What is semiconductor?
Materials that have the resistance levels between those of a conductor and an insulator are
referred to as semiconductors. They are quite common, found in almost all electronic devices.
Semiconductor materials: germanium, selenium, and silicon.
A semiconductor is a substance, usually a solid chemical element or compound, that can conduct
electricity under some conditions but not others, making it a good medium for the control of
electrical current.
The specific properties of a semiconductor depend on the impurities, or dopants, added to it.

An N-type semiconductor
carries
current
mainly in
the
form
of
negatively-
charged electrons, in a manner similar to the conduction of current in a wire.

A P-type semiconductor
carries
current
predominantly as
electron
deficiencies
called holes. A hole has a positive electric charge, equal and opposite to the charge on an
electron. In a semiconductor material, the flow of holes occurs in a direction opposite to
the flow of electrons.
Elemental semiconductors include antimony, arsenic, boron, carbon, germanium, selenium,
silicon, sulfur, and tellurium. Silicon is the best-known of these, forming the basis of most
integrated circuits (ICs). Common semiconductor compounds include gallium arsenide, indium
antimonide, and the oxides of most metals. Of these, gallium arsenide (GaAs) is widely used in
low-noise, high-gain, weak-signal amplifying devices.
Carbon, silicon and germanium (germanium, like silicon, is also a semiconductor) have a unique
property in their electron structure -- each has four electrons in its outer orbital. This allows
them to form nice crystals. The four electrons form perfect covalent bonds with four
neighboring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In
silicon, the crystalline form is a silvery, metallic-looking substance.
In a silicon lattice, all silicon atoms bond perfectly to four neighbors, leaving no free electrons
to conduct electric current. This makes a silicon crystal an insulator rather than a conductor.
Metals tend to be good conductors of electricity because they usually have "free electrons" that
can move easily between atoms, and electricity involves the flow of electrons. While silicon
crystals look metallic, they are not, in fact, metals. All of the outer electrons in a silicon crystal are
involved in perfect covalent bonds, so they can't move around. A pure silicon crystal is nearly
an insulator -- very little electricity will flow through it.
But we can change all this through a process called doping.
What is doping?
Doping is the process of adding impurities to intrinsic semiconductors to alter their
properties. Normally Trivalent and Pentavalent elements are used to dope Silicon and
Germanium.

When an intrinsic semiconductor is doped with Trivalent impurity it becomes a P-Type
semiconductor. The P stands for Positive, which means the semiconductor is rich in holes
or Positive charged ions.

When we dope intrinsic material with Pentavalent impurities we get N-Type
semiconductor, where N stands for Negative. N-type semiconductors have Negative
charged ions or in other words have excess electrons in it.
Why doping is used?
Because the band gap is so small for semiconductors, doping with small amounts of impurities
can dramatically increase the conductivity of the material. Doping, therefore, allows scientists to
exploit the properties of sets of elements referred to as “dopants” in order to modulate the
conductivity of a semiconductor.
Type of semiconductor??
What is N-type semiconductor?
An N-type semiconductor is a type of material used in electronics.
It is made by adding an impurity to a pure semiconductor such as silicon or germanium. The
impurities used may be phosphorus, arsenic, antimony, bismuth or some other chemical element.
They are called donor impurities. The impurity is called a donor because it gives a free electron to
a semiconductor. The purpose of doing this is to make more charge carriers, or electron wires
available in the material for conduction. The final material is a lot more conductive than the
original silicon or germanium.
Manufacture: N type semiconductor??
N-type semiconductors are manufactured by doping pure semiconductor material. The amount of
impurity added is very small compared to the amount of semiconductor. The way this new
semiconductor works is changed by controlling the quantity of the dopant.
Holes and Electrons in Semiconductors???
Holes and electrons are the types of charge carriers accountable for the flow of current in
semiconductors.

Holes (valence electrons) are the positively charged electric charge carrier.

Electrons are the negatively charged particles. Both electrons and holes are equal in
magnitude but opposite in polarity.
P type semiconductor?
When a pure semiconductor is doped with a trivalent impurity (B, Al, In, Ga) then, the three
valence electrons of the impurity bonds with three of the four valence electrons of the
semiconductor.
This leaves an absence of electron (hole) in the impurity. These impurity atoms which are ready
to accept bonded electrons are called “Acceptors“.
With the increase in the number of impurities, holes (the positive charge carriers) are increased.
Hence, it is called p-type semiconductor.
Crystal as a whole is neutral, but the acceptors become an immobile negative ion. As conduction
is due to a large number of holes, the holes in the p-type semiconductor are MAJORITY
CARRIERS and electrons are MINORITY CARRIERS.
Difference between Intrinsic and Extrinsic Semiconductors?
Intrinsic Semiconductor
Pure semiconductor
Extrinsic Semiconductor
Impure semiconductor
Density of electrons is equal to the density of Density of electrons is not equal to the density of
holes
holes
Electrical conductivity is low
Electrical conductivity is high
Dependence on temperature only
Dependence on temperature as well as on the
amount of impurity
No impurities
Trivalent impurity, pentavalent impurity
Applications of Semiconductors?
Let us now understand the uses of semiconductors in daily life. Semiconductors are used in almost
all electronic devices. Without them, our life would be much different.
Their reliability, compactness, low cost and controlled conduction of electricity make them ideal
to be used for various purposes in a wide range of components and devices. transistors, diodes,
photosensors, microcontrollers, integrated chips and much more are made up of semiconductors.
Uses of Semiconductors in Everyday life?

Temperature sensors are made with semiconductor devices.

They are used in 3D printing machines

Used in microchips and self-driving cars

Used in calculators, solar plates, computers and other electronic devices.

Transistor and MOSFET used as a switch in Electrical Circuits are manufactured using the
semiconductors.
Industrial Uses of Semiconductors?
The physical and chemical properties of semiconductors make them capable of designing
technological wonders like microchips, transistors, LEDs, solar cells, etc.
The microprocessor used for controlling the operation of space vehicles, trains, robots, etc is made
up of transistors and other controlling devices which are manufactured by semiconductor
materials.
Importance of Semiconductors??

They are highly portable due to the smaller size

They require less input power

Semiconductor devices are shockproof

They have a longer lifespan

They are noise-free while operating