As the number of holes are …
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Dr. Kamlapati Bhatt 6 years, 10 months ago
Considering an equilibrium established between the number of holes and the number of free electrons in a semiconductor at a particullar temperature.at equilibrium let
, no be the equilibrium free electron concentration in conduction band ,, [ cm-3 ]
po be the equilibrium hole concentration in valency band , [ cm-3 ]
Certainly , then in intrinsic semiconductor :
.............no = po = ni
where, ni represents intrinsic - carrier concentration.
As T increases , then ni increases .
As Eg increases , ni decreases.
We can consider this equilibria .........bond <----------> e- + h+ using an anology to chemical reaction H2O <------------> H+ + OH-
Applying law of mass action ,
..................................................................K = [ e- ] [ h+ ] / [ bond ]...................................................................& K = [ H+ ] [ OH- ] / [ H2 O ]
........................................................................{tex}\approx{/tex} exp [ - Eg / k T ]...................................................................................{tex}\approx{/tex} [ - E / k T ]
where , [ bonds ] is the concentration of unbroken bonds , k is rate constant & E , Eg represents respective activation energies..
again , since [ bonds ] >> no , po
..................{tex}\therefore{/tex} [ bonds ] = constant
In general , relatively few bonds are broken to form an electron hole , therefore, the number of bonds are approximately constant .Hence ,
......................Number of holes are equal to number of free electrons
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