The barrier height formation mechanism and bulk inhomogeneity in ZnSnN2 Schottky junctions

To reveal the formation mechanism of Schottky barrier heights, inter-diffusion and chemical reaction between ZnSnN2 and the metals (Cu or Ag) are studied. Nitrogen and selective cation out-diffusion are observed, besides stronger Cu and weaker Ag in-diffusion. The Schottky barrier heights are consistent with the Schottky–Mott theory based on the improved work functions of ZnSnN2 layers and metals due to oxygen contamination. The Fermi level is pinned at about 1/3 of the forbidden bandgap below the conduction band bottom. Each layer in ZnSnN2 is electronically homogeneous with the chemical reaction limited to the interface region. The ZnSnN2 layer in ZnSnN2 is bulk inhomogeneous with one smaller work function from the minor phase resulting from Cu in-diffusion and suppressed oxygen out-diffusion besides the larger one from the original major phase, while the Cu layer is also bulk inhomogeneous, resulting from the higher chemical activity of Cu, which leads to the observed barrier height inhomogeneity and quenches the photovoltaic effect.