bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling microscopy of the surface topography and surface etching of nanoscale structures on the high-temperature superconductors
Authors: Harmer Mark A. , Fincher Curtis R. , Parkinson Bruce A.
Published: July 2002

We report on the use of the scanning tunneling microscope (STM) for etching both single crystal and thin film, YBa2Cu3O7−x. Nanoscale features can be generated with the STM by ablation of atoms rastered by the microscope tip. The etching process can be controlled to remove layers of material which are multiples of the c axis (12 Å). Various geometric features have been fabricated ranging from fine lines to square etch pits. The STM has also been used to study the growth mechanism and surface topography of thin films of YBa2Cu3O7−x produced by in situ laser deposition (Jc typically 1×106 A cm−2 at 77 K). Step features equal to the c axis of the material can be readily identified which form pinnacles or chip like morphologies at the surface. These surfaces can also be etched with the STM to reveal a more continuous substructure consistent with the high Jc’s observed.
A thermodynamic and kinetic study of chemical vapor deposition of tungsten from WF6 and GeH4
Authors: van der Jeugd C. A. , Leusink G. J. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

In this paper a thermodynamic and kinetic study of the deposition of tungsten on silicon (100) from tungsten hexafluoride (WF6) and germane (GeH4) is presented. Thermodynamic calculations, as well as experiments with a closed reactor, indicate that the reaction occurring during deposition is WF6+3GeH4→W+3GeF2+6H2. The growth rate as a function of process parameters is obtained for depositions in the temperature range from 600 to 800 K and a total pressure range from 150 to 1000 mTorr. Experiments show that the germane reduction of tungsten hexafluoride is of 0.9 order in WF6, −0.2 order in GeH4, and zero order in H2. The activation energy is 34 kJ/mol. The deposition rate does not change when SiH4 is added to the GeH4/WF6 mixture, while, on the contrary, a small amount of GeH4 reduces the growth rate from a SiH4/WF6 mixture considerably. The kinetic data indicate that the formation of GeF2 might be the rate-limiting step.
Pockels’ effect in polycrystalline ZnS planar waveguides
Authors: Wong B. , Jessop P. E. , Kitai A. H.
Published: July 2002

The Pockels’ effect has been demonstrated in thermally evaporated polycrystalline thin films of ZnS. The strongly (111)-oriented films were found to have an electro-optic constant of r41 = 3.3 × 10−13 m/V for fields perpendicular to the (111) planes. Extinction ratios of up to 85% have been observed in an optical waveguide modulator. Analysis indicates a stress-related birefringence that manifests itself upon temperature change. The temperature coefficient of stress in the polycrystalline films was found to be 3.0×105 N m−2/°C.
Radiation-induced interface-state generation in reoxidized nitrided SiO2
Authors: Rao V. Ramgopal , Vasi J.
Published: July 2002

Reoxidized nitrided oxide is compared with nitrided oxides and dry SiO2 for radiation-induced interface-state generation (ΔDitm) and midgap voltage shifts (ΔVmg). The suppression of ΔDitm observed with heavy nitridation or reoxidation is explained in terms of the trapped-hole recombination model together with the shifting of the location of the trapped positive charge away from the Si interface. This model can also explain the effect of nitrogen annealing on nitrided oxides.
Morphological and magnetic effects of compaction pressure on YBa2Cu3O7−x-silver nonrandom composites
Authors: Knoll Peter , Reich Shimon
Published: July 2002

The effect of compaction pressure, 50–750 MPa, on YBa2Cu3O7−x-silver nonrandom composites is presented. It is found that the size distribution of open porosity in the final sintered product is determined by the compaction pressure prior to the sintering process. Low pressure leads to a higher density and hardness in the sintered composite. A larger value for the magnetic shielding is observed for samples compacted at lower pressures. These phenomena are connected with the process of grain growth during the sintering process. High pressures lead to small grains while small pressures facilitate the grain growth process.
Effect of ordered structure on the acceptor energy level of Be-doped Al0.5In0.5P
Authors: Yokotsuka T. , Suzuki T. , Takamori A. , Nakajima M.
Published: July 2002

The acceptor energy level of Be-doped Al0.5In0.5P grown by gas source molecular beam epitaxy has been studied as a function of doping level using temperature-dependent Hall measurements and transmission electron diffraction patterns. Activation energies of acceptors increased from 40 to 170 meV with Be doping levels ranging from 2×1018 to 5×1019 cm−3. The acceptor energy levels were ascribable to the local atomic arrangements on the column III sublattice.
The effect of oxygen incorporation in semi-insulating (AlxGa1−x)yIn1−yP
Authors: McCalmont J. S. , Casey H. C. , Wang T. Y. , Stringfellow G. B.
Published: July 2002

Oxygen-doped, semi-insulating layers of (AlxGa1−x)yIn1−yP with x=0.4 were grown on GaAs using organometallic vapor phase epitaxy (OMVPE). Secondary-ion mass spectrometry measurements show that the oxygen incorporation is proportional to the flow rate of O2 into the OMVPE reactor. Two-terminal metal-insulator-semiconductor devices were fabricated and used to evaluate the electrical characteristics of the (AlxGa1−x)yIn1−yP. Traps into the (AlxGa1−x)yIn1−yP bulk behave like DX centers, and are believed to be related to residual Si contamination. Increasing the oxygen concentration in the (AlxGa1−x)yIn1−yP layer decreases the trap concentration by the formation of oxygen complexes with the Si atoms.
High-speed 1.3-μm InGaAsP buried crescent lasers with Fe-doped InP current blocking layers grown by organometallic vapor phase epitaxy using tertiarybutylphosphine
Authors: Huang Rong-Ting , Keo S. , Cheng W. H. , Wolf D. , Buehring K. D. , Agarwal R. , Jiang C.-L. , Renner Daniel
Published: July 2002

Fe-doped semi-insulating InP layers grown by low-pressure organometallic vapor phase epitaxy with tertiarybutylphosphine have been used as a current block layer for high-speed 1.3-μm InGaAsP buried crescent lasers. The performance characteristics of such lasers are comparable to those of lasers with a PH3-grown Fe-doped semi-insulating InP current blocking layer over a measurement temperature range of 25 to 85 °C. A 3-dB modulation bandwidth of 17.5 GHz has been obtained at room temperature and a cw bias current of 100 mA.
Annealed indium oxide transparent ohmic contacts to GaAs
Authors: Cunningham Thomas J. , Guido Louis J. , Beggy J. C. , Barker R. C.
Published: July 2002

The current–voltage characteristics of annealed In2O3–GaAs devices have been investigated for the purpose of fabricating transparent ohmic contacts to GaAs. A detailed study of the reverse current for as-deposited structures with degenerately doped n-type In2O3 on lightly doped n-type GaAs yields a 0.67-V high Schottky barrier. After annealing, the barrier height is only slightly modified, but the reverse current increases dramatically. This reverse current follows a voltage dependence that is consistent with a Fowler–Nordheim tunneling mechanism, for which the electric field is enhanced around localized asperities. These data suggest that an optimized annealing schedule might be used to fabricate low-resistance, transparent In2O3 ohmic contacts to GaAs-based optoelectronic devices.
Quasinondestructive readout of holograms stored in photorefractive sillenites
Authors: Zhivkova S.
Published: July 2002

A drift mechanism of holographic recording in bipolar photorefractive sillenites is discussed. The influence of the external field on the parameters of the ‘‘fixed’’ hologram is presented.
Effect of isothermal annealing on the magnetic behavior of amorphous ferromagnets with composition near the percolation threshold. I. Outside the critical region
Authors: Kaul S. N. , Mohan Ch. V.
Published: July 2002

Results of detailed ferromagnetic resonance measurements taken on amorphous (a-) Fe90+XZr10−X alloys with X=0 and 1 in the horizontal-parallel and vertical-parallel sample configurations at a fixed microwave frequency of ≂9.23 GHz in the temperature range 77 to 300 K before and after these alloys have undergone isothermal annealing treatment at 400 K for durations of time, tA, ranging from 10 to 240 min are presented and discussed. While only a single (primary) resonance is observed for T≲TC (the Curie temperature), an additional (secondary) resonance first appears at T≂TC and then gets fully resolved for T≳(TC+10 K). For the primary resonance (i) the ‘‘in-plane’’ uniaxial anisotropy field, Hk, and the Gilbert damping parameter, λ, both scale with the saturation magnetization, MS, in the temperature ranges 77 K≤T≲TC and 0.5TC≲T≲0.8TC, respectively, at all tA including tA=0; (ii) isothermal annealing has essentially no effect on MS(T), the ‘‘peak-to-peak’’ linewidth, ΔHpp(T), ΔH0 (the frequency- and temperature-independent contribution to ΔHpp) and λ(T); (iii) with increasing Fe concentration, the value corresponding to the peak in λ(T) decreases, λ(0.5TC) increases while λ(300 K) stays constant at 1×108 s−1, and (iv) isothermal annealing up to a time duration of 30 min results in an enhancement of about 1.5% in TC and a reduction of nearly 40% in the characteristic temperature T0 (which is a measure of the re-entrant transition temperature) whereas no further change occurs in both TC and T0 at higher annealing times.

By contrast, for the secondary resonance, (a) Hk≂0 at all temperatures T≳TC and values of tA covered in the present experiments, (b) isothermal annealing leaves the resonance field unaltered, and (c) a steep decline in the value of ΔHpp′ occurs for tA≤10 min but at higher values of tA, ΔHpp′ remains constant for a-Fe90Zr10 whereas it increases at first and then saturates in the case of a-Fe91Zr9. The effect of isothermal annealing on the quantities of interest, i.e., TC, T0, ΔHpp, etc., can be qualitatively understood in terms of a finite spin clusters plus an infinite ferromagnetic matrix model.
Dependence of the properties of boron-trifluoride-based amorphous silicon carbide on preparation conditions
Authors: Gutiérrez M. T. , Cárabe J. , Gandía J. J.
Published: July 2002

p-type fluorinated and hydrogenated amorphous silicon carbide (a-Si:C:F:H) thin films have been prepared by plasma-enhanced chemical vapor deposition, using mixtures of silane (SiH4), methane (CH4), and boron trifluoride (BF3). The influence of preparation conditions on the optical and electrical properties of the films has been systematically studied with the aim of confirming the validity of BF3 to make p-type amorphous silicon carbide alloys and getting a better understanding of this material for its use in the preparation of p-type window layers of amorphous silicon solar cells. It has been found that the use of a low process pressure tends to prevent film growth as a consequence of the combination of a low density of radicals in the plasma and a high probability of desorption of species. High RF-power densities favor the incorporation of relatively large amounts of fluorine and the formation of defects. These two factors determine a poor doping efficiency and film quality. It has been shown that it is possible to prevent optical gap degradation if BF3 is used instead of B2H6. The effect is attributed to the incorporation of fluorine. Optimum dopant-gas concentrations seem to be of the order of 100%, instead of 1% as is the case for B2H6. This is due to the high tightness of the B-F bond. Our best films have an optical gap of 2.1 eV, a conductivity of 2.7×10−7 (Ω cm)−1 and an extended-state conductivity activation energy of 0.49 eV. Such properties make them suitable for their use as p-type window layers for amorphous silicon solar cells.
Plasma breakdown behavior of hydrogen azide (HN3) gas mixtures
Authors: Wright M. W. , Schlie L. A. , Black G.
Published: July 2002

Plasma breakdown studies in HN3 and its mixtures with inert gases showed Paschen type behavior independent of electrode geometries. For pressures above 3.3 Torr and with nonsharp electrodes, a breakdown induced detonation always produced a complete volumetric decomposition verified by mass spectrometric analysis and doubling of the initial pressure. NH(A3Π→X3∑−) spectra at 3360 (0,0) and 3371 Å (1,1) were observed with an NH(A) yield of 0.002% relative to the initial HN3 concentration. Examination of the transient spectra suggested the HN3 volumetric decomposition was promoted by heating at the compression wave shock front.
Single-energy, MeV implant isolation of multilayer III-V device structures
Authors: Elliman R. G. , Ridgway M. C. , Jagadish C. , Pearton S. J. , Ren F. , Lothian J. , Fullowan T. R. , Katz A. , Abernathy C. R. , Kopf R. F.
Published: July 2002

A single-energy, implant isolation scheme for thick (≥1.5 μm) III-V semiconductor device structures such as heterojunction bipolar transistors (HBTs) is described. A 5-MeV O+ implant at doses around 1015 cm−2 produces an almost uniform damage profile over ∼2 μm, sufficient to isolate structures containing highly doped (p=7×1019 cm−3) individual layers. The heavily damaged region associated with the end of the O+ ions range is placed in the underlying semi-insulating substrate. Resistivities above 108 Ω/⧠ are obtained in GaAs/AlGaAs HBTs with such an implant, following annealing at ∼550 °C. High-quality, 2×5 μm2 HBTs with gains of 25 for base doping of 7×1019 cm−3 have been fabricated using this isolation scheme. A considerable simplification is achieved over the use of conventional keV implants, where up to ten separate ion energies are required to isolate an HBT structure.
Effects of spacer layer in modulation-doped GaAs/AlGaAs heterostructures on a localization in quantized Hall resistance
Authors: Noh S. K. , Lee J. I. , Hwang J.-S. , Ihm G. , Yoo K. H.
Published: July 2002

The quantum Hall effect measurements have been applied on modulation-doped GaAs/AlGaAs heterostructures with various spacer-layer thicknesses (0–100 Å) for investigating the effects of an undoped layer on localization. The fraction of localized states (α) of Landau levels has been evaluated from the plateau widths in the quantized Hall resistance, and its functional dependences are proposed in terms of electron mobility and magnetic field. The mobility dependence gives an exponential profile, α∼exp(−μ/μ0), which results from a change in the long-range interaction by the variation of spacer-layer thickness. The characteristic mobility, μ0, is within (2.55±0.20)×105 cm2/V s for all step indices from i=4 to i=10, but the localized fraction has an additional dependence on step index. The fraction of localized states as a function of magnetic field shows B3/4 dependence which may be attributed to short-range contribution by interface states or interface roughness between the AlGaAs undoped layer and the GaAs buffer layer.
Analysis of the guidance of electromagnetic waves by a deformed planar waveguide with parabolic cylindrical boundaries
Authors: Choudhury P. K. , Khastgir P. , Ojha S. P. , Singh L. K.
Published: July 2002

An analytical study of a waveguide with two parabolic cylindrical surfaces separating the guiding region of refractive index n1 from two cladding regions of common refractive index n2 with n1≳n2 is presented. The cutoff conditions for modes are derived as equations containing trigonometric functions. The modes show a bunching tendency instead of well-defined discreteness, and several mode bunches occur because the distance of separation between the two interfaces does not remain constant but continues to increase as one moves away from the region near the vertices of the parabolas. Unlike the planar waveguide, a nonzero cutoff is deduced which may be attributed to the curvature of the boundaries, and the flare.
A vectorial finite element formulation for electromagnetic wave propagation in helical systems
Authors: Igarashi H. , Honma T.
Published: July 2002

This paper describes a vectorial finite element method for the analysis of electromagnetic waves propagating in helical systems. The present method can be as easily used as the methods for guided electromagnetic waves in systems with translational and axial symmetries. The functional for the vector Helmholtz equation is minimized using twisted coordinates in which the problem becomes two-dimensional. The spurious solutions, which do not satisfy the divergence-free condition, are removed on the basis of the penalty method. Two finite element equations for the covariant and contravariant components of electromagnetic fields are derived and boundary conditions for both formulations are described. The present method is applied to the analysis of a twisted waveguide with a rectangular cross section and the numerical solutions are shown to be in good agreement with the perturbed solutions for a small helical pitch.
Disordering of AlGaAs/GaAs quantum well structures using low dose oxygen implantation
Authors: Weiss B. L. , Bradley I. V. , Whitehead N. J. , Roberts J. S.
Published: July 2002

We report the photoluminescence study of low-energy, low-dose oxygen implantation induced compositional disordering of AlGaAs/GaAs quantum well structures. Significant disordering of both single and multiple AlGaAs/GaAs quantum wells has been achieved using low-energy (155 keV) oxygen ion implantation with doses as small as 5 × 1013 cm−2 after a moderate annealing step. These doses are significantly lower than those reported previously (500 keV and 1016 cm−2).
Study of the initial formation of silicon carbide by reaction of tetraethyl silane with silicon
Authors: Bermudez V. M.
Published: July 2002

The growth of SiC films on Si by reaction with tetraethyl silane (SiEt4) has been studied using Auger and electron energy-loss spectroscopies, low-energy electron diffraction, and external-reflection infrared reflection absorption spectroscopy (IRRAS). IRRAS is used to monitor the chemisorption of the reagent molecule on polycrystalline Si at substrate temperatures below the point where complete dissociation occurs. The electron techniques are used to characterize the structure and composition of SixC1−x (0≤x≤1) layers formed on Si(100) at higher temperatures during dosing with SiEt4. Near room temperature, IRRAS data indicate adsorption of undissociated -C2H5 groups with the C—C bond oriented nearly normal to the surface. Under growth conditions, the relative rates of deposition and indiffusion of C control the stoichiometry of the initial SixC1−x phase. At lower temperatures (∼750–1000 K), a partially noncarbidic phase occurs. Annealing this surface or dosing the clean surface at higher temperature leads to formation of a SiC layer which then acts to slow further diffusion. Subsequent layer growth occurs mainly by pyrolysis of the SiEt4 molecule. However, the underlying Si substrate continues to function as either a C sink or a Si source.
Probing of high T
c sample texturing with a potentiometric ring
Authors: Krause Thomas W. , Nkum R. K. , Datars W. R. , Gridin Vladimir V.
Published: July 2002

An inhomogeneously textured ring prepared from a diffused Bi2Sr2CaCu2O thick film has been arranged for the measurement of longitudinal, VL, and transverse, VT, voltages with three diametrical pairs of contacts. The film was deliberately grown in such a way that one half of the ring has a high degree of texturing with the a axis perpendicular to the sample plane. In the second, less textured half, a finer granular structure is present implying the presence of more grain boundaries. The application of an external magnetic field perpendicular and parallel to the sample plane clearly shows that an anisotropic weak link behavior from the inhomogeneous texturing is responsible for the minimum observed in VT below Tc. The reduction of this minimum with increasing magnetic field is explained in terms of the loss of superconducting paths due to increased dissipation at grain boundaries in the more textured branch.
Longitudinal mode stability difference in Se- and Si-doped AlGaAs lasers
Authors: Sugiura H. , Noma A. , Yuri M. , Hirose M. , Kume M. , Ohta I. , Kazumura M.
Published: July 2002

The longitudinal mode behavior of AlGaAs lasers with n-type cladding layers doped with Se and Si is reported. The longitudinal mode of the lasers with highly Se-doped cladding layer is stabilized, and large hysteresis of mode jump is observed as temperature changes. In the case of highly Si-doped cladding layers, however, the mode hops to the adjacent one and no hysteresis is observed. These phenomena are explained by the difference in thermal activation energy between Se- and Si-related DX centers.
Some electrical properties of amorphous silicon/amorphous silicon nitride interfaces: Top nitride and bottom nitride configurations in MNS and TFT devices
Authors: Godet C. , Kanicki J. , Gelatos A. V.
Published: July 2002

Top nitride (TN) and bottom nitride (BN) configurations of the a-SiN1.6:H/a-Si:H interface produced by plasma enhanced chemical vapor deposition (PECVD) have been characterized by using metal/a-SiN1.6:H/a-Si:H (MNS) devices and thin-film transistors (TFT). We observed that: (i) for MNS devices, the resonant frequency activation energy Eac from admittance, saturates at a higher value for the TN (≂0.3 eV) than for the BN (≂0.1 eV) MNS devices and the resonant frequency preexponential factors are found to be, respectively, in the 1012 s−1 and 108 s−1 range, (ii) in strong accumulation, the source-drain current activation energy is nearly similar for TN and BN TFTs (Edc≂0.1 eV), a slightly higher value being found in the latter configuration, (iii) the analysis of the transfer characteristics yields a very similar density of deep interface states (DOS) ≂4–5×1012 cm−2 eV−1 in both configurations, and (iv) the effective field-effect mobility is higher for the BN (μFE≳0.5 cm2/V s) than for the TN (μFE≲0.3 cm2/V s) TFTs.

The observed difference in mobilities for both TFTs structures is most likely associated with very high source/drain contact resistances in the TN TFT rather than with the quality of both interfaces. To explain some of these experimental results, the surface- and buried-channel models are proposed for TN and BN TFT configurations, respectively. The buried-channel concept is based on evidence of recycling/intermixing of nitrogen atoms into a-Si:H deposited on a-SiN1.6:H by PECVD. The nitrogen tail would produce a Si-rich a-SiNx:H alloy transition layer, followed by a nitrogen-doped n-type layer. The doped layer corresponding to the buried-channel formation is predicted to be located beyond 30 Å from the BN interface. In contrast, the surface-channel proposed for the TN interface is based upon this interface being considered as atomically sharp. The MNS results (i) are consistent with this model. In the case of TN MNS they are explained by thermionic emission of electrons from the traps to the conduction band edge in a-Si:H and in the case of BN MNS by hopping in the defective a-SiNx:H interlayer. The result (ii) on TFTs may be attributed to a broadening of the linear part of the conduction band tail of a-Si:H in the channel region, due to recycled nitrogen atoms.
Spin-dependent transport at silicon grain boundaries
Authors: Seager C. H. , Venturini E. L. , Schubert W. K.
Published: July 2002

The transport of electronic carriers across grain boundaries in n- and p-type silicon has been measured as a function of magnetic field in the presence of a microwave field. The spin-dependent-transport (SDT) signal is observed to have a distinctively different character depending on whether the samples are illuminated with band-gap light or are in the dark. Despite the approximate symmetry of the dark I-V curves, the dark SDT signals, which are only observed for n-type boundaries, are asymmetric, displaying an increased impedance at the resonance condition for one current direction and a decrease for the other. With band-gap illumination, a symmetric SDT signal is seen for all samples which becomes quite large at high light intensities. The line shapes and g values seen for these resonances are similar to those attributed to Si dangling-bond-like defects. The dark SDT effect may be associated with a spin-flip k-vector change which must take place for conduction-band electrons that are thermionically emitted over the grain-boundary double depletion layer. The light-induced SDT effect is well modeled as a spin-dependent change of the light-generated minority carrier flux that modulates the trapped majority-carrier density at the grain-boundary plane.
Local mode spectroscopy of proton- and deuteron-implanted InP
Authors: Fischer D. W. , Manasreh M. O. , Matous G.
Published: July 2002

We have introduced hydrogen into single crystal InP:Fe by implanting samples with 2 MeV protons and/or deuterons at fluences between 1×1016 and 5×1017 cm−2. This results in the creation of four local vibrational modes (LVMs) in infrared absorption which are all due to the stretching vibration of bonds formed between phosphorous and the implanted atom with various lattice defects or impurities at nearest-neighbor sites. Our implant-created LVMs are much sharper than those reported by previous workers and we observe two additional well separated peaks. The two main LVMs show a strong fluence dependence and are probably associated with lattice defects. The two weakest LVMs are not as fluence-dependent and may be associated with impurities. Two samples were implanted with both protons and deuterons in an attempt to observe the formation of complexes containing both isotopes, but no evidence of such complexes could be found.
Fracture studies of diamond films on silicon
Authors: Mecholsky J. J. , Tsai Y. L. , Drawl W. R.
Published: July 2002

Diamond coatings were prepared on silicon substrates for fracture studies. Two thicknesses of coatings were evaluated: 6 and 12 μm. The diamond films increased the strength of the silicon for the same size fracture initiating crack and thus caused an apparent toughness increase from 1.2 MPam1/2 for the uncoated silicon to about 1.6 MPam1/2 for the 12 μm coated silicon. Fractography showed that the indentation impression on the coated surface was altered by the coating, but this did not alter the formation of the radial crack beneath the surface so that indentation fracture mechanics can be used for thin coatings with thicknesses below 12 μm. Fractography also showed that the coatings separated from the substrate under and near the indentation site, but was still intact away from the indentation. Most of the fracture in the diamond coating was transgranular indicating good intergranular adhesion.
Strength of direct optical transition between conduction subbands of a Si/GexSi1−x superlattice
Authors: Yoo Jay S. , Lee Hong H.
Published: July 2002

Two lowest conduction subbands of Si/GexSi1−x superlattice can be tailored to allow for direct optical transition between the subbands in the infrared range (10–15 meV). The optical-absorption strength for the subbands is only two orders of magnitude smaller than that for GaAs. A monolayer well can be inserted into the barrier part of the usual superlattice period to increase the strength by almost an order of magnitude, up to slightly less than 0.1 a.u.
Electronic and photoluminescent properties of InP prepared by flow modulation epitaxy
Authors: Neuhalfen A. J. , Wessels B. W.
Published: July 2002

Epitaxial InP has been prepared by flow modulation epitaxy (FME) over the temperature range of 350–600 °C. The growth and properties of the epitaxial InP were studied as a function of modulation period, reactant partial pressure, and growth temperature. The growth rate was dependent on the trimethylindium reactant partial pressure and growth temperature, with growth rates ranging from 6 Å/cycle to 145 Å/cycle. The desorption of trimethylindium was rate-limiting at intermediate temperatures, and the decomposition of trimethylindium was rate-limiting at low temperatures. The deposited layers were n type with room-temperature carrier concentrations ranging from 7 × 1015 cm−3 to 9.5× 1016 cm−3 for layers deposited at intermediate growth temperatures of 520 to 600 °C and Hall mobilities ranging from 3000 cm2/V s to 4100 cm2/V s. For layers grown at 350 °C the carrier concentrations ranged from 4 × 1013 cm−3 to 2 × 1017 cm−3 with Hall mobilities typically less than 750 cm2/V s. The photoluminescence spectra of the as-deposited layers were dominated by intense near-band edge (NBE) emission at 1.414 eV and an acceptor related emission at 1.377 eV. No significant deep level luminescence was observed in the FME-deposited layers. The full width at half maximum values of the NBE luminescence ranged from 5 meV for layers deposited at 580 °C to 20 meV for layers deposited at 350 °C.
Interfacial reactions in the Pd/a-Si/c-Si system
Authors: Edelman F. , Cytermann C. , Brener R. , Eizenberg M. , Weil R. , Beyer W.
Published: July 2002

Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy (TEM) have been used to study the kinetics and morphology of phase transformations in two-layer structures of Pd/a-Si deposited on silicon substrates. Different kinds of a-Si were used: undoped, hydrogenated-deuterated, and fluorinated (a-Si, a-Si:H:D, and a-Si:F, respectively). It was found that the as-deposited Pd/a-Si interface included an intermixed region with a composition close to Pd2Si, for all samples studied. This region widened during room temperature aging. Heat treatments in the temperature range of 200–400 °C resulted in the formation of an oriented, textured, palladium silicide (Pd2Si). The morphology of the Pd2Si region depended on the thicknesses of the Pd and a-Si films. Fractal-like colonies of the Pd2Si silicide formed in the nonsupported double layer films of Pd/a-Si:F during in situ heat treatment in TEM. The growth of these Pd2Si dendrites had 0.1–1 μm/s velocity and was a diffusion controlled process. Kinetic parameters of the silicidation process were obtained from the x-ray diffraction data. The growth of the crystalline Pd2Si layer in thick films was also found to be controlled by a diffusion limited process with an activation energy of 1.5 eV in all samples. The presence of F in a-Si promoted the formation of Pd2Si both in the room-temperature processes and following heat treatments.
Effective mass and ground state of AlAs quantum wells studied by magnetoresistance measurements
Authors: Maezawa Koichi , Mizutani Takashi , Yamada Syoji
Published: July 2002

Transport properties of electrons confined in AlAs quantum wells were studied using low temperature magnetoresistance measurement. The structure used is quantum wells consisting of AlAs channel layers sandwiched by Si-doped Al0.45Ga0.55As barrier layers. This structure enables us to confine electrons in the X valleys of AlAs. The electron confinement in the AlAs quantum wells were confirmed by a mobility enhancement at low temperatures. Magnetoresistance measurements showed clear Shubnikov–de Haas oscillations for the magnetic field parallel to the growth direction. A large effective mass of (0.55±0.05) m0, which is close to √mtml (mt:transverse effective mass, ml:longitudinal effective mass), was obtained from the temperature dependence of the oscillations. This indicates that the ground state is Xx, Xy, even though Xz was expected to be the ground state due to its large effective mass parallel to the growth direction. This changeover of AlAs X valley states can most likely be attributed to a strain-induced energy shift caused by the small lattice mismatch between GaAs and AlAs.
Competing anisotropies and magnetization processes in the pseudoternary (HoxEr1−x)Fe10V2 tetragonal system
Authors: Algarabel P. A. , Pareti L. , Marquina C. , Solzi M. , Ibarra M. R. , Marusi G.
Published: July 2002

A study of temperature and composition dependence of the magnetic anisotropy in the tetragonal (HoxEr1−x)Fe10V2 polycrystalline compounds was made by means of the singular point detection technique. At 293 K the easy magnetization direction lies along the tetragonal c axis [001] in all the samples and the anisotropy field increases linearly with increasing Ho content. However, with decreasing temperature the competition among the anisotropy of the different magnetic sublattices gives rise to a spin reorientation transition axis to cone in Er containing samples. The TSR value increases with increasing Er content. A significant in-plane anisotropy was found in all the compounds. This planar anisotropy is larger in HoFe10V2, where it favors the [100] direction of the basal plane, while in ErFe10V2 the [110] is the preferred direction. The difference between the anisotropy field along [100] and [110] directions was found to decrease with increasing Er content. A first-order magnetization process of type 1 was observed below 120 K in all the compounds when the magnetic field is applied along the [100] direction.
Electron-paramagnetic-resonance study of the Cr3+ and Ni2+ ions and the (SCl)2− defect in FeS2
Authors: Yu Jiang-Tsu , Wu Ching-Jiun , Huang Ying-Sheng , Lin Shoei-Sheng
Published: July 2002

An electron-paramagnetic-resonance study of the iron pyrite crystals grown by the method of chemical-vapor transport is reported. Cr3+ and Ni2+ ions were detected as substitutional impurities. An effective spin S =1/2 defect species that exhibits hyperfine couplings to the two natural isotopes of chlorine was detected in sulfur-deficient FeS2 grown by using ICl3 as a transport agent. This species can be identified as the defect species (SCl)2−. The similarity and differences exhibited by this defect species in the sulfur-deficient Fe pyrite and the chalcogen-deficient Ru pyrites are discussed.
Automatic quasiphase matching for second-harmonic generation in a periodically poled LiNbO3 waveguide
Authors: Shinozaki K. , Fukunaga T. , Watanabe K. , Kamijoh T.
Published: July 2002

A novel technique is proposed and experimentally demonstrated to achieve a quasiphase matching (QPM) condition for second-harmonic generation (SHG) in a nonlinear optical waveguide with a periodically poled LiNbO3 waveguide. The fundamental wave satisfying the QPM conditions is automatically generated when the laser diode (LD) and the optical waveguide are optically connected. Using the proton-exchanged LiNbO3 waveguide with a periodically poled grating, which was fabricated by Ti diffusion and the InP/InGaAsP LD with antireflection-coated facets, it was confirmed that the LD oscillated at the wavelength satisfying the QPM condition, and SHG was observed simultaneously. Using a Ti:sapphire laser, it was also confirmed that the SHG was realized at the third order of QPM condition, as was expected.
Solution of the vector wave equation using Green’s function techniques
Authors: Kahen K. B.
Published: July 2002

Polarized solutions of the vector wave equation are computed for two-dimensional waveguides using a Green’s function perturbative approach. By solving the vector wave equation, the discontinuities in the normal electric field across internal boundaries are automatically taken into account, which obviates the need for imposing internal boundary conditions. Both the effective indices and the electric field profiles can be obtained for structures containing arbitrary index of refraction profiles. In order to obtain field profiles to the same order of accuracy as the effective indices, the iterated Galerkin method is used to improve the wave equation eigenfunctions. Compared with comparable finite element or finite difference-based codes, the computed effective indices and electric field profiles are determined to be in excellent agreement.
Low threshold current and high differential gain in ideal tensile- and compressive-strained quantum-well lasers
Authors: Ghiti A. , Silver M. , O’Reilly E. P.
Published: July 2002

We use an idealized band structure to compare the characteristics of tensile- and compressive-strained quantum-well lasers. We show that although the threshold carrier density increases as expected in tensile-strained lasers, both the radiative current density and differential gain can be comparable to or improved over compressively strained lasers.
Novel high mobility Ga0.51In0.49P/GaAs modulation-doped field-effect transistor structures grown using a gas source molecular beam epitaxy
Authors: Jiang Z. P. , Fischer P. B. , Chou S. Y. , Nathan M. I.
Published: July 2002

A standard Ga0.51In0.49P/GaAs modulation-doped field-effect transistor (MODFET) structure and a novel Ga0.51In0.49P/GaAs MODFET structure where the Ga0.51In0.49P spacer layer was replaced by an undoped Al0.3Ga0.7As layer were grown using a gas source molecular beam epitaxy. The Hall mobility of the novel MODFET’s structures are 6600 and 36 400 cm2/V s at room temperature and 77 K, respectively, which are more than twice as high as that in the ordinary Ga0.51In0.49P/GaAs MODFETs structure. The mobility is attributed to better carrier confinement and smoother heterointerface. Furthermore, it is found that both ordinary and novel MODFET’s structures have small photo-persistant conductivity effects at low temperatures and that the FETs made in these materials had no threshold voltage shift at low temperatures after illumination.
The effects of GaSb/InAs broken gap on interband tunneling current of a GaSb/InAs/GaSb/AlSb/InAs tunneling structure
Authors: Chen J. F. , Cho A. Y.
Published: July 2002

We propose and study a new GaSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling diode by varying the thicknesses of the InAs layer. A twice-higher peak current density and a three-times-higher peak-to-valley current ratio in the proposed structure with a 30-Å-thick InAs layer were observed relative to the structure with no InAs layer. This result indicates that the characteristic of the negative differential resistance can be improved simply by placing a thin effective InAs barrier on the GaSb side of the GaSb/AlSb/InAs single-barrier structure. The increase of the peak current is interpreted as the result of forming a quasi-bound state in the GaSb well. This interpretation is supported by the observation that the current-voltage characteristic of the proposed structure is similar to that of a conventional GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling structure.
Structural characterization of SimGen strained layer superlattices
Authors: Adams P. M. , Bowman R. C. , Ahn C. C. , Chang S. J. , Arbet-Engels V. , Kallel M. A. , Wang K. L.
Published: July 2002

SimGen strained layer superlattice (SLS) structures were grown by molecular beam epitaxy on GexSi1−x buffer layers on 〈100〉 Si substrates to determine the effects of buffer layer composition, SLS thickness ratio, and superlattice periodicity, on the overall quality of these structures. X-ray diffraction methods were used to determine how closely actual periodicities and compositions met targeted values, and to evaluate the quality of these samples. In most instances the as-grown structures matched the targeted values to within 10%, though in some instances deviations of 20–25% in either the period or composition were observed. The quality of the SLS structures was greatly dependent on the composition of the buffer layer on which it was grown. SimGen SLS structures grown on Si- and Ge-rich buffer layers were of much higher quality than SimGem SLSs grown on Ge0.50Si0.50 layers, but the x-ray rocking curves of the SimGen samples indicated that they were far from perfect and contained moderate levels of defects. These results were confirmed by cross sectional transmission electron microscopy, which showed that the SimGem structures contained significant numbers of dislocations and that the layers were nonuniform in thickness and wavy in appearance. SimGen structures, however, displayed fewer defects but some dislocations and nonparallelism of layers were still observed.
An effective correction to the theoretical curve of magnetobirefringence of magnetic fluid
Authors: Pan Yingtian , Liu Xiande , Du Chongwu , Li Zaiguang
Published: July 2002

Previously theoretical models for magnetically induced birefringence (M-B) of magnetic fluid ignored interparticle interactions and accordingly resulted in considerable deviation from the experiments at low field. Under such circumstances, we measure the Curie-Weiss behaviors of two ferrofluid samples from −50 °C to 80 °C and correct the M-B models by means of mean-field approximation (Weiss model). Experiments show that the corrected model coincides with the experiments quite well even for concentrated ferrofluid samples.
The magneto-optical Kerr effect of trilayer
Authors: Zhou S. M. , Lu M. , Zhang H. Y. , Zhai H. R.
Published: July 2002

In this paper the magneto-optical polar Kerr rotation spectra of trilayers Fe/Ag/Cu, Fe/Cu/Ag, Fe/Au/Cu, and Fe/Cu/Au were measured and calculated. The experimental results coincided well with the calculated results. It was found that for trilayers Fe/Cu/Ag and Fe/Ag/Cu, with a 100 Å thickness of the top Fe layer, there were two Kerr rotation peaks in their rotational magneto-optical Kerr rotation spectra, located near 320 nm (the plasma edge of Ag) and 560 nm (the absorption edge of Cu). For Fe/Cu/Au and Fe/Au/Cu, with a 100 Å thickness of the top Fe layer, there was only one Kerr rotation peak, which shifts slightly with the intermediate layer thickness. Trilayers Fe/Au/Cu and Fe/Cu/Au with suitable thickness of the top Fe layer are useful at present for magneto-optical storage with a read-out laser of long wavelength; Fe/Ag/Au and Fe/Cu/Ag will be useful in the future for magneto-optical storage with read-out laser of short wavelength.
Impact ionization thresholds in GexSi1−x alloys and strained layers
Authors: Czajkowski I. K. , Allam J. , Adams A. R. , Gell M. A.
Published: July 2002

Impact ionization rates in GexSi1−x alloys and strained layers are expected to be strongly influenced by the threshold energies for ionization. We have calculated the threshold energies along the principal crystal axes from empirical pseudopotential band structures for Ge, Si, and GexSi1−x alloys (x=0.25, 0.5, 0.75). Both relaxed (cubic) and strained [tetragonal, grown on (001) cubic Si] alloys were examined. The ionization process with the lowest threshold energy in Si is different from that in Ge, for both electron- and hole-initiated ionization. For the cubic alloys, the lowest thresholds are ‘‘Si-like’’ for compositions up to approximately x=0.65. The effect of strain on the GexSi1−x alloys is to increase the ratio of the lowest hole threshold to the lowest electron threshold for all compositions, suggesting the possibility that GexSi1−x strained layer avalanche photodiodes may exhibit superior noise properties.
1H relaxation and diffusion of water and their dependence on suspended γ-Al2O3 particles
Authors: Kwag J. O. , Jang E. K. , Yu I.
Published: July 2002

The 1H spin-lattice relaxation time of water molecules is measured for the aqueous colloidal suspensions of γ-alumina (Al2O3) particles. We observe that the spin-lattice relaxation time T1(c) decreases gradually as the concentration c of the alumina particles is increased. We also observe a parallel decrease in the diffusion constant D(c). We attribute the simultaneous decrease of T1(c) and D(c) as c gets larger to the increase in the effective viscosity of the suspension, as explained in the light of the Bloembergen–Purcell–Pound [Phys. Rev. 73, 679 (1948)] theory of spin relaxation in liquids.
Grating coupling and intersubband absorption at 10 μm in GaAs/AlxGa1−xAs infrared quantum well waveguides
Authors: Ralston J. D. , Gallagher D. F. G. , Bittner P. , Fleissner J. , Dischler B. , Koidl P.
Published: July 2002

Grating coupling and intersubband absorption of ∼10-μm CO2 laser radiation are demonstrated in GaAs/AlxGa1−xAs mid-infrared single-mode waveguides grown by molecular beam epitaxy. The samples contain ten Si-doped GaAs quantum wells embedded within the waveguide core. Grating coupling in mesa waveguides fabricated from such samples is studied as a function of the wavelength and polarization of the incident laser light. The devices demonstrate selective absorption of TM polarized light, as dictated by intersubband absorption selection rules. The measured wavelength dependence of the optimal coupling angle is in good agreement with a simple grating-coupler analysis. Potential applications for infrared detection and integrated optics are discussed.
A comparative study of Si- and GaAs-based devices for repetitive, high-energy, pulsed switching applications
Authors: Hadizad P. , Hur J. H. , Zhao H. , Gundersen M. A.
Published: July 2002

A study is performed to assess Si and GaAs as materials for realization of repetitive, high-energy, pulsed switches in applications where the switching parameters are blocking voltages (VB) exceeding 1 kV in the off state and conduction currents (IF) in excess of 500 A in the on state, the current risetime being less than 1 μs and the pulse length being longer than 50 ns. Theoretical and technological limitations associated with the switching characteristics of Si- and GaAs-based majority carrier (unipolar) and minority carrier (bipolar) devices in the low-field, high-mobility, and high-field velocity saturation regimes are analyzed and discussed. It is concluded that for medium power applications (VBIF<300 kW,VB≳1 kV), majority carrier devices are best suited for fast switching processes in the low-field, low current density (J<100 A/cm2) regime. Under such conditions, the high drift mobility of GaAs allows for realization of field-effect devices exhibiting fast switching speeds and low on-state conduction losses. For pulsed switching in the high-power regime (300 kW<VBIF<30 MW, VB≳1 kV), bipolar structures exhibit the most desirable characteristics, while compared to their Si counterparts, the on-state conduction losses of GaAs-based devices are extremely high. These considerations are extended to stacked Si bipolar devices and semi-insulating GaAs photoconductive switches for ultrahigh-power (≳30 MW) switching applications.
The different characteristics for heavy- and light-hole resonant tunneling in Si1−xGex/Si double barrier structures
Authors: Shen G. D. , Xu D. X. , Willander M. , Hansson G. V.
Published: July 2002

A new approach to analyze the transport characteristics of resonant tunneling structures has been developed. It is shown that the Fermi-level Ef position per se, the temperature variations of the Fermi-level, the effective mass, and the mobility, have important influences on the resonant tunneling transport properties. Both calculations and experiments have shown very different features for heavy-hole and light-hole resonant tunneling in SiGe/Si resonant tunneling structures. These different features can for the first time be explained coherently. The calculated subband energy at current resonance can be much higher or lower than the Fermi level and the peak current can decrease or increase with temperature, depending on the device structure, the carrier type, and the working conditions. The calculations have predicted an interesting result that, in the low-temperature region, the valley current for the first heavy-hole resonance decreases with temperature, and that is confirmed by our experiments. The calculated temperature dependences of heavy- and light-hole transport, such as peak and valley currents/voltages and their variations with the well width, agree very well with our observations and other published results.