Influence of Hydrogen on Si-Doped GaAs(100) in the Space Charge Regime

Abstract

The influence of hydrogen on collective excitations of free electrons in the conduction band (surface/interface plasmons) for homogeneously doped (Si) (≈7.5×1018 cm−3) GaAs(100)-c(4×4) surfaces was studied by high-resolution electron-energy-loss spectroscopy (HREELS). A simple two-layer model based on the semiclassical dipole approach was applied to analyse the experimental energy-loss spectra. A spatial dispersion of the surface plasmons in the form of the long-wavelength limit of random-phase approximation (Thomas-Fermi model) and the nonparabolicity of the conduction band were incorporated to the model for fitting the measured HREELS spectra. It was shown that the two competing effects of free-electron compensation and band bending, which modify the spatial dispersion of the surface plasmon, are responsible for the red shift of the surface plasmon energy observed at high hydrogen exposures. Furthermore, results about the influence of hydrogen exposure upon annealed GaAs(100)-c(8×2) surfaces are presented. The findings of the present study prove that the effective in-diffusion of hydrogen atoms occurs and that the creation of hydrogen-induced acceptor levels in the bandgap of heavily-doped n-type GaAs is accompanied by an appreciable reduction of free-electron density in the conduction band. Simultaneously, the high hydrogen exposures cause the large band bending of GaAs(100).