Changes in collector and base currents for AlGaAs/GaAs heterojunction bipolar transistors

The changes in the collector and base currents after a 5-min operation with a collector current density of more than 2.5 × 104 A/cm2 has been investigated for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with a Be doped base layer. Their dependence on the V/III flux ratio during molecular beam epitaxy (MBE) growth and on ion implantation conditions for emitter isolation were examined. A larger change in the collector current was observed for HBTs which were grown under a lower V/III ratio or fabricated under a heavier implantation condition. A change in the base current has also been found even when the change in the collector current was small. The change has been attributed to a decrease in the non-radiative recombination rate. A high V/III flux ratio growth and a low damage implantation are needed to suppress the changes.