9. SiC Planar MOSFET Structures

In Chap. 1, it was demonstrated that the specific on-resistance of power MOSFET devices can be greatly reduced by replacing silicon with wide band gap semiconductors. Among wide band gap semiconductors, the most progress with creating power MOSFET structures has been achieved using silicon carbide. Silicon carbide power device structures have been discussed in detail in a previous book [1]. In that book, it was shown that the conventional planar power D-MOSFET structure, developed and widely utilized for silicon, is not suitable for the development of silicon carbide devices. Two problems are encountered when utilizing the conventional power D-MOSFET structure for silicon carbide. The first problem is the much larger threshold voltage required to create an inversion layer in silicon carbide due to its much greater band gap. The doping concentration required in the P-base region to achieve a typical threshold voltage of 2 V is so low that the device cannot sustain a high blocking voltage due to reach-through of the depletion layer in the base region. The second problem is the very high electric field generated in the gate oxide because the electric field in the silicon carbide drift region under the gate is an order to magnitude larger than for silicon devices. This leads to rupture of the gate oxide at large blocking voltages.