4.3 Article

Tunneling-Related Leakage Currents in Coaxial GaAs/InGaP Nanowire Heterojunction Bipolar Transistors

Journal

Publisher

WILEY-V C H VERLAG GMBH
DOI: 10.1002/pssb.202000395

Keywords

coaxial nanowires; heterojunction bipolar transistors; leakage currents; pn-junctions; tunneling

Funding

  1. German Research Foundation (DFG) [265982007, 428769263]

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In this study, the leakage mechanisms in epitaxially grown nanowire heterojunction bipolar transistors were analyzed in detail. Tunneling was identified as the dominant leakage mechanism in highly doped nanowire pn-junctions, and by adjusting the tunneling barrier width, the junction leakage current density was successfully reduced. This suppression of tunneling also increased the number of electrons injected from the n-emitter into the p-base, enabling the functionality of bipolar transistors.
Herein, a detailed analysis of leakage mechanisms in epitaxially grown nanowire heterojunction bipolar transistors (NW-HBTs) is presented. Coaxial npn-GaAs/InGaP core-multishell nanowires are grown via gold-catalyzed metalorganic vapor phase epitaxy, processed to three terminal devices and electrically characterized. The key for successful NW-HBT device functionality is the identification of tunneling as the dominant leakage mechanism in highly doped nanowire pn-junctions. The suppression of forward tunneling currents by adjustment of the tunneling barrier width reduces the junction leakage current density into the nA cm(-2)regime, which is further verified by tunneling-related electroluminescence measurements. In addition, the suppressed tunneling accordingly increases the number of electrons that are injected from the n-emitter into the p-base. The latter effect influences the performance of pn-junction based devices and is found to enable bipolar transistor functionality. Measured common emitter Gummel plots of the NW-HBT exhibit a current gain of up to 9 and the transistor function is additionally verified by current-controlled output characteristics.

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