Comparative studies on optoelectronic properties of epitaxial MgxCr2-xO3 and AlxCr2-xO3 (x = 0, 0.1, 0.2 and 0.3) thin films deposited on sapphire substrates

Abstract

In this report, we have investigated the comparative studies on structural, optical, and electrical properties of pristine Cr2O3 (PCO), magnesium (Mg) substituted Cr2O3 (MCO), and aluminium (Al) substituted Cr2O3 (ACO) thin films. The epitaxial pristine Cr2O3, MgxCr2-xO3, and AlxCr2-xO3 (x = 0.1, 0.2, and 0.3) thin films having a thickness of ∼74 ± 2 nm were deposited on (0001) sapphire substrates using pulsed laser deposition (PLD) technique. X-ray diffraction (XRD) results showed that all thin films are single crystalline with (006) orientation, and exhibited rhombohedral structure with space group R3−c. And crystal structure of Cr2O3 thin films remains unaffected with Mg and Al substitution. Also, ϕ-scan diffraction patterns confirmed the epitaxial growth of as-deposited thin films. Atomic force microscopy (AFM) illustrated the smooth morphology with extremely low roughness of thin films. Optical studies demonstrated that PCO thin film is highly transparent in the visible region with an optical band gap of 3.64 eV. However, optical band gap energy found to be decreasing with Mg content, while on the other hand, blue shift has been observed with Al substitution into Cr2O3 thin films. Room temperature electrical measurements revealed that PCO is insulating in nature. But a reduction in resistivity value has been observed from 126.19 (PCO) to 2.52 Ω-cm at x = 0.2 of Mg content (MCO) while retaining the p-type character. On the contrary, the substitution of Al into Cr2O3 thin films leads to an insulating sample. This work can lead to the development of a new class of p-type transparent conducting c-axis oriented MCO thin films as a potential candidate for optoelectronic devices-based applications.