Twist Defects in Compound Semiconductors

Both intrinsic and extrinsic point defects can significantly alter the properties of semiconductors, impacting the performance and stability of devices. We investigate the diffusion and stability of a 'twist' point defect, an intrinsic defect characterized by a tilted bond rotation, in GaAs and GaN via density functional theory (DFT) calculations. First, we find that the formation energies for the twist defects are of order 5 eV in GaN and of order 3 eV in GaAs and that, despite being stoichiometric defects, have thermodynamic charge transition levels indicating the ability for excess charge trapping. We also find that twist defects have low thermal stability with energy barriers of less than 1 eV to anneal either to a pristine-crystal structure or other related metastable defects like the antisite pair. Neither possible twist defect configuration is lower in energy than the antisite pair in GaAs. However, in GaN, the twist defect is significantly lower in energy than the antisite pair. These results indicate that the existence of twist defects in low-temperature, low-energy ion irradiation damage environments is plausible and further reveals that the stability and annealing process for such defects relies on other metastable defect configurations.