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{\Large \bf Photoexcited transients in disordered semiconductors:}

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 {\Large \bf Kinematically induced {\boldmath $e$ -- $h$}  correlation}


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\noindent
{\large \it A. Kalvov\'{a}$\,^{\dagger}$,
B. Velick\'{y}$\,^{\ddagger}$} \\[5mm]
Institute of Physics, Academy of Sciences of the Czech
Republic,\\ Na Slovance 2, CZ-180 40 Praha 8, Czech Republic
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In the linear optical response of electrons in disordered semiconductors,
the correlation between the disorder in the valence and conduction bands
leads to a kinematical correlation between the electrons and the holes
which may be described, in analogy to the excitons, by an optical
vertex, or, equivalently, by the so-called Elliott factor entering
the Golden Rule matrix element.

This mechanism acts also in the non-linear regime, as induced by strong short optical
pulses. The new features as compared with the linear regime concern the correlation in
the electron and hole photoexcited populations, and also an additional transient light
induced band hybridization which modifies the full optical vertex.

For the initial time range when the disorder is still the dominant source of scattering,
the problem is conveniently treated by a
 direct solution of the Kadanoff--Baym (differential Dyson) equations for
 non-equilibrium Green functions. We concentrate to substitutional alloys and
 employ a self-consistent and conserving
single-site approximation for the self-energy.
}
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\b\b\b\n
$\,^{\dagger}$ {\tt kalvova@fzu.cz}\\
$\,^{\ddagger}$ Also: {\it Faculty of Mathematics and Physics, Charles University,
Prague}

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