bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging of photogenerated acid in a chemically amplified photoresist
Authors: Bukofsky S. J. , Feke G. D. , Wu Q. , Grober R. D. , Dentinger P. M. , Taylor J. W.
Published: July 2002

Chemically amplified photoresists are widely used throughout the semiconductor industry due to the need for high throughput in the lithography process. Knowledge of the location of acid molecules in chemically amplified resists is of paramount importance for the process control of the image formation of almost all the lithographic techniques used in the semiconductor industry today. We have demonstrated a technique based on pH-dependent fluorescence which can measure directly the spatial distribution of the photoacid in photoresist films without the need of any other subsequent process after exposure. By adding a small amount of fluorescent material to the resist, a latent image can be formed when photogenerated acid molecules quench the fluorescence in exposed areas. We demonstrate images formed after exposure of SAL605 resist films to x-ray radiation, with no post-exposure bake, and show that the optical contrast is a function of dose. We also show that the same technique can be utilized for rapid evaluation of photoacid generator efficiency.
Analysis of terrace size fluctuations of B-induced stripe structures on the Si (001) surface
Authors: Fujita Ken , Ichikawa Masakazu
Published: July 2002

Terrace size fluctuations of B-induced stripe structures on Si (001) were analyzed by using scanning tunneling microscopy. The terrace size was varied independently of the substrate temperature by supplying diborane (B2H6). Histograms of the terrace size were fitted by Gaussian distributions and the standard deviation was proportional to the square root of the mean terrace size. These results indicate that the B-induced stripe structures arise from the competition between the stress anisotropy and step energy on Si (001), and mean that the surface anisotropy is almost independent of the B concentration.
X-ray diffraction analysis of SiGe/Si heterostructures on sapphire substrates
Authors: Mooney P. M. , Ott J. A. , Chu J. O. , Jordan-Sweet J. L.
Published: July 2002

Si/Si 1−x Ge x heterostructures on improved silicon-on-sapphire substrates were grown epitaxially by ultrahigh vacuum chemical vapor deposition for application as p-channel field effect transistors. High-resolution triple-axis x-ray diffraction was used to analyze these structures quantitatively and to evaluate their thermal stability. Outdiffusion of Ge from the strained Si1−xGex quantum well was observed after annealing at 850 °C. The amount of outdiffusion was comparable to that observed in Si1−xGex structures on bulk Si wafers.
A highly transmittive semiconductor base for ballistic electron emission microscopy
Authors: Heer R. , Smoliner J. , Strasser G. , Gornik E.
Published: July 2002

Ballistic electron emission spectroscopy and ballistic electron emission microscopy offer the unique possibility of probing subsurface quantum states. To improve the spectroscopic sensitivity, it is important to increase the amount of electrons, which are able to penetrate into the sample. In this work, we show that the transmission coefficient and the attenuation length of the base layer can be enhanced by more than one order of magnitude, if the commonly used thin metal film is replaced by a molecular beam epitaxy grown InAs layer. At low temperatures (T=100 K), a passivated InAs layer yields an attenuation length in the order of 70–90 nm instead of 5 nm obtained on Au films.
Surface phases of GaAs and InAs (001) found in the metalorganic vapor-phase epitaxy environment
Authors: Li L. , Han B.-K. , Hicks R. F.
Published: July 2002

We have characterized the (2×4) and (4×2) reconstructions of GaAs and InAs (001) that are present in a metalorganic vapor-phase epitaxy (MOVPE) reactor. Scanning tunneling micrographs show that these surfaces are terminated with arsenic and gallium (or indium) dimers. The (2×4) dimer row exhibits a mottled appearance, which is ascribed to the adsorption of alkyl groups on some of the sites. On the (4×2), <10% of the surface is covered with small (2×4) islands. These results show that, in the MOVPE environment, the GaAs and InAs surface structures are nearly the same as those found in ultrahigh vacuum molecular beam epitaxy.
A field emitter array with an amorphous silicon thin-film transistor on glass
Authors: Gamo H. , Kanemaru S. , Itoh J.
Published: July 2002

We have designed and fabricated a field emitter array (FEA) with an amorphous silicon thin-film transistor (a-Si TFT) monolithically, as an emission control device, on a glass substrate. The TFT was fabricated on the glass substrate at a low temperature, less than 350 °C. The measured emission characteristics showed that the FEA had saturated emission currents with the aid of the a-Si TFT; thus the a-Si TFT is expected to stabilize the emission current. The emission current of the FEA was controlled in the range of 0–0.12 μA with the TFT-gate voltage from 0 to 15 V.
Unusually low surface recombination and long bulk lifetime in n-CdTe single crystals
Authors: Cohen R. , Lyahovitskaya V. , Poles E. , Liu A. , Rosenwaks Y.
Published: July 2002

We present a study of time-resolved photoluminescence (TRPL) measurements of n-type CdTe single crystals doped by a novel procedure. The measurements show that the surface recombination velocity of low doped n-type (n0=1.5×1016 cm−3) samples was below 200 cm/s and the nonradiative bulk recombination time was around 180 ns. By conducting the TRPL measurements under different carrier injection levels, it was found that radiative bulk recombination was the dominant mechanism in the low doped crystals. This enabled us to obtain the bulk radiative recombination rate constant, B, which was found to be 3±0.5×10−9 cm3 s−1.
Fabrication and properties of metal/ferroelectrics/semiconductor diodes on 4H–SiC
Authors: Mou D. , Petersson C. S. , Linnros J. , Rao K. V.
Published: July 2002

Polycrystalline PbTiO3 (PTO) films with pure perovskite phase were deposited directly on 4H n-type SiC substrates by pulsed laser ablation. By subsequent gold metallization, metal/ferroelectrics/semiconductor (MFS) diodes were fabricated. At room temperature the leakage current exhibits ohmic behavior at low voltages (<3 V), but at higher voltages (⩾6 V), it is Schottky emission dominated. Both the dielectric constant and the resistivity of the PTO layers are frequency dependent, decreasing monotonically with the increasing frequency. The capacitance–voltage (C–V) curves of the diodes demonstrate the typical hysteresis loop of a MFS diode structure, and carrier injection and memory effects are observed in the C–V measurements. The investigated MFS diode structure has tentative applications as a gate structure in a SiC field effect transistor or a nonvolatile memory cell on a SiC substrate.
Hydrogen effusion from epitaxial ZnSe layers grown by metalorganic vapor phase epitaxy
Authors: Hahn B. , Preis H. , Blümel S. , Gebhardt W.
Published: July 2002

The thermal outdiffusion of hydrogen from undoped ZnSe layers grown by metalorganic vapor phase epitaxy has been investigated. The samples were grown using dimethyl-zinc-triethylamine, di-tert.-butylselenide as precursors with hydrogen and nitrogen as carriergas. The typical atomic hydrogen concentrations of the samples is nH=1018 cm−3, which originates from pyrolysis products of the organometallic precursors. The incorporation from the carrier gas is negligible. Control samples grown by molecular beam epitaxy in the presence of atomic and molecular hydrogen in the growth chamber showed no hydrogen incorporation. The outdiffusion process was investigated using transient effusion experiments. The experiments are explained by diffusion controlled effusion with a diffusion coefficient of D(T)=1.4×10−11 exp[−0.33(±0.03) eV/(kBT)]cm2/s.
Two-dimensionally conjugated molecules: The importance of low molecular symmetry for large third-order nonlinear optical effects
Authors: Gubler U. , Spreiter R. , Bosshard Ch. , Günter P. , Tykwinski R. R. , Diederich F.
Published: July 2002

Low molecular symmetry with regard to the conjugation path of the delocalized electrons was found to be a good guideline towards linearly conjugated molecules with large second-order hyperpolarizabilities γ. We show that this guideline is also valid for two-dimensionally conjugated systems. We experimentally demonstrate this by third-harmonic generation measurements of two-dimensionally conjugated organic molecules, and show that the observed effects can be explained by the symmetry of the electronic wave functions. In addition, the positive impact of the substitution of phenyl rings by thienyl rings on γ is discussed.
Fermi-edge singularity observed in a modulation-doped AlGaN/GaN heterostructure
Authors: Zhang Jian-Ping , Sun Dian-Zhao , Wang Xiao-Liang , Kong Mei-Ying , Zeng Yi-Ping , Li Jin-Min , Lin Lan-Ying
Published: July 2002

In this letter, we report on the observation of Fermi-edge singularity in a modulation-doped AlGaN/GaN heterostructure grown on a c-face sapphire substrate by NH3 source molecular beam epitaxy. The two-dimensional electron gas (2DEG) characteristic of the structure is manifested by variable temperature Hall effect measurements down to 7 K. Low-temperature photoluminescence (PL) spectra show a broad emission band originating from the recombination of the 2DEG and localized holes. The enhancement in PL intensity in the high-energy side approaching Fermi level was observed at temperatures below 20 K. At higher temperatures, the enhancement disappears because of the thermal broadening of the Fermi edge.
Faster grating buildup characteristics in low silanol-containing polysilane-based photorefractive polymer
Authors: Nishida Fumito , Kushibiki Nobuo , Tomita Yasuo
Published: July 2002

The effect of silanol content on the grating buildup dynamics was examined by preparing two different lots of polymethylphenylsilane (PMPS). While the high silanol-containing PMPS showed very sluggish grating formation time, the lower silanol-containing PMPS exhibited very rapid grating formation in a diffraction efficiency measurement. The diffraction efficiency, on the other hand, was found to be unaffected. The results suggest that the silanol is acting as hole trap and a reduction of its content is a key to improving the response characteristics of polysilane-based photoconducting electro-optic polymer composite for photorefractive applications.
Resistive and structural properties of La1.85Sr0.15Cu1−yZnyO4 films
Authors: Cieplak Marta Z. , Karpińska K. , Domagała J. , Dynowska E. , Berkowski M. , Malinowski A. , Guha S. , Croft M. , Lindenfeld P.
Published: July 2002

Single-phase c-axis aligned La1.85Sr0.15Cu1−yZnyO4 films were grown by pulsed laser deposition with Zn contents up to a value of y of 0.12. The film properties indicate the existence of defects, in addition to the Zn impurities, that are unintentionally introduced during the film growth. These defects are probably oxygen vacancies, and have a distinctly different effect on Tc from the Zn. The separation of the two effects resolves earlier ambiguities in the observed rates of Tc depression.
Electron paramagnetic resonance evidence for reversible transformation of thermal donor into shallow donor-type center in hydrogen-implanted silicon
Authors: Rakvin B. , Pivac B. , Tonini R. , Corni F. , Ottaviani G.
Published: July 2002

Electron paramagnetic resonance spectrum of the proton-related thermal donor (TD) assigned as NL8 paramagnetic center has been detected at 110 K after heat treatment of the hydrogen-implanted Czochralski-Si at 773 K. The effect of temperature on reversible transformations of the anisotropic spectrum of NL8 center into the isotropic singlet line was studied in the temperature region from 110 to 240 K. The analysis of the singlet provides an evidence that this signal originates from the proton-related shallow donor type at g=1.9987. The changes in the linewidth have been used to evaluate the parameters [1/τ=0.66×1012 exp(−ΔE/kT); ΔE=169 meV] for thermally activated electron emission to the conduction band from the second donor state of the NL8 center. These results represent direct experimental evidence of reversible transformation of the TD+ charged center into the shallow donor-type center.
Direct fabrication of polyimide waveguide grating by synchrotron radiation
Authors: Kobayashi Junya , Maruno Tohru , Ishii Tetsuyoshi , Tamamura Toshiaki , Horiuchi Toshiyuki
Published: July 2002

Synchrotron radiation induces a change in the refractive index of a fluorinated polyimide by an order of 10−2, which is about ten times larger than the change it induces in silica glass irradiated by ultraviolet light, presumably due to fluorine detachment and subsequent volume compaction. We have fabricated a 0.51-μm-period grating structure in an embedded waveguide through a 15-μm-thick overcladding by using an x-ray mask with a spatially modulated pattern. The grating is fabricated at a dose of 160 A s and shows a reflectivity of 60% and a full width at half maximum as narrow as 0.25 nm at around a wavelength of 1.55 μm.
Investigation of broadband p-type quantum-well infrared photodetectors
Authors: Chu J. , Li Sheng S. , Singh A.
Published: July 2002

Typical quantum-well infrared photodetectors (QWIPs) exhibit rather narrow spectral bandwidths of 1–2 μm. For certain applications, such as spectroscopy, sensing of a broad range of infrared photons is necessary. In this letter, we report on the design of two p-type broadband (BB) QWIPs for detection in the 7–14 μm long-wavelength infrared band. Two different QWIP structures were designed: QWIP-A with three wells of different InxGa1−xAs(x=0.2,0.25,0.3) compositions and QWIP-B with three wells of In0.25Ga0.75As of different thicknesses (4.5, 5.5, and 6.2 nm) and an undoped GaAs barrier (40 nm thick) to form a unit cell, which are then repeated 20 times to create the BB-QWIPs. The spectral response for QWIP-A covers the wavelengths from the 7 to 11 μm range, while QWIP-B has a broader spectral response bandwidth from 7 to 14 μm. A maximum responsivity of 25 mA/W was obtained for QWIP-B at Vb=1.1 V, λp=10.2 μm, and T=40 K with a spectral bandwidth of Δλ/λ=63%, a cut-on wavelength at 6.2 μm, and a cut-off wavelength around 14 μm.
Surface defect scattering of surface plasmon polaritons: Mirrors and light emitters
Authors: Sánchez-Gil J. A.
Published: July 2002

We study the near-field and the angular distribution of radiation resulting from the scattering of surface plasmon polaritons from a surface defect by means of numerical calculations based on the use of the impedance boundary condition. Maximum reflection (plasmon mirrors) is found for half widths on the order of the inverse of the surface plasmon wavevector, either protuberances or indentations, as predicted by a perturbation-theoretic argument. Maximum radiation (light emitters) occurs for wider protuberances, with coupling efficiencies beyond 80%.
Visible light emission from dyes excited by simultaneous absorption of two different frequency beams of light
Authors: Rapaport Alexandra , Ayrault Karine , St. Matthew-Daniel Eyitope , Bass Michael
Published: July 2002

Emission of visible light by dyes in both liquid and polymer hosts is reported when excited by simultaneous absorption of infrared light from two different wavelength sources. By moving the intersection point of these two beams about within the volume of the dye-doped medium, one can create a true, real-time, three-dimensional display.
Ion channeling and x-ray diffraction study of tensely strained GaInP layers on InP
Authors: Cohen G. M. , Ritter D. , Richter V. , Kalish R.
Published: July 2002

Layers of Ga0.25In0.75P were grown on InP by metalorganic molecular beam epitaxy and studied by ion channeling and asymmetric high-resolution x-ray diffraction. The angular difference between the substrate and the layer channeling angles agreed with the corresponding angular difference calculated from the x-ray results. Negligible relaxation was found in Ga0.25In0.75P layers up to a thickness of 50 nm. Thicker layers were found to be partially relaxed. In the channeling experiments an additional minimum in the substrate angular scan profile at an angle corresponding roughly to the layer’s minimum yield was found. This extra minimum was attributed to the steering effect at the strained GaInP/InP interface [S. Hashimoto, Y. Q. Feng, W M. Gibson, L. J. Schowalter, and B. D. Hunt, Nucl. Instrum. Methods B 13, 45 (1986)], and was confirmed by a comparison with the x-ray diffraction measurements.
Molecular beam epitaxial growth of InAs/(Al, Ga)Sb quantum-well structures on germanium substrates
Authors: Behet M. , De Boeck J. , Borghs G. , Mijlemans P.
Published: July 2002

Growth of InAs/(Al, Ga)Sb quantum-well structures was performed on germanium substrates by molecular beam epitaxy. The structural and electrical quality was characterized by x-ray diffractometry, transmission electron microscopy, and Hall transport measurements. An optimization of the GaAs buffer layer growth enabled the deposition of InAs/Al0.2Ga0.8Sb quantum wells with electron mobilities of 27 500 cm2/V s at 300 K and 260 000 cm2/V s at 4.2 K. These values are comparable to those measured for identical structures grown on GaAs substrate. Our results demonstrate the feasibility of using germanium as an alternative cheap substrate instead of commonly used GaAs for the growth of InAs/Al0.2Ga0.8Sb quantum-well magnetic sensor devices.
Electrical and structural characterization of AlxGa1−xN/GaN heterostructures grown on LiGaO2 substrates
Authors: Kang Sangbeom , Doolittle William A. , Brown April S. , Stock Stuart R.
Published: July 2002

In this letter, we report on the properties of a AlxGa1−xN/GaN heterostructure grown on LiGaO2. A two-dimensional electron gas (2DEG) is observed with mobility of 731 cm2/V s at room temperature and 2166 cm2/V s at 77 K. A comparison of the structural quality of the heterostructure as determined by x-ray diffraction shows significant improvement in comparison to a similar structure grown on a sapphire substrate. Secondary ion mass spectroscopy analysis indicates that lithium diffuses into the GaN during growth. The concentration decreases by two orders of magnitude from the substrate to the surface in a 0.8 μm thick GaN film. The enhancement of the mobility of the 2DEG compared to that of electrons in a uniformly doped film is due, in part, to the proximity of the 2DEG to the film surface, where the Li concentration is lower. In addition, we believe that the surface roughness plays a role in the mobility of the 2DEG. Despite these extrinsic factors, the good conductivity of the 2DEG shows the promise of LiGaO2 as a substrate for device-quality GaN.
Bias-controlled wavelength switching in coupled-cavity In0.4Ga0.6As/GaAs self-organized quantum dot lasers
Authors: Zhou Weidong , Qasaimeh Omar , Phillips Jamie , Krishna Sanjay , Bhattacharya Pallab
Published: July 2002

Efficient wavelength switching is demonstrated in an In0.4Ga0.6As/GaAs self-organized quantum dot laser with an intracavity absorber section. A wavelength shift of ∼15 nm, believed to be caused by a shift of lasing between the bound states of the quantum dot, is obtained for a bias change of 6 V.
Oxidation of Si beneath thin SiO2 layers during exposure to HBr/O2 plasmas, investigated by vacuum transfer x-ray photoelectron spectroscopy
Authors: Donnelly V. M. , Klemens F. P. , Sorsch T. W. , Timp G. L. , Baumann F. H.
Published: July 2002

Thin SiO2 layers were exposed to an HBr/O2 plasma for a variety of short periods, reproducing the over-etching process after polycrystalline Si gate electrodes have been etched and the gate oxide layer is exposed. Samples were transferred under vacuum to an x-ray photoelectron spectrometer for analysis. After relatively thick (>60 Å) films were exposed to a 10% O2/HBr plasma at an average ion energy of ∼150 eV, the near-surface region becomes brominated, and the thickness of the film decreases, indicating an etching rate of ∼1–2 Å/s. When the starting film thickness is between 10 and 20 Å, however, exposure to the plasma results in an increases in the thickness of the film, and is enhanced with the increasing addition of oxygen to the feed gas. At mean ion energies of 40 or 150 eV, the transition from etching to deposition occurs at oxygen additions of ∼1% or ∼8%, respectively. The increase in SiO2 thickness is ascribed mainly to oxidation of the Si at the oxide-substrate interface, and not to deposition resulting from sputtering of reactor materials. Consumption of crystalline Si beneath a 12 Å thick SiO2 gate oxide, adjacent to a 600 Å linewidth, polycrystalline gate electrode was also observed after etching of this transistor structure, as confirmed by transmission electron microscopy.
Effects of stress on the growth of TiSi2 thin films on (001)Si
Authors: Cheng S. L. , Huang H. Y. , Peng Y. C. , Chen L. J. , Tsui B. Y. , Tsai C. J. , Guo S. S.
Published: July 2002

Tensile stress induced by backside CoSi2 films on a silicon substrate has been found to enhance the growth of C54–TiSi2 on (001)Si. In contrast, compressive stress induced by backside oxide films on the silicon substrate was found to retard significantly the growth of C54–TiSi2 on (001)Si. For Ti on stressed (001)Si after rapid thermal annealing at 800 °C for 30 s, the thickness of the C54– TiSi2 films was found to increase and decrease with the tensile and compressive stress levels, respectively. The retarded growth is attributed to the hindrance of the migration of Si through the Ti/Si interface by the compressive stress. On the other hand, the presence of tensile stress promotes the Si diffusion to facilitate the formation of Ti silicide thin films.
Direct observation of strained substrate in graded Si1−xGex/Si heterostructures
Authors: Tao M. , Lyding J. W.
Published: July 2002

Cross-sectional scanning tunneling microscopy is used to study strain relaxation in a graded Si1−xGex/Si heterostructure. Two strain relaxation mechanisms are observed on the (111) cleaved surface. One is through stressing the substrate, and the strained region in the substrate can extend several hundred Angstroms from the interface. The other strain relaxation mechanism is through defect formation, i.e., atomic steps, on the cleaved surface. This is analogous to misfit dislocations in bulk strain relaxation. Interaction between these two strain relaxation mechanisms is also observed, with the presence of atomic steps reducing the strained region in the substrate.
Improved blue luminescence in Ag-codoped SrS:Ce thin films made by atomic layer epitaxy and ion implantation
Authors: Li Wei-Min , Ritala Mikko , Leskelä Markku , Lappalainen Reijo , Soininen Erkki , Niinistö Lauri , Barthou Carlos , Benalloul Paul , Benoit Jacques
Published: July 2002

Silver ions were implanted into SrS:Ce3+ thin films grown by atomic layer epitaxy (ALE) to examine the effects of Ag+ codoping on the luminescence of SrS:Ce3+ used in thin-film electroluminescent (TFEL) devices. High-temperature annealing (800 °C) of the standard ALE SrS:Ce prepared at 510 °C caused a pronounced blueshift of the photoluminescence (PL) emission, but the intensity was decreased. Codoping by ion implantation of Ag+ and high-temperature annealing (800 °C) caused no further blueshift but the PL intensity was more than double that of the nonimplanted samples. The implanted SrS:Ce, Ag also exhibited the longest decay value (SN=22 ns at 520 nm with 420 nm excitation) reported for ALE SrS:Ce thin films. The improved PL properties show that codoping with Ag+ can be advantageous in ALE SrS:Ce3+ thin films used for electroluminescent multicolor and full-color flat panel displays. The results also suggest the potential of the ion implantation technique in TFEL device preparation.
Instability of nanocavities in amorphous silicon
Authors: Zhu Xianfang , Williams J. S. , Llewellyn D. J. , McCallum J. C.
Published: July 2002

This letter demonstrates that, whereas nanocavities are quite stable in crystalline Si (c-Si), they are unstable in amorphous Si (a-Si). This behavior is illustrated by introducing a band of nanocavities into c-Si by H implantation, followed by annealing at 850 °C. Amorphization of the c-Si surrounding the nanocavities led to their disappearance. Transmission electron microscopy, Rutherford backscattering, and channeling and time resolved (optical) reflectivity were used to provide details of the cavity instability process by studying the amorphous Si after implantation and subsequent crystallization. Two possible reasons are suggested for the instability of nanocavities in a-Si.
Mesoscopic composition fluctuations in semiconductor alloys: Effect on infrared devices
Authors: Muller M. W. , Sher A.
Published: July 2002

Semiconductor alloys like Hg1−xCdxTe and Al1−xGaxAs, where there is a close lattice constant match between the constituents, are nearly random. Consider mesoscopic size scales of radius r that are large compared with a lattice constant (∼25 A<r<∼250 A), but small compared with typical device dimensions. In such regions the number of substitutional sites is small enough so the root-mean-square concentration fluctuation 〈(Δx)2〉1/2 is sufficiently large to produce random arrays of mesoscopic “quantum dots” that adversely affect many device properties. The influence of the adverse effects differ among various properties—for example, electron and hole mobilities, lifetimes, and so on—but, in general, are worse the smaller the fundamental gap becomes. These kinds of fluctuations are suppressed in lattice-mismatched alloys like Hg1−xZnxTe and Ga1−xInxAs because there is a long-range strain energy penalty associated with them. Thus, lattice-mismatched alloys are more spatially uniform than lattice-matched alloys.
Direct observation of localized high current densities in GaN films
Authors: Brazel E. G. , Chin M. A. , Narayanamurti V.
Published: July 2002

Local high current densities in areas around dislocations with a screw component might be responsible for the observed high leakage currents in GaN-based electronic devices. Using ballistic electron emission microscopy, threading dislocations with a screw component are found to be accompanied by high current densities and low effective Schottky barrier heights. The electronic states responsible for this extremely nonuniform behavior of GaN films are metastable trap states. The experimental results show that acceptor- and donor-like charge traps coexist in the vicinity of dislocations with a screw component.
Direction-oriented quasiparticle injection and microwave emission in an ErBa2Cu3Oy superconductor
Authors: Lee K. , Yamaguchi H. , Wang W. , Kume E. , Iguchi I.
Published: July 2002

We report the anisotropic microwave emission properties of ErBa2Cu3Oy/insulator/Au (S/I/N) tunnel junctions due to the direction-oriented quasiparticle injection. Two types of samples with different S/I/N tunnel junction geometries are prepared: one allows the quasiparticle injection mainly along the c axis and the other only into the ab plane. The results show the presence of strong anisotropic behavior of microwave emission according to the direction of quasiparticle injection.
Interfacial reactions and evolution of the magnetic anisotropy in Tb/Fe multilayers irradiated by swift heavy ions
Authors: Juraszek J. , Fnidiki A. , Teillet J. , Richomme F. , Duc N. H. , Toulemonde M. , Keune W.
Published: July 2002

The magnetic and structural transformations in Tb/Fe multilayers irradiated with high energy Pb ions have been studied by Fe57 conversion electron Mössbauer spectrometry. Compositionally modulated amorphous FeTb alloy regions are formed at the interfaces in the vicinity of the ion path, accompanied by a loss of the perpendicular magnetic anisotropy. A phenomenological model, proposed earlier, has been used to explain the evolution of the magnetic anisotropy.
InAs-doped silica films for saturable absorber applications
Authors: Bilinsky I. P. , Fujimoto J. G. , Walpole J. N. , Missaggia L. J.
Published: July 2002

InAs-doped thin silica films having saturable absorption properties were fabricated using rf sputtering. The films contain semiconductor nanoparticles preserving the zincblende crystal structure of bulk InAs. We have investigated the linear and nonlinear optical as well as structural properties of the films. Rapid thermal annealing in nitrogen was successfully used to tailor the optical absorption saturation dynamics. The films having saturable absorber properties were applied to Kerr lens mode locking initiation in a Ti:Al2O3 laser resulting in self-starting mode locking operation with pulses as short as 25 fs.
Electroluminescence and carrier transport of SiO2 film containing different density of Ge nanocrystals
Authors: Zhang Jia-Yu , Ye Yong-Hong , Tan Xi-Lin
Published: July 2002

Luminescent SiO2 films containing Ge nanocrystals (nc-Ge) are synthesized by implanting Ge ions into SiO2 films thermally grown on crystalline silicon, and the nc-Ge density was controlled by Ge+ implantation doses. The current–voltage measurements of their metal–oxide–semiconductor structures illustrate that the density and the distribution of nc-Ge have significant effects on their electroluminescence and carrier transport. The temperature-dependent current behavior is weaker in the films with low density, but stronger in the films with high density. Electroluminescent spectra indicate that high electric field can be established only in the films with low density.
Plasmon energy shift in mesoporous and double length-scale ordered nanoporous silica
Authors: Yin J. S. , Wang Z. L.
Published: July 2002

Electron energy-loss spectroscopy studies are reported on three different types of structures: solid silica spheres, mesoporous silica, and the double length-scale ordered (DLSO) porous silica. The mesoporous silica has porosity at the length scale of nanometers. The DLSO porous silica has an additional ordering on submicron hollows created by the template polystyrene spheres. The plasmon energy of the porous silica shows a significant shift in comparison to that of the bulk, suggesting that the local density of the bound electrons in the porous structures is lower than that in the bulk. This gives the possibility of tuning the electronic structure of silica by varying its porosity, leading to even lower dielectric loss.
An ordered long-period superlattice structure of the B2 lattice
Authors: Shao Guosheng
Published: July 2002

Formation of an ordered long-period superlattice structure in the B2 phase has been observed. The results of electron diffraction analysis have been well explained using kinematical electron diffraction theory. The long-period superlattice structure is generated by periodic arrangements of antiphase domain boundaries between every four B2 cells along the 〈100〉B2 directions and the shift vectors for the formation of the antiphase domain boundaries are 〈12 12 12〉aB2.
Lateral migration of point defects in Si induced by localized ion implantation
Authors: Matsukawa T. , Yokoyama K. , Sawara S. , Ohdomari I.
Published: July 2002

Novel experimental approach to investigate lateral migration of point defects in Si induced by ion implantation has been proposed. The point defects induced by localized irradiation using a focused Si ion beam with an energy of 60 keV were monitored by deep level transient spectroscopy while changing the separation among a number of line-shaped irradiated regions. A result of the experiment that the defect formation is suppressed at a smaller separation is explained by the lateral migration of self-interstitials and annihilation with vacancy-type defects. The migration distance of the interstitials is also evaluated quantitatively and discussed in comparison with the trap-limited-diffusion model.
Effect of low-energy nitrogen molecular-ion impingement during the epitaxial growth of GaAs on the photoluminescence spectra
Authors: Shima Takayuki , Makita Yunosuke , Kimura Shinji , Sanpei Hirokazu , Fukuzawa Yasuhiro , Sandhu Adarsh , Nakamura Yoichi
Published: July 2002

Low-energy (∼100 eV) nitrogen molecular ions (N2+) were impinged during molecular beam epitaxial growth of GaAs at the substrate temperature of 550 °C. In the low-temperature (2 K) photoluminescence (PL) spectra, extremely sharp N-related emissions (Xi, i=1, 2, and 5) were observed in as-grown condition. These emissions were roughly two orders of magnitude stronger than those formed by the impingement of nitrogen atomic ions (N+). The results indicate that nitrogen (N) atoms are in situ substituted at As sites without inducing large structural damages and become quite efficient radiative recombination centers as isoelectronic impurities in GaAs. Further, to study the substitutional condition of N isoelectronic impurity, N isotope (15N) doped GaAs was grown by N152+ ion impingement. When N15 is doped, PL peak energy of X5 shifted towards higher energy side by 1.8 meV. The value is fairly close to the expected one of 1.9 meV when N15 replaces N14N. Together from energy separation between X2 emission (∼60 meV), origin of X5 was ascribed to the local vibrational mode of X2 emission.
Effects of inductively coupled plasma oxidation on the properties of polycrystalline silicon films and thin film transistors
Authors: Choi Yong Woo , Park Sang Won , Ahn Byung Tae
Published: July 2002

We investigated the effects of inductively coupled plasma (ICP) oxidation on the properties of polycrystalline silicon (poly-Si) films and thin film transistors (TFTs). The ICP oxidation in oxygen plasma passivated the dangling bonds in the poly-Si films, not by oxygen incorporation but by hydrogen incorporation; but the incorporated hydrogen diffused out during the TFT fabrication, so that the effect of the dangling bond passivation was not obtained in the TFT. The ICP oxidation did not remove the intragranular defects such as microtwins and stacking faults, but it reduced the interface trap density and also improved the performance of the poly-Si TFT. The field effect mobility of TFT with an ICP oxide and low-pressure chemical vapor deposited (LPCVD) oxide double layer was 30.6 cm2/V s, while that of TFT with only a LPCVD oxide was 17.2 cm2/V s.
Polarity- and voltage-controlled color-variable light-emitting devices based on conjugated polymers
Authors: Wang Y. Z. , Sun R. G. , Wang D. K. , Swager T. M. , Epstein A. J.
Published: July 2002

There is increased interest in developing multilayer color-variable light-emitting devices. So far, the multilayer color-variable light-emitting devices mainly have focused on polarity-controlled two-color light-emitting devices. We report here the fabrication and study of voltage- and polarity-controlled multilayer multicolor light-emitting devices based on pyridine-containing conjugated polymers and derivatives of polyacetylene. The devices emit red light under forward bias and multiple colors of light (from orange-red to green) under reverse bias. The colors under reverse bias are controlled by the magnitude of the applied voltages.
Resonant absorption of a short-pulse laser in a doped dielectric
Authors: Ang L. K. , Lau Y. Y. , Gilgenbach R. M.
Published: July 2002

A simple model is used to calculate the energy absorption efficiency when a laser of short pulse length impinges on a dielectric slab that is doped with an impurity with a resonant line at the laser frequency. It is found that the energy absorption efficiency is maximized for a certain degree of doping concentration (at a given pulse length) and also for a certain pulselength (at a given doping concentration). Dimensionless parameters are constructed, allowing calculations with one set of parameters be used to infer the results expected for other sets of parameters.
Detecting work-function differences in scanning tunneling microscopy
Authors: Müller A.-D. , Müller F. , Hietschold M.
Published: July 2002

Variations of the work-function differences between tip and sample over distance have been investigated by a special procedure with a scanning tunneling microscope. This procedure allows the measurement of displacement current Ic dependencies on the voltage U. For a Pt tip on a Au surface and for a W tip on a Pt surface, work-function differences among 0, 2 and 0, 6 eV were found. They increase with increasing distance. From the slope of the Ic(U) characteristics in different distances, the diameter of the tip is estimated.
Stability of trapped electrons in SiO2
Authors: Fleetwood D. M. , Winokur P. S. , Flament O. , Leray J. L.
Published: July 2002

Thermally stimulated current and capacitance voltage methods are used to investigate the thermal stability of trapped electrons associated with radiation-induced trapped positive charge in metal–oxide–semiconductor capacitors. The density of deeply trapped electrons in radiation-hardened 45 nm oxides exceeds that of shallow electrons by a factor of ∼3 after radiation exposure, and by up to a factor of 10 or more during biased annealing. Shallow electron traps anneal faster than deep traps, and exhibit response that is qualitatively consistent with existing models of compensated Eγ′ centers in SiO2. Deeper traps may be part of a different dipole complex, and/or have shifted energy levels that inhibit charge exchange with the Si.
Temperature dependence of continuous wave threshold current for 2.3–2.6 μm InGaAsSb/AlGaAsSb separate confinement heterostructure quantum well semiconductor diode lasers
Authors: Garbuzov D. , Maiorov M. , Lee H. , Khalfin V. , Martinelli R. , Connolly J.
Published: July 2002

The dependence of spontaneous emission intensity on both current and temperature has been studied for 2.3–2.6 μm InGaAsSb/AlGaAsSb separate-confinement-heterostructure quantum well diode lasers operating in the continuous wave and pulsed regimes. We have used the temperature dependence of the nonradiative recombination processes in the active region to determine the dependence of threshold current on temperature for lasers operating in this wavelength range. The high T0 value (T0=110 °C) observed at T<65 °C for 2.3 μm lasers has been identified with monomolecular nonradiative process dominating in their active regions. Low T0 of 40–50 °C for 2.3 μm lasers at T>65 °C and for 2.6 μm lasers in the whole temperature range studied has been identified with an enhancement of the Auger recombination process.
Phosphidization of GaAs by a remote phosphine plasma process and its application to surface passivation of GaAs metal–semiconductor field-effect transistors
Authors: Sugino Takashi , Nozu Satoshi , Nakajima Shigeru
Published: July 2002

Surface passivation of GaAs due to phosphidization is investigated. GaAs surfaces are treated with a remote plasma of phosphine (PH3) diluted with Ar. X-ray photoelectron spectroscopy analysis reveals that the PH3 plasma treatment removes native oxide from GaAs surfaces and that generation of As oxide is suppressed on phosphidized surfaces. Photoluminescence intensity is enhanced for phosphidized GaAs. The PH3 plasma treatment is applied to surface passivation of GaAs metal–semiconductor field-effect transistors. A significant increase of the drain current and the transconductance is achieved. These results strongly suggest that the surface states have been passivated.
Analysis of temperature dependence of the threshold current in 2.3–2.6 μm InGaAsSb/AlGaAsSb quantum-well lasers
Authors: Andreev Aleksey D. , Donetsky Dmitry V.
Published: July 2002

We have carried out the microscopic calculations of Auger recombination and interband absorption in InGaAsSb/AlGaAsSb quantum-well (QW) lasers operating within wavelength range 2.3–2.6 μm. The calculations show that the dominant Auger process in these laser structures is the process with hole excitation from the quantized level in QW to the continuous spectrum. The total Auger coefficient shows a weak temperature dependence. Based on the results of calculations and recent measurements of the heterobarrier hole leakage current and modal gain in 2.3 μm InGaAsSb QW lasers, we have calculated the temperature dependence of the threshold current. It was shown that a significant value of the Auger coefficient and the temperature dependence of laser gain are the major factors determining the temperature dependence of the threshold current in 2.3–2.6 μm InGaAsSb/AlGaAsSb QW lasers.
Time-resolved characteristics of phase conjugation in metal–semiconductor phase transition in VO2
Authors: Berger N. K. , Shuker R.
Published: July 2002

The change in the reflection behavior of VO2 films for the 1.06 μm wavelength at the semiconductor–metal phase transition was investigated. The nonlinearity caused by photoinduced transition was used for phase conjugation of a pulsed Nd:YAG laser. At 60 Hz Q-switching rate and average intensities of the pump and probe waves at 1 and 0.3 W/cm2, respectively, the reflection coefficient of the conjugated wave was ∼1%, the threshold energy density was 8 mJ/cm2, the rise time of the signal was 30 ns. The response rate of the phase conjugation via the VO2 films is discussed.
Force modulation microscopy study of phase separation on blend polymer films
Authors: Lin Heh-Nan , Hung Tien-Tsan , Chang En-Chung , Chen Show-An
Published: July 2002

We report force modulation microscopy study of phase separation on blend polymer films of ether-type phenylene vinylene based copolymer and cyano-substituted poly(2,5-didecyloxy- p-phenylene vinylene). Three different tips with spring constants of 0.6, 3, and 60 N/m, and various modulation frequencies between 5 and 10 kHz have been employed. It is found that consistent and correct image contrast can be obtained only with the stiffest tip. Theoretical calculation based on Sneddon mechanics also predicts a tip-sample stiffness close to that of the preferred tip. These results suggest strongly that the tip spring constant used in force modulation microscopy should be comparable to (or greater than) the interaction stiffness.
Multilayer stacked electroluminescent devices
Authors: Park W. , Jones T. C. , Wagner B. K. , Summers C. J.
Published: July 2002

A device concept, the multilayer stacked electroluminescent device is presented. This device consists of a series of double insulating-layer electroluminescent units stacked up on top of one another, separated by transparent electrodes and alternately biased in opposite directions. This unique design allows independent control of the drive voltage and the total phosphor thickness. The drive voltage depends only on the individual phosphor layer thickness while the total phosphor thickness, and thus the total brightness, can be increased by increasing the number of layers. The anticipated enhancement in brightness was predicted by equivalent circuit analysis and demonstrated by prototype devices fabricated by atomic layer epitaxy.
A traveling-wave THz photomixer based on angle-tuned phase matching
Authors: Matsuura Shuji , Blake Geoffrey A. , Wyss Rolf A. , Pearson J. C. , Kadow Christoph , Jackson Andrew W. , Gossard Arthur C.
Published: July 2002

A traveling-wave THz photomixer based on a free-space optical-THz phase-matching scheme is proposed. A dc-biased coplanar strip line fabricated on low-temperature-grown GaAs serves as the active area of the device, and is illuminated by two noncollinear laser beams which generate interference fringes that are accompanied by THz waves. The device with the laser-power-handling capability over 300 mW and a 3-dB bandwidth of 1.8 THz was experimentally demonstrated. The results show that traveling-wave photomixers have the potential to surpass small-area designs.
In-plane uniaxial magnetic anisotropy of cobalt-doped Y3Fe5O12 epitaxial films
Authors: Dale Darren , Hu G. , Balbarin Vincent , Suzuki Y.
Published: July 2002

We have grown magnetically harder single-crystalline thin films of Y3Fe5O12 doped with Co2+ on (110)-oriented Ga3Gd5O12 substrates. Ge4+ and Ce4+ have been substituted to compensate for the charge differential between Co2+ and Fe3+. These garnet films, prepared using pulsed-laser deposition, exhibit excellent crystallinity as determined from x-ray diffraction and Rutherford backscattering spectroscopy. The addition of Co2+ in Y3Fe5O12 films enhances the in-plane uniaxial anisotropy over an order of magnitude, depending on composition.
Reflection from dual-domains in a holographically-formed polymer-dispersed liquid crystal material
Authors: Bowley Chris C. , Crawford Gregory P. , Yuan Haiji
Published: July 2002

A holographically-formed polymer-dispersed liquid crystal is reported with two distinctive reflective states brought about by a single laser exposure of a liquid crystal-rich emulsion. The two reflective states are the result of two structurally different domains that are formed during the holographic cure. A simple phenomenological model is presented that describes the dual-domain effect.
Threshold behavior analysis of in-plane switching mode liquid-crystal cells with asymmetrical surface condition
Authors: Yoneya Makoto , Kondo Katsumi
Published: July 2002

The threshold behavior of the in-plane switching (IPS) mode liquid-crystal cells with different (asymmetric) anchoring strength at two liquid-crystal/substrate interfaces was investigated by linear stability analysis. Similarity in stability characteristics between the IPS mode and the surface stabilized ferroelectric mode was clarified. The analysis showed that, with parallel rubbing of the two substrate surfaces, only the (symmetric) switching initialized from the center of the liquid-crystal layer will occur even with the asymmetric surface condition. This means that the basic switching process of the IPS mode does not change with the asymmetricities of the surface conditions.
Ultrasonic anomalies in La0.67Ca0.33MnO3 near the Curie temperature
Authors: Zhu Changfei , Zheng Renkui , Su Jinrui , He Jiang
Published: July 2002

The ultrasonic velocity (V) and attenuation (α) have been measured for both longitudinal and transverse waves in the single-phase polycrystalline colossal-magnetoresistance compound La0.67Ca0.33MnO3 near the Curie temperature Tc. A dramatic increase in V is observed at the ferromagnetic transition temperature and accompanied by a sharp peak in α for both longitudinal and transverse waves. This simultaneous occurrence of magnetic, transport, and lattice anomalous features implies extremely strong spin–phonon and electron–phonon interaction, and gives direct evidence for the spontaneous linear magnetostriction effect. The longitudinal attenuation (αI) was carefully measured over a wide temperature range. The temperature dependence of critical attenuation is given by (T−Tc)−1.55 for T>Tc.
Laser generation of ultrasound in films and coatings
Authors: Murray T. W. , Krishnaswamy S. , Achenbach J. D.
Published: July 2002

A model for the pulsed laser generation of ultrasound in an isotropic film on a semi-infinite substrate is presented. The model gives the time domain displacement of the system as a function of the density and mechanical properties of the film and substrate and the thermal properties of the film. The model has been verified experimentally using a 1 ns Nd:YAG laser source for acoustic wave generation and a stabilized Michelson interferometer for detection. Experimental and theoretical signals agree well for both the case of a fast layer on a slow substrate (zirconium nitride/steel) and a slow layer on a fast substrate (titanium/aluminum).
Ground state lasing from a quantum-dot oxide-confined vertical-cavity surface-emitting laser
Authors: Zou Z. , Huffaker D. L. , Csutak S. , Deppe D. G.
Published: July 2002

Data are presented on the room-temperature, continuous-wave ground state lasing characteristics from a quantum dot vertical-cavity surface-emitting laser. A threshold current of 703 μA is obtained for a 10-μm-diameter oxide aperture using a three-stack active region, with the lasing wavelength of ∼1.06 μm. Lasing is obtained for apertures as small as 2 μm square with threshold current of 268 μA. The threshold conditions are discussed with an emphasis on the spontaneous and stimulated decay rates due to resonant excitation.