Grafted InGaAsP light emitting diodes on glass channel waveguides

Optically pumped lambda =1.3 mu m InGaAsP LEDs have been integrated with glass channel waveguides using epitaxial liftoff. Coupling of light from the grafted LEDs to the waveguides has been achieved with the aid of an overlayer film with tapered ends. Under pulsed operation, devices exhibit a laser-like threshold but without spectral narrowing.<>     

高亮度LED调光技术

高亮度发光二极管(HB LED)在各种领域应用普及.并要求HB LED具备有调光功能.在现有的几种调光技术中,从简单的可变电阻负载到复杂的脉冲宽度调制(PWM)开关,每一种方法均有其利弊.PWM调光的效率最高,电流控制也最精准.论述了HB LED在调光时的特性,介绍了LM3405评估板及其功能.包括其布局、原理图和元件清单.     

Saturation behavior of extrinsic photoconductivity in GaP light emitting diodes at high infrared intensities

Saturation of extrinsic photoconductivity in GaP:N(Zn, Te) diodes could be achieved by excitation with a TEA-CO₂-laser. At wavelengths in the 10 μm range intensities of several 100 kW/cm² being near the damage threshold were applied. Carrier lifetimes of 60 ps at 4.2 K and 200 ps at 77 K could be estimated. The only conceivable mechanism explaining these short time constants is the capture of infrared excited holes by ionized shallow acceptors in the highly compensated p-side of the diode.     

Materials for light emitting diodes

III–V semiconductor display diodes fall into three material categories: direct, indirect, and diode-phosphor combinations. The light generation mechanisms are well understood in each case. On the basis of the luminous efficacy achieved in the laboratory, the merit of the various materials is in the order: GaP: N (green), GaP: Zn, O (red), GaInP (yellow), GaAsP (red), GaAlAs (red) and GaAs-phosphor combinations (red, green, blue). A more comprehensive assessment of quality must take into account factors such as the economic feasibility of the methods of synthesis, the applicability to monolithic arrays, and the suitability of spectra (hue, contrast, saturation, etc.). The degree of importance of these matters and the limitations of the various materials are less well-defined at present. New developments which may have an impact on the future of display diodes include the use of Al_xGa_1-xP in place of GaP to shift spectra to shorter wavelengths, the possible development of very bright direct alloys of InP with either GaP or A1P, and the doping of GaAsP with N to extend its range of colors.     

High-brightness AlGaInP light emitting diodes

First commercially introduced in 1990, AlGaInP light emitting diodes (LEDs) currently are the highest (luminous) efficiency visible solid-state emitters produced to date in the red through yellow spectral regime. The attainment of this high-efficiency performance is a result of the development of advanced metalorganic chemical vapor deposition crystal growth techniques, which have facilitated the high-quality growth of this quaternary alloy as well as the implementation of complex device designs. Furthermore, the highest efficiency family of AlGaInP devices (based upon a transparent-substrate platform and commercially introduced in 1994) have been realized as result of the development and implementation of direct compound semiconductor wafer bonding technology. As a result, the luminous efficiency of AlGaInP LEDs exceeds or rivals that of unfiltered incandescent lamps and other conventional lighting sources. Further improvements in these techniques (and the realization of efficient, high-power LEDs) are expected to make AlGaInP LEDs even more competitive with conventional lamp technology, thus enhancing the position of LED's in many applications as a preferred lighting source     

高p型掺杂对高亮度发光二极管的作用

根据统计学理论系统分析了p掺杂在高亮度发光二极管中(HB-LED)的作用,研究了p型限制层掺杂浓度及浓度梯度变化时导带势垒的变化,由此得到对提高电子有效约束的浓度范围;提高电流扩展层的掺杂浓度,减小电阻率,使得注入器件的电流得到充分的扩展.两者是提高器件的外量子效率非常有效的方法.实验证明了理论分析是正确的.     

Theory and experiment for silicon Schottky barrier diodes at high current density

Metal-silicon Schottky barrier diodes exhibit n values which theoretically vary as a function of doping and applied voltage. The expected variation depends on which theoretical model is used to describe the current transport.Titanium n-type silicon barriers were prepared. At a doping level of 3 × 10¹⁵ cm^?3 the barrier height and n-value measured at 100 mV were 0.485±0.005 V and 1.02±0.01 whereas for a doping level of 2 × 10¹⁴ cm^?3 the corresponding values were 0.500±0.005 V and 1.18±0.05.The experimental variation of the diode n value as a function of semiconductor band bending showed good agreement with the thermionic-diffusion model of Crowell and Beguwala: n values increased rapidly as the band bending β → 2, and n values were highest at a given β for diodes with the lowest doping concentration. Similar results were obtained by measurements on magnesium and aluminium barriers on n-type silicon.An analysis of the results has shown that the variation of the diode saturation current I_s follows the predictions of the thermionic-diffusion theory, although there were some anomalies at high current densities. The anomalies did not result from variation of the width of the undepleted region of the epitaxial silicon layer or from diode self-heating effects.     

Homogeneous degradation of surface emitting type InGaAsP/InP lightemitting diodes

The homogeneous degradation modes of InGaAsP/InP light-emitting diodes (LED) with either a Au-Zn ohmic type or a Ti/Pt/Au Schottky type p-side electrode are discussed. In LEDs with a Au-Zn electrode homogeneous degradation goes through two distinct stages: an initial period of very slowly decreasing optical output power followed by a period of rapidly decreasing optical output power. Both modes are caused by electrode metal diffusion and alloy reactions between the electrode and the cap, cladding, and active layers during aging. In Ti/Pt/Au electrode LEDs homogeneous degradation is accompanied by a series resistance increase, which is caused by the formation of In- and Ga-depleting interfacial layers between the electrode and the cap layer. This study indicates that homogeneous degradation depends on the interface stability between the p-side electrode and the cap layer     

Degradation of AlGaN-based ultraviolet light emitting diodes

Aging the LEDs by driving at high current, results in the decrease of optical power proportional to the reciprocal square route of stress time. With aging time, change in the current–voltage characteristics indicates decrease of the current at low voltage below the light emission threshold, decrease of the forward voltage drop at high currents and usually no change in the series resistance. No change in the peak wavelength and half bandwidth were found with aging. Low frequency noise measured at low and high currents either did not depend on aging time or decreased. No correlation between noise, the device power, and the rate of the power degradation were found. These results are in strong contrast to previous studies of longer wavelength GaN-based LEDs. The possible degradation mechanism is the diffusion of the Al atoms out from the p-type cladding layer and lowering of the cladding layer potential barrier as a result.     

Improved efficiency roll-off at high brightness in simplified phosphorescent organic light emitting diodes with a crossfading-host

We report a high efficiency and low efficiency roll-off green phosphorescent organic light emitting diode using both hole- and electron-transporting host materials in a crossfading profile. To eliminate the energy barrier and reduce the charge carrier accumulation, the host materials are used as transporting layers as well, which also simplifies the device fabrication. It is found out that the recombination zone of gradient doping host sample is not only wider but also extended at high current density, which contributes to the suppressed efficiency roll-off at high luminance. An external quantum efficiency of 21.0% at 1000 cd/m² is obtained, and maintains to 19.3% at 10,000 cd/m².     

Red hot [light emitting diodes]

Light-emitting diodes are ubiquitous in today's high-tech world. But no matter what their application or color, their origin can be traced to the red LED created in 1962 by Nick Holonyak Jr., the winner of this year's IEEE Medal of Honor. The article describes Holonyak's career and the work which produced the first LED, and shows how his influence permeates the industry today.     

Subscriber loop transmission using low operating current light emitting diodes subjected to temperature extremes

A unique edge-emitting LED has been developed that has characteristics particularly attractive for use in loop transmission equipment. At low operating currents of 20-25 mA, sufficient optical power is launched into a Single-mode fiber to transmit data rates typical of the present day loop plant, 1.5-45 Mbit/s. In the system experiments reported here, 45-Mbit/s data was transmitted 12.9 km while operating the LED at a low drive current of 20-mA peak and at temperatures from -20 to +70°C. These experiments and related analyses confirm that the LED offers a reliable, low cost, and easy to use alternative to diode lasers and high drive current LED's in the telephone loop plant.     

Semi-insulating selective regrowth of surface light emitting diodes

Selective regrowth of indium phosphide (InP) using organometallic vapor phase epitaxy (OMVPE) on a circular shaped mesa has been demonstrated for the first time. Inclusion of an interfacial layer of indium gallium arsenide phosphide between the circular dielectric mask and the underlying material produces a favorable smooth mesa profile by controlling the level of undercut during mesa etching. This combination of profile and undercut was found to be critical for successful selective regrowth and planarization. To the best of our knowledge, this is the first time that a surface light emitting diode has been demonstrated with a selective OMVPE semi-insulating regrowth. The semi-insulating InP layer reduces parasitic capacitance and improves the heat dissipation out of the device. These salient features make these devices suitable for high speed digital and analog communication applications.     

Reduction of shot noise with light emitting diodes

The authors find that the optical shot noise and the electrical shot noise in light emitting diodes have the identical fluctuation due to spontaneous emission as far as the quantum efficiency is unity. The 0.45-dB reduction of noise below the standard shot-noise limit is achieved by using such correlation between the two kinds of shot noise     

Ⅲ族氮化物基发光二极管制造工艺

Ⅲ族氮化物是近年来半导体发光器件研究领域中的热点。由于InN,GaN,AlN及由其组成的连续变化固溶体合金所构成的半导体微结构材料,具有宽禁带宽电子漂移饱和速度高、介电常数小及导热性能好等特点,使其在制作短波长、高亮度的发光器件方面具有极其光明的前景。本文系统介绍了以氮化镓为代表的Ⅲ族氮化物基发光二极管的制造工艺。从工作原理、材料生长、掺杂和欧姆接触等各方面,介绍了各种氮化物二极管的不同器件结构和制造工艺。在介绍国际上最新制造技术的同时,对其发展前景做出了展望。     

1.3?m InGaAsP/InP light emitting diodes with internally defined emission area prepared by single-step LPE technique

An LPE single-step process is described for the fabrication of InGaAsP/InP double heterostructure surface emitting LEDs with internally defined emission area. The technique provides a simple production method which lends itself to simple upside-up mounting of LED chips and application of back surface mirrors for enhancement of light extraction efficiency.     

Ultraviolet light emitting diodes using III-N quantum dots

(Al,Ga)N-based quantum dots (QDs) grown on Al_0.5Ga_0.5N by molecular beam epitaxy have been studied as the active region for the fabrication of ultra-violet (UV) light emitting diodes (LEDs). In the first part, using both “polar” (0001) and “semipolar” (112¯2) surface orientations, the structural and optical properties of different QD structures are investigated and compared. In particular, their propensity to get an emission in the UV range is analyzed in correlation with the influence of the internal electric field on their optical properties. In a second part, (0001) and (112¯2)-oriented LEDs using GaN/Al_0.5Ga_0.5N QD as active regions have been fabricated. Their main current-voltage characteristics and electroluminescence properties are discussed, with a focus on the LED emission wavelength range reached for both surface orientations: it is shown that a large part of the UV-A region can be covered, with longer wavelengths-from 415 to 360 nm-for the “polar” LEDs, and shorter ones-from 345 to 325 nm-for the “semipolar” LEDs. In addition, the influence of the internal electric field on the QD-LEDs working operation is shown.     

Gravure printed flexible small-molecule organic light emitting diodes

Small-molecule based flexible organic light-emitting diodes (SMOLEDs) were fabricated by gravure printing. In order to modify rheological properties of the functional ink, the green emitter was embedded into an ultrahigh molecular weight polystyrene (UHMW-PS) matrix. The viscosity of the ink was characterized as a function of the small molecule:UHMW-PS weight ratio and solvent type. The gravure printed SMOLEDs exhibited a maximum luminance of 850 cd m⁻², a maximum efficiency of up to 7.7 cd A⁻¹, and turn on voltage of ∼3.5 V. The gravure printed SM:UHMW-PS device exhibits ∼67% higher luminance efficiency comparing to the spin-coated pristine SM device.     

Proton bombarded GaAlAs:GaAs light emitting diodes

High-speed high-radiance luminescent diodes for optical transmission systems have been fabricated. Proton bombardment is used for confining the area of the active region. Modulation cutoff frequencies of 170 MHz and a radiance of 11 W/ sr. cm²at a diode current of 100 mA have been measured.     

Ageing in ZnSe:Mn light emitting diodes

We report the fabrication of ZnSe light emitting diodes with useful lifetimes of at least 10⁴ hr, whereas early ZnSe Schottky diodes suffered from degradation after a few tens of hours of operation. This ageing took the form of an increase in series resistance, logarithmic with time for the initial 10³ hr, and later increasing as the square root of time. The change is consistent with the current-assisted growth of an insulating layer beneath the Schottky contact. The initial growth rate is probably controlled by oxidation proceeding preferentially at stress-relieving cracks in the layer, and the later rate is characteristic of oxidation limited by transport through the layer. Both processes can be inhibited: by adding a known insulating layer before deposition of the Schottky contact, to seal any cracks which may develop, and by using effective epoxy encapsulation.