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What is a Semiconductor ?

A solid substance whose electrical conductivity lies between that of an insulator and a conductor, either due to the addition of impurities or because of temperature effects. When two differently doped regions exist in the same crystal, a semiconductor junction is created.

Devices made by semiconductors, notably silicon, are essential components of most electronic circuits. Semiconductor devices can display a range of useful properties, such as passing current more easily in one direction than the other, showing variable resistance, and sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by doping, or by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion.

Types of Semiconductor

Semiconductors fall into two broad categories:

  1. Intrinsic semiconductors are composed of only one kind of material; silicon and germanium are two examples. These are also called “undoped semiconductors” or “I-type semiconductors. “

  2. Extrinsic semiconductors, on the other hand, are intrinsic semiconductors with other substances added to alter their properties — that is to say, they have been doped with another element.

  • N-Type Semiconductors are a type of extrinsic semiconductor in which the dopant atoms are capable of providing extra conduction electrons to the host material (e.g. phosphorus in silicon). This creates an excess of negative (n-type) electron charge carriers.

  • P-Type Semiconductors: -A p-type (p for “positive”) semiconductor is created by adding a certain type of atom to the semiconductor to increase the number of free charge carriers.

What is a semiconductor ?
What is a semiconductor ?

N-type Semiconductor

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.

An N-type semiconductor is created by doping this pure silicon crystal lattice with a pentavalent impurity element like Antimony (Sb). In an N-type semiconductor, the atom of pentavalent impurity element Antimony (Sb) is in between silicon atoms. The Silicon atoms have four electrons in the valence shell. Each of the silicon atoms creates a covalent bond with an electron of the prevalent impurity atom. The Antimony (Sb) impurity element electron form covalent bonds with only four silicon atoms. The fifth electron of the impurity atom is not bonded with any semiconductor atom in the crystal lattice. This electron is loosely bonded to its parent impurity atom. Thus, as external voltage or heat is applied this fifth electron easily breaks its bond with the parent atom and takes part in conduction. This fifth electron majorly contributes to the current in an N-type semiconductor. In the N-type Semiconductor, the electrons become the majority carrier.

P-type Semiconductor

A p-type semiconductor is a type of semiconductor. When the trivalent impurity is added to an intrinsic or pure semiconductor (silicon or germanium), then it is said to be a p-type semiconductor. Trivalent impurities such as Boron (B), Gallium (Ga), Indium(In), Aluminum(Al), etc. are called acceptor impurity. Ordinary semiconductors are made of materials that do not conduct (or carry) an electric current very well but are not highly resistant to doing so. They fall halfway between conductors and insulators. An electric current occurs when electrons move through a material. In order to move, there must be an electron 'hole' in the material for the electron to move into. A p-type semiconductor has more holes than electrons. This allows the current to flow along with the material from hole to hole but only in one direction. Semiconductors are most often made from silicon. Silicon is an element with four electrons in its outer shell. To make a p-type semiconductor extra materials like boron or aluminum are added to the silicon. These materials have only three electrons in their outer shell. When the extra material replaces some of the silicon it leaves a 'hole' where the fourth electron would have been in the semiconductor was pure silicon.

P-type Semiconductor
P-type Semiconductor

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