| ZnO is a II-VI compound semiconductor with a wide direct band gap of 3.37eV atroom temperature, a large exciton binding energy of 60meV, and a hexagonal wurtzitestructure. Its lattice parameters are a = 0.3249nm and c = 0.5206nm. Traditionally, Zincoxide is a piezoelectric material which has a reasonably large piezoelectric coefficient.Acoustoelectric devices, such as surface acoustic wave devices (SAW) have beenfabricated with ZnO. Due to its unique conducting mechanism based on oxygenvacancies, zinc oxide is also used in oxygen gas sensors. Furthermore, like indiumoxide and tin oxide, ZnO is both transparent in the visible region and electricallyconductive with appropriate dopants such as aluminum, this unique property has beenwidely studied for transparent conducting electrodes for flat panel displays, and solarcells. In recent years, ZnO, as a wide band semiconductor, has gained more and moreattention. Compared with GaN, the most successful wide-band semiconductor materialat present, ZnO has many promising advantages. High-quality ZnO with very lowdefect densities can be synthesized at relatively low temperature. It possesses lowerliminal power for photoluminescence and stimulated emission and take on higherefficiency of energy conversion. ZnO has large excitonic binding energy (60mev at RT),which promises strong UV stimulated emission from bound excitonic emissions at roomtemperature. Photoelectron devices with excellent quality, such as detectors, laserdiodes (LDs) and light emitting diodes (LEDs), can be made using ZnO films.To achieve the requirements of different applications, many techniques, such asmolecular beam epitaxy, magnetron sputtering, metal organic chemical vapor deposition,pulsed laser deposition, spray pyrolysis, sol-gel process, and reactive deposition havebeen used to deposit ZnO films. Each of these techniques has its merits and demerits.The key to the application of ZnO films is high quality for the purpose. For variousapplications, highly preferred c-axis orientation of ZnO films is usually important. Inthis work, ZnO films were prepared using pulsed laser deposition (PLD) techniques.PLD has advantages in comparison with other methods, such as simple operation, quickreactive process, realization of one-step synthesis, stable film composition, anddeposition in a relatively high oxygen-partial pressure and lower temperature. ZnOfilms deposited on silicon (111) substrates by PLD generally produced by the KrFexcimer laser with the wavelength of 248 nm or Nd: YAG laser operating at 355 nm. Inthis study, the effect of various substrate, oxygen pressure, substrate temperature andannealing temperature on the microstructure and optical properties of ZnO films grownby PLD using a Nd: YAG laser with the wavelength of 1064 nm was investigated.Uniform and compact ZnO films with the highly preferred c-axis orientation and ahexagonal wurtzite structure can be prepared by PLD under optimized condition.Crystal orientation and quality of ZnO films were examined with Rigaku D/max-rBX-ray diffraction (XRD) meter. Measurements of photoluminescence (PL) spectra werecarried out with a SL50-B and a FLS920 fluorescence spectrophotometer at anexcitation of 280nm and 310nm from a Xe lamp excitation source to examine opticalproperties of the films. The film morphologies and surface structures were characterizedusing a Hitachi S-570 scanning electron microscopy (SEM) and an PARKAUTOPROBE CP atomic force microscopy (AFM). The grain sizes and selected-areaelectron diffraction (SAED) were measured with a Hitachi H-800 transmission electronmicroscopy (TEM). The composition of the samples was examined by VG ESCALABMKII X-ray photoelectron spectroscopy (XPS) meter. TENSOR 27 Fourier transforminfrared spectrophotometer (FTIR) was employed to measure chemical states of thefilms. Resistivity of ZnO films were measured by SZ-85 digital four-probemeasuremeter. All measurements were carried out at room temperature. |
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