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In a semiconductor, what happens to the resistance when the temperature increases?
Increases
Decreases
Remains same
Becomes zero
Decreases
In a semiconductor, resistance decreases as temperature increases due to the significant rise in the number of charge carriers. This behavior is fundamentally different from conductors, where resistance increases with temperature due to lattice scattering.
In a semiconductor, resistance decreases as temperature increases due to the significant rise in the number of charge carriers. This behavior is fundamentally different from conductors, where resistance increases with temperature due to lattice scattering.
niтАЛ=NCтАЛNVтАЛтАЛeтИТ2kTEgтАЛтАЛ тАФ intrinsic carrier concentration as a function of temperature
╧Г=q(n╬╝nтАЛ+p╬╝pтАЛ) тАФ conductivity formula where ╧Г increases as n and p rise
Semiconductors have a covalent bond structure. As temperature rises, thermal energy breaks more covalent bonds, generating a large number of electron-hole pairs. Although lattice scattering increases slightly, the exponential increase in the carrier concentration (niтАЛ) dominates, leading to a net decrease in resistivity (╧Б=╧Г1тАЛ=q(n╬╝nтАЛ+p╬╝pтАЛ)1тАЛ).
Semiconductors possess a negative temperature coefficient (NTC) of resistance.
Thermal excitation promotes electrons from the valence band to the conduction band.
The energy gap EgтАЛ remains relatively stable while carrier concentration increases exponentially.
Higher thermal energy overcomes the band gap barrier, increasing conductivity.
Useful for thermal sensing (Thermistors).
Essential for electronic switching and amplification.
High thermal sensitivity can lead to thermal runaway in high-power devices.
Requires heat sinking to maintain stable operating points.
Temperature sensors (NTC thermistors).
Active electronic components like Diodes, Transistors, and MOSFETs.
| Feature | Conductors | Semiconductors |
|---|---|---|
Temperature Coefficient of Resistance | Positive (PTC) | Negative (NTC) |
For conductors, RtтАЛ=R0тАЛ(1+╬▒╬ФT) where ╬▒>0.
Option A is incorrect as it describes the behavior of metals/conductors.
Option C is incorrect as it describes ideal insulators or specialized alloys like Manganin over small ranges.
Option D is only achieved by superconductors below their critical temperature (TcтАЛ).
B is correct тАФ Semiconductors exhibit a negative temperature coefficient, meaning their resistance decreases as temperature increases due to thermal generation of charge carriers.
Always remember that while mobility (╬╝) decreases with temperature in semiconductors due to increased scattering, the exponential growth in the number of carriers (n) far outweighs the loss in mobility, leading to lower overall resistance.