bluuebunny/crossref_metadata_2025 huggingface dataset:
Comment on “The effect of dust charge fluctuations on ion cyclotron wave instability in the presence of an ion beam in a plasma cylinder” [Phys. Plasmas 6, 444 (1998)]
Authors: Ostrikov K. N. , Yu M. Y.
Published: July 2002

The applicability of the dust charging model used by Sharma and Sugawa [Phys. Plasmas 6, 444 (1998)] is discussed. The model has to be used with caution in general. In particular, a more accurate account of the external magnetic field in the model is needed for the problem investigated.
Role of computer modeling of plasmas in the 21st century
Authors: Dawson John M.
Published: July 2002

For much of their history plasmas have been characterized by complex unpredictable behavior. This stemmed from their general nonlinear turbulent behavior, from the difficulties of carrying out controlled experiments, and from the limitations of theory. Recently this situation has changed quite dramatically with the phenomenal growth in the capabilities of computer modeling. Contact between predictions and experiments have been made over a broad range of problems. In the 21st century the power of modeling will continue to grow; the techniques for using the tool will grow and our ability to understand the complex results will improve. In this endeavor the most critical factor is the human factor. Humans must create the models; they must make sense of the results; they must condense the results to a simplified form that is useful to others. Given the importance of plasmas to human activities and in the universe, these advances point to important developments.
Simple model for the electronic relaxation during the expansion of a plasma generated in an Ar–O2 mixture
Authors: Lebéhot A. , Kurzyna J. , Lago V. , Dudeck M. , Nishida M.
Published: July 2002

The local properties of a plasma free jet are calculated with a collisional-radiative model where electron density and temperature are included as parameters. The kinetic equations are written for all the electronic states of the atomic species Ar and O. In the first step, only excitation and de-excitation by electron collisions are taken into account, together with spontaneous radiative decay. This allows the problem to be treated as a linear system of equations represented by a matrix. In the second step, collisional processes with atoms and residual molecules are included. The number of adjustable parameters is limited to the normalization factor of the reaction rate constants for excitation by electrons, the degree of dissociation of oxygen at the nozzle exit, and to the relative number of singly charged ions for oxygen and argon along the axis. Electron temperature and density are measured experimentally, or obtained separately from another calculation. Then, the population density of any level can be obtained in any point of the free jet. The results are compared, on the axis, with those of three different experiments, and the agreement is quite satisfactory in any case.
Photoluminescence studies of the neutralization of acceptors in silicon by atomic hydrogen
Authors: Thewalt M. L. W. , Lightowlers E. C. , Pankove J. I.
Published: July 2002

A number of recent electrical transport studies have shown that low-temperature treatment in plasmas containing atomic H can neutralize acceptors in Si. We have studied this process by monitoring the bound exciton luminescence associated with the implanted acceptor impurities B, In, and Tl. Treatment in an atomic H plasma was found to substantially reduce the acceptor bound exciton luminescence while leaving unchanged the lines due to an implanted donor, As, thus verifying the conclusions of the transport studies.
Oxygen content of heavily doped silicon
Authors: Pearce C. W. , Jaccodine R. J. , Filo A. J. , Lin W.
Published: July 2002

We have determined the oxygen content of heavily doped n- and p-type silicon using charged particle activation analysis. Specifically, when crystals are grown using the Czochralski technique and keeping growth parameters constant, the oxygen content does not vary with dopant additions for p− and n+ crystals but does seem to increase for p+ crystals.
Reflection extended x-ray absorption fine structure recorded using a laser-produced plasma x-ray source
Authors: Eason R. W. , Bradley D. K. , Dobson P. J. , Hares J. D.
Published: July 2002

This letter describes the first use of a laser plasma x-ray source for the recording of surface reflection EXAFS (extended x-ray absorption fine structure), or reflexafs. A powerful technique in which a subnanosecond pulse of x rays is used to record the reflection spectrum over a range of incidence angles and wavelengths in a single shot is described. Reflexafs spectra for aluminum are presented which compare favorably with spectra recorded in transmission mode.
Proton ring trapping in a gated magnetic mirror
Authors: Pedrow P. D. , Greenly J. B. , Hammer D. A. , Sudan R. N.
Published: July 2002

An axis-encircling proton ring has been trapped for times (≊4 μs) much longer than the ion cyclotron period (≊80 ns). The rings, with mean radius 10 cm and with particle energies ≤430 keV, made eight passes through the 1.5-m-long magnetic mirror well with static and puffed hydrogen used for space-charge neutralization. The measured proton inventory was typically 2 × 1015 protons during the first pass and 2 × 1013 protons during the eighth and final pass. With a central solenoidal field of 0.8 T, the peak diamagnetism and azimuthal current density of the injected ring were typically 10 mT (100 G) and 10 A/cm2, respectively.
A 720 mV open circuit voltage SiOx:c-Si:SiOx double heterostructure solar cell
Authors: Yablonovitch E. , Gmitter T. , Swanson R. M. , Kwark Y. H.
Published: July 2002

For maximal performance solar cells should resemble semiconductor lasers, i.e., they should be constructed in the form of a double heterostructure. We have found rather good performance in SIPOS-crystalline silicon-SIPOS double heterostructure solar cells, where SIPOS≡SiOx. The processing of these solar cells gives insights into the truly outstanding performance of the n+-SIPOS: p-Si heterojunction which has a forward saturation current coefficient J0=10−14 A/cm2, or equivalently an ‘‘emitter Gummel number’’ Ge=3.3×1015 s/cm4. This suggests that crystalline silicon solar cells can be much more efficient than had been suspected.
Growth of InAs1−xSbx (0<x<1) and InSb-InAsSb superlattices by molecular beam epitaxy
Authors: Lee G. S. , Lo Y. , Lin Y. F. , Bedair S. M. , Laidig W. D.
Published: July 2002

Thin films of InAs1−xSbx (0<x<1) have been deposited on GaAs and InSb substrates in the temperature range 300–400 °C using molecular beam epitaxy. The solid composition was found to be quite sensitive to the Sb flux and less sensitive to As flux. InSb-InAsSb superlattice structures have also been grown and studied. Both the ternary alloy and the superlattice structures can be potential material systems for detectors covering the 8–12-μ range.
Formation of GdSi2 under UHV evaporation and i
n s
i
t
u annealing
Authors: Suu H. V. , Petõ G. , Mezey G. , Pászti F. , Kótai E. , Fried M. , Manuaba A. , Zsoldos E. , Gyulai J.
Published: July 2002

GdSi2 was prepared under ultrahigh vacuum conditions. Prior to processing, a clean interface was produced using diluted HF dipping. It is pointed out that the ‘‘critical temperature’’ for formation published earlier is probably an artifact and correlation between the interface native oxide and the critical temperature is established.
Optical studies of hydrogenated amorphous carbon plasma deposition
Authors: Wagner J. , Wild Ch. , Pohl F. , Koidl P.
Published: July 2002

Optical emission spectroscopy was applied to study the rf glow discharge in hydrocarbons used for the deposition of amorphous hydrogenated carbon (a-C:H). The optical data in conjunction with mass spectrometric measurements show that the species found in the glow region are very specific for the hydrocarbon used (e.g., benzene), but they are not directly related to the structure of the a-C:H film deposited. In the vicinity of the negatively self-biased cathode strong emission from CH is observed, irrespective of which hydrocarbon is used. The excited CH radicals are shown to result from fragmentation of the impacting hydrocarbon molecules. We conclude that this fragmentation upon impact is the key mechanism for the formation of hard a-C:H, irrespective of the type of hydrocarbon used for the deposition.
Photoresponse of the EL2 absorption in undoped semi-insulating GaAs
Authors: Dischler B. , Fuchs F. , Kaufmann U.
Published: July 2002

The response of the EL2 absorption band to monochromatic secondary illumination has been studied in undoped semi-insulating GaAs. Photoinduced changes of the absorption band are spectrally nonuniform. In addition, the changes are nonmonotonic in time similar to the EL2 photocapacitance transients: A fast enhancement in absorption is followed by a slow quenching. These data can be explained in terms of the EL2 properties known from photocapacitance studies. A comparison with recent electron paramagnetic resonance (EPR) results for the AsGa antisite provides direct evidence that the EL2 absorption band and the As+Ga EPR are induced by the same defect.
Resonant tunneling hot-electron transistor with current gain of 5
Authors: Mori Toshihiko , Ohnishi Hiroaki , Imamura Kenichi , Muto Syunichi , Yokoyama Naoki
Published: July 2002

By optimizing its structure, we have improved the current gain and collector-current peak-to-valley ratio of a resonant tunneling hot-electron transistor. The device has an asymmetric resonant tunneling barrier with an optimal well thickness to attain a higher peak-to-valley ratio for the collector current. Also, the device uses a graded collector barrier and decreased base thickness, exhibiting a common emitter current gain of 5.1 (at 77 K), the highest value ever reported for an AlGaAs/GaAs hot-electron transistor.
Effect of surface preparation on Ge overlayer growth on (HgCd)Te
Authors: Davis G. D. , Beck W. A. , Kelly M. K. , Mo Y. W. , Margaritondo G.
Published: July 2002

The interactions between thin Ge overlayers and both cleaved and ion-sputtered Hg1−xCdxTe surfaces have been examined using synchrotron radiation. Ge forms an unreactive layer on cleaved substrates of x=0.21 and x=0.28 with only a small loss of Hg (∼20%) from the interface. In contrast, deposition of Ge onto sputtered substrates results in approximately two (x=0.21 material) or three (x=0.28 material) times the Hg loss relative to the clean surface. The difference in behavior of the sputtered and cleaved material is due to sputter-induced defects at the surface. The increased loss of Hg from the sputtered x=0.28 material is a result of a greater number of these defects caused by the weaker Hg–Te bonding and the corresponding increase in the preferential sputtering of Hg from the surface. No difference was observed between sputtered p-type and n-type material. These results are a consequence of GeTe and HgTe having very similar heats of formation; as such, deposition of Ge provides an indication of the reactivity of (HgCd)Te surfaces.
New measurement technique: cw electro-optic probing of electric fields
Authors: Zhu Z. H. , Weber J-P. , Wang S. Y. , Wang S.
Published: July 2002

This letter describes a new nondestructive measurement technique—cw electro-optic probing, and reports results of experiments on GaAs coplanar waveguide sample. The technique is simple in instrumentation and convenient in applications. We believe that it can become a powerful tool for studying the electric field in various devices and integrated circuits.
Growth of semi-insulating GaAs crystals with low carbon concentration using pyrolytic boron nitride coated graphite
Authors: Inada Tomoki , Fujii Takashi , Kikuta Toshio , Fukuda Tsuguo
Published: July 2002

It has been determined that the incorporation of carbon into GaAs crystals grown by the liquid encapsulated Czochralski method occurs as the result of a reaction between the GaAs melt and gaseous oxides of carbon, rather than carbon particles. The incorporation occurs during growth as well as during synthesis. The incorporation of carbon was particularly large when a commercially available large puller was used because of the greater number of carbon components in the hot zone which act as sources. Crystals with a low carbon concentration of 1×1015 cm−3 have been successfully grown by employing pyrolytic boron nitride coated graphite components in the large puller.
Electrical activation of arsenic ion-implanted polycrystalline silicon by rapid thermal annealing
Authors: Wong C. Y. , Komem Y. , Harrison H. B.
Published: July 2002

Doped polycrystalline silicon films have often been used as a diffusion source in the formation of shallow junctions. Conventional furnace annealing of these films with high electrical activation usually results in junctions too deep for submicron devices. In this letter, we report on the results of rapid thermal annealing in the temperature range from 1000 to 1150 °C of arsenic ion-implanted polycrystalline silicon, characterized by secondary ion mass spectroscopy, Rutherford backscattering and channeling, transmission electron microscopy, and four-point probe measurements. We demonstrate that with rapid thermal annealing at 1150 °C for 5 s, we can achieve simultaneously a sheet resistance of 20 Ω/⧠ in the polycrystalline silicon and a diffusion profile of 50 nm into the single-crystal silicon substrate.
Kinetics of silicon-induced mixing of AlAs-GaAs superlattices
Authors: Mei P. , Yoon H. W. , Venkatesan T. , Schwarz S. A. , Harbison J. P.
Published: July 2002

The intermixing of AlAs-GaAs superlattices has been investigated as a function of Si concentration following anneals in the range of 500 to 900 °C. The superlattice samples were grown by molecular beam epitaxy and the near surface layers were doped with silicon at concentrations of 2×1017 to 5×1018 cm−3. Si and Al depth profiles were measured with secondary ion mass spectrometry (SIMS). The diffusion length and activation energy of Al as a function of silicon dopant concentration were derived from the SIMS data. In the temperature range studied a single activation energy for the Al diffusion of ∼4 eV was observed, and the Al diffusion coefficients increased rapidly with Si concentration.
Pressure dependence of electron transport in InP
Authors: Patel D. , Sites J. R. , Spain I. L.
Published: July 2002

Photoconductivity and Hall measurements in InP are presented for pressures up to 4 GPa using a diamond anvil cell. The application of pressure increases the direct energy band gap (E0), as seen by the shift of the photoconductivity edge to lower wavelength with increasing pressure. Hall measurements show a decrease in the electron mobility (μe) with pressure, due mainly to an increasing effective mass (m*e). Analysis of the pressure dependence of μe shows that polar optical scattering is the dominant mechanism.
Photoconductive response of PbTe doping superlattices
Authors: Jantsch W. , Lischka K. , Eisenbeiss A. , Pichler P. , Clemens H. , Bauer G.
Published: July 2002

Doping superlattices made of PbTe exhibit excellent photoconductive response with a peak detectivity D*≥8×1010 cm Hz1/2 W−1, which is close to the theoretical limit at 6 μm wavelength. Lifetime and far-infrared magneto-optical investigations show that photogenerated electron-hole pairs are separated in the periodic electrostatic potential, leading to a lifetime enhancement by nearly two orders of magnitude as compared to homogeneous bulk crystals.
Phase diagram and superconductivity in the Y-Ba-Cu-O system
Authors: Hinks D. G. , Soderholm L. , Capone D. W. , Jorgensen J. D. , Schuller Ivan K. , Segre C. U. , Zhang K. , Grace J. D.
Published: July 2002

We have determined the phase diagram of the Y-Ba-Cu-O system through structural, superconducting critical temperature and critical current density characterization. Our results show that a single-phase compound with a stoichiometry YBa2Cu3Oy is responsible for the high-temperature superconductivity (92.5 K) in this system.
Beam propagation study of nonlinear coupling between transverse electric modes of a slab waveguide
Authors: Finlayson N. , Wright E. M. , Seaton C. T. , Stegeman G. I. , Silberberg Y.
Published: July 2002

The evolution of an optical field along a symmetrical slab waveguide capable of supporting two TE modes in the linear regime is investigated using the beam propagation method (BPM) where the waveguide and cladding media have a uniform, self-focusing Kerr law nonlinearity. BPM calculations agree well with coupled-mode theory at low input powers, but diverge at powers approaching the coupled-mode value of the critical power and above, due to self-focusing of the field. At high power, the beam splits into two parts which generate unusual long-range collision effects.
Dot lithography for zero-dimensional quantum wells using focused ion beams
Authors: Kubena R. L. , Joyce R. J. , Ward J. W. , Garvin H. L. , Stratton F. P. , Brault R. G.
Published: July 2002

A 50-keV focused Ga+ beam formed in a two-lens microprobe column with prefinal lens deflection was used to expose dot arrays in a negative acting bilevel resist. Dot arrays 600 μm×600 μm with 600-Å-diam resist posts on 0.6 μm centers (incorporating 1024×1024 dots) were fabricated with ion exposure times of 18 s. By reducing the beam dwell time by a factor of 2, roughly 300-Å-diam posts were fabricated. Since the ions stop in the bottom resist layer and do not enter the substrate, the optical properties of underlying material should not be altered by damage from the exposure process.
Secondary ion mass spectrometry of hyper-abrupt doping transitions fabricated by limited reaction processing
Authors: Turner J. E. , Amano Jun , Gronet C. M. , Gibbons J. F.
Published: July 2002

Secondary ion mass spectrometry (SIMS) is used to quantify the abruptness of hyper-abrupt B-doping profiles in epitaxial silicon grown by limited reaction processing (LRP). By measuring the abruptness of dopant profiles as a function of SIMS primary beam energy and extrapolating to zero energy, doping roll-off decay lengths less than 20 Å are found for both the trailing and leading edges of LRP structures fabricated at 900 °C. Doping abruptness is limited by diffusional broadening during subsequent epitaxial growth. An asymmetry in leading and trailing edges of doping profiles is shown to be a SIMS sputter artifact, and the ratio of extracted decay lengths at these interfaces is predicted from elementary recoil events. A proportionality is found between sputter broadening of the doping profile and Monte Carlo calculations of dopant recoil depth.
Transmission electron microscopy of (001) CdTe on (001) GaAs grown by metalorganic chemical vapor deposition
Authors: Petruzzello J. , Olego D. , Ghandhi S. K. , Taskar N. R. , Bhat I.
Published: July 2002

The nature of dislocations in (001) CdTe-(001) GaAs heterostructures was investigated by transmission electron microscopy. The samples were grown by metalorganic chemical vapor deposition with CdTe layer thicknesses h ranging from 0.1 to 2.2 μm. The interface contains an array of misfit dislocations spaced about 31 Å apart, independent of h. These dislocations do not relax all of the lattice mismatch (14.6%) in the CdTe layers with h<1 μm. Above the interfaces, surface nucleated dislocations are observed in the CdTe layers and their density depends on h. No evidence of an oxide or foreign interface layer was found in these samples.
Magnetic and structural properties of melt-spun erbium-iron-boron ribbons
Authors: Meisner G. P.
Published: July 2002

Melt-spun ribbons of Er0.135Fe0.813B0.052 have a relatively large coercivity of nearly 5 kOe. The coercivity is a sharply peaked function of wheel speed (quench rate) with the optimally quenched ribbons having a wheel speed of 14 m/s and a Br of 4 kG. This also coincides with the maximum in energy product of 2.9 MGOe. The abrupt degradation of coercivity with increasing quench rate corresponds precisely to the lack of crystallinity of the ribbons as determined by x-ray powder diffraction.
Polarization switching in semiconductor lasers driven via injection from an external radiation
Authors: Sapia A. , Spano P. , Daino B.
Published: July 2002

Switching between transverse electric (TE) and transverse magnetic (TM) polarization states in the output from a semiconductor laser is experimentally obtained through injection locking from an external TM polarized radiation. Switching, which is connected to the loss reduction of the TM modes caused by the injection-locking mechanism, is faster than a few nanoseconds, the resolution limit of our apparatus.
High-temperature observation of heavy-hole and light-hole excitons in InGaAs/InP multiple quantum well structures grown by metalorganic molecular beam epitaxy
Authors: Kawaguchi Yoshihiro , Asahi Hajime
Published: July 2002

Heavy-hole (hh) and light-hole (lh) excitons were clearly observed at temperatures as high as 450 K in the optical absorption spectrum for the 1.5 μm wavelength range InGaAs/InP multiple quantum well (MQW) structures for the first time. Temperature dependence of the hh excitonic half-width was found to be weaker than that for InGaAs/InAlAs MQW structures. The MQW wafers were grown on (100) InP substrates by metalorganic molecular beam epitaxy (MOMBE) using trimethylindium, triethylgallium, arsine, and phosphine. Intense 77 K photoluminescence (PL) emission was also observed from the quantum well with thickness as narrow as 10 Å. The full width at half-maximum of 77 K PL spectrum for the 60 Å well as narrow as 11.7 meV and the double peak structures induced by the monolayer thickness fluctuation were observed in the thinner wells.
Direct observation of growth front movement in electron beam recrystallization of silicon layer on insulator
Authors: Inoue Tomoyasu , Hamasaki Toshihiko
Published: July 2002

A high-speed movie technique was used to investigate the growth front movement during electron beam recrystallization of thin silicon layers on insulating material. In a laterally epitaxial growth process, it was clearly observed that the molten zone shape dramatically changes across a seed opening, which is due to nonuniformity in heat dissipation toward the substrate in the vicinity of the seed opening. The molten zone width and velocities of the melt front and growth front were quantitatively analyzed using digital film motion analysis. The growth front velocity was found to drastically change by ∼30% across the seed opening.
Resonant tunneling in a GaAs/AlGaAs barrier/InGaAs quantum well heterostructure
Authors: Reed M. A. , Lee J. W.
Published: July 2002

Resonant tunneling through a GaAs contact/double AlGaAs barrier/single InGaAs quantum well strained-layer heterostructure was investigated. The structure exhibits negative differential resistance up to 275 K due to tunneling through the first excited state of the quantum well. Comparison of the observed peak positions with theory indicates that the conduction-band offset of the AlGaAs/InGaAs heterojunction is nearly 100%. Using the magnetic field dependence of the current-voltage characteristics, we have measured the effective mass of an electron while transiting a multicomponent quantum well tunneling structure. An effective mass for electrons in the InGaAs quantum well of approximately half the bulk effective mass is obtained.
Phase conjugate master oscillator-power amplifier using BaTiO3 and AlGaAs semiconductor diode lasers
Authors: Stephens R. R. , Lind R. C. , Giuliano C. R.
Published: July 2002

A double pass phase conjugate master oscillator-power amplifier has been demonstrated at 820 nm using AlGaAs gain elements and BaTiO3 in a self-pumped ring configuration. Single frequency operation with diffraction-limited output beam quality was achieved at output powers in excess of 50 mW cw.
Plasma enhanced chemical vapor deposition of fluorinated silicon nitride using SiH4-NH3-NF3 mixtures
Authors: Livengood R. E. , Hess D. W.
Published: July 2002

Fluorinated silicon nitride films are deposited by the plasma enhanced reaction of SiH4-NH3-NF3 gas mixtures. The deposition rate with NF3 increases to a maximum of approximately six times that of SiNxHy deposited using only SiH4 and NH3. Optical and electrical properties of the SiNxHy films are also affected. The addition of NF3 to the deposition atmosphere significantly reduces the concentration of H bonded to Si. The films display dielectric properties similar to SiNxHy films deposited using SiH4 and NH3. All films containing F hydrolyze on exposure to air. When less than 10 at. % F is present in the as-deposited films, film stability is achieved after initial hydrolysis. Essentially total hydrolysis to SiO2 occurs when the F content exceeds 10 at. %.
Very high transconductance InGaAs/InP junction field-effect transistor with submicrometer gate
Authors: Raulin J. Y. , Thorngren E. , di Forte-Poisson M. A. , Razeghi M. , Colomer G.
Published: July 2002

A very high transconductance (260 mS/mm) has been achieved for the first time with an InGaAs/InP junction field-effect transistor. The transistor was fabricated using a chemical etching technique which allowed the fabrication of submicrometer gate (0.5 μm). Very low values of access resistance were obtained using a self-aligned technology.
Direct overwrite in amorphous rare-earth transition-metal alloys
Authors: Hansen P.
Published: July 2002

The thermomagnetic writing and erasure process has been investigated, paying special attention to the case of zero applied magnetic field. Concerning bubblelike domains, writing can easily be performed by the demagnetizing field while erasure requires an external magnetic field larger than the collapse field. However, in alloys exhibiting a compensation temperature above ambient temperature erasure can be achieved in the absence of an external field via the creation and annihilation of a ring domain which opens the capability of direct overwrite.
Nonlinear optical absorption in bulk GaInAs/InP at room temperature
Authors: Fox A. M. , Maciel A. C. , Ryan J. F. , Scott M. D.
Published: July 2002

We report cw measurements of band-gap resonant nonlinear absorption in bulk Ga0.47In0.53As/InP at room temperature. A tunable Co:MgF2 laser was used for these experiments. The nonlinear absorption coefficient α2 is determined by measuring saturation of the optical absorption, and from this the nonlinear refractive index n2 is calculated in the band-tail region. We find α2≊−6 cm W−1 at 1.67 μm and n2≊−4×10−5 cm2 W−1 at 1.69 μm. Within the band-tail region the nonlinear optical quality factor ‖n2/α‖ is found to lie between 0.9 and 1.8×10−8 cm3 W−1.
Nondestructive measurement of indium content in semi-insulating GaAs substrates and ingots
Authors: Kirillov D. , Vichr M. , Powell R. A.
Published: July 2002

We report the use of room-temperature photoluminescence to determine low levels of indium in semi-insulating GaAs intended for use as low dislocation material for substrates of integrated circuits. We have compared this technique with other optical methods such as low-temperature (4.2 K) photoluminescence and Raman scattering and find it more convenient for this application. Room-temperature photoluminescence easily allows measurement of In content in InxGa1−xAs in the range of 0.1–2% with a standard deviation of 0.1%, which is sufficient for most practical applications. The technique is nondestructive and rapid. The measurement can be done on polished, sawed, or etched surfaces, or on side surfaces of as-grown ingots without any treatment. To illustrate its use, we have measured variations in the In content of semi-insulating GaAs due to segregation of In in the melt during liquid encapsulated Czochralski growth.
Microstructural investigation of Nd-Fe-B with the scanning tunneling microscope
Authors: Corb B. W. , Ringger M. , Güntherodt H.-J. , Pinkerton F. E.
Published: July 2002

The first investigation of rapidly quenched Nd-Fe-B permanent magnet material with the scanning tunneling microscope revealed that Nd-Fe-B has a faceted spheroidal grain structure with a grain size of 200 Å. Barrier height measurements indicate that the grains are often either of slightly different chemical compositions or more likely of different crystallographic orientation.
Infrared studies of the dynamics of transformations between normal and metastable state of the EL2 center in GaAs
Authors: Fuchs F. , Dischler B.
Published: July 2002

The bleaching of the EL2 absorption and its thermal regeneration are typical time-dependent processes. Compared to the conventional time transient analysis, faster and more accurate data acquisition is described. This technique is based on the combined use of optical absorption and its time derivative, measured while either the energy of the bleaching light or the sample temperature is varied. The peak of the spectral response for bleaching shifts to lower energies in the temperature range 10 to 130 K. The activation energy for thermal regeneration can decrease by a factor of 6 between semi-insulating and n-type samples. We report the first optical identification of persistent electrons, which are photogenerated during EL2 bleaching at 10 K. The thermal disappearance of persistent electrons and holes has also been studied.
Relationship between superconductivity and lattice distortion in Y-Ba-Cu-O compounds
Authors: Zeng Xiaobiao , Jiang Xiaoping , Qi Hongbo , Pang Dexing , Zhu Naiping , Zhang Ze
Published: July 2002

The letter presents an explanation for the reversal of peak intensities in x-ray diffraction patterns of Y-Ba-Cu-O compounds with the same nominal compositions but distinctive properties of superconductivity due to different cooling conditions. Structural differences between the phases caused by different lattice distortions as well as the effect of these distortions on superconductivity are also discussed.
Photoluminescence microscopy of epitaxial GaAs on Si
Authors: Gourley P. L. , Longerbone M. , Zhang S. L. , Morkoç H.
Published: July 2002

We report microscopic photoluminescence images and corresponding spectra of epitaxial GaAs on Si substrates, prepared by molecular beam epitaxy. High magnification (3000×) images directly reveal dislocations present in the epilayer. Several substrate orientations are investigated including nominal (001) tilted 4° toward 〈110〉. The GaAs samples include structures grown with and without superlattice buffer layers. Some samples were annealed at several temperatures from 650 to 850 °C. The dislocation density versus depth is studied by varying the optical probe wavelength and by studying samples that had been beveled and etched. In addition, the images and spectra are studied over a wide temperature range.
Molecular stream epitaxy of ultrathin InGaAs/GaAsP superlattices
Authors: Katsuyama T. , Tischler M. A. , Karam N. H. , El-Masry N. , Bedair S. M.
Published: July 2002

Molecular stream epitaxy allows several molecular beam epitaxy (MBE) concepts to take place in a metalorganic chemical vapor deposition reactor. In this technique, the growth of InGaAs/GaAsP superlattices proceeds by rotating the substrate between two gas streams, one containing trimethylgallium (TMG), triethylindium, and AsH3 and the other containing TMG, PH3, and AsH3. This technique eliminates gas flow transients and provides a method to mechanically shear off the gaseous boundary layer between successive exposures. Ultrathin strained-layer superlattices (SLS’s) with 8-Å-thick films have been obtained. The optical properties of these SLS’s are comparable to those obtained for equivalent superlattices by gas source MBE.
Molecular beam epitaxial growth and luminescence of InxGa1−xAs/InxAl1−xAs multiquantum wells on GaAs
Authors: Chang Kevin H. , Berger Paul R. , Singh Jasprit , Bhattacharya Pallab K.
Published: July 2002

This letter reports the successful molecular beam epitaxial growth of high-quality InxGa1−xAs/InxAl1−xAs directly on GaAs. In situ observation of dynamic high-energy electron diffraction oscillations during growth of InxGa1−xAs on GaAs indicates that the average cation migration rates are reduced due to the surface strain. By raising the growth temperature to enhance the migration rate and by using misoriented epitaxy to limit the propagation of threading and screw dislocations, we have grown device-quality In0.15Ga0.85As/In0.15Al0.85As multiquantum wells on GaAs with a 0.5–1.0 μm In0.15Ga0.85As buffer layer. The luminescence efficiency of the bound exciton peak increases with misorientation and its linewidth varies from 11 to 15 meV.
First observation of quantum Hall effect in a GaInAsP-InP heterostructure grown by metalorganic vapor deposition
Authors: Razeghi M. , Maurel P. , Omnes F. , Defour M. , Acher O. , Tsui D. , Wei H. P. , Guldner Y. , Vieren J. P.
Published: July 2002

We report the first observation of quantum Hall effect in a Ga0.25In0.75As0.5P0.5 heterostructure grown by metalorganic chemical vapor deposition growth technique.
Ion beam hydrogenation of amorphous silicon
Authors: Tsuo Y. S. , Smith E. B. , Deb S. K.
Published: July 2002

A Kaufman ion beam source was used to implant hydrogen atoms into glow-discharge-deposited amorphous silicon materials in which the hydrogen content had been driven out by heating. We found that the hydrogen atoms introduced by this low-energy (less than 700 eV) ion implantation method bonded predominantly as SiH. An air mass one, photo-to-dark-conductivity ratio as high as 5.6×105 has been obtained with hydrogen-implanted materials. No light-induced reduction of the photo- and dark conductivities has been observed in these materials after 20 h of AMl illumnination.
Nonselective etching of GaAs/AlGaAs double heterostructure laser facets by Cl2 reactive ion etching in a load-locked system
Authors: Vawter G. Allen , Coldren Larry A. , Merz James L. , Hu Evelyn L.
Published: July 2002

Reactive ion etching was used for etching laser facets of GaAs/AlGaAs transverse junction stripe lasers. A new load-locked reactive ion etching system was developed to dramatically reduce the background partial pressure of O2 and H2O in the chamber, substantially reducing the oxidation of AlGaAs and permitting equal rate etching of GaAs and AlGaAs with smooth vertical facets. Etching is performed with a chlorine plasma at a low pressure (0.5 mTorr), and bias voltage (−350 V) at a rate of ∼850 Å/min. This simple, single-step dry etching process is suitable for optoelectronic integration and eliminates the requirement of unreliable wet chemical etching or microcleaving techniques. This new system is used to fabricate transverse junction stripe lasers with facet reflectivities of more than 16%. These high quality dry etched facets result in only a 7.5% increase of the threshold current above that of lasers with cleaved facets.
Modulation-doped multiquantum wells in InP/In0.53Ga0.47As grown by atmospheric pressure metalorganic chemical vapor deposition
Authors: Taylor L. L. , Kane M. J. , Bass S. J.
Published: July 2002

Here we present the first report of electrical transport measurements (Hall effect and Shubnikov de Haas) on modulation-doped InP/In0.53Ga0.47As multiquantum wells grown by atmospheric pressure metalorganic chemical vapor deposition. Measurements were made on samples containing from 4 to 50 doped quantum wells. The carrier density per well was observed to be constant, approximately 1×1012 cm−2 independent of the number of wells, with 4 K mobilities from 70 000 to 90 000 cm2 V−1 s−1. Very little persistent photoconductivity was observed in any of the multiple quantum well structures.
Simulation of electron beam induced current at GaAs/AlGaAs heterojunctions under forward bias
Authors: Munnix S. , Bimberg D.
Published: July 2002

The influence of the charge collecting barrier on the electron beam induced current (EBIC) is studied by numerical solution of the current transport equations in the case of AlGaAs/GaAs heterojunctions. EBIC line scans are simulated as a function of external bias. It is found that the signal cannot be reduced to zero value, in accordance with experimental results. This effect is explained by a non-negligible potential drop outside of the space-charge region under high injection conditions. As a consequence, a more careful treatment is needed when using EBIC to determine band offsets.
Elucidation of the organometallic vapor phase epitaxial growth mechanism for InP
Authors: Buchan N. I. , Larsen C. A. , Stringfellow G. B.
Published: July 2002

Organometallic vapor phase epitaxy has achieved remarkable recent success, becoming the most promising technique for the ultimate production of III/V materials and device structures. Unfortunately, our understanding of the growth process remains primitive. In this letter we report a new technique for tracing the reactions by conducting the epitaxial growth in a D2 ambient using a time-of-flight mass spectrometer to analyze the product molecules. The pyrolysis reactions were studied for PH3, both alone and in the presence of trimethylindium (TMIn), and for TMIn alone and in the presence of PH3. For the reactants alone, the PH3 pyrolysis is completely heterogeneous at the InP surface, while TMIn pyrolyzes mostly homogeneously in the gas phase. For TMIn and PH3 together, the reaction mechanism is entirely different, and the pyrolysis temperatures for both PH3 and TMIn are lowered. Since the reaction produces only CH4 molecules, with a complete absence of CH3D at high ratios of PH3 to TMIn, we hypothesize that InP growth is initiated by the direct interaction of TMIn and PH3 in the vapor phase.
Sensitivity of Si diffusion in GaAs to column IV and VI donor species
Authors: Deppe D. G. , Holonyak N. , Baker J. E.
Published: July 2002

Secondary ion mass spectroscopy and carrier concentration measurements are used to characterize Si diffusion into GaAs wafers containing two fundamentally different forms of donors, the column IV donors Si or Sn and the column VI donors Se or Te. A decrease in the Si diffusion rate is found in GaAs containing the column VI donors compared to the column IV donors. This trend is consistent with the model in which the Si diffuses as donor-gallium-vacancy complexes. The decrease in the Si diffusion coefficient is attributed to the greater binding energy of column VI donor-gallium-vacancy nearest-neighbor complexes, thus reducing the concentration of free-gallium vacancies available to complex with the Si.
Ballistic electron transport across collector barriers in AlGaAs/GaAs hot-electron transistors
Authors: Kuzuhara M. , Kim K. , Arnold D. , Hess K.
Published: July 2002

A Monte Carlo calculation has been performed to simulate the experiment of Heiblum and co-workers [Phys. Rev. Lett. 55, 2200 (1985)], regarding ballistic electron transport and the electron transit time across the AlGaAs collector barrier region in AlGaAs/GaAs tunneling hot-electron transfer amplifier devices. Ballistic transport is proven to be highly probable across a 1000-Å-thick collector barrier under retarding field and hot-electron injection conditions at 4.2 K. Applying accelerating fields in the barrier results in almost negligible ballistic fraction of the transmitted hot electrons because of electron scattering into the satellite valleys. This result seems paradoxical at first sight. However, it is typical for electronic transport in heterolayers and fully consistent with the interpretation of the experiments by Heiblum and co-workers. There exists a negative collector-base bias range which minimizes the collector barrier transit time, corresponding to the condition of large ballistic probability and simultaneously relatively little deceleration of the electrons by the applied retarding field.
Reflectance-difference spectroscopy system for real-time measurements of crystal growth
Authors: Aspnes D. E. , Harbison J. P. , Studna A. A. , Florez L. T.
Published: July 2002

We describe a reflectance-difference spectroscopy system for real-time in situ optical studies of crystal growth. Either changes in surface chemistry or surface structure can be monitored depending on wavelength.
Molecular beam epitaxial growth and characterization of 2-in.-diam Hg1−xCdxTe films on GaAs (100) substrates
Authors: Lange M. D. , Sivananthan S. , Chu X. , Faurie J. P.
Published: July 2002

Hg1−xCdxTe films with 2 in. diameters have been grown by molecular beam epitaxy on GaAs (100) substrates. These films were grown in both the (100) and (∼(111)) B crystallographic orientations and in both conduction types. They were characterized by in situ electron diffraction, infrared absorption, and van der Pauw dc Hall measurements. Their surfaces were shiny and mirrorlike from center to edge. The Cd concentrations (x) of these films were very uniform, exhibiting standard deviations (Δx) as low as 0.7% of the mean (x̄). Their thicknesses also were uniform within 0.6%. These films were completely uniform in their conduction types; that is, the n-type films were entirely n type, and likewise for the p-type films. The Hall mobilities of these films show them to be of high quality, with values as high as 6.7×102 cm2 V−1 s−1 for the p-type (x=0.22) and 1.8×105 cm2 V−1 s−1 for the n-type films (x=0.21). These results represent an important achievement toward the future of infrared detector technology.
Barrier and recombination effects in the base-emitter junction of heterostructure bipolar transistors
Authors: Tiwari Sandip , Frank D. J.
Published: July 2002

We show that high current densities with minimal space charge region recombination current can be obtained by a suitable choice of alloy grading parameters and doping of the junction. It is also shown that compositionally graded, but uniformly doped emitter junctions require a minimum doping level in the emitter in order to suppress an excess barrier that results from alloy grading in the presence of high current injection. The complexity of recombination phenomenon at a heterojunction due to its dependence on doping, alloy grading, and bias is demonstrated and related to the injection behavior. We conclude that use of a minimum doping with parabolic alloy grading is an adequate compromise between high injection behavior and recombination behavior for practical devices.
Infrared photodiodes fabricated with Hg1−xCdxTe grown by molecular beam epitaxy
Authors: Arias J. M. , Shin S. H. , Pasko J. G. , Gertner E. R.
Published: July 2002

Device-quality Hg1−xCdxTe (0.26<x<0.33) epilayers with thicknesses in the range 10–20 μm were grown on (111)B CdTe substrates by molecular beam epitaxy (MBE). The as-grown layers were p type, and typically had carrier concentrations in the low 1016 cm−3 range and hole mobilities greater than 220 cm2/V s at 77 K. The n+-p junction was formed by Be ion implantation; unpassivated mesa photodiodes were fabricated by standard photolithographic techniques. Resistance-area products (R0A) at zero bias were 5.2×106 and 1.4×104 Ω cm2 at 77 K for Hg1−xCdxTe with cutoff wavelengths of 4.0 and 5.7 μm, respectively. These R0A values approach typical ones obtained by liquid phase epitaxy and represent a very promising initial effort for MBE-grown Hg1−xCdxTe.
‘‘Soft threshold’’ result in impact ionization derived from ‘‘hard-sphere’’ model
Authors: Woods R. C.
Published: July 2002

It has previously been shown that a result similar to the Keldysh formula [L. V. Keldysh, Sov. Phys. JETP 37, 509 (1960)], for the probability of impact ionization in an avalanching semiconductor, can be derived using a purely classical model. In this letter an even simpler model, the hard-sphere model, is used to derive an analogous relation, showing that the ‘‘soft threshold’’ effect is due largely to the geometry of the interaction between the particles concerned, rather than the nature of the interaction itself.
15% efficiency (1 sun, air mass 1.5), large-area, 1.93 eV AlxGa1−xAs (x=0.37) n-p solar cell grown by metalorganic vapor phase epitaxy
Authors: Chung B-C. , Hamaker H. C. , Virshup G. F. , Werthen J. G.
Published: July 2002

1.93 eV AlxGa1−xAs (x=0.37) n-p solar cells with areas of 4 cm2 have been fabricated by metalorganic vapor phase epitaxy. Under 1 sun, air mass 1.5, simulated conditions, the cell exhibiting a conversion efficiency as high as 15% is characterized by a short-circuit current density of 12.0 mA/cm2, an open-circuit voltage of 1.42 V, and a fill factor of 0.87. The realization of these high-quality AlGaAs solar cells at a band gap of 1.93 eV implies the potential for other promising optoelectronic devices in the visible spectrum.
Scaling and renormalization in transmittance of thin metal films near the percolation threshold
Authors: Yagil Y. , Deutscher G.
Published: July 2002

Recent transmittance measurements of thin metal films near the percolation threshold Pc [Y. Yagil and G. Deutscher, Thin Solid Films 152, 456 (1987)] are interpreted by scaling arguments reflecting the special structure of the film near Pc. Based on the claim that the relevant length scale over which the optical properties are measured is the optical wave number 1/k=λ/2π, we present an argument showing how the optical transmittance scales with this quantity. Our interpretation, based on real-space renormalization, yields a power law wavelength dependence near the percolation threshold, with a coefficient that vanishes at Pc.
Effects of heavy impurity doping on electron injection in p+-n GaAs diodes
Authors: Klausmeier-Brown M. E. , Lundstrom M. S. , Melloch M. R. , Tobin S. P.
Published: July 2002

Measurements of electron injection currents in p+-n diodes are presented for a range of p-type dopant concentrations. A successive etch technique was used to characterize the electron injection current in terms of the product (noDn). Measurements are presented for Zn-doped GaAs solar cells with p-layer hole concentrations in the range 6.3×1017−1.3×1019 cm−3. The results demonstrate that so-called band-gap narrowing effects substantially increase the injected electron current in heavily doped p-type GaAs. These heavy doping effects must be accounted for in the modeling and design of GaAs solar cells and heterostructure bipolar transistors.
Molecular beam epitaxy and metalorganic chemical vapor deposition growth of epitaxial CdTe on (100) GaAs/Si and (111) GaAs/Si substrates
Authors: Nouhi A. , Radhakrishnan G. , Katz J. , Koliwad K.
Published: July 2002

Epitaxial CdTe has been grown on both (100)GaAs/Si and (111)GaAs/Si substrates. A combination of molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) has been employed for the first time to achieve this growth: the GaAs layers are grown on Si substrates by MBE and the CdTe film is subsequently deposited on GaAs/Si by MOCVD. The grown layers have been characterized by x-ray diffraction, scanning electron microscopy, and photoluminescence.
Metal contacts to GaAs with 1 eV Schottky barrier height
Authors: Waldrop J. R. , Grant R. W.
Published: July 2002

Metal Schottky barrier contacts to n-type (100) GaAs are described in which a 1 eV Schottky barrier height φB is achieved by using a very thin Si interface layer to influence the interface Fermi energy EiF. The metals investigated are Au, Cr, and Ti. The contact structure consists of a thick metal in combination with a ∼15–30 Å heavily p-type Si interface layer. The EiF and interface composition during initial contact formation were obtained by x-ray photoemission spectroscopy (XPS); the φB for the corresponding thick contacts was measured by current-voltage (I-V) and capacitance-voltage (C-V) techniques. The XPS, I-V, and C-V measurements gave consistent results. The 1 eV φB for the Si interface layer contact structure is independent of the contact metal.
Misfit stress relaxation phenomena in GaAsP-InGaAs strained-layer superlattices
Authors: Radzimski Z. J. , Jiang B. L. , Rozgonyi G. A. , Humphreys T. P. , Hamaguchi N. , Parker C. , Bedair S. M.
Published: July 2002

Misfit stress relaxation phenomena were investigated in InGaAs-GaAsP strained-layer superlattice layers as a function of period thickness using x-ray diffraction topography and electron-beam-induced current techniques. By controlling the thickness of the individual layer, as well as the total thickness of an InGaAs/GaAsP strained-layer superlattice, we have achieved a defect density reduction in GaAs epilayers grown on GaAs substrates. Several strained-layer superlattice buffer layers whose period thickness varied from 80 to 120 nm have been studied.