High temperature implantation of Tm in GaN

Thulium ions were implanted into MOCVD grown GaN films with a fluence of 2.5×10¹⁵ at/cm² at temperatures between 20 and 500°C. The lattice damage introduced by the implantation and the effect of post-implant annealing were investigated using the Rutherford backscattering/channeling (RBS/C) technique. Whereas for room temperature implantation the implanted layer becomes amorphous, high temperature implantation inhibits amorphisation. For implantation temperatures higher than 300°C the RBS/C results clearly show two different damage regions - one at the surface and the second deeper in the crystal coinciding with the Tm depth profile. Annealing causes a decrease of the surface damage as well as initiating regrowth from the unimplanted bulk GaN. For the samples that were not completely amorphous a large part of the Tm atoms were found to be incorporated in Ga-sites. The optical properties of the ion implanted GaN films have been studied by room temperature cathodoluminescence. Directly following the implantation no Tm-related luminescence was observed. Subsequent annealing of the samples achieved optical activation, revealing well-defined emissions due to intra-4f-shell transitions of the Tm³⁺ ions in the blue spectral range at 477 nm and in the near infra-red at 804 nm.