A microscopic theory is adapted to compute the time-resolved terahertz (THz) probe response of a dynamically evolving, strong-field ionized electron-ion plasma. The numerical solutions show that the relaxation of the initially highly anisotropic carrier distributions leads to a polarization dependent short-time THz response. This THz polarization discrimination gradually vanishes as the plasma approaches a thermodynamic equilibrium configuration via electron-electron and electron-ion scattering. The detailed carrier-relaxation dynamics causes a strongly nonmonotonic time-development of the THz absorption. DOI: 10.1103/PhysRevE.87.033106

Rigorous quantum calculations of the femtosecond ionization of hydrogen atoms in air lead to highly anisotropic electron and ion angular (momentum) distributions. A quantum Monte-Carlo analysis of the subsequent many-body dynamics reveals two distinct relaxation steps, first to a nearly isotropic hot nonequilibrium and then to a quasi-equilibrium configuration. The collective isotropic plasma state is reached on a picosecond timescale well after the ultrashort ionizing pulse has passed.

Experimental gain spectra of 450 and 490 nm laser diodes on c-plane GaN are analyzed by detailed comparison with the results of a fully microscopic theory. The gain calculation shows the importance of electron LO-phonon coupling. The whole spectral gain shape, not only the low energy tail, is strongly influenced by the LO-phonon contribution. The inhomogeneous broadening parameter increases by a factor of about two for the cyan laser diode in comparison with the blue laser structure. This indicates an increase in alloy and thickness fluctuations for the longer wavelength material.

Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN/GaN quantum wells. Since the usual direct band-to-band Auger losses are too small to explain the experimentally observed droop of the external quantum efficiency in such structures, phonon assisted Auger processes are discussed. First numerical estimates indicate that the resulting losses constitute an important intrinsic loss process in InGaN/GaN quantum wells. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fully microscopic many-body models are used to study the importance of radiative and Auger carrier losses in InGaN∕GaN quantum wells. Auger losses are found to be negligible in contrast to recent speculations on their importance for the experimentally observed efficiency droop. Good agreement with experimentally measured threshold losses is demonstrated. The results show no significant dependence on details of the well alloy profile.

Charge and spin currents generated by ultrafast two-colour laser excitation of semiconductor quantum wells are computed using Bloch equations formulated in the basis of k⋅p wave functions. The optically induced interband and intraband excitations are treated nonperturbatively for a consistent description of phototransport in the high-excitation regime. The analysis shows that the photoexcited charge and spin currents depend on the amplitudes of the incident ω and 2ω beams in a highly nonlinear fashion. It is predicted that Rabi flopping should be observable experimentally leading to intensity-dependent changes of the current directions.

A brief overview of a consistent microscopic approach to model the optical and electronic properties of semiconductor nanostructures is presented. Coupled semiconductor Bloch and Maxwell equations are used to investigate the performance of semiconductor microcavity structures, photonic band gap systems, and lasers. The predictive potential of the microscopic theory is demonstrated for several examples of practical importance. Optical gain and output characteristics are computed for modern vertical external cavity surface emitting laser structures. It is shown how design flexibilities can be used to optimize the device performance. Nanostructures are proposed where semiconductor quantum wells are embedded in one-dimensional photonic crystals. For field modes spectrally below the photonic band edge it is shown that the optical gain and absorption can be enhanced by more than one order of magnitude over the value of the homogeneous medium. The increased gain can be used for laser action by placing quantum wells and a suitably designed photonic crystal structure inside a microcavity.

Significant aspects of the light-matter interaction can be strongly modified in suitably designed systems consisting of semiconductor nanostructures and dielectric photonic crystals. To analyze such effects, a microscopic theory is presented, which is capable of describing the optoelectronic properties of such hybrid systems via a self-consistent solution of the dynamics of the optical field and the photoexcitations of the material, The theory is applied to investigate the local excitonic resonances, which arise as a Consequence of the modified Coulomb interaction in the vicinity of a structured dielectric medium, The excitation of a coherent superposition of the spatially inhomogeneous optical transitions induces an intricate wave packet dynamics. In the presence of dephasing and relaxation processes, the coherent oscillations are damped and the photoexcited carriers relax into spatially inhomogeneous quasi-equilibrium distributions.

The optical properties of semiconductor quantum wells embedded in one-dimensional photonic crystal structures are analyzed by a self-consistent solution of Maxwell's equations and a microscopic many-body theory of the material excitations. For a field mode spectrally below the photonic band edge it is shown that the optical absorption and gain are enhanced, exceeding by more than 1 order of magnitude the values of a homogeneous medium. For the photonic crystal structure inside a microcavity the gain increases superlinearly with the number of wells and for more than five wells exceeds the gain of a corresponding vertical-cavity surface-emitting laser.

The optical and electronic properties of semiconductor heterostructures in the vicinity of photonic crystals are discussed. The theoretical approach provides a self-consistent solution of the dynamics of the electromagnetic field and the material excitations. Due to the influence of the structured dielectric environment on the Coulomb interaction, the exciton resonances and the quasiequilibrium carrier densities in the spatially homogeneous semiconductor become space dependent. It is demonstrated that these inhomogeneities lead to distinct modifications of the optical absorption and gain spectra. As an application, numerically calculated density-dependent optical spectra are analyzed for an array of semiconductor quantum wires which are close to a two-dimensional photonic crystal. The spatial inhomogeneities result in novel excitonic absorption features and modification of the optical gain in these structures.

c © 2003 by John von Neumann Institute for Computing Permission to make digital or hard copies of portions of this work for personal or classroom use is granted provided that the copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise requires prior specific permission by the publisher mentioned above.

Optical properties of a semiconductor quantum well in the vicinity of a two-dimensional photonic crystal are investigated. Due to the periodic spatial modulation of the dielectric environment the effective Coulomb interaction potential exhibits the periodicity of the photonic crystal. As a consequence, the excitonic binding energy varies periodically by up to 50% depending on the spatial position of the exciton relative to the structured dielectric. The self image charge effects result in a position dependent shift of the single-particle bandgap such that the spectral position of the absorption spectrum also develops the periodicity of the photonic surrounding. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Absorption spectra of semiconductor structures in photonic crystal environments are investigated numerically. It is shown that the periodic dielectric structuring changes the local optical and Coulomb interaction properties of semiconductor electron–hole excitations. The structurally induced modifications offer the possibility to design important aspects of the optoelectronic semiconductor properties.