Influence of exciton localization on recombination line shapes:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">In</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi mathvaria

Schnabel, R.; Zimmermann, R.; Bimberg, D.; Nickel, H.; Lösch, R.; Schlapp, W.

doi:10.1103/physrevb.46.9873

Cited by 94 publications

(50 citation statements)

References 22 publications

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“…1 are density dependent and vary from 13.5 K at the lowest density to 20.7 K at the highest density. Even at later times, they never reach the lattice value of 4 K [15,16,17]; the lowest temperature measured was 10.5±0.5 K (2.8 ns after excitation for an initial carrier density of n eh = 2.9 × 10 8 cm −2 ).For a lattice temperature of 50 K, our measurements show identical lattice and carrier temperatures after 0.1 ns.To compare many spectra as a function of density and temperature, it is convenient to define a single parameter β to characterize each spectrum. In thermodynamic equilibrium, one expects the PL to be proportional to the absorption coefficient α times a Bose distribu-…”

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confidence: 51%

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confidence: 90%

“…We then define β = I PL (1s)/I eq PL (1s) as in [17]. I eq PL (hω) is found by multiplying the measured nonlinear α by a Boltzmann factor to approximate the Bose function, using the temperature extracted from the measured continuum emission and normalizing it to agree with the measured continuum PL; see dashed lines in Fig.…”

Section: Introductionmentioning

confidence: 99%

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Excitonic Photoluminescence in Semiconductor Quantum Wells: Plasma versus Excitons

et al. 2004

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Time-resolved photoluminescence spectra after nonresonant excitation show a distinct 1s resonance, independent of the existence of bound excitons. A microscopic analysis identifies excitonic and electron-hole plasma contributions. For low temperatures and low densities the excitonic emission is extremely sensitive to even minute optically active exciton populations making it possible to extract a phase diagram for incoherent excitonic populations. 1 For a long time, photoluminescence (PL) at the spectral position of the 1s exciton resonance has been considered as evidence for the existence of excitons. The rise of the 1s PL after nonresonant excitation of a semiconductor was interpreted as buildup of an excitonic population [1,2,3,4,5,6], and the PL decay was used to describe exciton recombination [7,8]. However, recently a microscopic theory predicted that PL at the 1s resonance can also originate from correlated plasma emission [9]. Accordingly, PL at the spectral position of the 1s resonance would not prove the existence of excitons, and previous interpretations may be in question. Indeed, in nonresonantly excited time resolved PL measurements the 1s resonance is developed on a sub-ps timescale at 100 K [10], much faster than any expected exciton formation time.Information about exciton formation can be gained by performing THz experiments [11].However, currently the THz results are inconclusive: Kaindl et al. [12] observed the buildup of the induced absorption corresponding to the excitonic 1s to 2p transition showing excitonic populations with formation times on a rather slow timescale of 100's of ps to ns. They claim to observe a nearly completely excitonic system 1 ns after excitation, while Chari et al. [13] only plasma contributions. Also, THz absorption is sensitive to both dark and bright excitons, and cannot answer if and how excitonic populations influence the PL.Here we address the following questions. Is the 1s PL ever dominated by plasma emission?If so, is it always dominated by plasma emission, i.e. what can we learn about excitonic populations from the 1s PL and nonlinear absorption?After ps continuum excitation, time resolved PL and corresponding probe absorption measurements are performed under identical conditions on a ns timescale. The sample (DBR42) consists of 20 MBE-grown 8 nm In 0.06 Ga 0.94 As quantum wells with 130 nm GaAs barriers; both sides are anti-reflection coated. This indium concentration places the 1s exciton resonance at 1.471 eV at 4 K, avoiding absorption in the bulk GaAs substrate that leads to impurity emission at 1.492 eV from unintentional carbon in the substrate. The results, checked on several other samples including a sample grown in a different MBE system, are insensitive to exciton linewidths or to interfacial or alloy disorder. Single-quantum-well data were noisier but exhibited a similar behavior, excluding significant radiative coupling effects.We excite nonresonantly 13.2 meV above the 1s resonance, into the heavy-hole continuum but below the light-h...

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Excitonic Photoluminescence in Semiconductor Quantum Wells: Plasma versus Excitons

et al. 2004

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“…14,16 In reasonable good quality QWs the amplitude of the confinement energy fluctuations are typically one order of magnitude smaller than the binding energy of the 1S exciton. 3 In this limit the relative exciton motion described by the effective wave function 1S ( eh ) may be assumed undistorted by disorder. Disorder affects significantly only the center of mass ͑COM͒ motion through an effective potential V(r).…”

Section: ͓S0003-6951͑00͒04044-4͔mentioning

confidence: 99%

Imaging spectroscopy of quantum wells with interfacial fluctuations: A theoretical description

Stefano

Savasta

Martino

et al. 2000

Applied Physics Letters

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We present a theoretical approach for the simulation of scanning local optical spectroscopy in disordered quantum wells ͑QWs͒. After a single realization of the disorder potential, we calculate spectra on a mesh of points on the QW plane, thus obtaining a three-dimensional matrix of data from which we construct two-dimensional spectroscopic images of excitons laterally localized at interface fluctuations. Our simulations are in close agreement with the experimental findings, and contribute to the interpretation of spatially resolved spectra in QWs. ͓S0003-6951͑00͒04044-4͔Optoelectronics based on very thin active layers of semiconductor, such as quantum wells ͑QWs͒ are now currently used for many commercial applications. The performance of such devices is influenced by interface roughness, impurity concentration, and alloy homogeneity of the QW. Optical spectra of QWs yield valuable information on the quality of the interfaces and the growth process. 1,2 Disorder in a QW results in an effective two dimensional ͑2D͒ potential spatially correlated which tend to localize the center of mass of the exciton. This image was put forth on the basis of detailed theoretical simulations 3-5 and of observed homogeneous and inhomogeneous linewidths. 1 Macroscopic optical probes 1,2 have proven to be powerful techniques for probing localized excitons and hence interface fluctuations of quantum structures, however they perform a spatial averaging of the spectral signal, providing information at best on an inhomogeneous ensemble of quasi-0D ͑zero-dimensional͒ localized exciton states. Recently, techniques of very high spatial resolution optical spectroscopy allowed several groups to study the individual exciton eigenstates laterally localized at interface fluctuations. [6][7][8][9][10][11] Stimulated by the relevance of the experimental results cited above, theoretical approaches modeling the interaction of quantum structures with highly inhomogeneous light fields have been recently presented. 5,[12][13][14][15][16] In this letter, we present theoretical results for scanning local optical spectroscopy in QWs obtained after the simulation of a disorder potential with prescribed statistical properties. We will consider an input light field with a given profile g centered around the beam position R. In experiments done by both illuminating and collecting with the same tip ͑reflec-tion mode͒, the relevant optical signal that can be detected by a general near-field setup is proportional to 17 S ϭ͐dz drP*(r,z)•E(r,z), where P(r,z, ) is the macroscopic polarization of the sample induced by the electromagnetic field E(r,z, ). We have indicated with rϵ(x,y) the projection of the position vector on the plane of the QW and with z the coordinate along the growth direction. Via interferometric techniques it is possible in principle to measure both the phase and the amplitude of S, thus obtaining information on the local complex susceptibility of a sample. 18 Following the general linear response theory, the linear macroscopic polarization P(r...

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“…In systems with extended wave-functions such as semiconductors nonlocality plays a relevant role [13,14]. In reasonable good quality QWs the amplitude of the confinement energy fluctuations are typically one order of magnitude smaller than the binding energy of the 1S exciton [15]. In this limit, the susceptibility tensor is given by [13,14] $ cðr; r 0 ; z; z 0 Þ ¼ $ cðr; r 0 Þ qðzÞ qðz 0 Þ, where qðzÞ is the product of the electron and hole envelope functions along the growth axis and…”

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Imaging the wavefunctions of a quantum dot system

Stefano

Savasta

Martino

et al. 2003

phys. stat. sol. (c)

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We describe how, exploiting the current scanning near-field optical techniques, it is possible to map phase and modulus of the wavefunctions of a quantum dot system. In particular we propose an experimental setup based on an interferometric technique able to measure simultaneously modulus and phase of wavefunctions. We present numerical calculations simulating the measurements on dots arising from interface fluctuations of GaAs quantum wells.Recent measurements based on spatially-resolved photoluminescence provided direct information on the spatial and energy distribution of light emitting nanometric centers [1-5] of semiconductor quantum structures. However spatially resolved photoluminescence provides only an indirect probe of the electronic structure. Recently Guest et al. [6] presented a technique that combines coherent nonlinear spectroscopy with near-field microscopy providing a means to map the local optical density of states (LDOS) of the system in analogy to scanning tunneling microscopy measurements [7,8] that mapped out the electronic LDOS. Coherent optical control and optical manipulation play a fundamental role in the functioning of proposed devices. Proposed device architectures ultimately rely on tuning the interactions between individual electronic states, that requires direct access to eigenstates with spectral and spatial selectivity [9].Here we show that it is possible to go beyond LDOS measurements, thus achieving the ultimate characterization tool for a mesoscopic quantum system. We propose a near-field optical technique able to map modulus and phase of the wavefunctions of a quantum dot system. Recently Phillips et al. [10] advanced from the more traditional use of the scanning near-field optical microscope (SNOM) for electromagnetic imaging measuring both the light intensity and phase in the near field. We show that, when the probed region of the sample is comparable or lower than the spatial variations of the excitonic wavefunction, the phase and modulus of the collected light can be related to the phase and modulus of the excitonic wavefunction. In order to simulate the measurements, we consider a system of quantum dots arising from interface fluctuations of GaAs quantum wells. The numerical calculations consist of two steps in close analogy with real experiments. The first step is the growth of the sample corresponding to a single realization of disorder with given statistical properties. Once the sample has been obtained, we calculate the SNOM signal acquired in collection mode. In collectionmode SNOM, the sample is usually illuminated by a laser focussed onto the sample surface. An optical fiber (waveguide) with a sharp tip is scanned along the sample at subwavelength distance (in the near-field region), and the signal delivered by an optical detector at the end of the fiber is recordered. In experiments done in collection mode the relevant optical field that can be detected by a

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Influence of exciton localization on recombination line shapes:InxGa1

Cited by 94 publications

References 22 publications

Excitonic Photoluminescence in Semiconductor Quantum Wells: Plasma versus Excitons

Excitonic Photoluminescence in Semiconductor Quantum Wells: Plasma versus Excitons

Imaging spectroscopy of quantum wells with interfacial fluctuations: A theoretical description

Imaging the wavefunctions of a quantum dot system

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