Characterization of anisotropic wet etching of Gallium Nitride for surface orientations of the <0001> crystallographic zone in H3PO4 etchant

Based on the utilization of numerous wagon-wheel structures fabricated on Gallium Nitride (GaN) (0 0 0 1) substrate, this paper reports the characteristics of the wet etching rate distribution for the GaN< 0001 > crystal zone in H3PO4 etchant with various temperatures (130 ℃, 140 ℃, 150 ℃ and 158 ℃) and different concentrations (85%wt and 75%wt). Owing to the benefits of Focused Ion Beam (FIB), the wagon-wheel structures are manufactured by this technology. The results show that GaN, as a representative of the hexagonal system, exhibit a six-fold symmetrical anisotropy about the c-axis in the < 0001 > crystallographic zone. And compared with the reported GaN etched by AZ400K, the surface roughness and the etch rate fluctuation of GaN etched by H3PO4 are both lower. Meanwhile, for any orientation, the corresponding apparent activation energy in the GaN< 0001 > crystal zone can be calculated by the obtained etch rates at various temperatures. Moreover, the dependence of the etch rate on concentration is investigated in this paper. Finally, against the GaN< 0001 > crystal zone, for purpose of explaining the etching rate anisotropy at the atomic scale, the step flow theory is successfully applied here, which demonstrates that the corresponding wet chemical etching rate model can be established based on this theory.