Wet etching in beta-Ga2O3 bulk single crystals

Beta-phase gallium oxide (beta-Ga2O3) bulk single crystals have received increasing attention due to their fantastic performances and widespread use in power devices and solar-blind photodetectors. Wet etching has proved to be a simple and effective approach for visualization of defects, polishing of wafers, and patterning of substrates. Recently, a large number of different strategies have been developed for wet etching of beta-Ga2O3 substrates. Here we review recent advances in wet etching of beta-Ga2O3 substrates with an aim to comprehensively understand the etching behavior and mechanism. We classify wet etching into conventional etching including chemical etching, defect-selective etching, patterning, and chemical mechanical polishing and unconventional etching (i.e., electrochemical and electroless etchings including photo- and/or metal-assisted ones) depending on the input of extra assistance or not. In each category, the key parameters that control the etching kinetics were discussed and a number of examples were highlighted. This review intends to shed light on how to design appropriate etching strategies for various purposes and applications.