In situ monitoring of ZnS/GaP and ZnSe/GaAs metalorganic vapor phase epitaxy using reflectance anisotropy spectroscopy and spectroscopic ellipsometry

Abstract

Oxide desorption, homoepitaxial III–V buffer growth and the subsequent metalorganic vapor phase epitaxy of ZnS layers on GaP(001) and ZnSe layers on GaAs(001) were monitored in situ at 350°C using reflectance anisotropy spectroscopy and spectroscopic ellipsometry. Thermal oxide desorption in a II–VI reactor without stabilization by a group V partial pressure leads to rough III–V substrate surfaces with a group VI termination. Application of a proper stabilization induces a well-defined c(4×4) and a (2×1) surface reconstruction on GaAs and GaP, respectively. Atomic force microscopy proves the formation of smooth surfaces with monoatomic steps. Growth of II–VI epilayers was started under various conditions. Anisotropies of the dielectric function that originate from the II–VI surface or from the buried II–VI/III–V interface were calculated from the reflectance spectra. The separated contribution of the interface to the dielectric anisotropy is distinctly affected by different growth starts particularly for ZnS epilayers on GaP.