Electrical and Electronic Engineering - Research Publications
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ItemElectrical tuning of reflectance of graphene metasurface for unpolarized long wavelength infrared light(OSA, 2018-01-01)We demonstrate a graphene-metal metasurface for unpolarized long wavelength infrared light with electrically-tunable reflectance. By applying a gate voltage, we shift the wavelength of a resonant reflectance dip centered at ~9.4 micron by~156 nm.
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ItemMid-infrared Magnetic Mirror Based on a Hybrid Metal/Dielectric Metasurface(IEEE, 2018)We propose a hybrid metal/dielectric metasurface that functions as a mid-infrared magnetic mirror. It consists amorphous silicon cuboids on gold. The physical mechanism is explained by image theory. Measured reflection spectra agree with simulations.
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ItemNanostructured Fishnet Silicon Photodetector Pixels as a Fully-Contained Microspectrometer Chip(IEEE, 2018)We experimentally demonstrate a microspectrometer comprising twenty silicon photodetector pixels, whose responsivities are engineered via nanostructured fishnet patterns. We computationally reconstruct the spectrum of light that illuminates the chip from the measured pixel photocurrents.
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ItemSolution-Synthesized High-Mobility Tellurium Nanoflakes for Short-Wave Infrared Photodetectors(AMER CHEMICAL SOC, 2018-07)Two-dimensional (2D) materials, particularly black phosphorus (bP), have demonstrated themselves to be excellent candidates for high-performance infrared photodetectors and transistors. However, high-quality bP can be obtained only via mechanical exfoliation from high-temperature- and high-pressure-grown bulk crystals and degrades rapidly when exposed to ambient conditions. Here, we report solution-synthesized and air-stable quasi-2D tellurium (Te) nanoflakes for short-wave infrared (SWIR) photodetectors. We perform comprehensive optical characterization via polarization-resolved transmission and reflection measurements and report the absorbance and complex refractive index of Te crystals. It is found that this material is an indirect semiconductor with a band gap of 0.31 eV. From temperature-dependent electrical measurements, we confirm this band-gap value and find that 12 nm thick Te nanoflakes show high hole mobilities of 450 and 1430 cm2 V-1 s-1 at 300 and 77 K, respectively. Finally, we demonstrate that despite its indirect band gap, Te can be utilized for high-performance SWIR photodetectors by employing optical cavity substrates consisting of Au/Al2O3 to dramatically increase the absorption in the semiconductor. By changing the thickness of the Al2O3 cavity, the peak responsivity of Te photoconductors can be tuned from 1.4 μm (13 A/W) to 2.4 μm (8 A/W) with a cutoff wavelength of 3.4 μm, fully capturing the SWIR band. An optimized room-temperature specific detectivity ( D*) of 2 × 109 cm Hz1/2 W-1 is obtained at a wavelength of 1.7 μm.
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ItemHigh-resolution mid-infrared spectral reconstruction using a subwavelength coaxial aperture array(OSA & IEEE, 2019-01-01)We demonstrate mid-infrared computational spectroscopy using an array of coaxial aperture filters. We experimentally determine material transmission spectra using an algorithm whose inputs are the transmission spectra and the power transmitted through each filter.
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ItemMachine learning design of plasmonic apertures for optical nanotweezers(OSA, 2019-01-01)We present a new approach to design plasmonic structures for optical trapping. Using a simulated annealing algorithm, the shape of a nanoaperture is optimized. An order of magnitude increase in trapping potential is predicted.
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ItemMid-infrared computational spectroscopy with an electrically-tunable graphene metasurface(OSA - Optical Society of America, 2019-01-01)We demonstrate graphene-plasmonic metasurfaces whose mid-infrared reflection spectra are electrically-tunable. Using measurements of the power reflected by the metasurfaces at different drive voltages, the source spectrum is computationally reconstructed by the recursive least squares method.
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ItemNanostructured all-Silicon Photodetector Pixels with Tailored Responsivity Spectra(SPIE-INT SOC OPTICAL ENGINEERING, 2019)We experimentally demonstrate nanostructured silicon photodetectors which consist of subwavelength arrays of verticallyoriented waveguides etched into a P-I-N photodiode. Our device combines both spectral-filtering and photocurrentgeneration in one all-Si structure. We show that absorption and responsivity spectra of these nanophotonic devices can be tuned by appropriate geometric design.
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ItemVertically stacked silicon nanowire photodetectors for spectral reconstruction(OSA & IEEE, 2019-01-01)We experimentally demonstrate the use of vertically stacked silicon nanowire photodetectors for computational spectral reconstruction at visible wavelengths. The method is based on the photodetectors having tailored responsivity spectra, achieved by standard nanofabrication processes.