Effect of substrate temperature and oxygen partial pressure on phase transformation in zirconia thin films prepared by pulsed laser deposition

In the present work zirconia thin films were deposited on Si (100) and quartz substrates using pulsed laser deposition method, with the aim to understand the effect of substrate temperature and oxygen partial pressure on the formation of tetragonal and monoclinic phases of zirconia thin films. The substrate temperature and oxygen partial pressure was varied from 300 to 973 K and 2 x 10-2 to 2x10-5 mbar respectively. It is observed that the volume fraction of the monoclinic phase decreases with increasing substrate temperature at all oxygen partial pressure. The volume fraction of monoclinic phase varies from 19 to 90% at different substrate temperature and oxygen partial pressure. Crystallite size of monoclinic phase shows an increase with increase in the substrate temperature up to 673 K and then decreases. At temperatures exceeding 673 K, the tetragonal phase is formed and is also influenced by residual stress in the films. The films processed at low substrate temperatures (< 773)show a single band gap and the films deposited at 873 K show two band gaps. The optical band gap of films containing predominantly monoclinic phase shows an increase from 5.62 eV to 5.76 eV as the substrate temperature increases from 473 to 873 K. Band gap energy of 5.20 eV corresponding to the tetragonal phase is observed for the films deposited at a temperature of 873K