Photoluminescence Spectroscopy of Band Gap Shrinkage in GaN
  We present an experimental investigation of band-gap shrinkage in n-type GaN using photoluminescence spectroscopy, as a function of electron concentration and temperature. The observed systematic shift of the band-to-band transition energy to lower energies with increasing electron concentration has been interpreted as many-body effects due to exchange and correlation among majority and minority carriers. The band-to-band transition energy also shifts to lower energy with increasing temperature. The parameters that describe the temperature dependence red-shift of the band-edge transition energy are evaluated using different models and we find that the semi-empirical relation based on phonon-dispersion related spectral function leads to excellent fit to the experimental data. 
Niladri Sarkar and Subhasis Ghosh