Investigation of the space charge regime of epitaxially grown GaAs (100) by high-resolution electron energy-loss spectroscopy

High-resolution electron energy-loss spectroscopy (HREELS) has been used in situ to investigate the space charge regime of homogeneously doped and delta-doped (Si) GaAs (100) samples, which were grown by molecular beam epitaxy (MBE). The simplest model we applied to fit the experimental energy-loss spectra of homogeneously doped samples is based on a step-like distribution of free electrons with the Drude dielectric response function. In this case, the spatial dispersion of plasmon excitations is neglected, whereas in the Thomas-Fermi (or Debye-Hückel) model it is considered. The results of the fitting carried out show that the Drude model gives the higher values for both the free-electron density and the plasmon damping when compared to the Thomas-Fermi model. It thus appeared to provide a more adequate description of the collective dynamic response of free electrons. Post-annealing of the homogeneously doped GaAs (100) samples reveals a significant reduction (compensation) of the free-electron density due to the localization of free electrons on defects diffused from the surface to the bulk.