RUI: Atomically thin monolayer semiconductors for ultrasensitive UV photodetectors

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Title: Atomically thin semiconductors for ultrasensitive UV PhotodetectorsNon-technical Abstract: This research focuses on atom-thick, two-dimensional semiconductors derived from transition metal dichalcogenides (TMDs) with the ultimate goal to lay the foundation for developing an ultrasensitive, gigahertz speed photodetector in the ultraviolet (UV) range. Currently, such a semiconductor-based UV photodetector is not available, which hampers many high speed and low signal applications. TMD semiconductors reveal remarkable properties. Their unique crystal structure leads to the creation of a unique type of strongly bound excitons, known as van Hove singularity excitons that are created when a UV photon interacts with a TMD semiconductor. TMD materials will be studied to understand the basic physical properties of these excitons and to utilize them for optoelectronic applications in the UV region and ultimately for the development of a new ultrafast, fast-response, and high-sensitivity UV photodetector. This research is expected to have significant technological impacts ranging from everyday life to new communication tools. It will be conducted at a Primarily Undergraduate Institution and will involve undergraduate and Master's students and students from local high schools. The active participation in the project will provide students an excellent nanoscience research experience and an outstanding opportunity to train in nanoscale optoelectronics preparing them for careers in industry and academia. The principal investigator will reach out to the local community at the Annual Bay Area Science Festival to showcase the underlying principles of nanotechnology seeding public interest in science and encouraging young adults to pursue science degrees.Technical-Abstract: Newly developed atomically thin van der Waals crystals reveal remarkable electronic, optical, and optoelectrical properties and show great promise for the development of novel nanoscale optoelectronic devices. The goal of the project is to advance the fundamental understanding of such devices by studying the intriguing properties of monolayer transition metal dichalcogenides (TMDs). Ultimately a prototype of a nanoscale, ultrasensitive (~few photons) and fast UV photodetector will be developed by exploiting van Hove singularity assisted excitonic transitions in atomically thin monolayer TMDs derived from MoS2, MoSe2, WS2 and WSe2. The unique crystal structures of these semiconductors create a Mexican hat-like optical band structure. The joint density of states diverges at the bottom of the Mexican hat creating the van Hove singularity. The objectives of the project are: (i) Investigate the van Hove singularity assisted optoelectronic properties of monolayer TMDs derived from bulk crystals by measuring the photocurrent spectra, photoresponsivity, and time responses. (ii) Investigate the intrinsic optoelectronic properties of large-scale chemical vapor deposited TMDs and measure their photocurrent and time responses to elucidate how line defects and grain boundaries affect the optoelectronic properties. (iii) Stack monolayer TMDs to develop a UV photodetector that exhibits high absorption, a GHz photoresponse speed, and a few photon detection ability. This research will advance the fundamental understanding of novel, many-body excitonic phenomena in physics, not only in 2D systems, but also in other nanoscale systems ranging from Bose-Einstein condensation to excitonic solar cells and has great promise for the development of scalable nanophotonic devices.