Observation of resonant Raman lines during the photoluminescence of doped GaN

Abstract

P-type doping of molecular beam epitaxy grown GaN has been investigated using beryllium, magnesium and carbon, the sample being characterized by luminescence under optical excitation by He - Cd laser light of energy 3.815 eV. Doping resulted in a strong reduction of the band-edge luminescence in some samples and the appearance of deep level bands at around 2.3 and 2.5 eV. Photoluminescence spectra in the region of the band gap using high gain revealed the presence of narrow lines at positions 3.541, 3.449, 3.357 and 3.266 eV in a wide variety of these samples. These lines were constant in position with respect to temperature over the range of 5 K to 300 K and it was noted that they are separated by the GaN longitudinal optical phonon energy of 92 meV. It is believed that these lines are caused by resonant Raman scattered replicas appearing in the photoluminescence spectra.