bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of annealed heavily C-doped p+-AlGaAs
Authors: Watanabe Kazuo , Yamazaki Hajime
Published: July 2002

This paper systematically analyzes the sources of the degradation of majority- and minority-carrier characteristics in annealed/as-grown heavily carbon-doped Al0.12–0.13Ga0.88–0.87As epilayers grown by metalorganic chemical vapor deposition. Hydrogen atoms in the as-grown epilayers act as acceptor killers for majority carriers with one-to-one correspondence but not as very effective recombination centers for minority carriers. The hydrogen atoms occupy bond-centered positions and relax the lattice contraction due to carbon doping by a ratio of about 2.5×10−3 A per 1020 cm−3 atoms. Post-growth annealing in nitrogen decreases these hydrogen atoms. On the other hand, annealing in a mixture of hydrogen and arsine increases the number of hydrogen atoms, but all the introduced hydrogen atoms do not necessarily act as acceptor killers. Sources other than hydrogen atoms, which are created by annealing above 600 °C, and those of as-grown apparently act as both compensation centers for majority carriers and as very effective nonradiative recombination centers for minority carriers. These sources seem to relax the lattice contraction by the ratio of about 8×10−3 A or less per 1020 cm−3 majority-carrier decrease and may have structures containing interstitial carbon.
Exciton photoluminescence of quantum wells affected by thermal migration and inherent interface fluctuation
Authors: Ping Er-Xuan , Dalal Vikram
Published: July 2002

Exciton photoluminescence (PL) of quantum wells (QW), affected by the thermal migration and the inherent interface roughness, has been studied by a model which includes exciton transfer between the growth islands with one atomic layer difference in well thickness. Analytical expressions, showing a red shifting and linewidth changing compared to the exciton PL spectra without thermal migration, are obtained. At low temperature, the red shifting and the linewidth changing are uniquely determined by the geometry of the QW. At high temperature, the red shift and the linewidth changing depends on the temperature, structure, and inherent interface fluctuation of the QW. Under the influence of the thermal migration, the inconsistency of the PL and PL excitation spectra has been reexamined and quantitatively obtained as a function of the temperature, quality, and structure of the QW.
Microwave production by an intense ion beam propagating through a magnetized background plasma
Authors: Kraft R. , Kusse B. R.
Published: July 2002

Measurements of the microwave radiation produced when an intense pulsed ion beam propagated from a field-free region into a magnetized plasma are presented. The ion beam was initially charge and current neutralized by a comoving electron population. Upon entering the magnetized plasma, some of the neutralizing electrons were stripped from the ion beam by the magnetic field and replaced by plasma electrons which were accelerated to high velocities by a space-charge imbalance within the ion beam. Electron plasma waves at the background plasma frequency were driven unstable by the high-velocity plasma electrons.
Response to ‘‘Comment on ‘Steady-state temperature profile for a thin-film resistor under bias’ ’’ [J. Appl. Phys. 74, 5290 (1993)]
Authors: Sabeti Roya , Charlson E. M. , Charlson E. J.
Published: July 2002

Although the thermal conductivities of silicon and silicon dioxide do vary with temperature, minimal change would result from a temperature rise of 50 °C, from room temperature to 350 °C. as is the case in the application in question.
Constraints on effective volumes assigned to atoms in ion implantation calculations
Authors: Collins R.
Published: July 2002

Most calculations of atomic depth distributions in solids produced by high-speed ion bombardment use the concept of the effective displacement volume Ωk of an atom of species k in a multicomponent system. General equations are given here to calculate the set {Ωk} from density-composition data. It is further shown that if the {Ωk} vary with local composition, then these variations cannot be independent, but must satisfy equations of constraint, which are derived here. The case of a binary system is considered in more detail.
Temperature effects in second harmonic generation in AgGaSe2 crystal
Authors: Bhar G. C. , Das S. , Chatterjee U. , Rudra A. M. , Route R. K. , Feigelson R. S.
Published: July 2002

The prospect of temperature tunability in an AgGaSe2 crystal for use in infrared nonlinear optics is explored for the first time. Tunable second harmonic generation from CO2 laser radiation is studied at different temperatures of the crystal. The tuning offered is small and the experimental finding is consistent with dispersion measurement.
In0.2Ga0.8As single strained quantum well lasers with GaAs/AlGaAs short-period superlattice barrier layers grown by molecular beam epitaxy
Authors: Hayakawa T. , Matsumoto K. , Horie H. , Nagai M. , Morishima M. , Ishigame Y. , Isoyama A.
Published: July 2002

In0.2Ga0.8As single strained quantum well lasers with GaAs/Al0.45Ga0.55As short-period superlattice barrier (SPSB)layers have been successfully prepared using molecular beam epitaxy although a part of SPSB has been grown in the forbidden temperature region for AlGaAs, where the specular smooth bulk AlGaAs cannot be grown. The averaged AlAs mole fraction of the present SPSB is 0.25, which gives the heterobarrier height larger than that of the conventional GaAs barrier layers. The threshold temperature sensitivity factor T0 of the laser with SPSB has been measured to be as low as 240 K, which is much larger than that of 90 K in the laser with GaAs barrier layers. This improvement results from the reduction of carrier leakage from quantum well to barrier layers.
Characteristics of Hg0.8Cd0.2Te/PbS heterostructures
Authors: Khlyap G. M. , Andrukhiv M. G. , Shkumbatiuk P. S. , Bochkariova L. V.
Published: July 2002

The heterostructures Hg1−xCdxTe/PbS (x=0.2) and their electrophysical and optical characteristics are investigated. Some electrophysical parameters are determined from I-U and C-V measurements.
Guided electromagnetic waves in anisotropic dielectric plates
Authors: Lee P. C. Y. , Yu J. D.
Published: July 2002

Guided electromagnetic waves in an infinite dielectric plate with general crystal symmetry surrounded by free space are studied in terms of the three-dimensional Maxwell’s equations. To exhibit as how the crystal symmetry may affect the propagation, symmetry, and coupling of the waves, the study is divided into four cases: (I) β11,β22,β33≠0; (II) β11,β22,β33,β12≠0; (III) β11,β22,β33,β23≠0; (IV) all βij≠0; where βij is the impermeability tensor referred to the rectangular axes xi with the x2 axis normal to the plate faces. Closed-form solutions are obtained and then the dispersion relations and modes are computed and studied for each case. It is found that in case I, solutions can be separated into the transverse-electric or TE waves and the transverse-magnetic or TM waves; TE and TM waves can be further separated into the symmetric and antisymmetric waves. In case II, the solutions for the TE waves remain the same as those in the case I; however, TM waves cannot be separated into symmetric and antisymmetric waves. In case III, solutions cannot be separated into the TE and TM waves, but they can still be separated into the symmetric and antisymmetric waves. In case IV, solutions can neither be separated into the TE and TM waves nor into the symmetric and antisymmetric waves. In case the solutions are not separable, the resulting waves can always be expressed as the sum of symmetric and antisymmetric waves which differ by a phase angle of π/2. Numerical computations are made for singly and doubly rotated cuts of lithium niobate corresponding to the four cases of symmetry.
Fluttering fountains: Simplified models
Authors: Casperson Lee W.
Published: July 2002

Fluttering oscillations are sometimes observed in the falling sheets of water associated with dams and waterfall fountains, and a theoretical simulation of this phenomenon was recently reported. In this study approximate analytical solutions of the previous model are described and compared with the experimental and theoretical observations.
Impurity doping in InP layer grown by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and organic doping sources
Authors: Horita M. , Suzuki M. , Matsushima Y. , Utaka K.
Published: July 2002

Impurity doping in InP layer grown by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and organic doping sources is presented. Diethylzinc and diethylselenide were used as the p-type and n-type doping sources, respectively. Electrical properties and surface morphology of the impurity-doped layers together with their growth condition dependence were investigated. Good controllability and reproducibility of the doping level were confirmed. The maximum doping levels of 1.8×1018 and 1×1019 cm−3 were successfully attained for p-InP and n-InP, respectively. These results promise further safe metalorganic vapor-phase epitaxy by using organic compounds for all precursors.
Waveguide effects in quantum wires with double-bend discontinuities
Authors: Wu J. C. , Wybourne M. N. , Weisshaar A. , Goodnick S. M.
Published: July 2002

Quantum waveguide structures with double-bend discontinuities were fabricated in modulation-doped AlGaAs/GaAs heterojunctions using a split-gate technique. The low field ac-conductance measurements at 50 mK show resonant peaks in the lowest quantized conductance plateau. The number of peaks increases with the effective cavity length of the double bend. This observation may be explained in terms of the allowed standing waves in the bend cavity, which is consistent with the theoretical predictions of a generalized mode-matching theory. Beyond the simple waveguide behavior, we find that the measured peak conductivity decreases as the channel length increases, which is believed to be associated with elastic scattering due to channel inhomogeneities. Magnetic field studies show that the resonance features are suppressed as the cyclotron radius approaches the one-dimensional channel width.
Photoluminescence of GaAs epitaxial layers on Si with growth assisted by electron-beam irradiation
Authors: Kim D. Y. , Kang T. W. , Leem J. Y. , Kim T. W.
Published: July 2002

GaAs films grown on untilted Si substrates and prepared by molecular-beam epitaxy were characterized by low-temperature photoluminescence (PL) spectroscopy. The GaAs layer was irradiated in situ with a 50 keV electron beam during growth. The PL spectrum of the electron-beam-irradiated GaAs/Si consisted of four well-resolved peaks at 1.502, 1.488, 1.471, and 1.434 eV. The peaks at 1.502 and 1.488 eV are related to the intrinsic emissions, and the peaks at 1.471 and 1.434 eV originate from the extrinsic emission band. The full width at half-maximum of the 1.488 eV emission band is only 2.8 meV, which is much smaller than the value obtained from the unirradiated GaAs/Si. The strain induced in the GaAs layer was estimated from the intrinsic peaks observed in the temperature range of 5–200 K. The PL properties of the species after postgrowth treatment, such as rapid thermal annealing are discussed.
Impact ionization and light emission in GaAs metal-semiconductor field effect transistors
Authors: Neviani A. , Tedesco C. , Zanoni E. , Canali C. , Manfredi M. , Cetronio A.
Published: July 2002

A study of light emission from GaAs metal-semiconductor field effect transistors and its connection with impact ionization phenomena is presented. First, the electrical behavior of the device in the preavalanche regime is characterized by measuring the excess gate current. Numerical simulations are performed, showing that the excess gate current is due to the collection of impact-ionization-generated holes at the gate electrode. Then, the energy distribution of the emitted photons in the range 1.5–3.1 eV is analyzed. The integrated intensity of photons emitted with energy above 1.5 eV is shown to be proportional, for large negative gate biases, to the product of gate and drain currents, suggesting direct recombination of channel hot electrons with impact-ionization-generated holes as the dominant emission mechanism. The deviation from simple proportionality at gate voltages around 0 V indicates that in implanted devices in open channel conditions other mechanisms, such as bremsstrahlung, may significantly contribute to the intensity of the emitted light.
Observation of X-band electron quantum interference and transport through virtual states in AlxGa1−xAs/AlAs heterostructures
Authors: Shieh Tung-Ho , Wu Chung-Cheng , Lee Si-Chen
Published: July 2002

The X-band conduction electron quantum interference and its transport through Γ virtual state were observed in the AlxGa1−xAs/AlAs/AlxGa1−xAs/AlAs/AlxGa1−xAs heterostructures with x=0.42, 0.45, and 0.5. Due to the existence of the deep donors, the carriers in AlxGa1−xAs electrodes were frozen out at low temperature, and the current-voltage (I-V) characteristics could only be measured under illumination. For x=0.45 and 0.5, the interference patterns were clearly observed in the differential conductance (dI/dV) versus voltage plot at 8.2 K and they disappear at about 15 K for x=0.45 and 25 K for x=0.5. For x=0.42, however, the interference pattern is seen only in the d2I/dV2 vs V characteristics under low carrier concentration. The observation of this quantum interference effect leads to the conclusions that the scattering rate for X-band electrons in AlxGa1−xAs was 1.13×1012 s−1 at 25 K for x=0.5 and 8.75×1011 s−1 at 15 K for x=0.45, respectively. For x=0.42, the scattering events at 8.2 K were dominated by electron–electron and X–Γ intervalley scattering.
Strain and quantum-confinement effects on differential gain of strained InGaAsP/InP quantum well lasers
Authors: Seki Shunji , Yokoyama Kiyoyuki
Published: July 2002

The effects of both strain and quantum confinement on the differential gain of strained InGaAsP/InP quantum well lasers (QWLs) are studied on the basis of valence-band structures calculated by k⋅p theory. Using an InGaAsP quaternary compound as an active layer makes it possible to separate the effect of strain (both tensile and compressive) from the quantum-confinement effect. In tensile-strained quantum wells, both strain and quantum-confinement effects exert a significant influence not only on the valence-band density of states (DOS) but also on the valence-subband energy spacings. In compressive-strained wells, on the other hand, the strain and quantum-confinement effects play an independent role in determining the DOS and the subband energy spacings, respectively. On the basis of these characteristic features of the valence-band structure of strained quantum wells, we discuss basic design principles for strained QWLs with larger differential gain.
Interaction of optical waveguide modes with magnetostatic transverse surface eigenmodes in a channel yttrium iron garnet waveguide
Authors: Matyushev V. V. , Stashkevich A. A. , Lukyanov A. I.
Published: July 2002

Optical probing of transverse ‘‘width’’ surface modes of magnetostatic waves (MSW) in narrow yttrium iron garnet–gadolinium gallium garnet waveguides 1.14- and 0.49-mm wide has been performed. It has been shown that the resolution of the optical technique using four first couples of optical waveguide modes TEi, TMi (i=0,1,2,3) is sufficient to detect diffraction peaks of numerous transverse magnetostatic modes (n=1,2,3,4,5,6). The method makes it possible to directly measure the efficiency of excitation of transverse MSW modes (symmetric as well as antisymmetric) in a narrow channel waveguide, which cannot be realized by means of microwave measurements.
Thin foil x-ray converters pumped by subpicosecond excimer lasers
Authors: Casperson D. E. , Cobble J. A. , Fulton R. D. , Kyrala G. A. , Schappert G. T. , Taylor A. J. , Wahlin E.
Published: July 2002

We have measured the conversion efficiency, as well as the spectral and temporal x-ray output of H- and He-like carbon line emission, from a thin foil of polypropylene that has been irradiated with subpicosecond KrF laser pulses. The effect of amplified spontaneous emission prepulse on the x-ray conversion process, as well as the application of these x-ray ‘‘flashlamps’’ toward pumping soft x-ray lasers, is discussed.
Inductance mode characteristics of a ceramic YBa2Cu3O7−x radio-frequency superconducting quantum interference device at 77 K
Authors: Il’ichev E. V. , Andreev A. V. , Jacobsen C. S.
Published: July 2002

Experimental results on some radio-frequency superconducting quantum interference device (rf-SQUID) signal properties are presented. The quantum interferometer was made of ceramic YBa2Cu3O7−x and was due to a low critical current operated in the inductance or nonhysteretic mode. With bias current as reference, amplitude variation, and phase shift of the voltage over the tank circuit coupled to the SQUID were measured simultaneously. It is shown that there is qualitative agreement between calculations based on the resistivity shunted junction model and the data. Moreover, using phase detection, signal instabilities predicted for the rf-SQUID inductance mode were observed. These signal instabilities may be exploited to enhance the transfer coefficient for measured flux-to-output signal.
Synchronous mode locking in a closed cavity electron cyclotron maser
Authors: McCurdy A. H.
Published: July 2002

It is theoretically demonstrated that mode locked operation can be achieved in a closed cavity electron cyclotron maser (gyrotron). This work is unique in two respects. First, the cavity provides a highly dispersive guiding structure for the electromagnetic wave, hence, the mode frequency spacing varies by an amount comparable to the average spacing between modes. The dispersive properties of the electron beam are used to compensate that of the cavity to allow eight longitudinal TE11n modes to lock together. Second, the locking is obtained by rf modulation of the axial velocity of the electron beam. A numerical example shows that subnanosecond radiation pulses can be generated at 16 GHz with an order of magnitude increase in power level over the free-running maser.
Room temperature carrier recombination in InGaAs/GaAs quantum wells
Authors: Marcinkevičius S. , Olin U. , Treideris G.
Published: July 2002

Room temperature recombination in InGaAs/GaAs single quantum wells has been studied by steady-state photoluminescence. Nonradiative recombination has been determined to be the prevailing recombination process. It occurs via the thermal carrier activation out of the well, followed by recombination in the barriers. The temperature dependence of the quantum well photoluminescence peak energy allows us to conclude that the main mechanism of radiative recombination at room temperature is of band-to-band origin.
The interaction between electron and phonon localized in a double-barrier resonant tunneling diode
Authors: Fu Y. , Willander M.
Published: July 2002

The electron-phonon interaction (the transition probability from the initial electronic state to the final state via the electron-phonon interaction) is analyzed when electrons and phonons are either extended or localized in a quantum system. Compared with the situation of the bulk material where all wave functions are extended, it is generally found that the electron-phonon interaction is reduced when one state is localized while it will be enhanced when more states involved in the interaction process become localized. It has been shown that the electron-phonon interaction is inversely proportional to the well width when all the states involved are localized. Special attention is then focused on the double-barrier resonant tunneling diode. A simple Monte Carlo scheme is developed to include the electron-phonon interaction process in the quantum well between two barriers. The numerically calculated I-V characteristics agrees much better with the experimental spectra if the electron-phonon interaction has been taken into account.
Stress induced anisotropy and temperature dependence of the magnetostriction in Fe73.5Cu1Nb3Si13.5B9 amorphous alloy
Authors: Murillo N. , González J. , Blanco J. M. , Vázquez M.
Published: July 2002

The magnetic anisotropy, Kσ, induced by heating under applied tensile stress has been studied for the Fe73.5Cu1Nb3Si13.5B9 amorphous alloy as a function of the annealing temperature. The induction process was carried out by means of current annealing in samples as-quenched and preannealed (TP.A.=400 °C during 2 min). It is found that the easy axis of this anisotropy is transverse to the tensile stress. The dependence of the stress induced anisotropy on annealing temperature is, in both cases, similar to that reported in other different metallic glasses when annealing at temperature below Tc=350 °C, while Kσ is practically constant (≊500 J m−3) in the annealing temperature range from 350 to 525 °C. On the other hand, the magnetostriction constant, λs, was determined as a function of the measuring temperature within the range from 4.2 K up to 600 K. The results can be well accounted for by the single-ion model up to 350 K, while above this temperature the contribution of two-ion mechnism is also inferred.
Thermal stability of internal electric field and polarization distribution in blend of polyvinylidene fluoride and polymethylmethacrylate
Authors: Tsutsumi Naoto , Ueda Yoshiaki , Kiyotsukuri Tsuyoshi , DeReggi Aimé S. , Davis G. Thomas
Published: July 2002

It is confirmed that a melt-quenched and annealed blend of 80 wt % polyvinylidene fluoride and 20 wt % polymethylmethacrylate has the β-crystal form of PVDF with optical clarity and other properties that are desirable for a host material in a guest-host system where the guest is an optically nonlinear dye that is orientationally stabilized by the strong internal electric field of a poled ferroelectric. Combined measurements, in such a blend, of the internal electric field Ei, the pyroelectric coefficient Cpyro, and the polarization distribution after electrically poling and subsequently thermally aging for 2 h intervals at temperatures up to 120 °C are reported. Ei and Cpyro increase with increasing poling field Ep. Ei was found to be as large as three times Ep. An unexpected thermal stability of Ei was observed at annealing temperatures above the glass transition temperature of 60 °C up to 100 °C when significant loss of Cpyro was measured. Thermal pulse results yield polarization distributions that may be attributed in part to dipolar polarization and in part to space charge. The prolonged thermal stability of Ei is ascribed to space charge that does not contribute to Cpyro. The poled blend shows second-harmonic generation with a nonlinear coefficient d33 of around 1 pm/V (9×10−9 esu).
Kinetic model of Au-GaAs interfacial reaction
Authors: Barcz Adam J.
Published: July 2002

Open-system annealing of Au/GaAs leads to vaporization of As species and migration of Ga atoms into Au. These processes are simultaneous only on a macroscale. A simple kinetic model is developed in which they are treated sequential by introducing specific fluxes F(Ga) and F(As). In view of a high diffusivity of Ga in Au, F(Ga) is calculated assuming linear flow at the phase boundary. F(As) is set constant for a given external pressure of arsenic. Conservation of bulk stoichiometry of GaAs implies that the decomposition rate of GaAs is controlled by the slower process. The model accurately describes the observed reaction rate in both capped and open configuration. It is shown that, upon heating, the instantaneous composition of the GaAs surface in contact to the metal evolves from initially As rich to Ga rich when Au becomes saturated with Ga.
Effect of coherent electromagnetic radiation on the ultrafast electron dynamics of laser excited bulk photoconductors
Authors: Joshi R. P. , Dharamsi A. N.
Published: July 2002

We analyze the role of coherent terahertz radiation on the ultrafast electron dynamics of laser excited photoconductors. Generation of electromagnetic radiation is included within the framework of the usual hot carrier transport theory. A Monte Carlo scheme is used to study the resulting changes in the nonequilibrium electronic energy and transient drift velocity. Our results reveal a density dependent decrease in both quantities, due to reductions in the internal electric fields caused by radiative energy outflow. At densities above 2×1017 cm−3, we obtain a decrease in the transient velocity and expect delays in the onset of phonon emission.
Anomalous optogalvanic line shapes of argon metastable transitions in a hollow cathode lamp
Authors: Ruyten W. M.
Published: July 2002

Anomalous optogalvanic line shapes were observed in a commercial hollow cathode lamp containing argon buffer gas. Deviations from Gaussian line shapes were particularly strong for transitions originating from the 3P2 metastable level of argon. The anomalous line shapes can be described reasonably well by the assumption that two regions in the discharge are excited simultaneously, each giving rise to a purely Gaussian line shape, but with different polarities, amplitudes, and linewidths.
Plasma edge and its application to infrared measurement and detection
Authors: Qian Dingrong
Published: July 2002

A steep plasma edge in infrared reflectivity spectra of Hg1−xCdxTe and HgSe:Fe has been observed. It is predicted that the edge is sensitive to the variation of carrier concentration, which indicates the possibility of developing a fast light-controlled switch for infrared radiation as well as a new approach of infrared modulation and detection. The modulation gain in power and detectivity limited by the generation-recombination process has been calculated and compared with the photoconductive counterpart.
Transition from relaxed to derelaxed amorphous silicon: Optical characterization
Authors: Reitano R. , Grimaldi M. G. , Baeri P. , Bellandi E. , Borghesi S. , Baratta G.
Published: July 2002

Optical constants of relaxed, derelaxed, and partially relaxed amorphous silicon (a-Si) in the range 0.4–0.9 μm are reported. The thermodynamical state of amorphous silicon (a-Si) has been changed either by thermal treatments or low dose ion implantation. Ellipsometry has been used to evaluate the complex refractive index for several amorphous states with enthalpy content between that of the fully relaxed and fully derelaxed a-Si. We observed a strong correlation between the electronic structure as probed by our optical measurements and the topological short-range order as probed by Raman scattering.
Low-temperature epitaxial growth of GaAs on on-axis (100) Si using ionized source beam epitaxy
Authors: Yun S. J. , Yoo M. C. , Kim K.
Published: July 2002

The epitaxial growth of GaAs films on on-axis (100) Si was studied at growth temperatures in the range 160–280 °C using ionized source beam epitaxy. Single-crystal GaAs films could be grown at a temperature as low as 160 °C with the acceleration of a partially ionized As-source beam, whereas at the same temperature only amorphous films were possible with neutral beams or with the ionized source beam with no acceleration. The use of an ionized As-source beam even without beam acceleration greatly improved the surface flatness of the GaAs film, and suppressed the formation of antiphase domains. The acceleration of the ionized As beam further improved the surface quality of the film.
Submillimeter wave low-temperature admittance of n-GaAs and n-InP diode structures
Authors: Krowne Clifford M. , Blakey Peter A.
Published: July 2002

Numerical simulation results for n+nn+ GaAs and InP diode structures in the 1–5 THz frequency range are presented. Cryogenic temperatures from 4 through about 77 K as well as some cases above liquid-nitrogen temperature are examined to obtain the two-terminal admittance. Earlier work has suggested possible negative conductivity at or below 4.2 K, but nothing consistent above 77 K. Implications of the Monte Carlo data for generation of submillimeter waves at intermediate lattice temperatures between 4 and 60 K are discussed for GaAs. Furthermore, numerical results are obtained at elevated lattice temperatures (200 and 300 K) to form a more complete view of transport in InP. The GaAs and InP results strongly suggest negative conductance behavior will be found below 20 K.
Fabrication of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy coplanar junctions and their anisotropic current-voltage characteristics
Authors: Kanke Yoko , Kasai Masahiro , Ohno Toshiyuki , Kozono Yuzoo
Published: July 2002

Two types of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy (YBCO-LCMO-YBCO) coplanar-type junctions with a 0.2 μm gap were fabricated by electron-beam lithography and Ar-ion-beam milling. One is a junction in which a current flows into the a-b plane (ferromagnetic spin arrangement) of the LCMO and then passes through the channel along the c axis (antiferromagnetic arrangement), and the other is a junction in which the current only passes through the a-b plane. In the former junction the current-voltage characteristics show nonlinearity which suggests a superconductive linkage, while the latter has linear characteristics. This anisotropy of the proximity effect is attributed to anisotropy of the spin structure, because the LCMO film has a small anisotropy of the normal decay length in the a-b plane and along the c axis.
Laser processing of Nb3Al(Ge, Si) high-field superconductors
Authors: Schaper W. , Bormann R. , Freyhardt H. C.
Published: July 2002

The laser irradiation process is a promising method for the fabrication of metastable Al5–Nb3Al(Ge,Si) compounds. Thereby Nb-sheathed Nb-25 at. % Al(Ge,Si) microcomposite tapes are prepared by a conventional powder metallurgical method and heat treated by a high-intensity CO2-laser beam. The parameters selected during laser beam irradiation of the composite determine the relative amounts of molten, heat-affected or unreacted material. In order to obtain large overall superconducting currents, it is favorable to melt a large fraction of the microcomposite without melting the surrounding Nb sheath. The cooling rate after laser beam irradiation determines the structure and the formation of metastable phases in the resolidifying material. The sequences of the process are simulated by heat flow calculations, which consider laser power, beam diameter, tape velocity, thickness, and microstructure, as well as heat transfer coefficients. From these calculations we could deduce optimum conditions for the laser treatment, leading to Jc values of 105 A cm−2 at 10 T and 104 A cm−2 at 16 T.
Pressure dependence of photoluminescence in ordered Ga0.5In0.5P grown on (001) GaAs by organometallic vapor phase epitaxy
Authors: Kobayashi Toshihiko , Ohtsuji Michiya , Deol Rajpal S.
Published: July 2002

Photoluminescence (PL) measurements on Ga0.5In0.5P grown by organometallic vapor phase epitaxy on (001) GaAs substrates at various growth temperatures have been made as a function of pressure up to about 4.5 GPa at 77 K. The PL spectrum shows a markedly sublinear shift to higher energies with pressure up to about 3.8 GPa; this corresponds to a sublinear increase in the E0 direct band gap. The pressure coefficients were obtained through a quadratic fit to the data between atmospheric pressure and 3.5 GPa. The sample grown at the highest temperature shows a significantly smaller linear coefficent than that grown at the lowest temperature. The tendency of saturation or weakly negative pressure shift above 4.0 GPa was also observed. The proposed origin of these results is the presence of repulsion between Γ-folded states in the CuPt-type ordered structure of GaInP samples, in which the ordering is not perfect nor homogeneous but rather consists of domains of ordered and disordered phases, depending on the growth conditions.
Theoretical investigation of different formulations of the electron-plasmon interaction under transient conditions
Authors: Mansour Nabil S. , Brennan Kevin F.
Published: July 2002

We present a comparison of two different methods of including the electron-electron long-range interaction on the dynamics of hot electrons in degenerate GaAs under transient conditions in two different hot electron transistor structures of 60- and 120-nm base widths, respectively. The first approach is quantum mechanically based while the second follows a semiclassical prescription. The calculated energy spectrum, velocity distribution, and percentage of injected carriers collected in the hot electron transistors are determined under three different conditions: the inclusion of the plasmon interaction through the quantum-mechanical formulation, the inclusion of the plasmon interaction through the semiclassical technique, and with no plasmon interaction. The calculated energy spectrums within the two plasmon models are qualitatively similar. They differ only by the extent to which the peaks are broadened and the absolute ratio of collected to injected carriers. Because of the very different energy relaxation within the plasmon models, the ratio of collected to injected electrons is predicted to be far smaller using the quantum-mechanical model than the semiclassical model. Subsequently, knowledge of the absolute ratio of the collected to injected carriers in a hot electron transistor would give some indication of the appropriateness of each model.
Germanium-doped gallium phosphide obtained by neutron irradiation
Authors: Goldys E. M. , Barczynska J. , Godlewski M. , Sienkiewicz A. , Heijmink Liesert B. J.
Published: July 2002

Results of electrical, optical, electron spin resonance and optically detected magnetic resonance studies of thermal neutron irradiated and annealed at 800 °C n-type GaP are presented. Evidence is found to support the view that the main dopant introduced via transmutation of GaP, germanium, occupies cation sites and forms neutral donors. This confirms the possibility of neutron transmutation doping of GaP. Simultaneously, it is shown that germanium is absent at cation sites. Presence of other forms of Ge-related defects is deduced from luminescence and absorption data. Some of them are tentatively identified as VGa-GeGa acceptors leading to the self-compensation process. This observation means that the neutron transmutation as a doping method in application to GaP is not as efficient as for Si.
Depth distribution and thermal stability of implanted Hg ions in silicon
Authors: Wang Ke-Ming , Shi Bo-Rong , Ma Shi-Jie , Zhai Hong-Ying , Liu Xiang-Dong , Liu Ji-Tian , Liu Xi-Ju
Published: July 2002

50–400 keV Hg+ was implanted into silicon seven years ago. The depth distribution and temperature effect of the implanted Hg+ were recently investigated by Rutherford backscattering of 2.1 MeV 4He2+. The results show that the implanted Hg+ in silicon is still stable at room temperature after seven years. After 1000 °C annealing, the implanted Hg ions disappeared. The depth distributions of implanted Hg+ in Si can be well described by the transport of ions in matter (trim’90). In addition, the values of mean projected range and range straggling obtained from the present measurements are compared with those of TRIM’90 and the calculation procedure based on Biersack’s angular diffusion model.
Importance of confined longitudinal optical phonons in intersubband and backward scattering in rectangular AlGaAs/GaAs quantum wires
Authors: Jiang W. , Leburton J. P.
Published: July 2002

The important role of confined longitudinal optical (LO) and surface optical (SO) phonons is investigated for different types of individual scattering processes in AlGaAs/GaAs quantum wires. Electron wave function tailing due to finite barrier height has been properly taken into account. We demonstrate that for highly confined wires structures Ly=Lz=40 Å, forward and backward scattering are dominated by SO phonons. For 80 Å×80 Å structures, forward scattering is still predominately by SO phonons while backward scattering is dominated by confined LO phonons. Finally, for 150 Å×150 Å, confined phonons control both forward and backward scattering. However, we demonstrate that confined LO phonons play a dominant role in intersubband transitions even in highly confined structures, and that it has the most significant effect on the backward scattering in quantum wires of Ly=Lz≳80 Å.
Detection of S2F10 produced by a single-spark discharge in SF6
Authors: Sauers I. , Mahajan S. M.
Published: July 2002

Improvement in detection sensitivity of S2F10 in SF6 down to concentrations below 10 parts per billion, using a cryogenic enrichment-gas chromatography technique, has permitted the detection of S2F10 produced by a single-spark discharge in SF6. The spark yield of S2F10 was found to fall in the range of yields found in earlier work on more highly decomposed SF6. Based on preliminary data the spark discharge may provide a suitable and reproducible reference source of S2F10.
Role of temporal parameters of excitation in short-pulse low-pressure N2-TE lasers
Authors: Kukhlevsky S. V. , Kozma L.
Published: July 2002

To examine how laser pulses around 1 ns can be attained in a low-pressure N2-TE laser with a typical thyratron switch, we have shown that by decreasing the duration of the exciting current impulses the laser pulses can be reduced to 1 ns.
Photocurrent and photoluminescence from quantum-confined electrons in periodically δ-doped Si-GaAs
Authors: Maaref H. , Mejri H. , Priester C. , Barrau J. , Bacquet G. , Bourgoin J. C.
Published: July 2002

Photocurrent and photoluminescence experiments performed on periodical δ-doped GaAs reveal a signature of quantum-confined interband transitions. We present in this structure the observation of the transition energy at low temperature in the photocurrent spectrum.
Growth and characterization of Ga0.65In0.35P orange light-emitting diodes by metalorganic vapor–phase epitaxy
Authors: Lin Jyh-Feng , Wu Meng-Chyi , Jou Ming-Jiuun , Chang Chuan-Ming , Chen Chin-Yuan , Lee Biing-Jye
Published: July 2002

p-n Ga0.65In0.35P homostructure light-emitting diodes grown on GaAs0.7P0.3 substrates have been fabricated by low-pressure metalorganic vapor-phase epitaxy. The growth and characterization of undoped, Si-, and Zn-doped layers are described in detail. The optimum growth condition to grow the high-quality Ga0.65In0.35P epitaxial layers is at the growth temperatures of 700–740 °C and V/III ratios of 100–200. The strongest photoluminescence peak intensity occurs at 2×1018 and 7×1017 cm−3 for electron and hole concentrations, respectively. Diodes fabricated from the p-n homostructure are characterized by current-voltage measurement, electroluminescence, and external quantum efficiency. A forward-bias turn-on voltage of 1.68 V with an ideality factor of 2.5 and a breakdown voltage of 9 V are obtained from the current-voltage measurements. The emission peak wavelength and full width at half-maximum of electroluminescence are around 610 nm and 79 meV at 20 mA. The external quantum efficiency of the uncoated diode is about 0.015%.
Dependence of valence-subband structures on the substrate orientation in ZnSxSe1−x/ZnyMg1−ySzSe1−z quantum wells
Authors: Xie X. , Wang W. I.
Published: July 2002

We present a theoretical investigation of the growth orientation dependence of valence-subband structures in ZnSxSe1−x/ZnyMg1−ySzSe1−z quantum wells grown in the [001], [115], [113], [112], and [111] directions. The results indicate that the in-plane effective mass of the heavy-hole subband in the [111]-oriented structure is substantially smaller than that in the [001] quantum wells. For applications to quantum-well lasers, the lighter effective mass will lead to a smaller threshold current density, and therefore a better laser performance. Our investigations should provide useful guidelines for the design of II-VI quantum-well blue lasers.
Dwell time in doped double-barrier heterostructures
Authors: Pandey Lakshmi N. , George Thomas F.
Published: July 2002

A time-dependent Schrödinger equation has been solved numerically for a double-barrier and a quantum-well resonant tunnelling structure. Special emphasis has been paid to the system where barriers are doped specially by negative delta-function potentials (δ potentials) which broaden the widths of the resonances and in turn decrease the dwell times. The strengths of the delta functions could be such that they may form bound states in the barrier regions, but the states bound to δ potentials are very shallow. Delta-function potentials are replaced by equivalent barriers of different heights and widths which are easy to incorporate into the numerical calculation of the propagation of the wave packet, and the corresponding physical structures can be conveniently fabricated. It is found that for a certain strength of the δ potential or parametric value of the equivalent barriers in the barriers of the resonant tunneling structure, there are three resonance states very close together. The square of the wave functions trapped in the well region for the states oscillates in time for a broad wave packet in k space, whereas the wave function trapped in the whole structure decays exponentially. The oscillating part has a resemblance with the quantum beats. There are no oscillations for a narrow wave packet in k space.
Electron beam modification of GaAs surface potential: Measurement of Richardson constant
Authors: Lindsay S. M. , Hemsky J. W. , Look D. C.
Published: July 2002

The surface potential of GaAs is strongly modified in the presence of a high-energy electron beam due to the creation of electron-hole pairs in the depletion region and the subsequent drift of the holes to the surface where they neutralize surface states. This effect is modeled in terms of a parameter K=A*T2/Ib(dE/dz)η, where Ib is the beam current density, A* is the effective Richardson constant, dE/dz is the beam energy loss per unit length, and η−1 is the average energy required to create an electron-hole pair. For the sample studied here, an 0.25-μm layer with n≂3×1017 cm−3, we obtain a value K≂(7.5±0.8)×104 cm at T=296 K and Ib=0.33 μA/cm2, which gives A*≂0.44 A/cm2 K2. Although this value of A* is much lower than the theoretical estimate of 8 A/cm2 K2, it is in good agreement with other recent results.
X-ray induced modification of metal/fluoropolymer interfaces
Authors: Shi Ming-Kun , Lamontagne Boris , Martinu Ludvik , Selmani Amine
Published: July 2002

Metal adhesion to polymers depends on the chemical structure at the interface. In the present work, we study the evaporation of Cr, Ti, and Au onto Teflon PFA (perfluoromethyl-vinyl-ether) substrates, and we modify the interface by post-deposition x-ray irradiation. In situ x-ray photoelectron spectroscopy shows that deposition of reactive metals such as Cr and Ti leads immediately to crosslinking and to the formation of carbide and fluoride species. Less reactive metals, such as Au, cause only small loss of fluorine without formation of any new species. The metal/PFA interface is strongly affected by x-ray irradiation in the case of Cr and Ti: remarkably enhanced crosslinking has been observed, which further increases with the metal coverage, while the carbides and fluorides remain basically unaffected. On the other hand, crosslinking increases only very slightly for pure PFA and for the Au/PFA interface, regardless of the Au thickness. These results suggest that radical recombination reactions are responsible for crosslinking at the interface between PFA and reactive metals.
Water vapor controlling selective reactive ion etching of SiO2/Si in NF3 plasma
Authors: Konuma M. , Bauser E.
Published: July 2002

Water vapor added to NF3 plasma during reactive ion etching controls the ratio of the etch rates of SiO2 and Si. Selectivity rises from a value of 0.14 at water-free 100% NF3 to 1.99 for an initial gas composition of 35% H2O-65% NF3. The results of mass and energy analysis of the plasma yield a basis for discussing the mechanisms which effect the selectivity. The NF3/H2O plasma removes native oxides from Si surfaces.
Elastic anomalies of barium titanate
Authors: Subramanyam B. , Viswanathan K. S.
Published: July 2002

The anomalies of the second-, third-, and fourth-order elastic constants have been derived for barium titanate and related compounds for the phase transition from cubic to tetragonal and from the tetragonal to the orthorhombic phases. The equilibrium values of the three components of the order parameter and the strain variables in the two phases have been obtained from the stability conditions. The fluctuations in the order parameter in the two phases have been derived from the Landau–Khalatnikov equations. Expressions have been given for the shift in the zero point energy in the tetragonal and orthorhombic phases, and these are shown to be proportional to (T−Tc)2. The anomalies for all the second-order elastic constants have been derived for both phases, and relations among them have been reported. It is shown that the elastic anomalies suffer a discontinuity at the transition temperature for both the phases. Our expressions give the temperature variation of the third-order elastic and fourth-order elastic constants for the phase transition from the tetragonal to the orthorhombic phase.
Charge transfer cross section of He+ in collisional helium plasma using the plasma immersion ion implantation technique
Authors: Qin Shu , Chan Chung , Browning Jim , Meassick Steve
Published: July 2002

The charge transfer collision cross section of He+ ions in a collisional helium plasma has been determined based on the ion energy distribution at the target during the plasma immersion ion implantation (PIII) process. The ion energy distribution is obtained by inferring data from a secondary-ion mass spectroscopy measurement and a simple collisional theory. The value of the charge transfer cross section in the collisional plasma was found to be higher than previously published values. The cross-section value determined by the PIII technique was used in a plasma simulation and was found to agree with our experimental observations.
Reply to ‘‘Comment on ‘A theory on the x-ray sensitivity of a silicon surface-barrier detector including a thermal charge-diffusion effect’ ’’ [J. Appl. Phys. 72, 3363 (1992)]
Authors: Cho T. , Hirata M. , Takahashi E. , Teraji T. , Kohagura J. , Yamaguchi N. , Matsuda K. , Takeuchi A. , Ogura K. , Kondoh T. , Osawa A. , Yatsu K. , Tamano T. , Miyoshi S.
Published: July 2002

The effect of thermal-diffusion charge on the x-ray energy response of silicon surface-barrier (SSB) detectors have generally been ignored; consequently, the SSB response has been believed to be analyzed using the thickness of the depletion layer alone. Our new theory on the SSB x-ray response [J. Appl. Phys. 72, 3363 (1992)] was prepared for addressing recent confusion on plasma x-ray analyses using SSB detectors [Rev. Sci. Instrum. 59, 1380 (1988); 61, 693 (1990); 63, 4850 (1992)]. This approach was made under the assumption of a dominant contribution of the diffusion-charge signal in the vicinity of the x-ray incident location because of the strong reduction of the x-ray produced charge within the thermal-diffusion length. In this report, the comparison between this approximation (having an approximated solution) and the exact numerical calculation (using an integral form) is carried out. Necessity and importance of such three-dimensional treatments for the data analyses as well as the design of multichannel semiconductor-array detectors developed for plasma x-ray tomography diagnostics are highlighted. Furthermore, for the total diffusing-charge amount, the calculated results from our theory and the values using the comment from Donolato agree well within the accuracy of 1%.