In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.

Linear and nonlinear optical properties of semiconductor quantum wells

Quasi-periodic structure can be introduced into nonlinear optical materials such as LiTaO3 crystals. Such structures were used for quasi–phase-matching second-harmonic generation. These materials are now shown to be able to couple second-harmonic generation and sum-frequency generation through quasi–phase-matching. The approach led to a direct third-harmonic generation with high efficiency through a coupled parametric process. The result verifies that high-order harmonics may be generated in a quadric nonlinear medium by a number of quasi–phase-matching processes, and therefore, exhibits a possible important application of quasi-periodic structure materials in nonlinear optics.

http://science.sciencemag.org/content/sci/278/5339/843.full.pdf

Quasi-phase-matched third-harmonic generation in a quasi-periodic optical superlattice

Wave transmission in nonlinear lattices

In this work we consider the role of aperiodic order in different domains of science and technology from an interdisciplinary approach. To start with, we introduce some general classification schemes for aperiodic arrangements of matter. Afterwards, we review the main physical properties and possible applications of quasiperiodic crystals. Several conceptual links between quasiperiodic crystals and the hierarchical structure of biopolymers are then discussed in connection with the charge transfer properties of both biological and synthetic DNA chains. The widespread presence of Fibonacci numbers and the golden mean in different physical contexts is also discussed. Promising technological applications of aperiodic systems are finally reviewed by considering both current and potential applications. In particular, we analyse the capability of exploiting aperiodic order in the design of novel devices based on semiconductor heterostructures and dielectric multilayers.

https://iopscience.iop.org/article/10.1088/0034-4885/69/2/R03/pdf

The role of aperiodic order in science and technology

The authors studied the effects of changing the barrier design of GaAs-Al/sub x/Ga/sub 1-x/As quantum wells on the electroabsorption, exciton saturation, and carrier sweep-out times. Five samples with x values ranging from 0.2 to 0.4 and barrier thicknesses from 35 to 95 AA were studied. Within this range, the authors find that the electroabsorption is not very sensitive to the barrier thickness, but that the ionization field of the excitons approximately doubles for an increase of x from 0.2 to 0.4. The samples with high, thick barriers have lower internal quantum efficiencies than those with low, thin barriers. It was found that the exciton saturation intensity increases with increasing applied field, and decreasing barrier thickness or height. Time-resolved electroabsorption measurements confirm the variation in sweep-out rates between samples, and indicate that the escape mechanism at low field is probably a thermally-assisted tunneling process. >

Quantum well carrier sweep out: relation to electroabsorption and exciton saturation

We report the first realization of a quasiperiodic (incommensurate) superlattice. The sample, grown by molecular-beam epitaxy, consists of alternating layers of GaAs and AlAs to form a Fibonacci sequence in which the ratio of incommensurate periods is equal to the golden mean $\ensuremath{\tau}$. X-ray and Raman scattering measurements are presented that reveal some of the unique properties of these novel structures.

Quasiperiodic GaAs-AlAs Heterostructures

Raman scattering by acoustic phonons in Fibonacci GaAs-AlAs superlattices.

Raman scattering by acoustic phonons and structural properties of fibonacci, thue-morse and random superlattices

Photoluminescence linewidths and transition energies have been measured in GaAs-AlGaAs multiple quantum wells with large (equal to or greater than 160 A) barrier widths as a function of applied transverse electric field. The experimental data agree well with values calculated by using a recently developed variational technique. It is apparent that heterointerface roughness is the dominant line broadening mechanism. The emission intensity decreases rapidly with field, principally due to carrier tunneling at high fields. At 80 kV/cm a shift of 20 meV in the emission energy is observed.

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Field‐dependent linewidths and photoluminescence energies in GaAs‐AlGaAs multiquantum well modulators

The electric field dependence of ${c}_{0}$\ensuremath{\rightarrow}${c}_{1}$ intersubband transitions of photoexcited electrons has been studied in a 264-A\r{} GaAs-${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As quantum-well structure using Raman spectroscopy. Experimental results for the Stark shifts are in very good agreement with theoretical predictions. The intensity of the intersubband peak increases rapidly with applied field due to parity mixing. In contrast to the enhanced broadening shown by exciton resonances, the width of ${c}_{0}$\ensuremath{\rightarrow}${c}_{1}$ is nearly independent of the field. This feature is attributed to effects of structural disorder.

K. Bajema

Papers

Quasiperiodic GaAs-AlAs Heterostructures

Raman scattering by acoustic phonons in Fibonacci GaAs-AlAs superlattices.

Raman scattering by acoustic phonons and structural properties of fibonacci, thue-morse and random superlattices

Field‐dependent linewidths and photoluminescence energies in GaAs‐AlGaAs multiquantum well modulators

Stark effect in GaAs- Al x Ga 1 − x As quantum wells: Light scattering by intersubband transitions