P-type semiconductor
Encyclopedia
A P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor
in order to increase the number of free charge carrier
s (in this case positive holes).
When the doping material is added, it takes away (accepts) weakly bound outer electron
s from the semiconductor atoms. This type of doping agent is also known as an acceptor material and the vacancy left behind by the electron is known as a hole
.
The purpose of P-type doping is to create an abundance of holes. In the case of silicon
, a trivalent atom (typically from Group 13 of the periodic table
, such as boron
or aluminium
) is substituted into the crystal lattice. The result is that one electron is missing from one of the four covalent bond
s normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atom's covalent bond to complete the fourth bond. This is why such dopants are called acceptors. The dopant atom accepts an electron, causing the loss of half of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negatively charged dopant ion, and the semiconductor remains electrically neutral
as a whole. However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron when you have 3 electrons and 1 hole surrounding a particular nucleus with 4 protons. For this reason a hole behaves as a quantity of positive charge. When a sufficiently large number of acceptor
atoms are added, the holes greatly outnumber the thermally excited
electrons. Thus, the holes are the majority carriers, while electrons are the minority carriers in P-type materials. Blue diamond
s (Type IIb), which contain boron
(B) impurities, are an example of a naturally occurring P-type semiconductor.
Therefore, to a first approximation, sufficiently doped P-type semiconductors can be thought of as only conducting holes.
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
in order to increase the number of free charge carrier
Charge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
s (in this case positive holes).
When the doping material is added, it takes away (accepts) weakly bound outer electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s from the semiconductor atoms. This type of doping agent is also known as an acceptor material and the vacancy left behind by the electron is known as a hole
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
.
The purpose of P-type doping is to create an abundance of holes. In the case of silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, a trivalent atom (typically from Group 13 of the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
, such as boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
or aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
) is substituted into the crystal lattice. The result is that one electron is missing from one of the four covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
s normal for the silicon lattice. Thus the dopant atom can accept an electron from a neighboring atom's covalent bond to complete the fourth bond. This is why such dopants are called acceptors. The dopant atom accepts an electron, causing the loss of half of one bond from the neighboring atom and resulting in the formation of a "hole". Each hole is associated with a nearby negatively charged dopant ion, and the semiconductor remains electrically neutral
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
as a whole. However, once each hole has wandered away into the lattice, one proton in the atom at the hole's location will be "exposed" and no longer cancelled by an electron when you have 3 electrons and 1 hole surrounding a particular nucleus with 4 protons. For this reason a hole behaves as a quantity of positive charge. When a sufficiently large number of acceptor
Acceptor (semiconductors)
In semiconductor physics, an acceptor is a dopant atom that when added to a semiconductor can form p-type regions.For example, when silicon , having four valence electrons, needs to be doped as a p-type semiconductor, elements from group III like boron or aluminium , having three valence...
atoms are added, the holes greatly outnumber the thermally excited
Electron excitation
Electron excitation is the movement of an electron to a higher energy state. This can either be done by photoexcitation , where the original electron absorbs the photon and gains all the photon's energy or by electrical excitation , where the original electron absorbs the energy of another,...
electrons. Thus, the holes are the majority carriers, while electrons are the minority carriers in P-type materials. Blue diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
s (Type IIb), which contain boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
(B) impurities, are an example of a naturally occurring P-type semiconductor.
Therefore, to a first approximation, sufficiently doped P-type semiconductors can be thought of as only conducting holes.
See also
- Acceptor (semiconductors)Acceptor (semiconductors)In semiconductor physics, an acceptor is a dopant atom that when added to a semiconductor can form p-type regions.For example, when silicon , having four valence electrons, needs to be doped as a p-type semiconductor, elements from group III like boron or aluminium , having three valence...
- I-type semiconductor
- N-type semiconductorN-type semiconductorN-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....
- SemiconductorSemiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
- TransistorTransistorA transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
- n-p-n transistor
- p-n-p transistor