What is the difference between an n-type and a p-type semiconductor?
a) n-type semiconductors are better conductors than n-type semiconductors. b) n-type semiconductors are doped with electrons whereas p-type semiconductors are doped with protons.
c) n-type semiconductors are doped with impurities that increase the number of holes in the crystal lattice, whereas p-type semiconductors are doped with impurities that increase the number of electrons in the crystal lattice.
d) n-type semiconductors contain donor impurity atoms and have a preponderance of electrons compared to holes, whereas p-type semiconductors contain acceptor impurity atoms and have a preponderance of holes compared to electrons.
e) There is no difference, they are both semiconductors.
The Correct Answer and Explanation is:
The correct answer is:
d) n-type semiconductors contain donor impurity atoms and have a preponderance of electrons compared to holes, whereas p-type semiconductors contain acceptor impurity atoms and have a preponderance of holes compared to electrons.
Explanation:
Semiconductors are materials whose electrical conductivity lies between that of conductors and insulators. Their conductivity can be modified by introducing impurities, a process called doping. This creates two main types of semiconductors: n-type and p-type, which differ fundamentally in the type of charge carriers responsible for conduction.
- N-type Semiconductors:
- Doping with donor impurities: In n-type semiconductors, atoms with more valence electrons than the semiconductor material are added. For example, silicon (Si) has 4 valence electrons, so doping it with elements from Group V of the periodic table like phosphorus (P) or arsenic (As) (which have 5 valence electrons) adds extra electrons.
- Excess electrons: These extra electrons are free to move, acting as the majority charge carriers, increasing electrical conductivity. The donor atoms “donate” electrons to the conduction band, hence the name donor impurities.
- Minority carriers: Holes (positive charge carriers) exist but are much fewer compared to electrons.
- P-type Semiconductors:
- Doping with acceptor impurities: In p-type semiconductors, atoms with fewer valence electrons than the semiconductor are introduced. For example, silicon doped with Group III elements like boron (B), which has 3 valence electrons, creates “holes” because boron lacks one electron compared to silicon’s 4.
- Excess holes: These “holes” act as majority charge carriers because they represent the absence of an electron in the crystal lattice and can move as electrons jump to fill them.
- Acceptor impurities: These impurities “accept” electrons, creating holes that facilitate conduction.
- Why other options are incorrect:
- (a) Repeats “n-type” twice; no comparison.
- (b) Is incorrect because semiconductors are not doped with protons; protons are part of the nucleus and not involved in conduction.
- (c) Reverses the roles of electrons and holes in n-type and p-type doping.
- (e) Incorrect because n-type and p-type differ in doping and charge carriers.
In summary, the key difference is in the type of impurity atoms introduced and the resulting majority charge carriers: electrons for n-type (donor impurities) and holes for p-type (acceptor impurities). This distinction is crucial in semiconductor devices like diodes and transistors where the junction between n-type and p-type materials controls current flow.
