how temperature effects on metals and semiconductor resistance?
Answers
It seems to me that there are two separate processes that occur when the temperature rises.
The atoms move further apart (on average) because they are vibrating with greater amplitudes. This leads to less overlap of orbitals and a reduced number of free electrons.
The electrons have more energy and this increases the liklihood of the electrons being able to move up into the conduction band.
In metals, the outer electrons are in the conduction band, the inner electrons are nowhere near. Raising the temperature reduces the number of free electrons because of the greater separation between atoms. Inner electrons do not get anywhere near enougfh energy to become mobile. Net effect- conductivity decreases ( resisatnce increases).
In semiconductors- the separation of atoms will still tend to reduce the degree of orbital overlap and increase the eenrgy gap between the valence electons and the conduction band. At the same time the increae in the energy ofthe eelectromns due to the raised thermal energy has agreater impact due to the Boltzmann Factor ( e^(-E/kT)). Increasing T means that a greater fraction of the outer electrons can move to the conduction band. More charge carriers so greater conductivity (less resisatnce).
Both effects apply in both materials. The magnitude of the effects varies.