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In a p-type semiconductor, it is said that the hole current is greater than the electron current, which makes no sense to me..

The hole current is due to the electron current, right? Electrons jump from one hole to another. Thus, we can say the holes are moving OR the electrons are moving. So to me, it seems that the hole current should be greater than the electron current. But in my textbook it is clearly mentioned that the hole current is greater than the electron current in a p-type semiconductor. Where am I wrong?

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    $\begingroup$ Hole current is, indeed, the net result of electron motion in the valence band. We focus on holes there because (1) a full valence band has no net current, and (2) by considering the holes we can establish a relation between the equilibrium between (holes in the valence band) and (electrons in the conduction band). So, embrace the concept of holes - it will make things much easier in semiconductor physics. $\endgroup$
    – Jon Custer
    Feb 24, 2016 at 15:19

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Start with an intrinsic semiconductor: the valence band is full so when an electron is knocked out -- by thermal motion -- it produces an electron-hole pair. The pair is subject to rapid recombination due to the poor mobility of both the hole and the electron in an intrinsic semiconductor due to the full valence shell.

N-doped semiconductors have a controlled concentration of doping with an electron donor atom. In this case when an electric field is applied an electron current can be supported. N-doped semiconductors have a supply of easily freed electrons in addition to the intrinsic electron-hole pairs; phosphorus doped silicon is an example.

P-doped semiconductors are doped with electro-acceptor atoms, such as boron in silicon. This creates locations with holes in the valance band which can accept electrons from nearby or even not so nearby. When intrinsic electron-hole pairs are created the electrons can recombine or move to an acceptor site; this vastly increases the mobility of the holes.

For picturez see http://www.allaboutcircuits.com/textbook/semiconductors/chpt-2/electrons-and-holes/

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The terms "electron current" and "hole current" have the following meanings in any Semiconductor Physics book

  1. Electron current is associated with the movement of electrons in the Conduction Band of the semiconductor

  2. Hole current is associated with the movement of holes in the Valence Band of the semiconductor

As you pointed out, holes move due to electrons, but this is referred to as the hole current & not electron current.

Now, for a p-type semiconductor, due to the acceptor states near the valence band edge, there are more holes in the valence band than electrons in the conduction band.

$$n_h >> n_p$$

And thus, $$\text{Hole Current} >> \text{Electron Current}$$

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Electron current is due to the movement of electrons in the conduction band :-) Hole current is due to the movement of electrons between adjacent atoms' valence bands to fill vacancy created by hole, which implies the literal movement of holes :-) In intrinsic semicinductors, CB = empty, VB is full at 0K. But some electrons leave VB to CB, and eventually no.of holes in VB = no.of electrons in CB, when temp > 0K ( known as thermally generated/intrinsic careers) . So both currents are same in intrinsic semiconductors. In n-type, no. of electrons in CB> no.of holes in VB when temp > 0K , cz of doping + thermally generated carriers....so electron current > hole current In p-type, exactly opposite condition.

Summary 1) electron current is in CB, hole current is in VB only 2) electrons have more mobility than holes cz they require only lesser energy to move in CB( far from nucleus) compared to hole movement in VB. 3) if electron from CB moves to hole of VB ,it's called recombination ,that hole/ electron does not exist anymore.

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