The diffusion of fluorine ions in GaN was investigated using time-of-flight secondary ion mass spectrometry. Instead of incorporating the fluorine ions close to the sample surface by means of a fluorine plasma treatment, 180keV fluorine ion implantation was used to implant fluorine ions deep into the GaN bulk; thus preventing surface effects from affecting the data. It was found that the diffusion of fluorine ions in GaN was a dynamic process which featured initial out-diffusion followed by in- diffusion and final stabilization. A vacancy-assisted diffusion model was proposed in order to explain the experimental observations. It was also consistent with the results of molecular dynamics simulations. The fluorine ions tended to occupy the Ga vacancies introduced by ion-implantation, and diffused to vacancy-rich regions. The number of continuous vacancy chains could be significantly reduced by dynamic thermal annealing. As a result, strong local confinement and stabilization of fluorine ions could be obtained.

Diffusion Mechanism and the Thermal Stability of Fluorine Ions in GaN after Ion Implantation. M.J.Wang, L.Yuan, K.J.Chen, F.J.Xu, B.Shen: Journal of Applied Physics, 2009, 105[8], 083519