bluuebunny/crossref_metadata_2025 huggingface dataset:
Transverse magnetic and transverse electric polarized inter-subband absorption and photoconductivity in p-type SiGe quantum wells
Authors: Fromherz T. , Kruck P. , Helm M. , Bauer G. , Nützel J. F. , Abstreiter G.
Published: July 2002

We have investigated the polarization dependence of subband absorption and photoconductivity in Si/SiGe quantum wells. For samples with a hole concentration of ps=2.8×1012 cm−2 both transverse magnetic and transverse electric polarized absorptions have been observed, and transitions to several excited states are clearly identified by comparison with self-consistent Luttinger–Kohn type calculations. The photoconductivity is surprisingly little sensitive to the polarization, which indicates the importance of the subsequent transport process on the photocurrent responsivity.
Resistless, area-selective ultrashallow P+/N junction fabrication using projection gas immersion laser doping
Authors: Kramer K.-Josef , Talwar Somit , Lewis Isabella T. , Davison John E. , Williams Kenneth A. , Benton Keith A. , Weiner Kurt H.
Published: July 2002

The selective fabrication of ultrashallow p+/n junctions in silicon using projection gas immersion laser doping is reported. The method offers substantial improvement and simplification in junction formation to integrated circuit manufacturers, since several processing steps required for conventional doping techniques like ion implantation are eliminated. Spatially selective incorporation of boron into silicon without the use of any masking layer on the wafer surface is achieved. A pulsed excimer laser beam is patterned using a chromeless reticle and the pattern is transferred through a projection system onto a wafer that is kept in a BF3 dopant gas ambient. The depth of the fabricated junctions is 60 nm with a surface concentration of 5×1019 cm−3. The vertical and lateral distribution of boron in silicon after patterned laser processing is investigated using secondary ion mass spectroscopy (SIMS) and time-of-flight SIMS (ToF-SIMS). Vertical and lateral dopant profiles are steep and clearly resolved.
Room-temperature operation of an Yb-doped Gd3Ga5O12 buried channel waveguide laser at 1.025 μm wavelength
Authors: Shimokozono M. , Sugimoto N. , Tate A. , Katoh Y. , Tanno M. , Fukuda S. , Ryuoh T.
Published: July 2002

An epitaxially grown ytterbium-doped gadolinium gallium garnet (Yb:GGG) buried channel waveguide laser is prepared on an yttrium substituted GGG substrate (Y:GGG). The effective light guiding structure is obtained as a result of the difference of refractive indices of Yb:GGG and Y:GGG. The Yb:GGG waveguide exhibits single-mode 1.025 μm lasing operation at room temperature. The incident threshold and slope efficiency of the 5-mm-long waveguide laser when pumped at 0.941 μm are 80 mW and 13.4%, respectively.
Fine structure in 1.4 eV luminescence band from plasma deposited amorphous silicon layers on silicon substrates
Authors: Rao K. S. R. K. , Sreedhar A. K. , Bhat H. L. , Singh R. A. , Dubey G. C. , Kumar Vikram
Published: July 2002

Fine structure has been observed in the 1.4 eV luminescence band of thin (≊100 Å) amorphous silicon (a-Si:H) layers deposited on silicon substrates. The energy separation between the peaks is ≊20 meV. A similar luminescence band observed in layers grown on glass substrates under the same conditions is several orders of magnitude lower in intensity and is without perceptible fine structure. There is no change in the nature of the fine structure and the peak energies in films deposited at different substrate temperatures (150–300 °C). The dependence of the luminescence band on illumination intensity and on temperature has also been measured. This indicates probable excitonic nature of the luminescence. Possible causes for the observed phenomena are discussed.
Specific heat capacity of undercooled magnetic melts
Authors: Wilde G. , Görler G. P. , Willnecker R.
Published: July 2002

The specific heat capacities of (Co, Ni, Fe)–Pd alloys were determined in the crystalline and metastable undercooled liquid state using differential heat flow calorimetry. Applying the melt fluxing technique, the liquid alloys were undercooled by more than 330 K below their respective liquidus temperatures. For Co100−xPdx (x=20 and 25 at. %) the undercooled liquid approached the temperature regime of the ferromagnetic crystalline phase. The heat capacity of the liquid samples as a function of temperature shows a cusplike rise in the vicinity of the Curie temperature of the solid state. For (Fe, Ni)–Pd alloys, where the Curie temperatures are far below the crystallization temperatures achieved in undercooling experiments, an almost constant specific heat at the same levels of undercooling is observed. These results, together with recent magnetization measurements, indicate the existence of a magnetic phase transition in the undercooled liquid state of the Co–Pd alloys.
Silicon based light emitting gels
Authors: Vinod M. P. , Vijayamohanan K.
Published: July 2002

Light emitting properties of a silicon-containing gel formed by the controlled reaction between acetone and tetrachlorosilane is reported here. Although infrared spectroscopic analysis shows that the gel has a siloxane network (1000–1100 cm−1), UV absorption with a maximum of 328 nm suggests that it is not a simple siloxane polymer. A photoluminescence (PL) spectrum of the compound gives a broad peak in the range of 800–950 nm, attributed to the structural features associated with carbonyl conjugated siloxane groups.
Planar microwave devices fabricated by ion-implantation patterning of high-temperature superconductors
Authors: DeGroot D. C. , Rudman D. A. , Zhang Kuan , Ma Q. Y. , Kato H. , Jaeger N. A. F.
Published: July 2002

We have applied ion-implantation inhibit patterning as a new method of fabricating low-loss microwave transmission lines in high-temperature superconductor thin films. To determine the effectiveness of this technique, we fabricated coplanar waveguide transmission lines in YBa2Cu3O7−δ thin films that had been deposited on LaAlO3 substrates using pulsed laser deposition. Microwave characterizations of these lines are compared to a reference line fabricated with conventional ion milling. At 76 K and 12 GHz, the attenuation constants of the ion-implanted transmission lines are approximated 0.02 dB/mm, and the overall loss response is indistinguishable from that of the ion-milled device.
Output performance of a dye-doped sol-gel silica laser in the near UV
Authors: Ye Chao , Lam King-Shun , Chik Kin-Pong , Lo Dennis , Wong Kin-Hung
Published: July 2002

Visibly transparent near-UV dye (Exalite 377E)-doped silica in the form of parallelepiped were prepared by the low-temperature sol-gel process. The laser output performance of dye-doped sol-gel silica samples pumped by a short pulse (1 ns) N2 laser at 337 nm was reported. With a grating as the wavelength selection element, the laser was tuned from 367 to 387 nm with a laser linewidth of 2 nm. Using a resonator cavity consisting of two flat mirrors, the sol-gel laser showed a slope efficiency of 34.7% and a pump energy threshold of 20 μJ. The variation of sol-gel laser energy output as a function of the number of pulses under repetitive N2 laser excitation was investigated. The laser output energy decreased initially with the number of shots. The output energy recovered to its original intensity after a ten minute interruption in pumping. In this way, the dye-doped samples showed no signs of long term degradation after being irradiated at 337 nm for tens of thousand shots.
Observation of step configuration conversion on single-domain Si(001) 1×2 surface by scanning tunneling microscope
Authors: Zhou J. M. , Lin N. , Guo L. W. , Zhang M. H. , Huang Q. , Cue N. , Chen T.
Published: July 2002

We have observed a conversion of step configuration of 3.5° miscut Si(001) surface after depositing several monolayers of Ge by using a scanning tunneling microscope. For a 3.5° miscut Si(001) surface, terraces are spaced by double-atom height steps and all dimer rows, either on the upper terrace or on the lower terrace of a step, are normal to the step edge, defined as single-domain (1×2) surface. After depositing 2 ML of Ge, the surface is still single domain, but dimer rows have changed their direction, running parallel to the step edge and single domain (2×1) appeared. The reason for such conversion is attributed to the strain that existed on the epilayer of Ge.
Double injection and negative resistance in stripe-geometry oxide-aperture AlyGa1−yAs–GaAs–InxGa1−xAs quantum well heterostructure laser diodes
Authors: Wierer J. J. , Maranowski S. A. , Holonyak N. , Evans P. W. , Chen E. I.
Published: July 2002

Data are presented demonstrating double injection and negative resistance in stripe-geometry oxide-aperture AlyGa1−yAs–GaAs–InxGa1−xAs quantum well heterostructure lasers. The buried oxide laser structures are defined, in current and cavity, by laterally oxidizing the higher Al composition upper and lower cladding layers from a mesa edge (a ridge), thus, forming a narrow oxide-defined buried aperture (∼2μm). Post fabrication annealing (425 °C in N2) removes the negative resistance, indicating that the crystal growth and oxidation processes introduce products such as H and OH in the active region that compensate the dopants.
Development of an optically recording velocity interferometer system for laser induced shock waves measurements
Authors: Moshe E. , Dekel E. , Henis Z. , Eliezer S.
Published: July 2002

An optically recording velocity interferometer system, ORVIS, was developed for measurements of the time evolution of the free surface and the particle velocity in laser induced shock waves experiments. This system produces interference fringe shifts which are proportional to the Doppler shift of a laser beam reflected from the moving surface. These fringe shifts are recorded with a high speed electronic streak camera, which has a 70 ps time resolution. Using this method, the free surface velocity was measured with an accuracy better than 5% and the pressure in laser shocked aluminum targets was calculated. Shock waves of order of hundreds of kilobars are produced by a Nd:YAG laser system with a wavelength of 1.06 μm, pulse width of 5 ns (FWHM) and energy in the range (30–50) J, focused to spots diameters in the range (200–1000) μm. The dynamic spall strength reported here for Al is (14.47±1.45) kbar for a strain rate of ε̇∼8×106s−1, consistent with studies performed with other methods.
Quantum-well activated phosphors: A new concept for electroluminescent displays
Authors: Engelmann R. , Ferguson J. , Solanki R.
Published: July 2002

The development of a completely new class of artificially engineered phosphors for electroluminescent displays is proposed in which deep quantum wells embedded in a high band gap material act as radiative centers. The proof of concept of such phosphor activation by quantum wells (QWs) has been demonstrated in the CdSe/SrS multi-quantum well system prepared by atomic layer epitaxy. Various QW widths (3–15 nm) were studied. The reduction in QW width shifts the emission towards shorter wavelength and the emission spectra exhibit multiple peaks, believed to be the result of transitions from several QW levels.
An amorphous silicon thin film transistor fabricated at 125 °C by dc reactive magnetron sputtering
Authors: McCormick C. S. , Weber C. E. , Abelson J. R. , Gates S. M.
Published: July 2002

We deposited hydrogenated amorphous silicon-based thin film transistors using dc reactive magnetron sputtering at a substrate temperature of 125 °C. We characterize the structural properties of the a-Si:H channel and a- SiNx:H dielectric layers using infra-red absorption, thermal hydrogen evolution, and refractive index measurements, and evaluate the electrical quality using conductivity, capacitance–voltage, and leakage current measurements. Inverted staggered thin film transistors made with these layers exhibit a field effect mobility of 0.3 cm2/V s, a Ion/Ioff ratio of 5×105, a subthreshold slope of 0.8 V/decade, and a threshold voltage of 3 V.
Room-temperature electroluminescence of erbium-doped amorphous hydrogenated silicon
Authors: Gusev O. B. , Kuznetsov A. N. , Terukov E. I. , Bresler, M. S. , Kh. Kudoyarova V. , Yassievich I. N. , Zakharchenya B. P. , Fuhs W.
Published: July 2002

We have observed strong room-temperature electroluminescence at 1.54 μm induced by erbium ions in amorphous hydrogenated silicon (a-Si:H). The device consisted of an Al/a-Si:H(Er)/n-c-Si/Al structure. A mechanism for electronic excitation of the erbium ions in the amorphous matrix is proposed that is based on defect-related Auger excitation.
Third-order nonlinear optical properties of chalcogenide glasses
Authors: Kanbara Hirohisa , Fujiwara Seiji , Tanaka Koichiro , Nasu Hiroyuki , Hirao Kazuyuki
Published: July 2002

Third-order nonlinear optical properties of chalocogenide glasses were investigated through third-harmonic generation (THG), optical Kerr shutter (OKS), and degenerate four-wave mixing (DFWM) measurements. We examined the dependence of the THG susceptibility on the absorption edge, thereby showing that the susceptibility rapidly increased as the absorption edge red shifted. Moreover, the THG susceptibility was compared with the OKS susceptibility. It was found that both susceptibilities almost coincided within the range of experimental errors. The OKS and DFWM experiments indicated that a high-speed compact optical switching device was obtained using the chalcogenide glasses.
Photoluminescence of LiTaO3:Pr
Authors: Ryba-Romanowski W. , Sokólska I. , Gołab S. , Łukasiewicz T.
Published: July 2002

Single crystals of LiTaO3 doped with praseodymium were grown by the Czochralski method from congruent melt and their optical properties were examined. It has been found that the Pr3+ ions in LiTaO3 occupy several nonequivalent sites differing in the crystal field strength. In addition, the structural disorder associated with Li deficiency gives rise to strong inhomogeneous broadening of both the optical absorption and emission lines. In contrast to isostructural LiNbO3:Pr, the relaxation of the excited P03 level of praseodymium is governed by radiative transitions, which terminate on excited multiplets and make the LiTaO3:Pr3+ crystals promising for four-level lasing in the visible range.
Barrier-layer-thickness control of selective wet oxidation of AlGaAs for embedded optical elements
Authors: Blum O. , Ashby C. I. H. , Hou H. Q.
Published: July 2002

Selective wet oxidation of AlGaAs layers can be used to form embedded optical elements, such as buried lenses and current control apertures in vertical cavity structures. Oxidation rates of buried Al0.94Ga0.06As layers were controlled by varying the thickness of GaAs barrier layers between layers of Al0.94Ga0.06As and Al0.98Ga0.02As. This phenomenon can be attributed to the superposition of a vertical oxidation component due to species diffusing through the barrier layer and a constant lateral oxidation component. The magnitude of the vertical component is controlled by the GaAs barrier thickness, which determines the concentration of additional oxidizing species in the Al0.94Ga0.06As layer.
Femtosecond differential transmission measurements on low temperature GaAs metal–semiconductor–metal structures
Authors: Keil Ulrich D. , Hvam Jo/rn M. , Tautz Sönke , Dankowski Stefan U. , Kiesel Peter , Döhler Gottfried H.
Published: July 2002

We report on differential transmission measurements on low temperature grown (LT)-GaAs with and without applied electrical fields at different wavelengths. Electrical fields up to 100 kV/cm can be applied via an interdigitated contact structure to our LT GaAs samples which have been removed from the substrate by epitaxial lift off. In the presence of an electric field, both, the absorption bleaching due to phase space filling and field induced absorption changes due to the Franz–Keldysh effect contribute to the transmission changes. We observe an extended carrier lifetime with applied field. The response time of a biased metal–semiconductor–metal detector, therefore, exceeds the carrier life time of the substrate material.
Intersubband photoluminescence of GaAs quantum wells under selective interband excitation
Authors: Sauvage S. , Boucaud P. , Julien F. H. , Gauthier-Lafaye O. , Berger V. , Nagle J.
Published: July 2002

We report on infrared spontaneous emission between subbands in GaAs quantum wells excited by an interband optical pumping. The active region consists of 15 periods of four coupled quantum wells which are embedded in a mid-infrared optical waveguide. Electrons are selectively injected from the valence band in the excited subbands of the quantum wells using interband optical pumping. Intersubband spontaneous emission is observed at low temperature between the E5 and E4 subbands of the quantum wells (E5−E4≈162 meV≈7.7 μm). The intersubband luminescence vanishes when the E5 subband is not selectively populated. The emission is polarized along the growth axis of the quantum wells as expected for intersubband transitions. The collected infrared power exhibits a linear dependence with the interband optical power with a slope ≈560 pW/W.
Strong polarization selectivity in 780-nm vertical-cavity surface-emitting lasers grown on misoriented substrates
Authors: Ju Young-Gu , Lee Yong-Hee , Shin Hyun-Kuk , Kim Il
Published: July 2002

We report that the 780 nm quantum well vertical-cavity surface-emitting lasers (VCSELs) grown on a 2° off misoriented (001) substrate toward (111)A exhibit a high polarization suppression ratio over a few hundred. The main polarization is always along the [−110] direction for all the lasers over the entire operating currents. To understand the physical origin of this polarization selectivity, the gain/loss difference between two competing polarization modes in VCSELs is investigated by measuring the subthreshold spectral linewidth. The obtained modal gain/loss difference is about 3.0 cm−1, which is sufficiently large for polarization stabilization and amounts to 4% of the threshold modal gain. Comparison with the subthreshold measurement and previous theoretical work shows significant discrepancy, which implies the possibility of other polarization selection mechanisms inducing such large gain/loss differences in 780 nm quantum wells grown on a misoriented substrate. In addition, it is found that the 780 nm VCSEL made of a bulk active medium grown on a misoriented substrate also shows a high polarization selectivity as quantum well lasers.
Space-charge controlled conduction in low-temperature-grown molecular-beam epitaxial GaAs
Authors: Kordoš P. , Marso M. , Förster A. , Darmo J. , Betko J. , Nimtz G.
Published: July 2002

Current transport in low-temperature (LT) molecular-beam epitaxial GaAs grown at 200-300 °C on an n+ GaAs substrate is studied by means of current–voltage–temperature characteristics. The resistivity of LT GaAs at low electric fields is ρ⩾108 Ω cm, much higher than resulting from van der Pauw measurements. It is found that the measured resistivity decreases with increasing the LT GaAs thickness. This is explained by space-charge effect in the vicinity of n+/LT GaAs junction and subsequent suppression of hopping conduction in the high-field junction region.
Observation of coherent modes of Josephson vortices in Bi2Sr2CaCu2Ox
Authors: Lee J. U. , Guptasarma P. , Hornbaker D. , El-Kortas A. , Hinks D. , Gray K. E.
Published: July 2002

We report strong evidence for coherent modes of moving Josephson vortices in mesas patterned on the surface of Bi2Sr2CaCu2Ox single crystals. The vortex flow current–voltage curves are characterized by a sharp up-turn and the appearance of multiple branches as the current is ramped up and down at a fixed magnetic field and temperature. These results are consistent with weakly damped motion of Josephson vortices in which different coherent modes can occur in a close stack of Josephson coupled multilayers.
Antenna-coupled bolometer with a micromachined-beam thermal link
Authors: Osterman D. P. , Patt R. , Hunt R. , Peterson J. B.
Published: July 2002

We present the design of a novel bolometer intended for measurement of radiation within a waveguide. The thermal link in the bolometer is a low-thermal conductance micromachined beam. Power is coupled from an antenna to a resistive termination at the center of the beam. The optimization of the design for an astronomical measurement leads to an operating temperature of 0.48 K, accessible with a He3 refrigerator. Measurements on the antenna absorber in a waveguide show an average absorption of 94% from 33 to 50 GHz.
Nonradiative recombination of hot photoelectrons in CdS nanocrystals embedded in glass
Authors: Juršėnas S. , Kurilčik G. , Strumskis M. , Žukauskas A.
Published: July 2002

Transient luminescence spectra are investigated in highly photoexcited CdS nanocrystals (average radii 5.4–100 nm) embedded in glass. Luminescence-intensity kinetics exhibits distortion attributed to carrier-temperature-activated nonradiative recombination due to multiphonon emission. The distortion enhances with reduced crystallite size indicating that the photomodified semiconductor-glass interface originates deep traps with localization barrier of 130 meV.
Point-contact electrodes to probe charging effects in individual ultrasmall cobalt clusters
Authors: Desmicht R. , Faini G. , Cros V. , Fert A. , Petroff F. , Vaurès A.
Published: July 2002

A new technique to probe a single nanometer-scale magnetic particle by measuring the tunneling current through point-contact electrodes is described. The tunnel junctions are formed by a bulk cobalt bottom electrode, a monolayer of ultrasmall Co clusters sandwiched between two Al2O3 barriers and a point-contact top electrode, defined by e-beam lithography and permitting to study the quantum transport through an isolated cluster. We report on single electron charging effects such as Coulomb blockade and Coulomb staircase which are undoubtedly consistent with the tunneling through a single Co cluster. One of our devices exhibits a Coulomb gap of 380 mV which is, to our knowledge, one of the largest values ever reported in metallic granular systems.
Nanometer-scale imaging with an ultrafast scanning tunneling microscope
Authors: Steeves G. M. , Elezzabi A. Y. , Freeman M. R.
Published: July 2002

We present experimental data demonstrating the spatial resolution of an ultrafast junction mixing scanning tunneling microscope (JM-STM). The experiment uses a patterned metal-on-metal (Ti/Au) surface to establish electronic structure contrast on a short length scale. Our measurements achieve a spatio-temporal resolution of 20 nm–20 ps, limited only by the sample properties. The fine spatial resolution proves that the time-resolved signal is generated in the tunnel junction, indicating that atomic resolution should be possible in the JM-STM mode of operation.
Generation of millimeter waves with a GaAs/AlAs superlattice oscillator
Authors: Schomburg E. , Brandl S. , Hofbeck K. , Blomeier T. , Grenzer J. , Ignatov A. A. , Renk K. F. , Pavel’ev D. G. , Koschurinov Yu. , Ustinov V. , Zhukov A. , Kovsch A. , Ivanov S. , Kop’ev P. S.
Published: July 2002

We report on a semiconductor superlattice oscillator for generation of millimeter waves (frequency 65 GHz). The main element of the oscillator is a doped short-period GaAs/AlAs superlattice with negative differential conductance. The oscillator is due to current oscillations caused by charge density domains. The oscillator delivered, at an efficiency of 0.2% for the conversion of electrical power to radiation power, a power of 100 μW in a bandwidth of the order of 200 kHz.
Femtosecond dynamics in semiconductor lasers: Dark pulse formation
Authors: Kauer M. , Cleaver J. R. A. , Baumberg J. J. , Heberle A. P.
Published: July 2002

We track the dynamic response of GaAs quantum-well semiconductor diode lasers after injection of a femtosecond pulse, using ultrafast upconversion. The continuous-wave emission shows gain dynamics and relaxation oscillations on timescales of 1–100 ps. The recirculating femtosecond pulse evolves into an ultrafast “dark pulse” in the wake of subpicosecond oscillations.
Enhancement of acoustic- and optic-phonon generation by terahertz radiations in a two-dimensional electron system
Authors: Lei X. L. , Dong B.
Published: July 2002

We present a theoretical study on the angular and frequency distributions of the acoustic and optic-phonon generation by hot electrons during the terahertz-driven transport in a GaAs-based quantum well. Based on the detailed solution of the nonlinear balance equations in the presence of an oscillating electric field of arbitrary strength, we find that, when the system is exposed to an intense terahertz radiation, emissions of acoustic and optic phonons are significantly enhanced, especially along the polarized direction of the electric field.
Capacitance–voltage characteristics of Bi4Ti3O12/p-Si interface
Authors: Fu Liwei , Liu Kun , Zhang Bo , Chu Junhao , Wang Hong , Wang Min
Published: July 2002

Electrical properties of the interface between Bi4Ti3O12 ferroelectric film and p-Si substrate have been studied by capacitance–voltage (C–V) characteristics. It is found that the interface barrier can be broken down temporally because of the charge injection from Si substrate into the ferroelectric thin film, and this charge injection behavior induces hump and valley structures in the C–V curves. It is also found that the polarization in the Bi4Ti3O12 film is aligned along a preferential direction from semiconductor to ferroelectric thin film, which is attributed to the ferroelectric/p-Si contact.
High slope efficiency, “cascaded” midinfrared lasers with type I InAsSb quantum wells
Authors: Kurtz S. R. , Allerman A. A. , Biefeld R. M. , Baucom K. C.
Published: July 2002

Lasers and light-emitting diodes with multistage, type I InAsSb/InAsP quantum well active regions are reported. These ten stage, cascaded devices were grown by metalorganic chemical vapor deposition. The broadband light-emitting diodes produced high average powers, >2 mW (∼80 K, 3.7 μm) and >0.1 mW (∼300 K, 4.3 μm). A 3.8–3.9 μm laser structure operated up to T=180 K. At 80 K, peak power >100 mW and a slope efficiency of 48% (4.8% per stage) were observed in our gain guided lasers. The slope efficiency was strongly dependent on cavity length, and analysis of efficiency data suggests an internal differential quantum efficiency >1 and a loss coefficient ⩾100 cm−1.
Studies of metallic species and oxygen incorporation during sputter-deposition of SrBi2Ta2O9 films, using mass spectroscopy of recoiled ions
Authors: Im J. , Krauss A. R. , Dhote A. M. , Gruen D. M. , Auciello O. , Ramesh R. , Chang R. P. H.
Published: July 2002

We have recently developed a mass spectroscopy of recoiled ions technique which is suitable for monolayer-specific surface analysis of thin films during growth. We present initial results using this technique to study the effect of different bottom electrode layers on metallic species and oxygen incorporation in the early stages of SrBi2Ta2O3 (SBT) film growth via ion beam-sputter deposition. The work discussed here has been focused on studying the incorporation of Sr, Bi, and Ta during growth of SBT on Pt/Ti/SiO2/Si, Pt/MgO, Ti, and Si substrates. We found that the incorporation of Bi in sputter-deposited SBT films depends critically on the bottom electrode surface composition and the growth temperature.
Stress development during deposition of CNx thin films
Authors: Broitman E. , Zheng W. T. , Sjöström H. , Ivanov I. , Greene J. E. , Sundgren J.-E.
Published: July 2002

We have investigated the influence of deposition parameters on stress generation in CNx (0.3<x<0.5) thin films deposited onto Si(001) substrates by reactive magnetron sputtering of C in pure N2 discharges. Film stress, σ, which in all cases is compressive, decreases with an increase in the N2 pressure, PN2, due to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. The film stress σ is also a function of the film growth temperature, Ts, and exhibits a maximum value of ∼5 GPa at 350 °C. Under these conditions, the films have a distorted microstructure consisting of a three-dimensional, primarily sp2 bonded, network. In contrast, films deposited at Ts<200 °C with a low stress are amorphous. At 350 °C<Ts<600 °C, σ gradually decreases as Ts is increased and the microstructure becomes more graphitic and contains fewer defects. Nanoindentation measurements show that the films grown at 350 °C exhibit the highest hardness and elasticity.
A sensitive detection method for capacitive ultrasonic transducers
Authors: Ergun A. S. , Atalar A. , Temelkuran B. , Özbay E.
Published: July 2002

We report a sensitive detection method for capacitive ultrasonic transducers. Detection experiments at 1.6 MHz reveal a minimum detectable displacement around 2.5×10−4 Å/Hz. The devices are fabricated on silicon using surface micromachining techniques. We made use of microwave circuit considerations to obtain a good displacement sensitivity. Our method also eliminates the dependence of the sensitivity on the ultrasound frequency, allowing the method to be used at low audio frequency and static displacement sensing applications.
Multiple-wavelength vertical-cavity laser arrays based on postgrowth lateral-vertical oxidation of AlGaAs
Authors: Fiore A. , Akulova Y. A. , Ko J. , Hegblom E. R. , Coldren L. A.
Published: July 2002

We demonstrate that combined lateral-vertical oxidation of AlGaAs can be used to change the resonant wavelength of an optical cavity after the single epitaxial growth. A multiple-wavelength array of vertical-cavity surface-emitting lasers with a 48 nm wavelength span has been realized using this technique.
Plasma–wall sheath in a positive biased duct of the vacuum arc magnetic macroparticle filter
Authors: Keidar M. , Beilis I. I.
Published: July 2002

A model of the electrical sheath between plasma and a positively biased wall has been developed for the case of the magnetic field perfectly parallel to the wall. The magnetized sheath and relatively large positive wall potential with respect to the plasma are considered, so that only electron current is present in the sheath. We show that the sheath thickness increases linearly with duct current density. There is good quantitative agreement between the calculated and experimental current–voltage duct characteristics.
Properties of superconducting Nd1+xBa2−xCu3O7−δ thin films deposited by dc magnetron sputtering
Authors: Salluzzo M. , Maggio-Aprile I. , Fischer O/.
Published: July 2002

We report the superconducting properties of Nd1+xBa2−xCu3O7−δ thin films deposited by dc magnetron sputtering from stoichiometric Nd1Ba2Cu3O7−δ and off-stoichiometric Nd1.12Ba1.88Cu3O7−δ targets. Highly epitaxial c-axis oriented samples with thicknesses ranging from 5 to 100 nm were obtained on SrTiO3(100) substrates from both targets. A suppression of screw-dislocation mediated growth for off-stoichiometric films is observed by STM, resulting in smooth surfaces with roughness of 2–3 nm on a 1 μm2 area. The effects of the deposition conditions on the structural and superconducting properties are investigated and discussed in relation to the Nd–Ba substitution in the Nd1+xBa2−xCu3O7−δ system.
Strain relaxation of boron nitride thin films on silicon
Authors: Donner W. , Dosch H. , Ulrich S. , Ehrhardt H. , Abernathy D.
Published: July 2002

Exploiting the high brilliance of synchrotron radiation, we performed surface-sensitive and depth-resolved x-ray scattering experiments on thin films of boron nitride grown on Si(001) substrates. In-plane strains of different structural phases, namely turbostratic and cubic, grain sizes and textures were determined. Annealing the films up to temperatures of 1000 °C leads to large strain relaxation of about 70%, while the grain size stays constant at 80 Å.
Polarized luminescence from ZnSe-based laser structures and the role in laser operation
Authors: Worschech L. , Ossau W. , Behr Th. , Nürnberger J. , Landwehr G.
Published: July 2002

We report on the anisotropic polarization of the luminescence observed in ZnSe-based heterostructure lasers. It has been found that light originating from the radiative recombination of electrons and holes confined in the ZnCdSe quantum well of the laser is linearly polarized collinearly to one 〈110〉 crystallographic direction after having passed the p-type region of the laser diode. A strong dependence of the laser operation on the two possible 〈110〉 directions of cleaved facets is observed.
GaN epitaxial lateral overgrowth and optical characterization
Authors: Li X. , Bishop S. G. , Coleman J. J.
Published: July 2002

We demonstrate the epitaxial lateral overgrowth (ELO) of GaN from narrow stripes with triangular cross sections by atmospheric pressure metal organic chemical vapor deposition, and characterize the optical properties of these stripes at each stage of the growth using spatially resolved cathodoluminescence spectroscopy, wavelength imaging, and line scans. An improvement of the optical quality of the GaN materials grown by the ELO technique is clearly shown by the appearance of a free exciton peak, the enhancement of bandedge emission, and the weakening of the yellow emission.
Intermediate temperature grown GaAs/AlGaAs photodetector with low dark current and high sensitivity
Authors: Culp James , Nabet Bahram , Castro Francisco , Anwar Amro
Published: July 2002

A photodetector in which Schottky metal laterally contacts the molecular beam epitaxy grown heterointerface of intermediate-temperature GaAs and Al0.24Ga0.76As is reported. The device processed on 400 °C shows very low dark current, less than 25 fA/μm2 (0.5 pA/μm), with a high dc responsivity of about 10 A/W at low optical power levels. The device is process compatible with high electron mobility transistor technology.
Optical parametric oscillation out to 6.3 μm in periodically poled lithium niobate under strong idler absorption
Authors: Lefort L. , Puech K. , Ross G. W. , Svirko Y. P. , Hanna D. C.
Published: July 2002

The very high gains, achieved when using mode-locked pulses to synchronously pump an optical parametric oscillator based on periodically poled lithium niobate, permit oscillation even with strong idler absorption. Oscillation has been achieved at idler wavelengths out to 6.3 μm. Idler power was directly measured, out to 5.41 μm. Beyond this, idler generation was inferred from the observed signal. We present an analysis of operation in the presence of strong idler absorption.
Low-temperature-grown GaAs enhanced wet thermal oxidation of Al0.98Ga0.02As
Authors: Reese H. , Chiu Y. J. , Hu E.
Published: July 2002

The effects of incorporating low-temperature-grown GaAs (LT GaAs) into the layer structure of Al0.98Ga0.02As/GaAs are studied. Results show that the structures containing a 300 nm layer of LT GaAs have faster oxidation rates and lower oxidation temperatures compared to reference samples without the LT GaAs layer. This letter will discuss the mechanisms involved in the oxidation rate increase, attributed to the LT GaAs enhancing the transport of As species during the oxidation process.
1.55 μm single-mode lasers with combined gain coupling and lateral carrier confinement by focused ion-beam implantation
Authors: König H. , Reithmaier J. P. , Forchel A. , Gentner J. L. , Goldstein L.
Published: July 2002

Laterally gain-coupled distributed feedback GaInAsP/InP lasers were fabricated by focused ion-beam implantation and rapid thermal annealing of ridge waveguide structures. An absorption grating, which interacts with the evanescent light field, is formed by a periodic reduction of the band-gap absorption in the passive sections along the ridge. Room-temperature single-mode emission was observed at 1.5 μm with a 30 dB side-mode suppression ratio. Simultaneously, the increase of the band gap in the implanted section results in improved carrier confinement, which reduces the leakage current and improves the laser performance in comparison to unimplanted ridge waveguide lasers.
Majority carrier traps in proton-irradiated GaInP
Authors: Dekker J. R. , Tukiainen A. , Jaakkola R. , Väkeväinen K. , Lammasniemi J. , Pessa M.
Published: July 2002

The majority carrier traps formed in p-GaInP following room temperature irradiation with 3.1 MeV protons have been investigated using deep level transient Fourier spectroscopy. The radiation damage consists of several closely spaced peaks, one of which may have existed in the as-grown material. Energy levels of three of these new traps are reported although in the presence of such closely spaced peaks the energy parameters could only be reliably measured after annealing was used to eliminate shoulder peaks. The spectrum and its annealing behavior are explainable in terms of GaP and InP levels being superimposed. Among the observed peaks, two of the radiation induced levels have been associated with a gallium vacancy defect and a phosphorous Frenkel.
Spectral identification of transverse lasing modes of multimode index-guided vertical-cavity surface-emitting lasers
Authors: Burak D. , Kemme S. A. , Kostuk R. K. , Binder R.
Published: July 2002

The identification of lasing modes in vertical-cavity surface-emitting lasers (VCSELs) is usually based on the polarization-resolved near-field pattern identification, a method difficult to apply in the presence of multiple transverse modes. We study lasing modes of a multitransverse mode index-guided VCSEL under dc pumping conditions by considering in detail the modes’ spectral positions. The experimentally observed spectra are compared with theoretical calculations, based on a recently developed method for vectorial VCSEL eigenmodes [D. Burak and R. Binder, Appl. Phys. Lett. 72, 891 (1998)]. This allows for the identification of transverse lasing modes as a function of the pumping current. Two main effects that influence the spectral characteristics of the VCSEL are considered in our approach: temperature-induced linear shift of lasing wavelengths with increasing pumping current and switching of the lasing mode between different eigenmodes of the VCSEL cavity. The obtained temperature-dependent shift of the lasing frequencies agrees reasonably well with the value known from previous experimental estimations.
A thin-film diamond phototransistor
Authors: Lansley Stuart P. , Looi Hui Jin , Wang Yanyang , Whitfield Michael D. , Jackman Richard B.
Published: July 2002

A phototransistor fabricated from thin-film diamond is reported. Polycrystalline diamond grown by chemical vapor deposition, which is p-type by virtue of near-surface hydrogen, has been used to realize optically activated metal–semiconductor field-effect transistors (FETs). Devices with thin (30 nm) Al Schottky gates and Au source and drain contacts operate as effective enhancement-mode metal–semiconductor field-effect transistors at room temperature; illumination of an electrically isolated gate leads to increased channel current, although saturation is still evident. At deep UV wavelengths (<220 nm), a photodetector gain of around 4 has been measured; the mechanism of operation has been identified as photodiode-like turn-on followed by FET amplification.
Oxygen diffusion in heavily antimony-, arsenic-, and boron-doped Czochralski silicon wafers
Authors: Ono Toshiaki , Rozgonyi George A. , Asayama Eiichi , Horie Hiroshi , Tsuya Hideki , Sueoka Koji
Published: July 2002

The effect of dopant-type, antimony (Sb), arsenic (As), and boron (B), on the outdiffusion of oxygen in heavily doped Czochralski (Cz) silicon wafers has been investigated using secondary ion mass spectroscopy. The results indicate that, although oxygen diffusion in Cz silicon is retarded in heavily B- and As-doped wafers during low temperature annealing (800 °C), it is not influenced by heavy Sb doping. This indicates that charge effects and atom size effects have negligible influence on the diffusion of oxygen. The B and As diffusion retardation effect is attributed to the existence of dopant-oxygen complexes. The oxygen solubility was largest in the most heavily B-doped samples annealed at low temperature.
Photoconductivity investigation of the electron dynamics in GaAs grown at low temperature
Authors: Stellmacher Max , Schnell Jean-Phillipe , Adam Didier , Nagle Julien
Published: July 2002

We present detailed measurements of photoconductivity as functions of illumination power and temperature on metal–semiconductor–metal photodetectors made of low-temperature GaAs grown at different temperatures (225–350 °C). The extracted carrier lifetimes show the expected dependence as a function of growth temperature. Additionally, our experiments show an order-of-magnitude variation of the extracted lifetimes as functions of measurement temperature and illumination intensity. We propose a simple model based on the one-center-Shockley Read-recombination equation which gives good qualitative agreement over the whole range of temperature (20–120 °C) and illumination power (2×10−4 to 20 W/cm2). We show that the recombination properties are determined by the exact position of the electronic quasi-Fermi level in the partially filled midgap donor band, which is strongly influenced by the acceptor concentration.
The influence of the p-n junction induced electric field on the optical properties of InGaN/GaN/AlGaN light emitting diode
Authors: Wang T. , Sugahara T. , Sakai S. , Orton J.
Published: July 2002

The temperature dependence of photoluminescence measurement was performed on an undoped In0.126Ga0.874N/GaN multiple quantum well (MQW) structure and a light emitting diode (LED) structure using this MQW as an active region. The emission energy of the LED structure showed a red shift of about 230 meV at room temperature compared with the undoped In0.126Ga0.874N/GaN MQW. This behavior of the LED structure is attributed to the quantum-confined Stark effect due to its p-n junction induced electric field. This conclusion was confirmed by a calculation and a detailed discussion based on the theory of the quantum-confined Stark effect.
Remanent photoinduced birefringence in thin photochromic sol–gel films
Authors: Peretti J. , Biteau J. , Boilot J.-P. , Chaput F. , Safarov V. I. , Lehn J.-M. , Fernández-Acebes A.
Published: July 2002

High remanent optical anisotropy in photochromic sol–gel films is shown to be photoinduced by discoloration with linearly polarized visible light. This anisotropy results in a linear dichroism in the visible absorption band and in an important birefringence in the near-infrared transparency region. The kinetics of the whole process are quantitatively well described by a simple analytical model. Intrinsic characteristics of the individual molecule, such as the photochemical quantum yield and the anisotropy of their optical properties, are determined. The potential application of this effect to optical data storage is discussed.
Kinetics of nickel-induced lateral crystallization of amorphous silicon thin-film transistors by rapid thermal and furnace anneals
Authors: Lam Lawrence K. , Chen Szu-ke , Ast Dieter G.
Published: July 2002

The activation energy for nickel-induced lateral crystallization of amorphous silicon heated in an inert atmosphere was investigated, and was found to be 1.75 eV for rapid thermal annealing and 1.86 eV for furnace annealing. Polycrystalline silicon thin-film transistors fabricated in furnace recrystallized and rapid thermal recrystallized material had similar device characteristics, even though the crystallization velocity differed by a factor of 3.
Ferroelectricity of a hemicyanine dye in ultrathin organized molecular films: hysteresis and pyroelectric effects
Authors: Ma Shihong , Yan Mei , Lu Xingze , Wang Wencheng , Chen Zhanghai , Liu Pulin , Qu Cuifeng , Lin Shenwei , Ding Aili
Published: July 2002

Pyroelectricity of the optical nonlinear hemicyanine dye in organized molecular films has been demonstrated by using the electric polarization and second harmonic generation measurements. The typical hysteresis loop of the samples confirmed existence of the remnant polarization of hemicyanine molecules which is 600 μC m−2. The pyroelectric coefficient of hemicyanine was found to be 12 μC m−2 K−1 at room temperature and enhanced with increasing temperature monotonically which was well explained by using a molecular dipole reorientation model.
Migration and coalescence of Xe nanoprecipitates in Al induced by electron irradiation at 300 K
Authors: Allen C. W. , Birtcher R. C. , Donnelly S. E. , Furuya K. , Ishikawa N. , Song M.
Published: July 2002

Effects of 1 MeV electron irradiation on Xe precipitates in Al, formed by ion implantation, have been observed in situ by high-voltage transmission electron microscopy. Individual Xe precipitates undergo melting and recrystallization, migration which leads to coalescence, and shape changes. These processes are driven by the production of defects without either cascade defect production or the introduction of additional Xe atoms. Precipitate migration is due to an irradiation-induced surface diffusion process on the Xe/Al interfaces. Coalescence of close precipitates is enhanced by directed motion as a result of the net displacement of Al atoms out of the volume between them.
Elliptical grain growth in the solid-phase crystallization of amorphous SrBi2Ta2O9 thin films
Authors: Choi J. H. , Lee J. Y. , Kim Y. T.
Published: July 2002

During the crystallization process of amorphous SrBi2Ta2O9 (SBT) thin films at 800 °C in a dry O2 ambient, we have found elliptical nuclei in the initial nucleation state. These elliptical grains are preferentially oriented to [110] direction in the [11̄0] direction of projection. Elliptical grain growth keeps [110] as increasing the annealing time at 800 °C. Transmission electron microscopy and selected-area electron diffraction pattern indicate that the origin of 〈110〉-oriented crystallization is due to the highest ionic packing (001) SBT plane which includes TaO6 octahedra and the nearest bonding direction of TaO6 octahedra in SBT plane is the 〈110〉 direction.
Characteristics of a barrier discharge in monatomic and molecular gases
Authors: Sankaranarayanan R. , Pashaie B. , Dhali S. K.
Published: July 2002

We show that, in a parallel-plate dielectric-barrier discharge, monatomic gases behave very differently from molecular gases. Time-resolved images show diffused discharge for monatomic gases and filamentary discharge for molecular gases. In addition, current waveforms also show a marked difference. An empirical relationship for power and voltage is derived which shows good agreement with experimental results for both monatomic and molecular gases.
Tailoring of high-Tc Josephson junctions by doping their electrodes
Authors: Schneider C. W. , Schulz R. R. , Goetz B. , Schmehl A. , Bielefeldt H. , Hilgenkamp H. , Mannhart J.
Published: July 2002

Appropriate doping of the electrodes of high-Tc Josephson junctions provides a means to systematically adjust the junctions’ electronic properties. This is demonstrated for the exemplary case of grain boundary junctions in bicrystalline Ca-doped YBa2Cu3O7−δ films. It is found that the critical current density is strongly increased and the normal state resistivity significantly reduced in comparison with the values obtained for equivalent junctions in undoped films.
Coexistence of hexagonal and orthorhombic structures in NiSi films containing Pt
Authors: Dai J. Y. , Mangelinck D. , Lahiri S. K.
Published: July 2002

The structure of Ni(Pt)Si films was investigated using high-resolution electron microscopy (HREM), electron microdiffraction and image simulation techniques. Such films with 5 at. % Pt were sputter deposited onto (111) Si and annealed for 1 min at 500 °C by rapid thermal annealing. Analysis of the HREM pictures, diffraction patterns, and simulation results has revealed that NiSi films containing Pt can assume both hexagonal and orthorhombic structures that can coexist in the same film. The presence of film stresses and Pt seems to play a role in the formation of hexagonal NiSi.