Significant Effect of Emitter Area on the Efficiency, Stability and Reliability of Picosecond Switching in a GaAs Bipolar Transistor Structure

A drastic reduction in the residual voltage (from _~ 100 V to a few volts) and a significant (factor of _~ 2) increase in the dU/dt switching rate is demonstrated experimentally in the superfast ( _~ 200 ps) avalanche switching of a GaAs bipolar junction transistor with increased emitter area. This result is not a trivial one as only a small number of conductive channels of a few micrometers in diameter participate in the transient independently of the emitter size, while the remaining (passive) part of the structure supplies the switching channels with the currents circulating inside the chip, which makes the impact ionization in the filaments even more powerful. Excellent agreement was found between the experiment and a ¿two-transistor¿ model specially developed here, with one transistor simulating the switching channels and the other the nonswitched part of the structure. Much higher switching stability and reproducibility and much lower power dissipation were observed in the structure with increased emitter area.