Epitaxial growth of an Al0.2Ga0.8N(0001) film by metalorganic chemical vapor deposition (MOCVD) at 1050 °C on a Si(111) substrate via a ZrB2(0001) buffer layer has been accomplished free of unintentional Si doping. The in-plane lattice mismatch between Al0.2Ga0.8N(0001) and ZrB2(0001) is only 0.3% and good epitaxial relation is established with [112_0]AlGaN//[112_0]ZrB2//[1_10]Si. The cathodoluminescence (CL) spectrum of the Al0.2Ga0.8N shows a band-edge emission at 3.87 eV with full width at half maximum (FWHM) of 40 meV. Both the intensity and FWHM of the CL emission are comparable to those from a high-quality undoped Al0.2Ga0.8N film grown by MOCVD on sapphire. The close lattice match and the reflective nature of the ZrB2(0001) buffer layer are both attributes accountable for the optical quality of the Al0.2Ga0.8N grown on Si(111). © 2004 American Institute of Physics.