Lub teeb Emitting Diode (LED) yog qhov tseem ceeb ntawm PN junction semiconductor diode uas emits ib lub teeb monochromatic (ib xim) lub teeb thaum ua haujlwm nyob rau hauv ib qho kev coj ncaj ncees. Cov qauv hauv paus ntawm LED muaj cov khoom siv tuag lossis lub teeb ci emitting semiconductor, cov kab hlau lead uas qhov chaw tuag yog qhov tseeb, thiab encapsulation epoxy uas nyob ib puag ncig thiab tiv thaiv cov tuag (Daim duab 1). Thawj cov LEDs uas siv tau ua lag luam tau tsim nyob rau xyoo 1960 los ntawm kev sib txuas peb lub ntsiab lus: gallium, arsenic thiab phosphorus (GaAsP) kom tau txais 655nm lub teeb liab. Txawm hais tias qhov luminous siv tau tsawg heev nrog qhov ci ci ntawm kwv yees li 1-10mcd @ 20mA, lawv tseem pom siv ntau yam kev siv, feem ntau yog cov ntsuas. Tom qab GaAsP, GaP, lossis gallium phosphide, LEDs liab tau tsim. Cov cuab yeej no tau pom tias muaj kev ua tau zoo quantum siab heev, txawm li cas los xij, lawv tsuas yog ua lub luag haujlwm me me hauv kev loj hlob ntawm cov ntawv thov tshiab rau LEDs. Qhov no yog vim ob qho laj thawj: Ua ntej, 700nm wavelength emission yog nyob rau hauv ib cheeb tsam spectral uas qhov rhiab heev ntawm tib neeg lub qhov muag yog tsawg heev (Daim duab 2) thiab yog li ntawd, nws tsis "tso" yuav ci heev txawm tias cov efficiency. yog siab (qhov tib neeg lub qhov muag yog feem ntau teb rau daj-ntsuab teeb). Qhov thib ob, qhov kev ua haujlwm siab no tsuas yog ua tiav ntawm cov dej ntws qis. Raws li qhov tam sim no nce, qhov ua tau zoo txo. Qhov no ua pov thawj los ua qhov tsis zoo rau cov neeg siv xws li sab nraum zoov cov lus kos npe cov tuam txhab uas feem ntau muab lawv cov LEDs ntawm cov tam sim no siab kom ua tiav qib ci ci zoo ib yam li DC txuas ntxiv ua haujlwm. Yog li ntawd, GaP liab LEDs tam sim no siv nyob rau hauv tsuas yog ib tug tsawg tus naj npawb ntawm daim ntawv thov. Raws li LED thev naus laus zis tau nce mus txog xyoo 1970, cov xim ntxiv thiab cov wavelengths tau dhau los ua muaj. Cov khoom siv feem ntau yog GaP ntsuab thiab liab, GaAsP txiv kab ntxwv los yog high efficiency liab thiab GaAsP daj, tag nrho cov tseem siv niaj hnub no (Table3). Txoj kev mus rau kev siv tswv yim ntxiv kuj tau pib tsim. LEDs tau pom nyob rau hauv cov khoom xws li lub laij lej, digital watches thiab cov khoom siv ntsuas. Txawm hais tias kev ntseeg siab ntawm LEDs yeej ib txwm ua tau zoo tshaj plaws ntawm cov teeb pom kev zoo, neon thiab lwm yam, qhov tsis ua haujlwm ntawm cov khoom siv thaum ntxov tau ntau dua li cov thev naus laus zis tam sim no ua tiav. Qhov no yog vim nyob rau hauv ib feem ntawm qhov tseeb tivthaiv los ua ke uas yog feem ntau phau ntawv nyob rau hauv cov xwm. Cov neeg ua haujlwm ib leeg tau ua cov haujlwm xws li xa cov epoxy, tso cov tuag rau hauv txoj haujlwm, thiab sib tov epoxy tag nrho ntawm tes. Qhov no ua rau muaj qhov tsis xws luag xws li "epoxy slop" uas ua rau VF (rau pem hauv ntej voltage) thiab VR (rov qab voltage) to los yog luv luv ntawm PN junction. Tsis tas li ntawd, txoj kev loj hlob thiab cov khoom siv tsis tau ua kom zoo zoo li niaj hnub no. Cov lej loj ntawm qhov tsis xws luag hauv cov khoom siv lead ua, substrate thiab epitaxial txheej ua rau txo qis kev ua haujlwm thiab siv lub neej luv dua.
Gallium Aluminium Arsenide
Nws tsis yog txog thaum xyoo 1980's thaum cov khoom siv tshiab, GaAlAs (gallium aluminium arsenide) tau tsim, qhov kev loj hlob sai ntawm kev siv LEDs pib tshwm sim. GaAlAs thev naus laus zis tau muab kev ua haujlwm zoo tshaj li yav dhau los LEDs. Lub ci ci tau dhau 10 npaug ntau dua li cov qauv LEDs vim muaj kev ua tau zoo thiab ntau txheej, heterojunction hom qauv. Qhov hluav taws xob xav tau rau kev ua haujlwm tau qis dua ua rau tag nrho lub zog txuag. Cov LEDs kuj tuaj yeem yooj yim pulsed lossis multiplexed. Qhov no tso cai rau lawv siv hauv cov lus sib txawv thiab cov paib sab nraud. LEDs kuj tau tsim los rau hauv cov ntawv thov xws li bar code scanners, fiber optic cov ntaub ntawv xa mus, thiab cov khoom siv kho mob. Txawm hais tias qhov no yog qhov kev ua txhaum loj hauv LED thev naus laus zis, tseem muaj qhov cuam tshuam tseem ceeb rau cov khoom siv GaAlAs. Ua ntej, nws tsuas yog muaj nyob rau hauv liab 660nm wavelength. Qhov thib ob, lub teeb tso zis degradation ntawm GaAlAs yog ntau dua li ntawm cov txheej txheem thev naus laus zis. Nws tau ntev lawm ib qho kev xav tsis zoo nrog LEDs tias lub teeb tso zis yuav txo qis 50% tom qab 100,000 teev ntawm kev ua haujlwm. Qhov tseeb, qee qhov GaAlAs LEDs tuaj yeem txo 50% tom qab tsuas yog 50,000 -70,000 teev ntawm kev ua haujlwm. Qhov no muaj tseeb tshwj xeeb tshaj yog nyob rau hauv qhov kub thiab/los yog high humidity ib puag ncig. Tsis tas li thaum lub sijhawm no, daj, ntsuab thiab txiv kab ntxwv pom tsuas yog kev txhim kho me me hauv qhov ci thiab kev ua haujlwm tau zoo uas yog vim muaj kev txhim kho hauv kev loj hlob siv lead ua thiab optics tsim. Lub hauv paus qauv ntawm cov khoom tseem tsis tau hloov.
Yuav kom kov yeej cov teeb meem nyuaj no yuav tsum tau siv tshuab tshiab. LED designers tig mus rau laser diode technology rau kev daws teeb meem. Nyob rau tib lub sijhawm nrog kev txhim kho sai hauv LED thev naus laus zis, laser diode thev naus laus zis kuj tau ua tiav. Nyob rau xyoo 1980's laser diodes nrog cov zis tawm hauv qhov pom kev pom tau pib ua lag luam rau cov ntawv thov xws li cov ntawv nyeem bar code, ntsuas thiab ntsuas cov kab ke thiab cov cim cia tom ntej. Cov neeg tsim qauv LED tau saib siv cov tswv yim zoo sib xws los tsim cov teeb ci siab thiab kev ntseeg siab LEDs. Qhov no ua rau kev txhim kho ntawm InGaAlP (Indium Gallium Aluminium Phosphide) pom LEDs. Kev siv InGaAlP raws li cov khoom siv luminescent tso cai rau kev hloov pauv hauv kev tsim ntawm LED tso zis xim yooj yim los ntawm kev kho qhov loj ntawm lub zog band sib txawv. Yog li, ntsuab, daj, txiv kab ntxwv thiab liab LEDs tag nrho tuaj yeem tsim siv tib lub thev naus laus zis. Tsis tas li ntawd, lub teeb tso zis degradation ntawm InGaAlP cov ntaub ntawv tau txhim kho zoo txawm tias qhov kub thiab av noo siab.
Kev txhim kho tam sim no ntawm LED Technology InGaAlP LEDs tau nce ntxiv hauv kev ci ntsa iab nrog kev txhim kho tshiab los ntawm Toshiba, tus thawj coj ntawm LEDs. Toshiba, siv MOCVD (Metal Oxide Chemical Vapor Deposition) txheej txheem kev loj hlob, muaj peev xwm tsim tau cov qauv cuab yeej uas cuam tshuam txog 90% lossis ntau dua ntawm cov teeb ci tsim tawm los ntawm cov txheej txheem nquag mus rau substrate rov qab los ua cov khoom siv hluav taws xob (Daim duab 4). Qhov no tso cai rau yuav luag ob zaug nce hauv LED luminance tshaj li cov khoom siv ib txwm siv. LED kev ua tau zoo tau txhim kho ntxiv los ntawm kev nthuav qhia cov txheej thaiv tam sim no rau hauv cov qauv LED (Daim duab 5). Qhov thaiv txheej txheej no tseem ceeb tshaj qhov tam sim no los ntawm cov cuab yeej kom ua tiav cov cuab yeej zoo dua. Raws li qhov tshwm sim ntawm cov kev txhim kho no, ntau qhov kev loj hlob rau LEDs nyob rau hauv 1990's yuav yog concentrated nyob rau hauv peb qhov chaw tseem ceeb: thawj yog nyob rau hauv lub tsheb tswj cov cuab yeej xws li nres teeb, neeg taug kev teeb liab, barricade teeb thiab txoj kev phom sij. Qhov thib ob yog nyob rau hauv cov kab lus sib txawv xws li ib qho nyob hauv Times Square New York uas qhia cov khoom muag, xov xwm thiab lwm yam ntaub ntawv. Qhov thib peb concentration yuav yog nyob rau hauv automotive daim ntaub ntawv. Lub teeb pom kev LED tau los ntev heev txij li nws cov lus qhia yuav luag 40 xyoo dhau los thiab tseem tsis tau pom muaj cov tsos mob ntawm kev qeeb. Lub Blue LED, uas tau los ua muaj nyob rau hauv ntau lawm nyob rau hauv 1990's, ua rau tag nrho tiam ntawm daim ntawv thov tshiab. Blue LEDs vim lawv lub zog photon siab (> 2.5eV) thiab qhov muag tsis tshua muaj qhov muag tau ib txwm nyuaj rau kev tsim khoom. Ntxiv rau qhov thev naus laus zis tsim nyog los tsim cov LEDs no txawv heev thiab tsis tshua muaj siab tshaj li cov khoom siv LED. Cov LEDs xiav muaj hnub no suav nrog GaN (gallium nitride) thiab SiC (silicon carbide) kev tsim kho nrog qhov ci ntsa iab ntau tshaj 10,000mcd @ 20mA rau GaN li. Txij li thaum xiav yog ib qho ntawm cov xim tseem ceeb, (lwm ob yog liab thiab ntsuab), tag nrho cov xim ntawm lub xeev LED cov paib, TV's thiab lwm yam tau dhau los ua lag luam. Lwm daim ntawv thov rau xiav LEDs suav nrog cov cuab yeej kuaj mob thiab photolithography.
LED Xim Nws kuj tseem tuaj yeem tsim lwm cov xim siv tib yam GaN thev naus laus zis thiab kev loj hlob. Piv txwv li, lub siab ci ntsuab (kwv yees li 500nm) LED tau raug tsim tawm uas tau hloov lub teeb ntsuab hauv teeb pom kev. Lwm cov xim xws li ntshav thiab dawb kuj ua tau. Nrog rau kev taw qhia ntawm xiav LEDs, nws muaj peev xwm ua tau dawb los ntawm kev xaiv qhov sib xyaw ua ke kom zoo ntawm lub teeb liab, ntsuab thiab xiav. Cov txheej txheem no txawm li cas los xij, xav tau cov software tsim nyog thiab kho vajtse tsim los siv. Tsis tas li ntawd, qhov ci ntsa iab yog qis thiab tag nrho cov teeb pom kev zoo ntawm txhua RGB tuag raug siv degrades ntawm tus nqi sib txawv uas ua rau muaj xim tsis sib xws. Lwm txoj hauv kev ua kom ua tiav lub teeb pom kev zoo, yog siv cov phosphor txheej (Yttrium Aluminium Garnet) rau saum npoo ntawm lub teeb xiav LED. Hauv cov ntsiab lus, LEDs tau dhau los ntawm cov me nyuam mos mus rau cov hluas thiab tab tom ntsib qee qhov kev lag luam loj tshaj plaws ntawm lawv lub neej. Los ntawm kev siv cov khoom siv InGaAlP nrog MOCVD raws li cov txheej txheem kev loj hlob, ua ke nrog kev xa tawm ntawm cov teeb pom kev zoo thiab siv tau zoo ntawm kev txhaj tshuaj tam sim no, qee qhov ci ntsa iab, zoo tshaj plaws thiab txhim khu kev qha LEDs tam sim no muaj. Cov thev naus laus zis no ua ke nrog lwm cov qauv tshiab LED yuav ua kom muaj kev siv dav ntawm LEDs. Kev tsim kho tshiab hauv xiav spectrum thiab ntawm lub teeb pom kev zoo yuav lav qhov kev nce ntxiv hauv kev siv ntawm cov teeb pom kev lag luam no.
