bluuebunny/crossref_metadata_2025 huggingface dataset:
rf-diode sputtered Permalloy film
Authors: Yang M. M. , Aboaf J. A.
Published: July 2002

Permalloy films were deposited by rf-diode sputtering on silicon and glass substrates. The in-plane film stress was measured as a function of film thickness. The cause of stress changes with film thickness is discussed. The deposition rate and the in-plane stress have been correlated with various process parameters, such as rf power, argon pressure, and substrate bias. A regression analysis yields an excellent fit to the experimental data. The in-plane stress in the film was measured using the wafer-bending method and the x-ray method. The stress of Permalloy films on silicon wafer can be either compressive or tensile, depending on the deposition parameters. The stress increases with increased deposition rate. Stress-free films on silicon can be obtained for a deposition rate of about 7.5 nm/min. The films have good magnetic properties when deposited in these conditions.
Misfit dislocations in pseudomorphic In0.23Ga0.77As/GaAs quantum wells: Influence on lifetime and diffusion of excess excitons
Authors: Grundmann M. , Christen J. , Bimberg D. , Fischer-Colbrie A. , Hull R.
Published: July 2002

The recombination dynamics of excess charge carriers around misfit dislocations in strained layer GaAs/In0.23Ga0.77As/GaAs quantum wells are directly imaged with spectrally and time-resolved infrared cathodoluminescence imaging with subnanosecond time resolution. This unique experimental approach for the first time allows the imaging of excitonic lifetime around dislocations in such quantum wells. A strong reduction is observed. The quenching by more than two orders of magnitude of the quantum efficiency upon an increase of the line dislocation density from 4×103 to 5×106 m−1 is explained quantitatively by a diffusion model. The critical layer thickness is determined to agree well with the ‘‘mechanical equilibrium of forces’’ model.
Properties of conductive zinc oxide films for transparent electrode applications prepared by rf magnetron sputtering
Authors: Schropp R. E. I. , Madan A.
Published: July 2002

High-quality zinc oxide (ZnO) films have been deposited by rf magnetron sputtering from a zinc oxide target. The material has been obtained with resistivities ranging from about 1 Ω cm to 4.6×10−4 Ω cm, whereas the average transmission was always greater than 90% between 400 and 800 nm. A relatively high deposition rate usually leads to low resistivity of films. The films with the lowest resistivity differ from higher-resistivity films by their surface morphology, as observed by scanning electron microscopy and by their x-ray diffraction pattern. In particular, good quality films have a diffraction peak at 2Θ≂30.5°. The best films have also been characterized by Hall-effect measurements, Auger electron spectroscopy, and infrared transmission data. It is suggested that the film properties are dependent on the flux of energetic neutral oxygen atoms to the growing surface, which can be varied by changing the sputtering conditions, such as the target to substrate distance. These films have considerable potential in amorphous silicon solar cell technology as well as other photovoltaic and nonphotovoltaic applications.
Femtosecond probes of magnetic phenomena: Spin-polarization spectroscopy in dilute-magnetic-semiconductor quantum wells (invited)
Authors: Freeman M. R. , Awschalom D. D.
Published: July 2002

The spin-scattering times of charge carriers in dilute-magnetic-semiconductor multiple quantum-well structures are observed directly in a time-resolved experiment. Luminescence measurements with a temporal resolution of 150 fs, obtained via the sum-frequency-generation optical gating technique, monitor the evolution of carrier populations optically prepared to have nonequilibrium spin polarizations. This method enables measurements of spin scattering on shorter time scales than have hitherto been accessible. Spin-relaxation times of a few picoseconds are measured for quantum-confined electrons, and these times are found to be surprisingly insensitive to the presence of magnetic ions in the wells. The strong carrier-ion spin-spin–exchange mechanism is therefore not the dominant spin-scattering channel in these structures, contrary to theoretical expectations.
Theoretical analysis of residual stress effects on the magnetostrictive properties of amorphous wires
Authors: Liu J. , Malmhäll R. , Arnberg L. , Savage S. J.
Published: July 2002

A theoretical analysis of the origin of residual stresses in amorphous wires and their effect on the magnetostrictive properties has been made. The residual stress distribution (compression in the surface and tension in the center) in the wire is attributed to the different cooling rates experienced during solidification by different regions of the wire. Theoretically calculated results agree well with reported experimental data obtained from magnetic measurements.
Interfacial microstructure and electrical properties of the Pt/Ti ohmic contact in p-In0.53Ga0.47As formed by rapid thermal processing
Authors: Chu S. N. G. , Katz A. , Boone T. , Thomas P. M. , Riggs V. G. , Dautremont-Smith W. C. , Johnston W. D.
Published: July 2002

The interfacial microstructure and electrical properties of the Pt/Ti ohmic contact to p-In0.53Ga0.47As (Zn: 5×1018 cm−3) formed by rapid thermal processing (RTP) were intensively studied. Significant interdiffusion of Ti, In, and As across the interface, driven by RTP, occurred at temperatures of, or above, 350 °C for a heating duration of 30 s. A minimum specific contact resistance (9.0×10−6 Ω cm2) was achieved after heating at 450 °C. Cross-sectional transmission electron microscopy of this sample revealed an interfacial reaction zone with complicated microstructure, and the dominant interfacial compound was identified to be InAs. Further increase in RTP temperature resulted in a change in the microstructure, and degradation of the contact resistance. The temperature-dependence characteristic of the specific contact resistance of as-deposited Pt/Ti contact to InGaAs revealed a thermionic-emission-dominated carrier-transport mechanism with an effective barrier height φb, of 0.13 V. RTP treatment to the sample at elevated temperatures up to 450 °C decreased the temperature dependence of the contact resistance. This phenomenon strongly suggests a partial conversion of the dominant carrier-transport mechanism across the contact area from thermionic emission to field emission. This was further verified by fitting the temperature dependence of the measured contact resistance to a phenomenological theory based on a linear combination of the two different types of carrier-transport mechanisms operating at isolated area segments distributed uniformly across the interface.
A model for resonant and sequential tunneling in the presence of scattering
Authors: Khondker A. N.
Published: July 2002

In this paper we present a model to calculate the coherent and the sequential tunneling (or incoherent) transmission probabilities across a double-barrier heterojunction in the presence of scattering centers. The model, based on the previously reported transmission-line technique, provides a simple, yet powerful method to integrate these two different tunneling mechanisms. It is shown that if the scattering processes are taken into account, the coherent tunneling mechanism is strongly affected near the resonant peaks. On the other hand, the incoherent tunneling process, which arises due to the presence of scattering centers, dominates as the scattering lifetime is decreased. Effects of the scattering process on the current-voltage characteristics are investigated.
Correlation between interface nitrogen and the fixed charge in thermally nitrided silicon dioxide on silicon
Authors: Munukutla L. V. , Morady B. , Fordemwalt J. N. , Moore M. R. , Evans K.
Published: July 2002

Silicon dioxide layers of 250 Å thick were grown on Si at 1000 °C in a dry O2/TCA ambient. Thermal nitridation of the samples was performed in a pure ammonia ambient at temperatures from 900 to 1100 °C with one hour time intervals up to a maximum of 4 h. The fixed charge state densities at the interface of the samples were determined from high frequency C-V measurements, and the breakdown fields from I-V curves. Secondary ion mass spectroscopy depth profiles show low levels of contaminants, and high levels of nitrogen at the interface for samples annealed at temperature greater than or equal to 1000 °C and for periods longer than 2 h. Post metal annealing of the nitrided samples appears to help in reducing the trapped charges. Better quality films with lower Qf and VFB shifts, and higher breakdown fields were achieved for samples annealed at 1100 °C. Metal-oxide-semiconductor device quality nitrided films with a Qf of 1010/cm2 were achieved by optimizing the process conditions at 1100 °C. The fixed charge build up for lower nitridation temperatures (<1000 °C) and times (<2 h)is due to the dissociation of Si—O bonds in the presence of hydrogen, and is in accordance with the earlier results in the literature. However, the reduction in the fixed charge buildup at 1100 °C, we believe, is due to the increased levels of nitrogen.
Polymer diffusion as a probe of damage in ion or plasma etching
Authors: Tead S. F. , Vanderlinde W. E. , Marra G. , Ruoff A. L. , Kramer E. J. , Egitto F. D.
Published: July 2002

Dry etching of polystyrene (PS) with oxygen, using ion beams or plasmas is found to affect the diffusion characteristics of molten PS. Four different techniques, reactive ion beam etching (RIBE), reactive ion etching (RIE), and plasma etching in barrel and downstream reactors are used. Polymer molecules lying near the surface of an etched sample are found to have been immobilized, and thus unable to diffuse. The quantity of material affected in this manner is found to increase with polymer molecular weight, and to be greater in samples etched by RIBE and RIE than in the pure plasma methods. Etching is also found to reduce the permeability of the sample surface to diffusion by unetched polymers. The permeability is found to decrease with the penetrant polymer’s molecular weight, and to decrease more drastically in RIBE and RIE treated samples than the plasma treated samples. Surface wrinkling of RIBE samples upon annealing above the glass transition temperature is also seen. The results are found to yield a consistent picture of polymer damage during dry etching consisting of crosslinking and chain scission. These experiments demonstrate the utility of polymer diffusion in the characterization of topological damage to polymer molecules.
Low field mobility and thermopower in one-dimensional electron gas
Authors: Kundu S. , Sarkar C. K. , Basu P. K.
Published: July 2002

A scattering theory of one-dimensional electron gas formed in a narrow channel GaAs-AlGaAs high electron mobility transistor has been developed. The mobility values for the different scattering mechanisms have been computed and their variation with temperature has been presented. The various scattering processes include acoustic phonon scattering for both deformation potential and piezoelectric scattering mechanisms, impurity scattering, and surface roughness scattering at lower temperatures and polar optic phonon scattering at higher temperatures. The effect of dynamic screening has also been included. Finally, the temperature variation of thermopower for different 1D electron concentrations has been shown and attempts have been made to interpret the results obtained.
The mechanism of ac stabilization in ferroelectric liquid-crystal-filled cells
Authors: Elston S. J. , Sambles J. R. , Clark M. G.
Published: July 2002

The use of ac stabilization in ferroelectric liquid-crystal (FLC) devices is commonplace: It enhances the bistability and increases the extinction angles seen in a cell. The mechanism involved in this process is investigated here. Examining the optic tensor profile across an ac-stabilized FLC layer has revealed that it is very similar to that present under a forward bias dc field. Comparing the dc/dipole and ac/dielectric interaction energies shows conclusively the presence of biaxiality in the dielectric tensor. This biaxiality is measured through the comparison of the ac and dc electric energy densities in a cell.
Deep level transient spectroscopy of irradiated p-type InP grown by metalorganic chemical vapor deposition
Authors: McKeever S. W. S. , Walters R. J. , Messenger S. R. , Summers G. P.
Published: July 2002

Results are presented of a deep level transient spectroscopy study of radiation-induced defects in p-type (Zn-doped) InP grown by metalorganic chemical vapor deposition. Three major hole traps (H3, H4, and H5) and two electron traps (EA and EB) were observed. The electron trap structure in particular is significantly different from that reported in the literature for p-type InP grown by other methods. Activation energies of 0.22 eV (EA) and 0.76 eV (EB) have been measured, and capture cross sections (σ∞) of 4.4×10−15 cm2 (EA), and 1.4×10−12 cm−2 (EB) have been determined. The H5 center has a thermally activated capture cross section with an energy barrier of 0.35 eV. The measured injection annealing rate of the primary hole trap (H4) was different than previously observed.
Origin of the first-order phase change at the Curie temperature in KNbO3
Authors: Cross L. Eric , Rossetti George A.
Published: July 2002

As judged by the difference between Curie temperature Tc and Curie-Weiss temperature Θ (Tc−Θ∼53 °C) KNbO3 goes through a very strongly first-order phase change at Tc into a tetragonal ferroelectric phase. For BaTiO3, it is known that the weaker first-order change at Tc (Tc−Θ∼10 °C) derives from the electrostrictive coupling and that the strain-free crystal would go directly to rhombohedral symmetry by a second-order transition. It is the purpose of this note to point up the fact that in spite of the much stronger first-order change in KNbO3, the origin is again in the electrostrictive coupling, and that the cubically clamped crystal would go through a second-order phase change.
Optical reflectance of aluminum-doped zinc oxide powders
Authors: Rafla-Yuan H. , Cordaro J. F.
Published: July 2002

Changes in the electronic properties of zinc oxide powders doped with aluminum were related to the optical reflectance characteristics. ZnO powders doped as a solid solution, having from 0.035 to 1.00 mol % Al, were characterized. Diffuse optical reflectance was measured over near-ultraviolet and visible wavelengths from 340 to 700 nm. Diffuse infrared reflectance was used to characterize the free-electron density in each powder. Free-electron densities ranged from 2.5×1014 cm−3 for undoped ZnO to 3.5×1017 cm−3 for the 1.00-mol % Al powder. The Al-doped powders showed significant resistance to color center formation, whereas the undoped powder did not. The suppression of the optical absorption at approximately 400 nm in the Al-doped powder may be related to the suppression of a band state to localized defect state charge transfer.
Examination of thin SiO2 films on Si using spectroscopic polarization modulation ellipsometry
Authors: Jellison G. E.
Published: July 2002

A series of SiO2 films with thicknesses varying from 3 to 325 nm have been grown on silicon using standard dry oxygen growth techniques and examined using the two-channel polarization modulation ellipsometer, which has increased sensitivity for very thin insulating films on silicon. Using a biased estimator fitting technique, the ellipsometric data are fit to either an air-SiO2-Si model or an air-SiO2-interface-Si model, where the optical functions of the SiO2 layer are approximated using an isotropic one-term Sellmeier approximation. The results from the one-term Sellmeier approximation show that the refractive index of the SiO2 layer increases with decreasing film thickness, while the interfacial layer thickness decreases with decreasing film thickness.
Effect of indium replacement by gallium on the energy gaps of InAs/GaAs thin-layer structures
Authors: Sato Michio , Horikoshi Yoshiji
Published: July 2002

Energy gaps of InAs/GaAs thin-layer structures are calculated using a modified finite square well model, which takes into account In-Ga replacement during growth. We compare the calculated results with the experimental energy gaps of structures grown by flow-rate modulation epitaxy, which is based on an alternate supply of gaseous sources, and molecular-beam epitaxy. The results indicate that In-Ga replacement is rare in flow-rate modulation epitaxy, but about 90% of the surface In atoms are replaced with the Ga atoms in molecular-beam epitaxy. Arsenic has a low sticking coefficient on the In surface, so it is difficult to achieve high As coverages on the In surface in molecular-beam epitaxy. In flow-rate modulation epitaxy and metalorganic chemical vapor deposition, the dangling bonds of the surface As atoms are probably terminated by hydrogen atoms. The surface As atoms are stabilized by establishing stable sp3 orbitals and prevent In-Ga replacement.
Spin-Peierls and spin-liquid phases of Kagomé quantum antiferromagnets
Authors: Marston J. B. , Zeng C.
Published: July 2002

The ground state of the spin-1/2 nearest-neighbor Heisenberg quantum antiferromagnet on the Kagomé lattice probably lacks spin order; therefore, conventional spin-wave analysis breaks down. To ascertain the ground state, we instead use a systematic 1/n expansion with SU(n) fermions. Two distinct states occur in the large-n limit, depending on the size of the biquadratic interaction J̃. When J̃=0, there are an infinite number of degenerate ground states consisting of disconnected dimers. At finite n, however, this degeneracy is broken by local resonance. In contrast, a globally resonating chiral spin-liquid phase with no spin-Peierls modulation is the likely large-n ground state at sufficiently large J̃. For intermediate values of J̃, a phase transition from the dimer state to the chiral phase occurs as the temperature increases. At a higher temperature, there is a second transition to a paramagnetic state. We comment on the possibility that these phases are experimentally realized by the nuclear magnetic moments of a second layer of 3He atoms lying on a graphite surface.
Multilayer Permalloy films grown by molecular-beam epitaxy
Authors: Rook K. , Zeltser A. M. , Artman J. O. , Laughlin D. E. , Kryder M. H. , Chrenko R. M.
Published: July 2002

Single and multilayer [111]-textured films of Permalloy and Cu were grown by molecular-beam epitaxy (MBE) on (111) Si substrates. The magnetic properties of the films were measured by ferromagnetic resonance and M-H loop tracer. The microstructure was observed by transmission electron microscopy, reflection high-energy electron diffraction, and x-ray diffraction. Even the single-layer films had lower easy axis coercivity Hce (≊0.6 Oe) and a lower in-plane anisotropy field (≊1.1 Oe) than permalloy films of similar thickness (≊80 nm) deposited by sputtering. In these single-layer films, the grain size and Hce both increased with improved pre-MBE cleaning of the Si substrate. The multilayers consisted of five identical thickness Permalloy layers separated by Cu interlayers. Multilayers with total magnetic thickness greater than 100 nm exhibited lower Hce than equivalent single-layer films. 4πMs, measured by a combination of ferromagnetic resonance and M-H loop tracer in very thin (<5 nm) permalloy layers was found to drop off relative to the bulk value of 9.5 kG; a value of 5.0 kG was measured for a multilayer with 1-nm-thick Permalloy layers.
X-ray results from a modified nozzle and double gas puff z pinch
Authors: Chang T-F , Fisher A. , Van Drie A.
Published: July 2002

The nozzle and the anode of the UCI (University of California, Irvine) z-pinch facility were modified to study the influence of the anode-cathode geometrical structure on the stability of the pinch and the x-ray yield of the pinch. The anode was modified from a honey-comb to a hollow cylinder with a 4-cm diameter and a ∼3.5-mm wall thickness, placed 2 cm below the cathode. The cavity in the center of the cathode was enlarged from 6-mm diameter to 36 mm. The design of the cathode and the anode showed a marked improvement of the pinch stability over the previous design. Both zirconium and carbon-carbon nozzle were used for the Kr and Ne z pinches. After a few tens of shots the Zr nozzle was melted at the edge and the pinch degraded, while the carbon-carbon nozzle did not sustain any damage for more than 300 shots. Some shots showed the di/dt at the implosion is ∼5 times higher than the di/dt at the beginning of the discharge, this has never been obtained at UCI before. This ratio of the initial di/dt to pinch di/dt is a measure of the pinch quality. By serendipity it was found that double gas puff z pinch increased the hard x-ray (>1 keV) output by about an order of magnitude. The nozzle was then modified to allow double puff operation. A 3.4-mm-diam hole was opened at the center of the nozzle and a plunger was inserted from the top to control the mass of the gas entering the hole. The diagnostics include di/dt coil, soft, and hard x-ray diodes. Soft and hard x-ray emission are both enhanced by the double gas puff z pinch.
Subband structures and wave functions of electrons in quantum wires and in-plane superlattices consisting of grid-inserted quantum-well structures
Authors: Sugawara H. , Schulman J. N. , Sakaki H.
Published: July 2002

We study theoretically the wave functions and dispersion relation of electrons in grid-inserted GaAs quantum-well structures, where very thin AlAs rods are periodically inserted in the middle of quantum wells with a typical spacing of 100 Å. It has been found that when the grid thickness is even a few monolayers, the electronic motion along the lateral direction is strongly modified, resulting in the formation of both quantum-wire states and in-plane superlattice states. For example, when the width and spacing of the grid are 81 Å, the ground miniband width becomes as small as 12 meV for the grid thickness of one monolayer (ML) and can be further reduced to 4 meV when the grid thickness is 5 ML. It is further shown that the effect of grid potential is strongly dependent on the shape of the wave functions, and the lateral confinement is effective only for those having high amplitude in the central portion of the quantum well.
A practical predictive formalism to describe generalized activated physical processes
Authors: Miller S. L. , McWhorter P. J. , Miller W. M. , Dressendorfer P. V.
Published: July 2002

A predictive formalism is developed that is applicable to the large class of activated physical systems described by a differential equation of the generic form: ∂n(φ,t)/∂t =−n(φ,t)F(t) exp(−(φ−R(t))/A(t)). Practical techniques to predict the behavior of activated physical systems for arbitrary time-dependent environments are both intuitively and mathematically developed. Useful techniques to experimentally determine the initial distribution of activation energies, utilizing arbitrary time-dependent laboratory environments, are presented. A number of fundamental results regarding the correct use and interpretation of common diagnostic techniques, such as Arrhenius plots, are derived. It is shown how the predictive results significantly enhance the ability to quantitatively evaluate the reliability of physical systems whose rate-limiting mechanisms are activated processes obeying the above differential equation. Specific issues regarding integrated circuit reliability are examined as potential applications of this predictive formalism, including time-dependent dielectric breakdown, metal electromigration, nonvolatile memory retention, annealing of radiation-induced trapped charge, and thin ferroelectric film switching properties.
High field electrical conduction and breakdown in silicon incorporated polyethylene films
Authors: Liu D. , Kan L. , Kao K. C.
Published: July 2002

The current-voltage (I-V) characteristics of silicon-incorporated polyethylene films fabricated by plasma polymerization have been measured at very high electric fields. The experimental results show that the electric conduction at high fields is due mainly to Fowler–Nordheim type tunneling injection of holes from the anode, and that the incorporation of silicon in polyethylene creates hole traps, thus suppressing the conduction current and enhancing the breakdown strength. The amount of positive space charge resulting from the hole trapping increases with increasing magnitude and duration of the applied field for a fixed silicon content, and increases with increasing silicon content for a fixed magnitude and duration of the applied field. This positive space charge tends to suppress the actual field at the hole injecting contact and to enhance the actual field at the electron injecting contact. For fields higher than a certain critical value, the rate of the current increase with field changes rapidly. This phenomenon is attributed to the onset of double injection. This means that the contribution of the electron current to the total current becomes significant due to the gradual enhancement of the field at the electron injecting contact by the large amount of accumulated positive space charge. It is concluded that silicon incorporated in polyethylene introduces new hole traps which in turn reduces the hole mobility and creates more positive trapped space charge. The overall effect would be to reduce the conduction current and to increase the breakdown strength of the polyethylene if a proper amount of silicon is incorporated in it.
Effect of Sn incorporation on the growth mechanism of sprayed SnO2 films
Authors: Agashe Chitra , Takwale M. G. , Bhide V. G. , Mahamuni Shailaja , Kulkarni S. K.
Published: July 2002

In order to probe into the growth mechanism of sprayed SnO2 films, the films were deposited with different Sn concentrations in the precursor solution. The orientational properties were determined using grazing incidence x-ray diffraction. The preferred growth changed from [110] to [200] direction as the Sn incorporation was increased. Such a change in growth can be anticipated from structure factor calculations. The compositional analysis was done using x-ray photoelectron spectroscopy. The Hall effect measurements indicated that the carrier concentration and mobility are sensitively dependent on the orientation and composition of the films.
Raman scattering by interface phonons in GaAs-AlAs multiple-quantum-well structures: Correlation between Raman and high-resolution electron microscopy results
Authors: Tsen K. T. , Smith David J. , Tsen S.-C. Y. , Kumar Nathan S. , Morkoc H.
Published: July 2002

The effects of shallow impurity and interface roughness on resonant Raman scattering by interface phonons in GaAs-AlAs multiple quantum-well structures have been studied. By correlating the Raman results with observations by high-resolution electron microscopy, it has been demonstrated that Raman scattering from interface phonons depends strongly on the sample quality. For a relatively smooth interface with about 1–2 monolayers of interface roughness, the Raman signal is governed primarily by the impurity if the impurity concentration inside the GaAs layers is greater than about 2×1016 cm−3. On the other hand, for nominally undoped quantum-well structures, the Raman signal can be dominated by interface roughness if the interfaces are sufficiently distorted.
Atmospheric impregnation of porous silicon at room temperature
Authors: Canham L. T. , Houlton M. R. , Leong W. Y. , Pickering C. , Keen J. M.
Published: July 2002

Microporous and mesoporous Si layers contain a very large surface area that affects both their optical and electrical properties. Secondary ion mass spectroscopy (SIMS) analysis is used for the first time to simultaneously monitor all the major impurities on that surface. SIMS data on a microporous layer demonstrate that its chemical composition changes dramatically with time during ambient air exposure. Similar trends are observed for mesoporous layers. Extended storage in air at room temperature converts the hydride surface of freshly anodized layers to that of a contaminated native oxide. Characterization techniques need to take the metastability of the hydride surface into account since the structural, optical, and electrical properties of porous Si can consequently change with time upon exposure to ambient air. Low-temperature photoluminescence and spectroscopic ellipsometry data on freshly anodized and ‘‘aged’’ microporous and mesoporous layers are chosen to illustrate typical changes in optical properties and the timescales involved. Spreading resistance analysis is also shown for the first time to provide depth information on the resistivities of porous layers and their variation with extended exposure to air. Implications for other characterization techniques are briefly discussed.
Auger generation suppression in narrow-gap semiconductors using the magnetoconcentration effect
Authors: Djurić Zoran , Jakšić Zoran , Vujanić Aleksandar , Piotrowski J.
Published: July 2002

A method is presented for the Auger generation suppression in narrow-gap semiconductors using the magnetoconcentration effect for the case when all the generation-recombination mechanisms (Auger, radiative, and Shockley–Read) are taken into account. A numerical solution is given for the kinetic equation determining carrier concentration distribution in a thin semiconductor slab placed in an electric and a magnetic field. The results of the numerical calculation show that the Auger generation suppression becomes very efficient when the concentration of Shockley–Read recombination centers is small enough.
Numerical simulation of 3-level charge pumping
Authors: Ancona M. G. , Saks N. S.
Published: July 2002

The 3-level charge-pumping technique for characterizing electron and hole capture cross sections of fast interface traps in metal-oxide−semiconductor devices is studied via quasistatic one-dimensional numerical simulation. In general, these simulations confirm our understanding of the operation of the 3-level technique for carrier capture and emission. The simulations show that the previously developed simplified analysis of 3-level charge pumping is reasonably accurate in the emission regime. In contrast, previous simple analysis of the capture regime is found to be in error. For quantitatively accurate results, the effect of the trapped charge on band bending must be included. A revised analytical approach for the capture regime is developed which corrects this error.
Energy distribution of trapping states at grain boundaries in polycrystalline silicon
Authors: Yamamoto Ichiro , Kuwano Hiroshi , Saito Yoji
Published: July 2002

A method to obtain the energy distribution of traps at grain boundaries in polycrystalline silicon films from the activation energy of resistivity measured as a function of doping concentration is proposed. The energy distribution of trapping states in the energy gap for plasma-hydrogenated and nonhydrogenated polycrystalline silicon films doped with boron are determined: nonhydrogenated films have a Gaussian distribution with a peak at the midgap, and after plasma hydrogenation the peak at the midgap has diminished. The validity of the monoenergetic trap model applied to the conduction in nonhydrogenated and plasma-hydrogenated polycrystalline silicon films is discussed.
Control of interfacial morphology: NiSi2/Si(100)
Authors: Sullivan J. P. , Tung R. T. , Schrey F.
Published: July 2002

The structure and morphology of thin and ultrathin epitaxial NiSi2 layers on Si(100) grown by various techniques have been studied in detail. Very high-quality single-crystal NiSi2 layers have been grown on Si(100). Codeposition of stoichiometric NiSi2 at low temperatures followed by subsequent annealing at high temperatures (≥700 °C) has been shown to eliminate the most common problem for this epitaxial system, namely, faceting at the interface. Line defects, associated with interface roughness, were also greatly reduced in films grown by this method. Interfacial faceting and defects at interface domain boundaries appear to be related to the growth kinetics and are not due to energetic advantages, as previously thought. Discrete spots around the (01/2 1/2)-related reflections were observed by transmission electron diffraction from some planar NiSi2 layers, suggesting the existence of superstructures at portions of the NiSi2/Si interface. Low-energy electron diffraction indicated the existence of a highly ordered surface reconstruction for well-annealed films. Possible growth models, as well as the implications of possible structural inhomogeneity on interface electron transport measurements, are discussed.
Positive charge generation in SiO2 by electron-impact emission of trapped electrons
Authors: Thompson Scott E. , Nishida Toshikazu
Published: July 2002

Experiments are presented that firmly establish a common defect center for both positive and negative charges generated in thermally grown thin silicon oxide films and indicate the bridging oxygen vacancy as its probable origin (which is the well-established paramagnetic E′ center in crystalline and fused quartz and optical fibers). The positive oxide charge arises when one of the bound electrons at an initially neutral bridging oxygen vacancy, [(Si-O)3≡Si⋅⋅Si≡(O-Si)3], is emitted (released) by electron impact, VO0+e−*(kinetic energy≥7 eV)→VO++2e−. The measured electron impact threshold energy is 7 eV. An equal amount of negative oxide charge is generated at the same location (centroid about 9 nm from the SiO2/Si interface) by electron capture into the initially neutral oxygen vacancy, VO0+e−→VO−, whose peak density of charged state is located at 1 eV below the SiO2 conduction-band edge. The probable oxygen vacancy origin is deduced from an increase in the density of the shallow trap [VO−] and a higher positive charge generation rate at the deeper trap, d[VO+]/dt, in samples annealed in oxygen-deficient ambient (nitrogen and silicon gate) at 1000 °C, and from comparing the measured energies, (Ec−1 eV and Ec−7 eV), with the bound-state energies calculated by Fowler, Robinson, and associates. This origin is further supported by the oxide-electric-field dependence of the electron-impact emission coefficient of trapped electron at VO+, αnn=3500 cm−1 exp(−33 MV cm−1/EOX), and the electron capture cross section at a Coulombic VO+, σn∝EOX−n (n=2–4 and EOX=0.6–7.0 MV/cm); and by the steady-state balance between impact emission and thermal capture, which limits the buildup of positive oxide charge during electron injection into the oxide.
Ion kinetic-energy distributions in argon rf glow discharges
Authors: Olthoff J. K. , Van Brunt R. J. , Radovanov S. B.
Published: July 2002

Kinetic-energy distributions have been measured for different mass-selected ions sampled from 13.56 MHz rf glow discharges in argon inside a ‘‘GEC rf reference cell.’’ The electrode geometry of this cell produces an asymmetric discharge and the cell is operated in a pressure regime where ion-molecule collisions in the sheath region of the discharge are significant. Ions are sampled from the side of the plasma perpendicular to the interelectrode axis using an electrostatic energy analyzer coupled to a quadrupole mass spectrometer. Kinetic-energy distributions for Ar+, Ar2+, Ar++, and ArH+ are presented as functions of applied rf voltage, gas pressure, and distance of the mass spectrometer entrance aperture from the edge of the electrodes. The distributions obtained for the sampling orifice placed close enough to the electrodes to allow formation of a sheath in front of the orifice exhibit features similar to those observed previously when sampling ions through the grounded electrode of a parallel-plate reactor. The Ar+ and Ar++ distributions exhibit secondary maxima predicted to result from the formation of low-energy (thermal) ions in the sheath region, such as by charge-exchange and high-energy electron collisions. Kinetic-energy distributions for Ar2+ and ArH+ exhibit no secondary maxima and are peaked at high energies indicative of the sheath potential, and consistent with a formation mechanism involving relatively low-energy collisions in the bulk plasma (glow region).
Morphology of AlGaAs layer grown on GaAs(111)A substrate plane by organometallic vapor phase epitaxy
Authors: Umemura Masashi , Kuwahara Kazuhiro , Fuke Shunro , Sato Masahiro , Imai Tetsuji
Published: July 2002

Growth behavior of AlGaAs heteroepitaxial layers on GaAs (111)A planes has been studied for atmospheric pressure organometallic vapor phase epitaxy. The Al composition as well as the arsine partial pressure and the growth temperature are the influential factors for the surface morphology of epitaxial layers on (111)A planes. By increasing the Al composition of grown layers, the range of growth conditions for obtaining a smooth surface morphology does not change so much. But the range for controlling defect structures, such as pyramidal shape, shifts to lower arsine partial pressures, and/or higher growth temperatures. The Al0.3Ga0.7As growth rate remains constant even at a lower arsine partial pressure than for the GaAs growth. This indicates that the morphology change is due to the increase in the arsine dissociation efficiency when the trimethylaluminum partial pressure increases.
Photoexcited escape probability, optical gain, and noise in quantum well infrared photodetectors
Authors: Levine B. F. , Zussman A. , Gunapala S. D. , Asom M. T. , Kuo J. M. , Hobson W. S.
Published: July 2002

We present a detailed and thorough study of a wide variety of quantum well infrared photodetectors (QWIPs), which were chosen to have large differences in their optical and transport properties. Both n- and p-doped QWIPs, as well as intersubband transitions based on photoexcitation from bound-to-bound, bound-to-quasicontinuum, and bound-to-continuum quantum well states were investigated. The measurements and theoretical analysis included optical absorption, responsivity, dark current, current noise, optical gain, hot carrier mean free path, net quantum efficiency, quantum well escape probability, quantum well escape time, as well as detectivity. These results allow a better understanding of the optical and transport physics and thus a better optimization of the QWIP performance.
Electrical properties of highly ordered and amorphous thin films of pentacene doped with iodine
Authors: Minakata Takashi , Imai Hideaki , Ozaki Masaru
Published: July 2002

Studies on electrical properties of highly ordered and amorphous thin films of pentacene (PEN) doped with iodine have been made. Highly ordered film heavily doped with iodine (PEN1I2.2) showed electrical conductivity of 150 Ω−1 cm−1 with a hole mobility of 0.2 to 1 cm2 V−1 s−1 at room temperature. Metallic temperature dependence of the conductivity of the film from 240 to 4 K was observed as the first metallic transport phenomenon ever noted in an acenic compound. In contrast, amorphous film of PEN doped with iodine showed a conductivity of 10−3 Ω−1 cm−1 with an estimated hole mobility of 2×10−5 cm2 V−1 s−1 and semiconductive transport. These results revealed that the electrical properties of PEN thin films are strongly correlated with the degree of molecular orientation.
Magnetic characteristics of the Sm1−xPrxCo4−yFeyB system
Authors: Ido H. , Ogata H. , Maki K.
Published: July 2002

Magnetic properties of Sm1−xPrxCo4−yFeyB with various values of x and y have been observed mainly from the viewpoint of permanent magnet material. Pr substitution for SmCo4B results in an increase of the saturation moment; however, it leads to a decrease of the anisotropy field. The Curie temperature remains constant. On the other hand, the Fe substitution increases both the Curie temperature and the saturation moment significantly, and does not give vital damage to the original huge anisotropy field of SmCo4B. A possibility of the above system for a candidate of permanent magnet material is discussed in addition to discussion of the fundamental magnetic properties.
X-ray photoelectron spectroscopy study of CaS:Eu and SrS:Eu phosphors
Authors: Han Moonsup , Oh S.-J. , Park Jong Hee , Park H. L.
Published: July 2002

The phosphors of alkali-earth sulfides SrS:Eux (x=0.05 and 0.10 mole per mole of SrS), SrSO:Eux (x=0.05), and CaS:Eux (x=0.0005, 0.05, and 0.10) were studied by x-ray photoelectron spectroscopy. The CaS:Eu phosphors were found to be stabilized against atmospheric water vapor and carbon dioxide by annealing at high temperature for several hours. The S 2p core level shows that the chemical state of sulfur changes abruptly from −2 to +6 between the annealing temperature of 900 and 1100 °C. The Ca core level, on the other hand, does not show much change depending on the annealing temperature. From the Eu 3d core-level spectra of SrS:Eux and CaS:Eux (x=0.10) phosphors, we confirm that the valence state of Eu in these phosphors is Eu3+.
Observation of radio-frequency discharges at various driving frequencies
Authors: Ohtsu Yasunori , Okuno Yoshihiro , Fujita Hiroharu
Published: July 2002

Radio-frequency discharges at various driving frequencies f in the range of 1.9–28 MHz are observed, especially from the viewpoint of the sheath structure. The results reveal that for f≥10 MHz, the sheath thickness Zs measured by an emissive probe varies directly as f−1, while for f≤10 MHz, Zs∝f−1/2. The electron density estimated from the ion saturation current of a needle probe is almost proportional to f2 in the former case. High-energy electrons accelerated by the expanding rf sheath can contribute to sustaining rf plasmas in the high-frequency region, whereas in the low-frequency region, secondary electrons emitted from an electrode can contribute to it in a similar manner to dc and ac discharges.
Measurements of electron energy distribution function in an asymmetric radio-frequency discharge plasma
Authors: Okuno Yoshihiro , Ohtsu Yasunori , Komatsu Chihiro , Fujita Hiroharu
Published: July 2002

Electron energy distribution functions in an asymmetric radio-frequency (rf) discharge helium plasma were measured using an electrostatic energy analyzer looking opposite ways toward both the powered electrode and the bulk plasma. The grid and collector in the analyzer were connected to a series of parallel inductance-capacitance (L-C) filters to minimize rf interference. Electrons with high energies (15–30 eV) flowing from the electrode toward the bulk plasma were observed near the electrode. The energy is caused by the acceleration mechanism due to the rf sheath expansion, which should be the rf discharge sustaining mechanism. The electrons with high energies decreased in number with the distance from the electrode and became Maxwellian far from it. Electrons directed toward the electrode from the plasma were almost Maxwellian, and this situation was almost independent of the distance from the electrode.
The effects of gas phase convection on mass transfer in spin coating
Authors: Bornside David E. , Brown Robert A. , Ackmann Paul W. , Frank John R. , Tryba Anthony A. , Geyling Franz T.
Published: July 2002

The thickness uniformity of photoresist films deposited by spin coating critically influences the resolution of photolithography. This thickness uniformity depends on uniform evaporation from the film during drying. Simple scaling arguments demonstrate that, if the mass transfer coefficient at the surface of the wafer does not vary with radial position, then the dry coated resist film thickness will be independent of radial position. A model is presented for the compressible, laminar, steady-state, axisymmetric air flow in a spin coating apparatus for 6-in.-diam wafers. Flow fields computed by a finite-element–Newton method are used to evaluate the radial profile of the mass transfer coefficient at the surface of the rotating wafer, and to calculate the trajectories of particles that are generated as photoresist is flung from the edge of the spinning wafer. At a spin speed of 2000 revolutions/min and exhaust flow rate of 100 ℓ/min through the coater, the calculations predict that the mass transfer coefficient should be independent of radius. Comparison with film contours measured from experiments at these conditions indicates radial nonuniformities in the film thickness and suggests the importance of hydrodynamic instabilities in the gas on the uniformity of the coating.
Universality in two-dimensional magnetic systems
Authors: Bramwell S. T. , Holdsworth P. C. W.
Published: July 2002

Two-dimensional magnetic behavior in thin films and in layered magnets apparently falls into one of only two universality classes. The first is that of the 2D Ising model, characterized by a magnetization exponent β=1/8. The second, with β≊0.23, is observed in systems with planar spin symmetry. Recently it has been shown, using a modified renormalization group calculation, that β=0.23 is a property of a finite size XY model. Although there is no broken symmetry in this system, correlations below the Kosterlitz–Thouless transition temperature decay so slowly that a magnetization occurs in any realizable system, and β=0.23 is a result of two-dimensional fluctuations. By considering a large number of experimental situations we demonstrate that this rule is generally obeyed, and can be used as a test to identify two-dimensional behavior.
Photoluminescence properties of the Al0.48In0.52As/InP interface and the diffusion of carriers thereto
Authors: Olsthoorn S. M. , Driessen F. A. J. M. , Giling L. J.
Published: July 2002

A study of the photoluminescence (PL) and photoluminescence excitation (PLE) properties of the interface luminescence of the staggered-aligned Al0.48In0.52As/InP is presented, together with a study of the diffusion of carriers to this interface. Two PL peaks originating from the interface were measured at energies higher than commonly reported. This is the result of growth of the Al0.48In0.52As layer directly on the semi-insulating InP substrate, which results in a much sharper triangular well in the conduction band than when grown on an n-type InP buffer layer. Data from PL in a magnetic field and from PLE both showed that the PL transitions are excitonic in character. Furthermore, an inverted S-shape temperature dependence was found for the PL energy, which is characteristic of carrier localization. PLE measurements showed that at 4.2 K both electrons and holes participating in the interface PL are provided by exciton diffusion from the InP, while at 70 K they are provided by exciton diffusion from the Al0.48In0.52As. The difference arises from carrier localization in the Al0.48In0.52As top layer below 50 K. Unexpectedly, for the InP at 4.2 K the PL intensities of both excitonic and donor-to-acceptor transitions were independent of the absorption of laser light in the Al0.48In0.52As top layer.
Periodic mesoscopic step arrays by step bunching on high-index GaAs surfaces
Authors: Nötzel R. , Eissler D. , Hohenstein M. , Ploog K.
Published: July 2002

The direct formation of mesoscopic surface corrugations on high-index GaAs substrates during growth by molecular-beam epitaxy is reported. The accumulation of microscopic steps on GaAs (210) to produce one-dimensional step arrays with a 230 Å lateral periodicity is followed by reflection high-energy electron diffraction. The surprisingly high uniformity of the resulting mesoscopic step array is directly confirmed by atomic force microscopy. The shape of the steps is imaged by high-resolution transmission electron microscopy. Being comparable to the exciton Bohr radius in GaAs this length scale of the lateral periodicity is of particular importance for modulating the electronic properties of GaAs-based heterostructures. Pronounced red shifts in the luminescence of undoped GaAs/AlAs multilayer structures and an enhanced intensity at room temperature are observed. n-type modulation-doped heterostructures exhibit an anisotropic conductivity.