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12 Sep 2011

Volume 99, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 113501 (2011); http://dx.doi.org/10.1063/1.3634072 (3 pages)

Asif Islam Khan, Debanjan Bhowmik, Pu Yu, Sung Joo Kim, Xiaoqing Pan, Ramamoorthy Ramesh, and Sayeef Salahuddin
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Formation of optical barriers with excellent thermal stability in single-crystal sapphire by hydrogen ion implantation and thermal annealing

William T. Spratt, Mengbing Huang, Chuanlei Jia, Lei Wang, Vimal K. Kamineni, Alain C. Diebold, and Hua Xia

Appl. Phys. Lett. 99, 111909 (2011); http://dx.doi.org/10.1063/1.3637613 (3 pages) | Cited 1 time

Online Publication Date: 16 September 2011

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We report a study on the use of hydrogen ion implantation to form optical barriers with excellent thermal stability in single-crystal sapphire. Sapphire crystals are implanted with H ions of energies 0.2–1 MeV to doses 1016–1017 cm−2, followed by thermal annealing between 600–1200 °C. Prism coupling experiments and spectroscopic ellipsometry indicate the formation of an optical barrier with decreased refractive index around the projected range of H ions in sapphire. The refractive index reduction is found to increase with annealing temperatures, reaching a maximum of ∼3.2% following annealing at 1200 °C. The correlation of the structural properties with the formation of optical barriers and their thermal stability in sapphire crystals, is duscussed.
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61.72.up Other materials
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.43.Nr Desorption kinetics
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments

Magnesium, nitrogen codoped Cr2O3: A p-type transparent conducting oxide

E. Arca, K. Fleischer, and I. V. Shvets

Appl. Phys. Lett. 99, 111910 (2011); http://dx.doi.org/10.1063/1.3638461 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2011

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A p-type transparent conductive oxide (TCO) was synthesised by codoping of poorly conducting chromium oxide (Cr2O3) with magnesium and nitrogen. We demonstrated that the codoping produced a TCO with good figure of merit despite using spray pyrolysis for deposition. The nitrogen enhances the specular transparency of the films in the visible range (400-700 nm), and Mg improves the conductivity while retaining the p-type character of the material. Co-doping with both elements produces a p-type oxide with a low resistivity of 3 Ω cm and transmission up to 65% for a 150 nm thick film. A comparison with other known p-type materials is given.
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81.05.Hd Other semiconductors
81.15.Rs Spray coating techniques
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.66.Li Other semiconductors

Dislocation reduction in heteroepitaxial Ge on Si using SiO2 lined etch pits and epitaxial lateral overgrowth

Darin Leonhardt and Sang M. Han

Appl. Phys. Lett. 99, 111911 (2011); http://dx.doi.org/10.1063/1.3632113 (3 pages)

Online Publication Date: 16 September 2011

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We report a technique that significantly reduces threading dislocations in Ge on Si heteroepitaxy. Germanium is first grown on Si and etched to produce pits in the surface where threading dislocations terminate. Further processing leaves a layer of SiO2 only within etch pits. Subsequent selective epitaxial Ge growth results in coalescence above the SiO2. The SiO2 blocks the threading dislocations from propagating into the upper Ge epilayer. With annealed Ge films grown on Si, the said method reduces the defect density from 2.6 × 108 to 1.7 × 106 cm−2, potentially making the layer suitable for electronic and photovoltaic devices.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
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Spin-dependent electron transport in waveguide with continuous shape

Yue Ban and E. Ya. Sherman

Appl. Phys. Lett. 99, 112101 (2011); http://dx.doi.org/10.1063/1.3636410 (3 pages) | Cited 2 times

Online Publication Date: 12 September 2011

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We study effects of the shape of a two-dimensional waveguide on the spin-dependent electron transport in the presence of spin-orbit coupling. The transition from classical motion to the tunneling regime can be controlled there by modulating the strength of spin-orbit coupling if the waveguide has a constriction. The spin precession strongly depends on the shape of the waveguide.
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73.23.-b Electronic transport in mesoscopic systems
73.40.Gk Tunneling
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Metallic-like conduction in Co-phthalocyanine/Fe-phthalocyanine composite films grown on sapphire substrates

Arvind Kumar, Ajay Singh, S. Samanta, A. K. Debnath, D. K. Aswal, and S. K. Gupta

Appl. Phys. Lett. 99, 112102 (2011); http://dx.doi.org/10.1063/1.3637050 (3 pages) | Cited 3 times

Online Publication Date: 12 September 2011

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Charge transport properties of pure and composite thin films of cobalt phthalocyanine (CoPc) and iron phthalocyanine (FePc) deposited on (0001) sapphire substrate has been investigated. Temperature dependence of resistivity showed that composite films are in metallic regime, while pure films are in the critical regime of metal–insulator transition. Composite films showed trap free space charge limited conduction (SCLC) along with two order of magnitude higher mobility (∼110 cm2 V−1 s−1) compared to pure films. Pure films showed SCLC with exponential distribution of traps. High mobility and better structural ordering in composite films is attributed to the formation of CoPc-FePc dimers.
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73.61.Ph Polymers; organic compounds
77.22.Jp Dielectric breakdown and space-charge effects
73.50.Fq High-field and nonlinear effects
72.20.Ht High-field and nonlinear effects
68.55.am Polymers and organics

Native oxidation and Cu-poor surface structure of thin film Cu2ZnSnS4 solar cell absorbers

M. Bär, B.-A. Schubert, B. Marsen, S. Krause, S. Pookpanratana, T. Unold, L. Weinhardt, C. Heske, and H.-W. Schock

Appl. Phys. Lett. 99, 112103 (2011); http://dx.doi.org/10.1063/1.3637574 (3 pages) | Cited 5 times

Online Publication Date: 12 September 2011

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Air-exposed Cu2ZnSnS4 (“CZTS”) thin-film solar cell absorbers have been investigated by surface-sensitive x-ray photoelectron and x-ray-excited Auger electron spectroscopy, as well as by bulk-sensitive energy dispersive x-ray spectroscopy. We find a native surface oxidation of (mainly) tin, but also (to a lesser extent) of zinc and sulfur as well as evidence for a Cu-poor region at the surface of the absorber, best described by a Cu-free Zn-Sn-S surface layer.
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42.79.Ek Solar collectors and concentrators
88.40.H- Solar cells (photovoltaics)

Graphitization of n-type polycrystalline silicon carbide for on-chip supercapacitor application

Fang Liu, Albert Gutes, Ian Laboriante, Carlo Carraro, and Roya Maboudian

Appl. Phys. Lett. 99, 112104 (2011); http://dx.doi.org/10.1063/1.3638468 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2011

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Synthesis of silicon carbide-derived carbon films with excellent supercapacitor characteristics is demonstrated by a process that is fully compatible with standard microfabrication technology. NiTi alloy deposited on nitrogen-doped polycrystalline SiC films is shown to result in the growth of a rough, porous, high conductivity, nanocrystalline graphitic carbon film upon rapid thermal annealing to 1050 °C. Electrodes fabricated in this manner exhibit high charge/discharge rates with a time constant of about 0.062 s. Analysis shows that the incorporated nitrogen in the carbon electrode may induce pseudo-capacitance, and the electrodes exhibit the capacitance/area values comparable to those reported on carbon nanotube-based supercapacitors.
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68.55.ag Semiconductors
61.43.Gt Powders, porous materials
61.72.Cc Kinetics of defect formation and annealing
82.45.Fk Electrodes
82.47.Uv Electrochemical capacitors; supercapacitors
84.32.Tt Capacitors

Low-field microplasma breakdown in a-As2Se3 thin films

E. N. Voronkov and E. M. Eganova

Appl. Phys. Lett. 99, 112105 (2011); http://dx.doi.org/10.1063/1.3640220 (3 pages)

Online Publication Date: 13 September 2011

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It is shown that increasing external field stimulates appearance of the conductive microplasma channels in a-As2Se3 thin films. Cooling a sample under high field causes the disabling of microplasmas and decreases the sample conductance by several orders of magnitude in a rather narrow temperature range. The diameter of a microplasma channel was estimated to be one nanometer. We conclude that some negative centers near the metal—a-As2Se3 interface are causing a local barrier height lowering, stimulating the injection of carriers and formation of a microplasma.
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73.61.Jc Amorphous semiconductors; glasses
52.80.-s Electric discharges
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

Resistive detection of optically pumped nuclear polarization with spin phase transition peak at Landau level filling factor 2/3

K. Akiba, S. Kanasugi, K. Nagase, and Y. Hirayama

Appl. Phys. Lett. 99, 112106 (2011); http://dx.doi.org/10.1063/1.3640215 (3 pages) | Cited 1 time

Online Publication Date: 14 September 2011

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Nuclear spins in a single quantum well are polarized by optical pumping and its polarization is detected by resistance change in quantum Hall regime, that is, a shift in the resistance peak of the spin-phase-transition at Landau level filling factor ν = 2/3. The resistive readout of optical nuclear polarization is directly confirmed from resonant features by applying an RF magnetic field. The obtained nuclear magnetic field is at least 0.62 T. The dependence of the peak shift on laser polarization, intensity, duration time, and illumination position shows the sensitivity of polarization distribution and the capability to control optical nuclear orientation.
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73.63.Hs Quantum wells
76.60.-k Nuclear magnetic resonance and relaxation
73.43.-f Quantum Hall effects
71.70.Di Landau levels

Characteristics of a sensitive micro-Hall probe fabricated on chemical vapor deposited graphene over the temperature range from liquid-helium to room temperature

Chiu-Chun Tang, Ming-Yang Li, L. J. Li, C. C. Chi, and J. C. Chen

Appl. Phys. Lett. 99, 112107 (2011); http://dx.doi.org/10.1063/1.3640218 (3 pages) | Cited 5 times

Online Publication Date: 15 September 2011

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We have investigated the transport and noise properties of a micron-sized Hall probe, fabricated on chemical vapor deposited (CVD) graphene, from 300 K to 4.2 K. The field sensitivity of the Hall probe was tunable within ∼0.031-0.12 Ω/G, while the field resolution could reach ∼0.43-0.09 G/Hz1/2 at room temperature. The characteristics of graphene Hall probes (GHPs) were found to be comparable to present Hall sensors. Our results indicate that the fundamental limitation of the field sensitivity and the field resolution are respectively restricted by intrinsic and extrinsic defects. Our study paves the way for the use of CVD GHPs for scanning Hall probe with high field sensitivity and submicron spatial resolution at room temperature.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.79.-v Scanning probe microscopes and components

Remarkable enhancement in photocurrent of In0.20Ga0.80N photoanode by using an electrochemical surface treatment

Mingxue Li, Wenjun Luo, Bin Liu, Xin Zhao, Zhaosheng Li, Dunjun Chen, Tao Yu, Zili Xie, Rong Zhang, and Zhigang Zou

Appl. Phys. Lett. 99, 112108 (2011); http://dx.doi.org/10.1063/1.3640223 (3 pages) | Cited 4 times

Online Publication Date: 15 September 2011

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The photocurrent and incident photon conversion efficiency of In0.20Ga0.80N increased about 2 times after a simple electrochemical surface treatment. X-ray photoelectron spectroscopy and photoluminescence analysis suggested that In-rich InGaN region on the surface of the In0.20Ga0.80N electrode was removed by using the electrochemical surface treatment. The enhancement of the photocurrent was attributed to the removal of In-rich InGaN phases caused by indium segregations on the surface of the electrode, which played a major role as surface recombination centers of photo-generated electron-hole pairs.
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72.40.+w Photoconduction and photovoltaic effects
68.47.Fg Semiconductor surfaces
78.55.Cr III-V semiconductors
82.45.Vp Semiconductor materials in electrochemistry
68.35.Dv Composition, segregation; defects and impurities
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Electron scattering in Ge metal-oxide-semiconductor field-effect transistors

H.-S. Lan, Y.-T. Chen, William Hsu, H.-C. Chang, J.-Y. Lin, W.-C. Chang, and C. W. Liu

Appl. Phys. Lett. 99, 112109 (2011); http://dx.doi.org/10.1063/1.3640237 (3 pages)

Online Publication Date: 15 September 2011

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The electron mobility of n-channel metal-oxide-semiconductor field-effect transistors using Ge/GeO2/Al2O3 gate stack on (001) Ge substrates is analyzed theoretically and experimentally. Phonon scattering, Coulomb scattering, and interface roughness scattering are taken into account. The Ge peak mobility exceeding Si universal in our device by a factor of 1.3 is due to the reduction of Coulomb scattering of the interface states. As compared to Si, the faster roll-off of the Ge mobility at the effective field larger than 0.3 MV/cm is due to larger interface roughness scattering.
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85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
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High hole carrier concentration realized by alternative co-doping technique in metal organic chemical vapor deposition

Yoshinobu Aoyagi, Misaichi Takeuchi, Sohachi Iwai, and Hideki Hirayama

Appl. Phys. Lett. 99, 112110 (2011); http://dx.doi.org/10.1063/1.3641476 (3 pages)

Online Publication Date: 15 September 2011

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A method of alternative co-doping in metal organic chemical deposition was used to realize high hole carrier concentrations of about 6 × 1018/cm3 in AlxGa1−xN (x = 0.4) and 2 × 1019/cm3 for GaN at room temperature. This technique opens up a new avenue for fabricating electronic p-channel devices, such as p-channel high electron mobility transistor, and vertical current flow type devices, such as deep ultra violet light emitting diodes.
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72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
81.05.Ea III-V semiconductors

Metal-insulator transition in low dimensional La0.75Sr0.25VO3 thin films

Tran M. Dao, Partha S. Mondal, Y. Takamura, E. Arenholz, and Jaichan Lee

Appl. Phys. Lett. 99, 112111 (2011); http://dx.doi.org/10.1063/1.3638065 (3 pages) | Cited 5 times

Online Publication Date: 15 September 2011

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We report on the metal-insulator transition that occurs as a function of film thickness in ultrathin La0.75Sr0.25VO3 films. The metal-insulator transition displays a critical thickness of 5 unit cell. Above the critical thickness, metallic films exhibit a temperature driven metal-insulator transition with weak localization behavior. With decreasing film thickness, oxygen octahedron rotation in the films increases, causing enhanced electron-electron correlation. The electron-electron correlations in ultrathin films induce the transition from metal to insulator in addition to Anderson localization.
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71.30.+h Metal-insulator transitions and other electronic transitions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.Fz Weak or Anderson localization
73.61.Ng Insulators
68.55.aj Insulators
68.55.jd Thickness

Electronic properties of vacancy related defects in ZnO induced by mechanical polishing

V. Quemener, L. Vines, E. V. Monakhov, and B. G. Svensson

Appl. Phys. Lett. 99, 112112 (2011); http://dx.doi.org/10.1063/1.3638470 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2011

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Electronic properties of defects induced by mechanical polishing in hydrothermally grown n-type ZnO have been investigated by capacitance versus voltage measurements and deep level transient spectroscopy (DLTS). The DLTS measurements have been performed in the temperature range 80-600 K enabling exploration of deep-level states in the vicinity of the middle of the energy bandgap. The results show that mechanical polishing forms defects in the near surface region which strongly compensate and/or passivate the dominant shallow donors. Two pronounced polishing-induced defects are revealed with energy level positions around 1.0 eV and 1.2 eV below the conduction band edge. These levels are assigned to vacancy-related defect centers and substantially reduced in strength by post-polishing etching in diluted hydrofluoric acid.
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71.20.Nr Semiconductor compounds
81.65.Ps Polishing, grinding, surface finishing
61.72.jd Vacancies

III-V-on-nothing metal-oxide-semiconductor field-effect transistors enabled by top-down nanowire release process: Experiment and simulation

J. J. Gu, O. Koybasi, Y. Q. Wu, and P. D. Ye

Appl. Phys. Lett. 99, 112113 (2011); http://dx.doi.org/10.1063/1.3638474 (3 pages) | Cited 4 times

Online Publication Date: 15 September 2011

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III-V-on-nothing (III-VON) metal-oxide-semiconductor field-effect transistors (MOSFETs) are experimentally demonstrated with In0.53Ga0.47As as channel and atomic layer deposited Al2O3 as gate dielectric. A hydrochloric acid based release process has been developed to create an air gap beneath the InGaAs channel layer, forming the nanowire channel with width down to 40 nm. III-VON MOSFETs with channel lengths down to 50 nm are fabricated and show promising improvement in drain-induced barrier lowering, due to suppressed short-channel effects. The top-down processing technique provides a viable pathway towards fully gate-all-around III-V MOSFETs.
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85.30.Tv Field effect devices

Ammonium sulfide vapor passivation of In0.53Ga0.47As and InP surfaces

Alireza Alian, Guy Brammertz, Clement Merckling, Andrea Firrincieli, Wei-E Wang, H. C Lin, Matty Caymax, Marc Meuris, Kristin De Meyer, and Marc Heyns

Appl. Phys. Lett. 99, 112114 (2011); http://dx.doi.org/10.1063/1.3638492 (3 pages) | Cited 1 time

Online Publication Date: 15 September 2011

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The efficiency of the ammonium sulfide vapor (ASV) treatment, as opposed to the wet treatment in the liquid ammonium sulfide solution, on the performance improvement of the In0.53Ga0.47As surface-channel as well as InP-capped buried-channel metal-oxide-semiconductor field-effect-transistors (MOSFET) was demonstrated for the first time. MOSFETs were fabricated with either HCl or ASV surface treatments prior to the gate oxide deposition. ASV treatment was found to be very efficient in boosting the drive current of the transistors compared to that of the HCl treatment. It was also found that the ASV treatment leads to a lower border trap density and slightly higher oxide/semiconductor interface defect density compared to that of the HCl treatment. X-ray photoelectron spectroscopy (XPS) studies of In0.53Ga0.47As native oxide regrowth after both surface treatments identified indium sub-oxides as a possible cause of the performance degradation of the HCl treated devices. Based on this work, ASV treatment could be an efficient solution to the passivation of III-V surfaces.
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81.65.Rv Passivation
85.30.Tv Field effect devices
79.60.Bm Clean metal, semiconductor, and insulator surfaces

SiNx charge-trap nonvolatile memory based on ZnO thin-film transistors

Eunkyeom Kim, Youngill Kim, Do Han Kim, Kyoungmi Lee, Gregory N. Parsons, and Kyoungwan Park

Appl. Phys. Lett. 99, 112115 (2011); http://dx.doi.org/10.1063/1.3640221 (3 pages)

Online Publication Date: 16 September 2011

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We have demonstrated the fabrication and application of a nonvolatile thin-film transistor memory with SiNx charge traps using a ZnO thin film as the active channel layer. The thin film of ZnO was deposited using an atomic-layer deposition process and was subsequently post-annealed in an O2-filled atmosphere. X-ray diffraction and x-ray photoemission results indicated that the O2 annealing process was effective for the crystallinity and stoichiometry of the ZnO films. A saturation field-effect mobility of 6 cm2/Vs, on/off ratio of ≈105, subthreshold slope of 0.7 V/decade, and threshold voltage of −5 V were obtained in transistor operations. Threshold-voltage shift measurements performed for various stress voltages and time durations revealed that these devices had a large memory window of 5.4 V and a long retention time (>10 years) in nonvolatile memory operations.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Non-equilibrium charge stability diagrams of a silicon double quantum dot

M. G. House, H. Pan, M. Xiao, and H. W. Jiang

Appl. Phys. Lett. 99, 112116 (2011); http://dx.doi.org/10.1063/1.3640236 (3 pages) | Cited 1 time

Online Publication Date: 16 September 2011

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We report on the experimental characterization of an electrostatically defined, few-electron double quantum dot in a silicon metal-oxide-semiconductor (MOS) structure. The device incorporates two quasi-one-dimensional channels for sensing the charge states of the double quantum dot. Charge sensor stability diagrams obtained at finite source-drain bias are interpreted and used to find the absolute energy scale of the quantum dots based on a matrix representation of the coupling between the dots and the gates.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Tv Field effect devices

Gates controlled parallel-coupled double quantum dot on both single layer and bilayer graphene

Lin-Jun Wang, Guo-Ping Guo, Da Wei, Gang Cao, Tao Tu, Ming Xiao, Guang-Can Guo, and A. M. Chang

Appl. Phys. Lett. 99, 112117 (2011); http://dx.doi.org/10.1063/1.3638471 (3 pages) | Cited 3 times

Online Publication Date: 16 September 2011

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We present quantum transport measurements of gates controlled parallel-coupled double quantum dot (PDQD) device on both bilayer and single layer graphenes. The interdot coupling strength can be effectively tuned from weak to strong by in-plane plunger gates. All the relevant energy scales and parameters can be extracted from the honeycomb charge stability diagrams. The present method of designing and fabricating graphene PDQD is demonstrated to be general and reliable and will enhance the realization of graphene nanodevice and desirable study of rich PDQD physical phenomena in graphene.
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81.05.ue Graphene
81.07.Ta Quantum dots
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Fluxgate based detection of magnetic nanoparticle dynamics in a rotating magnetic field

Jan Dieckhoff, Meinhard Schilling, and Frank Ludwig

Appl. Phys. Lett. 99, 112501 (2011); http://dx.doi.org/10.1063/1.3639276 (3 pages) | Cited 3 times

Online Publication Date: 14 September 2011

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We have developed a measurement setup allowing the investigation of the dynamics of magnetic nanoparticle suspensions in a rotating magnetic field. To determine the vector of the sample magnetization, sensitive fluxgate magnetometers are utilized detecting the sample’s stray field. The phase lag between sample magnetization and rotating magnetic field vector is determined via the cross correlation spectrum. The phase lag spectra measured for various rotating field amplitudes on aqueous magnetite nanoparticle suspensions show good agreement with theory if the multidispersity of core and hydrodynamic size is taken into account.
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07.55.Ge Magnetometers for magnetic field measurements
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Electronic depiction of magnetic origin in undoped and Fe doped TiO2−d epitaxial thin films

Komal Bapna, R. J. Choudhary, S. K. Pandey, D. M. Phase, S. K. Sharma, and M. Knobel

Appl. Phys. Lett. 99, 112502 (2011); http://dx.doi.org/10.1063/1.3640212 (3 pages) | Cited 6 times

Online Publication Date: 15 September 2011

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We have investigated the electronic and magnetic properties of the pulsed laser deposited epitaxial thin films of undoped and Fe doped (4 at. %) anatase TiO2−d by photoemission, magnetization measurements, and ab-initio band structure calculations. These films show room temperature magnetic ordering. It is observed that Fe ions hybridize with the oxygen vacancy induced Ti3+ defect states. Our study reveals the formation of local magnetic moment at Ti and Fe sites to be responsible for magnetic ordering. A finite density of states at the Fermi level in both undoped and Fe doped films is also observed, suggesting their degenerate semiconducting nature.
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71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Fg Pulsed laser ablation deposition
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
73.20.At Surface states, band structure, electron density of states

Magnetic field influence on the transient photoresistivity of defect-induced magnetic ZnO films

C. Zapata, M. Khalid, G. Simonelli, M. Villafuerte, S. P. Heluani, and P. Esquinazi

Appl. Phys. Lett. 99, 112503 (2011); http://dx.doi.org/10.1063/1.3640231 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2011

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Magnetic field dependent photoresistivity was measured at 280 K in ZnO ferromagnetic films grown on r-plane Al2O3 under a N2 atmosphere. A correlation between the negative magneto photoresistivity and the existence of defect-induced magnetic order was found. The effect of magnetic field on the transient photoresistivity is to slow down the recombination process enhancing the photocarriers density. The experimental results demonstrate the possibility of tuning photocarriers life time using magnetic field in diluted magnetic semiconductors.
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73.50.Pz Photoconduction and photovoltaic effects
81.05.Dz II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Switching-probability distribution of spin-torque switching in MgO-based magnetic tunnel junctions

Takayuki Seki, Akio Fukushima, Hitoshi Kubota, Kay Yakushiji, Shinji Yuasa, and Koji Ando

Appl. Phys. Lett. 99, 112504 (2011); http://dx.doi.org/10.1063/1.3637545 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2011

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The time-evolution of the switching characteristics of spin-torque switching in MgO-based magnetic tunnel junctions (MTJs) during more than 109 write/read cycles was measured experimentally. In the measurements, the magnetic field and current conditions were chosen to give a switching probability (Psw) of about 0.5, where Psw is most sensitive to changes in the magnetic properties of an MTJ cell. Interestingly, some MTJ cells showed small jumps of Psw, which can be attributed to random transitions between states with slightly different magnetic configurations. Such time-evolution measurement can be used to evaluate the stability of the switching characteristics of memory cells.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
02.70.Rr General statistical methods
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Ferroelectric Zr0.5Hf0.5O2 thin films for nonvolatile memory applications

J. Müller, T. S. Böscke, D. Bräuhaus, U. Schröder, U. Böttger, J. Sundqvist, P. Kücher, T. Mikolajick, and L. Frey

Appl. Phys. Lett. 99, 112901 (2011); http://dx.doi.org/10.1063/1.3636417 (3 pages) | Cited 7 times

Online Publication Date: 12 September 2011

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We report the observation of ferroelectricity in capacitors based on hafnium-zirconium-oxide. Hf0.5Zr0.5O2 thin films of 7.5 to 9.5 nm thickness were found to exhibit ferroelectric polarization-voltage hysteresis loops when integrated into TiN-based metal-insulator-metal capacitors. A remnant polarization of 16 μC/cm2 and a high coercive field of 1 MV/cm were observed. Further proof for the ferroelectric nature was collected by quasi-static polarization-voltage hysteresis, small signal capacitance-voltage, and piezoelectric measurements. Data retention characteristics were evaluated by a Positive Up Negative Down pulse technique. No significant decay of the initial polarization state was observed within a measurement range of up to two days.
Show PACS
84.32.Tt Capacitors
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.50.Gk Non-volatile ferroelectric memories
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