Physics 2003 JAMB Past Questions - Question 49: The major difference between a pure semiconductor and a pure metal is that

Correct Answer

C

Explanation

experiment shows that increase in temperature increases the resistance of a pure metal but decreases the resistance of a pure semi conductor.The major difference between a pure semiconductor and a pure metal lies in their electrical conductivity and the behavior of electrons in their atomic structures.

1. Electrical Conductivity:
  - Pure Semiconductor: In a pure semiconductor, such as silicon or germanium, electrical conductivity is relatively low at room temperature. This is because the electrons in the semiconductor's crystal lattice are tightly bound to their respective atoms and there are relatively few free electrons available for conduction. Semiconductors can conduct electricity, but their conductivity is much lower compared to metals.
  - Pure Metal: In a pure metal, like copper or aluminum, electrical conductivity is very high. This is because metals have a "sea of electrons" in their atomic structure, where many electrons are delocalized and free to move throughout the material. This abundance of free electrons allows metals to conduct electricity very effectively.

2. Energy Band Structure:
  - Pure Semiconductor: Semiconductors have a bandgap in their electronic band structure. This bandgap is the energy difference between the valence band (where electrons are bound to atoms) and the conduction band (where electrons are free to move). Electrons in the valence band cannot easily move to the conduction band at low temperatures because they require energy greater than the bandgap to do so. However, this transition becomes easier with increased temperature or with the introduction of impurities or other factors.
  - Pure Metal: Metals do not have a bandgap in their electronic band structure. In metals, there is significant overlap between the valence and conduction bands, allowing electrons to move easily from one band to the other. This is why metals have high electrical conductivity, as electrons can move through the material without needing a significant energy input.

In summary, the primary distinction between a pure semiconductor and a pure metal is their electrical conductivity and the nature of their electronic band structures. Semiconductors have a bandgap and lower conductivity, while metals have no bandgap and high conductivity due to the free movement of electrons.