bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of carbon adsorption to Si(100) surface by thermal desorption spectroscopy and x-ray photoelectron spectroscopy
Authors: Matsuo N. , Kagawa K. , Miyoshi T.
Published: July 2002

Carbon adsorption to the Si(100) surface in the atmosphere with large or with small concentrations of organic carbons is examined by using thermal desorption spectroscopy or x-ray photoelectron spectroscopy. The number of carbon atoms on a Si(100) wafer stored in the pure water, in which the total organic carbon is 285 ppb, becomes larger until a certain time with increasing time stored in pure water, and it keeps constant over that time. On the other hand, that stored in the air in the clean bench, where the concentration of the organic carbon is thought to be low, becomes small, and the increasing rate of the carbon atoms adsorbed on the Si(100) surface is very small. The difference between these results is due to whether the dominant step is the transportation of organic carbons in the atmosphere or it is the adsorption of organic carbons on the Si surface. The former process occurs for the small concentration of the organic carbons in the atmosphere, and the latter process occurs for the large concentration of them. Adsorption of the organic carbons dominates in the entire process in pure water under the present condition, and the transportation of them dominates in the entire process in the air of the clean bench under the present condition. From the relationship between C1s integral intensity and thickness of the native oxide, it is found that the adsorption of the carbon atoms has a close relationship with the growth of the native oxide on the Si surface. The adsorption site of the carbon atoms is also discussed from the viewpoint of stepped growth of the native oxide.
Frequency readout of relaxation oscillation superconducting quantum interference devices in the GHz regime
Authors: van Duuren M. J. , Adelerhof D. J. , Brons G. C. S. , Kawai J. , Uehara G. , Kado H. , Flokstra J. , Rogalla H.
Published: July 2002

The output of relaxation oscillation superconducting quantum interference devices (ROSs) consists of a sequence of voltage pulses with a frequency that depends on the flux that is applied to the ROS. In this paper, a theoretical model for the flux-to-frequency conversion of a ROS is presented, and this model is validated in practice for oscillation frequencies up to 7 GHz. The experiments have been performed on more than ten different ROSs and the model was able to fit all measured data, which illustrates the versatility of the model. Furthermore, a simple flux locked loop based on frequency readout of a ROS in the GHz regime is presented. The measured flux noise, √SΦ=2.5μΦ0/√Hz, corresponding to an energy resolution ε≊600h, is probably not intrinsic to the ROSs, but due to the readout electronics.
Photoconductive sampling of subpicosecond pulses using mutual inductive coupling in coplanar transmission lines
Authors: Jacobsen R. H. , Uhd Jepsen P. , Keiding S. R. , Larsen B. H. , Holst T.
Published: July 2002

We demonstrate the generation and detection of subpicosecond pulses by photoconductive sampling in a three-line coplanar transmission line structure. Due to a mutual inductive coupling between adjacent striplines a differential sampling is obtained. Voltage pulses as short as 390 fs have been measured in a long-lifetime photoconductive switch. We emphasize that differential coupling can be used for the detection as well as the generation of subpicosecond pulses in long-lifetime photoconductors.
C+-energy-dependent residual ion damage in GaAs:C grown by the low-energy ion-beam doping method
Authors: Iida Tsutomu , Makita Yunosuke , Shima Takayuki , Kimura Shinji , Horn Joachim , Hartnagel Hans L. , Uekusa Shin-ichiro
Published: July 2002

The effects of residual ion damage in low-energy (30 eV–30 keV) C+-doped GaAs were investigated with regard to the electrical and optical activation of C as a function of C+ ion acceleration energy EC+. Systematic variation of EC+ demonstrated that, in the energy range of EC+<170 eV, the net hole concentration (|NA−ND|) slightly increases as EC+ increases and the highest |NA−ND| was obtained at EC+=170 eV under the constant C+ ion-beam current density. For EC+≳170 eV, an increase in EC+ gave rise to an abrupt decrease of |NA−ND| down to two orders of magnitude smaller than that obtained at EC+=170 eV. In low-temperature (2 K) photoluminescence spectra for as-grown samples with EC+=240 and 350 eV, a novel emission ascribable to residual ion damage was observed instead of an essential acceptor–acceptor emission of [g−g]β. However, subsequent annealing at 850 °C made this novel emission disappear and the proper [g−g]β emission was merely observed. An activation process observed for EC+=5, 10, and 30 keV samples was very similar to that by high-energy ion implantation, indicating low activation rate of 10%–15%. Minority-carrier lifetime measurements using scanning tunneling microscope stimulated time-resolved luminescence demonstrated the presence of residual ion damage in as-grown samples at EC+=240 and 350 eV and annealed ones at EC+=5, 10, and 30 keV while no ion damage was observed in as-grown sample at EC+=30 eV. The incorporation and activation behaviors of C atoms that take the form of low-energy ions were found to be considerably affected by changes in ion–surface interaction with increasing EC+ and by the presence of residual ion damage in the layer.
Dynamics of a ring with three Josephson junctions
Authors: Geigenmüller U.
Published: July 2002

The dynamics of a current biased superconducting ring with three Josephson junctions is investigated theoretically. For suitable magnetic frustration, the current–voltage (I–V) characteristic shows a surprising series of cusps. This feature, as well as the critical current, are discussed in detail, and explained using an extension of the familiar ‘‘tilted washboard’’ model. The stability of the new structure in the I–V curves against changes of various parameters is studied. An estimate shows that experimental observation should be feasible.
Direct measurement of the polarization-dependent absorption and saturation in an InGaAs/InGaAsP single quantum well
Authors: Gontijo I. , Tessier G. , Livingstone M. , Galbraith I. , Walker A. C.
Published: July 2002

A simple technique has been used to measure the two polarization-dependent absorption edges in a single quantum well around 1.5 μm. The broadband spontaneous emission of an AR-coated semiconductor laser chip was used as the spatially coherent light source in conjunction with a grating spectrometer. Absorption edges for both TE and TM polarized light have been measured in single quantum well InGaAs/InGaAsP waveguides and modeled by the k⋅p method. By pumping the devices with a 1.3 μm semiconductor laser, absorption saturation was also studied. The resulting changes in the refractive index were calculated from a Kramers–Kronig transformation of the absorption changes.
Emittance tailoring of electron beams for propagation in dense gas
Authors: Myers M. C. , Fernsler R. F. , Meger R. A. , Antoniades J. A. , Murphy D. P. , Hubbard R. F.
Published: July 2002

An intense relativistic electron beam injected into dense gas characteristically propagates in a self-pinched mode but is susceptible to the resistive hose instability. This convective instability typically leads to large amplitude beam motion and the disruption of propagation. Theory and computation suggest that, although resistive hose cannot be completely suppressed, its convective growth can be reduced by varying the average betatron oscillation frequency from head to tail in the beam pulse. We report here on experiments designed to implement this variation by tailoring the beam emittance using an ion-focused regime ‘‘conditioning’’ cell. Conditioning effectiveness is assessed by using measured beam quantities to evaluate a detuning parameter η(t). This information is correlated with beam propagation measurements to determine the optimum conditioning for resistive hose suppression.
Effects of hydrogen addition on C44 and ultrasonic attenuation of vanadium single crystals
Authors: Kojima H. , Sanada T. , Koike S.
Published: July 2002

Examination was made of ultrasonic attenuation α44 and elastic constant C44 of vanadium single crystals with hydrogen between 4.2 and 220 K, as a function of temperature, hydrogen concentration, frequency, and rates of cooling and heating. Attenuation in the V–H α phase at 210 K increased in proportion to the square of hydrogen concentration, while C44 was linear. At a cooling rate of 3.0 K/min, attenuation of the specimen with 1000 at. ppm H increased below the critical solution temperature and showed a peak. At 0.1 K/min, discontinuous decrease was observed at the temperature. During isothermal annealing below this temperature, attenuation at the higher cooling rate decreased with time in two stages and approached the value for the lower cooling rate. The results are discussed based on ultrasonic double refraction due to the volume array of hydrogens and hydride particles formed under the influence of C44-mode ultrasonic waves.
Diffusion-limited layer growth in spherical geometry: A numerical approach
Authors: Costa L. , Vilar R.
Published: July 2002

In this article we present a detailed numerical analysis of the problem of diffusion-controlled growth of a solid intermediate phase from two saturated solutions (solid solute and solid or liquid solvent). Spherical geometry is considered and the quasi-steady-state approximation used in earlier analytical models is eliminated. Comparison between our results and those from Larson’s model allows us to conclude that the use of a numerical scheme may lead to a significant gain in accuracy except when a solute-rich sphere is converting into a dilute phase.
Sulphur diffusion at the Si/GaAs(110) interface
Authors: Xia H. , Lennard W. N. , Huang L. J. , Lau W. M. , Baribeau J.-M. , Landheer D.
Published: July 2002

The depth distribution of sulphur near the Si/GaAs(110) interface has been measured using particle induced x-ray emission (PIXE) in conjunction with Rutherford backscattering spectrometry (RBS); ozone oxidation and a hydrofluoric acid step-etching technique were used for sequential removal of Si/GaAs atomic layers. The depth resolution was also calibrated via 16O(d,p)17O nuclear reaction analysis and x-ray photoemission spectroscopy. PIXE/RBS measurements found a half monolayer of sulphur on the H2Sx passivated GaAs(110) surface. Upon deposition of 15 Å silicon on the S-passivated GaAs(110), the total amount of sulphur remained constant as compared to that before Si deposition. However, no orientated S–Ga bonds were detected via the x-ray absorption measurement and the depth profile revealed that the sulphur atoms diffused into both the GaAs substrate and the Si heterolayer.
Temperature dependence of galvanomagnetic properties for Er-doped and undoped n-type InSe
Authors: Yildirim M. , Gürbulak B. , Abay B. , Efeoğlu H. , Tüzemen S. , Yoğurtçu Y. K.
Published: July 2002

The magnetoresistance and the Hall-effect measurements in undoped n-InSe (InSe) and Er-doped InSe (InSe:Er) samples in the temperature range 10–340 K were carried out. The InSe sample and the InSe:Er sample exhibit a null transverse magnetoresistance effect for T≳160 and T≳140 K, respectively, and a zero longitudinal magnetoresistance effect for T≳160 and T≳100 K, respectively. As the temperature increases, the carrier concentration obtained from the Hall-effect measurements in the InSe sample increases up to 40 K, decreases in the range 40–100 K, and increases for T≳100 K, although the carrier concentration in the InSe:Er sample increases up to 300 K. In the same samples, the Hall mobility of the InSe sample increases up to 80 K and obeys to μH∝T−1.86 for T≳80 K, although the Hall mobility of the InSe:Er sample decreases up to 340 K and obeys to μH∝T−1.51 for T≳80 K. The electrical conductivity, which is proportional to a product of the Hall mobility and the carrier concentration, of the InSe sample and the InSe:Er sample decreases with increasing temperature for T≳60 and T≳100 K, respectively.
An analytic model for the polymer grid triode
Authors: McElvain J. , Heeger A. J.
Published: July 2002

The polymer grid triode (PGT) is a novel semiconductor device constructed using a self-assembling porous conducting polyaniline (PANI) network placed between two semiconducting polymer layers, and sandwiched between metal electrodes. The structure behaves as a three-terminal device capable of current amplification, with the PANI network functioning as the control grid. An analysis of the generalized field-assisted carrier injection by tunneling, controlled by the grid voltage, is presented to model the charge injection and transport in the PGT. The results are in good agreement with the measured current–voltage characteristics. Further, an effective diode model for the PGT is introduced, and a simple, intuitive expression for charge transport in the presence of the grid network is obtained. In the effective diode regime, the current through the PGT is a function of (Vac−PVag); i.e., Iac≊I(Vac−PVag) where P is a geometric factor, as required for use in image processing applications. Other application possibilities for the PGT are surveyed, and the limitations of this device when placed in common circuit configurations are discussed.
Optical and magneto-optical properties of NdTbFeCo thin films
Authors: Peng Chubing , Kim W. M. , Cheong Byung-ki , Lee S. K. , Kim S. G.
Published: July 2002

Three series of NdxTbyFe1−x−y−zCoz films have been fabricated for their potential application in magneto-optical recording: (i) x=0–0.20, Tb was adjusted so that the coercivity at room temperature was 5–10 kOe; (ii) x+y=0.28–0.32 with x in the range of 0 to 0.25; and (iii) x+y=0.21–0.23 with x in the range of 0 to 0.17. These films have been characterized both optically and magneto-optically by Kerr hysteresis trace, variable angle of incidence ellipsometry, and normal angle of incidence Kerr spectroscopy. From these measurements, the optical constants (n and k), magneto-optical constants (Q1 and Q2), and maximum possible figure of merit (FOM) have been determined at wavelengths of 405, 546, and 633 nm. Results demonstrate that the magneto-optical behavior of NdTbFeCo films is sensitive to the concentration of both Nd and Tb in the film. For samples in the series (i), the addition of Nd into TbFeCo alloys was shown not to enhance their magneto-optic behavior at the short wavelengths. For samples in the series (ii) and (iii), the substitution of Nd improves the magneto-optical performance greatly at blue light. But at red and green wavelengths it has little effect on the magneto-optical properties in samples in the series (iii) or degrades in samples in the series (ii). The maximum enhancement in the FOM is about 25% at x∼10% for blue light.
Subgap excitation of defect band photoluminescence in phosphorous doped hydrogenated amorphous silicon
Authors: Yi S. , Liu S. , Gangopadhyay S. , Herbst W. , Schröder B.
Published: July 2002

This article presents a study of the effect of temperature on the defect band photoluminescence (PL) of moderately phosphorous doped amorphous silicon thin films deposited by magnetron sputtering. We have identified two types of recombination processes responsible for the observed temperature dependence of the defect PL band produced by subgap excitation. One of the processes is similar to that observed in intrinsic hydrogenated amorphous silicon and may originate from the recombination of carriers at band tail states and dangling bonds. The donor-defect pairs at nearest neighbor sites may be responsible for the second recombination process.
Angular-selective optical transmittance through obliquely evaporated Cr films: Experiments and theory
Authors: Mbise G. W. , Niklasson G. A. , Granqvist C. G. , Palmer S.
Published: July 2002

Strongly angular-selective thin Cr films were made by oblique angle evaporation. The optical transmittance could be quantitatively modeled by the Bruggeman effective medium theory applied to inclined structural units.
As and Ga dimers in core-level spectroscopy of S-passivated GaAs(001)
Authors: Chiaradia P. , Paget D. , Bonnet J. E. , Martin-Gago J. , Berkovits V. L.
Published: July 2002

We performed a correlated study of sulfide-passivated GaAs(001) surfaces, using x-ray photoelectron spectroscopy and reflection anisotropy spectroscopy. The reflection anisotropy spectra reveal after desorption of the sulfide overlayer the presence of As and Ga dimers analogous to ones observed on As-decapped surfaces. We identify in the 3d core-level spectra the surface components due to As and Ga dimers: their chemical shifts are −0.28 and −0.35 eV, respectively. We propose an interpretation of the main surface components in the framework of a simple model, based on charge neutrality, electron counting, and electronegativity concepts.
Plastic deformation in high critical current melt-textured YBa2Cu3O7
Authors: Martínez B. , Sandiumenge F. , Vilalta N. , Piñol S. , Obradors X. , Rabier J.
Published: July 2002

The effect of high-temperature creep under different conditions in melt-textured YBa2Cu3O7–Y2BaCuO5 composites, with high critical currents before deformation, is investigated. Transmission electron microscopy studies show that the low-temperature oxygenation process causes a strong modification of the as-deformed microstructure and leads to a clear degradation of the superconducting performances. This behavior of the superconducting properties is well correlated with the formation of extended planar defects such as large stacking faults and microcracks that severely diminish the vortex cutting length, thus enhancing the thermal activation effects on the critical currents and the irreversibility line.
Magnetic relaxation of a one-dimensional model for small particle systems with dipolar interaction: Monte Carlo simulation
Authors: Ribas R. , Labarta A.
Published: July 2002

Monte Carlo simulations have been performed to study the magnetic relaxation of a small particle system with dipolar interaction. The simulated system is a simplified version of the real situation in a small particle system with a random distribution of anisotropy axes and long range dipolar interaction among the particles. This model consists on a one-dimensional Ising model with dipolar interaction and a distribution of uniaxial anisotropy strengths. The anisotropy axes were considered perpendicular to the line connecting the spins. These choices allow us to focus on the influence of the demagnetizing part of the dipolar interaction on the magnetic relaxation by taking into account the main features of the system. The Tln(t/τ0) scaling variable is used to determine the effective distribution of energy barriers for the different interaction strengths showing an enhancement in the number of the lowest energy barriers as the interaction strength is increased. Moreover, the histograms of the energy barrier distribution as a function of the time are analyzed and this study leads to a deeper knowledge of the microscopic processes involved in the magnetic relaxation.
Mid-infrared and near-infrared properties of SrTiO3 from transmission and reflection measurements
Authors: Dore P. , Paolone A. , Trippetti R.
Published: July 2002

We measured transmittance and reflectance spectra of commercial SrTiO3 crystals in the infrared region (25–12 000 cm−1). The reflectance R(ν) spectra confirm recent results. The transmittance T(ν) spectra show that SrTiO3 is transparent above 1000 cm−1, while the model usually employed to describe the complex dielectric function of SrTiO3 predicts a negligible transmittance in all the infrared region. By combining T(ν) and R(ν) spectra, we directly determine the frequency dependence of the refractive indices n and k which accounts for the spectra measured in the mid-infrared and near-infrared range. This result will be important for a correct analysis of the infrared spectra of films deposited on SrTiO3.
Scattering of evanescent light by a finite-size probe in near-field scanning optical microscopy
Authors: Fukuzawa Kenji , Kuwano Hiroki
Published: July 2002

Scattering of the evanescent light by a finite-size SiO2 probe is calculated using a point matching method in order to improve the efficiency collecting the near-field optical signal. The scattered-light patterns can be classified into three categories. Category 1 is where the probe tip radius is very small (<λ/13). Category 3 is where the probe radius is very large (≳λ/6). Category 2 is the intermediate case (λ/13<radius<λ/6). When the radius is in category 1, the scattered light is able to be treated as a field radiated by the point dipole induced by the evanescent light at the probe tip. When the tip radius is in category 2 (λ/13<radius<λ/6), in order to obtain the angular distribution of the scattered light, the induced multipoles should be calculated, considering the probe radius and the incident angle. When the tip radius is in category 3 (radius ≳λ/6), the scattered light becomes larger in the parallel direction to a prism surface due to the forward scattering of the evanescent light.
Far-infrared intersubband transitions in a two-dimensional GaAs/(Al,Ga)As hole system: Direct comparison of experiment and calculation
Authors: Cole B. E. , Chamberlain J. M. , Henini M. , Nakov V. , Gobsch G.
Published: July 2002

Measured far-infrared (FIR) intersubband absorption in two p-type modulation-doped GaAs/(Al,Ga)As multiquantum wells is compared with k⋅p modeling of the two-dimensional heavy- and light-hole (HH, LH) subband structure. Strong absorption for both HH1–HH2 and HH1–LH1 transitions is found. Self-consistent modeling was performed within a 4×4 k⋅p scheme for heavy and light holes. There is an excellent agreement between the theoretical and experimental FIR intersubband transitions at k∥=0 and at the Fermi wave vector kf.
Raman scattering of interface modes in ZnTe–CdSe superlattices
Authors: Sugie R. , Ohta H. , Harima H. , Nakashima S. , Fujiyasu H.
Published: July 2002

Raman spectra have been measured for ZnTe/CdSe superlattices grown by hot wall epitaxy. A mechanical vibrational interface phonon (MVIF) mode localized at the Zn–Se interface is distinctly observed in addition to quasiconfined longitudinal optic (LO) modes. The relative intensity of the MVIF mode is increased as the period of the superlattice becomes short. Raman spectral profiles calculated by use of a linear chain model and a bond polarizability model explain this behavior qualitatively. The quasiconfined LO modes show resonant enhancement for excitations at the band gap energies of ZnTe and CdSe. The effect of atomic diffusion on the interfacial structure has been examined in thermally annealed superlattices by Raman measurement. It is shown that Raman scattering of the interface mode provides information about the interdiffusion of atoms and the sharpness of the heterointerfaces.
Structural and optical investigations of high quality InGaAs/InAlAs short period superlattices grown on an InGaAs quasisubstrate
Authors: Tominaga K. , Hosoda M. , Ohtani N. , Watanabe T. , Inomata H. , Fujiwara K.
Published: July 2002

Unstrained InGaAs (4.5 nm)/InAlAs (1.0 nm) short-period superlattices grown on a (100) GaAs substrate were studied. To achieve this growth, an In-composition-graded buffer layer and a thick InGaAs buffer layer were adopted. Structural properties were investigated by x-ray diffraction, atomic force microscopy, and a compositional analysis by the thickness fringe method. X-ray diffraction patterns showed clear periodicity in the superlattices and atomic force spectroscopy images showed cross-hatch morphology for the main ridge along the (011̄) direction. Clear thickness fringes in the bright-field electron microscope images for the superlattice region and ambiguous fringes for the graded buffer layer indicate that misfit dislocation due to lattice mismatch concentrates in the graded buffer and a high-quality superlattice is successfully grown in spite of the large lattice mismatch between the superlattice and the substrate. Optical characteristics measured by photocurrent spectroscopy reveal a clear Wannier–Stark localization effect at room temperature. The experimental absorption energies agree well with calculated values by a transfer matrix method using parameters for bulk InGaAs and InAlAs.
Effect of addition of Au on the physical, electrical and optical properties of bulk glassy As2S3
Authors: Kawaguchi Takeshi , Maruno Sigeo , Elliott Stephen R.
Published: July 2002

Bulk glasses in the (As0.4S0.6)100−xAux system have been prepared by melt-quenching in air. Homogeneous glasses were limited in composition up to 0.5 at. % Au and precipitation of pure Au particles was observed above 0.5 at. %. The physical properties have been studied and compared with those of Ag-doped bulk glasses. The compositional trends of the density, Vickers hardness, and glass-transition temperature were found to be significantly different between the Au and Ag systems. The optical gap and activation energy of the Au-doped glasses were less than those of the Ag-doped glasses with the same dopant concentration. The Au atoms incorporated into As2S3 glass are suggested to be located in and/or between the As–S network and behave as neutral atoms or form some weak bond with surrounding S atoms, in contrast to Ag atoms that break up the network through the formation of Ag—S ionic bonds. An increase in the randomness of the As–S network structure with the addition of Au may mainly affect the electronic band structure of the Au-doped glasses.
Monte Carlo model for the deposition of electronic energy in solid argon thin films by keV electrons
Authors: Vidal R. , Baragiola R. A. , Ferrón J.
Published: July 2002

The motion of keV electrons in a film of solid argon and the depth distribution of ionizations and excitations are studied using a Monte Carlo simulation. This method does not only allow for accurate inclusion of individual cross sections but also for easy inclusion of finite size effects. We have analyzed the effect of the substrate on electron trajectories and found an important enhancement of the number of electron–hole pairs and excitons produced near the interface by electrons reflected from heavy substrates.
Study of relaxed InxGa1−xAs epilayers on GaAs by grazing incidence x-ray diffraction
Authors: Imperatori P. , Lamelas F. J. , Fuoss P. H.
Published: July 2002

Partially relaxed InxGa1−xAs films with high In content (x=0.35, 0.47), grown on GaAs(001) substrates, have been studied using grazing incidence x-ray diffraction techniques. By measuring the separation between the film peak and the substrate peak along different crystallographic directions, the in-plane lattice mismatch along these directions has been directly determined. We observed an asymmetric distribution of strain relief, the two [110] directions showing a stronger relaxation than the [100] direction. From the shift of peak positions as a function of the x-ray penetration depth, a strain relaxation gradient within the film has been determined, with the top layers more relaxed than those near the interface. In the thinnest films (5 nm thick) the presence of stacking faults was also found to relax the misfit strain. We used the grazing incidence x-ray diffraction technique for these measurements, with a novel approach that allowed the entire profile of the strain relaxation as a function of depth to be recorded in one measurement.
Photoexcited states of DX centers in Si doped AlxGa1−xAs
Authors: Jia Y. B. , Grimmeiss H. G.
Published: July 2002

Deep level transient spectroscopy (DLTS) and single shot capacitance techniques were used to investigate Si doped AlxGa1−xAs with Al compositions ranging from 0.30 to 0.59. Under illumination, an additional DLTS peak was observed in samples with Al compositions close to x=0.38. This peak has been shown to originate from a localized state with an energy level shallower than the DX ground state and energy barriers for both electron emission and capture processes. Persistent photoconductivity effects related to this state were observed below 50 K. Evidence is provided that this state is a metastable state of the Si donor. Its origin is discussed in terms of the intermediate state of a negative U DX center and a metastable negative U configuration of the Si donor. A further photoinduced DLTS peak was observed within a narrow Al composition range that has been identified as the shallowest DX level of the four distinct DX levels originating from different local environments of the donors.
Electrical and optical properties of plasma-deposited a-SiGe:H alloys: Role of growth temperature and postgrowth anneal
Authors: Kuznetsov V. I. , Zeman M. , Vosteen L. L. A. , Girwar B. S. , Metselaar J. W.
Published: July 2002

Basic properties of hydrogenated amorphous silicon–germanium (a-SiGe:H) alloys deposited by plasma-enhanced chemical-vapor deposition were studied. We found that there is an optimal growth temperature in the range 250–280 °C. Infrared-absorption spectra measurements show that in this temperature range the alloys have optimal composition of hydrogen content and bonding, providing a minimum in dangling bond defect density Ns and a high photoconductivity σph. Growth at lower temperatures results in hydrogen-rich alloys with high Ns. Hydrogen in these alloys is mainly bonded as SiH2 and as clusters on internal voids. Growth at temperatures above the optimal value gives less deterioration of the properties of a-SiGe:H than the growth below this optimal temperature. We found two different dependencies of σph on Ns: in optimized alloys σph changes proportionally to N−1s and in low-temperature alloys σph decreases more steeply with N−1s due to a decrease in electron mobility. It is shown that annealing of a-SiGe:H causes a sharp increase in Ns starting at annealing temperatures about 20 °C below the temperature at which the alloy was grown. We observed a new phenomenon that during annealing Ns increases much more (by two orders of magnitude) than the photoconductivity decreases (only factor of 5). The entropy-based model was applied to explain this experimental phenomenon. We found that annealing shifted the centrum energy of the D+/0 dangling bond levels to the valence-band edge. The rate of electron recombination lowers due to this shift and the change in the effective electron capture crosssection of the defects, and therefore the decrease in σph is smaller than the increase in Ns.
Comment on ‘‘Temperature dependence of the barrier height of metal–semiconductor contacts on 6H-SiC’’ [J. Appl. Phys. 79, 301 (1996)]
Authors: Fröjdh C. , Petersson C. S.
Published: July 2002

In this paper we comment on the interpretation of CV data in the presence of deep levels or interfacial layers. In order for the barrier height extracted from CV measurements to be reliable, no frequency dependence should exist at the measurement frequencies, and the slope of the 1/C2 vs voltage curve should not be temperature dependent. This is illustrated by data from Schottky barriers on 6H–SiC.
Bulk anisotropic magnet of Sm2Fe17 type produced from the carbide by gas-solid reaction after sintering
Authors: Chen X. , Altounian Z. , Ström-Olsen J. O.
Published: July 2002

Bulk anisotropic magnets with the composition of Sm2(Fe,M)17CxNy (M=metal) have been produced by conventional powder sintering of the carbide, followed by gas-solid reaction. The results show that this is a very promising technique for producing high-performance bulk anisotropic magnets based on intercalated rare-earth–iron compounds.
Resistivity, charge diffusion, and charge depth determinations on charged insulator surfaces
Authors: Liesegang J. , Senn B. C.
Published: July 2002

A method and theory presented earlier by the authors, for the straightforward measurement of resistivity in the surface region of charged insulators, in the initial phase of charge decay, is demonstrated also to be valid for much longer time scales. This is achieved with the use of a theoretical charge transport model, enabling a direct comparison between experimental and theoretical data. This comparison enabled the accurate determination of both the diffusion coefficient (D) and the layer of surface charge (Δz). Results are presented for glass, plexiglas (perspex), and polyethylene covering a useful resistivity range in the insulator class. The surface charge transport behavior of small rectangular samples is also studied using this computational model, focusing on the potential and charge distributions involved. From this study, some insight is gained into the way the charge in the surface region of insulators decays away with time when one end of a charged sample is earthed. The method provides a ready means of measuring the resistivity, carrier diffusion coefficient, and carrier occupancy depth in surface charged insulators.
Optimum channel thickness of Al0.3Ga0.7As/In0.25Ga0.75As/GaAs heterostructures for electron transport applications
Authors: Haddab Y. , Bonard J.-M. , Haacke S. , Deveaud B.
Published: July 2002

We have grown high-electron mobility transistor structures in the Al0.3Ga0.7As/In0.25Ga0.75As/GaAs material system with In0.25Ga0.75As channel thicknesses in the range 40–200 Å. We have monitored the onset of channel relaxation using Hall mobility measurements, polychromatic cathodoluminescence mapping, time-resolved photoluminescence, transmission electron microscopy, low-frequency noise, and deep-level transient spectroscopy measurements. It appears that the first relaxation symptom, the Stransky–Krastanow growth mode, is observed only by the last three techniques. This shows that the onset of relaxation is not detected by characterization techniques which measure global properties of the material. On the other hand, it is detected by low-frequency noise, deep-level transient spectroscopy, and transmission electron microscopy measurements, which yield an estimation of the defect density in the material.
(100) Si/SiO2 interface states above midgap induced by Fowler-Nordheim tunneling electron injection
Authors: Inoue Masao , Shirafuji Junji
Published: July 2002

It has been found from ac conductance measurement that two kinds of interface states are generated in the upper half of the gap when (100) n-Si metal/oxide/semiconductor capacitors are subjected to Fowler-Nordheim tunneling electron injection. The generation efficiency of these interface states varies in a quite similar fashion with the oxide voltage, although the magnitude is somewhat different from each other. The electron capture cross section for both interface states shows a curious behavior that its value decreases with increasing interface-state density when exceeding about 1.5×1011 cm−2eV−1. This behavior is explained in terms of the occurrence of additional tunneling to defect states in the oxide.
Depletion mode optoelectronic modulation spectroscopy
Authors: Wang Q. H. , Swanson J. G.
Published: July 2002

The depletion mode of opto-electronic modulation spectroscopy (OEMS), spectroscopically senses the electrical response to wavelength modulated monochromatic illumination as trap states in the depletion region of a semiconductor device are cyclically excited. The method is demonstrated using metal–Si3N4–GaAs field-effect transistors in which the charge in the gate depletion region is detected through its effect on the channel current. The optical transition energies of trap levels were revealed and the charge exchange mechanisms identified unambiguously by examining the phase of the detected signal with reference to the phase of the photon energy variation. In-phase responses originate from electron trap states while responses of opposite sign derive from hole traps. Many of the states corresponded closely in energy with ones previously reported in vapor-phase-epitaxy GaAs materials. Charge exchange with energetically discrete and continuously distributed traps is theoretically described when they are excited by photons having periodic energy modulation. The results indicate that the magnitude and phase of the OEMS response spectra are determined by the relative thermal and optical emission rates of trapped charges. Deep level transient spectroscopy (DLTS) measurements made on the same samples could not reveal the responses of bulk levels that the OEMS technique showed were present; this was because the DLTS spectra were dominated by the interface continuum response. This illustrates clearly an important advantage of the technique. The method is equally applicable to other devices in which a space-charge region regulates the channel current.
Composition dependence of activation energy in solid phase epitaxial growth of Si1−xGex alloys
Authors: Suh K. Y. , Lee Hong H.
Published: July 2002

A theoretical model called the ‘‘multibody model’’ is developed for the composition dependence of the activation energy. The model that is based on the diffusion required of the recrystallization for the solid phase epitaxy does not involve any adjustable parameters and is shown to represent experimental data satisfactorily. For the Si1−xGex alloys that are of diamond structure, the most logical choice is the ‘‘five-body model’’ involving five atoms. The model is equally applicable to any other binary alloy.
Giant magnetoresistance in granular array
Authors: Chang Ching-Ray , Lo Kuo-Hung
Published: July 2002

An analytic expression for the magnetoresistance of a symmetric granular array is derived from a semiclassical transport equation, and the solution is applied to a simple cubic structured system. The influence of granular size, packing density, conductivity, electron mean free path, and interfacial resistance on magnetoresistance in granular systems is discussed in detail.
Correlation of buffer strain relaxation modes with transport properties of two-dimensional electron gases
Authors: Goldman R. S. , Kavanagh K. L. , Wieder H. H. , Robbins V. M. , Ehrlich S. N. , Feenstra R. M.
Published: July 2002

We have investigated the effects of buffer strain relaxation on the transport properties of two-dimensional electron gases (2DEGs). The 2DEGs consist of modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterostructures grown lattice-mismatched to GaAs via compositionally step-graded InxGa1−xAs buffers, with different composition gradients, or lattice-matched to InP. We find a variation in 2DEG electronic properties which occurs simultaneously with large differences in epilayer tilt and mosaic spread in the step-graded buffers. This indicates a correlation between the mechanism of buffer strain relaxation and the 2DEG transport properties.
Study of interface stresses in heterostructures using infrared piezobirefringence
Authors: Dutta Soumyo , Dutta Aloke K.
Published: July 2002

A general algorithm for the simulation of stress field images in III–V heterostructures, using infrared piezobirefringence, is presented in this article. As a first step, the algorithm is applied for the simulation of stress fields associated with step deposited SiO2 on GaAs substrates, under two assumptions—one that of distributed loading along the film, and the other that of concentrated loading at the two edges of the film. The simulated images are presented, and these are seen to be functions of film and sample thicknesses, and polarization angle of the incident light. Next, the algorithm was applied for III–V heterostructures (with and without misfit dislocations), and the simulated images are presented. These images are functions of substrate thickness, film thickness, dislocation density at the interface, and polarization angle of the incident light. In principle, any arbitrary heterostructure can be placed under a dark field polariscope, and the experimental images of the interface obtained for varying polarization angles of the incident light. Then an image matching procedure between the experimentally observed images and the simulated ones can yield the information about the defects present at the interface. This technique offers a superior speed advantage over other conventional methods, and permits testing of each individual sample without going in for statistical estimates. This can tremendously boost the yield. Some experimental results and their match with the theoretical ones are also presented.
Argon incorporation and surface compositional changes in InP(100) due to low-energy Ar+ ion bombardment
Authors: Pan J. S. , Wee A. T. S. , Huan C. H. A. , Tan H. S. , Tan K. L.
Published: July 2002

Angle-resolved x-ray photoelectron spectroscopy (ARXPS) has been used to study the Ar incorporation and surface compositional changes in InP(100) after 1–5 keV Ar+ bombardment at various ion fluences. The ARXPS measurements showed that the incorporated Ar concentration achieved saturation at ion bombardment fluences of >1016 cm−2. The surface Ar concentration decreased with increasing bombardment energy. No Ar bubbles were observed by atomic force microscopy, suggesting that Ar bubble formation was not the main Ar trapping mechanism. The altered layers were, on average, In rich up to the sampling depth of the ARXPS technique. However, the altered layers were inhomogeneous as a function of depth and appeared more In rich at the surface than in the subsurface region. The results are compared with those obtained by other authors and discussed in the context of preferential sputtering, radiation-enhanced diffusion and segregation, and Ar incorporation. Although the altered layers were In rich, a P-rich phase induced by Ar+ bombardment was identified in the altered layers.
Time-resolved measurements of x-ray damage to optical coatings
Authors: Elton R. C. , Grun J. , Burkhalter P. G. , Burris H. R. , Ripin B. H. , Newman D. A. , Millard J. R. , Bey D.-M. , Manka C. K. , Konnert J.
Published: July 2002

Thin film optical coatings are susceptible to damage by high intensity x rays. Time-resolved measurements of this damage are required to better understand the mechanism, so that more rugged coatings can be developed. In the present experiment, dark-field shadowgraphy was used to temporally map the x-ray damage across the surface of certain anti-reflecting (AR) coatings. Two beams from the NRL PHAROS III high power Nd:glass laser system were utilized to generate a point source of plasma x rays, which in turn was used to irradiate and damage the optical coatings. Thin, opaque filters, coupled with permanent magnets and pinholes, were used to shield the optical samples from ultraviolet and charged-particle damage, respectively. The absolute, time-integrated x-ray fluence was measured with a crystal spectrograph, and also was temporally resolved with an x-ray diode. The surface morphology of the damaged optical samples was examined after each shot visually, and later with a profilometer as well as with both scanning electron- and atomic-force microscopes. A measured threshold fluence for damage of 0.049±30% cal/cm2 agrees very well with a radiation-damage code prediction of 0.046 cal/cm2.
Photoeffect in porous silicon
Authors: Hlávka Jan
Published: July 2002

A new contactless technique makes possible the measurement of spectral dependences of the photoeffect and the photoeffect time relaxations in porous silicon. From these photoeffect measurements the following results have been obtained. The onset of excess carrier generation at about 1.35 eV was found. The photoeffect time relaxation constant ranges from 0.15 to 10 ms. The dominant components of the measured photoeffect were produced in the depletion space charge regions near both surfaces. Strong trapping of excess carriers near the sample surfaces was observed.
Amorphization and crystallization in high-dose Zn+-implanted silicon
Authors: Kalitzova M. , Simov S. , Yankov R. A. , Angelov Ch. , Vitali G. , Rossi M. , Pizzuto C. , Zollo G. , Fauré J. , Killian L. , Bonhomme P. , Voelskow M.
Published: July 2002

The nature of amorphization and crystallization of Si brought about by 50 keV Zn ion implantation within the dose range 2×1017–1×1018 cm−2 is studied. The structures are evaluated in the as-implanted state by transmission electron microscopy, transmission electron diffraction, reflection high-energy electron diffraction, selected-area electron diffraction, x-ray energy-dispersive analysis, and Rutherford backscattering spectrometry. It is found that, contrary to the theoretical predictions, the Zn concentration profile does not reach saturation even at a dose as high as 1×1018 cm−2. A common feature of the microstructure of these high-dose implants is the formation of a continuous amorphous layer and concurrent crystallization of Zn and Si in small crystalline clusters. Microscopic beam-heating effects are also believed to play an appreciable role in the development of the specific morphologies observed. The results are interpreted in terms of two recent models proposed in the literature and the concept of critical dose ranges.
Fast proton conducting glasses: Creation by proton implantation and a requirement for fast proton conduction
Authors: Hosono Hideo , Kawamura Ken-ichi , Kawazoe Hiroshi , Matsunami Noriaki , Abe Yoshihiro
Published: July 2002

Fast proton conducting glasses have been obtained in Mg(PO3)2 glasses by implantation of protons at 120 keV to a fluence of 1×1018 cm−2. The dc conductivity and the activation energy of the conduction in the implanted glasses are 5×10−4 s cm−1 at room temperature and 0.18 eV, respectively. No fast proton conduction was observed for H+-implanted SiO2 and Ca(PO3)2 glasses. Infrared absorption spectra revealed that implanted protons are present in the form of X–OH (X=Si or P) in SiO2 and Ca(PO3)2 glasses implanted with H+ ions to 1×1018 cm−2, but exist as POH groups and molecular water H2O in Mg(PO3)2 glasses. A quantitative discussion on the proton conductivity led to the conclusion that the coexistence of acidic groups such as POH and molecular water H2O is a structural requirement for the emergence of fast proton conduction in oxide glasses. The formation of H2O in Mg(PO3)2 was understood by considering its thermodynamic stability over SiO2 and Ca(PO3)2 glasses.
Characterization of InxGa1−xAs single quantum wells, buried in GaAs[001], by grazing incidence diffraction
Authors: Rose D. , Pietsch U. , Zeimer U.
Published: July 2002

The depth profile of the chemical composition in InxGa1−xAs single quantum wells (SQWs), epitaxially grown onto a GaAs[001] substrate and covered by a GaAs cap layer, has been determined by use of grazing incidence diffraction (GID). This method allows the scattering signal from the SQW to be enhanced and the scattering depth to be tailored. The coherently illuminated area is large, due to the small incident angle αi; this makes GID a unique technique for investigating buried thin layers over a lateral length scale of several microns. In the case of very thin SQWs the measurements could be described assuming a Gaussian-like distribution of the In content with depth. The broad In profile seen using this method is in contrast with the sharp monolayer signal achieved by photoluminescence measurements. This can be explained by the assumption of a terracelike In distribution and the very different lateral integration length of both experiments. For thicker SQWs we could verify that at least one of the two interfaces is not sharp but shows a gradient in the chemical composition.
Early stages of latent image formation in AgCl grains undoped or doped with iridium ions
Authors: Oikawa Tokuju , Kaneda Takuji
Published: July 2002

The behavior of photoelectrons captured by traps and early stage latent image formation in undoped or Ir-doped AgCl grains was studied by photoconductivity-modulation techniques. Silver atoms were formed at the grain surface of undoped grains in ∼10−4 s and near Ir ions of Ir-doped grains several seconds after exposure of the samples to a light pulse.