Esaki diodes in van der Waals heterojunctions with broken-gap energy band alignment

TL;DR

This paper demonstrates room temperature Esaki tunnel diodes in van der Waals heterostructures of black phosphorus and tin diselenide, revealing negative differential resistance due to electron tunneling, confirmed by experiments and theoretical modeling.

Contribution

First realization of room temperature Esaki diodes in vdW heterostructures with broken-gap band alignment, advancing understanding and potential applications of 2D layered materials.

Findings

Negative differential resistance observed at room temperature

Excellent agreement between experimental data and theoretical model

Broken-gap band alignment confirmed by photoresponse and TEM

Abstract

Van der Waals (vdW) heterojunctions composed of 2-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibit novel physics phenomena that can power high performance electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature (RT) Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions, and widen the potential applications base of 2D layered materials.