Studies On Growth And Doping Of ZnO Thin Films By PLD

Zno is a wide band gap semiconductor with optical transparency in the visible range. It′s crystallizes is a hexagonal wurtzite structure with 3.37eV band gap and large exciton binding energy of 60meV at room temperature.Zno is a kind of very promising materials for making the optoelectronics devices such as UV/blue light-emitting diodes and short-wavelength semiconductor diode laser devices and put in application. In recent years,the fabrication of Zno films has attracted a considerable amount of interest due to their potential appliection in flat-paned displays,solar cells,gas sensors and optical waveguides,which makes it a promising material for using in many fields. In this thesis,a series of ZnO films were prepared by using a KrF excimer laser at different deposited condition.preparation and doping of ZnO films have been studied by X-ray diffraction (XRD), photoluminescence spectra(PL),scan electron microscopy(SEM), atomic force microscopy(AFM) and Hall measurements . The results are as follows:1. The ZnO films were prepared at different substrate temperature.XRD results suggested that all samples have c-axis orientation.As the substrate temperature changes from 500℃to 650℃,the FWHM of ZnO(002) diffraction peaks become narrower.The crystallinity of the samples is improved.The surface morphology of the sample grown at 600℃is even-orderly,compact and clear-cut.The sample grown at 600℃has the strongest UV emission.2. The ZnO films were prepared at different oxygen partial pressure.As the oxygen pressure for the thin films deposition increases from 5 Pa to 60 Pa,all samples have c-axis orientation.As the oxygen pressure at 25 Pa, the (002) diffraction peak of the thin film is strongest,the surface morphology is clear and the UV is strongest,it may be due to some capabilities of the ZnO films related to the structural defect.3. The ZnO films were prepared at different laser frequencies.As the laser frequencies for the thin films deposition increases from 3Hz to 20Hz, all samples have c-axis orientation.As the laser frequencies at 3Hz,the quality of thin film is highest,it may be due to the interval of ZnO gotten to substrate surface related to the structural defect.4. The doped ZnO films were prepared at different percentage of Al. XRD results suggested that all samples have c-axis orientation.As the percentage of Al changes from 0.2% to 3.7%.As the percentage of Al increasing,the ZnO(002) diffraction peaks become weakener.Hall test results suggested AZO has the lowest resisitivity at percentage of 1.7 of Al, it may be due to the carrier concentration increased related to the Al atom affiliated,thus it induce the decline of resisitivity. However, As the Al-doped with more than 1.7 percent, as percentage of Al a further increasing, the resisitivity increased ,it may be due Al limited solid-thickness in ZnO films caused excessive Al atom can not be completely into the crystal lattice of ZnO, which makes some Al atoms and O atoms formed a non-conductive Al2O3 cluster, some of the lattice in the state of disorder encumber the electronic movement.