Numerical Modelling of Terahertz Response from a HEMT Structure
Authors
Jakobsen, Kristian Nedergaard ; Larsen, Niklas Linaa
Term
4. term (FYS10)
Education
Publication year
2019
Submitted on
2019-06-10
Abstract
This thesis examines how plasma waves form in the two-dimensional electron gas (2DEG) of high electron mobility transistors (HEMTs) and how their terahertz resonance frequencies can be predicted numerically. The goal is to model a HEMT’s response to incident electromagnetic waves to determine terahertz resonances and explore how they depend on parameters such as gate length and the 2DEG depth, with a particular focus on AlGaN/GaN HEMT structures. The approach uses classical electromagnetism (Maxwell’s equations with electromagnetic boundary conditions) and Fourier analysis to develop a method for calculating the gate current. An initial point-matching scheme showed inconsistent convergence, which was significantly improved by employing second-order basis functions. The structure was also analyzed for guided modes; assuming an infinitesimally thin 2DEG, the resulting resonance frequencies agreed with those from the numerical model. Overall, the method successfully identified terahertz resonances for given structures, largely consistent with expectations; relationships between resonance frequencies, gate length, and 2DEG distance were investigated, though detailed quantitative outcomes are not provided in this excerpt.
Dette speciale undersøger, hvordan plasma-bølger opstår i to-dimensionelle elektrongasser (2DEG) i high electron mobility transistorer (HEMT), og hvordan deres resonansfrekvenser i terahertz-området kan forudsiges numerisk. Formålet er at modellere en HEMTs respons på indfaldende elektromagnetiske bølger for at bestemme terahertz-resonanser og belyse, hvordan disse afhænger af blandt andet gatens længde og afstanden til 2DEG-laget, med særligt fokus på AlGaN/GaN-HEMT-strukturer. Metodisk bygger arbejdet på klassisk elektromagnetisme (Maxwells ligninger og tilhørende randbetingelser) og Fourier-analyse og udvikler en beregningsmetode for strømmen i HEMT-gaten. En indledende point-matching-tilgang gav inkonsistent konvergens, som blev væsentligt forbedret ved at anvende andenordens basisfunktioner. Derudover blev strukturen analyseret for guidede modes; under antagelse af en uendeligt tynd 2DEG gav dette resonansfrekvenser i overensstemmelse med den numeriske model. Overordnet set lykkedes det at bestemme resonansfrekvenser i terahertz-området for givne strukturer med resultater, der i store træk matchede forventningerne; relationer mellem resonansfrekvenser, gatelængde og 2DEG-afstand blev undersøgt, men uden detaljerede kvantitative konklusioner i det foreliggende uddrag.
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