Fe-Centers in GaN as Candidates for Spintronics Applications

ABSTRACT The potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 400 µm thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 5×1

Superconductivity in silicon nanostructures

We present the findings of the superconductivity observed in the silicon nanostructures prepared by short time diffusion of boron on the n-type Si(100) surface. These Si-based nanostructures represent the p-type ultra-narrow self-assembled silicon quantum wells, 2nm, confined by the delta - barriers heavily doped with boron, 3nm. The EPR and the thermo-emf studies show that the delta - barriers appear to consist of the trigonal dipole centres, which are caused by the negative-U reconstruction of the shallow boron acceptors. Using the CV and thermo-emf techniques, the transport of two-dimensional holes inside SQW is demonstrated to be accompanied by single-hole tunneling through these negative-U centres that results in the superconductivity of the delta - barriers. The values of the correlation gaps obtained from these measurements are in a good agreement with the data derived from the temperature and magnetic field dependencies of the magnetic susceptibility, which reveal a strong diamagnetism and additionally identify the superconductor gap value.Comment: 4 pages, 6 figures, presented at the 4th International Conference on Vortex Matter in Superconductors, Crete, Greece, September 3-9, 200

Lithium related deep and shallow acceptors in Li-doped ZnO nanocrystals

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 107, 024311 (2010) and may be found at https://doi.org/10.1063/1.3275889.We study the existence of Li-related shallow and deep acceptor levels in Li-doped ZnO nanocrystals using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. ZnO nanocrystals with adjustable Li concentrations between 0% and 12% have been prepared using organometallic precursors and show a significant lowering of the Fermi energy upon doping. The deep Li acceptor with an acceptor energy of 800 meV could be identified in both EPR and PL measurements and is responsible for the yellow luminescence at 2.2 eV. Additionally, a shallow acceptor state at 150 meV above the valence band maximum is made responsible for the observed donor-acceptor pair and free electron-acceptor transitions at 3.235 and 3.301 eV, possibly stemming from the formation of Li-related defect complexes acting as acceptors.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Spin interference in silicon one-dimensional rings

We present the first findings of the spin transistor effect caused by the Rashba gate-controlled ring embedded in the p-type self-assembled silicon quantum well that is prepared on the Si (100) surface. The coherence and phase sensitivity of the spin-dependent transport of holes are studied by varying the value of the external magnetic field and the gate voltage that are perpendicular to the plane of the double-slit ring. Firstly, the quantum scatterers connected to two one-dimensional leads and the quantum point contact inserted in the one of the arms of the double-slit ring are shown to define the amplitude and the phase of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations. Secondly, the amplitude and phase sensitivity of the 0.7 feature of the hole quantum conductance staircase revealed by the quantum point contact inserted are found to result from the interplay of the spontaneous spin polarization and the Rashba spin-orbit interaction.Comment: 2 pages, 2 figures, presented at the 5th International Conference on Strongly Correlated Electron Systems, SCES'05, Vienna, Austria, 26-30 July, 200

Magnetic and structural properties basic solid state physics of transition metal doped zinc-oxide nanostructures

We report on the magnetic and structural properties of two types of nanostructures doped with Co or Mn, namely, ZnO nanowires and colloidal ZnO nanocrystals. Electron paramagnetic resonance (EPR) spectra have been measured and analysed to extract information on the incorporation of the ions in the lattice. A detailed analysis by means of simulations of the experimental EPR spectra confirms that the transition metal (TM) ions were mainly incorporated as TM2+, occupying the Zn2+ sites in the wurtzite structure of ZnO. Furthermore, for both types of nanostructures, the EPR spectra are composed of more than one signal, revealing locally distorted environments or core-shell structures, proved by surface modifications via inorganic coatings