Short-wave infrared photocurrent spectroscopy to probe narrow-gap 2D materials

Abstract The capability of characterizing low-bandgap two-dimensional (2D) materials is crucial for a wide range of applications from fundamental science to commercial implementation. Current techniques rely heavily on expensive characterization equipment and thus hinder focused research on low-bandgap materials, compared to their counterparts in the visible range of the electromagnetic spectrum. This work demonstrates a cost-efficient and easily rebuildable optical setup to probe low-bandgap 2D materials using photocurrent spectroscopy. The heart of the setup consists of a supercontinuum laser in combination with a diffraction grating to create a tunable light source working from 500 to 2000 nm, allowing to access bandgaps in the short-wave infrared (IR), far from what is possible using standard silicon detector technology. Apart from a complete technical guide to facilitate reproduction of the system, two popular narrow-gap materials (MoTe 2 and black phosphorus) have been studied to extract bandgaps and excitonic features of these materials. The results highlight the simple, yet powerful approach of utilizing photocurrent spectroscopy in the IR and thus expanding the analysis toolbox for narrow-gap 2D semiconductor research.