Improvement of Ni/Si/4H-SiC ohmic contacts by VLS grown sub-contact layer

This work presents results of using VLS epitaxial Si-Ge-type structure as a sub-contact layer designated for Ni/Si ohmic contacts. The epitaxial growth was performed at 1240 and 1414 °C in various types of atmosphere in a processing chamber. The prepared layers had mostly smooth surface. XPS analysis showed that germanium escape from the structure occurred during the process of the epitaxial growth. An important result is that silicon and carbon bind in the form of SiC already at the surface of the structure, which proves silicon carbide formation during the epitaxial growth. Ni/Si-type contact metallization was deposited onto all epitaxial structures. After annealing we received ohmic contacts with contact resistivity equal or lower compared to the standard contact structure Ni/Si/SiC prepared on the same substrate. The best value of contact resistivity was 4 × 10⁻⁵ Ω cm². The doping concentration in the VLS epitaxial layers is reaching the value (6-7) × 10¹⁸ cm⁻³.