EEE 209
Lecture-3
Ref: Principles of Electronic Materials & Devices by S.O.
Kasap (4th edition)- Chapter 4 & B.G. Streetman (Chapter
3)
Fermi Distribution
Takes into account Pauli exclusion
principle.
EF is the Fermi energy level → energy at
which f(E)=0.5 for T>0
Density of states
Number of allowed states per unit energy per unit
volume → density of states
For 3D materials
Density of carriers
If the band starts at Ec then
Density of electrons
Physical Source of holes
Intrinsic Material
Pure material
If one of the Si valence electrons is broken away
from its position in the bonding structure such that
it becomes free to move about in the lattice, a
conduction electron is created and a broken bond
(hole) is left behind.
At equilibrium
Extrinsic Materials
Doped materials → a
common technique for
altering the conductivity of
materials.
N-type dopants As, P, Sb
n type materials
A small amount of thermal energy
enables this extra electron to
overcome its coulombic binding to
the impurity atom and be donated
to the lattice as a whole.
Thermal
energy
N type dopants are also called donors
p type materials
P type dopants B, Al, In
p type materials
With a small amount of thermal energy, this incomplete bond
can be transferred to other atoms as the bonding electrons
exchange positions.
P type dopants B, Al, In
Thermal
energy
p type dopants are also called acceptors