Effect of Oxygen Precursors on Growth Mechanism in High-Quality β-Ga₂O₃ Epilayers on Sapphire by Molecular Beam Epitaxy and Related Solar-Blind Photodetectors

In this work, we report on high-quality $\beta $ -Ga2O3 epilayers on sapphire substrates by molecular beam epitaxy (MBE) using ozone and oxygen plasma precursors, respectively. A systematic examination of the surface morphology, nucleation process, and epilayer compositions of the $\beta $ -Ga2O3 epilayers is conducted to elucidate the impact of ozone and oxygen plasma precursors on the growth mechanism. Compared to $\beta $ -Ga2O3 epilayers using ozone precursor, which exhibit a Volmer–Weber growth mode with early stage nucleation gaps, the epilayers using oxygen plasma show a Stranski–Krastanow (S–K) growth mode under the modification of the oxygen plasma. In addition, metal–semiconductor–metal solar-blind photodetectors (PDs) are then constructed using the optimized $\beta $ -Ga2O3 epilayers. The oxygen plasma-grown $\beta $ -Ga2O3 PDs display a dark current of 3.2 nA, a photo-dark current ratio (PDCR) of $2.98\times 10^{4}$ , and a specific detectivity of $6.51\times 10^{{13}}$ Jones, while the ozone-grown $\beta $ -Ga2O3 PDs manifest a low dark current of 7.5 pA, a higher PDCR of $1.31\times 10^{{7}}$ , and a higher specific detectivity of $1.31\times 10^{{15}}$ Jones at 10 V, which originate from the lower oxygen vacancy in ozone-grown $\beta $ -Ga $_{{2}}~\text{O}_{{3}}$ epilayers. This work reveals the heteroepitaxial growth mechanism of $\beta $ -Ga2O3 on sapphire by MBE, offering a facile, cheap, and effective approach for high-performance and large-area solar-blind PDs.