Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N : The relationship 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.

[1]  Hoffmann,et al.  Fe3+ center in ZnO. , 1992, Physical review. B, Condensed matter.

[2]  Umesh K. Mishra,et al.  Growth of Fe doped semi-insulating GaN by metalorganic chemical vapor deposition , 2002 .

[3]  A. Marty,et al.  High-Curie-temperature ferromagnetism in self-organized Ge1−xMnx nanocolumns , 2006, Nature materials.

[4]  H. Jacobs,et al.  Structure determination of ζ-Fe2N by neutron and synchrotron powder diffraction , 1996 .

[5]  E. Carter,et al.  Diffusion of interstitial hydrogen into and through bcc Fe from first principles , 2004 .

[6]  Walker,et al.  Site-specific Mössbauer evidence of structure-induced magnetic phase transition in fcc Fe(100) thin films. , 1995, Physical review letters.

[7]  C. Pickering,et al.  In situ optical monitoring of AlGaN thickness and composition during MOVPE growth of AlGaN/GaN microwave HFETs , 2001 .

[8]  S. Pearton,et al.  Use of ion implantation to facilitate the discovery and characterization of ferromagnetic semiconductors , 2002 .

[9]  David C. Look,et al.  Comment on: Recombination of excitons bound to oxygen and silicon donors in freestanding GaN , 2002 .

[10]  Kazunori Sato,et al.  First principles materials design for semiconductor spintronics , 2002 .

[11]  Magnetic properties of 3d-impurities substituted in GaAs , 2001, cond-mat/0110405.

[12]  X. Xu,et al.  Structural and electronic properties of Fe 3+ and Fe 2+ centers in GaN from optical and EPR experiments , 2006 .

[13]  H. Bender,et al.  Growth and characterization of low-temperature grown GaN with high Fe doping , 2000 .

[14]  Krzysztof P. Korona,et al.  Dynamics of excitonic recombination and interactions in homoepitaxial GaN , 2002 .

[15]  Hiroshi Katayama-Yoshida,et al.  High Curie Temperature and Nano-Scale Spinodal Decomposition Phase in Dilute Magnetic Semiconductors , 2005 .

[16]  J. Coey,et al.  Anisotropic ferromagnetism in substituted zinc oxide. , 2004, Physical review letters.

[17]  K. Hingerl,et al.  In situ spectroscopic ellipsometry of MOCVD-grown GaN compounds for on-line composition determination and growth control , 2003 .

[18]  Michael Kunzer,et al.  Determination of the GaN/AlN band offset via the (/0) acceptor level of iron , 1994 .

[19]  D. Boerma,et al.  Mechanisms of epitaxial growth and magnetic properties of gamma '-Fe4N(100) films on Cu(100) , 2004 .

[20]  B. Monemar.  Bound excitons in GaN , 2001 .

[21]  H. Sitter,et al.  In‐situ and real‐time monitoring of MOCVD growth of III‐nitrides by simultaneous multi‐wavelength‐ellipsometry and X‐ray‐diffraction , 2006 .

[22]  S. Pearton,et al.  Characterization of High Dose Mn, Fe, and Ni implantation into p-GaN , 2002 .

[23]  J. Coey,et al.  Sample size, position, and structure effects on magnetization measurements using second-order gradiometer pickup coils , 2006 .

[24]  A. Vantomme,et al.  Direct evidence for implanted Fe on substitutional Ga sites in GaN , 2001 .

[25]  K. Žďánský,et al.  Temperature change of Hall and Seebeck coefficient sign in InP doped with transition metals , 2004 .

[26]  Martin S. Brandt,et al.  Prospects for carrier‐mediated ferromagnetism in GaN , 2003 .

[27]  X. Xu,et al.  Internal E 5 → T 2 5 transition of Fe 2 + in GaN , 2006 .

[28]  H. Sitter,et al.  Doping of GaN with Fe and Mg for spintronics applications , 2006 .

[29]  H. Munekata,et al.  Preparation of wurtzite GaN-based magnetic alloy semiconductors by molecular beam epitaxy , 2001 .

[30]  Stuart A. Wolf,et al.  Spintronics : A Spin-Based Electronics Vision for the Future , 2009 .

[31]  R. Dronskowski,et al.  Theoretical calculations on the structures, electronic and magnetic properties of binary 3d transition metal nitrides , 1999 .

[32]  H. Krenn,et al.  Magnetic properties of a new spintronic material—GaN:Fe , 2006 .

[33]  H. Akinaga,et al.  Fluorescence x-ray absorption fine structure study on local structures around Fe atoms heavily doped in GaN by low-temperature molecular-beam epitaxy , 2001 .

[34]  Kim,et al.  Dimer-vacancy defects on the Si(001)-2 x 1 and the Ni-contaminated Si(001)-2 x n surfaces. , 1995, Physical review. B, Condensed matter.

[35]  H. Sitter,et al.  Simultaneous determination of composition and growth rate of MOCVD nitrides by in situ multiple wavelength ellipsometry , 2005 .

[36]  A. Fouchet,et al.  TOPICAL REVIEW: Oxide-diluted magnetic semiconductors: a review of the experimental status , 2003 .

[37]  H. Amano,et al.  Iron Acceptors in Gallium Nitride (GaN) , 1993 .

[38]  Tomasz Dietl,et al.  Self-organized growth controlled by charge states of magnetic impurities , 2006, Nature materials.

[39]  Martin M. Frank,et al.  Absence of magnetism in hafnium oxide films , 2005 .

[40]  Electronic structure and magnetism of Mn-doped GaN , 2003, cond-mat/0308527.

[41]  D. Boerma,et al.  1D lattice distortions as the origin of the (2 x 2)p4gm reconstruction in gamma'-Fe4N(100): a magnetism-induced surface reconstruction. , 2005, Physical review letters.

[42]  Umesh K. Mishra,et al.  Growth and characteristics of Fe-doped GaN , 2003 .

[43]  W. Richter,et al.  In situ monitoring of GaN metal-organic vapor phase epitaxy by spectroscopic ellipsometry , 2000 .

[44]  Dejun Fu,et al.  Ferromagnetic behavior of p-type GaN epilayer implanted with Fe+ ions , 2004 .

[45]  K. Volz,et al.  Overgrowth experiments of ferromagnetic (MnGa)As-cluster layers by MOVPE , 2003 .

[46]  A. Zieba,et al.  Image and sample geometry effects in SQUID magnetometers , 1993 .

[47]  B. H. Blott,et al.  The determination of magnetic moments of extended samples in a SQUID magnetometer , 1993 .

[48]  B. Delley,et al.  Magnetic metastability in tetrahedrally bonded magnetic III-nitride semiconductors. , 2006, Physical review letters.

[49]  H. Amano,et al.  Infrared luminescence of residual iron deep level acceptors in gallium nitride (GaN) epitaxial layers , 1994 .

[50]  T. Chikyow,et al.  Molecular Beam Epitaxy of Wurtzite GaN-Based Magnetic Alloy Semiconductors , 2001 .

[51]  David P. Norton,et al.  Wide band gap ferromagnetic semiconductors and oxides , 2003 .

[52]  In situ X-ray diffraction during MOCVD of III-nitrides : An optimized wobbling compensating evaluation algorithm , 2007 .