Name: Lori B.
Status: student
Age: 18
Location: N/A
Country: N/A
Date: Saturday, May 25, 2002
Question:
Why does the conductivity of a semiconductor increase as
temperature increases?
Replies:
Lori,
A semiconductor is very different from a conductor. In fact, a
semiconductor is almost an insulator. The only difference between
semiconductor and insulator is energy levels. An insulator requires a great
deal of energy (maybe 10 eV) to break an electron free from an atom. A
semiconductor requires only about 1 eV to free an electron. A conductor has
some electrons free to move without any added energy.
When a semiconductor is extremely cold, almost all electrons are held
tightly by individual atoms. It is hard to make them move through the
material. When a semiconductor is heated, the heat energy knocks loose some
of the electrons. These loose electrons can move through the material
easily. The conductivity is higher. As more heat energy is added, more
electrons break away from individual atoms, becoming free to move through
the semiconductor. Higher temperature means greater conductivity. This is
NOT true for conductors. Conductors already have plenty of loose electrons.
Higher temperature tends to go into these loose electrons. Adding energy
makes the loose electrons move in less organized patterns. It becomes more
difficult to control the direction of the electrons. This makes the
conductor have less conductivity when temperature is higher.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
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