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24 May 2010

Volume 96, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 213701 (2010); http://dx.doi.org/10.1063/1.3431628 (3 pages)

Satish Rao, Saurabh Raj, Stefan Balint, Carlota Bardina Fons, Susana Campoy, Montserrat Llagostera, and Dmitri Petrov
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Low-lying spectra of massless Dirac electron in magnetic dot and ring

C. M. Lee, Richard C. H. Lee, W. Y. Ruan, and M. Y. Chou

Appl. Phys. Lett. 96, 212101 (2010); http://dx.doi.org/10.1063/1.3435478 (3 pages) | Cited 2 times

Online Publication Date: 24 May 2010

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Both the size and the magnetic-field dependences of low-lying spectra of two-dimensional (2D) graphene based magnetic dot and ring in perpendicular inhomogeneous magnetic fields, where the magnetic field is zero inside the dot and ring, and constant elsewhere, are studied by the massless Dirac–Weyl equation. Numerical results obtained from direct diagonalization with 2D harmonic basis show that, under nonuniform magnetic fields, the higher Landau levels (N ≥ 1) for such massless Dirac electron interacting system in general become nondegenerate and split into discrete angular momentum states with level crossings with the lowest one (N = 0) being an exception.
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73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electrometry using the quantum Hall effect in a bilayer two-dimensional electron system

L. H. Ho, L. J. Taskinen, A. P. Micolich, A. R. Hamilton, P. Atkinson, and D. A. Ritchie

Appl. Phys. Lett. 96, 212102 (2010); http://dx.doi.org/10.1063/1.3428778 (3 pages)

Online Publication Date: 24 May 2010

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We discuss the development of a sensitive electrometer that utilizes a two-dimensional electron gas (2DEG) in the quantum Hall regime. As a demonstration, we measure the evolution of the Landau levels in a second, nearby 2DEG as the applied perpendicular magnetic field is changed, and extract an effective mass for electrons in GaAs that agrees within experimental error with previous measurements.
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07.68.+m Photography, photographic instruments; xerography
73.43.Fj Novel experimental methods; measurements
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.70.Di Landau levels

Anisotropic conductivity of doped graphene due to short-range nonsymmetric scattering

F. T. Vasko

Appl. Phys. Lett. 96, 212103 (2010); http://dx.doi.org/10.1063/1.3431667 (3 pages)

Online Publication Date: 24 May 2010

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The conductivity of doped graphene is considered taking into account scattering by short-range nonsymmetrical defects, when the longitudinal and transverse components of conductivity tensor appear to be different. The calculations of the anisotropic conductivity tensor are based on the quasiclassical kinetic equation for the case of monopolar transport at low temperatures. The effective longitudinal conductivity and the transverse voltage, which are controlled by orientation of sample and by gate voltage (i.e., doping level), are presented.
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72.80.Vp Electronic transport in graphene
72.20.Dp General theory, scattering mechanisms
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Metal-insulator transition in ZnO nanopowder during thermal cycling by impedance spectroscopy

M. Nadeem, Amina Farooq, and T. J. Shin

Appl. Phys. Lett. 96, 212104 (2010); http://dx.doi.org/10.1063/1.3431298 (3 pages) | Cited 4 times

Online Publication Date: 25 May 2010

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We have investigated the electrical response on the pellet of ZnO nanopowder by impedance spectroscopy. Different trends of impedance plane plots have been discussed due to the modulations of relaxation time with temperatures. Thermal cycling induces irreversible changes in the resistance of the material which has been explained by incorporating the role of extended defects like oxidation of Zn interstitials at surfaces and intrinsic/extrinsic grain boundaries. Metal-insulator transition has been reported and discussed in term of combined effects of Zn interstitials and oxygen vacancies. Irreversible increase in the values of dielectric constant have been conferred with thermal cycling’s.
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71.30.+h Metal-insulator transitions and other electronic transitions
77.22.Ch Permittivity (dielectric function)
61.72.jj Interstitials
61.72.Mm Grain and twin boundaries

AlGaN/GaN high electron mobility transistors based on InGaN/GaN multiquantum-well structures

K. H. Lee, P. C. Chang, S. J. Chang, Y. K. Su, and C. L. Yu

Appl. Phys. Lett. 96, 212105 (2010); http://dx.doi.org/10.1063/1.3421392 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2010

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We report an AlGaN/GaN high electron mobility transistors (HEMTs) based on InGaN/GaN multiquantum-well (MQW) structure. When InGaN/GaN MQW structure was inserted, InGaN layer has an opposite piezoelectric polarization field compared to AlGaN, which results in a very sharp rise of the conduction band. The raised potential barrier can help to improve carrier confinement and obtain a larger main peak transconductance of 111 mS/mm and satellite peak transconductance of 24 mS/mm, corresponding to AlGaN/GaN heterojunction and InGaN layer. MQW-based metal-oxide-semiconductor-HEMT was also fabricated and significantly reduced the leakage current and increased transconductance as a result of passivation by Ta2O5 gate oxide.
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85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Transverse-optical phonons excited in Si using a high-numerical-aperture lens

Daisuke Kosemura and Atsushi Ogura

Appl. Phys. Lett. 96, 212106 (2010); http://dx.doi.org/10.1063/1.3441042 (3 pages) | Cited 8 times

Online Publication Date: 27 May 2010

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We demonstrate excitation of transverse-optical (TO) phonons in a strained-Si on insulator (SSOI) by using a high-numerical-aperture oil-immersion lens. Using this technique, the TO phonons are excited, even under the (001) Si backscattering configuration. The wave numbers of the TO phonons in SSOI thus excited are different from that of the longitudinal-optical (LO) phonon. This result indicates the coefficients of Raman wave number shift and biaxial stress are different in the LO- and TO-phonon modes. The excitation of the TO phonons allows us to study stress tensors in Si.
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63.20.dd Measurements
78.30.Am Elemental semiconductors and insulators

Proposal for efficient generation of spin-polarized current in silicon

L. K. Castelano and L. J. Sham

Appl. Phys. Lett. 96, 212107 (2010); http://dx.doi.org/10.1063/1.3441407 (3 pages)

Online Publication Date: 27 May 2010

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We propose a spin-dependent resonant tunneling structure to efficiently inject spin-polarized current into silicon. By means of a heavily doped polycrystalline Si between the ferromagnetic metal and Si, the Schottky barrier resistance is reduced and consequently the tunneling current density is raised. The small Fermi sea of the charge carriers in Si focuses the tunneling electrons to the resonant spin states within a small region of transverse momentum in the ferromagnet which creates the spin polarization of the current.
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72.25.Dc Spin polarized transport in semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.61.Cw Elemental semiconductors

Topological confinement in graphene bilayer quantum rings

L. J. P. Xavier, J. M. Pereira, Andrey Chaves, G. A. Farias, and F. M. Peeters

Appl. Phys. Lett. 96, 212108 (2010); http://dx.doi.org/10.1063/1.3431618 (3 pages) | Cited 6 times

Online Publication Date: 27 May 2010

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We find localized electron and hole states in a ring-shaped potential kink in biased bilayer graphene. Within the continuum description, we show that for sharp potential steps the Dirac equation describing carrier states close to the K (or K′) point of the first Brillouin zone can be solved analytically for a circular kink/antikink dot. The solutions exhibit interfacial states which exhibit Aharonov–Bohm oscillations as functions of the height of the potential step and/or the radius of the ring.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.Tx Fullerenes and related materials; intercalation compounds

Addition of aluminum to solution processed conductive indium tin oxide thin film for an oxide thin film transistor

J. H. Jeon, Y. H. Hwang, B. S. Bae, H. L. Kwon, and H. J. Kang

Appl. Phys. Lett. 96, 212109 (2010); http://dx.doi.org/10.1063/1.3442482 (3 pages) | Cited 5 times

Online Publication Date: 28 May 2010

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Aluminum was added to a solution-processed conductive indium tin oxide thin film to be optimized as a channel layer for a thin film transistor (TFT). The conductive crystalline thin film becomes an amorphous semiconductor as the band gap enlarges with increasing Al content. Also, systematic variation in TFT characteristics was observed clearly, displaying transformation to a semiconductor. At the final composition of (Al2O3)0.3(In2O3)0.6(SnO2)0.1, the film channel layer exhibits a high mobility of 13.3 cm2 V−1 s−1, a high on-to-off ratio of 107 and a low subthreshold swing of 1.01 V/dec.
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85.30.Tv Field effect devices
81.05.Gc Amorphous semiconductors
68.55.ag Semiconductors

Pinning of recombination-enhanced dislocation motion in 4H–SiC: Role of Cu and EH1 complex

Bin Chen, Hirofumi Matsuhata, Takashi Sekiguchi, Takasumi Ohyanagi, Akimasa Kinoshita, and Hajime Okumura

Appl. Phys. Lett. 96, 212110 (2010); http://dx.doi.org/10.1063/1.3442907 (3 pages) | Cited 3 times

Online Publication Date: 28 May 2010

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We report on the pinning of recombination-enhanced dislocation motion in 4H–SiC by the implantation of Cu. The Cu was found to be preferentially gettered at basal plane dislocations (BPDs). Both EH1 and Z1/2 center were detected in 4H–SiC by cathodoluminescence. It was noticed that the EH1 has high luminescence intensity at the central part of the BPDs, while the Z1/2 does not. The complex of Cu and EH1 is regarded to be the cause for the pinning effect. The possible reason for the pinning is discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Yx Interaction between different crystal defects; gettering effect
78.60.Hk Cathodoluminescence, ionoluminescence
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