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.