bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-beam-induced conductivity in polymer films
Authors: Venkatesan T. , Forrest S. R. , Kaplan M. L. , Murray C. A. , Schmidt P. H. , Wilkens B. J.
Published: February 2003

Polymer films darken upon irradiation with energetic ion beams. At high doses (1016–1017 cm−2) of 2-MeV Ar+ ions, the resistivity of these insulating films decreases dramatically to 3.5×10−3 Ω cm. Furthermore, over a wide range of doses (1014–1015 cm−2) these films exhibit a temperature-dependent resistivity characteristic of carrier transport via hopping between isolated conducting islands. Rutherford backscattering measurements indicate that while a substantial amount of the carbon is retained in the film, other constituent elements are lost. Raman spectra show that the films are highly disordered at large ion doses.
Theory of bulk gettering
Authors: Knize R. J. , Cecchi J. L.
Published: February 2003

A theory describing bulk better operation is presented. The theory is applicable to a diatomic gas which adsorbs dissociatively on a getter material which exhibits a time independent sticking coefficient. The theory includes the effects of surface reactions and bulk diffusion. Exact numerical solutions are presented for the particular cases of pumping and desorption. In addition, approximate analytical solutions are derived and used to illustrate the characteristics of the particular operational regimes. The theory is applied to the analysis of the pumping and desorption behavior of the Zr-Al alloy bulk getter. The predictions of the theory are in excellent agreement with the experimentally measured Zr-Al performance.
Copper-related deep level defects in III–V semiconductors
Authors: Kullendorff N. , Jansson L. , Ledebo L-Å.
Published: February 2003

Copper-diffused InP and GaAs have been studied using junction space-charge spectroscopy. Two dominant copper-related deep level defects are observed in both materials. Photoionization cross sections of holes and electrons, thermal hole emission rates, and one electron capture cross section have been measured. In InP one of the ionization spectra exhibits a pronounced phonon-related structure. The results, together with previous work on GaAs:Cu, GaP:Cu, GaAs:Cu, and AlGaAs:Cu, indicate a common geometrical structure for each of the two copper-related defects in all the materials.
Field drift and hydrogenation of deep level defects associated with 1-MeV ion-implanted oxygen in germanium diodes
Authors: Tavendale A. J. , Pearton S. J.
Published: February 2003

Deep level hole-(Ev+0.39 eV) and electron-trapping (Ec−0.34 eV) centers associated with oxygen ion implanted at 1 MeV (1014 ions cm−2) have been detected in Schottky barrier germanium diodes by deep level transient spectroscopy, following thermal anneals under molecular hydrogen. No traps were present after heating under atomic hydrogen from a radiofrequency induced plasma, indicating passivation by hydrogenation. Drift of the peaked, electron trap distribution formed at the projected ion range was observed across the depletion layer of a reverse biased Schottky diode with an average mobility of 5.5±1×10−15 cm2 V−1 s−1 at 25 °C.
Carrier multiplication in semiconductors induced by the absorption of high-intensity CO2 laser light
Authors: James R. B.
Published: February 2003

A calculation is presented to describe the modification of the carrier distribution due to the presence of high-intensity CO2 laser radiation for several semiconductors. In the calculation the intercarrier collision rates are assumed to be sufficiently large that the distribution can be described by a carrier temperature, which may be much larger than the lattice temperature. The steady-state carrier temperature is calculated as a function of the light intensity by equating the rate of energy which the carriers receive from the electromagnetic field and the rate of energy which the carriers lose to the lattice by the emission of phonons. For sufficiently high light intensities, a significant fraction of the total free carrier density can have kinetic energies which exceed the band gap. These hot carriers are energetically capable of relaxing by undergoing an inelastic pair-producing scattering event. This impact ionization process can lead to the formation of a laser-induced plasma by the absorption of light well below the band gap of the material. Explicit values are presented for the intensity thresholds at which the impact ionization process becomes important for light in the 9–11 μm region. Comparison of the results with transmission measurements indicate that this mechanism may be responsible for the nonlinear absorption observed in several semiconductors by high-intensity pulsed CO2 laser light.
The effect of surface states and fixed charge on the field effect conductance of amorphous silicon
Authors: Powell M. J. , Pritchard J.
Published: February 2003

We have developed a computer program to calculate the field effect conductance for an amorphous semiconductor including the effects of surface states and fixed charge at both surfaces of the thin semiconductor film. For undoped films with a bulk density of states of less than 1017 cm−3 eV−1, the space-charge region extends to a depth of 0.5 μm. A complete description of the potential distribution in the semiconductor must include the contribution of surface charge from the surface opposite the gate electrode. This is of practical importance in thin film transistors, for example, where different transistor structures and processing of devices can affect the charge density of this surface.
A study of the 0.1-eV conversion acceptor in GaAs
Authors: Look D. C. , Pomrenke Gernot S.
Published: February 2003

Two semi-insulating liquid-encapsulated Czochralski GaAs cyrstals, one Cr-doped and the other undoped, were annealed at 750 °C for 15 min in flowing H2. Each sample converted to conducting p type in the near-surface region, due to the formation of acceptors at Ev+0.1 eV. We have studied this phenomenon by electrical, optical, and analytical profiling techniques, and have determined conclusively that the acceptors in our samples are not related to Mn accumulation, a commonly accepted explanation. It is argued that the 0.1-eV center may arise from several possible sources, each exhibiting a VGa -like state at this energy.
Electrical properties of polyacetylene/polysiloxane interface
Authors: Ebisawa F. , Kurokawa T. , Nara S.
Published: February 2003

Polyacetylene/polysiloxane interface states have been investigated using metal-insulator-semiconductor (MIS) diodes. The 1-mm2 MIS diodes (Al/polysiloxane/polyacetylene) have been fabricated by use of a conventional photolithographic technique. The I-V and C-V measurements were used to explore the polyacetylene/polysiloxane interface electrical properties. The electrical conduction mechanism in this interface was found to be a Schottky-Richardson mechanism. Using the C-V measurements to determine the interface states density distribution, it was found that the distribution had a U shape in the gap and its minimum value was 6×1013 eV−1 cm−2. An attempt was made to fabricate an insulating gate field-effect transistor which worked as a depletion-type transistor with a very low transconductance, gm =13 nΩ−1.
Beam-plasma discharge in a Kyoto beam-plasma-ion source
Authors: Ishikawa Junzo , Takagi Toshinori
Published: February 2003

A beam-plasma type ion source employing an original operating principle has been developed by the present authors. The ion source consists of an ion extraction region with an electron gun, a thin long drift tube as the plasma production chamber, and a primary electron beam collector. An electron beam is effectively utilized for the dual purpose of high density plasma production as a result of beam-plasma discharge, and high current ion beam extraction with ion space-charge compensation. A high density plasma of the order of 1011–1013 cm−3 was produced by virtue of the beam-plasma discharge which was caused by the interaction between a space-charge wave on the electron beam and a high frequency plasma wave. The plasma density then produced was 102–103 times the density produced only by collisional ionization by the electron beam. In order to obtain a stable beam-plasma discharge, a secondary electron beam emitted from the electron collector should be utilized. The mechanism of the beam-plasma discharge was analyzed by use of a linear theory in the case of the small thermal energy of the electron beam, and by use of a quasilinear theory in the case of the large thermal energy. High current ion beams of more than 0.1 A were extracted even at a low extraction voltage of 1–5 kV.
Simulation of rectangular arrays of large charged spheres of alternating sign by sets of point charges
Authors: Zimmels Y.
Published: February 2003

A new method is described for evaluation of electric field around rectangular arrays of large charged spheres of alternating sign. It is shown that the arrays can be simulated by three pairs of point charges per unit cell. The relation between spacing of charges, their intensity, and radius of the spheres yields the required field. The method provides superior accuracies for different unit cell proportions, including a cube and rectangular parallelepipeds, with the point charges appropriately arranged so as to satisfy boundary conditions.
Numerical analysis of an optically pumped D2O far infrared laser
Authors: Okada T. , Behn R. , Dupertuis M. A. , Morgan P. D. , Siegrist M. R.
Published: February 2003

The performance of a pulsed D2O laser pumped longitudinally by a CO2 laser and emitting at 385 μm is investigated numerically. These studies point out the limitations in pumping efficiency due to the ‘‘bottleneck’’ effect in the vibrational deexcitation of D2O. The influence of a buffer gas on the saturation behavior is discussed. The results of this numerical simulation are in good agreement with experimental measurements. Design parameters are predicted for a D2O laser system suitable for Thomson scattering diagnostics of a Tokamak plasma.
Coupling of Love waves with the bulk elastic waves in the substrate
Authors: Seshadri S. R.
Published: February 2003

In an elastically isotropic thin film having a free surface with a weak periodic corrugation, deposited on a semi-infinite substrate of another elastically isotropic material, the interaction between the Love wave guided along the film and the horizontal shear bulk elastic wave propagating in the substrate is investigated for the propagation directions lying in a plane perpendicular to the film and containing the grating vector. The transport equation for the guided Love wave incorporating the effect of the coupling with the bulk elastic wave is deduced. The theory is applied to obtain the characteristics of the output coupler in which the Love wave guided along the film radiates a bulk elastic wave in the substrate as well as those of an input coupler in which a bulk elastic wave incident on the grating region of the film launches the Love wave along the film. Energy conservation principle and the reciprocity between the output and the input couplers are examined.
Propagation of a large-amplitude surface wave in a plasma column sustained by the wave
Authors: Mateev E. , Zhelyazkov I. , Atanassov V.
Published: February 2003

The axial electron number density distribution of a plasma produced by a rf surface wave launcher has been found theoretically. The results obtained are expressed in the form of universal curves which are applicable to a wide range of experimental conditions (wave frequency, collision frequency, tube radius). The theory agrees well with the available experimental data.
Effect of hydrogen impurity on the electrical characteristics of neon-argon gas mixtures. II. Deionization processes in afterglow plasmas
Authors: Bhattacharya A. K.
Published: February 2003

The effect of small amounts of H2 (0.005–1.0%) on the deionization processes in Ne-A discharges was measured by microwave cavity techniques. At low charged particle densities the deionization of discharges produced in Ne-A mixtures is determined by the ambipolar diffusion of electrons and molecular argon ions (A+2). The charged particle density in the deionization period following a pulsed discharge decays exponentially with time. For a discharge tube of 7 mm i.d. filled with Ne-A mixtures at a pressure of  20 Torr, the deionization of the plasma occurs with a time constant of 1.3 ms. The presence of a small amount of H2 (0.005%) enhances the deionization process drastically. The charged particle density decreases much more rapidly (time constant of 0.61 ms) than in the pure mixture. A similar increase in the deionization rate was measured in pure A. At low charge particle densities the deionization rate is determined by the ambipolar diffusion of a highly mobile hydrogen ion, possibly H+3, compared to relatively less mobile argon ions.
Effect of modulated high-pressure mercury discharges on the shape of self-reversed lines
Authors: Damelincourt J. J. , Aubes M. , Fragnac P. , Karabourniotis D.
Published: February 2003

The variation of the principal characteristics of the mercury visible triplet self-reversed lines is studied as a function of radial and temporal profiles of the temperature and of the species densities in high pressure mercury discharges (∼2 and ∼3 atm) operating on 50 Hz ac. An investigation is made into the effect of different theoretical and experimental parameters on the shape of calculated self-reversed lines. By comparison between experimental and theoretical results an estimation is made of the broadening constants and of the transition probabilities of the lines.
Detection of traps in high conductivity ZnSe by optical transient capacitance spectroscopy
Authors: Christianson K. A. , Wessels B. W.
Published: February 2003

Deep level defects in high-conductivity ZnSe have been observed with optical deep level transient spectroscopy. An electron trap and hole trap with energy levels at Ec  −0.33 and Ev +0.71 eV, respectively, were detected in the as-grown material. Trap concentrations were in the range of 0.4–2.0×1015 cm−3. For zinc annealed samples, a trap at Ev +0.21 eV was also observed in concentrations as high as 9×1015 cm−3. The chemical identity of the hole traps remain undetermined, but experimental evidence indicates they may involve native defects.
Bounds on the effective conductivity of a composite by the finite element method
Authors: Nakamura Mitsunobu , Hirasawa Masahide
Published: February 2003

An upper and a lower bound on the effective conductivity of inhomogeneous materials were computed by the finite element method. Here we calculate by the method bounds for a composite with a channeling pattern, and compare them with the results by the effective medium theory, with the Hashin–Shtrikman bounds and with the conductivity of the equivalent resistor network. The results make it clear that the composite has a very conductive structure and that we can predict by the finite element method and the Hashin–Shtrikman bounds whether geometrical configurations of composites are conductive or not.
Saturated photocurrent method for measurement of the optical-absorption coefficient in a semiconductor
Authors: Shimizu T. , Takeda K. , Yanagawa H. , Ohta E. , Sakata M.
Published: February 2003

A new method, named saturated photocurrent, has been developed for measuring the optical-absorption coefficient of the semiconductor with consideration of the effect of the interfacial oxide layer. By using this method we can discuss the transmission coefficient for the carriers through the interfacial layer produced on the Schottky barrier solar cell as well as the absorption coefficient of the semiconductor.
Flocculation of diamagnetic particles in high magnetic fields
Authors: van Kleef R. P. A. R. , Myron H. W. , Wyder P. , Parker M. R.
Published: February 2003

The combined influence of high magnetic fields and concentration of a paramagnetic electrolyte on the stability of a suspension of diamagnetic quartz particles has been investigated. For the first time, formation of magnetically induced binary pairs of particles has been observed over a broad range of electrolyte concentration and is explained in terms of an extended Derjaguin–Landau–Verwey–Overbeek (DLVO)-theory. Anomalous effects at low fields are shown to be caused by particle rotation due to an anisotropic magnetic susceptibility.
Effect of surface preparation on the 77 K photoluminescence of CdTe
Authors: Myers T. H. , Schetzina J. F. , Edwards S. T. , Schreiner A. F.
Published: February 2003

Photoluminescence spectra were obtained at 77 K for three undoped CdTe single crystal specimens whose surfaces were prepared by mechanical, conventional chemimechanical, and modified hydroplane polishing techniques, respectively. The hydroplane polished sample was found to be a much brighter source of photoluminescence than either of the other two specimens. In addition, hydroplane polishing produced a photoluminescence spectrum in which nearly all of the emission occurred in a band centered at 1.58 eV rather than in the well-known defect band at 1.42 eV. We interpret these results as providing evidence that hydroplane polishing of CdTe produces a surface having a low density of defects.
Mobile elements in steels studied by Auger spectroscopy
Authors: Biggiero Giovanni , Luzzi Giulio
Published: February 2003

A new technique of investigation, consisting in mechanically scraping a sample surface and then performing Auger measurements on the zone, is described in this paper. Large Cl quantities are found in steels, that have been previously degreased in freon. This Cl presence seems to be due to free and mobile atoms, presumably contained in sinks at grain boundaries.
Surface resistance due to trapped magnetic flux of superconducting lead at X band
Authors: Momose Takashi , Yamashita Tsutomu , Onodera Yutaka
Published: February 2003

The surface resistance due to trapped magnetic flux of superconducting lead at X band is described. A TM010 mode cavity was prepared by deep drawing copper substrates and electroplating lead on the substrates. Measurements were made on the cavity at rf input power less than 3 mW. Residual surface resistance values of 0.06 and 7.4 μΩ were obtained. The apparent surface resistance [R(H,T)] of lead due to the trapped magnetic flux has a temperature dependence of (1−t2)−1(1−t4)−1/2 at t=T/Tc<0.6 and a relationship is established for trapped flux field dependence, R(H,T)∝2ScRH, where RH is the surface resistance of lead due to trapped flux and Sc is the cross section area of the cavity to the field direction. A new equation for RH(T=0) is given as R(H,T=0)×(Stot/2Sc). The results prepared using the new equation show good agreement with the published results shown to date for superconducting lead cavities having differences in mode, structure, and frequency. To obtain Rres≤0.001 μΩ, an ambient magnetic field should be set less than 1 mG. The field dependence of R(H,T)+Rres in the case of Rres=7.4 μΩ approaches gradually to that of Rres=0.06 μΩ as the field increases. A model to explain the relationship between the two cases is also described.
The movement of magnetic bubbles in a rotating field gradient
Authors: Breed D. J. , Nederpel P. Q. J.
Published: February 2003

Magnetic bubbles can move in steady state under the influence of rotating field gradients. In the experiments reported in this paper the rotating field gradient method, as described by Jones et al., was used. Some technical improvements were introduced and two garnet films with uniaxial anisotropy were studied. The observed bubble mobilities compare very well with the mobilities obtained by the conventional bubble translation technique. The present method appears to be very suitable for studying the dynamic behavior of the magnetic bubbles near critical drive fields.
Analytical solutions of bubble tracks in periodical propagation structures
Authors: Ruigrok Jaap J. M.
Published: February 2003

In this paper a general expression is derived that describes tracks of bubbles in current-access devices, the rotating gradient experiment, etc. A resonance phenomenon resulting from this equation is experimentally verified: The periodical motion of a hard bubble shows a sharp maximum at a certain frequency of operation. This resonance frequency is proportional to the steepness of the magnetic potential well in which the bubble is captured and inversely proportional to the gyrotropic constant of the bubble. Even unichiral bubbles in low damping material may show this phenomenon. From this resonance frequency the gyrotropic constant of the bubble can be accurately determined. The experimental technique of applying a bias field modulation to counter the effects of wall motion coercivity is used. An attempt is made to include this mechanism in the theoretical description.
Conduction and dielectric polarization in neodymium fluoride thin films
Authors: Dharmadhikari Vineet S.
Published: February 2003

Measurements are reported on the capacitance, loss tangent, and permittivity of vacuum-deposited films of neodymium fluoride in the frequency range 0.050–100 kHz, thickness range 400–900 nm, and over a wide temperature range extending from 80–400 K. A detailed examination of these results reveals the contribution of dipolar orientation polarization to the dielectric dispersion. It is shown, based on the modified Debye theory, that the observed relaxation is a true dielectric dispersion phenomena resulting from the orientation of dipoles. The dipoles are shown to arise from a fluorine deficiency within the film. The density of equivalent dipoles estimated is about 1020 cm−3. The activation energy for this relaxation process is determined to be 1.02 eV. The physical and chemical nature of the deposited films is characterized by x-ray diffraction and x-ray photoelectron spectroscopy.
A comparison of secondary electron yields from accelerated water cluster ions (M/z<50 000) striking Al2O3 and copper surfaces
Authors: Beuhler Robert J.
Published: February 2003

A comparison of the yields of secondary electrons (γ) ejected by water cluster ions, with M/z ratios from 18 to 49 000 and kinetic energies from 40 to 250 kV, striking copper and aluminum oxide surfaces is detailed. For clusters striking Al2O3 with M/z in the range 21 000–49 000, threshold velocities of 1×106 cm/sec were observed, lower than previously measured values from Cu. Threshold for secondary electron emission for cluster ions occurs when the estimated depth of penetration, based on standard stopping power formulae, is less than one atomic layer. For the oxide surface it is shown that the electron yields do not obey an additive relationship. The yields are always less than one would predict by summing the electron yields from each water molecule in the cluster. Lack of additivity is also shown in the yields resulting from small water clusters striking Cu. Electron yields from both surfaces are compared to a model which relates γ to the energy deposited in the target within the electron escape depth. For the oxide surface, a reduced electron yield can be qualitatively explained by the formation of a positive charge at the surface which can retard the escape of secondary electrons. Some implications for the practical use of these two surfaces as detection dynodes in high molecular weight mass spectroscopy are discussed.
Comparison between electron-beam and furnace rapid isothermal anneals of phosphorus-implanted solar cells
Authors: Lulli G. , Merli P. G. , Negrini P. , Ostoja P. , Solmi S.
Published: February 2003

Solar cells have been fabricated using single crystal silicon wafers, implanted at 10-keV energy with 2×1015 P+/cm2. Rapid isothermal heat treatments at temperatures ranging between 500 and 1000 °C were used to anneal the implanted damage. Two different methods have been used: electron-beam and furnace annealing for times ranging between 0.5 and 5 min, and between 2 and 5 min, respectively. Characterization of P+-implanted layers and of completed solar cells allowed us to demonstrate that rapid isothermal anneals with furnace and electron beam give equivalent results. The efficiency of solar cells which are annealed using these rapid isothermal processes is fairly good (13.5%), even if slightly lower than that obtained with conventional anneals (750 °C for 30 min). The reduced efficiency is a consequence of the lower value of the open circuit voltage. It is demonstrated that this effect is caused by residual defects in the space-charge region, produced by ion implantation.
Composition and structure of thermal oxides of indium phosphide
Authors: Nelson Art , Geib Kent , Wilmsen C. W.
Published: February 2003

The thermal oxidation of InP has been studied for growth temperatures of 400 to 700 °C using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) profiles and x-ray diffraction. For T<600 °C the composition of the oxide is layered. The outer layer is composed of In2O3 and InPO4 and the inner layer is primarily InPO4 with elemental P at the interface. For T>650 °C the oxide composition is primarily InPO4 throughout the layer although the roughness of the high temperature oxide may distort the XPS sputter profiles. From x-ray diffraction data, the oxides grown at T<650 °C appear noncrystalline. At T=700 °C the oxide is crystalline InPO4.
Radiation measurements from an inverted relativistic magnetron
Authors: Close R. A. , Palevsky A. , Bekefi G.
Published: February 2003

We report microwave emission measurements from an inverted relativistic magnetron comprising an outer cylindrical field emission cathode and an inner coaxial anode with embedded vane resonators. The magnetron operates in the π mode at a frequency ∼3.6 GHz, and voltages of 1–2 MV. The rf power is ∼500 MW.
Magnetization distributions in ion-implanted bubble garnet films
Authors: Wilson Lynn O. , Nelson T. J.
Published: February 2003

We solved coupled differential equations that govern the magnetization in the storage layer and the drive layer in an ion-implanted magnetic bubble film. We treat specific numerical cases with film properties and applied fields typical of 8-μm period bubble devices based on ion-implanted propagation patterns. The transition field region is approximately 0.07 μm wide, which is twice as large as one previous approximate theory predicts, but which agrees well with another approximate model. We also compute the magnetization direction in the layer as a function of the drive field direction and compare our results (a) with an approximate analytical method which assumes that the polar angle θ is nearly constant and (b) with another numerical study which neglected effects of coupling to the storage layer. Our results are in agreement with the latter, but the variation of polar angle with drive field direction is quite small (∼0.5°) compared to the estimate (∼6°) of the former.
Thin film recording head efficiency and noise
Authors: Hughes Gordon F.
Published: February 2003

Analytic formulas for thin film recording head efficiency and thermal noise are presented. Paton’s transmission line model is replaced by two-dimensional eddy currents in four regions: the coil region, the gap region, and two permeable pole regions. Predicted efficiencies are lower, and close to actual thin film heads. Basically, a four-region solution is needed because the gap region is a reluctive load on the coil region’s pole reluctance, which lowers the predicted efficiency substantially below that of the unloaded Paton two region (coil and pole) transmission line. Paton efficiency formulas seem to often predict either too high an efficiency, or too low a permeability. For typical head dimensions, the four region efficiency formulas reduces to hand calculator simplicity. Eddy currents in the drive coils and conductive (permalloy) poles can cause the impedance phase angle θ of these heads to hover closer to 45° than to a purely inductive 90° (eddy currents in a permeable, plane slab have 45° average phase angle). Such eddy currents can give an unusual impedance Z( f), and can raise the real part of the head impedance (‖Z‖cos θ) an order of magnitude higher than the dc resistance, and thereby similarly raise the mean-square thermal noise from the head. Magnetic field formulas from the four-region eddy current equations are used to calculate this impedance and the excess noise factor.
Silicon-stabilized grey tin
Authors: Gallerneault W. M. T. , Vnuk F. , Smith R. W.
Published: February 2003

Melt-spun Sn–Si alloy tapes were transformed to the grey modification at −30 °C to give compact specimens. On subsequent heating, the grey tin phase was seen to be stable to elevated temperatures, e.g., 90 °C for the Sn–0.6 wt % S alloy.
Symmetry determination for deep states in semiconductors from stress-induced dichroism of photocapacitance
Authors: Stavola M. , Kimerling L. C.
Published: February 2003

We have developed a junction capacitance spectroscopy that provides the means to obtain structural information for semiconductor defects. We combine stress alignment and photocapacitance measurements that are made with polarized infrared light to determine that the electron irradiation induced level H(0.21 eV) in p-type silicon that is observed by deep level transient spectroscopy has the same symmetry as the divacancy. The recovery kinetics of the stress alignment follow closely the microscopic reorientation rate of the divacancy. On the basis of this information we have unambiguously assigned H(0.21 eV) to the divacancy.
Nitrogen related deep electron trap in GaP
Authors: Ferenczi G. , Krispin P. , Somogyi M.
Published: February 2003

The most common electron trap in nitrogen doped GaP (0.45 eV below the conduction band) was studied in detail. It was established that the trap concentration quadratically depends on the N concentration and nearly linearly on the net donor concentration. Recombination enhanced anneal of this trap is accompanied by an increase of the nearest-neighbor nitrogen pair luminescence. A tentative model is suggested to identify this trap as a nitrogen split interstitial pair on phosphorous site.
Temperature dependence of electrical transport properties of n-type solar grade polycrystalline silicon
Authors: Mathur P. C. , Sharma R. P. , Shrivastava Renuka , Saxena P. , Kotnala R. K.
Published: February 2003

The effect of temperature on the electronic conduction mechanism and grain-boundary states has been observed through the measurements of Hall coefficient (RH), resistivity ( ρ), and Hall mobility (μH=RH/ρ), on n-type solar grade polycrystalline silicon having columnar grains in the temperature range ∼77–500 K. It is found that electronic conduction in the low-temperature range is determined by the hopping of the charge carriers in the localized states at the Fermi-level and RH is a slow function of temperature. In the intermediate temperature range the conduction is dominated by the thermionic emission of electrons over the grain boundaries. At a critical temperature Tc where the barrier height (φb) and hence the width of the space-charge region near the grain boundaries tends to zero, a crossover from the barrier-limited to the mobility-limited resistivity occurs. RH is found to be thermally activated over the temperature range where the conduction mechanism is governed by grain-boundary barriers. The experimental results are explained on the basis of a grain-boundary trapping model combined with the two-phase model and are used to determine various parameters, viz., grain size, trap-state density, and the amount of band bending at the grain boundary.
Impurity-limited mobility of semiconducting thin wire
Authors: Lee Johnson , Spector Harold N.
Published: February 2003

Sakaki [Jpn. J. Appl. Phys. 19, L735 (1980)] has investigated the mobility of semiconducting thin wire structures when the mobility of the wire is limited by scattering from ionized impurities which are located a fixed distance outside the wire. We have used a similar model to theoretically calculate the impurity-limited mobility of such semiconducting thin wires for the cases where the impurities are either in the wire itself (background impurities) or are distributed outside the wire (remote impurities) or are distributed uniformly both inside and outside the wire. For the case of scattering from the background impurities, we find that the mobility decreases with decreasing wire radius d as [ln (kd)]−2 where k is either the thermal or Fermi wave vector of the carriers. For the case of scattering from remote impurities, the size dependence of the impurity-limited mobility depends upon how the remote impurities are distributed outside the wire. When the distribution of ionized impurities outside the wire is uniform, the mobility is independent of the wire radius while, if the ionized impurities are separated from the wire by a fixed distance, we recover the results previously obtained by Sakaki. When the impurities are distributed uniformly both inside and outside the wire, the mobility again is size independent.
Analysis of the interaction of an electron beam with back surface field solar cells
Authors: von Roos Oldwig , Luke Keung L.
Published: February 2003

In this paper the short circuit current ISC induced by the electron beam of a scanning electron microscope in a back surface field solar cell will be determined theoretically. It will be shown that, in a configuration used previously for solar cells with an ohmic back surface, the ISC gives a convenient means for estimating the back surface recombination velocities and thus the quality of back surface field cells. Numerical data will be presented applicable to a point source model for the electron–hole pair generation.
Temperature dependent light induced conductivity changes in hydrogenated amorphous silicon
Authors: Jang Jin , Lee Choochon
Published: February 2003

The light induced changes for undoped and phosphorus doped hydrogenated amorphous silicon films deposited by dc glow discharge decomposition have been studied. It is observed that the conductance change after illumination is large for the undoped films deposited near the cathode, and deposited with high silane flow rate. The 0.1%–0.5% phosphorus doped samples show the increase of dark- and photoconductance after illumination. The rate of dark- and photoconductance change are observed to be accelerated as the temperature during the illumination is elevated. The activation energies for the recovery of the conductance changes are observed to be 1.5 and 1.0 eV for undoped and 0.1% phosphorus doped films, respectively. The field effect measurements for 0.1-μm-thick undoped a-Si:H film before and after the illumination show that the gap state density is not changed after illumination. The results are explained on the basis of material heterogeneity. The trapping regions, considered to be contained in tissue, should be assumed to exist in the material to explain the results. The transfer of electrons (or holes for p type samples) between islands and the trapping regions give rise to the light induced changes in conduction.
Theory of electron–hole kinetics in amorphous semiconductors under illumination: Application to solar cells
Authors: Lagos R. E. , Suhl H. , Tiedje T.
Published: February 2003

A general kinetic theory of the generation and recombination of electron–hole pairs for an illuminated amorphous semiconductor with an arbitrary distribution of gap states is presented. The basic assumptions of the theory are first, that sharp mobility edges separate localized states from extended states, and second that the localized states can communicate with each other only via the extended states. In the limit that mobile carriers are concentrated at the band edges, the coupled nonlinear integral equations for the occupation functions can be reduced to quadratures. The theory is applied to calculate the current–voltage characteristic of amorphous silicon solar cells, in the ‘‘lumped circuit’’ model where the spatial dependence is neglected. The open circuit voltage, the fill factor and the upper limit for the solar conversion efficiency of such devices are calculated as functions of the gap density of states.
Effects of controlled hydrogenation by ion implantation on the localized states in vacuum evaporated amorphous silicon
Authors: Lee T. C. , Neudeck G. W.
Published: February 2003

Hydrogen incorporation into electron beam vacuum-evaporated amorphous silicon films has been performed by ion implantation followed by a low temperature thermal activation at 230 °C. After hydrogenation, a field effect conductance change of 4 orders of magnitude was observed. A comparison of the samples before hydrogenation and after hydrogenation demonstrates that almost 3 orders of magnitude reduction (from about 1022/cm3 eV to about 1019/cm3 eV) in the density of localized states near the Fermi level in the energy gap has been achieved. Varying the hydrogen implantation dosage between samples from 1×1016 to 1.5×1017/cm2, with all other sample preparation procedures fixed, causes a decrease in the density of localized states near the Fermi level of the amorphous silicon from 8.6×1020 to 1×1019/cm3 eV.
Mass spectrometric studies of impurities in silane and their effects on the electronic properties of hydrogenated amorphous silicon
Authors: Corderman R. R. , Vanier P. E.
Published: February 2003

The concentration of volatile impurities in silane (SiH4) and disilane (Si2H6) used to prepare hydrogenated amorphous silicon (a-Si:H) thin films by glow-discharge deposition has been measured by modulated molecular beam mass spectrometry with a sensitivity of 1 ppm. From dark conductivity measurements on these films the location of the Fermi energy EF was determined. The Fermi levels of a-Si:H films were progressively lower with increasing concentrations of chlorine-containing molecules (mostly HCl and SiH3Cl) in the silane, indicating that these species can act as weak p-type dopants in a-Si:H. Oxygen-containing species (mostly SiH3OSiH3) were also detected in silane. It is clear from these results that large variations in electronic properties of glow discharge a-Si:H can be attributed to differences in purity of silane used in the deposition.
Photoemission studies of molecular beam epitaxially grown GaAs (001) surfaces exposed to a nitrogen plasma
Authors: Gourrier S. , Smit L. , Friedel P. , Larsen P. K.
Published: February 2003

GaAs(001) surfaces prepared in situ by molecular beam epitaxy (MBE) have been investigated by reflection electron diffraction, valence-band photoemission and core level photoemission after exposures to nitrogen plasmas. The nitridation leads to disordered surfaces. The Fermi level (EF) which for the clean surface is situated at 0.4 eV above the GaAs valence-band maximum (VBM) shifts as a function of the plasma exposure towards a saturation value of 1.1 eV above VBM. Strong nitrogen derived peaks are found in the valence-band spectra at energies 5 to 8 eV below EF. As(3d) and Ga(3d) core level spectra show chemical shifts towards higher binding energies due to the nitridation. The shift is 0.7–0.8 eV for the Ga(3d) level. For the As(3d) level shifts in the range 1.4–2.2 eV are observed. The dependence of the chemical shifts and the linewidths on the plasma exposure and on subsequent heat treatments are explained by the presence of different As nitrides having different binding energies and volatilities, whereas only one Ga nitride (GaN) is formed by the nitridation.
Pile up of implanted phosphorus during palladium silicide formation and the characteristics of Schottky barrier diodes
Authors: Kikuchi Akira
Published: February 2003

Schottky barrier diodes are fabricated on silicon surfaces whose impurity concentrations are controlled by ion implantation of phosphorus. The barriers are produced from Pd2Si or Al–Si. The forward voltages of Schottky barrier diodes made from Pd2Si show a much greater lowering than those made from Al–Si for implanted doses of 5×1013 cm−2 and higher. Spreading resistance measurements show that the implanted phosphorus atoms are piled up at the Pd2Si–Si interface during Pd2Si formation. This causes reduction in the effective barrier height.
Capacitance temperature analysis of midgap states in hydrogenated amorphous silicon
Authors: Jousse D. , Deleonibus S.
Published: February 2003

Simultaneous low frequency capacitance-temperature and conductance-temperature measurements on Schottky diodes in the range 180–450 K enable us to deduce the real density of bulk midgap states N(E) of hydrogenated amorphous silicon in the zero frequency limit. The analysis of the results indicates that the interaction kinetics is controlled by the thermal release time of the midgap states. The response times are consistent with an electron capture cross section ranging from 2×10−16 to 5×10−15 cm2, very similar to the value reported for crystalline Si–SiO2 interface states. Furthermore, results show that thermal equilibrium is established directly with conduction band electrons at high temperature or through intermediate states at temperature lower than 300 K. The high accuracy of the method is demonstrated by detecting 15% variations of N(E) due to light-induced effects. The physical nature of midgap states is also discussed.
Deep traps in metal–insulator–chemically vapor-deposited amorphous SiNx diodes
Authors: Sasaki Goro , Fujita Shizuo , Sasaki Akio
Published: February 2003

The dependence of capacitance of chemically vapor-deposited (CVD) amorphous SiN0.2 metal–insulator–semiconductor (MIS) diodes on frequency and temperature is measured and discussed. The results show that the MIS diode includes slow states and fast states. The response time of slow states is 2.4×10−9 exp(−0.6 eV/kBT) s above 130 °C. The fast states fully respond to 95 Hz at 130 °C. It cannot be distinguished whether these states originate from the interface states or the a-SiN0.2 gap states. The densities are evaluated to be 6×1017 cm−3 eV−1 (fast states) and 6×1018 to 2×1019 cm−3 eV−1 (slow states) as the CVD a-SiN0.2 gap states, or 6.9×1011 cm−2 eV−1 (fast states) and 6.2×1012 to 1.2×1013 cm−3 eV−1 (slow states) as the interface states.
Ablative organic films for optical recording
Authors: Mitsuya Munehisa , Terao Motoyasu , Taniguchi Yoshio , Kaku Toshimitsu , Shigematsu Kazuo , Akagai Motoo
Published: February 2003

This work presents a new type of optical recording medium for a diode laser which is three times more sensitive than a chalcogenide thin film. This medium has a tetralayer structure of n–hexatriacontane, zinc stearate, Sb2S3 and Bi. The Bi layer absorbs a recording light beam and organic layers are ablated by heat evolved in the Bi layer. The high sensitivity characteristic of this medium is attributed to the use of low-melting-point material as the ablating layer and the effective use of the incident beam.
A kinetic model of the sustained discharge HgBr laser
Authors: McGeoch M. W. , Hsia J. C. , Klimek D. E.
Published: February 2003

A kinetic model of the sustained discharge Ar/HgBr2 laser is developed from an experimental base. The choice of Ar as the buffer gas is supported by measurements of the specific fluorescence and laser efficiency in the buffer mixtures (Ar, Ar+5% Xe, Ne+10% Xe, Ne+10% N2). A computational treatment of the coupled photon and kinetic equations is described. Gain measurements determine a peak HgBr (B-X) stimulated emission cross section of 1.6×10−16 cm2±20% at 502 nm. Absorption measurements between 515 and 530 nm show the presence of a large, broad band absorption tentatively assigned to HgBr+2 with a cross section of 2×10−18 cm2. An upper bound of 5×10−9 cm3 sec−1 is placed on the rate constant for electron collisional quenching of the HgBr(B) state. The laser extraction efficiency of 65% is modeled by a lower level collisional deactivation by Ar with a rate constant 6.0×10−12 cm3 sec−1. Discharge impedance is measured as a function of E/N and the ionizing electron beam current density. Using the new data a good description of laser efficiency is demonstrated if the ratio of HgBr(B-X) fluorescence power to discharge input electical power is set to 6.1%, for 0.8% HgBr2 in Ar at E/N=8×10−17 V cm2.
Surface roughness and the attenuation length of guided waves in optical fibers
Authors: Mazur P. , Mills D. L.
Published: February 2003

We consider the influence of surface roughness on the attenuation length of electromagnetic waves guided by a dielectric cylinder. Fluctuations in the radius of the cylinder allow the guided wave to radiate energy into the vacuum outside the guide. We find that a perfectly sinusoidal modulation of the radius of the guide leads to a contribution to the attenuation coefficient propertional to ω2, if the wavelength of the guided mode is small compared to the radius of the guide, and if the spatial period of the sinusoid is in the appropriate range. Random fluctuations in the radius on a spatial scale small compared to the wavelength of the mode lead to a contribution proportional to ω3, in the limit of large guide radius. Our theoretical results will be compared to the data reported by Harrington, who studied the scattering produced by waves with wavelength in the 2–10 μm range in thallium halide fibers.
Fundamental defect centers in glass: Electron spin resonance and optical absorption studies of irradiated phosphorus-doped silica glass and optical fibers
Authors: Griscom D. L. , Friebele E. J. , Long K. J. , Fleming J. W.
Published: February 2003

Defect centers induced by ionizing radiation (50–100-keV x rays, 60Co γ rays) in high purity P-doped silica glass have been observed and elucidated by ESR spectroscopy. Four generic species are well characterized on the basis of the observed 31P hyperfine splittings and g values as defects analogous to PO2−3 (phosphoryl), PO4−4 (phosphoranyl), PO2−2 (phosphinyl), and PO2−4 radicals. The latter species, also termed the phosphorus-oxygen-hole center (POHC), is shown to occur in two variants comprising holes trapped on one or two nonbridging oxygens. Radiation-induced Si E′ centers with and without P next-nearest-neighbors were also identified, and a singlet resonance S due to E′ type defects such as (OSi2)Si⋅ and/or (O2Si)Si⋅ was observed to grow in with annealing above ∼800 K, regardless of whether or not the sample was irradiated. The structures, formation mechanisms, and precursors of these defects have been determined or inferred for all centers. Radiation-induced optical absorption spectra over the range 0.5–6.2 eV have been obtained for bulk glass and fiber samples after irradiation and following anneals to various temperatures up to 1250 K. Gaussian resolutions of the spectra into component bands have been performed and isochronal anneal data have been used to identify optical absorptions of the PO2−3, PO4−4, PO2−2, POHC, and S centers. The PO2−3 defect was found to absorb at ∼0.8 eV in the region of interest for fiber optic communication. Oscillator strengths are calculated for all bands.
Linear theory and adiabatic wave amplitude variation in the converging guide accelerator
Authors: Sullivan D. J. , Godfrey B. B.
Published: February 2003

A linear numerical analysis of the converging guide accelerator incorporating a radially inhomogeneous beam equilibrium and finite axial magnetic field is conducted. It is shown that these characteristics cannot explain the latest experimental results involving large amplitude waves. The slow phase velocity of these waves rely on nonlinear effects. A study of the adiabatic variation of wave amplitude in the accelerator indicates the importance of using high frequency waves for efficient operation.