Evaluation of GaAs Schottky gate bipolar transistor (SGBT) by electrothermal simulation

Abstract

A GaAs alternative to the Si IGBT, employing an implanted lateral channel in place of the usual MOSFET inversion channel, is proposed. A simplified analytical model shows that the relatively high ratio of electron to hole mobility in GaAs allows much lower anode emitter injection efficiencies to be used without compromising conductivity modulation of the base region. This, in turn, means that a higher proportion of the total device current is carried by electrons. Design strategies for the GaAs SGBT are investigated and applied in the design of an optimised unit cell. The optimised structure is compared with an equivalent Si IGBT structure by means of electrothermal and transient simulation. Electrothermal simulation shows the GaAs device to have useable performance at junction temperatures in excess of 300°C, a feature which is consistent with the wide band-gap of GaAs. Transient simulations show reduced minority carrier tailing effects at both turn-on and turn-off, with initial turn-off tail currents being reduced by a factor of 5 compared to the Si IGBT. The resulting reduction in turn-off loss allows switching frequencies to be increased by a factor of 4 for the same total losses. The excellent switching performance derives from the relatively low proportion of hole current needed to ensure effective conductivity modulation of the structure.