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2 Dec 2002

Volume 81, Issue 23, pp. 4315-4476

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Comparative study on the broadening of exciton luminescence linewidth due to phonon in zinc-blende and wurtzite GaN epilayers

S. J. Xu, L. X. Zheng, S. H. Cheung, M. H. Xie, S. Y. Tong, and Hui Yang

Appl. Phys. Lett. 81, 4389 (2002); http://dx.doi.org/10.1063/1.1526450 (3 pages) | Cited 8 times

Online Publication Date: 25 November 2002

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Linewidth broadening of exciton luminescence in wurtzite and zinc-blende GaN epilayers was investigated as a function of temperature with photoluminescence. A widely accepted theoretical model was used to fit the experimental data, so that the coupling parameters between exciton and acoustic and longitudinal optical phonons were obtained for both structures. It was found that the coupling constants of both exciton–acoustic optical phonon coupling and exciton–longitudinal optical phonon coupling for zinc-blende GaN are almost twice as much as the corresponding values of wurtzite GaN. These results show that the relatively strong exciton–phonon scattering seems to be characteristic to zinc-blende GaN film. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.Gg Exciton-mediated interactions
63.20.kk Phonon interactions with other quasiparticles

Pulsed atomic-layer epitaxy of ultrahigh-quality AlxGa1−xN structures for deep ultraviolet emissions below 230 nm

J. P. Zhang, M. Asif Khan, W. H. Sun, H. M. Wang, C. Q. Chen, Q. Fareed, E. Kuokstis, and J. W. Yang

Appl. Phys. Lett. 81, 4392 (2002); http://dx.doi.org/10.1063/1.1528726 (3 pages) | Cited 54 times

Online Publication Date: 25 November 2002

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In this letter, we report the pulsed atomic-layer epitaxy of ultrahigh-quality AlN epilayers and AlN/Al0.85Ga0.15N multiple quantum wells (MQWs) on basal plane sapphire substrates. Symmetric and asymmetric x-ray diffraction (XRD) measurements and room-temperature (RT) photoluminescence (PL) were used to establish the ultrahigh structural and optical quality. Strong band-edge RT PL at 208 and 228 nm was obtained from the AlN epilayers and the AlN/Al0.85Ga0.15N MQWs. These data clearly establish their suitability for sub-250-nm deep UV emitters. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.07.St Quantum wells
68.65.Fg Quantum wells
81.05.Ea III-V semiconductors

Realization of wide electron slabs by polarization bulk doping in graded III–V nitride semiconductor alloys

Debdeep Jena, Sten Heikman, Daniel Green, Dario Buttari, Robert Coffie, Huili Xing, Stacia Keller, Steve DenBaars, James S. Speck, Umesh K. Mishra, and Ioulia Smorchkova

Appl. Phys. Lett. 81, 4395 (2002); http://dx.doi.org/10.1063/1.1526161 (3 pages) | Cited 21 times

Online Publication Date: 25 November 2002

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We present the concept and experimental realization of polarization-induced bulk electron doping in III–V nitride semiconductors. By exploiting the large polarization charges in the III–V nitrides, we are able to create wide slabs of high-density mobile electrons without introducing shallow donors. Transport measurements reveal the superior properties of the polarization-doped electron distributions than comparable shallow donor-doped structures, especially at low temperatures due to the removal of ionized impurity scattering. Such polarization-induced three-dimensional electron slabs can be utilized in a variety of device structures owing to their high conductivity and continuously changing energy gap. © 2002 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.uj III-V and II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
71.55.Eq III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
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Origin of antiphase domain boundaries and their effect on the dielectric constant of Ba0.5Sr0.5TiO3 films grown on MgO substrates

Hao Li, H. Zheng, L. Salamanca-Riba, R. Ramesh, I. Naumov, and K. Rabe

Appl. Phys. Lett. 81, 4398 (2002); http://dx.doi.org/10.1063/1.1523632 (3 pages) | Cited 7 times

Online Publication Date: 25 November 2002

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Epitaxial Ba1−xSrxTiO3 (BST) with x = 0.5 films were grown on MgO substrates using pulsed-laser deposition. We have observed a high density of antiphase domain boundaries (ADB) in these BST films. We attribute the formation of the ADBs to the different crystal symmetry of the film and the substrate. Adjacent domains have an in plane phase shift of ½[110], or ½[1math0] thus creating a phase shift of the in plane lattice planes of ½[010] or ½[100] across the boundary. We have used first-principles calculations to obtain the effect of the ADBs on the dielectric constant of SrTiO3 and found that they lower the effective in plane dielectric constant in the direction normal to the ADB. Upon annealing, the density of ADBs decreases and the dielectric properties improve. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Tbit/inch2 ferroelectric data storage based on scanning nonlinear dielectric microscopy

Yasuo Cho, Kenjiro Fujimoto, Yoshiomi Hiranaga, Yasuo Wagatsuma, Atsushi Onoe, Kazuya Terabe, and Kenji Kitamura

Appl. Phys. Lett. 81, 4401 (2002); http://dx.doi.org/10.1063/1.1526916 (3 pages) | Cited 83 times

Online Publication Date: 25 November 2002

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Nanosized inverted domain dots in ferroelectric materials have potential applications in ultrahigh-density rewritable data storage systems. Here, a data storage system based on scanning nonlinear dielectric microscopy and thin films of ferroelectric single-crystal lithium tantalite is presented. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density of 1.50 Tbit/in.2. © 2002 American Institute of Physics.
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85.50.Gk Non-volatile ferroelectric memories
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films

Correlation between infrared phonon modes and dielectric relaxation in Bi2O3–ZnO–Nb2O5 cubic pyrochlore

Juan C. Nino, Michael T. Lanagan, Clive A. Randall, and Stanislav Kamba

Appl. Phys. Lett. 81, 4404 (2002); http://dx.doi.org/10.1063/1.1524699 (3 pages) | Cited 29 times

Online Publication Date: 25 November 2002

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Analysis of the dielectric relaxation phenomena in Bi2O3–ZnO–Nb2O5 cubic pyrochlore utilizing the Arrhenius equation is revisited to include recent high-frequency measurements. The fitting parameters obtained are further analyzed by comparison with theoretical and experimental activation energies of better understood relaxation systems such as dipolar glasses and relaxor ferroelectrics. The attempt jump frequency obtained from the Arrhenius fit (ν0 ∼ 4.385 THz) is found in correspondence with the resonant frequencies of the polar phonon modes previously identified by infrared spectroscopy. This correlation, and in particular the role of the O–A–O and O′–A–O′ bending phonon modes in driving the relaxation, is discussed. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Supercritical carbon dioxide extraction to produce low-k plasma enhanced chemical vapor deposited dielectric films

J. A. Lubguban, J. Sun, T. Rajagopalan, B. Lahlouh, S. L. Simon, and S. Gangopadhyay

Appl. Phys. Lett. 81, 4407 (2002); http://dx.doi.org/10.1063/1.1525390 (3 pages) | Cited 4 times

Online Publication Date: 25 November 2002

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A treatment to reduce the dielectric constant of plasma enhanced chemical vapor deposition (PECVD) films is presented. The method involved extracting low molecular weight or CO2 soluble species in the films by post deposition supercritical CO2 pressurization (SCCO2). We observed a decrease in k value of about 10%–14% in a composite film of organosilicate and a-C:F after SCCO2 treatment at 200 °C for 8 h. The composite films were deposited by PECVD using C4F8 and tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) liquid source and H2 carrier gas at room temperature. As-deposited films were also annealed at 200 °C for 8 h in N2 atmosphere to compare the effect of thermal annealing without SCCO2 treatment. The result shows that there is no change in the k of the films after annealing. Thus, SCCO2 extraction is a good method for reducing the dielectric constant of these PECVD composite films. Supercritical CO2 pressurization of the film deposited using TVTMCTS and H2 only without the addition of C4F8 has no effect on the dielectric properties of the film while SCCO2 treatment of a-C:F samples deposited using C4F8 only dissolved the film. Therefore, in the composite film, we expect that CFx species dissolve during SCCO2 treatment while the organosilicate structure is preserved. Analysis of the Fourier-transform infrared spectra of the samples supports this hypothesis based on the decrease in the C–F absorption intensity after SCCO2 treatment. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.40.Tv Optical and dielectric properties related to treatment conditions
77.22.Ch Permittivity (dielectric function)
61.72.Cc Kinetics of defect formation and annealing
81.05.U- Carbon/carbon-based materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.05.Rm Porous materials; granular materials
78.66.Nk Insulators

Kinetic of phase transformation of SrBi2Ta2O9 deposited by metalorganic decomposition on platinum electrodes

M. Moert, T. Mikolajick, G. Schindler, N. Nagel, W. Hartner, C. Dehm, H. Kohlstedt, and R. Waser

Appl. Phys. Lett. 81, 4410 (2002); http://dx.doi.org/10.1063/1.1526926 (3 pages) | Cited 2 times

Online Publication Date: 25 November 2002

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SrBi2Ta2O9 thin films were prepared by metalorganic decomposition on Pt/Ti/SiO2/Si substrates and subsequently crystallized at temperatures ranging from 600 to 700 °C for 40 to 225 min. Data of the Aurivillius surface coverage taken from atomic force microscopy measurements were used to model the kinetics of isothermal phase transformation from the fluorite to the Aurivillius phase. A two-dimensional growth mechanism at a decreasing nucleation rate can be deduced. By evaluating the temperature dependence of the growth rates, an activation energy for phase transformation of 318 kJ/mol is determined. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.B- Phase transitions and Curie point
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Nanometer-scale pores in low-k dielectric films probed by positron annihilation lifetime spectroscopy

C. L. Wang, M. H. Weber, K. G. Lynn, and K. P. Rodbell

Appl. Phys. Lett. 81, 4413 (2002); http://dx.doi.org/10.1063/1.1526923 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2002

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We measured positron annihilation lifetime spectra in mesoporous low dielectric constant (low-k) methyl-silsesquioxane (MSSQ) films versus porogen load Φ from Φ = 0% to 50%. The ortho-positronium lifetime parameters were obtained using both the maximum entropy and discrete lifetime analyses. Open and closed porosity distributions and the average radius of closed pores were obtained. The total porosity and the fraction of open/closed porosities were evaluated. The total porosity increases linearly with porogen load, consistent with the porosity obtained from density measurements. Open porosity occurs from 20% porogen load upwards. © 2002 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
78.70.Bj Positron annihilation
77.22.Ch Permittivity (dielectric function)

Effects of nitridation of silicon and repeated spike heating on the electrical properties of SrTiO3 gate dielectrics

Chih-Yi Liu, Hang-Ting Lue, and Tseung-Yuen Tseng

Appl. Phys. Lett. 81, 4416 (2002); http://dx.doi.org/10.1063/1.1526914 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2002

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Electrical properties of SrTiO3 (STO) gate dielectrics on Si substrates grown by rf-magnetron sputtering were studied. We employed the surface nitridation and repeated spike heating to improve the interfacial properties of STO/Si. The nitrogen was moderately incorporated at the interface by first growing a thin SiON layer and then removing this sacrificial layer before growing STO gate dielectric. The experimental results indicate that this nitridation treatment may retard the formation of thin interfacial layer during the high-temperature growth of STO gate dielectric and consequently decrease the equivalent oxide thickness (EOT) by about 10% toward 24% at various deposition pressures. The STO gate dielectric with this nitridation treatment exhibited slightly lower leakage current at an accumulation region and nearly 2 orders of magnitude lower leakage current at an inversion region. The repeated spike heating technique was also employed to deposit a STO gate dielectric at repeated oscillating temperatures. The results show that this thermal treatment reduced the interfacial trap states and the leakage current was also reduced by about 1 order of magnitude at the same EOT. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
77.55.-g Dielectric thin films
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)
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Effect of particle size on magnetic properties of zinc chromite synthesized by sol–gel method

X. H. Chen, H. T. Zhang, C. H. Wang, X. G. Luo, and P. H. Li

Appl. Phys. Lett. 81, 4419 (2002); http://dx.doi.org/10.1063/1.1526921 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2002

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Spinel zinc chromite nanocrystals with various grain sizes ranging from 6.8 to 32 nm have been synthesized using a formalin sol–gel method. Samples were characterized by x-ray diffraction, transmission electron micrograph, and superconducting quantum interference device magnetometer. An effect of particle size on magnetic properties is observed. The decrease in particle size leads to a large enhancement of magnetization. Antiferromagnetic transition disappears when the particles reach a critical size, which can be explained by the deviation from the normal spinel structure in the cation distribution induced by particle size. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ee Antiferromagnetics
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

“Gentle lithography” with benzene on Si(100)

Peter Kruse and Robert A. Wolkow

Appl. Phys. Lett. 81, 4422 (2002); http://dx.doi.org/10.1063/1.1526459 (3 pages) | Cited 15 times

Online Publication Date: 25 November 2002

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A scanning tunneling microscopy (STM) based nanolithographic method has been demonstrated. The previously reported tip-induced desorption of benzene from Si(100) was utilized to pattern the surface with close to atomic precision. This kind of lithography can take place under very mild conditions. Writing occurs with a STM tip bias of 2.8 V. No heating, etching, or exposure to photons is required. The method is best suited for small to medium sized molecules and can be said to be reliable for resolutions of 2 nm and above. In this letter, we have demonstrated patterning areas of the surface with ethylene and vinyl ferrocene. © 2002 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
81.16.Ta Atom manipulation

Cu/SiO2−x nanowires with compositional modulation structure grown via thermal evaporation

Y. G. Wang, A. Z. Jin, and Z. Zhang

Appl. Phys. Lett. 81, 4425 (2002); http://dx.doi.org/10.1063/1.1526453 (3 pages) | Cited 5 times

Online Publication Date: 25 November 2002

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One-dimensional compositional modulation has been achieved in Cu/SiO2−x nanowires prepared at the substrate temperature of 1000 °C by thermal evaporation of a cuprous oxide and silicon mono-oxide mixture. The synthesized nanowires consist of the Cu spheres uniformly piled up along the longitudinal direction of the nanowires to form a modulation structure with an average period of about 140 nm. This periodicity could be adjusted by changing the CuO concentration in the source materials mixture. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Measurement of three-dimensional force fields with atomic resolution using dynamic force spectroscopy

H. Hölscher, S. M. Langkat, A. Schwarz, and R. Wiesendanger

Appl. Phys. Lett. 81, 4428 (2002); http://dx.doi.org/10.1063/1.1525056 (3 pages) | Cited 60 times

Online Publication Date: 25 November 2002

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Using dynamic force microscopy and spectroscopy in an ultrahigh vacuum (“noncontact atomic force microscopy”) at low temperatures, we measured three-dimensional force fields with atomic resolution. The method is based on the systematic recording of the frequency shift of a cantilever oscillating near the sample surface. The presented experimental results were obtained on a NiO(001) sample surface with an iron-coated silicon tip, but the measurement principle can be extended to any tip–sample system. © 2002 American Institute of Physics.
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68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Lh Atomic force microscopes

Fabrication of 70 nm channel length polymer organic thin-film transistors using nanoimprint lithography

Michael D. Austin and Stephen Y. Chou

Appl. Phys. Lett. 81, 4431 (2002); http://dx.doi.org/10.1063/1.1526457 (3 pages) | Cited 108 times

Online Publication Date: 25 November 2002

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We report on the fabrication of short-channel polymer organic thin-film transistors (OTFTs) using nanoimprint lithography. Currently, there is significant interest in OTFTs due to their potential application in inexpensive, large-area electronics. However, polymer carrier mobilities are typically poor, and thus to increase the OTFT drive current per unit area, there is a need for short-channel devices. We have fabricated working devices with channel lengths from 1 μm down to 70 nm with high yields. The performance of these devices was studied as the channel length was reduced. We find that drive current density increases as expected, while the on/off current ratio remains 104. However, at short-channel lengths, OTFTs no longer saturate due to space charge limiting current effects. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Fabrication and thermal stability of arrays of Fe nanodots

Kai Liu, J. Nogués, C. Leighton, H. Masuda, K. Nishio, I. V. Roshchin, and Ivan K. Schuller

Appl. Phys. Lett. 81, 4434 (2002); http://dx.doi.org/10.1063/1.1526458 (3 pages) | Cited 60 times

Online Publication Date: 25 November 2002

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We have fabricated arrays of 60-nm-size magnetic Fe nanodots over a 1-cm2-size area using nanoporous alumina membranes as shadow masks. The size and size distribution of the nanodots correlate very well with that of the membrane pores. By placing an antiferromagnetic FeF2 layer underneath the Fe nanodots, an exchange anisotropy can be introduced into the Fe/FeF2 system. We have observed an increase in the magnetic hysteresis loop squareness in biased nanodots, suggesting that exchange bias may be used as a tunable source of anisotropy to stabilize the magnetization in such nanodots. © 2002 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.Bc Nanocrystalline materials

Fabrication of nanoporous gold nanowires

Chunxin Ji and Peter C. Searson

Appl. Phys. Lett. 81, 4437 (2002); http://dx.doi.org/10.1063/1.1526920 (3 pages) | Cited 53 times

Online Publication Date: 25 November 2002

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We report a method for the fabrication of nanoporous nanowires with high surface area and well-defined pore morphology. The nanoporous nanowires are formed in a two-step process involving electrochemical deposition of a single-phase, two-component AxB1−x alloy into a nanoporous template, and subsequent chemical etching of one component from the alloy after removal from the template. Here, we demonstrate the fabrication of nanoporous gold nanowires and also show that nonporous segments can be incorporated into multisegment nanowires. © 2002 American Institute of Physics.
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81.07.Vb Quantum wires
81.05.Bx Metals, semimetals, and alloys
81.05.Rm Porous materials; granular materials
81.07.Bc Nanocrystalline materials
68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials

Optical characteristics of SiO2 photonic band-gap crystal with ferroelectric perovskite oxide

Bog G. Kim, Kunjal S. Parikh, Geoffrey Ussery, Anvar Zakhidov, Ray H. Baughman, Eli Yablonobitch, and Bruce S. Dunn

Appl. Phys. Lett. 81, 4440 (2002); http://dx.doi.org/10.1063/1.1526163 (3 pages) | Cited 9 times

Online Publication Date: 25 November 2002

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We have made SiO2 photonic band-gap crystal infiltrated with ferroelectric perovskite oxide (BaTiO3, PbTiO3, SrTiO3) by using self-assembly and sol-gel methods. Microscopic optical reflectivity has been measured to characterize pseudogap properties of small single crystallites with different orientations. We have found significant redshift of pseudogap in opal infiltrated with BaTiO3 or PbTiO3, whereas negligible shift in opal with SrTiO3 infiltration. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics

Photon mapping of quantum dots using a scanning tunneling microscope

U. Håkanson, M. K.-J. Johansson, M. Holm, C. Pryor, L. Samuelson, W. Seifert, and M.-E. Pistol

Appl. Phys. Lett. 81, 4443 (2002); http://dx.doi.org/10.1063/1.1527239 (3 pages) | Cited 16 times

Online Publication Date: 25 November 2002

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Scanning tunneling microscopy (STM) and scanning tunneling luminescence (STL) have been used to investigate the geometric and optical properties of individual self-assembled InP quantum dots overgrown with a thin layer of GaInP. STL spectra and monochromatic photon maps were used to correlate the surface topography with the optical properties of single quantum dots. We find a spatial resolution of about 10 nm in the photon maps. Theoretical emission spectra were calculated by six-band k⋅p theory using a realistic shape of the dot as well as of the cap layer. The calculated emission spectrum of a single dot is in good agreement with the experimental findings. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.15.-m Methods of electronic structure calculations

Variation of Raman feature on excitation wavelength in silicon nanowires

Shu-Lin Zhang, Wei Ding, Yan Yan, Jiang Qu, Bibo Li, Le-yu Li, Kwok To Yue, and Dapeng Yu

Appl. Phys. Lett. 81, 4446 (2002); http://dx.doi.org/10.1063/1.1527228 (3 pages) | Cited 20 times

Online Publication Date: 25 November 2002

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A variation of Raman feature on excitation wavelength in silicon nanowires was observed. Based on the quantum size confinement effect, the resonant Raman scattering phenomenon and the existence of different sizes of Si grains in the samples, a plausible mechanism to interpret the novel feature was proposed and supported by experimental facts. © 2002 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials

Spontaneous localization in InAs/GaAs self-assembled quantum-dot molecules

Weidong Sheng and Jean-Pierre Leburton

Appl. Phys. Lett. 81, 4449 (2002); http://dx.doi.org/10.1063/1.1526167 (3 pages) | Cited 23 times

Online Publication Date: 25 November 2002

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Spontaneous localization of hole states is predicted at all separations in vertically stacked InAs/GaAs self-assembled quantum dots. Eight-band k⋅p theory shows that valence band mixing enhanced by the unique three-dimensional strain distribution, subjects holes to very different environment than electrons. As a result, low energy holes are confined to their respective dots without forming bonding or antibonding states. This localization plays the same role as a vertically applied electric field in coupled quantum systems, and substantially decreases the exciton binding energy, which may be an impediment to the formation of entangled states in quantum-dot molecules. © 2002 American Institute of Physics.
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73.21.La Quantum dots
73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations
03.67.Lx Quantum computation architectures and implementations

Spontaneous growth of an InAs nanowire lattice in an InAs/GaSb superlattice

B. Z. Nosho, B. R. Bennett, L. J. Whitman, and M. Goldenberg

Appl. Phys. Lett. 81, 4452 (2002); http://dx.doi.org/10.1063/1.1526164 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2002

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We describe a lattice of InAs nanowires that spontaneously organizes in three dimensions within an InAs/GaSb superlattice grown under high As4 flux. As characterized by x-ray diffraction and cross-sectional scanning tunneling microscopy, the periodic nanowires are ∼10 nm high, 120 nm wide, and many microns long along [110], with face-centered cubic-like vertical ordering within the superlattice. The unusual vertical ordering creates a lateral composition modulation with half the period of the nanowires. The structure appears to arise from the InAs misfit stress combined with specific InAs and GaSb growth kinetic effects. © 2002 American Institute of Physics.
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68.65.Cd Superlattices
81.07.Vb Quantum wires
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Nanomechanical resonant structures in nanocrystalline diamond

L. Sekaric, J. M. Parpia, H. G. Craighead, T. Feygelson, B. H. Houston, and J. E. Butler

Appl. Phys. Lett. 81, 4455 (2002); http://dx.doi.org/10.1063/1.1526941 (3 pages) | Cited 79 times

Online Publication Date: 25 November 2002

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We report the fabrication and the operation of nanomechanical resonant structures in nanocrystalline diamond. For this purpose, continuous diamond films as thin as 80 nm were grown using microwave plasma enhanced chemical vapor deposition. The lateral dimensions of the fabricated structures were as small as 50 nm and the measured mechanical resonant frequencies were up to 640 MHz. The mechanical quality factors were in the range of 2500–3000 at room temperature. The elastic properties of these films obtained via the resonant measurements indicate a Young’s modulus close to that of single-crystal diamond. © 2002 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.U- Carbon/carbon-based materials
62.25.-g Mechanical properties of nanoscale systems
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
62.20.D- Elasticity
07.10.Cm Micromechanical devices and systems

Nanowire resonant tunneling diodes

M. T. Björk, B. J. Ohlsson, C. Thelander, A. I. Persson, K. Deppert, L. R. Wallenberg, and L. Samuelson

Appl. Phys. Lett. 81, 4458 (2002); http://dx.doi.org/10.1063/1.1527995 (3 pages) | Cited 157 times

Online Publication Date: 25 November 2002

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Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures. © 2002 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Surface passivation of n-type crystalline Si by plasma-enhanced-chemical-vapor-deposited amorphous SiCx:H and amorphous SiCxNy:H films

I. Martín, M. Vetter, A. Orpella, C. Voz, J. Puigdollers, and R. Alcubilla

Appl. Phys. Lett. 81, 4461 (2002); http://dx.doi.org/10.1063/1.1527230 (3 pages) | Cited 20 times

Online Publication Date: 25 November 2002

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Excellent passivation of n-type crystalline silicon surface is demonstrated by means of intrinsic amorphous silicon carbide (a-SiCx:H) thin films. An optimum CH4/SiH4 ratio is determined, leading to an effective surface recombination velocity, Seff, lower than 54 cm s−1. By adding a constant flow of N2 to the precursor gases, the surface passivation is improved to Seff ⩽ 16 cm s−1. From infrared spectroscopy measurements of these films, it can be deduced that the N2 flow increases the carbon content of the layers for a constant CH4/SiH4 ratio. The dependence of the effective lifetime, τeff, on the excess charge carrier density, Δn, is measured using the quasisteady-state photoconductance technique, and these curves are simulated through an electrical model based on an insulator/semiconductor structure. © 2002 American Institute of Physics.
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81.65.Rv Passivation
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
78.66.Jg Amorphous semiconductors; glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering
82.80.Dx Analytical methods involving electronic spectroscopy
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