Lateral and Vertical Diffusion of Magnesium in Ion-Implanted Halide Vapor Phase Epitaxy Gallium Nitride

The paper is oriented on magnesium diffusion in gallium nitride samples implanted with this element. This is an importnt issue in the production chain of GaN-based electronics. Both vertical and lateral diffusion is considered.abstract:In the present study, the diffusion of magnesium in gallium nitride was investigated. In order to ensure high structural quality and purity of the analyzed material, bulk crystals, grown by Halide Vapor Phase Epitaxy on ammonothermal native seeds, were used. Samples of polarity (0001), (10-10) and (11-20) were prepared from them and implanted with magnesium ions with fluence of 1×1016 cm-2 and 230 keV energy. X-ray diffraction was used to assess the structural quality of the samples at each stage of the study. Ultra-high-pressure annealing was carried out in the temperature range of 1250-1450°C to activate the dopant and remove post-implantation damage. Diffusion of the implanted species was a consequence of the annealing process. Secondary ion mass spectrometry was used to assess the in-depth concentration of magnesium in the annealed samples. Strong diffusion anisotropy was observed for the crystallographic directions analyzed, with [000-1] being the most susceptible to diffusion and [10-10] being the most resistant. Using the finite element method for numerical analysis of the measured profiles, the diffusion coefficients were determined. Substitutional diffusion involving gallium vacancies was found to be the dominant mechanism in the analyzed samples. The temperature-independent diffusion coefficient was calculated. Its value was 1.7×10-4 cm2/s for the [0001] direction and one order of magnitude less for non-polar directions. The activation energy was similar for all cases studied and ranged from 2.26 eV to 2.38 eV.abbreviations:XRD - X-ray diffractionSIMS - secondary ion mass spectrometryMg - magnesiumH - hydrogen