Optical constants of cubic GaN/GaAs(001): Experiment and modeling

Abstract

The optical constants ε(E)=ε1(E)+iε2(E) of unintentionally doped cubic GaN grown on GaAs(001) have been measured at 300 K using spectral ellipsometry in the range of 1.5–5.0 eV. The ε(E) spectra display a structure associated with the critical point at E0 (direct gap) and some contribution mainly coming from the E1 critical point. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden–Muñoz model dielectric function [M. Muñoz et al., J. Appl. Phys. 92, 5878 (2002)]. This model is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E0, E0+Δ0 and the E1, E1+Δ1, doublet. In addition to evaluating the energy of the E0 critical point, the binding energy (R1) of the two-dimensional exciton related to the E1 critical point was estimated using the effective mass/k⋅p theory. The line shape of the imaginary part of the cubic-GaN dielectric function shows excitonic effects at room temperature not withstanding that the exciton was not resolved.