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

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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.