What is Semiconductor | Semiconductor Types

What is Semiconductor | Semiconductor Types


Semiconductor is a material which has a resistance is in between the conductor and insulators. Resistivity of semiconductor is 10-4 to 107. We have two types of semiconductors are there. One is extrinsic semiconductor and another one is intrinsic semiconductor.


Properties of Semiconductor:

1.    Semiconductors having moderate resistivity.
2.    Semiconductor always obeys negative (-ve) temperature coefficient
3.    Valence electrons of semiconductors are bounded and some are loosely coupled to their atoms.
4.    Semiconductors requires energy less than an insulators and more than conductors to remove electrons from parent atoms.

Types of semiconductors

We have two types of semiconductors are there. One is extrinsic semiconductor and another one is intrinsic semiconductor.
·       Extrinsic Semiconductor
·       Intrinsic Semiconductor

Intrinsic Semiconductor:

A semiconductor in its purest form is known as the intrinsic semiconductor. These are the intrinsic semiconductors.
Ex: Pure silicon, Pure germanium.
      In intrinsic semiconductors even at room temperature it can creates electron-hole pairs. Whenever we applied electric field to the intrinsic semiconductor then it will start conduction. Conduction takes place because of movement of electrons and holes opposite direction in conduction band and valance bands.

The numbers of conduction electrons are equal to number of holes. The energy band diagram of intrinsic semiconductor is shown in below.
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Intrinsic Semiconductor


Extrinsic Semiconductor

For getting good conducting properties, we will add some impurity atoms or doping agent is added to pure semiconductor (intrinsic semiconductor).

The process of adding impurity to the pure semiconductors is called “Doping”. Why we add some impurity or doping agent to the pure semiconductor is “to increase the conducting properties of either free electrons or free holes in semiconductors.

Extrinsic semiconductors are classified as two types because depending upon the impurity added to the semiconductors.

  1. ·       N-Type Semiconductor
  2. ·       P-Type Semiconductor


N-Type Semiconductor

N-Type Semiconductor is formed when a pentavalent impurity is added to the pure semiconductor (Intrinsic Semiconductor). The pentavalent impurities are 5th group elements.
Ex: Arsenic, antimony, Phosphorus, Al, Sb, In etc..

    Suppose if we take a antimony atom, each antimony atom forms the four covalent bands to with their surrounding silicon or germanium atoms with the help of four electrons. But antimony has 5 electrons so the 5th electron is superfluous and also it is loosely coupled to the antimony atom. It is easily removed from the conduction band by applying small electric field. This type of semiconductor is known as N-Type semiconductor. In this n-type semiconductor electrons are majority and it’s impurity is called as a “donor impurity”.  Because these are donate free electrons to the semiconductor materials.

  After donating free electron to semiconductor material it became as a positive donor ion. Therefore this type of semiconductors electrons are more than holes.

The N-type semiconductor is electrically neutral. The energy band diagram as shown in below.
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N-Type Semiconductor


P-Type Semiconductor

P-Type Semiconductor is formed when a trivalent impurity is added to the pure semiconductor (Intrinsic Semiconductor). The trivalent impurities are 3rd group elements.

Ex: Boron, Gallium etc..

    Suppose if we take a boron atom, each boron atom forms the four covalent bands to with their surrounding silicon or germanium atoms. But one band is left incomplete and also it gives a hole. This will cause boron and trivalent impurity atoms are called as “Acceptor impurity” atoms cause many holes are created in silicon or germanium band diagram. These types of semiconductors are called as a P-type semiconductor. In this type of semiconductors holes are majority than the electrons.
P-type semiconductor is electrically neutral.
 
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P-Type Semiconductor