Reduction in point defects of sol–gel derived ZnO thin films with oxygen ambient

• Highly c-axis orientated ZnO thin films deposited with sol-gel spin coating process.
• Reduction in point defects with the oxygen availability during post annealing.
• Resistivity can be tailored in ZnO thin films by oxygen flow rate during annealing.
• Ferromagnetic properties influenced with the availability of oxygen during annealing.

The influence of oxygen as an annealing ambient on the native point defects of ZnO thin films has been investigated. ZnO films were derived by sol-gel spin coating method. Films were annealed at 700 °C in vacuum, air and with different oxygen flow rates from 1.5 to 5.0 Standard Cubic Centimetres per Minute (SCCM). Intensity of characteristic XRD peak (002) increased intensively with the increment in oxygen, which indicates the improvement in crystal stoichiometry. In photoluminescence (PL) measurements yellow-green emission reduced while near band edge ultraviolet emission enhanced gradually, which is a sign of reduction in native defects (VO/Zni) and improvement in optical quality of films. Resistivity of the films, measured in Van der Pauw geometry, increased significantly as the oxygen flow increased during the annealing. Ferromagnetism in the films was also observed, although at very low scale, which may be due to one or more types of native defects. It is found that saturated magnetic moment (Ms) reduced with the availability of oxygen during annealing.