Tunable band-gap engineering of ZnSnN₂ via cation disorder from first-principles calculations

Heterovalent ternary alloys offer a rich space to search for the next-generation optoelectronic materials. Unlike their III-V counterpart, cation disorder can greatly alter the electronic properties of II-IV-V₂ compounds by breaking the octet-rule locally. Thus, intentional introduction of cation disorder can provide a new route to tune the electronic band gap of heterovalent ternary compound besides conventional alloying. To demonstrate this possibility, we performed first-principles calculations based on hybrid density functional theory to study the cation disorder effect in ZnSnN₂, which is a promising solar material in the II-IV-V₂ family. We found a direct relationship between the band gap of ZnSnN₂ and the long-range order parameter S, which characterizes the Zn/Sn disorder. Such band gap variations arise from the presence of octet-rule breaking motifs in the lattice (Zn3Sn, ZnSn3, Zn4, Sn4). Our findings reveal the correlations between cation disorder and the band gap of ZnSnN₂, and suggest the possibility of alloy-free band gap tuning in heterovalent ternary compounds.