bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavily Si-doped GaAs grown by metalorganic chemical vapor deposition
Authors: Furuhata Naoki , Kakimoto Koichi , Yoshida Masaji , Kamejima Taibun
Published: July 2002

Heavily Si-doped GaAs layers were grown by a metalorganic chemical vapor deposition method using disilane (Si2H6) as a silicon dopant source gas. The grown layers were characterized by the van der Pauw, secondary ion mass spectroscopy, and low-temperature Fourier transformation infrared spectroscopy (FTIR) method. The carrier concentration has no growth temperature dependence from 550 to 700 °C temperature range. However, it has temperature dependence below 550 °C and above 700 °C. The carrier concentration of Si-doped GaAs is usually saturated at 6×1018 cm−3 level. Further, Si doping makes the carrier concentration decrease. By using the low-temperature FTIR method, absorption bands for SiGa, SiAs, SiGa-SiAs pair, and lower energy bands (374 and 369 cm−1) were observed in heavily Si-doped GaAs. The peak intensity for SiGa is smaller than that for SiAs, and the peak heights at 374 and 369 cm−1 are relatively larger than that for the other peaks. These facts suggest that, in heavily Si-doped GaAs, a part of SiGa formed SiGa related defects, which act as new donor centers.
Dislocation effect on the activation efficiency profile in Si-implanted and SiN-capped annealed GaAs
Authors: Hyuga Fumiaki
Published: July 2002

Depth profiles of carrier concentration and photoluminescence (PL) intensities are measured for Si-implanted and SiN-capped annealed GaAs. The peak carrier concentration decreases far from dislocations without a change in the effective thickness of the active layer. Moreover, the activation efficiency of the implanted Si decreases and the PL intensity of the Si on the arsenic site (SiAs) acceptor increases in the surface region of the active layer. These results suggest that the As vacancy concentration increases during the annealing process, and this enhances the effect of dislocations which creates an electrical nonuniformity of the Si-implanted GaAs layer.
Temporal intensity modulation of spectral lines in a low-frequency discharge in argon
Authors: Seeböck R. J. , Köhler W. E.
Published: July 2002

The time-dependent modulation of the emission intensities of several Ari and Arii spectral lines was measured with the time-to-amplitude conversion method for an argon discharge at 50 kHz occurring between the electrodes of an asymmetric parallel plate etch reactor. Under the assumptions that the life time of an emitting state is short compared to the electric field period and that the state is populated by electron impact from the ground state, the line intensity becomes proportional to the corresponding excitation rate coefficient. This time-dependent rate coefficient is calculated from the electron energy distribution obtained by solving the quasistationary Boltzmann equation where the plasma electric field is taken to be proportional to the measured electrode potential. Good agreement between the time dependencies of measured and calculated line intensities is achieved for the selected 6d(1/2)01 →4p(1/2)1 transition in Ari if the amplitude of the plasma field is adjusted to 13 V/cm.
Correlation between electrical and photoluminescence measurements in high-quality p-type CdTe
Authors: Seto Satoru , Tanaka Akikazu , Kawashima Mitsuo
Published: July 2002

High-quality p-type CdTe crystals grown by the gradient freeze method were characterized by the radial resistivity distribution, Hall-effect, and photoluminescence (PL) measurements. These measurements were performed over the crystal ingot as a function of position along the growth direction. The resistivity and the carrier concentration monotonically varied from 200 to 20 Ω cm and from 1×1014 to 1×1015 cm−3 along the growth direction, respectively. All photoluminescence spectra measured have well-resolved spectra. It was found that both the resistivity and the carrier concentration strongly correlate to the photoluminescence intensity ratios of the neutral donor-bound to the neutral acceptor-bound exciton lines. The Hall mobility slightly decreased along the growth direction, and this result corresponded to the broadening of one longitudinal-optic-phonon replica of free excitons in the PL spectra. This good correspondence between the electrical properties and the PL spectra has provided useful means for characterizing the high-quality CdTe. The electrical properties in high-quality p-type CdTe was dominated mainly by Cd vacancy/donor complexes, which act as shallow acceptors, due to a deviation from the stoichiometry.
Grain-boundary compositions in YBa2Cu3O7−x from Auger electron spectroscopy of fracture surfaces
Authors: Kroeger D. M. , Choudhury A. , Brynestad J. , Williams R. K. , Padgett R. A. , Coghlan W. A.
Published: July 2002

Comparison of Auger electron spectra obtained from intergranular and transgranular areas exposed on fracture surfaces of sintered YBa2Cu3O7−x specimens indicates that most grain-boundary surfaces are deficient in oxygen and rich in copper compared to the bulk. The thickness of this region of altered composition is estimated to be in the range of 15–50 Å. No evidence of segregation of impurities to grain boundaries was seen. The results suggest that the grain-boundary layer is nonsuperconducting and a likely contributor to the problem of low critical current densities in these materials. It is believed that carbon at grain boundaries which has been reported results from incomplete calcination in material which is slightly off stoichiometry.
Oxygen bubbles along individual ion tracks in O+ implanted silicon
Authors: Maszara W. P.
Published: July 2002

Silicon wafers with and without a protective thermal oxide were implanted with oxygen at 150 keV with doses of 1.6–2.0×1018 cm−2. Transmission electron microscopy and secondary-ion mass spectroscopy were used to study the silicon layer above the implanted buried oxide. A regular array of spheroidal bubbles, postulated to be filled with oxygen gas, was observed only in the samples that were not protected by the oxide. The bubbles were aligned in individual columns whose orientation matched the direction of the implantation. The origin and kinetics of their formation are discussed. A model for column formation involving the overlap of ionization thermal spikes is proposed. It is also proposed that the observed phenomenon is a solid-state analog of the bubble chamber effect.
Argon sputtering analysis of the growing surface of hydrogenated amorphous silicon films
Authors: Lin Guang Hai , Doyle James R. , He Muzhi , Gallagher Alan
Published: July 2002

The surface of freshly deposited hydrogenated amorphous silicon (a-Si:H)films are studied by argon sputtering and mass-spectrometer detection of the sputtered neutral molecules. The surface density of H atoms in the top H-rich layers of the film is established from the initial surge of sputtered H-containing molecules. This shows that the growing film has a hydrogen-rich surface layer of multiply H bonded Si atoms about five monolayers thick on a room-temperature substrate. At the ∼240 °C substrate temperature typical of film production, the thickness of this hydrogen-rich layer decreases to about one monolayer.
Thermomagnetic writing in Tb-Fe: Modeling and comparison with experiment
Authors: Suits J. C. , Rugar D. , Lin C. J.
Published: July 2002

Computer model calculations and experimental comparison are presented for thermomagnetic writing in TbFe media. Two models are discussed which are appropriate for two observed types of writing behavior. A ‘‘bubble’’ type writing model is found to give good experimental agreement when wall motion processes dominate and the laser-written marks exhibit single-domain behavior. This model accurately accounts for the writing behavior of Tb0.23Fe0.77. The gradient of the domain-wall energy is found to be an important factor in the writing process and can cause nucleation to be delayed until some cooling has occurred. This results in written domain sizes which are a strong function of the applied bias field. For compositions which exhibit multiple domain writing behavior, a ‘‘nucleation field’’ model is found to be appropriate. This model predicts the observed weak dependence of mark size on applied bias field. In addition, the nucleation field model is used to calculate the bias fields which correspond to the onset of writing (onset field) and single-domain mark formation (saturation field).
Interfacial reactions of cobalt thin films on BF+2 ion-implanted (001) silicon
Authors: Lur W. , Chen L. J.
Published: July 2002

Interfacial reactions of cobalt thin films on BF+2 -implanted (001)Si have been studied by both cross-sectional and plan-view transmission electron microscopy as well as by sheet resistance measurements. The implantation-amorphous samples were found to favor the formation of CoSi2 at 400 °C and laterally uniform growth of the phase at higher temperatures. Two discrete layers of fluorine bubbles were observed in cobalt silicides in all BF+2 -implanted samples annealed at 400–800 °C. In 800–900 °C annealed samples, large bubbles were often observed to distribute near the CoSi2 grain boundaries. The results indicated that (1) fluorine atoms diffuse rapidly at a temperature as low as 400 °C, and (2) appreciable amounts of fluorine atoms are present with low solubility in cobalt silicides after annealing at 400–900 °C. The residual interstitial defects in BF+2 -implanted samples were completely annihilated by CoSi2 formation at 800–900 °C. The elimination of all interstitial defects in these samples is attributed to the injection of a high density of vacancies which were generated during silicide formation. The electrical resistivity of CoSi on blank silicon was measured to be about 350 μΩ cm. The presently measured electrical resistivity value is believed to be one of the most accurate values obtained for CoSi to date. Factors influencing the formation of cobalt silicides and defect structure are discussed.
Ultrafast imaging of optical damage dynamics and laser-produced wave propagation in polymethyl methacrylate
Authors: Kim Hackjin , Postlewaite Jay C. , Zyung Taehyoung , Dlott Dana D.
Published: July 2002

A high-power ultrafast laser spectrometer with image acquisition capability, the ‘‘picosecond microscope’’ is used to study optical surface damage processes in a transparent polymer, polymethyl methacrylate. Optical damage is a fast, violent, inhomogeneous solid-state chemical reaction. We observe three distinct fast processes: creation and growth of a dark absorbing damage volume, the ‘‘damage core,’’ creation and propagation of a hypersonic shock wave in the surrounding atmosphere, and creation of large amplitude acoustic waves which propagate outward from the core at the velocity of sound.
Electron transport in AlGaAs/GaAs tunneling hot electron transfer amplifiers
Authors: Kim K. , Hess K.
Published: July 2002

A Monte Carlo code has been developed to study electron transport at 4.2 K in AlGaAs/GaAs tunneling hot electron transfer amplifier devices. Our model includes the effects of coupled plasmon-phonon interaction and the Pauli exclusion principle along with more conventional features. The numerical results demonstrate the existence of nearly ballistic transport in the base and the collector barrier, and confirm that the experiments by Heiblum et al. [Phys. Rev. Lett. 55, 2200 (1985)] indeed measure the exact energy distribution of injected ballistic electrons. The device characteristics such as transfer ratio and transit time have also been investigated in detail and are discussed along with the optimum operating conditions.
Electric field effects in excitonic absorption for high-quality InGaAs/InAlAs multiple-quantum-well structures
Authors: Nojima S. , Kawamura Y. , Wakita K. , Mikami O.
Published: July 2002

The electric field effects in excitonic absorption characteristics are studied for high-quality InGaAs/InAlAs multiple-quantum-well structures grown by molecular beam epitaxy. The minute comparison between the experimental and theoretical results verifies the following: first, the variations of exciton levels in the first subband show excellent agreement with the calculations; second, the exciton level in the second subband shows a shift to the higher energy (blue shift).
Thermal-wave imaging of voids in structural ceramics
Authors: No Kwangsoo , McClelland John F.
Published: July 2002

Laser-excited thermal-wave magnitude and phase images were acquired by photoacoustic detection in the 20- to 1000-Hz modulation frequency range on surface and bulk laser absorbing ceramics having 20- to 50-μm-diam. voids and compared to optical photomicrographs made in reflection and transmission. Thermal-wave images were more straightforward to interpret for the voids in the ceramics which absorb light at the irradiated surface (surface thermal-wave generation) rather than in the bulk (bulk thermal-wave generation) because the bulk generated thermal-wave signal also involved the light reflection at the void interface.
Prolonged and rapid thermal annealing of boron implanted silicon
Authors: Peter C. R. , de Souza J. P. , Hasenack C. M.
Published: July 2002

We studied the annealing of silicon substrates implanted with a medium dose of boron ions (3×1014 cm−2, 150 keV) employing conventional furnace annealing (FA) and rapid thermal annealing (RTA) processes performed in a nitrogen atmosphere. The annealing efficiency was monitored by visual inspection of the implanted surface with an optical microscope after steam oxidation and Secco etching. The FA is more efficient when performed at a high temperature, but even so, it is not capable of suppressing completely the implantation damage. On the other hand, the RTA was observed to be more efficient than any FA cycle. We discuss this fact taking into account the influence of the very high heating rates (∼250 °C/s) the samples underwent during the RTA cycle on the annealing behavior of implantation damage.
Semiconductor alloys for fast thermal sensors
Authors: Krishnamurthy Srinivasan , Sher A. , Madou M. , Chen A.-B.
Published: July 2002

The electron mobility in the semiconductor alloys near compositions where the direct-to-indirect gap transition takes place can be a rapidly varying function of lattice temperature. Electron mobility limited by scattering mechanisms such as acoustic phonons, optical phonons, and alloy disorder is calculated for several semiconductor alloys as a function of alloy concentration and lattice temperature. Our results show that the positive temperature coefficients of GaAsxP1−x, GaxIn1−xP, and GaxAl1−xAs alloys at the critical concentrations are two-to-three times larger than that of commercially used platinum.
A new method to detect energy-band bending using x-ray photoemission spectroscopy
Authors: Ogama T.
Published: July 2002

A new method to detect energy-band bending using x-ray photoemission spectroscopy has been proposed which measures the changes in the binding energy with the change in the detection angle of photoelectrons. This method was applied to crystalline silicon of various doping conditions with a thin surface oxide and after removing it by ion sputtering. The change in the binding energy with the change in the detection angle was observed only in heavily doped p-type silicon before sputtering, but not in other silicon specimens studied in this work. All specimens showed an identical binding energy independent of the detection angle after removing surface oxides by sputtering. These results are explained semiquantitatively using a simple band-bending model.
Range distributions of 11B+ in Co, CoSi2, Ti, and TiSi2
Authors: Delfino M. , Morgan A. E. , Maillot P. , Broadbent E. K.
Published: July 2002

The range distributions of 10–120 keV 11B+ in polycrystalline Co, Ti, CoSi2, and TiSi2 targets have been measured by secondary ion mass spectrometry. The obtained projected ranges Rp and projected range stragglings ΔRp are within 25% and 10%, respectively, of those predicted using the Monte Carlo computer program trim. By comparison the one-dimensional Boltzmann transport calculation in suprem-3 tends to overestimate Rp by as much as 300% at the highest ion energies.
Luminescence of GaAs/(Al,Ga)As superlattices grown on Si substrates, containing a high density of threading dislocations: Strong effect of the superlattice period
Authors: Liu T. Y. , Petroff P. M. , Kroemer H.
Published: July 2002

In heavily dislocated material (dislocation density of mid-107 cm−2), the low-temperature cathodoluminescence intensity of a sufficiently short-period superlattice comes remarkably close to that of comparison structures grown on low-dislocation material. We attribute this effect to a redistribution of the recombination-active sites along the dislocation cores taking place in the material. The driving force of such redistribution may be electrical or chemical in nature.
Domination of the thermionic-field emission in the reverse I-V characteristics of n-type GaAs Schottky contacts
Authors: Horváth Zs. J.
Published: July 2002

The reverse I-V characteristics of GaAs-Cr/Au planar and mesa Schottky devices have been investigated as a function of the free electron concentration in the range of 3×1014–3×1017 cm−3. It has been obtained that the reverse characteristics have a linear region. The slope of these linear regions is higher for the planar structures than for the mesa ones. The ratio of the slopes for the planar and mesa structures with the same concentration is in agreement with the ratio of the breakdown voltages obtained on the same devices, and both of them correlate with the − 1/4 power of the concentration. The reverse characteristics calculated for the thermionic-field (TF) emission, taking into account the image force lowering and the slopes of the linear regions, are in very good agreement with the experimental results obtained on the mesa structures. The results indicate the domination of the TF emission in the reverse characteristics of the examined devices with concentration above 8×1014 cm−3 for a large voltage range. They also suggest that the effect of the image force lowering may be taken into account by its simple substitution into equations derived for the TF emission. On the other hand, its effect may be considered as a superposition to the effect of the TF emission.
Al/n-GaAs Schottky barrier height modified with rare-earth metal interlayer
Authors: Hirose K. , Tsuda H. , Mizutani T.
Published: July 2002

Schottky barrier heights are measured by current-voltage and capacitance-voltage methods for Al/n-GaAs contacts with a rare-earth metal (Sm, Dy, Yb) interlayer, which forms a stable alloy with Al but does not form an electrically active site in GaAs. The Schottky barrier height for each contact is found to be lowered with diode factor n<1.06, compared to ideal Al/n-GaAs and rare-earth metal/n-GaAs contacts. The mechanisms for the lowering are discussed from standpoints of alloy formation and diffusion across the interface.
A high-speed InP-based InxGa1−xAs Schottky barrier infrared photodiode for fiber-optic communications
Authors: Kim Jae-Hoon , Li Sheng S. , Figueroa Luis , Carruthers Thomas F. , Wagner Ronald S.
Published: July 2002

We report on a new high-speed InP-based InxGa1−xAs Schottky barrier photodiode for infrared detection. The photodiodes were fabricated on both p- and n-InGaAs epilayers. For this application, Schottky barrier height enhancement on InGaAs has been demonstrated. The photodiodes had responsivities as high as 0.55 A/W and quantum efficiencies of up to 45% in the range of 1.3–1.6 μm without antireflection coating. The response speed of photodiodes was measured by the impulse response and autocorrelation methods; rise times of 85 ps for p-InGaAs and 180 ps for n-InGaAs photodiodes were obtained. Recently, a barrier height enhancement of 0.35 eV was obtained in n-InGaAs photodiodes, resulting in a great reduction of leakage currents. This would lead to further improvement in the device performance of the photodiodes. Based on measured RC time constants, we estimate the intrinsic response speed to be 12 GHz for n-InGaAs and 18 GHz for p-InGaAs photodiodes. These results show that InP-based InxGa1−xAs Schottky barrier photodiodes can be very useful for high-speed infrared receivers in fiber-optic communications.
Growth of SiO2 thin film by double-excitation photoinduced chemical vapor deposition incorporated with microwave excitation of oxygen
Authors: Inoue Kohji , Nakatani Yoshiki , Okuyama Masanori , Hamakawa Yoshihiro
Published: July 2002

A new technology for low-temperature growth of good-quality silicon dioxide (SiO2) thin films has been developed. The film growth technology is a double-excitation photoinduced chemical vapor deposition using vacuum ultraviolet and ultraviolet lights from source gases of Si2H6 and microwave-excited O2 in the substrate temperature region of 25–300 °C. Growth rate is about 140 Å/min at 25 °C and does not change with the substrate temperature. Infrared absorption peak of the Si  H bond completely disappears in the films deposited even at 25 °C. The interface state density is extremely low and its minimum density is 7×1010 cm−2 eV−1 for the film deposited at 100 °C. The reaction and deposition mechanisms are discussed from mass spectroscopic analysis. O3 molecules are increased by the microwave excitation of O2 and chemically active oxygen radicals are produced by the irradiation of the D2 and Hg lamps. Si2OH5, SiH2, and H2 molecules are also increased by either the photo- or microwave excitation, but H2O and OH are not increased.
Magnetic properties of amorphous ferromagnets (invited)
Authors: Chudnovsky Eugene M.
Published: July 2002

Some magnetic properties of amorphous ferromagnets are well described within the random-anisotropy real-space model. This model assumes that the neighboring spins are ferromagnetically coupled with each other, and that there is a local magnetic anisotropy whose axes are correlated over a small length Ra due to short-range structural order. The system is characterized by a small parameter λ∼R2aK/A which depends on temperature and on the concentration of magnetic atoms via the local anisotropy K and exchange constant A. In zero magnetic field the local magnetization smoothly rotates over the solid with a characteristic length Rf =Ra/λ2. The zero-field susceptibility is very sensitive to the exchange, the anisotropy, and the amorphous structure: χ∝A3K−4R−6a. The magnetization law in approaching saturation (M→M0) is universal (M0−M)∝1/(H)1/2 for H<2A/M0R2a. These and other predictions of the model seem to be in a good agreement with many recent experimental results.
Magnetostriction of amorphous GdFeCo and YFeCo thin films
Authors: Yoshino S. , Masuda M. , Takahashi H. , Tsunashima S. , Uchiyama S.
Published: July 2002

The contribution of Gd and/or (Fe,Co) to the saturation magnetostriction constant λs of pseudobinary Gdx(Fe100−yCoy)100−x (9<x<65, y=100, 74,38, or 0) films has been examined by substituting nonmagnetic Y for Gd or nonmagnetic Cu for (Fe,Co) and comparing λs of these alloys at 300 and 80 K. The magnetostriction of Gdx(Fe,Co)100−x as well as Yx(Fe,Co)100−x films are positive and the composition (x) dependence of λs in Gd alloys is similar to Y alloys, but λs of Gd alloys are larger than Y alloys. It was further found that GdxCu100−x (35<x<60) shows positive λs at 80 K. These facts indicate positive contribution of Gd to λs in amorphous Gd-(Fe,Co) alloys.
Low core loss rotating flux transformer
Authors: Krause R. F. , Del Vecchio R. M.
Published: July 2002

A rotating magnetic induction at saturation generates no hysteresis losses. In addition, because domain walls are absent, there are no anomalous eddy current losses. Thus, only classical eddy current losses are present. In materials with high resistivity such as ferrites or materials fabricated into thin sheets such as amorphous metals, these classical losses are small. A transformer has been designed which utilizes this principle. It consists of a hollow toroidal core with toroidal windings wrapped outside the core and poloidal windings wrapped through the interior channel. When these windings are energized by currents 90 electrical degrees apart or, with suitable winding schemes, by three-phase currents, rotating flux is generated throughout the core volume.
Surface and bulk defects in hydrogenated amorphous silicon and silicon-based alloy films
Authors: Shimizu Tatsuo , Xu Xixiang , Kidoh Hideo , Morimoto Akiharu , Kumeda Minoru
Published: July 2002

The surface and bulk defects in a-Si:H, a-Si1−xCx:H, and a-Si1−xNx:H films were investigated by electron spin resonance (ESR) and constant photocurrent method. The thickness of the surface defective layer in a-Si:H films was determined for the first time by ESR. Applying various surface treatments, the free-surface layer proved to be much more defective than the interface layer. Both surface and bulk defect densities in a-Si1−xCx:H and a-Si1−xNx:H alloy films were also determined by ESR. The origin of the surface states is discussed, and the experimental results are explained by a simplified model of the distribution of surface defects.
Graded multigap solar cells
Authors: Sassi G.
Published: July 2002

A multigap cascade solar cell system which incorporates graded composition layers is proposed. The new design adds other useful benefits to the advantages of both cascade systems and graded gap regions. Moreover, the pair generation rate in each cell is a bell-shaped curve and it will be approximated by a normal distribution curve, with the result that the photocurrent will be formally determined. Such a procedure could be of some use even for generical generation rates, as it will be discussed. Efficiencies for 2, 3, and 4 cells will be worked out under AM1.5 solar spectrum and the influence of different air mass conditions will be analyzed. Finally, a comparison of these results with the limiting efficiency of multigap cascade structures will be considered and the presence of a particular intrinsic loss usually not contemplated will be shown.
Temperature dependence of silicon nitride etching by atomic fluorine
Authors: Loewenstein Lee M.
Published: July 2002

The temperature dependence of the etch rate of silicon nitride by atomic fluorine has been measured using a discharge-flow reactor. The activation energy of this process is 3.55±0.28 kcal/mol, quite similar to activation energies of Si and SiO2 etching, which were also measured (3.02±0.31 and 3.36±0.40 kcal/mol, respectively).
The effect of rapid thermal annealing on the precipitation of oxygen in silicon
Authors: Hawkins G. A. , Lavine J. P.
Published: July 2002

We report observations of the effect of heat pulses on the precipitation of oxygen in single-crystal silicon. In our experiments, heat pulses are applied for various durations at a fixed temperature of 1200 °C prior to a two-step precipitation sequence. When no pulse is applied, precipitation is at a maximum and is close to that expected from considerations of solid solubility, provided account is taken of the loss of oxygen due to evaporation. For very short pulses (e.g., 2 s), precipitation is suppressed by several fold. As the length of the pulse is increased to roughly 100 s, the precipitation recovers to its initial value. For very long pulses (greater than 10 000 s), precipitation decreases to nearly zero. There are no further changes in the precipitation characteristics for pulse times up to 50 000 s. We interpret these results in terms of a model in which the thermal pulses modify an initial distribution of heterogeneous nucleation sites. The fraction of heterogeneous sites that survive the two-step precipitation cycle is assumed to decrease continuously during the pulse due to thermal dissolution of sites. For short pulses, the decrease in sites accounts for the suppressed precipitation. For longer pulse times (about 100 s), we believe the recovery of precipitation is due to a reduction by out-diffusion of silicon self-interstitials which otherwise limit the rate of precipitation. For very long pulses (10 000 s), all nuclei have dissolved, so that negligible precipitation occurs. This interpretation is supported by experiments in which the interstitial population is altered by changes in ambient and by experiments in which the effects of more complex pulse sequences are investigated. It is suggested that studies of this type can be used to characterize the defect population of silicon for device applications as well as to investigate precipitation processes.
The role of hydrogen in altering the electrical properties of gold, titanium, and tungsten films
Authors: Rodbell K. P. , Ficalora P. J.
Published: July 2002

Hydrogen was found to alter the electrical properties of gold (Au), titanium (Ti), and tungsten (W) thin films deposited on SiO2/Si substrates. Specifically, the addition of H2 was found to reduce both hillock growth and the rate of electromigration in Au and Ti films. The resistance and 1/f noise of unpassivated Au, Ti, and W films was also found to decrease in H2. The influence of H2 adsorption, absorption, compound formation, and film crystal structure [Au (fcc), Ti (hcp), and W (bcc)] on the rate of electromigration is explored. The data suggest that a modification of the stress state at the metal film/substrate interface is responsible for the decreased resistance, 1/f noise, and electromigration rates observed in H2.
Growth and characterization of atomic layer doping structures in Si
Authors: van Gorkum A. A. , Nakagawa K. , Shiraki Y.
Published: July 2002

A new method to fabricate atomic layer doping structures in silicon using a combination of molecular-beam epitaxy and solid-phase epitaxy is developed. The antimony dopants are restricted to a thickness less than the resolution limit of secondary ion mass spectrometry, and exhibit extremely sharp C-V carrier profiles of less than 2 nm for a single Sb monolayer (ML). Hall and resistivity data show full activation for 0.1 ML and saturation at 8×1013 electrons cm−2. Measurements down to 4 K show metallic conduction for highly doped samples (above 0.05 ML) two-carrier conduction for intermediate levels, and strong freezeout for low amounts of Sb (below 0.01 ML). The two-dimensional electron gas is shown to exist by angular dependence of magnetoresistance.
Nonequilibrium behavior of charged point defects during phosphorus diffusion in silicon
Authors: Richardson W. B. , Mulvaney B. J.
Published: July 2002

A new nonequilibrium kinetic model for phosphorus diffusion in silicon is presented. Concentrations of charged defects and defect-impurity pairs are determined explicitly by solving a system of quasilinear evolution equations, each of a drift-diffusion-reaction form with constant diffusivities. This formulation subsumes a hierarchy of models from the literature. Calculated profiles for a 10-min predeposition show both a tail and a well-defined kink plateau. The latter results directly from the kinetic model under the assumption of a strong bimolecular recombination.
Thermal noise-limited sensitivity of the pulse-biased SQUID magnetometer
Authors: Fujimaki Norio , Tamura Hirotaka , Imamura Takeshi , Hasuo Shinya
Published: July 2002

We numerically calculated and obtained an approximate expression for the thermal noise-limited sensitivity of the pulse-biased SQUID sensor used in the integrated magnetometer. We found that the sensitivity is inversely proportional to the bias frequency and inversely proportional to the critical current of the Josephson junction to the 4/3 power. The sensitivity is also proportional to the temperature to the 4/3 power, and is nearly independent of the bias pulse duration. The sensitivity expression is similar to that of the rf SQUID, however, the coefficient is more than one order of magnitude smaller. The best sensitivity has the same order of magnitude as that of the dc SQUID. The quantum limit is attained at a bias frequency of 0.9 GHz at 4.2 K with the typical junction parameters. This sensitivity is available for the SQUID magnetometer operated in the digital feedback loop.
The temperature dependence of the anomalous Hall effects in p-type HgCdTe
Authors: Chen M. C.
Published: July 2002

The anomalous Hall effects of narrow-band-gap p-type HgCdTe, which manifest themselves as negative Hall coefficients at low temperatures, have caused serious problems in material characterization in the past two decades. These phenomena are now widely recognized as being caused by the inverted surface effect describable by Petritz’s two-layer model [Phys. Rev. 110, 1254 (1958)]. We report results from variable-temperature Hall measurements on p-type HgCdTe liquid-phase epitaxy and bulk slices with bare, anodically sulfidized, and anodically oxidized surfaces. We show that the Hall anomalies can be eliminated by depositing an anodic sulfide layer on the surface and subsequently can be restored by removing the sulfide layer. Based on Petritz’s two-layer model, we were able to use the same set of bulk transport parameters and different sets of surface transport parameters to fit the experimental temperature-dependent Hall coefficient and Hall mobility curves of the same sample with surfaces that have been subjected to different chemical treatments. It was demonstrated that the Hall anomalies occurred when the n-type surface conductivity increased relative to the p-type bulk conductivity. The surface conductivity is mainly controlled by the density of fixed positive surface charges which was found to be larger on an anodically oxidized surface and smaller on an anodically sulfidized surface than on a bare surface.
Spatially resolved second-harmonic-generation investigations of proton-induced refractive-index changes in LiNbO3
Authors: Schmidt N. , Betzler K. , Grabs M. , Kapphan S. , Klose F.
Published: July 2002

Doping profiles generated by electric-field-assisted proton diffusion in LiNbO3 bulk material are investigated, spatially resolved by absorption and by second-harmonic-generation measurements. The results allow a direct correlation of the refractive-index changes with the local proton density. It is shown that protons are the only mobile ions under the experimental conditions applied (600 °C, 100 V/cm), whereas lithium ions do not move under these conditions. Similar results were obtained for samples doped with deuterium.
The slow-mode surface plasmon in planar metal-oxide-metal tunnel junctions
Authors: Soole J. B. D. , Ager C. D.
Published: July 2002

We present calculations of the properties of the slow-mode surface plasmon supported by certain planar metal-oxide-metal tunnel junctions. We study the Al–Al oxide–Ag and Al–Al oxide–Au device structures commonly used in light-emission experiments and give the dispersion, propagation decay length, and field profile of the mode in devices of typical dimensions over the energy range 1.4–3.8 eV. We also consider the dependence of the dispersion and decay length on the thickness of the oxide barrier and the likely effect of interface roughness. The bearing of these results on roughness-coupled interconversion between the slow- and fast-mode plasmons is discussed, and we comment on the possibilty of obtaining radiation directly from the slow mode.
Annealing of GaAs single crystal: Relationship between electrical properties and structural defects
Authors: Lee Byung-Teak , Bourret Edith D. , Gronsky Ronald , Park In-shik
Published: July 2002

The behavior of As-related structural defects (dislocation loops and As precipitates) and the changes in EL2 concentration during bulk annealing of an As-rich GaAs crystal were studied in the temperature range of 500–900 °C. Results show that the EL2 concentration increases and that some structural defects dissolve during bulk annealing above 600 °C, indicating that the source of point defects necessary to form EL2 during bulk annealing is the excess As condensed during crystal growth in various forms. It was observed that the excess As condenses as point defects, dislocation loops, and/or As precipitates, depending upon the cooling rate from high temperatures and availability of nucleation sites (dislocations). It was also determined that the solvus temperature for the crystal studied, with an excess As concentration of about 1016/cm3, lies between 600 and 700 °C.
Defect production during ion implantation of various AIIIBV semiconductors
Authors: Wesch W. , Wendler E. , Götz G. , Kekelidse N. P.
Published: July 2002

The present paper gives a survey about the defect generation caused by ion implantation of GaAs, InAs, GaP, and InP. By combining Rutherford backscattering spectrometry, optical spectroscopy, and transmission electron microscopic methods, further information concerning the kinetics of the defect production as well as the type of defects created is obtained. Generally, the defect concentration in the region of implantation parameters investigated can be described by the energy density deposited into nuclear processes. Below critical values of the nuclear deposited energy density in GaAs weakly damaged layers containing point defects and point defect clusters are produced. With increasing nuclear deposited energy density an increasing number of amorphous zones is created due to manifold overlap of the initial defect clusters. The results indicate that in GaAs and InAs already at relatively low implantation temperatures, the amorphization occurs via homogeneous defect nucleation. The results obtained for GaP and InP, on the other hand, point at a remarkable contribution of heterogeneous defect nucleation already at room temperature, leading to amorphization at markedly lower nuclear deposited energy densities in spite of nearly identical values of the nuclear deposited energy. It is therefore concluded that defect recombination and annealing at room temperature is much less pronounced in the phosphides than in the arsenides.
Determination of the fluorine content in a-Si:H:F by infrared spectroscopy, electron probe microanalysis, x-ray photoelectron spectroscopy, and secondary ion mass spectrometry
Authors: Langford A. A. , Fleet M. L. , Nelson A. J. , Asher S. E. , Goral J. P. , Mason A.
Published: July 2002

We have measured the fluorine content in a-Si:H:F with 0%–10% F by electron probe microanalysis (EPMA), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and infrared (IR) spectroscopy. The techniques differ in accuracy and availability of calibration standards. EPMA is the most reliable of these measurements, with a calibration to internal standards that is accurate to ±1 at. % F. XPS measures only the top 30 Å which, after Ar+ sputtering, has 2.0±0.3 times less fluorine than the bulk. We compared SIMS to EPMA and XPS and found that the ratio of the F/Si SIMS intensities is linear in F content. The sum of the integrated IR absorbances of the Si-F stretches is proportional to the F content with 11±1 cm−1/at. % F. After correcting for the systematic variation in Si density with F content, this gives an average absorption cross section of 16±1 cm2/mM. The correlation between IR absorbance and F content is contrasted with previous reports and we find that this cross section may be applied to a-Si:H:F and a-SiGe:H:F deposited by photochemical vapor deposition or glow discharge. As IR spectroscopy is a readily available technique, this will facilitate the reporting of F content and thus allow comparisons between different studies of fluorinated materials.
Ferroelectric-ferroelastic properties of K3Fe5F15 and the phase transition at 490 K
Authors: Ravez J. , Abrahams S. C. , de Pape R.
Published: July 2002

K3Fe5F15 has previously been predicted to be both ferroelectric and ferroelastic, with a phase transition at 535 K, on the basis of the atomic coordinates given in Acta Crystallogr. Sect. B 29, 1654 (1973). Subsequently, the dielectric permittivity has been found to reach a maximum at 495(10) K as the dielectric loss undergoes a change in slope, characteristic of ferroelectric behavior. Furthermore, the heat capacity exhibits a λ-type anomaly at 490(10) K, with a corresponding entropy change of ΔS=5.5(2) J mol−1 K−1. The entropy change at the phase transition calculated from the predicted change in structure is 5.42 J mol−1 K−1. Ferroelastic domains present at room temperature disappear sharply on heating above 490(10) K, as K3Fe5F15 transforms from orthorhombic to tetragonal symmetry, and reappear on cooling below 480(10) K. The ferroelectric-ferroelastic properties in the orthorhombic phase are shown to be fully coupled.
Substrate rotation-induced composition modulation in epitaxial AlGaAs grown by molecular-beam epitaxy
Authors: Chu S. N. G. , Chand N. , Sivco D. L. , Macrander A. T.
Published: July 2002

We observe a periodic variation of Al mole fraction along the growth direction in AlGaAs grown by molecular-beam epitaxy on GaAs substrate by cross-sectional transmission electron microscopy (TEM). The wavelength of such composition modulation in AlGaAs is inversely proportional to the substrate rotation speed during growth and is independent of the growth temperature used. Uniform composition along the growth direction is achieved by increasing the rotation speed such that the modulation period merges into a continuum composition. The minimum change in the Al mole fraction required to obtain a visible periodic contrast in the [200] dark-field TEM images is estimated semiempirically to be about 6% in Al0.3Ga0.7As. Composition modulation was not observed in Al0.7Ga0.3As, indicating an improvement in the uniformity of the Al-beam flux profile across the wafer at a high source temperature. Although Hall measurements and high-resolution x-ray diffractometry did not show any difference in layers grown with and without composition modulation, both the photoluminescence intensity and its uniformity across the wafer improved considerably in Al0.3Ga0.7As with increasing rotation speed from 5 to 16 rpm. A deep donor-acceptor recombination with an activation energy around 157 meV was observed in Si-doped Al0.36Ga0.64As.
Evaluation of structural quality of a silicon carbide (6H-SiC) single crystal grown by a vapor transport method by Rutherford backscattering spectroscopy
Authors: Kobayashi Takane , Iwaki Masaya , Sakairi Hideo , Aono Masakazu , Inomata Yoshizo
Published: July 2002

The structural quality of a silicon carbide (6H-SiC) single crystal grown by a vapor transport method, in which silicon vapor from molten silicon is transported to a growth cavity made of graphite, has been evaluated by Rutherford backscattering spectroscopy (RBS) experiments in the [0001] channeling conditions using a beam of 4He+ of 1.5 MeV. The axial half-angle ψ1/2 and the minimum yield χmin in the [0001] channeling were measured to be 0.64±0.07° and 0.040±0.001, respectively. By comparing these experimental values with corresponding theoretical values (ψ1/2=0.61°, χmin=0.016), it is found that the 6H-SiC single crystal has a high structural quality with only a small amount of imperfections comparable to the detection limit of RBS (about 0.1%).
Mechanism of electrostatic potential conduction in semi-insulating substrates
Authors: Ohno Yasuo , Goto Norio
Published: July 2002

According to Shockley–Read–Hall statistics for deep traps, it has been estimated that the electrostatic potential propagates in semi-insulating substrates. In n-i-n structures made on hole-trap-rich substrates, a negative electric potential applied on an n region is carried to the vicinity of the other electrode. On the other hand, substrates with electron traps act like usual insulators. This phenomenon may be the primary origin of GaAs metal-semiconductor field-effect transistor side-gating effects.
Relaxation of strain within multilayer InGaAs/GaAs pseudomorphic structures
Authors: Grey R. , David J. P. R. , Claxton P. A. , Gonzalez Sanz F. , Woodhead J.
Published: July 2002

Strained-layer superlattice structures (SLSs) have been grown in InGaAs/GaAs with various GaAs barrier layer thicknesses. Photoluminescence measurements indicate that, in structures with thin barriers, the strained layers interact leading to the relaxation of strain, even though each individual well does not exceed the critical thickness for a single quantum well. These results suggest that a fuller understanding of the mechanisms by which strain relaxes in SLSs is important in order that the constraints on the design of devices using such structures can be known.
Theoretical investigations of microwave-driven Josephson junctions in a large frequency range
Authors: Mikolajczak B. , Meyer H.-G. , Seidel P.
Published: July 2002

Based on the Werthamer model [Phys. Rev. 147, 255 (1966)] we investigate the current-voltage characteristic of Josephson tunnel junctions irradiated by a microwave. Within the first harmonic approximation we derive relations for the constant-voltage steps and the corresponding stability conditions. The results are compared with investigations in the frame of the Stewart–McCumber model. [Appl. Phys. 12, 277 (1968); J. Appl. Phys. 39, 3113 (1968)].
Preparation of BaF2 films by metalorganic chemical vapor deposition
Authors: Singh R. , Sinha S. , Chou P. , Hsu N. J. , Radpour F. , Ullal H. S. , Nelson A. J.
Published: July 2002

To date thin films of II(a) fluorides (CaF2, BaF2, SrF2, and their mixtures) have only been deposited by physical vapor deposition techniques. We report for the first time the deposition of BaF2 films on silicon and yttrium-stabilized zirconia substrates by metalorganic chemical vapor deposition at a substrate temperature as low as 400 °C.
Epitaxial InAs-coupled superconducting junctions
Authors: Akazaki Tatsushi , Kawakami Tsuyoshi , Nitta Junsaku
Published: July 2002

Homoepitaxial n-type InAs-coupled superconducting junctions are investigated. The n-type channel layer on a p-type substrate has nearly the same mobility as bulk crystal and the layer can be isolated electrically from the substrate by the built-in potential at the p-n interface. As a result, the critical current-normal resistance (IC RN ) product of the homoepitaxial n-type InAs-coupled junction is at least 30 times better than those of the bulk n-type ones. The coherence length ξN is calculated using the experimentally obtained carrier concentration, mobility, and effective mass. Temperature dependence of IC agrees with calculations based on the proximity effect theory which can be applied to the intermediate regime between the clean and dirty limits.
Current-voltage characteristics of n-amorphous low-pressure chemical vapor deposited silicon films on p-crystalline silicon
Authors: Du N. , Salkalachen S. , Yao J. , Froelich H. R. , John P. K. , Tong B. Y. , Wong S. K.
Published: July 2002

Heterojunction devices have been fabricated by a low-pressure chemical vapor deposition technique whereby n-type amorphous or microcrystalline silicon films were grown on p-type crystalline silicon substrates. Heterostructures produced under various conditions of thin film deposition were subjected to detailed I-V curve analysis. It is seen that for amorphous-crystalline heterojunctions the current transport is through tunneling in the low bias range and limited by electron-hole recombination in the high bias range. For the microcrystalline-crystalline junctions however, recombination current at the interface dominates the current transport process. Illuminated I-V curves corresponding to films deposited at different substrate temperatures (Ts ) and dopant gas-to-silane ratios (R) show that the high values of the short-circuit current (Isc), open-circuit voltage (Voc ), and fill factor (FF) are achieved at values close to Ts ∼620 °C and R ∼4×10−3 in conformance with dark I-V characteristic data.