Correct Answer: C
Explanation:
In semiconductor physics, an acceptor is a dopant atom that when added to a semiconductor can form a p-type region.
Boron atom acting as an acceptor in the simplified 2D Silicon lattice.
For example, when silicon (Si), having four valence electrons, needs to be doped as a p-type semiconductor, elements from group III like boron (B) or aluminium (Al), having three valence electrons, can be used. The latter elements are also called trivalent impurities. Other trivalent dopants include indium (In) and gallium (Ga).
When substituting for a Si atom in the crystal lattice, the three valence electrons of boron form covalent bonds with three of the Si neighbours but the bond with the fourth neighbour remains unsatisfied. The unsatisfied bond attracts electrons from the neighbouring bonds. At room temperature, an electron from a neighbouring bond will jump to repair the unsatisfied bond thus leaving a hole (a place where an electron is deficient). The hole will again attract an electron from the neighbouring bond to repair this unsatisfied bond. This chain-like process results in the hole moving around the crystal and able to carry a current thus acting as a charge carrier. The initially electroneutral acceptor becomes negatively charged (ionised).
In semiconductor physics, a donor is a dopant atom that, when added to a semiconductor, can form an n-type region.
Phosphorus atom acting as a donor in the simplified 2D Silicon lattice.
For example, when silicon (Si), having four valence electrons, needs to be doped as an n-type semiconductor, elements from group V like phosphorus (P) or arsenic (As) can be used because they have five valence electrons. A dopant with five valence electrons is also called a pentavalent impurity. Other pentavalent dopants are antimony (Sb) and bismuth (Bi).
When substituting a Si atom in the crystal lattice, four of the valence electrons of phosphorus form covalent bonds with the neighbouring Si atoms but the fifth one remains weakly bonded. At room temperature, all the fifth electrons are liberated, can move around the Si crystal and can carry a current and thus act as charge carriers. The initially electroneutral donor becomes positively charged (ionised).