Correlation between the photoreflectance response at E1 and carrier concentration in n- and p-GaAs

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Abstract
We investigated the photoreflectance (PR) response of metalorganic chemical vapor deposition-grown n- and p-type GaAs at the higher-energy transition E1(≊2.9 eV). The doping level range of interest was 2×1016–4×1018 cm−3 for Si:GaAs and 6×1016– 1×1019 cm−3 for Zn:GaAs. Both the position and the broadening parameter, Γ1, of the E1 transition within the doping concentration range were investigated. The evaluation of Γ1’s, based on the curve fitting of the PR response and the Kramers–Kronig analyzed data reveal a nearly linear relation between Γ1 and the logarithm of the carrier concentration. This observation has the potential application for contactless determination of carrier concentration in moderate and heavily doped nanoscale films. Secondary-ion mass spectroscopy measurements show that there is relatively large compensation in Si:GaAs samples, but it does not correlate with the broadening of the E1 structure.