Oxygen partial pressure effect on structural and electrical behavior of pulsed laser deposited Zn0.98Co0.02O thin films

Thin Zn0.98Co0.02O films were grown by pulsed laser deposition at different oxygen partial pressure (PO2) and its influence on their structural and electrical properties was investigated. Raman and photoluminescence studies revealed that zinc interstitial defects significantly decreased with increase of PO2. Complex impedance spectroscopy has been made to elucidate conduction mechanism and electronic relaxation process in Zn0.98Co0.02O films. Resistivity/impedance in the films grown at 0.1 mbar decreased as the temperature increases while the films grown at 0.01 and 0.001 mbar have shown opposite trend. The change in resistivity/impedance with temperature in the films grown at low and high PO2 is attributed to annihilation of defects and thermal activation of free carriers respectively. The relaxation time in the films grown at low PO2 increases with the temperature. It exhibits an exponential dependence on the inverse temperature with three different slopes. The corresponding energies estimated from Arrhenius type relation are very close to the energies for electronic relaxation of zinc interstitials, zinc antisities and oxygen vacancies respectively. Impedance analysis and current–voltage characteristics suggest that the resistivity of Zn0.98Co0.02O films is mainly due to bulk effect of the films.

► The native point defects were characterized by impedance spectroscopy.
► Zinc interstitial defects significantly decreased with increase of oxygen partial pressure.
► The conduction mechanism in the films grown at low pressures is governed by native defects.
► The impedance and I–V characteristics suggest that the resistivity is mainly due to bulk effect of the films.