Photo-enhanced metal-assisted chemical etching of α-gallium oxide grown by halide vapor-phase epitaxy on a sapphire substrate and its applications

The development of an etching process with controllable etching rate and high selectivity is key to fabricating high-performance electronic and optoelectronic devices. In this paper, we report the photo-enhanced metal-assisted chemical (PE-MAC) etching of an ultrawide-bandgap (UWBG) alpha-phase gallium oxide (α-Ga₂O₃) semiconductor grown using a halide vapor-phase epitaxy technique. Using the PE-MAC etching process, the reproducible etch of an α-Ga₂O₃ epilayer was demonstrated at a rate of 8.24 nm min⁻¹ at room temperature; the extent of the reaction increased linearly with increasing time. The Arrhenius plot of the etching rate indicated that this process is an activation-controlled reaction with a high activation energy of 0.90 eV (86.7 kJ mol⁻¹). The Pt metal electrode, which can be removed using an acid solution, created a depletion region, making the exposed α-Ga₂O₃ epilayer etched with a smooth and tilted sidewall. The effects of the roughness at different etch temperatures were also investigated. An α-Ga₂O₃-based metal-semiconductor-metal (MSM) photodetector was fabricated by using the proposed PE-MAC etching process, and the fabricated MSM photodetector exhibited improved time-dependent photoresponse characteristics with reduced defect-related time constants, confirming that our PE-MAC etching is a damage-free fabrication process with high anisotropy and selectivity. Our study demonstrates that the PE-MAC etching is an effective wet process for manufacturing electronic and optical devices based on UWBG α-Ga₂O₃ semiconductors at room temperature without vacuum plasma equipment.