Question

The most widely used semiconductors are: (i) silicon(ii) germanium(iii) phosphorus(iv) arsenic
A) (i) and (ii)
B) (ii) and (iii)
C) (iii) and (iv)
D) (i), (ii), (iv),(iii)

Answer 1

Semiconductors are such types of material which have the electrical conductivity that falls between conductors and insulators. For practical application purpose, some impurities are injected with the inductors to make its effective use. Semiconductors are widely used in various electronic devices like transistors and integrated circuits.

Explanation:
Silicon and Germanium: Both silicon and germanium are group 14 elements of periodic table. They have half-filled outermost shells i.e. they have exactly 4 electrons in the outermost shell and that provides them the ability to gain or lose electrons at the same time. Normally, each atom of both silicon and germanium makes covalent bonds with neighboring four other silicon or germanium atoms and forms a sheet of these semiconducting materials. They are the most used semiconductor for electronic devices. When energy is provided to these materials either in terms of heat or using heavy potential difference, then these bonds start breaking and those newly available electrons start conducting current with higher conductivity.

Phosphorus and Arsenic: Both phosphorus(P) and arsenic(As) are group 15 elements of periodic table with 5 electrons in the outermost shell. So, within the semiconductor made by silicon(Si) or germanium(Ge) some of the Si or Ge are replaced by P or As. This method is known as doping. Since P or As has 5 electrons in their valence shell, there is always one free electron for each P or As. These free electrons increase the conductivity of the semiconductor.

Correct answer:The most widely used semiconductors are (a) (i) and (ii).

Note: For doped semiconductors, P and As remain present in it. But that doesn’t mean that they consist of semiconductors. Main ingredients for most used semiconductors are Si and Ge. Hence, the correct answer should be option (a), not option (d).