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

In this paper, the different designs of emitter-base junction including the employment of the delta-doping sheet and setback layer are presented and studied. A theoretical model is used to analyze the performances of the proposed different InGaP/GaAs heterojunction bipolar transistors (HBTs). Experimentally, a new InGaP/GaAs HBT with a delta-doping sheet and a setback layer inserting between emitter-base heterointerface is fabricated successfully. From the theoretical analysis and experimental results, it is found that the insertion of the delta-doping sheet and the setback layer can effectively eliminate the undesired potential spike at N-InGaP/p(+)-GaAs heterointerface. The experimental common-emitter current gain of 280 at collector current of 85 mA and a low offset voltage of 55 mV are achieved. In addition, a current gain of 11 at very small collector current of 0.5 mu A without passivation is obtained. (C) 1998 Elsevier Science Ltd. All rights reserved.