Current Modulation of a Heterojunction Structure by an Ultra-Thin Graphene Base Electrode

Abstract

Graphene has been proposed as the current controlling element of vertical transport in heterojunction transistors, as it could potentially achieve high operation frequencies due to its metallic character and 2D nature. Simulations of graphene acting as a thermionic barrier between the transport of two semiconductor layers have shown cut-off frequencies larger than 1 THz. Furthermore, the use of n-doped amorphous silicon, (n)-a-Si:H, as the semiconductor for this approach could enable flexible electronics with high cutoff frequencies. In this work, we fabricated a vertical structure on a rigid substrate where graphene is embedded between two differently doped (n)-a-Si:H layers deposited by very high frequency (140 MHz) plasma-enhanced chemical vapor deposition. The operation of this heterojunction structure is investigated by the two diode-like interfaces by means of temperature dependent current-voltage characterization, followed by the electrical characterization in a three-terminal configuration. We demonstrate that the vertical current between the (n)-a-Si:H layers is successfully controlled by the ultra-thin graphene base voltage. While current saturation is yet to be achieved, a transconductance of ~230 sans-serifμnormalS was obtained, demonstrating a moderate modulation of the collector-emitter current by the ultra-thin graphene base voltage. These results show promising progress towards the application of graphene base heterojunction transistors.

Electron Transport across Vertical Silicon/MoS2/Graphene Heterostructures: Towards Efficient Emitter Diodes for Graphene Base Hot Electron Transistors

“…Graphene base transistors (GBTs), where graphene replaces the metallic base electrodes, have been proposed to exploit the high conductivity and ultrathinness of graphene as the base material in HETs to minimize the base transit time and achieve high cutoff frequencies. − Although experimental demonstration of GBTs is limited to direct current (DC) characteristics, simulations clearly show that the performance greatly depends on the properties of the injection barrier that isolates the emitter and the base. In fact, high-level on-state collector currents ( I ON ) can be achieved only by choosing injection barriers that form relatively small conduction band (CB) offsets with respect to the emitter. − Thus, vertical heterostructures with low barriers, similar to compound semiconductor structures investigated by Heiblum et al, , have been proposed to enable high-frequency performance reaching (theoretically) the THz regime. − An illustration of the structure and operation of a GBT with molybdenum disulfide (MoS 2 ) as the emission barrier is shown in Figure S1.…”

Facile and Green Synthesis of Graphene-Based Conductive Adhesives via Liquid Exfoliation Process

“…As a two-dimensional material, graphene has attracted wide attention due to its stable structure and excellent performance. These materials have drawn an intensive attention towards a variety of research fields to utilize their exceptional thermal, mechanical, optical and electrical properties [14,15,16]. Theoretical and experimental studies of graphene show they may possess high thermal conductivity (5000 W·m −1 ·K −1 ), high Young’s modulus (~1 TPa), large surface area (~2600 m 2 ·g −1 ) [17,18] and great electrical conductivity (6000 S·cm −1 ) [19].…”

Emerging 2D Materials and Their Van Der Waals Heterostructures

“…The heterojunction formed by graphene with traditional 3D materials, which has been a promising research topic [34][35][36][37], is experimentally investigated by Luongo and coworkers [35]. They fabricate graphene/n-Si junctions by transferring graphene on the flat surfaces of Si nanopillars, etched into a Si substrate, and obtain devices with rectifying behavior, remarkable photo-response, and photovoltaic capability.…”