Electrical characteristics of tantalum and tantalum carbide Schottky diodes on n- and p-type silicon carbide as a function of temperature

This study reports on the electrical stability of Ta/SiC and TaC/SiC interfaces at potential device operating temperatures (25 to 40 degrees C). In contrast to previous reports on thermal stability of contacts, which report the electrical properties after high temperature annealing, this study reports the electrical properties of contacts measured both at room temperature (prior to an subsequent to annealing) and at elevated temperatures in air. Tantalum on p-type 6H-SiC (0001) showed good diode characteristics with low reverse leakage currents to 350 degrees C (less-than-or-equal-to 5x10(-7) A/cm(2) at 5 V). The results indicate that current transport across the interface is dominated by thermionic emission only at temperatures above 300 degrees C. The ideality factors decreased from 2.24 at R.T. to 1.07 at 400 degrees C. Thus, Schottky barrier heights (SBH's) calculated from these measurements are believed to be underestimated for the lower temperatures, where current transport is believed to be dominated by recombination. On n-type 4H-SiC, Ta contacts also displayed good diode behavior at 25 degrees C with significant increases in reverse leakage as low as 100 degrees C. As expected from its low work function (Fomenko, 1966; Kosolapova, 1971), Ta on lightly doped (4.1x10(16) cm(-3)) n-type SiC resulted in leaky diodes at R.T. These contacts showed ohmic behavior at temperatures above 200 degrees C. Tantalum carbide contacts on p-type (2x10(15) cm(-3)) material displayed diode behavior with low reverse leakage currents to 250 degrees C. Good reversibility of the current-voltage characteristics of all of these contacts after cycling between R.T. and 400 degrees C was observed. These results indicate the absence of interfacial reactions and, hence, the potential for thermally stable contacts to 400 degrees C.