Shallow versus Deep Nature of Mg Acceptors in Nitride Semiconductors

Abstract

We investigate the properties of Mg acceptors in nitride semiconductors with hybrid functional calculations. We find that although the thermodynamic transition level is relatively close to the valence band in GaN (260 meV), Mg(Ga) exhibits key features of a deep acceptor: the hole is localized on a N atom neighboring the Mg impurity, inducing a large local lattice distortion and giving rise to broad blue luminescence. We show that the ultraviolet photoluminescence peak attributed to Mg acceptors in GaN is likely related to Mg-H complexes, explaining the results of photoluminescence and electron paramagnetic resonance experiments. Predictions for Mg acceptors in AlN and InN are also presented.

Precise lattice location of substitutional and interstitial Mg in AlN

“…The χ 2 [ Fig.2(a)-(c)] displays clear minima for displacements from the ideal S Al sites of at most 0.1Å. At first sight, if one assumes that all the substitutional Mg dopants in our samples are in the neutral state, our results seem to support the prediction of Szabó et al 12 and contradict that of Lyons et al 17 : if an elongation of Mg-N c-axis bond length does occur, it must be accommodated by a displacement of the N neighbor, without significantly displacing the Mg atom from the ideal Al site. On the other hand, if all substitutional Mg acceptors in our samples are in the ionized state (compensated by native donor defects, possibly created upon 27 Mg implantation), our results are perfectly consistent with the prediction of Lyons et al 17 , i.e.…”

“…On the other hand, the ab initio calculations of Szabó et al 12 suggest for the acceptor state elongations of the Mg-N bond lengths by ∼0.2Å along the c-axis and ∼0.13Å basal to it, which should result in only small displacements of Mg from the ideal Ga site. These inconsistencies, which in fact also exist for Mg in GaN, [17][18][19] can only be clarified by a precise experimental determination of the Mg lattice location. In this letter, we report on direct lattice location studies of implanted Mg in AlN.…”

“…15 In most theoretical work, only substitutional Mg Al on ideal Al sites has been considered, since interstitial Mg, which acts as donor, 16 was suggested to be unstable. 10 Based on ab initio calculations for substitutional Mg Al in AlN, Lyons et al 17 have recently proposed that in the ionized state (Mg − Al ) Mg occupies a near-ideal Al site, whereas in the neutral state (Mg 0 Al ) the Mg atom is displaced from the ideal substitutional Al site. The shift results from the localization of the Mg-related hole on a N neighbor along the c-axis, which leads to an increase in the Mg-N bond length by 18% (0.34Å), accommodated by displacements of both the Mg atom and its N neighbor (along the c-axis).…”

Native point defects in CuIn1−xGaxSe2: hybrid density functional calculations predict the origin of p- and n-type conductivity

“…Finally, ∆V (q) is the difference in reference potential of the supercell without defect and with defect. J. L. Lyons et al have studied several corrections for the effects of the finite size supercell and have reported the correction scheme based on ∆V (q) to be consistent with other correction schemes, such as the Madelung correction 32 . From Eq.…”

The effects of screening length in the non-local screened-exchange functional

“…However, semi-local XC functional are unlikely to get transition levels correct, due to the band gap problem. Moreover, the electron delocalisation problem of semi-local DFT can lead to the incorrect ground state for some defects [67,68,69,70]. The sX hybrid functional is known to correct these problems in several semiconductors and insulators [35,39,66,71,72].…”