GaN/AlGaN超晶格透射电镜分析

用MOCVD法生长了120周期的GaN/Al0.14Ga0.86N超晶格,激光剥离技术被有效地用于GaN/AlGaN超晶格截面透射电镜样品的制作.用透射电子显微镜观察到了清晰的超晶格及晶胞周期结构,电子衍射也表明生长的超晶格样品质量较好.在透射电镜图中看到了Al,Ga原子的聚居点,这些聚居点达到应力临界时将可能成为新缺陷的起点.同时观察到GaN缓冲层中的线缺陷大多呈现弯曲的弧形,这是外延生长导致的.     

GaN基激光器多量子阱结构的性能表征与结构优化

研究了包括四元合金在内的三种多量子阱结构,对以此为有源层的激光器进行了性能表征和比较分析.通过对阈值电流和外微分量子效率的测量以及增益分布的模拟分析,证实了四元合金用于量子阱结构生长对提高激光器性能的作用.此外对优化的量子阱结构激光器的漏电流和增益饱和带来的影响进行了研究.     

GaN/AlGaN超晶格透射电镜分析

用MOCVD法生长了120周期的GaN/Al0.14Ga0.86N超晶格，激光剥离技术被有效地用于GaN/AlGaN超晶格截面透射电镜样品的制作. 用透射电子显微镜观察到了清晰的超晶格及晶胞周期结构，电子衍射也表明生长的超晶格样品质量较好. 在透射电镜图中看到了Al, Ga原子的聚居点，这些聚居点达到应力临界时将可能成为新缺陷的起点. 同时观察到GaN缓冲层中的线缺陷大多呈现弯曲的弧形，这是外延生长导致的.     

Improvement of Properties of p-GaN by Mg Delta Doping

The Mg-delta-doped GaN structure has been grown by low-pressure metalorganic chemical vapour deposition.The Hall-effect measurements reveal that the electrical properties are enhanced. The hole concentration is enhanced twice and hole mobility is enhanced three times by Mg-delta doping. Both the etch pit density data and the x-ray diffraction data demonstrate that Mg-delta doping can reduce the threading dislocation density of p-type GaN epilayer.     

Effect of Interface Nanotexture on Light Extraction of InGaN-Based Green Light Emitting Diodes

We report the enhancement of the light extraction of InGaN-based green light emitting diodes （LEDs） via the interface nanotexturing. The texture consists of high-density nanocraters on the surface of a sapphire substrate with an in situ etching. The width of nanocraters is about 0.5 μm and the depth is around 0.1 μm. It is demonstrated that the LEDs with interface texture exhibit about a 27% improvement in luminance intensity, compared with standard LEDs. High power InGaN-based green LEDs are obtained by using the interface nanotexture. An optical ray-tracing simulation is performed to investigate the effect of interface nanotexture on light extraction.     

Optical Defect in GaN-Based Laser Diodes Detected by Cathodoluminescence

GaN-based laser diodes （LDs） with 399 nm wavelength are grown on sapphire substrates by metal organic chemical vapour deposition （MOCVD）. Electroluminescence spectra of the fabricated LDs show that the LDs from some grown wafers failed to emit laser. The SEM and XRD results show the similar surface morphology and interface qualities of multi quantum wells （MQWs） and super-lattices between LDs that succeed and fail to emit laser. However, the cathodoluminescence （CL） measurements reveal a kind of optical defect rather than structural defect in un-emitted LDs. Further depth-dependent CL imaging observation indicates that such optical defects originate from the MQWs to the surface of LDs as a non-irradiative recombination centre that should cause the failure of laser emitting of LDs.     

成核层退火压力对形成高阻GaN的作用

采用了MOCVD生长技术来获得高阻GaN,发现GaN的方块电阻会随着成核层退火压力的降低而迅速升高.当成核层退火压力降到75torr时,形成了高阻GaN,方块电阻达到1011Ω/□以上.原子力显微镜结果显示高阻GaN的表面非常平整,表面粗糙度只有0.15nm.在位激光检测发现高阻样品的成核层经过退火后会形成密度较高的成核岛.样品的X射线分析结果表明,随着退火压力的改变,刃型位错相对于螺型位错会有较大变化.说明刃型位错是GaN电阻变化的主要原因.     

Microstructure Study on Heterostructures of AIInGaN/GaN/Al2O3 by Using Rutherford Backscattering/Channelling and XRD

A quaternary AlInGaN layer is grown by metal-organic chemical vapour deposition on a sapphire （0001） substrate with a thick （〉 1μm） GaN intermediate layer. The compositions of In and A1 are determined by Rutherford backscattering （RBS）. The low ratio between the channelling yield and random yield according to the spectra of RBS/C （χmin = 1.44%） means that the crystal quality of the AllnGaN film is perfect. The perpendicular and the parallel elastic strain of the AIlnGaN layer, e^⊥=-0.15% and e^//= 0.16%, respectively, are derived using a combination of XRD and RBS/channelling.     

线形拟合在X射线衍射研究GaN薄膜材料结构时的必要性

利用高分辨X射线衍射仪(XRD)分析了长时间退火前后的GaN样品.通过对各个样品的(0002)面摇摆曲线进行线形拟合及分析,发现虽然退火后摇摆曲线的半峰宽变大,但面外倾斜角(tilt)的值却变小,从而螺型穿透位错(TD)密度变小,这与化学腐蚀实验的结果一致.我们的结果表明,线形拟合在利用XRD研究GaN薄膜材料结构的过程中是十分必要的,而不能用摇摆曲线的展宽直接表征TD密度.     

Effect of Al Doping in the InGaN/GaN Multiple Quantum Well Light Emitting Diodes Grown by Metalorganic Chemical Vapour Deposition

The effect of Al doping in the GaN layer of InGaN/GaN multiple quantum-well light emitting diodes （LEDs） grown by metalorganic chemical vapour deposition is investigated by using photoluminescence （PL） and highresolution x-ray diffraction. The full width at half maximum of PL of A1 doped LEDs is measured to be about 12nm. The band edge photoluminescence emission intensity is enhanced significantly. In addition, the in-plane compressive strain in the Al-doped LEDs is improved significantly and measured by reciprocal space map. The output power of Al-doped LEDs is 130mW in the case of the induced current of 200mA.