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Model for localised recombination in quantum dots

A new generation of diode lasers is being developed using quantum dots as the gain generating medium. A detailed understanding of the carrier recombination mechanisms and optical gain generation is essential for optimisation of their performance. The aim of this work is to further understand the optical processes occurring in quantum dots. In particular, the effect of the localisation of the energy states in the dots on the recombination mechanisms and the gain/absorption is studied. It is often assumed that the rates of nonradiative recombination via defects, radiative recombination and Auger recombination are proportional to linear, quadratic and cubic functions of the carrier number respectively. The derivation of these functional forms is possible in quantum well and bulk structures because the extended electronic states make it meaningful to talk of a global carrier population. In a quantum dot system the dependence of the recombination processes on the total number of electrons populating the dots is modified by the localisation of all the recombination processes. In this thesis a computer model has been developed in which the dots are occupied by integer numbers of electrons and holes, with electron and hole occupancies controlled by Fermi-Dirac statistics. The recombination processes have similar dependences on the electron number and there is no clear transition from one process to another as the injection level is increased. These dependences cannot be represented by simple power law functions of the carrier number. An alternative model, in which each dot is electrically neutral, has also been studied, and the two models show significant differences for the hole distribution as the injection is increased. It is found that analyses based on power law relations between recombination rates and carrier number, as used for extended state systems, cannot be applied to localised recombination in dots.
Date January 2006
CreatorsPask, Helen J.
PublisherCardiff University
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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