PL characterization of GaN scintillator for radioluminescence-based dosimetry

Via photoluminescence (PL) measurements, we have investigated GaN (which is a widely employed material in optoelectronics) to be used as scintillator for developing implantable dosimetric probes. The studied Si-doped n-type GaN samples have common dominant band-edge emission at room temperature, with a strong doping-dependence on their PL spectra. Si-doped GaN with 1018 cm−3 concentration exhibits a non-negligible yellow luminescence (YL) or red luminescence broad band contribution, which is probably due to Ga vacancy native defect. However, heavily-doped GaN (∼1.5 × 1019 cm−3) has much more intense band-edge emission, with no significant contributions of lower-energy bands. The dominant band-edge emission peak remains unchanged at 3.4 eV for both concentrations, and may be accounted for by considering combined effects of band-gap narrowing and Fermi level rising. It has also been demonstrated by back-side PL collection that, due to bulk self-absorption, the dominant peak is shifted to 3.25 eV DAP (donor–acceptor-pair) or e–A (conduction-band-to-acceptor) band. At low temperatures (up to 200 K), PL intensity of heavily-doped GaN is dominated by a DBE (donor-bound exciton) line (D0XA at 3.467 eV for T = 10 K). When further increasing the temperature, band-to-band recombination becomes dominant with red-shift of the emission peak in connection with gap narrowing. The shift in peak wavelength from 10 K to room temperature is about 5 nm, while the corresponding PL integrated intensity is decreased only by 30%. Irradiating samples at room temperature to a 200 Gy dose with 6 MeV photon and electron beams causes a slight increase on defect-related DAP or e–A line and YL broad band, but the effect is not noticeable for heavily-doped GaN.