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5 Nov 2007

Volume 91, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 91, 191106 (2007); http://dx.doi.org/10.1063/1.2804016 (3 pages)

A. Pikulin, N. Bityurin, G. Langer, D. Brodoceanu, and D. Bäuerle
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Angular dependence of the photoelectron energy distribution of InP(100) and GaAs(100) negative electron affinity photocathodes

Dong-Ick Lee, Yun Sun, Zhi Liu, Shiyu Sun, and Piero Pianetta

Appl. Phys. Lett. 91, 192101 (2007); http://dx.doi.org/10.1063/1.2805775 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2007

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Energy distribution of the photoelectrons from InP(100) photocathodes are investigated with a photon energy range from 0.62 to 2.76 eV. When the photon energy is less than 1.8 eV, only electrons emitted from the Γ valley are observed in the energy distribution curves. At higher photon energies, electrons from the L valley are observed. The angular dependence of the electron energy distributions of InP and GaAs photocathodes are studied and compared. The electrons emitted from the L valley have a larger angular spread than the ones from the Γ valley due to the larger effective mass of the L valley minimum.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Effect of charge modulation in (LaVO3)m(SrVO3)n superlattices on the insulator-metal transition

W. C. Sheets, B. Mercey, and W. Prellier

Appl. Phys. Lett. 91, 192102 (2007); http://dx.doi.org/10.1063/1.2805222 (3 pages) | Cited 6 times

Online Publication Date: 7 November 2007

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A series of epitaxial (LaVO3)6m(SrVO3)m superlattices having the same nominal composition as La6/7Sr1/7VO3, a Mott-Hubbard insulator, was grown with pulsed-laser deposition on [001]-oriented SrTiO3 substrates, and their superlattice period was varied. When m = 1, the insulating resistivity of bulklike La6/7Sr1/7VO3 is obtained; however, an increase in the periodicity (m ≥ 2) results in metallic samples. Comparison of the superlattice periodicity with the coherence length of charge carriers in perovskite oxide heterostructures is used to understand these observations. A filling-controlled insulator-metal transition was induced by placing a single dopant layer of SrVO3 within LaVO3 layers of varying thickness.
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71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Fg Pulsed laser ablation deposition
73.21.Cd Superlattices
73.61.Ng Insulators

Reproducible resistive switching in nonvolatile organic memories

Frank Verbakel, Stefan C. J. Meskers, René A. J. Janssen, Henrique L. Gomes, Michael Cölle, Michael Büchel, and Dago M. de Leeuw

Appl. Phys. Lett. 91, 192103 (2007); http://dx.doi.org/10.1063/1.2806275 (3 pages) | Cited 49 times

Online Publication Date: 7 November 2007

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Resistive switching in nonvolatile, two terminal organic memories can be due to the presence of a native oxide layer at an aluminum electrode. Reproducible solid state memories can be realized by deliberately adding a thin sputtered Al2O3 layer to nominal electron-only, hole-only, and bipolar organic diodes. Before memory operation, the devices have to be formed at an electric field of 109 V/m, corresponding to soft breakdown of Al2O3. After forming, the structures show pronounced negative differential resistance and the local maximum in the current scales with the thickness of the oxide layer. The polymer acts as a current limiting series resistance.
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84.30.Sk Pulse and digital circuits
85.60.Jb Light-emitting devices

Huge magnetoresistive effects using space charge limited current in ZnO/SiO2 system

Shintaro Miyanishi, Motoji Yagura, Nobuaki Teraguchi, Kazuhiko Shirakawa, Keiichi Sakuno, Yoshiteru Murakami, Kunio Kojima, Akira Takahashi, and Kenji Ohta

Appl. Phys. Lett. 91, 192104 (2007); http://dx.doi.org/10.1063/1.2807279 (3 pages) | Cited 4 times

Online Publication Date: 8 November 2007

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Huge magnetoresistive effects were observed in a metal/insulator current-in-plane (CIP) diode feeding space charge limited (SCL) current. The insulator laterally toward opposite gold (Au) electrodes was fabricated on a SiO2 substrate by the standard photolithography method using dry etching. The insulator consisted of a SiO2/ZnO/SiO2/ZnO multilayer sputtered on the substrate. Current-voltage curves showed Ohmic property and SCL current characteristics accompanied by Child-Langmuir and Mott-Gurney laws derived from first order differential calculus. Current-magnetic field curves indicated the huge magnetoresistive effects up to 1010% under the magnetic field of 0.3 T at room temperature. The current-magnetic field curves have even symmetry for the applied magnetic field. The Au/insulator CIP diode is abruptly switched between a conducting state and an insulating state by the applied magnetic field.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Enhanced Seebeck coefficient of quantum-confined electrons in SrTiO3/SrTi0.8Nb0.2O3 superlattices

Yoriko Mune, Hiromichi Ohta, Kunihito Koumoto, Teruyasu Mizoguchi, and Yuichi Ikuhara

Appl. Phys. Lett. 91, 192105 (2007); http://dx.doi.org/10.1063/1.2809364 (3 pages) | Cited 20 times

Online Publication Date: 8 November 2007

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We report two-dimensional Seebeck coefficients (∣S∣2D) of [(SrTiO3)x/(SrTi0.8Nb0.2O3)y]20 (x = 1–60, y = 1–20) superlattices, which were grown on the (100) face of insulating LaAlO3 substrates to clarify the origin of the giant ∣S∣2D values of the SrTiO3 superlattices [ H. Ohta et al., Nat. Mater. 6, 129 (2007) ]. The ∣S∣2D values of the [(SrTiO3)17/(SrTi0.8Nb0.2O3)y]20 superlattices increased proportionally to y−0.5 and reached 320 μV K−1 (y = 1), which is approximately five times larger than that of the SrTi0.8Nb0.2O3 bulk (∣S∣3D = 61 μV K−1). The slope of the log∣S∣2D-log y plots was −0.5, proving that the density of states in the ground state for SrTiO3 increases inversely proportionally to y. The critical barrier thickness for quantum electron confinement was also clarified to be 6.25 nm (16 unit cells of SrTiO3).
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73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
73.21.Cd Superlattices
73.61.Le Other inorganic semiconductors

Vacancy-arsenic clusters in germanium

A. Chroneos, R. W. Grimes, B. P. Uberuaga, S. Brotzmann, and H. Bracht

Appl. Phys. Lett. 91, 192106 (2007); http://dx.doi.org/10.1063/1.2805773 (3 pages) | Cited 31 times

Online Publication Date: 8 November 2007

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Electronic structure calculations are used to investigate the structures and relative energies of defect clusters formed between arsenic atoms and lattice vacancies in germanium and, for comparison, in silicon. It is energetically favorable to form clusters containing up to four arsenic atoms tetrahedrally coordinated around a vacancy. Using mass action analysis, the relative concentrations of arsenic atoms in different vacancy-arsenic clusters, unbound arsenic atoms, and unbound vacancies are predicted. At low temperatures the four arsenic-vacancy cluster is dominant over unbound vacancies while at higher temperatures unbound vacancies prevail. In terms of concentration, no intermediate size of cluster is ever of significance.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Bb Theories and models of crystal defects
71.20.Mq Elemental semiconductors

Electronic transport in locally gated graphene nanoconstrictions

Barbaros Özyilmaz, Pablo Jarillo-Herrero, Dmitri Efetov, and Philip Kim

Appl. Phys. Lett. 91, 192107 (2007); http://dx.doi.org/10.1063/1.2803074 (3 pages) | Cited 50 times

Online Publication Date: 8 November 2007

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We have developed the combination of an etching and deposition techniques that enables the fabrication of locally gated graphene nanostructures of arbitrary design. Employing this method, we have fabricated graphene nanoconstrictions with local tunable transmission and characterized their electronic properties. An order of magnitude enhanced gate efficiency is achieved adopting the local gate geometry with thin dielectric gate oxide. A complete turn off of the device is demonstrated as a function of the local gate voltage. Such strong suppression of device conductance was found to be due to both quantum confinement and Coulomb blockade effects in the constricted graphene nanostructures.
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73.63.Fg Nanotubes
73.23.Hk Coulomb blockade; single-electron tunneling

Self-separated freestanding GaN using a NH4Cl interlayer

Hyun-Jae Lee, S. W. Lee, H. Goto, Sang-Hyun Lee, Hyo-Jong Lee, J. S. Ha, Takenari Goto, M. W. Cho, T. Yao, and Soon-Ku Hong

Appl. Phys. Lett. 91, 192108 (2007); http://dx.doi.org/10.1063/1.2806912 (3 pages) | Cited 2 times

Online Publication Date: 8 November 2007

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Thick GaN films were grown on void buffer layer by hydride vapor phase epitaxy. The void-buffer layers were consisted of NH4Cl, GaN dots, and low-temperature (LT) GaN buffer layer. Instead of GaN, NH4Cl was easily synthesized in NH3 and HCl atmospheres by simply lowering the growth temperature to 500 °C, and LT GaN buffer growth was followed during increasing substrate temperature to 600 °C. The LT GaN buffer acted as a protecting layer against evaporation of the NH4Cl and a seeding layer for the high temperature (HT) GaN. The NH4Cl layer between a sapphire substrate with GaN dots and the LT GaN buffer were fully evaporated during the HT GaN growth at 1040 °C. Many voids were formed at interface caused by evaporation of the NH4Cl layer, which strongly assisted self-separation of thick HT GaN during cooldown after the growth resulting in a 200 μm thick freestanding (FS) GaN. The FS GaN showed smooth surface morphology and absence of any crack. The a-axis and c-axis lattice constants of FS GaN were 3.189 and 5.185 Å, respectively, which well agrees with those of strain-free bulk GaN. The observed donor-bound exciton emission peak at 3.4718 eV agreed with the peak position of bulk GaN. All these features indicate that the obtained FS GaN through the self-separation process is nearly strain-free.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Nondestructive electrical characterization of integrated interconnect line-to-line spacing for advanced semiconductor chips

Fen Chen, Paul S. McLaughlin, and Kaushik Chanda

Appl. Phys. Lett. 91, 192109 (2007); http://dx.doi.org/10.1063/1.2806916 (3 pages)

Online Publication Date: 8 November 2007

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Poor process controls may cause huge line spacing variation across a semiconductor wafer during back-end-of-the-line integration in advanced semiconductor integrated circuit fabrication. As a consequence, significant degradation in yield, performance, and reliability may be observed. Line spacing variation also imposes challenges for accurate time dependent dielectric breakdown reliability lifetime projection. In this paper, a nondestructive, fast electrical method for determining a line-to-line spacing of a semiconductor chip is proposed. The method includes experimentally determining a slope from capacitance measurement (kCA), experimentally determining a slope from current-voltage measurement (kSE), and finally determining a line-to-line spacing from the slope kCA and the slope kSE. The line-to-line spacing determined from this method shows an excellent agreement with constructional analysis data.
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77.22.Jp Dielectric breakdown and space-charge effects
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing

Effect of tensile and compressive strains on the transport properties of SmNiO3 layers epitaxially grown on (001) SrTiO3 and LaAlO3 substrates

Florine Conchon, Alexandre Boulle, René Guinebretière, Cécile Girardot, Stéphane Pignard, Jens Kreisel, François Weiss, Eric Dooryhée, and Jean-Louis Hodeau

Appl. Phys. Lett. 91, 192110 (2007); http://dx.doi.org/10.1063/1.2800306 (3 pages) | Cited 12 times

Online Publication Date: 9 November 2007

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This paper deals with the role of epitaxial strain on the structure and electronic transport properties of metastable SmNiO3 layers grown by metal-organic chemical vapor deposition onto SrTiO3 and LaAlO3 substrates. The characterization of these layers is carried out by high resolution x-ray diffraction and four-probe resistivity measurements. It is found that the SmNiO3 phase is stabilized by in-plane compressive strain whereas in-plane tensile strain induces the creation of oxygen vacancies that induces an annihilation of the metal-insulator transition and a huge increase of the resistivity.
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73.61.Ng Insulators
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Impact of high-pressure deuterium oxide annealing on the blocking efficiency and interface quality of metal-alumina-nitride-oxide-silicon-type flash memory devices

Man Chang, Musarrat Hasan, Seungjae Jung, Hokyung Park, Minseok Jo, Hyejung Choi, and Hyunsang Hwang

Appl. Phys. Lett. 91, 192111 (2007); http://dx.doi.org/10.1063/1.2812570 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2007

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We have investigated the effect of high-pressure deuterium oxide annealing (HPDOA) on metal-alumina-nitride-oxide-silicon-type flash memory device. HPDOA was performed in a high-pressure wet vapor ambient (N2:D2O = 10 atm:2 atm) at 250 °C for 5 min. HPDOA devices achieved the improvements of blocking oxide quality as well as tunneling oxide/Si interface quality. The improvement of blocking oxide induced the lower charge loss through the blocking oxide, lower leakage current density, lower erase saturation level, and a larger memory window after the program/erase cycles. In addition, the presence of deuterium at the tunneling oxide/Si improved the interface quality by the formation of Si–D bonds.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Threshold voltage stability of organic field-effect transistors for various chemical species in the insulator surface

Kouji Suemori, Sei Uemura, Manabu Yoshida, Satoshi Hoshino, Noriyuki Takada, Takehito Kodzasa, and Toshihide Kamata

Appl. Phys. Lett. 91, 192112 (2007); http://dx.doi.org/10.1063/1.2812573 (3 pages) | Cited 28 times

Online Publication Date: 9 November 2007

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The relationship between the threshold voltage (Vt) stability and the chemical species of the insulator surface was investigated by using organic field-effect transistors with different types of self-assembled monolayers on a SiO2 insulator. The Vt shift induced by gate bias stressing was considerably increased by the introduction of long-chain chemical species to the SiO2 surface. In order to obtain high-performance and high-stability organic transistors, insulator surfaces with short-chain chemical species that can improve transistor performance without degrading stability are required.
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85.30.Tv Field effect devices

Scanning gate microscopy of copper phthalocyanine field effect transistors

Nobuyuki Aoki, Kouhei Sudou, Kazuya Okamoto, Jonathan P. Bird, and Yuichi Ochiai

Appl. Phys. Lett. 91, 192113 (2007); http://dx.doi.org/10.1063/1.2812575 (3 pages) | Cited 4 times

Online Publication Date: 9 November 2007

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Various techniques are developed to implement ambient scanning gate microscopy (SGM) as a tool for the characterization of organic-thin-film field-effect transistors (OFETs). OFETs comprising copper phthalocyanine have been investigated by this technique and their SGM response has been observed only at the edges of the metal electrodes, thereby providing visualization of the Schottky barrier at the boundary between the organic channel and the metal electrode.
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85.30.Tv Field effect devices

Low resistance, nonalloyed Ohmic contacts to InGaAs

Adam M. Crook, Erik Lind, Zach Griffith, Mark J. W. Rodwell, Jeremy D. Zimmerman, Arthur C. Gossard, and Seth R. Bank

Appl. Phys. Lett. 91, 192114 (2007); http://dx.doi.org/10.1063/1.2806235 (3 pages) | Cited 13 times

Online Publication Date: 9 November 2007

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We report extremely low specific contact resistivity (ρc) nonalloyed Ohmic contacts to n-type In0.53Ga0.47As, lattice matched to InP. Contacts were formed by oxidizing the semiconductor surface through exposure to ultraviolet-generated ozone, subsequently immersing the wafer in ammonium hydroxide (NH4OH, 14.8 normality), and finally depositing either Ti/Pd/Au contact metal by electron-beam evaporation or TiW contact metal by vacuum sputtering. Ti/Pd/Au contacts exhibited ρc of (0.73±0.44) Ω μm2—i.e., (7.3±4.4)×10−9 Ω cm2—while TiW contacts exhibited ρc of (0.84±0.48) Ω μm2. The TiW contacts are thermally stable, showing no observable degradation in resistivity after a 500 °C annealing of 1 min duration.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
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