版權(quán)說明:本文檔由用戶提供并上傳,收益歸屬內(nèi)容提供方,若內(nèi)容存在侵權(quán),請進(jìn)行舉報或認(rèn)領(lǐng)
文檔簡介
Semiconductors,diodes,transistors
(HorstWahl,QuarkNetpresentation,June2001)ElectricalconductivityEnergybandsinsolidsBandstructureandconductivitySemiconductorsIntrinsicsemiconductorsDopedsemiconductorsn-typematerialsp-typematerialsDiodesandtransistorsp-njunctiondepletionregionforwardbiasedp-njunctionreversebiasedp-njunctiondiodebipolartransistoroperationofbipolarpnptransistorFETELECTRICALCONDUCTIVITYinorderofconductivity:superconductors,conductors,semiconductors,insulatorsconductors:materialcapableofcarryingelectriccurrent,i.e.materialwhichhas“mobilechargecarriers”(e.g.electrons,ions,..) e.g.metals,liquidswithions(water,moltenioniccompounds),plasma
insulators:materialswithnoorveryfewfreechargecarriers;e.g.quartz,mostcovalentandionicsolids,plasticssemiconductors:materialswithconductivitybetweenthatofconductorsandinsulators;e.g.germaniumGe,siliconSi,GaAs,GaP,InPsuperconductors:certainmaterialshavezeroresistivityatverylowtemperature.somerepresentativeresistivities():R=L/A,R=resistance,L=length,A=crosssectionarea;resistivityat20oC
resistivityinm
resistance(in)(L=1m,diam=1mm)aluminum 2.8x10-8 3.6x10-2brass 8x10-8 10.1x10-2copper 1.7x10-8 2.2x10-2platinum 10x10-8 12.7x10-2silver 1.6x10-8 2.1x10-2carbon 3.5x10-5 44.5germanium 0.45 5.7x105silicon 640 6x108porcelain 1010-1012 1016-1018teflon 1014 1020blood 1.5 1.9x106fat 24 3x107ENERGYBANDSINSOLIDS:Insolidmaterials,electronenergylevelsformbandsofallowedenergies,separatedbyforbiddenbands valenceband=outermost(highest)bandfilledwithelectrons(“filled”=allstatesoccupied)conductionband=nexthighestbandtovalenceband(emptyorpartlyfilled)“gap”=energydifferencebetweenvalenceandconductionbands,=widthoftheforbiddenbandNote: electronsinacompletelyfilledbandcannotmove,sinceallstatesoccupied(Pauliprinciple);onlywaytomovewouldbeto“jump”intonexthigherband-needsenergy;electronsinpartlyfilledbandcanmove,sincetherearefreestatestomoveto.Classificationofsolidsintothreetypes,accordingtotheirbandstructure:insulators:gap=forbiddenregionbetweenhighestfilledband(valenceband)andlowestemptyorpartlyfilledband(conductionband)isverywide,about3to6eV;semiconductors:gapissmall-about0.1to1eV;conductors:valencebandonlypartiallyfilled,or(ifitisfilled),thenextallowedemptybandoverlapswithitBandstructureandconductivityINTRINSICSEMICONDUCTORSsemiconductor=materialforwhichgapbetweenvalencebandandconductionbandissmall;
(gapwidthinSiis1.1eV,inGe0.7eV).atT=0,therearenoelectronsintheconductionband,andthesemiconductordoesnotconduct(lackoffreechargecarriers);atT>0,somefractionofelectronshavesufficientthermalkineticenergytoovercomethegapandjumptotheconductionband;
fractionriseswithtemperature;
e.g.at20oC(293K),Sihas0.9x1010conductionelectronspercubiccentimeter;at50oC(323K)thereare7.4x1010.electronsmovingtoconductionbandleave“hole”(covalentbondwithmissingelectron)behind; underinfluenceofappliedelectricfield,neighboringelectronscanjumpintothehole,thuscreatinganewhole,etc.
holescanmoveundertheinfluenceofanappliedelectricfield,justlikeelectrons; bothcontributetoconduction.inpureSiandGe,thereareequallymanyholes(“p-typechargecarriers”)asthereareconductionelectrons(“n-typechargecarriers”);puresemiconductorsalsocalled“intrinsicsemiconductors”.Intrinsicsilicon:DOPEDSEMICONDUCTORS:“dopedsemiconductor”:(also“impure”,“extrinsic”)=semiconductorwithsmalladmixtureoftrivalentor pentavalentatoms;n-typematerial
donor(n-type)impurities:
dopantwith5valenceelectrons(e.g.P,As,Sb)4electronsusedforcovalentbondswithsurroundingSiatoms,oneelectron“l(fā)eftover”;leftoverelectronisonlylooselybound
onlysmallamountofenergyneededtoliftitintoconductionband(0.05eVinSi)
“n-typesemiconductor”,hasconductionelectrons,noholes(apartfromthefewintrinsicholes)example:dopingfraction
of10-8
SbinSiyieldsabout5x1016conductionelectronspercubiccentimeteratroomtemperature,i.e.gainof5x106overintrinsicSi.p-typematerialacceptor(p-type)impurities:
dopantwith3valenceelectrons(e.g.B,Al,Ga,In)
only3ofthe4covalentbondsfilled
vacancyinthefourthcovalentbond
hole“p-typesemiconductor”,hasmobileholes,veryfewmobileelectrons(onlytheintrinsicones).advantagesofdopedsemiconductors:can”tune”conductivitybychoiceofdopingfractioncanchoose“majoritycarrier”(electronorhole)canvarydopingfractionand/ormajoritycarrierwithinpieceofsemiconductorcanmake“p-njunctions”(diodes)and“transistors”DIODESANDTRANSISTORSp-nJUNCTION:
p-njunction=semiconductorinwhichimpuritychangesabruptlyfromp-typeton-type;“diffusion”=movementduetodifferenceinconcentration,fromhighertolowerconcentration;inabsenceofelectricfieldacrossthejunction,holes“diffuse”towardsandacrossboundaryinton-typeandcaptureelectrons;electronsdiffuseacrossboundary,fallintoholes(“recombinationofmajoritycarriers”);
formationofa“depletionregion”
(=regionwithoutfreechargecarriers)
aroundtheboundary;chargedionsareleftbehind(cannotmove):negativeionsleftonp-side
netnegativechargeonp-sideofthejunction; positiveionsleftonn-side
netpositivechargeonn-sideofthejunction
electricfieldacrossjunctionwhichpreventsfurtherdiffusion.PnjunctionFormationofdepletionregioninpn-junction:DIODEdiode=“biasedp-njunction”,i.e.p-njunctionwithvoltageappliedacrossit“forwardbiased”:p-sidemorepositivethann-side;“reversebiased”:n-sidemorepositivethanp-side;forwardbiaseddiode:thedirectionoftheelectricfieldisfromp-sidetowardsn-side
p-typechargecarriers(positiveholes)inp-sidearepushedtowardsandacrossthep-nboundary,
n-typecarriers(negativeelectrons)inn-sidearepushedtowardsandacrossn-pboundary
currentflowsacrossp-nboundaryForwardbiasedpn-junctionDepletionregionandpotentialbarrierreducedReversebiaseddiodereversebiaseddiode:appliedvoltagemakesn-sidemorepositivethanp-side
electricfielddirectionisfromn-sidetowards p-side
pusheschargecarriersawayfromthep-n
boundary
depletionregionwidens,andnocurrentflows
diodeonlyconductswhenpositivevoltageappliedtop-sideandnegativevoltageton-side
diodesusedin“rectifiers”,toconvertacvoltagetodc.ReversebiaseddiodeDepletionregionbecomeswider, barrierpotentialhigherTRANSISTORS(bipolar)transistor=combinationoftwodiodesthatsharemiddleportion,called“base”oftransistor;othertwosections:“emitter''and“collector”;usually,baseisverythinandlightlydoped.twokindsofbipolartransistors:pnpandnpntransistors“pnp”meansemitterisp-type,baseisn-type,andcollectorisp-typematerial;in“normaloperationofpnptransistor,applypositivevoltagetoemitter,negativevoltagetocollector;operationofpnptransistor:ifemitter-basejunctionisforwardbiased,“holesflow”frombatteryintoemitter,moveintobase;someholesannihilatewithelectronsinn-typebase,butbasethinandlightlydoped
mostholesmakeitthroughbaseintocollector,holesmovethroughcollectorintonegativeterminalofbattery;i.e.“collectorcurrent”flowswhosesizedependsonhowmanyholeshavebeencapturedbyelectronsinthebase;thisdependsonthenumberofn-typecarriersinthebasewhichcanbecontrolledbythesizeofthecurrent(the“basecurrent”)thatisallowedtoflowfro
溫馨提示
- 1. 本站所有資源如無特殊說明,都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
- 2. 本站的文檔不包含任何第三方提供的附件圖紙等,如果需要附件,請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
- 3. 本站RAR壓縮包中若帶圖紙,網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽,若沒有圖紙預(yù)覽就沒有圖紙。
- 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
- 5. 人人文庫網(wǎng)僅提供信息存儲空間,僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理,對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯,并不能對任何下載內(nèi)容負(fù)責(zé)。
- 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容,請與我們聯(lián)系,我們立即糾正。
- 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時也不承擔(dān)用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。
最新文檔
- 《寶馬銷售流程》課件
- 《電動力學(xué)chapter》課件
- 《寶葫蘆的秘密》電影觀后感10篇
- 《康師傅廣告文化》課件
- 跨學(xué)段項(xiàng)目化學(xué)習(xí)的核心任務(wù)設(shè)計(jì)探析
- 大學(xué)生幼兒園實(shí)習(xí)報告(15篇)
- 金融高效辦公技能
- 策劃招商洽談活動方案
- 七年級歷史下冊期末復(fù)習(xí)課件第二單元
- 研學(xué)旅游可持續(xù)發(fā)展研究-洞察分析
- 區(qū)塊鏈原理與實(shí)踐全套完整教學(xué)課件
- 運(yùn)動神經(jīng)元病小講課
- 工會的財務(wù)管理制度〔13篇〕
- 新版醫(yī)務(wù)人員法律法規(guī)知識培訓(xùn)課件
- 2024年土地市場研究分析服務(wù)協(xié)議
- 物業(yè)管理公文寫作培訓(xùn)
- 2023醫(yī)療質(zhì)量安全核心制度要點(diǎn)釋義(第二版)對比版
- 家庭教育大講堂實(shí)施方案
- 部編版《道德與法治》四年級下冊教材解讀與分析文檔
- 2024-2030年中國機(jī)場跑道異物碎片(FOD)檢測系統(tǒng)行業(yè)市場發(fā)展趨勢與前景展望戰(zhàn)略研究報告
- 學(xué)校體育學(xué)智慧樹知到答案2024年湖南科技大學(xué)
評論
0/150
提交評論