bluuebunny/crossref_metadata_2025 huggingface dataset:
A new compressively strained-layer p-type InGaAs/AlGaAs/GaAs step bound to miniband quantum well infrared photodetector with a detection peak at 10.4 μm
Authors: Chu J. , Li Sheng S. , Ho Pin
Published: July 2002

Investigation of a InGaAs/AlGaAs/GaAs p-type step bound-to-miniband compressively strained layer quantum well infrared photodetector grown on (100) semi-insulating GaAs has been made. A long wavelength infrared detection peak at 10.4 μm with a full width at half-maximum bandwidth, Δλ/λp=20% was obtained for this detector. The measured spectral peak is in good agreement with our theoretical prediction. A responsivity of 28 mA/W was obtained at T=65 K and V=3.0 V, with a spectral detectivity D* of 1.4×109 cm√Hz/W at T=65 K and V=1.0 V. The detector was under the background limited performance condition at T=40 K and V≤2.0 V.
Combined influence of design and carrier scattering on the ultrafast emission dynamics of quantum well microcavity lasers
Authors: Jahnke F. , Schneider H. C. , Koch S. W.
Published: July 2002

A microscopic theory for vertical-cavity surface-emitting lasers (VCSELs) with quantum-well active layers is applied to study the transient gain dynamics, nonequilibrium carrier effects and the influence of the laser design. We investigate how the laser response on femtosecond pulse excitation can be controlled in terms of (i) excitation conditions of the VCSEL, (ii) the mirror design, which allows to change the cavity quality and the resonance frequency, and (iii) the number and position of active semiconductor quantum-wells.
Stability of undoped hydrogenated amorphous silicon multilayer film grown with alternating substrate temperature
Authors: Yoon Jong-Hwan , Lee Czang-Ho
Published: July 2002

Undoped hydrogenated amorphous silicon films have been grown in multilayers with alternating substrate temperature between optimal and nonoptimal temperature for device-quality films. Compared to the single layer films grown at optimal substrate temperature, the multilayer films show improved stability in the light-induced state. Under intense light illumination of 3 W/cm2, the steady-state defect density of the layered film reaches a saturation of 2×1016 cm−3, while the single layer film saturates at 6×1016 cm−3. It is found that in the completely degraded state, the photoconductivity in the multilayer film is also improved by a factor of 3 compared to the single layer film.
Effect of Al-rich surface on Se δ-doped GaAs grown by low-pressure metalorganic chemical vapor deposition
Authors: Kim J.-H. , Lim D. H. , Yang G. M. , Shin Y. G. , Lim K. Y. , Lee H. J.
Published: July 2002

We study Se δ-doped GaAs grown by low-pressure metalorganic chemical vapor deposition using hydrogen selenide as a doping precursor. The results of capacitance–voltage measurements show that the very sharp doping profile can be obtained by Se δ-doping on an Al-rich surface and Se segregation is also reduced by making an Al-rich surface after δ-doping. It is essential to utilize the δ-doping sequence which does not have a post-δ-doping purge step to minimize the Se evaporation.
Spectroscopic ellipsometry of germanium growth on hydrogen-terminated silicon (111)
Authors: Barth Michael , Hess Peter
Published: July 2002

The nucleation and coalescence of high-quality amorphous hydrogenated germanium (a-Ge:H) films produced by ArF laser-induced chemical vapor deposition on different substrates was investigated by real-time spectroscopic ellipsometry (RTSE). The ellipsometric studies reveal a significant influence of the substrate surface on the nucleation stage which, in fact, determines the optical, electronic and mechanical properties of the bulk material. Coalescence of initial clusters occurs at 16 Å film thickness for atomically smooth hydrogen-terminated c-Si(111) substrates, whereas on native oxide covered c-Si(100) substrates the bulk volume void fractions are not reached until 35 Å film thickness. The formation of Si1−xGex (x=0.12) alloy was observed on the H-terminated Si(111) interface.
Holographic recording in indium–oxide (In2O3) and indium–tin–oxide (In2O3:Sn) thin films
Authors: Mailis S. , Boutsikaris L. , Vainos N. A. , Xirouhaki C. , Vasiliou G. , Garawal N. , Kiriakidis G. , Fritzsche H.
Published: July 2002

Holographic recording in polycrystalline indium–oxide (InOx) and indium–tin–oxide (ITO) thin films, grown by dc magnetron sputtering, is demonstrated. This recording, performed at relatively low optical power levels in the ultraviolet (UV) wavelength range (325 nm), exhibits very large coupling strength and a slow but dynamic behavior. The observed phenomena are attributed to localized photorefractive effects and appear to be independent of the electrical characteristics of the films.
GaAs-based multiple quantum well tunneling injection lasers
Authors: Zhang X. , Yuan Y. , Gutierrez-Aitken A. , Bhattacharya P.
Published: July 2002

We report the modulation characteristics of multiple quantum well tunneling injection lasers designed for 0.98 μm emission wavelength. Electrons are injected into the active region through a single barrier via tunneling. The active region has four quantum wells with different well widths. Improved high frequency performance, compared to similar separate confinement heterostructure lasers, has been demonstrated. The modulation response at 21 GHz is above 0 dB and the extrapolated −3 dB modulation bandwidth is ∼30 GHz under pulsed bias.
Second-order optical nonlinearities in dilute melt proton exchange waveguides in z-cut LiNbO3
Authors: Veng Torben , Skettrup Torben , Pedersen Kjeld
Published: July 2002

Planar optical waveguides with different refractive indices are made in z-cut LiNbO3 with a dilute proton exchange method using a system of glycerol containing KHSO4 and lithium benzoate. The optical second-order susceptibilities of these waveguides are measured by detecting the 266 nm reflected second-harmonic signal generated by a 532 nm beam directed onto the waveguide surface. It is found for this kind of waveguides that in the waveguide region all the second-order susceptibilities take values of at least 90% of the original LiNbO3 values for refractive index changes less than ∼0.013 at the 632.8 nm wavelength, whereas the susceptibilities are strongly reduced for larger index changes.
Preferential precipitation sequence of metastable phase during crystallization of (Fe0.99Mo0.01)78Si9B13 metallic glass
Authors: Li Jian-Min , Quan Ming-Xiu , Hu Zhuang-Qi
Published: July 2002

A preferential precipitation sequence of metastable phase formation during crystallization of an amorphous alloy (Fe0.99Mo0.01)78Si9B13 was revealed as following: α-Fe(Si, Mo) (bcc) → (Fe,Mo)3B (BCT), (Fe,Mo)3.5B (BCT), and (Fe,Mo)23B6 (fcc) →Fe2B. An ordering process of atom cluster occurs prior to the crystallization. Above experimental sequence of crystallization of (Fe0.99Mo0.01)78Si9B13 metallic glass could be understood in terms of the Gaskell model. There is a high strain (0.33%) in the α-Fe(Si, Mo) (bcc) grain with 37 nm, and the strain relaxation leads to the distortion in the lattice parameter of nanocrystallite.
Optical lock-in vibration detection using photorefractive frequency domain processing
Authors: Hale Thomas Chatters , Telschow Ken
Published: July 2002

An optical method for vibration detection and spectral analysis based on photorefractive frequency domain processing is presented. The method utilizes the photorefractive effect in selected materials (bismuth silicon oxide) for synchronous detection of the optical phase shift of an object beam scattered from a vibrating specimen surface. Four-wave mixing and lock-in detection allow measurement of both the vibration amplitude and phase. Narrow-bandwidth detection can be achieved at frequencies from the photorefractive response limit to the reciprocal of the photoinduced carrier recombination time.
Two kinds of dopant activation in boron-doped hydrogenated amorphous silicon–carbon
Authors: Isomura Masao , Tanaka Makoto , Tsuda Shinya
Published: July 2002

Dopant activation occurs via both thermal annealing and light-soaking in boron-doped hydrogenated amorphous silicon–carbon prepared at a relatively low temperature. Both kinds of dopant activation probably originate from the same boron sites, because they both cause almost the same increase in dark conductivity, and no light-induced activation occurs after the thermally induced activation has been attained. The light-induced states show relaxation even at room temperature and are bistable sites, but the thermally induced states show no significant relaxation and have a more stable configuration. Perhaps, the light-induced states are caused by microscopic change and the thermally induced states are created with larger scale restructuring.
Offset of the electrical characteristics of alternating-current thin-film electroluminescent devices
Authors: Shih S. , Keir P. D. , Hitt J. , Wager J. F.
Published: July 2002

Offset is observed in the charge–voltage (Q–V) or internal charge–phosphor field (Q–Fp) characteristics of certain alternating-current thin-film electroluminescent (ACTFEL) devices. This offset arises from a displacement along the voltage axis of a transient curve measured across a sense capacitor in the electrical characterization setup. A procedure for adjusting this offset is proposed that allows ACTFEL devices manifesting offset to be meaningfully analyzed. Two possible sources of offset are deduced from simulation and are associated with an asymmetry in the interface state energy depths at the two phosphor–insulator interfaces or with an asymmetry in the location of space charge generation in the phosphor.
Atomic hydrogen cleaning of GaSb(001) surfaces
Authors: Bell G. R. , McConville C. F.
Published: July 2002

We show that the (001) surface of GaSb can be cleaned efficiently by exposure to atomic hydrogen at substrate temperatures in the range 400–470 °C. This treatment removes carbon and oxygen contamination, leaving a clean, ordered surface with a symmetric (1×3) reconstruction after a total H2 dose of approximately 150 kL. An ordered but partially oxidized surface is generated during cleaning, and the removal of this residual oxide is the most difficult part of the process. Auger electron spectroscopy and low energy electron diffraction were used to monitor the chemical cleanliness and the ordering of the surface during the cleaning process, whereas high resolution electron energy loss spectroscopy was used to probe the electronic structure in the near-surface region. The results obtained indicates that this cleaning procedure leaves no residual electronic damage in the near-surface region of the Te-doped (n∼5×1017 cm−3) samples of GaSb(001) studied.
High resistivity and ultrafast carrier lifetime in argon implanted GaAs
Authors: Walukiewicz W. , Liliental-Weber Z. , Jasinski J. , Almonte M. , Prasad A. , Haller E. E. , Weber E. R. , Grenier P. , Whitaker J. F.
Published: July 2002

We have investigated the optoelectronic and structural properties of GaAs that has been implanted with Ar ions and subsequently annealed. The material exhibits all the basic optical and electronic characteristics typically observed in nonstoichiometric, As implanted or low-temperature-grown GaAs. Annealing of Ar implanted GaAs at 600 °C produces a highly resistive material with a subpicosecond trapping lifetime for photoexcited carriers. Transmission electron microscopy shows that, instead of As precipitates, characteristic for the nonstoichiometeric GaAs, voids ranging in size from 3 to 5 nm are observed in Ar implanted and annealed GaAs.
Thin-film YBa2Cu3O7−x direct current SQUIDs with Josephson junctions made by direct electron beam writing
Authors: Nadgorny B. , Shokhor S. , Gurvitch M. , Hou S. Y. , Phillips Julia M.
Published: July 2002

We have investigated dc superconducting quantum interference devices (SQUIDs) with loop areas 8 and 64 μm2 made by direct electron beam writing in YBa2Cu3O7−x films with thickness 25 and 50 nm. The SQUIDs have maximum peak-to-peak voltage modulation of about 20 μV, which corresponds to the transfer factor dV/dΦ0∼50–60 μV/Φ0 at 30–40 K. By measuring the mutual inductance of the SQUID signal line as a function of temperature and comparing the data with the numerical calculations and the two-fluid model, we extracted the values of the London penetration depth for YBa2Cu3O7−x thin films.
Simultaneous determination of the strain/stress tensor and the unstrained lattice constants by x-ray diffraction
Authors: Wieder Thomas
Published: July 2002

The main prerequisite for residual stress evaluation by x-ray diffraction is the knowledge of the unstrained lattice constants a0,m (m=1,2,3). Often the a0,m are unknown. A method is presented which gives the stress and strain tensor together with the a0,m simultaneously from the same set of data.
Optical losses of Al-free lasers for λ=0.808 and 0.98 μm
Authors: Yi H. , Diaz J. , Lane B. , Razeghi M.
Published: July 2002

In this work, we study the origin of the optical losses in Al-free InGaAsP/GaAs (λ=0.808 μm) and InGaAs/GaAs/InGaP (λ=0.980 μm) lasers. Theoretical modeling and the experimental results indicate that the scattering of the laser beam by refractive index fluctuation in the alloys is the dominant loss in our lasers, and the loss due to the free-carrier absorption and scattering by interface roughness are negligible.
Different epitaxial growth modes of Bi2Sr2Ca2Cu3Ox on MgO
Authors: Ohkubo M. , Brecht E. , Linker G. , Geerk J. , Meyer O.
Published: July 2002

The epitaxial growth of Bi2Sr2Ca2Cu3Ox (BSCCO 2223) films has been realized on (001)MgO with a cylindrical sputtering gun. The 2223 films with the c axis perpendicular to (001)MgO exhibit three types of in-plane epitaxial relations, i.e., [100]BSCCO∥〈100〉MgO, [100]BSCCO∥〈150〉MgO, and [100]BSCCO∥〈110〉MgO. Individual domains possess respective in-plane mosaic distributions, which manifest that different epitaxial growth modes take place.
Photoluminescence study of high quality InGaN–GaN single heterojunctions
Authors: Sun C. J. , Yang J. W. , Chen Q. , Lim B. W. , Anwar M. Zubair , Khan M. Asif , Temkin H. , Weismann D. , Brenner I.
Published: July 2002

In this letter we report the results of room-temperature continuous wave and pulsed photoluminescence measurements on InGaN–GaN single heterojunctions. These InGaN–GaN heterojunctions were deposited over basal plane sapphire substrates using low pressure metalorganic chemical vapor deposition. We suggest the use of vertical cavity stimulated emission instead of spontaneous emission peak position as a good measure of the InGaN band edge.
Measurement of the extent of strain relief in InGaAs layers grown under tensile strain on InP(100) substrates
Authors: Maigné P. , Gendry M. , Venet T. , Tahri Y. , Hollinger G.
Published: July 2002

High resolution x-ray diffraction has been used to investigate the structural properties of InxGa1−xAs epitaxial layers grown under tension on InP(100) substrates. The nominal indium composition (x=0.42) corresponds to a small lattice mismatch and a two dimensional growth mode. We have also included for comparison two samples grown under compression covering the mostly strained and the mostly relaxed regimes. Our results show that the residual strain and the asymmetry in strain relaxation along 〈011〉 directions are always larger for layers under tension. This can be explained by the difference in dislocation glide velocity induced by a different indium content, by the dissociation of perfect dislocations and partially by the difference in thermal expansion coefficients between substrate and epilayer. The larger asymmetry in strain relaxation for tensile strain layers is interpreted by the existence of microcracks aligned in the [011] direction.
Current transport across YBa2Cu3O7–Au interfaces
Authors: Grove M. , Dittmann Regina , Bode M. , Siegel M. , Braginski A. I.
Published: July 2002

Current transport across each of the two YBa2Cu3O7–Au interfaces in a step-edge superconductor–normal metal–superconductor (SNS) Josephson junction could be investigated independently, due to contacts to the Au interlayer. The I–V characteristics of each superconductor–normal metal (SN) interface showed dc and ac Josephson-like effects fitting well to a model, which takes into account the influence of proximity effect in the normal metal layer on the transport across the SN interface, and Andreev reflection at the interface. In the investigated junctions, both SN interfaces of the step SNS junctions had similar transparencies.
The spectro-photovoltaic characteristics of a carbonaceous film/n-type silicon (C/n-Si) photovoltaic cell
Authors: Yu H. A. , Kaneko T. , Yoshimura S. , Suhng Y. , Otani S. , Sasaki Y.
Published: July 2002

A photovoltaic cell with carbonaceous thin film/n-type silicon (C/n-Si) was fabricated utilizing a process in which a carbonaceous thin film was deposited on an n-type silicon substrate by chemical-vapor deposition of 2,5-dimethyl-p-benzoquinone at 500 °C. Under illumination of 15 mW cm−2 light with wavelengths between 400 and 800 nm (xenon arc lamp), a power conversion efficiency (η) of 6.45% was achieved from this photovoltaic cell. This C/n-Si cell has shown a normalized short-circuit-current efficiency of more than 0.85 under illumination of 30 μW cm−2 monochromatic light from 500 to 950 nm.
Processing independent photoluminescence response of chemically etched porous silicon
Authors: Winton M. J. , Russell S. D. , Wolk J. A. , Gronsky R.
Published: July 2002

Room temperature photoluminescence spectra from samples of chemically etched porous silicon were analyzed as a function of dopant type, dopant concentration, etchant chemistry, and etching times. In stark contrast to electrochemically etched porous silicon, no significant variations in peak location or width were observed to result from stain etching. This invariance of peak location is presumed to be due to either chemical or electronic passivation of the luminescent silicon nanostructures that prevents subsequent modification after their initial formation.
Influence of the light-induced degradation on the extended state mobility in hydrogenated amorphous silicon
Authors: Schmidt J. A. , Cutrera M. , Buitrago R. H. , Arce R. D.
Published: July 2002

We measured the effects of light soaking on the extended state electron mobility in intrinsic and n-type doped hydrogenated amorphous silicon samples. We obtained the temperature dependence of the mobility in the range 0–80 °C, using a recently proposed method [Dawson et al., Appl. Phys. Lett. 63, 955 (1993)]. We found a decrease of the mobility as the degree of light-induced degradation increased. We suggest that these changes in the extended state transport are caused by an enhancement in the magnitude of the potential fluctuations introduced by the extra created charged defects.
Optical detection of quantum oscillations in InP/InGaAs quantum structures
Authors: Buyanova I. A. , Chen W. M. , Buyanov A. V. , Bi W. G. , Tu C. W.
Published: July 2002

A magnetooptical method based on optical detection of quantum oscillations via photoluminescence in a magnetic field is applied for characterization of the electronic structure and recom- bination mechanisms in modulation-doped semiconductor quantum structures. By studying modulation-doped InP/InGaAs two-dimensional (2D) quantum structures as an example case, the method is shown to be capable of obtaining information on: (i) the electronic structure, filling of quantum subbands, as well as the effective mass of 2D carriers and band nonparabolicity; (ii) both equilibrium and nonequilibrium concentration of 2D carriers and the dependence of the carrier concentration and lifetime on injection level.
Study of ultrathin Y3Fe5O12/Gd3Ga5O12 superlattices
Authors: Chern M. Y. , Fang C. C. , Liaw J. S. , Lin J. G. , Huang C. Y.
Published: July 2002

High quality Y3Fe5O12/Gd3Ga5O12 (YIG/GGG) superlattices have been grown on (111)GGG substrates by pulsed laser deposition. The superlattices are investigated with the thickness of the YIG layer varied from six to one unit cells while keeping the GGG layer fixed at one unit cell. The thicknesses of the YIG and GGG layers are confirmed with grazing angle x-ray reflectivity (GAXR). The good quality of the samples is indicated by the small interface roughness, no more than 6 Å, also measured with GAXR. While the magnetization of the samples decreases when the thickness of the YIG layer is decreased, the superlattice remains magnetic even when the YIG layer is only one unit cell. Ferrimagnetic resonance indicates that there exists a surface anisotropy favoring in-plane magnetization.
A nonlinear interaction of two acoustic beams on the solid interface
Authors: He X. , Shui Y. , Mao Y. , Jiang W.
Published: July 2002

Two incident ultrasonic shear wave beams of 7.5 MHz interact at glass-metal interface, and the reflected longitudinal wave of 15 MHz normal to the interface are investigated. This effect is identified as a nonlinear interface effect and the sum frequency signal is the convolution of two input signals. The convolution efficiency is measured as about 106 dBm for glass-iron interface. The observation reveals that the quality of interface bonding has a significant influence on the convolution output. So the nonlinear effect is found to be useful for implementation of convolution or nondestructive evaluation of bonding layer. Theoretical analysis and experimental measurements on the effect are presented in this letter.
Investigation of film growth for amorphous Nb/Si multilayers
Authors: Zhang Ming , Wang W. K.
Published: July 2002

In this letter, film growth for amorphous Nb/Si multilayers has been studied by using x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM). Results from XRD and XTEM show that the structures of amorphous Nb/Si multilayers deposited at room temperature and 550 °C are quite different. The influences of surface mobility of adatoms and interfacial reaction on interfacial roughness are discussed.
p-type InGaAs/InP quantum well infrared photodetector with peak response at 4.55 μm
Authors: Sengupta D. K. , Jackson S. L. , Ahmari D. , Kuo H. C. , Malin J. I. , Thomas S. , Feng M. , Stillman G. E. , Chang Y. C. , Li L. , Liu H. C.
Published: July 2002

Lattice-matched InGaAs/InP quantum well intersubband photodetectors (QWIPs) have been grown on an InP substrate by gas source molecular beam epitaxy. Detection at 4.55 μm was observed for a narrow well p-type InGaAs QWIP which, when complimented by a high responsivity 8.93 μm n-type InGaAs/InP QWIP, demonstrates the possibility of dual band, monolithically integrated QWIPs on the same InP substrate. Theoretical calculations of the photocurrent spectra are in excellent agreement with the experimental data.
Dynamic response of electro-optic effect in free-standing ferroelectric liquid crystal film
Authors: Uto Sadahito , Ohtsuki Hideyo , Ozaki Masanori , Yoshino Katsumi
Published: July 2002

A study of an electro-optic response in a free-standing ferroelectric liquid crystal film has been carried out. The response time becomes shorter with increasing electric field and, especially at a certain threshold of electric field, it changes in stepwise by three orders of magnitude. The response time of the faster kind of response that appears in the higher field region is several hundred milliseconds and is about one thousand times faster than the slower kind of response at lower fields.
Polymeric optical intensity modulator optimized in quasi-single mode operation
Authors: Hwang Wol-Yon , Kim Jang-Joo
Published: July 2002

An electro-optic polymer intensity modulator designed in the heavily multimode region but operating as a quasi-single mode waveguide has been demonstrated. The device relaxes much of the trade-off relationship between the modulation voltage and coupling efficiency without the sacrifice of the modulation extinction ratio. The device poled at 1.5 MV/cm shows half-wave voltage–length product of 7.2 V cm, modulation extinction ratio better than 20 dB, and mode diameters of about 4 and 9 μm in vertical and lateral directions, respectively.
Site-specific reaction kinetics for gallium arsenide metalorganic vapor-phase epitaxy
Authors: Adamson S. D. , Han B. K. , Hicks R. F.
Published: July 2002

We have developed a kinetic model for arsine decomposition on GaAs(001) that accounts for the effect of the surface reconstructions on the rates of As4 and As2 desorption. The main assumption of the model is that As2 desorbs more slowly from Ga sites than from As sites. The model accurately simulates the temperature-programmed desorption of arsenic from GaAs(001). In addition, it reveals how the As coverage and the As2 and As4 production rates depend on the conditions employed during GaAs metalorganic vapor-phase epitaxy.
Structure of high resistivity GaAs film grown by low-temperature metalorganic chemical vapor deposition
Authors: Chen Wen-Chung , Chang C.-S. , Chan S. H.
Published: July 2002

The structure of a low-temperature GaAs layer grown by low-pressure metalorganic chemical vapor deposition with precursors of triethylgallium and arsine is reported. Dense particles containing Ga clusters are found in a high resistivity GaAs film grown at 420 °C. The size and concentration of particles are about 800–1000 nm and 7×1011 cm−3, respectively.
Strain field imaging on Si/SiGe(001)-(2×1) surfaces by low-energy electron microscopy and scanning tunneling microscopy
Authors: Jones D. E. , Pelz J. P. , Hong Y. , Tsong I. S. T. , Xie Y.-H. , Silverman P. J.
Published: July 2002

We show that ultrahigh-vacuum low-energy electron microscopy and scanning tunneling microscopy can be used to image residual uniaxial strain fields on (001) surfaces of SiGe heterostructures. We find that the surface crosshatch morphology on these films is highly correlated with large spatial variations in the residual uniaxial strain fields, confirming the importance of local strain fields in the formation of crosshatch.
Electron-beam-enhanced precipitation in highly carbon-doped GaAs layers
Authors: Werner P. , Gösele U. , Kohda H.
Published: July 2002

Highly carbon-doped GaAs layers grown by metalorganic vapor phase epitaxy were investigated by transmission electron microscopy (TEM). Secondary-ion-mass spectroscopy as well as Hall measurements indicated that nearly all the doping atoms incorporated are electrically active. Electron irradiation has been applied to generate point defects interacting with native defects, e.g., substitutional carbon. Owing to this irradiation periodically arranged striations perpendicular to the growth direction were induced, which were observed in situ by TEM. Furthermore, precipitates (O/=10–15 nm) occurred incorporating noncrystalline material, which most likely is gallium.
Giant magnetoresistance effect in bulk La1/3Nd1/3Ca1/3MnO3 at low field
Authors: Rao G. H. , Sun J. R. , Liang J. K. , Zhou W. Y. , Cheng X. R.
Published: July 2002

A magnetoresistance ratio as high as −96% in a low field of 0.67 T is achieved in bulk La1/3Nd1/3Ca1/3MnO3. The magnetization exhibits a transition from a low moment state to a high moment state with decreasing temperature, accompanied by a thermal hysteresis of the magnetization. The magnetic transition might be an order-order transition and would be responsible for the observed giant magnetoresistance effect in the compound at low field.
Hot-electron induced passivation of silicon dangling bonds at the Si(111)/SiO2 interface
Authors: Cartier E. , Stathis J. H.
Published: July 2002

It is demonstrated that pre-existing silicon dangling bonds in Al-gate metal-oxide-semiconductor capacitors on (111) silicon substrates are passivated during hot-electron stress, while defects—of an as yet unidentified nature—are simultaneously generated. This degradation behavior mimics the interface degradation caused by atomic hydrogen from a remote plasma, suggesting that hydrogen release by hot electrons leads to interface degradation, but the silicon dangling bond is not the dominant interface defect.
Anomalous surface segregation of Sb in Si during epitaxial growth
Authors: Kimura K. , Endoh Y. , Mannami M. , Gossmann H.-J. , Gilmer G. H. , Feldman L. C.
Published: July 2002

A delta-function-shaped Sb doping spike in Si is prepared by deposition of Sb on Si(001) followed by low-temperature molecular beam epitaxy of Si. The depth profile of the Sb atoms is measured using high-resolution Rutherford backscattering spectroscopy, yielding a depth resolution of 0.3 nm. The observed profile shows two peaks corresponding to the δ-doped layer (of width 0.5 nm) and Sb atoms on the surface. The latter are due to surface segregation of Sb atoms during the growth of the Si cap layer. The surface segregation rate is derived from the observed results at temperatures 70–280 °C. It is larger than the value extrapolated from high-temperature (≳400 °C) data by several orders of magnitude and shows a very weak temperature dependence as compared to the high-temperature data. These features indicate a new surface segregation mechanism at low temperature. A mechanism for this anomalous segregation is discussed.
On the voltage stability of lateral barriers in in-plane-gated structures
Authors: Baumgartner P. , Engel C. , Abstreiter G.
Published: July 2002

Lateral barriers in a two-dimensional electron gas were fabricated by laser-induced doping of GaAs/AlGaAs quantum well structures. The barrier heights of these insulating lines were analyzed as a function of voltage by temperature-dependent current measurements. The barrier height saturates for large bias voltages. This is connected with surprisingly high breakdown voltages of the sub-μm lateral barriers. We propose a model for in-plane-gated structures which can explain these effects by taking into account surface leakage currents and surface charges. The lateral band diagram and the barrier height as a function of voltage were calculated self-consistently using this model. The model and the calculations are in good agreement with experimentally determined barrier heights, depletion lengths, and time-dependent leakage currents.
Photoluminescence and photostimulated luminescence of BaFBr:Eu Eu2+,Eu3+
Authors: Chen Wei , Su Mianzeng
Published: July 2002

In the photoluminescence (PL) of BaFBr:Eu2+,Eu3+, the emissions of Eu2+, carrier electron-hole (e-h) recombination, and Eu3+ are observed, while in the photostimulated luminescence (PSL) only the emission of Eu2+ is exhibited. This disappearance of e-h recombination in PSL is considered to be caused by carrier migration during photo-stimulation.
Formation of pseudo one-dimensional photonic band in visible region by grating pair method
Authors: Todori Kenji , Hayase Shuzi
Published: July 2002

We have succeeded in fabricating a pseudo one-dimensional photonic band system in the visible region using two facing gratings. The transmittance spectra of 3600 and 1800 grooves/mm grating pairs were measured. The results, along with calculations of one-dimensional photonic bands, show that a photonic band exists and the band edges are near 530 THz.
Measurement of saturation intensities in ion doped solids by transient nonlinear refraction
Authors: Pilla V. , Impinnisi P. R. , Catunda T.
Published: July 2002

The transient response of the Z-scan signal ΔT(t) was used to investigate the nonlinearity of ion doped solids. n2 measurements in ruby and alexandrite were performed using an Ar+ laser. We observed that the nonlinearity response time τ decreases with the laser intensity as τ−1=τ0−1(1+I/Is), where τ0 is the excited state lifetime and Is the transition saturation intensity. So, by measuring the transient response at different laser intensities, we were able to determine not only the nonlinear complex refractive index n2 but also τ0 and Is for Cr+3 in ruby and in the two alexandrite sites.
Experimental determination of the absolute temperature modulation in photothermal microscopy of Y1Ba2Cu3O7 crystals
Authors: Studenmund W. R. , Fishman I. M. , Kino G. S. , Giapintzakis J.
Published: July 2002

We present a technique to experimentally determine the value of the temperature perturbation δT in photothermal microscopy. Knowledge of δT is necessary for proper analysis of the differential optical reflectivity (∂R/∂T) data obtained from untwinned Y1Ba2Cu3O7 crystals. We measure δT to be 0.2 K, consistent with previous theoretical predictions from thermal diffusion data.
Direct fabrication of microrelief patterns by electron-beam exposure in Ag–As–S glasses
Authors: Yoshida Norimitsu , Tanaka Keiji
Published: July 2002

Convex relief patterns can be produced in Ag–As–S glasses only by exposure to focused electron beams accelerated at ∼10 kV. The lateral size of the patterns is greater than 1 μm and the height increases to ∼6 μm. The volume expansion seems to be caused by accumulation of Ag+ ions into exposed regions.
Receiver with optical thyristors operating at 155 Mbit/s with 3 femto-Joule optical inputs
Authors: Bickel G. , Heremans P. , Kuijk M. , Vounckx R. , Borghs G.
Published: July 2002

A receiver for digital optical inputs is presented which is based on a differential pair of optical thyristors. Modification of the conventional differential pair allows the electrical readout of its ON and OFF states. Optical input pulses with an energy of about 3 femto-Joule (at a wavelength of 830 nm) are sufficiently large for detection. In its present size, the receiver works up to 155 Mbit/s.
Use of oxygen-stabilized C60 films for selective chemical vapor deposition
Authors: McGinnis Sean , Norin Lars , Jansson Ulf , Carlsson Jan-Otto
Published: July 2002

Thin C60 films exposed to ultraviolet/visible light in the presence of oxygen were used as a selective mask for tungsten chemical vapor deposition on silicon substrates. An uptake of oxygen in the fullerene films as well as a significant increase in their thermal stability resulted from the simultaneous exposure to the radiation and oxygen. The thermal stability and inertness of these films to tungsten hexaflouride, which is readily reduced by silicon to form the metal at 350 °C, allowed selective deposition of tungsten in both ultrahigh vacuum and low pressure environments. X-ray photoelectron spectroscopy and x-ray fluorescence spectroscopy were used to characterize the tungsten deposited on the C60 mask and the unmasked silicon substrate.
Dopant accumulation during substitutional–interstitial diffusion in semiconductors
Authors: Lyubomirsky Igor , Lyahovitskaya Vera , Cahen David
Published: July 2002

When p–n junctions are formed by doping with a dopant that diffuses via a dissociative diffusion mechanism, dopant diffusion is suppressed and dopants can pile up near the junction, well above their original concentration. Calculations confirm this, if no local neutrality is assumed. The results agree well with published and our own experimental data for Zn diffusion in InP. The increased built-in electric field due to this pileup is expelled nearly completely to the side of the junction without the pileup. This effect has important consequences for devices containing thin and/or small regions doped with such dopants because such regions may be completely depleted.
A 3 bit single flux quantum shift register based on high-Tc bicrystal Josephson junctions operating at 50 K
Authors: Oelze B. , Ruck B. , Sodtke E. , Kirichenko A. F. , Kupriyanov M. Yu. , Prusseit W.
Published: July 2002

A 3 bit single flux quantum (SFQ) shift register based on high-Tc bicrystal Josephson junctions has been designed, fabricated, and experimentally tested. The circuit consists of 26 bicrystal Josephson junctions and includes the shift register itself, two dc-SFQ converters, one readout superconducting quantum interference device, serving as a SFQ-dc converter, and three Josephson transmission lines. The correct operation of all circuit components has been demonstrated by low frequency testing at a temperature of 50 K.
Amorphous KNbO3 thin films with ferroelectriclike properties
Authors: Xiao R. F. , Sun H. D. , Siu H. S. , Zhu Y. Y. , Yu P. , Wong G. K. L.
Published: July 2002

Amorphous KNbO3 films are prepared by a low-cost sol–gel method. These films show a smooth surface morphology and have good waveguiding properties. Ferroelecticlike hysteresis loops are observed in these amorphous KNbO3 films with a remanant polarization of about 6μC/cm2. After corona poling, a stable effective second harmonic generation coefficient of 0.523 pm/V is achieved.
Direct identification of diamond growth precursor using almost pure CH4 or C2H2 near growth surface
Authors: Wu Jih-Jen , Hong Franklin Chau-Nan
Published: July 2002

Diamond growth was studied by injecting thermally decomposed Cl atoms into CH4/H2 or C2H2/H2. Owing to the extremely short residence time (25 μs) and low gas temperature (<1000 °C) in the decomposition system, the gas reaction is insignificant. Therefore, the carbon species near the substrate surface can be nearly identical to the input carbon source. With 0.3% CH4 being the input carbon source, CH4 remained the dominant carbon species near the surface (only 2.5% C2H2 was formed), and an almost continuous diamond film was deposited after 2 h growth. Raman spectra confirmed the formation of diamond. With 0.15% C2H2 being the input carbon source, C2H2 remained the dominant carbon species near the surface (10% CH4 was formed), but only a few very small particles were deposited. Therefore, we conclude that CH3 radicals seem the only diamond growth precursor under the Cl-rich conditions, whereas C2H2 is not efficient to grow diamond.
High efficiency photoemission from Cs–K–Te
Authors: Bisero D. , van Oerle B. M. , Ernst G. J. , Verschuur J. W. J. , Witteman W. J.
Published: July 2002

Cs–K–Te films have been fabricated under ultrahigh vacuum by vapor deposition of Te, K, and Cs onto a Mo substrate into the preparation chamber of the free electron laser of the University of Twente. Their photoemission properties are reported in this letter. The average quantum efficiency at 259 nm measured on 5 evaporated Cs–K–Te photocathodes is 22.5%, whereas the best quantum efficiency obtained at 259 nm is 23.4%. To our knowledge, this is the highest quantum efficiency at 259 nm reported so far, being about twice that of Cs2Te photocathodes. The reported results demonstrate that Cs–K–Te photocathodes are very promising for the use in photoinjectors.
SiH bond-bending modes of the HSi-(OSi)3 group in amorphous hydrogenated silicon dioxide
Authors: Lin Shu-Ya
Published: July 2002

The cluster-Bethe-lattice method is used to investigate SiH bond-bending modes of the HSi-(OSi)3 group in a-SiO2:H alloys. When the HSi-(OSi)3 group has C3 symmetry, the SiH bond-bending mode has a double degenerate frequency at 876 cm−1 as found by experiments. But when the HSi-(OSi)3 group does not have C3 symmetry, the nonsymmetrical coupling between SiH and its local bonding environment may cause the SiH bond-bending mode to split off and have an additional feature in the spectrum that is not revealed by experiments.
Blue photo- and electroluminescence from poly(benzoyl-1,4-phenylene)
Authors: Edwards A. , Blumstengel S. , Sokolik I. , Dorsinville R. , Yun H. , Kwei T. K. , Okamoto Y.
Published: July 2002

Optical and electroluminescent properties of a new poly(p-phenylene)-type polymer, poly(benzoyl-1, 4-phenylene) (PBP) were studied. PBP is soluble in common organic solvents, has high thermal stability and shows bright blue photoluminescence. Light-emitting diodes fabricated with PBP as the active layer emit blue electroluminescence with a peak wavelength at 446 nm and a brightness of about 100 cd/m2.
Electrical characterization of partially relaxed InxGa1−xAs/GaAs multiple quantum well structures
Authors: Moon C. R. , Kim In , Lee Jeong Seok , Choe Byung-Doo , Kwon S. D. , Lim H.
Published: July 2002

Electronic properties of partially relaxed InxGa1−xAs/GaAs multiple quantum well (MQW) structures are investigated using capacitance–voltage (C–V) profiling and deep level transient spectroscopy (DLTS). As the In composition becomes large, the depletion of carriers confined in QWs and the concentration of dislocation-related deep traps are increased. The carrier depletion is observed to occur predominantly in the QWs adjacent to the bottom layer. This depletion is believed to be due to electron capture at the acceptor-like misfit dislocation-related traps. Our results thus show that the C–V and DLTS measurements, combined with the numerical simulation of C–V profiles, can be used to study the influence of nonuniformly distributed misfit dislocations on the carrier distribution in MQW structures.
Misfit grainlets: Point strain sources compensating misfit during epitaxial growth
Authors: Albrecht M. , Christiansen S. , Strunk H. P.
Published: July 2002

We propose a misfit relaxation mechanism that may occur during growth in highly misfitting layers. It is based on a misfit compensating distribution of physical point strain sources at the interface between layer and substrate instead of misfit dislocations. These point strain sources are realized by interfacial islands (misfit grainlets) that have a lattice misfit opposite in sign to that of the surrounding epitaxial layer, in most cases brought about by an orientation relationship different from that of the surrounding layer to the substrate. We demonstrate the effectiveness in strain relaxation of misfit grainlets with an analysis of the interface structure of GaN on sapphire and discuss the formation of misfit grainlets in terms of a self-organized island growth process.
Electronic properties of osmium disilicide
Authors: Filonov A. B. , Migas D. B. , Shaposhnikov V. L. , Dorozhkin N. N. , Borisenko V. E. , Lange H.
Published: July 2002

Electronic property calculation of OsSi2 performed by the linear muffin-tin orbital method within the local density approximation scheme has shown the material to be an indirect gap semiconductor with a gap value of 0.95 eV. A direct transition with appreciable oscillator strength at 1.14 eV is predicted.
Deposition of silicon dioxide films on amorphous carbon films by plasma enhanced chemical vapor deposition for low dielectric constant interlayer dielectrics
Authors: Endo Kazuhiko , Tatsumi Toru , Matsubara Yoshihisa
Published: July 2002

Deposition of silicon dioxide films on fluorinated amorphous carbon films (a-C:F) for low dielectric constant interlayer dielectrics was investigated. Both SiO2 and a-C:F films were deposited by helicon wave plasma enhanced chemical vapor deposition with C4F8 for a-C:F and SiH4+O2 mixtures for SiO2. The SiO2 films on the a-C:F films peeled off soon after deposition. However, the peeling was suppressed by inserting a thin a-C:H buffer layer grown from CH4 between them. The adhesion between the films was increased by making the stoichiometry of SiO2 Si-rich. It was found that the Si–C bonds formed at the interface increased the adhesion.
Subband separation energy dependence of intersubband relaxation time in wide quantum wells
Authors: Luo Kejian , Zheng Houzhi , Lu Zhendong , Xu Jizong , Xu Zhongying , Zhang Ting , Li Chengfang , Yang Xiaoping , Tian Jinfa
Published: July 2002

Subband separation energy dependence of intersubband relaxation time in a wide quantum well (250 Å) was studied by steady-state and time-resolved photoluminescence. By applying a perpendicular electrical field, the subband separation energy in the quantum well is continuously tuned from 21 to 40 meV. As a result, it is found that the intersubband relaxation time undergoes a drastic change from several hundred picoseconds to subpicoseconds. It is also found that the intersubband relaxation has already become very fast before the energy separation really reaches one optical phonon energy.
Large Tc depression at low angle [100] tilt grain boundaries in bulk Bi2Sr2CaCu2O8+δ bicrystals
Authors: Li Qiang , Tsay Y. N. , Zhu Y. , Suenaga M. , Gu G. D. , Koshizuka N.
Published: July 2002

Large depression of Tc at 7° [100] tilt grain boundaries was observed in bulk Bi2Sr2CaCu2O8+δ (Bi2212) bicrystals by measuring the zero-field electrical transport properties of the grain boundaries and the constituent single crystals over an extended range of currents and voltages. The Tc-depressed region was determined to be around 20 nm, comparable to the width of the strain field associated with the observed array of grain-boundary dislocations. Superconducting coupling of the grain boundaries increases sharply as temperature decreases below the grain-boundary Tc≅68 K.
Measurement of absorption line wing structure by wavelength modulation spectroscopy
Authors: Bullock A. M. , Dharamsi A. N. , Chu W. P. , Poole L. R.
Published: July 2002

The application of wavelength modulation absorption spectroscopy in the characterization of lineshape functions of molecular spectra is discussed theoretically, and experimental results for the weak spin-forbidden, magnetic dipole-driven transitions of the oxygen A band are provided. Factors affecting the accuracy of the method are discussed, and it is shown that the technique allows one to accurately probe absorption lineshape functions by using a simple, cost-effective apparatus. The advantages of using detection harmonics greater than the commonly used second are discussed, including an investigation of wing structures of absorption lines and the measurement of collision cross sections.
An enhancement of pump efficiency of a Ti:sapphire tube laser with an inner spectrum converter
Authors: Seo Jae-Tae , Han Kwang S. , Lee Ja H.
Published: July 2002

An inner spectrum converter was employed to enhance the pump efficiency of a Ti:sapphire laser system. The inner converter was inserted along the hollow of the laser tube for additional spectrum conversions of the photons transmitted through the outer converter jacket and the laser-tube wall. The pump source was an array of hypocycloidal pinches that produced intense broad-band, rich in the near-ultraviolet, emissions. The increase of laser efficiency is attributable to the inner converter which offered an efficient spectral coupling into the center of the Ti:sapphire absorption band and a better geometric coupling than the outer converter.
Spatial soliton robustness against spatially anisotropic phase perturbations
Authors: Kang Jin U. , Hamilton C. J. , Aitchison J. S. , Stegeman G. I.
Published: July 2002

We demonstrate experimentally that spatial solitons in AlGaAs waveguides are resilient against spatially anisotropic perturbations in their phase caused by introducing a wedge in the soliton propagation path. In agreement with numerical simulations, the solitons maintained their initial beam shape and width, independent of the fraction of the soliton beam intercepted by the wedge.
Room temperature infrared intersubband photoluminescence in GaAs quantum wells
Authors: Sauvage S. , Moussa Z. , Boucaud P. , Julien F. H. , Berger V. , Nagle J.
Published: July 2002

We have observed mid-infrared photoluminescence at λ≈10 μm between conduction subbands in GaAs quantum wells. As for regular band-to-band interband photoluminescence spectroscopy, carriers are optically generated in the quantum wells using an interband optical pumping. At room temperature, the excited subbands of the quantum wells are thermally populated. Most of the carriers recombine nonradiatively through electron–phonon interactions, but a fraction of the carriers in the excited subbands recombine radiatively and give rise to the intersubband spontaneous emission in the 10 μm wavelength region. The intersubband photoluminescence is polarized along the growth axis of the quantum wells as expected from intersubband polarization selection rules. The emitted optical power is in the nW range and the quantum efficiency is found in agreement with calculations taking into account the radiative subband lifetimes. The emission is analyzed in terms of a blackbody emission of an electron gas in a two-dimensional confined system.