Thin Solid Films, Vol.669, 306-314, 2019
High-temperature reliability of Ni/Nb ohmic contacts on 4H-SiC for harsh environment applications
High-temperature stability of the Nb/Ni and Ni/Nb Ohmic contacts to n-type 4H-SiC was investigated and compared after being aged at 400 degrees C for 100 h in N-2 ambient. The electrical properties and surface morphologies of the contacts were characterized by using the combination of the current-voltage measurements and microscopic imaging. While the Nb/Ni/4H-SiC ohmic contact failed after 10-h aging, the Ni/Nb/4H-SiC contact still exhibited good ohmic characteristics with a slight increase of specific contact resistance after being aged for 100 h. According to the microscopic imaging results, though the Ni/Nb/4H-SiC contact has a rougher surface morphology compared to that of the Nb/Ni/4H-SiC contact, the Ni/Nb/4H-SiC has a better ability to collect excess carbon atoms at the interface, ensuring stable operation in a high temperature environment. The ability to collect excess carbon atoms of the Ni/Nb/4H-SiC is revealed by the formation of Nb6C5 which is confirmed by two-dimensional X-ray diffraction, hard X-ray photoelectron spectroscopy, and transmission electron microscopy analysis. The experimental results indicated that the Ni/Nb/4H-SiC ohmic contact is a potential candidate for high temperature and harsh environment applications.