Spectra of electroreflection from silicon surface subjected to ion bombardment

A study of the shapes of electroreflection spectra in the range of photon energies 3.0 to 5.0 eV and at 300 K has been carried out on the silicon surfaces both etched and bombarded by argon and helium ions. It has been found, that the critical point energy changes from 3.42 eV for the etched surface to 3.6 eV for the ion-bombarded surface with maximum dose of approximately 1017 ion/cm2. At the same time, the energy of the higher critical point E2=4.3 eV showed no change with the bombardment dose D. Also, a sharp increase of the broadening parameter from 110 to 450 meV at maximal D has been found, as well as a decrease in the amplitude of electroreflection peaks, correlated with the growth of the density of the surface electronic states. The possible causes of the changes mentioned are discussed. It is noted, in particular, that the dominating mechanism of the change in the band structure of a bombarded surface is the rise of heterogeneously distributed mechanical tensions and electric fields in the surface layer of silicon