We report on the growth and characterization of In0.28Ga0.72N/GaN multiple-quantum wells (MQW) on GaN/Si(111) by metalorganic vapor phase epitaxy. First, the GaN epitaxy was grown on Si(1 1 1) using AlGaN/AlN composite buffer layer. Even though the optimized AlGaN/AlN CBL improved the quality of GaN on Si and reduced melt-back etching during growth, the surface image of GaN epitaxy observed by SEM showed some cracks, which were resulted from the large difference in thermal expansion coefficient between GaN and Si. The full-width at half-maximum (FWHM) of the double-crystal X-ray rocking curve for GaN(0002) was 886 arcsec. Cross-sectional transmission electron microscopy (XTEM) shows that the predominant crystallographic defects in the GaN are threading dislocations. Next, In0.28Ga0.72N/GaN MQW structures were grown on this high-quality GaN/Si(1 1 1). From the XTEM image, it was found that the typical V-defects of uncapped In0.28Ga0.72N/GaN MQW structure originate from threading dislocations. Indium-rich InGaN precipitates were readily detected in the ln(0.28)Ga(0.72)N/GaN MQW by high-resolution transmission electron microscopy image. The photoluminescence (PL) spectrum at room temperature from the In0.8Ga0.72N/GaN MQW on Si(1 1 1) was separated into two peaks of strong intensity, whose FWHMs are 22 nm for the peak at 500 and 24 nm for the peak at 525 nm. The PL peak at longer wavelength side is believed to come from the In-rich phases by the interdiffusion of indium in the InGaN well layers. (C) 2002 Elsevier Science B.V. All rights reserved.