Carrier-induced changes in the phase resolved reflection of GaAs quantum wells

Nacke, Ch.; Stolz, H.; Manzke, G.; Henneberger, K.

doi:10.1140/epjb/e2002-00383-6

Cited by 10 publications

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“…In [30], we have demonstrated for a bulk semiconductor (ZnSe) that there is a pronounced influence of manybody effects on the chemical potentials even at higher excitation around the Mott transition. In this paper, we extend the earlier treatments for quantum wells [28,50] and include the renormalized carrier energies in the distributions f a,0 (e a k ) → f a (ε a k ). The change of chemical potentials µ a has to be determined for a given density n * a and temperature T of carriers from…”

Section: Ionization Equilibrium and Mott Transition-the Thermodynamicmentioning

confidence: 97%

“…The results of our theoretical concept were confirmed in [11], where it was shown how to circumvent the Shindo approximation in the derivation of the Bethe-Salpeter equation. The theoretical approach was successfully applied to the description of subtleties of polariton propagation in bulk semiconductors [25,27] and quantum wells [28]. However, the excitation in the experiments was rather low with densities of excited carriers well below the Mott transition.…”

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Mott transition of excitons in GaAs-GaAlAs quantum wells

2012

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We investigate the breakup of bound electron-hole pairs, known as Mott transition of excitons, in GaAs-GaAlAs quantum wells with increasing excitation, comparing two different theoretical approaches. Firstly, a thermodynamic approach is used to investigate the ionization equilibrium between electrons, holes and excitons, where the abrupt jump of the degree of ionization from 0 to 1 indicates the Mott density. It is extended to a self-consistent quasi-particle approximation (QPA) for the carrier properties, including dynamical screening of the Coulomb interaction between carriers. Secondly, a spectral approach based on the semiconductor Bloch equations within linear optical response is used, considering the quasi-particle (QP) properties of carriers and the dynamical screening between electron-hole pairs. While the first is effectively a one-particle approach, in the second the whole twoparticle spectrum is analyzed. Within the thermodynamic approach, a simple criterion for the Mott transition can be given: namely, if the sum of chemical potentials of carriers, reflecting the effective shrinkage of the band edge, crosses the exciton energy with increasing excitation. We demonstrate that this simple picture cannot be maintained in the two-particle approach. Here, a compact quantity, which describes the behavior of the band edge, does not exist. In fact, the behavior of the single states in the spectrum is generated by the interplay of dynamical screening in the interband self-energy and the effective interaction of the electron-hole pairs. Moreover, the band edge cannot be clearly resolved, 2 since it is merged with excited exciton states (e.g. 2s state), which show up only for densities far below the Mott density. Instead of a Mott density, only a density range can be given, where the Mott transition appears. We demonstrate that a small damping as a prerequisite for the validation of the extended QPA in the thermodynamic approach breaks down, analyzing (i) the dephasing processes with increasing excitation, (ii) the strong increase of the excitonic linewidth and (iii) comparing with the lifetime of carriers in the QP description. Contents

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Section: Ionization Equilibrium and Mott Transition-the Thermodynamicmentioning

confidence: 97%

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confidence: 99%

Mott transition of excitons in GaAs-GaAlAs quantum wells

2012

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Quantum kinetics and linear optical response of semiconductors

Manzke

Klähn

Henneberger

2003

phys. stat. sol. (c)

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We investigate the influence of quantum-kinetic effects on the linear optical properties of semiconductors near the band edge. These effects arise from a non-Markovian treatment of the scattering terms in the semiconductor Bloch equations and result in a strong dependence of many-body effects on the energy. We compare with results using a Markovian approximation of scattering, where the many-body effects do not depend on energy and correspond to those in a quasi-particle approximation. We demonstrate, that within such a treatment both linewidth and shift of the exciton are strongly overestimated. Finally, the Mott density of excitons differs by a factor of two. The importance of the quantum-kinetic approach for the explanation of polariton-pulse propagation experiments is shown.1 Introduction Ultra-short laser pulses in the order of a few femto-seconds have opened the possibility to study the temporal evolution of many-body effects in a laser excited semiconductor. This includes as well the generation and dephasing of the laser induced coherent polarization and the formation of carriers populations and their relaxation into quasi-equilibrium. A new concept for the theoretical description of the coupled kinetics of coherent polarization and carriers had to be developed in order to explain the experimental findings. The main point in this quantum-kinetic description (for a review see [1][2][3]) is the non-Markovian treatment of scattering between carriers, polarization and elementary excitations, as plasmons and phonons. Evidence for quantum-kinetic effects both in Coulomb and LO-phonon scattering was found in several experiments, investigating the decay of the four-wave mixing signal [4][5][6].However, these time resolved investigations give no spectral information and cannot be performed for lower excitations, where excitonic effects become important, in particular the limit of linear response cannot be achieved. In this paper we focus on this limit. We consider a pump-probe experiment, where carriers are pumped and relaxed into quasi-equilibrium, and the optical response is detected by a weak probe pulse. We demonstrate, that (i) quantum-kinetic effects in the scattering of the probe-induced polarization with the elementary excitations (plasmons, LO-phonons) in the electron-hole plasma play an important role, even at lowest excitations, and (ii) give new insight and better understanding of these many-body effects from the viewpoint of Green's function description for the excited semiconductor.

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Phase resolved polariton interferences in a ZnSe‐ZnSSe heterostructure

Seemann

Kieseling

Stolz

et al. 2006

Phys. Status Solidi (c)

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PACS 71. 71.36.+c, 71.45.Gm, 78.20.Bh, 78.67.De Applying the method of spectral interferometry we analyze amplitude and phase of reflected light at a ZnSe-ZnSxSe1−x heterostructure. Beside the 1s-heavy hole (hh), the 2s-heavy hole and the 1s-light hole (lh) excitons a series of peaks are found in the amplitude caused by interfering polariton modes propagating through the ZnSe layer. The phase shows pronounced changes at the corresponding energies. A strong increase by 2π appears for lower hh-and lh-polariton modes. The behavior can be explained considering spatial dispersion in the dielectric model, Pekar's additional boundary conditions for the polariton propagation and a penetration of the excitonic polarization into the cladding layers.

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Carrier-induced changes in the phase resolved reflection of GaAs quantum wells

Cited by 10 publications

References 1 publication

Mott transition of excitons in GaAs-GaAlAs quantum wells

Mott transition of excitons in GaAs-GaAlAs quantum wells

Quantum kinetics and linear optical response of semiconductors

Phase resolved polariton interferences in a ZnSe‐ZnSSe heterostructure

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