A semiconductor doped with a pentavalent impurity such as phosphorus becomes
- A. n type, with electrons as the majority carriers
- B. p type, with holes as the majority carriers
- C. an insulator
- D. a conductor with no charge carriers
Explanation
A pentavalent atom has five valence electrons but only four are needed for bonding, so the fifth is loosely bound and becomes a free electron, making electrons the majority carriers. Doping with a trivalent impurity such as boron leaves a vacancy, a hole, and gives p type material. The crystal as a whole stays electrically neutral in both cases.