Question

The temperature coefficient of a semi-conductor is

• A. positive
• B. Negative
• C. Zero
• D. Infinity

Hint:

A simple way to remember this is: \begin{itemize} \item \textbf{Conductors}: Get "more resistive" (hotter) with heat \(\rightarrow\) \textbf{Positive} \(\alpha\). \item \textbf{Semi-conductors}: Get "less resistive" (more conductive) with heat \(\rightarrow\) \textbf{Negative} \(\alpha\). \end{itemize} This behavior is a defining characteristic that distinguishes semiconductors from metals.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The temperature coefficient of resistance (\(\alpha\)) describes how the electrical resistance of a substance changes with a change in temperature. A positive coefficient means resistance increases with temperature, while a negative coefficient means resistance decreases with temperature.
Step 2: Detailed Explanation:
Conductors (Metals): In metals, as temperature increases, the positive ions vibrate more vigorously. This increases the frequency of collisions for the free electrons moving through the material, which in turn increases the electrical resistance. Therefore, conductors have a positive temperature coefficient of resistance.
Semi-conductors: In semi-conductors (like silicon and germanium), the electrical conductivity depends on the number of charge carriers (electrons and holes). At absolute zero, a pure semiconductor behaves like an insulator. As the temperature rises, thermal energy breaks covalent bonds, creating more electron-hole pairs. This increase in the number of charge carriers drastically increases the conductivity, and consequently, decreases the resistance.
Since the resistance of a semiconductor decreases as its temperature increases, it has a negative temperature coefficient of resistance.
Step 3: Final Answer:
The temperature coefficient of a semi-conductor is negative. Option (B) is correct.