bluuebunny/crossref_metadata_2025 huggingface dataset:
Focused ion beam fabrication of single grain Bi2Sr2Ca1Cu2Ox submicron bridges
Authors: Zitkovsky I. D. , Hu Qing , Orlando T. P. , Melngailis J. , Tao Tao
Published: July 2002

Superconducting microbridges have been patterned by direct milling of the Bi2Sr2Ca1Cu2Ox polycrystalline thin films using focused ion beam. Several single grain and multigrain bridges of sizes as small as 0.3 μm have been fabricated. Single grain microbridges exhibit a linear temperature dependence of the critical current density with Jc=106 A/cm2 at 8 K, and zero magnetic field. Larger 50–100 μm bridges show lower critical current densities of Jc=104–105 A/cm2. The current-voltage (I-V) and the Jc vs T characteristics show two qualitatively different types of superconducting weak links. The single grain microbridges behave as homogeneous superconductors with transport exhibiting flux creep and flux flow. The large bridges can be characterized as granular superconductors with weakly connected grains, and their I-V and the Jc vs T characteristics are dependent on processing conditions.
Donor-acceptor pair formation in InP doped simultaneously with Si and Zn during metalorganic chemical vapor deposition
Authors: Blaauw C. , Hobbs L.
Published: July 2002

Deposition of InP by metalorganic chemical vapor deposition, simultaneously doped with both a donor (Si) and an acceptor (Zn) species during the growth, has been carried out. The incorporation of Si is not affected by the presence of Zn, but the Zn incorporation is substantially enhanced by the presence of Si. These results are consistent with the formation of donor-acceptor pairs, which has been suggested earlier to explain Zn diffusion profiles in Si-doped InP.
Measurements of transmitted diffraction profiles on Bragg angles at π/2
Authors: Giles C. , Cusatis C.
Published: July 2002

Transmitted diffraction profiles of a thin Ge 620 crystal at Bragg angles around and including π/2 were obtained for different crystal temperatures using Co Kα1 radiation. A grooved crystal monochromator operating at Bragg angles near 89.5°, providing a highly monochromatic beam in the forward direction, is described. Rocking curves widths of 30 arcmin and energy resolution ΔE/E=1.66×10−5 were measured. Great sensitivity with crystal temperature and incident wavelength were observed. An intensity enhancement at the normal incidence position due to multiple diffraction occurrence was detected.
Ultrashort pulse generation from a Q-switched AlGaAs laser with cw injection
Authors: Stelmakh N. , Lourtioz J-M. , Barthelemy A.
Published: July 2002

Injection of a weak cw radiation in a Q-switched AlGaAs laser diode is shown to produce single-mode pulses with a quasi-linear downchirp of very large amplitude. Strong pulse compression can be achieved by using single-mode dispersive fibers at the laser output. Time-resolved spectroscopic measurements of the laser pulses are presented. Optical solitary pulses shorter than 2 ps are obtained after compression, which corresponds to a pulse compression factor larger than 15. Although the laser-fiber coupling is not fully optimized, peak powers exceeding 3 W are measured at the fiber output. These performances are believed to be the best ever reported for an electrically pumped Q-switched AlGaAs laser diode.
Highly sensitive NpnP optoelectronic switch by AlAs regrowth
Authors: Kuijk M. , Heremans P. , Borghs G.
Published: July 2002

A double-heterostructure NpnP optoelectronic switching device, with an extreme optical sensitivity and low holding power, has been fabricated. A decrease in breakover voltage of 650 mV is obtained at a light illumination of only 5 nW for a 50×50 μm2 device. To achieve this high sensitivity, the surface generation/recombination currents at the edges of the devices have been reduced by passivating the device perimeter with a regrowth of 50 nm AlAs (lowly p doped).
Enhancement of deposition rates in the reactive sputtering of silicon exposed to an argon-oxygen plasma
Authors: Ohwaki Takeshi , Taga Yasunori
Published: July 2002

Silicon oxide films were prepared by the reactive radio frequency (rf) sputtering in an Ar-O2 plasma. The deposition rates were measured as a function of oxygen mole fraction in the sputtering gas and sputtering power. It was found that the deposition rate was abruptly enhanced at a critical oxygen mole fraction in an Ar-O2 plasma. This enhancement was attributed to chemical sputtering of the Si target by argon ion bombardment in the oxygen atmosphere. Thus, the reactive sputtering of a Si target in an argon-oxygen plasma was found to consist of three modes, namely, (i) physical sputtering of oxidized target surface, (ii) chemical sputtering, i.e., release of species having very low energy, and (iii) physical sputtering of metallic target surface.
Wide area near afterglow oxygen radical source used as a polymer resist asher
Authors: Yu Zengqi , Collins George , Hattori Shuzo , Sugimoto Dai , Saita Masahiro
Published: July 2002

An active oxygen plasma of disk shape is used to ash photoresist films with ±5% variation in the uniformity over 15-cm-diam wafers located in a field-free downstream region which we term the near afterglow. In the near afterglow the resist surface is exposed primarily to both an atomic oxygen flux (1018 atoms cm−2 s−1) as well as a flux of 130.6 nm oxygen resonance radiation (10−3 W cm−2 Sr−1). Under these conditions an ashing rate of 1.5 μm/min for OFPR-800 resist is obtained at 100 °C substrate temperature, with an etch activation energy of 1.1 kcal/mol.
Molecular beam epitaxy and characterization of HgCdTe(111)B on Si(100)
Authors: Sporken R. , Lange M. D. , Sivananthan S. , Faurie J. P.
Published: July 2002

Up to 10-μm-thick HgCdTe(111)B films with 3 in. and 5 in. diameter were grown on Si(100) substrates. The films are n type, and Hall mobilities higher than 5×104 cm2 V−1 s−1 have been measured at 23 K for Cd concentration 0.26. Double-crystal rocking curves of the HgCdTe(333) x-ray diffraction peak with full width at half maximum as low as 180 arcsec were measured, indicating that the crystalline quality of the HgCdTe is significantly better than that of the CdTe. The Cd concentration of these films is very uniform, with a standard deviation of 2.4% of the average concentration for 5 in. samples and 0.6% for 3 in. samples.
Comparison of the theoretical and experimental differential gain in strained layer InGaAs/GaAs quantum well lasers
Authors: Lester L. F. , Offsey S. D. , Ridley B. K. , Schaff W. J. , Foreman B. A. , Eastman L. F.
Published: July 2002

A theoretical model that uses simple, analytic valence band equations to calculate the differential gain in strained layer InGaAs/GaAs quantum wells shows good agreement with experimental differential gain values obtained from multiple quantum well strained layer lasers. The differential gain in these devices is 7 times greater than in bulk, p-type doped InGaAsP lasers. Calculations including nonlinear damping effects indicate that modulation bandwidths exceeding 60 GHz should be achievable in strained layer quantum well lasers.
Time-resolved phonon-assisted stimulated emission in AlGaAs-GaAs quantum wells
Authors: Benjamin S. D. , Lo Y. C. , Kolbas R. M.
Published: July 2002

Time-resolved photoluminescence of phonon-assisted stimulated emission is reported for the first time. The temporal characteristics of the phonon-assisted stimulated emission are distinct from the stimulated emission from the quantum states. The phonon-assisted recombination is always delayed in time with respect to the confined particle transitions and has a larger full width at half maximum than the confined particle transitions. The dynamics of stimulated phonon emission along with the smaller transition probability for the phonon-assisted process may account for the distinct temporal characteristics. Data are presented on the emission intensity versus wavelength versus time from which the dependence of the delay on excitation intensity is extracted.
Stress-free GaAs grown on Si using a stress balance approach
Authors: Freundlich A. , Grenet J. C. , Neu G. , Stobl G.
Published: July 2002

A novel technique, based on a stress balance principle, is proposed to control residual stress magnitude in GaAs layers grown on Si substrates. It is demonstrated that, using a suitable GaAs1−xPx buffer layer, room (300 K) or low (2 K) temperature stress-free GaAs can be grown on Si (100).
Piezoelectrically induced stress tuning of electro-optic devices
Authors: Hung C.-Y. , Schlesinger T. E. , Reed M. L.
Published: July 2002

Photoluminescence measurements have been made on GaAs samples stressed with piezoelectric bimorphs. We show that measurable shifts in the energy gap can be obtained by mechanically stressing the semiconductor with a piezoelectric transducer. This principle can be applied to fabricate a class of wavelength-tunable electro-optic devices, such as tunable semiconductor lasers, light-emitting diodes, and photodetectors.
Conduction band structure of GexSi1−x using spatially resolved electron energy-loss scattering
Authors: Batson P. E. , Morar J. F.
Published: July 2002

Transmission electron energy-loss spectroscopy has been used to follow the positions of the Δ1 and L1 conduction-band minima, and the L3 saddle point, as a function of Ge content in GexSi1−x (x=0–0.95) alloys. By analyzing the shape of the Si 2p→conduction-band (CB) spectra we find that L3 and Δ1 shift largely together, as the band-structure compatibility relations predict. L1 shifts rapidly downwards with respect to Δ1 as the Ge content increases. Measurements were carried out in a scanning transmission electron microscope at a spatial resolution of better than 2 nm. Based on these results, this technique can be used to identify the composition of thin GexSi1−x alloys with a precision of better than 5%.
Transient electric field generated by nonequilibrium states in superconducting Pb films
Authors: Hu Xin-Hua , Juhasz T. , Bron W. E.
Published: July 2002

Nonequilibrium states can be excited in superconducting Pb films with laser pulses of picosecond duration. We used the technique of electro-optic sampling to observe the transient electric field generated by these states in the presence of a supercurrent. It follows from our experiment that the switching between the superconducting and normal states occurs within 1 ps after the laser excitation.
Raman intensity enhancement of the Si peak by CdS thin films
Authors: Dai C. M. , Chuu D. S. , Hsieh W. F.
Published: July 2002

A method, which utilizes interference enhanced Raman scattering and resonant Raman scattering techniques, is used to overcome the low efficiency of Raman methods to diagnose highly reflective materials. As applied to the p-type Si wafer, the enhanced gain is up to nearly a factor of 80 at 4880 Å excitation. Because of the strong absorption of the scattered light, it is recommended that the suitable deposited thickness of CdS films should not be thicker than 700 Å.
Accurate measurement of the vacancy equilibrium concentration in silicon
Authors: Zimmermann H.
Published: July 2002

A procedure is described which allows the measurement of the equilibrium concentration of vacancies in silicon at 800 °C. During a long lasting temperature treatment under inert and very clean conditions, the equilibrium concentration of the vacancies is established. According to the dominance of the Frank–Turnbull mechanism during platinum diffusion at 800 °C, the equilibrium concentration of vacancies C*V can then be determined from platinum diffusion profiles. A value of 4.1×1013 cm−3 at 800 °C for C*V is calculated using an analytical expression, which can be deduced from the equations of the Frank–Turnbull mechanism. For the vacancy diffusion coefficient in silicon, the result is 1.3×10−10 cm2 s−1. Numerical simulations show the self-consistency of the vacancy parameters.
Formation of monolithic masks for 0.25 μm x-ray lithography
Authors: Celler G. K. , Trimble L. E. , Frackoviak J. , Jurgensen C. W. , Kola R. R. , Novembre A. E. , Weber G. R.
Published: July 2002

We have constructed monolithic masks for proximity x-ray lithography by forming 1 μm thick polycrystalline Si membranes directly on glass support frames. Finished masks are 78 mm in diameter and ∼5 mm thick, with the Si membrane spanning 27 mm. The monolithic design provides simple processing and unprecedented flatness of 30 nm across the membrane and <500 nm across the entire disk. Mask blanks were metallized with 500 nm of W that was sputter deposited under conditions that hold the film stress <50 MPa. Tungsten was patterned by reactive ion etching to form features as small as 0.25 μm.
Oxygen-vacancy ordering in Y2Ba4Cu7O15−ε
Authors: Krekels T. , Van Tendeloo G. , Amelinckx S. , Karpinski J. , Kaldis E. , Rusiecki S.
Published: July 2002

Y2Ba4Cu7O15−ε samples prepared at high oxygen pressures were investigated by means of electron microscopy. Often grains show modulations along the a[100] direction, identified as oxygen-vacancy chain ordering of the type previously observed in the 123 compound. This identification is suggested by electron diffraction and high resolution data and is supported by image simulations. Compared to the original model of chain ordering in the CuO layer a deformation of the neighboring BaO layers is included here.
1.3 μm InGaAsP/InP multiquantum well buried heterostructure lasers grown by chemical-beam epitaxy
Authors: Tsang W. T. , Choa F. S. , Logan R. A. , Tanbun-Ek T. , Wu M. C. , Chen Y. K. , Sergent A. M. , Wecht K. W.
Published: July 2002

High performance InGaAsP/InP multiquantum well (MQW) buried heterostructure lasers emitting around 1.3 μm were prepared for the first time by chemical-beam epitaxy. At 20 °C, continuous-wave (cw) threshold currents were 5–8 mA and quantum efficiencies were 0.35–0.45 mW/mA for 250 μm long lasers having one facet ∼85% reflective coated. At 80 °C, the cw threshold currents remained low, 23 mA, quantum efficiency stayed high, 0.22 mW/mA, and output power of ∼10 mW was achieved. cw power output as high as 125 mW was achieved with 750 μm long lasers having AR–HR (∼5%–85%) coatings. Lasers with bulk active were also studied for comparison. Though they also have excellent device performance, in general, they are somewhat inferior to MQW lasers.
Mechanisms affecting long conduction time plasma opening switches
Authors: Parks Donald , Waisman Eduardo , Katz Ira
Published: July 2002

Experimental evidence suggests that long conduction time (≥ (R18)1 μs) plasma opening switches open more slowly than expected on the basis of magnetic forces, and perhaps even on the basis of plasma erosion. We propose that the slow opening is associated with charge exchange with and/or electron ionization of neutral particles produced in the switch gap during and/or prior to the power pulse. The possibility of such mechanisms bears on the choice of switch plasma and on surface conditioning procedures in the development of fast opening switch technology.
Control of hydrocarbon radicals and film deposition by using a whistler wave discharge in range of radio frequency
Authors: Mieno T. , Shoji T. , Kadota K.
Published: July 2002

Production of hydrocarbon radicals is controlled by using a whistler wave discharge in range of radio frequency in a low pressure region (∼0.1 Pa). Plasma density of 1010–1013 cm−3, electron temperature of 2–20 eV is obtained for the discharge of the admixture of Ar and small content of source gases (CH4, C2H2, CO). Spectroscopic measurement indicates that densities of CH and H radicals and the deposition rate of amorphous carbon:H film increase with electron density, electron temperature, and source gas pressure. The etching effect of H atoms influences on the deposition rate and a high deposition rate (90 μm/h for CO/Ar discharge) is obtained even in a low neutral pressure discharge.
Patterning of epitaxial YBa2Cu3Ox insulator multilayers with a high-temperature-resistant lift-off mask
Authors: Roas B.
Published: July 2002

A new process for patterning of YBa2Cu3Ox-insulator multilayers is described, using a high-temperature-resistant CaO process mask, which can be evaporated directly onto previously patterned YBa2Cu3Ox layers and removed after film deposition. A crossover contact of two 3 μm wide and 30 μm long YBa2Cu3Ox striplines has been fabricated by laser deposition, using this patterning technique. The upper and the lower stripline of the crossover contact show Tc values of ≊89 K and a critical current density jc (77 K) of 2 and 4×106 A/cm2, respectively. The contact between the upper and the lower stripline is superconducting below 87 K. At 100 K, the normal conducting contact resistivity is 5×10−8 Ω cm2, based on a contact area of 3×3 μm.
Surface-emitting laser-based optical bistable switching device
Authors: Zhou Ping , Cheng Julian , Sun S. Z. , Schaus C. F. , Hains C. , Myers D. R. , Vawter G. A.
Published: July 2002

The first experimental demonstration of a surface-normal bistable optical switching device based on the monolithic integration of a vertical-cavity surface-emitting laser and a pnpn photothyristor is reported. By the use of ion implantation, it is shown that the positive feedback in the photothyristor can be controlled, thus enabling the integration of both bistable and latching optical switches on the same epitaxial structure. High contrast (30 dB) and an optical gain of 8 are demonstrated.
Realignment of As doped polycrystalline Si films by double step annealing
Authors: Benyaïch F. , Priolo F. , Rimini E. , Spinella C. , Ward P.
Published: July 2002

The realignment by rapid thermal annealing of polycrystalline silicon layers deposited onto 〈100〉 Si substrates can occur either through the planar movement of the interface towards the surface or through the lateral growth of columnar epitaxial islands. An anneal at 1075 °C for 15 s, followed by As implantation, is shown to cause planar growth even at subsequent anneal temperatures as low as 900 °C. In contrast, the direct annealing of As implanted samples induces columnar realignment. Further, the As redistribution throughout the polycrystalline layers and its diffusion in the crystalline substrate is considerably reduced in the case of the double step annealing. The different regrowth modes are related to the morphology of the interfacial oxide layer and to the microcrystalline structure of the polycrystalline layers during the initial stages of the realignment process.
Fe-P-B ultrafine amorphous particles produced by chemical reduction
Authors: Shen Jianyi , Hu Zheng , Hsia Yuanfu , Chen Yi
Published: July 2002

A new kind of ultrafine amorphous particles Fe82P11B7 have been successfully prepared by the reaction of Fe(III) chloride, sodium hypophosphite and potassium borohydride in aqueous solution. X-ray diffraction and Mössbauer spectroscopy confirmed the amorphous structure of the particles and scanning electron microscopy showed that the particles are nearly spherical with the diameters from 150 to 350 nm. The structure relaxation and crystallization of the amorphous particles were also studied by Mössbauer spectroscopy. It is found that the particles began to crystallize when annealed at 573 K, below which, no crystalline phases were formed, but the amorphous structure significantly varied. The particles crystallized to form α-Fe and Fe3(P0.6B0.4) completely when annealed at 673 and 773 K.
Solid phase epitaxial seed for laser-crystallized silicon on glass substrates
Authors: Doi Atsutoshi , Kumikawa Masa-ichi , Konishi Jyun-ichi , Nakamizo Yoshiyuki
Published: July 2002

A new method for obtaining thin silicon film on glass substrates (SOG) has been introduced. This technique uses solid phase epitaxy (SPE) and laser crystallization to fabricate an orientation-controlled SOG structure. Heat treatment of amorphous SOG substrate in contact with mesa striped (100)-oriented Si seed crystal was performed at 543 °C for 16 h to form the SPE layer. The most important feature of the present external seeding technique is the separation of the seed from the substrate after SPE. Successful demonstration of seeded laser crystallization shows the usefulness of the external seed SPE.
Epitaxial YBa2Cu3Ox thin films on sapphire using a Y-stabilized ZrO2 buffer layer
Authors: Schmidt H. , Hradil K. , Hösler W. , Wersing W. , Gieres G. , Seeböck R. J.
Published: July 2002

Epitaxial, c-oriented YBa2Cu3Ox thin films were deposited by dc sputtering on (11̄02)-sapphire substrates with an intermediate buffer layer of Y-stabilized ZrO2 (YSZ), which was grown by rf magnetron sputtering. The epitaxy of the YSZ and the YBa2Cu3Ox films was proved by Rutherford backscattering spectrometry combined with ion channeling. The YBa2Cu3Ox films exhibited transition temperatures of 90 K and had critical current densities exceeding 1.2×106 A/cm2 at 77 K in zero magnetic field.
Triangular structures on tungsten diselenide induced and observed by scanning tunneling microscopy
Authors: Akari S. , Möller R. , Dransfeld K.
Published: July 2002

By applying voltage pulses of about −5 V at the tip of a scanning tunneling microscope triangular structures have been created on the atomically flat WSe2 surface. The evolution from a cluster-like structure directly after the pulse to an equilateral triangle occurs within minutes. The growth of the triangles has been investigated for times up to 1 h. For a given orientation of the substrate all the triangles have the same orientation thereby reducing the sixfold symmetry at the atomic Se surface to the threefold symmetry of a full molecular WSe2 layer.
Measurement and modeling of the fast collapse of HgCdTe metal-insulator-semiconductor devices
Authors: Meyassed M. , Nemirovsky Y.
Published: July 2002

Hg1−xCdxTe metal-insulator-semiconductor (MIS) devices with x≂0.22 often exhibit very short storage times that are determined by minority-carrier dark currents. This study describes a novel system, for measuring the fast collapse of such devices. The measurement and modeling of the dark current during the fast collapse process is presented. A quantitative correlation is noticeable between the experimental results and theoretical calculations which assume that thermal-trap-assisted tunneling is the dominant dark process. The results demonstrate the importance of trap-assisted tunneling in narrow band-gap HgCdTe, and that this process causes short storage times.
Low-frequency magnetic field mixing near period doubling bifurcation of a fiber-optic magnetometer
Authors: Vohra S. T. , Bucholtz F.
Published: July 2002

A magnetically driven magnetostrictive sample, which is used as the sensing element in a fiber-optic magnetometer, is known to exhibit strain bifurcations. Standard techniques for fiber-optic magnetostrictive magnetometers employ demodulation at a carrier frequency ωc but, typically, the resolution is limited by 1/f noise around ωc. We present a novel technique for the detection of low-frequency magnetic signals which employs the frequency associated with a period doubling bifurcation ωc/2, and which avoids upconverted 1/f noise near ωc. The signal-to-noise ratio of low-frequency magnetic signals near ωc/2 remains flat in the range 0.025–10 Hz, with a resolution of 5 nT/√Hz for a sensor using only 5 mm of fiber, limited by the phase noise of the fiber interferometer.
Current controlled GaAs/AlGaAs multiple quantum well phase shifter operating at 0.9 μm
Authors: Chuang C. L. , Yoon T. , Jin R. , Xu J. , Khitrova G. , Gibbs H. M. , Fu R. , Hong C. S.
Published: July 2002

An optical phase shifter with current injection has been demonstrated in a GaAs/AlGaAs multiple quantum well (MQW) single mode waveguide. Phase shifts at different wavelengths have been measured and compared with the theory in L. Banyai and S. W. Koch, Z. Physik B 63, 283 (1986). A 3π phase shift has been achieved in a 400-μm-long waveguide with almost no material absorption.
Multiple-quantum-well nonlinear waveguide grating device
Authors: Cada M. , Vasey F. , Stauffer J. M. , Reinhart F. K.
Published: July 2002

We report on the preliminary experimental demonstration of a multiple-quantum-well waveguide grating element. Due to optical nonlinearities in a multiple-quantum-well layer incorporated into the structure, the out-coupling angle of the grating is varied by the intensity of light in a guided mode. Experiments with GaAs-based planar as well as rib waveguide samples confirmed theoretical predictions. Changes in the coupling angle obtained are on the order of minutes. The demonstrated principle can be employed in fine tuning of the coupling angle, fine focusing of the output beam, or as a nonlinear beam-steering method for dispersion measurements.
Thermally stable, low-resistance NiInWNx ohmic contacts to n-type GaAs prepared by sputter deposition
Authors: Murakami Masanori , Lustig Naftali , Price W. H. , Fleischman A.
Published: July 2002

A new thermally stable, low-resistance In-based ohmic contact to n-type GaAs has been developed. The contacts consist of ion-beam sputtered Ni (5 nm)/In (5 nm)/Ni (5 nm) layers with a magnetron sputtered WNx overlayer. A low-contact resistance of ∼0.3 Ω mm was obtained by rapid thermal annealing at 750 °C for ∼5 s. The contact resistance and the excellent contact morphology remained unchanged after annealing at 400 °C for more than 100 h. The present deposition technique provides several advantages over previously reported electron-beam evaporated In-based contacts. In particular, the ability to deposit a thick WNx overlayer simplifies GaAs integrated circuit (IC) fabrication by (a) eliminating the need for separate diffusion barrier deposition and patterning steps, and (b) providing for low-sheet resistance (∼2 Ω/⧠) IC interconnect capabilities. In addition, sputter deposition allows for the controlled incorporation of n-type dopants into the metallization if further reduction of the contact resistance is required.
SiO2 film decomposition reaction initiated by carbon impurities located at a Si-SiO2 interface
Authors: Raider S. I. , Herd S. R. , Walkup R. E.
Published: July 2002

We have annealed Si-SiO2 structures at an elevated temperature in He(g) with SiO(g) added to the ambient. A SiO2 decomposition reaction that normally forms large voids in a thin SiO2 film during annealing in He(g) is not detected with the added SiO(g). Instead, chemically reactive SiC impurity sites which initiate the SiO2 decomposition reaction are found segregated along crystallographic planes in the substrate at the Si-SiO2 interface. The mechanism and technological importance of this interfacial reaction are discussed.
Electron-paramagnetic-resonance study of the isolated arsenic antisite in electron irradiated GaAs and its relation to the EL2 center
Authors: Rong F. C. , Buchwald W. R. , Harmatz M. , Poindexter E. H. , Warren W. L.
Published: July 2002

Arsenic antisites produced in GaAs by room-temperature electron irradiation (RTEI) are examined by electron paramagnetic resonance (EPR). For the first time, this RTEI antisite, which has been believed to be the isolated antisite, is found to be metastable. The most efficient photon energy for photoquenching is found to be approximately 1.15 eV, which is very close to that observed for the well-known EL2 center in undoped semi-insulating GaAs. However, the thermal recovery temperature is about 200–250 K, much higher than that for the EL2 center.
Selective plasma etching of Ge substrates for thin freestanding GaAs-AlGaAs heterostructures
Authors: Venkatasubramanian R. , Timmons M. L. , Colpitts T. S.
Published: July 2002

Selective plasma etching of Ge with a CF4/O2 mixture is used to produce freestanding GaAs-AlGaAs thin films. The etch rate of Ge substrates is as high as 150 μm/h at temperatures of 75 °C under optimized conditions and with a negligible etch rate for GaAs and AlGaAs materials. This plasma etching technique, combined with a lattice-matched growth of GaAs-AlGaAs structures on Ge substrates, has a variety of potential device applications. The characteristics of this etch process and the photoluminescence of freestanding AlGaAs-GaAs structures are presented.
High-power cw operation of InGaAs/GaAs surface-emitting lasers with 45° intracavity micro-mirrors
Authors: Ou S. S. , Jansen M. , Yang J. J. , Mawst L. J. , Roth T. J.
Published: July 2002

High-power cw operation of horizontal-cavity, monolithic InGaAs/GaAs surface-emitting lasers with all dry etched micro-mirrors has been demonstrated for the first time. The 45° and 90° micro-mirrors of the devices were fabricated by ion-beam etching and reactive ion etching techniques, respectively. Threshold-current densities of less than 500 A/cm2, external differential quantum efficiencies of 10% (0.12 W/A) from the emitting facet, and output powers in excess of 100 mW were achieved from uncoated devices driven under cw operation.
In situ observation of phase transition in potassium niobate single crystal by synchrotron radiation topography
Authors: Zhao Jiyong , Yang Ping , Jiang Shusheng , Jiang Xiaoming , Jiang Jianhua , Xian Dingchang , Geng Zhaohua , Zou Qun
Published: July 2002

The structure of domains and their evolution with temperature in potassium niobate (KNbO3) single crystals were studied by synchrotron radiation topography at Beijing Synchrotron Radiation Laboratory. The 90° domain disappears after the phase transition at about 224 °C, while the 60° (or 120°) domain still exists in the specimen.
Excimer-laser-induced sub-0.5-μm patterning of WO3 thin films
Authors: Rothschild M. , Forte A. R.
Published: July 2002

Amorphous WO3 thin films have been deposited in a plasma-enhanced chemical vapor deposition system, and were patterned with a 193-nm excimer laser (one pulse, 10–25 mJ/cm2). Negative-tone, sub-0.5-μm lines and spaces were obtained following dry development in a low-power CF4 plasma. The mechanism for laser-induced etch selectivity was studied with angle-resolved x-ray photoelectron spectroscopy. It was inferred from the fluorine photoelectron spectra that the laser induces atomic rearrangements that impede the etch process initiated by fluorine-containing radicals. A possible interpretation is that the rearrangements, which may be partially thermally activated, reduce the volume of the microvoids present in WO3.
Ultracompact monolithic integration of polarization diversity waveguide/photodiodes
Authors: Deri R. J. , Hawkins R. J. , Caneau C. , Pennings E. C. M. , Andreadakis N. C.
Published: July 2002

We demonstrate a monolithically integrated waveguide polarization diversity photodector on InP with total length below 210 μm. High quantum efficiency (87% TE) and extinction ratios of 10.6 dB (TE) and 16 dB (TM) are achieved at 1.5 μm wavelength with simple fabrication processes. The device employs extremely short (21 and 31 μm) waveguide photodiodes that are suitable for high bandwidth operation.
Structural modulations of Bi2Sr2CuO6 studied by in situ x-ray diffraction
Authors: Shen Y. , Richards D. R. , Hinks D. G. , Mitchell A. W.
Published: July 2002

High-temperature x-ray diffraction has been carried out on a superconducting single-phase sample of pseudo-tetragonal Bi2Sr2CuO6+y, which was obtained from crystallization of thin glassy platelets. The sample displayed (00l) preferred orientation, which made it possible to determine the incommensurate modulation by conventional θ−2θ x-ray scans. The existence of the modulation peaks (800 °C) indicates that the modulation cannot be caused solely by oxygen ordering. As temperature increased, it was observed that a decrease in the intensity of modulation lines was associated with an increase in intensity of fundamental reflection, which was similar to the order-disorder phase transition. By removing 0.045(5) oxygen atom per formula unit, the components of modulation satellites along the b* and c* directions changed from bmod=0.183(9) and cmod=0.315(4) to 0.184(6) and 0.260(4), respectively. This demonstrates that oxygen, while not the sole cause, does play a role in the formation of the structural modulation. However, the invariance of bmod with respect to the change in oxygen content does not support the model which explained the modulation by inserting extra oxygen in BiO plane.
Freely suspended liquid crystal film transfer: A new method of creating thin smectic films on solid substrates
Authors: Maclennan Joseph , Decher Gero , Sohling Ulrich
Published: July 2002

A novel method of creating ultrathin, well-ordered organic multilayer films is described, in which freely suspended smectic liquid crystal films are transferred to solid substrates. X-ray and optical measurements show that both the smectic layering and the in-plane director field, which are the defining characteristic structures of the original free film, are maintained after transfer. This method, in contrast to traditional techniques of organic film deposition, offers the possibility of orienting the initial freely suspended liquid crystal films using applied fields to obtain highly organized monodomain structures after transfer.
Evidence for surface chemical reactions between gold and BiCaSrCuO
Authors: Hwu Y. , Lozzi L. , La Rosa S. , Onellion M. , Berger H. , Gozzo F. , Lévy F. , Margaritondo G.
Published: July 2002

We explored the reactivity of gold on cleaved 2212 BiCaSrCuO by synchrotron-radiation photoemission spectroscopy. We found no evidence for reactivity when the substrate was at room temperature, similar to what has been reported for very low temperatures (20 K). At intermediate temperatures (100 K), however, clear evidence was found of a chemical reaction with formation of a localized nonmetallic phase. These findings have potentially important implications for the manufacturing of devices based on BiCaSrCuO.
Ideal electronic properties of a p-Ge/p-Al0.85Ga0.15As interface
Authors: Venkatasubramanian R. , Timmons M. L. , Hutchby J. A.
Published: July 2002

The isotype p+-Ge/p-Al0.85Ga0.15As interface is examined in this study. It is shown that a lattice-matched epitaxial layer of p-Al0.85Ga0.15 on p+-Ge acts like a minority-carrier mirror. Evidence for this action comes from improved short-wavelength response of a p+-n Ge solar cell and from a tenfold reduction in the dark saturation current of a p+-n Ge junction. At the same time, the p+-Ge/p-Al0.85Ga0.15As interface is electrically transparent to majority-carrier hole transport. Similarity of measured specific resistivities of Ti/Au ohmic contacts directly to Ge and through a p-Al0.85Ga0.15As layer to p+ Ge leads to this conclusion in spite of about 1 eV valence-band offset at the Ge-Al0.85Ga0.15As heterojunction interface. A possible mechanism for the hole transport through such an interface is discussed.
Picosecond optical nonlinearities in lead chalcogenide semiconductors
Authors: Klann Robert , Buhleier Rainer , Elsaesser Thomas , Lambrecht Armin
Published: July 2002

Optical nonlinearities of PbSe are studied in picosecond pump-probe experiments at wavelengths from 4 to 8 μm. Excitation of an electron-hole plasma leads to a shift of the absorption edge to higher energies and to large changes of the refractive index by up to −0.1 for a carrier density of 4×1017 cm−3. The optical nonlinearities result from band filling by both electrons and holes. The time-dependent absorption change shows a partial recovery within 100 ps, giving evidence of enhanced recombination rates. Theoretical calculations of the absorption change are in agreement with the experimental data.
Influence of cobalt substitution on critical currents of YBa2Cu3O7−s
Authors: Kulkarni R. G. , Baldha G. J. , Bichile G. K. , Kuberkar D. G. , Deshmukh Smita
Published: July 2002

Co-doped YBa2Cu3O7−s samples prepared under identical conditions have been investigated by magnetization measurements as a function of temperature and field exhibiting pronounced M(H) hysteresis loops indicative of large flux pinning even as T approaches Tc. It is believed that the flux pinning arises due to the preferential substitution of Co in Cu(1) site, which acts as pinning center. A critical current density, Jc, of ∼106 A/cm2 is deduced from M(H) data at 13 K in a field of 1.5 kOe for YBa2(Cu1−xCox)3O7−s at x=0.01, which is nearly five times larger than the Jc of the pristine 1-2-3. The variation of Jc with atomic percent of Co-substitution in 1-2-3 shows a structural transition (orthorhombic to tetragonal) at 4 at. % of Co indicating structural dependence on Jc.
Relief of thermal stress in heteroepitaxial GaAs on Si by mesa release and deposition
Authors: De Boeck J. , Van Hoof C. , Deneffe K. , Mertens R. P. , Borghs G.
Published: July 2002

We demonstrate a mesa release and deposition (MRD) technology to realize stress relief in GaAs layers on Si, useful in practical device applications. A thin AlAs layer is incorporated in the heteroepitaxial GaAs layer about 1 μm from the GaAs/Si interface. Mesas are etched down to the AlAs release layer and subsequently underetched in a 5% HF solution at room temperature. Photoresist clamps keep the mesas in their exact position during the underetch process which results in a self-aligned redeposition on the substrate after resist removal. We used spatially resolved photoluminescence on 100×200 μm2 GaAs-on-Si mesas before and after the MRD process to demonstrate the stress relief. Uniform stress relief is found and the residual strain observed in the photoluminescence spectra at 77 K (0.05±0.02%) is attributed to strain thermally induced upon cooling from 300 to 77 K.
Method for measuring diffusion of moisture in polyimide
Authors: Chang Li-Hsin , Tompkins Harland
Published: July 2002

A method of easily measuring the diffusion coefficient for the diffusion of moisture in polyimide is proposed. A polyimide film which is sandwiched between a silicon wafer and a metal film is exposed at the edge to moisture for various lengths of time. The progression of the diffusion process is delineated by placing the sample on a hot plate at about 350 °C. The pressure of the moisture causes the metal film to bubble. Diffusion coefficients are calculated for two different forms of polyimide.
Photoluminescence excitation measurements of the absorption band gap in heavily carbon-doped GaAs
Authors: Wang Lei , Aitchison B. J. , Haegel N. M.
Published: July 2002

Photoluminescence excitation (PLE) spectroscopy has been used to study the optical absorption in epitaxial layers of heavily carbon-doped GaAs. Shifts of the PLE spectra with temperature and doping were observed. The location of the Fermi level was estimated to be 0.08, 0.22, and 0.24 eV below the top of the valence band in samples doped to 6.2×1019 cm−3, 1.6×1020 cm−3, and 4.1×1020 cm−3, respectively.
Electronic structure of BaSn1−xSbxO3, for 0.0≤x≤0.2
Authors: Eibschutz M. , Cava R. J. , Krajewski J. J. , Peck W. F. , Reiff W. M.
Published: July 2002

The Mössbauer effect of the 37.2 keV transition of 121Sb and the 23.88 keV γ transition of 119Sn has been employed to study the electronic configuration of Sb and Sn ions in the conducting materials BaSn1−xSbxO3 for 0≤x≤0.2. A single-resonance absorption line is observed for each isotope. The isomer shifts change slightly with Sb content and fall in the region corresponding to Sb(V) and Sn(IV) valence states, respectively. The Sb isomer shift (IS) of 7.5 mm/s is significantly depressed (∼1 mm/s) relative to its value in a typical Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm5pn hybridization. The Sn IS of 0.1 mm/s indicates that the Sn atoms in BaSn1−xSbxO3 are more covalent than in BaSnO3. Charge disproportionation of the Sn and Sb into Sn(II) and Sn(IV) or Sb(III) and Sb(V) has not been observed.
Boron diffusion in Co74Ti26 amorphous alloy
Authors: La Via F. , Janssen K. T. F. , Reader A. H.
Published: July 2002

Boron diffusion in implanted Co74Ti26 amorphous alloy has been studied by secondary ion mass spectrometry (SIMS). Auger electron spectroscopy depth profiling, Rutherford backscattering spectroscopy, and x-ray diffraction have been used to control the crystallization and the interaction with the Si substrate. By comparing computer simulations with the SIMS profiles, the diffusion coefficients of B in Co74Ti26 have been found in the temperature range between 300 and 400 °C. An activation energy of 1.63±0.05 eV and a preexponential factor of 1.77×10−3 cm2/s for the diffusion equation have been found. These values agree with an experimental correlation that appears to be valid for the diffusion in amorphous alloys of all elements with the exception of hydrogen.
Measurement of the conduction-band discontinuity in pseudomorphic InxGa1−xAs/In0.52Al0.48As heterostructures
Authors: Huang J.-H. , Chang T. Y. , Lalevic B.
Published: July 2002

Compositional dependence of the conduction-band discontinuity ΔEc in InxGa1−xAs/In0.52Al0.48As pseudomorphic heterostructures has been measured as a function of InAs mole fraction over the range of 0.44≤x≤0.64 using both current-versus-voltage-versus-temperature and capacitance-versus-voltage measurements on semiconductor-insulator-semiconductor structures. The results show a monotonic increase of effective ΔEc with InAs mole fraction x according to ΔEc≊0.384+0.254x for x≤0.54 and an abrupt shift to ΔEc≊0.344+0.487x for x≥0.58. The effects of the conduction-band nonparabolicity and the lattice strain on the Fermi potential have been taken into account in deducing ΔEc from the measured barrier height across the InxGa1−xAs/In0.52Al0.48As heterojunction.
Gated photoluminescence method for interface state density determination
Authors: Iyer R. , Lile D. L.
Published: July 2002

We have investigated the use of gated photoluminescence (PL) to estimate interface state density in III–V metal-insulator-semiconductor (MIS) structures. Low-temperature PL measurements have been recorded as a function of bias applied to the semi-transparent gate of a MIS diode. An analysis of these data resulted in surface state densities in the low 1010/cm2 eV range on sulfur passivated SiO2 coated InP. The present technique is more sensitive than the conventional 1 MHz capacitance-voltage (C-V) method, and less dependent on low leakage currents in the dielectric, when compared to the quasi-static C-V technique.
Annealing characteristics and thermal stability of electron beam evaporated ruthenium Schottky contacts to n-GaAs
Authors: Myburg G. , Auret F. D.
Published: July 2002

High quality ruthenium Schottky barrier diodes were fabricated on epitaxially grown n-GaAs, by the electron beam evaporation of Ru. Annealing studies were carried out in vacuum and in air. The effective barrier height and the flatband barrier height of the as-deposited Schottky contacts were 0.86 and 0.91 eV, respectively. These barrier heights reached their respective maximum values of 0.93 and 0.96 eV, after annealing at 450 °C in vacuum. The electrical characteristics of a third set of contacts, which was subjected to prolonged (1000 min) annealing at 400 °C in vacuum, showed no measureable signs of degradation.
Undepleted pump regime of Hill grating formation in optical fibers
Authors: Guo Baiming , Anderson Dana Z.
Published: July 2002

A bleaching model describing the dynamics of Hill grating formation in optical fibers, [K.O. Hill, Y. Fujii, D. C. Johnson, and B. S. Kawasaki, Appl. Phys. Lett. 32, 647 (1978)], is analytically solved in an undepleted pump approximation. This regime provides quantitative predictions about grating dynamics in the early stages of grating growth. A series of experiments in which heating effects and surface reflections from the input end of the fiber have been eliminated show quantitative agreement with the theory to 2%.
Superconducting electron focusing and guiding based on the Andreev reflection mechanism
Authors: Xiao Gang , Xue Deng-Ping
Published: July 2002

Based on the principle of Andreev reflection, we suggest a novel normal-metal-superconductor composite structure capable of electron focusing and guiding. Such a structure may be used as a switching device. The resolution and performance of a model system have been evaluated numerically.
Fluorine concentration in doped tin oxide films prepared by chemical vapor deposition
Authors: Yueyuan Xia , Lennard W. N. , Akano U.
Published: July 2002

Concentration distributions of 19F-doped tin oxide thin films prepared by chemical vapor deposition have been studied using the 19F(p,αγ)16O resonant nuclear reaction at ER=340.46 keV. Large fluctuations are observed in the fluorine concentration as a function of depth, which arise during the deposition process. Using secondary ion mass spectrometry measurements in conjunction with ion beam analysis, the density of the films is found to be 6.1 g cm−3, i.e., similar to that of the bulk material; this observation contrasts markedly with an earlier report.
Experimental determination of the influence of gain saturation on the temperature dependence of threshold current in short AlGaAs-GaAs quantum-well lasers
Authors: Jung H. , Schlosser E. , Deufel R.
Published: July 2002

In GaAs-AlGaAs single and multiple quantum-well (SQW and MQW) ridge lasers, grown by molecular beam epitaxy, the temperature dependence of the threshold current, expressed by the characteristic temperature T0, is investigated as a function of the cavity length (L) at temperatures between 20 °C and 93 °C. SQW lasers, in contrast to MQWs, show at room temperature a strong decrease in T0 from 250 K to about 100 K when the length is reduced from 400 to 200 μm. We found that by further reducing L to about 130 μm, a strong increase in T0 up to 250 K occurs and T0 decreases again to 80 K for 60 μm SQW lasers. This T0 behavior in SQW lasers is directly correlated to the gain saturation of the n=1 transition and the switch of the laser emission to the n=2 transition. In MQW lasers, T0 is constant at all cavity lengths, even at high temperatures, indicating that no gain saturation occurs.
Nd3+ active sites in Nd:MgO:LiNbO3 lasers
Authors: Tocho J. O. , Jaque F. , García Solé J. , Camarillo E. , Cussó F. , Muñoz Santiuste J. E.
Published: July 2002

The fluorescence (excitation and emission) spectra of Nd3+ in Nd:MgO:LiNbO3 have been systematically investigated in order to identify the Nd3+ sites responsible for the two, π (1.085 μm) and σ (1.093 μm), infrared laser lines. Experimental results reveal that Nd3+ ions entering both Li+ and Nb5+ lattice sites are responsible for the π emission line (1.085 μm), whereas Nd3+ ions perturbed by close Mg2+ ions, called Nd-Mg sites, are the sites producing the σ emission line (1.093 μm).
Alloy scattering-limited mobility in narrow quantum wells
Authors: Mukhopadhyay Sanghamitra , Nag B. R.
Published: July 2002

Alloy scattering-limited mobility is calculated for narrow quantum wells of GaAs/Ga0.7Al0.3As, Ga0.47In0.5As/InP, and Al0.48In0.5As/Ga0.47In0.53As systems with widths down to 0.5 nm, taking into account the energy-band nonparabolicity and the effects of wave-function penetration into the barrier layer. Values of mobility are found to be significantly different from those given by the formulas derived earlier for wide wells.
Silicon epitaxial solar cell with 663-mV open-circuit voltage
Authors: Blakers A. W. , Werner J. H. , Bauser E. , Queisser H. J.
Published: July 2002

Silicon films of 20 μm thickness have been grown epitaxially on silicon substrates by liquid-phase epitaxy. Solar cells fabricated on such layers display open-circuit voltages as high as 663 mV (AM1.5, 25 °C), a value which exceeds previous data by a large margin. High open-circuit voltages are a prerequisite for thin-film solar cells with high efficiencies. Our result has applications to both space cells and to low-cost terrestrial cells.
Measurements of noise and temperature coefficient of resistance on YBa2Cu3O7−δ thin films in magnetic field
Authors: Çelik-Butler Zeynep , Yang Wiyi , Butler Donald P.
Published: July 2002

We measured low-frequency noise and temperature coefficient of resistance β=(dR/dT)/R on YBa2Cu3O7−δ thin films at varying temperatures around superconducting transition. Magnetic field densities of 18–88 G were applied to the films. We found Tc to decrease slightly with magnetic field even though β at the respective Tc remained constant. At the superconducting transition, the voltage noise power spectral density over the 10–1000 Hz frequency range decreased with magnetic field, whereas no change in noise behavior was observed with varying the magnetic field in normal state. At a constant temperature in transition, as the magnetic field density was varied, the noise magnitude followed the β2 dependence as predicted by the local thermal fluctuations theory of 1/f noise.