Temperature-dependent optical band gap of the metastable zinc-blende structure β-GaN

The temperature-dependent (10–300 K) optical band gap ${\mathit{E}}_0$(T) of the epitaxial metastable zinc-blende-structure β-GaN(001)4×1 has been determined by modulated photoreflectance and used to interpret low-temperature photoluminescence spectra. ${\mathit{E}}_0$ in β-GaN was found to vary from 3.302±0.004 eV at 10 K to 3.231±0.008 eV at 300 K with a temperature dependence given by ${\mathit{E}}_0$(T) =3.302–6.697×${10}^{\mathrm{-}4}$ ${\mathit{T}}^2$/(T+600) eV. The spin-orbit splitting ${\mathrm{\Delta }}_0$ in the valence band was determined to be 17±1 meV. The oscillations in the photoreflectance spectra were very sharp with a broadening parameter Γ of only 10 meV at 10 K. The dominant transition observed in temperature-dependent photoluminescence was attributed to radiative recombination between a shallow donor, at ≃11 meV below the conduction-band edge and the valence band.