Atomic-Scale Simulation for Pseudometallic Defect-Generation Kinetics and Effective NIEL in GaN

We have employed large-scale molecular dynamics simulations to study defect production, clustering, and its evolution in GaN for energies of a primary knock-on atom ranging from 500 eV to 40 keV. In the presence of proton radiation, a large number of atoms will be displaced during the collisional phase with a compacted cascade volume, but a great number of displaced atoms recombine significantly with vacancies at the same time, i.e., a pseudometallic behavior (PMB). This leads to the result that the majority of surviving defects are just single interstitials or vacancies for all recoil energies considered with only a small number of defects forming clusters. The total number of defects simulated in GaN can be very well predicted by the simplified Norgett, Robison, and Torrens (NRT) formula due to the PMB, in contrast to GaAs where the defect number becomes much larger than the NRT value. Moreover, the damage density within a cascade core is evaluated and applied to construct a model to calculate an energy-partition function for studying the nonionizing energy loss (NIEL) in GaN. The calculated NIEL in GaN is often found to be smaller than that predicted by a model based on the simple Kinchin-Pease formula. The comparisons of defect creation, density, and effective NIEL in GaN to those of GaAs suggest that GaN may be much more resistant to displacement damage than GaAs at low temperatures.