Basing on the ability of a
material that whether it can pass the current through it are not,the materials
can be divided into three categories.
The materials that can pass the
current through them because they’re having the free availability of the
charges are called conductors. Almost all the metals and human bodies of the
some of the examples for the conductors .
The materials who cannot pass the
current through them because they are not having the availability of the free
charges are called insulators.Plastic, rubber, cotton and paper are some of
the examples of the insulators.
The materials who behave like insulators at absolute zero temperature
but behaves like conductors once if the temperature is raised a little bit is
called a semiconducting material. Silicon and germanium are some of the
examples of the semiconducting materials.
Here we are going to have further
detailed discussion regarding the semiconducting materials.Many are for
modern-day electronic gadgets are having a lot of the integrated parts of the
semiconducting materials. It is impossible to imagine electronic gadgets without having a semiconducting material inside it. Diodes, transistors,
integrated circuits(IC’s) are very much made up of
semiconducting materials.
Properties of the semiconducting
materials:
1. The resistivity is more than that of the conductors but less than that of the insulators.
2. They have negative temperature
coefficient which means with the increase in temperature corresponding
resistance is going to decrease.
3. At absolute zero there is no
availability of the free charges and hence it behaves like insulators.
4. Its conductivity can be
increased by adding a little bit of impunity to it and this phenomena is called
doping.
Energy band theory:
To explain the conducting nature
of a given material we can depend on the energy band theory.We know that it
electrons are distributed in the different orbits like S, P, D,F. The electrons
in the outer orbits are called as valency electrons and they are always having
a chance of going to some other body if they got enough energy. The valency
electrons in the outermost orbits are bit close to each other and their form
together like a band. This band of electrons is called valency electrons and it
is either completely filled are partially filled in any kind of material.
Once if this electrons becomes
free they’re ready to conduct and all that kind of electrons together could be
called as conduction electrons.The conduction band is either partially filled
are completely empty depending on the nature of the material.
The band gap between the valency
band in the conduction band is called forbidden band gap. The size of this gap
depends on the nature of the material.
In the case of the conductor
valency band and conduction band overlap with each other electrons from valency
band can easily move to the conduction band and hence there is a flow of
current quite easily.
In the case of insulators there
is a big gap between these two bands and hence it becomes very difficult for
the valency electrons to travel from that band to the conduction band and hence
it always behaves like insulators.
In the case of the semiconducting
material the band gap is somewhere in between the conductors and insulators. By
default the charges have not enough energy to cross this band and hence it
behaves like insulators. Once if the temperature is raised a little bit, the
charges get enough energy to cross the and hence the start behaving like a conductors.
Types of semiconducting
materials:
Semiconducting materials are
broadly of two types. Those who are naturally available are called pure
semiconducting materials or intrinsic semiconducting materials. If a electron
leaves a place in a energy band , there is an empty place left in the band that
empty spaces called hole. In the case of a intrinsic semiconducting material ,number of electrons is equal to the number of holes. The flow of current in
this kind of semiconducting materials is equal due to both electrons and holes.
At 0° Kelvin in the crystalline
structure of the semiconducting material who is having four valency
electrons and each electron is having a covelent bond with its neighboring electron. There’s no electron is free and
hence it is behaving like insulators. Once if a little bit of temperature is
given, by obserbing that heat energy some of the covalent bonds can break and
hence it starts behaving like a conductor because of the availability of the
free charges.
Anyway practically use of this
kind of intrinsic semiconductor is very much limited because they are by
default behaving like insulators. We are looking for a semiconducting material
or can pass the current directly without raising the temperature and for that
sake we are going to use a phenomena called doping. Doping is the phenomenon of
adding a little bit of impunity to the pure semiconducting material therefore
there will be availability of the free charges.
When we are doping we have two
options.We can add tiavalent impunity
and hence there will be one excess hole and hence it start behaving like a P
type semiconducting material who is having access holes.
We can also had a pentavalent and
impurity to the semiconducting material and hence there will be availability of
excess electrons in the material. This type of the material is called N type.
These are called impure semiconducting materials or extrinsic semiconducting
materials.
In practical life we use extrinsic semi conductor materials in making electronic devices because of its ability to conduct current at ordinary temperatures.
Distance and displacement comparison
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