Chapter 7Unipolar and Bipolar Power Diodes

7.1 Introduction to SiC Power Switching Devices

The majority of silicon carbide devices developed to date can be grouped into three general classes: power switching devices, microwave devices, and specialty devices (sensors, high-temperature integrated circuits, etc.). Of these, by far the most important and most fully developed are the power switching devices. Accordingly, Chapters 7–11 will be devoted to SiC power devices, and other SiC device applications will be considered in Chapter 12.

Power switching devices attempt to emulate an ideal switch. An ideal switch carries infinite current in the on state with zero voltage drop, and hence zero power dissipation. In the off state it blocks infinite voltage with zero leakage current, and it switches instantly between states using zero switching energy. Of course, real semiconductor switches only approach these ideals, and the degree to which they achieve these goals is indicated by the performance specifications of the device. Most critical of these are blocking voltage, maximum on-state current, on-state and off-state power dissipation, and switching loss. Since maximizing performance involves trade-offs between parameters, researchers have developed figures of merit (FOMs) that define the theoretical envelope of maximum performance and quantify the degree to which actual devices approach these theoretical limits. Device performance depends on fundamental material parameters, as well ...

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