Anisotropic Properties and Atomic-Scale Etching Mechanisms of Ga-Face GaN: A Comparative Study of Acidic and Alkaline Solutions

Wet chemical etching serves as a critical fabrication process for gallium nitride (GaN)-based devices, while precisely measuring the overall etch rates of GaN is essential for both precise control and mechanism research of this process. In this study, the anisotropic etching behavior of Ga-face GaN in 5 wt % KOH/ethylene glycol (EG) solution (110-130 °C) is systematically investigated for the first time. By innovatively designing samples containing micrometer-level hemisphere and wagon-wheel structures, the overall etching rates of Ga-face GaN in the KOH/EG system are experimentally determined accurately. Subsequently, this research compares the etching rate distribution differences between the H₃PO₄ and KOH/EG systems for Ga-face GaN, and determines the activation energies of arbitrary crystal planes that can be calculated by the overall etching rate distribution in the KOH/EG system at different temperatures (110-130 °C). Furthermore, in this paper, the anisotropic mechanism of the etching rate is established under the assumption of step flow, the etching mechanism is given based on the calculated removal rate of atomic clusters, and the reasons for the etching rate distribution in different etchants are explained on the atomic scale. In addition, in GaN microstructure etching experiments, the evolution of the etching morphology of the hexagonal concave structure is accurately predicted based on the experimentally determined etching rate data of the overall crystal planes. The results of this paper provide critical experimental paths, overall etching rate distribution data, and theoretical support for the precision control of wet etching of GaN micro- and nanostructures.