Papers by Author: Markku Leskelä

Abstract: Aluminum-based high-k dielectric materials have been studied for their potential use as passivation for SiC devices. Metal-insulator-semiconductor structures were prepared and their dielectric properties were analyzed using capacitance-voltage and current-voltage measurements. Atomic layer deposition was used for the deposition of dielectric layers consisting of AlN with or without a buffer layer of SiO2, and also a stack of alternating AlN and Al2O3 layers. It has been observed that AlN has a polycrystalline structure which provides leakage paths for the current through the grain boundaries. However, adding alternate amorphous layers of Al2O3 prevent this leakage and give better overall dielectric properties. It is also concluded that the breakdown of the dielectric starts from the degradation of the thin interfacial SiO2 layer.

Abstract: Aluminium oxide and titanium oxide films were deposited using the Atomic Layer Deposition method on n-type 4H SiC and p-type Si {001} substrates, with doping 6×1015cm-3 and 2×1016cm-3, respectively, and on 1.2 kV PiN 4H SiC diodes for passivation studies. The Al2O3 and SiC interface was characterised for the existence of an effective negative charge with a density of 1×1012-2×1012 cm-2. The dielectric constant of Al2O3 as determined from capacitance-voltage data was about 8.3. The maximum electric field supported by the Al2O3 film was up to 7.5 MV/cm and 8.4 MV/cm on SiC and Si, respectively.

Abstract: The successive ionic layer adsorption and reaction (SILAR) technique was used to grow double layer structures of CdS-PbS. The growth of thin films by the SILAR technique from diluted aqueous solutions was achieved, ionic layer by ionic layer, at room temperature and normal pressure. The thin films on silicon were characterized by XRD, AFM, XPS. It was established that a double layer could be grown on crystalline silicon and that the morphology and crystallinity of the films could be controlled by changing the lead precursor.