bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron beam modification of the Schottky diode characteristics of diamond
Authors: Glesener J. W. , Morrish A. A. , Snail K. A.
Published: July 2002

Electron beam irradiation from a scanning electron microscope has been shown to improve the rectification characteristics of a boron doped diamond sample, as evidenced by measurement of a lowered reverse current in Al Schottky diodes. The sample processing procedure consisted of cleaning in heated CrO3/H2SO4 and NH4OH/H2O2 mixtures, exposure to an electron beam, a post-exposure cleaning in NH4OH/H2O2, and metallization. Since published information on the effect of CrO3/H2SO4 and NH4OH/H2O2 mixtures on the diamond surface is lacking, we hypothesize that the exposure of the diamond surface to an electron beam releases hydrogen from the surface, while the post-irradiation clean in boiling NH4OH/H2O2 may oxygenate the diamond surface. This result is consistent with previous work which demonstrated that annealing in hydrogen and oxygen ambients affected the surface resistance of diamond. These results indicate a high surface resistance is necessary to form good Schottky junctions in diamond.
Molecular beam epitaxy growth interrupt and temperature studies on doped and undoped single quantum well pseudomorphic structures
Authors: Miller B. A. , Kirby P. B.
Published: July 2002

Variable temperature Hall and low-temperature photoluminescence measurements have been used to monitor changes in the transport properties of electrons in modulation doped GaAs/InGaAs/AlGaAs structures that result from growth interruptions and varying temperature growth profiles during deposition by molecular beam epitaxy. Growth interruptions at the InGaAs/AlGaAs interface can lead to higher two-dimensional electron gas mobilities since the AlGaAs near the heterojunction interface can be grown nearer its optimum growth temperature. Changes in carrier mobilities as a result of growth variations are correlated with differences in the energy dependence of the photoluminescence spectrum.
New analog memory devices demonstrated using heterojunction acoustic charge transport device technology
Authors: Cullen D. E. , Miller M. J.
Published: July 2002

A new analog memory (AM) has been demonstrated using heterojunction acoustic charge transport (HACT) technology. The initial HACT AMs had storage time capabilities of 100 μs at 25 °C. The Schottky electrode storage array had 36 memory cells, each cell holding 2 charge packets, giving a maximum signal frequency of half the Nyquist frequency. Hold voltages in the 6–8 V range were found to be adequate, and effective storage was obtained at the same dc transport current level that resulted in the best charge transport efficiency. Storage times in the millisecond range are possible with cooling.
New self-electro-optic effect device using two wavelengths in InGaAs/AlGaAs multiple quantum wells
Authors: Giugni Stephen , Kawashima Kenji , Fujiwara Kenzo , Sano Naokatsu
Published: July 2002

A new self-electro-optic effect device is proposed and demonstrated in an InGaAs/AlGaAs multiple quantum well diode structure by using different wavelengths for the signal and control wavelengths. The single resistor biased device exhibits optical transmission bistability between two stable states of the signal beam at λ1 when the control beam power at λ2 is varied. The two wavelengths λ1 and λ2 may be widely separated so that one is absorbed in the substrate and the other transmitted eliminating the need for substrate removal. The separate wavelengths also eliminate interference effects simplifying the design of vertical device arrays enhancing the possibility of system integration.
Importance of the high-velocity projectile-z3 term in modified Bethe–Bloch stopping power theory
Authors: Porter L. E.
Published: July 2002

Modified Bethe–Bloch theory of stopping power provides for inclusion of several parameters in the Bethe–Bloch formula. These parameters include the target mean excitation energy and those associated with target shell corections, with the low-velocity projectile-z3 (Barkas effect) term, and with an effective charge factor. Fits of stopping power measurements permit extraction of one or two (and sometimes three) parameter values while the remaining parameters are assigned fixed values based on other studies. Omission of one or more of the required correction terms or factors induces distortions in the values of the extracted parameters. A recent development has been omission of the (parameter independent) high-velocity Barkas effect term in an analysis where projectile energies were sufficiently high to necessitate inclusion of this term. The importance of incorporating all pertinent terms and factors into the modified Bethe–Bloch formula is strenuously emphasized.
Correlation between structural and optical properties in proton-exchanged LiNbO3
Authors: Hsu Wei-Yung , Braunstein Gabriel , Gopalan Venkatraman , Willand Craig S. , Gupta Mool C.
Published: July 2002

We present a correlation of the structural characterization of proton-exchanged LiNbO3 provided by ion beam and x-ray analysis with the optical characterization provided by refractive index and second-harmonic generation measurements. The process of proton exchange induces disorder in the crystal lattice of LiNbO3. Subsequent thermal annealing removes only partially the lattice disorder and, in particular, the near surface region of the samples generally remains highly distorted. Results of x-rays studies indicate that the proton exchange induces a strain in the lattice and thermal annealing partially recovers it.
Distribution of Ge in O+ implanted silicon
Authors: Twigg M. E. , Zvanut M. E. , Stahlbush R. , Godbey D. J. , Jenkins W. C.
Published: July 2002

We have studied 50 nm Si0.8Ge0.2 buried layers and 800 nm Si0.9Ge0.1 layers, grown by molecular beam epitaxy, which were implanted with 200 keV oxygen O+ ions to a dose of 1.8×1018/cm2. This implantation procedure is similar to that used in the formation of SIMOX (separation by implantation of oxygen), although it was not followed by the usual high temperature anneal. Because the initial implantation profile extends as far as 600 nm below the Si surface, the 50 nm Si0.8Ge0.2 layers were embedded in Si at depths of 600, 500, 400, and 300 nm from the Si surface. The effects of Ge incorporation could then be studied as a function of distance from the surface and position within the implantation profile. Using a scanning transmission electron microscope equipped with energy dispersive x-ray spectroscopy, we examined cross-sectional specimens for the distribution of the Ge in and around the implanted oxide layer. We found that the Ge tended to be excluded from the oxide in all the samples with the 50 nm buried layer. For the case where the oxide was implanted into the midst of an 800 nm layer, the Ge remained in the oxide.
Fabrication of periodically inverted domain structures in LiTaO3 and LiNbO3 using proton exchange
Authors: Makio Satoshi , Nitanda Fumio , Ito Kohei , Sato Masayoshi
Published: July 2002

We report on the fabrication of a first-order periodically inverted domain structure in LiTaO3 and LiNbO3 for quasi-phase-matched devices using proton exchange with one-directional heating. First-order periodically inverted domains with a 3.2 μm period and more than 40 μm depth were formed beyond the proton exchanged region. This domain inversion took place during the proton exchange process, far below the Curie temperatures. Taking advantage of these deep domains, we demonstrated second-harmonic generation without fabricating a channel waveguide.
Electron-beam-assisted dry etching for GaAs using electron cyclotron resonance plasma electron source
Authors: Watanabe Heiji , Matsui Shinji
Published: July 2002

Electron-beam (EB)-assisted dry etching of GaAs using Ar electron cyclotron resonance (ECR) plasma as an electron shower source is developed to achieve a low energy and high current density electron beam (EB). The rate of EB-assisted dry etching is more than ten times larger than for Cl2 gas etching.It is confirmed, through photoluminescence measurement, that this etching method causes less damage than ion beam techniques and is very effective for damaged layer removal. Using this technique, a 0.4 μm linewidth low-damage fine structure of GaAs was fabricated.
Metalorganic chemical vapor deposition route to epitaxial neodymium gallate thin films
Authors: Han B. , Neumayer D. , Schulz D. L. , Marks T. J. , Zhang H. , Dravid V. P.
Published: July 2002

Phase-pure epitaxial thin films of the YBa2Cu3O7−δ lattice-matched, low dielectric loss perovskite insulator NdGaO3 have been grown on (110) LaAlO3 substrates by a metalorganic chemical vapor deposition (MOCVD)/post-annealing process. Amorphous Nd-Ga-O films are first prepared by MOCVD using the volatile metalorganic β-diketonate precursors Nd(dpm)3 and Ga(dpm)3 (dpm=dipivaloylmethanate). Subsequent postannealing affords phase pure, highly oriented [(001) and/or (110) orientations perpendicular to the substrate surface] and epitaxial NdGaO3 films as assessed by x-ray diffraction θ-2θ, ω, and φ scans. Cross-sectional high-resolution electron microscopic images show that the epitaxial growth occurs with atomically abrupt film-substrate interfaces and with coexisting NdGaO3 (001) and (110) orientation domains.
Controlled deposition and lateral growth of an ordered monolayer of carbon on Mo(100) observed in situ
Authors: Garcia Adrian , Wang Congjun , Kordesch Martin E.
Published: July 2002

A two-dimensional ordered carbon monolayer has been deposited on oxygen covered Mo(100) at 1300 K from a 5% methane in hydrogen gas mixture passed over a tungsten filament at 2300 K. The carbon layer grows laterally by occupying surface sites freed by the removal of adsorbed oxygen. A well-defined growth front is observed with photoemission electron microscopy, as well as a transitional species localized at the carbon-oxygen growth boundary.
Low-frequency noise in very high mobility modulation-doped structures
Authors: Phillips J. R. , Tsubaki K. , Saku T. , Tarucha S.
Published: July 2002

We report here on the observation of low-frequency (1–100 Hz) noise characteristics as a function of current in very high mobility four-terminal structures at 4.2 K. At low currents, the noise levels are too low to be observed with our measurement system. When the mobility is decreased by a change in gate voltage, or when the injected current is increased, noise levels increased. At currents where excess noise is observable, the channel current-voltage characteristics are nonlinear and the noise current dependence is superquadratic. The steep current-dependence results from the degradation of mobility due to electron heating, with the subsequent rapid noise increase due to optical phonon scattering.
Generation of carrier concentrations as high as 5×1019 cm−3 in GaAs by Si doping using a KrF excimer laser
Authors: Sugioka K. , Toyoda K.
Published: July 2002

Extremely high carrier concentrations have been generated in GaAs by KrF excimer laser doping with Si using SiH4 gas. The carrier profile of the doped region shows a boxlike profile with a carrier concentration as high as 5×1019 cm−3 in a nonthermal equilibrium state and a depth of 170 nm. The formation of the nonthermal equilibrium state has a close connection with the transient melting and cooling process of the excimer laser doping. In addition, the thermal stability of the doped region by postannealing is investigated.
Picosecond recombination processes in lead selenide
Authors: Klann Robert , Höfer Thomas , Buhleier Rainer , Elsaesser Thomas , Lambrecht Armin
Published: July 2002

Picosecond recombination processes of photoexcited electron-hole plasma in PbSe are directly monitored by time-resolved pump-probe experiments in the wavelength range from 3 to 9 μm. At temperatures T≤70 K, a rapid decrease of carrier density within 100 ps is found for excitation densities higher than 7×1017 cm−3. This behavior is due to recombination by stimulated emission, as is evident from comparative measurements of midinfrared luminescence spectra. At T=300 K, Auger recombination on a time scale of 2 ns is observed below the threshold of stimulated emission. The data for a carrier density of 3×1018 cm−3 give an Auger coefficient of c≂10−28 cm6/s.
Dispersion in Nb microstrip transmission lines at submillimeter wave frequencies
Authors: Javadi H. H. S. , McGrath W. R. , Bumble B. , LeDuc H. G.
Published: July 2002

We have measured the effects of dispersion on the resonant mode frequencies of open-ended Nb-SiOx-Nb microstrip transmission lines over a frequency range from 50 to 800 GHz. Submicron Nb/Al-AlOx/Nb Josephson junctions were used as both voltage-controlled oscillators and detectors to sample the high order modes of the resonators. The resonator modes are equally spaced up to about 550 GHz where the mode spacing start to decrease gradually to a minimum above the gap frequency fg≊700 GHz and then increases. Results are in good agreement with the expected theoretical behavior based on the Mattis–Bardeen conductivity of the superconductor line.
Calculation of slow mode surface plasmon polariton properties related to experimental observations
Authors: Connolly M. P. , Whitaker M. A. B. , Dawson P.
Published: July 2002

Recent experimental results definitively showed, for the first time, optical radiation mediated by the slow mode surface plasmon polariton of metal-oxide-metal tunnel junctions. Here, dispersion curves for this mode are calculated. They are consistent with first-order grating coupling to light at the energies of the experimental emission peaks. The curves are then used to analyze second-order and high-energy (≳2.35 eV) grating coupling of the polaritons to radiation. Finally, variation of slow mode damping as a function of energy is used to explain qualitatively the relative experimental peak emission intensities and the absence of radiation peaks above 2.35 eV.
Reactive ion etch damages in inverted, trilayer thin-film transistor
Authors: Kuo Yue
Published: July 2002

Plasma damages on the inverted, trilayer a-Si:H thin-film transistor from an n+ RIE process have been detected. These damages include a high threshold voltage, a high off current, and the divergence of the transfer characteristic curves under different drain voltages. Both the bulk of the films and the film-film interfaces were damaged by the plasma. The former was proved by the relation between the threshold voltage shift and the gate dielectric layer thickness and materials. The latter was demonstrated by the plasma radiation exposure experiment. Plasma radiation, instead of the charge buildup on devices, is the major cause of the thin-film transistor’s abnormality. All damages were easily repaired with a thermal annealing step.
Selective growth of Si crystals from the agglomerated Si seeds over amorphous substrates
Authors: Yamagata K. , Yonehara T.
Published: July 2002

Selective growth of Si crystals over amorphous substrates, seeded by the agglomerated single domained Si crystals is demonstrated. Si crystal seeds are formed from the minutely patterned polycrystalline Si films over amorphous SiO2 by the solid-state agglomeration phenomenon. Periodically placed seeds are grown selectively up to 100 μm by CVD selective epitaxial growth technique. An n-channel metal oxide semiconductor (NMOS) transistor is fabricated inside a planarized Si island on a fused quartz substrate and operated with an electron mobility of up to 600 cm2/V s.
Gate-voltage dependence of the critical current of the superconducting field effect transistor
Authors: Okamoto M. , Ohkura Y. , Katayama K. , Nishino T.
Published: July 2002

The saturation of the critical current as a function of the gate voltage found in the Nb-Si-Nb superconducting field effect transistor is analyzed numerically using the de Gennes expression for the proximity effect. According to the analysis, (i) the Schottky barrier effect is found to be negligible under experimental conditions, (ii) mobility of silicon fitted to the experimental curve shows a power relation to the gate voltage with exponent of about −0.81. This exponent is consistent with the results from independent experiments and a simple theory of surface scattering. The results indicate that the surface scattering effect causes the saturation phenomenon.
Optical spectroscopic study of the growth dynamics of radio-frequency-sputtered YBa2Cu3O7−x thin films
Authors: Lucía M. L. , Hernández-Rojas J. L. , Santamaría J. , Mártil I. , González-Díaz G. , Sánchez-Quesada F.
Published: July 2002

An optical spectroscopic study of the plasma produced during rf sputtering of an YBa2Cu3O7−x target was performed to analyze two basic properties of the deposition process: resputtering effects and oxidation mechanisms. Strong emissions of all the species above a value of the target voltage were found. These observations are associated to a strong secondary electron emission of the target which originates a negative self-bias of the substrate and a subsequent resputtering by argon cations. The addition of different amounts of oxygen to the discharge reveals that preoxidation in the gas phase may decrease the oxygen content in the films: the oxidation of the films is dominated by atomic oxygen.
Influence of a thin adhesion layer on the damping of surface acoustic waves
Authors: Teubner U. , Dahint R. , Schickfus M. v. , Hunklinger S.
Published: July 2002

The attenuation of surface acoustic waves (SAWs) on YZ-LiNbO3 crystals, coated with an aluminum layer of several hundred angstroms, has been measured as a function of temperature in the range from 0.3 K to room temperature. A peak in attenuation was found between 50 and 250 K dependent on layer thickness and SAW frequency. Addition of an adhesion layer with a thickness of about 15 Å, placed between substrate material and metal coating, drastically lowers the attenuation at higher temperatures. In this case, the attenuation rises slowly with temperature and no peak occurs.
Negative output differential resistance in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Gao G. B. , Fan Z. F. , Morkoç H.
Published: July 2002

A thermal-electrical model is presented to describe the negative output differential resistance in AlGaAs/GaAs heterojunction bipolar transistors. Included in this model are the base band-gap shrinkage due to heavy doping, temperature dependence of AlGaAs and GaAs band gaps, and valence band discontinuity. The experimental results unambiguously support the predictions of the model.
30 nm CoSi2 surface layers for contact metallization in complementary metal-oxide-semiconductor processes
Authors: Audet Sarah A. , White Alice E. , Short Ken T. , Hsieh Yong-Fen , Ross Frances M. , Rafferty Conor S.
Published: July 2002

Thin, low resistivity CoSi2 and TiSi2 surface layers have been realized through room-temperature ion implantation of Co+ and Ti+, respectively, followed by low-temperature annealing. TEM studies show that the layers are polycrystalline with large, uniformly thick grains. The results of leakage current measurements performed on junctions fabricated with and without CoSi2 surface layers illustrate the potential of this technique for contact metallization in sub-half-micron CMOS processes.
Investigations of laser array for parallel optical data link applications
Authors: Dutta N. K. , Wang S. J. , Wynn J. D. , Lopata J. , Logan R. A.
Published: July 2002

Very low threshold (Ith∼1 mA) lasers emitting near 1.3 μm have been fabricated using multiquantum-well active region, short cavity length, and high reflectivity facet coatings. A laser-array transmitter utilizing these lasers can be operated without prebias and has negligible timing skew for 1 Gb/s operation. No crosstalk is observed when adjacent elements of the laser array are modulated.
Nonlinear optical studies of polar polymeric Langmuir–Schaefer films
Authors: Ou S. H. , Mann J. A. , Lando J. B. , Zhou L. , Singer K. D.
Published: July 2002

We report on the successful fabrication of X-deposited multilayer films using the Langmuir–Schaefer technique incorporating nonlinear optical chromophores. This technique was used on films of a polysiloxane copolymer containing both a mesogenic and a nonlinear optical side chain. Both x-ray and nonlinear optical studies of mono- and multilayer films reveal the head-to-tail deposition characteristic of X deposition. Both studies also indicate a highly polar noncentrosymmetric structure with nearly perpendicular orientation of the chromophore with respect to the film plane. The nonlinear optical studies also indicate a more tilted structure for the first layer and a second-harmonic coefficient of d⊥⊥=5.3±0.5×10−9 esu.
YBa2Cu3O7−x to Si interconnection for hybrid superconductor/ semiconductor integrationa)
Authors: Harvey T. E. , Moreland J. , Jeanneret B. , Ono R. H. , Rudman D. A.
Published: July 2002

We have successfully made low resistance contacts between high-quality films of YBa2Cu3O7−x (YBCO) and single-crystal Si substrates through Ag-Au interconnections. The YBCO films were deposited by laser ablation on an epitaxial yttria-stabilized zirconia buffer layer on Si and had zero-resistance critical temperatures of 83–85 K after patterning into lines. Specific contact resistivities (resistance-area products) of the YBCO to Si interconnection, limited by the Au to Si interface, of 10−6 Ω cm2 were achieved on heavily doped Si after deposition and patterning of the YBCO film. This demonstrates the use of high-temperature superconductors as a wiring layer compatible with conventional Si metal-oxide-semiconductor processing.
NF3 plasma generation by commercial 50 Hz alternating current discharge for dry etching
Authors: Konuma M. , Bauser E.
Published: July 2002

We generate NF3 plasma for the first time by commercial 50 Hz ac discharge. Mass and energy analysis of the plasma shows the predominant positive ion NF2+, followed by the NF3+ parent ion, NF+, and F+. The measured energy distribution of the ions corresponds to the energy distribution expected from the time dependent plasma potential in a 50 Hz discharge. The plasma can be applied for native oxide removal from Si substrates.
Schottky barrier heights of the amorphous interlayer/Si interfaces in titanium thin films on (001)Si
Authors: Liauh H. R. , Chen M. C. , Chen J. F. , Chen L. J.
Published: July 2002

Schottky barrier heights (SBHs) of amorphous interlayer/Si interfaces in Ti thin films on (001)Si have been measured by forward current-voltage technique. A-interlayers were observed to form by cross-sectional transmission electron microscopy in both Ti thin films on n- and p-type silicon systems in samples annealed at temperatures of and lower than 450 °C for 30 s. Although the SBHs vary for about 0.05–0.08 eV for samples annealed over a temperature range from room temperature to 900 °C, SBHs at the a-interlayer/n-Si and a-interlayer/p-Si were measured to be 0.52–0.54 and 0.59–0.57 eV, respectively. Formation of homogeneous metal a-interlayer/Si interfaces correlated with their SBHs in a number of refractory metal-silicon systems promises to greatly clarify the SBH formation mechanisms.
Alloying behavior of gold atoms into nm-sized copper clusters
Authors: Yasuda H. , Mori H. , Komatsu M. , Takeda K.
Published: July 2002

Alloying behavior of gold atoms into copper clusters has been studied using a 200 kV transmission electron microscope (TEM) equipped with a double source evaporator in the specimen chamber. Isolated copper clusters of approximately 4 nm in diameter were first prepared on a supporting film of amorphous carbon, and then gold atoms were deposited onto the same film kept at room temperature. Upon the deposition of gold, the copper clusters quickly changed into homogeneously mixed Cu-Au alloy clusters. The gold diffusivities in the clusters estimated from the experimental results are at least 19 orders of magnitude faster than those in the bulk copper.
Device-quality copper using chemical vapor deposition of β-diketonate source precursors in liquid solution
Authors: Zheng Bo , Eisenbraun Eric T. , Liu Jun , Kaloyeros Alain E.
Published: July 2002

Device-quality copper films were produced by chemical vapor deposition from copper(II) β-diketonate precursors using a liquid delivery approach. This liquid delivery method exploits the high solubility of copper(II) β-diketonate precursors in selected solvents, such as isopropanol and ethanol, to provide highly accurate, reproducible, and controllable flow rates of precursor and solvent mixtures to the reaction zone. The approach was successfully employed to produce high-quality copper files from predetermined mixtures of bis(hexafluoroacetylacetonato) copper(II) and ethanol or isopropanol. Plasma-assisted chemical vapor deposition (PA-CVD) was used with substrate temperatures of 160–170 °C, reactor working pressures of 1.0–1.7 Torr, hydrogen flow rates between 500 and 1200 cc/min, and hydrogen plasma power density ranging from 0.13 to 0.25 W/cm2. The films were subsequently characterized by Rutherford backscattering spectroscopy, cross-section SEM (scanning electron microscopy), and a four-point resistivity probe. These studies indicated that the films thus grown were pure, dense, highly uniform, and displayed resistivities of 1.7–1.9 μΩ cm. Films produced on patterned test structures exhibited conformal step coverage and complete hole and via fill. Growth rates over large-area substrates were around 250 Å/min for via filling.
Liquid precursor two-step aluminum thin-film deposition on KrF-laser patterned palladium
Authors: Lehmann O. , Stuke M.
Published: July 2002

High quality aluminum films are deposited using a two-step process. KrF-laser mask patterned palladium catalyst areas are selectively covered with aluminum using triethylamine alane as precursor. The precursor is supplied directly in the liquid phase, so this technique can also work under atmospheric pressure conditions in an inert gas atmosphere. One micrometer thick aluminum metal films can be generated spatially selective with high deposition rate (t≲10 s).
Apparent super resolution in high-contrast photoresists
Authors: Peckerar Martin , Rebbert Milton , Gopalakrishnan Ganesh
Published: July 2002

Optoelectronic modulators and couplers frequently require high-aspect ratio feature definition in thick (≥10 μm) gold. The common process used involves up plating with a photoresist guide. Theory argues that feature boundaries would be degraded due to both diffractive spreading and scattering of the incident light in the resist. This is not observed and near-90° sidewalls appear obtainable. This letter demonstrates this effect and proposes an explanation for it.
Third-order optical nonlinearities of a processable main chain polymer with symmetrically substituted tris-azo dyes
Authors: Kurihara Takashi , Tomaru Satoru , Mori Yuhei , Hikita Makoto , Kaino Toshikuni
Published: July 2002

A new third-order nonlinear optical (NLO) polymeric material for all-optical waveguide devices is designed, which is a main chain polymer with symmetrically donor-substituted NLO units as part of the polymer backbone. On the basis of the molecular design, the polymer has large third-order NLO susceptibility, χ(3), potentially low propagation loss and high processability for channel waveguide fabrication. The magnitude of χ(3)(−3ω;ω,ω,ω) for the polymer film was 1.5×10−10 esu at the three-photon resonant wavelength. This is the largest value for highly processable polymers.
Electronic structure and optical properties of silicon crystallites: Application to porous silicon
Authors: Proot J. P. , Delerue C. , Allan G.
Published: July 2002

We have calculated the electronic structure of spherical silicon crystallites containing up to 2058 Si atoms. We predict a variation of the optical band gap with respect to the size of the crystallites in very good agreement with available experimental results. We also calculate the electron-hole recombination time which is of the order of 10−4–10−6 s for crystallites with diameters of 2.0–3.0 nm. We conclude that small silicon crystallites can have interesting optical properties in the visible range. These results are applied to porous silicon for which we confirm that a possible origin of the luminescence is the quantum confinement.
HgTe-CdTe superlattices for infrared detection revisited
Authors: Myers T. H. , Meyer J. R. , Hoffman C. A. , Ram-Mohan L. R.
Published: July 2002

Selected properties of HgTe-CdTe superlattices are re-examined in light of the new consensus that the valence-band offset is large. We conclude that while the cutoff wavelength for infrared detectors remains easier to control in superlattices than in the corresponding Hg1−xCdxTe alloy, the advantage is less than was predicted earlier assuming a small offset. The reduction of tunneling noise and minority carrier collection efficiency are discussed on the basis of revised electron and hole masses in the growth direction.
In situ growth of epitaxial TlBa2CaCu2O7 thin films
Authors: Face D. W. , Nestlerode J. P.
Published: July 2002

Epitaxial TlBa2CaCu2O7 thin films have been grown on single-crystal LaAlO3 and NdGaO3 substrates by in situ off-axis magnetron sputtering in the presence of Tl2O vapor. X-ray diffraction shows that the films are highly epitaxial with the c axis perpendicular to the substrate surface and [100] TlBa2CaCu2O7 aligned with pseudo-cubic [100] NdGaO3 and LaAlO3. The full width at half maximum of the rocking curve for the best films is 0.2°. X-ray diffraction finite size effects show that the film surface is smooth to within several unit cells (∼40 Å). The films are superconducting as deposited with a Tc (onset) of about 80 K and a Tc (R=0) of about 8 K. In situ oxygen treatment of the films at 675 °C has produced films with a Tc(R=0) as high as 40 K. Ex situ annealing in O2 and Tl2O vapor at 800 °C has produced films with a Tc(R=0) as high as 97 K while still retaining a very smooth surface.
Epitaxial growth of YBa2Cu3O7 films on GaAs with MgO buffer layers
Authors: Prusseit W. , Corsépius S. , Baudenbacher F. , Hirata K. , Berberich P. , Kinder H.
Published: July 2002

We have grown epitaxial YBa2Cu3O7 films on GaAs using MgO buffer layers similar to Fork, Nashimoto, and Geballe [Appl. Phys. Lett. 60, 1621 (1992)]. However, the YBa2Cu3O7 was deposited by thermal coevaporation at an even lower substrate temperature of 620 °C. We obtained substantially improved quality [Tc=86.8 K, jc(77 K)=1.2×106 A/cm2, ρ(100 K)≤100 μΩ cm] and smooth surfaces free of outgrowth. An important aspect is preventing As contamination from the gas phase. This was achieved by encapsulating the free sample surface.
Insensitivity of Rb3C60 to γ irradiation
Authors: Yep G. L. , Adrian F. J. , Cowan D. O. , Bohandy J. , Kim B. F. , Moorjani K.
Published: July 2002

The effects of 60Co γ irradiation on a granular sample of Rb3C60 have been examined, using magnetically modulated microwave absorption to measure the superconducting Rb3C60 component. The microwave responses indicate the sample consists of superconducting grains connected by intergranular weak links. No decrease in superconductivity was found up to doses of 5.1 Mrad.
Organometallic chemical vapor deposition of tungsten metal, and suppression of carbon incorporation by codeposition of platinum
Authors: Niemer Burkhard , Zinn Alfred A. , Stovall William K. , Gee Paul E. , Hicks Robert F. , Kaesz Herbert D.
Published: July 2002

Highly reflecting, amorphous, thin films of tungsten are obtained by the decomposition of bis-cyclopentadienyltungstendihydride, (η-C5H5)2WH2, in 1 atm of hydrogen at 350 °C. Auger depth profiling reveals that the carbon and oxygen content of the films are 25.1 and 3.1 at. %, respectively. Simultaneous chemical vapor deposition of tungsten with a small amount of platinum reduces the carbon and oxygen content of the film to 5.3 and 1.8 at. %. The platinum is deposited from cyclopentadienylplatinumtrimethyl, (η-C5H5)Pt(CH3)3, and its concen- tration in the film is 3.3%. Annealing at 750 °C in hydrogen converts the tungsten into a polycrystalline deposit which exhibits an x-ray diffraction pattern characteristic of the metal. The sheet resistivities of the amorphous films are 52±4 μΩ cm.
New coherent detector for terahertz radiation based on excitonic electroabsorption
Authors: Sha W. , Norris T. B. , Burm J. W. , Woodard D. , Schaff W. J.
Published: July 2002

We demonstrate a new technique for the coherent measurement of free-space THz electrical transients, based on the parallel-field excitonic electroabsorption effect in GaAs quantum wells. A THz transient generated from a photoconductive dipole antenna is measured with a rise time of 290 fs and a full width at half maximum of 360 fs. The initial rise of the THz wave form is abrupt, and does not display the exponential leading edge apparent in waveforms measured with photoconductive techniques. The detector sensitivity is sub-100 mV/cm.
In0.53Ga0.47As p-i-n photodiodes with transparent cadmium tin oxide contacts
Authors: Berger Paul R. , Dutta Niloy K. , Zydzik George , O’Bryan H. M. , Keller Ursula , Smith Peter R. , Lopata John , Sivco D. , Cho A. Y.
Published: July 2002

A new type of p-i-n In0.53Ga0.47As photodiode having an optically transparent composite top electrode consisting of a thin semitransparent metal layer and a transparent cadmium tin oxide (CTO) layer was investigated. The composite functions as the n or p contact, an optical window, and an antireflection coating. The transparent contact also prevents shadowing of the active layer by the top electrode, thus allowing greater collection of incident light. Since the CTO contact is nonalloyed, interdiffusion into the i-region is not relevant avoiding an increased dark current. The photodiodes exhibited leakage currents of ≤8 nA and some as low as 23 pA, with reverse breakdown voltages of ≥15–17 V. Responsivity was measured using a 1.55 μm InGaAsP diode laser focused onto an unpassivated 60 μm diam p-i-n photodiode and was ≥0.41 A/W. Photoresponse of the diodes to 3 ps pulses from a Nd:YLF laser (λ=1.047 μm) was 169 and 86 ps for the 60 and 9 μm diodes, respectively. The maximum frequency response of the 9 μm diode is packaging limited, and is expected to have an intrinsic response time of 20–30 ps.
CO2 laser power transmission and laser induced breakdown in AgClxBr1−x crystals, polycrystals, and fibers
Authors: Nagli L. , Katzir A.
Published: July 2002

Laser-induced breakdown (LIB) thresholds in AgClxBr1−x crystals, polycrystals, and fibers were studied under CO2 pulse laser excitation. The limit value of LIB threshold Pc of the bulk crystals is about 4×108 W/cm2 for x=1 and 8×108 W/cm2 for x=0 under 100 ns transversely excited atmospheric pressure laser excitation. The LIB threshold in fibers is much smaller; about 2×107 W/cm2. The dependence of the LIB on composition and temperature suggests that the main cause for LIB is electron avalanche combined with multiphonon absorption at 10.6 μm in silver halide crystals.
Gain and saturation intensity measurements of a discharge pumped F2 laser at high excitation rates
Authors: Kakehata Masayuki , Yang Chuen-Huei , Ueno Yoshiaki , Kannari Fumihiko
Published: July 2002

Small-signal gain and saturation intensity of a discharge pumped F2 laser at 157 nm, operated at high pressures (<10 atm) and high excitation rates (7–39 MW/cm3), were measured in an oscillator-amplifier configuration. The small-signal net gain reaches 37±4%/cm at an excitation rate of ∼26 MW/cm3 for a 6-atm laser gas. A saturation intensity, which depends on a nonsaturable absorption coefficient, was estimated.
ac Josephson effect in superconducting all-Nb thin-film nanobridges up to 693 GHz
Authors: Uzawa Yoshinori , Kawate Etsuo , Hirose Nobumitsu , Motohashi Isao , Harada Yuichi , Sekine Matsuo , Miki Yukinobu , Okaji Masahiro
Published: July 2002

All-niobium thin-film nanobridges were fabricated with bridge sizes of 40-nm length, 50-nm width, and 100-nm thickness. We investigated the performance of the nanobridges by monitoring Shapiro steps induced on the current-voltage curves by an optically pumped far-infrared laser. These steps have been observed up to 693 GHz (433 μm). This is a twofold increase over that previously reported on thin-film nanobridges.
High-speed all-optical switching experiment in Mach–Zehnder configuration using GaAs waveguide
Authors: Nakamura S. , Tajima K. , Hamao N. , Sugimoto Y.
Published: July 2002

We report the results of a high-speed all-optical switching experiment in Mach–Zehnder configuration using a GaAs waveguide. The all-optical switching is based on the nonlinear refractive index change induced by the band-filling effect in the GaAs waveguide. To achieve high-speed operation without being limited by the slow carrier relaxation time, a dc electric field is externally applied to the nonlinear waveguide to sweep carriers away from the light guiding region. The FWHM (full width at half maximum) of the switching waveform without the externally applied electric field is about 800–900 ps. As the electric field is increased, the FWHM is reduced to about 80–90 ps.
Increased pinning energies and critical current densities in heavy-ion-irradiated Bi2Sr2CaCu2O8 single crystals
Authors: Cutro J. A. , Rudman D. A. , Orlando T. P. , van Dover R. B. , Schneemeyer L. F. , White A. E. , Gyorgy E. M. , Waszczak J. V. , Felder R. J.
Published: July 2002

We report a significant increase in the pinning energy of vortices in single-crystal Bi2Sr2CaCu2O8 when irradiated with heavy ions such as Ar+. This is in contrast with the results of light ion (H+, He+) irradiations which give pinning energies comparable with those of unirradiated crystals. The stronger pinning is attributed to defects larger than point defects, e.g., clusters or amorphized regions. As a result of higher pinning energies, critical currents persist at markedly higher temperatures and fields.
Aligned and twinned growth of α-Fe thin films on atomically cleaned (111)Si at room temperature
Authors: Wang M. H. , Chen L. J.
Published: July 2002

Epitaxial α-Fe thin films have been grown on atomically cleaned (111)Si at room temperature under ultrahigh vacuum condition. The α-Fe epitaxy on (111)Si was analyzed by transmission electron microscopy (TEM) to be predominantly of twinned epitaxy with a small fraction of epitaxy being aligned with respect to the substrate. High resolution TEM showed that the interface between the epitaxial iron thin film and Si substrate is atomically flat with the presence of a low density of atomic steps. Interfacial dislocations were found to be of edge type with 1/2<11̄0≳ Burgers vectors. The average spacing of interfacial dislocations was found to be close to the theoretically predicted value.
Study on the photoconductivity characteristics of porous Si
Authors: Yeh C. C. , Hsu Klaus Y. J. , Samanta L. K. , Chen P. C. , Hwang H. L.
Published: July 2002

We utilized the conventional planar fabrication technique and the electrochemical etching method to prepare porous Si layers in the p-type region of a p-n junction, which makes the study on the transverse transport property of this material possible. The junctions were fabricated by low energy ion implantation, with porous Si formed perpendicular to the junction and between two metal contacts. This structure confines currents to the direction parallel to the surface. Distinct photoconductivity and photovoltaic effects have been clearly revealed from the I-V curves.
Millimeter-wave monolithic barrier n-n+ diode grid frequency doubler
Authors: Qin Xiaohui , Domier C. , Luhmann N. C. , Liu H-X L. , Chung E. , Sjogren L. , Wu Wenhsing
Published: July 2002

A monolithic quasioptical frequency multiplier array, comprised of approximately 1760 Ga0.5Al0.5As/GaAs barrier n-n+ (BNN) diodes, has been successfully fabricated. The BNN diode, first fabricated in these studies, possesses strongly nonlinear capacitance-voltage (C-V) characteristics, thereby offering the potential for a highly efficient device for millimeter-wave frequency multiplication applications. A frequency doubled power of 2.1 W at 66 GHz has been observed with a conversion efficiency of 7.5%.
Vacancy-mediated disordering of AlGaAs-GaAs superlattices by group IV or VI impurity in-diffusion
Authors: Olmsted B. L. , Houde-Walter S. N.
Published: July 2002

We report on a study of disordering by the in-diffusion of a variety of group IV and VI n-type impurities. In all cases, the n-type dopants enhance the Al-Ga interdiffusion coefficient over that due to the As overpressure alone. The Si-induced enhancement has been previously attributed to the change in the Fermi-level position with doping and therefore, should account for disordering using other n-type impurities. However, we observe important differences in the interdiffusion characteristics induced by Si or Ge, and that by S or Se. The disordering is attributed to the enhancement in the group III-vacancy concentration for each of these n-type impurities, as is also the case in undoped crystals disordered by an As ambient alone at 855 °C.
Cyclotron resonance studies of two-dimensional holes in strained Si1−xGex/Si quantum wells
Authors: Cheng J.-P. , Kesan V. P. , Grutzmacher D. A. , Sedgwick T. O. , Ott J. A.
Published: July 2002

Far-infrared magnetotransmission spectroscopy has been employed to study p-type modulation-doped strained Si1−xGex/Si quantum wells grown by atmospheric pressure chemical vapor deposition at magnetic fields up to 23 T. The cyclotron resonance (CR) mass of the two-dimensional hole gas (2DHG) in a strained 7.5 nm Si0.63Ge0.37 quantum well was determined to be (0.29±0.02)m0 for a 2D hole density of 2.3×1012/cm2 at 3 K. The CR mass of 2DHGs in strained Si1−xGex is comparable to previous measurements of the CR mass of 2DHGs in strained InyGa1−yAs with similar 2D hole densities.
Annealing effects on multilayered Co/Pt and Co/Pd sputtering films
Authors: Yamane H. , Maeno Y. , Kobayashi M.
Published: July 2002

Effects of air annealing on magnetic properties and structures of multilayered Co/Pt and Co/Pd sputtering films were studied. The dual-source rf magnetron sputtering method was employed in fabricating the films. The thicknesses of the Co layer and Pt layer of the Co/Pt films were 4.3 and 10.0 Å, respectively: the total thickness was 4300 Å. The thicknesses of Co layer and Pd layer of the Co/Pd films were 3.6 and 11.8 Å, respectively: the total thickness was 5600 Å. Residual magnetizations and coercivities of the Co/Pt and Co/Pd films increased with air-annealing at 250–350 °C for 30 min to 2.5–3 kG and 2–3 kOe, respectively. The increases were observed only during air annealing, but not in vacuum annealing. Saturated magnetizations and intensities of the superlattice x-ray peak decreased uniformly relative to annealing temperature.
Ultralow timing jitter in electrically gain-switched vertical cavity surface emitting lasers
Authors: Pepeljugoski P. , Lin J. , Gamelin J. , Hong M. , Lau K. Y.
Published: July 2002

We report that contrary to common belief, it is possible to achieve very low timing jitters of less than (≊100 fs) in gain-switched semiconductor lasers, which is comparable to actively mode-locked semiconductor lasers. A vertical cavity surface emitting laser was used to achieve these results, with a gain-switched pulse width of 12 ps.
Carrier-carrier scattering induced capture in quantum well lasers
Authors: Blom P. W. M. , Haverkort J. E. M. , van Hall P. J. , Wolter J. H.
Published: July 2002

We present calculations of the carrier capture efficiency into various types of quantum well lasers. The carrier capture into a quantum well can be due to either optical phonon emission or carrier-carrier scattering. Both capture mechanisms have been calculated and show oscillations as a function of the quantum well thickness. By optimizing the carrier capture efficiency the carrier accumulation in the barrier layers can be reduced, resulting in an improved modulation response and threshold current.
Step equalization in epitaxial growth: A noise limited process
Authors: Williams D. R. M. , Krishnamurthy Mohan
Published: July 2002

We present results from the Monte Carlo simulation of terrace size evolution by vapor phase growth on vicinal surfaces. We show that as a function of the number of added monolayers, the standard deviation of the step length distribution rapidly falls to a constant equilibrium value. We argue that recent analytical and numerical work indicating that the standard deviation falls continuously is incorrect because of a statistical preaveraging of the evolution equations. This has experimental importance as it shows that increasing the number of monolayers beyond a certain limit has no effect on the step size distribution.
Picosecond photoconductivity in polycrystalline gallium arsenide grown by molecular beam epitaxy
Authors: Morse Jeffrey D. , Mariella Raymond P. , Adkisson James W. , Anderson George D. , Harris James S. , Dutton Robert W.
Published: July 2002

Picosecond photoconductivity in polycrystalline gallium arsenide (GaAs) layers grown on silicon dioxide by molecular beam epitaxy has been investigated. Photocurrent transient responses having full width at half-maximum of ∼2.2 ps were measured by photoconductive sampling techniques. Interdigitated metal-semiconductor-metal photodiodes have been fabricated from the polycrystalline GaAs with 1.5- and 5-μm electrode spacing. The corresponding responsivities measured are 40 mA/W and 0.15 A/W, respectively, at 10 V/μm bias voltage and 820-nm wavelength. The corresponding effective mobility of this material is estimated to be μeff∼80 cm2/V s, making this photodetector competitive with alternative technologies for ultrahigh speed applications.
Single depressed-index cladding ridge waveguide laser with a low aspect ratio
Authors: Kahen K. B. , Shantharama L. G. , Shepherd J. P. , Peterson D. L.
Published: July 2002

A novel ridge waveguide semiconductor laser diode is introduced, which contains a single depressed-index cladding layer. Deployment of this layer significantly reduces the transverse beam divergence, while maintaining reasonable values for the optical confinement factor, Γ, and the lateral index step. For lasers with 500 Å active layers and ridge widths of 4 μm, we measured transverse and lateral far-field beam divergences of 16.4° and 8.2°, respectively, and threshold currents of 67 mA for 500-μm-long devices.
Dimerization induced Be segregation in GaAs
Authors: Cunningham J. E. , Goossen K. W. , Chiu T. H. , Williams M. D. , Jan W. , Storz F.
Published: July 2002

We report the observation of a Be segregation rate in GaAs that depends linearly on Be content. When δ-Be is codoped with δ-Si this segregation dependence changes and is observed to follow a model of segregation we develop based on Be dimerization. Further, we present the first evidence that GaAs surfaces order upon δ-Be deposition. The observed surface reconstructions could also result from Be dimerization. The energy gained from dimerization causes Be to segregate during growth.
Semi-insulating crystalline silicon formed by oxygen doping during low-temperature chemical vapor deposition
Authors: Schwartz P. V. , Liu C. W. , Sturm J. C.
Published: July 2002

In this letter we demonstrate the use of oxygen as a dopant in silicon to create semi-insulating, crystalline silicon films grown by chemical vapor deposition. The films contain oxygen concentrations that exceed the peak solid solubility of oxygen in silicon by several orders of magnitude, yet they remain crystalline. The resistivities of these films reach levels of 106 Ω cm at room temperature and the electronic properties of the films exhibit classical characteristics of space-charge-limited current associated with insulators containing trap states within the band gap. We then demonstrate that metal-oxide-semiconductor transistors with bulk-like mobilities can be fabricated in crystalline silicon layers grown without oxygen on top of the semi-insulating films.