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In semiconductors free electrons are in conduction bands.
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Why n type and p type are electrically neutral?
An N-type semiconductor is obtained by carrying out a process of doping, that is, by adding an impurity of valence-five elements to a valence-four semiconductor in order to increase the number of free charge carriers. When the doping material is added, it gives away weakly-bound outer electrons to the semiconductor atoms. This type of doping agent is also known as donor material since it gives away some of its electrons. The purpose of N-type doping is to produce an abundance of mobile or carrier electrons in the material. To help understand how n-type doping is accomplished, consider the case of silicon (Si). Si atoms have four valence electrons, each of which is covalently bonded with each of the four adjacent Si atoms. If an atom with five valence electrons, such as those from group 15 of the periodic table , is incorporated into the crystal lattice in place of a Si atom, then that atom will have four covalent bonds and one unbonded electron. This extra electron is only weakly bound to the atom and can easily be excited into the conduction band. At normal temperatures, virtually all such electrons are excited into the conduction band. Since excitation of these electrons does not result in the formation of a hole, the number of electrons in such a material far exceeds the number of holes. In this case the electrons are the majority carriers and the holes are the minority carriers. Because the five-electron atoms have an extra electron to donate, they are called donor atoms. Note that each movable electron within the semiconductor is never far from an immobile positive dopant ion, and the N-doped material normally has a net electric charge of zero.
Can you dope a semiconductor with holes instead of electrons?
Doping with Group III elements, which are missing the fourth valence electron, creates "broken bonds" (holes) in the silicon lattice that are free to move. The result is an electrically conductive p-type semiconductor.
What is hole current?
There are two type of carriers in any semiconductor. For a given sample, these carriers have a specific concentration and mobility. The current flow due to the holes carriers in any semiconductor is the hole current.Answer'Holes' are imaginary positive, mobile, charge carriers used as a model to represent the behaviour of electric current in p-type semiconducting material. A 'model' is simply a means of explaining complex behavior in terms of something we can easily understand or picture in our minds. In reality, therefore, holes do not exist, but offer a convenient way of explaining current flow in semiconductors in an understandable way. A 'hole' is simply a vacant position, formally occupied by an electron, rather than a real entity. As electrons move in one direction, relative to those electrons, these imaginary holes behave as though they move in the opposite direction (in rather the same way that scenery seems to be moving backwards when you look from a train whereas, in reality, it's the train that's moving forward!). So, as electrons move from negative to positive, holes appear as though the electrons are actually stationary and it's the holes that are moving from positive to negative.So it's convenient to think of current flow through 'p-type' material, in particular. in terms of imaginary holes moving in the opposite direction to electron flow.(You see a similar effect with led message boards. The message is formed by bright led dots that appear to move in one direction; but you can also argue that the message is formed by the unilluminated leds that appear to move in the opposite direction! You can think of the illuminated leds as electron flow and the unilluminated leds as hole flow.)Diouly-dcp's answerfirst lets look at what is holehole: is when an external voltage source of energy acquire to a piece of silicon or other,it allows the valence electrons to thermally jump from the valence bond to the conduction bond, when they moved, a vacancy is left. this vacancy is called holehole current: another type of current occurs at the valence level where the holes created by the free electron exist. Electrons remaining in the Valence Bond are still attached to their atoms and are not free to move randomly in the crystal structure as are the free electron, however a valence electron can move into a near by whole with little change in it's energy level thus leaving another hole where it came from. effectively the hole has more from one place to another in the crystal structure, this is called hole current.(electrons in the valence bond are moving from one hole to another in the valence bond it self, but not to the conduction bond)
What is electron diffusion?
Metals have "free" electrons, the free electrons in metals help to transfer heat together with the vibrating atoms.
Why is diamond a good of heat like metals but a bad conductor of electricity unlike metals?
this is due to the fact that diamond has perfect lattice structure which helps it to conduct heat but due to the absence of free electrons it cannot conduct electricity. there are two modes to conduct heat :1) thraugh free electron transfer 2) thraugh lattice vibration .in diamond lattice vibration is dominant. for further study read conduction heat tranfer .
Why does aluminum conduct?
Because it has a free electron in the conduction energy band.
A conductor with a high temperature is likely to have a high?
Since you are talking about conductors, a high temperature one will have a high resistance. Reason being that the distance between the conduction and the valence band keeps on increasing on the increase of temperature. A substance is said to be conducting if it has FREE electron in its conduction band. Since the distance b.w the to bands increases, less number of electrons are able to jump from valence band to conduction band, hence more resistance...
Why does aluminum conduct electricity?
Because it has a free electron in the conduction energy band.
What is the difference between Free Electron Theory and Band Theory of solids?
Free Electron Theory:This theory tells that, metals conduct electricity because of the presence of free electrons in it. The outermost shells of metal atoms will be loosely bound with their nucleus. So the electrons in it are free to move anywhere in the solid.These electrons are called free electrons and they are responsible for the conduction of electricity.Band theory of solids:A solid is assumed to contain many bands in which the electrons in it are packed. The most important are valence band and conduction band. The energy of electrons in these bands will be different.The difference in energies of valence band and conduction band determines whether the solid is a conductor, semi - conductor or insulator.For insulators, the difference between energies of them ( energy gap ) will be very high, and for conductor, these bands overlap each other.The conduction band carries the electrons that conduct electricity, but the valence band has all the electrons in the ground state. Whether they go into the conduction band depends on the temperature and the energy gap between the bands. In a conductor, these bands overlap, and hence many electrons can become conducting. Thus, Band Theory explains distinction between metals and insulators, which Free Electron theory cannot do (since it assumes all valence electrons become conducting). Calculations are be performed to see which materials will have big energy gaps and which will have overlapping bands.
Why are metal conductive?
Lots of free electrons in conduction band. This is commonly referred to as the electron gas.
How does the energy of core electron compare with the energy of valence electron?
valence electrons are bound to atoms and are used to bind atoms into molecules. free electron are free, either they are in the conduction band "electron gas" of a metal or they are in a vacuum (perhaps in a vacuum tube).
How many valence electrons does insulator have?
It is not the number of valence electrons that an insulator has that is important. It is the way the valence electrons are "arranged" in the structure of the material that matters. If not all the valence electrons of a substance are "involved" in the structure of the material, then these electrons are said to be free electrons. They move about in the substance, and are free to contribute to electron flow. The metals are examples. In contrast with this, if all the electrons are bound up in a material, they are not free to support current flow, and the material is said to be an insulator. Said another way, if the valence electrons in a material are in a Fermi energy level that overlaps the conduction band for that material, the material is a conductor. In an insulator, the valence electrons are all in Fermi energy levels that are below the conduction band for that material, and it is an insulator. Applying a voltage to an insulator will not "lift" the valence electrons up into the conduction band to allow them to support current flow.
Is doping is used to increase the conductivity of intrinsic semi conductor material?
Doping a semiconductor provides additional charge carriers to the material. The dopant atoms are easily ionized, and this provides the semiconductor with either free electrons in the conduction band or electron vacancies (or holes) in the valence band, both of which allow the semiconductor to conduct electricity.
If a pure Si crystal has a million free electrons inside it how many holes does it have.what happens to the no of free electrons and holes if the ambient temperature increases?
If the crystal is pure Si (no dopants or impurities) then the number of free electrons in the conduction band will be equal to the number of holes in the valence band. Each electron leaves behind a hole when it is thermally excited into the conduction band. If the ambient temp. increases, there will be more thermal energy available which will increase both the number electrons and the number of holes.
What happens when heat is added to pure silicon?
An intrinsic (pure) silicon crystal at room temperature has sufficient heat (thermal) energy for some valence electrons to jump the gap from the valence band into the conduction band, becoming free electrons.
Why is phosperous donar impurity?
because it adds extra electrons to semiconductor crystal lattice. these electrons having no place in valence band move up to conduction band, where they are free to move.
What is classical free electron theory of metal?
Classical free electron theory is modeled by drude - Lorentz to explian elctrical conductivity in metals. According to this free electron in a metal (valence electron) move randdomly at room temperature and these free electron are drifted in opposite to the direection of the applied electric field. This is repsonsible for the conduction. Here all the free elctron are are considered as equal in all aspect.
