Production of cuprous oxide, a solar cell material, by thermal oxidation and a study of its physical and electrical properties

Abstract Cuprous oxide (Cu 2 O) is a non stoichiometric defect semiconductor. It is envisaged that this semiconductor could be utilised for the fabrication of low-cost solar cells. Copper foil samples, were oxidised in air between 200°C and 1050°C. The oxide films grown were then investigated by means of both XRD and SEM. The electrical characteristics of Cu 2 O films were analysed by means of the hot-probe thermoelectric method, resistivity and mobility measurements. Oxide films formed between 1040°C and 1050°C were observed to consist entirely of Cu 2 O and showed p-type semiconductivity while those grown between 200°C and 970°C consists of a mixture of cupric oxide (CuO) and Cu 2 O. The CuO layer formed was found to be also p-type semiconducting. Thermodynamic calculations indicate that CuO in the mixed oxide layer could be explained in terms of the oxidation of Cu 2 O. Cu 2 O layers grown in air without the annealing process gave resistivities in the range 2×10 3 –3×10 3  Ω cm. A substantial reduction in the resistivity of the samples was achieved by doping with chlorine during growth and annealing. An average mobility of 75 cm 2  V −1 s  −1 , at room temperature, was obtained for eight unannealed Cu 2 O samples. This average value increased to 130 cm 2  V −1  s −1 , after doping the samples with chlorine and annealing.