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24 Nov 2008

Volume 93, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 93, 214101 (2008); http://dx.doi.org/10.1063/1.3025819 (3 pages)

Brian Abbey, Garth J. Williams, Mark A. Pfeifer, Jesse N. Clark, Corey T. Putkunz, Angela Torrance, Ian McNulty, T. M. Levin, Andrew G. Peele, and Keith A Nugent
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High-quality quantum point contact in two-dimensional GaAs (311)A hole system

J. Shabani, J. R. Petta, and M. Shayegan

Appl. Phys. Lett. 93, 212101 (2008); http://dx.doi.org/10.1063/1.3036011 (3 pages) | Cited 3 times

Online Publication Date: 24 November 2008

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We studied ballistic transport across a quantum point contact (QPC) defined in a high-quality GaAs (311)A two-dimensional hole system using shallow etching and top gating. The QPC conductance exhibits up to 11 quantized plateaus. The ballistic one-dimensional subbands are tuned by changing the lateral confinement and the Fermi energy of the holes in the QPC. We demonstrate that the positions of the plateaus (in gate voltage), the source-drain data, and the negative magnetoresistance data can be understood in a simple model that takes into account the variation, with gate bias, of the hole density and the width of the QPC conducting channel.
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73.23.Ad Ballistic transport
73.50.Fq High-field and nonlinear effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.-b Electronic transport in nanoscale materials and structures

Charge detection in graphene quantum dots

J. Güttinger, C. Stampfer, S. Hellmüller, F. Molitor, T. Ihn, and K. Ensslin

Appl. Phys. Lett. 93, 212102 (2008); http://dx.doi.org/10.1063/1.3036419 (3 pages) | Cited 31 times

Online Publication Date: 24 November 2008

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We report measurements on a graphene quantum dot with an integrated graphene charge detector. The quantum dot device consists of a graphene island (diameter of ∼ 200 nm) connected to source and drain contacts via two narrow graphene constrictions. From Coulomb diamond measurements a charging energy of 4.3 meV is extracted. The charge detector is based on a 45 nm wide graphene nanoribbon placed approximately 60 nm from the island. We show that resonances in the nanoribbon can be used to detect individual charging events on the quantum dot. The charging induced potential change on the quantum dot causes a steplike change in the current in the charge detector. The relative change in the current ranges from 10% up to 60% for detecting individual charging events.
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71.10.Pm Fermions in reduced dimensions (anyons, composite fermions, Luttinger liquid, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.U- Carbon/carbon-based materials
81.07.Ta Quantum dots

Similarities in the kinetics of photocrystallization and photodarkening in a-Se

Robert E. Tallman, A. Reznik, B. A. Weinstein, S. D. Baranovskii, and J. A. Rowlands

Appl. Phys. Lett. 93, 212103 (2008); http://dx.doi.org/10.1063/1.3026173 (3 pages) | Cited 1 time

Online Publication Date: 24 November 2008

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The onset time of photocrystallization (PC) as a function of temperature in a-Se films designed for avalanche photodetectors is explored using Raman scattering experiments. The PC onset time τon is compared to the time-constant τIPD for irreversible photodarkening (IPD) studied in earlier work. Both τon and τIPD exhibit activated thermal behavior mediated by an energy barrier EB ∼ 0.7–0.95 eV. We suggest that the formation kinetics of PC and IPD in a-Se are governed by the same energy surface and configuration changes, occurring via photoinduced defects during the primary stage of crystallization.
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64.70.K- Solid-solid transitions
78.20.-e Optical properties of bulk materials and thin films
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys

Energy barriers at interfaces of (100)GaAs with atomic layer deposited Al2O3 and HfO2

V. V. Afanas’ev, M. Badylevich, A. Stesmans, G. Brammertz, A. Delabie, S. Sionke, A. O’Mahony, I. M. Povey, M. E. Pemble, E. O’Connor, P. K. Hurley, and S. B. Newcomb

Appl. Phys. Lett. 93, 212104 (2008); http://dx.doi.org/10.1063/1.3021374 (3 pages) | Cited 17 times

Online Publication Date: 24 November 2008

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Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Scaling behaviors of reset voltages and currents in unipolar resistance switching

S. B. Lee, S. C. Chae, S. H. Chang, J. S. Lee, S. Seo, B. Kahng, and T. W. Noh

Appl. Phys. Lett. 93, 212105 (2008); http://dx.doi.org/10.1063/1.3036532 (3 pages) | Cited 28 times

Online Publication Date: 25 November 2008

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The wide distributions of switching voltages in unipolar switching currently pose major obstacles for scientific advancement and practical applications. Using NiO capacitors, we investigated the distributions of the reset voltage and current. We found that they scaled with the resistance value Ro in the low resistance state and that the scaling exponents varied at Ro ≈ 30 Ω. We explain these intriguing scaling behaviors and their crossovers by analogy with percolation theory. We show that the connectivity of conducting filaments plays a crucial role in the reset process.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
72.60.+g Mixed conductivity and conductivity transitions

Spin-glass-like behavior caused by Mn-rich Mn(Ga)As nanoclusters in GaAs

C. H. Chang and T. M. Hong

Appl. Phys. Lett. 93, 212106 (2008); http://dx.doi.org/10.1063/1.3039058 (3 pages) | Cited 1 time

Online Publication Date: 26 November 2008

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We simulate the indirect exchange interaction between Mn-rich Mn(Ga)As nanoclusters in GaAs by analytical means. In contrast to the conventional Ruderman–Kittel–Kasuya–Yosida (RKKY) formula, which considers the mediation by the carriers in the medium, we also include the contribution from those inside the clusters. Since the carrier concentration is higher in the clusters, this modification allows the RKKY oscillation to change its sign. Consequently, while the previous approach only favors ferromagnetism for this system, an antiferromagnetic coupling is in fact possible. Since the Mn-rich Mn(Ga)As nanoclusters are naturally formed and bound to have different sizes, their spin orientation is likely to be frustrated due to mixed preferences from different neighbors. We argue that this is likely the source of the spin-glass-like behavior that plagues this system. By tuning the size and narrowing its distribution, normal ferromagnetism can be restored with a Curie temperature higher than previously thought.
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68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
68.35.Rh Phase transitions and critical phenomena
46.65.+g Random phenomena and media

Surface potential of n- and p-type GaN measured by Kelvin force microscopy

S. Barbet, R. Aubry, M.-A. di Forte-Poisson, J.-C. Jacquet, D. Deresmes, T. Mélin, and D. Théron

Appl. Phys. Lett. 93, 212107 (2008); http://dx.doi.org/10.1063/1.3028639 (3 pages) | Cited 17 times

Online Publication Date: 26 November 2008

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n- and p-type GaN epitaxial layers grown by metal-organic chemical vapor deposition with different doping levels have been characterized by Kelvin probe force microscopy (KFM). To investigate the surface states of GaN beyond instrumental and environmental fluctuations, a KFM calibration procedure using a gold-plated Ohmic contact as a reference has been introduced, and the reproducibility of the KFM measurements has been evaluated. Results show that the Fermi level is pinned for n- and p-type GaN over the available doping ranges, and found 1.34±0.15 eV below the conduction band and 1.59±0.18 eV above the valence band, respectively.
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68.37.Ps Atomic force microscopy (AFM)
61.72.uj III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states
71.20.Nr Semiconductor compounds
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