1. Increased Carrier Concentration:
* Intrinsic Semiconductors: In intrinsic semiconductors, the number of free charge carriers (electrons and holes) is relatively low at low temperatures. As temperature increases, more valence electrons gain enough energy to break free from their bonds and become conduction electrons, leaving behind holes in the valence band. This increase in both electrons and holes directly contributes to increased conductivity.
* Extrinsic Semiconductors: In extrinsic semiconductors (doped with impurities), the temperature-dependent increase in carrier concentration is even more significant. As temperature rises, more impurity atoms donate or accept electrons, leading to a substantial increase in the number of free carriers.
2. Increased Carrier Mobility:
* At higher temperatures, the atoms in the semiconductor lattice vibrate more vigorously. This vibration makes it harder for charge carriers to move freely, leading to a decrease in carrier mobility. However, the increase in carrier concentration due to thermal excitation outweighs the decrease in mobility, resulting in a net increase in conductivity.
3. Band Gap Reduction:
* The energy gap between the valence band and conduction band decreases slightly with increasing temperature. This reduction in band gap makes it easier for electrons to jump from the valence band to the conduction band, further increasing the number of free carriers and conductivity.
Overall:
The increase in carrier concentration is the dominant factor contributing to the increase in conductivity with temperature in semiconductors. Although carrier mobility decreases with temperature, the increase in carrier concentration is much larger, resulting in a net increase in conductivity.
Important Note:
* The conductivity of a semiconductor does not increase indefinitely with temperature. At extremely high temperatures, the semiconductor may reach a point where its conductivity decreases. This happens because the increase in lattice vibrations and scattering effects overwhelm the increase in carrier concentration.
* Different types of semiconductors (intrinsic vs. extrinsic) exhibit different temperature dependencies in their conductivity.
This explanation provides a basic understanding of why semiconductor conductivity increases with temperature. For a more in-depth analysis, consider researching the specific properties of different types of semiconductors and their behavior at various temperatures.
