Technological breakthroughs in light-activated thyristors for pulsed power

Recently, a number of key technology breakthroughs have enabled a class of high di/dt (up to 30 kA/musec/cm²), high peak current density (up to 4 kA/cm²) and high charge transfer (up to 400 mCb/pulse/cm²) laser-activated thyristors with working voltages of up to 16.5 kV for a single device. These devices have been operated in single shot as well as repetitive applications, with designed lifetimes of from 10² to 10¹⁰ shots. The dominant technical advances that enable such performance levels include the development of high voltage compatible edge treatments and passivation techniques, high power laser diodes at near band-edge wavelengths for silicon, and advanced interfacing techniques for coupling light into the devices. Two generic embodiments of these devices have resulted: an on-board integrated device in which the laser diode bars are an integral part of the thyristor electrode structure, and, an off-board integrated device in which the light source is fiber-coupled to the thyristor. Because laser diode/diode-bar output power is typically orders of magnitude less than that of an Nd:YAG laser, it is desirable to have the laser diodes operate for the entire time that the thyristor is conducting current, in some applications. Our modeling has shown reduced forward dissipation with this mode of operation and the LGPT (Laser Gated and Pumped Thyristor) was hence conceived. The paper will discuss the theory of operation of these devices, numerous supporting developmental efforts, modeling results, and the most current laboratory tests and demonstrations. Present and projected applications will also be discussed