Photoluminescence from GaN transmuted by neutrons

Undoped n-type GaN films on Al2O3 substrates were irradiated by KUR reactor. By neutron irradiation, 69Ga and 71Ga in films were transmuted into 70Ge and 72Ge. Channeling experiments by Rutherford Back Scattering (RBS) indicated the presence of interstitial Ga ions after irradiation. Four Raman lines observed before irradiation were not detected after irradiation, but after annealing at 800 degC the lines recovered. The lattice distortion caused by irradiation recovered with an increase of annealing temperature. A photoluminescence peak due to bound excitons was observed at 3.49 eV before irradiation, but the peak after irradiation disappeared. After heat treatment at 600 degC after irradiation, a photoluminescence peak observed at 2.84 eV was attributed to interstitial Ge atoms. After annealing at 1000 degC, two photoluminescence peaks were observed at 2.90 and 2.25 eV, respectively. The peak at 2.90 eV was assigned to DX states, which are defined as Ge ions substituted at Ga lattice sites and trapping electrons, and the other peak at 2.25 eV was presumed to be due to complex defects consisting of Ga vacancies and transmuted Ge ions. Free electron carriers after irradiation were estimated to be 1.5 x 1017 cm-3 from the A1(LO) phonon mode by Raman scattering. (Y. Kazumata)