Electroreflection spectra of the surface of ion-bombarded silicon

The electroreflection spectra were determined for silicon surfaces subjected to etching and bombardment with argon and helium ions. The investigation was carried out in the photon energy range 3.0--5.0 eV at 300degreeK. The energy of the critical point E$sub 1$(E'$sub 0$) changed from 3.42 eV (for an etched surface) to 3.6 eV (for a surface bombarded with the maximum dose of approx.10$sup 17$ cm$sup -2$ argon ions). The energy of another critical point E$sub 2$=4.3 eV was found to be independent of the radiation dose D. Moreover, the broadening parameter GAMMA increased from 110 to 450 meV at the maximum dose and the amplitudes of the electroreflection peaks decreases; this was correlated with a increase in the density of the surface electron states. Possible causes of these bombardment-induced changes were considered. The appearance of heterogeneously distributed mechanical stresses and electric fields in the surface layer of silicon subjected to bombardment was identified as the dominant mechanism responsible for changes in the energy-band structure.