Mechanisms of carriers transport in Ni/n-SiC, Ti/n-SiC ohmic contacts

A mechanism of carriers transport through metal-semiconductor interface created by nickel or titanium-based ohmic contacts on Si-face n-type 4H-SiC is presented herein. The mechanism was observed within the temperature range of 20 °C ÷ 300 °C which are typical for devices operating at high current density and at poor cooling conditions. It was found that carriers transport depends strongly on concentration of dopants in the epitaxial layer. The carriers transport has thermionic emission nature for low dopant concentration of 5×1016 cm−3. The thermionic emission was identified for moderate dopant concentration of 5×1017 cm−3 at temperatures higher than 200 °C. Below 200 °C, the field emission dominates (for the same doping level of 5×1017 cm−3). High dopant concentration of 5×1018 cm−3 leads to almost pure field emission transport within the whole investigated temperature range.