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23 Mar 2009

Volume 94, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 94, 122502 (2009); http://dx.doi.org/10.1063/1.3100783 (3 pages)

Junhua Wang, Yisheng Shi, Juexian Cao, and Ruqian Wu
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Room temperature spontaneous emission enhancement from quantum dots in photonic crystal slab cavities in the telecommunications C band

R. Hostein, R. Braive, M. Larqué, K.-H. Lee, A. Talneau, L. Le Gratiet, I. Robert-Philip, I. Sagnes, and A. Beveratos

Appl. Phys. Lett. 94, 123101 (2009); http://dx.doi.org/10.1063/1.3104855 (3 pages) | Cited 5 times

Online Publication Date: 23 March 2009

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We report on the control of the spontaneous emission dynamics from InAsP self-assembled quantum dots emitting in the telecommunications C band and weakly coupled to the mode of a double heterostructure cavity etched on a suspended InP membrane at room temperature. The quality factor of the cavity mode is 44×103 with an ultralow modal volume of the order of 1.2(λ/n)3, inducing an enhancement in the spontaneous emission rate of up a factor of 2.8 at 300 K.
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78.66.Fd III-V semiconductors
42.70.Qs Photonic bandgap materials
68.18.-g Langmuir-Blodgett films on liquids

Resonant behavior observed in electron field emission from acid functionalized multiwall carbon nanotubes

S. M. Lyth and S. R. P. Silva

Appl. Phys. Lett. 94, 123102 (2009); http://dx.doi.org/10.1063/1.3094755 (3 pages) | Cited 6 times

Online Publication Date: 24 March 2009

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Acid functionalized multiwall carbon nanotube ink was deposited onto carbon fiber fabric via dip coating. Repeatable staircaselike current-field curves were observed in the field emission data. These atypical curves are attributed to resonant tunneling through localized surface states in a quantum well structure, which arises due to the presence of the surface carboxylic functional group.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.21.Fg Quantum wells
73.43.Jn Tunneling
73.63.Fg Nanotubes
73.20.At Surface states, band structure, electron density of states
81.07.De Nanotubes

High-performance, fully transparent, and flexible zinc-doped indium oxide nanowire transistors

W. F. Zhang, Z. B. He, G. D. Yuan, J. S. Jie, L. B. Luo, X. J. Zhang, Z. H. Chen, C. S. Lee, W. J. Zhang, and S. T. Lee

Appl. Phys. Lett. 94, 123103 (2009); http://dx.doi.org/10.1063/1.3100194 (3 pages) | Cited 16 times

Online Publication Date: 24 March 2009

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We report the fabrication of fully transparent and flexible nanowire transistors by combining a high-quality In2O3:Zn nanowire channel, a SiNx high-κ dielectric, and conducting Sn-doped In2O3 electrodes on a polyethylene terephthalate substrate. The devices show excellent operating characteristics with high carrier mobilities up to 631 cm2 V−1 s−1, a drain-source current on/off modulation ratio ∼ 1×106, a high on-state current ∼ 1×10−5 A, a small subthreshold gate voltage swing of 120 mV decade−1, and a near zero threshold voltage. The devices further show high reproducibility and stable performance under bending condition. The high-performance nanowire transistors would enable application opportunities in flexible and transparent electronics.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Coherent diffraction tomography of nanoislands from grazing-incidence small-angle x-ray scattering

O. M. Yefanov, A. V. Zozulya, I. A. Vartanyants, J. Stangl, C. Mocuta, T. H. Metzger, G. Bauer, T. Boeck, and M. Schmidbauer

Appl. Phys. Lett. 94, 123104 (2009); http://dx.doi.org/10.1063/1.3103246 (3 pages) | Cited 5 times

Online Publication Date: 25 March 2009

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The combination of grazing-incidence small-angle x-ray scattering with tomographic and phase retrieval methods is presented for the reconstruction of the three-dimensional (3D) electron density of nanometer sized objects. The measured 3D intensity distribution in reciprocal space is used for the phase retrieval and reconstruction of the shape and electron density of epitaxial SiGe islands with the shape of truncated pyramids with a 200 nm square base. A spatial resolution below 20 nm demonstrated in this work cannot be achieved by traditional tomographic methods.
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78.70.Ck X-ray scattering
68.55.ag Semiconductors
61.46.-w Structure of nanoscale materials
61.05.cf X-ray scattering (including small-angle scattering)

Size and composition dependent electronic and optical properties of GaxAl1−xAs and AlxGa1−xAs alloyed nanocrystals

Chanchal Ghosh, Sougata Pal, Pranab Sarkar, and Thomas Frauenheim

Appl. Phys. Lett. 94, 123105 (2009); http://dx.doi.org/10.1063/1.3109783 (3 pages)

Online Publication Date: 25 March 2009

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By using density-functional tight-binding method, we have shown the size and composition dependent variation of band gap and excitation spectra of both GaxAl1−xAs and AlxGa1−xAs alloyed semiconductor nanocrystals. The two systems differ with respect to the surface atoms, while in one case the surface atoms are Ga, while in another case it is Al, and hence the effect of structural relaxations in GaxAl1−xAs and AlxGa1−xAs are different leading to different final structures and properties. We observed a bowing effect in the band gap values as it is experimentally found in many semiconductor alloys.
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73.22.-f Electronic structure of nanoscale materials and related systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Hc Quantum dots
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.21.La Quantum dots

Directional light extraction enhancement from GaN-based film-transferred photonic crystal light-emitting diodes

Chun-Feng Lai, Chia-Hsin Chao, Hao-Chung Kuo, His-Hsuan Yen, Chia-En Lee, and Wen-Yung Yeh

Appl. Phys. Lett. 94, 123106 (2009); http://dx.doi.org/10.1063/1.3106109 (3 pages) | Cited 23 times

Online Publication Date: 25 March 2009

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Experimental investigation of the directionality in the far-field pattern and light extraction enhancement in collected cone were performed in GaN-based film-transferred photonic crystal (PhC) light-emitting diodes (FTLEDs). Angular-resolved measurement revealed directional profile and azimuthal anisotropy in the far-field distribution with guided modes extraction. Good agreement according to Bragg’s diffraction theory and free photon band structure were achieved. The light enhancement in PhC FTLEDs compared to non-PhC FTLEDs within the collection cone angle was obtained according to measured three-dimensional far-field patterns. In a ±20° collection cone, collected light was enhanced by a factor of ∼ 2.4 for the collimated PhC FTLED.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors

Atomic layer deposition of Cu2S for future application in photovoltaics

Alex B. F. Martinson, Jeffrey W. Elam, and Michael J. Pellin

Appl. Phys. Lett. 94, 123107 (2009); http://dx.doi.org/10.1063/1.3094131 (3 pages) | Cited 15 times

Online Publication Date: 26 March 2009

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Alternating exposure to bis(N,N′-di-sec-butylacetamidinato)dicopper(I) and hydrogen sulfide is shown to produce high quality chalcocite (Cu2S) thin films by atomic layer deposition on silicon and fused silica substrates. The layer-by-layer chemical vapor deposition method enables conformal growth of the phase-pure material at 130 °C. X-ray diffraction reveals that polycrystalline high-chalcocite films are deposited preferentially oriented in the 〈00l〉 plane. The optical properties of this naturally p-type absorber compare well with previous reports on single crystals, highlighting the applicability of the technique to nanostructured photovoltaics.
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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.)
85.40.Sz Deposition technology
68.55.A- Nucleation and growth
78.66.-w Optical properties of specific thin films

Room-temperature stability of Pt nanogaps formed by self-breaking

F. Prins, T. Hayashi, B. J. A. de Vos van Steenwijk, B. Gao, E. A. Osorio, K. Muraki, and H. S. J. van der Zant

Appl. Phys. Lett. 94, 123108 (2009); http://dx.doi.org/10.1063/1.3109784 (3 pages) | Cited 9 times

Online Publication Date: 26 March 2009

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We present a method to make Pt nanometer-spaced electrodes that are free of metallic particles and stable at ambient conditions. The nanogaps are fabricated using feedback-controlled electromigration to form few-atom contacts. When performing this procedure at elevated temperatures (>420 K), the Pt contacts undergo self-breaking so that nanometer separated electrode pairs are formed. Once cooled down to lower temperatures, the nanogaps stabilize and can be characterized in detail. We find that current-voltage characteristics can be well fitted to a Simmons model for tunneling and gap-size fluctuations at room temperature determined from these fits stay within 0.6 Å for at least 50 h.
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81.16.-c Methods of micro- and nanofabrication and processing
66.30.Qa Electromigration
73.63.-b Electronic transport in nanoscale materials and structures
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Bx Metals, semimetals, and alloys
73.40.Gk Tunneling

Periodic alignment of Si quantum dots on hafnium oxide coated single wall carbon nanotubes

Mario Olmedo, Alfredo A. Martinez-Morales, Gang Liu, Emre Yengel, Cengiz S. Ozkan, Chun Ning Lau, Mihrimah Ozkan, and Jianlin Liu

Appl. Phys. Lett. 94, 123109 (2009); http://dx.doi.org/10.1063/1.3103547 (3 pages) | Cited 3 times

Online Publication Date: 26 March 2009

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We demonstrate a bottom up approach for the aligned epitaxial growth of Si quantum dots (QDs) on one-dimensional (1D) hafnium oxide (HfO2) ridges created by the growth of HfO2 thin film on single wall carbon nanotubes. This growth process creates a high strain 1D ridge on the HfO2 film, which favors the formation of Si seeds over the surrounding flat HfO2 area. Periodic alignment of Si QDs on the 1D HfO2 ridge was observed, which can be controlled by varying different growth conditions, such as growth temperature, growth time, and disilane flow rate.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots

Dielectric breakdown of MgO magnetic tunnel junctions

D. V. Dimitrov, Zheng Gao, Xiaobin Wang, Wonjoon Jung, Xiaohua Lou, and Olle G. Heinonen

Appl. Phys. Lett. 94, 123110 (2009); http://dx.doi.org/10.1063/1.3109792 (3 pages) | Cited 5 times

Online Publication Date: 26 March 2009

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We have investigated high-quality MgO tunnel junctions with a range of barrier thickness in order to identify the underlying physical mechanism responsible for dielectric breakdown. Two types of dielectric breakdown (“soft” and “hard”) were observed. Soft breakdown was observed in a few percent of the devices. This breakdown mode is not intrinsic and is attributed to tunnel junction imperfections. The hard breakdown occurs because a critical electric field is reached across the tunnel barrier. Other possible breakdown mechanisms, such as thermally driven mass diffusion or charge trapping, were not consistent with the hard dielectric breakdown data and were ruled out.
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77.22.Jp Dielectric breakdown and space-charge effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Fast determination of phases in LixFePO4 using low losses in electron energy-loss spectroscopy

P. Moreau, V. Mauchamp, F. Pailloux, and F. Boucher

Appl. Phys. Lett. 94, 123111 (2009); http://dx.doi.org/10.1063/1.3109777 (3 pages) | Cited 7 times

Online Publication Date: 27 March 2009

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Experimental valence electron energy-loss spectra, obtained on different phases of LixFePO4, are analyzed with first principles calculations based on density functional theory. In the 4–7 eV range, a large peak is identified in the FePO4 spectrum but is absent in LiFePO4, which allows the easy formation of energy filtered images. The intensity of this peak, nonsensitive to the precise orientation of the crystal, is large enough to rapidly determine existing phases in the sample and permit future dynamical studies.
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79.20.Uv Electron energy loss spectroscopy
61.50.-f Structure of bulk crystals

Mechanisms of interdot coupling in (In,Ga)As/GaAs quantum dot arrays

Yu. I. Mazur, V. G. Dorogan, E. Marega, Jr., G. G. Tarasov, D. F. Cesar, V. Lopez-Richard, G. E. Marques, and G. J. Salamo

Appl. Phys. Lett. 94, 123112 (2009); http://dx.doi.org/10.1063/1.3103312 (3 pages) | Cited 6 times

Online Publication Date: 27 March 2009

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Interdot coupling in (In,Ga)As/GaAs quantum dot arrays is studied by means of steady state and time-resolved photoluminescence (PL). A peculiar dependence of the PL decay time on the excitation and detection energy is revealed and ascribed to the peculiarities of the carrier and energy relaxation caused by both immediate electronic interdot coupling and long-range coupling through the radiation field.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots

Anisotropic electron spins in self-assembled quantum dots

Weidong Sheng

Appl. Phys. Lett. 94, 123113 (2009); http://dx.doi.org/10.1063/1.3109789 (3 pages) | Cited 3 times

Online Publication Date: 27 March 2009

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Electron g-factors in self-assembled InAs/GaAs quantum dots are studied theoretically by means of a tight-binding method. The anisotropy in the electron g-factor, induced by the band-mixing effect, is found to be much more sensitive to the chemical composition of the dot than the aspect ratio of the structure. The modulus of the vertical electron g-factor is usually seen smaller than the in-plane component in pure InAs dots while the situation could be reversed in highly intermixing InGaAs dots. A microscopic theory is presented to reveal the dependence of the anisotropy in the electron g-factor on the proportion of the valence-band components in the electronic states. Our study indicates the possibility of tuning electron g-factor anisotropy in quantum dots.
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73.21.La Quantum dots
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
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