Ternary and quaternary wurtzite-type oxide semiconductors: β-CuGaO2 and its related materials

β-NaFeO₂ structure is an orthorhombic and ternary wurtzite-derived structure. Recently, we found a new oxide semiconductor possessing this structure, β-CuGaO₂, of which energy band gap is 1.47 eV, and it exhibits p-type electrical conduction. In this presentation, we introduce optical and electrical properties of β-CuGaO₂ and band gap engineering of this material by alloying with β-CuAlO₂ and β-LiGaO₂. Wurtzite-type β-NaFeO₂-type phases were obtained in 0<;under><;<;/under>x<;under><;<;/under>0.7 and the band gap was widened up to 2.1 eV in Cu(Ga_1-xAl_x)O₂ system. In (Cu_1-xLi_x)GaO₂ system, wurtzite-type phases were obtained in 0<;under><;<;/under>x<;under><;<;/under>1, and the band gap was adjustable between 1.47 and 5.6 eV. These new quaternary oxide semiconductors possessing wurtzite-derived structure expanded the energy region that the oxide semiconductors cover into visible and near-infrared region.