Experimental Studies of Surface Diffusion on Semiconductor Materials

利用表面二次谐波产生技术（SHG）对吸附质浓度曲线进行直接成像，研究了半导体表面的扩散。在锑锗（111）体系中的研究表明，SHG方法避免了与其他方法相关的许多问题，允许在没有参数化的情况下提取扩散系数的覆盖依赖性，并允许观察环境气体压力对表面扩散的影响。目前的工作集中在III-V吸附（包括砷化镓）在硅和锗上。活化能和扩散的指数前因子作为表面浓度和表面台阶的密度和取向的函数来测量。这种方法也被扩展到气态吸附物，如三乙基镓。考察了各种因素对扩散的影响；这些包括光子通量、平行于表面的电场和周围的惰性气体。表面扩散通常在控制表面反应速率方面起主要作用，特别是对于那些通过化学气相沉积或分子束外延形成半导体薄膜的反应。由于缺乏表面扩散的数据，对工艺和产品质量的控制受到阻碍。这项研究为获取这类信息提供了一种有效和通用的方法。

Surface diffusion on semiconductors is examined by direct imaging of adsorbate concentration profiles using surface second harmonic generation (SHG). Work in the antimony on germanium (111) system has demonstrated that the SHG method avoids many of the problems associated with other methods, permits extraction of the coverage dependence of the diffusivity without paramaterization, and allows observation of the effects of ambient gas pressure on surface diffusion. The present effort focusses on III-V adsorbates (including gallium arsenide) on silicon and germanium. Activation energies and preexponential factors for diffusion are measured as functions of surface concentration and of the density and orientation of surface steps. The approach is also being extended to gaseous adsorbates such as triethylgallium. The effects of various factors on diffusion are examined; these include photon flux, electric fields directed parallel to the surface, and ambient noble gases. Surface diffusion often has a primary role in governing the rates of surface reactions, particularly for those involved in the formation of thin films of semiconductors by chemical vapor deposition or molecular beam epitaxy. Control of the process and of the quality of the product are hampered by a lack of data on surface diffusion. This research produces an efficient and general methodology for obtaining such information.