78-79-A39饶晓仕.doc

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1、CHAPER3TheSemiconductorinEquilibriumSolutionTheparametervaluesatT=350KarefoundasAndTheprobabilitythatanenergystateatE=Ev–kTisemptyisgivenbyOrTheholeconcentrationisOr■CommentTheparametervaluesatanytemperaturecaneasilybefoundusingthe300Kvaluesandthetemperaturedependenceoftheparameter

2、.ExerciseProblemEX3.2Calculatethethermal-equilibriumholeconcentrationinsiliconatT=300KforthecasewhentheFermilevelis0.20eVabovethevalence-bandenergyEv.Theeffectivedensityofstatesfunctions,NcandNv,areconstantforagivensemiconductormaterialatafixedtemperature.Table3.1givesthevalusofthe

3、densityofstatesfunctionandoftheeffectivemassesforsilicon,galliumarsenide,andgermanium.NotethatvalueofNcforgalliumarsenideissmallerthanthetypicalvalue.Thisdifferenceisduetothesmallelectroneffectivemassingalliumarsenide.Thethermal-equilibriumconcentrationsofelectronsintheconductionba

4、ndandofholesinthevalencebandaredirectlyrelatedtotheeffectivedensityofstatesconstantsandtotheFermienergylevel.3.1ChargeCarriersinSemiconductorsTable3.1EffectivedensityofstatesfunctionandeffectivemassvaluesSilicon1.080.56Galliumarsenide0.0670.48Germanium0.550.373.1.3TheIntrinsicCarri

5、erConcentrationForanintrinsicsemiconductor,theconcentrationofelectronsintheconductionbandisequaltotheconcentrationofholesinthevalenceband.Wecandenoteandastheelectronandholeconcentrations，respectively,intheintrinsicsemiconductor.Theseparametersareusuallyreferredtoastheintrinsicelect

6、ronconcentrationandintrinsicholeconcentration.However,ni=pi,sonormallywesimplyusetheparameterastheintrinsiccarrierconcentration,whichreferstoeithertheintrinsicelectronorholeconcentration.TheFermienergylevelfortheintrinsicsemiconductoriscalledtheintrinsicFermienergy,or=.IfweapplyEqu

7、ations(3.11)and(3.19)totheintrinsicsemiconductor,thenwecanwrite（3.20）And（3.21）IfwetaketheproductofEquations(3.20)and(3.21),weobtain（3.22）or（3.23）whereEgisthebandgapenergy.Foragivensemiconductormaterialataconstanttemperature,thevalueofniisaconstant,andindependentoftheFermienergy.The

8、intrinsiccarrierconcentrat