1. When Electric field is applied to free electrons

2. When Electric field is applied to bloch electrons

17. Standard labels of the symmetry points of the B.Z.

18. Band structure of GaAs

24. Fermi level (chemical potential)

27. Extrinsic semiconductor
extrinsic semiconductor : introducing small amounts of impurities  n ≠ p
n-type doping IV V VI
doping : 1 impurity atom per ~106 host atoms
 keeping diamond crystal structure
pentavalent (valency of 5) element ( As, P, Sb)
 one electron left unbounded
electron e− orbing around As+ ionic center
 same as hydrogen atom in a silicon environment
binding energy of the electron in H atom
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28. [o  r o (r : relative permittivity of Si)]
binding energy of the electron in H atom
binding energy of electron to As+ site in Si crystal
[o  r o (r : relative permittivity of Si)]
: comparable with average thermal energy at RT ~ 3/2 kT (~ 0.04 eV)
free electron in CB
 readily free the fifth valence electron
donor atom : donates an electron into CB
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29. Nd : donor atom concentration
Ed : energy required to take electron
away from donor atom into CB
here, Ed ~ 0.03 eV below Ec
Nd : donor atom concentration
in the crystal : Nd >> ni
at RT,
electron concentration in CB ≈ Nd
 n ≈ Nd
 mass action law :
conductivity :
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Principles of Electronic .., S.O.Kasap (©McGraw-Hill)