Real-time analysis of III-V-semiconductor epitaxial growth

This paper summarizes recent results in optical real time analysis of epitaxial growth. Emphasis is placed on reflectance anisotropy spectroscopy (RAS) and spectroscopic ellipsometry (SE) which by their accuracy and sensitivity seem to be the most promising tools for analysis in the three main epitaxial methods: metal-organic vapour phase epitaxy (MOVPE), molecular beam epitaxy (MBE) and metal-organic MBE (MOMBE). Both optical techniques exploit the polarisation changes imposed by the surface upon reflection. Thereby RAS, sensing the anisotropic part of the reflectance, turns out to be extremely surface sensitive in materials which are otherwise (in the bulk) optically isotropic. This is the case for all semiconductors with diamond or zincblende structure. After giving a basic understanding of RAS, chemical trends in the presently available data of different III-V-semiconductor surfaces are discussed. Using GaAs(001) as a well studied example, differences in growth dynamics and growth mechanisms in the three epitaxial growth techniques are presented. From these basic studies useful applications are derived for growth monitoring including substrate conditioning before growth (group V stabilisation, temperature), control of thickness and stoichiometry during growth as well as monitoring the switching procedures during the growth of heterostructures.