Effect of air annealing on the structural, electrical, and optical properties of V-doped β-Ga2O3 single crystals

V impurities were intentionally introduced into β-Ga2O3 crystals as n-type dopants to improve the n-type conductivity of single-crystal substrates. A high-quality 0.20 mol% V-doped β-Ga2O3 single crystal was fabricated, and the effects of air annealing on the structure and the electrical and optical performances of V-doped β-Ga2O3 single crystals were systematically studied. The V-doped β-Ga2O3 crystal exhibited a high crystal quality, smooth surface, and high carrier concentration. In comparison, the crystalline quality of β-Ga2O3 was improved, and it showed a flat surface after the annealing treatment. Compared with that before annealing, the carrier concentration decreased from 5.90 × 1018 to 9.51 × 1017 cm−3, the optical transmittance increased in the near-infrared region, and the peak intensity of the Ag(3), mid-frequency Ag(8),Ag(9), and Ag(10) phonons were changed, which were attributed to the electron traps of the gallium vacancy (VGa) and the two cation vacancies paired with one cation interstitial atom (2VGa1-Gai) complex. After annealing, the oxygen vacancy (VO) was compensated, and the Ga3+ content decreased, which were related to the decrease in the free electron concentration. The variations in the VO and VGa concentrations resulted in a decrease in the blue luminescence peak area ratio and the formation of a green luminescence peak, respectively. These results can facilitate a better comprehension of the structural and property changes in V-doped β-Ga2O3 crystals owing to air annealing.