First-principles studies of the role of cation disorder on electronic structure of ZnTiN₂

Cation disorder is often found in divalent ternary nitride semiconductors, with significant consequences for optoelectronic properties. For example, recently synthesized wurtzite-derived ZnTiN₂ exhibits cation disorder on its Zn and Ti sites, and has a measured band gap of about 2 eV, 1.5 eV smaller than that predicted for its cation-ordered structure by density functional theory (DFT) calculations with hybrid functionals [1]. ZnTiN₂ has great potential in photoelectric applications due to its band gap in the visible, good integration with high-performing semiconductors, and the potential for a stable self-passivating surface layer (e.g., ZnO, TiO₂) under operating conditions. Using state-of-the-art first principles DFT calculations with optimally-tuned range-separated hybrid functionals, we demonstrate that cation disorder in ZnTiN₂ creates locally charge-unbalanced nitrogen centered motifs that further introduce states near band edges, leading to band gap reduction. We study how the cation disorder affects local chemical environment, energetics, electronic structure, and optoelectronic properties in ZnTiN₂ and discuss its properties in light of possible photocatalytic applications.