Band Gap-Tunable (Mg, Zn)SnN₂ Earth-Abundant Alloys with a Wurtzite Structure

Abstract

Herein, wurtzite-type MgSnN2–ZnSnN2 alloys (Mg x Zn1–x SnN2) are proposed as earth-abundant and band gap-tunable semiconductors with fundamental band gaps in the range of 1.5–2.3 eV. The alloys do not exhibit immiscibility, unlike the InN–GaN system, because the lattice mismatch between the endmembers is smaller than 1% in both a- and c-axis directions. The Mg x Zn1–x SnN2 alloys can be epitaxially grown on GaN(001) in the whole x range, and their fundamental band gap can be tuned from 1.5 to 2.3 eV with the increase in x from 0 to 1. Moreover, the Mg x Zn1–x SnN2 epilayers with x > 0.53 exhibit a green-light photoluminescence emission near room temperature, which indicates that they are direct-gap semiconductors. Direct-gap semiconductors with band gaps of 1.8–2.5 eV are eagerly anticipated for the development of green light-emitting diodes (LEDs) and top cells in high-efficiency tandem solar cells, though such wurtzite- or zincblende-type compounds that can be epitaxially integrated with conventional semiconductors are quite rare. Therefore, Mg x Zn1–x SnN2 alloys are attractive nitride semiconductors toward the development of green-LEDs and tandem solar cells.

Pressure-Induced Transition from Wurtzite and Epitaxial Stabilization for Thin Films of Rocksalt MgSnN2

“…It has been reported that sputtered films and high-pressure synthesized powders of MTN are often contaminated with oxygen. ,, Thus, the oxygen concentrations in the precursor and high-pressure heat-treated films with x = 0.02 were semi-quantitatively measured with XPS depth profiling. Figure a,b shows the depth profiles of the oxygen concentration (represented by the O/(N + O) atomic ratio) for the wz-MTN precursor layer and the high-pressure heat-treated rs-MTN films, respectively.…”

“…The oxygen concentrations within the film were comparable with or lower than the values reported for sputtered wz-MTN films. 20,22 The oxygen contamination is believed to have originated from water vapor in the residual gas within the sputtering chamber. High-pressure heat treatment promoted oxygen contamination in the surface region (Figure 7b), thereby widening the oxygen-rich surface region.…”

“…MgSnN 2 (MTN) is a new member of II–IV–N 2 compounds, and its first theoretical and experimental studies were reported in 2016 and 2019, respectively. Recently, MTN has been suggested to have a high-pressure phase. − In most experiments, MTN has been studied in its thin-film form, ,− and the films usually had a wurtzite (WZ)-type crystal structure (wz-MTN), as shown in Figure a (which was visualized using the software VESTA). We found that high-pressure synthesis yielded rocksalt (RS)-type MTN (rs-MTN) in powder form (Figure b), , although its presence had not previously been predicted.…”

Li and group-III impurity doping in ZnSnN2 : Potential and limitations

“…This material system attracts considerable attention, partially due to its strong similarities to the parent material system, i.e., the AlN-InN-GaN system, where the III-nitride cation is substituted by heterovalent group-II and -IV cations. For the ternary nitride system used for band gap engineering, e.g., Zn(Sn, Ge)N 2 [1] or (Zn,Mg)SnN 2 [2], ZnSnN 2 exhibits the lowest band gap for this category of materials, as summarized in the review by Greenaway et al [3]. In particular, ZnSnN 2 is of specific interest in applications of II-IV nitrides as top cell components in tandem solar cells together with silicon, as the band gap is close to the optimum for the top cell.…”

A first-principles study of MgSnN2 films using a DFT-1/2 approach

“…MgGeN 2 and MgSnN 2 have smaller band gaps of 3.2 eV [8] and 2.3 eV [9], respectively. Their counterparts in Zn-IV-N 2 family are of 3.7 eV [10], 3.1 eV [11] and 1.5 eV [9]. However, more works are still needed for further understanding of this class of materials in order to boost their applications, e.g., Dumre et al studied three crystal forms of MgSnN 2 on their mechano-electronic properties and bonding properties [12].As known, some II-IV-N 2 compounds can be used for nonlinear optical applications.…”