holes and electrons
I have read in some books that holes are physical entities. I do not understand how can a hole be a physical entity when it is actually an absence of electron from the valency orbit. Please explain?
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a hole has no exsistence. its actually the abscence of an electron. its actually like coldness. coldness itself is nothing its just the abscence of heat.
Yet Holes attract electrons, so to speak the hole doesn't actually move, electrons do phyically as it is replaced almost instantly. Not just one electron moves though a conductor, think of how energy is transmitted though those swinging ball thingys.
Example:
As a charge or voltage is applied one electron moves from one valance to a valance hole created by the potential difference. As the electron leaves the valance the hole is created and then in which attracts the next electron given the provided flow. So essencially the holes move the opposite way of electrons, but they really don't physically move the way electrons jump to valences of the next hole.
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remeber that the it is silicon that is being used
Silicon has 14 protons and thus 14 electrons in its shells. In its outer shell it has 4 electrons.
In a silicon crystal Silicon bonds with 4 other silicon atoms and thus fills up its outer most shell with a total of 8 electron by sharing an electron from the silicon it is bonding with (stable shell configuration). - Covalent bonds
Pure silicon crystal is an electrical insulator since it has no electrons available to flow. it is charge-neutral
When you "dope" silicon you put into the silicon crystal mix either phosphorous atoms or boron .
phosphorous has 5 electrons in it outer shell. Thus when it bond with 4silicon atoms around it, there is 1 electron not being used in covalent bonds - this electron is thus available for conduction. Such a material is N-type doped. It has more electrons than protons in the phosphorous-4Silicon thus it is NET negative charged
boron on the other hand only has 3 electrons in its outer shell. It really wants 8 electrons. It will bond with 4 silicon atoms as well, but this time one of the silicon atoms will be donating one elctron but will not get one in return. Thus there is gap in the outer shell of that boron atom and a silicon atom. This lattice now has more protons than electrons thus it has a NET positive charge.
It is easy to talk abt electrons moving. BUT holes (ie lack of an electron) do not, all that happens is an electron being used in electrical conduction completes the boron-silicon electron shell, it is then pushed out by an electron behind it (being forced around by a battery) thus it "appears" that the hole si moving but in fact it is electrons moving
Arsenic was a popular doping material in the old days as well. I seem to remember a play titled, "Arsenic and Hole Lace" or something like that.
Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).
R.I.P.
ouch!!
gerty
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