Simulating gain and absorption spectra of InAs/GaAs quantum dot material

Jakobs, Ben 2025. Simulating gain and absorption spectra of InAs/GaAs quantum dot material. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Quantum dot structures were numerically and experimentally investigated for the purpose of modelling absorption and gain spectra for varying biases. Such models already exist for bulk or quantum well materials and are widely used to simulate photonic integrated circuits. The 8-band k.p approximation was implemented to simulate InAs quantum dots. The strain tensor and the piezoelectric potential were identified, leading to detailed descriptions of the energy levels and wavefunction of individual dots. By extrapolating the results from the simulations of individual dots the absorption of quantum dot epitaxial structures was simulated. Excellent agreement was achieved between simulation results and measured absorption, assuming the individual dots are asymmetric or two growth modes are present. A rate equation model was used in combination with a commercially available diode solver to identify the occupation probabilities of dot states. From this, modal gain was simulated, and a calibration of recombination lifetimes was employed to yield good experimental agreement. The temperature induced shift in the absorption spectrum was measured and quantified. Including temperature dependent recombination lifetimes into the gain model, the modal gain spectrum for three different samples at various temperatures was simulated. Good agreement was obtained between simulations and measurements. The impact of an electric field on different dot structures was investigated, revealing inconsistencies in their responsiveness to an electric field. In comparison to simulations, insights into the dimensions and material composition of the individual dots were obtained. The model was expanded to simulate the gain of doped dot structures. p-type modulation showed increased gain and differential gain. The presence of a n-dopant in individual quantum dots was simulated, showing an increase in transition energy and a reduction in wavefunction overlaps. The overall impact of the n-dopant on the modal gain was simulated to be minimal.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	1300 nm emission Quantum Dot 8-band k.p theory 3D Strain Solver Quantum Dots Simulated Gain Spectrum Simulated Absorption Spectrum Simulated p-doped gain Simulated n-doped quantum dot Simulated n-doped gain spectrum Segmented Contact Method
Funders:	EPSRC (CDT)
Date of First Compliant Deposit:	5 March 2026
Last Modified:	05 Mar 2026 16:50
URI:	https://orca.cardiff.ac.uk/id/eprint/185545

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