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1
Tasmin, Tania. "Design of SiGe/Si quantum-well optical modulators." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/27904.
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An electro-optic modulator containing a single SiGe/Si quantum-well has been designed for operation at λ₀= 1.55 µm. This single quantum-well modulator has a lower VπLπ than the 3 quantum-well modulator recently designed and optimized by Maine et al. for operation at λ₀= 1.31 µm, for which the VπLπ product was 1.8 V•cm [25]. Both modulators are derived from the detailed design given for their modulator in [40]. This single quantum-well modulator contains a Si₀.₈Ge₀.₂ quantum-well with Non-Intentionally Doped (NID) and P⁺ highly doped layers on either side. With no field applied, holes from the P⁺ layers are captured by and confined in the quantum-well and when a reverse bias is applied holes are released from the quantum well and drift to the P⁺ contact layer. Variations of the hole distribution lead to changes in the free-carrier absorption and the refractive index of each layer and subsequently to phase modulation of guided TE modes. The VπLπ product of the single quantum-well modulator is estimated 1.09 V•cm for low voltage linear modulation and 1.208 V•cm for 0 to 1.6 V digital modulation, whereas the 3 quantum-well modulator gives a VπLπ of 2.039 V•cm for 0 to 6 V digital modulation for operation at λ₀= 1.55 µm. Also, the optical loss in the single quantum-well (5.36 dB/cm at V=0 V) is lower than that of the 3 quantum-well structure (5.75 dB/cm at V=0 V). This single quantum-well modulator should also offer higher frequency operation than the 3 quantum-well modulator.
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Becker, Christian Eberhard. "Transport properties of modulation doped Si/SiGe quantum well structures." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404404.
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Cho, Eun Chel Electrical Engineering UNSW. "Optical transitions in SiO2/crystalline Si/SiO2 quantum wells and nanocrystalline silicon (nc-Si)/SiO2 superlattice fabrication (Restricted for 24 months until Feb. 2006)." Awarded by:University of New South Wales. Electrical Engineering, 2003. http://handle.unsw.edu.au/1959.4/22492.
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Innovation in photovoltaic technology may offer cost competitive options to other energy sources and become a viable solution for the energy and environmental challenges of the 21st century. One proposed innovative technology is based on all-silicon tandem cells, which are constructed using superlattices consisting of environmental friendly Si and its compounds. The well and barrier materials in superlattices are restricted to silicon and silicon oxide during the present study. Single crystalline Si/SiO2 quantum wells (QWs) have been fabricated by thermal oxidation of silicon-on-insulator (SOI) wafers. It is found that oxide properties in QWs are important for SOI wafers prepared by the SIMOX (Separation by Implantation of Oxygen) technique. However, QWs fabricated from SOI wafers prepared by the ELTRAN (Epitaxial Layer TRANsfer) approach show the effect of quantum confinement without evidence of strong oxide interfacial transitions. In these wafers, evidence for an apparently ordered silicon oxide was found with 1.92?atomic fringe spacing along the (110) direction of the Si structure and with the thickness about 17?along the (100) direction of the Si structure. Luminescence wavelength ranges are from 700nm to 918nm depending on the Si thickness. The luminescence measurements on other positions of the sample show peak and shoulder spectra, which are explained by monolayer fluctuations in QW thicknesses, previously observed in III-V QWs and II-VI QWs. Si/SiO2 superlattices are fabricated by RF magnetron sputtering. Si density is the key issue in crystallizing the superlattice. High-density Si layers crystallize either under high temperature furnace annealing or rapid thermal process annealing. However, low density Si would not crystallize even at high temperature. Crystallized nanocrystals in the Si layers are observed by high resolution transmission electron microscopy (HRTEM) when the Si layer is thicker than 3nm. When Si layers are thinner than 3nm, the Si layers are discontinuous and finally deteriorate into small nanocrystals. The suitability of such superlattices for surface passivation and antireflection coatings is reviewed. Initial attempts to fabricate heterojunctions between Si wafers and Si/SiO2 superlattices resulted in open circuit voltage of 252mV. However, it is expected that better results would be obtained if Si/SiO2 superlattices were fully crystallized.
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Corbin, Elizabeth Ann. "Infra-red optical properties of SiGe/Si heterostructures." Thesis, University of Newcastle Upon Tyne, 1995. http://hdl.handle.net/10443/810.
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We present full-scale relativistic pseudopotential calculations of the first-order susceptibility in p-type SiGe/Si multiple quantum well structures with a view to exploring the suitability of such systems for infrared applications in the 3-5yrn and 8-15itm ranges. A derivation of an expression for the linear susceptibility, or absorption, is given and the frequency dependence of the linear response due to transitions between the valence minibands is determined. The microscopic origin of the absorption is demonstrated for both parallel and normal incident light. Comparisons between calculated and experimental results are presented and shown to be in good agreement. The effects of changing well width, temperature, doping concentration and germanium concentration in the well are considered. We also consider Auger recombination and discuss the possibility of engineering the miniband structure in order to prevent certain Auger processes occuring, Preliminary results from full scale Auger calculations are also presented.
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Shin, Dong Hoon. "Magnetotransport phenomena in modulation doped N-channel Si/ Si[subscript 0.7]Ge[subscript 0.3] quantum well structures." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393626.
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Liang, Hu. "Fabrication of high power InGaN/GaN multiple quantum well blue LEDs grown on patterned Si substrates /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20LIANG.
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Weiss, Bernard Lawson. "Modelling and characterisation III-V semiconductor quantum well structures and Si based structures for optoelectronic applications." Thesis, University of Surrey, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267875.
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Gadir, Mazin A. "Theoretical studies of GaAs / AlGaAs and SiGe / Si mid- and far-infrared (Terahertz) quantum well infrared photodetectors." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417888.
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Aslan, Bulent. "Physics And Technology Of The Infrared Detection Systems Based On Heterojunctions." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604801/index.pdf.
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The physics and technology of the heterojunction infrared photodetectors having different material systems have been studied extensively. Devices used in this study have been characterized by using mainly optical methods, and electrical measurements have been used as an auxiliary method. The theory of internal photoemission in semiconductor heterojunctions has been investigated and the existing model has been extended by incorporating the effects of the difference in the effective masses in the active region and the substrate, nonspherical-nonparabolic bands, and the energy loss per collisions. The barrier heights (correspondingly the cut-off wavelengths) of SiGe/Si samples have been found from their internal photoemission spectrums by using the complete model which has the wavelength and doping concentration dependent free carrier absorption parameters. A qualitative model describing the mechanisms of photocurrent generation in SiGe/Si HIP devices has been presented. It has been shown that the performance of our devices depends significantly on the applied bias and the operating temperature. Properties of internal photoemission in a PtSi/Si Schottky type infrared detector have also been studied. InGaAs/InP quantum well photodetectors that covers both near and mid-infrared spectral regions by means of interband and intersubband transitions have been studied. To understand the high responsivity values observed at high biases, the gain and avalanche multiplication processes have been investigated. Finally, the results of a detailed characterization study on a systematic set of InAs/GaAs self-assembled quantum dot infrared photodetectors have been presented. A simple physical picture has also been discussed to account for the main observed features.
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Ariyawansa, Gamini. "Semiconductor Quantum Structures for Ultraviolet-to-Infrared Multi-Band Radiation Detection." Digital Archive @ GSU, 2007. http://digitalarchive.gsu.edu/phy_astr_diss/17.
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In this work, multi-band (multi-color) detector structures considering different semiconductor device concepts and architectures are presented. Results on detectors operating in ultraviolet-to-infrared regions (UV-to-IR) are discussed. Multi-band detectors are based on quantum dot (QD) structures; which include quantum-dots-in-a-well (DWELL), tunneling quantum dot infrared photodetectors (T-QDIPs), and bi-layer quantum dot infrared photodetectors (Bi-QDIPs); and homo-/heterojunction interfacial workfunction internal photoemission (HIWIP/HEIWIP) structures. QD-based detectors show multi-color characteristics in mid- and far-infrared (MIR/FIR) regions, where as HIWIP/HEIWIP detectors show responses in UV or near-infrared (NIR) regions, and MIR-to-FIR regions. In DWELL structures, InAs QDs are placed in an InGaAs/GaAs quantum well (QW) to introduce photon induced electronic transitions from energy states in the QD to that in QW, leading to multi-color response peaks. One of the DWELL detectors shows response peaks at ∼ 6.25, ∼ 10.5 and ∼ 23.3 µm. In T-QDIP structures, photoexcited carriers are selectively collected from InGaAs QDs through resonant tunneling, while the dark current is blocked using AlGaAs/InGaAsAlGaAs/ blocking barriers placed in the structure. A two-color T-QDIP with photoresponse peaks at 6 and 17 µm operating at room temperature and a 6 THz detector operating at 150 K are presented. Bi-QDIPs consist of two layers of InAs QDs with different QD sizes. The detector exhibits three distinct peaks at 5.6, 8.0, and 23.0 µm. A typical HIWIP/HEIWIP detector structure consists of a single (or series of) doped emitter(s) and undoped barrier(s), which are placed between two highly doped contact layers. The dual-band response arises from interband transitions of carriers in the undoped barrier and intraband transitions in the doped emitter. Two HIWIP detectors, p-GaAs/GaAs and p-Si/Si, showing interband responses with wavelength thresholds at 0.82 and 1.05 µm, and intraband responses with zero response thresholds at 70 and 32 µm, respectively, are presented. HEIWIP detectors based on n-GaN/AlGaN show an interband response in the UV region and intraband response in the 2-14 µm region. A GaN/AlGaN detector structure consisting of three electrical contacts for separate UV and IR active regions is proposed for simultaneous measurements of the two components of the photocurrent generated by UV and IR radiation.
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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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Valloggia, Sylvie. "SPECTROSCOPIE DE PHOTOLUMINESCENCE LOCALE DANS LES SEMICONDUCTEURS MASSIFS (Si, InP) ET LES PUITS QUANTIQUES (GaAs/GaAlAs)." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619041b.
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Sidiki, Tamim Peter. "Structural and optical characterisation of Si/Si1-xGex multiple quantum wells." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962699195.
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Quiroga, Jean-Manuel. "Étude des propriétés optiques de multicouches a-Si:H/a-SiO2." Grenoble 1, 1998. http://www.theses.fr/1998GRE10124.
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L'etude porte sur les proprietes optiques de puits nanometriques multiples a-si:h/a-sio#2 elabores par pecvd (he+sih#4+o#2). Les caracteristiques des materiaux de reference sont determinees par diverses techniques de spectroscopie optique. Nous montrons la necessite de simuler les spectres en tenant compte des reflexions multiples afin d'eviter des erreurs importantes sur la valeur du coefficient d'absorption. Des mesures in situ de la teneur en oxygene dans le plasma nous ont permis de determiner une procedure de depot des multicouches reduisant la largeur des interfaces. La modulation de la composition chimique dans l'epaisseur est observee par des mesures de met, de rayons x et de spectrometrie infrarouge. La simulation des spectres de transmission infrarouge de la multicouche consideree comme un milieu effectif montre que l'interface a-sio#2/a-si:h est la plus large. La variation de l'epaisseur des motifs pour des series de multicouches de largeur de puits (d#a#-#s#i#:#h) ou de barriere constante permet d'elaborer des profils-modele de la composition d'oxygene en epaisseur x(d) en tenant compte de la reduction de la couche de silice et de l'oxydation de celle du silicium amorphe par le plasma lors du depot des couches ulterieures. Nous presentons enfin les mesures d'absorption et de photoluminescence des multicouches. La reduction de la largeur du puits conduit a une augmentation apparente du gap (e#g) mais une analyse plus fine s'appuyant sur le modele physico-chimique montre que la valeur apparente de e#g ne correspond pas a la separation minimale entre les bandes de valence et de conduction. Une emission de lumiere visible a l'il a temperature ambiante est observee pour des largeurs de puits nominales inferieures a 20a. Contrairement aux predictions du modele de confinement quantique, la position du pic de photoluminescence est independante de d#a#-#s#i#:#h. Nous concluons que la presence de sous-oxydes au fond du puits est a l'origine de l'emission observee.
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Sagnes, Isabelle. "Propriétés électro-optiques des hétérostructures épitaxiées sur silicium." Université Joseph Fourier (Grenoble ; 1971-2015), 1994. http://www.theses.fr/1994GRE10100.
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Les progres des techniques de croissance cristalline permettent aujourd'hui de fabriquer sur un substrat de silicium une large variete d'heterostructures epitaxiees a base de siliciures metalliques ou d'alliages silicium-germanium. Les proprietes de discontinuite de bandes electroniques dans les heterojonctions sige/si et les barrieres schottky permettent d'une part d'etendre jusqu'a l'infra-rouge lointain la detection sur silicium du rayonnement electro-magnetique, d'autre part d'obtenir le confinement bidimensionnel (2d) de gaz de porteurs libres a forte morbilite, tres prometteur pour des applications de transistors et circuits rapides sur silicium. C'est a l'etude et a la comprehension des proprietes electriques et electro-optiques de ces deux effets que nous nous sommes interesses durant cette these. Nous rappelons tout d'abord les proprietes de photo-emission interne de l'interface metal-semiconducteur ainsi que celles des structures metal-si-metal (tips) dont la reponse spectrale est modulable par l'application d'une tension entre les deux electrodes. Nous presentons ensuite les resultats experimentaux et theoriques obtenus dans les structures tips utilisant le disiliciure d'erbium et l'alliage silicium-germanium. La modelisation des differentes reponses spectrales du tips a necessite l'etude des proprietes d'absorption optique de ces structures. Dans la continuite de cette etude, nous nous sommes interesses aux multi-puits quantiques sige ou nous venons de mettre en evidence une forte absorption inter-sous bande de valence liee au confinement 2d des porteurs libres, ainsi qu'au silicium poreux, ou nous avons montre que le decalage vers le bleu du spectre d'absorption est lie au confinement a od dans les nanocristallites de silicium. Ce travail nous a enfin conduit a etudier les proprietes de transport et de magneto-transport des gaz 2d de porteurs libres dans les heterostructures a modulation de dopage sige/si
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Li, Cheng Che, and 李政哲. "Impurity Enhanced Intermixing in SiGe/Si Quantum Well Structure." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/13235051664378262492.
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Wang, Tzong-Liang, and 王宗良. "Study of Si/SiGe Multiple Quantum Well(MQW) Infrared Photodetector." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/30489586710397035336.
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碩士<br>大葉大學<br>電機工程學系碩士班<br>94<br>The SiGe based separate-absorption-multiplication avalanche-photodiode（SAMAPD）and has been implemented for the first time. The structure of SAMAPD, in our work, is P +-Si/MQW-(SiGe/Si)/ i-SiGe/N+-Si, in which the i-SiGe and quantum well structure of SiGe/Si are deposited by ultra-high-vacuum chemical-vapor-deposition (UHVCVD) system. In this structure，the thickness of i-Si0.8Ge0.2 layer is about 150nm and quantum structure is of Si (25 nm)/Si0.8Ge0.2( 5 nm) with five periods.
Experiment results shows that the current increases sharply at about 2 V reverse bias, we speculates that the avalanche effect occurred at this voltage. Two structures of dot and net are processed in our studies. We found that the photo-to-dark current ratio of Iphoto/Idark was 15.19 without and 17.9 with covered by Al thin film for dot electrodes at 1 V reverse bias voltage. A higher photo-to-dark current ratio was obtained for net electrodes, the Iphoto/Idark is 52.6 without covered by Al thin film; after covered by Al thin film, the Iphoto/Idark achieved a high value of 134.
In addition, the solar cell performance with this structure is measured by using a simulated solar source of 1000W/cm2 and a high conversion efficiency of 8.26% is obtained for dot electrodes with Al thin films.
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Chiu, Chien-Wei, and 邱建維. "Enhancement of Silicon Light Emission with Si/SiGe Quantum Well Structure." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/32938837991899689774.
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碩士<br>國立臺灣大學<br>電子工程學研究所<br>94<br>The advantage of the optoelectronic component of Silicon Germanium is fully compatible with the Si-based microelectronic chips. In addition, the progress of the growth techniques for quantum hetero-junction structure is in advanced. So the hetero-junction structure of Silicon Germanium is studied far and wide in recent years. In this thesis, a method with band bending effect to enhance silicon light emission was proved successfully by real fabricated devices and theoretical simulation results. Within simulation, we could know detail physical phenomenon which could not be observed in the lab easily. By comparing the simulation result and experiment data, we could improve our simulation accuracy and simulation result would help us to build a reliable physical model.
We used TCAD simulator named ATLAS which was developed by SILVACO. For experiment, we designed a LED with ten periods Si/SiGe MQW and grew it by UHVCVD system. After processing, we could get I-V data and EL spectrum. We utilized ATLAS to simulate this device and ATLAS let us to know insight physics. From the experiment data, Silicon light intensity increased as injection current is increased at room temperature. By simulation, we found that there is a hetero-junction between Silicon buffer layer and Si/SiGe MQW structure. As injection current is increased; a barrier was formed at the hetero-junction because of band bending effect. This barrier would block hole to flow into wells and then a lot of hole would be accumulated at the top Silicon buffer layer. Thus recombination rate at this layer would increase and Silicon light intensity would increase simultaneously.
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Hsieh, Wen-Yao, and 謝文耀. "Structure and Optical Properties of Ge-based Multiple-quantum-well on Si." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/83pa5t.
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碩士<br>國立中正大學<br>機械工程學系暨研究所<br>103<br>Compared to electronic communications, optical communications has many advantages. So the development of optical communication components will play an important role in the field of communications at the future. In order to produce the light emitting element which can be integrated in today's integrated circuits. This paper discusses the structure and optical properties of Ge-based multiple-quantum-well on Si.
We use Raman spectroscopy to know raman shift of Ge and SiGe layer in Ge / SiGe MQW. Then we determined the tensile strain of Ge layer is 0.21%, the tensile strain of SiGe layer is 1.01%, and the concentration of Ge is 89%by empirical formula. We discover the thickness of buffer layer in Ge / SiGe MQW by TEM is only 120nm. It will reduce the optical loss in produce waveguide type PIN-emitting element at Future By Photoluminescence, We observe that the wavelength of luminescence move to 1540nm which is the lowest energy loss in optical communication. In luminous efficiency, The power factor of old QW structure is 1.39. And MQW with tensile strain is 2.25. The luminous efficiency is better than the old one. And luminescence is dominated by excitonic transition which is produced primarily by the excitation light source.
For the purpose to investigate the impact between GeSn/Ge MQW and Ge film. We have two samples, GeSn/Ge MQW as experimental group and GeSn film as the control group. We observed the defects were absorbed in the buffer layer by TEM. And we find out the concentration of Sn in GeSn/Ge MQW is 2.27% by SIMS. By Photoluminescence, we aware of the luminescence wavelength of GeSn/Ge MQW is 1725nm and Ge film is 1755nm.The reason is the quasi-fermi level will move to the bottom of the conductive band and the top of valence band by quantum confinement effect.The power factor of GeSn/Ge MQW is 2.57 and Ge film is 1.73. The luminous efficiency is better than Ge film. And luminescence is dominated by excitonic transition which is produced primarily by the excitation light source.
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Lin, Wei-Chung, and 林威沖. "Electrooptical Properties of the Si delta-doped GaAs/GaInP quantum well system." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/54286892199997342370.
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碩士<br>國立臺灣師範大學<br>物理學系<br>84<br>We use the method of photo-refraction to measure modulation
spectra of delta-doped GaAs/GaInP quantum well system.All the
spectra clearly showed the Franz-Keldyshoscillation at different
temperature. By varying temperature from 75K to 150K,we found
the exciton transition near energy-gap.The effect of delta-doped
are not only built-in electric field, also making wellpotential
deeper and sharper.By analyzing Franz-Keldysh oscillation for
allspectra, we can deduce relation of built-in electric field
varying with temperature.Due to the effect of photovoltage, we
predict built-in electric field decreaseswhen lower sample
temperature,and ,as expect, it matches with experimental
results.We also use triangular well model to calculate the
lowest transition energy,andthis theoretical result is agree
with the energy deduced from experimental data.
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Jhang, Jhih-Hao, and 張致豪. "Electronic transport properties of a Si quantum well studied in tilted magnetic field." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/48383837315935407509.
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Liu, Yen-Hung, and 劉彥宏. "Study on InGaN/GaN Quantum Well Structures on Si Substrate with Transmission Electron Microscopy." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/25988065222972125041.
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碩士<br>國立臺灣大學<br>光電工程學研究所<br>100<br>The difference of thermal expansion coefficient between GaN and Si results in a strong tensile stress on the GaN epitaxial layer during the cooling process. In our study, we create a compressive thermal stress by using an AlN buffer layer grown with graded temperatures to compensate the tensile thermal stress. The InGaN/Gan quantum well (QW) sample with the largest number of graded-temperature growth stages has the weakest residual tensile stress, shortest emission wavelength, and highest emission internal quantum efficiency. In this study, the variation trend of indium composition of the QW samples grown on Si and the control sample grown on sapphire based on strain state analysis is shown to be the same as that based on the X-ray diffraction measurement and fitting. However, the variation range becomes larger. Also, from the cross-sectional transmission electron microscopy study, it is found that the threading dislocation (TD) density decreases with decreasing residual stress. The TD density above the GaN/AlN superlattice inter-layer is lower than that below the inter-layer, indicating that the inter-layer can block the TDs.
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Chen, Hung-Ming, and 陳宏銘. "Electroluminescence characteristics of LED with Si/SiGe multiple quantum well under different doping conditions." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/66129598288356015929.
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碩士<br>國立臺灣大學<br>電子工程學研究所<br>94<br>In this thesis we demonstrated 1.3~1.4μm wavelength light emission from 10-period Si/Si0.85Ge0.15 quantum-well (QW) structures. There are two different samples in our investigation: p-i-n and p-p-n structures, grown by UHVCVD system. For the p-i-n sample, the QW structure is in the depletion region of diode, while for the p-p-n sample it is in the electron diffusion region of diode.
According to our experiment results, the luminescence of QW dominates and the luminescence of Si is only observed at high bias for p-i-n sample at low temperature. However, the luminescence intensity of QW decreases with temperature because the carriers get more energy to escape the well. For p-p-n sample, the luminescence intensity of Si is enhanced because of the high p-type doping in the Si buffer layer, which causes lots of electron-hole recombination.
At room temperature, the efficiency is low for both samples. At low temperature, the efficiency of the p-p-n sample is higher than that of the p-i-n sample. The high hole-concentration in the electron diffusion region (p-type region) may enhance the recombination rate. We also discussed the temperature dependence of the QW luminescence and the activation energy of holes in the well. The activation energy decreases as the current injection increases. The difference in activation energy between these two samples is about 23meV at the same injection condition.
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Tsai, Wen-Chung, and 蔡文忠. "Physics and Device Applications of Si/Si1-xGex Quantum Well Structures Grown by Ultrahigh Vacuum Chemical Vapor Deposition." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/17263886108099700011.
Full textAbstract:
碩士<br>國立交通大學<br>電子工程學系<br>85<br>In this thesis, the growth of Si and strained Si1-xGex alloy
epitaxial layer have been investigated by ultrahigh vacuum
chemical vapor deposition (UHV/CVD) in the temperature range of
600 - 475℃. The physical properties and devices applications,
including p-type MODFETs and p-type QWIPs detectors of the Si/
Si1-xGex quantum well heterostructures have been demonstrated.
In the epitaxial layers growth, the deposition of excellent
quality Si epitaxy and strained Si1-xGex alloy epitaxial layers,
and strained Si/Si1-xGex superlattices have been grown. From the
HRXRD measurement of the Si1-xGex alloy layer, the in-wafer
deviation of maximum and minimum Ge composition x is 0.2 %, and
average uniformity is 0.75 %. The boron concentration of boron-
doped Si and Si1-xGexepitaxial layers can achieve 4.0 x 1021 to
1.0 x 1021 cm-3 far beyond the solid solubility of boron in Si
and Si1-xGex layers by some times or more orders of magnitude.
SIMS measurements demonstrate no Ge segregation at Si/Si1-xGex
interfaces grown during 575℃-525℃. The XRR measurement and the
HRXRD measurement are used to evaluate the structure parameters
of the Si/ Si1-xGex SLS. The interface roughnessesare 0.1 nm for
Si and SiGe layers grown at 525 ℃while 0.2 nm grown at 550 ℃
that are obtained by XRR measurement. The Ge compositions x of
Si/Si1-xGex SLS are measured from HRXRD and found to increase
with layer thickness for the same gas phase composition. A
simple model is proposed to explained this phenomena. From this
model, the transition region thickness and the transition time
can be extracted. The transition regions are in the range from
1.01 nm to 1.46 nm grown at 550 ℃, while from 0.34 nm to 0.66
nm grown at 525 ℃. We conclude that the interface abruptness in
UHV/CVD growth is determined by the quantity of surface hydrogen
coverage during growth, and the two competing rate-limiting
processes could result in a nonmonotonic tread of the growth
rate as Ge composition varying during fine-structure growth.
The Si/Si1-xGex/Si p-type normal modulation-doped
heterostructures are fabricated with an extremely high hole
mobility and high sheet carrier concentration, and show a 2DHG
hole mobility as high as 12500 cm2/V.s at 0.65 K, at a sheet
carrier density ns of 3.45 x 1011 cm-2 for x = 0.12. The study
also reveals the hole effective mass m* to be 0.295 m0 ±
0.01m0, which is independent of temperature and magnetic field.
The major factors that limit the 2DHG mobility are both the
interface roughness and the alloy abruptness at the Si/SiGe
heterointerface. The p-type Si1-xGex modulation-doped field
effect transistors with a 2DHG SiGe channel are grown by UHV/CVD
onto Si substrate to demonstrate the basic compatibility with
Si-based technologies. A p-type Si0.72Ge0.28 MODFET with gate
length 5 mm, the extrinsic transconductance gme is 9.3 mS/mm and
the intrinsic transonductance gmi 36.3 mS/mm. We observed
that the decrease of the spacer thickness of QW structures
increasethe concentration of holes confined in QW and the local
electric field induced. Thus, the perpendicular conductance
increases strongly due to a larger tunneling transparency of the
potential barriers. The confined holes creates also an
effectivequantum well for electrons which was studied by
photoluminescence. We observed a shift of the band-edge
photoluminescence in dependence on the spacer thickness, which
is Stark effect induced by local electric field. We have
demonstrated the intervalence subband transition at normal
incidence in p-type Si/Si1-xGex QWIP detectors. These 400 x 400
mm2 devices show the detectivitD*(4.8 mm) = 2.5 x 108 cm.Hz1/2/
Watt, the responsivity R(4.8 mm) = 5.65 mA/Watt at bias Vb =
-0.3 V at 77 K. The detector show a broad photoreponse at the
wavelength range from 2 mm to 7 mm. The Si/Si1-xGex QWIP
detectors have very good intrinsic performance, such as high
responsivity and high detectivity. So it is expected that these
devices have a potential application with Si integrated circuit
in fabricating large focal plane arrays.
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Tu, Li-Ping, and 杜麗萍. "High-Sensitivity Planar Si-Based MSM Photodetector with Very Thin Amorphous Silicon-Alloy Quantum-Well-Like Barrier Layers." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/96627656920503519878.
Full textAbstract:
碩士<br>國立中央大學<br>電機工程研究所<br>91<br>Abstract
The planar Si-based metal-semiconductor-metal photodetectors (MSM-PDs) with a-Si:H/a-SiC:H (or a-Si:H/a-SiGe:H) multi-layers to reduce device dark current had been studied. For the ones with a-Si:H/a-SiC:H multi-layers, their sensitivity could be enhanced very effectively. Under a very weak incident light power (0.5 μW) and with a 4 V bias-voltage, the device photo- to dark- current ratio (Ip/Id) could be 103 times higher than that of the previously reported one. Also, the average full-width-at-half-maximum (FWHM) and fall-time of the device temporal response were 68.18 and 294.7 ps, respectively, as measured with a periodic 0.83μm 60 ps light pulse and a 10 V bias-voltage. Comparing to the previously reported various Si-based PDs, this device exhibited significant improvements in device sensitivity and temporal-response due to the employed quantum-well-like amorphous silicon-alloy barrier layers. Moreover, the Si-based MSM-PDs with a-Si:H/a-SiGe:H multi-layers also had been investigated. The effects of multi-layer thickness and structure, and H2-plasma treatment of a-SiGe:H films on device performances had been studied also.
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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.
Full textAbstract:
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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Choi, Miri. "Monolithic integration of functional perovskite structures on Si." Thesis, 2014. http://hdl.handle.net/2152/26052.
Full textAbstract:
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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Cho, Eun Chel. "Optical transitions in SiO2/crystalline Si/SiO2 quantum wells and nanocrystalline silicon (nc-Si)/SiO2 superlattice fabrication /." 2003. http://www.library.unsw.edu.au/~thesis/adt-NUN/public/adt-NUN20040105.171835/index.html.
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Zhu, Li Huan, and 朱立寰. "Persistent photoconductivity in Si1-xGex/Si quantum wells." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/60484668283517265317.
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Wang, Ke-Yao, and 王科堯. "Magneto-Photoluminescence study of strained Si/SiGe multi-quantum wells." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/89673670055537466458.
Full textAbstract:
碩士<br>國立臺灣大學<br>電子工程學研究所<br>95<br>Strained Si/SiGe heterostructure has attracted great attention recently for its application in high speed and optoelectronic devises. However, the basic parameters such as band alignment are still not so clear due to the complexity of the band shifting and splitting as a result of strain effect between Si/SiGe lattice mismatch. For optoelectronic applications, band alignment (type-I and type-II) with different oscillation strength can cause extreme different optical transition efficiency. In this thesis, magneto-luminescence measurement was performed for Si/SiGe multi-quantum wells with different strain distribution. Under magnetic fields, the transitions associated with quantum well begin to shift. From the behavior of energy shifting, two kinds of excitons (type-I and type-II) are observed. Theoretical modeling of the diamagnetic shifting both considering cyclotron energy and Zeeman effect was performed, and the agreement between observation and calculation is quite well. With a proper strain manipulation, it is possible to form type-I band alignment which in principle has larger oscillation strength for more efficient light emission than the type-II alignment.
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Wang, Ke-Yao. "Magneto-Photoluminescence study of strained Si/SiGe multi-quantum wells." 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2507200711153300.
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TSAI, LING-CHUN, and 蔡玲君. "Study of Persistent Photoconductivity in SiGe/Si and AlGaSb/InAs quantum wells." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/77048456121442343108.
Full textAbstract:
碩士<br>國立臺灣大學<br>物理學系研究所<br>86<br>In this thesis,we present a detailed study of persistent photoconductivityef
fects in SiGe/Si quantum wells as well as AlGaSb/InAs quantum wells.I. SiGe/Si
quantum wells Persistent Photoconductivity (PPC) has been observed in boron-
doped SiGe/Siquantum wells. The decay kinetics of the PPC effect can be well d
escribed by a stretched-exponential function,I(t)=I(0)exp[-(t/τ)^β](0<β<1),
which is usually observed in many disorder materials. Through the studies of t
he PPCeffect under various conditions, such as different temperature, differen
t photon energy of photoexcitation, and different Ge content, we identify that
the alloy potential fluctuations induced by compositional disorder are theorig
in of the PPC effect in SiGe/Si quantum wells.II. AlGaSb/InAs quantum wells T
he "positive" persistent photoconductivity (PPC) and "negative" persistentphot
oconductivity (NPPC) have been studied in AlGaSb/InAs quantum wells. Comp-arin
g with the published reports, several new results have been observed,andthey c
an not be explained by previously proposed models. Through the studiesof the N
PPC and PPC effects under various conditions, such as different photonenergy o
f excitation,different temperature, and different Al composition x, wesuggest
that the NPPC and PPC effects are caused by two competing processes.At low tem
perature, electrons in InAs layer are photoexcited into the valence band on A
lGaSb layer. The return of the photoexcited electrons are prohibitedby the bar
rier due to interface band bending,and thus the NPPC occurs. At high temperat
ure, the photoconduction is dominated by the photogenerated electrons in the I
nAs well, in which the relaxation of the excess electrons is prohibitedby an e
nergy barrier due to the trapping of photoexcited holes by deep defectsin the
InAs well.
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Zheng, Yu-Shiang, and 鄭羽翔. "Strain analysis on semipolar nanopyramidal InGaN quantum wells grown on (100) Si substrates." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/8mmy98.
Full textAbstract:
碩士<br>國立中央大學<br>光電科學與工程學系<br>107<br>In this study, the effect of lattice strain before and after substrate transfer on the optoelectrionic properties of nanostructured InGaN quantum wells (QWs) structures was investigated. The nanostructure QWs were grown on (100) Si substrates by metal-organic chemical vapor deposition (MOCVD), employing ZnO nanorods as the buffer layer to release the huge stratin between Si and the nitride epilayer.
Using the small lattice mismatch between ZnO and GaN, we successfully grew the (10-11) semi-polar nanopyramidal QWs on the (100) Si substrate. The diffusion of Zn into GaN during the epitaxial growth also allows us to achieve the naturally formed p-type GaN, producing the desired p-side-down structure for QWs with enhanced interal quantum efficiency. During the growth, three different flow rates of Bis(cyclopentadienyl)-magnesium Mg(C5H5)2, i.e. 40, 80, and 120 sccm were adopted with the attempt to study the effect of p-type doping on the strain and the quantum efficiency of the QWs.
Due to the large thermal mismatch between the GaN epilayer and the Si substrate, huge lattice strain is expected in the epilayer after the MOCVD growth. The strain decreased the internal quantum efficiency of the InGaN QWs via the quantum-confinement Stark effect. The semipolar nanostructured QWs produced in this study are expected to exhibit improved radiative recombination efficiency becoause of the alleived QCSE. In addition, we transferred the epitaxial layer from the Si substrate to a silver substrate using a wet-etching technique, releasing the stress on the samples and increasing reflectivity at the epilayer/substrate interface. The released stress and enhanced interface reflectivity should lead to improved external quantum efficiency of the nanopyramidal QWs.
Scanning electron microscopy was used to observe the microstructure of the samples and a simulation software is used to analyze the relationship between the film thickness and the reflection wavelength. The samples were also characterized by x-ray diffraction (XRD) and Raman spectroscopy. According to these characterizations, it is found that the sample with less magnesium doping exhibits less tensile stress, and thus the higher internal quantum efficiency.
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Sidiki, Tamim Peter [Verfasser]. "Structural and optical characterisation of Si/Si1-xGex multiple quantum wells / submitted by Tamim P. Sidiki." 2001. http://d-nb.info/962699195/34.
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Su, Wei-shiang, and 蘇暐翔. "Studies of GaN thin films and InGaN/GaN quantum wells on Si substrates with AlN buffer layers." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/80232853635099693506.
Full textAbstract:
碩士<br>國立臺南大學<br>材料科學系碩士班<br>100<br>We use micro-Raman spectra, scanning electron microscope, atomic force microscope, and photoluminescence spectra to study the properties of III-V nitride semiconductor materials grown on (111) Si substrates with different growth conditions of AlN buffer layers.
The studies are divided into two parts. The first part is the growth of multiple AlN buffer layers with the decrease of growth temperature from 1000 to 700 oC. For the increase of the numbers of AlN buffer layer, it shows the blue shift of near band edge light emission energy and intensity, high energy shift of E2high and A1(LO) scattering modes of GaN from micro-Raman spectra, pronounced decrease of cracks density in scanning electron microscope images, and the reduced surface roughness in atomic force microscope images. These results indicate that such growth conditions of AlN buffer layers can help in decreasing tensile stress in GaN on (111) Si substrates.
The second part of the researches follow the first part. We also prepared the samples with AlN buffer layers on (111) Si substrates to improve the quality of GaN thin film. Furthermore, the InGaN/GaN multiple quantum wells were deposited on high quality GaN thin films. The near-band edge emission energies and intensities of samples show blue shift and increase respectively with the increase of the numbers of AlN buffer layer. This is due to the reduction of piezoelectric fields as well as the quantum confined Stark effect in InGaN/GaN multiple quantum wells. Also, the shift of E2high and A1(LO) modes of GaN from micro-Raman spectra were observed. The tensile stress in GaN on (111) Si substrates was decreased effectively .
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Huang, Wei-Lun, and 黃偉綸. "Structural and Optical Properties of ZnO/MgxZn1-xO Multiple Quantum Wells Using a Y2O3 Buffer Layer on Si (111)." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/68410280135324073908.
Full textAbstract:
碩士<br>國立交通大學<br>工學院加速器光源科技與應用碩士學位學程<br>104<br>This thesis reports the growth and physical properties of ten-period ZnO/MgxZn1-xO multiple quantum wells (MQWs) prepared on the most widely used semiconductor material, Si. The introduction of a nm-thick Y2O3 transition layer between Si (111) substrate and a ZnO buffer layer significantly improves the structural perfection of the MQWs grown on top of it. Single phase MgxZn1-xO with Mg contents x approximately higher than 0.33, as determined from its lattice constants and cathodoluminescence emitted peak position, was adopted as the barrier material. The high structural quality of the ZnO/MgxZn1-xO MQWs is evidenced by the appearance of pronounced high order satellite peaks in X-ray crystal truncation rods; high resolution cross-sectional TEM images also confirmed the regularly arranged well and barrier layers. We studied the dependence of the near-band edge (NBE) emission transition in ZnO/MgxZn1-xO MQWs on well layer thickness in details. The dominated PL peak of the MQWs shows a significant blue shift with decreasing well width, which is consistent with the quantum confinement effect. From the power-dependent PL spectra conducted at 10k, we observed that built-in electric field effect in MQWs can be negligible when the well width is less than ZnO excition Bohr radius (~3 nm). Moreover, the temperature dependence of PL spectra is investigated to reveal the localization, relaxation and recombination mechanisms of the photo-generated carriers. Our results indicate that ZnO/MgxZn1-xO MQWs integrated on Si have great potential in UV optoelectronic device applications.
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LAI, HO-CHINE, and 賴和謙. "(I) Investigation of surface plasmon resonance behaviors of GaxZn1-xO thin films and (II) influence of AlN buffer layers on GaN films and InGaN/GaN quantum wells grown on Si substrates." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/d9wng5.
Full textAbstract:
碩士<br>國立臺南大學<br>材料科學系碩士班<br>107<br>There are two parts of investigations in this thesis. The first part is the study of plasmonic resonance of characteristics of GaxZn1-xO thin films grown on sapphire substrate with molecular beam epitaxy (MBE). Three series of samples are prepared for the variations of Ga and Zn effusion cell temperature and substrate temperature. The results exhibit that electron concentration of GaxZn1-xO thin films can reach 1020~1021 cm-3. Preferential orientation along (002) of X-ray diffraction (XRD) pattern is demonstrated in GaxZn1-xO thin films. For the GaxZn1-xO thin film with the x content of Ga 6.26 % and substrate temperature 250 °C, it shows the strongest peak intensity of (002), high electron concentration 8.18×1020 cm-3, high electron mobility 30.1 cm2/Vs, low electron resistivity 2.54×10-4 Ω-cm, lower strain of the film, and better micro-photoluminescence (micro-PL) and crystalline structure. Besides Hall effect measurements, spectroscopic ellipsometry (SE) provides an nondestructive and contactless method to obtain electrical properties of semiconductor material with plasmonic behaviors.
The second part of the researches is the influence of AlN buffer layers on GaN films and InGaN/GaN quantum wells grown on Si substrates. Graded decrease of growth temperature from 1000 to 700 oC in depositing multiple AlN buffer layers can effectively reduce the cracks of GaN and hence increase crystalline quality and PL intensity. Two-photon excitation microscopy could help in-depth analysis of formation of GaN thin films.
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Wang, Bo-Yan, and 王博彥. "Studies of (I) the influence of Mn composition on CdMnTe epilayers grown on Si substrate and (II) the effect of silicon doping in part of barriers on 8 periods InGaN/GaN quantum wells." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/j493pm.
Full textAbstract:
碩士<br>國立臺南大學<br>材料科學系碩士班<br>103<br>There are two parts in this research. The first part is the study of effects of Mn content in Cd1-xMnxTe grown by molecular beam epitaxy (MBE) on silicon (Si) (111) substrate. Owing to different binding energy of atoms, Te-Te binding shows the lower forming energy than Cd-Te, results in the production of Te-Te binding defects. Incorporation of Mn atoms into CdTe demonstrates that the lower binding energy of Mn-Te than Te-Te can cause the reduction of Te-Te binding defects in CdTe:Mn. In this report, the ternary alloy of Cd1-xMnxTe with Mn content in 0, 2, 21 % were prepared. The integrated intensity of photoluminescence (PL) spectra exhibits three times larger than other samples in sample with Mn content 21 %. The Stokes shift (SS) characterized by peak energy of PL spectra and bandgap energy of photoreflectance (PR) spectra show the greater value in Mn 21 % than others. The results indicate that the larger the Mn content in Cd1-xMnxTe, the more the composition fluctuations of Mn content in Cd1-xMnxTe showing larger SS. Scan electron microscope (SEM) images give the direct behavior of materialmicrostructures. The results indicates that Mn 21 % sample have relatively flat surface of the film. Micro-Raman spectra also exhibit the diminished intensity of scattering modes of A1 and E that are related to Te-Te binding defects. The consequence is that the better condition of Mn content is 21 % in Cd1-xMnxTe for superior optical and material properties.
The second part of the research is the study of optical behaviors of blue light emitting diodes (LEDs) with multiple quantum wells (MQs) containing part of Si doping. The Si doping layers are the first two, three, four, and five barriers of QWs in the growth sequence from sapphire substrate of four samples. The results indicate that the reduction of piezoelectric field in QWs were occurred in all samples for the blue shift in PL peak energy compared with the undoped Si sample. First four Si-doped barrier samples show larger PL spectra intensity with greater carrier localization in QWs and smaller quantum confined Stark effect (QCSE). Soft confinement potential of QWs was observed in first four Si-doped barrier samples due to the existence of strong absorption intensity in the bandgap energy between quantum wells and barriers. The uniform spreading of carriers in QWs were expected in this sample. Blue LED with first four Si-doped barrier, thus having better output power and external quantum efficiency (EQE) under high current injection. Therefore, first four Si-doped barrier is the favorite condition for light emission of blue LED having 8 QWs.