Comparative Study of Defect Properties in GaN: Ab Initio and Empirical Potential Calculations
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Comparative Study of Defect Properties in GaN: Ab Initio and Empirical Potential Calculations Fei Gao, Eric J. Bylaska, Anter El-Azab and William J. Weber Pacific Northwest National Laboratory, MS K8-93, P. O. Box 999, Richland, WA 99352, USA ABSTRACT Density functional theory (DFT) is used to study the formation, properties and atomic configurations of monovacancies, antisite defects and possible interstitials in GaN. The relaxation around a vacancy is generally small, but the relaxation around antisite defects is large, particularly for a Ga antisite defect, which is not stable and converts to an N-N split interstitial. All N interstitials, starting from any possible site, eventually transfer into the N-N split interstitials, forming N2 molecules with one N-N bond, but also some covalent bonds to the surrounding atoms. In the case of Ga interstitials, the most favorable configuration is the Ga octahedral interstitial. However, it is found that the Ga-Ga< 1120 > split interstitial can bridge the gap between non-bonded Ga atoms along the < 1120 > direction, which leads to the formation of Ga atomic wires in GaN, with bond distance (2.3Å) close to those noted in bulk Ga. In addition, two representative potentials, namely Stillinger-Weber and Tersoff-Brenner potentials, have been employed to determine the formation of defects using molecular dynamics (MD) method in GaN. The MD results are discussed and compared to DFT calculations. The present DFT and MD results provide guidelines for evaluating the quality and fit of empirical potentials for largescale simulations of ion-solid interaction and thermal annealing of defects in GaN. INTRODUCTION Gallium nitride (GaN) is a semiconductor compound material with a high application potential in a variety of opto-electronic and electronic devices operating at high temperature and high power [1]. The large band gap, strong interaction bonds, and a high thermal conductivity of GaN make its use especially as a basic material for the realization of light-emitting diodes and lasers in the blue and UV regions [2]. It is well known that the electronic quality of semiconductors is largely controlled by the nature and concentration of their native defects and impurities, which can be introduced during growth or by ion implantation. Therefore, it is of great technological importance to fundamentally understand the formation and properties of these defects, as well as their behavior in various processing steps such as ion implantation and thermal annealing. Several experimental efforts have been carried out to detect point defects in GaN. Positron annihilation spectroscopy has been applied to study Ga vacancies and related complexes under 2MeV electron irradiation [3]; whereas optical detection of electron paramagnetic resonance has been used to identify Ga interstitial [4]. However, it is impossible to distinguish the defect allocations among all possible defect sites, particularly for interstitials among which there are little energy differences. Therefore, theoretical studies
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