1 Optoelectronics, Department of Photonics Engineering, Technical University of Denmark2 Department of Photonics Engineering, Technical University of Denmark3 Nanophotonics, Department of Photonics Engineering, Technical University of Denmark4 Department of Informatics and Mathematical Modeling, Technical University of Denmark
This thesis describes modeling of carrier relaxation processes in self-assembled quantum-dot-structures, with particular emphasis on carrier capture processes in quantum dots. Relaxation by emission of lontitudinal optical (LO) phonons is very efficient in bulk semiconductors and nanostructures of higher dimensionality. Here, we investigate carrier capture processes into quantum dots, mediated by emission of one and two LO phonons. In these investigations is is assumed that the dot is empty initially. In the Case of single-phonon capture we also investigate the influence of the presence of a charge in the quantum-dot state to which the capture takes place. In general, capture rates are of the same order as capture rates into an empty dot state, but in some cases the dot-size interval for which the capture process is energetically allowed, is considerably reduced.The above calculations are performed by assuming that the incident carrier is a free carrier described by a plane wave. Therefore, the influence of waves are scattered by the quantum dot have been neglected. At certain wavelengths and dot sizes, the quantum dot can act as a Fabry-Perot mirror in which the incident carrier travels back and forth in the dot leading to a quasi-bound state of finite linewidth that resembles the bound states. We investigate the coupling of carriers in quasi-bound states with LO phonons and demonstrate that they can couple strongly with phonons. This leads to the formation of a mixed carrier-phonon mode that is called a polaron.Capture processes mediated by carrier-carrier scattering (Auger processes) are investigated and their dependence on quantum-dot geometry is studied in detail.