Laser pumping of 5kV silicon thyristors for fast high current rise-times

Abstract

There are many applications currently using spark gap switches which would like to have the long lifetime of a solid state switch such as a silicon thyristor. This was not possible till now due to the relatively long turn-on times of silicon thyristors. The turn-on time of a silicon thyristor can be improved by providing the charge carriers using a laser source rather than an electrical source. Then the limit of the turn-on time is not the rate at which the charge carriers can be generated but on how fast the device can be seeded with photo-generated charge carriers. Previous experiments have tried to create devices based on fast optical gating of high voltage silicon thyristors. However, these used thick expensive prototype devices. We examined the use of standard commercial silicon thyristors. The advantage of using commercial thyristors is their lower cost and smaller thickness. Thinner devices have a faster turn-on time with lower optical energy requirements. We previously demonstrated 50ns turn-on times using 125W laser diode pumping of 5kV commercial devices that were designed for electrical triggering and had been modified for optical triggering. These devices were tested at up to 5kA peak current. This paper will describe how 500W laser pumping of silicon thyristors achieves turn-on times of less than 40ns using commercial devices designed for laser pumping and using a compact laser diode source.