Chemically deposited copper oxide thin films: structural, optical and electrical characteristics

Thin films of copper oxide with thickness ranging from 0.05–0.45 mm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–908C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu2O. Annealing the films in air at 3508C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV direct.to 1.75 eV direct.. The films show p-type conductivity, ;5=10y4 Vy1 cmy1 for a film of thickness 0.15 mm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW my2 tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 4008C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 4008C, is high, 7=10y3 Vy1 cmy1. These films are also photoconductive. q1999 Elsevier Science B.V. All rights reserved.