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GROWTH AND CHARACTERIZATION OF MAGNETIC SEMICONDUCTORS GeMn

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  • Tesi Di Dottorato
Disciplines
  • Engineering
  • Physics

Abstract

Recently, diluted magnetic semiconductors (DMS) have attracted the attention of both scientific and industry community. This class of materials is made of some ordinary semiconductors containing a small fraction of magnetic impurities in their lattice. DMSs have some unique properties, which enhance their potential use in a wide range of opto-electronic devices. They behave in a similar way to their non-magnetic counterpart semiconductors, in the absence of any applied external magnetic field. The lattice constant and the band gap can be tuned by changing the concentration of the added magnetic impurities. The possibility for band gap engineering in these systems makes them useful for different device applications, while the tunability of the lattice parameter with magnetic ion content, also extends their application to the field of heterostructures, where lattice matching is fundamental. The presence of substituted magnetic ions in the DMS results in magnetic properties that distinguish them from ordinary semiconductors. In DMSs an applied magnetic field changes the energy band and impurity level parameters but, most of all, a ferromagnetic order can be induced in the material, coexisting with the ordinary semiconducting behaviour. A unique and important feature of DMSs is the spin-spin exchange interaction between the localized magnetic moment of a magnetic ion and the charge carrier in the conduction or valence band. This interaction affects the energy band, electronic structure and impurity level parameters of the semiconductors, resulting in new physical effects particularly when in presence of strong magnetic fields. The consequences may be quite dramatic: g-factor is effectively enhanced by up to two order of magnitude, Faraday rotations become very large and the magneto-resistance can become negative, reaching exceptionally large values and leading to an insulator to metal transition induced by increasing magnetic field. So far, the most extensively studied DMSs are II-Mn-VI compound systems, which can accommodate the highest possible magnetic ion content without destroying the structure of the host II-VI semiconductors. VI

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