Temperature dependence of conduction, Metals, Phonon, semiconductors

1. Temperature dependence of
conduction

2. • electrical resistivity of metals increases with
temperature
• electrical resistivity of semi conductors
decrease with temperature

3. Metals

4. Phonon
• It is a description of an elementary vibrational
motion in which a lattice of atoms or
molecules uniformly oscillates at a single
frequency
• It is a normal mode of vibration according to
the classical mechanics

5. • The carrier (electrons in conduction band)
concentration changes very slowly with
temperature in metals
• So, can not consider its effect

6. • Atoms at absolute zero sit locked into their
lattice sites and don't move; they are frozen in
place
• But at any temperature warmer than absolute
zero, they bounce and wiggle around, causing
them to move slightly out of their lattice sites
• Called phonons

7. • These warmer atoms can begin to choke off
the channels through the lattice and to
interfere with electrons travelling through the
channels
• The warmer they are, the more they wiggle
and the more interfere
• Effectively, they start to block electrons on
their path, causing electrons to scatter

8. • The more motion of atoms, the more
interference
• The more phonons, the more interferences
• The more interference, slower the motion of
electrons
• Slower the motion of electrons, higher the
resistance

9. Semi conductors

10. • Carrier concentration increases as temperature goes up, due to
excitations across the band gap
• s= ne2t/m* (s=conduction)
• n is proportional to exp{-Eg/2kT}
• When T increases, term exp{-Eg/2kT} increases, so “n” increases (n
= # of charge carriers)
• t inversely proportional to T (when T increase, t decrease) so, s
decreases
• Two terms, opposite actions (n & t)
• But, exponential term dominates, increasing the conduction with
temperature
• So, mainly due to the increasing charge carriers
• T = temperature
• t = term in equation

11. THANK YOU