Improving carrier transport in Cu₂O thin films by rapid thermal annealing

Cuprous oxide (Cu₂O) is a promising material for large scale photovoltaic applications. The efficiencies of thin film structures are, however, currently lower than those for structures based on Cu₂O sheets, possibly due to their poorer transport properties. This study shows that post-deposition rapid thermal annealing (RTA) of Cu₂O films is an effective approach for improving carrier transport in films prepared by reactive magnetron sputtering. The as-deposited Cu₂O films were poly-crystalline, p-type, with weak near band edge (NBE) emission in photoluminescence spectra, a grain size of ~100 nm and a hole mobility of 2-18 cm² V^-1 s^-1. Subsequent RTA (3 min) at a pressure of 50 Pa and temperatures of 600-1000 °C enhanced the NBE by 2-3 orders of magnitude, evidencing improved crystalline quality and reduction of non-radiative carrier recombination. Both grain size and hole mobility were increased considerably upon RTA, reaching values above 1 µm and up to 58 cm² V^-1 s^-1, respectively, for films annealed at 900-1000 °C. These films also exhibited a resistivity of ~50-200 Ω cm, a hole concentration of ~10¹⁵ cm^-3 at room temperature, and a transmittance above 80%.