## Acoustoelectric effect in semiconductors / by S. B. Joshi

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##### Author

Joshi, S. B.

##### Subject

SemiconductorsMomentum and energy transfer

Acoustical scattering

Optical non-polar scattering

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The possibility of electron temperature decreasing below
the lattice temperature in the presence of an external electric field
(electron cooling) has been pointed out by Paranjape and Ambrose (1964).
In the present works we show that under suitable conditions an external
sound wave may produce the phenomenon of electron cooling in a semiconductor.
We have shown that a decrease in electron temperature may occur
when (1) the electrons are predominantly scattered by optical polar or
non-polar optical modes of the lattice vibrations and (2) when the incident
sound wave energy flux is greater than a certain critical value
WQ (which depends on the type of semiconductor). Chapter I consists of
a description of the model and a brief outline,of the calculations. In
Chapter II, using a displaced Maxwellian function, we have calculated
the rates of energy and momentum transfer from the electrons to the lattice
for acoustical, optical polar and non-polar optical types of scattering.
The rates of energy and momentum transfer from the sound wave
to the electrons are calculated in Chapter II, Section (2.b,l). Using
these rates in conservation conditions (1.11) and (1.12), we obtain the
expression for the electron temperature T as a function of the energy
flux W (Eqn. (3.6)). Inequality conditions (3.7) and (3.8) are the main
results of our calculations. Condition (3.7) is equivalent to the electron
cooling condition obtained by Paranjape and de Alba (1965) in the
case of an electric field, while (3.8) gives the minimum sound wave energy
flux P/Q required to produce electron cooling. In non-polar and polar substances, the required predominance of optical scattering over
acoustical scattering is expressed by the ratios (see document for formula)
in Eqns. (3.24) and (3.30), respectively. In Sections (S.b.l) and
(3.b.2), v/e have obtained the expressions for the sound absorption
coefficient a and acoustoelectric current in terms of the energy
flux W.