| Gallium nitride films were implanted at several temperatures and fluences with magnesium, silicon, calcium, and germanium ions. The affects of the implantations on the optical, microstructural, and electrical properties of the material were investigated. Several high temperature post-implantation annealing procedures were attempted in order to achieve activation of the implanted impurities. The optical properties of GaN are greatly affected by the ion implantation process resulting in a complete loss of the luminescence even for low implantation doses due to the introduction of efficient nonradiative recombination centers. Partial recovery of the luminescence and optical activation of the implanted dopants is possible after high temperature (>1100°C) thermal treatments given sufficient time at temperature. The crystal structure of GaN is very resistant to ion bombardment with no significant disorder until a displacement per atom of ∼1 is achieved. A sigmoidal dependence of disorder on dose has been observed and is consistent with cascade overlap, nucleation and growth, or direct-impact/defect-amorphization models. Computer simulations of the damage usually overestimate the damage compared to that experimentally observed. The discrepancy is due to an unusually large displacement energy resulting from the strong ionic bonding of GaN. The implantation damage removal is diffusion limited, which requires high temperature anneals (>1100°C) and long periods of time (>1 hour) due to the high thermal stability of the implantation-induced defects. The implantation defects generate deep level states in the band gap that act as electronic traps, which reduce the free carrier concentration in the GaN. Partial recovery of the electrical properties and removal of the deep level traps is possible after high temperature (>1100°C) thermal treatments. Activation of the implanted dopants was achieved after high temperature (1100–1200°C) thermal treatments. Characteristic photoluminescence emission at 3.25 eV, 3.33 eV, and 3.36 eV was observed for Mg, Ge, and Ca implanted GaN, respectively. A reduction in the free carrier concentration by compensation of the background n-type carriers was observed for both Mg and Ca implantation. Electrical activation of implanted Si and Ge was achieved with Carrier activation percentages of ∼100% and ∼45%, respectively. |
