bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of oxygen incorporated in molecular-beam epitaxy grown GaAs-on-AlAs interfaces and AlAs layers by secondary ion mass spectrometry
Authors: Someya T. , Akiyama H. , Kadoya Y. , Noda T. , Matsusue T. , Noge H. , Sakaki H.
Published: July 2002

By employing a long growth interruption (GI) in molecular beam epitaxy, we have successfully determined the concentration of oxygen incorporated in GaAs/AlAs interfaces and AlAs layers by secondary ion mass spectrometry. The concentration of oxygen atoms incorporated on AlAs surfaces during GI is found to be proportional to the period of GI when the incoming fluxes of residual oxygen-related species reach steady-state values. The net incorporation rate of oxygen on the AlAs surface is found to be constant for a wide range of substrate temperatures from 540 to 620 °C, indicating that the oxygen desorption is negligible.
Dislocation density reduction in CdZnTe(100) on GaAs using strained layer superlattices
Authors: Reno J. L. , Chadda Saket , Malloy Kevin
Published: July 2002

We have inserted Cd0.91Zn0.09Te/CdTe(100) strained layer superlattices of various periods into Cd0.955Zn0.045Te grown on GaAs(100). X-ray diffraction was used as a means to optimize the period of the strained layer superlattice to maximize the quality of the material. Transmission electron microscopy demonstrated that a dramatic decrease (a total of five orders of magnitude) in the dislocation density occurred due to the insertion of the strained layer superlattices. The dislocation density achieved is in a range usable as a substrate material for HgCdTe infrared detectors.
InGaAs/InGaAsP integrated tunable detector grown by chemical beam epitaxy
Authors: Choa F. S. , Tsang W. T. , Logan R. A. , Gnall R. P. , Koch T. L. , Burrus C. A. , Wu M. C. , Chen Y. K. , Kapre R.
Published: July 2002

By controlling the thickness of the grating depth with chemical beam epitaxy (CBE) growth time, we report in this letter the design and performance of an integrated tunable detector. A carefully designed tunable active filter, which allows only one below threshold Fabry–Perot mode for operation, is integrated with a waveguide detector. The full tuning range of this kind of tunable device can now be utilized for system applications.
Surface morphology of metalorganic vapor phase epitaxy grown GaAs observed by atomic force microscopy
Authors: Hsu C. C. , Wong T. K. S. , Wilson I. H.
Published: July 2002

Steps of monolayer height (0.28 nm) are observed by atomic force microscope on a metalorganic vapor phase epitaxy grown GaAs surface. Monolayer terrace width was found to be as large as 430 nm, the same as the vicinal substrate surface. The growth mechanism is according to the classical Burton–Cabrera–Frank theory. We may have a larger (≳500 nm) terrace width and surface diffusion length if an exactly oriented [100] substrate is used.
High-pressure conductivity of Au(dmit)2 Langmuir–Blodgett films
Authors: Miura Yasuhiro F. , Isotalo Heikki , Kawaguchi Kenji , Nakamura Takayoshi , Matsumoto Mutsuyoshi
Published: July 2002

The conductivity of the mixed Langmuir–Blodgett films of tridecylmethylammonium- Au(dmit)2 and icosanoic acid after electrochemical oxidation in LiClO4 aqueous solution was measured under pressure up to 14 kbar. The room-temperature conductivity (σRT=12 S/cm) increased with an increase in pressure reaching 2.85 times larger value at 14 kbar compared to that under ambient pressure. The temperature at which the film exhibits its maximum conductivity was shifted to lower temperature upon applying pressure without pronounced saturation.
Wavelength dependence of saturation and thermal effects in multiple quantum well modulators
Authors: Boyd G. D. , Cavaillès J. A. , Chirovsky L. M. F. , Miller D. A. B.
Published: July 2002

Experiments are described in biased AlGaAs/GaAs quantum well reflection modulators demonstrating that the degradation in continuous wave modulator performance due to absorption saturation at wavelengths λ≳λ0, is significantly reduced compared to that at λ0, the zero field exciton wavelength, which in this case is 850 nm. This is of importance in the selection of operating wavelengths for the self-electro-optic effect device (SEED) used in photonic switching or optical interconnect applications.
Potential structure in silane radio-frequency discharge containing particles
Authors: Okuno Yoshihiro , Fujita Hiroharu , Shiratani Masaharu , Watanabe Yukio
Published: July 2002

Potential structures are clarified experimentally with an emissive probe in silane-helium radio-frequency (rf) discharges containing particles. The results reveal, compared with a pure helium rf discharge, that both the crest and trough instantaneous plasma potentials in an rf oscillation shift toward the negative side, especially in the particle localized region near the plasma-sheath boundary. The absolute value of the self-bias potential of the powered electrode is reduced. A considerable electric field exists even in the bulk plasma region and the strength increases with the concentration ratio of silane to helium.
Substrate temperature and collimator aspect ratio effects in titanium sputtering
Authors: Meikle S. , Kim S.
Published: July 2002

We investigated the relationship of substrate temperature and collimator aspect ratio to sputtered titanium thin-film properties. Titanium films were deposited in a configuration with a collimating mesh between the target and substrate over collimator aspect ratios of 0.7–2.0 and substrate temperature ranges of 150–450 °C, respectively. We found that a morphology transition occurs with rising deposition temperature and falling collimator aspect ratio where film stress switches from compressive to tensile, roughness increases 50%, grain size doubles, and resistivity increases 20%. We propose that the transition phenomenon is based on a film growth mechanism where substrate heating and surface bombardment have competing effects on the formation of surface clusters.
Transient effects of tin oxide CO sensors in the presence of water vapor
Authors: Vlachos D. S. , Skafidas P. D. , Avaritsiotis J. N.
Published: July 2002

During the experimental study of CO sensitivity of SnO2 resistive-type gas sensors in the presence of water vapor, a transient effect was observed which elucidates the CO sensing mechanism in tin oxide. More precisely, after the removal of CO, an increase of the measured conductance was observed, depending on substrate temperature. An explanation of this phenomenon is proposed, which is based on the conductance modulation due to three different mechanisms: Formate desorption, occupation of lattice sites by oxygen molecules, and diffusion of lattice oxygen vacancies to sensor’s bulk.
Diamond film growth on Ti-implanted glassy carbon
Authors: Brewer M. A. , Brown I. G. , Evans P. J. , Hoffman A.
Published: July 2002

The growth of diamond thin films on glassy carbon substrates has been investigated as a function of deposition time for different surface treatments. Implantation of Ti to a dose of 1.7×1017 cm−2 and abrasion with diamond powder have both been examined to determine their effect on film nucleation and growth. At the shorter deposition times studied, diamond nucleation was observed on all test samples with those subjected to the abrasive pretreatment exhibiting the higher growth rates. However, the adhesion and uniformity of films on unimplanted glassy carbon were found to deteriorate significantly following deposition runs of 14 and 21 h duration. This was attributed to a destabilization of the underlying surface caused by plasma erosion.
Selective epitaxy of GaAs on indium oxide mask followed by in situ removal of the mask
Authors: Ozasa Kazunari , Ye Tianchun , Aoyagi Yoshinobu
Published: July 2002

The selective epitaxy of GaAs has been investigated on indium-oxide films prepared by vacuum deposition. It was found for the first time that gallium atoms supplied on the indium-oxide surface were absorbed into the oxide, resulting in the suppression of GaAs deposition on the oxide. The selective epitaxy on a patterned indium-oxide mask and subsequent in situ removal of the mask by radical hydrogen irradiation have been demonstrated. The investigation shows that indium oxide is a promising mask material for in situ processing since selective epitaxy up to 550 °C and in situ removal of the mask can be achieved on any kind of semiconductor.
Optical field enhanced multiphoton photoemission in copper mirrors
Authors: Srinivasan-Rao T. , Fischer J. , Tsang T.
Published: July 2002

Photoemission from diamond turned copper mirror with laser beams of intensity 1011 W/cm2 at the photon energy of 2 eV and pulse duration of ∼300 fs indicates that the electric field associated with the photons enhances the photoemission. At the optimum incident angle, the electron yield with p-polarized light was 75 times larger than that with s-polarized light and 4 times larger than that at normal incidence for a constant energy. These enhancements were underestimated by the changes in the absorption and were attributed in this letter to the optical field effect.
Ballistic-electron-emission microscopy of (100)CoGa/n-type GaAs interfaces grown by molecular beam epitaxy
Authors: Tsau Liming , Kuo T. C. , Wang K. L.
Published: July 2002

A scanning tunneling microscope (STM) was used for the first time to investigate the (100)CoGa/GaAs interfaces grown by molecular beam epitaxy. The surface image indicates a vertical variation of about 7.5 Å with some domains of dimensions of about 170 Å. Furthermore, ballistic-electron-emission-microscopy spectra of this metal/semiconductor interface show two turn-on voltages, which account for the change of transmission probabilities for electrons with energies above the L minima and X minima of GaAs, respectively. The transmission into the X valleys of GaAs is found to be relatively stronger than that into the L valleys. This is explained by the CoGa band structure and the conservation of energy and transverse momentum for ballistically injected electrons. So far no ballistic electron current flowing into the Γ valley has been observed. For this reason, Schottky barrier height and its spatial variation measured by STM were not directly from the anticipated turn-on voltage at the Γ minimum, but instead, from the thresholds corresponding to transmission into higher valleys.
Low resistance Ohmic contacts for p-type ZnTe
Authors: Ozawa M. , Hiei F. , Takasu M. , Ishibashi A. , Akimoto K.
Published: July 2002

Low resistance Ohmic contacts of Au(Pt)Pd to p-ZnTe were studied. The specific contact resistance of these contacts depends strongly on the annealing temperature and the Pd layer thickness. The specific contact resistance, measured by the transmission line model, is as low as 5×10−6 Ω cm2 when a sample is annealed at 200 °C. The optimum Pd layer thickness is 5–10 nm. This value of the specific contact resistance is two orders of magnitude lower than that of Au or Pt contacts to p-ZnTe. The depth profiles of these contacts were investigated by Auger electron spectroscopy. The possible role of the Pd layer is discussed.
Atom and bond centered localized valence-band states in Cd0.5Zn0.5Te alloys
Authors: Niles David W. , Höchst Hartmut
Published: July 2002

Angle-resolved valence-band photoemission spectroscopy is used to analyze the local electronic structure in Cd0.5Zn0.5Te(100) alloy films. Localized alloy valence-band states may be divided into two categories: (1) Atom centered states associated with Cd 4d and Zn 3d core-like states, and (2) bond centered states associated with the X6 critical point of the split-off band. While the atom centered states show distinct emission and no intermixing between Cd 4d and Zn 3d bands near the Γ point, bond centered X6 states are mixed but split by ∼0.4 eV. We discuss our experimental results within the framework of Wei and Zungers structural model, and show how far experimental evidence corroborates their theory.
Femtosecond reflectivity of 60 K Y-Ba-Cu-O thin films
Authors: Shi L. , Gong T. , Xiong W. , Weng X. , Kostoulas Y. , Sobolewski Roman , Fauchet P. M.
Published: July 2002

We report systematic studies of the femtosecond transient reflectivity at 2 eV in partially oxygen-depleted Y-Ba-Cu-O thin films exhibiting the resistive superconducting transition at 60 K. Our measurements, performed at room temperature, reveal that in 60 K films, the Fermi level in the Cu-O2 plane lies approximately 2 eV above the filled copper d9/d10 band. By mapping the transient optical response across a 1 cm2 film, we show that the position of the Fermi level is very sensitive to the apparent local variations of the film oxygen content, which gives rise to dramatically different transient optical responses. We also observe a strong transient reflectivity dependence on intensity, which can be attributed to the shift of the Fermi level caused by nonequilibrium hole heating.
Flux-flow transistors based on long YBa2Cu3O7−δ bicrystal grain boundary junctions
Authors: Zhang Y. M. , Winkler D. , Nilsson P. Å. , Claeson T.
Published: July 2002

Josephson flux-flow transistors were made from long YBa2Cu3O7−δ bicrystal grain boundary junctions. A normal metal loop, separated from the junction by an SiO layer, was used as the current control line. The line modulated the critical current, Ic , which for temperatures ≤60 K showed the typical dependence for a long junction, while at higher temperatures the regular small junction modulation was seen. Current gain larger than unity was obtained below 70 K. The current gain increased with the junction length, and varied roughly like √Ic when decreasing the temperature. A transresistance larger than 5 Ω was obtained at 15 K. Better performance is expected from junctions with higher current densities.
Short-pulse supersonic nozzle beam epitaxy: A new approach for submonolayer controlled growth
Authors: Zhang Suian , Cui Jie , Tanaka Akihiko , Aoyagi Yoshinobu
Published: July 2002

A new approach for submonolayer controlled growth using short-pulse supersonic nozzle beam epitaxy (SSBE) was demonstrated. The growth behavior of GaAs was studied by reflection high-energy electron diffraction. As the pulse width of trimethylgallium source was increased from 5 to several hundred ms, a systematic change in the specular beam intensity and in the diffraction pattern was observed. The results showed that the epitaxial growth was easily controlled on a submonolayer level by simply adjusting the pulse width and by counting the number of short pulses. This suggests that the SSBE has the ability to manipulate atomic arrays in the realization of highly confined nanostructure fabrication.
High-performance Zn-doped-base InP/InGaAs double-heterojunction bipolar transistors grown by metalorganic vapor phase epitaxy
Authors: Kurishima K. , Nakajima H. , Yamahata S. , Kobayashi T. , Matsuoka Y.
Published: July 2002

We report the successful growth of high-quality InP/InGaAs double-heterojunction bipolar transistors with heavily Zn-doped base layers (p=4×1019 cm−3) using metalorganic vapor phase epitaxy. Interrupting the growth for 30 min after growing a heavily Si-doped subcollector (n=2×1019 cm−3) is shown to eliminate the excessive nonequilibrium group III interstitials that enhance abnormal Zn diffusivity in the subsequently grown base region. Gummel plots of the fabricated microwave transistors show that they have ideal turn-on characteristics in spite of having only 5-nm-thick undoped spacer layers inserted between the emitter and base. The transistors obtain a maximum oscillation frequency fmax of 178 GHz and a current gain cutoff frequency fT of 126 GHz.
Investigation on higher order bands in irradiated Czochralski silicon
Authors: Shi Y. , Zheng Y. D. , Suezawa M. , Imai M. , Sumino K.
Published: July 2002

Using Fourier transform infrared absorption spectroscopy and Hall-effect measurements we have investigated the higher order bands (HOB) in the fast neutron irradiated Czochralski silicon. Introducing the thermal donors (TD) to alter the Fermi level, the defect level giving rise to the HOB is analyzed, which is proposed to be located slightly below the TD(+/++) level. Furthermore, the observation for the characteristics of the photoexcitation and decay of both the HOB and the TD+ supports the assumption that this characteristic of the HOB is associated with a slow relaxation of photoexcited carriers.
Improvements in strain-balanced InGaAs/GaAs optical modulators for 1047-nm operation
Authors: Goodwill D. J. , Walker A. C. , Stanley C. R. , Holland M. C. , McElhinney M.
Published: July 2002

We demonstrate a self-electro-optic effect device (SEED) designed to work at 1047 nm to match the high power available from a Nd:YLF laser. The device uses a strain-balanced InGaAs/GaAs multiple quantum well grown on a GaAs substrate with an InGaAs buffer layer of linearly graded composition. It has improved performance compared to previous devices in this system. We have obtained a single pass modulation contrast ratio of 1.74 by applying 13-V reverse bias, and have found 99% photodetection quantum efficiency under the built-in junction field. Bistability in a resistor-SEED configuration is demonstrated.
New photorefractive polymer based on multifunctional polyurethane
Authors: Chen Y. M. , Peng Z. H. , Chan W. K. , Yu L. P.
Published: July 2002

A new photorefractive polymer containing a photocarrier generator, a hole transporting compound, and a nonlinear optical chromophore covalently linked to the polymer backbone has been synthesized. Two-beam coupling experiments have clearly demonstrated asymmetric energy exchange under zero-field condition, a sign for photorefractivity and a maximum optical gain of 0.88 cm−1 was measured. Although it is not a net gain, the result reported here demonstrates the feasibility of rational designs of photorefractive polymers.
Influence of steps on quantum well states in Cu/Co(100) multilayers
Authors: Ortega J. E. , Himpsel F. J.
Published: July 2002

Interface roughness is known to have a large effect on oscillatory magnetic coupling and giant magnetoresistance in magnetic multilayers, but the origin of this effect is still uncertain. In order to obtain a quantitative measure we have used vicinal Cu/Co(100) interfaces with well-defined step spacing and have determined the amplitude of quantum oscillations in the density of states that are correlated with oscillatory magnetic coupling. For a step spacing of 10 Å the oscillation amplitude decreases by a factor of 1.8. This distance corresponds to the lateral extent of the quantized states in the film.
Electrically controlled continuous tilt of optical axis in ferroelectric chiral smectic liquid crystal cell
Authors: Mori Takeshi , Toyoda Yoshihiko , Mikami Noboru , Masumi Tatsuo , Nunoshita Masahiro
Published: July 2002

A continuous tilt of an apparent optical axis caused by an applied ac voltage in a ferroelectric chiral smectic C liquid crystal cell is observed. The cell under crossed Nicols modulates the incident light with the voltage applied between −10 and 10 V. Dispersions of the optical modulation intensity and the dielectric constant have the same relaxation frequency (2 kHz). Observation of the dielectric behavior of the cell suggests that the relaxation in the optical modulation corresponds to that of the Goldstone mode. The deformation of the splay structure in the liquid crystal cell supposedly causes the continuous tilt of apparent optical axis.
New model of ion-induced crystallization and amorphization of silicon
Authors: Wang Zhong-Lie , Itoh Noriaki , Matsunami Noriaki
Published: July 2002

A new model for ion-induced crystallization and amorphization at the interface is presented. The model is based on the general concept for ion-induced processes between two solid phases with different free energies; the presence of pure ballistic and thermally enhanced processes. The parameters that can fit quantitatively to the temperature, flux, and stopping power dependencies of crystallization/amorphization rates for Si are obtained.
Titanium nitride for transparent conductors
Authors: Kiuchi Masato , Chayahara Akiyoshi
Published: July 2002

The transparency of thin films of the electroconductive titanium nitride was demonstrated. Titanium nitride has a high hardness and a high resistance against corrosion, and it is electroconductive. Its color is gold, and it is usually not transparent. Materials can be transparent if they are much thinner than the wavelength of visible light. Formerly, there was no technique available to form such a thin TiN film which is also electroconductive, because very thin TiN crystals grow as small islands. However, by using the dynamic ion beam mixing technique, we succeeded in forming continuous, transparent, and conductive TiN films.
Performance improvement of amorphous silicon thin-film transistors with SiO2 gate insulator by N2 plasma treatment
Authors: Kim Jeong Hyun , Oh Eui Yeal , Ahn Byung Chul , Kim Donggil , Jang Jin
Published: July 2002

We studied the performance improvement of hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) using atmospheric pressure chemical vapor deposition (APCVD) SiO2 as a gate insulator. The threshold voltage and the subthreshold swing decrease remarkably by N2 plasma treatment on the APCVD SiO2 surface even though the field effect mobility changes little, indicating that the interface state density around the Fermi level is reduced significantly by N2 plasma treatment. We obtained the high performance a-Si:H TFT with the field effect mobility of 1.25 cm2/V s, the threshold voltage of 3.5 V and the subthreshold swing of 0.45 V/dec.
Epitaxial growth and properties of YBa2Cu3O7−y/LaSrGaO4/YBa2Cu3O7−y trilayer structures
Authors: Hontsu S. , Mukai N. , Ishii J. , Kawai T. , Kawai S.
Published: July 2002

We report the successful synthesis of insulating LaSrGaO4(LSGO) thin films and YBa2Cu3O7−y(YBCO)/LSGO heteroepitaxial multilayer structures using a pulsed laser deposition technique. SrTiO3(STO)(100) was used as a substrate. The formation of highly c-axis oriented YBCO/LSGO/YBCO trilayer structures is demonstrated. Epitaxial YBCO films on LSGO//STO and LSGO/YBCO//STO have a zero resistance temperature of 88.5 and 88.3 K, respectively. Sandwich-type YBCO/LSGO/YBCO junctions were produced by a suitable patterning technique. The observed (dI/dV)-V characteristics exhibit a clear single gap structure (width ∼26 meV) at temperatures below 30 K.
Injection locking of a self-mode locking CuBr laser
Authors: Geng Jihong , Wu Yanqing , Zhang Guiyan , Song Xiudong , Lin Fucheng
Published: July 2002

A longitudinal discharge-pumped large-scale CuBr laser has been injection locked with self-mode locking CuBr laser pulse trains for the first time. High average output power of mode-locked pulses has been obtained in a wide range of delay tine between the master and slave laser by extracting energy from the slave laser. Injection locking of the green laser line and the yellow occurs simultaneously.
Fast linear electro-optical switching properties of polymer-dispersed ferroelectric liquid crystals
Authors: Lee Kyehun , Suh Seong-Woo , Lee Sin-Doo
Published: July 2002

A fast linear electro-optic effect is demonstrated in ferroelectric liquid crystal/polymer composites suitable for display applications. Both the ferroelectric liquid crystal (FLC) and the polymer matrix are oriented by the rubbing process which remarkably improves the electro-optic characteristics of the composites. Depending on the phase transition sequence and the pitch of the FLC, the size as well as the shape of the droplets vary in the polymer matrix. The associated relaxation dynamics can be understood within a simplified model which contains the essential features of the experimental data. The switching times are on the order of a hundred μs.
Low power all-optical bistability in InGaAs-AlInAs superlattices: Demonstration of a wireless self-electro-optical effect device operating at 1.5 μm
Authors: Couturier J. , Voisin P. , Harmand J. C.
Published: July 2002

We report the observation of optical transmission bistability at low temperature in unprocessed InGaAs-AlInAs superlattice p-i-n structures. Bistability results, in analogy with the self-electro-optical effect device, from a positive feedback mechanism due to the interplay between Wannier–Stark effect, built-in field, and screening by photocarriers.
Subharmonic instability taking into account higher harmonics
Authors: Serrano E. , Carrascosa M. , Agulló-López F. , Solymar L.
Published: July 2002

It is shown that a large number of higher harmonics are needed for determining a region of subharmonic instability. For the examples calculated, the final result is qualitatively similar to that obtained considering only the imposed interference pattern.
Simultaneous shallow-junction formation and gate doping p-channel metal-semiconductor-oxide field-effect transistor process using cobalt silicide as a diffusion/doping source
Authors: Chen Wei-Ming , Lin Jengping , Banerjee Sanjay K. , Lee Jack C.
Published: July 2002

Submicron p-metal-semiconductor-oxide field-effect transistors (MOSFETs) have been fabricated using cobalt silicide as a diffusion source for forming shallow p-n junctions and as a doping source for undoped as-deposited amorphous silicon gate (SADDS). The thermal stability of CoSi2 on polycrystalline silicon is shown to be significantly improved by using as-deposited amorphous silicon instead of as-deposited polycrystalline silicon as the gate material. The p-MOSFETs fabricated using the SADDS process exhibit excellent characteristics and open up the possibility of eliminating several masks and implants in more complicated complimentary metal-oxide semiconductor processes.
cw He-Kr+ laser with transverse radio frequency excitation
Authors: Reich N. , Mentel J. , Jakob G. , Mizeraczyk J.
Published: July 2002

A cw He-Kr+ laser was excited with a capacitively coupled transverse radio frequency discharge. The laser was operated in a simple 40-cm active length alumina oxide tube which ends off via ceramic glass transitions in Brewster windows. Transformation of the laser discharge tube impedance to the 50 Ω output resistance of the rf source and symmetrization of the rf voltage were performed by a special matching network. cw lasing was obtained at 469.4, 458.3, 438.7, and 431.8 nm. The output power of all lines amounts to 35 mW at an input power of 600 W. The rms noise of the laser intensity did not exceed 0.6%.
Antiresonant reflecting optical waveguides in strip configuration
Authors: Gehler J. , Bräuer A. , Karthe W. , Jäger M.
Published: July 2002

A monomode antiresonant reflecting optical strip waveguide has been realized in SiON. The lateral confinement is provided by strip-loaded reflectors fabricated by reactive ion beam etching.
Graduated heterojunction in GaAs/AlAs quantum wells
Authors: Proctor M. , Oelgart G. , Rhan H. , Reinhart F.-K.
Published: July 2002

Molecular-beam epitaxy grown decoupled nominally square GaAs/AlAs multiquantum wells, producing levels deep in the well, have been studied by x-ray diffraction, photoluminescence excitation, and emission. The well width and period fluctuation (AlAs/GaAs/AlAs interface roughness) of the multiquantum wells were obtained by x-ray diffraction investigations. Using a smoothed profile of the interface as suggested by D. F. Nelson, R. C. Miller, C. W. Tu, and S. K. Sputz, Phys. Rev. B 36, 8063 (1987), the earlier verified theoretical approach [see Oelgart et al. Phys. Rev. B 49 (March 1994)] excellently predicts the experimentally observed transition energies.
InAs1−xSbx/In1−yGayAs multiple-quantum-well heterostructure design for improved 4–5 μm lasers
Authors: Liau Z. L. , Choi H. K.
Published: July 2002

A new strained-layer multiple-quantum-well (MQW) heterostructure comprising InAs1−xSbx wells and In1−yGayAs barrier layers is proposed for improved 4–5 μm lasers. Both well and barrier compositions are close to InAs and are potentially well suited for high-quality crystal growth of MQWs on either InAs or GaSb substrates. Simple modeling shows favorable valence-band alignment suitable for carrier confinement, free of the staggered band alignment problem generally found in the conventional designs. Perturbation calculation of the effect of the compressive strain in the wells also shows sufficient valence subband separation. This and the reduced hole mass are expected to considerably lower the threshold carrier density and Auger recombination.
Heterodyne mixing with Nb tunnel junctions above the gap frequency
Authors: de Lange G. , Honingh C. E. , Kuipers J. J. , Schaeffer H. H. A. , Panhuyzen R. A. , Klapwijk T. M. , van de Stadt H. , de Graauw M. M. W. M.
Published: July 2002

The noise and gain of a heterodyne waveguide mixer employing Nb/Al2O3/Nb superconducting tunnel junctions with an on-chip integrated tuning element are measured and analyzed at 680–750 GHz and at 840 GHz. The lowest receiver noise temperatures are 400 K (double side band) at 720 GHz and 1500 K (3000 K including the beam splitter loss) at 840 GHz. We compare data of the pumped I–V curves with the quantum theory of mixing and demonstrate good agreement at frequencies well above the gap frequency.
Origin and suppression of misfit dislocations in heavily boron-doped (100) silicon wafers
Authors: Lee Ho-Jun , Jeon Young-Jin , Han Chul-Hi , Kim Choong-Ki
Published: July 2002

It has been found that misfit dislocations in heavily boron-doped layers originate from wafer edges. Moreover, the propagation of the misfit dislocation into a region can be suppressed by placing a surrounding undoped region formed by a chemical-vapor deposited (CVD) oxide ring pattern before boron doping. A heavily boron-doped layer with no misfit dislocations can be obtained by using a CVD oxide ring up to a boron dose of 5.4×1016 cm2 for an area of 2 cm×2 cm and up to a dose of 1.48×1017 cm2 for an area of 400 μm×400 μm.
Broadly tunable vertical-coupler filtered tensile-strained InGaAs/InGaAsP multiple quantum well laser
Authors: Kim I. , Alferness R. C. , Koren U. , Buhl L. L. , Miller B. I. , Young M. G. , Chien M. D. , Koch T. L. , Presby H. M. , Raybon G. , Burrus C. A.
Published: July 2002

Using tensile-strained InGaAs/InGaAsP multiple quantum well material to increase the gain bandwidth, we demonstrate a tuning range of 74.4 nm with sidemode-suppression ratio of ≳25 dB and as high as 34 dB in a broadly tunable vertical-coupler filtered laser at 1.55 μm. Due to its wide gain bandwidth and significant gain-peak shift to shorter wavelengths with gain current increase, the tensile-strained quantum well material is well suited for broadly tunable lasers.
YBa2Cu3O7 direct current–superconducting quantum interference devices with artificial PrBa2Cu3O7 barriers above 77 K
Authors: Schilling M. , Reimer D. , Merkt U.
Published: July 2002

Direct current–superconducting quantum interference devices (dc-SQUIDs) from YBa2Cu3O7 with PrBa2Cu3O7 barriers and insulating MgO layers that modulate up to a temperature of 85 K are prepared by laser deposition with a KrF excimer laser and an ex situ patterning process. In order to utilize the longer coherence length of c-axis oriented YBa2Cu3O7 films in the a-b plane, an edge geometry is used for the definition of the Josephson junctions. By the variation of the barrier thickness the critical current of the junctions can be controlled within close limits and can be chosen for optimum dc-SQUID performance at a given working temperature. At 80 K we find a flux-voltage modulation of 3.4 μV.
AlGaAs/InGaAs/GaAs single electron transistors fabricated by Ga focused ion beam implantation
Authors: Fujisawa Toshimasa , Hirayama Yoshiro , Tarucha Seigo
Published: July 2002

Single electron transistors are formed in an AlGaAs/InGaAs/GaAs modulation-doped heterostructure by Ga focused ion beam implantation. The AlGaAs/InGaAs/GaAs system has a high two-dimensional electron gas density and facilitates a lateral constriction whose depletion length is much smaller than that in a conventional AlGaAs/GaAs system. A dot structure confined by a small depletion spreading of less than 0.15 μm is formed by the ion implantation. This ion implantation is also employed to form in-plane gates for controlling the tunneling junctions between the dot and reservoirs, and the number of electrons in the dot. Coulomb oscillations and a Coulomb staircase have been clearly observed by controlling three in-plane gates.
GaAs/AlGaAs multiquantum well resonant photorefractive devices fabricated using epitaxial lift-off
Authors: Kyono C. S. , Ikossi-Anastasiou K. , Rabinovich W. S. , Bowman S. R. , Katzer D. S. , Tsao A. J.
Published: July 2002

This letter deals with resonant photorefractive devices fabricated from multiquantum wells of GaAs/Al0.3Ga0.7As and operated in a quantum-confined Stark effect geometry. Details of the processing are presented. Epitaxial lift-off was used to remove the active device from the substrate. Low-temperature Al0.3Ga.07As was used as an insulator to form metal-insulator-semiconductor structures on both sides of the multiquantum wells. Proton implant damage was used to improve the fringe visibility. Photorefractive wave mixing with a diffraction efficiency of ∼0.03% was demonstrated. The incorporation of a nitride layer between the top electrode and the low-temperature AlGaAs increased the efficiency to 0.5%. The improvement is attributed to a reduction in the conduction of carriers across the low-temperature layer into the electrode.
Use of multiphoton photoelectric process to generate a high brightness electron beam for free-electron lasers
Authors: Asakawa Makoto , Mima Kunioki , Nakai Sadao , Fujita Masayuki , Imasaki Kazuo , Yamanaka Chiyoe
Published: July 2002

This letter describes a photocathode of tungsten driven by a frequency-doubled Nd:YAG laser. In this case, photoelectrons emerged by two-photon photoelectric process. The current density quadratically depended on the incident laser intensity, and the quantum yield then increased linearly with the laser intensity. Furthermore, by heating the cathode, we could improve the quantum yield. At a temperature around 1600 °C, the peak current was measured to be 5.8 A with an irradiation of 3.2 MW, and then the quantum yield was to be 2.4×10−6.
Thiapyrylium dye sensitization of photorefractivity in a polymer composite
Authors: Zhang Yue , Spencer Christopher A. , Ghosal Saswati , Casstevens Martin K. , Burzynski Ryszard
Published: July 2002

An ionic thiapyrylium dye has been used as a photocharge sensitizer for the first time in a photorefractive polymer composite containing poly(9-vinylcarbazole) and 4-(N,N-diethylamino)- (β)-nitrostyrene. Photorefractive gratings are written at a wavelength of 703 nm and four-wave mixing diffraction efficiencies as high as 2% have been achieved in films less than 200 μm thick. Asymmetric energy transfer has been observed and a two-beam coupling gain of 7 cm−1 has been obtained. Holographic image recording and retrieving have also been demonstrated.
High-resolution transmission electron microscopic study of the γ-FeSi2/Si(111) interface
Authors: Müller E. , Grindatto D. P. , Nissen H. -U. , Onda N. , von Känel H.
Published: July 2002

The atomic structure of the B-type γ-FeSi2/Si(111) interface has been determined by high-resolution transmission electron microscopy combined with dynamical calculations of the image contrast. Among four models for the interface considered here, only one is found to agree with the observations. In this model the Fe atoms at the interface are bonded to the substrate silicon atoms and 8-fold coordinated, as are the Co atoms in the case of CoSi2/Si(111), which is isostructural.
Amphoteric substitutionality and lattice distortion of Ge in InP
Authors: Yu Kin Man , Moll A. J. , Walukiewicz W. , Derhacobian N. , Rossington C.
Published: July 2002

We have studied the electrical and structural properties of InP implanted with Ge ions (2×1015/cm2). The implantation was performed at both room temperature (RT) and liquid nitrogen temperature (LNT). After annealing at 850 °C for 5 s, both sets of samples exhibited n-type conductivity. The n-type activation efficiency in the RT implanted sample was about a factor of 2 higher than that in the LNT sample (15% and 8%, respectively). Extended x-ray absorption fine structure spectroscopy (EXAFS) shows direct evidence of the amphoteric substitutionality of the Ge atoms in InP for both samples. The ratios of Ge on In sites to Ge on P sites, derived from the EXAFS results, are consistent with the electrical behavior of the samples. The EXAFS results also reveal that the Ge—In and Ge—P bond lengths in the RT sample are very similar to their theoretical values, but are very different from the original In—P bond length. A relaxation in the Ge—In bond is observed in the LNT sample, resulting in a Ge—In bond length very similar to the original In—P bond length.
Measurement of the 4Pi-confocal point spread function proves 75 nm axial resolution
Authors: Hell S. W. , Lindek S. , Cremer C. , Stelzer E. H. K.
Published: July 2002

In a 4Pi-confocal microscope the specimen is illuminated and observed coherently from above and below such that the numerical aperture is increased [S. W. Hell, European Patent Application 91121368.4 (filed 1990, published 1992), S. W. Hell and E. H. K. Stelzer, J. Opt. Soc. Am. A 9, 2159 (1992)]. The point spread functions of 4Pi-confocal and confocal microscopes were measured. Our measurements prove a three- to seven-fold increase of axial resolution, thus opening the prospect for a powerful three-dimensional imaging technique with an axial resolution down to 75 nm.
Irreversibility line for a Pb-doped Hg-Ba-Ca-Cu-O superconductor
Authors: Isawa Kazuyuki , Higuchi Takamitsu , Machi Takato , Tokiwa-Yamamoto Ayako , Adachi Seiji , Murakami Masato , Yamauchi H.
Published: July 2002

By measuring the magnetization hysteresis, we studied the critical current density, Jc, and irreversibility fields, Hirr, of a c-axis aligned Hg-Ba-Ca-Cu-O sample doped with Pb containing the Hg-1223 phase as the main phase. Anisotropy in ΔM was clearly observed in two different magnetic field directions. Even though the Hg-1223 phase contains three CuO2 sheets, the Hirr vs [1-(T/Tc)] curve was located at roughly the same positions as those reported for the Hg-1201 and Hg-1212 phases, indicating that the higher Tc phase, i.e., Hg-1223, is advantageous to the other phases in practical uses.
Nearly degenerate four-wave mixing in a vertical-cavity surface-emitting laser
Authors: Jiang Shijun , Dagenais Mario , Morgan Robert A.
Published: July 2002

We report the measurement of the frequency response of nearly degenerate four-wave mixing in a vertical-cavity surface-emitting laser. High efficiency conjugate signal generation is demonstrated. A superlinear dependence between the square of relaxation oscillation frequency and the output power is observed. The experimental observation is well described by present theories.
Composition modulation in lattice matched Zn1−xMgxSySe1−y/ZnSe buffer layer/GaAs heterostructures
Authors: Kuo L. H. , Salamanca-Riba L. , Wu B. J. , DePuydt J. M. , Haugen G. M. , Cheng H. , Guha S. , Haase M. A.
Published: July 2002

[100] composition modulation as well as [101] and [1̄01] tweed strain contrast were observed in lattice matched Zn1−xMgxSySe1−y epitaxial films grown on ZnSe buffer layers. The composition modulation corresponds to regions with different S and Mg concentration in a direction perpendicular to the growth direction. Very high quality lattice matched Zn1−xMgxSySe1−y films with a ZnSe quantum well were grown on As stabilized GaAs substrates exposed to Zn for a short time. The density of defects in these samples was less than 5×104/cm2. Other samples showed rough interfaces and high densities of Frank partial dislocations. The roughness is believed to result from an As-rich GaAs surface produced after the desorption of oxide under As overpressure.
Identification of VSe-impurity pairs in ZnSe:N
Authors: Kennedy T. A. , Glaser E. R. , Murdin B. N. , Pidgeon C. R. , Prior K. A. , Cavenett B. C.
Published: July 2002

Optically detected magnetic resonance (ODMR) of heavily nitrogen-doped ZnSe at 24 GHz reveals an anisotropic spectrum which can be assigned to a deep donor comprised of a Se vacancy paired with an impurity. The newly resolved spectrum is trigonal along 〈111〉 with g∥=2.0072(2) and g⊥=2.0013(2). Comparison of this g tensor with previous work leads to the assignment of the spectrum to VSe-X, where X is most probably Cu or Ag. Combining this result with previous photoluminescence and ODMR work shows that ZnSe:N has three distinct donors which include both impurities and intrinsic defects.
Low-energy separation by implantation of oxygen structures via plasma source ion implantation
Authors: Zhang L. , Shohet J. L. , Dallmann D. , Booske J. H. , Speth R. R. , Shenai K. , Goeckner M. J. , Kruger J. B. , Rissman P. , Turner J. E. , Perez-Albuerne E. , Lee S. , Meyyappan N.
Published: July 2002

The initial results from an investigation into the feasibility of using plasma source ion implantation (PSII) to produce separation by implantation of oxygen structures in silicon are reported. Oxygen ions are implanted into p-type (111) oriented silicon wafers using a −30 kV acceleration potential and an oxygen plasma at a pressure of 0.2 mTorr. The effects of ion dose and high-voltage pulse width were examined. Some of the implanted wafers were annealed. Both the as-implanted and annealed wafers were examined using secondary-ion-mass spectroscopy and Auger electron spectroscopy. The initial results show that oxygen can be implanted by PSII and suggest that a buried layer of silicon dioxide has been formed in the implanted wafers.
High-power InGaAsP/GaAs 0.8-μm laser diodes and peculiarities of operational characteristics
Authors: Diaz J. , Eliashevich I. , He X. , Yi H. , Wang L. , Kolev E. , Garbuzov D. , Razeghi M.
Published: July 2002

High-power operation of 3 W in pulse mode, 750 mW in quasi-continuous wave and 650 mW in continuous wave per uncoated facet from 100-μm aperture has been demonstrated for 1-mm-long cavity InGaAsP/GaAs 808-nm laser diodes prepared by low-pressure metalorganic chemical vapor deposition. Threshold current density of 300 A/cm2, differential efficiency of 1.1 W/A, T0=155 °C, transverse beam divergence of 27°, and less than 2-nm linewidth at 808 nm have been measured. No degradation has been observed after 1000 h of operation in a quasi-continuous wave regime.
Pulse measurements on ferroelectric capacitors simulating memory switching
Authors: Dormans G. J. M. , Larsen P. K.
Published: July 2002

Pulse switching investigations of ferroelectric PbZr0.44Ti0.56O3 capacitors prepared by organometallic chemical vapor deposition were done to simulate a ferroelectric memory. The released charge from the ferroelectric capacitor was measured with a reference capacitor, representing the bitline capacitances in a memory. A large reference capacitor will result in complete switching at low voltages, but gives a small detection signal. For a small reference capacitor partial switching and substantial backswitching of the ferroelectric material occurs. Here, a higher detection signal and improved endurance (≳1012 cycles) are found. Scaling the results indicates the feasibility of 0.2 μm2 capacitors operating at 3 V.
Effect of Ag2O addition in Y0.9Ca0.1Ba2Cu4O8 on the contact characteristics of Y0.9Ca0.1Ba2Cu4O8/Ag interface
Authors: Chen Y. C. , Yang C. K. , Meen T. H. , Yang H. D.
Published: July 2002

Effects of an Ag2O addition in Y0.9Ca0.1Ba2Cu4O8 on the contact characteristics of Y0.9Ca0.1Ba2Cu4O8/Ag interfaces have been investigated by the measurement of contact resistivity. The lowest ohmic-contact resistivity about 4.55×10−5 Ω cm2 at 300 K and less than 10−8 Ω cm2 below Tc for Ag2O-free system are observed by annealing at 600 °C for 1 h under one oxygen atmosphere. With addition of 25 wt % Ag2O in Y0.9Ca0.1Ba2Cu4O8, the optimal annealing condition for the lowest ohmic-contact for Y0.9Ca0.1Ba2Cu4O8/Ag interface can be achieved without any thermal annealing just by the addition of 25 wt % Ag2O in Y0.9Ca0.1Ba2Cu4O8. These results indicate that the addition of Ag2O can upgrade effectively the characteristics of Y0.9Ca0.1Ba2Cu4O8/Ag interfaces to get the better ohmic contact even without annealing, resulting in a lower annealing temperature and contact resistivity.
Deep-oxide planar buried-heterostructure AlGaAs–GaAs quantum well heterostructure laser diodes
Authors: Krames M. R. , Chen E. I. , Holonyak N.
Published: July 2002

Data are presented on deep-oxide planar buried-heterostructure AlGaAs–GaAs quantum well heterostructure laser diodes fabricated using a self-aligned process that combines native oxide and impurity-induced layer disordering (IILD) technologies. Silicon IILD intermixes the waveguide layers on either side of an active area stripe and allows ‘‘wet’’ oxidation to penetrate and create a low-index (n∼1.7) deep-oxide structure for electrical and optical confinement. Continuous-wave (cw) threshold currents of ∼3.4 mA are measured for ∼3.5-μm-wide active regions (L∼250 μm), with maximum cw output powers greater than 29 mW/facet and external differential quantum efficiencies as high as 70% (300 K, uncoated facets).
Sensitivity of ion induced charge pulses to the electrical and crystallographic properties of 60° dislocations
Authors: Breese M. B. H. , King P. J. C. , Grime G. W.
Published: July 2002

This letter reports evidence that the size of MeV ion induced charge pulses measured from epitaxial Si0.875Ge0.125/Si depends on both the crystallographic and electrical properties of the 60° misfit dislocations present. The results are correlated with both backscattered and transmission ion channeling analysis. With the sample in nonchanneled alignment the measured ion induced charge pulses depend on the number of charge carriers which recombine at the dislocations. With the sample in channeled alignment the rotated (110) and (11̄0) planes around the 60° dislocations affect the local rate of carrier generation and so alter the size of the measured ion induced charge pulses.
Experimental observation of transverse effects in microchip solid-state lasers
Authors: Longhi S. , Cerullo G. , Taccheo S. , Magni V. , Laporta P.
Published: July 2002

We report on the observation of transverse effects in a microchip solid-state laser due to gain-guiding, demonstrating that the transverse modulation of the gain profile and detuning play a fundamental role in the control of the longitudinal lasing mode. The observed behavior is interpreted in the framework of the Maxwell–Bloch equations as a symmetry breaking between the two sides of the atomic resonance.
Optical differentiator based on rapid collapse of Wannier–Stark localization due to space charge field screening
Authors: Hosoda M. , Tominaga K. , Watanabe T. , Fujiwara K.
Published: July 2002

An optical differentiator operation is demonstrated using a GaAs/AlAs short-period superlattice near an optical absorption band edge. This operation is clearly explained by a rapid collapse of Wannier–Stark localization due to electric field screening by photogenerated space charges, because the screening causes a positive feedback loop between restoration of blueshifted wavelength of absorption band edge to the red side and an increase in optical absorption which causes an additional field screening.
Observation of nonlinear accompanying electric potential wave in piezoelectric crystals
Authors: Jiang Wenhua , Du Gonghuan
Published: July 2002

The theory of three-field acoustic interactions in nonlinear piezoelectric crystals predicts that the second-harmonic acoustic wave is accompanied by the second-harmonic electric potential wave due to the electroacoustic nonlinearities of the media. An experiment to demonstrate the phenomenon carried out for crystal LiNbO3 is described in this letter. Ultrasonic waves excited by a 30 MHz quartz transducer propagate along the z direction of LiNbO3 crystal. The nonlinear electric potential wave accompanying with the acoustic wave is directly detected by use of the capacitive detector. To the author’s knowledge, this kind of observation has not been made before.