Abstract

In recent years we have witnessed an explosion of interest in two dimensional (2D) materials, due to their unique physical properties. Excitement surrounds the promise of replacing conventional bulk photodetectors with devices based on 2D materials, allowing better integration, flexibility and potentially improving performance. However, the low inherent light absorption of 2D materials is an outstanding issue to be solved. In this chapter we review two independent approaches to tackling this problem, which have the potential to be combined to find a robust solution. The first approach involves patterning the substrate with a rod-type photonic crystal (PhC) cavity structure, which is shown to increase the light absorption into a 2D material flake coupled spatially to the cavity mode. Secondly, we review 2D–compatible solid immersion lenses (SILs) and their ability to increase both the optical magnification of the structures they encapsulate, and the longevity of the material. SILs have been shown to reduce the requirements for complex optics in the implementation of 2D materials in optoelectronic devices, and also in preserving the photodetector’s optical performance over long periods of time. Finally, we show how by combining rod-type PhC cavities with SILs, we can improve the performance of 2D material-based photodetectors.

Highlights

  • Two-dimensional transition metal dichalcogenides (TMDs) are a class of semiconducting materials, which can be exploited for a range of diverse applications [1]

  • S-solid immersion lenses (SILs) have a higher magnification than hemispherical shape (h-SILs), scaling as the refractive index of the SIL squared as opposed to a direct linear relationship for a h-SIL

  • For optimum efficiency, our proposed scheme for a 2D material based photodetector involves the transfer of a flake on top of a rod-type photonic crystal (PhC) cavity, and spatial coupling of the monolayer and the cavity mode maximum via the flake’s declining into the cavity structure

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Summary

Introduction

Two-dimensional transition metal dichalcogenides (TMDs) are a class of semiconducting materials, which can be exploited for a range of diverse applications [1]. Sobhani et al in [23] have observed that by tuning plasmonic core-shell nanoparticles to the direct bandgap of monolayer MoS2 and depositing them sparsely onto the monolayer’s surface, the photocurrent achieved through the monolayer increases 3-fold, promising a model for more sensitive TMD based photodetectors Other structures such as nanocubes [27] and bowtie antennae [28, 29] have been utilized for enhancing light emission, resulting in up to 2000 fold increase in material’s absorption. A rod-type PhC is used to achieve an increased light to monolayer coupling This PhC can be combined with a high refractive index solid immersion lens (SIL) [34, 35], which is placed directly above the cavity. We discuss how the combination of the two structures can provide an efficient optical package for use in photodetection

Coupling 2D materials to photonic crystals
Photonic crystal cavity design
Enhancing light collection using photopolymer lenses
SIL fabrication
Enhanced light coupling
Improved device longevity
Findings
Conclusions and outlook

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