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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