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由于发射结(EB结)价带存在着能量差ΔEv,电流增益β不再主要由发射区和基区杂质浓度比来决定,给HBT设计带来了更大的自由度。为减小基区电阻和防止低温载流子冻析,可增加基区浓度。但基区重掺杂导致禁带变窄,禁带变窄的非均匀性产生的阻滞电场使基区渡越时间增加,退化了频率特性,特别是在低温下更为严重
Due to the energy difference ΔEv in the valence band of the emitter junction (EB junction), the current gain β is no longer determined mainly by the impurity concentration ratio of the emitter region to the base region, giving the HBT design more freedom. To reduce the base resistance and prevent cryogenic carrier cryogenic analysis, can increase the base concentration. However, heavy doping in the basement leads to the narrowing of the forbidden band and the stagnant electric field caused by the inhomogeneity of the forbidden band increases the transit time of the basement and degenerates the frequency characteristics, especially at low temperatures