Creating room temperature Ohmic contacts to 4H-SiC: studied by specific contact resistance measurements and X-ray photoelectron spectroscopy

The use of a silicon interface pre-treatment to produce low resistance Ohmic nickel contacts to 4H-SiC, circumventing the need for contact post annealing, is reported. The effects of two different SiC pre-metal deposition surface preparation techniques: RCA cleaning (control sample) and a silicon interlayer pre-treatment (SIP), are discussed. Electrical characterization of contacts on treated surfaces, using circular transfer length measurements (CTLM), revealed that contacts to RCA cleaned samples were Schottky in nature, unless annealed at temperatures greater than 700 °C. In contrast, contacts formed on SIP SiC surfaces exhibited Ohmic behaviour directly after fabrication, without the need for post metallisation annealing. Average contact resistances as low as 1.3E−05 Ω cm² have been recorded for SIP samples. This fabrication process has distinct technological advantages compared to standard techniques for forming Ohmic contacts to SiC. To consolidate our findings the chemical and electrical nature of the SIP nickel-SiC interface, as it was sequentially formed and annealed, was examined using X-ray photoelectron spectroscopy (XPS). Based on these results, a model is proposed to explain the as-deposited Ohmic contact nature of the SIP sample.