RESUMO
The combination of specific van der Waals semiconductors in vertical stacks leads to atomically sharp heterointerfaces with unique properties, offering versatility and additional functionality for thin, flexible, optoelectronic devices. In this work, we demonstrate heterostructures built from single-layer MoS2 (n-type) and multilayer FePS3 (p-type) as multifunctional p-n junctions where robust photoluminescent light emission and broadband electrical photo-response coexist. This is made possible by the inherent properties of the materials involved and the precise energy band alignment at their interface, which preserves the photoluminescent emission provided by the single-layer MoS2 and confers exceptional tunability to the system. Indeed, through small changes in the applied voltage across the junction, the interplay between photoluminescence and photocurrent generation can be tuned, allowing for a precise control of the light emission of single-layer MoS2 - from severely quenched to an order of magnitude enhancement. Additionally, the broadband photo-response of the system presents an enhanced performance under ultraviolet illumination, in contrast to other van der Waals heterostacks containing single-layer semiconductors. Furthermore, this photo-response can be adjusted by the application of an external electric field, enabling photocurrent generation under both reverse and forward bias, thereby contributing to the overall functionality and versatility of the system.
RESUMO
The absorption and emission of light in single-layer transition metal dichalcogenides are governed by the formation of excitonic quasiparticles. Strain provides a powerful technique to tune the optoelectronic properties of two-dimensional materials and thus to adjust their exciton energies. The effects of large compressive strain in the optical spectrum of two-dimensional (2D) semiconductors remain rather unexplored compared to those of tensile strain, mainly due to experimental constraints. Here, we induced large, uniform, biaxial compressive strain (â¼1.2%) by cooling, down to 10 K, single-layer WS2, MoS2, WSe2, and MoSe2 deposited on polycarbonate substrates. We observed a significant strain-induced modulation of neutral exciton energies, with blue shifts up to 160 meV, larger than in any previous experiments. Our results indicate a remarkably efficient transfer of compressive strain, demonstrated by gauge factor values exceeding previous results and approaching theoretical expectations. At low temperatures, we investigated the effect of compressive strain on the resonances associated with the formation of charged excitons. In WS2, a notable reduction of gauge factors for charged compared to neutral excitons suggests an increase in their binding energy, which likely results from the effects of strain added to the influence of the polymeric substrate.
RESUMO
Single-layer semiconducting transition metal dichalcogenides (2H-TMDs) display robust excitonic photoluminescence emission, which can be improved by controlled changes to the environment and the chemical potential of the material. However, a drastic emission quench has been generally observed when TMDs are stacked in van der Waals heterostructures, which often favor the nonradiative recombination of photocarriers. Herein, we achieve an enhancement of the photoluminescence of single-layer MoS2 on top of van der Waals FePS3. The optimal energy band alignment of this heterostructure preserves light emission of MoS2 against nonradiative interlayer recombination processes and favors the charge transfer from MoS2, an n-type semiconductor, to FePS3, a p-type narrow-gap semiconductor. The strong depletion of carriers in the MoS2 layer is evidenced by a dramatic increase in the spectral weight of neutral excitons, which is strongly modulated by the thickness of the FePS3 underneath, leading to the increase of photoluminescence intensity. The present results demonstrate the potential for the rational design of van der Waals heterostructures with advanced optoelectronic properties.