Effects of deposition time and temperature on the optical properties of air-annealed chemical bath deposited CdS films

US films of over 1-mu m thickness were deposited onto glass substrates by chemical bath deposition (CBD). Deposition temperature and time were varied from 40 degrees C to 60 degrees C and from 30 min to 4 h, respectively. The highest deposition rate, 6.39 nm/min, was obtained with samples deposited for 90 min at 60 degrees C. The films deposited at 60 degrees C for 4 h were found to have the best adhesion and without defects. The optical properties, in particular the optical band gap, depended on film thickness, the deposition and annealing temperatures. Annealing in air resulted in a shift of the absorption edge towards higher wavelengths, i.e., a decrease in the gap value from 2.45 eV to 2.38 eV. The optical band edges of the films were not constant but depended on the annealing temperature. The refractive index, calculated by applying the envelope method on the transmission of the films in wavelengths from 550 rim to 850 nm, was in the range 1.95-2.26. The resistivity determined from dark conductivity measurement, as a function of the annealing temperature, was found to be in the order of 10(5) Omega cm for samples annealed in air at 250 degrees C, 3 h, and the activation energy was about 0.22 eV (c) 2006 Elsevier B.V. All rights reserved.