bluuebunny/crossref_metadata_2025 huggingface dataset:
Etch masks for microfabrication produced by electron beam sublimation of graphitic carbon deposited as semimetallic amorphous carbon thin films
Authors: Porkolab G. A. , Wolf E. D.
Published: July 2002

High quality etch masks for nanometer plasma processing can be formed from thin films of semimetallic amorphous carbon that are deposited by electron beam sublimation of graphitic carbon. These films are amorphous, hard, semimetallic, and mirror-reflective. These electron beam sublimation deposited (EBSD) semimetallic amorphous carbon (semimetallic a-C) thin films can be routinely deposited up to at least 400 nm thick and patterned by SF6 plasma reactive ion etching (RIE) via standard photoresist masks. They are demonstrated to be excellent etch masks on gallium arsenide, silicon, and germanium substrates using chemically assisted ion beam etching (CAIBE), also known as ion beam assisted etching (IBAE), reactive ion beam etching (RIBE), and RIE. The carbon etch masks have fine grain, low chemical reactivity, low sputter rates, and high thermal stability. Finally, the EBSD semimetallic a-C can be readily stripped by SF6 or O2 or H2 plasmas.
Depth and radial profiles of defects in Czochralski-grown silicon
Authors: Sharma S. C. , Hyer R. C. , Hozhabri N. , Pas M. F. , Kim S.
Published: July 2002

We have studied the depth and spatial profiles of vacancies in Czochralski-grown silicon wafers by positron annihilation spectroscopy. By using a variable energy positron beam and γ-ray spectroscopy, we have obtained depth profiles of defects in as-grown, annealed, and 〈100〉 epitaxial Si wafers. We discuss these results in terms of vacancies and oxygen precipitates. The bulk position lifetime measurements, made as a function of axial displacement of a positron source, resolve vacancies, and divacancies in the wafer.
Superconducting transition temperature enhancement in YBa2Cu3O7 by chemical substitution and the implications thereof for the upper critical magnetic field
Authors: Neumeier J. J.
Published: July 2002

Chemical substitution of La+3 for Ba+2 in compounds of nominal composition YBa2−xLaxCu3O7−δ is shown to increase the superconducting transition temperature Tc by ∼2 K and the electrical resistivity ρ(100 K) by 90% for x=0.06. The increase of Tc is argued to result from a reduction of the hole carrier density. These results lead to the speculation that the upper critical magnetic field Hc2 may be increased by as much as 50% through this simple substitution.
Low-leakage superconductive tunneling in all-YBa2Cu3O7−x edge junctions
Authors: Ying Q. Y. , Hilbert C. , Kroger H.
Published: July 2002

All-YBa2Cu3O7−x (YBCO) superconductor-insulator-superconductor (SIS) edge-type tunnel junctions have been fabricated. This leads to the observation of superconductive tunneling with very low small-bias conductance for the first time in fabricated all-YBCO junctions. The presence of a superconductive gap of YBCO with a complete suppression of the density of states at the Fermi surface is evident from dynamic conductance measurements. The approach to all-YBCO SIS edge junctions is discussed.
Arsenic doping of GeSi epitaxial layers grown in the dichlorosilane/germane system
Authors: Liu W. H. , Leighton J. D. , Campbell S. A.
Published: July 2002

In this letter we detail the effects of arsine on Ge1−xSix growth rate and doping. We have observed for the first time that the growth process is no longer well described by a simple first-order reaction. The growth-rate data instead are consistent with a second-order reaction, with a substantial change in the activation energy. The electron carrier concentration and mobility have been measured as functions of arsine flow and compared to similar data from silicon growth.
1×16 photonic switch operating at 1.55 μm wavelength based on optical amplifiers and a passive optical splitter
Authors: Koren U. , Young M. G. , Miller B. I. , Newkirk M. A. , Chien M. , Zirngibl M. , Dragone C. , Glance B. , Koch T. L. , Tell B. , Brown-Goebeler K. , Raybon G.
Published: July 2002

An InP based 1×16 optical switch is demonstrated. The sixteen output ports are spaced 250 μm apart, and the total device length is 5.9 mm. Optical amplifiers are used to gate the optical signals and to provide optical gain. The total loss of the device, excluding coupling, is less than 2.5 dB and loss free operation was observed at low input powers. The output extinction ratios are lower than 18 dB and the uniformity spread of the sixteen channels is as low as 6.7 dB.
Nuclear magnetic resonance spin-echo studies in evaporated Co/Pt multilayers
Authors: Le Dang K. , Veillet P. , Krishman R. , Lassri H.
Published: July 2002

Multilayered Co/Pt films with Co layer thickness ranging from 10 to 26 Å have been studied by the NMR spin-echo method at 2 K. The rapid increase of the signal around 210 MHz as the Co layer thickness is decreased indicates the alloy formation at the interfaces. This signal coincides with the resonance spectrum of Co3Pt alloy. The latter corresponds to a disordered alloy and is coherent with the shifts of the satellite lines observed in a dilute alloy. The layer thickness of Co forming Co3Pt alloy at each interface is estimated to be about 4 Å.
YBa2Cu3O7−y microbridges on Y2O3/yttria-stabilized zirconia/SiO2/Si(100)
Authors: Hontsu S. , Mukai N. , Ishii J. , Kawai T. , Kawai S.
Published: July 2002

YBa2Cu3O7−y (YBCO) microbridges have been fabricated on a SiO2/Si substrate using Y2O3/YSZ (yttria-stabilized zirconia) buffer layer. Using polycrystalline silicon layer overlaid on oxidized Si(100) single crystal, the bridge is microprocessed by means of electron beam lithography and dry etching. The fabricated configuration serves as a mask for depositing YSZ and Y2O3 double buffer layers. The YBCO layer is deposited on the substrate by means of laser ablation deposition. The dimension of the bridge is 1.7 μm wide and 1.3 μm long. The microbridge junctions show a critical temperature of 86 K, and microwave-induced steps are observed indicating the presence of a Josephson junction-type behavior. The IcRn product is 0.5 mV at 30 K.
Electromigration failure due to interfacial diffusion in fine Al alloy lines
Authors: Hu C-K. , Small M. B. , Rodbell K. P. , Stanis C. , Blauner P. , Ho P. S.
Published: July 2002

Damage formation at grain boundary junctions has long been recognized as the dominant electromigration failure mechanism in metal lines. We report the results of drift-velocity experiments on fine lines with no reservoirs and find that the interfacial mass transport, along the edges of the lines, is faster than that along grain boundaries. This causes mass depletion at the cathode end of the line, leading to electromigration failure. The result demonstrates a new failure mechanism due to electromigration in submicron lines with bamboo grain structures.
Highly thermally stable electrical compensation in oxygen implanted p-InAlAs
Authors: Krauz Ph. , Rao E. V. K. , Thibierge H. , Harmand J. C.
Published: July 2002

The electrical compensation induced by oxygen ion implants in Be doped p-type In0.52Al0.48As epilayers has been investigated. By performing hot implants (∼250 °C) and high temperature (as high as 800 °C) furnace anneals, we have ascertained the formation of thermally stable electrically compensated layers. Similar data obtained by varying oxygen implant dose and Be background doping level are permitted to confirm unambiguously the involvement of oxygen atoms in the compensation mechanism. These results are satisfactorily explained assuming the formation of a deep donor center involving the participation of oxygen atoms.
Negative longitudinal resistance in a mesoscopic wire
Authors: Cumming D. R. S. , Blaikie R. J. , Ahmed H.
Published: July 2002

We have demonstrated that a negative four-terminal longitudinal resistance may be measured in a mesoscopic wire with a long electron mean free path. This is a geometrical effect which arises when the voltage probes nearest to the current source are shadowed in such a way that direct ballistic transport of electrons into these probes is not possible. A billiard ball model is used to simulate the magnetoresistance of the fabricated wires and the effects of diffuse boundary scattering and random impurity scattering are used to give a good explanation of our measurements.
Cross-sectional transmission electron microscopy parallel to the active stripe of degraded buried heterostructure distributed feedback laser devices
Authors: Chu S. N. G. , Nakahara S.
Published: July 2002

We demonstrate for the first time that cross-sectional transmission electron microscopy can be applied parallel to the active stripe of a distributed feedback buried heterostructure laser diode to identify the cause for degradation during reliability qualification. A dominant defect mechanism is found to be the generation of dislocation loops at or near the grating/waveguide-layer interface which subsequently propagate up through the multilayer structure. The vertical segments of the loops tend to be trapped onto the {111} planes to form a V-shaped configuration as revealed in the (011) cross section. A dislocation reaction mechanism is proposed to explain the observed dislocation configuration. Furthermore, complicated dislocation loops are grown out of the segments of dislocation threading through the active region forming <100≳ dark line defects revealed by the electroluminescence. The defect growth mechanism is believed to be a condensation of point defects induced by the nonradiative recombination assisted point defect migration process similar to that previously observed in degraded channeled substrate buried heterostructure lasers. The nucleation of dislocations at or near the grating/waveguide layer interface is consistent with a high interfacial strain observed in the degraded devices.
Wannier–Stark quantization by internal field in the HgTe/CdTe superlattice
Authors: Lo Ikai , Mitchel W. C. , Harris K. A. , Yanka R. W. , Mohnkern L. M. , Reisinger A. R. , Myers T. H.
Published: July 2002

The Stark ladder can be formed in a semiconductor superlattice by an applied electric field. The localization of electrons by an external electric field is known as Wannier–Stark quantization. We have performed the Shubnikov–de Haas measurements with a tilted magnetic field and the photoluminescence measurement on a HgTe/CdTe superlattice in the absence of an external electric field. From the observation of a two-dimensional electron gas and a blueshift of the photoluminescence spectrum, we conclude that the Stark ladder exists in the HgTe/CdTe superlattice and it is formed due to the Wannier–Stark quantization by the internal electrostatic field.
Comparative analysis of the intersubband versus band-to-band transitions in quantum wells
Authors: Khurgin Jacob
Published: July 2002

The strengths of the intersubband and band-to-band transitions in quantum wells are compared using simple k⋅p analysis, and contrary to the prevalent opinion, found to be nearly equal. The implications for the design of detectors and nonlinear optical devices are considered.
Ultrahigh-brightness, femtosecond ArF excimer laser system
Authors: Mossavi K. , Hofmann Th. , Tittel F. K. , Szabó G.
Published: July 2002

An ultrahigh-brightness ArF excimer laser system is described that is capable of generating pulse energies of 60 mJ with a pulse duration of ∼700 fs. The system utilizes a newly developed seed pulse generation scheme based on spectrally compensated sum-frequency mixing in beta-barium metaborate (BBO), and a double-pass discharge pumped ArF excimer preamplifier followed by an electron beam pumped power amplifier.
Hybrid integration of bipolar transistors and microlasers: Current-controlled microlaser smart pixels
Authors: Bryan Robert P. , Fu Winston S. , Olbright Greg R.
Published: July 2002

We describe the hybrid integration of GaAs/AlGaAs heterojunction bipolar transistors with GaAs/AlGaAs (850 nm operation) and InGaAs/AlGaAs (980 nm operation) vertical-cavity microlasers to form ultra-low-drive-current microlaser smart pixels. We achieved a single-mode, low divergence, 1 mW output with a 70 μA base injection current and digital electronics matched input impedance. The integration technology is appropriate for the integration of optoelectronic integrated circuits to GaAs and Si microelectronics circuits.
Electrical switching in methyltriphenylarsonium-(TCNQ)2 under pressure
Authors: Ravindran T. , Subramanyam S. V.
Published: July 2002

Electrical switching has been observed in methyltriphenylarsonium-(TCNQ)2 (7,7,8,8-tetracyanoquinodimethane) at different pressures up to 8 GPa at a temperature of 300 K. At high fields ∼3×103 V/cm, the sample switches from an off state of several kΩ resistance to low resistance on state of several ohms. Pulsed current-voltage characteristics reveal heating contribution to nonohmic conduction and switching. The switching time recorded is 0.5 ms. Nonohmic conduction is discussed in terms of space charge limited currents possibly leading to a structural phase transition.
Transport mechanisms in low-resistance ohmic contacts to p-InP formed by rapid thermal annealing
Authors: Clausen T. , Leistiko O.
Published: July 2002

Thermionic emission across a very small effective Schottky barrier (0–0.2 eV) are reported as being the dominant transport process mechanism in very low-resistance ohmic contacts for conventional AuZn(Ni) metallization systems to p-InP formed by rapid thermal annealing. The barrier modulation process is related to interdiffusion and compound formation between the metal elements and the InP. The onset of low specific contact resistance is characterized by a change in the dominant transport mechanism; from predominantly a combination of thermionic emission and field emission to purely thermionic emission.
Infrared photoconductor fabricated with HgTe/CdTe superlattice grown by molecular beam epitaxy
Authors: Qiu Yueming , He Li , Li Jie , Yuan Shixin , Becker C. R. , Landwehr G.
Published: July 2002

An infrared photoconductor fabricated with a HgTe/CdTe superlattice grown on a GaAs substrate by molecular beam epitaxy is described here for the first time. The growth procedure, device fabrication, and measurement results are described. The results show that the device has relatively high uniformity and 1000 K black-body detectivity 2.4×109 cm Hz1/2 W−1. The photoconductivity decay method was used for determining carrier lifetime of the HgTe/CdTe superlattice, the measured lifetime is 12 μs at 77 K, which is the longest lifetime ever reported for HgTe/CdTe superlattices and we believe that the increase of lifetime is mainly due to the reduction of dimensions.
Triple slab radio-frequency discharged CO2 laser
Authors: Lapucci A. , Cangioli G.
Published: July 2002

The operation of a laser having both the advantages of large area discharges and those of laser arrays is reported. The laser consists of three parallel optical channels (slabs) with a rectangular section. Locked emission due to distributed coupling of the three slabs is observed. The resulting far-field pattern displays the presence of a symmetric central lobe corresponding to a 2 Mrad divergence and some residual sidelobes due to the laser periodic structure in one transverse direction. Such a far-field can be handled by Talbot imaging techniques, and the structure can be scaled to a higher number of channels.
Electron paramagnetic resonance study of the two-dimensional electron gas in Ga1−xAlxSb/InAs single quantum wells
Authors: von Bardeleben H. J. , Jia Y. Q. , Manasreh M. O. , Stuz C. E.
Published: July 2002

The Shubnikov–de Haas oscillations of the two-dimensional electron gas in semimetallic undoped Ga1−xAlxSb/InAs single quantum wells with compositions x=0.1,0.2,0.5,0.8,1.0 are studied by X-band electron paramagnetic resonance spectroscopy in the 4–20 K temperature range. The thermal equilibrium carrier concentrations vary from 4×1011 cm−2 for x=0.2 to 1×1012 cm−2 for x=1.0; from the temperature dependence of the Shubnikov–de Haas oscillations amplitudes in the 1–2 T magnetic field range the effective mass is determined to 0.026m0. Photoexcitation, with a low-energy threshold of 0.7 eV, gives rise to a negative persistent photoconductivity (NPPC) for alloy compositions x≥0.2; no NPPC is observed for x=0.1.
Colliding pulse mode locking of a semiconductor laser in an external ring cavity
Authors: Lin C. F. , Tang C. L.
Published: July 2002

Colliding pulse mode locking of a semiconductor laser is achieved by monolithically integrating an absorber in the center of a laser diode structure with chemically assisted ion beam etched angled facets in an external ring cavity. Minimum deconvolved pulses as short as 1.6 ps before compression and near-transform-limited pulses of 0.35 ps after compression are measured.
Nucleation enhancement of diamond with amorphous films
Authors: Barnes Paul N. , Wu Richard L. C.
Published: July 2002

The nucleation and growth of diamond on pretreated Si substrates were studied. The diamond films were produced by microwave plasma enhanced chemical vapor deposition (PECVD). The pretreatment consisted of an amorphous carbon film also deposited by microwave PECVD. The Si was previously scratched with 0.5 μm diamond paste and cleaned in acetone. This pretreatment of Si resulted in diamond nucleation at densities averaging around 3×1010 cm−2, several orders of magnitude higher than scratched Si alone.
Decay time of the blue luminescence in ZnSe at room temperature
Authors: Zheng Jia Zhen , Allen J. W. , Spence D. E. , Sleat W. E. , Sibbett W.
Published: July 2002

The decay time of the blue luminescence at room temperature in n-type ZnSe grown by metalorganic chemical vapor deposition has been measured, using a mode-locked laser as excitation source and a streak camera for detection. Over an uncompensated donor concentration range 1017–1018 cm−3 the decay time is of the order of 100 ps. The short time is a result of strong nonradiative recombination: it is argued that the concentration of Hall–Shockley–Read recombination centers is high.
Generation of 415.9–482.6 nm tunable intense picosecond single pulse in LiB3O5
Authors: Huang Fang , Huang Liu , Yin Bao-lu , Hua You-nian
Published: July 2002

An intelligent type II noncritically phase-matched LiB3O5 optical generator pumped by 30 ps 355 nm laser pulse is reported. Tunable wavelengths of 482.6–415.9 nm (21–450 °C) with linewidths as low as 0.15 nm, a pump-to-signal energy conversion efficiency up to 37.6%, and 211 MW peak-power single pulse have been achieved.
Residual strains in epitaxial fluorides on Si(111) substrates
Authors: Schowalter Leo J. , Li Weidan
Published: July 2002

Growth conditions for molecular beam epitaxy of SrF2 directly on Si(111) have been optimized for excellent crystal quality. A χmin of 2.6% was demonstrated. Lattice distortion measurements were carried out by ion channeling along off-normal channeling directions in the strained SrF2 layers. The measured residual tensile strain versus the film thickness demonstrated a special thickness: When films were thinner than this thickness, their strain dropped dramatically as thickness decreased, and when films were grown thicker than it, the strain gradually decreased with increasing film thickness. This unique behavior was successfully modeled as the result of competition between the large lattice mismatch between SrF2 and Si and the large difference in thermal coefficients of expansion. Residual strain remained even in SrF2 films thicker than 600 nm, unlike CaF2 on Si(111) for which CaF2 films thicker than 300 nm were observed to have no strain.
Thermal quenching and relaxation in doped hydrogenated amorphous silicon deposited by plasma-enhanced chemical vapor deposition from He-diluted silane
Authors: Meaudre R. , Meaudre M. , Roca i Cabarrocas P.
Published: July 2002

The stability of n-type and p-type rf glow discharge amorphous silicon (a-Si:H) deposited from silane-helium mixtures has been studied. Dark dc conductivity measurements were made after quenching or slow cooling and the time dependence of isothermal relaxation at different temperatures has been investigated. The equilibration temperatures are ∼155 and ∼125 °C for n- and p-type films, respectively. These values are greater than those commonly reported on conventional rf glow discharge films (130 and 90 °C). In comparison with conventional films, at any given temperature the relaxation times are longer with activation energies of 1 and 1.39 eV for n- and p-type films. The improved stability of the films has been discussed in relation with their particular hydrogen-related structure.
High carrier-to-noise ratio achieved on magneto-optic recording disks using a plurality of magneto-optic recording layers
Authors: Lin C.-J.
Published: July 2002

Very high carrier-to-noise ratios of 67 dB (30 kHz bandwidth) were achieved on magneto-optic recording disks that utilize two thin magneto-optic layers. This improvement came primarily from the reduction in the disk writing noise. We explain this noise reduction through the statistical averaging of the written magnetic transition positions in these two active layers. In principle the disk writing noise can be further reduced when more active layers are utilized in the disk structure.
Switching characteristics of multi-ion-beam reactive sputter deposited Pb(Zr,Ti)O3 thin films
Authors: Hu H. , Krupanidhi S. B.
Published: July 2002

The switching of the multi-ion-beam reactive sputter deposited Pb(Zr0.5,Ti0.5)O3 thin films has been characterized by using several parameters such as switching time (ts), switched charge density (Qs), nonswitched charge density (Qns), and activation field (α). Comparison was made between films grown with and without low-energy oxygen ion bombardment. It was found that while there is not much difference in ts between the two kinds of films, the bombarded films show higher Qs/Qns, lower ts/Qs, and lower α. These results are consistent with previous results on the remanent polarization (Pr) and coercive field (Ec) and indicate that the bombardment has induced changes towards facilitating the domain reversal in the films.
Oscillator strength enhancement for [110]-polarized light in compressively strained GaInP ordered crystals used in AlGaInP lasers
Authors: Ueno Yoshiyasu
Published: July 2002

This letter studies the effect of compressive strain on the polarization-dependent oscillator strength in GaInP CuPt-type ordered crystals. The hole eigenstates are obtained by diagonalizing the total Hamiltonian consisting of the Hamiltonian for ordered GaInP and a perturbed term caused by the strain. Our calculation reveals that the strain squeezes the hole wave function and that the oscillator strength between an electron and the upper-valence-band hole increases for [110]-polarized light. The oscillator strength for [110]-polarized light increases with the strain, reaching 14% at +0.98% strain.
Iron-induced alternating current surface photovoltages in n-type silicon wafers
Authors: Shimizu Hirofumi , Munakata Chusuke
Published: July 2002

Alternating current surface photovoltage (SPV) is observed in n-type silicon wafers, which are treated with an iron (Fe)-contaminated alkaline solution composed of ammonia hydroxide, hydrogen peroxide, and water, indicating that the negative charge appears at wafer surfaces. With the removal of the native oxide, where the residual concentration of Fe is 4.6×1016 atoms/m2, Fe concentration is reduced to the detection limit (4.4×1013 atoms/m2) at the wafer surface, and then the ac SPV vanishes. This result provides evidence that Fe in the native oxide contributes to the negative charge induction, similar to results previously reported for aluminum.
Frequency tuning of a double-heterojunction AlGaAs/GaAs-vertical-cavity surface-emitting laser by a serial integrated in-cavity modulator diode
Authors: Gmachl C. , Köck A. , Rosenberger M. , Gornik E. , Micovic M. , Walker J. F.
Published: July 2002

The frequency tuning of a vertical-cavity surface-emitting laser through current injection is reported herein. This was achieved by integrating an AlGaAs graded-index p–n-modulator diode with a double-hetero GaAs/AlGaAs laser diode in a vertical cavity formed by an AlAs/AlGaAs-Bragg reflector and a metallic mirror. Experimental results show an obtained gradient of frequency shift up to 0.93 GHz/mA by the modulator current. This effect is at present restricted to approximately 40 mA due to thermal effects. A theoretical model based on the plasma effect and thermal effects agrees with the experimental values and predicts a maximum value for the gradient of frequency shift of 1.15 GHz/mA with the presented structure.
Unexpected time dependence of ac losses in multifilamentary NbTi superconductors
Authors: Schmidt Curt
Published: July 2002

Losses of NbTi multifilament superconductors in a copper matrix in alternating magnetic fields were measured using a specially developed sensitive calorimetric method. The investigated samples have filament diameters in the micrometer range and exhibit a strong proximity effect. The measured losses at fixed ac frequency and field amplitude showed an unexpected time dependence on a very long time scale of hours, compared to the ac field cycle time, which was in the millisecond range. This time dependence is probably a consequence of slowly decaying proximity currents.
Photoconduction in germanium and phosphorus doped silica waveguides
Authors: Kashyap Raman , Maxwell Graeme D. , Williams Doug L.
Published: July 2002

Photoconduction measurements on Ge-P doped silica planar ridge waveguides exposed to several miliwatts of ultraviolet radiation are reported. It is shown that there is a strong reduction in the photocurrent with time of exposure pointing to a depletion in the available photoactivated carriers. The density of defects is directly inferred from the measurements.
Fiber compatible fast acousto-optic modulator using a gradient index lens as the interaction medium
Authors: Abdulhalim I. , Pannell C. N. , Payne D. N.
Published: July 2002

A novel fiber-compatible acousto-optic modulator is described in which the interaction between the optical and acoustic waves occurs in a graded-index lens which can also function as an ‘‘expanded-beam’’ fiber-to-fiber connector in the case of a half-pitch device, or as a collimator in the case of a quarter-pitch device. Initial results using a quarter-pitch lens are diffraction efficiences of 3%, and diffraction loss of 7%, using 0.5 W power of 80 MHz rf under cw operation and under pulsed operation, using pulse widths down to 40 ns. A 14 ns switching time was measured.
Symmetric switching in strong anchoring surfaces of large-core-angle ferroelectric liquid crystal
Authors: Bawa S. S. , Biradar A. M. , Chandra Subhas
Published: July 2002

The polymer rubbed, polar surface anchoring effect in a thin homogeneously aligned sample of large-core (high-tilt)-angle ferroelectric liquid crystal which undergoes an isotropic-chiral nematic-smectic C* phase transition is reported herein. It has been found that symmetric switching characteristics can be obtained by applying an appropriate bias field to the samples even though the difference between the polar anchoring energy on two surfaces is quite large. The temperature dependence of the anchoring strength is also studied in the smectic C* phase.
Laser-assisted liquid film etching
Authors: Lim P. , Brock J. , Trachtenberg I.
Published: July 2002

Laser-assisted liquid film etching (LALFE) is a new technique for maskless patterning of silicon substrates. This technique involves forming a thin liquid film of etchant on a silicon substrate and focusing a laser beam on the portion to be etched. Results are given for direct-writing, orientation dependent LALFE on (100) and (111)n-Si using films of polyvinyl alcohol (PVA) as a wetting agent for hydrofluoric acid on n-Si.
Si3N4/Si/In0.53Ga0.47As depletion-mode metal-insulator-semiconductor field-effect transistors with improved stability
Authors: Mui D. S. L. , Wang Z. , Biswas D. , Demirel A. L. , Teraguchi N. , Reed J. , Morkoç H.
Published: July 2002

We report on the electrical characteristics of in situ deposited Si3N4/Si/In0.53Ga0.47As depletion-mode metal-insulator-semiconductor field-effect transistors (MISFETs). MISFETs with 2.2-μm gate lengths fabricated by a self-aligned gate process exhibited extrinsic transconductances of over 200 mS/mm. The drain current drifted by only 1% during the first 10 h of operation. This small shift is attributed to the reduction of traps at the interface by a pseudomorphic Si layer, incorporated at the interface between the dielectric and the In0.53Ga0.47As channel.
Interband near-infrared second-harmonic generation with very large ‖χ(2)(2ω)‖ in AlSb/GaSb-InAsSb/AlSb asymmetric quantum wells
Authors: Scandolo Sandro , Baldereschi Alfonso , Capasso Federico
Published: July 2002

We propose a novel steplike quantum-well structure for second-harmonic generation with very large ‖χ(2)(2ω)‖ in the near infrared, based on interband doubly resonant transitions. The structure is engineered so as to maximize the second-order susceptibility χ(2)(2ω), which requires, in particular, avoiding too much overlap between the heavy-hole and the lowest electron envelope functions. We show that the choice of a steplike asymmetry and of GaSb-InAsSb compounds, instead of the conventional AlGaAs, leads to an enhancement of the second-order susceptibility by about 30 times with respect to bulk GaAs, at pump wavelengths of 1.5 μm.
One-point contact measurement of spherical resonances
Authors: Hsieh C. P. , Khuri-Yakub B. Y.
Published: July 2002

Ceramic bearing balls are desirable for use in high-temperature and nonlubricative environments because of their ability to retain high mechanical strength and reduced wear. However, because ceramics are brittle, it is very important to inspect ceramic parts for the existence of small (1–10 μm) surface defects. The contact–contact resonant sphere technique has been shown to be able to detect the presence of surface defects in spherical objects. This technique, however, has certain limitations that are especially important when inspecting small spheres. In this letter we present a true one-point-contact technique to circumvent these limitations. We excite resonances of spheres at both low and high frequencies. Resonances are generated by forming a one-point Hertzian contact between the sphere and a spherical depression in a buffer rod with a transducer. The resonance spectrum is detected from the opposite pole of excitation using an optical interferometer. At low frequencies, bulk resonances of the sphere are excited, and material properties are determined. At high frequencies, surface-wave resonances of the sphere are excited, and the dispersion relation of the waves is measured. The measured dispersion relation of the sphere is correlated to the surface wave velocity on the sphere and to the presence of surface defects.
Microstructure of laser-deposited superconducting Nd1.85Ce0.15CuO4−y films
Authors: Beesabathina D. Prasad , Salamanca-Riba L. , Mao S. N. , Xi X. X. , Venkatesan T.
Published: July 2002

The morphology and microstructure of Nd1.85Ce0.15CuO4−y (NCCO) films grown epitaxially on (100) LaAlO3 (LAO) by pulsed laser deposition were studied by selected-area electron diffraction and high-resolution electron microscopy. The films were composed primarily of c-axis oriented grains and did not contain any polytypoidic faulting. The in-plane epitaxial relationship of the films was found to be [100]NCCO //[001]LAO. The Nd1.85Ce0.15CuO4−y-LaAlO3 interface is sharp and free of defects. A weak peak around the (110) position of NCCO(T′) structure in x-ray diffraction was observed. Using microdiffraction and energy-dispersive x-ray analysis, we confirmed that this peak corresponds to the (004) reflection of cubic Ce0.5Nd0.5O1.75.
Below band-gap laser ablation of diamond for transmission electron microscopy
Authors: George T. , Foote M. C. , Vasquez R. P. , Fortier E. P. , Posthill J. B.
Published: July 2002

A 248 nm excimer laser was used to thin naturally occurring type 1a diamond substrates at normal and glancing (22°) incidence. Perforation of a 250-μm-thick substrate was achieved in about 15 min at normal incidence. While the substrate thinned at glancing incidence was found to have large electron-transparent areas, that thinned at normal incidence required additional argon-ion milling to achieve electron transparency. X-ray photoelectron spectroscopy of the back surface of the diamond failed to detect any graphite or glassy carbon, confirming that damage due to laser ablation occurs only at the incident surface. Samples prepared using this technique imaged in the transmission electron microscope were observed to have retained the nitrogen platelets characteristic of such type 1a diamonds.
Determination of the layer structure of embedded strained InGaAs multiple quantum wells by high resolution x-ray diffraction
Authors: Choi Woo-Young , Fonstad Clifton G.
Published: July 2002

High resolution x-ray diffraction (HRXRD) has been used to determine the layer compositions and thicknesses of compressively strained InGaAs multiple-quantum-well (MQW) structures embedded in thick cladding layers that are nominally lattice matched to InP. The entire layer structure was accurately determined from the results of HRXRD measurements for a simple strained MQW structure in which barriers and claddings are of the same composition. The estimated margins of error are less than 1% for the quantum-well indium composition and ±2.5 Å for well and barrier thicknesses. The layer structure of the active region in a complete InGaAlAs graded-index separate confinement strained MQW laser diode has also been determined by HRXRD.
Synchrotron radiation assisted Si epitaxial growth: Comparison of growth characteristics between Si2H6 and SiH2Cl2 gases
Authors: Urisu Tsuneo , Akutsu Tetsuo , Kuchitsu Kozo
Published: July 2002

Effects of synchrotron radiation (SR) irradiation on the Si epitaxial growth using Si2H6 and SiH2Cl2 gases were investigated in the substrate temperature range of 400–600 °C. Single-crystal growth was observed in the whole temperature region for SiH2Cl2, but only at certain high temperatures, where the growth rate showed a significant temperature dependence, for Si2H6. Gas-phase excitation mechanism became dominant in the low-temperature deposition. SR-assisted desorption of hydrogen is found to be important in the process of crystallization in the case of Si2H6, whereas chemical processes such as desorption in the form of HCl are considered as probable for SiH2Cl2.
Intersubband optic phonon resonances in electrostatically confined quantum wires
Authors: Jovanovic Dejan , Leburton Jean-Pierre , Ismail Khalid , Bigelow Jeffrey M. , Degani Marcos H.
Published: July 2002

We investigate the occurrence of resonant intersubband optic phonon scattering in an array of quantum wires at high temperatures. Self-consistent solutions of the Schrödinger and Poisson equations with a subsequent Monte Carlo analysis of intersubband scattering reveal a strong resonant polar optic phonon coupling between subbands at the gate bias indicated by the experimental data. The observation of resonant scattering is only possible because the quasi-1D form of Gauss’ law shows an opposite trend to that for 2D systems in the dependence of the eigenenergy spectrum on gate bias.
In situ investigation of amorphous silicon/silicon nitride interfaces by infrared ellipsometry
Authors: Shirai H. , Drévillon B. , Ossikovski R.
Published: July 2002

A detailed in situ study by infrared phase-modulated ellipsometry of interfaces between plasma-deposited amorphous silicon (a-Si:H) and silicon nitride (a-SiNx) is presented. The structure of the interface is affected by the deposition sequence. A behavior compatible with a sharp interface is observed when a-SiNx is deposited on top of a-Si:H, the underlayer material being very weakly influenced by the deposition of the overlayer. In contrast, a graded transition is observed when a-SiNx is deposited first. In the latter case, the infrared measurements directly reveal a nitrogen tail incorporated in the first monolayers of a-Si:H (10–20 Å thick). The formation mechanisms of the interfaces are discussed.
Microstructural analysis of nickel silicide formed by nickel/silicon-on-oxide annealing
Authors: Yang H. , Pinizzotto R. F. , Luo L. , Namavar F.
Published: July 2002

Microstructures of crystalline nickel disilicide thin films formed on SIMOX (separation by implantation of oxygen) Si-on-oxide substrates were analyzed using electron microscopy. The samples were examined both in the top-down plane-view orientation and in cross section along a [110] direction. The nickel silicide films were formed through thermal reaction of metallic nickel deposited on the top Si layer of the SIMOX substrates. The results were compared with epitaxial NiSi2 layers grown on single crystal silicon substrates. Twin boundaries were observed at the silicide/oxide interface. The oxide layer acts as a diffusion barrier which prevents nickel from diffusing into the substrate resulting in uniform NiSi2 on a SiO2/Si substrate.
Crystalline linkage and defect structures in bulk zone melt textured YBa2Cu3O7 observed by transmission electron microscopy
Authors: Zanota A. , Kvam E. P. , Balkin D. , McGinn P. J.
Published: July 2002

The microstructural features of zone melt textured wires of YBa2Cu3O7 (123) with and without additions of Y2BaCuO5 have been examined by transmission electron microscopy. The 123 phase is observed to form well aligned platelets, which are of limited extent along [001], but extremely long in the perpendicular directions. Although platelet boundaries are wetted by a second phase, junctions are commonly observed to interconnect the plates. This suggests the possibility that the wires are actually highly defective single crystals. High densities of stacking faults are also observed, particularly at Y2BaCuO5/YBa2Cu3O7 interfaces and at dislocation arrays. It is suggested that these result from a drive for phase conversion to YBa2Cu4O8, and that they may be associated with flux pinning.
Monolithic integration of a light-emitting diode array and a silicon circuit using transfer processes
Authors: Dingle B. D. , Spitzer M. B. , McClelland R. W. , Fan J. C. C. , Zavracky P. M.
Published: July 2002

This letter reports the attainment of a monolithically integrated light-emitting diode array on a silicon integrated circuit. The emitters are first formed epitaxially on a lattice-matched substrate and are subsequently transferred to the silicon. Interconnections are made using thin-film techniques between the 128 separately addressable light-emitting diodes and the driver circuit. This work demonstrates attainment of a high level of optoelectronic/logic integration.
Removal of GaAs surface contaminants using H2 electron cyclotron resonance plasma treatment followed by Cl2 chemical etching
Authors: Hong M. , Freund R. S. , Choquette K. D. , Luftman H. S. , Mannaerts J. P. , Wetzel R. C.
Published: July 2002

We report a novel dry process to remove the surface contaminants C, Si, and O from GaAs substrates. This method utilizes an electron cyclotron resonance hydrogen plasma to remove the native oxides, followed by a very brief Cl2 chemical etching of GaAs to further reduce C and Si residues, and a final vacuum anneal. Characterization by secondary ion-mass spectrometry (SIMS) typically reveals the removal of C, Si, and O at the overgrown/processed interface to the levels below the SIMS detection limit. The as-processed GaAs surface, a Ga-stabilized reconstructed (4×6), is atomically smooth, and is as clean as a surface of freshly grown GaAs epilayers.
Detection of two-dimensional electron gases in undoped heterojunctions with magnetophotoluminescence
Authors: Driessen F. A. J. M. , Olsthoorn S. M. , Giling L. J.
Published: July 2002

We report the observation of a magnetoexciton in undoped GaAs/AlxGa1−xAs heterojunctions by photoluminescence. The exciton originates from photoexcited holes and two-dimensional electrons, which are confined in the shallow potential at the heterointerface. The observation of this exciton is particularly useful for identification of unintended two-dimensional electron gases in cases where detection by temperature-dependent Hall measurements is difficult.
Enhanced characteristics of InGaAsP buried quaternary lasers with pressures up to 1.5 GPa
Authors: Patel D. , Menoni C. S. , Temkin H. , Logan R. A. , Coblentz D.
Published: July 2002

Pressure dependent measurements of the threshold current, differential quantum efficiency, and lasing wavelength of a ∼1.3 μm bulk InGaAsP semiconductor laser performed in a diamond anvil cell up to 1.5 GPa are reported. Results show a 40% decrease in the threshold current and a simultaneous enhancement in the differential quantum efficiency of approximately 350%. Large wavelength tunability of 140 nm is observed in this pressure range at room temperature. Calculations indicate that a reduction of the Auger recombination rate is likely to be the dominant loss mechanism responsible for the observed changes in the laser threshold current in this pressure range.
Metal-semiconductor-metal photodetector with integrated Fabry–Perot resonator for wavelength demultiplexing high bandwidth receivers
Authors: Prank U. , Mikulla M. , Kowalsky W.
Published: July 2002

Surface operating metal-semiconductor-metal photodetectors with a monolithically integrated asymmetrical Fabry–Perot resonator are presented. Because of the low capacitance of the planar electrode configuration, frequency limits exceeding 35 GHz can easily be obtained. Wavelength demultiplexing of closely spaced channels is achieved by an integrated Fabry–Perot resonator. An optical bandwidth of 1.0 nm and a contrast ratio exceeding 10:1 are demonstrated.
Fourier transform diagnostics of gaseous species during microwave assisted diamond deposition
Authors: Campargue A. , Chenevier M. , Fayette L. , Marcus B. , Mermoux M. , Ross A. J.
Published: July 2002

High resolution Fourier transform spectra of the microwave plasma used for diamond deposition has been obtained in the 3 μm range. The results show that methane is nearly totally dissociated in the plasma. The recombination of the products of dissociation gives mostly acetylene and methane which have been detected 20 cm downstream.
Evolution of monolayer terrace topography on (100) GaAs annealed under an arsine/hydrogen ambient
Authors: Epler J. E. , Jung T. A. , Schweizer H. P.
Published: July 2002

The topographical evolution of the (100) GaAs surface annealed under an arsine/hydrogen ambient is studied by in situ orientation-resolved light scattering and ex situ atomic force microscopy (AFM). The light scattering system provides real-time monitoring of the magnitude and crystal orientation of topographical features of 0.3 μm scale. The AFM images of the GaAs surface, quenched at various annealing temperatures, vividly depict the randomly oriented high density monolayer steps evolving into an atomically smooth terracelike structure.
Stability of ultrathin silicon nitride films on Si(100)
Authors: Huang L. J. , Kwok R. W. M. , Lau W. M. , Tang H. T. , Lennard W. N. , Mitchell I. V. , Schultz P. J.
Published: July 2002

Ultrathin silicon nitride films on Si(100) have been studied using x-ray photoelectron spectroscopy, medium energy ion scattering, Raman spectroscopy, and variable-energy positron annihilation spectroscopy. Films ∼10-nm-thick were prepared by remote microwave plasma chemical vapor deposition. A compressive stress of about 0.4 GPa was found by measuring the Raman shift of the fifth-harmonic LO mode of the silicon substrate. The film properties, however, changed significantly upon vacuum annealing. Annealing at 100 °C for 1 h resulted in an increase of nitrogen concentration near the film surface, probably because of nitrogen surface segregation. Annealing at 100–500 °C also released film induced stress and a complete stress release was achieved by annealing at 500 °C for 1 h. Positron annihilation results showed that vacuum annealing only affected the film but not the substrate.
Atomistic calculation of the self-interstitial diffusivity in silicon
Authors: Maroudas Dimitris , Brown Robert A.
Published: July 2002

Formation and migration properties of self-interstitial atoms in silicon are calculated using systematic atomistic simulations based on the Stillinger–Weber interatomic potential [F. H. Stillinger and T. A. Weber, Phys. Rev. B 31, 5262 (1985)]. The lowest energy configuration of an interstitial atom is calculated to be an extended configuration with a formation energy that is 1.2 eV lower than the formation energy of the higher symmetry configuration with lowest energy. A mechanism for the interpretation of dopant diffusion data is proposed based on this result. The calculated lower bound for the diffusion coefficient of self-interstitials described by a simple migration path is in good agreement with experimental data over the temperature range 733 K<T<1473 K.
High-speed InP/InGaAs double-heterostructure bipolar transistors with suppressed collector current blocking
Authors: Kurishima K. , Nakajima H. , Kobayashi T. , Matsuoka Y. , Ishibashi T.
Published: July 2002

InP/InGaAs double-heterostructure bipolar transistors (DHBTs), incorporating a new collector structure featuring ‘‘pn pair doping’’ in the heterointerface vicinity, have been fabricated using a low-pressure metalorganic chemical vapor deposition (MOCVD) method. These transistors provide high collector current densities over 1×105 A/cm2, indicating the successful suppression of current blocking. S-parameter measurements determine the high current gain cutoff frequencies of 130 GHz. These values favorably compare with those of conventional InGaAs-collector HBTs fabricated for comparison, suggesting that the InP collectors have excellent electron transport properties.
Atomic layer epitaxy of GaAs with a 2 μm/h growth rate
Authors: Dip Anthony , Eldallal Gamal M. , Colter Peter C. , Hayafuji N. , Bedair S. M.
Published: July 2002

Atomic layer epitaxy (ALE) of GaAs with a growth rate as high as 2 μm/h was achieved in a specially designed reactor based on the rotating susceptor concept. High deposition rates are made possible by a unique partition system that permits rapid rotation of substrates between simultaneous streams of columns III and V reactant gases. Mixing of the gas streams at high rotational speeds is avoided by the gas shearing effect provided by the partition system. Background carbon levels in the GaAs films with high growth rates varied from mid 1017 cm−3 at 650 °C to mid 1018 cm−3 at 550 °C. When the growth rate was reduced to 0.3 μm/h, carbon background doping in the 1015 cm−3 was achieved.
Porous silicon formation: Morphological stability analysis
Authors: Kang Ying , Jorné Jacob
Published: July 2002

Morphological stability analysis for the photoelectrochemical etching of n-type Si is performed, in which the stability of the back-illuminated Si-electrolyte interface is theoretically investigated. Both the transport of holes in the semiconductor and ions in the diffusion layer are considered, together with the electrochemical reaction and surface energy. The roles and the effects of the various parameters, such as applied voltage, dopant concentration, current density, illumination intensity, surface energy, and electrolyte concentration, on the morphology of porous silicon are studied. The results show that porous silicon is formed when the dissolution process is controlled by the supply of holes in the semiconductor, and the density of porous silicon is both material- and process-dependent.