Binding of Biexcitons in GaAs/AlGaAs Superlattices

Physical Review B, 1999

Physical review. B, Condensed matter, 1989

Superlattices and Microstructures, 1997

The formation of spatially indirect excitons in superlattices with narrow minibands is theoretically and experimentally investigated. We identify the experimental conditions for the observation of interwell excitons and find a distinct excitonic state energetically located between the 1s exciton and the onset of the miniband absorption. The interwell exciton is similar to the first Wannier-Stark localized exciton of an electrically biased superlattice. However, in the present case the localization is mediated by the Coulomb interaction of the electron and the hole without external fields.

1991

Solid State Communications, 2000

We perform time integrated degenerate four-wave mixing (DFWM) measurements to investigate exciton dephasing in a GaAs/AlAs lateral superlattice (LSL) with a tunable band gap modulation. The excitons are resonantly excited by femtosecond laser pulses. Under optimal conditions of growth layer alignment, the ground state excitons in the LSL are 1D. When the LSL growth is highly tilted, the 1D confining potential vanishes and the LSL effectively becomes a 2D system. The DFWM measurements for the 1D and 2D excitons show that the exciton-exciton scattering strength is significantly reduced in the 1D case. We find that disorder in the LSL cannot fully explain the observed large reduction. It is likely that reduction in dimensionality plays an important role in this.

Physical review B, 1987

We have studied the optical properties of a short-period superlattice composed of 20.4-Å GaAs and 14.7-Å AlAs layers. The superlattice behaves as an indirect-gap material. A slow and nonexponential decay of the luminescence can be interpreted as the emission from the Λ indirect excitons ...

Superlattices and Microstructures, 2001

The temperature dependence of the recombination dynamics of excitons is investigated by time-resolved photoluminescence spectroscopy in (GaAs) n /(AlAs) n superlattices, where n denotes the layer thickness in monolayers, for different types of band structures. In directgap superlattices with a layer thickness of the order or larger than the exciton Bohr radius, the carrier dynamics is dominated by the transfer from light-hole to heavy-hole excitons. When the layer thickness becomes smaller than the exciton radius, the dynamics of free excitons is controlled by localization. vb In quasi-direct and indirect-gap superlattices, the influence of lateral potential fluctuations due to interface roughness completely governs exciton recombination.

Superlattices and Microstructures, 1992

We report a study of the photoluminescence spectra of GaAs-G~.65A10.ssAs superlattice under an electric field of about 10 kVcm-l, from 9 K up to 80 K ; the ratio p = I-l/I0 of the intensities of the -1 and 0 peaks of the Wannier-Stark ladder varies with the temperature T. To fit these variations, we assume for both transitions, a trapped exciton density of states with a gaussian distribution of eigenenergies, and a two dimensional density of states for free excitons. We show that above about 50 K there is a thermal equilibrium between direct and crossed free excitons whereas at low temperatures, the equilibrium statistics am not respected : the excitons trap into the direct state rather than to the crossed one.

Philosophical Magazine, 2006

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Journal of Luminescence, 2012

The dependencies of the binding energies of the lowest four 1s-like exciton states in GaAs-(Ga,Al)As coupled double quantum wells (CDQW) on the geometric parameters of the system are theoretically studied. A variational approach, together with the parabolic band and effective mass approximations, were considered in order to perform the numerical calculations. It is shown that in the case of a symmetric system there is a degeneracy between the heavy-hole even and odd states and this degeneracy can be removed by the presence of a sufficiently narrow middle barrier. In contrast to this fact, the electron even and odd states are never degenerated. It is detected that, if the system is asymmetric, there will appear binding energies anticrossings between the heavy-hole states at the point of the asymmetricsymmetric QW transition.

Journal of Luminescence, 1989

Time-resolved photoluminescence has been used to study the carrier transport in superlattice minibands (vertical transport). Transport of electrons and holes can be studied separately by using appropriate excitation densities and doping levels. Their diffusion coefficients are estimated and studied both as a function of the superlattice period and of the lattice temperature. The different behaviour of electrons and hole mobilities as a function of the SL period is evidenced. The temperature behaviour of the transport properties is similar in a superlattice and in the A1GaAs alloy with an equivalent Al concentration.

Le Journal de Physique IV, 1993

We report photoluminescence studies on some GaInAsIAIGaInAs superlattices lattice matched to InP. An electric field was applied along the growth axis. The spectra recorded at temperatures between 10 K and 300 K, present only one peak, the energy of which does not vary with the strength of the electric field. Moreover, the intensity of the peak does not monotonely vary with the temperature. These results are interpreted in a model which involves centers of nonradiative recombination, a density of states with a gaussian distribution of eigenenergies for the trapped excitons and a two dimensional density of states which takes into account fluctuations of composition and of well and barrier width for the free excitons.

Physics Letters A, 1984

The Keldysh model of a two-dimensionaUy confined exciton in a heterojunction superiattice, which corresponds to a maximal deviation from the isotropic semiconductor, is analyzed and solved numerically. The results suggest that the high angular momentum provides a reliable diagnostic of the dimensionality of the exciton, even when details of the potential are not known.

Microelectronic Engineering, 1998

In this work we have investigated the temperature dependence of photoluminescence (PL) properties of GaAs /AlAs ultrathin-layer superlattices (UTLS) grown by molecular beam epitaxy on high index surfaces. The temperature dependence reveals an anomalous decrease of the PL linewidth with the increase of the temperature, which is explained in terms of the exciton thermal activation energy transfer between nanometre-steps formed in the corrugated interfaces.

2001

The linear combination of bulk bands method recently introduced by Wang, Zunger [Phys. Rev. Lett. 78, 2819 (1997)] is applied to a calculation of energy bands and optical constants of (GaAs)n/(AlAs)n and (GaAs)n/(vacuum)n (001) superlattices with n ranging from 4 to 20. Empirical pseudopotentials are used for the calculation of the bulk energy bands. Quantumconfined induced shifts of critical point energies are calculated and are found to be larger for the GaAs/vacuum system. The E1 peak in the absorption spectra has a blue shift and splits into two peaks for decreasing superlattice period; the E2 transition instead is found to be split for large-period GaAs/AlAs superlattices. The band contribution to linear birefringence of GaAs/AlAs superlattices is calculated and compared with recent experimental results of Sirenko et al. [Phys. Rev. B 60, 8253 (1999)]. The frequency-dependent part reproduces the observed increase with decreasing superlattice period, while the calculated zero-frequency birefringence does not account for the experimental results and points to the importance of local-field effects.