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Professor Ryan Lewis, Engineering Physics, McMaster University

Event Date: 
Monday, January 28, 2019 - 3:30pm to 4:30pm

Engineering Surface and Strain Effects in Semiconductor Nanostructures

Semiconductor nanostructures—such as nanowires and quantum dots—have many conceptual advantages over conventional device structures based on planar heterostructures (planar layers grown on a bulk substrate). As the surface-to-volume ratio of nanostructures is extremely large, surface effects play a dominant role in their formation. Furthermore, the flexibility of these structures enables them to accommodate enormous strains, thus presenting exciting opportunities for manipulating material properties through unconventional strain engineering.

In this talk, I will show that strained monolayer-thick InAs films can be directed “on-demand” to reassemble into quantum dots, by exposing them to a surface-energy-modifying Bi surfactant. This effect presents a novel way to provoke and control quantum dot self-assembly. We employ this approach to realize quantum dots on GaAs surfaces on which quantum dots do not normally form. These structures are promising for applications in quantum optics.

In the second part of the talk, I will show that large strain gradients can be realized in nanowires comprising highly asymmetric core−shell heterostructures. Strain sharing across the nanowire heterostructures can bend vertical nanowires completely over to contact the substrate, presenting new possibilities for the bottom-up fabrication of nanowire biosensors and interconnects. Photoluminescence spectroscopy on bent-nanowire heterostructures reveals that strain gradients induce charge carrier drift, which can be exploited for light emission applications. These results open up new degrees of freedom for unconventional strain and device engineering.

Ryan Lewis obtained his B.Sc. (Physics) from Dalhousie University, and his M.A.Sc. (Engineering Physics) and Ph.D. (Physics) from the University of British Columbia. From 2014–2018 he was a postdoc and Alexander von Humboldt guest scientist at the Paul Drude Institute for Solid-State Electronics in Berlin, Germany. Since the fall of 2018 he has been an Assistant Professor of Engineering Physics at McMaster University. His research interests include the synthesis of semiconductor nanostructures, materials and heterostructures, and the development of optoelectronic devices and sensors based on these structures.


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