Analyses of the picosecond range transient in a high-power switch based on a bipolar GaAs transistor structure

The superfast (∼200 ps) switching observed lately in a GaAs bipolar-junction transistor (BJT) structure is analyzed. Contrary to all known bipolar semiconductor switches, a superfast transient occurs in this GaAs BJT due to practically homogeneous and simultaneous high-rate carrier generation across the entire thickness of the blocking region. This generation is provided by a comb of powerfully avalanching Gunn domains moving across the blocking n₀ layer and covering whole layer thickness at each instant. Generation of the multiple avalanching Gunn domains is accompanied by current filamentation, and at first glance the total area of the structure should not affect the switching process. It is shown however, that the charge accumulated in the barrier capacitance of the collector junction can cause a further drastic reduction in the switching time and in the residual voltage across the switch. Simulations performed with the barrier capacitance taken into account show excellent agreement with the experimental data for a transistor prototype, while a further significant reduction in the switching time to several dozens of picoseconds, and in the residual voltage to a dozen volts, is predicted for a device area that is an order of magnitude larger.