Effect of a Constant Electrical Field on Germanium Fast Surface States

The experimental evidence regarding the effect of electric fields on the fast states of germanium is, at present, contradictory: Litovchenko and Lyashenko explained their experimental results by assuming the fields only affect the density of states but not their energy, this would support the current view on charge transfer through the semiconductor oxide layer. Rzhanov et al., on the other hand, reported field-induced changes in energy as well as density. To resolve this question, careful measurements of surface recombination velocity and surface conductivity were performed before and after application of dc fields of about 2×${10}^6$ volts/cm. Though the effect of the field on the surface state density was much smaller than that found by Litovchenko and Lyashenko, the experimental results indicated clearly that the energy and ratio of capture cross sections were indeed unaffected by the field. It was also found that in wet ambients an ac field shifted the unperturbed surface potential by more than $+5\mathrm{kT}$.