Structure and characterization of the sputtered ZnO, Al-doped ZnO, Ti-doped ZnO and Ti, Al-co-doped ZnO thin films

Transparent conductive thin films such as ZnO, Al-doped ZnO (AZO), Ti-doped ZnO (TZO), and Ti, Al-codoped ZnO (TAZO) were prepared on the STN glass substrate by radio frequency sputtering. The thickness of as-prepared films was approximately 700 nm and the concentration of dopants was controlled by adjusting the electrical power of sputtering. Results from X-ray diffraction patterns clearly showed that all samples were in wurtzite structure with (002) preferential orientation. They all possessed smooth surfaces with the mixture of column and core texture as indicated by the field emission scanning electronic microscope analyses. The average transmittance ranging from 400 to 800 nm wavelength, determined by means of UV-visible spectra, TAZO (93%) was higher than AZO (90%), TZO (91%), and ZnO (86%). Electrical resistivity determined by four-point probe followed the order of TAZO (0.91 mΩ cm) < AZO (3.61 mΩ cm)∼TZO (3.84 mΩ cm)<<ZnO (289 mΩ cm). Observed lower resistivity of TAZO was likely attributed to the high density of crystal defects i.e., stacking faults as indicated by the high resolution transmission electron microscopy analyses.