Elaboration et caractérisation des couches minces de ZnO dopées cobalt et indium

Abstract

Zinc oxide (ZnO) is a binary semiconductor material with direct band gap (3,37 eV) because of their good optoelectronics properties, ZnO films find several applications such as: solar cells, gas sensors, piezoelectric sensors, waves guides... etc. ZnO thin films can be prepared by several techniques, such as: spray, thermal evaporation, reactive sputtering, sol gel, laser ablation... etc. In the present work and in the order to obtain conducting transparent layers, ZnO thin films were deposited by ultrasonic spray technique on glass substrates. Our interest is on the optimization of the parameters influence as a molarity, growth time and substrate temperature on the physical properties of ZnO thin films. On the other object is to improve the quality of these films in the study of the doping level influence and substrate temperature on the structural, optical and electrical properties of ZnO thin films. One has used two sources of dopants; CoCl3 6H2O, InCl3. Each time, the doping level was varied from 0 to 4 % by weigth. The DRX analyses indicated that undoped ZnO films deposited at different conditions have polycrystalline nature and hexagonal wurtzite structure with (002) preferential orientation and the maximum average crystallite size of 33.28 nm for the ZnO thin deposited at 350 °C for 2 min to deposition and in an concentration of 0.1 mol/l. are optimal conditions regardless the starting solution. The optical transmittance spectra showed transmittance higher than 80 % within the visible wavelength region. Hence, the values of the gap were found to be between 3.11 to 3.25 eV with the deposition parameters. The minimum resistivity of the ZnO films is 0.13 Ω.cm. The analysis by the method of X-ray diffraction revealed that CZO and IZO films crystallize in the hexagonal wurtzite structure of ZnO with a preferential orientation along the (002) plane with the maximum average crystallite size of ZnO:In and ZnO:Co were 45,78 and 55,46 nm, respectively. Transmission spectra and optical absorption indicates that the CZO films are haily transparency in the visible range and low absorption for IZO films. The band gap energy of the thin films increased after doping Co from 3.25 to 3.36 eV, which result in narrawing the conduction band and the valence band. And decrease for the IZO from 3.25 to 3.18 eV. The electrical conductivity of ZnO films improved with increasing in the doping level of 7.63 and 7.82 (Ω.cm) -1 of CZO and IZO, respectively. As a result, the crystallinity, the optical and electrical properties of IZO thin films are improved with annealing temperature can be influenced by oxygen diffusion with annealing temperature.