Experimental Studies of Surface Diffusion on Semiconductor Materials

点击翻译按钮获取中文摘要

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.