Cation-Disorder-Enhanced Unintentional Doping in ${\mathrm{Mg}\mathrm{Sn}\mathrm{N}}_{2}$

Cation-Disorder-Enhanced Unintentional Doping in ${Mg Sn N}_{2}$

Feng Ning, Jing Huang, and Jun Kang

Phys. Rev. Applied 19, 054046 – Published 12 May 2023

Abstract

${Mg Sn N}_{2}$ has recently attracted significant interest as a promising candidate for applications in green light-emitting diodes and photovoltaic absorbers. However, the experimentally synthesized ${Mg Sn N}_{2}$ 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 ${Mg Sn N}_{2}$ . It is found that the cation antisite defect ${Sn}_{Mg}$ is the predominant donor defect, contributing an electron concentration as high as $10^{17} {cm}^{- 3}$ to cation-ordered ${Mg Sn N}_{2}$ . However, this value is 2–3 orders of magnitude lower than experimental observations ( $10^{19} - 10^{20} {cm}^{- 3}$ ). We further show that cation disorder significantly decreases the formation energies of defects, leading to a much higher electron concentration ( $10^{19} {cm}^{- 3}$ ) 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.

Received 8 February 2023
Accepted 17 April 2023

DOI:https://doi.org/10.1103/PhysRevApplied.19.054046

Physics Subject Headings (PhySH)

Defects Optoelectronics

Disordered systems Doped semiconductors LEDs Semiconductor compounds Solar cells

Density functional calculations

Condensed Matter, Materials & Applied PhysicsEnergy Science & Technology

Authors & Affiliations

Feng Ning^1,2, Jing Huang¹, and Jun Kang ^1,*

¹Beijing Computational Science Research Center, Beijing 100193, China
²School of Physics and Electronics, Nanning Normal University, Nanning 530001, China

^*jkang@csrc.ac.cn

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Vol. 19, Iss. 5 — May 2023

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Figure 1
(a) Conventional cell of cation-ordered ${Mg Sn N}_{2}$ with the Pna2₁ space group. (b) Band structures calculated using the PBE and HSE06 methods. (c) Chemical potential region (in red shadow) stabilizing ${Mg Sn N}_{2}$ with respect to binary competing phases with activated $N$ source. Four distinct points, A, B, C, and D, are selected as the growth conditions for calculating defect-formation energies.
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Figure 2
Formation energies of native point defects and $O_{N}$ impurities in ${Mg Sn N}_{2}$ as a function of Fermi level under chemical potential points (a) A, (b) B, (c) C, and (d) D, as labeled in Fig. 1. Gray arrows indicate the self-consistently calculated Fermi level. (e) Defect charge-state transition levels within the band gap of ${Mg Sn N}_{2}$ . (f),(g) Charge-density distributions of donor and acceptor states for ${Sn}_{Mg}$ and ${Mg}_{Sn}$ under neutral states, respectively. Isosurface value is 0.0003 e/bohr³.
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Figure 3
(a) Calculated Fermi levels (referenced to the VBM) and (b) electron concentrations in cation-ordered ${Mg Sn N}_{2}$ with native point defects and $O_{N}$ impurities at a growth temperature of 700 K under different chemical potential conditions from points A to D.
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Figure 4
(a) Example of cation-disordered ${Mg Sn N}_{2}$ structure generated from the MC simulation. Local environment of a nitrogen site is denoted as $N$ (nMg, nSn), where nMg and nSn correspond to the numbers of $Mg$ and $Sn$ atoms in the tetrahedron. Each cation site is coordinated by four neighboring $N$ atoms with different local environments. For example, $Mg$ (0,1,3) represents the local environment of the $Mg$ atom coordinated by one $N$ (2,2) and three $N$ (3,1) motifs, and $Sn$ (3,1,0) represents the $Sn$ atom coordinated by three $N$ (1,3) and one $N$ (2,2) motifs. Formation-energy difference, $Δ H_{f}^{diff}$ , of the (b) ${Sn}_{Mg}$ , (c) ${Mg}_{Sn}$ , (d) $V_{N}$ , and (e) $O_{N}$ defects under different local environments in three host structures (S1, S2, and S3) picked from the MC calculations. $Δ H_{f}^{diff}$ is referenced to the lowest formation energy obtained among the considered defect sites. All the $Δ H_{f}^{diff}$ values are calculated using the HSE06 functional.
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Figure 5
(a) Effective formation energies of ${Sn}_{Mg}^{2 +}$ , ${Mg}_{Sn}^{2 -}$ , $V_{N}^{1 +}$ , and $O_{N}^{1 +}$ as a function of Fermi level for cation-disordered and -ordered ${Mg Sn N}_{2}$ at chemical potential point D, calculated using the HSE06 method. Two gray solid vertical lines represent the average band-edge positions of cation-disordered S1, S2, and S3 ${Mg Sn N}_{2}$ structures. (b) Electron concentrations of cation-disordered and -ordered ${Mg Sn N}_{2}$ at a growth temperature of 700 K under different chemical potential conditions from points A to D.
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Physical Review Applied

Cation-Disorder-Enhanced Unintentional Doping in MgSnN2

Feng Ning, Jing Huang, and Jun Kang

Phys. Rev. Applied 19, 054046 – Published 12 May 2023

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Cation-Disorder-Enhanced Unintentional Doping in ${Mg Sn N}_{2}$