Effect of post thermal annealing on the structural and optical properties of ZnO thin films prepared from polymer precursor

ZnO thin films were synthesised by a new method which uses polyvinyl alcohol (PVA) as polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and annealing time. All the films possess tensile strain which relaxes as the annealing temperature and the annealing time increases. The photoluminescence (PL) spectra contain only ultraviolet (UV) peaks at low temperature, but as the annealing temperature and time increase we observe peaks at blue and green regions with variation of the intensities of these peaks with annealing temperature and annealing time.