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High quality GaN layers were grown on Si(111) 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 pre-seeding Al to Si surface is a critical condition for AlN growth on Si. Two-dimensional growth of AlN was achieved under optimized conditions. Raman scattering shows a narrow GaN E₂ peak and broad AlN E₂, E₁ peaks. At room temperature, the investigated films are unintentionally doped n-type. The carrier concentration is about 1.3×10¹⁷cm⁻³ and the Hall mobility is about 210cm²/Vs. Metal–semiconductor–metal photoconductive detectors were fabricated on the GaN/Si …