Wet etching of (−102) β-Ga ₂ O ₃ 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.