Temperature dependence of the band gap shrinkage due to electron-phonon   interaction in undoped n-type GaN
  The photoluminescence spectra of band-edge transitions in GaN is studied as a function of temperature. The parameters that describe the temperature dependence red-shift of the band-edge transition energy and the broadening of emission line are evaluated using different models. We find that the semi-empirical relation based on phonon-dispersion related spectral function leads to excellent fit to the experimental data. The exciton-phonon coupling constants are determined from the analysis of linewidth broadening. 
Niladri Sarkar and Subhasis Ghosh