Electronic structures and optical properties of dilute nitride quantum dots

Dilute nitride III-V compounds are potential candidate materials for the next generation of telecommunication optoelectronic device such as laser and photodetector. In this thesis, we have investigated the electronic structure and optical properties of quantum dots (QDs) using eight-band or ten-band...

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Main Author: Chen, Jian
Other Authors: Fan Weijun
Format: Theses and Dissertations
Language:English
Published: 2012
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Online Access:https://hdl.handle.net/10356/50705
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-507052023-07-04T16:21:05Z Electronic structures and optical properties of dilute nitride quantum dots Chen, Jian Fan Weijun School of Electrical and Electronic Engineering DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics Dilute nitride III-V compounds are potential candidate materials for the next generation of telecommunication optoelectronic device such as laser and photodetector. In this thesis, we have investigated the electronic structure and optical properties of quantum dots (QDs) using eight-band or ten-band k.p methods with the strain distribution calculated by the valence force field (VFF) model. Because of QD’s novel electrical and optical properties and quantum confinement effects, we simulate and study these QDs for better understanding. The optical gains are calculated using the zero-dimensional optical gain formula taking into consideration inhomogeneous broadening due to QD size fluctuation. With variations of pyramidal InAs(N) QD size, shape and nitrogen(N) composition, we find that when N composition is higher, the ground state (GS) of conduction band c1 is forced to be lower so that the c1-h1 GS transition energy is less, and the intersubband energy separation c2-c1 is greater so that the higher excited states transition is harder to occur. The incorporated N can facilitate to achieve shorter emission wavelength 1.3 μm or even 1.55 μm, with higher maximum optical gain and less detrimental effect induced by higher excited state transition. If we truncate the full pyramidal shape, the QD height in z-direction is reduced. This truncation changes the strain distribution and increases the confinement in z-direction resulting in greater GS transition energy, greater transition matrix element (TME), less detrimental effect of higher excited transition, higher saturation gain and differential gain. For pyramidal InAsPN/GaP(N) QDs, with GaP barrier, for smaller InAsPN QDs, the GS transition energy is smaller at a lower phosphorus (P) composition of InAsPN. But for larger InAsPN QDs, the GS transition energy increases as P composition increases due to the increased bandgap. To obtain laser materials with a lattice constant comparable to Si, we incorporated 2% of N into GaP barrier. So the conduction band offset and the quantum confinement are reduced resulting in a smaller transition energy and longer wavelength. Meanwhile the optical gains are less than those without N in the barrier at a low carrier density, but the maximum GS optical gain increases faster and surpass to reach a greater saturation optical gain when the carrier density increases. DOCTOR OF PHILOSOPHY (EEE) 2012-09-11T04:27:38Z 2012-09-11T04:27:38Z 2011 2011 Thesis Chen, J. (2011). Electronic structures and optical properties of dilute nitride quantum dots. Doctoral thesis, Nanyang Technological University, Singapore. https://hdl.handle.net/10356/50705 10.32657/10356/50705 en 144 p. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
spellingShingle DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
Chen, Jian
Electronic structures and optical properties of dilute nitride quantum dots
description Dilute nitride III-V compounds are potential candidate materials for the next generation of telecommunication optoelectronic device such as laser and photodetector. In this thesis, we have investigated the electronic structure and optical properties of quantum dots (QDs) using eight-band or ten-band k.p methods with the strain distribution calculated by the valence force field (VFF) model. Because of QD’s novel electrical and optical properties and quantum confinement effects, we simulate and study these QDs for better understanding. The optical gains are calculated using the zero-dimensional optical gain formula taking into consideration inhomogeneous broadening due to QD size fluctuation. With variations of pyramidal InAs(N) QD size, shape and nitrogen(N) composition, we find that when N composition is higher, the ground state (GS) of conduction band c1 is forced to be lower so that the c1-h1 GS transition energy is less, and the intersubband energy separation c2-c1 is greater so that the higher excited states transition is harder to occur. The incorporated N can facilitate to achieve shorter emission wavelength 1.3 μm or even 1.55 μm, with higher maximum optical gain and less detrimental effect induced by higher excited state transition. If we truncate the full pyramidal shape, the QD height in z-direction is reduced. This truncation changes the strain distribution and increases the confinement in z-direction resulting in greater GS transition energy, greater transition matrix element (TME), less detrimental effect of higher excited transition, higher saturation gain and differential gain. For pyramidal InAsPN/GaP(N) QDs, with GaP barrier, for smaller InAsPN QDs, the GS transition energy is smaller at a lower phosphorus (P) composition of InAsPN. But for larger InAsPN QDs, the GS transition energy increases as P composition increases due to the increased bandgap. To obtain laser materials with a lattice constant comparable to Si, we incorporated 2% of N into GaP barrier. So the conduction band offset and the quantum confinement are reduced resulting in a smaller transition energy and longer wavelength. Meanwhile the optical gains are less than those without N in the barrier at a low carrier density, but the maximum GS optical gain increases faster and surpass to reach a greater saturation optical gain when the carrier density increases.
author2 Fan Weijun
author_facet Fan Weijun
Chen, Jian
format Theses and Dissertations
author Chen, Jian
author_sort Chen, Jian
title Electronic structures and optical properties of dilute nitride quantum dots
title_short Electronic structures and optical properties of dilute nitride quantum dots
title_full Electronic structures and optical properties of dilute nitride quantum dots
title_fullStr Electronic structures and optical properties of dilute nitride quantum dots
title_full_unstemmed Electronic structures and optical properties of dilute nitride quantum dots
title_sort electronic structures and optical properties of dilute nitride quantum dots
publishDate 2012
url https://hdl.handle.net/10356/50705
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