extrinsic and intrinsic semiconductor

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    INTRINSIC

    SEMICONDUCTOR

    qA pure semiconductor.

    qIts conductivity is low.

    qIt has thermally generated current carries.

    qExamples of pure or intrinsic semiconductorused frequently

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    qAt 0 K, all the covalent bonds is complete . Therefore, nofree electron is available in the crystal for the conduction of

    current . Hence, silicon crystal behaves as an insulator at 0 K.

    qAt room temperature, a covalent bond breaks, an electronbecomes free. The electron which leave the bonds is calledfree electron and the vacancy created in the covalent bonddue to the release of electron is called a hole.

    qIf the potential difference is applied across an intrinsicsemiconductor, electrons will moves towards the positive

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    q Ne= Nh = NiNe- Number of free electrons per unit volumeNh- Number of holes per unit volume

    Ni Number density of intrinsic carries

    q Total current inside the semiconductor = currentsdue to free electron + currents due to holes

    q The process of adding suitable impurities in theintrinsic is called doping. The impurities added in theintrinsic semiconductor to increased its conductivityare known as dopant.

    qA semiconductor obtained after adding impuritiesatoms in the intrinsic semiconductor is called extrinsicor doped semiconductor.

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    EXTRINSIC SEMICONDUCTOR

    Pentavalent Impurities - The elements whose each atomhas five valence electrons. For example Arsenic, Antimony,Phosphorus etc.

    Trivalent Impurities The elements whose each atom has

    three valence electorns. For example , Indium, Gallium ,Aluminium etc.

    v When Trivalent Impurity is added to pure germanium orsilicon crystal , we get extrinsic semiconductor known as p-type semiconductor. Majority charge carries in p-type

    semiconductor are holes and minority charge carries areelectrons which are thermally generated.

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    oWhen pentavalent impurities is added to the puregermanium or silicon crystal, we get an extrinsic

    semiconductor known as n-type semiconductor.

    o Majority charge carries in n-type semiconductorare electrons and minority charge carries are holeswhich are thermally generated. Since each

    pentavalent impurity atom dontes one electron tothe crystal, so it is known as donor impurities.

    Ne = Nh = Ni

    Nh

    > Ne

    . In p-type semiconductor Ne > Nh . In n-type semiconductor

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    THE DIFFERENCE OFINTRINSICSEMICONDUCTOR

    EXTRINSIC

    SEMICONDUCTOR

    It is pure elements

    like Ge and Silicon.Ne = Nh

    Low conductivity

    Conductivity mainlydepend on theirtemperature.

    It is impure

    elements.Ne Nh

    High conductivity

    Conductivitydepends on thetemperature as wellas the amount of