High-Frequency Graphene Base Hot-Electron Transistor

High current density heterojunction bipolar transistors with 3D-GaN/2D-WSe2 as emitter junctions

With the continuous advancement of electronic technology, there is an increasing demand for high-speed, high-frequency, and high-power devices. Due to the inherently small thickness and absence of dangling bonds of two-dimensional (2D) materials, heterojunction bipolar transistors (HBTs) based on 2D layered materials (2DLMs) have attracted significant attention. However, the low current density and limited structural design flexibility of 2DLM-based HBT devices currently hinder their applications. In this work, we present a novel vertical GaN/WSe2/MoS2 HBT with three-dimensional (3D)-GaN/2D-WSe2 as the emitter junction. Harnessing the high carrier concentration and wide bandgap of 3D-GaN, an HBT with a current density of about 260 A cm-2 is obtained. In addition, by selecting an adequate position for the collector electrode, we achieve efficient carrier collection through a collector junction smaller than the emitter junction area, obtaining a common-base current gain of 0.996 and a remarkable common-emitter current gain (β) of 12.4.

Ultrafast all-optical modulation based on graphene-microfiber

We proposed and studied an all-optical modulator based on graphene-microfiber (GMF), and prepared GMF by transferring graphene to the surface of the tapered region of the microfiber. The all-optical modulation characteristics and ultrafast all-optical modulation characteristics of GMF under different light source combinations were studied, and the all-optical modulator was completed. The experimental results show that GMF can achieve all-optical modulation, and broadband pump light can modulate single-pulse signal light. When the pump light is a 1550 nm ASE light source, and the signal light is a single-pulse light source of 852 nm, the maximum modulation depth is 3.92 dB. A single-pulse pump light can modulate single-pulse signal light. When the pump light is a 980 nm single-pulse laser, and the signal light is a 1550 nm single-pulse laser, the maximum modulation depth is 2.966 dB. The all-optical modulator proposed in this paper has ultrafast all-optical modulation characteristics. When using a femtosecond pulse laser as pump light, the average response time of the all-optical modulator is 51.43 μs, and the average equivalent modulation rate is 19.44 kHz. The all-optical modulator based on the GMF we proposed provides a new, to the best of our knowledge, idea for the design of graphene-based all-optical devices and shows great application potential in ultrafast all-optical networks.

High Current Gain MoS2 Bipolar Junction Transistor Based on Metal-Semiconductor Schottky Contacts

Bipolar junction transistors (BJTs) are crucial components in high-power electronic applications. However, while two-dimensional (2D) semiconductors with exceptional electrical properties have been extensively studied in field-effect transistors, their application in BJTs has received far less attention. In this study, we demonstrate high-gain MoS2 BJTs based on metal-semiconductor Schottky contacts. The emitter-base junction uses the thermal ionization properties of a Schottky diode to emit electrons, while the collector-base junction leverages the Schottky barrier to collect electrons. This design enables thermal ionization of electrons into the base region, where they are subsequently accelerated and transferred to the collector region under the influence of the collector-base junction voltage. Our MoS2 BJTs achieves a common-base current gain 0.99 and a remarkable common-emitter current gain of 1967, representing the highest performance reported for BJTs based on 2D semiconductors to date, which is comparable to traditional silicon-based BJTs.

3D Porous Graphene Architecture Integrated with Cu2O for Enhanced Electrochemical Sensing Performance

Construction and functionalization of a 3D graphene architecture are crucial to harness and extend the unique features of graphene and thus essential for its numerous conventional and novel applications. Herein, a 3D honeycomb-patterned porous graphene architecture is constructed through a facile and low-cost self-assembly process and then integrated with Cu2O nanoparticles via a simple electrodeposition procedure. The 3D porous graphene structure is prepared by the breath figure method using a graphene oxide (GO)-based complex in which GO is modified by a surfactant as the casting material. Benefiting from the intercalation of the surfactant between the GO nanosheets and the fabrication of a 3D porous structure, the aggregation inhibition of GO nanosheets and increases in accessible surface area are realized at both nano- and microscales, resulting in good electrochemical performance. Moreover, the deposition of Cu2O nanoparticles can further improve the electrochemical sensing performance of the porous reduced graphene oxide (rGO) structure. Extremely low detection limit (30.72 nM) with a linear range of 0 μM to 30 μM, excellent anti-interference, repeatability, reproducibility, stability, and high accuracy for actual sample testing are shown when the 3D porous Cu2O/rGO film is applied as an electrochemical sensor for DA detection. This work provides not only a superior electrochemical biosensor but also a simple, yet effective and general strategy for the construction and functionalization of a 3D graphene structure.

GaN/Gr (2D)/Si (3D) Combined High-Performance Hot Electron Transistors

To overcome the problem of minority carrier storage time in bipolar transistors, a hot electron transistor (HET) has been proposed. This device has the advantage of high working speed and some complex logic functions can be completed by using one component. Here, we demonstrate a mixed-dimensional HET composed of GaN/AlN microwires, graphene (Gr), and Si. The electrons between GaN/AlN are injected into graphene by an F-N tunneling mechanism to achieve high speed hot electrons, then cross graphene by ballistic transport, and are collected in a nearly lossless manner through a low-barrier Si. Therefore, the device shows a record DC gain of 16.2, a collection efficiency close to the limit of 99.9% based on the graphene hot electron transistor (GHET), an emitter current density of about 68.7 A/cm², and a high on/off current ratio reaching ∼10⁷. Meanwhile, the current saturation range is wide, beyond those of most GHETs. It has potential applications as a power amplifier.

Dual-mode frequency multiplier in graphene-base hot electron transistor

Since quantum computers have been gradually introduced in countries around the world, the development of the many related quantum components that can operate independently of temperature has become more important for enabling mature products with low power dissipation and high efficiency. As an alternative to studying cryo-CMOSs (complementary metal-oxide-semiconductors) to achieve this goal, quantum tunneling devices based on 2D materials can be examined instead. In this work, a vertical graphene-based quantum tunneling transistor has been used as a frequency modulator. The transistor can operate via different quantum tunneling mechanisms and generates, by applying the appropriate bias, voltage-resistance curves characteristic of variable nonlinear resistance for both base and emitter voltages. We experimentally demonstrate frequency modulation from input signals over the range of 100 kHz to 10 MHz, enabling a tunable frequency doubler or tripler in just a single transistor. This frequency multiplication with a tunneling mechanism makes the graphene-based tunneling device a promising option for frequency electronics in the emerging field of quantum technologies.