In doped ZnO thin films

Highlights: → Generally ZnO thin films are doped with Al or In in order to produce n-type semiconductor the doping level does not exceed 4% ratio. → In the present study, we have investigated the effect of a larger In doping ratio range (up to 8%) on the structural, optical and electrical properties of indium doped zinc oxide thin films deposited by ultrasonic spray with a non aqueous starting solution. → The films crystallinity and electrical conductivity are improved with increasing the doping level. → The optical gap are reduced with increasing the doping level. - Abstract: ZnO thin films were deposited by ultrasonic spray technique, zinc acetate was used as starting solution with a molarity of 0.1 M. A set of indium (In) doped ZnO (between 2 and 8 wt%) thin films were grown on glass substrate at 350 deg. C. The present work is focused on the influence of the doping level on the structural, optical and electrical films properties. Optical film characterization was carried by using UV-visible transmission spectroscopy, the optical gap was deduced from absorption. From X ray diffraction (XRD) analysis, we have deduced that ZnO films are formed with nanocrystalline structure with preferential (0 0 2) orientation. The grain size is increased with In doping from 28 to 37 nm. Electrical characterization was achieved using two-probes coplanar structure, the measured conductivity varies from 2.3 to 5.9 Ω cm-1 when increasing the doping level. However the optical gap is reduced from 3.4 to 3.1 eV.