bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence studies of ultrahigh-purity epitaxial silicon
Authors: Thewalt M. L. W. , Steele A. G. , Huffman J. E.
Published: July 2002

Photoluminescence has been used to identify bulk and interfacial contaminants in ultrahigh-purity epitaxially grown silicon. When combined with depth profiling using spreading resistance analysis, it provides a powerful characterization technique which may be used for determining optimal layer growth parameters. Identification of impurities has been demonstrated at concentrations which are orders of magnitude below the sensitivity limit of other methods suitable for epitaxial layer characterization.
Spatial resolution and nature of defects produced by low-energy proton irradiation of GaAs solar cells
Authors: Kachare R. , Anspaugh B. E.
Published: July 2002

AlGaAs/GaAs solar cells with ∼0.5-μm-thick Al0.85Ga0.15As window layers were irradiated using isotropic and normal incidence protons having energies between 50 and 500 keV with fluences up to 1×1012 protons/cm2. Although the projected range for these protons varies from 0 to more than 4.5 μm, the recombination losses due to the irradiation-induced defects were observed to be maximum in the vicinity of the AlGaAs/GaAs interface and the space-charge region irrespective of the proton energy. This was found by analyzing spectral response measurements. The results are explained by using a model in which the interaction of as-grown dislocations with irradiation-induced point defects is considered.
Contact structure formed in the Ni/Al/Si system due to rapid thermal melting
Authors: Katz A. , Komem Y.
Published: July 2002

The interface reaction induced by means of rapid thermal melting (RTM) of the Ni(30 nm)/Al(10 nm)/Si system, using heat treatment times of a few seconds at temperatures around the aluminum melting point, has been investigated. The RTM occurred at the Al-Si eutectic melting temperature (577 °C). As a result of this melting a polycrystalline intermediate layer, 60 nm thick, composed of NiSi and Ni2Si was formed adjacent to the Si substrate with a relative smooth interface while the Al was repelled to the outer region of the contact and two successive separate layers of polycrystalline Al3Ni and Ni(Al0.5Si0.5) were formed, both 10 nm thick. The results indicate that RTM can be used to obtain a unique interface reaction in a controlled manner.
Model for heteroepitaxial growth of CdTe on (100) oriented GaAs substrate
Authors: Cohen-Solal G. , Bailly F. , Barbé M.
Published: July 2002

A model is described, based on chemical bonding and lattice matching considerations, to account for the heteroepitaxy of CdTe on (100) GaAs substrate. The two main features of the proposed model are that the initial growth of CdTe starts with the formation of stable clusters of chemically bond Te, and that two types of cluster configurations are obtained depending only on the atomic structure of the (100)GaAs surface: the first one, made up of tetrahedral unit cells is formed on an As-deficient surface and leads to (111) orientation, whereas the second one, formed by twin-tetrahedral structures developed on an As- or Ga-stabilized surface gives rise to (100) orientation.
Interface charge polarity of a polar on nonpolar semiconductor GaAs/Si with Ga and As prelayers
Authors: Won T. , Munns G. , Houdré R. , Morkoç H.
Published: July 2002

We have studied the electrical characteristics of p-GaAs/n-Si (100) heterojunction diodes grown by molecular beam epitaxy in an effort to determine the interface polarity. A Ga or As pre-exposure was used prior to the growth of p-GaAs on n-Si substrates to prevent antiphase domains. The Ga prelayer induces a shift in the built-in voltage of −0.2 V, while the As prelayer shifts it as much as +2.0 V depending upon the As coverage. From the shift, the electrical charge and its polarity can be determined which is not possible by structural analysis. These electrical measurements are very sensitive to the interface charge properties and show very clearly that even with a submonolayer pre-exposure, antiphase domain-free material can be obtained.
Fabrication of small laterally patterned multiple quantum wells
Authors: Scherer A. , Craighead H. G.
Published: July 2002

A technique of high voltage electron beam lithography and BCl3/Ar reactive ion etching for laterally patterning GaAs/Al0.3Ga0.7As multiple quantum wells is described. The resulting structures were analyzed using scanning electron microscopy and a novel reflection electron microscopy technique, and their geometries are shown. Narrow columns 40 nm in diameter etched 230 nm through the quantum wells were reproducibly fabricated.
Diffusion model for the laser oxidation of metallic samples in air
Authors: Ursu I. , Nanu L. , Mihăilescu I. N.
Published: July 2002

A model is developed to explain several experimental data previously obtained with laser oxidation of metal samples in air. The main assumption is that the diffusion coefficient of the charged particles changes under the action of laser radiation.
Interdiffusion and wavelength modification in In0.53Ga0.47As/ In0.52Al0.48As quantum wells by lamp annealing
Authors: Seo K. S. , Bhattacharya P. K. , Kothiyal G. P. , Hong S.
Published: July 2002

In0.53Ga0.47As/ In0.52Al0.48As single quantum well structures grown by molecular beam epitaxy were pulse annealed by a halogen lamp to determine the stability of their optical properties after such thermal treatment. The annealing time and temperature were 5 s and 650–850 °C, respectively. The shift in energy of the main peak in the low-temperature photoluminescence spectra was modeled by considering Al-Ga interdiffusion at the heterointerface and solving the appropriate Schrödinger equation for this region. The estimated interdiffusion constants D are ∼10−16–10−15 cm2/s in this temperature range, which are almost three orders higher than the corresponding values reported for GaAs/ AlxGa1−xAs. For longer annealing times, up to 30 min, the linewidth (full width at half-maximum) of the excitonic transition in the 11 K photoluminescence spectrum continuously decreased from 12.5 to 7.7 meV, while the intensity maintained a high value.
Plasma-enhanced metalorganic chemical vapor deposition of GaAs
Authors: Huelsman A. D. , Reif R. , Fonstad C. G.
Published: July 2002

High quality specular epilayers of GaAs were grown using a plasma enhanced metalorganic chemical vapor deposition process. The GaAs epilayers were grown from trimethyl gallium and arsine at very low pressures (2–3 Torr) using an rf discharge to dissociate arsine. Specular single-crystal layers of unintentionally doped n-type GaAs were deposited on semi-insulating GaAs substrates both with and without plasma enhancement. The reactor design allowed the group V sources (in this case arsine) to be dissociated by a plasma localized to an area above the substrate. Films deposited with and without an rf plasma had good mobility and photoluminescence, but as the temperature was lowered films deposited with the plasma were better than those deposited without the plasma.
Specular beam intensity behavior in reflection high-energy electron diffraction during molecular beam epitaxial growth of Al0.3Ga0.7As on GaAs(100) and implications for inverted interfaces
Authors: Cho N. M. , Chen P. , Madhukar A.
Published: July 2002

Results on the specular beam intensity behavior in reflection high-energy electron diffraciton during molecular beam epitaxial growth of Al0.3Ga0.7As on GaAs(100) are reported. The behavior of steady-state intensity as a function of substrate temperature exhibits irreversible character. The results indicate that the Al reactivity with As and residual impurities is the dominant factor controlling the surface morphology and hence the nature of inverted interfaces. A critical need for choosing optimal growth conditions prior to initiation of Al0.3Ga0.7As growth thus emerges.
Low pressure metalorganic vapor phase epitaxy of InP using a trimethylindium-trimethylphosphine adduct source
Authors: Lee M. K. , Wuu D. S. , Tung H. H.
Published: July 2002

Metalorganic vapor phase epitaxy of InP prepared by a trimethylindium-trimethylphosphine (TMIn-TMP) adduct and PH3 was first grown in a low pressure vertical reactor. The adduct with its irreplaceable merit of high stability has been successfully used in this study. The lowest carrier concentration of undoped InP epilayers is 5×1014 cm−3 with a 77 K mobility of 75 000 cm2/V s. The full width at half-maximum of the 77 K photoluminescence spectrum was as narrow as 10 meV. These results can compete with all previous data from adduct sources. The growth rate was not limited by the relatively low vapor pressure of the TMIn-TMP adduct and could reach to 8 μm/h. It suggests the high growth efficiency of this growing process.
Surface quantum wells
Authors: Cohen R. M. , Kitamura M. , Fang Z. M.
Published: July 2002

Surface quantum wells of InP have been grown, by organometallic vapor phase epitaxy, on top of graded GaxIn1−xP epitaxial layers. The surface quantum well is confined on one side by vacuum, and on the other side by the graded GaxIn1−xP. Photoluminescence measurements show two transitions for electron-hole recombination within the surface quantum well. Surface recombination appears to be saturated by the high density of carriers collected in the well, and plays a minor role. The bending of the conduction and valence bands in the GaxIn1−xP leads to a high collection efficiency of excess carriers near the surface, and suggests that high efficiency surface light emitters could be built in similar structures.
Compound formation at the interface between cobalt thin films and single-crystal GaAs
Authors: Genut M. , Eizenberg M.
Published: July 2002

Interfacial reactions between cobalt thin films and single-crystal GaAs substrates have been studied by means of Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction. The interaction starts at ∼325 °C by the formation of a ternary phase, most probably Co2GaAs, which grows highly oriented with respect to the (001) substrate, with a lattice mismatch of ∼−10%. The reaction kinetics has been studied and found to be diffusion controlled with an activation energy of 0.7±0.1 eV. Cobalt was determined as the dominant diffusion species. The oriented ternary phase co-exists with randomly oriented CoGa and CoAs at the temperature range of 325–500 °C, while at higher temperatures only the binary compounds prevail.
O+ implantation and annealing in n-type InAlAs
Authors: Lee Wai , Fonstad Clifton G.
Published: July 2002

The dependence of the electrical properties of oxygen-implanted p+-n In0.52Al0.48As diodes on annealing temperatures has been studied. Current-voltage and capacitance-voltage measurements reveal that a semi-insulating layer is created by oxygen implantation in n-InAlAs which is found to be stable up to at least 720 °C. The presence of this semi-insulating layer significantly reduces the junction capacitance of the diode and the diode current at high bias levels.
Dislocation gettering in semi-insulating GaAs investigated by cathodoluminescence
Authors: Ding Jian , Chang James S. C. , Bujatti Marina
Published: July 2002

The cathodoluminescence (CL) imaging technique is applied to the characterization of semi-insulating GaAs substrates after an extrinsic gettering treatment. A reverse contrast CL image is found for the gettered material. This study provides evidence for the physical mechanism taking place in the gettering process and contributes to the understanding of the effect of dislocations on device performance.
Fluorine distributions in a chemical vapor deposited tungsten silicide/polycrystalline silicon composite gate structure
Authors: Fukumoto Masanori , Ohzone Takashi
Published: July 2002

A tungsten silicide/polycrystalline silicon composite gate structure has been fabricated in which tungsten silicide layers on polycrystalline silicon have been deposited by the low-temperature chemical vapor deposition method (at 360 °C) using a WF6/SiH4 gas mixture. The fluorine distributions in this structure have been studied by secondary ion mass spectrometry. In samples with as-deposited tungsten silicide, it has been confirmed clearly that almost all of the fluorine resides in the silicide layer. After high-temperature annealing (above 950 °C), however, fluorine is found to diffuse easily into the gate SiO2 through the polycrystalline silicon, that is, the gate oxide has been changed into the fluorine-doped oxide.
Hydrogen in crystalline silicon: A deep donor?
Authors: Capizzi M. , Mittiga A.
Published: July 2002

An analysis of the hydrogen concentration profiles obtained from secondary ion mass spectrometry in boron-doped silicon points to a deep donor hydrogen state located ∼0.1 eV above the Fermi level for intrinsic material. The theoretical model takes into account both neutral and ionized hydrogen diffusion, the latter enhanced by a built-in electric field associated with the hydrogen doping gradient. The activation energies for the two diffusion processes are ∼1.2 and ∼0.8 eV, respectively. A formerly reported discrepancy between low- and high-temperature results is lifted.
Coupled-stripe AlxGa1−xAs-GaAs quantum well lasers defined by vacancy-enhanced impurity-induced layer disordering from (Si2)y(GaAs)1−y barriers
Authors: Guido L. J. , Plano W. E. , Jackson G. S. , Holonyak N. , Burnham R. D. , Epler J. E.
Published: July 2002

Data are presented showing that high-performance (>100 mW) AlxGa1−xAs-GaAs quantum well heterostructure (QWH) coupled-stripe laser arrays can be realized by vacancy-enhanced impurity-induced layer disordering (IILD) employing an internal (Si2)y(GaAs)1−y barrier. This form of Si IILD (i.e., layer disordering from a ‘‘finite’’ internal Si source) results in coupled-emitter laser operation, even for relatively large stripe (7–10 μm) and spacing dimensions (2 μm), at currents just above threshold and higher. As a separate issue, the Si IILD QWH laser cross sections show that Si diffusion from a surface source is ‘‘slower’’ than the simultaneous vacancy diffusion from an SiO2 surface encapsulant (‘‘cap’’).
Index-guided AlxGa1−xAs-GaAs quantum well heterostructure lasers fabricated by vacancy-enhanced impurity-induced layer disordering from an internal (Si2)y(GaAs)1−y source
Authors: Guido L. J. , Jackson G. S. , Plano W. E. , Hsieh K. C. , Holonyak N. , Burnham R. D. , Epler J. E. , Thornton R. L. , Paoli T. L.
Published: July 2002

A unique form of Si impurity-induced layer disordering (Si IILD) is described that utilizes a ‘‘buried’’ Si source, a (Si2)y(GaAs)1−y barrier, and a patterned external source of column III vacancies, an SiO2 cap, to define the layer disordering. This form of Si IILD is used to fabricate stripe-geometry index-guided laser diodes that are capable of kink-free single-mode operation.
Reduced KNbO3 crystals for fast photorefractive nonlinear optics
Authors: Voit E. , Zha M. Z. , Amrhein P. , Günter P.
Published: July 2002

Reduced KNbO3 crystals are shown to have the fastest photorefractive response times for applications in the visible wavelength region. Grating build-up times at cw illumination in the microsecond region are reported which allow the use of such crystals for real-time applications. The reduction treatment and a new method for the investigation of the photorefractive homogeneity during reduction are presented.
Theoretical formalism to understand the role of strain in the tailoring of hole masses in p-type InxGa1−xAs (on GaAs substrates) and In0.53+xGa0.47−xAs (on InP substrates) modulation-doped field-effect transistors
Authors: Jaffe Mark , Sekiguchi Yoshihiko , Singh Jasprit
Published: July 2002

Recently, experimental studies have suggested that strained p-channel modulation-doped field-effect transistors (MODFET’s) display enhanced characteristics due to a decrease in hole masses. In this letter, we examine the potential of using biaxial compressive strain to lower the effective mass of the hole gas. The Kohn–Luttinger Hamiltonian is used to describe the hole states in a strained channel. Using this, the Schrödinger equation is solved self-consistently with the Poisson equation. The coupling between light- and heavy-hole states is found to be critical to get accurate properties of the hole gas. A decrease in the effective hole mass of more than three times is found at low temperatures in the presence of the biaxial strain. The theoretical technique described here is not variational in nature and can be applied to an arbitrarily shaped confining potential profile with different material parameters across interfaces. This technique should be quite useful in designing and understanding strained p-MODFET devices.
Optical polarization bistability with high switching speed in a TM wave injected buried heterostructure laser
Authors: Mori Yoshihiro , Shibata Jun , Kajiwara Takao
Published: July 2002

We demonstrate optical polarization bistability in a semiconductor laser for the first time. Only the optical signal pulses are used as triggers for switching the transverse mode of the laser. The two stable states are identified as the transverse electric mode and the transverse magnetic mode, respectively, while the optical input consists of the transverse magnetic wave. Switching speeds up to a few hundred picoseconds have been achieved for both switch-up and switch-down.
Monolithic integration of a transparent dielectric waveguide into an active laser cavity by impurity-induced disordering
Authors: Thornton Robert L. , Epler John E. , Paoli Thomas L.
Published: July 2002

In this letter we report the successful combination of a low-loss buried waveguide providing two-dimensional optical confinement with an active gain medium. We have thereby realized a planar and monolithic composite cavity laser where the laser cavity consists of distinct regions of optical gain combined with distinct regions of low-loss optical waveguide. The low threshold currents of these strucures (<10 mA) confirm the low loss and waveguiding nature of the waveguide regions. The ability to make these types of structures has applications for window lasers, monolithic waveguides, and monolithic integration of electrical and optical components.
Proximity effect depression of the critical temperature in two-phase Nb-Ti superconductors
Authors: Meingast C. , Daeumling M. , Lee P. J. , Larbalestier D. C.
Published: July 2002

The superconducting critical temperature of high critical current density Nb-Ti composites has been measured at various stages in the critical current optimization process. This process involves heat treatment steps which cause precipitation of normal α-Ti and make the matrix more Nb rich. Tc rises from 9.1 to 9.5 K during this stage. The final optimization stage involves extensive wire drawing during which the α-Ti precipitates are reduced to less than a coherence length in thickness. This does not result in a reduction in Jc but Tc is found to fall from 9.44 to 8.7 K during this step. The depression of Tc is found to be in fair agreement with the predicted proximity effect suppression of Tc. Wires of optimum transport critical current density are seen to have Tc of around 9 K.
Volume production of Li− in a small multicusp ion source
Authors: Walther S. R. , Leung K. N. , Kunkel W. B.
Published: July 2002

Negative lithium ions, generated by volume processes, have been extracted from a small magnetically filtered multicusp ion source. Current densities of 1.9 mA/cm2 have been obtained with a discharge voltage of 40 V and a discharge current of 4 A.
Operation of a Y-Ba-Cu-O rf SQUID at 81 K
Authors: Zimmerman J. E. , Beall J. A. , Cromar M. W. , Ono R. H.
Published: July 2002

An rf superconducting quantum interference device (SQUID) has been made from bulk Y-Ba-Cu-O. The device displays quantum interference effects and operates with useful signal levels up to 81 K. The SQUID is formed from a ring of Y-Ba-Cu-O which is broken in the cryogenic environment and then recontacted. Estimates of the SQUID noise performance are given.
Optical bistability and nonlinear switching due to increasing absorption in single-crystal ZnSe waveguides
Authors: Kim B. G. , Garmire E. , Shibata N. , Zembutsu S.
Published: July 2002

Optical nonlinear switching and bistability due to increasing absorption have been observed in single-crystal ZnSe waveguides with contrast ratios of 16/1 and switching times of 10 μs at 15 mW of argon laser light. Switching energy is improved over the bulk by a factor of 200.
Degradation of micron-sized CrSi2 lines on polycrystalline silicon
Authors: Phillips J. R. , Zheng L. R. , Mayer J. W.
Published: July 2002

The thermal stability of CrSi2 fine lines on undoped chemical vapor deposited polycrystalline silicon was investigated. Heat treatments were in vacuum at temperatures between 500 and 950 °C. Hillock growth resulting from dissolution of silicon and subsequent regrowth in the silicide resulted in degradation at temperatures as low as 650 °C. We found that the degradation occurs preferentially at line edges. It is suggested that the edge preference is due to silicide deformation that is required at recrystallization sites.
Trap generation and occupation in stressed gate oxides under spatially variable oxide electric field
Authors: Avni E. , Shappir J.
Published: July 2002

The spatial variation of the oxide field in metal-oxide-silicon devices due to charge trapping under electron injection stress is included in a self-consistent trapping model. The model predicts the spatial distribution of the stress-generated trapping sites and their occupation level under different conditions of applied voltages and total injected charge. The calculated results agree quite well with the experimental results of prolonged charge injection, as expressed in shifts of the flatband voltage.
Dual-wavelength emission from a twin-stripe single quantum well laser
Authors: Tokuda Yasunori , Abe Yuji , Matsui Teruhito , Tsukada Noriaki , Nakayama Takashi
Published: July 2002

We demonstrate a dual-wavelength laser constructed from a single quantum well structure. The device includes twin-stripe waveguides which differ in width. The two constituent emitters in the device of appropriate cavity lengths operate at widely different wavelengths, which are based on the lowest (n=1) and the second (n=2) quantized state transitions. Lasing behavior is interpreted in terms of the difference of the internal cavity loss of the waveguides.
Microscopic origin of light-induced changes in hydrogenated amorphous silicon
Authors: Jang Jin , Lee Chang Geun , Park Seung Chul , Lee Choochon
Published: July 2002

Light-induced changes in the stretching mode absorption of Si-H and Si-H2 have been studied for hydrogenated amorphous silicon (a-Si:H) films. The absorption below 2000 cm−1 decreases greatly, but a small change has been observed above 2100 cm−1. The magnitude of the overall change increases as the substrate temperature is lowered and little change is observed for a-Si:H films deposited at above 200 °C. The change in boron-doped a-Si:H is small compared with the undoped film deposited at the same substrate temperature. Based on experimental results, it is suggested that the hydrogen in the bulk of a-Si:H diffuses to the microvoids during light illumination.
Identification of the titanium-related levels in GaP
Authors: Roura P. , Bremond G. , Nouailhat A. , Guillot G. , Ulrici W.
Published: July 2002

Deep level transient spectroscopy, deep level optical spectroscopy, and optical absorption experiments were carried out in n- and p-type Ti-doped GaP crystals grown by the liquid encapsulated Czochralski technique. The single acceptor level of substitutional titanium Ti3+/Ti2+ was identified by deep level transient spectroscopy at an energy of 0.50±0.02 eV from the conduction band. The Ti2+ intracenter transitions were detected by deep level optical spectroscopy and optical absorption about 0.63 and 1.03 eV. The Ti4+/Ti3+ donor level was found at about 1±0.2 eV from the top of the valence band. The position of these two levels is found in complete agreement with the position of titanium-related levels in GaAs and in InP.
High mobility, selectively doped InP/GaInAs grown by organometallic vapor phase epitaxy
Authors: Aina Leye , Mattingly M. , Potter Bob
Published: July 2002

Selectively doped InP/GaInAs heterostructures with electron mobilities over 100 000 cm2/V s at 9 K, 72 000 cm2/V s at 77 K, and 11 300 cm2/V s at 300 K have been grown by organometallic vapor phase epitaxy. These layers have sheet concentrations ranging from 7.5×1011 to 2×1012 cm−2. These are the highest electron mobility/sheet concentration values reported so far for GaInAs/InP heterostructures grown by any technique.
SiFx and SFx molecular ion implantations into GaAs
Authors: Tamura Akiyoshi , Inoue Kaoru , Onuma Takeshi , Sato Minoru
Published: July 2002

We have investigated fundamental electrical characteristics of GaAs implanted with SiFx and SFx (x=1, 2, and 3) molecular ions at energies which give the same dopant atom (Si or S) ion ranges. Three kinds of annealing methods were compared. Characterization of these implanted GaAs layers was carried out by the Hall effect, capacitance-voltage, and secondary ion mass spectrometry measurements.
Thermal conversion of AlxGa1−xAs layers grown by molecular beam epitaxy
Authors: Adachi Sadao , Yamahata Shoji
Published: July 2002

We report the observation of thermal conversion of AlxGa1−xAs alloys grown by molecular beam epitaxy (MBE) from undoped, high-resistivity AlxGa1−xAs to low-resistivity, p-type material after annealing beyond the growth temperature (∼650 °C). The phenomenon occurs only in the Al-containing layers and not in the GaAs. Electrical measurements indicate that a substantial concentration of residual C acceptors causes the thermal conversion of the AlxGa1−xAs layers. A possible mechanism of C incorporation during MBE is examined from a thermodynamical point of view.
Biaxially stressed excitons in GaAs/AlGaAs quantum wells grown on Si substrates
Authors: Jagannath C. , Zemon S. , Norris P. , Elman B. S.
Published: July 2002

Photoluminescence and photoluminescence excitation spectroscopies are utilized to study excitons in GaAs/AlGaAs quantum wells (QW’s) fabricated by molecular beam epitaxy on a GaAs buffer layer grown on a Si substrate. The buffer layer was grown by metalorganic vapor phase epitaxy. The experimental results are understood in terms of a uniform biaxial tension of approximately 3 kbar present in the plane of growth for both the QW’s and the GaAs buffer. An important consequence of the biaxial tension is that for QW’s with well widths larger than ≊15 nm the light-hole and heavy-hole subbands cross each other in energy, resulting in a light-hole exciton energy lower than that of the heavy-hole exciton, opposite to the case of QW’s grown on GaAs substrates.
Deep level transient spectroscopy studies of epitaxial silicon layers on silicon-on-insulator substrates formed by oxygen implantation
Authors: McLarty P. K. , Cole J. W. , Galloway K. F. , Ioannou D. E. , Bernacki S. E.
Published: July 2002

Deep level transient spectroscopy was applied to study silicon epitaxial layers of varying thickness grown on silicon-on-insulator substrates formed by oxygen implantation. For 3-μm-thick layers no traps were detected. For 1.0-, 2.0-, and 2.5-μm-thick layers electron traps were found with levels 0.34, 0.32, and 0.37 eV below the conduction-band edge, and corresponding capture cross sections of ∼2.0×10−7, 6.0×10−18, and 5.0×10−7 cm2. These levels were found to be uniformly distributed across the wafer. It was also observed that the trap concentration is a decreasing function of epilayer thickness.
Observation of periodical short pulse trains in free-electron laser oscillations
Authors: Kawamura Y. , Toyoda K. , Kawai M.
Published: July 2002

Periodical short pulse trains were observed in a long pulse, low current, low voltage waveguide mode free-electron laser. The pulse width and the pulse train intervals of the periodical short pulse trains were about a few ns and about 23 ns, respectively. These pulse trains can be explained as self-mode-locked oscillations of a free-electron laser.
High-quality amorphous silicon germanium produced by catalytic chemical vapor deposition
Authors: Matsumura Hideki
Published: July 2002

High-quality amorphous silicon germanium (a-SiGe:H) films are produced by a new ‘‘catalytic chemical vapor deposition (CTL CVD)’’ method. In the method, a SiH4, GeH4, and H2 gas mixture is decomposed without using any plasmas or photochemical excitation, but using only the thermal or the catalytic reaction with a heated tungsten catalyzer. Photoconductive properties of CTL CVD a-SiGe:H are apparently not degraded as the Ge content increases. The photoconductivity and the photosensitivity for AM-1 of 100 mW/cm2 are 10−5–10−4 (Ω cm)−1 and 104, respectively, even for the sample of optical band gap of 1.40–1.45 eV.
Low-threshold and wide-bandwidth 1.3 μm InGaAsP buried crescent injection lasers with semi-insulating current confinement layers
Authors: Cheng W. H. , Su C. B. , Buehring K. D. , Ure J. W. , Perrachione D. , Renner D. , Hess K. L. , Zehr S. W.
Published: July 2002

A hybrid growth technique has been used to fabricate low-threshold, high-modulation bandwidth, and high-power 1.3 μm InGaAsP buried crescent injection lasers. The technique involves a first growth of an Fe-doped semi-insulating current confinement layer by low-pressure metalorganic chemical vapor deposition followed by a liquid phase epitaxy regrowth. The lasers have cw threshold currents as low as 10 mA at 25 °C, total differential quantum efficiency over 50%, high-temperature operation up to 100 °C, and output power more than 33 mW/facet. A 3-dB modulation bandwidth of 8.4 GHz has been achieved at 5 mW/facet.
Nondestructive characterization of multilayer structures by resonant attenuated total reflection spectroscopy
Authors: Bosacchi Bruno , Oehrle Robert C. , Grosse Eric
Published: July 2002

A new technique for the nondestructive characterization of semiconductor heterostructures is presented. The technique consists of a measurement of the attenuated total reflection (ATR) spectrum of the structure. This spectrum is characterized by sharp interference patterns and deep resonance minima, corresponding to the excitation of various resonant modes. From the analysis of the ATR spectrum, detailed information can be obtained on the geometrical and compositional parameters of the structure. The technique, which is nondestructive and fast, is a natural candidate for general use in semiconductor technology (microelectronics, optoelectronics, integrated optics). To illustrate its potential, we discuss its application to the case of the thickness characterization of the wafers used to manufacture GaAlAs heterostructure lasers.
Diffusion of oxygen in superconducting YBa2Cu3O7−δ oxide upon annealing in helium and oxygen ambients
Authors: Tu K. N. , Park S. I. , Tsuei C. C.
Published: July 2002

Superconducting YBa2Cu3O7−δ oxide specimens (Tc∼91 K) formed by sintering were annealed in He gas ambient at constant temperatures ranging from 300 to 440 °C. Outdiffusion of oxygen during the annealing procedure was monitored by in situ electrical resistivity measurement. Below 350 °C, no resistivity changes were observed with time. From 370 to 440 °C, resistivity increased linearly with annealing time except the very initial period. Indiffusion of oxygen monitored by switching He to O2 (or air) during the annealing occurred extremely rapidly as indicated by a precipitous drop of resistivity. Assuming that the outdiffusion of oxygen is interfacial-reaction limited, an activation energy of 1.7 eV was measured. The effects of oxygen diffusion on resistivity indicate that oxygen atoms mediate majority carriers in the oxide.
Improved detection of carbon in GaAs by secondary ion mass spectroscopy: The influence of hydrocarbons in metalorganic vapor phase epitaxy
Authors: Scilla G. J. , Kuech T. F. , Cardone F.
Published: July 2002

The quantitative analysis of carbon levels in thin layers of semiconductor materials is usually limited by poor detection limits. While several qualitative techniques for detecting carbon exist, secondary ion mass spectroscopy (SIMS) has been the primary tool for obtaining depth profiles of carbon in thin films. The presence of carbon compounds in the residual gas background of the SIMS instrument typically limits the carbon detection limits to ∼1017 cm−3 under standard operating conditions. If the carbon contamination in material processing could be studied with 13C labeled compounds, detection sensitivities should be far better. We have shown here that with this approach and the judicial choice of the analyte ion As13C− the detection sensitivity can be lowered by more than two orders of magnitude. We have applied this technique to the study of the incorporation of carbon from isotopically enriched CH4, C2H2, and C2H4 during the epitaxial growth of GaAs by the metalorganic vapor phase epitaxy technique. We find no additional incorporation of carbon into these layers when substantial amounts of the hydrocarbons are introduced into the growth ambient. The use of isotopically enriched sources, together with these improved SIMS techniques, permits the routine detection of carbon at very low levels without the interference present in the conventional SIMS approach.
Ultrathin Au films studied with the scanning tunneling microscope: Topography of insulating surfaces
Authors: Jaklevic R. C. , Elie L. , Shen Weidian , Chen J. T.
Published: July 2002

The scanning tunneling microscope (STM) can produce high-resolution topographic images of surfaces which, normally, are electrically conducting. We have made STM images of a variety of insulating surfaces which are made conducting by a smooth ultrathin (>20 Å thickness) Au overlay film. Topographic features of the underlying substrate as small as 10 Å are resolved. Surprisingly, no features of the overlay Au film are seen. These films are useful for obtaining topographic images of a wide variety of surfaces and for STM measurements where a stable conducting surface is required for support of molecules or other microscopic structures.
Thermomagnetic direct overwrite in TbFe using thermally induced domain wall energy gradient
Authors: Rugar D. , Suits J. C. , Lin C.-J.
Published: July 2002

A method is described for thermomagnetic direct overwrite in amorphous Tb23 Fe77 . Using long (500 ns) laser pulses, micron-size domains can be written with diameters significantly smaller than the diameter of the Curie temperature isotherm. The relatively small domain size is due to the collapsing effect of the thermally generated domain wall energy gradient. Without switching the magnetic bias field, the domains can be collapsed to submicron size using short (50 ns) laser pulses. Domains can be completely erased by firing short pulses in succession as the recording medium is moved slowly with respect to the optical beam.
Enhanced infrared attenuated-total-reflection spectra of p-nitrobenzoic acid with Ag films
Authors: Badilescu S. , Ashrit P. V. , Truong Vo-Van
Published: July 2002

Enhanced infrared attenuated-total-reflection spectra of p-nitrobenzoate with overcoated and undercoated thin Ag films have been observed. The role of Ag-sample chemical interactions in the enhancement mechanism is considered.
Narrowing the far field of a Y-junction laser array using a customized spatial filter in an external cavity
Authors: Berger Josef , Welch David F. , Streifer William , Scifres Donald R.
Published: July 2002

A study of the spatially resolved spectrum of individual emitters in a Y-junction laser array shows that the array is not completely locked. The use of an external cavity with a novel, customized spatial filter is demonstrated to yield a stable output beam, which increases from 1.25 times the diffraction limit at low power to 1.6 times the diffraction limit at 120 mW without shifting.
High-efficiency extraction study of an electron beam pumped ArF laser amplifier with an atmospheric-pressure Ar-rich mixture
Authors: Lee Young-Woo , Kumagai Hiroshi , Ashidate Shu-ichi , Obara Minoru
Published: July 2002

The characteristics of an electron beam excited ArF laser amplifier were investigated from the small-signal region to the strongly saturated region (≥10 MW/cm2) as a function of Ar concentration. A single-pass (L=50 cm) amplifier experiment was performed with atmospheric Ar/F2 and Ne/Ar/F2 gas mixtures pumped by an intense electron beam (1.3 MV, 90 kA, 65 ns full width half-maximum). The extracted intensity (output intensity minus input intensity) from this single-pass amplifier was maximized at input intensities ranging from 6.7 to 9.5 MW/cm2. The power efficiencies obtained were 13, 14.4, and 15.7%, and the extraction efficiencies were 65, 59.7, and 59.4% for Ar concentrations of 40, 70, and 99.6%, respectively. The amplifier parameters (small-signal gain g0, nonsaturable absorption coefficient α, and saturated intensity Is) were estimated for each mixture using a Rigrod analysis [J. Appl. Phys. 36, 2487 (1965)].
Radiation-enhanced diffusion of Au in amorphous Si
Authors: Priolo F. , Poate J. M. , Jacobson D. C. , Linnros J. , Batstone J. L. , Campisano S. U.
Published: July 2002

The radiation-enhanced diffusion of implanted Au markers in amorphous Si has been measured in the temperature range 77–693 K. Samples were irradiated with 2.5 MeV Ar ions. The diffusion coefficients show three well-defined regions. For temperatures <400 K, diffusion is athermal and due to ballistic mixing. For temperatures in the range 400–700 K diffusion is Arrhenius-type with an activation energy of 0.37 eV and is considerably enhanced over the normal thermal diffusion. The defects that cause the enhanced diffusion come from nuclear energy loss processes. Thermal diffusion, with an activation energy of 1.42 eV, dominates at temperatures greater than 750 K.
Epitaxial growth of GaAs/NiAl/GaAs heterostructures
Authors: Sands T. , Harbison J. P. , Chan W. K. , Schwarz S. A. , Chang C. C. , Palmstro/m C. J. , Keramidas V. G.
Published: July 2002

Epitaxial GaAs/NiAl/GaAs heterostructures consisting of buried NiAl layers and GaAs overlayers that are monocrystalline and well aligned have been fabricated by a combination of solid-phase reactions and molecular beam epitaxy. The structures have been characterized by reflection high-energy electron diffraction, electron microscopy, and ion channeling. The achievement of these stable and epitaxial buried-metal heterostructures makes possible the fabrication of metal-base and permeable-base transistors, buried interconnects, and buried ground planes.
Resistivity of boron-doped polycrystalline silicon
Authors: Ghannam M. Y. , Dutton R. W.
Published: July 2002

The doping dependence of the resistivity of polycrystalline silicon deposited by low-pressure chemical vapor deposition and implanted with boron is investigated. At doping concentrations <1018 cm−3, the resistivity is almost two orders of magnitude larger than that of crystalline silicon. At very large doping levels (=1020 cm−3), the resistivity is comparable to that of crystalline silicon though slightly higher. Boron segregation at grain boundaries is not observed for doping levels <1019 cm−3. At 1020 cm−3, boron segregation or additional clustering at grain boundaries causes a reversible change in the resistivity upon changing the annealing temperature.
High T
c superconducting films of Y-Ba-Cu oxide prepared by low-pressure plasma spraying
Authors: Tachikawa K. , Watanabe I. , Kosuge S. , Kabasawa M. , Suzuki T. , Matsuda Y. , Shinbo Y.
Published: July 2002

A low-pressure plasma spraying technique for depositing high Tc Y-Ba-Cu-O thick films has been developed. Films with a thickness range of 20–100 μm have been prepared by using Y0.3Ba0.7CuOx powders. After post-annealing in oxygen for 1 h at 950 °C, the films, which were deposited on a nimonic alloy substrate heated at 650 °C during spraying, exhibited a zero resistance temperature of 90.6 K with a transition width (90%–10%) of 2 K and a critical current density (77 K, 0 T) of 690 A/cm2.
High-field transport in an InGaAs-InP superlattice grown by chemical beam epitaxy
Authors: Vuong T. H. H. , Tsui D. C. , Tsang W. T.
Published: July 2002

We report the observation of high-field-domain formation in the transport through an In0.53Ga0.47As-InP superlattice. The current-voltage characteristics show two series of sharp negative differential resistances which are due to tunneling from the 1 to 2 and from the 1 to 3 subbands, respectively. Within each series the negative differential resistances occur at nearly equal intervals in the bias voltage. For the first series, the period in the bias voltage increases as the sample is cooled from 77 to 4.2 K. In contrast, the period for the second series remains constant within the same temperature range. We explain these observations by the effect of phonon scattering on the various subbands.
Laser-induced bulk damage in potassium dihydrogen phosphate crystal
Authors: Singleton M. F. , Cooper J. F. , Andresen B. D. , Milanovich F. P.
Published: July 2002

Potassium dihydrogen phosphate (KDP) is widely used for high-power laser frequency conversion. Its applications, however, are limited by a characteristically low laser damage threshold. This damage is associated with extrinsic impurity inclusions, whose exact nature has not been previously identified. We have now demonstrated that KDP grown in solutions containing organic impurities incorporates select organic compounds into the crystal matrix. Furthermore, we have observed a strong correlation between the concentration of these compounds and the crystal laser damage threshold and density.
Combined Rayleigh and Raman scattering study of AlxGa1−xAs grown via molecular beam epitaxy under reflection high-energy electron diffraction determined growth conditions
Authors: Tang W. C. , Lao P. D. , Madhukar A. , Cho N. M.
Published: July 2002

Rayleigh and Raman scattering studies reveal a direct correlation between the degree of disorder and growth kinetics attendant to the chosen growth conditions in molecular beam epitaxial growth. This inference is derived from studies on AlxGa1−xAs alloys grown under growth conditions indicated by reflection high-energy electron diffraction intensity dynamics to be near optimal and away from optimal.
Auger study of grain boundaries in large-grained YBa2Cu3Ox
Authors: Verhoeven J. D. , Bevolo A. J. , McCallum R. W. , Gibson E. D. , Noack M. A.
Published: July 2002

A scanning Auger microscopy study has been carried out on fractured surfaces of YBa2Cu3Ox samples prepared by standard sintering procedures from powders. It is concluded that in the large-grained samples examined, a majority of the grain boundaries are sufficiently ‘‘open’’ that standard metallographic preparation causes them to become contaminated with C. This suggests that an actual loss of contact at the grain boundaries during sample preparation is responsible for the low Jc values observed in bulk-sized large-grained YBa2Cu3Ox.
Surface kinetic processes and the morphology of equilibrium GaAs(100) surfaces: A Monte Carlo study
Authors: Ogale S. B. , Thomsen M. , Madhukar A.
Published: July 2002

The morphological behavior of model static surfaces of compound semiconductors, as well as dynamic growth fronts relaxing towards their equilibrium behavior upon termination of growth, is studied via Monte Carlo simulations based upon the configuration-dependent reactive incorporation model. It is found that anion desorption, cation migration, and surface reconstruction play a crucial role in controlling the surface morphology and their interplay can explain the experimentally observed dependence of morphology on the substrate temperature.
Secondary ion mass spectrometry study of e
x s
i
t
u annealing of epitaxial GaAs grown on Si substrates
Authors: Radhakrishnan G. , McCullough O. , Cser J. , Katz J.
Published: July 2002

Samples of epitaxial GaAs grown on (100) Si substrates using molecular beam epitaxy were annealed at four different temperatures, from 800 to 950 °C. Following annealing, the samples were analyzed using secondary ion mass spectrometry. Depth profiles of Ga, As, and Si reveal optimum conditions for annealing, and place a lower limit on a damage threshold for GaAs/Si substrates.
Characterization of GaAs film grown on Si substrate by photoluminescence at 77 K
Authors: Huang Yihe , Yu Peter Y. , Lee Henry , Wang Shyh
Published: July 2002

Photoluminescence of GaAs films grown on Si substrate has been investigated quantitatively at 77 K. The peak shift and splitting of the exciton luminescence are shown to result from tensile stress in the film. Information on carrier lifetime has been deduced from the line shape of the photoluminescence.
High-frequency modulation of AlGaAs/GaAs lasers grown on Si substrate by molecular beam epitaxy
Authors: Chen H. Z. , Paslaski J. , Yariv A. , Morkoç H.
Published: July 2002

We report on the frequency response of quantum well lasers on Si substrates grown by molecular beam epitaxy. Ridge waveguide lasers of 10 μm×380 μm having threshold currents as low as 40 mA were used in this study. Measurements were performed up to a frequency of 4.5 GHz with a resultant modulation corner frequency of 2.5 GHz when the laser was operated about 20% above the threshold.
Ordering-induced changes in the optical spectra of semiconductor alloys
Authors: Bernard J. E. , Wei S.-H. , Wood D. M. , Zunger Alex
Published: July 2002

It is shown how the recently predicted and subsequently observed spontaneous long-range ordering of pseudobinary A0.5B0.5C isovalent semiconductor alloys into the (AC)1(BC)1 superlattice structure (a CuAuI-type crystal) gives rise to characteristic changes in the optical and photoemission spectra. We predict new direct transitions and substantial splittings of transitions absent in the disordered alloy.
Free-electron laser study of the nonlinear magnetophotoconductivity in n-GaAs
Authors: Kaminski J. , Spector J. , Prettl W. , Weispfenning M.
Published: July 2002

The University of California at Santa Barbara free-electron laser was used to investigate the kinetics of electrons bound to shallow donors in n-GaAs by saturation spectroscopy. The resonant photothermal conductivity arising from 1s–2p+ shallow donor excitations in a magnetic field was measured at intensities greatly exceeding that of earlier investigations and saturation of bound-to-free photoionization transitions was achieved. The impurity resonance photoconductive signal shows a distinct intensity dependence caused by competing bound-to-free transitions which saturate differently. This permits a more detailed evaluation of the electron recombination kinetics than was previously possible, yielding the ionization probability of the 2p+ state, the transition time of electrons from the 2p+ level to the gound state, and the recombination time of free carriers.
Large-numerical-aperture InP lenslets by mass transport
Authors: Liau Z. L. , Diadiuk V. , Walpole J. N. , Mull D. E.
Published: July 2002

Lenslets with diameters up to 130 μm and numerical apertures of 0.39–0.75 have been formed in InP substrates by using mass transport to smooth out chemically etched multilevel mesa structures. The lenslets show a smooth surface with an accurately controlled profile (i.e., curvatures) and are capable of forming clear images. Some lenslets (with a diameter of approximately 67 μm) have been used to collimate the output of a buried-heterostructure diode laser (of 1.3 μm wavelength) and resulted in a nearly diffraction-limited beam divergence of 1.4°.