Plasma-free anisotropic selective-area etching of β-Ga₂O₃ using forming gas under atmospheric pressure

We demonstrate a facile and safe anisotropic gas etching technique for β-Ga₂O₃ under atmospheric pressure using forming gas, a H₂/N₂ gas mixture containing 3.96 vol% H₂. This etching gas, being neither explosive nor toxic, can be safely exhausted into the atmosphere, simplifying the etching system setup. Thermodynamic calculations confirm the viability of gas-phase etching above 676°C without the formation of Ga droplets. Experimental verification was achieved by etching ( $$ 02) β-Ga₂O₃ substrates within a temperature range of 700-950°C. Moreover, selective-area etching using this method yielded trenches and fins with vertical and flat sidewalls, defined by (100) facets with the lowest surface energy density, demonstrating significant anisotropic etching capability.