Effect of thermal annealing on photoexcited carriers in nitrogen-ion-implanted β-Ga2O3 crystals detected by photocurrent measurement

Acceptor impurity doping is recognized as a functional tool to extend the capabilities and applications of β-Ga2O3. The effect of thermal annealing on photoexcited carriers was characterized by measuring the photocurrent spectra of nitrogen (N)-ion-implanted β-Ga2O3 crystals, where the N was found to cause less crystal damage to the crystal and much lower thermal diffusivity than Mg. The photocurrent intensity at 4.5–5.5 eV showed an increase with an increase in external bias, and the increase was attributed to the photo-generated non-equilibrium electrons and holes. The spectra under a positive external bias showed a distinct onset at 3.0–3.5 eV owing to optical transitions involving deep donor levels formed by the N-implantation. Spectrally integrated responsivity showed a significant change with the annealing temperature by reflecting the recovery of crystallinity and the thermal activation of N impurities. The results also indicate the formation of additional nonradiative recombination centers due to N-implantation.