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31 Oct 2005

Volume 87, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 183103 (2005); http://dx.doi.org/10.1063/1.2126118 (3 pages)

X. M. Cai, A. B. Djurišić, M. H. Xie, C. S. Chiu, and S. Gwo
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High-performance operation of single-mode terahertz quantum cascade lasers with metallic gratings

Lukas Mahler, Alessandro Tredicucci, Rüdeger Köhler, Fabio Beltram, Harvey E. Beere, Edmund H. Linfield, and David A. Ritchie

Appl. Phys. Lett. 87, 181101 (2005); http://dx.doi.org/10.1063/1.2120901 (3 pages) | Cited 31 times

Online Publication Date: 24 October 2005

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A periodic array of thin slits opened on a metallic surface can act as a one-dimensional photonic crystal for the propagation of surface-plasmon waves. We have used such structure for the implementation of distributed feedback resonators in quantum cascade lasers emitting near 2.5 THz. Single-mode emission, stable at all injection currents and operating temperatures, was achieved both in pulsed and continuous wave. The devices exhibited output powers of several milliwatts with low threshold current densities of ∼ 100 A/cm2.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.79.Dj Gratings
42.70.Qs Photonic bandgap materials
78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Bistable lasing in twin microdisk photonic molecules

Satoru Ishii and Toshihiko Baba

Appl. Phys. Lett. 87, 181102 (2005); http://dx.doi.org/10.1063/1.2120906 (3 pages) | Cited 18 times

Online Publication Date: 24 October 2005

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We demonstrate the bistable lasing in a photonic molecule consisting of twin microdisks. When the photonic molecule was nonuniformly photopumped, the bistability and/or mode switching were observed with an effective pump power of <100 μW. The rate equation analysis indicated that the operation was based on saturable absorption and gain switching, which depended on the nonuniformity, disk diameter detuning, and Q factors of coupled modes. Such a bistable laser, particularly showing the mode switching, will be applied for ultrasmall high-speed optical memories, flip-flops, and so on.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Observation of the interferences between the emitted beams in a 4Pi microscope by partial coherence interferometry

N. Sandeau, H. Giovannini, P.-F. Lenne, and H. Rigneault

Appl. Phys. Lett. 87, 181103 (2005); http://dx.doi.org/10.1063/1.2120908 (2 pages)

Online Publication Date: 24 October 2005

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We propose a modified 4Pi microscope setup for observing solely the interference resulting from the superposition of the beams emitted by fluorescent species placed between two microscope objectives. A scanning Michelson interferometer is coupled to the 4Pi microscope. Interferences between the beams emitted by fluorophores deposited on a cover glass are observed, thanks to partial coherence interferometry technique.
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07.60.Pb Conventional optical microscopes
07.60.Ly Interferometers

Subpicosecond saturation of intersubband absorption in (CdS/ZnSe)/BeTe quantum-well waveguides at telecommunication wavelength

R. Akimoto, B. S. Li, K. Akita, and T. Hasama

Appl. Phys. Lett. 87, 181104 (2005); http://dx.doi.org/10.1063/1.2123379 (3 pages) | Cited 24 times

Online Publication Date: 25 October 2005

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Ultrafast all-optical switching at an optical communication wavelength has been investigated by utilizing an intersubband transition (ISBT) of II–VI-based multiple quantum wells (MQWs) fabricated in high-mesa waveguide devices. The waveguide structure consists of a CdS/ZnSe/BeTe MQW core layer and two top and bottom ZnMgBeSe quaternary cladding layers grown by molecular beam epitaxy on a (001) GaAs substrate. A marked increase in waveguide transmittance was observed only for transverse-magnetic-polarized subpicosecond pulse with increasing incident pulse energy at λ = 1.57 μm, indicative of the ISBT absorption saturation. The pulse energy necessary for a 10 dB transmittance increase is as low as 13.3 pJ for a waveguide device with 2.7 μm mesa, and the saturation pulse energy can be even further reduced by employing a narrower mesa structure. Ultrafast gate switching within a time window of 0.56 ps was also demonstrated with pump pulse at λ = 1.57 μm and probe pulse at λ = 1.63 μm in this waveguide device.
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42.79.Gn Optical waveguides and couplers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Wi Nonlinear waveguides
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Diffusion-controlled optical elements for optofluidics

Daniel B. Wolfe, Dmitri V. Vezenov, Brian T. Mayers, George M. Whitesides, Richard S. Conroy, and Mara G. Prentiss

Appl. Phys. Lett. 87, 181105 (2005); http://dx.doi.org/10.1063/1.2119412 (3 pages) | Cited 26 times

Online Publication Date: 26 October 2005

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Diffusion at the interface between two streams of liquids with different refractive indices, flowing laminarly, creates a controllable concentration gradient and a corresponding refractive index gradient. Using flow rate to change the time over which diffusion occurs in a liquid-liquid (L2) optical waveguide, we demonstrate an optical splitter and a wavelength filter. The optical splitter comprises two parallel L2 waveguides which smoothly merge into a single L2 waveguide by diffusion. The wavelength filter comprises an optical splitter in which the two L2 waveguides contain an absorbing dye.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Gn Optical waveguides and couplers
42.79.Ci Filters, zone plates, and polarizers
42.79.Fm Reflectors, beam splitters, and deflectors
66.10.C- Diffusion and thermal diffusion
47.15.-x Laminar flows
47.85.Np Fluidics

Line-defect-induced bending and splitting of self-collimated beams in two-dimensional photonic crystals

Sun-Goo Lee, Sang Soon Oh, Jae-Eun Kim, Hae Yong Park, and Chul-Sik Kee

Appl. Phys. Lett. 87, 181106 (2005); http://dx.doi.org/10.1063/1.2112186 (3 pages) | Cited 31 times

Online Publication Date: 26 October 2005

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We show that line defects can give rise to the bending and splitting of self-collimated beams in two-dimensional photonic crystals from the equifrequency contour calculations and the finite-difference time-domain simulations. The power ratio between two split self-collimated beams can be controlled systematically by varying the radii of rods or holes in the line defect. We also show that the bending and controllable splitting of self-collimated beams can be useful in steering the flow of light in photonic crystal integrated light circuits.
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42.70.Qs Photonic bandgap materials
42.25.Gy Edge and boundary effects; reflection and refraction
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

High-performance GaN-based light-emitting diode using high-transparency Ni/Au/Al-doped ZnO composite contacts

Sung-Pyo Jung, Denise Ullery, Chien-Hung Lin, Henry P. Lee, Jae-Hong Lim, Dae-Kue Hwang, Ja-Yeon Kim, Eun-Jeong Yang, and Seong-Ju Park

Appl. Phys. Lett. 87, 181107 (2005); http://dx.doi.org/10.1063/1.2120913 (3 pages) | Cited 11 times

Online Publication Date: 26 October 2005

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We report on a high-transparency low-resistance composite contact structure on p-GaN for light-emitting diode applications. The structure consists of a thin Ni (5 nm)/Au (5 nm) layer overcoated with a sputtered Al-doped ZnO (170 nm) layer. Enhancement in light emission intensity as high as 74% at 40 mA and forward operating voltages in the range of 3.36–3.48 V at 20 mA are obtained for these devices using a two-step thermal annealing process.
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85.60.Jb Light-emitting devices
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing

Dynamics of a high-Q vertical-cavity organic laser

M. Koschorreck, R. Gehlhaar, V. G. Lyssenko, M. Swoboda, M. Hoffmann, and K. Leo

Appl. Phys. Lett. 87, 181108 (2005); http://dx.doi.org/10.1063/1.2125128 (3 pages) | Cited 25 times

Online Publication Date: 27 October 2005

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We investigate the dynamics of the organic laser guest-host composite of tris-(8-hydroxy quinoline) aluminium and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran embedded in a high-Q (Q ≈ 4500) double distributed Bragg reflector microcavity using subpicosecond up-conversion techniques. Lasing is observed at a threshold of 0.4 nJ/20 μJ cm−2 with a linewidth of 0.05 nm (resolution limit). We observe a strongly nonlinear intensity-dependent delay of the emitted radiation burst. All experimental results are successfully modeled by a set of nonlinear rate equations, emphasizing the importance of a feedback mechanism for lasing.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Controlled transition between parametric and Raman oscillations in ultrahigh-Q silica toroidal microcavities

Bumki Min, Lan Yang, and Kerry Vahala

Appl. Phys. Lett. 87, 181109 (2005); http://dx.doi.org/10.1063/1.2120921 (3 pages) | Cited 6 times

Online Publication Date: 28 October 2005

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A controllable and reversible transition between parametric and Raman oscillations in an ultrahigh-Q silica toroidal microcavity is experimentally demonstrated and theoretically analyzed. By direct change of cavity loading and indirect adjustment of frequency detuning, parametric and/or Raman oscillation can be accessed selectively without modification of cavity geometry in a toroidal microcavity with a large enough aspect ratio. Based on an effective cavity gain theory, this transition is analyzed in terms of cavity loading and frequency detuning leading to a better understanding of the combined effects of parametric and Raman processes in silica microcavities.
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42.65.Yj Optical parametric oscillators and amplifiers
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.79.-e Optical elements, devices, and systems
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Enhancement of microarcing at a grounded chamber wall by nonvanishing ion sheath in a radio-frequency capacitive discharged plasma

Dixon T. K. Kwok, Yongbai Yin, Marcela M. M. Bilek, and David McKenzie

Appl. Phys. Lett. 87, 181501 (2005); http://dx.doi.org/10.1063/1.2126126 (3 pages) | Cited 5 times

Online Publication Date: 27 October 2005

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One-dimensional hybrid particle-in-cell simulations in cylindrical r coordinate, with particle ions and Boltzmann’s distribution of electrons, are used to investigate the arcing effect in radio-frequency (rf) capacitively coupled discharged plasma. The simulation shows that the arcing at the chamber wall is enhanced by the nonvanishing ion sheath at the surface, such that the emission electrons current will last for several tens of rf cycles. On the other hand, at the inner electrode, the electron emission occurs only during certain phases of the rf cycle and does not promote arc growth.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.40.Hf Plasma-material interactions; boundary layer effects
52.40.Kh Plasma sheaths
52.80.Pi High-frequency and RF discharges
52.65.Rr Particle-in-cell method
52.25.Fi Transport properties
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Pressure-induced structural phase transition in CaCrO4: Evidence from Raman scattering studies

Y. W. Long, W. W. Zhang, L. X. Yang, Y. Yu, R. C. Yu, S. Ding, Y. L. Liu, and C. Q. Jin

Appl. Phys. Lett. 87, 181901 (2005); http://dx.doi.org/10.1063/1.2117624 (3 pages) | Cited 12 times

Online Publication Date: 24 October 2005

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Raman spectroscopic studies have been carried out on CaCrO4 under pressure up to 26.2 GPa at ambient temperature. The Raman spectra showed that CaCrO4 underwent a continuous structural phase transition started near 6 GPa, and finished at about 10 GPa. It was found that the high-pressure phase could be quenched to ambient conditions. Pressure dependence of the Raman peaks suggested that there existed four pressure regions related to different structural characters. We discussed these characters and inferred that the nonreversible structural transition in CaCrO4, most likely was from a zircon-type (I41/amd) ambient phase to a scheelite-type high-pressure structure (I41/a).
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics

Improved GaN layer morphology by hydride vapor phase epitaxy on misoriented Al2O3 wafers

Ferdinand Scholz, Peter Brückner, Frank Habel, Matthias Peter, and Klaus Köhler

Appl. Phys. Lett. 87, 181902 (2005); http://dx.doi.org/10.1063/1.2120916 (3 pages) | Cited 6 times

Online Publication Date: 24 October 2005

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Crack-free thick GaN layers have been grown by hydride vapor phase epitaxy on on-axis as well as on off-axis GaN-Al2O3 templates. A dramatic difference in surface quality could be traced back to the misorientation of the substrates: Mirror-like layers have been obtained for slightly off-oriented substrates, whereas pyramids and other surface structures were found on samples grown on exactly oriented wafers. Such excellent surfaces may make further surface treatment prior to a subsequent use of these wafers in further epitaxial processes obsolete.
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68.47.Fg Semiconductor surfaces
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)

Low-temperature pathways to Ge-rich Si1−xGex alloys via single-source hydride chemistry

C.-W. Hu, J. Menéndez, I. S. T. Tsong, J. Tolle, A. V. G. Chizmeshya, Cole Ritter, and J. Kouvetakis

Appl. Phys. Lett. 87, 181903 (2005); http://dx.doi.org/10.1063/1.2117620 (3 pages) | Cited 7 times

Online Publication Date: 25 October 2005

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We report rapid low-temperature (300–470 °C) growth of Si0.50Ge0.50, Si0.33Ge0.67, Si0.25Ge0.75, and Si0.20Ge0.80 alloys on Si(100) using heavy single-source hydride molecular compounds (H3Ge)nSiH4−n (n = 1–4). Incorporation of the entire SiGe, SiGe2, SiGe3, and SiGe4 framework of these precursors into the film provides precise control of morphology, composition, and strain. Low-energy electron microscopy analysis indicates that the (H3Ge)xSiH4−x (x = 2–4) species are highly reactive, with H2 desorption characteristics comparable to those of Ge2H6, despite the presence of strong Si–H bonds in their molecular structure.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.47.Fg Semiconductor surfaces
68.43.Mn Adsorption kinetics
68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology

Evidence of a rearrangement of the surface structure in titanium phthalocyanine sensors induced by the interaction with nitrogen oxides molecules

A. Generosi, B. Paci, V. Rossi Albertini, P. Perfetti, A. M. Paoletti, G. Pennesi, G. Rossi, and R. Caminiti

Appl. Phys. Lett. 87, 181904 (2005); http://dx.doi.org/10.1063/1.2119429 (3 pages) | Cited 9 times

Online Publication Date: 25 October 2005

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Thin-film samples of titanium phthalocyanine, a sensor of environmental pollutants, were studied by time resolved energy-dispersive x-ray reflectivity (EDXR). This original method demonstrated to be an ideal tool to follow the evolution of the films morphology upon gas exposure, in situ, also allowing an unexpected response of the sensors to be detected. Indeed, while the increase in thickness showed the characteristic feature of a “breathing-like” expansion, already observed in other metal-Pc, the curve of roughness versus exposure time exhibited a peak. This effect, in some cases evident by observation with the naked eye the EDXR data, was attributed to a surface structure rearrangement process.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.47.Fg Semiconductor surfaces
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.47.-p Spectroscopy of solid state dynamics
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Atomic scale morphology of thin GaNAs films: Effects of nitrogen content and growth temperature

W. M. McGee, P. A. Bone, R. S. Williams, and T. S. Jones

Appl. Phys. Lett. 87, 181905 (2005); http://dx.doi.org/10.1063/1.2120917 (3 pages) | Cited 6 times

Online Publication Date: 25 October 2005

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The surface morphology of 8 nm GaNAs layers grown by molecular-beam epitaxy on GaAs(001) substrates has been studied as a function of nitrogen content and growth temperature using scanning tunneling microscopy (STM). Increasing the nitrogen content from 0%–3% leads to a pronounced increase in surface roughness, caused by the appearance of deep pits. Raising the growth temperature from 400–500 °C produces the same effect. We propose that pit formation is symptomatic of phase segregation. STM images show that the GaNAs layers adopt an (n×3) surface reconstruction, suggesting that a disproportionately high concentration of N is present on the postgrowth surface compared with that incorporated into the layer during growth.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
64.75.-g Phase equilibria

Effect of rapid thermal annealing on the ordering of AlInP grown by metal-organic vapor-phase epitaxy

Xiaohong Tang, Jinghua Zhao, Mee Koy Chin, Ting Mei, Zongyou Yin, Sentosa Deny, and An Yan Du

Appl. Phys. Lett. 87, 181906 (2005); http://dx.doi.org/10.1063/1.2120897 (3 pages) | Cited 6 times

Online Publication Date: 25 October 2005

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Spontaneous CuPt ordering is observed in AlxIn1−xP layers grown by metal-organic vapor-phase epitaxy in pure nitrogen ambient with tertiarybutylphosphine as phosphorus precursor. Changes of the degree of ordering of the AlxIn1−xP epilayer versus annealing temperature have been investigated by using photoluminescence and transmission electron diffraction. The degree of ordering of the AlxIn1−xP layers is reduced after annealing the sample at a temperature higher than the sample growth temperature. It becomes completely disordered when the annealing temperature reaches 900 °C and above.
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61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Monodisperse spherical core-shell-structured phosphors obtained by functionalization of silica spheres with Y2O3:Eu3+ layers for field emission displays

H. Wang, C. K. Lin, X. M. Liu, J. Lin, and M. Yu

Appl. Phys. Lett. 87, 181907 (2005); http://dx.doi.org/10.1063/1.2123382 (3 pages) | Cited 53 times

Online Publication Date: 25 October 2005

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Spherical SiO2 particles have been coated with Y2O3:Eu3+ phosphor layers (SiO2@Y2O3:Eu3+) by a Pechini sol-gel process. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, and cathodoluminescence spectra were utilized to characterize the SiO2@Y2O3:Eu3+ core-shell-structured phosphor particles. The obtained core-shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution. The thickness of Y2O3:Eu3+ shell could be easily controlled by changing the number of deposition cycles (60 nm for three deposition cycles). The SiO2@Y2O3:Eu3+ core-shell particles show a strong red emission corresponding to math-math (611 nm) of Eu3+ under the excitation of ultraviolet (250 nm) and low-voltage electron beams (2–6 kV), which have potential application for field emission displays.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
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)
85.45.Fd Field emission displays (FEDs)

Role of Sb in the growth and optical properties of 1.55 μm GaInN(Sb)As/GaNAs quantum-well structures by molecular-beam epitaxy

H. D. Sun, S. Calvez, M. D. Dawson, J. A. Gupta, G. I. Sproule, X. Wu, and Z. R. Wasilewski

Appl. Phys. Lett. 87, 181908 (2005); http://dx.doi.org/10.1063/1.2123383 (3 pages) | Cited 8 times

Online Publication Date: 25 October 2005

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High-quality GaInN(Sb)As/GaNAs double quantum wells (QWs) which emit at 1.54 μm wavelength at room temperature with a narrow linewidth of ∼ 34 meV (12 meV at 5 K) were fabricated by molecular-beam epitaxy on GaAs substrates. Photoluminescence and photoluminescence excitation spectroscopy were used to study the electronic states and optical properties of these heterostructures. By characterizing samples grown using different fluxes of Sb, the role played by Sb in the growth process and optical properties was elucidated. At low Sb flux, Sb atoms act mainly as a surfactant which improves the microstructure of the QWs and enhances the photoluminescence intensity. With an increase of Sb flux, some of the Sb atoms may incorporate into GaInNAs to form a quinary compound. In the latter case, the incorporation of Sb could also enhance the N composition in the QWs, which may be responsible for the further reduction of the band gap.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Photoinduced stress in a ZnSe/GaAs epilayer containing 90°α partial dislocations

Yutaka Ohno

Appl. Phys. Lett. 87, 181909 (2005); http://dx.doi.org/10.1063/1.2123392 (3 pages) | Cited 2 times

Online Publication Date: 25 October 2005

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Photoinduced stress in a ZnSe/GaAs epilayer containing 90°α partial dislocations was observed in situ by means of polarized cathodoluminescence spectroscopy under light illumination in a transmission electron microscope. A dislocation glided under the illumination of a monochromatic light whose photon energy was above 2.07–2.40 eV, presumably due to a recombination-enhanced effect. The glide accompanied with a variation of the compression stress along [110] in the epilayer; the stress decreased at the temperature of 35 K, while it increased at higher temperatures.
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79.20.Ds Laser-beam impact phenomena
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
68.37.Lp Transmission electron microscopy (TEM)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.Nn Stacking faults and other planar or extended defects

Mechanisms of arsenic segregation to the Ni2Si/SiO2 interface during Ni2Si formation

M. A. Pawlak, T. Janssens, A. Lauwers, A. Vantomme, W. Vandervorst, K. Maex, and J. A. Kittl

Appl. Phys. Lett. 87, 181910 (2005); http://dx.doi.org/10.1063/1.2125124 (3 pages) | Cited 1 time

Online Publication Date: 26 October 2005

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We have investigated the mechanisms of As redistribution during Ni2Si formation on polycrystalline Si/SiO2 and amorphous Si/SiO2 stacks on (100) Si by secondary ion mass spectroscopy measurements. We found a significant impact of the Si crystallinity and pre-silicidation thermal treatments on the dopant redistribution. There is a significantly higher dose of As accumulated in the vicinity of SiO2 after full Ni2Si silicidation on poly-Si ( ∼ 51%) than on amorphous-Si ( ∼ 13%). We demonstrate that the As redistribution during Ni2Si formation on amorphous silicon is dominated by snowplow of As in front of the growing silicide. In contrast, when Ni2Si is formed on recrystallized poly-silicon there are three segregation mechanisms: (1) thermal diffusion during high temperature recrystallization annealing ( ∼ 17%), (2) snowplow during silicidation ( ∼ 13%), not dependent on the substrate crystallinity and (3) diffusion along poly-Si grain boundaries during silicidation ( ∼ 22%).
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64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.up Other materials
66.30.Xj Thermal diffusivity
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.Mm Grain and twin boundaries

Electronic structure and optoelectronic properties of strained InAsSb/GaSb multiple quantum wells

Thomas Koprucki, Michael Baro, Uwe Bandelow, Tran Q. Tien, Fritz Weik, Jens W. Tomm, Markus Grau, and Markus-Christian Amann

Appl. Phys. Lett. 87, 181911 (2005); http://dx.doi.org/10.1063/1.2125126 (3 pages) | Cited 1 time

Online Publication Date: 26 October 2005

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A study of the optical properties of a set of InAsxSb1−x/Al0.15In0.85As0.77Sb0.23/GaSb multiple quantum wells (0.82<x<0.92) with built-in strains in the −0.62% to +0.05% range is presented. The energy of the lowest quantum-confined optical transition is calculated by k∙p perturbation theory and experimentally determined by absorption measurements. Stokes shifts of photoluminescence, photocurrent, and of the emission from light-emitting devices against the absorption edge of the quantum well are quantified. The impact of the decreasing carrier confinement in the InAsxSb1−x quantum-well system with increasing mole fraction is analyzed theoretically, and experimentally demonstrated by photoluminescence measurements. Our results allow for the improvement of optoelectronic devices, in particular for tailoring emission spectra of light-emitting diodes.
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73.21.Fg Quantum wells
78.67.De Quantum wells
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
61.66.Bi Elemental solids
61.66.Dk Alloys

Combined hydride and metal organic vapor-phase epitaxy of GaN on sapphire

G. S. Solomon, D. J. Miller, M. Ramsteiner, A. Trampert, O. Brandt, and K. H. Ploog

Appl. Phys. Lett. 87, 181912 (2005); http://dx.doi.org/10.1063/1.2119408 (3 pages) | Cited 2 times

Online Publication Date: 26 October 2005

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We describe a method to produce GaN epitaxial layers in a single chamber where a low-temperature buffer layer is deposited using metalorganic vapor-phase epitaxy (MOVPE), followed by conventional hydride vapor-phase epitaxy (HVPE) of GaN at higher temperatures. While a typical 12 μm sample is investigated here, the GaN film thickness can vary between 2 and 200 μm, with HVPE growth rate ranging from 5 to 60 μm/h. Cross-sectional transmission-electron microscope images show a dense network of mixed dislocations, whose density is significantly reduced after 6 μm to the high 107 cm−2 range. 10 K photoluminescence shows bound exciton dominated emission associated with the A and B valence bands and phonon replicas. No yellow emission is observed. This versatile process can be extended to produce additional device layers by MOVPE.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Cr 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
71.20.Nr Semiconductor compounds
63.20.-e Phonons in crystal lattices
71.35.-y Excitons and related phenomena

Third-order nonlinear optical properties of a cadmiun sulfide-dendrimer nanocomposite

Michael Etienne, Anna Biney, Ardie D. Walser, Roger Dorsinville, David L. V. Bauer, and Valeria Balogh-Nair

Appl. Phys. Lett. 87, 181913 (2005); http://dx.doi.org/10.1063/1.2123385 (3 pages) | Cited 8 times

Online Publication Date: 26 October 2005

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We have investigated the nonlinear optical response of thin films consisting of a poly(propyleneimine) dendrimer matrix having diaminobutane core with and without small 2.2 nm diameter CdS quantum dots. Large nonlinear coefficients and low nonlinear absorption losses were observed at 532 and 1064 nm. The high nonlinearity and low two-photon absorption yielded promising figures of merit for nonlinear optical switching applications.
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42.70.Jk Polymers and organics
42.65.An Optical susceptibility, hyperpolarizability
78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors

Spectral-resolved microprobe cathodoluminescence investigations of Al-doped single-crystalline Ba0.6Sr0.4TiO3 thin films

T. L. Chen, X. M. Li, K. S. Wan, W. L. Zhu, and G. Pezzotti

Appl. Phys. Lett. 87, 181914 (2005); http://dx.doi.org/10.1063/1.2125109 (3 pages) | Cited 10 times

Online Publication Date: 27 October 2005

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Single-crystalline Al-doped Ba0.6Sr0.4TiO3 (BST) thin films have been pulsed-laser deposited onto Ir/MgO buffered Si substrates. Spectral-resolved microprobe cathodoluminescence measurements of Al-doped BST thin films at room temperature clearly showed three detectable luminescence bands in the wavelength range between 200 and 900 nm. We assigned the first shoulder peak to saturation of phonon-assisted processes, with a band gap transition resulting in the second sharp band. The band-maximum position of a third (defect-related) broad luminescence band varied with varying the concentration of Al dopant. By fitting this latter band as the sum of three superimposed Gaussian curves, it was revealed that the incorporation of Al dopant into the BST crystal lattice had a direct impact on the defect population existing in the single-crystalline film. For perovskite ABO3-structured BST thin films, it is suggested that the Al dopant occupies the B site (Ti) in a low range of dopant concentrations, while at higher dopant concentrations Al might occupy both A sites (Ba or Sr) and B sites.
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78.66.Nk Insulators
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Discovering inch-diameter metallic glasses in three-dimensional composition space

H. Ma, L. L. Shi, J. Xu, Y. Li, and E. Ma

Appl. Phys. Lett. 87, 181915 (2005); http://dx.doi.org/10.1063/1.2126794 (3 pages) | Cited 101 times

Online Publication Date: 27 October 2005

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We have discovered low-cost bulk metallic glasses (BMGs) with diameters as large as 16 to 25 mm based on the ordinary engineering metal Mg. We also use this example to present a new strategy, to illustrate how to navigate in three-dimensional composition space for locating the best glass-forming compositions. The extraordinary glass-forming ability demonstrated by the inch-sized BMGs has implications for future development and applications of amorphous metals.
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61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
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