Authors: Göhring, Holger
Title: Structural investigation of the impact of magnetostriction on GaMnAs thin film lattices and the thermal expansion of (In,Ga)As/GaAs quantum dots
Language (ISO): en
Abstract: The combination of semiconductor based materials with magnetic properties in so called diluted magnetic semiconductors could revolutionize the field of spintronics. Here, the charge and spin properties of such devices can be utilized for the processing and storage of data. The magnetic properties of gallium manganese arsenide (GaMnAs), which is a promising candidate for ferromagnetic ordering at room temperature, have been extensively studied over the years. Especially, the Curie temperature could be enhanced up to 250 K in special hybrid systems, since its first realization in 1996. This thesis deals with the investigation of the effect of magnetostriction on GaMnAs thin film lattices grown epitaxially on a GaAs substrate. The magnetostriction occurs during the magnetization process of the GaMnAs sample induced by the second-order phase transition occurring at the Curie temperature. The effect of magnetostriction was studied for two samples with Curie temperatures of 50 K and 110K on a temperature range from 30 K to 180 K. For this purpose, a continuous flow cryostat setup for high-resolution x-ray diffraction was constructed and developed at BL9 at DELTA. Here, measurements reveal changes in the GaMnAs lattice constant with a resolution on an order of magnitude of 10 -4 Å. The obtained results are analyzed in two independent approaches, investigating the angular separation of the positions of the GaAs and GaMnAs (004) Bragg reflections and the modelling of the measured crystal truncation rods. The discussion of both obtained results leads consistently to a relative change in lattice constant on the order of (2.8 ± 1.1) ∙10 -4 Å. Within a second project the thermal expansion of GaAs and (In,Ga)As/GaAs quantum dots were also investigated with the constructed high-resolution x-ray diffraction setup. It was found that the differences in thermal expansion of these samples are small compared to the effect of thermal heating. Therefore, it is highly unlikely, that the observed tetragonal lattice distortion of the quantum dot sample can be assigned to a sole thermal effect. It is further discussed, that this distortion is induced by the polaron formation due to the optical excitement of the carriers.
Subject Headings: Magnetostriction
Diluted magnetic semiconductors
High-resolution x-ray diffraction
Subject Headings (RSWK): Magnetischer Halbleiter
Issue Date: 2017
Appears in Collections:Experimentelle Physik I

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