bluuebunny/crossref_metadata_2025 huggingface dataset:
Low energy carbon ion bombardment on indium phosphide and its implications for alkane-based reactive ion etching
Authors: Meharg P. F. A. , Ogryzlo E. A. , Bello I. , Lau W. M.
Published: July 2002

Carbon ion bombardment in the energy range of 20–500 eV, which occurs in reactive ion etching using alkanes, has been performed on InP with a mass-separated carbon ion beam in an ultrahigh vacuum chamber. The sample structure consisted of an ultrathin, epitaxial InP (40 Å) layer on InGaAs. In situ polar-angle dependent x-ray photoelectron spectroscopy was used to measure sputtering, deposition on, and damage of the InP layer, and to determine if any damage had propagated to the underlying InGaAs. An investigation of damage removal was also carried out by in situ thermal annealing, and by exposure to ultraviolet radiation and ozone. It was found that carbon ion bombardment led to carbon incorporation and to a gross change in the surface composition of the semiconductor. A complex, heterogeneous In-P-C alloy was formed. Sputtering of InP and preferential removal of P were also evident. Further carbon ion bombardment resulted in the deposition of an amorphous carbon residue. The degree of residual damage increased with bombarding energies. At 20 eV, the damage was confined to the 40 Å InP layer, but at 100 eV, significant broadening of the As 3d peak was observed, which suggests that the underlying InGaAs layer was also damaged at this higher energy. Bombardment with 500 eV ions caused severe damage to both the InP and InGaAs layers. Heating of the irradiated samples at 350 °C in vacuum was ineffective in annealing the damage, although a reduction of the surface Fermi level position from 0.95 to 0.75 eV (relative to the valence band maximum) was measured for 20 eV carbon ion bombarded samples. This is attributed to the acceptor behavior of the incorporated carbon. Exposure to ultraviolet light/ozone was also found to be ineffective in removing the carbon residue.
Hysteresis of the work function of Co(0001) surface resulting from an allotropic transformation
Authors: Saito S. , Takeda K. , Soumura T. , Ohki M. , Tani T. , Maeda T.
Published: July 2002

The influence of the crystallographic phase transformation on the work function was studied on a Co(0001) surface by a precise measurement of the contact potential difference. The characteristic hysteresis of the work function due to the hcp⇄fcc allotropic transformation was found. The work function changes abruptly by about 2 meV with the phase transformation while decreasing monotonically with temperature except in the transformation range. The contributions of the surface dipole barrier and the chemical potential of electrons to the work function are discussed from the point of view of cellular approximation.
Epitaxial growth of YBa2Cu3O7−x thin films on Si(100) with zirconia buffers of varying crystalline quality and structure
Authors: Lubig A. , Buchal Ch. , Schubert J. , Copetti C. , Guggi D. , Jia C. L. , Stritzker B.
Published: July 2002

Thin epitaxial films of monoclinic pure and cubic yttria-stabilized (YSZ) ZrO2 were deposited onto Si(100) by electron-beam evaporation. The degree of crystalline perfection was controlled by the growth temperature. Epitaxial YBa2Cu3O7−x films were grown on these buffer layers by KrF excimer laser ablation. Optimum crystalline and electrical quality, characterized by a transition temperature Tc0 of 86–89 K, a critical current density jc of 106 A/cm2 at 77 K, and a channeling minimum yield of 12% was obtained on YSZ buffers showing a minimum yield of 7%. Even a 14-nm-thick YSZ buffer enabled the growth of an YBa2Cu3O7−x film with Tc0 of 86 K and a minimum yield of 12%. With decreasing quality of the YSZ buffer layers the crystalline quality of the superconductor also decreased. The disorder in the YBa2Cu3O7−x films, however, increased more slowly than in the buffer layers, so that even on an amorphous buffer the YBa2Cu3O7−x exhibited a pronounced texture with a minimum yield of 72%. The comparatively rough surface of the monoclinic pure ZrO2 severely hampered the c-axis alignment of the YBa2Cu3O7−x, resulting in superconductor films of inferior quality.
Abnormal Jc changes against temperature of the Bi1.6Pb0.4Sr2Ca2Cu3Ox
Authors: Nishi Yoshitake , Nozaki Kazuo , Ichimura Shinichi
Published: July 2002

The temperature dependence of the superconducting critical current density (Jc) is investigated for the high Tc Bi1.6Pb0.4Sr2Ca2Cu3Ox. An abnormal Jc change is found from 50 to 80 K.
Positron annihilation studies in the field induced depletion regions of metal-oxide-semiconductor structures
Authors: Asoka-Kumar P. , Leung T. C. , Lynn K. G. , Nielsen B. , Forcier M. P. , Weinberg Z. A. , Rubloff G. W.
Published: July 2002

The centroid shifts of positron annihilation spectra are reported from the depletion regions of metal-oxide-semiconductor (MOS) capacitors at room temperature and at 35 K. The centroid shift measurement can be explained using the variation of the electric field strength and depletion layer thickness as a function of the applied gate bias. An estimate for the relevant MOS quantities is obtained by fitting the centroid shift versus beam energy data with a steady-state diffusion-annihilation equation and a derivative-gaussian positron implantation profile. Inadequacy of the present analysis scheme is evident from the derived quantities and alternate methods are required for better predictions.
Orientational optomechanical media for microwave applications
Authors: Rogovin D. , Shen T. P.
Published: July 2002

We show that three-dimensional arrays of electrically small, anisotropic particles are excellent media for wave-mixing processes at microwave and millimeter wavelengths. Electrostrictive torques rotate the particles in such a way as to form orientational index gratings that can control the attributes of microwave or millimeter wave radiation. Theory asserts that this medium is highly favorable for phase conjugation via quasidegenerate four-wave mixing at these wavelengths.
Resonator amplification of microwave emission from a relativistic beam-plasma system
Authors: Benford Gregory , Baranga A. Ben-Amar
Published: July 2002

Electromagnetic emission produced by a propagating electron beam in a cylindrical drift chamber can be amplified by axially reflecting screens. Radiation appears at the first and second plasma harmonics with linewidths ∼0.1 νp. Amplification scales with νp2 and lags electron-beam voltage by several hundred nanoseconds, implying that electrostatic waves moving at the electron thermal speed must traverse the resonator before amplification begins. Rotating the reflectors beyond 30° lessens amplification, suggesting a broad reflection property.
Scanning tunneling microscope-promoted growth of nanometer-scale, uniform gold stripes on reconstructed Au(111) surfaces
Authors: Wang Zhouhang , Moskovits Martin
Published: July 2002

Scanning the scanning tunneling microscopy (STM) tip on a Au(111) (22±1)×√3 reconstructed surface causes monatomic stripes to grow preferentially on the fcc portions of the surface. Stripes several 100 nm’s in length, ∼4 nm wide, and separated by spaces ranging from 2 to ∼4 nm (the hcp regions of the reconstructed surface) can be grown. Stripe formation only takes place when the scan direction corresponds, more or less, with the [1,1,−2] primary direction of the reconstruction. Growth occurs much more rapidly than can be accounted for by diffusion alone, leading to the conclusion that the STM tip transports gold, previously picked up from other portions of the surface, to the growing ends of the stripes. Stripes grown in this way may serve as convenient templates for subsequent growth of quantum wire structures by molecular beam epitaxy.
Characterization of GaAs/AlxGa1−xAs multiple quantum well infrared detector structures using photoreflectance
Authors: Dafesh P. A.
Published: July 2002

Photoreflectance (PR) spectroscopy at 295 K was used to characterize GaAs/AlxGa1−xAs multiple quantum well (MQW) 10 μm infrared detector structures. From PR measurements of a representative structure, GaAs/Al0.20Ga0.80As, at different positions, the aluminum fractions were found to vary negligibly across the sample, while the variation in band-to-band MQW transition energies and E0 alloy linewidths was appreciable. The measured interband transitions of several structures designed for x=0.28 were then compared to the results of envelope-function calculations. Good agreement was found between measured and theoretical interband transitions for both heavy and light hole-to-conduction subbands. Other features observed in the spectra may be attributed to spin-orbit splittings as well as n=2 subband to subband transitions. The dominant features in the spectra were used to access well width, composition, and peak wavelengths for the MQW detector structures. Additionally, an anomalously narrow linewidth (<9 meV) was observed in the room temperature E0 spectrum of an undoped AlxGa1−xAs reference sample grown on the same system as the MQW samples. The corresponding doped sample was observed to severely broaden.
Limitations on models describing the kinetics of light-induced defect creation in hydrogenated amorphous silicon
Authors: Bube Richard H. , Redfield David
Published: July 2002

Two quite different models have indicated their ability to describe the experimental data for the kinetics of light-induced defect creation in hydrogenated amorphous silicon at or quite near room temperature. These have been called the ‘‘t1/3’’ model and the ‘‘stretched exponential’’ model. When measurements are made at different temperatures, however, the experimental data can still be described completely by the stretched exponential model with a change in the value of the stretch parameter, which may reasonably be a function of temperature, but they no longer follow a t1/3 dependence. Since the t1/3 dependence is based on a particular physical mechanism for defect creation, it is concluded that this mechanism is not applicable to hydrogenated amorphous silicon.
Whispering gallery modes along a bent channel waveguide
Authors: Hayata K. , Tsuji Y. , Koshiba M.
Published: July 2002

Whispering gallery modes (WGMs) that propagate along a bent dielectric waveguide with two-dimensional field confinement are analyzed with a self consistent field approximation (weighted index theory). WGMs are quasi-modes (leaky modes) with their field shape distorted toward the outermost boundary of a bend. Numerical results are shown for the modes in an optical embedded channel waveguide whose center of curvature is on an arbitrary location. Calculation of the leakage loss is included as well.
Thermally induced structural relaxation in amorphous rare-earth–transition metal thin films
Authors: Bartholomeusz Brian J. , Kopalidis Peter M. , Stinson Douglas G.
Published: July 2002

In the course of practical usage, amorphous optical data storage media are subject to multiple write-erase cycles. The laser heating that this entails can result in an appreciable change in material properties including those relevant to data recording and retention. Media lifetime predictions based on conventional Arrhenian considerations have, in the past, proven inaccurate. We simulated the thermally induced structural relaxation of rare-earth–transition metal media assuming the existence of a spectrum of activated processes and provided a rationale for some experimental observations within this framework.
Warm and hot hole drift velocity in GaAs studied by Monte Carlo simulation
Authors: Brudevoll T. , Lund B. , Fjeldly T. A.
Published: July 2002

We have studied hole mobilities and drift velocities in undoped GaAs at 77 and 300 K using the Monte Carlo method. Two different sets of valence band parameters were used (V1: A=7.98, B=5.16, C=6.56; V2: A=7.65, B=4.82, C=7.7). The results show that the low-field mobility is sensitively dependent on the particular choice of valence band parameters. The low-field mobilities obtained were 440 cm2/V s(V1) and 330 cm2/V s(V2) at 300 K, and 17 150 cm2/V s(V1) and 11 400 cm2/V s(V2) at 77 K. The warm hole transport coefficients β0 and γ0 were extracted from the drift velocity data. At 77 K, β0=−7×10−9 m2/V2 and γ0 was estimated to be 2×10−10 m2/V2(V1). At 300 K the corresponding estimated values were −2×10−13 m2/V2 and 5×10−14 m2/V2, respectively. The warm hole region is limited to E<0.04 kV/cm at 77 K and to E<10 kV/cm at 300 K. Anisotropy in the drift velocity is negligible in the warm hole region and relatively small at higher electric fields. Complete velocity saturation was not observed for the electric fields considered here (E<60 kV/cm).
Dielectric constant of ice at 26.5–40 GHz
Authors: Koh Gary
Published: July 2002

The complex dielectric constant, ε=ε′+iε″, of ice at 26.5–40 GHz was determined using free-space measurement technique. A network analyzer-based system was used to measure the phase velocity and attenuation of a synthesized pulse propagating in bubble-free ice which was grown from distilled de-ionized water. Based on the phase velocity measurement, ε′ was determined to be 3.155±0.005 and virtually independent of frequency. The loss factor in ice was observed to be frequency dependent so that ε″ increased from approximately 0.002 at the lower frequencies to 0.004 at the higher frequencies. No temperature dependence of ε′ and ε″ was observed at ice temperatures of −2.5 and −15 °C.
Morphological stability of growing particles and maximum growth rate principle
Authors: Liu Zi-Kui
Published: July 2002

The maximum growth rate (MGR) principle is discussed in connection with the morphological stability of growing particles. It is suggested that the MGR principle may be applicable to the growth of a platelike particle when there is no sidebranching. The suggestion is based on a stability analysis indicating that MGR principle would hold at least approximately unless the supersaturation is too large. For large supercooling, the stability analysis breaks down, but the MGR principle still presents reasonable values.
Damage generation and annealing in Ga+ implanted GaAs/(Ga,Al)As quantum wells
Authors: Vieu C. , Schneider M. , Launois H. , Descouts B.
Published: July 2002

The damage generation and its annealing behavior in GaAs/(Ga,Al)As quantum wells after Ga+ implantation at room temperature is investigated by transmission electron microscopy. Its relations with the disordering of the layered structures is explored by low temperature photoluminescence spectroscopy. We find that at low doses the intermixing is activated during annealing through the diffusion of point defects, while at high doses the disordering is produced by cascade mixing. A strong segregation of the defects in the GaAs layers is observed. During implantation of a GaAs/Ga0.65Al0.35As single quantum well, the GaAs quantum-well layer accumulates damage more rapidly than the Ga0.65Al0.35As barriers. At high dose this leads to a differential amorphization of the two compounds. Using the critical damage energy density model, the amorphization thresholds of GaAs and Ga0.65Al0.35As are estimated around 26 eV/molecule and 960 eV/molecule, respectively, in our conditions of implantation. The influence of barriers in AlAs is studied. AlAs is more resistant to amorphization than Ga0.65Al0.35As and delays the amorphization of the GaAs quantum-well layer. This effect is attributed to the in situ recombination of point defects during irradiation in AlAs material as well as to some intermixing of the layers. After annealing it appears that defects can easily diffuse in Al rich materials but are trapped in GaAs. It is concluded that the ability of AlAs to prevent damage accumulation in GaAs quantum wells and to drain off the defects during annealing can be exploited for device applications. The general trends for an optimized GaAs/GaAlAs quantum well dedicated to mixing applications such as the fabrication of quantum-well wires by masked implantation is finally proposed.
Electron acoustic signal of metallic layers over a semiconductor substrate
Authors: Bresse J. F.
Published: July 2002

Calculations have been made for the electron acoustic signal in the case of one and two metallic layers deposited over a semiconductor substrate. The temperature repartition as a function of the depth has been determined by taking into account the absorbed power in the metallic layers and the substrate. We have considered strain-free and constrained layers. Experimental results have been obtained for a single metallic layer (Au, W, Pd, Mo, Mn, Ti) deposited over GaAs and for Au-Ti contacts. Comparison between experiments and calculations allows us to determine whether the layers are constrained or not.
The increase in the in-plane acceleration sensitivity of the plano-convex resonator resulting from its thickness asymmetry
Authors: Tiersten H. F. , Zhou Y. S.
Published: July 2002

It has recently been shown that the in-plane acceleration sensitivity of contoured quartz resonators vanishes for a perfectly symmetric combined resonator plus support system. This indicates that a biconvex resonator will have lower resultant in-plane acceleration sensitivity than a plano-convex one because of its inherent additional symmetry. Since a plano-convex resonator is easier to fabricate, an analysis of the degradation in the in-plane acceleration sensitivity that arises from the contour being on one side only is performed. The calculations show that the in-plane sensitivity of the plano-convex resonator increases with decreasing radius of curvature and that the magnitude ranges over a few parts in 1012 per g.
Dynamics of the detonation products of lead azide. I. Hydrodynamics
Authors: Tzuk Y. , Bar I. , Ben-Porat T. , Rosenwaks S.
Published: July 2002

The present paper is the first of a series reporting on a comprehensive study of the hydrodynamics, kinetics, and spectroscopy of the transient species formed following the detonation of lead azide (LA). The spatial and temporal behavior of the detonation products expanding into vacuum is obtained via high-speed framing photography, transmission of a HeNe laser beam, and chemiluminescence from excited Pb atoms. The photography reveals that following the initiation of LA the products form an expanding, bell-shaped cloud. The HeNe beam is attenuated when the cloud of products traverses its route. The attenuation starts 4–15 μs after initiation and depends on the height of the beam above the LA sample. The chemiluminescence consists of two components: the first, appearing 1–2 μs after initiation, is obtained from excited products formed by the detonation near the surface of the sample, while the second, starting 2–14 μs after initiation, originates from the expanding cloud of products.

The intensity and the temporal behavior of the second component of chemiluminescence depend on the distance to a barrier placed above the LA sample. The cloud contains gaseous products and solid particles which propagate perpendicular to the LA surface with a maximum velocity of 4.48±0.10 km/s and 3.78±0.18 km/s, respectively. To reproduce the experimental results, two alternative hydrodynamic models are applied: Stanyukovich’s model [K. P. Stanyukovich, Unsteady Motion of Continuous Media (Pergamon, London, 1960), pp. 498–501] for isentropic expansion and London and Rosen’s model [R. A. London and M. D. Rosen, Phys. Fluids 29, 3813 (1986)] for exploding foil. The latter model is preferred and when incorporating Beer’s law and Mie’s theory [C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light in Small Particles (Wiley, New York, 1983), p. 77] it reproduces very well both the temporal behavior of the second component of chemiluminescence and the attenuation of the HeNe beam and suggests that lead particles with radius of 0.05–0.15 μm are involved in the attenuation. The model also provides an estimate of the composition of the product cloud and of the density of the gaseous and solid species as a function of time and distance from the LA sample.
Strong magnetoresistance reduction at the coercive-field crossover of two uncoupled magnetic films
Authors: Vélu E. , Dupas C. , Nabhan W. , Trigui F. , Renard J. P. , Renard D.
Published: July 2002

The variation of the magnetoresistance (MR) with temperature T in the range 1.4–300 K has been studied in three dissymmetric structures Au/M1/Au/M2/Au where M1 and M2 are two ultrathin films of either Co or Fe with perpendicular anisotropy. In the Fe sample, the low-temperature MR is 7.6%, showing for the first time the spin-valve effect in this system. In all samples, the variation of the coercive fields Hc1 and Hc2 vs T exhibits a crossover leading to a reduction by a factor one-half of the MR at the same temperature. The fit of the MR curves versus T in the frame of the Camley–Barnas model leads to the values of the electron mean-free-path and spin-dependent transmission coefficients at the interfaces in these samples.
Effect of hydrogenation on deep-level traps in InP on GaAs
Authors: Chen Y. F. , Sung K. C. , Chen W. K. , Lue Y. S.
Published: July 2002

Deep levels in the heteroepitaxial undoped InP layers grown directly on GaAs substrates by organometallic vapor-phase epitaxy have been investigated by deep-level transient spectroscopy. Two electron traps have been observed with activation energies of 0.4 and 0.57 eV in the temperature range between 150 and 310 K. The trap concentrations of these levels are in the order of 1015 cm−3 for samples with a carrier concentration of 1016 cm−3. Incorporation of atomic hydrogen into the InP layer by a photochemical vapor deposition system produces substantial decreases of the trap concentrations to 1014 cm−3 and of the carrier concentration to 1015 cm−3.
High-frequency properties of superconducting Y-Ba-Cu-oxide thin films
Authors: Ramakrishnan E. S. , Su Ming-Yih , Howng Wei-Yean
Published: July 2002

rf and microwave properties of superconducting YBa2Cu3O7−x thin films were measured and analyzed using a coplanar resonator structure. The films were developed by sequential electron-beam evaporation of the metals followed by postanneal processing. dc properties of the films were obtained from resistance-temperature and current-voltage measurements to evaluate the transition temperature and current densities. High-frequency properties were measured from 70 to 10 K and in the frequency range 1–3 GHz to determine the film characteristics as compared to pure copper films on the same substrates.
Growth and characterization of GaAlAs/GaAs and GaInAs/InP structures: The effect of a pulse metalorganic flow
Authors: Sacilotti M. , Horiuchi L. , Decobert J. , Brasil M. J. , Cardoso L. P. , Ossart P. , Ganière J. D.
Published: July 2002

GaAlAs/GaAs and GaInAs/InP thick layers, single and multiple quantum wells were grown by atmospheric pressure metalorganic vapor phase epitaxy. Auger electron spectroscopy, wedge transmission electron microscopy, x-ray diffraction, low-temperature photoluminescence, and scanning electron microscopy were used to analyze the crystal quality. These analysis techniques show that layers grown using high vapor pressure metalorganic sources present fluctuations in the ternary alloy composition. We propose that these fluctuations are due to the pulse character of the high vapor pressure metalorganic flow. Bubbling experiments were performed to show the relationship between ternary layer composition fluctuation and the pulse character of the metalorganic flow. High vapor pressure metalorganic source like trimethylgallium presents tens of Angströms growth rate per pulse or bubble whereas a low vapor pressure source like triethylgallium presents few Angströms growth rate per bubble.
Structure, magnetization, and thermal stability of (100) FeCu films deposited on Pd/Cu/Si(100)
Authors: Chang Chin-An
Published: July 2002

(100)-oriented FeCu films, containing 80 and 50 at. % Fe, have been deposited on (100) Si using (100) Pd/Cu seed layers. Heating of the samples helps identify the structures of the FeCu films, especially the one with 50 at. % Fe. The FeCu(50/50) film shows a structure with possibly two phases: one with a lattice spacing close to that of (100) Fe, and one to that of (100) Cu, henceforth assigned to the Fe- and Cu-stabilized FeCu phases, respectively. The FeCu(80/20) film shows only one phase, with a lattice spacing close to that of (100) Fe. Ferromagnetic characteristics are detected up to an anneal of 30 min at 600 °C for the FeCu(80/20) films, with a reduced saturation magnetization above 400 °C. For the FeCu(50/50) films, their ferromagnetic characteristics remain little changed up to 300 °C, with reduced saturation magnetization at 400 °C, and disappear completely after an anneal at 500 °C. The results are compared with those containing elemental Fe layers deposited on different metal seeds, and the reaction mechanisms of the present structures are discussed.
Time-resolved photoluminescence in anodically etched silicon
Authors: Pearsall T. P. , Adams Jeff C. , Wu Jen E. , Nosho Brett Z. , Aw Chak , Patton J. C.
Published: July 2002

We have studied the time response of visible, red photoluminescence in anodically etched p− silicon films. The principal features of our measurements are luminescence with two wavelength components, and a temperature dependent rise time of 24 μs and a decay time of 47 μs at room temperature. Results from our samples show some similarities to characteristics measured in amorphous Si, suggesting that some low-dimensional or disordered Si phase may play a role in the observation of visible light from this new photonic material.
The influence of ion beam mixed TiSi2 layers on reverse characteristics of diodes
Authors: Dehm C. , Burte E. P. , Gyulai J. , Zimmermann H.
Published: July 2002

Diodes with shallow p+n junctions were contacted with titanium silicide films which were formed by ion beam mixing with germanium. The leakage current of these diodes was observed to be dominated by a generation mechanism in the space charge layer. Deep level transient spectroscopy and secondary-ion mass spectroscopy measurements revealed that ion beam mixing with heavy ions leads to recoil implantation of titanium atoms into the silicon substrate. The temperature and reverse bias behavior of the leakage current could be consistently explained by Shockley–Read–Hall generation mechanism [Phys. Rev. 87, 385, 387 (1952)] and by Poole-Frenkel barrier lowering [Phys. Rev. 54, 647 (1938)] of the double donor level Ti+/++ at Ev+0.2 eV.4
On the transmission coefficient of graded composition GaAs/AlxGa1−xAs heterojunctions under an electric field
Authors: Freire Valder N. , Farias Gil A. , Auto Margarida M.
Published: July 2002

The effect of an electric field on the electrons transmission across graded composition GaAs/AlxGa1−xAs heterojunctions is presented. Analytical expressions for the transmission coefficient were obtained by solving the Schrödinger equation in all space. We assume a heterointerface region of width l, with a linear growth of aluminum molar fraction. An increase in the interfacial heterojunction width is responsible for an enhancement and a shift of the transmission coefficient towards low energies. In contrast, an increase of the applied electric field intensity shifts the nonabrupt transmission coefficient towards high energies.
Contactless characterization of the Si+ ion-implanted semi-insulating GaAs
Authors: Ito Akira , Usami Akira , Wada Takao
Published: July 2002

Si+ ion-implanted semi-insulating GaAs substrates have been characterized by the contactless measurement of the optically injected carrier concentration using the reflectance microwave probe method. The signal intensity decreases with dosage because of implantation damage. After rapid thermal annealing (RTA), the signal intensity becomes larger than those of the as-implanted samples. However, the signal intensity decreases with dosage even after RTA. From observation of the dosage dependence, it is found that the implantation damage is not fully annealed after RTA. The measurement with the He-Ne laser is sensitive enough to evaluate the implantation damage because most excess carriers are injected near the surface. It is found that this method is effective in evaluating the condition of the ion-implanted GaAs substrates.
Comment on ‘‘Infrared study of the Si-H stretching band in a-SiC:H’’ [J. Appl. Phys. 69, 7805 (1991)]
Authors: Sacher E.
Published: July 2002

Contrary to the conclusions of Koropecki, Alvarez, and Arce [J. Appl. Phys. 69, 7805 (1991)], it is shown that the Si-Hn peak positions in a-SiC:H are influenced by inductive effects.
Reply to ‘‘Comment on ‘Infrared study of the Si-H stretching band in a-SiC:H’ ’’ [J. Appl. Phys. 69, 7805 (1991)]
Authors: Koropecki R. R. , Alvarez F. , Arce R.
Published: July 2002

We show that the theoretical arguments used in the preceding comment do not apply to our experiments, and that our interpretation of the behavior of the Si-H stretching band in a-SiC:H in terms of structural influences is correct.
63Cu nuclear magnetic resonance spectra of Cu59Zr41 powders during amorphization
Authors: Li Baiqin , Xiao Keqin
Published: July 2002

The variations of the 63Cu nuclear magnetic resonance (NMR) spectra have been studied for the powder mixtures of Cu59Zr41 after different times of ball milling. Other relevant samples such as the ball-milled pure copper powders and the prealloyed intermetallic compound Cu59Zr41 have also been investigated. Ball milling the Cu–Zr powder mixtures influences all of the 63Cu NMR spectral parameters of the samples. The most pronounced changes are in the position and intensity of the 63Cu resonance peak, which compares with the characteristics of Cu59Zr41 powders unmilled and other samples. During amorphization progress, a new broad 63Cu resonance peak around K=1490 ppm developed in the milled Cu59Zr41 powder samples. The detailed physical discussion on correct identification of these peaks has proceeded. The spectrum of 63Cu resonance in the ball-milled Cu59Zr41 is a superposition of two resonance peaks, the narrow one with Knight shift of about 2400 ppm corresponding to the resonance in unalloyed copper powders, and another broader one with Knight shift value around 1490 ppm which is attributed to the resonance of active nuclei 63Cu in the amorphous phase. Compared with results of x-ray diffraction, the 63Cu NMR analysis seems more sensitive to the subtle microstructural changes of the Cu–Zr powder mixtures during mechanical alloying. The importance of the NMR measurement to reveal the amorphization mechanism by ball milling has been emphasized briefly.
Laser patterning of diamond films
Authors: Narayan J. , Chen X.
Published: July 2002

We report here selective deposition and fine-scale patterning of hot filament deposited diamond films by the use of pulsed laser irradiation on silicon and copper substrates. The substrates were abraded with diamond and alumina powders before hot-filament chemical vapor deposition. A drastic enhancement in diamond nucleation (using hot-filament chemical vapor deposition) was observed on specimens treated with diamond powder, whereas enhancement on specimens pretreated with alumina powder was relatively insignificant. We have found that the seeding of diamond crystals was substantially reduced by pulsed laser annealing/melting which removes the plastic damage as well as the seed crystals introduced by diamond powder pretreatment. The selective deposition or fine-scale patterning of diamond films was achieved either by a shadow masking or by scanning a focused laser beam to generate desired patterns. The nucleation can also be enhanced by laser deposition of thin films, such as diamond-like carbon and tungsten carbide (WC), and selective deposition and patterning achieved by controlled removal or deposition of the above films.
Real-time Raman measurement of Si(111) under low-energy Ar+ ion irradiation
Authors: Nakamura K. G. , Kitajima M.
Published: July 2002

Real-time Raman measurements have been performed on Si(111) under Ar+ ion irradiation with a time resolution of 15 s. Ion flux of 3×1011 ions cm−2 s−1 and ion energy of 3 and 5 keV are used. Decrease in the intensity of the TO line (at 521 cm−1) has been observed as irradiation time increases. The reduction rate of 5-keV irradiation is larger than that of 3-keV irradiation.
Suppression of anomalous diffusion of ion-implanted boron in silicon by laser processing
Authors: Juang M. H. , Wan F. S. , Liu H. W. , Cheng K. L. , Cheng H. C.
Published: July 2002

Anomalous diffusion of ion-implanted boron in silicon has been suppressed by using the laser annealing (LA) technique. For the rapid thermal annealing process, the high-dosage boron implant significantly enhanced the anomalous diffusion of boron in Si largely due to increased density of interstitial clusters. The mechanism that electrically active dopants contribute to diffusion is confirmed. The dopant activation is primarily determined from the heating process rather than the holding time interval. Hence, the optimum annealing regime, attaining high-performance shallow p+-n junctions, is to increase the dopant activation efficiency during the temperature-ramping process as well as to shorten the holding interval. Having an ultrahigh heating rate, the LA technique serves as an excellent annealing scheme to significantly suppress the anomalous diffusion and considerably promote the dopant activation.
Electric fields associated with transient surface currents
Authors: McAllister I. W.
Published: July 2002

The boundary condition to be fulfilled by the potential functions associated with a transient surface current is derived and expressed in terms of generalized orthogonal coordinates. From the analysis, it can be deduced that the use of the method of separation of variables is restricted to three surface geometries, viz. a plane, a circular cylinder, and a sphere.
Interdiffusion in polystyrene crosslinked by keV ion irradiation
Authors: Calcagno L. , Foti G.
Published: July 2002

Mass transport properties of polymers are deeply influenced by the presence of crosslinks between chains, induced by high-energy ion irradiation. Diffusion coefficients in polystyrene, measured after irradiation with 300-keV protons in the fluence range 1012–1014 ions/cm2, show strong variation up to two orders of magnitude. Diffusion process has been studied in deuterated/hydrogenated polystyrene bilayer by using the forward recoil analysis technique with 2.0-MeV He beam. The adopted experimental procedure allows us to detect diffusion coefficients in the range 5×10−13–10−15 cm2/s. Two molecular weights have been chosen for the hydrogenated polystyrene (7500 and 575 000 amu), in both experiments the molecular weight of deuterated polystyrene has been maintained constant (27 000 amu). Combining diffusion, molecular weight distribution, and solubility measurements performed in the same irradiation conditions, we have tested that diffusion process is slowed down when branching of chains or formation of a large unsoluble fraction occurs in the original polymer structure.
The influence of substrate-epitaxial layer chemical impurities on heterostructure electrical characteristics
Authors: Gray M. L. , Ebert C. W.
Published: July 2002

Molecular beam epitaxial (MBE) layer heterostructures have been grown on GaAs wafers that received several different predeposition surface treatments. The electrical properties of the epitaxial structures have been correlated with the electrically active chemical impurities present at the substrate-epitaxial layer interface. Direct evidence has been found that relates the interface condition to the population of deep levels in the MBE structures. Photoreflectance modulation spectroscopy was used to qualitatively determine the electric field strengths of the epitaxial buffer layer regions.
Lock-on effect in pulsed-power semiconductor switches
Authors: Gundersen M. A. , Hur J. H. , Zhao H. , Myles Charles W.
Published: July 2002

Certain high-voltage pulsed-power switches based on semi-insulating GaAs or InP exhibit a ‘‘lock-on’’ effect. In this paper, this effect is argued to be fundamentally a transferred-electron effect, and its experimentally observed characteristics are explained. The lock-on effect causes high forward drop and high power dissipation for certain pulsed-power switches based on GaAs and various other direct-gap materials.
Normal incidence infrared photoabsorption in p-type GaSb/GaxAl1−xSb quantum wells
Authors: Xie H. , Katz J. , Wang W. I. , Chang Y. C.
Published: July 2002

Absorption of infrared radiation at normal incidence from intervalence-subband transitions is investigated in p-type GaSb/Ga1−xAlxSb quantum wells. Normal incidence absorption is allowed in conventional p-type quantum wells due to the favorable properties of the p-like valence-band Bloch states and the heavy- and light-hole mixing. By using GaSb as the quantum-well material, which has the smallest heavy-hole effective mass of the commonly used III-V semiconductors, absorption can be further enhanced. We find that normal incidence absorption of 3000–6000 cm−1 can be easily achieved in these proposed quantum wells with well widths of 55–90 Å for the wavelength range of 8–12 μm and typical sheet doping concentrations of 1012 cm−2. This absorption strength is comparable to that in the intrinsic Hg1−xCdxTe detector. Strong absorption of normally incident radiation makes this structure a good candidate for infrared photodetection.
Ion mixing of III-V compound semiconductor layered structures
Authors: Xia W. , Pappert S. A. , Zhu B. , Clawson A. R. , Yu P. K. L. , Lau S. S. , Poker D. B. , White C. W. , Schwarz S. A.
Published: July 2002

Compositional disordering of III-V compound superlattice structures has received considerable attention recently due to its potential application for photonic devices. The conventional method to induce compositional disorder in a layered structure is to implant a moderate dose of impurity ions (∼1015/cm2) into the structure at room temperature, followed by a high-temperature annealing step (this process is referred to as IA here). Ion irradiation at room temperature alone does not cause any significant intermixing of layers. The subsequent high-temperature annealing step tends to restrict device processing flexibility. Ion mixing (IM) is capable of enhancing compositional disordering of layers at a rate which increases exponentially with the ion irradiation temperature. As a processing technique to planarize devices, ion mixing appears to be an attractive technology. In this work, we investigate compositional disordering in the AlGaAs/GaAs and the InGaAs/InP systems using ion mixing. We found that the ion mixing behavior of these two systems shows a thermally activated regime as well as an athermal regime, similar to that observed for metal-metal and metal-semiconductor systems. Ion mixing is observed to induce compositional disordering at significantly lower temperatures than that for the IA process. We have compared the two processes in terms of five parameters: (1) irradiation temperature, (2) dose dependence, (3) dose rate dependence, (4) annealing, and (5) ion dependence (including electrical effects and mass dependence). We found that the IM process is more efficient in utilizing the defects generated by ion irradiation to cause disordering. Both the physical mechanism of ion mixing and possible device implications will be discussed.
Effects of interface roughness in a multilayer system on neutron reflectivity
Authors: Tasaki Seiji
Published: July 2002

The neutron reflectivity of a multilayer system with interface roughness is studied on the basis of the neutron optical method. The reduction of the specular reflection by the incoherent effect is taken into account by introducing imaginary phase factors in characteristic matrices. The modification of the optical potential by the coherent effect is considered by introducing an intermediate layer at each potential boundary, where the optical potential changes smoothly. Numerical calculation shows that the incoherent effect lowers the reflectivity on the whole, whereas the coherent effect reduces mainly the intensity of the second-or the higher-order Bragg peaks. It is found that these two effects explain experimental results reasonably well in cases of Ni/Ti multilayers.
Growth of InAlAs/InGaAs and InGaAlAs/InGaAs heterojunction bipolar transistors on Si-implanted InP substrates by molecular beam epitaxy
Authors: Dodabalapur A. , Chang T. Y. , Tell B. , Brown-Goebeler K. F.
Published: July 2002

We describe procedures to grow InAlAs/InGaAs and InGaAlAs/InGaAs heterojunction bipolar transistors (HBTs) on Si-implanted InP substrates by molecular beam epitaxy (MBE). The combined effects of ion implantation and annealing necessitates a significant modification of MBE growth conditions in order to obtain high quality epilayers and heterojunctions. Approximately 50% higher As4 flux is needed, especially during the initial heat cleaning step, to obtain layers with good surface morphology and HBTs with dc characteristics similar to those of HBTs grown on regular InP substrates. InGaAlAs/InGaAs HBTs grown under modified conditions on implanted and annealed InP have dc current gains of 2000 at a current density of 2 kA/cm2 . Similar MBE growth conditions can be used to grow other minority-carrier lifetime sensitive devices directly on implanted and annealed InP wafers.
Consequences of the cooling induced by voltage taps at the extremities of electromigration test structures
Authors: Jeuland F. , Lormand G. , Normandon Ph. , Boudou A.
Published: July 2002

The difference between the rupture localizations observed on two types of electromigration test structures, with or without several width variations, is explained by the effect of the cooling due to voltage taps at the extremities of the structures. The influence of this cooling on the ion flow divergence resulting from the thermal gradient at the extremities of the test structures is studied. Whereas a current density acceleration exponent of 3 is found for temperature-gradient-induced failures at moderated current densities, a value of 1 is predicted for high-current-density accelerated tests.
Microscopic manipulation of homojunction band lineups
Authors: Marsi M. , La Rosa S. , Hwu Y. , Gozzo F. , Coluzza C. , Baldereschi A. , Margaritondo G. , McKinley J. T. , Baroni S. , Resta R.
Published: July 2002

We tested the theoretical prediction that the band structures on the opposite sides of a homojunction can be artificially displaced in energy with respect to each other by means of double intralayers of atomiclike thickness, producing band discontinuities of potential interest for practical applications. Evidence of such discontinuities was found when Ga-As, Al-As, Ga-P, or Al-P intralayers were inserted between Si and Si or Ge and Ge.
A two-dimensional ensemble Monte Carlo simulation of hole transport in heavily doped small n-type emitters
Authors: Pan Y.
Published: July 2002

An ensemble Monte Carlo simulation of hole transport in the emitters of ultrasmall npn bipolar transistors is presented in this paper. A small number of holes in a heavily doped emitter permit us to follow the entire history of all holes in the emitter over a long period of time. Most of the important scattering mechanisms and the band-to-band Auger recombination are included in the simulator. The minority-hole mobility was calculated and compared with the best existing measurement results. Reasonable agreement between the theory and experiments has been achieved. The fluctuation in the base current, which is a fundamental limitation in scaling bipolar transistors operating at very high speed, was extensively studied.
Amorphous phase transition mechanism by the mechanical alloying of the Fe–W system
Authors: Shen T. D. , Wang K. Y. , Quan M. X. , Wang J. T.
Published: July 2002

The Fe–W binary system exhibits a zero heat of mixing in the amorphous state. Thus, there is no chemical driving force for the crystal-to-amorphous transformation. However, the crystal-to-amorphous transition was observed in a mechanically alloyed mixture of pure Fe and W powders. A structural study by x-ray diffraction showed that supersaturated solid solutions of W in Fe [Fe(W) SSS] and Fe in W [W(Fe) SSS] were produced during the early stage of the mechanical alloying. Iron atoms were already totally involved in the solid-state amorphization reaction after 24 h of milling. The end products were W(Fe) SSS and amorphous Fe–W alloy. The amorphization by mechanical alloying of the Fe–W system is attributed to a solid-state amorphization reaction in which lattice distortion induced by supersaturation of W in Fe and a refinement of grain size may raise the free energy of Fe(W) SSS above that of the amorphous phase and make the Fe(W) SSS destabilize.
Room-temperature hydrogenation effect on Si- and Be-ion-implanted GaAs
Authors: Cho Hoon Young , Kim Eun Kyu , Lee Ho Sub , Min Suk-Ki
Published: July 2002

Hydrogenation effects on Si- and Be-ion-implanted GaAs exposed to the hydrogen plasma were investigated. In the sample hydrogenated for 60 min at room temperature, electron mobilities were increased about 21% at 300 K and 1400 cm2/V s at 150 K, showing a little change of the activated Si donor profile. Also, by using deep-level transient spectroscopy and optical deep-level transient spectroscopy, it was observed that the electron and hole traps at Ec−0.62- and Ev+0.68-eV levels, which have been reported as defects due to the implanted damage, were efficiently decreased during the room-temperature hydrogenation. This effect persists during the anneal at 400 °C during 5 min in an argon ambient.
On the evolution of GaInAs/GaAs strained epitaxial layers
Authors: Brafman O. , Fekete D. , Sarfaty R.
Published: July 2002

We find that in a highly lattice-mismatched heteroepitaxial growth, as critical thickness is reached, defects are formed within a thin layer at the surface and do not necessarily propagate to the interface. At that thin layer the strain is locally decreased resulting in a larger lattice parameter, which persists until the next step takes place. This procedure is inferred from the Raman scattering data of InxGa1−xAs/GaAs. Disorder induced Raman spectroscopy in a scattering forbidden configuration is shown to be an extremely sensitive tool for observing this stepwise release of the strain.
Dopant-surface migration and interactions from reflection high-energy electron diffraction dynamics
Authors: Wood Colin E. C.
Published: July 2002

The effect of silicon and beryllium atom coverage on the intensity of electrons specularly reflected from vicinal (100) GaAs is reported. Intensities typically drop to minima when concentrations approach gallium step-site densities, and increase to broad maxima associated with changes in dominant reconstruction order. Transient relaxation effects are also reported together with possible applications to surface migration kinetics, dopant flux calibrations, and determination of misorientation angles.
Ordering effect on the performance of Ga0.5In0.5P visible light-emitting diodes grown by metalorganic chemical vapor deposition
Authors: Horng R. H. , Lee M. K.
Published: July 2002

Ordering effect on the performance of Ga0.5In0.5P visible light-emitting diodes (LEDs) has been reported. The GaInP LEDs were fabricated on GaAs substrates at 675 and 730 °C by metalorganic chemical vapor deposition, with ordered and disordered structures. A sample with an ordered structure shows anomalous device performance, where emitting wavelength change, low light intensity, and early saturation were observed from the current-light intensity relationship. From the current-voltage measurement, it was found that the sample with ordered structure also yields an inferior diode performance. These phenomena could be due to the existence of antiphase boundaries in the ordered structures. The antiphase boundaries can act as generation-recombination centers and result in the anomalous behavior of the ordered GaInP LED.