T. R. Nielsen

Polarons in semiconductor quantum dots and their role in the quantum kinetics of carrier relaxation

While time-dependent perturbation theory shows inefficient carrier-phonon scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic description of carrier-phonon interaction predicts fast carrier capture and relaxation. The considered processes do not fulfill energy conservation in terms of free-carrier energies because polar coupling of localized quantum-dot states strongly modifies this picture.

Influence of carrier-carrier and carrier-phonon correlations on optical absorption and gain in quantum-dot systems

A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of a coherent excitation and line shifts of the interband transitions due to carrier-carrier Coulomb interaction and carrier-phonon interaction are determined from a quantum kinetic treatment of correlation processes. We investigate the density dependence of both mechanisms and clarify the importance of various dephasing channels involving the localized and delocalized states of the system.

Coulomb scattering in nitride-based self-assembled quantum dot systems

We study the carrier capture and relaxation due to Coulomb scattering in group-III nitride quantum dots on the basis of population kinetics. For the states involved in the scattering processes the combined influence of the quantum-confined Stark effect and many-body renormalizations is taken into account. The charge separation induced by the built-in field has important consequences on the capture and relaxation rates. It is shown that its main effect comes through the renormalization of the energies of the states involved in the collisions and leads to an increase in the scattering efficency.

Many-body theory of carrier capture and relaxation in semiconductor quantum-dot lasers

For quantum dots on a wetting layer, the role of Coulomb scattering and carrier-phonon interaction for carrier capture and relaxation of carriers between the quantum-dot levels are studied theoretically

Quantum kinetic effects in the optical absorption of semiconductor quantum-dot systems

A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of the coherent polarization due to carrier-carrier Coulomb interaction and carrier-phonon interaction is determined from quantum kinetic equations. We investigate the density dependence of the dephasing mechanisms, and compare the relevance of various interaction processes. The failure of frequently used approximations based on the GKBA with free single-particle energies is demonstrated for pure dephasing processes involving only the localized quantum-dot states.

Many-body theory of optical gain in semiconductor quantum dot lasers

Central ingredients for a theoretical description of optical gain spectra for self-assembled quantum dots are presented. The importance of a quantum kinetic treatment of carrier-carrier Coulomb interaction and carrier-phonon interaction is discussed.

Quantum kinetics of phonon-assisted carrier transitions in semiconductor quantum dots

Results for carrier-phonon scattering in semiconductor quantum dots are presented on the basis of a quantum-kinetic theory. In contrast to time-dependent perturbation theory fast capture and relaxation processes are obtained.