Electron And Hole Equilibrium Concentrations 24 February 2014

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Electron And Hole Equilibrium Concentrations 24 February 2014

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Electron And Hole Equilibrium Concentrations 24 February 2014

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- Return and discuss Quiz 2
- Chapter 4 Topics-Two burning questions:
- What is the density of states in the conduction and valence bands?
- How do you find an exact position of the Fermi Level?

Concentration of Electrons at Equilibrium

Thermal-equilibrium concentration of electrons (#/cm3) in the conduction band

Assume that EF is within the energy bandgap and

there is

So for energy levels in the conduction band

(kT ≈ 25.9 meV for T=300K). So for energy levels in the conduction band

Page 87 Text, Equation 3.69

Concentration of Electrons at Equilibrium

Define effective density of states in the conduction band

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Concentration of Holes at Equilibrium

Thermal-equilibrium concentration of holes (#/m3) in the conduction band

Assume that EF is within the energy bandgap and

there is

So for energy levels in the conduction band

then for energy levels in the conduction band

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Concentration of Holes at Equilibrium

Define effective density of states in the valence band

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Carrier Concentrations in Intrinsic Semiconductors

For an intrinsic semiconductor, the concentration of electrons in the conduction band is equal to the concentration of holes in the valence band

is the Fermi-level for the intrinsic semiconductor, i.e., intrinsic Fermi-level

For a given semiconductor, at constant temperature, ni isconstant

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The Intrinsic Fermi-Level position

If

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Fermi-Energy Levels In Extrinsic Semiconductors

Electron and Hole Concentrations in Extrinsic Semiconductor Summary

For both undoped material and doped material under equilibrium condition

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Position of Fermi Energy in Extrinsic Semiconductors

Position of Fermi-level:

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Variation of Fermi-Energy with Doping Concentration

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Variation of Fermi-Energy with Temperature

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