Numerical Modeling Of Algaas Gaas Heterojunction Bipolar Transistors

Author : Mohan K. Chirala
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (57 download)

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Download or read book Design, Simulation and Modeling of Collector-up GalnP/GaAs Heterojunction Bipolar Transistors written by Mohan K. Chirala and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The immense demand for communication systems world wide has created an enormous market for semiconductors devices in variegated applications. While scaled CMOS is consolidating its stronghold in the analog and RF domains, the wide gamut of microwave frequencies is being competed for by the various types of III-V heterojunction based semiconductor devices, which were made amenable to high-volume production, thanks to rapid improvements in bulk-processing and fabrication techniques in the last decade. Among these devices, the quest for faster, more powerful and low cost transistors has led researchers to investigate innovative topologies. The availability of powerful CAD tools that incorporate the most intricate physical phenomenon in the modeling process has provided a much needed impetus to this ongoing research. Of the scores of disparate devices that have been investigated, Heterojunction Bipolar Transistors (HBTs) have carved a niche for themselves owing to their high speeds and greater power handling capabilities. In this work, the design of an innovative HBT with a collector-up topology, i.e., with the collector situated on top of the device and emitter on the substrate side, is carried out and optimized for maximizing the high frequency performance. The material system used here is Ga x In 1-x P/GaAs (with x=0.51 indicating lattice matched composition), which has relatively superior material properties and etching characteristics than the conventional Al x Ga 1 -xAs/GaAs material system. The material properties of the ternary were investigated and the most suitable values were ascertained through meticulous research. These parameters, along with the mobility models (that were derived by investigating published results), were made compatible to an emitter-up HBT and incorporated into a two dimensional, physically-based, numerical simulator called ATLAS by Silvaco Inc. The motive was to verify the correctness of the material parameters and models derived. The simulation results compared favorably with the published results. With these verified material parameters and mobility models, a collector-up GaInP/GaAs HBT structure with unetched extrinsic emitter was simulated. After a performance appraisal with the emitter-up structure, the impact of having an undercut in the extrinsic base region was investigated. It was found that this undercut drastically improved the high frequency performance as well as DC characteristics of the collector-up structure. This was documented by a significant increase in cutoff frequency (f T) from 109 GHz to 140 GHz. It was even more pronounced in maximum frequency of oscillation (f max), which is more practically useful than cutoff frequency, from 76 GHz to 233 GHz. These simulation results are much better than the practically experimented values. The high frequency parametric values described here were achieved after scrupulously optimizing the collector-up HBT structure.