Low-Temperature Luminescence of GaN

Photoluminescent properties of GaN at low temperatures (1.5°–150°K) have been studied mostly in powder samples. The near-uv emissions at 4.2°K consist of one peak at 3.476 eV, another at about 3.43 eV (dependent on doping), and further a repetitive pattern of emissions in the region 3.0–3.3 eV (so-called satellite emissions). The emission with the highest peak energy is probably due to the recombination of a free exciton. Thus the bandgap of GaN is estimated to 3.48 eV at 4.2°K in good agreement with excitation spectra. The second peak around 3.43 eV is apparently of extrinsic origin. The satellite emissions show at least four peaks at approximately 3.27, 3.18, 3.09, and 3.00 eV. The origin of these emissions is discussed.