Physical properties of electroless CoO thin filins

Abstract

Thin films of cobalt II oxide were prepared by the chemical bath deposition process using aqueous ammonia (30%) as a complexing agent. A post-deposition annealing treatment of the as-deposited films at 350°C for 30 mins in a controlled oxygen atmosphere (100-130 kPa/cm 2 ) was found to be a necessary precondition for obtaining good-quality CoO thin films. The films are p-type and semi-insulating with low carrier density of about 1011 em -3, high resistivity, and very low photosensitivity. From the study of the optical transmission spectra in the UV, visible and near-IR regions it was observed that the films had less than 10% transmittance in the UV,~50 % in the mid-visible region and 86% at a wavelength of 1100 nm. The optical constants were computed from the reflectance and transmittance spectra. The refractive-index values in the near-infrared region were fitted to the single oscillator Sellmeier dispersion model, yielding an undispersed refractive index of 1.80. The films showed both direct and indirect optical bandgaps E g , of 4.14 ± 0.05 eV and 3.89 ± 0.02 eV, respectively. PACS 81.15 -Methods of deposition of films and coatings; film growth and epitaxy. PACS 81.15.Lm -Liquid phase epitaxy; deposition from liquid phases (melts, solutions and surface layers on liquids).

Thermal-annealing-induced effects in chemically deposited cobalt sulphide thin films

“…These results correlated well with the results of XRD and electrical and optical studies of the as-deposited and annealed films. The properties of the CoO thin films described here are comparable to those reported in the literature on chemically deposited CoO films [4,15].…”

“…A careful observation of the optical transmission spectra for the 100 and 200 • C air annealed Co 3 S 4 films reveals that the absorption edge is not well defined, which is expected for an indirect-bandgap semiconductor. The transmission spectrum for the 270 • C air-annealed film corresponds to the mixed Co 3 S 4 -CoS 2 phase and the onset of its transformation to CoO film is evident in the spectrum for the sample air annealed at 310 • C. Figure 2 also indicates a well defined absorption edge and a shift of the absorption edge to shorter wavelengths for samples annealed at 350 and 400 • C, which correspond to the optical absorption edge of CoO [13][14][15]. Air annealing at higher temperatures up to 450 • C did not change the optical transmittance appreciably.…”