Dissertation / PhD Thesis/Book

PreJuSER-55214

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Mit Mangan und Eisen ko-dotiertes Germanium: Ein ferromagnetischer Halbleiter?

Braak, H. (Corresponding author)FZJ*

2006
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/2541

Report No.: Juel-4223

Abstract: This thesis describes the synthesis and characterization of diluted magnetic semiconductors. The potential of co-doping germanium with manganese and iron to increase the Curie-temperature of diluted magnetic semiconducting Ge(Mn)-films is explored. Epitaxial Ge(Mn,Fe)films are prepared by evaporating the three elements layer-by-layer in a MBE-system. Post annealing intermixes the sequentially evaporated films by diffusion. Adding a small amount of iron to Ge(Mn)-films results in a drastically different magnetization behavior of the films. The Mn$_{11}Ge_{8}$-phase, which is detected in the Ge(Mn)-films, vanishes and the contribution of the Mn$_{5}Ge_{3}$-phase to the magnetization strongly increases compared to the Ge(Mn)-films. An unknown magnetic low-temperature phase (LT-phase) with a Curie-temperature of 210K appears. The contribution of this LT-phase to the magnetization is very small. Transport measurements reveal for these samples p-type semiconducting properties and the anomalous Hall effect is negligible. The microstructure analysis shows a strongly inhomogeneous sample with Mn-containing clusters. Decreasing the annealing temperature significantly reduces the number of clusters, which can be attributed to the Mn$_{5}Ge_{3}$-phase. The temperature dependence of the magnetization shows again the presence of the two magnetic phases. The contribution of the LT-phase to the magnetization is strongly increased and much larger than that of the cluster phase. The film contains cylindrical inhomogeneities with higher Mn- and Fe-concentrations than the surrounding matrix. The anomalous Hall effect shows contributions for both the LT-phase and the cluster phase. The formation of the cluster phase is suppressed by optimizing the relative Mn- and Fe-concentrations, and the magnetization measurements reveal only the LT-phase. The crystal structure of the cylindrical inhomogeneities has a precise eptiaxial relation to the matrix. The optimized p-type semiconducting Ge(Mn,Fe)-film shows an almost one magnitude higher anomalous Hall effect of the LT-phase than the Ge(Mn,Fe)-film containing clusters. Only further experiments addressing the intrinsic carrier-induced ferromagnetism can answer the question, whether the optimized, single-phase Ge(Mn,Fe)-film with a Curie-temperature of 210K is a diluted ferromagnetic semiconductor. The presence of the anomalous Hall effect is a necessary but not sufficient condition for a ferromagnetic semiconductor, because - as shown here - cluster phases can also give rise to an anomalous Hall effect.

Note: Record converted from VDB: 12.11.2012
Note: Köln, Univ., Diss., 2006

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Research Program(s):

1. Grundlagen für zukünftige Informationstechnologien (P42)

Appears in the scientific report 2006

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