Difference between Intrinsic and Extrinsic Semiconductor

Computers, the internet, smartphones, and tablet services are just a few examples of electrical equipment that uses semiconductors. In the modern world, they are commonly used. Without semiconductors, it wouldn't be impossible to produce all of these gadgets. Thomas Johan Seebeck first identified a semiconductor-related effect in 1821. Early in the 1830s, studies on semiconductors were conducted in laboratories. Michael Faraday conducted experiments with silver sulphide in 1833 and found that the conductivity of silver sulphide increased with the rise in temperature. Unlike metals like copper, whose conductivity declines as temperature rises, silver sulphide behaves in the exact opposite way.

A material that is conductive and lies halfway between an insulator and a conductor is said to be a semiconductor. Compared to a conductor and an insulator, semiconductors conduct more slowly. A semiconductor material has an electrical characteristic that lies halfway between an insulator and a conductor. The best semiconductors to use are Si and Ge. Basically, there are two categories of semiconductors based on their purity. Extrinsic and intrinsic semiconductors. Extrinsic semiconductors are those that contain impurities as opposed to intrinsic semiconductors, which are semiconductors that are pure. Extrinsic conductivity will be at a minimum at room temperature, whereas intrinsic conductivity will be at zero. At absolute zero, the intrinsic semiconductor's valence band is entirely filled, while the conduction band is entirely empty. The valance electrons jump to the conduction band and leave holes in the valance band if applied at a certain temperature. Because of this, resistance decreases and conduction rises as the temperature rises. We introduce impurities to enhance the number of free electrons and holes in the semiconductor.

Intrinsic semiconductor

An intrinsic semiconductor is one that is extremely pure. At room temperature, the conductivity of this semiconductor will be zero, according to the energy band theory. Inherent semiconductors include Si and Ge.

The conduction band in the energy band diagram below is empty, but the valence band is completely filled. Once the temperature has been raised, some heat energy can be supplied to it. Electrons from the valence band are supplied to the conduction band as a result of exiting the valence band. When moving from the valence band to the conduction band, electrons will move at random. Additionally, any direction can be freely traversed by the crystal's holes.

This semiconductor's TCR (temperature coefficient of resistance) will be negative as a result. The TCR shows a decrease in resistance and an increase in conductivity as the temperature rises.

Extrinsic semi-conductor

Extrinsic semiconductors are semiconductors to which an impurity has been added at a controlled rate to make them conductive. Both intrinsic semiconductors and extrinsic semiconductors can be created by doping materials that are now insulating to make their semiconductors.

The effect of doping is the division of extrinsic semiconductors into two groups: atoms with an extra electron (n-type for negative, from group V), and atoms with one less electron (p-type for positive, from group III). Doping is the deliberate addition of impurities to an extremely pure or intrinsic semiconductor to modify its electrical properties. Impurities are based on the type of semiconductor. Extrinsic semiconductors have a light to moderate amount of doping.

Doping

Doping is the process of adding an impurity to a semiconductor. The sort and quantity of impurities that must be added to the material in order to produce extrinsic semiconductors must be closely regulated. In most circumstances, one impurity atom is added for every 108 semiconductor atoms.

An impurity is utilised to increase the number of free electrons or holes in a semiconductor crystal, making it more conductive. If a pentavalent impurity with five valence electrons is added to a pure semiconductor, there will be a large number of free electrons. If a trivalent impurity with three valence electrons is added, a large number of holes will be present in the semiconductor. The conductivity of a semiconductor is altered via doping. Semiconductors are frequently made from fourth-group elements like germanium and silicon in the periodic table. Tetravalent crystals of the following two types of dopants can be added to the tetravalent crystals of silicon and germanium. Phosphorous (Pi), antimony (Sb), arsenic (As), and other elements with a valency of five are examples of pentavalent atoms. Aluminium (Al), Indium (In), Boron (B), and other trivalent elements are examples. The third and fifth groups of the periodic table, which are close to the fourth group, are made up of pentavalent and trivalent dopants, respectively. Therefore, the atoms' size is essentially not much different from that of the atoms of the fourth group of elements.

Based on the type of impurity injected, extrinsic semiconductors are categorised into two categories: N-type and P-type.

Types of Extrinsic Semiconductors

N-type semiconductors

Extrinsic semiconductors called N-type semiconductors allow dopant atoms to supply more conduction electrons to the host material (e.g. phosphorus in silicon). This leads to excess negative (n-type) electron charge carriers. Oftentimes, doping atoms have one more valence electron than the host atoms. The most frequent scenario is group-V element atomic substitution in group-IV solids. The problem gets trickier when the host has a variety of atom kinds. In III-V semiconductors like gallium arsenide, silicon, for instance, can operate as an acceptor when it substitutes arsenic and as a donor when it replaces gallium. Some donors, including alkali metals, which are donors in most solids, have fewer valence electrons than the host.

P-type semiconductors

When a doping agent is added, semiconductor atoms that have weakly bound outside electrons are removed (accepted). This kind of doping agent is also referred to as an acceptor material. A hole is a void that the electron leaves behind. P-type doping aims to generate a lot of holes. A trivalent atom replaces the crystal lattice in the case of silicon. As a result, one of the four covalent bonds that ordinarily make up the silicon lattice is missing an electron. As a result, the dopant atom can accept an electron from the covalent link of an atom close by to complete the fourth bond. These dopants are known as acceptors.

The neighbouring atom loses half of its linkage when a dopant atom accepts an electron, resulting in the formation of a hole. An electrically neutral semiconductor is produced as a result of the connections between each hole and a nearby negatively charged dopant ion. One proton in the atom will become "exposed" once each hole has wandered into the lattice, meaning it will no longer be cancelled by an electron. The nucleus of this atom, which has four protons, will have one hole in addition to three electrons. A hole acts as a positive charge as a result. The number of thermally excited electrons is significantly outweighed by the number of holes when an adequate supply of acceptor atoms is present. Holes dominate in p-type materials.

Extrinsic and intrinsic semiconductors differ primarily in the following ways:

• While extrinsic semiconductors are produced by doping impurities into pure semiconductors, intrinsic semiconductors are always present in their most pure state.
• Extrinsic semiconductors have a high electrical conductivity in comparison to other materials at room temperature, while intrinsic semiconductors have a low electrical conductivity.
• In intrinsic semiconductors, the number of electrons and holes is equal, however, this is not the case in extrinsic semiconductors.
• Temperature alone determines the behaviour of intrinsic semiconductors, whereas extrinsic semiconductors are influenced by both temperature and the number of impurities present.
• While N-type and p-type semiconductors are two categories of extrinsic semiconductors, intrinsic semiconductors are not further subdivided.
• Examples of intrinsic semiconductors include silicon and germanium.

Application of Extrinsic semi-conductor

The majority of electronic gadgets are mostly made of extrinsic semiconductors. Here are a few examples:

• Electronic equipment needs a specific unidirectional current flow, which is why diodes are installed in them.
• A P-N junction is created when semiconductors of both the P and N types come together.
• Bipolar junction transistors and field-effect transistors both utilise extrinsic semiconductors.
• The majority of extrinsic semiconductors function as switches.