1. Semiconductor Laser Diodes 2. Basic Concepts 3. Free-Carrier Theory 4. Coulomb Effects 5. Many-Body Gain 6. Band Mixing and Strain in Quantum Wells 7. Semiclassical laser Theory 8. Multimode Operation 9. Quantum Theory of the Laser 10. Propagation Effects 11. Beyond Quasiequilibrium Theory, Appendices A-e, Index

Semiconductor-Laser Physics

The application of femtosecond spectroscopy to the study of ultrafast dynamics in semiconductor materials and nanostructures is reviewed with particular emphasis on the physics that can be learned from it. Excitation with ultrashort optical pulses in general results in the creation of coherent superpositions and correlated many-particle states. The review comprises a discussion of the dynamics of this correlated many-body system during and after pulsed excitation as well as its analysis by means of refined measurements and advanced theories. After an introduction of basic concepts—such as coherence, correlation and quantum kinetics—a brief overview of the most important experimental techniques and theoretical approaches is given. The remainder of this paper is devoted to specific results selected in order to highlight how femtosecond spectroscopy gives access to the physics of coherences, correlations and quantum kinetics involving charge, spin and lattice degrees of freedom.First examples deal with the dynamics of basic laser-induced coherences that can be observed, e.g. in quantum beat spectroscopy, in coherent control measurements or in experiments using few-cycle pulses. The phenomena discussed here are basic in the sense that they can be understood to a large extent on the mean-field level of the theory. Nevertheless, already on this level it is found that semiconductors behave substantially differently from atomic systems. Subsequent sections report on the occurrence of coherences and correlations beyond the mean-field level that are mediated either by carrier–phonon or carrier–carrier interactions. The corresponding analysis gives deep insight into fundamental issues such as the energy–time uncertainty, pure dephasing in quantum dot structures, the role of two-pair or even higher correlations and the build-up of screening. Finally results are presented concerning the ultrafast dynamics of resonantly coupled excitations, where a combination of different interaction mechanisms is involved in forming new types of correlations. Examples are coupled plasmon–phonon and Bloch–phonon oscillations.The results reviewed in this paper clearly reveal the central role of many-particle correlations and coherences for the ultrafast dynamics of dense semiconductor systems. Both the presence of strong correlation effects and the formation of coherences in a genuine many-particle system have important implications for the controllability of optical signals from this class of materials, which is of utmost importance for applications in present-day and future optoelectronic devices.

https://iopscience.iop.org/article/10.1088/0034-4885/67/4/R01/pdf

Femtosecond spectroscopy in semiconductors: a key to coherences, correlations and quantum kinetics

This article reviews the application of the non-equilibrium Green's function formalism to the simulation of novel photovoltaic devices utilizing quantum confinement effects in low dimensional absorber structures. It covers well-known aspects of the fundamental NEGF theory for a system of interacting electrons, photons and phonons with relevance for the simulation of optoelectronic devices and introduces at the same time new approaches to the theoretical description of the elementary processes of photovoltaic device operation, such as photogeneration via coherent excitonic absorption, phonon-mediated indirect optical transitions or non-radiative recombination via defect states. While the description of the theoretical framework is kept as general as possible, two specific prototypical quantum photovoltaic devices, a single quantum well photodiode and a silicon-oxide based superlattice absorber, are used to illustrated the kind of unique insight that numerical simulations based on the theory are able to provide.

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Theory and simulation of quantum photovoltaic devices based on the non-equilibrium Green's function formalism

We use the finite-difference time-domain (FDTD) solution of the full-wave vectorial Maxwell-Bloch equations for a two-level quantum system developed earlier , to investigate the nonlinear gain spatio-temporal dynamics of active optical waveguides and semiconductor microcavities. The numerical model has been successfully validated against density matrix theory of gain saturation in homogeneously broadened two-level quantum systems for optical waveguides containing resonant gain nonlinearities. The semiclassical equations have been extended employing the Langevin formalism to account for the quantum noise and the spontaneous emission. We have numerically demonstrated the time evolution of the coherent oscillations build up at the output laser facet identifying the lasing threshold and the fast relaxation oscillations until the settlement of a steady-state emission. Our simulation predictions of the lasing wavelength in a number of vertical-cavity surface-emitting laser geometries, when the spontaneous emission is the only source of radiation, agree very well with standard results and, thus, allow us to infer and subsequently optimize important emission characteristics, such as the spontaneous emission rate, the laser line shape, and the relaxation oscillation frequencies and decay rates.

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FDTD simulation of the nonlinear gain dynamics in active optical waveguides and semiconductor microcavities

/pdf/theory-and-simulation-of-quantum-photovoltaic-devices-based-54k0ex315a.pdf

Semiconductor light emission is analyzed as a paradigm of a nonequilibrium quantum mechanical many-body problem. The medium excitations and the quantized light field inside and outside a semiconductor slab are treated consistently. Splitting the photon density of states into a medium and a vacuum induced contribution the arbitrarily strong semiconductor emission is described as spontaneous emission into the vacuum induced part. With increasing gain narrowing peaks of growing intensity evolve for each propagation direction, whereas under laser conditions one propagation direction is favored by the cavity.

S. W. Koch

Papers

Quantum kinetics of semiconductor light emission and lasing.