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Graduate Student Seminar - 11/17/2017

"Hot carrier generation in nanoscale optical coatings for short wavelength infrared photodetection"

by Lisa Krayer

Friday, November 17, 2017 -- 12:00 p.m.
Large Conference Room, 1207 Energy Research Facility

Advisor:  Associate Professor Jeremy Munday

Abstract: Optical confinement in nanometer scale films through excitation of zeroth order Fabry-Perot (FP) modes has recently been utilized to obtain tunable, high absorption in ultra-thin semiconductor films on metal substrates. Here we propose and experimentally demonstrate an alternative material system that enables hot carrier generation and photon detection in the short wavelength infrared based on this phenomenon. We extend the bandwidth of traditional semiconductor devices through absorption and hot carrier generation in nanoscale metal contacts. While plasmonic nanostructures have been shown to enable sub-bandgap photodetection in semiconductors, their fabrication often requires costly lithography processes and are difficult to incorporate into commercial devices. Our proposed device is enabled by simple, lithography free fabrication and is compatible with commercial processes. By selecting metals with approximately equal real and imaginary components of their refractive index (n ~ k for m = n + ik), it is possible to absorb ~80% of the broadband, sub-bandgap radiation in planar films as thin as 10 nm. The absorbed photons excite hot carriers that are injected into the semiconductor, enabling photocurrent generation from light with energy below the semiconductor bandgap energy.

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