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13 Jun 2011

Volume 98, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 243101 (2011); http://dx.doi.org/10.1063/1.3598468 (3 pages)

M. Beleggia, T. Kasama, R. E. Dunin-Borkowski, S. Hofmann, and G. Pozzi
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Conductance and shot noise in graphene superlattice

Xiao-Xiao Guo, De Liu, and Yu-Xian Li

Appl. Phys. Lett. 98, 242101 (2011); http://dx.doi.org/10.1063/1.3599447 (3 pages) | Cited 8 times

Online Publication Date: 13 June 2011

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The conductance and the shot noise were investigated in graphene superlattice. A new Dirac point appears in the graphene superlattice and the position of the new Dirac point depends on the ratio of the width of the barriers to that of the wells. At the new Dirac point the conductance is minimum and the Fano factor reaches its max value 1/3. This Dirac point is robust against the magnetic field. In the energy window below the Dirac point, the magnetic field weakens the conductance but enhances the Fano factor.
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72.70.+m Noise processes and phenomena
68.65.Cd Superlattices
72.25.Dc Spin polarized transport in semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Epitaxial growth of high mobility Bi2Se3 thin films on CdS

X. F. Kou, L. He, F. X. Xiu, M. R. Lang, Z. M. Liao, Y. Wang, A. V. Fedorov, X. X. Yu, J. S. Tang, G. Huang, X. W. Jiang, J. F. Zhu, J. Zou, and K. L. Wang

Appl. Phys. Lett. 98, 242102 (2011); http://dx.doi.org/10.1063/1.3599540 (3 pages) | Cited 16 times

Online Publication Date: 13 June 2011

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We report the experiment of high quality epitaxial growth of Bi2Se3 thin films on hexagonal CdS (0001) substrates using a solid source molecular-beam epitaxy system. Layer-by-layer growth of single crystal Bi2Se3 has been observed from the first quintuple layer. The size of surface triangular terraces has exceeded 1 μm. Angle-resolved photoemission spectroscopy clearly reveals the presence of Dirac-cone-shape surface states. Magneto-transport measurements demonstrate a high Hall mobility of ∼ 6000 cm2/V s for the as-grown Bi2Se3 thin films at temperatures below 30 K. These characteristics of Bi2Se3 thin films promise a variety of potential applications in ultrafast, low-power dissipation devices.
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68.55.aj Insulators
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ng Insulators
73.20.At Surface states, band structure, electron density of states
72.20.My Galvanomagnetic and other magnetotransport effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Hot electron injection effect on the microwave performance of type-I/II AlInP/GaAsSb/InP double-heterojunction bipolar transistors

K. Y. Donald Cheng, C. C. Liao, H. Xu, K. Y. Norman Cheng, and M. Feng

Appl. Phys. Lett. 98, 242103 (2011); http://dx.doi.org/10.1063/1.3599582 (3 pages) | Cited 2 times

Online Publication Date: 13 June 2011

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A type-I/II double heterojunction bipolar transistor (DHBT) with a layer structure of AlInP(emitter)/GaAsSb(composition graded base)/InP(collector) was designed and grown by molecular beam epitaxy technique. The band alignment of the type-I AlInP/GaAsSb emitter-base interface provides hot electron injection into the base to enhance the effective base velocity to 2.54×107 cm/s, resulting in an improved device gain and high frequency performance. We have fabricated a submicron emitter (AE = 0.35×4 μm2) type-I/II DHBT with a demonstrated current gain of β = 50 and a breakdown voltage of BVCEO = 4.2 V, with a cutoff frequency of fT = 455 GHz and fMAX = 400 GHz at a collector current density, JC = 10 mA/μm2.
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85.30.Pq Bipolar transistors
85.30.Tv Field effect devices
85.40.Sz Deposition technology

Spin current depolarization under high electric fields in undoped InGaAs

N. Okamoto, H. Kurebayashi, K. Harii, Y. Kajiwara, H. Beere, I. Farrer, T. Trypiniotis, K. Ando, D. A. Ritchie, C. H. W. Barnes, and E. Saitoh

Appl. Phys. Lett. 98, 242104 (2011); http://dx.doi.org/10.1063/1.3599599 (3 pages)

Online Publication Date: 13 June 2011

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Carrier spin polarization in In0.13Ga0.87As under high electric fields has been investigated. The spin polarization was created by optical spin orientation techniques and the inverse spin-Hall effect was employed to measure the spin polarization. For moderate electric fields, the spin polarization was constant, whereas the significant change in the spin polarization was found in the high electric field range. The spin-density rate equation, together with carrier transport analysis, clarifies that the observed change is attributed to the voltage-induced Auger process which modifies the carrier number in InGaAs.
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72.25.Dc Spin polarized transport in semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
79.20.Fv Electron impact: Auger emission
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Boron nitride substrates for high mobility chemical vapor deposited graphene

W. Gannett, W. Regan, K. Watanabe, T. Taniguchi, M. F. Crommie, and A. Zettl

Appl. Phys. Lett. 98, 242105 (2011); http://dx.doi.org/10.1063/1.3599708 (3 pages) | Cited 21 times

Online Publication Date: 13 June 2011

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Chemical vapor deposited (CVD) graphene is often presented as a scalable solution to graphene device fabrication, but to date such graphene has exhibited lower mobility than that produced by exfoliation. Using a boron nitride underlayer, we achieve mobilities as high as 37 000 cm2/V s, an order of magnitude higher than commonly reported for CVD graphene and better than most exfoliated graphene. This result demonstrates that the barrier to scalable, high mobility CVD graphene is not the growth technique but rather the choice of a substrate that minimizes carrier scattering.
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85.30.De Semiconductor-device characterization, design, and modeling
72.20.Fr Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Nonthermal phase transition in phase change memory cells induced by picosecond electric pulse

D. Q. Huang, X. S. Miao, Z. Li, J. J. Sheng, J. J. Sun, J. H. Peng, J. H. Wang, Y. Chen, and X. M. Long

Appl. Phys. Lett. 98, 242106 (2011); http://dx.doi.org/10.1063/1.3597792 (3 pages) | Cited 5 times

Online Publication Date: 13 June 2011

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The ultrafast amorphization phenomenon induced by a single picosecond electric pulse was studied. The RESET operations were performed on phase change memory cells with 50 nm and 150 nm thick Ge2Sb2Te5 layers by a self-built test system, respectively. The ultrafast amorphization of only 0.2 ns was observed in phase change memory cell. The dependence of RESET resistance on the pulse amplitude was investigated. Thermal simulations with a RESET pulse width of 50 and 0.8 ns using finite element method were compared. Experimental and simulation results suggest that the amorphization in phase change memory cells induced by a picosecond electric pulse exhibits nonthermal nature.
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84.30.Sk Pulse and digital circuits

Spin polarized photoemission from strained Ge epilayers

Federico Bottegoni, Giovanni Isella, Stefano Cecchi, and Franco Ciccacci

Appl. Phys. Lett. 98, 242107 (2011); http://dx.doi.org/10.1063/1.3599493 (3 pages) | Cited 5 times

Online Publication Date: 14 June 2011

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We report on spin polarized electron photoemission experiments on compressively strained Ge/SiGe/Si(001) layers. Spin polarization of conduction band electrons up to P = 62% at T = 120 K has been observed, well above the theoretical limit of P = 50% valid for bulk materials. Such spin polarization increase, can be attributed to the strain-induced removal of the heavy-hole light-hole degeneracy in the valence band. A set of Ge epilayers with different strain levels has been characterized, achieving an experimental correlation between the measured polarization and the strain in the epilayer.
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72.25.Dc Spin polarized transport in semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Mq Elemental semiconductors
68.55.-a Thin film structure and morphology

p-type conduction induced by N-doping in α-Fe2O3

Takeshi Morikawa, Kousuke Kitazumi, Naoko Takahashi, Takeo Arai, and Tsutomu Kajino

Appl. Phys. Lett. 98, 242108 (2011); http://dx.doi.org/10.1063/1.3599852 (3 pages) | Cited 3 times

Online Publication Date: 14 June 2011

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A p-type N-doped α-Fe2O3 was developed by magnetron sputtering of a Fe2O3 target in a plasma containing N2 and Ar followed by postannealing. Photoelectrochemical measurement under visible light irradiation (>410 nm) showed that N–Fe2O3 exhibits a typical cathodic photocurrent originated from the p-type conduction. X-ray photoemission spectroscopy indicated that the atomic N incorporated substitutionally at O sites was responsible for the p-type conduction. The concentration of acceptors was very close to that for Zn-doped Fe2O3, a typical p-type α-Fe2O3. This finding would stimulate further research on p-type Fe2O3 for solar fuel generation, etc.
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73.61.Le Other inorganic semiconductors
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
81.05.Hd Other semiconductors
82.50.-m Photochemistry
82.45.-h Electrochemistry and electrophoresis

Light-induced stochastic resonance in a nanoscale resonant-tunneling diode

F. Hartmann, L. Gammaitoni, S. Höfling, A. Forchel, and L. Worschech

Appl. Phys. Lett. 98, 242109 (2011); http://dx.doi.org/10.1063/1.3600329 (3 pages)

Online Publication Date: 14 June 2011

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Resonant tunneling diodes (RTDs) have been often invoked as a primary nanoelectronic device candidate for cellular neural network physical implementation and for mimicking biological neuronlike behaviors. In this letter we report on the light-induced behavior of trench-etched RTDs capable of undergoing complex stochastic dynamics where electronic noise and light can cooperate for reproducing the stochastic resonance phenomenon previously observed in real biological neurons. The experimental measurements presented here add a missing piece to the quest for the optimal mimicking of bio-neural simulation by improving the functionality and thus the potential role of nanoscale RTDs.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Measurement of SiO2/InZnGaO4 heterojunction band offsets by x-ray photoelectron spectroscopy

E. A. Douglas, A. Scheurmann, R. P. Davies, B. P. Gila, Hyun Cho, V. Craciun, E. S. Lambers, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 98, 242110 (2011); http://dx.doi.org/10.1063/1.3600340 (3 pages) | Cited 7 times

Online Publication Date: 14 June 2011

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X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (ΔEv) of SiO2/InZnGaO4 (IGZO) heterostructures deposited by low temperature plasma enhanced chemical vapor deposition and sputtering at <50 °C, respectively. A value of ΔEv = 1.43±0.15 eV was obtained by using the Ga and Zn 2p3 and In 3d3 and 3d5 energy levels as references. Given the experimental bandgap of 3.2 eV for the IGZO, this would indicate a conduction band offset ΔEC of 4.27 eV in this system.
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71.20.Lp Intermetallic compounds
79.60.Jv Interfaces; heterostructures; nanostructures

Recombination models for spatio-temporal Monte Carlo transport of interacting carriers in semiconductors

Diksha Sharma, Yuan Fang, Fahad Zafar, Karim S. Karim, and Aldo Badano

Appl. Phys. Lett. 98, 242111 (2011); http://dx.doi.org/10.1063/1.3599602 (3 pages)

Online Publication Date: 16 June 2011

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multimedia

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When the secondary electron generated from an x-ray interaction within a photoconductor deposits energy, clouds of charge carriers (electron–hole pairs) with random spatial and energy distributions are created. Even under high electric field bias, a fraction of the carriers recombine affecting the detection statistics. We propose and compare modeling approaches for recombination including a nearest-neighbor model (NN) and a first-hit model (FH) that recombines the first pair from the vector of candidate carriers. We find that the mean of the NN model correlates with the mean of the FH model but differs for individual clouds.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Studies of temperature dependent ac impedance of a negative temperature coefficient Mn-Co-Ni-O thin film thermistor

Lin He and Zhiyuan Ling

Appl. Phys. Lett. 98, 242112 (2011); http://dx.doi.org/10.1063/1.3596454 (3 pages) | Cited 1 time

Online Publication Date: 16 June 2011

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Mn1.85Co0.3Ni0.85O4 thin films with single cubic spinel phase and compact surface were prepared by chemical solution deposition method on Al2O3 substrates. Temperature dependent ac impedance spectroscopy was employed to analyze the contributions of grain boundary (GB) and grain to the conduction mechanism. The major characteristics (hopping type, resistance versus temperature behavior, and characteristic temperature T0) of the GB and grain were obtained. The hopping type of GB is nearest-neighbor-hopping (NNH), and that of grain might be a transition from variable-range-hopping to NNH. The GB shows dominating resistance while the grain shows stronger temperature dependence.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Delta-doped epitaxial La:SrTiO3 field-effect transistor

K. Nishio, M. Matvejeff, R. Takahashi, M. Lippmaa, M. Sumiya, H. Yoshikawa, K. Kobayashi, and Y. Yamashita

Appl. Phys. Lett. 98, 242113 (2011); http://dx.doi.org/10.1063/1.3600782 (3 pages)

Online Publication Date: 17 June 2011

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We show that by delta doping a deep depletion layer at a SrTiO3/CaHfO3 interface with La, it is possible to achieve a separation of physical dopants from the current transport layer in SrTiO3. This allows us to construct an epitaxial top-gate field-effect transistor that can switch a channel with a physical dopant density of ∼ 1014 cm−2 between insulating and metallic states with a finite threshold shift and without carrier mobility degradation at low temperature.
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85.30.Tv Field effect devices

Spectromicroscopy of tantalum oxide memristors

John Paul Strachan, Gilberto Medeiros-Ribeiro, J. Joshua Yang, M.-X. Zhang, Feng Miao, Ilan Goldfarb, Martin Holt, Volker Rose, and R. Stanley Williams

Appl. Phys. Lett. 98, 242114 (2011); http://dx.doi.org/10.1063/1.3599589 (3 pages) | Cited 13 times

Online Publication Date: 17 June 2011

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We report experiments to measure material changes in tantalum oxide-based memristive devices. The high endurance and low power demonstrated in this material system suggests a unique mechanism for the switching, which we investigated using x-ray based spectromicroscopy and nanospectroscopy. Our study nondestructively identified a localized (<150nm diameter) Ta-rich phase surrounded by nano- or polycrystalline Ta2O5.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
85.35.-p Nanoelectronic devices

Effect of ion bombardment on the a-Si:H based surface passivation of c-Si surfaces

A. Illiberi, P. Kudlacek, A. H. M. Smets, M. Creatore, and M. C. M. van de Sanden

Appl. Phys. Lett. 98, 242115 (2011); http://dx.doi.org/10.1063/1.3601485 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2011

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We have found that controlled Ar ion bombardment enhances the degradation of a-Si:H based surface passivation of c-Si surfaces. The decrease in the level of surface passivation is found to be independent on the ion kinetic energy (7–70 eV), but linearly proportional to the ion flux (6×1014–6×1015 ions cm−2 s−1). This result suggests that the ion flux determines the generation rate of electron–hole pairs in a-Si:H films, by which metastable defects are created at the H/a-Si:c-Si interface. Possible mechanisms for the ion induced generation of electron–hole pairs are discussed.
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81.65.Rv Passivation
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Defects at nitrogen site in electron-irradiated AlN

N. T. Son, A. Gali, Á. Szabó, M. Bickermann, T. Ohshima, J. Isoya, and E. Janzén

Appl. Phys. Lett. 98, 242116 (2011); http://dx.doi.org/10.1063/1.3600638 (3 pages)

Online Publication Date: 17 June 2011

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In high resistance AlN irradiated with 2 MeV electrons, an electron paramagnetic resonance (EPR) spectrum, labeled EI-1, with an electron spin S = 1/2 and a clear hyperfine (hf) structure was observed. The hf structure was shown to be due the interaction between the electron spin and the nuclear spins of four 27A nuclei with the hf splitting varying between ∼ 6.0 and ∼ 7.2 mT. Comparing the hf data obtained from EPR and ab initio supercell calculations we suggest the EI-1 defect to be the best candidate for the neutral nitrogen vacancy in AlN.
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61.72.jd Vacancies
61.80.Fe Electron and positron radiation effects
76.30.Lh Other ions and impurities
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