Design consideration of emitter-base junction structure for InGaP/GaAs heterojunction bipolar transistor

An InGaP/GaAs heterojunction bipolar transistor (HBT) with an 50 Å undoped spacer and δ-doping sheet at base-emitter heterointerface is fabricated and studied. A common-emitter current gain of 280 and an offset voltage as small as 55 mV are obtained, respectively. This results show that high current gain and low offset voltage can be attained simultaneously without the passivation of emitter-base junction. From the experimental results, it shows that the potential spike is indeed reduced by the employment of an δ-doped layer and spacer simultaneously. On the other hand, theoretical consideration also shows that the potential spike is removed by inserting a δ-doping sheet between the emitter-base heterointerface