Influence of the free-electron concentration on the optical properties of zincblende GaN up to 1×1020 cm-3

Abstract

We analyze the optical properties of zincblende gallium-nitride in the infrared and ultraviolet spectral range (≈27meV-6.5eV) experimentally by spectroscopic ellipsometry and provide a quantitative description of these results by k·p perturbation theory. Free-electron concentrations above 1020cm-3 are achieved by introducing germanium as a donor. We determine the dielectric function as well as band filling effects like the Burstein-Moss shift and band gap renormalization. The Kane model for the band structure of semiconductors near the Γ-point allows to calculate the effective electron mass and to determine the nonparabolicity of the conduction band. At the same time, these results can be used to derive the free-electron concentration all-optically. The combination of Kane's model, Burstein-Moss shift, and band-gap renormalization can be used to expertly describe the measured transition energies up to ≈3.7eV dependent on the carrier concentration, yielding an averaged hole mass of ≈0.61me for the contributing valence bands.