bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel electron interferometers using field-induced decoupling in double quantum well structures
Authors: Okuda Masahiro , Fujii Kazuhito , Shimizu Akira
Published: July 2002

Novel Aharonov–Bohm type electron interferometers are proposed, which have no curved electron waveguide structures to form a ring geometry. But instead the ring geometry is effectively constructed in a straight double quantum well structure, by the control of the shapes of the wave functions by electric fields. The interferometer has a perfect single-mode channel in each arm of the interferometer as well as the exact 1:1 branching ratio to the two arms, for each electron moving in the plane of the ring.
Improvement of the KrF(B→X) excimer lamp with 248 and 193 nm dual wavelength emission using an Ar buffer
Authors: Nakamura Ichiro , Kannari Fumihiko , Obara Minoru
Published: July 2002

A quasi-continuous KrF(248 nm:B→X)fluorescence of over 8 ms pulse duration with a 100 Hz operation frequency was observed in a microwave-discharge-pumped KrF lamp with an Ar buffer gas in place of the He/Ne buffer. With an average microwave power deposition of 517.1 W, the maximum average KrF fluorescence power was 58.2 W obtained at a KrF intrinsic efficiency of 11.2% with the lamp gas mixture of F2/Kr/Ar=4/2/94(%) at 50 Torr and simultaneously an average ArF(193 nm:B→X) fluorescence power of 17.4 W with over 8 ms pulse duration at a 100 Hz operation frequency was also obtained. Based on the total fluorescence power of ArF and KrF, the intrinsic efficiency becomes as high as 14.6%. The maximum KrF intrinsic efficiency was 13.8% obtained with a lamp gas mixture of F2/Kr/Ar=2/2/96(%) at 50 Torr. The maximum average KrF fluorescence power and KrF intrinsic efficiency with the Ar buffer has exceeded the maximum average KrF fluorescence of 53 W and the corresponding KrF intrinsic efficiency of 8.3% achieved previously with the lamp gas mixture of F2/Kr/He/Ne=2/1/48.5/48.5(%) at 50 Torr. Dual wavelength emission should be useful for those that need both the 248 and 193 nm wavelengths.
Dynamic observation of Si (111) surface using a fast scanning tunneling microscope
Authors: Hosaka Sumio , Hasegawa Tsuyoshi , Hosoki Shigeyuki , Takata Keiji
Published: July 2002

Atomic structures of a Si (111) surface are dynamically observed at a 2 s/frame velocity over a scanning field about 150 Å×150 Å using a fast scanning tunneling microscope (FSTM). A FSTM has been developed and it features a compensation method for probe tip servo position error in the constant current mode. The compensation value is derived from the ratio of tunnel current fluctuation and tunnel current (Δ I/I) in differential-type tunnel current equation. The FSTM provides first dynamic observation of a residual gas molecule adsorption on atomic defects in 7×7 Si adatom reconstructions using a video tape recorder. In addition, a thermal drift of about 10 Å /s, about 30 min after direct electric flash heating of the sample for Si surface cleaning, can be easily observed.
High-power, widely tunable, picosecond coherent source from optical parametric amplification in barium borate
Authors: Huang J. Y. , Zhang J. Y. , Shen Y. R. , Chen C. , Wu B.
Published: July 2002

We report the performance of a type-I barium borate optical parametric amplifier pumped by 15 ps, 355 nm laser pulses. We show that it is possible to obtain narrowband (≂3 Å), high-energy (≥200 μJ), widely tunable (0.4–2 μm) picosecond pulses with a maximum pump-to-signal energy conversion better than 30%.
Photoconductivity of chemically deposited CdS:Y films
Authors: Bhushan S. , Sharma S. K.
Published: July 2002

Photoconductive CdS:Y films prepared by chemical bath technique show photocurrent to dark current ratios of the order of 105. From scanning electron micrographs, a combination of crystalline and noncrystalline growths are inferred. In the presence of Y a maximum transmission of the order of 60% is found. Traps at depths 0.68 and 0.72 eV are found effective.
(√3×√3)B structure on a (5×5)GexSi1−x/Si (111) surface
Authors: Tatsumi T. , Hirosawa I. , Niino T. , Hirayama H. , Mizuki J.
Published: July 2002

A (√3×√3)B structure was found to be formed on a (5×5) GexSi1−x/Si (111) surface on which Ga or Sn atoms did not form any superstructures. The critical B coverage at which a (7×7) pattern disappeared and only a (√3×√3) pattern was visible increased as the fraction (x) of Ge in the substrate layer increased. A Si epitaxial overlayer was grown on the (√3×√3)B/50 Å Ge0.4Si0.6/Si (111) structure at a growth temperature of 300 °C. The observed (−2/3,4/3) reflection intensity in grazing x-ray diffraction was 50 times larger than that of a Si epitaxial layer grown on a (√3×√3)B/Si (111) structure under the same condition. On a GexSi1−x substrate, the B(√3×√3) structure is well preserved at the interface probably because of relief of the interface strain that results from the small size of the boron atom.
Dependence of InGaAs/InP multiquantum well laser characteristics on the degree of substrate misorientation
Authors: van der Ziel J. P. , Logan R. A. , Tanbun-Ek T. , Monberg E. M. , Sergent A. M.
Published: July 2002

The threshold current density, internal quantum efficiency, internal loss, and emission wavelength of InGaAsP/InP multiquantum well lasers, grown by atmospheric pressure metalorganic chemical vapor deposition, were measured as a function of substrate orientation on and away from the (001) towards the nearest [011] and [111]A. The laser parameters are optimized for (001) oriented substrates. Substrate misorientations of more than 3° in either direction yield lasers with increased threshold current density and lower internal quantum efficiency. The internal loss increases and the surface morphology becomes visually poorer for substrate misorientations of 6°. The laser emission shifts to longer wavelength with increasing misorientation.
New nondestructive depth profile measurement by using a refracted x-ray fluorescence method
Authors: Sasaki Yuji C. , Hirokawa Kichinosuke
Published: July 2002

We demonstrated analysis of the nondestructive depth profile near the surface of As ion-implanted Si substrate by using the refracted x-ray fluorescence method. Experimental results show that the angular distribution of the measured x-ray fluorescence is dependent on the surface roughness of the substrate.
Effect of operating electric power on the dynamic behavior of quantum well vertical-cavity surface-emitting lasers
Authors: Chang-Hasnain C. J. , Zah C. E. , Hasnain G. , Harbison J. P. , Florez L. T. , Stoffel N. G. , Lee T. P.
Published: July 2002

We investigated the effect of high operating voltage and series resistance on the dynamic behavior of strained InGaAs/GaAs quantum well vertical-cavity surface-emitting lasers (VCSELs). A large wavelength chirp in the lasing spectrum is observed for the lasers with high voltage/resistance even under low-duty-cycle pulse operation due to resistive heating close to the laser junction. Using an optimized laser design, VCSELs with 2.6 V threshold voltage and 40 Ω resistance are achieved. We believe this is the lowest threshold voltage and resistance reported to date for a 20 μm VCSEL with as-grown mirrors. The wavelength chirp is reduced by nearly two orders of magnitude for these improved lasers.
Electron cyclotron resonance plasma-induced damage in AlGaAs/GaAs/AlGaAs single quantum wells
Authors: Swaminathan V. , Asom M. T. , Chakrabarti U. K. , Pearton S. J.
Published: July 2002

Changes in cathodoluminescence (CL) intensity from a buried single AlGaAs/GaAs/AlGaAs quantum well (QW) as a result of exposure to electron cyclotron resonance (ECR) hydrogen or argon discharges are reported. For additional dc biases of 150 V on the sample during either H2 or Ar plasma exposure, we observe substantial decreases in CL intensity from the well. Ar+ ion bombardment creates damage more resistant to annealing than does H+ ion bombardment at the same energy. The ECR discharges alone with zero additional dc bias cause degradation in the well luminescence due possibly to defects created by energetic electron bombardment or ultraviolet illumination. At intermediate bias voltages (50 V) strong hydrogen passivation of nonradiative centers is observed, leading to 500% increases in CL intensity from the well. The initial characteristics of the QW under these conditions are restored by annealing at 400 °C.
Low radio frequency biased electron cyclotron resonance plasma etching
Authors: Samukawa Seiji , Toyosato Tomohiko , Wani Etsuo
Published: July 2002

A radio frequency (rf) biased electron cyclotron resonance (ECR) plasma etching technology has been developed to realize an efficient ion acceleration in high density and uniform ECR plasma for accurate Al-Si-Cu alloy film etching. In this technology, the substrate is located at the ECR position (875 G position) and the etching is carried out with a 400 kHz rf bias power. This Al-Si-Cu etching technology achieves a high etching rate (more than 5000 A/min), excellent etching uniformity (within ±5%), highly anisotropic etching, and Cu residue-free etching in only Cl2 gas plasma. These etching characteristics are accomplished by the combination of the dense and uniform ECR plasma generation at the ECR position with the efficient accelerated ion flux at the ECR position by using 400 kHz rf bias.
Observation of resonant tunneling in InSb/AlInSb double-barrier structures
Authors: Söderström J. R. , Yao J. Y. , Andersson T. G.
Published: July 2002

We report the first observation of resonant tunneling in the InSb/AlxIn1−xSb material system. Five samples with InSb quantum well thicknesses ranging from 70 to 110 Å and Al0.5In0.5Sb barrier thicknesses ranging from 22 to 36 Å were grown by molecular beam epitaxy on GaAs(100) substrates at a temperature of 420 °C. The best sample, which had 22-Å-thick barriers and a 110-Å-thick quantum well, displayed a peak-to-valley current ratio of 1.4(3.9) at room temperature (77 K) with a corresponding peak current density of 3.6×104 A/cm2. Transmission electron microscopy revealed threading dislocations, misfit dislocations, and microtwins in the barrier region.
Sharp boron spikes in silicon grown by fast gas switching chemical vapor deposition
Authors: Roksnoer P. J. , Maes J. W. F. M. , Vink A. T. , Vriezema C. J. , Zalm P. C.
Published: July 2002

Boron-doping spikes in Si have been grown by fast gas switching chemical vapor deposition at 800 or 850 °C using Si2H6 in 0.03 or 0.1 atm H2, respectively. The B2H6 doping gas was added for 2 s in two ways, viz. during growth, or as a flush while the Si2H6 was interrupted. High-resolution secondary-ion mass spectrometry (HR-SIMS) analysis has revealed the sharpest as-measured SIMS dopant profiles reported for Si grown by deposition from the gas phase. Electrical measurements show the sheet resistivity of the B spikes to be as low as 580 Ω/⧠.
Demonstration of a heterostructure field-effect laser for optoelectronic integration
Authors: Taylor G. W. , Claisse P. R. , Cooke P.
Published: July 2002

A new laser structure suitable for optoelectronic integration is reported. It utilizes field effect at a heterointerface within the same structure used to build field-effect transistors. A threshold current density of 560 A/cm2 and a differential quantum efficiency of 56% were achieved.
Low-resistivity p-type ZnSe through surface Fermi level engineering
Authors: Woodall J. M. , Hodgson R. T. , Gunshor R. L.
Published: July 2002

Low-resistivity p-type ZnSe is difficult to make. This has been associated with the equilibrium thermodynamics of self-compensation of the p-type dopant by donor-like Se vacancies. We suggest that the bulk Se vacancy concentration can be vastly reduced by positioning the surface Fermi level near the conduction-band edge during the low-temperature epitaxial growth of p-doped ZnSe. This procedure is expected to minimize the equilibrium Se vacancy concentration at the surface, leading to a much lower than equilibrium Se vacancy concentration in the bulk. Experiments which could test this concept include liquid phase epitaxy growth of ZnSe from As or Li doped low work function melts such as Sn, and As doping during molecular beam epitaxy growth of ZnSe on (111)A surfaces.
Growth of microcrystal silicon by remote plasma chemical vapor deposition
Authors: Kim Sung Chul , Jung Moon Hyun , Jang Jin
Published: July 2002

We have studied the growth of microcrystal silicon films by remote plasma chemical vapor deposition as growth parameters of substrate temperature and rf power. With increasing substrate temperature, the growth rate increases because of the decrease of the etch rate. The rf power dependence shows that the growth rate decreases with increasing rf power at high power levels. The results indicate that the chemical equilibrium between the deposition and etching of Si on the growing surface gives rise to the growth of microcrystal Si, resulting in the optimum rf power and substrate temperature for the growth of microcrystalline silicon.
Investigation of the thermalization of sputtered atoms in a magnetron discharge using laser-induced fluorescence
Authors: Park W. Z. , Eguchi T. , Honda C. , Muraoka K. , Yamagata Y. , James B. W. , Maeda M. , Akazaki M.
Published: July 2002

The thermalization of sputtered atoms in a magnetron discharge was investigated using laser-induced fluorescence. The results clearly indicated for the first time that the velocity distribution agrees well with the Thompson formula [M. W. Thompson, Philos. Mag. 18, 377 (1968)] for d/λ≪1, while a thermalized component becomes appreciable for d/λ≳1, where d is the distance from the cathode surface and λ is the mean free path of sputtered atoms for collisions with filling gas atoms.
High-power, cw, diffraction-limited, GaAlAs laser diode array in an external Talbot cavity
Authors: Waarts Robert , Mehuys David , Nam Derek , Welch David , Streifer William , Scifres Donald
Published: July 2002

A 20-element linear array of single transverse mode semiconductor lasers is operated in an external Talbot cavity. A total cw output power of 250 mW in a diffraction-limited far field and 29% differential efficiency is obtained with a 50% output coupler. By decreasing the output mirror reflectivity to 20%, 900 mW cw in a 1.7 times diffraction-limited radiation pattern with an increased differential efficiency of 38% is obtained. The low fill factor of the array (1:12) acts as a spatial mode-selective filter resulting in strong mode discrimination.
Spontaneous emission and laser oscillation properties of microcavities containing a dye solution
Authors: Yokoyama H. , Suzuki M. , Nambu Y.
Published: July 2002

An experimental study on spontaneous and stimulated emission properties of planar optical microcavities confining an organic dye solution is reported. The lasing threshold in an input-output curve became indistinct by decreasing the distance between a pair of dielectric reflectors. The coupling ratio of spontaneous emission into a laser mode was as large as 0.2 for a cavity half a wavelength distance. Differences between the spontaneous emission dominant regime and the stimulated emission dominant regime were also examined with emission spectra and emission lifetime measurements.
Hydrogenation effect on electrical and optical properties of GaAs epilayers grown on Si substrates by metalorganic chemical vapor deposition
Authors: Kim Eun Kyu , Cho Hoon Young , Kim Yong , Kim Hyeon Soo , Kim Moo Sung , Min Suk-Ki
Published: July 2002

Hydrogenation effects on electrical and optical properties in GaAs epilayers grown on Si substrate by metalorganic chemical vapor deposition have been investigated. In as-grown GaAs layers on Si substrates, typically four deep levels at 0.81, 0.68, 0.57, and 0.53 eV below the conduction band were observed by deep level transient spectroscopy. After hydrogen plasma exposure at 250 °C for 2.5 h, the 0.68 eV level disappeared. In addition, the reverse leakage current in the hydrogenated sample decreased by three orders of magnitude compared to the untreated sample. These effects persist after dehydrogenation process with a 5 min, 400 °C anneal. The results indicate that the hydrogenation for GaAs-on-Si has some benefits to its device application.
Single-mode very wide tunability in laterally coupled semiconductor lasers with electrically controlled reflectivities
Authors: Griffel Giora , Chen Howard Z. , Gravé Ilan , Yariv Amnon
Published: July 2002

Tunable, single longitudinal mode spectrum of a novel monolithic, laterally coupled semiconductor stripe laser has been demonstrated. A tuning range of 14.2 nm, which is the widest observed so far in a monolithic device, has been achieved.
Thermally stable and nonspiking Pd/Sb(Mn) ohmic contact to p-GaAs
Authors: Han C. C. , Wang X. Z. , Lau S. S. , Potemski R. M. , Tischler M. A. , Kuech T. F.
Published: July 2002

A thermally stable, nonspiking ohmic contact to p-GaAs has been developed based on the solid-phase regrowth mechanism. The contact metallization consists of a layered structure of Pd(250 Å)/Sb(100 Å)/Mn(10 Å)/Pd(250 Å)/p-GaAs. Thermal annealing of the contact between 300 and 600 °C for 10 s yields contact resistivities in the range of low 10−6 Ω cm2 on substrates doped to 2.5×1018 cm−3. A contact resistivity of 4.5×10−7 Ω cm2 can be obtained after annealing at 500 °C on samples with a doping concentration of 4.5×1019 cm−3. The contact metallization remains uniform in thickness and the contact interface is flat after the contact is formed. The consumption of the substrate is limited to less than a hundred angstroms. Contact resistivities are stable at 400 °C.
Raman scattering from InxGa1−xAs/GaAs strained-layer superlattices
Authors: Wu Chuanyong , Lao Pudong , Shen S. C.
Published: July 2002

Measurements of room-temperature Raman scattering were performed on InxGa1−xAs/GaAs strained-layer superlattices, grown by molecular beam epitaxy, with superlattice periods of 230 Å and In concentration x values of 0.1 and 0.2. We use, for the first time, the ‘‘spatial correlation’’ model as well as the splitting mechanism of the corresponding Raman peaks to account for the line shape of the Raman peak around 291 cm−1.
Gas source molecular beam epitaxy growth of short period GaP/AlP(001) superlattices
Authors: Asahi Hajime , Asami Kumiko , Watanabe Tetsuya , Yu Soon Jae , Kaneko Tadaaki , Emura Shuichi , Gonda Shun-ichi
Published: July 2002

Short period GaP/AlP superlattices are grown on GaP and GaAs substrates at 600 °C by gas source molecular beam epitaxy with growth interruption. Alternating monolayer growth of GaP and AlP is confirmed by the observation of the reflection high-energy electron diffraction intensity oscillations during growth. The formation of short period superlattice structures and the zone-folded LO phonons are observed in the x-ray diffraction rocking curves and Raman spectra, respectively.
Channel waveguides in electro-optic polymers using a photopolymer cladding technique
Authors: Ashley Paul R. , Tumolillo Thomas A.
Published: July 2002

Reported here is a new fabrication technique for forming channel waveguides in organic electro-optic (EO) polymer materials. The process uses projection printing to directly expose inverted ridge channel patterns in a UV curing optical epoxy cladding layer. This technique is noncontact, requires no post processing, minimizes wall roughness, and can be used with any spin coatable EO polymer. Single-mode channel waveguides have been demonstrated and characterized as well as phase modulator devices.
High-pressure photoluminescence study of ordered Ga0.5In0.5P alloys grown on GaAs by organometallic vapor phase epitaxy
Authors: Kobayashi Toshihiko , Deol Rajpal S.
Published: July 2002

Photoluminescence (PL) measurements on Ga0.5In0.5P grown by organometallic vapor phase epitaxy on GaAs substrates at various growth temperatures have been made as a function of pressure up to about 4.5 GPa. In the pressure range 0–3.8 GPa the PL spectrum exhibits a shift to higher energies. It is found that the pressure coefficient of the PL peak energy depends significantly on the growth temperature and hence on the degree of ordering. These results are partly explained in terms of repulsion between the Γ-folded energy states in the CuPt-type ordered structure.
High-quality YBa2Cu3O7−x thin films by plasma-enhanced metalorganic chemical vapor deposition at low temperature
Authors: Zhao J. , Li Y. Q. , Chern C. S. , Lu P. , Norris P. , Gallois B. , Kear B. , Cosandey F. , Wu X. D. , Muenchausen R. E. , Garrison S. M.
Published: July 2002

Single-crystalline epitaxial YBa2Cu3O7-x thin films with a sharp superconducting transition temperature of 90 K and a critical current density of 3.3×106 A/cm2 at 77 K were prepared by a plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. The films were formed in situ on (100) LaAlO3 substrates at a temperature of 670 °C in 2 Torr partial pressure of N2O. X-ray analysis indicated that films grew epitaxially with the c-axis perpendicular to the substrate and the a and b axes uniformly aligned along the LaAlO3 [100] directions. High-resolution transmission electron microscopy along with electron diffraction revealed that the films grew epitaxially with atomically abrupt film-substrate interfaces. The high degree of epitaxial crystallinity of the films was also confirmed by Rutherford backscattering spectroscopy which gave a minimum channeling yield of 9%.
Parameter ranges for ultrahigh frequency mode locking of semiconductor lasers
Authors: Palaski J. , Lau K. Y.
Published: July 2002

The inclusion of an intracavity saturable absorber for ultrahigh-frequency passive mode locking of semiconductor lasers also produces intensity self-pulsation in many instances. We examined experimentally and theoretically the deleterious effect of self-pulsation on ultrahigh-frequency mode locking, and arrived at the conclusion that lasers with high reflectivity coatings can most reliably achieve mode locking without being adversely affected by self-pulsation.
Low temperature and low pressure diamond synthesis in a microwave electron cyclotron resonance discharge
Authors: Chang J. J. , Mantei T. D. , Vuppuladhadium Rama , Jackson Howard E.
Published: July 2002

High quality diamond films have been grown at low temperature (540–650 °C) and low pressure (2–20 Torr) in a microwave electron cyclotron resonance CH4-O2-H2 discharge. The films were characterized by microprobe Raman spectroscopy and scanning electron microscopy. Diamond crystals grown at ∼600 °C and 10 Torr with 2% oxygen exhibit a characteristic Raman peak at 1334 cm−1 with no accompanying nondiamond carbon peaks.
High quality InGaAsP/InP multiple quantum wells for optical modulation from 1 to 1.6 μm
Authors: Chiu T. H. , Zucker J. E. , Woodward T. K.
Published: July 2002

We show that extremely high quality InGaAsP/InP superlattices grown by chemical beam epitaxy meet the stringent requirements for optical modulator application in the wavelength range from 1 to 1.6 μm. Double crystal x-ray diffraction from multiple quantum well samples of 20 to 100 periods show that the satellite peaks have widths comparable to or narrower than the substrate peak width, which indicates very reproducible thickness and composition control along the growth direction. For optical modulation, a p–i–n waveguide structure consisting of 20 periods 90/90 Å InGaAsP/InP exhibits very sharp excitonic feature and large quantum confined Stark effect near 1.5 μm. A room temperature exciton shift of about 25 meV has been measured for a bias voltage of 100 kV/cm in the photocurrent spectra.
Energy relaxation and dephasing dynamics of colored filter glasses
Authors: Nakano H. , Ishida Y. , Yanagawa T.
Published: July 2002

The energy relaxation and the dephasing time constants of colored filter glass are measured as functions of temperature and the wavelength of the incident light by degenerate four-wave mixing. To investigate the influence of the photodarkening effect on the relaxation time constants, fresh and photodarkened samples are measured. The two samples have almost the same dephasing time constants but their energy relaxation time constants are quite different.
Calculated performance of p+n InP solar cells with In0.52Al0.48As window layers
Authors: Jain R. K. , Landis G. A.
Published: July 2002

We have calculated the performance of indium phosphide solar cells with lattice matched wide band-gap In0.52Al0.48As window layers using the PC-1D computer code. The conversion efficiency of p+n InP solar cells is improved significantly by the window layer. No improvement is seen for n+p structures. The improvement in InP cell efficiency was studied as a function of In0.52Al0.48As layer thickness. The use of the window layer improves both the open circuit voltage and short circuit current. For a typical In0.52Al0.48As window layer thickness of 20 nm, the cell efficiency improves in excess of 27% to a value of 18.74%.
Optical investigation of interface roughness and defect incorporation in GaAs/AlGaAs quantum wells grown with and without growth interruption
Authors: Gurioli M. , Vinattieri A. , Colocci M. , Bosacchi A. , Franchi S.
Published: July 2002

We report a comparative analysis of photoluminescence and photoluminescence excitation of GaAs/AlGaAs quantum well structures grown by molecular beam epitaxy with and without growth interruption, which clearly indicates the improvement of interface quality when interruptions are used during growth. Time resolved spectroscopy, together with the temperature dependence of the integrated radiative recombination intensity, are used as a sensitive probe of the defect incorporation, which is usually observed to increase as a consequence of growth interruptions. We find that a significant increase of both extrinsic photoluminescence and nonradiative processes is not a necessary consequence of growth interruptions, unlike recent reports in the literature. We conclude that growth interruptions are compatible with the growth of high quality quantum well structures with a very high radiative efficiency.
Optically induced excitonic electroabsorption in a periodically δ-doped InGaAs/GaAs multiple quantum well structure
Authors: Larsson A. , Maserjian J.
Published: July 2002

Large optically induced Stark shifts have been observed in a periodically δ-doped InGaAs/GaAs multiple quantum well structure. With an excitation intensity of 10 mW/cm2 we have measured an absolute quantum well absorption change of 7000 cm−1 with a corresponding differential absorption change as high as 80%. The associated maximum change in the quantum well refractive index is 0.04. This material is promising for device development for all-optical computing and signal processing.
Bistability of donor-hydrogen complexes in silicon: A mechanism for debonding
Authors: Estreicher S. K. , Seager C. H. , Anderson R. A.
Published: July 2002

The {D,H}+ complex in silicon, with D=P or As, is studied near the ab initio Hartree–Fock level. The results show that the transitions between {D,H}0 and {D,H}+ involve a drastic change in the equilibrium geometry and electronic structure of the complex. The implications of these results on the observed dependence of the debonding rates on majority- and minority-carrier concentrations for both As and P donors are discussed.
Planar native-oxide index-guided AlxGa1−xAs-GaAs quantum well heterostructure lasers
Authors: Kish F. A. , Caracci S. J. , Holonyak N. , Dallesasse J. M. , Hsieh K. C. , Ries M. J.
Published: July 2002

A new form of planar index-guided laser diode is demonstrated with a relatively thick (∼0.4 μm) native oxide employed to define the lateral optical waveguide (transverse to the laser stripe). Oxidation of high-gap AlxGa1−xAs in a ‘‘wet’’ ambient results in the transformation of most of the upper confining layer to a lower-index current-blocking native oxide outside of the active stripe. Planar quantum well heterostructure (QWH) AlxGa1−xAs-GaAs laser diodes fabricated by this process exhibit both optical and current confinement. Continuous 300 K threshold currents as low as 10 mA (uncoated facets) and kink-free single-longitudinal-mode operation are demonstrated for ∼2-μm-wide active region devices.
High-superconducting critical current densities in YBa2Cu3O7/PrBa2Cu3O7 superlattices
Authors: Jakob G. , Przyslupski P. , Stölzel C. , Tomé-Rosa C. , Walkenhorst A. , Schmitt M. , Adrian H.
Published: July 2002

Well-ordered [(YBa2Cu3O7)nY/(PrBa2Cu3O7)nPr)]m superlattices with high superconducting critical temperatures were prepared by sequential reactive dc sputtering. The superconducting critical current density at 4.5 K reaches values as high as 1.1×107 A/cm2 for a sample with nY = 2 and nPr = 1 and 3.8×106 A/cm2 for nY = 1 and nPr = 3, indicating that the coupling of the CuO2 layers is not necessary for high-jc values. The angular dependence jc(φ) is determined by the component of the magnetic field perpendicular to the a-b planes and shows that these superlattices are two-dimensional systems.
Bistable self-electro-optic operation of strained In0.1Ga0.9As/GaAs asymmetric Fabry–Perot modulators
Authors: Sale T. E. , Woodhead J. , Pabla A. S. , Grey R. , Claxton P. A. , Robson P. N. , Moloney M. H. , Hegarty J.
Published: July 2002

We report bistable operation of a strained-layer InGaAs/GaAs asymmetric Fabry–Perot optical modulator configured as a self-electro-optic effect device (SEED) operating in reflection mode. Bistable loops are observed from 949 to 962 nm with switching powers down to submicrowatt levels. The contrast ratio between on and off states is as large as 5:1 (7 dB) and the device will hold in either state indefinitely. A 600-μm-diam device has a switching time of 20 μs for 2.1 fJ μm−2 switching energy. Large optical latch arrays are envisaged using this device.
High power cw operation of GaAs/GaAlAs surface-emitting lasers mounted in the junction-up configuration
Authors: Ou S. S. , Jansen M. , Yang J. J. , Sergant M.
Published: July 2002

High power cw operation of horizontal cavity monolithic GaAs/GaAlAs surface-emitting lasers with all dry etched micromirrors in the junction-up configuration has been demonstrated for the first time. The 45° and 90° mirrors of the devices were fabricated by ion beam etching and reactive ion etching techniques, respectively. Typical threshold current densities of less than 360 A/cm2, external differential efficiencies of 22% (0.34 W/A) from the emitting facet, and output powers in excess of 280 mW were achieved under cw operation.
High contrast ratio asymmetric Fabry–Perot reflection light modulator based on GaAs/InGaAs multiple quantum wells
Authors: Hu Kezhong , Chen Li , Madhukar Anupam , Chen Ping , Rajkumar K. C. , Kaviani Kian , Karim Zaheed , Kyriakakis Chris , Tanguay Armand R.
Published: July 2002

We report the realization of both high contrast ratio (66:1) and dynamic range (30%) at room temperature in a strained GaAs/InGaAs(100) multiple quantum well based asymmetric Fabry–Perot reflection modulator. The p-i-n configuration modulator also acts as a photodetector and exhibits a high quantum efficiency (∼80%).
Super-Gaussian reflectivity unstable resonator for excimer lasers
Authors: Perrone M. R. , Mezzolla F. , Cali’ C. , Pace C.
Published: July 2002

High-mode-volume, good optical quality laser beams of 55 mJ, of 19 ns duration and with a brightness of 3×1013 W cm−2 Sr−1, have been extracted from a high-gain, short-pulse XeCl laser, with an unstable resonator using a super-Gaussian reflectivity mirror. The misalignment angle of the output coupler to decrease the normalized output energy by 20% was 3.5 mrad.
Comparative study of the perovskite phase microstructure evolution and electrical properties of lead zirconate titanate thin-film capacitors annealed in oxygen and nitrogen ambients
Authors: Chikarmane Vinay , Sudhama Chandra , Kim Jiyoung , Lee Jack , Tasch Al , Novak Steve
Published: July 2002

Lead zirconate titanate [PZT, Pb(ZrxTi1−x)O3, x=0.65, 400 nm] thin-film capacitors with very low leakage current and large stored charge densities (Q′c=Pmax–Pr) for ultralarge scale integration dynamic random access memory (ULSI DRAM) memory applications have been fabricated by reactive dc magnetron sputtering followed by an annealing step. In this letter, we present a comparative study of the significant influence of the use of an oxidizing (O2) as against a nonoxidizing annealing ambient (N2) on the evolution of the perovskite phase microstructure and the electrical properties of PZT capacitors. The phase transformation kinetics are faster in a N2 annealing ambient at low temperatures, yielding capacitors with a large Q′c at low annealing thermal budgets. However, N2 annealed films exhibit a lower breakdown field and time to breakdown which is in agreement with a degradation model based on the field-induced concentration polarization of oxygen vacancies.
Enhancement in critical current density of Bi-Pb-Sr-Ca-Cu-O tapes by thermomechanical processing: Cold rolling versus uniaxial pressing
Authors: Haldar P. , Hoehn J. G. , Rice J. A. , Motowidlo L. R.
Published: July 2002

Critical current densities up to 24 000 A/cm2 (Ic∼23.6 A) at 77 K, zero field, have been measured in short tape samples of silver-sheathed Bi-Pb-Sr-Ca-Cu-O superconductors made by the powder-in-tube technique. These samples carried 3000 A/cm2 at 1 T and 1000 A/cm2 at 2 T, also at liquid-nitrogen temperature. A repeated cold work (rolling and pressing) together with an intermediate heat treatment were required to achieve these properties. Without the pressing, tapes were made with Jc’s as high as 15 000 A/cm2 at 77 K, zero field. The role of uniaxial pressing as compared to rolling is discussed and its implications to long length conductor fabrication described.
Dependence of Al-Ga interdiffusion in AlGaAs on stoichiometry between Ga-rich and As-rich solidus limits
Authors: Olmsted B. L. , Houde-Walter S. N.
Published: July 2002

The effect of stoichiometry on the Al-Ga interdiffusion of undoped AlGaAs/GaAs multiple quantum wells is investigated over the full composition range of the GaAs solidus. The 2 orders of magnitude increase observed in the interdiffusion coefficient suggests that interdiffusion in an intrinsic crystal is mediated predominantly by column III vacancies throughout the whole solidus range. In addition, we observe that the photoluminescence intensity of the Ga-rich crystal is more than 3 orders of magnitude stronger than that of the As-rich crystal.
Photo-modulation of light up-conversion in light transducer using high-gain photoresponsive amorphous silicon carbide combined with organic electroluminescent diode
Authors: Hiramoto Masahiro , Yoshimura Kanji , Yokoyama Masaaki
Published: July 2002

Photo-modulation of light up-conversion was successfully demonstrated in a new type of light transducer using a high-gain photoresponsive amorphous silicon carbide (a-SiC:H) combined with an organic electroluminescent (EL) diode. Green EL output up-converted from red input-light was reversibly photo-modulated by the simultaneously irradiated ultraviolet light due to the effective suppression of photocurrent multiplication in a-SiC:H film. The present device can be applicable to the logic device for two-dimensional optical computing.
All-optical reflectivity tuning and logic gating in a GaAs/AlAs periodic layered structure
Authors: Cada M. , He J. , Acklin B. , Proctor M. , Martin D. , Morier-Genoud F. , Dupertuis M.-A. , Glinski J. M.
Published: July 2002

The optical nonlinearity of a GaAs/AlAs periodic layered structure was experimentally investigated for the first time. The shift of the reflectivity peak with increasing intensity was observed. A reflectivity contrast of about 10:1 was obtained by varying the incident intensity. Hysteresis loops due to the response delay of both the electronic and the thermal nonlinearity were observed. All-optical logic operations were also demonstrated. A further improvement of the structure may lead to a new type of optical bistable device.
Theoretical studies of defect-initiated particle emission from GaP(110) surfaces: Basis for a new technique of generating perfect surfaces
Authors: Itoh N. , Hattori K. , Nakai Y. , Kanasaki J. , Okano A. , Ong C. K. , Khoo G. S.
Published: July 2002

We have calculated the energy needed to eject P atoms from several types of defects on the GaP (110) surface as well as from the perfect surface. It is found that most types of defects have a Ga or P atom bonded less strongly than those on the perfect surface. In view of the result of calculation, and of recent experimental observation that less strongly bonded atoms are ejected by irradiation with laser pulses of lower fluences, we suggest a new method of producing perfect surfaces using laser irradiation to eliminate steps and adatoms and deposition to eliminate vacancies.
Modulation excitation spectroscopy: A method to determine the symmetry of electronic states
Authors: Armelles G. , Alonso M. I. , Castrillo P. , Domínguez P. S.
Published: July 2002

In this letter we present a new method to determine the character of the optical transitions. We apply this method to a single quantum well of GaAs/AlGaAs. We compare a conventional photoluminescence excitation (PLE) spectrum and a piezomodulated PLE spectrum. The observed relative intensity of the light-hole and heavy-hole transitions is different in the former case than in the latter. This method allows us to assign the character of the optical transitions using only one measurement, and is very sensitive and selective.
Composite reaction texturing of superconducting ceramic composites
Authors: Soylu B. , Adamopoulos N. , Glowacka D. M. , Evetts J. E.
Published: July 2002

Textured composite Bi2Sr2Ca1Cu2O8+a (2212) conductors have been fabricated by a novel method termed composite reaction texturing (CRT) that makes use of inert whiskers or fibers to align superconducting grains and control their morphology. The process has two stages, the initial alignment of fibre material in a precursor followed by a composite reaction stage to develop a textured microstructure. In this work, disk-shaped pellets with whisker alignment in the pellet plane were reacted to produce CRT material with a transport critical-current density in excess of 4×103 A cm−2 at 77 K (B=0). At 4.5 K, the critical-current density was ∼105 A cm−2 in zero field and 2.104 A cm−2 at 12 T. The method clearly has promise for the production by a wind-and-react technique of high critical-current conductors with large cross sections.
Thermally stable operation of a bistable Fabry–Perot etalon with a bulk GaAs spacer
Authors: Acklin B. , Bagnoud C. , Dupertuis M. A. , Proctor M. , Morier-Genoud F. , Martin D.
Published: July 2002

We report thermally stable latched operation of a nonlinear Fabry–Perot device without heat sinking other than through the 0.5-mm GaAs substrate. The device has a 2-μm GaAs spacer and integrated dielectric mirrors with reflectivities of 91% and 99%. Operated in reflection at a wavelength of 886 nm, thresholds as low as 1 mW, and contrast ratios of 10:1 have been observed. Measurements of the threshold dependence on the size of the excited spot give evidence for carrier diffusion and light-diffraction effects.
Enhanced growth of device-quality copper by hydrogen plasma-assisted chemical vapor deposition
Authors: Eisenbraun Eric T. , Zheng Bo , Dundon Christopher P. , Ding Pei Jun , Kaloyeros Alain E.
Published: July 2002

A hydrogen plasma-assisted chemical vapor deposition (PACVD) process has been developed for the growth of device-quality copper films on large-area substrates. The process takes advantage of the high concentration of reactive hydrogen species present in the low-power plasma to enhance the clean reduction of copper β-diketonate precursors such as bis(hexafluoroacetylacetonato)copper(II). Copper films were produced at substrate temperatures of 160–170 °C, reactor working pressures of 1.3–1.7 Torr, hydrogen flow rates between 700 and 1200 cc/min, and hydrogen plasma power ranging from 15 to 30 W (with an equivalent power density of ∼0.10–0.25 W/cm2. The films were characterized by x-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, scanning electron microscopy (SEM), and cross-section SEM. These studies indicate that PACVD processes pure, dense, highly uniform films, and allows conformal step coverage and complete hole filling of patterned test structures. Growth rates over large-area substrates were as high as 1000 Å/min.
High-quality Nb/HfOx-Hf/Nb Josephson junction
Authors: Morohashi Shin’ichi , Imamura Takeshi , Hasuo Shinya
Published: July 2002

We fabricated a niobium (Nb) Josephson junction with a hafnium (Hf) overlayer. The Hf native oxide (HfOx), formed by thermal oxidation, was used as the new tunneling barrier. Hf was selected as an overlayer because of its good affinity to Nb and strong oxygen affinity. The junction was fabricated the same way as Nb/AlOx-Al/Nb junctions. The junction showed excellent I-V characteristics (Vm=40 mV and Vg=3.0 mV). The critical current of the junction did not change with annealing up to 250 °C.
The Si/Pd(Si,Ge) ohmic contact on n-GaAs
Authors: Wang L. C. , Li Y. Z. , Kappes M. , Lau S. S. , Hwang D. M. , Schwarz S. A. , Sands T.
Published: July 2002

A modified Si/Pd ohmic contact to n-GaAs has been developed based on the solid-phase regrowth mechanism. The Si/Pd contact usually yields a contact resistivity of 2×10−6 Ω cm2. A thin (∼15 Å) layer of additional Ge or Si embedded in the Pd layer of the Si/Pd contact structure is used to reduce the contact resistivity from ∼2×10−6 to 2–4×10−7 Ω cm 2 without suffering from a loss of thermal stability. The reduction in the contact resistivity is explained in terms of the formation of an n+ GaAs surface layer via solid-phase regrowth. The modified contacts show uniform surface and interface morphologies. The contact resistivity of the modified contacts remains in the mid-10−6 Ω cm2 range after annealing at 400 °C for 50 h.
Reactive ion etching of ZnSe by gas mixture of ethane and hydrogen
Authors: Ohtsuka K. , Imaizumi M. , Sugimoto H. , Isu T. , Endoh Y.
Published: July 2002

ZnSe epitaxial layers grown by gas source molecular beam epitaxy were etched by reactive ion etching (RIE) with a gas mixture of ethane and hydrogen (C2H6/H2). Smooth etching surfaces were obtained under the following RIE conditions: an ethane concentration (flow fraction) of 3%, total flow (C2H6+H2) of 55 sccm, total pressure of 15 Pa and radio frequency power density of 0.6 W/cm2. This ethane concentration is smaller than that in III–V semiconductors, 5%–7%. The etching rate of ZnSe was 21 nm/min and smaller than that of III–V semiconductors.
Anomalous magnetoresistance at a mesoscopic bend
Authors: Cumming D. R. S. , Ahmed H. , Thornton T. J.
Published: July 2002

We have carried out magnetoresistance measurements on a mesoscopic cross formed from two split gates on a GaAs/AlGaAs 2DEG and have observed anomalous peaks in the bend resistance before the electron collimation is finally destroyed by the magnetic field. We have considered two possible explanations for this effect, and have rejected the possibility of quantum mechanical effects in favor of a classical one in which we postulate the presence of an impurity close to the center of the active region.
Second-harmonic generation and optical rectification using intersubband transitions in a biased p-type semiconductor quantum well
Authors: Tsang Leung , Chuang Shun L.
Published: July 2002

We present new theoretical results for the second-harmonic and optical rectification coefficients due to intersubband transitions within the valence subbands of a p-type quantum well in a biased external electric field. The results are based on the density matrix approach. Both the parabolic band model and the heavy-hole/light-hole valence band mixing model are utilized. With a moderate electric field of 10 and 150 kV/cm, it is shown that the second-order susceptibilities are many times larger than those of bulk GaAs. The valence band mixing model also gives rise to a broader resonance phenomenon than the parabolic band model.
Low temperature synthesis of boron nitride from condensed diborane and ammonia using synchrotron radiation
Authors: Strongin D. R. , Mowlem J. K. , Ruckman M. W. , Strongin Myron
Published: July 2002

Synchrotron radiation was used to form boron nitride from a mixture of diborane (B2H6) and ammonia condensed on a silver substrate at 78 K. Photoemission and near-edge x-ray absorption fine structure results show valence band and near-edge features characteristic of the hexagonal phase of boron nitride.
All-optical modulation in crystalline organic semiconductor waveguides
Authors: Zang D. Y. , Forrest S. R.
Published: July 2002

We demonstrate all-optical modulation in crystalline organic semiconductor waveguides grown by the ultrahigh vacuum process of organic molecular-beam deposition. Two light beams with wavelengths of 1.06 and 0.514 μm were used as the guided and the pump light sources, respectively. A refractive index change of 5.4×10−5 at 1.06 μm was observed at a pump intensity of 1.0 W/cm2. This large nonlinear effect is attributed to free electron-hole pairs produced by the dissociation of excitons generated by the short wavelength beam. A carrier lifetime of (17±1) μs which determines the modulator switching time is in good agreement with theoretical predictions. To our knowledge, this is the first observation of free-carrier-induced index modulation in crystalline organic waveguides.
Transmission electron microscopy study of chemical-vapor-deposited diamond by a side-view method
Authors: Goto Yasuyuki , Kurihara Kazuaki , Sawamoto Yumiko , Kitakohji Toshisuke
Published: July 2002

The initial growth of synthetic diamond by dc plasma-jet chemical vapor deposition was studied with a transmission electron microscope by a side-view method. Both diamond particles and β-SiC particles were observed on the Si substrate. Si atoms in the substrate were etched clearly by the plasma jet except beneath diamond particles.
Growth of GaAs and AlGaAs by metalorganic molecular beam epitaxy using tris-dimethylaminoarsenic
Authors: Abernathy C. R. , Wisk P. W. , Bohling D. A. , Muhr G. T.
Published: July 2002

Due to the extreme toxicity of AsH3, safer alternatives for III–V epitaxy are highly desirable. In addition, the AsH3 molecule is too stable to decompose on the wafer surface at the temperature and pressure conditions normally used during growth by metalorganic molecular beam epitaxy (MOMBE). This requires the use of high-temperature cracker cells to decompose the AsH3 to elemental As prior to entry to the growth chamber and as a result leads to significant As buildup within the chamber. In this letter we report for the first time MOMBE growth at low temperatures (≤525 °C) using a novel As precursor, tris-dimethylaminoarsenic (DMAAs) without precracking. Specular surface morphologies were obtained over a wide range of growth temperatures, 375–525 °C, for both GaAs and AlGaAs. Carbon concentrations measured by SIMS analysis in GaAs layers deposited from triethylgallium were lower than those obtained using a similar flux of AsH3, while carbon was reduced more than two orders of magnitude in films grown with trimethylgallium and DMAAs as compared to AsH3. No difference in oxygen content was observed between AlGaAs grown with DMAAs and AsH3.
Intersubband absorption in Sb δ-doped Si/Si1−xGex quantum well structures grown on Si (110)
Authors: Lee Chanho , Wang K. L.
Published: July 2002

Strong electron intersubband infrared absorption is observed for Sb δ-doped Si/Si1−xGex multiple quantum well structures grown on (110) Si substrates. The intersubband absorption is shown to be allowed for both the optical field components perpendicular and parallel to the quantum wells due to the tilted ellipsoidal of constant energy surfaces. About 90% infrared absorption is measured by a Fourier transform infrared spectrometer using a waveguide structure with 10 internal reflections. For various samples used in experiments, absorption peaks ranging from 4.9 to 5.8 μm are observed. The peak energy is shown to be tunable by changing the Ge composition in the Si1−xGex barriers and the doping concentration in the Si quantum wells.