12. Class 12th Physics |Semiconductor & its Types | Generation & Recombination of e-h Pairs


let us discuss an important phenomena in semiconductors
that is generation and recombination of electron hole pairs, as we have already discussed that
, in a pure semiconductor , concentration of electrons is equal to concentration of
holes. and we can write that , due to . thermal agitation. continuously , new electron hole
pairs . are generated. per unit volume of the semiconductor , and
other electron hole pair , other means the electron hole pairs which are generated earlier
. these disappears . due to, recombination , here recombination refers to the phenomena
where we can say , falling off. an electron from, conduction band to a hole. in valence
band . to regenerate . the covalent bond, again . and release energy, this phenomena
we call as recombination, as we know well that when electron is excited to higher energy
level after small duration of its life time .
it drops down to the. lower energy state, if there are vacancies in it, so once when
electron hole pairs are generated, individual electrons and holes exist for a small duration,
which is called life time of electrons and holes, after which, these electrons and holes
recombine not necessary that this electron will recombine with the same hole , covalent
bond which , was broken when pair was created it can drop in any hole in the valence band
. and it releases energy and generated covalent bonds again, this phenomena we call, recombination
of electron hole pair. there are few important fact we need to write
about it that, at a given temperature. due to continuous. generation, and recombination,
of electron hole pairs, average concentration, of electrons and holes, remains constant , which
changes with temperature only , so due to continuous generation and recombination of
electron hole pairs the quantity of electrons in conduction band and the quantity of hole
in valence band almost remains constant. another important fact about it , thermal
energy . absorbed . in generation of , electron hole pairs . and released energy . during
recombination . keeps the lattice. in, thermal equilibrium, this is also important otherwise
if thermal energy is absorbed by electrons when these are excited to , conduction band,
then the lattice will cool down due to absorption of lattice energy by electrons , so , after
some time when these recombine, we can state that continuous generation and recombination
continuously absorbs energy as well as releases energy due to which, the lattice remains in,
thermal equilibrium , this phenomena is important , generation and recombination of electron
hole pairs, in a semiconductor.

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9 thoughts on “12. Class 12th Physics |Semiconductor & its Types | Generation & Recombination of e-h Pairs”

  1. Seema Phadke says:

    Ashish Arora Sir what a explanation !!!!!1111 sir . super take a bow!!!

  2. Anshul Kohli says:

    sir if p.d. is applied across lattice then recombination will take place (lattice will remain in thermal equilibrium?

  3. Vatsal Mavani says:

    sir can you please just speed up the videos???
    it really gets very boring when you have to complete the chapter in small time….

  4. pewkew ter says:

    Sir what is the reason of recombination.

  5. रौशन कुमार says:

    Sir where covelant bond formed

  6. Repudi Rajasekhar says:

    Superrrr sir

  7. 63pverma says:

    Is this imp for jee

  8. Rohan Jadamali says:

    How will lattice cool down by absorption of thermal energy by electron?

  9. Vaibhav Tambade says:

    @4:25 sir Please explain, not understanding, why if thermal energy is absorbed by electrons leafs to cooling down of lattice..?

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