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

Automated summary

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.