  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.
