Preparation And Photoelectric Properties Of Ti-doped ZnO Thin Films

The Ti0.015Zn0.985O ceramic prepared by the solid-state reaction method was used as a target,and the TZO thin films were deposited on four different substrates of common glass,quartz,ITO and Si wafer by RF magnetron sputtering method.The effects of different substrates on the crystal structures and photoelectric properties of TZO thin films were studied.The TZO thin films deposited on the quartz substrates were grown in an oxygen atmosphere with different oxygen fluxes,then these samples were then annealed at 400℃ for 40 min in hydrogen,and the effect of hydrogen annealing on the photoelectric properties of the thin film samples was studied.A varistor with n-TZO/p-Bi2O3/n-TZO three-layer composite thin film was sputter-deposited on an ITO substrate.The crystal structure and surface morphology of the TZO thin films were characterized by XRD and SEM.The optical transmittance of the TZO thin films in the wavelength range from 200nm to 800 nm was measured by an ultraviolet-visible spectrophotometer UV-2700,and the optical band gap was calculated.The emission spectra of TZO thin film excited by a light with a wavelength of about 325 nm were measured by a PL spectrometer.The Hall coefficient,carrier concentration,and resistivity of the TZO thin films were measured by a Hall effect analyzer.The I-V characteristic curves of the n-TZO/p-Bi2O3/n-TZO composite films were measured by a Digital Source Meter.The following main experimental results were abtained:(1)The Ti-doped zinc oxide(TZO)thin films were deposited on common glass,quartz,ITO and P-Si wafer substrates,respectively.Different substrates have a significant effect on the structures and optoelectronic properties of TZO films.The average grain sizes of the TZO films grown on Si,ITO,common glass and quartz substrate were 19.32nm,22.43nm,21.93 nm and 24.11 nm,respectively.The average transmittances of the TZO thin films deposited on ITO,common glass and quartz substrate in the visible light range(400-760 nm)were 76.9%,80.5%and 80.7%,respectively.The resistivity of the TZO thin films deposited on common glass,quartz,ITO and Si wafer were 2.61 ×10-3 Ω·cm,1.94×10-3 Ω·cm,5.09×10-4 Ω·cm,2.65×10-Ω·cm,respectively.(2)The optical transmittance of the TZO films in visible light(400-760 nm)increased when the films were annealed in a hydrogen atmosphere.The average transmittance of the TZO film,which was prepared by sputtering at an oxygen flow rate of 15 seem,was increased from 84.9%(before annealing in a hydrogen atmosphere)to 91.6%(after annealing in a hydrogen atmosphere).It was found that the electrical properties of the TZO thin films changed remarkably when they were subjected to anneal in a hydrogen atmosphere,for example,the resistivity of the TZO thin film,which was prepared by sputtering at an oxygen flow rate of 15 seem,was reduced from 1.15 × 10 2 Ω·cm to 7.6 ×10-2 Ω.cm;its carrier concentration and mobility increase from-3.11 × 1016(/cm3)and 1.62(cm2/vs)to-2.72×1019(/cm3)and 3.06(cm2/vs),respectively.(3)The varistor consist of n-TZO/p-Bi2O3/n-TZO composite films were prepared by RF magnetron sputtering.XRD results show that the Bi2O3 thin film prefers to growing on the(201)crystal surface.HALL Effect experimental results show that the TZO thin film was a n-type semiconductor,its resistivity was relatively lower;Bi2O3 thin film was a p-type semiconductor,and its resistivity was relatively higher.The I-V characteristic curve of n-TZO/p-Bi2O3 was measured,which had the volt-ampere characteristic of a pn junction;the I-V characteristic curve of the n-TZO/-Bi2O3/n-TZO three-layer composite film was measured,and it had the volt-ampere characteristic of a varistor.