Enhanced Performance of PECVD-Grown β-Ga2O3 MSM Solar-Blind Ultraviolet Photodetectors via a SiO2 Buffer Layer

Heteroepitaxial growth of β-Ga2O3 thin films on Si for solar-blind ultraviolet photodetectors faces severe challenges due to lattice mismatch and interfacial oxidation, leading to high dark current and low responsivity. In this work, β-Ga2O3 thin films were deposited on n-Si(100), p-Si(100), and p-Si(100) substrates with a 100 nm thermally oxidized SiO2 buffer layer using plasma-enhanced chemical vapor deposition. Metal-semiconductor-metal structured solar-blind ultraviolet photodetectors were subsequently fabricated. The effects of the SiO2 buffer layer on the crystalline quality, interfacial characteristics, and optoelectronic performance of the devices were systematically investigated. Results show that the SiO2 buffer layer possibly relieves the mismatch-induced stress in Ga2O3 films on Si, suppresses the formation of an uncontrollable interfacial layer tentatively assigned as SiOx-like (x ≤ 2) during the initial deposition stage, and significantly improves the crystalline quality of β-Ga2O3 films. Compared with devices on bare Si substrates, the photodetector based on the SiO2-buffered substrate exhibits a significantly reduced dark current, a photo-to-dark current ratio of 5.01 × 103, a responsivity of 3.32 A/W, a theoretical shot-noise-limited specific detectivity of 1.14 × 1013 Jones, and a UV-to-visible rejection ratio as high as 8.12 × 105 at 5 V. The overall performance of the SiO2-buffered device is markedly superior to that of bare Si devices, albeit with a slight decrease in response speed. Mechanism analysis reveals that the dense SiO2 buffer layer blocks the vertical leakage path of carriers toward the Si substrate, simultaneously relieving the mismatch-induced stress and improving film quality. This work provides a feasible technical pathway toward low-cost, CMOS-compatible high-performance silicon-based solar-blind ultraviolet photodetectors.