Charge Separation at Mixed-Dimensional Single and Multilayer MoS₂/Silicon Nanowire Heterojunctions

Abstract

Layered two-dimensional (2-D) semiconductors can be combined with other low-dimensional semiconductors to form nonplanar mixed-dimensional van der Waals (vdW) heterojunctions whose charge transport behavior is influenced by the heterojunction geometry, providing a new degree of freedom to engineer device functions. Toward that end, we investigated the photoresponse of Si nanowire/MoS heterojunction diodes with scanning photocurrent microscopy and time-resolved photocurrent measurements. Comparison of n-Si/MoS isotype heterojunctions with p-Si/MoS heterojunction diodes under varying biases shows that the depletion region in the p-n heterojunction promotes exciton dissociation and carrier collection. We measure an instrument-limited response time of 1 μs, which is 10 times faster than the previously reported response times for planar Si/MoS devices, highlighting the advantages of the 1-D/2-D heterojunction. Finite element simulations of device models provide a detailed understanding of how the electrostatics affect charge transport in nanowire/vdW heterojunctions and inform the design of future vdW heterojunction photodetectors and transistors.

Low‐dimensional nanomaterial/Si heterostructure‐based photodetectors

“…As a typical 2D layered TMDC, molybdenum disulfide (MoS 2 ) can be integrated with Si into a heterostructure with desirable performance. This property is consistent with the observation of the single and multilayer MoS 2 /Si nanowire heterojunction photodetector generated by Lauhon and coworkers, where the p‐n heterojunction boosted exciton dissociation and carrier collection . They also utilized finite element simulations to investigate whether electrostatics affect charge transport in heterojunctions.…”

“…Similar to graphene, TMDCs have many excellent properties, such as good mechanical flexibility and thermal stability, and have been widely used in optical and electrical devices . Although TMDCs have a lower mobility than graphene, they have higher optical absorptivity and a tunable bandgap due to the different number of layers.…”

“…Similar to graphene, TMDCs have many excellent properties, such as good mechanical flexibility and thermal stability, and have been widely used in optical and electrical devices. [76][77][78][79][80][81][82][83][84][85] Although TMDCs have a lower mobility than graphene, they have higher optical absorptivity and a tunable bandgap due to the different number of layers. As a typical 2D layered TMDC, molybdenum disulfide (MoS 2 ) can be integrated with Si into a heterostructure with desirable performance.…”

“…This property is consistent with the observation of the single and multilayer MoS 2 /Si nanowire heterojunction photodetector generated by Lauhon and coworkers, where the p-n heterojunction boosted exciton dissociation and carrier collection. 78 They also utilized finite element simulations to investigate whether electrostatics affect charge transport in heterojunctions. The photoresponse time for a multilayer MoS 2 /p-Si nanowire photodetector (<1 μs) was faster than that for the corresponding monolayer device.…”

Direct synthesis of two-dimensional MoS2 on p-type Si and application to solar hydrogen production

“…The elementary building blocks of p-n junctions are vital for semiconductor electronic devices such as integrated circuits, photodetectors, solar cells, LEDs, diodes, and transistors [20][21][22][23][24] . Recently, the integration of lowdimensional TMD materials with single-crystal traditional semiconductors (e.g., Si, GaAs, and InP) has significantly impacted the development of functional electronic devices, including field effect transistors (FETs), diodes, photodetectors, and photoelectrochemical cells 21,[25][26][27] .…”