Fermi-level pinning of GaAs at room temperature directly determined by the amplitude of photoreflectance spectra

Abstract

Photoreflectance (PR) measurements on an n-GaAs epitaxial layer as a function of the intensity of pumping light are reported. Based on the thermionic emission theory and current-transport theory, the pinning position of surface Fermi level can be determined from the dependence of the PR signal on the pumping light intensity. Experiments demonstrated that the PR amplitude depends upon the optical excitation intensity I as ln((gamma) I), which is normally the case experimentally and theoretically. From the analysis of the dependence on the amplitude of PR on optical excitation intensity, the surface Fermi level of GaAs at room temperature about 0.72 +/- 0.02 eV below conduction band was evaluated easily and directly. This result is consistent with those accurately reported results using PR to characterize samples with specially designed complex surface-intrinsic-doped structures for obtaining a uniform Franz-Keldysh oscillations and derived the built-in electric fields then evaluated the Fermi level pinning position indirectly.