4.4.1.1 SBD Structure

Fig. 4.5 shows the cross section of a typical SBD in SiC. A lightly doped n-type blocking layer is grown by chemical vapor deposition on an n+ 4H-SiC substrate that is disoriented about $8^\circ$ off the normal to the (0001) silicon face (see Section 2.3.3.2). The doping and thickness of the epilayer are chosen to achieve the desired blocking voltage from Fig. 4.4.

Figure 4.5: Cross section of the Schottky barrier diode in SiC.

The Schottky junction on the top surface of the blocking layer is formed by implanting an edge termination ring at the surface, then depositing the Schottky metal. The edge termination ring is needed to prevent field crowding at the periphery of the metal in the blocking state, which would significantly reduce the blocking voltage. Two types of edge termination rings are currently in use: a resistive termination extension (RTE) [173] and a junction termination extension (JTE) [174]. 4H-SiC is preferred over 6H-SiC for this application because it has higher and more isotropic electron mobility than 6H-SiC. For the 1200 kV 4H-SiC SBDs available today in markets, an epilayer thickness of 6.5 $\mu$m with a doping concentration of 2$\times$10$^{16}$cm$^{-3}$ is expected to show a good device FOM. T. Ayalew: SiC Semiconductor Devices Technology, Modeling, and Simulation