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24 Apr 2000

Volume 76, Issue 17, pp. 2325-2474

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Features of hydrogenated amorphous silicon films developed under an unexplored region of parameter space of radio-frequency plasma-enhanced chemical vapor deposition

Sukti Hazra, A. R. Middya, C. Longeaud, and Swati Ray

Appl. Phys. Lett. 76, 2340 (2000); http://dx.doi.org/10.1063/1.126339 (3 pages) | Cited 4 times

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Searching to improve stability of electronic properties under intense light illumination, hydrogenated amorphous silicon (a-Si:H) films have been fabricated by radio-frequency plasma-enhanced chemical vapor deposition with helium dilution of silane. The deposition conditions which correspond to the transition between the α regime and the powder regime have not been explored properly yet. The resulting materials show many new features: hydrogen bonding mostly monohydride, lower bonded hydrogen content, compact structure, higher efficiency-mobility-lifetime product (ημτ) and density of states (DOS) above Fermi level lower than the reported values of the state-of-the-art a-Si:H films. The saturation time under light-soaking (AM 1) is fast (within 20 h) and the saturated value of ημτ and the DOS above the Fermi level is comparable to that of annealed state standard a-Si:H films. © 2000 American Institute of Physics.
Show PACS
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Repeated crystallization in undercooled Zr41Ti14Cu12Ni10Be23 liquids

Jan Schroers, William L. Johnson, and Ralf Busch

Appl. Phys. Lett. 76, 2343 (2000); http://dx.doi.org/10.1063/1.126340 (3 pages) | Cited 27 times

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Isothermal crystallization studies are performed on Zr41Ti14Cu12Ni10Be23 melts. Undercooling experiments are carried out repeatedly at 907, 860, and 750 K. The scattering of the time to reach the onset of crystallization is investigated. Results from experiments performed at 907 K show a large scatter of the onset time of crystallization. For the experiments carried out at 860 and 750 K, scattering of the onset time is two orders of magnitude smaller. These results indicate that, at high temperatures, the crystallization is governed by the time scale of the statistical nucleation events. At low temperatures, the crystallization is controlled by diffusion, resulting in a well-defined onset time for crystallization. © 2000 American Institute of Physics.
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64.70.D- Solid-liquid transitions
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.10.Fq Growth from melts; zone melting and refining
64.60.Q- Nucleation

Direct synthesis of silicon nanowires, silica nanospheres, and wire-like nanosphere agglomerates

J. L. Gole, J. D. Stout, W. L. Rauch, and Z. L. Wang

Appl. Phys. Lett. 76, 2346 (2000); http://dx.doi.org/10.1063/1.126341 (3 pages) | Cited 79 times

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Elevated temperature synthesis has been used to generate virtually defect free SiO2 sheathed crystalline silicon nanowires and silica (SiO2) nanospheres which can be agglomerated to wire-like configurations impregnated with crystalline silicon. The SiO2 passivated (sheathed) crystalline silicon nanowires, generated with a modified approach using a heated Si–SiO2 mix, with their axes parallel to 〈111〉 are found to be virtually defect free. Modifications to the system allow the simultaneous formation of SiO2 nanospheres (d ∼ 10–30 nm) as virtually monodisperse gram quantity powders which form large surface area catalysts for the selective conversion of ethanol to acetaldehyde. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
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
81.05.Cy Elemental semiconductors
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Manganese surface segregation in NiMnSb

Delia Ristoiu, J. P. Nozières, C. N. Borca, B. Borca, and P. A. Dowben

Appl. Phys. Lett. 76, 2349 (2000); http://dx.doi.org/10.1063/1.126342 (3 pages) | Cited 43 times

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A quantitative analysis of the surface composition of the Heusler alloy NiMnSb has been undertaken using angle-resolved x-ray photoemission spectroscopy and the surface composition characterized. With sufficient annealing cycles, the stoichiometric surface evolves to a surface that is manganese rich. This indicates that the surface enthalpy is different from the bulk for the Heusler alloy NiMnSb. © 2000 American Institute of Physics.
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64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities
81.05.Bx Metals, semimetals, and alloys
65.20.-w Thermal properties of liquids
65.40.gd Entropy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Unusual disparity in electroluminescence and photoluminescence spectra of vacuum-evaporated films of 1,1-bis ((di-4-tolylamino) phenyl) cyclohexane

J. Kalinowski, G. Giro, M. Cocchi, V. Fattori, and P. Di Marco

Appl. Phys. Lett. 76, 2352 (2000); http://dx.doi.org/10.1063/1.126343 (3 pages) | Cited 64 times

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The electroluminescence (EL) and photoluminescence (PL) spectra of thin films of 1,1-bis((di-4-tolyloamino)phenyl) cyclohexane (TAPC) appear to be completely different. Whereas the broad PL spectra reveal major maxima at ≅370 and 450 nm, a strong regular band at 580 nm is characteristic of the EL spectra. It is shown that in contrast to PL, which is composed of molecular exciton (monomer) and excimer emission, EL can be explained by the direct cross recombination transition between electrons and holes trapped on tritolylamine (TTA) subunits of different TAPC molecules. Such a pair of trapped carriers, formed selectively under recombination of statistically independent (here injected at opposite electrodes) electrons and holes, is considered as a particular excited state (“electromer”) responsible also for the EL emission of some other compounds containing TTA or triphenylamine moieties, as for example an amino-substituted triphenylbenzene. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Exciton-related photoluminescence in homoepitaxial GaN of Ga and N polarities

V. Kirilyuk, A. R. A. Zauner, P. C. M. Christianen, J. L. Weyher, P. R. Hageman, and P. K. Larsen

Appl. Phys. Lett. 76, 2355 (2000); http://dx.doi.org/10.1063/1.126344 (3 pages) | Cited 25 times

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A photoluminescence (PL) study of GaN homoepitaxial layers grown by metal–organic chemical-vapor deposition demonstrates the high optical quality of N-face layers deposited on vicinal (000math) GaN substrates. In contrast to broad PL emission in exact (000math) layers, narrow-bound (0.9 meV) and free- (A and B) excitonic transitions are observed. By following the PL spectra as a function of temperature and excitation power, the main optical transitions in the Ga- and the misoriented N-face layers are found to be the same. Observed differences are related to the distinct creation of donor and acceptor states in the samples of different polarities. © 2000 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
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Effect of plasma-induced damage on interfacial reactions of titanium thin films on silicon surfaces

T. Yamaguchi, H. Nikoh, A. Hama, N. Fujimura, and T. Ito

Appl. Phys. Lett. 76, 2358 (2000); http://dx.doi.org/10.1063/1.126345 (3 pages) | Cited 1 time

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Solid-state reactions of titanium thin films on Si surfaces damaged and amorphized by CHF3/O2 plasma treatment were investigated. The formation temperature of the C49–TiSi2 phase increased due to plasma-induced damage and contamination from decomposed gas elements. The presence of a plasma-induced damage layer suppressed the interdiffusion of Ti and Si. The Ti5Si3 phase was formed initially at an annealing temperature of 400 °C when a plasma-induced damage layer was present at the interface. The increase of the C49–TiSi2 formation temperature may be caused by the transformation of the Ti5Si3 phase into C49–TiSi2 rather than by the direct nucleation of the C49–TiSi2 phase with a clean interface. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.65.Cf Surface cleaning, etching, patterning
73.40.Ns Metal-nonmetal contacts
61.80.Jh Ion radiation effects

Narrow photoluminescence peaks from localized states in InGaN quantum dot structures

Osamu Moriwaki, Takao Someya, Koichi Tachibana, Satomi Ishida, and Yasuhiko Arakawa

Appl. Phys. Lett. 76, 2361 (2000); http://dx.doi.org/10.1063/1.126346 (3 pages) | Cited 69 times

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Microscopic photoluminescence spectra were measured for self-assembled InGaN quantum dots (QDs) grown by metalorganic chemical vapor deposition. A thin aluminum layer with 400 nm square apertures was formed on the sample surface to reduce the number of QDs measured. We observed very sharp peaks whose spectral linewidths were typically 170 μeV at 3.5 K, the linewidth being limited by spectral resolution. Such sharp lines were not observed in similar experiments on a reference sample having single InGaN quantum well structure. These experimental results suggest that excitons are strongly confined in our InGaN QD structure. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Long-term thermal stability of Ti/Al/Pt/Au Ohmic contacts to n-type GaN

Ching-Ting Lee and Hsiao-Wei Kao

Appl. Phys. Lett. 76, 2364 (2000); http://dx.doi.org/10.1063/1.126347 (3 pages) | Cited 78 times

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We present a study of the long-term thermal stability and low specific contact resistance of Ti/Al/Pt/Au multilayer contacts to n-type GaN. The Ohmic performance can be maintained up to 60 and 540 min for thermal annealing at 950 and 850 °C, respectively, and even longer than 600 min for thermal annealing at 750 °C. By comparing the specific contact resistances for Ti/Al/Pt/Au and Ti/Al/Au Ohmic contacts to n-type GaN, the long-term thermal stability may be deduced as due to the contribution of the Pt barrier for preventing Au penetration. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
73.61.Ey III-V semiconductors
68.60.Dv Thermal stability; thermal effects

Controlling the diameter, growth rate, and density of vertically aligned carbon nanotubes synthesized by microwave plasma-enhanced chemical vapor deposition

Young Chul Choi, Young Min Shin, Young Hee Lee, Byung Soo Lee, Gyeong-Su Park, Won Bong Choi, Nae Sung Lee, and Jong Min Kim

Appl. Phys. Lett. 76, 2367 (2000); http://dx.doi.org/10.1063/1.126348 (3 pages) | Cited 97 times

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Vertically aligned carbon nanotubes were synthesized on Ni-deposited Si substrates using microwave plasma-enhanced chemical vapor deposition. The grain size of Ni thin films varied with the rf power density during the rf magnetron sputtering process. We found that the diameter, growth rate, and density of carbon nanotubes could be controlled systematically by the grain size of Ni thin films. With decreasing the grain size of Ni thin films, the diameter of the nanotubes decreased, whereas the growth rate and density increased. High-resolution transmission electron microscope images clearly demonstrated synthesized nanotubes to be multiwalled. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Mechanically induced Si layer transfer in hydrogen-implanted Si wafers

K. Henttinen, I. Suni, and S. S. Lau

Appl. Phys. Lett. 76, 2370 (2000); http://dx.doi.org/10.1063/1.126349 (3 pages) | Cited 23 times

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Show Abstract
Mechanically induced layer transfer of single-crystal silicon by hydrogen ion implantation, low-temperature wafer bonding, and subsequent mechanical splitting of the implanted wafer has been investigated. The bond strength measurements using the crack opening method in room environment yield a surface energy of ≥ 2000 mJ/m2 after exposure to oxygen plasma and subsequent hydrophilic silicon/silicon dioxide bonding at 200 °C. Mechanically induced layer transfer was carried out for silicon wafers implanted to a dose of 5×1016 H2/cm2 at 100 keV and annealed for 2 h at 200 °C. No feature was observed by atomic force microscopy (AFM) measurements on the unbonded free surface after this heat treatment. For lower doses of implantation, annealing at higher temperatures is required to enable the mechanical transfer. AFM measurements on the split silicon surface indicate that low-temperature wafer bonding and mechanical transfer yield a root mean square surface roughness of 4 nm which is less than in the standard Smart-Cut® process. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.65.-b Surface treatments
68.35.Md Surface thermodynamics, surface energies
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)

Low temperature deposition of nanocrystalline silicon carbide thin films

S. Kerdiles, A. Berthelot, F. Gourbilleau, and R. Rizk

Appl. Phys. Lett. 76, 2373 (2000); http://dx.doi.org/10.1063/1.126350 (3 pages) | Cited 36 times

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Silicon carbide thin films have been deposited by reactive magnetron sputtering in a pure hydrogen plasma at substrate temperatures, Ts, ranging between 100 and 600 °C. The infrared (IR) absorption spectra and the transmission electron microscopy observations reveal an onset of crystallization at Ts as low as 300 °C. The crystalline fraction increases with Ts and reaches a value of about 60% for Ts = 600 °C. Both refractive index n and room temperature dark conductivity σd(RT) show quite consistent behaviors with the structural evolution of the layers. Thus n increases from 1.9 to 2.4 and σd(RT) improves by six orders of magnitude when Ts is raised from 100 to 600 °C. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
73.50.Pz Photoconduction and photovoltaic effects
73.61.Le Other inorganic semiconductors

Experimental and theoretical scaling laws for transverse diffusive broadening in two-phase laminar flows in microchannels

Rustem F. Ismagilov, Abraham D. Stroock, Paul J. A. Kenis, George Whitesides, and Howard A. Stone

Appl. Phys. Lett. 76, 2376 (2000); http://dx.doi.org/10.1063/1.126351 (3 pages) | Cited 164 times

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This letter quantifies both experimentally and theoretically the diffusion of low-molecular-weight species across the interface between two aqueous solutions in pressure-driven laminar flow in microchannels at high Péclet numbers. Confocal fluorescent microscopy was used to visualize a fluorescent product formed by reaction between chemical species carried separately by the two solutions. At steady state, the width of the reaction–diffusion zone at the interface adjacent to the wall of the channel and transverse to the direction of flow scales as the one-third power of both the axial distance down the channel (from the point where the two streams join) and the average velocity of the flow, instead of the more familiar one-half power scaling which was measured in the middle of the channel. A quantitative description of reaction–diffusion processes near the walls of the channel, such as described in this letter, is required for the rational use of laminar flows for performing spatially resolved surface chemistry and biology inside microchannels and for understanding three-dimensional features of mass transport in shearing flows near surfaces. © 2000 American Institute of Physics.
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47.55.Kf Particle-laden flows
47.70.Fw Chemically reactive flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.15.-x Laminar flows
47.80.-v Instrumentation and measurement methods in fluid dynamics
07.60.Pb Conventional optical microscopes
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.45.-a Nonlinear dynamics and chaos
05.60.-k Transport processes
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