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Question
Write two characteristic features to distinguish between n-type and p-type semiconductors ?
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Solution
In n-type semiconductor, the semiconductor is doped with pentavalent impurity. In it the electrons are majority carriers and holes are minority carrier or ne >> nh [ne − number density of electrons, nh − number density of holes]
In energy band diagram of n-type semiconductor the donor energy level ED is slightly below the bottom of EC conduction band and thus the electron can move to conduction band thus the electron can move to conduction band with even small supply of energy,
In p-type semiconductor, the semiconductor is doped with trivalent impurity. In this the holes are the majority carries and electrons are the minority carriers i.e nh >> ne
In energy-band diagram of p-type, the accepter energy level in slightly above the top of valence band EV.
Thus even with small supply of energy electron from valence band can jump to level EA and ionize the acceptor negatively.
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A p-type semiconductor is
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(Use Planck constant h = 4.14 × 10-15 eV-s, Boltzmann constant k = 8·62 × 10-5 eV/K.)
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Useful data
`1/(4pi∈_0) = 8.99 xx 10^-34`N m2 C-2; e = 1.60 10-19 C; h = 6.63 10-34 Js; me = 9 × 10-3 kg
The valance of an impurity added to germanium crystal in order to convert it into p-type semiconductor is
- Assertion (A): In insulators, the forbidden gap is very large.
- Reason (R): The valence electrons in an atom of an insulator are very tightly bound to the nucleus.
