First-principles investigation of chlorine adsorption onto GaN(0001) during atomic layer etching

Atomic layer etching of GaN in chlorinated plasmas requires a detailed understanding of plasma–surface interaction mechanisms at the atomic scale. In this work, the adsorption of radical chlorine on the wurtzite GaN(0001) surface is investigated using density functional theory calculations. The preferred adsorption sites, the adsorption energies, and the diffusion barriers are determined. Charge transfer mechanisms are analyzed using Bader charge analysis and charge density difference calculations. The results indicate that chlorine adsorption occurs preferentially near surface Ga atoms with adsorption energies up to −3.6 eV. Projected density of states calculations reveal the formation of localized surface states associated with Cl–Ga bonding. Surface diffusion barriers toward the most stable Ga adsorption sites are below 0.1 eV, promoting rapid migration of Cl. The influence of chlorine surface coverage is also investigated and shows a progressive decrease in adsorption energy with increasing chlorine coverage. These results provide atomistic insight into chlorine adsorption and surface diffusion mechanisms relevant to the surface modification step of GaN in atomic layer etching processes [T. Rasoanarivo et al., J. Vac. Sci. Technol. A 44, 022608 (2026)].