Morphological and stoichiometric optimization of Cu2O thin films by deposition conditions and post-growth annealing

Thin films of copper oxide were grown by radio frequency-magnetron sputtering in an oxygen-argon environment onto silicon substrates at two different oxygen partial pressures (15% and 23%). Post deposition annealing in vacuum environment was conducted on the films at different temperatures (between 250 °C and 550 °C). We investigated the thin films by Scanning Electron Microscopy, Energy Dispersive X-ray, X-ray diffraction, Raman spectroscopy, Atomic Force Microscopy and Kelvin Probe Force Microscopy. These studies show that post-growth annealing in vacuum results in thin films with different morphological and stoichiometric properties. Furthermore, the oxygen partial pressure conditions during deposition have an impact over the obtained oxide phases: high oxygen partial pressure leads to the formation of two different oxide phases, i.e. CuO and Cu2O, while low oxygen partial pressure leads to the formation of Cu2O thin films. Notably, we also uncovered a parasitic crystallite growth as a result of aging on the pristine and low-temperature annealed samples, and we found out that high temperature annealing prevents this kind of aging.