Comparison of reflectance difference spectroscopy and surface photoabsorption used for the investigation of anisotropic surfaces

Abstract

Reflectance difference spectroscopy (RDS) and surface photoabsorption (SPA) are two optical characterization techniques that are now in common use for monitoring and controlling epitaxial growth. Here we establish the connection of SPA data to the surface dielectric response, using an anisotropic three phase model (substrate, anisotropic overlayer, ambient). In contrast to the generally accepted picture, our calculations show, that the contribution to the SPA signal from the dielectric component normal to the surface is negligible, and that the major contribution arises from the projection of the dielectric tensor on the line formed by the intersection of the surface and the plane of incidence. It follows, that the difference between SPA data taken with the plane of incidence along the different principal axis is related to, and in fact can be calculated from, RDS spectra. By comparing published data to our database of RD spectra, we are able to find the surface reconstruction present during flow modulated organo metallic chemical vapour epitaxial growth of GaAs epilayers.