Structural, morphological, and electrical characterization of heteroepitaxial ZnO thin films deposited on Si (100) by pulsed laser deposition: Effect of annealing ( 800 ° C ) in air

Pulsed laser deposition technique was used for growing thin films of ZnO on Si (100) substrate held at different temperatures ( T s ) . All the as-deposited films have shown a preferential c -axis orientation associated with varying grain size as a function of T s ranging from 100 to 600 ° C . Current-voltage ( I - V ) characteristics of these films show Ohmic behavior over the entire T s range studied. These films were subjected to annealing at 800 ° C in air ambient for 4 h . The grain size was observed to increase after the annealing process for all the films deposited at different T s . Interestingly, these annealed films show nonlinear variation of current with applied voltage, very similar to the one observed in doped ZnO varistors. The nonlinear parameters such as the asymmetric behavior of change in current on the polarity reversal of voltage, the plateau region, and the break down voltage are observed to depend on T s . This nonlinear behavior can perhaps be explained on the basis of electronic conduction model proposed for the bulk, doped ZnO varistors. The role of insulating intergranular layers between the disoriented microcrystallites is expected to be similar to that played by insulating intergranular layers in the doped ZnO varistors.