Study of Doping In Zinc Oxide in Thin Films Grown by Spray Pyrolysis Technique

Abstract

The main objective of present work is to study the effect of doping on the optical and electrical properties of spray deposited zinc oxide (ZnO) thin films. The optimum conditions required to obtain quality of ZnO thin films is determined initially by varying the deposition parameters such as substrate temperature, spray rate and precursor molarity. Later film thickness and annealing temperature is fixed by considering the transmittance and conductivity of the films. ZnO thin films obtained under optimum conditions were found to be crystalline in nature with the combination of visible region transmittance of 78 % and room temperature conductivity of 0.156 S/cm. XPS analysis has been shown that the as-deposited film is oxygen deficient and annealed films are oxygen rich. Further, ZnO films were doped with group V and group III dopants to improve their conductivity. Investigation has been carried out to know the optimum percentage of dopant to be added to retain the transmittance of the films by varying dopant concentration from 0 to 5%. The effect of group V elements as dopants in the form of pure metals has been studied by doping the film with antimony and bismuth separately. A slight improvement in the conductivity of the films was observed with antimony and bismuth doping without changing optical transmittance in the visible region. ZnO film doped with Sb (3% and above) shows ptype conductivity. Role of group III elements as n-type dopants in the form of pure metals is studied by doping the film with aluminium, indium and gallium separately. It has been observed that all the doped films possess transparent and highly conducting properties. The 3% doping concentration and annealing at 450°C for 4hr is the optimum condition to achieve transparent and high conductive ZnO films doped with Al, In and Ga. From the structural, optical and electrical properties of these doped ZnO films it is found that all films have smooth surface with visible region transparency of 80% and significantly high electrical conductivity of the order of 102 S/cm at room temperatures, which are well suited for the transparent electrodes application.