Abstract
Van der Waals materials with narrow energy gaps and efficient response over a broadband optical spectral range are key to widen the energy window of nanoscale optoelectronic devices. Here, we characterize FePS3 as an appealing narrow-gap p-type semiconductor with an efficient broadband photo-response, a high refractive index, and a remarkable resilience against air and light exposure. To enable fast prototyping, we provide a straightforward guideline to determine the thickness of few-layered FePS3 nanosheets extracted from the optical transmission characteristics of several flakes. The analysis of the electrical photo-response of FePS3 devices as a function of the excitation energy confirms a narrow gap suitable for near IR detection (1.23 eV) and, more interestingly, reveals a broad spectral responsivity up to the ultraviolet region. The experimental estimate for the gap energy is corroborated by ab-initio calculations. An analysis of photocurrent as a function of gate voltage and incident power reveals a photo-response dominated by photogating effects. Finally, aging studies of FePS3 nanosheets under ambient conditions show a limited reactivity of the outermost layers of flakes in long exposures to air.
Highlights
Two-dimensional crystals (2D materials), owning strong in-plane covalent bonds and weak van der Waals interlayer interactions, have attracted big attention since the isolation of graphene sheets by exfoliation of bulk graphite[1]
The family of transition metal dichalcogenides (TMDCs) has been of great interest for optoelectronic applications owing to their intrinsic bandgap in the visible range and their strong luminescent excitonic features[2,3,4]
A very simple method to estimate the thickness of layered material flakes consists in the comparison of the relative transmittance images[19] through their comparison to atomic force microscopy (AFM)
Summary
Two-dimensional crystals (2D materials), owning strong in-plane covalent bonds and weak van der Waals interlayer interactions, have attracted big attention since the isolation of graphene sheets by exfoliation of bulk graphite[1]. We report on the photo-response of a few-layer FePS3 field-effect device in the UV–VIS–NIR spectral range and we determine the bandgap of this material toward the two-dimensional limit.
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