Computationally predicted energies and properties of defects in GaN

Abstract

Recent developments in theoretical techniques have significantly improved the predictive power of density-functional-based calculations. In this review, we discuss how such advancements have enabled improved understanding of native point defects in GaN. We review the methodologies for the calculation of point defects, and discuss how techniques for overcoming the band-gap problem of density functional theory affect native defect calculations. In particular, we examine to what extent calculations performed with semilocal functionals (such as the generalized gradient approximation), combined with correction schemes, can produce accurate results. The properties of vacancy, interstitial, and antisite defects in GaN are described, as well as their interaction with common impurities. We also connect the first-principles results to experimental observations, and discuss how native defects and their complexes impact the performance of nitride devices. Overall, we find that lower-cost functionals, such as the generalized gradient approximation, combined with band-edge correction schemes can produce results that are qualitatively correct. However, important physics may be missed in some important cases, particularly for optical transitions and when carrier localization occurs.

Detection of deep-level defects and reduced carrier concentration in Mg-ion-implanted GaN before high-temperature annealing

“…There is a possibility that the defects generated by the Mg ion implantation caused carrier compensation. Since several types of deep-level states have been predicted to be located at the mid-gap and near the valence band, 17 we cannot determine the origin of the observed reduction in the carrier density at this stage.…”

“…In a previous report, 16 deep-level states were detected at E C -E = 0.67 eV after N ion implantation with a dosage of 1×10 11 cm -2 (a similar dosage to the present samples), and the density of the deep-level states was found to decrease after subsequent annealing at 900 o C. It was proposed that a possible origin of the deep-level defects was a N interstitial, N i . However, a theoretical study 17 showed that the N i produced an acceptor-like defect level at E C -E = 0.99 eV. If this amount of discrepancy in the energy location is allowed, the following discussion is possible.…”

“…Thus, it is possible that the annealing at 800 o C generated the deep-level states near the GaN surface. It has been predicted by calculation that simple defects, V Ga and anti-site defects, produce states near this energy location, 17 while some V N -related defects are also likely to be the origin considering the annealing temperature. The measured C-V curves indicated that the reduction and recovery of the carrier concentration occurred upon the implantation and subsequent annealing, respectively.…”

“…However, since the interface-fixed charges might have caused a shift of the C-V curve as large as 10 V, we cannot completely rule out the possibility of the detected states being acceptor-like states, e.g., N i , V Ga , and Ga antisites. 17 Nevertheless, the shift of the C-V curve by 10 V requires a high density of interface-fixed charges of 1.5×10 13 cm -2 , which seems unlikely. On the other hand, Ref.…”

“…A Si-doped GaN epitaxial layer was grown by metalorganic vapor phase epitaxy on a free-standing n + -GaN (0001) substrate produced by hydride vapor phase epitaxy. The thickness and carrier concentration of the n-type GaN epitaxial layer were 3 µm and 5×10 17 …”