Conductivity and Temperature: Extrinsic Semiconductors vs. Metals

The relationship between conductivity and temperature differs significantly between extrinsic semiconductors and metals due to the nature of their charge carriers and band structures.

Extrinsic Semiconductors:

• Conductivity increases with increasing temperature, up to a point.
• This behavior is due to the thermal excitation of electrons from donor levels (n-type) or acceptor levels (p-type) to the conduction band.
• More free charge carriers lead to higher conductivity.
• However, this increase has a limit. Once all the dopant-related electrons (or holes) are excited, further temperature rise doesn't significantly increase conductivity.

Metals:

• Conductivity generally decreases with increasing temperature.
• Metals have a sea of delocalized electrons in the conduction band readily available for conduction.
• As temperature increases, the metal atoms vibrate more, causing increased collisions between the electrons and the vibrating atoms.
• These collisions hinder the movement of electrons, reducing their average velocity and therefore, the overall conductivity.

Here's a table summarizing the key points:

MaterialConductivity vs. TemperatureExplanationExtrinsic SemiconductorIncreases initially, then plateausThermal excitation of electrons/holes from dopant levels to conduction band, limited by available dopants.MetalDecreasesIncreased collisions between electrons and vibrating atoms hinder their movement.

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Additional Points:

• The specific effects of temperature on conductivity can vary depending on the material and its properties.
• Doping concentration in extrinsic semiconductors can also influence the temperature dependence of conductivity.

Overall, understanding the interplay between temperature and conductivity is crucial for designing and utilizing materials effectively in various applications, like electronics and energy devices.

Dr Murtadha Shukur thank you for your contribution to the discussion

Electrical conductivity increases in semiconductors with increasing temperature, because, as temperature increases, the number of electrons from the valence band is able to jump to the conduction band. The electrical conductivity of an extrinsic semiconductor increases with a rise in temperature such that semiconductors have a negative temperature coefficient of resistance. With increase in temperature of extrinsic semiconductor, minority charge carriers increase because of bond breakage and minority charge carriers may become almost equal with majority charge carriers. Thus, extrinsic semiconductor behaves almost as an intrinsic semiconductor with increase in temperature. Clearly, conductivity significantly depends on majority charge carriers generated due to impurity doping. It means conductivity of metal is highly dependent on free electrons. If we increase the temperature of metal then lattice vibration increase so restrictions in the path of free electrons also increases. So conductivity increase by lattice vibration but decrease due to less flow of free electrons. As the temperature of the conductor rises, the velocity of the free-charged particles increases and the increased temperature also affects the amplitude of vibration due to this the vibration rate of metallic atoms also increases.For metals we have positive temperature coefficient of resistance. For semiconductors we have negative temperature coefficient of resistance i.e. as temperature increases then conductivity increases and resistance decreases. The electrical conductivity of semiconductors increases rapidly with increasing temperature, whereas the electrical conductivity of metals decreases slowly with increasing temperature.