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时间:2019-08-11
《Omar_Elementary Solid State Physics_Lecture9》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
1、Chapter7Weshalldiscuss:•thep-njunction=⇒explainitsrectificationpropertyandshowhow:•thejoiningof2p-njunctionsleadstothejunctiontransistorwhichactsasanamplifier.7.2Thep-njunction:TheRectifierThep-njunctionis:•aspecimenmadeofasingle–crystalsemiconductorinwhichtherearetwoad-jacen
2、tregions(seeFig.7.1):–ann-type–ap-typethen-regionisdopedwithdonorimpurities;thep-regionwithacceptorimpurities.Nd=donorconcentrationNn=acceptorconcentration.Notethatthewholejunctionisonesinglepieceofcrystalinwhich:•thetwosidesaredopeddifferentlyratherthantwodifferentpiecesjoi
3、nedto-gether.Themostinterestingelectricalproperty:•apotentialdifference,thecontactpotential,developsacrossthejunction,be-cause•electronsbegintodiffuseacrossjunctionfromntopregion•holesdiffusefromptonregion.Duetolargeconcentrationgradientatthejunction:⇓pregionacquiresnetnegati
4、vechargebecause•electronsenterthatregion•holesleavethatregion.⇓CONTACTPOTENTIALDEVELOPSNote:RefertotheFig.7.2whereenergyonp-sideishigherthanenergyonn-sidebyeφwhereφ=potentialdifference=contactpotential.ContactPotentialimpedesflowofdiffusioncurrents:dφelectricfield=E0=−dxactsto
5、opposefurtherdiffusionoftheelectronsandholes,andonly•thoseelectronswithkineticenergy>eφcandiffusefromn-sidetop-side.Aschargetransfercontinues,potentialcontinuestoincrease=⇒diffusionfluxcontinuestodecreaseuntil:Diffusionfluxofelectronsfromntopsidebecomesbalancedbyanelectronfluxfro
6、mptonsidecalledthe“GenerationFlux”2WHATISTHESOURCEOFTHEGENERATIONFLUX?•Onp-side,electronsandholesarecreatedthermally.Theseelectronsandholesrecombine,BUTanelectronfluxflowingtonregionresults,andanysuchelectronreachingthejunctionis=⇒quicklysweptawaytonsidebythestrongelectricfie
7、ldinsidethejunction.Thus,therearetwoelectronfluxesacrossthejunction:1.Afluxfromntopsideduetolargeelectronconcentrationonn-side.ThisiscalledtherecombinationfluxJnr,becauseelectronsflowingintothepregioneventuallycombinewiththeholesthere.2.ThegenerationfluxJng,flowingfromptonside.E
8、QUILIBRIUMREQUIRES:Jnr0=Jng0.Bysimilararguments:•holesinthevalencebandflowacrossjunction−→
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