bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain relaxation and ordering in SiGe layers grown on (100), (111), and (110) Si surfaces by molecular-beam epitaxy
Authors: Kuan T. S. , Iyer S. S.
Published: July 2002

Si0.5Ge0.5/Si superlattices and thick Si0.5Ge0.5 layers grown on (100), (111), and (110) Si surfaces by molecular-beam epitaxy (MBE) exhibit different growth morphologies and defect structures. The best morphology is achieved on (100) surfaces at low temperatures (∼400 °C), while thin and defect-free SiGe layers grown at higher temperatures (∼600 °C) tend to exhibit undulated surfaces due to the mismatch strain. Strained SiGe layers grown on (111) and (110) surfaces are much more susceptible to twin formation. SiGe layers grown on (100) surfaces at low temperatures exhibit a long-range order along the 〈111〉 directions. Our results indicate that such ordering occurs only in thick and relaxed SiGe layers but not in thin SiGe layers strained in a SiGe/Si superlattice structure. No ordering was observed in SiGe layers grown on (111) and (110) surfaces.
High sensitivity optical image processing device based on CdZnTe/ZnTe multiple quantum well structures
Authors: Partovi A. , Glass A. M. , Olson D. H. , Zydzik G. J. , Short K. T. , Feldman R. D. , Austin R. F.
Published: July 2002

We present results on the operation of a high sensitivity semi-insulating multiple quantum well device for optical image processing. This device operates in the visible spectrum using II-VI CdZnTe/ZnTe multiple quantum well structures. Incident light creates charge carriers that screen an applied ac electric field modulating the absorption and refractive index of the structure through the quantum confined Stark effect. In this way, an incident intensity pattern is recorded as an absorption and refractive index variation. The semi-insulating nature of the material eliminates the need for pixelation. In a wave-mixing experiment, a peak diffraction efficiency of 0.25% was observed from 2.25 μm active layer of the device. Two-beam-coupling gain coefficients of ∼500 cm−1 at wavelengths longer than the exciton absorption peak should be possible.
Control of porous Si photoluminescence through dry oxidation
Authors: Shih S. , Tsai C. , Li K.-H. , Jung K. H. , Campbell J. C. , Kwong D. L.
Published: July 2002

We demonstrate the applicability of thermal oxidation to control the photoluminescence (PL) from quantum-sized structures in porous silicon. Uniform photoluminescence samples with intense visible light observed under ultraviolet light at room temperature were quickly obtained without a long time hydrofluoric acid (HF) immersion. Applying different oxidation times or temperatures provides a very practical technique to control the luminescence color. By this way, we have observed a shift in the luminescence peak from 7600 to 6200 Å and a reduction in the spectral width from ∼1600 to ∼950 Å.
Resonant tunneling through a bend in a quantum wire
Authors: Wang Jian , Guo Hong
Published: July 2002

We study the transmission properties of a two-dimensional L-shaped quantum wire where a double potential barrier is placed at the corner. The localized state at the corner region without the barriers is pushed into the continuum in the presence of the barriers, resulting in resonant tunneling. Through resonant tunneling, reflection at the corner can be eliminated. The transmission is sharply peaked at resonant energies which can be tuned by applying a voltage. We propose that this system can be used as a basic element for connecting quantum devices in a circuit where bending of the connecting wire is necessary.
Elemental boron-doped p+-SiGe layers grown by molecular beam epitaxy for infrared detector applications
Authors: Lin T. L. , George T. , Jones E. W. , Ksendzov A. , Huberman M. L.
Published: July 2002

SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p+-SiGe layers on p−-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during molecular beam epitaxy (MBE) growth, and high doping concentrations (≳5×1020 cm−3) have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature (350 °C), resulting in improved crystalline quality and smooth surface morphology of the Si0.7Ge0.3 layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.
InAs0.85Sb0.15 infrared photodiodes grown on GaAs and GaAs-coated Si by molecular beam epitaxy
Authors: Dobbelaere W. , De Boeck J. , Heremans P. , Mertens R. , Borghs G. , Luyten W. , Van Landuyt J.
Published: July 2002

We report on the first InAs0.85Sb0.15 infrared photodiodes, grown on GaAs and GaAs-coated Si substrates by molecular beam epitaxy. Transmission electron microscopy images reveal a good structural quality. The electrical characteristics of the photodiodes were analyzed using current-voltage, current-temperature, and capacitance-voltage measurements. The spectral response and detector noise were measured at 77 K, resulting in a peak detectivity at 3.8 μm of 1.5×1011 cm Hz1/2/W for InAs0.85Sb0.15/GaAs and 5.0×1010 cm Hz1/2/W for InAs0.85Sb0.15/GaAs/Si.
Formation of stoichiometric SiGe oxide by electron cyclotron resonance plasma
Authors: Li P. W. , Liou H. K. , Yang E. S. , Iyer S. S. , Smith T. P. , Lu Z.
Published: July 2002

Electron cyclotron resonance (ECR) plasma oxidation of SiGe alloys was investigated at temperatures from room temperature to 500 °C. Both Si and Ge are shown to be fully oxidized, forming SiO2 and GeO2. Auger depth profiling reveals that there is no Ge-rich SiGe layer after oxidation. With increasing temperature up to 500 °C, the oxide is stoichiometric and it does not lose its GeO2 component. Oxidation has also been carried out at both positive and negative sample bias in order to identify the role of ions, electrons, and neutrals. From biasing experiments negative oxygen ions and atomic neutrals appear to be the major reaction species.
Direct observation of Si delta-doped GaAs by transmission electron microscopy
Authors: Liu D. G. , Fan J. C. , Lee C. P. , Tsai C. M. , Chang K. H. , Liou D. C. , Lee T. L. , Chen L. J.
Published: July 2002

Direct observation of the Si delta-doped layer in GaAs has been achieved by high resolution transmission electron microscopy. Samples with different Si doses, from half a monolayer to two monolayers, were studied. The observed spreading of the delta-doped layer showed that Si atoms are largely confined in five monolayers at most (in the highest dose case), indicating excellent confinements of dopants in GaAs. From the images, the Si atoms were uniformly distributed in the doped layer, no cluster formation was observed. For delta-doped GaAs grown at low temperature (480 °C), stacking faults originated from the doped layers were observed. These faults were thought to be caused by the large unrelaxed strain in the low-temperature grown GaAs.
Magnetically hard Sm2Fe17Nx prepared by nitriding melt-spun ribbons
Authors: Pinkerton F. E. , Fuerst C. D.
Published: July 2002

We have obtained magnetically hard Sm-Fe-N ribbons with a room-temperature intrinsic coercivity Hci=23 kOe by nitriding melt-spun Sm-Fe precursor ribbons. Best results are obtained by grinding the ribbons to a <25 μm powder, then heat treating the powder in vacuum for 1 h at 700 °C prior to nitriding in N2 gas at 450–480 °C. X-ray diffraction shows that the primary phase is rhombohedral Sm2Fe17Nx, or possibly the disordered hexagonal modification of this phase having the TbCu7 structure. Higher coercivities will be obtainable if the volume fraction of soft magnetic impurity phases, such as α-Fe, can be reduced by optimizing the composition and processing.
Visible electroluminescence from porous silicon np heterojunction diodes
Authors: Namavar Fereydoon , Maruska H. Paul , Kalkhoran Nader M.
Published: July 2002

We report the preparation of silicon-based visible light-emitting diodes, configured as heterojunctions between porous silicon (formed by electrochemical etching of p-type silicon wafers), and n-type indium tin oxide (ITO). The transparent ITO film allows light emission through the top surface of the device, under a forward electrical bias of several volts across the junction. Photogenerated currents are observed under reverse biases. A tentative model for this electroluminescence is presented, based on injection of minority carriers through a narrow interphase region into the porous silicon structure, where radiative recombination occurs.
Growing thin magnetic films with a mask: Distinguishing between magnetic and instrumental asymmetries
Authors: Allenspach R. , Bischof A. , Stampanoni M. , Kerkmann D. , Pescia D.
Published: July 2002

A simple technique is presented which allows a very small spin polarization to be distinguished from a vanishing one in spin polarized scanning electron microscopy (spin-SEM). Ferromagnetic thin films are evaporated through a mask onto a nonmagnetic substrate, thus producing a patterned area. Spin polarization and the element specificity of the secondary electron yield are combined to determine a local ‘‘asymmetry zero’’ where the spin polarization vanishes. With this technique it is possible to distinguish between a single domain thin film and a nonmagnetic one in spin-SEM. This is exemplified by monolayer Co/Cu (100) films.
High current and directional electron beams produced from gold photocathodes by ultrashort excimer laser pulses
Authors: Moustaizis S. D. , Tatarakis M. , Kalpouzos C. , Fotakis C.
Published: July 2002

The surface photoelectric effect induced by 500 fs excimer laser pulses in a gold metallic target has been studied. Unexpectedly high current densities of 4 kA/cm2, induced by laser intensities in the 3 GW/cm2 range have been measured. Intense photoelectron emission could also be observed at laser intensities up to 10 GW/cm2 without plasma formation. Furthermore, an electron angular distribution of 18°±2° was obtained for laser intensities in the range of 1–3 GW/cm2. These results are compared to those obtained in previous work for single-photon and multiphoton photoeffects by using longer laser pulses, and their potential exploitation for free-electron laser and accelerator applications is discussed.
Direct determination of the valence-band offsets at Ga0.47In0.53As/InP and InP/Ga0.47In0.53As heterostructures by ultraviolet photoemission spectroscopy
Authors: Landesman J. P. , Garcia J. C. , Massies J. , Maurel P. , Jezequel G. , Hirtz J. P. , Alnot P.
Published: July 2002

Ultraviolet photoemission spectroscopy has been used to study the valence-band offsets at GaInAs/InP and InP/GaInAs heterostructures grown by metalorganic molecular-beam epitaxy. High-resolution In-4d/Ga-3d core levels were used. The measured values are 440±50 meV for the ‘‘direct’’ (GaInAs grown on InP) interface and 260±50 meV for the ‘‘inverse’’ interface. This band-offset asymmetry is attributed to a difference in the chemical natures of the two interfaces, deduced from the detailed analysis of the core-level spectra.
Two-dimensional electron gas effects in the electromodulation spectra of a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation-doped quantum well structure
Authors: Yin Yichun , Qiang H. , Pollak Fred H. , Streit Dwight C. , Wojtowicz Michael
Published: July 2002

We have studied the electroreflectance and photoreflectance spectra from a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation-doped quantum well (MDQW) structure in the temperature range 79<T<304 K. The features from the InGaAs MDQW can be accounted for on the basis of a two-dimensional density of states and a Fermi level filling factor. A detailed line shape fit makes it possible to evaluate the Fermi energy, and hence the two-dimensional electron gas concentration (Ns), as well as other important parameters of the structure. Our value for Ns is in good agreement with a Hall measurement.
Co/Ni multilayers with perpendicular magnetic anisotropy: Kerr effect and thermomagnetic writing
Authors: den Broeder F. J. A. , van Kesteren H. W. , Hoving W. , Zeper W. B.
Published: July 2002

Perpendicular magnetic anisotropy has recently been predicted and confirmed for a Co1/Ni2 multilayer [G. H. O. Daalderop, P. J. Kelly, and F. J. A. den Broeder, Phys. Rev. Lett. 68, 682 (1992)]. This letter reports on some magneto-optical properties of this new multilayer. Its polar Kerr effect appeared to be considerably larger than for a Co1/Pd2 multilayer and comparable to a Co1/Pt2 multilayer. For certain vapor deposition conditions, the perpendicular magneto-optic hysteresis loop of a 120 Å Co1/Ni2 layer showed 100% remanence with a coercivity as high as 140 kA/m. Thermomagnetic writing was possible despite the high Curie temperature.
Cathodoluminescence imaging and spectroscopy of dislocations in Si and Si1−xGex alloys
Authors: Higgs V. , Lightowlers E. C. , Tajbakhsh S. , Wright P. J.
Published: July 2002

Dislocations in float-zone Si which has been plastically deformed and deliberately copper contaminated, and misfit dislocations in a relaxed Si1−xGex alloy layer grown on a Si substrate by molecular beam epitaxy, have been investigated by monochromatic and panchromatic cathodoluminescence imaging and by cathodoluminescence spectroscopy. The measurements show that the D3 and D4 luminescence features originate on the slip lines in plastically deformed Si and at the misfit dislocations in the Si1−xGex alloy layer whereas the D1 and D2 bands are dominant between the slip lines and the misfit dislocations.
Diamond deposition from CF4-H2 mixed gas by microwave plasma
Authors: Kadono M. , Inoue T. , Miyanaga A. , Yamazaki S.
Published: July 2002

We have deposited diamond films from CF4-H2 mixed gas by microwave plasma chemical vapor deposition method. The diamond films were characterized by scanning electron microscopy, x-ray diffraction, Raman spectrometry, and secondary ion mass spectrometry. (111) peak line of diamond crystal observed by x-ray diffraction and the peaks at 1333 cm−1 in the Raman spectroscopies of the deposited films showed that the films consisted of diamond. We observed that the quality of diamond films got better as the concentration (from 2.5% to 40%) of CF4 (tetrafluoromethane) got lower. It was observed from the optical emission spectra that CF, CF2, CF3, CH, and C2 fragments existed in the microwave plasma of CF4-H2 mixed gas. But it was observed from secondary ion mass spectroscopies that impurities (Si, F, and H) were present in the diamond films.
Femtosecond index nonlinearities in InGaAsP optical amplifiers
Authors: Hall K. L. , Darwish A. M. , Ippen E. P. , Koren U. , Raybon G.
Published: July 2002

We present the first femtosecond measurements of refractive index nonlinearities in diode laser amplifiers at 1.5 μm. Our results are obtained with a novel measurement technique, based on a time domain interferometer with heterodyne detection that allows the study of polarization anisotropy in the refractive index nonlinearities. We observe index changes due to carrier heating and stimulated transitions, as well as an instantaneous refractive index change similar to that observed in AlGaAs devices.
Interpretation of photoluminescence excitation spectroscopy of porous Si layers
Authors: Wang Lei , Wilson M. T. , Haegel N. M.
Published: July 2002

Photoluminescence excitation (PLE) measurements allow one to obtain direct information on the absorption processes in porous Si leading to the strong visible luminescence which has recently been reported. This technique does not need a free-standing porous Si sample, but the effect of layer thickness should be included in the interpretation of PLE data. In our PLE spectra, two separate absorption edges are observed and the initial one shifts to higher energies with storage time. The trends of these changes are consistent with the quantum wire model.
Two-photon pumped blue lasing in bulk ZnSe and ZnSSe
Authors: Yang X. H. , Hays J. M. , Shan W. , Song J. J. , Cantwell E.
Published: July 2002

We have studied laser action of ZnSe and ZnS0.05Se0.95 samples grown by seeded physical vapor phase transport (SPVT) technique in the near resonant two-photon absorption regime. The two-photon pumped lasing was observed using a tunable near-infrared nanosecond laser (830–890 nm). Blue lasing could be observed up to 200 K and the two-photon pumped lasing threshold was measured to be ∼7 MW/cm2 at 10 K. This work demonstrates the applicability of using near-infrared diode lasers as pumping sources to excite the ZnSe-based materials. By comparing the energy position of two-photon pumped lasing with that of the one-photon pumped lasing and examining the red shift of the energy position, we suggest that the free-exciton free-exciton scattering and resultant band filling are the dominant processes involved in the lasing action of ZnSe and ZnSSe alloy crystals at low temperature.
Diffusion of Fe in InP via the kick-out mechanism
Authors: Zimmermann H. , Gösele U. , Tan T. Y.
Published: July 2002

The diffusion of iron in indium phosphide is found to proceed via the kick-out diffusion mechanism. A Fe diffusion profile in InP available from the literature is simulated using the complete set of three partial differential equations for the kick-out mechanism. A value for the contribution of indium self-interstitials to the self-diffusion coefficient of InP is extracted and found to be much smaller than the known self-diffusion coefficient determined from indium tracer diffusion measurements. Possible reasons for the observed difference are discussed. Furthermore, an analogy of diffusion in InP to diffusion in GaAs is suggested.
Control and characterization of ordering in GaInP
Authors: Su L. C. , Pu S. T. , Stringfellow G. B. , Christen J. , Selber H. , Bimberg D.
Published: July 2002

Ga0.51In0.49P layers have been grown by organometallic vapor phase epitaxy on GaAs substrates with [110]-oriented grooves on the surface that have an important effect on the formation of Cu-Pt ordered structures during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, single domains of the (1̄11) and (11̄1) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow grooves produce large domains on each side of the groove containing small domains of the other variant. For deep grooves, only a single variant is formed on each side of the groove, but the domains are small. For substrates with deep grooves on a GaAs substrate misoriented by 9°, every groove contains large regions of highly ordered and completely disordered material separated by a few micrometers. This allows a direct determination of the effect of ordering on the band gap of the material using cathodoluminescence spectroscopy, allowing the first direct demonstration that ordering reduces the energy band gap of a III/V alloy.
Nanocrystalline Ge in SiO2 by annealing of GexSi1−xO2 in hydrogen
Authors: Liu W. S. , Chen J. S. , Nicolet M.-A. , Arbet-Engels V. , Wang K. L.
Published: July 2002

We have synthesized nanocrystalline Ge in vitreous SiO2 by annealing amorphous Ge0.38Si0.62O2 in hydrogen at 700 °C. The germanium dioxide in Ge0.38Si0.62O2 is thermodynamically unstable in the presence of hydrogen and thus precipitates out as elemental Ge. Elemental Si is not needed in this reduction process. Cross-sectional transmission electron microscopy reveals that the nucleation process is homogeneous, leading to a uniform distribution of small Ge crystallites imbedded in the remaining vitreous SiO2.
Roughness of the silicon (001)/SiO2 interface
Authors: Tang Mau-Tsu , Evans-Lutterodt K. W. , Higashi G. S. , Boone T.
Published: July 2002

We use synchrotron x-ray diffraction to characterize the roughness of the buried Si(001)/SiO2 interface, for three types of oxide, without modification of the interface. We show that the thermal oxide interface is 0.5±0.1 times as rough as the native oxide interface, suggesting that the oxide growth decreases the roughness slightly. We also measure the roughness of a chemically grown oxide interface.
Silicon interstitial absorption during thermal oxidation at 900 °C by extended defects formed via silicon implantation
Authors: Roth David J. , Huang Robert Y. S. , Plummer James D. , Dutton Robert W.
Published: July 2002

Extended defect damage created by high-dose silicon implants is used to study the interaction between extended defects and silicon interstitials introduced via thermal oxidation. A buried epitaxial layer of boron was used as an interstitial monitor, and a layer of extended defects was formed between the surface and the buried layer via silicon implants. Samples were oxidized at 900 °C in wet O2, and the amount of oxidation-enhanced diffusion was measured. For a silicon implant of 1×1013 cm−2, the enhancement was very similar in regions that had and had not been implanted. For an implant of 1×1015 cm−2, the enhancement was reduced in regions that had been implanted. The difference is explained by the absorption of the injected interstitials by a layer of extended defects.
Direct determination of the ambipolar diffusion length in strained InxGa1−xAs/InP quantum wells by cathodoluminescence
Authors: Lee Robert B. , Vahala Kerry J. , Zah Chung-En , Bhat Rajaram
Published: July 2002

The ambipolar diffusion length is measured in strained InxGa1−xAs/InP quantum wells for several mole fractions in the interval 0.3<x<0.8 by cathodoluminescence. The ambipolar diffusion length is found to have a significantly higher value in the lower indium mole fraction samples corresponding to tensile-strained wells. This longer diffusion length for the tensile samples is consistent with results of carrier lifetime experiments by M. C. Wang, K. Kash, C. E. Zah, R. Bhat, and S. L. Chuang [Appl. Phys. Lett. 62, 166 (1993)].
Ellipsometric study of boron nitride thin-film growth on Si(100)
Authors: Ren S. L. , Rao A. M. , Eklund P. C. , Doll G. L.
Published: July 2002

Variable angle spectroscopic ellipsometry over the photon energy (E) range 1.5≤E≤5.5 eV has been used to study the structure and optical properties of thin (<400 Å) laser-deposited boron nitride films grown on Si(100). The data are interpreted to indicate that initially the film grows next to the substrate in the cubic phase, followed by a reasonably sharp transition after 50–100 Å of film growth to an amorphous phase.
Study of the effects of aging on the relaxation luminance in atomic layer epitaxy ZnS:Mn alternating-current thin-film electroluminescent devices
Authors: Morton D. C. , Koh J. , Hogh C. P. , Khormaei R.
Published: July 2002

A study of the relaxation luminance peak and the electro-optical aging effects in atomic layer epitaxy (ALE) normally doped ZnS:Mn alternating-current thin-film electroluminescent (ACTFEL) devices is presented. The relaxation luminance occurs when the applied voltage goes to zero. The changes in the luminance versus time L(t), current versus time I(t), and characteristics of luminance versus voltage, as a function of aging are discussed in terms of a model which includes bulk traps, space charge, and shallow trap levels. This relaxation luminance peak observed in ALE devices provides a means of gaining insight into ACTFEL devices.
Electroreflectance-photoreflectance technique for studies of built-in electric field in layered materials
Authors: Sydor M. , Badakhshan Ali , Dale D. A. , Alavi K. , Pathak R.
Published: July 2002

We use a new modulation technique to investigate photoreflectance from layered electronic materials. The technique can be used to determine the direction of the electric field, and separate the effects of electric field modulation from extraneous modulations due to laser generated charge carriers.
Fabrication of GaAs quantum wires (∼10 nm) by metalorganic chemical vapor selective deposition growth
Authors: Tsukamoto S. , Nagamune Y. , Nishioka M. , Arakawa Y.
Published: July 2002

GaAs triangular-shaped quantum wires with the lateral width of ∼10 nm are fabricated by metalorganic chemical vapor selective deposition growth technique. The lateral dimension is determined by both photoluminescence (PL) measurement and a high-resolution scanning electron micrograph observation. A systematic change in the size of the quantum wire exhibits consistent blue shifts of the PL peak keeping high intensities, which demonstrates enhanced two-dimensional quantum confinement with the material of high quality.
Optical investigation of confinement and strain effects in CdTe/(CdMg)Te quantum wells
Authors: Kuhn-Heinrich B. , Ossau W. , Heinke H. , Fischer F. , Litz T. , Waag A. , Landwehr G.
Published: July 2002

We present optical investigations on CdTe/(CdMg)Te single quantum wells (QWs) and demonstrate the high structural quality of the pseudomorphic grown QWs structure which shows high photoluminescence efficiency up to room temperature. Due to the large band-gap difference between CdTe and Cd0.51Mg0.49Te of more than 0.8 eV remarkable strong confinement effects are observable. A strong enhancement of the exciton binding energies is found by decreasing well width. In the 50-Å-wide QW the binding energy is more than two times larger compared with that of bulk CdTe. In addition, a strong functional dependence of the localization energy of donor bound excitons on the well thickness is found. A valence-band offset of 30% in the strain-free limit is determined from the energy difference between heavy- and light-hole excitons which is consistent with the strong blue shift of exciton energies by decreasing well widths and the observed effective electron-hole confinement.
Optical characterization of porous silicon by synchrotron radiation reflectance spectra analyses
Authors: Koshida Nobuyoshi , Koyama Hideki , Suda Yoshiyuki , Yamamoto Yuko , Araki Minoru , Saito Tadashi , Sato Katsuaki , Sata Noriko , Shin Shik
Published: July 2002

The electronic structure of porous Si(PS) has been characterized by optical reflectance spectra analyses. The reflectance spectra of PS were measured in the photon energy range of 2–27 eV using a synchrotron radiation source. The reflectance at the low energy region was calibrated by the corresponding absolute value which was separately determined from spectroscopic ellipsometry. The spectral response of optical constants were calculated by the Kramers–Kronig analysis. Our results indicate that PS retains some of the characteristic optical features of crystalline Si, and that a blue shift in the absorption edge occurs in PS.
Ozone-induced rapid low temperature oxidation of silicon
Authors: Kazor A. , Boyd Ian W.
Published: July 2002

We report the use of ozone enriched oxygen to induce rapid oxidation of silicon at temperatures up to 550 °C. The growth rates induced under these conditions were well over an order of magnitude larger than those achieved using pure dry oxygen. At 550 °C films up to 260 Å in thickness were grown 4 h producing a growth rate comparable to that for conventional oxidation at 850 °C.
Magnetic spectromicroscopy from Fe(100)
Authors: Schneider C. M. , Holldack K. , Kinzler M. , Grunze M. , Oepen H. P. , Schäfers F. , Petersen H. , Meinel K. , Kirschner J.
Published: July 2002

Magnetic domains on an Fe(100) surface have been imaged by means of energy-resolved photoemission microscopy. We excited the photoelectrons with circularly polarized synchrotron radiation in the soft x-ray region, and employed the effect of magnetic circular dichroism in the emitted photoelectrons in order to obtain contrast between differently oriented magnetic domains. This new approach offers a surface sensitive way to combine chemical and magnetic information on a microscopic scale.
Pulsed laser deposition of thick YBa2Cu3O7−δ films with J
c≥1 MA/cm2
Authors: Foltyn S. R. , Tiwari P. , Dye R. C. , Le M. Q. , Wu X. D.
Published: July 2002

Using pulsed laser deposition, YBa2Cu3O7−δ (YBCO) films ranging in thickness from 0.065 to 6.4 μm have been deposited on yttria-stabilized zirconia substrates with an intermediate layer of CeO2. The thinnest films have critical current densities of over 5 MA/cm2 at 75 K with zero applied field; as film thickness is increased, Jc decreases asymptotically to 1 MA/cm2. X-ray analysis of a 2.2-μm-thick film shows that the YBCO is predominantly c-axis oriented and textured in-plane, while a Rutherford backscattering spectrometry minimum channeling yield of ≊75% indicates that the film contains disordered material at this thickness.
Reversible electron-beam writing on a submicron scale in a superionic amorphous film
Authors: Oldale J. M. , Elliott S. R.
Published: July 2002

The direct writing of patterns in amorphous silver chalcogenide materials by electron-beam exposure is reported. At sufficiently low beam-current densities, the written patterns comprise regions depleted of silver; complete hole drilling of films does not occur. The phenomenon is postulated to arise from a combination of thermal gradient and electronic excitation effects.
Cathodoluminescence of single quantum wires and vertical quantum wells grown on a submicron grating
Authors: Gustafsson A. , Samuelson L. , Malm J.-O. , Vermeire G. , Demeester P.
Published: July 2002

We present cathodoluminescence (CL) investigations of a corrugated GaAs/AlGaAs single quantum well (QW) structure grown on a submicron grating. The CL spectra have four distinct emission peaks. Using plan-view and cross-sectional CL imaging together with cross-sectional transmission electron microscope imaging, we have assigned the four peaks: They originate in the nominal QW, a quantum wire (QWR), a vertical quantum well (VQW), and the barrier, respectively. We have CL-imaged and -characterized single QWRs and VQWs.
Stress-controlled silicon nitride film with high optical transmittance prepared by an ultrahigh-vacuum electron cyclotron resonance plasma chemical-vapor deposition system
Authors: Ahn Jinho , Suzuki Katsumi
Published: July 2002

An ultrahigh-vaccuum electron cyclotron resonance plasma chemical-vapor deposition system with a substrate heating component has been applied to deposit silicon nitride film. Low background pressure (∼5×10−9 Torr) and efficient plasma excitation at a low deposition pressure (<10−3 Torr) result in a low oxygen impurity content in the silicon nitride film. Process flexibility of this system, i.e., control of the SiH4 to NH3 flow ratio, deposition pressure, and substrate temperature, allows the deposition of near-stoichiometry silicon nitride film with a high optical transmittance as well as a suppressed amount of hydrogen impurity and a low film stress.
Doping of zinc-selenide-telluride
Authors: Faschinger W. , Ferreira S. , Sitter H.
Published: July 2002

We investigate the doping behavior of ZnSe/ZnTe short period superlattices. p-type doping is achieved with a dc nitrogen plasma source, n-type doping with chlorine from a ZnCl2 Knudsen source. Even a small Te content has a strong positive effect on p doping: Doping levels in the upper 1019 cm−3 range are achieved, and ohmic contacts can be obtained even for low carrier concentrations. The data are in excellent agreement with a theory based on the amphoteric native defect model. The opposite is valid for n doping: At Te concentrations above 20% electron concentrations are below 1016 cm−3. As a possible way to get both good n- and p-type doping at the same lattice constant we propose the use of the quaternary compound Zn(1−y)Mg(y)Se(1−x)Te(x).
Electron collision cross sections of boron trichloride
Authors: Nagpal Rajesh , Garscadden Alan
Published: July 2002

Three vibrational and two dissociation cross sections of BCl3 in the range 0–30 eV have been unfolded from recent electron drift velocity data in BCl3/Ar and BCl3/He mixtures.
Structures and optical properties of organic/inorganic superlattices
Authors: Tokito Shizuo , Sakata Jiro , Taga Yasunori
Published: July 2002

A new class of superlattice materials consisting of alternating layers of organic and inorganic materials has been prepared from 8-hydroxyquinoline aluminum (Alq) and MgF2 by vacuum deposition. The Alq layer thickness in the superlattices was varied from 10 to 50 Å. Small-angle x-ray diffraction measurements indicate that the superlattices have very uniform layered structure throughout the entire stack, and the interfacial roughness is much smaller than 10 Å. From the optical absorption and photoluminescence measurements, it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness. The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.
Highly efficient TE/TM mode switching of GaAsP/AlGaAs strained quantum-well laser diodes
Authors: Tanaka Hidenao , Shimada Jun-ichi , Suzuki Yoshio
Published: July 2002

TE/TM mode switching is demonstrated in GaAsP/AlGaAs tensilely strained quantum-well laser diodes with two electrodes. The laser diode oscillated in the TM mode when current was injected into both electrodes, and oscillated in the TE mode when current was injected only into the longer electrode. The mode was switched by controlling the injection current of the two electrodes. The modulation efficiency of the TM-mode output selected by a polarizer was very high (15 W/A) in this mode switching.
Interaction of amorphous fluoropolymer with metal
Authors: Wu P. K. , Yang G.-R. , Ma X. F. , Lu T.-M.
Published: July 2002

The bonding structure of an amorphous fluoropolymer, AF 1600, with Al, Ag, Au, and Cu were examined using x-ray photoelectron spectroscopy. 100 Å thick films of AF 1600 were deposited on various metal films. AlF3 was found at the AF 1600/Al interface. F detached from the −CF3 functional group of the AF 1600, diffused into the Al/Al2O3 matrix and formed AlF3. The diffusion depth of F is estimated to be ≳150 Å. An Al film was evaporated onto an AF 1600 film. The Al film was then mechanically peeled off and the remaining polymer surface examined. AlF3 was again found. For the spin-on AF 1600 film on Ag, Au, and Cu, no chemical reaction between the metal and the polymer were found.
Annealing induced refractive index and absorption changes of low-temperature grown GaAs
Authors: Dankowski S. U. , Kiesel P. , Knüpfer B. , Kneissl M. , Döhler G. H. , Keil U. D. , Dykaar D. R. , Kopf R. F.
Published: July 2002

Large changes of the refractive index (Δn≊0.25) and absorption coefficient (Δα≊16 000 cm −1) of GaAs grown by molecular beam epitaxy (MBE) at low substrate temperature (LT-GaAs) induced by annealing are reported. The refractive index difference between the LT-GaAs layer and the GaAs substrate are determined from both, the amplitude of the Fabry–Pérot oscillations and the shift of their extrema towards shorter wavelengths yielding nearly the same results. With increasing anneal temperature the excess refractive index as well as the strong absorption at photon energies below the GaAs band gap (determined by transmission measurements) disappear around 700  °C.
Absorption spectroscopy studies of strained InGaAs/GaAs single-quantum wells
Authors: Shen W. Z. , Tang W. G. , Shen S. C. , Wang S. M. , Andersson T.
Published: July 2002

Strained In0.20Ga0.80As/GaAs single-quantum well (SQW) structures with the GaAs capping layer thickness ranging from 5 to 500 nm have been studied directly by absorption spectroscopy. The absorption peaks are shifted to lower energy while the GaAs capping layer thickness decreases due to the strain relaxation in InGaAs/GaAs SQW structures induced by the GaAs capping layer. The best fit gives the conduction-band offset ratio Qc=0.70±0.05. The pronounced exciton peaks are observed in the absorption spectra at room temperature. The strength of the exciton–phonon coupling is determined from linewidth analysis and is found to be much larger than that of strained InGaAs/GaAs MQW structures.
Study on photorefractive effect in KTiOPO4 waveguides
Authors: Shi L. P. , Karthe W. , Rasch A.
Published: July 2002

Photorefractive effects (PRE) in KTiOPO4 channel waveguides were studied at the wavelengths 0.633 and 0.83 μm. The 4 μm-wide waveguides were fabricated by Rb ion exchange on the z-face of the crystals and along the y axis. At 0.633 μm, crystals from one source showed conventional photorefractive response with a saturation index change Δn of 2×10−5, but samples from a different source were not photorefractive. Neither type of crystals displayed photorefractive behavior in response to 0.83 μm light at guided-wave power flow of 2.4×107 W/m2. Differences in bicrystal structure are suggested as a possible cause of differing PRE between the two samples. On crystals from the first source, the relaxation time of generating PRE is related to power flow of the irradiating beam. The relaxation time of PRE disappearance after stop irradiation is also related to power flow of the irradiating light.
Electronic band structure of AlGaInP grown by solid-source molecular-beam epitaxy
Authors: Mowbray D. J. , Kowalski O. P. , Hopkinson M. , Skolnick M. S. , David J. P. R.
Published: July 2002

The compositional dependence of the electronic band structure of (AlxGa1−x)0.52In0.48P lattice matched to GaAs is reported. Epitaxial layers, grown by solid-source molecular-beam epitaxy, with excellent structural and optical quality are obtained over the whole compositional range. Optical spectroscopic techniques are used to study the electronic band structure as a function of composition. The low-temperature, direct excitonic band gap is found to be given by Eg(x)=1.979+0.704x eV and the lowest band gap becomes indirect for xc=0.50±0.02. The low-temperature excitonic direct band gap of Al0.52In0.48P is measured to be 2.680 eV.
Operation of bicrystal junction high-T
c direct current-SQUID in a portable microcooler
Authors: Khare Neeraj , Chaudhari P.
Published: July 2002

A bicrystal junction high-Tc direct current-SQUID has been operated successfully at 77 K in a portable battery operated microcooler. The microcooler products magnetic signals which are harmonics of 43 Hz and a band of frequencies from 400 Hz to 4 kHz. It is possible to operate the SQUID in a flux-locked-loop mode using a 10 kHz modulation signal. The performance of the SQUID in the microcooler, in the frequency range 1–10 Hz, is almost identical to that in a Dewar.
High-spatial-resolution photoluminescence measurements on AlxGa1−xAs grown on a nonplanar substrate by metalorganic vapor phase epitaxy
Authors: Olsthoorn S. M. , Bongers M. M. G. , Giling L. J.
Published: July 2002

High-spatial-resolution photoluminescence measurements are reported of AlxGa1−xAs grown on nonplanar substrates by metalorganic vapor phase epitaxy. The aluminum fractions are determined of the various facets of three grooves with varying widths. The (111)A facets on the side walls of the grooves have an aluminum fraction 6.3% higher than that of the unpatterned area. The narrowest groove is exactly V-shaped showing only these (111)A facets. Higher index facets in the corners of the bottom of the two broader grooves show a 27.8% reduction in aluminum fraction as compared with the unpatterned area. The aluminum fractions of the (100) facets at the bottom of the grooves depend strongly on the groove widths.
Josephson fluxonic diode
Authors: Raissi F. , Nordman J. E.
Published: July 2002

A nonuniform magnetic field has been applied to a long Josephson junction to create two separated vortex and antivortex regions. Such a configuration is the Josephson version of the so-called fluxonic diode, an electrical dual to the semiconductor p-n junction diode. Volt-ampere relations of a junction subjected to this magnetic field are compared with those obtained using a unidirectional magnetic field. The study, supported by simulation, shows a number of unique characteristics including rectification and fluxon injection across the junction. Both are necessary phenomena for realization of a bipolar transistor dual.
Fabrication of highly concentrated Er3+ doped aluminosilicate films via sol-gel processing
Authors: Ryu Choon Kun , Choi Hyungsoo , Kim Kyekyoon
Published: July 2002

Optically active highly concentrated Er3+–Al3+ codoped silica thin films were fabricated on fused silica substrates by sol-gel method. The synthesis of the Er3+–Al3+ double alkoxide was intended to prevent the optically harmful Er clustering by the selective coordination of Al3+ around Er3+ ions. The molar Er ion concentration was varied from 3811 to 23719 ppm. Photoluminescence (PL) measurements indicated that Er ions were optically active in all films of different Er concentrations. A broadband peak was observed at 1531 nm with the full width at half-maximum (FWHM) of 42 nm, which corresponds to the 4I13/2→4I15/2 transition. The shape, peak position, and FWHM of the PL signals from the sol-gel derived Er3+ doped silica were quite comparable to those prepared by other methods. The PL peak showed maximum intensity at an Er concentration of 8535 ppm. This implies the concentration quenching at higher Er concentrations.
Four-frame holographic probing system for plasma density measurement (invited)
Authors: Busch Garland E. , Shepard C. L. , Siebert L. D. , Tarvin J. A.
Published: July 2002

An important upgrade of UV holographic interferometry is now in use. Many hundreds of laser fusion-type target plasmas have been probed at KMS Fusion, Inc. using the holographic technique. The data obtained with this diagnostic include high-resolution images and plasma electron density distributions at various probe times. The diagnostic system now produces a sequence of four interferograms of an evolving plasma. The times of the 20-ps pulses in the sequence are fully adjustable and known within 10 ps. The experiments to which this diagnostic has been adapted will be described along with details of problems and their solutions. Selected sets of recent interferograms of plasmas produced by irradiation of thin foils will be presented along with their inversions.
Semiautomated method for the determination of density profiles from Mach–Zehnder interferograms
Authors: Chen Hai-Tao , Christiansen Walter H.
Published: July 2002

The determination of a density field by means of digital imaging of a Mach–Zehnder interferogram and processing by a microcomputer is described. The apparatus used in this study are an optical single-bit digitizer, a microcomputer, and a dot matrix printer. Photographs of the interferograms are semiautomatically digitized by the apparatus. The fringe count and the spatial locations of the fringes are calculated using basic programs, and the density field is plotted as an output.
Automatic recording of direct current singularity amplitudes in Josephson junctions
Authors: Costabile G. , Gambardella U. , Pagano S.
Published: July 2002

We have designed and tested an electronic circuit to record the amplitude of any current singularity in the current-voltage characteristic of a Josephson tunnel junction. The detection of the peak current occurs only when the junction voltage is within a range that can be centered and narrowed conveniently. We describe the circuit in detail and illustrate its operation in the recording of some typical dc singularities.
Retarding-field differential-output energy prefilter for high-performance secondary ion mass spectrometry
Authors: Thompson Patrick M. , Taylor James W. , Negri Ronald E.
Published: July 2002

A retarding-field differential-output energy prefilter has been optically matched to a quadrupole mass spectrometer to produce a high-performance secondary ion quadrupole mass spectrometer. The sample area was designed to be field free to allow for sample charge compensation and to prevent secondary ion trajectories from being affected by electric fields. Design considerations for optically matching the energy prefilter to the quadrupole mass filter (QMF) are discussed. The overall transmission of the instrument was 1.8×10−4 at a mass resolution of 100 M/ΔM (1–100 amu range) for copper and 1.7×10−5 at a mass resolution of 400 M/ΔM (10–250 amu range) for tungsten.
High-temperature Mössbauer-effect measurements with a precision furnace
Authors: Kolk B. , Bleloch A. , Hall D. B. , Zheng Y. , Patton-Hall K. E.
Published: July 2002

A furnace system is presented for Mössbauer-effect spectroscopy at temperatures up to 1200 K with a temperature stability better than 0.03 K. This system allows the study of samples at high temperatures in an external magnetic field of a few kG with a homogeneity of better than 1%. Our measurements show that a few degrees above the Curie temperature TC, such an external field induces a considerable hyperfine field at 57Fe nuclei in iron. In addition, the magnetic hyperfine field and the isomer shift of 57Fe in metallic iron are measured over a temperature range of 300 to 1100 K. It is shown that a relatively small nonlinear behavior of the Mössbauer velocity drive system may result in a pseudodiscontinuity in the isomer shift δ near the Curie temperature, explaining the anomalous behavior observed for δ of iron and of some iron alloys in this region.
Polarization interferometer for angular measurements
Authors: Niay P. , Bernage P. , Ledee J. J.
Published: July 2002

A new interferometric system measuring change of birefringence through anisotropic crystals induced by change in the direction of an expanded laser beam has been developed in order to measure small angular displacements of an external mirror. In a low-cost version of the apparatus, pitch and yaw measurements were simultaneously performed with 0.1-arc s sensitivity, 20-Hz bandwidth, and a measuring range ±600 arc s at a working distance of 1 m. The major advantages of this interferometer are that it is fast, easy to use, and convenient to drive a servomechanism, locking the X-Y angular position of a target moving in the Z direction.
Adapting an electrostatic voltmeter for ultrahigh-vacuum operation
Authors: Loubriel G. M.
Published: July 2002

A modification of a commercial electrostatic voltmeter which operates on the Kelvin–Zisman principle is described which permits operation inside a vacuum system at pressures below 5.0×10−8 Torr. This allows for in-vacuum electrostatic measurements of voltages of up to 5 kV.
Static seal for high gas pressures
Authors: Verbrugge R. , Schouten J. A. , Trappeniers N. J.
Published: July 2002

A new design of closure is described which is capable of sealing pressure vessels up to 15 kbar. The sealing ring is made of Be–Cu and has a triangular cross section with an angle of 90° at its largest diameter. It is easy to construct and suitable for gases as well as liquids.
Rotary probe traversing mechanism
Authors: Hokenson Gustave J.
Published: July 2002

A simple mechanical device is presented which allows a probe to scan a plane in space without translating the probe support. The mechanism relies on the rotation of two shafts, one of which rotates the probe through space and the other controls the probe offset from the axis of rotation. The characteristic width of the area swept out is four times the characteristic width of the device. A simple ratcheting gear allows adjacent planes to be scanned for the purpose of obtaining gradients. Computerized control of the shafts rotations also allows noncircular domains to be scanned.
High-performance electrode profile generation method
Authors: Elizondo Juan M. , Benze Jay W. , Moeny William M. , Small James G.
Published: July 2002

High-performance electrodes for gas discharge devices such as lasers often require surfaces of compound curvature which are both difficult to describe and difficult to manufacture. This paper describes a simple microcomputer method for generating sophisticated electrode shapes on a numerically controlled milling machine. As an example, a Rogowski cross-section electrode with end profiling was fabricated using an Apple IIe computer with an RS-232 serial interface to the milling machine.