Semiconductors and Doping

topicmedium63 MCQ

Energy bands in conductors, insulators and semiconductors; intrinsic and extrinsic types. (Physics › Electronic Devices, NEET UG syllabus.)

What is Semiconductors and Doping?

A material where the valence and conduction bands overlap, allowing free movement of electrons and high electrical conductivity.

Key formula / rule: Mass Action Law

Classify materials into conductors, insulators, and semiconductors based on energy band theory.
Explain the concept of intrinsic semiconductors and their properties.
Define doping and explain its purpose.
Differentiate between n-type and p-type semiconductors, including their formation and majority/minority carriers.

Confusing donor impurities with acceptor impurities (pentavalent vs. trivalent).

Term: Conductor
Meaning: A material where the valence and conduction bands overlap, allowing free movement of electrons and high electrical conductivity.

Term: Insulator
Meaning: A material with a large energy gap between the valence and conduction bands, preventing electron movement and exhibiting very low electrical conductivity.

Term: Semiconductor
Meaning: A material with an electrical conductivity between that of a conductor and an insulator, characterized by a small forbidden energy gap.

Term: Valence Band
Meaning: The highest energy band occupied by electrons at absolute zero temperature.

Term: Conduction Band
Meaning: The lowest unoccupied energy band, where electrons can move freely and contribute to electrical conduction.

Term: Energy Gap (Forbidden Gap)
Meaning: The energy difference between the top of the valence band and the bottom of the conduction band, where no electron states can exist.

Term: Intrinsic Semiconductor
Meaning: A pure semiconductor material where the number of thermally generated electrons equals the number of holes (n_e = n_h).

Term: Extrinsic Semiconductor
Meaning: A semiconductor whose electrical properties have been modified by doping with impurities.

Term: Doping
Meaning: The intentional process of adding a small amount of impurity atoms to a pure semiconductor to alter its electrical conductivity.

Term: Donor Impurity
Meaning: A pentavalent impurity atom (e.g., P, As) that donates an extra electron to the conduction band when added to a semiconductor.

Term: Acceptor Impurity
Meaning: A trivalent impurity atom (e.g., B, Al) that accepts an electron from the valence band, thereby creating a hole, when added to a semiconductor.

Term: n-type Semiconductor
Meaning: An extrinsic semiconductor formed by doping with donor impurities, where electrons are the majority charge carriers.

Term: p-type Semiconductor
Meaning: An extrinsic semiconductor formed by doping with acceptor impurities, where holes are the majority charge carriers.

Term: Majority Carrier
Meaning: The type of charge carrier (electron or hole) that is present in the largest concentration in an extrinsic semiconductor.

Term: Minority Carrier
Meaning: The type of charge carrier (electron or hole) that is present in the smallest concentration in an extrinsic semiconductor.

Classify materials into conductors, insulators, and semiconductors based on energy band theory.
Explain the concept of intrinsic semiconductors and their properties.
Define doping and explain its purpose.
Differentiate between n-type and p-type semiconductors, including their formation and majority/minority carriers.
Describe the role of donor and acceptor impurities and their associated energy levels.
Apply the Mass Action Law to calculate carrier concentrations in extrinsic semiconductors.

Name: Mass Action Law
Note: Relates electron (n_e) and hole (n_h) concentrations in an extrinsic semiconductor to the intrinsic carrier concentration (n_i) at a given temperature.
Expression: n_e \· n_h = n_i^2

Confusing donor impurities with acceptor impurities (pentavalent vs. trivalent).
Incorrectly identifying majority and minority carriers in n-type and p-type semiconductors.
Believing that n-type semiconductors are negatively charged or p-type are positively charged (they are electrically neutral overall).
Not understanding that doping creates new energy levels within the forbidden gap.
Forgetting the Mass Action Law and its implications for carrier concentrations.

Which of the following elements is typically used as a donor impurity to create an N-type semiconductor from silicon?…
medium
Which of the following best describes a semiconductor material?…
easy
At absolute zero (0 K), an intrinsic semiconductor behaves as which of the following?…
easy