Unraveling the strain and inherent onsite-correlation effect on the electronic structure of pure and iso-electronic Ag doped copper nitride

Promising optoelectronic properties of semiconducting copper nitride (Cu3N), have brought the material into limelight for numerous device applications. As band gap (Eg), undoubtedly is a key parameter in determining proficiency of a semiconductor in optoelectronics, hence its modulation needs clear understanding both from the fundamental and application perspectives. The present study discusses the impact of inherent onsite Coulomb-correlation (through Hubbard U) and strain on the electronic properties of pure and iso-electronic element (Ag) doped Cu3N using density functional calculations. A slow rate of increase in Eg with U recognizes Cu3N a weakly correlated system. Alternately, U for the doped system (Cu2AgN) is discovered to have further weaker effect on the Eg, nearly independent for U > 2 eV. However, doping of the 4d electronic element in the 3d transition metal nitride predicts an increased carrier mobility which will subsequently improve electrical conductivity. While examining the effect of strain in pristine Cu3N, the lowest conduction band is found to have both approaching and avoiding feature with respect to the Fermi level at two different high symmetry k-points. Consequently, Eg decreases (increases) for the compressive (tensile) strain which is attributed to the higher (lower) dispersive nature of the valence bands due to stronger (weaker) p-d hybridization. In case of Cu2AgN, though a similar shifting in the lower conduction band is observed, the variation of Eg with strain is quite different to that of Cu3N. While Eg increases (decreases) for the uniaxial compressive (tensile) strain, it decreases both for tensile and compressive strains corresponding to the isotropic deformations.