Design of van der Waals Interfaces for Broad-Spectrum Optoelectronics

TL;DR

This paper demonstrates that engineering type-II van der Waals interfaces with specific band alignments enables radiative optical transitions regardless of lattice mismatch or layer alignment, broadening optoelectronic applications of 2D materials.

Contribution

It introduces a method to create vdW heterostructures with radiative interlayer transitions by selecting materials with band edges at the Γ-point, overcoming previous momentum mismatch issues.

Findings

Type-II interfaces with Γ-point band edges enable radiative transitions.

Lattice mismatch and layer misalignment do not suppress optical coupling in these structures.

The approach is robust across different material types and configurations.

Abstract

Van der Waals (vdW) materials offer new ways to assemble artificial electronic media with properties controlled at the design stage, by combining atomically defined layers into interfaces and heterostructures. Their potential for optoelectronics stems from the possibility to tailor the spectral response over a broad range by exploiting interlayer transitions between different compounds with an appropriate band-edge alignment. For the interlayer transitions to be radiative, however, a serious challenge comes from details of the materials --such as lattice mismatch or even a small misalignment of the constituent layers-- that can drastically suppress the electron-photon coupling. The problem was evidenced in recent studies of heterostructures of monolayer transition metal dichalcogenides, whose band edges are located at the K-point of reciprocal space. Here we demonstrate experimentally that the solution to the interlayer coupling problem is to engineer type-II interfaces by assembling atomically thin crystals that have the bottom of the conduction band and the top of the valence band at the $\Gamma$-point, thus avoiding any momentum mismatch. We find that this type of vdW interfaces exhibits radiative optical transition irrespective of lattice constant, rotational/translational alignment of the two layers, or whether the constituent materials are direct or indirect gap semiconductors. The result, which is robust and of general validity, drastically broadens the scope of future optoelectronics device applications based on 2D materials.