4°偏轴SiC衬底外延工艺研究

4°偏轴SiC衬底上生长的外延薄膜容易出现台阶形貌,外延薄膜表面的台阶形貌对后续制作的器件性能有着一定的影响。主要研究了进气端C/Si比及生长前刻蚀工艺对4°偏轴衬底外延的影响。采用外延生长前的氢气刻蚀工艺,结合掺杂浓度缓变的缓冲层设计,在4°偏轴的SiC衬底上制得了表面无台阶形貌的SiC SBD结构外延材料。利用优化工艺生长的4°偏轴衬底上的SBD结构外延材料目前已经全面应用于600～1 700V SBD器件的研制。     

InGaAs/InP材料的MOCVD生长研究

研究了InGaAs/InP材料的MOCVD生长技术和材料的性能特征。InP衬底的晶向偏角能够明显影响外延生长模型以及外延层的表面形貌,用原子力显微镜(AFM)观察到了外延层表面原子台阶的聚集现象(step-bunching现象),通过晶体表面的原子台阶密度和二维生长模型解释了台阶聚集现象的形成。对外延材料进行化学腐蚀,通过双晶X射线衍射(DCXRD)分析发现异质结界面存在应力,用异质结界面岛状InAs富集解释了应力的产生。通过严格控制InGaAs材料的晶格匹配,并优化MOCVD外延生长工艺,制备出厚层InGaAs外延材料,获得了低于1×1015cm-3的背景载流子浓度和良好的晶体质量。     

Kinetics and Thermodynamics Induced Step-bunching Instability on Semiconductor Surface

This paper introduces the basic kinetic and thermodynamic factors affecting step-bunching instability and derive the one-dimensional(1D) step motion equation based adatom diffusion equation for further analysis.The step-bunching instability is analyzed for different cases.     

Step structure of GaInAsSb grown by organometallic vapor phase epitaxy

The surface step structure of Ga_1−xIn_xAs_ySb_1−y grown by organometallic vapor phase epitaxy on GaSb substrates has been studied by atomic force microscopy. Epilayers were grown at 525°C and 575°C on (001) GaSb substrates misoriented 2° toward (101) or 6° toward (1 1)B. For Ga_0.88In_0.12As_0.1Sb_0.9 grown at 575°C, the surface exhibits step-bunching on both types of substrates. When the composition is increased to Ga_0.86In_0.14As_0.12Sb_0.88, the periodic step structure breaks down and the surface becomes irregular. The deterioration of the step structure is a consequence of phase separation at the surface of the metastable GaInAsSb epilayer, which leads to the formation of GaAs- and InSb-rich regions. The photoluminescence (PL) of such layers show significant broadening due to carrier recombination in the lower energy gap InSb-rich quaternary regions. On the other hand, the surface of GaInAsSb epilayers grown at a lower temperature of 525°C is vicinal with steps heights of one to two monolayers. The PL FWHM values are considerably smaller for these layers. This improvement in material quality is related to smaller adatom lifetimes at the lower growth temperature. The importance of surface kinetics as it influences the step structure and thermodynamically driven phase separation is discussed.     

ZTS晶体(100)面台阶聚并现象的AFM非实时研究

通过对301 K时,不同过饱和度以及掺杂2.5%(摩尔分数)尿素(σ=0.09)条件下生长的ZTS晶体进行AFM非实时扫描,对其(100)面的基本台阶以及聚并形成宏观台阶的形貌情况进行了研究。发现ZTS晶体(100)面在低过饱和度下(σ=0.03),以基本台阶推移为主,台阶高度约为0.553nm,近似为晶格参数a值的一半;在高过饱和度下(σ=0.09),以台阶聚并后的宏观台阶推移为主。而在同样的过饱和度下掺入尿素则会加剧台阶聚并的程度,该实验结果很好地符合了杂质诱导产生非对称台阶动力学系数理论模型。