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Energy Bands in Semiconductors

Energy Bands in Semiconductors. Overlapping of energy bands – presence of mixed states s 2 +p 6  2 ( s+p )-Bands = 2 x ( s 1 +p 3 ) In the ground state at 0K: valence band is completely filled, conduction band is empty. Electron configurations in semiconductors:

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Energy Bands in Semiconductors

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  1. Energy Bands in Semiconductors Overlapping of energy bands – presence of mixed states s2+p6 2 (s+p)-Bands = 2 x (s1+p3) In the ground state at 0K: valence band is completely filled, conduction band is empty

  2. Electron configurations in semiconductors: 4 electrons at the highest atomic energy level Group IV (C, Si, Ge): 2  s2 + 2  p2 Group III-V (GaAs, GaP, AlN, GaN): 2  s2 + p1 + p3 Group II-VI (ZnO, CdS, CdTe): 2  s2+ p4

  3. Pure (intrinsic) semiconductors Electrons with (): Population density: Density of state: Fermi function: Number of electrons in the conduction band: (e-in the CB)

  4. Fermi Energy in Semiconductors Fermi energy: Temperature T = 0K T > 0K Energy The Fermi energy (Fermi level) of semiconductors at 0K is located in the middle of the energy gap

  5. Electrons and Holes EC

  6. Electrons in the Conduction Band Fermi function:

  7. Number of Electrons in Conduction Band

  8. Electrons in the Conduction Band Number of electrons in the conduction band: Fermi energy: Effective mass: Number of electrons in the conduction band (per unit of volume):

  9. Number of Charge Carriers and Electrical Conductivity

  10. Mobility of electrons and holes Electrical conductivity Density of the charge carriers

  11. Electrical Properties of some Semiconductors Effective mass

  12. Table 14.6. gap energy, mobility of electrons and holes and the effective mass of conduction electrons Lattice parameter(Å) Diamond 3.5670 4.3585 5.4300 5.6568 5.6533 6.0954 6.056 6.4867

  13. Correlation between the lattice parameter and the gap size

  14. Energy Transition of Electrons between Valence Band and Conduction Band* Thermal excitation Photon Electron Optical transition Phonon Cutoff frequency of absorption: * Quantum jump

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