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Band Gap and Temperature
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),
á and â 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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Update: June 2012
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