X-Ray-Excited Luminescence of High-Quality Doped GaN Single Crystals

X-Ray-induced luminescence behavior of Si/Ge-doped GaN single crystals is observed and analyzed in combination with undoped GaN. Similarities between radioluminescence (RL) and photoluminescence (PL) indicate an analogous physical process. Under X-Ray irradiation, the gallium nitride (GaN) single crystals doped with Si/Ge elements intensely emit tunable visible light ranging from 1.8 to 2.2 eV, and an ultraviolet (UV) emission of approximate to 3.3 eV is aroused by the intrinsic direct band-edge transition of GaN. Due to the difference in the physical properties of excitation source and the self-absorption effect, the UV signal in RL has a dramatic reduction (especially for undoped GaN) and redshift, which is also considered to be the obvious difference between the two spectra. RL results obtained herein along with PL demonstrate that the visible luminescence of Si/Ge-doped GaN is mainly attributed to DAP or/and e-A recombination, which is supported by density functional theory (DFT) calculations.