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Optimizations of structured MXene surfaces for THz polarization and plasmonic photodetection applications
Thesis   Open access

Optimizations of structured MXene surfaces for THz polarization and plasmonic photodetection applications

Mostafa K. Ismail
Master of Science (M.S.), Drexel University
Jun 2020
DOI:
https://doi.org/10.17918/00000158
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Abstract

Optical detectors Plasmonics Polarizers (Light)
Structured metasurfaces such as periodic surfaces enable unique applications including polarization and photodetection of electromagnetic waves. Polarizers are used in semiconductor lasers, integrated isolators, fiber-optic sensor, photodiode, light-emitting diode, and imaging sensors. In this thesis we examine the use of these structures as wire grid polarizers (WGPs) which are linear polarizers that pass only transverse magnetic (TM) waves and are usually made with gold or other metals This research uses the recently discovered 2D material - MXene - which can be an excellent candidate material for WGPs. MXenes are relatively cheap, easy and facile to be fabricated and can be used for terahertz frequency polarization. MXene-based WGP (MX-WGP) can also be integrated in photonic devices due to their planar two-dimensional structure. Several devices were fabricated and tested using Terahertz time-domain spectroscopy (THz-TDS). The results of this simple fabrication process were promising and show that these MX-WGPs perform well and give extinction ratio (ER) of up to 5 dB. Simulations using finite-difference time-domain (FDTD) were done to optimize the MX-WGP by enhancing the extinction ratios. The optimization shows that with proper geometry an ER of about 32 dB, which is 226 times more than the best presently fabricated device, is possible. This allows for further optimization and fabrication of better MX-WGP that can compete commercially with the existing metal based WGP. A second application discussed in this thesis is the enhancement of sensitivity of the metal-semiconductor-metal (MSM) photodetectors using plasmonic MXene structures acting as lenses. The need for high speed photodetectors, which converts optical signals to electrical signals, is booming especially for applications in Internet of Things (IOT), virtual reality, autonomous vehicles, and artificial intelligence. The MXene lenses can couple photons to plasmons causing the surface plasmon polariton (SPP) waves to travel at the interface between the metal and the dielectric (air). This waveguiding technique results in an increase of transmission of TM waves in the active area of the MSM. Simulations are performed in order to optimize the integrated plasmonic MXene lens resulting in about 3 times more transmission in the active area hence substantial increase in device sensitivity while maintaining its speed of response.

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