Long-term stability of nickel-based ohmic contacts with n-type and p-type 4H-SiC in a high-temperature environment

Abstract

Long-term thermal stability of specific contact resistance (ρc) in cross-bridge kelvin resistors (CBKRs), with an Al/TiN/Ti/Ni2Si/4H-SiC layered structure was studied. In hightemperature-storage tests at 500°C, ρc of p-type SiC increased after it decreased to 1/100 from its initial value; however, in high-temperature-storage tests at 300°C, it was stable up to 1000 hr. The initial decline of ρc was due to formation of titanium-silicide alloy, whose barrier height is lower than that of Ni2Si phase. It was found that ρc increased when the aluminum electrode disappeared because aluminum displaced silicon in the silicon-dioxide layer. In thermal-shock tests (-40°C/300°C), ρc hardly changed up to 2000 cycles, and that trend was constant regardless of SiC carrier type. In both tests, almost no thermal deterioration of ρc around 300°C was observed even in air, so it is concluded that the CBKR structure is robust enough for installation in a high-temperature environment such as a nuclear power plant under decommissioning.