Dynamic behavior of hot-electron–hole plasma in highly excited GaN epilayers

The room-temperature spontaneous luminescence of electron–hole plasma was investigated in GaN epilayers under extremely high quasi-steady-state photoexcitation. The photoluminescence spectra were measured for excitation power densities up to 200 MW/cm2 both under quasiresonant and off-resonant excitation conditions. High carrier temperatures up to 1000 K were observed under off-resonant excitation. A nonmonotonous dependence of the luminescence band peak position Ep on the excitation power density was observed. We attribute this nonmonotonous behavior of Ep to two competing mechanisms: (i) band-gap shrinkage due to carrier screening effects (redshift); and (ii) nonequilibrium carrier heating (blueshift). The obtained results are in a good agreement with finite-temperature theory of the band-gap renormalization.