Structural, optical, and electrical properties of manganese-doped nickel oxide thin films synthesized by spray pyrolysis technique

Abstract

Nickel oxide (NiO) and manganese (Mn)-doped NiO thin films were synthesized on to glass substrate at the substrate temperature of 450 ℃ using the spray pyrolysis technique. As deposited undoped NiO films showedtriangle-shaped porous structure, which was explored by field emission scanning electron microscopy. Doping changed the morphology of Mn-doped NiO thin films. Surface morphology turnedgradually into triangle-shaped clusters up to 2 at% Mn-doped NiO films. Surface morphology was changed to random-shaped particles as the Mn concentration was raised to 4 at%. The crystalline structure of the deposited films was detected using X-ray diffraction analysis. All the samples were observed to have face-centered cubic structure, where the crystal growth had a preferential orientation along the (111) plane.The crystallite size dropped from 39 to 22 nm as the amount of Mn-doping increasedfrom 0 to 4 at%. UV-vis spectroscopy was used in the 300-1100 nm wavelength range to investigate the transmittance of the samples,while undoped NiOexhibited the lowest transmittance within the visible spectrum. Transmittance of NiO thin films increased up to 2 at% Mn-doping. The maximum transmittance is recorded about 90% for 2 at% Mn-doped NiO film. Transmittance decreased with the further riseinMn-doping concentration. The estimated range of band gap values was 3.17–4.03 eV. Room-temperature and temperature-dependent resistivity were measured by the two-point probe method. The highest room-temperature resistivity (2.01×105 Ω cm) was observed for 2 at% Mn-doped NiO film. Activation energy was estimated for all the samples in the range of 300 to 373 K.2 at% Mn-doped NiO film showed two conduction regions with the minimum activation energy (0.12 eV) at higher temperature region (348-373 K).