FAA Aviation Mechanic General (AMG)Fundamentals of Electricity and ElectronicsHard
A technician wants to create P-type semiconductor material by doping pure silicon, which has four valence electrons per atom. Which type of impurity atom should be added to achieve this?
- AAn atom with five valence electrons, creating excess free electrons
- BAn atom with eight valence electrons, filling the outer shell completely
- CAn atom with four valence electrons identical to silicon
- DAn atom with three valence electrons, creating electron deficiencies called holes
Show answer & explanationAnswer & explanation
Correct answer: D. An atom with three valence electrons, creating electron deficiencies called holes
P-type semiconductor material is created by doping silicon with a trivalent impurity, such as boron, which has only three valence electrons. This creates electron deficiencies known as holes, which act as majority charge carriers.
Why the other options are wrong
- A. Adding a pentavalent (five-electron) impurity creates N-type material with excess electrons, not P-type.
- B. An atom with eight valence electrons would not bond properly into the silicon lattice.
- C. An impurity identical to silicon would not create doping effects at all.
P-Type Semiconductor Doping
P-type material is created by adding trivalent impurity atoms (3 valence electrons) to pure silicon, creating electron-deficient holes as majority carriers.
- Trivalent dopants: e.g., boron, gallium, indium
- Holes act as positive majority charge carriers
- Opposite is N-type, made with pentavalent dopants like arsenic
Memory trick: P for 'Positive holes' — three electrons leaves a gap to fill.