Electronic structure of the substitutional versus interstitial manganese in GaN

TL;DR

This study uses density-functional theory to compare the electronic structures of substitutional and interstitial manganese in GaN, revealing differences in impurity states, hybridization effects, and implications for doping efficiency and optical properties.

Contribution

It provides a detailed comparison of Mn impurity states in GaN, highlighting how site position affects electronic behavior and potential passivation mechanisms.

Findings

Mn_Ga acts as a deep acceptor, Mn_I as a donor.

Formation of Coulomb-stabilized complexes may passivate Mn acceptors.

Hybridization causes wave functions to spread far from impurities.

Abstract

Density-functional studies of the electron states in the dilute magnetic semiconductor GaN:Mn reveal major differences for the case of the Mn impurity at the substitutional site Mn_Ga versus the interstitial site Mn_I. The splitting of the two-fold and the three-fold degenerate Mn(d)states in the gap are reversed between the two cases, which is understood in terms of the symmetry-controlled hybridization with the neighboring atoms. In contrast to Mn_Ga, which acts as a deep acceptor, Mn_I acts as a donor, suggesting the formation of Coulomb-stabilized complexes such as (Mn_Ga Mn_I Mn_Ga), where the acceptor level of Mn_Ga is passivated by the Mn_I donor. Formation of such passivated clusters might be the reason for the observed low carrier-doping efficiency of Mn in GaN. Even though the Mn states are located well inside the gap,the wave functions are spread far away from the impurity center. This is caused by the hybridization with the nitrogen atoms, which acquire small magnetic moments aligned with the Mn moment. Implications of the differences in the electronic structure for the optical properties are discussed.