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

The temperature-dependent (10--300 K) optical band gap E₀(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. E₀ 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 E₀(T) =3.302--6.697×{}10^-4{T}²$/(T+600) eV. The spin-orbit splitting ${{{Δ}}}₀$ 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.