Ga₂O₃/GaN-based solar-blind phototransistors fabricated using a thermal oxidation process performed on the GaN p-n junction layers

In this article, β-Ga₂O₃/GaN-based solar-blind phototransistors are fabricated using a thermal oxidation process performed on the p-GaN layer of a p-GaN/n-GaN junction to form the β-Ga₂O₃/p-GaN/n-GaN heterostructure. The thermal-oxidized β-Ga₂O₃ films exhibit a (2̅01)-orientated crystal phase and high-resistivity property. The high-resistivity β-Ga₂O₃ layer can be converted into an n-type β-Ga₂O₃ layer through Si ion implantation and a subsequent thermal annealing process. The typical electron concentration and mobility of the Si-implanted β-Ga₂O₃ are as high as 3.2 × 10²⁰ cm⁻³ and 177 cm²v⁻¹s⁻¹, respectively. The n-type β-Ga₂O₃ and unimplanted β-Ga₂O₃ layers serve as the collector associating with the p-GaN and n-GaN layers, which function as the base and emitter, respectively, to construct the heterojunction phototransistors (HPTs). The HPTs exhibit a distinct cut-off wavelength at around 260 nm, indicating that the photocurrents result from the β-Ga₂O₃ layers rather than the p-GaN and n-GaN layers. The HPTs also show a significant bias-dependent responsivity in the deep UV (λ < 260 nm) region. This increased responsivity can be attributed to band discontinuity, resulting in the accumulation of photogenerated carriers at the β-Ga₂O₃/p-GaN interface. The preliminary results suggest that the β-Ga₂O₃/GaN-based HPTs can be achieved through the thermal oxidation of a p-GaN/n-GaN epitaxial structure.