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 similar to 100 nm and a hole mobility of 2-18 cm(2) V-1 s(-1). Subsequent RTA (3 min) at a pressure of 50 Pa and temperatures of 600-1000 degrees 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 mu m and up to 58 cm(2) V-1 s(-1), respectively, for films annealed at 900-1000 degrees C. These films also exhibited a resistivity of similar to 50-200 Omega cm, a hole concentration of similar to 10(15) cm(-3) at room temperature, and a transmittance above 80%.