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Conduction in Solids Part - 1 : Basic electronics

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CONDUCTION IN SOLIDS

ELECTRON MOTION  AND HOLE TRANSFER


Conduction occurs in any material when an applied voltage causes electrons in the material to move in a particular direction . This may be due to one or both of two processes : electron motion and hole transfer . In electron motion free electrons in the condition band are moved under the influence of the applied electric field thus creating an electric current . Since electrons have a negative charge , they are repelled from the negative terminal of the applied voltage and attracted toward the positive terminal . Hole transfer involves electrons which are still attached to atoms ( Those in the valence band ).

If some of the electron positions in the  valence shell of an atom are not occupied by electrons, there are holes where electrons could exist . when sufficient energy is applied, an electron may be made to jump from one atom to a hole in another atom . When it jumps the electron leaves a hole behind it. And consequently the hole has moved in a direction opposite to that of the electron .

Holes may be thought of as positively charged particles and as such they move through an electric field in a direction opposite to that of electrons.  Or positive particles are attracted toward the negative terminal of  an applied voltage  . where there are few free electrons it is more convenient to think of hole  movement than of electrons jumping from atom to atom.

Since the flow of electric current is constituted by the movement of electrons and holes electrons and holes are referred to as charge  carriers . Each time a hole moves ,an electron must be supplied  with enough energy to enable it to escape from its atom . Free electrons can be moved with less application of energy than the holes because they are already disconnected from their atoms. For this reason , electrons have greater mobility than holes.

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