Synergistic Photon Management and Strain-Induced Band Gap Engineering of Two-Dimensional MoS2 Using Semimetal Composite Nanostructures

TL;DR

This paper demonstrates a novel method using semimetal composite nanostructures to enhance light absorption and engineer the band gap of 2D MoS2, improving its performance in photonic devices through synergistic photon management and strain application.

Contribution

Introduces self-assembled semimetal nanostructures for synergistic photon management and strain-induced band gap engineering in 2D MoS2 without complex nanolithography.

Findings

Achieved >15x absorption enhancement at 650-950 nm with Sn nanodots.

Achieved 20-30x absorption enhancement at 700-900 nm with SnOx nanoneedles.

Induced up to 3.5% biaxial tensile strain, reducing band gap by ~0.35 eV.

Abstract

2D MoS2 attracts increasing attention for its application in flexible electronics and photonic devices. For 2D material optoelectronic devices, light absorption of the molecularly thin 2D absorber would be one of the key limiting factors in device efficiency, and conventional photon management techniques are not necessarily compatible with them. In this paper, we show two semimetal composite nanostructures for synergistic photon management and strain-induced band gap engineering of 2D MoS2: (1) pseudo-periodic Sn nanodots, (2) conductive SnOx (x<1) core-shell nanoneedle structures. Without sophisticated nanolithography, both nanostructures are self-assembled from physical vapor deposition. 2D MoS2 achieves up to >15x enhancement in absorption at {\lambda}=650-950 nm under Sn nanodots, and 20-30x at {\lambda}=700-900 nm under SnOx (x<1) nanoneedles, both spanning from visible to near infrared regime. Enhanced absorption in MoS2 results from strong near field enhancement and reduced MoS2 band gap due to the tensile strain induced by the Sn nanostructures, as confirmed by Raman and photoluminescence spectroscopy. Especially, we demonstrate that up to 3.5% biaxial tensile strain is introduced to 2D MoS2 using conductive nanoneedle-structured SnOx (x<1), which reduces the band gap by ~0.35 eV to further enhance light absorption at longer wavelengths. To the best of our knowledge, this is the first demonstration of a synergistic triple-functional photon management, stressor, and conductive electrode layer on 2D MoS2. Such synergistic photon management and band gap engineering approach for extended spectral response can be further applied to other 2D materials for future 2D photonic devices.