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International Journal of Modern Physics B

SEMICONDUCTOR EXCITON OPTICAL BISTABILITY AS INFLUENCED BY FREE CARRIERS

Nguyen Ba An, NGUYEN TRUNG DAN, Hoang Xuan Nguyen

Published Dec 30, 1993• 0 citations
Publisher

Abstract

Exciton density in an optically excited semiconductor is calculated as a function of pumping light intensity. In a certain domain in the detuning-intensity plane there may appear bistability of exciton density which is shown considerably influenced by the presence of free carriers. The carrier-induced effect manifests itself in the modification of phase diagrams leading to changes of the hysteresis loop size in both intensity-controlled and frequency-controlled bistabilities.

DOI
10.1142/s021797929300384x

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Exciton density in an optically excited semiconductor is calculated as a function of pumping light intensity. In a certain domain in the detuning-intensity plane there may appear bistability of exciton density which is shown considerably influenced by the presence of free carriers. The carrier-induced effect manifests itself in the modification of phase diagrams leading to changes of the hysteresis loop size in both intensity-controlled and frequency-controlled bistabilities.
A resonant monochromatic pump laser generates coherent excitons in an n-type-doped semiconductor. Both exciton–exciton and exciton–donor interactions come into play. The former interaction can give rise to the appearance of optical bistability, which is heavily influenced by the latter one. When optical bistability occurs at a fixed laser frequency both its holding intensity and hysteresis-loop size are shown to decrease with increasing donor concentration. Two possibilities are suggested for experimentally determinng one of the two parameters of the system, the exciton–donor coupling constant or the donor concentration if the other is known.
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The influence of the exciton and phonon spectra of layer semiconductors on the conditions of optical bistability (OB) realization in the exciton absorption region is investigated by means of the Green function method. Using the 2H-polytype PbI2 as an example, it has been found that an effective exciton scattering by an oscillation of the bending wave (BW) type leads to the short wave shift of the OB realization region, the decrease of its size, the widening of the OB observing temperature region and to the shift of the hysteresis loop in the direction of greater intensities, the decrease of its height and width. The possibility of observing the polarizable OB, connected with the direction of spreading and the insident light polarization dependence ofthe layer crystal exciton spectra is substantiated in this paper.