bluuebunny/crossref_metadata_2025 huggingface dataset:
Layer disordering of n-type (Se) and p-type (C) AlxGa1−xAs-GaAs superlattices by S diffusion
Authors: Major J. S. , Dallesasse J. M. , Guido L. J. , Baker J. E. , Plano W. E. , Sugg A. R. , Vesely E. J. , Richard T. A. , Holonyak N.
Published: July 2002

Data are presented showing limited layer disordering (or intermixing) of S-diffused Se-doped or C-doped AlxGa1−xAs-GaAs superlattices. The S diffusion is characterized via secondary-ion mass spectroscopy, shallow angle beveled cross sections, and absorption measurements. Limited intermixing of column-III-site atoms (Al⇄Ga) as well as minimal displacement of the column-V-site acceptor C is observed. The S diffusion depth is much greater than that of the layer disordering, the magnitude of which is similar to that of native-defect vacancy-assisted disordering (vacancy VIII).
Semiconductor lasers with uniform longitudinal intensity distribution
Authors: Schrans Thomas , Yariv Amnon
Published: July 2002

Power-dependent nonuniform longitudinal intensity distribution leading to spectral and spatial instabilities is a major problem in semiconductor lasers. It is shown theoretically that a proper choice of the longitudinal distribution of the gain as well as that of the magnitude of the grating coupling coefficient will lead to a uniform intensity distribution in distributed feedback lasers. We also show that the widely used phase, rather than magnitude, control of the coupling coefficient cannot lead to a uniform intensity distribution when the facet reflectivities are zero.
Direct imaging of δ-doped layers in GaAs
Authors: Ourmazd A. , Cunningham J. , Jan W. , Rentschler J. A. , Schröter W.
Published: July 2002

We report the direct imaging of Be δ-doped layers in GaAs, in the concentration range (0.5–2)×1014/cm2, comparing samples grown by gas source molecular beam epitaxy (MBE) and conventional MBE. The gas source MBE δ layers are ∼15 Å wide, and at least at high concentrations, consist of clusters ∼12 Å in diameter. At 2×1014 Be atoms/cm2, the MBE δ layer is an order of magnitude wider than that grown at the same temperature by gas source MBE. Our results imply that layers with Be concentrations in excess of 1021/cm3 can be fabricated by gas source MBE.
In situ time-resolved reflectivity measurements of Al under excimer laser planarization conditions
Authors: Carey Paul G. , Woratschek Bertram J. , Bachmann Friedrich
Published: July 2002

In situ time-resolved reflectivity (TRR) measurements have been made on unpatterned 800 nm pure Al films located on top of different underlying layers (e.g., substrate, diffusion barrier, or oxide) under XeCl (λ=308 nm, pulse width 40 ns) excimer laser planarization conditions. The reflectivity change observed when using a HeNe (λ=632.8 nm) probe beam is assumed to indicate layer melting. Results show that Al melt durations increase with laser energy fluence, oxide thickness, and substrate temperature. In addition, under certain processing conditions Al areas with a thick underlying oxide remain molten for over 1000 ns while no Al melting is observed where it directly contacts the silicon substrate. This work explains why substrate heating during excimer laser planarization is necessary in order to completely fill high aspect ratio contact holes.
Optical determination of oxygen outdiffusion in epitaxial silicon grown on n-type Czochralski substrates
Authors: Geddo M. , Pivac B. , Borghesi A. , Stella A. , Pedrotti M.
Published: July 2002

Oxygen solid-state outdiffusion from the substrate to the epitaxial layer was investigated by using micro-Fourier transform infrared measurements in a transversal wafer cross-section configuration. Interstitial oxygen concentration, obtained by analyzing the 1107 cm−1absorption band, indicated that an oxygen content, clearly detectable by the infrared technique, is present in the epitaxial layer near the interface. To our knowledge this is the first evidence of oxygen outdiffusion from the substrate into the epitaxial layer.
Rapid thermal annealing of Ge-implanted InP
Authors: Kringho/j P. , Gribkovskii V. V. , Nylandsted Larsen A.
Published: July 2002

Results from n-type doping by Ge implantation at 200 keV into 〈100〉 p-type InP are reported. The degree of recrystallization and electrical activity after capless annealing by rapid thermal annealing was investigated as a function of dose, implantation, and annealing temperature by a combination of Rutherford backscattering spectrometry/channeling, differential Hall/resistivity, and secondary-ion mass spectrometry measurements. Room-temperature implantations resulted in continuous amorphous layers even at a dose of 2×1013cm−2 in contrast to hot implantations at 200 °C where no amorphous layers were created even for a dose as high as 5×1014 cm−2. For the latter dose an activation percentage of 37 and a maximum carrier concentration of 1×1019 cm−3 were achieved after rapid thermal annealing at 830 °C for 1 s.
Effect of confining layer aluminum composition on AlGaAs-GaAs-InGaAs strained-layer quantum well heterostructure lasers
Authors: York P. K. , Langsjoen S. M. , Miller L. M. , Beernink K. J. , Alwan J. J. , Coleman J. J.
Published: July 2002

Data are presented on laser threshold current density and emission wavelength of strained-layer InGaAs-GaAs-AlxGa1−xAs single quantum well lasers having confining layer aluminum compositions in the range 0.20≤x≤0.85. A decrease in threshold current density with increasing confining layer composition is related to the increased confinement factor of the waveguide structure. An increase in the laser emission wavelength is observed as a consequence of reduced bandfilling.
Tunneling real-space transfer induced by wave function hybridization in modulation-doped heterostructures
Authors: Bigelow J. M. , Leburton J. P.
Published: July 2002

We report a new tunneling mechanism in modulation-doped heterostructures based on wave function hybridization. We show that hybrid wave functions can be formed across the heterojunction by growing highly doped n-p layers below the undoped GaAs layer. The hybridization creates the condition for hot electrons to transfer by tunneling from the high-mobility GaAs channel through the heterojunction to the low-mobility AlGaAs layer and results in a negative differential resistance. The hybrid nature of the wave functions and the smaller energies needed to achieve the transfer across the heterojunction suggest that this effect will occur at lower applied fields than for thermionic emission or tunneling between localized states in adjacent quantum wells.
Lateral quantization induced emission energy shift of buried GaAs/AlGaAs quantum wires
Authors: Maile B. E. , Forchel A. , Germann R. , Straka J. , Korte L. , Thanner C.
Published: July 2002

Buried GaAs/AlGaAs quantum wires were prepared by Al0.2Ga0.8As overgrowth of deep etched wires defined by high-resolution electron beam lithography and dry etching. The overgrown wires show a dramatic decrease of the optically inactive sidewall layer compared to open wires. For wires with a lateral dimension Lx=50 nm we observe a spectral shift to higher energies of the excitonic emission, in good agreement with calculations of the two-dimensional confinement effects.
Single and double quantum well lasers with a monolithically integrated passive section
Authors: Werner J. , Lee T. P. , Kapon E. , Colas E. , Stoffel N. G. , Schwarz S. A. , Schwartz L. C. , Andreadakis N. C.
Published: July 2002

Single (SQW) and double (DQW) quantum well composite cavity GaAs/AlGaAs lasers with an integrated passive section were fabricated and compared. Si implantation was used for partial quantum well disordering in the passive section. Implanted DQW lasers with a 2.6-mm-long cavity had threshold currents of 26.3 mA compared to 33 mA for implanted SQW lasers. The measured resonant absorption in the passive section showed an exponential roll-off in agreement with Urbach’s law. The characteristic energy E0 associated with Urbach’s law was 6 meV for untreated SQW and DQW lasers and ≊11 meV for implanted SQW and DQW lasers.
Mössbauer spectra of nanocrystalline Fe and Fe-Cr particles in sol-gel-derived SiO2 glass
Authors: Chatterjee A. , Das D. , Chakravorty D. , Choudhury K.
Published: July 2002

Ultrafine iron particles prepared by a sol-gel route are characterized by Mössbauer spectroscopy and transmission electron microscopy. The Mössbauer absorption patterns consist of a ferromagnetic component superposed on a superparamagnetic doublet. The intensity of the superparamagnetic doublet is found to be larger for particles having smaller average diameter. For very fine particles a diffused electron diffraction pattern is observed. It is also shown that the sol-gel technique could be used to prepare fine particles of a Fe-Cr alloy.
Using a neural network to proximity correct patterns written with a Cambridge electron beam microfabricator 10.5 lithography system
Authors: Cummings K. D. , Frye R. C. , Rietman E. A.
Published: July 2002

This letter describes our initial results of using a theoretical determination of the proximity function and an adaptively trained neural network to proximity correct patterns written on a Cambridge electron beam lithography system. The methods described are complete and may be applied to any electron beam exposure system that can modify the dose during exposure. The patterns produced in resist show the effects of proximity correction versus noncorrected patterns.
Electronic properties of a pulse-doped GaAs structure grown by organometallic vapor phase epitaxy
Authors: Nakajima Shigeru , Kuwata Nobuhiro , Nishiyama Naoki , Shiga Nobuo , Hayashi Hideki
Published: July 2002

A pulse-doped GaAs structure was grown by organometallic vapor phase epitaxy using a conventional doping technique. Existence of a two-dimensional electron gas confined in this structure was confirmed by Schubnikov–de Haas measurement. Electron mobility and concentration are evaluated by Hall measurement. Electron mobility and concentration dependence on temperature of a pulse-doped GaAs are similar to those of a δ-doped GaAs.
Prediction of direct band gaps in monolayer (001) and (111) GaAs/GaP superlattices
Authors: Dandrea Robert G. , Zunger Alex
Published: July 2002

The bulk GaAs0.5P0.5 alloy with lattice constant a(0.5) has an indirect band gap. First-principles self-consistent pseudopotential band structure calculations show that the monolayer (GaAs)1 (GaP)1 superlattice (SL) in either the (001) or the (111) layer orientation G is also indirect if constrained epitaxially on a substrate whose lattice constant is a(0.5). However, if grown coherently on a GaAs substrate we predict that both of these SLs will have a direct band gap. This is explained in terms of the deformation potentials of the underlying materials. Predicted band offsets are given for both (001) and (111) GaP/GaAs.
Optical beam deflection signal from a single microparticle
Authors: Wu Jiaqi , Kitamori Takehiko , Sawada Tsuguo
Published: July 2002

The optical beam deflection (OBD) method was applied to the measurement of a single microparticle, and the signal from one resin microparticle of 200–600 μm in diameter could be detected. Based on the frequency characteristics and size dependence of the OBD signal, this method was found to be more sensitive for a smaller particle, and more effective than the photoacoustic method. Theoretical considerations showed that these characteristics were attributable to the enhancement of the temperature field gradient due to the curvature of the microparticle.
Epitaxial growth of diamond thin films on cubic boron nitride {111} surfaces by dc plasma chemical vapor deposition
Authors: Koizumi S. , Murakami T. , Inuzuka T. , Suzuki K.
Published: July 2002

Diamond thin films have been grown epitaxially on high-pressure synthesized cubic boron nitride (c-BN) particles by using dc plasma chemical vapor deposition. At the early growth stage of the film on c-BN{111} surfaces, the island structure is observed and the number density of islands is about 1011 cm−2. The growth and the coalescence of islands are also found by scanning electron microscopy observation. The continuous film is obtained at the thickness of about 2000 Å and the surface of the film is rather smooth. The Raman peak of the epitaxial diamond film shows the shift toward the lower wave number due to the tensile stress involved in the film.
Electron beam irradiation enhancement of Al-Ga interdiffusion at GaAs/AlGaAs quantum well interfaces
Authors: Li Y. J. , Tsuchiya M. , Petroff P. M.
Published: July 2002

The effect of room-temperature electron beam irradiation on the Al-Ga interdiffusion at GaAs/AlGaAs quantum well heterointerfaces is investigated with low-temperature cathodoluminescence spectroscopy. The interdiffusion is enhanced by defects generated through an irradiation with a 400 keV electron beam. After room-temperature irradiation with a dose of ∼1.5×1017–2.5×1017/cm2 and subsequent rapid thermal annealing at 900 °C for 1 min, an interdiffusion length of 3–5 Å is obtained. The electron beam induced damage tends to saturate with increasing irradiation dose, and the formation of defect cluster at high dose limits the defect introduction and, thus, the interdiffusion at the interface.
Atomic layer epitaxy of AlGaAs
Authors: Gong J. R. , Jung D. , El-Masry N. A. , Bedair S. M.
Published: July 2002

Atomic layer epitaxy (ALE) has been employed to grow AlGaAs in the temperature range 550–700 °C. Monolayer growth was achieved independent of the column III flux. Al incorporates during ALE more efficiently than in metalorganic chemical vapor deposition (MOCVD). The ALE films grown at low temperature have superior photoluminescence properties when compared with the MOCVD-grown films. The as-grown ALE films are p type with carrier concentrations in the 1017–1019/cm3 range, depending on the growth conditions.
Incorporation of carbon in heavily doped AlxGa1−xAs grown by metalorganic molecular beam epitaxy
Authors: Abernathy C. R. , Pearton S. J. , Manasreh M. O. , Fischer D. W. , Talwar D. N.
Published: July 2002

Hole concentrations in excess of 1020 cm−3 have been achieved in AlxGa1−xAs using carbon doping during metalorganic molecular beam epitaxy. Hall and secondary-ion mass spectrometry measurements show a 1:1 correspondence between the hole density and carbon concentration in as-grown samples, although post-growth annealing at 900 °C leads to a reduction in the net free-carrier concentration (typically a decrease of ∼40% for 30 s anneals). The carbon-localized vibrational modes (LVMs) show fine structure due to the presence of three different symmetries for substitutional carbon CAs, namely Td, C2v, and C3v. The experimental CAs LVM line positions are in remarkable agreement with the predictions of a rigid ion model.
Surface Fermi-level changes in n-type GaAs determined from Hall-effect measurements
Authors: Miller W. R. , Stillman G. E.
Published: July 2002

Changes in the surface Fermi-level position in n-type epitaxial GaAs samples are determined by Hall-effect measurements of the corresponding changes in the sheet concentrations and theoretical calculations of the surface depletion thickness. The changes are induced and reversed repeatedly by alternating wet chemical treatments in hydrogen peroxide and ammonium hydroxide. This is the first known use of hydrogen peroxide to restore the surface Fermi level to near its starting value and demonstrate the repeated variation of the surface Fermi level by ammonium hydroxide. The results agree with the predictions of the advanced unified defect model and with published reports of increased band bending on n-type material, rather than with conflicting reports of decreased band bending. The results also indicate that problems may exist with other techniques used to measure surface- potential changes.
Origin and improvement of interface roughness in AlGaAs/GaAs heterostructures grown by molecular beam epitaxy
Authors: Chand Naresh , Chu S. N. G.
Published: July 2002

We show that the likely reason of interface roughness of AlxGa1−xAs/GaAs heterostructures is the surface segregation of background impurities present in the AlGaAs layer. The roughness increases with x and is worse for x=1. In our system, Al is considered to be the main source of impurities in AlGaAs. When grown using a less pure Al source, AlxGa1−xAs/GaAs interfaces show waviness with wavelength ranging from a few hundred to few thousand Å even for x=0.1. Such wavy AlGaAs/GaAs interfaces were not observed when a purer Al source was used irrespective of the AlGaAs thickness, value of x, growth rate, growth temperature (<630 °C), As4:Ga flux ratio, and other growth conditions. The AlAs/GaAs interface smoothness was further improved by using 2° to 4° off (100) towards 〈111〉A GaAs substrates, and by incorporating thin layers of GaAs at regular intervals in AlAs.
Secondary-ion mass spectrometry on δ-doped GaAs grown by molecular beam epitaxy
Authors: Schubert E. F. , Luftman H. S. , Kopf R. F. , Headrick R. L. , Kuo J. M.
Published: July 2002

Improved resolution of secondary-ion mass spectrometry (SIMS) is obtained on Be δ-doped GaAs grown by molecular beam epitaxy at a temperature of 500 °C. The measured impurity distribution width is 29 Å, which corresponds to a SIMS resolution of ΔzR=25 Å. Impurity diffusion lengths of ≤10 Å can be detected by the technique. The surface segregation of Si impurities in δ-doped GaAs grown at 660 °C is investigated as a function of doping density. The segregation length increases with the Si density and is consistent with a segregation model based on the pinning of the Fermi level at the growing GaAs surface.
Gain mechanism of the vertical-cavity surface-emitting semiconductor laser
Authors: Deppe D. G.
Published: July 2002

The vertical-cavity surface-emitting single quantum well laser is examined in terms of the short Fabry–Perot cavity’s effect on optical gain. It is suggested that for this vertical- cavity structure the optical gain mechanism is fundamentally altered as compared to the case of the more standard edge-emitting device with longer cavity lengths. The short cavity and highly reflecting mirrors of the vertical cavity structure lead to an enhanced gain coefficient at fixed carrier densities, due to enhanced spontaneous emission into the Fabry–Perot modes of the optical cavity, and the resultantly reduced spontaneous linewidth.
Low angle x-ray reflection study of ultrathin Ge films on (100) Si
Authors: Baribeau J.-M.
Published: July 2002

We report a glancing incidence x-ray reflection study of ultrathin (1–12 monolayers) Ge films grown on (100) Si by molecular beam epitaxy. Thin buried Ge layers were characterized by analyzing intensity oscillations arising from the interference of the x rays reflected at the Si/Ge interface and at the surface of a Si capping layer. Strong interference fringes were detected even for a 1-monolayer-thick Ge film. The intensity of the fringes was found to increase with the Ge thickness up to 6 monolayers. A damping of the fringes was observed for a thicker film, suggesting a breakdown of two-dimensional growth. This interpretation was corroborated by a transmission electron microscopy investigation which showed evidence of three-dimensional growth only in the 12 monolayer film.
Amplification by stimulated emission from optically pumped nickel vapor in an ultraviolet region
Authors: Hirata K. , Yoshino S. , Ninomiya H.
Published: July 2002

Amplification by stimulated emission has been observed from an optically pumped nickel vapor on the transitions at 347 and 381 nm. Nickel vapor was produced by direct laser vaporization, and the nickel atoms were optically pumped by a N2 laser at 337 nm. The amplification factor at 347 nm reaches a maximum after the amplification factor at 381 nm reaches a maximum. The maximum amplification factors are 1.62 and 1.69, respectively.
Multi-beam-bulk model for electron transport during commutation in an optically triggered pseudospark thyratron
Authors: Pak Hoyoung , Kushner Mark J.
Published: July 2002

The electron energy distribution in low-pressure pulsed power plasma switches is typically not in equilibrium with the local electric field. To simulate electron transport under these conditions a computer model has been developed and has been applied to the optically triggered pseudospark, or back-lit-thyratron (BLT). The model uses many groups of electrons divided into the ‘‘bulk’’ and the ‘‘beam’’. The bulk is represented by a fluid while the beam electrons are ballistic in nature and have not undergone significant energy-loss collisions after generation. To account for beam electrons being generated at arbitrary locations in the BLT, multiple beams are employed in the model. The commutation phase of switching in the BLT is investigated and the onset of a hollow cathode effect during switching is predicted.
Vacuum lithography for in situ fabrication of buried semiconductor microstructures
Authors: Wang Y. L. , Temkin H. , Harriott L. R. , Hamm R. A. , Weiner J. S.
Published: July 2002

We have developed a complete lithographic process combining focused ion beam writing, dry etching, and molecular beam epitaxy for in situ preparation of buried InP-based microstructures. A focused ion beam is used to locally remove an ultrathin oxide imaging layer grown in situ on the surface of InP. The pattern is transferred into the underlying semiconductor by free Cl2 etching with the patterned oxide layer acting as an etch mask. After removal of the oxide mask, GaInAs/InP heterostructures with excellent morphology and high luminescence efficiency can be grown on the patterned substrate. The entire process of mask formation, lithography, and regrowth can be carried out in situ repeatedly, and used for creating fully buried microstructures.
Microstructure and critical current density of zone melt textured YBa2Cu3O6+x
Authors: McGinn P. , Chen W. , Zhu N. , Lanagan M. , Balachandran U.
Published: July 2002

Zone melting has been used to produce texture in extruded YBa2Cu3O6+x wires. Highly aligned microstructures are produced with a-b planes oriented along the axis of the wires. Microstructural observations show that changes in alignment orientation can occur, and can result in the inability to carry a transport current. Pulsed transport Jc measurements on oriented samples indicate a zero field critical current density greater than 4×104 A/cm2.
Reactive partially ionized beam deposition of BaTiO3 thin films
Authors: Li P. , Lu T.-M.
Published: July 2002

A dual-source reactive partially ionized beam deposition has been employed to deposit thin BaTiO3 films on the Si(100) substrate at room temperature. It is shown that with a small amount (3%) of Ti and oxygen ions in the beam one can dramatically control the electrical properties of the films. From the capacitance versus voltage (C-V) characteristics, the flatband voltage and the total interface charge density were measured to be 0.3 V and 1×1011/cm2, respectively. These ferroelectric compound oxide thin films with high-dielectric constant are potentially useful in high density memory applications.
Optical spectroscopic study of inverted cylindrical magnetron sputtering of YBa2Cu3O7−x
Authors: Xi X. X. , Wu X. D. , Inam A. , Li Q. , Hemmick D. , Findikoglu A. , Venkatesan T. , Chang C. C. , Howard R.
Published: July 2002

Optical spectroscopic studies of the plasma generated by inverted cylindrical magnetron sputtering of the high-temperature superconductor YBa2Cu3O7−x reveal strong ionic emissions from cation elements as well as from the sputter gases. The emissions of cationic ions are weakened drastically when O2 is added into the sputter gas indicating the dominating role of ions in the reaction with oxygen to form gas phase oxides. The formation of gas phase oxides is proposed to be an important precursor step for the in situ deposition of YBa2Cu3O7−x thin films.
Lattice recovery of oxygen-implanted YBa2Cu3O7−δ superconductor
Authors: Martínez J. A. , Wilkens B. , Stoffel N. G. , Hart D. , Nazar L. , Venkatesan T. , Inam A. , Wu X. D.
Published: July 2002

The regrowth of an oxygen-implanted YBa2Cu3O7−δ thin film was studied by Rutherford backscattering, ion channeling, and x-ray diffraction studies. The atomic composition of the thin film was preserved even after a 1 h anneal at 990 °C, reflecting the high chemical stability of the material obtained by the pulsed laser deposition technique. Two distinct activation energies were determined during the regrowth process: 0.42±0.04 eV at lower temperatures, corresponding to epitaxial growth from the interface, and 0.18±0.03 eV at higher temperatures, presumably associated with homogeneous nucleation and reorientation.
Laser writing of superconducting patterns on YBa2Cu3Ox films
Authors: Dye R. C. , Muenchausen R. E. , Nogar N. S. , Mukherjee A. , Brueck S. R. J.
Published: July 2002

A novel process for the direct laser writing of thin-film high Tc patterns is demonstrated. The process consists of deposition of a high quality film (308 nm laser ablation from a YBa2Cu3Ox target with a 750 °C substrate temperature and a 150 mTorr O2 ambient), annealing in an inert atmosphere (Ar at 400 °C for 5–20 min) to reduce the oxygen content and depress or eliminate the superconducting transition temperature, and direct-write laser heating (1.06 μm at ≊0.5 kW/cm2 for ≊5 min) in an oxygen atmosphere at ≊590 Torr to selectively regenerate the high Tc material. rf eddy current and four-point resistivity probe results confirm this process for both SrTiO3 and LaAlO3 substrates. Scanning electron micrographs indicate that this is a very mild processing sequence with no observable changes in film morphology.
Interaction of Cu with CoSi2 with and without TiNx barrier layers
Authors: Olowolafe J. O. , Li Jian , Blanpain B. , Mayer J. W.
Published: July 2002

Thermally induced interactions of Cu with CoSi2, with and without interposed TiNx layers, have been studied using Rutherford backscattering spectrometry, Auger electron spectroscopy, and x-ray diffraction. Cu diffuses through a preformed CoSi2 layer to form the structure Cu/CoSi2/Cu3Si/Si at temperatures above 300 °C, and no dissociation of CoSi2 occurs. A 50 nm TiNx(x≊1) layer is observed to be an effective diffusion barrier up to about 500 °C between Cu and CoSi2.
Possible presence of 2234 phase with T
c(zero) of 95 K in a Bi-Pb-Sb-Sr-Ca-Cu-O ceramic
Authors: Wang Hong , Wang Xiaolin , Shang Shuxia , Wang Zhuo , Lu Zhikuan , Jiang Minhua
Published: July 2002

Samples of Bi1.84Pb0.34Sb0.1Sr2Ca2Cu3Oy ceramic were prepared by a direct sintering and air quenching method. A new phase with Tc(zero) of 95 K is detected inside multiphased samples by resistivity and susceptibility measurements. Powder x-ray diffraction analysis indicates that the structure is orthorhombic with cell parameters a=5.41 Å, b=5.44 Å, c=43.35 Å. The (Bi, Pb)2Sr2Ca3Cu4Oy composition is determined by x-ray energy dispersion analysis.
Electron spin resonance of antisite defects in as-grown and plastically deformed GaP
Authors: Palm J. , Kisielowski-Kemmerich C. , Alexander H.
Published: July 2002

In as-grown GaP we investigated two phosphorous antisite related electron spin resonance spectra with respect to ligand hyperfine (lhf) interactions: basing upon a linewidth analysis, we attribute a hyperfine doublet with unresolved lhf structure (PA3) in n-GaP:S to a P-antisite defect with cubic symmetry. The lhf interaction of the well known lhf resolved PP4 doublet (PA1) in semi-insulating GaP:Cr was found to be temperature dependent. In plastically deformed GaP the two spectra showed contrary linewidth changes. In highly deformed n-GaP:S both signals were detectable. A new spectrum of low symmetry (GA1) was observed which we attribute to a gallium antisite related defect.
Critical currents and magnetization in c-axis textured Bi-Pb-Sr-Ca-Cu-O superconductors
Authors: Jin S. , van Dover R. B. , Tiefel T. H. , Graebner J. E. , Spencer N. D.
Published: July 2002

Transport critical currents and magnetization behavior in c-axis textured Bi-Pb-Sr-Ca-Cu-O superconductor ribbons have been studied. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport Jc values as high as 2.3×105 A/cm2 at 4.2 K, H=8 T (H⊥ab) have been obtained. The high Jc at H≥5 T is maintained to temperatures near 20 K but it vanishes completely at or above ∼30 K, thus showing the limitation in useful, high-field operating temperatures for the Bi-system superconductors. A comparison of Jc (transport) and Jc (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders-of-magnitude-smaller grain size. This demonstrates that the a-b grain boundaries in the melt-processed ribbons are not weakly coupled. The time decay of magnetization has also been studied.
Anomalous compositional dependence in in situ growth of YBaCuO films at low oxygen pressure
Authors: Shinohara K. , Matijasevic V. , Rosenthal P. A. , Marshall A. F. , Hammond R. H. , Beasley M. R.
Published: July 2002

The roles of composition and oxygen pressure in in situ growth of superconducting YBaCuO films have been studied. Anomalous results are observed at low oxygen pressure. Off-stoichiometric, Ba-deficient films have superior superconducting properties and more bulk-like crystal structure compared to films made on the 1:2:3 stoichiometry. Films made at low pressure have an expanded c axis compared to the bulk value, although their Tc’s are only slightly depressed. Tc and c-axis lattice parameters are reported as a function of the deposition conditions.
Sequential deposition growth of Bi-Sr-Ca-Cu-O systems observed using in situ reflection high-energy electron diffraction
Authors: Yoshida I. , Kamei M. , Suzuki K. , Morishita T. , Tanaka S.
Published: July 2002

The crystal growth mechanism in Bi-Sr-Ca-Cu-O thin films has been revealed by sequential deposition with an electron cyclotron resonance (ECR) oxygen plasma using in situ reflection high-energy electron diffraction (RHEED) observation. A series of RHEED patterns presents clear evidence that the unit cell of the Bi-Sr-Ca-Cu-O structure is completed as the Bi layers have sandwiched Sr, Ca, and Cu layers. This crystalline process is not an atomic layer by atomic layer growth but a ‘‘unit cell by unit cell’’ growth.
Organometallic chemical vapor deposited layers of stabilized zirconia on sapphire as a substrate for laser ablated YBa2Cu3O7−x thin films
Authors: Schieber M. , Schwartz M. , Koren G. , Aharoni E.
Published: July 2002

Substrates of (11̄02) sapphire single crystals were covered with Y2O3 stabilized ZrO2 (YSZ) thin films deposited from 2,2,6,6 tetramethyl-3, 5-heptanedione precursors of Zr and Y by organometallic chemical vapor deposition. The YSZ layers were indeed oriented on the (100) planes as established by x-ray diffraction. Thin films of YBa2Cu3O7−x (YBCO) were then deposited on top of the YSZ layer by laser ablation. A critical temperature (R=0) of 90 K was obtained which is among the highest observed for YSZ. However, the critical current density at 77 K was only of the order of 103 A/cm2, which is common of polycrystalline YBCO deposited on YSZ.
Optically pumped Hg1−xZnxTe lasers grown by liquid phase epitaxy
Authors: Ravid A. , Zussman Z. , Sher A. , Shapira Yoram
Published: July 2002

Optically pumped stimulated emission is reported for the first time from Hg1−xZnxTe (x≊0.23) epilayers grown by liquid phase epitaxy. Pulsed lasing was observed up to 70 K. Maximum single mirror peak power output of 23 and 2 mW was measured at 12 and 70 K, respectively. The laser emission spectra consisted of a strong line around 5.4 μm, and a weaker one, 6–7 meV below it, which were attributed to band-to-band and to band-to-acceptor transitions. Far-field patterns with angular width of θ⊥=4° and θ∥≊2.5° have been observed perpendicular and parallel to the layer plane, respectively.
Anisotropy of critical current density in textured Bi2Sr2Ca1Cu2Ox tapes
Authors: Kumakura H. , Togano K. , Maeda H. , Kase J. , Morimoto T.
Published: July 2002

Anisotropy in Jc with respect to field direction for a textured Bi2Sr2Ca1Cu2Ox tape was measured at various temperatures and magnetic fields. Anisotropy at 4.2 K was small enough for practical applications in fields up to 25 T. However, the anisotropy increases rapidly with increasing temperature. Angular dependence of Jc shows a history effect, which is characteristic of ceramic superconductors.
Interface between Y-Ba-Cu-O thin film and cubic zirconia substrate
Authors: Hwang D. M. , Ying Q. Y. , Kwok H. S.
Published: July 2002

The interface between laser deposited Y-Ba-Cu-O thin films and yttria-stabilized cubic zirconia substrates was studied using high-resolution transmission electron microscopy and in situ resistivity measurements. It was found that a ∼5 nm layer of low resistivity compound was formed at the interface, at a substrate temperature of ∼650 °C. This result is qualitatively different from other substrates such as SrTiO3 and MgO, where the interface compounds are high resistivity oxides. This in situ Y-Ba-Cu-O thin film is superconducting with a Tc of 88 K and a Jc of 2×106 A/cm2 at 77 K.
High critical current densities in epitaxial YBa2Cu3O7−δ thin films on silicon-on-sapphire
Authors: Fork D. K. , Ponce F. A. , Tramontana J. C. , Newman N. , Phillips Julia M. , Geballe T. H.
Published: July 2002

The use of silicon on sapphire (SOS) as a substrate for YBa2Cu3O7−δ allows the growth of thick (∼4000 Å) films without the thermally induced cracking characteristic of epitaxial films on bulk Si substrate. Epitaxy is sustained and reaction is prevented by an intermediate buffer layer of yttria-stabilized (YSZ). The transport critical current density is as high as 4.6×106 A/cm2 at 77 K, and surface resistance measurements at 4.2 K are reported. Microtwin propagation from Si into YSZ is shown not to occur.
Direct measurement of transient macroscopic volume change induced by generation of electron-hole pairs in GaP and GaAs
Authors: Sugiyama Toshinobu , Tanimura Katsumi , Itoh Noriaki
Published: July 2002

We have carried out a direct measurement of the macroscopic volume change of GaP and GaAs induced by irradiation with an electron pulse by means of the photoelastic technique. We find that metastable states lasting over 1 ms in both GaAs and GaP are formed and that their yield increases as the temperature increases.
Amorphization and recrystallization of epitaxial ReSi2 films grown on Si(100)
Authors: Kim Kun Ho , Bai G. , Nicolet Marc-A. , Mahan John E. , Geib Kent M.
Published: July 2002

We used 2 MeV 4He backscattering spectrometry, x-ray diffractometry, and the van der Pauw technique to study how epitaxial ReSi2 films on Si(100) change structurally and electrically upon room-temperature implantation of 300 keV 28Si or 380 keV 40Ar. The as-grown film has a minimum channeling yield of ∼2% for Re, and a resistivity of ∼23 mΩcm at room temperature. Ion implantation produces damage in the film, which increases monotonically with dose. At a dose of either 5×1014 28Si/cm2 or 1×1014 40Ar/cm2, the entire ReSi2 film becomes both x-ray and channeling amorphous. The resistivity of the film decreases monotonically with dose. The amorphous film has a resistivity of ∼1.2 mΩcm at room temperature. Upon annealing in vacuum at 700 °C for 30 min, the damage anneals out and the amorphous ReSi2 film recrystallizes epitaxially, once again exhibiting a minimum channeling yield of ∼2% for Re and a resistivity of ∼23 mΩcm.
Extremely low threshold current strained InGaAs/AlGaAs lasers by molecular beam epitaxy
Authors: Williams R. L. , Dion M. , Chatenoud F. , Dzurko K.
Published: July 2002

Using solid source molecular beam epitaxy we have grown strained layer InGaAs/AlGaAs graded index separate confinement heterostructure lasers operating at 1.01 μm. For broad-area, uncoated Fabry–Perot devices with cavity lengths in excess of 3000 μm, the threshold current density is 56 A/cm2, a value which we believe to be the lowest ever reported for laser diodes in any materials system. The internal quantum efficiency for these lasers is 88%, while the materials losses are 1.8 cm−1.
Hybrid optical bistability based on voltage-controlled changes of persistent spectral holes
Authors: Hartmannsgruber N. , Maier Max
Published: July 2002

Electric field induced changes of the absorption in the center of a persistent spectral hole were used to operate a hybrid optical bistable device. The hole was burned in the inhomogeneously broadened S0–S1 transition of perylene in an amorphous polyvinylbutyral matrix. The external feedback was realized by detecting the zero-phonon fluorescence light of the dye molecules with a photomultiplier and applying the amplified voltage to the sample.
Noncritically phase-matched second-harmonic generation and optical parametric amplification in a lithium triborate crystal
Authors: Huang J. Y. , Shen Y. R. , Chen Chuangtian , Wu Bochang
Published: July 2002

We evaluate the potential of lithium triborate (LBO) temperature-tuned to achieve type-I noncritical phase matching, for picosecond high-power second-harmonic generation (SHG) and tunable optical parametric amplification (OPA). Pumped by 35 ps, 1.064 μm laser pulses, a conversion efficiency of 65% was obtained from SHG. The output of OPA, pumped by 0.532 μm was tunable from 0.75 to 1.8 μm with an efficiency better than 20%.
Preparation of a-axis oriented Y1Ba2Cu3O7−δ films by laser metalorganic chemical vapor deposition
Authors: Ushida T. , Higa H. , Higashiyama K. , Hirabayashi I. , Tanaka S.
Published: July 2002

Superconducting Y1Ba2Cu3O 7−δ (YBCO) thin films were prepared on MgO(100) substrates by metalorganic chemical vapor deposition. The films were partly irradiated by ArF excimer laser during deposition. We found that the irradiated parts were strongly a-axis oriented normal to the surface of the substrate for YBCO films prepared at 650–700 °C, whereas the x-ray diffraction pattern of the unirradiated parts consisted of the peaks of the (110), (00l), and (h00) planes. The surface morphology of the laser irradiated part of the films was very smooth, whereas that of the unirradiated parts was relatively rough. The zero-resistance temperature of the unirradiated and the irradiated parts of YBCO films prepared at 650 °C were 45 and 72 K, respectively.
Direct observation of SiH3 on a 1%-HF-treated Si(111) surface by scanning tunneling microscopy
Authors: Morita Y. , Miki K. , Tokumoto H.
Published: July 2002

Scanning tunneling microscopy (STM) has been made on an as-prepared Si(111) surface by the 1%-HF treatment. The STM images for both the empty and filled states exhibit regular dots with the threefold symmetry on the flat parts of the surface: the distance between dots measures 2.2 Å. The origin of these dots can be ascribed to the H atoms of the trihydride (SiH3) phase on the Si(111) surface. The electrons can tunnel from or to the tail states of the σ (filled) states or the σ* (empty) states around the H atoms for the SiH3 radicals, respectively.
Nonbolometric photoresponse of YBa2Cu3O7−δ films
Authors: Johnson Mark
Published: July 2002

Current biased films of YBa2Cu3O7−δ (YBCO) are illuminated by short pulses of laser light and transient voltages are measured for a range of temperature 10 K <T < 250 K. Near the superconducting transition temperature Tc a bolometric response is observed. Below Tc signals are observed that cannot be explained by a bolometric mechanism. These signals, with decay times of the order of hundreds of picoseconds, are characterized and discussed.
Effects of plasma and/or 193 nm excimer laser irradiation on the surface in chemical vapor deposition of boron films from B2H6+He
Authors: Komatsu Shojiro , Kasamatsu Mitsuo , Yamada Kawakatsu , Moriyoshi Yusuke
Published: July 2002

Micromorphological boron columns were found to grow toward 193 nm light in a low-pressure B2H6+He plasma, as a direct evidence of a photoinduced growth. Its growth mechanism was discussed; the micromorphological growth rate which resulted from photoinduced growth reactions reflects a grading distribution of laser intensity on the initial hemispherical nucleus surface. Activation energies for the growth were positive in the plasma-enhanced chemical vapor deposition while they were negative in the pyrolysis; this was discussed based on a previously proposed growth model.
Gold gettering induced by rapid thermal doping using spin-on sources
Authors: Hartiti B. , Muller J. C. , Siffert P.
Published: July 2002

Transition metals are known to degrade the device performances. Gettering is now widely used to reduce the effects of these contaminants. Rapid thermal processing (RTP) has been shown to advantageously replace conventional long time temperature cycles in various types of applications. Moreover, recent works have evidenced that a gettering of impurities can occur during the RTP cycle. In this letter, we report that RTP diffusion of phosphorus or boron from a spin-on deposited layer can also induce a gettering effect in silicon. For gold-contaminated samples, the redistribution of the Au acceptor level is followed by deep level transient spectroscopy measurements. After a 1000 °C/10 s cycle, gold is depleted in the regions below the surfaces, indicating that gettering has occurred. The mechanism of this RTP-induced gettering is discussed.
Oscillatory magnetic coupling in Ag/Ni superlattices
Authors: dos Santos C. A. , Rodmacq B. , Vaezzadeh M. , George B.
Published: July 2002

Ag/Ni superlattices have been prepared by triode dc sputtering on glass substrates at 100 K. X-ray diffractometry with the scattering vector perpendicular to the superlattice plane suggests structural coherence and interface sharpness whatever the thickness of the elemental layers. All the samples present (111) textures for both Ag and Ni. Magnetic measurements performed with a superconducting quantum interference device magnetometer indicate in-plane anisotropy of the magnetization and oscillatory interlayer magnetic coupling. This is confirmed by magnetoresistance measurements.
In situ observations of dc and ac electromigration in passivated Al lines
Authors: Castaño E. , Maiz J. , Flinn P. , Madden M.
Published: July 2002

In situ experiments have been carried out using a field emission scanning electron microscope (Hitachi S-800) in order to characterize the dynamic behavior of electromigration (EM) voids under high spatial resolution. These experiments have shown how the EM voids move against the electron wind either in passivated or unpassivated lines under dc and low-frequency ac currents.
In situ single-chamber laser processing of YBa2Cu3O7−δ superconducting thin films on yttria-stabilized zirconia buffered (100)GaAs
Authors: Tiwari P. , Sharan S. , Narayan J.
Published: July 2002

Superconducting YBa2Cu3O7−δ(YBCO) thin films have been deposited in situ on GaAs(100) by laser evaporation using yttria-stabilized zirconia (YSZ) as a buffer layer. The YSZ buffer layer was deposited at room temperature initially, followed by a deposition at 650 °C. The YBCO layers were deposited subsequently at substrate temperature of 650 °C. All the depositions were carried out in a single chamber equipped with a multitarget holder using KrF excimer laser, λ=248 nm. The morphology and structure of the buffer layer and YBCO films were determined using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Auger spectroscopy. The nature of YSZ films was determined to be polycrystalline with partial texturing. The YBCO superconducting thin films on these YSZ-coated GaAs specimens exhibited strong (00l) orientation with peak intensities similar to those observed on single-crystal YSZ substrates. The superconducting transition temperature Tc (onset) of 92 K and Tc0(zero resistance) of 73 K were achieved for YBCO thin films on GaAs with YSZ buffer layers.
In situ determination of phosphorus composition in GaAs1−xPx grown by gas-source molecular beam epitaxy
Authors: Hou H. Q. , Liang B. W. , Chin T. P. , Tu C. W.
Published: July 2002

We report for the first time an in situ determination of phosphorus compositions in a mixed group-V compound, such as GaAs1−xPx, grown by gas-source molecular beam epitaxy. Reflection high-energy electron diffraction intensity oscillations from As-limited and (As+P)-limited growth are observed on a Ga-rich GaAs surface. The phosphorus composition is therefore deduced from the different growth rates. Viability of this technique is strongly confirmed by the good agreement with the phosphorus compositions determined ex situ by x-ray rocking curve measurements on GaAs/GaAsP strained-layer superlattice structures.
Optimal growth conditions for molecular-beam epitaxy of Nd3+ doped CaF2
Authors: Bausá L. E. , Muñoz-Yagüe A.
Published: July 2002

Nd3+ incorporation in CaF2 layers grown by molecular-beam epitaxy on CaF2 substrates is investigated by making use of the photoluminescence lines associated with Nd3+ centers involving one or several Nd3+ ions. It is shown that the substrate crystal orientation has no effect on the aggregation state of Nd3+ while the growth temperature greatly influences the formation of Nd3+ aggregate centers. An optimum growth temperature around 500 °C is determined, leading to CaF2 layers of good crystal quality in which the main emission, related to single Nd3+ centers, is optimized. The results have been obtained for Nd3+ concentrations as high as 3.6 wt % Nd and growth rates in the range of 0.2–1 μm/h.
Nanometer scale pattern replication using electron beam direct patterned SiO2 as the etching mask
Authors: Pan X. , Allee D. R. , Broers A. N. , Tang Y. S. , Wilkinson C. W.
Published: July 2002

Because of its unique properties and well-established processing techniques, SiO2 has wide application in the integrated circuit industry. The ability to directly pattern SiO2 with nanometer resolution by electron beam irradiation is therefore of great importance in the fabrication of both ultrasmall conventional and quantum devices. In this letter we demonstrate the replication of trenches with feature sizes as small as 10 nm into polycrystalline silicon and single-crystal and via reactive ion etching by using electron beam direct patterned SiO2 as the mask.
Cation site ordering and conduction electron scattering in GaInP2
Authors: Friedman D. J. , Kibbler A. E. , Olson J. M.
Published: July 2002

We present Hall mobility data μ(T) in the range T=300–600 K for GaInP2, an alloy whose band gap has been shown to decrease with increasing compositional ordering. Samples grown to give high ordering are found to have consistently lower mobilities than samples with low ordering, suggesting that the mobility is limited by cluster scattering by ordered domains. We analyze μ(T) in terms of a cluster scattering model developed by Marsh [Appl. Phys. Lett. 41, 732 (1982)] and others to estimate the relative volume fraction of cluster scattering sites in the ordered and disordered material.
Observation of third order optical nonlinearity due to intersubband transitions in AlGaAs/GaAs superlattices
Authors: Walrod D. , Auyang S. Y. , Wolff P. A. , Sugimoto M.
Published: July 2002

We report the first observations of large third order optical nonlinearities in AlGaAs/GaAs superlattices due to intersubband transitions. The process is triply resonant when the first intersubband transition matches the radiation from CO2 lasers. The intersubband relaxation time has also been estimated from the dispersion of χ(3) with the laser difference frequency Δω and found to be in good agreement with other published values. The magnitude and frequency dependence of the intersubband mechanism have been calculated using the diagrammatic technique.
Many-body effects in the gain spectra of strained quantum wells
Authors: Pereira M. F. , Koch S. W. , Chow W. W.
Published: July 2002

A many-body theory for the optical susceptibility in highly excited strained-layer quantum wells is presented. Gain spectra are computed for the example of InxGa1−xAs/InP and different In concentrations, yielding zero, tensile, and compressive strain.