REFLECTANCE-DIFFERENCE SPECTROSCOPY STUDY OF THE FERMI-LEVEL POSITIONOF LOW-TEMPERATURE-GROWN GAAS

The results of a reflectance-difference spectroscopy study of GaAs gro wn on (100) GaAs substrates by low-temperature molecular-beam epitaxy (LT-GaAs) are presented. In-plane optical anisotropy resonances which come from the linear electro-optic effect produced by the surface elec tric field are observed. The RDS line shape of the resonances clearly shows that the depletion region of LT-GaAs is indeed extremely narrow (much less than 200 Angstrom). The surface potential is obtained from the RDS resonance amplitude without the knowledge of space-charge dens ity. The change of the surface potential with post-growth annealing te mperatures reflects a complicated movement of the Fermi level in LT-Ga As. The Fermi level still moves for samples annealed at above 600 degr ees C, instead of being pinned to the As precipitates. This behavior c an be explained by the dynamic properties of defects in the annealing process.