Effect of Cr doping on optical and electrical properties of ZnO thin films deposited by spray pyrolysis technique

Abstract

The aim of this work is to study the effect of chromium doping and nozzle-substrate distance on the optical and electrical properties of zinc oxide thin films to ameliorate these properties, which makes it an important candidate in many technological applications such as: gas sensors, photocatalysts, and solar cells. In this work, we have prepared chromium doped zinc oxide thin films (ZnO: Cr) at different atomic percentages (0, 2, 4, 6 and 8 at. %) onto glass substrates by the ultrasonic spray pyrolysis technique from aqueous solution of zinc acetate dihydrate and chromium chloride hexahydrate as precursors. Where, the experimental conditions (substrate temperature (T_S), deposition time (t_D), molarity (C) and solution flow rate (φ_S) were kept constant throughout the sedimentation process with two different distances between the spray nozzle and the substrate (dN-S) for studied the effect the chromium concentration and nozzle-substrate distance on the properties of ZnO thin films deposited by spray pyrolysis. The UV-Visible spectrophotometry and four- point probe method were used to determinate the optical and electrical properties of ZnO:Cr thin films. We observed that the optical and electrical properties are influenced with the variation of chromium doping percentage and nozzle-substrate distance. The films obtained give the best physical properties (good adhesion and high optical transparency in visible range). It should be noted that with the increase of doping percentage or the decrease of nozzle substrate distance, the refractive index and the optical band gap decreases with increase in the Urbach energy and the film thickness, this is from one hand. On the other hand, the electrical conductivity also decreasing with the increasing of Cr percentage or as the substrate approaches the solution outlet. It should be noted that the sample that has the best electrical conductivity is the undoped ZnO that was prepared at a far distance from spray nozzle in addition to its high transparency in the visible range