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27 Sep 2010

Volume 97, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 133303 (2010); http://dx.doi.org/10.1063/1.3491815 (3 pages)

Yoshihide Fujisaki, Yoshiki Nakajima, Daisuke Kumaki, Toshihiro Yamamoto, Shizuo Tokito, Takahiro Kono, Jun-ichi Nishida, and Yoshiro Yamashita
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Role of graphene/substrate interface on the local transport properties of the two-dimensional electron gas

S. Sonde, F. Giannazzo, C. Vecchio, R. Yakimova, E. Rimini, and V. Raineri

Appl. Phys. Lett. 97, 132101 (2010); http://dx.doi.org/10.1063/1.3489942 (3 pages) | Cited 9 times

Online Publication Date: 27 September 2010

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The electron mean free path (lgr) is “locally” evaluated by scanning capacitance spectroscopy on graphene obtained with different preparation methods and on different substrates, i.e., graphene exfoliated from highly oriented pyrolitic graphite (HOPG) and deposited (DG) on 4H-SiC(0001) and on SiO2 and epitaxial graphene grown on 4H-SiC(0001) (EG). lgr in DG on SiC was more than four times larger than in DG on SiO2. The improved mean free path is explained by the higher permittivity of SiC compared to SiO2, yielding a better dielectric screening of charged-impurities, and by the weaker coupling of graphene two-dimensional-electron-gas with surface polar phonons of SiC. On the other hand, lgr on EG is on average ∼ 0.4 times that on DG-SiC and exhibits large variations from point to point, due to the presence of a laterally inhomogeneous positively charged layer at EG/SiC interface.
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81.05.ue Graphene
77.22.Ch Permittivity (dielectric function)
73.63.-b Electronic transport in nanoscale materials and structures
73.22.Pr Electronic structure of graphene
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Impact of InGaAs surface nitridation on interface properties of InGaAs metal-oxide-semiconductor capacitors using electron cyclotron resonance plasma sputtering SiO2

T. Hoshii, M. Yokoyama, H. Yamada, M. Hata, T. Yasuda, M. Takenaka, and S. Takagi

Appl. Phys. Lett. 97, 132102 (2010); http://dx.doi.org/10.1063/1.3464170 (3 pages) | Cited 6 times

Online Publication Date: 27 September 2010

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We perform InGaAs surface nitridation using electron cyclotron resonance (ECR) plasma and study the effect on interface properties of ECR-sputtered SiO2/InGaAs metal-oxide-semiconductor (MOS) capacitors. We demonstrate that the InGaAs surface nitridation, combined with in situ ECR SiO2 sputtering and annealing, effectively reduces the interface state density (Dit) of SiO2/InGaAs MOS capacitors and realizes a minimum Dit value of as low as 2×1011 cm−2 eV−1. It is found from x-ray photoelectron spectroscopy (XPS) analyses of the MOS interfaces that the MOS interfaces have almost no As oxides and that the nitridation and the subsequent annealing can reduce Ga oxides of InGaAs surfaces and form Ga–N bonds at the surfaces. It is suggested from the comparison in C-V and XPS data with and without nitridation that the Ga–N bond formation can be a key for the reduction in Dit, in addition to the suppression of Ga oxides and As oxides.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Virtual scanning tunneling microscopy: A local spectroscopic probe of two-dimensional electron systems

A. Sciambi, M. Pelliccione, S. R. Bank, A. C. Gossard, and D. Goldhaber-Gordon

Appl. Phys. Lett. 97, 132103 (2010); http://dx.doi.org/10.1063/1.3492440 (3 pages) | Cited 1 time

Online Publication Date: 27 September 2010

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We propose a probe technique capable of performing local low-temperature spectroscopy on a two-dimensional electron system (2DES) in a semiconductor heterostructure. Motivated by predicted spatially-structured electron phases, the probe uses a charged metal tip to induce electrons to tunnel locally, directly below the tip, from a “probe” 2DES to a “subject” 2DES of interest. We test this concept with large-area (nonscanning) tunneling measurements, and predict a high spatial resolution and spectroscopic capability, with minimal influence on the physics in the subject 2DES.
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07.79.Cz Scanning tunneling microscopes

Thermoelectric properties of electrostatically tunable antidot lattices

Srijit Goswami, Christoph Siegert, Saquib Shamim, Michael Pepper, Ian Farrer, David A. Ritchie, and Arindam Ghosh

Appl. Phys. Lett. 97, 132104 (2010); http://dx.doi.org/10.1063/1.3493268 (3 pages)

Online Publication Date: 27 September 2010

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We report on the fabrication and characterization of a device which allows the formation of an antidot lattice (ADL) using only electrostatic gating. The antidot potential and Fermi energy of the system can be tuned independently. Well defined commensurability features in magnetoresistance as well as magnetothermopower are observed. We show that the thermopower can be used to efficiently map out the potential landscape of the ADL.
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85.35.Ds Quantum interference devices
85.35.Gv Single electron devices
85.80.Fi Thermoelectric devices
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Tunnel barrier parameters derivation from normalized differential conductance in Hg/organic monomolecular layer-Si junctions

C. Godet, A. B. Fadjie-Djomkam, S. Ababou-Girard, and F. Solal

Appl. Phys. Lett. 97, 132105 (2010); http://dx.doi.org/10.1063/1.3493650 (3 pages) | Cited 3 times

Online Publication Date: 27 September 2010

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The shape of tunnel barrier junctions is derived from experimental current density versus bias, J(V), using the normalized differential conductance, NDC = d log J/d log V, to discriminate barrier height, ΦT, and barrier width, dT, effects. Parameterization of the Simmons model for a rectangular tunnel barrier, with NDC ≈ dTV/(ΦT-qV)1/2, provides physical (dT,ΦT) values for Hg∥monomolecular layer—n Si(111) junctions incorporating functionalized n-alkyl layers covalently bonded to silicon.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.65.+h Molecular electronic devices

Effect of O2 adsorption on electron scattering at Cu(001) surfaces

J. S. Chawla, F. Zahid, H. Guo, and D. Gall

Appl. Phys. Lett. 97, 132106 (2010); http://dx.doi.org/10.1063/1.3489357 (3 pages) | Cited 5 times

Online Publication Date: 27 September 2010

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The electrical resistance of epitaxial Cu(001) sequentially increases, decreases, and again increases when exposed to 10−3–105 Pa s of O2. This is attributed to partial specular surface scattering for smooth clean Cu(001) and for the surface with a complete adsorbed monolayer, but diffuse scattering at partial coverage and after chemical oxidation. A model relates the surface coverage to the specularity parameter and finds adatom and advacancy scattering cross-sections of 0.8±0.2 and 0.06±0.03 nm2, which are qualitatively validated by nonequilibrium ab initio transport simulations. The rates for resistance change are proportional to the O2 partial pressure.
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73.61.At Metal and metallic alloys
73.25.+i Surface conductivity and carrier phenomena
68.43.Mn Adsorption kinetics
68.55.-a Thin film structure and morphology
68.35.bd Metals and alloys
81.65.Mq Oxidation

Phase change memory cell using Ge2Sb2Te5 and softly broken-down TiO2 films for multilevel operation

Byung Joon Choi, Seol Choi, Taeyong Eom, Sang Ho Rha, Kyung Min Kim, and Cheol Seong Hwang

Appl. Phys. Lett. 97, 132107 (2010); http://dx.doi.org/10.1063/1.3494084 (3 pages) | Cited 2 times

Online Publication Date: 27 September 2010

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A phase change memory cell was fabricated by stacking plasma-enhanced cyclic chemical-vapor-deposited Ge2Sb2Te5 (GST) and atomic layer deposited TiO2 thin films. Different pairs of resistance states were obtained by controlling the current flow, which can be used to achieve higher memory density by multilevel operation. The multiresistance states of the stacked cell were explained by the resistance switching phenomena of TiO2 and the thermoelectric phase change properties of GST. The phase change characteristics of GST could be altered by controlling the degree of filament formation in the TiO2 layer, which eventually changed the phase change volume in the GST.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Lw Thermoelectric effects

Nanoscale resistive switching and filamentary conduction in NiO thin films

J. Y. Ye, Y. Q. Li, J. Gao, H. Y. Peng, S. X. Wu, and T. Wu

Appl. Phys. Lett. 97, 132108 (2010); http://dx.doi.org/10.1063/1.3494267 (3 pages) | Cited 9 times

Online Publication Date: 28 September 2010

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We fabricate regular arrays of nanoelectrodes on NiO thin films via nanosphere lithography and directly probe the nanoscale resistive switching using a conductive atomic force microscope. The unipolar resistive switching is consistent with the conducting filament formation/rupture mechanism, and the switching power is as low as 10−9 W. We find that only about half of devices are switchable, and the Monte Carlo simulation suggests strong correlations between the switching reliability, the electrode size, and the filament dimension and density.
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68.55.-a Thin film structure and morphology
81.16.Nd Micro- and nanolithography
82.45.Fk Electrodes
68.37.Ps Atomic force microscopy (AFM)
61.43.Bn Structural modeling: serial-addition models, computer simulation

Surface states induced high P-type conductivity in nanostructured thin film composed of Ge nanocrystals in SiO2 matrix

B. Zhang, S. Shrestha, M. A. Green, and G. Conibeer

Appl. Phys. Lett. 97, 132109 (2010); http://dx.doi.org/10.1063/1.3496031 (3 pages) | Cited 1 time

Online Publication Date: 29 September 2010

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Highly conductive thin films composed of Ge nanocrystals (Ge-NCs) embedded in SiO2 matrix were prepared using a low thermal budget process. P-type behavior in the undoped films was attributed to the hole accumulation caused by acceptor-like surface states. Quantitative analysis has demonstrated that the density of surface states was sufficient to cause the measured electrical conductivity. The charge transport mechanism was identified as thermally activated charge hopping from one NC to its nearest neighbor. Postgrowth rapid thermal annealing dramatically increased the conductivities and this was tentatively explained by the modification of Ge-NCs’ surface structure and reduction in defects in SiO2 matrix.
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81.05.Cy Elemental semiconductors
68.35.bg Semiconductors
73.20.At Surface states, band structure, electron density of states
61.72.Cc Kinetics of defect formation and annealing
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.ag Semiconductors

Lateral, high-quality, metal-catalyzed semiconductor growth on amorphous and lattice-mismatched substrates for photovoltaics

Nathaniel J. Quitoriano

Appl. Phys. Lett. 97, 132110 (2010); http://dx.doi.org/10.1063/1.3495799 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2010

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Solar-derived energy is universally available but is not yet cost-competitive. Next generation solar cells are expected to have high efficiencies, associated with single-crystalline semiconductors, at reduced costs, associated with amorphous substrates. Here we report the growth of high-quality semiconductors (Ge and Si) on amorphous and lattice-mismatched substrates using metal-catalyzed, lateral growth. Using this technique, we engineer the location of crystal nucleation, by controlling the catalyst location, and can thus prevent the formation of grain boundaries, typical when crystals grow together. The results presented here provide a foundation upon which next generation photovoltaics may be built.
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81.16.Hc Catalytic methods
81.07.Vb Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
81.05.Cy Elemental semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.07.Gf Nanowires

Interfacial chemical states of resistance-switching metal/Pr0.7Ca0.3MnO3 interfaces

R. Yasuhara, T. Yamamoto, I. Ohkubo, H. Kumigashira, and M. Oshima

Appl. Phys. Lett. 97, 132111 (2010); http://dx.doi.org/10.1063/1.3496033 (3 pages) | Cited 12 times

Online Publication Date: 30 September 2010

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The relationship between interfacial chemical states and resistance-switching (RS) behaviors at the metal/Pr0.7Ca0.3MnO3 (PCMO) interfaces has been studied by photoemission spectroscopy and x-ray absorption spectroscopy. For Al/PCMO interfaces that exhibit RS behavior, redox reactions between Al and Mn ions occur at the interface. In sharp contrast, no chemical reactions occur at Pt/PCMO interfaces that do not exhibit RS behavior. These results strongly suggest that the interfacial transition layer due to the redox reactions is responsible for the RS behavior at metal/PCMO interfaces.
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73.40.Ns Metal-nonmetal contacts
78.70.Dm X-ray absorption spectra
79.60.Jv Interfaces; heterostructures; nanostructures
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
72.60.+g Mixed conductivity and conductivity transitions
73.25.+i Surface conductivity and carrier phenomena

Electron band alignment between (100)InP and atomic-layer deposited Al2O3

Hsing-Yi Chou, V. V. Afanas’ev, A. Stesmans, H. C. Lin, P. K. Hurley, and S. B. Newcomb

Appl. Phys. Lett. 97, 132112 (2010); http://dx.doi.org/10.1063/1.3496039 (3 pages) | Cited 9 times

Online Publication Date: 30 September 2010

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Energy barriers at interfaces of (100)InP with atomic-layer deposited Al2O3 are determined using internal photoemission of electrons. The barrier height between the top of the InP valence band and bottom of the alumina conduction band is found to be 4.05±0.10 eV corresponding to a conduction band offset of 2.7 eV. An interlayer associated with the oxidation of InP may result in a lower barrier for electron injection potentially leading to charge instability of the insulating stack. A wide-gap P-rich interlayer has a potential to reduce this degrading effect as compared to In-rich oxides.
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79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Ps Other inorganic compounds
81.65.Mq Oxidation
73.20.At Surface states, band structure, electron density of states

Delocalized-localized transition in a semiconductor two-dimensional honeycomb lattice

G. De Simoni, A. Singha, M. Gibertini, B. Karmakar, M. Polini, V. Piazza, L. N. Pfeiffer, K. W. West, F. Beltram, and V. Pellegrini

Appl. Phys. Lett. 97, 132113 (2010); http://dx.doi.org/10.1063/1.3493189 (3 pages) | Cited 1 time

Online Publication Date: 30 September 2010

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We report the magnetotransport properties of a two-dimensional electron gas in a modulation-doped AlGaAs/GaAs heterostructure subjected to a lateral potential with honeycomb geometry. Periodic oscillations of the magnetoresistance and a delocalized-localized transition are shown by applying a gate voltage. We argue that electrons in such artificial-graphene lattices offer a promising approach for the simulation of quantum phases dictated by Coulomb interactions.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Indium segregation in AlInN/AlN/GaN heterostructures

A. Minj, D. Cavalcoli, and A. Cavallini

Appl. Phys. Lett. 97, 132114 (2010); http://dx.doi.org/10.1063/1.3489433 (3 pages) | Cited 13 times

Online Publication Date: 30 September 2010

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AlInN/AlN/GaN heterostructures were characterized by atomic force microscopy. V-defects and channels were observed. In phase-contrast mode, these features were found related to inhomogeneities associated with In-segregation (and/or In-diffusion) and Al-rich surface reconstruction. The electrical characterization via conductive atomic force microscopy showed enhanced conductivity regions related to In-rich traces within channels and V-defects.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
66.30.-h Diffusion in solids
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.-y Defects and impurities in crystals; microstructure
81.05.Ea III-V semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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