ZnSeO alloys with O composition to 11.5% were grown on sapphire substrates by plasma-assisted molecular beam epitaxy. The absorption coefficients, alpha((h) over bar omega)), determined from the transmittance measurements are higher than 1 x 10(4) cm(-1) for these ZnSeO thin films and manifest themselves very suitable for photovoltaic devices. The absorption coefficient following the square law of photon energy indicated that the ZnSeO has a direct band gap. Based on the quadratic band gap function, a bowing parameter of 6.9 eV was obtained. Cl doping in ZnSeO films grown on GaAs substrates were first demonstrated with carrier electron concentration varying from 1.2 x 10(17) cm(-3) to 5.4 x 10(18) cm(-3) with 2.2% oxygen content. The activation energy of 123 meV for Cl dopant in ZnSeO was also deduced from temperature dependent Hall measurements. (c) 2013 Elsevier B.V. All rights reserved.