Effect of vacuum-ultraviolet irradiation on structure and resistivity of epitaxial copper oxide thin films

The structural and property control of copper oxide thin films driven by vacuum ultraviolet irradiation at room temperature in air was determined in this study. Cu2O(110) thin films were epitaxially grown as precursor crystals on MgO(100) substrates using pulsed laser deposition. The Cu2O thin films were subsequently irradiated with vacuum ultraviolet light ( = 172 nm) using a xenon excimer lamp for up to 120 min. Structural analyses by in-plane X-ray diffraction, reciprocal space mapping, and reflection high-energy electron diffraction observation indicated the phase transition of Cu2O to CuO crystals in the near-surface area, maintaining the oriented structure. The bi-epitaxial relationships were as follows: CuO(010)[100] // Cu2O(110)[001] // MgO(100)[011] and CuO(010)[001] // Cu2O(110)[110] // MgO(100)[011]. Significant improvement of conductivity in the order of 10(3 )was demonstrated, that the resistivity decreased from -2.1 x 10(3) Omega cm to -1.2 Omega cm after irradiation of 120 min. The present light-driven formation of epitaxial heterostructures of both Cu2O and CuO p-type semiconductors will be useful for the development and property control of devices.