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 400°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 and 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°C (⩽5×10^-7 A/cm² at 5 V). The results indicate that current transport across the interface is dominated by the thermionic emission only at temperatures above 300°C. The ideality factors decreased from 2.24 at R.T. to 1.07 at 400°C. Thus, Schottky barrier heights (SBHs) 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°C with significant increases in reverse leakage at temperatures as low as 100°C. As expected from its low work function (Fomenko, 1966; Kosolapova, 1971), TaC on lightly doped (4.1×10 ¹⁶ cm^-3) n-type SiC resulted in leaky diodes at R.T. These contacts showed ohmic behavior at temperatures above 200°C. Tantalum carbide contacts on p-type (2×10¹⁵ cm^-3) material displayed diode behavior with low reverse leakage currents to 250°C. Good reversibility of the current-voltage characteristics of all of these contacts after cycling between R.T. and 400°C was observed. These results indicate the absence of interfacial reactions and, hence, the potential for thermally stable contacts to 400°C