Quantum oscillation in carrier transport in two-dimensional junctions

TL;DR

This paper reveals that most 2D device structures inherently form lateral monolayer-bilayer-monolayer junctions, leading to quantum oscillations in carrier transmission due to potential wells, which are crucial for device design.

Contribution

It demonstrates that 2D devices act as lateral junctions with quantum wells affecting transport, challenging the belief that vertical structures function as vertical junctions.

Findings

Quantum oscillations in transmission coefficients are observed.

Potential wells in bilayer regions influence charge transport.

Vertical electric fields can tune quantum transmission.

Abstract

Two-dimensional (2D) device structures have recently attracted considerable attention. Here, we show that most 2D device structures, regardless vertical or lateral, act as a lateral monolayer-bilayer-monolayer junction in their operation. In particular, a vertical structure cannot function as a vertical junction as having been widely believed in the literature. Moreover, due to a larger electrostatic screening, the bilayer region in the junction always has a smaller band gap than its monolayer counterpart. As a result, a potential well, aside from the usual potential barrier, will form universally in the bilayer region to affect the hole or electron quantum transport in the form of transmission or reflection. Taking black phosphorus as an example, we show that an oscillation in the transmission coefficient can be clearly resolved in a two-electrode prototypical device by non-equilibrium Green function combined with density functional theory calculations and the results can be qualitatively understood using a simple quantum well model. The presence of the quantum well is vital to 2D device design, including the effective tuning of quantum transmission by a vertical electric field.