Showing papers on "Diode published in 2002"
TL;DR: Conjugated polymers and indium arsenide–based nanocrystals were used to create near-infrared plastic light-emitting diodes that effectively covers the short-wavelength telecommunications band.
Abstract: Conjugated polymers and indium arsenide–based nanocrystals were used to create near-infrared plastic light-emitting diodes. Emission was tunable from 1 to 1.3 micrometers—a range that effectively covers the short-wavelength telecommunications band—by means of the quantum confinement effects in the nanocrystals. The external efficiency value (photons out divided by electrons in) is ∼0.5% (that is, >1% internal) and is mainly limited by device architecture. The near-infrared emission did not overlap the charge-induced absorption bands of the polymer.
1,286 citations
TL;DR: A redshift that is strongly dependent on pump power supports the idea that the electron–hole plasma mechanism is primarily responsible for the gain at room temperature and is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet–blue coherent light sources.
Abstract: There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices, including lasersand nonlinear optical frequency converters. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet-blue light-emitting diodes, lasers and photodetectors. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films. Here we report the observation of ultraviolet-blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry-Perot modes (Q approximately 10(3)) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV microJ x cm(-2)) supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet-blue coherent light sources.
1,207 citations
TL;DR: Electroluminescence from a single quantum dot within the intrinsic region of a p-i-n junction is shown to act as an electrically driven single-photon source for applications in quantum information technology.
Abstract: Electroluminescence from a single quantum dot within the intrinsic region of a p-i-n junction is shown to act as an electrically driven single-photon source. At low injection currents, the dot electroluminescence spectrum reveals a single sharp line due to exciton recombination, while another line due to the biexciton emerges at higher currents. The second-order correlation function of the diode displays anti-bunching under a continuous drive current. Single-photon emission is stimulated by subnanosecond voltage pulses. These results suggest that semiconductor technology can be used to mass-produce a single-photon source for applications in quantum information technology.
1,110 citations
Patent•
16 Jul 2002TL;DR: In this paper, the fabrication and growth of sub-microelectronic circuitry is described, and the arrangement of such articles to fabricate electronic, optoelectronic, or spintronic devices and components.
Abstract: The present invention relates generally to sub-microelectronic circuitry, and more particularly to nanometer-scale articles, including nanoscale wires which can be selectively doped at various locations and at various levels. In some cases, the articles may be single crystals. The nanoscale wires can be doped, for example, differentially along their length, or radially, and either in terms of identity of dopant, concentration of dopant, or both. This may be used to provide both n-type and p-type conductivity in a single item, or in different items in close proximity to each other, such as in a crossbar array. The fabrication and growth of such articles is described, and the arrangement of such articles to fabricate electronic, optoelectronic, or spintronic devices and components. For example, semiconductor materials can be doped to form n-type and p-type semiconductor regions for making a variety of devices such as field effect transistors, bipolar transistors, complementary inverters, tunnel diodes, light emitting diodes, sensors, and the like.
598 citations
TL;DR: In this paper, the authors reviewed the current available semiconductor laser sources for spectroscopy in the near and mid-infrared spectral region based upon gallium arsenide, indium phosphite, antimonides and lead-salt containing compounds.
555 citations
TL;DR: In this article, the authors proposed a solution for the phosphor conversion of light-emitting diode light for white light sources and some monochrome applications, which takes into account specific issues if aimed at high power output.
Abstract: Phosphor conversion of light-emitting diode light for white light sources and some monochrome applications requires particular phosphor properties and has to take into account specific issues if aimed at high-power output. Limitations and solutions will be discussed, giving special considerations to drive and temperature dependencies. Efficiencies of 32 lm/W for white with good color rendering at 4600 K and 35 lm/W for green (535 nm) have been demonstrated.
478 citations
TL;DR: In this article, a functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires are presented.
Abstract: Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures.
460 citations
TL;DR: In this article, the authors improved the extraction efficiency of emission light from the InGaN-based light-emitting diode (LED) chips grown on sapphire substrates.
Abstract: We markedly improved the extraction efficiency of emission light from the InGaN-based light-emitting diode (LED) chips grown on sapphire substrates Two new techniques were adopted in the fabrication of these LEDs One is to grow nitride films on the patterned sapphire substrate (PSS) in order to scatter emission light Another is to use the Rh mesh electrode for p-GaN contact instead of Ni/Au translucent electrode in order to reduce the optical absorption by the p-contact electrode We fabricated near-ultraviolet (n-UV) and blue LEDs using the above-mentioned techniques When the n-UV (400 nm) LED was operated at a forward current of 20 mA at room temperature, the output power and the external quantum efficiency were estimated to be 220 mW and 355%, respectively When the blue (460 nm) LED was operated at a forward current of 20 mA at room temperature, the output power and the external quantum efficiency were estimated to be 188 mW and 349%, respectively
390 citations
TL;DR: In this article, a small-molecule organic light-emitting diode where the intrinsic emitter layer is sandwiched by n- and p-doped transport layers with appropriate blocking layers was realized.
Abstract: We have realized a small-molecule organic light-emitting diode where the intrinsic emitter layer is sandwiched by n- and p-doped transport layers with appropriate blocking layers. The diodes based on this pin concept have exponential forward characteristics up to comparatively high current densities. The diodes reach high brightness at very low operating voltage: for instance, 1000 cd/m2 at a voltage of 2.9 V. Despite the highly doped transport layers, the devices reach very high efficiency for the given emitter system up to high brightness.
373 citations
Patent•
01 Feb 2002TL;DR: Light emitting diodes include a substrate having first and second opposing faces and that is transparent to optical radiation in a predetermined wavelength range and patterned to define, in cross-section, a plurality of pedestals that extend into the substrate from the first face towards the second face as discussed by the authors.
Abstract: Light emitting diodes include a substrate having first and second opposing faces and that is transparent to optical radiation in a predetermined wavelength range and that is patterned to define, in cross-section, a plurality of pedestals that extend into the substrate from the first face towards the second face. A diode region on the second face is configured to emit light in the predetermined wavelength range, into the substrate upon application of voltage across the diode region. A mounting support on the diode region, opposite the substrate is configured to support the diode region, such that the light that is emitted from the diode region into the substrate, is emitted from the first face upon application of voltage across the diode region. The first face of the substrate may include therein a plurality of grooves that define the plurality of triangular pedestals in the substrate. The grooves may include tapered sidewalls and/or a beveled floor. The first face of the substrate also may include therein an array of via holes. The via holes may include tapered sidewalls and/or a floor.
296 citations
TL;DR: In this paper, the authors review the recent progress of AlGaInP high brightness light-emitting diodes, and discuss several approaches of high efficiency devices for light extraction.
Abstract: This paper reviews the recent progress of AlGaInP high brightness light-emitting diodes. After the discussion of some basic material properties and the general problem of light extraction we will discuss several approaches of high efficiency devices.
TL;DR: In this paper, a general applicable model is presented to describe the potential barrier shape in ultrasmall Schottky diodes, and it is shown that for diode smaller than a characteristic length lc (associated with the semiconductor doping level) the conventional description no longer holds.
Abstract: A generally applicable model is presented to describe the potential barrier shape in ultrasmall Schottky diodes. It is shown that for diodes smaller than a characteristic length lc (associated with the semiconductor doping level) the conventional description no longer holds. For such small diodes the Schottky barrier thickness decreases with decreasing diode size. As a consequence, the resistance of the diode is strongly reduced, due to enhanced tunneling. Without the necessity of assuming a reduced (non-bulk) Schottky barrier height, this effect provides an explanation for several experimental observations of enhanced conduction in small Schottky diodes.
TL;DR: In this paper, the design, fabrication, and characterization of a 130 A Schottky diode, 4.9 kV 4H-SiC SiC PiN diode and 8.6 kV SiC power diodes are described in detail.
Abstract: The present state of SiC power Schottky and PiN diodes are presented in this paper. The design, fabrication, and characterization of a 130 A Schottky diode, 4.9 kV Schottky diode, and an 8.6 kV 4H-SiC PiN diode, which are considered to be significant milestones in the development of high power SiC diodes, are described in detail. Design guidelines and practical issues for the realization of high-power SiC Schottky and PiN diodes are also presented. Experimental results on edge termination techniques applied to newly developed, extremely thick (e.g., 85 and 100 /spl mu/m) 4H-SiC epitaxial layers show promising results. Switching and high-temperature measurements prove that SiC power diodes offer extremely low loss alternatives to conventional technologies and show the promise of demonstrating efficient power circuits. At sufficiently high on-state current densities, the on-state voltage drop of Schottky and PiN diodes have been shown to be comparable to those offered by conventional technologies.
TL;DR: In this paper, the authors studied the electrical characteristics and optical properties of GaN/InGaN multiple quantum well (MQW) light-emitting diodes (LEDs) grown by metalorganic chemical vapor deposition.
Abstract: We have studied the electrical characteristics and optical properties of GaN/InGaN multiple quantum well (MQW) light-emitting diodes (LEDs) grown by metalorganic chemical vapor deposition. It appears that there is an essential link between material quality and the mechanism of current transport through the wide-bandgap p-n junction. Tunneling behavior dominates throughout all injection regimes in a device with a high density of defects in the space-charge region, which act as deep-level carrier traps. However, in a high-quality LED diode, temperature-dependent diffusion-recombination current has been identified with an ideality factor of 1.6 at moderate biases. Light output has been found to follow a power law, i.e., L /spl prop/ I/sup m/ in both devices. In the high-quality LED, nonradiative recombination centers are saturated at current densities as low as 1.4 /spl times/ 10/sup -2/ A/cm/sup 2/. This low saturation level indicates that the defects in GaN, especially the high density of edge dislocations, are generally optically inactive.
TL;DR: In this paper, a sputter deposition of n-ZnO films on p-Si substrates was used to construct a photodiode with an Ar/O 2 ratio of 6:1.
TL;DR: In this paper, the authors demonstrate lowvoltage inverted transparent vacuum deposited organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode.
Abstract: We demonstrate low-voltage inverted transparent vacuum deposited organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode. The devices comprise an intrinsic 8-tris-hydroxyquinoline aluminum (Alq3) emitting layer sandwiched in between n- and p-doped charge transport layer with appropriate blocking layers. They exhibit low driving voltages (∼4 V for a luminance of ∼100 cd/m2). The devices are about 50% transparent in the Alq3 emission region and emit green light from both sides with a total external current efficiency of about 2.5 cd/A.
TL;DR: In this article, AlGaN multiple-quantum-well (MQW)-based deep ultraviolet light-emitting diodes over sapphire with peak emission at 278 nm were presented.
Abstract: We report on AlGaN multiple-quantum-well (MQW)-based deep ultraviolet light-emitting diodes over sapphire with peak emission at 278 nm. A new buffer layer growth process was used to reduce the number of defects and hence the nonradiative recombination. The improved material quality and carrier confinement resulted in pulsed powers as high as 3 mW at 278 nm and a significantly reduced deep-level-assisted long-wavelength emission.
TL;DR: In this article, a 2.8-μm-thick GaN-based light-emitting diode structure on 2 in. Si(111) substrates was grown by metalorganic chemical-vapor deposition.
Abstract: Thick, entirely crack-free GaN-based light-emitting diode structures on 2 in. Si(111) substrates were grown by metalorganic chemical-vapor deposition. The ∼2.8-μm-thick diode structure was grown using a low-temperature AlN:Si seed layer and two low-temperature AlN:Si interlayers for stress reduction. In current–voltage measurements, low turn-on voltages and a series resistance of 55 Ω were observed for a vertically contacted diode. By in situ insertion of a SixNy mask, the luminescence intensity is significantly enhanced. A light output power of 152 μW at a current of 20 mA and a wavelength of 455 nm is achieved.
07 Aug 2002
TL;DR: In this paper, a new technique to manufacture vertical Resurf devices is presented, in which the alternating p-n junctions in the drift region are formed by a combination of trench etching and vapor phase doping (VPD).
Abstract: A new technique to manufacture vertical Resurf devices is presented, in which the alternating p-n junctions in the drift region are formed by a combination of trench etching and vapor phase doping (VPD). Scanning capacitance microscopy (SCM) was performed to investigate these deep p-n junctions, showing a uniform doping profile along the full depth of the devices. Electrical measurements on such Resurf diodes display an increase in breakdown voltage from 30 V to 145 V for a device with a 10 /spl mu/m deep drift region doped at 3.5/spl times/10/sup 16/ cm/sup -3/. Such a concept leads to prediction of a specific on-resistance well below the silicon limit for an equivalent MOSFET.
Patent•
25 Jan 2002TL;DR: Light emitting diodes include a substrate having first and second opposing faces and that is transparent to optical radiation in a predetermined wavelength range and patterned to define, in cross-section, a plurality of pedestals that extend into the substrate from the first face towards the second face.
Abstract: Light emitting diodes include a substrate having first and second opposing faces and that is transparent to optical radiation in a predetermined wavelength range and that is patterned to define, in cross-section, a plurality of pedestals that extend into the substrate from the first face towards the second face. A diode region on the second face is configured to emit light in the predetermined wavelength range, into the substrate upon application of voltage across the diode region. A mounting support on the diode region, opposite the substrate is configured to support the diode region, such that the light that is emitted from the diode region into the substrate, is emitted from the first face upon application of voltage across the diode region. The first face of the substrate may include therein a plurality of grooves that define the plurality of triangular pedestals in the substrate. The grooves may include tapered sidewalls and/or a beveled floor. The first face of the substrate also may include therein an array of via holes. The via holes may include tapered sidewalls and/or a floor.
TL;DR: An overview of highly efficient resonant-cavity light-emitting diodes is presented in this article, where the basics of dipole emission in planar cavities are reviewed.
Abstract: An overview of highly efficient resonant-cavity light-emitting diodes is presented. First, the basics of dipole emission in planar cavities are reviewed. From these, a number of design rules are derived. We point out some guidelines for comparison of high-efficiency light-emitting diodes, and use these to review the state-of-the-art devices in different material systems and at different wavelengths. We also discuss some advanced techniques based on gratings or photonic crystals to improve the efficiency of these devices.
TL;DR: In this article, a series of seven polybenzobisazoles were investigated as electron transport materials in arylene vinylene polymer-based electroluminescent devices.
Abstract: A series of seven polybenzobisazoles were investigated as electron transport materials in arylene vinylene polymer-based electroluminescent devices. A large enhancement in performance and stability was observed in poly(p-phenylene vinylene) and poly(2-methoxy-5(2‘-ethyl-hexyloxy)-1,4-phenylene vinylene) light-emitting diodes by using polybenzobisthiazoles and poly(p-phenylene benzobisoxazole) as electron-transport materials. Devices using polybenzobisazole electron transport layers and aluminum cathodes had a turn-on voltage as low as 2.8 V, a luminance of up to 1400 cd/m2, and an external quantum efficiency of up to 2.5%. These polymer devices and their performances were stable under repeated testing over a period of 9−10 months storage in air. The superior performance of the polybenzobisazole thin films as electron-transport and hole-blocking materials in polymer light-emitting diodes is due to their high glass-transition temperature, environmental resistance, and photochemical/electrochemical stability...
Journal Article•
TL;DR: In this article, two types of high-efficiency white light-emitting diodes (LEDs) composed of an InGaN multi-quantum well (MQW), which emit light of two or three different colors without phosphors, were fabricated.
Abstract: We fabricated two types of high-efficiency white light-emitting diodes (LEDs) composed of an InGaN multi-quantum well (MQW), which emit light of two or three different colors without phosphors. The Type-1 white LED emits light of two colors (blue and yellow) from the MQW active layer, while the Type-2 LED emits light of three colors (blue, green and red). When the Type-1 white LED was operated at a forward current of 20 mA at room temperature, the color temperature (Tcp), average color rendering (Ra) and luminous efficiency were 7600 K, 42.7 and 11.04 lm/W, respectively. When the Type-2 white LED was operated at a forward current of 20 mA at room temperature, Tcp, Ra and luminous efficiency were 5060 K, 80.2 and 7.94 lm/W, respectively.
Patent•
14 May 2002
TL;DR: In this article, the design of monolithically integrated diodes for use in planar, thin-film, photovoltaic devices, such as solar cells, is described.
Abstract: The present invention relates to the design of and includes monolithically integrated diodes for use in planar, thin-film, photovoltaic devices, such as solar cells.
TL;DR: In this article, the authors numerically model the effect of surface plasmon (SP) modes on the efficiency of organic light-emitting diodes and show that SP modes can significantly detract from device efficiency, particularly those based on small molecules.
Abstract: Organic light-emitting diodes typically take the form of an optical microcavity in which one layer is a metallic cathode. Coupling between emissive species in the light emitting layer and surface plasmon (SP) modes associated with the metallic cathode result in a loss of efficiency; an aspect often discussed but not so far fully quantified. Here we numerically model the extent of this problem, both for organic light-emitting diodes based on small molecules (Alq/sub 3/) and those based on conjugated polymers (MEH-PPV). We show that SP modes can significantly detract from device efficiency, particularly those based on small molecules. We then report measurements of photo- and electroluminescence from organic light-emitting diodes incorporating wavelength scale periodic structure. These data demonstrate the existence of the SP modes in organic light-emitting diodes. Finally we consider ways in which the problems associated with SPs might be overcome, and may even be turned to advantage.
TL;DR: In this article, double-barrier resonant tunneling diodes (DB-RTDs) were fabricated on (0001) Al2O3 substrates by molecular-beam epitaxy, using a rf-plasma nitrogen source.
Abstract: AlN/GaN double-barrier resonant tunneling diodes (DB–RTDs) were fabricated on (0001) Al2O3 substrates by molecular-beam epitaxy, using a rf-plasma nitrogen source. The AlN/GaN DB–RTDs were designed to have a 3-ML-thick GaN quantum well and 4-ML-thick AlN barrier layers sandwiched by Si-doped n-type GaN contact layers. The current–voltage characteristics of mesa diode samples showed clear negative differential resistance (NDR) at room temperature. The NDR was observed at 2.4 V with a peak current of 2.9 mA, which corresponds to 180 A/cm2. A peak-to-valley current ratio as high as 32 was obtained.
TL;DR: In this paper, a laser plasma thruster for micro-and nanosatellites is proposed, based on the commercial availability of diode lasers with sufficient brightness and 100% duty cycle to produce a repetitively pulsed or continuous vapor or plasma jet on a surface in vacuum.
Abstract: We developed an entirely new type of orientation thruster for micro- and nanosatellites. The laser plasma thruster is based on the recent commercial availability of diode lasers with sufficient brightness and 100% duty cycle to produce a repetitively pulsed or continuous vapor or plasma jet on a surface in vacuum. A low-voltage semiconductor switch can drive the laser. A lens focuses the laser diode output on the ablation target, producing a miniature jet that provides the thrust. Single-impulse dynamic range is nearly five orders of magnitude, and the minimum impulse bit is 1 nN/s in a 100-„s pulse. Even with diffraction-limited focusing optics, at least 0.5-W optical power is needed to produce thrust from selected ablator materials. Thrust-to-power ratio Cm is 50 to 100„N/W and specific impulse Isp is 200‐500 s with a 1-W laser, depending partially on the illumination mode. Transmission and reflection (R) illumination modes are discussed. R mode gives about 50% better Isp and two times better Cm. Improved results are anticipated from higher laser power in the reflection mode. The prototype engine we are developing is intended to provide lifetime on-orbit steering for a 5-kg satellite, as well as reentering it from low Earth orbit.
TL;DR: In this paper, a detailed high-pump-current study of self-heating effects in ultraviolet light-emitting diodes (LEDs) grown on sapphire was presented.
Abstract: We present a detailed high-pump-current study of self-heating effects in ultraviolet light-emitting diodes (LEDs) grown on sapphire. For deep ultraviolet LEDs on sapphire, our results establish self-heating to be a primary cause of premature power saturation under dc pumping. Even the flip-chip packaged devices undergo a steady-state temperature rise to about 70 °C at a dc pump current of only 50 mA (at 8 V) resulting in a significant decrease in LED output. Temperature rise values estimated from peak emission wavelength shifts and from micro-Raman mapping of the active devices were in good agreement.
TL;DR: In this paper, a detailed quantitative analysis of the light extraction and loss mechanisms in high-efficiency GaAs-AlGaAs surface-textured thin-film light-emitting diodes (LEDs) is presented based on a Monte Carlo simulation.
Abstract: We present a detailed quantitative analysis of the light extraction and loss mechanisms in high-efficiency GaAs-AlGaAs surface-textured thin-film light-emitting diodes (LEDs). The analysis is based on a Monte Carlo simulation. Most input parameters, including scattering of photons at the textured surface, sub-bandgap absorption, and absorption at the metal mirror are obtained from experiments or from literature. The simulation also takes into account the effect of photon recycling and the realistic geometry of the diodes. The only remaining fitting parameter is the internal quantum efficiency, which is deduced to be about 80% at room temperature for the experimentally realized 850-nm LEDs with an external quantum efficiency of 44%. The analysis shows further that the most important loss mechanism is reabsorption in the active layer, and in particular in those parts of the active layer that are not electrically pumped. This conclusion is also valid for other types of high-efficiency LEDs. We could furthermore verify the validity of the Monte-Carlo simulation results by conducting experiments at low temperatures, where nonradiative recombination processes are reduced, resulting in the internal quantum efficiency approaching unity. The measured external quantum efficiency at 90 K is 68%, which is close to the theoretically predicted efficiency for a perfect active layer. The results demonstrate that the light extraction from surface-textured LEDs is fully understood and can be quantitatively modeled by a simple raytracing algorithm.
TL;DR: In this paper, the authors analyzed the high-temperature continuous-wave performance of 1.3/spl mu/m AlGaInAs/InP laser diodes grown by digital alloy molecular-beam epitaxy.
Abstract: We analyze the high-temperature continuous-wave performance of 1.3-/spl mu/m AlGaInAs/InP laser diodes grown by digital alloy molecular-beam epitaxy. Commercial laser software is utilized that self-consistently combines quantum-well bandstructure and gain calculations with two-dimensional simulations of carrier transport, wave guiding, and heat flow. Excellent agreement between simulation and measurements is obtained by careful adjustment of material parameters in the model. Joule heating is shown to be the main heat source; quantum-well recombination heat is almost compensated for by Thomson cooling. Auger recombination is the main carrier loss mechanism at lower injection current. Vertical electron escape into the p-doped InP cladding dominates at higher current and causes the thermal power roll-off. Self-heating and optical gain reduction are the triggering mechanisms behind the leakage escalation. Laser design variation is shown to allow for a significant increase in the maximum output power at high temperatures.