Lecture #5.ppt

Lecture#5OUTLINEIntrinsicFermilevelDeterminationofEFDegeneratelydopedsemiconductorCarrierpropertiesCarrierdriftRead:,,EiTofindEFforanintrinsicsemiconductor,usethefactthatn=p:2SemiconductorDevicesforIntegratedCircuits*n(ni,Ei)andp(ni,Ei)Inanintrinsicsemiconductor,n=p=niandEF=Ei:3SemiconductorDevicesforIntegratedCircuits*Example:Energy-banddiagramQuestion:WhereisEFforn=1017cm-3?4SemiconductorDevicesforIntegratedCircuits*DopantIonizationConsideraphosphorus-dopedSisampleat300KwithND=1017cm-?Answer:Supposeallofthedonoratomsareionized. ThenProbabilityofnon-ionization5SemiconductorDevicesforIntegratedCircuits*NondegeneratelyDopedSemiconductorRecallthattheexpressionsfornandpwerederivedusingtheBoltzmannapproximation,*DegeneratelyDopedSemiconductorIfasemiconductorisveryheavilydoped,=300K:Ec-EF<3kTifND>-3 EF-Ev<3kTifNA>-:“n+”degeneratelyn-Ec“p+”degeneratelyp-Ev7SemiconductorDevicesforIntegratedCircuits*BandGapNarrowingIfthedopantconcentrationisasignificantfractionofthesiliconatomicdensity,theenergy-bandstructureisperturbedthebandgapisreducedbyDEG:N=1018cm-3:DEG=35meVN=1019cm-3:DEG=75meV8SemiconductorDevicesforIntegratedCircuits*urinsideasemiconductor:Drift::-generation(R-G)9SemiconductorDevicesforIntegratedCircuits*ElectronsasMovingParticlesF=(-q)E=moaF=(-q)E=mn*awheremn*istheelectroneffectivemassInvacuumInsemiconductor10SemiconductorDevicesforIntegratedCircuits*