Reflection anisotropy spectroscopy study of the near-surface electric fields in undoped,n- andp-doped low-temperature grown GaAs (001)

We have evaluated the effective surface electric fields, effective depletion widths, and the sign (n-type/upward band bending) of the near-surface electric fields in undoped as well as n-(5×10¹⁸cm^-3) and p-(5×10¹⁸cm^-3 and 2×10¹⁹cm^-3) doped low-temperature grown (LTG) GaAs (001) using the optical method of reflection-anisotropy (RA) spectroscopy in the vicinity of the spin-orbit split E₁, E₁+Δ₁ optical features. Even for the highest p doping the surface band bending is still n type, indicating the strong influence of the large donor trap densities. Our results are in good agreement with a self-consistent Poisson's calculation of the near-surface electric fields assuming deep donor (1×10²⁰cm^-3) and acceptor (1×10¹⁹cm^-3) trap densities and midgap surface Fermi-level pinning. This experiment provides valuable information about the defect density and position in LTG:GaAs. Our results will be compared to the recent RA spectroscopy experiment and interpretation of Chen et al. [Phys. Rev. B 55, R7379 (1997)].