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 n- and 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) Omega cm(2) to 10(-6) Omega cm(2)) have been obtained after high-temperature (> 800A degrees C) annealing. Moreover, great efforts have been made to achieve good Ohmic contact performance (10(-6) Omega cm(2) to 10(-5) Omega cm(2)) under low-temperature annealing (< 600A degrees C) or even without annealing. During long-term aging at high temperature (300A degrees C to 1000A degrees 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.