The comparative investigation of spectra of characteristic energy losses of electrons reflected from the surface of semiconductors and their alloys

The spectra of electrons backscattered from the surfaces of semiconductors (Si,Ge) and their alloys (Si + Ge) were studied using the reflected electro n energy loss spectroscopy (REELS) at 500-2000 eV primary beam energies. Se ven peaks corresponding to different energy losses have been revealed in th e spectra. Based on an analysis of the experimental data on the REEL spectr a measured for different primary energies and angles of incidence of the el ectron beam as well as on Brillouin zone diagrams and electron density dist ributions in both the valent band and the conduction band the following fea tures have been established. In addition to two peaks resulting from the su rface - and bulk plasmon oscillations of valent electrons there are four pe aks from the interband electron transitions and one (sometimes two) connect ed with the electron polarisation of the ion cores. An oscillator model of a the dielectric function of a solid taking into account the weight of the functions of bulk - and surface energy losses has been proposed to account for the REEL spectra. The model takes into consideration the fact that the energy losses of primary electrons are connected not only with excitation o f plasmons but also with electron transitions from the valent band to the c onduction band. For the calculation of the REEL spectra in terms of the mod el we used information on the band structure of the solid under investigati on. It has been shown that the REEL spectra calculated with the proposed mo del agree with the experimental ones. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.