Infrared reflectance studies of bulk and epitaxial-film n-type GaAs

Abstract

The reflectance spectra of n-type GaAs samples with carrier densities from 3×1016 to 3×1018 cm−3 have been measured in the spectral range 55–1000 cm−1. Except for slight discrepancies in the vicinity of the reflectance minima, the classical Drude model provides an excellent description of the free-carrier effects in the reflectance. The discrepancies may be accounted for by a depletion layer at the surface or by a quantum-mechanical scattering theory. Inhomogeneities in the carrier density are measured by scanning the surface of the sample with a small aperture at a fixed frequency. The effect of mechanical polishing on the reflectance is analyzed in terms of a damaged layer. Reflectance measurements are also used to characterize samples consisting of epitaxial films of GaAs on GaAs substrates.