Characterization of ZnO–SnO 2 thin film composites prepared by pulsed laser deposition

Abstract

Thin films of ZnO–SnO 2 composites have been deposited on Si(1 0 0) and glass substrates at 500 °C by pulsed laser ablation using different composite targets with ZnO amount varying between 1 and 50 wt%. The effect of increasing ZnO-content on electrical, optical and structural properties of the ZnO–SnO 2 films has been investigated. X-ray diffraction analysis indicates that the as-deposited ZnO–SnO 2 films can be both crystalline (for ZnO <1 wt%) and amorphous (for ZnO ≥ 10 wt%) in nature. Atomic force microscopy studies of the as-prepared composite films indicate that the surfaces are fairly smooth with rms roughness varying between 3.07 and 2.04 nm. The average optical transmittance of the as-deposited films in the visible range (400–800 nm), decreases from 90% to 72% for increasing ZnO concentration in the film. The band gap energy ( E g) seems to depend on the amount of ZnO addition, with the maximum obtained at 1 wt% ZnO. Assuming that the interband electron transition is direct, the optical band gap has been found to be in the range 3.24–3.69 eV for as-deposited composite films. The lowest electrical resistivity of 7.6 × 10 −3 Ω cm has been achieved with the 25 wt% ZnO composite film deposited at 500 °C. The photoluminescence spectrum of the composite films shows a decrease in PL intensity with increasing ZnO concentration.