2, University of Michigan, Ann Arbor, Michigan, United States
Although silicon-based electronics are used to power light-emitting diodes and electric vehicles, their utility in high power applications is limited by a low breakdown voltage. Wide-bandgap semiconductors, such as gallium nitride and related alloys have been proposed as alternatives, but the effective p-type doping at high concentrations remains elusive. For example, Mg dopant activation following ion implantation, selective diffusion, and metal-organic vapor deposition requires high temperature annealing which may disrupt active device structure. In the case of molecular-beam epitaxy, surfactants and co-dopants such as O and Si have been explored, but the concentration of substitutional Mg is often limited, leading to limited p-type doping efficiency. Here, we are developing a novel approach to enhance the p-type doping of GaN and related allows. We describe a combined computational-experimental approach consisting of focused ion-beam (FIB) nano-implantation of Mg in GaN during molecular-beam epitaxy (MBE), followed by computational and experimental ion channeling studies of the Mg incorporation mechanisms. This approach is likely to result in p-type doping at ultra-high concentrations, without the need for subsequent high temperature annealing. We will discuss the development of a modified Mg-Ga alloy source for nano-implantation and our progress towards its implementation in a modular MBE-FIB system. We also present our Monte Carlo-Molecular dynamics simulations of ion channeling in wurtzite GaN crystals, and discuss our progress towards quantifying the influence of growth and annealing sequences on Ga and/or N vacancy formation and the result substitutional vs interstitial incorporation of Mg in GaN. We have examined the influence of Mg defect type in GaN on the , [10-10], and [11-20] channeling yields.