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4 Apr 2011

Volume 98, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 141903 (2011); http://dx.doi.org/10.1063/1.3548546 (3 pages)

H. Hattab, A. T. N’Diaye, D. Wall, G. Jnawali, J. Coraux, C. Busse, R. van Gastel, B. Poelsema, T. Michely, F.-J. Meyer zu Heringdorf, and M. Horn-von Hoegen
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Fabrication and characterization of topological insulator Bi2Se3 nanocrystals

S. Y. F. Zhao, C. Beekman, L. J. Sandilands, J. E. J. Bashucky, D. Kwok, N. Lee, A. D. LaForge, S. W. Cheong, and K. S. Burch

Appl. Phys. Lett. 98, 141911 (2011); http://dx.doi.org/10.1063/1.3573868 (3 pages) | Cited 6 times

Online Publication Date: 6 April 2011

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In the recently discovered class of materials known as topological insulators, the presence of strong spin-orbit coupling causes certain topological invariants in the bulk to differ from their values in vacuum. The sudden change in invariants at the interface results in metallic, time reversal invariant surface states whose properties are useful for applications in spintronics and quantum computation. However, a key challenge is to fabricate these materials on the nanoscale appropriate for devices and probing the surface. To this end we have produced 2 nm thick nanocrystals of the topological insulator Bi2Se3 via mechanical exfoliation. For crystals thinner than 10 nm we observe the emergence of an additional mode in the Raman spectrum. The emergent mode intensity together with the other results presented here provide a recipe for production and thickness characterization of Bi2Se3 nanocrystals.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.-c Methods of micro- and nanofabrication and processing
73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
78.30.Hv Other nonmetallic inorganics

Thermal-vacancy-assisted phase transition in FePt thin films

X. H. Li, F. Q. Wang, B. T. Liu, D. F. Guo, and X. Y. Zhang

Appl. Phys. Lett. 98, 141912 (2011); http://dx.doi.org/10.1063/1.3575558 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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Understanding the ordering transition from A1 to L10 structure in FePt thin films is of great significance for developing L10-FePt films as ultrahigh density magnetic recording media. Here, the L10-ordering transition of FePt films has been investigated based on activation volume measurements. A large activation volume ΔV∗ = 10–11 Å3 = (0.75–0.8) Ω, where Ω is average atomic volume of FePt, is determined for atomic diffusions in the L10-ordering transition, indicating a thermal-vacancy-assisted phase transition. This transition is suggested to be predominantly dependent on the diffusion of Fe atoms. These findings have direct implications for yielding L10-FePt films at low temperatures and optimizing their microstructures.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
66.30.Fq Self-diffusion in metals, semimetals, and alloys
75.50.Ss Magnetic recording materials

Room temperature homogeneous flow in a bulk metallic glass with low glass transition temperature

K. Zhao, X. X. Xia, H. Y. Bai, D. Q. Zhao, and W. H. Wang

Appl. Phys. Lett. 98, 141913 (2011); http://dx.doi.org/10.1063/1.3575562 (3 pages) | Cited 8 times

Online Publication Date: 7 April 2011

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We report a high entropy metallic glass of Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 via composition design that exhibiting remarkable homogeneous deformation without shear banding under stress at room temperature. The glass also shows properties such as low glass transition temperature (323 K) approaching room temperature, low density and high specific strength, good conductivity, polymerlike thermoplastic manufacturability, and ultralow elastic moduli comparable to that of bones. The alloy is thermally and chemically stable.
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81.05.Kf Glasses (including metallic glasses)
64.70.pe Metallic glasses
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Spontaneous polarization estimation from the soft mode in strain-free epitaxial polar axis-oriented Pb(Zr,Ti)O3 thick films with tetragonal symmetry

Yoshitaka Ehara, Satoru Utsugi, Mitsumasa Nakajima, Tomoaki Yamada, Takashi Iijima, Hiroki Taniguchi, Mitsuru Itoh, and Hiroshi Funakubo

Appl. Phys. Lett. 98, 141914 (2011); http://dx.doi.org/10.1063/1.3575565 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2011

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The ferroelectric property, crystal structure, and A1(1TO) soft mode of almost strain-free epitaxial polar axis-oriented tetragonal lead zirconate titanate thick films grown on CaF2 substrates were investigated by changing the Zr/(Zr+Ti) ratio and the temperature. The square of spontaneous polarization (Ps), Ps2, monotonically increased as tetragonal distortion, (c/a)−1, increased where a and c are the lattice parameters of the films and as the square of frequency in A1(1TO), ω2[A1(1TO)], increased. Additionally, the relationships of Ps2, (c/a−1), and ω2[A1(1TO)] were experimentally obtained, which confirmed the Ps value obtained from (c/a−1) and ω[A1(1TO)] without direct polarization measurements.
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77.22.Ej Polarization and depolarization
61.66.Fn Inorganic compounds
77.84.Cg PZT ceramics and other titanates
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.80.Dj Domain structure; hysteresis
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Electronic-grade GaN(0001)/Al2O3(0001) grown by reactive DC-magnetron sputter epitaxy using a liquid Ga target

M. Junaid, C.-L. Hsiao, J. Palisaitis, J. Jensen, P. O. Å. Persson, L. Hultman, and J. Birch

Appl. Phys. Lett. 98, 141915 (2011); http://dx.doi.org/10.1063/1.3576912 (3 pages) | Cited 7 times

Online Publication Date: 7 April 2011

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Electronic-grade GaN (0001) epilayers have been grown directly on Al2O3 (0001) substrates by reactive direct-current-magnetron sputter epitaxy (MSE) using a liquid Ga sputtering target in an Ar/N2 atmosphere. The as-grown GaN epitaxial films exhibit low threading dislocation density on the order of ≤ 1010 cm−2 determined by transmission electron microscopy and modified Williamson–Hall plot. X-ray rocking curve shows narrow full-width at half maximum (FWHM) of 1054 arc sec of the 0002 reflection. A sharp 4 K photoluminescence peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. The high structural and optical qualities indicate that MSE-grown GaN epilayers can be used for fabricating high-performance devices without the need of any buffer layer.
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81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors

Manipulating stress in Cu/low-k dielectric nanocomposites

Conal E. Murray, Paul R. Besser, E. Todd Ryan, and Jean L. Jordan-Sweet

Appl. Phys. Lett. 98, 141916 (2011); http://dx.doi.org/10.1063/1.3578192 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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The interaction of x-rays with organic dielectric materials, which alters their mechanical properties, affects values of stress generated within encapsulated Cu structures. In particular, the evolution of stress within submicron Cu interconnect structures encapsulated by an organosilicate glass can be investigated in situ using synchrotron-based x-ray diffraction. The overall geometry of the composite, along with the amount of irradiation, dictates the change in stress of the Cu features. A quantitative comparison of these findings to mechanical modeling results reveals two modes of modification within the dielectric film: a densification that changes the effective eigenstrain followed by an increase in elastic modulus.
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68.60.Bs Mechanical and acoustical properties
62.23.Pq Composites (nanosystems embedded in a larger structure)
62.20.de Elastic moduli
77.55.Bh Low-permittivity dielectric films

Strong luminescence of two-dimensional electron gas in tensile-stressed AlGaN/GaN heterostructures grown on Si substrates

Ki-Won Kim, Dong-Seok Kim, Ki-Sik Im, Jung-Hee Lee, Bong-Joon Kwon, Ho-Sang Kwack, Seol Beck, and Yong-Hoon Cho

Appl. Phys. Lett. 98, 141917 (2011); http://dx.doi.org/10.1063/1.3578399 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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We have investigated the photoluminescence (PL) characteristics of AlGaN/GaN heterostructure with an extremely high two-dimensional electron gas (2DEG) density. A very high 2DEG density was obtained by controlling the tensile stress during the growth of the heterostructure on silicon substrate. Strong PL emission peaks corresponding to both the band edge and the 2DEG were observed in the highly tensile-stressed heterostructure. Furthermore, the strong longitudinal optical (LO) phonon replicas (1-LO2DEG and 2-LO2DEG) of the 2DEG peak were also observed in the heterostructure.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
68.35.Gy Mechanical properties; surface strains
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Effect of impurities on thermal stability of pseudomorphically strained Si:C layer

Yao-Teng Chuang, Sheng-Hao Wang, and Wei-Yen Woon

Appl. Phys. Lett. 98, 141918 (2011); http://dx.doi.org/10.1063/1.3572339 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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We investigate the thermal stability of pseudomorphically strained Si:C layer using high resolution x-ray diffraction (HRXRD) and Fourier transform infrared (FTIR) spectroscopy. Far below β-SiC precipitation threshold, almost complete strain relaxation is found without significant substitutional carbon (Csub) loss. FTIR shows the strain relaxation is related to volume compensation by Csub-interstitial complex formation through oxidation injection of interstitial. By multilayer HRXRD kinematical simulation, we find correlation of the enhanced strain relaxation to P distribution, implying P’s role as additional interstitial promoter during postannealing treatment. We relate our findings to recent reports on strain relaxation issues in Si:C devices fabrication.
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71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
81.40.Gh Other heat and thermomechanical treatments

Lattice thermal conductivity of graphene nanoribbons: Anisotropy and edge roughness scattering

Z. Aksamija and I. Knezevic

Appl. Phys. Lett. 98, 141919 (2011); http://dx.doi.org/10.1063/1.3569721 (3 pages) | Cited 12 times

Online Publication Date: 7 April 2011

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We present a calculation of the thermal conductivity of graphene nanoribbons (GNRs), based on solving the Boltzmann transport equation with the full phonon dispersions, a momentum-dependent model for edge roughness scattering, as well as three-phonon and isotope scattering. The interplay between edge roughness scattering and the anisotropy of the phonon dispersions results in thermal conduction that depends on the chiral angle of the nanoribbon. Lowest thermal conductivity occurs in the armchair direction and highest in zig-zag nanoribbons. Both the thermal conductivity and the degree of armchair/zig-zag anisotropy depend strongly on the width of the nanoribbon and the rms height of the edge roughness, with the smallest and most anisotropic thermal conductivities occurring in narrow GNRs with rough edges.
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66.70.Df Metals, alloys, and semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Effect of postgrowth hydrogen treatment on defects in GaNP

D. Dagnelund, X. J. Wang, C. W. Tu, A. Polimeni, M. Capizzi, W. M. Chen, and I. A. Buyanova

Appl. Phys. Lett. 98, 141920 (2011); http://dx.doi.org/10.1063/1.3576920 (3 pages) | Cited 3 times

Online Publication Date: 8 April 2011

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Effect of postgrowth hydrogen treatment on defects and their role in carrier recombination in GaNP alloys is examined by photoluminescence (PL) and optically detected magnetic resonance. We present direct experimental evidence for effective activation of several defects by low-energy subthreshold hydrogen treatment ( ≤ 100 eV H ions). Among them, two defect complexes are identified to contain a Ga interstitial. Possible mechanisms for the H-induced defect activation and creation are discussed. Carrier recombination via these defects is shown to efficiently compete with the near band-edge PL, explaining the observed degraded optical quality of the alloys after the H treatment.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.jj Interstitials
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Giant mesoscopic photoconductance fluctuations in Ge/Si quantum dot system

N. P. Stepina, E. S. Koptev, A. V. Dvurechenskii, A. I. Nikiforov, J. Gerharz, J. Moers, and D. Gruetzmacher

Appl. Phys. Lett. 98, 142101 (2011); http://dx.doi.org/10.1063/1.3574022 (3 pages) | Cited 2 times

Online Publication Date: 4 April 2011

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We studied the impact of weak photon flux on the electron transport in strongly localized quantum dot system. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. This phenomenon has the potential to detect a single photoexcited carrier for a wide range of wavelength. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photoinduced fluctuations on the light intensity and the steplike response of conductance on the pulse excitation.
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72.40.+w Photoconduction and photovoltaic effects
72.20.-i Conductivity phenomena in semiconductors and insulators
72.20.Ee Mobility edges; hopping transport
73.50.Dn Low-field transport and mobility; piezoresistance
81.07.Ta Quantum dots

High-temperature thermoelectric properties of nanostructured Ca3Co4O9 thin films

Min-Gyu Kang, Kwang-Hwan Cho, Seung-Min Oh, Jin-Sang Kim, Chong-Yun Kang, Sahn Nahm, and Seok-Jin Yoon

Appl. Phys. Lett. 98, 142102 (2011); http://dx.doi.org/10.1063/1.3574530 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2011

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We prepared nanostructured Ca3Co4O9 (CCO) thin films by promoting localized epitaxial growth on polycrystalline Al2O3 substrates. The thermoelectric properties of the CCO films were studied in the temperature range 300 to 1023 K. We confirmed that localized epitaxial growth occurred on the seed grains that dominate the (006) plane. The nanostructured CCO thin films were found to have a maximum Seebeck coefficient of 206 μV/K and a power factor (at 920 K) of 0.514 mW/mK2. Moreover, the presence of nanostructure was found to reduce the thermal conductivity, and thus, should enhance the overall performance of CCO films in thermoelectric devices.
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73.50.Lw Thermoelectric effects
81.15.Cd Deposition by sputtering
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.55.ag Semiconductors
73.61.Le Other inorganic semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization

Electronic structure of cation-codoped TiO2 for visible-light photocatalyst applications from hybrid density functional theory calculations

Run Long and Niall J. English

Appl. Phys. Lett. 98, 142103 (2011); http://dx.doi.org/10.1063/1.3574773 (3 pages) | Cited 4 times

Online Publication Date: 4 April 2011

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The electronic structures of Mg/Ca- and/or Mo/W- (mono- and co-) doped anatase TiO2 have been investigated via generalized Kohn–Sham theory with the Heyd–Scuseria–Ernzerhof hybrid functional for exchange-correlation { J. Heyd et al., [J. Chem. Phys. 118, 8207 (2003)] , J. Heyd et al., [J. Chem. Phys. 124, 219906 (2006)] , and J. Paier et al., [J. Chem. Phys. 125, 249901 (2006)] }, in the context of density functional theory. Gap narrowing is small for monodoping, which also creates impuritiy bands in the “forbidden gap,” either as acceptor or donor states, limiting possible utility as visible-light photocatalysts. However, codoping of Mg/Ca and Mo/W not only induces appreciable gap narrowing, but also serves to passivate the impurity bands, which can harvest visible-light to a greater extent. Considering ionic radii, Mg and Mo should constitute the best cation-pair.
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71.20.Nr Semiconductor compounds
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.50.Hp Processes caused by visible and UV light
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.40.Fy Semiconductors
61.72.up Other materials

Si/SiGe quantum dot with superconducting single-electron transistor charge sensor

Mingyun Yuan, Feng Pan, Zhen Yang, T. J. Gilheart, Fei Chen, D. E. Savage, M. G. Lagally, M. A. Eriksson, and A. J. Rimberg

Appl. Phys. Lett. 98, 142104 (2011); http://dx.doi.org/10.1063/1.3572033 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2011

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We report a robust process for fabrication of surface-gated Si/SiGe quantum dots (QDs) with an integrated superconducting single-electron transistor (SSET) charge sensor. A combination of a deep mesa etch and AlOx backfill is used to reduce gate leakage. After the leakage current is suppressed, Coulomb oscillations of the QD and the current-voltage characteristics of the SSET are observed at a temperature of 0.3 K. Coupling of the SSET to the QD is confirmed by using the SSET to perform sensing of the QD charge state.
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81.07.Ta Quantum dots
85.35.Gv Single electron devices

Heteromaterial gate tunnel field effect transistor with lateral energy band profile modulation

Ning Cui, Renrong Liang, and Jun Xu

Appl. Phys. Lett. 98, 142105 (2011); http://dx.doi.org/10.1063/1.3574363 (3 pages) | Cited 2 times

Online Publication Date: 5 April 2011

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A tunnel field effect transistor (TFET) device with a heteromaterial gate structure was introduced, and the influence of the lateral energy band profile modulation effect on the performance of TFET devices has been investigated. The two-dimensional numerical simulations demonstrated that a local minimum of the conduction band in the channel was formed by work function mismatch, which resulted in the abrupt transition between the on- and off-states and significant drive current enhancement. In particular, these unique features could be manipulated by engineering the heteromaterial and the gate length. This work reveals an effective method to improve the performance of nanoscale TFETs.
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85.30.Tv Field effect devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Correlation of thermoelectric and microstructural properties of p-type CeFe4Sb12 melt-spun ribbons using a rapid screening method

Y. G. Yan, W. Wong-Ng, J. A. Kaduk, G. J. Tan, W. J. Xie, and X. F. Tang

Appl. Phys. Lett. 98, 142106 (2011); http://dx.doi.org/10.1063/1.3570690 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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We have demonstrated the effect of gradients in phase composition and microstructure of p-type CeFe4Sb12 melt-spun ribbons on Seebeck coefficient by using a thermoelectric (TE) screening tool in conjunction with x-ray diffraction. The spatial Seebeck coefficient variation was found to correlate with the changes in the phase composition and microstructure. The observed gradient was the result of a postannealing effect caused by the thermal lag between the contact surface with the roller and the free surface. Our results illustrate the application of our screening tool to the three-dimensional variation in Seebeck coefficient in a model TE material.
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72.15.Jf Thermoelectric and thermomagnetic effects
81.40.Gh Other heat and thermomechanical treatments
81.20.-n Methods of materials synthesis and materials processing

Direct determination of the band alignment at the (Zn,Mg)O/CISSe interface

F. Erfurth, A. Grimm, J. Palm, T. P. Niesen, F. Reinert, L. Weinhardt, and E. Umbach

Appl. Phys. Lett. 98, 142107 (2011); http://dx.doi.org/10.1063/1.3565972 (3 pages) | Cited 1 time

Online Publication Date: 6 April 2011

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The electronic and chemical properties of the (Zn1−x,Mgx)O/CuIn(S,Se)2 interface, prepared by sputtering of thin (Zn,Mg)O layers, were investigated with direct and inverse photoelectron spectroscopy on in situ prepared samples. With the combination of both techniques we have determined the band alignment at this interface as a function of Mg-content in the range 0 ≤ x ≤ 0.30. We find that the band alignment at the interface can be tailored between a “cliff” (downward step) in the conduction band for pure ZnO and a “spike” (upward step) for high Mg-contents. A direct influence of the band alignment modifications on the solar cell parameters is found.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Cd Deposition by sputtering
79.60.Jv Interfaces; heterostructures; nanostructures

Ohmic contact between ZnO and Pt by InSb layer in a ZnO Schottky diode

Seung Hyun Jee, Nitul Kakati, Seok Hee Lee, Hyon Hee Yoon, and Young Soo Yoon

Appl. Phys. Lett. 98, 142108 (2011); http://dx.doi.org/10.1063/1.3574933 (3 pages) | Cited 2 times

Online Publication Date: 6 April 2011

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The surface of the ZnO thin films was modified by a thin InSb layer by using a thermal evaporator to increase the work function without altering the physical properties of the film. We expected that the InSb thin layer with a high work function could achieve the Ohmic contact between the ZnO and Pt electrodes by reducing an energy barrier due to increase in the ZnO thin film. The Ohmic contact was achieved in the interface between the ZnO and Pt electrodes by the InSb thin layer.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices

Resistively detected nuclear magnetic resonance via a single InSb two-dimensional electron gas at high temperature

K. F. Yang, H. W. Liu, K. Nagase, T. D. Mishima, M. B. Santos, and Y. Hirayama

Appl. Phys. Lett. 98, 142109 (2011); http://dx.doi.org/10.1063/1.3579257 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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We report on the demonstration of the resistively detected nuclear magnetic resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at elevated temperatures up to 4 K. The RDNMR signal of 115In in the simplest pseudospin quantum Hall ferromagnet triggered by a large direct current shows a peak-dip line shape, where the nuclear relaxation time T1 at the peak and the dip is different but almost temperature independent. The large Zeeman, cyclotron, and exchange energy scales of the InSb 2DEG contribute to the persistence of the RDNMR signal at high temperatures.
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76.60.Es Relaxation effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.43.-f Quantum Hall effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions

Magnetotransport properties of (In,Zn)As/InAs p-n junctions

K. H. Gao, Q. W. Wang, G. Yu, T. Lin, H. Y. Deng, N. Dai, and J. H. Chu

Appl. Phys. Lett. 98, 142110 (2011); http://dx.doi.org/10.1063/1.3576922 (3 pages) | Cited 1 time

Online Publication Date: 7 April 2011

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We study the magnetotransport properties of nonmagnetic (In,Zn)As/InAs p-n junctions prepared by liquid phase epitaxy. The junctions show a clear rectifying behavior. A relatively large positive magnetoresistance is observed and its maximum value is greater than 140% at 12 K and gets to 38% at 292 K when a small magnetic field of 1.38 T is applied, which is not related to the series resistance. We attribute the observed magnetoresistance to the impurity-assisted tunneling mechanism.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification
81.05.Ea III-V semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
72.20.My Galvanomagnetic and other magnetotransport effects

Band gap shift in Al1−xInxN/AlN/GaN heterostructures studied by surface photovoltage spectroscopy

Daniela Cavalcoli, Saurabh Pandey, Beatrice Fraboni, and Anna Cavallini

Appl. Phys. Lett. 98, 142111 (2011); http://dx.doi.org/10.1063/1.3576938 (3 pages) | Cited 6 times

Online Publication Date: 7 April 2011

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GaN based heterostructures have recently gained increased interest due to their applications for high electron mobility transistors. In this letter AlInN/AlN/GaN heterojunctions grown by metal-organic chemical-vapor deposition with different AlN thicknesses have been investigated by surface photovoltage spectroscopy. The density of the two-dimensional electron gas (2DEG) forming at the interface has been measured by Hall effect. A band gap shift has been detected and its dependence on the 2DEG electron density at the AlN/GaN interface has been analyzed on the basis of the Moss–Burstein and renormalization effects.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
73.21.Cd Superlattices
72.40.+w Photoconduction and photovoltaic effects

Effects of hydrostatic pressure on the electrical properties of hexagonal Ge2Sb2Te5: Experimental and theoretical approaches

B. Xu, Y. Su, Z. G. Liu, C. H. Zhang, Y. D. Xia, J. Yin, Z. Xu, W. C. Ren, and Y. H. Xiang

Appl. Phys. Lett. 98, 142112 (2011); http://dx.doi.org/10.1063/1.3577606 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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A combination of experiments and first-principles method calculations has been applied to investigate the influence of the hydrostatic pressure on the electrical properties of the phase-change material hexagonal Ge2Sb2Te5 (h-GST). Experimentally, it is found that the resistance of h-GST declines monotonically with increasing hydrostatic pressure up to 0.7 GPa. Theoretically, the band-structure calculations revealed that the electronic band gap also decreases with the pressure. The hydrostatic pressure increases the conductivity of h-GST by reducing the electronic band gap. The dEg/dP obtained from theoretical calculations and the d ln ρ/dP by experimental result are in the same order of magnitude.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ng Disordered solids
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
62.50.-p High-pressure effects in solids and liquids

Atomic layer deposition ZnO:N flexible thin film transistors and the effects of bending on device properties

Jae-Min Kim, Taewook Nam, S. J. Lim, Y. G. Seol, N.-E. Lee, Doyoung Kim, and Hyungjun Kim

Appl. Phys. Lett. 98, 142113 (2011); http://dx.doi.org/10.1063/1.3577607 (3 pages) | Cited 5 times

Online Publication Date: 7 April 2011

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ZnO:N flexible thin film transistors were fabricated by atomic layer deposition on polyethylene naphthalate substrates and the effects of bending on the device properties investigated. The threshold voltage and saturation mobility were observed to change with respect to the amount of substrate bending. These modulations can be explained in terms of piezoelectric nature of in ZnO. In comparison with the previously reported single crystal nanowires ZnO field effect transistors, the amount of the electrical property modulation under bent condition is significantly reduced and our report shows a much improved stability for ZnO:N as a flexible device material.
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85.30.Tv Field effect devices

Quasi one-dimensional transport in single GaAs/AlGaAs core-shell nanowires

D. Lucot, F. Jabeen, J.-C. Harmand, G. Patriarche, R. Giraud, G. Faini, and D. Mailly

Appl. Phys. Lett. 98, 142114 (2011); http://dx.doi.org/10.1063/1.3574026 (3 pages) | Cited 10 times

Online Publication Date: 7 April 2011

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We present an original approach to fabricate single GaAs/AlGaAs core-shell nanowire with robust and reproducible transport properties. The core-shell structure is buried in an insulating GaAs overlayer and connected as grown in a two-probe setup using the highly doped growth substrate and a top diffused contact. The measured conductance shows a non-Ohmic behavior with temperature and voltage-bias dependences following power laws, as expected for a quasi one- dimensional system.
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81.07.Gf Nanowires
81.05.Ea III-V semiconductors
81.07.Vb Quantum wires
81.16.Nd Micro- and nanolithography
73.63.Nm Quantum wires

Ballistic transport and electrical spin signal enhancement in a nanoscale three-terminal spintronic device

Lei Zhu and Edward T. Yu

Appl. Phys. Lett. 98, 142115 (2011); http://dx.doi.org/10.1063/1.3567922 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2011

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Ballistic electron transport at nanoscale dimensions is investigated and exploited in a nanoscale three-terminal, all-electrical spintronic semiconductor device. Charge current cancellation under appropriate device biasing yields a large, spin-dependent current signal even with modest spin injection efficiency into the semiconductor, while reliance on ballistic, rather than diffusive, carrier transport is expected to enable robust scalability to smaller dimensions. Magnetocurrent in excess of 200% is measured with spin injection efficiency of 5%, and a spin-dependent ballistic carrier transport model is shown to yield accurate, quantitative predictions of current-voltage behavior.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.De Semiconductor-device characterization, design, and modeling
85.35.-p Nanoelectronic devices
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