ZnO layers were grown on (0 0 0 1) GaN/sapphire substrates by molecular beam epitaxy (MBE) with the use of hydrogen peroxide as an oxidant. Single-crystal ZnO films were found to grow at substrate temperatures from 400degreesC to 650degreesC, whereas textured ZnO layers were prepared at the temperatures below 400degreesC. Structural and optical properties as well as surface morphology of the single-crystal ZnO films were investigated as a function of growth parameters. The single-crystal material showed strong bound-exciton (BE) emission with a full-width at half-maximum down to 4.7meV. The increase in both substrate temperature and Zn flux was found to result in higher crystal perfection and stronger BE emission. The data obtained prove the feasibility of the peroxide-assisted MBE for the growth of high-quality ZnO layers. (C) 2004 Elsevier B.V. All rights reserved.