Structural and optoelectronic properties of epitaxial Ni-substituted Cr2O3 thin films for p-type TCO applications

Abstract

Transparent and conducting epitaxial thin films of pristine chromium oxide (Cr2O3) and nickel (Ni) substituted Cr2O3 were deposited on the sapphire substrates using pulsed laser deposition (PLD) technique. Co-precipitation method was used to prepare targets of Cr2O3 nanomaterials with varying Ni content (i.e. x = 0, 0.03, 0.05 and 0.1). In-plane diffraction (i.e. ϕ-scan) measurements confirmed that all thin films were epitaxially grown on sapphire substrates. X-ray diffraction (XRD) patterns illustrated that all thin films orienting along (006) plane only and crystallize in the rhombohedral structure of Cr2O3, and structure remains unchanged with Ni-substitution. Consequently, Cr cations were replaced by Ni counter-cations in Cr2O3 structure, which lead to the delocalization of holes and improve mobility. Moreover, an increase in Ni-content also leads to upsurge in the carrier concentration. Hence, both factors contributed to the improvement in Ni-substituted Cr2O3 thin films' conductivity and retained the p-type character as well. UV–Vis spectra demonstrated that pristine Cr2O3 thin film acquired an optical band gap energy of 3.64 eV, decreasing to 3.48 eV with Ni-substitution. Furthermore, optical transmittance spectra illustrated the average transparency of 77–81% for as-deposited thin films in the visible region. Therefore, this material can render a wide variety of applications in the field of optoelectronics.