High quality GaN layers were grown on Si(1 1 1) substrates using high-temperature-grown AlN as buffer layer by rapid thermal process low-pressure metalorganic chemical vapor deposition. The growth and characteristics of AlN buffer layer and the GaN layers were investigated by using scanning electron microscope, X-ray diffraction, photoluminescence (PL), Raman scattering, and Hall measurements at room temperature. It was found that preseeding Al to Si surface is a critical condition for AlN growth on Si. Two-dimensional growth of AIN was achieved under optimized conditions. Raman scattering shows a narrow GaN E-2 peak and broad AIN E-2,E- E-1 peaks. At room temperature, the investigated films are unintentionally doped n-type. The carrier concentration is about 1.3 x 10(17)cm(-3) and the Hall mobility is about 210 cm(2)/V a. Metal-semiconductor-metal photoconductive detectors were fabricated on the CaN/Si(1 1 1) films. These detectors show a sharp cut-off wavelength at 363 nm. A maximum responsivity of 6.9 A/W was achieved at 357 nm under a 5.0 V bias. These results indicate that high quality GaN films on Si(1 1 1) can be obtained using the AIN buffer layer, and the potential application of GaN films based on Si substrates.