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

Lasers have been used to control semiconductor switching devices either by laser gating or laser triggering. Laser gating requires the optical source to generate of all charge carriers which would be prohibitively expensive in terms of optical power to use with high current devices. Laser triggering only generates charge carriers in the gate region of the device which still results in a slow turn-on time as those charges create conducting channels between the anode and cathode. Laser pumping is an alternative that combines these two concepts, seeding all of the initial charge carriers using optical power while using thyristor action to maintain conduction. By selecting the appropriate wavelength, the charge carries can be generated throughout the bulk of the thyristor. This significantly reduces the costs of the optical power while still providing a very fast turn-on as the limit of the turn-on time is not the rate at which the initial charge carriers can be generated but on how fast the device can be seeded with photo-generated charge carriers. Previously reported results demonstrated turn-on times of less than 40ns to 2500A. These tests were done using commercial devices with windows etched into the anode metalization to permit laser pumping and described the development of a compact laser diode source. This paper will describe the development and comparative performance of laser pumped silicon thyristor switches capable of <50ns risetimes and peak currents of >5kA. The turn-on time was improved through the development of devices designed specifically for laser pumping. Two types of devices were fabricated, some with optical windows on the anode side and electrical triggering available on the cathode side while the others have optical windows on the cathode side and cannot be electrically triggered. A higher power compact laser source was also developed.