Phase memory of the electronic polarization in transient nonlinear optical spectra of gallium arsenide at 2 eV

Bohne, Gotthold; Sure, Thomas; Ulbrich, R. G.; Schäfer, Wilfried

doi:10.1103/physrevb.41.7549

Cited by 33 publications

(9 citation statements)

References 41 publications

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“…While the absolute energy of the 1s exciton stays nearly unchanged in bulk samples over a wide range of carrier densities its oscillator strength disappears due to band gap shrinkage. This was proved in many experiments [1][2][3] and explained qualitatively by strong compensation of gap shrinkage and weakening of the Coulomb interaction due to screening inspecting the effective Wannier equation of an exciton embedded in a thermal plasma [4][5][6][7]. The situation is rather different in quantum wells, where a blueshift of the exciton with increasing density was observed [8,9].…”

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confidence: 84%

Density Dependence of the Exciton Energy in Semiconductors

et al. 1998

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We investigate both experimentally and theoretically the excitonic absorption in ZnSe in a temperature range between 2 and 60 K with increasing densities of carriers. For higher temperatures a weak redshift of the exciton resonance is found which turns into a blueshift for lower temperatures. While the widely used simplified treatment of the scattering processes within a static screening approximation fails completely to describe this thermally induced crossover, it can be explained by the interplay between Coulomb-Hartree-Fock renormalizations and carrier-carrier and carrier-polarization scattering including the dynamical screening. [S0031-9007 (98)06251-6] PACS numbers: 71.35.CcThe nonlinear behavior of the excitonic absorption is one of the most investigated manifestations of many-particle effects in a highly excited narrow-gap semiconductor. For instance the Mott transition observed for increasing excitation densities is well understood as a consequence of screening of the Coulomb interaction between charge carriers. While the absolute energy of the 1s exciton stays nearly unchanged in bulk samples over a wide range of carrier densities its oscillator strength disappears due to band gap shrinkage. This was proved in many experiments [1-3] and explained qualitatively by strong compensation of gap shrinkage and weakening of the Coulomb interaction due to screening inspecting the effective Wannier equation of an exciton embedded in a thermal plasma [4][5][6][7]. The situation is rather different in quantum wells, where a blueshift of the exciton with increasing density was observed [8,9]. Qualitatively, this behavior is caused by the reduced dimensionality, which leads to a reduction of the Coulomb interaction between carriers [10] as was confirmed by more elaborated calculations for a dense exciton gas model [11]. In GaAs͞Ga 12x Al x As quantum wells the transition from quasi-2D to 3D behavior was found to occur at well widths of 19 nm, i.e., already at less than two exciton Bohr radii [9,12].The present situation is characterized by two aspects. At first, recent experimental results shed new light on the commonly accepted view that the excitonic resonance stays nearly constant in a large density region. In GaAs͞Ga 12x Al x As quantum wells of 21 nm width the exciton shift was found to change from a weak blueshift under resonant excitation to a weak redshift under nonresonant excitation [13]. Also in bulk ZnSe, where the influence of many-particle effects on the exciton can be observed much more pronounced than in the III-V semiconductors (GaAs) due to the larger exciton binding energy, a weak blueshift of the exciton [14] at resonant excitation and low temperatures has been found recently. Second, substantial progress has been achieved during the last few years to find out which many-particle effects have to be included into the semiconductor-Bloch equations (SBE) in order to describe the nonlinear absorption features of laser pulses. In particular, inclusion of carrier-polarization scattering processes was sh...

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confidence: 84%

Density Dependence of the Exciton Energy in Semiconductors

et al. 1998

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“…A straightforward extension introduces the screening of the interaction, Together with corresponding exchange diagrams (3.1) leads to the well-known Born approximation for the description of scattering processes. Within the Marcovian approximation the corresponding contributions to relaxation and dephasing have been evaluated earlier [6]. In general the propagator of the longitudinal field D(21') describes the excitation of the collective modes of the system causing relaxation and dephasing of the electronic states.…”

Section: Self-energiesmentioning

confidence: 99%

“…An improvement in comparison with the phenomenological time constant is a Marcovian approximation for the scattering contributions in the kinetic equations [6]. This approach is based on the assumption of the separability of microscopic (difference variables) and macroscopic (centre-of-mass variables) time scales and leads to the characteristic feature that scattering processes depend instantaneously on one-particle distribution and polarization functions.…”

Section: Introductionmentioning

confidence: 99%

Real Time Approach to Relaxation and Dephasing Processes in Semiconductors

Hartmann

Schäfer

1992

Physica Status Solidi (b)

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Starting from the kinetic equations for the nonequilibrium Green's functions, a practical method is proposed which allows to solve the set of equations for the two-time propagators numerically. In contrast to the usual semiconductor Bloch equations with phenomenological damping relaxation and dephasing processes are treated microscopically for the case of coupling to a bath of LO-phonons. Beside a standard approximation for the treatment of LO-phonon scattering, no further approximations are performed. For the low-density limit we compare exact results with approximate treatments, as the Marcovian and non-Marcovian approximations resulting from a density matrix approach. First results concerning nonlinear optical properties are presented.

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“…Different models of screening were discussed in this context, in particular the effect of dynamical screening [4][5][6], which requires the use of the so-called Shindoapproximation in the BSE. The results turn out to be restricted to lower carrier densities, since divergencies appear if the sum of the carrier distribution functions of electrons and holes approaches unity.…”

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confidence: 99%

“…mn; q ðt; t 0 Þ in the scattering integral (4) depends on two times, Eq. (1) together with the corresponding equations for the carrier distributions is not a closed set of equations for the two-band density matrix (5). In order to get closed equations, one has to apply an appropriate ansatz to reduce G mn; q ðt; t 0 Þ to f ?…”

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confidence: 99%

Quantum-Kinetic Effects in the Linear Optical Response of GaAs Quantum Wells

Manzke

Henneberger

2002

phys. stat. sol. (b)

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We investigate the influence of quantum-kinetic effects on the linear optical properties of GaAs quantum wells. We demonstrate that these effects arising from a non-Markovian treatment of the scattering terms in the semiconductor Bloch equations lead in the linear optical response to a dependence of many-body effects on the energy. A non-Markovian treatment of scattering terms corresponds to a quasi-particle approximation of many-body effects, where they are independent of the energy. We compare both treatments and show that the quasi-particle treatment (i) overestimates both energy shift and broadening of the exciton resonance and (ii) fails to give quantitative description of the excitonic Mott transition with increasing excitation.Introduction The dielectric response of semiconductors for frequencies close to the fundamental gap is dominated by electron-hole correlations. To lowest order in density, electrons and holes form excitonic pair states. With increasing excitation the dielectric polarization is influenced by many-body effects between excited carriers and the exciton resonance becomes more and more broadened. The Mott transition of excitons as a consequence of screening of the Coulomb interaction between carriers is well understood. The two basic effects of band gap shrinkage and weakening of the Coulomb interaction cancel nearly complete, leading to a widely unchanged exciton position, while the sharp line feature is broadened and disappears in the shrinking band edge. This was first shown by Zimmermann et al.[1] reducing the Bethe-Salpeter Equation (BSE) for an electron-hole pair in an equilibrium electron-hole plasma to an effective wave equation of the Wannier exciton, and verified in several experiments (see Ref. [2] for GaAs).The basic idea of [1] was developed further in a series of papers (for a review see [3]), directly solving the BSE for the optical polarization, and giving experimental evidence. Different models of screening were discussed in this context, in particular the effect of dynamical screening [4][5][6], which requires the use of the so-called Shindoapproximation in the BSE. The results turn out to be restricted to lower carrier densities, since divergencies appear if the sum of the carrier distribution functions of electrons and holes approaches unity. Another aspect is the use of the quasi-particle concept [7] for the one-particle Green's functions in order to reduce the numerical effort for the solution of the BSE.New insight into the role of many-body effects came into play with the development of the Semiconductor-Bloch Equations (SBE) [8], describing the time evolution of the

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Phase memory of the electronic polarization in transient nonlinear optical spectra of gallium arsenide at 2 eV

Cited by 33 publications

References 41 publications

Density Dependence of the Exciton Energy in Semiconductors

Density Dependence of the Exciton Energy in Semiconductors

Real Time Approach to Relaxation and Dephasing Processes in Semiconductors

Quantum-Kinetic Effects in the Linear Optical Response of GaAs Quantum Wells

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