Evolution in morphological features, enhancement of optical transparency and band gap broadening in Manganese doped nickel oxide thin films for optoelectronics applications

Abstract

Nickel (II) oxide (NiO) and manganese (Mn) doped NiO thin films were synthesized by a low-cost thermal spray pyrolysis technique. Mn concentration was varied from 1 to 4 at% in the doped thin films. In field emission scanning electron microscopic analysis, NiO's surface morphology was transformed from agglomeration of triangular nanoparticles to clusters of random-sized nanoparticles because of Mn-doping. In the X-ray diffraction analysis, all the films were observed to have face-centered cubic structures with preferential orientation along the (111) plane. The crystallite size was calculated using the Scherrer formula, Williamson-Hall analysis, and the size-strain plot. Lattice constant of the films were determined using Neilson-Relay plots. Transmittance of NiO films was found to be 90 % for 2 at% Mn-doping. The band gap of NiO film widened significantly owing to Mn doping. Urbach energy was estimated using absorbance data. The highest room-temperature resistivity observed for 2 at% Mn-doped NiO film was 2.01×10⁵ Ω-cm. The 2 at% Mn-doped NiO film had the minimum activation energy (0.12 eV) in temperature range 348–373 K. Conclusively, 2 at% Mn-doped NiO thin film reveals the highest Haacke's figure of merit of 2.55$\times$10⁻¹² Ω⁻¹, promoted to five orders of magnitude, worthy of optoelectronic applications.