Wet etching of (-102) β-Ga₂O₃ with tetramethylammonium hydroxide (TMAH)

We investigated wet etching of (-102) β-Ga₂O₃ substrates using heated 25 wt% tetramethylammonium hydroxide (TMAH). The (-102) plane exhibited an etching rate that was one order of magnitude higher than those of the widely used (100), (010), (001), and (-201) orientations. In addition, the temperature dependence of the etching rate over the range 50°C-90°C was well described by the Arrhenius equation, with an activation energy that was nearly independent of carrier concentration. These two features indicate that the (-102) orientation is suitable for fast and highly controllable wet-etch patterning. The morphologies of the resulting etched sidewalls on the (-102) surface were dominated by the emergence of flat (001) and (-201) facets. By exploiting the pronounced development of these two facets, we obtained well-defined V-shaped trenches with a crystallographic opening angle of 130.0° when the etching windows were aligned along the [010] direction. In contrast to plasma-based dry etching, where the outcomes often depend heavily on the specific apparatus and processing conditions, we expect this crystallography-driven facet-formation approach to enable the fabrication of highly reproducible V grooves. Given the wide bandgap of β-Ga₂O₃, the proposed method is potentially applicable to V-groove-trench metal-oxide-semiconductor field-effect transistors and transmission-type blazed gratings.