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15 Jun 2004

Volume 95, Issue 12, pp. 7561-8489

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Yellow-green strained-InGaP quantum-well epitaxial-transparent-substrate light emitting diodes

L. McGill, J. W. Wu, and E. A. Fitzgerald

J. Appl. Phys. 95, 7561 (2004); http://dx.doi.org/10.1063/1.1736330 (6 pages) | Cited 2 times

Online Publication Date: 4 June 2004

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We present a strained-InGaP quantum-well light emitting diode (LED) operating in the green to yellow region of the visible spectrum. The active layer consists of an undoped, compressively strained In0.32Ga0.68P or In0.37Ga0.63P quantum well deposited via metalorganic chemical vapor deposition on a transparent In0.22(Al0.2Ga0.8)0.78P/∇x[Inx(Al0.2Ga0.8)1−xP]/GaP virtual substrate. Epitaxial-transparent-substrate LEDs based on this structure emit with a primary peak at 590 nm and a secondary peak at 560 nm. The highest LED power of 0.18 μW per facet at 20 mA was observed for a quantum well composition of In0.32Ga0.68P and a threading dislocation density on the order of 7×106 cm−2. The same device structure intentionally grown with a threading dislocation density on the order of 5×107 cm−2 exhibited an identical spectral shape with a reduced power of 0.08 μW per facet at 20 mA. Based upon superspots present in transmission electron diffraction from the quantum well region, the observed spectrum is the result of emission from ordered and disordered domains in the active region. Devices with a quantum well composition of In0.37Ga0.63P and an overall threading dislocation density on the order of 5×107 cm−2 emit at a single peak wavelength of 588 nm with a power of 0.06 μW per facet at 20 mA. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.65.Fg Quantum wells

Identifying Au-based Te alloys for optical data storage

D. Wamwangi, R. Detemple, H.-W. Woeltgens, M. Wuttig, and X. Zhang

J. Appl. Phys. 95, 7567 (2004); http://dx.doi.org/10.1063/1.1736332 (6 pages) | Cited 2 times

Online Publication Date: 4 June 2004

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Au18Sb23Te59 and Au19In26Te55 have been investigated to determine their suitability as phase change recording alloys. Recrystallization experiments identify Au18Sb23Te59 as a suitable phase change material with a recrystallization time of 110 ns and high optical contrast. Coupled to the high optical contrast is a considerable density increase of 4% upon crystallization which allows phase change recording for the Au18Sb23Te59 alloy. On the other hand no recrystallization has been observed optically for Au19In26Te55 due to its low optical contrast of less than 1%. This is related to a lower density contrast of 2%. The crystallization for the Au18Sb23Te59 and Au19In26Te55 alloys observed from temperature-dependent sheet resistance measurements have yielded transition temperatures of 113 and 175 °C, and activation barriers of 1.61±0.01 eV and 2.42±0.02 eV, respectively. We report a cubic structure (a=2.99±0.002 Å) for the Au18Sb23Te59 alloy and a chalcopyrite structure (a=6.50±0.018 Å and 12.27±0.025 Å) for the Au19In26Te55 material. These results confirm that suitable phase change alloys possess cubic structures rather than the chalcopyrite structure typical for sp3 bonded semiconductors. © 2004 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.55.-a Thin film structure and morphology
73.61.Jc Amorphous semiconductors; glasses
61.66.Dk Alloys

Field fluctuations and spectral line shape in semiconductor lasers subjected to optical feedback

Moustafa Ahmed and Minoru Yamada

J. Appl. Phys. 95, 7573 (2004); http://dx.doi.org/10.1063/1.1738525 (11 pages)

Online Publication Date: 4 June 2004

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This article reports on extensive investigations of the influence of external optical feedback (OFB) on the spectral line shape and the associated spectra of relative intensity noise (RIN) and frequency noise (FN) in semiconductor lasers. The study is based on a generalized simulation model that treats the OFB as a multiple-roundtrip time delay of the lasing field in the external cavity. We present criteria to apply the famous Lang–Kobayashi model to predict the operation characteristics of lasers under OFB. The accuracy of approximated models of calculating the spectral linewidth from the low-frequency components of the frequency noise is examined. We characterize the spectral line shape and the spectra of the RIN and FN in five distinct operating regions, namely, continuous-wave (cw), weak OFB-induced pulsation, period-doubling route-to-chaos, chaos or coherence collapse, and strong OFB-induced pulsation. InGaAsP lasers emitting in a wavelength of 1.5 μm are included in the calculations. The results show that the line shape is most enhanced with sharp central and satellite peaks when strong OFB induces either high-frequency pulsation or cw operation. The moderate range of OFB induces coherence collapse operation, which is characterized by most suppressed and most broadened central and satellite peaks. The cw operation induced under very strong OFB is characterized by RIN and FN levels lower than those of the case of cw operation induced under low OFB. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Mi Dynamical laser instabilities; noisy laser behavior
42.60.Pk Continuous operation
42.55.Ah General laser theory

Measurements of optical losses in mid-infrared semiconductor lasers using Fabry–Pérot transmission oscillations

D. G. Revin, L. R. Wilson, D. A. Carder, J. W. Cockburn, M. J. Steer, M. Hopkinson, R. Airey, M. Garcia, C. Sirtori, Y. Rouillard, D. Barate, and A. Vicet

J. Appl. Phys. 95, 7584 (2004); http://dx.doi.org/10.1063/1.1738523 (4 pages) | Cited 7 times

Online Publication Date: 4 June 2004

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We present a Fabry–Pérot resonator technique for room temperature optical loss measurements on mid-infrared (λ∼2–4 μm) lasers. The quality of optical waveguides for λ≈2.3 μm InGaAsSb/AlGaAsSb/GaSb interband lasers and a λ≈3.7 μm strain-compensated InGaAs/InAlAs/InP quantum cascade laser have been estimated using this method. The optical losses for these lasers lie in the range 15–25 cm−1 for interband lasers and 4–5 cm−1 (transverse electric polarization) and 21–23 cm−1 [transverse magnetic (TM) polarization] for the quantum cascade laser. The considerably higher losses for TM polarization in the case of quantum cascade laser are explained by intersubband absorption in the active layers. The method may be applied to structures with only a minimum amount of device processing, facilitating rapid progress in development of mid infrared laser designs in new materials systems. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Gn Optical waveguides and couplers

Collinear phase-matched terahertz-wave generation in GaP crystal using a dual-wavelength optical parametric oscillator

T. Taniuchi and H. Nakanishi

J. Appl. Phys. 95, 7588 (2004); http://dx.doi.org/10.1063/1.1751238 (4 pages) | Cited 21 times

Online Publication Date: 4 June 2004

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Tunable terahertz (THz)-wave generation in GaP crystal was theoretically and experimentally investigated using collinear difference frequency mixing. The wavelength range and length of GaP crystal for efficient difference frequency generation (DFG) were determined by calculating the phase-matching conditions. THz waves from 0.5 to 4.5 THz were generated by collinear phase-matched DFG using a dual-wavelength optical parametric oscillator with two KTiOPO4 crystals in the range of 930–1000 nm. A maximum THz output energy of 5.3 nJ/pulse (peak power of 0.66 W) at 1.9 THz was obtained when the pump energy was 1.2 mJ/pulse. © 2004 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Tunable wavelength-selective waveguiding of photoluminescence in Si-rich silica optical wedges

Leonid Khriachtchev, Markku Räsänen, Sergei Novikov, and Jouko Lahtinen

J. Appl. Phys. 95, 7592 (2004); http://dx.doi.org/10.1063/1.1751639 (10 pages) | Cited 13 times

Online Publication Date: 4 June 2004

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We report accurate tuning of spectral peaks built up upon guiding of broadband light by annealed Si-rich silica layers with varying optical thickness. The optical wedges are characterized with various methods (photoluminescence, Raman spectroscopy, visible absorption, and x-ray photoelectron spectroscopy) showing that their properties change smoothly from point to point along the sample surface. As measured in the conventional transverse detection geometry, the annealed (1100 °C) Si-rich silica material exhibits well-known broad photoluminescence (PL) with maximum at ∼800 nm conventionally connected with Si nanocrystals. In the waveguiding detection geometry, the guiding of PL light by the silica layer containing Si nanocrystals is wavelength-dependent, and the detected spectrum exhibits narrow (down to 100 cm−1) and linearly polarized spectral peaks. As the central observation of the present work, these spectral peaks can be accurately tuned over the whole PL spectral region by moving the optical wedges across the laser beam. For our samples, the tuning coefficient is ∼150 cm−1/mm. It is shown that tuning of the transmission peaks is caused by change of both refractive index (from 1.6 to 1.9) and thickness (from 1.4 to 2.0 μm) of the prepared optical wedges. The propagation loss for the guided light is found to increase for shorter wavelengths and for materials with larger Si concentration. The propagation losses reliably below 0.5 cm−1 are observed in the broad spectral interval in sample areas with smaller Si concentrations. © 2004 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.72.Cc Kinetics of defect formation and annealing
78.30.Am Elemental semiconductors and insulators
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Asymmetric injection of cathodic arc plasma into a macroparticle filter

André Anders and Robert A. MacGill

J. Appl. Phys. 95, 7602 (2004); http://dx.doi.org/10.1063/1.1707200 (5 pages)

Online Publication Date: 4 June 2004

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The cathodic arc plasmas produced by cathode spots usually include macroparticles, which is undesirable for many applications. A common way of removing macroparticles is to use curved solenoid filters that guide the plasma from the source to the substrate. In this work, an arc source with a relatively small cathode is used, limiting the possible locations of plasma production. The relative position of cathodic arc source and macroparticle filter was systematically varied and the filtered plasma current was recorded. It was found that axis-symmetric plasma injection lead to maximum throughput only if an anode aperture was used, which limited the plasma to near-axis flow by scraping off plasma at larger angles to the axis. When the anode aperture was removed, more plasma could enter the filter. In this case, maximum filtered ion current was achieved when the plasma was injected off-axis; namely, offset in the direction where the filter is curved. Such behavior was anticipated because the plasma column in the filter is known to be shifted by E×B and centrifugal drift as well as by non-axis-symmetric components of the magnetic field in the filter entrance and exit plane. The data have implications for plasma transport variations caused by different spot locations on cathodes that are not small compared to the filter cross section. © 2004 American Institute of Physics.
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52.50.Dg Plasma sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Light emission in a laser-initiated transient glow discharge in argon and air with butane

Y. Hoshi, A. Yokota, H. Yoshida, and J. Akedo

J. Appl. Phys. 95, 7607 (2004); http://dx.doi.org/10.1063/1.1737808 (4 pages) | Cited 1 time

Online Publication Date: 4 June 2004

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By observing light emissions from flares, we systematically investigated transient phenomena from glow to arc discharges under designated durations. To describe properly the discharge flare behavior, we introduced a parameter νa defined as (electrode gap)/(flare traveling time). The main findings are as follows. The parameter νa is proportional to the initial electrode voltage. The maximum value of νa is obtained at a certain gas pressure and it falls on the Paschen curve. The flare behavior follows Townsend’s theory at each instant, therefore, it is governed by the state of the electrolytic dissociation of the gas. © 2004 American Institute of Physics.
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52.80.Hc Glow; corona
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Dy Low-field and Townsend discharges
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Characterization of the plasma in a radio-frequency magnetron sputtering system

A. Palmero, E. D. van Hattum, W. M. Arnoldbik, A. M. Vredenberg, and F. H. P. M. Habraken

J. Appl. Phys. 95, 7611 (2004); http://dx.doi.org/10.1063/1.1728295 (8 pages) | Cited 11 times

Online Publication Date: 4 June 2004

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In order to understand the fundamental mechanisms in a radio-frequency magnetron sputtering system, the main properties of the argon plasma used in the process have been measured. A complete three-dimensional map of the ion density, electron temperature, and plasma potential has been obtained using a Langmuir probe. The electron temperature as well as the ion density have been found to increase in the region of the so called race track at the cathode. Furthermore, from the plasma potential map, the time-averaged local electric field has been obtained, pointing out the race track as the region where the most intense ion bombardment takes place. Besides, only the ions produced near the race track are accelerated towards the cathode, whereas those produced in the remaining volume move towards the anode. Finally, the dependence of the plasma quantities on the incident radio-frequency power and deposition pressure has been studied. The plasma potential measured using the Langmuir probe has been found to agree with that determined using an energy resolved mass spectrometer in all studied conditions. © 2004 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.77.Dq Plasma-based ion implantation and deposition

Characterization of extreme ultraviolet light-emitting plasmas from a laser-excited fluorine containing liquid polymer jet target

B. Abel, J. Assmann, M. Faubel, K. Gäbel, S. Kranzusch, E. Lugovoj, K. Mann, T. Missalla, and Ch. Peth

J. Appl. Phys. 95, 7619 (2004); http://dx.doi.org/10.1063/1.1737051 (5 pages)

Online Publication Date: 4 June 2004

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The operation of a liquid polymer jet laser-plasma target and the characterization of the absolute x-ray emission in the extreme ultraviolet wavelength window from 9–19 nm is reported. The target is a liquid polymer (perfluoro-polyether) that is exposed to pulsed and focused laser light at 532 nm in the form of a thin, liquid microjet (d=40 to 160 μm) in vacuum. The spectral brightness of the source in the 13 nm range is relatively high because a large fraction of radiative energy is emitted in one single line only, which is assigned to be the 2p–3d FVII doublet at 12.8 nm, with a laser energy conversion efficiency of 0.45% (2π sr, 2% bandwidth) in our initial experiment. A further increase of the relative emission has been found in the wavelength range between 7 and 17 nm when the jet diameter was increased from 40 to 160 μm. The two-dimensional spatial profile of the source plasma (d=40 to 50 μm) has been analyzed with a pinhole camera. © 2004 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.75.-d Plasma devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Filtered pulsed carbon cathodic arc: Plasma and amorphous carbon properties

Dongping Liu, Günther Benstetter, Edgar Lodermeier, Jialiang Zhang, Yanhong Liu, and Johann Vancea

J. Appl. Phys. 95, 7624 (2004); http://dx.doi.org/10.1063/1.1753081 (8 pages) | Cited 12 times

Online Publication Date: 4 June 2004

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The carbon plasma ion energies produced by the filtered pulsed cathodic arc discharge method were measured as a function of filter inductance. The energy determination is based on the electro-optical time-of-flight method. The average ion energies of the pulsed ion beams were found to depend upon the rise time and duration of pulsed arc currents, which suggests that a gain of ion kinetic energy mainly arises from the electric plasma field from the ambipolar expansion of both electrons and ions, and an electron drag force because of the high expansion velocity of the electrons. The tetrahedral amorphous carbon (ta-C) films with a sp3 fraction of ∼70% were deposited on silicon substrates at the average ion energies of >6 eV in the highly ionized plasmas. The ta-C films were found to be covered with a few graphitelike atomic layers. The surface properties of ultrathin carbon films, such as nanoscale friction coefficients, surface layer thickness, and silicon contents were strongly dependent on the ion energies. The growth of amorphous carbon films was explained in terms of the thermal spike migration of surface carbon atoms. In terms of this model, the thermal spike provides the energy required to release surface atoms from their metastable positions and leads to the formation of the sp3 bonded carbon on a sp3 bonded matrix. The experimental results indicate that the low-energy (<3 eV) carbon ions have insufficient energies to cause the rearrangement reaction within the film and they form graphitelike structures at film surface. © 2004 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
61.43.Dq Amorphous semiconductors, metals, and alloys
52.70.Nc Particle measurements
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In situ measurements of thickness changes and mechanical stress upon gasochromic switching of thin MoOx films

J. Okumu, F. Koerfer, C. Salinga, and M. Wuttig

J. Appl. Phys. 95, 7632 (2004); http://dx.doi.org/10.1063/1.1728309 (5 pages) | Cited 6 times

Online Publication Date: 4 June 2004

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Thin films of MoOx coated with platinum as a catalyst were prepared by dc magnetron sputtering from a molybdenum target in an oxygen and argon atmosphere. The films were colored and bleached by exposure to diluted hydrogen gas and air, respectively. In situ measurements of x-ray reflectance and substrate curvature were performed during switching cycles. Upon hydrogen exposure a remarkable thickness decrease of 11% and a density increase of 6.5% are observed by x-ray reflectance measurements. Corresponding changes in optical transmittance and mechanical stress up to several hundreds of MPa are also observed. These changes are not fully reversible as revealed by measurements of multiple switching cycles. Both the change of thickness and density, as well as the change of optical transmittance and mechanical stress can be explained by the existence of a mixed phase of edge and corner sharing MoO3 octahedra whereupon the first coloration the ratio between edge and corner sharing octahedra is changed. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
78.66.Nk Insulators
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)

Two-color photorefractive properties in near-stoichiometric lithium tantalate crystals

Youwen Liu, Kenji Kitamura, Shunji Takekawa, Masaru Nakamura, Yasunori Furukawa, and Hideki Hatano

J. Appl. Phys. 95, 7637 (2004); http://dx.doi.org/10.1063/1.1737046 (8 pages) | Cited 1 time

Online Publication Date: 4 June 2004

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The two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively. The key parameters in characterizing two-color photorefractive effect, light-induced absorption change, two-color sensitivity, refractive index change, readout characteristics, and dark decay were measured by changing intensities of gating and writing beams, wavelengths of gating and writing beams for the crystals with different near-stoichiometric crystal compositions, and proton concentrations. The results showed that there exists an optimal crystal composition of around 49.65% for both sensitivity and refractive index change together with moderate lifetime of small polarons. The achieved refractive index change was on the order of 10−4, and the obtained maximum sensitivity was 0.18 cm/J. The extrapolated lifetime of holograms at room temperature in the crystals without observable OH− absorption was longer than 50 yr. The measurements of UV-induced absorption change at room temperature and low temperature of 77.3 K suggested that the unintentional impurity of Fe and intrinsic defects were responsible for two-color photorefractive effect. The excellent two-color photorefractive properties of undoped as-grown near-stoichiometric lithium tantalate crystals were discussed based on this mechanism and the physical properties of lithium tantalate. © 2004 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.66.Bi Elemental solids
61.66.Dk Alloys
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
61.72.-y Defects and impurities in crystals; microstructure

Structure and morphology of the As-rich and the stoichiometric GaAs(114)A surface

J. Márquez, P. Kratzer, and K. Jacobi

J. Appl. Phys. 95, 7645 (2004); http://dx.doi.org/10.1063/1.1707212 (10 pages) | Cited 5 times

Online Publication Date: 4 June 2004

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GaAs(114)A surfaces were prepared using molecular beam epitaxy followed by annealing in As2 pressure as well as in ultrahigh vacuum. Based on low-energy electron diffraction, in situ scanning tunneling microscopy measurements, and ab initio first-principles electronic-structure calculations the surface reconstructions are determined. Under As-rich conditions GaAs(114)A develops a β2(2×1) and/or β2c(2×2) reconstruction which is analogous to the GaAs(001)β2(2×4) one. Although a low surface free energy (46 meV/Å2 for As-rich conditions) is found for GaAs(114)Aβ2(2×1), it is split up into mesoscopic (113) and (115) facets. Also typical steps between 150 Å wide terraces are observed along [1math0]. The stoichiometric GaAs(114)A surface is mesoscopically very flat and develops a α2(2×1) reconstruction of a low surface free energy of 53 meV/Å2. The surface free energies for the α(2×1) and a newly introduced ω(2×1) variant are larger. © 2004 American Institute of Physics.
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68.47.Fg Semiconductor surfaces
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Md Surface thermodynamics, surface energies
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.15.-m Methods of electronic structure calculations
73.20.At Surface states, band structure, electron density of states

Enhanced photothermal displacement spectroscopy for thin-film characterization using a Fabry-Perot resonator

Eric D. Black, Ivan S. Grudinin, Shanti R. Rao, and Kenneth G. Libbrecht

J. Appl. Phys. 95, 7655 (2004); http://dx.doi.org/10.1063/1.1728312 (5 pages) | Cited 4 times

Online Publication Date: 4 June 2004

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We have developed a technique for photothermal displacement spectroscopy that is potentially orders of magnitude more sensitive than conventional methods. We use a single Fabry-Perot resonator to enhance both the intensity of the pump beam and the sensitivity of the probe beam. The result is an enhancement of the response of the instrument by a factor proportional to the square of the finesse of the cavity over conventional interferometric measurements. In this paper we present a description of the technique, and we discuss how the properties of thin films can be deduced from the photothermal response. As an example of the technique, we report a measurement of the thermal properties of a multilayer dielectric mirror similar to those used in interferometric gravitational wave detectors. © 2004 American Institute of Physics.
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07.60.Ly Interferometers
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
65.40.De Thermal expansion; thermomechanical effects

Normally black reflective twisted-nematic cell for microdisplay application

Xinyu Zhu and Shin-Tson Wu

J. Appl. Phys. 95, 7660 (2004); http://dx.doi.org/10.1063/1.1751234 (5 pages)

Online Publication Date: 4 June 2004

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A normally black reflective twisted-nematic mode is proposed for microdisplay application. This mode is based on the polarization rotation effect of a twisted-nematic liquid crystal. In the dark state, the cell exhibits a large gap tolerance and weak color dispersion. For twist angle ranging from 45° to 65°, the maximum normalized reflectance can achieve 100% through d/p (cell gap over pitch) ratio optimization. Particularly, when the twist angle equals to 52°, the normalized reflectance can reach 100% without any chiral dopant. The twist angle and polarizer angle also make important contributions to the bright state optical efficiency and dark state spectral bandwidth. © 2004 American Institute of Physics.
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42.70.Df Liquid crystals
42.25.Ja Polarization
42.25.Gy Edge and boundary effects; reflection and refraction
42.79.Kr Display devices, liquid-crystal devices

Reactive magnetron sputtering of molybdenum sulfide thin films: In situ synchrotron x-ray diffraction and transmission electron microscopy study

V. Weiss, W. Bohne, J. Röhrich, E. Strub, U. Bloeck, I. Sieber, K. Ellmer, R. Mientus, and F. Porsch

J. Appl. Phys. 95, 7665 (2004); http://dx.doi.org/10.1063/1.1736323 (9 pages) | Cited 5 times

Online Publication Date: 4 June 2004

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The nucleation and growth of magnetron sputtered MoSx films has been investigated by in situ energy dispersive x-ray diffraction, electron microscopy, and elastic recoil detection analysis. The MoSx films (0.5⩽x⩽2) were prepared by reactive magnetron sputtering from a molybdenum target in an argon–hydrogen sulfide mixture at substrate temperatures up to 700 °C. Using time-resolved in situ x-ray diffraction it was found that the films start to grow with (001) orientation where the van der Waals planes are parallel to the substrate surface. Depending on the deposition conditions a crossover of texture to the (100) orientation occurs, which leads to very rough surfaces. This texture crossover occurs earlier at low substrate temperatures and/or high deposition rates and/or high energetic particle bombardment of the growing films. The MoSx films exhibit significant lattice strain (up to 4%) in the c direction, i.e., perpendicular to the van der Waals planes, which decreases at high substrate temperatures and/or low deposition rates. This lattice expansion is not caused by film stress. Instead, it seems to be connected with disturbed or turbostratic growth due to crystallographic defects induced by energetic bombardment of the films. Also, intercalation of hydrogen could be responsible for lattice expansion, since significant amounts of hydrogen were detected by elastic recoil detection analysis. The sulfur deficiency (up to 20%) found in films that were deposited at temperatures higher than 200 °C could have been initiated by the reducing effect of the atomic hydrogen in our Ar/H2S plasma. © 2004 American Institute of Physics.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Lp Transmission electron microscopy (TEM)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Mechanism of solid-state amorphization of Se induced by mechanical milling

Y. H. Zhao, Y. T. Zhu, and T. Liu

J. Appl. Phys. 95, 7674 (2004); http://dx.doi.org/10.1063/1.1737478 (7 pages)

Online Publication Date: 4 June 2004

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In this work, the solid-state amorphization process of elemental trigonal Se via mechanical milling was studied. Trigonal Se has a unique crystal structure consisting of helical [–Se–]n chains with strong intrachain covalent bonds and with weak interchain van der Waals bonds. It was found that the interchain coordination distance increased while the intrachain coordination distance decreased with increasing milling time. The crystalline Se transformed to the amorphous state once the interchain coordination distance reached a critical value. The intrachain coordination distance of amorphous Se continued to decrease with milling time, suggesting that molecular chain length decreased with milling time. Combined with the x-ray absorption near-edge structure calculations, it was concluded that the mechanical milling destroyed the interchain bonds of crystalline Se, resulting in the amorphization, while the intrachain bonds were strengthened during amorphization. The present results support a previous crystallite-destabilization model for solid-state amorphization. © 2004 American Institute of Physics.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
78.70.Dm X-ray absorption spectra
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Influence of surface roughness and internal strain on defect spectrum and intensity of low-temperature photoluminescence of thin Si1−xGex layers

V. Ligatchev, T. K. S. Wong, and S. F. Yoon

J. Appl. Phys. 95, 7681 (2004); http://dx.doi.org/10.1063/1.1739288 (9 pages) | Cited 6 times

Online Publication Date: 4 June 2004

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Microstructure, surface roughness, morphology, defect spectrum, and low-temperature photoluminescence of thin (10–125 nm) strained Si1−xGex layers (0.1⩽x⩽0.3), deposited by chemical vapor deposition (CVD) at 650 °C on silicon wafers have been studied. Nominally undoped layers with crystalline orientations of 〈100〉 and 〈111〉 have been investigated. Local strain within the layers was estimated from x-ray diffraction data. It decreases with the layer thickness in the 〈100〉-oriented samples, but rises in the 〈111〉-oriented ones. Nanoscale (∼10–30 nm) and microscale (∼0.2–1 μm) morphologies have been found on the surface of the Si1−xGex layers by atomic-force microscopy. The lateral sizes of the morphologies and surface roughness depend on the thickness, germanium concentration x, and crystalline orientation of the layers. The spectrum of defect states N(E) in the band gap of these samples has been experimentally studied by the deep-level-transient-spectroscopy (DLTS) technique. The standard D1(P1), D2, P3, and P4 defect peaks were observed. The N(E) spectrum is strongly influenced by germanium concentration, crystalline orientation, and surface roughness of the films (especially at Ec−E<0.4 eV). Photoluminescence (PL) was excited with argon ion (Ar+) laser at a sample temperature of about 5 K. Both “no-phonon” and phonon-assisted PL peaks around 1.1 eV, as well as a strong peak at 0.80 eV were observed. These peaks originated, respectively, from the no-phonon line from the Si substrate, transverse optical/acoustical phonon replica and dislocation-related Si1−xGex band, D1. Intensities of these PL peaks are influenced by the layer thickness, internal strain, surface roughness, and germanium concentration x. Possible mechanisms of relationship between the local strain, film roughness, the defect spectrum N(E), and the D1 line strength are discussed. © 2004 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
78.55.Hx Other solid inorganic materials
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
71.55.-i Impurity and defect levels
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.20.Ps Other inorganic compounds

Be–Se double-phonon behavior in Zn1−x−yMgyBexSe alloy

O. Pagès, M. Ajjoun, D. Bormann, and E. Tournié

J. Appl. Phys. 95, 7690 (2004); http://dx.doi.org/10.1063/1.1738522 (4 pages) | Cited 2 times

Online Publication Date: 4 June 2004

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The longitudinal optical (LO) and transverse optical (TO) phonons of zincblende Zn1−x−yMgyBexSe with x,y∼0.15 are identified by Raman scattering. The Be–Se region exhibits a two-mode behavior similar to that observed with the random Zn1−xBex(Se,Te) systems. This indicates that the percolation picture set for the latter mixed crystals with contrasted bond stiffness extends to Be-based multinaries. Accordingly the low- and high-frequency modes refer to Be–Se bonds within the Be-rich hard-like region and the (Zn,Mg)-rich soft-like one, respectively. Besides, we derive the (x,y) values together with the fraction p of Be atoms in the hard-like region from combined contour modeling of the TO and LO Raman line shapes. We find p∼x, as in the ZnBe(Se,Te) references. We deduce that the Be incorporation is random in ZnMgBeSe. © 2004 American Institute of Physics.
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63.20.K- Phonon interactions
78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

The role of contaminants in the variation of adhesion, friction, and electrical conduction properties of carbide-coated scanning probe tips and Pt(111) in ultrahigh vacuum

M. Enachescu, R. W. Carpick, D. F. Ogletree, and M. Salmeron

J. Appl. Phys. 95, 7694 (2004); http://dx.doi.org/10.1063/1.1738536 (7 pages) | Cited 5 times

Online Publication Date: 4 June 2004

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Scanning probe microscopy was used to investigate the tribological properties of nanoscale tips in contact with a Pt(111) single-crystal surface under ultrahigh vacuum conditions. The tips were coated with a tungsten carbide film, which contained a significant fraction of oxygen. The electrically conductive tip made it possible to alternate between contact measurements and noncontact scanning tunneling microscopy. Several types of interfaces were found depending on the chemical state of the surfaces. The first type is characterized by strong irreversible adhesion followed by material transfer between tip and sample. Low adhesion and no material transfer characterize a second type of contact, which are associated with the presence of passivating adsorbates in both (full passivation) or in one of the two contacting surfaces (half-passivation). Half-passivated contacts in which the clean side is the Pt(111) sample gave rise to periodic stick-slip friction behavior with a period equal to the atomic lattice constant of the Pt(111) surface. Local electrical conductivity measurements show a clear correlation between electronic and friction properties, with ohmic behavior on clean regions of the Pt surface and semiconductor-like behavior on areas covered with adsorbates. © 2004 American Institute of Physics.
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68.35.Np Adhesion
68.35.Af Atomic scale friction
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.65.Rv Passivation
73.40.Ns Metal-nonmetal contacts
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Optical properties of an all-plastic WO3⋅H2O-based infrared modulator

A. Bessière, L. Beluze, M. Morcrette, B. Viana, J.-M. Frigerio, C. Andraud, and V. Lucas

J. Appl. Phys. 95, 7701 (2004); http://dx.doi.org/10.1063/1.1737807 (6 pages) | Cited 1 time

Online Publication Date: 4 June 2004

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WO3⋅H2O powder embedded in a plastic matrix has demonstrated attractive properties as a flexible emissivity modulator driven by the electrochemical insertion of lithium. The near infrared optical properties of LixWO3⋅H2O are investigated as a function of the lithium intercalation level x for 0⩽x⩽2.65. The reflectivity at 2.5 μm, measured through a glass window, was found to vary between 0.15 and 0.4 over the α intercalation phase (0⩽x<0.3), i.e., demonstrating an emissivity contrast of ∼0.25. For x⩾0.1 the LixWO3⋅H2O-based plastic device exhibits a Drude behavior comparable to that of monoclinic tungsten oxide (m-WO3) thin films. For larger intercalation levels, the performances are affected by some irreversible structural modifications of the LixWO3⋅H2O lattice. © 2004 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
82.47.-a Applied electrochemistry
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.30.-j Infrared and Raman spectra

Absence of island–island interaction during formation of isolated Ge islands in small windows

T. Stoica, L. Vescan, and E. Sutter

J. Appl. Phys. 95, 7707 (2004); http://dx.doi.org/10.1063/1.1736312 (5 pages) | Cited 2 times

Online Publication Date: 4 June 2004

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Isolated Ge islands, i.e., islands not connected by a wetting layer can be obtained by selective epitaxial growth in voids of ultrathin oxides of thickness 1–2 nm. Voids of 30–600 nm size were created before epitaxy during a high temperature anneal of the ultrathin oxide. The formation of one island per window was investigated at 700 °C as a function of Ge thickness and void size. Islands nucleate mainly at the edge of the void and for this reason they have an anisotropic shape. In voids smaller than 300 nm only one island is nucleated. Islands form only in voids greater than a critical size (30–80 nm) which depends on the total amount of Ge deposited. We observe that height, width, and aspect ratio of isolated islands increase with void size for a given Ge thickness. A metastable state of Ge in small windows was observed. Moreover, the Si interdiffusion is strongly reduced with decreasing island size (i.e., with void size) reaching only ∼10% in comparison with ∼50% in islands on large areas. © 2004 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Cc Kinetics of defect formation and annealing
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Effects of finite crystal size in the quartz crystal microbalance with dissipation measurement system: Implications for data analysis

Ilya Reviakine, Alexander N. Morozov, and Fernanda F. Rossetti

J. Appl. Phys. 95, 7712 (2004); http://dx.doi.org/10.1063/1.1737049 (5 pages) | Cited 7 times

Online Publication Date: 4 June 2004

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A quartz crystal microbalance with dissipation, or QCM-D, allows the properties of a loaded quartz oscillator—resonance frequency and dissipation [1/(the quality factor)]—to be monitored on several overtones. The frequency and the dissipation factor of the loaded oscillator are functions of the physical properties (such as thickness, density, viscosity, elasticity, roughness) of the media loading the resonator (e.g., a liquid, a thin polymer film, a phospholipid bilayer, etc.) and the frequency at which the measurement was performed. In this contribution, it is shown that the frequencies measured with the QCM-D instrument on the first, third, fifth, and seventh overtones do not agree with those expected of an ideal, infinite crystal. Therefore, the results of QCM-D measurements cannot be directly compared with theoretical models that require the resonance frequency of an unloaded crystal to be used as one of the input parameters. A phenomenological procedure for dealing with this problem is proposed. © 2004 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
06.30.Ft Time and frequency
06.30.Dr Mass and density
07.10.Lw Balance systems, tensile machines, etc.

Temperature dependence of energy transfer mechanisms in Eu-doped GaN

Chang-Won Lee, Henry O. Everitt, D. S. Lee, A. J. Steckl, and J. M. Zavada

J. Appl. Phys. 95, 7717 (2004); http://dx.doi.org/10.1063/1.1738529 (8 pages) | Cited 16 times

Online Publication Date: 4 June 2004

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The temperature dependent behavior of continuous-wave and time-resolved photoluminescence of Eu-doped GaN in the visible region is measured for both the 5D0→7F2 and 5D0→7F3 transitions. The radiative decay of these transitions, following pulsed laser excitation of the GaN host, is monitored by a grating spectrometer and photomultiplier tube detector system. In addition to these two radiative energy transfer pathways within Eu3+, the data reveal two nonradiative energy transfer paths between Eu3+ and the host GaN. Decay constants for the relaxation processes are extracted from the data using a numerically solved rate equation model. Although the dominant radiative relaxation processes decayed with a temperature insensitive decay constant of 166 μs, a prominent role for nonradiative transfer between Eu3+ and impurities within the GaN host was deduced above 180 K. © 2004 American Institute of Physics.
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78.55.Cr III-V semiconductors
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