On the recombination currents effect of heterostructure-emitter bipolar transistors (HEBTs)

We demonstrate the effect of recombination current on the electrical properties of heterostructure-emitter bipolar transistors (HEBTs). For comparison, an AlGaAs/GaAs and an AlInAs/GaInAs HEBT are fabricated with the layer structure. For the AlGaAs/GaAs HEBT, the hole diffusion length is larger than the emitter thickness, so that most holes can be reflected back at the confinement layer because the hole recombination current is low in the neutral-emitter region. Thus, high emitter injection efficiency and current gain can be achieved simultaneously. On the other hand, for the AlInAs/GaInAs HEBT, the increase of recombination current in the neutral emitter regime and the existence of a potential spike could reduce the emitter injection efficiency at large V_BE voltage. Hence, the non-1KT component of collector current is enhanced and the transistor characteristics are degraded. However, a lower offset voltage of 40 mV is obtained attributed to the low base surface recombination current for the AlInAs/GaInAs HEBT