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Applied Physics Letters

Excitonic absorption saturation in ternary alloy Al x Ga1− x As/AlAs multiple-quantum-well structures

Maurizio Dabbicco, R. Cingolani, Michele Ferrara, Klaus Ploog, A. Fisher

Published Sep 16, 1991• 5 citations
Publisher

Abstract

The bleaching of the n=1 and n=2 heavy-hole exciton absorption has been observed at room temperature in ternary alloy Al0.37Ga0.63As/AlAs multiple-quantum-well structures by nanoseconds pump-and-probe spectroscopy. The relative variation of the absorption coefficient [(−Δα)/α0] are about 15% and 8%, respectively. The nonlinear absorption coefficient (α2) and the nonlinear absorption cross section has been deduced. The value of the saturation density deduced from our spectra is in good agreement with the theoretical predictions. The influence of the staggered band alignment on the observed process is also discussed.

DOI
10.1063/1.105299

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Journal of the Physical Society of Japan•Jan 15, 1986•24 citations
The bleaching of the n=1 and n=2 heavy-hole exciton absorption has been observed at room temperature in ternary alloy Al0.37Ga0.63As/AlAs multiple-quantum-well structures by nanoseconds pump-and-probe spectroscopy. The relative variation of the absorption coefficient [(−Δα)/α0] are about 15% and 8%, respectively. The nonlinear absorption coefficient (α2) and the nonlinear absorption cross section has been deduced. The value of the saturation density deduced from our spectra is in good agreement with the theoretical predictions. The influence of the staggered band alignment on the observed process is also discussed.
This report describes progress in measuring and modeling the nonlinear optical properties of and picosecond carrier dynamics in bulk ternary alloys and multiple quantum wells (MQWs). Studies of the bulk alloy Al(x)Ga(1-x)As have been produced the first experimental isolation of the electron exchange energy in a dense electron-hole plasma, and the observation of enhanced band-gap renormalization as a consequence of alloy disorder, stimulated emission from the indirect gap for x-values as large as 0.52, and large optical nonlinearities from band filling, band-gap renormalization, and screening of the excitonic continuum states. The latter appear promising for room temperature absorptive and dispersive optical bistability. An exact theory of the influence of an intense radiation field on the excitonic energy levels of a MQW has been developed and has led to the prediction of two-wave mixing gain. Keywords: Nonlinear optics; Ultrafast phenomena; Multiple quantum wells; Band gap renormalization; Alloy disorder; Optical bistability.
We present here the first observation of quasisteady state optical nonlinearities in the absorption and photoluminescence (PL) spectra of GaAs/AlAs type II heterostructures. Using pump-probe spectroscopy we observed deep modulation, ΔT ~ 0.5 (Δα =−50,000 cm−1), due to a >40-meV blue shift and bleaching of the heavy hole exciton absorption peak. In addition, a blue shift of up to ~10 meV of the indirect PL line is observed with increasing PL excitation intensity. These nonlinearities are understood in terms of spatially separated layers of electrons and holes that are produced by the optical excitation process.
Abstract : In this paper we describe a detailed study of the complete time evolution of the optical nonlinearities of type-11 GaAs/AlAs quantum wells using nanosecond and femtosecond pump/probe spectroscopy. We explain these nonlinearities by solving the generalized Wannier equation for the case of a type-II quantum-well structure. In contrast to the usual type-I quantum-wells, we observe different shifts and saturations of light- and heavy-hole excitons as well as the absence of gain. The dominant effects are a blue shift and saturation of the heavy-hole (HH) exciton.
The saturation behavior of the nonlinear index δnNL in the band tail of GaAs/AlGaAs multiple quantum wells is experimentally studied in quasi-steady state and in a low absorption region (below 300 cm−1), where dispersive optical bistability is observed. Measurements at different detunings from the exciton resonance allow us to study the absorption dependence of the saturation parameters. The saturation intensity IS is found inversely proportional to the linear absorption coefficient, while the saturating nonlinear index δnS is approximately constant. This evidences that the nonlinear index saturation is due to a saturation of the carrier density versus light intensity, due to the saturation of the band tail absorption itself.