Effects of Al doping on the structural, electrical, and optical properties of rock-salt ZnCdO thin films grown by molecular beam epitaxy. (April 2022)

• Record Type: Journal Article
• Authors: Jang, HyoChang; Saito, Katsuhiko; Guo, Qixin; Yu, Kin Man; Tanaka, Tooru
• Is Part Of: Journal of physics and chemistry of solids. Volume 163(2022)
• Publication Date: 2022-04
• Subjects: ZnCdO -- Thin film -- MBE growth; Solids -- Periodicals; Solides -- Périodiques; Solids; Periodicals; 530.41
• DOI: 10.1016/j.jpcs.2021.110571
• Languages: English
• ISSNs: 0022-3697

Abstract

Abstract: The effects of Al doping on the structural, electrical, and optical properties of rock-salt (RS)-Zn1- x Cd x O (ZnCdO) thin films were investigated. The films were grown by molecular beam epitaxy under various Al cell temperatures. Reflection high-energy electron diffraction and compositional analyses indicated that single-crystal RS-ZnCdO ( x ≈ 0.83) layers were obtained with up to 7.8% Al incorporation. The electron concentration in the thin films increased with increasing Al cell temperature and was 1.5 × 10 21 cm −3 at ∼7.8% Al. Al-doped RS- and wurtzite (WZ)-ZnCdO thin films with various Cd concentrations were grown under the same Al cell temperatures. The ZnCdO films had an electron concentration of 10 21 cm −3 for Cd content x ranging over 0.27–1.0, regardless of the crystal structure. Al-doped RS-ZnCdO films had a 3.45-eV optical band gap at x = 0.7 because of the high electron concentration that led to a Burstein-Moss shift. This was the highest-energy optical band gap reported for RS-ZnCdO. Therefore, Al doping was very effective in expanding the optical band gap, as well as increasing the RS-ZnCdO electrical conductivity, making the films suitable as transparent conductors for full-spectrum solar cells. Highlights: Al-doped Zn1- x Cd x O thin films were grown on MgO substrate by molecular beam epitaxy. Effect of Al doping on the structural, electrical, and optical properties of RS-ZnCdO thin films was investigated systematically. A large optical band gap of 3.45 eV was achieved in RS-ZnCdO thin film with x ≈ 0.7 with a low resistivity of ∼1 × 10 −4 Ω-cm.