Bandgap tuning in ZnO thin films and enhanced n-type properties through Mn doping synthesized by a simple spray pyrolysis

Abstract

Undoped and manganese (Mn)-doped zinc oxide (ZnO) thin films have been deposited onto glass substrates at 300[Formula: see text]C using a low cost spray pyrolysis technique. Structural, optical and electrical properties of the as-deposited films have been investigated. Scanning electron microscopy images show the existence of clusters with well-defined nucleation centers consisting of highly dense ganglia-like fibers over a large area around the nucleation center. Chemical compositions of the ZnO and Mn-doped ZnO thin films are studied by using energy dispersive X-ray (EDX) analysis. X-ray diffraction spectra depict that the films have polycrystalline wurtzite structure. The average crystallite sizes are calculated in the range of 8–16 nm by Williamson–Hall method and found in good agreement with Scherer method. Optical transmittance of the films is about 80% in the visible region. Bandgap energy is tuned to 2.83 eV from 3.10 eV with increasing Mn doping. Electrical resistivity at room-temperature decreases significantly with increasing Mn doping as well as increasing temperature from 300–440 K. The activation energies in the temperature ranges 300–350 K and 350–440 K are found to be in the range of 0.25–0.16 eV and 0.35–0.59 eV, respectively. Hall Effect measurements show that the thin films have negative Hall co-efficient indicating [Formula: see text]-type conductivity at room-temperature. Carrier concentration is found to be of the order of 10[Formula: see text] cm[Formula: see text].