The role of the low temperature buffer layer and layer thickness in the optimization of OMVPE growth of GaN on sapphire

In agreement with previous work,¹² a thin, low temperature GaN buffer layer, that is used to initiate OMVPE growth of GaN growth on sapphire, is shown to play a critical role in determining the surface morphology of the main GaN epilayer. X-ray analysis shows that the mosaicity of the main GaN epilayer continues to improve even after several μm of epitaxy. This continuing improvement in crystal perfection correlates with an improvement in Hall mobility for thicker samples. So far, we have obtained a maximum mobility of 600 cm²/V-s in a 6 μm GaN epilayer. Atomic force microscopy (AFM) analysis of the buffer layer and x-ray analysis of the main epilayer lead us to conclude that the both of these effects reflect the degree of coherence in the main GaN epitaxial layer. These results are consistent with the growth model presented by Hiramatsu et al., however, our AFM data indicates that for GaN buffer layers partial coherence can be achieved during the low temperature growth stage.     

InGaAs／AlGaAs 941 nm高功率半导体激光二极管阵列

利用金属有机化合物气相淀积(MOCVD)技术生长了InGaAs／GaAs／AlGaAs分别限制应变单量子阱激光器材料。利用该材料制成半导体激光器线阵的峰值波长为941nm，光谱的半高全宽(FWHM)为3．3nm，在400μs、50Hz的输入电流下，输出峰值功率达到67．9W，斜率效率高达0．85W／A(64％)。     

Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina‐forming alloy. Part III: The use of two stage oxidation experiments and in situ X‐ray diffraction to understand the oxidation mechanisms

The aim of this work was to investigate several different yttrium introduction routes to improve the high temperature oxidation resistance of a Fe‐20Cr‐5Al model alloy. Y₂O₃ sol‐gel coatings, Y₂O₃ metal‐organic chemical vapor deposition (MOCVD) coatings, yttrium ion implantation and yttrium as alloying element (0.1 wt.%) were the different methods of introduction of the reactive element. Both isothermal and cyclic oxidation tests showed that the surface introduction of yttrium or yttrium oxide did not drastically improve the oxidation behavior of the steel. Complementary experiments were performed to understand the lack of major beneficial effects of the so‐treated samples. Two stage oxidation experiments under 200 mbar ¹⁶O₂ and ¹⁸O₂ followed by secondary neutral mass spectrometry (SNMS) were performed to understand the alumina scale growth mechanisms, according to the introduction route of the reactive element. The results exhibited that the yttrium induced an increase of the inward transport of oxygen through the alumina scale compared to the untreated specimen. Nevertheless, the outward transport of aluminum was generally observed, except for the specimen containing Y as alloying element, which exhibited only a single¹⁸O peak close to the metal/oxide interface. Phase transformations during the oxidation at 1100°C were registered by in‐situ X‐ray diffraction (XRD). The untreated alloy was only covered by a thin layer of α‐Al₂O₃. For implanted specimens, yttrium was incorporated in Y₃Al₅O₁₂ and YAlO₃ phases. All the YAlO₃ is transformed into Y₃Al₅O₁₂ after less than 10 h. For the MOCVD or the sol‐gel coated samples, the primary formed YAlO₃ phase was progressively transformed into Y₃Al₅O₁₂. For the Fe‐20Cr‐5Al‐0.1Y alloy, no yttrium containing phases could be detected, even after 40 h of oxidation test at 1100°C.     

Diffusion Growth Model of Doping—impurity Longitudinal Profile in Grown Material by MOCVD and Chloride VPE

The program process of the longitudinal impurity profile introduced in the quantum well(QW)laser and microwave electronic materials in analysed,based on the growth system by metalorganic chemical vapor deposition(MOCVD)and microwave electronic materials and chloride vapor phase epitaxy(VPE).The quantitative solution of the final longitudinal direction impurity distribution using the mathematical physics model of impurity carrier-gas transport drift and rediffusion in growth process was carried out.A technology for giving a reference to grown imputity profile of abrupt doping and uniform longitudinal direction based on the theory is presented.     

Surface photoabsorption monitoring of the growth of GaAs and InGaAs at 650°C by MOCVD

By monitoring the cyclic behavior of surface photoabsorption (SPA) reflectance changes during the growth of GaAs at 650°C and with sufficient H₂ purging time between the supply of trimethylgallium and AsH₃, we have been able to achieve controlled growth of GaAs down to a monolayer. Our results show, as confirmed by photoluminescence (PL) measurements, the possibility of growing highly accurate quantum well heterostructures by metalorganic chemical vapor deposition at conventional growth temperatures. We also present our PL measurements on the InGaAs single quantum wells grown at this temperature by monitoring the SPA signal.     

Study of indium droplets formation on the InxGa1−xN films by single crystal x-ray diffraction

Indium droplet formation during the epitaxial growth of In_xGa_1−xN films is a serious problem for achieving high quality films with high indium mole fraction. In this paper, we studied the formation of indium droplets on the In_xGa_1−xN films grown by metalorganic chemical vapor deposition (MOCVD) using single crystal x-ray diffraction. It is found that the indium (101) peak in the x-ray diffraction spectra can be utilized as a quantitative measure to determine the amounts of indium droplets on the film. It is shown by monitoring the indium diffraction peak that the density of indium droplets increases at lower growth temperature. To suppress these indium droplets, a modulation growth technique is used. Indium droplet formation in the modulation growth is investigated and it is revealed in our study that the indium droplets problem has been partially relieved by the modulation growth technique.     

InGaAs（P）／InP应变量子阱和超晶格的光电性质

利用低压金属有机化合物化学汽相沉积（ＭＯＣＶＤ）生长技术在ＩｎＰ衬底上生长ＩｎＧａＡｓ／ＩｎＰ应变量子阱，超晶格和ＩｎＧａＡｓＰ／ＩｎＰ量子阱结构材料，利用７７Ｋ光荧光（ＰＬ）测量这一应变量了阱和量子阱的光学性质，利用双晶Ｘ光测量应变超晶格的性质。     

Ni－Cr衬底上MOCVD法制备YSZ过渡层的研究

用ＭＯＣＶＤ方法在柔性金属衬底上沉积超导膜是潜在的实用高温超导成材方法。用适当方法原位快速地制备有择优取向的防扩散过渡层是其中的关键。本文报导用有机源Ｙ（ｄｐｍ）_３和Ｚｒ（ｄｐｍ）_４，采用ＭＯＣＶＤ方法在Ｎｉ基合金衬底上沉积了Ｙ稳定的ＺｒＯ_２立方相过渡层，厚度约０．５μｍ。文中研究了氧分压和沉积温度对ＹＳＺ结晶和择优取向的影响。结果表明，在生长压力为１３０Ｐａ时，氧分压低至２０Ｐａ，制备出（１１１）取向为主的ＹＳＺ多晶膜，氧分压为５０～１００Ｐａ，则制备出（ｈ００）择优取向为主的ＹＳＺ膜。衬底温度太低，将导致ＹＳＺ膜质量变差。     

MOCVD生长1．06μm InGaAs／GaAs量子阱LDs

用低压MOCVD生长应变InGaAs/GaAs量子阱,采用中断生长、应变缓冲层(SBL)、改变生长速度和调节Ⅴ/Ⅲ等方法改善InGaAs/GaAs量子阱的光致发光(PL)质量。PL结果表明,10s生长中断结合适当的SBL生长的量子阱PL谱较好。该量子阱应用于1.06μm激光器的制备,未镀膜的宽条激光器(100μm×1000μm)有低阈值电流密度(110A/cm2)和高的斜率效率(0.256W/A,per.facet)。     

ZnO薄膜的XPS研究

利用等离子体增强型MOCVD设备,在C面蓝宝石上生长出了C轴取向的未退火、生长后一次退火和生长过程中多次退火的ZnO薄膜样品,并通过X光衍射和X光电子能谱对样品进行了表征,结果表明生长过程中多次退火的样品具有较高的质量,O/Zn原子比较大,且受空气中氧和水汽的影响最小.