Cation disorder in stoichiometric MgSnN2 and ambipolar self-doping behavior in off-stoichiometric MgSnN2

TL;DR

This study investigates cation disorder and doping behavior in MgSnN2, revealing how disorder affects band gaps and optical properties, and demonstrating ambipolar self-doping depending on Mg/Sn ratio.

Contribution

It provides a comprehensive analysis of cation disorder effects and doping mechanisms in MgSnN2 using first principles calculations and cluster expansion methods.

Findings

Cation disorder reduces band gap due to octet rule violation.

Local disorder impacts optical absorption by altering band gap.

Mg-rich and Sn-rich compositions exhibit p-type and n-type self-doping, respectively.

Abstract

Investigations on II-Sn-N2 (II = Mg, Ca) have been started very recently compared to the intense research of the Zn-IV-N2 (IV = Si, Ge, Sn). In this work, we perform a comprehensive study of cation disorder in stoichiometric MgSnN2 and crystal structure characteristic, doping behavior of off-stoichiometric Mg1+xSn1-xN2 (x = -0.8, -0.6, -0.5, -0.4, -0.2, 0.2, 0.4, 0.5, 0.6, 0.8) by using the cluster expansion method and first principles calculations. It is found that cation disorder in stoichiometric MgSnN2 induces a band gap reduction because of a violation of the octet rule. Moreover, the local disorder, namely forming (4,0) or (0,4) tetrahedra, would lead to an appreciable band gap reduction and hinder the enhancement of the optical absorption. An off-stoichiometric Mg/Sn ratio can strongly affect the morphology of Mg1+xSn1-xN2 samples due to the higher ionicity of the Mg-N bonds in comparison with Zn-N bonds. Furthermore, Mg1+xSn1-xN2 compounds show an ambipolar self-doping behavior, i.e., Mg-rich Mg1+xSn1-xN2 show p-type doping while Sn-rich ones exhibit n-type doping owing to the formation of acceptor-type antisite defect MgSn or donor-type antisite defect SnMg, respectively.