Why conductivity of semiconductor increases with temperature and conductivity of semiconductor depends on impurities?
Murtadha Shukur
Semiconductors behave uniquely when it comes to conductivity compared to conductors and insulators, and here's why their conductivity changes with temperature and impurities:
Temperature dependence:
- Inherent structure: Semiconductors have a unique electronic structure with a filled "valence band" and a higher energy, empty "conduction band." Normally, electrons cannot easily jump this gap, preventing current flow.
- Thermal excitation: When temperature rises, thermal energy excites some electrons from the valence band to the conduction band. These additional free electrons become mobile charge carriers, increasing conductivity.
Impurity dependence (doping):
- Pure semiconductors: In their pure state, the number of mobile charge carriers in a semiconductor is very low, resulting in low conductivity.
- Doping: Introducing controlled impurities, called dopants, drastically alters conductivity. Two main types of doping exist:N-type doping: Adding elements with one extra electron (e.g., phosphorus) creates "donor states" near the conduction band. These readily donate electrons, significantly increasing the number of mobile charge carriers and conductivity. P-type doping: Adding elements with one missing electron (e.g., boron) creates "holes" in the valence band. These "holes" behave like positively charged particles and can move, contributing to current flow and increasing conductivity.
Therefore, both temperature and impurities play a crucial role in determining the conductivity of semiconductors. By manipulating these factors, we can control the flow of electricity in these materials, making them valuable for various electronic applications like transistors and integrated circuits.
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