Highly efficient silicon light emitting diodes produced by doping engineering

This paper reviews our recent progress on silicon (Si) pn junction light emitting diodes with locally doping engineered carrier potentials.Boron implanted Si diodes with dislocation loops have electrol...     

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.     

Materials for polymer-light emitting diodes

Polymer light-emitting diodes have become feasible when suitable materials were available. The various relevant properties are interrelated parameters. The solubility can be improved in various ways but here the introduction of side-chains has been found most successful. Colour tuning is achieved by attaching electron withdrawing or donating side-chains. Some polymer defects in PPV are shown. Special functionalities can be built-in. As an example a self-doped PPV is given.     

A new degradation phenomenon in blue light emitting silicon carbide diodes

In 6H-SiC blue emitting diodes prepared by sawing epitaxial wafers the development of greenish striations in the luminescing layer is observed together with a decrease in external quantum efficiency. It is proposed that this degradation is due to the development of numerous stacking faults leading to an intermediate (cubic?) state of lower band gap than the 6H modification.     

High-efficiency monolithic GaAs IMPATT diodes

Impedance-matching circuits were integrated on the same chip as the IMPATT diodes to produce monolithic impatt diodes for millimetre-wave applications. A drastic reduction of device-to-circuit parasitic elements was achieved by placing the external circuitry very close to the device. Oscillators fabricated in this fashion gave the highest efficiencies reported so far in the 30?35 GHz range with 28% conversion efficiency using hybrid-Read structures.     

MOCVD生长双波长发光二极管

根据白光照明和可变换波长的光通信中对单芯片双波长发光二极管(LED)要求,在分析了反向偏置隧道结性质的基础上,设计了用反向偏置隧道结连接两个有源区的单芯片双波长LED,用金属有机化学气相沉积技术(MOCVD)在GaAs衬底上一次外延生长了同时发射两种波长的LED,其包含一个AlGaInP量子阱有源区和一个GaInP量子阱有源区,两个有源区由隧道结连接;通过后工艺制备了双波长LED器件,在20mA电流注入下,可以同时发射626nm和639nm两种波长,光强是127mcd,正向电压是4.17V。与传统的单有源区LED进行对比表明,双波长LED有较强的光强;对比单有源区LED的2.08V正向电压,考虑到双波长LED包含隧道结和两个有源区,隧道结上的压降很小。     

Light emitting diodes reliability review

The increasing demand for light emitting diodes (LEDs) has been driven by a number of application categories, including display backlighting, communications, medical services, signage, and general illumination. The construction of LEDs is somewhat similar to microelectronics, but there are functional requirements, materials, and interfaces in LEDs that make their failure modes and mechanisms unique. This paper presents a comprehensive review for industry and academic research on LED failure mechanisms and reliability to help LED developers and end-product manufacturers focus resources in an effective manner. The focus is on the reliability of LEDs at the die and package levels. The reliability information provided by the LED manufacturers is not at a mature enough stage to be useful to most consumers and end-product manufacturers. This paper provides the groundwork for an understanding of the reliability issues of LEDs across the supply chain. We provide an introduction to LEDs and present the key industries that use LEDs and LED applications. The construction details and fabrication steps of LEDs as they relate to failure mechanisms and reliability are discussed next. We then categorize LED failures into thirteen different groups related to semiconductor, interconnect, and package reliability issues. We then identify the relationships between failure causes and their associated mechanisms, issues in thermal standardization, and critical areas of investigation and development in LED technology and reliability.     

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     

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     

具有纳米级结构出光面的AlGaInP基发光二极管

研究了一种利用金属自组装纳米掩膜和ICP刻蚀对AlGaInP基发光二极管(LED)表面进行粗化的技术,使光输出得到了提高.粗化了的AlGaInP基LED比常规的AlGaInP基LED,光强提高了27%,光功率提高了12.6%,实验结果具有可重复性.可以进一步优化Au颗粒的周期和分散程度,提高AlGaInP基LED的提取效率.     

Thin film AlGaInP light emitting diodes with different reflectors

The reflectivity versus incident angle of a GaP/Au reflector,a GaP/SiO_2/Au triple ODR(omni-directional reflector) and a GaP/ITO/Au triple ODR was calculated.Compared to AlGaInP LEDs with a GaAs absorbing substrate, thin film LEDs with a Au reflector,a SiO_2 ODR and an ITO ODR were fabricated.At a current of 20 mA,the optical output power of four samples was respectively 1.04,1.14,2.53 and 2.15 mW.The Au diffusion in the annealing process reduces the reflectivity of the Au/GaP reflector to 9%.The differe...     

Green emitting Zn-diffused LPE GaP diodes

The growth of liquid phase epitaxial (LPE) layers of n-type GaP on GaP substrates was investigated using a multi-wafer growth system constructed of fused quartz which had provisions for gas phase saturation and doping of the gallium melt. The effect of growth temperature, substrate orientation, doping level, and repeated use of the same melt on the properties of zinc diffused electroluminescent diodes fabricated from these epitaxial layers were investigated. After an initial increase, the carrier concentration remained relatively constant (1.7 × 10¹⁷/cc) throughout a series of eighteen runs from the same melt. Using conventional commercial techniques, zinc diffused diodes with efficiencies of 0.05% at 30A/cm² and a brightness of 1200 fL at 10A/cm² were produced. These diodes had a limited area n and p-type contact and had an epoxy dome. Layers grown on the 〈 111 〉P orientation had the best surface quality whereas those grown on the 〈 100 〉 plane incorporated less background impurities. The use of relatively low growth starting temperatures (∼ 920°C) was found to minimize the background impurity of the layers and the substrate surface deterioration due to the reaction with ammonia. This work was, in part, sponsored by the Air Force Materials Laboratory under the direction of Mrs. E. H. Tarrants, contract number F33615-71-C-1621     

High-performance polymer light emitting diodes with interface-engineered graphene anodes

Recently, graphene-based organic light emitting diodes (OLEDs) were successfully demonstrated using graphene as anodes. However, the graphene electrodes have not been utilized for polymer light emitting diodes (PLEDs) yet, although the simpler device structure and the solution-based fabrication process of PLEDs are expected to be more advantageous in terms of time and cost. Here we demonstrate high-performance polymer light emitting diodes (PLEDs) with simple two-layer structures using interface-engineered single-layer graphene films as anodes. The single-layer graphene synthesized by chemical vapor deposition methods was transferred onto a glass substrate utilizing an elastic stamp, and its work function was engineered by varying the duration and the power of ultraviolet ozone (UVO) treatment. Thus, we were able to optimize the contact between silver electrodes and the graphene anodes, leading to the considerable enhancement of light-emitting performance.     

薄膜AlGaInP发光二极管中不同反光镜的研究

本文计算了GaP/Au 反光镜, GaP/SiO2/Au 三层ODR and GaP/ITO/Au 三层ODR的反射率随角度的变化值。制作了GaAs衬底的AlGaInP LED,Au反光镜、SiO2 ODR和ITO ODR的薄膜AlGaInP LED。在20mA下,四种样品光输出功率分别为1.04mW, 1.14mW, 2.53mW and 2.15mW。制作工艺退火后,Au扩散使Au/GaP反光镜的反射率降至9％。1/4波长的ITO和SiO2透射率不同造成了两种薄膜LED光输出功率不同。ITO ODR中加入Zn可以大大降低LED的电压,但并不影响LED的光输出。     

Efficient white organic light emitting diodes with solution processed and vacuum deposited emitting layers

The white light emitting diode based on small molecules, which have double emitting layers, was fabricated by combining a solution process and a vacuum deposition process. The organic light emitting diode that we have prepared utilizes a three phosphorescent guest materials, iridium(III)bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, fac tris(2-phenylpyridine) iridium (III) and tris[1-phenylisoquinolinato-C2,N] iridium (III), exhibits a high color rendering index of over 82. Despite its ease of fabrication, the peak power efficiency was about 16 lm/W. The high efficiency was attributed to the distribution of the emitting region over the two emitting layers, which is caused by energy transfer between the phosphorescent guests.     

Thermal management for high-power photonic crystal light emitting diodes

An effective heat dissipation structure is a crucial element for stable thermal management in ensuring thermal stability of high power photonic crystal light emitting diodes (PC-LEDs). New integrated structure for effective thermal management is put forward for high power PC-LEDs to reduce the thermal resistance between the chip and heat dissipation device, which can be composed by the heat pipes or an active heat dissipation device. Based on the thermal resistances analyzed, 3D thermal distributions for the device CSM360 with the nominal electric power of 80 W are simulated and analyzed by using of ANSYS. Compared with the general metal fins model, the heat pipes integrated model improves the heat dissipation efficiency of CSM360 by 36.61%, while the active heat dissipation device integrated model improves the heat dissipation efficiency by 60.2% at the temperature of 50 °C on the cold end of the device. The results show that the integrated structure can obtain a significant improvement in thermal management and achieve a reduction in temperature in the working status of CSM360. Heat dissipation experiments are also conducted, and the values of temperature distributions are validated to be coincident with those from simulations.     

Colloidal quantum dot active layers for light emitting diodes

In this paper the preliminary results of incorporating a novel active layer into a GaN light emitting diode (LED) are discussed. Integration of colloidal CdSe quantum dots into a GaN LED active layer is demonstrated. Properties of p-type Mg doped overgrowth GaN are examined via circular transmission line method (CTLM). Effects on surface roughness due to the active layer incorporation are examined using atomic force microscopy (AFM). Electroluminescence of LED test structures is reported, and an ideality factor of n = 1.6 is demonstrated.     

Organic light emitting diodes with highly conductive micropatterned polymer anodes

We use a soft lithography technique to pattern a high conductive poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) acting as anode in organic light emitting diodes. In this method all the polymer layers except for the desired pattern are lifted up from the substrate surface. We are able to define the emissive zones of our devices on a large area in a cheap and fast way. By comparing the devices realized using the patterned polymeric anode with an untreated indium tin oxide substrate, we obtained current efficiency values that have the same order of magnitude: this is the first step for the realization of low cost devices suitable for flexible substrates.     

阴极为半透明Ce/Au的有机发光二极管

在p型硅基底的阳极上制得的顶出光有机发光器件(TOLEDs)采用Ce(xnm)/Au(15nm)(x:4～16)沉积层作为半透明阴极材料.当有机层NPB(60 nm)/Alq3(60 nm)保持不变时,研究了Ce层厚度对透光度和器件性能的影响.结果表明:沉积层为Ce(11nm)/Au(15nm)的阴极透光度达到46％,...