PHOTOREFLECTANCE SPECTRA FROM THE SURFACE AND GAAS GAAS INTERFACES OFDOPED MBE GAAS FILMS/

We report on photoreflectance (PR) measurements of the electric fields at the surface and GaAs/GaAs interface of doped GaAs films prepared b y molecular beam epitaxy (MBE). By using He-Ne and He-Cd lasers altern ately as the pump light, PR signals from the surface and interface of the films can be effectively separated because of the difference in th e penetration depths of these two pump beams. Electric fields at the s urface and interface were evaluated from PR spectra. Film interference effects on modulation spectroscopy have been studied. The origin of t he electric field at interfaces has also been discussed.