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Name: James
Status: student
Grade: n/a
Country: Brazil
Date: Fall 2010



Question:
Is possible the band gap of a semiconductor vary as function of the temperature? If it is possible, how does it work?


Replies:
James

A good explanation of the band gap of a semiconductor is provided at this URL:

http://en.wikipedia.org/wiki/Band_gap

As Wikipedia states (with a little bit of editing for clarity): In solid state physics, a band gap is an energy range in a solid where no electron states can exist. In a graph of the electronic band structure of a solid, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band which is found in insulators and semiconductors. It is the amount of energy required to free an outer shell (valence) electron from its orbit about the nucleus to become a mobile charge carrier, able to move freely within the solid material as a (conduction) electron. In conductors, the two bands often overlap, so they may not have a band gap.

Further down in the Wikipedia article is this: "The band gap energy of semiconductors tends to decrease with increasing temperature" And then the article goes on to present the mathematical equations.

So, it is possible for the band gap of a semiconductor to vary as a function of temperature. The Wikipedia article explains how it works. Look for this part of the article:

"The relationship between band gap energy and temperature can be described by Varshni's empirical expression,

E(T) = Eg(0) - (alpha x T^2) / (T + Beta), where Eg(0),

รก and รข are material constants."

Sincere regards,
Mike Stewart


James,

Typically changes in the temperature of a material will result in variation of its lattice constant (i.e. thermal expansion or contraction). This parameter is crucial in determining the electronic structure of a substance, and hence its band gap. I guess maybe you are thinking of the experiment where an LED is placed in liquid nitrogen?

- Isaac Tamblyn



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