500 degrees C high-temperature reliability of Ni/Nb ohmic contact on n-type 4H-SiC

The reliability of Ni/Nb ohmic contact on n-type 4H-SiC at 500 degrees C was investigated. The current-voltage characteristics showed that, while the Ni(50)/Nb(50)/4H-SiC sample without applying the CF4:O-2 etching process degraded just after 25 h and lost ohmic behavior after 50 h aging, the Ni(75)/Nb(25)/4H-SiC contact undergone CF4:O-2 surface treatment still showed excellent stability after aging for 100 h at 500 degrees C. Though X-ray diffraction results indicated that the chemical compounds remained stable during the aging process, transmission electron microscopy showed that there was a redistribution of the chemical compounds at the interface of the contact after 500 degrees C aging. The depth distribution of the elements and energy-dispersive X-ray analyses revealed that the contribution of carbon agglomeration at the interface accounted for the degradation of the sample without applying the etching process. Whereas the well-controlled excess carbon atoms of the contact undergone CF4:O-2 treatment ensured the stability of this contact when operating at a high ambient temperature.