bluuebunny/crossref_metadata_2025 huggingface dataset:
Arsenic pressure variations during oxide desorption from gallium arsenide prior to epitaxial deposition
Authors: SpringThorpe A. J. , Majeed A. , Priest A. D.
Published: July 2002

Prior to epitaxial deposition of gallium arsenide by molecular beam epitaxy it is necessary to remove surface oxide films in situ. Changes in the system pressure can be measured during the desorption process. The largest pressure changes are found for ion gauges that can directly measure the flux of arsenic atoms that are reflected or scattered from the substrate surface. It is found that there is a reproducible drop in apparent pressure of ∼25% as the oxide is desorbed, which is independent of whether an As2 or As4 overpressure is used to stabilize the surface. There are, however, qualitative differences between the two arsenic species, which can be attributed to the way they interact with the GaAs surface. Nevertheless, the pressure changes correlate precisely with the oxide removal, and they provide a reproducible monitoring tool for the calibration of substrate temperatures and the establishment of appropriate epitaxial growth conditions.
Operation of a single quantum well heterojunction field-effect photodetector
Authors: Sargood S. K. , Taylor G. W. , Vang T. , Cooke P. , Burrus C. A. , Tell B. , Brown-Goebeler K.
Published: July 2002

The single quantum well heterojunction field-effect photodetector is demonstrated for the first time as a GHz bandwidth waveguide heterostructure, and as the optoelectronic counterpart to the single quantum well heterojunction field-effect transistor. For a 1 μm gate-length device a responsivity of 0.16 A/W, external quantum efficiency of 0.35, and test-laser limited rise time of 100 ps are obtained.
In situ all-laser process for deposition of Y1Ba2Cu3O7−δ film on stainless steel involving use of Y-ZrO2-Ag composite as a barrier layer
Authors: Ogale S. B. , Koinkar V. N. , Viswanathan R. , Roy S. D. , Kanetkar S. M.
Published: July 2002

Highly c-axis oriented good-quality (Tc of 88 K and Jc of 105 A/cm2 at 20 K) thin films of Y1Ba2Cu3O7−δ have been deposited on stainless-steel substrates by an in situ all-laser process involving use of laser-deposited Y-ZrO2-Ag composite film as a barrier layer. These results are compared with those obtained for the case of the use of a bilayer configuration of Ag and Y-ZrO2 to emphasize the importance of employing a composite film as a barrier layer.
Second harmonic conversion in cubic silicon carbide at 1.06 μm
Authors: Harris G. L. , Jones E. W. , Spencer M. G. , Jackson K. H.
Published: July 2002

In this letter, we describe second harmonic conversion in cubic silicon carbide (β-SiC) at a wavelength of 1.06 μm. Epitaxial layers of β-SiC formed by vapor phase growth on silicon are indeed birefringent, and thus phase matchable. Phase matched films of β-SiC have respectable conversion efficiencies even in the presence of adsorption at 532 nm. Our measured value of the effective second order nonlinear susceptibility for β-SiC is χ(2)eff=1.05±0.3×10−9 esu.
Formation kinetics of oxygen thermal donors in silicon
Authors: Wijaranakula W.
Published: July 2002

The formation kinetics of oxygen thermal donors in silicon was investigated. The result indicates that the diffusivity of interstitial oxygen can be used to explain the aggregation process of oxygen atoms at the thermal donor annealing temperatures. For the annealing time <105 s, the thermal donor concentration increases linearly with increasing time, while the number of oxygen atoms per donor remains unchanged. This result implies that an equilibrium concentration of oxygen atoms in the electrically active clusters could exist at the donor anneal temperature.
Photovoltage amplification and quasi-photovoltaic operation of an infrared hot-electron transistor
Authors: Choi K. K. , Taysing-Lara M. , Fotiadis L. , Chang W. , Iafrate G. J.
Published: July 2002

Under proper external bias, we showed that photovoltage amplification can be achieved from an infrared hot-electron transistor, and hence the transistor structure can be used to increase the voltage responsivity of a multiple quantum well photoconductor. In addition, the ouput voltage of the transistor can be very small when there is no signal light source, similar to a photovoltaic detector. As a result, the transistor is able to dc couple to a high-gain voltage amplifier for further signal amplification without reducing its detectivity.
High resolution electron microscopy study of damage created in Si-implanted InP
Authors: Zheng P. , Ruault M.-O. , Pitaval M. , Descouts B. , Krauz P. , Gasgnier M. , Crestou J.
Published: July 2002

{011} oriented InP crystals were implanted with 50 keV Si+ ions (doses: 5×1012 and 1014 Si/cm2). The individual cluster density and size were compared with those previously obtained in {001} oriented crystals. The high-resolution electron microscopy observations are consistent with an amorphous nature of these strained clusters. Further annealing of the amorphous zone obtained at the highest implantation dose shows lattice deformation or microtwins in the epitaxial recrystallized InP. Moreover, many InP undetermined and incoherent ‘‘precipitates’’ are observed.
Dependence of misfit dislocation velocities upon growth technique and oxygen content in strained GexSi1−x/Si(100) heterostructures
Authors: Hull R. , Bean J. C. , Noble D. , Hoyt J. , Gibbons J. F.
Published: July 2002

Misfit dislocation velocities in strained GexSi1−x/Si(100) heterostructures are compared for layers grown by molecular beam epitaxy and limited reaction processing. We demonstrate that velocities are substantially lower in structures with oxygen concentrations ∼1020 cm−3 compared to layers with oxygen concentrations ∼1018 cm−3. For layers with the lower oxygen concentration, the sample growth technique does not appear to be a significant factor affecting misfit dislocation velocity.
Ultrashort carrier lifetimes in H+ bombarded InP
Authors: Lamprecht K. F. , Juen S. , Palmetshofer L. , Höpfel R. A.
Published: July 2002

We studied the lifetimes of photoexcited carriers in H+ bombarded InP for different damage doses by means of femtosecond luminescence spectroscopy. The lifetime decreases down to 95 fs for a dose of 1×1016 cm−2. To our knowledge this is the shortest decay time for spontaneous light emission ever observed. The luminescence spectrum of the most damaged sample is inverted, indicating nonthermalized carrier distributions.
New high T
c superconductor: (In,Pb,Cu)Sr2(Ca,Y)Cu2O7−δ
Authors: Liu R. S. , Hu S. F. , Edwards P. P.
Published: July 2002

Bulk superconductivity was observed in the new system (InxPb0.75−xCu0.25)Sr2(Ca0.5Y0.5)Cu2 O7−δ. An increase in indium doping, 0≤x≤0.2, into the Pb sites results in an increase in the superconducting transition temperature Tc from 45 K for x=0 to 60 K for x=0.2. For nominal compositions x≳0.2, a decrease in Tc was observed, and an increase in the concentration of an impurity phase. From the results of the x-ray diffraction and energy- dispersive spectrometry, we identify the phase responsible for the superconductivity to be [In0.06(1)Pb0.69(1)Cu0.25]Sr1.99(7)[Ca0.47(1)Y 0.53(2)]Cu2O7−δ; this phase resulted from the synthesis of a sample of nominal composition (In0.2Pb0.55Cu0.25)Sr2(Ca0.5Y0.5)Cu2 O7−δ.
A periodic index separate confinement heterostructure quantum well laser
Authors: Wu M. C. , Chen Y. K. , Hong M. , Mannaerts J. P. , Chin M. A. , Sergent A. M.
Published: July 2002

A novel edge-emitting periodic index separate confinement heterostructure (PINSCH) semiconductor quantum well laser is proposed and demonstrated for the first time. Periodic semiconductor multilayers are used as optical confinement layers to simultaneously reduce the transverse beam divergence and increase the maximum output power. Self-aligned ridge-waveguide InGaAs/GaAs/AlGaAs PINSCH quantum well lasers emitting at 980 nm are fabricated. The 5×750 μm device has far-field angles of 10° by 20°, a threshold current of 45 mA, an external differential quantum efficiency of 1.15 mW/mA (90%), and an output power exceeding 620 mW, all measured at room temperature under CW operation. A record high fiber coupling efficiency of 51% has been achieved with a lensed fiber of 5 μm core diameter.
Leakage current and reliability of thin nitride films on as-deposited rugged polycrystalline silicon
Authors: Fazan P. C. , Mathews V. K. , Chan H. C. , Ditali A.
Published: July 2002

The leakage current and reliability characteristics of thin oxide/nitride (ON) storage dielectrics on as-deposited rugged polycrystalline silicon layers are discussed. Rugged capacitors showing capacitance improvements as high as 53% exhibit only a slight increase in leakage current when compared to smooth structures. Even though these capacitors have a shorter lifetime at high electric fields, time-dependent dielectric breakdown data at various fields show that their field acceleration coefficient is larger. However, lifetime extrapolations to low operating fields might be inaccurate if the field enhancement at the electrode asperities is not taken into account for the rugged capacitors.
Study of the oxygen depletion in the film-substrate interface of superconducting YBa2Cu3O7−x films
Authors: Colino J. , Sacedón J. L. , Vicent J. L.
Published: July 2002

Auger electron spectroscopy (AES) depth profiles were carried out on c-axis oriented YBa2Cu3O7−x films grown in situ onto SrTiO3 (100) and polycrystalline yttria-stabilized zirconia substrates. These films were grown by on-axis single-target dc planar magnetron sputtering, and they show zero resistance as high as 90.2 K and critical currents above 105 A/cm2 (77 K). The AES depth profiles reveal a clear oxygen loss at the interface. This oxygen deficiency corresponds to an atomic decrease from 7 to 6.6–6.3 per unit cell, in good agreement with the tetragonal structure oxygen composition. This confirms the oxygen-deficient first stages of YBa2Cu3O7−x film growth on some usual cubic substrates, and that those first layers do not become fully oxidized after the oxygen intake on the cooling in O2 atmosphere.
Transistor-based studies of heavy doping effects in n-GaAs
Authors: Patkar M. P. , Lundstrom M. S. , Melloch M. R.
Published: July 2002

The n2ieDp product (where n2ie is the np product and Dp is the minority hole mobility) in heavily doped n-GaAs has been measured by electrical characterization of p-n-p GaAs homojunction transistors with base dopings ranging from approximately 1×1017 to 9×1018 cm−3. The measured n2ieDp product decreases as the doping density increases. These results suggest that nie is roughly constant with doping density, in sharp contrast to the large increase observed for p-type GaAs. This work shows that when designing GaAs bipolar devices, it is important to consider the large difference in effective band gap between n+ and p+ regions.
Effects of nearest-neighbor pairs on the energy transfer in Nd:YAG
Authors: Lupei V. , Lupei A. , Georgescu S. , Ursu I.
Published: July 2002

An analysis of the luminescence quenching of 4F3/2 level of Nd3+ in YAG is presented in terms of two models: uniform random distribution and nonuniform placement of activators. It is shown that the correlated placement model for Nd3+ ions, assuming the absence, based on ionic size arguments, of Nd3+ ions in nearest-neighbor sites, is in contradiction with high resolution absorption spectra as well as quantum yield data. The anomalous decay can be described by energy transfer theory for a uniform distribution with a short-range interaction connecting the nearest-neighbor pairs and with dipolar interaction inside the other donor-acceptor pairs.
Response to ‘‘Comment on ‘Observation of two in-plane epitaxial states in YBa2Cu3O7−δ films on yttria stabilized ZrO2’ ’’
Authors: Garrison S. M. , Newman N. , Cole B. F. , Char K. , Barton R. W.
Published: July 2002

The superconducting properties of epitaxial YBa2Cu3O7−δ on yttria stabilized ZrO2 and LaAlO3 substrates depend on substrate-film interactions. The reduction in Jc was observed. (AIP)
Astigmatism correction in x-ray scanning photoemission microscope with use of elliptical zone plate
Authors: Ade H. , Ko C.-H. , Anderson E.
Published: July 2002

We report the impact of an elliptical, high resolution zone plate on the performance of an initially astigmatic soft x-ray scanning photoemission microscope. A zone plate with carefully calibrated eccentricity has been used to eliminate astigmatism arising from transport optics, and an improvement of about a factor of 3 in spatial resolution was achieved. The resolution is still dominated by the source size and chromatic aberrations rather than by diffraction and coma, and a further gain of about a factor of 2 in resolution is possible. Sub 100 nm photoemission microscopy with primary photoelectrons is now within reach.
Remarkable reduction of threshold current density by substrate misorientation effects in 660 nm visible light lasers with GaInP bulk active layers
Authors: Kikuchi Akihiko , Kishino Katsumi
Published: July 2002

660 nm wavelength GaInP/AlInP visible lasers with 60 nm thick GaInP active layers were grown on misoriented (100) GaAs substrates by gas source molecular beam epitaxy. A remarkable reduction in threshold current density Jth was observed with increasing substrate misorientation angle (SMA) from the (100) surface toward the [011] direction. Jth was 1.23 kA/cm2 on average for SMA of 0°, and 841 A/cm2 for SMA of 15° (both cavity lengths were 600 μm). For 1.1 mm long cavity lasers, a minimum Jth was 702 A/cm2 which was obtained for ordinary bulk-crystal active layers without strain and quantum-well effects. Such misorientation effects on reduction of Jth was systematically discussed in relation to various lasing parameters.
Photoluminescence of porous silicon buried underneath epitaxial GaP
Authors: Campbell J. C. , Tsai C. , Li K.-H. , Sarathy J. , Sharps P. R. , Timmons M. L. , Venkatasubramanian R. , Hutchby J. A.
Published: July 2002

Recent observations of visible, room-temperature photoluminescence in porous Si have stimulated research aimed at the realization of efficient, Si-based electroluminescent devices. To achieve electroluminescence, it may be beneficial to generate carriers with sufficient energy to populate the states of the quantum-confined Si structures. A viable method to accomplish this is to utilize a wide-band-gap heterojunction injector, such as GaP. Toward that end, we report the successful formation of porous Si buried underneath GaP islands, and we demonstrate that the buried porous Si layer exhibits strong photoluminescence (λ≊7000 Å).
Luminescence from Si/Si1−xGex heterostructures and superlattices
Authors: Northrop G. A. , Wolford D. J. , Iyer S. S.
Published: July 2002

A detailed study of near-gap photoluminescence (PL) from strained Si1−xGex alloy layers (x=0.01–0.05) and Si/Si0.95Ge0.05 multiquantum-wells (MQWs) has failed to show either free or dopant-bound excitons in as-prepared molecular beam epitaxial (MBE) layers. Low-temperature PL was, however, successfully induced in these same heterostructures by the selective introduction of relatively shallow (137 and 186 meV) radiation-damage bound-exciton centers, I1 and G, (respectively). The I1 center, in particular, produced alloy-broadened spectra which are shown clearly to emanate from the epitaxial layers, with separate and distinguishable components originating from both Si and Si1−xGex (x=0.01–0.05). This is among the first such reports of luminescence verifiably originating from within a Si/Si1−xGex multiple heterostructure.
Piezoexcitation of Rayleigh-type acoustic waves induced by near-surface absorption of laser pulses
Authors: Telenkov S. A. , Zhang X. R. , Gusev V. E.
Published: July 2002

We have investigated the generation of Rayleigh-type surface acoustic waves in high-resistance CdS crystals under the action of the third harmonic of the YAG:Nd3+ pulsed laser. A linear dependence of the acoustic signal amplitude with applied external electric field and its saturation with increasing illumination intensity has been observed. Experimental results show that the acoustic wave excitation is due to the inverse piezoeffect in which an external electric field is screened by a dense photogenerated electron-hole plasma. The saturation effect is caused by a nonlinear recombination of nonequilibrium carriers that prevents from increasing the screened part of the crystal volume.
Nanofeatures on GaAs (111)B via photolithography
Authors: Rajkumar K. C. , Kaviani K. , Chen J. , Chen P. , Madhukar A.
Published: July 2002

Mesas defined on GaAs(111)B substrates by photolithography followed by wet chemical etching are found to be triangular pyramids with truncated tops. The areal dimensions of the unetched tops of the pyramidal mesas diminish with etch time and can be reduced to an apex on continued etching. Transmission electron microscopy is used to examine a post-growth etched GaAs/Al0.3Ga0.7As multilayer structure grown on GaAs(111)B. A three-dimensionally confined GaAs volume of the order of 105 atoms is observed.
Electric-field effect on the minigap state in semiconductor superlattices
Authors: Huang F. Y. , Morkoç H.
Published: July 2002

Electric-field effect on the confined minigap states in coupled semiconductor superlattices is studied theoretically. Due to the perturbation of periodicity in the superlattice by an applied field, delocalization of the confined states is observed. In the weak field regime, delocalization of the minigap states is similar to the quantum confined Stark effect in single quantum wells. In the strong field regime, confined states disappear, and additional states from the original superlattice miniband are introduced to form semibound states due to the mixing of localized Stark ladders with the gap mode. Our numerical simulation will have an impact on confirmation of the proposed confined states in experimental observations. Possible device applications are discussed.
Quasi-continuous lasing from optically pumped CdZnTe/ZnTe multiple quantum wells at room temperature
Authors: Lee D. , Johnson A. M. , Zucker J. E. , Burrus C. A. , Feldman R. D. , Austin R. F.
Published: July 2002

We demonstrate the first room-temperature operation of optically pumped II-VI quantum-well lasers in a quasi-continuous mode. This result shows promise for high repetition rate, short-pulse operation, and cw operation of future wide-gap II-VI diode lasers at room temperature.
Center electrode effects in a long-conduction-time plasma-opening switch
Authors: Véron L. , Etlicher B. , Rouillé C.
Published: July 2002

We present the results of an experimental study of a coaxial, long-conduction-time plasma-opening switch. Our experiments show that the use of an 80% transparent inner electrode can significantly increase the opening speed. From measurements of the current into a load, the use of the grid improves the value of dI/dt by more than 60%, compared to results obtained with a solid center electrode.
Raman scattering and the π-orbitals in amorphous carbon films
Authors: Sinha K. , Menéndez J. , Sankey O. F. , Johnson D. A. , Varhue W. J. , Kidder J. N. , Pastel P. W. , Lanford W.
Published: July 2002

We report a Raman study of amorphous carbon films grown by different techniques. We compare Raman line shapes, depolarization ratios, and excitation profiles obtained from samples grown by rf-plasma deposition or sputtering as opposed to arc-evaporated carbon films. We find that all features of the Raman spectra are closer to results from crystalline graphite for samples deposited with an electron cyclotron resonance plasma using either a hydrocarbon gas source or a graphite sputtering target. This is surprising in view of the much larger optical band gap of these samples and also in view of recent e-2e scattering results which suggest that the π orbitals are more graphitelike in arc-evaporated carbon films. We offer a possible explanation of this paradox based on a reinterpretation of the optical properties of amorphous carbon which takes into account the special characteristics of the electronic states derived from π orbitals.
Synthesis of diamond filaments in an oxyacetylene torch
Authors: Morrison Philip W. , Cosgrove Joseph E. , Solomon Peter R.
Published: July 2002

This research reports the growth of diamond filaments using chemical vapor deposition (CVD). The growth reactor consists of an oxyacetylene torch that impinges on a cooled Mo wire tip. By controlling the tip temperature with a flow of Ar and carefully positioning the tip in the flame, one successfully nucleates a diamond seed. Slowly retracting the wire tip from the flame produces a filament of diameter 200–250 μm and length of 1 mm in 6–8 h. We have demonstrated that, in principle, there is no limit to the length of the filament. X-ray diffraction shows that the filament is cubic diamond and that it is not randomly oriented polycrystalline diamond but does have some features of orientational texture. Throughout the deposition, a video camera focused through a microscope records the nucleation and growth of the diamond.
Optical studies of erbium excited states in Ga0.55Al0.45As
Authors: Benyattou T. , Seghier D. , Guillot G. , Moncorge R. , Galtier P. , Charasse M. N.
Published: July 2002

Photoluminescence experiments have been carried out on erbium doped Ga0.55Al0.45As under continuous wave and pulsed laser excitation. For the first time the emissions arising from the two first Er3+ excited states 4I11/2, 4I13/2 and their temperature dependence have been systematically studied. From these results the nature and the excitation-deexcitation processes of these photoluminescences are discussed. With the help of these spectroscopic data we give an estimate of the stimulated emission cross section and the laser applications of such rare-earth doped III-V materials are examined.
On the high speed modulation bandwidth of quantum well lasers
Authors: Zhao B. , Chen T. R. , Yariv A.
Published: July 2002

A recent formulation of the gain in conventional three-dimensional double heterostructure (DH) and two-dimensional quantum well (QW) semiconductor lasers has been used to study the high speed modulation in such lasers. The emphasis is on the differential gain and nonlinear (i.e., intensity dependent) gain suppression in these material systems. We conclude that, in variance with earlier predictions, the expectation of higher modulation speed in QW lasers is not warranted at room temperature. The advantage of using multiple QW structure for high speed performance has been analyzed.
Micromachined vertical hall magnetic field sensor in standard complementary metal oxide semiconductor technology
Authors: Paranjape M. , Ristic Lj.
Published: July 2002

A novel vertical Hall magnetic field sensor which incorporates two important microsensor features is presented. First, the device is fabricated using a standard complementary metal oxide semiconductor (or CMOS) process and therefore possesses all characteristics inherent with integrated circuit manufacturing. Second, the magnetic field sensor is subjected to a post-processing step which involves CMOS-compatible micromachining techniques. This combination of micromachining and CMOS processing led to the superior results for a micromachined sensor when compared with a non-micromachined magnetic field sensor.
Organometallic vapor-phase homoepitaxy of gallium arsenide assisted by a downstream hydrogen afterglow plasma in the growth region
Authors: Pihlstrom B. G. , Sheng T. Y. , Thompson L. R. , Collins G. J.
Published: July 2002

In situ generated arsenic hydrides are reacted downstream with trimethylgallium (TMGa), both in the presence of and in the absence of a downstream hydrogen afterglow plasma. The homoepitaxial activation energy dramatically changes from 62 kcal/mol for the pure thermal to 21 kcal/mol for the plasma-assisted growth. The carbon incorporation mechanism for the plasma-assisted growth at temperatures less than 400 °C has a distinct activation energy for carbon incorporation of 23 kcal/mol, independent of V-III ratios. At temperatures above 400 °C, the level of carbon incorporated in the films reaches a level that appears to be dependent on the gas-phase precursor V-III ratio. The activation energy of the low-temperature region is consistent with the surface decomposition of arsenic hydrides.
Astigmatically compensated, high gain cooperative upconversion laser
Authors: Xie P. , Rand S. C.
Published: July 2002

We demonstrate a cw Er:LiYF4 trio laser in a 3-mirror cavity configuration, and investigate details of the mechanism yielding stimulated upconversion well above liquid nitrogen temperatures with an efficiency of 20%.
Γ effect: Key intermodal-discrimination mechanism in arrays of antiguided diode lasers
Authors: Botez D. , Mawst L. J.
Published: July 2002

By using results of the Bloch-function method applied to infinite-extent antiguided arrays, a closed-form expression has been derived, for the first time, for Γ, the two-dimensional array-mode confinement factor. When array modal behavior is analyzed, as the interelement-region width varies, domains of in-phase (i.e., single-lobe) array operation are found to occur periodically around the resonance points of in-phase modes. It is made clear why coupled-mode theory failed to predict how to obtain single-lobe phase-locked operation. Results of an exact analysis of a 20-element array are discussed, with the main conclusion being that the Γ effect, while being the key mechanism for selecting single-lobe array operation, does not insure purely diffraction-limited beams to high powers.
Effect of thermal history on the transport properties and the location of Fe in YBa2Cu3O7 thin films
Authors: Bridges Frank , Boyce J. B. , Johnson R. I.
Published: July 2002

Epitaxial Fe-substituted YBa2Cu3O7 films on LaAlO3 substrates prepared by pulsed-laser deposition exhibit a large variation in Tc with changes in the cooldown rate of the films in an O2 environment immediately after deposition. A rapid cooldown rate (200 °C/min) yields surprisingly high-Tc films with Tc≳75 K for 13% of the Cu replaced by Fe, while a slow cooldown of 10 °C/min results in low-Tc films with Tc→0 at 11% Fe, a greater suppression than reported for bulk materials. In addition, post-deposition anneals in O2 affect Tc significantly, even for anneal temperatures as low as 370 °C. These results are interpreted in terms of isolated- and clustered-Fe atoms substituted on the Cu chains sites.
In incorporation in GaInAs grown by molecular beam epitaxy
Authors: Woodbridge Karl
Published: July 2002

A study of In segregation during molecular beam epitaxial growth of GaInAs is reported. We find that In segregates to the surface during growth above approximately 550 °C and a constant surface concentration forms at low In flux. If the In flux is increased, a continuous buildup of In can occur due to the segregation rate not being balanced by the re-evaporation rate. Up to two monolayers of In may have segregated onto the surface during the growth of 200 Å of Ga0.75In0.25As at 560 °C. The In surface buildup appears to be suppressed by increasing the arsenic to group III flux ratio. A continuing incident Ga flux, after the In flux has been terminated, significantly prolongs the surface recovery time. The implications of these results for the growth of GaAs/GaInAs multiple quantum well layers is discussed.
Vertical microcavity surface-emitting ring laser
Authors: Lin J. , Gamelin J. K. , Du G. T. , Wang S. , Hong M. , Mannaerts J. P.
Published: July 2002

We report the performance of a novel surface-emitting laser of ring structure (RSEL). The far-field emission pattern of the RSEL remains a near-diffraction limited single lobe at 3 times the threshold current level. The structure may also be used to achieve beam width much less than that of the diffraction limit of Gaussian near-field distribution.
Optical second-harmonic generation in laterally asymmetric quantum dots
Authors: Allam Jeremy , Wagner Mathias
Published: July 2002

We investigate laterally asymmetric quantum dots (LAQDs) as second-order nonlinear optical elements in which symmetry-forbidden intersubband transitions become allowed due to lateral asymmetry. The susceptibility for second-harmonic generation (χ2ω(2)) of a two-dimensional LAQD with three equispaced energy levels was studied by calculating the product of the intersubband transition dipole moments. The product was as large as 0.95×10−3 Lx3 for a dot of length Lx confined by an infinite-potential barrier. The product was increased to 3.0×10−3 Lx3 by varying the aspect ratio (Ly/Lx) of the LAQD and decreasing the barrier height. The lateral asymmetry can be controlled by a gate electrode in semiconductor devices, leading to a device with tunable wavelength and nonlinear coefficients, suitable for quasi-phase matching in nonlinear optical waveguides.
Identification of segregation from borophosphosilicate glass films during annealing
Authors: Imai S. , Yabuuchi Y. , Terai Y. , Yasui T. , Kudo C. , Nakao I. , Fukumoto M.
Published: July 2002

The structure and crystallinity of a segregation on a borophosphosilicate glass (BPSG) film have been clarified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), transmission electron diffraction (TED), and electron energy loss spectroscopy (EELS). The segregation arises on the BPSG film surface after annealing in nitrogen ambient. Its size is below 0.5 μm. The segregation is identified as crystalline BPO4 from the results of TED and EELS. In this letter, TED pattern of crystalline BPO4 is indicated in detail. The growth mechanism of crystalline BPO4 is proposed on the basis of a series of the results.
Electrical properties of oxide-nitride dielectric films incorporating passivation oxide on polycrystalline silicon for advanced dynamic random access memory stacked capacitors
Authors: Chan Hiang C. , Mathews Viju K. , Fazan Pierre C.
Published: July 2002

We demonstrate that electron trapping in oxide/nitride (ON) dielectric films with a passivation oxide on rugged polycrystalline silicon is lower than in those without passivation oxide. The leakage current at high field through the Si3N4 films incorporating a passivation oxide is smaller than through Si3N4 films without passivation oxide. The deposited passivation oxide allows the formation of thinner Si3N4 films and also reduces the leakage current through Si3N4 films at high field. Our results show that oxide-nitride layers on deposited passivation oxides have the low leakage current, tight dielectric breakdown distribution, and trapping characteristics suitable for advanced dynamic random access memory (DRAM) stacked capacitors.
GaAs surface modification by room-temperature hydrogen plasma passivation
Authors: Yoon Euijoon , Gottscho Richard A. , Donnelly Vincent M. , Luftman Henry S.
Published: July 2002

The role of hydrogen atoms in enhancing photoluminescence (PL) intensity of native-oxide-contaminated GaAs during room temperature, short-time exposure to a H2 plasma is studied. Room-temperature D2 plasma passivations, annealing experiments in vacuum at 400 °C, D atom depth profiling with secondary ion mass spectroscopy, and chemical etching of residual surface oxides after passivation are all consistent with a reduction in surface recombination velocity leading to enhanced PL. By contrast, passivation of deep level defects in bulk GaAs cannot account for all the observations. The passivated surface is stable up to 400 °C in vacuum for at least an hour with only a slight reduction in PL intensity. Thus, it is possible to reactivate inadvertently neutralized donors and acceptors after passivation without affecting the reduction in surface recombination velocity.
High temperature superconducting YBa2Cu3O7−x films on metallic substrates grown in situ by off-axis sputtering
Authors: Jia Q. X. , Anderson W. A.
Published: July 2002

High temperature superconducting YBa2Cu3O7−x (YBCO) thin films were deposited on metallic substrate of Hastelloy C-276 using in situ off-axis rf magnetron sputtering from a single stoichiometric YBa2Cu3O7−x target. Highly c-axis oriented films with a zero resistance temperature of 84 K and critical current density of 1.6×104 A/cm2 at 77 K were obtained where BaTiO3 was used as a buffer layer. Scanning electron microscopy (SEM) surface scan showed quite good surface morphology of the films. The clear interfaces among different regions, confirmed by cross-sectional SEM analysis and Auger electron spectroscopy depth profiling, demonstrated BaTiO3 to be an effective buffer layer between YBCO and Hastelloy at a temperature as high as 640 °C.
Effects of deposition parameters on the refractive index in plasma polymerized methyl methacrylate thin films
Authors: Tobin J. A. , Denton D. D.
Published: July 2002

Plasma polymerization can be used to deposit thin films whose properties significantly differ from those of conventionally synthesized linear or cross-linked polymers. We investigate the plasma polymerization of methyl methacrylate for use in microelectronic and photonic applications. The deposition system is a 13.56 MHz parallel plate reactor. The effects of varying rf power and neutral pressure on deposition rate and refractive index in the visible are examined. It is found that the deposition rate can be varied from 50–500 Å/min over a pressure range of 40–300 mT. In addition, the refractive index can be varied from 1.5 to 1.6 in the visible by varying the rf power from 10 to 50 W. Possible applications in photonics include smoothly varying graded index and multilayer structures.
Single-crystal Al films grown by sputtering on (111)Si substrates
Authors: Niwa H. , Kato Masaharu
Published: July 2002

Single-crystal growth of Al films deposited by the sputtering method on (111)Si substrates was investigated in detail by transmission electron microscopy studies. A single-crystal epitaxial Al film 500 nm thick was obtained by conducting an appropriate heat treatment during and after the deposition.
Supercritical shear in shocked pentaerythritol tetranitrate
Authors: Dick J. J.
Published: July 2002

Supercritical shear occurs when the shear stress exceeds the strength of the perfect crystal. An estimate of the theoretical strength of the molecular crystal pentaerythritol tetranitrate is compared to experimental observations of the shock response of this explosive. It is concluded that supercritical shear may be occurring at shock stresses of several GPa in underdriven shocks where there is an elastic wave followed by a slower plastic wave. The induced simultaneous slip on sterically crowded cystallographic planes may be the mechanism for shock initiation of detonation in this explosive, at least in the low stress regime.
Photoemission from thick overlying epitaxial layers of CaF2 on Si(111)
Authors: Quiniou B. , Schwarz W. , Wu Z. , Osgood R. M. , Yang Q. , Phillips Julia M.
Published: July 2002

A tunable pulsed UV laser has been used to investigate photoemission from epitaxial films on Si(111). We find that internal photoemission from the Si surface provides significant electron emission through overlayers as thick as 8000 Å. The attenuation length in the epitaxial CaF2 films is found to be 2600 Å.
Generation and anneal of a new kind of interface state in stressed and high-temperature annealed metal-oxide-semiconductor devices
Authors: Berger M. , Avni E. , Shappir J.
Published: July 2002

Polycrystalline silicon (poly) gate metal-oxide-semiconductor (MOS) transistors were electrically stressed by constant-current tunneling. After the stress the devices were thermally annealed for variable times in the temperature range between 800 and 950 °C, and a second tunneling stress was performed. Capacitance-voltage (C-V) curve broadening and a charge pumping (CP) technique were used to detect interface state generation. It was found that the stress generated interface states are totally annealed by the thermal treatment. On the other hand, generation rates and saturation values, due to the second stress after annealing, exceed those of the fresh devices. Analysis of the generation process indicates that two types of interface states are generated: one, similar in its generation rate and saturation value to that of a fresh device, and another one, which is characterized by a higher generation rate and saturation value, is attributed to a new type of latent site. The density of this new type of latent interface states site decays exponentially with the annealing time. The annealing rate follows a temperature-dependent Arrhenius function. The anneal of this new type of interface state is characterized by an activation energy of 3.47 eV.
Hot-carrier effect on current transport in epitaxial YBa2Cu3Oy thin films
Authors: Matsui Ken-ichi , Sakuta Ken , Kobayashi Takeshi
Published: July 2002

The significant current saturation against the 20-ns-wide pulsed electric field above the threshold value Eth (∼2 kV/cm) was observed in the semiconducting phase YBa2Cu3Oy epitaxial films at low temperatures. Although Eth increased up to 3–7 kV/cm, the superconducting phase films also showed the same nonlinearity in their normal conduction at low temperatures. The value of Eth lowered with reducing temperature where the carrier concentration and mobility decreased and increased, respectively. These characteristic features are explained by the well-known hot-carrier effect in the familiar semiconducting materials.
Growth of DyBa2Cu3O7−x studied by scanning tunneling microscopy
Authors: Chandrasekhar N. , Agrawal V. , Achutharaman V. S. , Goldman A. M.
Published: July 2002

Scanning tunneling microscopy (STM) has been used to investigate the microstructure of DyBa2Cu3O7−x films grown on (100) SrTiO3 by ozone-assisted molecular beam epitaxy. The surface roughness is found to be higher than that reported for sputtered films of YBa2Cu3O7−x. Intensity oscillations were observed in the specular spot of in situ reflection high energy electron diffraction patterns, a result which suggests that surface smoothness is not a requisite for the observation of such intensity oscillations. The observation of spiral morphology in STM pictures indicates the presence of screw dislocations, in excess of 109 cm−2. A zeroth order approximation has been used to evaluate the shapes of the spirals and reasonable agreement is obtained with experiment.
Nonlinear far-infrared photoacoustic magnetospectroscopy of n-GaAs at low temperatures
Authors: Schilz A. , Huber L. , Prettl W. , Kaminski J.
Published: July 2002

The far-infrared magnetoabsorption of shallow donors in n-GaAs has been investigated as a function of irradiation intensity applying a low-temperature photoacoustic cell. Optical cross sections and saturation intensities of various optical transitions were quantitatively determined yielding recombination times of excited electrons.
Modeling the cycling degradation of silicon-oxide-nitride-oxide-semiconductor transistors
Authors: Everist S. C. , Miller S. L. , McWhorter P. J.
Published: July 2002

A model has been developed to predict cycling-induced threshold voltage shifts of silicon-oxide-nitride-oxide-semiconductor transistors. The model is based on the mechanism of hole transport through the tunnel oxide. It has been experimentally demonstrated that the model accurately predicts cycling behavior for a wide range of cycling parameters. Only two simple experiments are required to determine the model parameters.
Effect of spatial correlation of DX centers on the mobility in heavily doped n-type GaAs
Authors: Maude D. K. , Eaves L. , Portal J. C.
Published: July 2002

The persistent photoconductivity effect at low temperatures and under hydrostatic pressure is used to study the effect of spatial correlation of DX centers on the mobility and Shubnikov–de Haas oscillations in heavily doped n-type GaAs. Upon illumination, the transport mobility and the quantum relaxation time τs decrease rapidly with increasing carrier concentration. This is due to the destruction of the correlated distribution of DX centers by the random photoionization process. The enhancement of τs due to correlations is estimated.
55 GHz microstrip bandpass filter made from YBa2Cu3O7−x superconductor thin film
Authors: Gergis I. S. , Cheung J. T. , Trinh T. N. , Sovero E. A. , Kobrin P. H.
Published: July 2002

We report the first mm wave passive component made with high temperature superconducting thin films. Microstrip bandpass filters, with bandwidth of 2.2 GHz and a center frequency of 55 GHz, were made using YBa2Cu3O7−x filter patterns on MgO substrates with Au ground planes. The best results were obtained for a film grown with a thin SrTiO3 buffer layer and had Tc=89 K and Jc=106 A/cm2 at 84 K. The filter showed insertion loss of 1.7 db at 77 K, and 1.5 db at 70 K, compared to 7.3 db for Au filters at 77 K. Subtracting the losses in the Au ground plane, we estimated that the superconductor surface resistance is lower than one fourth that of Au at 77 K and 55 GHz.
Epitaxial growth of double hexagonal close-packed Nd on the α-Fe (111) surface
Authors: Cheng Yang-Tse , Chen Yen-Lung
Published: July 2002

Epitaxial double hexagonal close-packed (dhcp) Nd layers have been grown on the (111) surface of α-Fe at 320 °C by electron beam evaporation in an ultrahigh vacuum environment. Conventional θ-2θ diffraction and transmission electron microscopy show that the dhcp Nd films are oriented with the dhcp Nd (0001) plane parallel to the α-Fe(111) plane and with the dhcp Nd [112̄0] direction parallel to the Fe[11̄0] direction in the plane of the substrate. An epitaxial Fe/Nd/Fe trilayer structure with the same orientational relationships has also been made.
Scanning tunneling microscopic studies of growth spirals in bulk single crystals of superconducting YBa2Cu3O7 and flux pinning
Authors: Narlikar A. V. , Dutta P. K. , Samanta S. B. , Srivastava O. N. , Ramasamy P. , Sabarwal S. C. , Gupta M. K. , Padalia B. D.
Published: July 2002

Growth spirals have been observed in the basal plane of bulk single crystals of Y-123 high Tc cuprate, using scanning tunneling microscope with the unit cell resolution. The density of screw dislocations present is of the order of 107–108/cm2, close to the recently reported values for the sputtered epitaxial thin films of Y-123. The growth steps or terraces which are generally shown to possess a step height equal to the c parameter of the unit cell, have been further resolved into substeps corresponding to each of the triple perovskite block. Further, in the limit of ultimate resolution we have been able to demonstrate the substep heights corresponding to the individual atomic layers of the unit cell and thus provide a persuasive evidence that single crystals of Y-123 grow via layer-by-layer growth on the atomic scale within the purview of the spiral growth mechanism. Growth features are briefly discussed and it is argued that the observed screw dislocation density is still too low and the orientation is not favorable for realizing optimum flux pinning in these HTSC systems.
New method of measuring second harmonic generation efficiency using powder crystals
Authors: Kiguchi M. , Kato M. , Okunaka M. , Taniguchi Y.
Published: July 2002

A new method of measuring second-harmonic generation (SHG) efficiency using powder crystals is proposed. The second harmonic, which is generated by the evanescent wave under total reflection conditions, is phase matched for every element of the second-order optical nonlinear coefficient, whether each element is phase matchable in a bulk crystal or not. Observing this phase-matched second-harmonic power gives the SHG efficiency, regardless of the phase matchability in a bulk crystal, even if powder crystals are used as a sample.
Vertical cavity surface emitting laser with a submonolayer thick InAs active layer
Authors: Benjamin S. D. , Zhang T. , Hwang Y. L. , Mytych M. S. , Kolbas R. M.
Published: July 2002

We report photopumped operation of a vertical cavity surface emitting laser where the active region consists of a single pseudomorphic InAs-GaAs quantum well that is less than one monolayer thick. This represents the thinnest active layer to support stimulated emission when the optical feedback is perpendicular to the layer. Lasing action supported across a submonolayer thick quantum well can be understood by considering the effects on the carrier collection process and the gain across an ultrathin quantum well due to the spreading out of the electron and hole wavefunctions. Pulsed lasing due to gain across the InAs quantum well is confirmed for photoexcitation energies above and below the band edge of the GaAs confining layers at 17 and 77 K.
Photoluminescence study of lateral carrier confinement and compositional intermixing in (Al,Ga)Sb lateral superlattices
Authors: Chalmers S. A. , Weman H. , Yi J. C. , Kroemer H. , Merz J. L. , Dagli N.
Published: July 2002

We have compared the photoluminescence properties of an (Al,Ga)Sb lateral superlattice (LSL) quantum well to those of an (Al,Ga)Sb alloy quantum well, with respect to recombination energy and polarization dependence. From the results we have deduced the compositional intermixing and lateral carrier confinement present in the LSL structure. We found that the LSL well luminesces at 36 meV lower than the alloy well, and that emitted light from the LSL well is more than twice as intense when its electric field is polarized parallel versus perpendicular to the LSL ‘‘wires.’’ From these data we calculate that the lateral content of the LSL varies periodically between approximately 24% and 42% AlSb, and the maximum:minimum carrier density ratios are about 4:1 and 6:1 for electrons and heavy holes, respectively.
Dual wavelength optical bistability and multistability in a symmetric self-electro-optic effect device based on Wannier–Stark localization
Authors: Kawashima K. , Fujiwara K. , Yamamoto T. , Kobayashi K.
Published: July 2002

A tunable optical switch has been studied of a symmetric self-electro-optic effect device based on Wannier–Stark localization (WSL) in GaAs/AlAs superlattices. This device is driven by two different wavelengths for a signal beam and a control beam. Clear bistability and/or triple stability are demonstrated by controlling the illumination wavelengths. The tunability of the switching properties is clearly explained by the WSL mechanism.
Growth of GaAs on hydrogen-fluoride treated Si (100) surfaces using migration-enhanced epitaxy
Authors: Sudersena Rao T. , Nozawa K. , Horikoshi Y.
Published: July 2002

Heteroepitaxial growth of GaAs has been successfully achieved for the first time using migration-enhanced epitaxy (300 °C) on HF treated Si substrates which have been subjected to an initial in situ pre-heat treatment in the range of 350–620 °C and without the customary high-temperature Si oxide desorption step. High quality GaAs on Si exhibiting double-crystal x-ray rocking curve full-width at half-maximum value of 280 arcsec was obtained by using two-step growth technique MEE(300 °C)/MBE (580 °C). Secondary-ion mass spectrometry studies indicated 0.05 (monolayer) ML of oxygen at the interface of GaAs and HF treated Si substrate. The photoluminescence spectra at 10 K for GaAs grown on HF treated Si substrates was dominated by sharp excitonic related peaks and no carbon acceptor related emission could be detected.
Improved mode locking of a femtosecond titanium-doped sapphire laser by intracavity second harmonic generation
Authors: Petrov V. , Georgiev D. , Stamm U.
Published: July 2002

The inclusion of a frequency doubling crystal in a self mode-locked titanium-doped sapphire laser stabilizes the mode-locking regime. 125 fs pulses at ∼800 nm are generated at 90 MHz repetition rate. Femtosecond second harmonic pulse trains of 10 mW average power are obtained for the first time in the spectral region around 400 nm.
Direct observation of chemical vapor deposited diamond films by atomic force microscopy
Authors: Baranauskas V. , Fukui M. , Rodrigues C. R. , Parizotto N. , Trava-Airoldi V. J.
Published: July 2002

Diamond polycrystals deposited by the hot-filament chemical vapor deposition method on silicon (100) substrates have been examined by atomic force microscopy (AFM) in air. Measurements of the diamond unit cell show periodic spacings between 0.34 to 0.37 nm in a very good agreement with the theoretical value of the bulk constant of natural diamond (0.356 nm). Hybridized sp3 bonds can also be observed at the (111) surface.