bluuebunny/crossref_metadata_2025 huggingface dataset:
Shallow p+ junction formation by a reverse-type dopant preamorphization scheme
Authors: Ganin E. , Davari B. , Harame D. , Scilla G. , Sai-Halasz G. A.
Published: July 2002

Device grade ultrashallow p+ junctions have been fabricated by a novel ion implantation scheme. The novelty of the method is in using antimony to amorphize silicon prior to a low-energy boron implantation. Antimony satisfies a combination of two requirements lacking from all previously applied preamorphization schemes. First, due to the heavy mass of antimony, amorphization of silicon is achieved with a minimal amount of implantation damage. Second, and most important, antimony is a dopant of an opposite type than boron. Because of this, the inevitable implant tail of the preamorphizing species serves to confine the depth of the p layer. The optimized conditions for the application of this scheme have been determined. Junctions below 100 nm in depth, with less than 200 Ω/⧠ sheet resistance and junction leakage of 10 nA/cm2, have been achieved. The electrical results have been correlated with the residual defect structure observed by cross-sectional transmission electron microscopy.
Imaging of current-induced superconducting-resistive transitions by scanning electron microscopy in laser-deposited superconducting thin films of Y1Ba2Cu3O7−x
Authors: Frenkel A. , Clausen E. , Chang C. C. , Venkatesan T. , Lin P. S. D. , Wu X. D. , Inam A. , Lalevic B.
Published: July 2002

We have investigated the transport current-induced resistive transitions in predominantly c-axis oriented crystalline Y1Ba2Cu3O7−x superconducting thin films with scanning electron microscopic (SEM) imaging and its correlation with dc current-voltage (I-V) measurements. We find that there is a nonlinear gradual transition region in the I-V curves that is caused by macroscopic effects (current ‘‘crowding’’, substrate defects, film thickness variation, etc.) and by microscopic dissipation effects. At a high current there is an abrupt transition to the normal state in the I-V curve due to Joule heating. The SEM mapping provides a direct image of the above effects and is useful for characterization and study of fundamental transport properties of high Tc thin films.
Ion beam mixing in Ag-Pd alloys
Authors: Klatt J. L. , Averback R. S. , Peak David
Published: July 2002

Ion beam mixing during 750 keV Kr+ irradiation at 80 K was measured on a series of Ag-Pd alloys using Au marker atoms. The mixing in pure Ag was the greatest and it decreased monotonically with increasing Pd content, being a factor of 10 higher in pure Ag than in pure Pd. This large difference in mixing cannot be explained by the difference in cohesion energy between Ag and Pd in the thermodynamic model of ion beam mixing proposed by Johnson et al. [W. L. Johnson, Y. T. Cheng, M. Van Rossum, and M-A. Nicolet, Nucl. Instrum. Methods B 7/8, 657 (1985)]. An alternative model based on local melting in the cascade is shown to account for the ion beam mixing results in Ag and Pd.
Low-temperature photoluminescence from CdTe grown by hot-wall epitaxy on GaAs
Authors: Lischka K. , Schmidt T. , Pesek A. , Sitter H.
Published: July 2002

The low-temperature near-band-edge photoluminescence of thick (d≊36 μm) (100)CdTe epilayers grown on (100)GaAs substrates is investigated. Besides a dominating bound exciton emission, evidence for free-exciton emission (n=1 and 2) and two electron transitions (TETs) of donor-bound excitons is found. The defect involved in the TET is most likely a gallium-related donor. This is concluded from the TET line wavelength adopting recent bulk CdTe TET data. A new emission line at 781.4 nm (1586.7 meV) is observed. It is tentatively assigned to a TET of a free exciton.
Model for the diffusion of zinc in gallium arsenide
Authors: Kahen K. B.
Published: July 2002

The anomalous shape of the Zn diffusion profile in GaAs has been quantitatively explained. The Frank–Turnbull mechanism is invoked to govern the interchange between interstitial and substitutional Zn, via the Ga vacancies. These vacancies are proposed to be either neutral or singly ionized, depending on the position of the Fermi level. In addition, two physical phenomena are proposed. Substitutional Zn thermally generates interstitial Zn-Ga vacancy pairs and there is pairing between the donor, interstitial Zn, and the acceptor, substitutional Zn. The model is found to be in good agreement with the experimental data.
Transition metal silicide precipitation in silicon induced by rapid thermal processing and free-surface gettering
Authors: Kola R. R. , Rozgonyi G. A. , Li J. , Rogers W. B. , Tan T. Y. , Bean K. E. , Lindberg K.
Published: July 2002

We have investigated the effect of nickel and copper on defect formation in silicon employing the rapid thermal processing (RTP) scheme. Treatment by RTP induces haze in the silicon wafer front side when its back side is contaminated by either nickel or copper. Transmission electron microscopy studies showed that the haze consisted of metal silicide precipitates, which negates a previous suggestion that ‘‘oxidation-induced stacking faults’’ are the main defect forming the haze. The morphology and nature of these precipitates have been analyzed. The nickel silicide precipitates were found to be NiSi2 and the copper silicide precipitates are most likely CuSi (zinc blende structure). Both kinds of precipitates exhibited an epitaxial relationship with the silicon substrate and adopted the shape of an inverted pyramid or section of a pyramid. The present CuSi precipitate morphology differs totally from that obtained using furnace annealing, and is attributed to the availability of free-silicon surface as the main silicon self-interstitial sink. Implications for low-temperature ultralarge scale integration processing are discussed.
Electron focusing in two-dimensional systems by means of an electrostatic lens
Authors: Spector J. , Stormer H. L. , Baldwin K. W. , Pfeiffer L. N. , West K. W.
Published: July 2002

We introduce an electrostatic lens for ballistic electrons in two-dimensional (2D) systems and demonstrate its focusing action in very high mobility GaAs-(AlGa)As heterostructures. This is the first refractive element for the control of 2D electrons. It exemplifies the close analogy between ballistic propagation in 2D electron systems and traditional geometrical optics.
Improving tunneling junction in amorphous silicon tandem solar cells
Authors: Shen D. S. , Schropp R. E. I. , Chatham H. , Hollingsworth R. E. , Bhat P. K. , Xi J.
Published: July 2002

We report new results on a tunneling junction in amorphous silicon tandem solar cells using the metal oxide, niobium oxide (NbOx ), as the recombination layer and the advanced doping gas, trimethylboron [B(CH3 )3 ], in the p+ layer. The new tunneling junction has a low series resistance and minimizes optical loss. The advantage of the NbOx layer is its high transparency, hence a relatively thick (∼10 nm) layer can be used. The ability to use a thick oxide layer is important for the implementation of the tunneling junction in the production of large-area panels.
Te doping study in molecular beam epitaxial growth of GaSb using Sb2Te3
Authors: Chiu T. H. , Ditzenberger J. A. , Luftman H. S. , Tsang W. T. , Ha N. T.
Published: July 2002

Te evaporated from a Sb2Te3 compound source has been used to dope GaSb grown by molecular beam epitaxy. Te concentrations up to 2×1019 cm−3 followed a simple Arrhenius behavior with respect to source temperature. Efficient incorporation of Te remained insensitive to growth temperature until above 540 °C. Carrier density was found very close to Te doping level up to about 2×1018 cm−3. Above that, electron mobility as well as crystallinity deteriorated with increasing Te concentration. A dependence of surface reconstruction on Te doping level was observed. A complete change from (1×3) to (2×1) pattern occurred when Te concentration considerably exceeded its solubility limit in GaSb.
Deposition of SiC films by pulsed excimer laser ablation
Authors: Balooch M. , Tench R. J. , Siekhaus W. J. , Allen M. J. , Connor A. L. , Olander D. R.
Published: July 2002

Thin films of β-SiC were grown on Si substrates by excimer laser pulse ablation of bulk SiC. The films were examined by Auger electron, x-ray, and photoelectron spectroscopies and laser ionization mass analysis techniques. The film was smooth as monitored by scanning electron microscopy. Scanning electron and scanning tunneling microscopy (STM) showed inclusions in the deposited SiC films, and laser ionization mass analysis detected SiC dimers in the vapor plume emitted from the target.
Crossover from tunneling to metallic behavior in superconductor-semiconductor contacts
Authors: Kleinsasser A. W. , Jackson T. N. , McInturff D. , Rammo F. , Pettit G. D. , Woodall J. M.
Published: July 2002

We describe current-voltage measurements on superconducting Nb/InGaAs junction field-effect transistors which reveal a crossover from tunneling-dominated to Andreev scattering-dominated transport at the superconductor-semiconductor contacts as Schottky barrier thickness decreases with increasing interfacial dopant concentration. These measurements are the first demonstration of such a crossover in a thin-film structure, and are of interest for investigations of hybrid superconductor-semiconductor devices, proximity effect boundary conditions, and transport in ohmic contacts to semiconductors.
rf plasma aerosol deposition of superconductive Y1Ba2Cu3O7−δ films at atmospheric pressure
Authors: Wang X. W. , Zhong H. H. , Snyder R. L.
Published: July 2002

Superconducting films of Y1Ba2Cu3O7−δ were produced by a radio frequency (rf) plasma aerosol evaporation technique at atmospheric pressure. Aqueous solutions of the ions were generated as an aerosol and the mist was injected into the plasma region, and then deposited onto substrates outside of both the plasma and flame regions. The substrate temperature was about 600 °C. The deposition rate is 0.01–100 μm/(min cm2) and the film thickness is 1–200 μm. For an ‘‘as-deposited’’ film on a single-crystalline MgO substrate (100), the onset temperature of the superconducting transition is 100 K, with a transition width (10–90%) of 3 K, and zero resistance at 91 K. For another film post annealed at 850±10 °C for 1 h, the onset temperature is 105 K, with a width of 6 K, and zero resistance at 91 K. Since this technique does not require a vacuum environment, it has potential for large scale production of thin films.
Persistent photoconductivity in low-energy argon ion-bombarded semi-insulating GaAs
Authors: Vaseashta A. , Burton L. C.
Published: July 2002

Time-dependent phototransport measurements are presented for low-energy argon ion-bombarded semi-insulating liquid-encapsulated Czochralski GaAs. Distinct changes caused by ion beam etching were persistent photoconductivity and an increase in photosensitivity. The time dependence of photoconductivity indicated direct participation of the EL2 center. An ion beam induced and optically generated metastable defect state is suggested in the near-surface disordered region to describe the observed phenomena.
In situ extended x-ray absorption fine structure spectroscopy of thin-film nickel hydroxide electrodes
Authors: Capehart T. W. , Corrigan D. A. , Conell R. S. , Pandya K. I. , Hoffman R. W.
Published: July 2002

A convenient in situ electrochemical cell has been developed which permits x-ray absorption measurements on thin-film electrodes under electrochemical polarization. Extended x-ray absorption fine structure spectra from highly disordered α-Ni(OH)2 films, before and after polarization, provided quantitative results on the lattice contraction accompanying oxidation. Upon oxidation of α-Ni(OH)2, the Ni-O distance contracted from 2.05 to 1.86 Å, and the Ni-Ni distance contracted from 3.09 to 2.82 Å. The observed 10% contraction in the brucite plane is consistent with the 3.67 nickel valence in a K(NiO2)3 phase. The present technique extends x-ray absorption spectroscopy to the study of a variety of unstable materials not amenable to ex situ techniques.
Si doping efficiency in GaAs grown at low temperatures
Authors: Winer K. , Kawashima M. , Horikoshi Y.
Published: July 2002

The doping efficiency of Si (≡[e−]/[Si]) has been measured as a function of substrate temperature Ts, beam-equivalent As4-to-Ga fluence ratio R, and beam supply conditions to probe the kinetic limitations of low-temperature GaAs homoepitaxy. The doping efficiency decreases strongly with increasing R at low Ts due, we suggest, to electron trapping at defects caused by excess As incorporation.
Increased x-ray power from a transition-radiation source
Authors: Piestrup M. A. , Boyers D. G. , Pincus C. I. , Harris J. L. , Bergstrom J. C. , Caplan H. S. , Silzer R. M. , Skopik D. M.
Published: July 2002

Soft x rays were produced by a stack of 12 aluminum foils, each 1.0 μm thick, which were bombarded by a relativistic electron beam whose maximum power was ∼10 kW. The maximum total soft x-ray flux was measured to be 8 mW, a factor of 10 over the previous value. The maximum average power per unit area was ∼0.3 mW/cm2 over 8.5 cm2 area at 3 m from the transition radiator. Using an Intel mask, we obtained lithographs with features of 0.5 μm. Exposure times of the bare resist were as short as 150 s for 4.3 cm2 of wafer area (the resist had a 230 mJ/cm2 energy dose per unit area). The shortest time for mask/wafer exposure was 300 s for 8.5 cm2. We reduced the exposure time of the photoresist by a factor of 9 from the previous value.
Extrinsic transient diffusion in silicon
Authors: Giles Martin D.
Published: July 2002

The effect of extrinsic background doping on the transient enhancement of dopant diffusion for an ion-implanted dopant is investigated to gain insight into the role of point defect charge states. The transient effect is found to be greatly increased for extrinsic background doping of the same type as the implanted ion, and reduced for background doping of the opposite type. Analysis of the relative enhancements for boron and phosphorous allows the position of the donor and acceptor levels for the silicon self-interstitial to be extracted. The results are in good agreement with earlier work based on extrinsic oxidation-enhanced diffusion.
Monoatomic step observation on Si(111) surfaces by force microscopy in air
Authors: Suzuki M. , Kudoh Y. , Homma Y. , Kaneko R.
Published: July 2002

The structure of a vicinal Si(111) stepped surface is analyzed by force microscopy in air to reveal a fine structure in a step bunching area, and a monoatomic step in a terrace region. Step heights of one to three monoatomic layers were also observed on a debunched Si(111) surface. These steps have low crystallographic indices [112̄], [101̄], [01̄1], [213̄], and [ 1̄2̄3]. The force microscope images were in good agreement with scanning electron microscope and reflection electron microscope images observed in ultrahigh vacuum just after sample annealing by resistive heating.
Light-emitting devices based on the real-space transfer of hot electrons
Authors: Luryi Serge
Published: July 2002

The real-space transfer of hot electrons into semiconductor layers, where the transferred electrons are minority carriers, results in a generation of light by recombination. Based on this principle, several optoelectronic devices of varying degree of complexity are proposed in the present work. In particular, we propose a new class of vertical-cavity surface-emitting lasers that can be implemented in a number of heterostructures, including long wavelength materials (over 1.5 μm). An advantage of these structures is that the injection can be arranged without any current passing through the dielectric mirror stacks forming an optical cavity. Real-space transfer lasers can be used as logic devices with optical output functionally related to two or more electrical inputs.
Photovoltaic GaAs quantum well infrared detectors at 4.2 μm using indirect AlxGa1−x barriers
Authors: Levine B. F. , Gunapala S. D. , Kopf R. F.
Published: July 2002

We have demonstrated the first bound to continuum state GaAs/AlxGa1−xAs quantum well infrared detector which has a peak response λp=4.2 μm in the center of the midwavelength (λ=3–5 μm) infrared band. Although the detector uses indirect AlxGa1−xAs barriers, excellent hot-electron transport and a high detectivity D*λ=1012 cm√Hz/W were achieved.
Energy-dependent electron wave coupling between two asymmetric quantum well waveguides
Authors: Yang Rui Q. , Xu J. M.
Published: July 2002

We present an analysis of the electron wave directional coupling in two parallel asymmetric quantum well waveguides. By taking into account the effective mass difference between the wells we show that the transfer coefficient depends on the energy of the incident electron wave. A realistic configuration as an example of these kinds of electron wave couplers is examined. Its possible operation as an electron filter is suggested.
Self-consistency of magnetic domain wall calculation
Authors: Aharoni Amikam , Jakubovics J. P.
Published: July 2002

Minimum energy states of a rather general domain wall are determined by a set of differential equations. By using these equations, the energy of any of those states is shown to be equal to the value given by an expression that contains second derivatives, and is, therefore, very sensitive to the wall structure. The closeness of the two values can thus be taken as a measure of the closeness of the computed structure to the real energy minimum. This is a generalization of a criterion that has only been used before for 180° walls. Several other cases are treated in detail, and for the particular case of 90° walls, numerical values are given for some published wall structures.
Thermal treatment studies of the photoluminescence intensity of porous silicon
Authors: Tsai C. , Li K.-H. , Sarathy J. , Shih S. , Campbell J. C. , Hance B. K. , White J. M.
Published: July 2002

Thermal annealing studies of the photoluminescence (PL) intensity and Fourier-transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.
Local electrical dissipation imaged by scanning force microscopy
Authors: Denk Winfried , Pohl Dieter W.
Published: July 2002

The low internal damping of micromachined monolithic silicon levers with integrated probe tip has been exploited to detect nonconservative components in the interaction forces between the probe tip and sample. This is accomplished by monitoring the mechanical Q while scanning the surface. The gap width was controlled by keeping the lever’s resonance frequency detuning, caused by the gradient of the force between tip and surface, fixed to a preset value. Nonconservative components are present even in Coulomb attraction since, whenever a voltage is applied between tip and substrate, currents are induced by the lever’s oscillation leading to Joule dissipation of energy at a rate that depends on the local conductivity. Strong damping contrast was observed in layered GaAs/AlGaAs semiconductor heterostructures. It depended on the type of material, dopant concentration, illumination, and the applied voltage. Damping variations were resolved over distances of less than 20 nm.
Low-voltage, high-saturation, optically bistable self-electro-optic effect devices using extremely shallow quantum wells
Authors: Morgan R. A. , Asom M. T. , Chirovsky L. M. F. , Focht M. W. , Glogovsky K. G. , Guth G. D. , Przybylek G. J. , Smith L. E. , Goossen K. W.
Published: July 2002

Symmetric self-electro-optic effect devices (S-SEEDs) using extremely shallow GaAs/Al0.04Ga0.96As multiple quantum wells are demonstrated. By exploiting mainly exciton ionization, rather than the usual quantum-confined Stark shift, room-temperature optical bistability is obtained with no applied bias. The extremely shallow symmetric-SEED (symmetric E-SEED) exhibits contrast ratios (CRs)≂3.5, with biasses<5 V, demonstrating system applicability and compatability with electronics. Large system tolerances Δλ≂6 nm and maximum bistability loop width ≂70% are also obtained. Moreover, due to fast carrier escape times, the symmetric E-SEED exhibits useful CRs≳2 even at continuous-wave intensities ≳70 μW/μm2.
Sensitivity of resonant excitation and photoluminescence excitation measurements to exciton localization effects in GaAs/AlGaAs quantum wells
Authors: Reynolds D. C. , Evans K. R. , Stutz C. E. , Yu P. W.
Published: July 2002

Low temperature (2 K) photoluminescence (PL), PL excitation (PLE), and resonant excitation (RE) measurements on a very high quality, 150-Å-wide GaAs/Al0.3Ga0.7As multiquantum well structure are reported, with a focus on exciton localization effects. The PL spectra show evidence of effective submonolayer well width fluctuations. Excitons observed via RE are found to be predominantly localized; i.e., they decay from the same effective well-width region in which they are formed, while both localized and delocalized excitons are observed in PLE measurements. Delocalized excitons are free to diffuse to differing effective well-width regions which are energetically accessible. These results are supported by time-resolved PL measurements, which show essentially identical time-responses for differing effective well-width regions under resonant excitation conditions, thereby demonstrating the localized nature of resonantly created excitons.
Monte Carlo analysis of the transient spectral density of velocity fluctuations in semiconductors
Authors: González Sánchez T. , Velázquez Pérez J. E. , Gutiérrez Conde P. M. , Pardo Collantes D.
Published: July 2002

A multiparticular Monte Carlo method has been developed to calculate the spectral density of velocity fluctuations in transient conditions, when the electric field applied to a semiconductor changes. This method has been employed in the study of an instantaneous change in the electric field from 1 to 25 kV/cm in N-type GaAs. The results obtained are interpreted in terms of the phenomena occurring during the transient. The evolution of the transient spectral density for long times was found to converge at the steady state one of the final field.
Enhancement of change in the refractive index in an asymmetric quantum well
Authors: Susa Nobuhiko , Nakahara Tatsushi
Published: July 2002

A three-step quantum well is proposed that increases the electric-field-induced change in refractive index and reduces transmission loss. The oscillator strength of the n=1 heavy hole exciton can be reduced by more than an order of magnitude when an electric field is applied. This property results in a large change in refractive index and reduction in transmission loss. A low operating voltage is also possible.
Polarity dependence of hot-electron-induced trap creation in metal-oxide-semiconductor capacitors
Authors: Buchanan D. A.
Published: July 2002

Using thin metal gate electrodes, we have injected electrons into silicon dioxide films from the gate electrode and from the silicon substrate using internal photoemission. We have measured the hot-electron-induced electron trap density and centroid as a function of the average applied field and bias polarity for samples that have been in storage for a number of years and for samples recently fabricated. We found a greater density of traps generated for injection from the gate than from the silicon substrate. For the ‘‘aged’’ samples, the charge centroid of the electron traps is found close to the aluminum/silicon dioxide interface for low electric fields implying a large density of background traps close to this interface. For the ‘‘dry’’ samples the low-field centroid is found close to the center of the silicon dioxide film. As the field exceeds the electron heating threshold (≂1.5 MV/cm), the charge centroid for all samples is found to move towards the cathode/silicon dioxide interface.
Simultaneous detection of optical constants ε1 and ε2 by Brewster angle reflectivity measurements
Authors: Dietz N. , Lewerenz H. J.
Published: July 2002

A new method for determination of the dielectric function ε is presented. The experiment is based on the simultaneous measurement of the Brewster angle φB and the reflectivity Rp for light polarized parallel to the plane of incidence. ε1 and ε2 as a function φB and Rp were calculated and the results plotted as contour plots with the optical constants as parameters. Spectral measurements yield ε1 and ε2 as a function of photon energy. Results obtained on GaAs are evaluated and correspond well to literature data.
Si-SiO2 interface states enhanced by oxidation-induced stacking faults
Authors: Yoshida H. , Ohmori M. , Niu H. , Kishino S. , Tanaka H. , Nakashizu T.
Published: July 2002

It has been observed for the first time that interface states of Si metal-oxide-semiconductor diode are enhanced by the influence of oxidation-induced stacking faults (OSF). The observation has been carried out by isothermal capacitance transient spectroscopy measurement, using two kinds of samples. The samples are cut from the same CZ-Si wafer with ‘‘ring OSF.’’ One is prepared from the region with ‘‘ring OSF’’ and the other is prepared from the defect-free region.
Surface reconstruction phase diagram and growth on GaAs(111)B substrates by molecular beam epitaxy
Authors: Yang K. , Schowalter L. J.
Published: July 2002

A three-dimensional phase diagram is introduced to describe the dependence of GaAs(111)B surface reconstruction phases as observed by reflection high-energy electron diffraction (RHEED) on growth parameters. The 2×2, transitional, and √19 ×√19 surface reconstructions correspond to different zones in the phase diagram. A simple equation is found to be good approximation in representing the boundaries that separate these zones. From RHEED pattern studies, As coverages are evaluated to be a larger than 0.79 for the 2×2 reconstruction and smaller than 0.58 for the√19 ×√19 reconstruction. The dependence of surface morphology and crystal quality on growth condition are discussed in terms of RHEED patterns and growth parameters.
Magnetic and magneto-optic properties of epitaxial ferromagnetic τ-MnAl/(Al,Ga)As heterostructures
Authors: Cheeks T. L. , Brasil M. J. S. P. , Sands T. , Harbison J. P. , Aspnes D. E. , Keramidas V. G. , Allen S. J.
Published: July 2002

We have investigated the magnetic and magneto-optic properties of epitaxial τ MnAl/AlAs/GaAs heterostructures grown by molecular beam epitaxy. The ferromagnetic τ phase of MnAl was observed, and perpendicular anisotropy was confirmed by the nearly square hysteresis loops. The polar magneto-optic Kerr rotation of thin 10 nm τ MnAl films is nearly constant at 0.11° from 220 to 820 nm.
Noncontact monitoring of laser ablation using a miniature piezoelectric probe to detect photoacoustic pulses in air
Authors: Leung Wing P. , Tam Andrew C.
Published: July 2002

We show for the first time the use of pulsed photoacoustic detection using a miniature piezoelectric transducer to study and monitor photoablation in air by an ultraviolet KrF excimer laser. At incident laser fluences below the ablation threshold, the photoacoustic signal is produced by the thermal expansion of the air near the irradiated surface (‘‘thermal-piston signal’’) and propagates at the speed of sound. Above the ablation threshold, the photoacoustic signal contains an additional component due to the ejection of ablated materials (‘‘ablative-piston signal’’); this propagates initially at supersonic speeds. The amplitude of the ablative-piston signal is found to be a monotonic function of the etch-depth per pulse. Hence, by accumulating the amplitude of the ablative acoustic pulse, the total etch depth can be monitored in real time.
Activation energy for the photoluminescence W center in silicon
Authors: Schultz Peter J. , Thompson T. D. , Elliman R. G.
Published: July 2002

This work presents a systematic study of the substrate temperature dependence for the formation of the photoluminescent W center during high energy self-ion irradiation of silicon. All previous studies of this center were for postirradiation annealing, and we show that the formation is well described by a thermally activated process involving both the release of point defects from secondary defect complexes and the rate-limited activation of the center itself. We deduce an activation energy of Ea∼0.85 eV for the growth of the W center, and discuss the relationship of this type of experiment to conventional annealing studies.
Magnetic field imaging by using magnetic force scanning tunneling microscopy
Authors: Gomez R. D. , Burke E. R. , Adly A. A. , Mayergoyz I. D.
Published: July 2002

Magnetic fields on previously recorded magnetic disk are measured and analyzed using a modified scanning tunneling microscope. The technique employs the interaction of local magnetic field with a flexible thin-film magnetic probe. The dependence of resolution and image contrast on spatial orientation of the probe with respect to the sample is theoretically investigated. The predictions of this model, in limiting cases, are supported and illustrated by experimental results. A method for a controlled batch fabrication of probe tips is also discussed.
Ultrafast carrier capture and long recombination lifetimes in GaAs quantum wires grown on nonplanar substrates
Authors: Christen J. , Grundmann M. , Kapon E. , Colas E. , Hwang D. M. , Bimberg D.
Published: July 2002

The recombination kinetics of the quasi-one-dimensional (1D) carriers confined in quantum wires grown by organometallic chemical vapor deposition on nonplanar, patterned substrates is reported for the first time. Due to the small (240 nm) wire spacing, excited carriers are efficiently captured into the wires on a sub-ps time scale. The radiative recombination lifetime of the captured 1D carriers is longer than 310 ps. Time-resolved cathodoluminescence spectra directly monitor thermalization of the carriers within the wire.
Scanning tunneling microscopy of GaAs multiple pn junctions
Authors: Gwo S. , Smith A. R. , Shih C. K. , Sadra K. , Streetman B. G.
Published: July 2002

Scanning tunneling microscopy and spectroscopy is used to study GaAs multiple pn junction samples cleaved in ultrahigh vacuum. Direct topographic contrast over the pn junctions can be observed in the constant current imaging mode. The topographic height in the p-type regions appears much lower (by about 5 Å) than that in the n-type regions. Tunneling spectroscopy measurements show consistency with the assignment of the p- and n-type regions. We discuss a possible mechanism for the observed contrast.
Photorefractive effect in annealed proton-exchanged LiNbO3 waveguides
Authors: Fujiwara Takumi , Cao Xiaofan , Srivastava Ramakant , Ramaswamy Ramu V.
Published: July 2002

We compare the photorefractive effect in proton-exchanged (PE) and annealed proton-exchanged (APE) LiNbO3 optical waveguides at the irradiation wavelength of 488 nm. We measure the intensity dependence of the saturated index change, the build-up time constant, and the photorefractive sensitivity in PE and APE waveguides. In APE waveguides the photorefractive sensitivity is about three times that of PE waveguides up to an irradiation intensity of 100 W/cm2. The contribution of the dark conductivity to the photorefractive effect in PE and APE waveguides is found to be dominant in the intensity range used in our experiments.
Intervalence-subband transition in SiGe/Si multiple quantum wells−normal incident detection
Authors: Park J. S. , Karunasiri R. P. G. , Wang K. L.
Published: July 2002

Normal incident infrared absorption is observed in intervalence-subband transition of Si1−xGex/Si multiple quantum wells for the first time. The observed absorption peak wavelength, strength, and broadness are shown to be strongly dependent on the Ge content in the well. The intervalence-subband absorption peak shows up at a shorter wavelength with the beam polarized parallel to the growth plane (normal incidence), compared with the previously reported intersubband transition between two heavy hole subbands, which occurs when the optical field is polarized along the growth direction. The dependence of the absorption peak height with the Ge composition and thus the direct gap energy in the quantum well indicates that the origin of this transition is due to the intervalence-subband transition from the heavy hole ground state to another valence subband. The normal incident detection suggests the convenient fabrication of focal plane infrared detector arrays using Si1−xGex/Si multiple quantum wells.
Electromigration-induced failure in passivated aluminum-based metallizations−The dependence on temperature and current density
Authors: Li C.-Y. , Bo/rgesen P. , Korhonen M. A.
Published: July 2002

A new dynamic picture of electromigration-induced failure in passivated narrow lines allows the prediction of the variation of lifetimes with temperature and current density. According to the model, damage is usually nucleated by thermal stress-induced voiding. Small voids are trapped and grow at grain and phase boundaries. After reaching a critical size, voids then begin to migrate and coalesce, eventually leading to line severance. In most cases this leads to lifetimes varying approximately as the square of the current density j for low and moderate j, and faster for large j. The temperature dependence is determined by a combination of bulk, surface, and grain boundary diffusivities.
Observation and modeling of quasiepitaxial growth of a crystalline organic thin film
Authors: Burrows P. E. , Zhang Y. , Haskal E. I. , Forrest S. R.
Published: July 2002

We directly observe, using the scanning tunneling microscope, a two-dimensional crystal of the organic compound 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA). The surface unit cell dimension is found to be 21.6±2.2 Å by 15.2±1.6 Å, or approximately 20% larger than the bulk unit cell. Furthermore, the organic lattice is oriented with respect to the graphite substrate even though the two lattices are incommensurate. These observations are consistent with reflection high energy electron diffraction measurements, and energy minimization calculations, assuming that the van der Waals bond is the predominant intermolecular force which determines the equilibrium crystal structure. The combination of measurement and theory provides the first step in developing tools for predicting the conditions which lead to quasiepitaxial growth of these technologically important van der Waals solids.
Normal incidence infrared detector using intervalence-subband transitions in Si1−xGex/Si quantum wells
Authors: Karunasiri R. P. G. , Park J. S. , Wang K. L.
Published: July 2002

Normal incidence infrared detection due to intervalence band transitions of holes is demonstrated using Si1−xGex/Si multiple quantum-well structures. Two samples with Ge composition (x) of 30% and 60% are used in this study and broad photoresponse peaks (∼100 meV) at near 3 and 2 μm, respectively, are observed. The peak positions of the photoresponse are in close agreement with those observed in the absorption measurement using a waveguide geometry. The low-temperature photocurrent spectrum for each sample shows that the broad absorption peak at room temperature consists of many peaks due to several transitions. From the calculated energy levels due to different hole bands, we conclude that the transitions are from the heavy-hole ground state to the split-off and continuum states. This principle of normal incidence detection can be readily implemented for focal plane infrared detection in the 3–5 μm (and 8–12 μm) range with potential for monolithic integration with Si signal processing circuits.
Long pulse KrCl excimer laser at 222 nm
Authors: Hueber J-M. , Fontaine B. L. , Bernard N. , Forestier B. M. , Sentis M. L. , Delaporte Ph. C.
Published: July 2002

A long pulse (up to 185 ns FWHM) KrCl laser at λ=222 nm has been achieved by combining x-ray preionization and double discharge (spiker/sustainer) with fast ferrite magnetic switch. A relatively low pumping power (0.5 to 1 MW/cm3) and 25 cm gain length allows a maximum extracted energy of 115 mJ in 135 ns FWHM, with an overall energy efficiency of 0.75%.
Visible photoluminescence in crystallized amorphous Si:H/SiNx:H multiquantum-well structures
Authors: Chen Kunji , Huang Xinfan , Xu Jun , Feng Duan
Published: July 2002

Visible photoluminescence has been observed in crystallized a-Si:H/a-SiNx:H multiquantum-well structures at room temperature. The MQW heterostructures consisting of 72 layers were formed by computer controlled plasma-enhanced chemical-vapor deposition method and then crystallized by Ar+ laser annealing technique. The crystallinity and average grain size of the silicon microcrystals were determined by means of Raman and x-ray diffraction spectroscopy. The crystallized samples with well-layer thickness Ls=40 Å showed an intense photoluminescence which is peaked at 2.1 eV with a full width at half-maximum of 0.25 eV. This is consistent with calculations based on the quantum confinement model.
Nuclear magnetic resonance study on Si-H microstructure in hydrogenated amorphous silicon prepared by diluted-hydrogen and hydrogen-atom-treatment methods
Authors: Hsu Kuo-Chiang , Hwang Huey-Liang
Published: July 2002

Silicon-hydrogen microstructures in hydrogenated amorphous silicon films are characterized by nuclear magnetic resonance (NMR) measurements. Spectral differences are associated with hydrogen incorporation for several novel fabrication methods. It is found that hydrogen dilution of the SiH4/H2 mixture can produce a significant effect on the NMR results and that the NMR spectra tend to show a sharp line shape as the substrate temperature (Ts) is increased to about 300 °C. The hydrogen-atom-treatment method also produces the same effect even at a lower substrate temperature of about 250 °C.
Investigation of rapid-thermal-oxidized porous silicon
Authors: Li K.-H. , Tsai C. , Campbell J. C. , Hance B. K. , White J. M.
Published: July 2002

We report that the photoluminescence of porous Si that was quenched by low-temperature thermal annealing was restored by further annealing in an oxygen atmosphere at high temperature (750 °C≤T≤1100 °C). The intensity of the photoluminescence recovered to near the as-anodized value and the peak wavelength was red shifted by approximately 100 nm. The oxidized porous Si has been found to have lower resistance and higher photoelectric efficiency than as-anodized material.
Epitaxial growth kinetics on patterned substrates
Authors: Haider N. , Wilby M. R. , Vvedensky D. D.
Published: July 2002

The temperature dependence of the growth kinetics on V-grooved substrates is studied by computer simulation, with attention focused upon the evolution of the morphology. We find a distribution of growth rates on GaAs(001) at high temperatures due to surface diffusion of adatoms from one facet to the other. However, at low temperatures, where surface migration processes are less important, growth on these substrates proceeds in a shape-preserving manner. Comparison with scanning microprobe reflection high-energy electron-diffraction intensity oscillations on GaAs(001) near (111) surfaces shows that our results are in qualitative agreement with observed behavior.
Time resolved electroluminescence in hydrogenated amorphous silicon
Authors: Wang Keda , Han Daxing , Kemp Mathieu , Silver Marvin
Published: July 2002

The electroluminescence lifetime distribution of a-Si:H is measured. We find that the distribution is double peaked. The first peak occurs at 10−6 s independent of temperature. The second peak changes from 10−3 to 10−6 s with increasing temperature. A model including the Coulomb interaction between electrons and holes and transport limited recombination is discussed.
Stochastic model for thin film growth and erosion
Authors: Stearns D. G.
Published: July 2002

A linearized, stochastic theory of thin film growth and erosion is presented to describe the evolution of surface roughness in the case of good layer formation far from equilibrium, as is generally found in energetic growth techniques such as ion-assisted vapor deposition. The variation of the power spectral density and root-mean-square roughness is studied for growth on smooth and rough substrates.
Modification of the microstructure in epitaxial erbium silicide
Authors: Kaatz F. H. , Graham W. R. , Van der Spiegel J.
Published: July 2002

Several growth techniques in the formation of thin (<100 Å) epitaxial rare-earth silicide films have been investigated. Low temperature processing of a thin (3–4 Å) template layer results in distinct changes of the low energy electron diffraction patterns, with a 1×1 pattern occurring below 400 °C and a √3 ×√3 pattern occurring for higher temperature anneals. We present corresponding real and reciprocal space data showing that an appropriate template will produce structurally continuous films with no evidence of a vacancy superstructure that can occur in films prepared under less well-controlled conditions.
Gamma-rays irradiation: An effective method for improving light emission stability of porous silicon
Authors: Fu J. S. , Mao J. C. , Wu E. , Jia Y. Q. , Zhang B. R. , Zhang L. Z. , Qin G. G. , Wui G. S. , Zhang Y. H.
Published: July 2002

We report a study on gamma irradiated porous Si. The electron paramagnetic resonance study on porous Si irradiated by gamma rays shows that the observed signals come from an intrinsic defect, a Si dangling bond, at the interface of Si/SiOx in porous Si. The photoluminescence measurements show that the gamma irradiation not only increases the intensity of the photoluminescence but also greatly improves its stability. The spectra of the Fourier transform infrared absorption show that the gamma irradiation is an effective method for accelerating oxidation of porous Si. All experimental results can be explained by the increase of the oxidation layer thickness which decreases the nonradiative recombination probability of electron-hole pairs.
Photoluminescence spectra of Zn3P2-Cd3P2 thin films
Authors: Nayak A. , Rao D. R.
Published: July 2002

Photoluminescence (PL) spectra of electron beam evaporated (ZnxCd1−x)3P2 thin films with composition (x) equal to 0.0, 0.2, 0.4, 0.5, 0.8, and 1.0 have been recorded at 100 K. The radiative transitions associated with the different PL peaks are correlated considering the distribution of native defects which act either as acceptor (A)- or donor (D)-like centers. In the case of (Zn0.5Cd0.5)3P2 films, which showed some satellite structure, the emission at 0.92 eV is related to the DA pairs (associated phosphorous interstitials and vacancies) with the distance of separation estimated in the range of 10–30 Å.
Electroluminescence from porous silicon with conducting polymer film contacts
Authors: Li Kun-hsi , Diaz Dennis C. , He Yuesong , Campbell Joe C. , Tsai Chaochieh
Published: July 2002

Visible electroluminescence with a peak wavelength of 6300 Å is observed from forward-biased porous Si p-n diodes with conducting polymer contacts. These devices have brighter electroluminescence than similar devices with thin, gold-film contacts. Electroluminescence is also observed from conducting polymer/n-porous Si diodes.
Femtosecond studies of interfacial electron-hole recombination in aqueous CdS colloids
Authors: Zhang J. Z. , O’Neil R. H. , Roberti T. W.
Published: July 2002

We report the measurements of the electron-hole recombination rate in aqueous CdS colloids on the femtosecond time scale. A fast 2-ps decay and a slower 45-ps decay have been observed, and the decay dynamics are found to be very sensitive to the excitation laser intensity. Geminate electron-hole recombination, responsible for the 45-ps decay, dominates the decay process at low excitation intensities, while nongeminate recombination, accounting for the 2-ps decay, becomes more important at high excitation intensities.
Near field measurements of optical channel waveguides and directional couplers
Authors: Choo Ahn Goo , Jackson Howard E. , Thiel Udo , De Brabander Gregory N. , Boyd Joseph T.
Published: July 2002

Near field microscopy is used to investigate the guided mode intensity distribution of optical channel waveguides and directional couplers with subwavelength spatial resolution. The directional coupler consisted of two single mode optical ridge channel waveguides formed with silicon nitride deposited on a lower cladding layer of SiO2 on a silicon substrate. A near field measurement of the guided mode intensity profile in the transverse direction parallel to the waveguide surface was performed across one of the optical channel waveguides. These variations are compared with model calculations. Similar transverse measurements of light propagating through a directional coupler were performed at many locations along the coupler, providing a view of the evolution of optical power transfer.
Selective growth of zinc-blende, wurtzite, or a mixed phase of gallium nitride by molecular beam epitaxy
Authors: Cheng T. S. , Jenkins L. C. , Hooper S. E. , Foxon C. T. , Orton J. W. , Lacklison D. E.
Published: July 2002

We report on the growth of GaN with a zinc-blende, wurtzite, or a mixed phase structure on (001)GaP and (001)GaAs substrates by a low-temperature modified molecular beam epitaxy technique. By systematically varying the incident arsenic overpressure, films grown at a moderate substrate temperature of ≊620 °C show predominately wurtzite α-GaN, zinc-blende β-GaN, or a mixed phase of the two. Films containing only the metastable phase β-GaN were achieved by using a relatively high growth temperature of ≊700 °C and with an arsenic overpressure of ≊2.4×10−5 Torr. X-ray diffraction measurements indicate an improved crystalline quality for the layers grown at ≊700 °C compared to those grown at ≊620 °C as evident by a narrower full width at half-maximum of 35 min for β-GaN, which is among the narrowest reported to date.
Apparatus for programmed high-performance purification of surfactant solutions
Authors: Lunkenheimer K. , Pergande H.-J. , Krüger H.
Published: July 2002

Generally, surfactants contain trace impurities that will falsify their adsorption properties enormously. To carry out reliable experiments with surfactant solutions necessitates removing those trace impurities beforehand. A programmed apparatus for removing surface-active trace impurities from surfactant solutions has been constructed and tested. It takes advantage of the contaminants’ stronger surface activity and considerably lower content in comparison with the main surfactant component. Surface-active material of the solution to be purified is allowed to adsorb at its surface. After considerable reduction of the solution surface area, the adsorbed material is sucked off from the surface in a definite manner by using a fine capillary. The single operating steps are repeated periodically and automatically until the solution reaches the state of ‘‘surface chemical purity.’’ The apparatus can be utilized for a wide range of different conditions given by the individual surfactant properties simply by changing the operating parameters. The instrument favorably and effectively provides that peculiar grade of surfactant purity necessary for all kinds of fundamental surfactant research and characterization.
Differential polarization microscope using an image dissector camera and phase-lock detection
Authors: Beach D. A. , Wells K. S. , Husher F. , Bustamante C.
Published: July 2002

A polarization modulation microscope designed to detect and spatially resolve the distribution of optically anisotropic domains in microscopic objects is described. An image dissector camera is used as the detection device. The polarization of the light is modulated by means of a photoelastic modulator and a synchronous demodulation amplifier (lock-in) is utilized to obtain the difference image between the images formed using two orthogonal forms of the incident polarization on the sample. Preliminary results are described for the linear dichroism imaging measurements of polymerized hemoglobin (HbS) in red blood sickle cells. The present limitations of this design are discussed along with various strategies to improve its performance.