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    Question

    A silicon sample is doped such that the number of holes

    far exceeds the number of electrons. Which of the following is true about its conductivity?
    A Controlled by electrons only Correct Answer Incorrect Answer
    B Controlled by both electrons and holes equally Correct Answer Incorrect Answer
    C Controlled primarily by holes Correct Answer Incorrect Answer
    D Zero Correct Answer Incorrect Answer

    Solution

    When a silicon sample is doped in such a way that the number of holes far exceeds the number of electrons, it implies the use of trivalent impurity atoms (like Boron), which create acceptor levels near the valence band. These acceptor impurities capture electrons from the valence band, creating a large number of holes . Since holes are much greater in number compared to electrons, they act as the majority charge carriers , while electrons become the minority carriers. In such p-type semiconductors , electrical conductivity is governed primarily by the drift of holes under an applied electric field. Though minority electrons do contribute to conduction, their role is minimal in comparison.

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