CVD-based tungsten carbide Schottky contacts to 6H-SiC for very high-temperature operation

In this study, tungsten carbide, with its hardness, chemical inertness, thermal stability and low resistivity (25 mu Omega cm)(1) is shown as a reliable contact material to n- and p-type 6H-SiC for very high temperature applications. WC films with thicknesses of 100-150 nm were deposited by chemical vapor deposition (CVD) from a WF6/C3H8/H-2 mixture at 1173 K. A method to pattern CVD-tungsten carbide is suggested. TEM analysis of as deposited samples displayed a clear and unreacted interface. The electrical investigations of the p-type 6H-SiC Schottky contacts revealed a high rectification ratio and a low reverse current density (6.1 x 10(-5) A cm(-2), -10 V) up to 713 K. On n-type, a low barrier (Phi(Bn) = 0.79 eV) at room temperature was observed. The low Phi(Bn) value suggests WC to be promising as an ohmic contact material on highly doped n-type epi-layers. We will show a temperature dependence for the barrier height of tungsten carbide contacts that can be related to the simultaneous change in the energy bandgap, which should be considered when designing SiC devices intended for high temperature operation.