Dopant distribution in high fluence Fe implanted GaN

Undoped wurtzite GaN epilayers implanted at room temperature with 50-325 keV Fe(+) ions in the fluence range of 10(15)-10(17) ions/cm(2) are studied by a combination of Rutherford backscattering/channeling spectrometry and time-of-flight elastic recoil detection analysis. The results show an enhanced Fe concentration close to the surface for high ion fluences (>1 X 10(16) cm(-2)), which increases with the ion fluence. Annealing at 800 degrees C for 30 min has a negligible effect on the Fe distribution in the material bulk, but further increases the Fe concentration near the surface. Our findings can be understood by radiation enhanced diffusion during ion implantation and an increased Fe diffusivity in the near surface region with distorted stoichiometry, or formation of secondary phases and precipitates for the highest doses. The simulation shows that, if enhanced diffusion is the reason for Fe buildup at the surface, both radiation enhanced diffusion and the thermal diffusion of Fe atoms near the surface, need to be at least five times larger than ordinary bulk diffusion to explain the increased Fe surface concentration. (C) 2008 American Institute of Physics.