Question

A semiconductor is doped with a donor impurity then [more than one option may be correct]

• A. the hole concentration increases
• B. the hole concentration decreases the electron concentration increases
• C. the electron concentration increases
• D. the electron concentration decreases

Answer 1

Answer: (B), (C)

the electron concentration increases
the hole concentration decreases the electron concentration increases

Options B and C are correct.

B Donor impurity is a pentavalent impurity which donates one free electron as the result of which the the electron concentration increases.The hole concentration decreases as the number of charge carriers(Product of number of electrons and holes per unit volume) in the semiconductor remains constant; so when the electron concentration increases the hole concentration decreases.(Formula)

C The pentavalent impurity added has five electrons in its outermost shell; four of the electrons are used for forming covalent bond and one electron is free as the result of which the electron concentration increases.(View image for more clearance of the concept)

A The hole concentration decreases and the electron concentration increases as the number of charge carriers remains constant.

D The electron concentration increases due to pentavalent impurity being added which has five electrons in its outermost shell ; uses four electrons to form covalent bond and one electron is free which increases the electron concentration.