A critical challenge in modern electronics lies in achieving high-speed operation without sacrificing power efficiency or device stability. In this context, vertical graphene base hot-electron transistors (GHETs) based on van der Waals heterostructures offer a compelling solution due to their ability to exploit ballistic electron transport and quantum tunneling at the atomic scale. This study presents a tunable GHET device featuring a bilayer dielectric collector-base barrier composed of MoS₂/h-BN, enabling precise control over radio frequency (RF) performance through external bias modulation.
The device structure is built upon a heavily doped n++ silicon emitter, with a thin native SiO₂ layer (1.2 nm) serving as the emitter-base insulator (EBI). A monolayer graphene base is transferred via PMMA-assisted exfoliation and integrated into the architecture. The key innovation lies in the collector-base region, where a dual-layer insulator—first a low-barrier FL1 (MoS₂) followed by a high-resistance FL2 (h-BN)—forms a selective tunneling junction. This configuration effectively blocks cold electrons while allowing only high-energy hot carriers from the emitter to pass through, ensuring a high ON/OFF current ratio and minimal leakage.
Electrical characterization confirms that the device operates under Fowler-Nordheim tunneling dominance. At VBE > 1.08 V, the emitter current increases sharply, indicating successful injection of hot electrons. The common base current gain (*), defined as |IC|/|IE|, reaches up to 99.2% across a wide range of biases, demonstrating near-unity carrier transfer efficiency. This performance is significantly enhanced compared to earlier designs using Al₂O₃ or HfO₂ barriers, primarily due to the reduced energy barrier height difference between graphene and the MoS₂/h-BN layers (Δ = 2.56 eV vs. 3.3 eV in previous devices).
Further analysis reveals that the intrinsic current gain cutoff frequency (fT) can be tuned from 54 GHz to 65 GHz by varying the collector-base voltage (VCB).Phospho-PLC γ1 Antibody Cancer At VCB = –4.6 V, fT reaches approximately 54 GHz, while increasing VCB to –2 V or higher raises fT to 65 GHz. This tunability stems from the electric field-dependent bending of the h-BN tunneling barrier, which modulates the effective width and height of the potential barrier for hot carriers. RF measurements conducted using deembedded h-parameter analysis show a clear frequency response, with current gain H₂₁ decreasing gradually beyond 50 GHz but maintaining measurable amplification up to 65 GHz.
Energy band diagrams illustrate the transition between off-state (VCB = 0 V) and on-state (VCB = –2 V) conditions. In the off-state, the h-BN barrier remains too high for hot electrons to tunnel through, resulting in negligible collector current. Upon applying a negative VCB, the barrier bends downward, enabling hot electron transmission and triggering the on-state operation. The device’s ability to switch between states rapidly supports its suitability for high-frequency signal amplification.KLHL2 Antibody Formula
The use of atomically thin 2D materials such as MoS₂ and h-BN not only enables sub-nanometer precision in barrier engineering but also reduces parasitic capacitance and enhances thermal stability.PMID:34880106 However, device-to-device variability persists, likely due to thickness fluctuations in the native SiO₂ layer and imperfections in the MoS₂/h-BN interface. These challenges highlight the need for improved growth and transfer techniques, particularly for scalable integration.
This work demonstrates that bilayer dielectric GHETs can achieve tunable high-frequency operation exceeding 60 GHz, marking a significant step toward practical applications in millimeter-wave communication, radar systems, and ultrafast digital logic. With continued optimization of material quality and fabrication uniformity, such devices may soon enable compact, low-power, high-speed electronic platforms capable of operating in the terahertz regime.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
