bluuebunny/crossref_metadata_2025 huggingface dataset:
Continuous, high-power operation of a strained InGaAs/AlGaAs quantum well laser
Authors: Bour D. P. , Gilbert D. B. , Elbaum L. , Harvey M. G.
Published: July 2002

Continuous wave (cw), high-power operation of a strained In0.2Ga0.8As/ AlGaAs quantum well laser, grown by atmospheric pressure organometallic vapor phase epitaxy, is reported. The laser active region consists of a single 70 Å In0.2Ga0.8As/Al0.2Ga0.8As quantum well, with optical confinement provided by a graded index separate confinement heterostructure. The threshold current density and differential quantum efficiency of a 90 μm×600 μm stripe with uncoated facets are ∼200 A/cm2 and 46%, respectively. Lasing wavelength is ∼930 nm, and the cw single ended power versus current characteristic is linear up to 250 mW (1 A current). In the short-cavity (<300 μm) regime, these devices have high thresholds and have been observed to lase at shorter wavelength, presumably due to a saturation of gain at the lowest energy transition. The characteristic temperature is 150 K and decreases somewhat with cavity length. This suggests that some nonradiative process, most likely Auger recombination, contributes significantly to quantum well gain saturation.
One-dimensional electronic systems in ultrafine mesa-etched single and multiple quantum well wires
Authors: Demel T. , Heitmann D. , Grambow P. , Ploog K.
Published: July 2002

Ultrafine mesa-etched structures with lateral geometrical dimensions of 250 to 550 nm have been prepared in modulation-doped AlGaAs/GaAs heterostructures and multiple quantum well systems. From magnetotransport measurements at low temperatures (T=2.2 K) on these single and multiple quantum well wire structures we find that the lateral carrier confinement leads to the formation of one-dimensional electronic subbands of typically 2 meV energy separation. The width of the electron channel is smaller than the geometrical width, indicating a lateral depletion length of about 100 to 150 nm at the mesa edge.
Selectively Se-doped AlGaAs/GaAs heterostructures with reduced D
X center concentrations grown by molecular beam epitaxy
Authors: Ishikawa Tomonori , Maeda Takeshi , Kondo Kazuo
Published: July 2002

We studied the DX center concentration in Se-doped AlxGa1−x As layers grown by molecular beam epitaxy. In the shallow to DX transition region around x=0.2, the concentration of DX centers was far lower when compared to that of Si-doped layers. We applied Se-doped AlGaAs layers to selectively doped AlGaAs/GaAs heterostructures to avoid the influence of DX centers. By optimizing growth conditions, electron mobilities as high as 74 000 cm2 /V s (x=0.26) and 44 000 cm2 /V s (x=0.19) were achieved at 77 K for heterostructures with 60-Å-thick spacer layers.
Growth and characterization of Ge/Si strained-layer superlattices
Authors: Chang S. J. , Huang C. F. , Kallel M. A. , Wang K. L. , Bowman R. C. , Adams P. M.
Published: July 2002

Ultrathin Ge/Si strained-layer superlattices (SLS’s) with periodicities of a few monolayers have been successfully grown and characterized by Raman scattering spectroscopy. Structures with alternating Ge and Si layers were grown on Si substrates of different orientations. A thick 200 nm Ge0.4Si0.6 buffer layer was grown prior to the growth of the superlattice to make the strain distribution of the superlattice symmetrical and thus to maintain the pseudomorphic growth of the superlattices. Folded acoustic phonon peaks observed from these Ge/Si SLS samples can be used to determine the superlattice periodicity. The observed optical phonon frequencies were found to depend strongly on superlattice periodicity. A quantitative interpretation of this phenomenon was presented. Subsequent annealing of these samples reveals that the transition from pure Ge and/or Si layers to GexSi1−x alloy becomes more pronounced as the annealing time and temperature increase.
Physical meaning of electron capture kinetics on D
X centers
Authors: Bourgoin J. C. , Feng S. L. , von Bardeleben H. J.
Published: July 2002

The capture kinetics of electrons on DX centers are interpreted in terms of a simple model taking only into account the fact that the concentrations of the DX centers and of the doping impurities are equal. It is shown that there is no need to introduce an alloying effect in order to explain the capture as well as the emission kinetics, in agreement with the nonobservation of this effect in optical transitions. This is understood if the DX center is itself the donor impurity.
Y-Ba-Cu-O superconducting films prepared on SrTiO3 substrates by chemical vapor deposition
Authors: Yamane H. , Masumoto H. , Hirai T. , Iwasaki H. , Watanabe K. , Kobayashi N. , Muto Y. , Kurosawa H.
Published: July 2002

High Tc superconducting YBa2 Cu3 O7−x films were prepared by chemical vapor deposition using β-diketonates of Y, Ba, and Cu as source materials. The films were epitaxially grown on SrTiO3 (100) substrates. The c-axis orientation perpendicular to the plane of the substrates was observed. A sharp resistive superconducting transition with Tc (R=0) at 84 K was obtained. The maximum critical-current density at 77 K was 2×104 A/cm2 .
Interdiffusion and interfacial reaction between an YBa2Cu3Ox thin film and substrates
Authors: Nakajima H. , Yamaguchi S. , Iwasaki K. , Morita H. , Fujimori H. , Fujino Y.
Published: July 2002

Interdiffusion and interfacial reaction between a sputter-deposited YBa2Cu3Ox thin film and substrates (MgO, sapphire, quartz, and Si) have been investigated by 2.7 MeV 4He+ Rutherford backscattering spectrometry. The diffusivities of Cu in the substrates and of the substrate elements (Mg, Al, and Si) in the Y-Ba-Cu-O thin films have been determined over the annealing temperature range from 876 to 1226 K in an oxygen atmosphere. Among three metallic elements of Y, Ba, and Cu, Cu diffuses the fastest into the substrates. Copper silicide is observed in the interfacial region between the film and the Si substrate. Among these substrates, MgO is suggested to be the most stable on annealing.
Intrinsic superconductor/normal-metal/superconductor-like weak links in Y1Ba2Cu3O7−x thin films
Authors: England P. , Venkatesan T. , Wu X. D. , Inam A. , Hegde M. S. , Cheeks T. L. , Craighead H. G.
Published: July 2002

Magnetotransport measurements on micron-sized wires of the thin-film high Tc superconductor Y1 Ba2 Cu3 O7−x made by pulsed laser deposition reveal an exponential suppression of the critical current with magnetic field, and a power law dependence of the critical current on reduced temperature. We ascribe this behavior to crystallographic defects in the film which behave as superconductor/normal-metal/superconductor weak links in a magnetic field. From the measurements we estimate a critical current density of 106 A cm−2 in a field of 16 T at 4.2 K.
High-temperature stability of Si/SiO2 interfaces and the influence of SiO flux on thermomigration of impurities in SiO2
Authors: Celler G. K. , Trimble L. E.
Published: July 2002

We analyze experimentally unidirectional mass transport of As implanted into a SiO2 film covered with Si and heated to 1405 °C in a temperature gradient. The data can only be explained if we postulate that the thermomigration process is mediated by a flux of SiO molecules, flowing from the Si/SiO2 interfaces into the oxide. From the delay times before the onset of As drift, we estimate diffusivity of SiO at ∼4×10−13 cm2 /s at 1405 °C. The data also explain the apparent dichotomy between high-temperature dissociation of SiO2 , measured experimentally and predicted by thermodynamic arguments, and the ability to heat Si-coated SiO2 up to the melting point of Si at 1412 °C without any loss of the oxide integrity. The latter is possible because coated SiO2 saturates with SiO, resulting in steady-state conditions.
Pb1−xEuxS films prepared by hot wall epitaxy
Authors: Ishida A. , Nakahara N. , Okamura T. , Sase Y. , Fujiyasu H.
Published: July 2002

Pb1−x EuxS films were prepared for the first time using hot wall epitaxy technique. X-ray diffraction and optical transmission measurements were performed for the films. Films with energy gaps up to 0.9 eV (up to x=0.2) were obtained. Lattice constants of the films were very close to that of PbS as is expected from the small lattice mismatch between PbS and EuS. It was found that the energy band gap increases very rapidly with the EuS content up to x=0.05 (dEg/dx=5 eV).
Sequential electron beam evaporated films of Tl2CaBa2Cu2Oy with zero resistance at 97 K
Authors: Ginley D. S. , Kwak J. F. , Hellmer R. P. , Baughman R. J. , Venturini E. L. , Morosin B.
Published: July 2002

Thin unoriented polycrystalline films in the Tl-Ca-Ba-Cu-O system were prepared by sequential electron beam evaporation of multiple Tl, Ca, Ba, and Cu layers and a two-stage anneal under controlled Tl and oxygen overpressures. These films show zero resistance as high as 97 K and transport critical current densities at 76 K up to 110 000 A/cm2 with typical values of 50 000 A/cm2. The critical currents exhibit a modest magnetic field dependence. Meissner effect data show an onset at 110 K and a superconducting fraction of 75%. Compositional and structural studies indicate that the films, although polyphase, are predominantly Tl2Ca1Ba2Cu2Oy. There is no evidence of other superconducting phases.
Plasma oxidation of Ba2YCu3O7−y thin films
Authors: Tamura H. , Yoshida A. , Morohashi S. , Hasuo S.
Published: July 2002

We studied the effects of plasma oxidation on the electrical properties of Ba2YCu3O7−y thin films. Films were prepared by electron beam evaporation, then annealed in oxygen. Plasma oxidation, performed in a barrel reactor, lowered the room-temperature resistivity of films and raised the zero-resistance temperature. Film resistivity increased a few percent a day after plasma oxidation. The rate of resistivity increase is several times that of untreated samples. Changes in resistivity and critical temperature could be completely reversed by repeated plasma treatment.
Internal photoemission and band discontinuities at Ga0.47In0.53As-InP heterojunctions
Authors: Haase M. A. , Pan N. , Stillman G. E.
Published: July 2002

Internal photoemission has been observed in the spectral response of specially designed Ga0.47In0.53As-InP p+N− heterojunction photodiodes. Power-law fits to the internal photoemission as a function of photon energy allow precise determination of threshold energies from which the conduction-band discontinuity is easily and accurately deduced to be ΔEc=203±15 meV at room temperature. These measurements have been performed at temperatures from 135 to 297 K. The temperature dependence of ΔEc is described by ∂(ΔEc)/∂T=−0.2±0.1 meV/K.
Effect of boron on the deep donors (D
X centers) in GaAs:Si
Authors: Li M. F. , Yu Peter Y. , Shan W. , Hansen W. , Weber E. R.
Published: July 2002

We found that, when boron was introduced into GaAs:Si, the deep donors induced by pressure exceeding 20 kbar reported previously by M. Mizuta, M. Tachikawa, H. Kukimoto, and S. Minomura [J. Appl. Phys. 24, L143 (1985)] disappeared while new donor levels with reduced binding energies and capture barrier heights appeared. It is proposed that B atoms paired up with Si donor atoms and the resultant change in the short-range potential of the Si donor atoms depressed the capture barrier height of the pressure-induced deep donor.
One-dimensional subbands and mobility modulation in GaAs/AlGaAs quantum wires
Authors: Ismail K. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

Devices consisting of 100 parallel, modulation-doped GaAs/AlGaAs wires, each about 40 nm wide, have been fabricated and tested at 4.2 and 77 K. The wires were created by ion milling a shallow grating into the doped AlGaAs layer. The mask for etching the grating was produced by x-ray nanolithography, and lift-off of Ti/Au. The grating period was 200 nm and the linewidth about 85 nm. Backgate bias or illumination was used to modulate the charge density in the wires. Conductance measurements at 4.2 K provide clear evidence of quasi-one-dimensional density of states. A corresponding modulation of the electron mobility, above and below values in the two-dimensional system, was observed.
Quantum-confined subband transitions of a GaAs sawtooth doping superlattice
Authors: Ullrich B. , Zhang C. , Klitzing K. v.
Published: July 2002

In this letter we present for the first time the observation of quantum-confined transitions of a short-period sawtooth doping superlattice in photocurrent and luminescence. The luminescence was investigated with different laser intensities. Due to the nature of the band modulation of sawtooth doping superlattices, the resonant energies for optical transitions are dependent on the intensity of the laser beam. We present a model, which incorporates both the Kronig–Penney energy dispersion and the self-consistent intensity-dependent internal field to explain the observed energy shift. Furthermore, the differences between photocurrent and luminescence measurements are discussed.
Multiple quantum well passive mode locking of a NaCl color center laser
Authors: Islam M. N. , Sunderman E. R. , Bar-Joseph I. , Sauer N. , Chang T. Y.
Published: July 2002

Using multiple quantum well (MQW) saturable absorbers, we passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses with τ as short as 275 fs and peak power as high as 3.7 kW. Because of exciton ionization with a 200±30 fs time constant, the MQW shows a fast absorption recovery that is comparable to our pulse widths. This fast component plays a major role in pulse shaping and may limit the pulse width. We also show that the wavelength for the short pulses can be tuned from 1.59 to 1.7 μm by choosing MQWs with different band gaps.
Angular-selective optical properties of Cr films made by oblique-angle evaporation
Authors: Mbise G. , Smith G. B. , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Thin Cr films were made by oblique-angle evaporation onto glass. Electron microscopy showed an inclined columnar microstructure. Spectrophotometry yielded a strongly angular-selective p-polarized transmittance, consistent with recent theoretical notions, of potential interest for energy-efficient windows.
Infrared diodes fabricated with HgCdTe grown by molecular beam epitaxy on GaAs substrates
Authors: Arias J. M. , DeWames R. E. , Shin S. H. , Pasko J. G. , Chen J. S. , Gertner E. R.
Published: July 2002

Infrared photodiodes fabricated with HgCdTe epilayers grown on GaAs substrates by molecular beam epitaxy (MBE) are reported here for the first time. Growth was carried out on the (211)B orientation of GaAs, and the as-grown epilayer (x=0.24) was p type. The n-p junction was formed by Be ion implantation, the resistance-area product (R0 A) at zero bias was 1.4×103 Ω cm2 , the wavelength cutoff was 8.0 μm, and the quantum efficiency was 22%; all were measured at 77 K. We show that in the diffusion regime diodes fabricated with MBE HgCdTe/GaAs have comparable R0 A product values to those made with HgCdTe grown by bulk techniques. This result discloses new possibilities for advanced monolithic HgCdTe devices based on GaAs integrated circuit technology.
Persistent photoquenching and anion antisite defects in neutron-irradiated GaAs
Authors: Goltzene A. , Meyer B. , Schwab C.
Published: July 2002

A potential origin for the reported discrepancies on the low-temperature photosensitivity of particle-induced anion antisites in GaAs is revealed by a systematic study of the relative fraction of photoquenchable paramagnetic As4+Ga centers as a function of neutron fluence and annealing temperature. The electron paramagnetic resonance data show that the As4+Ga centers can be split into two subsets.
Planar Ge/Pd and alloyed Au-Ge-Ni ohmic contacts to n-AlxGa1−xAs (0≤x≤0.3)
Authors: Marshall E. D. , Yu L. S. , Lau S. S. , Kuech T. F. , Kavanagh K. L.
Published: July 2002

Specific contact resistivity ρc of planar Ge/Pd ohmic contacts to n-type AlxGa1−xAs is measured as a function of AlAs mole fraction x and anneal temperature Tann. The functional dependence of ρc on Tann is the same for all x, decreasing to a minimum at 275–325 °C. This indicates that the ohmic contact formation mechanism is independent of x(0≤x≤0.3) as verified by MeV Rutherford backscattering spectrometry and Read camera glancing angle x-ray diffraction. Decomposition of an epitaxial Pd-AlxGa1−xAs phase is correlated with the onset of ohmic behavior and may result in a thin solid phase regrown interfacial AlxGa1−xAs layer. An undoped 20 nm GaAs cap layer reduces ρc by about one order of magnitude. Ge/Pd contacts display greater dependence of ρc on x and much smoother surface morphology compared with those of standard Au-Ge-Ni contacts on AlxGa1−xAs (0≤x≤0.3).
Properties of ultrathin thermal nitrides in silicon Schottky barrier structures
Authors: Sobolewski M. A. , Helms C. R.
Published: July 2002

Thermally grown silicon nitride layers ≤30 Å thick have been investigated as interfacial layers in silicon Schottky barrier structures. Current-voltage characteristics of these devices show modified barrier heights with near unity ideality factors, more ideal than those obtained using silicon dioxide films of the same thickness. By appropriate choice of metal or of nitride layer thickness barrier heights in any desired range can be produced. Barrier heights of different metals are ‘‘unpinned’’: they differ by a fixed constant, independent of the thickness, indicating that interface trap states are not present in sufficient quantity to affect the barrier height. The barrier height varies roughly linearly with nitride thickness, for both as-grown and etched films, suggesting the presence of a constant quantity of positive fixed charge located at the silicon-silicon nitride interface.
Selective epitaxial silicon growth in the 650–1100 °C range in a reduced pressure chemical vapor deposition reactor using dichlorosilane
Authors: Regolini J. L. , Bensahel D. , Scheid E. , Mercier J.
Published: July 2002

Selective epitaxial silicon layers have been grown in a reduced pressure (<2 Torr) reactor in the 650–1100 °C temperature range using only dichlorosilane (DCS) gas diluted in hydrogen. The growth rate plotted in Arrhenius coordinates (log G vs 1/T) shows an activation energy of 59 kcal/mol in the 650–800 °C range. A comparison is made between the DCS system and our previous results concerning the SiH4/HCl/H2 system.
Electric field induced localization in GaAlAs-GaAs superlattices
Authors: Feng S. L. , Bourgoin J. C. , Qin G. G.
Published: July 2002

Using deep level transient spectroscopy we have observed electron emission in a 50–50 Å uniformly n-type doped GaAs-GaAlAs superlattice placed in the space-charge region of a Schottky barrier. This emission arises from carriers localized in the wells by the electric field above the barriers. This observation demonstrates that electric field induced localization in superlattices can be monitored using capacitance techniques.
Ion mixing of metal/Al bilayers near 77 K
Authors: Ma E. , Workman T. W. , Johnson W. L. , Nicolet M-A.
Published: July 2002

The efficiency of interfacial ion mixing is measured for metal/Al (metal=Ti, Cr, Ni, and Mo) thin-film bilayers irradiated with 285 keV Xe+ ions near 77 K. The results indicate that, as a group, mixing of 3d-metal/Al pairs irradiated by Xe can be explained by neither a pure binary collision cascade nor a pure thermal spike model. Such a situation should exist; that it should be found at the average atomic numbers of the present bilayers is consistent with recent theoretical predictions.
Characteristics of the off-centered apertured mirror external cavity laser array
Authors: Chang-Hasnain C. J. , Dienes A. , Whinnery J. R. , Streifer W. , Scifres D. R.
Published: July 2002

We present experimental data and a self-consistent analysis to explain the behavior of laser arrays in an off-centered apertured mirror external cavity. The eigensolutions of the composite cavity are superpositions of the orthonormal modes supported by the laser array itself. The thresholds, near- and far-field intensity distributions of the cavity modes are calculated for various mirror positions and widths. Good agreement is obtained between the calculations and the experimental data.
Ar ion laser-assisted metalorganic molecular beam epitaxy of GaAs
Authors: Sugiura H. , Iga R. , Yamada T. , Yamaguchi M.
Published: July 2002

Selective growth of GaAs using an Ar+ laser beam is reported. The laser irradiation during growth in the substrate temperature range 400–525 °C forms a GaAs spot of 400 μm in diameter. The spot growth rate increases up to 1.3 μm/h with laser power and does not depend on the type of substrate conductivity. Temperature rise due to the irradiation is revealed to be 7° at 120 °C for the laser power of 500 mW (laser beam diameter 400 μm). A concentric circle pattern can be formed by diffracting a laser beam. These results strongly suggest that the growth rate enhancement arises from the photodissociation of metalorganic molecules.
Conductance characteristics of ballistic one-dimensional channels controlled by a gate electrode
Authors: Hirayama Y. , Saku T.
Published: July 2002

Ballistic one-dimensional channels are fabricated using a highly resistive region induced by focused Ga ion beam scanning. Both wide and narrow channels are fabricated using this process. Transport characteristics of these channels are controlled by a voltage applied to the Schottky electrode on the channel. The channels show multiple-step structures in their transport characteristics at low temperature when the gate voltage is varied. This is probably due to the ballistic transport through one-dimensional quantized electron states. For narrower channels, the number of the observed steps becomes fewer. Instead, the structures are observable at higher temperature.
Single-crystal germanium grown on (11̄02) sapphire by molecular beam epitaxy
Authors: Godbey D. J. , Qadri S. B. , Twigg M. E. , Richmond E. D.
Published: July 2002

Crystalline germanium films have been successfully grown on the (11̄02) sapphire surface using molecular beam epitaxy. Growth at temperatures above 700 °C and after preannealing the sapphire substrates above 1100 °C resulted in germanium films with a (110) orientation. A 500 nm germanium film grown at 800 °C after preannealing the sapphire substrate at 1400 °C gave an x-ray rocking curve width that measured 317 arcsec at half maximum for the (220) reflection.
Electro-optical switching in a GaAs multiple quantum well directional coupler
Authors: Cada M. , Keyworth B. P. , Glinski J. M. , Rolland C. , SpringThorpe A. J. , Hill K. O. , Soref R. A.
Published: July 2002

Theoretical and experimental results are reported on electro-optical switching in a GaAs-based multiple quantum well coupled planar nonlinear optical directional coupler. It is shown that a careful selection of the wavelength of operation can lead to an efficient, practically constant loss, low electric field controlled transfer of light energy from one slab waveguide to the other. The quantum-confined Stark effect in the multiple quantum well coupling layer is employed as the switching mechanism. Results are compared with those achieved with nonlinear all-optical switching in the same structure. It is believed that this is the first semiconductor ΔK switch.
Strained-layer InGaAs-GaAs-AlGaAs graded-index separate confinement heterostructure single quantum well lasers grown by molecular beam epitaxy
Authors: Offsey S. D. , Schaff W. J. , Tasker P. J. , Ennen H. , Eastman L. F.
Published: July 2002

Strained-layer Ga0.7In0.3As-AlGaAs-GaAs graded-index separate confinement heterostructure single quantum well lasers have been grown by molecular beam epitaxy with growth conditions selected to optimize the growth of each material. The lasers emit at a wavelength of 1.03 μm at 300 K. These lasers have threshold currents of 12 mA for 3 μm×400 μm devices and average threshold current densities of 174 A/cm2 for 40 μm×800 μm devices. Studies of threshold current versus cavity length and width are compared with theoretical formulations. The threshold currents for lasers of various lengths and widths are significantly lower than those for previous strained-layer lasers grown by molecular beam epitaxy and lower than those for strained-layer lasers grown by organometallic vapor phase epitaxy.
Reduction in interfacial recombination velocity by superlattice buffer layers in GaAs/AlGaAs quantum well structures
Authors: Iwata H. , Yokoyama H. , Sugimoto M. , Hamao N. , Onabe K.
Published: July 2002

The values of interfacial recombination velocities in GaAs/AlGaAs double heterostructures and quantum wells grown by molecular beam epitaxy with and without superlattice cladding layers are obtained with photoluminescence time-decay measurements. The authors show that superlattice layers reduce the interfacial recombination velocity from 330 cm/s, the value for double heterostructures with alloy cladding layers, to 40 cm/s, and that they have small effect on the GaAs bulk lifetime.
Photocurrent spectroscopy of InxGa1−xAs/GaAs multiple quantum wells
Authors: Yu P. W. , Sanders G. D. , Evans K. R. , Reynolds D. C. , Bajaj K. K. , Stutz C. E. , Jones R. L.
Published: July 2002

Photocurrent spectra of InxGa1−xAs/GaAs multiple quantum well structures grown by molecular beam epitaxy are studied in the presence of electric fields perpendicular to the heterointerface. Several Δn=0 allowed and Δn≠0 forbidden excitonic transitions are observed. Both negative and positive shifts of exciton transitions are found. Good agreement is found between the photocurrent observations and calculations using a multiband effective-mass approach, taking into account the strain-induced splitting.
Noise and hysteresis in flux-locked TlBaCaCuO SQUIDs
Authors: Foglietti V. , Koch R. H. , Gallagher W. J. , Oh B. , Bumble B. , Lee W. Y.
Published: July 2002

Measurements of TlBaCaCuO-based dc superconducting quantum interference devices (SQUIDs) performed using a practical feedback circuit gave a flat frequency response and an energy sensitivity of 6×10−30 J/Hz at 5 kHz and 77 K with an 80 pH SQUID. Flux-locked loop operation was demonstrated to be strongly effective in eliminating the magnetic field hysteresis of the SQUID. The SQUIDs were operated in the flux-locked loop at temperatures over 90 K and the 1/f noise was found to decrease with increasing temperature near 77 K.
CO2 large-area discharge laser using an unstable-waveguide hybrid resonator
Authors: Jackson P. E. , Baker H. J. , Hall D. R.
Published: July 2002

A one-dimensional unstable resonator combining free-space and waveguide propagation is used to efficiently extract power from a large-area gain medium in a slab waveguide CO2 laser. A power of 240 W in a near-diffraction-limited beam has been attained at 12% conversion efficiency from a 38 cm gain length in a compact sealed-off laser head, corresponding to a specific power extraction of 14 kW m−2 of discharge area.
Depth dependence of silicon donor passivation and reactivation in hydrogenated GaAs
Authors: McCluskey F. P. , Pfeiffer Loren , West K. W. , Lopata J. , Schnoes M. Lamont , Harris T. D. , Pearton S. J. , Dautremont-Smith W. C.
Published: July 2002

The depth dependence of silicon donor passivation and reaction in hydrogenated GaAs is directly determined for the first time by using 1000 Å layers of 1017 cm−3 Si-doped GaAs, buried at various depths in undoped GaAs. Low-frequency hydrogen plasma exposure for 30 min at 250 °C reduces the carrier density by only a factor of 3 in layers buried 3 μm deep, but by three orders of magnitude in layers buried 0.3 μm deep. Annealing at 400 °C for 5 min restores 100% of the original carrier density in the 3-μm-deep layer but only 73% in the 0.3-μm-deep layer. Plasma exposure and 400 °C annealing together do not improve the mobility in the molecular beam epitaxial samples at any depth. Hydrogen-related acceptors seen by photoluminescence account for these effects.
Resonant Raman scattering of In+-implanted CdTe and Cd0.23Hg0.77Te
Authors: Lusson A. , Wagner J. , Ramsteiner M.
Published: July 2002

In+ -implanted CdTe and Cd0.23 Hg0.77 Te have been studied by resonant Raman scattering. Dipole-forbidden but defect-induced scattering by one longitudinal optical (LO) phonon as well as Fröhlich-induced two-LO phonon scattering is strongly affected by implantation of 350 keV In+ with doses ranging from 1011 to 5×1014 ions/cm2 . The intensity ratio of the one-LO and the two-LO phonon lines is found to be a measure of the implantation damage in CdTe and in the alloy Cd0.23 Hg0.77 Te. The observed implantation effects on resonant Raman scattering by LO phonons are due to a broadening and an energy shift of the corresponding resonances as demonstrated for the E0 +Δ0 gap resonance in CdTe.
Bulk dc SQUID in a Tl-based ceramic: Shapiro steps, signal, and noise properties at 77 K
Authors: Robbes D. , Sing M. Lam Chok , Monfort Y. , Bloyet D. , Provost J. , Raveau B.
Published: July 2002

The current-voltage characteristic at 77 K of a constricted thallium-based high Tc superconducting sample exhibits Shapiro steps and is modulated by a dc magnetic field. This device operates as a dc superconducting quantum interference device with a maximum critical current Ic of 350 μA, a dynamic resistance up to 30 Ω, and a transfer parameter as high as 1.5 mV/Φ0 for an estimated inductance of 40 pH. The measured spectral density of the flux noise in the white noise region is 1.4×10−10 Φ20/Hz. The 1/f noise at 1 Hz is 2.1×10−7 Φ20/Hz and is reduced by a factor of 10 by a synchronous detection. Implications for thin-film devices are examined.
Low-temperature deposition of Y-Ba-Cu-O films on a CaF2/GaAs substrate
Authors: Mizuno K. , Miyauchi M. , Setsune K. , Wasa K.
Published: July 2002

Superconducting thin films of Y-Ba-Cu-O were fabricated on a CaF2/GaAs(100) substrate using the rf planar magnetron sputtering technique. Substrates were heated as low as 450 °C during deposition. The as-deposited films without high-temperature post-annealing have a transition temperature of 75 K and zero resistance temperature of 45 K. The perovskite structure usually observed in this system was not observed. The critical current (Jc) value of 2×103 A/cm2 was measured at 4.2 K.
Organometallic chemical vapor deposition of high T
c superconducting Bi-Sr-Ca-Cu-O films
Authors: Zhang Jiming , Zhao Jing , Marcy Henry O. , Tonge Lauren M. , Wessels Bruce W. , Marks Tobin J. , Kannewurf Carl R.
Published: July 2002

Films of the high Tc Bi-Sr-Ca-Cu-O superconductor have been prepared by organometallic chemical vapor deposition using the volatile metalorganic precursors Cu(acetylacetonate)2 , Sr(dipivaloylmethanate)2 , and Ca(dipivaloylmethanate)2, and triphenylbismuth. Deposition is carried out at 2 Torr with argon as the carrier gas and oxygen and water vapor as reactants. Film growth rates of 2–3 μm/h are achieved. After annealing under oxygen, energy dispersive x-ray analysis and x-ray diffraction data reveal that such films on [100] single-crystal MgO consist predominantly of the Bi2(Sr,Ca)3Cu2Ox, Tc=85 K, phase and have preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four-probe resistivity measurements reveal the onset of film superconductivity at ∼110 K and zero resistance by 75 K.
Interface analysis of Y-Ba-Cu-O films on Al-coated Si substrates
Authors: Asano T. , Tran K. , Byrne A. S. , Rahman M. M. , Yang C. Y. , Reardon J. D.
Published: July 2002

Y-Ba-Cu-O films were deposited on Al-coated Si substrates by the plasma-spray method. The Al buffer layer appears to be effective in yielding crack-free adhesive Y-Ba-Cu-O films. Resistance measurements indicate that the films exhibit a superconducting phase below 90 K. Results of x-ray microanalysis and x-ray photoelectron spectroscopy confirm that the Al buffer forms an Al2O3 layer and prevents precipitation of Cu at the film/substrate interface.
Effects and loss of lead in doped Bi-Sr-Ca-Cu-O films
Authors: Dew S. K. , Osborne N. R. , Mulhern P. J. , Parsons R. R.
Published: July 2002

Films of Bi-Sr-Ca-Cu-O, with and without lead doping, were prepared by rf magnetron sputtering of oxide targets. The films were annealed in oxygen for varying durations and characterized by electron microprobe and x-ray diffraction. The results show a drastic loss of lead during annealing. Films with the lead-enhanced Bi2Sr2Ca2Cu3Oy (2223) phase had no detectable lead after annealing. The films were seen to grow in stages of 2201, 2212, and finally 2223 phases. The lead affected film development through these stages.
Epitaxial film growths of artificial (Bi-O)/(Sr-Ca-Cu-O) layered structures
Authors: Fujita J. , Tatsumi T. , Yoshitake T. , Igarashi H.
Published: July 2002

Epitaxial film growth of artificial (Bi-O)/(Sr-Ca-Cu-O) layered structures on MgO substrates was carried out using reactive-oxygen-gas dual ion beam sputtering and shuttering technique. A 12 Å Sr-Ca-Cu-O buffer layer seems suitable for perfect epitaxial film growth. Single-phase films having periodicities of 12, 15, and 18 Å (which correspond to bulk 24, 30, and 36 Å phases in Bi oxide superconductors) were selectively grown by adjusting the thickness of a Sr-Ca-Cu-O layer sandwiched by Bi-O bi-planes. A high Tc phase film with a total thickness of about 300 Å showed an onset Tc of 110 K and a zero resistivity temperature of 45 K without post-deposition annealing. The shuttering technique seems to enable the layer-by-layer film growth, and it is very effective for the formation of smooth and perfect epitaxial structures.
High-power low-threshold graded-index separate confinement heterostructure AlGaAs single quantum well lasers on Si substrates
Authors: Kim Jae-Hoon , Lang Robert J. , Radhakrishnan Gouri , Katz Joseph , Narayanan Authi A. , Craig Richard R.
Published: July 2002

A high-power low-threshold graded-index separate confinement heterostructure AlGaAs single quantum well laser on Si substrates has been demonstrated for the first time by a hybrid growth of migration-enhanced molecular beam epitaxy followed by metalorganic vapor phase epitaxy. The quantum well laser showed an output power of more than 400 mW per facet under pulsed conditions. A room-temperature threshold current of 300 mA was obtained with a differential quantum efficiency of 40% without facet coating. The threshold current density was 550 A/cm2 for a cavity length of 500 μm. These results show the highest peak power reported to date for low-threshold lasers on Si substrates. The full width at half maximum of the far-field pattern parallel to the junction was 6°. Threshold current densities as low as 250 A/cm2 were obtained for lasers on GaAs substrates.
Doping of diamond by coimplantation of carbon and boron
Authors: Sandhu G. S. , Swanson M. L. , Chu W. K.
Published: July 2002

We have implanted boron ions into insulating natural diamonds which were predamaged by carbon ion implantation in order to enhance the doping efficiency. All implantations were performed at liquid-nitrogen temperature. Subsequent rapid thermal annealing at 1100 °C produced strong new optical absorption bands near 1060 cm−1, and a sharp absorption at 2962 cm−1 (0.37 eV) which is close to that attributed to substitutional boron in type IIB diamond. We obtained resistivity of the order of 100 Ω cm and carrier activation energy of 0.1 eV for a sample implanted with 2×1015 C and 3×1014 B per cm2, indicating a high substitutional fraction of boron atoms.
Stimulated emission from a Hg1−xCdxTe epilayer grown by molecular beam epitaxy
Authors: Mahavadi K. K. , Bleuse J. , Chu X. , Faurie J. P.
Published: July 2002

We report on the observation of stimulated emission from a (100) oriented Hg1−xCdxTe epilayer grown by molecular beam epitaxy. The cleaved epilayers were cooled and optically pumped by a Nd:YAG laser and were found to lase continuously up to 40 K.
Metalorganic chemical vapor deposition of indium phosphide by pulsing precursors
Authors: Chen W. K. , Chen J. C. , Anthony L. , Liu P. L.
Published: July 2002

We have grown InP by supplying precursors alternately into the reactor of a metalorganic chemical vapor deposition system. Epitaxial growth has been obtained with a substrate temperature as low as 330 °C. The growth process is mass transport limited in the temperature range of 420–580 °C. It is kinetic controlled below 400 °C. At 340 °C, we have achieved monolayer growth in each cycle, i.e., atomic layer epitaxy.
Doppler profile measurement of Ar and Ar+ translational energies in a divergent magnetic field electron cyclotron resonance source
Authors: McKillop John S. , Forster John C. , Holber William M.
Published: July 2002

High-resolution optical emission spectroscopy has been used to measure Doppler profiles of Ar and Ar+ transitions in a divergent magnetic field electron cyclotron resonance (ECR) source, yielding average translational energies between 0.1 and 0.6 eV (Ar), and 1.0 and 2.5 eV (Ar+). ECR magnetic field configuration strongly affects Ar+ energies, although little variation with Ar pressure (0.1–1.5 mTorr) is found. The average Ar energy increases slightly with pressure. These observations suggest that thermal ion and neutral excitation primarily results from collisional degradation of directed downstream ion energies arising from the unique ambipolar potential created in ECR sources.
Reduction of trap concentration and interface roughness of GaAs/AlGaAs quantum wells by low growth rates in molecular beam epitaxy
Authors: Maierhofer Ch. , Munnix S. , Bimberg D. , Bauer R. K. , Mars D. E. , Miller J. N.
Published: July 2002

A simultaneous reduction of interface roughness and of impurity and trap incorporation in GaAs/AlGaAs quantum wells is observed for a decrease of the molecular beam epitaxy growth rate below its standard value 1 μm/h, down to 0.1 μm/h, at a substrate temperature of 620 °C. Thus, layer quality is drastically improved at low, nonstandard growth rates. Incorporation of impurities from the background is observed to induce a transition from two- to three-dimensional growth. The conclusions are based on a detailed study and line shape analysis of quantum well luminescence.
Analysis of defect-assisted tunneling based on low-frequency noise measurements of resonant tunnel diodes
Authors: Weichold M. H. , Villareal S. S. , Lux R. A.
Published: July 2002

The results of an experimental apparatus and procedure using noise measurement techniques to identify conduction mechanisms in resonant tunneling diodes due to defect-assisted tunneling are presented. The activation energies and capture cross sections of the traps are determined for each of three distinct levels detected. These values are in good agreement between the forward bias and inverted bias cases. A conjecture is made as to the physical location of the traps. This interpretation yields qualitative behavior consistent with the known bias and temperature dependence of the experimental results.
Numerical calculation of particle trajectories and tunneling times for resonant tunneling barrier structures
Authors: Jensen K. L. , Buot F. A.
Published: July 2002

The Wigner particle trajectories in phase space for double-barrier semiconductor quantum well structures are investigated by numerically calculating the Wigner distribution function. The determination of the particle dynamics of the phase points allows for an estimation of tunneling times, particle currents, and particle energies associated with the statistics of bound and open trajectories across the double-barrier structures.
X-ray diffraction from ordered regions in GaInP ternary alloys
Authors: Okuda Hiroshi , Anayama Chikashi , Narita Satoyasu , Kondo Makoto , Tanahashi Toshiyuki , Ueda Osamu , Nakajima Kazuo
Published: July 2002

Ordered structure in GaInP alloys grown on (001) GaAs substrates by low-pressure metalorganic vapor phase epitaxy has been investigated by means of x-ray diffraction and transmission electron microscopy. We found a broad peak of CuPt I type (111)B ordering in the x-ray measurements. X-ray results gave the total amount of ordered region and the average size of each ordered domain. Room-temperature photoluminescence peak energy anomalies were found to be related to the amount of the order phase.
Electroabsorption and refraction by electron transfer in asymmetric modulation-doped multiple quantum well structures
Authors: Wegener M. , Chang T. Y. , Bar-Joseph I. , Kuo J. M. , Chemla D. S.
Published: July 2002

We present a novel heterostructure that exhibits large electroabsorption and refraction. The structure is periodic with a stackable building block, thus it allows large contrast and waveguide operation. The mechanism used is the quenching of absorption produced by transfer of electrons from a reservoir into a quantum well. We demonstrate the principle by presenting differential absorption and refraction spectra on a ten-period device.
Dual-transistor method to determine threshold-voltage shifts due to oxide-trapped charge and interface traps in metal-oxide-semiconductor devices
Authors: Fleetwood D. M.
Published: July 2002

A new technique is proposed to evaluate the radiation response of metal-oxide-semiconductor (MOS) transistors. The method requires that otherwise identical n- and p-channel transistors be irradiated under the same conditions. Using assumptions similar to those of widely accepted ‘‘single-transistor’’ methods, standard threshold-voltage and mobility measurements are combined to accurately estimate threshold-voltage shifts due to oxide-trapped charge and interface traps. This approach is verified for several MOS processes. The dual-transistor method can be applied to devices with much larger parasitic leakage, and at shorter times following a radiation pulse, than subthreshold current or charge-pumping techniques.
Growth of Cd1−xMnxTe films by pulsed laser evaporation and epitaxy
Authors: Wrobel J. M. , Dubowski J. J.
Published: July 2002

Epitaxial layers of (111) Cd1−xMnxTe (x=0.05) were grown on (111) GaAs substrates by pulsed laser evaporation and epitaxy. A XeCl excimer laser beam was directed at a Cd0.95Mn0.05Te target to produce the vapors necessary for deposition. A simultaneously operating pulse Nd:YAG laser was used to create the overpressure of Cd needed in the growth of stoichiometric films. In situ reflection high-energy electron diffraction, as well as scanning electron microscopy, energy-dispersive x-ray analysis, and photoluminescence study showed that the films had characteristics comparable to the best CdMnTe epilayers grown so far by molecular beam epitaxy or metalorganic chemical vapor deposition.
Spike train generation and current-to-frequency conversion in silicon diodes
Authors: Coon D. D. , Perera A. G. U.
Published: July 2002

A device physics model is developed to analyze spontaneous neuron-like spike train generation in current driven silicon p+-n-n+ devices in cryogenic environments. The model is shown to explain the very high dynamic range (107) current-to-frequency conversion and experimental features of the spike train frequency as a function of input current. The devices are interesting components for implementation of parallel asynchronous processing adjacent to cryogenically cooled focal planes because of their extremely low current and power requirements, their electronic simplicity, and their pulse coding capability, and could be used to form the hardware basis for neural networks which employ biologically plausible means of information coding.
All-silicon integrated optical modulator for 1.3 μm fiber-optic interconnects
Authors: Hemenway B. R. , Solgaard O. , Bloom D. M.
Published: July 2002

We report an all-silicon fiber-optic light modulator which relies on free-carrier optical dispersion and mode filtering in single-mode fibers. Greater than 10% peak-to-peak intensity modulation over a 200 MHz bandwidth for 10 mA rf current modulation at 1.3 μm wavelength is demonstrated.
Electrical charging of percolating samples in the scanning electron microscope
Authors: Barkay Z. , Dwir B. , Deutscher G. , Grünbaum E.
Published: July 2002

Electrical properties of indium percolating samples were investigated by the charging effect in the scanning electron microscope. The finite clusters and the infinite cluster were identified due to the difference in their charging images. The finite clusters exhibited a capacitor-like behavior. An electric breakdown in a tree-like structure was obtained in the indium insulating films.
Efficient generation at 421 nm by resonantly enhanced doubling of GaAlAs laser diode array emission
Authors: Goldberg Lew , Chun Myung K.
Published: July 2002

The 842-nm diffraction-limited emission from an injection-locked laser diode array was frequency doubled using a monolithic spherical-mirror KNbO3 crystal cavity. Maximum unidirectional external 421 nm power of 24 mW was generated with 167 mW of pump power. Maximum total internal second-harmonic power and conversion efficiency of 64 mW and 45% were obtained. Effects of heating in the crystal are described.
Reconstruction of the spatial structure of current filaments in n-GaAs in a magnetic field
Authors: Brandl A. , Völcker M. , Prettl W.
Published: July 2002

The spatial pattern of current filaments generated by impurity breakdown has been investigated in a semiconductor for the first time as a function of the magnetic field. Large asymmetries of shallow impurity excited-state population were observed occurring at opposite edges of a filament normal to the magnetic field. Deformation of filament boundaries evolves at very low field strengths being comparably small to those which destabilize current flow yielding current fluctuation and chaos.
Generation of misfit dislocations in GaAs grown on Si
Authors: Tsai H. L. , Matyi R. J.
Published: July 2002

The misfit dislocation configurations in initial GaAs islands grown on silicon were studied by high-resolution electron microscopy. Misfit dislocations, especially 60° type and stacking faults, were observed to generate from near the edges of the islands. Large steps on the substrate surface were observed to help the nucleation of these dislocations. The presence of threading dislocations in thicker films is attributed to the misfit dislocation segments in initial GaAs islands. A mechanism is proposed to explain the propagation and multiplication of misfit dislocations during the coalescence of islands and their subsequent growth.
Etch rate enhancement of photoresist in nitrogen-containing plasmas
Authors: Premachandran V.
Published: July 2002

It is shown that the etch rate of photoresist can be greatly enhanced by adding 1% of nitrogen into the oxygen plasma. An increase in the atomic oxygen concentration is shown to be responsible for this enhancement in the etch rate. A further enhancement in the etch rate is obtained by introducing CF4 into the O2 -N2 plasma. The enhancement in the etch rate of photoresist in the CF4 -N2 -O2 mixture is the result of an increase in the atomic concentrations of oxygen and fluorine in the plasma.
Capacitance properties in n-type AlxGa1−xAs
Authors: Izpura I. , Muñoz E. , Hill G. , Roberts J. , Pate M. A. , Mistry P. , Hall N. Y.
Published: July 2002

The electrical properties of n-type AlxGa1−x As, for x>0.2, are governed by deep donor states (formerly called DX centers) created by the isolated donor atoms. We have studied the capacitance properties of such layers for Si and Sn dopants. The meanings of the capacitance-voltage carrier profiling and of the capacitance dependence with temperature have been considered. The deep donor energy position with respect to the Γ minimum has been determined.
Optical depth profiling of ion beam etching induced damage in InGaAs/InP heterostructures
Authors: Germann R. , Forchel A. , Grützmacher D.
Published: July 2002

We have investigated the energy dependence and depth distribution of the damage caused by ion beam etching using Ar/O2−ions with energies in the range between 175 and 1200 eV. The damage was created by partially etching the upper InP barrier of In0.53Ga0.47As single quantum wells. The optical emission from the quantum wells is used as a high-resolution local probe for the damage. From the decay of the quantum efficiency as a function of the etch depth we determine an effective damage range of about 8.4 nm for 250 eV ions in InP.