Recent Progress in Ohmic Contacts to Silicon Carbide for High-Temperature Applications

During the past few decades, silicon carbide (SiC) has emerged as the most promising wide-bandgap semiconductor for high-temperature, high-frequency, and high-power applications. All its attractive properties depend critically on and are often limited by the formation of Ohmic contacts to SiC. Although impressive progress has been made, improvements to further reduce the specific contact resistance without lowering the stability of Ohmic contacts during long-term aging are still indispensable. In this regard, we present a review of recent progress in Ohmic contacts to nand p-type SiC reported in literature. The mechanism of Ohmic contact to SiC, surface preparation methods, and performance of Ohmic contacts are discussed. Emphasis is placed on the thermal stability of Ohmic contacts to SiC. To date, extremely low specific contact resistance values (10 7 X cm to 10 6 X cm) have been obtained after high-temperature (>800 C) annealing. Moreover, great efforts have been made to achieve good Ohmic contact performance (10 6 X cm to 10 5 X cm) under low-temperature annealing (<600 C) or even without annealing. During long-term aging at high temperature (300 C to 1000 C), surface morphology degradation, formation of unwanted Kirkendall voids, interdiffusion between metallization stacks and/or SiC substrates, and especially severe oxidation in oxygen-containing atmospheres can be responsible for electrical degradation of Ohmic contacts. These critical issues are discussed along with future perspectives.