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7 Jan 2008

Volume 92, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 011101 (2008); http://dx.doi.org/10.1063/1.2828458 (3 pages)

F. Pedaci, S. Barland, E. Caboche, P. Genevet, M. Giudici, J. R. Tredicce, T. Ackemann, A. J. Scroggie, W. J. Firth, G.-L. Oppo, G. Tissoni, and R. Jäger
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Ballistic electron emission spectroscopy/microscopy of self-assembled InAs quantum dots of different sizes embedded in GaAs/AlGaAs heterostructure

J. Walachová, J. Zelinka, V. Malina, J. Vaniš, F. Šroubek, J. Pangrác, K. Melichar, and E. Hulicius

Appl. Phys. Lett. 92, 012101 (2008); http://dx.doi.org/10.1063/1.2821846 (3 pages) | Cited 2 times

Online Publication Date: 2 January 2008

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Self-assembled InAs quantum dots embedded in GaAs/GaAlAs heterostructure were visualized by ballistic electron emission microscopy. The spectroscopic characteristics on individual quantum dots were examined. Quantum dots had images of elliptical shapes. Their length was from about 10 to 20 nm. Below one-electron p1-like state, one-electron and two-electron ground states and excited two-electron states were observed. The Coulomb interaction and exchange energies between two electrons in quantum dots were determined and compared with the previously published theoretical results.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.La Quantum dots
73.63.Kv Quantum dots
FREE

Tunable Coulomb blockade in nanostructured graphene

C. Stampfer, J. Güttinger, F. Molitor, D. Graf, T. Ihn, and K. Ensslin

Appl. Phys. Lett. 92, 012102 (2008); http://dx.doi.org/10.1063/1.2827188 (3 pages) | Cited 76 times

Online Publication Date: 2 January 2008

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We report on Coulomb blockade and Coulomb diamond measurements on an etched, tunable single-layer graphene quantum dot. The device consisting of a graphene island connected via two narrow graphene constrictions is fully tunable by three lateral graphene gates. Coulomb blockade resonances are observed and from Coulomb diamond measurements, a charging energy of ≈ 3.5 meV is extracted. For increasing temperatures, we detect a peak broadening and a transmission increase of the nanostructured graphene barriers.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.21.La Quantum dots

Selective formation of Ohmic junctions and Schottky barriers with electrodeposited ZnO

Shawn Chatman, Bernard J. Ryan, and Kristin M. Poduska

Appl. Phys. Lett. 92, 012103 (2008); http://dx.doi.org/10.1063/1.2828702 (3 pages) | Cited 8 times

Online Publication Date: 2 January 2008

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Constant-potential electrochemical synthesis of ZnO on metal substrates enables selective formation of either Ohmic or Schottky-barrier contacts. Using a mildly acidic nitrate-based aqueous electrolyte, there is a substrate-dependent deposition potential below which electrodeposited ZnO heterojunctions display Schottky response with high contact resistances ( ∼ 105 Ω) and above which Ohmic behavior and low contact resistances ( ∼ 1 Ω) occur. Voltammetric evidence for Zn metal deposition, in conjunction with Schottky-barrier heights that are consistent with values expected for a ZnO–Zn junction, suggests that more negative deposition potentials create a Zn-based interface between the substrate and ZnO that leads to rectifying behavior.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Cg Contact resistance, contact potential
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
82.45.Vp Semiconductor materials in electrochemistry

Valence band offset of ZnO/GaAs heterojunction measured by x-ray photoelectron spectroscopy

P. F. Zhang, X. L. Liu, R. Q. Zhang, H. B. Fan, A. L. Yang, H. Y. Wei, P. Jin, S. Y. Yang, Q. S. Zhu, and Z. G. Wang

Appl. Phys. Lett. 92, 012104 (2008); http://dx.doi.org/10.1063/1.2828860 (3 pages) | Cited 9 times

Online Publication Date: 2 January 2008

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X-ray photoelectron spectroscopy has been used to measure the valence band offset at the ZnO/GaAs heterojunction interface. The valence band offset is determined to be 2.39±0.23 eV. As a consequence, a type-II heterojunction with a conduction band offset of −0.44±0.23 eV is found. The directly obtained value is in good agreement with the result of theoretical calculations based on the interface-induced gap states and the chemical electronegativity theory.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.20.Nr Semiconductor compounds

Thermoelectric properties of directionally solidified half-Heusler compound NbCoSn alloys

Yoshisato Kimura, Yukio Tamura, and Takuji Kita

Appl. Phys. Lett. 92, 012105 (2008); http://dx.doi.org/10.1063/1.2828713 (3 pages) | Cited 4 times

Online Publication Date: 2 January 2008

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Single- and multiphase samples of the n-type half-Heusler NbCoSn were prepared by directional solidification using the optical floating zone melting method, and the thermoelectric properties of these samples were evaluated. NbCoSn has an excellent thermoelectric power which exceeds −250 μV K−1 at around 900 K and a relatively high carrier concentration, 4.82×1026 m−3. A metalliclike temperature dependence of the electrical resistivity indicates that NbCoSn is a degenerate semiconductor. NbCoSn also shows an excellent power factor, 2.5 mW m−1 K−2 at about 650 K, even without any tuning of the electrical properties which are susceptible to coexisting metallic phases.
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72.15.Jf Thermoelectric and thermomagnetic effects
64.70.kd Metals and alloys
81.10.Fq Growth from melts; zone melting and refining

Excitonic bright-to-dark transition induced by spin-orbit coupling

Jian-Wei Wang and Shu-Shen Li

Appl. Phys. Lett. 92, 012106 (2008); http://dx.doi.org/10.1063/1.2828861 (3 pages) | Cited 2 times

Online Publication Date: 2 January 2008

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The center-of-mass motion of quasi-two-dimensional excitons with spin-orbit coupling is calculated within the framework of effective mass theory. The results indicate that the spin-orbit coupling will induce a controllable bright-to-dark transition in a quasi-two-dimensional exciton system. This procedure can work as a way to increase the lifetime of excitons.
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71.35.-y Excitons and related phenomena
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Charge transport mechanisms in microcrystalline silicon

S. J. Konezny, M. N. Bussac, and Libero Zuppiroli

Appl. Phys. Lett. 92, 012107 (2008); http://dx.doi.org/10.1063/1.2828991 (3 pages) | Cited 8 times

Online Publication Date: 3 January 2008

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A heterogeneous charge transport model for microcrystalline silicon based on fluctuation-induced tunneling is presented that fits the low-temperature saturation observed in dark conductivity measurements and accounts for the film microstructure. Excellent agreement is found when the model is applied to data reported in the literature, particularly for highly crystalline samples, which produce the highest performance transistors. Values obtained for the three fitting parameters are consistent with typical measurements of microcrystalline silicon film morphology and the conduction band offset between amorphous and crystalline silicons.
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73.61.Cw Elemental semiconductors
71.20.Mq Elemental semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.50.Pz Photoconduction and photovoltaic effects
73.40.Gk Tunneling

Magnetically responsive elastic microspheres

Suili Peng, Mengying Zhang, Xize Niu, Weijia Wen, Ping Sheng, Zhengyou Liu, and Jing Shi

Appl. Phys. Lett. 92, 012108 (2008); http://dx.doi.org/10.1063/1.2830620 (3 pages) | Cited 12 times

Online Publication Date: 3 January 2008

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We report the design, fabrication, and characterization of magnetically responsive elastic microspheres consisting of polydimethylsioxane (PDMS) and magnetic nano-/microparticles. The microspheres can have either core-shell or solid structure, fabricated by using a microfluidic technique. The mechanical characteristics are determined with a modified electronic balance, and the results show that the microspheres exhibit magnetostrictive effect. Such microspheres can in addition behave as a smart material controllable through an external magnetic field. Owing to the transparency, biocompatibility and nontoxicity of PDMS, the magnetically responsive elastic microspheres may have potential applications in drug delivery, biosensing, bioseparation, and medical diagnosis.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.80.+q Magnetomechanical effects, magnetostriction

Cyclotron mass of two-dimensional holes in (100) oriented GaAs/AlGaAs heterostructures

T. M. Lu, Z. F. Li, D. C. Tsui, M. J. Manfra, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 92, 012109 (2008); http://dx.doi.org/10.1063/1.2830016 (3 pages) | Cited 2 times

Online Publication Date: 3 January 2008

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Microwave cyclotron resonance of low-density high-mobility two-dimensional hole gases of different densities in (100) oriented GaAs/AlGaAs heterostructures has been measured at 4.2 K. The measurements show that the hole effective mass depends strongly on the confining potential. For holes in a 20 nm quantum well, the cyclotron mass decreases from 0.48me at density p = 6.9×1010/cm2 to 0.29me at p = 0.8×1010/cm2. The cyclotron mass for holes confined at a heterojunction is fairly insensitive to the density and has a value of approximately 0.5me.
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73.21.Fg Quantum wells
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
76.40.+b Diamagnetic and cyclotron resonances

Real-time observation of the dry oxidation of the Si(100) surface with ambient pressure x-ray photoelectron spectroscopy

Yoshiharu Enta, Bongjin S. Mun, Massimiliano Rossi, Philip N. Ross, Jr., Zahid Hussain, Charles S. Fadley, Ki-Suk Lee, and Sang-Koog Kim

Appl. Phys. Lett. 92, 012110 (2008); http://dx.doi.org/10.1063/1.2830332 (3 pages) | Cited 15 times

Online Publication Date: 3 January 2008

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We have applied ambient-pressure x-ray photoelectron spectroscopy with Si 2p chemical shifts to study the real-time dry oxidation of Si(100), using pressures in the range of 0.01–1 Torr and temperatures of 300–530 °C, and examining the oxide thickness range from 0 to  ∼ 25 Å. The oxidation rate is initially very high (with rates of up to ∼ 225 Å/h) and then, after a certain initial thickness of the oxide in the range of 6–22 Å is formed, decreases to a slow state (with rates of ∼ 1.5–4.0 Å/h). Neither the rapid nor the slow regime is explained by the standard Deal-Grove model for Si oxidation.
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68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Characterization of doped silicon in low carrier density region by terahertz frequency Faraday effect

Yohei Ikebe and Ryo Shimano

Appl. Phys. Lett. 92, 012111 (2008); http://dx.doi.org/10.1063/1.2830697 (3 pages) | Cited 13 times

Online Publication Date: 4 January 2008

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We report on optical characterization of doped semiconductors by using terahertz Faraday rotation measurements in Cross-Nicole configuration. The detection sensitivity of Faraday rotation angle as small as 0.5 mrad is obtained. The scheme is applied to an n-type silicon wafer of 525 μm thickness in carrier freeze-out temperature region. The carrier density below N = 1×1014 cm−3 is evaluated under magnetic field B = 1 T.
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72.80.Cw Elemental semiconductors
72.30.+q High-frequency effects; plasma effects
78.20.Ls Magneto-optical effects

Charge trapping properties in TiO2/HfSiO/SiO2 gate stacks probed by scanning capacitance microscopy

Y. Naitou, H. Arimura, N. Kitano, S. Horie, T. Minami, M. Kosuda, H. Ogiso, T. Hosoi, T. Shimura, and H. Watanabe

Appl. Phys. Lett. 92, 012112 (2008); http://dx.doi.org/10.1063/1.2828863 (3 pages) | Cited 9 times

Online Publication Date: 7 January 2008

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The charge-trapping properties of the high-permittivity titanium oxide–hafnium silicate–silicon dioxide (TiO2/HfSiO/SiO2) gate stacks have been studied using scanning capacitance microscopy. From the bias stress examination of the gate stacks, we concluded that there were electron traps within the films, and these trap densities increased with an increase in the oxidation temperature used for the fabrication of TiO2 top dielectrics. Furthermore, we found that the distribution of these charged defects was inhomogeneous within the gate stacks. These results are attributed to Ti diffusion through the dielectric layers, which caused electrical defects within the gate stacks.
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77.55.-g Dielectric thin films
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ng Insulators
81.65.Mq Oxidation

Inelastic electron tunneling spectroscopy study of metal-oxide-semiconductor diodes based on high-κ gate dielectrics

S. L. You, C. C. Huang, C. J. Wang, H. C. Ho, J. Kwo, W. C. Lee, K. Y. Lee, Y. D. Wu, Y. J. Lee, and M. Hong

Appl. Phys. Lett. 92, 012113 (2008); http://dx.doi.org/10.1063/1.2831717 (3 pages) | Cited 3 times

Online Publication Date: 7 January 2008

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Inelastic electron tunneling spectroscopy (IETS) was applied to characterize the microstructure, interface, and trap-related states in silicon metal-oxide-semiconductor devices consisting of high-κ gate dielectrics HfO2, Y2O3, and stacked HfO2/Y2O3 bilayer by molecular beam epitaxy and atomic layer deposition under various heat treatments. Reproducible vibrational modes of monoclinic HfO2 and cubic Y2O3 were identified from IETS spectra, along with phonon modes related to interfacial structures for a given metal-oxide-semiconductor fabrication process. A simple modeling was employed to analyze the trap related features in IETS spectra of stacked HfO2/Y2O3 bilayers, and showed that most traps are located near the HfO2/Y2O3 interface due to dissimilar charge distributions of two ionic oxides of different cation valences, and the presence of interfacial strains of dissimilar structures.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.35.Ct Interface structure and roughness
73.20.-r Electron states at surfaces and interfaces
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Kk Junction diodes

Investigation of oxygen growth pressure effects on TiO2−δ:Co

E. Hu, S. von Molnár, P. A. Stampe, R. J. Kennedy, and Y. Xin

Appl. Phys. Lett. 92, 012114 (2008); http://dx.doi.org/10.1063/1.2824626 (3 pages) | Cited 3 times

Online Publication Date: 8 January 2008

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We find that depending on the oxygen pressure during growth (PO2), the TiO2−δ:Co films show dramatically different magnetic behaviors. The magnetic properties are dominated by cobalt nanoparticles and are sensitive to the nanoparticle size. Hopping transport behavior expected in multiphase granular metal systems is observed for most of the samples in the measured temperature range and the linear I-V regime. Concomitantly, voltage induced tunneling conduction is observed in high electrical fields (nonlinear I-V regime) and at very low temperature (0.35 K). Cross sectional transmission electron microscopy images provide further corroboration of the multiphase structure of these materials.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.15.Fg Pulsed laser ablation deposition
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Fabrication and transport properties of ZnO/Nb-1 wt %-doped SrTiO3 epitaxial heterojunctions

Yunlong Wu, Liuwan Zhang, Guanlin Xie, Jia-Lin Zhu, and Yonghai Chen

Appl. Phys. Lett. 92, 012115 (2008); http://dx.doi.org/10.1063/1.2831913 (3 pages) | Cited 7 times

Online Publication Date: 8 January 2008

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(110) ZnO/(001) Nb-1 wt %-doped SrTiO3 n-n type heteroepitaxial junctions were fabricated using the pulse laser deposition method. A diodelike current behavior was observed. Different from conventional p-n junctions or Schottky diodes, the diffusion voltage was found to increase with temperature. At all temperatures, the forward current was perfectly fitted on the thermionic emission model. The band bending at the interface can qualitatively explain our results, and the extracted high ideality factor at low temperatures, as well as large saturation currents, is ascribed to the deep-level-assisted tunneling current through the junction.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Fg Pulsed laser ablation deposition

A sequential logic device realized by integration of in-plane gate transistors in InGaAs/InP

Jie Sun, Daniel Wallin, Yuhui He, Ivan Maximov, and H. Q. Xu

Appl. Phys. Lett. 92, 012116 (2008); http://dx.doi.org/10.1063/1.2825575 (3 pages) | Cited 3 times

Online Publication Date: 9 January 2008

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An integrated nanoelectronic circuit is fabricated from a high-mobility In0.75Ga0.25As/InP heterostructure. The manufactured device comprises two double in-plane gate transistors with a current channel of 1.1 μm in length and 100 nm in width. The two transistors are coupled to each other in a configuration that the source of one transistor is directly connected with one in-plane gate of the other transistor. Electrical measurements reveal that this device functions as an SR (set-reset) latch (a sequential logic device) with a gain of ∼ 4 in the logic swing at room temperature. The demonstrated device provides a simple circuit design for SR latches.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Resistive switching memory effect of ZrO2 films with Zr+ implanted

Qi Liu, Weihua Guan, Shibing Long, Rui Jia, Ming Liu, and Junning Chen

Appl. Phys. Lett. 92, 012117 (2008); http://dx.doi.org/10.1063/1.2832660 (3 pages) | Cited 34 times

Online Publication Date: 10 January 2008

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The Au/Cr/Zr+-implanted-ZrO2/n+-Si sandwiched structure exhibits reversible bipolar resistive switching behavior under dc sweeping voltage. The resistance ratio (Rratio) of high resistive state and low resistive state is as large as five orders of magnitude with 0.5 V readout bias. Zr+-implanted-ZrO2 films exhibit good retention characteristics and high device yield. The impact of implanted Zr+ ions on resistive switching performances is investigated. Resistive switching of the fabricated structures is explained by trap-controlled space charge limited current conduction.
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84.30.Sk Pulse and digital circuits

Measurement of electronic structure at nanoscale solid-solid interfaces by surface-sensitive electron spectroscopy

Hui-Qiong Wang, Eric I. Altman, and Victor E. Henrich

Appl. Phys. Lett. 92, 012118 (2008); http://dx.doi.org/10.1063/1.2831000 (3 pages) | Cited 1 time

Online Publication Date: 10 January 2008

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We explore the use of electron spectroscopy that samples the near-surface region of a crystal to study the electronic structure at the buried interfaces between two dissimilar transition-metal oxides. The interface is probed by comparing experimental ultraviolet photoelectron spectra to model spectra and by taking sequential differences between the experimental spectra as one oxide is grown on another. Using (100) Fe3O4–NiO and Fe3O4–CoO interfaces grown by molecular beam epitaxy, we show that there is a much higher density of electronic states at the Fe3O4–CoO interface than at the Fe3O4–NiO interface. The origin of this difference is discussed.
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73.20.At Surface states, band structure, electron density of states
71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ambipolar transistor behavior in p-doped InAs nanowires grown by molecular beam epitaxy

B. S. Sørensen, M. Aagesen, C. B. Sørensen, P. E. Lindelof, K. L. Martinez, and J. Nygård

Appl. Phys. Lett. 92, 012119 (2008); http://dx.doi.org/10.1063/1.2821372 (3 pages) | Cited 8 times

Online Publication Date: 10 January 2008

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We present the electric properties of p-InAs nanowire field-effect transistors showing ambipolar conduction. Be doped nanowires are grown by the vapor-solid-solid mechanism using molecular beam epitaxy with in situ deposited Au catalyst particles. P-type conduction in InAs nanowires is challenging because of the Fermi-level pinning above the conduction band edge at the nanowire surface that leads to creation of an electron inversion layer. We demonstrate that this task is possible without a modified surface and report a strong temperature dependence (10–105) of the on-off ratio caused by the surface inversion layer.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Negative magnetoresistance in ultrananocrystalline diamond: Strong or weak localization?

T. C. Choy, A. M. Stoneham, M. Ortuño, and A. M. Somoza

Appl. Phys. Lett. 92, 012120 (2008); http://dx.doi.org/10.1063/1.2826542 (3 pages) | Cited 4 times

Online Publication Date: 11 January 2008

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Electronic transport of ultrananocrystalline diamond involves the interplay between disorder, Anderson localization, and phase coherence. We show that variable range hopping explains many key features of the conductivity including the large low temperature negative magnetoresistance. Our numerical studies suggest two regimes where the (negative) magnetoresistance varies with magnetic field B such as B2 or B1/2, respectively, depending on the ratio of the cyclotron orbital radius and the hopping distance. This agrees with experiment, which also points to the expected T−1/2 temperature dependence of the hopping distance at the critical field.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.20.Fz Weak or Anderson localization
73.63.Bd Nanocrystalline materials

Characterization of carriers in GaSb/InAs superlattice grown on conductive GaSb substrate

T. V. Chandrasekhar Rao, J. Antoszewski, L. Faraone, J. B. Rodriguez, E. Plis, and S. Krishna

Appl. Phys. Lett. 92, 012121 (2008); http://dx.doi.org/10.1063/1.2831666 (3 pages) | Cited 2 times

Online Publication Date: 11 January 2008

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We report on mobility spectrum analysis of electrical transport in a GaSb/InAs superlattice (SL) grown on GaSb substrate. Despite domineering contribution to conduction from the substrate, it was possible to discern and characterize carriers from SL. A single electron specie with an ambient temperature mobility of ∼ 104 cm2/V s was found to emanate from SL. We show that this carrier has an activation energy of 0.27 eV and is associated with the SL band gap.
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72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
71.20.Nr Semiconductor compounds

Amplification of magnetoresistance of magnetite in an Fe3O4–SiO2–Si structure

Xianjie Wang, Yu Sui, Jinke Tang, Cong Wang, Xingquan Zhang, Zhe Lu, Zhiguo Liu, Wenhui Su, Xiankui Wei, and Richeng Yu

Appl. Phys. Lett. 92, 012122 (2008); http://dx.doi.org/10.1063/1.2823609 (3 pages) | Cited 7 times

Online Publication Date: 11 January 2008

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Film of Fe3O4 was prepared with laser molecular beam epitaxy deposition on a Si substrate with a native SiO2 layer. When the temperature is increased above 250 K, the resistance drops rapidly because the conduction path starts to switch from the Fe3O4 film to the inversion layer underneath the SiO2 via thermally assisted tunneling. A greatly magnified low field negative magnetoresistance of Fe3O4 is observed at 280 K. The effect is similar to a metal-oxide-semiconductor field-effect transistor. The magnetoresistance becomes positive with further increase in the magnetic field due to the Lorentz force and other effects on the carriers in the inversion layer.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Gg Ferrimagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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