bluuebunny/crossref_metadata_2025 huggingface dataset:
A quasilinear wide-range radiometer amplifier implemented with correlated phase-sensitive detection
Authors: Shaw Sen-Yen , Hsiao Yu-Wei
Published: July 2002

A radiometer amplifier capable of wide-range optical measurement is described. Based on a novel automatically ranged electrometer and amplifier circuit, the radiometer provides a quasilinear analog output for the measurement of input radiation over ten orders of magnitude. Together with the scheme of phase-sensitive detection of modulated optical signals, the circuit resulted in an output voltage of low noise and offset drift. It can be applied directly to various kinds of photodetectors. The application of standard integrated circuits and lock-in amplifiers makes the whole system low cost and it can be readily built.
A flexible high-current lead for use in high-magnetic-field cryogenic environments
Authors: Kirkpatrick P. E. , Ekin J. W. , Bray S. L.
Published: July 2002

A flexible high-current lead for use at cryogenic temperatures and in high-magnetic fields has been developed using high purity aluminum. Readily available high purity aluminum has distinct advantages over copper, namely lower resistivity at liquid-helium temperature, lower magnetoresistance, lower yield stress, lower density, lower cost for material with comparable conductivity, and room temperature annealing. Aluminum may also be used in high magnetic fields, where flexible superconductors cease to function. Practical issues encountered in the design and fabrication of such flexible leads are discussed, such as geometrical considerations where sample loading and heating are important issues.
A charge-coupled device-based laser photofragment fluorescence spectrometer for detection of mercury compounds
Authors: Tong Xiaomei , Barat Robert B. , Poulos Arthur T.
Published: July 2002

The use of a charge-coupled device (CCD) camera for the detection of mercuric bromide (HgBr2) vapor at low concentrations by laser photofragment fluorescence (PFF) spectroscopy was investigated. The CCD detection system (camera+monochromator) offers reasonable sensitivity plus spectral information, thus enhancing PFF as a technique for the environmental monitoring of airborne mercury compounds. The experiment used laser radiation at 222 nm to photolyze HgBr2 and produce excited atomic mercury (Hg*). The PFF was monitored at 253.7 nm. Our unenhanced CCD detection limit was about 30 ppb HgBr2 in the absence of air. The CCD response remained linear up to 20 ppm. Observed nonlinearity of the PFF signal at higher concentrations is discussed. With the same collection optics and under the same experimental conditions, the sensitivity of a photomultiplier tube (PMT) with interference filters (253.7 nm) was also investigated for comparison. The detection limit for our PMT system was 10 ppb without signal averaging, but the linear dynamic range ended at 0.7 ppm. It is expected that the CCD detection system would be more versatile for measuring metal compound species by PFF spectroscopy in any future airborne metals monitor.
Generation and characterization of high intensity electron beams generated from rough photocathodes
Authors: Nassisi V. , Perrone M. R.
Published: July 2002

In this work, the generation and the characterization of high current electron beams from rough photocathodes induced by an ultraviolet excimer laser are reported. The cathodes were rough Cu disks. In order to study the influence of the cathode surface, the electron emission from different surface roughnesses was investigated. To establish the electromagnetic and geometric parameters a Rogowski coil and a new slit–slit emittance meter were used. The laser beam utilized was obtained by a mixture of Kr and Cl which generated coherent light at 222 nm. Fixing the laser energy at 0.5 mJ and the laser spot into 4 mm2, the maximum current as well as the maximum emittance value were obtained with the cathode that had the highest surface roughness which resulted in 1 A and 46 π mm mrad, respectively. A low current and a low emittance were obtained with the cathode that had the lowest roughness, namely, 410 mA and 19 π mm mrad, respectively. A quantum efficiency value of 1.2×10−4 was reached with the cathode with the highest amount of roughness.
Correlation between the hot-electron dynamics and the afterglow currents in electron cyclotron resonance ion sources
Authors: Kidera Masanori , Lamoureux Michele , Mironov Vladimir , Nakagawa Takahide , Shirkov Grigori
Published: July 2002

Time-resolved x-ray spectra were recorded at the RIKEN 18 GHz electron cyclotron resonance ion source (ECRIS) run in a pulsed mode, in order to understand why the best operating conditions are different in continuous and afterglow modes. The production of the largest afterglow currents of highly charged ions appears to be correlated with the building up of an important hot-electron component during the heating stage. The sudden drop of the corresponding hard x-ray emission at the microwave power turn-off is also studied. These observations support the view that the boosting afterglow effect is due to a fast modulation of the ECRIS plasma potential.
Determination of fundamental frequency of a physical oscillator by the period fitting method
Authors: Hu Zhong-Kun , Luo Jun
Published: July 2002

A period fitting method, which is a variant of the classical least-square fitting method, is proposed to determine the fundamental frequency of a physical oscillator. The root mean square deviation used as the criterion in this method is a single-parameter function of the fundamental frequency of the oscillator, so it makes the fitting process optimize the period fit at the expense of a lesser evaluation of the other parameters such as the amplitude and the phase. Theoretical analysis shows that this method is intrinsically independent of the disturbances of the high order harmonic frequencies oscillation, and the computer simulation experiments show that it is effective to overcome the disturbances of the finite quality factor and the monotonic drift of an oscillator system, as well as the white noise, and this method can determine the fundamental frequency or period of a physical oscillator with a relative precision of 10−7 orders.
Design and performance of an electrospray ionization time-of-flight mass spectrometer
Authors: Håkansson Kristina , Zubarev Roman A. , Håkansson Per , Laiko Viktor , Dodonov Alexander F.
Published: July 2002

In order to circumvent the limitations of a quadrupole mass filter, which so far has been the most common mass analyzer for use with electrospray ionization, a mass spectrometer coupling electrospray with time-of-flight mass analysis has been constructed. The design of this spectrometer, including a simple electrospray ion source, an atmosphere–vacuum interface without a rf-only quadrupole/multipole that discriminates against low mass ions which can be used for internal calibration, orthogonal extraction, and a reflectron, is presented together with its performance characteristics. A resolving power of 7500 was obtained for the +5 ion of bovine insulin and the detection limit for the same molecule was shown to be 1 f mol. Mass accuracy using a conventional two-point calibration is 60 ppm for internal calibration on low mass ions and better than 100 ppm for external calibration on peptide ions. An improved mass accuracy equal to 10 ppm was achieved using internal three-point calibration on low mass ions naturally present in the spectra. The dynamic range of a single sample was found to be at least 400:1.
Three-dimensional beam tracking for optical lever detection in atomic force microscopy
Authors: Nakano Katsushi
Published: July 2002

For the requirement to move a probe with respect to a large specimen like a silicon wafer, a three-dimensional beam tracking for optical lever force detection in atomic force microscopy has been developed. This beam tracking is not an approximate solution but an ideal solution in three-dimensional scanning. A set of tracking mirrors that are attached at the middle of a tube scanner steers a laser beam to a probe and to a detector during scanning. Tracking errors achieved were 2 and 7 nm in horizontal and vertical direction scans over 50 μm scanning. A simple theoretical error estimate revealed that less than 2 nm error is obtainable with moderate mirror mounting accuracy. To reduce the thickness of the scanner for coaxial optical microscope observation, the tube scanner was arranged sideways, resulting in 12 mm scanner thickness. A twist probe, pointed in the vertical direction to enter its tip into a narrow trench, was used for the probe. This system could obtain a semiconductor trench image successfully.
Novel imaging system for measuring microscale curvatures at high temperatures
Authors: Tada Haruna , Kumpel Amy E. , Lathrop Richard E. , Slanina John B. , Nieva Patricia , Zavracky Paul , Miaoulis Ioannis N. , Wong Peter Y.
Published: July 2002

An innovative system was designed to optically measure the curvature of microelectromechanical system at high temperatures. The system takes advantage of the limited numerical aperture of the imaging system to detect the curvature of cantilever beams. Images of the beam are used to determine beam curvature at high temperatures of up to 850 °C by analyzing the apparent change in beam length as seen by the camera during an experimental trial. The system is designed to operate at very high temperatures, which is difficult in conventional microscale curvature measurement techniques such as scanning electron microscopy or stylus profilometry due to excess heating of peripheral equipment. The system can measure curvatures as small as 300 m−1, which corresponds to tip deflections of 1.5 μm for a 100 μm beam. The resolution of the system is limited by the image resolution of the charge-coupled device camera, and increases at large curvatures. The maximum curvature that can be measured by the system is limited by the increase in system resolution, and is estimated to be 4500 m−1, corresponding to 22 μm deflection for a 100 μm beam. The apparatus was demonstrated to measure the thermally induced curvature of multilayered thin-film cantilever beams. The beams bend at high temperatures due to mismatch in thermal expansion coefficients between the layers. One innovative application of such curvature measurement is the determination of thermophysical properties of thin films at elevated temperatures. This article presents the experimental setup and operational theory of apparatus, as well as curvature measurements obtained by the system. The thermal expansion coefficient of polycrystalline silicon, determined from the curvature measurements, are also discussed.
Measurement of solute dipole moments in dilute solution: A simple three-terminal cell
Authors: Breitung Eric M. , Vaughan Worth E. , McMahon Robert J.
Published: July 2002

The construction of a simple, thermostated, three-terminal cell for the measurement of the dipole moment of polar solutes in nonpolar solvents is described. Using a General Radio Company bridge, we demonstrate the accurate measurement of the dielectric constants of p-xylene and benzene, as well as the molecular dipole moments of acetonitrile in p-xylene and p-nitroaniline in benzene. Capacitance measurements of dilute solutions (10−2–10−3 M) using less than 10 ml of solution are possible with this apparatus. The Debye and Hedestrand equations are used to extract the dipole moments from the capacitance measurements.
A new telemetry system for a balloon-borne far-infrared astronomical telescope
Authors: D’Costa S. L. , Ghosh S. K. , Naik M. V.
Published: July 2002

A new telemetry system (NTS) is described here, which has been developed for a balloon-borne far-infrared astronomical telescope. The NTS includes two space borne encoders (TEs) and the ground station decoder and display subsystems. The design of the TEs uses several novel ideas which simplify on-board hardware implementation. The NTS has shown satisfactory in-flight performance and is now a standard package for regular balloon flight experiments.
A linear pulse amplifier for space flight applications
Authors: Lampton M. , Penegor G.
Published: July 2002

We describe a charge pulse amplifier developed for the medium energy neutral atom experiment aboard the IMAGE geophysical observatory. Its purpose is to receive and amplify event pulses from a large area microchannel plate detector. Its design emphasizes low input impedance (∼20 Ω), good dynamic range (>10 000:1), and timing accuracy (<1 ns) sufficient for neutral-atom time-of-flight determination in the 1–30 keV energy range. The design is robust and free of adjustments, and is expected to tolerate a space radiation environment in which a 300 krad dose will be accumulated.
Lifetime determination for high-lying excited states using Z scan
Authors: Wei Tai-Huei , Huang Tzer-Hsiang , Lin Huang-Der , Lin Sheng-Hsien
Published: July 2002

We report a method of determining the lifetimes of the high-lying excited singlet states of dye molecules in solution. The method is based on the Z-scan technique and the observation of saturation of excited state absorption in dye solutions using laser pulses having Gaussian temporal and spatial distributions. This leads to the important finding that the use of laser pulses as long as tens of picosecond can resolve subpicosecond lifetimes. The method is demonstrated by measuring an upper excited singlet state lifetime of 900 fs using 30 ps full width at half maximum input pulses on a chloroaluminum phthalocyanine dye.
Normal incident InGaAs/GaAs multiple quantum well infrared detector using electron intersubband transitions
Authors: Karunasiri Gamani , Park Jin Suk , Chen John , Shih Robert , Scheihing J. F. , Dodd M. A.
Published: July 2002

A normal incident infrared detector has been fabricated using electron intersubband transition in a InGaAs/GaAs quantum well structure. With the light polarized in the plane of the layers (normal incident) a nominally forbidden absorption peak was observed. Such an absorption is most likely a result of spin-flip intersubband transitions induced by the spin-orbit coupling. In addition, for the light polarized in the plane of incidence, the usual intersubband absorption due to envelope function transition is observed. The responsivity of 0.2 A/W was obtained for the normal incident infrared on the detector. This work demonstrates the fabrication of high sensitivity quantum well infrared detectors operating in the normal incident mode without fabricating grating structures on the device for focal plane applications.
Carrier capture in cylindrical quantum wires
Authors: Mansour N. S. , Sirenko Yu. M. , Kim K. W. , Littlejohn M. A. , Wang J. , Leburton J. P.
Published: July 2002

We present quantum mechanical calculations of electron capture rates in cylindrical quantum wires via polar-optical phonon scattering. The capture rate dependence on quantum wire radius and lattice temperature is investigated. An oscillatory behavior of the electron capture rate is observed as a function of the quantum wire radius at the temperatures considered in this study (20–300 K). However, the amplitude of these oscillations decreases significantly at large wire radii and high lattice temperatures.
Amorphous silicon/silicon carbide photodiodes with excellent sensitivity and selectivity in the vacuum ultraviolet spectrum
Authors: Cesare G. de , Irrera F. , Palma F. , Tucci M. , Jannitti E. , Naletto G. , Nicolosi P.
Published: July 2002

An innovative family of thin-film photodetectors optimized for the ultraviolet (UV) spectrum is presented here. The devices are made of hydrogenated amorphous silicon (a-Si:H) and silicon carbide (a-SiC:H) on glass substrates. At room temperature, the photodetectors exhibit values of quantum efficiency of 21% in the vacuum UV and 0.08% at 750 nm, without external voltage. The great advantage of this technology lies in the possibility to produce low-cost, large-area arrays of photodetectors on glass or flexible substrates. All these features candidate the a-Si/SiC:H photodetectors as possible, concurrent to specialized commercial devices.
A normal force distance regulation scheme for near-field optical microscopy
Authors: Stephenson R. J. , Welland M. E.
Published: July 2002

A near-field optical microscope (NFOM) has been developed that combines the features of a near-field optical microscope and an atomic force microscope. Improved control over tip-sample separation has led to improved optical imaging and independent surface topography information. The tip oscillation is normal to the sample plane thereby reducing lateral forces—important for nonperturbative imaging of soft samples. Both topographic images and reflection near-field optical images are presented which demonstrate the capability of the system.
Phosphorus doping of Si and Si1−xGex grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4
Authors: Chen L. P. , Huang G. W. , Chang C. Y.
Published: July 2002

100 ppm PH3 diluted in hydrogen is used as the n-type dopant gas in Si and Si1−xGex epilayers grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6 and GeH4. The phosphorus concentration in Si increases linearly at a small PH3 flow rate and becomes nearly saturated at higher flow rates, while the phosphorus concentration in Si1−xGex only shows a nearly linear behavior with PH3 flow rate. The growth rates of Si and Si1−xGex epilayers decrease seriously (∼50%) and slightly (∼10%) with the increase of PH3 flow rate, respectively. These results can be explained by a model based on the enhancement of hydrogen desorption rate at smaller PH3 flow rates and different levels of the effects of phosphorus blocking of surface-activated sites between Si and Si1−xGex epilayers at higher PH3 flow rates.
InAs monolayers and the controlled introduction of deep levels in AlGaAs alloys
Authors: Colombelli Raffaele , Jancu Jean-Marc , Beltram Fabio , Sorba Lucia , Bertho Denis , Jouanin Christian
Published: July 2002

InAs monolayers and submonolayers have been introduced by means of molecular beam epitaxy in AlxGa1−xAs structures. Our photoluminescence and photoluminescence excitation measurements represent the first results on heterostructures with In sheets in AlxGa1−xAs. It is argued that these results together with their tight-binding modeling here presented provide a valid framework to implement a new class of heterostructures based on engineered deep centers.
Ga0.25In0.75As/InP quantum wells with extremely high and anisotropic two-dimensional electron gas mobilities
Authors: Ramvall P. , Carlsson N. , Omling P. , Samuelson L. , Seifert W. , Stolze M. , Wang Q.
Published: July 2002

Measurements of modulation-doped Ga0.25In0.75As/InP quantum wells show, in the 〈−110〉 direction, a record electron mobility of 520 000 cm2/V s at 300 mK. A mobility difference of 15% between the 〈110〉 direction and the 〈−110〉 direction is observed. This anisotropy is tentatively attributed to an ordering effect. The mobilities at room temperature and at 77 K were 16 100 and 170 000 cm2/V s, respectively. By separating out the ionized impurity scattering from other scattering processes in the quantum well, we conclude that at low electron concentrations ionized impurity scattering is limiting the mobility, while alloy scattering has a strong influence on the mobility at high electron concentrations. From this result we determine the first experimental value of the alloy-scattering potential as ΔV=0.3 eV.
Potential chirp-free characteristics (negative chirp parameter) in electroabsorption modulation using a wide tensile-strained quantum well structure
Authors: Yamanaka Takayuki , Wakita Koichi , Yokoyama Kiyoyuki
Published: July 2002

The possibility of nearly chirp-free electroabsorption (EA) characteristics in intensity modulation at an operating wavelength of 1.55 μm is studied theoretically. The TE-polarized EA spectra, their Kramers–Krönig (K–K) transformed refractive index changes, and the chirp parameters derived under both small-signal and large-signal conditions are calculated including excitonic effect within the framework of the effective mass theory. We investigate on the basis of the simulated EA results how to keep chirp parameters always negative. This can be accomplished by following two successive steps: (1) Widen the well width to increase the Stark shift. This makes it easier for the chirp parameter to turn negative at smaller applied electric field. (2) Apply tensile strain to the wide QW to induce a negative refractive index changes even in the vicinity of zero electric fields, indicating that there exists a desirable condition where the chirp parameter is negative independently of applied fields.
Rapid two-dimensional self-consistent simulation of inductively coupled plasma and comparison with experimental data
Authors: Wise Richard S. , Lymberopoulos Dimitris P. , Economou Demetre J.
Published: July 2002

A methodology has been developed to achieve rapid two-dimensional self-consistent simulation of plasma transport and reaction in an inductively coupled source of arbitrary geometry and with arbitrary plasma and surface chemistries. In this modular finite element fluid simulation the reactor was divided into bulk plasma and sheath. The bulk plasma was assumed quasineutral and the electrons were assumed to be in Boltzmann equilibrium. Separate modules computed the power deposition into the plasma, electron temperature, charged species densities, and neutral species densities. Simulation results agreed favorably with available experimental data, taken in a chlorine plasma in a Gaseous Electronics Conference reference cell, without using any adjustable parameters. Rapid convergence makes the simulation tool especially attractive for technology computer-aided design (TCAD) applications.
Near-infrared contact mode collection near-field optical and normal force microscopy of modulated multiple quantum well lasers
Authors: Ben-Ami U. , Tessler N. , Ben-Ami N. , Nagar R. , Fish G. , Lieberman K. , Eisenstein G. , Lewis A. , Nielsen J. M. , Mo/eller-Larsen A.
Published: July 2002

Contact near-field and far-field imaging of multiple quantum well (MQW) structures emitting at 1.54 μm is reported using bent normal force/near-field optical elements for simultaneous imaging of the light distribution, topography, and modulation of the normal force signal with laser modulation. Excellent registration and correlation of each of these images is reported. Alterations in the distribution of the light emission in going from the near to the far-field is detected in agreement with theoretical deductions. Nonetheless, differences are also noted in this light distribution from standard understandings.
Reduction of internal stress in sputter-deposited films by energetic ion bombardment
Authors: Nowak R. , Horino Y. , Ando Y. , Maruno S.
Published: July 2002

Considerable relaxation of the high internal stresses which arise in HfN thin films during their deposition by a sputtering method has been accomplished through bombarding the films with energetic silicon ions. The internal stresses have been estimated from the measurements of the surface curvature. Our results indicate a relaxation of the internal compressive stresses in the films, which occurs via a transport of the interstitial defects within the thermal spikes created by a post-deposition energetic ion bombardment. The mechanical properties of HfN films before and after the treatment have been studied by depth-sensing indentation technique while the structural analysis has been made using x-ray diffraction, Rutherford backscattering, and Auger electron spectroscopy. Ion bombardment did not affect resistivity of the thin films while improving their plastic properties.
Ultrafast optical sampling pump-probe measurement of exciton spin relaxation in GaAs/AlGaAs quantum wells
Authors: Adachi Satoru , Takeyama Shojiro , Takagi Yoshihiro , Tackeuchi Atsushi , Muto Shunichi
Published: July 2002

Spin dynamics in GaAs/AlGaAs multiple quantum wells at room temperature are studied in subpicosecond to nanosecond time region by using the optical sampling nondegenerate pump-probe technique. Polarization-dependent absorption signals resonant to the light-hole (lh) exciton revealed the subpicosecond spin relaxation time which was several tens of times shorter than that of the heavy-hole (hh) exciton. Resonant pumping to lh and probing at hh exhibited no spin dependence within the time resolution, showing the spin memory being washed out completely during the energy relaxation from lh to hh.
Infrared reflection of GaN and AlGaN thin film heterostructures with AlN buffer layers
Authors: Wetzel C. , Haller E. E. , Amano H. , Akasaki I.
Published: July 2002

Infrared reflection spectroscopy is applied to state-of-the-art thin film heterostructures of group-III nitrides on sapphire and Si substrates. The individual layers of GaN and AlGaN and the AlN buffer layer are identified by their phonon frequencies. Under non-perpendicular incidence of the light, A1(LO) phonon modes are observed in the wurtzite system. The presence of the very thin AlN buffer layer manifests itself in clear features of the AlN phonons. The A1(LO) phonon mode energy is determined in AlxGa1−xN for x≊0.15. Raman spectra confirm our findings.
Corrugated quantum well infrared photodetectors for normal incident light coupling
Authors: Chen C. J. , Choi K. K. , Tidrow M. Z. , Tsui D. C.
Published: July 2002

In this letter, we report a quantum well infrared photodetector geometry for normal incidence light coupling. The new optical coupling scheme utilizes total internal reflection at the sidewalls of triangular wires to create favorable optical polarization for infrared absorption. These wires are created by chemically etching an array of V grooves through the detector active region along a specific crystallographic direction. Experimental results from the initial single color as well as two-color detectors with linear wires and unthinned substrate show efficient light coupling comparable to the standard 45° edge coupling, without the undesirable wavelength dependence or spectral narrowing effect of a conventional grating structure. At the same time, the dark current density is substantially reduced due to the partial material removal. Further improvement is expected by creating a two-dimensional coupling structure with substrate thinning.
All-optical integrated Mach–Zehnder switching due to cascaded nonlinearities
Authors: Baek Y. , Schiek R. , Stegeman G. I. , Krijnen G. , Baumann I. , Sohler W.
Published: July 2002

We demonstrate all-optical switching using the cascaded second order nonlinearity in a fully integrated, asymmetric Mach Zehnder interferometer implemented in lithium niobate channel waveguides. We obtained an 8:1 switching ratio.
Residual strain in GaN epilayers grown on sapphire and (6H)SiC substrates
Authors: Li Wei , Ni Wei-Xin
Published: July 2002

A high-resolution multiple-crystal reflection diffractometer was used to determine the residual strain in GaN epilayers grown on different substrates. Our results show that the GaN epilayers with thickness of about 1 μm are not fully relaxed. The strain situation in a GaN epilayer grown on SiC substrate is totally different from that in GaN layer on sapphire, which are the main reason for the scatter in the recent data on the optical properties of group III nitrides.
Preparation of low dielectric constant F-doped SiO2 films by plasma enhanced chemical vapor deposition
Authors: Woo Lim Sang , Shimogaki Yukihiro , Nakano Yoshiaki , Tada Kunio , Komiyama Hiroshi
Published: July 2002

Signal delays in interlayer films limit the performance of very large scale integrated (VLSI) circuits. Signal delays can be reduced by using interlayer films with low dielectric constants, such as fluorine-doped (F-doped) SiO2 films. We were able to fabricate F-doped SiO2 films with dielectric constants as low as 2.3 and with good step coverage, by adding CF4 to SiH4/N2O plasma-enhanced chemical vapor deposition (PECVD). The reduction of the dielectric constant apparently results from a decrease of the ionic polarization. The improvement of step coverage is due to a decrease of the sticking probability of the film-forming species.
Real-time investigation of In surface segregation in chemical beam epitaxy of In0.5Ga0.5P on GaAs (001)
Authors: Mesrine M. , Massies J. , Deparis C. , Grandjean N. , Vanelle E.
Published: July 2002

Surface segregation processes during the growth of Ga0.5In0.5P/GaAs heterostructures by chemical beam epitaxy have been investigated in real time using reflection high-energy electron diffraction (RHEED). It is shown that In segregation occurs at both GaInP on GaAs and GaAs on GaInP interfaces. Resulting composition profiles are deduced from the RHEED data.
Observation of inverse reactive ion etching lag for silicon dioxide etching in inductively coupled plasmas
Authors: Doemling M. F. , Rueger N. R. , Oehrlein G. S.
Published: July 2002

The slowdown of the oxide etch rate with width of submicrometer structures is known as reactive ion etching (RIE) lag and has been explained by ion shadowing and differential charging of the sidewalls, among other effects [R. A. Gottscho and co-workers, J. Vac. Sci. Technol. B 10, 2133 (1992)]. Here we show for an inductively coupled high density plasma reactor working in the pressure regime from 6 to 20 mTorr that inverse RIE lag is primarily observed, i.e., the etch rates increase as the width of the microstructures decrease. Inverse RIE lag, which was first discussed by Vitkavage et al. [Tegal Plasma Proceedings Symposium, San Francisco, 1991 (unpublished)], may be explained by considering the neutral flux distribution at the structure bottom. The neutral flux has a stronger dependence on the aspect ratio than the ion flux due to its isotropic velocity distribution. The neutral flux distribution has been modeled and is consistent with etching profiles observed at high pressure.
Energy level bending and alignment at the interface between Ca and a phenylene vinylene oligomer
Authors: Park Y. , Choong V. , Ettedgui E. , Gao Y. , Hsieh B. R. , Wehrmeister T. , Müllen K.
Published: July 2002

We have studied the interface formation of a vinylene phenylene oligomer with a Ca substrate using photoemission spectroscopy. The evolution of core and valence spectra during the deposition of the oligomer on Ca has indicated the molecular energy level bending. The total energy level bending was 0.5 eV and the thickness of the level bending region was about 100 Å. We propose an energy level diagram of the oligomer-Ca interface based on the information obtained from the photoemission spectra.
Self-consistent modeling of accumulation layers and tunneling currents through very thin oxides
Authors: Rana Farhan , Tiwari Sandip , Buchanan D. A.
Published: July 2002

Poisson and Schrödinger equations are solved self-consistently for accumulated layers in metal-oxide-semiconductor devices and applied to the calculation of tunneling currents at 300 K and 77 K and extraction of parameters for very thin oxides. Calculations at 300 K show strong agreement with measured tunneling currents and also point out the sources of inaccuracies in extracting thicknesses of oxides by electrical methods such as through measurement of capacitance. Direct tunneling current in thin oxides (1.5–2.0 nm) are shown to achieve larger than 1  A /cm2 current density for applied voltages smaller than 3 V, pointing to possibilities of achieving high endurance injection across thin oxides. Comparison of calculations using a classical approach and self-consistent approach shows fortuitous agreements in tunneling currents despite large differences in the physical models. Appropriate methods for calculating tunneling currents from bound and extended quantum states are also described.
Atomic-scale structure and electronic properties of GaN/GaAs superlattices
Authors: Goldman R. S. , Feenstra R. M. , Briner B. G. , O’Steen M. L. , Hauenstein R. J.
Published: July 2002

We have investigated the atomic-scale structure and electronic properties of GaN/GaAs superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional scanning tunneling microscopy (STM) and spectroscopy, we show that the nitrided layers are laterally inhomogeneous, consisting of groups of atomic-scale defects and larger clusters. Analysis of x-ray diffraction data in terms of fractional area of clusters (determined by STM), reveals a cluster lattice constant similar to bulk GaN. In addition, tunneling spectroscopy on the defects indicates a conduction band state associated with an acceptor level of NAs in GaAs. Therefore, we identify the clusters and defects as nearly pure GaN and NAs, respectively. Together, the results reveal phase segregation in these arsenide/nitride structures, in agreement with the large miscibility gap predicted for GaAsN.
Disordering of the ZnCdSe single quantum well structure by Cd diffusion
Authors: Momose M. , Taike A. , Kawata M. , Gotoh J. , Nakatsuka S.
Published: July 2002

The effects of annealing on a ZnCdSe single quantum well (SQW) structure with ZnCdSSe/ZnSSe superlattice optical guiding layers are investigated. X-ray diffraction and photoluminescence (PL) measurements showed disordering of a ZnCdSSe/ZnSSe superlattice after annealing at about 500 °C. The PL peak energy of the SQW shifted to the higher energy side, and the linewidth narrowed in the sample annealed at 300 °C. Cadmium diffusion was confirmed by secondary ion mass spectrometry. We found that the disordering of the ZnCdSSe/ZnSSe superlattice and the changes in the emissions from the SQW were due to the Cd diffusion.
Carrier dynamics in InP with metallic precipitates
Authors: Marcinkevičius S. , Krotkus A. , Adomavičius R. , Leon R. , Jagadish C.
Published: July 2002

Time-resolved photoluminescence and photoconductivity studies were performed on InP with nanometer-size metallic precipitates. InP samples with precipitates had been prepared by Cu diffusion and subsequent quenching. The carrier lifetimes for minority holes and majority electrons have been found to be of the order of tens of picoseconds and a nanosecond, respectively. Observed reduction of nonequilibrium carrier trapping times and temporal changes of the photoluminescence spectra are attributed to the effects of the built-in electric fields in the space–charge regions around metallic precipitates.
A Si-based light-emitting diode with room-temperature electroluminescence at 1.1 eV
Authors: Tsybeskov L. , Moore K. L. , Duttagupta S. P. , Hirschman K. D. , Hall D. G. , Fauchet P. M.
Published: July 2002

We have achieved room-temperature electroluminescence (EL) at 1.1 eV from a light-emitting diode with an active layer prepared by high-temperature partial oxidation of electrochemically etched crystalline silicon. The EL is easily measurable under a forward bias ≥ 1 V and a current density <10 mA/cm2 and is only weakly temperature dependent from 12 to 300 K. The luminescence is due to Si band edge radiative recombination and originates from large silicon clusters within a nonstoichiometric silicon-rich silicon oxide matrix.
Surface-emitted blue light from [112]-oriented (In,Ga)As/GaAs quantum well edge-emitting lasers
Authors: Ramos P. A. , Towe E.
Published: July 2002

Second-harmonic generation of surface-emitted blue light has been achieved in (In,Ga)As/GaAs quantum well edge-emitting lasers. The blue light is generated by the nonlinear interaction of the internal fundamental fields of a continuously pumped laser. These lasers exhibit room temperature threshold current densities as low as 200 A/cm2 and produce about 2.6 nW of blue light for 9.8 mW of fundamental power. The peak emission of the blue light is at 487 nm and the spectral spread is about 1.7 nm.
Photocurrent decay in n-type GaN thin films
Authors: Qiu C. H. , Melton W. , Leksono M. W. , Pankove J. I. , Keller B. P. , DenBaars S. P.
Published: July 2002

Minority carrier relaxation in undoped n-type gallium nitride (GaN) thin films was studied by photoconductivity decay measurements in the time span from 50 ns to 50 s. The decay is characterized by an initial exponential decay followed by a quasi-power-law decay for decades of time longer than 1 μs. The decay rate is insensitive to the electron concentration and is only slightly temperature dependent. The results are discussed in terms of hole trapping at gap states and subsequent recombination. The studies revealed that the dominant recombination mechanism is very different from recombination through dislocations and that the valence band-tail states in n-type GaN seem to be negatively charged.
Comparison of partially relaxed InGaAs/GaAs based high performance phototransistors
Authors: Ghisoni M. , Sjölund O. , Larsson A. , Wang S. M.
Published: July 2002

We report on heterojunction phototransistors (HPTs) operating at GaAs substrate transparent wavelengths beyond 900 nm, utilizing a strained InGaAs quantum well based absorbing region. High performances have been measured with responsivities of ≊80 and 200 A/W at 10 and 50 μW, respectively. The results correspond to electrical current gains of up to 3000 for currents of ≊10 mA, the best reported results for such phototransistor structures. The effect of strain relaxation on device performance is examined, and it is seen that it can cause a degradation both in terms of the transistor and photodiode characteristics of the HPT.
A voltage-tunable multicolor triple-coupled InGaAs/GaAs/AlGaAs quantum-well infrared photodetector for 8–12 μm detection
Authors: Chiang Jung-Chi , Li Sheng S. , Tidrow M. Z. , Ho P. , Tsai M. , Lee C. P.
Published: July 2002

A voltage-tunable multicolor triple-coupled quantum-well infrared photodetector (TC-QWIP) has been developed for 8–12 μm detection. The TC-QWIP consists of three coupled quantum wells formed by an enlarged Si-doped InxGa1−xAs quantum well and two undoped GaAs quantum wells separated by two thin AlyGa1−yAs barriers. Two TC-QWIP structures with varying indium and aluminum compositions were designed and demonstrated. Due to the strong coupling effect of the asymmetrical quantum wells, three bound states (E1, E2, E3) are formed inside the quantum wells of the TC-QWIP. The main detection peak wavelength is due to E1→E3 bound states transition for both devices, while two secondary detection peaks due to E1→E2 and E1→Ec continuum states transitions under different biases were also observed. In addition, a strong quantum-confined Stark shift effect for the E1→E3 transition was observed in the wavelength range of 8.2–9.1 and 10.8–11.5 μm for QWIP-A and QWIP-B, respectively; both devices exhibit a linear dependence of detection peak wavelength on the applied bias voltage. A spectral responsivity of Ri=0.05 A/W and background limited performance (BLIP) detectivity DBLIP*=6.1×109 cm√Hz/W were obtained at Vb=5 V, λp=8.6 μm, and TBLIP=66 K for QWIP-A, while Ri=0.33 A/W and DBLIP* =1.63×1010 cm√Hz/W at Vb=4 V, λp=11.2 μm, and TBLIP=50 K were obtained for QWIP-B.
Thin film channel waveguides fabricated in metalorganic chemical vapor deposition grown BaTiO3 on MgO
Authors: Gill D. M. , Block B. A. , Conrad C. W. , Wessels B. W. , Ho S. T.
Published: July 2002

We report on the fabrication of channel waveguides in epitaxial grown BaTiO3 layers on MgO. Layers were prepared by metalorganic chemical vapor deposition. Ridge waveguides with ridge heights ranging from 15 to 200 nm were fabricated in a 0.2-μm-thick film. Single mode waveguide throughput, scattering loss, and mode profiles are reported. Coating waveguides with spin on glass significantly increase waveguide throughput. Throughputs of up to 10.4% were measured in 15 nm ridge waveguides which were 2.85 mm long and coated with spin on glass. Waveguide throughput is found to increase significantly with an increase in wavelength from 1.06 to 1.55 μm.
Asymmetric GaAs/AlGaAs T wires with large confinement energies
Authors: Gislason H. , Langbein W. , Hvam J. M.
Published: July 2002

We report on the design and growth of asymmetric T-shaped quantum wires with large one-dimensional confinement energies. Prior to growth, the optimal structure for a given (110) well width is determined by a calculation. The structures are made by molecular beam epitaxy cleaved edge overgrowth. We demonstrate a confinement of 54 meV in an experimental structure consisting of a narrow (110) oriented GaAs/Al0.3Ga0.7As quantum well overgrown on much wider (001) oriented Al0.14Ga0.86As/Al0.3Ga0.7As wells.
Imaging and magnetometry of switching in nanometer-scale iron particles
Authors: Gider S. , Shi J. , Awschalom D. D. , Hopkins P. F. , Campman K. L. , Gossard A. C. , Kent A. D. , von Molnár S.
Published: July 2002

The reversal mechanisms in arrays of nanometer-scale (<40 nm diameter) iron particles are studied by low-temperature Hall magnetometry and room-temperature magnetic force microscopy. Rotation of the net array magnetization at low temperatures (20 K) occurs by both reversible and irreversible modes, the latter revealed by Barkhausen jumps. Spatially resolved measurements at room temperature show the particles to be single domain with remanence and coercivity indicating they are not superparamagnetic. Individual particles are observed to switch irreversibly over a small field range (<10 Oe) between preferred magnetic directions parallel to the growth direction of the particles. Scaling of the arrays offers the possibility of magnetic storage at the 45 Gbit/in.2 level, nearly 50 times greater than current technology.
Measurements of density fluctuations by modulation spectroscopy
Authors: Dharamsi A. N. , Bullock A. M.
Published: July 2002

Theoretical and experimental results describing the application of wavelength modulation spectroscopy to density fluctuations are given. The effects of concurrent amplitude modulation, which often occurs when such experiments are performed with diode lasers are accounted for. It is shown that the characteristics of the signal magnitude at line center as a function of density include the expected increase with density, n, in the Doppler regime. In the effective collision broadened regime the signal magnitude at line center falls approximately as n−N, where N is the order of the harmonic at which detection is performed. This result incorporates the well-known result for direct absorption (N=0) in which the signal magnitude at line center stays constant while the linewidth increases in the collision broadened regime. It is shown that the sensitivity to density fluctuations measured by wavelength modulation spectroscopy around any ambient value depends strongly on the order of the detection harmonic employed, and that in many instances this sensitivity can be increased by using detection harmonics of order greater than the commonly used second order.
Flux penetration in bicrystal-substrate thin-film YBa2Cu3O7−δ Josephson junctions
Authors: Hinaus B. M. , Redwing R. D. , Rzchowski M. S.
Published: July 2002

We experimentally investigate the effect of flux penetration into the electrodes of a thin-film YBa2Cu3O7−δ grain boundary Josephson junction using the field-dependent critical current as a probe. Above a temperature-dependent threshold field for flux trapping we observe that the maximum critical current Icmax is reduced, and occurs at an applied field Hpeak shifted from zero. The critical current also has an increasingly complex field-dependent structure. Despite this complexity, we experimentally find that Icmax follows a simple power law Hpeak−0.30. We present a model that predicts Icmax∝Hpeak−1/3 due to fluxons trapped in the electrodes.
Atomic force microscope study of photo-polymerized and photo-dimerized epitaxial C60 films
Authors: Hassanien A. , Gasperič J. , Demsar J. , Muševič I. , Mihailovic D.
Published: July 2002

We have used an atomic force microscope to analyze the surface of C60 thin films, which have been grown epitaxially on a mica surface and illuminated with a 514.5 nm laser light at different temperatures. Two regimes of light-induced polymerization are observed. If the illumination temperature Tp is lower than 320 K, the illuminated surface shows polymer chains typically six molecules long with an intermolecular distance of 9.2±0.1 Å . Because of the strain associated with the shorter inter-C60 distance in the polymer compared to the bulk, the surface is buckled with a period of ∼100 Å and amplitude of ∼5 Å resulting in a characteristic herringbone three-dimensional structure. For films, illuminated above 350 K, the surface shows primarily dimers and trimers with an unusually short inter-C60 distance of 8.8±0.1 Å, this being the shortest interbuckyball distance reported so far. We also find large changes in the adhesive forces on the polymerized films compared to unpolymerized ones, suggesting that the polymer is substantially more hydrophyllic than normal C60.
Electron beam induced reliefs in chalcogenide glasses
Authors: Tanaka Keiji
Published: July 2002

Surface deformations appear in chalcogenide glasses when irradiated by scanned or pulsed electron beams accelerated at 10–30 kV. The deformation consists of a central expansion which accompanies peripheral depressions, and the scale is typically micrometer. The deformation seems to be produced by electrostatic force and electro-induced fluidity.
Repetition rate dependence of gray-tracking in KTiOPO4 during second-harmonic generation at 532 nm
Authors: Fève J. P. , Boulanger B. , Marnier G. , Albrecht H.
Published: July 2002

The aim of this work is to study gray tracking during type II second-harmonic-generation 1064→532 nm in halide flux grown KTiOPO4 crystals. The repetition rate of the laser varies from 1 to 20 kHz. We experimentally demonstrate that the gray-tracking threshold, expressed by the harmonic peak power density, is a decreasing exponential function of the Q-switch frequency. The corresponding 532 nm average power density, however, remains constant.
Effects of phosphorus doping on boron transient enhanced diffusion in silicon
Authors: Huang M. B. , Simpson T. W. , Mitchell I. V.
Published: July 2002

The effects of phosphorus predoping on transient enhanced diffusion (TED) of boron, ion implanted into silicon, were studied using secondary ion mass spectroscopy (SIMS). Boron ions of 40 keV energy were implanted to a dose of 3×1014 cm−2 into Si(100), which had been uniformly predoped with P at atomic concentrations varying between ∼3×1019 and ∼1×1020 cm−3. The effective boron diffusivity in the TED distribution and the amount of immobile boron are extracted from SIMS profiles. Our results show that both decrease with increasing P doping level, saturating beyond a P-doping level of ∼6×1019 cm−3 after the low temperature anneal. The implications of these results for different models of modified TED behavior of boron are discussed.
A nondiamond phase at the interface between oriented diamond and Si(100) observed by confocal Raman spectroscopy
Authors: Nishitani-Gamo Mikka , Ando Toshihiro , Yamamoto Kazuo , Watanabe Kenji , Dennig Paul A. , Sato Yoichiro , Sekita Masami
Published: July 2002

We have characterized bias-assisted chemical vapor deposition diamond using the nondestructive technique of confocal Raman spectroscopy to investigate the interfacial structures and the variation in structure and quality with depth. The spectral depth profiles of oriented diamond showed that a band centered at 1210 cm−1 and the diamond peak at 1332 cm−1 coexisted at the interface between the oriented diamond and Si substrate. The relative intensity of the 1210 cm−1 band compared to that of the diamond peak varied with depth. The intensity of the band decreased and that of the diamond peak increased from the interface to the diamond surface. The quality of the oriented diamond improved with the growth time. In contrast, for the case of a randomly oriented diamond, a band centered at 1550 cm−1 was observed, the diamond peak was shifted between −6 and 6 cm−1 from the single crystal diamond peak at 1332.5 cm−1, and the spectral profile did not change with depth. No band at 1210 cm−1 was seen in this case. We conclude that a nondiamond phase with a Raman band at 1210 cm−1 and a diamond phase coexist at the interface between the oriented diamond and the Si substrate, and that this 1210 cm−1 phase is therefore a characteristic feature of the nature of the diamond-substrate bonding in oriented films.