We investigated the optical bandgap engineering of ZnO based quaternary alloy films of wurtzite Zn1-y(MgxCd1-x)(y)O for photodiodes in visible spectral range. Quaternary alloy films were successfully synthesized by remote-plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The wurtzite alloy system has an optical bandgap energy between 2.16 eV and 3.25 eV, which was controlled by the flow ratio of metalorganic sources. The crystal structure and composition was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This revealed that carrier compensation effects by alloying with MgO in Zn1-xCdxO system decreases carrier concentration. Strong compensation effects were observed in the bandgap range of Zn1-y(MgxCd1-x)(y)O between 3.0 eV to 3.25 eV and the carrier concentration decreased to 10(15)-10(18) cm(-3). Schottky diodes of PEDOT: PSS/Zn1-y(MgxCd1-y)(y)O with optical bandgaps in the visible spectral range were fabricated to confirm the viability of photovoltaic applications. The diodes performed photovoltaic characteristics under a Xe-Hg lamp illumination through Schottky junctions. The photoresponse spectra showed a photosensitivity with cutoff energy of 2.23 eV and peak energy of 2.90 eV at 0 V biasing. (C) 2016 Elsevier B.V. All rights reserved.