Reflectance modulation produced by an intense secondary light beam (photoreflectance) has been studied for wavelength near the fundamental edge in silicon doped epitaxial layers of GaAs as a function of doping, and intensity of the modulating light beam. As the doping concentration increases, the built-in electric field at the surface increases. For all but the heavily doped sample, the line shapes are independent of the modulating light beam, being consistent with the model that the secondary light beam is only slightly modifying the surface electric field. However, in the heavily doped sample, the band gap becomes slightly larger and the broadening parameter increases as much as twice those of lesser doped samples. This may attribute to the band filling effect.
