Plasma-free anisotropic selective-area etching of β-Ga 2 O 3 using forming gas under atmospheric pressure.

We demonstrate a facile and safe anisotropic gas etching technique for β-Ga 2 O 3 under atmospheric pressure using forming gas, a H 2 /N 2 gas mixture containing 3.96 vol% H 2 . 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 ( 1 - 02) β-Ga 2 O 3 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.