Optical characterization of pure and Al-doped ZnO prepared by sol-gel method

During the last years, ZnO coatings have been studied extensively due to their potential applications in piezoelectric and optoelectronic devices as conductive gas sensors, transparent conductive, electrodes, solar cell windows, varistors, UV-filters or photovoltaic cells. It is II–VI semiconductor with wide-band gap of 3.37 eV and large exciton binding energy of 60meV. Pure ZnO coatings, grown by various techniques including sol-gel method are generally found to be n-type conductive due to the presence of O2- vacancies and Zn2+ interstitials. Furthermore, it is possible to further improve the conductivity of ZnO coating by intentionally doping ZnO with aluminium ions during preparation process. Such transparent and conducting thin films, known as AZO (Aluminium Zinc Oxide) films, are very good candidate for application as transparent conducting materials in many optoelectronic devices.
In this paper the preparation process and optical characterization of pure and Al3+ doped zinc oxide coatings will be presented. The well-known sol-gel method is used for preparation of solution, coated on glass substrates by dip coating process. Prepared samples were investigated by Raman and UV-VIS spectroscopy. Transmittance as well as specular and diffuse reflectance spectroscopy methods were used for studies of optical parameters. We found that Al admixture influences on optical bandgap of ZnO.