Analysis of and process development for high-frequency indium gallium phosphide/gallium arsenide heterojunction bipolar transistors
Hanson, Allen William
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https://hdl.handle.net/2142/22174
Description
Title
Analysis of and process development for high-frequency indium gallium phosphide/gallium arsenide heterojunction bipolar transistors
Author(s)
Hanson, Allen William
Issue Date
1994
Doctoral Committee Chair(s)
Stillman, Gregory E.
Department of Study
Electrical and Computer 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
Language
eng
Abstract
The In$\rm\sb{0.5}Ga\sb{0.5}$P/GaAs materials system has been investigated for use in heterojunction bipolar transistor applications. This material possesses several properties which make it attractive as a potential replacement for AlGaAs as the wide band gap emitter material. These properties include the availability of highly selective etches, an energy band alignment favorable for high injection efficiency devices, and the absence of DX centers.
A comparison of the dc characteristics of MOCVD-grown, Npn In$\rm\sb{0.5}Ga\sb{0.5}$P/GaAs single- and double-heterojunction bipolar transistors (SHBTs and DHBTs, respectively) with carbon-doped bases is presented. A base doping level of 2.5 $\times$ 10$\sp{19}$ cm$\sp{-3}$ was employed in both device structures, resulting in a base sheet resistance of 500 $\Omega$/sq. Common-emitter current gains as high as 210 and 150 were measured for the SHBTs and DHBTs respectively. Results of a dc performance optimization study indicate that a 15 to 25 A undoped setback layer at the emitter-base junction provides optimal common-emitter current gain. The DHBTs exhibited a 40% improvement in common-base breakdown voltage compared to SHBTs (25 V versus 18 V), indicating that In$\rm\sb{0.5}Ga\sb{0.5}$P/GaAs DHBTs may prove suitable for power device applications.
Details concerning the design and development of a high-frequency HBT process utilizing this materials system are also given. A unity current gain cutoff frequency, $f\sb{t}$, of 14.6 GHz was obtained for a double heterojunction In$\rm\sb{0.5}Ga\sb{0.5}$P/GaAs HBT. This device featured a 1 $\mu$m In$\rm\sb{0.5}Ga\sb{0.5}$P collector region and exhibited common-base breakdown voltage $BV\sb{CBO}$ of 45 V. The high-frequency device characteristics of the DHBTs are presented, and an estimation of the high-field electron velocity for n-type In$\rm\sb{0.5}Ga\sb{0.5}$P is determined from the results.
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