I'm trying to understand the concept of semiconductors, as far as I know whenever an electron moves it leaves a hole, so how can we say (for example) that n-type semiconductor has a majority of \$e^-\$, won't every electron let a hole?
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2\$\begingroup\$ No, because that's not how a hole is defined. A hole is a vacancy in the valence orbital resulting from having fewer electrons than a full orbital. \$\endgroup\$– Ignacio Vazquez-AbramsCommented Oct 3, 2016 at 12:32
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\$\begingroup\$ See the picture of the lattice structure at hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html \$\endgroup\$– Peter SmithCommented Oct 3, 2016 at 12:36
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\$\begingroup\$ An n-type semiconductor has extra electrons only because it is doped with materials which by nature have more than 4 electrons to make bonds with in their normal states. Since silicon can only make four bonds, and these dopant atoms are forced into a silicon structure, their 5th electron has nothing to make a stable bond with, and so it floats about the lattice - free to drift under the influence of electric fields and contribute to conduction. \$\endgroup\$– jbord39Commented Oct 6, 2016 at 23:53
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What you are confusing is the application/use of semiconductors with the manufacture of the semiconductors.
The of type semiconductor is determined by the type of "impurities" added by the manufacturer to the silicon. If the impurity has more electrons than it needs, it is an n-type, if it has fewer electrons than it needs, it is a p-type. These materials, when vapor deposited "next to each other", form a p-n junction (band).
Now, when you apply a forward bias the junction, the electrons of the n-type material will be pushed into the "holes" of the p-type material leaving holes on the n-type side of the junction (which will be filled with new electrons coming from the negative side of the supply). The electrons that went into the p-type are attracted to the positive side of the supply leaving holes on the p-type side of the junction.
So it is clear that a "hole" is created when an electron moves, but the electron would not be able to move, in the first place, if there were no "holes," to move into!
