Si1－ZGeZ基区杂质和Ge组份分布对HBT基区渡越时间的影响

EFFECTS OF DOPING AND Ge FRACTION PROFILE IN THE Si 1-Z Ge Z BASE ON THE BASE TRANSIT TIME OF HBTs

在Ｓｉ１－ＺＧｅＺ基区ＨＢＴ中，Ｇｅ组份Ｚ缓变（进而能隙缓变）产生自建电场，基区杂质浓度向发射极侧的减小产生了阻滞电场，基区杂质浓度向集电极侧的减小产生了加速电场．文中研究了这些电场对基区渡越时间的影响．研究结果表明，随基区发射极侧杂质浓度的不同，因阻滞电场而产生的延迟时间占基区总渡越时间的４０％～８０％．同时还发现，选用无阻滞电场产生的基区杂质分布，采用大的Ｇｅ组份线性缓变和利用集电结空间电荷区电子速度过冲效应。

In this paper, effects of the accelerating field due to the base doping grading down towards the collector, the built in field due to the base Ge fraction grading, and the retarding field from the base graded doping profile down towards the emitter on the base transit time of the SiGe base heterojunction bipolar transistors(HBTs) are studied. It is shown that the retarding field has between 40%～80% contribution to the base transit time depending on the doping level near the emitter. It is also found that 100 GHz SiGe base HBTs will be possible if the retarding field is diminished, a large base Ge fraction grading is used, and the electron velocity overshoot in the collector space charge region is available.