Date of Graduation

8-2023

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

Magda El-Shenawee

Committee Member

Hugh Churchill

Second Committee Member

Morgan Ware

Keywords

Antenna, EBL, LT-GaAs, Photoconductive, THz, Time-Domain Spectroscopy

Abstract

This thesis presents the fabrication and measurement of LT-GaAs based terahertz (THz) photo conductive antennas (PCAs) and arrays. The LT-GaAs THz PCAs are fabricated to serve as reference devices to new 2D material black phosphorous (BP) based THz PCAs. The LT-GaAs and BP devices have identical metallic electrodes, allowing for a comparison of emitted THz intensity and bandwidth. All PCAs have been measured using an open bench pulsed time-domain spectroscopy (TDS) system with a usable bandwidth from 0.1-4 THz, pumped with a 780nm Ti:Sapphire femtosecond laser. The results have shown LT-GaAs devices outperforming BP devices in signal amplitude and bandwidth at identical DC bias voltages and pump powers. Three other electrode shape designs were achieved: circular, slotted, and fractal, fabricated on LT-GaAs. The effect of electrode shape on the amplitude and bandwidth of the THz pulse has been experimentally characterized. A comparison of all four shapes has shown that the bowtie electrodes provide a nominal increase in pulse amplitude under identical biasing conditions. Further, a polarization study using an x-cut quartz rotator was conducted, validating that all four electrode shapes are highly linearly polarized. Results show that the co-polarized THz pulse is two orders of magnitude greater than the cross-polarized THz pulse. In addition, two element THz PCAs with electrode spacings of 75µm, 150µm, and 300µm have been investigated. A novel feed network using two beam splitters has been designed, and implemented into the existing open bench TDS system. This feed network gives individual control over the position and path length of the beams feeding each elements. Further, a DC bias splitting PCB and switchboard were designed to allow each element to be turned on and off, aiding in laser alignment validation. The measurement of all three devices have shown the array THz pulse having a higher amplitude than either individual element, however, an insignificant effect on the array bandwidth has been observed.

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