Al doped ZnO thin films obtained by spray pyrolysis technique: Influence of different annealing time

Abstract

Zinc oxide films which belong to II-VI group and have common use in opto-electronic applications are attracting attention as wide band gap semiconductor materials. ZnO films have various application areas such as solar cells, transparent electrodes, chemical sensors and diodes. There have been many works focused on the development of the physical properties of such a popular material in technology. One of the alternative ways of this is to dope this film with different elements. In this work, ZnO:Al films have been produced for 8 at.% Al ratio with ultrasonic spray pyrolysis technique (USP) at the substrate temperature of 350 ± 5 °C. The films produced have been annealed at 400 °C for 1.5, 3 and 6 h in air. The effect of annealing time on the structural, surface, optical and electrical properties of films have been studied using X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), and UV–Visible spectrophotometry, four-point probe method. XRD pattern confirmed the growth of polycrystalline hexagonal wurtize structure of ZnO with preferred orientation along (101) direction. Surface analysis showed that the grains were agglomerated with an island-like structure over the entire surface of substrates. Mean Root Square (RMS) obtained from AFM decreased from 34 nm to 12 nm with increasing annealing time. Despite the fact that optical characteristics have revealed low transmittance values (~40–60%), all the films have been exhibited large optical gap (Eg = ~3.3 eV). Minumum electrical resistivity has been obtained for the 3h annealing time and its value was 1.39x10 1 Ωcm with films thickness of 94 nm. Finally, it has been concluded that annealing time has an important effect on the optical, structural, electrical and surface properties of the films. • Al doped ZnO thin films were successfully deposited via ultrasonic spray pyrolysis technique. • Effect of annealing time on properties of Al doped ZnO thin films was investigated. • The Al doped ZnO films can be used for optoelectronic applications in near future.