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In article <1992Apr7.160355.2968@darwin.ntu.edu.au>, 910436a@darwin.ntu.edu.au writes:
> Hot Phonon effect
> 
> Could anybody out there explain what a hot phonon effect is...what are the 
> chracteristics of a hot phonon...higher frequencies?
> 
> Ms Thila
> NTU
> Australia


"Hot" in hot phonons doesn't mean their energies are higher.
It just means the population of phonons is higher than that
governed by thermal equilibrium with the lattice temperature. Normally,
the occupation probability of a phonon mode is given by a Bose
distribution:

    N = 1/(exp(hw/kT)-1)

When we have more phonons than N (which is per unit cell here)
given by lattice temperature T, it means the phonon temperature 
is higher than T.

I don't know much about hot phonons other than in semiconductor
transport.  When we have high electron-phonon scattering rates, the 
probability of phonon emission is proportional to (N+1) as opposed
to N for the probability of phonon absorption. Hence as carriers
encounter phonon scattering processes, the phonon population rises
above the thermal equilibrium population and becomes hot. The 
implication is that the scattering rates are now increased, and more
phonons are produced. This is important since energy loss rates are
increased, especially in high field (hot electron) low dimensional devices. 
This is termed as the "hot phonon bottleneck". 

Hope this helps. 

Selim Guncer



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