ELCT363_Lecture13_FermiLevel_in_DopedSemiconductor_CarrierMobility

ELCT363_Lecture13_FermiLevel_in_DopedSemiconductor_CarrierMobility

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Unformatted text preview: ELCT 363: Intro. to Microelectronics Lecture 13; Slide Mandal/Fall 2011 Fermi level in n-type semiconductor In the n-type material most of the mobile charges are free electrons. Therefore, the average energy of mobile charges is close to EC: EF EC EFn Phosphorus (P) has 5 outer shell electrons. Extra free electron EC EV EFi 1 ELCT 363: Intro. to Microelectronics Lecture 13; Slide Mandal/Fall 2011 Position of Fermi level in n-Type Semiconductor n0 ni Nc e-(Ec-E F )/kT = Nc e-(Ec-Ei)/kT = eE F /k T eE i /kT = e(E F-E i ) /kT (EF-E i ) = kT ln (n0/ni ) E c Ei E F EV EF - Ei ln (n0/ni ) = (EF-E i )/kT n-type semiconductor: n0 = ND (EF-E i ) = kT ln (ND/ni ) Position of Fermi level depends on doping concentration. 2 ELCT 363: Intro. to Microelectronics Lecture 13; Slide Mandal/Fall 2011 Fermi level in p-type semiconductor In the p-type material most of the mobile charges are holes. Therefore, the average energy of mobile charges is close to EV: EF EV EFp EC EV Boron (B) has 3 outer shell electrons. Extra electron vacancy or hole EFi 3 ELCT 363: Intro. to Microelectronics Lecture 13; Slide Mandal/Fall 2011 Position of Fermi level in p-Type Semiconductor p0 pi N V e-(EF-Ev)/kT = N V e-(Ei-Ev)/kT = e-E F /kT e- E i /kT = e(E i-E F ) /kT (Ei-E F ) = kT ln (p0/pi ) Ec Ei E F EV Ei - EF Similarly, ( Ei-E F ) = kT ln (p0/ni ) Since ni = pi, p-type semiconductor: p0 = NA (Ei-E F ) = kT ln (NA/ni ) 4 ELCT 363: Intro. to MicroelectronicsELCT 363: Intro....
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ELCT363_Lecture13_FermiLevel_in_DopedSemiconductor_CarrierMobility

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