Ohmic Contacts for Power Devices on SiC

An ohmic contact in semiconductor devices consists of an electrode (metal) and a semiconductor, and it plays an important role in current injection and ejection. Because a voltage drop at the contact increases the power loss and deteriorates the device performance, the contact resistance must be negligible relative to the total resistance of the device (its on-resistance) [1]. Contacts through which a high-density current flows horizontally must have the lowest resistivity possible because their effective contact area is very small due to current crowding at the contact edges [2]. Source contacts in vertical DMOSFETs are one example of such contacts. Increasing the size of the contact area to make it larger than that of the effective area does not reduce contact resistance. The only way to minimize contact resistance is to reduce the specific contact resistivity, ρC, itself. High-power and high-frequency SiC devices need horizontal contacts with a ρC in the range of 10−6 Ωcm2 or lower [3].

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