bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray investigation of the ordered structure in AlGaInP quaternary alloys
Authors: Okuda Hiroshi , Anayama Chikashi , Tanahashi Toshiyuki , Nakajima Kazuo
Published: July 2002

The ordered structure occurring in AlGaInP quaternary alloys grown on GaAs substrates by low-pressure metalorganic vapor phase epitaxy has been investigated by means of x-ray diffraction measurements. The order spot became strong as the Al content increased, and was observed only for the (1/2 ∼(1/2) 1/2) diffraction, corresponding to CuPt-type (111)B ordering. Kinematical analysis implies that the full width at half maximum of the order spot is strongly affected by the antiphase boundary, whereas the integrated intensity is not.
High-power, narrow single-lobe operation from 20-element phase-locked arrays of antiguides
Authors: Mawst L. J. , Botez D. , Jansen M. , Roth T. J. , Peterson G.
Published: July 2002

Pure in-phase-mode operation is obtained from 20/21-element AlGaAs/GaAs antiguided arrays grown by two-step metalorganic chemical vapor deposition. Oscillation of out-of-phase modes is substantially suppressed by a built-in spatial filter: two sets of noncollinear antiguides separated by a 50-μm-long laterally unguided region, corresponding to the half-Talbot distance. Design considerations for 20- vs 10-element arrays are discussed. Diffraction-limited-beam operation (i.e., 0.8° lobewidth) is obtained to 1.5×threshold (90 mW, both facets). Beams with 1.3° lobewidth (1.6×diffraction limit) are obtained at 3×threshold and 300 mW (both facets). Devices with optimized facet coatings operate in a single, 1.5°-wide lobe (i.e., 1.8×diffraction limit) at 330 mW front-facet emitted power. The main lobe contains 80–87% of the total power.
New model for dopant redistribution at interfaces
Authors: Orlowski M.
Published: July 2002

A new model for dopant redistribution at an interface is derived and verified by data from segregation and outdiffusion experiments. In the present model, a third phase, the interface layer itself (interphase), is considered in addition to the adjacent bulk phases for the first time. The dynamics of the three-phase system is described in terms of rate equations. In case that all three phases are identical, i.e., constitute one single homogeneous phase, this model effectively reduces to an ordinary diffusion equation for a bulk phase. The immediate advantage of this formulation is that the coupling between the redistribution at the interface and the diffusion in adjacent bulk phases can be described in an unambiguous and consistent way derived from first principles. In the limit of equilibrium segregation, the interface dynamics and bulk diffusion decouple, and the model reduces to diffusion equations in bulk phases supplied with Dirichlet boundary conditions at the interface given by analytic solutions of the equilibrium interface dynamics.
Dislocations in In0.1Ga0.9As/GaAs multilayers epitaxially grown on Si substrates
Authors: Morita Tatsuo , Furukawa M. , Shimizu M. , Nakajima Y. , Sakurai T.
Published: July 2002

Dislocations in In0.1Ga0.9As/GaAs multilayers grown on Si substrates have been examined by using transmission electron microscopy. It is found that two types of misfit dislocations exist at the interfaces of multilayers which are composed of layers thicker than the critical thickness (hc). One is a 60° dislocation and the other is a pure edge dislocation. It is considered that a 60° dislocation can glide to adjacent layers from the interface, while a pure edge dislocation can also go out of the interface. The stress field caused by closely located dislocations introduces bowing of dislocation lines followed by cross slipping.
Strong enhancement of the photoluminescence of n-type indium phosphide under a cathodic polarization
Authors: Etcheberry A. , Vigneron J. , Sculfort J. L. , Gautron J.
Published: July 2002

A strong enhancement of the photoluminescence emitted by n-type indium phosphide (n-InP), in contact with an aqueous electrolyte, takes place under a cathodic polarization. Neither the dead-layer model nor a modification of the optical properties of the semiconductor surface can explain such a phenomenon and it is necessary to involve a large variation in the surface recombination velocity. The decrease in this velocity is due to the passivating action of hydrogen which evolves during the reduction of the water.
Irreversible behavior of the transport critical current in polycrystalline YBa2Cu3Oy
Authors: Obara H. , Yamasaki H. , Kimura Y. , Kosaka S.
Published: July 2002

Temperature and magnetic field dependence of the critical current density Jc and magnetization of the polycrystalline high Tc oxide superconductor YBa2Cu3Oy have been measured. At low temperature, Jc shows a different temperature dependence between field cooling and zero-field cooling, that is, the Jc value measured when the sample was cooled in a fixed magnetic field was larger than that measured when the sample was cooled in zero magnetic field and then a magnetic field was applied. This irreversible behavior of Jc disappeared at a reduced temperature difference 1–t proportional to H2/3 (H is the magnetic field). Moreover, we have observed that the slope dV/dJ just above Jc began to increase rapidly with increasing temperature above 70 K. These experimental results can be attributed to the effects of grain boundaries.
Spectral characteristics of an injection-controlled XeF(C→A) excimer laser
Authors: Dane C. B. , Yamaguchi S. , Hofmann Th. , Sauerbrey R. , Wilson W. L. , Tittel F. K.
Published: July 2002

The spectral output characteristics of an injection-controlled XeF(C→A) excimer laser pumped by a short pulse (10 ns), high current density (250 A/cm2) electron beam are reported. A tuning bandwidth of 50 nm full width half maximum, centered at 490 nm, with a peak specific energy density of 1.3 J/ℓ was measured using an injection laser intensity of ∼2 MW/cm2. Continuously tuned output across the entire blue-green region (450–530 nm) with an energy density exceeding 0.2 J/ℓ was achieved. Injection beam spectral linewidths as narrow as 0.001 nm were shown to be preserved in the XeF(C→A) laser output.
Fermi edge singularity in the luminescence of modulation-doped Ga0.47In0.53As/Al0.48In0.52As single heterojunctions
Authors: Zhang Yong-Hang , Jiang De-Sheng , Cingolani R. , Ploog K.
Published: July 2002

Modulation-doped Ga0.47In0.53As/Al0.48In0.52As single heterojunctions have been investigated by means of optical spectroscopy and magnetotransport measurements. Strong radiative recombination of the two-dimensional electron gas (2DEG) with photogenerated holes has been observed. The recombination is not k conserving, since the holes are weakly localized at the heterointerface opposite to the 2DEG region. At low temperature strong Fermi edge enhancement occurs in the luminescence of single heterojunctions with, for example, a dense electron sheet concentration of 2.5×1012 cm−2. The results show clear evidence for the influence of carrier concentration and temperature on the Fermi edge singularity. The linewidths of the luminescence spectra agree well with those estimated from the electron sheet carrier concentrations, which were determined from the Shubnikov–de Haas oscillations, using an ideal 2DEG model.
Epitaxial Al Schottky contacts formed on (111) GaAs
Authors: Ueno Kazuyoshi , Yoshida Takayoshi , Hirose Kazuyuki
Published: July 2002

Epitaxial (111)A1/(111)GaAs Schottky contacts are formed using molecular beam epitaxy. The epitaxial relationship is determined by transmission electron microscopy. The interface is found to be abrupt and of an atomic order. Schottky barrier heights are measured by current-voltage and capacitance-voltage methods. The Schottky barrier height for a (111) surface is found to be stable under 450 °C annealing in a N2 atmosphere.
GaAs/AlGaAs photonic integrated circuits fabricated using chemically assisted ion beam etching
Authors: Grande W. J. , Johnson John E. , Tang C. L.
Published: July 2002

Photonic integrated circuits with a virtually complete set of active and passive devices are fabricated in the GaAs/AlGaAs system by single-step chemically assisted ion beam etching. Using this straightforward processing technique, photonic integrated circuits consisting of etched facet ridge waveguide lasers coupled to passive waveguides, beamsplitters, etched turning mirrors, and photodetectors are demonstrated. The results presented point to the promise of this technique for the fabrication of future high-complexity photonic integrated circuits.
Magnetotransport in narrow In0.53Ga0.47As/InP wires
Authors: Menschig A. , Forchel A. , Roos B. , Germann R. , Pressel K. , Heuring W. , Grützmacher D.
Published: July 2002

We have fabricated dry etched In0.53Ga0.47As quantum wires with geometrical widths varying from 80 nm to 50 μm from modulation-doped heterostructures. All wires show finite resistances even at 40 mK without illumination. The magnetotransport measurements show clearly the depopulation of one-dimensional subbands, universal conductance fluctuations, and an anomalous magnetoresistance peak.
Mechanistic investigations of nanometer-scale lithography at liquid-covered graphite surfaces
Authors: Penner Reginald M. , Heben Michael J. , Lewis Nathan S. , Quate Calvin F.
Published: July 2002

Pulse-induced nanometer-scale lithography has been performed on graphite surfaces that were in contact with pure water or other organic liquids. Very reproducible control over the pit diameter was observed in aqueous solutions, and a well-defined voltage threshold (4.0±0.2 V) was also apparent. Near the threshold voltage, 7 Å diameter×2 Å high protrusions were formed, while larger initial pulse voltages resulted in pits of diameter≳20 Å.
Extrinsic photoconductivity in chemical vapor deposition diamond
Authors: Jeng David G. , Tuan H. S. , Salat Robert F. , Fricano Glenn J.
Published: July 2002

Photoconductivity in the visible region has been studied in diamond films (DF) grown by the chemical vapor deposition process. It was found that the photocurrent increased linearly with the external bias voltage within the experimental range (30 V). Moreover, by exposing both boron-doped and undoped DF samples in air mass 1 (AM1) condition, the photocurrent produced by the former was approximately an order higher than that by the latter.
Strain-induced nonlinear energy-band splitting of Si1−xGex alloys coherently grown on (111) and (110) oriented Ge substrates
Authors: Ma Q. M. , Wang K. L.
Published: July 2002

A multi-band semi-empirical tight-binding method was used to calculate the band structures of Si1−xGex alloys coherently grown on (111) and (110) oriented Si1−yGey substrates. The results show that the lowest conduction band X5 at point X in the [001] directions of the Si1−xGex alloy is split into two bands with even and odd parities, due to the reduction of symmetry by strain. This is the first calculation that shows a kind of nonlinear band-edge splitting in the coherently grown Si1−xGex alloys. The results here can be approximated by adding a new deformation potential Ξ′u to the linear deformation potential formula, which was used earlier for bulk Si under external [111] and [110] uniaxial stress cases. For coherently grown layers with a large lattice mismatch, the nonlinear splittings should not be neglected when analyzing the electronic properties.
Hole intersubband absorption in δ-doped multiple Si layers
Authors: Park J. S. , Karunasiri R. P. G. , Mii Y. J. , Wang K. L.
Published: July 2002

The hole intersubband infrared absorption in δ-doped Si multiple quantum wells is observed for the first time. The structures used consist of ten periods of boron-doped Si quantum wells and undoped Si barriers. Near 100% infrared absorption is measured by a Fourier transform infrared spectrometer using waveguide structures. The observed absorption peaks ranging between 3 and 7 μm, which are mainly due to the transition between the first two heavy hole subbands. This absorption peak can be tuned by varying the doping concentration in the δ-doped layer. The polarization-dependent spectra show good agreement with the intersubband selection rule. The estimated peak energy positions using a self-consistency calculation with exchange effects as a perturbation agree reasonably well with the experimental observation. This observation suggests the use of multiple quantum well for IR detector application using Si technology
Field-induced refractive index variation spectrum in a GaInAs/InP quantum wire structure
Authors: Ravikumar K. G. , Kikugawa T. , Aizawa T. , Arai S. , Suematsu Y.
Published: July 2002

We report the electric field induced refractive index variation spectrum in a GaInAs/InP multilayered (three layers) quantum wire structure (λg∼1.48 μm) in the range 1.484–1.65 μm with the maximum positive index variation of 4% at around 1.52 μm at an applied reverse bias voltage of 3 V. We have also observed the anisotropic property of the index variation with respect to the quantum wire direction to the input light. These multilayered quantum wire structures were fabricated by low-pressure electron cyclotron resonance reactive ion beam etching and low-pressure organometallic vapor phase epitaxy methods.
Double-phase conjugated mirror and double color pumped oscillator in photorefractive InP:Fe
Authors: Vieux V. , Gravey P. , Wolffer N. , Picoli G.
Published: July 2002

We report on double-phase conjugation at 1.06 μm wavelength in InP:Fe with applied continuous electric field. Conversion efficiencies up to 74% with a grating period of 9 μm are obtained. The dependence of this efficiency on intensity, applied field, and grating period is reported and the results are compared with numerical simulations taking into account space-charge field nonlinearities. Double color (1.06 and 1.32 μm) pumped oscillation is also observed with conversion efficiencies higher than 30%.
Synchrotron radiation excited Si epitaxial growth using disilane gas source molecular beam system
Authors: Takahashi Jun-ichi , Utsumi Yuichi , Akazawa Housei , Kawashima Izumi , Urisu Tsuneo
Published: July 2002

Silicon photoepitaxy excited by synchrotron radiation (SR) has been observed for the first time. The epitaxial growth is observed even at lower than a 400 °C substrate temperature. The surface of the as-grown film exhibits a 2×1 reconstruction reflection high-energy electron diffraction pattern, indicating two-dimensional growth. At lower than 600 °C, the SR-irradiation growth rate is larger than that of thermal growth. This result suggests that SR irradiation enhances the dynamic surface reactions, such as desorption of hydrogen and surface migration of adsorbed species.
Existence of threshold density in silicon surface cleaning using hydrogen electron cyclotron resonance plasma
Authors: Nakashima Kenji , Ishii Masahiko , Tajima Ichiro , Yamamoto Minoru
Published: July 2002

Silicon surfaces were cleaned using hydrogen electron cyclotron resonance (ECR) plasma, and were analyzed by x-ray photoelectron spectroscopy after exposure to air. For cleaning a silicon surface, a threshold density exists to remove a surface oxide layer using hydrogen ECR plasma. Cleaning was promoted when the electron density was higher than the threshold density. The threshold density seems to depend on the base pressure. In the experiment, the threshold density was about 1010 cm−3 at the base pressure of 8×10−7 Torr.
Epitaxial CeO2 films as buffer layers for high-temperature superconducting thin films
Authors: Wu X. D. , Dye R. C. , Muenchausen R. E. , Foltyn S. R. , Maley M. , Rollett A. D. , Garcia A. R. , Nogar N. S.
Published: July 2002

We have prepared epitaxial (100)CeO2 thin films on LaAlO3, sapphire, and yttria-stabilized zirconia using pulsed laser deposition. It is demonstrated in this letter that the CeO2 films are chemically and structurally compatible to the high-temperature superconductor YBa2Cu3O7−δ (YBCO). Epitaxial YBCO films on CeO2/LaAlO3 had a zero resistance temperature and critical current density in a zero field of 90 K and 5.9×106 A/cm2 at 75 K, respectively. Furthermore, epitaxial multilayers of CeO2/YBCO were prepared. This work demonstrated that CeO2 is an excellent buffer layer material for the high-temperature superconductors.
Novel microscopy using stimulated light scattering by laser-induced transient reflecting gratings on metallic surfaces
Authors: Harata Akira , Sawada Tsuguo
Published: July 2002

A novel microscopic method, based on the technique of laser-induced transient reflecting gratings, is proposed to monitor ion implantation in silicon by noncontact and nondestructive ways. Some unique advantages of this technique, such as high sensitivity to ion dose and potential real time imaging capability, are demonstrated.
Application of superlattice bandpass filters in 10 μm infrared detection
Authors: Choi K. K. , Dutta M. , Moerkirk R. P. , Kuan C. H. , Iafrate G. J.
Published: July 2002

Recently, experimental evidence has revealed that the energy distribution of the dark current in a typical multiple quantum well GaAs infrared detector is extremely broad, in contrast to the narrowly distributed photocurrent. In this letter, we present the current transfer ratio of an infrared hot-electron transistor with a superlattice collector filter. From the current transfer characteristics, we demonstrate that the superlattice is able to collect electrons with specific energy against a broad background. The energy filtering characteristics can be attributed to the underlying band structure of the superlattice. When the filter is applied to infrared radiation detection, the detectivity of the transistor is improved.
Influence of ballistic electrons on the device characteristics of vertically integrated resonant tunneling diodes
Authors: Rascol J. J. L. , Martin K. P. , Carnahan R. E. , Higgins R. J. , Cury L. A. , Portal J. C. , Park B. G. , Wolak E. , Lear K. L. , Harris J. S.
Published: July 2002

We present a systematic study of the ballistic electron contribution to the current-voltage (I-V) characteristics of vertically integrated resonant tunneling diodes (RTDs) separated by doped spacer layers (Wsp). A magnetic field (B) transverse to the tunneling direction was used to tune the electron’s longitudinal energy. The results confirm the isolated circuit element picture of the Wsp=1000 Å sample and the strongly coupled description of the 0 Å sample. This work shows that even for some nominally isolated RTDs (in this work for Wsp= 400 and 500 Å), the I-V characteristics can undergo striking B-induced changes. This effect is due to resonant charge buildup in the well of the collector RTD from the relatively weak ballistic component of the current traversing the doped spacer region. A simple model that includes a calculation of the conduction-band profile and quantum well energy levels under bias gives good agreement with the data.
Laser writing and rewriting on YBa2Cu3O7 films
Authors: Shen Y. Q. , Freltoft T. , Vase P.
Published: July 2002

High-resolution patterning (4 μm) has been achieved on epitaxial thin films of the high-temperature superconductor YBa2Cu3O7−δ using laser writing. A focused laser beam is applied to write semiconducting patterns on superconducting films in a vacuum or in a nitrogen atmosphere. The semiconducting patterns are shown to be formed by a reduction of the oxygen content due to local heating caused by the laser beam. The process does not cause any structural damage and does not change the surface morphology. When reapplying the same laser beam and rewriting the film in an oxygen atmosphere, it is possible to restore the superconductive properties. The application of this method for production of superconducting microelectronic circuits is discussed.
Third-order nonlinear optical susceptibilities of electroconductive oxide thin films
Authors: Ueda Naoyuki , Kawazoe Hiroshi , Watanabe Yuichi , Takata Masasuke , Yamane Masayuki , Kubodera Ken’ichi
Published: July 2002

Third-order nonlinear optical susceptibilities (χ(3)) were estimated by third-harmonic generation for some electroconductive oxide thin films with wide band gaps (∼3.5 eV). Tin dioxide (SnO2) films showed the highest χ(3) as 3.8×10−12 esu, which is comparable with that of polydiacethylene (PDA) casting films that possess conjugated π electron systems.
Wet etch process for patterning insulators suitable for epitaxial high T
c superconducting thin film multilevel electronic circuits
Authors: Eidelloth W. , Gallagher W. J. , Robertazzi R. P. , Koch R. H. , Oh B. , Sandstrom R. L.
Published: July 2002

We describe a wet etch process for patterning insulators suitable for multilayer epitaxial highTc superconductor-insulator-superconductor structures down to micronmeter-scale dimensions. A solution of 7% HF in water gives convenient etch rates for SrTiO3 and MgO insulators (about 1500 Å/min for single crystals), and easily stops on thin high Tc superconducting layers, due to the high selectivity of this etchant between these insulators and the cuprate superconductors. Using entirely wet etching patterning processes, we have fabricated 5-turn (20-turn) coils with zero resistance at 89 K (79 K) and critical currents at 77 K of 2.5 mA (6 μA).
Direct imaging of the fragments produced during excimer laser ablation of YBa2Cu3O7−δ
Authors: Gupta A. , Braren B. , Casey K. G. , Hussey B. W. , Kelly Roger
Published: July 2002

The evolution dynamics of the fragments produced during KrF excimer laser (248 nm, 25 ns) ablation of YBa2Cu3O7−δ has been observed by ultrafast photography using a synchronized dye laser beam (∼1 ns) to probe above the target surface. The images show that fragment removal is initiated near the beginning of the laser pulse (≳10 ns), continues for a maximum of a few hundred nanoseconds, and has an expansion front velocity suggesting a target temperature varying from about 1500 to 4000 K or greater. The shock wave formed due to interaction of the ablated fragments with background oxygen gas has also been photographed, and its temporal evolution as a function of oxygen pressure has been shown to agree better with a planar than spherical model. The overall picture is that of an ablation process showing pronounced but understandable gas-dynamic effects.
Picosecond absorption dynamics of photoexcited InGaP epitaxial films
Authors: Thiagarajan P. , Schmerge J. F. , Menoni C. S. , Marconi M. , Martinez O. E. , Rocca J. J. , Hafich M. J. , Lee H. Y. , Robinson G. Y.
Published: July 2002

The absorption recovery of a photoexcited InGaP epitaxial film 0.4 μm thick was investigated using the pump-probe laser technique and found to have a time constant of 55 ps at room temperature. Measurements done in the temperature range of 300–50 K show the decay of the photoexcited carrier distribution to be dominated by ambipolar diffusion and surface recombination. The measured absorption recovery time constant corresponds to an ambipolar diffusion coefficient D≳2.8 cm2/s and a surface recombination velocity of S≳4×105 cm/s at room temperature.
Very low threshold current density 1.5 μm GaInAs/AlGaInAs graded-index separate-confinement-heterostructure strained quantum well laser diodes grown by organometallic chemical vapor deposition
Authors: Kasukawa A. , Bhat R. , Zah C. E. , Koza M. A. , Lee T. P.
Published: July 2002

Very low threshold current densities of 200 and 400 A/cm2 were obtained in 1.5 μm GaInAs/AlGaInAs tensile and compressive strained-layer quantum well laser diodes (SL-QW LDs), grown by organometallic chemical vapor deposition, with continuously graded-index separate-confinement-heterostructure. The differential quantum efficiency of SL-QW LDs showed less sensitive to temperature in contrast to that of a lattice matched QW LD. This is attributed to the decrease of intervalence band absorption due to the strain-induced reduction in the valence band density of state. The polarization of output power for a tensile SL-QW LD showed transverse magnetic (TM) mode, while that for a lattice matched and a compressive SL-QW LDs showed transverse electric (TE) mode.
Influence of an electric charge during quench aging of a low-carbon steel
Authors: Lu Hao An , Conrad Hans
Published: July 2002

We report here the first investigation on the quench aging of a low-carbon steel under the influence of an electric charge produced by 6.7 kV dc voltage between the specimen and a parallel electrode separated by 5 mm. This arrangement produced the following effects: (a) retarded the aging kinetics and (b) reduced the peak hardness. Fitting the results to a thermally activated rate equation indicated that the activation energy was increased from 0.65 to 0.85 eV. TEM observations revealed significant changes in precipitate size, morphology, and distribution near the grain boundaries and in the grain interior. It is proposed that the existing electrical conditions enhanced the migration of quenched-in vacancies from the grain interior to the grain boundaries.
Phase-locked CO2 laser array using diagonal coupling of waveguide channels
Authors: Abramski K. M. , Colley A. D. , Baker H. J. , Hall D. R.
Published: July 2002

Continuous coupling of square-bore CO2 waveguide lasers by geometrical overlap in the diagonal direction has been used for phase locking of a five-channel array. A radio-frequency discharge excited device has produced 125 W in phase-locked operation, with power per channel equal to independent single channels. The dependence of phase-locking range on the coupling geometry, and dimensional tolerances has been demonstrated. The array radiates approximately 65% of its power in the axial lobe.
In situ patterning and overgrowth for the formation of buried GaAs/AlGaAs single quantum-well structures
Authors: Kawanishi H. , Sugimoto Y. , Ishikawa T. , Hidaka H.
Published: July 2002

Buried GaAs/AlGaAs single quantum-well structures have been fabricated for the first time by in situ electron beam (EB) lithography. The process includes the molecular beam epitaxy of a GaAs/AlGaAs single quantum well, electron-beam direct writing, Cl2 gas etching, and overgrowth of an AlGaAs layer. A thin GaAs oxide layer was used as the etching mask, which was selectively formed on a clean GaAs surface by EB irradiation under an O2 ambient. Subsequent Cl2 gas etching resulted in the formation of isolated quantum wells. Prior to the overgrowth, thermal cleaning with atomic hydrogen was employed for removing the oxide mask. The cathodoluminescence image of the buried quantum well demonstrates the high quality of the resultant structure formed by in situ EB lithography.
Narrow-linewidth operation of broad-stripe single quantum well laser diodes in a grazing incidence external cavity
Authors: Gavrilovic P. , Chelnokov A. V. , O’Neill M. S. , Beyea D. M.
Published: July 2002

An external-cavity semiconductor laser employing a grazing-incidence grating and 100-μm stripe gain-guided laser diodes is described. The laser oscillates in a single axial and spatial mode at currents below the free-running threshold of the diode. A maximum single-frequency power of 30 mW is obtained. The lasing wavelength is tunable over 300 Å. At higher drive currents, the output contains multiple axial and spatial modes, with a linewidth of 4 GHz. The maximum continuous output power is 230 mW.
Nanocrystalline germanium synthesis from hydrothermally oxidized Si1−xGex alloys
Authors: Paine David C. , Caragianis Christine , Shigesato Yuzo
Published: July 2002

We have used low temperature (475 °C), high pressure (25 MPa) hydrothermal oxidation to form compositionally congruent oxides from epitaxial thin film alloys of Si90Ge10. The resulting Si90Ge10O2 oxide alloys are shown to be thermodynamically unstable when in contact with Si but remain microstructurally unchanged on annealing at 700 °C for 1 h. After annealing for 1 h at 800 °C, Raman spectroscopy and cross-sectional transmission electron microscopy reveal the presence of crystalline Ge precipitates in the oxide. Transmission electron microscopy was used to show that these precipitates are distributed through the oxide thickness, and range in size from 1 to 20 nm after a 1 h, 800 °C anneal.
δ-doped AlGaAs and AlGaAs/InGaAs high electron mobility transistor structures grown by metalorganic chemical vapor deposition
Authors: Yang G. M. , Park S. G. , Seo K. S. , Choe B. D.
Published: July 2002

We have successfully grown δ-doped AlGaAs structures and δ-doped AlGaAs/InGaAs pseudomorphic high electron mobility transistor (HEMT) structures by atmospheric pressure metalorganic chemical vapor deposition (MOCVD). Capacitance-voltage (C-V) profiles with full-width at half-maximum as small as 32 Å demonstrate very narrow doping profiles of δ-doped AlGaAs layers grown at 650–700 °C. Theoretical C-V profiles of δ-doped AlGaAs have been self-consistently calculated with the L valley taken into account and compared with the experimental results. A δ-doped AlGaAs/InGaAs pseudomorphic HEMT structure with a 30 Å spacer layer yields a sheet carrier concentration of 2.25×1012 cm−2 with an electron mobility of 20 300 cm2/V s at 77 K.
Mechanically alloyed and gas-phase carbonated highly coercive Sm2Fe17Cx
Authors: Kuhrt C. , Katter M. , Wecker J. , Schnitzke K. , Schultz L.
Published: July 2002

Microcrystalline Sm2Fe17Cx powders with high carbon content (x≊2) were prepared by mechanical alloying and a subsequent solid-gas reaction in acetylene atmosphere to introduce carbon atoms interstitially into the 2:17 lattice. Such processing results in magnetically isotropic material with a room-temperature coercivity of up to 18.5 kA/cm (23.2 kOe) and a maximum energy product of 59 kJ/m3 (7.4 MGOe). It is unstable at high temperatures and decomposes into the equilibrium phases SmC and α-Fe upon heating to 700 °C in vacuum.
Gain compression in tensile-strained 1.55 μm quantum well lasers operating at first and second quantized states
Authors: Wu T. C. , Kan S. C. , Vassilovski D. , Lau K. Y. , Zah C. E. , Pathak B. , Lee T. P.
Published: July 2002

Gain compression coefficients in tensile-strained 1.55 μm single quantum well lasers are measured using an optical injection method. Lasers operating in the first and second quantized states are used. An explicit linear dependence of nonlinear gain on the differential gain is obtained from these measurements. These results are quantitatively compared to a recently proposed model involving carrier transport in and out of the quantum well.
Accelerated stability test for amorphous silicon solar cells
Authors: Rossi M. C. , Brandt M. S. , Stutzmann M.
Published: July 2002

Fast light-induced degradation of amorphous silicon p-i-n solar cells has been investigated by replacing cw illumination by light pulses of the same average intensity. This method allows us to evaluate the long-term device performance with exposure times of the order of minutes and avoids complication due to cell temperature increase.
Spectroscopic ellipsometry of epitaxial Si {100} surfaces
Authors: Nayar V. , Leong W. Y. , Pickering C. , Pidduck A. J. , Carline R. T. , Robbins D. J.
Published: July 2002

The dielectric spectra of Si {111} and Si {100} orientations are shown to be equivalent using ex situ spectroscopic ellipsometry on clean epitaxial surfaces. The peak values for the real and imaginary parts (εr, i) of the dielectric function exceed those previously reported, values of εi (at 4.25 eV)≥47 being obtained. Surface features with lateral scales of ≊0.5–2 μm, do not affect the dielectric spectra significantly. The high dielectric function peaks indicate that the nanometer lateral-scale roughness on these epitaxial surfaces is very small.
Critical current of a high Tc Josephson grain boundary junction in high magnetic field
Authors: Däumling M. , Sarnelli E. , Chaudhari P. , Gupta A. , Lacey J.
Published: July 2002

The critical current (Ic) of YBa2Cu3O7−δ grain boundary Josephson junctions was measured up to magnetic fields of 5 T. Magnetic field history dependent Ic values were observed even after correction for self-field effects stemming from hysteretic shielding currents in the grain adjacent to the boundary. A novel feature observed is an anomalous increase in Ic in high magnetic fields of several Telsa.
Atmosphere-temperature-time relationships for the formation of 110 K phase in the Bi-(Pb)-Sr-Ca-Cu-O high T
c superconductor system
Authors: Zhu Wen , Nicholson Patrick S.
Published: July 2002

The influence of atmosphere (PO2=10−5–1 atm), temperature (T=810–890 °C) and time (6–60 h) on the formation of the Bi(Pb)2SrCa2Cu3O10 (110 K) phase in the Bi-Pb-Sr-Ca-Cu-O high TC superconductor system of composition Bi:Pb:Sr::Ca:Cu=1.84:0.34:1.91:2.03:3.06 has been studied. The relationships between the fraction 110 K phase, heating atmosphere, temperature, and time have been mapped via experimental data.
21 W broad area near-diffraction-limited semiconductor amplifier
Authors: Goldberg L. , Mehuys D.
Published: July 2002

A 600 μm wide broad area single pass GaAlAs traveling wave amplifier emitted 21 W in pulsed operation. The far-field was dominated by a near-diffraction limited 0.08° wide lobe, with 16 W measured in a 0.9° angular aperture. Current dependent scattering of the output beam power to outside of the diffraction-limited lobe was observed.
Electroluminescence in p-n junction using p-ZnTe/ZnS doping superlattices
Authors: Yokogawa Toshiya , Narusawa Tadashi
Published: July 2002

p-n junction blue light-emitting diodes (LEDs) using p-ZnTe/ZnS doping SLs have been demonstrated for the first time. These LED structures emit blue light at room temperature. These heterostructures also provide p-type conduction and are very useful for the carrier and optical confinement. We believe the present study sheds light on blue LDs using II-VI semiconductors.
Fragmentation process induced by nanosecond laser pulses
Authors: Rink K. , Delacrétaz G. , Salathé R. P.
Published: July 2002

A fiber-optic stress sensing technique is applied to evaluate the fragmentation mechanism induced by nanosecond laser pulses. We demonstrate that fragmentation is achieved in response to the shock induced by the laser initiated plasma expansion. This shock is followed by a second shock of similar magnitude observed some hundreds of microseconds later, which originates from the collapse of the induced cavitation bubble. The strength of this second shock is able to induce further fragmentation of the target. This is in contrast to the fragmentation process observed with microsecond pulses where the shock induced by the cavitation bubble collapse is the governing phenomenon.
Minority carrier capture cross section of the EL2 defect in GaAs
Authors: Zaidi M. A. , Maaref H. , Bourgoin J. C.
Published: July 2002

The EL2 defect in GaAs possesses two levels E1 and E2 located in the gap at 0.75 eV below the conduction band (E1) and 0.5 eV above the valence band (E2) for which only the majority carrier (electron for E1 and hole for E2) capture cross sections have been determined. We present a study in which the occupancy of the E1 level under minority carrier injection, monitored by deep level transient spectroscopy, provides the value of the capture cross section of holes on the E1 level. This enables us to estimate the contribution of the EL2 defect to the minority carrier lifetime in GaAs materials
Filtered arc deposition of amorphous diamond
Authors: Lossy Richard , Pappas David L. , Roy Ronnen A. , Cuomo Jerome J. , Sura Vivek M.
Published: July 2002

A cathodic arc with beam filter is employed for the deposition of hydrogen-free amorphous carbon films. A linear filter is used to prevent macroparticles and nonionized carbon atoms from reaching the substrate. The deposited films are characterized by their optical and mechanical behavior. Depending on the deposition conditions, optical band gaps in the range 2.1–2.4 eV are measured. Mechanical properties are investigated using the nanoindentation method and are shown to approach those of natural diamond. To our knowledge, the data obtained thus far reveal these films to be more diamondlike than those prepared using any other method for the deposition of nonhydrogenated amorphous diamond.
Arsine flow requirement for the flow modulation growth of high purity GaAs using adduct-grade triethylgallium
Authors: Pitts B. L. , Emerson D. T. , Shealy J. R.
Published: July 2002

Using arsine and triethylgallium with flow modulation, organometallic vapor phase epitaxy can produce high purity GaAs layers with V/III molar ratios near unity. We have estimated that under appropriate growth conditions the arsine incorporation efficiency into epitaxial GaAs can exceed 30%. The arsine flow requirement for obtaining good morphology has been identified over a range of substrate temperatures using adduct-grade triethylgallium. The process described reduces the environmental impact and life safety risk of the hydride based organometallic vapor phase epitaxial method.
Picosecond signal recovery in type II tunneling bi-quantum well etalon
Authors: Tackeuchi Atsushi , Inata Tsuguo , Nakata Yoshiaki , Nakamura Satoshi , Sugiyama Yoshihiro , Muto Shunichi
Published: July 2002

We demonstrate picosecond signal recovery in all optical gate operation using a type II tunneling bi-quantum well (TBQ) etalon. The type II TBQ consists of a series of GaAs wells, AlGaAs barriers, and AlAs layers. In this structure, photoexcited electrons in the GaAs wells escape by tunneling through the AlGaAs barriers toward X states in the AlAs layers. Therefore, the time for recovery from excitonic absorption bleaching in GaAs wells is controlled directly by the AlGaAs barrier thickness. The type II TBQ etalon with 1.7 nm barriers showed a fast signal recovery of 17 ps by carrier tunneling.
Optical investigations of GaAs-GaInP quantum wells grown on the GaAs, InP, and Si substrates
Authors: He Xiaoguang , Razeghi Manijeh
Published: July 2002

We report the first photoluminescence investigation of GaAs-Ga0.51In0.49P lattice matched multiquantum wells grown by the low pressure metalorganic chemical vapor deposition simultaneously in the same run on GaAs, Si, and InP substrates. The sharp photoluminescence peaks indicate the high quality of the samples on three different substrates. The temperature dependence of the photoluminescence indicates that the intrinsic excitonic transitions dominate at low temperature and free-carrier recombinations at room temperature. The photoluminescence peaks of the samples grown on Si and InP substrates shift about 15 meV from the corresponding peaks of the sample grown on the GaAs substrate. Two possible interpretations are provided for the observed energy shift. One is the diffusion of In along the dislocation threads from GaInP to GaAs and another is the localized strain induced by defects and In segregations.
Strained-layer InGaAs/GaInAsP/GaInP quantum well lasers grown by gas-source molecular beam epitaxy
Authors: Zhang G.
Published: July 2002

We demonstrate the first strained-layer InGaAs/GaInAsP/GaInP separated confinement heterostructure multiple quantum well lasers which emit at a wavelength of 0.98 μm. These lasers, grown by gas-source molecular beam epitaxy, exhibit a low threshold current density of 169 A/cm2 and high characteristic temperatures of 235 K for a cavity length of 1200 μm. The internal waveguide loss and internal quantum efficiency are 5.0 cm−1 and 83%, respectively. Single mode continuous wave operation is found up to an output power of 25 mW per facet at room temperature for an uncoated 5.5 μm×800 μm ridge waveguide laser.
Ultralow damage depth by electron cyclotron resonance plasma etching of GaAs/InGaAs quantum wells
Authors: Bickl T. , Jacobs B. , Straka J. , Forchel A.
Published: July 2002

Dry etch induced damage of GaAs/InGaAs/GaAs heterostructures in an electron cyclotron resonance (ECR) argon discharge has been investigated as a function of additional radio frequency self-biasing of the sample and process pressure in argon ECR discharges. We used depth resolved photoluminescence measurements to determine the influence of the etch process on the samples. We observe a decreasing damage depth for smaller bias voltages reaching its lowest value of 1.7 nm at 20 V bias and a pressure of 0.15 Pa. For lower pressures we observe a strong increase of the damage, which is attributed predominantly to high energetic vacuum ultraviolet radiation from the ECR region.
Similarity of scanning tunneling microscopy and atomic force microscopy images of YBa2Cu3O7 thin-film spiral growth patterns
Authors: Sheats James R. , Merchant Paul
Published: July 2002

The surface morphology of highly oriented c-axis YBa2Cu3O7 films grown by off-axis sputtering on MgO has been examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) at room temperature. Spiral growth patterns were well resolved by both techniques, and the shape of the structures is qualitatively and semiquantitatively similar. The terraces tend to be uneven, with troughs near the steps. The mean height of the steps is close to a multiple of the unit cell, but individual step heights are often not. We conclude that the observed surface topography is not artifactual. The YBa2Cu3O7 appears to be covered by a thin layer (of unknown composition or structure) whose thickness may vary by several Å, and whose electrical properties are temperature dependent.
Multihundred-watt CO laser power delivery through chalcogenide glass fibers
Authors: Sato Shunichi , Igarashi Kaoru , Taniwaki Manabu , Tanimoto Kenichi , Kikuchi Yutaka
Published: July 2002

Power transmission characteristics for the 5-μm band CO laser through chalcogenide glass fibers have been measured. With 1000-μm core diameter, 1-m-long, As-S and Ge-As-S glass fibers, the maximum transmitted powers have reached as high as 226 and 180 W, respectively. By applying antireflection coatings to the fibers, drastic increases in transmission efficiency have been demonstrated.
In situ noble metal YBa2Cu3O7 thin-film contacts
Authors: Ekin J. W. , Russek S. E. , Clickner C. C. , Jeanneret B.
Published: July 2002

Thin-film contacts to YBa2Cu3O7 have been fabricated by an in situ noble-metal process and patterned down to 2×2 μm2; at this small size, the contacts carry transport current over 106 A/cm2 while maintaining a specific contact resistivity ρc in the 10−8 to 10−9 Ω cm2 range. No oxygen annealing was used in the processing, thus avoiding the problem of silver or gold agglomeration, as well as preserving a sharp interface for Josephson-device applications. ρc was measured to increase only ∼25% as temperature was increased from 4 to 90 K. The measurements were carried out on a series of film morphologies using both superconductor-normal metal and superconductor-normal metal-superconductor test structures; a carefully designed test pattern was used to correct for spreading conduction in the noble-metal contact layer. The contacts were ohmic with voltage-current characteristics that were linear over more than four orders of magnitude.
Mg doping of InP and InGaAs grown by metalorganic molecular beam epitaxy using bis-cyclopentadienyl magnesium
Authors: Abernathy C. R. , Wisk P. W. , Pearton S. J. , Ren F.
Published: July 2002

We have investigated the feasibility of Mg doping using bis-cyclopentadienyl magnesium (Cp2Mg) during growth of InP and InGaAs by metalorganic molecular beam epitaxy. In InP, hole concentrations between 5×1016 and 4×1018 cm−3 were readily attained without degradation of the surface morphology. Comparison with secondary ion mass spectrometry analysis shows good electrical activation for concentrations ≤2×1018 cm−3 though compensation at low doping levels was observed due to compensation from carbon and oxygen impurities which were present at levels of 9×1016 and 5×1016 cm−3, respectively. Mg profiles in InGaAs tended to be more abrupt than those in InP and hole concentrations up to 1019 cm−3 were achieved. p-InGaAs/n-InP structures annealed at 600 °C for 10 s showed no evidence of Mg diffusion.
Negative differential resistance of metal (CoSi2)/insulator (CaF2) triple-barrier resonant tunneling diode
Authors: Watanabe Masahiro , Suemasu Takashi , Muratake Shigeki , Asada Masahiro
Published: July 2002

The electron transport and negative differential resistance in metal–insulator nanometer-thick heterostructures are reported for the first time. The structure of the samples is a resonant tunneling diode with three-barriers of 0.9-nm-thick CaF2 layers and two wells of 1.9- and 2.8-nm-thick CoSi2 layers. These layers were grown by means of partially ionized beam epitaxy for CaF2 and a two step growth technique for CoSi2. In the current-voltage characteristics at 77 K, negative differential resistance was observed in the significant number of samples and the typical peak-to-valley ratio was as high as 2. The negative differential resistance observed here can be attributed to the electron transport through the resonant levels in metal/insulator multilayered heterostructures.
Preparation of CaTiO3 heteroepitaxial thin films by excimer laser deposition
Authors: Fujii Tatsuhiko , Fujishima Akira , Hirano Takashi , Kobayashi Takeshi
Published: July 2002

CaTiO3 thin films were prepared by a 193 nm ArF excimer laser deposition method. Epitaxial CaTiO3 thin films were obtained on SrTiO3 (100) substrate and YBa2Cu3Oy (001) deposited on MgO (100) single-crystal substrate. The grown CaTiO3 thin films orientated to (010) direction and the unit cell of CaTiO3 rotated 45° around the [100] axis of the SrTiO3 substrate. It also happened in CaTiO3/YBa2Cu3Oy/MgO system. The static dielectric constant was 120 at room temperature and reached 175 at lower temperatures.
Effects of heat treatment on sharp-line photoluminescence of GaAs grown by low-temperature molecular beam epitaxy
Authors: Yu P. W. , Talwar Devki N. , Stutz C. E.
Published: July 2002

We report the effects of heat treatment on sharp-line photoluminescence spectra from GaAs layers grown by low-temperature molecular beam epitaxy. The photoluminescence consists of no-phonon lines of three different centers and associated phonon sidebands of both lattice and localized vibrational modes. By considering the calculated values of local phonon modes, the photoluminescence features, and layer growth conditions, we attribute the three no-phonon lines to the nearest neighbor C3v-type arsenic interstitial complexes: Asin-VGa, Asin-CAs and Asin-AsGa. Heat treatments at 300–500 °C considerably increase the concentration of Asin, and thereby, of Asin-CAs and Asin-AsGa.
A 75 GHz silicon metal-semiconductor-metal Schottky photodiode
Authors: Alexandrou Sotiris , Wang Chia-Chi , Hsiang Thomas Y. , Liu M. Y. , Chou S. Y.
Published: July 2002

The ultrafast characteristics of crystalline-silicon metal-semiconductor-metal (MSM) photodiodes with 300 nm finger width and spacing were measured with a subpicosecond electro-optic sampling system. Electrical responses with full width at half maximum as short as 5.5 and 11 ps, at corresponding 3 dB bandwidths of 75 and 38 GHz, were generated by violet and red photons, respectively. The difference is attributed to the photon penetration depth which is much larger than the diode finger spacing at red, but smaller at violet. Light-intensity dependence was also examined at different wavelengths, indicating a linear relation and a higher sensitivity in the violet. These results not only demonstrated the fastest silicon photodetector reported to date, but also pinpointed the dominant speed-limiting factor of silicon MSM photodiodes. A configuration is suggested to improve the speed of these detectors at long wavelengths.
p-type conduction in pyrite single crystals prepared by chemical vapor transport
Authors: Blenk O. , Bucher E. , Willeke G.
Published: July 2002

Pyrite (FeS2) single crystals have been prepared by chemical vapor transport from the elements, using additional phosphorus as a possible dopant source. Hall as well as thermoprobe measurements clearly indicated p-type conduction. Carrier concentrations of between 1 and 8×1018 cm−3 and Hall mobilities of 0.42–0.76 cm2/V s were deduced.