Electrical Properties of Semiconductors
It goes without saying that electrons rotate round the nucleus
in specific circular orbits under theinfluence of nuclear forces
which are the short range attractive forces. If the influence of
electronis strong enough to conquer this force of attraction, it
can be designated as conductors. If theenergy of electrons, on the
other hand, is least to overcome the nuclear short range forces, it
iscalled as insulators. In simple words, the materials which reveal
intermediate behavior inbetween insulators and conductors, and both
are termed as semiconductors. Depending on theirconducting
properties, semiconductors can be classified into 2 types:
Intrinsic semiconductorsand Extrinsic semiconductors.
Intrinsic Semiconductors:
Basically electrons and holes are charge carriers present in
semiconductors, holes as +velycharged and electrons being -vely
charged. The unique characteristic property of
intrinsicsemiconductors is the possession neutralisation current.
As a consequence of this currentintrinsic semiconductor, they only
have carrying capability of little current. This is to enhance
itsconducting properties that need to be modified in the case of
intrinsic semiconductors. Doping isthe property that enhances the
conductivity of semiconductors. The amount of doping should
bemoderate. Extrinsic semiconductors are formed by intiating doping
process.
Extrinsic Semiconductors:
Extrinsic semiconductors present in an impure form. The
impurities added belongs to 3rd and 5thgroup in the periodic table,
the trivalent impurities are 3rd group elements such as
aluminium,boron, gallium, indium and pentavalent impurities. For
the 5th group elements are arsenic,phosphorous, antimony, bismuth.
Germanium and Silicon semiconductors are tetravalent innature. When
phosphorous, the pentavelent impurity, is added to silicon, take
note that 4 valenceelectrons of silicon form a covalent bond with 4
valence electrons of silicon, but one electronwill lie free without
any participation.
Therefore, adding a small amount of impurity, electrons are
generated, thus thesesemiconductors are n-type extrinsic
semiconductors. By adding trivalent impurities, such asboron to a
semiconductor 3 valence electrons of silicon form covalent bond
with 3 valenceelectrons of impure atom. While one electron is
electron deficient, the semiconductor completesits bonding process
by stealing an electron from its neighboring atom. By adding
trivalentimpurity, there is a vacancy created. Thus, these
impurities are known as acceptor impurities,while the
semiconductors are called as p-type semiconductors.
Currents In Semiconductors
The current in semiconductors is usually carried by holes and
electrons. The currents insemiconductors are of two types depending
on the application of the external field. The first oneis the drift
current, and the second one is the diffusion current.
Applications
