Dear friend,

Donot know whether am correct or wrong. But i think hole is nothing but the vacancy created due to the electron displacement. Suppose due to some excitation that may be thermal or any other field, then electron is displaced from its position(site) then it leaves a vacancy there which we call a hole. Likewise another electron comes to fill up the vacant site and hole moves to the site where the electron came from. Like wise another electron comes to the hole site and hole replaces the electron's site and so on. In this way continuous movement of electron and holes takes place.  As there is movement is taking place for both the electron as well as holes inside the materials hence it is supposed that the holes exist. And about the existence of holes inside the atom i have no idea.

Thank you

Dear Prakash,

A hole is only a theoretical concept to explain the deficiency of an electron and it does not exist in reality. Suppose a stone is there in the field. If we take out the stone, then it creates a hole in the field. Similarly, if we take out an electron, then the vacant space is termed as hole. I also do not understand why the scientists termed it so. if there is no electron, then it should have been a positive charge having the same magnitude of electron but it is positive (say, positron). Any other name should have been there instead of the so called hole. But we have to follow what the great scientists has dictated to us. I also have so many other doubts regarding electronics. Lets keep our fingers crossed that one day we can get a absolute perfect answer.

Regards   

All the current commenters share valuable information. The following is my brief answer.

Holes are not considered particles and are the infinitesimal area or point(s) of positive charge when an electron is transported (moves)  from a valence band to a conduction band. Holes are not positrons or antimatter. Holes are the absence of electrons' negative charge caused by transport. The discovery of the positive charge arising from displacement of an electron led to the improvement (by doping) of semiconductor materials performance. The negative and positive charges (electrons and holes) conduct through the lattice. In this manner of speaking, ions, electrons and holes are charge carriers or traveling charges. The existence and presence of charges are real and quantitative, even if holes are considered imaginary or theoretical.

The following online link describes electrons and holes in semiconductors quite well.

http://www.allaboutcircuits.com/vol_3/chpt_2/5.html

"Thermal energy may occasionally free an electron from the crystal lattice ... . This electron is free for conduction about the crystal lattice. When the electron was freed, it left an empty spot with a positive charge in the crystal lattice known as a hole. This hole is not fixed to the lattice; but, is free to move about. The free electron and hole both contribute to conduction about the crystal lattice. That is, the electron is free until it falls into a hole. This is called recombination. If an external electric field is applied to the semiconductor, the electrons and holes will conduct in opposite directions. Increasing temperature will increase the number of electrons and holes, decreasing the resistance. This is opposite of metals, where resistance increases with temperature by increasing the collisions of electrons with the crystal lattice."

I appreciate all the answers. Hole is never seen experimentally. But how do you all say that the vacancy created by electron should be a positive charge, i dont understand it. If the electron and hole exist at a place then it should be neutral. But before the elctron moved it was a negative charge. When the negatively charged electron moved away, it left a positively charged hole. How come this is possible ? I think i donot have that much knowledge to explain this hole concept.....

But as hole is moving opposite to the electron thatswhy it is taken as +vely charged, but not sure..I think it may be

This is how I think of it.  For a "hole band" we have a roughly concave down parabola so that the filling reduces the size of the k-vectors.  If we deform this fermi surface to give net right k vectors we have to have lower velocity electrons on the right and slower on the left.  This is why the Hall coefficient is negative.  Of course, only electrons are actually flowing but the overall constraints of the fermi sea for "not hot" electrons creates collective constraints that give "negative mass" or equivalently "positive charge" behavior.  Is there specific example you want to apply the concept to?  

I have to disagree with Don.  I find some of these heuristic engineering descriptions less than worthless.  They lead to no calculational value and don't get to the heart of the matter.  

Thank you for all, I am getting good information, But if I try to determine the hole mobility, is it positive, if not what is the sign of hole?

Most of the previous answers have inaccuracies, irrelevant statements, and statements which do not make sense.

Concept of Hole: A hole represents an allowed state or energy in the valence band, which is not occupied by an electron, i.e. basically an unoccupied state in the valence band. If all the allowed states in the valence band are filled with electrons, then these electrons are not free charge carriers, as they cannot move under an electric field, as there is no higher allowed state empty to move to. Remember that under an applied electric field, an electron has to gain energy from the field, and consequently has to be lifted to a higher energy state. Also remember Pauli's exclusion principle - an electron cannot be excited to a filled state. A vacant energy state in the valence band (i.e. a hole) is a free carrier, because an electron can be excited to this state under an applied electric field. In an applied electric field, the so-called hole moves in a direction opposite of the electron occupying its state - this is why it is assigned a positive charge. Unfortunately, the name "hole" may give a wrong impression; it is nothing but an unoccupied state inside the valence band.

Hole Mobility: Drift velocity is proportional to the applied electric field; the constant of proportionality is called the mobility. Both electrons in the conduction band and holes in the valence band contribute to the drift current. Mobility is inversely proportional to the second derivative of the energy E with respect to the wave-vector k. In other words, hole mobility is determined by the E(k) relation of the valence band. 

Note: There is no such thing as "electron hole", or there is no such thing as "hole in an atom". We only talk of holes in the valence band, and not inside an atom. A valence band is a collection of energy levels allowed by quantum mechanics.

I so often lament the notion of "hole" was ever invented.  I think it was Rudolf Peierls.  For electrons that are scattered regularly the currents can be described as close to the Fermi surface.  The scattering by impurities and phonons determined the mobility.  The shape of the fermi surface can apply pretty much arbitrarily large constraining forces on these currents even though they are doing no work on them.  These forces sometimes makes it seem like the masses of these negative electrons are negative because it forces them to bend them "wrong" way.  +m->-m, -q->+q gives an equivalent calculation.  That is all there really is to the notion of hole.  Excitons are a special case but all the fancy field theory states and dressing of particles just disguises this even though they are a useful way to compute many things.  

Inside an atom one can have excited states from deeper inside the electron core or ejection as in Augur processes.  You can call  these vacated regions holes but they don't have any mass.  The mass is where the electrons are.  Maybe one can find a way to make the concept useful here.  It is hard to see how it could be useful in the limit where electron correlations matter but stranger things have happened.  

In valence band there is no electron,we denoted that is hole. In conduction band there is no electron that is empty states

A Hole in principle is a lack of electron, it is a purely theoretical concept to facilitate the understanding of a p-doped semiconductor. if an electron from the valence band gets excited to the conduction band, it "leaves behind" an empty place, which can be seen a decrease of negative charge in the valence band or an increase in positive charge in that manner. such "empty place"  seen as a positive charge is the hole. A hole like an electron has mass, charge and volume. you can calculate its mobility. when applying voltage to a semiconductor the fermi level splits to quasi electron fermi level and quasi hole fermilevel. for me the easiest way to view a hole is by looking at the band diagram from upside down...

I hope this helps

Interesting thought process would be to look at it from the electrostatic point of view and realize that holes in atoms can be attributed to the deficiency in charge balance - due to absence of an electron. So just because it denotes absence of electrons - we could think of it as a missing charge of -e and hence the charge +e and a positive mass.

But from the quantum mechanical point -.holes could be just missing wave functions in terms of inter-electron interactions. 

http://stacks.iop.org/0022-3700/7/i=14/a=006

A golf ball in hole- Electron

When the ball is out- Hole (can be imagined as a place for electron hideout)

Holes are generated in semiconductors once bound electrons are made free by thermal or photon energy absorption. When the electrons in the free state (conduction band) can contribute to conduction, the holes in the bound state (valence band) can also contribute to the conduction, because it helps the nearby electron to move through it. In fact hole movement is nothing but electron movement in the valence band. To distinguish the bound electron movement from free electron movement, the concept of holes was introduced. Since the free and bound electrons (holes) move from different states, respectively, from free (conduction band) and bound (valence band) states their effective masses will be different.

[He] has two electrons. When an electron leaves ( for whatever reason), it leaves [ He ] with one electron only. Now, [ He ] becomes [He+]. There is a space on [ He+ ] on which an electron can be placed and I am going to call that place a-hole...Just because that's what everybody else calls it.