A comparative study of wet etching and contacts on (2¯01) and (010) oriented β-Ga2O3

We report on the effect of β-Ga2O3 crystal orientation on wet etching and Ohmic contact formation. The photochemical etching rate in KOH solutions of (2¯01) oriented, n-type bulk single crystals grown by the edge-defined film-fed growth method is ∼3-4 times higher than for the (010) planes. The activation energy for etching was 0.498 eV and 0.424 eV for (2¯01) and (010) orientations, respectively, suggesting the etching is reaction-limited with the same rate-limiting step. Ti (200 Å)/Au (1500 Å) metallization deposited on the two different orientations and annealed at 450 °C showed Ohmic current-voltage (I-V) behavior for (2¯01) but rectifying characteristics for (010). For (010) Ga2O3, there exists 2 types of surfaces having Ga and O atomic densities of 0.58 and 0.87 × 1015 cm−2, respectively. By contrast, for (2¯01) Ga2O3 surfaces, there exist 2 types of surface, with each type terminated with only Ga or O. If the surface is terminated with O, the dangling bond densities of O are 1.78 and 2.68 × 1015 cm−2, respectively. We found that (2¯01)-oriented Ga2O3 is etched at higher rates and is easier to form Ohmic contacts than (010) Ga2O3. The higher density of oxygen dangling bonds on the (2¯01) plane correlates with the faster etch rates and pronounced Ohmic behavior from deposited metals.