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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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