| Summary: | 碩士 === 國立成功大學 === 電機工程研究所 === 81 === In this thesis, an analytical model for the heterojunction
emitter bipolar transistors (HEBTs) is developed. The HEBT,
which has a homojunction emitter with a heterojunction
confinement layer on top of it, combines the merits of
homojunction and regular heterojucntion bipolar transistors and
is simple for fabrication. In the present model, the model
parameters are directly related to device parameters such as
doping densities, dimensions, and band offset, etc. The effects
of carrier recombination at the heterointerface of the narrow-
and wide-bandgap emitters, in the quasi-neutral emitter and
base regions, in the e-b SCR, and at the surface of the e-b SCR
edge have been considered. Physical insight of the influence of
the thickness, the valence band discontinuity, and the junction
velocity of the narrow-bandgap emitter layer on device
performance is investigated. Based on an AlGaAs/GaAs HEBT, the
calculated results obtained from this analytical model are
compared with experimental data. It is found that the common-
emitter I-V characteristics from the present model are in good
agreement with the experimental data. In addition, the modeling
of current-dependent cutoff frequency has been also
investigated. The proposed analytical equations discribe very
well for high-current base-widening, current-dependent b-c
junction capacitance, etc. Optimization of HEBT design is
discussed based on current-dependent analysis. This model can
be used for homojunction BJTs, both single and double
heterojunction bipolar transistors, and heterojunction emitter
bipolar transistors.
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