The role of annealing temperature on the optical and electrical transport properties of NiOx films

• Published in: Optical materials 2024-05, Vol.151, p.115398, Article 115398
• Main Authors: Beisembekov, M.K., Omarbekova, G.I., Tazhibayev, S.K., Aimukhanov, A.K., Baltabekov, A.S., Ziyat, A.Z., Zeinidenov, A.K.
• Format: Article
• Language: English
• Subjects: Absorption coefficient; Annealing temperature; Dispersion index; Electrical transport characteristics; Nickel oxide; Optical band gap; Sol-gel technology
• ISSN: 0925-3467
• DOI: 10.1016/j.optmat.2024.115398

In this paper, we studied the effects of the annealing temperature of nickel oxide (NiOx) thin films on the structural, optical, and electrical transport properties. Thin NiOx was synthesized by the sol-gel method, followed by annealing at different temperatures varying from 200 to 450 °C. From the obtained AFM image data, an increase in the surface Ra value is observed with rising film annealing temperature. The decrease in film thickness with increasing annealing temperature is associated with significant densification of NiOx. During thermal annealing, a change in the redistribution of Ni/O elements is seen in the films. The increase in the intensity of the (1P)LO scattering peak in NiOx with rising annealing temperature is associated with a growth in the density of defects due to Ni vacancies. When the annealing temperature reaches 250 °C, an increase in Eg = 3.49 eV is detected; a further rise of the annealing temperature leads to a decrease in Eg = 2.92 eV. The increase in the index n of films with rising annealing temperature is associated with the formation of a denser and more ordered NiOx film. A rise in the annealing temperature of NiOx films leads to an increase in the value of the total resistance of the films, a decrease in the resistance of hole recombination at the NiOx/electrode interface, and the value of the conditional mobility of holes. •An increase in the RMS value of films with increasing annealing temperature is associated with an increase in grain size on the surface.•At an annealing temperature of 250 °C, an increase in Eg is observed; a further increase in the annealing temperature leads to a decrease in Eg.•An increase in the extinction coefficient and dispersion index is associated with the densification of the NiOx film with increasing annealing temperature.•An increase in film density with increasing annealing temperature leads to an increase in the NiOx resistance and a decrease in the value of the conditional hole mobility.