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30 Jun 2003

Volume 82, Issue 26, pp. 4633-4843

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Appl. Phys. Lett. 82, 4797 (2003); http://dx.doi.org/10.1063/1.1587262 (3 pages)

Ongi Englander, Dane Christensen, and Liwei Lin
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Light amplification in semiconductor nanocrystals: Quantum rods versus quantum dots

H. Htoon, J. A. Hollingworth, A. V. Malko, R. Dickerson, and V. I. Klimov

Appl. Phys. Lett. 82, 4776 (2003); http://dx.doi.org/10.1063/1.1586460 (3 pages) | Cited 52 times

Online Publication Date: 24 June 2003

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We perform side-by-side comparison of optical gain properties of spherical and elongated nanocrystals (quantum dots and quantum rods, respectively). This comparison indicates that elongated nanoparticles provide several features beneficial for lasing applications, such as enhanced absorption cross sections (and hence reduced lasing threshold and improved photostability), increased optical gain lifetime, and extended optical gain spectral range through the use of transitions that involve both ground and excited electronic states. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Lt Quantum wires
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots
73.21.Hb Quantum wires
81.07.Vb Quantum wires
73.21.La Quantum dots
81.07.Ta Quantum dots
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Yj Optical parametric oscillators and amplifiers
78.55.-m Photoluminescence, properties and materials

Two-dimensional periodic positioning of self-assembled Ge islands on prepatterned Si (001) substrates

Zhenyang Zhong, A. Halilovic, T. Fromherz, F. Schäffler, and G. Bauer

Appl. Phys. Lett. 82, 4779 (2003); http://dx.doi.org/10.1063/1.1581986 (3 pages) | Cited 70 times

Online Publication Date: 24 June 2003

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Two-dimensional (2D) periodic arrays of Ge islands were realized on prepatterned Si (001) substrates by solid-source molecular-beam epitaxy. Atomic-force microscopy images demonstrate that the Ge islands are formed in the 2D laterally ordered pits of patterned substrates. The 2D periodicity of the substrate pattern is replicated throughout a stack of Ge island layers by strain-driven vertical ordering. Photoluminescence spectra of the ordered Ge islands show well-resolved peaks of the no-phonon signal and the transverse-optical phonon replica. These peaks are observed at nearly the same energy as those of random Ge islands deposited under the same conditions on unpatterned Si substrates. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Vertical nanowire transistor in flexible polymer foil

Jie Chen and R. Könenkamp

Appl. Phys. Lett. 82, 4782 (2003); http://dx.doi.org/10.1063/1.1587258 (3 pages) | Cited 23 times

Online Publication Date: 24 June 2003

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Fabrication and operation of a vertical nanowire field-effect transistor is reported. The device is prepared by growing vertical wires in the cylindrical pores of a polymer foil stack. The nanowire diameter is approximately 100 nm, the packing density up to 108 cm−2. The polymer foil stack consists of two polymer layers and an intermediate metal layer. Cylindrical holes are prepared in this stack by using fast ion irradiation and subsequent etching. Well-defined cylindrical openings with diameters between 50 and 150 nm are obtained. The semiconductor growth involves electrodeposition of the p-type quaternary compound CuSCN. Electrical measurements on first devices show transistor action with some gate leakage, which may be improved in future designs. The arrangement of inorganic device material embedded in soft polymer matrix is structurally robust, and the devices show low sensitivity to mechanical strain of the foil. Single electron effects may be expected in these devices, when the dimensions are further reduced. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

Spatially direct and indirect transitions observed for Si/Ge quantum dots

M. Larsson, A. Elfving, P. O. Holtz, G. V. Hansson, and W.-X. Ni

Appl. Phys. Lett. 82, 4785 (2003); http://dx.doi.org/10.1063/1.1587259 (3 pages) | Cited 19 times

Online Publication Date: 24 June 2003

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The optical properties of Ge quantum dots embedded in Si were investigated by means of photoluminescence, with temperature and excitation power density as variable parameters. Two different types of recombination processes related to the Ge quantum dots were observed. A transfer from the spatially indirect to the spatially direct recombination in the type-II band lineup was observed with increasing temperature. A blueshift of the spatially indirect Ge quantum-dot-emission energy with increasing excitation power is ascribed to band bending at the type-II Si/Ge interface for high carrier densities. Comparative studies were performed on uncapped Ge dot structures. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Ap Elemental semiconductors

Influence of coupling effect in the operation of vertically coupled quantum-dot lasers

B. Shi and Y. H. Xie

Appl. Phys. Lett. 82, 4788 (2003); http://dx.doi.org/10.1063/1.1587881 (3 pages) | Cited 4 times

Online Publication Date: 24 June 2003

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The influence of the coupling effect in the operation of vertically coupled quantum-dot lasers is studied by solving coupled rate equations including the terms representing carrier coupling between vertically stacked quantum dots. The calculation results show a much narrower spectral width above the lasing threshold compared with the uncoupled case. The single-mode output power is also enhanced by the coupling effect, especially when there is a large fluctuation in dot size. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.La Quantum dots
73.63.Kv Quantum dots
78.67.Hc Quantum dots
42.60.By Design of specific laser systems
81.07.Ta Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Ah General laser theory

Synthesis and optical properties of S-doped ZnO nanowires

B. Y. Geng, G. Z. Wang, Z. Jiang, T. Xie, S. H. Sun, G. W. Meng, and L. D. Zhang

Appl. Phys. Lett. 82, 4791 (2003); http://dx.doi.org/10.1063/1.1588735 (3 pages) | Cited 50 times

Online Publication Date: 24 June 2003

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S-doped ZnO nanowires with an average diameter of 80 nm and length up to several tens of micrometers were produced through a simple physical evaporation approach. The nanowires had a single-crystal hexagonal structure and grew along the [102] direction. Photoluminescence (PL) measurements showed that the doping of sulfur shifted the PL spectrum peak towards short wavelengths, and the doping quantity was found responsible for the different characteristics. © 2003 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.uj III-V and II-VI semiconductors

Self-assembled growth of single-walled carbon nanotubes by pyrolysis of metalorganic precursor

A. R. Harutyunyan, G. Chen, and P. C. Eklund

Appl. Phys. Lett. 82, 4794 (2003); http://dx.doi.org/10.1063/1.1587257 (3 pages) | Cited 12 times

Online Publication Date: 24 June 2003

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Carbon nanotubes with controllable diameters from ∼ 1 to 200 nm were synthesized by pyrolysis of iron phthalocyanine at ∼ 900 °C under argon gas flow. Diameters of nanotubes were controlled by varying the metal concentration, using the solid phase dilution of iron phthalocyanine with metal-free phthalocyanine to various degrees. Self-assembled single-walled carbon nanotubes were obtained by using iron phthalocyanine precursor diluted with metal-free phthalocyanine in 1:24 molar ratio. © 2003 American Institute of Physics.
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81.07.De Nanotubes
81.16.Dn Self-assembly
61.46.-w Structure of nanoscale materials

Local synthesis of silicon nanowires and carbon nanotubes on microbridges

Ongi Englander, Dane Christensen, and Liwei Lin

Appl. Phys. Lett. 82, 4797 (2003); http://dx.doi.org/10.1063/1.1587262 (3 pages) | Cited 44 times

Online Publication Date: 24 June 2003

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Resistive heating of microline resistors was used to activate vapor-deposition synthesis of silicon nanowires and carbon nanotubes in a room-temperature chamber. The process is compatible with on-chip microelectronics and eliminates the necessity of postsynthesis assembly of nanostructures to form more complicated devices. The process is localized, selective, and scalable. The synthesized nanowire dimensions are 30–80 nm in diameter and up to 10 μm in length, while nanotubes 10–50 nm in diameter and up to 5 μm in length have been demonstrated. Growth rates of up to 1 μm/min for silicon nanowires and up to 0.25 μm/min for carbon nanotubes were observed. This method facilitates the integration of nanotechnology with larger-scale systems. © 2003 American Institute of Physics.
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81.07.Lk Nanocontacts
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.35.Kt Nanotube devices
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)

Comparative current–voltage characteristics of nicked and repaired λ-DNA

B. Hartzell, B. McCord, D. Asare, H. Chen, J. J. Heremans, and V. Soghomonian

Appl. Phys. Lett. 82, 4800 (2003); http://dx.doi.org/10.1063/1.1588738 (3 pages) | Cited 28 times

Online Publication Date: 24 June 2003

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We report on current–voltage characteristics obtained at room temperature on λ-DNA molecules, modified at both ends with disulfide groups and spanning Au electrodes. A comparison is drawn between the characteristics of the λ-DNA, which after modification features a gap between 3′ and 5′ sites (nicked DNA), and λ-DNA where this gap has been ligated (repaired DNA). The repaired DNA double helices show a close-to-linear current–voltage characteristic, and a dc conductivity estimated at ∼ 1×10−3 S cm−1. In contrast, the nicked DNA shows pronouncedly nonlinear and rectifying behavior, with a conductivity gap of ∼3 eV. The low-field conductivity of the nicked DNA is approximately a factor 20 lower than the repaired DNA’s conductivity. © 2003 American Institute of Physics.
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87.14.G- Nucleic acids
87.15.-v Biomolecules: structure and physical properties

InAs/InP quantum dots in SiO2/Ta2O5-based microcavities

D. Dalacu, D. Poitras, J. Lefebvre, P. J. Poole, G. C. Aers, and R. L. Williams

Appl. Phys. Lett. 82, 4803 (2003); http://dx.doi.org/10.1063/1.1588369 (3 pages) | Cited 5 times

Online Publication Date: 24 June 2003

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Planar InAs/InP quantum-dot microcavities using multilayer SiO2/Ta2O5 Bragg reflectors have been studied in emission. For an eight-pair mirror design, the stop band extends from 700 to 900 meV and the cavity linewidth is ∼ 500 μeV for emission at 850 meV. Measurements as a function of incident power show quantum-dot saturation behavior, with the emission intensity going to the wetting layer outside the cavity stop band. Saturation behavior at fixed pump power is also observed as a function of decreasing temperature. Dispersion measurements as a function of emission angle show polarization splitting in reasonable agreement with theory. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots

Dual-mode mechanical resonance of individual ZnO nanobelts

X. D. Bai, P. X. Gao, Z. L. Wang, and E. G. Wang

Appl. Phys. Lett. 82, 4806 (2003); http://dx.doi.org/10.1063/1.1587878 (3 pages) | Cited 206 times

Online Publication Date: 24 June 2003

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The mechanical resonance of a single ZnO nanobelt, induced by an alternative electric field, was studied by in situ transmission electron microscopy. Due to the rectangular cross section of the nanobelt, two fundamental resonance modes have been observed corresponding to two orthogonal transverse vibration directions, showing the versatile applications of nanobelts as nanocantilevers and nanoresonators. The bending modulus of the ZnO nanobelts was measured to be ∼ 52 GPa and the damping time constant of the resonance in a vacuum of 5×10−8 Torr was ∼ 1.2 ms and quality factor Q = 500. © 2003 American Institute of Physics.
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77.65.Fs Electromechanical resonance; quartz resonators
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
61.46.-w Structure of nanoscale materials

Direct and subdiffraction-limit laser nanofabrication in silicon

S. M. Huang, M. H. Hong, B. S. Luk’yanchuk, and T. C. Chong

Appl. Phys. Lett. 82, 4809 (2003); http://dx.doi.org/10.1063/1.1589167 (3 pages) | Cited 17 times

Online Publication Date: 24 June 2003

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We propose a method for nanofabrication at a resolution much below the diffraction limit for projection optical lithography using a backside-irradiation method. Feature sizes below λ/260 have been achieved in silicon. An infrared laser (CO2, λ=10.6 μm) was used to illuminate the backside of a Si substrate with Au particles on its polished surface. The morphologies of created features were characterized by atomic force microscope and field emission scanning electron microscope. The formation mechanisms of these nanofeatures have been discussed and associated with localized optical excitations in Au colloid aggregates with a fractal structure. This backside-irradiation laser-assisted nanofabrication method may also be extended to various metals, particle shapes, particle sizes, substrates, and other lasers. It can be used to investigate optical excitations and near fields in these systems. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
68.47.Fg Semiconductor surfaces
85.40.Hp Lithography, masks and pattern transfer
81.07.Wx Nanopowders
68.37.Ps Atomic force microscopy (AFM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Vj Field emission and field-ion microscopy
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

The role of free carriers and excitons on the lasing characteristics of InAs/InGaAs quantum-dot lasers

A. Dikshit and J. M. Pikal

Appl. Phys. Lett. 82, 4812 (2003); http://dx.doi.org/10.1063/1.1588377 (3 pages) | Cited 1 time

Online Publication Date: 24 June 2003

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Temperature-dependent lasing characteristics of InAs/InGaAs quantum-dot lasers operating at 1.3 μm are theoretically analyzed. In particular, we investigated the effect of different carrier distribution models, free and bound electron–hole pairs, on gain and the lasing characteristics. In contrast to lasers of higher dimensionality, the results of this work indicate that it is the bound electron–hole pairs (excitons) that mainly contribute to gain in these lasers. However, the ratio of the number of free carriers to excitons is very important and significantly affects the threshold current and its temperature dependence. Our calculations show that the characteristic temperature T0 drops from 356 K when only excitons are included in the model, to a more realistic 83 K when both excitons and free carriers are considered. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.La Quantum dots
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
71.35.Gg Exciton-mediated interactions
78.67.Hc Quantum dots
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