Effect of temperature on semiconductors' conductivity

In summary, the conductivity of semiconductors increases with temperature because more electrons are freed. However, the scattering and vibrations of the lattice affect the conductivity in semiconductors as in metals, and the effect of additional free electrons outweighs the effect of the greater vibrations of the lattice, so the overall resistance will decrease.
  • #1
Entanglement
439
13
I've known that the conductivity of semiconductors increase with temperature because more electrons are freed,
But why doesn't the scattering and vibrations of the lattice affect the conductivity in semiconductors as in metals?
 
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  • #2
Does the effect of additional free electrons outweighs the effect of the greater vibrations of the lattice so the overall resistance will decrease ??
 
  • #3
Temperature changes have many different effects upon semiconductors; they are well discussed here:
http://www.springer.com/cda/content/document/cda_downloaddocument/9781461407478-c1.pdf?SGWID=0-0-45-1268751-p174130080

The link will download a pdf.
 
  • #4
UltrafastPED said:
Temperature changes have many different effects upon semiconductors; they are well discussed here:
http://www.springer.com/cda/content/document/cda_downloaddocument/9781461407478-c1.pdf?SGWID=0-0-45-1268751-p174130080

The link will download a pdf.
That's quite complicated to me I just want a normal answer . :smile:
 
  • #5
In metals the number of free charge carriers is constant. As the temperature goes up their mobility goes down. Because the carriers can't move as much there is higher resistance.

In semiconductors the number of charge carriers increase exponentially with temperature and this overrides the decrease in mobility.

It turns out that we're lucky. Semiconductors have a complex behavior over a wide range of temperatures. It just so happens that they behave like useful semiconductors at temperatures that we're accustomed to on Earth.

EDIT: I should have said that conductivity is a function of the number of free charge carriers multiplied by their mobility. If the number of carriers increases faster than the decrease in mobility then conductivity can increase with temperature.

If a device's resistance goes down with temperature then we say that it has a negative temperature coefficient. This is not necessarily directly related to the conductivity of the device's material makeup. Other physical processes can affect the temperature coefficient.

Some things that have negative coefficients:
-light bulbs
-diodes
-bipolar junction transistors

Some things that have positive coefficients:
-metal wires
-Field effect transistors
 
Last edited:
  • #6
Incandescent bulb filaments have a positive temperature coefficient.

I believe a carbon rod will show a negative coefficient.
 
  • #7
Okefenokee said:
In metals the number of free charge carriers is constant. As the temperature goes up their mobility goes down. Because the carriers can't move as much there is higher resistance.
In semiconductors the number of charge carriers increase exponentially with temperature and this overrides the decrease in mobility.
It turns out that we're lucky. Semiconductors have a complex behavior over a wide range of temperatures. It just so happens that they behave like useful semiconductors at temperatures that we're accustomed to on Earth.
EDIT: I should have said that conductivity is a function of the number of free charge carriers multiplied by their mobility. If the number of carriers increases faster than the decrease in mobility then conductivity can increase with temperature.
If a device's resistance goes down with temperature then we say that it has a negative temperature coefficient. This is not necessarily directly related to the conductivity of the device's material makeup. Other physical processes can affect the temperature coefficient.
Some things that have negative coefficients:

-light bulbs

-diodes

-bipolar junction transistors
Some things that have positive coefficients:

-metal wires

-Field effect transistors
An Excellent reply, thanks ! :smile:
 

1. What is the effect of temperature on the conductivity of semiconductors?

The conductivity of semiconductors generally increases as temperature increases. This is because at higher temperatures, more electrons are able to break free from the valence band and become conductive, leading to a higher conductivity.

2. How does temperature affect the band gap of semiconductors?

As temperature increases, the band gap of semiconductors decreases. This is due to the increased movement of electrons, which can fill in the band gap and decrease its energy.

3. Can temperature changes cause permanent damage to semiconductors?

Yes, extreme temperature changes can cause permanent damage to semiconductors. This is because high temperatures can cause the atoms in the semiconductor to move and disrupt the crystal structure, leading to a loss of conductivity.

4. Are there any materials that are not affected by temperature changes when used as semiconductors?

No, all materials are affected to some degree by temperature changes when used as semiconductors. However, some materials may have a smaller change in conductivity compared to others.

5. Is there an optimal temperature for semiconductor conductivity?

Yes, there is an optimal temperature for semiconductor conductivity. This temperature is typically referred to as the "room temperature" and varies depending on the specific material being used. For example, silicon's optimal conductivity temperature is around 300 K (27 °C or 80 °F).

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