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21 Jan 2008

Volume 92, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages)

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha
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Migration and luminescence enhancement effects of deuterium in ZnO/ZnCdO quantum wells

W. Lim, D. P. Norton, S. J. Pearton, X. J. Wang, W. M. Chen, I. A. Buyanova, A. Osinsky, J. W. Dong, B. Hertog, A. V. Thompson, W. V. Schoenfeld, Y. L. Wang, and F. Ren

Appl. Phys. Lett. 92, 032103 (2008); http://dx.doi.org/10.1063/1.2836946 (3 pages) | Cited 7 times

Online Publication Date: 22 January 2008

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ZnO/ZnCdO/ZnO multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150 °C. The deuterium showed migration depths of ∼ 0.8 μm for 30 min plasma exposures, with accumulation of 2H in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased by factors of 5 at 5 K and ∼ 20 at 300 K as a result of the deuteration, most likely due to passivation of competing nonradiative centers. Annealing up to 300 °C led to increased migration of 2H toward the substrate but no loss of deuterium from the sample and little change in the PL intensity. The initial PL intensities were restored by annealing at ≥ 400 °C as 2H was evolved from the sample ( ∼ 90% loss by 500 °C). By contrast, samples without in situ annealing showed a decrease in PL intensity with deuteration. This suggests that even moderate annealing temperatures lead to degradation of ZnCdO quantum wells.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.65.Rv Passivation
52.77.-j Plasma applications

Sources of unintentional conductivity in InN

Anderson Janotti and Chris G. Van de Walle

Appl. Phys. Lett. 92, 032104 (2008); http://dx.doi.org/10.1063/1.2832369 (3 pages) | Cited 40 times

Online Publication Date: 23 January 2008

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Using first-principles methods, we investigate the effects of monatomic hydrogen in InN. We find that hydrogen can occupy interstitial and substitutional sites. Interstitial hydrogen is stable in the bond-center configuration and acts exclusively as a shallow donor, with a H–N stretching vibration at 3050 cm−1. Hydrogen can also substitute for nitrogen in InN, bonding equally to the four In nearest neighbors in a multicenter-bond configuration. Substitutional hydrogen has low formation energy and, counterintuitively, is a double donor. Our results suggest that monatomic hydrogen is a plausible cause of the unintentional n-type conductivity that is often observed in as-grown InN.
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78.66.Fd III-V semiconductors
72.80.Ey III-V and II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Ge 3d core-level shifts at (100)Ge/Ge(Hf)O2 interfaces: A first-principles investigation

G. Pourtois, M. Houssa, A. Delabie, T. Conard, M. Caymax, M. Meuris, and M. M. Heyns

Appl. Phys. Lett. 92, 032105 (2008); http://dx.doi.org/10.1063/1.2833696 (3 pages) | Cited 23 times

Online Publication Date: 23 January 2008

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First-principles calculations of Ge 3d core-level shifts on (100)Ge/Ge(Hf)O2 interface models, presenting a GeOx transition region that samples different possible oxidation states for Ge atoms near the interface are reported. The fractional densities of these different oxidation states present in the modeled structures are consistent with those inferred from x-ray photoelectron spectroscopy data on thermally oxidized (100)Ge surfaces. The computed relative Ge 3d core-level shifts are in overall fair agreement with the experimental values reported in the literature, especially for the Ge–O–Hf bonds that are likely formed at the GeO2/HfO2 interface. The computed core-level shifts increase linearly with the partial atomic charges on the Ge atoms, consistently with a classical charge-transfer model usually used for the interpretation of experimental data on (100)Ge/Ge(Hf)O2 interfaces.
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73.20.-r Electron states at surfaces and interfaces

Time-resolved photoluminescence of type-II quantum dots and isoelectronic centers in Zn–Se–Te superlattice structures

M. C.-K. Cheung, A. N. Cartwright, I. R. Sellers, B. D. McCombe, and I. L. Kuskovsky

Appl. Phys. Lett. 92, 032106 (2008); http://dx.doi.org/10.1063/1.2835699 (3 pages) | Cited 9 times

Online Publication Date: 23 January 2008

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Spectrally and time-resolved photoluminescence of a ZnTe/ZnSe superlattice reveals a smooth transition of the photoluminescence (PL) lifetime from ∼ 100 ns at 2.35 eV to less than a few nanoseconds at 2.8 eV. The significant increase of the lifetime in the low energy region is strong evidence to support the formation of type-II quantum dots (QDs), since in these nanostructures the spatial separation of carriers is increased. The shorter lived emission above 2.5 eV is attributed to excitons bound to Te isoelectronic centers in the ZnSe matrix. The smooth transition of the PL lifetime confirms that clusters of these Te atoms evolve into type-II ZnTe/ZnSe QDs.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Et II-VI semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
71.35.-y Excitons and related phenomena

Band alignment between amorphous Ge2Sb2Te5 and prevalent complementary-metal-oxide-semiconductor materials

Lina Wei-Wei Fang, Ji-Sheng Pan, Rong Zhao, Luping Shi, Tow-Chong Chong, Ganesh Samudra, and Yee-Chia Yeo

Appl. Phys. Lett. 92, 032107 (2008); http://dx.doi.org/10.1063/1.2837189 (3 pages) | Cited 3 times

Online Publication Date: 23 January 2008

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Band alignment of amorphous Ge2Sb2Te5 and various substrates was obtained using high-resolution x-ray photoelectron spectroscopy. The valence band offset of Ge2Sb2Te5 on various complementary-metal-oxide-semiconductor (CMOS) materials, i.e., Si, SiO2, HfO2, Si3N4 and NiSi, were investigated with the aid of the core level, valence band, and energy loss spectra. Energy band lineups of Ge2Sb2Te5 on these materials were thus determined which can be used as for phase change memory device engineering and integration with CMOS technology.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Investigation of Zr–Si–N/Zr bilayered film as diffusion barrier for Cu ultralarge scale integration metallization

Ying Wang, Fei Cao, Yun-tao Liu, and Ming-Hui Ding

Appl. Phys. Lett. 92, 032108 (2008); http://dx.doi.org/10.1063/1.2837190 (3 pages) | Cited 12 times

Online Publication Date: 23 January 2008

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The effectiveness of ZrSiN/Zr bilayered films to serve as diffusion barriers in Cu/Si contacts has been investigated. Annealing studies for Cu/ZrSiN/Zr/Si contact systems were carried out in N2/H2(10%) ambient. X-ray diffraction data suggest that Cu film has preferential (111) crystal orientation and Cu silicide cannot be observed up to 700 °C. Scanning electron microscopy micrographs show that the Cu film was integrated and free from agglomeration after annealing at 700 °C. Auger electron spectroscopy depth profiles of the Cu/ZrSiN(10 nm)/Zr(20 nm)/Si samples have no noticeable change except Zr silicide grows with annealing temperature up to 700 °C. The results indicate excellent barrier property for ZrSiN(10 nm)/Zr(20 nm) bilayer structure for Cu metallization.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Observation of SrTiO3 in-gap states by depletion mode field effect

Keisuke Shibuya, Tsuyoshi Ohnishi, Takayuki Uozumi, Taisuke Sato, Kazunori Nishio, and Mikk Lippmaa

Appl. Phys. Lett. 92, 032109 (2008); http://dx.doi.org/10.1063/1.2837627 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2008

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We have fabricated SrTiO3 (100) single crystal field-effect transistors with epitaxial and amorphous DyScO3 gate insulator layers. The devices showed an on-off ratio of 107 with a field-effect mobility of over 100 cm2/V s at 50 K. The residual oxygen vacancy concentration in the transistor channel was adjusted so that the off-state current was high at room temperature but dropped sharply upon cooling. The temperature dependence of the channel current under a carrier-depleting gate bias was used to show that oxygen vacancies form an in-gap impurity state at about 0.24 eV below the SrTiO3 mobility edge.
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85.30.Tv Field effect devices
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Role of metallic cobalt in room temperature dilute ferromagnetic semiconductor Zn0.95Co0.05O1−δ

Q. Liu, C. L. Gan, C. L. Yuan, and G. C. Han

Appl. Phys. Lett. 92, 032501 (2008); http://dx.doi.org/10.1063/1.2835702 (3 pages) | Cited 14 times

Online Publication Date: 22 January 2008

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Using two suitably designed thin film systems, the impact of metallic cobalt nanodots on the mechanism of ferromagnetism (FM) in ZnO thin films was studied. At a relatively higher oxygen partial pressure, Co nanodots embedded ZnO thin films no longer show FM, as compared to Co-doped ZnO dilute magnetic semiconductor (DMS). The structural and magnetic properties of these two systems support the hypothesis that (1) the FM of DMS thin films is due to bound magnetic polarons instead of cobalt nanoclusters and (2) the critical defect concentration is the key parameter which controls the FM properties in DMS thin films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.38.-k Polarons and electron-phonon interactions

Control of interlayer magnetostatic coupling in submicron-sized Fe/Au/Fe rings

T. Miyawaki, M. Kohda, A. Fujita, and J. Nitta

Appl. Phys. Lett. 92, 032502 (2008); http://dx.doi.org/10.1063/1.2830702 (3 pages) | Cited 3 times

Online Publication Date: 23 January 2008

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We have investigated the inner diameter dependence of magnetostatic coupling in Fe/Au/Fe pseudospin valve (PSV) rings by the magneto-optical Kerr effect. Hysteresis loops of the soft layer with smaller inner diameter are considerably different from those found in single-layer rings maintaining the outer diameter. This is explained by the attenuation of circumferential shape anisotropy as the inner diameter decreases. The magnetostatic coupling is enhanced between the two Fe layers due to an increase of a stray field from ring edges. These results indicate that the magnetostatic coupling in the PSV rings is controlled by changing the inner diameter.
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78.20.Ls Magneto-optical effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Detection of the magnetostructural phase coexistence in MnAs epilayers at a very early stage

J. Milano, L. B. Steren, A. H. V. Repetto Llamazares, V. Garcia, M. Marangolo, M. Eddrief, and V. H. Etgens

Appl. Phys. Lett. 92, 032503 (2008); http://dx.doi.org/10.1063/1.2837178 (3 pages) | Cited 1 time

Online Publication Date: 23 January 2008

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We report on the appearance of magnetic stripes in MnAs/GaAs(100) epilayers at temperatures well below the ferromagnetic transition of the system. The study has been performed by ferromagnetic resonance (FMR) experiments on MnAs epilayers grown on the (100) and (111) GaAs substrates. The FMR spectra of the MnAs/GaAs(100) samples at 180 K reveal the appearance of zones of different magnetic behaviors with respect to the low-temperature homogeneous ferromagnetic phase. The angular and the temperature dependences of the spectra serve us to detect the intergrowth of the nonmagnetic phase into the ferromagnetic phase at a very early stage of the process. The experimental data show that the paramagnetic phase nucleates in a self-arranged array of stripes in MnAs/GaAs(100) thin films while it grows randomly in the same films grown on GaAs(111).
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
64.60.Q- Nucleation

The rf magnetic-field vector detector based on the spin rectification effect

L. H. Bai, Y. S. Gui, A. Wirthmann, E. Recksiedler, N. Mecking, C.-M. Hu, Z. H. Chen, and S. C. Shen

Appl. Phys. Lett. 92, 032504 (2008); http://dx.doi.org/10.1063/1.2837180 (3 pages) | Cited 8 times

Online Publication Date: 23 January 2008

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Ferromagnetic resonances on three Permalloy strips under an in-plane external magnetic field are detected electrically. By measuring and analyzing the angular dependence of the photovoltage induced by the spin rectification effect, an approach is demonstrated for making microwave detectors capable of detecting the rf magnetic field vector at subwavelength scale.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Bb Fe and its alloys
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.50.Pz Photoconduction and photovoltaic effects
73.40.Ei Rectification

Magnetic switching of ferromagnetic nanotubes

R. Sharif, S. Shamaila, M. Ma, L. D. Yao, R. C. Yu, X. F. Han, and M. Khaleeq-ur-Rahman

Appl. Phys. Lett. 92, 032505 (2008); http://dx.doi.org/10.1063/1.2836272 (3 pages) | Cited 15 times

Online Publication Date: 24 January 2008

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The magnetic switching of ferromagnetic nanotubes as function of geometrical parameters has been investigated. The modes of magnetization reversal are observed to depend on the geometry of the nanotubes. Time dependent magnetization properties reveal that the nanotubes have strong magnetic viscosity effects. The values of magnetic viscosity coefficient (S) for different applied fields are high near the coercive field.
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75.60.Jk Magnetization reversal mechanisms
75.60.Lr Magnetic aftereffects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
75.50.Bb Fe and its alloys

Acoustic-assisted magnetic-field-induced strain and stress output of Ni–Mn–Ga single crystal

Ratchatee Techapiesancharoenkij, Jari Kostamo, Jesse Simon, David Bono, Samuel M. Allen, and Robert C. O’Handley

Appl. Phys. Lett. 92, 032506 (2008); http://dx.doi.org/10.1063/1.2837195 (3 pages) | Cited 8 times

Online Publication Date: 24 January 2008

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The application of acoustic energy input from a piezoelectric actuator is observed to increase the magnetic-field-induced strain (MFIS) and decrease the threshold field in Ni–Mn–Ga ferromagnetic shape memory alloys (FSMAs). To appreciate better the benefit of the acoustic assistance, the stress and strain outputs of the quasistatic FSMA actuation under acoustic assistance are studied systematically. With acoustic assistance, the maximum reversible strain increases from 3% to 4.5% and appears in a broader range of stress output between 0.4 and 1.2 MPa. Elastic stress wave analysis explains quantitatively the effect of acoustic assistance on MFIS.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.fg Shape-memory effect; yield stress; superelasticity

Magnetic properties of Fe-5d (Os, Ir, and Pt) nanowires encapsulated in carbon nanotubes

Junhua Wang, Chulsu Jo, and Ruqian Wu

Appl. Phys. Lett. 92, 032507 (2008); http://dx.doi.org/10.1063/1.2837541 (3 pages) | Cited 6 times

Online Publication Date: 24 January 2008

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Using the first-principles density functional calculations, we explored the magnetic properties of Fe–X (X = Os, Ir, and Pt) nanowires encapsulated in a (4,4) carbon nanotubes. It is found that these wires possess giant magnetic anisotropy energies due to sizable spin-orbit coupling along with induced magnetization of 5d metals.
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75.75.-c Magnetic properties of nanostructures
75.30.Gw Magnetic anisotropy
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Magnetic domain wall propagation in a submicron spin-valve stripe: Influence of the pinned layer

J. Briones, F. Montaigne, D. Lacour, M. Hehn, M. J. Carey, and J. R. Childress

Appl. Phys. Lett. 92, 032508 (2008); http://dx.doi.org/10.1063/1.2835201 (3 pages) | Cited 9 times

Online Publication Date: 25 January 2008

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The propagation of a domain wall in a submicron ferromagnetic spin-valve stripe is investigated using giant magnetoresistance. A notch in the stripe efficiently traps an injected wall stopping the domain propagation. The authors show that the magnetic field at which the wall is depinned displays a stochastic nature. Moreover, the depinning statistics are significantly different for head-to-head and tail-to-tail domain walls. This is attributed to the dipolar field generated in the vicinity of the notch by the pinned layer of the spin valve.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.47.De Giant magnetoresistance

Magnetic-field-induced martensitic transformation in MnNiGa:Co alloys

L. Ma, H. W. Zhang, S. Y. Yu, Z. Y. Zhu, J. L. Chen, G. H. Wu, H. Y. Liu, J. P. Qu, and Y. X. Li

Appl. Phys. Lett. 92, 032509 (2008); http://dx.doi.org/10.1063/1.2838343 (3 pages) | Cited 26 times

Online Publication Date: 25 January 2008

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With a high Curie temperature and low entropy change, the magnetic-field-induced martensitic transformation has been obtained in ferromagnetic shape memory alloys MnNiGa by doping a small amount of Co. Due to the ferromagnetic activation effect of Co, a large amount of antiferromagnetically aligned Mn moments are turned into ferromagnetic ordering, which is verified by our electronic structural calculation and experimental observation. Consequently, the magnetization rises up to 70 emu/g and the magnetization difference between two phases increases about ten times, resulting in a considerable dT/dH of 4 K/T and a well-defined reversed transformation induced by a magnetic field.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Cc Other ferromagnetic metals and alloys
61.72.up Other materials
81.30.Kf Martensitic transformations
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Low-loss materials for high Q-factor Bragg reflector resonators

Jean-Michel le Floch, Michael E. Tobar, Dominique Cros, and Jerzy Krupka

Appl. Phys. Lett. 92, 032901 (2008); http://dx.doi.org/10.1063/1.2828025 (3 pages) | Cited 2 times

Online Publication Date: 23 January 2008

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A Bragg resonator uses dielectric plates within a metallic cavity to confine the energy within a central free space region. The importance of the permittivity is shown with a better Q factor possible using higher permittivity materials of larger intrinsic dielectric losses. This is because the electric energy in the reflectors decreases proportionally to the square root of permittivity and the coupling to the metallic losses decrease linearly. In a sapphire resonator with a single reflector pair a Q factor of 2.34×105 is obtained, which may be improved on by up to a factor of 2 using higher permittivity materials.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings
41.20.-q Applied classical electromagnetism
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Sol-gel derived morphotropic phase boundary 0.37BiScO3–0.63PbTiO3 thin films

Jingzhong Xiao, Aiying Wu, and Paula M. Vilarinho

Appl. Phys. Lett. 92, 032902 (2008); http://dx.doi.org/10.1063/1.2834366 (3 pages) | Cited 6 times

Online Publication Date: 23 January 2008

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Dielectric/ferroelectric properties of morphotropic phase boundary 0.37BiScO3–0.63PbTiO3 thin films with a PbTiO3 seed layer deposited on platinized silicon substrates by sol-gel are examined. Room temperature dielectric constant of >1600 and dielectric loss of 0.02 are achieved (100 Hz). A well-defined hysteresis loop was observed with a Pr of ∼ 23 μC/cm2. In particular, the remarkable low Ec of ∼ 33 kV/cm of these films adds value to the potential application of BiScO3–PbTiO3 films in high temperature ferroelectric memories. The influence of PbTiO3 seed layer on the electric properties and the relation with the phase formation process, crystallinity, and microstructure of the films is discussed.
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77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Terahertz evanescent field microscopy of dielectric materials using on-chip waveguides

J. Cunningham, M. Byrne, P. Upadhya, M. Lachab, E. H. Linfield, and A. G. Davies

Appl. Phys. Lett. 92, 032903 (2008); http://dx.doi.org/10.1063/1.2835705 (3 pages) | Cited 6 times

Online Publication Date: 23 January 2008

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We demonstrate an evanescent field modality for terahertz frequency time-domain measurements, based on the interaction between a sample and the evanescent field extending above lithographically defined terahertz waveguides. We quantify this interaction using freely positionable dielectric samples (GaAs) moved in close proximity to the waveguide (a terahertz microstrip line), finding a reduction in the microstrip-propagating pulse amplitude and an increase in its time delay when the dielectric is brought into the microstrip evanescent field. We also show that the frequency response of resonant passive circuit elements (stub band-stop filters), integrated into the microstrip line, can be used to determine the terahertz frequency properties of scanned samples, opening the way for a terahertz subwavelength imaging modality, the resolution of which is limited by lithographic constraints, rather than by free-space diffraction.
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82.45.Un Dielectric materials in electrochemistry
84.40.Az Waveguides, transmission lines, striplines
84.30.-r Electronic circuits

Diffuse second harmonic generation under the ferroelectric switching in Sr0.75Ba0.25Nb2O6 crystals

D. V. Isakov, M. S. Belsley, T. R. Volk, and L. I. Ivleva

Appl. Phys. Lett. 92, 032904 (2008); http://dx.doi.org/10.1063/1.2830993 (3 pages) | Cited 8 times

Online Publication Date: 24 January 2008

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In this work, we present observations of the polarization process in strontium barium niobate Sr0.75Ba0.25Nb2O6 (SBN-0.75) crystals by measuring the diffuse generation of the second harmonic converted by the random ferroelectric domains. The ability of a field-controlling intensity of the diffuse second harmonic generation is analyzed and discussed in terms of the specific switching scenario in SBN crystals.
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77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Strain and vacancy cluster behavior of vanadium and tungsten-doped Ba[Zr0.10Ti0.90]O3 ceramics

F. Moura, A. Z. Simões, L. S. Cavalcante, M. Zampieri, J. A. Varela, E. Longo, M. A. Zaghete, and M. L. Simões

Appl. Phys. Lett. 92, 032905 (2008); http://dx.doi.org/10.1063/1.2837196 (3 pages) | Cited 10 times

Online Publication Date: 25 January 2008

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Strain and vacancy clusters behavior of polycrystalline vanadium (V) and tungsten (W)-doped Ba[Zr0.10Ti0.90]O3, (BZT:2%V) and (BZT:2%W) ceramics obtained by the mixed oxide method was evaluated. Substitution of V and W reduces the distortion of octahedral clusters, decreasing the Raman modes. Electron paramagnetic resonance data indicate that the addition of dopants leads to defects and symmetry changes in the BZT lattice. Remnant polarization and coercive field are affected by V and W substitution due the electron-relaxation mode. The unipolar strain E curves as a function of electric field reach its maximum value for BZT:2%V and BZT:2%W ceramics.
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81.05.Mh Cermets, ceramic and refractory composites
61.72.jd Vacancies
87.80.Lg Magnetic and paramagnetic resonance

Switchable and tunable strontium titanate electrostrictive bulk acoustic wave resonator integrated with a Bragg mirror

Alexandre Volatier, Emmanuel Defaÿ, Marc Aïd, Amy N’hari, Pascal Ancey, and Bertrand Dubus

Appl. Phys. Lett. 92, 032906 (2008); http://dx.doi.org/10.1063/1.2837616 (3 pages) | Cited 7 times

Online Publication Date: 25 January 2008

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The realization and the radio-frequency characterization of a tunable strontium titanate (STO) electrostrictive solidly mounted acoustic resonator (SMR) bulk acoustic wave are reported. For a 430 nm thick strontium titanate layer, the resonance frequency at 2.2 GHz can be switched on with a bias voltage of 6 V and tuned ±0.85% with a bias voltage between 6 and 30 V. No hysteresis is observed. The SMR tunability is found to be affected by (i) the variation of coupling factor versus bias which is the dominant effect and (ii) the variation of SrTiO3 stiffness at constant electric displacement.
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43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
42.79.Bh Lenses, prisms and mirrors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Inversion-type enhancement-mode HfO2-based GaAs metal-oxide-semiconductor field effect transistors with a thin Ge layer

Hyoung-Sub Kim, I. Ok, M. Zhang, F. Zhu, S. Park, J. Yum, H. Zhao, Jack C. Lee, Jungwoo Oh, and Prashant Majhi

Appl. Phys. Lett. 92, 032907 (2008); http://dx.doi.org/10.1063/1.2838294 (3 pages) | Cited 20 times

Online Publication Date: 25 January 2008

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Using a thin germanium (Ge) interfacial passivation layer (IPL), GaAs HfO2-based inversion-type enhancement-mode metal-oxide-semiconductor field effect transistors (MOSFETs) are realized. The n-channel MOSFETs on semi-insulating GaAs substrate clearly show surface modulation and excellent current control by gate bias. The threshold voltage of ∼ 0.5 V, the transconductance of ∼ 0.25 mS/mm, the subthreshold swing of ∼ 130 mV/decade, and the drain current of ∼ 162 μA/mm (normalized to the gate length of 1 μm) at Vd = 2 V and Vg = Vth+2 V are obtained. In comparison with previous reports, the dc characteristics of the inversion-type GaAs MOSFETs with a Ge IPL and HfO2 dielectric demonstrate much similar results.
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85.30.Tv Field effect devices
81.65.Rv Passivation
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Vertical quantum dot with a vertically coupled charge detector

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha

Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages) | Cited 2 times

Online Publication Date: 22 January 2008

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We fabricated a vertical quantum dot equipped with a charge detector. The dot current flows vertically between the top and bottom contacts. The charge detector is formed at the bottom contact layer with a current channel constricted to the region just under the dot. This channel current is reduced by addition of an extra electron onto the dot due to the electrostatic coupling to the dot. The charge state of the vertical dot was detected, starting from zero electrons. The sensitivity of the charge detector was comparable to that previously reported for lateral dots with nearby quantum point contacts.
Show PACS
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
06.30.Ka Basic electromagnetic quantities

Measuring the electrical characteristics of individual junctions in the SnO2 capped ZnO nanowire arrays on Zn substrate

Y. Liu, S. Wang, Z. Y. Zhang, L.-M. Peng, L. Shi, and Quan Li

Appl. Phys. Lett. 92, 033102 (2008); http://dx.doi.org/10.1063/1.2837060 (3 pages) | Cited 4 times

Online Publication Date: 23 January 2008

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Direct measurements on electrical characteristics have been carried out in situ inside a scanning electron microscope using a multiple nanoprobe system on individual SnO2 capped ZnO nanowires (NWs) within a NW film on a Zn substrate. It is shown that while good Ohmic contacts can be made at Zn–ZnO NW and ZnO NW–SnO2 cap (when heavily doped with Zn) junctions, the overall I-V characteristics of the Zn–ZnO–SnO2 junction system differ significantly among different NWs, suggesting doping inhomogeneity in the NW film.
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73.63.Nm Quantum wires
72.80.Ey III-V and II-VI semiconductors
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