Aluminum nitride (AlN) thin films were prepared on p-type Si (100) wafers using a sequential injection of trimethylaluminum (TMA) and ammonia under ultraviolet (UV) radiation at a temperature of 370 degrees C. Films containing low carbon concentration (< 0.5 atom%) were deposited with a dielectric constant of similar to 7.9. UV radiation effects were investigated for two different radiation conditions (UV exposure during the TMA and NH3 injection step, respectively). A reduction in the hydrogenated nitrogen concentration was observed by X-ray photoelectron spectroscopy when UV photons were radiated during the TMA injection step. The leakage current of a 9.5-nm-thick AlN film followed the Poole-Frenkel conduction mechanism, and an optical dielectric constant of 4.2 and a trap energy depth of 0.83 eV were extracted from the Poole-Frenkel fitting of the current-density-voltage results at temperatures ranging from 20 to 170 degrees C. The film deposited under UV radiation during TMA injection showed a higher dielectric constant than the films deposited without radiation.