Explanation: current carrier, called carrier.stayphysicsIn, the carrier refers to the free movingchargeOfCorpuscle, such asElectronicsandIons。staysemiconductorIn physics, the vacancy (hole lead) left on the covalent bond due to electron loss is regarded as a carrier.There are electrons in metals and two kinds of carriers in semiconductors, namely, electrons and holes.Charged particles that can move directionally under the action of an electric field.Such as free electrons and holes in semiconductors, free electrons in conductors, positive and negative ions in electrolyte, ions in discharge gases, etc.
Carriers are particles with electric charge and can move to transport current, including electrons, ions, etc.There are two kinds of carriers in semiconductors, namely, negatively charged free electrons and positively charged free holes.In fact, holes are also valence bond vacancies in semiconductors, and the movement of a vacancy is equivalent to the movement of a large group of valence electrons;It is much more convenient to use the concept of fewer holes to describe the movement of a large number of valence electrons.So, in essence, a hole is just another expression of a large group of valence electrons.
Academic explanation
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Explanation of "carrier" in academic literature:
1. WhetherN-type semiconductorFree electrons in, orP-type semiconductorInholeThey all participate in conducting electricity and are collectively referred to as "carriers""Carrier" conduction is unique to semiconductors.
2. As we all know about gas conduction, conductors are easy to conduct because "there are a large number of free moving charged material particles in the conductor, called carriers. Under the effect of the external electric field, the carriers make directional movement, forming an obvious current".
Academic definition
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staysemiconductorThe charged particles, electrons and holes, which carry current in, are also called free carriers.At a certain temperature, the semiconductor isheat balanceState, the concentration of conductive electrons in semiconductor n0 andholeThe concentration p0 keeps a stable value. The conductive electrons and holes in the thermal equilibrium state are calledheat balanceCarrier.
Extrapolation formula
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stayIntrinsic semiconductorWhen only thermal excitation occurs in, the number of electrons is equal to the number of holesheat balanceThe carrier concentration is
Extrapolation formula
Where, mzeroIs the electronic mass, kg; mn*Is electronicEffective quality,kg; mp*Is the effective mass of the hole, kg; k isBoltzmannConstant, J/K; Eg is the band gap width, eV; niIs the intrinsic carrier concentration, cm-3;T is the absolute temperature, K.
If yessemiconductorExternal action (such as light or electricity) is applied to destroyheat balanceConditionsemiconductorIn andHeat balance stateThe state of phase deviation is called unbalanced state.Is notEquilibrium stateThe part of the carrier that is more than that in the equilibrium state is calledUnbalanced carrier。In type NsemiconductorThe non-equilibrium electrons are called non-equilibriumMajority carrierThe nonequilibrium holes are called nonequilibrium minority carriers.For P typesemiconductorThe opposite is true.staysemiconductorIn devices, unbalanced minority carriers often play an important role.[1]
Unbalanced carrierstayreunite withThe average lifetime before is the abbreviation of unbalanced carrier lifetime.stayheat balanceIn case of electronic andholeThe production rate of is equal toreunite withThe concentration of the two is in balance.Under the action of external conditions (such as light), additionalUnbalanced carrier, that is, electronic -holeyes;After the external conditions are revokedreunite withWhen the rate is greater than the generation rate, the unbalanced carriers will gradually recombine and disappear, and finally return toheat balanceState.Unbalanced carrierThe attenuation law of concentration with time generally follows the relationship of exp (- t/τ), and the constant τ indicates that the non-equilibrium carrierreunite withThe average survival time before is calledNonequilibrium carrier lifetime 。In semiconductor devices, because unbalanced minority carriers play a leading role, τ is often called unbalancedMinority carrier lifetime, short foryoungest sonlife.The range of τ value is generally 10-1 ～ 103 μ s.The recombination process can be roughly divided into two types:conduction bandandPrice bandThe direct transition between the two leads to the disappearance of a pair of electrons and holes, which is calledDirect recombination；The electron hole pair may also pass through the energy level in the band gap（Composite center）To compound, calledIndirect recombination。Eachsemiconductorτ of is not a fixed value, which will depend on the chemical composition andcrystal structureTherefore, life is a sensitive parameter of structure.The τ value is not always the greater the better.For the static characteristics of Si single crystal rods and transistors, we hope that the τ value is larger.However, for switches used at high frequencies, doping (diffusion gold) is often required to increase the gold impurityComposite center, reduce the τ value and increase the switching speed.stayPower electronic devicesIn production, electron beam irradiation is often used instead of gold doping to reduce τ value.In the production process of Si and GaAs materials, devices and integrated circuits, τ value is an important parameter that must be frequently measured.[2]
The relationship between carriers and semiconductors
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Carriers are charged material particles that can move freely to form current.The properties of semiconductors are different from those of conductors and insulators because of their different energy band structures;The conductivity of semiconductors can be controlled, mainly because the type and number of carriers are different from those of conductors and insulators, and can be controlled. The regulation means is "doping", that is, doping impurities into pure semiconductors to change the number, distribution and movement trend of carriers, thereby changing the overall conductivity.
The carriers of insulators and metal conductors are electrons, while in semiconductors, besides electrons, there is another kind of carrier called hole.In addition, positive ions and negative ions are also charged, but they generally do not flow in semiconductors, so we think that the carriers of semiconductors are electrons and holes.
It is easy to understand that electrons are carriers, because atoms in matter are composed of atomic nuclei and electrons, and free electrons that break free from atomic nuclei can move under certain conditions, thus generating current.A hole is a vacancy left by the absence of electrons.This is like the relationship between cars and parking spaces. Suppose there are five parking spaces in a row, four cars are parked in order from the left, and there is one vacancy on the right. If the leftmost car moves to the rightmost vacancy, then the leftmost parking space will be empty.It seems that the empty space moves from right to left, which is a relative movement. The movement of the car from left to right is equivalent to the movement of the empty space from right to left.In the same way, the movement of negatively charged electrons can be seen as the opposite movement of positively charged holes.In pure semiconductors without impurities, the number of moving electrons generated by thermal excitation is equal to the number of holes, because negatively charged electrons and positively charged holes will be compounded. When the number is roughly equal, "generation" and "recombination" will reach a dynamic balance, so that no effective current will be generated from the macro view.In order to improve its conductivity, doping is introduced.
carrier
For integrated circuits, the most important semiconductor material is silicon.The silicon atom has four valence electrons, which are located at the four top corners of the tetrahedron centered on the nucleus.These valence electrons will form covalent bonds with the valence electrons of other silicon atoms, and a large number of silicon atoms will combine with each other in this way to form crystals with regular structure.If arsenic (or phosphorus) is added to it, there are five electrons in the outermost layer of arsenic, and four of them will also form covalent bonds with four valence electrons of silicon atom to fix the arsenic atom in the lattice of silicon material.At this time, 1 morefree electronThe energy required for this electron to transition to the conduction band is low, and it is easy to move in the silicon lattice, thus generating current.This kind of semiconductor doped with impurities that can provide extra electrons to obtain conductivity is calledN-type semiconductor, "N" means Negative, which means negative charge.If we add boron (B) into pure silicon, because there are only three valence electrons of boron, we need to attract another electron to form a covalent bond with the four valence electrons of silicon atom, so that a hole will be formed as an additional introduced carrier to provide conductive energy.This kind of semiconductor doped with impurities that can provide holes is called P-type semiconductor. "P" is positive, meaning positive charge.[3]
It should be noted that the semiconductor doped with impurities still has both electron and hole carriers, but their numbers are different.In N-type semiconductors, the majority of electrons (negatively charged) are called majority carriers, and holes (positively charged) are called minority carriers.In P-type semiconductors, the opposite is true: holes are majority carriers and electrons are minority carriers;It can be referred to as "many children" and "few children" respectively.
