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12 Mar 2001

Volume 78, Issue 11, pp. 1463-1639

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Enhancing the active lifetime of luminescent semiconducting polymers via doping with metal nanoshells

G. D. Hale, J. B. Jackson, O. E. Shmakova, T. R. Lee, and N. J. Halas

Appl. Phys. Lett. 78, 1502 (2001); http://dx.doi.org/10.1063/1.1343854 (3 pages) | Cited 29 times

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We report a dramatic, concentration-dependent decrease in the rate of photo-oxidation of semiconducting polymers due to the addition of small amounts of metal nanoshells to the polymer. In each case, the nanoshell resonances are tuned to the triplet exciton-ground state energy of the polymer. The nanoshell dopants slow the oxidation rate yet do not affect the photoluminescent properties of the polymers to which they have been added. © 2001 American Institute of Physics.
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61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
71.20.Rv Polymers and organic compounds
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
82.35.Cd Conducting polymers
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
82.50.-m Photochemistry
82.20.Pm Rate constants, reaction cross sections, and activation energies
71.35.-y Excitons and related phenomena
78.55.Kz Solid organic materials
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
81.07.Bc Nanocrystalline materials
71.55.Ht Other nonmetals

Doping by metal-mediated epitaxy: Growth of As delta-doped Si through a Pb monolayer

O. D. Dubon, P. G. Evans, J. F. Chervinsky, M. J. Aziz, F. Spaepen, J. A. Golovchenko, M. F. Chisholm, and D. A. Muller

Appl. Phys. Lett. 78, 1505 (2001); http://dx.doi.org/10.1063/1.1352692 (3 pages) | Cited 5 times

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In molecular-beam epitaxy a monolayer of Pb on the Si(111) surface induces single-crystal growth at temperatures well below those required for similar growth on a bare surface. We demonstrate that the suppression of dopant segregation at the lower temperatures attainable by Pb-mediated growth allows the incorporation of As donors at concentrations reaching a few atomic percent. When Pb and Si are deposited on an As-terminated Si(111) substrate at 350 °C, the Pb segregates to the surface without doping the Si film while the As is buried within nanometers of the substrate–film interface. The resulting concentration of electrically active As, 1.8×1021 cm−3, represents the highest concentration of As donors achieved by any delta-doping or thin-film deposition method. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
68.35.Dv Composition, segregation; defects and impurities
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
85.40.Ry Impurity doping, diffusion and ion implantation technology

Near-field photoluminescence study of GaNAs alloy epilayer at room and cryogenic temperature

K. Matsuda, T. Saiki, M. Takahashi, A. Moto, and S. Takagishi

Appl. Phys. Lett. 78, 1508 (2001); http://dx.doi.org/10.1063/1.1353815 (3 pages) | Cited 27 times

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We have measured the spatial distribution of the optical properties of a GaNAs (N∼0.8%) epilayer to investigate the carrier recombination mechanism at both room temperature and cryogenic temperature using a near-field scanning optical microscope. A difference between the macro and near-field photoluminescence (PL) spectra at room temperature was not observed. At low temperature, we found spatial inhomogeneity of the optical properties and sharp features in the near-field PL spectrum. These findings indicate that the dominant emission mechanism changes from recombination of delocalized carriers at room temperature to recombination of localized carriers (excitons) trapped in the local potential minimum due to compositional fluctuation at low temperature. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors

Epitaxial growth of ZnO films on Si substrates using an epitaxial GaN buffer

Ahmed Nahhas, Hong Koo Kim, and Jean Blachere

Appl. Phys. Lett. 78, 1511 (2001); http://dx.doi.org/10.1063/1.1355296 (3 pages) | Cited 49 times

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We report on epitaxial growth of ZnO films on Si(111) substrates using an epitaxial GaN buffer layer. A rf magnetron sputtering process has been developed and utilized in growing epitaxial GaN buffers on Si, and then ZnO films on the GaN-buffered Si substrates. X-ray diffraction analysis shows that both the ZnO and GaN films are of a monocrystalline wurtzite structure with an epitaxial relationship of ZnO[0001]//GaN[0001]//Si[111] along the growth direction and ZnO[11math01]//GaN[11math0]//Si[1math0] along the in-plane direction. The successful growth of epitaxial ZnO/GaN films on Si demonstrates the feasibility and promise of integrating various functional devices on the same substrate. © 2001 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Simulation of the transformation from the C49 to the C54 phase of TiSi2 in blanket films and narrow conductors

S. Privitera, C. Spinella, F. La Via, M. G. Grimaldi, and E. Rimini

Appl. Phys. Lett. 78, 1514 (2001); http://dx.doi.org/10.1063/1.1354669 (3 pages) | Cited 2 times

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The C49–C54 phase transition has been simulated by Monte–Carlo calculations in blanket films and conductors using a unitary model based on transient nucleation and growth which takes into account the temperature dependence of the nucleation parameters. The output of the model has been compared with experimental data from electrical measurements in blanket films and 0.5 μm wide conductors. The comparison allows us to determine the density of available nucleation sites and to interpret the spread of experimental data, observed in the case of lines, as fluctuations in the number of sites and in their random location. © 2001 American Institute of Physics.
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64.70.K- Solid-solid transitions
64.60.Q- Nucleation
68.55.A- Nucleation and growth
85.40.Ls Metallization, contacts, interconnects; device isolation
02.70.Uu Applications of Monte Carlo methods
73.61.At Metal and metallic alloys

Study of ultrathin Al2O3/Si(001) interfaces by using scanning reflection electron microscopy and x-ray photoelectron spectroscopy

Manisha Kundu, Noriyuki Miyata, and Masakazu Ichikawa

Appl. Phys. Lett. 78, 1517 (2001); http://dx.doi.org/10.1063/1.1355294 (3 pages) | Cited 27 times

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Al2O3/Si(001) interfaces were investigated using scanning reflection electron microscopy and x-ray photoelectron spectroscopy. A uniform and stoichiometric ultrathin Al2O3 film of ∼0.6 nm was grown on an atomically flat Si(001)-2×1 surface, and the resulting Al2O3/Si(001) interface was atomically abrupt. Furthermore, an intentional high-pressure oxidation shows that we can grow Si oxide at the Al2O3/Si(001) interface with atomic-scale uniformity as this oxidation proceeds in a layer-by-layer manner. The resulting Si oxide/Si(001) interface was also atomically abrupt. In addition, the rate of oxidation of Si at the Al2O3/Si(001) interface depends strongly on the O2 pressure. © 2001 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
81.65.Mq Oxidation
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
79.60.Jv Interfaces; heterostructures; nanostructures

Atomic resolution structure of growth and etching patterns at the surface of microwave plasma chemical vapor deposited diamond films

P. B. Lukins, M. H. Zareie, and J. Khachan

Appl. Phys. Lett. 78, 1520 (2001); http://dx.doi.org/10.1063/1.1352046 (3 pages) | Cited 3 times

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Scanning tunneling microscopy and spectroscopy of microwave chemical vapor deposited diamond films prepared using a methane/hydrogen gas mixture indicates that the predominant diamond surface structure is (001) 1×1: 2H with a wide variety of facet shapes and orientations, and that the film surface is diamond-like and semiconductive but with a surface band gap (∼1.1 eV) that is smaller than the band gap of normal bulk diamond. Significant differences are observed in the electronic properties, resolution, and contrast between newly deposited surface carbon atoms and those bound in the underlying lattice. The composition of the deposition gas mixture is important in determining both the crystal structure and the type of bond termination at the surface. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.U- Carbon/carbon-based materials
68.55.A- Nucleation and growth
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states

Magneto-optical properties of a GaAs:MnAs hybrid structure sandwiched by GaAs/AlAs distributed Bragg reflectors: Enhanced magneto-optical effect and theoretical analysis

H. Shimizu, M. Miyamura, and M. Tanaka

Appl. Phys. Lett. 78, 1523 (2001); http://dx.doi.org/10.1063/1.1354657 (3 pages) | Cited 27 times

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We have fabricated a multilayer structure consisting of a semiconductor-magnetic hybrid material GaAs:MnAs and GaAs/AlAs distributed Bragg reflectors, that is a one-dimensional semiconductor-based magnetophotonic crystal. Significant enhancement of magneto-optical effect was demonstrated at a controlled wavelength at room temperature. Magneto-optical spectra of this multilayer system were well explained by theoretical calculations, and the mechanism for the enhancement of magneto-optical effect was shown. Also, the required conditions for application to optical isolators are discussed and some potential solutions are indicated. Since our structure is composed of all semiconductor-based materials, the present results potentially lead to semiconductor based magneto-optical devices integrated with III–V-based optoelectronics. © 2001 American Institute of Physics.
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78.20.Ls Magneto-optical effects
85.70.Sq Magnetooptical devices
42.79.Wc Optical coatings
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.30.Fs III-V and II-VI semiconductors
75.50.Pp Magnetic semiconductors

Strain and composition dependence of the E1(TO) mode in hexagonal Al1−xInxN thin films

A. Kasic, M. Schubert, J. Off, and F. Scholz

Appl. Phys. Lett. 78, 1526 (2001); http://dx.doi.org/10.1063/1.1355010 (3 pages) | Cited 15 times

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Infrared spectroscopic ellipsometry is used to study the influence of strain and composition on the transverse-optical phonon mode of E1 symmetry in hexagonal Al1−xInxN films for 0.12 ⩽ x ⩽ 0.21. The 0.1–0.2-μm thick films were grown on slightly compressively strained hexagonal GaN buffer layers, or directly on [0001] sapphire by metalorganic vapor phase epitaxy. The Al1−xInxN E1(TO) phonon shows a one-mode behavior in contrast to recent theoretical predictions [H. Grille, C. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Films grown on GaN reveal the influence of strain on the phonon mode frequencies due to pseudomorphic film growth. Al1−xInxN deposited directly on sapphire possesses phonon modes which indicate fully relaxed film growth. © 2001 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties

V-shaped defects connected to inversion domains in AlGaN layers

B. Pécz, Zs. Makkai, M. A. di Forte-Poisson, F. Huet, and R. E. Dunin-Borkowski

Appl. Phys. Lett. 78, 1529 (2001); http://dx.doi.org/10.1063/1.1355996 (3 pages) | Cited 18 times

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Thick AlGaN layers and AlGaN/GaN superlattices have been grown on GaN using metalorganic chemical vapor deposition. Cross-sectional transmission electron microscopy has been used to show that V-shaped surface pits on these samples differ from similar features observed in the InGaN system. Inversion domains and segregated Al are found in the middle of each V pit, and superlattice layers are observed to follow the pit sidewalls. © 2001 American Institute of Physics.
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68.65.Cd Superlattices
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Spontaneous formation of horizontal chevrons in smectic-C∗ liquid crystals

G. Strangi, D. A. Coleman, J. E. Maclennan, M. Copic, and N. A. Clark

Appl. Phys. Lett. 78, 1532 (2001); http://dx.doi.org/10.1063/1.1352661 (3 pages) | Cited 3 times

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We report an unusual structural formation observed in surface-stabilized ferroelectric liquid crystal cells with asymmetrically treated surfaces of 3-Glycidoxypropyl trimethoxysilane and nylon. On cooling the material W415 from the smectic-A∗ to the smectic-C∗ phase, the bookshelf smectic layers spontaneously rearrange to form a horizontal chevron structure, manifested optically as a periodic texture of uniform stripes. The polarization is perpendicular to the boundary plates and reverses direction from stripe to stripe, while the director is oriented in the plane of the cell and alternates symmetrically about the stripe direction. In an applied field the cells show a V-shaped (analog) electro-optic response. © 2001 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.70.Df Liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
78.20.Jq Electro-optical effects
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena

Co cluster coalescence behavior observed by electrical conduction and transmission electron microscopy

D. L. Peng, T. J. Konno, K. Wakoh, T. Hihara, and K. Sumiyama

Appl. Phys. Lett. 78, 1535 (2001); http://dx.doi.org/10.1063/1.1354158 (3 pages) | Cited 13 times

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We deposited monodispersed Co clusters with mean diameters d = 6, 8.5, and 13 nm on quartz and microgrid substrates using a plasma-gas-condensation-type cluster beam deposition system. The cluster–cluster coalescence behavior of the Co cluster assemblies was investigated by in situ electrical conductivity measurements and ex situ transmission electron microscopy (TEM). The electrical conductivity measurement indicates that, below temperature T ≈ 100 °C, the Co clusters with d = 8.5 nm maintain their original size as deposited at room temperature, while the cluster–cluster coalescence takes place at their interface at T>100 °C. The TEM observation indicates that the morphology of the cluster distribution shows no marked change at substrate temperatures Ts<250 °C. Above Ts = 300 °C, the interfacial area of coalesced clusters is crystalline, and has its own orientation, different from that of two connected cluster cores. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Effects of GaAlN barriers and of dimensionality on optical recombination processes in InGaN quantum wells and quantum boxes

P. Lefebvre, T. Taliercio, A. Morel, J. Allègre, M. Gallart, B. Gil, H. Mathieu, B. Damilano, N. Grandjean, and J. Massies

Appl. Phys. Lett. 78, 1538 (2001); http://dx.doi.org/10.1063/1.1352664 (3 pages) | Cited 34 times

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We compare several InGaN-based low-dimensional systems, by time-resolved photoluminescence (PL), versus temperature (8<T<280 K). We investigate the influence of growing or not an AlGaN barrier on top of the active layer. We address the differences between quantum wells and quantum boxes 5–10 nm in diameter and 2 nm in height. Our results are consistent with carrier localization on potential fluctuations with spatial extension much smaller than the size of the quantum boxes. Growing an AlGaN barrier reduces the carrier mobility between fluctuations, thus maintaining an effective PL dominated by localized carriers up to room temperature. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
68.65.Hb Quantum dots (patterned in quantum wells)
78.47.-p Spectroscopy of solid state dynamics

High-resolution spectral hole burning in CdSe/ZnS core/shell nanocrystals

Phedon Palinginis and Hailin Wang

Appl. Phys. Lett. 78, 1541 (2001); http://dx.doi.org/10.1063/1.1355666 (3 pages) | Cited 27 times

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We report studies of the homogeneous linewidth in CdSe/ZnS core/shell nanocrystals by means of high-resolution spectral hole burning under low excitation levels. The hole burning spectrum reveals a sharp spectral hole as well as clearly resolved acoustic phonon sidebands. Homogeneous linewidths as narrow as 32 μeV were obtained. At low temperature, the temperature dependence of the homogeneous linewidth deviates from the usual linear dependence, reflecting the effects of phonon quantization. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
61.46.-w Structure of nanoscale materials

Origins of threading dislocations in GaN epitaxial layers grown on sapphire by metalorganic chemical vapor deposition

V. Narayanan, K. Lorenz, Wook Kim, and S. Mahajan

Appl. Phys. Lett. 78, 1544 (2001); http://dx.doi.org/10.1063/1.1352699 (3 pages) | Cited 37 times

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The origins of threading dislocations (TDs) in GaN epitaxial layers grown on (0001) sapphire have been investigated by examining different stages of high-temperature (HT) GaN growth on low-temperature GaN nucleation layers (NLs) by transmission electron microscopy. Results indicate that after 20 s of HT growth, GaN islands were free of TDs. After 75 and 120 s of growth, most of the islands contained pure screw (c type) and pure edge (a type) TDs with an interspersion of mixed (c+a type) TDs. Most of the TDs originated from faulted regions located within NLs. TDs move toward the island top surface (c type) or curve toward island side facets (a, c+a type). Coalescence of HT GaN islands did not give rise to either a, c, or c+a type TDs. After 240 s of growth, most TDs were predominantly of a type and could result from climb and glide of basal plane (BP) dislocations that form by the dissociation of Shockley partials located within the faulted regions. BP dislocations are also observed attached to the side facets of islands away from the faulted regions and their possible origins are discussed. c and c+a type TDs form primarily by the coalescence of Frank partials near the GaN/sapphire interface. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
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