Aluminum nitride ͑AlN͒ thin films were prepared on p-type Si ͑100͒ wafers using a sequential injection of trimethylaluminum ͑TMA͒ and ammonia under ultraviolet ͑UV͒ radiation at a temperature of 370°C. Films containing low carbon concentration ͑ Ͻ0.5 atom%͒ were deposited with a dielectric constant of ϳ7.9. UV radiation effects were investigated for two different radiation conditions ͑UV exposure during the TMA and NH 3 injection step, respectively͒. 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°C. The film deposited under UV radiation during TMA injection showed a higher dielectric constant than the films deposited without radiation. have attracted a great deal of interest as gate dielectrics of future metal-oxide-semiconductor field-effect transistor ͑MOSFET͒ devices because the continuous scaling down of the SiO 2 gate oxide reaches its physical thickness limit. 1-8 However, there are several problems to overcome in order to apply high-k films as gate dielectrics. Most vapor-phase grown high-k thin films appear to have interfacial layers ͑IL͒ having a lower-k value at the interface with the Si substrate due to the presence of excess oxidizing elements, 1-4 and the concurrent Si diffusion into the growing films. 5 This reduces the overall capacitance density, and should therefore be minimized in order to realize the high-k characteristics. High-temperature post-annealing is inevitable for current MOSFET fabrication processes. During post-annealing, the structural and electrical performance of high-k films is usually degraded. The compatibility with the polycrystalline Si ͑poly-Si͒ gate is another problem of high-k oxides. During activation annealing, dopant penetration such as boron and phosphorus from the poly-Si gate results in a shift of the flatband voltage and an increase of the leakage current. 6 Therefore, nitride films or oxynitride films have been studied to suppress the interface layer formation and diffusion. 1,3 AlN is promising as a reaction barrier dielectric in near-future MOSFET devices because the AlN film works as a good reaction barrier layer ͑RBL͒ between a high-k film and Si substrate by suppressing the formation of SiO 2 or silicate. 9-11 AlN has a higher k value compared to Si 3 N 4 , thereby minimizing the capacitance loss when it is adopted as RBL. The nitride film also suppresses boron penetration from the poly-Si gate electrode. 6 However, the growth and characterization of AlN films as RBL for high-k applications by either chemical vapor deposition or atomic layer deposition, which are believed to be the processes of choice for mass production, have rarely been reported.In th...