3,661 research outputs found

    The effect of dislocation loops on the light emission of silicon LEDs

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    Recently, different and apparently contradicting results were published regarding the influence of crystal defects on the light emission efficiency of silicon LEDs at room temperature (Wai Lek Ng). In this paper we report our results on light emission of silicon p/sup +/n diodes with various defect engineering approaches. The p/sup +/ region was formed either by ion implantation or by diffusion; and optionally, additional lattice damage was created by silicon ion implantation. The experiments clearly indicate that lattice defects have a detrimental effect on light emission, contrary to the results published in recent years

    Influence of dislocation loops on the near infrared light emission from silicon diodes

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    The infrared light emission of forward-biased silicon diodes is studied. Through ion implantation and anneal, dislocation loops were created near the diode junction. These loops suppress the light emission at the band-to-band peak around 1.1 μm. The so-called D1 line at 1.5 μm is strongly enhanced by these dislocation loops. We report a full study of photoluminescence and electroluminescence of these diodes. The results lead to new insights for the manufacturing approach of practical infrared light sources in integrated circuit

    Room temperature magneto-optic effect in silicon light-emitting diodes

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    In weakly spin-orbit coupled materials, the spin-selective nature of recombination can give rise to large magnetic-field effects, for example on electro-luminescence from molecular semiconductors. While silicon has weak spin-orbit coupling, observing spin-dependent recombination through magneto-electroluminescence is challenging due to the inefficiency of emission due to silicon's indirect band-gap, and to the difficulty in separating spin-dependent phenomena from classical magneto-resistance effects. Here we overcome these challenges to measure magneto-electroluminescence in silicon light-emitting diodes fabricated via gas immersion laser doping. These devices allow us to achieve efficient emission while retaining a well-defined geometry thus suppressing classical magnetoresistance effects to a few percent. We find that electroluminescence can be enhanced by up to 300\% near room temperature in a seven Tesla magnetic field showing that the control of the spin degree of freedom can have a strong impact on the efficiency of silicon LEDs

    Voltage modulated electro-luminescence spectroscopy and negative capacitance - the role of sub-bandgap states in light emitting devices

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    Voltage modulated electroluminescence spectra and low frequency ({\leq} 100 kHz) impedance characteristics of electroluminescent diodes are studied. Voltage modulated light emission tracks the onset of observed negative capacitance at a forward bias level for each modulation frequency. Active participation of sub-bandgap defect states in minority carrier recombination dynamics is sought to explain the results. Negative capacitance is understood as a necessary dielectric response to compensate any irreversible transient changes in the minority carrier reservoir due to radiative recombinations mediated by slowly responding sub-bandgap defects. Experimentally measured variations of the in-phase component of modulated electroluminescence spectra with forward bias levels and modulation frequencies support the dynamic influence of these states in the radiative recombination process. Predominant negative sign of the in-phase component of voltage modulated electroluminescence signal further confirms the bi-molecular nature of light emission. We also discuss how these states can actually affect the net density of minority carriers available for radiative recombination. Results indicate that these sub-bandgap states can suppress external quantum efficiency of such devices under high frequency operation commonly used in optical communication.Comment: 21 pages, 4 sets of figure

    Fabrication and characterization of nanocrystalline silicon LEDs : a study of the influence of annealing

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    This thesis describes the fabrication of a set of bright, visible light-emitting silicon LEDs. These devices were fabricated in-house at the University of Saskatchewan using a custom plasma ion implantation tool, an annealing furnace, and a physical vapour deposition system. A high-fluence (F = 4 × 1015 cm^−2) implantation of molecular hydrogen ions extracted from an RF inductively coupled plasma at an energy of 5 keV was used to create a heavily damaged region in the silicon centered approximately 40 nm below the silicon surface with a width of approximately 56 nm. A matrix of annealing (e.g. thermal processing) processes at 400 ºC and 700 ºC and different durations (30 minutes and 2 hours) as well as an aluminum gettering procedure were tested with the goal of increasing the output electroluminescence intensity. Current-voltage characterization was used to extract information about the defect-rich nanocrystalline, light-emitting layer as well as the Schottky barrier height. This enabled comparison of these new devices with previous silicon LEDs based on porous silicon and other approaches. The processes which were used to fabricate these devices are compatible with standard CMOS processing techniques and could provide one solution to the problem of optical interconnect on multi-core chips. The scientific significance of this work is the demonstration of bright, visible light emission at mean photon energies ∼1.84 eV corresponding to a photon wavelength of λ ≈ 675 nm. This is remarkable given that ordinary crystalline silicon is an indirect bandgap material with a bandgap energy of 1.1 eV, in which band-to-band radiative recombination is forbidden by momentum conservation. The devices fabricated in this thesis have light emission properties similar to previous silicon LEDs based on nanocrystalline or nanoporous silicon. They have the advantage of being easily electrically driven. The nanocrystalline region which is the source of the light emission was nucleated from the ion-implanted layer below the surface of the silicon. This makes these devices mechanically robust and insensitive to environmental conditions. The engineering significance of this work is the production of CMOS compatible light emitters. This study demonstrated increased light emission efficiency at higher annealing temperatures which is likely due to enhanced diffusion and nucleation of silicon nanocrystals in the ion-implant damaged layer

    Active-matrix GaN micro light-emitting diode display with unprecedented brightness

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    Displays based on microsized gallium nitride light-emitting diodes possess extraordinary brightness. It is demonstrated here both theoretically and experimentally that the layout of the n-contact in these devices is important for the best device performance. We highlight, in particular, the significance of a nonthermal increase of differential resistance upon multipixel operation. These findings underpin the realization of a blue microdisplay with a luminance of 10⁶ cd/m²

    Silicon based microcavity enhanced light emitting diodes

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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.: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 / Versicherun

    The Role Of Photonics In Energy

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    Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)In celebration of the 2015 International Year of Light, we highlight major breakthroughs in photonics for energy conversion and conservation. The section on energy conversion discusses the role of light in solar light harvesting for electrical and thermal power generation; chemical energy conversion and fuel generation; as well as photonic sensors for energy applications. The section on energy conservation focuses on solid-state lighting, flat-panel displays, and optical communications and interconnects. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.5Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)U.S. National Science Foundation [DMR-1309459, ECCS 1408051, DMR 1505122]U.S. Office of Naval ResearchEngineering and Physical Sciences Research Council of the UK [EP/K00042X, EP/L012294]European Research Council of the European Union [321305]Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
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