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

Abstract

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.

Thermodynamics Controlled Sharp Transformation from InP to GaP Nanowires via Introducing Trace Amount of Gallium

“…Nanowires show advantages in strain relaxation, heterojunction formation as well as crystal phase engineering and thus are developing rapidly during the last decade [ 1 – 4 ]. III–V semiconductor nanowires, thanks to their superior optical and electronic properties, have been widely used in both application fields (such as photovoltaics [ 5 ], photodetectors [ 6 , 7 ], photodiodes [ 8 ], and electronic devices [ 9 ]) and basic science researches [ 10 ]. For the bottom-up nanowire fabrication, metal organic chemical vapor deposition (MOCVD) [ 11 , 12 ] and molecular beam epitaxy (MBE) [ 13 ] techniques are widely applied to synthesize high-quality nanowires.…”

Electrical Properties of the Base‐Substrate Junction in Freestanding Core‐Shell Nanowires

“…In addition, since the tunneling probability depends exponentially on the width of the space charge region (SCR), [43] the tunneling current should be suppressed by an additional intrinsic inner shell, as already shown by Liborius et al [5] In sample B, the intrinsic shell at the NW base region has a diameter of 239 nm ± 12 nm as measured by SEM images, which is more than five times thicker than in the reference. [5] Therefore, the tunneling current should be strongly suppressed. Furthermore, a p-i-n structure is the ideal way to realize a charge-selective contact for electrons and holes according to Würfel et al; [44] in this way, electrons and holes are separated at the different p-i and i-n contacts.…”

“…Depending on various factors, such as the different conductivity channels (surface, interface, and bulk) [7] of the different shells, the current path can cross the intrinsic GaInP layer at different locations. However, in analogy to Liborius et al [5] , the i-GaInP interlayer with a thickness of ≈240 nm provides a strong suppression of the tunneling contribution. Since the I-V characteristic of the MT-STM measurement does not exhibit a strong suppression of the current contribution according to Liborius et al, [5] we infer a superposition of current path 2 (black) in figure 4b).…”

“…The virtues of bottom‐up grown III‐V semiconducting nanowire (NW) device structures offer a huge potential for advanced functional electronic and optoelectronic applications. Due to their high charge carrier mobility, [ 1 ] as well as their tunable electronic structure through selective adaptation of the material composition, [ 2 ] and the possibility of integrating heterocontacts for tunnel junctions, [ 3 ] charge‐selective contacts, [ 4 ] or tunnel barriers, [ 5,6 ] a multitude of applications can be targeted. In order to realize these types of device components, special attention must be paid to their surfaces and interfaces, since their electrical properties can be strongly influenced by surface termination and the sequence of layer deposition, especially in the case of core‐shell structures.…”

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structure through selective adaptation of the material composition, [2] and the possibility of integrating heterocontacts for tunnel junctions, [3] charge-selective contacts, [4] or tunnel barriers, [5,6] a multitude of applications can be targeted. In order to realize these types of device components, special attention must be paid to their surfaces and interfaces, since their electrical properties can be strongly influenced by surface termination and the sequence of layer deposition, especially in the case of core-shell structures.

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