Indirect interband transition in hexagonal GaN

In this paper, we report on optical investigations with Raman experiment to underline a new ultraviolet (UV) luminescence band in hexagonal gallium nitride (GaN) at 4.56?eV. GaN is a direct band gap semiconductor, the photoluminescence peak corresponding to the energy gap at 3.43?eV dominates the spectrum. Nevertheless, other electronic interband transitions can appear on the spectrum: the electronic indirect interband transitions. We attribute one of them to the observed new photoluminescence band at 4.56?eV. This interpretation is supported by photoluminescence spectra obtained on three different samples at room temperature and at ?50??C with UV excitation source: mbd-266?nm solid laser (4.66?eV) and by the study of three criteria: the partly opposite parities of initial and final wave function, the implication of acoustic phonons and temperature control.