Theory of ultrafast phenomena in photoexcited semiconductors

Abstract

The 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 nonequilibrium 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. CONTENTS

The role of phonons for exciton and biexciton generation in an optically driven quantum dot

“…Most often, these methods fully account for the dotlight coupling but treat the exciton-phonon interaction within further approximations. Examples of such approaches are the time-convolutionless approach [116,120,121], the correlation expansion [122,123,124,125,126], different types of master equations [116,53,64,127,88,128,93] or time-dependent perturbation theory [129,125]. For the Hamiltonian dynamics within the model established by Eqs.…”

Relaxation Dynamics in Graphene

“…A variety of dynamical phenomena, such as the appearance of a signi cant carrier multiplication and transient optical gain, have been theoretically predicted [30 33] and experimentally con rmed [32,34,35]. A consistent treatment of the relaxation dynamics containing all important scattering contributions can be realized within the density matrix approach [17,36,37]. 1.…”

Theory of optical excitations in dipole-coupled hybrid molecule-semiconductor layers: Coupling of a molecular resonance to semiconductor continuum states

“…Our microscopic approach is based on a Heisenberg equation of motion technique [15,16]. In the Heisenberg picture, the equation of motion for an operator O is given…”

“…Our approach is based on a Heisenberg equation of motion technique [15,16] to derive the optical many-body Bloch equations of the hybrid system in the Hartree-Fock limit [17,18]. This approach is computationally less expensive than the aforementioned fully time resolved first-principles calculations, but retains the microscopic description of the charge carrier dynamics, if parameterized with first-principles input.…”