190 nm thick aluminium nitride (AlN) with a dielectric constant of 8.8 was deposited by physical vapour deposition (PVD) on n- and p-type Si and n-type 4H-SiC samples. The Metal-Insulator-Semiconductor, MIS, structures were analysed by IV and CV techniques and 1.2 kV SiC diodes were used to evaluate leakage current before and after AlN deposition. The samples were prepared both with and without 5% HF dip after UV exposure, prior to the AlN deposition. Structural AlN analysis showed polycrystalline composition with a dominant [002] phase, a density of 3.27 g/cm(3) and stochiometry of Al0.4N0.6. Surface pre-treatment did not have much influence on the IV characteristics of Si samples (breakdown field similar to 3 MV/cm). However, the non-HF-etched sample is characterised by 2.5 times smaller CV hysteresis for the p-type sample at 100 kHz. The SiC MIS structures have a high leakage current, nevertheless a beneficial influence of UV irradiation is observed in the case of the non-HF-etched sample (soft breakdown field similar to 3 MV/cm compared to similar to 2 MV/cm for HF-etched sample). The diode reverse current was about 2 pA before UV irradiation and 4 and 600 pA after AlN deposition at room temperature and at 150 degrees C, respectively. (c) 2006 Elsevier B.V. All rights reserved.