Improving carrier transport in Cu ₂ O thin films by rapid thermal annealing

Abstract

Abstract Cuprous oxide (Cu 2 O) 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 Cu 2 O sheets, possibly due to their poorer transport properties. This study shows that post-deposition rapid thermal annealing (RTA) of Cu 2 O films is an effective approach for improving carrier transport in films prepared by reactive magnetron sputtering. The as-deposited Cu 2 O 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 cm 2 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 µ m and up to 58 cm 2 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 ~10 15 cm −3 at room temperature, and a transmittance above 80%.