Characterization of tungsten-nickel simultaneous Ohmic contacts to p- and n-type 4H-SiC

Ohmic contacts to p- and n-type 4H-SiC using refractory alloyed W:Ni thin films were investigated. Transfer length measurement test structures to p-type 4H-SiC (N_A = 3 � 10²⁰ cm^-3) revealed Ohmic contacts with specific contact resistances, ρ_c, of ∼10^-5 Ω cm² after 0.5 h annealing in argon at temperatures of 1000 �C, 1100 �C, 1150 �C, and 1200 �C. Contacts fabricated on n-type 4H-SiC (N_D = 2 � 10¹⁹ cm^-3) by similar methods were shown to have similar specific contact resistance values after annealing, demonstrating simultaneous Ohmic contact formation for W:Ni alloys on 4H-SiC. The lowest ρ_c values were (7.3 � 0.9) � 10^-6 Ω cm² for p-SiC and (6.8 � 3.1) � 10^-6 Ω cm² for n-SiC after annealing at 1150 �C. X-ray diffraction shows a cubic tungsten-nickel-carbide phase in the Ohmic contacts after annealing as well as WC after higher temperatures. Auger electron spectroscopy depth profiles support the presence of metal carbide regions above a nickel and silicon-rich region near the interface. X-ray energy dispersive spectroscopy mapping showed tungsten-rich and nickel-rich regions after annealing at 1100 �C and above. W:Ni alloys show promise as simultaneous Ohmic contacts to p- and n-SiC, offering low and comparable ρ_c values along with the formation of W_xNi_yC.