bluuebunny/crossref_metadata_2025 huggingface dataset:
Superconducting YBa2Cu3O7−x thin films on alkaline earth fluorides
Authors: Chan Siu-Wai , Chase E. W. , Wilkens B. J. , Hart D. L.
Published: July 2002

Alkaline earth fluorides have low dielectric constants and large band gaps. In addition, they are chemically compatible with and several can be grown epitaxially on silicon and compound semiconductors. We have deposited YBa2Cu3O7−x thin films (200–500 nm thick) directly on (001) SrF2, (001) BaF2, (001) MgF2, and unoriented CaF2 single crystals by laser deposition. The substrate temperature was about 720 °C and the vacuum chamber was at 350 mTorr of oxygen. For this work, no additional annealing outside the deposition chamber was done after deposition. The deposited YBa2Cu3O7−x films were superconducting and exhibited transition temperatures Tc (R=0) of 83, 73, and 74 K on MgF2, SrF2, and BaF2, respectively. Structural studies by x-ray diffraction showed that YBa2Cu3O7−x films on MgF2, SrF2, and BaF2 were polycrystalline and exhibited some (00L) textures. Deposition on CaF2 substrates resulted in yellowish, insulating films with Ca- and Ba-rich interfacial reaction products.
Reduction in magnetic field induced broadening of the resistive transition in laser-deposited YBa2Cu3O7−x thin films on MgO
Authors: Rogers C. T. , Gregory S. , Venkatesan T. , Wilkens B. J. , Wu X. D. , Inam A. , Dutta B. , Hegde M. S.
Published: July 2002

The magnetic field induced broadening of the normal to superconducting resistive transition of YBa2Cu3O7−x thin films laser deposited on (100) MgO substrates for field oriented parallel to the c axis is found to be significantly reduced in comparison with that found previously in single crystals and in films deposited on SrTiO3. This reduction in broadening is associated with a high density of defects which, while causing a slight decrease in Tc and an increase in the zero-field transition width, seems to provide strong vortex pinning centers that reduce flux creep.
Stability limits of the perovskite structure in the Y-Ba-Cu-O system
Authors: Bormann R. , Nölting J.
Published: July 2002

The equilibrium (molecular) oxygen partial pressure of the Y1Ba2Cu3O7−x phase has been measured by an electrochemical method. The investigations are focused on the low-temperature range between 560 and 750 °C and on oxygen stoichiometries close to the oxygen-poor phase boundary. In particular, the oxygen partial pressure has been determined below which the perovskite structure becomes thermodynamically unstable. This critical value should be considered during the preparation of high Tc Y1Ba2Cu3O7−x superconductors, especially in the case of an in situ preparation of thin films.
Microwave noise emission from high T
c thin films
Authors: Jung G. , Konopka J. , Gierl/owski P. , Kula W.
Published: July 2002

A pronounced X-band microwave noise emission from Y-Ba-Cu-O thin films has been observed. Emission depends strongly on temperture, bias current, and magnetic field. Two types of emission lines can be distinguished in the power versus dc bias spectra. The lines which remain at stable current positions against temperature we tentatively ascribe to the interaction of depinned flux flow with a two-dimensional Josephson junction array. The lines that appear at fixed voltage positions may be attributed to the Josephson radiation of a distributed network of junctions. No significant emission was detected from Bi-Ca-Sr-Cu-O films.
I
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u formation of YBa2Cu3Ox thin films by physical sputtering
Authors: Yeh J.-J. , Hong M. , Felder R. J.
Published: July 2002

We have found that in situ superconducting Y-Ba-Cu-O thin films can be produced by sputtering without the aid of any external O2 source during deposition. The films were produced by rf magnetron sputtering from a composite target onto MgO(100) substrates heated at 650 °C. Films made in a pure Ar pressure of 24 mTorr and fast cooled in N2 ambient contain the tetragonal YBa2Cu3Ox phase with x estimated to be 6.1. Films made under the same sputtering conditions but cooled in 30 mTorr oxygen after deposition, show a superconducting transition Tc(R=0) at 71 K with an onset at 85 K. The Tc(R=0) rises to 80 K if 0.5 mTorr oxygen was added during sputtering. The experimental results provide conclusive evidence that sufficient oxygen can be incorporated into the films to form the tetragonal YBa2Cu3Ox phase simply by physical sputtering from an oxide target. The films absorb additional oxygen and transform into the orthogonal, superconducting phase when subsequently cooled in partial O2.
High-density Bi-Pb-Sr-Ca-Cu-O superconductor prepared by rapid thermal melt processing
Authors: Moon B. M. , Lalevic B. , Kear B. H. , McCandlish L. E. , Safari A. , Meskoob M.
Published: July 2002

A high quality, dense Bi-Pb-Sr-Ca-Cu-O superconductor has been successfully synthesized by rapid thermal melt processing. Conventionally sintered pellets were melted at 1200 °C, cooled rapidly, and then annealed. As-melted samples exhibited semiconductor behavior, which upon annealing became superconducting at 115 K [Tc(zero)=105 K]. A detailed study of various processing techniques has been carried out.
Self-interstitials and the 935 cm−1 band in silicon
Authors: Stein H. J.
Published: July 2002

Substitutional carbon in Czochralski Si is found to decrease the formation rate for a 935 cm−1 infrared absorption band under neutron irradiation while that for a 965 cm−1 band (interstitial carbon trapped at interstitial oxygen) increases. The observations support a controversial previous assignment of the 935 cm−1 band to a center with interstitial Si trapped by interstitial oxygen.
Gettering of gold by rapid thermal processing
Authors: Hartiti B. , Vu-Thuong-Quat  , Eichhammer W. , Muller J.-C. , Siffert P.
Published: July 2002

We report on the first direct evidence of a gettering effect induced by rapid thermal processing (RTP). Homogeneously gold-doped silicon is studied before and after RTP by deep level transient spectroscopy measurements of the Au acceptor level. After a 1000 °C/10 s cycle, gold is depleted in three regions below the surfaces, indicating a gettering effect. The mechanism for this RTP-induced gettering is discussed.
Electric field response of a semiconductor superlattice optical mirror from electroreflectance spectra
Authors: Fritz I. J. , Gourley P. L. , Drummond T. J.
Published: July 2002

We report low-field electroreflectance (ER) spectra of an all-semiconductor multilayer optical mirror structure. The structure, consisting of alternating blocks of AlAs/Al0.5Ga0.5 As and Al0.5Ga0.5As/GaAs multiple quantum well layers, was grown by molecular beam epitaxy without wafer rotation. Thickness variations across the wafer produce a position-dependent reflectance spectrum. The observed line shape of the band-edge exciton depends on its wavelength position relative to the mirror spectrum and cannot be explained by ordinary ER theory, due to the rapidly varying background mirror reflectance. Computer simulations, using the matrix method to calculate the reflectance for different layer thicknesses and exciton energies, agree qualitatively with the data. A strong enhancement in ER response is predicted near the minima in the mirror spectrum. This enhancement is important in electo-optic reflectance modulators.
Numerical study of entrained soliton motion in long Josephson junctions
Authors: Davidson A. , Pedersen N. F.
Published: July 2002

We present the results of numerical simulations of entrainment by microwaves of a soliton in Josephson junctions of both the overlap and in-line geometries. The computation was based on the full partial differential equations with boundary conditions, making no use of perturbation theory or Fourier expansion. We confirm the perturbation prediction for the range of phase lock for overlap junctions, but we observe a major departure for the in-line geometry, due to soliton creation and annihilation. Outside the range of entrainment, the perturbation predictions are not reliable in either case: we observe quasiperiodicity, intermittency, or chaotic creation and annihilation, depending on junction geometry and parameter values.
Enhancement of modulation bandwidth in InGaAs strained-layer single quantum well lasers
Authors: Lau K. Y. , Xin S. , Wang W. I. , Bar-Chaim N. , Mittelstein M.
Published: July 2002

It is shown that the unique properties of strained-layer quantum well lasers can be identified by measuring the relaxation oscillation frequency as a function of optical gain. These measurements are insensitive to effects due to nonradiative recombinations and leakage currents, which can mask the beneficial effects in terms of a lower threshold current due to a reduced hole mass in strained quantum wells. The conclusion, both theoretically and experimentally, is that strained-layer quantum well lasers have a higher differential gain but saturate at a lower gain level as compared to regular quantum well lasers. As a consequence, for a strained single quantum well, slightly higher relaxation oscillation frequency results, but only for certain limited ranges of device parameters. A multiple strained-layer quantum well can in theory take better advantage of the higher differential gain.
Role of the crystallographic orientation on the incorporation of indium in HgCdTe epilayers grown by molecular beam epitaxy
Authors: Sou I. K. , Wijewarnasuriya P. S. , Boukerche M. , Faurie J. P.
Published: July 2002

In-doped HgCdTe films have been grown by molecular beam epitaxy (MBE) on CdTe substrates in the (100) crystallographic orientation. They were characterized by Hall and secondary-ion mass spectroscopy measurements. The results are compared with those of In-doped HgCdTe layers grown in the (111)B orientation. In the (111)B orientation indium is incorporated in the metal site whereas in the (100) orientation it appears that indium is mainly incorporated interstitially. The results agree with a Te antisite model as a possibility for explaining the electrical behavior of (100) HgCdTe grown by MBE.
Dependence of external differential efficiency on laser length and reflectivities in multiple quantum well lasers
Authors: Wilcox J. Z. , Ou S. , Yang J. J. , Jansen M. , Peterson G. L.
Published: July 2002

The external efficiency ηd of quantum well (QW) lasers is maximum at some characteristic laser length, which is dependent upon mirror reflectivities and the number of QWs in the active layer. The observed decrease in ηd in short lasers is caused by increased optical absorption associated with a high concentration of free carriers in the QW and the surrounding waveguide layer. The carriers spill into the waveguide because of QW subband filling in short cavity lasers with high threshold gains.
Ballistic-electron-emission microscopy investigation of Schottky barrier interface formation
Authors: Hecht M. H. , Bell L. D. , Kaiser W. J. , Grunthaner F. J.
Published: July 2002

Ballistic-electron emission microscopy (BEEM) has been used to investigate the origin of defects at the Au/GaAs(100) Schottky barrier interface. In addition, molecular beam epitaxy (MBE) and in situ fabrication methods have been employed to control Schottky barrier interface properties. BEEM characterization combined with MBE methods has enabled the development of a near-ideal Schottky barrier interface with drastically reduced defect density.
Detecting transition regions in magneto-optical disk systems
Authors: Mansuripur Masud
Published: July 2002

Several combinations of incident polarization and detection schemes suitable for direct detection of transitions in magneto-optical disk systems are described. One such combination uses a circularly polarized light with a single split detector in the far field. Another scheme uses linear polarization in conjunction with differential detection. In the first scheme the medium must be optimized for Kerr rotation while the second method requires maximum ellipticity.
Tunable stimulated emission of radiation in GaAs doping superlattices
Authors: Schubert E. F. , van der Ziel J. P. , Cunningham J. E. , Harris T. D.
Published: July 2002

Tunable stimualted emission of radiation is achieved in AlxGa1−xAs/GaAs double heterostructures, in which the waveguiding GaAs region consists of a delta-doped doping superlattice. The low-temperature emission energy is 45 meV below the bulk band gap of GaAs for homogeneous optical excitation of the Fabry–Perot cavity. The emission energy is continuously tunable over 35 Å by inhomogeneous excitation of the cavity.
GaAs metal-semiconductor field-effect transistor with extremely low resistance nonalloyed ohmic contacts using an InAs/GaAs superlattice
Authors: Kumar N. S. , Chyi J.-I. , Peng C. K. , Morkoç H.
Published: July 2002

GaAs metal-semiconductor field-effect transistors (MESFETs) with extremely low resistance nonalloyed ohmic contacts have been demonstrated. The contact structure consists of an n+-InAs/GaAs strained-layer superlattice and an InAs cap layer. Contact resistances as low as 0.036 Ω mm have been measured. These results represent the smallest figures reported to date for GaAs field-effect transistors. Nonalloyed MESFETs with 1 μm gate lengths had transconductances of about 210 mS/mm.
Growth of textured diamond films on foreign substrates from attached seed crystals
Authors: Geis M. W.
Published: July 2002

A technique has been developed to grow (111) textured diamond films on smooth substrates using attached diamond seeds. The degree of texture is defined by the initial texture of the seeds. This initial texture depends upon the seed size and the cleaning procedure. Under the best conditions, over 90% of the seeds exhibit a (111) texture with a tip angle of less than 0.25°. Further growth of diamond on these seeds does not affect the texture, and diamond films obtained by such growth are expected to have smoother surfaces and more controlled doping than nontextured polycrystalline films.
Low-resistance nonalloyed ohmic contacts on p-type GaAs using GaSb/GaAs strained-layer superlattices
Authors: Chyi J.-I. , Chen J. , Kumar N. S. , Kiely C. , Peng C. K. , Rockett A. , Morkoç H.
Published: July 2002

Employing a GaSb/GaAs strained-layer superlattice and a GaSb cap, specific contact resistivities as low as 3.2×10−7 Ω cm2 have been realized for nonalloyed ohmic contact to p-type GaAs. This contact structure is shown to give low contact resistances irrespective of the contact metals, including AuBe, AuGe/Ni/Au, and Au. Excellent thermal stability for AuBe contacts was obtained when sintered.
Quantum device microfabrication: Resolution limits of ion beam patterning
Authors: Scherer A. , Roukes M. L.
Published: July 2002

We have achieved precise control of the lateral electrical damage accompanying ion beam patterning of submicron electron devices from semiconductor materials. In situ transport measurements, made in the etching chamber during the definition process, provide an exact and reproducible means of end-point detection, irrespective of material structure and ion beam parameters. We apply this to routinely fabricate conducting channels having widths below 100 nm from high-mobility GaAs/AlGaAs heterojunctions. Subsequent low-temperature magnetotransport measurements and successive optimization of processing conditions enable us to systematically obtain the minimum conducting width. Through these studies we explore the ultimate resolution limits of the ion beam patterning process.
Leaky-wave modes in nonlinear output prism couplers
Authors: Lin L. , Tamir T. , Leung K. M.
Published: July 2002

By using the resonance property of modal fields, we derive leaky-wave modes supported by nonlinear layered media of the Kerr type and apply the results to obtain the beam field emitted by an output prism coupler containing such a nonlinear layer.
Gain measurements of the C VI 3d–2p transition (18.2 nm) from the wall-confined carbon plasmas produced by a CO2 laser
Authors: Miura E. , Daido H. , Kitagawa Y. , Sawai K. , Kato Y. , Nishihara K. , Nakai S. , Yamanaka C.
Published: July 2002

We propose a 1-cm-long cylinder-type target as the gain medium of a recombination-pumped extreme-ultraviolet (XUV) laser. The gain medium plasma was pumped by a long-pulse CO2 laser (400 J energy in 50 ns pulse duration). At the C VI 3d–2p transition (18.2 nm) we obtained the gain-length product up to 2.4, which was estimated from the line intensity ratio of the axial to transverse directions. The electron temperature of 54 eV and density of 1.2×1019 cm−3 near the cylinder wall measured using soft-x-ray spectroscopy satisfied the condition for the generation of the population inversion between n=3 and 2 levels of the C VI ions.
Growth control of CdTe/CdZnTe (001) strained-layer superlattices by reflection high-energy electron diffraction oscillations
Authors: Lentz G. , Ponchet A. , Magnea N. , Mariette H.
Published: July 2002

We have used reflection high-energy electron diffraction (RHEED) and x-ray diffraction to study the growth of CdTe/Cd0.90 Zn0.10 Te (001) heterostructures by molecular beam epitaxy (MBE). A growth process involving an excess of Cd and growth interruptions at the well-barrier interfaces has been found necessary to observe strong and persistent RHEED oscillations during the epitaxy of quantum wells and superlattices. This method gives accurate in situ thickness measurements of all the layers during the growth of CdTe/Cd0.90 Zn0.10 Te superlattices, in good agreement with x-ray diffraction data. The sharpness of x-ray diffraction satellites confirms the high crystalline quality of the superlattices with a period fluctuation of less than one monolayer.
Beam breakup in recirculating induction accelerators
Authors: Lau Y. Y. , Colombant D. G.
Published: July 2002

Estimates of beam breakup instability (BBU) growths are given for multiturn recirculating induction accelerators currently under active study. The dispersion relation based on a simple model shows that BBU growth cannot be completely suppressed by just reducing the quality factor Q alone. Various methods of BBU control are discussed.
Optical intensity modulator for integrated optics by use of a heterojunction bipolar transistor waveguide structure
Authors: Okada Yoshitaka , Ishikawa Takuya , Tada Kunio
Published: July 2002

Device fabrication and basic experimental results obtained with a heterojunction bipolar transistor waveguide structure optical intensity modulator, whose device structure is particularly suitable for possible monolithic integrated circuits, are described for the first time. Common emitter dc current gain hFE obtained with a 0.25-μm-thick base/waveguide was 38, and the switching times have been determined as 1.5 ns. Free-carrier injection modulates the absorption coefficient α in the waveguide mainly by the band filling and plasma dispersion effects and consequently, the output light intensity can be modulated. The optical on/off modulation ratio of up to 2.1:1, corresponding to a modulation efficiency of Δα/α∼89%, has been demonstrated at a base current of 3 mA for a device with an emitter/waveguide width of 7 μm and a length of 190 μm.
16.7% efficient, laser textured, buried contact polycrystalline silicon solar cell
Authors: Zolper John C. , Narayanan Srinivasamohan , Wenham Stuart R. , Green Martin A.
Published: July 2002

In the evolution of single-crystal silicon solar cells, crystallographic texturing of the cell surface using anisotropic etches was an important step in improving cell performance. Unfortunately, this technique is ineffective for polycrystalline silicon solar cells due to generally unfavorable grain orientation. This limitation has been overcome by employing a new laser texturing technique on the top surface of a laser grooved, buried top contact polycrystalline silicon solar cell. This approach has demonstrated an independently confirmed 16.7% (air mass 1.5, 25 °C) efficiency for a 10.5 cm2 polycrystalline silicon solar cell, the highest efficiency ever reported for a polycrystalline cell of this size.
Selective deposition of i
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u doped polycrystalline silicon by rapid thermal processing chemical vapor deposition
Authors: Hsieh T. Y. , Chun H. G. , Kwong D. L.
Published: July 2002

Selective polycrystalline silicon was successfully deposited and in situ doped wih arsenic for the first time by rapid thermal processing chemical vapor deposition (RTPCVD). The growth kinetics of SiH2Cl2/AsH3/H2 gas system have been studied by examining the dependence of growth rate on deposition temperature, volume percentage of SiH2Cl2, and AsH3 mole fraction. Submicron polycrystalline silicon layers with excellent selectivity and precise thickness control have been achieved with proper deposition conditions. The growth rate decreases as doping levels increase, and drastically decreases when the AsH3 mole fraction is higher. In addition, the growth rate is linearly proportional to the SiH2Cl2 flow rate for a fixed AsH3 flow rate.
Decomposition of trimethylgallium in the downstream region of a near afterglow plasma
Authors: Sheng T. , Pihlstrom B. , Yu Z. , Collins G. J.
Published: July 2002

The downstream region of a near afterglow plasma (Δt=100 μs) has been used to decompose trimethylgallium (TMGa) and the products analyzed using a mass spectrometer. The major TMGa dissociation products with a hydrogen plasma were identified as methane and ethane while with a helium plasma ethane, ethylene, and acetylene were the main dissociation species. Time-resolved optical emission originating from the downstream reaction zone shows that decomposition of TMGa occurs primarily via photodissociation with the hydrogen plasma while both photon and metastable species (He 21 S and 23 S) contributed to the TMGa decomposition with the helium plasma. VUV transmitting and VUV absorbing windows placed between the upstream hydrogen plasma and the downstream TMGa source provided further direct evidence of the role of VUV photodissociation in the TMGa decomposition.
Strained-layer InGaAs/GaAs/AlGaAs single quantum well lasers with high internal quantum efficiency
Authors: Larsson Anders , Cody Jeffrey , Lang Robert J.
Published: July 2002

Low threshold current density strained-layer In0.2Ga0.8As/GaAs/AlGaAs single quantum well lasers, emitting at 980 nm, have been grown by molecular beam epitaxy. Contrary to what has been reported for broad-area lasers with pseudomorphic InGaAs active layers grown by metalorganic chemical vapor deposition, these layers exhibit a high internal quantum efficiency (∼90%). The maximum external differential quantum efficiency is 70%, limited by an anomalously high internal loss possibly caused by a large lateral spreading of the optical mode. In addition, experimental results supporting the theoretically predicted strain-induced reduction of the valence-band nonparabolicity and density of states are presented.
Fluctuating deep level trap occupancy model for bulk 1/f noise in field-effect transistors
Authors: Folkes P. A.
Published: July 2002

A quantitative theoretical model for bulk 1/f noise in semiconductor resistors has been developed. The model uses the fact that random fluctuations of the steady-state deep level trapped electron density at some point in a depletion layer decay exponentially with a time constant which depends on the local free-electron density. The model was used to derive an exact integral expression and a simple approximate analytic expression for the spectral density of bulk 1/f and generation noise in unsaturated field-effect transistors. Excellent agreement with experimental results is obtained. The relationship between bulk 1/f and generation noise spectra is discussed.
New type of compensation wall in ferrimagnetic double layers
Authors: Hansen P.
Published: July 2002

A new type of compensation wall located at the interface of thin rare-earth transition-metal double layers was studied in terms of a simple wall model. The magnetic field dependence of the wall energy and thickness was calculated yielding a variation of both by a factor of 3 in fields up to 1.6×106 A/m. Strong changes of the relative magnetization result for wall thicknesses that are comparable with the film thickness. The calculated variation of the relative magnetization with the field indicates that these changes can be directly observed by magnetization measurements. This opens new possibilities in the study of domain wall structures.
Structure of hexagonal and cubic CdS heteroepitaxial layers on GaAs studied by transmission electron microscopy
Authors: Cullis A. G. , Smith P. W. , Parbrook P. J. , Cockayne B. , Wright P. J. , Williams G. M.
Published: July 2002

The initial heteroepitaxial growth and structure of thin CdS layers on GaAs has been studied by conventional and high-resolution transmission electron microscopy. The work highlights the dependence of CdS crystal type on GaAs substrate orientation. Wurtzite-structure CdS is formed on (111)A GaAs and it is found to relieve misfit stresses by the introduction of interfacial defects, often associated with steps at the interface. Sphalerite-structure CdS is produced by initial growth on (001)GaAs and, in this case, misfit stresses are more slowly relieved, first with the formation of an asymmetrical array of interfacial dislocations and inclined stacking faults.
Thermal stability of Si/Si1−xGex/Si heterojunction bipolar transistor structures grown by limited reaction processing
Authors: Noble D. B. , Hoyt J. L. , Gibbons J. F. , Scott M. P. , Laderman S. S. , Rosner S. J. , Kamins T. I.
Published: July 2002

The thermal stability of Si/500-Å-thick Si0.77Ge0.23 bilayers grown on Si by limited reaction processing is studied as a function of Si capping layer thickness. After annealing for 4 min at 850 °C, misfit dislocation spacings increase monotonically with cap thickness from 0.5 μm for an uncapped film to greater than 50 μm for a layer with a 500-Å-thick cap. Thus, an epitaxial Si cap of sufficient thickness prevents significant misfit dislocation formation during this anneal. Experimental observations are reported which indicate that the Si cap enhances thermal stability by inhibiting both dislocation nucleation and propagation. These results are very encouraging since they suggest that high-temperature processing of Si/Si1−xGex device structures may be possible without significant misfit dislocation formation.
Model of growth of single-domain GaAs layers on double-domain Si substrates by molecular beam epitaxy
Authors: Varrio J. , Asonen H. , Lammasniemi J. , Rakennus K. , Pessa M.
Published: July 2002

Growth of single-domain GaAs (100) layers on double-domain Si (100) substrates by molecular beam epitaxy has been investigated. It has been shown that domain orientation of the top layer of GaAs depends on the surface structure of a buffer layer. The size of atomic step heights on the Si surface and the As-Si interaction temperature before film growth are not important factors in controlling domain orientation. Suppression of an antiphase disorder is explained in terms of nonstoichiometric antiphase boundary annihilation operative during growth.
Dislocation-accelerated impurity-induced layer disordering of AlxGa1−xAs-GaAs quantum well heterostructures grown on GaAs-on-Si
Authors: Plano W. E. , Nam D. W. , Hsieh K. C. , Guido L. J. , Kish F. A. , Sugg A. R. , Holonyak N. , Matyi R. J. , Shichijo H.
Published: July 2002

Data are presented showing that dislocations and Si autodiffusion promote accelerated layer disordering of AlxGa1−xAs-GaAs quantum well heterostructures grown on GaAs-on-Si ‘‘substrates’’ via metalorganic chemical vapor deposition. The accelerated impurity-induced layer disordering is more extreme at higher temperatures (>800 °C) and virtually nonexistent at lower temperatures (≲775 °C).
Wide-bandwidth, high-efficiency reflection modulators using an unbalanced Fabry–Perot structure
Authors: Yan R. H. , Simes R. J. , Coldren L. A.
Published: July 2002

A normally-on electroabsorptive multiple quantum well asymmetric Fabry–Perot reflection modulator with an on/off ratio of 22, insertion loss of 3.7 dB, and optical bandwidth of 3.4 nm for a voltage swing of 11 V has been measured. The trade-off between low insertion loss and high contrast in such devices will be discussed in the present letter and is shown to be due to the relative placement in wavelength between the Fabry–Perot resonant mode and the heavy hole exciton position in the multiple quantum well active region.
Interference filters using indium phosphide-based epitaxial layers grown by metalorganic vapor phase epitaxy
Authors: Ritchie S. , Spurdens P. C. , Hewett N. P. , Aylett M. R.
Published: July 2002

Bandpass interference filters with center wavelengths between 1.3 and 1.7 μm have been made with InGaAsP/InP epitaxial layers grown by metalorganic vapor phase epitaxy. The transmission spectra measured exhibit a full width half maximum of 7 nm with peak rejections up to 20 dB and are in good agreement with the results obtained from theoretical modeling of the 81-layer single half-wave Fabry–Perot structure used. This indicates very good control of the composition and thickness of the layers grown, which is confirmed by transmission electron microscopy of the structure.
Electrical characterization of plasma generation in KrF laser Cu ablation
Authors: Dyer P. E.
Published: July 2002

Ionization onset in the ablation plume from KrF laser-irradiated Cu targets in vacuum leads to a fast-rising voltage transient on the target. This, together with ion probe measurements, provides information on the plasma parameters. With 30 ns pulses, plasma initiates at ∼108 W cm−2; electron temperatures of 7 eV and ion energies of several hundred volts are produced at 2.2×108 W cm−2 .
Substructure in short optical pulses from gain-switched semiconductor lasers
Authors: Weber A. G. , Böttcher E. H. , Bimberg D.
Published: July 2002

The spike-like substructure in picosecond optical pulses from gain-switched multimode injection lasers is analyzed. A theoretical description based on the interference of the randomly phased longitudinal laser modes and the transient shift of the envelope of the mode spectrum under gain-switched operation is presented. Single shot, streak camera records and autocorrelation traces are simulated, describing all essential experimental features of the substructure like its random variation from pulse to pulse and inherent periodicity.
Fine structure of the oxygen-related local mode at 714 cm−1 in GaAs
Authors: Alt H. Ch.
Published: July 2002

Infrared absorption measurements on a new third state of the Ga-O-Ga center in GaAs are reported. This state gives rise to a local mode at 714 cm−1, B′, which is shifted from the band B to lower energy by 0.67 cm−1. The B′ state acts as an intermediate state for the photoinduced conversion from the 730 cm−1 band, A, to B. The kinetics is quantitatively described by a model considering successive capture of conduction-band electrons, which have been photoexcited from the EL2 level. The reappearance of the band A after quenching of EL2 occurs through the corresponding sequence B→B′→A. The experimental results favor the interpretation of B′ in terms of a third charge state being not accessible at thermal equilibrium conditions.
Space-charge recombination in N-AlGaAs/p+-GaAs heterojunction diodes
Authors: Low T. S. , Mars D. E.
Published: July 2002

Space-charge recombination currents were measured in N-AlGaAs/p+-GaAs heterojunction diodes grown by molecular beam epitaxy (MBE) under various growth conditions. The diode epilayer structure was designed to simulate the emitter-base junction of a heterojunction bipolar transistor.The diodes were fabricated using a fast turnaround mesa process, and their forward current-voltage characteristics were fit to a simple model to extract the recombination current density. The space-charge recombination decreased steeply with increasing growth temperature Ts between 560 and 610 °C, and it decreased when the As4/Ga ratio was reduced from 3 to 1. It was lower for misoriented substrates (6° off 〈100〉 toward 〈111〉A) than for 〈100〉 oriented substrates, and it decreased significantly as the result of a post-growth anneal in the MBE system.
New and simple optical method for i
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u etch rate determination and endpoint detection
Authors: Heinrich F. , Stoll H.-P. , Scheer H.-C.
Published: July 2002

Optical emission spectroscopy has been established as a simple method for simultaneous etch rate determination and endpoint detection in ion beam etching. During the sputtering of a thin layer with a refractive index different from the substrate interference is detected in the reflected light emitted by excited beam particles. This method will be very useful for other plasma and beam-assisted processes too, like deposition, reactive ion etching, and reactive ion beam etching. In contrast to the conventional methods, no additional light source is required.
Modification of Y2Ba4Cu8O16 thin-film surfaces by interaction with a radio frequency excited oxygen plasma
Authors: Budhani R. C. , Ruckman M. W.
Published: July 2002

The use of rf excited oxygen plasma for oxidizing and possible etching of SrTiO3 (100) supported Y2Ba4Cu8O16 thin films is studied by photoemission. Oxygen plasma modifies the surface and eliminates photoemission features identified with surface impurities like BaCO3. The resulting surface is barium deficient but shows a Fermi level suggesting it is metallic. Application of a −200 V dc bias to the sample to increase the kinetic energy of the incident oxygen ions enhances either surface sputtering or atomic mixing and produces a surface which resembles YBa2Cu3O7, because the photoemission spectra are similar to those published for cleaved crystal surfaces or films.
Y-Ba-Cu-O superconducting films produced by long-pulse laser vaporization
Authors: Balooch M. , Olander D. R. , Russo R. E.
Published: July 2002

Deposition of superconducting thin films from YBa2Cu3O7 targets using a long-pulse (ms) Nd-glass laser with 50 J/pulse energy has been demonstrated. The deposition rate was approximately 100 nm/pulse and the film stoichiometry was close to that of the target. Scanning electron microscopy revealed spherical inclusions in the film. Scanning tunneling microscopy in air showed a terrace-ledge structure on the uniform portion of the film. A film produced by four pulses on a SrTiO3 substrate, held at 540 °C, and post-annealed in O2 at 850 °C for about 2h exhibited an onset transition at 78 K and zero resistance at 61 K. This new approach can provide fast deposition rates and broad-area film coverage per laser shot.
Preparation of superconducting Bi-Sr-Ca-Cu-O fibers
Authors: LeBeau S. E. , Righi J. , Ostenson J. E. , Sanders S. C. , Finnemore D. K.
Published: July 2002

Procedures have been developed for the preparation of long slender fibers of Bi-Sr-Ca-Cu-O using a gas jet to shape and freeze the material. The fibers emerge in amorphous form and are converted to the Bi2Sr2Ca1Cu2Ox phase by subsequent heat treatment. Magnetization and scanning electron microscopy studies show the material to be a very fine grained bulk superconductor with intragranular critical currents of 7×106 A/cm2 at 5 K and 1.8 T.
Y-Ba-Cu-O superconducting thin films prepared by plasma-assisted flash evaporation
Authors: Yasuda Yukio , Koide Yasuo , Zaima Shigeaki , Sano Naoki
Published: July 2002

Superconducting thin films of Y-Ba-Cu-O oxide have been prepared on (100) MgO substrates by flash evaporation in oxygen plasma. The as-grown films deposited at substrate temperatures from 385 to 550 °C show superconducting properties with a critical temperature Tc of about 90 K. Transmission electron diffraction indicates that a film deposited at below 430 °C has both amorphous and polycrystalline regions, and that a film at above 430 °C is polycrystalline.
Domain observation during direct overwrite on magneto-optical recording films
Authors: Suzuki Yoshio , Ohta Norio , Takahashi Masahiko , Yonezawa Seiji
Published: July 2002

Domain patterns were observed with a polarized microscope during direct thermomagnetic overwrite at a fixed bias magnetic field. The size of a recorded domain can be changed reversibly by irradiation of laser pulses with various durations. By scanning a rapidly pulsed laser beam on a film, a stripe domain can be written, erased, and manipulated. This technique may be used in a new type of rewritable memory device. These overwrite behaviors can be explained with a model which assumes that an initial domain formed during laser pulse heating shrinks during cooling.
Intersubband infrared absorption in GexSi1−x/Si superlattice by photocurrent measurement
Authors: Karunasiri R. P. G. , Park J. S. , Wang K. L. , Cheng Li-Jen
Published: July 2002

The intersubband infrared absorption of holes in a GexSi1−x /Si superlattice is observed for the first time. In the experiment, the photocurrent is measured as a function of applied bias which is used to inject holes to the minibands of the superlattice. Two peaks in the photocurrent as a function of bias across the device are observed due to intersubband absorption between the ground to the first and the first to the second light hole minibands. The polarization dependence measurement is used to study the nature of the transitions and is in good agreement with the selection rules.
Single-monolayer quantum wells of GaInAs in InP grown by metalorganic vapor phase epitaxy
Authors: Seifert W. , Fornell J.-O. , Ledebo L. , Pistol M.-E. , Samuelson L.
Published: July 2002

GaInAs/InP quantum wells differing in thickness between 1 and 20 monolayers (1 monolayer≊2.93 Å) have been grown by low-pressure (50 mbar) metalorganic vapor phase epitaxy and investigated by 2 K photoluminescence. To our knowledge this is the first observation of the one monolayer quantum well. Well-resolved photoluminescence peaks were observed and were attributed to recombination of excitons bound to quantum wells of defined monolayer thickness. The growth rate could be adjusted to produce a one monolayer quantum well. Its photoluminescence peak was observed at 1.245 eV, corresponding to a quantum confinement shift of 434 meV. The full width at half maximum of this peak was only 8 meV.
Double-heterostructure GaAs/AlGaAs lasers on Si substrates with reduced threshold current and built-in index guiding by selective-area molecular beam epitaxy
Authors: Lee Henry P. , Liu Xiaoming , Wang Shyh
Published: July 2002

We report successful fabrication of GaAs/Al0.26Ga0.74As double-heterostructure laser diodes grown on patterned Si substrates by molecular beam epitaxy. The patterned substrates consist of exposed Si stripes with widths ranging from 9 to 70 μm and surrounded by 900 Å of SiN films on both sides. Oxide-defined contact stripe lasers with stripe widths ranging from 3 to 50 μm (corresponding to each of the SiN-defined stripe windows) were fabricated. Reduction of laser threshold current densities compared to similar lasers grown on nonpatterned Si substrates is observed, and is attributed to current confinement effect by the high-resistivity polycrystalline GaAs/AlGaAs films surrounding the active devices. From the measurements on the longitudinal mode spectrum and far-field patterns, lateral index guiding is also observed for the 10-μm-wide selective-area grown laser.
Low-loss GaAs/AlGaAs optical waveguides and phase modulator on silicon substrate grown by molecular beam epitaxy
Authors: Kim Y. S. , Lee S. S. , Ramaswamy R. V. , Sakai S. , Kao Y. C. , Shichijo H.
Published: July 2002

We report on the fabrication and the characterization of low-loss, single-mode GaAs/AlGaAs single heterostructure ridge waveguides and a linear electro-optic phase modulator on silicon substrate. The waveguides and the phase modulator were grown by molecular beam epitaxy and were characterized at a 1.3 μm wavelength. The average TE mode propagation loss of 1.24 dB/cm, obtained for a 6-μm-wide ridge waveguide, is the lowest loss so far reported. The measured phase shift efficiency of the phase modulator was 3.5°/V mm.
Electrical characteristics of p+-Ge/(N-GaAs and N-AlGaAs) junctions and their applications to Ge base transistors
Authors: Ünlü M. S. , Strite S. , Gao G. B. , Adomi K. , Morkoç H.
Published: July 2002

Electrical properties of p+-Ge/N-AlGaAs (and N-GaAs) are studied as a function of temperature and current conduction mechanisms are outlined. Junctions with Ge grown on GaAs and AlGaAs show ideality factors of unity and 1.03 at room temperature, respectively. Temperature-dependent current-voltage (I-V) and room-temperature capacitance-voltage (C-V) characterization are employed to determine the built-in voltage (Vbi) of the two diode structures. For Ge/GaAs, a valence-band discontinuity of 0.49±0.05 eV is measured which is in good agreement with the value deduced from photoemission studies. Implications of p+-Ge base in AlGaAs/Ge/GaAs double-heterojunction bipolar transistors (DHBTs) are discussed.
Simultaneous measurement of spontaneous emission rate, nonlinear gain coefficient, and carrier lifetime in semiconductor lasers using a parasitic-free optical modulation technique
Authors: Eom J. , Su C. B. , LaCourse J. , Lauer R. B.
Published: July 2002

An optical modulation technique is used to determine three important parameters for 1.3 μm InGaAsP diode lasers: the rate of spontaneous emission into the guided modes, the nonlinear gain coefficient, and the carrier lifetime at threshold. These results are unaffected by electrical parasitics, and are essential to understanding the noise and modulation properties of diode lasers.
1/2 〈100〉 {100} dislocation loops in a zinc blende structure
Authors: Chu S. N. G. , Nakahara S.
Published: July 2002

We report, for the first time, the identification of extrinsic dislocation loops lying on the {100} planes with 1/2〈100〉 types of Burgers vectors in a zinc blende structure in InGaAsP lattice matched to InP. These dislocation loops generated only in nonradiative recombination assisted point-defect motion process under intensed laser light, and form the 〈100〉 type dark line defects in degraded 1.3 μm wavelength laser diodes.
Attractor crowding in Josephson junction arrays
Authors: Tsang Kwok Yeung , Wiesenfeld Kurt
Published: July 2002

Large arrays of coupled nonlinear oscillators can suffer a noise sensitivity due to competition between huge numbers of coexisting states. We have found direct numerical evidence that a Josephson junction series array can exhibit attractor crowding. Thus, for the parameter values considered, no matter how small the noise level, there is a limit to the size of the array beyond which noise corrupts the in-phase dynamical state.
Growth of pseudomorphic high electron mobility heterostructures by atmospheric pressure metalorganic chemical vapor deposition
Authors: Pan N. , Carter J. , Zheng X. L. , Hendriks H. , Hoke W. E. , Feng M. S. , Hsieh K. C.
Published: July 2002

Pseudomorphic high electron mobility heterostructures are demonstrated by atmospheric pressure metalorganic chemical vapor deposition for the first time. Transmission electron microscopy (TEM), variable temperature Hall effect measurements, Shubnikov–de Haas measurements, and photoreflectance were applied to characterize the heterostructures. TEM micrographs of the cross section reveal sharp heterojunction interfaces. Variable temperature Hall effect measurements show a monotonic increase in mobility as the temperature is lowered. With a spacer thickness of 120 Å, a peak mobility of 80 000 cm2/V s at 20 K and a sheet carrier concentration of 1.05×1012 cm−2 are obtained. Similarly, a thinner spacer (60 Å) shows a peak mobility of 57 000 cm2/V s at 25 K with a sheet carrier concentration of 1.40×1012 cm−2. Shubnikov–de Haas measurements in magnetic fields up to 18.5 T show clear oscillations and the quantum Hall effect confirming the existence of a two-dimensional electron gas.
InGaP/GaAs single quantum well structure growth on GaAs facet walls by chloride atomic layer epitaxy
Authors: Usui Akira , Sunakawa Haruo , Stützler Frank J. , Ishida Koichi
Published: July 2002

InGaP/GaAs single quantum well(SQW) structure growth on GaAs facet wall is achieved by atomic layer epitaxy (ALE) using chloride source gases, such as InCl and GaCl. GaAs facets are formed on GaAs(100) surface openings by conventional hydride vapor phase epitaxy, which have {011} sidewalls perpendicular to the surface, {111}B and (100) faces. ALE growth of SQWs onto these faces results in a very smooth and uniform surface, as shown by scanning electron microscopy observation and cathodoluminescence measurements. The self-limiting mechanism for ALE is also retained in such selective sidewall growth of heterostructures.
Transconductance degradation and interface state generation in metal-oxide-semiconductor field-effect transistors with oxynitride gate dielectrics under hot-carrier stress
Authors: Lo G. Q. , Ting W. C. , Shih D. K. , Kwong D. L.
Published: July 2002

The hot-carrier immunity of submicrometer (0.8 μm) n-channel metal-oxide-semiconductor field-effect transistors with thin (∼8.6 nm) oxynitride gate dielectrics prepared by rapid thermal reoxidation (RTO) of rapidly thermal nitrided (RTN) SiO2 has been studied. The hot-carrier immunity was evaluated in terms of hot-carrier-induced transconductance degradation (ΔGm/Gm0) and interface state generation (ΔDit/Dit0) which was measured by using charge pumping current (Icp) measurement. It is found that for improved device performance and reliability, there exists an optimum RTO condition for a given RTN SiO2. In addition, a strong correlation between ΔDit/Dit0 and ΔGm/Gm0 has been observed.
Surface melting of metal deposits during laser-induced chemical vapor deposition with a modulated continuous-wave laser
Authors: Comita Paul B. , Price Peter E. , Kodas Toivo T.
Published: July 2002

Thermal laser-induced chemical vapor deposition of gold crystals on alumina substrates has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when the laser source is modulated. Time-resolved reflectance measurements have been used to study the time evolution of the surface reflectance during growth with both modulated and unmodulated laser light. These experiments suggest that the surface melting observed with a modulated laser source is primarily due to the heat released by the exothermic decomposition of reactant adsorbed on the surface during the time that the laser intensity is off.
Low surface recombination velocity and contact resistance using p+/p carbon-doped GaAs structures
Authors: de Lyon T. J. , Kash J. A. , Tiwari S. , Woodall J. M. , Yan D. , Pollak F. H.
Published: July 2002

A reduction of the GaAs surface recombination velocity due to a heavily carbon-doped GaAs overlayer is reported. Metalorganic molecular beam epitaxy using trimethylgallium, triethylgallium, and elemental arsenic sources has been used to grow an epitaxial structure consisting of 1000 nm of p=1×1017 cm−3 capped with 10 nm of p=1×1020 cm−3 GaAs. Time-resolved photoluminescence (PL) and PL excitation spectroscopy showed this p+/p structure to have a 3.2 ns carrier lifetime and strong band-edge PL emission, whose intensity was nearly constant over an excitation photon energy range of 1.5–3.3 eV. The same wafer with the p+ cap etched off exhibited a much shorter carrier lifetime and PL intensity that decreased exponentially with increasing photon energy, which is indicative of carrier losses to surface recombination. The specific contact resistivity of nonalloyed ohmic contacts to these heavily doped layers was observed to be in the mid 10−7 Ω cm2 range, independent of measurement temperature from 77 to 340 K, suggesting a tunneling contact due to the narrow surface depletion layer.
Chemical beam epitaxial growth of InAs using trimethylindium and arsine
Authors: Chiu T. H. , Ditzenberger J. A.
Published: July 2002

We report the growth study of InAs by chemical beam epitaxy. Growth conditions for high quality epilayer has been determined from in situ reflection high-energy electron diffraction measurement, surface morphology, photoluminescence, and Hall measurement. The growth rate measurement shows that the pyrolysis characteristics of trimethylindium are qualitatively similar to that of triethylgallium which have previously been simulated by a surface chemical kinetics model. The boundary condition between In- and As-stabilized surface in the previously unexplored temperature range of 520–560 °C gives an activation energy of 3.1 eV for the As desorption from the InAs surface.