Theoretical and optical investigations of some III-V based quantum wells and modulation doped heterostructures
Abstract: This thesis is based on a combination of theoretical calculations and optical studies of the electronic structure and the radiative recombination processes in some III-V based quantum wells and ?-type modulation doped heterostructures. The optical studies includes photoluminescence (PL) spectroscopy, PL excitation (PLE) spectroscopy, and time-resolved PL. The PL experiments have been performed under various external perturbations, such as magnetic or electric fields. The theoretical calculations of the electronic structure in the studied quantum wells and ?-type modulation doped heterostructures, are based on a single band envelope function approximation. A number of different heterostructure material systems have beenstudied in this work: GaAs/ A1GaAs, InGaAs/InP and GaN/ A1GaN.In the GaAs/ A1GaAs system, the radiative recombination process in n-type modulation doped heterostructure has been studied. The spatially indirect recombination between the electrons in the 2DEG and photo-created holes in the valence band is highly dependent on the experimental conditions such as the excitation power and the electric field perturbation. The stationary as well as the dynamical properties have been studied in the PL experiments. The experimental result has been compared to self-consistent calculations of the electronic structure in the heterostructure, including a fully self-consistent simulation of the radiative decay process.In the In? Ga? As/InP material, the effects of strain, induced by the lattice mismatch between the ln? Ga1-? As well material and the InP barrier material, both in quantum wells and modulation doped heterostructures, have been studied as a function of the composition ?. The conditions for observing the Fermi-edge-singularity (FES) in luminescence have been investigated in n-type modulation doped lattice matched In0.53 Ga0.47As/InP heterostructures as a function of the 2DEG density. The FES luminescence is a many-body phenomena providing an enhancement of the optical matrix element in the vicinity of the Fermi-edge of the 2DEG.In the GaN / A1GaN system, a modulation doped heterostructure has been studied. Luminescence originating from the 2DEG formed in the GaN well has been observed. The experiments have been compared with self-consistent calculations of the energy levels in the 2DEG.
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