Role of W in W/Ni Bilayer Ohmic Contact to n-Type 4H-SiC From the Perspective of Device Applications

Ohmic contacts to n-type 4H-SiC using Ni layer and W/Ni bilayer were investigated and compared. The phase composition, electronic states, and carbon structural evolution of the contact layer were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The surface roughness and cross-sectional morphology were characterized by atomic force microscopy and high-resolution transmission electron microscopy. The Keithley 4200-SCS semiconductor parameter analyzer was used to measure the current-voltage curves of the contacts. The specific contact resistance rho(c) was calculated based on the circular transmission line model. rho(c) is 3.2 x 10(-5) Omega . cm(2) for W/Ni/SiC and 4.2 x 10(-4) Omega . cm(2) for Ni/SiC. Ni2Si with minor W substitution and tungsten carbide with minor Ni substitution were identified as the dominant phases for W/Ni/SiC after annealed. The contact surface morphology is improved, and the content of free carbon and the quantity of voids at the interface are reduced when W is introduced into Ni/SiC. The wire bonding is easy to carry out and the thermal stability of ohmic contact is greatly enhanced. From the perspective of device applications, W/Ni bilayer ohmic contact to n-type 4H-SiC is very competitive.