【Member Papers】The Effect of Air Annealing on the Optical and Luminescence Properties of Bi-Doped β-Ga₂O₃ Single Crystals

      Researchers from the Tongji University have published a dissertation titled "The Effect of Air Annealing on the Optical and Luminescence Properties of Bi-Doped β-Ga₂O₃ Single Crystals" in Journal of Luminescence.

Project Support

      This work was financially supported by Shanghai Science and Technology Plan Project (No.23511102302), National Natural Science Foundation of China (Nos.12375181 and 12275194).

Background

      Gallium oxide (Ga₂O₃) has emerged as a promising fourth-generation ultrawide bandgap semiconductor material, demonstrating significant potential for UV solar-blind detection and power devices due to its ~ 4.9 eV bandgap and dopant compatibility. When grown via the optical floating zone (OFZ) method, β-Ga₂O₃ offers distinct advantages including rapid growth cycles and crucible-free processing, enabling high-quality bulk single crystal production. These characteristics position β-Ga₂O₃ as a standout material in semiconductor optics research with substantial application prospects.

      In this work, the effects of 1000 °C air annealing on the structure, morphology, and optical properties of Bi-doped β-Ga₂O₃ single crystals were investigated. By comparing the changes in crystal structure, surface morphology, and optical properties between as-grown and air-annealed samples, the influence of air annealing on surface elemental distribution and roughness was revealed. Furthermore, through spectroscopic analyses, the regulatory mechanisms of vacancy defects induced by annealing on luminescence properties were explored. These findings would help deepen the understanding of the optical properties and recombination transition processes in Bi-doped β-Ga₂O₃ single crystals.

Abstract

      β-Ga₂O₃, as a highly promising fourth-generation ultra-wide bandgap semiconductor material, can be grown as Bi-doped single crystals using the optical floating zone method. This work investigated the effects of air annealing on the optical and luminescence properties of Bi-doped β-Ga₂O₃ single crystals. Comparing the as-grown and air-annealed samples revealed that annealing reduced the concentration of V_O in Bi-doped β-Ga₂O₃ single crystal through environmental oxygen compensation. After annealing, transmission spectra indicated a significant decrease in carrier concentration, while the PL spectra exhibited enhanced intensity and prolonged decay time, with an increased proportion of GL emission, attributed to the increase in V_Ga. This phenomenon is due to the effective suppression of Auger recombination by the reduced carrier concentration, thereby enhancing the radiative recombination-dominated luminescence process. These findings not only elucidate the effect of annealing on the optical properties of Bi-doped β-Ga₂O₃ single crystals but also further expand our understanding of their recombination transitions.

Highlights

      · The effect of air annealing on Bi-doped β-Ga₂O₃ single crystals was investigated.

      · After annealing, the fluorescence intensity was significantly enhanced and the decay time prolonged.

      · Although annealing, the ultra-wide bandgap characteristic remained unchanged.

Conclusion

      In conclusion, this work investigated the effect of air annealing at 1000 °C on the fundamental properties of Bi-doped β-Ga₂O₃ single crystals, with a particular focus on their optical properties. It was found that annealing induces recrystallization in the crystals, leading to increased surface roughness and non-uniform crystalline quality, but simultaneously enhancing visible light transmittance. Moreover, air annealing compensates for the concentration of V_O through environmental oxygen, yet increases the concentration of V_Ga, thereby significantly enhancing GL emission associated with V_Ga. Additionally, the PL decay time was prolonged after annealing, which may be related to the suppression of non-radiative transitions. These findings not only reveal the effect of annealing on the optical properties of Bi-doped β-Ga₂O₃ single crystals but also further deepen the understanding of their recombination transitions. Future research will extend the annealing temperature and time range and combine defect evolution calculations with corrosion analysis to optimize device preparation and improve performance.