Study On Transparent And Conductive ZAO Thin Films By Sol-Gel Technique

Transparent conductive oxide thin films exhibit outstanding optical and electrical properties, such as low resistivity and high transmittance in the visible rang etc, because of high carrier concentration and wide optical band gap. At present transparent conductive oxide thin films are widely applied in solar cell, transparent electrodes of flat panel display, defend screen of electromagnetism and infrared reflection coating of architectural glass. Al3+-doped ZnO(ZAO) thin films are emerging as an alternative potential candidate for ITO(Sn-doped In2O3) films recently not only because of their comparable optical and electrical properties to ITO films, but also because of their excellence of the abundance of the materials in nature, simple production procedure, low cost absence of toxicity, high thermal and chemical stability。There are many techniques used to deposition ZnO thin films, such as Magnetron sputtering, chemical vapor deposition (CVD), pulsed laser deposition (PLD), spray pyrolysis, molecular beam epitaxy (MBE),sol-gel technique and so on. However, from a practical standpoint, these processes have the disadvantage of the need for vacuum apparatus. Yet, the sol-gel technique has voided the disadvantage. The sol-gel method is easy to doped of atomic class and the dopant can be accurately controlled. Moreover it has the potential for preparation of films of large area and complicated forms on various substrates.In this paper, the A13+-doped ZnO thin films were deposited on common substrates by sol-gel technique from 2-methoxyethanol solutions prepared by Zinc acetate as precursor, DEA as stabilizer, DCCA as defending cracker。Homogenous, transparent, polycrystalline ZAO thin film was formed finally by spinning coating, film-plate on substrate conducted by drying, pre-heat-treatment and annealing.Optimum study of technological parameters for the preparation of ZAO thin films by sol-gel method was carried through L9(34) orthogonal design. The optimum technological parameters for the best optical and electrical properties of ZAO thin films were that the sol concentration was 0.6mol/L, the dopant concentration was 4at%, and pre-heat- treatment was temperature was 300℃,the annealing temperature was 600℃. It is revealed that the annealing temperature is significant to properties of ZAO thin films.X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM) were used to characterize the crystallization behavior, orientation and surface morphology of the ZAO thin films. The result proved that the thin films with strongly preferred orientation of c-axis perpendicular to the substrate surface; which surface was homogenous, dense and crackfree was the crystalline phase of hexagonal wurtzite. The surface roughness was small. The crystals were growing with columniations, which crystal dimension approximate to 30-90nm. The annealing temperature, sol concentration and the dopant concentration, having strong influence on the microstructure and composition of ZAO transparent conductive film, has been found.Study for optical spectra of the films with ultra-violet spectrometer and infrared reflection spectrometry, the result indicates that the average value of the optical transmittance of the films in the visible region exceeds 80%. With the annealing temperature increasing, the average optical transmittance increases little and the absorption edge of the transmission curve of the films moves toward short wavelength. The optical transmittance was higher with the increase of ZAO thin films thickness. In the region, the infrared reflectance has raised with the increase of ZAO thin films thickness. Conducting mechanism of the ZAO thin films was discussed. Investigation for electrical properties of the films indicates that dopant concentration, annealing temperature and annealing time have strong influence on the sheet resistance of the films. With increasing the annealing temperature and annealing time, the sheet resistance perform decreasing previously and increasing later. The lowest sheet resistance of ZAO thin films was about 515?/口.