2 MeV proton radiation damage studies of gallium nitride films through low temperature photoluminescence spectroscopy measurements

Gallium nitride (GaN) thin film samples were grown by ammonia-molecular beam epitaxy. Through room temperature transport measurements, electron mobilities of 560 cm²/Vs were observed for layers with a carrier density of 1.5×10¹⁷ cm^-3 . Room temperature photoluminescence (PL) spectroscopy revealed the bound exciton transition at 363.0 nm and a weak yellow emission whose intensity was sample dependent. At 22 K, the main photoluminescence signal sharpened, shifted to 356.9 nm (3.474 eV), and the maximum intensity increased by a factor of one hundred; the intensity of the yellow emission decreased. The samples were irradiated at room temperature with 2 MeV protons at fluences of 10⁹, 10 ¹⁰, 10¹¹, 10¹², 10¹³, 10¹⁴, 10¹⁵, and 10¹⁶ cm^-2. The intensity changes were within experimental error up to 10¹³ cm^-2. The drop in intensity of the bound exciton transition was 16% at 10¹⁴ cm^-2 and 99% at 10¹⁵ cm^-2. The radiation damage constant associated with the main PL peak at 3.474 eV in GaN is (1.4±0.3)×10^-13 cm², compared with (4±1)×10^-11 cm² associated with the main PL, peak at 1.492 eV in GaAs. For photonic applications, GaN is more robust than GaAs with respect to displacement damage