Abstract
Ultrafast photodetectors based on two-dimensional materials suffer from low responsivities and high dark currents. Interlayer exciton dissociation in type-II vertical heterojunctions of transition metal dichalcogenides is a viable mechanism for achieving higher responsivities with picosecond response times. Here, we propose a novel device concept based on these structures, with potential for self-powered photodetector applications characterized by an unprecedented trade-off between speed and responsivity with zero dark current. In order to assess the realistic performance to be expected in the proposed device, we have purposely devised a simulation approach able to provide a detailed investigation of the physics at play, while showing excellent predictive capabilities when compared with experiments on interlayer exciton transport available in the literature. The proposed high-performance photodetectors with tunable responsivities are at reach with available fabrication techniques and could help in paving the way towards monolithically integrated artificial neural networks for ultrafast machine vision in speed sensitive applications.
Highlights
By including the main physical phenomena of interest for interlayer exciton drift-diffusion and free-carrier transport (Fig. 1d), we show that the photodetectors here designed operate in a photovoltaic mode with zero dark current, and are characterized by picosecond response times (B4 ps) and increased responsivities (B50 mA WÀ1) compared to high-speed stateof-the-art devices employing 2D materials
Even though outstanding experimental research efforts are currently undertaken on the manipulation of exciton complexes in 2D materials, a detailed physical description of the mechanisms at play in devices based on interlayer exciton transport in van der Waals heterostructures is still lacking
We have proposed novel photodetectors through the development of a purposely devised simulation platform for interlayer exciton transport in van der Waals heterostructures of 2D materials
Summary
Two-dimensional (2D) materials have brought new perspectives to the research on photonic and optoelectronic devices, with graphene and transition metal dichalcogenides (TMDCs) as leading players.[1,2] While graphene is characterized by high carrier mobilities and proven integrability with silicon photonic platforms,[3] strong light-matter coupling and high absorptionper-layer factors turn in favor of direct bandgap TMDCs for light-detecting applications.[4,5] Several experimental works on a Dipartimento di Ingegneria dell’Informazione, University of Pisa, Pisa, Italy b Departamento de Electronica y Tecnologıa de Computadores, Universidad de Communication trade-off is aggravated by the hurdles in maintaining high responsivities without increasing the dark current, the main factor affecting sensitivity. The smallest dark currents are obtained in photovoltaic mode with zero bias, which in turn limits the responsivity of the detector. This type of operation in photovoltaic mode is ideal in terms of power consumption, allowing for the integration of devices in self-powered systems, such as photodiode arrays in artificial neural networks for machine vision applications.[10] Even though zero-bias photodetection in graphene has been achieved on a photonic defect crystal waveguide, with responsivities of 48 mA WÀ1, the reported bandwidth is limited to 18 GHz The promising optical characteristics of direct bandgap monolayer TMDCs have enabled photodetectors operating with zero dark currents and ultrafast responses in the picosecond range, though showing responsivities intrinsically limited to few mA WÀ1 (ref. 12 and 13)
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