Date of Graduation

7-2021

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Degree Level

Graduate

Department

Electrical Engineering

Advisor/Mentor

El-Shenawee, Magda O.

Committee Member

Churchill, Hugh O.H.

Second Committee Member

Ware, Morgan E.

Keywords

Computational Model; Computational Physics; COMSOL Multiphysics; Optoelectronics; Photoconductive Antenna; Terahertz

Abstract

This thesis presents computational models of terahertz (THz) photoconductive antenna (PCA) emitter using COMSOL Multiphysics commercial package. A comparison of the computer simulated radiated THz signal against that of an experimentally measured signal of commercial reference LT-GaAs emitter is presented. The two-dimensional model (2D) aimed at calculating the photoconductivity of a black phosphorus (BP) PCA at two laser wavelengths of 780 nm and 1560 nm. The 2D model was applied to the BP PCA emitter and the LT-GaAs devices to compare their simulated performance in terms of the photocurrent and radiated THz signal pulse. The results showed better performance of the BP PCA compared with that of LT-GaAs emitter. The three-dimensional model (3D) improved the accuracy of the solution by eliminating some assumptions included in the 2D model of the BP PCA such as the application of the actual bowtie geometry of the electrodes and the inclusion of the distribution of the laser footprint in x- and y- directions. Furthermore, the 3D model investigated the temperature variation in the BP PCA emitter due to the Joule heating from the conduction of the current induced by the bias voltage and the laser heating produced by the electromagnetic power dissipation of the laser. However, the 3D model introduced computational challenges (i.e., solution time, CPU, and memory, RAM) because of the multi-scale nature of the BP configuration from nanoscale to microscale. The parallel version of the COMSOL package was executed on the supercomputer of XSEDE at Pittsburg and the AHPCC at the University of Arkansas to successfully overcome these challenges. This helped to simulate a large case of total number of unknown of 313, 252,784.00 that required 3,202.98 GB RAM and 25 h CPU time on XSEDE Bridges. In addition, the TeraAlign THz experimental system, purchased from TeraView, Cambridge, UK, was used to measure the THz signal radiation of the commercial LT-GaAs emitters, demonstrating good agreement in terms of the pulse width and shape.

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