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1
Blenkhorn, William Eric. "Optical studies of polar InGaN/GaN quantum well structures." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-polar-ingangan-quantum-well-structures(7f610cae-ba98-44d8-ae54-dbc4c44725d4).html.
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In this thesis, I will present and discuss research performed on InGaN/GaN multiple quantum well (QW) structures. The results of which were taken using photoluminescence (PL) spectroscopy and PL time decay spectroscopy. In the first two experimental chapters, I report on the effects of QW growth methodology on the optical properties of c-plane InGaN/GaN QWs. I compare structures grown using the single temperature (1T), quasi-two temperature (Q2T), temperature bounced (T-bounced) and two temperature (2T) QW growth methodologies. The T-bounced and 2T structures are observed to have gross well width fluctuations (GWWF), where the QW width varies from 0 to 100 % created when the QWs are exposed to a temperature ramp. Whereas, the 1T and Q2T structures have continuous QWs with only one or two monolayer well width fluctuations. The structures with GWWFs are observed to have a larger room temperature internal quantum efficiency (RT-IQE) at low excitation conditions i.e. below efficiency droop compared to those without. The larger RT-IQE is ascribed to several factors which include an increased radiative recombination rate, increased thermal activation energy of non-radiative recombination and reduced defect density of the QWs. The effect of barrier growth temperature is also investigated. No clear trend is observed between barrier growth temperature and RT-IQE.In the last experimental chapter I report on studies of carrier localisation in InGaN/GaN QWs using resonant PL spectroscopy. The effect of carrier localisation on the independently localised electrons and holes are investigated and the resonant PL spectrum is studied in detail. The InGaN/GaN QW structure is observed to exhibit an effective mobility edge at 12 K where delocalised carriers are created above a particular excitation energy. The emission from the resonantly excited localised states which are accompanied by the emission of a longitudinal optical phonon (resonant LO feature) is investigated as a function of temperature and excitation energy. The integrated PL intensity of the resonant LO feature is observed to quench rapidly with temperature up to around 45 K, independent of excitation energy. The integrated PL intensity of the resonant LO feature is fitted to an Arrhenius model and a thermal activation energy of ∼ 1(±1) meV is extracted. This activation energy is speculated to be consistent with the localisation energy of electrons.
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Guptah, Vinod Kumar. "Growth on patterned substrates for optoelectronic device applications." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267027.
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Barnes, Jennifer M. "An experimental and theoretical study of GaAs/InGaAs quantum well solar cells and carrier escape from quantum wells." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319305.
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Höglund, Linda. "Growth and characterisation of InGaAs-based quantum dots-in-a-well infrared photodetectors." Doctoral thesis, Linköpings universitet, Materiefysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15774.
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This thesis presents results from the development of quantum dot (QD) based infrared photodetectors (IPs). The studies include epitaxial growth of QDs, investigations of the structural, optical and electronic properties of QD-based material as well as characterisation of the resulting components. Metal-organic vapour phase epitaxy is used for growth of self-assembled indium arsenide (InAs) QDs on gallium arsenide (GaAs) substrates. Through characterisation by atomic force microscopy, the correlation between size distribution and density of quantum dots and different growth parameters, such as temperature, InAs deposition time and V/III-ratio (ratio between group V and group III species) is achieved. The V/III-ratio is identified as the most important parameter in finding the right growth conditions for QDs. A route towards optimisation of the dot size distribution through successive variations of the growth parameters is presented. The QD layers are inserted in In0.15Ga0.85As/GaAs quantum wells (QWs), forming so-called dots-in-a-well (DWELL) structures. These structures are used to fabricate IPs, primarily for detection in the long wavelength infrared region (LWIR, 8-14 μm). The electron energy level schemes of the DWELL structures are revealed by a combination of different experimental techniques. From Fourier transform photoluminescence (FTPL) and FTPL excitation (FTPLE) measurements the energy level schemes of the DWELL structures are deduced. Additional information on the energy level schemes is obtained from tunneling capacitance measurements and the polarization dependence studies of the interband transitions. From tunneling capacitance measurements, the QD electron energy level separation is confirmed to be 40-50 meV and from the polarization dependence measurements, the heavy hole character of the upper hole states are revealed. Further characterisation of the IPs, by interband and intersubband photocurrent measurements as well as dark current measurements, is performed. By comparing the deduced energy level scheme of the DWELL structure and the results of the intersubband photocurrent measurements, the origin of the photocurrent is determined. The main intersubband transition contributing to the photocurrent is identified as the QD ground state to a QW excited state transition. Optical pumping is employed to gain information on the origin of an additional photocurrent peak observed only at temperatures below 60 K. By pumping resonantly with transitions associated with certain quantum dot energy levels, this photocurrent peak is identified as an intersubband transition emanating from the quantum dot excited state. Furthermore, the detector response is increased by a factor of 10, when using simultaneous optical pumping into the quantum dots states, due to the increasing electron population created by the pumping. In this way, the potentially achievable responsivity of the detector is predicted to be 250 mA/W. Significant variations of photocurrent and dark currents are observed, when bias and temperature are used as variable parameters. The strong bias and temperature dependence of the photocurrent is attributed to the escape route from the final state in the QW, which is limited by tunneling through the triangular barrier. Also the significant bias and temperature dependence of the dark current could be explained in terms of the strong variation of the escape probability from different energy states in the DWELL structure, as revealed by interband photocurrent measurements. These results are important for the future optimisation of the DWELL IP. Tuning of the detection wavelength within the LWIR region is achieved by means of a varying bias across the DWELL structure. By positioning the InAs quantum dot layer asymmetrically in a 8 nm wide In0.15Ga0.85As/GaAs quantum well, a step-wise shift in the detection wavelength from 8.4 to 10.3 μm could be achieved by varying the magnitude and polarity of the applied bias. These tuning properties could be essential for applications such as odulators and dual-colour infrared detection.<br>On the day of the defence date the status on article IV was: Accepted.
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Höglund, Linda. "Growth and characterisation of InGaAs-based quantum dot-in-a-well infrared photodetectors /." Linköping : [Department of Physics, Chemistry and Biology, Linköping University], 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-15774.
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Hollander, Jonathan Lee. "Defect-reduced growth and characterisation of off-basal III-nitride quantum well structures." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609372.
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BANAL, RYAN GANIPAN. "MOVPE Growth of AlN and AlGaN/AlN Quantum Wells and their Optical Polarization Properties." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/78005.
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Eker, Ömer F. "A hybrid prognostic methodology and its application to well-controlled engineering systems." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9269.
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This thesis presents a novel hybrid prognostic methodology, integrating physics-based and data-driven prognostic models, to enhance the prognostic accuracy, robustness, and applicability. The presented prognostic methodology integrates the short-term predictions of a physics-based model with the longer term projection of a similarity-based data-driven model, to obtain remaining useful life estimations. The hybrid prognostic methodology has been applied on specific components of two different engineering systems, one which represents accelerated, and the other a nominal degradation process. Clogged filter and fatigue crack propagation failure cases are selected as case studies. An experimental rig has been developed to investigate the accelerated clogging phenomena whereas the publicly available Virkler fatigue crack propagation dataset is chosen after an extensive literature search and dataset analysis. The filter clogging experimental rig is designed to obtain reproducible filter clogging data under different operational profiles. This data is thought to be a good benchmark dataset for prognostic models. The performance of the presented methodology has been evaluated by comparing remaining useful life estimations obtained from both hybrid and individual prognostic models. This comparison has been based on the most recent prognostic evaluation metrics. The results show that the presented methodology improves accuracy, robustness and applicability. The work contained herein is therefore expected to contribute to scientific knowledge as well as industrial technology development.
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Fuchs, Christian [Verfasser], and Wolfgang [Akademischer Betreuer] Stolz. "Epitaxial growth and characterization of GaAs-based type-II (GaIn)As/Ga(AsSb)/(GaIn)As “W”-quantum well heterostructures and lasers / Christian Fuchs ; Betreuer: Wolfgang Stolz." Marburg : Philipps-Universität Marburg, 2018. http://d-nb.info/1171424728/34.
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Bierwagen, Oliver. "Growth and anisotropic transport properties of self assembled InAs nanostructures in InP." Doctoral thesis, [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985352930.
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Küpers, Hanno. "Growth and properties of GaAs/(In,Ga)As core-shell nanowire arrays on Si." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19402.
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Diese Arbeit präsentiert Untersuchungen zum Wachstum von GaAs Nanodrähten (NWs) und (In,Ga)As Hüllen mittels Molekularstrahlepitaxie (MBE) mit sekundärem Fokus auf den optischen Eigenschaften solcher Kern-Hülle Strukturen. Das ortsselektive Wachstum von GaAs NWs auf mit Oxidmasken beschichteten Si Substraten wird untersucht, wobei der entscheidende Einfluss der Oberflächenpreparation auf die vertikale Ausbeute von NW Feldern aufgedeckt wird. Basierend auf diesen Ergebnissen wird ein zweistufiger Wachstumprozess präsentiert der es ermöglicht NWs mit dünner und gerade Morphologie zu erhalten ohne die vertikale Ausbeute zu verringern. Für die detaillierte Beschreibung der NW Form wird ein Wachstumsmo- dell entwickelt, das die Einflüsse der Veränderung der Tropfen Größe während des Wachstums sowie direktes des Wachstums auf den NW Seitenwänden umfassend beschreibt. Dieses Wachstumsmodell wird benutzt für die Vorhersage der NW Form über einen großen Parameterraum um geeignete Bedingungen für die Realisierung von erwünschten NW Formen und Dimensionen zu finden. Ausgehend von diesen NW Feldern werden die optimalen Parameter für das Wachstum von (In,Ga)As Hüllen untersucht und wir zeigen, dass die Anordnung der Materialquellen im MBE System die Materialqualität entscheidend beeinflusst. Die dreidimensionale Struktur der NWs in Kombination mit der Substratrotation und der Richtungsabhängigkeit der Materialflüsse in MBE resultieren in unterschiedlichen Flusssequenzen auf der NW Seitenfacette welche die Wachstumsdynamik und infolgedessen die Punktde- fektdichte bestimmen. An Proben mit optimaler (In,Ga)As Hülle und äußerer GaAs Hülle zeigen wir, dass thermionische Emission mit anschließender nichtstrahlender Rekombination auf der Oberfläche zu einem starken thermischen Verlöschen der Lumineszenz Intensität führt, welches durch das Hinzufügen einer AlAs Barrierenhülle zur äußeren Hüllenstruktur erfolgreich unterdrückt werden kann. Abschließend wird ein Prozess präsentiert der das ex-situ Tempern von NWs bei hohen Temperaturen ermöglicht, was in der Reduzierung von Inhomogenitäten in den (In,Ga)As Hüllenquantentöpfen führt und in beispiellosen optischen Eigenschaften resultiert.<br>This thesis presents an investigation of the growth of GaAs nanowires (NWs) and (In,Ga)As shells by molecular beam epitaxy (MBE) with a second focus on the optical properties of these core-shell structures. The selective-area growth of GaAs NWs on Si substrates covered by an oxide mask is investigated, revealing the crucial impact of the surface preparation on the vertical yield of NW arrays. Based on these results, a two-step growth approach is presented that enables the growth of thin and untapered NWs while maintaining the high vertical yield. For a detailed quantitative description of the NW shape evolution, a growth model is derived that comprehensively describes the NW shape resulting from changes of the droplet size during elongation and direct vapour-solid growth on the NW sidewalls. This growth model is used to predict the NW shape over a large parameter space to find suitable conditions for the realization of desired NW shapes and dimensions. Using these GaAs NW arrays as templates, the optimum parameters for the growth of (In,Ga)As shells are investigated and we show that the locations of the sources in the MBE system crucially affect the material quality. Here, the three-dimensional structure of the NWs in combination with the substrate rotation and the directionality of material fluxes in MBE results in different flux sequences on the NW sidefacets that determine the growth dynamics and hence, the point defect density. For GaAs NWs with optimum (In,Ga)As shell and outer GaAs shell, we demonstrate that thermionic emission with successive nonradiative recombination at the surface leads to a strong thermal quenching of the luminescence intensity, which is succesfully suppressed by the addition of an AlAs barrier shell to the outer shell structure. Finally, a process is presented that enables the ex-situ annealing of NWs at high temperatures resulting in the reduction of alloy inhomogeneities in the (In,Ga)As shell quantum wells and small emission linewidths.
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Zippel, Jan. "Gepulste Laserabscheidung und Charakterisierung funktionaler oxidischer Dünnfilme und Heterostrukturen." Doctoral thesis, Universitätsbibliothek Leipzig, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-100358.
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In der vorliegenden Arbeit wird das Hauptaugenmerk auf die Untersuchung der Auswirkungen einer Modifikation der zugänglichen Prozessparameter auf die funktionalen Eigenschaften oxidischer Dünnfilme während der gepulsten Laserabscheidung (PLD) gelegt.
Der erste Teil der Arbeit stellt die Herstellung von BaTiO3/SrTiO3-Mehrfach-Heterostrukturen auf thermisch und chemisch vorbehandelten SrTiO3-Substraten mittels gepulster Laserabscheidung (PLD) vor. Die zugängliche in-situ Wachstumskontrolle durch ein reflection high-energy electron diffraction (RHEED)-System ermöglicht es die Wachstumsprozesse in Echtzeit zu überwachen. Angestrebt wird ein stabiler zwei-dimensionaler Wachstumsmodus, der neben glatten Grenzflächen auch eine hohe Dünnfilmqualität ermöglicht. Es wird erstmals die prinzipielle Anwendbarkeit von BaTiO3/SrTiO3-Heterostrukturen als Bragg-Spiegel aufgezeigt. Für BaTiO3- sowie SrTiO3-Dünnfilme wurden die PLD-Parameter Substrattemperatur, Sauerstoffpartialdruck, Energiedichte des Lasers sowie Flussdichte der Teilchen variiert und die Auswirkungen auf die strukturellen, optischen und Oberflächeneigenschaften mittels Röntgendiffraktometrie (XRD), spektraler Ellipsometrie (SE) und Rasterkraftmikroskopie (AFM) beleuchtet.
Im zweiten Teil werden ZnO/MgxZn1−xO-Quantengrabenstrukturen hetero- und homoepitaktisch auf thermisch vorbehandelten a-Saphir- respektive m- und a-orientierten ZnO-Einkristallen vorgestellt. Die Realisierung eines zwei-dimensionalen „layer-by-layer“ Wachstumsmodus wird für die Quantengrabenstrukturen aufgezeigt. Die Quantengrabenbreite lässt sich aus beobachteten RHEED-Oszillationen exakt bestimmen. Ein Vergleich zwischen, mittels Photolumineszenz gemessenen Quantengrabenübergangsenergien als Funktion der Grabenbreite mit theoretisch ermittelten Werten wird vorgestellt, wobei der Unterschied zwischen polaren und nicht-polaren Strukturen mit Blick auf eine Anwendung aufgezeigt wird. Für c-orientierte ZnO-Dünnfilme wird das Wachstum im Detail untersucht und ein alternativer Abscheideprozess im so genannten Intervall PLD-Verfahren vorgestellt.
Die Verifizierung der theoretischen Prognose einer ferromagnetischen Ordnung mit einer Curie-Temperatur oberhalb Raumtemperatur (RT) für kubische, Mangan stabilisierte Zirkondioxid (MnSZ)-Dünnfilme stellt den dritten Teil der Arbeit dar. Die strukturellen Eigenschaften der Dünnfilme werden mittels XRD, AFM sowie Transmissionselektronenmikroskopie (TEM) untersucht. Die Bedingungen einer erfolgreichen Stabilisierung der kubischen Kristallphase durch den Einbau von Mn wird aufgezeigt. Mittels Röntgenphotoelektronenspektroskopie (XPS) sowie Elektronenspinresonanz (EPR) wird der Ladungszustand der, in der Zirkondioxidmatrix eingebauten, Mn-Ionen ermittelt. Die elektrischen Eigenschaftenwerden durch Strom-Spannungsmessungen(IU) sowie der Leitungstyp durch Seebeck-Effekt Messungen charakterisiert. Zur Erhöhung der Leitfähigkeit werden die MnSZ Dünnfilme in verschiedenen Atmosphären thermisch behandelt und Veränderungen durch IU-Messungen aufgezeigt. Ergebnisse von optischen Untersuchungen mittels Transmissionsmessungen und KL werden
präsentiert. Superconducting quantum interference device (SQUID)-Magnetometrie wird zur
Charakterisierung der magnetischen Eigenschaften genutzt. Magnetische Ordnungen im Bereich zwischen 5 K ≤ T ≤ 300 K werden untersucht und der Einfluss von Defekten sowie einer thermischen Behandlung in verschiedenen Atmosphären auf die magnetischen Eigenschaften diskutiert.
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Guille, Claire. "Etude de la formation par epitaxie par jets moleculaires des interfaces entre inas et gaas." Paris 6, 1987. http://www.theses.fr/1987PA066415.
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Malgre le fort desaccord parametrique existant entre gaas et inas (7,2%), il est possible de realiser des couches pseudomorphes de l'un des materiaux sur l'autre, en se limitant a des couches d'epaisseurs inferieures a une dizaine d'a. Dans ces conditions,l'interface inas/gaas est plane et chimiquement abrupte, a la demi-couche pres. L'interface inverse est diffuse et rugueuse a l'echelle atomique. Au cours de la formulation de cette heterojonction, il y a segregation d'in en surface et formation d'un compose ternaire. Ce type de phenomene de segregation d'in se produit egalement dans les composes ternaires ingaas et peut etre a l'origine de leur rugosite superficielle. Etude comparative avec d'autres systemes iii-as
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DUPONT-NIVET, ERIC. "Epitaxie en phase vapeur aux organometalliques de gainp et algainp sur gaas : application a la realisation de diodes et de lasers a heterojonctions." Paris 7, 1987. http://www.theses.fr/1987PA077108.
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Principes de base de la methode movpe et problemes poses par sa mise en oeuvre. Cas particuliers de gainp et de algainp. Analyse des mecanismes de la methode movpe. Proprietes des interfaces gainp/gaas, algainp/gaas et algainp/gainp et presentation de puits quantiques algainp/gainp. Realisation de dispositifs optoelectroniques: presentations de diodes electroluminescentes a homojonctions en gainp et algainp, examen des travaux des principales equipes epitaxiant algainp, presentation de lasers a heterojonctions algainp/gainp/algainp
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Fan, Wen-Chung, and 范文忠. "Growth and optical study of type-II quantum well and quantum dot structures." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/09425140675312570973.
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博士<br>國立交通大學<br>電子物理系所<br>99<br>Type-II ZnSeTe/ZnSe multiple quantum wells (MQWs), ZnTe/ZnSe quantum dots (QDs), ZnMnTe/ZnSe QDs, and ZnTe/ZnMnSe QDs were grown by molecular beam epitaxy (MBE). The photoluminescence (PL), temperature dependent PL, time-resolved PL and magneto-PL were used to investigate the interesting physical properties.
The tunability of the emission energy, oscillator strength and PL efficiency by varying the well thickness and excitation density was demonstrated in the ZnSe0.8Te0.2/ZnSe multiple quantum wells. A significant blueshift about 260 meV of the PL peak energy was observed as the well width decreased from 5 to 1 nm. An extraordinary long lifetime (300 ns) of the recombination for the widest sample was detected. The binding energy of the indirect excitons is determined as 12 meV for the thinnest sample. The reduction of PL efficiency by thermal energy is greatly suppressed by employing a high excitation power.
The optical properties of type-II ZnTe QDs were also investigated by temperature-dependent and time-resolved PL spectroscopy. The initial decrease then increase with temperature for the full width at half maximum (FWHM) of PL is attributed to the hole thermal escape from the smaller QDs then transfer and re-capture to the neighboring-larger QDs. The non-mono-exponential decay profiles reflect the processes of carrier transfer and recapture. We show that the Kohlrausch’s stretching exponential well fits the decay profile of ZnTe/ZnSe QDs.
ZnMnTe/ZnSe QD structures have distinguished difference in magneto-optical properties from ZnTe/ZnSe QD structures due to the existence of Mn in the QDs. Different growth modes of ZnMnTe/ZnSe QDs were studied by using MBE. The ZnMnTe QD system grown by opened the Mn for a few seconds and then Zn+Te growth mode exhibit better emission efficiency. The σ+ and σ– circularly polarized time-integrated and time-resolved PL were employed to investigate the carrier spin dynamics of ZnMnTe/ZnSe QDs grown on GaAs substrates by molecular beam epitaxy. The Kohlrausch’s stretching exponential function well correlates both the σ+ and σ– decay profiles. The measured spin relaxation time is about 23 ns. In addition, we present a magneto-optical study of magnetic polarons (MP) in ZnMnTe/ZnSe QDs. The polarons are found due to the exchange coupling between the spins of the holes and those of the Mn ions, both of which are localized in the QDs. In this system, the MP was detected at temperature up to 100 K and the formation energy is roughly independent of temperature.
Finally, the ZnTe QDs were grown in ZnMnSe matrix. The magnetic field dependence of PL circular polarization degree follows the Brillouin function and evidences the Mn magnetism in ZnTe/ZnMnSe QDs. The magnetic field dependence of PL circular polarization degree shows the long spin relaxation time of about 35 ns. The magnetic polaron formation was observed in low temperature. The ZnTe/ZnMnSe QDs have better PL emission efficient than ZnMnTe/ZnSe QDs.
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邱信豪. "Molecular Beam Epitaxy growth of InN/InGaN Multiple Quantum Well Structures." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/48326711955563336050.
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碩士<br>國立彰化師範大學<br>電子工程學系<br>100<br>Abstract
InN has drawn intensive research interest due to its lower effective mass, higher
mobility, and lowest energy band gap among nitride semiconductors. The fabrication
of InN/InGaN quantum well (QW) structure is a key technology to implement the
fabrication of advanced InN based devices. By measuring the in-situ reflectivity, the
accumulation of indium and the formation of InN by irradiating indium with nitrogen
plasma on the growth front during molecular beam epitaxy can be monitored. An
alternate shutter sequence of metal and nitrogen fluxes was designed to achieve layer
by layer growth of InN quantum wells and minimize the formation of indium clusters
while InGaN barrier layers are grown under metal rich growth condition used
previously to improve smooth morphology and material quality. Then buffer layers
were added to improve the material quality, which was confirmed by low-temperature
photoluminescence study. The structural quality and surface morphology were
measured by x-ray diffraction and atomic force microscopy, respectively.
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Liao, Che-Hao, and 廖哲浩. "Growth and Characterization of Regularly Patterned InGaN/GaN Quantum-well Nanorod Arrays." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/00347952445074740781.
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博士<br>國立臺灣大學<br>光電工程學研究所<br>100<br>In this dissertation, we first demonstrate the growth of high-quality GaN nanorods (NRs) on c-plane sapphire substrate by metalorganic chemical vapor deposition with various hole patterns on the templates. With the nano-imprint technique, the selective-area growth leads to the growth of regularly patterned GaN NRs. The growth of GaN NRs starts with a hole-filling process, followed by NR growth with the pulsed growth mode through switching on and off alternatively the TMGa and NH3 flows. Regularly arranged GaN NRs of uniform geometry are formed.
Then, a regularly-patterned, c-axis nitride NR array of quite uniform geometry with simultaneous depositions of top-face, c-plane disc-like and sidewall, m-plane core-shell InGaN/GaN quantum well (QW) structures is formed. The differences of geometry and composition between these two groups of QW are studied with scanning electron microscopy, cathodoluminescence (CL), and transmission electron microscopy (TEM). In particular, the strain state analysis results in TEM observations provide us with the information about the QW width and composition. It is found that the QW widths are narrower and the indium contents are higher in the sidewall m-plane QWs, when compared with the top-face c-plane QWs. Also, in the sidewall m-plane QWs, the QW width (indium content) decreases (increases) with the height on the sidewall. The observed results can be interpreted with the migration behaviors of the constituent atoms along the NR sidewall from the bottom.
Next, the cross-sectional sizes of the GaN NRs and QW NRs of different heights and different hexagon orientations between different hole patterns, including different hole diameters and pitches, are demonstrated. The cross-sectional size of the GaN NRs is controlled by the hole diameter and has little to do with the NR height and pitch. On the other hand, the cross-sectional size of the QW NRs is mainly determined by the NR height and is slightly affected by the hexagon orientation. The cross-sectional size variation of GaN NRs is interpreted by the three-dimensional nature of the formed catalytic Ga droplet. The cross-sectional size variation of QW NRs is explained by the condition of constituent atom supply in the gap volume between the neighboring NRs. Also, the plan-view and cross-sectional CL emission wavelengths, including the whole scale and local measurements, among those samples are compared. The emission wavelength depends on the NR height, cross-sectional size, pitch of the pattern, and hexagon orientation. It involves in the factors of indium incorporation rate and well layer thickness and shows a complicated combination of various affecting factors. Generally speaking, the QW NRs with a shorter QW NR, a larger cross-sectional size, or a larger pitch have a longer emission wavelength. The NRs with the side-by-side hexagon orientation have longer emission wavelengths, when compared with those with the edge-to-edge hexagon orientation.
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HUANG, ZHEN-WANG, and 黃振旺. "The growth and characterizations of in GaAs/GaAs strained layer quantum well structure." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/27262674762779253260.
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Chen, Y. J., and 陳育志. "Effect of incorporation and growth rate on electric properties of InAs/InGaAs quantum dots and InGaAsN single quantum well." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/90182226085313635138.
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碩士<br>國立交通大學<br>電子物理系<br>91<br>Abstract
The effect of N incorporation into the 1.3μm InAs/InGaAs quantum dots(QDs) is investigated by current-voltage(I-V),capacitance-voltage(C-V),admittance and deep-level transient spectroscopy﹒For the QD sample without any incorporation, C-V profile shows two quantum peaks which are probably originated from quantum well(QW) and QD, respectively﹒From their peak separation in voltage, the QD level is estimated at energy position of 0.2eV below the QW level﹒For the QD sample with the N(0.4~1%) incorporation into the InGaAs well, only single quantum peak is observed﹒All the quantum peaks in these samples are found to be frequency-independent, indicating that the emission time from QW and QD must be less than 10-6s at 18K﹒Quality of these quantum structures is good since no traps are observed either by admittance spectroscopy or DLTS﹒However, for the QD sample with the N(17%) incorporation directly into the QD,C-V spectra show significant dispersion over frequency with carrier depletion at low temperatures and carrier accumulation at high temperatures around the QW/QD region﹒From C-F spectra, we determine the emission time for electrons from around QW/QD to be ~10-4s(at 300K),with activation energy of 0.42eV(2.32*10-14cm2)﹒combining with the poor PL spectra, we believe that N incorporation directly into the QD would introduce around the QW/QD region defect traps(at 0.42ev) which cause the carrier depletion﹒
We continue this investigation by studying the effect of growth rate on the properties of InGaAsN single QW structures which emit at 1.3μm﹒The PL results show a quantum emission at 1.3μm for the high-growth-rate sample and very broad spectra for the low-growth-rate sample﹒While the high-growth-rate sample shows frequency-independent quantum peak, the low-growth-rate sample shows two frequency-dependent capacitance dispersions due to two different traps: one appears at low temperatures(~80K) around -2V where the QW locates and the other appears at high temperatures(~300K) around -4V﹒We believe that these two trap locate at same region around the QW and the bigger bias (-4V) just indicates a deeper energy position﹒From admittance and DLTS, we determine their activation energies to be 12~83meV and 0.21eV﹒These two traps deplete the free electrons around the QW region and are probably responsible for the poor PL spectra observed﹒In contrast to a flat QW interfaces in the high-growth-rate sample, TEM data show a 3-D growth of the InGaAsN layer probably due to N clusterization in the low-growth-rate sample﹒Therefore, we conclude that these defect taps are probably related to the nonuniform
N distribution﹒
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Hsu, Yu-Chi, and 徐鈺淇. "Growth and characterization of GaN heterophased quantum well microdisk and InGaN/GaN quantum well microdisk grown on gamma-LiAlO2 substrate by plasma-assisted molecular beam epitaxy." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/79673648526784456969.
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博士<br>國立中山大學<br>物理學系研究所<br>101<br>In this thesis, the GaN thin film was grown on γ-LiAlO2 (LAO) substrate by plasma assisted molecular beam epitaxy. The LAO substrate provides two basal planes which are rectangular and hexagonal basal planes; therefore we grew M-plane GaN thin film and self-assembled c-plane single crystal GaN microdisk and micropyramid at the same time. To simulate the mechanism of self-assemble c-plane single crystal GaN microdisk and micropyramid, we realized the GaN microdisk was established with the capture of N atoms by most-outside Ga atoms to form the diverging growth. The GaN micropyramid was established due to the missing of most-outside N atoms to form converging growth.
In fabrication of GaN microdisk device, we have fabricated self-assembled wurtzite/zinc-blende/wurtzite GaN heterophased quantum well on GaN microdisk. The GaN wurtzite structure is stacking in ABAB… layer sequence, the phase transition is obtained with the development of C-layer by rotating the threefold symmetric N-Ga vertical bond of B-layer 60o and then repeats the ABCABC…layer sequence. The zinc-blende/wurtzite phase transition can be established, vice versa. Therefore, the sequence of ABABCABCABAB can be achieved to form wurtzite/zinc-blende/wurtzite GaN heterophased quantum well without lattice mismatch.
In addition, we have also grown InGaN/GaN quantum well atop GaN microdisk. By verifying the ratio of indium and gallium, we obtained the indium concentration of the InxGa1-xN/GaN quantum well to be 25% with a band gap energy of 2.31 eV, which is consistent with the bowing effect of bulk InxGa1-xN: Eg(x) = [3.42-x*2.65-x*(1-x)*2.4] eV.
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Fu, Hsueh, and 彭學甫. "The effect of growth temperature and doping for quantum dots-in-a-well laser." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/47368220717402007434.
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碩士<br>國立中山大學<br>光電工程學系研究所<br>100<br>The purpose of this thesis is to fabricate 12-layer InxGa1-xAs quantum dots grown on 2-nm In0.1Ga0.9As quantum wells (DWell) laser structures grown by molecular-beam epitaxy (MBE) on GaAs substrats. We expect to optimum the lasers performance by tune the epitaxial recipe and fabrication condition. For the carrier injection efficiency, DWell structure of quantum dots grown on quantum wells is proposed to enhance the carrier capture rate. So we analyze a series of DWell structure in this work. In the epitaxial recipe, we investigate the influences of p-type doping and change the quantum wells growth temperature for the laser structures.
In the laser fabrication, to transport the light wave in smaller dispersion loss single mode waveguide, dry etching photolithography processes are adapted in this study to fabricate 2.2mm width ridge waveguide. The as-cleaved facets are used as Fabry-Perot laser mirrors in ridge waveguide lasers. The pattern can be transferred effectively with less under-cut by dry etching compare with wet etching.
Finally, the P-type doping DWell laser exhibits high power/facet of 24mW, slope efficiency of 0.209W/A. The maximum power/facet of PWell580 laser reach to 24mW, slope efficiency of 0.238W/A after raising the growth temperature to 580oC.
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Lin, Jian-Ming, and 林健銘. "Growth Model of GaAsSb/GaAs Quantum Well by Using Gas Source Molecular Beam Epitaxy." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/87400636754354241865.
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博士<br>國立臺灣大學<br>電子工程學研究所<br>99<br>In this study, gas source molecular beam Epitaxy（GSMBE）was used to grow GaAsSb/GaAs multiple quantum wells with different compositions at various substrate temperatures. In the X-ray measurements, it was found that the Sb content in quantum well is varied with the As atom and reveals different incorporation behaviors. Strong photoluminescence intensity was observed in the grown quantum wells. The maximum wavelength for the sample is about 1.327μm（0.934eV）, which gives an evidence of application for 1.3μm band range. Moreover, blue shift in the type-II GaAsSb/GaAs quantum well was found.
To predict the results of epitaxy, a growth model is proposed by using the thermodynamic model. For a more accurate growth model for epitaxy, it is necessary to consider the desorption of two Group V elements, a combination of kinetic model and thermodynamic model is then proposed.
For the calculation of the combined theoretical model, it is found the competition between two Group V atoms resulting in different incorporation behaviors and composition curves. The only fitting parameter is also found linearly proportional to the substrate temperature. And the relation is useful for the prediction of the unknown variable.
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Chuo, Chang-Cheng, and 卓昌正. "Growth and Characterization of InGaN/GaN Quantum Well and Blue-violet Laser Diode Structures." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/42590454707279903961.
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Wu, Cheng-Hsien, and 吳政憲. "MOVPE Growth of (In)GaNAs and GaInNP for Quantum Well Lasers and Heterojunction Bipolar Transistors." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/95911527501031982551.
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博士<br>國立成功大學<br>微電子工程研究所碩博士班<br>92<br>In this dissertation, the III-N-V alloys and their heterostructures including GaNAs, InGaNAs, GaInNP, GaNAs/GaAs and InGaNAs/GaAs quantum wells have been grown by metal organic vapor phase epitaxy (MOVPE). Several material characterization techniques, such as high resolution X-ray diffraction (HRXRD), Modulation spectroscopy, photoluminescence (PL), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) have been performed to characterize the material quality of these epitaxial structures.
The influence of N incorporation on the band structure of (In)GaAs is described by a simple two-level “band anticrossing” model (BAC). A narrow band of highly localized N states interacts strongly with the extended conduction band edge states of the (In)GaAs host crystal. The N-induced perturbation is enhanced as the N composition increases. The resulting two levels are denotes as E+ and E�{, and the energy difference between them increases with increasing N composition. The level of E�{ is related to the fundamental bandgap transition energy of (In)GaNAs conduction band. The compositional assessment of grown In(x)Ga(1-x)N(y)As(1-y) alloys in this dissertation is also performed by using BAC model.
The local N configuration and hydrogen-induced bandgap tuning have been gave a detailed discussion in order to explain the variation of the emission wavelength of InGaNAs/GaAs quantum wells after annealing. The evolution towards more In-N bonds during annealing at elevated temperature is supposed to result in the bandgap blue shift. On the contrary, hydrogen-passivated is found to lead to a complete reversal of the drastic bandgap reduction caused by N, that is, elimination of hydrogen-passivated results in the bandgap red shift. These two factors described above can reasonably explain the variant bandgap after annealing.
The growth conditions of (In)GaNAs have been well studied in this dissertation. Many growth parameters including growth temperature, indium content, TBAs partial pressure, growth rate and the ratio of DMHy/(DMHy+TBAs) are found to effect the nitrogen incorporation. The temperature dependent photoluminescence is performed and it is found that InGaNAs has lower temperature bandgap dependence than InGaAs. The activation energy is increased with increasing nitrogen composition. In addition, In- and N-rich cluster and its abnormal optical characteristics observed in the highly nitrogen incorporated InGaNAs alloys is supposed to the highly compositional fluctuation of indium and nitrogen.
The structural and optical properties of GaInNP grown on GaAs substrate are also presented in this dissertation. The spontaneous ordering behavior and temperature dependent near band edge transition energy are also presented. The polarized- high-resolution x-ray rocking curves (HXRC), contactless electroreflectance (CER) and piezoreflectance (PzR) spectra at room temperature show anisotropic character along the [110] and directions, which can prove there exist some degree of the spontaneous ordering phenomenon in the GaInNP alloys. Ordering-induced superlattice-like microstructure observed in high-resolution transmission electron microscope (HTEM) images confirms the spontaneous ordering in the Ga0.46In0.54NxP1-x alloys.
For the device application, edge-emitting laser structures with InGaNAs quantum well active region has been grown by MOVPE and is fabricated as broad area laser diodes. The laser spectrum emits at 1.2 um, the slope efficiency is 1.94 W/A and the threshold current density is 600 A/cm2. In addition, the double heterojunction bipolar transistors (DHBTs) with low turn-on voltage by using InGaAs/GaAsP and InGaNAs as base material have been successfully fabricated and characterize. A turn-on voltage reduction of 225 mV over the conventional HBT with GaAs base layer is obtained. The device has a peak current gain of 85 and shows good high frequency characteristics of fT and fMAX are 55GHz and 45GHz, respectively.
The aim of this dissertation is to grow high quality InGaNAs quaternary alloys and quantum wells by MOVPE; the most important thing is application on the low power consumption heterojunction bipolar transistors (HBTs) and quantum well lasers toward 1.3 um emission for use as the principal devices in the transceiver module and thus contributes to the development of optical fiber communication.
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鍾宜縈. "Optical and material studies of InGaN/GaN ultiple quantum well structures of different well widths and their post-growth thermal annealing effects." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/09313169102625329341.
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Lee, Chien-Hung, and 李健鴻. "Growth of well-aligned Ge quantum dots by adjusting the inner morphology of nano-hole array on Si substrate." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/29359201902735440185.
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碩士<br>臺灣大學<br>電子工程學研究所<br>98<br>This thesis discusses systematically about how to achieve the well-aligned and size-homogeneous germanium quantum dots (Ge QDs).
The Si (001) substrates were fabricated by electron beam (E-beam) lithography and reactive ion etching (RIE), which result in circle-shape periodic nano-patterned on the surface. Then, Ge QDs were grown on the circle-patterned Si (001) template in ultrahigh vacuum chemical vapor deposition (UHV-CVD) chamber using Stranski-Krastanow (SK) growth mode. We successfully realize one Ge QD in one hole by modulating the inner morphology of hole array, the pitch of hole array, and the size of hole array. The samples were measured with scanning electron microscope (SEM) and atomic force microscope (AFM). Finally, we propose applying chemical potential model to understand physical mechanism of alignment of Ge QDs and also hope to forecast experiment results.
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You, Shuo-Ting, and 尤碩廷. "Growth of GaN thin film and AlGaN-based quantum well structure by plasma-assisted molecular beam epitaxy for optoelectronics application." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8pa8ub.
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博士<br>國立中山大學<br>物理學系研究所<br>105<br>In this dissertation, we discuss growth of GaN thin film and AlGaN-based quantum well structure by plasma-assisted molecular beam epitaxy for optoelectronics application. At the first, we grow non-polar plane GaN thin film on the low lattice mismatch substrate. We grow M-plane GaN on ZnO micro-rods (1010) under Ga-rich growth condition which was confirmed by TEM and polarization-dependent photoluminescence. We found that the ZnGa2O4 compound was formed at the M-plane hetero-interface which induce stacking fault defect in the epilayer. We demonstrated that the M-plane ZnO micro-rod surface can be used as an alternative substrate to grow high quality M-plane GaN epi-layers. We also grow M-plane GaN on the -LiGaO2 (100) and derive M-plane GaN Hooke’s law. By the TEM and Hooke’s law, we estimate anisotropic stress in the M-plane GaN epilayer.
In the growth of AlGaN-based quantum well, at the first, we grow AlxGa1-xN/GaN multi-quantum wells on the GaN template substrate. We find that growth of AlxGa1-xN/GaN multi-quantum wells as buffer layer can improve GaN epilayer quality. We also grow AlxGa1-xN/AlyGa1-yN multi-quantum wells on the GaN template. We find that the interlayer LT-AlN layer can avoid AlxGa1-xN/AlyGa1-yN multi-quantum well structure cracking and improve AlxGa1-xN/AlyGa1-yN multi-quantum wells structure.
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Choi, Miri. "Monolithic integration of functional perovskite structures on Si." Thesis, 2014. http://hdl.handle.net/2152/26052.
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Functional crystalline oxides with perovskite structure have a wide range of electrical properties such as ferroelectric, ferromagnetic, and superconductive, as well as unique properties that make them suited for a wide variety of applications including electro-optics, high-k dielectrics, and catalysis. Therefore, in order to realize the potential of perovskite oxides it is desirable to integrate them with semiconductors. Due to the high surface energy of oxides compared to that of semiconductors and the low number of oxides that are thermodynamically stable against SiO₂ formation, it has been extremely difficult to integrate epitaxial oxides with Si directly. However, in 1998, McKee and co-workers finally succeeded in depositing SrTiO₃ on Si directly using a Sr template via molecular beam epitaxy. This breakthrough opened the possibility of integrating the perovskite oxides with Si to realize potential device applications. In this dissertation, alkaline earth metal (Sr and Ba) templates on semiconductors, which enable epitaxial growth of complex oxides on semiconductors, are investigated using molecular beam epitaxy (MBE) for growth and in-situ X-ray/ultraviolet photoemission spectroscopy (XPS/UPS) for the electronic structure analysis. An epitaxial layer of SrTiO₃ on Si using such alkaline earth templates is used as a pseudo-substrate for the integration of perovskite oxides on Si. Through the use of post-deposition annealing as a function of oxygen pressure and annealing time, the strain relaxation behavior of epitaxial SrTiO₃ films grown on Si is also investigated to determine how the SiO₂ interlayer thickness affects the SrTiO₃ lattice constant. This ability to control strain relaxation can be used as a way to manipulate the properties of other perovskite oxides grown on SrTiO₃/Si. Additionally, SrTiO₃ can be made conductive by doping with La. Conductive SrTiO₃ can be used as a thermoelectric, a transparent conductive layer, and a quantum metal layer in a quantum metal field-effect transistor (QMFET). The structural, electrical, and optical properties of strained conductive La-doped SrTiO₃ are studied in order to understand the relation between elastic strain and electrical properties for electronic device applications. Oxide quantum well systems based on LaAlO₃/SrTiO₃ are also investigated using spectroscopic ellipsometry to understand how the quantum well layer structure affects the electronic structure. Such quantum well systems are good candidates for the monolithic integration of functional perovskites on semiconductors. Oxides quantum wells can be used in various device applications such as in quantum well cascade lasers, laser diodes and high performance transistors. As part of the growth optimization for high quality complex oxide heterostructures, the surface preparation of SrTiO₃ substrates using several different methods was also extensively studied using angle-resolved photoemission spectroscopy (ARPES). We found that acid-free water-based surface preparation is actually more effective at removing SrOx̳ crystallites and leaving the surface TiO₂-terminated compared to the more commonly used acid-based methods.<br>text
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"Polarization Effects in Group III-Nitride Materials and Devices." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.14643.
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abstract: Group III-nitride semiconductors have wide application in optoelectronic devices. Spontaneous and piezoelectric polarization effects have been found to be critical for electric and optical properties of group III-nitrides. In this dissertation, firstly, the crystal orientation dependence of the polarization is calculated and in-plane polarization is revealed. The in-plane polarization is sensitive to the lateral characteristic dimension determined by the microstructure. Specific semi-polar plane growth is suggested for reducing quantum-confined Stark effect. The macroscopic electrostatic field from the polarization discontinuity in the heterostructures is discussed, b ased on that, the band diagram of InGaN/GaN quantum well/barrier and AlGaN/GaN heterojunction is obtained from the self-consistent solution of Schrodinger and Poisson equations. New device design such as triangular quantum well with the quenched polarization field is proposed. Electron holography in the transmission electron microscopy is used to examine the electrostatic potential under polarization effects. The measured potential energy profiles of heterostructure are compared with the band simulation, and evidences of two-dimensional hole gas (2DHG) in a wurtzite AlGaN/ AlN/ GaN superlattice, as well as quasi two-dimensional electron gas (2DEG) in a zinc-blende AlGaN/GaN are found. The large polarization discontinuity of AlN/GaN is the main source of the 2DHG of wurtzite nitrides, while the impurity introduced during the growth of AlGaN layer provides the donor states that to a great extent balance the free electrons in zinc-blende nitrides. It is also found that the quasi-2DEG concentration in zinc-blende AlGaN/GaN is about one order of magnitude lower than the wurtzite AlGaN/GaN, due to the absence of polarization. Finally, the InAlN/GaN lattice-matched epitaxy, which ideally has a zero piezoelectric polarization and strong spontaneous polarization, is experimentally studied. The breakdown in compositional homogeneity is triggered by threading dislocations with a screw component propagating from the GaN underlayer, which tend to open up into V-grooves at a certain thickness of the InxAl1-xN layer. The V-grooves coalesce at 200 nm and are filled with material that exhibits a significant drop in indium content and a broad luminescence peak. The structural breakdown is due to heterogeneous nucleation and growth at the facets of the V-grooves.<br>Dissertation/Thesis<br>Ph.D. Physics 2012