Analysis of DC characteristics of GaAs double heterojunction bipolar transistors (DHBTs) with a pseudomorphic GaAsSb base

In this paper, DC characteristics in GaAs DHBTs with pseudomorphic GaAsSb base layer are investigated using an analytical approach. Devices using different GaAs1−xSbx base thickness with different Sb compositions were simulated to gain an in-depth understanding on the effect of base layer design on the device DC performance. Our calculated results show that, in the GaAsSb base with high Sb composition, the strain plays a non-negligible role in determining the overall device performance. The reduction of B-E turn-on voltage using a large Sb composition of GaAs1−xSbx could be partially compensated by strain in the base. Furthermore, for the devices using high Sb composition, a thin base layer has to be used to ensure elastic strain. In order to maintain reasonable base conductivity that is critical for device microwave performance, high base doping is required. However, our simulation reveals a drastic reduction of DC gain with the increase in base doping, while a high emitter doping may be helpful for the compensation of the degradation of β. A proper design of the device structure by taking the aforementioned issues into account is important for improving device DC and microwave performance.