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Information about Semiconductors

Published on April 25, 2009

Author: ankush85


Slide 1: 1 Semiconductors Slide 2: 2 Free Electron Bands Origin of Energy Bands Na: 1s22s22p63s1 Pauli’s Exclusion Principle Semiconductors : 3 Semiconductors X (real space) Slide 4: 4 K Space E k k Metal Semiconductor Forbidden gap Slide 5: 5 Band Gap Energy: Eg How is the Band Gap formed? : 6 How is the Band Gap formed? For free electron in metals: U 0 because of high electron density and short electrostatic screening length Electron wavefunction scattered by periodic potentialstanding wave when K= np/a (think about interference of light) Multiple Bands : 7 Multiple Bands Bandgap Formation : 8 Bandgap Formation Bandstructure of Si and GaAs : 9 Bandstructure of Si and GaAs Electrons and Holes : 10 Electrons and Holes Slide 11: 11 Charge Carrier Density Parabolic approx (free electron): m*: effective mass Electron: Hole: Slide 12: 12 f(E) and D(E) Intrinsic Semiconductor Doped Semiconductor Slide 13: 13 Law of mass action: Slide 14: 14 Intrinsic Semiconductors Slide 15: 15 Doped Semiconductors Slide 16: 16 Dopant Energy Level Slide 17: 17 Carrier Densities in Doped Semiconductors “Law of Mass Action” for semiconductors Charge accounting: Slide 18: 18 Charge neutrality (accounting): Occupation of donors by electrons: Occupation of acceptors by holes: Charge Density in Doped Semiconductors Slide 19: 19 where Slide 20: 20 I) Low temperature limit Carrier freeze-out II) Higher temperature limit Saturation III) Muy caliente limit: n ~ ni  intrinsic region Temperature Dependance of Carrier Concentration Slide 21: 21 HOT COLD Carrier Density vs. Temperature Carrier Transport in Semiconductors : 22 Carrier Transport in Semiconductors Current Density: Mobility: Electrical Conductivity: Drift Velocity: Slide 23: 23 Carrier Scattering Mechanisms Defect Scattering Phonon Scattering Boundary Scattering (Film Thickness, Grain Boundary) Carrier Scattering CarrierScattering : 24 CarrierScattering Intra-valley Inter-valley Inter-band Defect Scattering : 25 Defect Scattering Charged defect Perturb potential periodicity (i) Ionized defects (ii) Neutral defects Slide 26: 26 Scattering from Ionized Defects (“Rutherford Scattering”) 1/  <v>-3  T-3/2 Average Carrier Velocity in Semiconductors (not the drift velocity): Mean Free Time: Mobility: Carrier-Phonon Scattering : 27 Carrier-Phonon Scattering Phonon modulates the periodic potential Carrier scattered by moving potential 1/tph~ Slide 28: 28 Mobility Slide 29: 29 Electrical Conductivity

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