UBC Theses and Dissertations
Fabrication and modeling of composite-collector heterojunction bipolar transistors Ghodsian, Bahram
This thesis is concerned with processing and modeling aspects of heterojunction bipolar transistors (HBTs) with composite-collectors. HBTs with InGaAs/InP composite collectors were designed, fabricated and measured. Their dc characteristics are compared with those of a device which was structurally similar but with a conventional n-InGaAs collector. The measured data for both devices can be well-described by an analytical model. The model indicates the need to ensure that the InGaAs layer in the composite collector exceed a critical thickness if the current gain is to be preserved. It is also shown that the spacer layer between the emitter and base, which was used to prevent zinc diffusion into the emitter, must be considered in the model if the collector current is to be correctly predicted. The comparison of the experimental data also suggests that surface recombination is not a dominant base recombination current in the devices studied.
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