Development of tunnel field effect optoelectronic devices based on stacked 2D crystals with clean interfaces

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Nontechnical:Optical communication is based on converting electrical signals into optical signals by optoelectronic devices such as lasers and photodiodes. Devices based on conventional semiconductors such as silicon are reaching the ultimate limits for performance. New materials and structures are required to advance the state of the art. The discovery of graphene, a two-dimensional (2D) layer of carbon, shows how new electronic properties emerge when a bulk material is thinned down to a single layer. Other 2D materials include boron nitride, black phosphorous, and transition metal dichalcogenides. Different 2D materials can be assembled one layer at a time into vertically stacked thin films. Such heterostructures can achieve functions and performance not possible with a single material. The interface between different 2D materials is critical to maintaining the unique properties that make them attractive for device applications. The principal investigator will use a newly developed clean-transfer method to prepare 2D heterostructure materials with clean interfaces. A custom-built scanning probe microscope with nanometer-scale light sources at the tip will be used to study the optical and electronic properties of devices with unprecedented resolution. Results from this project will enrich the understanding of these materials and accelerate the development of nanoscale optoelectronics. This interdisciplinary project will integrate research into education of graduate and undergraduate students in material science, engineering, and nanomanufacturing. This project will also seek to broaden participation in science, technology, engineering and mathematics.Technical:This proposal will combine novel 2D-heterostructure material preparation techniques, near-field scanning optics microscopy and near-field scanning photocurrent microscopy to investigate the fundamental optoelectronic properties and photocarrier behaviors in van der Waals material-based heterostructures. The photocurrent imaging with high spatial resolution, below 10nm, can reveal rich physics in nanoscale features. These include local pn-junctions, domain boundaries, edges, dopants, and strains. Imaging such features can significantly improve the understanding and enhance the control of the electronic and photonic properties of this new material system. The objectives of this project are to: (1) demonstrate a prototype tapping-mode near-field scanning photocurrent microscopy to investigate heterostructure devices, (2) improve the spatial resolution of scanning photocurrent imaging technique to sub-10nm level, and (3) study the photoresponsivity of vertically-stacked heterostructures based on graphene, boron nitrides, transmission metal dichalcogenides such as WSe2, MoS2, and MoSe2, and (4) develop fundamental understanding of the roles of nanoscale features, such as edge terminations and interlayer defect formation on the optoelectronic properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.