Structural and paramagnetic properties of dilute Ga1-xMnxN

Systematic investigations of the structural and magnetic properties of single crystal (Ga,Mn)N films grown by metal organic vapor phase epitaxy are presented. High resolution transmission electron microscopy, synchrotron x-ray diffraction, and extended x-ray absorption fine structure studies do not reveal any crystallographic phase separation and indicate that Mn occupies Ga-substitutional sites in the Mn concentration range up to 1%. The magnetic properties as a function of temperature, magnetic field and its orientation with respect to the c-axis of the wurtzite structure can be quantitatively described by the paramagnetic theory of an ensemble of non-interacting Mn$^{3+}$ ions in the relevant crystal field, a conclusion consistent with the x-ray absorption near edge structure analysis. A negligible contribution of Mn in the 2+ charge state points to a low concentration of residual donors in the studied films. Studies on modulation doped p-type (Ga,Mn)N/(Ga,Al)N:Mg heterostructures do not reproduce the high temperature robust ferromagnetism reported recently for this system.Comment: 15 pages, 14 figure

Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N - relation between structural, electronic, and magnetic properties

We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and (Ga,Fe)N layers on c-sapphire substrates and their thorough characterization via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably FexN with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. In layers with iron content x<0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. We link the presence of ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced by TEM and EDS studies. This interpretation is supported by magnetization measurements after cooling in- and without an external magnetic field, pointing to superparamagnetic properties of the system. It is argued that the high temperature ferromagnetic response due to spinodal decomposition into regions with small and large concentration of the magnetic component is a generic property of diluted magnetic semiconductors and diluted magnetic oxides showing high apparent Curie temperature.Comment: 21 pages, 30 figures, submitted to Phys. Rev.

Soluciones creativas de intervención

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Magnetic Nanostructures Embedded in III-Nitrides: Assembly and Performance

III-Nitride semiconductors are the materials of choice for state-of-the-art opto-electronic and high-power electronic applications. Through the incorporation of magnetic ions, like transition metals and rare-earths, III-Nitrides have further extended their applicability to spintronic devices. However, in most III-Nitrides the low solubility of the magnetic ions leads to the formation of secondary phases that are often responsible for the observed magnetic behavior of the layers. The present review summarizes the research dedicated to the understanding of the basic properties, from the fabrication to the performance, of III-Nitride-based phase-separated magnetic systems containing embedded magnetic nanostructures as suitable candidates for spintronics applications

Tuning the Size, Shape and Density of ′-GayFe4yN Nanocrystals Embedded in GaN

Phase-separated semiconductor systems hosting magnetic nanocrystal (NCs) are attracting increasing attention, due to their potential as spintronic elements for the next generation of devices. Owing to their morphology- and stoichiometry-dependent magnetic response, self-assembled -GayFe4yN NCs embedded in a Fe -doped GaN matrix, are particularly versatile. It is studied and reported here, how the tuning of relevant growth parameters during the metalorganic vapour phase epitaxy process affects the crystalline arrangement, size, and shape of these self-assembled nanostructures. In particular, it is found that the Ga-flow provided during the -doping, determines the amount of Fe incorporated into the layers and the spatial density of the NCs. Moreover, the in-plane dimensions of the NCs can also be controlled via the Ga-flow, conditioning the aspect-ratio of the embedded nanostructures. These findings are pivotal for the design of nanocrystal arrays with on-demand size and shape, essential requirements for the implementation into functional devices.P22477P24471P26830V478227690(VLID)344806

Analytical electron microscopy study on gallium nitride systems doped with manganese and iron

Modulated structures of gallium nitride (GaN) doped with transition metal ions (here Fe, Mn) are investigated by analytical (scanning) transmission electron microscopy to gain insight into the structural arrangement and chemical composition of the material, known to be critically correlated to the magnetic response and hence the functionality of these technologically relevant systems. Three classes of samples are considered: (i) homogeneous (dilute) (Ga, Mn)N; (ii) δ-Mn-doped (Ga, δ-Mn)N and phase separated (Ga, Fe)N, containing Fe-rich nanocrystals. The combination of various microscopic techniques employed, allows for a quantitative determination of the distribution of the magnetic ions in the samples, providing essential information on the structural and chemical asset of these systems