Use band theory to explain the changes in the resistance of an intrinsic semiconductor as temper changes.
At low temperatures(0K), the conduction band is empty while the valence band if filled. As temperature increases, the electrons gain energy to go into the conduction band and leave positive holes in the valence band. The lattice vibration increase, but it is outweighed by increase in charge carriers. Hence the current increases and resistance decreases.
KG
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