UCLA

Magnesium ion implantation and subsequent activation annealing shows promise as an effective p-type doping method in Gallium Nitride (GaN). This dissertation relates implant-induced defects and the electrical performance. The implantation process introduces an elastic strain purely orthogonal to the (0001). Complete strain recovery is achieved by annealing at 1300 �C for 10 min (one GPa N2 overpressure) for dose level up to 1�1015 cm-2. However, extended defects such as stacking faults, dislocation loops, and inversion domains form during the anneal. Critical extended defects in the form of inversion domains were found to contain electrically inactive Mg after annealing at temperatures of 1300 �C (one GPa N2 overpressure), which results in a low dopant activation efficiency. A key finding of this work was to demonstrate that annealing at temperatures above 1300 �C eliminates the presence of the Mg-rich inversion domains. While other residual defects, such as dislocation loops, still exist after annealing at and above 1400 �C, chemical analysis shows no sign of Mg segregation at dislocation loops or other defects. Meanwhile, an overall decreasing trend in the dislocation loop size and density is observed after annealing at the higher temperatures and longer times. Electrical measurements show that annealing at 1400 �C leads to a dopant activation efficiency that is an order of magnitude higher than that observed at 1300 �C, which points to the benefits, in terms of defect density and p-type dopant activation, of using higher temperatures ( ≥ 1400 �C) annealing cycles to activate Mg acceptors. Novel characterization methods combining high resolution x-ray scattering and transmission electron microscopy were developed to understand the implant-induced strain recovery process and the evolution of extended defect structures after the dopant activation anneal. It was found that homoepitaxial GaN on high quality native substrates is necessary for clearly assessing the implant-induced defects by separating them from the pre-existing intrinsic defects. Results from this work are expected to bring the understanding of the key processing steps to achieve high activation efficiency selective area p-type doping for vertical GaN device structures in a scalable framework.