Metalorganic chemical vapour deposition of p-type delafossite CuCrO2 semiconductor thin films: characterization and application to transparent p-n junction

Transparent conducting oxides such as ITO, FTO or AZO, are currently used in a number of commercial applications, such as transparent electrodes for flat panel displays, light-emitting diodes and solar cells. These applications rely essentially on n-type conductive materials. The developments towards electronic devices based on transparent p-n junctions have triggered an intense research for the synthesis of p-type transparent conductors with sufficiently high quality. Copper-based delafossite materials are thought to hold one of the highest potential and among them CuCrO2 has exhibited strong potential in terms of trade off electrical conductivity and optical transparency. In this work, we report for the first time on CuCrO2 thin-films, grown using a pulsed injection MOCVD. We particularly highlight the influence of the growth temperature, the volume precursor ration and the oxygen partial pressure on chemical, morphological, structural, electrical and optical properties of the films. Delafossite CuCrO2 thin films are synthesized as low as 310°C on glass substrate, which is the lowest growth temperature reported to our knowledge. The films exhibit a carbon contamination below 1%, an excess of chromium and a p-type conductivity. Electrical conductivity at room temperature is measured as high as 17S.cm-1 with a moderate visible transparency at 50%. We report the highest trade off electrical conductivity and visible transparency of CuCrO2 thin films. We investigate the transport conduction with simultaneous electrical and thermoelectrical measurements and band conduction and small polaron models are controversially discussed. A functional transparent p-n junction CuCrO2/ZnO, based on only two-layers, is synthesized with a visible transparency of 45-50%. The junction shows a typical current-voltage characteristic of a diode, with high series resistance features. The device is efficiently acting as an UV detector.