bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-aligned polycrystalline silicon thin-film transistors by laser implantation
Authors: Coxon P. , Lloyd M. , Migliorato P.
Published: July 2002

Polycrystalline silicon thin-film transistors have been fabricated using photochemical doping with phosphorus from the gas phase by ultraviolet laser. The results obtained show the technique to be a viable alternative to ion implantation for applications such as three-dimensional very large scale integrated circuits.
Observations of subpicosecond dynamics in GaAlAs laser diodes
Authors: Stix Michael S. , Kesler Morris P. , Ippen Erich P.
Published: July 2002

We present results of pump-probe experiments on GaAlAs laser diodes indicating a 0.9-ps relaxation time associated with the device transmission. Subpicosecond, tunable near infrared pulses obtained by fiber compression were used to carry out the experiments. The data strongly support a model in which a nonequilibrium carrier temperature in the active layer is responsible for the observed signal.
Hydrogenated amorphous silicon formation by flux control and hydrogen effects on the growth mechanism
Authors: Toyoda H. , Sugai H. , Kato K. , Yoshida A. , Okuda T.
Published: July 2002

The composition of particle flux to deposit hydrogenated amorphous silicon films in a glow discharge is controlled by a combined electrostatic-magnetic deflection technique. As a result, the films are formed firstly without hydrogen ion flux, secondly by neutral flux only, and thirdly by all species fluxes. Comparison of these films reveals the significant role of hydrogen in the surface reactions. Hydrogen breaks the Si–Si bond, decreases the sticking probability of the Si atom, and replaces the SiH bond by a SiH2 bond to increase the hydrogen content of the films.
Edge effects on foil fuses
Authors: Waisman E. M. , Kennedy E. M. , Parks D. E.
Published: July 2002

We investigate the edge effect on foil fuses in a cylindrical enclosure containing a tamping medium. This type of fuse is being considered for use in microsecond switching of high power electromagnetic pulses. By using the exact magnetostatic solution for axial current lines in a cylindrical enclosure, we find a circuitlike model for the foil fuse and the driving external circuit. The foil resistivity is a function of the joule heat per unit volume dissipated at each position along the width of the foil. In the extreme example given in this letter, we find that the strong edge effects observed at the beginning of the pulses ‘‘heal’’ faster than the time it takes for the foil to switch and hence, edge effects, even in such cases are not important.
Pulsed laser treatment of diamondlike carbon films
Authors: Prawer S. , Kalish R. , Adel M.
Published: July 2002

Conducting (10−1 Ω cm) pathways have been directly written into an insulating (106 Ω cm) diamondlike carbon film using pulsed laser irradiation (0.53 μm). The morphological and structural changes caused by the laser suggest that the film has been transformed into a form of graphite preserving some of the diamondlike properties of the original coating.
Interelement coupling in gain-guided diode laser arrays
Authors: Hohimer J. P. , Hadley G. R. , Owyoung A.
Published: July 2002

Below-threshold studies of an injection-locked gain-guided diode laser array show a far-field emission pattern with several lobes whose angular widths decrease with increasing frequency of the injected radiation. The concurrent increase in the far-field emission angle with the frequency of the injected radiation provides strong evidence that the interelement coupling in a gain-guided diode laser array depends upon the tilt of the wave front in the array cavity. These results provide insight into the coupling mechanism that dominates gain-guided array behavior and strongly suggest that these devices should be viewed as perturbed broad-area devices in which plane waves are undergoing multiple reflections between facets. This contrasts sharply with the coupled-mode picture, which is more appropriate for index-guided arrays.
Low-loss optical waveguides made with molecular beam epitaxial In0.012Ga0.988As and In0.2Ga0.8As-GaAs superlattices
Authors: Das Utpal , Bhattacharya Pallab K. , Dhar Sunanda
Published: July 2002

We demonstrate for the first time low-loss optical guiding in In-doped GaAs. Ridge waveguides are made with single In0.012Ga0.988As ternary layers and In0.2Ga0.8As-GaAs superlattices. Attenuation constants of ∼1.3 dB/cm are measured and the principal loss mechanism is identified to be scattering at the ridge walls. It is expected that improved fabrication techniques will lead to guides with attenuation ≤0.5 dB/cm.
Performance of a hydrogen uranyl phosphate—carbon double-layer solid capacitor
Authors: Pham-Thi M. , Adet Ph. , Velasco G. , Colomban Ph.
Published: July 2002

A mixture of commercially available carbon black powders and hydrogen uranyl phosphate (HUP) precipitate can be used as the electrode material for miniaturized double-layer capacitors. A solid cell of C-HUP‖HUP‖C-HUP has a capacitance of 1 F which, given the device area and thickness of 0.8 cm2 and 0.2 cm respectively, corresponds to an energy density of more than 5 J/cm3. The charge×voltage factor is higher than 5×10−6 s and the working voltage is over 1.6 V. The leakage current is lower than 3 μA at room temperature. The electrolyte can be operated up to about 120 °C if the device is hermetically sealed.
Shifts in the flatband voltage of metal-oxide-silicon structure due to iodine in SiO2
Authors: Krusin-Elbaum L. , Sai-Halasz G. A.
Published: July 2002

We report the observation of positive shifts in the flatband voltage of metal-oxide-silicon structure as a consequence of iodine presence in the oxide. The positive shifts remain stable after thermal processing cycles, typical to very large scale integration, as well as under temperature-voltage stress. This flatband behavior is obtained by direct implantation of iodine into SiO2 and subsequent anneal in the inert ambient. In contrast, if Si is first implanted with iodine and then oxidized, the resulting flatband shifts are stable, but negative. The shifts of both polarities occur without significant increase in the interface state density. In each case, they are correlated with the presence of iodine in the oxide as determined by secondary ion mass spectrometry.
〈100〉 and 〈111〉 textures in unseeded, strip heater recrystallized silicon-on-insulator
Authors: Lee El Hang
Published: July 2002

The graphite strip heater technique was used to obtain strongly preferred 〈100〉 or 〈111〉 textures for thin-film silicon recrystallized on amorphous oxide and nitride substrates. Whereas 〈100〉 textures have been obtained in the liquid phase, 〈111〉 textures have been obtained in the solid phase at near-melting temperatures. Films of 〈100〉 orientation displayed the usual sub-boundaries, but 〈111〉 films revealed grainy textures mixed with pond ripple features. The lateral epitaxy model and the birth and spread model have been useful in distinguishing the two growth mechanisms. Films on Si3N4 substrates had characteristics similar to those on SiO2 substrates.
Raman microprobe analysis during the direct laser writing of silicon microstructures
Authors: Magnotta Frank , Herman Irving P.
Published: July 2002

Raman microprobe techniques are used for the first time as a real-time probe during local direct laser writing and also as an in situ probe after writing. The Stokes–Raman emission observed during pyrolytic deposition of micron-dimension structures of silicon on germanium and vitreous carbon substrates is found to be weaker, more asymmetric, and to peak at a smaller Raman shift than the corresponding spectrum of the same structure similarly probed in situ after deposition. Results of detailed post-deposition Raman analysis of these silicon microstructures are presented and compared to the Raman spectra of oven-heated silicon. Potential applications of these techniques are discussed.
cw helium-neon Raman laser
Authors: Assendrup J. , Grover B. , Hall L. , Jabr S.
Published: July 2002

Continuous lasing has been observed at 650 nm with a helium-neon electrical discharge placed in an ultrahigh finesse optical cavity. This new lasing line is attributed to a Stokes–Raman process between the 1s5 and 1s4 electronic states of neon atoms pumped by the 632.8-nm neon lasing line. A gain calculation based on a near-resonant stimulated electronic Raman process predicts a lasing threshold for the 650-nm line near that measured. Lasing output power was measured as a function of discharge current and helium-neon gas pressure for the pump line and for the Stokes line.
Greatly reduced losses for small-radius bends in Ti:LiNbO3 waveguides
Authors: Korotky S. K. , Marcatili E. A. J. , Veselka J. J. , Bosworth R. H.
Published: July 2002

We report the demonstration of a new concept that permits the fabrication of low-loss Ti:LiNbO3 waveguide bends with radii much smaller than previously achieved.
Acceleration sensitivity of surface acoustic wave resonators
Authors: Tiersten H. F. , Stevens D. S. , Weglein R. D.
Published: July 2002

The acceleration sensitivity of acoustic surface wave resonators (and delay lines) on quartz substrates supported uniformly at the base has been calculated. For normal acceleration the calculated sensitivity is almost two orders of magnitude lower than the lowest published measurements. For in-plane acceleration the calculated sensitivity is comparable to the best published measurements. This causes us to believe that uniform base support has not been realized in practice and, in fact, may be impossible to achieve. For normal acceleration and nonuniform base support the calculations indicate that increasing the thickness of the substrate decreases the acceleration sensitivity. Experimental verification of this is presented. However, for in-plane acceleration the calculations indicate that increasing the thickness of the substrate increases the acceleration sensitivity.
Corrections to the rate equation approximation for dynamic considerations in a semiconductor laser
Authors: Vahala Kerry
Published: July 2002

Corrections to the rate equation approximation are derived and applied to a semiconductor laser. Whereas these corrections do not affect the operating point of the device, they do alter the dynamic operation. To first order the correction produces a renormalization of familiar dynamic parameters. This renormalization, in turn, leads to a 20% correction to the field spectrum linewidth formula.
Neutron induced conductivity in trans-polyacetylene
Authors: Butler M. A. , Ginley D. S. , Bryson J. W.
Published: July 2002

Neutron induced conductivity is reported for the first time in an organic conductor. The induced conductivity is linear in total neutron flux over several decades and Seebeck measurements indicate that the conductivity is p type. Optical measurements show that acetonitrile plays an important role in the conductivity changes. The implication of these results for conduction mechanisms in polyacetylene is discussed. These results demonstrate a new method for producing uniform low doping in organic conductors and a potential mechanism for a new, fast neutron dosimetry.
Selective-area epitaxy of GaAs through silicon dioxide windows by molecular beam epitaxy
Authors: Hong J. M. , Wang S. , Sands T. , Washburn J. , Flood J. D. , Merz J. L. , Low T.
Published: July 2002

Optical-quality GaAs films were successfully grown by molecular beam epitaxy (MBE) through SiO2 insulator windows on GaAs (100) substrates, thus making this selective-area epitaxy applicable to the fabrication of GaAs optoelectronic integrated circuits. The photoluminescence spectra at 2.2 K consist of several exciton peaks near 820 nm and broader acceptor-related peaks centered at approximately 830 nm. The spectra are comparable to those observed in high quality planar MBE GaAs grown in other laboratories. The luminescence intensity from the epitaxial layer above the windows is shown by cathodoluminescence to be much higher than that from the polycrystalline GaAs deposited on top of SiO2. From transmission electron microscopy and x-ray diffractometry it is found that the GaAs grains on the SiO2 grow with their (111) planes preferentially parallel to the SiO2 surface.
Hot-electron induced interface traps in metal/SiO2/Si capacitors: The effect of gate-induced strain
Authors: Hook Terence B. , Ma T. P.
Published: July 2002

It is shown that the generation of interface traps by Fowler–Nordheim injection, like those generated by ionizing radiation, is a function of the mechanical strain at the silicon-silicon dioxide interface. However, because of the current enhancement at the edge of a metal-oxide-semiconductor gate when the gate serves as the hot-electron injector, this phenomenon may only be evident when the device is stressed with the gate biased positively. It is also shown that the capture rate of electrons in the silicon dioxide depends on the strain in the film.
X-ray photoelectron spectroscopy on surface oxidation of silicon by some cleaning procedures
Authors: Wong C. Y. , Klepner S. P.
Published: July 2002

X-ray photoelectron spectroscopy was used to analyze silicon surfaces after some standard cleaning procedures. Buffered hydrofluoric acid (BHF), RCA clean, and back door etch (BDE) result in less than one monolayer of suboxide coverage. RCA clean without BHF, heat treatment in nitrogen ambience, and prolonged explosure to air at room temperature all result in thicker self-passivating suboxides. Wafers with arsenic ion implantation yield thicker oxides even immediately after BHF or BDE clean. Arsenic ion implantation also causes an additional chemical shift of 0.3 eV on the Si 2p peak. The possible causes for these observations are discussed.
Measurements of x-ray dose required for multiatmospheric pressure CO2 laser discharge
Authors: Midorikawa K. , Okada M. , Tashiro H. , Namba S.
Published: July 2002

We have investigated the preionization characteristics of x ray for a transversely excited, multiatmospheric pressure CO2 laser amplifier with an active volume as large as 225 cm3. The x-ray dose required for uniform avalanche discharge is measured as a function of pressure up to 10 atm. The dependence of the input energy density of the main discharge on the x-ray dose is also investigated.
Design of a Bragg cavity for a millimeter wave free-electron laser
Authors: Wang M. C. , Granatstein V. L. , Kehs R. A.
Published: July 2002

This letter concerns a design of a Bragg cavity for TM modes that can be used with a free-electron laser (FEL) or other electron beam generator. If the corrugated wall in the FEL section meets the Bragg condition, the distributed feedback mechanism can function like mirrors in the usual laser cavity; however, the Bragg cavity eliminates the dead space between the interaction region and the reflectors so that it is a preferred design where the pulse duration of the electron beam is limited. The calculations indicate that high reflection coefficients that correspond to high cavity Q factor can be obtained if we carefully choose the parameters of the corrugated wall, such as period, amplitude, and length. Finally, we discuss factors to be considered in the design of a Bragg cavity for a FEL based on an intense relativistic electron beam and an electromagnetic pump wave.
Low current threshold AlGaAs visible laser diodes with an (AlGaAs)m(GaAs)n superlattice quantum well
Authors: Hayakawa T. , Suyama T. , Takahashi K. , Kondo M. , Yamamoto S. , Hijikata T.
Published: July 2002

Very short period (AlGaAs)m(GaAs)n superlattices (SL’s) have been used for single quantum wells (SQW’s) of visible laser diodes emitting in the wavelength region of 680–785 nm for the first time. The threshold current of graded-index separate-confinement-heterostructure (GRIN SCH) lasers with SL SQW’s is lower than that of lasers with AlGaAs alloy SQW’s. The ridge-waveguide structure GRIN SCH SL SQW laser emitting at 785 nm shows the low threshold current of 11 mA.
Electron-pumped high-efficiency semiconductor laser
Authors: Daneu V. , DeGloria D. P. , Sanchez A. , Tong F. , Osgood R. M.
Published: July 2002

We report on an efficient semiconductor laser array pumped by a high-energy electron gun. A peak power of 350 kW in a 4-ns pulse has been measured from a 25-mm2 CdS laser. For the materials studied (CdS, ZnxCd1−xS, and ZnSxSe1−x), laser action has been obtained in the blue-green region of the spectrum.
Optically pumped mode-locked multiple quantum well laser
Authors: Valk B. , Salour M. M. , Munns G. , Morkoç H.
Published: July 2002

We report the first optically pumped mode-locked Al0.3Ga0.7As/GaAs multiple quantum well (MQW) laser in external cavity. The MQW structure with a total thickness of 5 μm was grown by molecular beam epitaxy on a Si-doped GaAs substrate and was synchronously pumped by a mode-locked Kr+ laser (82 MHz) at 647.1 nm. The MQW laser emitted 10 ps pulses at 8085 Å with peak powers as high as 6 W. The demonstrated MQW laser combines desirable properties of quantum wells with advantages of an external cavity, such as specific band-gap design with high beam quality and the possibility of intracavity tailoring of the laser beam.
Vapor phase epitaxy of InP using flow modulation
Authors: Wang P. J. , Wessels B. W.
Published: July 2002

We report the first preparation of indium phosphide using flow modulation techniques in the hydride vapor phase epitaxial system. A conventional single barrel reactor was used. Layer growth rates as low as 25 Å/cycle were demonstrated. Room-temperature carrier concentrations for the unintentionally doped InP of 5×1015 cm−3 and electron mobilities of 3650 cm2/V s were achieved.
Determination of transport coefficients in high mobility heterostructure systems in the presence of parallel conduction
Authors: Syphers D. A. , Martin K. P. , Higgins R. J.
Published: July 2002

The effect of a parasitic parallel conducting layer on the measurement of longitudinal and transverse magnetoresistances of a high mobility two-dimensional (2D) electron gas in modulation-doped heterostructures is considered. A circuital analysis which takes into account the effect of circulating currents at the Hall contacts is presented, and previous descriptions of this situation are shown to be inapplicable. The resultant equations correctly predict the behavior of the longitudinal and transverse magnetoresistances at both high and low magnetic fields, and correlate well with the measured values. They also allow one to accurately determine the 2D mobility and density as well as the parallel layer resistivity.
Characterization of InGaAsP surface corrugation used for distributed feedback lasers by means of Raman spectroscopy
Authors: Kubo Minoru , Koga Keisuke , Ogura Mototsugu , Kohiki Shigemi
Published: July 2002

Thermally deformed surface corrugations on both an InP substrate and an InGaAsP layer have been analyzed by means of x-ray photoelectron spectroscopy and laser Raman spectroscopy. From the spectra of the deformed surface corrugations on an InP substrate on which a GaAs wafer was placed during its heat treatment, it has been found that material formed in the grooves is an InGaAsP alloy single crystal.
Measurement of air gap thickness underneath an opaque film by pulsed photothermal radiometry
Authors: Tam A. C. , Sontag H.
Published: July 2002

We describe an experimental method to detect and measure a thin air gap between an opaque film and a substrate. The method is pulsed photothermal radiometry with signal shape analysis at suitable delayed times. This relies on the use of a short light pulse to heat up the surface of the opaque film by∼10 °C, and detecting the infrared thermal emission from the surface as a function of time for a sufficiently long time. A numerical computation as well as an analytical approximation is developed to explain the dependence of the photothermal radiometry signal shape on the air gap thickness in the range of ten to hundreds of microns. Our work has applications not only for detecting subsurface air gaps and delaminations, but also for measuring the thermal resistance between layers for nondestructive characterization of adhesion bond strengths.
Experimental demonstration of longitudinal wiggler free-electron laser
Authors: Shraga I. , Goren Y. , Leibovitch C. , Eckhouse S. , Gover A.
Published: July 2002

The lowbitron—a longitudinal wiggler beam interaction device—as a novel source of submillimeter wave radiation was proposed and analyzed theoretically by McMullin and Bekefi [Phys. Rev. A 25, 1826 (1982)]. This letter reports the first experimental measurements of lowbitron radiation obtained with a 740-kV, 400-A electron beam. The measured power spectra in the W-band range for different wiggler field periods agree with the lowbitron interaction theory. They match the intersection points of the shifted fast cyclotron wave dispersion relation ω−(k+kw)v∥−Ω0/γ=0 and the TE01 electromagnetic waveguide mode.
Evidence for excitonic decay of excess charge carriers in high quality GaAs quantum wells at room temperature
Authors: Bimberg D. , Christen J. , Werner A. , Kunst M. , Weimann G. , Schlapp W.
Published: July 2002

A comparative study is presented of the room-temperature decay of laser excited microwave photoconductivity and of cathodoluminescence of high quality GaAs multiple quantum wells grown by molecular beam expitaxy and of high quality GaAs liquid phase epitaxial layers. The results from both experiments are in quantitative agreement and prove that carrier recombination in multiple quantum wells occurs via excitonic decay channels at excess carrier densities less than 1017 cm−3. In contrast, band-band recombination prevails in three-dimensional material.
Silicon nitride films grown on silicon below 300 °C in low power nitrogen plasma
Authors: Paloura E. , Nauka K. , Lagowski J. , Gatos H. C.
Published: July 2002

Device quality silicon nitride films ranging in thickness down to 30 Å were successfully grown on silicon at temperatures below 300 °C in a radio frequency (rf) nitrogen plasma. The growth rate was controlled in the range 5–100 Å/h by changing nitrogen pressure, rf power, and growth temperature. Electron microscopy and Auger spectroscopy showed that the films were amorphous, microcrack-free, close to stoichiometry Si3N4, and formed a sharp interface with the Si substrate. The breakdown voltage of Al-Si3N4-Si capacitors was about (1.3±0.2)×107 V/cm and the typical density of the leakage current was below 3×10−7 A/cm2 at 5 V bias for films 70 Å thick.
Effect of active layer thickness on differential quantum efficiency of 1.55 μm InGaAsP buried crescent injection lasers
Authors: Cheng W. H. , Renner D.
Published: July 2002

Comprehensive measurements of the differential quantum efficiency (ηd ) dependence on the active layer thickness (d) for 1.55 μm InGaAsP buried crescent (BC) injection lasers are presented. The results show that ηd increases rapidly as d decreases. The strong d dependence of ηd in 1.55 μm BC lasers suggests that a large value of optical absorption in the active region is one of the dominant mechanisms which determines the ηd of these InGaAsP lasers. The likely cause for large absorption in the active region is intervalence band absorption (IBA). Thus, by reducing the active layer thickness and hence, the effect of IBA, we have obtained 1.55 μm BC lasers which exhibit threshold currents as low as 9 mA at 25 °C, ηd over 45%, and high-temperature operation up to 100 °C.
Microstructure of magnetron co-sputtered CoCr thin films
Authors: Hong M. , Nakahara S. , van Dover R. B. , Boone T.
Published: July 2002

Magnetic CoCr films deposited on fused quartz substrates were prepared by the dual-gun magnetron co-sputtering technique. The cross-section transmission electron microscopy studies showed the establishment of a textured columnar structure of the hcp CoCr films. Furthermore, the columnar grains were found to nucleate at the surface of the substrates and grow with the c axis parallel to the film-normal direction. No initial layer of randomly oriented small equiaxed grains was observed.
Integrated external cavity laser
Authors: Dutta N. K. , Cella T. , Piccirilli A. B. , Brown R. L.
Published: July 2002

The fabrication and performance characteristics of single frequency integrated external cavity lasers of the coupled cavity type and the distributed Bragg reflector type are described. The active cavity section of these devices utilizes the double channel planar buried heterostructure scheme for current confinement. The lasers emit near 1.55 μm. The threshold current of these lasers is in the range 70–120 mA. cw linewidth of 7 MHz has been obtained for a 2-mm-long laser at an output power of 3 mW. We believe lasers with longer external cavity should exhibit lower cw linewidths.
Electrical and optical properties of sputtered TiNx films as a function of substrate deposition temperature
Authors: Thorpe T. P. , Qadri S. B. , Wolf S. A. , Claassen J. H.
Published: July 2002

Characterization results are given for a set of TiNx films grown on sapphire substrates at temperatures between 140 and 850 °C. A relationship between resistivity and spectral reflectivity is established, with highest reflectivities and lowest resistivities observed for the highest substrate temperatures. It is found that grain orientation within the films is random except at the highest deposition temperature where a preferred 100 orientation is indicated. Measurement of the superconducting transition temperature, lattice parameter, and microcrystalline texture of each film has been made and correlated with the stoichiometry, electrical, and optical properties.
Photoluminescence studies of the effects of interruption during the growth of single GaAs/Al0.37Ga0.63As quantum wells
Authors: Miller R. C. , Tu C. W. , Sputz S. K. , Kopf R. F.
Published: July 2002

Low-temperature excitation and photoluminescence spectra are described for single GaAs/Al0.37Ga0.63As quantum wells grown by molecular beam epitaxy with and without a 2-min interruption of growth at the heterointerfaces. The spectra from samples grown with interruption include well-resolved multiple sharp peaks which are due to changes in well thickness of one monolayer and to bound excitons. These peaks are as narrow as 1.0, 1.7, and 6.0 meV for single wells of width 57, 28, and 17 Å, respectively.
Surface-emitting GaAlAs/GaAs linear laser arrays with etched mirrors
Authors: Yang J. J. , Sergant M. , Jansen M. , Ou S. S. , Eaton L. , Simmons W. W.
Published: July 2002

Surface-emitting GaAlAs/GaAs linear laser arrays are fabricated using the ion milling technique. Low threshold current and differential quantum efficiency comparable to these of the cleaved device are obtained.
Epitaxial growth of β-SiC thin films on 6H α-SiC substrates via chemical vapor deposition
Authors: Kong H. S. , Glass J. T. , Davis R. F.
Published: July 2002

Epitaxial films of cubic β-SiC(111) have been grown via chemical vapor deposition at 1683 K on (0001) substrates of hexagonal 6H α-SiC. Optical microscopy of the surface indicated that a decrease in the ratio of the sum of the C and Si source gases to the H2 carrier gas changed the crystallization behavior from polycrystalline to monocrystalline. Cross-sectional transmission electron microscopy showed almost no line or planar defects at the substrate/film interface and very few defects within the bulk of the film.
Ohmic contact control in modulation-doped gallium arsenide field-effect transistors
Authors: Christou A. , Efthimiopoulos T. , Hatsopoulos Z.
Published: July 2002

Modulation-doped field-effect transistor structures grown by molecular beam epitaxy were excimer laser annealed at a wavelength of 248 nm and energy density of 75–160 mJ/cm2. A transconductance of over 100 mS/mm was obtained. Source resistance was minimized at 0.8–1.0 Ω mm. The energy density threshold for interdiffusion is 90 mJ/cm2.
Transverse junction stripe laser with a lateral heterobarrier by diffusion enhanced alloy disordering
Authors: Yang Y. J. , Lo Y. C. , Lee G. S. , Hsieh K. Y. , Kolbas R. M.
Published: July 2002

We report the first cw, room-temperature multiple quantum well transverse junction stripe laser (MQW TJS) with an alloy disordered heterobarrier. The addition of a lateral heterobarrier by zinc diffusion enhanced alloy disordering reduces the laser threshold by a factor of 3 compared to standard transverse junction stripe lasers processed simultaneously. The reduction in threshold and excellent single mode performance of the MQW TJS are attributed to the superior carrier and optical confinement of a single heterojunction compared to a homojunction. We demonstrate for the first time lateral injection in a multiple quantum well where the diffused junction plays an active (not passive) role in the injection process and that the transition region between complete disorder and no disorder forms the active region of the laser.
InGaAs/InP superlattice avalanche photodetectors grown by gas source molecular beam epitaxy
Authors: Temkin H. , Panish M. B. , Chu S. N. G.
Published: July 2002

Preparation and performance of separate avalanche and multiplication superlattice photodiodes are reported. The absorbing region of these devices consists of up to 100 InGaAs quantum wells separated by InP barriers grown by gas source molecular beam epitaxy. The well size varies from 50 to 20 Å with very well-resolved exciton structures visible at room temperature. With the p-n junction displaced into the InP layer, leakage currents as low as 0.1 nA are obtained at unity gain bias of 20 V. dc avalanche gain of up to 280 and rf gain of 20 are observed at a bias of 38 V.
Proposal for superstructure based high efficiency photovoltaics
Authors: Wagner M. , Leburton J. P.
Published: July 2002

A novel class of cascade structures is proposed which features multijunction upper subcells. These will be referred to as superstructure high efficiency photovoltaics (SHEP). The additional junctions enhance spectral response and improve radiation tolerance by reducing bulk recombination losses. This is important because ternary III-V alloys, which tend to have short minority-carrier diffusion lengths, are the only viable materials for the high band-gap upper subcells required for cascade solar cells. Realistic simulations of AlGaAs SHEP’s show that one sun AM0 efficiencies in excess of 26% are possible.
Relativistic trajectory equations for charged particles in general orthogonal curvilinear coordinates
Authors: Szilagyi M.
Published: July 2002

The relativistic trajectory equations are given in orthogonal curvilinear coordinates for charged particles moving in arbitrary electrostatic and magnetic fields without restrictions. The trajectory equations for Cartesian and cylindrical coordinates are presented as special cases.
Far-infrared study of alloying in the HgTe-CdTe superlattice
Authors: Perkowitz S. , Rajavel D. , Sou I. K. , Reno J. , Faurie J. P. , Jones C. E. , Casselman T. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

The far-infrared reflectivity spectra of three HgTe-CdTe superlattices from two sources [HgTe/CdTe thicknesses (Å/Å): 64/26, 7/35, 32/57] have been measured at 300, 77, and 6 K. Analysis of transverse optical phonon structure between 80 and 180 cm−1 with different alloying models shows that the first of these superlattices contains HgTe and CdTe with no evidence of significant mixing, whereas the others contain HgTe and homogeneous Hg1−xCdxTe. An earlier study of the HgTe-CdTe band gap also indicated homogeneous alloying. The reflectivity data were analyzed with a superlattice dielectric function which is shown to be valid in the far infrared.
In/GaAs reaction: Effect of an intervening oxide layer
Authors: Ding J. , Washburn J. , Sands T. , Keramidas V. G.
Published: July 2002

The effects of a thin (∼1.3 nm) intervening native GaAs oxide interface layer on the In/GaAs reaction have been investigated by comparing the reactions of In on GaAs substrates with the native oxide present or desorbed. Transmission electron microscopy of cross-sectional samples reveals that the thin native oxide layer, when present, disrupts the In/GaAs orientation relationship in as-deposited samples and prevents an extensive reaction between In and GaAs at 350 °C. These data also show that the In/GaAs reaction at 350 °C proceeds by dissolution of the GaAs substrate into the molten In followed by the subsequent nucleation and growth of epitaxial In1−xGaxAs particles with x≤0.2 or x≥0.8 only, indicating immiscibility. The In1−xGaxAs/GaAs interfaces are found to be structurally and compositionally abrupt to within ∼3 nm. The effects of the interfacial native oxide on the In/GaAs reaction and the suggested presence of an InAs-GaAs miscibility gap have implications for the fabrication of In/GaAs ohmic contacts by thermal reaction.
Deformation-free overgrowth of reactive ion beam etched submicron structures in InP by liquid phase epitaxy
Authors: Schilling M. , Wünstel K.
Published: July 2002

Submicron grating patterns written by electron beam lithography are transferred into InP substrates by reactive ion beam etching (RIBE) using an Ar/O2 gas mixture. Trapezoidal grating structures with a depth of 0.15 μm are generated. The influence of the preheating cycle prior to liquid phase epitaxy (LPE) on the grating shape is investigated as a function of different cover materials. We obtain deformation-free LPE overgrowth of the dry etched corrugations applying the GaAs cover technique. In contrast to wet chemically etched gratings identical grating profiles are formed in different crystallographic directions by RIBE and successfully overgrown by LPE.
High quality narrow GaInAs/InP quantum wells grown by atmospheric organometallic vapor phase epitaxy
Authors: Miller B. I. , Schubert E. F. , Koren U. , Ourmazd A. , Dayem A. H. , Capik R. J.
Published: July 2002

A series of GaInAs/InP quantum wells from 10 to 135 Å has been grown by atmospheric organometallic vapor phase epitaxy using pressure balancing techniques. These wells exhibit strong exciton peaks at 4 K and have quantized energy shifts of up to 326 meV. These energy shifts are compared with two simple finite well models (Kronig–Penney and envelope function approximation) using a conduction-band offset of Vc≊40% ΔEg(GaInAs) and are in close agreement with the latter model. The full width half-maximum linewidths indicate an average interface roughness of ≊1 monolayer.
Electrical measurements on n+-GaAs/undoped AlAs/n-GaAs and n+-GaAs/undoped AlAs:GaAs superlattice/n-GaAs capacitors
Authors: Kirby P. B. , Kerr T. M.
Published: July 2002

We report current versus voltage measurements as a function of temperature (I-V-T) and capacitance-voltage (C-V) measurements on n+-GaAs/insulator/n-GaAs capacitors where the insulators used are (i) AlAs and (ii) a GaAs:AlAs superlattice. For the n+-GaAs/AlAs/n-GaAs structures activation energies of 0.38 eV are observed over the temperature range 100–300 K indicating that conduction takes place by thermionic emission through the X-band states of AlAs. For the superlattice case a measured activation energy of ∼0.33 eV for thermionic emission has a contribution of ∼0.2 eV resulting from the band bending in the superlattice, as revealed by our C-V measurements. We discuss the implications of these results for transport in superlattices and as a technique for determining miniband energies.
High efficiency, multiple layer ZnO acoustic transducers at millimeter-wave frequencies
Authors: Hadimioglu B. , La Comb L. J. , Wright D. R. , Khuri-Yakub B. T. , Quate C. F.
Published: July 2002

We have fabricated multiple layer ZnO acoustic transducers for highly efficient sound wave generation at millimeter-wave frequencies. The transducers consist of half-wave-thick layers of ZnO with alternating crystal structure. The two-way untuned conversion loss values were 27 dB near 29 GHz and 50 dB at 96 GHz measured at liquid nitrogen temperatures.
New approach to the kinetics of silicon vapor phase epitaxy at reduced temperature
Authors: Robbins D. J. , Young I. M.
Published: July 2002

The rate of silicon homoepitaxy from SiH4/H2 mixtures has been studied between 750 and 850 °C using a new ultrahigh-vacuum-compatible low pressure reactor. The analysis of the experimental data is novel in including the effects of both nonepitaxial deposition within the reactor and of gas pumping speed. Epitaxy by pyrolysis of SiH4/H2 mixtures on clean Si substrates between 800 and 850 °C is first order in SiH4 pressure but zero order in H2 pressure at least to 1 mm Hg. The results do not support models of growth mechanism derived from previous studies.
High power with high efficiency in a narrow single-lobed beam from a diode laser array in an external cavity
Authors: Chang-Hasnain C. J. , Berger J. , Scifres D. R. , Streifer W. , Whinnery J. R. , Dienes A.
Published: July 2002

High output power (700 mW) in a nearly diffraction-limited (0.7°) single-lobed nonsteering output beam is obtained from a gain-guided diode laser array in a novel, easily fabricated external cavity configuration. The laser output beam is collimated in both lateral and vertical directions. Differential quantum efficiency as high as 70% has been measured along with excellent linearity of the optical power versus current characteristic. The power and efficiency are the highest reported for a coupled-stripe laser array emitting a narrow single-lobed beam.
Picosecond optical sampling by semiconductor lasers
Authors: Ketterer K. , Böttcher E. H. , Bimberg D.
Published: July 2002

It is shown that a semiconductor laser driven by short electrical current pulses represents a high-speed gate for external optical signals. Based on this finding a novel sampling technique for the detection of light pulses is demonstrated. Conventional semiconductor lasers can be used as sampling gates in a cross correlation arrangement. The time resolution is observed to be better than 10 ps under appropriate injection conditions of the sampling laser. Computer simulations of the sampling system are carried out in the framework of the rate equation model. The theoretical predictions on the time response and the dynamics of the sampling system agree with the experimental observations.
Ultrafast light-controlled optical-fiber modulator
Authors: Halas N. J. , Krökel D. , Grischkowsky D.
Published: July 2002

We report the ultrafast operation of a light-controlled optical-fiber modulator, driven by subpicosecond, compressed, and amplified (6000 Å) dye laser pulses, controlling frequency-doubled (5320 Å) yttrium aluminum garnet laser pulses. The operation of the modulator is based on the optical Kerr effect, and its main component is 7 mm of single-mode optical fiber. Using this system as a light-controlled shutter, we produced either 0.4 ps green light pulses or 0.5 ps holes on the much longer duration second harmonic pulses.
Photocurrent spectroscopy of lattice-matched superlattice electrodes in photoelectrochemical cells
Authors: Nozik A. J. , Thacker B. R. , Turner J. A. , Klem J. , Morkoç H.
Published: July 2002

Photocurrent spectra of GaAs/Al0.38Ga0.62As lattice-matched superlattice electrodes were obtained in photoelectrochemical cells containing nonaqueous liquid electrolyte; spectra were compared for two electron acceptors, cobalticinium and ferrocinium, having redox potentials (energy levels) that differ by 1.33 V. The spectra were found to be independent of acceptor energy levels, in sharp contrast to previous results with GaAs/GaAs0.5P0.5As strained-layer superlattices. These results indicate that for lattice-matched systems hot-electron transfer from upper quantum states in the quantum wells is not a dominant process. This is explained by the much lower surface trapping rates in lattice-matched superlattices compared to strained-layer superlattices.
Impurity-induced layer-disordered buried heterostructure AlxGa1−xAs-GaAs quantum well edge-injection laser array
Authors: Deppe D. G. , Jackson G. S. , Holonyak N. , Hall D. C. , Burnham R. D. , Thornton R. L. , Epler J. E. , Paoli T. L.
Published: July 2002

A laser array is described that makes use of edge injection into two sides (two ‘‘edges’’) of a stack of three AlxGa1−xAs-GaAs multiple quantum well active regions. The edge-injection array is realized by impurity-induced layer disordering, which forms a higher gap Si-doped n-type emitter that edge injects electrons into either side of a stack of three lower gap multiple quantum well p-type active regions. The far-field beam divergence in the vertical direction (θ⊥) of the array diode is reduced from 45° to 15° as determined by the laser operation, for comparison, of one of the quantum well active regions (oxide-defined stripe geometry diode).
Epitaxial Fe films on (100)GaAs substrates by ion beam sputtering
Authors: Tustison Randal W. , Varitimos Thomas , Van Hook Jerrold , Schloemann Ernst F.
Published: July 2002

We report the successful growth of single-crystal Fe films on GaAs substrates in (100) orientation by ion beam sputtering. Magnetic measurements show that the crystalline anisotropy field of these films is substantially the same as that of bulk single crystals.
680-nm band GaInP/AlGaInP tapered stripe laser
Authors: Ikeda M. , Sato H. , Ohata T. , Nakano K. , Toda A. , Kumagai O. , Kojima C.
Published: July 2002

A gain-guiding tapered stripe laser was fabricated using a Ga0.5In0.5P/(Al0.5Ga0.5)0.5In0.5P double heterostructure wafer grown by metalorganic chemical vapor deposition. The laser showed a continuous wave (cw) threshold current of 48 mA, a maximum temperature for cw operation of 81 °C, an aspect ratio of about 2, and an astigmatism near 25 μm. The emission wavelength was 684 nm. Thirty-two devices have been operating without significant degradation for more than 2000 h at 50 °C with a constant output power of 3 mW.
Excitation and decay mechanisms of the intra-4f luminescence of Yb3+ in epitaxial InP:Yb layers
Authors: Körber W. , Hangleiter A.
Published: July 2002

The decay and excitation processes of internal transitions of Yb3+(4f13) incorporated in InP were investigated by means of time-resolved photoluminescence and photoluminescence excitation spectroscopy. From the temperature dependence of the excited state lifetime we find several decay mechanisms, including a bound-exciton-like Auger process, energy transfer, and thermal depopulation. Excitation spectroscopy reveals that free carriers are needed during the excitation process of Yb centers.
Real time processing of picosecond and femtosecond laser pulses: Application to free-electron lasers
Authors: Cutolo Antonello , Benson Stephen V. , Madey John M.
Published: July 2002

An original and reliable technique, based on a three-wave interaction, has been designed and successfully tested to analyze the evolution of the modes and the pulse length of a free-electron laser during the buildup of the radiation. The technique was developed in order to study the effects of the optical guiding in the free-electron laser built at Stanford and driven by the MARK III linear accelerator. We explicitly mention that this technique can be easily exploited to monitor, in real time, the pulse-to-pulse fluctuations of the mode size and the pulse length of the pulses delivered by any laser independently of its pulse length from femtosecond to millisecond.
Stark spectroscopic measurement of spatially resolved electric field and electric field gradients in a glow discharge
Authors: Shoemaker J. R. , Ganguly B. N. , Garscadden A.
Published: July 2002

Spatially resolved Stark spectra of triplet helium Rydberg states have been measured in the cathode fall region of a normal glow discharge. It is demonstrated that Stark spectral intensity distribution of a single Stark manifold provides both the electric field and the electric field gradient. The spectra of appropriate manifolds typically are sensitive to 20 V/cm change across the width of the probe laser beam. The experimental method of determining the electric field gradient locally means that one can measure space-charge distributions in sheaths adjacent to electrodes, probes, and plasma boundaries.
Manipulation of nucleation sites and periods over amorphous substrates
Authors: Yonehara T. , Nishigaki Y. , Mizutani H. , Kondoh S. , Yamagata K. , Noma T. , Ichikawa T.
Published: July 2002

A selective nucleation based crystal growth technique over amorphous substrates is originated. The method manipulates nucleation sites and periods, and hence, controls the grain boundary location by modifying the substrate surface. In Si, Si3 N4 provides artificial nucleation sites, 1–2 μm in diameter, 100 μ m in period, which is surrounded by SiO2 . One Si nucleus is formed exclusively in a small portion of Si3 N4 . The highly faceted and periodically located nuclei grow over SiO2 up to 100 μm in diameter before impingement. A field-effect transistor fabricated inside the island operates comparably to the bulk Si control.
Chemical precursor to optical damage detected by laser ionization mass spectrometry
Authors: Estler R. C. , Nogar N. S.
Published: July 2002

Mass spectrometry was used in conjunction with Nomarski microscopy to characterize the initiation of optical damage in selected commercial optics. The reflective optics (351 nm) consisted of Sc2O3/SiO2 multilayer coatings on 7940 (glass) substrates. These samples were exposed to loosely focused 1.06 μm, 10 ns pulses at 10 Hz. At fluences above 100 mJ/cm2, transient iron signals were observed at each increasing fluence level, with concomitant appearance of small circular (10 μm) pits in the surface. The latter was observed by Nomarski microscopy. These small pits were also associated with macroscopic damage features resulting from threshold damage testing.
Optical nonlinearities of excitons in CuCl microcrystals
Authors: Masumoto Yasuaki , Yamazaki Makoto , Sugawara Hideyuki
Published: July 2002

Nonlinear optical properties of excitons in CuCl microcrystals in NaCl host crystals were studied by the absorption saturation method. Prominent absorption saturation of excitons was observed together with a blue shift. Optical nonlinearity was found to increase with an increase in the size of the CuCl microcrystals. The observed nonlinearities are very large compared with those in bulk CuCl crystals and GaAs quantum wells.
Selective constraints on the activation domain of transcription factor Pit-1.
Authors: Majumdar S , Irwin D M , Elsholtz H P
Published: July 2002

The POU transcription factor Pit-1 activates members of the prolactin/growth hormone gene family in specific endocrine cell types of the pituitary gland. Although Pit-1 is structurally conserved among vertebrate species, evolutionary changes in the pattern of Pit-1 RNA splicing have led to a notable "contraction" of the transactivation domain in the mammalian lineage, relative to Pit-1 in salmonid fish. By site-directed mutagenesis we demonstrate that two splice insertions in salmon Pit-1, called beta (29 aa) and gamma (33 aa), are critical for cooperative activation of the salmon prolactin gene. Paradoxically, Pit-1-dependent activation of the prolactin gene in rat is enhanced in the absence of the homologous beta-insert sequence. This apparent divergence in the mechanism of activation of prolactin genes by Pit-1 is target gene specific, as activation of rat and salmon growth hormone genes by Pit-1 splice variants is entirely conserved. Our data suggest that efficient activation of the prolactin gene in the vertebrate pituitary has significantly constrained the pattern of splicing within the Pit-1 transactivation domain. Rapid evolutionary divergence of prolactin gene function may have demanded changes in Pit-1/protein interactions to accommodate new patterns of transcriptional control by developmental or physiological factors.