Influence of One Monolayer Thickness Variation in GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well upon Electrorefractive Index Change

Abstract

The five-layer asymmetric coupled quantum well (FACQW) is a new potential-tailored quantum well (QW) for ultrafast and low-voltage optical modulators and switches. First, the influence of one monolayer (ML) thickness variation of a single layer in the GaAs/AlGaAs FACQW on the electrorefractive index change Δn is theoretically studied. The thickness variation of two thicker GaAs layers has a considerable influence on Δn of the FACQW, while the thickness variation of thin AlAs and AlGaAs barrier layers has a smaller influence on Δn. The ratio of the thicknesses of the two GaAs well layers significantly affects the Δn characteristics of the FACQW. The change Δn does not vary appreciably as long as the ratio is kept constant. Second, the influence of the statistical fluctuation of the layer thickness by 1 ML in all of the layers on the Δn characteristics of the FACQW is also discussed. Even when Δn decreases with the increase of the occurrence probability of a layer being thicker or thinner by 1 ML, the FACQW still has a much larger Δn than conventional rectangular quantum wells do.

GaAs/AlGaAs Five-Layer Asymmetric Coupled Quantum Well (FACQW) Mach-Zehnder Modulator

“…This value is about half of the theoretically expected one. This discrepancy is probably due to thickness fluctuations of each layer [3].…”

Robust Coupled-Quantum-Well Structure for Use in Electrorefraction Modulators

“…The Lorentzian broadening function used in the model is described in [9], and the refractive-index changes are obtained using the Kramers-Kronig relation [1]. Our model is very similar to that used in [3] and [10] except that, in our model, the refractive-index changes are obtained for a whole period of a CQW structure and not only for the quantum-well layers. Fig.…”

“…In [3], it is shown that even such small thickness variations can significantly modify the distributions of wave functions in CQW structures and, in turn, influence the absorption spectra and the refractive-index changes in these structures. Similarly, the InAs mole fractions in the three barriers and each quantum well are changed by ±0.02.…”

“…Although, in ER modulators, the magnitude of the electric-field-induced refractive-index change achievable with CQW structures is similar to that achievable with SQW structures, CQW structures have the advantage that they exhibit no significant absorption modulation [1]. An additional advantage of CQW structures is that they provide the refractive-index change for considerably lower applied electric field F (leading to much lower drive voltages in devices using them) [1]- [3]. Until now, CQW structures have had the disadvantage that they are typically very sensitive to layer thickness and compositional variations [2], [3], [5].…”

“…An additional advantage of CQW structures is that they provide the refractive-index change for considerably lower applied electric field F (leading to much lower drive voltages in devices using them) [1]- [3]. Until now, CQW structures have had the disadvantage that they are typically very sensitive to layer thickness and compositional variations [2], [3], [5]. Here, we introduce an InGaAs/InAlAs CQW structure (structure #1) that is very robust to these layer thickness and compositional variations.…”