First-Principles Exploration of Defect-Pairs in GaN

TL;DR

This study uses first-principles calculations to systematically analyze defect-pairs in GaN, revealing their stability, formation energies, and impact on electronic properties, which is crucial for understanding radiation damage in GaN.

Contribution

It provides a comprehensive first-principles analysis of all defect-pairs in GaN, including previously overlooked VN-VN pairs, and their effects on material properties under irradiation.

Findings

15 defect-pairs are stable during relaxation.

VN-VN pairs have very low formation energies, acting as deep donors.

Defect-pairs influence electrical and optical properties depending on Ga/N chemical potentials.

Abstract

Using first-principles calculations, we explored all the 21 defect-pairs in GaN and considered 6 configurations with different defect-defect distances for each defect-pair. 15 defect-pairs with short defect-defect distances are found to be stable during structural relaxation, so they can exist in the GaN lattice once formed during the irradiation of high-energy particles. 9 defect-pairs have formation energies lower than 10 eV in the neutral state. The vacancy-pair VN-VN is found to have very low formation energies, as low as 0 eV in p-type and Ga-rich GaN, and act as efficient donors producing two deep donor levels, which can limit the p-type doping and minority carrier lifetime in GaN. VN-VN has been overlooked in the previous study of defects in GaN. Most of these defect-pairs act as donors and produce a large number of defect levels in the band gap. Their formation energies and concentrations are sensitive to the chemical potentials of Ga and N, so their influences on the electrical and optical properties of Ga-rich and N-rich GaN after irradiation should differ significantly. These results about the defect-pairs provide fundamental data for understanding the radiation damage mechanism in GaN and simulating the defect formation and diffusion behavior under irradiation.