Photoluminescence Characteristics of Post-annealed Cu₂O Thin Films

Cuprous oxide (Cu₂O) thin films grown by radio-frequency magnetron sputtering were post-annealed at 700°C under various oxygen partial pressures (PO₂). Reduction and oxidation of oxygen were found in thin films annealed under PO₂ of 0.1 Pa and 2.0 Pa, respectively. We investigated the photoluminescence characteristics of the Cu₂O thin films measured at low temperature (30 K) and room temperature (300 K). When post-annealed at PO₂ of 0.3 Pa and 0.7 Pa, Cu₂O films presented dominant PL lines originating from transitions of excitons and doubly charged oxygen vacancies at low temperature, and solely excitonic recombination at room temperature. The temperature-dependent exciton spectra were well modeled in terms of phonon-assisted recombination of ortho-excitons. On the other hand, a broad luminescence band around 2.2 eV dominated in oxygen-deficient and over-oxidized Cu₂O thin films. By comparing the results of grazing-incident x-ray diffraction and luminescence spectra, we believe that the origin of this band, however, involves extrinsic bands induced by structural imperfections.