Direct evidence for implanted Fe on substitutional Ga sites in GaN

Wahl, Ulrich; Vantomme, André; Langouche, Guido; Correia, J. G.; Peralta, L.

doi:10.1063/1.1372201

Cited by 23 publications

(23 citation statements)

References 23 publications

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“…11,12 Furthermore, the emission channeling technique applied to Fe-implanted (Fe dose up to 10 19 cm −3 ) GaN samples confirmed the presence of a high percentage of TM ions (up to 80%) occupying substitutional Ga sites of the host crystal. 13 Moreover, GaN films doped with Fe, with concentrations up to 3 × 10 19 cm −3 were grown by molecular beam epitaxy (MBE) at substrate tempera-tures T S ranging from 20 to 380 • C directly on sapphire (0001) and ferromagnetic behavior with a Curie temperature T C = 100 K has been observed only in the samples grown at 400 • C. 14 Films of GaN:Fe (Fe density up to 6 × 10 21 cm −3 ) fabricated by means of MBE at T S = 500 -800 • C showed a superparamagnetic behavior 15,16 assigned to Ga-Fe and/or Fe-N inclusions. Extended x-ray absorption fine structure (EXAFS) analysis suggests that the decrease of T C leads to a structural transition from the wurtzite (wz) to the zinc-blende (zb) reconstruction, and this transition may be related to the origin of ferromagnetism in Fe-doped GaN films.…”

Section: Introductionmentioning

confidence: 99%

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

et al. 2007

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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. According to Hall effect measurements, electrons from residual donors are trapped by mid-gap Fe acceptor states in the limit of low iron content x 0.4%, indicating that the concentration of Fe 2+ ions increases at the expense of Fe ions in the 3+ charge state. This effect is witnessed by photoluminescence (PL) measurements as changes in the intensity of the Fe 3+ -related intra-ionic transition, which can be controlled by co-doping with Si donors and Mg acceptors. In this regime, EPR of Fe 3+ ions and Curie-like magnetic susceptibility are observed. As a result of the spin-orbit interaction, Fe 2+ does not produce any EPR response. However, the presence of Fe ions in the 2+ charge state may account for a temperature-independent Van Vleck-type paramagnetic signal that we observe by SQUID magnetometry. Surprisingly, at higher Fe concentrations, the electron density is found to increase substantially with the Fe content. The co-existence of electrons in the conduction band and Fe in the 3+ charge state is linked to the gradient in the Fe concentration. In layers with iron content x 0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. A set of precautions has been undertaken in order to rule out possible sources of spurious ferromagnetic contributions. Under these conditions, a ferromagnetic-like response is shown to arise from the (Ga,Fe)N epilayers, it increases with the iron concentration, it persists up to room temperature, and it is anisotropic -i.e., the saturation value of the magnetization is higher for in-plane magnetic field. 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.

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Section: Introductionmentioning

confidence: 99%

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

et al. 2007

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“…Note, nonetheless, that the incorporation of Mn impurities in N sites cannot be considered a direct effect of ion implantation, since it was not observed for Fe under very similar experimental conditions. 18 Fe is a 3d transition metal as well, with an atomic mass which is similar to that of Mn and, therefore, has similar incorporation kinetics. A more detailed description of the conditions under which N substitution by Mn impurities occurs in wurtzite GaN will require the assessment of the formation energies of such defects, as well as an experimental reassessment of the lattice location of Mn in GaN for different preparation methods and growth conditions, carefully taking into consideration the possibility of anion substitution.…”

Section: Discussionmentioning

confidence: 99%

“…We have previously used the emission channeling technique to determine the lattice location of other impurities in GaN (e.g. Fe, 18 As, 19 and several rare earths 20 ). The technique is particularly suited in cases where significant fractions of the impurity atoms occupy more than one lattice site.…”

Section: Methodsmentioning

confidence: 99%

Evidence of N substitution by Mn in GaN

et al. 2012

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We report on the lattice location of Mn in wurtzite GaN using β − emission channeling. In addition to the majority substituting for Ga, we locate up to 20% of the Mn atoms in N sites. We propose that the incorporation of Mn in N sites is enabled under sufficiently high concentrations of N vacancies, and stabilized by a highly charged state of the Mn cations. Since N substitution by Mn impurities in wurtzite GaN has never been observed experimentally or even considered theoretically before, it challenges the current paradigm of transition metal incorporation in wide-gap dilute magnetic semiconductors.

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“…Further calculations on the ratio of the integrated intensity counts, done on the L 3 and L 2 absorption edge of nickel, correspond to valence state of +2. In analogy with Wahl et al's report for Fe implanted GaN [3], we expect that some fraction of Ga is substituted by Ni after implantation. Moreover, the post-implantation annealing assured the migration to the correct (cation) lattice site of most of the implanted dopant ions [4].…”

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confidence: 89%

HRTEM and EELS Study in GaN-based Diluted Magnetic Semiconductor

Huang

Hsu

Kai

et al. 2005

MAM

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Diluted magnetic semiconductors (DMSs) based on III-V semiconductors, fabricated by incorporating a proper concentration of magnetic ions, have attracted considerable attentions in recent years because of the possibility involving charge and spin degrees of freedom in a single substance. It is expected to provide new functionality for microelectronic devices by exploiting the spin of charge carriers in the ferromagnetic semiconductors [1]. Also, it is desirable to exhibit robust ferromagnetism with Curie temperature Tc above room temperature without second magnetic phase or clusters [1]. However, to understand the correlation of magnetic properties and microstructure in DMSs with spatial resolution of near or even better than nanometer scale is required. The high spatial resolution available on a transmission electron microscopy (TEM) combined with the benefits of electron energy loss spectroscopy (EELS) allows detailed analysis in terms of microstructure and the white-line intensities of the transition metal at the onsets of the L 2 and L 3 absorption edges on the scale of nanometer. In our experiment, GaN-based DMSs with several annealing conditions are investigated by using high resolution TEM coupling with nano-beam energy dispersive x-ray spectroscopy (EDX) and EELS.In this study, for avoiding the formation of second phase (as shown in Fig. 1), we report on the use of a thin protecting layer during implantation with Ni at a dose of 5 × 10 16 cm -2 and the study of corresponding magnetic and structural properties after subsequent annealing. After etching off the protecting layer, subsequent annealing up to 800 o C under flowing N 2 resulted in a p-type GaN with apparent ferromagnetic behavior up to ∼ 320 K. In addition, the ferromagnetic behavior became more manifest with increasing annealing temperature that increases hole concentration. Neither presence of any other second phases nor clusters in the Ni-implanted region was identifiable, at least to the 0.2 nm point-to-point resolution of high resolution transmission electron microscopy. Although implantation damages are still abundant, there are no obvious extra spots contributed from secondary phases, and only the streaking diffraction spots from the GaN hexagonal crystal structure is observed. The streaking diffraction spots are resultant from lattice defects caused by the damages of ion implantation, including dislocation loops or stacking faults, as shown in Fig. 2. Since the 3-d shell is the outermost shell and known to be responsible for the magnetic properties for the 3-d transition metal group ions [2], this work will study the behavior of 3d state electrons in Ni-doped DMSs. Figure 2 shows the electron energy loss spectrum from several nanowires. The characteristic nickel L 2 and L 3 absorption edge can be seen. Further calculations on the ratio of the integrated intensity counts, done on the L 3 and L 2 absorption edge of nickel, correspond to valence state of +2. In analogy with Wahl et al.'s report for Fe implanted GaN [3], we expect that some ...

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Direct evidence for implanted Fe on substitutional Ga sites in GaN

Cited by 23 publications

References 23 publications

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

Evidence of N substitution by Mn in GaN

HRTEM and EELS Study in GaN-based Diluted Magnetic Semiconductor

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