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1、HowLightEmittingDiodesWorkbyTomHarrisLightemittingdiodes,commonlycalledLEDs,arerealunsungheroesintheelectronicsworld.Theydodozensofdifferentjobsandarefoundinallkindsofdevices.Amongotherthings,theyformthenumbersondigitalclocks,transmitinformationfromremotecontrols,lightupwatchesandtellyo
2、uwhenyourappliancesareturnedon.Collectedtogether,theycanformimagesonajumbotelevisionscreenorilluminateatrafficlight.Basically,LEDsarejusttinylightbulbsthatfiteasilyintoanelectricalcircuit.Butunlikeordinaryincandescentbulbs,theydon'thaveafilamentthatwillburnout,andtheydon'tgetespeciallyh
3、ot.Theyareilluminatedsolelybythemovementofelectronsinasemiconductormaterial,andtheylastjustaslongasastandardtransistor.Inthisarticle,we'llexaminethesimpleprinciplesbehindtheseubiquitousblinkers,illuminatingsomecoolprinciplesofelectricityandlightintheprocess.WhatisaDiode?Adiodeisthesimpl
4、estsortofsemiconductordevice.Broadlyspeaking,asemiconductorisamaterialwithavaryingabilitytoconductelectricalcurrent.Mostsemiconductorsaremadeofapoorconductorthathashadimpurities(atomsofanothermaterial)addedtoit.Theprocessofaddingimpuritiesiscalleddoping.InthecaseofLEDs,theconductormater
5、ialistypicallyaluminum-gallium-arsenide(AlGaAs).Inpurealuminum-gallium-arsenide,alloftheatomsbondperfectlytotheirneighbors,leavingnofreeelectrons(negatively-chargedparticles)toconductelectriccurrent.Indopedmaterial,additionalatomschangethebalance,eitheraddingfreeelectronsorcreatingholes
6、whereelectronscango.Eitheroftheseadditionsmakethematerialmoreconductive.AsemiconductorwithextraelectronsiscalledN-typematerial,sinceithasextranegatively-chargedparticles.InN-typematerial,freeelectronsmovefromanegatively-chargedareatoapositivelychargedarea.Asemiconductorwithextraholesisc
7、alledP-typematerial,sinceiteffectivelyhasextrapositively-chargedparticles.Electronscanjumpfromholetohole,movingfromanegatively-chargedareatoapositively-chargedarea.Asaresult,theholesthemselvesappeartomovefromapositively-chargedareatoanegatively-chargedarea.Adiodecomprisesasecti
