Simulation of optical and electronic characteristics of terahertz quantum cascade laser

Nowadays terahertz spectroscopy is fast becoming a method of choice both in industrial and security applications. This spectroscopic method requires a device that produces broadband THz radiation. Currently one of the techniques used to generate this radiation is by using a heterogeneous AlGaAs/GaAs...

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Main Author:	Mohd. Akil, Mohd. Asmu'i
Format:	Thesis
Language:	English
Published:	2021
Subjects:	QC Physics
Online Access:	http://eprints.utm.my/id/eprint/101845/1/MohdAsmuiMohdPFS2021.pdf
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spelling	my-utm-ep.1018452023-07-22T02:55:18Z Simulation of optical and electronic characteristics of terahertz quantum cascade laser 2021 Mohd. Akil, Mohd. Asmu'i QC Physics Nowadays terahertz spectroscopy is fast becoming a method of choice both in industrial and security applications. This spectroscopic method requires a device that produces broadband THz radiation. Currently one of the techniques used to generate this radiation is by using a heterogeneous AlGaAs/GaAs terahertz quantum cascade laser (THz QCL). Typically the device combines a few independent designs of active region that needs to be fabricated using very special, costly instruments and tested several times to improve its performance. A simulation model is critically needed to study the electronic transport properties of the individual designs and the optical performance of the waveguide used to support the broadband operation. Therefore the aim of this work is to establish a new model to study the electronic transport properties of four (4) experimentally established designs using the density matrix (DM) method and the optical characteristics of a narrow double metal waveguide using the finite element (FE) method. From these calculations several critical characteristics of THz QCL such as the threshold current densities, the average gain, the gain spectra, the optical mode confinement factor and the figure of merit (F.O.M) can be determined and their dependence on relevant design parameters can be studied. The results from the DM calculations show that the threshold current densities for these individual designs are in the range of 350 to 600 A cm-2 with the average gain of about 20 cm-1 and 100 cm-1, without and with the stimulated emission respectively. The calculated gain spectra exhibit Lorentzian pattern over a frequency range of 1 to 5 THz. The gain spectrum of the whole system based on a combination of each individual gain spectra leads to a bandwidth of around 3 THz which is bigger than the reported bandwidth from previous experimental broadband QCL designs. Meanwhile, the result from FE method for the calculated confinement factor value obtained for the waveguide increases from 90 % to 100 % in frequency range of 2 to 4 THz. The combined effects of all the design parameters lead to a figure of merit (F.O.M) that decreases with the increase of the operating frequency. As a conclusion, a reliable prediction tool based on the DM method and FE method has been demonstrated whereby it can be used not only as a guide for broadband QCL design but also to simulate its performance before the actual design is to be fabricated. 2021 Thesis http://eprints.utm.my/id/eprint/101845/ http://eprints.utm.my/id/eprint/101845/1/MohdAsmuiMohdPFS2021.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:147016 phd doctoral Universiti Teknologi Malaysia, Faculty of Science Faculty of Science
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	QC Physics
spellingShingle	QC Physics Mohd. Akil, Mohd. Asmu'i Simulation of optical and electronic characteristics of terahertz quantum cascade laser
description	Nowadays terahertz spectroscopy is fast becoming a method of choice both in industrial and security applications. This spectroscopic method requires a device that produces broadband THz radiation. Currently one of the techniques used to generate this radiation is by using a heterogeneous AlGaAs/GaAs terahertz quantum cascade laser (THz QCL). Typically the device combines a few independent designs of active region that needs to be fabricated using very special, costly instruments and tested several times to improve its performance. A simulation model is critically needed to study the electronic transport properties of the individual designs and the optical performance of the waveguide used to support the broadband operation. Therefore the aim of this work is to establish a new model to study the electronic transport properties of four (4) experimentally established designs using the density matrix (DM) method and the optical characteristics of a narrow double metal waveguide using the finite element (FE) method. From these calculations several critical characteristics of THz QCL such as the threshold current densities, the average gain, the gain spectra, the optical mode confinement factor and the figure of merit (F.O.M) can be determined and their dependence on relevant design parameters can be studied. The results from the DM calculations show that the threshold current densities for these individual designs are in the range of 350 to 600 A cm-2 with the average gain of about 20 cm-1 and 100 cm-1, without and with the stimulated emission respectively. The calculated gain spectra exhibit Lorentzian pattern over a frequency range of 1 to 5 THz. The gain spectrum of the whole system based on a combination of each individual gain spectra leads to a bandwidth of around 3 THz which is bigger than the reported bandwidth from previous experimental broadband QCL designs. Meanwhile, the result from FE method for the calculated confinement factor value obtained for the waveguide increases from 90 % to 100 % in frequency range of 2 to 4 THz. The combined effects of all the design parameters lead to a figure of merit (F.O.M) that decreases with the increase of the operating frequency. As a conclusion, a reliable prediction tool based on the DM method and FE method has been demonstrated whereby it can be used not only as a guide for broadband QCL design but also to simulate its performance before the actual design is to be fabricated.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Mohd. Akil, Mohd. Asmu'i
author_facet	Mohd. Akil, Mohd. Asmu'i
author_sort	Mohd. Akil, Mohd. Asmu'i
title	Simulation of optical and electronic characteristics of terahertz quantum cascade laser
title_short	Simulation of optical and electronic characteristics of terahertz quantum cascade laser
title_full	Simulation of optical and electronic characteristics of terahertz quantum cascade laser
title_fullStr	Simulation of optical and electronic characteristics of terahertz quantum cascade laser
title_full_unstemmed	Simulation of optical and electronic characteristics of terahertz quantum cascade laser
title_sort	simulation of optical and electronic characteristics of terahertz quantum cascade laser
granting_institution	Universiti Teknologi Malaysia, Faculty of Science
granting_department	Faculty of Science
publishDate	2021
url	http://eprints.utm.my/id/eprint/101845/1/MohdAsmuiMohdPFS2021.pdf
_version_	1776100785368596480

Simulation of optical and electronic characteristics of terahertz quantum cascade laser

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