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5 Jul 2004

Volume 85, Issue 1, pp. 1-159

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 145 (2004); http://dx.doi.org/10.1063/1.1769595 (3 pages)

J. U. Lee, P. P. Gipp, and C. M. Heller
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Waveguiding in air by total external reflection from ultralow index metamaterials

Brian T. Schwartz and Rafael Piestun

Appl. Phys. Lett. 85, 1 (2004); http://dx.doi.org/10.1063/1.1764596 (3 pages) | Cited 25 times

Online Publication Date: 29 June 2004

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Metamaterials composed of metal-dielectric nanostructures can be engineered to have the real part of the effective refractive index less than unity at optical wavelengths. These materials show intriguing optical properties including total external reflection. We utilize this effect to design and analyze slab waveguide structures that guide visible light in an air core.
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42.79.Gn Optical waveguides and couplers

Probing the dispersive and spatial properties of photonic crystal waveguides via highly efficient coupling from fiber tapers

P. E. Barclay, K. Srinivasan, M. Borselli, and O. Painter

Appl. Phys. Lett. 85, 4 (2004); http://dx.doi.org/10.1063/1.1767954 (3 pages) | Cited 31 times

Online Publication Date: 29 June 2004

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The demonstration of an optical fiber based probe for efficiently exciting the waveguide modes of high-index contrast planar photonic crystal (PC) slabs is presented. Fiber taper waveguides formed from standard silica single-mode optical fibers are used to evanescently couple light into the guided modes of a patterned silicon membrane. A coupling efficiency of ∼95% is obtained between the fiber taper and a PC waveguide mode suitably designed for integration with a previously studied ultrasmall mode volume high-Q PC resonant cavity [Srinivasan et al., Appl. Phys. Lett. 83, 1915 (2003)]. The micron-scale lateral extent and dispersion of the fiber taper is used as a near-field spatial and spectral probe to study the profile and dispersion of PC waveguide modes.
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42.79.Gn Optical waveguides and couplers
42.81.Qb Fiber waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials

Electrical characteristics of InGaN∕GaN light-emitting diodes grown on GaN and sapphire substrates

X. A. Cao, J. M. Teetsov, M. P. D’Evelyn, D. W. Merfeld, and C. H. Yan

Appl. Phys. Lett. 85, 7 (2004); http://dx.doi.org/10.1063/1.1767280 (3 pages) | Cited 46 times

Online Publication Date: 29 June 2004

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We report on the electrical characteristics of InGaN∕GaN multiple-quantum-well light-emitting diodes (LEDs) grown on sapphire and free-standing GaN substrates. As a result of defect reduction, the tunneling current in the homoepitaxially grown LED was remarkably suppressed and diffusion-recombination current dominated at intermediate forward bias. Temperature-dependent measurements showed that the remaining reverse current originated from carrier generation and tunneling associated with deep-level traps. In contrast, the LED on sapphire exhibited dominant tunneling characteristics over a wide range of applied bias. Nanoscale electrical characterization using conductive atomic force microscopy revealed highly localized currents at V-defects, indicating that the associated dislocations are electrically active and likely responsible for the high leakage current in the heteroepitaxially grown LED.
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85.60.Jb Light-emitting devices
68.37.Ps Atomic force microscopy (AFM)
71.55.Eq III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Tunable blue organic light emitting diode based on aluminum calixarene supramolecular complex

C. Legnani, R. Reyes, M. Cremona, I. A Bagatin, and H. E. Toma

Appl. Phys. Lett. 85, 10 (2004); http://dx.doi.org/10.1063/1.1767274 (3 pages) | Cited 14 times

Online Publication Date: 29 June 2004

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In this letter, the results of supramolecular organic light emitting diodes using a calix[4] arene complex thin film as emitter and electron transporting layer are presented. The devices were grown onto glass substrates coated with indium-tin-oxide layer and aluminum thick (150 nm) cathode. By applying a dc voltage between the device electrodes in forward bias condition, a blue light emission in the active area of the device was observed. It was found that the electroluminescent emission peak can be tuned between 470 and 510 nm changing the applied voltage bias from 4.3 to 5.4 V. The observed tunable emission can be associated with an energy transfer from the calixarene compound.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Fountain-pen-based laser microstructuring with gold nanoparticle inks

Tae Y. Choi, Dimos Poulikakos, and Costas P. Grigoropoulos

Appl. Phys. Lett. 85, 13 (2004); http://dx.doi.org/10.1063/1.1767281 (3 pages) | Cited 28 times

Online Publication Date: 29 June 2004

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Employing the fountain-pen principle, a micropipette is used to write an Au nanoparticle ink on glass substrates. A continuous-wave laser (488–515 nm) is subsequently used as a controlled, localized energy source to evaporate the carrier liquid (toluene) in the ink and sinter the nanoparticles together thus fabricating continuous gold stripes 5 μm in width and a few hundred nanometers in height. The scanning speed, the laser intensity, and the degree of defocusing are identified as important parameters to the successful manufacturing of the gold microstructures. The electrical resistivity of the stripes, within the parametric domain of the present work, is measured to be the order of 10−6 Ω m.
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61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.16.Rf Micro- and nanoscale pattern formation
81.05.Bx Metals, semimetals, and alloys
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Ultralow refractive index substrates–a base for photonic crystal slab waveguides

M. Schmidt, G. Boettger, M. Eich, W. Morgenroth, U. Huebner, R. Boucher, H. G. Meyer, D. Konjhodzic, H. Bretinger, and F. Marlow

Appl. Phys. Lett. 85, 16 (2004); http://dx.doi.org/10.1063/1.1767962 (3 pages) | Cited 24 times

Online Publication Date: 29 June 2004

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Out of plane radiation losses in two-dimensional (2D) photonic crystal (PC) waveguides occur due to a lack of total internal reflection at the core-substrate∕superstrate boundaries. In order to minimize these losses, either a high vertical refractive index contrast or deep etching into the substrate is required [G. Boettger, C. Liguda, M. Schmidt, and M. Eich, Appl. Phys. Lett. 81, 2517 (2002)]. The maximum vertical contrast is achieved in air bridge type PC waveguides, which are inherently fragile. In this article, we introduce a concept which combines the advantages of a high vertical index contrast of an air bridge with those of a solid substrate. This approach consists of mesoporous silica as substrate material with an ultralow refractive index (n=1.14 at 1.3 μm), close to that of air. Finite 2D PC line defect resonators consisting of an optical polymer as core and mesoporous silica as substrate were fabricated. Compared to ordinary substrates with higher refractive indices like silica or amorphous Teflon [C. Liguda, G. Boettger, A. Kuligk, M. Eich, H. Roth, J. Kunert, W. Morgenroth, H. Elsner, and H. G. Meyer, Appl. Phy. Lett. 78, 2434 (2001)], measurements show significantly increased transmission at the resonance wavelength and virtually no losses on the sensitive air band side.
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42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials
81.65.Cf Surface cleaning, etching, patterning

Continuous-wave laser oscillation at 929 nm from a Nd3+-doped LiNbO3:ZnO nonlinear laser crystal: A powerful tool for blue laser light generation

D. Jaque, J. A. Sanz García, and J. García Solé

Appl. Phys. Lett. 85, 19 (2004); http://dx.doi.org/10.1063/1.1768299 (3 pages) | Cited 16 times

Online Publication Date: 29 June 2004

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This work reports on room-temperature continuous-wave laser action at 929 nm from a Nd3+:LiNbO3 nonlinear laser crystal co-doped with ZnO. The spectroscopic parameters of the quasi-three-level 4F3∕2→4I9∕2 laser channel are discussed. In nonoptimal preliminary experiments, pump power at threshold was found to be as low as 105 mW.
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42.55.Rz Doped-insulator lasers and other solid state lasers
81.10.Fq Growth from melts; zone melting and refining
61.72.S- Impurities in crystals

Electroluminescence at 7 terahertz from phosphorus donors in silicon

P.-C. Lv, R. T. Troeger, T. N. Adam, S. Kim, J. Kolodzey, I. N. Yassievich, M. A. Odnoblyudov, and M. S. Kagan

Appl. Phys. Lett. 85, 22 (2004); http://dx.doi.org/10.1063/1.1769589 (3 pages) | Cited 33 times

Online Publication Date: 29 June 2004

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Terahertz (THz) emissions corresponding to intracenter transitions of phosphorus impurities in silicon have been observed up to 30 K. Electrical pulses (250 ns) with a repetition rate of 413 Hz were used for excitation, and the peak power was calculated to be ∼20 μW∕facet for a 190×120 μm2 device with a peak pumping current of 400 mA at 12 K. THz emission intensity increased linearly with pumping current and quenched when the sample temperature was above 30 K. The current–voltage characteristics suggested a conduction and excitation mechanism by injection of electrons from a Schottky barrier followed by impact ionization of the neutral impurities.
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78.66.Db Elemental semiconductors and insulators
78.60.Fi Electroluminescence
71.55.Cn Elemental semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
78.70.Gq Microwave and radio-frequency interactions

Spectral focusing: High spectral resolution spectroscopy with broad-bandwidth laser pulses

Thomas Hellerer, Annika M.K. Enejder, and Andreas Zumbusch

Appl. Phys. Lett. 85, 25 (2004); http://dx.doi.org/10.1063/1.1768312 (3 pages) | Cited 82 times

Online Publication Date: 29 June 2004

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In this work, we show how broad-bandwidth femtosecond pulses can be used to achieve high spectral resolution in nonlinear spectroscopy and microscopy. Our approach is based on chirping the excitation pulses in order to focus their entire bandwidth into a narrow spectral region. We show that spectral features which are 100 times narrower than the excitation light can be resolved with this simple spectral focusing. The gain in spectral selectivity and sensitivity makes its application to nonlinear microscopy very convenient. This is demonstrated with diffraction-limited coherent anti-Stokes Raman scattering microscopy.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Chirp characterization of ultrashort pulses utilizing molecular vibrations

Pedro Julian Rizo and Takayoshi Kobayashi

Appl. Phys. Lett. 85, 28 (2004); http://dx.doi.org/10.1063/1.1768303 (3 pages) | Cited 1 time

Online Publication Date: 29 June 2004

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A method is presented and demonstrated for chirp characterization of ultrashort laser pulses utilizing identical setup and detection systems of common pump–probe experiments. The coherent intramolecular vibrations that can be impulsively excited in a nonresonant manner in many common solvents are used to directly measure the spectral relative delay of femtosecond pulses. For pump–probe experiments on solutions, this method has the capability of isolating the phase of the signal due to the solute from the phase due to the solvent and to uncompensated chirp in the laser pulse. The method is not restricted to pulses with optical bandwidth narrower than an octave.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
63.50.-x Vibrational states in disordered systems
78.30.C- Liquids
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
78.47.-p Spectroscopy of solid state dynamics

Subpicosecond pulses from a gain-switched polymer distributed feedback laser

Mark Goossens, Arvydas Ruseckas, Graham A. Turnbull, and Ifor D. W. Samuel

Appl. Phys. Lett. 85, 31 (2004); http://dx.doi.org/10.1063/1.1767952 (3 pages) | Cited 10 times

Online Publication Date: 29 June 2004

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The emission dynamics of polymer distributed feedback lasers have been studied following excitation by femtosecond laser pulses. The lasers were found to generate pulses as short as 800 fs. The dynamics were investigated as a function of pump power and excitation spot size. Simple rate equations modeling the amplification of spontaneous emission are shown to describe the behavior of the lasing dynamics observed.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
42.70.Jk Polymers and organics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Wavelength conversion in silicon using Raman induced four-wave mixing

V. Raghunathan, R. Claps, D. Dimitropoulos, and B. Jalali

Appl. Phys. Lett. 85, 34 (2004); http://dx.doi.org/10.1063/1.1768310 (3 pages) | Cited 16 times

Online Publication Date: 29 June 2004

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Conversion of digital- and analog-modulated optical signals from the 1550 nm band to the 1300 nm band is demonstrated in silicon waveguides. The conversion is based on parametric Stokes to anti-Stokes coupling using the Raman susceptibility of silicon.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Wi Nonlinear waveguides
42.65.An Optical susceptibility, hyperpolarizability
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Photovoltaic effect in La0.7Ce0.3MnO3−δ∕SrTiO3‐Nb heterojunction and its oxygen content dependence

J. R. Sun, C. H. Lai, and H. K. Wong

Appl. Phys. Lett. 85, 37 (2004); http://dx.doi.org/10.1063/1.1769079 (3 pages) | Cited 16 times

Online Publication Date: 29 June 2004

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The photovoltaic effect (PVE) of a heterojunction composed of a La0.7Ce0.3MnO3 (LCE) film and a 0.5 wt. % Nb-doped SrTiO3 crystal has been experimentally studied. A strong PVE was observed, and the maximum photovoltage was ∼54.1 mV, when the LCE film was exposed to light with a wavelength (λ) of 460 nm and a power of ∼6.5 μW. The PVE remains significant up to λ=660 nm, though it decreases gradually with the increase of wavelength. Oxygen release of the LCE film depresses the PVE considerably and modifies the rectifying property of the junction. A logarithmic variation of photovoltage with junction resistance was observed. The weakening of the ferromagnetic order of the LCE film due to the incorporation of oxygen vacancies may be the reason for the depression of the PVE.
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72.40.+w Photoconduction and photovoltaic effects
73.61.Ng Insulators
75.50.Dd Nonmetallic ferromagnetic materials

Dominant carrier recombination mechanisms in GaInNAs∕GaAs quantum well light-emitting diodes

J. M. Ulloa, A. Hierro, J. Miguel-Sánchez, A. Guzmán, E. Tournié, J. L. Sánchez-Rojas, and E. Calleja

Appl. Phys. Lett. 85, 40 (2004); http://dx.doi.org/10.1063/1.1769078 (3 pages) | Cited 4 times

Online Publication Date: 29 June 2004

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The electroluminescence of GaInNAs∕GaAs quantum well light-emitting diodes is analyzed as a function of temperature and injection current. The relative influence of nonradiative carrier recombination, recombination from localized states, and conduction-band to valence-band recombination is discussed. The localized states are found to dominate the emission and the external quantum efficiency only at low temperatures and currents. When temperature and∕or injection level are increased, band-to-band transitions become the main recombination mechanism. Nonradiative recombination is strongly thermally activated, and becomes the dominant process above 75 K. As a result of postgrowth rapid thermal annealing, the device luminescence efficiency increases by over one order of magnitude due to a decrease in the density of nonradiative recombination centers.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
61.72.Cc Kinetics of defect formation and annealing
73.20.Fz Weak or Anderson localization
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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High-reflectivity AlxGa1−xN∕AlyGa1−yN distributed Bragg reflectors with peak wavelength around 350 nm

T. Wang, R. J. Lynch, P. J. Parbrook, R. Butté, A. Alyamani, D. Sanvitto, D. M. Whittaker, and M. S. Skolnick

Appl. Phys. Lett. 85, 43 (2004); http://dx.doi.org/10.1063/1.1766404 (3 pages) | Cited 16 times

Online Publication Date: 29 June 2004

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Al0.49Ga0.51N∕Al0.16Ga0.84N distributed Bragg reflectors (DBRs), designed for the ultraviolet spectral region, are reported. The crack-free structures are grown on sapphire substrates by metalorganic chemical vapor deposition. A peak reflectivity of 91% at 353 nm with a stop-band width of 17 nm was obtained at 300 K using a 25 pair DBR. Structures at 6 nm shorter wavelength show asymmetric spectra, a narrower stop band, and slightly decreased peak reflectivity. By studying the spectra as a function of temperature, the degradation is shown to arise from internal absorption at short wavelengths. Simulations based on transfer matrix theory agree well with the experimental data.
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81.05.Ea III-V semiconductors
42.79.Bh Lenses, prisms and mirrors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Photoluminescence of a tensilely strained silicon quantum well on a relaxed SiGe buffer layer

P. Boucaud, M. El Kurdi, and J. M. Hartmann

Appl. Phys. Lett. 85, 46 (2004); http://dx.doi.org/10.1063/1.1766073 (3 pages) | Cited 7 times

Online Publication Date: 29 June 2004

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We have investigated the photoluminescence of tensilely strained silicon layers grown on relaxed SiGe buffer layers. At low excitation densities, the photoluminescence is dominated by the radiative recombinations associated with the dislocations in the buffer layer and the band-edge luminescence of the relaxed SiGe layers. We show that the photoluminescence of a strained silicon quantum well capped by a relaxed SiGe layer can be observed at high excitation densities. The resonance energy of this photoluminescence, observed around 960 meV for the phonon-assisted transition, is in satisfying agreement with the calculated value of the bandgap of the type II strained heterostructure.
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78.67.De Quantum wells
78.55.Ap Elemental semiconductors

Metal delocalization and surface decoration in direct-write nanolithography by electron beam induced deposition

Vidyut Gopal, Eric A. Stach, Velimir R. Radmilovic, and Ian A. Mowat

Appl. Phys. Lett. 85, 49 (2004); http://dx.doi.org/10.1063/1.1765736 (3 pages) | Cited 19 times

Online Publication Date: 29 June 2004

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The ability to interconnect different nanostructures is crucial to nanocircuit fabrication efforts. A simple and versatile direct-write nanolithography technique for the fabrication of interconnects is presented. Decomposition of a metalorganic precursor gas by a focused electron beam resulted in the deposition of conductive platinum nanowires. The combination of in situ secondary electron imaging with deposition allows for the simultaneous identification and interconnection of nanoscale components. However, the deposition was not entirely localized to the electron beam raster area, as shown by secondary ion mass spectrometry measurements. The electrical impact of the metallic spread was quantified by measuring the leakage current between closely spaced wires. The origins of the spread and strategies for minimizing it are discussed. These results indicate that, while this direct-write methodology is a convenient one for rapid prototyping of nanocircuits, caution must be used to avoid unwanted decoration of nanostructures by metallic species.
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81.16.Nd Micro- and nanolithography
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Growth mechanism difference of sputtered HfO2 on Ge and on Si

Koji Kita, Kentaro Kyuno, and Akira Toriumi

Appl. Phys. Lett. 85, 52 (2004); http://dx.doi.org/10.1063/1.1767607 (3 pages) | Cited 47 times

Online Publication Date: 29 June 2004

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HfO2 films were deposited by the reactive sputtering on Ge and Si substrates simultaneously, and we found both the interface layer and the HfO2 film were thinner on Ge substrate than those on Si substrate. A metallic Hf layer has a crucial role for the thickness differences of both interface layer and HfO2 film, since those thickness differences were observed only when an ultrathin metallic Hf layer was predeposited before the reactive sputtering process. The role of metallic Hf in these phenomena is understandable by assuming the formation of a volatile Hf–Ge–O ternary compound at the early stage of the film growth. This result shows that the HfO2∕Ge system has an advantage over the HfO2∕Si system from the viewpoint of further reduction of the gate oxide film thickness.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Effect of corrugated substrates on light extraction efficiency and the mechanism of growth in pulsed laser deposited Y2O3:Eu3+ thin-film phosphors

Kee-Sun Sohn, Namsoo Shin, Yoon-Chang Kim, and Young Rag Do

Appl. Phys. Lett. 85, 55 (2004); http://dx.doi.org/10.1063/1.1766392 (3 pages) | Cited 33 times

Online Publication Date: 29 June 2004

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The luminance level of thin-film Y2O3:Eu3+ phosphors deposited by a pulsed laser deposition techniques are not candidates for field emission display because of their low extraction efficiency. A square lattice nanorod-type two-dimensional SiO2 photonic crystal layer (PCL) was built on a quartz glass substrate in an attempt to improve the efficiency of light extraction. The pitch of the PCL was varied, such that 500, 550, and 600 nm pitches were produced while maintaining the depth of the PCL fixed at 200 nm. The integrated photoluminescence efficiency of an Y2O2:Eu3+ thin-film phosphor deposited on the PCL was improved by 4.8 times and well matched with the calculated result based on the finite-difference time-domain method. The PCL played a significant role not only in enhancing the extraction efficiency but also aiding in the control of the film growth.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition

Solubility of nitrogen and phosphorus in 4H-SiC: A theoretical study

Michel Bockstedte, Alexander Mattausch, and Oleg Pankratov

Appl. Phys. Lett. 85, 58 (2004); http://dx.doi.org/10.1063/1.1769075 (3 pages) | Cited 14 times

Online Publication Date: 29 June 2004

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The n-type dopants phosphorus and nitrogen, and their complexes with intrinsic point defects are investigated in 4H-SiC by first-principles theory. The solubility and electrical activation of the dopants in thermodynamic equilibrium are calculated. For nitrogen, a saturation of the electrical activation above a certain critical concentration is found that is driven by a preferential incorporation of nitrogen into electrically passive nitrogen-vacancy complexes. This explains the observations of recent experiments. An almost complete phosphorus activation is found up to the solubility limit. We suggest that the low phosphorus doping achieved by sublimation growth is related to the growth kinetics.
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61.72.S- Impurities in crystals
71.15.-m Methods of electronic structure calculations
64.75.-g Phase equilibria
61.72.Yx Interaction between different crystal defects; gettering effect

“Soft” bulk metallic glasses based on cerium

B. Zhang, M. X. Pan, D. Q. Zhao, and W. H. Wang

Appl. Phys. Lett. 85, 61 (2004); http://dx.doi.org/10.1063/1.1768308 (3 pages) | Cited 55 times

Online Publication Date: 29 June 2004

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CeAlNiCu alloys can be readily cast into glassy rods with up to 5 mm in diameter. The Ce-based bulk metallic glasses (BMGs) exhibit a wide supercooled region up to 78 K, very low glass transition temperature (Tg=359 K), melting temperature (Tm=637 K), and Debye temperature (θD=144 K). Ultrasonic measurements demonstrate that these Ce-based BMGs are very soft, having the lowest elastic moduli in known BMGs. These features suggest that the “soft” BMGs are an ideal model system for investigating physical problems in glass transition, supercooled liquid and melt states, and have potential applications as a functional material as well.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.D- Solid-liquid transitions
62.20.D- Elasticity

Exciton and biexciton luminescence from single hexagonal GaN∕AlN self-assembled quantum dots

S. Kako, K. Hoshino, S. Iwamoto, S. Ishida, and Y. Arakawa

Appl. Phys. Lett. 85, 64 (2004); http://dx.doi.org/10.1063/1.1769586 (3 pages) | Cited 35 times

Online Publication Date: 29 June 2004

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We report single dot spectroscopy of hexagonal GaN∕AlN self-assembled quantum dots grown by metalorganic chemical vapor deposition. Through the reduction of the number of quantum dots using submicron mesa structures, we have obtained several isolated photoluminescence peaks emitted by individual quantum dots. With increasing excitation power, an additional peak emerges in the higher-energy side of an excitonic ground state. This additional peak shows quadratic power dependence, and is attributed to the photoluminescence from a biexciton state. The biexciton binding energy is negative and the magnitude is about 30 meV, which is explained by the effects of a strong built-in electric field.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)
68.18.-g Langmuir-Blodgett films on liquids
71.35.Gg Exciton-mediated interactions
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Hysteresis loops of the energy band gap and effective g factor up to 18 000 for metamagnetic EuSe epilayers

R. Kirchschlager, W. Heiss, R. T. Lechner, G. Bauer, and G. Springholz

Appl. Phys. Lett. 85, 67 (2004); http://dx.doi.org/10.1063/1.1771454 (3 pages) | Cited 4 times

Online Publication Date: 29 June 2004

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Hysteresis effects of the fundamental energy gap as a function of applied magnetic field are studied for metamagnetic EuSe layers grown by molecular-beam epitaxy. Below the phase transition temperature, the energy gap show large step-like red shifts of up to 150 meV with increasing magnetic field with pronounced hysteresis effects when the change in the magnetic field is reversed. Both, the steps and the hysteresis loops are caused by transitions between the aniferro-, ferri-, and ferromagnetic phases in EuSe. The large redshift of the band gap is directly proportional to the magnetization of the sample and results from the Zeeman spin splitting of the conduction band. The corresponding effective g factor deduced from our experiments reaches values up to 18 000 at the magnetic phase transitions.
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71.20.Ps Other inorganic compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Magnetic flux pinning enhancement in HgBa2CaCu2O6+δ films on vicinal substrates

Y. Y. Xie, J. Z. Wu, S. H. Yun, R. Emergo, R. Aga, and D. K. Christen

Appl. Phys. Lett. 85, 70 (2004); http://dx.doi.org/10.1063/1.1763985 (3 pages) | Cited 3 times

Online Publication Date: 29 June 2004

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High-temperature superconducting HgBa2CaCu2O6+δ films were fabricated on the vicinal surfaces of 4°-miscut SrTiO3 single crystal substrates in a cation-exchange process, with the purpose to induce additional growth defects via a step-flow growth mode on the miscut substrates. The critical current densities (Jc) of these films were measured using a standard four-probe method with magnetic fields applied perpendicular to the film surface. The vicinal Hg-1212 films indeed showed higher Jc’s in magnetic fields and irreversibility fields (Hirr) than that on 0°-cut SrTiO3. Hirr at 77 K is 2.1 T for the film grown 0°-cut SrTiO3, and is enhanced to 2.7 T for the one grown on 4°-miscut SrTiO3. If optimized so that the shape and the density of the defects can be controlled experimentally, this may be a promising way of improve magnetic flux pinning for many practical applications related to coated conductors.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.25.F- Transport properties

Giant Hall resistance in Pt-based ferromagnetic alloys

G. X. Miao and Gang Xiao

Appl. Phys. Lett. 85, 73 (2004); http://dx.doi.org/10.1063/1.1757645 (3 pages) | Cited 13 times

Online Publication Date: 29 June 2004

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We report on the observation of a dramatically increased extraordinary Hall Effect in Pt-based ferromagnetic alloy thin films with varying composition and thickness that were deposited using magnetron sputtering. Hall slope as high as 76.8 μΩ cm/T has been obtained at 110 K and 22.6 μΩ cm/T at 300 K. Excellent sensitivity, linearity, and a small temperature coefficient have been achieved in a particular composition, Fe35Pt65, for a film thickness of 10 nm. The optimized Fe–Pt thin films compare favorably with the commonly used semiconductor Hall sensors. © 2004 American Institute of Physics.
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75.50.Bb Fe and its alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
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