Relation of site disorder, band gap and localization in ZnGeN₂

In ZnGeN₂, site disorder is studied to manipulate the band gap to align with current technological deficiencies at green/amber emission wavelengths in light emitting diodes known as the “green gap,” while maintaining low lattice mismatch with GaN. We present cluster-based Monte Carlo simulations to evaluate site disorder in ZnGeN₂ at short- and long-range. Converged configurations are relaxed in volume and lattice parameters through Density Functional Theory. Band gap-corrected hybrid calculations are used to obtain the electronic structure of the 1,024 atom supercells and structural and electronic parameters are then used in device modeling to study the effects of site disorder on quantum well design for light emitting diodes. We calculate nitrogen coordination and Bragg-Williams short- and long-range order parameters, respectively, to relate order and electronic structure and analyze state localization as a means of differentiating defect states from band gaps which remain ill-defined in disordered systems. In ZnGeN₂, the non-isovalent character of the disordered species (Zn²⁺ and Ge⁴⁺) subjects the cation ordering to strong short-range order effects which influence band structure by decreasing the band gap relative to ordered ZnGeN₂ across a wide range.