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Mid-infrared plasmonics
Title
Mid-infrared plasmonics.
Creator
Khalilzadeh Rezaie, Farnood, Peale, Robert, Ishigami, Masa, Schoenfeld, Winston, Buchwald, Walter, Abdolvand, Reza, University of Central Florida
Abstract / Description
This dissertation reports investigations into materials for, and applications of, infrared surface plasmon polaritons (SPP). SPPs are inhomogeneous electromagnetic waves that are bound to the surface of a conductor. Tight confinement of electromagnetic energy, the primary virtue of SPPs for so-called (")plasmonic(") applications, requires plasma frequencies for the conductor near the intended infrared operational frequencies. This requires carrier concentrations that are much less than those...
Show moreThis dissertation reports investigations into materials for, and applications of, infrared surface plasmon polaritons (SPP). SPPs are inhomogeneous electromagnetic waves that are bound to the surface of a conductor. Tight confinement of electromagnetic energy, the primary virtue of SPPs for so-called (")plasmonic(") applications, requires plasma frequencies for the conductor near the intended infrared operational frequencies. This requires carrier concentrations that are much less than those of usual metals such as gold and silver. I have investigated the optical properties and SPP excitation resonances of two materials having infrared plasma frequencies, namely the semimetal bismuth and the transparent conducting fluorine-doped tin-oxide (FTO). The complex permittivity spectra for evaporated films of Bi were found to be distinctly different than earlier reports for crystal or polycrystalline films, and SPP excitation resonances on Bi-coated gratings were found to be disappointingly broad. Permittivity spectra for chemical spray deposited FTO were obtained to long-wave IR wavelengths for the first time, and nano-crystalline FTO-coated silicon lamellar gratings show remarkable conformity. SPP excitation resonances for FTO are more promising than for Bi. Thus, FTO appears to be a promising SPP host for infrared plasmonics, e.g. a planer waveguide plasmonic spectral sensor, whose design was elaborated and investigated as part of my research and which requires SPP-host coating on deep vertical side walls of a trench-like analyte interaction region. Additionally, FTO may serve as a useful conducting oxide for a near-IR plasmonic spectral imager that I have investigated theoretically.
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Date Issued
2015
Identifier
CFE0006222, ucf:51080
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006222
TERAHERTZ AND SUB-TERAHERTZ TUNABLE RESONANT DETECTORS BASED ON EXCITATION OF TWO DIMENSIONAL PLASMONS IN InGaAs/InP HEMTs
Title
TERAHERTZ AND SUB-TERAHERTZ TUNABLE RESONANT DETECTORS BASED ON EXCITATION OF TWO DIMENSIONAL PLASMONS IN InGaAs/InP HEMTs.
Creator
Nader Esfahani, Nima, Peale, Robert, Ishigami, Masa, Del Barco, Enrique, Buchwald, Walter, University of Central Florida
Abstract / Description
Plasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases,...
Show morePlasmons can be generated in the two dimensional electron gas (2DEG) of grating-gated high electron mobility transistors (HEMTs). The grating-gate serves dual purposes, namely to provide the required wavevector to compensate for the momentum mismatch between the free-space radiation and 2D-plasmons, and to tune the 2DEG sheet charge density. Since the plasmon frequency at a given wavevector depends on the sheet charge density, a gate bias can shift the plasmon resonance. In some cases, plasmon generation results in a resonant change in channel conductance which allows a properly designed grating-gated HEMT to be used as a voltage-tunable resonant detector or filter. Such devices may find applications as chip-scale tunable detectors in airborne multispectral detection and target tracking.Reported here are investigations of InGaAs/InP-based HEMT devices for potential tunable resonant sub-THz and THz detectors. The HEMTs were fabricated from a commercial double-quantum well HEMT wafer by depositing source, drain, and semi-transparent gate contacts using standard photolithography processes. Devices were fabricated with metalized transmission gratings with multiple periods and duty cycles. For sub-THz devices, grating period and duty cycle were chosen to be 9 ?m and 22%, respectively; while they were chosen to be 0.5 ?m and 80% for the THz device. The gratings were fabricated on top of the gate region with dimensions of 250 ?m (&)#215; 195 ?m.The resonant photoresponse of the larger grating-period HEMT was investigated in the sub-THz frequency range of around 100 GHz. The free space radiation was generated by an ultra-stable Backward Wave Oscillator (BWO) and utilized in either frequency modulation (FM), or amplitude modulation (AM) experiments. The photoresponse was measured at 4K sample temperature as the voltage drop across a load resistor connected to the drain while constant source-drain voltages of different values, VSD, were applied. The dependence of such optoelectrical effect to polarization of the incident light, and applied VSD is studied. The results of AM and FM measurements are compared and found to be in agreement with the calculations of the 2D-plasmon absorption theory, however, a nonlinear behavior is observed in the amplitude and the line-shape of the photoresponse for AM experiments. For detection application, the minimum noise-equivalent-power (NEP) of the detector was determined to be 235 and 113 pW/Hz1/2 for FM and AM experiments, respectively. The maximum responsivity of the detector was also estimated to be ~ 200 V/W for the two experiments. The far-IR transmission spectra of the device with nanometer scale period was measured at 4 K sample temperature for different applied gate voltages to investigate the excitation of 2D-plasmon modes. Such plasmon resonances were observed, but their gate bias dependence agreed poorly with expectations.
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Date Issued
2014
Identifier
CFE0005386, ucf:50461
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005386