A Ballistic Two-Dimensional Lateral Heterojunction Bipolar Transistor

TL;DR

This paper introduces a monolayer ballistic heterojunction bipolar transistor using 2D transition metal dichalcogenides, demonstrating high current modulation and potential for THz frequency operation without the need for gates.

Contribution

It presents the first detailed simulation and analysis of a monolayer lateral heterostructure bipolar transistor based on 2D materials, highlighting its intrinsic thinness and high performance.

Findings

Achieves I_ON/I_OFF ratio of ~10^8

Demonstrates current gain β~10^4

Predicts cutoff frequency in the THz range

Abstract

We propose and investigate the intrinsically thinnest transistor concept: a monolayer ballistic heterojunction bipolar transistor based on a lateral heterostructure of transition metal dichalcogenides. The device is intrinsically thinner than a Field Effect Transistor because it does not need a top or bottom gate, since transport is controlled by the electrochemical potential of the base electrode. As typical of bipolar transistors, the collector current undergoes a tenfold increase for each 60 mV increase of the base voltage over several orders of magnitude at room temperature, without sophisticated optimization of the electrostatics. We present a detailed investigation based on self-consistent simulations of electrostatics and quantum transport for both electron and holes of a pnp device using MoS$_2$ for the 10-nm base and WSe$_2$ for emitter and collector. Our three-terminal device simulations confirm the working principle and a large current modulation I$_\text{ON}$/I$_\text{OFF}\sim 10^8$ for $\Delta V_{\rm EB}=0.5$ V. Assuming ballistic transport, we are able to achieve a current gain $\beta\sim$ 10$^4$ over several orders of magnitude of collector current and a cutoff frequency up to the THz range. Exploration of the rich world of bipolar nanoscale device concepts in 2D materials is promising for their potential applications in electronics and optoelectronics.