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 us ed in situ to investigate the space charge regime of homogeneously dop ed and delta-doped (Si) GaAs (100) samples, which were grown by molecu lar beam epitaxy (MBE). The simplest model we applied to fit the exper imental 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 exc itations is neglected, whereas in the Thomas-Fermi (or Debye-Huckel) m odel it is considered, The results of the fitting carried out show tha t the Drude model gives the higher values for both the free-electron d ensity and the plasmon damping when compared to the Thomas-Fermi model . It thus appeared to provide a more adequate description of the colle ctive dynamic response of free electrons. Post-annealing of the homoge neously doped GaAs (100) samples reveals a significant reduction (comp ensation) of the free-electron density due to the localization of free electrons on defects diffused from the surface to the bulk.