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1
Shakoor, Abdul. "Silicon nanocavity light emitters at 1.3-1.5 µm wavelength." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3673.
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Silicon Photonics has been a major success story in the last decade, with many photonic devices having been successfully demonstrated. The only missing component is the light source, however, as making an efficient light source in silicon is challenging due to the material's indirect bandgap. The development of a silicon light source would enable us to make an all-silicon chip, which would find many practical applications. The most notable among these applications are on-chip communications and sensing applications. In this PhD project, I have worked on enhancing silicon light emission by combining material processing and device engineering methods. Regarding materials processing, the emission level was increased by taking three routes. In all the three cases the emission was further enhanced by coupling it with a photonic crystal (PhC) cavity via Purcell effect. The three different approaches taken in this PhD project are listed below. 1. The first approach involves incorporation of optically active defects into the silicon lattice by hydrogen plasma treatment or ion implantation. This process results in broad luminescence bands centered at 1300 and 1500 nm. By coupling these emission bands with the photonic crystal cavity, I was able to demonstrate a narrowband silicon light emitting diode at room temperature. This silicon nano light emitting diode has a tunable emission line in the 1300-1600 nm range. 2. In the second approach, a narrow emission line at 1.28µm was created by carbon ion implantation, termed “G-line” emission. The possibility of enhancing the emission intensity of this line via the Purcell effect was investigated, but only with limited success. Different proposals for future work are presented in this regard. 3. The third approach is deposition of a thin film of an erbium disilicate on top of a PhC cavity. The erbium emission is enhanced by the PhC cavity. Using this method, an optically pumped light source emitting at 1.54 µm and operating at room temperature is demonstrated. A practical application of silicon light source developed in this project in gas sensing is also demonstrated. As a first step, I show refractive index sensing, which is a simple application for our source and demonstrates its capabilities, especially relating to the lack of fiber coupling schemes. I also discuss several proposals for extending applications into on-chip biological sensing.
2
Germer, Susette. "Design and analysis of integrated waveguide structures and their coupling to silicon-based light emitters." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-172306.
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A major focus is on integrated Silicon-based optoelectronics for the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive and portable optical sensors in the environmental control and medicine follows in the development of integrated high resolution sensors [1]. In particular, since 2013 the quick onsite verification of pathogens, like legionella in drinking water pipes, is becoming increasingly important [2, 3]. The essential questions regarding the establishment of portable biochemical sensors are the incorporation of electronic and optical devices as well as the implementations of fundamental cross-innovations between biotechnology and microelectronics.
This thesis describes the design, fabrication and analysis of high-refractive-index-contrast photonic structures. Besides silicon nitride (Si3N4) strip waveguides, lateral tapers, bended waveguides, two-dimensional photonic crystals (PhCs) the focus lies on monolithically integrated waveguide butt-coupled Silicon-based light emitting devices (Sibased LEDs) [4, 5] for use as bioanalytical sensor components. Firstly, the design and performance characteristics as single mode regime, confinement factor and propagation losses due to the geometry and operation wavelength (1550 nm, 541 nm) of single mode (SM), multi mode (MM) waveguides and bends are studied and simulated. As a result, SM operation is obtained for 1550 nm by limiting the waveguide cross-section to 0.5 μm x 1 μm resulting in modal confinement factors of 87 %. In contrast, for shorter wavelengths as 541 nm SM propagation is excluded if the core height is not further decreased.
Moreover, the obtained theoretical propagation losses for the lowestorder TE/TM mode are in the range of 0.3 - 1.3 dB/cm for an interface roughness of 1 nm. The lower silicon dioxide (SiO2) waveguide cladding should be at least 1 μm to avoid substrate radiations. These results are in a good correlation to the known values for common dielectric structures. In the case of bended waveguides, an idealized device with a radius of 10 μm was developed which shows a reflection minimum (S11 = - 22 dB) at 1550 nm resulting in almost perfect transmission of the signal. Additionally, tapered waveguides were investigated for an optimized light coupling between high-aspect-ratio devices. Here, adiabatic down-tapered waveguides were designed for the elimination of higher-order modes and perfect signal transmission. Secondly, fabrication lines including Electron-beam (E-beam) lithography and reactive ion etching (RIE) with an Aluminum (Al) mask were developed and lead to well fabricated optical devices in the (sub)micrometer range.
The usage of focused ion beam (FIB) milling is invented for smoother front faces which were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). As a result, the anisotropy of the RIE process was increased, but the obtained surface roughness parameters are still too high (10 – 20 nm) demonstrating a more advanced lithography technique is needed for higher quality structures. Moreover, this study presents an alternative fabrication pathway for novel designed waveguides with free-edge overlapping endfaces for improving fiber-chipcoupling.
Thirdly, the main focus lies on the development of a monolithic integration circuit consisting of the Si-based LED coupled to an integrated waveguide. The light propagation between high-aspect-ratio devices is enabled through low-loss adiabatic tapers. This study shows, that the usage of CMOS-related fabrication technologies result in a monolithic manufacturing pathway for the successful implementation of fully integrated Si-based photonic circuits. Fourth, transmission loss measurements of the fabricated photonic structures as well as the waveguide butt-coupled Si-based LEDs were performed with a generated setup. As a result, free-edge overlapping MM waveguides show propagation loss coefficients of ~ 65 dB/cm in the range of the telecommunication wavelength. The high surface roughness parameters (~ 150 nm) and the modal dispersion in the core are one of the key driving factors. These facts clearly underline the improvement potential of the used fabrication processes.
However, electroluminescence (EL) measurements of waveguide butt-coupled Si-based LEDs due to the implanted rare earth (RE) ion (Tb3+, Er3+) and the host material (SiO2/SiNx) were carried out. The detected transmission spectra of the coupled Tb:SiO2 systems show a weak EL signal at the main transition line of the Tb3+-ion (538 nm). A second emission line was detected in the red region of the spectrum either corresponding to a further optical transition of Tb3+ or a Non Bridging Oxygen Hole Center (NBOHC) in SiO2. Unfortunately, no light emission in the infrared range was established for the Er3+-doped photonic circuits caused by the low external quantum efficiencies (EQE) of the Er3+ implanted Si-based LEDs.
Nevertheless, transmission measurements between 450 nm – 800 nm lead again to the result that an emission at 650 nm is either caused by an optical transition of the Er3+-ion or initialized by the NBOHC in the host. Overall, it is difficult to assess whether or not these EL signals are generated from the implanted ions, thus detailed statements about the coupling efficiency between the LED and the integrated waveguide are quite inadequate. Nevertheless, the principle of a fully monolithically integrated photonic circuit consisting of a Si-based LED and a waveguide has been successfully proven in this study.
3
Potfajova, J. "Silicon based microcavity enhanced light emitting diodes." Forschungszentrum Dresden-Rossendorf, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-27756.
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Realising Si-based electrically driven light emitters in a process technology compatible with mainstream microelectronics CMOS technology is key requirement for the implementation of low-cost Si-based optoelectronics and thus one of the big challenges of semiconductor technology. This work has focused on the development of microcavity enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si-diode was used, which was fabricated by ion implantation of boron into n-type silicon. Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138 nm with a reasonably high power efficiency of 0.1% [1]. Two MCLEDs emitting light at the resonant wavelength about 1150 nm were demonstrated: a) 1 MCLED with the resonator formed by 90 nm thin metallic CoSi2 mirror at the bottom and semitranparent distributed Bragg reflector (DBR) on the top; b) 5:5 MCLED with the resonator formed by high reflecting DBR at the bottom and semitransparent top DBR. Using the appoach of the 5:5 MCLED with two DBRs the extraction efficiency is enhanced by about 65% compared to the silicon bulk pn-junction diode.
4
Zabel, Thomas [Verfasser], Gerhard [Akademischer Betreuer] Abstreiter, Jonathan J. [Akademischer Betreuer] Finley, and Bougeard [Akademischer Betreuer] Dominique. "Study on silicon-germanium nanoislands as emitters for a monolithic silicon light source / Thomas Zabel. Gutachter: Jonathan J. Finley ; Bougeard Dominique ; Gerhard Abstreiter. Betreuer: Gerhard Abstreiter." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/103155176X/34.
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Potfajova, J. "Silicon based microcavity enhanced light emitting diodes." Forschungszentrum Dresden-Rossendorf, 2009. https://hzdr.qucosa.de/id/qucosa%3A21604.
Full textAbstract:
Realising Si-based electrically driven light emitters in a process technology compatible with mainstream microelectronics CMOS technology is key requirement for the implementation of low-cost Si-based optoelectronics and thus one of the big challenges of semiconductor technology. This work has focused on the development of microcavity enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si-diode was used, which was fabricated by ion implantation of boron into n-type silicon. Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138 nm with a reasonably high power efficiency of 0.1% [1]. Two MCLEDs emitting light at the resonant wavelength about 1150 nm were demonstrated: a) 1 MCLED with the resonator formed by 90 nm thin metallic CoSi2 mirror at the bottom and semitranparent distributed Bragg reflector (DBR) on the top; b) 5:5 MCLED with the resonator formed by high reflecting DBR at the bottom and semitransparent top DBR. Using the appoach of the 5:5 MCLED with two DBRs the extraction efficiency is enhanced by about 65% compared to the silicon bulk pn-junction diode.:List of Abbreviations and Symbols
1 Introduction and motivation
2 Theory
2.1 Electronic band structure of semiconductors
2.2 Light emitting diodes (LED)
2.2.1 History of LED
2.2.2 Mechanisms of light emission
2.2.3 Electrical properties of LED
2.2.4 LED e ciency
2.3 Si based light emitters
2.4 Microcavity enhanced light emitting pn-diode
2.4.1 Bragg reflectors
2.4.2 Fabry-Perot resonators
2.4.3 Optical mode density and emission enhancement in coplanar Fabry-Perot resonator
2.4.4 Design and optical properties of a Si microcavity LED
3 Preparation and characterisation methods
3.1 Preparation techniques
3.1.1 Thermal oxidation of silicon
3.1.2 Photolithography
3.1.3 Wet chemical cleaning and etching
3.1.4 Ion implantation
3.1.5 Plasma Enhanced Chemical Vapour Deposition (PECVD) of silicon nitride
3.1.6 Magnetron sputter deposition
3.2 Characterization techniques
3.2.1 Variable Angle Spectroscopic Ellipsometry (VASE)
3.2.2 Fourier Transform Infrared Spectroscopy (FTIR)
3.2.3 Microscopy
3.2.4 Electroluminescence and photoluminescence measurements
4 Experiments, results and discussion
4.1 Used substrates
4.1.1 Silicon substrates
4.1.2 Silicon-On-Insulator (SOI) substrates
4.2 Fabrication and characterization of distributed Bragg reflectors
4.2.1 Deposition and characterization of SiO2
4.2.2 Deposition of Si
4.2.3 Distributed Bragg Reflectors (DBR)
4.2.4 Conclusions
4.3 Design of Si pn-junction LED
4.4 Resonant microcavity LED with CoSi2 bottom mirror
4.4.1 Device preparation
4.4.2 Electrical Si diode characteristics
4.4.3 EL spectra
4.4.4 Conclusions
4.5 Si based microcavity LED with two DBRs
4.5.1 Test device
4.5.2 Device fabrication
4.5.3 LED on SOI versus MCLED
4.5.4 Conclusions
5 Summary and outlook
5.1 Summary
5.2 Outlook
A Appendix
A.1 The parametrization of optical constants
A.1.1 Kramers-Kronig relations
A.1.2 Forouhi-Bloomer dispersion formula
A.1.3 Tauc-Lorentz dispersion formula
A.1.4 Sellmeier dispersion formula
A.2 Wafer holder
List of publications
Acknowledgements
Declaration / Versicherung
6
Potfajova, Jaroslava. "Silicon based microcavity enhanced light emitting diodes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-25451.
Full textAbstract:
Realising Si-based electrically driven light emitters in a process technology compatible with mainstream microelectronics CMOS technology is key requirement for the implementation of low-cost Si-based optoelectronics and thus one of the big challenges of semiconductor technology. This work has focused on the development of microcavity enhanced silicon LEDs (MCLEDs), including their design, fabrication, and experimental as well as theoretical analysis. As a light emitting layer the abrupt pn-junction of a Si diode was used, which was fabricated by ion implantation of boron into n-type silicon. Such forward biased pn-junctions exhibit room-temperature EL at a wavelength of 1138 nm with a reasonably high power efficiency of 0.1%. Two MCLEDs emitting light at the resonant wavelength about 1150 nm were demonstrated: a) 1-lambda MCLED with the
resonator formed by 90 nm thin metallic CoSi2 mirror at the bottom and semitransparent distributed Bragg reflector (DBR) on the top; b) 5.5-lambda MCLED with the resonator formed by high reflecting DBR at the bottom and semitransparent top DBR. Using the appoach of the 5.5-lambda MCLED with two DBRs the extraction efficiency is enhanced by about 65% compared to the silicon bulk pn-junction diode.
7
Germer, Susette [Verfasser], Lars [Akademischer Betreuer] Rebohle, Wolfgang [Akademischer Betreuer] Skorupa, Johannes [Akademischer Betreuer] Heitmann, and Manfred [Akademischer Betreuer] Helm. "Design and analysis of integrated waveguide structures and their coupling to silicon-based light emitters / Susette Germer. Gutachter: Johannes Heitmann ; Manfred Helm. Betreuer: Lars Rebohle ; Wolfgang Skorupa." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://d-nb.info/1075123712/34.
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Germer, Susette Verfasser], Lars [Akademischer Betreuer] [Rebohle, Wolfgang [Akademischer Betreuer] Skorupa, Johannes [Akademischer Betreuer] Heitmann, and Manfred [Akademischer Betreuer] Helm. "Design and analysis of integrated waveguide structures and their coupling to silicon-based light emitters / Susette Germer. Gutachter: Johannes Heitmann ; Manfred Helm. Betreuer: Lars Rebohle ; Wolfgang Skorupa." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://d-nb.info/1075123712/34.
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Arciniegas, Carlos Andres Gonzalez. "Properties of the light emitted by a silicon on-chip optical parametric oscillator (OPO)." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-22112017-153330/.
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The Optical Parametric Oscillator (OPO) has been one of the most versatile source of non-classical states of light. Usual configurations of such devices are a macroscopic second order nonlinear crystals inside an optical cavity. Recently the use of silicon photonics techniques allowed the implementation of high quality factor microcavities and OPOs which include several technological advantages over usual configuration as a small size, bigger bandwidth, CMOS compatibility, facility to engineer the dispersion properties and compatibility with commercial optical fiber communications. Nevertheless the nonlinearity present within these systems is a third order nonlinearity for which theoretical calculations lack in the literature. Here we describe theoretically the quantum properties of the light generated in an OPO with a third order nonlinearity. We showed that the effects of phase modulation (which are not present in the second order nonlinearity) and dispersion are determinant in the way that oscillation and entanglement is produced in the system. Despite of these effects, bipartite and tripartite entanglement is predicted with the use of the Schmidt modes formalism. We also describe the system when there are more modes exited within the cavity and a frequency comb is formed. In such a situation, using again the Schmidt modes formalism, multipartite entanglement was predicted as well.O oscilador paramétrico ótico (OPO) tem sido uma fonte muito versátil de estados não clássicos da luz. A configuração usual destes OPOs consiste em um cristal macroscópico com não linearidade de segunda ordem no interior de uma cavidade ótica. Recentemente, devido ao desenvolvimento da fotonica de silício, foi possível a implementação de micro- cavidades óticas e OPOs que possuem varias vantagens sobre OPOs usuais. Não entanto a não linearidade destes sistemas é de terceira ordem. Neste trabalho, descrevemos teoricamente as propriedades quânticas da luz gerada num OPO com não linearidade de terceira ordem. Mostra-se que os efeitos de modulação de fase (não presentes na não linearidade de segunda ordem) e a dispersão são determinantes para a geração e o emaranhamento produzido no sistema. Emaranhamento bi e tri partito foi predito teoricamente usando o formalismo de modos de Schmidt. Também foi feita uma descrição quando mais modos da cavidade são excitados gerando um pente de frequência. Nesta situação. e utilizando novamente o formalismo de modos de Schmidt, foi predito emaranhamento multimodo destes sistemas.
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Lai, Jiun-Hong. "Development of low-cost high-efficiency commercial-ready advanced silicon solar cells." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52234.
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The objective of the research in this thesis is to develop manufacturable high-efficiency silicon solar cells at low-cost through advanced cell design and technological innovations using industrially feasible processes and equipment on commercial grade Czochralski (Cz) large-area (239 cm2) silicon wafers. This is accomplished by reducing both the electrical and optical losses in solar cells through fundamental understanding, applied research and demonstrating the success by fabricating large-area commercial ready cells with much higher efficiency than the traditional Si cells. By developing and integrating multiple efficiency enhancement features, namely low-cost high sheet resistance homogeneous emitter, optimized surface passivation, optimized rear reflector, back line contacts, and improved screen-printing with narrow grid lines, 20.8% efficient screen-printed PERC (passivated emitter and rear cell) solar cells were achieved on commercial grade 239 cm2 p-type Cz silicon wafers.
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Bates, R. "Silicon heterostructure intersubband emitters." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596474.
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It is believed that the Silicon Germanium (SiGe) materials system offers numerous benefits over GaAs/AlGaAs for operation within the THz gap - absorption coefficients are lower due to the non-polar nature of the SiGe lattice and the potential for integration with Si chips exists. Furthermore, operating within the valence band allows surface normal emission to be observed and vertical cavity surface emitting lasers to be fabricated using transitions between light (LH) and heavy (HH) hole subbands and poly-Si/silicon dioxide Bragg reflectors. This dissertation reports upon recent advances made in FIR Quantum Cascade Emitters (QCEs) based within the SiGe materials system. Initial measurements were designed purely to demonstrate the ability of the vertical intersubband transition to absorb radiation. Such structures were also observed to emit and spectroscopy was performed allowing the origin of such emission to be verified as being due to intersubband transitions. QCEs were then designed and processed, allowing the observation of the first surface-normal emission from a QCE in the absence of a grating to be observed. Further designs demonstrated the primary dependence upon the strain within the quantum wells of the energy of the LH1-HH1 transition. The scalability of the active regions has also been demonstrated - the strain symmeterised growth allowing hundreds of layers to be grown at a uniformly high standard. A shift from vertical (intrawell) to diagonal (interwell) transitions using photon assisted tunnelling lead to the theoretical observation of population inversion within the system. One of the key requirements for lasing, the existence of population inversion demonstrates both the potential and feasibility for a QCL to be fabricated in SiGe.
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Krishnan, Jagadamma Lethy. "Characterisation of nanostructured light emitters." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=17192.
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Group III-nitride semiconductors are the dominant inorganic solid state light emitting materials, spanning the UV to infra-red spectral range. InGaN/GaN based LEDs and lasers are commercially available and intense research is being pursued to improve their efficiency. One practical approach is the development of functionalised and/or improved materials patterned on a nanometre length scale. This thesis presents the optical, morphological and compositional characterisation of III-nitride based nanostructured light emitters. The III-nitride nanostructures studied are GaN coalesced above arrays of either nanopyramids or nanocolumns, semipolar and nonpolar InGaN QWs on the facets of GaN nanopyramids, and thin epilayers of AlInN and AlInGaN. Spatially resolved optical characterisation of nano-ELOG GaN layers revealed a shift in the exciton-related band edge emission across the coalesced layer. This is related to Si doping and to strain effects. Study of the semipolar {1011} InGaN QWs grown on the facets of GaN nanopyramids identified a blue shift in QW emission energy as the sampled region is moved up the pyramid facets. This shift is found to follow the release of the tensile strain towards the top of nanopyramid. Luminescence properties of nearly lattice matched AlInN epilayers investigated using CL, PL and PLE spectroscopic techniques revealed that the emission and bandgap energy of the AlInN layers are at higher energy than that of GaN. Results obtained from polarisation resolved PL measurements of AlInN epilayers point to two possible implications: the observed higher energy AlInN emission is either related to defects or this emission is due to carrier recombination occurring in InN clusters similar to those of InGaN epilayers. Optical properties of thin AlInGaN epilayers investigated using PL and PLE spectroscopy revealed a redshift in bandgap energy with increase in InN fraction. The observed spatial intensity fluctuations are discussed in terms of the InN compositional fluctuations and inhomogeneous strain effects.
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Stevens, Renaud. "Modulation Properties of Vertical Cavity Light Emitters." Doctoral thesis, Stockholm : Tekniska högsk, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3240.
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Wölfl, Friedrich. "Intensity noise studies of semiconductor light emitters." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342990.
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Chen, Li. "SILICON CARBIDE PRESSURE SENSORS AND INFRA-RED EMITTERS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1195161915.
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Tomczak, Nikodem. "Single light emitters in the confinement of polymers." Enschede : University of Twente [Host], 2005. http://doc.utwente.nl/57484.
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Fu, Wai-yuen, and 傅惠源. "A comprehensive approach to high efficiency light emitters." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42841537.
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The Best MPhil Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2008-2009published_or_final_version
Electrical and Electronic Engineering
Master
Master of Philosophy
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Girgel, Ionut. "Development of InGaN/GaN core-shell light emitters." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720648.
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Gallium nitride (GaN) and its related semiconductor alloys are attracting tremendous interest for their wide range of applications in blue and green LEDs, diode lasers, high-temperature and high-power electronics. Nanomaterials such as InGaN/GaN core-shell three-dimensional nanostructures are seen as a breakthrough technology for future solid-state lighting and nano-electronics devices. In a core-shell LED, the active semiconductor layers grown around a GaN core enable control over a wide range of wavelengths and applications. In this thesis the capability for the heteroepitaxial growth of a proof-of-principle core-shell LED is advanced. A design that can be applied at the wafer scale using metalorganic vapor phase epitaxy (MOVPE) crystal growth on highly uniform GaN nanorod (NR) structures is proposed. This project demonstrates understanding over the growth constraints of active layers and dopant layers. The impact of reactor pressure and temperature on the morphology and on the incorporated InN mole fraction was studied for thick InGaN shells on the different GaN crystal facets. Mg doping and effectiveness of the p-n junction for a core-shell structure was studied by extensive growth experiments and characterization. Sapphire and Si substrates were used, and at all the stages of growth and fabrication. The structures were optimized to achieve geometry homogeneity, high-aspect-ratio, incorporation homogeneity for InN and Mg dopant. The three-dimensional nature of NRs and their light emission provided ample challenges which required adaptation of characterization and fabrication techniques for a core-shell device. Finally, an electrically contacted core-shell LED is demonstrated and characterized. Achieving a proof-of-principle core-shell device could be the starting point in the development of nanostructure-based devices and new physics, or in solving technical problems in planar LEDs, such as the polarization of emitted light, the quantum-confined Stark effect, efficiency droop, or the green gap.
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Woodhead, Christopher Stephen. "Enhancing the light output of solid state emitters." Thesis, Lancaster University, 2017. http://eprints.lancs.ac.uk/88416/.
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The work in this thesis focuses on improving the light output of room temperature emitting materials, and nanostructures as a stepping stone for use as single photon sources. The primary nanostructures studied are III-V based type-II emitting quantum dots/quantum rings (QDs/QR’s), which emit at telecom wavelengths either in the O-band (GaSb/GaAs QRs) or the C-band (InAs/GaAs QDs capped with GaAsSb). Individual exciton emission at low temperature was observed in these samples using micro-photoluminescence for what we believe is the first time. This was achieved by reducing the excitation area of the sample using micropillars and gold aperture masks, combined with increasing the extraction efficiency of light using a solid immersion lens. The observation of individual exciton emission enabled their contribution to the power dependent blueshift of type-II quantum dots to be studied. The integration of the InAs/GaAs QDs with silicon was explored by studying their emission when they are grown on both GaAs and silicon substrates. Studies such as this are an important step towards integrating QDs with on-chip communications. Finally, solid immersion lenses formed from a UV-curable epoxy are explored as a method for increasing light out of 2D materials. It was found that for Tungsten Diselenide (WSe2) the solid immersion lens increased the intensity of the emitted photoluminescence, as well as preventing the monolayer from degrading. This method could prove to be an excellent method for increasing the light output of 2D material based LED’s, especially WSe2 based single photon sources.
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Fu, Wai-yuen. "A comprehensive approach to high efficiency light emitters." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42841537.
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Gold, Daniel Patrick. "Transmission electron microscope studies of emitters of silicon bipolar transistors." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:ec5f58c3-ced6-44fe-8f1f-d042cdb7b7b7.
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Transmission Electron Microscope (TEM) studies have been carried out of emitter regions in polysilicon contacted emitter bipolar transistors. The preparation of suitable TEM thin foils is described. In addition a technique is developed for the observation and quant jtative interpretation of the break-up of the interfacial oxide layers observed in these samples. The effect of annealing the samples prior to emitter dopant implantation (pre-annealing) is investigated for phosphorus and arsenic doped samples, implanted into a polysilicon layer 0.4μm thick, with a dose of 1x1016cm2. Two wafer pre-cleans have been used prior to polysilicon deposition to produce a thin oxide (0-8Å) and a thicker oxide (14Å). In the presence of the thinner oxide, the phosphorus doped samples enhance epitaxial regrowth of the polysilicon layer compared with the arsenic doped or undoped samples. In the presence of the thicker oxide, no difference is observed between the samples. A mechanism is proposed to explain this. The mechanisms controlling the gain of a phosphorus doped device are investigated and a model proposed to explain the observed electrical characteristics. It is concluded that there are two mechanisms responsible for the observed supression of hole current. Firstly tunnelling through the interfacial oxide and secondly some blocking effect of the interface. Carrier transport in the polysilicon is not believed to contribute to this supression. A dopant sensitive etch has been applied to TEM thin foils containing fully processed emitters in state-of-the-art devices. The shape of the emitter dopant distribution is revealed in such devices for the first time, and a 2-D profile is obtained from the emitter. It is shown that reduction in the emitter depth to 8OOÅ or less does not alter the emitter dopant geometry. The technique is demonstrated to be capable of resolving spatial separations of dopant iso-concentration contours of 100Å or less.
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Laws, Gerard Michael. "Design and processing of gallium nitride based light emitters." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326522.
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ZHOU, XIANGYU. "Physics-based multiscale modeling of III-nitride light emitters." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2639710.
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The application of computer simulations to scientific and engineering problems has evolved to an established phase over the last decades. In the field of semiconductor device physics, Technology CAD (TCAD) has been regarded as an indispensable tool for the interpretation and prediction of device behavior. More specifically, TCAD modeling and simulation of nanostructured III-nitride light emitters still have challenging problems and is currently a topic under active research.
This thesis devotes to the theoretical and numerical investigations of III-nitride bulk and quantum structures, following a bottom-up approach aimed at modeling and understanding photoluminescence and electroluminescence in these structures. In the first part, the calculation of electronic bandstructure is addressed, where a novel k · p model derived from Non-local Empirical Pseudopotential method(NL-EPM) is presented. Optical properties are then calculated employing both Poisson-k · p and a density-matrix based approach, gain and luminescence spectra can be extracted by solving the semiconductor-Bloch equation numerically. The last part of this thesis deals with the microscopic quantum transport, within the framework of the quantum-statistical nonequilibrium Greens function formalism(NEGF). While classical drift-diffusion models assume that bound carriers hold their coherence in the confined direction and unbound carriers are completely incoherent, NEGF does not distinguish between bound and unbound states and treats them on equal footing. In addition, NEGF also provides intuitive insights into energy-resolved carrier distributions, currents and coherence loss mechanisms.
The numerical computations alongside this thesis can be computationally very involved, some code developed along with this thesis is deployed on the clusters and able to scale up to more than 1000 CPU cores, thanks to the parallel implementation technique such as OpenMP and MPI, as well as HPC infrastructures available at CINECA computing center.
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Garner, D. M. "Silicon heterojunction bipolar transistors with wide band-gap amorphous semiconductor emitters." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599324.
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Firstly, the motivation behind the silicon HBT is discussed, followed by an investigation of tetrahedral amorphous carbon (ta-C) as a possible heteroemitter material. Silicon HBTs with n-type ta-C as a heteroemitter in npn transistors were studied first. Transistor action occurred, but the current gain was only 10-6. This was found to be due to the low electron affinity of ta-C creating a barrier to electron injection into the base, opposite to how an HBT should behave. The low electron affinity of ta-C motivated the fabrication of pnp transistors with p-type ta-C as the heteroemitter. These performed better, having a current gain approaching unity. The lack of thorough investigation of the silicon HBT with an amorphous silicon (a-Si:H) heteroemitter prompted an investigation into the static and dynamic characteristics of this device. Numerical simulation using device modelling software such as MEDICI is well-established for crystalline semiconductor materials but less so for amorphous materials. Therefore a physics-based model for a a-Si:H was incorporated into MEDICI and used to model the a-Si: emitter HBT under a range of collector and base dopings. The main observation from this work was that the low drift mobility of a-Si:H was a major impediment on its frequency response, limiting it to only 2.6GHz. The heteroemitter material properties were then varied to study their effect on transistor dynamic and static characteristics. The requirements on heteroemitter material parameters were found which produced a silicon HBT with superior performance to a silicon homojunction bipolar transistor. Silicon HBTs with a-Si:H emitters were fabricated, and the experimental characteristics compared well with the stimulations, verifying the a-Si:H model and the use of device simulation software to calculate the characteristics of silicon HBTs with amorphous emitters. Finally, a new 'pseudo'-HBT (PHBT) structure which has an n-type doped crystalline silicon emitter region between the heteroemitter material and the p-type base was elucidated and studied. This was found to increase the maximum cutoff frequency using an a-Si:H as the heteroemitter material from 2.8GHz to 6.4GHz.
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Heuser, Eike [Verfasser]. "Light-Emitting Polymers with On-Chain Triplet Emitters / Eike Heuser." Wuppertal : Universitätsbibliothek Wuppertal, 2016. http://d-nb.info/1104187329/34.
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Crutchley, Benjamin G. "Investigation into the efficiency limitations of InGaN-based light emitters." Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.583342.
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Seiferth, Frederick J. "Light emission from silicon /." Online version of thesis, 1994. http://hdl.handle.net/1850/11444.
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Haneder, Stephan. "Correlation Between Electronic Structure and Light Emission Properties in Phosphorescent Emitters." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-110988.
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Silverstone, Joshua Wimbridge. "Entangled light in silicon waveguides." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685546.
Full textAbstract:
Quantum computation will unlock a new class of computational complexity, allowing us to solve previously unsolvable problems, and understand previously unconscionable phenomena. A quantum computer must exert precise control over complex quantum systems, on a truly massive scale. It must freely wield entanglement- the ethereal connection between quantum particles-to operate. Photons, particles of light, have obvious use in the transmission of quantum information, but could also process it; their manipulation is aided by a millennium of human experience with optics. This thesis describes how to build a photonic quantum computer from the ground up, and applies today's most scalable optical technology-silicon integrated optics-to construct the first integrated devices which can produce photons and wield their entanglement. I detail the nonlinear process used to produce photons, spontaneous four-wave mixing, as well as the silicon optical technology used to control them. I demonstrate, via four experiments, a massive scaling-up of silicon quantum photonics. Finally, I provide a glimpse of possible technological routes towards universal quantum computation with photons.
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Marconi, Alessandro. "Silicon Nanocrystal Based Light Emitting Devices for Silicon Photonics." Doctoral thesis, Università degli studi di Trento, 2011. https://hdl.handle.net/11572/369171.
Full textAbstract:
This thesis presents experimental work developing silicon nanocrystal based light emitting devices for silicon photonics. The chapters are organized as follows:
In chapter 2, fabrication and characterization of silicon nanocrystal based devices are presented. In collaboration with Intel Corporation and Bruno Kessler Foundation and thanks to the support of European Commission through the project No. ICT-FP7-224312 HELIOS and through the project No. ICT-FP7-248909 LIMA, it is shown that layers and devices containing silicon nanocrystals can be formed in a production silicon-fab on 4 and 8 inch silicon substrates via PECVD and subsequent thermal annealing. Devices produced by single layer and multilayer deposition are studied and compared in terms of structural properties, conduction mechanisms and electroluminescence properties. Power efficiency is evaluated and studied in order to understand the relation between exciton recombination and electrical conduction. A band gap engineering method is proposed in order to better control carrier injection and light emission in order to enhance the electroluminescence power efficiency.
In chapter 3, the power efficiency of silicon nanocrystal light-emitting devices is studied in alternating current regime. An experimental method based on impedance spectroscopy is proposed and an electrical model based on the constant phase element (CPE) is derived. It is, then, given a physical interpretation of the electrical model proposed by considering the disordered composition of the active material. The electrical model is further generalized for many kinds of waveforms applied and it is generalized for the direct current regime. At the end, time-resolved electroluminescence and carrier injection in alternate current regime are presented.
In chapter 4, erbium implanted silicon rich oxide based devices are presented. The investigation of opto-electrical properties of LED in direct current and alternate current regime are studied in order to understand the injection mechanism and estimate the energy transfer between silicon nanocrystals and erbium. At the end a device layout and process flow for an erbium doped silicon nanocrystal based laser structure are shown.
In chapter 5, some other applications of silicon nanocrystal are presented. An example of all-silicon solar cell is shown. The photovoltaic properties and carrier transport of silicon nanocrystal based solar are studied. At the end, the combination of emitting and absorbing properties of silicon nanocrystal based LED are used to develop an all-silicon based optical transceiver.
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Marconi, Alessandro. "Silicon Nanocrystal Based Light Emitting Devices for Silicon Photonics." Doctoral thesis, University of Trento, 2011. http://eprints-phd.biblio.unitn.it/630/1/Tesi_PhD_Marconi_Alessandro.pdf.
Full textAbstract:
This thesis presents experimental work developing silicon nanocrystal based light emitting devices for silicon photonics. The chapters are organized as follows:
In chapter 2, fabrication and characterization of silicon nanocrystal based devices are presented. In collaboration with Intel Corporation and Bruno Kessler Foundation and thanks to the support of European Commission through the project No. ICT-FP7-224312 HELIOS and through the project No. ICT-FP7-248909 LIMA, it is shown that layers and devices containing silicon nanocrystals can be formed in a production silicon-fab on 4 and 8 inch silicon substrates via PECVD and subsequent thermal annealing. Devices produced by single layer and multilayer deposition are studied and compared in terms of structural properties, conduction mechanisms and electroluminescence properties. Power efficiency is evaluated and studied in order to understand the relation between exciton recombination and electrical conduction. A band gap engineering method is proposed in order to better control carrier injection and light emission in order to enhance the electroluminescence power efficiency.
In chapter 3, the power efficiency of silicon nanocrystal light-emitting devices is studied in alternating current regime. An experimental method based on impedance spectroscopy is proposed and an electrical model based on the constant phase element (CPE) is derived. It is, then, given a physical interpretation of the electrical model proposed by considering the disordered composition of the active material. The electrical model is further generalized for many kinds of waveforms applied and it is generalized for the direct current regime. At the end, time-resolved electroluminescence and carrier injection in alternate current regime are presented.
In chapter 4, erbium implanted silicon rich oxide based devices are presented. The investigation of opto-electrical properties of LED in direct current and alternate current regime are studied in order to understand the injection mechanism and estimate the energy transfer between silicon nanocrystals and erbium. At the end a device layout and process flow for an erbium doped silicon nanocrystal based laser structure are shown.
In chapter 5, some other applications of silicon nanocrystal are presented. An example of all-silicon solar cell is shown. The photovoltaic properties and carrier transport of silicon nanocrystal based solar are studied. At the end, the combination of emitting and absorbing properties of silicon nanocrystal based LED are used to develop an all-silicon based optical transceiver.
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Frey, Alexander [Verfasser]. "Industrial n-Type Silicon Solar Cells with Co-Diffused Boron Emitters / Alexander Frey." Konstanz : Bibliothek der Universität Konstanz, 2018. http://d-nb.info/1161342966/34.
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Fernández, Robledo Susana [Verfasser], and Eicke [Akademischer Betreuer] Weber. "Laser-induced forward transfer based boron selective emitters for crystalline silicon solar cells." Freiburg : Universität, 2021. http://d-nb.info/122665715X/34.
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Liang, Yu-Han. "Deep Ultraviolet Light Emitters Based on (Al,Ga)N/GaN Semiconductor Heterostructures." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/1008.
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Deep ultraviolet (UV) light sources are useful in a number of applications that include sterilization, medical diagnostics, as well as chemical and biological identification. However, state-of-the-art deep UV light-emitting diodes and lasers made from semiconductors still suffer from low external quantum efficiency and low output powers. These limitations make them costly and ineffective in a wide range of applications. Deep UV sources such as lasers that currently exist are prohibitively bulky, complicated, and expensive. This is typically because they are constituted of an assemblage of two to three other lasers in tandem to facilitate sequential harmonic generation that ultimately results in the desired deep UV wavelength. For semiconductor-based deep UV sources, the most challenging difficulty has been finding ways to optimally dope the (Al,Ga)N/GaN heterostructures essential for UV-C light sources. It has proven to be very difficult to achieve high free carrier concentrations and low resistivities in high-aluminum-containing III-nitrides. As a result, p-type doped aluminum-free III-nitrides are employed as the p-type contact layers in UV light-emitting diode structures. However, because of impedance-mismatch issues, light extraction from the device and consequently the overall external quantum efficiency is drastically reduced. This problem is compounded with high losses and low gain when one tries to make UV nitride lasers. In this thesis, we provide a robust and reproducible approach to resolving most of these challenges. By using a liquid-metal-enabled growth mode in a plasma-assisted molecular beam epitaxy process, we show that highly-doped aluminum containing III-nitride films can be achieved. This growth mode is driven by kinetics. Using this approach, we have been able to achieve extremely high p-type and n-type doping in (Al,Ga)N films with high aluminum content. By incorporating a very high density of Mg atoms in (Al,Ga)N films, we have been able to show, by temperature-dependent photoluminescence, that the activation energy of the acceptors is substantially lower, thus allowing a higher hole concentration than usual to be available for conduction. It is believed that the lower activation energy is a result of an impurity band tail induced by the high Mg concentration. The successful p-type doping of high aluminum-content (Al,Ga)N has allowed us to demonstrate operation of deep ultraviolet LEDs emitting at 274 nm. This achievement paves the way for making lasers that emit in the UV-C region of the spectrum. In this thesis, we performed preliminary work on using our structures to make UV-C lasers based on photonic crystal nanocavity structures. The nanocavity laser structures show that the threshold optical pumping power necessary to reach lasing is much lower than in conventional edge-emitting lasers. Furthermore, the photonic crystal nanocavity structure has a small mode volume and does not need mirrors for optical feedback. These advantages significantly reduce material loss and eliminate mirror loss. This structure therefore potentially opens the door to achieving efficient and compact lasers in the UV-C region of the spectrum.
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Galata, Sotiria. "Sulphur doped silicon light emitting diodes." Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/842933/.
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In this thesis light emission from sulphur related impurity in silicon has been reported. Although, sulphur related luminescence from silicon has been stated since the 1980's, no room temperature luminescence has been achieved and no compatible devices that can be integrated to the silicon technology have been invented. Photoluminescence and electroluminescence experiments were made on a set of samples implanted with only with sulphur at doses ranging from 1011-1014 S cm-2 at 30 keV, annealed at 1000 °C or 1100 °C for 10 s and on another set of samples implanted with sulphur as above and further implanted with boron at 1015 B cm-2 at 30 keV, further annealed at 950 °C for 1 min. The experiments revealed two major emissions at 1129.5 nm (1.0997 eV) which is due to the Si TO phonon assisted transition and at 1363 nm (0.9097 eV) which is due to sulphur related impurities. Variable temperature experiments were done at both PL and EL experiments. From the EL variable temperature measurements, it was observed that the two main lines were shifting towards longer wavelengths with the increase of temperature. Sulphur emission was present at room temperature with low intensity compared to the silicon emission which was more dominant at room temperature. Of great interest was the effect of power on silicon and sulphur emission. It has revealed a sublinear and a superlinear behaviour for the sulphur and silicon integrated intensity respectively with the increase of the injection condition, which can be attributed to the saturation of sulphur related levels responsible for the 1.33 nm emission at the high excitation levels. A model of the diffusion of sulphur concentration after the annealing treatments was presented, introducing the two cases of perfect reflection and perfect loss from the samples surfaces. Finally a model explaining our PL and EL power dependence experiments was provided which showed that there are two major radiative routes via the silicon and the sulphur that take place, which are competing at each other along with a non-radiative route coming from the sulphur related level. Our model describes the trends in our experimental data well. Finally, the energy related to the sulphur peak quenching was calculated to be 32.2 +/-1.4 meV.
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Siddiqui, Saiful Anam. "Erbium doped silicon light emitting diodes." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/843408/.
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Erbium, a rare earth element, has been shown to exhibit characteristic luminescence at 1.54mum due to its internal 4f transition from the first excited state (4pi3/2) to the ground state (4pi5/2). As this emission wavelength falls inside the maximum transmission window of silicon based optical fibers, erbium doped silicon might lead to the opportunity of silicon based optoelectronics. The introduction of erbium in silicon allows excitation through electron-hole recombination and subsequent radiative emission from the rare earth centers. The works reported here describe the structural, electrical and optical properties of crystalline silicon codoped with erbium and boron by ion implantation technique. Four sets of samples, co-implanted with erbium and boron at different Er dose, implantation energy and at different conditions, were prepared. Post-implantation annealing has been performed to recover the implantation damage to an acceptable value and to activate the dopant atoms optically and electrically. PL and EL measurements have been performed in the temperature range between 80K to room temperature. The sample with the lowest erbium concentration and energy gives the best PL and EL results. The observed emission peaks in both PL and EL measurements were at around 1.129mum, ~1.303mum, 1.50mum and 1.597mum at 80K. At higher temperatures, a broader peak at around 1.50mum with long tail towards the both end of wavelength has been observed. The peak at 1.129mum corresponding to the Si band edge emission, the reason for the peaks at around l.303mum has not been identified while the remaining two peaks correspond the Er3+ emission. Virtually no temperature quenching of Er luminescence is observed in some samples rather room temperature intensity is higher than that at 80K. The improvement of the temperature quenching effect on Er luminescence at room temperature has been attained in our results, which is significant improvement in comparison to the result found in the literature. The structural properties were studied by TEM in both cross-sectional and plan view configurations. TEM analyses showed dislocation loops and other defects of random size and distribution from the surface to 600nm below the surface. Er precipitates defects were also seen in the sample doped with Er comparatively at higher dose (1x1015Er/cm2) and energy (1.0 MeV). No detectable room temperature PL and EL signals were observed from the sample implanted at higher doses and energies.
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Squire, E. K. "Light emitting microstructures in porous silicon." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285287.
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Wang, Junjun [Verfasser]. "Three-dimensional InGaN/GaN based light emitters with reduced piezoelectric field / Junjun Wang." Ulm : Universität Ulm, 2018. http://d-nb.info/1158664257/34.
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O'Regan, Bryan J. "Resonantly enhanced thermal emitters based on nanophotonic structures." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7801.
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The manipulation of photons, especially the control of spontaneous emission, has become a core area of photonics research in the 21st century. One of the key challenges is the control of the broadband emission profile of thermal emitters. Recently, attention has focused on resonant nanophotonic structures to control the thermal emission with most of the work concentrating on the mid-infrared wavelength range and/or based on metallic nanostructures. However, the realisation of a high temperature, single wavelength, narrowband and efficient thermal source, remains a challenge. In this project, four individual nanophotonic resonant structures are presented for the control of thermal emission, all operating in the near-infrared (≈ 1.5 μm) wavelength range. The work is split over two different emission materials; gold and doped silicon. While I present two successful designs of narrowband thermal emitters from gold, the main backbone of the research is concentrated on doped silicon as the emission material. By combining the weak broadband absorption of doped silicon with a photonic crystal resonator, resonantly enhanced narrowband absorption is achieved. Using Kirchhoff's law of thermal radiation which equates the absorptivity and emissivity, narrowband absorption leads to narrowband emission, which is the underlying principle used throughout the work presented in this thesis to achieve narrowband thermal emission. One common oversight in many of the presented thermal emitter designs is the angular emission dependence, i.e. how the emission wavelength behaves away from surface normal. Typically, since the majority of the devices are based on periodic structures, the resonant emission wavelength changes with emission angle, which is not ideal. Here, the angular sensitivity is considered and addressed, by constructing a device that is based on localised confined resonances and not on propagating resonances, it is possible to achieve a truly monochromatic source i.e. one with the same emission wavelength in all directions, all the way up to an angle of 90°. Finally, the devices presented here demonstrate that weak absorption together with photonic resonances can be used as a wavelength-selection mechanism for thermal emitters, both for the enhancement and the suppression of emission away from the resonant wavelength.
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Xuan, Guangchi. "The fabrication and characterization of high temperature Terahertz emitters, and DNA-sensitive transistors based on silicon-germanium and silicon carbide materials." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 138 p, 2008. http://proquest.umi.com/pqdweb?did=1459914001&sid=11&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Lalic, Nenad. "Light emitting devices based on silicon nanostructures." Doctoral thesis, KTH, Electronic Systems Design, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2943.
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Although silicon is the dominant semiconductor today, lightemitting devices are currently based on compound semiconductorsdue to their direct band-gap, which promotes fast radiativerecombination. However, in nanometer-size silicon structures,carrier confinement enhances the radiative recombination,while, at the same time, suppresses diffusion to non-radiativerecombination centra, resulting in a significant increase inlight emission efficiency. Moreover, the band-gap is wideningas the crystal size is reduced (quantum confinement), enablinglight emission in the visible range. In this work, twodifferent approaches to manufacture a light emitting diode(LED) in silicon have been investigated. The first type ofsilicon LED's is based on porous silicon (PSi) and manufacturedby electrochemical etching of a previously formed pn diodestructure. After optimizing the etching process, PSi LED's wereproduced with an external quantum efficiency of ~0.2% underpulsed excitation, more than an order of magnitude higher thanpreviously reported. Tunability of the emission wavelength inthe range 1.6-2eV was demonstrated by varying the etchingparameters. The EL wavelength is determined by the band-gap ofthe nanocrystals, i. e. their size, as evidenced by a lowerthreshold for longer EL wavelengths, due to lower barriers forinjection into larger crystallites. The EL decay after the biaspulse follows a stretched exponential shape, in agreement witha model involving exciton migration in partially interconnectednanocrystals. Under constant bias, the EL and forward currentare decreasing, due to charging, caused by carrier trapping inthe porous network. After the etching the hydrogen passivatedporous silicon surface is being gradually oxidized, resultingin increased barriers, permanent conductivity reduction and ELdegradation. To improve stability, the second LED approach,based on Si nanocrystals embedded in SiO2, was studied. Nanocrystals were formed by theimplantation of Si into thermally grown SiO2and by subsequent annealing at high temperatures(mostly 1100°C). Photoluminescence investigation showedthat luminescence properties are dependent on nanocrystal sizeand similar to those of PSi. However, decay shapes and timeconstants revealed a stronger isolation of the nanocrystalsthan in PSi. For the EL, good current transport properties werenecessary. That required a thin SiO2layer and efficient injection, realized using anin-situ doped poly-Si cap layer. The Si nanocrystal LED's werestable, although the total light intensity was lower than inPSi, as a consequence of a thin active layer.
Key words: Electroluminescence, photoluminescence, lightemitting diode, porous materials, nanostructured materials,silicon, etching, anodized layers, ion implantation.
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Pitanti, Alessandro. "Light-matter interaction in silicon nanophotonic structures." Doctoral thesis, Università degli studi di Trento, 2010. https://hdl.handle.net/11572/368665.
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In this thesis light matter interactions in the weak coupling regime are investigated in Si-based photonic devices. At first, spectroscopic investigation of energy transfer among Er ions and Si-nanoparticles for optical amplification has been reported. Successively, light propagation in dielectric resonator and waveguides has been addressed, in particular considering photon Local Density of States modifications and the possible Purcell enhancement effect.
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Pitanti, Alessandro. "Light-matter interaction in silicon nanophotonic structures." Doctoral thesis, University of Trento, 2010. http://eprints-phd.biblio.unitn.it/208/1/Pitanti_PhDThesis.pdf.
Full textAbstract:
In this thesis light matter interactions in the weak coupling regime are investigated in Si-based photonic devices. At first, spectroscopic investigation of energy transfer among Er ions and Si-nanoparticles for optical amplification has been reported. Successively, light propagation in dielectric resonator and waveguides has been addressed, in particular considering photon Local Density of States modifications and the possible Purcell enhancement effect.
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Wang, Michael Wei-Ching McGill T. C. "Graded injector, wide bandgap light emitters and XPS studies of the InAs/GaSb heterointerface /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10262007-091414.
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Rahman, Tasmiat. "Light trapping structures for photovoltaics using silicon nanowires and silicon micro-pyramids." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/31858.
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The current photovoltaic industry is dominated by crystalline or poly-crystalline Si in a planar pn-junction configuration. The use of silicon nanowire arrays (SiNWA) within this industry has shown great promise due to its application as an anti-reflective layer, as well as benefits in charge carrier extraction. In this work, we use a metal assisted chemical etch process to fabricate SiNWAs onto a dense periodic array of pyramids that are formed using an alkaline etch masked with an oxide layer. The hybrid micro-nano structure acts as an anti-reflective coating with experimental reflectivity below 1% over the visible and near-infrared spectral regions. This represents an improvement of up to 11 and 14 times compared to the pyramid array and SiNWAs on bulk, respectively. In addition to the experimental work, we optically simulate the hybrid structure using the commercial Lumerical FDTD package. The results of the optical simulations support our experimental work, illustrating a reduced reflectivity in the hybrid structure. The nanowire array increases the absorbed carrier density within the pyramid by providing a guided transition of the refractive index along the light path from air into the silicon. Furthermore, electrical simulations which take into account surface and Auger recombination show an effi ciency increase for the hybrid structure of 56% over bulk, 11% over pyramid array and 8.5% over SiNWAs. Opto-electronic modelling was performed by establishing a tool flow to integrate the eff ective optical simulator Lumerical FDTD with the excellent fabrication and electrical simulation capability of Sentaurus TCAD. Interfacing between the two packages is achieved through tool command language and Matlab, off ering fast and accurate electro-optical characteristics of nano-structured PV devices.
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Famiyeh, Lord. "Electrodeposition of Silicon in Fluoride Melts : Production of Silicon Films." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16344.
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There has been considerable interest in electrodeposition of silicon from fluoride melts on a suitable substrate for its application in thin film solar cells. The goal of this work is to produce a high purity silicon films from LiF-KF-K2SiF6 (mol %) that could be suitable for solar grade applications, and to study electrodeposition of silicon in the same melt by performing electrochemical measurements. Cyclic voltammetry was carried out both in pure melt LiF-KF and LiF-KF-K2SiF6 (0.13mol/kg) at 750oC on Ag electrode to study the reduction mechanism of fluorosilicate. The reduction mechanism was found to be mass transport diffusion controlled. The diffusion coefficient was estimated to be 1.1x10-5cm2/s from Randles-Sevcik equation.Chronoamperometry was also carried out in LiF-KF-K2SiF6 (0.13mol/kg) at 750oC on Ag electrode at different cathodic potentials and the current-time response, reduction mechanism of silicate ion was studied. It was also found again that the reduction mechanism of fluorosilicate is diffusion controlled. The diffusion coefficient was calculated to be 4.6x10-4cm2/s using the Cottrell equation. The influence of electrolytic parameters such as temperature, concentration of the electroactive species K2SiF6, and current density on the morphology and purity of the deposits and the current efficiency of the electrolytic process was studied. Effect of temperature and concentration was studied on Ag substrate and current density on both Ag and Si substrate. The influence of the substrate (silver and silicon) was also studied. Before the start of each electrodeposition experiment pre-electrolysis was carried out to remove moisture and reduce impurities concentration to ppm level. The deposits obtained were cleaned in ultrasonic bath to get rid of salt inclusions. It was observed that not all the salt inclusions were completely removed and therefore the current efficiency calculated was described to be apparent (not accurate). A few selected deposits were characterized using scanning electron microscope and energy dispersive spectroscopy, the results are shown below. It was observed that at a temperature of 800oC the deposit was dense, coherent, good adhesion to the silver substrate and with less impurities and salt inclusions but at 550oC the deposit was powdered or dendritic with high content of impurities and salt inclusions. At 5mol% of K2SiF6 the deposit consists of homogeneous structure with less impurities and salt but at 20mol% on the microstructure seems to be elongated and contain high content of impurities and salts. On silicon substrate, at current density 101.5mAcm-2 the deposit was dendritic with no grains, weakly adhered to the silicon substrate and also contains more impurities and salts but at 35.5mAcm-2 the deposit contains large grains with columnar microstructure and less impurities and salts. On silver substrate, at 83.8mAcm-2 the deposit consists of fine microstructure with high content of impurities and salts but at 42.9mAcm-2 the deposit consists of bigger and elongated with high porosity and small content of impurities and salts. For the influence of the substrate, it was observed that on sliver the deposit was insoluble with fine microstructure but on silicon it was soluble and weakly adhered with non uniform microstructure which is powdered and dendritic. The deposit obtained on both silver and silicon contains high content of impurities and salts because of the high current density applied (83.8mAcm-2 on Ag and 80.5mAcm-2 on Si).
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Schiz, Frank Jochen Wilhelm. "The effect of fluorine in low thermal budget polysilicon emitters for SiGe heterojunction bipolar transistors." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287345.
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HU, CHENXI. "Simulation studies and design of AlInGaN-ZnSiGeN2 quantum wells for high-efficiency ultraviolet light emitters." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1589300145090549.
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Anutgan, Mustafa. "Nanocrystal Silicon Based Visible Light Emitting Pin Diodes." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612718/index.pdf.
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The production of low cost, large area display systems requires a light emitting material
compatible with the standard silicon (Si) based complementary metal oxide semiconductor
(CMOS) technology. The crystalline bulk Si is an indirect band semiconductor with very
poor optical properties. On the other hand, hydrogenated amorphous Si (a-Si:H) based wide
gap alloys exhibit strong visible photoluminescence (PL) at room temperature, owing to the
release of the momentum conservation law. Still, the electroluminescence (EL) intensity from
the diodes based on these alloys is weak due to the limitation of the current transport by the
localized states.
In the frame of this work, first, the luminescent properties of amorphous silicon nitride
(a-SiNx:H) thin films grown in a plasma enhanced chemical vapor deposition (PECVD) system
were analyzed with respect to the nitrogen content. Then, the doping effciency of p- and
n-type hydrogenated nanocrystalline Si (nc-Si:H) films was optimized via adjusting the deposition
conditions. Next, the junction quality of these doped layers was checked and further
improved in a homojunction pin diode.
Heterojunction pin light emitting diodes (LEDs) were fabricated with a-SiNx:H as the
luminescent active layer. The EL effciency of the fresh diodes was very low, as expected.
As a solution, the diodes were electro-formed under high electric field leading to nanocrystallization
accompanied by a strong visible light emission from the whole diode area. The
current-voltage (I-V) and EL properties of these transformed diodes were investigated in detail.
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Tu, Hoang. "High efficient infrared-light emission from silicon LEDs." Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/58014.
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