Chapter 5

Question 1

When do Fermi-Dirac reduce to Boltzmann statistics?

Answer 1

when Ec - Ef&raquo_space; kT or Ef - Ev&raquo_space; kT

Ef is a few kT away from the band edges

Question 2

intrinsic semiconductor

Answer 2

> number of electron and hole concentrations are equal

> no impurities

Question 3

Increase electron concenctration _______ hole concentration

Answer 3

reduces

Question 4

np = ni^2 always when

Answer 4

> in thermal equilibrium

> applies for intrinsic, n-type, and p-type

Question 5

energy difference between vacuum level and fermi energy level is

Answer 5

work function

Question 6

For a mat’l in thermal equilibrium and no photogeneration/electric field applied, fermi level in the mat’l is ______

Answer 6

uniform

Question 7

Fermi-Dirac function is based on ______

Answer 7

Pauli exclusion principle

Question 8

In a metal the average energy for conduction electrons is _____ and is relatively temperature ______

Answer 8

3/5Ef, independent

Question 9

Why can we exclude the Pauli exclusion principle in semiconductors? What statistics do we use then?

Answer 9

The conduction band is scarcely populated by electrons, so likelihood of two electrons populating the same state is slim. We use Boltzmann statistics then

Question 10

ψA overlap to give the ______

Answer 10

conduction band (empty)

Question 11

ψB overlap to give the ______

Answer 11

valence band (full)

Question 12

When an electric field is applied across a semiconductor, energy band bend up into the ___ direction, V(x) ______ and PE _______

Answer 12

x, decreases, increases