Surface Fermi level pinning in epitaxial InSb studied by electric-field-induced Raman scattering.

Electric-field-induced Raman scattering by longitudinal optical (LO) phonons has been used to study the surface Fermi level position in InSb layers grown by molecular beam epitaxy on (100) GaAs. From the analysis of a variety of layers it is found that the LO phonon scattering intensity, relative to that of intrinsic two-LO phonon scattering, decreases with increasing optical power density in n-type samples, but remains constant in p-type and undoped layers, which are residual p-type. The power dependence of the relative LO phonon intensity for n-type doping is shown to be caused by a surface electric field, the strength of which is reduced upon increasing illumination due to screening by photogenerated carriers. As this effect is only found in n-type layers, we conclude that the surface Fermi level is pinned at the valence band thus giving rise to a sizeable surface electric field in n-type but not in p-type material.