A comparison of single- and multi-layer ohmic contacts based on tantalum carbide on n-type and osmium on p-type silicon carbide at elevated temperatures

The thermal stability of TaC ohmic contacts with and without Au, Pt, and W/WC overlayers were investigated on n-type 6H-SiC (0001) substrates. Specific contact resistivities (SCRs) were calculated at temperatures ranging from 20 to 400 degreesC in air. The TaC contacts with Au overlayers had the minimum SCR at room temperature, which was 1.4 x 10(-6) Omega cm(2) on SiC with a doping level of 2.3x10(19) cm(-3). The SCRs for both the Au/TaC/SiC (5.3 x 10(-7) Omega cm(2)) and the Pt/TaC/SiC (7.5 x 10(-7) Omega cm(2)) samples decreased with measurement temperature to 200 and 400 degreesC, respectively, while the latter samples showed reversibility after heating to 400 degreesC. W/WC/TaC/SiC samples showed the best stability after annealing at 400 degreesC for 144 hrs in vacuum. Changes in the electrical characteristics were correlated with increases in O incorporation in the contacts as a result of annealing. Investigation of the TaC/SiC interface by transmission electron microscopy indicated that there was little or no reaction between the materials. The An, Pt and/or W/WC overlayers were required to prevent oxidation of the TaC and Os contacts during elevated temperature measurements. Osmium contacts annealed at 1020 degreesC for 1 h followed by 1075 degreesC for 15 min. displayed ohmic behavior on p-type (1 x 10(19) cm(-3)) SiC with SCRs of 6.8 x 10(-4) Omega cm(2).