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# Electron And Hole Equilibrium Concentrations 24 February 2014 - PowerPoint PPT Presentation

Electron And Hole Equilibrium Concentrations 24 February 2014. 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?.

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Electron And Hole Equilibrium Concentrations24 February 2014

• 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

Define effective density of states in the conduction band

5

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

7

Concentration of Holes at Equilibrium

Define effective density of states in the valence band

8

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

10

Electron and Hole Concentrations in Extrinsic Semiconductor Summary

For both undoped material and doped material under equilibrium condition

14

Position of Fermi-level:

15