Influence of Low Cd-Doping Concentration (0.5 and 3 wt.%) and Different Substrate Types (Glass and Silicon) on the Properties of Dip-Coated Nanostructured ZnO Semiconductors Thin Films

The investigation of semiconductor films of undoped ZnO and doped with two weight percentages of Cadmium (0.5 and 3) were grown on glass and silicon substrates under the same conditions using the dip-coating method. The X-ray diffraction patterns showed the growth of the wurtzite ZnO phase in a hexagonal crystal structure. Also, the effect of both cadmium concentration and substrate type is very clear, while the films those grown on glass substrate showed a crystallization with a highly c-axis preferred (002) orientation, those grown on a silicon substrate showed regular growth in all directions of the zinc oxide phase. The average crystallites size is of the nano-metric scale, more precise about 27 nm, supported with images taken with Environmental Scanning Electron Microscopy, furthermore from the latter technic (ESEM), we noticed a presence of three morphological types on the surface, were originated according to the substrate type and quantity of Cd-doping. The Rutherford Backscattering Spectrometry simulation spectra and the Auger Electron Spectroscopy by the relation with the stripping time emphasize the subsistence of starting (Zn) and doping (Cd) elements on the final specimens and in proportional quantities, to deduce that the undoped ZnO specimen thin film is the thickest. All the obtained films have an optical transmission of about 80% level within the visible range and a severe absorption beginning about 370 nm corresponding to the fundamental absorption limit, where the optical band gap energy decreased from 3.21 eV to 3.16 eV for the undoped ZnO and doped with 3 wt.% Cd respectively. The room-temperature luminescence emission spectra of all specimens were excited at the same conditions under 250 nm Xenon lamp excitation, where showed ultraviolet and visible emissions for all the films grown on a glass and silicon substrate, while an opposite reaction was recorded in the intensity of the spectra as the percentage of Cd increased.