Excess oxygen and 1-at% Mg co-doped CuScO2[3R](0001) epitaxial films were prepared on a-plane sapphire substrates by combining two-step deposition and post-annealing techniques. The optical and electrical transport properties of the co-doped epitaxial films were compared with those of the CuScO2[3R](0001) epitaxial films. No significant increase in optical absorption was observed in the co-doped epitaxial films, and the energy gap for direct allowed transition was estimated at 3.7 eV. The carrier concentration of CuScO2[3R](0001) epitaxial films was controlled from similar to 10(16) cm(-3) to similar to 10(18) cm(-3) at room temperature by adjusting the excess oxygen and Mg co-doping. The electrical conductivity, carrier concentration, and Hall mobility of the most conductive film were 3.6x10(-2) Scm(-1), 8.5x10(17) cm(-3) and 2.6x10(-1) cm(2)V(-1)s(-1) at room temperature, respectively. The temperature dependence of the electrical transport properties of the film exhibited semiconducting characteristics, and the activation energy estimated from the temperature dependence of the carrier concentration was 0.50 eV. (C) 2009 Elsevier B.V. All rights reserved.