bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the growth kinetics of glow-discharge hydrogenated amorphous silicon using a radical separation technique
Authors: Matsuda Akihisa , Tanaka Kazunobu
Published: July 2002

The deposition kinetics of hydrogenated amorphous silicon (a-Si:H) from a SiH4 glow-discharge plasma have been investigated by examining the diffusion of SiH3 monoradicals in the discharge-free space within a triode reactor. This experiment suggests that the SiH3 radicals are responsible for about 37% of the total deposition rate of a-Si:H in a conventional SiH4 glow-discharge process. The contribution of other radicals and atoms to the deposition rate is also discussed through the analysis of reaction-rate constants.
Studies of implanted iron in silicon by channeling and Rutherford backscattering
Authors: Wang P. W. , Cheng H. S. , Gibson W. M. , Corbett J. W.
Published: July 2002

Different amounts of 100-keV iron ions have been implanted into high-resistivity p-type FZ-silicon samples. The implantation damage, recovery of damage during various annealing periods and temperatures, movement of iron atoms under annealing and oxidation, and the kinds of defects created after implantation, annealing, or oxidation are all investigated by channeling and backscattering measurements. We have found that the critical fluence of 100-keV iron implanted into silicon at room temperature is ∼2.5×1014 Fe/cm2, and that iron atoms are gettered by silicon oxidation. In this supersaturated region iron atoms diffuse slightly towards bulk silicon during high-temperature annealing (≥1100 °C) but not at all during low-temperature annealing (≤1000 °C) in dry nitrogen ambient.
Organometallic growth and characterization of GaxIn1−xP (x=0.51, 0.65, 0.69)
Authors: Yuan J. S. , Tsai M. T. , Chen C. H. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

The growth and characterization of GaxIn1−xP (x=0.51, 0.65, 0.69) are described in this paper. The organometallic vapor-phase epitaxial (OMVPE) growth was carried out in an atomospheric pressure reactor using trimethylgallium (TMGa), trimethylindium (TMIn), and phosphine (PH3). GaAs and commercially available hydride vapor-phase epitaxial GaAs0.70P0.30 and GaAs0.61P0.39 were used as the substrates. The influence of growth temperature and V/III ratio on the properties of the OMVPE epilayers was studied. This resulted in the determination of an optimum growth temperature of 625 °C and an optimum V/III ratio range of 40–50. The results of the mismatch due to the different lattice constants of the GaxIn1−xP epilayer and the substrate were investigated. It was found that high-quality GaxIn1−xP epilayers can be obtained only when the mismatch ‖Δa/a0‖ is less than 1×10−3. Under the conditions mentioned above, epilayers were reproducibly obtained with featureless surface morphologies, and photoluminescence (PL) with high intensities and narrow half-widths (41–43 meV at 300 K). The dislocation etch pit densities  ρ of Ga0.65In0.35P and Ga0.69In0.31P epilayers were 7.4–8.6×104 cm−2, grown lattice matched to GaAs1−yPy ( y=0.30, 0.39) substrates with  ρ=6.4–7.5×105 cm−2. The degradation of PL intensity after annealing at temperatures between 400 and 600 °C in H2 or N2 indicates an increase in the surface recombination velocity for GaInP epilayers. Etching 30 Å from the surface was found to restore the original PL intensity.
Vacancy interactions in GaAs
Authors: Dannefaer S. , Kerr D.
Published: July 2002

Isochronal annealing of zinc- or silicon-doped GaAs as well as undoped semi-insulating or low-resistivity materials has been investigated by positron lifetime measurements. For impurity concentrations larger than 4.5×1017 cm−3, only monovacancy complexes such as ZnGaVAs,  SiAsVGa, or AsGaVGa are observed and they yield a positron lifetime of 265±5 ps. For impurity concentrations less than 1×1017 cm−3, divacancies dominate and yield a lifetime of 295±5 ps. The concentrations of grown-in vacancies, either VAs or VGa, are both estimated to be in the range of (1–4)×1017 cm−3.
The local structure of amorphous SnO2 by electron microscope techniques
Authors: Tafto J. , Rajeswaran G. , Vanier P. E.
Published: July 2002

Electron microscopy/diffraction and electron energy-loss spectroscopy, including low-loss and core-edge structures, were used to characterize and study the atomic arrangement in amorphous SnO2 prepared by reactive sputtering. The gross features in the energy-loss spectra are the same as for crystalline SnO2, whereas the fine structures are smeared out. The diffraction pattern of amorphous SnO2 is qualitatively well described by assuming each tin atom to be surrounded by six oxygen atoms at a distance of 2.05 Å, two tin atoms at 3.19 Å, and eight tin atoms at 3.71 Å, which suggests the same local atomic arrangement as in crystalline SnO2.
High-temperature hardness of Ga1−xInxAs
Authors: Guruswamy S. , Hirth J. P. , Faber K. T.
Published: July 2002

Substantial solid-solution strengthening of GaAs by In acting as InAs4 units has recently been predicted for an intermediate-temperature plateau region. This strengthening could account, in part, for the reduction of dislocation density in GaAs single crystals grown from the melt. Hardness measurements at high temperatures up to 900 °C have been carried out on (100) GaAs, Ga0.9975In0.0025As, and Ga0.99In0.01As wafers, all of which contain small amounts of boron. Results show a significant strengthening effect in In-doped GaAs. A nominally temperature-independent flow-stress region is observed for all three alloys. The In-doped GaAs shows a higher plateau stress level with increasing In content. The results are consistent with the solid-solution strengthening model. The magnitude of the solid-solution hardening is sufficient to explain the reduction in dislocation density with In addition.
Luminescence study of rapid thermal annealing of ion implantation damage in cadmium telluride
Authors: James K. M. , Merz J. L. , Jones C. E.
Published: July 2002

The results of photoluminescence analysis of ion-implanted and flash-annealed CdTe are reported here. Bound exciton lines in the spectrum of the CdTe were used to study the annealing of implantation-induced damage in the crystal. The intensity and width of these lines are a very good indicator of variations in lattice strain. Optimum flash annealing conditions were found to depend on both the energy and the dose of the implant. The photoluminescence indicates that flash annealing can provide complete annealing of the crystal damage following implantation. Implanting Cu or B ions into the lattice did not, however, lead to significant variations in the spectrum of the samples as compared to annealed, unimplanted samples. A comparison of flash and furnace annealing was made.
Photoluminescence studies of defects and impurities in annealed GaAs
Authors: van de Ven J. , Hartmann W. J. A. M. , Giling L. J.
Published: July 2002

Photoluminescence studies have been performed on undoped and silicon-doped GaAs crystals, which were annealed between 650 and 1000 °C under different arsenic pressures. Samples were also heat treated with the addition of pure elemental Ga, Mn, or Cu. Spectra were taken in the energy range 1.15–1.55 eV at the surfaces of the annealed crystals and at various depths below the surface. Newly observed zero-phonon emissions at 1.31 and 1.347 eV are concluded to be related to CuGa-(VAs)2 and CuGa-VAs, respectively. An emission at 1.467 eV also was found to be related to a CuGa-containing complex. A new emission at 1.342 eV was found to be related to a fast diffusing MnGa-containing complex. Most likely, the emission originates from a MnAs center. The nature of these defects is discussed on the basis of their emission characteristics, diffusion behavior, and dependence on annealing parameters. Through this study it appeared that arsenic vacancies play a crucial role both in the establishment of defect equilibria and in the formation of complexes with MnGa and CuGa. A new luminescence peak at 1.448 eV was found to be related to the VAs defect. Most probably, it has to be associated with the GaAs antisite. The presence of arsenic vacancies also induces a shift of the 1.492-eV emission to 1.484 eV. This shift is attributed to the replacement of CAs by SiAs acceptors. Some evidence was found that a peak at 1.38 eV is associated with VGa. It is concluded that solid-state equilibrium of native defects and impurities is only established at the surfaces but not in the bulk of the crystal during the heat treatments.
Uniform p-type doping profiles in Mg+24-implanted, rapidly annealed GaAs/AlGaAs heterostructures
Authors: Descouts B. , Duhamel N. , Daoud-Ketata K. , Krauz P. , Godefroy S.
Published: July 2002

A flat profile with p-type doping level of 1×1019 cm−3 can be obtained up to the surface in GaAs/GaAlAs heterostructures by multienergy implantations of Mg+24 at room temperature followed by a rapid thermal anneal by halogen lamps.
Calculated quasi-eigenstates and quasi-eigenenergies of quantum well superlattices in an applied electric field
Authors: Harwit Alex , Harris J. S. , Kapitulnik A.
Published: July 2002

We present a new technique utilizing computer simulations to determine the exact eigenstates of a quantum well superlattice of GaAs/AlGaAs in a perpendicular electric field. The technique is applied to quantify the tunability of a new infrared detector utilizing an intraconduction-band transition in the quantum well. Solutions found by this technique are compared with those found by a variational method and the Kronig–Penney model. The technique has several advantages over a conventional variational approach. It allows the easy calculation of the excited states in addition to the ground state. It is able to determine the energy levels in a finite period superlattice in addition to those in a single well. It also provides an indication of its own precision.
High-resolution imaging of the EL2 distribution in thin semi-insulating GaAs wafers: A comparison with x-ray topography
Authors: Alt H. Ch. , Packeiser G.
Published: July 2002

A detailed comparison of two-dimensional near-infrared absorption maps and x-ray topographs of commercial semi-insulating (100) GaAs wafers grown by the liquid-encapsulated Czochralski technique is reported. The absorption measurements with a spatial resolution up to 100×100 μm2 were performed using a highly sensitive silicon diode array as the detector element. Fluctuations of the EL2 concentration up to 60% are found in conventional undoped wafers. In preannealed wafers, these fluctuations are reduced by a factor of 2, approximately. The spatial one-to-one correlation of the EL2 distribution with grown-in dislocation networks, which is observed in both cases, is discussed. In indium-doped wafers of low dislocation density, the homogeneity of EL2 is better than 5% in the central area of about 40 mm in diameter. By investigating the EL2 distribution near peripheral slip lines, it is definitely established that gettering is a relevant process leading to nonuniformities.
Rapid annealing of GaAs: Uniformity and temperature dependence of activation
Authors: Cummings K. D. , Pearton S. J. , Vella-Coleiro G. P.
Published: July 2002

Scanning microwave photoconductance, capacitance-voltage profiling, and Hall effect measurements were used to investigate the uniformity of activation of Si-, Be-, and Mg-implanted 2- and 3-in.-diam, semi-insulating GaAs substrates after rapid thermal annealing in a commerical furnace. The results indicate that carrier lifetimes and mobilities for low-dose (3–4×1012 cm−2) implants and carrier densities for high-dose (1×1015 cm−2) implants are comparable or superior in rapidly annealed substrates to those obtained in thermally annealed implanted layers. The uniformity of these parameters is not significantly different for wafers annealed by either method. The temperature dependence of damage removal and carrier activation in the implanted regions during both furnace and transient annealing was also investigated, and demonstrates that the microwave photoconductance technique gives results for donor implantation correlating well with conventional backscattering and electrical measurements, respectively.
Propagation of intense ion beams across a plasma-filled magnetic cusp
Authors: Busby K. O. , Greenly J. B. , Hammer D. A. , Nakagawa Y. , Pedrow P. D.
Published: July 2002

Preionized plasma has been compared with vacuum and with neutral gas as a medium for the propagation of intense ion beams across magnetic fields. Two cusp-injection ion ring experiments have been used to study the effectiveness of these three cusp-fill media for space-charge neutralization, as shown by the subsequent spreading of the injected rings. In the ion ring experiment a ≲100-ns ion beam was injected into ∼20-eV plasma fills of ≲1012/cm3, giving much better propagation than vacuum, but not as good as 100-mTorr H2 gas. In the long-pulse ion ring experiment with ≳200-ns beam rise time, plasma fill and vacuum gave similar propagation. The results suggest that for complete neutralization of space charge in ion beams propagating across magnetic fields, background media must be provided to meet certain minimum requirements of conductivity and collisionality which depend upon the beam current and rise time.
Photoluminescence and excitation spectra of Zn1−xMnxSe films and superlattices grown by molecular-beam epitaxy
Authors: Bylsma R. B. , Kossut J. , Becker W. M. , Kolodziejski L. A. , Gunshor R. L. , Frohne R.
Published: July 2002

Measurements of photoluminescence and photoluminescence excitation spectra at liquid helium temperatures are presented for films of ZnSe, Zn1−xMnxSe (0≤x≤0.33), and multilayer structures ZnSe/Zn1−xMnxSe (x=0.23, 0.33, and 0.51) grown by molecular-beam epitaxy. All samples investigated had the zinc-blende structure. The temperature dependence of the luminescence from the superlattices has been studied up to 300 K. Good quality of the samples is evidenced by the reduction of impurity- or defect-related long wavelength emissions. Several new features in the photoluminescence spectra were resolved (e.g., a region of low-intensity luminescence ending with a sharp cut off at about 75 meV above the main line) which were not observable in bulk samples. The presence of internal strains in the epitaxially grown superlattice samples results in the observed splitting of the heavy- and light-hole valence bands. Furthermore, the strain present can actually dominate over the quantum confinement to produce a net red shift of the near band-edge features. Both the red shifts and the heavy-to-light-hole band splitting are consistent with the estimates of the lattice mismatch-induced strains.
Use of radiation from betatron oscillations as an electron-beam diagnostic
Authors: Chernin D. , Levush B.
Published: July 2002

It is generally difficult to diagnose the energy of an electron beam propagating in a focusing channel. Here we suggest observation of the Doppler-shifted radiation due to the electrons’ betatron motion in the channel as a sensitive, nonperturbing diagnostic. Sample spectra have been calculated for a specific type of channel used in a cyclic electron accelerator and their features are discussed.
Influence of oxygen precipitates on silicon resistivity in the 650 °C range
Authors: Kung C. Y.
Published: July 2002

A new kinetic model is proposed to explain the resistivity shift phenomenon at annealing temperatures of around 550–800 °C. In this model, thermal donor generation and acceptor annihilation both contribute to the resistivity shift, but the latter contributes most. The rodlike defect which can only grow at temperatures below 800 °C is speculated to act as a gettering center for the acceptors. This model is used to explain the most salient features of ‘‘new donor’’ activity.
Growth of GeSi/Si strained-layer superlattices using limited reaction processing
Authors: Gronet C. M. , King C. A. , Opyd W. , Gibbons J. F. , Wilson S. D. , Hull R.
Published: July 2002

SiGe/Si superlattices were grown using limited reaction processing. Each multilayer structure was fabricated in situ by changing the gas composition between high-temperature cycles. Commensurate SiGe alloy layers as thin as 15 nm were reproducibly deposited and were examined using transmission electron microscopy, sputtering Auger electron spectroscopy, and Rutherford backscattering. Si/SiGe interfaces are abrupt to within a few monolayers, establishing for the first time the use of a chemical vapor deposition technique to fabricate abrupt GeSi/Si-based heterostructures.
Role of oxygen and nitrogen in the titanium-silicon reaction
Authors: Kikuchi Akira , Ishiba Tsutomu
Published: July 2002

X-ray diffraction and Rutherford backscattering measurements were performed on titanium silicide, titanium oxide, and titanium nitride. These compounds were formed by the heat treatment of Ti film on single-crystal Si in O2, N2, or O2+N2 ambient. The heat treatment in O2 and O2+N2 at 600 °C resulted in the formation of TiO2 and TiSi2, whereas the heat treatment in N2 resulted in the formation of TiN, Ti5Si3, and TiSi. It was also observed that Ti5Si3 and TiSi were converted to TiSi2 during the post-annealing above 800 °C and that the resistivity of TiSi2 was lowered to about 25% that of TiSi and Ti5Si3. The refractive index of TiO2 formed in O2 ambient was similar to that of rutile bulk.
Equivalence of donor and acceptor fits of temperature-dependent carrier-concentration data
Authors: Look D. C. , Sizelove J. R.
Published: July 2002

It is shown that the usual charge-balance analysis of temperature-dependent carrier-concentration data cannot distinguish between the donor and acceptor behavior of a center which is emitting carriers to a particular band, even though the statistics are different in the two cases. Other data, such as mobility or analytical results are needed to make the distinction.
Influence of the excitation frequency on surface wave argon discharges: Study of the light emission
Authors: Boisse-Laporte C. , Granier A. , Bloyet E. , Leprince P. , Marec J.
Published: July 2002

We compare discharges produced by surface waves at 210 MHz and 2.45 GHz in argon at low pressure (0.1–10 Torr). For plasma lengths up to 1 m, the plasma and wave characteristics are determined (electron density, electric field, effective collision frequency, etc.) and the influence of the excitation frequency is shown. Studying the emission of the discharge, we have established relations between the intensities of Ar i and Ar ii lines and these characteristics, taking into account the wave frequency. That leads to practical criteria for the choice of the excitation frequency.
Fe-C film formation by dual ion beam sputtering
Authors: Kobayashi Toshio , Ootomo Shigekazu , Kumasaka Noriyuki
Published: July 2002

Fe-C films are formed by dual ion beam sputtering in which an ion beam irradiates the substrate during film formation. The magnetic properties and film structure of the resulting Fe-C films are investigated. As the acceleration voltage of the substrate beam increases, C concentration in the Fe-C films decreases, thereby changing the magnetostriction constant of the film from positive to negative. When films formed at an acceleration voltage of 0, 200, and 400 V are heated at 100, 300, and 400 °C, respectively, the relative permeability of each film reaches a maximum. The Fe-C film with 8 at. % C has a room-temperature saturation magnetic flux density of 2.2 T, a relative permeability of 900, and a magnetostriction constant near zero.
Transmission electron microscope study of the growth kinetics of TiSi2 epitaxy on (111)Si
Authors: Chu J. J. , Wu I. C. , Chen L. J.
Published: July 2002

The kinetics of the growth of epitaxial TiSi2 on (111)Si and accompanying microstructural changes have been investigated by examining the same region of a thin foil repeatedly in a transmission electron microscope with intermittent annealings in a diffusion furnace. The evolution of the different modes of C54-TiSi2 epitaxy was monitored. The dominance of the epitaxy with [101]TiSi2//[111]Si and (3̄13)TiSi2//(22̄0)Si (with about 1° deviation) was found to be due to a faster initial growth rate resulting in a much larger final size than that of the epitaxy with [100]TiSi2//[111]Si and (004)TiSi2//(022̄)Si. The difference in interface energy is conceived to be the dominant factor in affecting the epitaxial growth.
Induced inversion at a silicon ferroelectric copolymer interface
Authors: Langlois J.-M. , Noirhomme B. , Filion A. , Rambo A. , Caron L. G.
Published: July 2002

A copolymer of vinylidene fluoride and tetrafluoroethylene is solution cast on a p-type silicon wafer. The dipoles in the copolymer are aligned by corona charging the film or by biasing a subsequently evaporated aluminum gate. The field coupling to the semiconductor is studied by measuring the surface channel currents which flow between a metal-insulator-semiconductor source and drain. We show that the field coupling following corona injection is sufficient to induce a strong inversion in silicon and that this effect decays with a time constant which can vary between a few minutes to approximately one day.
Depletion corrections in variable temperature Hall measurements
Authors: Lepkowski T. R. , DeJule R. Y. , Tien N. C. , Kim M. H. , Stillman G. E.
Published: July 2002

The decrease in the measured Hall free-electron concentration with decreasing temperature near 300 K is often observed for thin high-purity GaAs layers. This has previously been interpreted as electron freezeout on deep donor sites. However, it can be quantitatively described by the decrease in carrier concentration per unit area associated with increasing surface and interface depletion region thicknesses. It is shown that when these depletion regions are included in the analysis of the Hall-effect data, the measured free-electron freezeout behavior can be accurately described by a simple shallow donor. If necessary, a deep donor may be included in the modeling. The results agree with the observed temperature variation of the capacitance-voltage (C-V) profiling data.
Experimental research and computer analysis of a completely demagnetized state microwave permeability for polycrystalline ferrites
Authors: Zhu Sheg-chuan , Zhao Li-qun , Wen Fan-ping , Meng Lu-zheng
Published: July 2002

The systematic experimental research and computer analysis of the completely demagnetized state microwave permeability has been done for a series of polycrystalline ferrites with various saturation magnetizations, magnetocrystalline anisotropies, and densities. The results show that the influence of the saturation magnetization and magnetocrystalline anisotropy is in agreement with Schloemann’s formula; and the action of porosity can be interpreted by the apparent saturation magnetization and additional magnetic anisotropy.
Well-defined uniaxial anisotropy in iron film formed by ion beam sputtering
Authors: Nagai Yasuhiro , Tago Akio , Yanagisawa Keiichi , Toshima Tomoyuki
Published: July 2002

This paper reports on the results of an experimental investigation into the magnetic properties of iron films formed by ion beam sputtering. Through the iron film formation at various nitrogen partial pressures and substrate angles, nitrogen ion bombardment is found to reduce the coercive force of the magnetic hard axis in addition to inducing uniaxial anisotropy. The decrease in the coercive force corresponds well to the increase in the nitrogen concentration and the anisotropy constant of the α-Fe-composed films. The uniaxial anisotropy is confirmed to mainly result from directional ordering rather than crystalline anisotropy. The magnetic properties of the film having well-defined uniaxial anisotropy are a coercive force of 0.3 Oe, a saturation magnetization of 2.2 T, an anisotropy field of 3.5 Oe, and a permeability of 5000.
Magnetic properties of BaFe12−2xCoxTixO19 fine particles prepared by coprecipitation tempering
Authors: Chou Fucheng , Feng Xiaofeng , Li Jun , Liu Yin
Published: July 2002

The magnetic properties of BaFe12−2xCoxTixO19 fine particles prepared by the coprecipitation tempering method were studied. The experimental data shows that the specific saturation magnetization σs decrease with an increase in the substitution x is not significant and the anisotropy constant K1 decrease is obvious. We believe that the Co2+ ions preferentially occupy 12k sites in the structure of magnetoplumbite, and the tendency of Co2+ ions to enter lattice sites has some temperature dependence.
Magnons and factons in diluted antiferromagnets (invited)
Authors: Orbach R. , Yu Kin-Wah
Published: July 2002

Site-diluted antiferromagnets with short-range interactions can serve as a model magnetic percolation system. A length scale ξ exists such that for length scales (1/q)>ξ the structure is continuous (hydrodynamic limit), and the magnetic excitations are antiferromagnetic magnons, with a stiffness constant which depends critically upon the magnetic concentration. For length scales (1/q)<ξ, the structure is fractal, and the magnetic excitations are fractons, with a characteristic dispersion law. The fracton excitations are (strongly) spatially localized. The magnons are expected to be extended in the very long length scale limit, with the possibility of Anderson (weak) localization for length scales longer than ξ. The magnetic excitations cross over from magnon to fracton at an energy ωc∝ξ−[1+(θ/2)], where θ is the anomalous diffusion exponent. We have calculated the scattering form factor I(q,ω) for magnetic excitations of a d=3 simple cubic antiferromagnet within the effective medium approximation (EMA), as a function energy transfer ω and momentum transfer q. We find that at small fixed q (within the magnon regime), p>pc, I(q,ω) is sharply peaked at the magnon frequency. Near to pc, a second (but small) peak at ωc is visible on the asymmetric high-energy tail of I(q,ω). For larger fixed q (within the fracton regime), I(q,ω) is centered about the fracton frequency, although it is quite broad, reflecting the strong spatial scattering of fractons.
The effect of molybdenum on the magnetic properties of the Nd-Fe-Co-B system
Authors: Shen Xufang , Wang Yongqiang , Diao Zhitao , Liu Xuefen
Published: July 2002

Experiments have been carried out using the Nd-Fe-Co-B-Mo alloy to study the improvement of thermomagnetic properties. The samples containing Mo have a set of typical characteristics as follows: Hc=9100 Oe, Hcj=19 400 Oe, and Hk=12 000 Oe. The SEM have been determined, and a new Mo-rich phase was found. The results and SEM obtained are discussed in this paper.
Photoluminescence study of the Si-implanted and rapid thermal annealed InP:Fe
Authors: Rao Mulpuri V.
Published: July 2002

Low-temperature photoluminescence has been used to characterize 200 keV/3×1012 cm−2 Si-implanted and rapid thermal annealed InP:Fe. A very low-optical activation was observed in the samples annealed for 15 s at less than 700 °C. A peak at 1.353 eV has been observed along with exciton peak (1.419 eV) and Zn-C acceptor peak (1.382 eV) in Si-implanted and annealed samples. The 1.353-eV peak which is not observed in unimplanted samples exhibited shallow donor-to-deep acceptor transition behavior and is believed to be due to the silicon-antisite defect-complex (In−−PSi+In)− acting as the deep acceptor. Analysis of variable temperature PL data gives an activation energy of 69.8 meV for this deep acceptor level. Due to compensating effect of this acceptor complex, a relatively poor electrical activation (≤35%) has been observed in the annealed samples.
Superconducting Sn/Sn-oxide/Sn tunneling junctions as high-resolution x-ray detectors
Authors: Twerenbold D. , Zehnder A.
Published: July 2002

In a superconducting detector, the energy resolution is expected to be superior than in a semiconductor detector, owing to the thousand times smaller energy gap Δ. The performance of Sn/Sn-oxide/Sn tunneling junctions (operated in the Giaever mode at T=0.32 K) exposed to 6-keV x-ray photons of a 55Fe source is presented. The best energy resolution observed is 67 eV (FWHM). Extrapolating to vanishing electronic noise, an intrinsic resolution of 0.7% (FWHM) is obtained. This is an order of magnitude worse than expected from the statistics of the 2.5×106 primary electron charges produced, and is believed to be due to geometrical effects in the films. The energy response of the detector is nonlinear, owing to the self-recombination of the free charge carriers. At a fixed bias voltage, the pulses generated in either film of the junction were observed to have the same sign. If the junctions are evaporated onto a silicon substrate, most of the pulses originate, via phonon backscattering, from x-ray photons interacting in the substrate. Quasiparticle diffusion is essential in explaining the observed data.
Phase-separated Fe and Co particles in a BN matrix
Authors: Edelstein A. S. , Das B. N. , Holtz R. L. , Koon N. C. , Rubinstein M. , Wolf S. A. , Kihlstrom K. E.
Published: July 2002

Using co-sputtering, 10–300 Å particles of Fe and Co have been prepared in an insulating BN matrix. The Fe particles have the α-Fe structure. The saturation magnetic moment of the iron particles per at. % Fe was found to be approximately independent of the Fe concentration and equal to the value of α-Fe. The system undergoes a metal–nonmetal transition at approximately 40 vol % Fe. For concentrations of Fe particles above this threshold the temperature dependence of the resistivity is metallic and the room-temperature coercivity is large (50–100 Oe). For the Co particles, the room-temperature coercivity is about twice as large as Fe above the metal–nonmetal threshold. Below the metal–nonmetal threshold the particles behave as superparamagnets and the coercivity is approximately zero.
D
X center analysis in Sn-doped AlGaAs layer of double heterostructures
Authors: Kaniewski J. , Kaniewska M. , Žďánský K.
Published: July 2002

Capacitance as well as photovoltage methods have been used to analyze deep centers in an n-type AlGaAs:Sn layer of double heterostructures. It is suggested that the trap with thermal activation energy equal to ΔE2=0.33±0.02 eV is associated with the L minimum of AlGaAs and could be interpreted as a DX center related to Sn. The observed changes of deep center concentration in double heterostructures are due to different Al contents within the depletion region.
Positron-lifetime studies of hydrogenated amorphous silicon
Authors: Bhide V. G. , Dusane R. O. , Rajarshi S. V. , Shaligram A. D. , David S. K.
Published: July 2002

Positron-lifetime studies have been carried out on hydrogenated amorphous silicon (a-Si:H) films prepared by the glow-discharge method. Films deposited and thermally annealed at different temperatures have been investigated for determination of microstructural aspects such as hydrogen content, microvoids, vacancies, etc. The appearance of a long-lifetime component (τ3>3 ns) in the lifetime spectrum together with a narrow peak in the two-dimensional angular correlation of positron-annihilation radiation confirms existence of large microvoids in the films. The systematics of the variation of the intensity of the long-lifetime component (I3) as a function of the deposition and annealing temperature is studied in detail. This study clearly shows that molecular hydrogen exists at high pressure in the microvoids and it effuses out at elevated temperature, leaving behind empty microvoids in the film. Two stages of effusion of hydrogen at 275 and 600 °C have been clearly identified in films deposited at 25 °C. Interestingly, the films deposited at 300 °C exhibit only the high-temperature effusion stage, establishing thereby that the low-temperature stage relates to trapped molecular hydrogen, while the one corresponding to high temperature (600 °C) relates to bonded hydrogen. The positronium lifetime (τ3) shows an increase with annealing temperature, representing growth of microvoid dimensions, presumably due to ensuance of an agglomeration process concurrent with hydrogen effusion. Information concerning the presence of quadrivacancies and pentavacancies in the films and their response to thermal treatment is also obtained from the study of the intensity (I2) and lifetime (τ2) corresponding to the trapped positron state. An attempt has been made to correlate the positronium component with electron-spin-resonance results.
Impurity scattering of a two-dimensional gas calculated in the charge-sheet approximation
Authors: Grinberg A. A.
Published: July 2002

A simplified form of the screened impurity potential is used in the calculation of the impurity-scattering limited mobility. The simplification is based on modeling the two-dimensional gas as a charge sheet removed from the interface by some distance. It is shown that for the practical values of electron concentrations (1011–1012 cm−2), a good agreement with the exactly calculated mobility can be reached if one takes this distance equal to 0.55zav, where zav is the average separation of the two-dimensional electrons from the interface. The relative error does not exceed 20% in the case of scattering by the interface impurity centers and 10% in the case of the scattering by the remote centers. In the latter case the error decreases with the increased thickness of an undoped spacer layer. The proposed sheet model of the two-dimensional gas can be used in numerical calculations of the impurity scattering effects where accuracy of the calculated mobility plays a secondary role.
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u Schottky contacts to molecular-beam epitaxially grown gallium antimonide
Authors: Poole I. , Lee M. E. , Missous M. , Singer K. E.
Published: July 2002

Rectifying contacts have been made by depositing epitaxial films of aluminum on both homo- and heteroepitaxial layers of n-type GaSb grown by molecular-beam epitaxy. The barrier heights determined from the current-voltage and capacitance-voltage characteristics of these contacts were 0.54 and 0.56 eV, respectively. The significance of these results is briefly discussed.
Distribution coefficient of carbon in melt-grown GaAs
Authors: Desnica U. V. , Cretella M. C. , Pawlowicz L. M. , Lagowski J.
Published: July 2002

The results of a detailed investigation of the distribution coefficient of carbon in GaAs are reported for a series of crystals grown at different pulling rates by the liquid-encapsulated Czochralski method. From localized vibration mode absorption measurements, it was found that the concentration of carbon always decreases along the length of the ingots and that the effective distribution coefficient increases strongly with a decrease in pulling rate. The equilibrium distribution coefficient determined from present data, K0=3.5, is higher than previously reported values for the effective distribution coefficient; however, it is consistent with chemical trends for group IV elements in GaAs.
Anomalous deposition rate dependence of hydrogenated amorphous silicon on substrate temperature
Authors: Ishihara Shin-ichiro , Kitagawa Masatoshi , Hirao Takashi
Published: July 2002

The deposition rate dependence of hydrogenated amorphous silicon prepared by capacitively coupled rf glow discharge upon substrate temperature has been studied using an optical emission spectroscopy. Both the plasma emission intensity and the deposition rate increased more than twice by changing the substrate temperature from 200 to 300 °C. Under the conditions of pure SiH4 60 sccm, 1 Torr, and electrode spacing 18 mm, the deposition rate is found to be proportional to the intensity of H2 continuum radiation at 200–500 nm.
Spatial distribution of free-carrier lifetime and deep-level luminescence across a semi-insulating GaAs wafer
Authors: Leo K. , Rühle W. W. , Haegel N. M.
Published: July 2002

The free-carrier lifetime, the near band-edge luminescence (band-to-band and band-to-acceptor transitions), and the near-infrared deep-level luminescence (two bands at 0.7 and 0.8 eV) are mapped across an undoped semi-insulating GaAs wafer. The carrier lifetime follows on a large scale a W-shaped profile across the wafer with lifetimes varying between 200 and 500 ps at T=5 K. The band-to-band, band-to-acceptor, and the 0.7-eV luminescence are intense wherever the lifetime is long. However, the intensity of the 0.8-eV luminescence is high where the lifetime is short. The intensity variation of the 0.8-eV luminescence could quantitatively explain the lifetime distribution. Comparison with near-infrared absorption data show that EL20 as mapped by near-infrared absorption is not responsible for the short lifetime. Additionally, the lifetime shows a short-distance variation with a cell size of about 300 μm.
Physical conditions of computer analysis of ion backscattering
Authors: Rauhala E.
Published: July 2002

The physical effects on computer data analysis of 4He and 1H ion backscattering have been investigated. The consequences of the low-energy tail effect, undetected elements, the nonunique correspondence between the sample and the spectrum, screening and nuclear effects on the scattering cross sections, and the energy response of the silicon surface barrier detector have been studied from the point of view of spectrum synthesis. Cases are pointed where these physical effects should be taken into account. Usually their consequences are neglected in ‘‘standard’’ computer programs since they are considered to have secondary importance. It is shown that ‘‘standard’’ procedures are well justified only in treating those parts of 4He backscattering spectra which arise near the surface region of the sample at about 2-MeV ion energy.
Generalized rate equations governing the light-induced degradation and the thermal recovery of a-Si:H films
Authors: Hong C. S. , Hwang H. L.
Published: July 2002

This paper examines the rate equations governing light-induced degradation and thermal recovery of undoped a-Si:H films. For early degradation the recombination came primarily from band-to-band transitions and the degradation rate (dN/dt) is proportional to the inverse of the square of the spin density (1/N2). When electron paramagnetic resonance active dangling bonds is greater than 1018 cm−3, the recombination through defects becomes more significant, and the degradation rate has a form of A(1/N2)−B(1/N)+C−DN. Furthermore, the temperature dependence on the changes of the photoconductivity decay and recovery indicates that both degradation and recovery are thermally activated processes, and an activation energy of ∼0.2 and ∼1.4 eV was derived for either process.
Temperature dependence of the picosecond carrier relaxation in silicon-irradiated silicon-on-sapphire films
Authors: Pfeiffer Th. , Kuhl J. , Göbel E. O. , Palmetshofer L.
Published: July 2002

The temperature dependence of the free-carrier relaxation in ion-irradiated silicon-on-sapphire films has been investigated by picosecond photoconductivity measurements in the temperature range 90–295 K. The relaxation time of the photoconductivity decreases markedly with decreasing temperature in samples irradiated with small doses (<1014 cm−2) of Si ions, whereas nearly amorphized samples show no temperature dependence. This behavior is well described within a multiple-trapping model taking into account structural defects that are built in during the evaporation of the films as well as introduced by the ion irradation.
Degradation and annealing characteristics of amorphous silicon-hydrogen alloys after a long-time test
Authors: Tzeng Wen-Jer , Tsai Hsiung-Kuang , Lee Si-Chen
Published: July 2002

The effect of long time (up to 1000 h) repeated light exposure combined with annealing at different temperatures (25–200 °C) on the photoconductivity of an intrinsic amorphous silicon-hydrogen alloy has been investigated. It was found that the degradation process was not entirely reversible and that the photoconductivity decay was enhanced after each test cycle. A new annealing behavior was observed; that is, the photoconductivity of the degraded films did not show any sign of recovery when annealed below the degradation temperature (25 °C) for 800 h, but started to improve slowly when annealed at a temperature above 50 °C. The light-soaking effect was also studied by using different light intensities and substrate temperatures. It was found that the nonreciprocity relation always holds, and the degradation is much improved when tested at a higher temperature. The bond-breaking model with a distribution of dangling-bond distance is used to explain all these results.
Anomalous Hall effect in p-type Hg1−xCdxTe liquid-phase-epitaxial layers
Authors: Zemel A. , Sher Ariel , Eger D.
Published: July 2002

This paper reports on the Hall characterization of narrow-gap p-type Hg1−xCdxTe epilayers grown by liquid-phase epitaxy. The characterization couples variable magnetic field (0.5–10 kG) and temperature (from 15 to 300 K) data with an analysis procedure which includes n-type conducting regions in the p-type material. It is shown that the analysis of the magnetic field dependence of the Hall coefficient is a useful tool to study the anomalous electrical properties in p-type Hg1−xCdxTe . The analysis, which is rather simple, yields consistent and meaningful results, and in some cases permits determination of the concentration of holes (in the p-type material) and electrons (in the n-type regions) and their mobilities. Although there is strong evidence that the n-type conducting regions are located at the surface of the Hg1−xCdxTe samples, the possibility that in some cases the n-type regions could be located within the material bulk or near the Hg1−xCdxTe substrate interface cannot be excluded.
A model of conduction in polycrystalline silicon films
Authors: Ada-Hanifi M. , Sicart J. , Dusseau J. M. , Robert J. L.
Published: July 2002

Conductivity and Hall measurements have been performed on n-type and p-type polycrystalline silicon films over a wide range of temperatures (30–400 K). We present an interpretation of the electrical behavior of polycrystalline semiconductors which for the first time takes into account intergranular fluctuations in potential. In this model, random distribution of potential among grains and fluctuations in barrier heights at grain boundaries (GB) result from nonuniformities in the grain size, impurity concentrations, and GB state densities. We separate the carriers into localized carriers and free carriers. This model explains both the high and low temperature conduction regimes. We estimate the intergranular disorder parameter and the threshold energy for several phosphorus or boron-doped silicon samples.
Localized epitaxial growth of TaSi2 on (111) and (001)Si by rapid thermal annealing
Authors: Wu I. C. , Chu J. J. , Chen L. J.
Published: July 2002

Localized epitaxial TaSi2 was grown on (111) and (001)Si by rapid thermal annealing in Ar ambient. The best epitaxy was obtained in samples annealed at 1300 °C for 300 s. Three major modes and one dominant mode of TaSi2 epitaxy were found to grow on (111) and (001)Si, respectively. The roles of lattice match in the growth of epitaxial TaSi2 are explored. The effects of gas ambient on the growth of TaSi2 epitaxy are discussed.
Localized epitaxial growth of ReSi2 on (111) and (001) silicon
Authors: Chu J. J. , Chen L. J. , Tu K. N.
Published: July 2002

Epitaxial ReSi2 has been grown locally on (111) and (001)Si. The best epitaxy was obtained in samples after two-step annealing at 500–1100 °C. In (111) samples, the orientation relationships were analyzed to be [110]ReSi2//[111]Si and (002)ReSi2//(2̄02)Si. About 70% in areal fraction of the epitaxial regions were found to be pseudomorphic. In (001) samples, two different modes of epitaxial silicides were observed: [110]ReSi2//[001]Si and (1̄10)ReSi2//(22̄0)Si (mode A′) and [110]ReSi2//[001]Si and (1̄12̄)ReSi2//(220)Si (mode B′). About 40% and 60% in areal fractions of the mode A′ and mode B′ epitaxial ReSi2 regions, respectively, were found to be pseudormorphic. The apparent insensitivity of the quality of the ReSi2 epitaxy to the lattice matches at silicide/silicon interfaces at room temperature may be explained in part by the considerable changes in lattice mismatches at the growth temperature arising from the substantial difference in thermal expansion coefficients between the ReSi2 overlayer and the substrate silicon. The results are in agreement with a theory which predicts that orientations with negative mismatches are favored for epitaxial growth over orientations with positive mismatches.
X-ray diffraction analysis of buffer layer effects on lattice distortions of strained layer superlattices
Authors: Kamigaki K. , Sakashita H. , Kato H. , Nakayama M. , Sano N. , Terauchi H.
Published: July 2002

Effects of In0.2Al0.8As buffer layers on the lattice distortions of the strained layer superlattices (In0.2Al0.8As)100 Å (GaAs)100 Å (30 periods) have been investigated by x-ray diffraction. We have found that for the buffer layer thickness hbuff≥5000 Å, the In0.2Al0.8As layers of both buffer layers and superlattices are in a strain-free state, while GaAs layers of superlattices show large tetragonal lattice distortions. This fact implies that for hbuff≥5000 Å, buffer layers dominate the strain fields of superlattices, i.e., buffer layers play the role of an ‘‘effective substrate.’’ Lattice distortions in buffer layers and superlattices against buffer layer thickness are discussed.
Optical investigation of quantum-well fluctuations in In0.53Ga0.47As/InP superlattices
Authors: Sauer R. , Harris T. D. , Tsang W. T.
Published: July 2002

Photoluminescence spectra of In0.53Ga0.47As/InP multiple quantum wells with well widths of 70–160 Å and barrier widths of 20–400 Å exhibit narrow doublet lines or more complex line structure. Such spectra are studied as a function of temperature, excitation level, and wavelength, and by photoluminescence excitation spectroscopy. It is shown that all lines are due to intrinsic excitons and that the multiplicity of the spectra arises from fluctuations in the quantum wells along the growth direction, which we identify with compositional changes of the InGaAs. The multiline spectra offer a convenient way to study interwell electron-hole transfer, and this process is shown to be efficient in the present crystals up to barrier widths of at least 200 Å.
Plasma-assisted etching of tungsten films: A quartz-crystal microbalance study
Authors: Fracassi F. , Coburn J. W.
Published: July 2002

The plasma-assisted etching of magnetron-sputtered polycrystalline tungsten films in CF4-H2 and CF4-O2 glow discharges has been studied as a function of ion energy using quartz-crystal microbalance methods supplemented by vacuum-transfer Auger electron spectroscopy and actinometric emission spectroscopy.
Theoretical evaluation of the buffer gas effects for a self-sustained discharge ArF laser
Authors: Ohwa Mieko , Obara Minoru
Published: July 2002

The effect of buffer gases on the operating performance of a self-sustained discharge ArF laser employing a charge transfer excitation circuit has been analyzed theoretically. By the analysis of the electron kinetics, the ArF* formation, the ArF* relaxation, and the absorption of the B→X laser radiation, the pump rate dependence of intrinsic efficiency, small-signal gain, and absorption could be clarified for the Ne- and He-diluted mixtures. It is found that there is no appreciable difference in the intrinsic efficiency of the ArF laser between Ne- and He-diluted mixtures when employing a laser resonator with a strong output coupling. After optimizing output coupling in each case, a higher efficiency is obtainable for the Ne diluent than for the He diluent. For a 4-atm mixture of 4.9% Ar and 0.1% F2 in Ne, an intrinsic efficiency of 4% is obtainable, while less than 2% is obtainable for the He-diluted mixtures. However, a higher specific output energy is achievable for the He-diluted mixtures than the Ne-diluted mixtures because the use of He-diluted mixtures can efficiently transfer the stored energy to the laser discharge load.