Growth and Optical Properties of Nanocrystalline Titania Films for Optoelectronics and Photovoltaics

Abstract

Nanoscaled titania is a modern material targeting, among others, to optoelectronic and photovoltaic applications. Titanium-based thin films are grown by radio frequency magnetron sputtering on glass, polyimide and silicon substrates inside a high vacuum chamber (base pressure 10–7 mbar). X-ray diffraction measurements show that if only Argon is used as the sputtering gas, then pure titanium metal films are formed. However, by controllable adding and increasing of the quantity of air through a fine (leak) valve in the vacuum chamber during the sputtering process, we manage to grow Ti(N)O and TiO2 films by reactive sputtering. Some of these films are found to be in an amorphous state or in a mixture of amorphous and nanocrystalline state. Post-annealing of the films under air at high temperatures (between 450–750 °C) results in the formation of nanocrystalline titania films; the phases of anatase and rutile are detected. Ultraviolet-visible absorption spectroscopy is used to measure the optical band gap of titania semiconductor. Finally, well-grown titania films show strong photoluminescence at near infrared as a result of a phonon-replica effect. Our work contributes to the better understanding of growth and optics of nanocrystalline titania films for largescale technological applications.