A carbon-doping related luminescence band in GaN revealed by below bandgap excitation

Carbon doped GaN grown by hydride vapor phase epitaxy was investigated by photoluminescence and photoluminescence excitation spectroscopy covering a broad range of carbon concentrations. Above bandgap excitation reveals typical transitions related to CN and CN−Hi that decrease with increasing carbon concentration. Besides the formation of nonradiative defects, the formation of complexes containing more than one carbon atom is proposed to be responsible for this reduction. Below bandgap excitation reveals an intense emission band around 1.62 eV for [C] >1018cm−3 that is shown by photoluminescence excitation spectroscopy to be most efficiently excited at 2.7 eV. The 1.62 eV transition thermally quenches above 80 K. A configuration-coordinate diagram model is proposed to explain the observed emission, excitation, and thermal quenching behavior. Based on the simultaneous increase in the concentration of tri-carbon complexes, this band is tentatively attributed to a transition involving a deep tri-carbon-related charge state transition level in the GaN bandgap.