摘要:

AbstractIn the frequency domain close to the intrinsic absorption threshold the dynamic polarization, accompanying propagation of a strong electromagnetic pulse, is a dense cloud of electron‐hole pairs, free or bound to excitons or both. In order to investigate the structure and properties of this system in a wide range of pumping field strengths and frequencies, including both the exciton resonance and continuum edge, two simplified models are introduced and discussed, both substituting an effective short‐range interaction instead of the usual Coulomb potential. To go beyond the mean‐field approximation (MFA) the correlation effects are accounted for phenomenologically in this interaction. Results for both ‐ (quasi‐) stationary regime and transient response ‐ are presented. Possible inelastic relaxation mechanisms and kinetics are discussed. For not too fast (in the “excitonic” time scale) varying pumping field strengths the Boltzmann equation for renormalized Galitskii‐Elesin quasi‐p

ISSN:0370-1972    

DOI:10.1002/pssb.2221880102

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA description of polariton effects on excitons in multiple quantum wells (MQWs), superlattices (SLs), and semiconductor microcavities is given, which is based on a nonlocal semiclassical theory in a transfer‐matrix formulation. The radiative width in MQWs atk= 0 increases first with the number of wellsN, then goes to zero asN→ ∞, where stationary polariton states are recovered. A very similar behavior is found by treating the MQW with a local dielectric model. In the SL limit, the exciton‐polariton dispersion at long wavelengths reduces to that of a light wave in a uniaxial material, described by an effective dielectric tensor. Comparing with the bulk, the polariton splitting is increased in SLs, and reduced in microcavities. Nevertheless, polariton effects in microcavities are easily observable, since spatial coherence along the growth direction is not r

ISSN:0370-1972    

DOI:10.1002/pssb.2221880103

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fundamental intrinsic radiative process associated with excitons in semiconductor multiple quantum wells is discussed within the context of exciton polaritons. Multiple quantum wells in which each well is randomly displaced from its ideal periodic position are discussed in order to investigate the effect of disorder on excitonic radiative widths. The coherent transpori of excitons in multiple quantum wells is discussed.

ISSN:0370-1972    

DOI:10.1002/pssb.2221880104

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe polariton reflection spectra in PbI‐based compounds – self‐organized semiconductor/insulator superlattices – for different polarizations of incoming light and within a nonlocal model for the exciton response are cal

ISSN:0370-1972    

DOI:10.1002/pssb.2221880105

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA theory of the optical decay and of the resonant two‐photon creation of an excitonic molecule (xx) in direct band gap semiconductors is given within the polariton picture. An xx Schrödinger equation which includes both the Coulombic exciton‐exciton attraction and the polariton coupling is derived and analyzed. The solution of this equation describes an xx as the quasibound two‐polariton complex. The real and imaginary parts of the xx energy give self‐consistently the inverse xx radiative lifetime Γxxand the radiative renormalization Δxxof the xx energy (the xx Lamb shift), respectively. For 3D (CuCl) the polariton effects result in a non‐parabolic xx dispersion with M xxeff→ ∞ at zero momentum; for quasi‐2D (GaAs) they lead to a “Mexican hat” structure in the xx dispersion at small momenta together with a considerable increase of both the xx effective binding energy ϵxxand lifetime Γxx. For quasi‐ID the influence of the polariton effects is so strong that an xx can exist only as

ISSN:0370-1972    

DOI:10.1002/pssb.2221880106

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo different theoretical models of the giant two‐photon absorption due to excitonic molecules (xx) are examined experimentally. The conventional model (Hanamura, 1973) follows the sequence: photon + photon → exciton + photon → xx, while the self‐consistent model (Ivanov and Haug, 1993) gives the other scenario of the two‐photon absorption: photon + photon → exciton + exciton → xx. Our high‐precision measurement of the frequency dependence of the two‐photon xx absorption coefficient in CuCl allows us to discriminate these two models and supports the new self

ISSN:0370-1972    

DOI:10.1002/pssb.2221880107

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA high‐density electron–hole system in one dimension (1D) is studied theoretically in terms of the photoinduced Fermi‐edge singularity (FES) in optical spectra, the anomaly of which results from the fluctuating exciton Bose condensation in 1D. Describing this system as thetwo‐bandTomonaga Luttinger (TL) liquid with the forward‐scattering correlations, the critical exponent of the FES is analytically obtained with the aid of the bosonization technique. Competition between the exciton condensation and other Fermi‐surface instabilities is also clarified within the framework of the two‐bandg‐ology. Comparison with the FES in ordinary 1D conductors (heavily‐doped 1D semiconductors), which are described as thesingle‐bandTL liquids, is made to clarify recoil effects of an optical hole on the FES. Effects of backward scatterings, random potentials, spin‐dependent electronic correlations, and spin splitting of the conduction ba

ISSN:0370-1972    

DOI:10.1002/pssb.2221880108

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIt is shown that plasmon‐assisted superconductivity can occur in an electron plasma of a modulationdoped quantum well structure or in an optically excited, cool quasi‐equilibrium electron–hole plasma in stressed quantum wells. For our analysis the quasi‐classical approximation (QCA) for non‐equilibrium Keldysh‐Green functions for carriers of a degenerate plasma is used. The screening is described in RPA, simplified further for some of the calculations by a damped plasmon‐pole approximation (PPA). Because the plasmon coupling is strong the appropriately modified Eliashberg equations are derived and analyzed for the complex frequency‐dependent normal and anomalous self‐energies. The plasmon frequency in a semiconductor plasma with a typical density of 1018cm−3is of the order of some 10 meV. If the spectral density of the plasmon is not too broad, a pairing instability is found also in the range of interparticle distances withrs<1, where QCA and RPA are valid. Depending on the material, transition plasma temperatures of up to 30 K are obtained which can be enhanced further by quantum confinement and special properties of the band structure. The underlying virtual exchange of plasmons can only be obtained in a fully dynamical description, and is absent in the commonly used quasi‐static quasi‐

ISSN:0370-1972    

DOI:10.1002/pssb.2221880109

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe development of a ground state of the squeezed quasi‐1D system of Wannier‐Mott excitons (x) into a quantum exciton crystal (EC) is examined. This quantum EC is due to repulsive interactions between singlet x (or biexcitons). Spatial squeezing of the x‐system can be realized by the surface and interface potentials of a quasi‐1D quantum wire. Stability and melting of the quantum EC are studied both within the Lindemann and Mott criteria. The phase diagram of the squeezed quasi‐1D x‐system is proposed. According to the estimates within the Heitler‐London approximation, the quantum EC can exist for moderate x densities (1

ISSN:0370-1972    

DOI:10.1002/pssb.2221880110

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAn experimental and theoretical study of the carrier capture time into a semiconductor quantum well is presented. Oscillations of the phonon emission induced capture time are experimentally observed and good agreement with theory is found. The calculations show that not only the LO‐phonon emission induced capture time (ph‐capture) oscillates as a function of well width, but also the carrier–carrier scattering induced capture time (c‐c capture) oscillates by more than one order of magnitude as a function of the active layer design. Recently it has been shown that the carrier capture time is directly related to the modulation band width in a quantum well laser. As a result, it might be possible to tailor the modulation band width by optimizing the capture efficiency using a proper design of the active layer in a quantum wel

ISSN:0370-1972    

DOI:10.1002/pssb.2221880111

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY