Interface structures of ZnO/MoO3 and their effect on workfunction of ZnO surfaces from first principles calculations

Abstract

Plane wave periodic Density Functional Theory (DFT) calculations were performed to investigate MoO3 surfaces and MoO3/ZnO interfaces to understand the effect of transition metal oxide overlayers on the workfunction of ZnO surfaces. To construct computationally feasible interfaces with small lattice mismatches, a set of strain variables was introduced to measure the lattice mismatch of interface models. Based on this, the MoO3 (010)/ZnO (0001) interface was constructed and fully relaxed within DFT. In order to accurately predict the workfunction of the interface, pseudo-hydrogen atoms were introduced to compensate the net dipole moment of the ZnO slab with (0001)/(0001¯) terminations. The results show that the workfunction of ZnO (0001) surface increased from 6.9eV to 7.4eV when it has one layer of MoO3 (010) overlayer. However, with further increases of the MoO3 slab thickness, no appreciable increase of workfunction was observed suggesting full coverage of a thin layer of transition metal oxide can be an effective way of increasing the workfunction of ZnO for display and flexible OLED applications.