Cation-Disorder-Enhanced Unintentional Doping in MgSnN2

Abstract

${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_{2}$ has recently attracted significant interest as a promising candidate for applications in green light-emitting diodes and photovoltaic absorbers. However, the experimentally synthesized ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_{2}$ samples suffer from a high concentration of unintentionally doped electrons, and their origin is not fully understood yet. By performing first-principles calculations, we investigate the properties of intrinsic point defects and oxygen impurities in cation-ordered and -disordered wurtzite ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_{2}$. It is found that the cation antisite defect ${\mathrm{Sn}}_{\mathrm{Mg}}$ is the predominant donor defect, contributing an electron concentration as high as ${10}^{17}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ to cation-ordered ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_{2}$. However, this value is 2--3 orders of magnitude lower than experimental observations (${10}^{19}\ensuremath{-}{10}^{20}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$). We further show that cation disorder significantly decreases the formation energies of defects, leading to a much higher electron concentration (${10}^{19}\phantom{\rule{0.25em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$) than in the case of the cation-ordered phase. The reduced formation energy can be understood by the energy gain due to the creation of energetically favorable local motif structures after the formation of defects. Hence, reducing the degree of cation disorder is beneficial for decreasing the densities of defects and self-doped carriers.