P-type spinel ZnCo2O4 thin films prepared using sol-gel process

Abstract

In the present study, the sol-gel process was used to deposited thin films of the p-type spinel ZnCo2O4 onto glass substrate. Spinel ZnCo2O4 thin films were obtained by annealing the sol-gel derived specimens at 300–400 °C in oxygen for 2 h, and were confirmed by four Raman active modes at approximately 470 cm−1, 514 cm−1, 600 cm−1, and 670 cm−1. The nanostructured and flat surface morphologies of the obtained ZnCo2O4 thin films were observed by field-emission scanning electron microscopy and atomic force microscopy. Uniform film thickness and good adhesion with the substrate were also observed. The binding energy of Zn-2p at 1020.7 ± 0.2 eV (2p3/2) and 1043.8 ± 0.2 eV (2p1/2) revealed the presence of Zn2+. Additionally, the presence of both divalent and trivalent Co cation was indicated by deconvolution of the binding energies at 779.5 ± 0.2 eV (2p3/2) and 795.1 ± 0.2 eV (2p1/2) for Co3+, and at 781.5 ± 0.2 eV (2p3/2) and 796.6 ± 0.2 eV (2p1/2) for Co2+. Two optical bandgaps of the obtained spinel ZnCo2O4 thin films were deduced at 2.38–2.39 eV and 3.95–3.99 eV. The p-type characteristic was confirmed using the hot-probe test. Furthermore, the resistivities of the spinel ZnCo2O4 thin films were 1.58 × 10 2 –2.45 × 103 Ω-cm with corresponding carrier concentrations of 5.57 × 1012-4.29 × 1014 cm−3. Hence, the sol-gel process provides a feasible method for the preparation of p-type spinel ZnCo2O4 thin films.