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6 Nov 2000

Volume 77, Issue 19, pp. 2943-3115

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Interface corrugation in GaAs/AlAs (311)A superlattices

A. B. Vorob’ev, A. K. Gutakovsky, V. Ya. Prinz, V. V. Preobrazhenskii, and M. A. Putyato

Appl. Phys. Lett. 77, 2976 (2000); http://dx.doi.org/10.1063/1.1322632 (3 pages) | Cited 5 times

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GaAs/AlAs (311)A superlattices are studied by cross-sectional high-resolution transmission electron microscopy X-HRTEM. An anisotropic relief on GaAs/AlAs (311)A interfaces with a height up to 6 ML is observed, predominantly aligned along the [math33] direction. A strong (up to 12 ML) highly anisotropic modulation of the thickness of the GaAs layers is found, which can explain the in-plane anisotropy of carrier transport previously observed in this system. At the same time, the thickness of the AlAs layers appeared to be nearly constant. The X-HRTEM studies have revealed no 32 Å periodicity of the GaAs/AlAs (311)A interfacial structure, although a distinct (8×1) surface reconstruction of both GaAs and AlAs surfaces was observed by reflection high-energy electron diffraction during growth. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness

Piezoelectric effects in In0.5Ga0.5As self-assembled quantum dots grown on (311)B GaAs substrates

A. Patanè, A. Levin, A. Polimeni, F. Schindler, P. C. Main, L. Eaves, and M. Henini

Appl. Phys. Lett. 77, 2979 (2000); http://dx.doi.org/10.1063/1.1322631 (3 pages) | Cited 29 times

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Photocurrent spectroscopy is used to investigate the quantum-confined Stark shift of In0.5Ga0.5As/GaAs self-assembled quantum dots grown on (100) and (311)B planes. By comparing the Stark shift for dots grown on (100) and (311)B planes, we find that in the (311)B dots, the electron and hole wave functions are displaced by a strain-induced piezoelectric field directed from the apex to the base of the dots. © 2000 American Institute of Physics.
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77.65.Ly Strain-induced piezoelectric fields
78.20.Jq Electro-optical effects
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
77.55.-g Dielectric thin films

Polarized photoluminescence from solid films of nematic and chiral-nematic poly(p-phenylene)s

D. Katsis, H. P. Chen, S. H. Chen, L. J. Rothberg, and T. Tsutsui

Appl. Phys. Lett. 77, 2982 (2000); http://dx.doi.org/10.1063/1.1323548 (3 pages) | Cited 3 times

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Thermotropic nematic and chiral-nematic poly(p-phenylene)s were prepared into well-aligned films between fused-silica substrates in which conjugated backbones were uniaxially and helically oriented. With unpolarized photoexcitation at 350 nm, a nematic film produced a degree of linear polarization of 9 near the emission peak at 410 nm with no evidence of excimer formation. With the same photoexcitation of a chiral-nematic film, the degree of circular polarization was found to vary from −1.3 in the 390–430 nm spectral region to between +0.3 and +0.9 beyond the edge of the selective reflection band. The crossover behavior unique to light emission from the selective reflection region remains inexplicable with existing theories on light propagation through periodically structured films. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
61.30.-v Liquid crystals

Lift-up growth of aligned carbon nanotube patterns

Bingqing Wei, Z. J. Zhang, G. Ramanath, and P. M. Ajayan

Appl. Phys. Lett. 77, 2985 (2000); http://dx.doi.org/10.1063/1.1323544 (3 pages) | Cited 19 times

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The fabrication of three-dimensional networks of carbon nanotubes with controlled orientation will be essential for building large-scale functional devices integrated with microelectronics circuits. We describe here our recent work on the controlled synthesis of vertically aligned carbon-nanotube patterns, grown under patterned metal layers on Si substrates by combining chemical-vapor deposition and conventional lithography. We show that metal patterns are lifted up by vertically aligned nanotubes during growth. This lift-up growth links the thin-film metal patterns and the Si substrate via nanotube assemblies, giving the possibility of creating nanotube architectures in three dimensions. The possible scenarios of the growth of aligned nanotube films leading to the lift up of the metal films are discussed. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Sz Deposition technology
85.40.Hp Lithography, masks and pattern transfer
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Dependence of composition fluctuation on indium content in InGaN/GaN multiple quantum wells

Yen-Sheng Lin, Kung-Jeng Ma, C. Hsu, Shih-Wei Feng, Yung-Chen Cheng, Chi-Chih Liao, C. C. Yang, Chang-Cheng Chou, Chia-Ming Lee, and Jen-Inn Chyi

Appl. Phys. Lett. 77, 2988 (2000); http://dx.doi.org/10.1063/1.1323542 (3 pages) | Cited 90 times

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The information on the variations of indium composition, aggregation size, and quantum-well width is crucially important for understanding the optical properties and, hence, fabricating efficient light-emitting devices. Our results showed that spinodal decomposition could occur in InGaN/GaN multiple quantum wells with indium content in the range of 15%–25% (grown with metal–organic chemical-vapor deposition). A lower nominal indium content led to a better confinement of indium-rich clusters within InGaN quantum wells. The InGaN/GaN interfaces became more diffusive, and indium-rich aggregates extended into GaN barriers with increasing indium content. It was also observed that indium-rich precipitates with diameter ranging from 5 to 12 nm preferred aggregating near V-shaped defects. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.35.Fx Diffusion; interface formation

Oswald ripening and shape transitions of self-assembled PbSe quantum dots on PbTe (111) during annealing

A. Raab and G. Springholz

Appl. Phys. Lett. 77, 2991 (2000); http://dx.doi.org/10.1063/1.1323733 (3 pages) | Cited 26 times

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The thermal stability of faceted self-assembled PbSe quantum dots during annealing is investigated. With increasing annealing time, the dot density is found to decrease rapidly with a simultaneous increase of the average island volumes. In addition, a shape transition from pyramidal islands to truncated pyramids is observed for islands exceeding a critical height of 160 Å. The evolution of island volumes and densities is consistent with Oswald ripening by interface-reaction-limited mass transfer. This is a clear indication that the as-grown islands do not represent an equilibrium structure and that their narrow size dispersion is a purely kinetic effect. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Dv Thermal stability; thermal effects
61.72.Cc Kinetics of defect formation and annealing
68.35.Rh Phase transitions and critical phenomena
68.35.Fx Diffusion; interface formation

Liquid-phase epitaxial growth of amorphous silicon during laser annealing of ultrashallow p+/n junctions

Y. F. Chong, K. L. Pey, Y. F. Lu, A. T. S. Wee, T. Osipowicz, H. L. Seng, A. See, and J.-Y. Dai

Appl. Phys. Lett. 77, 2994 (2000); http://dx.doi.org/10.1063/1.1323549 (3 pages) | Cited 8 times

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We have investigated the effect of laser annealing on the recrystallization of the preamorphized layer during the formation of ultrashallow p+/n junctions. The results from channeling Rutherford backscattering spectrometry clearly indicate that the preamorphized layer has been completely annealed with a single-pulse laser irradiation at 0.5 J/cm2. These data are further verified by high-resolution cross-sectional transmission electron microscopy. It is proposed that the preamorphized layer has recrystallized to a single-crystalline structure via liquid-phase epitaxy. No observable extended defects are present in the recrystallized region after laser annealing. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.43.Dq Amorphous semiconductors, metals, and alloys

Optical study of ZnSexTe1−x alloys using spectroscopic ellipsometry

Hosun Lee, S. M. Kim, B. Y. Seo, E. Z. Seong, S. H. Choi, S. Lee, and J. K. Furdyna

Appl. Phys. Lett. 77, 2997 (2000); http://dx.doi.org/10.1063/1.1323999 (3 pages) | Cited 6 times

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We report pseudodielectric function data 〈ϵ〉 = 〈ϵ1〉+i〈ϵ2〉 of ZnSexTe1−x samples grown on GaAs substrates. The data were obtained from 1.5 to 6.5 eV using spectroscopic ellipsometry. Critical-point parameters were obtained by fitting model line shapes to numerically calculated second-energy derivatives of 〈ϵ〉. The bowing parameters of E0, E1, and E1+Δ1 were determined and were comparable to that of E0 quoted from the literature. We observed a monotonic increase of the linewidth of the E1 gap up to x = 0.85, whereas that of E1+Δ1 showed a maximum value near x = 0.5. We attribute this anomalous broadening of the E1 gap to sample microstructures developed in the low-Te composition alloys. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Robust half metalicity in FexCo1−xS2

I. I. Mazin

Appl. Phys. Lett. 77, 3000 (2000); http://dx.doi.org/10.1063/1.1324720 (3 pages) | Cited 45 times

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The FexCo1−xS2 system is predicted, on the basis of density functional calculations, to be a half metal for a wide concentration range. Unlike most known half metals, the half metalicity in this system is expected to be very stable with respect to crystallographic disorder and other types of defects.
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71.20.Ps Other inorganic compounds
75.10.Lp Band and itinerant models
75.50.Dd Nonmetallic ferromagnetic materials
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.)
75.20.Ck Nonmetals

Implantation of size-selected Si clusters into graphite

R. Neuendorf, R. E. Palmer, and R. Smith

Appl. Phys. Lett. 77, 3003 (2000); http://dx.doi.org/10.1063/1.1324719 (3 pages) | Cited 3 times

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Molecular dynamics simulations have been performed to explore the implantation of silicon clusters into a graphite substrate to well-defined depths. The cluster sizes range from N = 20 up to N = 200 atoms per cluster, deposited with kinetic energies from E = 500 eV up to E = 5000 eV per cluster. We find that the clusters remain intact as coherent, amorphous structures after implantation. The implantation depth is well defined and scales with the kinetic energy of the clusters and the inverse of the cross-sectional area. This indicates a constant decelerating force, associated with the lateral displacement of carbon atoms as the cluster “drills a hole” in the substrate. The main dissipation channels for the energetic silicon clusters are the creation of phonons in the graphite substrate and the breaking of C–C bonds. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.35.Fx Diffusion; interface formation
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.50.Lt Crystal binding; cohesive energy
68.35.Ja Surface and interface dynamics and vibrations
61.43.Bn Structural modeling: serial-addition models, computer simulation

Annihilation of nonradiative defects on hydrogenated silicon surfaces under pulsed-laser irradiation

V. Yu. Timoshenko, Th. Dittrich, F. Koch, B. V. Kamenev, and J. Rappich

Appl. Phys. Lett. 77, 3006 (2000); http://dx.doi.org/10.1063/1.1324723 (3 pages) | Cited 6 times

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Annihilation of nonradiative recombination defects on hydrogenated Si surfaces has been found after irradiation with XeCl laser pulses of energies below the melting threshold. A decrease of the total numbers of the stretched Si–Hx (x = 1,2,3) bonds and an increase of the relative part of the Si–H bonds of the surface coverage have been established simultaneously by Fourier transform infrared spectroscopy. The drop of the number of surface nonradiative defects despite the efficient hydrogen desorption is explained by the mechanism of bonding of Si dangling bonds under the high electronic excitation induced by the XeCl laser pulse. © 2000 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Cn Elemental semiconductors
68.35.Dv Composition, segregation; defects and impurities
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors

Optical properties of a Fabry–Pérot microcavity with Er-doped hydrogenated amorphous silicon active layer

A. A. Dukin, N. A. Feoktistov, V. G. Golubev, A. V. Medvedev, A. B. Pevtsov, and A. V. Sel’kin

Appl. Phys. Lett. 77, 3009 (2000); http://dx.doi.org/10.1063/1.1324725 (3 pages) | Cited 13 times

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Fabry–Pérot hydrogenated amorphous silicon (a-Si:H)/amorphous-SiOx:H microcavities with an erbium-doped a-Si:H active region are fabricated by a plasma-enhanced chemical-vapor deposition technique in a single technological cycle without exposure to air between the intermediate operations. A metalorganic compound is used to incorporate erbium in the active a-Si:H layer. Transmission, reflection, and photoluminescence spectra of the microcavities are measured. The experimental data are compared to theoretical calculations performed in terms of field amplitudes generated by stochastic excitation sources. © 2000 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Ap Elemental semiconductors
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.40.Fy Semiconductors
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors

Effects of high-temperature annealing on the dielectric function of Ta2O5 films observed by spectroscopic ellipsometry

N. V. Nguyen, C. A. Richter, Yong Jai Cho, G. B. Alers, and L. A. Stirling

Appl. Phys. Lett. 77, 3012 (2000); http://dx.doi.org/10.1063/1.1324730 (3 pages) | Cited 15 times

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Postdeposition annealing of high-k dielectric Ta2O5 films to eliminate contaminations can adversely cause the films to crystallize, which can be detrimental to their complementary metal–oxide–semiconductor device performances. In this letter, we will show that spectroscopic ellipsometry can be used to quickly and nondestructively detect such crystallization by identifying the two relatively sharp absorption peaks at 4.7 and 5.2 eV in the complex dielectric function of the films. Such peaks are absent in amorphous Ta2O5 films. In general, these sharp structures in the dielectric function are expected from the presence of long-range order in materials, which produces singularities in their interband density of states. Using this approach, we will show that Ta2O5 films become crystalline when annealed at or above 750 °C and remain amorphous below 700 °C. © 2000 American Institute of Physics.
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78.66.Nk Insulators
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
61.72.Cc Kinetics of defect formation and annealing
68.55.Nq Composition and phase identification
78.40.Ha Other nonmetallic inorganics

Formation of metal nanowires on suspended single-walled carbon nanotubes

Y. Zhang and Hongjie Dai

Appl. Phys. Lett. 77, 3015 (2000); http://dx.doi.org/10.1063/1.1324731 (3 pages) | Cited 167 times

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Suspended single-wall carbon nanotubes are used as substrates for deposition of various metals by evaporation. Deposition of many types of metals normally forms discrete particles on nanotubes due to a weak interaction between the metals and nanotubes. However, continuous nanowires of virtually any metal are obtained by using titanium, a metal with strong interaction with carbon, as a buffer layer on nanotubes. The metal nanowires can be ⩽10 nm wide with continuous length up to tens of microns. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Bx Metals, semimetals, and alloys
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology

Laser ablation and column formation in silicon under oxygen-rich atmospheres

A. J. Pedraza, J. D. Fowlkes, and D. H. Lowndes

Appl. Phys. Lett. 77, 3018 (2000); http://dx.doi.org/10.1063/1.1324732 (3 pages) | Cited 16 times

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The microstructure formed at the surface of silicon by cumulative pulsed-laser irradiation in oxygen-rich atmospheres consists of an array of microcolumns surrounded by microcanyons and microholes. Formation of SiOx at the exposed surface of silicon is most likely responsible for the occurrence of etching/ablation that causes the continuous deepening of canyons and holes. The growth mechanism of columns that is supported by the experimental evidence presented here is a process in which the columns are fed at their tips by the silicon-rich ablation plasma produced during pulsed-laser irradiation. © 2000 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Cy Elemental semiconductors
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