Bipolar Transistors in Small Bandgap Semiconductors

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AbstractBipolar transistors that operate at a lower voltage than existing devices would have a big impact on wireless communications and other battery-powered applications. The operating voltage of a bipolar transistor is determined by the bandgap of the constituent semiconductor, thus bipolar transistors in low bandgap semiconductors are needed.The only viable semiconductor family with lower bandgaps than those already used for bipolar transistors is the so-called 6.1 material family, named after the value of their lattice constant.The heterojunction bipolar transistor (HBT) is the prevalent bipolar transistor design in III-V semiconductor material families. It would seem natural to develop HBT's in the low bandgap 6.1 materials, but this cannot be done. The HBT is incompatible with the 6.1 materials, so an alternate type of bipolar transistor is sought. Such a transistor is the tunneling emitter bipolar transistor (TEBT). This program will study the TEBT's in the low bandgap 6.1 semiconductors. The effort will be along three lines: physics, materials and device engineering. The physics involves certain tunneling processes required by the TEBT. The materials work is the development of the epitaxial structures for the TEBT in the 6.1 materials. The device engineering (and fabrication and testing) of TEBT's will initially aim at a transistor exhibiting a substantial (40) dc current gain, and follow up with engineering the device for rf performance.