Effect of surface and nonuniform fields in electroreflectance: Application to Ge

Abstract

The effect of crystal termination and nonuniform modulation fields is investigated theoretically in the one-electron approximation. Beginning with the nonlocal dielectric susceptibility expression previously obtained by Del Sole, it is shown that under suitable conditions the surface and field inhomogeneity contributions can be separated. Odd and even line shape components are obtained. The odd component, which at low fields varies linearly with the modulation field, arises from crystal termination. It depends on the mass difference between the electron and the hole and vanishes if the electron and hole masses are equal. The even component includes both crystal termination and field inhomogeneity effects and does not reduce completely to the Franz-Keldysh theory even in the uniform-field limit. Experimental results are presented for the odd electron reflectance component for the $E_0$ transition of Ge. The results are in good agreement with theory.