ANALOG ELECTRONICS:
SEMICONDUCTORS:
intrinsic semiconductors:
An intrinsic semiconductor, also
called an undoped
semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the
properties of the material itself instead of the amount of impurities. In
intrinsic semiconductors the number of excited electrons and the number of holes are equal: n = p.
The electrical conductivity of intrinsic semiconductors can be due
to crystallographic defects or electron
excitation. In an intrinsic semiconductor the number of electrons in the conduction band is equal to the number of holes in the valence band. An example is Hg0.8Cd0.2Te at room temperature.
Extrinsic semiconductror:
An extrinsic semiconductor is a semiconductor that has been doped, that is, into which a doping agent has been introduced, giving it
different electrical properties than the intrinsic (pure) semiconductor.
Doping
involves adding dopant atoms to an intrinsic semiconductor, which changes the electron and hole carrier concentrations of the semiconductor at thermal equilibrium. Dominant carrier concentrations
in an extrinsic semiconductor classify it as either an n-type or p-type semiconductor. The electrical
properties of extrinsic semiconductors make them essential components of many
electronic devices.
.
Intrinsic
semiconductor
|
Donor
atoms
|
Acceptor
atoms
|
|
Group
IV semiconductors
|
Silicon, Germanium
|
Phosphorus, Arsenic
|
Boron, Aluminium
|
Group
III-V semiconductors
|
Aluminum phosphide, Aluminum
arsenide, Gallium arsenide, Gallium
nitride
|
Selenium, Tellurium, Silicon,Germanium
|
Beryllium, Zinc, Cadmium, Silicon,Germanium
|
N-type semiconductors
Main article: N-type
semiconductor
Band structure of an n-type
semiconductor. Dark circles in the conduction band are electrons and light
circles in the valence band are holes. The image shows that the electrons are
the majority charge carrier.
Extrinsic
semiconductors with a larger electron concentration than hole concentration are
known as n-type semiconductors.
The phrase 'n-type' comes from the negative charge of the electron. In n-type
semiconductors, electrons are the majority
carriers and holes are the minority carriers. N-type
semiconductors are created by doping an intrinsic semiconductor with donor
impurities. In an n-type semiconductor, theFermi energy level is greater than that of the intrinsic
semiconductor and lies closer to the conduction
band than the valence band.
P-type semiconductors
Main article: P-type
semiconductor
Band structure of a p-type
semiconductor. Dark circles in the conduction band are electrons and light
circles in the valence band are holes. The image shows that the holes are the
majority charge carrier
As opposed
to n-type semiconductors, p-type
semiconductors have a larger hole
concentration than electron concentration. The phrase 'p-type' refers to the
positive charge of the hole. In p-type semiconductors, holes are the majority
carriers and electrons are the minority carriers. P-type semiconductors are
created by doping an intrinsic semiconductor with acceptor impurities. P-type
semiconductors have Fermi energy levels below the intrinsic Fermi energy level.
The Fermi energy level lies closer to the valence band than the conduction band
in
Drift current:
In condensed matter physics and electro chemistry, drift current is the electric current, or movement of charge carriers, which is due to the
applied electric field, often
stated as the electromotive force over
a given distance. When an electric field is applied across a semiconductor
material, a current is produced due to flow of charge carriers.
The drift velocity is the average velocity of the charge
carriers in the drift current. The drift velocity, and resulting current, is
characterized by the mobility;
for details, see electron
mobility (for solids) or electrical mobility (for a more general discussion).
Here
v=velocity
Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers (holes and/or electrons). Diffusion
current can be in the same or opposite direction of adrift current, that is formed due to the electric field in the semiconductor. At equilibrium in a p–n junction, the forward diffusion current in the depletion region is
balanced with a reverse drift current, so that the net current is zero. The
diffusion current and drift current together are described by the drift–diffusion equation.