Cu2O thin films obtained from sol-gel cuo films using a simple argon/dry-air microwave plasma. (February 2018)

• Record Type: Journal Article
• Authors: Badillo-Ávila, M.A.; Castanedo-Pérez, R.; Torres-Delgado, G.; Márquez-Marín, J.; Zelaya-Ángel, O.
• Is Part Of: Materials science in semiconductor processing. Volume 74(2018)
• Page Start: 203
• Page End: 209
• Publication Date: 2018-02
• Subjects: Cu2O by plasma -- Metastable copper -- Oxidation -- Reduction -- Home-made plasma; Semiconductors -- Periodicals; Integrated circuits -- Materials -- Periodicals; Semiconducteurs -- Périodiques; Circuits intégrés -- Matériaux -- Périodiques; Electronic journals; 621.38152
• DOI: 10.1016/j.mssp.2017.10.036
• Languages: English
• ISSNs: 1369-8001

Abstract

Abstract: Cu2 O thin films were obtained from CuO films using an argon/dry-air plasma treatment (PT) for times less than 30 s. CuO films were dip-coated on glass at a withdrawal speed of 8 cm/min from a sol-gel precursor solution. The as-prepared CuO samples were air-annealed conventionally at different temperatures, from 300 to 550 °C, to fabricate the CuO film-targets. An argon/dry-air PT was later applied to film-targets for 15, 20, 25 and 30 s in a modified microwave oven made with simple components. Cu2 O mixed with a low amount of Cu was identified by X-ray diffraction in films treated for 20 s or less. Films only constituted of Cu2 O were produced for most of the samples treated for 25 and 30 s. Depending on plasma processing time and CuO film-target annealing temperature, the crystallite size of Cu2 O was largely changed (from 6 to 25 nm). Bigger Cu2 O crystallite sizes were observed for targets with annealing of 400 °C. SEM studies showed surface morphology to depend on time of PT: grains grew, formed agglomerates and granules with longer exposure. These last caused a decrease in Cu2 O film transparency below 800 nm for 30 s of treatment, but not for larger wavelengths nor for shorter times. Band gap value for CuO was 1.20 eV, and around 2.35 eV for Cu2 O films below 25 s of plasma-treatment. However, 2.16 eV was calculated for the biggest crystallite size obtained at 30 s. Thickness and resistivity measurements were also performed. A strategic experiment showed that CuO films are reduced to metastable metallic copper with PT. This metallic copper readily oxidizes to Cu2 O in open atmosphere. The biggest advantage of this plasma processing lies in the simplicity, short time of treatment and, low cost of the home-made equipment. Highlights: Conversion of CuO films to Cu2 O films using an argon/dry-air microwave plasma. Dip-coated films used as targets for conversion of CuO to Cu2 O by microwave plasma. Cu2 O films exhibit a maximum crystallite size of 25 nm, corresponding Eg of 2.16 eV. Non-reported oxidation of metastable copper phase obtained from plasma processing. Fabrication of a home-made microwave plasma system for fast redox treatments.