on GaN and sapphire substrates by metalorganic vapor phase epitaxy and their electrical characteristics have been studied. For the diode on the GaN substrate, the reverse leakage current is lower and the breakdown voltage VB is higher than those on the sapphire substrate owing to the lower dislocation density. The breakdown voltage is further improved with decreasing Mg concentration in p-GaN layers. Analysis of the depletion-layer capacitance of pn diodes has revealed that the Mg acceptors are fully ionized in the depletion layer. By optimizing the growth conditions, the diodes on GaN substrates show extremely low leakage current and the ideal hard breakdown at -925 V. The breakdown field is estimated to be 3.27 MV/cm. The specific on-resistance RON of 6.3 mΩ cm 2 is obtained, leading to the figure of merit, VB2/R, of 136 MW/cm 2.

  5. Growth of a-plane GaN on lattice-matched ZnO substrates using a room-temperature buffer layer

    NASA Astrophysics Data System (ADS)

    Kobayashi, Atsushi; Kawano, Satoshi; Ueno, Kohei; Ohta, Jitsuo; Fujioka, Hiroshi; Amanai, Hidetaka; Nagao, Satoru; Horie, Hideyoshi

    2007-11-01

    Nonpolar a-plane GaN films were grown on nearly lattice-matched a-plane ZnO substrates by pulsed laser deposition. Growth of GaN on a-plane ZnO at conventional growth temperatures (around 700°C) resulted in the formation of polycrystalline materials, probably due to the interface reactions between GaN and ZnO. However, single crystalline a-plane GaN with an atomically flat surface can be grown on ZnO at room temperature in the layer-by-layer mode. X-ray diffraction and photoluminescence measurements revealed that high-quality a-plane GaN films can also be grown at elevated substrate temperatures (up to 700°C) by using a RT a-plane GaN film as a buffer layer.

  6. High-performance AlGaN /GaN lateral field-effect rectifiers compatible with high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Chen, Wanjun; Wong, King-Yuen; Huang, Wei; Chen, Kevin J.

    2008-06-01

    A high electron mobility transistor (HEMT)-compatible power lateral field-effect rectifier (L-FER) with low turn-on voltage is demonstrated using the same fabrication process as that for normally off AlGaN /GaN HEMT, providing a low-cost solution for GaN power integrated circuits. The power rectifier features a Schottky-gate-controlled two-dimensional electron gas channel between the cathode and anode. By tying up the Schottky gate and anode together, the forward turn-on voltage of the rectifier is determined by the threshold voltage of the channel instead of the Schottky barrier. The L-FER with a drift length of 10μm features a forward turn-on voltage of 0.63V at a current density of 100A/cm2. This device also exhibits a reverse breakdown voltage (BV) of 390V at a current level of 1mA/mm and a specific on resistance (RON,sp) of 1.4mΩcm2, yielding a figure of merit (BV2/RON,sp) of 108MW/cm2. The excellent device performance, coupled with the lateral device structure and process compatibility with AlGaN /GaN HEMT, make the proposed L-FER a promising candidate for GaN power integrated circuits.

  7. 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).

  8. 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)

  9. 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.

  10. Anisotropy of effective electron masses in highly doped nonpolar GaN

    SciTech Connect

    Feneberg, Martin Lange, Karsten; Lidig, Christian; Wieneke, Matthias; Witte, Hartmut; Bläsing, Jürgen; Dadgar, Armin; Krost, Alois; Goldhahn, Rüdiger

    2013-12-02

    The anisotropic effective electron masses in wurtzite GaN are determined by generalized infrared spectroscopic ellipsometry. Nonpolar (112{sup ¯}0) oriented thin films allow accessing both effective masses, m{sub ⊥}{sup *} and m{sub ∥}{sup *}, by determining the screened plasma frequencies. A n-type doping range up to 1.7 × 10{sup 20} cm{sup −3} is investigated. The effective mass ratio m{sub ⊥}{sup *}/m{sub ∥}{sup *} is obtained with highest accuracy and is found to be 1.11 independent on electron concentration up to 1.2 × 10{sup 20} cm{sup −3}. For higher electron concentrations, the conduction band non-parabolicity is mirrored in changes. Absolute values for effective electron masses depend on additional input of carrier concentrations determined by Hall effect measurements. We obtain m{sub ⊥}{sup *}=(0.239±0.004)m{sub 0} and m{sub ∥}{sup *}=(0.216±0.003)m{sub 0} for the parabolic range of the GaN conduction band. Our data are indication of a parabolic GaN conduction band up to an energy of approximately 400 meV above the conduction band minimum.

  11. High uniform growth of 4-inch GaN wafer via flow field optimization by HVPE

    NASA Astrophysics Data System (ADS)

    Cheng, Yutian; Liu, Peng; Wu, Jiejun; Xiang, Yong; Chen, Xinjuan; Ji, Cheng; Yu, Tongjun; Zhang, Guoyi

    2016-07-01

    The uniformity of flow field inner the reactor plays a crucial role for hydride vapor phase epitaxy (HVPE) crystal growth and its more important for large scale substrate. A new nozzle structure was designed by adding a push and dilution (PD) gas pipe in the center of gas channels for a 4-inch HVPE (PD-HVPE) system. Experimental results showed that the thickness inhomogeneity of 46 μm 4-inch GaN layer could reach ±1.8% by optimizing PD gas, greatly improved from ±14% grown with conventional nozzle. The simulations of the internal flow field were consistent with our experiment, and the enhancement in uniformity should be attributed to the redistribution of GaCl and NH3 upon the wafer induced by PD pipe. The full width at half maximum (FWHM) of X-ray diffraction rocking curves for the 4-inch GaN film were about 224 and 200 arcsec for (002) and (102) reflection. The dislocation density of as-grown GaN was about 6.4×107 cm-2.

  12. Patterning of GaN in high-density Cl{sub 2}- and BCl{sub 3}-based plasmas

    SciTech Connect

    Shul, R.J.; Briggs, R.D.; Han, J.; Pearton, S.J.; Lee, J.W.; Vartuli, C.B.; Killeen, K.P.; Ludowise, M.J.

    1997-05-01

    Fabrication of group-III nitride electronic and photonic devices relies heavily on the ability to pattern features with anisotropic profiles, smooth surface morphologies, etch rates often exceeding 1 {micro}m/min, and a low degree of plasma-induced damage. Patterning these materials has been especially difficult due to their high bond energies and their relatively inert chemical nature as compared to other compound semiconductors. However, high-density plasma etching has been an effective patterning technique due to ion fluxes which are 2 to 4 orders of magnitude higher than conventional RIE systems. GaN etch rates as high as {approximately}1.3 {micro}m/min have been reported in ECR generated ICl plasmas at {minus}150 V dc-bias. In this study, the authors report high-density GaN etch results for ECR- and ICP-generated plasmas as a function of Cl{sub 2}- and BCl{sub 3}-based plasma chemistries.

  13. 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.

  14. Highly mismatched crystalline and amorphous GaN(1-x)As(x) alloys in the whole composition range

    SciTech Connect

    Yu, K. M.; Novikov, S. V.; Broesler, R.; Demchenko, I. N.; Denlinger, J. D.; Liliental-Weber, Z.; Luckert, F.; Martin, R. W.; Walukiewicz, W.; Foxon, C. T.

    2009-08-29

    Alloying is a commonly accepted method to tailor properties of semiconductor materials for specific applications. Only a limited number of semiconductor alloys can be easily synthesized in the full composition range. Such alloys are, in general, formed of component elements that are well matched in terms of ionicity, atom size, and electronegativity. In contrast there is a broad class of potential semiconductor alloys formed of component materials with distinctly different properties. In most instances these mismatched alloys are immiscible under standard growth conditions. Here we report on the properties of GaN1-xAsx, a highly mismatched, immiscible alloy system that was successfully synthesized in the whole composition range using a nonequilibrium low temperature molecular beam epitaxy technique. The alloys are amorphous in the composition range of 0.17GaN to ~;;0.8 eV at x~;;0.85. The reduction in the band gap can be attributed primarily to the downward movement of the conduction band for alloys with x>0.2, and to the upward movement of the valence band for alloys with x<0.2. The unique features of the band structure offer an opportunity of using GaN1-xAsx alloys for various types of solar power conversion devices.

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

    SciTech Connect

    Kyle, Erin C. H. Kaun, Stephen W.; Burke, Peter G.; Wu, Feng; Speck, James S.; Wu, Yuh-Renn

    2014-05-21

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

  16. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy

    PubMed Central

    2012-01-01

    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. PMID:23270331

  17. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy.

    PubMed

    Zhong, Aihua; Hane, Kazuhiro

    2012-01-01

    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. PMID:23270331

  18. 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.

  19. Au-Free GaN High-Electron-Mobility Transistor with Ti/Al/W Ohmic and WN X Schottky Metal Structures for High-Power Applications

    NASA Astrophysics Data System (ADS)

    Hsieh, Ting-En; Lin, Yueh-Chin; Chu, Chung-Ming; Chuang, Yu-Lin; Huang, Yu-Xiang; Shi, Wang-Cheng; Dee, Chang-Fu; Majlis, Burhanuddin Yeop; Lee, Wei-I.; Chang, Edward Yi

    2016-07-01

    In this study, an Au-free AlGaN/GaN high-electron-mobility transistor (HEMT) with Ti/Al/W ohmic and WN x Schottky metal structures is fabricated and characterized. The device exhibits smooth surface morphology after metallization and shows excellent direct-current (DC) characteristics. The device also demonstrates better performance than the conventional HEMTs under high voltage stress. Furthermore, the Au-free AlGaN/GaN HEMT shows stable device performance after annealing at 400°C. Thus, the Ti/Al/W ohmic and WN X Schottky metals can be applied in the manufacturing of GaN HEMT to replace the Au based contacts to reduce the manufacturing costs of the GaN HEMT devices with comparable device performance.

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

    NASA Astrophysics Data System (ADS)

    Zhou, Hong; Du, Yuchen; Ye, Peide D.

    2016-05-01

    Herein, we report on achieving ultra-high electron density (exceeding 1014 cm-2) in a GaN bulk material device by ionic liquid gating, through the application of atomic layer deposition (ALD) of Al2O3 to passivate the GaN surface. Output characteristics demonstrate a maximum drain current of 1.47 A/mm, the highest reported among all bulk GaN field-effect transistors, with an on/off ratio of 105 at room temperature. An ultra-high electron density exceeding 1014 cm-2 accumulated at the surface is confirmed via Hall-effect measurement and transfer length measurement. In addition to the ultra-high electron density, we also observe a reduction of the contact resistance due to the narrowing of the Schottky barrier width on the contacts. Taking advantage of the ALD surface passivation and ionic liquid gating technique, this work provides a route to study the field-effect and carrier transport properties of conventional semiconductors in unprecedented ultra-high charge density regions.

  1. Ultrafast carrier dynamics in GaN nanorods

    SciTech Connect

    Yang, Chi-Yuan; Chia, Chih-Ta; Chen, Hung-Ying; Gwo, Shangjr; Lin, Kung-Hsuan

    2014-11-24

    We present ultrafast time-resolved optical spectroscopy on GaN nanorods at room temperature. The studied GaN nanorods, with diameters of ∼50 nm and lengths of ∼400 nm, were grown on the silicon substrate. After femtosecond optical pulses excited carriers in the GaN nanorods, the carriers thermalized within a few picoseconds. Subsequently, the electrons are trapped by the surface states on the order of 20 ps. After the surface electric field was reformed in the GaN nanorods, we found the lifetime of the residue carriers in GaN nanorods is longer than 1.7 ns at room temperature, while the lifetime of carriers in GaN thin film is typically a few hundred picoseconds. Our findings indicate that GaN nanorods have higher electrical quality compared with GaN thin film.

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

    SciTech Connect

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

    2015-02-07

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

  3. High-power blue laser diodes with indium tin oxide cladding on semipolar (202{sup ¯}1{sup ¯}) GaN substrates

    SciTech Connect

    Pourhashemi, A. Farrell, R. M.; Cohen, D. A.; Speck, J. S.; DenBaars, S. P.; Nakamura, S.

    2015-03-16

    We demonstrate a high power blue laser diode (LD) using indium tin oxide as a cladding layer on semipolar oriented GaN. These devices show peak output powers and external quantum efficiencies comparable to state-of-the-art commercial c-plane devices. Ridge waveguide LDs were fabricated on (202{sup ¯}1{sup ¯}) oriented GaN substrates using InGaN waveguiding layers and GaN cladding layers. At a lasing wavelength of 451 nm at room temperature, an output power of 2.52 W and an external quantum efficiency of 39% were measured from a single facet under a pulsed injection current of 2.34 A. The measured differential quantum efficiency was 50%.

  4. Effect of double superlattice interlayers on growth of thick GaN epilayers on Si(110) substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Shen, Xu-Qiang; Takahashi, Tokio; Ide, Toshihide; Shimizu, Mitsuaki

    2016-05-01

    The effect of double thin AlN/GaN superlattice interlayers (SL ILs) on the growth of thick GaN epilayers by metalorganic chemical vapor deposition (MOCVD) on Si(110) substrates is investigated. It is found that the GaN middle layer (GaN layer between the two SL ILs) can affect the strain state of the GaN epilayer. By comparison with the case of a single SL IL, it is shown that the double SL ILs can have a stronger compressive effect on the GaN epilayer grown on it, which results in lower residual tensile strain in the GaN film after the growth. By optimizing the GaN middle layer thickness, a 4-µm-thick crack-free GaN epilayer is successfully achieved. By this simple technique, it is expected that high-quality crack-free thick GaN can be grown on Si substrates for optical and electronic device applications.

  5. Optically generated giant traps in high-purity GaN

    NASA Astrophysics Data System (ADS)

    Reshchikov, M. A.; McNamara, J. D.; Usikov, A.; Helava, H.; Makarov, Yu.

    2016-02-01

    An unusual temperature dependence of the photoluminescence lifetime for the green luminescence (GL) band in GaN is explained. This GL is caused by an internal transition of electrons from an excited state to the ground state of the 0/+ transition level of the isolated CN defect. The excited state appears only after the CN defect captures two photogenerated holes. The electron capture by the excited state is nonradiative, yet the lifetime of such can be probed by the temperature variation of the GL lifetime, whose temperature dependence shows a classic case of electron capture by a giant trap.

  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. GaN etching in BCl{sub 3}Cl{sub 2} plasmas

    SciTech Connect

    Shul, R.J.; Ashby, C.I.H.; Willison, C.G.; Zhang, L.; Han, J.; Bridges, M.M.; Pearton, S.J.; Lee, J.W.; Lester, L.F.

    1998-04-01

    GaN etching can be affected by a wide variety of parameters including plasma chemistry and plasma density. Chlorine-based plasmas have been the most widely used plasma chemistries to etch GaN due to the high volatility of the GaCl{sub 3} and NCl etch products. The source of Cl and the addition of secondary gases can dramatically influence the etch characteristics primarily due to their effect on the concentration of reactive Cl generated in the plasma. In addition, high-density plasma etch systems have yielded high quality etching of GaN due to plasma densities which are 2 to 4 orders of magnitude higher than reactive ion etch (RIE) plasma systems. The high plasma densities enhance the bond breaking efficiency of the GaN, the formation of volatile etch products, and the sputter desorption of the etch products from the surface. In this study, the authors report GaN etch results for a high-density inductively coupled plasma (ICP) as a function of BCl{sub 3}:Cl{sub 2} flow ratio, dc-bias, chamber-pressure, and ICP source power. GaN etch rates ranging from {approximately}100 {angstrom}/min to > 8,000 {angstrom}/min were obtained with smooth etch morphology and anisotropic profiles.

  8. Refractive index of erbium doped GaN thin films

    SciTech Connect

    Alajlouni, S.; Sun, Z. Y.; Li, J.; Lin, J. Y.; Jiang, H. X.; Zavada, J. M.

    2014-08-25

    GaN is an excellent host for erbium (Er) to provide optical emission in the technologically important as well as eye-safe 1540 nm wavelength window. Er doped GaN (GaN:Er) epilayers were synthesized on c-plane sapphire substrates using metal organic chemical vapor deposition. By employing a pulsed growth scheme, the crystalline quality of GaN:Er epilayers was significantly improved over those obtained by conventional growth method of continuous flow of reaction precursors. X-ray diffraction rocking curve linewidths of less than 300 arc sec were achieved for the GaN (0002) diffraction peak, which is comparable to the typical results of undoped high quality GaN epilayers and represents a major improvement over previously reported results for GaN:Er. Spectroscopic ellipsometry was used to determine the refractive index of the GaN:Er epilayers in the 1540 nm wavelength window and a linear dependence on Er concentration was found. The observed refractive index increase with Er incorporation and the improved crystalline quality of the GaN:Er epilayers indicate that low loss GaN:Er optical waveguiding structures are feasible.

  9. Electrical detection of kidney injury molecule-1 with AlGaN /GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

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

    2007-11-01

    AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect kidney injury molecule-1 (KIM-1), an important biomarker for early kidney injury detection. The gate region consisted of 5nm gold deposited onto the AlGaN surface. The gold was conjugated to highly specific KIM-1 antibodies through a self-assembled monolayer of thioglycolic acid. The HEMT source-drain current showed a clear dependence on the KIM-1 concentration in phosphate-buffered saline solution. The limit of detection was 1ng/ml using a 20×50μm2 gate sensing area. This approach shows potential for both preclinical and clinical kidney injury diagnosis with accurate, rapid, noninvasive, and high throughput capabilities.

  10. Defect Reduction via Selective Lateral Epitaxy of GaN on an Innovative Masked Structure with Serpentine Channels

    NASA Astrophysics Data System (ADS)

    Li, Lei; Liu, Justin P. C.; Liu, Lei; Li, Ding; Wang, Lei; Wan, Chenghao; Chen, Weihua; Yang, Zhijian; Xie, Yahong; Hu, Xiaodong; Zhang, Guoyi

    2012-05-01

    We demonstrated an innovative lateral epitaxy method to grow c-plane GaN film using serpentine masked structures, which simplified the entire fabrication process with only one single epitaxial growth step and could efficiently block the threading dislocations. The microstructural and optical properties of GaN indicated that the crystalline quality was effectively improved. Unlike the conventional epitaxial lateral overgrowth (ELOG) or the double ELOG method, the presented serpentine masked structure needs no regrowth process for obtaining low-defect-density GaN materials, and is promising for growing high-performance III-nitride-based devices including laser diodes (LDs), power transistors, and light-emitting diodes (LEDs).

  11. A novel MOCVD reactor for growth of high-quality GaN-related LED layers

    NASA Astrophysics Data System (ADS)

    Hu, Shaolin; Liu, Sheng; Zhang, Zhi; Yan, Han; Gan, Zhiyin; Fang, Haisheng

    2015-04-01

    Gallium nitride (GaN), a direct bandgap semiconductor widely used in bright light-emitting diodes (LEDs), is mostly grown by metal-organic chemical vapor deposition (MOCVD) method. A good reactor design is critical for the production of high-quality GaN thin films. In this paper, we presented a novel buffered distributed spray (BDS) MOCVD reactor with vertical gas sprayers and horizontal gas inlets. Experiments based on a 36×2″ BDS reactor were conducted to examine influence of the process parameters, such as the operating pressure and the gas flow rate, on the growth efficiency and on the layer thickness uniformity. Transmission electron microscopy (TEM) and photoluminescence (PL) are further conducted to evaluate quality of the epitaxial layers and to check performance of the reactor. Results show that the proposed novel reactor is of high performance in growing high-quality thin films, including InGaN/GaN multiquantum wells (MQWs) structures.

  12. 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.

  13. 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.

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

    SciTech Connect

    Li, X.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Janzén, E.; Forsberg, U.; Bergsten, J.; Rorsman, N.

    2015-12-28

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

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

    NASA Astrophysics Data System (ADS)

    Li, X.; Bergsten, J.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Rorsman, N.; Janzén, E.; Forsberg, U.

    2015-12-01

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 1018 cm-3) epitaxial layer closest to the substrate and a lower doped layer (3 × 1016 cm-3) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 1018 cm-3) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  16. Vertical GaN based light emitting diodes on metal alloy substrate boosts high power LED performance

    NASA Astrophysics Data System (ADS)

    Doan, T.; Tran, C.; Chu, C.; Chen, C.; Liu, W. H.; Chu, J.; Yen, K.; Chen, H.; Fan, F.

    2007-09-01

    Vertical GaN based Light Emitting Diodes on metal alloy substrate (VLEDMS) were realized and characterized for solid state lighting application. An efficiency of more than 100 lumens/watt from a white LED was achieved. And, an efficiency of more than 80 lumens/watt from a high efficiency and high power green LED was achieved also. The dissipate heat more effectively than conventional and flip-chip LEDs, thanks to the higher thermal conductivity of a copper alloy substrate. This increases their maximum operating current and output power and makes them more suitable for solid-state lighting applications. In addition, these VLEDMS exhibit many advantages over those on sapphire under extreme operation conditions for general lighting application.

  17. Highly reliable and bright GaN vertical LED on metal alloy substrate using corrugated pyramid shaped surface technology

    NASA Astrophysics Data System (ADS)

    Chu, Jiunn-Yi; Chu, Chen-Fu; Cheng, Chao-Chen; Liu, Wen-Huan; Cheng, Hao-Chun; Fan, Feng-Hsu; Yen, Jui-Kang; Tran, Chuong Anh; Doan, Trung

    2008-02-01

    GaN vertical LED on metal alloy substrate (VLEDMS) is a desirable technology suitable for solid state lighting application from the viewpoint of reliability and lighting efficacy performance. A new top surface engineering technique for efficient light extraction is employed to VLEDMS to improve power conversion efficiency further. Corrugated pyramid shaped (CPS) surfaces are developed and formed on VLEDMS. By using such structure, VLEDMS exhibit a great enhancement of around 20% in light output power, and a high efficiency of over 100 lumens per watt can also be achieved by white LEDs. In the life test, the light output power of VLEDMS chips drop only by less than 10% within 3,000 hours, and the chips can also endure over 1000 cycles of thermal shocks without significant variations in electro-optical performance. Therefore, the highly reliable and bright VLEDMS using CPS surface engineering technique is very suitable for the solid-state lighting application.

  18. An aberration-corrected STEM study of structural defects in epitaxial GaN thin films grown by ion beam assisted MBE.

    PubMed

    Poppitz, David; Lotnyk, Andriy; Gerlach, Jürgen W; Lenzner, Jörg; Grundmann, Marius; Rauschenbach, Bernd

    2015-06-01

    Ion-beam assisted molecular-beam epitaxy was used for direct growth of epitaxial GaN thin films on super-polished 6H-SiC(0001) substrates. The GaN films with different film thicknesses were studied using reflection high energy electron diffraction, X-ray diffraction, cathodoluminescence and primarily aberration-corrected scanning transmission electron microscopy techniques. Special attention was devoted to the microstructural characterization of GaN thin films and the GaN-SiC interface on the atomic scale. The results show a variety of defect types in the GaN thin films and at the GaN-SiC interface. A high crystalline quality of the produced hexagonal GaN thin films was demonstrated. The gained results are discussed.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

    So, Hongyun; Senesky, Debbie G.

    2016-11-01

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

  1. Semi-polar GaN materials technology for high IQE green LEDs.

    SciTech Connect

    Koleske, Daniel; Lee, Stephen Roger; Crawford, Mary H; Coltrin, Michael Elliott; Fini, Paul

    2013-06-01

    The goal of this NETL funded program was to improve the IQE in green (and longer wavelength) nitride- based LEDs structures by using semi-polar GaN planar orientations for InGaN multiple quantum well (MQW) growth. These semi-polar orientations have the advantage of significantly reducing the piezoelectric fields that distort the QW band structure and decrease electron-hole overlap. In addition, semipolar surfaces potentially provide a more open surface bonding environment for indium incorporation, thus enabling higher indium concentrations in the InGaN MQW. The goal of the proposed work was to select the optimal semi-polar orientation and explore wafer miscuts around this orientation that produced the highest quantum efficiency LEDs. At the end of this program we had hoped to have MQWs active regions at 540 nm with an IQE of 50% and an EQE of 40%, which would be approximately twice the estimated current state-of-the-art.

  2. Electronic structure of ytterbium-implanted GaN at ambient and high pressure: experimental and crystal field studies.

    PubMed

    Kaminska, A; Ma, C-G; Brik, M G; Kozanecki, A; Boćkowski, M; Alves, E; Suchocki, A

    2012-03-01

    The results of high-pressure low-temperature optical measurements in a diamond-anvil cell of bulk gallium nitride crystals implanted with ytterbium are reported in combination with crystal field calculations of the Yb(3+) energy levels. Crystal field analysis of splitting of the (2)F(7/2) and (2)F(5/2) states has been performed, with the aim of assigning all features of the experimental luminescence spectra. A thorough analysis of the pressure behavior of the Yb(3+) luminescence lines in GaN allowed the determination of the ambient-pressure positions and pressure dependence of the Yb(3+) energy levels in the trigonal crystal field as well as the pressure-induced changes of the spin-orbit coupling coefficient.

  3. Correlation between the optical loss and crystalline quality in erbium-doped GaN optical waveguides.

    PubMed

    Feng, I-Wen; Zhao, Weiping; Li, Jing; Lin, Jingyu; Jiang, Hongxing; Zavada, John

    2013-08-01

    Erbium-doped GaN (GaN:Er) epilayers were synthesized by metal organic chemical vapor deposition. GaN:Er waveguides were fabricated based on four different GaN:Er layer structures: GaN:Er/GaN/Al2O3, GaN:Er/GaN/AlN/Al2O3, GaN:Er/GaN/Al(0.75)Ga(0.25)N/AlN/Al2O3, and GaN/GaN:Er/GaN/Al2O3. Optical loss at 1.54 μm in these waveguide structures has been measured. It was found that the optical attenuation coefficient of the GaN:Er waveguide increases almost linearly with the GaN (002) x-ray rocking curve linewidth. The lowest measured loss was ~6 dB/cm.

  4. Effective surface treatment for GaN metal-insulator-semiconductor high-electron-mobility transistors using HF plus N2 plasma prior to SiN passivation

    NASA Astrophysics Data System (ADS)

    Liu, Shih-Chien; Trinh, Hai-Dang; Dai, Gu-Ming; Huang, Chung-Kai; Dee, Chang-Fu; Yeop Majlis, Burhanuddin; Biswas, Dhrubes; Chang, Edward Yi

    2016-01-01

    An effective surface cleaning technique is demonstrated for the GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) passivation process. In this study, dilute HF solution and in situ N2 plasma treatments were adopted to remove the native oxide and recover the nitrogen-vacancy defects at the GaN surface before device passivation. To investigate the correlation between the properties of the SiN/GaN interface and the device performance, the GaN MIS-HEMTs were characterized using current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement, and X-ray photoelectron spectroscopy (XPS) analysis. With the application of this surface treatment technique, the device exhibits improved I-V characteristics with low leakage current, low dynamic ON-resistance, and good C-V response with a steep slope. Overall, the results reveal that the oxide-related bonds and nitrogen-vacancy defects at the SiN/GaN interface are the root cause of the GaN MIS-HEMTs performance degradation.

  5. Toward the realization of erbium-doped GaN bulk crystals as a gain medium for high energy lasers

    NASA Astrophysics Data System (ADS)

    Sun, Z. Y.; Li, J.; Zhao, W. P.; Lin, J. Y.; Jiang, H. X.

    2016-08-01

    Er-doped GaN (Er:GaN) is a promising candidate as a gain medium for solid-state high energy lasers (HELs) at the technologically important and eye-safe 1.54 μm wavelength window, as GaN has superior thermal properties over traditional laser gain materials such as Nd:YAG. However, the attainment of wafer-scale Er:GaN bulk or quasi-bulk crystals is a prerequisite to realize the full potential of Er:GaN as a gain medium for HELs. We report the realization of freestanding Er:GaN wafers of 2-in. in diameter with a thickness on the millimeter scale. These freestanding wafers were obtained via growth by hydride vapor phase epitaxy in conjunction with a laser-lift-off process. An Er doping level of 1.4 × 1020 atoms/cm3 has been confirmed by secondary ion mass spectrometry measurements. The freestanding Er:GaN wafers exhibit strong photoluminescent emission at 1.54 μm with its emission intensity increasing dramatically with wafer thickness under 980 nm resonant excitation. A low thermal quenching of 10% was measured for the 1.54 μm emission intensity between 10 K and 300 K. This work represents a significant step in providing a practical approach for producing Er:GaN materials with sufficient thicknesses and dimensions to enable the design of gain media in various geometries, allowing for the production of HELs with improved lasing efficiency, atmosphere transmission, and eye-safety.

  6. 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.

  7. 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

  8. Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

    SciTech Connect

    Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma; Krupanidhi, S. B.; Roul, Basanta

    2014-11-28

    We hereby report the development of non-polar epi-GaN films of usable quality, on an m-plane sapphire. Generally, it is difficult to obtain high-quality nonpolar material due to the planar anisotropic nature of the growth mode. However, we could achieve good quality epi-GaN films by involving controlled steps of nitridation. GaN epilayers were grown on m-plane (10-10) sapphire substrates using plasma assisted molecular beam epitaxy. The films grown on the nitridated surface resulted in a nonpolar (10-10) orientation while without nitridation caused a semipolar (11-22) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. X-ray rocking curves confirmed better crystallinity of semipolar as compared to nonpolar GaN which resulted in faster transit response of the device.

  9. 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.

  10. Ultralow nonalloyed Ohmic contact resistance to self aligned N-polar GaN high electron mobility transistors by In(Ga)N regrowth

    SciTech Connect

    Dasgupta, Sansaptak; Nidhi,; Brown, David F.; Wu, Feng; Keller, Stacia; Speck, James S.; Mishra, Umesh K.

    2010-04-05

    Ultralow Ohmic contact resistance and a self-aligned device structure are necessary to reduce the effect of parasitic elements and obtain higher f{sub t} and f{sub max} in high electron mobility transistors (HEMTs). N-polar (0001) GaN HEMTs, offer a natural advantage over Ga-polar HEMTs, in terms of contact resistance since the contact is not made through a high band gap material [Al(Ga)N]. In this work, we extend the advantage by making use of polarization induced three-dimensional electron-gas through regrowth of graded InGaN and thin InN cap in the contact regions by plasma (molecular beam epitaxy), to obtain an ultralow Ohmic contact resistance of 27 OMEGA mum to a GaN 2DEG.

  11. Design of an Ultra-Efficient GaN High Power Amplifier for Radar Front-Ends Using Active Harmonic Load-Pull

    NASA Technical Reports Server (NTRS)

    Thrivikraman, Tushar; Hoffman, James

    2012-01-01

    This work presents a new measurement technique, mixed-signal active harmonic load-pull (MSALP) developed by Anterverta-mw in partnership with Maury Microwave, that allows for wide-band ultra-high efficiency amplifiers to be designed using GaN technology. An overview of the theory behind active load-pull is presented and why load-pull is important for high-power device characterization. In addition, an example procedure is presented that outlines a methodology for amplifier design using this measurement system. Lastly, measured results of a 10W GaN amplifier are presented. This work aims to highlight the benefit of using this sophisticated measurement systems for to optimize amplifier design for real radar waveforms that in turn will simplify implementation of space-based radar systems

  12. Single-pass UV generation at 222.5 nm based on high-power GaN external cavity diode laser.

    PubMed

    Ruhnke, N; Müller, A; Eppich, B; Güther, R; Maiwald, M; Sumpf, B; Erbert, G; Tränkle, G

    2015-05-01

    We demonstrate a compact system for single-pass frequency doubling of high-power GaN diode laser radiation. The deep UV laser light at 222.5 nm is generated in a β-BaB2O4 (BBO) crystal. A high-power GaN external cavity diode laser (ECDL) system in Littrow configuration with narrowband emission at 445 nm is used as pump source. At a pump power of 680 mW, a maximum UV power of 16 μW in continuous-wave operation at 222.5 nm is achieved. This concept enables a compact diode laser-based system emitting in the deep ultraviolet spectral range.

  13. Role of quantum confinement in giving rise to high electron mobility in GaN nanowall networks

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    Origin of unprecedentedly high electron mobility observed in the c-axis oriented GaN nanowall networks is investigated by studying the depth distribution of structural, electrical and optical properties of several such high mobility samples grown by molecular beam epitaxy (MBE) technique for different time durations. It has been found that in two hour grown samples, walls are tapered continuously from the bottom to the top. While in four hour grown samples, walls are flat-topped with the top surface containing certain secondary tip structures. These additional features run along the length of the walls to form a well-connected network. Our study reveals that the carriers are quantum mechanically confined not only in the secondary tip structures but also in the wider part of the walls. The secondary tip structures, which are found to offer higher mobility than the rest of the network, are also identified as the regions of stronger confinement. The effect of mobility enhancement observed in these samples has been attributed to a 2D quantum confinement of electrons in the central vertical plane of the walls.

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

    PubMed

    Hayashi, Hiroaki; Konno, Yuta; Kishino, Katsumi

    2016-02-01

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

  15. Topical Review: Development of overgrown semi-polar GaN for high efficiency green/yellow emission

    NASA Astrophysics Data System (ADS)

    Wang, T.

    2016-09-01

    The most successful example of large lattice-mismatched epitaxial growth of semiconductors is the growth of III-nitrides on sapphire, leading to the award of the Nobel Prize in 2014 and great success in developing InGaN-based blue emitters. However, the majority of achievements in the field of III-nitride optoelectronics are mainly limited to polar GaN grown on c-plane (0001) sapphire. This polar orientation poses a number of fundamental issues, such as reduced quantum efficiency, efficiency droop, green and yellow gap in wavelength coverage, etc. To date, it is still a great challenge to develop longer wavelength devices such as green and yellow emitters. One clear way forward would be to grow III-nitride device structures along a semi-/non-polar direction, in particular, a semi-polar orientation, which potentially leads to both enhanced indium incorporation into GaN and reduced quantum confined Stark effects. This review presents recent progress on developing semi-polar GaN overgrowth technologies on sapphire or Si substrates, the two kinds of major substrates which are cost-effective and thus industry-compatible, and also demonstrates the latest achievements on electrically injected InGaN emitters with long emission wavelengths up to and including amber on overgrown semi-polar GaN. Finally, this review presents a summary and outlook on further developments for semi-polar GaN based optoelectronics.

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

    PubMed

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

    2016-02-10

    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.

  17. 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

  18. 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.

  19. High-quality vertical light emitting diodes fabrication by mechanical lift-off technique

    NASA Astrophysics Data System (ADS)

    Tu, Po-Min; Hsu, Shih-Chieh; Chang, Chun-Yen

    2011-10-01

    We report the fabrication of mechanical lift-off high quality thin GaN with Hexagonal Inversed Pyramid (HIP) structures for vertical light emitting diodes (V-LEDs). The HIP structures were formed at the GaN/sapphire substrate interface under high temperature during KOH wet etching process. The average threading dislocation density (TDD) was estimated by transmission electron microscopy (TEM) and found the reduction from 2×109 to 1×108 cm-2. Raman spectroscopy analysis revealed that the compressive stress of GaN epilayer was effectively relieved in the thin-GaN LED with HIP structures. Finally, the mechanical lift-off process is claimed to be successful by using the HIP structures as a sacrificial layer during wafer bonding process.

  20. Effect of buffer layer growth temperature on epitaxial GaN films deposited by magnetron sputtering

    SciTech Connect

    Mohanta, P.; Singh, D.; Kumar, R.; Ganguli, T.; Srinivasa, R. S.; Major, S. S.

    2012-06-05

    Epitaxial GaN films were deposited by reactive sputtering of a GaAs target in 100 % nitrogen at 700 deg. C on ZnO buffer layers grown at different substrate temperatures over sapphire substrates. High resolution X-ray diffraction measurements and the corresponding analysis show that the growth temperature of buffer layers significantly affects the micro-structural parameters of GaN epilayer, such as lateral coherence length, tilt and twist, while the vertical coherence length remains unaffected. The optimum substrate temperature for buffer layer growth has been found to be 300 deg. C. High epitaxial quality GaN film grown on such a buffer layer exhibited micro strain of 1.8x10{sup -4} along with screw and edge type dislocation densities of 7.87x10{sup 9} and 1.16x10{sup 11}, respectively.

  1. Epitaxial growth of GaN films on nearly lattice-matched hafnium substrates using a low-temperature growth technique

    NASA Astrophysics Data System (ADS)

    Kim, H. R.; Ohta, J.; Inoue, S.; Ueno, K.; Kobayashi, A.; Fujioka, H.

    2016-07-01

    We demonstrated epitaxial growth of GaN (0001) films on nearly lattice-matched Hf (0001) substrates by using a low-temperature (LT) epitaxial growth technique. High-temperature growth of GaN films results in the formation of polycrystalline films due to significant reaction at GaN/Hf heterointerfaces, while LT-growth allowed us to suppress the interfacial reactions and to obtain epitaxial GaN films on Hf substrates with a GaN [" separators=" 11 2 ¯ 0 ] / / Hf [" separators=" 11 2 ¯ 0 ] in-plane orientation. LT-grown GaN films can act as buffer layers for GaN growth at high temperatures. The interfacial layer thickness at the LT-GaN/Hf heterointerface was as small as 1 nm, and the sharpness of the contact remained unchanged even after annealing up to approximately 700 °C, which likely accounts for the dramatic improvement in GaN crystalline quality on Hf substrates.

  2. 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.

  3. High-voltage thin-film GaN LEDs fabricated on ceramic substrates: the alleviated droop effect at 670 W/cm(2).

    PubMed

    Tsai, M L; Liao, J H; Yeh, J H; Hsu, T C; Hon, S J; Chung, T Y; Lai, K Y

    2013-11-01

    High-voltage thin-film GaN LEDs with the emission wavelength of 455 nm were fabricated on ceramic substrates (230 W/m · K). The high-voltage operation was achieved by three cascaded sub-LEDs with dielectric passivation and metal bridges conformally deposited on the side walls. Under the driving power of 670 W/cm(2), the high-voltage LEDs exhibit much alleviated efficiency droop and the operative temperature below 80 °C. The excellent performances were attributed to the improved current spreading within each sub-LED and the superior heat sinking of the ceramic substrate.

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

    NASA Astrophysics Data System (ADS)

    Chen, Shuo-Wei; Li, Heng; Lu, Tien-Chang

    2016-04-01

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

  5. Self-induced growth of vertical GaN nanowires on silica

    NASA Astrophysics Data System (ADS)

    Kumaresan, V.; Largeau, L.; Oehler, F.; Zhang, H.; Mauguin, O.; Glas, F.; Gogneau, N.; Tchernycheva, M.; Harmand, J.-C.

    2016-04-01

    We study the self-induced growth of GaN nanowires on silica. Although the amorphous structure of this substrate offers no possibility of an epitaxial relationship, the nanowires are remarkably aligned with the substrate normal whereas, as expected, their in-plane orientation is random. Their structural and optical characteristics are compared to those of GaN nanowires grown on standard crystalline Si (111) substrates. The polarity inversion domains are much less frequent, if not totally absent, in the nanowires grown on silica, which we find to be N-polar. This work demonstrates that high-quality vertical GaN nanowires can be elaborated without resorting to bulk crystalline substrates.

  6. Transformation of c-oriented nanowall network to a flat morphology in GaN films on c-plane sapphire

    SciTech Connect

    Kesaria, Manoj; Shetty, Satish; Cohen, P.I.; Shivaprasad, S.M.

    2011-11-15

    Highlights: {yields} High quality wurtzite structures GaN nanowall network formed on c-plane sapphire. {yields} Tapering of nanowalls at the apex cause electron confinement effects. {yields} Temperature dependent transformation of the six fold nanowall network to a flat morphology. {yields} Growth kinetics is influenced by adatom diffusion, interactions and bonding for GaN layer. -- Abstract: The work significantly optimizes growth parameters for nanostructured and flat GaN film in the 480-830 {sup o}C temperature range. The growth of ordered, high quality GaN nanowall hexagonal honeycomb like network on c-plane sapphire under nitrogen rich (N/Ga ratio of 100) conditions at temperatures below 700 {sup o}C is demonstrated. The walls are c-oriented wurtzite structures 200 nm wide at base and taper to 10 nm at apex, manifesting electron confinement effects to tune optoelectronic properties. For substrate temperatures above 700 {sup o}C the nanowalls thicken to a flat morphology with a dislocation density of 10{sup 10}/cm{sup 2}. The role of misfit dislocations in the GaN overlayer evolution is discussed in terms of growth kinetics being influenced by adatom diffusion, interactions and bonding at different temperatures. The GaN films are characterized by reflection high energy electron diffraction (RHEED), field emission scanning electron (FESEM), high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL).

  7. GaN based nanorods for solid state lighting

    SciTech Connect

    Li Shunfeng; Waag, Andreas

    2012-04-01

    In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

  8. Epitaxial MoS2/GaN structures to enable vertical 2D/3D semiconductor heterostructure devices

    NASA Astrophysics Data System (ADS)

    Ruzmetov, D.; Zhang, K.; Stan, G.; Kalanyan, B.; Eichfeld, S.; Burke, R.; Shah, P.; O'Regan, T.; Crowne, F.; Birdwell, A. G.; Robinson, J.; Davydov, A.; Ivanov, T.

    MoS2/GaN structures are investigated as a building block for vertical 2D/3D semiconductor heterostructure devices that utilize a 3D substrate (GaN) as an active component of the semiconductor device without the need of mechanical transfer of the 2D layer. Our CVD-grown monolayer MoS2 has been shown to be epitaxially aligned to the GaN lattice which is a pre-requisite for high quality 2D/3D interfaces desired for efficient vertical transport and large area growth. The MoS2 coverage is nearly 50 % including isolated triangles and monolayer islands. The GaN template is a double-layer grown by MOCVD on sapphire and allows for measurement of transport perpendicular to the 2D layer. Photoluminescence, Raman, XPS, Kelvin force probe microscopy, and SEM analysis identified high quality monolayer MoS2. The MoS2/GaN structures electrically conduct in the out-of-plane direction and across the van der Waals gap, as measured with conducting AFM (CAFM). The CAFM current maps and I-V characteristics are analyzed to estimate the MoS2/GaN contact resistivity to be less than 4 Ω-cm2 and current spreading in the MoS2 monolayer to be approx. 1 μm in diameter. Epitaxial MoS2/GaN heterostructures present a promising platform for the design of energy-efficient, high-speed vertical devices incorporating 2D layered materials with 3D semiconductors.

  9. Spatially resolved and orientation dependent Raman mapping of epitaxial lateral overgrowth nonpolar a-plane GaN on r-plane sapphire

    PubMed Central

    Jiang, Teng; Xu, Sheng-rui; Zhang, Jin-cheng; Xie, Yong; Hao, Yue

    2016-01-01

    Uncoalesced a-plane GaN epitaxial lateral overgrowth (ELO) structures have been synthesized along two mask stripe orientations on a-plane GaN template by MOCVD. The morphology of two ELO GaN structures is performed by Scanning electronic microscopy. The anisotropy of crystalline quality and stress are investigated by micro-Raman spectroscopy. According to the Raman mapping spectra, the variations on the intensity, peak shift and the full width at half maximum (FWHM) of GaN E2 (high) peak indicate that the crystalline quality improvement occurs in the window region of the GaN stripes along [0001], which is caused by the dislocations bending towards the sidewalls. Conversely, the wing regions have better quality with less stress as the dislocations propagated upwards when the GaN stripes are along []. Spatial cathodoluminescence mapping results further support the explanation for the different dislocation growth mechanisms in the ELO processes with two different mask stripe orientations. PMID:26821824

  10. Spatially resolved and orientation dependent Raman mapping of epitaxial lateral overgrowth nonpolar a-plane GaN on r-plane sapphire.

    PubMed

    Jiang, Teng; Xu, Sheng-Rui; Zhang, Jin-Cheng; Xie, Yong; Hao, Yue

    2016-01-29

    Uncoalesced a-plane GaN epitaxial lateral overgrowth (ELO) structures have been synthesized along two mask stripe orientations on a-plane GaN template by MOCVD. The morphology of two ELO GaN structures is performed by Scanning electronic microscopy. The anisotropy of crystalline quality and stress are investigated by micro-Raman spectroscopy. According to the Raman mapping spectra, the variations on the intensity, peak shift and the full width at half maximum (FWHM) of GaN E2 (high) peak indicate that the crystalline quality improvement occurs in the window region of the GaN stripes along [0001], which is caused by the dislocations bending towards the sidewalls. Conversely, the wing regions have better quality with less stress as the dislocations propagated upwards when the GaN stripes are along []. Spatial cathodoluminescence mapping results further support the explanation for the different dislocation growth mechanisms in the ELO processes with two different mask stripe orientations.

  11. Heteroepitaxial VO{sub 2} thin films on GaN: Structure and metal-insulator transition characteristics

    SciTech Connect

    Zhou You; Ramanathan, Shriram

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO{sub 2}) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010){sub vo{sub 2}} parallel (0001){sub GaN} parallel (0001){sub A1{sub 2O{sub 3}}} and [100]{sub vo{sub 2}} parallel [1210]{sub GaN} parallel [0110]{sub A1{sub 2O{sub 3}}} from x-ray diffraction. VO{sub 2} heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO{sub 2}. Electrical characterization of VO{sub 2} films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO{sub 2} films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  12. Chlorine-based plasma etching of GaN

    SciTech Connect

    Shul, R.J.; Briggs, R.D.; Pearton, S.J.; Vartuli, C.B.; Abernathy, C.R.; Lee, J.W.; Constantine, C.; Baratt, C.

    1997-02-01

    The wide band gap group-III nitride materials continue to generate interest in the semiconductor community with the fabrication of green, blue, and ultraviolet light emitting diodes (LEDs), blue lasers, and high temperature transistors. Realization of more advanced devices requires pattern transfer processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 {micro}m/min. The utilization of high-density chlorine-based plasmas including electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) systems has resulted in improved GaN etch quality over more conventional reactive ion etch (RIE) systems.

  13. 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.

  14. 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

  15. Ensuring High Quality Research Services.

    ERIC Educational Resources Information Center

    Gardner, Bob

    This paper discusses ensuring high quality research services that meet client needs, based on experiences at the Research and Information Services of the Ontario Legislative Library (Canada). The first section is an introduction that provides an overview of the Research and Information Services and summarizes factors related to quality control.…

  16. High reflectance membrane-based distributed Bragg reflectors for GaN photonics

    NASA Astrophysics Data System (ADS)

    Chen, Danti; Han, Jung

    2012-11-01

    Preparation of highly reflective distributed Bragg reflectors (DBRs) from III-nitrides is an important building block for cavity photonics. In this work, we report the fabrication of a membrane-based GaN/air-gap DBR for blue/green light emitting devices. The formation of membrane DBRs relies on a recently discovered electrochemical procedure in which selective etch is achieved by adjusting the conductivity rather than chemical composition, thus relieving greatly the burden in creating epitaxial DBRs. Micro-reflectance measurement shows over 98% peak reflectance and a wide stopband with only four pairs of GaN/air-gap layers. Micro-photoluminescence spectra of InGaN multiple quantum wells (MQWs) on DBRs show reduced linewidth and improved emission efficiency. After capping the MQWs on DBRs with silver, a significant linewidth narrowing indicates the modification of spontaneous emission due to the presence of a planar microcavity.

  17. 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.

  18. Compact deep UV laser system at 222.5 nm by single-pass frequency doubling of high-power GaN diode laser emission

    NASA Astrophysics Data System (ADS)

    Ruhnke, Norman; Müller, André; Eppich, Bernd; Güther, Reiner; Maiwald, Martin; Sumpf, Bernd; Erbert, Götz; Tränkle, Günther

    2016-03-01

    Deep ultraviolet (DUV) lasers emitting below 300 nm are of great interest for many applications, for instance in medical diagnostics or for detecting biological agents. Established DUV lasers, e.g. gas lasers or frequency quadrupled solid-state lasers, are relatively bulky and have high power consumptions. A compact and reliable laser diode based system emitting in the DUV could help to address applications in environments where a portable and robust light source with low power consumption is needed. In this work, a compact DUV laser system based on single-pass frequency doubling of highpower GaN diode laser emission is presented. A commercially available high-power GaN laser diode from OSRAM Opto Semiconductors serves as a pump source. The laser diode is spectrally stabilized in an external cavity diode laser (ECDL) setup in Littrow configuration. The ECDL system reaches a maximum optical output power of 700 mW, maintaining narrowband emission below 60 pm (FWHM) at 445 nm over the entire operating range. By direct single pass frequency doubling in a BBO crystal with a length of 7.5 mm a maximum DUV output power of 16 μW at a wavelength of 222.5 nm is generated. The presented concept enables compact and efficient diode laser based light sources emitting in the DUV spectral range that are potentially suitable for in situ applications where a small footprint and low power consumption is essential.

  19. Role of the ganSPQAB Operon in Degradation of Galactan by Bacillus subtilis.

    PubMed

    Watzlawick, Hildegard; Morabbi Heravi, Kambiz; Altenbuchner, Josef

    2016-10-15

    Bacillus subtilis possesses different enzymes for the utilization of plant cell wall polysaccharides. This includes a gene cluster containing galactan degradation genes (ganA and ganB), two transporter component genes (ganQ and ganP), and the sugar-binding lipoprotein-encoding gene ganS (previously known as cycB). These genes form an operon that is regulated by GanR. The degradation of galactan by B. subtilis begins with the activity of extracellular GanB. GanB is an endo-β-1,4-galactanase and is a member of glycoside hydrolase (GH) family 53. This enzyme was active on high-molecular-weight arabinose-free galactan and mainly produced galactotetraose as well as galactotriose and galactobiose. These galacto-oligosaccharides may enter the cell via the GanQP transmembrane proteins of the galactan ABC transporter. The specificity of the galactan ABC transporter depends on the sugar-binding lipoprotein, GanS. Purified GanS was shown to bind galactotetraose and galactotriose using thermal shift assay. The energy for this transport is provided by MsmX, an ATP-binding protein. The transported galacto-oligosaccharides are further degraded by GanA. GanA is a β-galactosidase that belongs to GH family 42. The GanA enzyme was able to hydrolyze short-chain β-1,4-galacto-oligosaccharides as well as synthetic β-galactopyranosides into galactose. Thermal shift assay as well as electrophoretic mobility shift assay demonstrated that galactobiose is the inducer of the galactan operon regulated by GanR. DNase I footprinting revealed that the GanR protein binds to an operator overlapping the -35 box of the σ(A)-type promoter of Pgan, which is located upstream of ganS IMPORTANCE: Bacillus subtilis is a Gram-positive soil bacterium that utilizes different types of carbohydrates, such as pectin, as carbon sources. So far, most of the pectin degradation systems and enzymes have been thoroughly studied in B. subtilis Nevertheless, the B. subtilis utilization system of galactan, which is

  20. MOCVD growth of N-polar GaN on on-axis sapphire substrate: Impact of AlN nucleation layer on GaN surface hillock density

    NASA Astrophysics Data System (ADS)

    Marini, Jonathan; Leathersich, Jeffrey; Mahaboob, Isra; Bulmer, John; Newman, Neil; (Shadi) Shahedipour-Sandvik, F.

    2016-05-01

    We report on the impact of growth conditions on surface hillock density of N-polar GaN grown on nominally on-axis (0001) sapphire substrate by metal organic chemical vapor deposition (MOCVD). Large reduction in hillock density was achieved by implementation of an optimized high temperature AlN nucleation layer and use of indium surfactant in GaN overgrowth. A reduction by more than a factor of five in hillock density from 1000 to 170 hillocks/cm-2 was achieved as a result. Crystal quality and surface morphology of the resultant GaN films were characterized by high resolution x-ray diffraction and atomic force microscopy and found to be relatively unaffected by the buffer conditions. It is also shown that the density of smaller surface features is unaffected by AlN buffer conditions.

  1. Selective area growth and characterization of GaN nanocolumns, with and without an InGaN insertion, on semi-polar (11–22) GaN templates

    SciTech Connect

    Bengoechea-Encabo, A.; Albert, S.; Barbagini, F.; Sanchez-Garcia, M. A.; Calleja, E.; Trampert, A.

    2013-12-09

    The aim of this work is the selective area growth (SAG) of GaN nanocolumns, with and without an InGaN insertion, by molecular beam epitaxyon semi-polar (11–22) GaN templates. The high density of stacking faults present in the template is strongly reduced after SAG. A dominant sharp photoluminescence emission at 3.473 eV points to high quality strain-free material. When embedding an InGaN insertion into the ordered GaN nanostructures, very homogeneous optical properties are observed, with two emissions originating from different regions of each nanostructure, most likely related to different In contents on different crystallographic planes.

  2. Single crystalline Sc2O3/Y2O3 heterostructures as novel engineered buffer approach for GaN integration on Si (111)

    NASA Astrophysics Data System (ADS)

    Tarnawska, L.; Giussani, A.; Zaumseil, P.; Schubert, M. A.; Paszkiewicz, R.; Brandt, O.; Storck, P.; Schroeder, T.

    2010-09-01

    The preparation of GaN virtual substrates on Si wafers via buffer layers is intensively pursued for high power/high frequency electronics as well as optoelectronics applications. Here, GaN is integrated on the Si platform by a novel engineered bilayer oxide buffer, namely, Sc2O3/Y2O3, which gradually reduces the lattice misfit of ˜-17% between GaN and Si. Single crystalline GaN(0001)/Sc2O3(111)/Y2O3(111)/Si(111) heterostructures were prepared by molecular beam epitaxy and characterized ex situ by various techniques. Laboratory-based x-ray diffraction shows that the epitaxial Sc2O3 grows fully relaxed on the Y2O3/Si(111) support, creating a high quality template for subsequent GaN overgrowth. The high structural quality of the Sc2O3 film is demonstrated by the fact that the concentration of extended planar defects in the preferred {111} slip planes is below the detection limit of synchrotron based diffuse x-ray scattering studies. Transmission electron microscopy (TEM) analysis reveal that the full relaxation of the -7% lattice misfit between the isomorphic oxides is achieved by a network of misfit dislocations at the Sc2O3/Y2O3 interface. X-ray reflectivity and TEM prove that closed epitaxial GaN layers as thin as 30 nm can be grown on these templates. Finally, the GaN thin film quality is studied using a detailed Williamson-Hall analysis.

  3. Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

    NASA Astrophysics Data System (ADS)

    He, Yunlong; Li, Peixian; Wang, Chong; Li, Xiangdong; Zhao, Shenglei; Mi, Minhan; Pei, Jiuqing; Zhang, Jincheng; Ma, Xiaohua; Hao, Yue

    2015-08-01

    This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98-2.56) × 1012 cm-2 eV-1 is located at ET in a range of (0.37-0.44) eV in the thin sample, while the trap state density of (2.3-2.92) × 1012 cm-2 eV-1 is located at ET in a range of (0.33-0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

  4. Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

    SciTech Connect

    He, Yunlong; Wang, Chong Li, Xiangdong; Zhao, Shenglei; Mi, Minhan; Pei, Jiuqing; Zhang, Jincheng; Hao, Yue; Li, Peixian; Ma, Xiaohua

    2015-08-10

    This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 10{sup 12 }cm{sup −2} eV{sup −1} is located at E{sub T} in a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 10{sup 12 }cm{sup −2} eV{sup −1} is located at E{sub T} in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

  5. Analysis of GaN high electron mobility transistor switching characteristics for high-power applications with HiSIM-GaN compact model

    NASA Astrophysics Data System (ADS)

    Mizoguchi, Takeshi; Naka, Toshiyuki; Tanimoto, Yuta; Okada, Yasuhiro; Saito, Wataru; Miura-Mattausch, Mitiko; Jürgen Mattausch, Hans

    2016-04-01

    This paper presents a newly developed compact model HiSIM-GaN [Hiroshima University STARC IGFET Model for GaN high electron mobility transistors (HEMTs)]. The developed model includes two specific features of GaN-HEMT to reproduce the power efficiency accurately. One is the two-dimensional electron gas induced at the heterojunction, which is modeled by considering the potential distribution across the junction including the trap density contribution. The second feature is the field plate, which is introduced to delocalize the electric-field peak that occurs at the electrode edge. Using HiSIM-GaN, device characteristics have been simulated. It is demonstrated that measured DC/AC characteristics are well reproduced with the developed model. The model has also been applied to analyze circuit characteristics of a boost converter. It is shown that the waveform is well reproduced by considering one half of the trap density extracted with measured DC characteristics due to the time constant of trap events. Furthermore, it is verified that the power efficiency as a function of the load current is predicted within an accuracy of 1%. Influence of the trap density and the field plate on circuit performances is also discussed.

  6. 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.

  7. 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.

  8. Comparison of stress states in GaN films grown on different substrates: Langasite, sapphire and silicon

    NASA Astrophysics Data System (ADS)

    Park, Byung-Guon; Saravana Kumar, R.; Moon, Mee-Lim; Kim, Moon-Deock; Kang, Tae-Won; Yang, Woo-Chul; Kim, Song-Gang

    2015-09-01

    We demonstrate the evolution of GaN films on novel langasite (LGS) substrate by plasma-assisted molecular beam epitaxy, and assessed the quality of grown GaN film by comparing the experimental results obtained using LGS, sapphire and silicon (Si) substrates. To study the substrate effect, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectra were used to characterize the microstructure and stress states in GaN films. Wet etching of GaN films in KOH solution revealed that the films deposited on GaN/LGS, AlN/sapphire and AlN/Si substrates possess Ga-polarity, while the film deposited on GaN/sapphire possess N-polarity. XRD, Raman and PL analysis demonstrated that a compressive stress exist in the films grown on GaN/LGS, AlN/sapphire, and GaN/sapphire substrates, while a tensile stress appears on AlN/Si substrate. Comparative analysis showed the growth of nearly stress-free GaN films on LGS substrate due to the very small lattice mismatch (~3.2%) and thermal expansion coefficient difference (~7.5%). The results presented here will hopefully provide a new framework for the further development of high performance III-nitride-related devices using GaN/LGS heteroepitaxy.

  9. New approaches for calculating absolute surface energies of wurtzite (0001)/(000 1 ¯ ): A study of ZnO and GaN

    NASA Astrophysics Data System (ADS)

    Zhang, Jingzhao; Zhang, Yiou; Tse, Kinfai; Deng, Bei; Xu, Hu; Zhu, Junyi

    2016-05-01

    The accurate absolute surface energies of (0001)/(000 1 ¯ ) surfaces of wurtzite structures are crucial in determining the thin film growth mode of important energy materials. However, the surface energies still remain to be solved due to the intrinsic difficulty of calculating the dangling bond energy of asymmetrically bonded surface atoms. In this study, we used a pseudo-hydrogen passivation method to estimate the dangling bond energy and calculate the polar surfaces of ZnO and GaN. The calculations were based on the pseudo chemical potentials obtained from a set of tetrahedral clusters or simple pseudo-molecules, using density functional theory approaches. The surface energies of (0001)/(000 1 ¯ ) surfaces of wurtzite ZnO and GaN that we obtained showed relatively high self-consistencies. A wedge structure calculation with a new bottom surface passivation scheme of group-I and group-VII elements was also proposed and performed to show converged absolute surface energy of wurtzite ZnO polar surfaces, and these results were also compared with the above method. The calculated results generally show that the surface energies of GaN are higher than those of ZnO, suggesting that ZnO tends to wet the GaN substrate, while GaN is unlikely to wet ZnO. Therefore, it will be challenging to grow high quality GaN thin films on ZnO substrates; however, high quality ZnO thin film on GaN substrate would be possible. These calculations and comparisons may provide important insights into crystal growth of the above materials, thereby leading to significant performance enhancements in semiconductor devices.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  13. 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.

  14. Suppression of plasma-induced damage on GaN etched by a Cl2 plasma at high temperatures

    NASA Astrophysics Data System (ADS)

    Liu, Zecheng; Pan, Jialin; Kako, Takashi; Ishikawa, Kenji; Takeda, Keigo; Kondo, Hiroki; Oda, Osamu; Sekine, Makoto; Hori, Masaru

    2015-06-01

    Plasma-induced damage (PID) during plasma-etching processes was suppressed by the application of Cl2 plasma etching at an optimal temperature of 400 °C, based on results of evaluations of photoluminescence (PL), stoichiometric composition, and surface roughness. The effects of ions, photons, and radicals on damage formation were separated from the effects of plasma using the pallet for plasma evaluation (PAPE) method. The PID was induced primarily by energetic ion bombardments at temperatures lower than 400 °C and decreased with increasing temperature. Irradiations by photons and radicals were enhanced to form the PID and to develop surface roughness at temperatures higher than 400 °C. Consequently, Cl2 plasma etching at 400 °C resulted optimally in low damage and a stoichiometric and smooth GaN surface.

  15. Green high-power tunable external-cavity GaN diode laser at 515  nm.

    PubMed

    Chi, Mingjun; Jensen, Ole Bjarlin; Petersen, Paul Michael

    2016-09-15

    A 480 mW green tunable diode laser system is demonstrated for the first time to our knowledge. The laser system is based on a GaN broad-area diode laser and Littrow external-cavity feedback. The green laser system is operated in two modes by switching the polarization direction of the laser beam incident on the grating. When the laser beam is p-polarized, an output power of 50 mW with a tunable range of 9.2 nm is achieved. When the laser beam is s-polarized, an output power of 480 mW with a tunable range of 2.1 nm is obtained. This constitutes the highest output power from a tunable green diode laser system. PMID:27628345

  16. Green high-power tunable external-cavity GaN diode laser at 515  nm.

    PubMed

    Chi, Mingjun; Jensen, Ole Bjarlin; Petersen, Paul Michael

    2016-09-15

    A 480 mW green tunable diode laser system is demonstrated for the first time to our knowledge. The laser system is based on a GaN broad-area diode laser and Littrow external-cavity feedback. The green laser system is operated in two modes by switching the polarization direction of the laser beam incident on the grating. When the laser beam is p-polarized, an output power of 50 mW with a tunable range of 9.2 nm is achieved. When the laser beam is s-polarized, an output power of 480 mW with a tunable range of 2.1 nm is obtained. This constitutes the highest output power from a tunable green diode laser system.

  17. 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.

  18. Qualitative and quantitative analysis of the major constituents in Jin-Mu-Gan-Mao tablet by high-performance liquid chromatography with diode-array detection and quadrupole time-of-flight tandem mass spectrometry.

    PubMed

    Huang, Mingqing; Xu, Shuyu; Xu, Wen; Chen, Daxing; Chu, Kedan; Xu, Wei; Peng, Jun; Lu, Jinjian

    2014-12-01

    Jin-Mu-Gan-Mao tablet is a well-known traditional Chinese medicinal preparation, which has been used to treat the common cold in China. In this study, a systematic method was established for the qualitative and quantitative analysis of the major constituents in Jin-Mu-Gan-Mao tablet. First, a method of high-performance liquid chromatography with diode-array detection and quadrupole time-of-flight mass spectrometry was developed for identification of the multi-constituents. Thirty-one compounds including ten phenolic acids, 18 flavonoids, and three iridoid glycosides were clearly identified by comparison with the reference standards, and 11 compounds were deduced by comparison with the literature data. Second, a new quantitative analysis method of Jin-Mu-Gan-Mao tablet was established by high-performance liquid chromatography with diode-array detection. Twelve compounds, either with high contents or strong bioactivities, were chosen as marker components. This analytical method was validated through intra- and interday precision, repeatability, and stability, with respective relative standard deviations less than 1.74, 2.54, 2.44, and 2.48%. The limits of detection and quantification were less than 0.327 and 0.881 μg/mL, respectively. The overall recoveries ranged from 97.04-102.76% (relative standard deviation ≤ 2.91%). Then this validated method was applied to determine ten batches of Jin-Mu-Gan-Mao tablet. The results indicated that these new approaches can be applicable for the qualitative and quantitative analysis of Jin-Mu-Gan-Mao tablet.

  19. Photoluminescence enhancement from GaN by beryllium doping

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  20. Design of an Ultra-High Efficiency GaN High-Power Amplifier for SAR Remote Sensing

    NASA Technical Reports Server (NTRS)

    Thrivikraman, Tushar; Hoffman, James

    2013-01-01

    This work describes the development of a high-power amplifier for use with a remote sensing SAR system. The amplifier is intended to meet the requirements for the Sweep-SAR technique for use in the proposed DESDynI SAR instrument. In order to optimize the amplifier design, active load-pull technique is employed to provide harmonic tuning to provide efficiency improvements. In addition, some of the techniques to overcome the challenges of load-pulling high power devices are presented. The design amplifier was measured to have 49 dBm of output power with 75% PAE, which is suitable to meet the proposed system requirements.

  1. Visible fiber lasers excited by GaN laser diodes

    NASA Astrophysics Data System (ADS)

    Fujimoto, Yasushi; Nakanishi, Jun; Yamada, Tsuyoshi; Ishii, Osamu; Yamazaki, Masaaki

    2013-07-01

    This paper describes and discusses visible fiber lasers that are excited by GaN laser diodes. One of the attractive points of visible light is that the human eye is sensitive to it between 400 and 700 nm, and therefore we can see applications in display technology. Of course, many other applications exist. First, we briefly review previously developed visible lasers in the gas, liquid, and solid-state phases and describe the history of primary solid-state visible laser research by focusing on rare-earth doped fluoride media, including glasses and crystals, to clarify the differences and the merits of primary solid-state visible lasers. We also demonstrate over 1 W operation of a Pr:WPFG fiber laser due to high-power GaN laser diodes and low-loss optical fibers (0.1 dB/m) made by waterproof fluoride glasses. This new optical fiber glass is based on an AlF3 system fluoride glass, and its waterproof property is much better than the well known fluoride glass of ZBLAN. The configuration of primary visible fiber lasers promises highly efficient, cost-effective, and simple laser systems and will realize visible lasers with photon beam quality and quantity, such as high-power CW or tunable laser systems, compact ultraviolet lasers, and low-cost ultra-short pulse laser systems. We believe that primary visible fiber lasers, especially those excited by GaN laser diodes, will be effective tools for creating the next generation of research and light sources.

  2. Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Bai, J.; Hou, Y.; Smith, R. M.; Yu, X.; Gong, Y.; Wang, T.

    2016-02-01

    We demonstrate a great improvement in the crystal quality of our semi-polar (11-22) GaN overgrown on regularly arrayed micro-rod templates fabricated using a combination of industry-matched photolithography and dry-etching techniques. As a result of our micro-rod configuration specially designed, an intrinsic issue on the anisotropic growth rate which is a great challenge in conventional overgrowth technique for semi-polar GaN has been resolved. Transmission electron microscopy measurements show a different mechanism of defect reduction from conventional overgrowth techniques and also demonstrate major advantages of our approach. The dislocations existing in the GaN micro-rods are effectively blocked by both a SiO2 mask on the top of each GaN micro-rod and lateral growth along the c-direction, where the growth rate along the c-direction is faster than that along any other direction. Basal stacking faults (BSFs) are also effectively impeded, leading to a distribution of BSF-free regions periodically spaced by BSF regions along the [-1-123] direction, in which high and low BSF density areas further show a periodic distribution along the [1-100] direction. Furthermore, a defect reduction model is proposed for further improvement in the crystalline quality of overgrown (11-22) GaN on sapphire.

  3. High power, high beam quality regenerative amplifier

    DOEpatents

    Hackel, Lloyd A.; Dane, Clifford B.

    1993-01-01

    A regenerative laser amplifier system generates high peak power and high energy per pulse output beams enabling generation of X-rays used in X-ray lithography for manufacturing integrated circuits. The laser amplifier includes a ring shaped optical path with a limited number of components including a polarizer, a passive 90 degree phase rotator, a plurality of mirrors, a relay telescope, and a gain medium, the components being placed close to the image plane of the relay telescope to reduce diffraction or phase perturbations in order to limit high peak intensity spiking. In the ring, the beam makes two passes through the gain medium for each transit of the optical path to increase the amplifier gain to loss ratio. A beam input into the ring makes two passes around the ring, is diverted into an SBS phase conjugator and proceeds out of the SBS phase conjugator back through the ring in an equal but opposite direction for two passes, further reducing phase perturbations. A master oscillator inputs the beam through an isolation cell (Faraday or Pockels) which transmits the beam into the ring without polarization rotation. The isolation cell rotates polarization only in beams proceeding out of the ring to direct the beams out of the amplifier. The diffraction limited quality of the input beam is preserved in the amplifier so that a high power output beam having nearly the same diffraction limited quality is produced.

  4. High power, high beam quality regenerative amplifier

    DOEpatents

    Hackel, L.A.; Dane, C.B.

    1993-08-24

    A regenerative laser amplifier system generates high peak power and high energy per pulse output beams enabling generation of X-rays used in X-ray lithography for manufacturing integrated circuits. The laser amplifier includes a ring shaped optical path with a limited number of components including a polarizer, a passive 90 degree phase rotator, a plurality of mirrors, a relay telescope, and a gain medium, the components being placed close to the image plane of the relay telescope to reduce diffraction or phase perturbations in order to limit high peak intensity spiking. In the ring, the beam makes two passes through the gain medium for each transit of the optical path to increase the amplifier gain to loss ratio. A beam input into the ring makes two passes around the ring, is diverted into an SBS phase conjugator and proceeds out of the SBS phase conjugator back through the ring in an equal but opposite direction for two passes, further reducing phase perturbations. A master oscillator inputs the beam through an isolation cell (Faraday or Pockels) which transmits the beam into the ring without polarization rotation. The isolation cell rotates polarization only in beams proceeding out of the ring to direct the beams out of the amplifier. The diffraction limited quality of the input beam is preserved in the amplifier so that a high power output beam having nearly the same diffraction limited quality is produced.

  5. Tellurium n-type doping of highly mismatched amorphous GaN1-xAsx alloys in plasma-assisted molecular beam epitaxy

    DOE PAGES

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

    2014-10-01

    In this paper we report our study on n-type Te doping of amorphous GaN1-xAsx layers grown by plasma-assisted molecular beam epitaxy. We have used a low temperature PbTe source as a source of tellurium. Reproducible and uniform tellurium incorporation in amorphous GaN1-xAsx layers has been successfully achieved with a maximum Te concentration of 9×10²⁰ cm⁻³. Tellurium incorporation resulted in n-doping of GaN1-xAsx layers with Hall carrier concentrations up to 3×10¹⁹ cm⁻³ and mobilities of ~1 cm²/V s. The optimal growth temperature window for efficient Te doping of the amorphous GaN1-xAsx layers has been determined.

  6. Photo-assisted RIE of GaN in BCl{sub 3}/Cl{sub 2}/N{sub 2}

    SciTech Connect

    Medelci, N.; Tempez, A.; Berishev, I.; Starikov, D.; Bensaoula, A.

    1999-07-01

    Gallium nitride (GaN) has been under intense investigation due to its unique qualities (wide band gap, chemical and temperature stability) for optoelectronic and high temperature/high power applications. To this end, reactive ion etching (RIE) experiments were performed on GaN thin films using BCl{sub 3}/Cl{sub 2}/Ar. These resulted in etch rates of 1,400 {angstrom}/min at {minus}400 V dc bias. However, rough etched surfaces, nitrogen surface depletion and high chlorine content were observed. In order to remedy these shortcomings, a photo-assisted RIE process using a filtered Xe lamp beam was developed, resulting in higher etch rates but again in nitrogen depleted surfaces. Preliminary results on using nitrogen instead of argon in the process chemistry show a big improvement in photo-assisted etch rates (50%) and Ga/N ratio (0.78 versus 1.25). In this paper, the effects of epilayer doping, dc bias, nitrogen flow rate and photo-irradiation flux on GaN etch rates, surface morphology and composition are presented. Finally, preliminary results on the use of a KrF excimer laser beam in the GaN photo-assisted RIE process are presented.

  7. Charge transfer in Fe-doped GaN: The role of the donor

    SciTech Connect

    Sunay, Ustun; Dashdorj, J.; Zvanut, M. E.; Harrison, J. G.; Leach, J. H.; Udwary, K.

    2014-02-21

    Several nitride-based device structures would benefit from the availability of high quality, large-area, freestanding semi-insulating GaN substrates. Due to the intrinsic n-type nature of GaN, however, the incorporation of compensating centers such as Fe is necessary to achieve the high resistivity required. We are using electron paramagnetic resonance (EPR) to explore charge transfer in 450 um thick GaN:Fe plates to understand the basic mechanisms related to compensation so that the material may be optimized for device applications. The results suggest that the simple model based on one shallow donor and a single Fe level is insufficient to describe compensation. Rather, the observation of the neutral donor and Fe3+ indicates that either the two species are spatially segregated or additional compensating and donor defects must be present.

  8. Growth and characteristics of self-assembly defect-free GaN surface islands by molecular beam epitaxy.

    PubMed

    Hsu, Kuang-Yuan; Wang, Cheng-Yu; Liu, Chuan-Pu

    2011-04-01

    GaN surface nano-islands of high crystal quality, without any dislocations or other extended defects, are grown on a c-plane sapphire substrate by plasma-assisted molecular beam epitaxy. Nano-island growth requires special conditions in terms of V/III ratio and substrate temperature, distinct from either film or nanocolumn growth. The insertion of a nitrided Ga layer can effectively improve the uniformity of the nano-islands in both shape and size. The islands are well faced truncated pyramids with island size ranged from 30 to 110 nm, and height ranged from 30 to 55 nm. On, the other hand, the density and facet of the GaN surface islands would be affected by the growth conditions. An increase of the V/III ratio from 30 to 40 led to an increase in density from 1.4 x 10(9) to 4.3 x 10(9) cm(-2) and an evolution from {1-21-1} facets to {1-21-2} facets. The GaN layers containing the surface islands can moderate the compressive strain due to the lattice and thermal mismatch between GaN and c-sapphire. Conductive atomic force microscopy shows that the off-axis sidewall facets are more electrically active than those at the island center. The formation of the GaN surface islands is strongly induced by the Ehrlich-Schwoebel barrier effect of preexisting islands grown in the early growth stage. GaN surface islands are ideal templates for growing nano-devices.

  9. Less strained and more efficient GaN light-emitting diodes with embedded silica hollow nanospheres

    PubMed Central

    Kim, Jonghak; Woo, Heeje; Joo, Kisu; Tae, Sungwon; Park, Jinsub; Moon, Daeyoung; Park, Sung Hyun; Jang, Junghwan; Cho, Yigil; Park, Jucheol; Yuh, Hwankuk; Lee, Gun-Do; Choi, In-Suk; Nanishi, Yasushi; Han, Heung Nam; Char, Kookheon; Yoon, Euijoon

    2013-01-01

    Light-emitting diodes (LEDs) become an attractive alternative to conventional light sources due to high efficiency and long lifetime. However, different material properties between GaN and sapphire cause several problems such as high defect density in GaN, serious wafer bowing, particularly in large-area wafers, and poor light extraction of GaN-based LEDs. Here, we suggest a new growth strategy for high efficiency LEDs by incorporating silica hollow nanospheres (S-HNS). In this strategy, S-HNSs were introduced as a monolayer on a sapphire substrate and the subsequent growth of GaN by metalorganic chemical vapor deposition results in improved crystal quality due to nano-scale lateral epitaxial overgrowth. Moreover, well-defined voids embedded at the GaN/sapphire interface help scatter lights effectively for improved light extraction, and reduce wafer bowing due to partial alleviation of compressive stress in GaN. The incorporation of S-HNS into LEDs is thus quite advantageous in achieving high efficiency LEDs for solid-state lighting. PMID:24220259

  10. Comparison of AlGaN p-i-n ultraviolet avalanche photodiodes grown on free-standing GaN and sapphire substrates

    NASA Astrophysics Data System (ADS)

    Kim, Jeomoh; Ji, Mi-Hee; Detchprohm, Theeradetch; Dupuis, Russell D.; Ryou, Jae-Hyun; Sood, Ashok K.; Dhar, Nibir D.; Lewis, Jay

    2015-12-01

    We compare the performance characteristics of Al0.05Ga0.95N UV avalanche photodiodes (APDs) grown on different substrates. UV-APDs grown on a free-standing GaN substrate show lower dark-current densities for all fabricated mesa sizes than similar UV-APDs grown on a GaN/sapphire template. In addition, a stable avalanche gain higher than 5 × 105 and a significant increase in the responsivity of UV-APDs grown on a free-standing GaN substrate are observed. We believe that the high crystalline quality of Al0.05Ga0.95N UV-APDs grown on a free-standing GaN substrate with low dislocation density is responsible for the observed low leakage currents, high performance characteirstics, and reliability of the devices.

  11. 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.

  12. Thermal stability of deep level defects induced by high energy proton irradiation in n-type GaN

    SciTech Connect

    Zhang, Z.; Farzana, E.; Sun, W. Y.; Arehart, A. R.; Ringel, S. A.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; McSkimming, B.; Kyle, E. C. H.; Speck, J. S.

    2015-10-21

    The impact of annealing of proton irradiation-induced defects in n-type GaN devices has been systematically investigated using deep level transient and optical spectroscopies. Moderate temperature annealing (>200–250 °C) causes significant reduction in the concentration of nearly all irradiation-induced traps. While the decreased concentration of previously identified N and Ga vacancy related levels at E{sub C} − 0.13 eV, 0.16 eV, and 2.50 eV generally followed a first-order reaction model with activation energies matching theoretical values for N{sub I} and V{sub Ga} diffusion, irradiation-induced traps at E{sub C} − 0.72 eV, 1.25 eV, and 3.28 eV all decrease in concentration in a gradual manner, suggesting a more complex reduction mechanism. Slight increases in concentration are observed for the N-vacancy related levels at E{sub C} − 0.20 eV and 0.25 eV, which may be due to the reconfiguration of other N-vacancy related defects. Finally, the observed reduction in concentrations of the states at E{sub C} − 1.25 and E{sub C} − 3.28 eV as a function of annealing temperature closely tracks the detailed recovery behavior of the background carrier concentration as a function of annealing temperature. As a result, it is suggested that these two levels are likely to be responsible for the underlying carrier compensation effect that causes the observation of carrier removal in proton-irradiated n-GaN.

  13. 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.

  14. Electron Spin Resonance in GaN Thin Film Doped with Fe

    NASA Astrophysics Data System (ADS)

    Kashiwagi, Takanari; Sonoda, Saki; Yashiro, Haruhiko; Ishihara, Yujiro; Usui, Akira; Akasaka, Youichi; Hagiwara, Masayuki

    2007-02-01

    High-quality and high-resistivity semiconducting substrates are needed to fabricate high-frequency devices such as high-mobility transistors based on gallium nitride (GaN). A GaN thin film doped with Fe ions becomes one of such high-resistivity substrates. To obtain microscopic information on the Fe ions in the GaN:Fe film, we have performed electron spin resonance (ESR) measurements using a conventional X-band apparatus and home made Q-band equipment. The observed ESR signals were analyzed with a spin Hamiltonian given by considering the local symmetry of the Ga site (C3v) and assuming that the Fe3+ ions (S=5/2) are substituted for Ga3+ ions. As a result, the angular dependence of the resonance fields and the temperature dependence of the signal intensities are reproduced very well by the calculations. Consequently, we confirmed that the Fe3+ ions occupy some of the Ga sites in the GaN thin film.

  15. Temperature Dependence and High-Temperature Stability of the Annealed Ni/Au Ohmic Contact to p-Type GaN in Air

    NASA Astrophysics Data System (ADS)

    Zhao, Shirong; McFavilen, Heather; Wang, Shuo; Ponce, Fernando A.; Arena, Chantal; Goodnick, Stephen; Chowdhury, Srabanti

    2016-04-01

    We report on the temperature-dependent contact resistivity and high-temperature stability of the annealed Ni/Au ohmic contacts to p-type GaN in air. As the measure temperature increases from 25°C to 390°C, both the specific contact resistivity (ρ c) and sheet resistance (R sh) decrease by factors ˜10, contributing to the 10-fold increase in current at 390°C compared with that at 25°C. It was also observed that the ρ c was further reduced by 36%, i.e., from 2.2 × 10-3 Ω cm2 to 1.4 × 10-3 Ω cm2, during the 48-h high-temperature stability test at 450°C in air, showing excellent stability of the contacts. An increase in ρ c was observed after the contacts were subjected to 500°C in air. Higher temperature stress led to a significant increase in ρ c. The contacts show rectifying I-V characteristics after being subjected to 700°C for 1 h. The degradation mechanics were analyzed with the assistance of transmission electron microscopy and energy dispersive x-ray spectroscopy.

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

    PubMed

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

    2016-06-01

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

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

    PubMed

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

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts. PMID:27124605

  18. 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.

  19. Influence of post-deposition annealing on interfacial properties between GaN and ZrO2 grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Influence of post-deposition annealing on interfacial properties related to the formation/annihilation of interfacial GaOx layer of ZrO2 grown by atomic layer deposition (ALD) on GaN is studied. ZrO2 films were annealed in N2 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 GaOx layer associated with low surface defect states due to "clean up" effect of ALD-ZrO2 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.

  20. Impact of inhomogeneous broadening on optical polarization of high-inclination semipolar and nonpolar InxGa1 -xN /GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Mounir, Christian; Schwarz, Ulrich T.; Koslow, Ingrid L.; Kneissl, Michael; Wernicke, Tim; Schimpke, Tilman; Strassburg, Martin

    2016-06-01

    We investigate the influence of inhomogeneous broadening on the optical polarization properties of high-inclination semipolar and nonpolar InxGa1 -xN /GaN quantum wells. Different planar m-plane and (20 2 ¯1 ¯) samples were grown (including core-shell microrods) and have been characterized by excitation-dependent polarization-resolved confocal micro-photoluminescence. The measured degree of linear polarization (DLP) is compared to theoretical predictions obtained by Fermi-Dirac statistical filling of the electronic band structure calculated by the k .p envelope function method. We show that our measured DLP at room temperature, as well as values reported by other groups, are systematically higher than the theoretical predictions. We propose to solve this discrepancy between theory and experiment by introducing inhomogeneous broadening in our calculations. Considering indium content fluctuations and the localization lengths of electrons and holes, different effective broadenings are applied to different subsets of subbands. We thereby show that inhomogeneous broadening leads to an increase of the DLP at room temperature. Furthermore, the dependence of the optical properties on the excitation density is better reproduced. Looking at the DLP as a function of the temperature gives us insight into the thermalization dynamics of charge carriers.

  1. Interface control technologies for high-power GaN transistors: Self-stopping etching of p-GaN layers utilizing electrochemical reactions

    NASA Astrophysics Data System (ADS)

    Sato, Taketomo; Kumazaki, Yusuke; Edamoto, Masaaki; Akazawa, Masamichi; Hashizume, Tamotsu

    2016-02-01

    The selective and low-damaged etching of p-type GaN or AlGaN layer is inevitable process for AlGaN/GaN high-power transistors. We have investigated an electrochemical etching of p-GaN layer grown on AlGaN/GaN heterostructures, consisting of an anodic oxidation of p-GaN surface and a subsequent dissolution of the resulting oxide. The p-GaN layer was electrochemically etched by following the pattern of the SiO2 film that acted as an etching mask. Etching depth was linearly controlled by cycle number of triangular waveform at a rate of 25 nm/cycle. The AFM, TEM and μ-AES results showed that the top p-GaN layer was completely removed after 5 cycles applied, and the etching reaction was automatically sopped on the AlGaN surface. I-V and C-V measurements revealed that no significant damages were induced in the AlGaN/GaN heterostructures.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  3. Fabrication of low-density GaN/AlN quantum dots via GaN thermal decomposition in MOCVD.

    PubMed

    Zhang, Jin; Li, Senlin; Xiong, Hui; Tian, Wu; Li, Yang; Fang, Yanyan; Wu, Zhihao; Dai, Jiangnan; Xu, Jintong; Li, Xiangyang; Chen, Changqing

    2014-01-01

    With an appropriate high anneal temperature under H2 atmosphere, GaN quantum dots (QDs) have been fabricated via GaN thermal decomposition in metal organic chemical vapor deposition (MOCVD). Based on the characterization of atomic force microscopy (AFM), the obtained GaN QDs show good size distribution and have a low density of 2.4 × 10(8) cm(-2). X-ray photoelectron spectroscopy (XPS) analysis demonstrates that the GaN QDs were formed without Ga droplets by thermal decomposition of GaN.

  4. Wafer-scale epitaxial lift-off of optoelectronic grade GaN from a GaN substrate using a sacrificial ZnO interlayer

    NASA Astrophysics Data System (ADS)

    Rajan, Akhil; Rogers, David J.; Ton-That, Cuong; Zhu, Liangchen; Phillips, Matthew R.; Sundaram, Suresh; Gautier, Simon; Moudakir, Tarik; El-Gmili, Youssef; Ougazzaden, Abdallah; Sandana, Vinod E.; Teherani, Ferechteh H.; Bove, Philippe; Prior, Kevin A.; Djebbour, Zakaria; McClintock, Ryan; Razeghi, Manijeh

    2016-08-01

    Full 2 inch GaN epilayers were lifted off GaN and c-sapphire substrates by preferential chemical dissolution of sacrificial ZnO underlayers. Modification of the standard epitaxial lift-off (ELO) process by supporting the wax host with a glass substrate proved key in enabling full wafer scale-up. Scanning electron microscopy and x-ray diffraction confirmed that intact epitaxial GaN had been transferred to the glass host. Depth-resolved cathodoluminescence (CL) analysis of the bottom surface of the lifted-off GaN layer revealed strong near-band-edge (3.33 eV) emission indicating a superior optical quality for the GaN which was lifted off the GaN substrate. This modified ELO approach demonstrates that previous theories proposing that wax host curling was necessary to keep the ELO etch channel open do not apply to the GaN/ZnO system. The unprecedented full wafer transfer of epitaxial GaN to an alternative support by ELO offers the perspective of accelerating industrial adoption of the expensive GaN substrate through cost-reducing recycling.

  5. Thermodynamic theory of epitaxial alloys: first-principles mixed-basis cluster expansion of (In, Ga)N alloy film.

    PubMed

    Liu, Jefferson Zhe; Zunger, Alex

    2009-07-22

    Epitaxial growth of semiconductor alloys onto a fixed substrate has become the method of choice to make high quality crystals. In the coherent epitaxial growth, the lattice mismatch between the alloy film and the substrate induces a particular form of strain, adding a strain energy term into the free energy of the alloy system. Such epitaxial strain energy can alter the thermodynamics of the alloy, leading to a different phase diagram and different atomic microstructures. In this paper, we present a general-purpose mixed-basis cluster expansion method to describe the thermodynamics of an epitaxial alloy, where the formation energy of a structure is expressed in terms of pair and many-body interactions. With a finite number of first-principles calculation inputs, our method can predict the energies of various atomic structures with an accuracy comparable to that of first-principles calculations themselves. Epitaxial (In, Ga)N zinc-blende alloy grown on GaN(001) substrate is taken as an example to demonstrate the details of the method. Two (210) superlattice structures, (InN)(2)/(GaN)(2) (at x = 0.50) and (InN)(4)/(GaN)(1) (at x = 0.80), are identified as the ground state structures, in contrast to the phase-separation behavior of the bulk alloy. PMID:21828531

  6. Defect reduction in (112_O) a-plane GaN by two-stage epitaxiallateral overgrowth

    SciTech Connect

    Ni, X.; Ozgur, U.; Fu, Y.; Biyikli, N.; Xie, J.; Baski, A.A.; Morkoc, H.; Liliental-Weber, Z.

    2006-10-20

    In the epitaxial lateral overgrowth (ELO) of (11{bar 2}0) a-plane GaN, the uneven growth rates of two opposing wings, Ga- and N-wings, makes the coalescence of two neighboring wings more difficult than that in c-plane GaN. We report a two-stage growth method to get uniformly coalesced epitaxial lateral overgrown a-plane GaN using metalorganic chemical vapor deposition (MOCVD) by employing relatively lower growth temperature in the first step followed by enhanced lateral growth in the second. Using this method, the height differences between Ga-polar and N-polar wings at the coalescence front could be reduced, thereby making the coalescence of two wings much easier. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing areas was 1.0x10{sup 8}cm{sup -2}, more than two orders of magnitude lower than that in the window areas (4.2x10{sup 10}cm{sup -2}). However, high density of basal stacking faults of 1.2x104 cm-1 was still observed in the wing areas as compared to c-plane GaN. Atomic force microscopy and photoluminescence measurements on the coalesced ELO a-GaN sample also indicated improved material quality.

  7. Semipolar (202{sup ¯}1) GaN and InGaN quantum wells on sapphire substrates

    SciTech Connect

    Leung, Benjamin; Wang, Dili; Kuo, Yu-Sheng; Xiong, Kanglin; Song, Jie; Chen, Danti; Park, Sung Hyun; Han, Jung; Hong, Su Yeon; Choi, Joo Won

    2014-06-30

    Here, we demonstrate a process to produce planar semipolar (202{sup ¯}1) GaN templates on sapphire substrates. We obtain (202{sup ¯}1) oriented GaN by inclined c-plane sidewall growth from etched sapphire, resulting in single crystal material with on-axis x-ray diffraction linewidth below 200 arc sec. The surface, composed of (101{sup ¯}1) and (101{sup ¯}0) facets, is planarized by the chemical-mechanical polishing of full 2 in. wafers, with a final surface root mean square roughness of <0.5 nm. We then analyze facet formation and roughening mechanisms on the (202{sup ¯}1) surface and establish a growth condition in N{sub 2} carrier gas to maintain a planar surface for further device layer growth. Finally, the capability of these semipolar (202{sup ¯}1) GaN templates to produce high quality device structures is verified by the growth and characterization of InGaN/GaN multiple quantum well structures. It is expected that the methods shown here can enable the benefits of using semipolar orientations in a scalable and practical process and can be readily extended to achieve devices on surfaces using any orientation of semipolar GaN on sapphire.

  8. Effect of photocatalytic oxidation technology on GaN CMP

    NASA Astrophysics Data System (ADS)

    Wang, Jie; Wang, Tongqing; Pan, Guoshun; Lu, Xinchun

    2016-01-01

    GaN is so hard and so chemically inert that it is difficult to obtain a high material removal rate (MRR) in the chemical mechanical polishing (CMP) process. This paper discusses the application of photocatalytic oxidation technology in GaN planarization. Three N-type semiconductor particles (TiO2, SnO2, and Fe2O3) are used as catalysts and added to the H2O2-SiO2-based slurry. By optical excitation, highly reactive photoinduced holes are produced on the surface of the particles, which can oxidize OH- and H2O absorbed on the surface of the catalysts; therefore, more OH* will be generated. As a result, GaN MRRs in an H2O2-SiO2-based polishing system combined with catalysts are improved significantly, especially when using TiO2, the MRR of which is 122 nm/h. The X-ray photoelectron spectroscopy (XPS) analysis shows the variation trend of chemical composition on the GaN surface after polishing, revealing the planarization process. Besides, the effect of pH on photocatalytic oxidation combined with TiO2 is analyzed deeply. Furthermore, the physical model of GaN CMP combined with photocatalytic oxidation technology is proposed to describe the removal mechanism of GaN.

  9. Study of radiation detection properties of GaN pn diode

    NASA Astrophysics Data System (ADS)

    Sugiura, Mutsuhito; Kushimoto, Maki; Mitsunari, Tadashi; Yamashita, Kohei; Honda, Yoshio; Amano, Hiroshi; Inoue, Yoku; Mimura, Hidenori; Aoki, Toru; Nakano, Takayuki

    2016-05-01

    Recently, GaN, which has remarkable properties as a material for optical devices and high-power electron devices, has also attracted attention as a material for radiation detectors. We previously suggested the use of BGaN as a neutron detector material. However, the radiation detection characteristics of GaN itself are not yet adequately understood. For realizing a BGaN neutron detector, the understanding of the radiation detection characteristics of GaN, which is a base material of the neutron detector, is important. In this study, we evaluated the radiation detection characteristics of GaN. We performed I-V and energy spectrum measurements under alpha ray, gamma ray, and thermal neutron irradiations to characterize the radiation detection characteristics of a GaN diode. The obtained results indicate that GaN is an effective material for our proposed new BGaN-based neutron detector.

  10. Infrared absorption of hydrogen-related defects in ammonothermal GaN

    NASA Astrophysics Data System (ADS)

    Suihkonen, Sami; Pimputkar, Siddha; Speck, James S.; Nakamura, Shuji

    2016-05-01

    Polarization controlled Fourier transform infrared (FTIR) absorption measurements were performed on a high quality m-plane ammonothermal GaN crystal grown using basic chemistry. The polarization dependence of characteristic absorption peaks of hydrogen-related defects at 3000-3500 cm-1 was used to identify and determine the bond orientation of hydrogenated defect complexes in the GaN lattice. Majority of hydrogen was found to be bonded in gallium vacancy complexes decorated with one to three hydrogen atoms (VGa-H1,2,3) but also hydrogenated oxygen defect complexes, hydrogen in bond-center sites, and lattice direction independent absorption were observed. Absorption peak intensity was used to determine a total hydrogenated VGa density of approximately 4 × 1018 cm-3, with main contribution from VGa-H1,2. Also, a significant concentration of electrically passive VGa-H3 was detected. The high density of hydrogenated defects is expected to have a strong effect on the structural, optical, and electrical properties of ammonothermal GaN crystals.

  11. GaN and related alloys -- 1999. Materials Research Society symposium proceedings, Volume 595

    SciTech Connect

    Myers, T.H.; Feenstra, R.M.; Shur, M.S.; Amano, Hiroshi

    2000-07-01

    The symposium, GaN and Related Alloys, was held November 28--December 3 at the 1999 Materials Research Society Fall Meeting in Boston, Massachusetts. This symposium on GaN and associated materials focused on advances in basic science, as well as the rapidly maturing technologies involving blue/green light-emitters, detectors and high power electronics. Nichia Chemical reported on the commercialization of a laser operating at 405 nm wavelength with a 4,000 hour device lifetime. At 450 nm emission wavelength, significant reductions in lifetime are found, and are believed to arise from non-ideal properties of the InGaN alloy used in the active layer of the device. Transistors for microwave applications have achieved significant success in terms of device speed and high power capability. Improvements in the epitaxy of GaN were discussed, using both selective area growth techniques (lateral epitaxial overgrowth) and introduction of low-temperature intra-layers in the films. Advances in both molecular beam epitaxy and metal-organic vapor phase epitaxy were reported, including several studies of quantum dot formation in strained alloys. Hydride vapor phase epitaxy continues to show improvements, particularly for providing very thick films. As the material quality improves, advances in characterization (structural, optical, and electrical) have provided an increased understanding of the role of defects in the materials, and the effects of processing steps on material properties. One hundred thirty two papers have been processed separately for inclusion on the data base.

  12. Si in GaN -- On the nature of the background donor

    SciTech Connect

    Wetzel, C.; Chen, A.L.; Suski, T.; Ager, J.W. III; Walukiewicz, W.

    1996-08-01

    A characterization of the Si impurity in GaN is performed by Raman spectroscopy. Applying hydrostatic pressure up to 25 GPa the authors study the behavior of the LO phonon-plasmon mode in a series of high mobility Si doped GaN films. In contrast to earlier results on unintentionally doped bulk GaN crystals no freeze out of the free carriers could be observed in Si doped samples. The authors find that Si is a shallow hydrogenic donor throughout the pressure range studied. This result positively excludes Si incorporation as a dominant source of free electrons in previously studied bulk GaN samples.

  13. Structural defects in GaN revealed by Transmission Electron Microscopy

    SciTech Connect

    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.

  14. 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.

  15. Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

    NASA Astrophysics Data System (ADS)

    Puybaret, Renaud; Patriarche, Gilles; Jordan, Matthew B.; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean-Paul; Voss, Paul L.; de Heer, Walt A.; Berger, Claire; Ougazzaden, Abdallah

    2016-03-01

    We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5-8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

  16. Direct growth of GaN layer on carbon nanotube-graphene hybrid structure and its application for light emitting diodes.

    PubMed

    Seo, Tae Hoon; Park, Ah Hyun; Park, Sungchan; Kim, Yong Hwan; Lee, Gun Hee; Kim, Myung Jong; Jeong, Mun Seok; Lee, Young Hee; Hahn, Yoon-Bong; Suh, Eun-Kyung

    2015-01-01

    We report the growth of high-quality GaN layer on single-walled carbon nanotubes (SWCNTs) and graphene hybrid structure (CGH) as intermediate layer between GaN and sapphire substrate by metal-organic chemical vapor deposition (MOCVD) and fabrication of light emitting diodes (LEDs) using them. The SWCNTs on graphene act as nucleation seeds, resulting in the formation of kink bonds along SWCNTs with the basal plane of the substrate. In the x-ray diffraction, Raman and photoluminescence spectra, high crystalline quality of GaN layer grown on CGH/sapphire was observed due to the reduced threading dislocation and efficient relaxation of residual compressive strain caused by lateral overgrowth process. When applied to the LED structure, the current-voltage characteristics and electroluminescence (EL) performance exhibit that blue LEDs fabricated on CGH/sapphire well-operate at high injection currents and uniformly emit over the whole emission area. We expect that CGH can be applied for the epitaxial growth of GaN on various substrates such as Si and MgO, which can be a great advantage in electrical and thermal properties of optical devices fabricated on them. PMID:25597492

  17. Modeling and Design of GaN High Electron Mobility Transistors and Hot Electron Transistors through Monte Carlo Particle-based Device Simulations

    NASA Astrophysics Data System (ADS)

    Soligo, Riccardo

    In this work, the insight provided by our sophisticated Full Band Monte Carlo simulator is used to analyze the behavior of state-of-art devices like GaN High Electron Mobility Transistors and Hot Electron Transistors. Chapter 1 is dedicated to the description of the simulation tool used to obtain the results shown in this work. Moreover, a separate section is dedicated the set up of a procedure to validate to the tunneling algorithm recently implemented in the simulator. Chapter 2 introduces High Electron Mobility Transistors (HEMTs), state-of-art devices characterized by highly non linear transport phenomena that require the use of advanced simulation methods. The techniques for device modeling are described applied to a recent GaN-HEMT, and they are validated with experimental measurements. The main techniques characterization techniques are also described, including the original contribution provided by this work. Chapter 3 focuses on a popular technique to enhance HEMTs performance: the down-scaling of the device dimensions. In particular, this chapter is dedicated to lateral scaling and the calculation of a limiting cutoff frequency for a device of vanishing length. Finally, Chapter 4 and Chapter 5 describe the modeling of Hot Electron Transistors (HETs). The simulation approach is validated by matching the current characteristics with the experimental one before variations of the layouts are proposed to increase the current gain to values suitable for amplification. The frequency response of these layouts is calculated, and modeled by a small signal circuit. For this purpose, a method to directly calculate the capacitance is developed which provides a graphical picture of the capacitative phenomena that limit the frequency response in devices. In Chapter 5 the properties of the hot electrons are investigated for different injection energies, which are obtained by changing the layout of the emitter barrier. Moreover, the large signal characterization of the

  18. Dislocation-induced nanoparticle decoration on a GaN nanowire.

    PubMed

    Yang, Bing; Yuan, Fang; Liu, Qingyun; Huang, Nan; Qiu, Jianhang; Staedler, Thorsten; Liu, Baodan; Jiang, Xin

    2015-02-01

    GaN nanowires with homoepitaxial decorated GaN nanoparticles on their surface along the radial direction have been synthesized by means of a chemical vapor deposition method. The growth of GaN nanowires is catalyzed by Au particles via the vapor-liquid-solid (VLS) mechanism. Screw dislocations are generated along the radial direction of the nanowires under slight Zn doping. In contrast to the metal-catalyst-assisted VLS growth, GaN nanoparticles are found to prefer to nucleate and grow at these dislocation sites. High-resolution transmission electron microscopy (HRTEM) analysis demonstrates that the GaN nanoparticles possess two types of epitaxial orientation with respect to the corresponding GaN nanowire: (I) [1̅21̅0]np//[1̅21̅0]nw, (0001)np//(0001)nw; (II) [1̅21̅3]np//[12̅10]nw, (101̅0)np//(101̅0)nw. An increased Ga signal in the energy-dispersive spectroscopy (EDS) profile lines of the nanowires suggests GaN nanoparticle growth at the edge surface of the wires. All the crystallographic results confirm the importance of the dislocations with respect to the homoepitaxial growth of the GaN nanoparticles. Here, screw dislocations situated on the (0001) plane provide the self-step source to enable nucleation of the GaN nanoparticles.

  19. Spontaneous nucleation and growth of GaN nanowires: the fundamental role of crystal polarity.

    PubMed

    Fernández-Garrido, Sergio; Kong, Xiang; Gotschke, Tobias; Calarco, Raffaella; Geelhaar, Lutz; Trampert, Achim; Brandt, Oliver

    2012-12-12

    We experimentally investigate whether crystal polarity affects the growth of GaN nanowires in plasma-assisted molecular beam epitaxy and whether their formation has to be induced by defects. For this purpose, we prepare smooth and coherently strained AlN layers on 6H-SiC(0001) and SiC(0001̅) substrates to ensure a well-defined polarity and an absence of structural and morphological defects. On N-polar AlN, a homogeneous and dense N-polar GaN nanowire array forms, evidencing that GaN nanowires form spontaneously in the absence of defects. On Al-polar AlN, we do not observe the formation of Ga-polar GaN NWs. Instead, sparse N-polar GaN nanowires grow embedded in a Ga-polar GaN layer. These N-polar GaN nanowires are shown to be accidental in that the necessary polarity inversion is induced by the formation of Si(x)N. The present findings thus demonstrate that spontaneously formed GaN nanowires are irrevocably N-polar. Due to the strong impact of the polarity on the properties of GaN-based devices, these results are not only essential to understand the spontaneous formation of GaN nanowires but also of high technological relevance.

  20. Thermo-piezo-electro-mechanical simulation of AlGaN (aluminum gallium nitride) / GaN (gallium nitride) High Electron Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Stevens, Lorin E.

    Due to the current public demand of faster, more powerful, and more reliable electronic devices, research is prolific these days in the area of high electron mobility transistor (HEMT) devices. This is because of their usefulness in RF (radio frequency) and microwave power amplifier applications including microwave vacuum tubes, cellular and personal communications services, and widespread broadband access. Although electrical transistor research has been ongoing since its inception in 1947, the transistor itself continues to evolve and improve much in part because of the many driven researchers and scientists throughout the world who are pushing the limits of what modern electronic devices can do. The purpose of the research outlined in this paper was to better understand the mechanical stresses and strains that are present in a hybrid AlGaN (Aluminum Gallium Nitride) / GaN (Gallium Nitride) HEMT, while under electrically-active conditions. One of the main issues currently being researched in these devices is their reliability, or their consistent ability to function properly, when subjected to high-power conditions. The researchers of this mechanical study have performed a static (i.e. frequency-independent) reliability analysis using powerful multiphysics computer modeling/simulation to get a better idea of what can cause failure in these devices. Because HEMT transistors are so small (micro/nano-sized), obtaining experimental measurements of stresses and strains during the active operation of these devices is extremely challenging. Physical mechanisms that cause stress/strain in these structures include thermo-structural phenomena due to mismatch in both coefficient of thermal expansion (CTE) and mechanical stiffness between different materials, as well as stress/strain caused by "piezoelectric" effects (i.e. mechanical deformation caused by an electric field, and conversely voltage induced by mechanical stress) in the AlGaN and GaN device portions (both

  1. New CVD-based method for the growth of high-quality crystalline zinc oxide layers

    NASA Astrophysics Data System (ADS)

    Huber, Florian; Madel, Manfred; Reiser, Anton; Bauer, Sebastian; Thonke, Klaus

    2016-07-01

    High-quality zinc oxide (ZnO) layers were grown using a new chemical vapour deposition (CVD)-based low-cost growth method. The process is characterized by total simplicity, high growth rates, and cheap, less hazardous precursors. To produce elementary zinc vapour, methane (CH4) is used to reduce a ZnO powder. By re-oxidizing the zinc with pure oxygen, highly crystalline ZnO layers were grown on gallium nitride (GaN) layers and on sapphire substrates with an aluminum nitride (AlN) nucleation layer. Using simple CH4 as precursor has the big advantage of good controllability and the avoidance of highly toxic gases like nitrogen oxides. In photoluminescence (PL) measurements the samples show a strong near-band-edge emission and a sharp line width at 5 K. The good crystal quality has been confirmed in high resolution X-ray diffraction (HRXRD) measurements. This new growth method has great potential for industrial large-scale production of high-quality single crystal ZnO layers.

  2. 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.

  3. Nanoheteroepitaxy of GaN on AlN/Si(111) nanorods fabricated by nanosphere lithography

    NASA Astrophysics Data System (ADS)

    Lee, Donghyun; Shin, In-Su; Jin, Lu; Kim, Donghyun; Park, Yongjo; Yoon, Euijoon

    2016-06-01

    Nanoheteroepitaxy (NHE) of GaN on an AlN/Si(111) nanorod structure was investigated by metal-organic chemical vapor deposition. Silica nanosphere lithography was employed to fabricate a periodic hexagonal nanorod array with a narrow gap of 30 nm between the nanorods. We were successful in obtaining a fully coalesced GaN film on the AlN/Si(111) nanorod structure. Transmission electron microscopy revealed that threading dislocation (TD) bending and termination by stacking faults occurred near the interface between GaN and the AlN/Si(111) nanorods, resulting in the reduction of TD density for the NHE GaN layer. The full width at half-maximum of the X-ray rocking curve for (102) plane of the NHE GaN was found to decrease down to 728 arcsec from 1005 arcsec for the GaN layer on a planar AlN/Si(111) substrate, indicating that the crystalline quality of the NHE GaN was improved. Also, micro-Raman measurement showed that tensile stress in the NHE GaN layer was reduced significantly as much as 70% by introducing air voids between the nanorods.

  4. Study of GaN doping with carbon from propane in a wide range of MOVPE conditions

    NASA Astrophysics Data System (ADS)

    Lundin, W. V.; Sakharov, A. V.; Zavarin, E. E.; Kazantsev, D. Yu.; Ber, B. Ya.; Yagovkina, M. A.; Brunkov, P. N.; Tsatsulnikov, A. F.

    2016-09-01

    Complex studies of intentional GaN carbon doping from propane during MOVPE were performed in a wide range of growth conditions. A strong dependence of carbon doping efficiency on growth rate and ammonia flow is revealed, while dependence of carbon doping efficiency on reactor pressure is small. Atomic force microscopy confirms the good quality of the GaN:C layers for doping levels as high as 2*1019 cm-3 grown with growth rate up to 45 μm/h. The dependence of carbon incorporation into GaN is proportional to the propane concentration to the power 3/2 in most growth regimes, but for very high growth rate a linear or sub-linear component of the dependence becomes prominent.

  5. Effect of the duration of the growth process on the properties of GaN grown by the sublimation method

    SciTech Connect

    Wolfson, A. A.; Mokhov, E. N.

    2009-03-15

    Variation in the structural and morphological features and luminescent characteristics of thick epitaxial GaN layers grown by the sublimation sandwich method with the duration of the crystallization process has been studied. This was, in particular, done by means of scanning electron microscopy in the secondary-electron and color-cathodoluminescence modes. It was found that rather high-quality GaN layers with a thickness of up to 0.5 mm can be grown in a time of about 1.5 h, with their surface hardly exhibiting any luminescence in the visible spectral range. However, making the growth process longer in order to obtain thicker layers impairs the quality of a crystal being grown, which is accompanied by an increase in the intensity of cathodoluminescence from its surface layer in the visible (predominantly yellow) region of the spectrum. Reasons for the poorer quality of GaN layers in this case are discussed. It is suggested that, as the evaporation rate from the source decreases, the amount of active nitrogen near the growth surface becomes lower.

  6. Excellence through High-Quality Individualization.

    ERIC Educational Resources Information Center

    Burns, Richard W.; Klingstedt, Joe Lars

    1988-01-01

    Proposes a strategy employing challenge, functionalism, high-order learning, and originality to achieve high-quality individualization in course work. Asserts that individualized instruction better prepares students to solve problems, make decisions, and produce original ideas. (MM)

  7. Prospects for the application of GaN power devices in hybrid electric vehicle drive systems

    NASA Astrophysics Data System (ADS)

    Su, Ming; Chen, Chingchi; Rajan, Siddharth

    2013-07-01

    GaN, a wide bandgap semiconductor successfully implemented in optical and high-speed electronic devices, has gained momentum in recent years for power electronics applications. Along with rapid progress in material and device processing technologies, high-voltage transistors over 600 V have been reported by a number of teams worldwide. These advances make GaN highly attractive for the growing market of electrified vehicles, which currently employ bipolar silicon devices in the 600-1200 V class for the traction inverter. However, to capture this billion-dollar power market, GaN has to compete with existing IGBT products and deliver higher performance at comparable or lower cost. This paper reviews key achievements made by the GaN semiconductor industry, requirements of the automotive electric drive system and remaining challenges for GaN power devices to fit in the inverter application of hybrid vehicles.

  8. Broadband nanophotonic waveguides and resonators based on epitaxial GaN thin films

    NASA Astrophysics Data System (ADS)

    Bruch, Alexander W.; Xiong, Chi; Leung, Benjamin; Poot, Menno; Han, Jung; Tang, Hong X.

    2015-10-01

    We demonstrate broadband, low loss optical waveguiding in single crystalline GaN grown epitaxially on c-plane sapphire wafers through a buffered metal-organic chemical vapor phase deposition process. High Q optical microring resonators are realized in near infrared, infrared, and near visible regimes with intrinsic quality factors exceeding 50 000 at all the wavelengths we studied. TEM analysis of etched waveguide reveals growth and etch-induced defects. Reduction of these defects through improved material and device processing could lead to even lower optical losses and enable a wideband photonic platform based on GaN-on-sapphire material system.

  9. Broadband nanophotonic waveguides and resonators based on epitaxial GaN thin films

    SciTech Connect

    Bruch, Alexander W.; Xiong, Chi; Leung, Benjamin; Poot, Menno; Han, Jung; Tang, Hong X.

    2015-10-05

    We demonstrate broadband, low loss optical waveguiding in single crystalline GaN grown epitaxially on c-plane sapphire wafers through a buffered metal-organic chemical vapor phase deposition process. High Q optical microring resonators are realized in near infrared, infrared, and near visible regimes with intrinsic quality factors exceeding 50 000 at all the wavelengths we studied. TEM analysis of etched waveguide reveals growth and etch-induced defects. Reduction of these defects through improved material and device processing could lead to even lower optical losses and enable a wideband photonic platform based on GaN-on-sapphire material system.

  10. ECR, ICP, and RIE plasma etching of GaN

    SciTech Connect

    Shul, R.J.; McClellan, G.B.; Rieger, D.J.; Hafich, M.J.

    1996-06-01

    The group III-nitrides continue to generate interest due to their wide band gaps and high dielectric constants. These materials have made significant impact on the compound semiconductor community as blue and ultraviolet light emitting diodes (LEDs). Realization of more advanced devices; including lasers and high temperature electronics, requires dry etch processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 {mu}m/min. In this paper, we compare electron cyclotron resonance (ECR), inductively coupled plasma (ICP), and reactive ion etch (RIE) etch results for GaN. These are the first ICP etch results reported for GaN. We also report ECR etch rates for GaN as a function of growth technique.

  11. Comprehensive study of the electronic and optical behavior of highly degenerate p-type Mg-doped GaN and AlGaN

    SciTech Connect

    Gunning, BP; Fabien, CAM; Merola, JJ; Clinton, EA; Doolittle, WA; Wang, S; Fischer, AM; Ponce, FA

    2015-01-28

    The bulk and 2-dimensional (2D) electrical transport properties of heavily Mg-doped p-type GaN films grown on AlN buffer layers by Metal Modulated Epitaxy are explored. Distinctions are made between three primary p-type conduction mechanisms: traditional valence band conduction, impurity band conduction, and 2D conduction within a 2D hole gas at a hetero-interface. The bulk and 2D contributions to the overall carrier transport are identified and the relative contributions are found to vary strongly with growth conditions. Films grown with III/V ratio less than 1.5 exhibit high hole concentrations exceeding 2 x 10(19) cm(-3) with effective acceptor activation energies of 51 meV. Films with III/V ratios greater than 1.5 exhibit lower overall hole concentrations and significant contributions from 2D transport at the hetero-interface. Films grown with III/V ratio of 1.2 and Mg concentrations exceeding 2 x 10(20) cm(-3) show no detectable inversion domains or Mg precipitation. Highly Mg-doped p-GaN and p-AlGaN with Al fractions up to 27% similarly exhibit hole concentrations exceeding 2 x 10(19) cm(-3). The p-GaN and p-Al0.11Ga0.89N films show broad ultraviolet (UV) photoluminescence peaks, which intercept the valence band, supporting the presence of a Mg acceptor band. Finally, a multi-quantum-well light-emitting diode (LED) and p-i-n diode are grown, both of which demonstrate rectifying behavior with turn-on voltages of 3-3.5V and series resistances of 6-10 Omega without the need for any post-metallization annealing. The LED exhibits violet-blue luminescence at 425 nm, while the p-i-n diode shows UV luminescence at 381 nm, and both devices still show substantial light emission even when submerged in liquid nitrogen at 77 K. (C) 2015 AIP Publishing LLC.

  12. Comprehensive study of the electronic and optical behavior of highly degenerate p-type Mg-doped GaN and AlGaN

    SciTech Connect

    Gunning, Brendan P.; Fabien, Chloe A. M.; Merola, Joseph J.; Clinton, Evan A.; Doolittle, W. Alan; Wang, Shuo; Fischer, Alec M.; Ponce, Fernando A.

    2015-01-28

    The bulk and 2-dimensional (2D) electrical transport properties of heavily Mg-doped p-type GaN films grown on AlN buffer layers by Metal Modulated Epitaxy are explored. Distinctions are made between three primary p-type conduction mechanisms: traditional valence band conduction, impurity band conduction, and 2D conduction within a 2D hole gas at a hetero-interface. The bulk and 2D contributions to the overall carrier transport are identified and the relative contributions are found to vary strongly with growth conditions. Films grown with III/V ratio less than 1.5 exhibit high hole concentrations exceeding 2 × 10{sup 19} cm{sup −3} with effective acceptor activation energies of 51 meV. Films with III/V ratios greater than 1.5 exhibit lower overall hole concentrations and significant contributions from 2D transport at the hetero-interface. Films grown with III/V ratio of 1.2 and Mg concentrations exceeding 2 × 10{sup 20} cm{sup −3} show no detectable inversion domains or Mg precipitation. Highly Mg-doped p-GaN and p-AlGaN with Al fractions up to 27% similarly exhibit hole concentrations exceeding 2 × 10{sup 19} cm{sup −3}. The p-GaN and p-Al{sub 0.11}Ga{sub 0.89}N films show broad ultraviolet (UV) photoluminescence peaks, which intercept the valence band, supporting the presence of a Mg acceptor band. Finally, a multi-quantum-well light-emitting diode (LED) and p-i-n diode are grown, both of which demonstrate rectifying behavior with turn-on voltages of 3–3.5 V and series resistances of 6–10 Ω without the need for any post-metallization annealing. The LED exhibits violet-blue luminescence at 425 nm, while the p-i-n diode shows UV luminescence at 381 nm, and both devices still show substantial light emission even when submerged in liquid nitrogen at 77 K.

  13. High brightness GaN vertical light emitting diodes on metal alloyed substrate for general lighting application

    NASA Astrophysics Data System (ADS)

    Tran, Chuong Anh; Chu, Chen-Fu; Cheng, Chao-Chen; Liu, Wen-Huan; Chu, Jiunn-Yi; Cheng, Hao-Chun; Fan, Feng-Hsu; Yen, Jui-Kang; Doan, Trung

    2007-01-01

    The characteristics of the GaN-based vertical light emitting diodes on metal alloyed substrate (VLEDMS) were investigated. The VLEDMS exhibits very good current-voltage behaviour with low serial dynamic resistance of 0.7 Ω and low operated voltage of 3.2 V at 350 mA. High current operation up to 3 A in continuous mode was demonstrated without any performance deterioration. The high thermal conductivity of metal alloyed substrate exhibits excellent heat dissipation capability. Chip scaling without efficiency loss shows a unique property of VLEDMS. A light output efficiency of 70 lumens/W or better was achieved in single chip or multiple chips package. Coupled with good reliability and mass production ability, VLEDMS is very suitable for general lighting application.

  14. Roma Gans: Still Writing at 95.

    ERIC Educational Resources Information Center

    Sullivan, Joanna

    1991-01-01

    Recounts discussions with reading educator Roma Gans over a 25-year period. Presents Gans' views about reading, teachers, her family, and her years at Teachers College, Columbia. Notes that Gans has seen the teaching of reading come full circle since her first teaching assignment in 1919. (RS)

  15. Structural effects of field emission from GaN nanofilms on SiC substrates

    SciTech Connect

    Chen, Cheng-Cheng; Wang, Ru-Zhi Zhu, Man-Kang; Yan, Hui; Liu, Peng; Wang, Bi-Ben

    2014-04-21

    GaN nanofilms (NFs) with different structures are grown on SiC substrates by pulsed laser deposition under different conditions. The synthesized GaN NFs are studied by X-ray diffraction, field-emission (FE) scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The GaN NFs are composed of diversified GaN nanoparticles with a diameter of 9–38 nm, thickness of 10–50 nm, and roughness of 0.22–13.03 nm. FE from the GaN NFs is structure dependent, which is explained by stress changing the band gap of the NFs. By structure modulation, the turn-on field of GaN NFs can be as low as 0.66 V/μm at a current density of 1 μA/cm{sup 2}, with a current density of up to 1.1 mA/cm{sup 2} at a field of 4.18 V/μm. Fowler-Nordheim curves of some samples contain multiple straight lines, which originate from the structural change and diversification of GaN nanoparticles under an applied field. Overall, our results suggest that GaN NFs with excellent FE properties can be prepared on SiC substrates, which provides a new route to fabricate high-efficiency FE nanodevices.

  16. Two-domain formation during the epitaxial growth of GaN (0001) on c-plane Al{sub 2}O{sub 3} (0001) by high power impulse magnetron sputtering

    SciTech Connect

    Junaid, M.; Lundin, D.; Palisaitis, J.; Hsiao, C.-L.; Darakchieva, V.; Jensen, J.; Persson, P. O. A.; Sandstroem, P.; Helmersson, U.; Hultman, L.; Birch, J.; Lai, W.-J.; Chen, L.-C.; Chen, K.-H.

    2011-12-15

    We study the effect of high power pulses in reactive magnetron sputter epitaxy on the structural properties of GaN (0001) thin films grown directly on Al{sub 2}O{sub 3} (0001) substrates. The epilayers are grown by sputtering from a liquid Ga target, using a high power impulse magnetron sputtering power supply in a mixed N{sub 2}/Ar discharge. X-ray diffraction, micro-Raman, micro-photoluminescence, and transmission electron microscopy investigations show the formation of two distinct types of domains. One almost fully relaxed domain exhibits superior structural and optical properties as evidenced by rocking curves with a full width at half maximum of 885 arc sec and a low temperature band edge luminescence at 3.47 eV with the full width at half maximum of 10 meV. The other domain exhibits a 14 times higher isotropic strain component, which is due to the higher densities of the point and extended defects, resulting from the ion bombardment during growth. Voids form at the domain boundaries. Mechanisms for the formation of differently strained domains, along with voids during the epitaxial growth of GaN are discussed.

  17. Assuring quality in high-consequence engineering

    SciTech Connect

    Hoover, Marcey L.; Kolb, Rachel R.

    2014-03-01

    In high-consequence engineering organizations, such as Sandia, quality assurance may be heavily dependent on staff competency. Competency-dependent quality assurance models are at risk when the environment changes, as it has with increasing attrition rates, budget and schedule cuts, and competing program priorities. Risks in Sandia's competency-dependent culture can be mitigated through changes to hiring, training, and customer engagement approaches to manage people, partners, and products. Sandia's technical quality engineering organization has been able to mitigate corporate-level risks by driving changes that benefit all departments, and in doing so has assured Sandia's commitment to excellence in high-consequence engineering and national service.

  18. Electrical and structural degradation of GaN high electron mobility transistors under high-power and high-temperature Direct Current stress

    SciTech Connect

    Wu, Y. Alamo, J. A. del; Chen, C.-Y.

    2015-01-14

    We have stressed AlGaN/GaN HEMTs (High Electron Mobility Transistors) under high-power and high-temperature DC conditions that resulted in various levels of device degradation. Following electrical stress, we conducted a well-established three-step wet etching process to remove passivation, gate and ohmic contacts so that the device surface can be examined by SEM and AFM. We have found prominent pits and trenches that have formed under the gate edge on the drain side of the device. The width and depth of the pits under the gate edge correlate with the degree of drain current degradation. In addition, we also found visible erosion under the full extent of the gate. The depth of the eroded region averaged along the gate width under the gate correlated with channel resistance degradation. Both electrical and structural analysis results indicate that device degradation under high-power DC conditions is of a similar nature as in better understood high-voltage OFF-state conditions. The recognition of a unified degradation mechanism provides impetus to the development of a degradation model with lifetime predictive capabilities for a broad range of operating conditions spanning from OFF-state to ON-state.

  19. Curvature and bow of bulk GaN substrates

    NASA Astrophysics Data System (ADS)

    Foronda, Humberto M.; Romanov, Alexey E.; Young, Erin C.; Roberston, Christian A.; Beltz, Glenn E.; Speck, James S.

    2016-07-01

    We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.

  20. Are high-quality mates always attractive?

    PubMed Central

    Holveck, Marie-Jeanne; Verhulst, Simon; Fawcett, Tim W

    2010-01-01

    Sexual selection theory posits that females should choose mates in a way that maximizes their reproductive success. But what exactly is the optimal choice? Most empirical research is based on the assumption that females seek a male of the highest possible quality (in terms of the genes or resources he can provide), and hence show directional preferences for indicators of male quality. This implies that attractiveness and quality should be highly correlated. However, females frequently differ in what they find attractive. New theoretical and empirical insights provide mounting evidence that a female’s own quality biases her judgement of male attractiveness, such that male quality and attractiveness do not always coincide. A recent experiment in songbirds demonstrated for the first time that manipulation of female condition can lead to divergent female preferences, with low-quality females actively preferring low-quality males over high-quality males. This result is in line with theory on state-dependent mate choice and is reminiscent of assortative mating preferences in humans. Here we discuss the implications of this work for the study of mate preferences. PMID:20714411

  1. Fabrication of microchannels in single-crystal GaN by wet-chemical-assisted femtosecond-laser ablation

    NASA Astrophysics Data System (ADS)

    Nakashima, Seisuke; Sugioka, Koji; Midorikawa, Katsumi

    2009-09-01

    We investigated micro- and nano-fabrication of wide band-gap semiconductor gallium nitride (GaN) using a femtosecond (fs) laser. Nanoscale craters were successfully formed by wet-chemical-assisted fs-laser ablation, in which the laser beam is focused onto a single-crystal GaN substrate in a hydrochloric acid (HCl) solution. This allows efficient removal of ablation debris produced by chemical reactions during ablation, resulting in high-quality ablation. However, a two-step processing method involving irradiation by a fs-laser beam in air followed by wet etching, distorts the shape of the crater because of residual debris. The threshold fluence for wet-chemical-assisted fs-laser ablation is lower than that for fs-laser ablation in air, which is advantageous for improving fabrication resolution since it reduces thermal effects. We have fabricated craters as small as 510 nm by using a high numerical aperture (NA) objective lens with an NA of 0.73. Furthermore, we have formed three-dimensional hollow microchannels in GaN by fs-laser direct-writing in HCl solution.

  2. Synthesis of three kinds of GaN nanowires through Ga 2O 3 films’ reaction with ammonia

    NASA Astrophysics Data System (ADS)

    Dong, Zhihua; Xue, Chengshan; Zhuang, Huizhao; Wang, Shuyun; Gao, Haiyong; Tian, Deheng; Wu, Yuxin; He, Jianting; Liu, Yi'an

    2005-03-01

    A new method was employed to obtain GaN nanowires (NWs). In this method, SiC films were deposited with radio frequency (r.f.) magnetron sputtering onto silicon substrates and annealed at high temperature, and then Ga 2O 3 films were deposited on top of the SiC intermediate layers and annealed in NH 3 atmosphere. SiC layer was used to reduce thermal and lattice mismatch between GaN and Si, and improve NWs’ quality. After Ga 2O 3 films reacted with NH 3, a great quantity of GaN NWs with the shape of birch trunks and stalactites were found by transmission electron microscopy (TEM). At the same time, a few very even and uniform pillarlike NWs were observed. The electron diffraction patterns (EDP) show that birch trunk-shaped and pillarlike NWs are all single-crystalline structures. These NWs were also analyzed with the assistance of X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and high-resolution transmission electron microscopy (HRTEM) to show their properties.

  3. 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.

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

    SciTech Connect

    Szyszka, A. E-mail: adam.szyszka@pwr.wroc.pl; Haeberlen, M.; Storck, P.; Thapa, S. B.; Schroeder, T.

    2014-08-28

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

  5. Layer-transferred MoS{sub 2}/GaN PN diodes

    SciTech Connect

    Lee, Edwin W.; Lee, Choong Hee; Paul, Pran K.; Krishnamoorthy, Sriram; Arehart, Aaron R.; Ma, Lu; McCulloch, William D.; Wu, Yiying; Rajan, Siddharth

    2015-09-07

    Electrical and optical characterization of two-dimensional/three-dimensional (2D/3D) p-molybdenum disulfide/n-gallium nitride (p-MoS{sub 2}/n-GaN) heterojunction diodes are reported. Devices were fabricated on high-quality, large-area p-MoS{sub 2} grown by chemical vapor deposition on sapphire substrates. The processed devices were transferred onto GaN/sapphire substrates, and the transferred films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). On-axis XRD spectra and surface topology obtained from AFM scans were consistent with previously grown high-quality, continuous MoS{sub 2} films. Current-voltage measurements of these diodes exhibited excellent rectification, and capacitance-voltage measurements were used to extract a conduction band offset of 0.23 eV for the transferred MoS{sub 2}/GaN heterojunction. This conduction band offset was confirmed by internal photoemission measurements. The energy band lineup of the MoS{sub 2}/GaN heterojunction is proposed here. This work demonstrates the potential of 2D/3D heterojunctions for novel device applications.

  6. Highly chemical reactive ion etching of gallium nitride

    SciTech Connect

    Karouta, F.; Jacobs, B.; Moerman, I.; Jacobs, K.; Weyher, J.L.; Porowski, S.; Crane, R.; Hageman, P.R.

    2000-07-01

    A highly chemical reactive ion etching process has been developed for MOVPE-grown GaN on sapphire. The key element for the enhancement of the chemical property during etching is the use of a fluorine containing gas in a chlorine based chemistry. In the perspective of using GaN substrates for homo-epitaxy of high quality GaN/AlGaN structures they have used the above described RIE process to smoothen Ga-polar GaN substrates. The RMS value, measured by AFM, went from 20 {angstrom} (after mechanical polishing) down to 4 {angstrom} after 6 minutes of RIE. Etching N-polar GaN resulted in a higher etch rate than Ga-polar materials (165 vs. 110 nm/min) but the resulting surface was quite rough and suffers from instability problems. Heat treatment and HCl dip showed a partial recovery of Schottky characteristics after RIE.

  7. Oxygen in GaN.

    NASA Astrophysics Data System (ADS)

    van de Walle, Chris G.; Neugebauer, Jörg

    1997-03-01

    Oxygen is commonly present during epitaxial growth of GaN. We have proposed that unintentional incorporation of O, as well as Si, is responsible for the frequently observed n-type conductivity in as-grown GaN. Here we present results from comprehensive density-functional-pseudopotential studies of GaN:O under pressure, and of O interactions with native defects and dopant impurities. We find that the O donor undergoes a DX-like transition under pressure: a large outward relaxation introduces a deep level in the band gap. This behavior explains the carrier freezeout in GaN under pressure.^1 Si donors do not exhibit the transition, consistent with experiment. Results for these impurities in AlGaN will also be discussed. We have also investigated the interaction between O and native defects. Most notably we find a large binding energy between O and the gallium vacancy (V_Ga), which we have proposed to be the source of the yellow luminescence. Finally, we have studied the interaction between O and Mg acceptors. The incorporation of the O donor is significantly enhanced in Mg-doped material. In addition, we calculate a binding energy of 0.6 eV for Mg-O complexes. The presence of O during growth can thus be detrimental to p-type GaN. ^1 C. Wetzel et al., Proc. ICPS-23 (World Scientific, Singapore, 1996), p. 2929.

  8. The influence of Fe doping on the surface topography of GaN epitaxial material

    NASA Astrophysics Data System (ADS)

    Lei, Cui; Haibo, Yin; Lijuan, Jiang; Quan, Wang; Chun, Feng; Hongling, Xiao; Cuimei, Wang; Jiamin, Gong; Bo, Zhang; Baiquan, Li; Xiaoliang, Wang; Zhanguo, Wang

    2015-10-01

    Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 1019 cm-3. High resistivity GaN epitaxial material which is 1 × 109 Ω·cm is achieved. Project supported by the Knowledge Innovation Engineering of the Chinese Academy of Sciences (No. YYY-0701-02), the National Natural Science Foundation of China (Nos. 61204017, 61334002), the State Key Development Program for Basic Research of China, and the National Science and Technology Major Project.

  9. Current status and scope of gallium nitride-based vertical transistors for high-power electronics application

    NASA Astrophysics Data System (ADS)

    Chowdhury, Srabanti; Swenson, Brian L.; Hoi Wong, Man; Mishra, Umesh K.

    2013-07-01

    Gallium nitride (GaN) is becoming the material of choice for power electronics to enable the roadmap of increasing power density by simultaneously enabling high-power conversion efficiency and reduced form factor. This is because the low switching losses of GaN enable high-frequency operation which reduces bulky passive components with negligible change in efficiency. Commercialization of GaN-on-Si materials for power electronics has led to the entry of GaN devices into the medium-power market since the performance-over-cost of even first-generation products looks very attractive compared to today's mature Si-based solutions. On the other hand, the high-power market still remains unaddressed by lateral GaN devices. The current and voltage demand for high-power conversion application makes the chip area in a lateral topology so large that it becomes difficult to manufacture. Vertical GaN devices would play a big role alongside silicon carbide (SiC) to address the high-power conversion needs. In this paper vertical GaN devices are discussed with emphasis on current aperture vertical electron transistors (CAVETs) which have shown promising performance. The fabrication-related challenges and the future possibilities enabled by the availability of good-quality, cost-competitive bulk GaN material are also evaluated for CAVETs. This work was done at Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA.

  10. 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

  11. 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

    NASA Astrophysics Data System (ADS)

    Gunning, Brendan P.; Clinton, Evan A.; Merola, Joseph J.; Doolittle, W. Alan; Bresnahan, Rich C.

    2015-10-01

    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 N2 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 N2 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 × 1016 to 3.8 × 1019 cm-3 were achieved in GaN using Ge doping, and unintentionally doped GaN films exhibited low background electron concentrations of just 1-2 × 1015 cm-3. The highest growth rates resulted in macroscopic surface features due to Ga cell spitting, which is an engineering challenge still to be addressed. Nonetheless, the dramatically enhanced growth rates demonstrate

  12. Synthesis of p-type GaN nanowires

    NASA Astrophysics Data System (ADS)

    Kim, Sung Wook; Park, Youn Ho; Kim, Ilsoo; Park, Tae-Eon; Kwon, Byoung Wook; Choi, Won Kook; Choi, Heon-Jin

    2013-08-01

    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.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

  13. Characteristics of High-Quality Teachers

    ERIC Educational Resources Information Center

    Jones, Jason E.; Gulek, James C.

    2010-01-01

    The purpose of this study was to examine the characteristics of high-quality teachers who used a structured mathematics program for teaching, namely the Math Achievement Program (MAP[superscript 2]D), which demonstrated significant gains on student achievement as measured by California's Standards Test (CST) in mathematics. Specifically, the…

  14. Structural and Electronic Properties of GaN Films Grown on Sapphire.

    NASA Astrophysics Data System (ADS)

    Zhu, Q.; Botchkarev, A.; Kim, W.; Aktas, O.; Salvador, A.; Sverdlov, B.; Morkoc, H.; Tsen, S.-C. Y.; Smith, D. J.

    1996-03-01

    The structural characteristics of GaN films grown on sapphire substrates by molecular beam epitaxy (MBE) have been investigated using high-resolution synchrotron x-ray diffraction and electron microscopy, and compared to their electrical and optical properties. We find remarkable correspondence between the in-plane structural order (coherence length and mosaic spread) and the electrical and optical properties. Contrary to common belief, our observations show unequivocally that the out-of-plane structural features, which are considerably better developed than the in-plane counterparts, can not be used for determining the material quality with respect to their optical and electrical activity. In particular, the (00l) mosaic spread is not a good indicator of film quality. The structural correlations of the GaN film, the AlN buffer laryer and the sapphire substrate are also explored and compared to their growth conditions. The issue of in-plane stacking fault (hcp - fcc) is also addressed using x-ray scans along the (10l) direction. Work supported by the US Department of Energy, Division of Materials Science under contract No. DEAC0276CH00016, by NSF Grant DMR-9314326, by the Office of Naval Research with M. Yoder and Dr. Y. S. Park as monitors, and by the Air Force Office of Scientific Research with Dr. G. L. Witt as the monitor. H. M. was funded by AFOSR under a URRP program.

  15. Characterization of bulk grown GaN and AlN single crystal materials

    NASA Astrophysics Data System (ADS)

    Raghothamachar, Balaji; Bai, Jie; Dudley, Michael; Dalmau, Rafael; Zhuang, Dejin; Herro, Ziad; Schlesser, Raoul; Sitar, Zlatko; Wang, Buguo; Callahan, Michael; Rakes, Kelly; Konkapaka, Phanikumar; Spencer, Michael

    2006-01-01

    Sublimation method, spontaneously nucleated as well as seeded on SiC substrates, has been employed for growing AlN bulk crystals. For GaN growth, in addition to the sublimation method using sapphire substrates, ammonothermal growth (analogous to the hydrothermal method) on HVPE GaN seeds is also being used. Thick plates/films of AlN and GaN grown by these methods have been characterized by synchrotron white beam X-ray topography (SWBXT) and high resolution X-ray diffraction (HRXRD). Results from a recent set of growth experiments are discussed.

  16. Characterization of Bulk Grown GaN and AlN Single Crystal Materials

    SciTech Connect

    Raghothamachar,B.; Bai, J.; Dudley, M.; Dalmau, R.; Zhuang, D.; Herro, Z.; Schlesser, R.; Sitar, Z.; Wang, B.; Callahan, M.

    2006-01-01

    Sublimation method, spontaneously nucleated as well as seeded on SiC substrates, has been employed for growing AlN bulk crystals. For GaN growth, in addition to the sublimation method using sapphire substrates, ammonothermal growth (analogous to the hydrothermal method) on HVPE GaN seeds is also being used. Thick plates/films of AlN and GaN grown by these methods have been characterized by synchrotron white beam X-ray topography (SWBXT) and high resolution X-ray diffraction (HRXRD). Results from a recent set of growth experiments are discussed.

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

    SciTech Connect

    Lupina, L.; Zoellner, M. H.; Dietrich, B.; Capellini, G.; Niermann, T.; Lehmann, M.; Thapa, S. B.; Haeberlen, M.; Storck, P.; Schroeder, T.

    2015-11-16

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

  18. One-step graphene coating of heteroepitaxial GaN films.

    PubMed

    Choi, Jae-Kyung; Huh, Jae-Hoon; Kim, Sung-Dae; Moon, Daeyoung; Yoon, Duhee; Joo, Kisu; Kwak, Jinsung; Chu, Jae Hwan; Kim, Sung Youb; Park, Kibog; Kim, Young-Woon; Yoon, Euijoon; Cheong, Hyeonsik; Kwon, Soon-Yong

    2012-11-01

    Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as ~0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as 'pseudo-substrates' in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.

  19. Dislocation Reduction and Stress Relaxation of GaN and InGaN Multiple Quantum Wells with Improved Performance via Serpentine Channel Patterned Mask.

    PubMed

    Ji, Qingbin; Li, Lei; Zhang, Wei; Wang, Jia; Liu, Peichi; Xie, Yahong; Yan, Tongxing; Yang, Wei; Chen, Weihua; Hu, Xiaodong

    2016-08-24

    The existence of high threading dislocation density (TDD) in GaN-based epilayers is a long unsolved problem, which hinders further applications of defect-sensitive GaN-based devices. Multiple-modulation of epitaxial lateral overgrowth (ELOG) is used to achieve high-quality GaN template on a novel serpentine channel patterned sapphire substrate (SCPSS). The dislocation blocking brought by the serpentine channel patterned mask, coupled with repeated dislocation bending, can reduce the dislocation density to a yet-to-be-optimized level of ∼2 × 10(5) to 2 × 10(6) cm(-2). About 80% area utilization rate of GaN with low TDD and stress relaxation is obtained. The periodical variations of dislocation density, optical properties and residual stress in GaN-based epilayers on SCPSS are analyzed. The quantum efficiency of InGaN/GaN multiple quantum wells (MQWs) on it can be increased by 52% compared with the conventional sapphire substrate. The reduced nonradiative recombination centers, the enhanced carrier localization, and the suppressed quantum confined Stark effect, are the main determinants of improved luminous performance in MQWs on SCPSS. This developed ELOG on serpentine shaped mask needs no interruption and regrowth, which can be a promising candidate for the heteroepitaxy of semipolar/nonpolar GaN and GaAs with high quality.

  20. Dislocation Reduction and Stress Relaxation of GaN and InGaN Multiple Quantum Wells with Improved Performance via Serpentine Channel Patterned Mask.

    PubMed

    Ji, Qingbin; Li, Lei; Zhang, Wei; Wang, Jia; Liu, Peichi; Xie, Yahong; Yan, Tongxing; Yang, Wei; Chen, Weihua; Hu, Xiaodong

    2016-08-24

    The existence of high threading dislocation density (TDD) in GaN-based epilayers is a long unsolved problem, which hinders further applications of defect-sensitive GaN-based devices. Multiple-modulation of epitaxial lateral overgrowth (ELOG) is used to achieve high-quality GaN template on a novel serpentine channel patterned sapphire substrate (SCPSS). The dislocation blocking brought by the serpentine channel patterned mask, coupled with repeated dislocation bending, can reduce the dislocation density to a yet-to-be-optimized level of ∼2 × 10(5) to 2 × 10(6) cm(-2). About 80% area utilization rate of GaN with low TDD and stress relaxation is obtained. The periodical variations of dislocation density, optical properties and residual stress in GaN-based epilayers on SCPSS are analyzed. The quantum efficiency of InGaN/GaN multiple quantum wells (MQWs) on it can be increased by 52% compared with the conventional sapphire substrate. The reduced nonradiative recombination centers, the enhanced carrier localization, and the suppressed quantum confined Stark effect, are the main determinants of improved luminous performance in MQWs on SCPSS. This developed ELOG on serpentine shaped mask needs no interruption and regrowth, which can be a promising candidate for the heteroepitaxy of semipolar/nonpolar GaN and GaAs with high quality. PMID:27484167

  1. Composition and optical properties of dilute-Sb GaN1-xSbx highly mismatched alloys grown by MBE

    NASA Astrophysics Data System (ADS)

    Shaw, M.; Yu, K. M.; Ting, M.; Powell, R. E. L.; Sarney, W. L.; Svensson, S. P.; Kent, A. J.; Walukiewicz, W.; Foxon, C. T.; Novikov, S. V.; Martin, R. W.

    2014-11-01

    In this work the compositional and optical characterization of three series of dilute-Sb GaN1 - xSbx alloys grown with various Sb flux, under N and Ga-rich conditions, are presented. Using wavelength dispersive x-ray microanalysis and Rutherford backscattering spectroscopy it is found that the N-rich samples (Ga flux < 2.3 × 10-7 Torr) incorporate a higher magnitude of GaSb than the Ga-rich samples (Ga flux > 2.3 × 10-7 Torr) under the same growth conditions. The optical properties of the Ga-rich samples are measured using room temperature cathodoluminescence (CL), photoluminescence (PL) and absorption measurements. A broad luminescence peak is observed around 2.2 eV. The nature and properties of this peak are considered, as is the suitability of these dilute-Sb alloys for use in solar energy conversion devices.

  2. 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.

  3. Design, fabrication and characterising of 100 W GaN HEMT for Ku-band application

    NASA Astrophysics Data System (ADS)

    Chunjiang, Ren; Shichang, Zhong; Yuchao, Li; Zhonghui, Li; Yuechan, Kong; Tangsheng, Chen

    2016-08-01

    Ku-band GaN power transistor with output power over 100 W under the pulsed operation mode is presented. A high temperature A1N nucleation together with an Fe doped GaN buffer was introduced for the developed GaN HEMT. The AlGaN/GaN hetero-structure deposited on 3 inch SiC substrate exhibited a 2DEG hall mobility and density of ˜2100 cm2/(V·s) and 1.0 × 1013 cm-2, respectively, at room temperature. Dual field plates were introduced to the designed 0.25 μm GaN HEMT and the source connected field plate was optimized for minimizing the peak field plate near the drain side of the gate, while maintaining excellent power gain performance for Ku-band application. The load-pull measurement at 14 GHz showed a power density of 5.2 W/mm for the fabricated 400 μm gate periphery GaN HEMT operated at a drain bias of 28 V. A Ku-band internally matched GaN power transistor was developed with two 10.8 mm gate periphery GaN HEMT chips combined. The GaN power transistor exhibited an output power of 102 W at 13.3 GHz and 32 V operating voltage under pulsed operation mode with a pulse width of 100 μs and duty cycle of 10%. The associated power gain and power added efficiency were 9.2 dB and 48%, respectively. To the best of the authors' knowledge, the PAE is the highest for Ku-band GaN power transistor with over 100 W output power.

  4. Status of GaN HEMT performance and reliability

    NASA Astrophysics Data System (ADS)

    Green, Daniel S.; Brown, J. D.; Vetury, R.; Lee, S.; Gibb, S. R.; Krishnamurthy, K.; Poulton, M. J.; Martin, J.; Shealy, J. B.

    2008-02-01

    This report will focus on the status of GaN HEMT based amplifier technology development at RFMD. This technology is based around GaN on semi-insulating SiC substrates for optimal thermal performance. RFMD's 0.5μm gate technology features high performance advanced field plate structures, including a unit power cell producing high gain (21dB), high power density (3-5W/mm at 28V) and high efficiency (65-70 percent) at cellular frequencies. We will report on transistor and module performance relevant to applications ranging from high power, high bandwidth amplifiers, to switches and ICs for radar, electronic warfare, cellular infrastructure and homeland security. Additionally, we will report on reliability results that demonstrate capability for dependable, high voltage operation.

  5. 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.

  6. Heteroepitaxial growth of GaN on vertical Si{110} sidewalls formed on trench-etched Si(001) substrates

    NASA Astrophysics Data System (ADS)

    Gagnon, Jarod C.; Shen, Haoting; Yuwen, Yu; Wang, Ke; Mayer, Theresa S.; Redwing, Joan M.

    2016-07-01

    A maskless Si trench structure was developed to integrate crystallographically non-polar GaN microstructures with semi-polar facets on Si(001). GaN "fins" were preferentially grown by MOCVD on Si{110} trench sidewalls formed by deep reactive ion etching (DRIE) of Si(001) such that GaN(0001)//Si{110} and GaN(10-10)//Si(001), resulting in a non-polar crystal structure with respect to the Si(001) substrate surface. No masking layer was required to prevent GaN growth on the Si(001) top surface of the trenches, instead, it was found that GaN nucleated preferentially on the Si{110} trench sidewalls. GaN was also observed to nucleate at the top corner of the trenches due to Si etching and exposure of high-index Si facets during the pre-growth H2 anneal. This undesired GaN nucleation was successfully suppressed by reducing the H2 anneal time and/or increasing the growth temperature and decreasing the precursor V/III to enhance Ga-adatom diffusion. Cross-sectional TEM studies confirmed that the GaN fins were crystallographically non-polar with respect to the Si(001) substrate surface and were bounded by semi-polar and non-polar facets. The reported Si fabrication and GaN growth process shows promise for the integration of non-polar and semi-polar GaN microstructures on industry standard Si(001) substrates.

  7. GaN Initiative for Grid Applications (GIGA)

    SciTech Connect

    Turner, George

    2015-07-03

    For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -even for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral and

  8. Substitutional and interstitial carbon in wurtzite GaN

    NASA Astrophysics Data System (ADS)

    Wright, A. F.

    2002-09-01

    First-principles theoretical results are presented for substitutional and interstitial carbon in wurtzite GaN. Carbon is found to be a shallow acceptor when substituted for nitrogen (CN) and a shallow donor when substituted for gallium (CGa). Interstitial carbon (CI) is found to assume different configurations depending on the Fermi level: A site at the center of the c-axis channel is favored when the Fermi level is below 0.9 eV (relative to the valence band maximum) and a split-interstitial configuration is favored otherwise. Both configurations produce partly filled energy levels near the middle of the gap, and CI should therefore exhibit deep donor behavior in p-type GaN and deep acceptor behavior in n-type GaN. Formation energies for CN, CGa, and CI are similar, making it likely that CN acceptors will be compensated by other carbon species. CGa is predicted to be the primary compensating species when growth occurs under N-rich conditions while channel CI is predicted to be the primary compensating species under Ga-rich growth conditions. Self-compensation is predicted to be more significant under Ga-rich growth conditions than under N-rich conditions. Experimental evidence for self-compensation is discussed. Four carbon complexes are discussed. CN-VGa is found to be unstable when the Fermi level is above the middle of the gap due to the high stability of gallium vacancies (VGa). The CN-VGa complex was previously suggested as a source of the broad 2.2 eV luminescence peak often observed in n-type GaN. The present results indicate that this is unlikely. The CI-CN complex is capable of forming in carbon doped GaN grown under Ga-rich conditions if the mobility of the constituents is high enough. Experimental evidence for its existence is discussed.

  9. 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.

  10. Thermal Conductivity and Large Isotope Effect in GaN from First Principles

    SciTech Connect

    Lindsay, L.; Broido, D. A.; Reinecke, T. L.

    2012-08-28

    We present atomistic first principles results for the lattice thermal conductivity of GaN and compare them to those for GaP, GaAs, and GaSb. In GaN we find a large increase to the thermal conductivity with isotopic enrichment, ~65% at room temperature. We show that both the high thermal conductivity and its enhancement with isotopic enrichment in GaN arise from the weak coupling of heat-carrying acoustic phonons with optic phonons. This weak scattering results from stiff atomic bonds and the large Ga to N mass ratio, which give phonons high frequencies and also a pronounced energy gap between acoustic and optic phonons compared to other materials. Rigorous understanding of these features in GaN gives important insights into the interplay between intrinsic phonon-phonon scattering and isotopic scattering in a range of materials.

  11. Enhanced cell growth on nanotextured GaN surface treated by UV illumination and fibronectin adsorption.

    PubMed

    Li, Jingying; Han, Qiusen; Wang, Xinhuan; Yang, Rong; Wang, Chen

    2014-11-01

    Semiconductors are important materials used for the development of high-performance biomedical devices. Gallium nitride (GaN) is a well-known III-nitride semiconductor with excellent optoelectronic properties as well as high chemical stability and biocompatibility. The formation of tight interfaces between GaN substrates and cells would be crucial for GaN-based devices used for probing and manipulating biological processes of cells. Here we report a strategy to greatly enhance cell adhesion and survival on nanotextured GaN surface which was treated by UV illumination and fibronectin (FN) adsorption. Cell studies showed that the UV/FN treatment greatly enhanced cell adhesion and growth on nanotextured GaN surfaces. These observations suggest new opportunities for novel nanotextured GaN-based biomedical devices.

  12. Thermal-mechanical modeling of single crystal AlN and GaN

    NASA Astrophysics Data System (ADS)

    Karvanirabori, Payman

    In this work, thermal-mechanical models are being developed, based on underlying micromechanical behavior of III-nitride single crystals at growth temperatures, for use in process design. A crystal plasticity model that is capable of capturing the underlying mechanisms of dislocation motion, multiplication, and interactions in wurtzite structure (hexagonal) crystals is defined to accurately model the elastic-plastic behavior of GaN and AlN crystals at elevated temperatures. The model for AlN is extended from relations developed for GaN based on available experimental data. Algorithms for integrating the constitutive model and computing the consistent tangent modulus are formulated, and the material model is implemented into a crystal plasticity finite element framework. Finite element models of crystal growth for different processing conditions are simulated. The simulation predicts cracking and dislocation defect density in order to improve the yield and reduce the manufacturing cost of high quality III-nitride semiconductors. Furthermore, the resulting simulation capability can be used in conjunction with relevant experiments to backout key thermal-mechanical material properties at high temperatures.

  13. Decreased sleep quality in high myopia children.

    PubMed

    Ayaki, Masahiko; Torii, Hidemasa; Tsubota, Kazuo; Negishi, Kazuno

    2016-01-01

    The aim of the present study was to evaluate sleep quality in myopic children and adults. This cross sectional study surveyed 486 participants aged from 10 to 59 years with refractive errors using a questionnaire containing the Pittsburgh Sleep Quality Index (PSQI) and Hospital Anxiety and Depression Scale (HADS). Children (< 20 years) in the high myopia group exhibited the poorest PSQI scores (P < 0.01), while the adults showed no such correlations. Subscales of PSQI and HADS in children disclosed that the high myopia groups had the shortest sleep duration (P < 0.01), worst subjective sleep scores (P < 0.001), and latest bedtime (P < 0.05). Regression analyses in children significantly correlated myopic errors with PSQI (P < 0.05), sleep duration (P < 0.01), and bedtime (P < 0.01). Sleep efficacy (P < 0.05) and daytime dysfunction (P < 0.05) were significantly better in contact-lens users compared to the respective non-user groups across all participants. In conclusion, sleep quality in children was significantly correlated with myopic error, with the high myopia group worst affected. PMID:27650408

  14. Decreased sleep quality in high myopia children

    PubMed Central

    Ayaki, Masahiko; Torii, Hidemasa; Tsubota, Kazuo; Negishi, Kazuno

    2016-01-01

    The aim of the present study was to evaluate sleep quality in myopic children and adults. This cross sectional study surveyed 486 participants aged from 10 to 59 years with refractive errors using a questionnaire containing the Pittsburgh Sleep Quality Index (PSQI) and Hospital Anxiety and Depression Scale (HADS). Children (< 20 years) in the high myopia group exhibited the poorest PSQI scores (P < 0.01), while the adults showed no such correlations. Subscales of PSQI and HADS in children disclosed that the high myopia groups had the shortest sleep duration (P < 0.01), worst subjective sleep scores (P < 0.001), and latest bedtime (P < 0.05). Regression analyses in children significantly correlated myopic errors with PSQI (P < 0.05), sleep duration (P < 0.01), and bedtime (P < 0.01). Sleep efficacy (P < 0.05) and daytime dysfunction (P < 0.05) were significantly better in contact-lens users compared to the respective non-user groups across all participants. In conclusion, sleep quality in children was significantly correlated with myopic error, with the high myopia group worst affected. PMID:27650408

  15. Cross-stacked carbon nanotubes assisted self-separation of free-standing GaN substrates by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Wei, Tongbo; Yang, Jiankun; Wei, Yang; Huo, Ziqiang; Ji, Xiaoli; Zhang, Yun; Wang, Junxi; Li, Jinmin; Fan, Shoushan

    2016-06-01

    We report a novel method to fabricate high quality 2-inch freestanding GaN substrate grown on cross-stacked carbon nanotubes (CSCNTs) coated sapphire by hydride vapor phase epitaxy (HVPE). As nanoscale masks, these CSCNTs can help weaken the interface connection and release the compressive stress by forming voids during fast coalescence and also block the propagation of threading dislocations (TDs). During the cool-down process, thermal stress-induced cracks are initiated at the CSCNTs interface with the help of air voids and propagated all over the films which leads to full self-separation of FS-GaN substrate. Raman and photoluminescence spectra further reveal the stress relief and crystalline improvement of GaN with CSCNTs. It is expected that the efficient, low cost and mass-producible technique may enable new applications for CNTs in nitride optoelectronic fields.

  16. Cross-stacked carbon nanotubes assisted self-separation of free-standing GaN substrates by hydride vapor phase epitaxy

    PubMed Central

    Wei, Tongbo; Yang, Jiankun; Wei, Yang; Huo, Ziqiang; Ji, Xiaoli; Zhang, Yun; Wang, Junxi; Li, Jinmin; Fan, Shoushan

    2016-01-01

    We report a novel method to fabricate high quality 2-inch freestanding GaN substrate grown on cross-stacked carbon nanotubes (CSCNTs) coated sapphire by hydride vapor phase epitaxy (HVPE). As nanoscale masks, these CSCNTs can help weaken the interface connection and release the compressive stress by forming voids during fast coalescence and also block the propagation of threading dislocations (TDs). During the cool-down process, thermal stress-induced cracks are initiated at the CSCNTs interface with the help of air voids and propagated all over the films which leads to full self-separation of FS-GaN substrate. Raman and photoluminescence spectra further reveal the stress relief and crystalline improvement of GaN with CSCNTs. It is expected that the efficient, low cost and mass-producible technique may enable new applications for CNTs in nitride optoelectronic fields. PMID:27340030

  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. Abbreviated epitaxial growth mode (AGM) method for reducing cost and improving quality of LEDs and lasers

    DOEpatents

    Tansu, Nelson; Chan, Helen M; Vinci, Richard P; Ee, Yik-Khoon; Biser, Jeffrey

    2013-09-24

    The use of an abbreviated GaN growth mode on nano-patterned AGOG sapphire substrates, which utilizes a process of using 15 nm low temperature GaN buffer and bypassing etch-back and recovery processes during epitaxy, enables the growth of high-quality GaN template on nano-patterned AGOG sapphire. The GaN template grown on nano-patterned AGOG sapphire by employing abbreviated growth mode has two orders of magnitude lower threading dislocation density than that of conventional GaN template grown on planar sapphire. The use of abbreviated growth mode also leads to significant reduction in cost of the epitaxy. The growths and characteristics of InGaN quantum wells (QWs) light emitting diodes (LEDs) on both templates were compared. The InGaN QWs LEDs grown on the nano-patterned AGOG sapphire demonstrated at least a 24% enhancement of output power enhancement over that of LEDs grown on conventional GaN templates.

  19. Mass transport, faceting and behavior of dislocations in GaN

    SciTech Connect

    Nitta, S.; Kashima, T.; Kariya, M.; Yukawa, Y.; Yamaguchi, S.; Amano, H.; Akasaki, I.

    2000-07-01

    The behavior of threading dislocations during mass transport of GaN was investigated in detail by transmission electron microscopy. Mass transport occurred at the surface. Therefore, growing species are supplied from the in-plane direction. The behavior of threading dislocations was found to be strongly affected by the mass transport process as well as the high crystallographic anisotropy of the surface energy of the facets particular to GaN.

  20. Anelasticity of GaN Epitaxial Layer in GaN LED

    NASA Astrophysics Data System (ADS)

    Chung, C. C.; Yang, C. T.; Liu, C. Y.

    2016-10-01

    In this work, the anelasticity of the GaN layer in the GaN light-emitting-diode device was studied. The present results show that the forward-voltage of GaN LED increases with time, as the GaN light-emitting-diode was maintained at a constant temperature of 100 °C. We found that the increase of the forward-voltage with time attributes to the delay-response of the piezoelectric fields (internal electrical fields in GaN LED device). And, the delay-response of the internal electrical fields with time is caused by the anelasticity (time-dependent strain) of the GaN layer. Therefore, using the correlation of strain-piezoelectric-forward voltage, a plot of thermal strain of the GaN layer against time can be obtained by measuring the forward-voltage of the studied GaN LED against time. With the curves of the thermal strain of GaN epi-layers versus time, the anelasticity of the GaN compound can be studied. The key anelasticity parameter, characteristic relaxation time, of the GaN is defined to be 2623.76 min in this work.

  1. High quality factor indium oxide mechanical microresonators

    SciTech Connect

    Bartolomé, Javier Cremades, Ana; Piqueras, Javier

    2015-11-09

    The mechanical resonance behavior of as-grown In{sub 2}O{sub 3} microrods has been studied in this work by in-situ scanning electron microscopy (SEM) electrically induced mechanical oscillations. Indium oxide microrods grown by a vapor–solid method are naturally clamped to an aluminum oxide ceramic substrate, showing a high quality factor due to reduced energy losses during mechanical vibrations. Quality factors of more than 10{sup 5} and minimum detectable forces of the order of 10{sup −16} N/Hz{sup 1/2} demonstrate their potential as mechanical microresonators for real applications. Measurements at low-vacuum using the SEM environmental operation mode were performed to study the effect of extrinsic damping on the resonators behavior. The damping coefficient has been determined as a function of pressure.

  2. Synthesis and excellent field emission properties of three-dimensional branched GaN nanowire homostructures

    NASA Astrophysics Data System (ADS)

    Li, Enling; Sun, Lihe; Cui, Zhen; Ma, Deming; Shi, Wei; Wang, Xiaolin

    2016-10-01

    Three-dimensional branched GaN nanowire homostructures have been synthesized on the Si substrate via a two-step approach by chemical vapor deposition. Structural characterization reveals that the single crystal GaN nanowire trunks have hexagonal wurtzite characteristics and grow along the [0001] direction, while the homoepitaxial single crystal branches grow in a radial direction from the six-sided surfaces of the trunks. The field emission measurements demonstrate that the branched GaN nanowire homostructures have excellent field emission properties, with low turn-on field at 2.35 V/μm, a high field enhancement factor of 2938, and long emission current stability. This indicates that the present branched GaN nanowire homostructures will become valuable for practical field emission applications.

  3. Excitation and deexcitation dynamics of excitons in a GaN film based on the analysis of radiation from high-order states

    NASA Astrophysics Data System (ADS)

    Ishitani, Yoshihiro; Takeuchi, Kazuma; Oizumi, Naoyuki; Sakamoto, Hironori; Ma, Bei; Morita, Ken; Miyake, Hideto; Hiramatsu, Kazumasa

    2016-06-01

    The physical mechanism of excitation and deexcitation transitions of nonthermal exciton states in a GaN film is investigated at a measurement temperature of 23 K by time-resolved photoluminescence (PL) analysis involving phonon replica lines of the principal quantum number n  =  2 in addition to n  =  1 and bound states of the A exciton. A time region of 280 ps after a pulse excitation is mainly analyzed. The emission intensities of the constituent lines are obtained by spectrum fitting. Although the effective exciton temperature of the n  =  1 state shows a relaxation time within approximately 150 ps as a previous report, the temperature of the n  =  2 state is found to have a longer relaxation time. This is because the n  =  2 state strongly couples with the continuum by excitation and deexcitation transfers, while the n  =  1 state couples with the donor bound state. These two systems exhibit different dynamic properties. Overall population transfer is the direction of energy relaxation, however, cooling of the upper states is delayed when compared to the lower states by the increase in the excitation transfer rate to the continuum. This dynamics of the exciton has a similarity to that of hydrogen atoms in plasma.

  4. Fully porous GaN p-n junction diodes fabricated by chemical vapor deposition.

    PubMed

    Bilousov, Oleksandr V; Carvajal, Joan J; Geaney, Hugh; Zubialevich, Vitaly Z; Parbrook, Peter J; Martínez, Oscar; Jiménez, Juan; Díaz, Francesc; Aguiló, Magdalena; O'Dwyer, Colm

    2014-10-22

    Porous GaN based LEDs produced by corrosion etching techniques demonstrated enhanced light extraction efficiency in the past. However, these fabrication techniques require further postgrown processing steps, which increases the price of the final system. Also, the penetration depth of these etching techniques is limited, and affects not only the semiconductor but also the other elements constituting the LED when applied to the final device. In this paper, we present the fabrication of fully porous GaN p-n junctions directly during growth, using a sequential chemical vapor deposition (CVD) process to produce the different layers that form the p-n junction. We characterized their diode behavior from room temperature to 673 K and demonstrated their ability as current rectifiers, thus proving the potential of these fully porous p-n junctions for diode and LEDs applications. The electrical and luminescence characterization confirm that high electronic quality porous structures can be obtained by this method, and we believe this investigation can be extended to other III-N materials for the development of white light LEDs, or to reduce reflection losses and narrowing the output light cone for improved LED external quantum efficiencies.

  5. Reactive ion etching of high optical quality GaN/sapphire photonic crystal slab using CH{sub 4}-H{sub 2} chemistry

    SciTech Connect

    Bouchoule, S.; Boubanga-Tombet, S.; Le Gratiet, L.; Le Vassor d'Yerville, M.; Torres, J.; Chen, Y.; Coquillat, D.

    2007-02-15

    Reactive ion etching (RIE) using a CH{sub 4}-H{sub 2} plasma is investigated for the fabrication of a GaN one-dimensional (1D) photonic crystal (PhC) slab. The dominant control parameter for the etch rate and the sidewall profile is the dc bias. The influence of operating pressure, CH{sub 4}/H{sub 2} ratio, and total gas flow rate on the etching characteristics is also presented. An etch rate as high as 85 nm/min and an overcut angle as low as 5 degree sign obtained in this work are among the best values reported for conventional RIE technique. The CH{sub 4}-H{sub 2} process is used to etch 1D PhCs with a lattice parameter ranging from 700 to 350 nm and an air filling factor of 0.30 into a 600-nm-thick GaN/sapphire slab. Sharp peaks corresponding to the resonant modes of the nanopatterned structures are observed in the experimental reflection spectra for all the lattice periods. Furthermore, the good optical quality of the nanostructures is evidenced by a resonantly enhanced second-harmonic generation experiment around 400 nm. A second-harmonic generation enhancement factor as high as 10{sup 5} is obtained, compared with the unpatterned GaN reference slab. These results demonstrate that the CH{sub 4}-H{sub 2} conventional RIE technique is well adapted to the etching of GaN PhC for the fabrication of next generation photonic devices exploiting nonlinear processes.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  7. Growth and characterization of horizontal GaN wires on silicon

    SciTech Connect

    Zou, Xinbo; May Lau, Kei; Lu, Xing; Lucas, Ryan; Kuech, Thomas F.; Choi, Jonathan W.; Gopalan, Padma

    2014-06-30

    We report the growth of in-plane GaN wires on silicon by metalorganic chemical vapor deposition. Triangular-shaped GaN microwires with semi-polar sidewalls are observed to grow on top of a GaN/Si template patterned with nano-porous SiO{sub 2}. With a length-to-thickness ratio ∼200, the GaN wires are well aligned along the three equivalent 〈 112{sup ¯}0 〉 directions. Micro-Raman measurements indicate negligible stress and a low defect density inside the wires. Stacking faults were found to be the only defect type in the GaN wire by cross-sectional transmission electron microscopy. The GaN wires exhibited high conductivity, and the resistivity was 20–30 mΩ cm, regardless of the wire thickness. With proper heterostructure and doping design, these highly aligned GaN wires are promising for photonic and electronic applications monolithically integrated on silicon.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    Cui, Bentao; Cohen, P. I.

    2004-03-01

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

  10. A guide to highly effective quality programs.

    PubMed

    Byrnes, John; Fifer, Joe

    2010-01-01

    To dramatically improve quality while decreasing costs, hospitals should: ensure all executives are vocal and visible supporters of quality improvement; focus the board of directors on quality as a strategic priority; strategically target quality resources to improve care for the majority of patients; use the finance system as the foundation for automated quality reporting; form a strong alliance between the CFO and chief quality officer, with each playing a leadership role in the quality program; rely on a well-executed quality program to improve efficiency and decrease the cost of care. PMID:20088475

  11. 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.

  12. An economical route to high quality lubricants

    SciTech Connect

    Andre, J.P.; Hahn, S.K.; Kwon, S.H.; Min, W.

    1996-12-01

    The current rends in the automotive and industrial markets toward more efficient engines, longer drain intervals, and lower emissions all contribute to placing increasingly stringent performance requirements on lubricants. The demand for higher quality synthetic and non-conventional basestocks is expected to grow at a much faster rate than that of conventional lube basestocks to meet these higher performance standards. Yukong Limited has developed a novel technology (the Yukong UCO Lube Process) for the economic production of high quality, high-viscosity-index lube basestocks from a fuels hydrocracker unconverted oil stream. A pilot plant based on this process has been producing oils for testing purposes since May 1994. A commercial facility designed to produce 3,500 BPD of VHVI lube basestocks cane on-stream at Yukong`s Ulsan refinery in October 1995. The Badger Technology Center of Raytheon Engineers and Constructors assisted Yukong during the development of the technology and prepared the basic process design package for the commercial facility. This paper presents process aspects of the technology and comparative data on investment and operating costs. Yukong lube basestock product properties and performance data are compared to basestocks produced by conventional means and by lube hydrocracking.

  13. Behavior of aluminum adsorption and incorporation at GaN(0001) surface: First-principles study

    SciTech Connect

    Qin, Zhenzhen; Xiong, Zhihua Wan, Qixin; Qin, Guangzhao

    2013-11-21

    First-principles calculations are performed to study the energetics and atomic structures of aluminum adsorption and incorporation at clean and Ga-bilayer GaN(0001) surfaces. We find the favorable adsorption site changes from T4 to T1 as Al coverage increased to 1 monolayer on the clean GaN(0001) surface, and a two-dimensional hexagonal structure of Al overlayer appears. It is interesting the Al atoms both prefer to concentrate in one deeper Ga layer of clean and Ga-bilayer GaN(0001) surface, respectively, while different structures could be achieved in above surfaces. For the case of clean GaN(0001) surface, corresponding to N-rich and moderately Ga-rich conditions, a highly regular superlattice structure composed of wurtzite GaN and AlN becomes favorable. For the case of Ga-bilayer GaN(0001) surface, corresponding to extremely Ga-rich conditions, the Ga bilayer is found to be sustained stable in Al incorporating process, leading to an incommensurate structure directly. Furthermore, our calculations provide an explanation for the spontaneous formation of ordered structure and incommensurate structure observed in growing AlGaN films. The calculated results are attractive for further development of growth techniques and excellent AlGaN/GaN heterostructure electronic devices.

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

    PubMed

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

    2015-11-13

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

  15. ITON Schottky contacts for GaN based UV photodetectors

    NASA Astrophysics Data System (ADS)

    Vanhove, N.; John, J.; Lorenz, A.; Cheng, K.; Borghs, G.; Haverkort, J. E. M.

    2006-12-01

    Lateral Schottky ultraviolet detectors were fabricated in GaN using indium-tin-oxynitride (ITON) as a contact metal. The GaN semiconductor material was grown on 2 in. sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The Schottky contact has been realized using ITON that has been deposited using sputter techniques. I- V characteristics have been measured with and without UV illumination. The device shows photo-to-dark current ratios of 10 3 at -1 V bias. The spectral responsivity of the UV detectors has been determined. The high spectral responsivity of more than 30 A/W at 240 nm is explained by a high internal gain caused by generation-recombination centers at the ITON/GaN interface. Persistent photocurrent effect has been observed in UV light (on-off) switching operation, time constant and electron capture coefficient of the transition has been determined.

  16. 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.

  17. Quality assurance and high count rate

    SciTech Connect

    Lindstrom, R.M.

    1994-12-31

    A high count rate can distort the expected linear relation between the charge spectrum generated in a semiconductor gamma-ray detector and that recorded in the pulse-height analyzer. The busy time of the analog-to-digital converter (ADC) is accurately compensated for in commercial analyzers by extending the live counting time. As fast successive-approximation ADCs have become more generally used (note that 10{mu}s fixed digitizing time for 8192 channels is equivalent to an 800-MHz Wilkinson ADC), the resolution times of the other components in the counting system have become relatively more important limitations of the throughput of the total system and also more important sources of nonlinearity, which lead to biased measurements. A loss-free counting technique (LFC) has been developed which gives an undistorted spectrum and zero dead time so that decay equations can be solved. Tests of an LFC system have shown that, with systematic calibration, the system can give stable values in practice for a reference spectrum up to at least 100 kHz. To obtain higher quality data with confidence, quality control test are needed.

  18. High Image Quality Laser Color Printer

    NASA Astrophysics Data System (ADS)

    Nagao, Kimitoshi; Morimoto, Yoshinori

    1989-07-01

    A laser color printer has been developed to depict continuous tone color images on a photographic color film or color paper with high resolution and fidelity. We have used three lasers, He-Cd (441.6 nm), Ar4+ (514.5 nm), and He-Ne (632.8 nm) for blue, green, and red exposures. We have employed a drum scanner for two dimensional scanning. The maximum resolution of our system is 40 c/mm (80 lines/mm) and the accuracy of density reproduction is within 1.0 when measured in color difference, where most observers can not distinguish the difference. The scanning artifacts and noise are diminished to a visually negligible level. The image quality of output images compares well to that of actual color photographs, and is suitable for photographic image simulations.

  19. Method for synthesis of high quality graphene

    DOEpatents

    Lanzara, Alessandra; Schmid, Andreas K.; Yu, Xiaozhu; Hwang, Choonkyu; Kohl, Annemarie; Jozwiak, Chris M.

    2012-03-27

    A method is described herein for the providing of high quality graphene layers on silicon carbide wafers in a thermal process. With two wafers facing each other in close proximity, in a first vacuum heating stage, while maintained at a vacuum of around 10.sup.-6 Torr, the wafer temperature is raised to about 1500.degree. C., whereby silicon evaporates from the wafer leaving a carbon rich surface, the evaporated silicon trapped in the gap between the wafers, such that the higher vapor pressure of silicon above each of the wafers suppresses further silicon evaporation. As the temperature of the wafers is raised to about 1530.degree. C. or more, the carbon atoms self assemble themselves into graphene.

  20. Magnetic and structural properties of Fe-implanted cubic GaN

    NASA Astrophysics Data System (ADS)

    Righetti, V. A. N.; Gratens, X.; Chitta, V. A.; de Godoy, M. P. F.; Rodrigues, A. D.; Abramof, E.; Dias, J. F.; Schikora, D.; As, D. J.; Lischka, K.

    2016-09-01

    In this article, we report on structural and magnetic properties of cubic GaN epitaxial layers implanted with Fe ions and subsequently subjected to thermal annealing. The epitaxial quality of the layers was studied by X-ray diffraction rocking curves (ω-scans) and Raman spectroscopy. The results show that the implantation damages the crystal structure producing an expansion of the lattice parameter in the implanted region. These damages are partially removed by the thermal treatment. Room temperature ferromagnetism is observed for the sample implanted with a dose of 1.2 × 1016 cm-2, while samples implanted with 2.4 × 1016 cm-2 show a coexistence of ferromagnetism and paramagnetism due to disperse Fe3+. Thermal annealing changes these magnetic properties. For the low dose sample, the ferromagnetism is converted into paramagnetism while for the high dose we observed an enhancement of the ferromagnetic contribution characterized by a superparamagnetism behavior attributed to Fe-based particles.

  1. Localized vibrational modes of carbon-hydrogen complexes in GaN

    SciTech Connect

    Manasreh, M.O.; Baranowski, J.M.; Pakula, K.; Jiang, H.X.; Lin, J.

    1999-08-01

    Localized vibrational modes of carbon-hydrogen complexes in metalorganic chemical vapor deposition grown GaN on sapphire were studied using a Fourier-transform infrared spectroscopy technique. Three distinctive localized vibrational modes were observed around 2850, 2922, and 2959 cm{sup {minus}1} for undoped, Si-, and Mg-doped samples. These peaks are related to CH, CH{sub 2}, and CH{sub 3} defect complexes, respectively. However, the localized vibrational modes were not observed in some undoped samples, which is indicative of high quality grown epitaxial layers. It is also observed that the frequencies and intensities of the localized vibrational modes are sample dependent. {copyright} {ital 1999 American Institute of Physics.}

  2. Time-dependent threshold voltage drift induced by interface traps in normally-off GaN MOSFET with different gate recess technique

    NASA Astrophysics Data System (ADS)

    Sang, Fei; Wang, Maojun; Tao, Ming; Liu, Shaofei; Yu, Min; Xie, Bing; Wen, Cheng P.; Wang, Jingyan; Wu, Wengang; Hao, Yilong; Shen, Bo

    2016-09-01

    The time-dependent threshold voltage drift induced by fast interface traps in a fully gate-recessed normally-off GaN MOSFET is studied. It is found that the degree and time scale of the shift in threshold voltage are consistent with the density and time constant of interface traps at the MOS interface. The device based on wet etching delivers higher interface quality and threshold voltage stability than that based on dry etching. Nitrogen deficiency and high oxygen coverage are considered to be the origins of the high interface trap density in the MOSFET fabricated by dry etching.

  3. Synchrotron radiation x-ray topography and defect selective etching analysis of threading dislocations in GaN

    SciTech Connect

    Sintonen, Sakari Suihkonen, Sami; Jussila, Henri; Tuomi, Turkka O.; Lipsanen, Harri; Rudziński, Mariusz; Knetzger, Michael; Meissner, Elke; Danilewsky, Andreas

    2014-08-28

    The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid and non-destructive technique for dislocation analysis on a large scale. In this study, the defect structure of an ammonothermal c-plane GaN substrate was recorded using SR-XRT and the image contrast caused by the dislocation induced microstrain was simulated. The simulations and experimental observations agree excellently and the SR-XRT image contrasts of mixed and screw dislocations were determined. Apart from a few exceptions, defect selective etching measurements were shown to correspond one to one with the SR-XRT results.

  4. Optical properties of Yb ions in GaN epilayer

    NASA Astrophysics Data System (ADS)

    Jadwisienczak, W. M.; Lozykowski, H. J.

    2003-07-01

    In recent years, an important effort in semiconductor materials research has been devoted to III-nitrides semiconductors doped with rare earth ions due to the high potential of these materials in light-emitting device applications. Ytterbium (Yb 3+) is one of a few lanthanide ions which have not been investigated as an optically active center in these materials yet. In this paper we report the observation of luminescence from GaN films grown on sapphire (0 0 0 1) substrate by metal organic chemical vapor deposition and doped by implantation with Yb 3+ ions. The high resolution photo- and cathodoluminescence spectra of GaN:Yb 3+ were studied at different excitation conditions in temperatures ranging from 8 to 330 K and revealed weak thermal quenching. The luminescence emission lines are assigned to transitions between the spin-orbit levels 2F 5/2 → 2F 7/2 of Yb 3+ (4f 13). The analysis of the Yb luminescence spectra allowed us to suggest the energy level diagram of the crystal-field-split 4f 13 levels for the Yb ion center. The most probable lattice location of Yb in GaN is the substitutional Ga site. Furthermore, the luminescence kinetics of internal transitions of Yb 3+ incorporated in GaN was investigated by means of decay and time-resolved luminescence measurements. It was found that the ytterbium decay is non-exponential with dominant exponential term of ˜100 μs with little dependence on the ambient temperature. The results indicate that Yb-doped GaN epilayer may be suitable as a material for near infrared optoelectronic devices.

  5. Transport properties, specific heat and thermal conductivity of GaN nanocrystalline ceramic

    SciTech Connect

    Sulkowski, Czeslaw; ChuchmaLa, Andrzej; Zaleski, Andrzej J.; Matusiak, Marcin; Mucha, Jan; GLuchowski, PaweL; Strek, WiesLaw

    2010-10-15

    The structural and transport properties (resistivity, thermopower and Hall effect), specific heat and thermal conductivity have been measured for GaN nanocrystalline ceramic prepared by hot pressing. It was found that the temperature dependence of resistivity in temperature range 10-300 K shows the very low activation energy, which is ascribed to the shallow donor doping originating in amorphous phase of sample. The major charge carriers are electrons, what is indicated by negative sign of Hall constant and Seebeck coefficient. The thermopower attains large values (-58 {mu}V/K at 300 K) and was characterized by linear temperature dependence which suggests the diffusion as a major contribution to Seebeck effect. The high electron concentration of 1.3x10{sup 19} cm{sup -3} and high electronic specific heat coefficient determined to be 2.4 mJ/molK{sup 2} allow to conclude that GaN ceramic demonstrates the semimetallic-like behavior accompanied by very small mobility of electrons ({approx}0.1 cm{sup 2}/V s) which is responsible for its high resistivity. A low heat conductivity of GaN ceramics is associated with partial amorphous phase of GaN grains due to high pressure sintering. - Graphical Abstract: Thermal resistivity and thermopower measurements indicates the high phonon scattering and lack of phonon-drag contribution to thermopower in GaN nanoceramics pressed under 4 GPa at 800 {sup o}C.

  6. Simulation of optimum parameters for GaN MSM UV photodetector

    NASA Astrophysics Data System (ADS)

    Alhelfi, Mohanad A.; Ahmed, Naser M.; Hashim, M. R.; Al-Rawi, Ali Amer; Hassan, Z.

    2016-07-01

    In this study the optimum parameters of GaN M-S-M photodetector are discussed. The evaluation of the photodetector depends on many parameters, the most of the important parameters the quality of the GaN film and others depend on the geometry of the interdigited electrode. In this simulation work using MATLAB software with consideration of the reflection and absorption on the metal contacts, a detailed study involving various electrode spacings (S) and widths (W) reveals conclusive results in device design. The optimum interelectrode design for interdigitated MSM-PD has been specified and evaluated by effect on quantum efficiency and responsivity.

  7. Cubic and hexagonal GaN nanoparticles synthesized at low temperature

    NASA Astrophysics Data System (ADS)

    Qaeed, M. A.; Ibrahim, K.; Saron, K. M. A.; Salhin, A.

    2013-12-01

    This study involves a simple and low cost chemical method for the synthesis of Gallium Nitride (GaN) nanoparticles at low temperature. Structural and optical characterizations were carried out using various techniques in order to investigate the properties of the nanoparticles. The Field-Emission Scanning Electron Microscope (FESEM) images showed that the nanoparticles consist of cubic and hexagonal shapes, indicating crystallized structural quality of the GaN nanoparticles. The average size of the nanoparticles was found to be 51 nm. The X-ray Diffraction (XRD) and Raman analysis further confirmed the hexagonal and cubic phases of GaN nanoparticles. The room temperature photoluminescence deduced h-GaN energy gaps of 2.95, 3.12 and 3.13 eV.

  8. 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.

  9. Atomic layer deposition of epitaxial ZnO on GaN and YSZ

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Wei; Ke, Dong-Jie; Chao, Yen-Cheng; Chang, Li; Liang, Mei-Hui; Ho, Yen-Teng

    2007-01-01

    ZnO thin films were epitaxially grown by atomic layer deposition on both of GaN/c-sapphire and yttria-stabilized zirconia (YSZ) substrates for comparison. X-ray diffraction, cross-sectional transmission electron microscopy (TEM) and photoluminescence (PL) measurements show that epitaxial ZnO films have better structural qualities and optical properties on GaN than on YSZ, whereas atomic force microscopy (AFM) shows that the surface of ZnO films on YSZ is smoother than on GaN. From the ZnO thickness measured by TEM, the growth rate of ZnO on GaN is about one (0 0 0 2) monolayer per cycle, which is roughly four times of that on YSZ.

  10. Mechanical properties of nanoporous GaN and its application for separation and transfer of GaN thin films.

    PubMed

    Huang, Shanjin; Zhang, Yu; Leung, Benjamin; Yuan, Ge; Wang, Gang; Jiang, Hao; Fan, Yingmin; Sun, Qian; Wang, Jianfeng; Xu, Ke; Han, Jung

    2013-11-13

    Nanoporous (NP) gallium nitride (GaN) as a new class of GaN material has many interesting properties that the conventional GaN material does not have. In this paper, we focus on the mechanical properties of NP GaN, and the detailed physical mechanism of porous GaN in the application of liftoff. A decrease in elastic modulus and hardness was identified in NP GaN compared to the conventional GaN film. The promising application of NP GaN as release layers in the mechanical liftoff of GaN thin films and devices was systematically studied. A phase diagram was generated to correlate the initial NP GaN profiles with the as-overgrown morphologies of the NP structures. The fracture toughness of the NP GaN release layer was studied in terms of the voided-space-ratio. It is shown that the transformed morphologies and fracture toughness of the NP GaN layer after overgrowth strongly depends on the initial porosity of NP GaN templates. The mechanical separation and transfer of a GaN film over a 2 in. wafer was demonstrated, which proves that this technique is useful in practical applications.

  11. UV-Photoassisted Etching of GaN in KOH

    SciTech Connect

    Abernathy, C.R.; Auh, K.H.; Cho, H.; Donovan, S.M.; Han, J.; Lambers, E.S.; Pearton, S.J.; Ren F.; Shul, R.J.

    1998-11-12

    The etch rate of GaN under W-assisted photoelectrochemical conditions in KOH solutions is found to be a strong function of illumination intensity, solution molarity, sample bias and material doping level. At low e-h pair generation rates, grain boundaries are selectively etched, while at higher illumination intensities etch rates for unintentionally doped (n - 3x 10^12Gcm-3) GaN are 2 1000 .min-l. The etching is diffusion limited under our conditions with an activation energy of - 0.8kCal.mol-1. The etched surfaces are rough, but retain their stoichiometry. PEC etching is found to selectively reveal grain boundaries in GaN under low light illumination conditions. At high lamp powers the rates increase with sample temperature and the application of bias to the PEC cell, while they go through a maximum with KOH solution molarity. The etching is diffusion-limited, producing rough surface morphologies that are suitable in a limited number of device fabrication steps. The surfaces however appear to remain relatively close to their stoichiometric composition.

  12. Metal contacts on ZnSe and GaN

    SciTech Connect

    Duxstad, K J

    1997-05-01

    Recently, considerable interest has been focused on the development of blue light emitting materials and devices. The focus has been on GaN and ZnSe, direct band gap semiconductors with bands gaps of 3.4 and 2.6 eV, respectively. To have efficient, reliable devices it is necessary to have thermally and electrically stable Ohmic contacts. This requires knowledge of the metal-semiconductor reaction behavior. To date few studies have investigated this behavior. Much information has accumulated over the years on the behavior of metals on Si and GaAs. This thesis provides new knowledge for the more ionic wide band gap semiconductors. The initial reaction temperatures, first phases formed, and phase stability of Pt, Pd, and Ni on both semiconductors were investigated. The reactions of these metals on ZnSe and GaN are discussed in detail and correlated with predicted behavior. In addition, comparisons are made between these highly ionic semiconductors and Si and GaAs. The trends observed here should also be applicable to other II-VI and III-Nitride semiconductor systems, while the information on phase formation and stability should be useful in the development of contacts for ZnSe and GaN devices.

  13. 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.

  14. Spin and phase relaxation dynamics in GaN and GaN/AlGaN quantum wells (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Gallart, Mathieu; Ziegler, Marc; Hönerlage, Bernd H.; Gilliot, Pierre; Feltin, Eric; Carlin, Jean-François; Butté, Raphaël.; Grandjean, Nicolas

    2015-09-01

    By performing time-resolved optical non-degenerate pump-probe experiments, we study the relaxation dynamics of spin-polarized excitons in wurtzite epitaxial GaN and in nitride nanostructures. Those materials are indeed promising candidates for spintronic applications because of their weak spin-orbit coupling and large exciton binding energy (~ 17 meV and ~ 26meV in bulk GaN, respectively). In epilayers, we show that the high density of dislocations increases dramatically the spin relaxation of electrons and holes through the defect assisted Elliott-Yafet mechanism. That makes the exciton dephasing time very short. In high quality GaN/AlGaN quantum wells, both the exciton-spin lifetime S and the exciton dephasing-time T2 were determined via pump-probe spectroscopy using polarized laser pulses and time-resolved four wave-mixing experiments. The evolution of both quantities with temperature shows that spin relaxation occurs in the motional narrowing regime up to 80 K. Above this threshold, the thermal energy becomes large enough for excitons to escape from the QW. Such measurements demonstrate that GaN-based heterostructures can reach a very high degree of control that was previously mostly restricted to conventional III-V semiconductors and more specifically to the arsenide family.

  15. Influence of substrate quality on structural properties of AlGaN/GaN superlattices grown by molecular beam epitaxy

    SciTech Connect

    Schubert, F.; Merkel, U.; Schmult, S.; Mikolajick, T.

    2014-02-28

    Short-period AlGaN/GaN superlattices were established as versatile test structures to investigate the structural properties of molecular beam epitaxy (MBE)-grown GaN and AlGaN layers and their dependence on the GaN substrate quality. X-ray diffractometry data of the investigated superlattices allow access to relevant structural parameters such as aluminum mole fraction and layer thicknesses. The occurrence of theoretically predicted intense high-order satellite peaks and pronounced interface fringes in the diffraction pattern reflects abrupt interfaces and perfect 2-dimensional growth resulting in smooth surfaces. The data unambiguously demonstrate that the structural quality of the MBE grown layers is limited by the structural properties of the GaN substrate.

  16. Integrating Quality into the Textile and Apparel High School Curriculum.

    ERIC Educational Resources Information Center

    Meyer, Deborah J. C.; Kadolph, Sara J.; Cosbey, Sarah; Hillery, Julie; Haar, Sherry; Day, Marla; Keiser, Sandra; Brandes, Kendra

    2001-01-01

    Explains the importance of quality assurance in high school textiles and apparel instruction. Describes educational activities that integrate quality assurance concepts (teamwork, continuous improvement, customer focus, and empowerment). (Contains 23 references.) (SK)

  17. 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.

  18. Zn-dopant dependent defect evolution in GaN nanowires.

    PubMed

    Yang, Bing; Liu, Baodan; Wang, Yujia; Zhuang, Hao; Liu, Qingyun; Yuan, Fang; Jiang, Xin

    2015-10-21

    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¯3), (101¯1) and (202¯1), as well as Type I stacking faults (…ABABCBCB…), 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 (…ABABACBA…) 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.

  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. PMID:27363777

  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. 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.

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

    SciTech Connect

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

    2014-08-14

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

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

    SciTech Connect

    Koleske, Daniel David; Lee, Stephen Roger; Lemp, Thomas Kerr; Coltrin, Michael Elliott; Cross, Karen Charlene; Thaler, Gerald

    2009-07-01

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

  4. GaN detector development for particle and X-ray detection

    NASA Astrophysics Data System (ADS)

    Owens, Alan; Barnes, A.; Farley, R. A.; Germain, M.; Sellin, P. J.

    2012-12-01

    We report on preliminary alpha particle and X-ray measurements on a number of prototype GaN PIN diodes. The aim of the study was to investigate the potential use of GAN based radiation detectors for radiation hard, high temperature, solar blind space applications. The devices have a planar structure consisting of a 2 μm epitaxial GaN layer grown on a highly doped n-type AlxGa1-xN nucleation layer, which in turn is deposited on a p-type 4H-SiC substrate. Au ohmic contacts were applied to the top of the GaN layer and the bottom of the substrate. A number of different sized devices were tested with contact diameters ranging from 0.4 mm to 0.7 mm. All devices showed good diode behaviour with reverse leakage currents in the tens to hundreds of micro-amp range. C-V measurements showed that the GaN layers were fully depleted for biases >20 V. When exposed to a 5.5 MeV alpha particle source, the devices showed a spectroscopic response with energy resolutions of ∼25% FWHM at room temperature (RT) and 10 V bias and 20% FWHM at -50 °C. These values are consistent with the previous measurements. No response to 60 keV photons could be measured.

  5. 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. PMID:27483845

  6. High rate dry etching of GaN, AlN and InN in ECR Cl{sub 2}/CH{sub 4}/H{sub 2}/Ar plasmas

    SciTech Connect

    Vartuli, C.B.; Pearton, S.J.; Abernathy, C.R.; Shul, R.J.; Kilcoyne, S.P.; Crawford, M.H.; Howard, A.J.; Parmeter, J.E.

    1995-05-01

    Etch rates for binary nitrides in ECR Cl{sub 2}/CH{sub 4}/H{sub 2}/Ar are reported as a function of temperature, rf-bias, microwave power, pressure and relative gas proportions. GaN etch rates remain relatively constant from 30 to 125{degrees}C and then increase to a maximum of 2340 {angstrom}-min{sup {minus}1} at 170{degrees}C. The AlN etch rate decreases throughout the temperature range studied with a maximum of 960 {angstrom}-min{sup {minus}1} at 30{degrees}C. When CH{sub 4} is removed from the plasma chemistry, the GaN and InN etch rates are slightly lower, with less dramatic changes with temperature. The surface composition of the III-V nitrides remains unchanged over the temperatures studied. The GaN and InN rates increase significantly with rf power, and the fastest rates for all three binaries are obtained at 2 mTorr. Surface morphology is smooth for GaN over a wide range of conditions, whereas InN surfaces are more sensitive to plasma parameters.

  7. Analysis of high-quality modes in open chaotic microcavities

    SciTech Connect

    Fang, W.; Yamilov, A.; Cao, H.

    2005-08-15

    We present a numerical study of the high-quality modes in two-dimensional dielectric stadium microcavities. Although the classical ray mechanics is fully chaotic in a stadium billiard, all of the high-quality modes show a 'strong scar' around unstable periodic orbits. When the deformation (ratio of the length of the straight segments over the diameter of the half circles) is small, the high-quality modes correspond to whispering-gallery-type trajectories and their quality factors decrease monotonically with increasing deformation. At large deformation, each high-quality mode is associated with multiple unstable periodic orbits. Its quality factor changes nonmonotonically with the deformation, and there exists an optimal deformation for each mode at which its quality factor reaches a local maximum. This unusual behavior is attributed to the interference of waves propagating along different constituent orbits that could minimize light leakage out of the cavity.

  8. High Efficiency, Illumination Quality OLEDs for Lighting

    SciTech Connect

    Joseph Shiang; James Cella; Kelly Chichak; Anil Duggal; Kevin Janora; Chris Heller; Gautam Parthasarathy; Jeffery Youmans; Joseph Shiang

    2008-03-31

    The goal of the program was to demonstrate a 45 lumen per watt white light device based upon the use of multiple emission colors through the use of solution processing. This performance level is a dramatic extension of the team's previous 15 LPW large area illumination device. The fundamental material system was based upon commercial polymer materials. The team was largely able to achieve these goals, and was able to deliver to DOE a 90 lumen illumination source that had an average performance of 34 LPW a 1000 cd/m{sup 2} with peak performances near 40LPW. The average color temperature is 3200K and the calculated CRI 85. The device operated at a brightness of approximately 1000cd/m{sup 2}. The use of multiple emission colors particularly red and blue, provided additional degrees of design flexibility in achieving white light, but also required the use of a multilayered structure to separate the different recombination zones and prevent interconversion of blue emission to red emission. The use of commercial materials had the advantage that improvements by the chemical manufacturers in charge transport efficiency, operating life and material purity could be rapidly incorporated without the expenditure of additional effort. The program was designed to take maximum advantage of the known characteristics of these material and proceeded in seven steps. (1) Identify the most promising materials, (2) assemble them into multi-layer structures to control excitation and transport within the OLED, (3) identify materials development needs that would optimize performance within multilayer structures, (4) build a prototype that demonstrates the potential entitlement of the novel multilayer OLED architecture (5) integrate all of the developments to find the single best materials set to implement the novel multilayer architecture, (6) further optimize the best materials set, (7) make a large area high illumination quality white OLED. A photo of the final deliverable is shown. In

  9. Generation of high-quality petawatt pulses

    SciTech Connect

    Mourou, G; Bado, Philippe

    1991-01-01

    CPA sources need a front-end capable of generating very short seed pulses. To meet this requirement, present CPA sources rely on actively modelocked solid-state oscillators used in conjunction with non-linear fiber stages. This approach generates pulses with a residual frequency chirp, resulting in a limited peak-to-background intensity contrast ratio. The availability of an oscillator capable of producing directly (i.e. without fiber stage) picosecond or sub-picosecond pulses would significantly improve the quality of CPA sources. We have pursued different approaches to replace the standard modelocked oscillator front-end. In an initial phase, we investigated the possible use of Additive Pulse Modelocking (APM) color-center lasers as oscillators for CPA Nd:glass sources. Lately we have developed a Ti:Sapphire modelocked oscillator operating in the one-micron range. In order to generate pulses with very high peak to background contrast ratio, we have built a non-linear coupled-cavity oscillator generating 200-fs pulses. This color-center laser operates in the 1.5--1.6 micron range. A diagram of the oscillator is shown in Fig. 1. The laser is pumped with a modelocked Nd:YAG source. Both KCl and NaCl crystals were tested as gain media. NaCl was found to have a larger tuning range and to generate a higher average power (up to 150 mW). When synchronously mode-locked, the color-center generates pulses in the 10--20 ps range. Once interferometrically coupled to non-linear external-cavity, this oscillator produces very short pulses (85 to 260 fs). This oscillator was first operated with a 2 mm birefringent plate. 85 fs, near transform-limited pulses were generated at 1.54 micron. As the laser was tuned to longer wavelength, the pulse duration increased, as well as the bandwidth-duration product. With a 4 mm birefringent plate, 125 fs, transform-limited pulses were generated over the full tuning range.

  10. Measurement of the electrostatic edge effect in wurtzite GaN nanowires

    SciTech Connect

    Henning, Alex; Rosenwaks, Yossi; Klein, Benjamin; Bertness, Kris A.; Blanchard, Paul T.; Sanford, Norman A.

    2014-11-24

    The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference between the nanowire face and the hexagonal vertices, the surface state concentration and band bending of GaN NWs were estimated. The surface band bending is important for an efficient design of high electron mobility transistors and for opto-electronic devices based on GaN NWs. This methodology provides a way to extract NW parameters without making assumptions concerning the electron affinity. We are taking advantage of electrostatic modeling and the high precision that KPFM offers to circumvent a major source of uncertainty in determining the surface band bending.

  11. Lithographically defined carbon growth templates for ELOG of GaN

    NASA Astrophysics Data System (ADS)

    Burckel, D. B.; Fan, Hongyou; Thaler, G.; Koleske, D. D.

    2008-06-01

    We report the initial use of lithographically defined carbon growth templates for use as an epitaxial lateral overgrowth (ELOG) mask for metalorganic chemical vapor deposition (MOCVD) heteroepitaxial GaN on sapphire. Interferometric lithography is used to define high aspect ratio structures in SU-8, which are then pyrolyzed in a reducing atmosphere up to 1200 °C. The resist structures convert to amorphous carbon, shrinking 80% in the vertical direction and 53% in the horizontal direction, but maintain their pattern geometry and adhesion to the substrate. These templates are capable of surviving GaN nucleation layer growth temperatures (˜530 °C), GaN crystal growth and high-temperature annealing up to 1050 °C. This new approach to ELOG offers several advantages, requiring fewer processing steps, and favorable selectivity tendencies as well as the capability to create growth masks which are difficult or impossible to fabricate using a top-down etching approach.

  12. Properties of Gallium Disorder and Gold Implants in GaN

    SciTech Connect

    Jiang, Weilin; Weber, William J.; Thevuthasan, Suntharampillai; Shutthanandan, V; DB Poker, SC Moss, K-H Heinig

    2001-04-25

    Epitaxial single-crystal GaN films on sapphire were implanted 60? off the <0001> surface normal with 1 MeV Auor 3 MeV Au over a fluence range from 0.88 to 86.2 ions/nm2 at 180 and 300 K. The implantation damage was studied in-situ using 2 MeV He Rutherford backscattering spectrometry in channeling geometry (RBS/C). The disordering rate in the near-surface region is faster than at the damage peak. In all cases, results show an intermediate stage of Ga disorder saturation at the damage peak. Migration of Au implants in GaN is observed during ion implantation at 300 K. As a result of thermal annealing at 870 K for 20 min, some Au implants in GaN diffuse into the amorphized surface region, while the remaining Au atoms distribute around the mean ion-projected-range. These results suggest a high mobility of both Ga defects and Au implants in GaN. Deeper damage implantation by 3 MeV Au indicates that GaN cannot be completely amorphized up to the highest ion fluence (86.2 ions/nm) applied at 300 K.

  13. Synthesis, microstructure, and cathodoluminescence of [0001]-oriented GaN nanorods grown on conductive graphite substrate.

    PubMed

    Yuan, Fang; Liu, Baodan; Wang, Zaien; Yang, Bing; Yin, Yao; Dierre, Benjamin; Sekiguchi, Takashi; Zhang, Guifeng; Jiang, Xin

    2013-11-27

    One-dimensional GaN nanorods with corrugated morphology have been synthesized on graphite substrate without the assistance of any metal catalyst through a feasible thermal evaporation process. The morphologies and microstructures of GaN nanorods were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results from HRTEM analysis indicate that the GaN nanorods are well-crystallized and exhibit a preferential orientation along the [0001] direction with Ga(3+)-terminated (101̅1) and N(3-)-terminated (101̅1̅) as side facets, finally leading to the corrugated morphology surface. The stabilization of the electrostatic surface energy of {101̅1} polar surface in a wurtzite-type hexagonal structure plays a key role in the formation of GaN nanorods with corrugated morphology. Room-temperature cathodoluminescence (CL) measurements show a near-band-edge emission (NBE) in the ultraviolet range and a broad deep level emission (DLE) in the visible range. The crystallography and the optical emissions of GaN nanorods are discussed. PMID:24164686

  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. 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.

  16. Growth behavior of GaN nanowires on c-plane sapphire substrate by applying various catalysts

    NASA Astrophysics Data System (ADS)

    Kuppulingam, B.; Bhalerao, G. M.; Singh, Shubra; Baskar, K.

    2016-07-01

    Systematic reaction has been used to control the vapor-liquid-solid growth of gallium nitride nanowires (NWs) using different catalysts. GaN NWs were grown using Cu, Au, Pd/Au alloy catalysts on c-plane sapphire substrate. XRD and Raman analysis revealed the crystalline wurtzite phase of GaN synthesized at 900 °C. High density GaN NWs were studied using SEM and HRTEM. Elemental composition and impurities were analyzed by EDX. Diameter of individual NW, grown using Au catalyst is found to be ~50 nm. The diameter of NWs grown with the help of Cu catalyst was found to be ˜65 nm, whereas with Pd/Au catalyst, the diameter was about 100-200 nm. NBE emission observed from PL spectra for Cu catalyst (377 nm), Au catalyst (372 nm) as well as Pd/Au catalyst (385 nm) growth of GaN NWs respectively has been presented and discussed.

  17. The origin of yellow band emission and cathodoluminescence of Au-catalyzed wurtzite GaN nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, R. S.; Jiao, J. F.; Wu, X.

    2016-06-01

    GaN nanowires with large yield are directly synthesized by simply ammoniating the gallium oxide powders in the presence of ammonia gas at 1000 °C, under the assistance of Au nanocatalysts. The microstructure and crystallinity of as-synthesized GaN nanowires are well studied by using high-resolution transmission electron microscope (HRTEM) and some structural defects such as stacking faults are found in the GaN nano-crystal. Cathodoluminescence measurement shows that a strong near-band-edge (NBE) emission band centered at 384 nm and a broad yellow band in the range of 500-800 nm are observed. Finally, the growth mechanism and possible optical emission process of GaN nanowires are discussed.

  18. InGaN light emitting diodes with a nanopipe layer formed from the GaN epitaxial layer.

    PubMed

    Hsu, Wei-Ju; Chen, Kuei-Ting; Huang, Wan-Chun; Wu, Chia-Jung; Dai, Jing-Jie; Chen, Sy-Hann; Lin, Chia-Feng

    2016-05-30

    A Si-heavy doped GaN:Si epitaxial layer is transformed into a directional nanopipe GaN layer through a laser-scribing process and a selectively electrochemical (EC) etching process. InGaN light-emitting diodes (LEDs) with an EC-treated nanopipe GaN layer have a high light extraction efficiency. The direction of the nanopipe structure was directed perpendicular to the laser scribing line and was guided by an external bias electric field. An InGaN LED structure with an embedded nanopipe GaN layer can enhance external quantum efficiency through a one-step epitaxial growth process and a selective EC etching process. A birefringence optical property and a low effective refractive index were observed in the directional-nanopipe GaN layer.

  19. InGaN light emitting diodes with a nanopipe layer formed from the GaN epitaxial layer.

    PubMed

    Hsu, Wei-Ju; Chen, Kuei-Ting; Huang, Wan-Chun; Wu, Chia-Jung; Dai, Jing-Jie; Chen, Sy-Hann; Lin, Chia-Feng

    2016-05-30

    A Si-heavy doped GaN:Si epitaxial layer is transformed into a directional nanopipe GaN layer through a laser-scribing process and a selectively electrochemical (EC) etching process. InGaN light-emitting diodes (LEDs) with an EC-treated nanopipe GaN layer have a high light extraction efficiency. The direction of the nanopipe structure was directed perpendicular to the laser scribing line and was guided by an external bias electric field. An InGaN LED structure with an embedded nanopipe GaN layer can enhance external quantum efficiency through a one-step epitaxial growth process and a selective EC etching process. A birefringence optical property and a low effective refractive index were observed in the directional-nanopipe GaN layer. PMID:27410087

  20. 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.

  1. Enhance ferromagnetism by stabilizing the cation vacancies in GaN

    NASA Astrophysics Data System (ADS)

    Tang, Zhen-kun; Zhang, Deng-Yu; Tang, Li-Ming; Wang, Ling-Ling; Chen, Ke-Qiu

    2013-06-01

    The magnetic properties related to cation vacancies in GaN are investigated by first-principles calculations. The results show that a neutral Ga-vacancy induces 3 μ B magnetic moment in GaN, but is difficult to form due to the high formation energy. It is found that the Ga-vacancy formation energy can be reduced by adding electrons with uniform compensating positive background charge, by nano-structure engineering, or by co-doping donor-like defects. The Ga-vacancy induced colossal magnetic moment in Gd-doped GaN can be modulated by co-doping the donor like defects. It is suggested that ferromagnetism enhanced by stabilizing the cation vacancies may be applied to other wide band-gap semiconductors as well.

  2. Heteroepitaxial growth of InN on GaN intermediate layer by PA-MOMBE

    NASA Astrophysics Data System (ADS)

    Lai, Fang-I.; Kuo, Shou-Yi; Chen, Wei-Chun; Lin, Woei-Tyng; Wang, Wei-Lin; Chang, Li; Hsiao, Chien-Nan; Chiang, Chung-Hao

    2011-07-01

    In this paper, high-quality wurtzite indium nitride was epi-grown on sapphire substrates by plasma-assisted metal-organic molecule beam epitaxy system (PA-MOMBE). Structural and electrical properties of the InN films were significantly improved by employing a GaN buffer layer. In addition, high-resolution X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), Hall Effect, Raman and photoluminescence spectroscopy were carried out to characterize the effect of the growth temperature on structural and optoelectronic properties. It was found that highly c-axis oriented InN epilayer can be obtained by optimizing growth conditions. TEM images reveal that the epitaxially grown InN/GaN interface is sharp, and the spacing of the InN(0 0 0 2) lattice plane is about 0.57 nm. Raman spectra also show a sharp peak at 491 cm -1 attributed to the E 2(high) mode of wurtzite InN. These results indicate that the improvement of InN material quality can be achieved using heteroepitaxy on GaN/sapphire templates.

  3. 36 CFR 910.31 - High architectural quality.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 36 Parks, Forests, and Public Property 3 2011-07-01 2011-07-01 false High architectural quality... architectural quality. Development must maintain a uniformly high standard of architecture, representative of the best contemporary design and planning concepts. Great care and sensitivity must be shown in...

  4. Quality Assurance Strategy for Existing Homes. Final Quality Management Primer for High Performing Homes

    SciTech Connect

    Del Bianco, M.; Taggart, J.; Sikora, J.; Wood, A.

    2012-12-01

    This guide is designed to help Building America (BA) teams understand quality management and its role in transitioning from conventional to high performance home building and remodeling. It explains what quality means, the value of quality management systems, the unique need for QMS when building high performing homes, and the first steps to a implementing a comprehensive QMS. This document provides a framework and context for BA teams when they encounter builders and remodelers.

  5. Quality Assurance Strategy for Existing Homes: Final Quality Management Primer for High Performing Homes

    SciTech Connect

    Del Bianco, M.; Taggart, J.; Sikora, J.; Wood, A.

    2012-12-01

    This guide is designed to help Building America (BA) Teams understand quality management and its role in transitioning from conventional to high performance home building and remodeling. It explains what quality means, the value of quality management systems, the unique need for QMS when building high performing homes, and the first steps to a implementing a comprehensive QMS. This document provides a framework and context for BA teams when they encounter builders and remodelers.

  6. Germanium-catalyzed growth of single-crystal GaN nanowires

    NASA Astrophysics Data System (ADS)

    Saleem, Umar; Wang, Hong; Peyrot, David; Olivier, Aurélien; Zhang, Jun; Coquet, Philippe; Ng, Serene Lay Geok

    2016-04-01

    We report the use of Germanium (Ge) as catalyst for Gallium Nitride (GaN) nanowires growth. High-yield growth has been achieved with Ge nanoparticles obtained by dewetting a thin layer of Ge on a Si (100) substrate. The nanowires are long and grow straight with very little curvature. The GaN nanowires are single-crystalline and show a Wurtzite structure growing along the [0001] axis. The growth follows a metal-free Vapor-Liquid-Solid (VLS) mechanism, further allowing a CMOS technology compatibility. The synthesis of nanowires has been done using an industrial Low Pressure Chemical Vapor Deposition (LPCVD) system.

  7. Microstructural evolution in H ion induced splitting of freestanding GaN

    SciTech Connect

    Moutanabbir, O.; Scholz, R.; Senz, S.; Goesele, U.; Chicoine, M.; Schiettekatte, F.; Suesskraut, F.; Krause-Rehberg, R.

    2008-07-21

    We investigated the microstructural transformations during hydrogen ion-induced splitting of GaN thin layers. Cross-sectional transmission electron microscopy and positron annihilation spectroscopy data show that the implanted region is decorated with a high density of 1-2 nm bubbles resulting from vacancy clustering during implantation. These nanobubbles persist up to 450 deg. C. Ion channeling data show a strong dechanneling enhancement in this temperature range tentatively attributed to strain-induced lattice distortion. The dechanneling level decreases following the formation of plateletlike structures at 475 deg. C. Extended internal surfaces develop around 550 deg. C leading to the exfoliation of GaN thin layer.

  8. Inequality in Preschool Quality? Community-Level Disparities in Access to High-Quality Learning Environments

    ERIC Educational Resources Information Center

    Bassok, Daphna; Galdo, Eva

    2016-01-01

    In recent years, unequal access to high-quality preschool has emerged as a growing public policy concern. Because of data limitations, it is notoriously difficult to measure disparities in access to early learning opportunities across communities and particularly challenging to quantify gaps in access to "high-quality" programs. Research…

  9. Effective multidisciplinary working: the key to high-quality care.

    PubMed

    Ndoro, Samuel

    This article explores multidisciplinary team working, inter-disciplinary, trans-disciplinary and effective collaborative practice in order to provide high-quality patient care. It discusses different views on collaboration, some of the issues around cross-discipline and multi-agency working and concerns around promoting 'high-quality' care. It also discusses the importance of evidence-based practice in multidisciplinary teams. Issues around good-quality care, clinical governance and the audit cycle in MDTs are addressed. The article highlights the importance of the 6Cs (care, compassion, competence, communication, courage and commitment) in MDTs if quality care is to be achieved. The article also explores advantages and limitations of multidisciplinary team working, trans-disciplinary working and inter-professional working in developing and delivering high-quality patient-centred care. Further research is needed on how clinical audits can help to improve how MDTs function in order improve the quality of service provided to clients.

  10. Dislocation confinement in the growth of Na flux GaN on metalorganic chemical vapor deposition-GaN

    SciTech Connect

    Takeuchi, S. Asazu, H.; Nakamura, Y.; Sakai, A.; Imanishi, M.; Imade, M.; Mori, Y.

    2015-12-28

    We have demonstrated a GaN growth technique in the Na flux method to confine c-, (a+c)-, and a-type dislocations around the interface between a Na flux GaN crystal and a GaN layer grown by metalorganic chemical vapor deposition (MOCVD) on a (0001) sapphire substrate. Transmission electron microscopy (TEM) clearly revealed detailed interface structures and dislocation behaviors that reduced the density of vertically aligned dislocations threading to the Na flux GaN surface. Submicron-scale voids were formed at the interface above the dislocations with a c component in MOCVD-GaN, while no such voids were formed above the a-type dislocations. The penetration of the dislocations with a c component into Na flux GaN was, in most cases, effectively blocked by the presence of the voids. Although some dislocations with a c component in the MOCVD-GaN penetrated into the Na flux GaN, their propagation direction changed laterally through the voids. On the other hand, the a-type dislocations propagated laterally and collectively near the interface, when these dislocations in the MOCVD-GaN penetrated into the Na flux GaN. These results indicated that the dislocation propagation behavior was highly sensitive to the type of dislocation, but all types of dislocations were confined to within several micrometers region of the Na flux GaN from the interface. The cause of void formation, the role of voids in controlling the dislocation behavior, and the mechanism of lateral and collective dislocation propagation are discussed on the basis of TEM results.

  11. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    SciTech Connect

    Kushvaha, S. S. Pal, P.; Shukla, A. K.; Joshi, Amish G.; Gupta, Govind; Kumar, M.; Singh, S.; Gupta, Bipin K.; Haranath, D.

    2014-02-15

    We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 10{sup 8} cm{sup −2} at 750 °C) than that of the low temperature grown sample (1.1 × 10{sup 9} cm{sup −2} at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  12. On compensation and impurities in state-of-the-art GaN epilayers grown on sapphire

    SciTech Connect

    Wickenden, A.E.; Gaskill, D.K.; Koleske, D.D.; Doverspike, K.; Simons, D.S.; Chi, P.H.

    1996-11-01

    A comparison between 300 K electron transport data for state-of-the-art wurtzite GaN grown on sapphire substrates and corresponding theoretical calculations shows a large difference, with experimental mobility less than the predicted mobility for a given carrier concentration. The comparison seems to imply that GaN films are greatly compensated, but the discrepancy may also be due to the poorly known values of the materials parameters used in the calculations. In this work, recent analysis of transport and SIMS measurements on silicon-doped GaN films are shown to imply that the compensation, N{sub A}/N{sub D}, is less than 0.3. In addition, the determination of an activation energy of 34 meV in a GaN film doped to a level of 6 {times} 10{sup 16} cm{sup {minus}3} suggests either that a second, native donor exists in the doped films at a level of between 6 {times} 10{sup 16} cm{sup {minus}3} and 1 {times} 10{sup 17} cm{sup {minus}3}, or that the activation energy of Si in GaN is dependent on the concentration, being influenced by impurity banding or some other physical effect. GaN films grown without silicon doping are highly resistive.

  13. Effect of GaAs substrate orientation on the growth kinetic of GaN layer grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Laifi, J.; Chaaben, N.; Bouazizi, H.; Fourati, N.; Zerrouki, C.; El Gmili, Y.; Bchetnia, A.; Salvestrini, J. P.; El Jani, B.

    2016-06-01

    We have investigated the kinetic growth of low temperature GaN nucleation layers (LT-GaN) grown on GaAs substrates with different crystalline orientations. GaN nucleation layers were grown by metal organic vapor phase epitaxy (MOVPE) in a temperature range of 500-600 °C on oriented (001), (113), (112) and (111) GaAs substrates. The growth was in-situ monitored by laser reflectometry (LR). Using an optical model, including time-dependent surface roughness and growth rate profiles, simulations were performed to best approach the experimental reflectivity curves. Results are discussed and correlated with ex-situ analyses, such as atomic force microscopy (AFM) and UV-visible reflectance (SR). We show that the GaN nucleation layers growth results the formation of GaN islands whose density and size vary greatly with both growth temperature and substrate orientation. Arrhenius plots of the growth rate for each substrate give values of activation energy varying from 0.20 eV for the (001) orientation to 0.35 eV for the (113) orientation. Using cathodoluminescence (CL), we also show that high temperature (800-900 °C) GaN layers grown on top of the low temperature (550 °C) GaN nucleation layers, grown themselves on the GaAs substrates with different orientations, exhibit cubic or hexagonal phase depending on both growth temperature and substrate orientation.

  14. GaN Nanowire Devices: Fabrication and Characterization

    NASA Astrophysics Data System (ADS)

    Scott, Reum

    The development of microelectronics in the last 25 years has been characterized by an exponential increase of the bit density in integrated circuits (ICs) with time. Scaling solid-state devices improves cost, performance, and power; as such, it is of particular interest for companies, who gain a market advantage with the latest technology. As a result, the microelectronics industry has driven transistor feature size scaling from 10 μm to ~30 nm during the past 40 years. This trend has persisted for 40 years due to optimization, new processing techniques, device structures, and materials. But when noting processor speeds from the 1970's to 2009 and then again in 2010, the implication would be that the trend has ceased. To address the challenge of shrinking the integrated circuit (IC), current research is centered on identifying new materials and devices that can supplement and/or potentially supplant it. Bottom-up methods tailor nanoscale building blocks---atoms, molecules, quantum dots, and nanowires (NWs)---to be used to overcome these limitations. The Group IIIA nitrides (InN, AlN, and GaN) possess appealing properties such as a direct band gap spanning the whole solar spectrum, high saturation velocity, and high breakdown electric field. As a result nanostructures and nanodevices made from GaN and related nitrides are suitable candidates for efficient nanoscale UV/ visible light emitters, detectors, and gas sensors. To produce devices with such small structures new fabrication methods must be implemented. Devices composed of GaN nanowires were fabricated using photolithography and electron beam lithography. The IV characteristics of these devices were noted under different illuminations and the current tripled from 4.8*10-7 A to 1.59*10 -6 A under UV light which persisted for at least 5hrs.

  15. Size dictated thermal conductivity of GaN

    NASA Astrophysics Data System (ADS)

    Beechem, Thomas E.; McDonald, Anthony E.; Fuller, Elliot J.; Talin, A. Alec; Rost, Christina M.; Maria, Jon-Paul; Gaskins, John T.; Hopkins, Patrick E.; Allerman, Andrew A.

    2016-09-01

    The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3-4 μm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (1015-1018 cm-3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends—and their overall reduction relative to bulk—are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to the increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.

  16. Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods

    NASA Astrophysics Data System (ADS)

    Conroy, M.; Li, H.; Kusch, G.; Zhao, C.; Ooi, B.; Edwards, P. R.; Martin, R. W.; Holmes, J. D.; Parbrook, P. J.

    2016-05-01

    We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive X-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips' broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD's confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive X-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips' broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD

  17. Structural and luminescence properties of GaN nanowires grown using cobalt phthalocyanine as catalyst

    NASA Astrophysics Data System (ADS)

    Yadav, Shivesh; Rodríguez-Fernández, Carlos; de Lima, Mauricio M.; Cantarero, Andres; Dhar, Subhabrata

    2015-12-01

    Catalyst free methods have usually been employed to avoid any catalyst induced contamination for the synthesis of GaN nanowires with better transport and optical properties. Here, we have used a catalytic route to grow GaN nanowires, which show good optical quality. Structural and luminescence properties of GaN nanowires grown by vapor-liquid-solid technique using cobalt phthalocyanine as catalyst are systematically investigated as a function of various growth parameters such as the growth temperature and III/V ratio. The study reveals that most of the nanowires, which are several tens of microns long, grow along [ 10 1 ¯ 0 ] direction. Interestingly, the average wire diameter has been found to decrease with the increase in III/V ratio. It has also been observed that in these samples, defect related broad luminescence features, which are often present in GaN, are completely suppressed. At all temperatures, photoluminescence spectrum is found to be dominated only by a band edge feature, which comprises of free and bound excitonic transitions. Our study furthermore reveals that the bound excitonic feature is associated with excitons trapped in certain deep level defects, which result from the deficiency of nitrogen during growth. This transition has a strong coupling with the localized vibrational modes of the defects.

  18. Boiler for generating high quality vapor

    NASA Technical Reports Server (NTRS)

    Gray, V. H.; Marto, P. J.; Joslyn, A. W.

    1972-01-01

    Boiler supplies vapor for use in turbines by imparting a high angular velocity to the liquid annulus in heated rotating drum. Drum boiler provides a sharp interface between boiling liquid and vapor, thereby, inhibiting the formation of unwanted liquid droplets.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  20. Total quality management: A management philosophy for providing high quality construction

    NASA Astrophysics Data System (ADS)

    Beckwith, Paul D.

    Total Quality Management (TQM) is not a new concept. Only recently (within the past ten years or so) have American companies started to realize the potential of TQM as a means of ensuring high quality products and services. With this realization has come implementation in manufacturing and service companies. A commercial construction company, like any other business, must provide a top quality finished product to its customer if it intends to stay in business. TQM is one way to work to that end. This report explores the quality problems facing my fictitious construction company, which I believe are fairly typical among the commercial construction industry, existing management methods, and the TQM method to ensure top quality production. It will be shown why I believe TQM or a variation thereof is the best method for controlling the quality of products and service during the construction process. Under the philosophy of TQM, we build quality into the finished product.

  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. Stress related aspects of GaN technology physics

    NASA Astrophysics Data System (ADS)

    Suhir, Ephraim

    2015-03-01

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

  3. Highly Integrated Quality Assurance – An Empirical Case

    SciTech Connect

    Drake Kirkham; Amy Powell; Lucas Rich

    2011-02-01

    Highly Integrated Quality Assurance – An Empirical Case Drake Kirkham1, Amy Powell2, Lucas Rich3 1Quality Manager, Radioisotope Power Systems (RPS) Program, Idaho National Laboratory, P.O. Box 1625 M/S 6122, Idaho Falls, ID 83415-6122 2Quality Engineer, RPS Program, Idaho National Laboratory 3Quality Engineer, RPS Program, Idaho National Laboratory Contact: Voice: (208) 533-7550 Email: Drake.Kirkham@inl.gov Abstract. The Radioisotope Power Systems Program of the Idaho National Laboratory makes an empirical case for a highly integrated Quality Assurance function pertaining to the preparation, assembly, testing, storage and transportation of 238Pu fueled radioisotope thermoelectric generators. Case data represents multiple campaigns including the Pluto/New Horizons mission, the Mars Science Laboratory mission in progress, and other related projects. Traditional Quality Assurance models would attempt to reduce cost by minimizing the role of dedicated Quality Assurance personnel in favor of either functional tasking or peer-based implementations. Highly integrated Quality Assurance adds value by placing trained quality inspectors on the production floor side-by-side with nuclear facility operators to enhance team dynamics, reduce inspection wait time, and provide for immediate, independent feedback. Value is also added by maintaining dedicated Quality Engineers to provide for rapid identification and resolution of corrective action, enhanced and expedited supply chain interfaces, improved bonded storage capabilities, and technical resources for requirements management including data package development and Certificates of Inspection. A broad examination of cost-benefit indicates highly integrated Quality Assurance can reduce cost through the mitigation of risk and reducing administrative burden thereby allowing engineers to be engineers, nuclear operators to be nuclear operators, and the cross-functional team to operate more efficiently. Applicability of this case

  4. Devices for medical diagnosis with GaN lasers

    NASA Astrophysics Data System (ADS)

    Kwasny, Miroslaw; Mierczyk, Zygmunt

    2003-10-01

    This paper presents laser-induced fluroescence method (LIF) employing endogenous ("autofluroescence") and exogenous fluorophores. LIF is applied for clinical diagnosis in dermatology, gynaecology, urology, lung tumors as well as for early dentin caries. We describe the analysers with He-Ne, He-Cd, and SHG Nd:YAG lasers and new generation systems based on blue semiconductor GaN lasers that have been implemented into clinical practice till now. The LIF method, fundamental one for many medical applications, with excitation radiation of wavelength 400 nm could be appl,ied only using tunable dye lasers or titanium lasers adequte for laboratory investigations. Development of GaN laser shows possibility to design portable, compact diagnostic devices as multi-channel analysers of fluorescence spectra and surface imaging devoted to clinical application. The designed systems used for spectra measurement and registration of fluorescence images include lasers of power 5-30 mW and generate wavelengths of 405-407 nm. They are widely used in PDT method for investigation of superficial distribution of accumulation kinetics of all known photosensitizers, their elimination, and degradation as well as for treatment of superficial lesions of mucosa and skin. Excitation of exogenous porphrins in Soret band makes possible to estimate their concentration and a period of healthy skin photosensitivity that occurs after photosensitiser injections. Due to high sensitivity of spectrum analysers, properties of photosensitisers can be investigated in vitro (e.g. their aggregation, purity, chromatographic distributions) when their concentrations are 2-3 times lower in comparison to concentrations investigated with typical spectrofluorescence methods. Dentistry diagnosis is a new field in which GaN laser devices can be applied. After induction with blue light, decreased autofluorescence intensity can be observed when dentin caries occur and strong characteristic bands of endogenous porphyrines

  5. Can high quality cane be delivered to the mill economically

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cane quality is becoming increasingly important to the Louisiana sugarcane industry, with some processors offering premiums for high quality cane. Using a Cameco® 3500, we tested ground speeds of 2.5, 3.0, and 3.5 mph and fan speeds of 650, 850, and 1050 rpm. Ground speed had no effect on can...

  6. Reliability of AlGaN/GaN high electron mobility transistors on low dislocation density bulk GaN substrate: Implications of surface step edges

    SciTech Connect

    Killat, N. E-mail: Martin.Kuball@bristol.ac.uk; Montes Bajo, M.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk; Paskova, T.; Evans, K. R.; Leach, J.; Li, X.; Özgür, Ü.; Morkoç, H.; Chabak, K. D.; Crespo, A.; Gillespie, J. K.; Fitch, R.; Kossler, M.; Walker, D. E.; Trejo, M.; Via, G. D.; Blevins, J. D.

    2013-11-04

    To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gate leakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths. Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges of surface steps.

  7. High quality transparent conducting oxide thin films

    DOEpatents

    Gessert, Timothy A.; Duenow, Joel N.; Barnes, Teresa; Coutts, Timothy J.

    2012-08-28

    A transparent conducting oxide (TCO) film comprising: a TCO layer, and dopants selected from the elements consisting of Vanadium, Molybdenum, Tantalum, Niobium, Antimony, Titanium, Zirconium, and Hafnium, wherein the elements are n-type dopants; and wherein the transparent conducting oxide is characterized by an improved electron mobility of about 42 cm.sup.2/V-sec while simultaneously maintaining a high carrier density of .about.4.4e.times.10.sup.20 cm.sup.-3.

  8. Transmission electron microscopy study of microstructural properties and dislocation characterization in the GaN film grown on the cone-shaped patterned Al2O3 substrate.

    PubMed

    Park, Jung Sik; Yang, Jun-Mo; Park, Kyung Jin; Park, Yun Chang; Yoo, Jung Ho; Jeong, Chil Seong; Park, Jucheol; He, Yinsheng; Shin, Keesam

    2014-02-01

    Growing a GaN film on a patterned Al2O3 substrate is one of the methods of reducing threading dislocations (TDs), which can significantly deteriorate the performance of GaN-based LEDs. In this study, the microstructural details of the GaN film grown on a cone-shaped patterned Al2O3 substrate were investigated using high-resolution transmission electron microscopy and weak-beam dark-field techniques. Various defects such as misfit dislocations (MDs), recrystallized GaN (R-GaN) islands and nano-voids were observed on the patterned Al2O3 surfaces, i.e. the flat surface (FS), the inclined surface (IS) and the top surface (TS), respectively. Especially, the crystallographic orientation of R-GaN between the GaN film and the inclined Al2O3 substrate was identified as $[\\overline 1 2\\overline 1 0]_{{\\rm GaN}} \\hbox{//}[\\overline 1 101]_{{\\rm R - GaN} \\,{\\rm on}\\,{\\rm IS}} \\hbox{//}[\\overline 1 100]_{ {{\\rm Al}} _{\\rm 2} {\\rm O}_{\\rm 3}} $, $(\\overline 1 012)_{{\\rm GaN}} \\hbox{//}(1\\overline 1 02)_{{\\rm R - Ga}\\,{\\rm Non}\\,{\\rm IS}} \\hbox{//}(\\overline {11} 26)_{ {{\\rm Al}} _{\\rm 2} {\\rm O}_{\\rm 3}} $. In addition, a rotation by 9° between $(10\\overline 1 1)_{{\\rm R - GaN}} $ and $(0002)_{{\\rm GaN}} $ and between $(10\\overline 1 1)_{{\\rm R - GaN}} $ and $(0006)_{ {{\\rm Al}} _{\\rm 2} {\\rm O}_{\\rm 3}} $ was found to reduce the lattice mismatch between the GaN film and the Al2O3 substrate. Many TDs in the GaN film were observed on the FS and TS of Al2O3. However, few TDs were observed on the IS. Most of the TDs generated from the FS of Al2O3 were bent to the inclined facet rather than propagating to the GaN surface, resulting in a reduction in the dislocation density. Most of the TDs generated from the TS of Al2O3 were characterized as edge dislocations.

  9. Fabrication of high quality ferromagnetic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Weides, M.; Tillmann, K.; Kohlstedt, H.

    2006-05-01

    We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized regarding junction insulation and homogeneity of current transport. Using ion-beam-etching and anodic oxidation we defined and insulated the junction mesas. The additional 2 nm thin Cu-layer below the ferromagnetic NiCu (SINFS) lowered interface roughness and ensured very homogeneous current transport. A high yield of junctional devices with jc spreads less than 2% was obtained.

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

    PubMed

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

    2015-12-15

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

  11. Management of data quality of high level waste characterization

    SciTech Connect

    Winters, W.I., Westinghouse Hanford

    1996-06-12

    Over the past 10 years, the Hanford Site has been transitioning from nuclear materials production to Site cleanup operations. High-level waste characterization at the Hanford Site provides data to support present waste processing operations, tank safety programs, and future waste disposal programs. Quality elements in the high-level waste characterization program will be presented by following a sample through the data quality objective, sampling, laboratory analysis and data review process. Transition from production to cleanup has resulted in changes in quality systems and program; the changes, as well as other issues in these quality programs, will be described. Laboratory assessment through quality control and performance evaluation programs will be described, and data assessments in the laboratory and final reporting in the tank characterization reports will be discussed.

  12. Multicolor, High Efficiency, Nanotextured LEDs

    SciTech Connect

    Jung Han; Arto Nurmikko

    2011-09-30

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and green for Solid State Lighting applications. Accomplishments in the duration of the contract period include (i) heteroepitaxy of nitrogen-polar LEDs on sapphire, (ii) heteroepitaxy of semipolar (11{bar 2}2) green LEDs on sapphire, (iii) synthesis of quantum-dot loaded nanoporous GaN that emits white light without phosphor conversion, (iv) demonstration of the highest quality semipolar (11{bar 2}2) GaN on sapphire using orientation-controlled epitaxy, (v) synthesis of nanoscale GaN and InGaN medium, and (vi) development of a novel liftoff process for manufacturing GaN thin-film vertical LEDs. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  13. Selective-area growth of GaN microrods on strain-induced templates by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Lekhal, Kaddour; Bae, Si-Young; Lee, Ho-Jun; Mitsunari, Tadashi; Tamura, Akira; Deki, Manato; Honda, Yoshio; Amano, Hiroshi

    2016-05-01

    In this paper, we discuss the influence of parameters such as type of carrier gas and NH3/HCl flow ratio on the growth of vertical GaN microstructures by selective-area growth (SAG) hydride vapor phase epitaxy (HVPE). On various strain-induced templates such as GaN/sapphire, GaN/Si, and AlN/Si, regular arrays of Ga-polar GaN microrods were properly achieved by adjusting the growth parameters. The photoluminescence and micro-Raman measurements reveal not only the crystal quality of the GaN microrods but also strain distribution. These results will give insight into the control of the morphology of GaN microrods in terms of the strain induced from templates in SAG-HVPE. The precisely controlled arrays of GaN microrods can be used for next-generation light-emitting diodes (LEDs) by realizing InGaN/GaN multi-quantum wells (MQWs) with a radial structure.

  14. Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications.

    PubMed

    Mitchell, B; Timmerman, D; Poplawsky, J; Zhu, W; Lee, D; Wakamatsu, R; Takatsu, J; Matsuda, M; Guo, W; Lorenz, K; Alves, E; Koizumi, A; Dierolf, V; Fujiwara, Y

    2016-01-01

    The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform. PMID:26725651

  15. Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications

    DOE PAGES

    Mitchell, Brandon; Timmerman, D.; Poplawsky, Jonathan D.; Zhu, W.; Lee, D.; Wakamatsu, R.; Takatsu, J.; Matsuda, M.; Guo, Wei; Lorenz, K.; et al

    2016-01-04

    The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions thatmore » were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. Furthermore, these findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.« less

  16. Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications

    PubMed Central

    Mitchell, B.; Timmerman, D.; Poplawsky, J.; Zhu, W.; Lee, D.; Wakamatsu, R.; Takatsu, J.; Matsuda, M.; Guo, W.; Lorenz, K.; Alves, E.; Koizumi, A.; Dierolf, V.; Fujiwara, Y.

    2016-01-01

    The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform. PMID:26725651

  17. Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications.

    PubMed

    Mitchell, B; Timmerman, D; Poplawsky, J; Zhu, W; Lee, D; Wakamatsu, R; Takatsu, J; Matsuda, M; Guo, W; Lorenz, K; Alves, E; Koizumi, A; Dierolf, V; Fujiwara, Y

    2016-01-04

    The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.

  18. Si Donor Incorporation in GaN Nanowires.

    PubMed

    Fang, Zhihua; Robin, Eric; Rozas-Jiménez, Elena; Cros, Ana; Donatini, Fabrice; Mollard, Nicolas; Pernot, Julien; Daudin, Bruno

    2015-10-14

    With increasing interest in GaN based devices, the control and evaluation of doping are becoming more and more important. We have studied the structural and electrical properties of a series of Si-doped GaN nanowires (NWs) grown by molecular beam epitaxy (MBE) with a typical dimension of 2-3 μm in length and 20-200 nm in radius. In particular, high resolution energy dispersive X-ray spectroscopy (EDX) has illustrated a higher Si incorporation in NWs than that in two-dimensional (2D) layers and Si segregation at the edge of the NW with the highest doping. Moreover, direct transport measurements on single NWs have shown a controlled doping with resistivity from 10(2) to 10(-3) Ω·cm, and a carrier concentration from 10(17) to 10(20) cm(-3). Field effect transistor (FET) measurements combined with finite element simulation by NextNano(3) software have put in evidence the high mobility of carriers in the nonintentionally doped (NID) NWs. PMID:26426262

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

    SciTech Connect

    Gangopadhyay, Subhashis; Schmidt, Thomas Kruse, Carsten; Figge, Stephan; Hommel, Detlef; Falta, Jens

    2014-09-01

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

  20. Rode's iterative calculation of surface optical phonon scattering limited electron mobility in N-polar GaN devices

    SciTech Connect

    Ghosh, Krishnendu Singisetti, Uttam

    2015-02-14

    N-polar GaN channel mobility is important for high frequency device applications. Here, we report theoretical calculations on the surface optical (SO) phonon scattering rate of two-dimensional electron gas (2DEG) in N-polar GaN quantum well channels with high-k dielectrics. Rode's iterative calculation is used to predict the scattering rate and mobility. Coupling of the GaN plasmon modes with the SO modes is taken into account and dynamic screening is employed under linear polarization response. The effect of SO phonons on 2DEG mobility was found to be small at >5 nm channel thickness. However, the SO mobility in 3 nm N-polar GaN channels with HfO{sub 2} and ZrO{sub 2} high-k dielectrics is low and limits the total mobility. The SO scattering for SiN dielectric on GaN was found to be negligible due to its high SO phonon energy. Using Al{sub 2}O{sub 3}, the SO phonon scattering does not affect mobility significantly only except the case when the channel is too thin with a low 2DEG density.

  1. Growth of high quality and uniformity AlGaN/GaN heterostructures on Si substrates using a single AlGaN layer with low Al composition

    NASA Astrophysics Data System (ADS)

    Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Zhang, Jie; Wang, Jiaming; He, Chenguang; Zhang, Lisheng; Wang, Maojun; Xu, Fujun; Tang, Ning; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-03-01

    By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm2/Vs with an electron density of 9.3 × 1012 cm‑2. The sheet resistance is 313 ± 4 Ω/◻ with ±1.3% variation. The high uniformity is attributed to the reduced wafer bow resulting from the balance of the compressive stress induced and consumed during the growth, and the thermal tensile stress induced during the cooling down process. By a combination of theoretical calculations and in situ wafer curvature measurements, we find that the compressive stress consumed by the dislocation relaxation (~1.2 GPa) is comparable to the value of the thermal tensile stress (~1.4 GPa) and we should pay more attention to it during growth of GaN on Si substrates. Our results demonstrate a promising approach to simplifying the growth processes of GaN-on-Si to reduce the wafer bow and lower the cost while maintaining high material quality.

  2. Growth of high quality and uniformity AlGaN/GaN heterostructures on Si substrates using a single AlGaN layer with low Al composition

    PubMed Central

    Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Zhang, Jie; Wang, Jiaming; He, Chenguang; Zhang, Lisheng; Wang, Maojun; Xu, Fujun; Tang, Ning; Qin, Zhixin; Wang, Xinqiang; Shen, Bo

    2016-01-01

    By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm2/Vs with an electron density of 9.3 × 1012 cm−2. The sheet resistance is 313 ± 4 Ω/◻ with ±1.3% variation. The high uniformity is attributed to the reduced wafer bow resulting from the balance of the compressive stress induced and consumed during the growth, and the thermal tensile stress induced during the cooling down process. By a combination of theoretical calculations and in situ wafer curvature measurements, we find that the compressive stress consumed by the dislocation relaxation (~1.2 GPa) is comparable to the value of the thermal tensile stress (~1.4 GPa) and we should pay more attention to it during growth of GaN on Si substrates. Our results demonstrate a promising approach to simplifying the growth processes of GaN-on-Si to reduce the wafer bow and lower the cost while maintaining high material quality. PMID:26960730

  3. Size dictated thermal conductivity of GaN

    DOE PAGES

    Thomas Edwin Beechem; McDonald, Anthony E.; Fuller, Elliot James; Talin, Albert Alec; Rost, Christina M.; Maria, Jon -Paul; Gaskins, John T.; Hopkins, Patrick E.; Allerman, Andrew A.

    2016-04-01

    The thermal conductivity on n- and p-type doped gallium nitride (GaN) epilayers having thickness of 3-4 μm was investigated using time domain thermoreflectance (TDTR). Despite possessing carrier concentrations ranging across 3 decades (1015 – 1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends–and their overall reduction relative to bulk–are explained leveraging established scattering models where it is shown that size effects play a primary role in limiting thermal conductivity for layers even tens of microns thick. GaNmore » device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness.« less

  4. Nanoscale anisotropic plastic deformation in single crystal GaN.

    PubMed

    Huang, Jun; Xu, Ke; Fan, Ying Min; Niu, Mu Tong; Zeng, Xiong Hui; Wang, Jian Feng; Yang, Hui

    2012-01-01

    Elasto-plastic mechanical deformation behaviors of c-plane (0001) and nonpolar GaN single crystals are studied using nanoindentation, cathodoluminescence, and transmission electron microscopy. Nanoindentation tests show that c-plane GaN is less susceptible to plastic deformation and has higher hardness and Young's modulus than the nonpolar GaN. Cathodoluminescence and transmission electron microscopy characterizations of indent-induced plastic deformation reveal that there are two primary slip systems for the c-plane GaN, while there is only one most favorable slip system for the nonplane GaN. We suggest that the anisotropic elasto-plastic mechanical properties of GaN are relative to its anisotropic plastic deformation behavior.PACS: 62.20.fq; 81.05.Ea; 61.72.Lk.

  5. High quality factor, fully switchable terahertz superconducting metasurface

    SciTech Connect

    Scalari, G. Maissen, C.; Faist, J.; Cibella, S.; Leoni, R.

    2014-12-29

    We present a complementary THz metasurface realised with Niobium thin film which displays a quality factor Q = 54 and a fully switchable behaviour as a function of the temperature. The switching behaviour and the high quality factor are due to a careful design of the metasurface aimed at maximising the ohmic losses when the Nb is above the critical temperature and minimising the radiative coupling. The superconductor allows the operation of the cavity with high Q and the use of inductive elements with a high aspect ratio. Comparison with three dimensional finite element simulations highlights the crucial role of the inductive elements and of the kinetic inductance of the Cooper pairs in achieving the high quality factor and the high field enhancement.

  6. Concrete Waste Recycling Process for High Quality Aggregate

    SciTech Connect

    Ishikura, Takeshi; Fujii, Shin-ichi

    2008-01-15

    Large amount of concrete waste generates during nuclear power plant (NPP) dismantling. Non-contaminated concrete waste is assumed to be disposed in a landfill site, but that will not be the solution especially in the future, because of decreasing tendency of the site availability and natural resources. Concerning concrete recycling, demand for roadbeds and backfill tends to be less than the amount of dismantled concrete generated in a single rural site, and conventional recycled aggregate is limited of its use to non-structural concrete, because of its inferior quality to ordinary natural aggregate. Therefore, it is vital to develop high quality recycled aggregate for general uses of dismantled concrete. If recycled aggregate is available for high structural concrete, the dismantling concrete is recyclable as aggregate for industry including nuclear field. Authors developed techniques on high quality aggregate reclamation for large amount of concrete generated during NPP decommissioning. Concrete of NPP buildings has good features for recycling aggregate; large quantity of high quality aggregate from same origin, record keeping of the aggregate origin, and little impurities in dismantled concrete such as wood and plastics. The target of recycled aggregate in this development is to meet the quality criteria for NPP concrete as prescribed in JASS 5N 'Specification for Nuclear Power Facility Reinforced Concrete' and JASS 5 'Specification for Reinforced Concrete Work'. The target of recycled aggregate concrete is to be comparable performance with ordinary aggregate concrete. The high quality recycled aggregate production techniques are assumed to apply for recycling for large amount of non-contaminated concrete. These techniques can also be applied for slightly contaminated concrete dismantled from radiological control area (RCA), together with free release survey. In conclusion: a technology on dismantled concrete recycling for high quality aggregate was developed

  7. 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.

  8. U.S. Department of Energy, National Energy Technology Laboratory Solid-State Lighting Core Technologies Light Emitting Diodes on Semipolar Bulk GaN Substrate with IQE > 80% at 150 A/cm2 and 100 0C

    SciTech Connect

    Chakraborty, Arpan; David, Aurelien; Grundmann, Michael; Tyagi, Anurag; Craven, Michael; Hurni, Christophe; Cich, Michael

    2015-03-31

    GaN is a crucial material for light-emitting diodes (LEDs) emitting in the violet-to-green range. Despite its good performance, it still suffers from significant technical limitations. In particular, the efficiency of GaN-based LEDs decreases at high current (“current droop”) and high temperature (“temperature droop”). This is problematic in some lighting applications, where a high-power operation is required. This program studied the use of particular substrates to improve the efficiency of GaN-based LEDs: bulk semipolar (SP) GaN substrates. These substrates possess a very high material quality, and physical properties which are distinctly different from legacy substrates currently used in the LED industry. The program focused on the development of accurate metrology to quantify the performance of GaN-based LEDs, and on improvement to LED quality and design on SP substrates. Through a thorough optimization process, we demonstrated violet LEDs with very high internal quantum efficiency, exceeding 85% at high temperature and high current. We also investigated longer-wavelength blue emitters, but found that the limited strain budget was a key limitation.

  9. 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.

  10. Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

    SciTech Connect

    Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep

    2013-01-28

    We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

  11. Thermal boundary conductance between Al films and GaN nanowires investigated with molecular dynamics.

    PubMed

    Zhou, Xiao-Wang; Jones, Reese E; Hopkins, Patrick E; Beechem, Thomas E

    2014-05-28

    GaN nanowires are being pursued for optoelectronic and high-power applications. In either use, increases in operating temperature reduce both performance and reliability making it imperative to minimize thermal resistances. Since interfaces significantly influence the thermal response of nanosystems, the thermal boundary resistance between GaN nanowires and metal contacts has major significance. In response, we have performed systematic molecular dynamics simulations to study the thermal boundary conductance between GaN nanowires and Al films as a function of nanowire dimensions, packing density, and the depth the nanowire is embedded into the metal contact. At low packing densities, the apparent Kapitza conductance between GaN nanowires and an aluminum film is shown to be larger than when contact is made between films of these same materials. This enhancement decreases toward the film-film limit, however, as the packing density increases. For densely packed nanowires, maximizing the Kapitza conductance can be achieved by embedding the nanowires into the films, as the conductance is found to be proportional to the total contact area.

  12. GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium

    SciTech Connect

    Bartram, Michael E.; Creighton, J. Randall

    1999-05-26

    Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

  13. Epitaxial GaN films by hyperthermal ion-beam nitridation of Ga droplets

    SciTech Connect

    Gerlach, J. W.; Ivanov, T.; Neumann, L.; Hoeche, Th.; Hirsch, D.; Rauschenbach, B.

    2012-06-01

    Epitaxial GaN film formation on bare 6H-SiC(0001) substrates via the process of transformation of Ga droplets into a thin GaN film by applying hyperthermal nitrogen ions is investigated. Pre-deposited Ga atoms in well defined amounts form large droplets on the substrate surface which are subsequently nitridated at a substrate temperature of 630 Degree-Sign C by a low-energy nitrogen ion beam from a constricted glow-discharge ion source. The Ga deposition and ion-beam nitridation process steps are monitored in situ by reflection high-energy electron diffraction. Ex situ characterization by x-ray diffraction and reflectivity techniques, Rutherford backscattering spectrometry, and electron microscopy shows that the thickness of the resulting GaN films depends on the various amounts of pre-deposited gallium. The films are epitaxial to the substrate, exhibit a mosaic like, smooth surface topography and consist of coalesced large domains of low defect density. Possible transport mechanisms of reactive nitrogen species during hyperthermal nitridation are discussed and the formation of GaN films by an ion-beam assisted process is explained.

  14. GaN nano-pyramid arrays as an efficient photoelectrode for solar water splitting

    NASA Astrophysics Data System (ADS)

    Hou, Y.; Yu, X.; Syed, Z. Ahmed; Shen, S.; Bai, J.; Wang, T.

    2016-11-01

    A prototype photoelectrode has been fabricated using a GaN nano-pyramid array structure grown on a cost-effective Si (111) substrate, demonstrating a significant improvement in performance of solar-powered water splitting compared with any planar GaN photoelectrode. Such a nano-pyramid structure leads to enhanced optical absorption as a result of a multi-scattering process which can effectively produce a reduction in reflectance. A simulation based on a finite-difference time-domain approach indicates that the nano-pyramid architecture enables incident light to be concentrated within the nano-pyramids as a result of micro-cavity effects, further enhancing optical absorption. Furthermore, the shape of the nano-pyramid further facilitates the photo-generated carrier transportation by enhancing a hole-transfer efficiency. All these features as a result of the nano-pyramid configuration lead to a large photocurrent of 1 mA cm‑2 under an illumination density of 200 mW cm‑2, with a peak incident photon-to-current conversion efficiency of 46.5% at ∼365 nm, around the band edge emission wavelength of GaN. The results presented are expected to pave the way for the fabrication of GaN based photoelectrodes with a high energy conversion efficiency of solar powered water splitting.

  15. Self-catalyzed anisotropic growth of GaN spirals

    NASA Astrophysics Data System (ADS)

    Patsha, Avinash; Sahoo, Prasana; Dhara, S.; Tyagi, A. K.

    2012-06-01

    GaN spirals with homogeneous size are grown using chemical-vapor-deposition technique in a self catalytic process. Raman and photoluminescence (PL) studies reveal wurtzite GaN phase. Nucleation of GaN sphere takes place with the agglomeration Ga clusters and simultaneous reaction with NH3. A growth mechanism involving diffusion limited aggregation process initiating supersaturation and subsequent neck formation along with possible role of thermodynamic fluctuation in different crystalline facets of GaN, is described for the anisotropic spiral structures. Temperature dependent PL spectra show strong excitonic emissions along with the presence of free-to-bound transition.

  16. Later Leaders in Education: Roma Gans--Teacher of Teachers.

    ERIC Educational Resources Information Center

    Almy, Millie

    1990-01-01

    Retired teacher Roma Gans is described in terms of her early life and education, early teaching experience, teaching experience at Teachers College, publishing experience, citizenship, and retirement. (DG)

  17. Realization of high quality production schedules: Structuring quality factors via iteration of user specification processes

    NASA Technical Reports Server (NTRS)

    Hamazaki, Takashi

    1992-01-01

    This paper describes an architecture for realizing high quality production schedules. Although quality is one of the most important aspects of production scheduling, it is difficult, even for a user, to specify precisely. However, it is also true that the decision as to whether a scheduler is good or bad can only be made by the user. This paper proposes the following: (1) the quality of a schedule can be represented in the form of quality factors, i.e. constraints and objectives of the domain, and their structure; (2) quality factors and their structure can be used for decision making at local decision points during the scheduling process; and (3) that they can be defined via iteration of user specification processes.

  18. A Procedure for High Resolution Satellite Imagery Quality Assessment

    PubMed Central

    Crespi, Mattia; De Vendictis, Laura

    2009-01-01

    Data products generated from High Resolution Satellite Imagery (HRSI) are routinely evaluated during the so-called in-orbit test period, in order to verify if their quality fits the desired features and, if necessary, to obtain the image correction parameters to be used at the ground processing center. Nevertheless, it is often useful to have tools to evaluate image quality also at the final user level. Image quality is defined by some parameters, such as the radiometric resolution and its accuracy, represented by the noise level, and the geometric resolution and sharpness, described by the Modulation Transfer Function (MTF). This paper proposes a procedure to evaluate these image quality parameters; the procedure was implemented in a suitable software and tested on high resolution imagery acquired by the QuickBird, WorldView-1 and Cartosat-1 satellites. PMID:22412312

  19. Quality of life and the high-dependency unit.

    PubMed

    Brooks, N

    2000-02-01

    This study was designed to identify and measure the patients' perspective of the concept quality of life within the context of a high-dependency unit (HDU). Data were collected in two phases. In phase one, 55 patients were interviewed, which resulted in the concept clarification of quality of life as: physical, social, psychological and family/friends. In phase two, 51 patients undertook quality-of-life assessment using validated instruments the Quality of Life Index (Ferrans & Powers 1985) and the Global Quality of Life Scale (Hyland & Sodergren 1997). Post-HDU patients demonstrated improvements upon pre-admission scores in both instruments (the social domain in the quality of life index being the exception), although this only reached statistical significance P<0.05 in the overall index score and within the domains of health and family. When exploring variables of age and severity of illness (Apache 2 score, Knaus et al. 1980) it was the people who were older and physiologically compromised to an increased extent (P<0.05) who demonstrated higher levels of satisfaction with their resulting quality of life. This study has been successful in providing patients with an opportunity to participate more actively in service evaluation and has identified the need for future evaluation of HDUs to move beyond physiological measures, to incorporate the impact that illness leading to admission to an HDU has upon the patients' ability to function and their resulting quality of life. PMID:10790712

  20. Developing Visions of High-Quality Mathematics Instruction

    ERIC Educational Resources Information Center

    Munter, Charles

    2014-01-01

    This article introduces an interview-based instrument that was created for the purposes of characterizing the visions of high-quality mathematics instruction of teachers, principals, mathematics coaches, and district leaders and tracking changes in those visions over time. The instrument models trajectories of perceptions of high-quality…

  1. Process to Continuously Melt, Refine and Cast High Quality Steel

    SciTech Connect

    2005-09-01

    The purpose of this project is to conduct research and development targeted at designing a revolutionary steelmaking process. This process will deliver high quality steel from scrap to the casting mold in one continuous process and will be safer, more productive, and less capital intensive to build and operate than conventional steelmaking. The new process will produce higher quality steel faster than traditional batch processes while consuming less energy and other resources.

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

    NASA Astrophysics Data System (ADS)

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

    2001-11-01

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

  3. Growth and analysis of GaN nanowire on PZnO by different-gas flow

    NASA Astrophysics Data System (ADS)

    Shekari, L.; Hassan, H. Abu; Thahab, S. M.; Ghazai, A. J.; Hassan, Z.

    2012-06-01

    In this research we have used an inexpensive method to fabricate highly crystalline GaN nanowires (NWs) on porous zinc oxide (PZnO) on Si (1 1 1) wafer by thermal evaporation using commercial GaN powder, either in argon (Ar) gas atmosphere or a combination of Ar and nitrogen (N2) gas atmosphere without any catalyst. Micro structural studies by scanning electron microscopy (SEM) and transmission electron microscope (TEM) measurements reveal the role of different gas flowing, in the nucleation and alignment of the GaN NWs. The GaN NWs different diameters ranging between 50 and 200 nm for the NWs grown under flow of mix gases, but the NWs which were grown under Ar gas only, have uniform diameter of around 50-60 nm, also their lengths are almost the same (around 10 μm). Further structural and optical characterizations were performed using high resolution X-ray diffraction (HR-XRD), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL) spectroscopy. Results indicated that the NWs are of single-crystal hexagonal GaN with [0 0 0 1] and [1 0 1¯ 1] growth directions for NWs grown under Ar and mixed gas flow.

  4. 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.

  5. Growth of p-type and n-type m-plane GaN by molecular beam epitaxy

    SciTech Connect

    McLaurin, M.; Mates, T. E.; Wu, F.; Speck, J. S.

    2006-09-15

    Plasma-assisted molecular beam epitaxial growth of Mg-doped, p-type and Si-doped, n-type m-plane GaN on 6H m-plane SiC is demonstrated. Phase-pure, m-plane GaN films exhibiting a large anisotropy in film mosaic ({approx}0.2 deg. full width at half maximum, x-ray rocking curve scan taken parallel to [1120] versus {approx}2 deg. parallel to [0001]) were grown on m-plane SiC substrates. Maximum hole concentrations of {approx}7x10{sup 18} cm{sup -3} were achieved with p-type conductivities as high as {approx}5 {omega}{sup -1} cm{sup -1} without the presence of Mg-rich inclusions or inversion domains as viewed by cross-section transmission electron microscopy. Temperature dependent Hall effect measurements indicate that the Mg-related acceptor state in m-plane GaN is the same as that exhibited in c-plane GaN. Free electron concentrations as high as {approx}4x10{sup 18} cm{sup -3} were measured in the Si-doped m-plane GaN with corresponding mobilities of {approx}500 cm{sup 2}/V s measured parallel to the [1120] direction.

  6. Hydride VPE: the unexpected process for the fast growth of GaAs and GaN nanowires with record aspect ratio and polytypism-free crystalline structure

    NASA Astrophysics Data System (ADS)

    André, Yamina; Trassoudaine, Agnès.; Avit, Geoffrey; Lekhal, Kaddour; Ramdani, Mohammed R.; Leroux, Christine; Monier, Guillaume; Varenne, Christelle; Hoggan, Philip; Castelluci, Dominique; Bougerol, Catherine; Réveret, François; Leymarie, Joël.; Petit, Elodie; Dubrovskii, Vladimir G.; Gil, Evelyne

    2013-12-01

    Hydride Vapor Phase Epitaxy (HVPE) makes use of chloride III-Cl and hydride V-H3 gaseous growth precursors. It is known as a near-equilibrium process, providing the widest range of growth rates from 1 to more than 100 μm/h. When it comes to metal catalyst-assisted VLS (vapor-liquid-solid) growth, the physics of HVPE growth is maintained: high dechlorination frequency, high axial growth rate of nanowires (NWs) up to 170 μm/h. The remarkable features of NWs grown by HVPE are the untapered morphology with constant diameter and the stacking fault-free crystalline phase. Record pure zinc blende cubic phase for 20 μm long GaAs NWs with radii of 10 and 5 nm is shown. The absence of wurtzite phase in GaAs NWs grown by HVPE whatever the diameter is discussed with respect to surface energetic grounds and kinetics. Ni assisted, Ni-Au assisted and catalyst-free HVPE growth of wurtzite GaN NWs is also addressed. Micro-photoluminescence spectroscopy analysis revealed GaN nanowires of great optical quality, with a FWHM of 1 meV at 10 K for the neutral donor bound exciton transition.

  7. Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods.

    PubMed

    Conroy, M; Li, H; Kusch, G; Zhao, C; Ooi, B; Edwards, P R; Martin, R W; Holmes, J D; Parbrook, P J

    2016-06-01

    We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive X-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips' broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD's confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates. PMID:27174084

  8. Dislocation filtering in GaN nanostructures.

    PubMed

    Colby, Robert; Liang, Zhiwen; Wildeson, Isaac H; Ewoldt, David A; Sands, Timothy D; García, R Edwin; Stach, Eric A

    2010-05-12

    Dislocation filtering in GaN by selective area growth through a nanoporous template is examined both by transmission electron microscopy and numerical modeling. These nanorods grow epitaxially from the (0001)-oriented GaN underlayer through the approximately 100 nm thick template and naturally terminate with hexagonal pyramid-shaped caps. It is demonstrated that for a certain window of geometric parameters a threading dislocation growing within a GaN nanorod is likely to be excluded by the strong image forces of the nearby free surfaces. Approximately 3000 nanorods were examined in cross-section, including growth through 50 and 80 nm diameter pores. The very few threading dislocations not filtered by the template turn toward a free surface within the nanorod, exiting less than 50 nm past the base of the template. The potential active region for light-emitting diode devices based on these nanorods would have been entirely free of threading dislocations for all samples examined. A greater than 2 orders of magnitude reduction in threading dislocation density can be surmised from a data set of this size. A finite element-based implementation of the eigenstrain model was employed to corroborate the experimentally observed data and examine a larger range of potential nanorod geometries, providing a simple map of the different regimes of dislocation filtering for this class of GaN nanorods. These results indicate that nanostructured semiconductor materials are effective at eliminating deleterious extended defects, as necessary to enhance the optoelectronic performance and device lifetimes compared to conventional planar heterostructures. PMID:20397703

  9. GaN Based Electronics And Their Applications

    NASA Astrophysics Data System (ADS)

    Ren, Fan

    2002-03-01

    The Group III-nitrides were initially researched for their promise to fill the void for a blue solid state light emitter. Electronic devices from III-nitrides have been a more recent phenomenon. The thermal conductivity of GaN is three times that of GaAs. For high power or high temperature applications, good thermal conductivity is imperative for heat removal or sustained operation at elevated temperatures. The development of III-N and other wide bandgap technologies for high temperature applications will likely take place at the expense of competing technologies, such as silicon-on-insulator (SOI), at moderate temperatures. At higher temperatures (>300°C), novel devices and components will become possible. The automotive industry will likely be one of the largest markets for such high temperature electronics. One of the most noteworthy advantages for III-N materials over other wide bandgap semiconductors is the availability of AlGaN/GaN and InGaN/GaN heterostructures. A 2-dimensional electron gas (2DEG) has been shown to exist at the AlGaN/GaN interface, and heterostructure field effect transistors (HFETs) from these materials can exhibit 2DEG mobilities approaching 2000 cm2 / V?s at 300K. Power handling capabilities of 12 W/mm appear feasible, and extraordinary large signal performance has already been demonstrated, with a current state-of-the-art of >10W/mm at X-band. In this talk, high speed and high temperature AlGaN/GaN HEMTs as well as MOSHEMTs, high breakdown voltage GaN (>6KV) and AlGaN (9.7 KV) Schottky diodes, and their applications will be presented.

  10. Quality of service on high-speed data networks

    NASA Astrophysics Data System (ADS)

    Barbero, Ezio; Antonelli, Ferruccio

    1995-02-01

    Since the beginning of this century the issue of `quality' has been gaining increasing importance in a number of fields of human activities. For telecommunication services, too, the quality perceived by customers has been taken into account early on as an issue of strategic importance. Whilst for telephony the Quality of Service (QoS) has been already investigated and identified in terms of parameters and related test methodology, the situation for high speed data services (i.e. CBDS/SMDS, Frame Relay, etc.), provided by means of high speed network based on Asynchronous Transfer Moe (ATM) or Metropolitan Area Network technologies, can still be considered `under study'. There is a death of experience not only in terms of measurement instruments and procedures, but also in terms of knowledge of the relationship between the QoS provided at a network level and the quality perceived by the user on his or her terminal. The complexity of the equipment involved in setting up an end-to-end solution based on high speed data communications makes the problems of knowledge and supply of quality very hard to solve. Starting from the experience gained in carrying out high- speed network field trials based on Metropolitan Area Networks and, more recently, on ATM technology, the paper mainly deals with the problem of defining, measuring and then offering a specific QoS. First, the issue of what the user expects from the `high-speed network' is addressed. This analysis is carried out trying to gather what is peculiar to high-speed data communications from the user standpoint. Next, the focus is on how to cope with the requirements due to users' expectations, while carefully considering the basic principles of quality. Finally, a solution is proposed, starting from the experience gained from high speed networks installed in Italy.

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

    PubMed

    Kishino, Katsumi; Ishizawa, Shunsuke

    2015-06-01

    The growth of highly uniform arrays of GaN nanocolumns with diameters from 122 to 430 nm on Si (111) substrates was demonstrated. The employment of GaN film templates with flat surfaces (root mean square surface roughness of 0.84 nm), which were obtained using an AlN/GaN superlattice (SL) buffer on Si, contributed to the high-quality selective-area growth of nanocolumns using a thin Ti mask of 5 nm thickness by rf-plasma-assisted molecular beam epitaxy. Although the GaN template included a large number of dislocations (dislocation density ∼10(11) cm(-2)), the dislocation filtering effect of nanocolumns was enhanced with decreasing nanocolumn diameters (D). Systematic transmission electron microscopy (TEM) observation enabled us to explain the dependence of the dislocation propagation behavior in nanocolumns on the nanocolumn diameter for the first time. Plan-view TEM analysis was performed for nanocolumns with D = 120-324 nm by slicing the nanocolumns horizontally at a height of ∼300 nm above their bottoms and dislocation propagation through the nanocolumns was analyzed by the cross-sectional TEM observation of nanocolumns with D ∼ 200 nm. It was clarified that dislocations were effectively filtered in the bottom 300 nm region of the nanocolumns, the dislocation density of the nanocolumns decreased with decreasing D, and for narrow nanocolumns with D < 200 nm, dislocation-free crystals were obtained in the upper part of the nanocolumns. The dramatic improvement in the emission properties of GaN nanocolumns observed with decreasing diameter is discussed in relation to the decreased dislocation density. The laser action of InGaN/GaN-based nanocolumn arrays with a nanocolumn diameter of 170 nm and a period of 200 nm on Si under optical excitation was obtained with an emission wavelength of 407 nm. We also fabricated red-emitting InGaN-based nanocolumn light-emitting diodes on Si that operated at a wavelength of 652 nm, demonstrating vertical conduction

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

    PubMed

    Kishino, Katsumi; Ishizawa, Shunsuke

    2015-06-01

    The growth of highly uniform arrays of GaN nanocolumns with diameters from 122 to 430 nm on Si (111) substrates was demonstrated. The employment of GaN film templates with flat surfaces (root mean square surface roughness of 0.84 nm), which were obtained using an AlN/GaN superlattice (SL) buffer on Si, contributed to the high-quality selective-area growth of nanocolumns using a thin Ti mask of 5 nm thickness by rf-plasma-assisted molecular beam epitaxy. Although the GaN template included a large number of dislocations (dislocation density ∼10(11) cm(-2)), the dislocation filtering effect of nanocolumns was enhanced with decreasing nanocolumn diameters (D). Systematic transmission electron microscopy (TEM) observation enabled us to explain the dependence of the dislocation propagation behavior in nanocolumns on the nanocolumn diameter for the first time. Plan-view TEM analysis was performed for nanocolumns with D = 120-324 nm by slicing the nanocolumns horizontally at a height of ∼300 nm above their bottoms and dislocation propagation through the nanocolumns was analyzed by the cross-sectional TEM observation of nanocolumns with D ∼ 200 nm. It was clarified that dislocations were effectively filtered in the bottom 300 nm region of the nanocolumns, the dislocation density of the nanocolumns decreased with decreasing D, and for narrow nanocolumns with D < 200 nm, dislocation-free crystals were obtained in the upper part of the nanocolumns. The dramatic improvement in the emission properties of GaN nanocolumns observed with decreasing diameter is discussed in relation to the decreased dislocation density. The laser action of InGaN/GaN-based nanocolumn arrays with a nanocolumn diameter of 170 nm and a period of 200 nm on Si under optical excitation was obtained with an emission wavelength of 407 nm. We also fabricated red-emitting InGaN-based nanocolumn light-emitting diodes on Si that operated at a wavelength of 652 nm, demonstrating vertical conduction

  13. Characterization of M-plane GaN thin films grown on misoriented γ-LiAlO2 (100) substrates

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Chiao; Lo, Ikai; Wang, Ying-Chieh; Yang, Chen-Chi; Hu, Chia-Hsuan; Chou, Mitch M. C.; Schaadt, D. M.

    2016-09-01

    M-plane GaN thin films were grown on 11° misoriented γ-LiAlO2 substrates without peeling off or cracking by plasma-assisted molecular beam epitaxy. Because of anisotropic growth kinetics, which leads to an anisotropic compressive in-plane strain in the M-plane GaN films, the surface presents a rough morphology with worse crystal quality. The crystal quality of sample was optimally improved, XRD rocking curve FWHM of which is about 900 arcsec, by raising growth temperature to 800 °C with proper Ga/N flux ratio. As the crystal quality was improved, the polarization ratio decreased from the unity (less than 0.8) which could be attributed to the effect of exciton localization due to the partial increased in-plane strain.

  14. Growth of high-quality InN thin films on InGaN buffer layer by plasma-assisted molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Yang, Chen-Chi; Lo, Ikai; Shih, Cheng-Hung; Hu, Chia-Hsuan; Wang, Ying-Chieh; Lin, Yu-Chiao; Tasi, Cheng-Da; You, Shuo-Ting

    2015-03-01

    Four samples were grown on 2 inch c-plane (0001) sapphire substrates with 4 μm-thick GaN template. The InN thin films were grown on InGaN buffer layer by low-temperature plasma-assisted molecular beam epitaxy (PAMBE) system. These samples were grown under a varied temperature of InGaN buffer layers: 500°C, 540°C, 570°C, and 600°C. The structure properties of these samples were analyzed by X-ray diffraction (XRD). The interference fringes of InN grown on the sample 1 (the growth temperature of InGaN buffer layer at 500°C) exhibit prominent oscillations, which indicates that the sample has a high quality and layer by layer epitaxial structure. The surface morphology and microstructure of samples were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). We confirmed the smooth surface and high quality crystalline for the sample.

  15. Enhanced functionality in GaN and SiC devices by using novel processing

    NASA Astrophysics Data System (ADS)

    Pearton, S. J.; Abernathy, C. R.; Gila, B. P.; Ren, F.; Zavada, J. M.; Park, Y. D.

    2004-11-01

    Some examples of recent advances in enhancing or adding functionality to GaN and SiC devices through the use of novel processing techniques are discussed. The first example is the use of ion implantation to incorporate transition metals such as Mn, Cr and Co at atomic percent levels in the wide bandgap semiconductors to produce room temperature ferromagnetism. A discussion is given of the phase space within which single-phase material can be obtained and the requirements for demonstrating the presence of a true dilute magnetic semiconductor. The ability to make GaN and SiC ferromagnetic leads to the possibility of magnetic devices with gain, spin FETs operating at low voltages and spin polarized light emitters. The second example is the use of novel oxides such as Sc 2O 3 and MgO as gate dielectrics or surface passivants on GaN. True inversion behavior has been demonstrated in gated MOS-GaN diodes with implanted n-regions supplying the minority carriers need for inversion. These oxide layers also effectively mitigate current collapse in AlGaN/GaN HEMTs through their passivation of surface states in the gate-drain region. The third example is the use of laser drilling to make through-wafer via holes in SiC, sapphire and GaN. The ablation rate is sufficiently high that this maskless, serial process appears capable of achieving similar throughput to the more conventional approach of plasma etching of vias. The fourth example is the use of either ungated AlGaN/GaN HEMTs or simple GaN and SiC Schottky diodes as sensors for chemicals, biogens, radiation, combustion gases or strain. The sensitivity of either the channel carrier density or the barrier height to changes in surface condition make these materials systems ideal for compact robust sensors capable of operating at elevated temperatures.

  16. Fabrication of normally-off GaN nanowire gate-all-around FET with top-down approach

    NASA Astrophysics Data System (ADS)

    Im, Ki-Sik; Won, Chul-Ho; Vodapally, Sindhuri; Caulmilone, Raphaël; Cristoloveanu, Sorin; Kim, Yong-Tae; Lee, Jung-Hee

    2016-10-01

    Lateral GaN nanowire gate-all-around transistor has been fabricated with top-down process and characterized. A triangle-shaped GaN nanowire with 56 nm width was implemented on the GaN-on-insulator (GaNOI) wafer by utilizing (i) buried oxide as sacrificial layer and (ii) anisotropic lateral wet etching of GaN in tetramethylammonium hydroxide solution. During subsequent GaN and AlGaN epitaxy of source/drain planar regions, no growth occurred on the nanowire, due to self-limiting growth property. Transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping reveal that the GaN nanowire consists of only Ga and N atoms. The transistor exhibits normally-off operation with the threshold voltage of 3.5 V and promising performance: the maximum drain current of 0.11 mA, the maximum transconductance of 0.04 mS, the record off-state leakage current of ˜10-13 A/mm, and a very high Ion/Ioff ratio of 108. The proposed top-down device concept using the GaNOI wafer enables the fabrication of multiple parallel nanowires with positive threshold voltage and is advantageous compared with the bottom-up approach.

  17. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

    SciTech Connect

    Xu, Xingsheng

    2015-03-02

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

  18. Providing high-quality care in primary care settings

    PubMed Central

    Beaulieu, Marie-Dominique; Geneau, Robert; Grande, Claudio Del; Denis, Jean-Louis; Hudon, Éveline; Haggerty, Jeannie L.; Bonin, Lucie; Duplain, Réjean; Goudreau, Johanne; Hogg, William

    2014-01-01

    Abstract Objective To gain a deeper understanding of how primary care (PC) practices belonging to different models manage resources to provide high-quality care. Design Multiple-case study embedded in a cross-sectional study of a random sample of 37 practices. Setting Three regions of Quebec. Participants Health care professionals and staff of 5 PC practices. Methods Five cases showing above-average results on quality-of-care indicators were purposefully selected to contrast on region, practice size, and PC model. Data were collected using an organizational questionnaire; the Team Climate Inventory, which was completed by health care professionals and staff; and 33 individual interviews. Detailed case histories were written and thematic analysis was performed. Main findings The core common feature of these practices was their ongoing effort to make trade-offs to deliver services that met their vision of high-quality care. These compromises involved the same 3 areas, but to varying degrees depending on clinic characteristics: developing a shared vision of high-quality care; aligning resource use with that vision; and balancing professional aspirations and population needs. The leadership of the physician lead was crucial. The external environment was perceived as a source of pressure and dilemmas rather than as a source of support in these matters. Conclusion Irrespective of their models, PC practices’ pursuit of high-quality care is based on a vision in which accessibility is a key component, balanced by appropriate management of available resources and of external environment expectations. Current PC reforms often create tensions rather than support PC practices in their pursuit of high-quality care. PMID:24829023

  19. 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.

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

    SciTech Connect

    Wu, F.; Gao, K. H. Li, Z. Q.; Lin, T.; Zhou, W. Z.

    2015-04-21

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

  1. Characterization of high quality InN grown on production-style plasma assisted molecular beam epitaxy system

    SciTech Connect

    Gherasoiu, I.; O'Steen, M.; Bird, T.; Gotthold, D.; Chandolu, A.; Song, D. Y.; Xu, S. X.; Holtz, M.; Nikishin, S. A.; Schaff, W. J.

    2008-05-15

    In this work, the authors report step-flow growth mode of InN on [0001] oriented GaN templates, using a production-style molecular beam epitaxy system, Veeco GEN200 registered , equipped with a plasma source. Using adaptive growth conditions, they have obtained a surface morphology that exhibits the step-flow features. The root mean squared roughness over an area of 5x5 {mu}m{sup 2} is 1.4 nm with monolayer height terrace steps (0.281 nm), based on atomic force microscopy. It has been found that the presence of In droplets leads to defective surface morphology. From x-ray diffraction, they estimate edge and screw dislocation densities. The former is dominant over the latter. Micro-Raman spectra reveal narrow E{sub 2}{sup 2} phonon lines consistent with excellent crystalline quality of the epitaxial layers. The Hall mobility of 1 {mu}m thick InN layers, grown in step-flow mode, is slightly higher than 1400 cm{sup 2}/V s, while for other growth conditions yielding a smooth surface with no well-defined steps, mobility as high as 1904 cm{sup 2}/V s at room temperature has been measured. The samples exhibit high intensity photoluminescence (PL) with a corresponding band edge that shifts with free carrier concentration. For the lowest carrier concentration of 5.6x10{sup 17} cm{sup -3}, they observe PL emission at {approx}0.64 eV.

  2. Growth condition optimization and mobility enhancement through prolonging the GaN nuclei coalescence process of AlGaN/AlN/GaN structure

    NASA Astrophysics Data System (ADS)

    He, Xiao-Guang; Zhao, De-Gang; Jiang, De-Sheng; Zhu, Jian-Jun; Chen, Ping; Liu, Zong-Shun; Le, Ling-Cong; Yang, Jing; Li, Xiao-Jing; Zhang, Shu-Ming; Yang, Hui

    2015-09-01

    AlGaN/AlN/GaN structures are grown by metalorganic vapor phase epitaxy on sapphire substrates. Influences of AlN interlayer thickness, AlGaN barrier thickness, and Al composition on the two-dimensional electron gas (2DEG) performance are investigated. Lowering the V/III ratio and enhancing the reactor pressure at the initial stage of the high-temperature GaN layer growth will prolong the GaN nuclei coalescence process and effectively improve the crystalline quality and the interface morphology, diminishing the interface roughness scattering and improving 2DEG mobility. AlGaN/AlN/GaN structure with 2DEG sheet density of 1.19 × 1013 cm-2, electron mobility of 2101 cm2·V-1·s-1, and square resistance of 249 Ω is obtained. Project support by the National Natural Science Foundation of China (Grant Nos. 61474110, 61377020, 61376089, 61223005, and 61176126), the National Science Fund for Distinguished Young Scholars, China (Grant No. 60925017), the One Hundred Person Project of the Chinese Academy of Sciences, and the Basic Research Project of Jiangsu Province, China (Grant No. BK20130362).

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

    PubMed Central

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

    2016-01-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate. PMID:27756906

  4. Designing High Quality Research in Special Education: Group Experimental Designs.

    ERIC Educational Resources Information Center

    Gersten, Russell; Lloyd, John Wills; Baker, Scott

    This paper, a result of a series of meetings of researchers, discusses critical issues related to the conduct of high-quality intervention research in special education using experimental and quasi-experimental designs that compare outcomes for different groups of students. It stresses the need to balance design components that satisfy laboratory…

  5. Novel, high-quality surface plasmon resonance microscopy

    PubMed Central

    Thariani, Rahber; Yager, Paul

    2016-01-01

    A surface plasmon resonance microscope capable of high-quality speckle-free imaging has been designed that uses a laser as a source. An inexpensive acoustic transducer is used to reduce speckle and other image artifacts arising from the use of illumination from an inexpensive laser pointer. The microscope is described and operation of the system demonstrated.

  6. High-quality Health Information Provision for Stroke Patients

    PubMed Central

    Du, Hong-Sheng; Ma, Jing-Jian; Li, Mu

    2016-01-01

    Objective: High-quality information provision can allow stroke patients to effectively participate in healthcare decision-making, better manage the stroke, and make a good recovery. In this study, we reviewed information needs of stroke patients, methods for providing information to patients, and considerations needed by the information providers. Data Sources: The literature concerning or including information provision for patients with stroke in English was collected from PubMed published from 1990 to 2015. Study Selection: We included all the relevant articles on information provision for stroke patients in English, with no limitation of study design. Results: Stroke is a major public health concern worldwide. High-quality and effective health information provision plays an essential role in helping patients to actively take part in decision-making and healthcare, and empowering them to effectively self-manage their long-standing chronic conditions. Different methods for providing information to patients have their relative merits and suitability, and as a result, the effective strategies taken by health professionals may include providing high-quality information, meeting patients’ individual needs, using suitable methods in providing information, and maintaining active involvement of patients. Conclusions: It is suggested that to enable stroke patients to access high-quality health information, greater efforts need to be made to ensure patients to receive accurate and current evidence-based information which meets their individual needs. Health professionals should use suitable information delivery methods, and actively involve stroke patients in information provision. PMID:27569241

  7. Two-step epitaxial lateral overgrowth of a-plane GaN by MOCVD

    NASA Astrophysics Data System (ADS)

    Ni, X.; Özgür, Ü.; Morkoç, H.; Baski, A. A.; Liliental-Weber, Z.; Everitt, H. O.

    2007-02-01

    -plane epitaxial layers (<45 ps), and ratio of the slow decaying component magnitude to the fast decaying one was more than 1.5, showing considerable reduction of nonradiative centers by lateral overgrowth. In addition, room temperature near-field optical microscopy studies revealed the improved optical quality in the wing regions of the overgrown GaN. As revealed from far-field PL, the band edge luminescence at room temperature was more than two orders of magnitude weaker than the yellow luminescence. Therefore, the overall spectrally integrated near field PL was collected, and its intensity was noticeably stronger in the wing areas with both Ga and N polarity. The much weaker emission at the windows and meeting fronts of the two opposite wings were consistent with the observations of high density of dislocations in the window regions and new defects originating at the meeting boundaries from TEM.

  8. Method for producing high quality thin layer films on substrates

    DOEpatents

    Strongin, Myron; Ruckman, Mark; Strongin, Daniel

    1994-01-01

    A method for producing high quality, thin layer films of inorganic compounds upon the surface of a substrate is disclosed. The method involves condensing a mixture of preselected molecular precursors on the surface of a substrate and subsequently inducing the formation of reactive species using high energy photon or charged particle irradiation. The reactive species react with one another to produce a film of the desired compound upon the surface of the substrate.

  9. Method for producing high quality thin layer films on substrates

    DOEpatents

    Strongin, M.; Ruckman, M.; Strongin, D.

    1994-04-26

    A method for producing high quality, thin layer films of inorganic compounds upon the surface of a substrate is disclosed. The method involves condensing a mixture of preselected molecular precursors on the surface of a substrate and subsequently inducing the formation of reactive species using high energy photon or charged particle irradiation. The reactive species react with one another to produce a film of the desired compound upon the surface of the substrate. 4 figures.

  10. Numerical analysis on the origin of thickness unevenness and formation of pits at GaN thin film grown by HVPE

    NASA Astrophysics Data System (ADS)

    Han, Xue-Feng; Lee, Jae-Hak; Lee, Yoo-Jin; Song, Jae-Ho; Yi, Kyung-Woo

    2016-09-01

    In this study, we propose a 3D model for analyzing the fluid flow, mass fractions of reacting gases, GaN deposition thickness distribution and V/III ratio distribution at the GaN deposition surface in the multi-susceptor HVPE equipment. The GaN thin film is grown in the multi-susceptor HVPE equipment at 1213 K and 1 bar. The deposition thickness distribution from the calculation has been compared with the experimental results. Moreover, the standard deviations of deposition thickness of the films achieved from calculations and experiments have been compared. Besides, in the calculation results, we found that the V/III ratio at the GaN deposition surface increased from the center to the periphery and from low susceptor to high susceptor. Our calculation results have also been verified by 3D measuring laser microscope observation of the surface morphology of the GaN thin film. In according with the calculation results, the density of the pits also decreases from the center to the periphery as well as from low susceptor to high susceptor, demonstrating that the pit density at the surface of the GaN thin films could be reduced when the V/III ratio is increased.

  11. Highly qualified does not equal high quality: A study of urban stakeholders' perceptions of quality in science teaching

    NASA Astrophysics Data System (ADS)

    Miranda, Rommel Joseph

    By employing qualitative methods, this study sought to determine the perceptions that urban stakeholders hold about what characteristics should distinguish a high school science teacher whom they would consider to demonstrate high quality in science teaching. A maximum variation sample of six science teachers, three school administrators, six parents and six students from a large urban public school district were interviewed using semi-structured, in-depth interview techniques. From these data, a list of observable characteristics which urban stakeholders hold as evidence of high quality in science teaching was generated. Observational techniques were utilized to determine the extent to which six urban high school science teachers, who meet the NCLB Act criteria for being "highly qualified", actually possessed the characteristics which these stakeholders hold as evidence of high quality in science teaching. Constant comparative analysis was used to analyze the data set. The findings suggest that urban stakeholders perceive that a high school science teacher who demonstrates high quality in science teaching should be knowledgeable about their subject matter, their student population, and should be resourceful; should possess an academic background in science and professional experience in science teaching; should exhibit professionalism, a passion for science and teaching, and a dedication to teaching and student learning; should be skillful in planning and preparing science lessons and in organizing the classroom, in presenting the subject matter to students, in conducting a variety of hands-on activities, and in managing a classroom; and should assess whether students complete class goals and objectives, and provide feedback about grades for students promptly. The findings further reveal that some of the urban high school science teachers who were deemed to be "highly qualified", as defined by the NCLB Act, engaged in practices that threatened quality in science

  12. Identification of Si and O donors in hydride-vapor-phase epitaxial GaN

    NASA Astrophysics Data System (ADS)

    Moore, W. J.; Freitas, J. A.; Braga, G. C. B.; Molnar, R. J.; Lee, S. K.; Lee, K. Y.; Song, I. J.

    2001-10-01

    Donor impurity excitation spectra in the infrared from two high-quality, not-intentionally doped, hydride-vapor-phase epitaxial GaN wafers are reported. Two previously observed shallow donors which we designate N1 and N2 were observed in both wafers. However, spectra of one wafer are dominated by N1 and spectra of the other by N2. A comparison of infrared and secondary ion mass spectroscopic data allows identification of N1 as Si and N2 as O. Silicon is the shallowest uncompensated donor in these samples with an activation energy of 30.18±0.1 meV in the freestanding Samsung wafer. The activation energy of O is found to be 33.20±0.1 meV. An unidentified third donor with an activation energy of 31.23±0.1 meV also was observed. Integrated absorption cross sections are found to be 8.5×10-14 cm for Si and 8.6×10-14 cm for O.

  13. A partly-contacted epitaxial lateral overgrowth method applied to GaN material

    PubMed Central

    Xiao, Ming; Zhang, Jincheng; Duan, Xiaoling; Shan, Hengsheng; Yu, Ting; Ning, Jing; Hao, Yue

    2016-01-01

    We have discussed a new crystal epitaxial lateral overgrowth (ELO) method, partly-contacted ELO (PC-ELO) method, of which the overgrowth layer partly-contacts with underlying seed layer. The passage also illustrates special mask structures with and without lithography and provides three essential conditions to achieve the PC-ELO method. What is remarkable in PC-ELO method is that the tilt angle of overgrowth stripes could be eliminated by contacting with seed layer. Moreover, we report an improved monolayer microsphere mask method without lithography of PC-ELO method, which was used to grow GaN. From the results of scanning electron microscopy, cathodoluminescence, x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscope (AFM), overgrowth layer shows no tilt angle relative to the seed layer and high quality coalescence front (with average linear dislocation density <6.4 × 103 cm−1). Wing stripes peak splitting of the XRD rocking curve due to tilt is no longer detectable. After coalescence, surface steps of AFM show rare discontinuities due to the low misorientation of the overgrowth regions. PMID:27033154

  14. GaN metal-semiconductor-metal UV sensor with multi-layer graphene as Schottky electrodes

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Ju; Kang, Sang-Bum; Cha, Hyeon-Gu; Won, Chul-Ho; Hong, Seul-Ki; Cho, Byung-Jin; Park, Hongsik; Lee, Jung-Hee; Hahm, Sung-Ho

    2015-06-01

    We fabricated a GaN-based metal-semiconductor-metal (MSM)-type UV sensor using a multilayer graphene as transparent Schottky electrodes. The fabricated GaN MSM UV sensor showed a high photo-to-dark current contrast ratio of 3.9 × 105 and a UV-to-visible rejection ratio of 1.8 × 103 at 7 V. The as-fabricated GaN MSM UV sensor with graphene electrodes has a low bias dependence of maximum photoresponsivity and a noise-like response at a visible wavelength in the 500 nm region. These problems were successfully solved by treatment with a buffered oxide etcher (BOE), and the photoresponse characteristics of the fabricated GaN MSM UV sensor after the treatment were better than those before the treatment.

  15. Screw dislocation-driven epitaxial solution growth of ZnO nanowires seeded by dislocations in GaN substrates.

    PubMed

    Morin, Stephen A; Jin, Song

    2010-09-01

    In the current examples of dislocation-driven nanowire growth, the screw dislocations that propagate one-dimensional growth originate from spontaneously formed highly defective "seed" crystals. Here we intentionally utilize screw dislocations from defect-rich gallium nitride (GaN) thin films to propagate dislocation-driven growth, demonstrating epitaxial growth of zinc oxide (ZnO) nanowires directly from aqueous solution. Atomic force microscopy confirms screw dislocations are present on the native GaN surface and ZnO nanowires grow directly from dislocation etch pits of heavily etched GaN surfaces. Furthermore, transmission electron microscopy confirms the existence of axial dislocations. Eshelby twist in the resulting ZnO nanowires was confirmed using bright-/dark-field imaging and twist contour analysis. These results further confirm the connection between dislocation source and nanowire growth. This may eventually lead to defect engineering strategies for rationally designed catalyst-free dislocation-driven nanowire growth for specific applications.

  16. Hidden surface states at non-polar GaN (101xAF0) facets: Intrinsic pinning of nanowires

    NASA Astrophysics Data System (ADS)

    Lymperakis, L.; Weidlich, P. H.; Eisele, H.; Schnedler, M.; Nys, J.-P.; Grandidier, B.; Stiévenard, D.; Dunin-Borkowski, R. E.; Neugebauer, J.; Ebert, Ph.

    2013-10-01

    We investigate the electronic structure of the GaN(101¯0) prototype surface for GaN nanowire sidewalls. We find a paradoxical situation that a surface state at all k points in the bandgap cannot be probed by conventional scanning tunneling microscopy, due to a dispersion characterized by a steep minimum with low density of states (DOS) and an extremely flat maximum with high DOS. Based on an analysis of the decay behavior into the vacuum, we identify experimentally the surface state minimum 0.6 ± 0.2 eV below the bulk conduction band in the gap. Hence, GaN nanowires with clean (101¯0) sidewall facets are intrinsically pinned.

  17. Confocal microscopic analysis of optical crosstalk in GaN micro-pixel light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Li, K. H.; Cheung, Y. F.; Cheung, W. S.; Choi, H. W.

    2015-10-01

    The optical crosstalk phenomenon in GaN micro-pixel light-emitting diodes (LED) has been investigated by confocal microscopy. Depth-resolved confocal emission images indicate light channeling along the GaN and sapphire layers as the source of crosstalk. Thin-film micro-pixel devices are proposed, whereby the light-trapping sapphire layers are removed by laser lift-off. Optical crosstalk is significantly reduced but not eliminated due to the remaining GaN layer. Another design involving micro-pixels which are completely isolated is further proposed; such devices exhibited low-noise and enhanced optical performances, which are important attributes for high-density micro-pixel LED applications including micro-displays and multi-channel optical communications.

  18. Detection of High Quality Rainfall Data to Improve Flood Resilience

    NASA Astrophysics Data System (ADS)

    Hoang, T. C.; Tchiguirinskaia, I.; Schertzer, D. J.; Lovejoy, S.

    2012-12-01

    European flood management systems require reliable rainfall statistics, e.g. the Intensity-duration-Frequency curves for shorter and shorter durations and for a larger and larger range of return periods. Preliminary studies showed that the number of floods depends on the quality of available data, e.g. the time resolution quality. These facts suggest that a particular attention should be paid to the rainfall data quality in order to adequately investigate flood risk aiming to achieve flood resilience. The potential consequences of changes in measuring and recording techniques have been somewhat discussed in the literature with respect to a possible introduction of artificial inhomogeneities in time series. In this direction, we developed a first version of a SERQUAL procedure to automatically detect the effective time resolution of highly mixed data. We show that most of the rainfall time series have a lower recording frequency than that is assumed. This question is particularly important for operational hydrology, because an error on the effective recording high frequency introduces biases in the corresponding statistics. It is therefore essential to quantify the quality of the rainfall time series before their use. Due to the fact that the multiple scales and possible scaling behaviour of hydrological data are particularly important for many applications, including flood resilience research, this paper first investigates the sensitivity of the scaling estimates and methods to the deficit of short duration rainfall data, and consequently propose a few simple criteria for a reliable evaluation of the data quality. The SERQUAL procedure enable us to extract high quality sub-series from longer time series that will be much more reliable to calibrate and/or validate short duration quantiles and hydrological models.

  19. Depth profile characterization technique for electron density in GaN films by infrared reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Kamijoh, Takaaki; Ma, Bei; Morita, Ken; Ishitani, Yoshihiro

    2016-05-01

    Infrared reflectance spectroscopy is a noncontact measurement method for carrier density and mobility. In this article, the model determination procedure of layer-type nonuniform electron distribution is investigated, since the spectrum fitting hitherto has been conducted on the basis of a multilayer model defined in advance. A simplified case of a high-electron-density GaN layer embedded in a GaN matrix is mainly studied. The following procedure is found to be applicable. The first step is the determination of the high-density layer position in the vicinity of the surface, in the middle region, or in the vicinity of the interface. This is followed by the specification of the sheet electron density and the layer thickness of the high-density region. It is found that this procedure is also applicable to the characterization of two-dimensional electron gases in the vicinity of AlGaN/GaN heterointerfaces.

  20. Compact pulley-type microring resonator with high quality factor

    NASA Astrophysics Data System (ADS)

    Cai, Dong-Po; Lu, Jyun-Hong; Chen, Chii-Chang; Lee, Chien-Chieh; Lin, Chu-En; Yen, Ta-Jen

    2014-11-01

    A pulley-type microring resonator with ultra-small dimensions and ultra-high quality factor on a silicon-on-insulator wafer is fabricated and characterized. Simulation results show that the bending loss of the pulley-type microring resonator can be diminished by wrapping the curved waveguide around the microring, and that the energy loss from the output port can be decreased by tuning the width of the bus waveguide to achieve destructive interference. A quality factor of 1.73 × 105 is obtained in this experiment. The compact size of the pulley-type microring resonator with low bending loss is suitable for an integrated optical circuit.

  1. High Quality Factor Mechanical Resonators Based on WSe2 Monolayers.

    PubMed

    Morell, Nicolas; Reserbat-Plantey, Antoine; Tsioutsios, Ioannis; Schädler, Kevin G; Dubin, François; Koppens, Frank H L; Bachtold, Adrian

    2016-08-10

    Suspended monolayer transition metal dichalcogenides (TMD) are membranes that combine ultralow mass and exceptional optical properties, making them intriguing materials for opto-mechanical applications. However, the low measured quality factor of TMD resonators has been a roadblock so far. Here, we report an ultrasensitive optical readout of monolayer TMD resonators that allows us to reveal their mechanical properties at cryogenic temperatures. We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 1.6 × 10(4) at liquid nitrogen temperature and 4.7 × 10(4) at liquid helium temperature. This surpasses the quality factor of monolayer graphene resonators with similar surface areas. Upon cooling the resonator, the resonant frequency increases significantly due to the thermal contraction of the WSe2 lattice. These measurements allow us to experimentally study the thermal expansion coefficient of WSe2 monolayers for the first time. High Q-factors are also found in resonators based on MoS2 and MoSe2 monolayers. The high quality-factor found in this work opens new possibilities for coupling mechanical vibrational states to two-dimensional excitons, valley pseudospins, and single quantum emitters and for quantum opto-mechanical experiments based on the Casimir interaction. PMID:27459399

  2. High Quality Factor Mechanical Resonators Based on WSe2 Monolayers

    PubMed Central

    2016-01-01

    Suspended monolayer transition metal dichalcogenides (TMD) are membranes that combine ultralow mass and exceptional optical properties, making them intriguing materials for opto-mechanical applications. However, the low measured quality factor of TMD resonators has been a roadblock so far. Here, we report an ultrasensitive optical readout of monolayer TMD resonators that allows us to reveal their mechanical properties at cryogenic temperatures. We find that the quality factor of monolayer WSe2 resonators greatly increases below room temperature, reaching values as high as 1.6 × 104 at liquid nitrogen temperature and 4.7 × 104 at liquid helium temperature. This surpasses the quality factor of monolayer graphene resonators with similar surface areas. Upon cooling the resonator, the resonant frequency increases significantly due to the thermal contraction of the WSe2 lattice. These measurements allow us to experimentally study the thermal expansion coefficient of WSe2 monolayers for the first time. High Q-factors are also found in resonators based on MoS2 and MoSe2 monolayers. The high quality-factor found in this work opens new possibilities for coupling mechanical vibrational states to two-dimensional excitons, valley pseudospins, and single quantum emitters and for quantum opto-mechanical experiments based on the Casimir interaction. PMID:27459399

  3. 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.}

  4. Enhanced water splitting with silver decorated GaN photoelectrode

    NASA Astrophysics Data System (ADS)

    Hou, Y.; Syed, Z. A.; Smith, R.; Athanasiou, M.; Gong, Y.; Yu, X.; Bai, J.; Wang, T.

    2016-07-01

    By means of a cost-effective approach, we demonstrate a GaN-based photoelectrode decorated with self-organized silver nano-islands employed for solar powered hydrogen generation, demonstrating 4 times increase in photocurrent compared with a reference sample without using any silver. Our photoelectrode exhibits a 60% incident photon-to-electron conversion efficiency. The enhanced hydrogen generation is attributed to a significantly increased carrier generation rate as a result of strongly localized electric fields induced by surface plasmon coupling effect. The silver coating also contributes to the good chemical stability of our photoelectrode in a strong alkali electrolyte. This work paves the way for the development of GaN and also InGaN based photoelectrodes with ultra-high solar hydrogen conversion efficiency.

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

    NASA Astrophysics Data System (ADS)

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

    2006-04-01

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

  6. Fundamental Bulk/Surface Structure Photoactivity Relationships of Supported (Rh2-yCryO3)/GaN Photocatalysts

    SciTech Connect

    Phivilay, Somphonh; Roberts, Charles; Puretzky, Alexander A; Domen, Kazunari Domen; Wachs, Israel

    2013-01-01

    ABSTRACT. The supported (Rh2-yCryO3)/GaN photocatalyst was examined as a model nitride photocatalyst system to assist in the development of fundamental structure photoactivity relationships for UV activated water splitting. Surface characterization of the outermost surface layers by High Sensitivity-LEIS and High Resolution-XPS revealed for the first time that the GaN support consists of a GaOx outermost surface layer and a thin film of GaOxNy in the surface region. HR-XPS also demonstrates that the supported (Rh2-yCryO3) mixed oxide nanoparticles (NPs) exclusively consist of Cr+3 and Rh+3 cations and are surface enriched for the supported (Rh2-yCryO3)/GaN photocatalyst. Bulk analysis by Raman and UV-vis spectroscopy show that the bulk molecular and electronic structures, respectively, of the GaN support are not perturbed by the deposition of the (Rh2-yCryO3) mixed oxide NPs. The function of the GaN bulk lattice is to generate photoexcited electrons/holes, with the electrons harnessed by the surface Rh+3 sites for evolution of H2 and the holes trapped at the Ga oxide/oxynitride surface sites for splitting of water and evolving O2. These new structure-photoactivity relationships for supported (Rh2-yCryO3)/GaN also extend to the best performing visible light activated supported (Rh2-yCryO3)/(Ga1-xZnx)(N1-xOx) photocatalyst.

  7. Weld quality evaluation using a high temperature SQUID array

    SciTech Connect

    Clark, D. D.; Espy, M. A.; Kraus, Robert H., Jr.; Matlachov, A. N.; Lamb, J. S.

    2002-01-01

    This paper presents preliminary data for evaluating weld quality using high temperature SQUIDS. The SQUIDS are integrated into an instrument known as the SQUID Array Microscope, or SAMi. The array consists of ll SQUIDs evenly distributed over an 8.25 mm baseline. Welds are detected using SAMi by using an on board coil to induce eddy currents in a conducting sample and measuring the resulting magnetic fields. The concept is that the induced magnetic fields will differ in parts of varying weld quality. The data presented here was collected from three stainless steel parts using SAMi. Each part was either solid, included a good weld, or included a bad weld. The induced magnetic field's magnitude and phase relative to the induction signal were measured. For each sample considered, both the magnitude and phase data were measurably different than the other two samples. These results indicate that it is possible to use SAMi to evaluate weld quality.

  8. High-quality-factor photonic crystal ring resonator.

    PubMed

    Zhang, Yong; Zeng, Cheng; Li, Danping; Gao, Ge; Huang, Zengzhi; Yu, Jinzhong; Xia, Jinsong

    2014-03-01

    A design for enhancing the quality (Q) factor of a photonic crystal ring resonator (PCRR) is introduced. The highest Q factor based on simulations is 121,000. The analysis of momentum space distributions of the electric field profile for PCRR resonance shows that a high Q factor of a PCRR is attributed to the reduction of tangential k-vector component inside the leaky region. A high Q factor of 75,200 is experimentally demonstrated for a modified PCRR on a silicon-on-insulator wafer. The high-Q-factor PCRR demonstrated here will be beneficial for channel drop filters, lasers, sensors, and other applications. PMID:24690727

  9. High-Quality Ion Beam Generation in Laser Plasma Interaction

    NASA Astrophysics Data System (ADS)

    Nagashima, Toshihiro; Takano, Masahiro; Izumiyzma, Takeshi; Barada, Daisuke; Kawata, Shigeo; Gu, Yan Jun; Kong, Qing; Xiao Wang, Ping; Ma, Yan Yun; Wang, Wei Min

    We focus on a control of generation of high-quality ion beam. In this study, near-critical density plasmas are employed and are illuminated by high intensity short laser pulses; we have successfully generated high-energy ions by multiple-stages acceleration. We performed particle-in-cell simulations in this paper. Near-critical density plasmas are employed at the proton source and also in the post acceleration. A beam bunching method is also proposed to control the ion beam length.

  10. 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.

  11. 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.

  12. 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.

  13. Self-assembled growth and structural analysis of inclined GaN nanorods on nanoimprinted m-sapphire using catalyst-free metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Nam, Okhyun

    2016-04-01

    In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ˜57.5° to the [10-10]sapp direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]sapp. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to be mostly free of stacking fault-related defects using high-resolution transmission electron microscopy.

  14. 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.

  15. High-quality DNA from fingernails for genetic analysis.

    PubMed

    Preuner, Sandra; Danzer, Martin; Pröll, Johannes; Pötschger, Ulrike; Lawitschka, Anita; Gabriel, Christian; Lion, Thomas

    2014-07-01

    The availability of high-quality germline DNA is an important prerequisite for a variety of genetic analyses. We have shown previously that fingernail clippings provide an optimal source of autologous, constitutional DNA for PCR-based applications. However, most existing protocols for nucleic acid purification from nails do not provide sufficiently high yields of pure and intact DNA for more demanding downstream analyses such as next generation sequencing (NGS). We have extensively tested and systematically modified a number of different protocols for DNA purification from nail material to optimize the yield and quality. The integrity of DNA was determined by PCR amplification of short (<300 bp), mid-range (>400 bp), and long-range (>2 kb) sequences using different target genes. Among the methods tested, the Prepfiler Forensic DNA Extraction kit was identified as the most appropriate approach to isolation of high-quality DNA from nail clippings. A standardized input of 20 mg nail material (1 to 10 pieces of fingernail clippings) yielded a mean of 1 μg DNA (range, 0.5 to 2.3 μg). Subsequent PCR-analysis revealed efficient amplifiability of short and mid-range targets in 93% and 90%, and long-range fragments in 60% of the samples tested. The adequacy for next generation sequencing applications was demonstrated by successful high-resolution HLA-typing in ten transplant recipients. Hence, the protocol presented facilitates the exploitation of fingernail material even for demanding genomic analyses both in research and diagnostics.

  16. A high-throughput, high-quality plant genomic DNA extraction protocol.

    PubMed

    Li, H; Li, J; Cong, X H; Duan, Y B; Li, L; Wei, P C; Lu, X Z; Yang, J B

    2013-01-01

    The isolation of high-quality genomic DNA (gDNA) is a crucial technique in plant molecular biology. The quality of gDNA determines the reliability of real-time polymerase chain reaction (PCR) analysis. In this paper, we reported a high-quality gDNA extraction protocol optimized for real-time PCR in a variety of plant species. Performed in a 96-well block, our protocol provides high throughput. Without the need for phenol-chloroform and liquid nitrogen or dry ice, our protocol is safer and more cost-efficient than traditional DNA extraction methods. The method takes 10 mg leaf tissue to yield 5-10 µg high-quality gDNA. Spectral measurement and electrophoresis were used to demonstrate gDNA purity. The extracted DNA was qualified in a restriction enzyme digestion assay and conventional PCR. The real-time PCR amplification was sufficiently sensitive to detect gDNA at very low concentrations (3 pg/µL). The standard curve of gDNA dilutions from our phenol-chloroform-free protocol showed better linearity (R(2) = 0.9967) than the phenol-chloroform protocol (R(2) = 0.9876). The results indicate that the gDNA was of high quality and fit for real-time PCR. This safe, high-throughput plant gDNA extraction protocol could be used to isolate high-quality gDNA for real-time PCR and other downstream molecular applications. PMID:24222228

  17. Direct spontaneous growth and interfacial structural properties of inclined GaN nanopillars on r-plane sapphire

    SciTech Connect

    Adikimenakis, A.; Aretouli, K. E.; Tsagaraki, K.; Androulidaki, M.; Georgakilas, A.; Lotsari, A.; Dimitrakopulos, G. P. Kehagias, Th.; Komninou, Ph.

    2015-06-28

    The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with increasing the duration of the nitridation process and the power applied on the radio-frequency plasma source, as well as the III/V flux ratio, while variation of the first two parameters enhanced the roughness of the substrate's surface. Transmission electron microscopy (TEM) techniques were employed to reveal the structural characteristics of the NPs and their nucleation mechanism from steps on the sapphire surface and/or interfacial semipolar GaN nanocrystals. Lattice strain measurements showed a possible Al enrichment of the first 5–6 monolayers of the NPs. By combining cross-sectional and plan-view TEM observations, the three-dimensional model of the NPs was constructed. The orientation relationship and interfacial accommodation between the NPs and the nonpolar a-plane GaN film were also elucidated. The NPs exhibited strong and narrow excitonic emission, suggesting an excellent structural quality.

  18. Ultrathin GaN nanowires: Electronic, thermal, and thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Davoody, A. H.; Ramayya, E. B.; Maurer, L. N.; Knezevic, I.

    2014-03-01

    We present a comprehensive computational study of the electronic, thermal, and thermoelectric (TE) properties of gallium nitride nanowires (NWs) over a wide range of thicknesses (3-9 nm), doping densities (1018-1020 cm-3), and temperatures (300-1000 K). We calculate the low-field electron mobility based on ensemble Monte Carlo transport simulation coupled with a self-consistent solution of the Poisson and Schrödinger equations. We use the relaxation-time approximation and a Poisson-Schrödinger solver to calculate the electron Seebeck coefficient and thermal conductivity. Lattice thermal conductivity is calculated using a phonon ensemble Monte Carlo simulation, with a real-space rough surface described by a Gaussian autocorrelation function. Throughout the temperature range, the Seebeck coefficient increases while the lattice thermal conductivity decreases with decreasing wire cross section, both boding well for TE applications of thin GaN NWs. However, at room temperature these benefits are eventually overcome by the detrimental effect of surface roughness scattering on the electron mobility in very thin NWs. The highest room-temperature ZT of 0.2 is achieved for 4-nm-thick NWs, while further downscaling degrades it. In contrast, at 1000 K, the electron mobility varies weakly with the NW thickness owing to the dominance of polar optical phonon scattering and multiple subbands contributing to transport, so ZT increases with increasing confinement, and reaches 0.8 for optimally doped 3-nm-thick NWs. The ZT of GaN NWs increases with increasing temperature beyond 1000 K, which further emphasizes their suitability for high-temperature TE applications.

  19. High dose rate (HDR) brachytherapy quality assurance: a practical guide

    PubMed Central

    Wilkinson, DA

    2006-01-01

    The widespread adoption of high dose rate brachytherapy with its inherent dangers necessitates adoption of appropriate quality assurance measures to minimize risks to both patients and medical staff. This paper is aimed at assisting someone who is establishing a new program or revising one already in place into adhere to the recently issued Nuclear Regulatory Commission (USA) regulations and the guidelines from the American Association of Physicists in Medicine. PMID:21614233

  20. High quality fuel gas from biomass pyrolysis with calcium oxide.

    PubMed

    Zhao, Baofeng; Zhang, Xiaodong; Chen, Lei; Sun, Laizhi; Si, Hongyu; Chen, Guanyi

    2014-03-01

    The removal of CO2 and tar in fuel gas produced by biomass thermal conversion has aroused more attention due to their adverse effects on the subsequent fuel gas application. High quality fuel gas production from sawdust pyrolysis with CaO was studied in this paper. The results of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments indicate that the mass ratio of CaO to sawdust (Ca/S) remarkably affects the behavior of sawdust pyrolysis. On the basis of Py-GC/MS results, one system of a moving bed pyrolyzer coupled with a fluid bed combustor has been developed to produce high quality fuel gas. The lower heating value (LHV) of the fuel gas was above 16MJ/Nm(3) and the content of tar was under 50mg/Nm(3), which is suitable for gas turbine application to generate electricity and heat. Therefore, this technology may be a promising route to achieve high quality fuel gas for biomass utilization.

  1. High quality fuel gas from biomass pyrolysis with calcium oxide.

    PubMed

    Zhao, Baofeng; Zhang, Xiaodong; Chen, Lei; Sun, Laizhi; Si, Hongyu; Chen, Guanyi

    2014-03-01

    The removal of CO2 and tar in fuel gas produced by biomass thermal conversion has aroused more attention due to their adverse effects on the subsequent fuel gas application. High quality fuel gas production from sawdust pyrolysis with CaO was studied in this paper. The results of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments indicate that the mass ratio of CaO to sawdust (Ca/S) remarkably affects the behavior of sawdust pyrolysis. On the basis of Py-GC/MS results, one system of a moving bed pyrolyzer coupled with a fluid bed combustor has been developed to produce high quality fuel gas. The lower heating value (LHV) of the fuel gas was above 16MJ/Nm(3) and the content of tar was under 50mg/Nm(3), which is suitable for gas turbine application to generate electricity and heat. Therefore, this technology may be a promising route to achieve high quality fuel gas for biomass utilization. PMID:24486940

  2. Ground Albedo Neutron Sensing (GANS) method for measurements of soil moisture in cropped fields

    NASA Astrophysics Data System (ADS)

    Andres Rivera Villarreyes, Carlos; Baroni, Gabriele; Oswald, Sascha E.

    2013-04-01

    Measurement of soil moisture at the plot or hill-slope scale is an important link between local vadose zone hydrology and catchment hydrology. However, so far only few methods are on the way to close this gap between point measurements and remote sensing. This study evaluates the applicability of the Ground Albedo Neutron Sensing (GANS) for integral quantification of seasonal soil moisture in the root zone at the scale of a field or small watershed, making use of the crucial role of hydrogen as neutron moderator relative to other landscape materials. GANS measurements were performed at two locations in Germany under different vegetative situations and seasonal conditions. Ground albedo neutrons were measured at (i) a lowland Bornim farmland (Brandenburg) cropped with sunflower in 2011 and winter rye in 2012, and (ii) a mountainous farmland catchment (Schaefertal, Harz Mountains) since middle 2011. At both sites depth profiles of soil moisture were measured at several locations in parallel by frequency domain reflectometry (FDR) for comparison and calibration. Initially, calibration parameters derived from a previous study with corn cover were tested under sunflower and winter rye periods at the same farmland. GANS soil moisture based on these parameters showed a large discrepancy compared to classical soil moisture measurements. Therefore, two new calibration approaches and four different ways of integration the soil moisture profile to an integral value for GANS were evaluated in this study. This included different sets of calibration parameters based on different growing periods of sunflower. New calibration parameters showed a good agreement with FDR network during sunflower period (RMSE = 0.023 m3 m-3), but they underestimated soil moisture in the winter rye period. The GANS approach resulted to be highly affected by temporal changes of biomass and crop types which suggest the need of neutron corrections for long-term observations with crop rotation. Finally

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

    DOE PAGES

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; Lin, Yi -Hsuan; Machuca, Francisco; Weiss, Robert; Welsh, Alex; McCartney, Martha R.; Smith, David J.; Kravchenko, Ivan I.

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

  4. GaN for LED applications

    NASA Technical Reports Server (NTRS)

    Pankove, J. I.

    1973-01-01

    In order to improve the synthesis of GaN the effect of various growth and doping parameters has been studied. Although Be, Li, Mg, and Dy can be used to overcompensate native donors, the most interesting acceptor element is Zn. The emission spectrum and the luminescence efficiency depend on the growth temperature (below 800 C), on the partial pressure of the doping impurity, and on the duration of growth. Blue-green electroluminescence with a power efficiency of 0.1 percent and a brightness of 850 fL (at 0.6 mA and 22.5 V) was obtained. Some diodes allow the color of the emitted light to change by reversing the polarity of the bias. Continuous operation of a diode over a period of 5 months showed no evidence of degradation. The luminescence properties of ion-implanted GaN were studied. Delay effects were found in the electroluminescence of diodes, although, with a dc bias, a 70-MHz modulation was possible.

  5. High quality mask storage in an advanced Logic-Fab

    NASA Astrophysics Data System (ADS)

    Jähnert, Carmen; Fritsche, Silvio

    2012-02-01

    High efficient mask logistics as well as safe and high quality mask storage are essential requirements within an advanced lithography area of a modern logic waferfab. Fast operational availability of the required masks at the exposure tool with excellent mask condition requires a safe mask handling, safeguarding of high mask quality over the whole mask usage time without any quality degradation and an intelligent mask logistics. One big challenge is the prevention of haze on high advanced phase shift masks used in a high volume production line for some thousands of 248nm or 193nm exposures. In 2008 Infineon Dresden qualified a customer specific developed semi-bare mask storage system from DMSDynamic Micro Systems in combination with a high advanced mask handling and an interconnected complex logistic system. This high-capacity mask storage system DMS M1900.22 for more than 3000 masks with fully automated mask and box handling as well as full-blown XCDA purge has been developed and adapted to the Infineon Lithotoollandscape using Nikon and SMIF reticle cases. Advanced features for ESD safety and mask security, mask tracking via RFID and interactions with the exposure tools were developed and implemented. The stocker is remote controlled by the iCADA-RSM system, ordering of the requested mask directly from the affected exposure tool allows fast access. This paper discusses the advantages and challenges for this approach as well as the practical experience gained during the implementation of the new system which improves the fab performance with respect to mask quality, security and throughput. Especially the realization of an extremely low and stable humidity level in addition with a well controlled air flow at each mask surface, preventing masks from haze degradation and particle contamination, turns out to be a notable technical achievement. The longterm stability of haze critical masks has been improved significantly. Relevant environmental parameters like

  6. Migration mechanism of a GaN bicrystalline grain boundary as a model system

    NASA Astrophysics Data System (ADS)

    Lee, Sung Bo; Yoo, Seung Jo; Kim, Young-Min; Kim, Jin-Gyu; Han, Heung Nam

    2016-05-01

    Using in situ high-resolution transmission electron microscopy, we have explored migration mechanism of a grain boundary in a GaN bicrystal as a model system. During annealing at 500 °C, the grain-boundary region underwent a decrease in thickness, which occurred by decomposition or sublimation of GaN during annealing at 500 °C coupled with electron-beam sputtering. The decrease in thickness corresponds to an increase in the driving force for migration, because the migration of the grain boundary was driven by the surface energy difference. As the driving force increased with annealing time, the grain-boundary morphology turned from atomically smooth to rough, which is characterized by kinetic roughening. The observations indicate that a grain boundary exhibits a nonlinear relationship between driving force for migration and migration velocity, in discord with the general presumption that a grain boundary follows a linear relationship.

  7. Response of GaN to energetic ion irradiation: conditions for ion track formation

    NASA Astrophysics Data System (ADS)

    Karlušić, M.; Kozubek, R.; Lebius, H.; Ban-d'Etat, B.; Wilhelm, R. A.; Buljan, M.; Siketić, Z.; Scholz, F.; Meisch, T.; Jakšić, M.; Bernstorff, S.; Schleberger, M.; Šantić, B.

    2015-08-01

    We investigated the response of wurzite GaN thin films to energetic ion irradiation. Both swift heavy ions (92 MeV Xe23+, 23 MeV I6+) and highly charged ions (100 keV Xe40+) were used. After irradiation, the samples were investigated using atomic force microscopy, grazing incidence small angle x-ray scattering, Rutherford backscattering spectroscopy in channelling orientation and time of flight elastic recoil detection analysis. Only grazing incidence swift heavy ion irradiation induced changes on the surface of the GaN, when the appearance of nanoholes is accompanied by a notable loss of nitrogen. The results are discussed in the framework of the thermal spike model.

  8. Anisotropy of two-photon absorption and free-carrier effect in nonpolar GaN

    SciTech Connect

    Fang, Yu; Zhou, Feng; Yang, Junyi; Wu, Xingzhi; Xiao, Zhengguo; Li, Zhongguo; Song, Yinglin

    2015-03-30

    We reported a systematic study about the anisotropic optical nonlinearities in bulk m-plane and a-plane GaN crystals by Z-scan and pump-probe with phase object methods under picosecond at 532 nm. The two-photon absorption coefficient, which was measured as a function of polarization angle, exhibited oscillation curves with a period of π/2, indicating a highly polarized optical third-order nonlinearity in both nonpolar GaN samples. Furthermore, free-carrier absorption revealed stronger hole-related absorption for E⊥c than for E//c probe polarization. In contrast, free-carrier refraction was found almost isotropic due to electron-related refraction in the isotropic conduction bands.

  9. Strain modulating half-metallicity of semifluorinated GaN nanosheets

    NASA Astrophysics Data System (ADS)

    Xiao, Meixia; Ao, Zhimin; Xu, Tianhan; He, Cheng; Song, Haiyang; Wang, Lei

    2016-06-01

    Strain-dependent half-metallicity of two-bilayer GaN nanosheets (NSs) with fluorinated Ga atoms is studied using density-functional theory. Our results demonstrate that the band gaps in spin-up states and half-metallic gaps vary with biaxial strain and uniaxial compressive strain along the zigzag direction, while the metallic behaviors in spin-down states remain regardless of strain. However, biaxial strain has a better effect on the half-metallicity. Semifluorinated GaN NSs may undergo a structural phase transition from wurtzite to graphite-like phase at high biaxial tension. Therefore, biaxial strain tuning half-metallicity efficiently could provide a viable route to GaN-based spintronic nanodevices.

  10. Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

    SciTech Connect

    Corrion, A. L.; Wu, F.; Speck, J. S.

    2012-09-01

    c-plane GaN films were grown by ammonia molecular beam epitaxy on metal-organic chemical vapor deposition templates for a wide range of NH{sub 3}:Ga flux ratios and growth temperatures, and the resulting films were characterized using atomic force microscopy, reflection high-energy electron diffraction, and transmission electron microscopy. Three distinct nitrogen-rich growth regimes - unstable layer-by-layer, quasi-stable step flow, and dislocation-mediated pitting - were identified based on the growth mode and film properties. In addition, step flow growth was observed under conditions of gallium droplet accumulation. The results indicate the existence of two regimes for step-flow growth of GaN by ammonia MBE - both gallium-rich and nitrogen-rich. Growth mode instabilities and mound formation were observed and are discussed in the context of a step-edge energy barrier to adatom diffusion over a terrace.

  11. Migration mechanism of a GaN bicrystalline grain boundary as a model system

    PubMed Central

    Lee, Sung Bo; Yoo, Seung Jo; Kim, Young-Min; Kim, Jin-Gyu; Han, Heung Nam

    2016-01-01

    Using in situ high-resolution transmission electron microscopy, we have explored migration mechanism of a grain boundary in a GaN bicrystal as a model system. During annealing at 500 °C, the grain-boundary region underwent a decrease in thickness, which occurred by decomposition or sublimation of GaN during annealing at 500 °C coupled with electron-beam sputtering. The decrease in thickness corresponds to an increase in the driving force for migration, because the migration of the grain boundary was driven by the surface energy difference. As the driving force increased with annealing time, the grain-boundary morphology turned from atomically smooth to rough, which is characterized by kinetic roughening. The observations indicate that a grain boundary exhibits a nonlinear relationship between driving force for migration and migration velocity, in discord with the general presumption that a grain boundary follows a linear relationship. PMID:27210538

  12. Migration mechanism of a GaN bicrystalline grain boundary as a model system.

    PubMed

    Lee, Sung Bo; Yoo, Seung Jo; Kim, Young-Min; Kim, Jin-Gyu; Han, Heung Nam

    2016-01-01

    Using in situ high-resolution transmission electron microscopy, we have explored migration mechanism of a grain boundary in a GaN bicrystal as a model system. During annealing at 500 °C, the grain-boundary region underwent a decrease in thickness, which occurred by decomposition or sublimation of GaN during annealing at 500 °C coupled with electron-beam sputtering. The decrease in thickness corresponds to an increase in the driving force for migration, because the migration of the grain boundary was driven by the surface energy difference. As the driving force increased with annealing time, the grain-boundary morphology turned from atomically smooth to rough, which is characterized by kinetic roughening. The observations indicate that a grain boundary exhibits a nonlinear relationship between driving force for migration and migration velocity, in discord with the general presumption that a grain boundary follows a linear relationship. PMID:27210538

  13. 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.

  14. Nanopores in GaN by electrochemical anodization in hydrofluoric acid: Formation and mechanism

    NASA Astrophysics Data System (ADS)

    Chen, Danti; Xiao, Hongdi; Han, Jung

    2012-09-01

    We report the use of hydrofluoric acid (HF) as an electrolyte in etching and porosifying GaN. HF is found to be effective in rendering a wide range of nanoporous morphology, from curved branches to highly parallel straight pores. Under suitable conditions, the porosification proceeds at a rate greater than 100 μm/min. To elucidate the etching mechanism, cyclic voltammetry is performed, together with a parametric mapping of electrolysis variables such as the doping of GaN, the concentration of HF electrolyte, and the anodization voltage. We demonstrate that the formation of nanoporous structures is largely due to the local breakdown of the reverse-biased semiconductor junction. A quantitative agreement between the estimated width of space-charge region and the observed variation in morphology lends support to a depletion layer model developed previously in the etching of porous-Si.

  15. Evidence of satellite valley position in GaN by photoexcited field emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Yilmazoglu, O.; Pavlidis, D.; Hartnagel, H. L.; Evtukh, A.; Litovchenko, V.; Semenenko, N.

    2008-06-01

    GaN field emitter rods with nanometer diameter were fabricated by photoelectrochemical etching on a n+-GaN substrate. Their electron field emission properties were investigated under ultraviolet (UV) illumination. The Fowler-Nordheim plots of the emission current show different slopes for nonilluminated and UV illuminated devices. A model based on the electron emission from valleys having different specific electron affinities is proposed to explain the experimental results. In the absence of illumination, the GaN rods are almost fully depleted and emission takes place only from the lower valley. Upon UV illumination and presence of a high electric field at the emitter tip, the upper valley of the conduction band appears to be occupied by electrons generated at the valence band. The energy difference between the lower and upper valleys was determined to be 1.15eV and is in good agreement with formerly published theoretical and measured values.

  16. High-throughput Protein Purification and Quality Assessment for Crystallization

    PubMed Central

    Kim, Youngchang; Babnigg, Gyorgy; Jedrzejczak, Robert; Eschenfeldt, William H.; Li, Hui; Maltseva, Natalia; Hatzos-Skintges, Catherine; Gu, Minyi; Makowska-Grzyska, Magdalena; Wu, Ruiying; An, Hao; Chhor, Gekleng; Joachimiak, Andrzej

    2012-01-01

    The ultimate goal of structural biology is to understand the structural basis of proteins in cellular processes. In structural biology, the most critical issue is the availability of high-quality samples. “Structural biology-grade” proteins must be generated in the quantity and quality suitable for structure determination using X-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy. The purification procedures must reproducibly yield homogeneous proteins or their derivatives containing marker atom(s) in milligram quantities. The choice of protein purification and handling procedures plays a critical role in obtaining high-quality protein samples. With structural genomics emphasizing a genome-based approach in understanding protein structure and function, a number of unique structures covering most of the protein folding space have been determined and new technologies with high efficiency have been developed. At the Midwest Center for Structural Genomics (MCSG), we have developed semi-automated protocols for high-throughput parallel protein expression and purification. A protein, expressed as a fusion with a cleavable affinity tag, is purified in two consecutive immobilized metal affinity chromatography (IMAC) steps: (i) the first step is an IMAC coupled with buffer-exchange, or size exclusion chromatography (IMAC-I), followed by the cleavage of the affinity tag using the highly specific Tobacco Etch Virus (TEV) protease; [1] the second step is IMAC and buffer exchange (IMAC-II) to remove the cleaved tag and tagged TEV protease. These protocols have been implemented on multidimensional chromatography workstations and, as we have shown, many proteins can be successfully produced in large-scale. All methods and protocols used for purification, some developed by MCSG, others adopted and integrated into the MCSG purification pipeline and more recently the Center for Structural Genomics of Infectious Diseases (CSGID) purification pipeline, are

  17. Growth of low-defect-density nonpolar a-plane GaN on r-plane sapphire using pulse NH3 interrupted etching.

    PubMed

    Son, Ji-Su; Honda, Yoshio; Amano, Hiroshi

    2014-02-10

    Nonpolar a-plane (11-20) GaN (a-GaN) layers with low overall defect density and high crystalline quality were grown on r-plane sapphire substrates using etched a-GaN. The a-GaN layer was etched by pulse NH3 interrupted etching. Subsequently, a 2-µm-thick Si-doped a-GaN layer was regrown on the etched a-GaN layer. A fully coalescent n-type a-GaN layer with a low threading dislocation density (~7.5 × 10(8) cm(-2)) and a low basal stacking fault density (~1.8 × 10(5) cm(-1)) was obtained. Compared with a planar sample, the full width at half maximum of the (11-20) X-ray rocking curve was significantly decreased to 518 arcsec along the c-axis direction and 562 arcsec along the m-axis direction.

  18. 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.

  19. The Peculiarities of Strain Relaxation in GaN/AlN Superlattices Grown on Vicinal GaN (0001) Substrate: Comparative XRD and AFM Study.

    PubMed

    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

    2016-12-01

    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.

  20. NpN-GaN/InxGa1-xN/GaN heterojunction bipolar transistor on free-standing GaN substrate

    NASA Astrophysics Data System (ADS)

    Lochner, Zachary; Jin Kim, Hee; Lee, Yi-Che; Zhang, Yun; Choi, Suk; Shen, Shyh-Chiang; Doug Yoder, P.; Ryou, Jae-Hyun; Dupuis, Russell D.

    2011-11-01

    Data and analysis are presented for NpN-GaN/InGaN/GaN double-heterojunction bipolar transistors (HBTs) grown and fabricated on a free-standing GaN (FS-GaN) substrate in comparison to that on a sapphire substrate to investigate the effect of dislocations in III-nitride HBT epitaxial structures. The performance characteristics of HBTs on FS-GaN exhibit a maximum collector current density of ˜12.3 kA/cm2, dc current gain of ˜90, and maximum differential gain of ˜120 without surface passivation, representing a substantial improvement over similar devices grown on sapphire. This is attributed to the reduction in threading dislocation density afforded by using a homoepitaxial growth on a high-crystalline-quality substrate. The minority carrier diffusion length increases significantly owing to not only a mitigated carrier trap effect via fewer dislocations, but also possibly reduced microscopic localized states.