Si doped and undoped nanocrystalline aluminum nitride thin films were deposited on various substrates by direct current sputtering technique. X-ray diffraction analysis confirmed the formation of phase pure hexagonal aluminum nitride with a single peak corresponding to (1 0 0) reflection of AlN with lattice constants, a = 0.3114 nm and c = 0.4986 nm. Energy dispersive analysis of X-rays confirmed the presence of Si in the doped AlN films. Atomic force microscopic studies showed that the average particle size of the film prepared at substrate temperature 200 degrees C was 9.5 nm, but when 5 at.% Si was incorporated the average particle size increased to similar to 21 nm. Field emission study indicated that, with increasing Si doping concentration, the emission characteristics have been improved. The turn-on field (E-to) was 15.0 (+/- 0.7) V/mu m, 8.0 (+/- 0.4) V/mu m and 7.8 (+/- 0.5) V/mu m for undoped, 3 at.% and 5 at.% Si doped AlN films respectively and the maximum current density of 0.27 mu A/cm(2) has been observed for 5 at.% Si doped nanocrystalline AlN film. It was also found that the dielectric properties were highly dependent on Si doping. (C) 2008 Elsevier B.V. All rights reserved.