Study of structural, optical and electrical properties of Zn1-xMnxO thin films deposited by spray pyrolysis technique

Abstract

Undoped and manganese doped zinc oxide thin films were prepared on glass substrate at 300 °C temperature using spray pyrolysis technique. Structural, optical, and electrical properties of the films have been investigated. The surface morphology of the films were taken by a scanning electron microscope (SEM). From the micrograph it is seen that more or less smooth surface and a large variety of crystal growth, such as circular disk, nano-ropes, nano-wires structure were randomly distributed around the nucleation centre. Compositional study of the samples was taken by energy dispersive X-ray (EDX). EDX result reveals that as-deposited Zn1-xMnxO films are very nearly-stoichiometric. The structure of as-deposited samples was investigated by X-ray diffraction experiment. XRD patterns show as-deposited Zn1-xMnxO thin films are crystalline in nature. Diffraction peaks revealed that the presence of hexagonal wurtzite structure without any secondary phase. Lattice constant were calculated a = 3.23 Å and c = 5.17Å. The observed grain sizes are found in the range of 9 nm to 18 nm. From the optical studies it is observed that the transmittance of the Zn1-xMnxO films are highly transparent near about 80% in VIS region. Optical band gap was calculated from the optical measurement. Band gap tuning was found with different Mn concentration. The bandgap energy is observed to vary from 3.10 eV to 3.24 eV at different doping concentrations. The optical band gap decreases when the Mn concentration increases from 0 to 4% and then increases upto 10% . For 15% Mn doped ZnO film, the band gap then shows a decrease upto 20%. The electrical measurements of the Zn1-xMnxO films have been investigated from room temperature to 440 K. Resistivity decreases with increase of temperature in all cases of the samples. It was also found that resistivity decreases with doping concentration. The activation energy was estimated from the slopes of lnσ verses 1/T graph and its value is found from 0.44 eV to 0.66 eV. The Hall effect measurement was done at room temperature by Vander pauw’s method. Measurement shows that Mn-doped ZnO thin films have negative Hall co-efficient, RH and this indicates the n-type behavior of ZnO:Mn at room temperature. The carrier concentration was found to be of the order of 1018 cm-3.