The Light Emitting Diodes Engineering Essay

The Light Emitting Diodes Engineering tooshievasHistory of livelying pulls starts with kickoff efficient in dropdescent lamps, then coterminous came the CFL lamp. In the history of illuminationing devices, invention of conduct was a number point Light Emitting Diode or simply lead is an electronic device, which verbalizes scant(p) when electricity passes through it. conduct has a number of varied uses in day to day life. Its uses varies from a simple forcefulness on indicator to indicator to traffic signals. LED uses about 10% of the zipper traditional scant(p) bulb uses and they can last about cardinal ages longer.LED sportsmanlikes argon full(prenominal)ly efficient and cost exerciseive.Nano techno put downy has its receive role to play in lighting devices history. Invention of quantum back breakers and ionic liquidnesss replaced the subject of lighting industry. Quantum dits LEDs were manufactured employ quantum dots particles. QLEDs offer better lumin escence than embodiment LED lights. Introduction of bean Liquids (IL) was an other(a) turning point. Still in the beginning stage, bonce Liquids offer a better solution to the piece of lighting devices.2. Light Emitting Diodes (LED)A Light Emitting Diode or LED is a semi-conductor device which can be employ as a light- ascendant. Semiconductors atomic number 18 neither a good conductor nor an insulator. Semiconductors atomic number 18 sack up up of semiconducting materials bid Silicon or Germanium.A rectifying valve (also called as a PN junction semiconductor diode) has two destinations, anode(a) and cathode (k), anode is a demonstrable terminal and cathode is negative terminal- which allows electric current to pass only in bingle direction. A semiconductor diode can be comp ard to a fault or a one- authority valve.A Light Emitting Diode emits light when electric current passes through it.The colour emitted by an LED depends on the type of semiconductor material use d for its construction. Common colours on hand(predicate) for LEDs be atomic number 19, red, o govern, gloomful, yellow and white. Aluminium gallium indium phosphide (AlGaInp) alloy is used for obtaining red, yellow and orange lights. Indium gallium nitride (IaGaN) is used for numberting blue, green and white lights. whiteness and disconsolate LEDs are more than expensive than other colours. Apart from the above colours, Infra Red LEDS (also called IREDs-Infra Red Emitting Diodes) and Ultra purple LEDs are also avai laboratoryle. Staring into an Ultra Violet LEDS is harmful to the eyes.3. Quantum dot LEDs (QLEDs)Quantum Dots are very keen crystals, in nanotechnology terminology, they are nano particles of semiconductor materials, commonly its diameter varies amid 2 and 10 nano meters. Quantum dot particles were dis doged in early 80s by Louis Brus at Bell Laboratories. A Quantum Dot can contain either a single electron or thousands of electrons. primarily quantum dots ar e make from the sulphides or selenides of semi conductor materials like surface or Cadmium.Quantum dots electronic and optical characters are related to the surface and shape of each particles. When energy is applied (under excitation), electrons get energized and moved to higher(prenominal) bands, and when electrons get back to the stable state, the accessal energy is emitted as light be to a certain frequency. Its narrow emission spectrum is directly proportional to the size of the crystal. Smaller particles hold a blue shifted emission and commodiousr particles give a red shifted emission. Using a technique called size quantisation effect, quantum dots can be tuned to produce any colour during manufacturing.Quantum dot LEDs (QLED or QD LED) are devices which use quantum dots as their light emitting material. These dots are excited when electricity is applied and emits light according to the size of the dots. Larger dots produce more energy levels and darker colours and br okener dots create smaller energy levels and emits spark colour shades.Gold or silver nano particles are very versatile materials whose diameter varies from 1nm to 100nm. Gold nano particles are comparatively smaller that of Silicon Quantum Dots. And it s experimentally proven that, smaller particles generate better fluorescence than that of self-aggrandisingr particles. So, Quantum Dot LEDs manufactured from gold or silver nano particles increases the luminescence.4. noodle liquids (IL)Ionic liquid is the salt form of any material in liquid state. Ionic liquids are liquid salts. Ionic liquids are made up of, ions (charged atoms) or ion pairs. These ions or ion pairs are poorly coordinated in the liquid. This poor coordination of ions results in the liquid from below 100C. Ionic liquids are also cognise as liquid electrolytes or ionic fluids. When a salt melts without decomposing, it results to an Ionic Liquid. Ionic bond is much more stronger than the bond between the average Van der Waals forces in the molecules. Ionic liquid changes its form to ionic steadfast when it gets cooled. Ionic solids are seen in two forms, crystalline and glassy. At low temperature, ionic liquids acts like ionic solutions, which is a combination of both ions and nonsubjective molecules. Ionic liquids are also called designer solvents, be produce they are manufacturing in the lab for specific purpose.Properties of ionic liquids are they dont evaporate, and it is a good conductor of electricity, and it dissolves or so everything. The reason for their non-evaporate property is their non-volatile nature. So, Ionic liquids can replace some acids and natural solvents. Ionic liquids are used for electro polishing, metal plating, exceptionalcting metals from rocks. Applications for Ionic liquids are retentivity for chemical stalls, batteries, fuel electric cells and electro chronic devices for displays, cellulose processing, used as dispersants agents in paints, for bumble h andling and storage, for natural fuel processing, in food and bio-product industries, in cycle of plastic and synthetic wastes etc.5. Turn-On TimeTurn on time or rise time is the time required by a signal to change from low state to high state. The time it takes for the output of a system to change from a specified small percentage (usually 5 or 10) of its steady-state increment to a specified large percentage (usually 90 or 95). (www.answers.com)An LEDs turn-on-time is the time demanded by the device to turn from OFF state to ON state. Time needed to emit the light, after applying the electricity. LEDs are very fast devices and its turn-on time is 0.0001S or 0.1mS.Polymer light emitting diodes (PLED) uses an electro luminescent conductive polymer that emits light when connected to a power supply. PLEDs need very small amount of electricity to emit light and in that locationfore they are considered to be very efficient.A polymer light emitting diode use ionic liquids as one its a ctive material. Usually polymer light emitting diode has fast turn on time.6. Improved Efficiencies in LEDLED faculty can be improved by remunerative attention on packaging, halt structure and positive voltage applying.White LEDs are usually considered to be more efficient that the other Red, Green, Blue colour LEDs. White light in LED can be produced in two ways. One method is, using three somebody LEDs which producing the primary colours and then mixing them to produce the white light. another(prenominal) method is, using the principle which is using in fluorescent lights, a phosphor material is used to convert light from UV or blue LED to white light. The bright efficiency of blue/UV chip and the conversion efficiency of phosphorous determine the efficiency of white LED. luminous efficiency is highly influenced by temperature and current. Efficiency of LEDs fall with the increasing current. This effect is called droop. When operating temperature increases from 327K to 380K, the luminous efficiency dropped by 20%.When the temperature is rising, the shaft at the potential decreases which eventually cause a decrease in luminous efficiency. When operating current rises from 0mA to 350mA, the luminous efficiency of LED tend to be decreased by 35%. When current increases, more and more non-stable electrons easy out of potential well, thus decreasing the luminous efficiency.We can improve the luminous efficiency of a LED by improving the waken dissipation efficiency and increasing the width of potential well. Working stop of a LED should be under limited temperature and moderate current. The hot up generated in the LED, reduces the efficiency of lighting performance. A good packing technology is the way to solve the hot pants dissipation problem. But developing a heat dissipation technology for reducing the LEDs working temperature is a literal challenge. The efficiency and reliability of an LED depends on the thermal dissipation of an LED, because the heat generated in the junction affect the performance and effective operation of LED.LED efficiency can be improved by LED packaging. But, we need to over come the challenges facing in packaging stage to collide with the desired efficiency. The challenges facing in packaging are colour torso of light emitting, multi-chip packaging etc. Packaging technology used for high power LED are more complex and costly. In addition to packaging, chip structure and positive voltage also play a role in LED efficiency. Efficiency can be achieved if positive voltage can be controlled in a very small range.7.Studies of radiation footing in solar cells and LEDssolar cellsSolar cells or photovoltaic (PV) cells are devices which converts solar light to electricity. Working principle of a solar cell is just opposite to that of LED. A solar cell converts light to electricity while a LED converts electricity to light. In a solar cells, photovoltaic effect generates electricity.Solar cells are made up of semiconductor materials like te. When light hits on a solar cell, some portion of a light is absorbed by silicon material. That means, the energy in the light is shifted to the semi conductor material. This energy excites the electrons and make them to break the covalent bond, Breaking of covalent bonds in an atom results in free electrons. This free electrons start flowing and the flow of free electrons cause a current flow in the solar cell. A theme of solar cells are electrically connected to form a variety called solar panels. A solar panels are grouped to form large solar arrays.When sunlight hits the semiconductor, the electrons from P-type semiconductor springs up and is attracted towards the N-type semiconductor. This make negative charges in the N-type semiconductor and more positive charges in P-type semiconductor. Thus electricity is generated collectible to the flow of electrons. This is called photovoltaic effect. radioactivity distressRadiation damage is the sensual damage occurs to devices (solar cell or LED) in a radiation environment. visible light, also known as electromagnetic radiation, does not damage soalr cells or LED normally. But exposing to ultra violet (UV) light , which has more energy, can damage the cells overtime. Output parameters of the devices are affected by radiation damage. Radiation damage in solar cells and LEDs occur when highly massive particles like electrons, protons, or ions come in contact with semi conductor materials. The source of the highly massive particles may be nuclear reactions, gamma rays, space radiation etc. The particles having mass and energy can interact with materials in different ways, such as inelastic collision with electrons in a material, inelastic collisions with nucleus and elastic collisions with nucleus. ionization and atomic displacement are the two categories of radiation damage that occur to solar cells and LEDs. ionization ionization is the process when an atom becomes an io n. It happens, when electrons lose from an outer orbit or extra electrons are added to atom structure. High energy radiation cause ionisation in materials.The use of silicon is solar cells and LEDs cause a range of ionisation related radiation effects such as change magnitude leakage current, decreased gain etc.Atomic displacement When a fast particles collide with a crystal, silicon atoms may get displaced from their wicket gate structure. And this displacement may damage the silicon solar cells.Silicon Solar cell damageThere are different method to banknote silicon solar cell damage. One method is by touchstone the irradiation changes occurring in a solar cell and can be explained using basic solar cell equation. This method require data such as series resistance, shunt resistance, current generated by light and diode parameters such as saturation current and quality work out of diode.Solar cell damage can also be deliberate by observing the change in minority carrier dif fusion space. And this method is widely used because diffusion length is measurable. But there are many disadvantage to this method. One serious disadvantage is damage caused due to low energy protons. Low energy protons do a significant damage to the PN junction of a solar cell. This irregular damage increases the saturation and quality factor of the diode. This damage can cause a significant decrease in voltage. The output parameters of a solar cell can be described using the formulaIsc=Isc0Clog (1 +Phi/Phix), whereIsc is the cell short circuit currentPhix is the radiation fluence at which Isc starts to changeC is the Constant indicates the decrease in Isc per decadeThe relation between solar cell short circuit current and diffusion length can be represented as Isc=AlnL+B.Solar cells are more prone to radiation damage in space. The degradation of cover glass material of solar cell in space is more. Ionisation cause more damage to covering material than atom displacement. Ionisati on in material are directly depend on the radiation absorbed.Solar cells are usually made up of Si and GaAs which are more prone to radiation. Replacing these semiconductor material with InP during manufacturing is the best way to reduce damage due to radiation. InP is more resistant to radiation that Si or GaAs. InP substrate constructed with high carrier concentration has superior radiation resistance.LEDs are also prone to displacement damage. Shorter wave length AlGaAs and GaAs LEDs emitting light in the region 800-900nm are more prone to radiation damage. Manufacturing LEDs with higher wavelength is the answer to this radiation problem.8. CONCLUSIONLED lights are widely using these days commercially. The main advantage of LED is its reduced power consumption. They are highly efficient, cost effective, durable and long lasting. Inventions like quantum dot and Ionic Liquids in Nano Technology field, bring significant changes in Lighting. Quantum Dot LEDS are more efficient than n ormal LEDs, QLEDs use nano crystals as their lighting materials. delectation of gold or silver nano particles increases the luminescence emitted from the QLEDs. Introduction of Ionic Liquids, changed the manner of LED lights. Ordinary LED lights produces a harsh white lights. Implementing a layer of ionic liquids to the LED light, produces a warm light. Researches were made to take a chance the ways of improving the efficiencies of LED. When expose to space radiation solar cells and LEDs are more prone to damages. And it reduces the life span of these devices. Researches are still continuing in the field of nano technology, searching for finding new methods to improve the efficiency of lighting devices.