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1.
The effects of sapphire nitridation on GaN growth by metalorganic chemical vapour deposition 下载免费PDF全文
In situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above a low-temperature GaN buffer layer on a c-plane sapphire substrate by metalorganic chemical vapour deposition. It is found that the lateral growth of the GaN islands and their coalescence are promoted in the initial growth stage if optimized nitridation time and temperature are selected when the substrate is pre-exposed to ammonia. As confirmed by atomic force microscopy observations, the quality of the GaN epilayers is closely dependent on the surface morphology of the nitridated buffer layer, especially grain size and nucleation density. 相似文献
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2008年的数学高考考试大纲中,数列部分有一类能力要求为A,其余三类的能力要求均达到C级,它们分别是等差数列、等比数列以及数列的综合应用.对于能力C级,即为灵活和综合应用,要求学生系统地掌握知识的内在联系,能运用所列知识分析和解决较为复杂或综合性的问题.…… 相似文献
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Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well solar cells 下载免费PDF全文
Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well(MQW) solar cells are investigated. It is found that due to the reduction of piezoelectric polarization and the enhancement of tunneling transport of photo-generated carriers in MQWs, the external quantum efficiency(EQE) of the solar cells increases in a low energy spectral range(λ 370 nm) when the barrier thickness value decreases from 15 nm to 7.5 nm. But the EQE decreases abruptly when the barrier thickness value decreases down to 3.75 nm. The reasons for these experimental results are analyzed. We are aware that the reduction of depletion width in MQW region, caused by the high resistivity of the p-type GaN layer may be the main reason for the abnormally low EQE value at long wavelengths(λ 370 nm). 相似文献
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Reduction of Dislocations in GaN Epilayer Grown on Si (111) Substrates using a GaN Intermedial Layer 下载免费PDF全文
GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si(111) substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional (3D) mode to the 2I) one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy (TEM) measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer. 相似文献
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The novel Gd3(Fe0.978Ti0.022)29 compounds and their nitride have been synthesized. The X-ray diffraction patterns of the Gd3(Fe,Ti)29Ny and its parent compounds were indexed in the Nd3(Fe,Ti)29-type structure with a monoclinic symmetry and space group P21/c, Both the nitride and the parent compounds exhibit ferrimagnetlc coupling. Nitrogenatio led to an increase in Curie temperature and saturation magnetization. The Curie temperatures are 517K for the parent and 765K for the nitride. The saturation magnetizations σs at 4.2K are 101.9A·m2/kg for the parent and 128A·m2/kg for the nitride. Both the nitride and parent exhibit a planar anisotropy. Nitrogenation led to a decrease of the contribution of Fe-sublattice to planar anisotropy. The anisotropy fields at 4.2K are 9.8T for the parent and 6.5 T for the nitride. 相似文献
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合成了三缩四乙二醇一二一(g_A奎琳基)醚(I)配体,并首次合成了与十四个稀土硝酸盐的固体配合物二用IR,TCr; DTA等测试确定固体配合物组成为〔Ln(N03)3)}( I ),(Ln = La, Ce, Pr, Nd)和〔Ln(N03)3)s( I )}H,O(Ln=Sm-Yb和Y).配体(I}和配合物〔La(N03)3]3( I):核磁共振谱分析表明,醚链上的质子向低场位移,“奎咐环I质子向高场位移,这说明会闹与配体(I)中刀奎琳上的氮是直接配位的, 相似文献
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采用金属有机化合物化学气相沉积(MOCVD)方法制备了不同Al组分(x=0.19,0.22,0.25,0.32)的AlxGa1-xN/AlN/GaN 结构的高电子迁移率晶体管(HEMT)材料。研究了AlxGa1-xN势垒层中Al组分对HEMT材料电学性质和结构性质的影响。研究结果表明,在一定的Al组分范围内,二维电子气(2DEG)浓度和迁移率随着Al组分的升高而增大。然而,过高的Al组分导致HEMT材料表面粗糙度增大,2DEG迁移率降低,该实验现象在另一方面得到了原子力显微镜测试结果的验证。在最佳Al组分(25%)范围内,获得的 HEMT材料的2DEG浓度和室温迁移率分别达到1.2×1013 cm-2和1 680 cm2/(V·s),方块电阻低至310 Ω/□。 相似文献