bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the dissociation process of oxygen on the electron swarm parameters in oxygen
Authors: Kajita S. , Ushiroda S. , Kondo Y.
Published: July 2002

Previous theoretical studies assumed that the energy loss of a colliding electron has a discrete value for dissociative excitation of molecular oxygen. In the calculation of the rate coefficients for oxygen atom yields using the Boltzmann equation, the previous reports have used discrete energy loss values of 6.1 eV for A3Σ+u and 8.4 eV for B3Σ−u. In this paper, we take account of the fact that the excitation to B3Σ−u has a continuum energy loss spectrum and describe the effects on calculated swarm parameters that are important in the simulation of ozonizer discharges. It can be seen that the use of a continuum electron energy-loss spectrum as opposed to a discrete electron energy loss associated with excitation to the B3Σ−u state makes no significant difference in the calculated values of electron swarm parameters in oxygen. We also calculate the ozone yield as a function of E/N obtained from the analysis of the energy balance equation. In this case, the partial cross section for dissociation via B3Σ−u assuming a continuum electron energy-loss spectrum can have significant effects on the atomic oxygen yields at different E/N.
Morphology of gold films thinned by argon ion sputter etching
Authors: Hodgkinson Ian J. , Lemmon Joan
Published: July 2002

Evaporated gold films and gold films etched by argon ion bombardment to the same thickness are known to exhibit different optical and electrical properties. Transmission electron microscope observations presented in this paper confirm that these differences are caused by different growth/etch film morphologies. The density of islands in a globular film remains nearly constant during etching, in contrast to a steady decrease during deposition. Similarly, the particle density in a nested island film initially remains constant during etching but then increases slightly as some of the islands break up. Films that are initially fully coalesced remain continuous during etching until, when they are very thin, an array of holes of irregular shape and increasing size appears and finally they break up into islands of irregular shape.
Polytype formation in zirconium-silicon thin films
Authors: Bourret A. , d’Heurle F. M. , Le Goues F. K. , Charai A.
Published: July 2002

The structure of zirconium silicide (ZrSi2, orthorhombic C49; a=0.369 nm, b=1.47 nm, c=0.366 nm) thin films has been investigated by high-resolution electron microscopy. The crystals are heavily faulted in the 010 plane with an average distance between faults of 1.6 nm. The fault has been found to be a π/2-rotation twin around the b axis, the habit plane lying between two silicon layers. The crystals contain an equal number of 〈a〉- and 〈c〉-oriented slabs, giving rise to a strained lattice with an average a=c lattice parameter. On the basis of an elastic calculation, the fault energy is evaluated to be of the order of 5 ergs cm−2. This low energy explains the tendency to form polytypes which are mostly disordered, although some ordered sequences are favored at short range.
Doping in a superlattice structure: Improved hole activation in wide-gap II-VI materials
Authors: Suemune Ikuo
Published: July 2002

The activation energy of acceptors in ZnSe is about 110 meV and the ratio of the activated free holes to the doped acceptors is reduced for high doping. This paper proposes doping of acceptors in a superlattice structure to improve the activation ratio. The doping characteristics were analyzed considering self-consistent potential change due to the carrier distributions. The activation ratio is shown to be improved for the shorter period of the superlattice and free-hole concentrations of nearly 1×1019 cm−3 are expected in a ZnSe/ZnS0.18Se0.82 superlattice with a 60 Å period, which is about a 4–5 times improvement compared with the doping in ZnSe films.
Deep levels in Ga-doped ZnSe grown by molecular-beam epitaxy
Authors: Miyajima Takao , Akimoto Katsuhiro , Mori Yoshifumi
Published: July 2002

Deep levels in Ga-doped ZnSe films grown by molecular-beam epitaxy have been investigated through deep-level transient spectroscopy. Au/Ga-doped ZnSe Schottky diodes have two well-defined electron traps with activation energies of 0.26 eV (trap A), and 0.40–0.56 eV (trap B). The activation energy of trap B depends on the free-carrier concentration. The trap concentration in trap A and B is linearly proportional to the free-carrier concentration. The trap concentration, normalized by the free-carrier concentration, increases as the VI/II (Se/Zn) ratio increases. From these observations, we conclude that traps A and B can be ascribed to the complex of either the Zn vacancy and Ga or the interstitial Se and Ga.
Free molecular transport and deposition in long rectangular trenches
Authors: Cale T. S. , Raupp G. B. , Gandy T. H.
Published: July 2002

Integral equations are derived which describe free molecular flow and simultaneous film deposition in long rectangular trenches. The equations apply to flow in the absence of deposition and to both low-pressure chemical vapor deposition (LPCVD) and physical vapor deposition (PVD), i.e., over the full range of reactant sticking coefficient from zero to unity. A steady-state assumption is implicit in the formulation. In the absence of film deposition, the flux to the surface is spatially uniform. Analytical expressions are presented for the initial deposition profiles along the trench sides and bottom for PVD (unity sticking coefficient). Numerical inversion of the integral equations provides initial deposition profiles for LPCVD (low sticking coefficient). The calculated initial deposition profiles are consistent with empirical results which typically show poor uniformity in PVD and high uniformity in LPCVD, and also compare well with Monte Carlo based simulations of deposition processes.
Interaction of metallized tubules with electromagnetic radiation
Authors: Behroozi F. , Orman M. , Reese R. , Stockton W. , Calvert J. , Rachford F. , Schoen P.
Published: July 2002

Several diacetylenic lecithins form tubular microstructures (tubules) when their liposomes are cooled through the chain-melting transition. Recently, the tubules have been metal plated by an electroless technique. This paper reports on the interaction of permalloy coated tubules with electromagnetic radiation. At 10 vol % loading of tubules in an epoxy matrix has a real dielectric constant ε′≊50 at a frequency of 9.5 GHz. Simple electrodynamics accounts well for the observed results. Far higher values of ε′ may be achievable with longer tubules and with improved metal coatings.
Photothermal characterization of creep damage in SiC–SiO2
Authors: Inglehart L. J.
Published: July 2002

We demonstrate that ceramic composites with near surface damage may be characterized with photothermal methods in a noncontact, sensitive way through dependence on temperature. As an application we characterize a SiC–SiO2 composite with creep damage.
2.5 μm GaInAsSb lattice-matched to GaSb by liquid phase epitaxy
Authors: Tournié E. , Lazzari J.-L. , Pitard F. , Alibert C. , Joullié A. , Lambert B.
Published: July 2002

GaSb lattice-matched Ga1−xInxAsySb1−y has been grown by liquid phase epitaxy on (100) and (111)B oriented substrates using initial melt supersaturation ΔT varying from 10 to 30 °C, at growth temperatures >600 °C. It is shown that the band-gap cutoff wavelength, measured at room temperature by the electroreflectance method, is ∼2.38 μm for (100) layers whatever ΔT, and increases from 2.38 μm up to 2.51 μm for (111)B oriented layers when ΔT is increased from 15 to 25 °C. Photoluminescence experiments at 2 K confirm the band-gap reduction occurring at high ΔT with the (111)B orientation.
Spherical reflector as an electromagnetic-missile launcher
Authors: Shen Hao-Ming
Published: July 2002

A spherical reflector illuminated by a point source is found to be capable of launching an electromagnetic missile. Since the surfaces of the reflector are not complete spherical surfaces, the problem cannot be solved by simple boundary matching. The electromagnetic fields have to be solved in three regions separately. The general solutions are matched on the boundaries to obtain a set of coefficient equations. Under the conditions for an electromagnetic missile, the coefficient equations are solved asymptotically. The evaluation of the Poynting vector shows that the energy radiated from the reflector has the same slow rate of decay as for the spherical lens.
Modeling of two-junction, series-connected tandem solar cells using top-cell thickness as an adjustable parameter
Authors: Kurtz Sarah R. , Faine P. , Olson J. M.
Published: July 2002

Theoretical efficiencies are calculated for two-junction, series-connected solar cells using air mass 1.5 global and direct irradiance spectra. For band-gap combinations previously limited by a low bottom-cell current, thinning of the top cell is shown to result in significant increases in the theoretical efficiencies. The increases are primarily due to increased short-circuit currents, since current matching is achievable. Smaller gains are also seen in the open-circuit voltages of the thinner cells when a low surface-recombination velocity is assumed. Thus, a number of material combinations which previously could only be used in four-terminal configurations can now be considered for series-connected two-junction solar cells.
Observations of soft x-ray production in the speed 2 plasma focus
Authors: Bayley J. M. , Decker G. , Kies W. , Mälzig M. , Müller F. , Röwekamp P. , Westheide J. , Sidelnikov Y. V.
Published: July 2002

A new soft x-ray source has been developed and investigated. Argon is injected into a plasma focus through a hole in the anode. The pinch emits several Joules per shot of soft x rays at λ<0.5 nm from multiple micropinches well aligned along the axis of symmetry. When viewed end-on the pinch appears as a small source of 700 μm diam. The micropinches have the following characteristics: Range of size 40–250 μm (depending on radiation wavelength), density 1028 m−3, temperature 1.5 keV, and lifetime typically less than 1 ns. The helium-like emission from single micropinches lasts for 250 ps only, which is much shorter than previously reported.
Study on the sensing mechanism of tin oxide flammable gas sensors using the Hall effect
Authors: Ippommatsu Masamichi , Ohnishi Hisao , Sasaki Hirokazu , Matsumoto Takeshi
Published: July 2002

Measurements were made on the Hall effect of SnO2 thin-film inflammable gas sensors prepared by using the reactive sputtering method. The results revealed that when the electrical conductivity of the sensors changed with a change in the flammable gas concentration in air, the apparent carrier density changed significantly while apparent mobility hardly changed at all. However, detailed analysis revealed that these experimental results could not be explained by using the double Schottky model or the neck model that had been proposed. In order to provide satisfactory explanation of the experimental results, the authors clarified that for SnO2 thin films there exists no distinction between bulk and surface of the grain while the carrier densities of bulk and surface of the grain simultaneously change with a change in oxygen absorption of the SnO2 surface in the presence of flammable gas. This model was in good agreement with the results of transmission electron microscopy observations.
Mechanisms of thermal stress relaxation and stress-induced voiding in narrow aluminum-based metallizations
Authors: Korhonen M. A. , Paszkiet C. A. , Li Che-Yu
Published: July 2002

Thermal stress-induced voiding in narrow aluminum-based metallizations used as interconnects in microelectronic circuits has recently become a serious reliability concern. Room-temperature stress relaxation and associated physical phenomena in passivated and unpassivated aluminum-based metallizations, subsequent to exposure to high temperatures, are analyzed based both on theoretically estimated and experimentally determined thermal stresses. It is shown that stress relaxation at longer times involves mainly dislocation climb, while short-term relaxation during cool down from higher temperatures, and immediately thereafter, involves significant dislocation glide. Void growth, frequently observed in passivated metallizations, provides a new source of atoms to feed stress relaxation by the same processes as in the absence of voiding.
Substrate effects on the epitaxial growth of ZnGeP2 thin films by open tube organometallic chemical vapor deposition
Authors: Xing G. C. , Bachmann K. J. , Posthill J. B. , Timmons M. L.
Published: July 2002

In this paper, we report the growth of epitaxial films of ZnGeP2 on GaP and Si substrates of (001) and (111) orientations by open tube organometallic chemical vapor deposition. Generally, smaller growth rates are required to achieve similar film quality on (111) GaP as compared to growth on (001). For the growth on (001) GaP the c-axis strain determined by x-ray diffraction agrees with the expected strain for a lattice mismatch of 0.0026 between the a-axis lattice parameters of ZnGeP2 and GaP. Based on the continuous increase of the c-axis lattice parameters and the gradual weakening of the chalcopyrite structure superlattice reflections, a continuous transition is proposed from the ordered structure of ZnGeP2 towards diamond structure of Ge via partially disordered metastable solid solution of ZnGeP2-Ge. Cross-sectional transmission electron microscopy reveals twinning of epitaxial ZnGeP2-Ge films on (111) GaP. The twinning density is related to both the growth rate and the flow rate ratio of Zn(CH3)2 to GeH4 at constant flow rate of PH3 and H2. Twins are also formed in ZnGeP2 growth on Si substrates.
Model for the relation between shock velocity and particle velocity in weak shock waves in metals
Authors: Tonks D. L.
Published: July 2002

The weak-shock theory of D. C. Wallace [Phys. Rev. B 22, 1487 (1980)] is used to calculate shock velocities as a function of particle velocity. The calculated shock velocities are based on thermoelastic behavior, plasticity behavior, and precursor behavior. The results are calculated and compared with data for 6061T6 Al, Be, Cu, Fe, 21-6-9 stainless steel, and U. Except for Fe, the agreement is reasonable. The contributions to the shock velocity from material strength and precursor behavior are rather small but, nevertheless, are calculated fairly well with the present theory.
Preparation and ferroelectric properties of PbZr0.53Ti0.47O3 thin films by spin coating and metalorganic decomposition
Authors: Spierings G. A. C. M. , Ulenaers M. J. E. , Kampschöer G. L. M. , van Hal H. A. M. , Larsen P. K.
Published: July 2002

Films with a composition PbZr0.53Ti0.47O3 were prepared on different platinum bottom electrodes using a spin-coating process followed by metalorganic decomposition. The film morphology and structure were characterized by scanning electron microscopy and x-ray diffraction analysis. The morphology was strongly influenced by the heat cycle used to form the PbZr0.53Ti0.47O3 layer. Fast heating and high-fire temperatures produced smooth films, while slow heating and low-fire temperatures gave films having a rosette perovskite phase and an inter-rosette second phase. The films were characterized electrically by measuring hysteresis loops and capacitance and conductance versus bias voltage and by pulse-switching measurements. The dependence of the switched and nonswitched polarization on the number of switching cycles (i.e., the fatigue behavior) is found to be much better for fast-heated than for slowly heated films. Switching lifetimes exceeding 1011 cycles were measured. The type of platinum bottom electrode used was found to have a large influence on the ferroelectric properties of the lead zirconate titanate films.
Epitaxial orientation and morphology of β-FeSi2 on (001) silicon
Authors: Geib K. M. , Mahan John E. , Long Robert G. , Nathan Menachem , Bai G.
Published: July 2002

Epitaxially aligned films of β-FeSi2 were grown on (001) silicon by reactive deposition epitaxy (RDE), molecular-beam epitaxy (MBE), and solid-phase epitaxy (SPE). Although the matching crystallographic faces, FeSi2 (100)/Si(001), remained invariant throughout this study, two different azimuthal orientations predominated, depending on the deposition mode and growth temperature. Films with the FeSi2[010]∥Si〈110〉 orientation (grown by RDE at typically 500 °C) were of a genuine large-area single-crystal structure; however, the surface morphology was rough due to islanding which always preceeded the formation of a continuous film. Films of the alternative azimuthal orientation FeSi2[010]∥Si〈100〉 (which were grown by SPE at typically 250 °C or by MBE at temperatures as low as 200 °C on top of an SPE-grown template) have a much smoother surface morphology. However, there was some loss of purity in the epitaxial alignment at these extremely low temperatures. Excellent RHEED (reflection high-energy electron diffraction) streak patterns were observed for all the films; the technique was used for the determination of azimuthal orientation. In addition, we have shown that it is possible to determine the entire heteroepitaxial relationship using RHEED.
Transverse photothermal beam deflection within a solid
Authors: Spear Jonathan D. , Russo Richard E.
Published: July 2002

The mirage effect within a transparent solid substrate was used for monitoring optical absorption of a thin film. Refractive index gradients, which accompany thermal gradients below the film-coated surface, cause a probe laser beam to be deflected. The spectrum of copper, deposited onto a piece of clear acrylic, was recorded by this method of photothermal deflection. The influence of thermally induced mechanical stresses can alter the effective value of the thermo-optic coefficient of the solid, dn/dT.
Deep donor levels in Sn-doped AlxGa1−xAs
Authors: Huang Q. S. , Lin H. , Kang J. Y. , Liao B. , Tang W. G. , Li Z. Y.
Published: July 2002

The properties of the Sn-doped AlxGa1−xAs alloys with various compositions have been studied by deep level transient spectroscopy and photocapacitance methods. Two deep donor levels with the thermal activation energies of 0.19 and 0.32 eV are found in all of the samples. Detailed data for the thermal emission and capture activation energies, optical ionization energies, and their composition dependence are given for the first time. Because their electronic properties are similar to that of the typical Si DX level in AlxGa1−xAs, it is concluded that both Sn-related levels are the DX-like levels.
The energy of finite systems of misfit dislocations in epitaxial strained layers
Authors: Atkinson A. , Jain S. C.
Published: July 2002

Previous approaches to calculating the energy of a system of misfit dislocations in epitaxial strained layers have assumed that the system is infinite in the plane of the epitaxial interface and that the dislocations are uniformly spaced. Here a method is presented which is capable of dealing with finite systems of nonuniformly spaced dislocations of the type observed experimentally. The principle of the method is to explicitly account for the interactions between pairs of misfit dislocations. When the dislocations are infinite and uniformly spaced the present approach is shown to be equivalent to an earlier exact treatment. The present approach applied to finite systems of uniformly spaced dislocations shows that the energy per unit area converges to that of the infinite system very slowly; particularly when the spacing of the dislocations is less than the thickness of the epitaxial layer. Typically, systems must be larger than 30×30 dislocations for their energy per unit area to be within 10% of that of the infinite system. Similarly the infinite system will overestimate the energy of a 10×10 array by about 30%.
The dispersion relation in antiparallel coupled ferromagnetic films
Authors: Wigen P. E. , Zhang Z. , Zhou L. , Ye M. , Cowen J. A.
Published: July 2002

The dispersion relation of the system with two identical magnetic layers antiparallel coupled is modified from the normal antiferromagnetic material as well as that of the single ferromagnetic layer. With the external field in the film plane parallel to the in-plane easy axis, three unique regions exist as the antiparallel, canted and saturation region. The resonance field of the acoustic mode shifts significantly compared with that of a noncoupled layer system if the magnetization is not saturated. No antiparallel state exists with the external field perpendicular to the film plane and a minimum frequency, ω=2γHE, is required to observe the acoustic resonance mode. In each orientation the optical mode exists at a field of 2HE higher than that of the acoustic mode in the saturation region. These calculations are very helpful to understand the unusual ferromagnetic resonance spectrum in the strong antiparallel coupled bilayer system being investigated in this lab.
Structural characterization of photochemically grown silicon dioxide films by ellipsometry and infrared studies
Authors: Ashokan R. , Singh R. , Gopal V. , Anandan M.
Published: July 2002

Silicon dioxide films grown by photochemical vapor deposition at different deposition rates are investigated by ellipsometry and Fourier transform infrared measurements. Disagreement in the variation of refractive index with chamber pressure between thin and thick films is interpreted in terms of a deposition rate dependent buildup of internal stress in the film. Direct measurements of curvature show the presence of compressive stress in thick SiO2 films grown at chamber pressures ≳600 mTorr. Infrared transmission measurements also indicate a change in the structural characteristics of films (probably induced by stress), with increasing deposition rate. Molecular model calculations show a decrease in the Si—O—Si bond angle as the growth pressure increases. Ion implantation seems to release the stress in these films as evidenced by the shift observed in the stretching mode frequency. The relative concentrations of H2O, SiOH, and SiH groups in these films and the effect of annealing on the strength of these modes are also discussed. Reflection infrared measurements at 60° incidence reveal a disorder induced longitudinal-transverse optic pair at around 1200 cm−1.
Role of cladding layer thicknesses on strained-layer InGaAs/GaAs single and multiple quantum well lasers
Authors: Liu D. C. , Lee C. P. , Tsai C. M. , Lei T. F. , Tsang J. S. , Chiang W. H. , Tu Y. K.
Published: July 2002

The influences of cladding layer thicknesses on the performance of strained-layer InGaAs/GaAs graded-index separated confinement heterostructure quantum well lasers have been studied. The waveguiding property of the laser structure was analyzed using the transfer matrix method. In this work, experimental results and the calculated results showed that threshold current densities and external quantum efficiencies both were crucially dependent on the thicknesses of cladding layer for both single and multiple quantum well lasers. The minimum cladding layer thicknesses needed to maintain low threshold current densities and low internal total loss for both single and multiple quantum well devices were determined experimentally and theoretically.
Short pulse electron beam excitation of the high-pressure atomic Ne laser
Authors: Shon Jong W. , Rhoades Robert L. , Verdeyen Joseph T. , Kushner Mark J.
Published: July 2002

The high-pressure atomic Ne laser operates on four visible transitions between the 3p and 3s manifolds. Oscillation at 585 nm (3p′[1/2]0→3s′[1/2]10) at efficiencies of ≳1% have been demonstrated by others. The upper laser level is believed to be populated by dissociative recombination of Ne2+, while state-selective Penning reactions relax the lower laser levels. To investigate these pumping mechanisms, experimental and modeling studies have been performed on a short pulse e-beam excited Ne laser using He/Ne/Ar mixtures. We found that the electron temperature in the afterglow following the e-beam pulse largely determines the time at which oscillation starts. The electron temperature during the afterglow is partly controlled by a slow relaxation of excited states in Ar. Laser oscillation does not occur until these manifolds are depleted and the electron temperature decreases, thereby increasing the rate of dissociative recombination.
Electromagnetic modes and prism-film coupling in anisotropic planar waveguides of epitaxial (101) rutile thin films
Authors: Foster C. M. , Chan S.-K. , Chang H. L. M. , Chiarello R. P. , Zhang T. J. , Guo J. , Lam D. J.
Published: July 2002

We report optical waveguiding in single-crystal, epitaxial (101) oriented rutile (TiO2) thin films grown on (112̄0) sapphire (α-Al2O3) substrates using the metal-organic chemical vapor deposition technique. The electromagnetic field distributions and propagation constants for asymmetric planar waveguides composed of an anisotropic dielectric media applicable to these films are derived. Modifications to the prism-film coupling theory for this anisotropic case are also discussed. By application of this model to (101) oriented rutile thin films, we directly obtain values of the ordinary and extraordinary refractive indexes, n0 and ne, of the rutile thin films as well as film thicknesses. We obtain typical values of the refractive indexes (n0=2.5701±0.0005; ne=2.934±0.001) near to those for bulk rutile single crystals indicating the exceptional quality of these films.
Hierarchical domain structures and in situ domain migration in the antiferroelectric ceramic PLSnZT
Authors: Speck J. S. , De Graef M. , Wilkinson A. P. , Cheetham A. K. , Clarke D. R.
Published: July 2002

The crystallography and microstructure of an antiferroelectric ceramic of approximate composition Pb0.97La0.02(Zr0.65Sn0.25Ti0.10)O3 have been examined. Transmission electron microscopy (TEM), x-ray, and neutron powder studies were carried out. The cell is metrically tetragonal with a c/a ratio of 0.993 when indexed to the parent cubic perovskite cell. The structure exhibits both a commensurate supercell, believed to be associated with oxygen octahedra distortions, and an incommensurate modulation. The different crystallographic variants of the tetragonal antiferroelectric phase gave rise to a hierarchy of domain structures. Charging of TEM specimens having an incomplete conductive coating caused domain migration.
The nature of donor conduction in n-GaN
Authors: Khan M. Asif , Olson D. T. , Kuznia J. N. , Carlos W. E. , Freitas J. A.
Published: July 2002

Single crystal GaN thin films resulting from various deposition techniques are usually dominated by residual donors. To date, the true nature of this donor conduction is not known. Nitrogen vacancies, residual oxygen, and growth defects are cited as potential causes for the residual n-type conduction. In this communication we present the first systematic study of near conduction band edge states in n-type GaN samples deposited over basal plane sapphire substrates using low pressure metal organic chemical vapor deposition. Electron spin resonance, low temperature photoluminescence, and Van der Pauw–Hall measurements were used as the basis for our study. We concluded that the residual n-type conduction in GaN results from a band of delocalized donors.
Current flow mechanisms in GaAs planar-doped-barrier diodes with high built-in fields
Authors: Jiang Wei-Nan , Mishra Umesh K.
Published: July 2002

The existing models of the current flow across planar-doped-barrier (PDB) diodes are based on thermionic emission over the triangular barriers and have successfully predicted the characteristics of diodes with low barriers. However, experimental measurements on planar-doped-barrier (PDB) electron emitters suggest that tunneling can be the dominant transport mechanism across PDB structures with high built-in fields. In this work, we propose a model that takes into account the quantum mechanical effects of the scattering across the barrier and the tunneling through the energy band gap. Good agreement between the theory and experiments has been obtained.
Study of defects in silicon dioxide films on Si(100) by a variable-energy positron beam
Authors: Fujinami M. , Chilton N. B. , Ishii K. , Ohki Y.
Published: July 2002

Amorphous SiO2 films grown by both thermal oxidation and plasma chemical vapor deposition (CVD) in a tetraethylorthosilicate and O2 atmosphere were studied using variable-energy positron annihilation spectroscopy and infrared (IR) spectroscopy. For thermally grown SiO2 layers with growth temperatures of over 1000 °C it was found that the measured Doppler broadening parameter was identical for both wet and dry growth atmospheres. The measured Doppler broadening parameter in the case of SiO2 prepared by plasma CVD was found to be strongly influenced by the substrate temperature during deposition. For a substrate growth temperature of 600 °C, the data are essentially identical to those of the thermally grown oxide layers. IR analysis revealed that the concentration of Si–OH in the SiO2 layer is affected by the substrate temperature during growth. The level of the Doppler broadening parameter in the SiO2 film exhibited changes that can be correlated with this Si–OH concentration. We thus show that the concentration of Si–OH in amorphous SiO2 film is a factor that may affect the Doppler broadening parameter.
Electro-optic properties near the absorption edge of GaAs/AlGaAs multiple-quantum-well waveguides
Authors: Bloemer Mark J. , Myneni Krishna
Published: July 2002

Measurements are reported of the electro-optic properties of multiple-quantum-well p-i-n diodes at wavelengths where the waveguide propagation losses are small, 55–110 meV below the exciton resonance. Electroabsorptive and electrorefractive properties were measured as a function of polarization and crystal propagation direction. The electroabsorption and electrorefraction data show that there is a wavelength bandwidth of ∼25 nm where the quadratic electro-optic coefficient is large (1–7×10−15 cm2/V2) and the magnitude of the electroabsorption is <0.5 dB/mm for applied fields of up to 1×105 V/cm. Compact, high-dynamic-range interferometric modulators can be realized in this wavelength band.
Direct bonding of quartz crystal onto silicon
Authors: Eda Kazuo , Kanaboshi Akihiro , Ogura Tetsuyoshi , Taguchi Yutaka
Published: July 2002

A new method to bond a quartz crystal onto a silicon substrate, fabricating a quartz-crystal-on-silicon resonator, is reported together with its fabrication process, interface microstructure, and resonant characteristics. A one-chip quartz crystal oscillator employing the quartz-crystal-on-silicon resonator for mobile communication is also suggested.
rf excited 1.1 W/cm waveguide CO2 laser
Authors: Heeman-Ilieva M. B. , Udalov Yu. B. , Witteman W. J. , Peters P. J. M. , Hoen K. , Ochkin V. N.
Published: July 2002

The results of an optimization procedure performed for a continuous wave rf excited sealed CO2 waveguide laser are presented. Parameters that affect laser performance, such as the excitation frequency, the gas pressure, and composition, as well as the electrode temperature and different kinds of circuit losses have been analyzed. An output power of 41 W (17.7 kW/ℓ) with an efficiency of 12% has been obtained from an optimized laser with an active length 37 cm.
Epitaxial growth and magnetic properties of Fe(211)
Authors: Yaegashi Seiji , Kurihara Toshiya , Segawa Hideo
Published: July 2002

Epitaxial growth of Fe(211) was achieved at a room temperature on MgO(110) with a dc facing targets sputtering system. The epitaxial relation was confirmed by electron diffraction: 〈111〉 in the Fe(211) plane is parallel to 〈110〉 in the MgO(110) plane with a 6:5 coincident site lattice. Crystallographic and magnetic properties could be controlled by changing the rf power of substrate bias and substrate temperature. The magnetocrystalline anisotropy energy for Fe(211) was calculated and compared with experimental results. The film deposited at 400 °C with 10 W of rf bias had a small stress and showed almost theoretical behavior in a torque measurement. The difference in the in-plane anisotropy energy between the film and bulk was attributed to the effect of uniaxial anisotropy energy.
Brillouin scattering by localized acoustic modes in silicon-oxynitride–fused-silica optical waveguides
Authors: van Wijk R. J. , Arts A. F. M. , de Wijn H. W.
Published: July 2002

Brillouin scattering connecting guided optical modes is used to study the acoustic waves in a silicon-oxynitride–fused-silica double layer deposited onto a Si substrate. The frequencies of the acoustic modes as derived from the acoustic wave equation are found to reproduce those of the experiment. The scattering intensities are in agreement with a calculation based on the coupled-waveguide-mode formalism with due account of the elasto-optic effect and the corrugation of the surface and silicon-oxynitride–silica interface. Finally, the sound velocities and Pockels coefficients of the silicon-oxynitride layer are determined.
The growth and structure of short period (001) Hg1−xCdxTe-HgTe superlattices
Authors: Becker C. R. , He L. , Regnet M. M. , Kraus M. M. , Wu Y. S. , Landwehr G. , Zhang X. F. , Zhang H.
Published: July 2002

Molecular beam epitaxially grown short period (001) Hg1−xCdxTe-HgTe superlattices have been systematically investigated. Several narrow well widths were chosen, e.g., 30, 35 and 40 Å, and the barrier widths were varied between 24 and 90 Å for a particular well width. Both the well width and the total period were determined directly by means of x-ray diffraction. The well width was determined by exploiting the high reflectivity from HgTe and the low reflectivity from CdTe for the (002) Bragg reflection. Knowing the well and barrier widths we have been able to set an upper limit on the average Cd concentration of the barriers, x̄b, by annealing several superlattices and then measuring the composition of the resulting alloy. x̄b was shown to decrease exponentially with decreasing barrier width. The structure of a very short period superlattice, i.e., 31.4 Å, was also investigated by transmission electron microscopy, corroborating the x-ray diffraction results.
Output characteristics of a discharge-pumped F2 laser (157 nm) with an injection-seeded unstable resonator
Authors: Kakehata M. , Yang C.-H. , Ueno Y. , Kannari F.
Published: July 2002

To improve beam quality, an injection-seeded unstable resonator was applied to a discharge-pumped F2 laser, which is normally dominated by amplified spontaneous emission with a large beam divergence when using a normal stable cavity, due to the laser’s extremely high gain (a small-signal gain-length product ∼29). The time-dependent injection-seeding efficiency was obtained for various injection timings by measuring a ratio of the output laser intensity with the same polarization as the seed laser. Correlation of the injection-seeding efficiency with the temporal evolution of the laser-beam divergence was also studied. Both the time-dependent beam divergence and the injection-seeding efficiency showed degradation at a later part of the laser pulse.
Photoluminescence study of implantation-induced intermixing of In0.53Ga0.47As/InP single quantum wells by argon ions
Authors: Oshinowo J. , Dreybrodt J. , Forchel A. , Mestres N. , Calleja J. M. , Gyuro I. , Speier P. , Zielinski E.
Published: July 2002

We have performed systematical investigations of intermixing effects in In0.53Ga0.47As/InP single quantum wells induced by 30-keV Ar+-ion beam implantation with doses ranging from 1012 to 1014 cm−2 and a subsequent rapid thermal annealing (RTA) at temperatures between 600 and 900 °C. After implantation and RTA at 600 °C we observe a significant increase of the photoluminescence emission energy of about 60 meV in comparison with unimplanted heterostructures, indicating that the intermixing is determined by implantation. For RTA above 850 °C, in contrast, the energetic shifts up to 200 meV observed for the implanted samples are similar to the shift in unimplanted samples, indicating a predominant contribution of thermal interdiffusion. The significant decrease of Ga concentration after interdiffusion is confirmed quantitatively by Raman measurements.
Structural and transport properties of biaxially aligned YBa2Cu3O7−x films on polycrystalline Ni-based alloy with ion-beam-modified buffer layers
Authors: Iijima Y. , Onabe K. , Futaki N. , Tanabe N. , Sadakata N. , Kohno O. , Ikeno Y.
Published: July 2002

Biaxially aligned YBa2Cu3O7−x (YBCO) thin films were produced on polycrystalline Ni-based alloy, by using biaxial yttria-stabilized-zirconia (YSZ) intermediate layers formed by off-normal ion-beam-assisted deposition. Most explicit in-plane alignment was obtained when the YSZ layer formed with the beam-incident angle of 55° from substrate normal. Jc-B characteristics and angular dependence of Jc on the magnetic field were measured. 5.0×105 and 5.5×104 A/cm2 were obtained at 77 K with 0 and 8 T, respectively. The distribution of misorientation angles of in-plane a and b axes between YBCO grains was evaluated by both x-ray pole figure measurement and planar observations of transmission electron microscopy. 50% of the grains had the misorientation angles restricted within ±5°. From the image of dislocations, the elastic strains at grain boundaries were estimated to be relaxed with lower misorientation angle. The high-Jc properties are understood to be obtained by the current paths through low-angle grain boundaries.
Photopumped room-temperature continuous operation of native-oxide-embedded AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well-heterostructure lasers
Authors: Sugg A. R. , Chen E. I. , Richard T. A. , Holonyak N. , Hsieh K. C.
Published: July 2002

Data are presented on the 300 K (and 77 K) continuous photopumped laser operation of AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well heterostructures (QWHs) that have been oxidized (H2O vapor+N2, 425 °C) selectively along the high-band-gap heterolayers located on either side of a GaAs waveguide (WG) region with an InxGa1−xAs QW in its center. Transmission electron microscope images show that the oxide-embedded GaAs-InxGa1−xAs WG+QW active region remains unoxidized and thus is sandwiched between electrically insulating AlyGa1−yAs native oxide layers. The thresholds for photopumped 300 K continuous laser operation of the as-grown and oxide-embedded QWHs are approximately equal after differences in the Ar+-laser photopumping efficiencies are considered.
Preferential axis control of YBa2Cu3Ox thin film by quasilattice-match engineering
Authors: Mukaida Masashi , Miyazawa Shintaro
Published: July 2002

The lowest temperature for c-axis preferred oriented thin film growth is investigated for films on different substrate materials. This temperature has a maximum when the lattice constant of the substrate matches that of YBa2Cu3Ox. This result readily explains a-axis preferred oriented film growth by the template technique. We propose quasilattice-match engineering as a technique for controlling the preferential orientation axis of a part of a YBa2Cu3Ox thin film by using a seed layer whose lattice mismatch differs from that of the substrate. The part of the YBa2Cu3Ox thin film on a PrGaO3 seed layer is a-axis oriented and the film directly deposited on a SrTiO3 substrate is c-axis oriented.
Silicon donor-hydrogen complex in GaAs: A deep donor?
Authors: Morrow Richard A.
Published: July 2002

Post-hydrogenation anneals of shallow SiGa donors in GaAs indicate that their reactivation rate is enhanced in the presence of an applied electric field. We show that existing data are consistent with the SiGa-H complex being a deep donor dissociating only via its ionized state. The 0/+ level of this deep donor is found to be at EC−0.75 eV. There is no need to appeal to the existence of negatively charged hydrogen to account for the reactivation of SiGa donors.
Effects of rapid quenching on the impurity site location in Zn-diffused InP
Authors: Yu Kin Man , Walukiewicz W. , Chan L. Y. , Leon R. , Haller E. E. , Jaklevic J. M. , Hanson C. M.
Published: July 2002

The lattice locations of Zn atoms in heavily Zn-doped InP single crystal have been investigated by ion channeling techniques. The InP samples were rapidly quenched in diffusion pump oil after high-temperature Zn diffusion. Ion channeling experiments performed along various major crystal axes suggest that a large fraction (20%–30%) of the Zn atoms are in the tetrahedral interstitial position in the InP lattice. It has been found that although the maximum hole concentration is not significantly affected by the cooling rate, there is a substantial increase in the incorporation of Zn on substitutional and tetrahedral interstitial lattice locations in the rapidly cooled samples as compared to the slowly cooled samples. The consequences of these results for understanding the mechanisms leading to the saturation of the free-hole concentration in compound semiconductors are discussed.
Lateral thickness modulation of InGaAs/InP quantum wells grown by metalorganic molecular beam epitaxy
Authors: Cotta M. A. , Hamm R. A. , Chu S. N. G. , Harriott L. R. , Temkin H.
Published: July 2002

We have grown InGaAs quantum wells (QW), lattice matched to InP, with spatially modulated thickness along the [01̄1̄] direction of the crystal. Kinetic roughening alters the morphology of the underlying InP buffer layer and leads to the modulation of the well thickness. Photoluminescence (PL) emission reveals two distinct peaks, corresponding to excitons bound to well sections of different thicknesses. Comparison of PL spectra of 10 and 40 Å QW samples at different temperatures clearly indicates carrier confinement in the thicker well section. This effect is potentially useful for the preparation of quantum wires.
An exciton with a massive hole in a quantum dot
Authors: Nomura Shintaro , Kobayashi Takayoshi
Published: July 2002

An exciton with a massive hole trapped at an arbitrary position in a semiconductor quantum dot (QD) is studied theoretically. The energy spectra, wave functions, and dipole moments are obtained in the effective mass approximation. The contour maps of the density of the lowest state obtained clearly show the development of the wave function from the strong to weak confinement limit. The energy minimum for the lowest state is found for the trapped hole position from the center of a QD. The dipole moment of an exciton with the hole trapped on the surface is found to be proportional to R0 for small R0 and nearly constant for large R0.
Growth and modeling of cw-UV induced oxidation of silicon
Authors: Kazor A. , Boyd Ian W.
Published: July 2002

A report on the use of a low pressure Hg discharge lamp to grow 100 Å SiO2 layers on Si at 550 °C. The induced reaction rate is more than 12 times that for thermal oxidation of Si at 612 °C, indicating that the growth mechanism is photonically controlled. We tentatively suggest that the induced oxidation is based on space-charge controlled drift of ionic oxygen species created in the SiO2 by charge photoinjected from the Si. Simple modeling predicts a limiting thickness for film growth that is confirmed by experimental evidence. An activation energy of 0.56 eV extracted from the data compares with values of 0.14 – 0.7 eV previously reported for oxidation of silicon by O or O− species.
Long-wavelength λc=18 μm infrared hot-electron transistor
Authors: Lee C. Y. , Tidrow M. Z. , Choi K. K. , Chang W. H. , Eastman L. F. , Towner F. J. , Ahearn J. S.
Published: July 2002

A long-wavelength λc=18 μm infrared hot-electron transistor (IHET) with low dark current is demonstrated. In order to achieve long-wavelength absorption, a low barrier height is required, which in turn results in a large dark current. Therefore, operation of a normal long-wavelength quantum-well infrared photodetector (QWIP) structure is limited to very low temperatures and biases due to the thermally activated dark current. In the IHET, a high-energy pass filter placed after 30 periods of GaAs/AlGaAs quantum wells blocks the temperature-activated dark current while allowing high-energy photoexcited electrons to pass and be collected as photocurrent. A comparison of the dark current to the 300 K background photocurrent shows that the QWIP structure without the high-energy pass filter demonstrates background-limited infrared photodetection (BLIP) only at T≤35 K. Furthermore, in order to avoid saturating a typical readout circuit, detector operation of the QWIP is restricted to biases less than 0.08 V at 35 K. In contrast, the filtered dark current in the IHET is reduced by two to four orders of magnitude such that BLIP performance can be achieved for temperatures up to T=55 K without saturating the readout circuit. Because of the preferential current filtering effect, the noise equivalent temperature difference of the IHET can be improved by a factor of 100 at T=55 K. The dark-current-limited detectivity was found to be D*=1×1010 cm Hz1/2/W at λp=15 μm, Ve=−0.2 V, and T=55 K.
Strain relief of metastable GeSi layers on Si(100)
Authors: Bai G. , Nicolet M.-A. , Chern C. H. , Wang K. L.
Published: July 2002

Highly metastable pseudomorphic Ge0.3Si0.7 layers 570 nm thick were grown on Si(100) at ∼300 °C by molecular-beam epitaxy. The relief of strain in such metastable layers upon ex situ thermal annealing in vacuum is investigated by double-crystal x-ray diffractometry and MeV 4He channeling spectrometry. Upon isochronal annealing of 30 min, the strain relieves sharply at (375±25) °C, and reaches the thermal equilibrium value above 400 °C. Under isothermal annealing between 300 and 400 °C, the time evolution of the strain relief has the characteristics of a nucleation and growth transformation. The strain relief is very slow initially, increases approximately linearly as the strain is partially relieved, and saturates upon approaching equilibrium strain state. Two important results are drawn from the experimental data. First, a deformation-mechanism map is constructed from which the strain relief rate of a metastable GeSi/Si can be extrapolated for given stress state and temperature. Second, the rate of the strain relief when the strain is partially relieved increases with rising temperature, and follows an Arrhenius behavior as a function of the inverse temperature with a slope of 2.1±0.2 eV. This value coincides with the activation energy for dislocation glide in Ge0.3Si0.7. Furthermore, the strain-relief equation of a plastic flow model is solved and fits well the experimental strain-time dependence. One of the two fitting parameters, the time constant, has an Arrhenius temperature dependence. The slope, 1.9±0.2 eV, is assumed to be the activation energy for dislocation motion, and agrees with the previous value extracted from the simple rate-temperature dependence. In addition, as the strain is relieved, the x-ray-diffraction peak from the layer broadens and the channeling yield increases, confirming that the generation of misfit dislocations associated with the strain relief is accompanied by the generation of threading dislocations in the layer.
Characterization of InTlSb/InSb grown by low-pressure metal-organic chemical vapor deposition on a GaAs substrate
Authors: Choi Y. H. , Staveteig P. T. , Bigan E. , Razeghi M.
Published: July 2002

Optical properties of InTlSb, a new long wavelength infrared material, are investigated. InTlSb/InSb epilayers grown by low-pressure metal-organic chemical vapor deposition on semi-insulating GaAs substrates were characterized using Auger electron spectroscopy and Fourier transform infrared spectroscopy. Auger electron spectra confirm the presence of thallium. Transmission measurements at 77 K indicate an absorption shift from 5.5 μm for InSb up to 8 μm for InTlSb that is confirmed by photoconductivity measurements.