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15 Aug 2005

Volume 87, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 073101 (2005); http://dx.doi.org/10.1063/1.2010598 (3 pages)

Ji Ung Lee
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THz sideband generation at telecom wavelengths in a GaAs-based quantum cascade laser

S. S. Dhillon, C. Sirtori, S. Barbieri, A. de Rossi, M. Calligaro, H. E. Beere, and D. A. Ritchie

Appl. Phys. Lett. 87, 071101 (2005); http://dx.doi.org/10.1063/1.2010601 (3 pages) | Cited 11 times

Online Publication Date: 8 August 2005

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Terahertz sideband generation is demonstrated by using the nonlinear intracavity interaction between far-infrared and near-infrared modes in a GaAs waveguide. A low power near-infrared beam at 1.32 μm is coupled into a quantum cascade laser operating at 104 μm (2.9 THz), which acts as both the THz source and the nonlinear medium. The conversion efficiency of the resulting sidebands is found to be approximately 4.5×10−6.
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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
42.72.Ai Infrared sources
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Surface plasmon enhanced spontaneous emission rate of InGaN/GaN quantum wells probed by time-resolved photoluminescence spectroscopy

Koichi Okamoto, Isamu Niki, Axel Scherer, Yukio Narukawa, Takashi Mukai, and Yoichi Kawakami

Appl. Phys. Lett. 87, 071102 (2005); http://dx.doi.org/10.1063/1.2010602 (3 pages) | Cited 106 times

Online Publication Date: 8 August 2005

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We observed a 32-fold increase in the spontaneous emission rate of InGaN/GaN quantum well (QW) at 440 nm by employing surface plasmons (SPs) probed by time-resolved photoluminescence spectroscopy. We explore this remarkable enhancement of the emission rates and intensities resulting from the efficient energy transfer from electron-hole pair recombination in the QW to electron vibrations of SPs at the metal-coated surface of the semiconductor heterostructure. This QW-SP coupling is expected to lead to a new class of super bright and high-speed light-emitting diodes (LEDs) that offer realistic alternatives to conventional fluorescent tubes.
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78.67.De Quantum wells
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.68.+m Optical properties of surfaces
78.55.Cr III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.Cd Superlattices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.47.-p Spectroscopy of solid state dynamics
78.40.Fy Semiconductors

Optical nonlinearity of colloidal crystals

J. P. Huang and K. W. Yu

Appl. Phys. Lett. 87, 071103 (2005); http://dx.doi.org/10.1063/1.2008359 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2005

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We theoretically exploit a class of colloidal-crystal-based nonlinear optical materials, which are made of graded metallodielectric nanoparticles suspended in a host fluid. Such materials can have both an enhancement and a redshift of optical nonlinearity, due to the gradation inside the nanoparticles as well as the lattice effects arising from the periodic structure.
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42.70.Mp Nonlinear optical crystals
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
82.70.Dd Colloids
42.65.-k Nonlinear optics
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
82.70.Kj Emulsions and suspensions

Highly strained InGaAs/GaAs multiple quantum-wells for laser applications in the 1200–1300 nm wavelength regime

P. Sundgren, J. Berggren, P. Goldman, and M. Hammar

Appl. Phys. Lett. 87, 071104 (2005); http://dx.doi.org/10.1063/1.2010615 (3 pages) | Cited 15 times

Online Publication Date: 8 August 2005

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We report on metalorganic vapor-phase epitaxy growth optimization and properties of highly strained InGaAs/GaAs quantum-well (QW) structures with emission wavelength beyond 1200 nm. It is observed that a sufficiently high V/III ratio in combination with low growth temperature is critical for preserved layer integrity when increasing the strain. Multiple QWs with up to five wells are realized without any degradation in photoluminescence intensity or broad-area laser performance at an emission wavelength of 1240 nm with threshold current density below 70 A/cm2 per well.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells

Novelty filtering with a photorefractive lithium–niobate crystal

Vishnu Vardhan Krishnamachari, Oliver Grothe, Hendrik Deitmar, and Cornelia Denz

Appl. Phys. Lett. 87, 071105 (2005); http://dx.doi.org/10.1063/1.2007857 (3 pages) | Cited 8 times

Online Publication Date: 8 August 2005

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In this letter we present a technique which employs a photorefractive lithium–niobate crystal for novelty filtering. Due to the minimal trail formation exhibited by this novelty filter, it can be used for reliable quantitative phase measurement for time intervals of the order of a few hours. We present a simplified theoretical description of this filter based on a coupled wave theory [ N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, and V. L. Vinetskii, Ferroelectrics 22, 949 (1979) ; N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, and V. L. Vinetskii, Ferroelectrics22, 961 (1979) ]. We also demonstrate the first experimental results of employing this device in the field of microfluid dynamics for measuring the concentration changes produced due to the mixing of two transparent liquids in a microchannel.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials
47.80.-v Instrumentation and measurement methods in fluid dynamics

Effect of a dielectric coating on terahertz surface plasmon polaritons on metal wires

Nick C. J. van der Valk and Paul C. M. Planken

Appl. Phys. Lett. 87, 071106 (2005); http://dx.doi.org/10.1063/1.2011773 (3 pages) | Cited 22 times

Online Publication Date: 8 August 2005

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The authors present measurements and calculations on the effect of thin dielectric coatings on the propagation of terahertz pulses along the surface of metal wires. Our measurements show that propagation over only a few centimeters of wire having a thin dielectric coating, strongly distorts the terahertz pulse, which results in a several tens of picoseconds long chirped signal. We demonstrate that the terahertz pulses propagate along the wire as surface waves, and show how a thin coating of a nondispersive material makes this propagation strongly dispersive, giving rise to the chirped signal observed in the measurements. Our results show the potential of terahertz surface plasmon polaritons on metal wires for the sensitive detection of thin dielectric layers.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
77.55.-g Dielectric thin films
63.20.-e Phonons in crystal lattices

Ultralow threshold current terahertz quantum cascade lasers based on double-metal buried strip waveguides

Sukhdeep Dhillon, Jesse Alton, Stefano Barbieri, Carlo Sirtori, A. de Rossi, M. Calligaro, Harvey E. Beere, and David Ritchie

Appl. Phys. Lett. 87, 071107 (2005); http://dx.doi.org/10.1063/1.2001159 (3 pages) | Cited 16 times

Online Publication Date: 9 August 2005

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Terahertz (THz) quantum cascade lasers based on a buried cavity geometry are demonstrated by combining double-metal waveguides with proton implantation. Devices are realized with emission at 2.8 THz, displaying ultralow threshold currents of 19 mA (127 A/cm2) at 4 K in both pulsed and continuous wave operation. Owing to the semiconductor material on both sides of the active region and to the narrow width of the top metal strip, the thermal properties of these devices have been greatly improved. A decrease of the thermal resistance by over a factor of two compared to standard ridge double-metal lasers of similar size has been measured.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Combined electromagnetic and photoreaction modeling of CLD-1 photobleaching in polymer microring resonators

Yanyi Huang, Joyce K. S. Poon, Wei Liang, Amnon Yariv, Cheng Zhang, and Larry R. Dalton

Appl. Phys. Lett. 87, 071108 (2005); http://dx.doi.org/10.1063/1.2031945 (3 pages) | Cited 1 time

Online Publication Date: 9 August 2005

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By combining a solid-state photoreaction model with the modal solutions of an optical waveguide, we simulate the refractive index change due to the photobleaching of CLD-1 chromophores in an amorphous polycarbonate microring resonator. The simulation agrees well with experimental results. The photobleaching quantum efficiency of the CLD-1 chromophores is determined to be 0.65%. The combined modeling of the electromagnetic wave propagation and photoreaction precisely illustrates the spatial and temporal evolution of the optical properties of the polymer material as manifested in the refractive index and their effects on the modal and physical properties of the optical devices.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.−a
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.−m

Very large electro-optic coefficients from in situ generated side-chain nonlinear optical polymers

Jae-Wook Kang, Tae-Dong Kim, Jingdong Luo, Marnie Haller, and Alex K.-Y. Jen

Appl. Phys. Lett. 87, 071109 (2005); http://dx.doi.org/10.1063/1.2031931 (3 pages) | Cited 8 times

Online Publication Date: 10 August 2005

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A synthetic/processing method has been developed for achieving highly efficient nonlinear optical polymers. A maleimide-containing chromophore with large molecular nonlinearity was covalently attached onto a anthrathene-containing polymer to generate in situ a side-chain polymer via the Diels-Alder reaction. The poling and covalent side-chain attachment processes can be performed simultaneously in a solid state, resulting in high electro-optic (E-O) coefficients (r33 values up to 50 pm/V at 1310 nm) and temporal stability (85% retention of the original dipole alignment after isothermal heating at 85 °C for more than 500 h). A very high chromophore loading level (39 wt %) can be achieved by adding more chromophore into this side-chain polymer without causing any obvious phase separation. Poling of this chromophore-doped side-chain polymer (total dye content: 34 wt %) showed a significantly increased E-O coefficient, from 50 to 110 pm/V.
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42.70.Jk Polymers and organics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Jq Electro-optical effects
77.22.Ej Polarization and depolarization
81.40.Gh Other heat and thermomechanical treatments
42.65.-k Nonlinear optics

Epitaxial growth of a nanoscale, vertically faceted, one-dimensional, high-aspect ratio grating in III-V materials for integrated photonics

S. C. Lee, L. R. Dawson, and S. R. J. Brueck

Appl. Phys. Lett. 87, 071110 (2005); http://dx.doi.org/10.1063/1.1984085 (3 pages) | Cited 3 times

Online Publication Date: 12 August 2005

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Homoepitaxial selective growth of a GaAs nanoscale, high-aspect ratio, one-dimensional (1D) grating with vertical facets is reported. For a pattern direction along [110], the kinetics of faceting in selective molecular-beam epitaxy (MBE) induce (1math0)-type facets vertical to a GaAs(001) substrate near the boundary between an SiO2 mask and an open substrate area. On a 1.25-μm period, 1D stripe, SiO2-patterned GaAs(001) substrate with an opening width of ∼ 300 nm, vertical faceting results in a grating structure consisting of 2.8-μm-high, 820-nm-wide features. Kinetics of faceting in selective MBE is explained as a result of the minimization of total surface energy.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
68.47.Fg Semiconductor surfaces
68.35.Md Surface thermodynamics, surface energies

Enhanced light emission from InAs quantum dots in single-defect photonic crystal microcavities at room temperature

W.-Y. Chen, W.-H. Chang, H.-S. Chang, T. M. Hsu, Chien-Chieh Lee, Chii-Chang Chen, P. G. Luan, J.-Y. Chang, T.-P. Hsieh, and J.-I. Chyi

Appl. Phys. Lett. 87, 071111 (2005); http://dx.doi.org/10.1063/1.2008367 (3 pages) | Cited 6 times

Online Publication Date: 12 August 2005

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The optical properties of InAs quantum dots with photonic crystal microcavity emitting near 1.3 μm were investigated at room temperature. The photoluminescence (PL) intensity for quantum dots in cavity was enhanced by two orders of magnitude. The large PL enhancement was attributed to the effects combining the improved extraction efficiency and the enhanced spontaneous emission rate due to the Purcell effect. A threefold Purcell enhancement is observed at room temperature, which is predominantly achieved by the very small mode volume of the photonic crystal microcavity.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
42.70.Qs Photonic bandgap materials
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Gas heating in plasma-assisted sputter deposition

A. Palmero, H. Rudolph, and F. H. P. M. Habraken

Appl. Phys. Lett. 87, 071501 (2005); http://dx.doi.org/10.1063/1.2010609 (3 pages) | Cited 17 times

Online Publication Date: 8 August 2005

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We present a theoretical framework to deal with an important source of nonhomogeneity in plasma-assisted sputter deposition. The gas heating due to the interaction between the background gas and the flow of energetic sputtered particles seems to be of significance under realistic deposition conditions. The results illustrate that the decrease of the gas density due to this heating has to be taken into account for a proper description of the deposition process, even when the total pressure in the system remains constant. The Keller–Simmons equation, that describes the deposition rate in a parallel plate reactor, has been studied in the case of such a nonhomogeneous plasma. We determine the conditions for its applicability and find a direct relation between the throw distance, the temperature of the growing film and the cross section of elastic scattering of a sputtered atom on a gas particle.
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52.77.Dq Plasma-based ion implantation and deposition
52.50.Gj Plasma heating by particle beams
52.40.Mj Particle beam interactions in plasmas
52.25.-b Plasma properties
52.30.-q Plasma dynamics and flow
81.15.Cd Deposition by sputtering

Energy dependence of ion-assisted chemical etch rates in reactive plasmas

L. Stafford, J. Margot, M. Chaker, and S. J. Pearton

Appl. Phys. Lett. 87, 071502 (2005); http://dx.doi.org/10.1063/1.2031936 (3 pages) | Cited 10 times

Online Publication Date: 8 August 2005

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In a highly cited paper, Steinbrüchel [ C. Steinbrüchel, Appl. Phys. Lett. 55, 1960 (1989) ] has demonstrated that in the sub-keV region the etch yield scales like the square root of the ion energy. Based on this result, many authors have subsequently applied this specific energy dependence to ion-assisted chemical etch rates of various materials in different etch tools. In this work, it is demonstrated that in contrast to the etch yield, the etch rate cannot universally be modeled by a simple square-root energy dependence. A novel model accounting for the correct energy dependence of ion-assisted chemical etch rates is therefore proposed. Application of this model to the etching of SiO2 and ZnO in halogenated plasma chemistries provides a quantitative description of the simultaneous dependence of the etch rate on ion energy and on ion and reactive neutral fluxes.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.05.Dz II-VI semiconductors
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Fullerenelike arrangements in carbon nitride thin films grown by direct ion beam sputtering

R. Gago, G. Abrasonis, A. Mücklich, W. Möller, Zs. Czigány, and G. Radnóczi

Appl. Phys. Lett. 87, 071901 (2005); http://dx.doi.org/10.1063/1.2008366 (3 pages) | Cited 12 times

Online Publication Date: 8 August 2005

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Carbon nitride (CNx) thin films were grown by direct N2/Ar ion beam sputtering of a graphite target at moderate substrate temperatures (300–750 K). The resulting microstructure of the films was studied by high-resolution transmission electron microscopy. The images showed the presence of curved basal planes in fullerenelike arrangements. The achievement and evolution of these microstructural features are discussed in terms of nitrogen incorporation, film-forming flux, and ion bombardment effects, thus adding to the understanding of the formation mechanisms of curved graphitic structures in CNx materials.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.37.Lp Transmission electron microscopy (TEM)
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.60.Wm Other nonelectronic physical properties

Resonant Raman study of confined Se single helix and Se8 rings

I. L. Li, S. C. Ruan, Z. M. Li, J. P. Zhai, and Z. K. Tang

Appl. Phys. Lett. 87, 071902 (2005); http://dx.doi.org/10.1063/1.2009053 (3 pages) | Cited 6 times

Online Publication Date: 8 August 2005

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Electron-phonon coupling in Se species confined in the nanoporous matrix has been investigated by using resonant Raman spectra performed with several different laser lines from deep blue to near infrared. The spectra strongly depend on the energies of the excitation laser lines. The one-phonon symmetric A1 modes for Se single helix and Se8 rings are enhanced in the vicinity of their absorption bands. Detailed analysis shows that the Raman band in the high-frequency range of 450–550 cm−1 is composed of three individual second-order Raman bands for the confined Se species. These two-phonon Raman shifts occur at twice the frequency shift of the first-order Raman lines, and their intensities are also enhanced when the excitation laser energy matches an electronic transition in Se nanospecies.
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78.30.Hv Other nonmetallic inorganics
63.20.K- Phonon interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Impact of Ge on integration of HfO2 and metal gate electrodes on strained Si channels

Yanxia Lin, Mehmet C. Öztürk, Bei Chen, Se Jong Rhee, Jack C. Lee, and Veena Misra

Appl. Phys. Lett. 87, 071903 (2005); http://dx.doi.org/10.1063/1.2009809 (3 pages) | Cited 4 times

Online Publication Date: 8 August 2005

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Tensile-strained Si epitaxial layers (7.5 nm–17 nm) were grown on relaxed Si0.5Ge0.5 virtual substrates by ultrahigh-vacuum rapid thermal chemical vapor deposition. Metal-oxide-silicon capacitors were fabricated with SiO2 or HfO2 as gate dielectrics and Ru–Ta alloy or TaN as the metal gate electrodes. The results indicate that the interface trap density (Dit) increased as the strained silicon thickness decreased, which was attributed to the presence of Ge in the strained Si layer. Higher Dit was observed with SiO2 which may be due to Si consumption during oxidation, leading to a higher density of Ge at the interface. Leakage current density (Jg) was also observed to increase with increasing strained silicon thickness. This trend of increasing Dit and Jg with decreasing strained silicon thickness did not change after rapid thermal annealing. Both Ru–Ta and TaN gate electrodes were found to exhibit as good a performance on strained Si as on bulk Si.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Coherent thermal emission from one-dimensional photonic crystals

B. J. Lee, C. J. Fu, and Z. M. Zhang

Appl. Phys. Lett. 87, 071904 (2005); http://dx.doi.org/10.1063/1.2010613 (3 pages) | Cited 43 times

Online Publication Date: 9 August 2005

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Coherent thermal emission from surface relief gratings holds promise for spectral and directional control of thermal radiation but is limited to transverse magnetic waves, which can excite surface plasmon or phonon polaritons in the grating structure. We show in this letter that a coherent thermal source can be constructed with a thin polar material coated on a one-dimensional photonic crystal. The excitation of surface waves at the interface of the coated layer and the photonic crystal results in highly spectral and directional emission in the infrared for both the transverse electric wave and the transverse magnetic wave.
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42.72.Ai Infrared sources
42.70.Qs Photonic bandgap materials

High resolution, high collection efficiency in numerical aperture increasing lens microscopy of individual quantum dots

Zhiheng Liu, Bennett B. Goldberg, Stephen B. Ippolito, Anthony N. Vamivakas, M. Selim Ünlü, and Richard Mirin

Appl. Phys. Lett. 87, 071905 (2005); http://dx.doi.org/10.1063/1.2012532 (3 pages) | Cited 12 times

Online Publication Date: 9 August 2005

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We demonstrate the application of a subsurface solid immersion technique to the photoluminescence spectroscopy of individual quantum dots. Contrasted with the conventional solid immersion microscopy, we used a numerical aperture increasing lens and moved the interface between the sample and the solid immersion lens away from the focal plane, thus diminished the influence of interface artifacts on the images obtained in a two-dimensional scan. Meanwhile, our technique has achieved a high spatial resolution of λ/3 that is capable of resolving the spectroscopic features of single QDs. We also demonstrate that the collection efficiency of our system is six times better than that of a conventional confocal microscope with a high NA objective.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.-m Photoluminescence, properties and materials
81.07.Ta Quantum dots

Low-resistance Au and Au/Ni/Au Ohmic contacts to p-ZnMgO

Kelly Ip, Yuanjie Li, D. P. Norton, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 87, 071906 (2005); http://dx.doi.org/10.1063/1.2012518 (3 pages) | Cited 3 times

Online Publication Date: 9 August 2005

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Both electron-beam-deposited Au and Au/Ni/Au are found to produce low-resistance Ohmic contacts (ρC in the range 2.5×10−5–7.6×10−6 Ω cm2) to p-type ZnMgO (p ∼ 1016 cm−3) on sapphire substrates after annealing at 600 °C. The as-deposited contacts are rectifying in both cases. For the Au contact, the annealing produces a small amount of outdiffusion of Zn to the surface of the contact, whereas with the Au/Ni/Au, both Ni and Zn are found on the surface. In both cases, the formation of Zn vacancies may play a role in increasing the near-surface hole concentration in the ZnMgO.
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73.61.Ga II-VI semiconductors
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
61.72.J- Point defects and defect clusters

Existence and atomic arrangement of microtwins in hexagonal MnAs ferromagnetic epilayers grown on GaAs (100) substrates with monolayer InAs Buffers

H. S. Lee, S. Yi, T. W. Kim, D. U. Lee, H. C. Jeon, T. W. Kang, K. H. Lee, and J. Y. Lee

Appl. Phys. Lett. 87, 071907 (2005); http://dx.doi.org/10.1063/1.2011796 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2005

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Selected-area electron-diffraction pattern (SADP) and high-resolution transmission electron microscopy (HRTEM) measurements were carried out to investigate the existence and the atomic arrangement of microtwins in hexagonal MnAs ferromagnetic epilayers grown on GaAs (100) substrates with monolayer InAs buffer layers by using molecular beam epitaxy. The magnetization curve as a function of the magnetic field at 5 K showed that the MnAs thin films were ferromagnetic, and the magnetization curve as a function of the temperature revealed that the ferromagnetic transition temperature was as high as 325 K. The SADP and HRTEM results showed that an epitaxial relationship was formed among the hexagonal MnAs layer, the InAs layer, and the zincblende GaAs substrate. Microtwins existed between the MnAs grain boundaries on top of the InAs layers. Based on the SADP and HRTEM results, we present a possible atomic arrangement of the microtwins for the MnAs-InAs-GaAs heterostructure.
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75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.37.Lp Transmission electron microscopy (TEM)
61.72.Mm Grain and twin boundaries

Influence of dislocations on photoluminescence of InGaN/GaN multiple quantum wells

J. C. Zhang, D. S. Jiang, Q. Sun, J. F. Wang, Y. T. Wang, J. P. Liu, J. Chen, R. Q. Jin, J. J. Zhu, H. Yang, T. Dai, and Q. J. Jia

Appl. Phys. Lett. 87, 071908 (2005); http://dx.doi.org/10.1063/1.2012531 (3 pages) | Cited 14 times

Online Publication Date: 10 August 2005

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The influence of dislocations on photoluminescence (PL) of InGaN/GaN multiple quantum wells (MQWs) is investigated by triple-axis x-ray diffraction (TAXRD), transmission electron microscopy (TEM), and PL spectra. The ω scan of every satellite peak by TAXRD is adopted to evaluate the mean screw and edge dislocation densities in MQWs. The results show that dislocations can lead to a reduction of the PL-integrated intensity of InGaN/GaN MQWs under certain conditions, with edge dislocations playing a decisive role. Additionally, the dislocations can broaden the PL peak, but the effect becomes evident only under the condition when the interface roughness is relatively low.
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78.67.De Quantum wells
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
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
68.65.Fg Quantum wells

Significant stiffness reduction at ferroelectric domain boundary evaluated by ultrasonic atomic force microscopy

T. Tsuji, S. Saito, K. Fukuda, K. Yamanaka, H. Ogiso, J. Akedo, and Y. Kawakami

Appl. Phys. Lett. 87, 071909 (2005); http://dx.doi.org/10.1063/1.2012537 (3 pages) | Cited 9 times

Online Publication Date: 10 August 2005

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Two-dimensional resonance frequency mapping in the ultrasonic atomic force microscopy was applied to the investigation of the ferroelectric domain structure in lead zirconate titanate ceramics. This method can visualize the stiffness anisotropy due to the differently oriented domains. Moreover, the significant stiffness reduction at the ferroelectric domain boundary was discovered. The disorder of the lattice, the ability of the switching of the domain, and the reduction of the piezoelectric stiffening are possible explanations. The implication of this work is the characterization of novel functional materials on nanoscale and the nondestructive evaluation of the microelectromechanical systems and nanotechnology devices.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.65.-j Piezoelectricity and electromechanical effects
77.80.Fm Switching phenomena
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
68.37.Ps Atomic force microscopy (AFM)

Tuning stimulated emission of organic thin films by molecular reorientation

Hao-Wu Lin, Chun-Liang Lin, Chung-Chih Wu, Teng-Chih Chao, and Ken-Tsung Wong

Appl. Phys. Lett. 87, 071910 (2005); http://dx.doi.org/10.1063/1.2031940 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2005

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In this letter, employing the spectroscopic ellipsometry, we study the phenomena of molecular reorientation in amorphous thin films of a ter(9,9-diarylfluorene) compound T3 upon annealing around or above its glass transition temperature. Molecular reorientation results in changes in the in-plane optical constants, which in turn could alter the waveguiding characteristics of a thin-film slab waveguide. Employing such properties, we demonstrate continuous tuning of the wavelength of amplified spontaneous emission of a T3 slab waveguide within one sample. Such an approach has the particular advantage of permitting facile tuning of stimulated emission after device fabrication.
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42.79.Gn Optical waveguides and couplers
78.66.Qn Polymers; organic compounds
78.66.Jg Amorphous semiconductors; glasses
78.45.+h Stimulated emission
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing

Direct formation of Na3AlH6 by mechanical milling NaH/Al with TiF3

P. Wang, X. D. Kang, and H. M. Cheng

Appl. Phys. Lett. 87, 071911 (2005); http://dx.doi.org/10.1063/1.2001756 (3 pages) | Cited 7 times

Online Publication Date: 12 August 2005

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Na3AlH6 can be directly formed by mechanical milling NaH/Al with TiF3 under hydrogen atmosphere. The hydrogenation fraction of NaH increases with increasing the milling time, and reaches up to 0.61 after 20 h milling. Thus-formed Na3AlH6 exhibits unexpected polymorphic transformation and decomposition behaviors. This, together with the unusual hydrogen storage performance of the mechanically prepared materials, provides us a suggestive perspective to probe the favorable modification of the thermodynamics of Na3AlH6 and nature of active Ti-species in Ti-doped NaAlH4.
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81.20.Wk Machining, milling
84.60.-h Direct energy conversion and storage
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.75.-g Phase equilibria
65.40.G- Other thermodynamical quantities
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Transport properties of p-type phosphorus-doped (Zn,Mg)O grown by pulsed-laser deposition

Y. J. Li, Y. W. Heo, Y. Kwon, K. Ip, S. J. Pearton, and D. P. Norton

Appl. Phys. Lett. 87, 072101 (2005); http://dx.doi.org/10.1063/1.2010600 (3 pages) | Cited 39 times

Online Publication Date: 8 August 2005

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We report on carrier type in phosphorus-doped (Zn,Mg)O films grown by pulsed-laser deposition under a broad range of conditions. For film growth at 500 °C, increasing the oxygen partial pressure from 20 to 200 mTorr yielded a carrier type conversion from n to p type. Transport characteristics of as-grown P-doped (Zn,Mg)O films were determined by Hall-effect measurements at room temperature. The P-doped (Zn,Mg)O films grown at 150 mTorr oxygen partial pressure were marginally p type and exhibited a hole concentration of 2.7×1016 cm−3, a mobility of 8.2 cm2/V s, and a resistivity of 35 Ω cm. The films exhibited good crystallinity with c-axis orientation. These results indicate the importance of oxidation conditions in realizing p-type (Zn,Mg)O films.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.65.Mq Oxidation
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