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15 Apr 2005

Volume 97, Issue 8, Articles (08xxxx)

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Recombination, gain, band structure, efficiency, and reliability of 1.5-μm GaInNAsSb/GaAs lasers

Lynford L. Goddard, Seth R. Bank, Mark A. Wistey, Homan B. Yuen, Zhilong Rao, and James S. Harris

J. Appl. Phys. 97, 083101 (2005); http://dx.doi.org/10.1063/1.1873035 (15 pages) | Cited 12 times

Online Publication Date: 4 April 2005

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We present temperature-dependent measurements of the local Z parameter, which reflects the dominant recombination processes. At room temperature, Z increases with current from 1.2 at low bias up to a threshold value, Zth, of only 2.0, demonstrating the existence of significant amounts of monomolecular recombination. At elevated temperatures, Zth rises above 2.5. We calculate the laser’s band diagram and estimate 35 meV of band-gap renormalization at threshold through polarization-resolved measurements of exciton peaks in the absorption spectrum and inflection points of the absorption, spontaneous emission, and gain spectra. The small effective valence-band barrier height of 115 meV leads to hole leakage due to thermionic emission and carrier spillover into the barriers. This could explain the increase in Zth at elevated temperatures and decrease in internal quantum efficiency from 57% at 15 °C to 47% at 75 °C. We also analyze the spontaneous emission and gain spectra below and above threshold. The spontaneous emission clamped rather weakly at threshold, which also partially explains the low internal efficiency at room temperature. We present initial reliability measurements of over 100 h at 10-mW continuous-wave power from a single facet. After 50 h of life testing, the threshold current increased by 79% and the external differential quantum efficiency decreased by 39% of their respective pretest values. By comparing the local Z parameter versus current-density curves before and after life testing, we have identified an increase in monomolecular recombination as the main source of degraded device performance.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Femtosecond laser-induced refractive index modification in multicomponent glasses

V. R. Bhardwaj, E. Simova, P. B. Corkum, D. M. Rayner, C. Hnatovsky, R. S. Taylor, B. Schreder, M. Kluge, and J. Zimmer

J. Appl. Phys. 97, 083102 (2005); http://dx.doi.org/10.1063/1.1876578 (9 pages) | Cited 38 times

Online Publication Date: 4 April 2005

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We present a comprehensive study on femtosecond laser-induced refractive index modification in a wide variety of multicomponent glasses grouped as borosilicate, aluminum–silicate, and heavy-metal oxide glasses along with lanthanum–borate and sodium–phosphate glasses. By using high-spatial resolution refractive index profiling techniques, we demonstrate that under a wide range of writing conditions the refractive index modification in multicomponent glasses can be positive, negative, or nonuniform, and exhibits a strong dependence on the glass composition. With the exception of some aluminum–silicate glasses all other glasses exhibited a negative/nonuniform index change. We also demonstrate direct writing of waveguides in photosensitive Foturan® glass with a femtosecond laser without initiating crystallization by thermal treatment. Upon ceramization of lithium–aluminum–silicate glasses such as Foturan®, Zerodur®, and Robax® we observe switching of laser-induced refractive index change from being positive to negative. The measured transmission losses in the waveguides at 1550 nm agree with the index profile measurements in alkali-free aluminum–silicate glasses.
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42.70.Ce Glasses, quartz
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.62.-b Laser applications
42.79.Gn Optical waveguides and couplers

Optical lifting force under focused evanescent wave illumination: A ray optics model

Smitha Kuriakose, Xiasong Gan, James W. M. Chon, and Min Gu

J. Appl. Phys. 97, 083103 (2005); http://dx.doi.org/10.1063/1.1863453 (4 pages) | Cited 4 times

Online Publication Date: 11 April 2005

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We propose a ray optics model to calculate the trapping force on a dielectric particle located on the interface between two media and illuminated by a focused evanescent field beam. Such a focused evanescent beam is produced by a high numerical aperture objective with a central obstruction whose size satisfies the total internal reflection condition on the interface. The dependence of the lifting force on the obstruction size, the particle size, and the distance of the particle from the interface is revealed.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.15.-i Geometrical optics

Effect of strain relaxation and exciton localization on performance of 350-nm AlInGaN quaternary light-emitting diodes

T. Wang, G. Raviprakash, F. Ranalli, C. N. Harrison, J. Bai, J. P. R. David, P. J. Parbrook, J. P. Ao, and Y. Ohno

J. Appl. Phys. 97, 083104 (2005); http://dx.doi.org/10.1063/1.1877816 (4 pages) | Cited 7 times

Online Publication Date: 12 April 2005

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The optical and structural properties of AlInGaN quaternary single and multiple quantum-well structures have been investigated by means of photoluminescence and x-ray diffraction. This comparative study of single quantum-well (SQW) and multiple quantum-well (MQW) structures was carried out in terms of the exciton localization effect and the strain relaxation. A detailed analysis indicated that 13% strain relaxation occurs in the MQW compared to the SQW, which is assumed to be fully strained. Furthermore, the AlInGaN SQW structure showed a stronger localization effect than the MQW. Both these effects result in enhanced emission efficiency for the SQW structure, indicating that it is better suited as the active region for ultraviolet light-emitting diodes (UV-LEDs). Finally, the UV-LEDs with an emission wavelength of about 350 nm based on such SQW and MQW active regions were grown. The output power of the SQW UV-LEDs is around 2.3 times higher than that of MQW UV-LEDs.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
68.65.Fg Quantum wells
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Gy Mechanical properties; surface strains
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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Electron kinetic effects in atmospheric dielectric-barrier glow discharges

X. M. Zhu and M. G. Kong

J. Appl. Phys. 97, 083301 (2005); http://dx.doi.org/10.1063/1.1872192 (6 pages) | Cited 5 times

Online Publication Date: 6 April 2005

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Large-volume atmospheric dielectric-barrier discharges (DBD) are particularly useful for processing applications when they operate in their homogeneous mode. A vast majority of their theoretical studies is currently based on the hydrodynamic treatment in which electrons are assumed to be in equilibrium with the local electric field. Recognizing that this assumption is incorrect in the sheath region, we report the development of an electron-hybrid model to treat electrons kinetically and all other particles hydrodynamically. Through numerical examples, it is shown that the mainstream hydrodynamic model underestimates gas ionization and discharge current. Using the hybrid model, it is demonstrated that variation in the amplitude of the applied voltage does not significantly alter sheath characteristics in terms of the electric field and the electron mean energy. Also gas ionization in atmospheric DBD is found to be significant only over a short timescale of 1 μs. Compared with dc atmospheric pressure glow discharges, atmospheric DBD are shown to have a smaller electron mean energy and a larger sheath thickness.
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52.25.Fi Transport properties
52.80.Hc Glow; corona
52.40.Kh Plasma sheaths
52.65.Pp Monte Carlo methods
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On the microstructure of AlxGa1−xN layers grown on 6H-SiC(0001) substrates

Roland Kröger, Sven Einfeldt, Rosa Chierchia, Detlef Hommel, Zachary J. Reitmeier, Robert F. Davis, and Quincy K. K. Liu

J. Appl. Phys. 97, 083501 (2005); http://dx.doi.org/10.1063/1.1861152 (8 pages) | Cited 2 times

Online Publication Date: 31 March 2005

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The microstructural as well as the compositional evolution of AlxGa1−xN (x ∼ 0.15) layers grown on 6H-SiC(0001) substrates by metalorganic vapor phase epitaxy were analyzed by atomic force microscopy, X-ray diffraction, and transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy. The epitaxial growth was followed from the early nucleation stage on the substrate to the development of a thick bulk-like film. Phase separation was observed during the early stage of growth; that is, islands of two different shapes formed whose Al mole fractions were about 0.035 and 0.18, respectively. The AlxGa1−xN coalesced at a film thickness of about 100 nm with the domains of varying Al content being fully coherent. Such domains were not only found at the film∕substrate interface but also further away from the interface. They were arranged in layers that were shifted laterally against each other; that is, Al-deficient domains formed on top of Al-rich domains and vice versa. Increasing the film thickness to more than 100 nm finally led to a homogeneous Al distribution. Finite-element simulations were performed to calculate the strain distribution in these inhomogeneous systems. They allowed the experimental results to be explained by an interplay of strain minimization in the epitaxial film and growth kinetics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
64.60.Q- Nucleation
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
64.75.-g Phase equilibria
68.55.Nq Composition and phase identification
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effect of oxygen content on piezoresistivity of indium tin oxide thin films prepared by pulsed laser deposition

H. Fang, T. Miller, B. R. Rogers, R. H. Magruder, and R. A. Weller

J. Appl. Phys. 97, 083502 (2005); http://dx.doi.org/10.1063/1.1868062 (5 pages) | Cited 1 time

Online Publication Date: 31 March 2005

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The piezoresistivity of thin films of indium tin oxide prepared by pulsed laser deposition has been measured as a function of the O-to-(In+Sn) atom ratio. The oxygen-to-metal atom ratio was determined through Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy analyses. Gauge factors, defined as the fractional change of the film resistance to the applied strain, increase with the film’s oxygen content. The deposition under 50 mTorr oxygen pressure resulted in the film with the largest oxygen-to-metal atom ratio, 1.92, and a gauge factor of −14.5. A model based on hopping conduction is proposed. Results from this model are consistent with the sign and magnitude of the observed gauge factors.
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81.05.Hd Other semiconductors
73.61.Le Other inorganic semiconductors
68.55.Nq Composition and phase identification
73.50.Dn Low-field transport and mobility; piezoresistance
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.15.Fg Pulsed laser ablation deposition

Magnetron sputter epitaxy of wurtzite Al1−xInxN(0.1<x<0.9) by dual reactive dc magnetron sputter deposition

T. Seppänen, P. O. Å. Persson, L. Hultman, J. Birch, and G. Z. Radnóczi

J. Appl. Phys. 97, 083503 (2005); http://dx.doi.org/10.1063/1.1870111 (9 pages) | Cited 17 times

Online Publication Date: 31 March 2005

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Ternary wurtzite Al1−xInxN thin films with compositions throughout the miscibility gap have been grown onto seed layers of TiN and ZrN by magnetron sputter epitaxy (MSE) using dual reactive direct current magnetron sputter deposition under ultra high vacuum conditions. The film compositions were calculated using Vegard’s law from lattice parameters determined by x-ray diffraction (XRD). XRD showed that single-phase Al1−xInxN alloy films in the wurtzite structure with [0.10<x<0.90] could be obtained at substrate temperatures up to 600 °C by heteroepitaxial growth. Epitaxial growth at 600 °C gave the crystallographic relations Al1−xInxN(0001)//TiN,ZrN(111) and Al1−xInxN〈10-10〉//TiN,ZrN〈110〉. At higher substrate temperatures almost pure AlN was formed. The microstructure of the films was also investigated by high-resolution electron microscopy. A columnar growth mode with epitaxial column widths from 10 to 200 nm was observed. Rocking curve full-width-at-half-maximum measurements revealed highly stressed lattices for growth onto TiN at 600 °C. Pseudobinary MSE growth phase field diagrams for Al1−xInxN onto ZrN and TiN were established for substrate temperatures up to 1000 °C. Large regimes for single-phase solid solutions were thus identified with In being the diffusing species.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.37.Lp Transmission electron microscopy (TEM)

Simulating thermal explosion of cyclotrimethylenetrinitramine-based explosives: Model comparison with experiment

Jack J. Yoh, Matthew A. McClelland, Jon L. Maienschein, Jeffrey F. Wardell, and Craig M. Tarver

J. Appl. Phys. 97, 083504 (2005); http://dx.doi.org/10.1063/1.1863429 (11 pages) | Cited 5 times

Online Publication Date: 31 March 2005

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We compare two-dimensional model results with measurements for the thermal, chemical, and mechanical behavior in a thermal explosion experiment. Confined high explosives (HEs) are heated at a rate of 1 °C/h until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an Arbitrarily Lagrangian-Eulerian code (ALE3D) that can handle a wide range of time scales that vary from a structural to a dynamic hydrotime scale. During the preignition phase, quasistatic mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydrodynamic calculation is performed as a burn front propagates through the HE. Two cyclotrimethylenetrinitramine-based explosives, C-4 and PBXN-109, are considered, whose chemical-thermal-mechanical models are constructed based on measurements of thermal and mechanical properties along with small scale thermal explosion measurements. The simulated dynamic response of HE confinement during the explosive phase is compared to measurements in larger scale thermal explosion tests. The explosion temperatures for both HEs are predicted to within 5 °C. Calculated and measured wall strains provide an indication of vessel pressurization during the heating phase and violence during the explosive phase. During the heating phase, simulated wall strains provide only an approximate representation of measured values indicating a better numerical treatment is needed to provide accurate results. The results also show that more numerical accuracy is needed for vessels with lesser confinement strength. For PBXN-109, the measured wall strains during the explosion are well represented by the ALE3D calculations.
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82.33.Vx Reactions in flames, combustion, and explosions
82.20.Wt Computational modeling; simulation
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
66.30.Xj Thermal diffusivity
81.40.Gh Other heat and thermomechanical treatments
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Vw Pressure treatment
82.60.-s Chemical thermodynamics

Electrical activation characteristics of silicon-implanted GaN

Y. Irokawa, O. Fujishima, T. Kachi, and Y. Nakano

J. Appl. Phys. 97, 083505 (2005); http://dx.doi.org/10.1063/1.1863458 (5 pages) | Cited 12 times

Online Publication Date: 31 March 2005

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Electrical activation studies of Si-implanted GaN layers on sapphire were made as a function of annealing temperature (1100–1400 °C). For an ion dose of 1.0×1014 cm−2, the optimum annealing temperature was 1400 °C, exhibiting a nearly 100% electrical activation efficiency and a low sheet resistance of ∼ 450 Ω/square at room temperature. From variable temperature Hall-effect measurements, Si-implanted GaN films annealed below 1200 °C displayed deep ionization levels of ∼ 280 meV, whereas samples annealed above 1300 °C had shallow ones of ∼ 11 meV. For lateral Schottky diodes fabricated on Si-implanted GaN layers annealed below 1200 °C, capacitance frequency and thermal admittance measurements showed a typical dispersion effect characteristic of a single deep donor with an activation energy of ∼ 133 meV. These results illustrate that deep donor levels created by the Si implantation in GaN layers apparently annihilate and transit to shallow levels produced by the Si ion substitution for Ga in the GaN lattice (SiGa) by annealing at temperature greater than ∼ 1300 °C at these doses.
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73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.30.Kk Junction diodes
71.55.Eq III-V semiconductors
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance

Structure and luminescence of BaFBr:Eu2+ and BaFBr:Eu2+, Tb3+ phosphors and thin films

Wei Chen, Shaopeng Wang, Sarah L. Westcott, Jun Zhang, Kai Dou, Alan G. Joly, and David E. McCready

J. Appl. Phys. 97, 083506 (2005); http://dx.doi.org/10.1063/1.1875738 (8 pages) | Cited 4 times

Online Publication Date: 31 March 2005

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The inclusion of Tb3+ ions doped into the storage phosphor BaFBr:Eu2+ results in increased purity of the host material as well as an improvement in the linearity of the photostimulated luminescence (PSL) intensity versus the x-ray irradiation dose. Films produced by pulsed laser deposition (PLD) also show similar results, indicating that PLD is a powerful technique for producing high quality, high purity thin films. As a result, the PSL dose response is more linear in the thin films than in the powder samples. The emission intensity of Eu2+ in the phosphors increases with the increasing time of x-ray irradiation while the emission intensity of Tb3+ remains almost constant. This result may be explained by considering the reduction of impurity Eu3+ ions following trapping of the photoexcited electrons. The results demonstrate that these materials are not only potentially useful for medical imaging but also show promise for use in radiation dosimetry.
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68.55.-a Thin film structure and morphology
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.80.Cb X-ray effects
61.82.Ms Insulators

Noncontacting laser photocarrier radiometric depth profilometry of harmonically modulated band bending in the space-charge layer at doped SiO2‐Si interfaces

Andreas Mandelis, Jerias Batista, Jürgen Gibkes, Michael Pawlak, and Josef Pelzl

J. Appl. Phys. 97, 083507 (2005); http://dx.doi.org/10.1063/1.1850197 (11 pages) | Cited 2 times

Online Publication Date: 1 April 2005

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Laser infrared photocarrier radiometry (PCR) was used with a harmonically modulated low-power laser pump and a superposed dc superband-gap optical bias (a secondary laser beam) to control and monitor the space-charge-layer (SCL) width in oxidized p‐Si–SiO2 and n‐Si–SiO2 interfaces (wafers) exhibiting charged interface-state related band bending. Applying the theory of PCR-SCL dynamics [ A. Mandelis, J. Appl. Phys. 97, 083508 (2005) ] to the experiments yielded various transport parameters of the samples as well as depth profiles of the SCL exhibiting complete ( p-type Si) or partial (n-type Si) band flattening, to a degree controlled by widely different minority-carrier capture cross section at each interface. The uncompensated charge density at the interface was also calculated from the theory.
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07.60.Dq Photometers, radiometers, and colorimeters
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena
42.60.Fc Modulation, tuning, and mode locking
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Theory of space-charge layer dynamics at oxide-semiconductor interfaces under optical modulation and detection by laser photocarrier radiometry

Andreas Mandelis

J. Appl. Phys. 97, 083508 (2005); http://dx.doi.org/10.1063/1.1850198 (11 pages) | Cited 7 times

Online Publication Date: 1 April 2005

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The dynamic theory of the optically modulated space-charge layer (SCL) resulting from band bending at a Si–SiO2 interface was developed in terms of the density of interface charges occupying band-gap energy states. Expressions were derived for these interface charge densities, interacting with the free-carrier density wave generated in the SCL and in the quasineutral region (bulk) by an intensity-modulated super-band-gap laser. The residual and modulated interface charge coverage affects the band-edge-to-impurity state recombination and the concomitant near-infrared photon emission comprising the photocarrier radiometry (PCR) signal. The PCR theory incorporating these effects was further developed. It was found to involve the dc, fundamental, and entire harmonic spectrum of the excitation frequency as a result of the optical modulation of the curvature of the energy bands and the SCL width at the interface.
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77.22.Jp Dielectric breakdown and space-charge effects
73.20.At Surface states, band structure, electron density of states
71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
42.60.Fc Modulation, tuning, and mode locking

A model for heterogeneous materials including phase transformations

F. L. Addessio, B. E. Clements, and T. O. Williams

J. Appl. Phys. 97, 083509 (2005); http://dx.doi.org/10.1063/1.1885165 (12 pages) | Cited 3 times

Online Publication Date: 1 April 2005

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A model is developed for particulate composites, which includes phase transformations in one or all of the constituents. The model is an extension of the method of cells formalism. Representative simulations for a single-phase, brittle particulate (SiC) embedded in a ductile material (Ti), which undergoes a solid–solid phase transformation, are provided. Also, simulations for a tungsten heavy alloy (WHA) are included. In the WHA analyses a particulate composite, composed of tungsten particles embedded in a tungsten–iron–nickel alloy matrix, is modeled. A solid–liquid phase transformation of the matrix material is included in the WHA numerical calculations. The example problems also demonstrate two approaches for generating free energies for the material constituents. Simulations for volumetric compression, uniaxial strain, biaxial strain, and pure shear are used to demonstrate the versatility of the model.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.70.D- Solid-liquid transitions
65.40.G- Other thermodynamical quantities
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Nuclear-magnetic-resonance diffusion simulations in porous media

A. Valfouskaya, P. M. Adler, J.-F. Thovert, and M. Fleury

J. Appl. Phys. 97, 083510 (2005); http://dx.doi.org/10.1063/1.1871352 (12 pages) | Cited 2 times

Online Publication Date: 1 April 2005

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Nuclear-magnetic-resonance (NMR) diffusion simulations were performed numerically in unconsolidated and consolidated porous media. The curve of the apparent diffusion coefficient as a function of time was found to be a poor indicator of the pore structure. Various representations were tried to gather the data. A successful one uses a combination of surface-to-volume ratio, formation factor, and permeability; it can be used in different ways in order to derive these parameters from NMR measurements.
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76.60.-k Nuclear magnetic resonance and relaxation
66.30.Dn Theory of diffusion and ionic conduction in solids
61.43.Gt Powders, porous materials
68.35.Fx Diffusion; interface formation

Characterization of self-assembled InAs quantum dots with InAlAs/InGaAs strain-reduced layers by photoluminescence spectroscopy

K. P. Chang, S. L. Yang, D. S. Chuu, R. S. Hsiao, J. F. Chen, L. Wei, J. S. Wang, and J. Y. Chi

J. Appl. Phys. 97, 083511 (2005); http://dx.doi.org/10.1063/1.1886278 (4 pages) | Cited 9 times

Online Publication Date: 1 April 2005

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The optoelectronic characteristics of self-assembled InAs quantum dots (QDs) with strain-reduced layers (SRLs) were investigated using photoluminescence (PL) spectroscopy. Various SRLs that combine In0.14Al0.86As and In0.14Ga0.86As with the same total thickness were examined to ascertain their confining effect on carriers in InAs QDs. The emission wavelength is blueshifted as the thickness of InAlAs is increased. The energy separation between the ground state and the first excited state of QDs with InAlAs SRLs greatly exceeds that of QDs with InGaAs SRLs. Atomic force microscopic images and PL spectra of the QD samples demonstrated that high-quality InAs QDs with long emission wavelengths and a large energy separation can be generated by growing a low-temperature, thin InAlAs SRL onto self-assembled QDs.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
68.65.Hb Quantum dots (patterned in quantum wells)

Electrically switchable third-harmonic generation in photonic crystals

P. P. Markowicz, H. Tiryaki, P. N. Prasad, V. P. Tondiglia, L. V. Natarajan, T. J. Bunning, and J. W. Haus

J. Appl. Phys. 97, 083512 (2005); http://dx.doi.org/10.1063/1.1868081 (4 pages) | Cited 2 times

Online Publication Date: 4 April 2005

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We demonstrate electrically switchable third-harmonic generation in low refractive index contrast one-dimensional photonic crystals pumped by a near-infrared laser beam. A dramatic enhancement of the third-harmonic signal is observed on the short wavelength side of the photonic crystal stop band. The enhancement of the third-harmonic generation disappears when an electric field is applied, revealing the electrical switchability of the third-harmonic generation. The observed phenomenon of enhancement is explained theoretically with a coupled-mode model. We also show that up to a modulation frequency of 10 kHz the switching properties are supported in the photonic crystal.
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42.70.Qs Photonic bandgap materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Thermophysical properties of liquid Te: Density, electrical conductivity, and viscosity

C. Li, C.-H. Su, S. L. Lehoczky, R. N. Scripa, B. Lin, and H. Ban

J. Appl. Phys. 97, 083513 (2005); http://dx.doi.org/10.1063/1.1868881 (7 pages) | Cited 4 times

Online Publication Date: 4 April 2005

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The thermophysical properties of liquid Te, namely, density, electrical conductivity, and viscosity, were determined using the pycnometric and transient torque methods from the melting point of Te (723 K) to approximately 1150 K. A maximum was observed in the density of liquid Te as the temperature was increased. The electrical conductivity of liquid Te increased to a constant value of 2.9×105 Ω−1 m−1 as the temperature was raised above 1000 K. The viscosity decreased rapidly upon heating the liquid to elevated temperatures. The anomalous behaviors of the measured properties are explained as caused by the structural transitions in the liquid and discussed in terms of Eyring’s [ A. I. Gubanov, Quantum Electron Theory of Amorphous Conductors (Consultants Bureau, New York, 1965) ] and Bachinskii’s [ Zh. Fiz.-Khim. O-va. 33, 192 (1901) ] predicted behaviors for homogeneous liquids. The properties were also measured as a function of time after the liquid was cooled from approximately 1173 or 1123 to 823 K. No relaxation phenomena were observed in the properties after the temperature of liquid Te was decreased to 823 K, in contrast to the relaxation behavior observed for some of the Te compounds.
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65.20.-w Thermal properties of liquids
72.80.Ph Liquid semiconductors
66.20.-d Viscosity of liquids; diffusive momentum transport
64.70.D- Solid-liquid transitions

Dose-dependent precipitate evolution arising during implantation of Er into Si

S. M. Hogg, B. Pipeleers, A. Vantomme, H. Bender, O. Richard, and M. Swart

J. Appl. Phys. 97, 083514 (2005); http://dx.doi.org/10.1063/1.1874295 (8 pages)

Online Publication Date: 4 April 2005

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Implant dose effects arising from the implantation of math into Si(111) have been investigated. This study encompasses a wide dose range from 4×1015 to 1.2×1017 at. cm−2 and focuses on channeled implantation as random implantation leads to a high degree of self-sputtering and damage in the resultant silicide precipitates. Dramatic changes are observed in the shape of the implant profile as a function of dose. Buildup of damage to the crystalline lattice and increasing target density as the implant proceeds lead to a piling up of subsequently implanted Er. Concurrently, sputtering and redistribution of the implanted species cause the implant profile to broaden. The crystalline quality and elastic strain of the resulting ErSi1.7 precipitates have been studied using Rutherford backscattering and channeling spectrometry and high-resolution x-ray diffraction. Following implantation, the precipitates are under compressive elastic strain perpendicular to the sample surface. Its magnitude increases linearly with dose and is attributed to the accumulation of irradiation-induced defects. A two-step improvement in crystalline quality is ascribed to the rapidly improving coherence of the growing precipitates with the Si lattice, succeeded by a slow improvement as the peak Er concentration approaches the silicide stoichiometry. Transmission electron microscopy imaging reveals that the transition between the two regimes corresponds to the formation of a continuous silicide layer. These results have consequences for both precipitate and layer formation using ion implantation.
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
81.30.Mh Solid-phase precipitation
61.66.Bi Elemental solids
61.66.Dk Alloys
62.90.+k Other topics in mechanical and acoustical properties of condensed matter (restricted to new topics in section 62)
68.37.Lp Transmission electron microscopy (TEM)

Ultrathin epitaxial Al2O3 films grown on Nb(110)/sapphire(0001) investigated by tunneling spectroscopy and microscopy

Ch. Dietrich, B. Koslowski, and P. Ziemann

J. Appl. Phys. 97, 083515 (2005); http://dx.doi.org/10.1063/1.1876580 (6 pages) | Cited 6 times

Online Publication Date: 4 April 2005

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Structural as well as electronic properties of ultrathin epitaxial Al2O3 films prepared on Nb(110)/sapphire(0001) were analyzed in situ by applying scanning tunneling microscopy (STM) and spectroscopy as well as ultraviolet photoelectron spectroscopy, cathode luminescence, and low-energy electron diffraction. According to these experiments, the niobium base film is protected from oxidation, while the ultrathin Al film deposited onto the Nb is fully oxidized and (0001)-oriented with a very smooth surface. The STM-imaged topography of the oxide films in most cases reflects monatomic steps of the underlying Nb(110) film. In some cases (10% of all samples with low tunneling barriers) additional ∼ 0.4-nm-high steps are observed characteristic of monatomic Al2O3 steps. Furthermore, for growing tunneling voltages (>1 V), the STM-imaged topographies reveal an increasing density of small hillocks, which are attributed to localized defect states such as oxygen vacancies still present within the oxide layer.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
73.40.Ns Metal-nonmetal contacts
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.60.Dp Adsorbed layers and thin films
78.60.Hk Cathodoluminescence, ionoluminescence
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.40.Gk Tunneling
61.72.J- Point defects and defect clusters
81.65.Mq Oxidation
81.15.Cd Deposition by sputtering
78.66.Nk Insulators

Long-period martensitic structures of Ni-Mn-Ga alloys studied by high-resolution transmission electron microscopy

Jaume Pons, Rubén Santamarta, Volodymyr A. Chernenko, and Eduard Cesari

J. Appl. Phys. 97, 083516 (2005); http://dx.doi.org/10.1063/1.1861137 (7 pages) | Cited 22 times

Online Publication Date: 5 April 2005

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The layered martensitic structures formed in Ni-Mn-Ga alloys have been investigated by high-resolution transmission electron microscopy (including image simulations) in order to discern from two structural models reported in the literature. For the seven-layer martensite, the observations discard the model based on shuffling of the atomic positions (modulation) by a function with a period of seven planes and confirm its nanotwinned nature, which is inherent to the description as stacking of nearly close-packed planes derived from {110}aust with (5math) sequence, that is, the so-called 14M structure. The observed stacking sequence, however, is notably distorted [the perfect (5math) sequence is present only in small areas], although it preserves a predominant periodicity of seven planes. For another alloy composition, a nanotwinned martensite with periodicity of twelve planes and (7math) average stacking sequence has also been observed. In case of the five-layer martensite, the image simulations and atom projections obtained from the two structural models fit well with the experimental images, which makes it very difficult to discern between them.
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61.72.Bb Theories and models of crystal defects
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries
68.37.Lp Transmission electron microscopy (TEM)
61.46.-w Structure of nanoscale materials

High-temperature annealing of optical centers in type-I diamond

Alan T. Collins, Alex Connor, Cheng-Han Ly, Abdulla Shareef, and Paul M. Spear

J. Appl. Phys. 97, 083517 (2005); http://dx.doi.org/10.1063/1.1866501 (10 pages) | Cited 14 times

Online Publication Date: 5 April 2005

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Diamonds previously subjected to radiation damage have been annealed at temperatures up to 1750 °C at ambient pressure, and at 2300 °C using a stabilizing pressure of 5 GPa. The results have been compared with those from similar measurements using natural brown diamonds. The investigation has led to an improved understanding of the commercial process for enhancing the color of brown diamonds by high-pressure, high-temperature (HPHT) annealing. The study has confirmed that the H4 center is less stable than the H3 center, and shown that the destruction of the H4 center in irradiated type-IaB diamonds coincides with the formation of a number of optical centers found to occur naturally in brown diamonds. In type-IaA diamonds the annealing out of the H1b absorption coincides with the production of H2 centers. Annealing measurements on brown diamonds indicate that the plastic deformation, associated with the brown color, occurred at a late stage in the diamonds’ history. Optical centers, such as H3 and (NV)−, that are produced in brown diamonds by HPHT annealing, are destroyed by this process in irradiated dislocation-free diamonds. Formation of these centers during the HPHT annealing of brown diamonds occurs as a result of the release of vacancies from the dislocations, and the present results therefore indicate that the production of these centers is a dynamic process with the generation and annealing in competition.
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81.05.U- Carbon/carbon-based materials
81.40.Gh Other heat and thermomechanical treatments
61.72.J- Point defects and defect clusters
81.40.Tv Optical and dielectric properties related to treatment conditions
81.40.Vw Pressure treatment
81.40.Wx Radiation treatment (particle and electromagnetic)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Lm Deformation, plasticity, and creep
78.60.Hk Cathodoluminescence, ionoluminescence
62.20.F- Deformation and plasticity
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
62.50.-p High-pressure effects in solids and liquids
61.80.Fe Electron and positron radiation effects
61.82.Ms Insulators
61.80.Hg Neutron radiation effects

Shock-compression response of an alumina-filled epoxy

R. E. Setchell and M. U. Anderson

J. Appl. Phys. 97, 083518 (2005); http://dx.doi.org/10.1063/1.1868055 (8 pages) | Cited 15 times

Online Publication Date: 5 April 2005

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Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties. Complex behavior during shock compression and release can result, particularly at higher alumina loadings. In the current study, a particular material containing 43% alumina by volume was examined in planar-impact experiments. Laser interferometry was used to measure particle velocity histories in both reverse-impact and transmitted-wave configurations. Hugoniot states and release-wave velocities were obtained at shock stresses up to 10 GPa, and represented smooth extensions of previous data at lower stresses. Surprisingly high release-wave velocities continued to be the most notable feature. Measured profiles of transmitted waves show a gradual transition from viscoelastic behavior at high shock stresses to a more complex behavior at lower stresses in which viscous mechanisms produce a broadened wave structure. This wave structure was examined in some detail for peak stress dependence, evolution towards steady-wave conditions, and initial temperature effects.
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81.05.Qk Reinforced polymers and polymer-based composites
62.50.-p High-pressure effects in solids and liquids
64.30.-t Equations of state of specific substances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.35.Gy Mechanical properties; surface strains

Soft x-ray resonant magneto-optical Kerr effect as a depth-sensitive probe of magnetic heterogeneity: A simulation approach

Ki-Suk Lee, Dae-Eun Jeong, Sang-Koog Kim, and J. B. Kortright

J. Appl. Phys. 97, 083519 (2005); http://dx.doi.org/10.1063/1.1861969 (10 pages) | Cited 6 times

Online Publication Date: 6 April 2005

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We report a noticeable depth sensitivity of soft x-ray resonant magneto-optical Kerr effect able to resolve depth-varying magnetic heterostructures in ultrathin multilayer films. For various models of depth-varying magnetization orientations in an ultrathin Co layer of realistic complex layered structures, we have calculated the Kerr rotation, ellipticity, intensity spectra versus grazing incidence angle ϕ, and their hysteresis loops at different values of ϕ for various photon energies hν’s near the Co resonance regions. It is found from the simulation results that the Kerr effect has a much improved depth sensitivity and that its sensitivity varies remarkably with ϕ and hν in the vicinity of the resonance regions. These properties originate from a rich variety of wave interference effects superimposed with noticeable features of the refractive and absorptive optical effects near the resonance regions. Consequently, these allow us to resolve depth-varying magnetizations and their reversals varying with depth in a single magnetic layer and allow us to distinguish interface magnetism from the bulk properties in multilayer films. In this paper, the depth sensitivity of the Kerr effect with an atomic-scale resolution is demonstrated and discussed in details in several manners with the help of model simulations for various depth-varying spin configurations.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies
78.70.Dm X-ray absorption spectra

Phase-change recording materials with a growth-dominated crystallization mechanism: A materials overview

L. van Pieterson, M. H. R. Lankhorst, M. van Schijndel, A. E. T. Kuiper, and J. H. J. Roosen

J. Appl. Phys. 97, 083520 (2005); http://dx.doi.org/10.1063/1.1868860 (7 pages) | Cited 65 times

Online Publication Date: 6 April 2005

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The influence of phase-change material composition on amorphous phase stability, crystallization rate, nucleation probability, optical constants and media noise is reported for materials with a growth dominated crystallization mechanism. Two material classes have been studied, doped Sb–Te and doped Sb-based compositions. The material properties of both are greatly influenced by their composition, and in a similar way. For both materials systems hold that the antimony content especially influences the crystallization rate, amorphous phase stability and media noise of the phase-change material. Compositions rich in antimony generally show high crystallization rates, low archival life stability and high media noise. The material properties are further influenced by the presence of dopants like tellurium, germanium, gallium, indium or tin. Germanium and tellurium reduce the crystallization rate, but are essential to increase the amorphous phase stability. Dopants like tin or indium are added to increase the crystallization rate or to adjust the optical constants.
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64.70.K- Solid-solid transitions
64.60.Q- Nucleation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.S- Impurities in crystals
61.43.Dq Amorphous semiconductors, metals, and alloys
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