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19 Dec 2005

Volume 87, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 252501 (2005); http://dx.doi.org/10.1063/1.2149972 (3 pages)

R. Katoh, T. Hihara, D. L. Peng, and K. Sumiyama
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Highly efficient tunable tapered-polymer-fiber lasers

Qinjun Peng, Guiling Wang, Yong Bo, Xinjun Guo, Aicong Geng, Zuyan Xu, Liyong Ren, Yani Zhang, Yishan Wang, Wei Zhao, and Lili Wang

Appl. Phys. Lett. 87, 251101 (2005); http://dx.doi.org/10.1063/1.2149155 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2005

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A highly efficient tunable tapered-polymer-fiber (TPF) laser was demonstrated by use of a compound parabolic TPF doped with Rhodamine-6G (R6G) dye. The tuning ranges over 40 nm at the visible region for laser output with the maximum output energy of 600 μJ at 570 nm and the optical-optical conversion efficiency of 23% were achieved by a prism as a spectrally selective element. Moreover, the coupling efficiency for the taper exceeded 90%. Compared to traditional polymer fibers with a micrometer-size core diameter, the taper allows for a higher pump to be launched without damaging the fiber endfaces, and it can efficiently couple the light into the fiber and alleviate the alignment difficulty. So, the TPF laser not only possesses all of the advantages of traditional polymer-fiber lasers, and it can also obtain higher output energy and higher efficiency. Additionally, it is insensitive to geometrical displacements.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.55.Mv Dye lasers
42.79.Bh Lenses, prisms and mirrors
42.81.Qb Fiber waveguides, couplers, and arrays
42.70.Jk Polymers and organics

All optically tunable wavelength-selective reflector consisting of coupled polymeric microring resonators

Jacob Scheuer, George T. Paloczi, and Amnon Yariv

Appl. Phys. Lett. 87, 251102 (2005); http://dx.doi.org/10.1063/1.2149158 (3 pages) | Cited 12 times

Online Publication Date: 13 December 2005

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We present an all optically tunable wavelength-selective reflector for planar lightwave technology based on coupled microring resonators. By employing the Vernier effect, we demonstrate narrow-band reflection and strong side-lobe suppression in an optical polymer device fabricated by soft lithography. Wide and simple tuning of the reflection peak using an external control beam is demonstrated.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer

Quasiphase matched harmonic generation in a two-dimensional octagonal photonic superlattice

Boqin Ma, Ting Wang, Yan Sheng, Peigen Ni, Yiquan Wang, Bingying Cheng, and Daozhong Zhang

Appl. Phys. Lett. 87, 251103 (2005); http://dx.doi.org/10.1063/1.2138352 (3 pages) | Cited 14 times

Online Publication Date: 14 December 2005

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We have fabricated LiNbO3 nonlinear photonic crystals with a two-dimensional octagonal quasilattice. The effective collinear quasiphase matched second-harmonic orange and green lights, with conversion efficiencies of ∼ 38% and 23%, were realized. The noncollinear harmonic processes at multiple wavelengths were also observed with the conversion efficiency of around 5%. All the-same results can be obtained when the crystal is rotated by the integral multiples of π/4.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Mp Nonlinear optical crystals

Dual localizations for second-harmonic generations using left-handed materials

Jing Chen, Fang-Fang Ren, Rui Li, Nian-Hai Shen, Ya-Xian Fan, Jianping Ding, and Hui-Tian Wang

Appl. Phys. Lett. 87, 251104 (2005); http://dx.doi.org/10.1063/1.2149967 (3 pages)

Online Publication Date: 14 December 2005

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We show that dual localized modes can be achieved in defective one-dimensional photonic crystals containing left-handed materials. By inserting a nonlinear defect into a photonic crystal formed by stacked alternating left-handed materials and air layers, defective modes for fundamental wave and second-harmonic signal inside the zero-math gap and a Bragg gap are formed, respectively. We present a theory in designing the whole structure, and show that a giant enhancement of second-harmonic generation is achieved. The merits and character of such a scheme comparing with that in ordinary photonic crystals are discussed.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
42.70.Qs Photonic bandgap materials

Coded excitation of broadband terahertz using optical rectification in poled lithium niobate

T. Buma and T. B. Norris

Appl. Phys. Lett. 87, 251105 (2005); http://dx.doi.org/10.1063/1.2149969 (3 pages) | Cited 1 time

Online Publication Date: 14 December 2005

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We demonstrate coded excitation of broadband terahertz for imaging applications. The encoded transmitter uses optical rectification of femtosecond laser pulses in poled lithium niobate patterned with a 53-bit binary phase code. The terahertz wave forms are detected by electro-optic sampling in zinc telluride. A digital pulse compression filter decodes the binary wave forms, producing broadband pulses at 1.0 THz. A two-dimensional imaging experiment shows comparable performance between the encoded transmitter and a zinc telluride emitter.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Ci Filters, zone plates, and polarizers

Optimization of tapered semiconductor optical amplifiers for picosecond pulse amplification

E. Gehrig and O. Hess

Appl. Phys. Lett. 87, 251106 (2005); http://dx.doi.org/10.1063/1.2149177 (3 pages) | Cited 1 time

Online Publication Date: 15 December 2005

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We present results of a fundamental device simulation study aimed at an optimization of high-power tapered semiconductor optical amplifiers for picosecond pulse amplification. Thereby, the microscopic light-matter coupling is described on the basis of a spatially resolved Maxwell–Bloch–Langevin description that takes into account many-body-carrier interactions, energy transfer between the carrier and phonon systems and, in particular, the spatiotemporal interplay of stimulated and amplified spontaneous emission and the noise caused by spontaneous emission. Extensive simulation runs reveal the microscopic physical processes which are responsible for the beam quality of the amplified picosecond pulses and allow us to give concrete suggestions for the optimization of the amplifier structure and geometry. We discuss the influence of a curved waveguide or spatially patterned current contact, and identify the length of the unpumped area as the most critical parameter to be carefully optimized.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Design for a triply resonant vertical-emitting micro-optical parametric oscillator

C. Diederichs and J. Tignon

Appl. Phys. Lett. 87, 251107 (2005); http://dx.doi.org/10.1063/1.2150282 (3 pages) | Cited 6 times

Online Publication Date: 16 December 2005

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An approach is proposed for the realization of a vertical-cavity surface-emitting semiconductor micro-optical parametric oscillator that relies on the use of third-order excitonic nonlinearity in isotropic semiconductors. We demonstrate that a planar triple microcavity structure can be designed to provide triple resonance for the parametric frequencies together with built-in cavity phase-matching for all waves at normal incidence. An example is given of a monolithic structure consisting of three strongly coupled AlGaAs/GaAs lambda microcavities including single InGaAs quantum wells. Applications to the generation of twin photons or entangled photon pairs are discussed.
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42.65.Yj Optical parametric oscillators and amplifiers
42.65.Lm Parametric down conversion and production of entangled photons
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Optical gain from InAs nanocrystal quantum dots in a polymer matrix

Gang Chen, Ronen Rapaport, Dan T. Fuchs, Leah Lucas, Andrew J. Lovinger, Sahar Vilan, Assaf Aharoni, and Uri Banin

Appl. Phys. Lett. 87, 251108 (2005); http://dx.doi.org/10.1063/1.2149176 (3 pages) | Cited 13 times

Online Publication Date: 16 December 2005

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We report on the observation of optical gain from InAs nanocrystal quantum dots which emit at 1.55 microns and are imbedded in a novel polymer platform. The measurements are based on a three-beam time resolved pump-probe technique, which enables extracting the intrinsic gain cross section, lifetime, and recovery time. These experiments are another step toward the realization of active optical devices based on InAs nanocrystals.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Gw Other integrated-optical elements and systems

Impact of N on the lasing characteristics of GaInNAs/GaAs quantum well lasers emitting from 1.29 to 1.52 μm

J. M. Ulloa, A. Hierro, M. Montes, B. Damilano, M. Hugues, J. Barjon, J.-Y. Duboz, and J. Massies

Appl. Phys. Lett. 87, 251109 (2005); http://dx.doi.org/10.1063/1.2151249 (3 pages) | Cited 8 times

Online Publication Date: 16 December 2005

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The origin of the degradation with N of the threshold current density (Jth) and external differential quantum efficiency (ηd) of 1.29 to 1.52 μm GaInNAs/GaAs laser diodes is analyzed. Adding N to InGaAs leads to a ∼ 25% reduction of the carrier injection efficiency and thus to an increase of Jth and a decrease of ηd. This effect is likely related to carrier recombination losses in the barriers and is independent of the N content. The optical absorption losses and the internal transparency current density are found to increase with N content, accounting for the rest of the degradation in Jth. Modeling of the transparency carrier and radiative current densities identifies the increase of the defect-related recombination coefficient in GaInNAs as the dominant effect leading to the N dependence of Jtr.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Cadmium telluride bulk crystal as an ultrafast nonlinear optical switch

Satoshi Tatsuura, Takashi Matsubara, Hiroyuki Mitsu, Yasuhiro Sato, Izumi Iwasa, Minquan Tian, and Makoto Furuki

Appl. Phys. Lett. 87, 251110 (2005); http://dx.doi.org/10.1063/1.2151256 (3 pages) | Cited 6 times

Online Publication Date: 16 December 2005

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A semiconductor bulk crystal has several advantages as a nonlinear optical material, such as low processing cost, long interaction length, and alleviation of the free-carrier absorption caused by two-photon absorption (TPA). We examine optical properties of semiconductor bulk crystals with different orientations at 1.55 μm and find that CdTe[111] has favorable capabilities, such as nonlinear refractive index of 5.23×10−17 (m2 W), TPA coefficient of 18.3 (mm GW), and consequent figure of merit of 0.54. Optical three-dimensional measurements of reflective material are carried out using CdTe[111] as ultrafast optical Kerr shutter and clear images corresponding to surface steps are obtained.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.82.Gw Other integrated-optical elements and systems
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Scaling of domain size during spinodal decomposition: Dislocation discreteness and mobility effects

Mikko Haataja, Jennifer Mahon, Nikolas Provatas, and Francois Léonard

Appl. Phys. Lett. 87, 251901 (2005); http://dx.doi.org/10.1063/1.2147732 (3 pages) | Cited 7 times

Online Publication Date: 12 December 2005

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In this letter, we examine the effects of discrete mobile dislocations on spinodal decomposition kinetics in lattice mismatched binary alloys. By employing a novel continuum model, we demonstrate that the effects of dislocation mobility on domain coarsening kinetics can be expressed in a unified manner through a scaling function, describing a crossover from t1/2 to t1/3 behavior.
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64.70.K- Solid-solid transitions
64.75.-g Phase equilibria
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

High-quality nanothickness single-crystal Sc2O3 film grown on Si(111)

M. Hong, A. R. Kortan, P. Chang, Y. L. Huang, C. P. Chen, H. Y. Chou, H. Y. Lee, J. Kwo, M.-W. Chu, C. H. Chen, L. V. Goncharova, E. Garfunkel, and T. Gustafsson

Appl. Phys. Lett. 87, 251902 (2005); http://dx.doi.org/10.1063/1.2147711 (3 pages) | Cited 7 times

Online Publication Date: 12 December 2005

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High-quality single-crystal Sc2O3 films a few nanometer thick have been grown epitaxially on Si (111) despite a huge lattice mismatch. The films were electron-beam evaporated from a Sc2O3 target. Structural and morphological studies were carried out by x-ray diffraction and reflectivity, atomic force microscopy, high-resolution transmission electron microscopy, and medium-energy ion scattering, with the initial epitaxial growth monitored by in situ reflection high-energy electron diffraction. The films have the cubic bixbyite phase with a remarkably uniform thickness and high structural perfection. The film surfaces are very smooth and the oxide/Si interfaces are atomically sharp with a low average roughness of 0.06 nm. The films are well aligned with the Si substrate with an orientation relationship of Si(111)‖Sc2O3(111), and an in-plane expitaxy of Si[math10]‖Sc2O3[math01].
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Electron energy-loss spectrometry studies of bonding in nanoscale Ni–SiO2 multilayers

Seth T. Taylor and Ronald Gronsky

Appl. Phys. Lett. 87, 251903 (2005); http://dx.doi.org/10.1063/1.2147712 (3 pages) | Cited 1 time

Online Publication Date: 12 December 2005

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Electron energy-loss spectrometry in the transmission electron microscope is used to directly assess the nature of bonding at interfaces formed during alternating deposition of nanoscale Ni and SiO2 multilayers. Interfacial Ni–O bond formation near the interface is revealed by energy-loss near-edge structure preceding the O K edge threshold, indicating hybridization of O 2p with Ni 3d orbitals, and by characteristic white line structure associated with the Ni L2,3 edge. Interface spectra are compared to reference NiO spectra, verifying local Ni–O bonding at the Ni/SiO2 interface.
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79.20.Uv Electron energy loss spectroscopy
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Optical properties of thin films of [Ru(bpy)3][NaCr(ox)3] polymeric networks

Sebastien Rabaste, Nahid Amstutz, Andreas Hauser, and Anne Pillonnet

Appl. Phys. Lett. 87, 251904 (2005); http://dx.doi.org/10.1063/1.2143409 (3 pages)

Online Publication Date: 12 December 2005

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The optical properties of a thin film of the [Ru(bpy)3][NaCr(ox)3] network structure obtained by pulsed laser deposition are described. The luminescence shows the characteristic doublet of R lines at 14 400 cm−1 of the spin-forbidden ligand field transition math(t2g3)→math(t2g3) of the [Cr(ox)3]3− chromophore. The resonant energy migration within the R1 line shows that the three-dimensional crystallographic structure is preserved during the coating process. The observation of the R lines of [Cr(bpy)3]3+ at 13 710 cm−1 indicates that a small fraction of Cr3+ ions migrate from the oxalate network to the tris-bipyridine cation site in the cavities of the network.
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78.66.Qn Polymers; organic compounds
81.15.Fg Pulsed laser ablation deposition
42.70.Jk Polymers and organics
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
78.55.Kz Solid organic materials
81.65.-b Surface treatments

Nanoindentation of HgCdTe prepared by molecular beam epitaxy

M. Martyniuk, R. H. Sewell, C. A. Musca, J. M. Dell, and L. Faraone

Appl. Phys. Lett. 87, 251905 (2005); http://dx.doi.org/10.1063/1.2143411 (3 pages) | Cited 2 times

Online Publication Date: 12 December 2005

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Nanoindentation has been used to investigate the elastoplastic behavior of Hg0.7Cd0.3Te prepared by molecular beam epitaxy. It was found that Hg0.7Cd0.3Te had a modulus of elasticity of ∼ 50 GPa and hardness of ∼ 0.66 GPa. The HgCdTe response to nanoindentation was found to be purely elastic for low loads and developed into ∼ 10% elastic and ∼ 90% plastic response for higher-load indentation exhibiting significant amounts of creep. The onset of plasticity has been observed to be marked by discontinuities or “pop-in” events in the indenter load-penetration curves at sheer stresses of ∼ 1.8 GPa, and has been correlated with the homogeneous nucleation and propagation of dislocations.
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81.05.Dz II-VI semiconductors
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
62.20.F- Deformation and plasticity
62.20.Hg Creep
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Two-staged sorption isotherm of a nanoporous energy absorption system

Falgun B. Surani, Xinguo Kong, and Yu Qiao

Appl. Phys. Lett. 87, 251906 (2005); http://dx.doi.org/10.1063/1.2144280 (3 pages) | Cited 25 times

Online Publication Date: 12 December 2005

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To selectively absorb impact energy, the profiles of sorption isotherms of protection systems must be adjusted in a broad spectrum. In this article, a N-Lauroylsarcosine sodium salt (sarcosyl) of intermediate molecular size is used to control the pressure induced infiltration of a nanoporous silica. The experimental result shows that the infiltration plateau of this system is two-staged; that is, not only the activation pressure but also the infiltration volume can be modified. It is noticed that the sarcosyl molecule demands a “free volume” to enter a nanopore. The free volume size decreases nearly linearly as the sarcosyl concentration increases.
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68.43.Mn Adsorption kinetics
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials

Strain-facilitated process for the lift-off of a Si layer of less than 20 nm thickness

Lin Shao, Yuan Lin, J. G. Swadener, J. K. Lee, Q. X. Jia, Y. Q. Wang, M. Nastasi, Phillip E. Thompson, N. David Theodore, T. L. Alford, J. W. Mayer, Peng Chen, and S. S. Lau

Appl. Phys. Lett. 87, 251907 (2005); http://dx.doi.org/10.1063/1.2146211 (3 pages) | Cited 4 times

Online Publication Date: 12 December 2005

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We report a process for the lift-off of an ultrathin Si layer. By plasma hydrogenation of a molecular-beam-epitaxy-grown heterostructure of Si/Sb‐doped‐Si/Si, ultrashallow cracking is controlled to occur at the depth of the Sb-doped layer. Prior to hydrogenation, an oxygen plasma treatment is used to induce the formation of a thin oxide layer on the surface of the heterostructure. Chemical etching of the surface oxide layer after hydrogenation further thins the thickness of the separated Si layer to be only 15 nm. Mechanisms of hydrogen trapping and strain-facilitated cracking are discussed.
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81.05.Cy Elemental semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
52.77.-j Plasma applications
81.65.Cf Surface cleaning, etching, patterning

Self-assembly of steps and vacancy lines during the early stages of Ge/Si(001) heteroepitaxy

D. T. Tambe, C. V. Ciobanu, and V. B. Shenoy

Appl. Phys. Lett. 87, 251908 (2005); http://dx.doi.org/10.1063/1.2147720 (3 pages) | Cited 1 time

Online Publication Date: 13 December 2005

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The wetting layer formed during the early stages of Ge/Si(001) growth has been found in recent experiments to undergo a roughening process, where the SA surface steps affect the spatial organization of vacancy lines (VLs) by increasing (stretching) or decreasing (squeezing) their average spacing. Using a combination of atomistic simulations and elastic theory of surface defects, we have computed the interaction energy of the SA steps and VLs for each of the observed defect configurations. We find that the repulsive SA-VL interactions lead to an increase in the spacing of the VLs in the “stretch” arrangement, but do not significantly affect the VL spacing in the “squeeze” configuration, providing an explanation for the observed correlations in the wetting layer roughness.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
68.08.Bc Wetting
68.47.Fg Semiconductor surfaces

Effect of local ordering on the decomposition of an amorphous Cu–Zr–Ti alloy

Zs. Kovács and Á Révész

Appl. Phys. Lett. 87, 251909 (2005); http://dx.doi.org/10.1063/1.2149175 (3 pages) | Cited 3 times

Online Publication Date: 13 December 2005

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We present free-energy calculations based on the random solution model. These calculations support the fact that the Cu-based solid solution observed to form during decomposition in amorphous Cu60Zr30Ti10 alloy is an ordered metastable L12 Cu3(Zr,Ti) phase which can nucleate due to its small unit cell and high mixing preference of Zr with Cu atoms.
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61.43.Fs Glasses
64.60.Q- Nucleation
64.60.My Metastable phases
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Optical spectroscopy of trivalent chromium in sol-gel lithium niobate

J. K. Krebs and U. Happek

Appl. Phys. Lett. 87, 251910 (2005); http://dx.doi.org/10.1063/1.2149182 (3 pages) | Cited 2 times

Online Publication Date: 13 December 2005

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We report on the characterization of sol-gel derived lithium niobate via trivalent chromium probe ions, a study that is motivated by recent reports on the synthesis of high quality sol-gel lithium niobate (LiNbO3). In order to assess the quality of sol-gel derived LiNbO3, we incorporate Cr3+ during the hydrolysis stage of the sol-gel process. A comparison of the Cr3+ emission and photoexcitation data on both sol-gel and melt-grown LiNbO3 shows that the sol-gel derived material is highly stoichiometric.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
64.70.D- Solid-liquid transitions
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)

Photoluminescence of Si nanocrystal memory devices obtained by ion beam synthesis

Marzia Carrada, Anja Wellner, Vincent Paillard, Caroline Bonafos, Hubert Coffin, and Alain Claverie

Appl. Phys. Lett. 87, 251911 (2005); http://dx.doi.org/10.1063/1.2143130 (3 pages) | Cited 11 times

Online Publication Date: 13 December 2005

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In this letter, we propose an original method to investigate Si nanocrystal-based nonvolatile memory devices, taking benefit of the photoluminescence (PL) spectroscopy and the specific optoelectronic properties of Si nanocrystals (Si-NCs). Ordered two-dimensional-arrays of Si-NCs were synthesized by ultralow-energy ion implantation in 7-nm-thick SiO2 and subsequent annealing. The Si-NCs population characteristics (size and density) were adjusted by different oxidizing annealing. This allowed, at the same time, the progressive healing of the oxide matrix. The analysis of the spectra revealed the presence of two PL bands, one due to quantum confinement effects in Si-NCs, and the other one attributed to silicon-rich oxide. Therefore, the evolution in energy and intensity of the PL bands was correlated to the oxidizing conditions, thus to the change of the Si-NCs size and density, and to the formation of stoichiometric SiO2. These results are of great interest as being the first step in using PL spectroscopy as a nondestructive method to assess or monitor the electrical performances of the future memory devices, before any step of contact fabrication.
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78.55.Ap Elemental semiconductors
84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.65.Mq Oxidation

Optical properties of nanocluster-assembled ZnO thin films by nanocluster-beam deposition

Z. W. Zhao, B. K. Tay, J. S. Chen, J. F. Hu, X. W. Sun, and S. T. Tan

Appl. Phys. Lett. 87, 251912 (2005); http://dx.doi.org/10.1063/1.2149170 (3 pages) | Cited 7 times

Online Publication Date: 13 December 2005

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Nanocluster-assembled ZnO thin films have been synthesized by nanocluster-beam deposition, and the films exhibit a band-gap energy at 323.7 nm (3.84 eV) and ultraviolet (UV) light emission at 373 nm (3.32 eV) with an average particle size of 6 nm. A comparison of the optical properties of the annealed films with that of as-grown one is presented. It is found that, after the film is annealed, the shoulder in the absorbance spectra turns steeper and the intensity of UV light emission band becomes stronger. Moreover, blueshifts of band-gap energy and a UV emission band are both observed as decreasing the annealing temperature and ascribed to the quantum-confinement effect.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
78.66.Hf II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.40.Fy Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Role of substrate and transparent conducting oxide in impurity evolvement in polycrystalline thin-film devices

M. Emziane, K. Durose, D. P. Halliday, A. Bosio, and N. Romeo

Appl. Phys. Lett. 87, 251913 (2005); http://dx.doi.org/10.1063/1.2149990 (3 pages) | Cited 8 times

Online Publication Date: 13 December 2005

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A comparison of as-grown and processed CdTe/CdS solar cell structures deposited on sapphire substrate has been undertaken with those grown on glass. The device structures were depth-profiled using quantitative secondary ion mass spectrometry. It was shown that while Si concentration profiles are similar to those for structures grown on glass, Na was more than one order of magnitude lower when sapphire was used instead of glass, showing that Na diffused from the glass. It was also found that there was no measurable diffusion of Sn from the SnO2 layer into CdTe, and that the former played an important role in preventing the diffusion of In from In-containing transparent conducting oxide layer. Cl, O, Br, and F species were also investigated and while Cl and O were found to be independent of the nature of the substrate used, Br and F were shown to be affected by the processing.
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84.60.Jt Photoelectric conversion
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Ultrafast dynamics of femtosecond laser-induced periodic surface pattern formation on metals

Jincheng Wang and Chunlei Guo

Appl. Phys. Lett. 87, 251914 (2005); http://dx.doi.org/10.1063/1.2146067 (3 pages) | Cited 31 times

Online Publication Date: 13 December 2005

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In this paper, we perform a comparison study of periodic structures on the surfaces of three different noble metals, Cu, Ag, and Au, following femtosecond laser radiation. Under identical experimental conditions, laser-induced surface patterns show distinctly different level of morphological clearness on the three different metals. Simple calculations based on metal melting fail to explain the pattern differences. We show that our observation result from the competition of two ultrafast processes, electron-phonon energy coupling and hot electron diffusion, following femtosecond laser heating of metals.
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81.40.−z
79.20.Ds Laser-beam impact phenomena

Nanoair-bridged lateral overgrowth of GaN on ordered nanoporous GaN template

Y. D. Wang, K. Y. Zang, S. J. Chua, S. Tripathy, P. Chen, and C. G. Fonstad

Appl. Phys. Lett. 87, 251915 (2005); http://dx.doi.org/10.1063/1.2147716 (3 pages) | Cited 18 times

Online Publication Date: 13 December 2005

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We report the growth of high-quality GaN epilayers on an ordered nanoporous GaN template by metalorganic chemical vapor deposition. The nanopores in GaN template were created by inductively coupled plasma etching using anodic aluminum oxide film as an etch mask. The average pore diameter and interpore distance is about 65 and 110 nm, respectively. Subsequent overgrowth of GaN first begins at the GaN crystallite surface between the pores, and then air-bridge-mediated lateral overgrowth leads to the formation of the continuous layer. Microphotoluminescence and micro-Raman measurements show improved optical properties and significant strain relaxation in the overgrown layer when compared to GaN layer of same thickness simultaneously grown on sapphire without any template. Similar to conventional epitaxial lateral overgrown GaN, such overgrown GaN on a nanopatterned surface would also serve as a template for the growth of ultraviolet-visible light-emitting III-nitride devices.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.05.Rm Porous materials; granular materials
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
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