Carrier-Carrier and Carrier-Phonon Scattering in Self-Assembled Quantum Dots

Abstract

In this work theoretical investigations of the carrier-carrier interaction and the carrier-phonon interaction in self-assembled quantum dots are presented. Based on the nonequilibrium Green's function technique, equations of motion are derived for the one-particle Green's function. To demonstrate our method we focus on lens-shaped quantum dots grown on top of a wetting layer, using typical InGaAs and InGaN material parameters. For the carrier-carrier interaction, we study the carrier-carrier scattering processes leading to carrier capture into and relaxation inside the quantum dots. The corresponding scattering rates are evaluated within the Boltzmann approximation under quasi-equilibrium conditions. For the InGaAs material system we find at elevated carrier densities in the wetting layer that Coulomb scattering provides processes with capture (relaxation) times typically faster than 10ps (1ps). For the InGaN material system the combined influence of the quantum-confined Stark effect and many-body renormalizations is furthermore taken into account. The charge separation induced by the built-in electrostatic 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. The carrier-phonon scattering is studied for the InGaAs material system. The interaction of carriers with longitudinal-optical (LO) phonons at the Boltzmann level predicts inefficient scattering (phonon bottleneck) when the transition energies of the quantum dot states do not match the LO-phonon energy. In contrast, we demonstrate that a quantum kinetic description of the carrier-phonon interaction supports experimental observed fast scattering processes.