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半导体发光二极管
 
半导体光源是一种无灯丝的电光源，是一种将电能转化为光能的半导体器件，它是靠半导体化合物制成的特殊结构把电能转化成光能，，称为发光二极管，英文为Light Emitting Diodde，简称LED。发光二极管的结构主要由PN结芯片，电极和光学系统组成。当在电极上加正向偏压之后，使电子和空穴分别注入P区和N区，当非平衡载流子复合时，就会以辐射光子的形式将多余的能量转化为光能。其发光过程包括三个方面：正向偏压的载流子注入，复合辐射和光能传输。发光二极管有许多的优点，如工作电压低，耗电量少，性能稳定，使用寿命长（-1）、抗冲击、耐振动性强、重量轻、体积小、成本低、电路简单、使用方便。半导体灯开始只有一种颜色，现在发展为红色、黄色、绿色等多种发光颜色。加上其调制性能好，可制作成大面积显示屏作为动态广告和体育新闻传播只用，还可用于显示器的指示灯，应用前景好。
发光二极管发明与20世纪 60年代，在后数十年中，其基本用途是作为收录机等电子设备的指示灯。为了充分发挥发光二极管的照明潜力，近年来科学家们开发出用于照明的新型发光二极管灯泡。
早期的半导体发光二极管亮度小，视角窄，颜色仅红光一种，并且质量不稳定，近年来利用掺氧工艺和新的半导体材料，使发光二极管的亮度提高了10倍以上，达到1-5cd/m级水平，具有红、黄、绿、蓝和白等多种发光颜色，从而可以应用于国民经济的各种照明领域除了传统的小型指示器件外，还有图文显示、照明标志、汽车照明、交通信号灯等多种应用，具有效率高、使用寿命长、高度低、低功耗和相应快等其他传统光源难以比拟的优点，逐步占据了照明领域的一席之地。例如采用半导体发光二极管的标志灯，其发光亮度为20-30cd/m,有效寿命为h，可以使用25年以上，比普通的白炽灯长100倍。半导体发光而激光这种电光源有可能取代白炽灯和紧凑型荧光灯，有人预言10年后半导体发光二极管可以取代30%的白炽灯，引起产业界和科技界的极大关注，倍公认为是21世纪最有前途的电光源。据统计到2005年，LED的市场规模会迅速增长至30亿美元。
英国剑桥大学的科技人员在实验中研制出可发白光的发光二极管，这种发光二极管发出的光线与阳光十分接近，具有良好的应用前景。这种发光二极管可以做的很小，只有几毫米，将其安装在墙板或天花板上，如果不开灯，几乎感觉不到它们的存在。白光发光二极管的寿命很长，白炽灯的平均寿命为1000-1500h，质量最好的荧光灯管最多只能使用5h，这就是说如果每天开灯10小时，可以用15年。除经久耐用外，发光二极管在节能发面也有很大的潜力。据统计，如果每年美国的灯泡中有一半使用发光二极管照明，则可以关闭24座发电站，节省数10亿美元，二氧化碳的排放量也将明显下降。正因为如此，美国计划到2006年，所有的交通灯都将使用发光二极管灯泡，这样每个交叉路口每年可省下750美元。当然，用LED取代普通灯泡还需要相当长的时间，在现今的工艺条件下，制造一只3W的白色发光二极管成本约为 100美元，而与之亮度相当的60W大的白炽灯只需0.5美元。白色发光二极管的大批量生产也会大幅度降低成本，但价格上的差异，无疑是白色发光二极管取代普通照明灯泡的一大障碍。
目前的发光二极管主要用于显示器件和短距离 ,低速率的光纤通信用光源，如各种仪器仪表指示器的文字，数字及其他符号的显示器等。由于亮度和颜色等原因，目前LED还不能用于普通的照明场合，而这正是LED的重要的应用发展方向之一。目前，汽车的刹车灯，交通红绿灯等纷纷采用发光二极管。当今国内外现代化都市，不少标志性景观和夜景照明都开始使用LED这一类型的固体节能新光源。据专家预测，随着发光二极管的制作成本的降低，它必将在更多的领域发挥积极作用。从照明市场看，1999年全球白光LED销售额为0.88亿美元，2000年增长到1.18亿美元，2003年超过2.7亿美元，年增长超过预测的40%，未来需求量将继续上涨。
近年来，发光二极管的制造技术不断取得突破，应用越来越广泛，开发应用LED固体光源已成为本世纪的发展目标。美国，西欧，日本等国家与中国台湾地区，竞相投资开发白光LED绿色光源。我国国防部，国家科技部，发展委员会与信息产业部等有关部门共同组织实施的“国家半导体照明工程”正式启动，标志着中国亮度LED产业进入到加速发展的新阶段，为LED产业进入加速发展的新阶段，为LED产业的发展提供了良好契机。
半导体发光二极管和半导体激光器类似，也是一个PN结，也是利用外电源向PN结注入电子来发光的。半导体发光二极管记作LED，是由P型半导体形成的P层和N型半导体形成的N层，以及中间的由双异质结构成的有源层组成。有源层是发光区，其厚度为0.1～0.2μm左右。
半导体发光二极管的结构公差没有激光器那么严格，而且无谐振腔。所以，所发出的光不是激光，而是荧光。LED是外加正向电压工作的器件。在正向偏压作用下，N区的电子将向正方向扩散，进入有源层，P区的空穴也将向负方向扩散，进入有源层。进入有源层的电子和空穴由于异质结势垒的作用，而被封闭在有源层内，就形成了粒子数反转分布。这些在有源层内粒子数反转分布的电子，经跃迁与空穴复合时，将产生自发辐射光。
半导体发光二极管的结构简单，体积小，工作电流小，使用方便，成本低，所以在光电系统中的应用极为普遍。
在正向偏置下，半导体PN结或与其类似的结构能够发出可见光或近红外光，这种把电能直接转换为光能的器件称为发光二极管，简称LED。
发光是物体内部以某种方式储存的能量转化为光辐射的过程。发光物体的光辐射是材料中受激发的电子跃迁到基态时产生的。半导体（主要是元素周期表中Ⅲ族和Ⅴ族元素构成的化合物半导体）发光二极管属于电流激发的电致发光器件。
电致发光现象发现于1923年，当时并没有引起人们的注意。随着近代技术的发展，对发光器件提出了新的要求，希望发光管简单、可靠、寿命长、价格低、小型化。所以自60年代开始电致发光的研究非常活跃。
原子、分子和某些半导体材料，能分别吸收和放出一定波长的光或电磁波。根据固体能带论，半导体中电子的能量状态分为价带和导带，当电子从一个带中能态E1跃迁(转移)到另一带中的能态E2时,就会发出或吸收一定频率(υ)的光。υ与能量差(墹E＝E2-E1)成正比，即
　　υ＝墹E/h (Hz)
此式称为玻尔条件。式中h＝6.626×10-34J·s。 当发光二极管工作时，在正偏下，通常半导体的空导带被通过结向其中注入的电子所占据，这些电子与价带上的空穴复合，放射出光子，这就产生了光。发射的光子能量近似为特定半导体的导带与价带之间的带隙能量。这种自然发射过程叫作自发辐射复合（图1）。显然,辐射跃迁是复合发光的基础。注入电子的复合也可能是不发光的，即非辐射复合。在非辐射复合的情况下，导带电子失去的能量可以变成多个声子,使晶体发热,这种过程称为多声子跃迁；也可以和价带空穴复合,把能量交给导带中的另一个电子,使其处于高能态，再通过热平衡过程把多余的能量交给晶格，这种过程称为俄歇复合。随着电子浓度的提高，这种过程将变得更加重要。带间跃迁时，辐射复合和非辐射复合的两种过程相互竞争。有的发光材料表现为辐射复合占优势。
LED的结构依应用和材料掺杂情况而异。用于可见光指示和显示方面的LED,要求结构最佳化以获得高效率；用于光通信方面的LED,需要有高辐射度以把最大功率耦合入纤维，还希望有较大的调制能力,在低压(低于2伏)、小电流（几十毫安至200毫安）下工作,功耗小、体积小、可直接与固体电路连接使用；稳定、可靠、寿命长(105～106小时)；调制方便，通过调制LED的电流来调制光输出;光输出响应速度比较快（1～100兆赫）；价格便宜。 应用　LED可用作指示灯、文字-数字显示、光耦合器件、光通信系统光源等。
对LED的要求提高内量子效率,要求尽量减少晶体缺陷和有害杂质；提高外量子效率，结构要便于光收集、提取和发射；可以用携载信息的输出电流直接对光输出进行高速率的调制；结构要有利于散热，减少因结温上升引起光功率下降；要有高的辐射度，因此必须应用直接带隙半导体和能够在高电流密度下驱动的结构。
用作指示灯的LED有两种结构:径向引线结构和轴向引线结构。前者尺寸小、价格低，适宜安装在印刷电路板上；后者既可安装在仪器面板上，又可直接安装在印制线路板上。专为印制线路板设计的最小的LED指示灯，可与晶体管和集成电路兼容，用来指示电路状态和故障。LED可作为电视频道调谐指示器,还可用于高保真度收音机和录音机以及汽车、飞机和机电工业。大多数指示灯是单管芯，新发展的还有双色灯和多色灯。
LED用作袖珍计算器。数字手表和电子仪表的数字显示，一般为七段显示。但对台式计算器,更灵活的显示方式（产生全文字-数字）是35点矩阵，其中LED装成7×5阵列。35点矩阵价格较高、驱动电路复杂，其应用不及七段显示器件广泛。 光耦合器件 GaAs（或GaAsP）LED和Si－PN结探测器相结合，可以制成许多新型器件，进行光-电和电-光的传递，通常称为光耦合器件。熟知的是光耦合隔离器，它高速、可靠并可提供高至2.5千伏的电隔离。GaAsLED与Si晶体管相结合制成穿孔卡片或磁带的光电子读数头，比钨丝灯径向分布可靠、稳定、抗震和功耗小。采用光耦合器件的汽车点火装置，省油、易起动、工作平稳。GaAlAs负阻发光二极管可用作发光开关、可控发光整流器和光波长转换等。
通信、信息处理和光耦合等应用要求 LED有良好的方向性。适于光通信应用的两种主要光源是高辐射度LED和半导体注入激光器。LED稳定、可靠、寿命长、驱动电路简单、功率对温度不敏感，广泛用作中、短距离（铁路、电力、交通、公安等）光通信系统的光源。GaAlAs－GaAs面发光管的带宽为10～20兆赫，适用于二次群光通信系统(可传输120路电话),传输距离大于5公里。GaAlAs-GaAs快速边发光管带宽50～100兆赫，适用于三级群光通信系统(可传输480路电话)，传输距离数公里。InGaAsP-InP LED可用于更长距离(大于10公里)的传输系统。此外，LED还用于信息处理、图像传输、测距和传感等方面。
近年来，国外又相继开发出半导体孤子激光器、量子阱线或点激光器和垂直腔表面发射激光器等新型半导体激光二极管。 ，中国作为照明产品的生产和消费大国，中国的照明企业能否在新一轮照明技术革命与照明工业转型中占有一席之地，是共同面对的问题。望中国能秉承“更高、更快、更强”的奥运精神，冲出亚洲，走向世界，早日实现半导体照明产业的腾飞！
 
Semiconductor light-emitting diode
 
Semiconductor light sources is a non-filament light sources,is a semiconductor device of electrical energy into light energy, it is special structure made of compound semiconductors to transform electrical energy into light energy,, known as light-emitting diodes, English Light Emitting Diodde , Abbreviated as LED 。 Light emitting diode structure mainly consists of PN junction chips, electrodes and optical systems. After adding forward bias on the electrodes, electrons and holes injected respectively p and n when the non-equilibrium charge carriers when combined, there will be excess energy as a photon radiation into light Its luminous process consists of three areas: a forward bias of carrier injection and compound radiation and light transmission. LEDs have many advantages, such as low voltage, less power consumption, stable performance, service lifeLong  Strong resistance to impact, vibration-resistant, light weight, small size, low cost, the circuit is simple, easy to use. Semiconductor lamp start only one color, now developed for multiple light colors such as red, yellow, green. Combined with its modulation performance, can be made into large-area display as dynamic advertising and sports journalism, can also be used to monitor led, bright future.
Light emitting diode invention and 20 century, 60 years, decades after, its basic purpose is the recorder devices such as LEDs. In order to realize the full potential of light emitting diode lighting, in recent years, scientists have developed a new LED lamps for lighting.
Early semiconductor light-emitting diode light small, narrow the angle, color is red, and the inconsistent quality, in recent years the use of oxygen-doped semiconductor material technology and new, the brightness of light emitting diode increases 10 times, to1-5cd/mLevel level, has red, and yellow, and green, and blue and white, multiple glow color, to can should for national economy of various lighting area apart from traditional of small indicates devices outside, also has graphic displayed, and lighting flag, and car lighting, and traffic lights, multiple application, has efficiency high, and using life long, and height low, and low power and corresponding fast, other traditional light difficult to match of advantages, gradually occupies has lighting area of place. Such as the use of semiconductor light-emitting diode lamp, glow brightness20-30cd/m,Active life10h, You can use the 25 years, longer than normal incandescent lamps 100 times. Semiconductor light-emitting lasers that light sources have the potential to replace incandescent and compact fluorescent lamps, it was predicted that 10 years after the semiconductor light-emitting diode can be replaced 30% light bulbs, caused great concern among the industry and the scientific community, recognized as the 21 century's most promising light sources. According to statistics to 2005 year,LED the market size will rapidly grow to 30 billion dollars.
Technologists at the University of Cambridge experiments in the development of white light emitting diodes, this issue led light and is very close to the Sun, with good prospects. The LEDs can do very little, only a few mm, is installed on the wall or on the ceiling, if you do not turn on the light, almost feel their presence. White light-emitting diode lifetime is long, average lifespan of incandescent lamps for 1000-1500h, the best quality of fluorescent tubes can only be used5h, Which means that if the lights every day 10 hours for 15 years. Apart from durable, led in energy-saving leavened dough has a lot of potential. According to statistics, if the annual United States half of the light bulb using light-emitting diode lighting, you can turn off 24 power stations, save 10 dollars, carbon dioxide emissions also decreased significantly. Because of this, United States plan to 2006 year, all traffic lights are led light bulbs will be used, so that each intersection can be saved each year 750 dollars. Of course, LED to replace ordinary bulbs also require quite a long time, under the conditions of today, making a 3-watt white led cost about 100 dollars, and brightness of a 60W incandescent lamp just 0.5 USD. Mass production of white light-emitting diodes are also significantly lower cost, but the difference in price is undoubtedly the white light-emitting diode an obstacle to replace normal light bulbs.
Current light-emitting diodes are mainly used for display and short distance , low rates of light source for optical fiber communications, such as instrument and indicator text, numbers, and other symbols of the monitor. Due to factors such as the brightness and color, now LED cannot be used for general lighting, which LED one of the important development direction of. At present, the car's brake lights, traffic, such as traffic lights use light-emitting diodes. Today's modern city at home and abroad, many iconic landscape and lighting are starting to use LED solid for this type of energy-saving light sources. According to expert forecasts, with light-emitting diodes reduce production costs, it will play an active role in the field of more. From the lighting market,1999 global white light LED sales to 0.88 dollars,2000 year to 1.18 billion dollars,2003 year over 2.7 billion dollars, rose more than forecast of 40%, Demand will continue to rise in the future.
In recent years, manufacturing technology continues to achieve breakthrough in led, increasingly broad application, application development LED solid state light sources has become the development goal of the century. United States, Western Europe, Japan and other countries and China's Taiwan region, competing to develop white light LED green light. Ministry of defence, Ministry of science and technology, the Development Committee together with the relevant departments of the Ministry of information industry and other organizations to implement "National Semiconductor lighting project" was officially launched, marked the brightness of LED industry entering a new phase of accelerated development, LED industry entered a new phase of accelerated development, LED industry provides a good opportunity for development.
Semiconductor light emitting diodes and laser diode is similar, is a PN junction , is the use of external power supply to the PN junction injection to glow. Semiconductor light-emitting diode credited LED, is the p -type semiconductor formation of p -and n -type semiconductor to form n -tier, and middle double heterostructure becomes the active layer. Active layer is a light area, its thickness is 0.1~0.2 μm or so.
Semiconductor light-emitting diode structure tolerances not as strict as lasers and non-resonant cavity. So, the light emitted by is not a laser, fluorescence. LED is applied to the voltage of the device. Under forward bias,n- electrons will spread to the positive direction of the district, entering the active layer,p electrons will spread to the negative direction, entering the active layer. Upon entering the active layer of the electron and hole the heterostructure barrier function, and is enclosed within the active layer, distribution of a population inversion is formed. The population inversion in the active layer of electronic distribution, transitions and a hole when combined, will result in spontaneous emission of light.
Semiconductor light-emitting diode structure is simple, small, small current, easy to use, low cost, so in the electro-optical system is a common application of.
Under forward bias, semiconductor PN junction or similar structure to give visible or near-infrared light, which directly converts solar energy device called the power light-emitting diode, known as LED.
Light is inside the object to store in some way the process of radiation energy into light. Shiner light radiation excited electrons in the material when the transition is made to the ground state. Semiconductors (mainly in the periodic table of elements III and v family of elements of compound semiconductor) light emitting diodes are current excitation light-emitting devices.
Electro-luminescence phenomena discovered in 1923 years, did not attract the attention of people. With the development of modern technologies, make new demands on light emitting diodes, want led simple, reliable, long service life, low price, small size. Since 60 years began to study on electroluminescence of very active.
Atomic, molecular, and some semiconductor materials, absorbs and emits certain wavelengths of light or electromagnetic waves, respectively. According to the solid energy band theory, the energy of the electrons in the semiconductor into the valence band and conduction band, when electrons from one energy state e1 transitions ( transfer ) to another area energy state e2 Shi , Emits or absorbs certain frequencies (υ) . Υ and energy difference ( Jian e=e2-e1) proportional to the
　　Υ= Jian E/h (Hz)
This type is known as Bohr's condition. H=6.626x10-34J · s. When the led work, and downwards, usually empty conduction band of semiconductor occupies is injected through the knot to which electronic, these electrons and valence band holes on comp, radiate photons, it produces light. The photon energy emitted is rounded to the specified between the conduction band and the valence band of a semiconductor bandgap energy. This natural emission process known as spontaneous radiative recombination (figure 1). Obviously , radiative transitions are the basis of recombination. Injection of compound may also be light, that is, non-radiative recombination. In non-radiation composite of situation Xia, guide with electronic lost of energy can became multiple sound child , makes crystal fever , this process called more sound child jumped moved; also can and price with hole composite , to energy handed guide with in the of another electronic , makes its is high energy State, then by heat balance process to extra of energy handed lattice, this process called Russia break composite. As the electron concentration increases, this process will become more important. When you transition between, radiation hybrid and non-radiative recombination of two competing processes. Luminescent materials for radiative recombination advantage.
LED Application structure and materials of doped vary depending on the situation. For visible light indicating and display LED, require structural optimization to obtain efficient; for optical communications LED, of high radiation can also be coupled into maximum power fiber, also wants to have a larger capacity modulation , at low pressure ( Less than 2 volts ), little current (dozens of Ma to 200 MA) work , low power consumption, small size, can be used directly to a solid electrical connection; stable, reliable, long service life (105~106 hours ) ; Modulation through modulation LED Current modulation of light output ; Light output responds faster ( 1 ～ 100 MHz), and cheap. LED lights, text - figures, light optical coupling device, optical communication systems, etc.
LED Demands for higher quantum efficiency , Requirements as reduced crystal defects and harmful impurities; improve outside quantum efficiency, structure to easy light collection, and extraction and launches; can with carrying contains information of output current directly light output for high speed rate of modulation; structure to has conducive to thermal, reduced due to knot temperature rose caused light power fell; to has high of radiation of, so must application directly with gap semiconductor and to in high current density Xia drive of structure.
Used as the indicator LED There are two kinds of structure : Radial lead structures and axial lead structure. The former small size, low price, suitable for installation on a printed circuit board which can be mounted on the instrument panel, and can be installed directly on the printed circuit board. Designed for minimum of printed circuit board design LED lights, can be compatible with transistors and integrated circuits, used to indicate the circuit and fault. LED can be used as TV channel tuning indicator , also available for high fidelity radios and tape recorders as well as automobile, aircraft, and electrical and mechanical industries. Most of the light is a single core, development of new bi-color lights and many colored lights.
LED As a pocket calculator. Digital watch digital display and electronic instrument, typically a seven-segment display. But on a desktop calculator , more flexible way (full text - figures) is a 35 -point matrix, which LED into 7x5 array. 35 -point matrix driving circuit for high prices, complex, its application less than seven-segment display wide. Optical coupling device GaAs( GaAsP)LED and Si- PN Junction detectors combine can be made into many new devices, optical - Electric and electric - Transmission of light, often referred to as optical coupling device. Optical coupled isolators is familiar, fast, reliable, and can provide up to 2.5 kV electrical isolation. GaAsLED Si transistors made from combining the photoelectron reading punched cards or tape, reliable and stable than tungsten radial distribution, seismic and small power consumption. Optical coupling device of automobile ignition system, fuel economy, easy-starting, smooth. GaAlAs negative resistance light emitting diode can be used as light controllable light switches, rectifiers and optical wavelength conversion and so on.
Communications, information processing and optical coupling of application requirements LED A good direction. Two main light source is suitable for optical communication applications of high radiation LED and semiconductor injection lasers. LED driving circuit for stable, reliable, long life, simple, power is not sensitive to temperatures, widely used as, a short distance (railway, electricity, transportation, public safety, and so on) source of optical communication systems. GaAlAs-GaAs surface emitting pipe bandwidth for 10~20 MHz for secondary group communication system ( transmission 120 road ), transmission distances greater than 5 km. GaAlAs-GaAs Quick edge led bandwidth 50~100 MHz, applies to the three-level group of optical communication systems ( transmission 480 Road ), few km transmission distance. InGaAsP-InP LED can be used for long distances ( greater than 10 km ) transmission systems. In addition, theLED is also used for information processing and sensing, image transfer, ranging aspects.