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13 Aug 2007

Volume 91, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 071906 (2007); http://dx.doi.org/10.1063/1.2753092 (3 pages)

Cheng Zhang, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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Thermally driven defect formation and blocking layers at metal-ZnO interfaces

H. L. Mosbacker, C. Zgrabik, M. J. Hetzer, A. Swain, D. C. Look, G. Cantwell, J. Zhang, J. J. Song, and L. J. Brillson

Appl. Phys. Lett. 91, 072102 (2007); http://dx.doi.org/10.1063/1.2772664 (3 pages) | Cited 11 times

Online Publication Date: 16 August 2007

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The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe the temperature-dependent formation of native point defects and reaction layers at metal-ZnO interfaces and their effect on transport properties. These results identify characteristic defect emissions corresponding to metal-Zn alloy versus oxide formation. Au alloys with Zn above its eutectic temperature, while Ta forms oxide blocking layers that reduce current by orders of magnitude at intermediate temperatures. Defects generated at higher temperatures and/or with higher initial defect densities for all interfaces produce Ohmic contacts. These reactions and defect formation with annealing reveal a thermodynamic control of blocking versus Ohmic contacts.
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61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.60.Hk Cathodoluminescence, ionoluminescence

CO2 laser rapid-thermal-annealing SiOx based metal-oxide-semiconductor light emitting diode

Gong-Ru Lin and Chun-Jung Lin

Appl. Phys. Lett. 91, 072103 (2007); http://dx.doi.org/10.1063/1.2769962 (3 pages) | Cited 5 times

Online Publication Date: 16 August 2007

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Structural damage enhanced near-infrared electroluminescence (EL) of a metal-oxide-semiconductor light emitting diode (MOSLED) made on SiOx film with buried nanocrystallite Si after CO2 laser rapid thermal annealing (RTA) at an optimized intensity of 6 kW/cm2 for 1 ms is demonstrated. CO2 laser RTA induced oxygen-related defects are capable of improving Fowler-Nordheim tunneling mechanism of carriers at metal/SiOx interface. The CO2 laser RTA SiOx film reduces Fowler-Nordheim tunneling threshold to 1.8 MV/cm, facilitating an enhanced EL power of an indium tin oxide/SiOx/p-Si/Al MOSLED up to 50 nW at a current density of 2.3 mA/cm2.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices

Electronic transport studies of a systematic series of GaAs/AlGaAs quantum wells

D. R. Luhman, D. C. Tsui, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 91, 072104 (2007); http://dx.doi.org/10.1063/1.2767978 (3 pages) | Cited 5 times

Online Publication Date: 16 August 2007

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The results of experimental transport studies involving a series of five narrow Al0.1Ga0.9As/GaAs quantum wells with well widths ranging from 7.9 to 33.0 nm are reported. The total transport scattering rate measured in thin AlGaAs/GaAs quantum wells is typically limited by electron scattering from the interfacial roughness of the quantum well. For a relatively low constant electron density (ne ∼ 5.8×1010 cm−2), the authors find that interfacial roughness is the dominant scattering mechanism for L ⩽ 16.0 nm and describe the data using a finite quantum well model with adjustable interfacial roughness parameters. Temperature dependence data are also presented.
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73.63.Hs Quantum wells
73.25.+i Surface conductivity and carrier phenomena
68.35.Ct Interface structure and roughness

Study on the synthesis of high quality single crystalline Si1−xGex nanowire and its transport properties

S. J. Whang, S. J. Lee, W. F. Yang, B. J. Cho, and D. L. Kwong

Appl. Phys. Lett. 91, 072105 (2007); http://dx.doi.org/10.1063/1.2772665 (3 pages) | Cited 11 times

Online Publication Date: 17 August 2007

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In this wok, the authors report a synthesis of high quality single crystalline homogeneous Si1−xGex nanowires and investigate the effects of growth temperature on the microstructures, morphologies, and properties of Si1−xGex nanowires. Fabricated phosphorus-doped Si1−xGex nanowire metal-oxide-semiconductor (MOS) field effect transistor integrated with 5 nm HfO2, TaN/Ta metal gate, and Pd source/drain electrode demonstrated enhancement mode p-MOS operation with Ion/Ioff ∼ 104, subthreshold swing of ∼ 136 mV/decade, and small hysteresis of 90 mV.
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81.07.Bc Nanocrystalline materials
81.05.Hd Other semiconductors
73.63.Nm Quantum wires
61.46.Hk Nanocrystals
81.16.-c Methods of micro- and nanofabrication and processing
85.30.Tv Field effect devices

Nitrogen passivation of (0001) 4H-SiC silicon-face dangling bonds

G. Pennington and C. R. Ashman

Appl. Phys. Lett. 91, 072106 (2007); http://dx.doi.org/10.1063/1.2770653 (3 pages) | Cited 6 times

Online Publication Date: 17 August 2007

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The authors report a density functional theory study of nitrogen passivation of the (0001) Si face of 4H-SiC. Results indicate that (1) upon passivation dangling bond density is reduced near the conduction band and increased near the valence band and (2) stable nitrogen coverage is allowed only up to 1/3 of a monolayer. Although an oxygen environment is not considered, these findings concur with experimental studies of 4H-SiC metal-oxide-semiconductor field-effect transistors which have undergone gate oxide annealing in the presence of nitrogen. Simulations indicate that nitrogen may reduce interface state density by removing 4H-SiC Si-face dangling bonds.
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81.65.Rv Passivation
71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states

In situ imaging of electromigration-induced nanogap formation by transmission electron microscopy

Hubert B. Heersche, Günther Lientschnig, Kevin O’Neill, Herre S. J. van der Zant, and Henny W. Zandbergen

Appl. Phys. Lett. 91, 072107 (2007); http://dx.doi.org/10.1063/1.2767149 (3 pages) | Cited 20 times

Online Publication Date: 17 August 2007

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The authors imaged electromigration-induced nanogap formation in situ by transmission electron microscopy. Real-time video recordings show that edge voids form near the cathode side. The polycrystalline gold wires narrow down until a single-grain boundary intersects the constriction along which the breaking continues. During the last 50 ms of the break, a relatively large deformation of the constriction’s geometry occurs. The shape of the anode (blunt) and the cathode (sharp) is asymmetric when the wire breaks with a bias voltage applied, but symmetric when a narrow constriction breaks spontaneously.
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66.30.Qa Electromigration
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries

Observation of type-I and type-II excitons in strained Si/SiGe quantum-well structures

K. Y. Wang, W. P. Huang, H. H. Cheng, G. Sun, R. A. Soref, R. J. Nicholas, and Y. W. Suen

Appl. Phys. Lett. 91, 072108 (2007); http://dx.doi.org/10.1063/1.2771094 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2007

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The authors report photoluminescence (PL) measurement on a series of Si/SiGe quantum-well structures that had different internal strain distributions. When each sample was placed in a high magnetic field, the field-dependent energy shift of the relevant PL peaks revealed either type-I or type-II exciton formation depending on the strain distribution. This observation is in agreement with theoretical modeling. The present investigation shows that type-I band alignment—desired for electroluminescent devices—can be achieved by strain engineering.
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78.55.Ap Elemental semiconductors
78.67.De Quantum wells
71.35.-y Excitons and related phenomena

Current transport mechanism of Au/Ni/GaN Schottky diodes at high temperatures

S. Huang, B. Shen, M. J. Wang, F. J. Xu, Y. Wang, H. Y. Yang, F. Lin, L. Lu, Z. P. Chen, Z. X. Qin, Z. J. Yang, and G. Y. Zhang

Appl. Phys. Lett. 91, 072109 (2007); http://dx.doi.org/10.1063/1.2772182 (3 pages) | Cited 14 times

Online Publication Date: 17 August 2007

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Current transport mechanism in Au/Ni/GaN Schottky diodes has been investigated using current-voltage characterization technique between 27 and 350 °C. It is found that the ideality factor n of the diode decreases with increasing temperature when the temperature is lower than 230 °C, and then increases with increasing temperature when the temperature is higher than 230 °C. The corresponding Schottky barrier height (SBH) increases all through the temperature range. Thermionic-emission model with a Gaussian distribution of SBHs is thought to be responsible for the electrical behavior at temperatures lower than 230 °C, while the generation-recombination (GR) process takes place in at temperatures above 230 °C. The effective Richardson constant is determined to be 24.08 A cm−2 K−2, in excellent agreement with the theoretical value. The extrapolated activation energy of the GR process is determined to be 1.157 eV. Based on the cathodoluminescence measurements, it is suggested that the deep level defects inducing yellow luminescence facilitate the GR process of the current transport in the diodes.
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85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions

Giant magnetoresistance in oxide-based metallic multilayers

Mara Granada, J. Carlos Rojas Sánchez, and Laura B. Steren

Appl. Phys. Lett. 91, 072110 (2007); http://dx.doi.org/10.1063/1.2772237 (3 pages) | Cited 2 times

Online Publication Date: 17 August 2007

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The authors report on the first measurement of low-field giant magnetoresistance in metallic multilayers of perovskite oxides. The authors performed in-plane measurements of the magnetoelectric transport properties in La0.75Sr0.25MnO3/LaNiO3 trilayers and succeeded in distinguishing the giant magnetoresistance effect from other contributions to the total magnetoresistance. The samples were grown on single-crystalline SrTiO3 substrates by dc sputtering.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
81.15.Cd Deposition by sputtering
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Experimental realization of a silicon spin field-effect transistor

Biqin Huang, Douwe J. Monsma, and Ian Appelbaum

Appl. Phys. Lett. 91, 072501 (2007); http://dx.doi.org/10.1063/1.2770656 (3 pages) | Cited 18 times

Online Publication Date: 13 August 2007

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A longitudinal electric field is used to control the transit time (through an undoped silicon vertical channel) of spin-polarized electrons precessing in a perpendicular magnetic field. Since an applied voltage determines the final spin direction at the spin detector and hence the output collector current, this comprises a spin field-effect transistor. An improved hot-electron spin injector providing ≈ 115% magnetocurrent, corresponding to at least ≈ 37% electron current spin polarization after transport through 10 μm undoped single-crystal silicon, is used for maximum current modulation.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Low-temperature ordering of (001) granular FePt films by inserting ultrathin SiO2 layers

Yun-Chung Wu, Liang-Wei Wang, and Chih-Huang Lai

Appl. Phys. Lett. 91, 072502 (2007); http://dx.doi.org/10.1063/1.2770652 (3 pages) | Cited 40 times

Online Publication Date: 13 August 2007

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L10 granular FePt–SiO2 films with a (001) preferred orientation and well-separated grains of 5.14 nm were obtained by depositing atomic-scale Fe/Pt/SiO2 multilayers (MLs) on glass substrates and subsequently annealing MLs at a temperature of 350 °C. Large out-of-plane coercivity of 7700 Oe and a high ordering factor of 0.83 were achieved. Alternate atomic-scale depositions promoted the formation of (001) textures. Furthermore, because of the low surface energy of SiO2 layers, SiO2 tended to diffuse into grain boundaries of FePt during annealing, which may accelerate diffusion of Fe and Pt atoms, resulting in the low-temperature ordering.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
68.35.Fx Diffusion; interface formation

Synthesis and magnetic properties of (Nd1−xSmx)5Fe17 (x = 0–1) phase

Tetsuji Saito

Appl. Phys. Lett. 91, 072503 (2007); http://dx.doi.org/10.1063/1.2770771 (3 pages) | Cited 2 times

Online Publication Date: 13 August 2007

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An investigation of the synthesis of the (Nd1−xSmx)5Fe17 (x = 0–1) phase and its magnetic properties is presented. It was found that the (Nd1−xSmx)5Fe17 (x = 0–1) phase can be produced by annealing of the amorphous melt-spun ribbon, regardless of the Sm content of the phase. The Curie temperature and coercivity of the (Nd1−xSmx)5Fe17 (x = 0–1) phase increased with its Sm content.
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81.05.Bx Metals, semimetals, and alloys
75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments

Charge order suppression and weak ferromagnetism in La1/3Sr2/3FeO3 nanoparticles

F. Gao, P. L. Li, Y. Y. Weng, S. Dong, L. F. Wang, L. Y. Lv, K. F. Wang, J.-M. Liu, and Z. F. Ren

Appl. Phys. Lett. 91, 072504 (2007); http://dx.doi.org/10.1063/1.2768895 (3 pages) | Cited 13 times

Online Publication Date: 14 August 2007

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Perovskite-type polycrystalline La1/3Sr2/3FeO3 particles with different sizes (80–2000 nm) were prepared using a simple sol-gel technique. In samples of nanoparticles with a diameter of less than 300 nm, weak ferromagnetism was observed at room temperature, which was attributed to the lattice distortion. The magnetic and specific heat measurements suggest that the charge ordering state was largely suppressed due to the lowering of the particle size, but the charge ordering temperature remained unaffected.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Nuclear magnetic resonance in the earth’s magnetic field using a nitrogen-cooled superconducting quantum interference device

Longqing Qiu, Yi Zhang, Hans-Joachim Krause, Alex I. Braginski, Martin Burghoff, and Lutz Trahms

Appl. Phys. Lett. 91, 072505 (2007); http://dx.doi.org/10.1063/1.2771060 (3 pages) | Cited 23 times

Online Publication Date: 14 August 2007

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The authors recorded nuclear magnetic resonance (NMR) spectra of water, benzene, fluorobenzene, and 2,2,2-trifluoroethanol in the earth’s magnetic field (EMF) using a nitrogen-cooled superconducting quantum interference device (SQUID). In trifluoroethanol, the broadband detection characteristics of the SQUID with a noise floor of about 70 fT/√Hz enabled authors to simultaneously observe fluorine and proton spectra at 1940 and 2060 Hz Larmor frequency, reflecting their heteronuclear J coupling in the high-field limit without showing a measurable chemical shift. To reduce the noise in EMF-NMR, the authors suggest the use of frequency-adjusted averaging, which compensates line broadening due to EMF fluctuations.
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76.60.-k Nuclear magnetic resonance and relaxation
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Nonvolatile memory effect of capacitance in polycrystalline spinel vanadate

H. Takei, T. Suzuki, and T. Katsufuji

Appl. Phys. Lett. 91, 072506 (2007); http://dx.doi.org/10.1063/1.2771041 (3 pages) | Cited 5 times

Online Publication Date: 14 August 2007

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The authors found that capacitance of polycrystalline spinel FeV2O4 exhibits a magnetic-field dependence with hysteresis and takes two values at zero field depending on the direction of a small magnetic field ( ∼ 1000 G) applied prior to measurement. This behavior can be potentially used as a nonvolatile memory device in which the data are stored as a difference of capacitance through the change of magnetic-field directions.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.-y Studies of specific magnetic materials

X-ray magnetic circular dichroism characterization of GaN/Ga1−xMnxN digital ferromagnetic heterostructure

J. I. Hwang, M. Kobayashi, G. S. Song, A. Fujimori, A. Tanaka, Z. S. Yang, H. J. Lin, D. J. Huang, C. T. Chen, H. C. Jeon, and T. W. Kang

Appl. Phys. Lett. 91, 072507 (2007); http://dx.doi.org/10.1063/1.2769944 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2007

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The authors have investigated the magnetic properties of a GaN/Ga1−xMnxN (x = 0.1) digital ferromagnetic heterostructure (DFH) showing ferromagnetic behavior using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The Mn L2,3-edge XAS spectra were similar to those of Ga1−xMnxN random alloy thin films, indicating a substitutional doping of high concentration Mn into GaN. From the XMCD measurements, it was revealed that paramagnetic and ferromagnetic Mn atoms coexisted in the Ga1−xMnxN digital layers. Subtle differences were also found from the XMCD spectra between the electronic states of the ferromagnetic and paramagnetic Mn2+ ions. The ferromagnetic moment per Mn atom estimated from XMCD agreed well with that estimated from superconducting quantum interference device measurements, indicating that the ferromagnetic behavior of the GaN/Ga1−xMnxN DFH sample arises only from substitutional Mn2+ ions in the Ga1−xMnxN digital layers and not from ferromagnetic precipitates.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Pp Magnetic semiconductors

Dipole-induced magnetic anisotropy in γ-Fe2O3(001) epitaxial films

H. Yanagihara, J. Hagiwara, M. Nakazumi, Eiji Kita, and T. Furubayashi

Appl. Phys. Lett. 91, 072508 (2007); http://dx.doi.org/10.1063/1.2771062 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2007

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The authors investigated the magnetic anisotropy of epitaxial films of γ-Fe2O3(001) composed entirely of Fe3+. The cubic anisotropy term (K1) was negligibly small (K1 ≈ −2.7×104 erg/cm3), as expected for L ≈ 0 systems; however, substantially large uniaxial anisotropy energy (Ku ≈ 6.1×105 erg/cm3) was found as the thickness reached the bulk limit. A detailed characterization of both the in-plane and out-of-plane lattice parameters revealed that the c/a ratio of the unit cell was intrinsically elongated due to its vacancy-ordered supercell. This unexpectedly large Ku is reasonably explained by simple dipole sums if the authors take into account the slightly stretched unit cell (c′/a = 1.03) in the growth direction even without the spin-orbit interaction.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Controlled interface profile in Sm–Co/Fe exchange-spring magnets

Y. Choi, J. S. Jiang, J. E. Pearson, S. D. Bader, J. J. Kavich, J. W. Freeland, and J. P. Liu

Appl. Phys. Lett. 91, 072509 (2007); http://dx.doi.org/10.1063/1.2769755 (3 pages) | Cited 20 times

Online Publication Date: 16 August 2007

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In exchange-spring magnets with temperature-induced interfacial intermixing, differences in the extent of diffusion of constituent elements typically lead to local compositional changes. The authors demonstrate that adding an artificially created intermixed layer in Sm–Co/Fe exchange-spring permanent magnets enhances the exchange coupling effectiveness without modifying the local composition of the Sm–Co layer. Element- and depth-resolved magnetization measurements verify that the diffusion extent of Sm and Co is similar across the interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.50.Ww Permanent magnets
68.35.Fx Diffusion; interface formation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Exchange bias behavior in Ni–Mn–Sb Heusler alloys

Mahmud Khan, Igor Dubenko, Shane Stadler, and Naushad Ali

Appl. Phys. Lett. 91, 072510 (2007); http://dx.doi.org/10.1063/1.2772233 (3 pages) | Cited 59 times

Online Publication Date: 16 August 2007

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The authors report the observation of exchange bias in bulk polycrystalline Ni50Mn25+xSb25−x Heusler alloys. Shifts in hysteresis loops of up to 248 Oe were observed in the 5 T field cooled samples. The observed exchange bias behavior in Ni50Mn25+xSb25−x is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. Such behavior is an addition to the multifunctional properties of the Ni50Mn25+xSb25−x Heusler alloy system.
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75.30.Et Exchange and superexchange interactions
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Role of point defects in room-temperature ferromagnetism of Cr-doped ZnO

Hui Liu, Xiao Zhang, Luyan Li, Y. X. Wang, K. H. Gao, Z. Q. Li, R. K. Zheng, S. P. Ringer, Bei Zhang, and X. X. Zhang

Appl. Phys. Lett. 91, 072511 (2007); http://dx.doi.org/10.1063/1.2772176 (3 pages) | Cited 54 times

Online Publication Date: 17 August 2007

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Polycrystalline CrxZn1−xO films and powders are prepared by cosputtering and sol-gel method, respectively. While room-temperature ferromagnetism is found in as-deposited films, the powders exhibit paramagnetism. Comparison of the structural and magnetic properties of the as-deposited, annealed, and powdered samples indicates that the interstitial zinc, together with Cr doping, plays an important role in the ferromagnetic origin of Cr:ZnO. The ferromagnetism in films can be described by bound magnetic polaron models with respect to defect-bound carriers.
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81.05.Dz II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.-m Intrinsic properties of magnetically ordered materials

Linear and nonlinear electrodynamic responses of bulk CaC6 in the microwave regime

A. Andreone, G. Cifariello, E. Di Gennaro, G. Lamura, N. Emery, C. Hérold, J. F. Marêché, and P. Lagrange

Appl. Phys. Lett. 91, 072512 (2007); http://dx.doi.org/10.1063/1.2769763 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2007

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The linear and nonlinear responses to a microwave electromagnetic field of two c-axis oriented polycrystalline samples of the recently discovered superconductor CaC6 (TC ≈ 11.5 K) is studied in the superconducting state down to 2 K. The surface resistance RS and the third order intermodulation distortion, arising from a two-tone excitation, have been measured as a function of temperature and microwave circulating power. Experiments are carried out using a dielectrically loaded copper cavity operating at 7 GHz in a “hot finger” configuration. The results confirm recent experimental findings that CaC6 behaves as a weakly coupled, fully gapped, superconductor.
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74.25.N- Response to electromagnetic fields
74.25.F- Transport properties

Amplification of spin-current polarization

D. Saha, M. Holub, and P. Bhattacharya

Appl. Phys. Lett. 91, 072513 (2007); http://dx.doi.org/10.1063/1.2772660 (3 pages) | Cited 16 times

Online Publication Date: 17 August 2007

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A ferromagnet/semiconductor based electrically controlled spin-current amplifier using a dual-drain nonlocal lateral spin valve is demonstrated. The spin polarization injected by the source into the channel is amplified at the second drain contact. An amplified current spin polarization of 100% is measured. The controlled variation of amplifier gain with bias is also demonstrated. The observations are explained in the framework of the spin drift-diffusion model.
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72.25.Dc Spin polarized transport in semiconductors
72.25.Hg Electrical injection of spin polarized carriers
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Effect of annealing on the magnetic properties of Gd focused ion beam implanted GaN

M. A. Khaderbad, S. Dhar, L. Pérez, K. H. Ploog, A. Melnikov, and A. D. Wieck

Appl. Phys. Lett. 91, 072514 (2007); http://dx.doi.org/10.1063/1.2770762 (3 pages) | Cited 20 times

Online Publication Date: 17 August 2007

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The authors have studied the effect of annealing on the magnetic and the structural properties of Gd focused ion beam implanted GaN samples. Molecular beam epitaxy grown GaN layers, which were implanted with 300 keV Gd3+ ions at room temperature at doses 2.4×1011 and 1.0×1015 cm−2, are rapid thermally annealed in flowing N2 gas up to 900 °C for 30 s. X-ray diffraction results indicate the presence of Ga and N interstitials in the implanted layers. Their densities are also found to reduce upon annealing. At the same time, magnetic measurements on these samples clearly show a reduction in the saturation magnetization as a result of the annealing for the lowest Gd incorporated sample, while in the highest Gd incorporated sample it does not change. These findings suggest that Gd might be inducing magnetic moment in Ga and/or N interstitials in giving rise to an effective colossal magnetic moment of Gd and the associated ferromagnetism observed in Gd:GaN.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
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Influence of crystallographic steps on properties of ferroelectric ultrathin films: An ab initio study

S. Prosandeev and L. Bellaiche

Appl. Phys. Lett. 91, 072901 (2007); http://dx.doi.org/10.1063/1.2770764 (3 pages) | Cited 3 times

Online Publication Date: 13 August 2007

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A first-principles-based approach is used to investigate the effect of a crystallographic step on the existence and morphology of the recently discovered periodic nanostripe domains [ S. K. Streiffer et al., Phys. Rev. Lett. 89, 067601 (2002) ] in Pb(Zr1−xTix)O3 ultrathin films. It is found that these domain structures do not vanish in the presence of such defect but rather evolve to form original stripe configurations to accommodate this step. The morphology and energetics of these original configurations are provided. Their dependencies on the film’s thickness and the step’s height is also discussed.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity
61.50.-f Structure of bulk crystals

Stabilization of higher-κ tetragonal HfO2 by SiO2 admixture enabling thermally stable metal-insulator-metal capacitors

T. S. Böscke, S. Govindarajan, P. D. Kirsch, P. Y. Hung, C. Krug, B. H. Lee, J. Heitmann, U. Schröder, G. Pant, B. E. Gnade, and W. H. Krautschneider

Appl. Phys. Lett. 91, 072902 (2007); http://dx.doi.org/10.1063/1.2771376 (3 pages) | Cited 27 times

Online Publication Date: 14 August 2007

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The authors report the relationship between HfO2 crystalline phase and the resulting electrical properties. Crystallization of amorphous HfO2 into the monoclinic phase led to a significant increase in leakage current and formation of local defects. Admixture of 10% SiO2 avoided formation of these defects by stabilization of the tetragonal phase, and concurrently increased the permittivity to 35. This understanding enabled fabrication of crystalline HfO2 based metal-insulator-metal capacitors able to withstand a thermal budget of 1000 °C while optimizing capacitance equivalent thickness (<1.3 nm) at low leakage [J(1 V)<10−7 A/cm2].
Show PACS
84.32.Tt Capacitors
85.30.Tv Field effect devices
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