Modeling and Characterization of Heterojunction Bipolar Transistors
Mazhari, Baquer
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https://hdl.handle.net/2142/72017
Description
Title
Modeling and Characterization of Heterojunction Bipolar Transistors
Author(s)
Mazhari, Baquer
Issue Date
1993
Doctoral Committee Chair(s)
Morkoc, Hadis
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Abstract
Heterojunction bipolar transistor (HBTs) offer several advantages over their homo-junction counterparts resulting from the use of semiconductors in the emitter and base with different bandgaps. These advantages include high current gain, large cut-off frequency and short gate delay in digital logic circuits. This thesis selects a few important and critical issues connected with the operation of HBTs with a view to provide a clear and comprehensive understanding thereof.
The characteristics of HBT in saturation are examined first. Analytical models for collector-emitter offset voltage and minority carrier storage are developed and used to describe the performance of different kinds of HBT structures. The use of saturation characteristics for estimation of emitter and collector resistance is also analysed. The effect of improvement in saturation characteristics obtained using HBTs on the performance of Integrated Injection Logic ($I\sp2L$) circuits is investigated next. It is shown that improvement in intrinsic gate delay by an order of magnitude can be obtained using GaAs/AlGaAs heterostructure $I\sb2L$ circuits. The potential of rapidly emerging Si/SiGe heterostructure technology for $I\sb2L$ circuit application is also examined. It is shown that intrinsic gate delay as low as 11 ps for a fanout of 1 can be achieved. The problem of surface recombination in GaAs pn junctions and GaAs/AlGaAs HBTs is also analysed in detail. A new model is developed that clearly explains the origin of 2kT surface recombination current at the sidewalls of GaAs pn junctions. A simple model is also proposed for the comparison of different components of surface recombination current in HBTs.
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