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.