Zeeman Interaction in Low-Dimensional III-V Semiconductor Structures

Sammanfattning: The Zeeman interaction in low-dimensional III-V semiconductor nanostructures is studied. The effective g-value of bulk InGaAs is measured by two different spin resonance techniques. Experimental conditions were found to control the Overhauser effect, thus enabling a highly accurate determination of the g-value, g' = -4.070 ± 0.005, being a prerequisite for theoretical modeling of low-dimensional structures. Novel optically detected spin resonance experiments of the electron effective g-values in quantum wells with a type-I band alignment are reported. The material systems studied are InxGa1-xAs/InP and InxGa1-xAs/GaAs. These technologically important systems have not been studied before due to their large optical transition rates giving lifetimes of electrons of the order of 0.1 to 1 nanosec. This is too short for magnetic dipole-induced spin transitions, thus the feasibility of the present spin resonance experiments is surprising. Spin transitions induced by the electric dipole operator are identified as an explanation for these experiments. The g-values measured at the conduction bandedge are strongly dependent on quantum confinement, which can be explained by a k.p calculation using the envelope function approximation. The spin splittings are furthermore strongly anisotropic with axial symmetry. In a two-dimensional system of GaAs/AlGaAs the zero-magnetic-field-splitting for k-vectors higher up in the conduction band is determined by beatings in Shubnikov-de Haas oscillations. Results of magnetic field dependent photoluminescence experiments on Stranski-Krastanow quantum dots, so-called artificial atoms, are presented. In InAs dots indications for level anticrossings are found. For InAs and InP dots in various surroundings the diamagnetic shifts are presented. InP dots on a GaAs surface show luminescence peaks that stem from individual excited states of electrons in the dots. Very good agreement with a novel calculation scheme taking into account the realistic pyramidal shape of the dots is found. The accurate modeling, which is based on k.p theory, is facilitated by the knowledge of the shape and size of the dots as obtained by Atomic Force Microscopy on the same samples. Single InP quantum dots are investigated in magnetic field dependent micro-photoluminescence experiments. The measurements are based on a new experimental set-up using a telescope. The results indicate that theoretical modeling is at present too simple to explain the detailed and complex structure of the spectra. InAs self-assembled dots can be placed in a controlled manner to form regular arrangements. This is facilitated by pre-determining the sites where the dots nucleate during their growth using Electron Beam Lithography and wet chemical etching to pattern the substrate.