In this work, a buffer structure of a-GaAs/a-Si double amorphous layers was used for the epitaxial growth of GaAs on Si substrate by metal-organic vapor phase epitaxy. The atomic force microscopy (AFM) images exhibited that the root-mean-square (RMS) value of the surface morphology was only 1.331 nm. The full-width at half-maximum (FWHM) of the double crystal X-ray rocking curve in the (4 0 0) reflection was about 102 arcsec. The top-surface etch-pit density (EPD) revealed by molten KOH etching was lower than 10(6) cm(-2). From the material characterizations described above, the use of a-GaAs/a-Si buffer structure was found to be a very simple and effective approach for obtaining high-quality GaAs on Si for solar cell applications. (c) 2006 Elsevier B.V. All rights reserved.