Analysis of Zn diffusion in various crystallographic directions of GaN grown by HVPE

This work presents the diffusion mechanism of zinc in gallium nitride. Halide vapor phase epitaxy layers were deposited on native ammonothermal seeds of three crystallographic orientations: c - (0001), m - (10-10), and a - (11–20). The surfaces were prepared to an epi-ready state by mechanical and chemical-mechanical polishing. Zinc ions were then implanted with energy of 230 keV and fluence 1016 cm−2 to create an infinite-like source of zinc atoms near the surface. The implanted samples were annealed by ultra-high-pressure method in the temperature range 1250–1450 °C at nitrogen pressure of 1 GPa for 4.5 h to remove the post-implantation structural damage and trigger the diffusion of zinc into the depth of the gallium nitride layers. X-ray diffraction measurements were performed for samples at every stage of the process: as-grown, as-implanted and annealed in order to investigate the evolution of the structural quality. Secondary ion mass spectrometry was employed to analyze depth profiles of zinc and concentrations of impurities. Positron annihilation spectroscopy and low-temperature photoluminescence were employed to assess the defect evolution in the samples. The results showed a strong dependence of zinc diffusion on the crystallographic direction of gallium nitride crystal growth. The depth profiles measured for the analyzed crystallographic directions differed in shape and range of zinc penetration. Diffusion coefficients were calculated for all the analyzed temperatures. The pre-exponential diffusion factor and activation energy were determined.