Practical limits of high-voltage thyristors on wide band-gap materials

This article presents a detailed simulation study of the highest achievable voltage ratings on bi-directional semiconductor controlled rectifiers designed using wide band-gap materials. It is shown that the voltage ratings of 4H-SiC and GaN are limited by small carrier lifetimes, as a result of material defects or crystal structure. Symmetric thyristors rated up to 8 kV are possible with commercially available 4H-SiC wafers that have carrier lifetimes longer than 300 ns. With further improvements in wafer quality, devices with voltage rating higher than 15 kV may be achievable. The performance of 8 kV 4H-SiC thyristors is compared with that of 8 kV Si thyristors. It is shown that the on-state voltage of 4H-SiC thyristors has very little dependence on temperature up to 300 degreesC unlike Si thyristors, with a positive temperature coefficient. Finally, simulations suggest that symmetric GaN thyristors may be impractical primarily because of the low carrier lifetimes resulting from direct band structure. (C) 2000 American Institute of Physics. [S0021-8979(00)03901-9].