Interface roughness and homogeneous linewidths in quantum wells and superlattices studied by resonant acoustic-phonon Raman scattering

We investigate the homogeneous linewidth of localized type-I excitons in type-II GaAs/AlAs superlattices. These localizing centers represent the intermediate case between quasi-two-dimensional (Q2D) and quasi-zero-dimensional localizations. The temperature dependence of the homogeneous linewidth is obtained with high precision from microphotoluminescence spectra. We confirm the reduced interaction of the excitons with their environment with decreasing dimensionality except for the coupling to LO phonons. The low-temperature limit for the linewidth of these localized excitons is five times smaller than that of Q2D excitons. The coefficient of exciton-acoustic phonon interaction is 5 ∼ 6 times smaller than that of Q2D excitons. An enhancement of the average exciton-LO phonon interaction by localization is found in our sample. But this interaction is very sensitive to the detailed structure of the localizing centers.The homogeneous linewidth of exciton luminescence is one of the most important features in excitonic dynamics in semiconductors, since it contains directly the information about the interactions between excitons and their environment. During the past two decades, the homogeneous linewidth of excitons in several kinds of quantum well and superlattice systems has been investigated extensively in both time and frequency domains. In the time domain, the excitonic dephasing time was measured from four-wave mixing (FWM), and then the homogeneous linewidth could be deduced. [1,2,3,4,5] In the frequency domain, the linewidth was measured directly from photoluminescence, [6,7,8,9] transmission, reflection or absorption [10,11] and Raman spectroscopy [12]. By modeling of experimental data, extensive information about interactions between excitons and acoustic phonons, LO phonons, free carriers and other excitons has been deduced. In these investigations, excitons are quasi-two-dimensional (Q2D). That is, they can move freely in the wells or are localized weakly with a localization energy of several meV. On the other side, the homogeneous linewidth of quasi-zero-dimensional (Q0D) excitons confined in quantum dots, with localization energy of several hundreds of meV, has been studied by spatially resolved measurements. [13,14] The comparison of these two kinds of excitons provides information about the influence of quantum confinement on the interactions between excitons and their environment.In this paper, we report investigations on homogeneous linewidth of single type-I localized excitons in GaAs/AlAs superlattices which have a global band alignment of type II. The localization energies of these centers are several tens of meV. Thus we can regard these localized excitons as intermediate in dimensionality between Q2D excitons and Q0D excitons. Furthermore, since the investigated centers are found in a small area (1 µm in diameter) of the same sample, we can rule out any artificial effects which come about when comparing different samples. This enables us to discuss the influence of localization on exciton-phonon ...

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“…It has been found before [2,12] and confirmed again recently [9] that γ AC of Q2D excitons is smaller than that in bulk GaAs [ Fig. 4(b)II] .…”

supporting

confidence: 72%

Effect of quantum confinement on exciton-phonon interactions

2002

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“…Most of the work in low-dimensional structures was dedicated to GaAs/Al x Ga 1Ϫx As quantum wells ͑QW's͒. 1,2 Full width at half maximum ͑FWHM͒ linewidth-broadening coefficients of ϳ4 eV/K for acoustic phonons and ϳ17 meV for optical phonons have been reported by Gammon, et al 2 using temperature-dependent exciton linewidth analysis on GaAs/Al 0.3 Ga 0. 7 As quantum wells of different thicknesses.…”

Section: Introductionmentioning

confidence: 99%

Well-width dependence of exciton-phonon scattering inInxGa1−xA
Borri
¹
,
Langbein
²
,
Hvam
³

et al. 1999
Phys. Rev. B

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The temperature and density dependencies of the exciton dephasing time in In 0.18 Ga 0.82 As/GaAs single quantum wells with different thicknesses have been measured by degenerate four-wave mixing. The excitonphonon scattering contribution to the dephasing is isolated by extrapolating the dephasing rate to zero-exciton density. From the temperature dependence of this rate we have deduced the linewidth broadening coefficients for acoustic and optical phonons. We find acoustic-phonon coefficients that increase from 1.6 to 3 eV/K when increasing the well width from 1 to 4 nm. This is in quantitative agreement with theoretical predictions when the spatial extension of the exciton wave function, strongly penetrating into the GaAs barrier in thin In x Ga 1Ϫx As quantum wells, is taken into account. The optical-phonon coefficient does not show a systematic dependence on well thickness, and is comparable with the value for bulk GaAs. ͓S0163-1829͑99͒02103-7͔

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“…This model is in line with experimental studies of thermal conductivity on AlAs/GaAs superlattices (SL) [16][17][18][19] . In particular, the application of this model to the available data leads to estimated interface roughnesses raging from ~2.5-5 Å, that correlate well with the expected 1-2 monolayer thickness for the transition layer in high-quality SLs 20 . These values for the roughnesses will therefore be chosen as the initial parameters for the QW in the laser prior to the degradation.…”

Section: Thermomechanical Modelingmentioning

confidence: 74%

Mechanisms driving the catastrophic optical damage in high-power laser diodes

Souto

Pura

Rodriguez

et al. 2015

High-Power Diode Laser Technology and Applications XIII

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The catastrophic optical damage (COD) of laser diodes consists of the sudden drop off of the optical power. COD is generally associated with a thermal runaway mechanism in which the active zone of the laser is molten in a positive feedback process. The full sequence of the degradation follows different phases: in the first phase, a weak zone of the laser is incubated and the temperature is locally increased there; when a critical temperature is reached the thermal runaway process takes place. Usually, the positive feedback leading to COD is circumscribed to the sequential enhancement of the optical absorption in a process driven by the increase of the temperature. However, the meaning of the critical temperature has not been unambiguously established. Herein, we will discuss about the critical temperature, and the physical mechanisms involved in this process. The influence of the progressive deterioration of the thermal conductivity of the laser structure as a result of the degradation during the laser operation will be addressed.

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Interface roughness and homogeneous linewidths in quantum wells and superlattices studied by resonant acoustic-phonon Raman scattering

Cited by 73 publications

References 38 publications

Effect of quantum confinement on exciton-phonon interactions

Effect of quantum confinement on exciton-phonon interactions

Well-width dependence of exciton-phonon scattering inInxGa1−xA
Borri
¹
,
Langbein
²
,
Hvam
³

et al. 1999
Phys. Rev. B

Mechanisms driving the catastrophic optical damage in high-power laser diodes

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Interface roughness and homogeneous linewidths in quantum wells and superlattices studied by resonant acoustic-phonon Raman scattering

Cited by 73 publications

References 38 publications

Effect of quantum confinement on exciton-phonon interactions

Effect of quantum confinement on exciton-phonon interactions

Well-width dependence of exciton-phonon scattering inInxGa1−xABorri1, Langbein2, Hvam3 et al. 1999Phys. Rev. B

Mechanisms driving the catastrophic optical damage in high-power laser diodes

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Well-width dependence of exciton-phonon scattering inInxGa1−xA
Borri
¹
,
Langbein
²
,
Hvam
³

et al. 1999
Phys. Rev. B