Urbach–Martienssen tails in a wurtzite GaN epilayer

Effects of an interaction between the electronic and lattice systems on the optical spectra of a wurtzite GaN epilayer were investigated. The exponentially increasing absorption tail was well explained as an Urbach–Martienssen tail, giving the characteristic phonon energy of 30 meV. The result indicates that few longitudinal optical phonons contribute to the exciton-phonon coupling even at room temperature.