bluuebunny/crossref_metadata_2025 huggingface dataset:
GaAs-InGaAs double delta-doped quantum-well switching device prepared by molecular beam epitaxy
Authors: Hsu Wei-Chou , Liu Wen-Chau , Guo Der-Feng , Lour Wen-Shiung
Published: July 2002

A new GaAs negative-differential-resistance (NDR) switching device with a double delta-doped quantum-well structure, prepared by molecular beam epitaxy (MBE), has been fabricated and demonstrated. The double delta-doped sheets δ(p+) located in InGaAs quantum wells produce potential barriers for electron injection. Owing to the avalanche multiplication process and potential redistribution effect, the significant S-shaped NDR phenomenon is obtained. From experimental results, it is known that the temperature variation introduces an effective influence on the device properties. Consequently, the studied structure may produce a good potential for switching device applications.
Low-temperature decay of photocapacitance caused by Sn-related DX centers in AlxGa1−xAs
Authors: Žd’ánský K. , Peaker A. R.
Published: July 2002

Transients of capacitance and parallel conductance when illumination is switched off have been measured at various temperatures down to 25 K. It has been proved that the Sn-DX center is not an origin of persistent photocapacitance but the photocapacitance is only long lasting and decays with the temperature independent rate. It has been proposed that the decay is caused by quantum mechanical tunneling of the Sn donor with electron capture. Further, capacitance and conductance as a function of frequency were measured and the energy ED=30 meV of the negative charge state and ED=8 meV of the neutral charge state of the DX center were determined.
Room-temperature determination of two-dimensional electron gas concentration and mobility in heterostructures
Authors: Schacham S. E. , Mena R. A. , Haugland E. J. , Alterovitz S. A.
Published: July 2002

A technique for determination of room-temperature two-dimensional electron gas (2DEG) concentration and mobility in heterostructures is presented. Using simultaneous fits of the longitudinal and transverse voltages as a function of applied magnetic field, we were able to separate the parameters associated with the 2DEG from those of the parallel layer. Comparison with the Shubnikov–de Haas data derived from measurements at liquid helium temperatures proves that the analysis of the room-temperature data provides an excellent estimate of the 2DEG concentration. In addition we were able to obtain for the first time the room-temperature mobility of the 2DEG, an important parameter to device application. Both results are significantly different from those derived from conventional Hall analysis.
Photoemission from U and Mg using a pulsed XeCl laser
Authors: Ivri J. , Levin L. A.
Published: July 2002

We report results of photoemission from metal cathodes. The photon source was a pulsed XeCl laser of 10 ns width (FWHM). We obtained a photocurrent density of 600 A/cm2, a quantum efficiency of 8×10−5, and a calculated brightness of 1×108 A/(cm2 rad2) for a uranium cathode and a photocurrent of 60 A/cm2, a quantum efficiency of 8×10−6 and brightness of 1×107 A/(cm2 rad2) for a magnesium cathode. Space charge limited and emission limited photoelectrons were studied using high and low energy laser pulses, respectively. The uranium cathode was operated for over 50 h with no reduction of the photocurrent.
Formation of bulk Pd40Ni40P20 glass
Authors: Kui H. W.
Published: July 2002

Bulk amorphous Pd40Ni40P20 has been formed by fluxing the molten specimen in anhydrous boron oxide. In this study, a new method to form bulk amorphous Pd40Ni40P20 glass in the absence of boron oxide is introduced. Two kinds of Pd40Ni40P20 ingots were used in the experiment. In the first type, glassy alloys were used while the second kind involved alloys that had not been treated before. Both types could be undercooled to the glass state in bulk form.
Metalorganic chemical vapor deposition of InP using phosphine modulation
Authors: Lee M. K. , Hu C. C. , Lin M. H.
Published: July 2002

In this study, a new epitaxial growth process was developed using phosphine modulation using conventional metalorganic chemical vapor deposition. With this method, phosphine was switched off a short time in each cycle and provided a metal-rich growth surface. With higher surface mobility of indium atoms than that of InP molecules, crystal quality was improved significantly. Photoluminescence full width at half-maximum 5.6 meV at 77 K was achieved under optimum growth conditions.
Carrier transport into intermixed GaAs/AlGaAs quantum wires
Authors: Prins F. E. , Lehr G. , Fröhlich E. M. , Mayer G. , Schweizer H. , Straka J. , Forchel A. , Smith G. W.
Published: July 2002

We have realized GaAs/AlGaAs quantum wires using the implantation induced intermixing technique. The transport of carriers from the AlGaAs barriers into the intermixed quantum well (QW) is studied by comparing low temperature photoluminescence spectra at resonant and nonresonant excitation. It is shown that hardly any carriers generated in the AlGaAs are captured in the intermixed QW. At resonant excitation a large lateral diffusion length of carriers from the lateral barriers into the wires is observed which is reduced at higher temperatures due to implantation defects.
Spatially resolved Raman spectroscopy of a step graded GexSi1−x strain relief structure
Authors: Tsang J. C. , Dacol F. H. , Mooney P. M. , Chu J. O. , Meyerson B. S.
Published: July 2002

The structure of a strain relief region between a Si substrate and a low dislocation density Ge film has been measured by Raman spectroscopy. The composition of the structure has been determined with ≂1000 Å resolution in the growth direction, and the upper portions shown to be largely relaxed. The presence of microscopic inhomogeneities in these alloys is suggested.
Symmetric self-electro-optic effect device array grown by metalorganic vapor phase epitaxy using GaAs/Al0.04Ga0.96As shallow quantum wells
Authors: Lee S. W. , Kim T. M. , Chu K. U. , Park S. , Jeong M. S. , Kwon O’D.
Published: July 2002

A self-electro-optic effect device (SEED) epistructure grown by low-pressure metalorganic vapor phase epitaxy (MOVPE) is demonstrated. The symmetric SEED using GaAs/Al0.04Ga0.96As shallow quantum well (SQW) exhibits a contrast ratio of 2.9 at 5 V bias with 50 pairs of GaAs wells. This high contrast results from the low background carrier concentration of absorption region which is obtained by the temperature controlled compensation of the acceptors and donors. The absorption data suggest that the MOVPE technique is comparable to the MBE technique in growing the high performance SQW epistructure.
Tunable guided-wave optical polarization converters in lithium tantalate
Authors: Tang Z. , Eknoyan O. , Taylor H. F. , Swenson V. P.
Published: July 2002

Tunable guided-wave TE↔TM mode converters have been produced in LiTaO3 using strain-induced polarization mode coupling. The waveguides are formed by Zn diffusion from the vapor phase. Phase matched coupling is obtained by depositing a thick SiO2 film at an elevated temperature and delineating a spatially periodic pattern in the film at room temperature. The static shear strain resulting from the large thermal expansion mismatch between the substrate and film causes an off-diagonal change in the refractive index via the strain-optic effect and promotes TE↔TM coupling. Polarization conversion in excess of 98% was achieved at a wavelength of 627 nm in X-cut LiTaO3. The conversion efficiency is highly wavelength selective, with a spectral width of 7.3 nm in the 5.4 mm long device. Thermal and electro-optic tuning of the center wavelength was demonstrated.
X-ray diffraction method for characterization of thin surface layers and thin epitaxial films
Authors: Itoh Nobuo
Published: July 2002

A new convenient diffraction technique is proposed, which enables us to infer a depth distribution of crystalline quality in a thin crystal layer. When a crystal plate is laid on the side and its reflecting planes get arranged in the vertical with tilting of the surface by a given angle, x-ray diffraction from the thin surface layer can be obtained. Since glancing angles of x-ray beams are changed with turning of the crystal by an angle around the diffraction vector and thereby the x-ray penetration depth is changeable, the depth distribution can be measured. The applicability to characterization of surface damage layers of GaAs crystals and a thin InGaP epitaxial film on a GaAs substrate is demonstrated.
Hydrogen plasma removal of AlGaAs oxides before molecular beam epitaxy
Authors: Choquette Kent D. , Hong M. , Chu S. N. G. , Luftman H. S. , Mannaerts J. P. , Wetzel R. C. , Freund R. S.
Published: July 2002

We report a method for the removal of AlxGa1−xAs native oxides for 0≤x≤1, prior to molecular beam epitaxial overgrowth. The oxides formed on epilayers of AlGaAs after atmospheric exposure are removed in an electron cyclotron resonance hydrogen plasma with a substrate temperature less than 400 °C. Reflection high energy electron diffraction indicates the plasma-prepared AlGaAs surface are oxide-free and crystalline; after a vacuum anneal to 250–500 °C, GaAs or AlGaAs are epitaxially overgrown on these surfaces. Secondary ion mass spectroscopy detects C, O, and Si impurities at the interfaces, where their concentrations increase with increasing Al content of the exposed surface. The quality of the interface and the overgrown film, as observed by transmission electron microscopy, are found to be better for lower interface impurity densities.
Injection locking of leaky-wave coupled resonant optical waveguide arrays
Authors: Jansen M. , Botez D. , Mawst L. J. , Roth T. J. , Yang J. J. , Ou S. S. , Hayashida P. , Dozal L. A.
Published: July 2002

Injection locking of mutually coupled resonant antiguided arrays, consisting of up to four ten-element arrays, has been demonstrated. External injection causes single-longitudinal mode operation, and enhanced phase-locking of the coupled arrays. The injected signal is distributed via leaky-wave coupling, so that the master-oscillator signal injected into one element (3 μm) of one array locks the whole array ensemble (223 μm wide aperture). Wavelength tuning is achieved over a 12 Å spectral range for two coupled arrays, and has no impact on the coupled array far-field pattern.
Third-order nonlinear optical susceptibilities of amorphous SnO2−x thin films
Authors: Endo Hiroshi , Sakai Mitsuhiro , Watanabe Yuichi , Takata Masasuke
Published: July 2002

Amorphous SnO2−x (x=0–1) thin films are prepared on glass substrates by using a radio-frequency magnetron sputtering technique and the third-order nonlinear optical susceptibilities χ(3) (−3ω; ω, ω, ω) are evaluated by the third-harmonic generation (THG) method. The values of χ(3) are found to increase with decreasing the oxygen content in the samples. The χ(3) of the present sample is larger by several times than that of crystalline SnO2 thin film in which the χ(3) is about 10−12 esu order. These values are very large among those for inorganic materials at the nonresonant region.
Thermodynamic interpretation of quaternary (InGaAsP) layer uniformity grown by low-pressure metalorganic vapor phase epitaxy
Authors: Jordan A. S. , Robertson A. , Zilko J. L.
Published: July 2002

According to a recent study, the compositional nonuniformity for group V sites of quaternary (Q) In0.68Ga0.32As0.7P0.3 layers (λ=1.35 μm) grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) on 50 mm diam InP wafers was reduced from 3% to 1% when tertiary butyl phosphine (TBP)+AsH3 instead of PH3+AsH3 or TBP+tertiary butyl arsine (TBAs) were employed. In this letter we offer a thermodynamic interpretation of these observations. Under LP-MOVPE conditions at a total pressure of 0.08 atm for fully decomposed group V precursors diluted with H2, we show that while the dominant species are the tetramers, the concentration of the dimers is significant and becomes more prominent with rising temperature (T). Examining the [As/P] ratio in the gas phase as a function of reciprocal T, we demonstrate that in the MOVPE range (900–950 K) the slope of these curves changes from steep to moderate and then nearly flat for the sources AsH3+PH3, TBAs+TBP, and AsH3+TBP, respectively. The insensitivity of the [As/P] ratio to the ∼30 K gradient over the susceptor when combining AsH3 and TBP suggests a very effective method to assure compositional uniformity in Q layers prepared by LP-MOVPE. Uniformity results for atmospheric pressure MOVPE employing AsH3 and PH3 are also consistent with the thermodynamic argument.
Capacitive detection of subband structure in the electron gas in a wide parabolic GaAs/AlxGa1−xAs quantum well
Authors: Rimberg A. J. , Yang Scott , Dempsey Jed , Baskey J. H. , Westervelt R. M. , Sundaram M. , Gossard A. C.
Published: July 2002

Profiles of the capacitance C(Vg) between a front gate and the electron gas in a wide parabolic well and its derivative dC/dVg are used to study the subband structure and uniformity of the electron gas layer. Subband depopulation events are detected as peaks in the derivative profile dC/dVg as the width of the electron gas is reduced by application of the gate voltage Vg. To separate depopulation events from nonuniformities in electron density, derivative profiles are repeated for increasing in-plane magnetic fields: depopulation peaks move to smaller gate voltages and disappear at characteristic fields, while nonuniformities remain fixed and are accentuated in strong fields.
Direct current-94.92 MHz hybrid plasma magnetron sputtering for fabrication of YBa2Cu3O7−x thin films
Authors: Ito W. , Okayama S. , Homma N. , Oishi A. , Morishita T.
Published: July 2002

YBa2Cu3O7−x thin films have been prepared using a newly designed dc-94.92 MHz hybrid plasma magnetron sputtering system. The cathode current affected the crystalline orientation of the films as well as the deposition rate. Optical emission spectroscopic studies of this plasma indicate that the intensities of the emission lines from the ions increase with the increasing cathode current. The films showed an excellent crystallinity with the a-axis being perpendicular to the plane of the substrate; a full width at half-maximum value of 0.027° was measured for the (200) peak from the rocking curve measurement. The crystallinity of films has reached the level for the first time where the crystallinity essentially depends on the crystallinity of the substrate used.
Si diffusion and segregation in low-temperature grown GaAs
Authors: Kavanagh K. L. , Chang J. C. P. , Kirchner P. D. , Warren A. C. , Woodall J. M.
Published: July 2002

Heavily Si-doped (5×1019 cm−3) low-temperature GaAs (LT-GaAs) sandwiched between undoped LT-GaAs layers has been grown by molecular beam epitaxy and annealed to 900 °C. Transmission electron microscopy showed that within the first few minutes of annealing an accumulation of As precipitates formed near each Si-doped/undoped LT-GaAs interface. With further annealing Si segregation to As precipitates was detected with secondary ion mass spectroscopy in the form of deltalike peaks at the As precipitate accumulations. The Si diffusion coefficient was initially concentration independent at a value of 2.5×10−13 cm2/s, comparable to diffusion under intrinsic conditions in As-rich GaAs grown at normal temperatures. After a 60 min anneal the Si concentration in the As precipitates reached 2.5×1020 cm−3.
Effect of disorder on the optical properties of short period superlattices
Authors: Strozier J. A. , Zhang Y. A. , Horton C. , Ignatiev A. , Shih H. D.
Published: July 2002

The optical properties of disordered short period superlattices are studied using a one-dimensional tight-binding model. A difference vector and disorder structure factor are proposed to characterize the disordered superlattice. The density of states, participation number, and optical absorption coefficients for both ordered and disordered superlattices are calculated as a function of energy. The results show that introduction of disorder into an indirect band gap material enhances the optical transition near the indirect band edge.
Electrical conduction in low temperature grown InP
Authors: Khirouni K. , Maaref H. , Bourgoin J. C. , Garcia J. C.
Published: July 2002

Electric conduction has been studied vs frequency ω and temperature T in InP layers grown at low temperature. The T and ω behaviors of the conductivity are found to be typical of a hopping process in a partially defect filled band, very similar to the one observed in disordered materials. We have determined the location of the Fermi level. The results are analyzed in terms of a recent theory developed by D. Emin [Phys. Rev. B 46, 9419 (1992)].
Observations of the frequency range of self-mode locking and single longitudinal mode operation in CuBr lasers
Authors: Geng Jihong , Zhang Guiyan , Song Xiudong , Lin Fucheng
Published: July 2002

The lower and upper limits of the longitudinal mode spacing and self-mode locking behavior in CuBr lasers are reported for the first time, by using different optical cavity configurations. A proposed interpretation is given qualitatively. In addition, the first observation of single longitudinal mode operation in CuBr lasers with a multimirror cavity is described.
Time dependence of the surface Fermi level of GaAs in atmosphere
Authors: Ohbu I. , Takahama M. , Mizuta H.
Published: July 2002

This letter reports the time dependence of the surface Fermi level of GaAs grown by molecular-beam epitaxy and then exposed to atmosphere. The sheet resistance of sample structures for field effect transistors alternately increased, decreased, increased, and decreased to become nearly constant after about 500 h. These changes correspond to the surface Fermi level varying between 0.3 and 0.7 eV and finally settling 0.7 eV above the valence band maximum. Comparison between annealed and unannealed samples with low-temperature-grown GaAs layers showed that the pinning of the surface Fermi level at 0.7 eV above the valence band maximum is caused by arsenic antisite defects. The result supports the advanced unified defect model.
Multilevel ramp transitions in GaAs circuits
Authors: Hur Katerina Y. , Compton Richard C.
Published: July 2002

Two techniques for the integration of GaAs devices in multiple layer topologies are presented. An isotropic reactive ion etching technique is discussed for free-standing-metal interconnections within the same layer. A complementary approach for connections between different levels, based on chemically assisted ion beam etched ramps, is also described. In addition, both techniques can be used for device isolation.
Novel shadow mask molecular beam epitaxial regrowth technique for selective doping
Authors: Gulden K. H. , Wu X. , Smith J. S. , Kiesel P. , Höfler A. , Kneissl M. , Riel P. , Döhler G. H.
Published: July 2002

We present a novel molecular beam epitaxial regrowth technique which provides a simple and convenient way for the in situ lateral structuring of the doping profiles and growth rates on a μm scale. We achieve excellent selective contacts to the respective doping layers for device dimensions varying from several 100 μm down to several μm. Keldysh based n-i-p-i modulator structures, fabricated with our new method, exhibit an on/off ratio of 6:1 for a voltage swing of 7 V without enhancement by additional Bragg mirrors.
Linewidth measurements of Josephson flux-flow oscillators in the band 280–330 GHz
Authors: Zhang Y. M. , Winkler D. , Claeson T.
Published: July 2002

An integrated receiver consisting of two Josephson flux-flow oscillators and a superconductor-insulator-superconductor (SIS) mixer has been used to measure the linewidth of the oscillators. The oscillators are coupled to the SIS mixer using two centerfed interdigital capacitors, one of which with a fairly weak (−20 dB) coupling. By biasing the two oscillators (a few microvolt apart) on their velocity matching steps, the two resulting oscillations (280–330 GHz) were mixed in the SIS mixer. The difference frequency was amplified and detected on a spectrum analyzer. The combined linewidth of the two oscillators was 2.1 MHz throughout the band. The calculated available power incident on the SIS mixer was 430 nW at 320 GHz. The rf power from the oscillators, which could be tuned by changing the current bias, is high enough to pump the SIS mixer optimally.
New high-T
c cuprate (Tl1−xCrx) (Sr2−yBay)Ca2Cu3O9
Authors: Chen Z. Y. , Sheng Z. Z. , Tang Y. Q. , Li Y. F. , Wang L. M. , Pederson D. O.
Published: July 2002

A new series of 1223-type (Tl,Cr)-based cuprates, (Tl,Cr)(Sr,Ba)2Ca2Cu3Oz, have been successfully synthesized and identified by powder x-ray diffraction and electron diffraction analyses. Ba partial substitution for Sr promotes the formation of (Tl,Cr)-based 1223-type compounds. Nominal samples, (Tl1−xCrx)-(Sr2−yBay) Ca2Cu3Oz, with 0.15≤x≤0.50 and 0.50≤y≤1.50 are pure or nearly pure 1223 phase and exhibit Tc(ρ=0) in the range of 104–114 K. This new (Tl,Cr)-based high-Tc material may be of importance in practical applications.
Superconductivity and microstructure of n-type Ln1.85Ce0.15CuO4−y (Ln=Pr, Sm, Eu) produced under high-pressure sintering
Authors: Jin C. Q. , Yao Y. S. , Liu S. C. , Zhou W. L. , Wang W. K.
Published: July 2002

Using an unconventional reduction method, high-pressure sintering at 6.0 GPa and about 600 °C for 20 min, we have produced high-quality n-type Ln1.85Ce0.15CuO4−y (Ln=Pr, Sm, and Eu) superconductors from the as-prepared materials. The samples show higher critical temperatures, higher superconducting phase fractions, and much lower resistances in the normal state than those synthesized by conventional methods. The increase of critical temperature in Eu1.85Ce0.15CuO4−y is most obvious with an onset temperature Tonc and zero-resistance temperature Tc0 of 28.4 and 23.3 K, respectively. High-pressure sintering seems to be effective on the modulation of the fine crystal and electronic structures of n-type systems. In particular, metallic resistance versus temperature behaviors in normal states similar to those found in single crystals and epitaxial films are observed in Sm1.85Ce0.15CuO4−y and Eu1.85Ce0.15CuO4−y, in sharp contrast to the semiconductorlike behaviors in the conventionally prepared samples. From transmission electron microscopy studies, it is found that the compacting and regrowth of the polycrystal under high-pressure sintering greatly improves the weak links at grain boundaries.
Chemical vapor deposition of silicon carbide thin films on titanium carbide, using 1,3 disilacyclobutane
Authors: Chaddha A. K. , Parsons J. D. , Wu J. , Chen H-S. , Roberts D. A. , Hockenhull H.
Published: July 2002

Silicon carbide (SiC) thin films were deposited on titanium carbide (TiC) substrates by pyrolysis of 1,3 disilacyclobutane (C2H8Si2), at atmospheric pressure, in an inverted-vertical cold-wall chemical vapor deposition reactor. The growth rate, morphology, and crystallinity of the films were studied, at constant C2H8Si2 flow rate, as a function of substrate temperature (810 °C≤Ts≤1285 °C). The growth rate increased with increasing Ts. Film morphologies were dependent on Ts and slight differences in TiC substrate orientation at Ts≥1015 °C. A smooth, soft as-grown morphology was obtained at 810 °C. Hard, rough as-grown surfaces were obtained at Ts≥1066 °C. Films grown at Ts ≥1066 °C contained a SiC primary phase and a Si-rich second phase. Epitaxial growth of β-SiC was obtained only at 1210 °C.
Effect of point defect reactions on behavior of boron and oxygen in degenerately doped Czochralski silicon
Authors: Wijaranakula W.
Published: July 2002

The behavior of boron and oxygen in degenerately doped Czochralski silicon has been studied after an extended annealing at temperatures ranging between 750 and 900 °C in nitrogen ambient. The results from secondary ion mass analysis show an accumulation of boron atoms near the silicon surface while oxygen outdiffusion appears to be significantly retarded. Based upon the defect morphology examined using high resolution electron microscopy, it is concluded that degenerate silicon is saturated with interstitial defect species during an extended annealing. From the point defect reaction and dynamic clustering models, an accumulation of boron near the silicon surface is hypothesized to be due to boron outdiffusion which may be driven by the difference in chemical potential of boron saturation between the bulk and surface regions. A retardation of oxygen diffusion, on the other hand, may be caused by a strong pairing reaction between boron and oxygen atoms.
Effects of Al2O3 cap on the structural and electrical properties of Au/Te/Au contacts on an n-type GaAs substrate
Authors: Lin X. W. , Piotrowska A. , Kaminska E. , Liliental-Weber Z. , Washburn J. , Weber E.
Published: July 2002

Au/Te/Au contacts to n-type GaAs were prepared by sequential vapor deposition and subsequently annealed at temperatures in the range 420–480 °C. The structural and electrical characteristics of the contacts were characterized by transmission electron microscopy and current–voltage measurements. We found that the electrical behavior of the contacts depends dramatically on whether they are covered with an Al2O3 cap during annealing. While a cap-annealed Au/Te/Au contact remains rectifying, annealing without the cap results in ohmic behavior. In conjunction with the observed structural properties, this phenomenon can be understood in terms of the doping model for ohmic contact formation.
Spatially resolved electrical characterization of a YBa2Cu3O7−δ flux transformer
Authors: Husemann K.-D. , Gross R. , Huebener R. P. , Roas B.
Published: July 2002

We report the spatially resolved transport properties of a three-layer YBa2Cu3O7−δ flux transformer using low-temperature scanning electron microscopy. The seven-turn spiral coil is fabricated using a crossover technology with SrTiO3 as an insulator. The different layers were patterned with shadow masks or optical lithography. We show that the insulating SrTiO3 film has no shorts and that the overlaying YBa2Cu3O7−δ spiral reveals a reduced zero resistance critical temperature at the steps and edges of the insulator.
High-pressure sintering characteristics of Sm2Fe17Nx powder
Authors: Machida K. , Nakatani Y. , Adachi G. , Onodera A.
Published: July 2002

Sintering characteristics of Sm2Fe17Nx were studied under high-pressure conditions (pressure=3 GPa and temperatures=300, 550, and 800 °C) without any binding material. High-pressure treatments at 3 GPa and 550 °C succeeded in preparing the sintered materials without any decomposition, which possessed density values close to the theoretical one and good mechanical strength property, although the temperature of 300 °C was little enough for sintering of the Sm2Fe17Nx powder and the sample prepared at 800 °C provided a different x-ray diffraction (XRD) pattern from that of Sm2Fe17Nx. The result that the remanence values of Sm2Fe17Nx were almost similar to each other (6.5–7.0 kG) before and after the sintering at 3 GPa and 550 °C indicated that the high-pressure treatments never involved any serious undesirable effect on the magnetization property of resulting sintered materials.
Two-wavelength reversible holograms in azo-dye doped nematic liquid crystals
Authors: Chen Alan G. , Brady David J.
Published: July 2002

We describe reversible holographic effects in azo-dye doped liquid crystals. Surface-stabilized holograms are recorded at 514 nm using beams polarized parallel to the molecular director of the liquid crystals. While these holograms persist for several hours in the dark, complete erasure is achieved in a few seconds by exposure to 337 nm light.
Optical emission from GaAs/AlGaAs p-i-n multiquantum well structures grown on patterned Si substrates
Authors: Murray R. , Roberts C. , Woodbridge K. , Barnes P. , Parry G. , Norman C.
Published: July 2002

Photoluminescence and cathodoluminescence have been used to investigate the strain in GaAs/AlGaAs multiquantum well structures grown on a thick GaAs buffer layer on a patterned silicon substrate. By growing the epitaxial GaAs only on ‘‘islands’’ of Si the density of microcracks is reduced by nearly two orders of magnitude. Although the biaxial tension is reduced in the vicinity of a microcrack, the strain is almost eliminated at the island edges. Strain is still present in the center of the islands but reduces with decreasing island size offering the possibility of relatively strain and microcrack free, small area optical devices on silicon substrates.
Photoelastic waveguides formed by interfacial reactions
Authors: Yu L. S. , Guan Z. F. , Xia W. , Liu Q. Z. , Deng F. , Pappert S. A. , Yu P. K. L. , Lau S. S. , Florez L. T. , Harbison J. P.
Published: July 2002

The fabrication of low-loss photoelastic waveguides in GaAs/AlGaAs layered structures by thin film reactions is investigated. The waveguides are formed by opening a narrow window stripe, a few microns wide, in an otherwise continuous Ni layer under tension deposited on a semiconductor structure. The local tensile stress induced by the Ni layer in the semiconductor causes the local refractive index to increase, thus providing the guiding mechanism. Annealing the sample at 250 °C for 1 h induced an interfacial reaction between the Ni film and the substrate to form Ni3GaAs. The formation of an interfacial compound stabilizes the stresses, making the stress state independent of the deposition system and technique. Single-mode waveguide propagation losses as low as 1.4 dB/cm at 1.53 μm wavelength have been obtained on annealed waveguides. Further annealing up to 600 °C did not cause degradation in the optical confinement, thus indicating a thermally stable planar waveguide fabricated by this process. Other photoelastic optical devices such as polarizers, splitters, and couplers are also demonstrated.
Nanotube structure and electronic properties probed by scanning tunneling microscopy
Authors: Zhang Zhe , Lieber Charles M.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to investigate the structure and electronic properties of carbon nanotubes produced from a discharge between graphite electrodes. STM images of the nanotubes deposited onto polycrystalline gold substrates resolve the three-dimensional structure of the nanotubes and show that these tubes often exist as tightly packed bundles. In addition, bias-voltage dependent imaging studies indicate that the nanotubes studied are semiconductors. The implications of these new data to the application of nanotubes in structural composites and nanoelectronics is discussed.
GaAs single-domain growth on exact (100) Si substrate
Authors: Sprung K.-R. , Wilke K. , Heymann G. , Varrio J. , Pessa M.
Published: July 2002

Single-domain growth of a GaAs layer showing a relatively good crystal structure and specular surface has been demonstrated on a silicon substrate which has been cut along an exact (100) plane. The substrate was patterned with a sawtooth grating using electron beam lithography, and the layers were grown by molecular beam epitaxy.
Simple, extremely low resistance contact system to n-InP that does not exhibit metal-semiconductor intermixing during sintering
Authors: Weizer Victor G. , Fatemi Navid S.
Published: July 2002

Contact formation to InP is plagued by the violent metal-semiconductor intermixing that takes place during the contact sintering process. We have discovered a truly unique contact system, involving Au and Ge, which is easily fabricated, which exhibits extremely low values of contact resistivity, and in which there is virtually no metal-semiconductor interdiffusion, even after extended sintering. We present a description of this contact system and suggest possible mechanisms to explain the observed behavior.
Microstructure of porous silicon
Authors: Nakajima A. , Ohshima Y. , Itakura T. , Goto Y.
Published: July 2002

We examined the microstructure of luminescent porous silicon by cross-sectional high-resolution transmission electron microscopy and found a threadlike structure consisting of Si microcrystals. We also found Si microcrystals with sizes ranging about 3–20 nm randomly distributed throughout the porous silicon.
Photoluminescence of AlAs/GaAs superlattice quantum wells
Authors: Shih Y. C. Albert , Streetman B. G.
Published: July 2002

We report the results of low-temperature photoluminescence (PL) studies of AlAs/GaAs superlattice quantum wells (SLQWs), obtained by placing various periods of short-period AlAs/GaAs superlattices (SLs) between two Al0.45Ga0.55As confining layers. Structures with a constant well width and various combinations of AlAs and GaAs layer thicknesses in the SLs are synthesized by molecular beam epitaxy. Two distinct peaks are resolved in the PL spectra, which can be attributed to transitions involving heavy-hole and light-hole bands. Comparison of 4 and 77 K PL spectra reveal evidence of type-II band alignment in SLQWs with thin GaAs layers.
Real-time study of the reflection high energy electron diffraction specular beam intensity during atomic layer epitaxy of GaAs
Authors: Maa B. Y. , Dapkus P. D. , Chen P. , Madhukar A.
Published: July 2002

The intensity behavior of the specular beam in reflection high energy electron diffraction (RHEED) from GaAs (001) is investigated during the exposure of trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) in atomic layer epitaxy (ALE) of GaAs. The temporal behavior of RHEED specular beam intensity corresponding to the transient behavior of the reflectance difference (RD) at 632.8 nm reveals several phases of surface reactions in ALE using TMGa and TBAs. RHEED specular beam intensity relaxation after short exposure to TMGa shows a longer time constant than that observed by RD, suggesting that it is the result of the overall changes in the surface atomic arrangements and morphology whereas the latter is responding to the formation/annihilation of Ga dimers.
Impurity decoration of defects in float zone and polycrystalline silicon via chemomechanical polishing
Authors: McHugo Scott A. , Sawyer William D.
Published: July 2002

The behavior of impurities introduced in single and polycrystalline silicon via chemomechanical polishing was studied extensively. Using the electron beam induced current mode of a scanning electron microscope, chemomechanical polishing of boron-doped FZ silicon is shown to introduce impurities which decorate and electrically activate swirl defects. Undecorated swirl defects do not behave as carrier recombination sites. Chemomechanical polishing and preferential etching of boron-doped polycrystalline silicon produced etch pits which increased in concentration with decreasing resistivity, indicating an interaction between the polishing impurity and boron. The impurity is shown to form discrete points of electrical activity homogeneously in a thin surface region of the material as well as increase the electron beam induced current contrast of dislocations and grain boundaries.
Reflectance of a chiral plate absorber
Authors: Liao S. B. , Yin G. J.
Published: July 2002

This letter presents the dependence of the reflectance of a single layer of plate absorber constructed by a chiral material on the chiral parameter. The results show that the absorber constructed by the chiral material has great advantages over that constructed by the general electromagnetic material (achiral material).
Optical tri-state switching through a metastable state using short pulse excitation
Authors: Kawashima Kenji , Hosoda Makoto , Fujiwara Kenzo
Published: July 2002

Optical tri-state switching is obtained for the first time, using short pulse excitation in a symmetric self-electro-optic effect device based on the Wannier–Stark localization (WSL-SEED). A novel method, by controlling photoexcited charges, is proposed to set and reset the transmission states of the signal diode, which enables us to use a metastable state as an intermediate state in the tri-state device. By the use of a sequence of the optical pulses a clear switching among three stable states as well as optical adder/subtracter properties is demonstrated.
Monte Carlo investigation of minority electron transport in silicon
Authors: Dewey J. , Osman M. A.
Published: July 2002

The transport of minority electrons in silicon has been investigated using an ensemble Monte Carlo approach at room temperature with electron-hole scattering rates which take into account the ellipsoidal nature of the conduction band valleys. Mobility calculations showed quantitative agreement with experimental values at an acceptor concentration of 4.5×1016 cm−3 while qualitative agreement with the electron-hole drag effect was observed at 3.8×1018 cm−3. Transient calculations showed the electron-hole interactions decrease electron energy, reduce steady-state velocity, and decrease the transfer rate of electrons to the cold valleys.
Multilayer, nonlinear antiresonant waveguides for surface emitted optical mixing
Authors: Normandin R. , Dai H. , Janz S. , Delage A. , Brown J. , Chatenoud F.
Published: July 2002

A multilayered core nonlinear antiresonant reflecting optical waveguide (NARROW) was used to generate surface emitted frequency doubled light. High efficiencies were obtained with the NARROW while simultaneously keeping optimum antiresonant conditions at the fundamental wavelength.
Al2O3+x/Al interface formation by promoted oxidation using an alkali metal and removal of the catalyst
Authors: Huttel Y. , Bourdié E. , Soukiassian P. , Mangat P. S. , Hurych Z.
Published: July 2002

We report the effect of Na overlayers on the oxidation of Al thin films by core level photoemission spectroscopy using synchrotron radiation. The presence of a Na monolayer enhances the aluminum room temperature oxidation rate by 4 orders of magnitude with formation of alumina as Al2O3 and Na oxides, possibly as aluminates. Furthermore, the Na catalyst could be desorbed from the surface by a rapid thermal annealing at temperatures below 300 °C, leading to the growth of aluminum oxides having a binding energy larger than stoichiometric Al2O3. It indicates the formation at the surface of Al oxides having higher oxidation states.
High-resolution x-ray diffraction to determine the self-limiting growth in atomic layer epitaxy of InP and InAs/InP heterostructures
Authors: Tran C. A. , Masut R. A. , Brebner J. L. , Leonelli R.
Published: July 2002

High-resolution x-ray diffraction (HRXRD) can be used to quickly and precisely evaluate the self-limiting growth of atomic layer epitaxy (ALE) of III-V compounds and heterostructures. We have studied atomic layer epitaxy of InP and InAs/InP heterostructures in a conventional low pressure metalorganic vapor phase epitaxy reactor. We used the interference of x-ray wave fields in the grown structures to measure nondestructively the thickness of the deposited film with relatively high precision. A self-limiting growth close to 1 monolayer/cycle has been obtained for InP and InAs with a substrate temperature as low as 350–360 °C. HRXRD and photoluminescence measurements have demonstrated the structural and optical high quality of ALE-grown InP and InAs/InP heterostructures.
Nanometer scale fabrication in mercury cadmium telluride using methane/hydrogen electron cyclotron resonance microwave plasmas
Authors: Eddy C. R. , Dobisz E. A. , Hoffman C. A. , Meyer J. R.
Published: July 2002

The fabrication of nanometer scale features in the narrow gap, compound semiconductor mercury cadmium telluride has been demonstrated through the application of e-beam lithography and reactive ion etching with an electron cyclotron resonance (ECR) microwave generated methane/hydrogen plasma. The effects of methane concentration, substrate bias, total pressure, and substrate position with respect to the ECR condition on etch rate, anisotropy, and overall etch performance have been examined. The optimized process resulting from these studies has produced the first mercury-based nanostructures consisting of 30–60 nm features with sidewall angles of 88°.
Fabrication and characterization of YBa2Cu3O7 step-edge junction arrays
Authors: Reuter W. , Siegel M. , Herrmann K. , Schubert J. , Zander W. , Braginski A. I. , Müller P.
Published: July 2002

We investigated one-dimensional arrays with up to 600 step-edge Josephson junctions (SEJ) fabricated by pulsed laser deposition of YBa2Cu3O7 (YBCO) films on steep steps in epitaxial LaAlO3 substrates. The steps were prepared by Ar-ion milling and the YBCO thin films were patterned either by Ar-ion milling or by an inhibit process. The current-voltage (I-V) characteristics and the Josephson emission of a single SEJ show that it consists of two resistively shunted-junction-type (RSJ) weak links in series which have different critical currents, IC1 and IC2. The I-V characteristics of our arrays were also close to the RSJ-model. The number of series-connected weak links deduced from the I-V curves was usually higher than the number of steps. Histograms of the individual weak link ICs showed two peaks at IC1 and IC2. The IC spread was about ±20% to ±40% of these two values. Radiation from arrays was detected and an evidence of phase locking in Josephson junction clusters obtained.
Dynamic response of short-cavity semiconductor lasers
Authors: Jahnke F. , Koch S. W. , Henneberger K.
Published: July 2002

The influence of many-body, carrier-carrier, and carrier-photon interaction on the dynamic response of microcavity semiconductor lasers is investigated. It is shown how the switch-on dynamics is governed by the spectrally resolved gain-loss compensation. Transient instabilities and relaxation oscillations are discussed and their suppression through spontaneous emission enhancement is demonstrated.
Hall effect measurements on boron-doped, highly oriented diamond films grown on silicon via microwave plasma chemical vapor deposition
Authors: Stoner B. R. , Kao Chien-teh , Malta D. M. , Glass R. C.
Published: July 2002

A highly oriented, (100) textured diamond film was grown on a Si substrate, followed by the deposition of an epitaxial boron-doped layer for electrical characterization. Temperature-dependent Hall effect measurements were performed between 180 and 440 K. The 165 cm2/V⋅s hole mobility measured at room temperature is approximately five times greater than the highest reported mobilities for polycrystalline diamond. The relative improvement in the electronic quality of diamond films grown on Si, due to the reduction of misorientation and grain boundary angles, has been demonstrated. X-ray diffraction pole measurements were performed on the (100) oriented film in order to quantify the degree of misorientation.
SrTiO3 buffer layers and tunnel barriers for Ba-K-Bi-O junctions
Authors: Baumert B. A. , Talvacchio J. , Forrester M. G.
Published: July 2002

Epitaxial SrTiO3 films were used as buffer layers and tunnel barriers for Ba0.6K0.4BiO3 (BKBO) films and tunnel junctions, respectively. In contrast to BKBO films grown directly on LaAlO3, films grown on SrTiO3 (001) buffer layers on LaAlO3 had a single (001) growth orientation, with Tc’s of 26 K and Δω=0.7°. These values are both equal to those obtained for growth on a SrTiO3 single crystal. A similar improvement was obtained for BKBO grown on SrTiO3-buffered NdGaO3 substrates. Tunnel junctions consisting of BKBO(001)/SrTiO3/BKBO layers had substantial contributions to the gap voltage from both the base and top BKBO electrodes.
KrF excimer laser projection patterned deposition of aluminum from triethylamine alane as adsorbate precursor
Authors: Foulon F. , Stuke M.
Published: July 2002

KrF pulsed excimer laser-induced decomposition of the triethylamine alane [(C2H5)3NAlH3] precursor in the adsorbed phase is shown to allow projection patterned deposition of Al at room temperature. The deposited height increases linearly with the laser energy dose suggesting that the decomposition is photolytically driven. Mirrorlike Al films are deposited at rates up to about one Al monolayer per pulse which corresponds to rates up to 2 μm/min when photolyzing at 100 Hz. Al films with good adhesion and resistivities down to 7.5 μΩ cm (2.5 times bulk), were deposited on quartz, Al2O3, and GaAs substrates. The process has good spatial selectivity. Patterns with 1 μm resolution have been generated.
Direct measurements of electron-optical photon scattering rates in ultrathin GaAs-AlAs multiple quantum well structures
Authors: Tsen K. T. , Joshi R. , Morkoç H.
Published: July 2002

Electron-optical phonon scattering rates in ultrathin GaAs-AlAs multiple quantum well structures have been directly measured by using time-resolved Raman spectroscopy on a subpicosecond timescale. We have found that when the GaAs well width increases from 20 to 60 Å, electron-AlAs-like-optical phonon scattering rate decreases by a factor of about 3. The experimental results are explained with theoretical calculations of electron-optical phonon interactions recently carried out by K. Huang and B. Zhu [Phys. Rev. B 38, 13377 (1988)].
Photon-induced anisotropic oxidation along p-n junctions in AlxGa1−xAs-GaAs quantum well heterostructures
Authors: Maranowski S. A. , Holonyak N. , Richard T. A. , Kish F. A.
Published: July 2002

Data are presented demonstrating, in ‘‘wet’’ oxidation, anisotropic oxide formation at p-n junction edges in AlxGa1−xAs-GaAs quantum well heterostructures (QWHs). The QWH high gap AlxGa1−xAs upper confining layer is oxidized via H2O vapor at elevated temperatures (425–525 °C). The higher energy portion of ‘‘blackbody’’ radiation (the furnace ambient) at these temperatures generates sufficient electron-hole pairs to drive anodic oxidation at the edge of a QWH p-n junction. The anisotropic oxidation, on the p-type side of the junction, and possible reaction mechanisms are described.
Microcavity effects in the photoluminescence of GaAs microcrystals
Authors: Juen S. , Überbacher K. , Baldauf J. , Lamprecht K. F. , Höpfel R. A.
Published: July 2002

We have fabricated submicron GaAs crystals by pulverization of bulk material. Size selected crystals exhibit modified photoluminescence spectra with blue shifts of up to 10 meV. The observed behavior is explained by the enhancement and the inhibition of spontaneous emission in a three-dimensional optical microcavity formed by a semiconductor microcrystal.
New model for a capacitance increase of a capacitor with hemispherical grains
Authors: Matsuo Naoto
Published: July 2002

A new model that clarifies the dependence of the increase of a storage capacitance of the hemispherical grains (HSGs) capacitor both on the grain size and the oxide nitride oxide (ONO) thickness is proposed and discussed. This model assumes the effective area with a constant ONO thickness on the grain. The ratios of the storage capacitance of the HSGs capacitor to that of the conventional stacked capacitor calculated by this model coincide with the experimental data at the different ONO thickness and the different grain size. It is because the effective area increases that the ratios of the storage capacitance increase as the grain size becomes large and the ONO thickness becomes small.
Secondary ion mass spectrometry of InGaAs/InP (100) multiple layers grown by chemical beam epitaxy
Authors: Williams M. D. , Chiu T. H. , Storz F. G. , Shunk S. C. , Ferguson J. F.
Published: July 2002

Secondary ion mass spectrometry was used to study the effect of substrate temperature on the composition and growth rate of InGaAs/InP multilayers grown by chemical beam epitaxy. The dependence on the As overpressure was also studied for the first time by this technique. The substrate temperature effects that we observed are in good agreement with published results from x-ray diffraction and Auger electron spectroscopy studies. The Ga/In ratio was observed to decrease with increasing arsine flow rate in contradiction to previously reported results.
Electron holography in the study of the leakage field of magnetic force microscope sensor tips
Authors: Matteucci G. , Muccini M. , Hartmann U.
Published: July 2002

Electron holography is applied to the investigation of the leakage magnetic field produced by sharp ferromagnetic probes employed for magnetic force microscopy. Using the double exposure technique, interference fringes were obtained which show a good qualitative agreement with calculations based on a macroscopic dipole model for the sensor tips. Magnetic flux measurements are possible through the evaluation of the phase difference in the simulated map of the dipole field.