Fabrication and electro-optical properties of CuAl_0.8O₂/Zn_0.95Al_0.05O heterojunction films

CuAl_0.8O₂/Zn_0.95Al_0.05O heterojunction films were fabricated on quartz glass substrates. CuAl_0.8O₂ films were synthesised by the sol–gel method, and Zn_0.95Al_0.05O films were deposited onto a CuAl_0.8O₂-coated substrate through spray pyrolysis technique. The electro-optical properties of the CuAl_0.8O₂/Zn_0.95Al_0.05O heterojunction films were then investigated. The Zn_0.95Al_0.05O films deposited onto the CuAl_0.8O₂-coated substrate exhibited better crystallisation and larger grain size than those deposited onto quartz glass, and CuAl_0.8O₂ was not decomposed into other phases during the synthesis of Zn_0.95Al_0.05O films. The CuAl_0.8O₂/Zn_0.95Al_0.05O heterojunction films demonstrated rectifying I–V characteristics. Two optical transitions were observed in the CuAl_0.8O₂ films with optical gaps of 2.78 and 3.36 eV. Meanwhile, the average transmittance of the CuAl_0.8O₂/Zn_0.95Al_0.05O heterostructure films with a total thickness of 400 nm was over 75% in the 500–800 nm wavelength range. The CuAl_0.8O₂/Zn_0.95Al_0.05O heterostructure films achieved good electro-optical properties when the thickness ratio of the CuAlO₂ and Zn_0.95Al_0.05O films was in the range of 1:5–3:3 with a total thickness of 600 nm.