bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of carbon and beryllium-doped base GaAs/AlGaAs heterojunction bipolar transistors
Authors: Ren F. , Fullowan T. R. , Lothian J. , Wisk P. W. , Abernathy C. R. , Kopf R. F. , Emerson A. B. , Downey S. W. , Pearton S. J.
Published: July 2002

GaAs/AlGaAs heterojunction bipolar transitors (HBTs) utilizing highly Be-doped base layers display a rapid degradation of dc current gain and junction ideality factors during bias application at elevated temperature. For example, the gain of a 2×10 μm2 device with a 4×1019 cm−3 Be-doped base layer operated at 200 °C with a collector current of 2.5×104 A cm−2 falls from 16 to 1.5 within 2 h. Both the base emitter and base collector junction ideality factors also rise rapidly during device operation, and this current-induced degradation is consistent with recombination-enhanced diffusion of Be interstitials producing graded junctions. By sharp contrast, devices with highly C-doped (p=7×1019 cm−3) base layers operated under the same conditions show no measurable degradation over much longer periods (12 h). This high degree of stability is most likely a result of the fact that C occupies the As sublattice, rather than the Ga sublattice as in the case of Be, and also has a higher solubility than Be. The effect of nearby implant isolated regions in promoting Be diffusion is also reported.
Raman depth profiling by in situ sputtering
Authors: Ramsteiner M. , Wagner J. , Koidl P.
Published: July 2002

Raman scattering has been combined with in situ sputtering for a depth resolved Raman spectroscopic characterization of semiconductor structures. Using optical excitation in resonance with higher lying band gaps, such as the E1 band gap of GaAs, a depth resolution of a few nm can be achieved along with an enhanced sensitivity due to resonance effects in the scattering efficiency. The present experimental technique is demonstrated by recording a composition profile from a GaAs/AlxGa1−xAs multiple quantum well structure. Furthermore, the ability of lattice site selective depth profiling of dopant distributions is shown for Si incorporated on Ga and As lattice sites, respectively, in Si+ implanted and annealed GaAs.
Interfacial structure and its effect on nucleation and growth energetics in mesotaxial Si/CoSi2/Si structures
Authors: Hull R. , Hsieh Y. F. , White A. E. , Short K. T.
Published: July 2002

We show how analysis of the stacking sequences at CoSi2/Si interfaces formed by 100 kV Co+ implantation into Si (001) or (111) predicts the formation of partial dislocations or stacking faults at precipitate corners. The presence and nature of the stacking fault can uniquely identify the bonding coordination at the CoSi2/Si(111) interface. Consideration of the interfacial structure for twinned (B) and untwinned (A) {111} interfaces helps explain the competitive nucleation and growth of A vs B precipitates.
LaMgAl11O19:Nd microchip laser
Authors: Mermilliod N. , François B. , Wyon Ch.
Published: July 2002

A LMA (LaMgAl11O19) microchip laser close coupled to the fiber output of a laser diode has been tested. For a 1-mm-thick cavity and a 6×1020 cm−3 Nd concentration, an output power of 35 mW has been obtained, leading to an optical efficiency of 12%. The laser proved to be very stable with an intrinsic noise of 0.6% and an output power variation of only 5% for a 15 °C temperature change of the pump laser diode. Even near threshold two longitudinal modes were observed. The half divergence of this microchip laser was found to be 5±1 mrad.
Picosecond excite and probe nonlinear absorption measurements in CuCl quantum dots
Authors: Kippelen B. , Levy R. , Faller P. , Gilliot P. , Belleguie L.
Published: July 2002

We report nonlinear absorption around the Z3 exciton in CuCl microcrystallites embedded in a glass matrix. Our experiments are performed in a test-pump configuration with picosecond pulses at low temperature. In addition to a shift and a bleaching of the excitonic resonance, induced absorption on the high-energy side is found. The nonlinear index changes induced per exciton per unit volume of CuCl quantum dot could be determined by Kramers–Kronig transformations.
In situ measurements and numerical simulation of wave-electron interactions in a crossed-field amplifier
Authors: Browning J. , Chan C. , Ye J. , Dombrowski G. E. , Ruden T. E.
Published: July 2002

We report detailed two-dimensional in situ measurements of electron density inside an injected-beam crossed-field amplifier operating at 150 MHz. It is demonstrated that during amplification there is a spatial redistribution of the cycloidal electron beam as electrons are drawn to the anode. These measurements have been compared with a numerical simulation [G. E. Dombrowski, IEEE Trans. Electron. Devices 35, 2060 (1988)] which predicts a change in electron trajectories but gives a larger electron loss than was measured.
Dielectric properties of nonsquare AlGaAs/GaAs single quantum wells at photon energies below the band gap
Authors: Li E. Herbert , Weiss Bernard L.
Published: July 2002

The complex dielectric function of square and hyperbolic AlGaAs/GaAs single quantum wells have been calculated to predict the refractive index differences at photon energies below the band gap. The results show that, at these photon energies, the refractive index of a single hyperbolic quantum well exceeds that of the as-grown square quantum well during the initial stages of disordering, after which it decreases with increasing disorder. These results also predict the onset of antiguiding in multiple quantum well waveguides, which has been observed previously.
Phase-locked ridge waveguide InGaAs-GaAs-AlGaAs strained-layer quantum well heterostructure laser arrays
Authors: Beernink K. J. , Miller L. M. , Cockerill T. M. , Coleman J. J.
Published: July 2002

We report the characteristics of separate confinement heterostructure InGaAs/GaAs/AlGaAs strained-layer quantum well heterostructure (λ≳1 μm) ridge waveguide laser arrays grown by metalorganic chemical vapor deposition, and etched by reactive ion etching. The ten element arrays have ridge widths of 4 μm on 8 μm centers. Several etch depths are examined, covering the range from gain-guided to strongly index-guided elements. For these structures, values of effective index step, Δneff, below ∼6×10−3 are necessary to achieve interelement coupling. For Δneff=1.3×10−3, the devices lase in the highest array mode up to ∼1.5 times threshold with a nearly diffraction-limited double-lobed far-field pattern. For higher currents, additional structure in the far-field pattern is observed, and is accompanied by splitting of the longitudinal modes due to operation in additional array modes.
Comparative analysis of growth rate reductions on shadow masked substrates
Authors: De Vlamynck K. , Coudenys G. , Demeester P.
Published: July 2002

The growth on shadow masked substrates by atmospheric pressure metalorganic vapor phase epitaxy is investigated. An analytical description based on simple concepts for a complex geometry shows good agreement with the experimental results and enables the determination of quantum well thickness variations in optical waveguide structures. The growth rate reduction (or: ratio of growth rates) r(u) in the middle of the channel increases as the width-to-height ratio of the mask opening is increased.
Phase relationships in Cu-O thin films prepared by sputtering
Authors: Miller D. J. , Chiarello R. P. , Kim H. K. , Roberts T. , You H. , Kampwirth R. T. , Gray K. E. , Zheng J. Q. , Williams S. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

The conditions for deposition of Cu and Cu-oxide thin films by reactive dc sputtering have been investigated by characterizing the crystal structure of growing films both during and immediately following deposition using an in situ x-ray diffraction technique. The relationship between sputtering conditions and the phases deposited was established for a variety of conditions. At each temperature studied, increasing the oxygen pressure in the system resulted in a systematic change in the phases deposited. Of significant importance was the identification of temperature-pressure regimes in which CuO was stable during deposition but reverted to Cu2O after the sputtering plasma was extinguished, suggesting a shift in the oxidizing potential in the plasma environment. These results also suggest that the in situ analysis technique may be ideally suited for the investigation of phase relationships and phase diagrams in other systems.
Suppression of beam steering in an injection-locked laser diode array
Authors: Brewer Laurence R.
Published: July 2002

Experimental measurements were made to demonstrate that the degree of beam steering in an injection-locked laser diode array is related to the divergence of the master laser beam. For a collimated master laser beam the beam steering was suppressed. The injection-locked laser diode array beam steers with the master laser wavelength because only a portion of the divergent master laser beam satisfies the round trip mode condition.
Ion implantation profile modeling of nitrocellulose coated substrates
Authors: Merhari L. , Le Hüe C. , Belorgeot C. , Bahna Z.
Published: July 2002

The modification of a standard ion implantation profile is usually achieved by carrying out successive irradiations at variable ion incident energy. Keeping this latter parameter constant, we propose an alternative way which consists in implanting the substrate through a nitrocellulose thin film shrinking during ion irradiation. Making precise use of the self-developing mechanism of nitrocellulose when functioning as an ion beam resist, we describe a simple model predicting the new implantation profile and, in particular, the concentration enhancement obtained at the surface of the substrate. The model whose fundamentals and related mathematical derivations are given, is critically dependent on the diffusion mechanism of the implanted ions in the substrate. Comparison between simulated and preliminary experimental implantation profiles of Cs in polyparaphenylenesulfide is made and does not show a major divergence considering that the only diffusion mechanism taken into account is the thermal diffusion.
Superconducting race arbiter with subpicosecond timing discrimination
Authors: Lee G. S. , Ruby R. C. , Ko H. L. , Barfknecht A. T.
Published: July 2002

A novel race arbiter for ultrahigh resolution time discrimination is proposed and has been designed, fabricated, and tested in an all-niobium Josephson junction technology. The arbiter is based on a pair of quantum flux parametrons, which are single flux quantum switching devices, and is hence called a BiQFP for Bi-quantum Flux Parametron. High-speed experiments have demonstrated a rms single-shot time jitter of ±200–300 fs.
Comment on ‘‘E′ centers and nitrogen-related defects in silicon dioxide films’’
Authors: Warren W. L. , Lenahan P. M.
Published: July 2002

The defect centers in silicon dioxide films reported earlier (ref. 1), are discussed. ESR spectra were recorded at higher microwave power in order to facilitate detection of N dangling-bonds. Such bonds were not observed in any significant concentration.(AIP)
Dynamic reflection high-energy electron diffraction observation of 3C-SiC(001) surface reconstruction under Si2H6 beam irradiation
Authors: Yoshinobu Tatsuo , Izumikawa Iwao , Mitsui Hideaki , Fuyuki Takashi , Matsunami Hiroyuki
Published: July 2002

The transition of 3C-SiC(001) surface superstructures under Si2H6 gas molecular beam irradiation was dynamically observed by reflection high-energy electron diffraction. Starting from the C-terminated c(2×2) structure, the surface structure changed in the order of c(2×2)→(2×1)→(5×2)→(3×2) with continuing irradiation. The amounts of Si2H6 dose required for the transitions c(2×2)→(5×2) and c(2×2)→(3×2) were approximately 1.16 and 1.36 times as much as that for c(2×2)→(2×1). These ratios are interpreted as the relative amount of the constituent Si atoms of the superstructures. This experimental result supports the simple dimer model for (2×1) (1 monolayer of Si) and the additional dimer model for (5×2) (1.2 monolayer) and (3×2) (1.33 monolayer), respectively, as the proper configurations of these surface superstructures.
Properties of a new high-efficiency vacuum ultraviolet fluorine lamp excited by a microwave discharge
Authors: Kumagai Hiroshi , Toyoda Koichi
Published: July 2002

A vacuum ultraviolet fluorine lamp excited by continuous-wave microwave discharge was developed for the first time. This lamp provided a fluorescence spectrum which was comprised of two broad lines centered at 157 and 166 nm. Output performances were investigated in terms of gas mixture and total pressure. A total fluorescence power of 18.9 W was obtained with an intrinsic efficiency of 6.2%, when a microwave power of 310 W was coupled to the plasma.
Stress-driven void growth in narrow interconnection lines
Authors: Hu S. M.
Published: July 2002

We consider a model of stress-driven void growth in interconnection lines that are narrower than the metal grain size. The metal line is imbedded in an SiO2 matrix at a temperature T0, and incurs tensile stress after being brought down to an annealing temperature Tann. A void nucleates at a particular grain boundary, along which the diffusion is assumed to be so fast that the stress relaxation at that grain boundary is nearly complete in a very short time. This is assumed to occur before the void spans the width of the line. Thereafter, the void continues to grow by matter transport through bulk diffusion, cascading down sequential tiers of grain boundaries, resulting in a layer of extra matter at each grain boundary for strain relaxation. The kinetics of the void growth is given analytically. The consideration of climbing dislocations is deferred for future analysis.
AlGaAs/GaAs heterojunction bipolar transistor with a two-dimensional electron gas emitter
Authors: Wang Q. , Wang Y. , Longenbach K. F. , Yang E. S. , Wang W. I.
Published: July 2002

We report the operation of the first two-dimensional electron gas (2-DEG) emitter heterojunction bipolar transistor. This device, which was grown by molecular beam epitaxy, incorporates an undoped GaAs spacer between the emitter and base of a standard AlGaAs/GaAs single-heterojunction bipolar transistor. The introduction of the spacer layer causes the formation of a 2-DEG at the AlGaAs/GaAs interface. This 2-DEG defines the emitter side of the junction and produces an emitter-base characteristic similar to that of the collector GaAs homojunction. Using a 300 Å GaAs spacer, offset voltages as low as 30 mV have been attained. These devices also exhibit current gains greater than 10 at emitter current densities of 3 A/cm2 and gains up to 400 in the high current density regime.
Monolithic two-dimensional surface-emitting diode laser arrays mounted in the junction-down configuration
Authors: Jansen M. , Yang J. J. , Ou S. S. , Sergant M. , Mawst L. , Rozenbergs J. , Wilcox J. , Botez D.
Published: July 2002

We report on the first achievement of large area (0.5 cm2) monolithic two-dimensional surface-emitting arrays mounted in the junction-down configuration. Device fabrication involves dry etching of 45°, and vertical micromirrors with ±2° tolerances and <0.2 μm RMS smoothness, integration of 100-μm-thick current-spreading electrodes for minimizing ohmic loss, large area packaging, and mounting to heat exchangers for long pulse and minimum chirp operation. Uniform lasing is achieved from 0.2×0.5 cm2 and 0.5×1 cm2 active area junction-down monolithic arrays (120 and 600 emitters, respectively) using 100 μs long pulses at a 1% duty cycle. Differential quantum efficiencies of ≥ (R18)40% and 7% are achieved for rows of 12 emitters, and for 0.2×0.5 cm2 active area arrays, respectively. The decrease in efficiency with increased area is found to be due to current leakage, which in turn limits the 2-D array emitted optical-power density to 150 W/cm2. Wavelength chirp in these devices is measured to be <4 nm at twice the threshold current.
Highly stable silicon dioxide films deposited by means of rapid thermal low-pressure chemical vapor deposition onto InP
Authors: Katz A. , Feingold A. , Chakrabarti U. K. , Pearton S. J. , Jones K. S.
Published: July 2002

An attempt was made to deposit a high thermally stable silicon dioxide (SiO2) film onto InP substrates. The films were grown by rapid thermal, low-pressure chemical vapor deposition (RT-LPCVD), using pure oxygen (O2) and 2% diluted silane (SiH4) in argon (Ar) gas sources, in the temperature range of 350–550 °C and pressure range of 3–10 Torr. The SiO2/InP structures were heated, post-deposition, up to 1000 °C for durations of up to 5 min, resulting in negligible changes in the properties of the SiO2 films and a limited SiO2/InP interfacial reaction of about 15 nm thick. The higher the initial deposition temperature of the SiO2 the larger was the film compressive stress and the less the degree of densification the film underwent through the post-deposition heating cycles.
Generation of TE12 mode from cyclotron resonance maser driven by nonadiabatic electrostatically pumped electron beam
Authors: Yovchev I. , Spassovsky I. , Nikolov N. , Kostov K. , Velichkov J. , Spassov V. , Loza O.
Published: July 2002

Intense emission of the TE12 mode has been detected in an experiment based on the cyclotron resonance maser mechanism with nonadiabatic electrostatic pumping of an electron beam. The pitch-ratio α of beam electrons has been found experimentally and estimated from a computer simulation. Both results are in good agreement with each other.
Microvolume-secondary ion mass spectrometry analysis of nonvolatile sulfur residues in semiconductor process solutions
Authors: Chia V. K. F. , Bleiler R. J. , Sams D. B. , Craig A. Y. , Odom R. W.
Published: July 2002

The capability to detect and quantify sulfur at the part-per-billion (ppb) concentration level in ultrapure hydrochloric acid rinse solutions used in GaAs wafer fabrication is described. Nonvolatile residues formed from the deposition of nanoliter aliquots of solution onto high purity silicon wafers are analyzed using a high performance CAMECA IMS 4f ion microanalyzer. The dynamic SIMS analysis of microdroplet residues is referred to as Microvolume-SIMS (MV-SIMS). The Microvolume-SIMS analyses of two acid solutions are presented. The concentration of total sulfur detected in these solutions was 98 and 650 ppb; both values are below the SEMI specification standard of less than 1300 ppb total sulfur concentration. Despite this, the acid solution containing 650 ppb of total sulfur was responsible for causing an isolation failure halting wafer production. This finding corroborated electrical failure analyses using these same acids.
Second-harmonic generation at the Al and Cu surfaces for the fundamental wavelength of λ=532 nm
Authors: Petrocelli G. , Martellucci S. , Scudieri F. , Agostini A.
Published: July 2002

The angular dependence of the second-harmonic (SH) generation efficiency at the copper and aluminum surfaces has been measured. In aluminum the bulk and the parallel surface nonlinear polarization gives the main contribution to the SH generation. In copper the normal surface nonlinear polarization contributes significantly to the SH generation.
Substantial improvement by substrate misorientation in dc performance of Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As double-heterojunction NpN bipolar transistors grown by molecular beam epitaxy
Authors: Chand Naresh , Berger Paul R. , Dutta Niloy K.
Published: July 2002

Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As NpN double-heterojunction bipolar transistors have been grown simultaneously by molecular beam epitaxy on (100) and 3° off (100) towards 〈111〉A GaAs substrates. On the tilted substrate, the current gain is significantly higher, comparable to the maximum expected value, with a marked reduction of its dependence on current and device geometry. For 10 μm×40 μm emitter devices, maximum common emitter current gains (β) of 1630 and 725 were measured at a current density of ∼6.3 kA/cm2 on the tilted and flat substrates, respectively. On the tilted substrate, both the emitter injection efficiency and base transport factor are increased. We have used compositionally graded emitter-base (e-b) and abrupt base-collector (b-c) junctions. We find that the abrupt b-c junction does not result in an offset voltage but certainly reduces the electron collection efficiency, and hence the gain, in the region where it is forward biased. The device characteristics and the current gain on both substrates were essentially independent of temperature between 25 and 100 °C, except for a slight decrease of gain with increasing temperature.
Time- and frequency-resolved measurements of frequency modulation and switching of a tunable semiconductor laser
Authors: Kuznetsov M. , Stone J. , Stulz L. W.
Published: July 2002

We report measurements of intensity as a function of both time and frequency for frequency modulation and switching of a tunable semiconductor laser. Because of the uncertainty principle limitations, the measured time-frequency signal can have a complex structure and does not show the simple-minded picture of a laser spectrum whose center frequency varies in time. The observations are explained by a theory of the time-dependent spectral measurements, well known in the field of speech analysis. We discuss implications for channel switching speed and channel interference in switched, frequency-multiplexed optical networks.
Infrared optical properties of lateral superlattices on vicinal planes
Authors: Sham L. J.
Published: July 2002

In a quantum well on a vicinal plane, the lowest band gap caused by a lateral periodic potential due to artificial structures with the period of the steps is estimated. The absorption spectrum of transitions across the minigap is calculated. Factors leading to possible applications as opto-electronic devices are discussed.
Factors controlling resolution in the laser-induced aqueous etching of semiconductors using a focused cw beam
Authors: Li Shi , Scelsi Giuseppe , Ruberto Mark N. , Scarmozzino Robert , Osgood Richard M.
Published: July 2002

We present a study of selected factors which can control or improve the resolution of light-induced wet etching of semiconductors; specifically we examine the case of a focused Gaussian cw laser beam. The results have important implications for the recent application of the technique to the maskless fabrication of integrated optic device structures. Factors considered include semiconductor doping, solution composition, laser intensity, and the effect of applied bias. Results are discussed in the context of hole diffusion and drift in the semiconductor and transport through the solution/semiconductor interface.
Thermal stabilities and microstructures of tungsten compound contacts on n-GaAs fabricated by low-energy ion-beam-assisted deposition
Authors: Park Chul Soon , Lee Jae Shin , Kang Jin Young , Lee Jeong Yong
Published: July 2002

A low-energy ion-beam-assisted deposition (IBAD) technique has been developed to fabricate W-Si-N Schottky contacts of enhanced thermal stabilities on n-GaAs. By implementing remote sputtering and glancing angle low-energy N+ ion irradiation, the thermal stabilities of the W-Si-N/n-GaAs Schottky contacts were enhanced to be stable up to 850 °C, while keeping the Schottky barrier heights to the best values obtained with conventional sputtering. Thermal stabilities of the IBAD refractory metals/n-GaAs interfaces were investigated also for various W-Si-N compositions by examining the microstructure and Schottky diode characteristics. WSi0.3N0.4 showed the most stable Schottky contacts on n-GaAs of which the barrier height changed only 20 meV after thermal annealing between 700 and 850 °C, and that is proposed to be due to the stable metallurgical microstructure compared to the element tungsten and tungsten nitride.
Passive mode locking of a multistripe single quantum well GaAs laser diode with an intracavity saturable absorber
Authors: Zarrabi Joseph H. , Portnoi E. L. , Chelnokov A. V.
Published: July 2002

A multistripe, single quantum well GaAs laser diode is passively mode locked without an external cavity. The intracavity saturable absorber is formed by ion implantation of the laser diode’s facet. The dose and energy of implanted ions were adjusted to achieve mode locking. This monolithically integrated laser diode and saturable absorber generates 40 GHz optical pulses with a pulse width of 5 ps.
N-channel enhancement mode field-effect transistors in Hg1−xCdxTe grown by organometallic epitaxy (direct alloy growth process)
Authors: Bhat I. B. , Parat K. K. , Ehsani H. , Ghandhi S. K.
Published: July 2002

N-channel metal-insulator semiconductor field-effect transistors were fabricated in Hg1−xCdxTe layers grown by the organometallic vapor phase epitaxy, using the direct alloy growth technique. As-grown layers, which were p type due to Group II vacancies, were used as the starting material. Then n-type source and drain regions were formed using a planar process for selective annealing of the Hg1−xCdxTe. The gate insulator consisted of 200 Å of native anodic sulfide followed by 2500 Å of thermally evaporated zinc sulfide. Indium was used as the gate metal. Details of device fabrication and characteristics are described here.
Free hole gas and its coupling to phonons in ZnSe:Li layers
Authors: Olego D. J. , Petruzzello J. , Marshall T. , Cammack D.
Published: July 2002

The presence of a free hole gas and its coupling to longitudinal optical phonons were established with Raman spectroscopy in Li doped ZnSe layers grown by molecular beam epitaxy on GaAs substrates. The phonon spectra shift to higher frequencies and broaden with increasing acceptor concentration and temperature, according to the behavior of coupled phonon-plasmon modes. Values for the concentration and mobility of the holes were obtained from the analysis of the spectral line shapes. They agree with determinations by other methods. A linear relationship was found between the spectral broadening and the hole concentration.
Demonstration of the heterostructure field-effect transistor as an optical modulator
Authors: Taylor G. W. , Vang T. , Sargood S. K. , Cooke P. , Claisse P.
Published: July 2002

A new semiconductor waveguide absorption modulator is demonstrated utilizing the heterostructure field-effect transistor structure. The modulator of 300 μm length and 10 μm width achieves an extinction ratio of 8 for a gate voltage change of 2.5 V and an absorption change greater than 2300 cm−1. The transistor transconductance is 92 ms/mm for a 1 μm device and an identical structure has been reported as an edge-emitting laser providing an ideal combination for optoeletronic integration.
Magnetic field dependence of sputtering magnetron efficiency
Authors: Goree J. , Sheridan T. E.
Published: July 2002

A Monte Carlo simulation of electron transport is used to predict the dependence of the ionization efficiency on the magnetic field strength of a planar magnetron. This offers insight into the operation of the magnetron, and it also provides two valuable practical results. First, the efficiency increases with field strength only up to a saturation level. Operating a magnetron with a stronger field strength would only lead to an undesirable loss of target utilization. Second, a scaling law is found that is useful for designing magnetrons of different sizes.
Indirect-to-direct transition of stimulated emission in AlxGa1−xAs
Authors: Rinker M. , Kalt H. , Lu Y.-C. , Bauser E. , Ganser P. , Köhler K.
Published: July 2002

The sensitivity of the threshold for stimulated emission on temperature is typically described by the T0 parameter of a heuristic exponential law. This T0 parameter has a value of about 80 K in AlxGa1−xAs heterostructures with a direct fundamental gap, while it is rather large (300 K) in indirect-gap AlxGa1−xAs. Samples with an AlAs mole fraction (here x=0.43 and 0.44) close to the direct-to-indirect crossover change the nature of their fundamental gap, and thus the dominant channel for stimulated emission, from indirect to direct with rising lattice temperature. This temperature-induced change in bandstructure is reflected in a drastic change of the T0 parameter. As a direct consequence of the differential T0 values, indirect-gap Al0.46Ga0.54As has a room-temperature threshold comparable to the standard laser material Al0.33Ga0.77As.
AlGaSb/GaSb diodes grown by molecular-beam epitaxy
Authors: Longenbach K. F. , Wang W. I.
Published: July 2002

AlGaSb p-i-n diodes have been grown by molecular-beam epitaxy on (100) and (111) B substrates, with the devices grown on (111)B substrates exhibiting a higher breakdown voltage and lower leakage current than those grown on (100) substrates. The superior performance of devices fabricated on (111) substrates is attributed to the improved incorporation of Sb during growth on the Sb-rich (111)B face. Increasing the Sb incorporation reduces the density of p-type native defects and thus improves intrinsic layer quality. It is also shown that the best surface morphology is obtained by utilizing slightly misoriented (111)B substrates.
Picosecond optical gain in the mid-infrared by nonequilibrium split-off holes in p-type germanium
Authors: Woerner M. , Elsaesser T. , Kaiser W.
Published: July 2002

Transient excess populations of the split-off valence band created by picosecond infrared excitation of p-type germanium are monitored via optical gain at wavelengths around 4.7 μm. A transient gain coefficient of 5 cm−1 during the excitation pulse is found in spectrally and time-resolved pump-probe studies of the split-off→light-hole transition. The amplification is due to the very high generation rate of split-off holes, the different transient temperatures of split-off and light holes, and the exceptionally strong radiative transition probability.
On the role of mobility and saturated velocity in the dynamic operation of p-i-n and metal-semiconductor-metal photodetectors
Authors: Tiwari Sandip , Tischler Michael A.
Published: July 2002

We have employed the temperature dependence of the response of lateral p-i-n and metal-semiconductor-metal photodetectors fabricated with Ga0.47In0.53As active regions to determine the role of low and high-field transport properties of electrons and holes in the speed and frequency response. The p-i-n structures exhibit a response with two characteristic time constants and show a significantly larger improvement in response time at lower temperatures than that expected from improvements in saturated velocities alone. It is suggested that upon excitation by photons, the initial stage of the response is characterized by low-field ambipolar conditions with electron transport and collection dominating the response. This is followed by high-field unipolar conditions where hole transport and collection dominates the response. Thus, low-field mobility, which has a stronger temperature dependence, is also important to the operation of photodetectors.
Role of hydrogen in synchrotron-radiation-stimulated evaporation of amorphous SiO2 and microcrystalline Si
Authors: Akazawa H. , Takahashi J. , Utsumi Y. , Kawashima I. , Urisu T.
Published: July 2002

We report on the photostimulated evaporation of amorphous SiO2 and microcrystalline Si by synchrotron radiation in ultrahigh vacuum and in H2 ambients up to 0.08 Torr. For a-SiO2, the evaporation was slowed by introduction of H2, which suggests that the highly efficient decomposition process is hindered by hydrogen termination (-OH species formation). For μc-Si, the evaporation rate in ultrahigh vacuum was strongly affected by the degree of crystallization. The evaporation rate doubled with introduction of 0.08 Torr H2. Hydrogenation of the surface (SiHx species formation) slightly reduces the activation barrier for evaporation.
Laser surface modification for selective electroplating of metal: A 2.5 m/s laser direct write process
Authors: Malba Vincent , Bernhardt Anthony F.
Published: July 2002

A very fast laser direct write process is described. The process involves laser modification of an insulating seed multilayer to form a conducting surface which can be electroplated. The seed layer is composed of an adhesion layer of TiW, a conducting layer of Au, and a top insulating layer of α-Si. The laser forms a Au-Si mixture without substantially affecting the adhesion layer. Writing speeds of 2.5 m/s have been demonstrated. The laser patterning can be performed in air, and the process works over a broad range of laser power (Pmax/Pmin ∼ 5).
Enhanced two-wave mixing in a photorefractive waveguide having a periodically reversed c-axis by electrical poling technique
Authors: Ito Fumihiko , Kitayama Ken-ichi , Nakao Osamu
Published: July 2002

Propagation angle sensitivity of two-wave mixing is observed in a photorefractive BaTiO3 waveguide having a periodically reversed c-axis. The periodic reversal of the c-axis is realized for the first time by adopting an electrical poling technique in which the polarization of the applied electric field is cyclically reversed along the waveguide axis.
Large second-harmonic response of C60 thin films
Authors: Wang X. K. , Zhang T. G. , Lin W. P. , Liu Sheng Zhong , Wong G. K. , Kappes Manfred M. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

Second harmonic generation measurements were performed using 1.064 μm pulses provided by a Nd:YAG laser. A bulk second-order susceptibility χ(2)z, zz = 2.1 × 10 − 9 esu was observed at room temperature, which is about 1.5 times the χ(2) value of quartz. χ(2) values in a poling field were studied as a function of temperature; the largest value occurred at a nominal temperature of 140 °C where χ(2) is ten times larger than the room temperature value.
Study of As-doping and surface reconstructions in molecular beam epitaxy grown CdTe(100) on BaF2-CaF2/Si(100)
Authors: Tiwari A. N. , Blunier S. , Zogg H.
Published: July 2002

Heteroepitaxial As doped p-type CdTe (100) layers have been grown for the first time on Si(100) by molecular beam epitaxy using stacked BaF2-CaF2 as a buffer. The doping activation is accomplished using an extra Cd source and laser illumination of the substrate during growth. The surface reconstructions have been studied during the CdTe growth under different conditions and the induced effects on Te desorption, Cd migration, and As substitution on Te vacancy site have been correlated. The resistivity of As doped CdTe layers is down to 20 Ω cm. The 8 K photoluminescence spectra of such a layer shows a dominant (A°, X) peak at 1.590 eV with full width at half maximum of 1.2 meV, and the As acceptor level corresponds to a shallow level with ≊60 meV activation energy.
Patterned Y1Ba2Cu3Oy films on Y2BaCuO5 substrates by a surface diffusion process
Authors: Lee Kiejin , Park Gwangseo
Published: July 2002

A technique which combines the fabrication and the patterning of 10-μm-thick films of the high Tc superconducting Y1Ba2Cu3Oy directly on the Y2BaCuO5 ceramic substrates has been developed. The Ba3Cu5Oy(3BaCuO2+2CuO) powders were patterned on the substrate by silk-screen printing and then heat treated at 930 °C for 3 h in an oxygen atmosphere. Measurements of resistivity and critical current density at 77 K for a patterned Y1Ba2Cu3Oy film with a 250-μm width and 10-μm thickness show zero resistivity at 88 K and 103 A/cm2, respectively. The microwave loss measured on the Y2BaCuO5 substrate is found to be negligibly low below 77 K.
Absence of electrical activity at high-angle grain boundaries in zone-melt-recrystallized silicon-on-insulator films
Authors: Evans P. V. , Smith D. A. , Thompson C. V.
Published: July 2002

Zone-melt recrystallization (ZMR) of polycrystalline silicon-on-insulator films has been used to produce a variety of tilt grain boundaries for electrical characterization. Electron channeling patterns reveal the grains to have misorientations up to ∼25° and the parallel boundaries to be separated by distances of up to ∼1 mm. Current-voltage measurements indicate that the boundaries are electrically inactive, with no evidence of defect gap states even after long high-temperature anneals.
Effect of fluorine-ion implantation on buried nitride silicon-on-insulator structures
Authors: Virdi G. S. , Rauthan C. M. S. , Pathak B. C. , Khokle W. S.
Published: July 2002

Effect of fluorine-ion (19F+) implantation on the buried silicon nitride silicon-on-insulator (SOI) structures was investigated. Fluorine was introduced before and after the synthesis of buried Si3N4 layers in silicon by high-dose nitrogen ion (14N+) implantation. Infrared transmission spectropscopy and glancing angle x-ray diffraction studies show that 19F+ implantation before SOI synthesis inhibits the growth of larger-size polycrystalline Si3N4 grains, whereas after the synthesis it removes undesired polycrystalline silicon and helps to obtain larger-grain-size α-polycrystalline silicon nitride in few preferred planes.
Low threshold current grating-coupled surface-emitting strained-InGaAs single quantum well laser with GaAs optical confinement structure
Authors: Takigawa Shinichi , Bacher Ken , Aronson Lewis B. , Harris James S.
Published: July 2002

We have demonstrated low threshold current operation of a grating-coupled surface-emitting strained-InGaAs single quantum well laser with a distributed Bragg reflector. By considering the field discontinuity at the gain/grating section interface, our calculations show that the GaAs optical confinement structure can provide high effective reflectivity in the grating section. As a result, continuous wave threshold currents as small as 15 mA were attained at 22 °C, which is the lowest threshold current reported for a grating-coupled surface-emitting laser fabricated without epitaxial regrowth.
Ferroelectric liquid crystal modulator using twisted smectic structure
Authors: Patel J. S.
Published: July 2002

We describe an electro-optic modulator using ferroelectric liquid crystal. A smectic C* material with a 45° tilt angle is sandwiched between two glass plates with buffing directions perpendicular to each other. This produces a twisted smectic structure in absence of an electric field. When used with polarizers, the twisted structure can be electrically distorted to produce optical modulation on a sub-millisecond time scale using less than 1 V/μm.
Photon-gated photochemical hole burning by two-color sensitization of a photoreactive polymer via triplet-triplet energy transfer
Authors: Machida Shinjiro , Horie Kazuyuki , Yamashita Takashi
Published: July 2002

A new system of photon-gated photochemical hole burning is presented: zinc-tetratolyl-tetrabenzoporphine in glycidyl azide polymer matrix. The two-color irradiation with dye laser and Ar+ laser at 20 K forms holes 500 times more efficiently than the one-color irradiation with dye laser alone. No change in the area of Q-band in the absorption spectra of the guest molecules during hole formation indicates that the sensitized decomposition of azide groups via triplet-triplet energy transfer from the higher excited triplet state of the guest molecules causes the change in guest-host interaction leading to the hole formation.
Investigation of the nucleation of oxygen precipitates in Czochralski silicon at an early stage
Authors: Zimmermann H. , Falster R.
Published: July 2002

The nucleation of oxygen precipitates in Czochralski silicon is examined in an early stage by measuring vacancy profiles with platinum diffusion. Using an analytical expression, which was deduced from the equations of the Frank–Turnbull diffusion mechanism, the vacancy profiles are calculated from measured platinum diffusion profiles. The vacancy concentration of differently treated Czochralski (CZ) material is compared to the vacancy concentration of float zone (FZ) silicon. In CZ silicon a decrease of the vacancy concentration with increasing nucleation time and platinum diffusion time is found. This decrease cannot be explained by a supersaturation of silicon self-interstitials caused by nucleation and by recombination of self-interstitials and vacancies alone. A direct consumption of vacancies during nucleation also is present. The annihilation rate of the vacancies during nucleation can be estimated to be smaller than 5×108 cm−3 s−1 at 770 °C.
Distributed feedback operation of optically pumped ZnSe quantum-well lasers in the blue-green
Authors: Ishihara T. , Brunthaler G. , Walecki W. , Hagerott M. , Nurmikko A. V. , Samarth N. , Luo H. , Furdyna J.
Published: July 2002

Distributed feedback operation of optically pumped (Zn,Cd)Se/ZnSe quantum-well lasers has been realized at room temperature. The periodic grating structure was fabricated by short wavelength holographic lithography and dry etching techniques. These results are relevant also in the context of the new blue-green diode lasers, based on this same quantum-well system.
Evidence for the neutral charge state model of the DX center from low temperature Hall mobility measurements
Authors: Leith G. A. , Zukotynski S. , SpringThorpe A. J.
Published: July 2002

The dependence of the Hall mobility on DX center occupancy in a sample of Si-doped Al0.3Ga0.7As is measured at 40 K. The occupancy of the DX centers is adjusted by means of the persistent photoconductivity effect. The theoretical mobility is calculated for both the neutral and negative charge state models of the DX center. The calculation includes the effect of dynamic screening, and uses values of the impurity concentrations measured by both Hall effect and secondary ion mass spectroscopy. The experimental results are found to be in much better agreement with the neutral charge state model.
Thermoelectric cooling at very low temperatures
Authors: Kapitulnik Aharon
Published: July 2002

We present a theoretical analysis of a thermoelectric cooler that can operate below liquid-He temperatures. Using a metal close to its metal-insulator transition, we show that the figure of merit for such a thermoelectric cooler improves with decreasing temperature. With a proper choice of materials, such a cooler can be used in arbitrarily low temperatures and possibly replace devices such as a dilution refrigerator.
Properties of a SiNx/Si/GaAs system having amorphous and crystalline Si interlayers on (100) GaAs with different surface superstructures
Authors: Fujieda Shinji , Benoit Emmanuel , Baba Toshio
Published: July 2002

A variation of the electrical properties of SiNx/Si/GaAs system having amorphous and crystalline Si (a-Si, c-Si) interlayers on (100) GaAs with c(4×4), 2×4, and 4×6 surfaces is demonstrated. We interpret the findings in terms of Ga and As incorporation into the Si interlayers, which should form acceptor and donor levels, respectively. The dissimilar effects of a-Si and c-Si interlayers are attributed to Ga segregation during the growth of c-Si, which is suggested by the secondary-ion mass spectroscopy of c-Si films grown on GaAs.
Atomic resolved material displacement on graphite surfaces by scanning tunnelling microscopy
Authors: Moriarty Philip , Hughes Greg
Published: July 2002

Atomic scale modifications and subsequent atomic resolution imaging has been achieved on the highly oriented pyrolytic graphite surface in air. Application of short pulse voltages, above a minimum threshold voltage of 3.5 V, across the tunneling gap results in the displacement of a layer or more of atoms to form a hole and create a neighboring mound or ‘‘nanodot’’ from the displaced atoms. We have found a correlation between the hole and ‘‘nanodot’’ volume at the atomic level and observe an asymmetric displacement of material in all cases of feature creation. Nanofeatures as small as four carbon atoms at beta sites have been created. Our experimental observations are consistent with the modification process depending on the gradient in the electric field induced by the rise time of the bias pulse voltage and not the pulse duration. Interesting faceting behavior has also been observed around some hole edges. Tip bias pulsing sometimes induced a tip, and not a surface modification, resulting in a change in the observed tunneling image.
Torsional modulus of vapor-grown carbon fibers
Authors: Chen Jianhui , Lu Yan , Church Daniel B. , Patel Dinesh
Published: July 2002

The torsional modulus (G) of vapor-deposited carbon fibers of both as-grown and annealed samples were determined with a torsion pendulum. G is found to be both stress and size dependent. The extrapolated zero-stress value of torsional modulus is 105±5 GPa for a 5.4 μm diameter as-grown fiber and 200±10 GPa for a 8.4 μm diameter annealed fiber. G decreases with increasing diameter. These unusually high values of torsional moduli, compared to other types of carbon fibers, are believed to be the results of the tree-ring structural morphology and the degree of graphitization of these vapor-deposited carbon fibers.
Setback modulation doping of HgTe-CdTe multiple quantum wells
Authors: Hoffman C. A. , Meyer J. R. , Bartoli F. J. , Lansari Y. , Cook J. W. , Schetzina J. F.
Published: July 2002

Photoassisted molecular beam epitaxy has been used to achieve the first setback modulation doping of HgTe-CdTe heterostructures. A 43 Å setback is found to yield a factor-of-2 increase of the mobility over any measured previously for intentionally doped samples, and an 81 Å setback leads to further enhancement of the mobility.
Composition and wavelength dependence of the refractive index in Cd1−xMnxTe epitaxial layers
Authors: Schubert D. W. , Kraus M. M. , Kenklies R. , Becker C. R. , Bicknell-Tassius R. N.
Published: July 2002

We have investigated Cd1−xMnxTe thin films with Mn concentrations of x=0.12, 0.18, 0.30, 0.52, and 0.70. These single crystal layers were grown by molecular beam epitaxy on [001] CdTe substrates. The real part of the refractive index, n, was determined below the band-gap E0 in the range of 0.5–2.5 eV at T=300 K. The parallel reflectivity was measured near the Brewster angle at the YAG laser wavelength of 1.064 μm (hν=1.165 eV). Combining these results with the optical pathlength results (nd) of reflection measurements in a Fourier spectrometer we have determined n(x,ν) over a wide spectral range by utilizing a three parameter fit. The accuracy of these results for n should improve waveguide designs based on this material.
Plasma filled backward wave oscillator without an axial magnetic field
Authors: Botton M.
Published: July 2002

The linear growth rate of the electromagnetic and electrostatic instability in a plasma filled backward wave oscillator without a guiding axial magnetic field, are analyzed. It is shown that the absence of the external magnetic field has a small influence on the electromagnetic instability but profound effects on the electrostatic instability. The operation of a backward wave oscillator is found to be obtained when the space charge of the electron beam is neutralized by the plasma.
Separate confinement electroabsorption modulator for 633 nm light
Authors: Haase M. A. , Misemer D. K. , Olsen L. C. , Vernstrom G. D.
Published: July 2002

A novel guided-wave electroabsorption modulator, based on separate confinement of the optical modes and the applied electric field, is described. When demonstrated for 633 nm light using AlGaAs waveguide technology, the concept provides low insertion loss and extinction ratios as great as 100:1 (20 dB) while operating at less than 10 V. Other advantages include polarization insensitivity and low capacitance.
Formation of p+n junctions by Si++B+ implantation and laser annealing
Authors: Juang M. H. , Cheng H. C.
Published: July 2002

The effects of rapid thermal annealing (RTA) and laser annealing (LA) on the activation and diffusion of ion-implanted boron in Si substrate have been investigated. The implant and anneal regimes, forming good shallow junctions, were presented. The Si+-preamorphized samples boron implanted with a high dosage showed largely enhanced diffusion in RTA processing. The LA process serves as an excellent scheme to effectively activate the dopant and suppress the anomalous diffusion because of its very high heating rate. A high-quality p+/n junction with a leakage current density lower than 2 nA/cm2 and a forward ideality factor of about 1.01 was formed by laser processing.