Effect of thickness on the structural and optical properties of sputtered ZnO and ZnO:Mn thin films

We have deposited ZnO and 3% Mn doped ZnO (ZnO:Mn) thin films of different thickness by RF magnetron sputtering and studied the structural and optical properties. The deposited films were characterized by a host of characterization techniques, such as, X-ray diffraction, scanning electron microscopy, UV-visible transmittance and photoluminescence. The X-ray diffraction measurements on all the films show a preferential growth along c axis and the intensity of (0 0 2) peak is found to increase with increase of thickness up to 80 and 90 nm for ZnO and ZnO:Mn films respectively and decreases thereafter. The FESEM images of the films illustrate a hexagonal granular surface morphology for lower thickness and a growth of pyramidal nanostructures for higher thickness. The calculated values of the optical band gaps are found to decrease upon increasing the film thickness. Markedly, the band edge emission is large for 80 and 90 nm films of ZnO and ZnO:Mn respectively. The obtained optimized sputtering growth conditions will facilitate to exploit these ZnO and ZnO:Mn thin films for various device applications.