Influence of phonons on the temperature dependence of the band gap of AlN and Al_xGa_1-xN alloys with high AlN mole fraction

The temperature dependence of the optical band gap of AlN and Al _xGa_1-xN alloys, with x ∼ 0.6, has been studied using optical absorption spectroscopy. The band gap shrinkage is interpreted based on electron-phonon interactions using a two-phonon oscillator model. The two-oscillator model includes average acoustic and optic phonon energies and thermal occupation factor described by the Bose function. The temperature dependence of the transition width, from transparent to opaque, is also described based on electron-phonon interactions.