Role of defects in ferromagnetism in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Zn</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">Co</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>: A hybrid density-functional study

Patterson, Charles H.

doi:10.1103/physrevb.74.144432

Cited by 194 publications

(113 citation statements)

References 68 publications

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“…Also some other negatively charged ionized gas particles originating from and close to the filament area can be accelerated toward the sample causing damage to the sample. A defect with the same energy level as E4 has been reported by Patterson et al 25 from theory and has been explained as the unoccupied level for the doubly charged oxygen vacancy, V o 2þ . Since the identity of E3 is not clear as yet, there is a possibility that E3 is interstitial Zn related.…”

Section: Resultssupporting

confidence: 57%

A comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

Mtangi

Auret

Rensburg

et al. 2011

Journal of Applied Physics

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A systematic investigation to check the quality of Pd Schottky contacts deposited on ZnO has been performed on electron beam (e-beam) deposited and resistively/thermally evaporated samples using current-voltage, IV, and conventional deep level transient spectroscopy (DLTS) measurements. Room temperature IV measurements reveal the dominance of pure thermionic emission on the resistively evaporated contacts, while the e-beam deposited contacts show the dominance of generation recombination at low voltages, <0.30 V, and the dominance of pure thermionic emission at high voltages, greater than 0.30 V. The resistively evaporated contacts have very low reverse currents of the order of 10 À10 A at a reverse voltage of 1.0 V whereas the e-beam deposited contacts have reverse currents of the order of 10 À6 A at 1.0 V. Average ideality factors have been determined as (1.43 6 0.01) and (1.66 6 0.02) for the resistively evaporated contacts and e-beam deposited contacts, respectively. The IV barrier heights have been calculated as (0.721 6 0.002) eV and (0.624 6 0.005) eV for the resistively evaporated and e-beam deposited contacts, respectively. Conventional DLTS measurements reveal the presence of three prominent defects in both the resistive and e-beam contacts. Two extra peaks with energy levels of 0.60 and 0.81 eV below the conduction band minimum have been observed in the e-beam deposited contacts. These have been explained as contributing to the generation recombination current that dominates at low voltages and high leakage currents. Based on the reverse current at 1.0 V, the degree of rectification, the dominant current transport mechanism and the observed defects, we conclude that the resistive evaporation technique yields better quality Schottky contacts for use in solar cells and ultraviolet detectors compared to the e-beam deposition technique. The 0.60 eV has been identified as possibly related to the unoccupied level for the doubly charged oxygen vacancy, V o 2þ .

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Section: Resultssupporting

confidence: 57%

A comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

Mtangi

Auret

Rensburg

et al. 2011

Journal of Applied Physics

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“…In a wide gap semiconductor such as ZnO (E g 3:4 eV), this would place the minority spin Co t 2d states within the band gap, as has been reported from both optical and magnetic measurements for ZnO:Co [13][14][15]. Surprisingly, this is not the case in previous theoretical studies [5][6][7][8].From consideration of Co 3d band coupling, FM interactions between occupied majority t 2d states results in no net energy gain due to filled bonding and antibonding combinations, while AFM interactions can result in a small energy gain (Fig. 1).…”

mentioning

confidence: 84%

“…Extrinsic n-type doping (e.g., Al) has also been shown to have a similar effect [15]. In contrast, band structure studies of ZnO:Co have reported preference for both FM [5] and AFM [6] ordering, in addition to no preferred magnetic alignment [7].…”

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confidence: 99%

Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

2008

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Substitutional cobalt in ZnO has a weak preference for antiferromagnetic ordering. Stabilization of ferromagnetism is achieved through n-type doping, which can be understood through a band coupling model. However, the description of the transition to a ferromagnetic ground state varies within different levels of band theory; issues arise due to the density functional theory underestimation of the band gap of ZnO, and the relative position of the nominally unfilled Co t 2d states. We examine these limitations, including approaches to overcome them, and explain the contradictions in previous studies, which drastically overestimate the doping threshold for magnetic ordering. DOI: 10.1103/PhysRevLett.100.256401 PACS numbers: 71.20.Nr, 71.15.Mb, 75.10.ÿb, 75.50.Pp The potential to simultaneously tune both charge and spin in solid state materials has lead to great interest in the field of spintronics [1]. The ultimate aim is a controllable room temperature semiconducting ferromagnet, which could be used in magnetoelectric and magnetotransport devices. Intrinsically magnetic semiconductors generally possess relatively low Curie temperatures (T C ); however, it has been proposed that incorporating transition metal or rare earth ions into a nonmagnetic semiconductor host lattice, forming a dilute magnetic semiconductor (DMS), may help raise T C above room temperature [2,3].In DMS materials, magnetism is influenced and controlled by the presence of charge carriers in the form of holes (GaAs:Mn) or electrons (GaN:Gd). There is still great debate over the fundamental mechanism behind the origin of the observed high temperature magnetic alignment in many of these systems. The situation is not helped by large variation in both experimental and theoretical studies [4 -8].Cobalt doped ZnO has become a focus of attention due to its reported high T C of up to 700 K and, most promisingly, the reversible cycling of FM ordering [9]. Coupled with existing optical and electrical properties of ZnO, the addition of controllable magnetism could make it a technologically essential material. It has been reported that at Co concentrations of less than 10%, the solubility is good and Co occupies a substitutional Zn site in a 2 charge state [9,10]. B . The splitting between filled e d and empty minority t 2d states for tetrahedral Co is typically on the order of 1.5-2 eV [12]. In a wide gap semiconductor such as ZnO (E g 3:4 eV), this would place the minority spin Co t 2d states within the band gap, as has been reported from both optical and magnetic measurements for ZnO:Co [13][14][15]. Surprisingly, this is not the case in previous theoretical studies [5][6][7][8].From consideration of Co 3d band coupling, FM interactions between occupied majority t 2d states results in no net energy gain due to filled bonding and antibonding combinations, while AFM interactions can result in a small energy gain (Fig. 1). Partial occupation of the empty minority t 2d states will result in a transition to FM ordering through the energy gained from the fi...

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“…We use a combination of scanning TEM (STEM) imaging and electron energy-loss spectroscopy (EELS) to characterize grain boundaries, planar defects and interfaces in order to reveal structural features and possible chemical inhomogeneities, some of which have not been previously reported in transition-metaldoped oxides. We demonstrate that the presence of extended defects, which can be distinguished from simple point defects, 12 as well as non-stoichiometric layers of Co:ZnO, should be considered in realistic models of such DMS layers. …”

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confidence: 98%

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

Kovács

Ney

Duchamp

et al. 2013

Journal of Applied Physics

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Room-temperature ferromagnetic Co-doped ZnO nanoneedle array prepared by pulsed laser deposition Appl. Phys. Lett. 87, 173119 (2005) We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al 2 O 3 ), as well as the Co:ZnO/Al 2 O 3 interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers next to the Al 2 O 3 substrate. The stacking fault density is in the range of 10 17 cm À3 . We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties. V C 2013 AIP Publishing LLC.

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Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

Cited by 194 publications

References 68 publications

A comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

A comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

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