bluuebunny/crossref_metadata_2025 huggingface dataset:
The electric field induced photoluminescence properties of GaAs/AlxGa1−xAs quantum-well structures grown by molecular-beam epitaxy
Authors: Naganuma M. , Ishibashi T. , Horikoshi Y.
Published: July 2002

Photoluminescence spectra were measured with molecular-beam epitaxy grown layers containing five different single quantum wells in an electric field. The photoluminescence intensity changed with the applied bias voltage in various ways according to the well width. An anti-Stokes shift in the peak energy was observed with the 2- and 3-nm quantum wells, while normal quantum confined Stark shifts were observed in the quantum wells with larger widths. These results were qualitatively interpreted in terms of the recombination rates both at the hetero-interfaces and in the quantum wells. Experimental results suggest that the impurity concentration at an interface between AlGaAs and an overlying GaAs layer is higher than that at an interface between GaAs and an overlying AlGaAs layer.
Electrical properties of ion beam recrystallized and laser beam annealed arsenic-implanted silicon on sapphire
Authors: Alestig G. , Holmén G. , Linnros J.
Published: July 2002

A 300-keV neon ion beam has been used to epitaxially regrow an amorphous surface layer in silicon on sapphire at three different target temperatures, 350, 400, and 450 °C. The layer was produced by implantation of 40 keV, 1015 arsenic ions/cm2. After the ion beam induced recrystallization, only a few percent of the dopants were electrically active. However, the electrical activity increased to 70%–80% by a subsequent cw laser anneal. Channeling measurements showed that the crystal quality of these samples was better than that for samples subjected only to laser annealing. Measurements of the angular dependence of the backscattering yield showed that, for the ion beam recrystallized samples, the arsenic atoms were displaced from substitutional positions.
The structure of Ni5Si2 formed in Ni-Si thin-film lateral diffusion couples
Authors: Chen S. H. , Carter C. B. , Elgat Z. , Zheng L. R. , Mayer J. W.
Published: July 2002

The microstructure of the nickel silicide, Ni5Si2, which forms during solid-state reactions using self-supporting Ni-Si lateral-diffusion couples, has been studied using high-resolution electron microscopy (HREM) and selected-area electron diffraction. Two different structures for Ni5Si2 have been identified, one of which is consistent with the crystal structure which has been reported to have an actual composition of Ni31Si12. There is evidence for the existence of a third structure. Variations in the distribution of these structures and the presence of planar defects may account for the reported composition range of Ni5Si2 in the Ni-Si phase diagram. The observed HREM images are compared with computer simulated images.
Determination of gap state density distribution in hydrogenated amorphous silicon from light-induced effects
Authors: Chen Yang-Fang , Huang Ying-Sheng
Published: July 2002

Gap state density distribution in hydrogenated amorphous silicon has been obtained from the effect of light illumination on the dark conductivity. This new technique allows us to determine the bulk density of state distribution within approximately 400 meV below the Fermi level.
Effect of small amounts of hydrogen on the elastic behavior of lutetium
Authors: Greiner J. D. , Beaudry B. J. , Smith J. F.
Published: July 2002

The elastic constants of a well-characterized, high-purity single crystal were measured before and after hydrogen was added to change the hydrogen content from 500 at. ppm (3 wt. ppm) to 6900 at. ppm (40 wt. ppm). Comparison between the two sets of measurements shows that such a small change in hydrogen content has a disproportionately large effect on the elastic stiffness. In this case the increase in hydrogen content produced an increase in all directly measured elastic constants by the order of 0.5%. Further comparison of our data with earlier data indicates that other interstitial elements (e.g., C, N, and O) may also exert an inordinately large influence on the elastic stiffness.
Effects of interfacial microstructure on uniformity and thermal stability of AuNiGe ohmic contact to n-type GaAs
Authors: Shih Yih-Cheng , Murakami Masanori , Wilkie E. L. , Callegari A. C.
Published: July 2002

As part of the investigation of the use of AuNiGe as the ohmic contact to n-type GaAs at a high integration level, cross-sectional transmission electron microscopy was used to explore the uniformity at the metal/GaAs interface and the thermal stability of the AuNiGe contact after the ohmic contact formation. A close relation between spread of the contact resistance and nonuniformity of the interfacial microstructure of the contact was found. Deposition of 5-nm-thick Ni as the first layer of the AuNiGe ohmic contact significantly reduced the spread of the contact resistance and led to the formation of a uniform interface without large protrusions. The improvement in uniformity of compound distribution and the reduction of interface roughness are believed to be due to a change in the sequence of alloying reactions, compared to those in the contact without a Ni first layer. This suggests an ideal interface structure for a low resistance AuNiGe ohmic contact after alloying to be a uniform two layer structure: a high density of the NiAs(Ge) grains contacting the GaAs substrate, and a homogeneous β-AuGa phase close to the top surface. However, due to the existence of β-AuGa phases with a low melting point of around 375 °C, the thermal stability of the contact at 400 °C is of serious concern. Segregation of the NiAs(Ge) grains was observed after annealing at 400 °C for 10 h, which reduced the contact areas between the NiAs(Ge) grains and GaAs. During subsequent annealing at this temperature for up to 90 h, liquidlike flow of the β-AuGa phase was observed which deteriorated the interface uniformity, causing an increase in contact resistance. A typical contact edge slide distance after contact alloying at 440 °C for 2 min was measured to be 0.2 μm and the longest distance among specimens examined was 0.47 μm. This edge deterioration could limit the use of the AuNiGe contact in GaAs submicron devices.
Phosphorus redistribution in a WSi2/polycrystalline-silicon gate structure during furnace annealing
Authors: Torres J. , Thomas O. , Jourdain D. , Madar R. , Perio A. , Senateur J. P.
Published: July 2002

The phosphorus redistribution in a WSi2/polycrystalline-silicon structure after furnace annealing between 600 and 1000 °C was studied. When P is initially introduced into the polycrystalline-silicon, a secondary ion mass spectroscopy analysis shows a nearly equidistribution of the dopant within the sandwich. When the silicide layer is phosphorus implanted, it has been clearly shown that with the refractory metal the dopant forms a tungsten phosphide compound more stable than WSi2 up to a critical temperature Tc. The stability of the phosphide increases with the implanted dose. A complete characterization of the additional phase was obtained by thermal annealing of W-Si-P powders. Several other interesting features on the redistribution of the dopant in the polycrystalline-silicon/silicide structure have been established and discussed.
Reflection high-energy electron diffraction intensity oscillations during the growth of Pb on Si(111)
Authors: Jal/ochowski M. , Bauer E.
Published: July 2002

The growth of Pb on Si(111) at low temperatures is studied by reflection high-energy electron diffraction. Pronounced specular beam intensity oscillations are found which depend in detail upon the state of the surface, codeposition of trace amounts of other metals, residual gas pressure, and temperature. The consequences for the understanding of RHEED intensity oscillations and of the growth of ultrathin films are discussed.
Effects of boron implantation in films of iron-nickel
Authors: Ryu J. , Castell K. , Nowak W. , Vittoria C.
Published: July 2002

We have implanted boron ions into films of Fe-Ni alloy composition. A homogeneous distribution of boron was determined from the sputter Auger analysis with a concentration of 18% and 34% for low- and high-dose implantation, respectively. The resistivity of film was increased by a factor of 2 and 4 as a result of low- and high-dose implantation, respectively. The magnetic properties of these films are studied as a function of annealing temperature by using FMR measurements. Both the uniaxial anisotropy field and FMR linewidth are dramatically decreased as a result of annealing at elevated temperatures. The changes of effective magnetization of these films are strongly dependent on implanted boron concentration.
EL2 distributions in vertical gradient freeze GaAs crystals
Authors: Gray M. L. , Sargent L. , Blakemore J. S. , Parsey J. M. , Clemans J. E.
Published: July 2002

Spatial distributions of EL2 in undoped, semi-insulating GaAs crystals grown by a novel vertical gradient freeze (VGF) method are reported. As a result of the low-temperature gradients present during growth and post-solidification cooling, these crystals exhibit lower EL2 concentrations and lower dislocation densities than liquid-encapsulated Czochralski crystals. Both the EL2 distribution and dislocation density over the area of a wafer do not display the fourfold symmetric pattern prevalent for LEC-grown GaAs. The radial distributions of EL2 in as-grown VGF crystals have been found to be independent of the dislocation density. Axial and radial Hall-effect measurements are included. Thermal activation energies are also presented and the compensation mechanism for this material is discussed.
Hydrodynamic stability threshold of liquid metal current collectors
Authors: Woo J. T. , Pipkins J. F. , Brown S. H. , Sondergaard N. A. , Walker J. S.
Published: July 2002

A mechanism derived from hydrodynamic theory to explain the ejection instability of liquid metal current collectors is presented. The ejection mechanism is shown to be caused by the onset of the Kelvin–Helmholtz instability resulting from the gradient of azimuthal (primary) flow at the interface between the liquid metal and cover gas. This new mechanism differs from the previous theory developed by Eriksson [in Electrical Engineering Series, no. 48, edited by M. Luukkala (The Finnish Academy of Technical Sciences, Helsinki, Finland, 1982), who analyzed the onset of the Kelvin–Helmhotz instability resulting from the gradient of meridional (secondary) flow at the interface. Considering the solution to the linearized Navier–Stokes equations at the liquid metal and gas interface, the azimuthally driven (primary flow) instability mechanism for the onset of ejection is much more prevalent than the meridional (secondary) flow driven mechansim. Furthermore, Eriksson’s theory requires an empirical multiplicative fractional factor that is not physically justified to predict experimentally measured ejection points, whereas the present theory is more self-consistent. Calculations of minimum ejection values from both theories were compared with corresponding experimental ejection data. The present theory appears to give significantly better engineering estimates, both quantitively and qualitatively, for minimum ejection threshold than Eriksson’s theory. The basic mathemtical model presented can serve as the basis for developing a more complex mathematical model for liquid metal ejection.
The effect of Ga substitution on the magnetic properties of Nd2Fe14B, Pr2Fe14B, and PrCo5
Authors: Pedziwiatr A. T. , Sankar S. G. , Wallace W. E.
Published: July 2002

R2Fe14−xGaxB (R=Pr and Nd) and PrCo5−xGax alloys were synthesized and examined by powder x-ray diffraction at room temperature and by magnetometry in the temperature range 4.2–1100 K. Lattice parameters, Curie temperature, spin-reorientation temperatures, anisotropy fields, and saturation magnetizations were determined. Phase analysis revealed that single-phase materials exist only for x≤1 in the case of 2:14:1 alloys and for x≤2 for 1:5 alloys. An increase in lattice parameters is observed upon Ga substitution in all cases. About 20 K increase in the Curie temperature is observed for 2:14:1 alloys, whereas there is a dramatic decrease in 1:5 alloys. Saturation magnetization values decrease upon Ga substitution. The anisotropy field is slightly enhanced by Ga addition in the Nd2Fe14−xGaxB system. Spin-reorientation phenomena in Nd2Fe14−xGaxB and PrCo5−xGax are strongly affected by Ga addition. The observed behavior is discussed in terms of preferential substitution of Ga atoms into the Nd2Fe14B-type crystal structure and random substitution into the CaCu5-type crystal structure.
Magnetic structure of UCu2Si2 and U(Cu0.75Mn0.25)2Si2
Authors: Giorgi A. L. , Lawson A. C. , Goldstone J. A. , Volin K. J. , Jorgensen J. D.
Published: July 2002

The replacement of Cu by Mn in UCu2Si2 causes surprisingly large increases in both the Curie temperature and the coercivity of this ferromagnetic material. We have performed neutron powder diffraction experiments on a series of U(Cu,Mn)2Si2 alloys and found that UCu2Si2 is a simple ferromagnet with a magnetic moment of 2.0(1)μB on the U atoms pointing along the crystallographic c axis of the tetragonal unit cell. The alloy U(Cu0.75Mn0.25)2Si2 is also a ferromagnet with moments on both U and Mn pointing in the c direction. The moment on the U atoms is 1.7(1)μB, and the average moment on the (Cu,Mn) site is 0.16(5)μB. No indication of chemical ordering on the (Cu,Mn) site was detected.
Fe-Nd-B permanent magnet prepared by hot extrusion of rapidly solidified melt-spun filaments
Authors: Yang C. J. , Ray R.
Published: July 2002

A high-performance Fe-Nd-B permanent magnet containing a fine dispersion of hafnium diboride (HfB2) was produced by melt spinning and hot extrusion. The melt-spun filaments of Fe-Nd-B base alloys were hot extruded at 1000 °C into 100% dense bar-shaped magnets with an energy product of 16 MGOe. Magnetic properties of the hot extruded bars were anisotropic with highest-energy product values achieved along the directions perpendicular to the extrusion axis. Improved properties were achieved in magnets containing ultrafine Fe-Nd-B grains stabilized by HfB2 dispersions. A symptom of crystallographic texture was observed in the extruded magnets.
Interlayer exchange in magnetic superlattices (invited)
Authors: Yafet Y. , Kwo J. , Hong M. , Majkrzak C. F. , O’Brien T.
Published: July 2002

A simple model for calculating the Ruderman–Kittel–Kasuya–Yosida exchange interaction between layers of a magnetic rare-earth (RE) metal separated by yttrium is presented. The calculation is semiphenomenological and makes use only of previously measured or calculated quantities. It is valid when the thickness of the magnetic RE layers is much smaller than that of the Y layers. The coupling is found to be of fairly long range and to be consistent in sign with the ordering observed in Gd-Y superlattices. For the actual case of comparable layer thicknesses, a discussion of the superlattice wave functions is given. We show that our simple model is very plausible for constituent metals with simple band structures. For the actual band structure of Gd, eigenstates that are evanescent in the Gd region may provide a justification of our model and account for the agreement with experiment. Further theoretical and experimental work is necessary for understanding these systems.
Magnetic and structural properties of Fe(100)/Ag(100) single-crystal multilayer films with ultrathin Fe layers
Authors: Krebs J. J. , Jonker B. T. , Prinz G. A.
Published: July 2002

Multilayer single-crystal films with 57Fe(100)/Ag(100) periods have been grown with Fe layers only 1.7 monolayers thick, using molecular-beam epitaxy techniques. Reflection electron diffraction and Auger spectroscopy were used to establish the crystalline and chemical perfection of these samples. SQUID magnetometer measurements were made over 0–40 kOe and 10–300 K ranges. At 10 K it is easier to saturate the magnetization normal to the film than in its plane. Furthermore, there is a significant perpendicular remanence Mr. This indicates that the easy axis of magnetization is normal to the film. The strong temperature dependence of Mr suggests that thermally assisted domain-wall motion exists in these samples. Mössbauer studies of the same sample (reported elsewhere) are consistent with the above behavior.
The crystal growth and magnetic properties of sputtered Co-Ni films on bcc polycrystalline underlayers
Authors: Lee Hyung J.
Published: July 2002

The crystal growth and magnetic properties of sputtered Co-20 wt. % Ni films on Cr-based bcc polycrystalline underlayers were investigated. The crystal textures of sputtered Co-Ni films on Cr underlayers were initially determined by x-ray diffraction technique and related to their in-plane coercivities. By introducing N in Cr layers, the lattice spacing of the Cr-based bcc structure was expanded and the effects of larger lattice spacing on the crystal growth of Co-Ni films were studied. The microstructure and morphology of Co-Ni/Cr(N) thin layers were also studied by employing scanning electron microscopy and transmission electron microscopy. The preferred orientation texture of Co-Ni films on Cr(N) layers having d(110)=2.039 Å showed (101̄1), while Cr-N d(110) of larger than 2.039 Å gave (0002) preferred orientation texture of Co-Ni films. In this study, 〈101̄1〉 and 〈0002〉 of 750-Å-thick Co-Ni thin films on Cr(N) bcc polycrystalline layers, which are hard and easy axes of magnetization in the hcp structure, gave 750 and 277 Oe of in-plane coercivity, respectively. The difference in coercivities of Co-Ni films having different crystal textures are clearly explained by the crystal anisotropy in hcp Co-Ni sputtered film.
Magnetic anisotropy and granulometry of Ni/CeO2 catalyst
Authors: Mauger A. , Escorne M. , Paul-Boncour V. , Percheron-Guegan A. , Achard J. C. , Barrault J.
Published: July 2002

Ni supported on CeO2 are catalysts used for hydrogenation reactions. In this work, magnetic properties of two samples reduced at 250 and 400 °C in hydrogen are reported, with small nickel concentrations (6 vol %) so that magnetic interactions between nickel particles are negligible. Below 500 K, a progressive spin freezing of nickel particles is evidenced by the observation of a remanent magnetization and a deviation of the magnetic susceptibility from the Curie Weiss law. A model beyond the superparamagnetic approximation from which we derive the size distribution f(d) of the nickel particles is presented. It is found that the two samples differ by the particle size heterogeneity, although the mean size d is about the same (7–8 nm). It is shown that the blocking of the Ni particles is due to a strong strain anisotropy (3×106 erg cm−3), and conclude that the difference in the catalytic activity between the two samples is due to a strong interaction with the support, rather than a difference in the particle-size distribution.
Magnetization anomalies and temperature-dependent hole localization in the Ca2+Fe4+Ga3+: yttrium iron garnet system
Authors: Pardavi-Horváth M. , Thavendrarajah A. , Wigen P. E. , De Gasperis P.
Published: July 2002

The measurement of the temperature dependence of the magnetization, Ms, between 4.2 and 300 K of epitaxial films of Y3+3−xCa2+xFe3+5−y−x′ Ga3+yFe4+x′O2−12, with x<0.4 and 0≤y<1.6, has shown low-temperature deviations from the molecular field theory of a two-sublattice Néel model, generally applicable to yttrium iron garnet with nonmagnetic substitutions. Molecular field calculations of M(x,y,T) have been performed, assuming a temperature-dependent concentration of Fe4+ ions due to the gradual localization of the uncompensated hole at the tetrahedral Fe3+ sites with the lowering of the temperature. The Fe4+ ions are assumed to form a third magnetic sublattice, which is ferromagnetically coupled to the octahedral Fe3+. The hole localization energy is observed to be on the order of 1–4 meV. The calculations are in good agreement with the experimental results.
Effects of backsputtering and amorphous silicon capping layer on the formation of TiSi2 in sputtered Ti films on (001)Si by rapid thermal annealing
Authors: Chen L. J. , Wu I. W. , Chu J. J. , Nieh C. W.
Published: July 2002

The effects of backsputtering and amorphous silicon capping layer on the formation of TiSi2 in sputtered Ti films on (001)Si by rapid thermal annealing have been studied by scanning and transmission electron microscopy as well as Auger electron spectroscopy. Backsputtering cleaning of the silicon substrates was found to be effective in alleviating the island formation and in promoting the epitaxial growth. Auger depth profiles indicated that intermixing of Ti and Si occurred in samples with substrates cleaned by in situ backsputtering prior to depositions. High-resolution lattice images of cross-sectional samples revealed the presence of continuous amorphous layers between polycrystalline Ti grains and single-crystal Si substrates in the backsputtering-cleaned samples. An amorphous silicon capping layer was found to degrade the surface morphology and hinder the formation of silicide epitaxy. The formation and growth of epitaxial regions are more difficult in samples with amorphous silicon capping layer since an additional step is required for the polycrystalline grains in the upper layer to realign with the underlying epitaxial TiSi2 layer to form an epitaxial region. Better surface morphology is correlated with improved silicide epitaxy with its more favorable energetics.
Temperature effects on electron trap generation and occupation in SiO2
Authors: Avni E. , Loev L. , Shappir J.
Published: July 2002

The effects of charge injection under constant tunneling current through gate oxides of metal-oxide-silicon transistors are studied at different temperatures. For this study, a recently introduced novel characterization method for enduring charge injection effects in SiO2 is used. Results show that trapping–detrapping sites and saturation of surface state generation are independent of the temperature. It is shown that in the temperature range of −120–20 °C, the steady-state field-dependent occupation function is independent of the temperature. On the other hand, the rates for filling repulsive traps, generating new trapping sites, and generating surface states increase with increasing temperature.
A theoretical investigation of the cathode fall in a neon glow discharge
Authors: Moratz T. J.
Published: July 2002

A theoretical analysis of the cathode fall experiments of Doughty and co-workers [Phys. Lett. A 103, 41 (1984); Appl. Phys. Lett. 46, 352 (1985)] is presented, based on a Monte Carlo simulation of the electrons in the discharge. The nonlocal aspects of the electron kinetics (i.e., the average energy and the ionization coefficient) are emphasized and the connection is made with the work of Davies and Evans [J. Phys. D 13, L161 (1980)]. Further examples of the electron kinetics are the light output in the negative glow and the electron energy distribution at the anode. The ion kinetics concentrate on the ion drift velocity and the molecular ion (Ne+2) formation.
Effects of silicon and aluminum additions on magnetic properties of rapidly quenched Nd-Fe-B permanent magnets
Authors: Matsumoto F. , Sakamoto H. , Komiya M. , Fujikura M.
Published: July 2002

The effects of Si and Al on magnetic properties of melt-spun Nd-Fe-B base alloy permanent magnets were studied. The addition of Si to the Nd-Fe-B base alloy improves magnetic properties: it especially increases the maximum energy product (BH)max up to 20 MG Oe, remanence Br over 9 kG, and decreases intrinsic coercive force iHc. The addition of Si also increases Curie temperature and decreases reversible temperature coefficient. The combined addition of Si and Al spreads wheel surface velocity ranges to obtain (BH)max>15 MG Oe and Br>9 kG compared to the addition of Si only. The origin of high performance is discussed.
Optical properties of general double layer twisted and supertwisted nematic liquid crystal displays
Authors: Ong Hiap Liew
Published: July 2002

Analytic expressions are obtained using the generalized geometrical-optics approximation for the field-off state optical field and transmission of the general double layer twisted nematic and supertwisted nematic liquid crystal displays with arbitrary display parameters. A variety of display characteristics can be obtained from such structures. In particular, the strong interference colors in the field-off state single layer supertwisted nematic displays can be completely removed in a double layer supertwisted nematic display; thus, a black or white off state is possible. For the double layer 90° twisted nematic, besides the complete black or white field-off state, it can also exhibit off state display performance similar to that for either the single layer 180° supertwisted nematic or the optical mode interference display.
Intersubband transitions in single AlGaAs/GaAs quantum wells studied by Fourier transform infrared spectroscopy
Authors: Andersson J. Y. , Landgren G.
Published: July 2002

Infrared intersubband absorption in modulation-doped MOVPE-grown AlxGa1−xAs/GaAs single-quantum wells have been studied by Fourier transform infrared spectroscopy. High signal to noise ratio was obtained by utilizing the multiple internal reflection (MIR) technique and a quantitative model of the absorption for this geometry was developed. Overlapping from multiphonon absorption was eliminated by using radiation polarized in two orthogonal directions and taking the difference between the resulting spectra, only one of them exhibiting the intersubband peak. The absorption wavelengths and intensities were fitted to theoretical expressions and the dimensions of the quantum wells were compared with independent determinations by photoluminescence, double crystal x-ray diffraction, and Hall-effect measurements. A narrow linewidth of about 6 meV was measured, corresponding to a 0.1-ps lifetime of electrons in the excited state.
Temperature dependence of nonlinear absorption in InP doping superlattices
Authors: Kobayashi H. , Yamauchi Y. , Ando H. , Takahei K.
Published: July 2002

Absorptive optical nonlinearity in InP doping superlattices grown by vapor-phase epitaxy is investigated in a 2–300 K temperature range. The absorption spectra have tails below InP band-gap energy, caused by the Franz–Keldysh effect due to the internal electric field. The absorption tail is almost temperature independent. This means that the periodic electric potential in the doping superlattice, responsible for the nonlinearity, is unchanged across this temperature range. Nonlinear absorption is evaluated by the pump-probe method. The large reduction in absorption coefficient is obtained even with a weak excitation light intensity. This enhancement in nonlinearity is due to prolongation of the excited-carrier lifetime. Nonlinear absorption increases as temperature decreases. This is due to the temperature dependence of the carrier lifetime.
Electrically active point defects in amorphous silicon nitride: An illumination and charge injection study
Authors: Krick D. T. , Lenahan P. M. , Kanicki J.
Published: July 2002

We observe a strong correlation between changes in the density of paramagnetic silicon ‘‘dangling-bond’’ centers and changes in the space-charge density in amorphous silicon nitride films subjected alternately to illumination and both positive- and negative-charge injection. We demonstrate that ultraviolet illumination annihilates space charge and creates stable paramagnetic centers in silicon nitride. These centers can be passivated with a 1-h anneal at 250 °C. Our results provide the first direct experimental evidence associating a specific point defect with the trapping phenomena in amorphous silicon nitride. We also demonstrate both directly and for the first time the amphoteric nature of the silicon nitride dangling-bond center. Furthermore, our ability to cycle the defect between its paramagnetic neutral state and both its charged diamagnetic states suggests that the optical generation of dangling bonds in amorphous silicon nitride involves no complex structural rearrangement, but simply changes in the charge and spin states of the defect.
Mean projected range and range straggling of 50- to 400-keV Hg+ in glass
Authors: Wang Ke-Ming , Liu Xi-Ju , Wang Yi-Hua , Shi Bo-Rong , Liu Ji-Tian
Published: July 2002

The range profile of Hg+ implanted at energies from 50 to 400 keV in glass was measured by 4He+ Rutherford backscattering. The measured projected ranges are in good agreement with those predicted by the Biersack model. A marked improvement in the range straggling fit is obtained after considering the second-order energy loss.
An investigation of the oxidation of Ti:W
Authors: Tompkins Harland G. , Lytle Steve
Published: July 2002

The alloy Ti:W was oxidized in 100% O2 at temperatures ranging from 375 to 505 °C. The resulting oxides were analyzed with Auger electron spectroscopy, x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, and ellipsometry. The resulting oxide structure contains both Ti and W and appears to be simply a combination of TiO2 and WO3. The indices of refraction of the TiW metal and the oxide were determined to be Ns=2.84–3.08j and Nf=2.25–0.12j, respectively. Film thicknesses of the oxides formed at various temperatures and times were measured with ellipsometry and the resulting kinetics are presented. The growth kinetics were determined to be parabolic with an activation energy of 33.9 kcal per mole (1.47 eV).
The effect of coil design on materials synthesis in an inductively coupled plasma torch
Authors: McKelliget John W. , El-Kaddah Nagy
Published: July 2002

A mathematical model for the analysis and design of inductively coupled plasma torches is presented. The model is based upon a solution of the electromagnetic vector potential equation and is capable of predicting the two-dimensional velocity, temperature, and electromagnetic fields as well as the reaction kinetics inside the torch for any axisymmetric coil configuration. The model is used to study the effect of coil design on the thermal decomposition of silicon tetrachloride to silicon. The coil design is found to affect both the temperature field and the flow field and to have a significant effect on the reaction kinetics in the torch. It is demonstrated that through fundamental changes in the coil design it is possible to control the location of the reaction zone and to reduce silicon deposition on the wall of the reactor.
Stability of Te–Cu amorphous alloy thin films for optical recording
Authors: Carcia P. F. , Kalk F. D. , Bierstedt P. E. , Ferretti A. , Jones G. A. , Swartzfager D. G.
Published: July 2002

We have studied the structure and optical stability of Te–Cu thin film alloy candidates for write-once optical recording. Films prepared by rf diode sputtering with 20–50 at. % Cu are amorphous, as-sputtered. One of these, Te65 Cu35 , has a relatively high crystallization temperature (150 °C), as determined by x-ray diffraction. Near the eutectic composition (∼29 at .% Cu), alloy films have stable optical properties after accelerated aging at 60 °C and 85% relative humidity. The mechanism for film stability near the eutectic was studied by x-ray photoelectron spectroscopy and depth profiling using ion scattering spectroscopy. We found that a Cu-enriched surface oxide, formed at ambient conditions, passivates the film and is responsible for its subsequent stability after accelerated aging. We also demonstrated that a 14 in. diam, multilayer optical disk with a Te65 Cu35 recording medium exhibits excellent linearity for 3 and 8 MHz pulses, good written pulse length stability, and high signal-to-noise ratio. Thus, a Te–Cu recording medium can effectively use run-length-limited codes, which allow very high data storage capacity and data transfer rates.
Electrical properties of CdS/CdTe heterojunctions
Authors: Chu T. L. , Chu Shirley S. , Ang S. T.
Published: July 2002

The electrical properties of n-CdS/p-CdTe heterojunctions depend strongly on the cleanliness of the interface region. In this work, CdTe films were deposited on CdS/glass substrates by close-spaced sublimation (CSS) under various conditions. The dark current-voltage characteristics of the resulting heterojunctions were measured over a wide temperature range, and the capacitance-voltage characteristics were measured in the dark and under illumination. When the CdS surface is in situ cleaned prior to the deposition of the CdTe film, the current transport across the junction is controlled by a thermally activated process. Tunneling makes an important contribution to the interface recombination at temperatures below room temperature when the in situ cleaning of CdS is not used. The dark capacitance of CdS/CdTe heterojunctions prepared with in situ etching is essentially independent of the reverse bias due to intrinsic interface states. Under white light illumination, the 1/C 2 vs V relation is nearly linear. The CdS/CdTe heterojunctions without in situ cleaning showed different 1/C 2 vs V relations due to higher density of interface states. The in situ cleaning also has pronounced effects on the frequency dependence of dark and illuminated capacitances. Using the in situ cleaning technique, solar cells of about 1 cm2 area have achieved an AM 1.5 (global) efficiency of about 10.5%.
An improved effective dipole theory for band lineups in semiconductor heterojunctions
Authors: Ruan Ying-Chao , Wu Nanjien , Jiang Xinde , Ching W. Y.
Published: July 2002

An improved effective-interface quantum dipole model over the previous one for predicting band offsets in semiconductor heterojunctions was formulated. A more general tunneling solution explicitly involving the dipole effect was derived, and a better value for the parameter C1 in determining the number of the tunneling electrons was obtained. The exact formula for calculating the dipole potential drop in the interface region was presented. The model gives the same good results in predicting band offsets, but also gives much improved values for the widths of interface regions.
Theory of Co2+ exchange isolation in ferrimagnetic spinels and garnets
Authors: Dionne Gerald F.
Published: July 2002

The previously reported mechanism of exchange isolation that was proposed to explain the absence of strong positive magnetocrystalline anisotropy effects from Co2+ ions in LiTi spinel ferrite is approximated by a three-cation superexchange model. This simplified system is then analyzed in terms of the dependence of the single-ion Co2+ anisotropy contribution on magnetic dilution. To account for the reduced anisotropy effects in the presence of strong spin-lattice relaxation, Co2+ is considered to act as a paramagnetic ion through decoupling from the exchange fields of the iron sublattices by magnetic dilution. The exchange-isolation concept is based on selective clustering of Li1+ and Ti4+ dilutant ions that results from the minimization of the total energy comprised of (i) magnetic exchange energy, (ii) lattice electrostatic energy, and (iii) crystal-field stabilization energy. Each of these contributions is discussed in terms specific to the spinel lattice and, in particular, to the ionic distributions surrounding the octahedral site occupied by the Co2+ ion. The model is also tested qualitatively by comparing its predictions with published experimental results for the ferrimagnetic CaV garnet system.
Nonequilibrium macroscopic models of carrier dynamics in a semiconductor
Authors: Kunhardt E. E. , Cheng M. , Wu C.
Published: July 2002

A nonequilibrium macroscopic description of carrier dynamics in a semiconductor under the influence of space-time varying fields is discussed. The description is obtained by interpolating between the Boltzmann transport and moment formulations. The resulting model is used to simulate the response of electrons in GaAs to a step change in the applied electric field. In this illustration, the nonequilibrium model is implemented using a single-valley model for GaAs. The results for average velocity and mean energy obtained with this model are compared to those obtained from a Monte Carlo simulation using a three-valley model for GaAs. The results are in reasonably good agreement. The differences between them arise primarily from the limitations of the single-valley model for GaAs for fields at which the intervalley scattering of electrons is dominant.
Properties of molecular-beam-epitaxy-grown and O+-implanted GaAs and their application to the formation of a buried collector of an AlGaAs/GaAs heterojunction bipolar transistor
Authors: Ota Y. , Yanagihara M. , Inada M.
Published: July 2002

Changes in properties of molecular-beam-epitaxy-grown GaAs by oxygen-ion (O+) implantation and annealing, such as crystallinity, carrier concentration, and sheet resistance, are investigated. Using these results, we developed a method of O+ implantation through an external base area to form a small buried collector and to minimize the product, RbCbc, of the base-collector capacitance Cbc and the base resistance Rb in an AlGaAs/GaAs heterojunction bipolar resistance Rb in an AlGaAs/GaAs heterojunction bipolar transistor (HBT) fabricated by a multiple self-alignment process with one mask. High-frequency properties of HBT’s are improved by this method remarkably.
A precise angular spectrum of plane-waves diffraction theory for leaky wave materials
Authors: Hunt W. D. , Hunsinger B. J.
Published: July 2002

A computationally efficient diffraction theory technique is presented which very accurately describes leaky wave propagation in {100}-cut GaAs. This technique combines the angular spectrum of the plane-waves diffraction theory with the slowness surface measurement method of Murray and Ash [1977 Ultrasonics Symposium Proceedings, IEEE Cat. No. 77CH1264-1SU (IEEE, New York, 1977), p. 823] and extends them to deal with the anisotropic loss exhibited by the leaky wave. Both the magnitude and phase of beam profiles are predicted with great precision for beams propagating over long distances and through metallic grating structures. The implications of these results for acoustic charge transport devices on GaAs are discussed.
Investigation of electrodeposited CuInSe2 films by admittance spectroscopy
Authors: Qiu C. X. , Shih I.
Published: July 2002

Junctions of CuInSe2/CdS have been investigated using an admittance spectroscopy technique to obtain information on electrically active states in CuInSe2. The junctions studied were fabricated using electrodeposited p-type CuInSe2 films. The admittance experiments were carried out over a temperature range from 80 to 300 K with a frequency range from 1 to 100 kHz. In devices fabricated using CuInSe2 films with an In/Cu ratio of 1.10, peaks were observed in the conductance-temperature curves with an activation energy of about 50 meV. Characteristic peaks with an activation energy of about 160 meV were found in the devices fabricated using CuInSe2 films with an In/Cu ratio of about 1.25.
Characterization of deep-level defects in In1−xGaxAs/InP
Authors: Bacher F. R.
Published: July 2002

New characterization data are presented for the deep-level defects observed in photoluminescence (PL) spectra of InGaAs near 0.1 eV within the band gap. The literature regarding these defects is summarized and compared to the results of this study. Defects are seen to be present in In-rich, Ga-rich, and lattice-matched In1−xGaxAs/InP epilayers. The PL spectra vary depending on alloy composition and crystal growth conditions. PL spectra at 77 K for 0.46<x<0.50 and input laser powers of 9–18 W/cm2 are given for material grown by organometallic vapor phase epitaxy. Hall mobility and Auger electron specroscopy data are also give for these epilayers. The cause of the defects is unknown, but it is not InP substrate doping or growth impurities. Imperfect arsenic incorporation may be involved, as evidenced by the dependence of PL spectra on growth conditions.
Perpendicular anisotropy at the (001) surface of bulk Fe single crystals
Authors: Purcell S. T. , Heinrich B. , Arrott A. S.
Published: July 2002

We have used ferromagnetic resonance to measure the perpendicular surface anisotropy constant Ks on ultrahigh vacuum prepared bulk Fe single crystals covered by epitaxial Au and Ag overlayers and exposed to air. We find Ks∼0.5 ergs/cm2 for Au on Fe, Ks∼0.7 ergs/cm2 for Ag on Fe, and Ks>1 ergs/cm2 for an exposed Fe surface.
Mechanically alloyed isotropic and anisotropic Nd-Fe-B magnetic material
Authors: Schultz L. , Schnitzke K. , Wecker J.
Published: July 2002

Starting from elemental powders, hard-magnetic Nd-Fe-B can be produced by mechanical alloying and a solid-state reaction. Due to the short reaction time at relatively low temperatures (typically 30 min at 700 °C), the magnetically isotropic particles are microcrystalline and show a high coercivity. These powders can be compacted to dense isotropic magnets by hot uniaxial pressing. An additional deformation at elevated temperatures is used to form magnetically anisotropic samples. With regard to microstructure, magnetic properties, compaction, and formation of anisotropy, the magnetically alloyed material is comparable with the rapidly quenched Nd-Fe-B. The formation characteristics and the magnetic properties of resin-bonded powder, hot compacted isotropic material, and hot deformed anisotropic samples are described.
Domain wall nucleation by impurity ions in KNbO3 single crystals
Authors: Ingle S. G. , Dutta H. S. , David A. P.
Published: July 2002

It has been shown theoretically as well as experimentally that microwalls with linear dimensions of the order of 10−6–10−8 m can be nucleated in KNbO3 single crystals under the influence of the electric dc fields applied externally at the sites of the impurity ions. The critical field for nucleation is found to be about 8×103 V m−1. Since such low fields already exist in crystals at the nonferroelectric to ferroelectric phase transition, the mechanism is expected to be operative at that time, and a photographic evidence of it is also obtained. A model has been developed to explain the nucleation. Employing thermodynamic considerations, expressions have been derived for the critical length of the domain wall nucleated, and the activation energy of nucleation, both for 60° and 90° walls. The photomicrographs obtained after applying the dc fields show microwalls nucleated at the impurity sites, with their linear dimensions of the order given by the theory. Many other aspects of the domain wall nucleation have been made clear by the photomicrographs. Particularly, it has been found that the microwalls move after nucleation to lie linearly to reduce the strain energy of the crystal. The microwalls are not pinned at the impurities, and extend themselves so that they meet each other end to end, producing a continuous wall. It is possible to distinquish these microwalls from the microwalls nucleated by the dislocation loops. The expression for the activation energy of nucleation is also verified experimentally. It is suggested that the mechanism of domain wall nucleation can occur in other ferroelectric crystals also, and shown that the memory of domain walls, commonly observed in ferroelectrics, can be readily attributed to the impurity ions present in the crystals, and the phenomenon of domain wall nucleation operative at their sites.
An estimation of the impurities causing n- to p-type inversion of conduction in thin InSb films on mica substrates
Authors: Isai Masaaki , Ohshita Masahide
Published: July 2002

The 0.1–0.9-μm-thick thin InSb films were prepared on mica substrates by evaporation of InSb to obtain highly sensitive magnetoresistance elements. It was observed that films thinner than 0.15 μm show p-type conduction while films thicker than 0.2 μm show n-type conduction in the extrinsic temperature range. It was also observed that the film, thinned from 0.3 to 0.1 μm by etching from the surface side, showed p-type conduction. The cause of these phenomena was investigated using a secondary ion mass spectroscopy in-depth analysis. It was observed that K, Al, Si and O atoms, constituents of mica substrates, diffused into InSb films from mica substrates. In these atoms, it was estimated that K, Al, and Si atoms could act as acceptors in an InSb crystal contributing to the inversion of conduction type.
Radial focusing in a linear induction accelerator gap
Authors: Chen Yinbao , Reiser M.
Published: July 2002

The focusing properties of the electric field distribution in a linear induction accelerator gap are identical to those of a bipotential electrostatic lens if the particle gap-transit time is small compared with the time variation of the induced electric field. Bipotential lenses have been studied systematically only in the nonrelativistic case. In this paper we present the results of a theoretical study of the focusing properties of a symmetrical two-cylinder lens with identical radii and negligible separation for relativistic electron beams. Analytical formulas derived by using the thin-lens approximation are compared with the results of numerical integration of the relativistic paraxial ray equation and found to be sufficiently accurate for practical applications.
Pulsed laser-induced vaporization from the surface of a binary oxide (zinc ferrite) and its implications for synthesis of thin films
Authors: Nawathey Rashmi , Vispute R. D. , Chaudhari S. M. , Kanetkar S. M. , Ogale S. B. , Mitra A. , Date S. K.
Published: July 2002

The nature of pulsed ruby laser-induced vaporization from the surface of a binary oxide represented by ZnxFe3−xO4 (x∼1) is studied via morphological (scanning electron microscopy), compositional (energy-dispersive analysis of x ray), structural (small-angle x-ray diffraction), and microstructural (conversion electron Mössbauer) examination of the laser-processed surface and correlation of the related surface modification to the properties of thin films deposited therefrom, and subjected to similar examination. Zinc ferrite (ZnxFe3−xO4) films have been deposited on single-crystal Al2O3 substrates and the dependence of the film properties on the oxygen partial pressure and substrate temperature during deposition is studied to explore optimized conditions for deposition of near single-phase stoichiometric films.
Advantages of an indirect semiconductor quantum well system for infrared detection
Authors: Yang Chan-Lon , Pan Dee-Son , Somoano Robert
Published: July 2002

We have analyzed the infrared intersubband absorption process in quantum well systems with anisotropic bulk effective masses, which usually occurs in indirect semiconductors. We find that the anisotropic effective mass can be utilized to provide allowed intersubband transitions at normal incidence to the quantum well growth direction. This transition is known to be forbidden for cases of isotropic effective mass. This property can be exploited for infrared sensor application of quantum well structures by allowing direct illumination of large surface areas without using special waveguide structures. We have calculated the 10-μm intersubband absorption in quantum wells made of the silicon-based system Si/Si1−xGex. We find that it is readily possible to achieve an absorption constant of the order of 104 cm−1 in these Si quantum wells with current doping technology.
Optical properties of chemically ordered a-Si1−xCx:H alloys
Authors: Smith G. B. , McKenzie D. R.
Published: July 2002

The optical properties (n,k,ε,neff) of chemically ordered a-Si1−xCx:H alloys have been measured and then analyzed with the effective-medium theory. Included is the first experimental result for an amorphous binary semiconductor that is known to be almost fully chemically ordered, and represented by the formula a-SiC0.64:H. Chemical order is induced by heavy dilution of the plasma with hydrogen. Chemical ordering shifts absorption to shorter wavelengths. Analysis using a scaling theory to define optical constants of different tetrahedron components leads to serious errors in the a-Si1−xCx:H series.