Lawrence P Grana, MSEE 1
Summer, AY 2021-2022
A material that has energy bands either
completely empty or completely full is an
insulator.
The resistivity of an insulator is very large
or, conversely, the conductivity of an
insulator is very small.
There are essentially no charged particles
that can contribute to a drift current.
The bandgap energy Eg of an insulator is
usually on the order of 3.5 to 6 eV or larger
if an electric field is applied, the electrons
can gain energy, move to higher energy
states, and move through the crystal.
If an electric field is applied, the holes can
move and give rise to a current.
The bandgap energy may be on the order of 1
eV
This energy-band diagram represents a
semiconductor for T 0 K.
shows the case of a partially full band in which there are many electrons available for
conduction, so that the material can exhibit a large electrical conductivity
a case in which the conduction and valence bands overlap at the equilibrium interatomic distance
There are three distribution laws determining the
distribution of particles among available energy states.
Maxwell–Boltzmann probability function
The behavior of gas molecules in a container at fairly low
pressure
Bose–Einstein function
The behavior of photons, or black body radiation
Fermi–Dirac probability function
Electrons in a crystal obey this law
Equation (3.80) is known as the Maxwell–Boltzmann approximation, or simply the
Boltzmann approximation, to the Fermi–Dirac distribution function.