bluuebunny/crossref_metadata_2025 huggingface dataset:
InGaAs shallow junction fabrication using Langmuir–Blodgett film diffusion source
Authors: Shah D. M. , Chan W. K. , Bhat R. , Cox H. M. , Schlotter N. E. , Chang C. C.
Published: July 2002

A new source of cadmium diffusion in In0.53Ga0.47As has been developed. Langmuir–Blodgett (LB) deposited monolayers of cadmium arachidate have been used as a source of cadmium. The LB film has been characterized by grazing incidence infrared spectroscopy and Auger electron spectroscopy. Acceptor profiles obtained by differential Hall technique are presented. Highly doped (NA =2×1019 cm−3) shallow (xj ≊0.1–0.4 μm), p+-n junctions are obtained. Mesa-type p-i-n diodes with 125 μm diameter, ideality factor =1.3, Idark =5 nA at 20 V reverse bias, and Vbreakdown =30 V have been fabricated.
Grain boundary observation in polycrystalline CdSe by photoelectrochemical etching techniques
Authors: Sugiura Takashi , Hida Masanobu , Minoura Hideki , Ueno Yasusada
Published: July 2002

A new method for studying grain boundaries of polycrystalline CdSe semiconductors by the use of photoelectrochemical etching (photoetching) has been described. The selectivity of the photoetching site of CdSe depends on the grain structure, for instance on the presence of grain boundaries or on crystallographic orientation of the grain bulk. After the photoetching treatment of CdSe under weak anodic polarization, the grain boundaries are left undissolved. This finding makes it possible to observe directly the grain boundaries as separated from the grain bulk. A transmission electron micrograph and a selected area diffraction pattern of the grain boundary are shown.
Complete single-mode continuous-wave operation in 180° mode AlGaAs phased array lasers with dummy stripes
Authors: Sagawa M. , Kajimura T.
Published: July 2002

A new AlGaAs phased array laser structure with dummy stripes outside the stripe region is developed. The dummy stripes are dashed line stripes along both edge elements of the array stripes. Therefore, current in these dummy stripes does not cause lasing, but does increase the temperature of the edge elements. Thermal distribution in the array stripes, which mainly causes multimode oscillation in phased array lasers, is effectively unified by the dummy stripes. As a result, completely single lateral 180° mode continuous-wave operation is realized for the first time in this novel phased array laser.
Unusual orientation relationship for a copper film on Si(111)
Authors: Knorr D. B. , Bai P. , Lu T.-M.
Published: July 2002

The texture of a copper film deposited on bare Si(111) is studied. Deposition is done using the partially ionized beam technique where no potential is applied to the substrate. Pole figure analysis shows a very sharp texture where Cu{531} is parallel to Si(111). In the plane of the film, two variants of copper orientation are present with orientation relationships Si〈112̄〉//Cu〈13̄4〉and Si〈112̄〉//2.5° from Cu〈35̄0〉. The rotation between variants of 56.5° is less than the Cu(111) twin orientation. Possible reasons for the mismatch are discussed.
Effect of subband mixing and subband dispersion on the exciton line shape of superlattices
Authors: Zhou J. F. , Jung P. S. , Song J. J. , Tu C. W.
Published: July 2002

We have found a very unusual exciton line shape in the vicinity of n=2 heavy hole states (HH2) of GaAs/AlxGa1−xAs superlattices. The excitonic structure consisting of a step, a sharp peak, and a broad asymmetric hump results from valence-band mixing between HH2 and n=1 light hole states, in conjunction with subband dispersion due to well-to-well coupling of electrons and holes. In quantum well samples with negligible subband dispersion, a distinctly different exciton line shape is observed. The observed line shape is well fitted by a theory recently reported by Chu and Chang [Phys. Rev. B 39, 10861 (1989)].
Highly efficient pseudomorphic InGaAs/GaAs/AlGaAs single quantum well lasers for monolithic integration
Authors: Larsson A. , Cody J. , Forouhar S. , Lang R. J.
Published: July 2002

Highly efficient ridge waveguide pseudomorphic single quantum well lasers, emitting at 980 nm, have been fabricated from an In0.2Ga0.8As/GaAs/AlGaAs graded-index separate confinement heterostructure grown by molecular beam epitaxy. The lateral index guiding provided by the ridge reduces the anomalously large lateral loss of optical power found in gain-guided structures, thereby reducing the internal loss by more than 50%. The low threshold current (7.6 mA) and high differential quantum efficiency (79%) obtained under continuous operation as well as the transparency of the GaAs substrate to the emitted radiation render these lasers attractive for GaAs-based optoelectronic integration.
Achievement of high gain in a multiple quantum channel lateral heterojunction bipolar transistor
Authors: Thornton R. L. , Mosby W. J. , Chung H. F.
Published: July 2002

We describe refinements in the geometry of a lateral heterojunction bipolar transistor that have allowed us to greatly improve the dc characteristics of these devices. By reducing the base dimensions to 0.35 μm and improving the abruptness of the grading at the base-emitter p-n junction, we have achieved maximum current gains in excess of 600.
Microwave imaging by a moment-method solution to two-dimensional inverse scattering: Preliminary experimental results
Authors: Caorsi S. , Gragnani G. L. , Pastorino M.
Published: July 2002

Preliminary results are reported on an experimental reconstruction of dielectric scatterers, for microwave imaging purposes, via a moment-method solution to the inverse-scattering problem, in the case of two-dimensional geometries.
Proximity effect in electron beam patterned x-ray masks
Authors: Umbach C. P. , Broers A. N.
Published: July 2002

Electron beam exposures of 30 nm Au/5 nm Cr/2.2 μm Si x-ray lithography mask structures were carried out at 25, 50, 75, and 100 keV to study the reduction in the proximity effect at higher beam voltages resulting from the loss of backscattered electrons out the backside of the masks. Surprisingly, the thin Au/Cr plating base was found to be the major source of backscattering over distances <1.0 μm. In addition, the plating base served to limit the decrease in the ratio of the backscattered to forward scattered exposure that resulted from increasing the beam voltage. These results indicate that simply increasing the beam voltage will not completely eliminate the proximity effect due to backscattering that arises during the electron beam patterning of x-ray masks.
(Tl, Pb, Bi)Sr2Ca2Cu3Oz superconductors with zero resistance at 120 K
Authors: Kaneko Tetsuyuki , Wada Takahiro , Yamauchi H. , Tanaka Shoji
Published: July 2002

We have synthesized new superconductors of nearly single phase with zero-resistance temperatures around 120 K employing a novel method for sintering. The samples included a nominal composition of (Tl0.64Pb0.2Bi0.16)Sr2Ca3Cu4Oz. This sample was prepared from the mixture of presynthesized (Tl0.64Pb0.2Bi0.16)Sr2CaCu2Oz (1212 phase), CaO, and CuO powders. The mixed powder was sintered at 920 °C in O2 gas and post-annealed at 400–600 °C in O2 gas. The powder x-ray diffraction revealed that the sample was isostructural with the Tl-based (Tl, Pb, Bi)Sr2Ca2Cu3Oz (1223 phase). The sample exhibited a sharp superconducting transition at Tonsetc=125 K and TR=0c=120 K and the superconducting diamagnetic signal at 10 K was about 20% of a full Meissner effect.
Thermal instability of anodic sulfide films on Hg1−xCdxTe
Authors: Ma Zongfu , Li Rui
Published: July 2002

Thermal instability of anodic sulfide films on Hg1−xCdxTe was studied. Instead of using laser ionization or ion backscattering in studying oxidic films after heat treatment, we used x-ray photoelectron spectroscopy (XPS) in analyzing nonaqueous sulfidization. In this case, XPS is feasible, simpler, and has the advantage of better resolution. Hg evaporation was investigated here by measuring Te(3d5/2) of Te oxide peak rather than Hg lines. Correlation between thermal instability and composition x was obtained.
Sputtered BiPbSrCaCuO films on polycrystalline CuO substrates
Authors: Das S. K. , Suryanarayanan R. , Gorochov O.
Published: July 2002

BiPbSrCaCuO films have been deposited for the first time onto polycrystalline CuO substrates by dc sputtering. The films become superconducting after they are post-annealed in air. Zero resistivity is observed between 38 and 72 K depending on the annealing conditions. The sample showing an onset at 105 K gives an extrapolated zero resistivity at 90 K. The preparation and annealing conditions are described.
Planar stress relaxation in solid phase epitaxial CaF2 films grown on (111)Si by i
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u rapid isothermal processing
Authors: Singh R. , Kumar A. , Thakur R. P. S. , Chou P. , Chaudhuri J. , Gondhalekar V. , Narayan J.
Published: July 2002

Planar strain in CaF2 films on (111) Si substrate has been measured by an x-ray double-crystal diffraction technique using rocking curves. The films grown by a solid phase epitaxial approach using in situ rapid isothermal processing are almost free of tensile planar strain, and free from defects as observed by the transmission electron microscope diffraction pattern.
Radioactive metal tracer investigation of Pd2Si formation
Authors: Farmer J. , Wandt M. A. E. , Pretorius R.
Published: July 2002

A radioactive metal tracer technique has been developed with a view to identify the dominant diffusing species and the diffusion mechanism during silicide growth.The position of a thin band of radioactive metal, originally at the silicon/metal interface, is determined after silicide formation by alternate use of Rutherford backscattering spectrometry, γ spectrometry, and Ar ion sputter etching. Application of this procedure to the formation of Pd2Si yields a 109Pd activity profile, the position and shape of which indicates that mainly silicon moves during this reaction, while the observed spreading of the profile points to some palladium vacancy diffusion. The data obtained with this approach demonstrate that the technique is well suited for the determination of the predominantly diffusing species, and confirm results of other inert marker and 31Si tracer diffusion experiments.
Investigation of the ‘‘join’’ between the near edge and extended x-ray absorption fine structure
Authors: Lytle F. W. , Greegor R. B.
Published: July 2002

The L1 and L3 x-ray absorption fine structures from the same element in the same material were compared to illustrate the ‘‘join’’ between the x-ray absorption near edge structure (XANES) and the extended x-ray absorption fine structure (EXAFS). In the XANES region the two spectra differed because of the different selection rules; however, the EXAFS spectra were very similar when adjusted for the phase shift. For the oxide samples investigated the L1,3 spectra were similar for E>20 eV which identifies the demarcation between XANES and EXAFS.
Longitudinal electron transport in hydrogenated amorphous silicon/silicon nitride multilayer structures
Authors: Hattori R. , Shirafuji J.
Published: July 2002

Electron transport longitudinal to hydrogenated amorphous silicon/silicon nitride (a-Si:H/a-SiNx:H) multilayer structures (superlattices) with various barrier layer thicknesses has been measured by the time-of-flight method. The barrier thickness dependence of the electron drift velocity supports a transport model based on tunnel hopping from well to well under the influence of frequent trapping events in each well. The applied voltage dependence of the drift velocity is significantly superlinear in contrast with a linear character in bulk a-Si:H samples. The occurrence of the superlinearity is discussed by considering the applied voltage dependence of various effects which limit the longitudinal electron transport in superlattice structures. The occurrence of the superlinearity is possibly dominated by the existence of continuous distribution of deep traps in the gap of well layers rather than the applied voltage dependence of the tunneling rate, taking into account various possible effects.
Preparation of TiB2 films by photochemical vapor deposition using a D2 lamp
Authors: Motojima Seiji , Mizutani Hidetoshi
Published: July 2002

TiB2 films have been prepared by photochemical vapor deposition using a D2 lamp from a TiCl4-BCl3-H2-Ar gas mixture. The deposition temperature of the TiB2 films was lowered 50 °C by irradiation with a D2 lamp as compared to that without irradiation. The deposition rate was increased by 1.5–2.5 times with irradiation.
Continuously graded-index separate confinement heterostructure multiquantum well Ga1−xInxAs1−yPy/InP ridge waveguide lasers grown by low-pressure metalorganic chemical vapor deposition with lattice-matched quaternary wells and barriers
Authors: Ludowise M. J. , Ranganath T. R. , Fischer-Colbrie A.
Published: July 2002

Continuously graded-index separate confinement heterostructure multiple quantum well (four wells, Lz ∼50 Å) lasers fabricated in the Ga1−xInxAs1−yPy/InP system with lattice-matched quaternary wells (bulk emission wavelength λg=1.39 μm) and barriers (λg=1.2 μm) are reported. A 5-μm-wide ridge waveguide laser operates with laser threshold current Ith=34 mA at room temperature (λ∼1286 nm) with an external differential quantum efficiency of ∼19% per facet and a temperature coefficient T0 ∼40 K. Large-area threshold current density is measured at 1.1 kA/cm2 on a 40×300 μm2 device.
Operation of logic gate using YBa2Cu3O7−x/Ag/Pb-In superconducting weak links
Authors: Nishino T. , Tarutani Y. , Hasegawa H. , Fukazawa T. , Saitoh S. , Nakane H. , Kawabe U.
Published: July 2002

A logic gate has been fabricated with the partial use of high-temperature superconducting films and tested to study digital applications of such films. The logic gate consists of three YBa2Cu3O7−x/Ag/Pb-In superconducting weak links and three inductors. The current-voltage characteristics of the weak links are nonhysteristic. The logic gate successfully provides and and or logic results for two external digital inputs at 4.2 K.
Behavior of the first layer growth in GaAs molecular beam epitaxy
Authors: Liu D. G. , Lee C. P. , Chang K. H. , Wu J. S. , Liou D. C.
Published: July 2002

The first layer growth in GaAs molecular beam epitaxy has been studied by reflection high-energy electron diffraction (RHEED). The time between the growth start and the first RHEED intensity peak is found to be dependent on the starting surface condition and is different from the time needed for a single layer growth. Periodic flux interruption has been used to study the surface recovery behavior as a function of growth time. When the growth time is the same as the time for a single layer growth, sustained two-dimensional growth can be obtained.
Femtosecond-response, highly third-order nonlinear 4-(N, N-dimethylamino)-3-acetamidonitrobenzene crystal cored fiber
Authors: Yamashita Mikio , Torizuka Kenji , Uemiya Takafumi
Published: July 2002

A nonlinear refractive index n2.DAN of a 4-(N, N-dimethylamino)-3-acetamidonitrobenzene (DAN) single-crystal cored fiber of 3.9 mm length and 2.3 μm core radius is evaluated by observing the spectral broadening of a 250 fs pulse due to dispersive self-phase modulation in its fiber and that in a conventional fused-silica fiber. The result shows that the value of the femtosecond-response n2.DAN in the nonabsorbing wavelength region around 625 nm is 1.7×104 times as large as that of the latter’s glass fiber.
Charge density waves of 1T-TaS2 imaged by atomic force microscopy
Authors: Barrett R. C. , Nogami J. , Quate C. F.
Published: July 2002

The layer-structure transition-metal dichalcogenide 1T-TaS2 has been imaged in air at room temperature by atomic force microscopy (AFM). The images reveal both the atomic lattice and the periodic lattice distortion (PLD) associated with the charge density wave. The PLD period, orientation relative to the atomic lattice, and amplitude all agree with diffraction measurements. Under different imaging conditions the PLD can appear with a large amount of disorder or as a near-perfect superlattice. This difference is attributed to the tip-sample interaction. Simultaneous force and current images are shown that demonstrate the different imaging mechanisms of scanning tunneling microscopy and AFM.
Activation efficiency of a B√3×√3/Si(111) structure covered with molecular beam deposited amorphous Si or SiOx
Authors: Tatsumi T. , Hirosawa I. , Niino T. , Hirayama H. , Mizuki J.
Published: July 2002

The electric activation efficiencies for a-Si/B√3×√3/Si(111) and a-Si/B/Si(100) systems were measured before and after annealing by Hall measurement. The efficiency of the latter was lower than that of the former before annealing. But, after annealing, it rose to the former’s level, while the former’s level remained unchanged. This difference strongly suggests that almost all boron atoms are activated at the a-Si/Si(111) interface because of the √3×√3 structure formation. The B√3×√3 structure was also preserved at the interface between the Si(111) and the SiOx layer, which had been fabricated by the codeposition of Si and O2 molecular beams at room temperature. The electric activation efficiency for B√3×√3 at the interface between SiOx and Si(111) was lower than that between a-Si and Si(111). An a-Si overlayer was effective to activate the boron which formed a √3×√3 structure at the interface.
Pressure dependence of the intersubband transition in strained In0.15Ga0.85As/GaAs multiple quantum wells
Authors: Shan W. , Fang X. M. , Li D. , Jiang S. , Shen S. C. , Hou H. Q. , Feng W. , Zhou J. M.
Published: July 2002

The dependence of the intersubband transitions on pressure in strained In0.15Ga0.85As/GaAs multiple quantum wells has been studied in two samples with well widths of 8 and 15 nm, respectively, with photomodulated transmission spectroscopy by using a diamond anvil cell. The pressure coefficients of the energies for the intersubband transitions were found to depend significantly on the well widths and to be smaller than that of the band gap of constituents in bulk form. These results suggested that the critical thickness for strained In0.15Ga0.85As/GaAs layer should be smaller than 15 nm.
Two-dimensional electron gas magnetic field sensors
Authors: Heremans J. , Partin D. L. , Morelli D. T. , Fuller B. K. , Thrush C. M.
Published: July 2002

We describe the use of accumulation layers of electron charge in applications as magnetoresistive devices. We consider two such systems: an InGaAs/InP heterostructure in which we identify a two-dimensional electron gas from the observation of the quantum Hall effect, and InAs films, in which a strong surface accumulation of charge is inferred from depth profiling studies of the galvanomagnetic coefficients. Magnetoresistive devices fabricated from these materials exhibit outstanding field sensitivity and temperature stability due to the existence of electrons of relatively high density and mobility in the accumulation regions. We also model the magnetosensitivity of our devices.
GaAs traveling-wave directional coupler optical modulator/switch
Authors: Hayashi Hideki , Tada Kunio
Published: July 2002

Device structure, fabrication method, and experimental results of a GaAs/AlGaAs traveling-wave directional coupler optical modulator/switch operated at 1.06 μm wavelength are described for the first time. An extinction ratio of 13.7 dB has been measured at the switching voltage of 10.4 V, and a 3 dB bandwidth of 9.1 GHz has been demonstrated for a device with a waveguide width of 5.5 μm, waveguide spacing of 3.5 μm, and length of 8 mm.
Optical switching of quantum interference through exchange interactions between coherent electron waves and photoexcited virtual excitons
Authors: Yamanishi M. , Osaka Y. , Yamatani K. , Agou S.
Published: July 2002

Proposed and analyzed is an ultrafast modulation scheme for electron quantum interference based on exchange interactions between coherent electron waves and photoexcited virtual excitons in quantum wire interferometers.
Frequency stability and reproducibility of optically pumped far-infrared lasers
Authors: Crownover Richard L. , Everitt Henry O. , De Lucia Frank C. , Skatrud David D.
Published: July 2002

Direct measurements of the gain profile of optically pumped far-infrared lasers show that large shifts in the laser frequency can be caused by the absorption from thermal molecules on the laser transition. The absorption shifting greatly exacerbates pump frequency deviations, resulting in an extreme sensitivity to pump offsets and drifts. This pressure-dependent shifting mechanism is not present in transversely pumped lasers, which explains their superior frequency reproducibility compared to longitudinally pumped lasers, and reconciles two apparently conflicting results regarding laser stability.
Femtosecond gain dynamics and saturation behavior in InGaAsP multiple quantum well optical amplifiers
Authors: Hall K. L. , Lai Y. , Ippen E. P. , Eisenstein G. , Koren U.
Published: July 2002

Femtosecond pump-probe experiments on InGaAs/InGaAsP multiple quantum well optical amplifiers reveal ultrafast dynamics that are similar to, but quantitatively different from, those observed in bulk amplifiers. Pulse energy saturation of the amplifier gain is also studied using 150 fs and 20 ps pulses and is found to be pulsewidth dependent. The measured saturation energies are 200 fJ and 6 pJ, respectively.
Coherent linear and two-dimensional arrays of multiple quantum well grating-surface-emitting diode lasers emitting at 1.5 μm
Authors: Palfrey S. L. , Enstrom R. E. , VanGieson E. A. , Hammer J. M. , Martinelli Ramon U. , Carlson N. W. , Evans G. A. , Andrews J. T. , Appert J. , Stolzenberger R. , Triano A.
Published: July 2002

We have demonstrated linear and two-dimensional arrays of grating-surface-emitting lasers operating at 1.5 μm. The gain sections are 400-μm-long InGaAs/InGaAsP multiple quantum well ridge-guide diode lasers, connected by waveguide output sections of 300-μm-long distributed-Bragg-reflection gratings. These arrays exhibit coherent, mutual-injection-coupled laser action. The far-field patterns are characteristic of low-order array modes that are nearly diffraction limited. Predominantly single-wavelength-mode operation is observed.
Etch rate modeling for ion-irradiated nitrocellulose
Authors: Merhari L. , Belorgeot C. , Moliton J. P.
Published: July 2002

The self-developing mechanism of nitrocellulose when used as an ion beam resist is described by a model predicting the evolution of the etch rate versus irradiation time. Fundamentals of the model based on ion energy deposition dependent ablative development along with related mathematical derivations are given and briefly discussed. Comparison between theoretical results and experimental data available for protons at 20 keV and Ne+, Ar+, Kr+ ions at 150 keV is made and shows a good agreement. This result clearly does not conflict with our assumption that the nitrocellulose etch rate is dependent on the total ion deposited energy no matter how the energy is deposited.
Local electron concentration-dependent electronic stopping power model for Monte Carlo simulation of low-energy ion implantation in silicon
Authors: Klein K. M. , Park C. , Tasch A. F.
Published: July 2002

We have developed a new electronic (inelastic) stopping model for low-energy implanted ions which explicitly accounts for the effect of the local variation of the electron density between the lattice atoms in the silicon crystal target material on the amount and rate of energy loss due to electronic processes. Designed for incorporation into Monte Carlo simulation codes, this model more accurately predicts the energy loss of ions due to electronic processes, and it provides significantly better agreement with experimental profiles of boron implanted into single-crystal silicon over a wide range of energies and incident angles compared with the agreement obtained with other electronic stopping models.
Picosecond all-optical logic gate in a nonlinear organic étalon
Authors: Williams V. S. , Ho Z. Z. , Peyghambarian N. , Gibbons W. M. , Grasso R. P. , O’Brien M. K. , Shannon P. J. , Sun S. T.
Published: July 2002

An all-optical logic gate has been demonstrated in a nonlinear organic étalon using femtosecond laser pulses. The logic gate consists of a guest-host organic thin film, 7-[4-[(4-hexyloxyphenyl)azo](naphthyl)azo-(2,3-dihydro-1,3-dimethyl-2-octyl)] perimidine doped in poly(methyl methacrylate), sandwiched between two highly reflective mirrors. It shows a subpicosecond switch-on time and a switch-off or recovery time that has a fast, ≂4 ps component and slower components. A maximum contrast ratio of ≂2 between the switch-on and switch-off states of the optical gate was obtained. The nonlinear index of refraction is also measured from this Fabry–Perot interferometer to be Δn=0.005.
Angle-dependent laser-induced voltages in room-temperature polycrystalline wafers of YBa2Cu3O7−x
Authors: Tate K. L. , Hilinski E. F. , Foster S. C.
Published: July 2002

Room-temperature laser-induced voltages were observed in unsupported, polycrystalline wafers of YBa2Cu3O7−x in the absence of a transport current. Peak voltages of ∼1 V were detected in response to 40 mJ pulses of 532 nm light. The rise and fall times for the signals were detector limited. The half widths of the signals were instrument response limited (laser pulsed limited for a 10 ns laser pulse and digitizer limited for a 30 ps laser pulse). At fixed pulse energy, the induced peak voltage scales as the sine of the angle of incidence of the laser beam and is nulled at normal incidence. The magnitude of the signal as a function of sample thickness, preparation, and laser excitation wavelength is discussed.
Early stages of growth of GaAs on Si observed by scanning tunneling microscopy
Authors: Biegelsen D. K. , Bringans R. D. , Northrup J. E. , Swartz L. E.
Published: July 2002

Using a system coupling molecular beam deposition, scanning tunneling microscopy, and Auger spectroscopy in a connected ultrahigh-vacuum environment, we have observed the initial stages of GaAs growth on vicinal Si(100), including As termination, ordered Ga overlayers, and subsequent competition between two- and three-dimensional structures.
Influence of surface topography on depth profiles obtained with secondary-ion mass spectrometry
Authors: Walker A. J. , Borchert M. T. , Vriezema C. J. , Zalm P. C.
Published: July 2002

Lithographically generated well-defined surface topography of submicron dimensions has been etched into silicon (100) previously implanted with 25 keV 11B to a fluence of 2×1014 atoms/cm2. The thus-obtained samples were depth profiled via secondary-ion mass spectrometry (SIMS). The boron concentration distributions measured were contrasted against those found on undisturbed flat parts of the target. From this intercomparison the otherwise trivial observation that surface topography causes profile distortion becomes suddenly alarming as an apparent improvement of depth resolution occurs. Scanning electron microscope images enable identification of the origin of this remarkable phenomenon. The present results imply that (i) the hitherto commonly accepted assumption in the interpretation of SIMS depth profiles that perceived gradients are never steeper than actual ones is subject to revision; (ii) it may prove very difficult, if not impossible, to construct SIMS equipment for reliable on-chip analysis of submicron details.
Molecular beam epitaxial growth of high quality GaAs on untilted (001) Si substrates assisted by electron beam irradiation
Authors: Leem Jae-Young , Kim Deuk-Young , Kang Tae-Won , Lee Jae-Jin , Oh Jae-Eung
Published: July 2002

Using molecular beam epitaxy assisted by an electron beam irradiation with a beam energy of 50 keV at an angle of incidence 5°, we have successfully grown high quality GaAs layers on untilted (001)Si substrates. Raman spectra show that this technique reduces crystalline imperfections usually found in GaAs layers grown (001)Si substrates by a factor of 20, clearly demonstrating the effectiveness of this technique. Typical low-temperature photoluminescence spectra of undoped GaAs on Si contain four features at emission energies of 1.503, 1.488, 1.471, and 1.434 eV. The full width at half maximum (FWHM) of the bound excitonic peak with heavy holes is 2.8 meV, which can be one of the narrowest ever reported. The incident electron beam is expected to play several roles, such as cleaning Si surfaces by removing carbon/oxygen residuals, enhancement of migration rates of adatoms on the growing surface, and acceleration of the single-domain formation during the growth.
Wannier–Stark localization in a strained InGaAs/GaAs superlattice
Authors: Pezeshki B. , Thomas D. , Harris J. S.
Published: July 2002

We report the first room-temperature observation of Wannier–Stark localization in a strained InGaAs/GaAs superlattice. The localization effects are in close agreement to theory. At low electric fields, the room-temperature absorption data show a small Wannier exciton peak at the lower edge of the miniband, and a more prominent M1 exciton at higher energy. At higher fields, the miniband localizes to a single quantum well exciton with accompanying +1 and −1 transitions. At even higher fields the initial blue shift of the Wannier exciton changes to a Stark effect red shift with a Δα/α of about 3.
n-type doping of amorphous silicon using tertiarybutylphosphine
Authors: Gaughan K. , Nitta S. , Viner J. M. , Hautala J. , Taylor P. C.
Published: July 2002

The use of a liquid organic source for n-type doping in hydrogenated amorphous silicon (a-Si:H) is described. Tertiarybutylphosphine (TBP) vapor is added to silane in a rf glow discharge process to produce doped a-Si:H thin films. Impurity levels from parts per million to about 1% phosphorus have been incorporated into the film with this method. Measurements of dark conductivity, photoconductivity, conductivity activation energy, electron spin resonance, and sub-gap optical absorption of the TBP-doped films are compared to those published for films doped with phosphine.
Growth of oxide layers on gallium arsenide with a high kinetic energy atomic oxygen beam
Authors: Hoffbauer M. A. , Cross J. B. , Bermudez V. M.
Published: July 2002

Oxide layers have been formed on (110) and (100) GaAs wafers by exposure to a high kinetic energy beam of atomic O and characterized using x-ray photoemission spectroscopy (with Ar+ ion sputter profiling) and Raman spectroscopy. Photoemission shows the reacted layer, ∼500 Å thick, to be uniform in composition and fully oxidized. Raman spectroscopy shows that the substrate is not appreciably disordered during oxidation and in some cases no free-elemental As is present at the oxide-substrate interface at a detectable level.
High-power, diffraction-limited, monolithically integrated master oscillator/power amplifier
Authors: Welch D. F. , Waarts R. , Mehuys D. , Parke R. , Scifres D. , Craig R. , Streifer W.
Published: July 2002

Monolithically integrated master oscillator/power amplifiers have been fabricated with a single-mode distributed Bragg reflector laser as the oscillator and a chain of amplifier output couplers defined by a single-mode waveguide gain region and a second-order grating detuned from the gain peak. The output of the amplifier chain is a single frequency and can be phased to obtain a diffraction-limited output up to an output power of 485 mW.
Novel optical-power-controlled oscillator with multigigahertz oscillation frequency range
Authors: Choa F. S. , Koch T. L. , Koren U. , Burrus C. A.
Published: July 2002

An optical analogue of a voltage-controlled oscillator based on an optical resonant amplifier structure is proposed and experimentally demonstrated. By using tunable distributed Bragg reflector and distributed feedback laser diode amplifiers, we demonstrate oscillators with frequencies controllable from several hundred MHz into multiGHz range. Such devices may find applications in future all-optical signal processing and optical communication systems.
Frequency modulation and linewidth of gain-levered two-section single quantum well lasers
Authors: Lau K. Y.
Published: July 2002

The ‘‘gain lever’’ effect in two-section single quantum well lasers can be used in enhancing the frequency modulation (FM) efficiency of the laser without a corresponding increase in the FM noise, i.e., linewidth. Theoretical and experimental results of the FM efficiency, speed, tuning range, and linewidth will be discussed and compared to other tunable laser structures.
Negative differential conductance due to resonant states in GaInAs/InP hot-electron transistors
Authors: Miyamoto Yasuyuki , Yamaura Shinji , Furuya Kazuhito
Published: July 2002

We have observed dips with negative values in the curve of the differential conductance of the base versus the base-emitter voltage dIB/dVBE at 77 K in GaInAs/InP hot-electron transistors grown by organometallic vapor phase epitaxy. The efficiency of the hot-electron transmission across the 40-nm-thick base was more than 0.99. In comparison with a theoretical model considering that observed dips should have been caused by the resonant states in the base well, the phase relaxation time of the hot electron is estimated to be in the order of 0.1 ps or longer.
Large increase of refractive index and compactness in siloxane-type spin-on-glass induced by ion implantation
Authors: Moriya N. , Shacham-Diamand Y. , Kalish R.
Published: July 2002

Drastic changes in index of refraction and volume shrinkage of spin-on-glass films induced by P+ implantation are reported. An increase in refraction index (n) as large as 20% (from 1.38 to 1.79) has been measured following 1.6×1016 cm −2 implantations. The changes in n are accompanied by a volume shrinkage of similar magnitude. However, at doses exceeding ≊1015 cm−2 the shrinkage saturates while the index of refraction continues to increase indicating that material changes other than simple densification must be responsible for the observed rise in refractive index.
Preparation of Ag-coated superconducting Bi2Sr2CaCu2Ox glass-ceramic fibers
Authors: Komatsu T. , Hirose C. , Ohki T. , Sato R. , Matusita K. , Yamashita T.
Published: July 2002

The Ag-coated superconducting Bi2 Sr2 CaCu2 Ox glass-ceramic fibers were successfully prepared. The glass fibers with a length of 50 cm, a width of 100–200 μm, and a thickness of about 20 μm were first drawn from glass plates with a thickness of 1 mm and then silver pastes were coated on the smooth surface of glass fibers. The Ag-coated glass fibers were converted into superconductors after annealing at temperatures of 820–860 °C. The main crystalline phase in the glass-ceramic fibers was the superconducting low Tc phase. The Ag-coated glass-ceramic fibers obtained by annealing at 840 °C for 5 h in air exhibited superconductivity with a Tc (zero)=70 K and a critical current density (60 K, zero magnetic field) of more than 40 A/cm2 .
Peak electron mobilities between 2.75 and 3.32×105 cm2 V−1 s−1 in GaAs grown by molecular beam epitaxy with As2
Authors: Stanley C. R. , Holland M. C. , Kean A. H.
Published: July 2002

Exceptionally pure n-GaAs has been grown without intentional doping by solid-source molecular beam epitaxy (MBE) using arsenic dimers (As2). Peak electron mobilities in the range 2.75–3.32×105 cm2 V−1 s−1 at temperatures of ≊40–50 K with free-electron densities n=1×1014 cm−3 have been measured for a series of layers grown under a variety of conditions. These mobilities are among the highest recorded for MBE-grown GaAs.
Effect of AlGaAs window and buffer layers on the response characteristics of GaAs photoconductive detectors
Authors: Youn H. J. , Darling R. B. , Kuhn K. J.
Published: July 2002

Five comparative GaAs-based photoconductive detectors were fabricated to investigate the effects of AlGaAs window and buffer layers on device performance. Steady-state and transient photoconductive responses were measured on structures with and without an AlGaAs window layer over the photoconductive layer, and with and without an AlGaAs buffer layer between the photoconductive layer and substrate. The structure with both an AlGaAs window and AlGaAs buffer layer shows the lowest dark current (<1 nA) and the highest responsivity (∼ 0.2 A/W). However, the structure on a bare semi-insulating GaAs substrate shows the fastest pulse response of ∼ 800 ps full width at half maximum, indicating that interfacial rather than bulk properties dominate the photoconductive characteristics.
Intensity noise in the ultrahigh efficiency tandem-contact quantum well lasers
Authors: Gajić Dragan , Lau Kam Y.
Published: July 2002

We present theoretical and experimental results describing the intensity noise in the ultrahigh efficiency tandem-contact single quantum well laser. We find that the substantial increase in the modulation efficiency of these lasers is accompanied by only a marginal increase in the intensity noise.
Higher order electron cyclotron resonances in n-type HgTe-CdTe superlattices
Authors: Dobrowolska M. , Wojtowicz T. , Furdyna J. K. , Meyer J. R. , Feldman R. D. , Austin R. F. , Ram-Mohan L. R.
Published: July 2002

Temperature-dependent magneto-optical measurements on an n-type HgTe-CdTe superlattice have been compared to the results of a comprehensive new theory, which fully incorporates the complexities of the unusual superlattice band structure. The theory predicts that higher order cyclotron resonance processes should yield a separate transmission minimum which is distinct from that of the lowest order cyclotron transition, and the data provide an unambiguous confirmation of this prediction. Since the energy gap is near zero, interband transitions are also observed in the same spectral range as the cyclotron resonance.
Experimental verification of an ion-induced focus model for the recirculating electron beam injector
Authors: Poukey James W. , Mazarakis Michael G. , Platt R. C.
Published: July 2002

We present a model for the operation of a particular type of electron beam diode used in the Sandia Recirculating Linear Accelerator system. The critical element of the model is ion emission from the anode aperture, which neutralizes enough beam space charge to permit focusing. Recent experimental results are shown which support the model in several respects.
Observation of miniband formation in the CdTe/Cd1−xMnxTe quantum well system
Authors: Harwit Alex , Hsu C. , Agulló-Rueda F. , Chang L. L.
Published: July 2002

We report the effects of perpendicular electric fields on the eigenenergies of the CdTe/Cd1−xMnxTe quantum well system. The samples are probed at 6 K using photoluminescence. In an electric field, the photoluminescence spectra of wide-barrier quantum well samples red shifted, consistent with the quantum-confined Stark effect. The spectra of narrow-barrier superlattice samples blue shifted, indicative of miniband reduction to localized states. A linear blue shift was observed up to a field of 50 kV/cm after which saturation occurred. Additionally, we have observed luminescence which appeared to arise from transitions between adjacent wells. No striking effects were observed at the paramagnetic-spin glass transition temperature.
Observation of reduced current thresholds in GaAs/AlGaAs vertical-cavity surface-emitting lasers grown on 4° off-orientation (001) GaAs substrates
Authors: Wang Y. H. , Tai K. , Hsieh Y. F. , Chu S. N. G. , Wynn J. D. , Cho A. Y.
Published: July 2002

GaAs/AlGaAs vertical-cavity surface-emitting lasers (VCSELs) with two semiconductor distributed Bragg reflectors (DBRs) were grown by molecular beam epitaxy. The threshold current was found to be 20–50% less on an average for VCSELs grown on the 4° off-orientation (001) substrates than those on the on-orientation ones. The lower threshold current was attributed to the smoother interfaces of the Al0.1Ga0.9As/AlAs DBRs in the off-orientation growth observed by transmission electron microscopy. A threshold current and current density of 12 mA and 10.5 kA/cm2 were measured with an emission efficiency of 0.2 mW/mA.
Analysis of quantum-confined structures using the beam propagation method
Authors: Kim Inho , Gustafson T. K. , Thylén Lars
Published: July 2002

The beam propagation method has been applied to find confined energy eigenvalues and eigenfunctions for a III-V quantum well structure subjected to an external electric field. Quantum-confined Stark shifts for both electrons and holes and excitonic states for single and double quantum wells are calculated. Excellent agreement with analytical results where available is demonstrated. A comparison with experimental data published in the literature is given.
Effect of an AlAs/GaAs mirror on the spontaneous emission of an InGaAs-GaAs quantum well
Authors: Rogers T. J. , Deppe D. G. , Streetman B. G.
Published: July 2002

Data are presented demonstrating a strong influence of a closely spaced AlAs/GaAs distributed Bragg reflector on the spontaneous emission characteristics of an InGaAs-GaAs quantum well. The mirror to quantum well spacings on different crystal samples correspond to optical path lengths of either 1/4, 1/2, or 3/4 of the emission wavelength. The samples are characterized using photoluminescence, electroluminescence, and reflectivity measurements. Spontaneous emission is found to be greatly enhanced for a 1/2 wavelength spacing, while 1/4 and 3/4 spacings suppress the spontaneous emission by a factor of ≳1000.
Study of electrical characteristics of polyoxides grown by rapid thermal oxdidation
Authors: Lo G. Q. , Cheung A. W. , Kwong D. L. , Alvi N. S.
Published: July 2002

Thin (∼18 nm) polyoxide films have been grown on phosphorus-implanted polycrystalline silicon (poly-Si) by rapid thermal oxdiation (RTO). With an emphasis on the bias polarity dependence, we have studied the electrical characteristics of polyoxides, such as leakage current, breakdown field, and charge trapping. In comparison with polyoxides grown in conventional furnace, RTO polyoxides exhibit a significantly reduced leakage current. In addition, the dielectric breakdown strength and breakdown field distribution have been improved. When electrons were injected from the top poly-Si/SiO2 interface, RTO polyoxide shows a reduced trapping rate. However, when electrons were injected from the SiO2/bottom poly-Si interface, RTO polyoxide shows an increased trapping rate.
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i
t
u growth of YBa2Cu3O7−x high T
c superconducting thin films directly on sapphire by plasma-enhanced metalorganic chemical vapor deposition
Authors: Chern C. S. , Zhao J. , Li Y. Q. , Norris P. , Kear B. , Gallois B.
Published: July 2002

Highly c-axis oriented YBa2Cu3O7−x superconducting thin films have been, in situ, deposited directly on sapphire substrate by a remote microwave plasma-enhanced metalorganic chemical vapor deposition process (PE-MOCVD). The films were deposited at a substrate temperature of 730 °C followed by a fast cooling. The as-deposited films show attainment of zero resistance at 82 K and have critical current density of 104 A/cm2 at 70 K. ac susceptibility measurement indicated that the films contain a single superconducting phase. PE-MOCVD was carried out in a commercial-scale MOCVD reactor with capability of uniform deposition over 100 cm2 per growth run.
Temperature dependence of microwave losses in Y-Ba-Cu-O films
Authors: Pakulis E. J. , Sandstrom R. L. , Chaudhari P. , Laibowitz R. B.
Published: July 2002

We have made measurements of the T dependence of microwave absorption (at 22.7 GHz) in films of Y1Ba2Cu3Ox on SrTiO3 and LaGaO3 substrates. The superconducting transition temperatures were near 90 K. The film on SrTiO3 had predominantly c axis normal to the film, while the film on LaGaO3 was partially a axis oriented. The microwave losses L for both films followed the temperature dependence given by L∝t/√1−t, with t=T/Tc. In the macroscopic theory of Ginzburg–Landau, this expression is proportional to the number of normal electrons within a penetration depth of the surface of the film, provided (1−t)≪1. However, we find that the above expression fits the data well for a wide range of T.
Broad-area high-power semiconductor optical amplifier
Authors: Goldberg Lew , Weller J. F.
Published: July 2002

Operating characteristics of a high-power 400-μm-wide, 500-μm-long double-pass near-traveling-wave GaAlAs amplifier are described. In pulsed operation, 2.5 W of diffraction-limited emission at 820 nm was obtained with an external power gain of 10 dB and 24% electrical to optical conversion efficiency.
Electrically controlled frequency scanning by a photoconducting antenna array
Authors: Hu B. B. , Froberg N. , Mack M. , Zhang X.-C. , Auston D. H.
Published: July 2002

The radiation frequency of an electromagnetic wave from a spatial periodically biased photoconducting antenna array can be electrically scanned by varying the periodicity of the bias voltage on the antennas. Over 900 GHz frequency tuning bandwidth has been demonstrated.
Effect of strain on the resonant frequency and damping factor in InGaAs/InP multiple quantum well lasers
Authors: Fukushima T. , Bowers J. E. , Logan R. A. , Tanbun-Ek T. , Temkin H.
Published: July 2002

The intensity noise of strained InxGa1−xAs/InP multiple quantum well (MQW) lasers is measured for three types of strain: tensile strain (x=0.48), no strain (x=0.53), and compressive strain (x=0.65). From a comparison between the measured noise power spectral density and the theoretical one, the resonance frequency and the carrier damping factor of each type of lasers are calculated. Although compressive strained MQW lasers show abot 10% increase in resonance frequency compared to those of tensile strained and unstrained lasers, this increase is smaller than theoretically predicted. Most important, all three types of MQW lasers show about two to three times higher nonlinear gain saturation and lower maximum bandwidth than conventional double-heterostructure lasers. A solution to reduce this high damping is also discussed.
Crystallization of amorphous silicon by reconstructive transformation utilizing gold
Authors: Stoemenos J. , McIntosh J. , Economou N. A. , Bhatnagar Y. K. , Coxon P. A. , Lowe A. J. , Clark M. G.
Published: July 2002

A gold layer one order of magnitude thinner than the thickness of an amorphous silicon layer in intimate contact leads to the dissolution of the amorphous silicon into the liquid and the subsequent precipitation of crystalline Si as the liquid phase propagates into the amorphous phase at above eutectic temperatures. The crystalline Si precipitate has grain sizes of the order of 6 μm. The Si/Au liquid is very sensitive to constitutional supercooling and subsequent crystallization.
Phase-matched second-harmonic generation in periodically poled optical fibers
Authors: Kashyap Raman
Published: July 2002

Phase-matched second-harmonic generation is reported in periodically poled optical fibers for the first time. A periodic χ(2) was induced in optical fibers during phase-matched periodic-electric field-induced second-harmonic generation at a fundamental wavelength of 1064 nm. Further, it is shown that periodic poling can be achieved by photo excitation with radiation of 514.5 nm wavelength while applying a spatially periodic static field. In both cases, the mode interaction HEω11→HE2ω11 is quasi-phase matched at 1064 nm. Seeding is observed in fibers beyond the poled region. A photoinduced index change has been measured using electric field induced second-harmonic generation.
Atomic cadmium laser pumped by multiphoton ionization
Authors: Tünnermann A. , Henking R. , Wellegehausen B.
Published: July 2002

By multiphoton ionization of cadmium vapor with a high peak power femtosecond KrF-excimer laser system, a cold and dense plasma is generated. In a fast recombination process an inversion in the atom results, leading to strong short-pulse laser oscillation at λ=508 nm. Also superfluorescence phenomena have been observed.
Decay times of excitons in lattice-matched InGaAs/InP single quantum wells
Authors: Brener I. , Gershoni D. , Ritter D. , Panish M. B. , Hamm R. A.
Published: July 2002

A study of the photoluminescence decay times in lattice-matched InGaAs/InP single quantum wells grown by two different epitaxial techniques is presented. We show that these decay times can be measured directly using a nonlinear photoluminescence autocorrelation technique. A model based on the saturation of localized exciton states describes the temporal behavior and the optical nonlinearities observed very well.