1,721,208 research outputs found
Coherent phenomena in semiconductors
No full textA review of coherent phenomena in photoexcited semiconductors is presented. In particular, two classes of phenomena are considered. The first is concerned with the role played by optically induced phase coherence in the ultrafast spectroscopy of semiconductors; the other with the Coulomb-induced effects on the coherent optical response of low-dimensional structures.
All the phenomena discussed in this review are analysed in terms of a theoretical framework based on the density-matrix formalism. Due to its generality, this quantum-kinetic approach allows a realistic description of coherent as well as incoherent, i.e. phase-breaking, processes, thus providing quantitative information on the coupled - coherent versus incoherent - carrier dynamics in photoexcited semiconductors.
The primary goal of this review is to discuss the concept of quantum-mechanical phase coherence as well as its relevance to and implications for semiconductor physics and technology. In particular, we will discuss the dominant role played by optically induced phase coherence on the process of carrier photogeneration and relaxation in bulk systems. We will then review typical field-induced coherent phenomena in semiconductor superlattices such as Bloch oscillations and Wannier-Stark localization. Finally, we will discuss the dominant role played by Coulomb correlation on the linear and nonlinear optical spectra of realistic quantum-wire structures
The excitonic quantum computer
No full textA review of semiconductor-based schemes for the realization of quantum information processing devices is presented. After recalling the fundamentals of quantum information/computation theory, we shall discuss potential implementation schemes based on charge and/or spin degrees of freedom in semiconductor nanostructures. More specifically, we shall present an all-optical implementation scheme of quantum information processing with semiconductor macroatoms/molecules, where the computational degrees of freedom are interband optical transitions (excitonic states) manipulated/controlled by ultrafast sequences of multicolor laser pulses. We shall primarily focus on implementation schemes dealing with charge excitations in GaAs as well as GaN quasi-zero-dimensional structures. We shall finally discuss the possibility to combine charge and spin degrees of freedom, thus, allowing for fast-quantum gates, which do not translate into fast-decoherence times
Ultrafast carrier dynamics in semiconductor nanostructures: interplay between coherence and relaxation
No full textThe strong coupling between coherent and incoherent ultrafast phenomena in the electro-optical response of semiconductor nanostructures is discussed theoretically within a density matrix formalism. In particular, the problem of scattering-induced damping of Bloch oscillations in superlattices is reviewed. Moreover, a generalization to ‘open systems' of the conventional semiconductor Bloch equations is discussed. The presence of spatial boundary conditions manifests itself through self-energy corrections and additional source terms in the kinetic equations. As an example, some simulated experiments of quantum transport phenomena through double-barrier structures are reviewed
Quantum Fermi's golden rule for semiconductor nanodevices
No full textWe shall revisit the conventional adiabatic or Markov approximation, stressing its intrinsic failure in describing the proper quantum-mechanical evolution of a generic subsystem interacting with its environment. In particular, we shall show that - contrary to the semiclassical case - the Markov limit does not preserve the positivedefinite character of the corresponding density matrix, thus leading to highly non-physical results. To overcome this problem, we shall propose an alternative adiabatic procedure which (i) in the semiclassical limit reduces to the standard Fermi's golden rule, and (ii) describes a genuine Limblad evolution, thus providing a reliable/robust treatment of energy-dissipation and dephasing processes in electronic quantum devices. Compared to standard master-equation formulations, the proposed approach does not involve/require any reduction or average procedure, exactly as for the derivation of the well known Fermi's golden rul
Theory of Semiconductor Quantum Devices
No full textA comprehensive survey of opto-electronic quantum devices. Deals with quantum phenomena in nanomaterials, various applications such as quantum cascade lasers and detectors, few-electron quantum devices as well as quantum logic gates. Quantum transport and coherent-optics phenomena on ultrasmall space and time scales are treated. Both a reference work for researchers and a textbook for graduate student
A quantum description of drift velocity overshoot at high electric fields in semiconductors
No full textA quantum description of transient charge transport in semiconductors is presented. In particular, we discuss the drift velocity overshoot in GaAs. The paper is intended to show how typical quantum features, such as intracollisional field effect and multiple collisions tend to modify the transient behavior of the system as predicted by semiclassical transport. This analysis has been performed by means of a quantum Monte Carlo procedure which takes into account the GaAs band structure through a many-valley model. The results of the quantum simulation, as regards drift velocity and upper valley population, have been compared with those of the classical theory and this comparison shows that in the case of GaAs quantum features are not relevant. For a better understanding, a semiconductor model, characterized by a very strong electron-phonon coupling constant, has been considered where quantum effects are appreciable and from this analysis it is possible to identify physical systems for which a full quantum treatment is required
Ultrafast phenomena in photoexcited semiconductors
Full text linkThe authors review the physics of ultrafast dynamics in semiconductors and their heterostructures, including both the observed experimental phenomena and the theoretical description of the processes.
These are probed by ultrafast optical excitation, generating nonequilibrium states that can be monitored by time-resolved spectroscopy. Light pulses create coherent superpositions of states, and the dynamics of the associated phase relationships can be directly investigated by means of many-pulse experiments. The commonly used experimental techniques are briefly reviewed. A variety
of different phenomena can be described within a common theoretical framework based on the density-matrix formalism. The important interactions of the carriers included in the theoretical description are the phonon interactions, the interactions with classical and quantum light fields, and the Coulomb interaction among the carriers themselves. These interactions give rise to a strong interplay between phase coherence and relaxation, which strongly affects the non equilibrium dynamics. Based on the general theory, the authors review the physical phenomena in various semiconductor structures including superlattices, quantum wells, quantum wires, and bulk media.
Particular results which have played a central role in understanding the microscopic origins of the relaxation processes are discussed in detail
Scattering nonlocality in quantum charge transport: Application to semiconductor nanostructures
No full textOur primary goal is to provide a rigorous treatment of scattering nonlocality in semiconductor nanostructures. On the one hand, starting from the conventional density-matrix formulation and employing as ideal instrument for the study of the semiclassical limit the well-known Wigner-function picture, we shall perform a fully quantum-mechanical derivation of the space-dependent Boltzmann equation. On the other hand, we shall examine the validity limits of such semiclassical framework, pointing out, in particular, regimes where scattering-nonlocality effects may play a relevant role; to this end we shall supplement our analytical investigation with a number of simulated experiments, discussing and further expanding preliminary studies of scattering-induced quantum diffusion in GaN-based nanomaterials. As for the case of carrier-carrier relaxation in photoexcited semiconductors, our analysis will show the failure of simplified dephasing models in describing phonon-induced scattering nonlocality, pointing out that such limitation is particularly severe for the case of quasielastic dissipation processe
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