Preparation Of Pure And Al-doped ZnO Films By RF Magnetron Sputtering And Study Of Their Properties

ZnO is a Ⅱ-Ⅵ group multifunctional material with wide direct band-gap and has a hexagonal wurtzite structure. ZnO thin films have recently gained much attention due to their good piezoelectric, photoelectric, gas sensitivity and stress sensitivity behaviors. Transparent conducting Al doped ZnO (ZAO) thin films have been extensively studied as photoelectron information materials also. ZAO thin film is comparable with the more commonly used indium tin oxide (ITO) films regarding to their electrical and optical properties. Moreover, the film is chemical stable in the presence of active hydrogen or hydrogen plasma atmosphere and will not reduce the activity of solar cell materials because its composition is hard to interact with hydrogen at high temperatures. ZAO film is a promising transparent conducting film. It is emerging as one of the best alternative candidates for ITO films, and its use will promote the development of cheap solar cells.Polycrystalline ZnO films were deposited by radio frequency (RF) magnetron sputtering technique and the as-deposited films were annealed. X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, spectrophotometer and four-point probe were employed to characterize and analyze the films.The investigation results showed that the preparation parameters, especially the substrate temperature and annealing temperature, affect the structure, electrical and optical properties significantly. As far as ZnO thin film, it has the strongest preferred orientation under 300℃ substrate temperature and the crystallization of film is the best after 500℃ annealing. The mean transmittance in the visible region is over 85% for both as-deposited and annealed ZnO films. After annealing, the crystallization of ZnO thin film deposited on Si(111) substrate was improved, the defect concentration associated with deep energy level in the film could be reduced. For ZAO thin film, the resistivity and visible transmittance is 2.59 Ω cm and 70% respectively. The low resistivity can be obtained by either doping Al or shifting to non-stoichiometry, but it will reduce visible transmittance at the same time because of dopants' scattering. The band-gap of ZAO film becomes widened due to Burstein-Moss shift effect as compared to ZnO film. After annealed at 500℃ in pure Ar atmosphere for 1 hour, the visible transmittance increased from 70% to 80% and the resistivity decreased from 2.59 Ω cm to 0.13 Ω cm.