What Is True About Semiconductors

Semiconductor that has been doped

An extrinsic semiconductor is one that has been doped; during industry of the semiconductor crystal a trace chemical element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it different electrical backdrop than the pure semiconductor crystal, which is called an intrinsic semiconductor. In an extrinsic semiconductor it is these strange dopant atoms in the crystal lattice that mainly provide the charge carriers which carry electric electric current through the crystal. The doping agents used are of 2 types, resulting in two types of extrinsic semiconductor. An electron donor dopant is an atom which, when incorporated in the crystal, releases a mobile conduction electron into the crystal lattice. An extrinsic semiconductor which has been doped with electron donor atoms is chosen an n-type semiconductor, because the majority of accuse carriers in the crystal are negative electrons. An electron acceptor dopant is an cantlet which accepts an electron from the lattice, creating a vacancy where an electron should be called a hole which can move through the crystal similar a positively charged particle. An extrinsic semiconductor which has been doped with electron acceptor atoms is called a p-blazon semiconductor, because the majority of accuse carriers in the crystal are positive holes.

Doping is the key to the extraordinarily broad range of electrical beliefs that semiconductors can exhibit, and extrinsic semiconductors are used to make semiconductor electronic devices such as diodes, transistors, integrated circuits, semiconductor lasers, LEDs, and photovoltaic cells. Sophisticated semiconductor fabrication processes similar photolithography can implant different dopant elements in unlike regions of the same semiconductor crystal wafer, creating semiconductor devices on the wafer's surface. For case a common blazon of transistor, the northward-p-n bipolar transistor, consists of an extrinsic semiconductor crystal with two regions of n-type semiconductor, separated by a region of p-type semiconductor, with metal contacts attached to each part.

Conduction in semiconductors [edit]

A solid substance can conduct electric current only if it contains charged particles, electrons, which are gratis to move about and not attached to atoms. In a metallic usher, information technology is the metal atoms that provide the electrons; typically each metal atom releases i of its outer orbital electrons to go a conduction electron which tin can move well-nigh throughout the crystal, and bear electrical current. Therefore the number of conduction electrons in a metal is equal to the number of atoms, a very large number, making metals good conductors.

Different in metals, the atoms that brand up the bulk semiconductor crystal do not provide the electrons which are responsible for conduction. In semiconductors, electrical conduction is due to the mobile charge carriers, electrons or holes which are provided past impurities or dopant atoms in the crystal. In an extrinsic semiconductor, the concentration of doping atoms in the crystal largely determines the density of charge carriers, which determines its electrical conductivity, also equally a not bad many other electrical backdrop. This is the key to semiconductors' versatility; their electrical conductivity can be manipulated over many orders of magnitude by doping.

Semiconductor doping [edit]

Semiconductor doping is the process that changes an intrinsic semiconductor to an extrinsic semiconductor. During doping, impurity atoms are introduced to an intrinsic semiconductor. Impurity atoms are atoms of a different element than the atoms of the intrinsic semiconductor. Impurity atoms human activity every bit either donors or acceptors to the intrinsic semiconductor, changing the electron and hole concentrations of the semiconductor. Impurity atoms are classified as either donor or acceptor atoms based on the effect they take on the intrinsic semiconductor.

Donor impurity atoms have more valence electrons than the atoms they replace in the intrinsic semiconductor lattice. Donor impurities "donate" their actress valence electrons to a semiconductor's conduction band, providing backlog electrons to the intrinsic semiconductor. Excess electrons increase the electron carrier concentration (due north₀) of the semiconductor, making it n-type.

Acceptor impurity atoms have fewer valence electrons than the atoms they replace in the intrinsic semiconductor lattice. They "accept" electrons from the semiconductor's valence band. This provides excess holes to the intrinsic semiconductor. Backlog holes increase the pigsty carrier concentration (p₀) of the semiconductor, creating a p-type semiconductor.

Semiconductors and dopant atoms are defined by the column of the periodic table in which they autumn. The column definition of the semiconductor determines how many valence electrons its atoms accept and whether dopant atoms human action every bit the semiconductor's donors or acceptors.

Group 4 semiconductors use grouping V atoms as donors and grouping III atoms as acceptors.

Grouping III–V semiconductors, the compound semiconductors, use grouping Half-dozen atoms as donors and grouping Two atoms as acceptors. Group 3–V semiconductors tin can likewise employ group Four atoms equally either donors or acceptors. When a group IV atom replaces the group Iii element in the semiconductor lattice, the group Four atom acts equally a donor. Conversely, when a group 4 atom replaces the group 5 element, the group Iv atom acts every bit an acceptor. Group IV atoms can human action as both donors and acceptors; therefore, they are known as amphoteric impurities.

	Intrinsic semiconductor	Donor atoms (n-Type Semiconductor)	Acceptor atoms (p-Type Semiconductor)
Group IV semiconductors	Silicon, Germanium	Phosphorus, Arsenic, Antimony	Boron, Aluminium, Gallium
Grouping Three–V semiconductors	Aluminum phosphide, Aluminum arsenide, Gallium arsenide, Gallium nitride	Selenium, Tellurium, Silicon, Germanium	Glucinium, Zinc, Cadmium, Silicon, Germanium

The ii types of semiconductor [edit]

N-type semiconductors [edit]

Ring structure of an northward-type semiconductor. Dark circles in the conduction band are electrons and light circles in the valence band are holes. The image shows that the electrons are the majority charge carrier.

N-type semiconductors are created by doping an intrinsic semiconductor with an electron donor chemical element during manufacture. The term n-type comes from the negative charge of the electron. In northward-type semiconductors, electrons are the majority carriers and holes are the minority carriers. A common dopant for n-type silicon is phosphorus or arsenic. In an n-type semiconductor, the Fermi level is greater than that of the intrinsic semiconductor and lies closer to the conduction band than the valence band.

Examples: phosphorus, arsenic, antimony, etc.

P-blazon semiconductors [edit]

Ring structure of a p-type semiconductor. Dark circles in the conduction ring are electrons and light circles in the valence ring are holes. The prototype shows that the holes are the bulk accuse carrier

P-type semiconductors are created by doping an intrinsic semiconductor with an electron acceptor element during manufacture. The term p-blazon refers to the positive charge of a pigsty. Equally opposed to n-blazon semiconductors, p-type semiconductors have a larger hole concentration than electron concentration. In p-blazon semiconductors, holes are the bulk carriers and electrons are the minority carriers. A mutual p-type dopant for silicon is boron or gallium. For p-type semiconductors the Fermi level is below the intrinsic semiconductor and lies closer to the valence ring than the conduction band.

Examples: boron, aluminium, gallium, etc.

Employ of extrinsic semiconductors [edit]

Extrinsic semiconductors are components of many mutual electrical devices. A semiconductor diode (devices that permit current in merely one direction) consists of p-type and north-type semiconductors placed in junction with ane another. Currently, most semiconductor diodes use doped silicon or germanium.

Transistors (devices that enable current switching) also make apply of extrinsic semiconductors. Bipolar junction transistors (BJT), which amplify current, are i type of transistor. The most common BJTs are NPN and PNP type. NPN transistors have two layers of n-type semiconductors sandwiching a p-type semiconductor. PNP transistors have two layers of p-blazon semiconductors sandwiching an n-type semiconductor.

Field-upshot transistors (FET) are another type of transistor which amplify current implementing extrinsic semiconductors. As opposed to BJTs, they are called unipolar considering they involve single carrier blazon operation – either N-channel or P-aqueduct. FETs are cleaved into ii families, junction gate FET (JFET), which are three last semiconductors, and insulated gate FET (IGFET), which are four last semiconductors.

Other devices implementing the extrinsic semiconductor:

Lasers
Solar cells
Photodetectors
Light-emitting diodes
Thyristors

See besides [edit]

Intrinsic semiconductor
Doping (semiconductor)
List of semiconductor materials

References [edit]

Neamen, Donald A. (2003). Semiconductor Physics and Devices: Basic Principles (3rd ed.) . McGraw-Colina Higher Instruction. ISBN0-07-232107-v.

External links [edit]

Howstuffworks: How Semiconductors Piece of work