05_carrier+density+calculation

# 05_carrier+density+calculation - Carrier Density...

This preview shows pages 1–7. Sign up to view the full content.

EECS-320, L.J. Guo 1 Carrier Density Calculation How to determine carrier density and the associated Fermi energy level? What are the necessary conditions to determine the carrier densities? What are intrinsic and extrinsic semiconductors? How can semiconductors be compensated? Carrier density as a function of temperature

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
EECS-320, L.J. Guo 2 Density Of States How many electron states are there at certain energy? Density Of States for conduction band and for valence band *3/ 2 1/ 2 23 2( ) () eC C mE E gE π = h *3/ 2 1/ 2 ) hV V E = h E ρ (E) E V E C Valence band Conduction band
EECS-320, L.J. Guo 3 Fermi Function and Fermi Energy Electronic states are not uniformly populated, but obey the F-D distribution At T=0, all states below E f are filled and all states above are empty; For metals, Fermi energy/level represents the highest energy level that is occupied by electrons. For semiconductors, Fermi level is a function of carrier density, as we will see later. Approach Boltzmann distribution () + = kT E E E f f exp 1 1 k = 8.617x10 -5 eV/ o K

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
EECS-320, L.J. Guo 4 Carrier Density Distribution ( ) ( ) ( ) C nE g E f E = () ( ) 1 V pE g E f E ⎡⎤ =− ⎣⎦
EECS-320, L.J. Guo Degenerate versus Non-Degenerate Define where Boltzmann approximation is valid E C E V For E V + 3kT < E f < E C – 3kT, Boltzmann approximation is accurate Semiconductor is said to be “non-degenerate” 3kT 3kT E F here: non-degenerate, Boltzmann valid E F here: degenerate (large n) E F here: degenerate (large p)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
EECS-320, L.J. Guo Alternative expression for n, p (non-degenerate) = kT E E N n C f C exp = kT E E N p f V V exp For Boltzmann approximation, exp iC EE nN kT
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 07/22/2011 for the course EECS 320 taught by Professor Sun during the Fall '10 term at University of Florida.

### Page1 / 21

05_carrier+density+calculation - Carrier Density...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online