Sol-gel Method Doped Zno Thin Films Optical And Electrical Properties

Zinc oxide(ZnO) is a novelⅡ-Ⅵcompound semiconductor with a wide direct bandgap(3.37eV at room temperature) and a hexagonal wurtzite strcture.ZnO is a unique material that exhibits optoelectronic,piezoelectric and ferromagnetic multiple properties.With its direct wide-bandgap and high exciton binding energe(60meV,cf. 25meV for GaN),ZnO is a potential candidate for applications in optoelectronic region.Due to the stability of its exciton,ZnO will favor efficient excitonic emission processes at room temperature.When Cd or Mg is added in ZnO,the bandgap energy of ZnO alloy thin films can be tuned by varying the compositions,which gives ZnO extended application in short-wavelength optoelectronic devices,including light emitting diodes(LEDs) and laser diodes(LDs).In this thesis,based on the introduction of past and current research on ZnO thin films,we deposit ZnO:Cd and ZnO:Mg alloy thin films by the sol-gel process using a spinning-techniques.The main results are obtained as follows:1.We have prepared Cd-doped(≤10at%) and Mg-doped(≤15at%) ZnO thin films by sol-gel method.X-ray diffraction(XRD),scanning electron microscope(SEM) and energy dispersive X-ray spectrometer(EDS) were used to characterize the crystalline structure,orientation and surface morphology of the ZnO thin films.It was revealed that wurtzite structure with(002) orientation ZnO thin films were obtained at any concentrations.As the Cd concentration is 8at%or Mg concentration is 9at%,the ZnO thin films were optimally crystallized.2.Ultraviolet-visible(UV-vis) spectrometer was used to measure the optical properties of the Zno thin films.It was found that their optical transmittance was over 75%in the visible region with a sharp fundamental absorption edge.Optical band-gap of the films was decreased to 3.11eV depending on the Cd doping concentration,and it was increased to 3.45eV when Mg doping concentration was 15at%.3.Photoluminescence spectrum was acquired in a SHIMADZU fluorespectrometer at room temperature.The shape of all the spectra was featured by a strong emission near UV and a deep level emission in blue region.As the Cd doping concentration was increasing,the UV emission peak shifted towards the longer wavelengths;on the contrary,the peak shifted to the shorter wavelengths when we increased the Mg concentration,which revealed the same result as the transmission spectrum.4.The electrical properties of the ZnO:Cd thin films were studied.A minimum resistivity of 8.47kΩ·cm was obtained at a doping concentration of 8at%;while the optimal electricity conduction at a annealing temperature of 600℃.