bluuebunny/crossref_metadata_2025 huggingface dataset:
Graded InGaAs/GaAs strained-layer single quantum well laser
Authors: Yoo Tae-Kyung , Spencer Robert , Schaff William J. , Eastman Lester F. , Chung Ki-Woong , Ahn Doyeol
Published: July 2002

A new graded InxGa(1−x)As/GaAs/AlGaAs strained-layer single quantum well (QW) laser diode has been proposed and experimentally characterized. Bias-dependencies of valence subbands and maximum optical gains of the InGaAs QW on the external bias are calculated taking into account the effects of the valence band mixing and intraband relaxation. Electron distributions in the conduction bands at threshold bias are also calculated by solving the Poisson and Schrödinger equation self-consistently. By a two-step grading of the InGaAs QW compositions, the higher peak value and smaller full width at half maximum of electron distributions can be obtained around the QW center even at the large external bias. Moreover, the electron-hole spatial separation is substantially reduced in the graded QW. A graded InxGa(1−x)As/GaAs strained-layer single QW laser diode with x=0.17–0.33 shows lower threshold current densities by 15% than those of the conventional In0.25Ga0.75As laser.
Effect of Cu content on the reaction growth and morphology of an Al12W compound between Al-Cu/Ti-W bilayers
Authors: Park M. , Krause S. J. , Wilson S. R.
Published: July 2002

The effect of Cu content on the reaction growth and morphology of the Al12W phase in annealed Al-Cu/Ti-W films was directly studied by cross-section transmission electron microscopy. After heat treatment at 450 °C for 30 min, spiked growths of the Al12W phase penetrated into the overlying Al-0.5 wt % Cu film. In contrast, increasing Cu concentration to 1.5% in the Al film suppressed the spiked growth of the Al12W phase, resulting in a smooth and discrete layer of Al12W between the Al-Cu and Ti-W films. It is suggested that an increasing amount of grain boundary segregation of Cu in the Al alloy film suppressed the Al12W spiked growth.
Helium-excited reactive magnetron sputtering for stress-free silicon nitride films
Authors: Sugimoto Iwao , Nakano Satoko
Published: July 2002

Compressive stress in reactively magnetron-sputtered silicon nitride films can be considerably reduced by helium-excited rf plasma. Plasma emission spectroscopy reveals that plasma consisting of the gas ratio of He/N2=11.5 preferentially produces the highly reactive N2+ ions through collisional ionization by the metastably excited helium atoms and suppresses the generation of energetic particles. Increasing plasma reactivity for Si—N bond formation and reduction of the peening effect both effectively reduce the resulting film stress.
New measurement techniques to determine magnetization and coercivity using a torque magnetometer
Authors: Hur Jeen , Shin Sung-Chul
Published: July 2002

We have developed new techniques to measure the magnetization and the coercivity of a uniaxial magnetic material using a torque magnetometer. The magnetization could be measured from the linear dependence at the low-field regime in a plot of the torque versus the applied magnetic field, where the direction of the applied field was perpendicular to the uniaxial orientation. The coercivity could be obtained by taking the value of the applied field where the torque is zero, when the direction of the applied field was (180+δ) degrees from the uniaxial orientation. The techniques were applied to determine the magnetizations and the coercivities of several Co/Pd multilayer thin films. The results were confirmed to be similar within a 2% difference to those obtained by a vibrating sample magnetometer.
Subnanosecond optically addressable generalized optical crossbar switch with an aggregate throughput rate of 4.2 Gbit/s
Authors: Pan Zeqi , Dagenais Mario
Published: July 2002

We report on a novel scheme to implement a high-performance optically addressable generalized optical crossbar switch based on Fabry–Perot nonlinear diode laser amplifiers. This approach permits fast, parallel optical reconfiguration and a potentially large switch size. By using discrete components, we have demonstrated a 1×3 optical crossbar switch with an aggregate throughput rate of 4.2 Gbit/s, and a reconfiguration time of less than 1 ns. In addition, we demonstrate wavelength conversion at bit rates up to 1.5 Gbit/s, with a facet-to-facet usable gain of 9.6 dB.
Transient growth rate change during gas source molecular beam epitaxy of Si1−xGex alloys
Authors: Ohtani N. , Mokler S. M. , Xie M. H. , Zhang J. , Joyce B. A.
Published: July 2002

Reflection high-energy electron diffraction intensity oscillations during gas source molecular beam epitaxy growth of Si1−xGex using disilane and germane are reported. Transient changes of the oscillation period and hence the growth rate are observed during the growth. Their origin is discussed on the basis of hydrogen desorption kinetics on the alloy surface and attributed to Ge surface segregation effects at the growth interface. This observation provides a unique opportunity for in situ investigations with monolayer-scale resolution, of Ge segregation effects in Si/Si1−xGex heterostructures.
Probable electron distribution in crystal and the maximum range evaluation
Authors: Nakagawa S. T.
Published: July 2002

The atomic Wigner–Seitz sphere approximation assigns a sphere to each atom in solid. This has often been used in combination with the binary collision approximation. However, it causes a lack or excess of electrons around the center of the channels. As an alternative to this approximation we propose a simple muffin-tin model. Making use of a cluster to represent each axial channel, the electronic stopping powers for channeled ions are figured according to a local density approximation. The present model reproduces reasonable maximum ranges in depth profiles on cases of channeling implantation. Results are shown for cases of B into Si〈100〉 and Si〈110〉.
Carbon doping for AlGaAs/GaAs heterojunction bipolar transistors by molecular-beam epitaxy
Authors: Ito Hiroshi , Nakajima Osaake , Ishibashi Tadao
Published: July 2002

Carbon doping in GaAs is investigated using solid-source molecular-beam epitaxy. The proportion of inactive C atoms in GaAs layers is found to increase when the free-carrier concentration is higher than about 1018/cm3. The current gain of AlGaAs/GaAs heterojunction bipolar transistors decreases rapidly with increasing base doping. The gradient of this tendency is much steeper than for inverse base doping, indicating the introduction of additional nonradiative recombination centers in heavily doped regions. A high current gain of 300 is achieved with a base doping of 2.5×1018/cm3.
High-power, single-frequency operation of an InGaAsP/InGaAs active-grating surface emitting amplifier at λ=1.7 μm
Authors: Carlson N. W. , Menna R. , Gardner P. , Liew S. K. , Andrews J. , Triano A. , Kirk J. , Reichert W.
Published: July 2002

We have demonstrated high-power, single-wavelength cw operation of an InGaAsP/InGaAs strained-layer multi-quantum-well active-grating surface-emitting amplifier operating at a wavelength of 1.7 μm. Single-wavelength operation was obtained with 38 dB suppression of amplified spontaneous emission at 107 mW cw power output.
Nonlinear optical susceptibility of ultrasmall CdS particles by means of the polarization-discriminated forward degenerate four-wave mixing in a resonant region
Authors: Nosaka Yoshio , Tanaka Kazunori , Fujii Nobuyuki
Published: July 2002

We report results of degenerate four-wave mixing (DFWM) measurements of resonant nonlinearity for ultrasmall CdS particles having diameters of 26–39 Å. The values of χxyyx(3) obtained by means of forward DFWM operating under polarization-discriminated conditions are the same order of magnitude as the reported χ(3) at a nonresonant wavelength.
Size effects in the epitaxial realignment of polycrystalline silicon films onto Si substrates
Authors: Benyaïch F. , Rimini E. , Spinella C. , Cacciato A. , Fallico G. , Ferla G. , Ward P.
Published: July 2002

The epitaxial realignment of As-doped polycrystalline silicon layers has been investigated by varying the dimensions of the contact area with the crystalline silicon substrate. Rectangular strips of width in the 0.2–100 μm range and length in the mm range were used. In the 1–100 μm strips the realignment proceeds by the two-dimensional growth of epitaxial columns, while in the 0.2–0.3 μm strips by the one-dimensional growth. The experimental realigned fractions quantitatively follow the trend predicted by the classical model of nucleation and growth in two and one dimension, respectively. The growth kinetics is slowed down in the small width geometry and the thermal budget to realign the films increases.
Influence of deposition temperature on giant magnetoresistance of Fe/Cr multilayers
Authors: Parkin S. S. P. , York B. R.
Published: July 2002

The giant magnetoresistance effect ΔR/R in magnetron-sputter deposited Fe/Cr multilayers is shown to depend strongly on deposition temperature. The largest values of ΔR and magnetoresistance are found in structures deposited at ≂125 °C. Structures deposited at lower (≂30 °C) or higher (≂200 °C) temperatures exhibit lower ΔR and ΔR/R values. Low angle x-ray reflectivity and rocking curve data show that all the structures have well defined layers. However the largest giant MR values are found in structures which have the lowest high field resistivities, R, the longest structural coherence lengths and the narrowest (110) rocking curve widths. These results suggest that more perfect structures have intrinsically higher giant magnetoresistance.
Dependence of steady-state defect density in hydrogenated amorphous silicon on carrier generation rate studied over a wide range
Authors: Hata Nobuhiro , Ganguly Gautam , Matsuda Akihisa
Published: July 2002

Measurements of the steady-state defect density (Nst) in hydrogenated amorphous silicon under illumination of pulse-laser light, as well as of continuous light, were carried out; and the dependence of Nst on the effective rate of carrier generation (G) is presented. The values of G ranged from 8×1021 to 2.4×1023 cm−3 s−1, while the illumination temperature was kept at 30 or 105 °C. The results showed trends of Nst increasing with G similarly to the trends in the literature, but covered a higher and wider G range, and fitted a defect model which assumes a limited number of possible defect states.
Formation of compositionally uniform tungsten silicide films using dichlorosilane in a single-wafer reactor
Authors: Telford S. G. , Eizenberg M. , Chang M. , Sinha A. K. , Gow T. R.
Published: July 2002

High quality chemical vapor deposited (CVD) WSix (2.2<x<2.6) films were deposited on 200 mm Si wafers using SiH2Cl2/WF6 chemistry. Earlier reported problems regarding silicide nucleation at the substrate interface were solved resulting in a highly uniform composition (vertically and laterally) regardless of the substrate type (SiO2 or polycrystalline Si). As-deposited resistivities of ∼750 μΩ cm were obtained for WSix (x=2.4–2.5) films grown at 550–600 °C. The films were completely crystalline, consisting predominantly of the hexagonal WSi2 phase. The as-deposited stress in the films was ∼1.3×1010 dyne/cm2 and after 900 °C anneal has reduced to ∼8×109 dyne/cm2. The films contained relatively low levels of impurities: F∼6×1016–2×1017 atoms/cm3, and Cl∼5×1017–5×1018 atoms/cm3.
Diffraction grating pitch modulation using lead lanthanum zirconate titanate
Authors: Bryan-Brown G. P. , Sambles J. R. , Welford K. R.
Published: July 2002

Interferographic exposure followed by fast atom etching is used to write a sinusoidal diffraction grating into the surface of a lead lanthanum zirconium titanate (PLZT) wafer. A silver overlayer evaporated onto the grating allows the excitation of surface plasmon polaritons by incident radiation thus leading to sharp resonance dips in the angular dependent reflectivity. A second silver layer is evaporated onto the back of the wafer to allow ac electric fields to be applied across the sample. The large electrostrictive effect in PLZT causes a significant modulation in the grating groove pitch and hence surface plasmon polariton resonance angle which is very accurately quantified using a lock-in differential measurement. This simple configuration is able to measure pitch changes as small as 4.2×10−4 nm (a strain of 4.8×10−7).
8×18 top emitting independently addressable surface emitting laser arrays with uniform threshold current and low threshold voltage
Authors: Vakhshoori D. , Wynn J. D. , Zydzik G. J. , Leibenguth R. E.
Published: July 2002

Fabrication of 8×18 independently addressable vertical cavity surface emitting laser arrays (VC-SELA) with uniform threshold current, threshold voltage, and high optical output power is reported. The top surface emitting array contains GaAs multiquantum well active regions and exhibits uniform characteristics over a 4×9 mm2 area. The cw threshold current is ≊4.2∓0.2 mA, the threshold voltage is 2.65∓0.1 V, and the output optical power is greater than 2 mW for the individual elements of the array. To realize these large VC-SELAs, a novel ion implantation mask fabrication was developed.
Lasing in atomic iodine with a nuclear-pumped XeBr* flash lamp
Authors: Williams W. H. , Miley G. H.
Published: July 2002

Excitation of the atomic iodine laser with a nuclear-pumped flash lamp is reported. The energetic reaction of thermal neutrons from a pulsed research reactor with 3He was used to excite the XeBr* excimer, and its spontaneous fluorescence at 282 nm, in turn, used to excite the iodine lasant (i-C3F7I). The peak fluorescence intensity was approximately twice the lasing threshold. Laser output at 1.31 μm closely followed the neutron flux shape (over the 12 ms pulse), suggesting long pulse or cw operation is feasible. This represents the first laser pumped with a nuclear-driven flash lamp.
Hetero-nipi band filling modulator with laterally interdigital contacts made by shadow mask molecular beam epitaxy regrowth
Authors: Wu X. , Gulden K. H. , Thomas M. , Smith J. S. , Whinnery J. R. , Malzer S. , Kiesel P. , Kneissl M. , Döhler G. H.
Published: July 2002

An AlGaAs/GaAs optical hetero-nipi modulator based on band filling effect with interdigital selective contacts has been fabricated by use of shadow mask molecular beam epitaxy (MBE) regrowth technique. There is a five order of magnitude change in I-V characteristics from forward to reverse junction bias, which indicates the high quality of the interdigital contacts. The measured reflectance spectra show a change of the absorption coefficient of about 7850 cm−1 with an applied bias voltage as low as 1.5 V.
Quasiparticle-tuned superconducting mixer
Authors: Ugras N. G. , Worsham A. H. , Winkler D. , Prober D. E.
Published: July 2002

We have successfully employed the recently observed quasiparticle admittance of a superconducting tunnel junction as the tuning element for a superconductor- insulator-superconductor mixer. This is the first demonstration of an electronic on-chip tuning element for a superconducting detector. We observe an increase in the dynamic resistance and an improvement in mixer gain and noise temperature as the dc bias voltage of the tuning junction array is varied. We compare our results with the quantum theory of mixing.
Identification of nonbolometric photoresponse in YBa2Cu3O7−δ thin films based on magnetic field dependence
Authors: Hegmann F. A. , Preston J. S.
Published: July 2002

Optically induced transient voltages across a current-biased bridge structure fabricated from an epitaxial YBa2Cu3O7−δ thin film are reported. A novel technique consisting of applying a small magnetic field perpendicular to the sample was used to identify any bolometric contribution to the photoresponse. Comparison to resistance versus temperature curves with and without the field establishes a slow component in the photoresponse as bolometric and unambiguously identifies a fast component as a nonthermal transient.
Optical absorption in quantum wells with two characteristic curvatures
Authors: Johnson N. F. , Vargas J. E.
Published: July 2002

Novel features are predicted in the infrared absorption spectrum of an interacting electron gas in a parabolic quantum well with two characteristic curvatures (biparabolic quantum well). A series of well-defined absorption peaks appears below the frequency of the usual center-of-mass absorption. These subfundamental peaks correspond to modes of the coupled electron gas and light system, and lie beyond the usual treatment of light absorption within first-order perturbation theory.
AlGaAs/GaAs buried quantum well laser diodes by one time selective metalorganic chemical vapor deposition growth on dielectric window stripes
Authors: Ogura M. , Chen Z. Y. , Kaneko H. , Fujii S. , Itoh H. , Mori M. , Watanabe M. , Mukai S. , Yajima H.
Published: July 2002

AlGaAs graded-index separate-confinement heterostructure lasers with lateral mode confinement are realized by one time metalorganic chemical vapor deposition with silicon dioxide stripes as selective masks and current blocking layers. The effect of the active region width on lasing characteristics is investigated. The threshold current and external quantum efficiency are around 12 mA and 70%, respectively, for narrow lasers. Elevated waveguide structure formed by the growth-rate difference between (100) and sidewall planes was effective for stable lateral mode characteristics.
Transient analysis of a nonlinear fiber ring resonator
Authors: Fraile-Peláez F. Javier , Prol Miguel , Santos David J. , Soto-Crespo José M.
Published: July 2002

In this letter we study the transient behavior of a nonlinear fiber ring resonator operating both as an optical bistable and as a differential amplifier. The speed of response of the structure is investigated, and some general considerations on the performance of these kinds of devices are presented.
Semi-insulation of undoped GaAs epitaxial layers by wafer annealing
Authors: Imaizumi T. , Okazaki H. , Oda O.
Published: July 2002

Wafer annealing was first applied to undoped p-type GaAs epitaxial layers grown by the chloride chemical vapor deposition method in order to realize semi-insulating GaAs epitaxial layers. It was found that by wafer annealing at temperatures higher than 950 °C, the semi-insulating epitaxial layers with the resistivity higher than 107 Ω cm and the mobility higher than 5000 cm2/V s can be obtained. The EL2 concentration was measured using Si-doped epitaxial layers and it was concluded that the semi-insulation of undoped p-type GaAs epitaxial layers is due to the increase of the EL2 concentration to the level of 1015 cm−3 by wafer annealing.
Effect of the Y-junction output coupler on the lasing threshold of semiconductor ring lasers
Authors: Hohimer J. P. , Craft D. C. , Vawter G. A.
Published: July 2002

We report the first measurements of the effect of a Y-junction output coupler on the continuous-wave (cw) lasing threshold of rib-waveguide semiconductor ring lasers. We show that the Y-junction induced loss in this type of ring diode laser depends on the ring radius (r), and increases the lasing threshold current density substantially for devices with r<200 μm. For our devices with radii of 50–100 μm, the Y-junction loss term is shown to be the dominant factor affecting the cw lasing threshold. We also report the first measurements of the dependence of the cw lasing threshold on the width (w) of the Y-junction output coupler, and show that the threshold current density increases linearly for 0≤w≤9 μm.
Positron annihilation and internal surfaces
Authors: Huang W. F. , Huang D. C.
Published: July 2002

Doppler broadened gamma spectra from positron annihilations in alumina and several zeolites were measured as a function of internal surfaces. In all cases, the gamma line shape parameter was found to vary proportionally with surface area. The results greatly enhance the potential of using positron annihilation spectroscopy as a microprobe for surface studies of porous materials.
Threshold height for movement of C60 molecules on Si(111)-7×7 with a scanning tunneling microscope
Authors: Maruno S. , Inanaga K. , Isu T.
Published: July 2002

Scanning tunneling microscope has been employed for intentional movement of C60 molecules adsorbed on Si(111)-7×7 surface. Threshold conditions at which a C60 molecule starts moving from its adsorption site are investigated in relation to tunnel current and tip bias voltage. We find that there exists threshold height for the movement process. The threshold height estimated from a planar electrode model is in agreement with the vertical height of the adsorbed C60 molecules. Present results evidence that direct contact or close proximity between a mechanical probe and C60 molecules is required for movement of the molecules to occur.
Influence of wettability on anodic bias induced electroluminescence in porous silicon
Authors: Halimaoui A.
Published: July 2002

Anodic oxidation in hydrochloric (HCl) acid and chemical dissolution in hydrofluoric (HF) acid solutions of porous silicon (PS) layers obtained from lightly doped p-type substrates have been investigated. It is shown that the wettability of PS, which is a highly hydrophobic and organophilic material, strongly affects its electroluminescence (EL) during anodic oxidation and its chemical etch rate in HF solutions. When the solutions do not penetrate the pores, a very weak EL intensity is obtained and the chemical etch rate in HF is found to be very slow. However, when the solutions infiltrate the pores, both the EL intensity and chemical etch rate are dramatically increased. In the first case, only the top surface of the porous layer is accessible to the liquids while in the second case the whole volume of the material and its vast inner surface are involved.
Investigation of the growth of gallium arsenide thin films by metalorganic molecular beam epitaxy using gallane-quinuclidine adduct
Authors: Foord J. S. , Whitaker T. J. , Downing E. N. , O’Hare D. , Jones A. C.
Published: July 2002

The use of gallane-quinuclidine adduct (GaH3[N(CH2CH2)3CH] ) as a chemical precursor in metal organic molecular beam epitaxy (MOMBE) and chemical beam epitaxy (CBE) has been investigated. The compound displays a long-term stability and can be readily admitted as a molecular beam into the growth chamber without significant decomposition. The surface decomposition pathway of the precursor on the growth surface is similar to that of the highly successful alane adduct precursors already in widespread use. Efficient MOMBE growth of GaAs is observed at much lower temperatures than is the case when conventional Ga alkyl precursors are employed. These results show that gallane adducts may have the potential to act as practical low carbon precursors in CBE and MOMBE.
New high-temperature superconducting phase spread alloy thin films
Authors: Lederman D. , Moran T. J. , Hasen J. , Schuller Ivan K.
Published: July 2002

We have prepared Gd1−xPrxBa2Cu3O7−δ phase spread alloy thin films with well-defined variations in the concentration of Pr across a single substrate. Their Pr concentrations were independently determined from electrical resistivity and Auger electron spectroscopy measurements. The results from both methods are in good agreement with each other. Using this technique several high-temperature superconducting thin-film alloys may be grown under virtually identical conditions. As an example of an important application of this technique, we measured the changes in the films’ resistivities and critical temperatures (Tc) induced by decreasing their oxygen concentration. The observed shifts in Tc of the oxygen-deficient samples appear to be slightly dependent on their Pr concentrations.
Resonant tunneling of X-band electrons from AlAs through GaAs/AlAs/GaAs double barrier structure
Authors: Shieh Tung-Ho , Lee Si-Chen
Published: July 2002

The negative differential resistance entirely due to X-band electron tunneling through the X-band profile in an AlAs/GaAs/AlAs/GaAs/AlAs diode which uses the AlAs as the X-band electrodes and tunneling well and the GaAs as the X-band barriers is observed. Two small inflection points in the current-voltage curve are measured at 8.8 K at low biases (24 and −48 mV) which disappear above 30 K. These peaks are found to be due to the Xl (normal to the interface) electrons in the AlAs electrode tunneling through the quasiquantized state of Xl valley in the AlAs well. Two tunneling peaks with negative differential resistance are also observed at 8.8 K which disappears above 100 K. The tunneling peak current density is 3.1 A cm−2 at a bias of −0.18 V and the peak to valley ratio is 1.4. This peak is attributed to the Xt (parallel to the interface) electrons in the AlAs electrode tunneling through the quasiquantized state of Xt valley in the AlAs well.
Large diffusion length enhancement in silicon by rapid thermal codiffusion of phosphorus and aluminum
Authors: Hartiti B. , Slaoui A. , Muller J. C. , Siffert P.
Published: July 2002

We have investigated the effects of simultaneous diffusion of phosphorus and aluminum in crystalline silicon on the minority carrier diffusion length as measured by the surface photovoltage technique. The diffusion is carried out by using a tungsten halogen lamp furnace (rapid thermal processing). We have shown that more than 100% bulk diffusion length improvement can be achieved in both float zone and Czochralski silicon material. The different contributions to this enhancement are discussed.
Carbon + argon co-implantation for GaAs p-channel metal-semiconductor field-effect transistors
Authors: Chan Yi-Jen , Chen Chun-Hung
Published: July 2002

Carbon (C), based on its high carrier density and low diffusivity, has been applied extensively in GaAs devices, where p-active layers are required. In this study, we used C as an implant source to form p-type active layers, rather than using the conventional epitaxial approach. The dopant activation increased dramatically if an additional argon (Ar) implantation was used. p-channel GaAs metal-semiconductor field-effect transistors were fabricated with this C plus Ar co-implantation technique and demonstrated a promising improvement on device performance.
Electroabsorption and saturation behavior of InGaAsP/InP/InAlAs multiple superlattice electron transfer optical modulator structures
Authors: Agrawal N. , Reier F. W. , Bornholdt C. , Weinert C. M. , Li K. C. , Harde P. , Langenhorst R. , Grosskopf G. , Berger L. , Wegener M.
Published: July 2002

We report substantial progress in the growth of multi-quantum-well electron transfer optical modulator structures by metalorganic vapor phase epitaxy, which is made possible as a consequence of the highly abrupt modulation doping of donors and acceptors in InP-reservoir and InAlAs-barrier layers, respectively. Due to a large thermionic emission barrier provided by the type II InP/InAlAs interface, the InGaAsP/InP/InAlAs devices exhibit extremely low leakage current densities. We observe distinct and sharp features related to absorption quenching in differential transmission spectroscopy. Moreover, the saturation intensities of electron transfer modulators are determined. The underlying physical mechanism is discussed.
Gas-source molecular beam epitaxy growth of GaxIn1−xAsyP1−y lattice matched to GaAs
Authors: Zhang G.
Published: July 2002

Gas-source molecular beam epitaxy growth of GaxIn1−xAsyP1−y layers lattice matched to GaAs is reported. X-ray diffraction, photoluminescence, and Hall measurements show that the layers are of good quality. High-quality GaAs/GaxIn1−xAsyP1−y heterojunction and (In)GaAs/GaxIn1−xAsyP1−y quantum well structures have also been prepared, as deduced from the device characteristics of heterojunction diodes and quantum well lasers.
High-resolution line-Q measurements of velocity-selective nonlinear Faraday rotation in Rb vapor
Authors: Lee W. D. , Heuring J. J. , Campbell J. C. , Buell W. F. , Davis C. L.
Published: July 2002

Optical feedback from velocity-selective nonlinear Faraday rotation in alkali metal vapors has been shown to be an effective technique for simultaneously stabilizing the frequency and reducing the linewidth of AlxGa1−xAs/GaAs lasers. The ultimate frequency stability of such a laser is limited by the quality factor Q=ν0/Δν of this frequency reference. In this letter we report the measurement of Q=6×106 for optical feedback from velocity-selective nonlinear Faraday rotation in Rb vapor.
Low-temperature synthesis of BaTiO3 thin films on silicon substrates by hydrothermal reaction
Authors: Bacsa R. R. , Dougherty J. P. , Pilione L. J.
Published: July 2002

Crystalline BaTiO3 thin films (0.2–1 μm) of dielectric constant 450–500 have been synthesized by the hydrothermal reaction of a titanium film (∼1 μm thickness) deposited on a silicon substrate with Ba(OH)2 solution (concentration 0.4 M) in the temperature range 100–200 °C. The reaction of the silicon substrate with the Ti film was prevented by deposition of a buffer layer of amorphous TiC between the Ti film and the Si substrate. The TiC not only prevented the diffusion of Si through the Ti layer but also allowed some reaction between itself and the Ti layer so that the adherence of the films was not degraded.
Quantum wires prepared by molecular beam epitaxy regrowth on patterned AlGaAs buffer layers
Authors: Eberl K. , Grambow P. , Lehmann A. , Kurtenbach A. , Klitzing K. v. , Heitmann D. , Dilger M. , Hohenstein M.
Published: July 2002

Modulation doped GaAs quantum wires are prepared by molecular beam epitaxy regrowth on patterned AlGaAs buffer layers. The structural properties are investigated by scanning electron microscopy and by transmission electron microscopy. Far-infrared spectroscopy provides information about the lateral confinement and the carrier density in the quantum wires. The measurements indicate a distinct dependence of the electronic width on the orientation of the quantum wires within the (100) plane. Confinement energies of 6.9, 9.3, and 11.7 meV are determined for the [011], [001], and the [01̄1] wire orientations, respectively.
Effects of propane and methane on carbonization and surface morphology in heteroepitaxial growth of β-SiC films on (100) Si via chemical vapor deposition
Authors: Bahavar B. , Chaudhry M. I. , McCluskey R. J.
Published: July 2002

Epitaxial β-SiC films have been produced on Si(100) substrates by chemical vapor deposition (CVD) with 90% of the carbon supplied by methane and 10% by propane as compared to 100% by propane (or 100% by any carbon source more reactive than methane). These films, grown at 1350 °C in a CVD reactor, are single crystalline with a three-dimensional surface morphology and have similar growth rates but lower carrier concentrations than films grown from propane and silane. The interplay of the chemistry of methane and evaporative loss of the Si substrate at ∼1100–1300 °C provide a reasonable explanation of our observations.
Defect control during solid phase epitaxial growth of SiGe alloy layers
Authors: Im Seongil , Washburn Jack , Gronsky Ronald , Cheung Nathan W. , Yu Kin Man
Published: July 2002

A systematic study of the processing procedures required for minimizing structural defects generated during the solid phase epitaxial (SPE) growth of SiGe alloy layers is described. It includes high dose Ge implantation into Si at liquid nitrogen temperature (LNT), sequential carbon implantation, and an 800 °C anneal. The LNT implantation step considerably reduces the density of end-of-range (EOR) defects relative to that found in SPE grown SiGe layers implanted at room temperature, while the sequential implantation of carbon ions before annealing effectively suppresses the formation of stacking faults that are found to form at a threshold peak concentration of about 6 at. % Ge in the absence of carbon.
Comparison of microsecond photoluminescence decay between as-prepared and dry-oxidized porous Si
Authors: Takazawa Akira , Tamura Tetsuro , Yamada Masao
Published: July 2002

Photoluminescence (PL) decay for as-prepared and dry-oxidized porous Si following by a nitrogen pulse laser excitation is reported. The PL decay of both samples is nonexponential. For the as-prepared samples, the PL lifetime decreases from 200 to 60 μs as the PL emission energy increases from 1.55 to 1.90 eV. The spread in values can be interpreted in terms of nonradiative tunneling of carriers between Si microcrystals. For the dry-oxidized samples, the PL lifetime depends little on the emission energy, and is about 100 μs. On the basis of these results, we conclude that photoluminescence cannot be explained by the tunneling model alone, suggesting that luminescence centers play a role in determining the PL mechanism of porous Si.
Transport properties in n-type InSb films grown by metalorganic chemical vapor deposition
Authors: Song S. N. , Ketterson J. B , Choi Y. H. , Sudharsanan R. , Razeghi M.
Published: July 2002

We have measured the temperature and magnetic field dependence of the Hall mobility and transverse magnetoresistance in n-type InSb films epitaxially grown on GaAs substrates by metalorganic chemical vapor deposition. The films show a giant magnetoresistance: e.g., at 240 K the resistivity increases over 20 times at a magnetic field of 5 T; the low field coefficient of resistivity at 77 K is as high as 47.5 μΩ cm/G. The Hall mobility decreases with magnetic field and saturates at higher fields. By taking the interface carrier transport into account, the observed field dependence of the Hall mobility and magnetoresistance may be understood based on a two-layer model.
Demonstration of demultiplexing with a rocking filter fiber
Authors: Krautschik C. G. , Wigley P. , Stegeman G. I. , Stolen R. H.
Published: July 2002

We show that the presence of a strong pump beam detuned from the center wavelength of a rocking filter fiber causes a signal beam at the filter resonance frequency to switch between polarization states. This process is used to switch out a pulse from a pulse train.
Ion beam mixing for enhanced electron tunneling in metal-oxide-silicon structures
Authors: Walker A. J. , Politiek J.
Published: July 2002

Metal-oxide-silicon (MOS) structures were fabricated to investigate enhanced Fowler–Nordheim tunneling in thin oxides due to ion beam mixing. Ions of germanium were implanted into a 100 nm polycrystalline silicon layer deposited on 10 nm thermal silicon dioxide such that the tail of the implant profile contains the thin oxide. Besides simple MOS capacitors and transistors, flash electrically erasable programmable read only memory (flash EEPROM) cells were fabricated for the first time using this technique. Using 1×1015 cm−2 at 80 keV the Fowler–Nordheim tunneling barrier reduced by about 0.9 eV at the polycrystalline gate/oxide interface and by 1.3 eV at the oxide/substrate interface. The consequently lower program/erase voltages in the flash EEPROM were measured. Flash EEPROM charge retention measurements show that the discharge process is logarithmic in time. This leads to the possibility of flash EEPROMs being programmed and erased at low voltages and having sufficient charge retention for several years operation.
Electrically induced light emission and novel photocurrent response of a porous silicon device
Authors: Shi Hongtao , Zheng Youdou , Wang Yongbin , Yuan Renkuan
Published: July 2002

An electrically induced visible light emitting porous silicon (PS) device was fabricated by laterally anodizing an n-type single-crystal silicon (Si) wafer. Al/PS Schottky junctions exhibited rectifying I-V characteristics with an ideality factor of 7. The intensity of current-induced light emission increased with applied electrical current. Novel photocurrent spectra of the device under different reverse biases were measured at room temperature and reported for the first time, which showed three peaks of light absorption pertinent to the quantized energy levels of the PS. Interpretation is given based on the quantum confinement model.
Low-temperature migration enhanced epitaxy of base material for AlGaAs/GaAs heterojunction bipolar transistors
Authors: Zhang Kai , Wu Der-Woei , Fu Jianming , Miller D. L. , Fukuda Mike , Yun Yong-Hoon , Schauer Stephen
Published: July 2002

Migration enhanced epitaxy (MEE) was used in this work to grow p+-GaAs at the substrate temperature of 300 °C for the base of AlGaAs/GaAs heterojunction bipolar transistors. The results indicated that the low-temperature MEE-grown p+-GaAs epitaxial layers (p=1×1019–1×1020 cm−3) exhibited a crystalline quality comparable to those grown by standard MBE at a substrate temperature of 570 °C. AlGaAs/GaAs HBTs with low-temperature MEE-grown bases doped at p≊2×1019 cm−3 were fabricated by using a self-alignment technique. For the devices with the conventional MBE-grown base, secondary ion mass spectroscopy depth profiles showed a significant Be diffusion into the AlGaAs emitter and as a consequence, the devices showed no current gain. For the devices with the low-temperature MBE-grown base, there was a negligible Be penetration into the emitter and the devices exhibited a common-emitter dc current gain of 13.
Dependence of femtosecond single-photon photoemission from gold on laser beam incidence and polarization
Authors: Girardeau-Montaut J. P. , Girardeau-Montaut C. , Moustaizis S. D. , Fotakis C.
Published: July 2002

We report here the measurements of single-photon photoelectric emission sensitivity of gold irradiated with 450 fs laser pulses at 248 nm and discuss the dependence of this sensitivity on the angle of incidence and the states of polarization of the laser beam. We compare our experimental data to the predictions from both the vectorial photoemission theory and the single-photon absorption corresponding to a pure energy coupling.
Observation of deep donor center related tunneling peak in the AlxGa1−xAs/AlAs/AlxGa1−xAs/AlAs/AlxGa1−xAs (0.40≤x≤0.50) resonant tunneling diodes
Authors: Shieh Tung-Ho , Lee Si-Chen
Published: July 2002

The tunneling peak due to electron transport through deep donor (DX) centers was observed in the AlxGa1−xAs/AlAs/AlxGa1−xAs/AlAs/AlxGa1−xAs resonant tunneling diodes (0.40≤x≤0.50). Since the carriers are frozen out in AlxGa1−xAs (x≥0.35) at low temperature, the current-voltage (I-V) characteristics can only be measured under laser illumination condition. It was found that this DX center related tunneling peak initially appeared at higher voltage when the laser was turned on, and it gradually shifted to lower voltage over several minutes. This peak eventually merged into the lower voltage tunneling peak at temperature below 76 K, but stayed apart at higher temperature. This unusual behavior is attributed to the simultaneous existence of the impurity band formed by the metastable DX states associated with X band [DX(X)] and their isolated double charged states [DX−(X)]. This tunneling peak is not observed when the AlAs mole fraction x is reduced to 0.35.
Spectral linewidth reduction in partly gain-coupled 1.55 μm strained multiple quantum-well distributed feedback laser
Authors: Lu H. , Li G. P. , Makino T.
Published: July 2002

The effective linewidth enhancement factor αeff and the spectral linewidth Δυ are reported for the first time for a partly gain-coupled distributed feedback laser with a gain corrugation in a strained multiple quantum-well active region emitting at 1.55 μm wavelength. The αeff value is estimated to be as low as 1 and is independent of the laser cavity length L, while a decrease in the linewidth-power product ΔυPo with L has been observed, with a measured linewidth of 2 MHz at 10 mW optical output power for 300-μm-long devices. The experimental results demonstrate that a small αeff is obtained due to the strain and the gain coupling effects, while further reduction of the spectral linewidth with L is the result of longitudinal index coupling effects.
Diffusion of sulfur-35 into silicon using an elemental vapor source
Authors: Rollert F. , Stolwijk N. A. , Mehrer H.
Published: July 2002

Diffusion of S into Si was investigated by the closed ampoule technique using the radioactive tracer 35S. Erfc-type penetration profiles determined by mechanical sectioning originated from exposure of the samples to evaporated elemental sulfur. Diffusion coefficients in the temperature range 1328–1671 K obey the Arrhenius law with an activation energy of 1.80 eV and a pre-exponential factor of 4.7×10−6 m2 s−1. This high diffusivity can be reconciled with the preferred incorporation of S on lattice sites by invoking substitutional-interstitial exchange. Within this concept the measured long-range transport appears to be controlled by a minority of interstitial S atoms.
Brick-wall structure in polycrystalline TlBa2Ca2Cu3Ox thick films with high critical currents
Authors: Miller D. J. , Hu J. G. , Hettinger J. D. , Gray K. E. , Tkaczyk J. E. , DeLuca J. , Karas P. L. , Sutliff J. A. , Garbauskas M. F.
Published: July 2002

Microstructural studies of TlBa2Ca2Cu3Ox(Tl-1223) thick films that exhibit high critical current densities (Jc) for nonepitaxial polycrystalline materials show that these films possess a ‘‘brick-wall’’ structure that may be partly responsible for high current densities. The magnetic field dependence of Jc is similar to that reported for Bi-Sr-Ca-Cu-O materials that exhibit this structure. Structural analyses indicate a high degree of c-axis alignment but little in-plane texture, suggesting that high-angle [001] tilt boundaries are prevalent. Scanning and transmission electron microscopy reveal that the microstructure consists of overlapping layers reminiscent of the brick-wall structure. These results suggest that high critical current densities may be achieved by percolative transport through this structure.
Small-signal gain measurements in an electron beam pumped F2 laser
Authors: Bastiaens H. M. J. , van Dam B. M. C. , Peters P. J. M. , Witteman W. J.
Published: July 2002

The net-small-signal gain of a molecular fluorine F2* laser pumped by a coaxial electron beam has been measured in gas mixtures of He/F2 and He/Ne/F2. A peak net-small-signal gain of 0.63 cm−1 has been measured in a mixture of He/Ne/F2 at a pressure of 8 bar and a pumping power density of 13 MW/cm3.
Design and fabrication of asymmetric strained layer mirrors for optoelectronic applications
Authors: Bean J. C. , Peticolas L. J. , Hull R. , Windt D. L. , Kuchibhotla R. , Campbell J. C.
Published: July 2002

The design of thin-film mirrors is optimized for strained layer materials systems. It is shown that the use of asymmetric structures produces only minor loss in reflectivity per mirror period, while greatly extending the number of periods that can be grown in a defect-free mode. As applied to the GexSi1−x/Si strained layer system, the net result is an enhancement of reflectivity, with 1.3 μm mirrors achieving peak values near 75%. The approach is applicable to other materials systems and should yield even higher reflectivities in situations where wider ranges in index of refraction are available.
Positron trap centers in x-ray and γ-ray irradiated SiO2
Authors: Khatri R. , Asoka-Kumar P. , Nielsen B. , Roellig L. O. , Lynn K. G.
Published: July 2002

Using Doppler broadening annihilation spectroscopy, we investigated the properties of irradiated samples of SiO2/Si(100) with 117 nm thick oxide layer, grown in dry O2 on p- and n-type substrates. These samples were irradiated with γ rays and x rays at doses in the range of 7×104–9×106 rad and 50–2000 mJ/cm2, respectively. The changes observed in the Doppler broadening line shape parameter after irradiation and its recovery during isochronal annealing were used to obtain an activation energy of 1.48–1.61 eV required for annealing the defects.
Electrochemically prepared Si(111) 1×1-H surface
Authors: Bitzer T. , Gruyters M. , Lewerenz H. J. , Jacobi K.
Published: July 2002

Si(111) surfaces have been prepared electrochemically. Using high resolution electron energy loss spectroscopy it is demonstrated that perfectly terminated and clean Si(111) 1×1-H surfaces can be achieved. The dark current observed during electrochemical preparation is shown to be a very reliable control parameter.
Pulsed laser deposition of cubic boron nitride films on silicon substrates
Authors: Qian F. , Nagabushnam V. , Singh R. K.
Published: July 2002

Quasicrystalline cubic boron nitride (cBN) thin films have been deposited on clean single crystal silicon substrates by the pulsed laser deposition technique. Different chamber gases (N2 and NH3) at pressures between 10−3 and 800 mTorr were employed for the deposition processes. Typically, boron-rich films were obtained, but the boron/nitrogen ratio was reduced when nitrogen or nitrogen/ammonia gases were incorporated during the deposition process. Under a wide range of deposition conditions, the films exhibited a quasicrystalline cubic phase near the film–substrate interface (∼150 Å thick). A completely amorphous phase was observed beyond this region, suggesting that the substrate plays an important role in the crystallization of cBN thin films.
Solid-phase epitaxial growth of lithium tantalate thin films deposited by spray-metalorganic chemical vapor deposition
Authors: Wernberg Alex A. , Braunstein Gabriel , Paz-Pujalt Gustavo , Gysling Henry J. , Blanton Thomas N.
Published: July 2002

We demonstrate the solid-phase epitaxial crystallization of thin films of lithium tantalate deposited on lithium niobate and sapphire substrates. An organometallic compound, formed by reaction of lithium dipivaloylmethanate and tantalum(V) ethoxide, is used as a single-source precursor for the deposition of amorphous thin films of lithium tantalate using a spray-metalorganic chemical vapor deposition process. Annealing of the amorphous films results in their epitaxial alignment with respect to the underlying LiNbO3 or Al2O3 substrates. X-ray diffraction, ion channeling, and scanning electron microscopy are used to evaluate and compare the crystalline quality of the films produced by this solid-phase epitaxial process to films that are crystalline as deposited.
Epitaxy of high resistivity InP on Si
Authors: Schnabel R. F. , Krost A. , Grundmann M. , Heinrichsdorff F. , Bimberg D. , Pilatzek M. , Harde P.
Published: July 2002

Low pressure metalorganic chemical vapor deposition of undoped and Fe-doped InP on vicinal Si(001) and Si(111) is reported. For concentrations up to 8×1016 cm−3 the incorporated Fe is found to be entirely electrically active. Semi-insulating InP on Si(111) with a resistivity of 3×107 Ω cm has been obtained. The resistivity increases strongly with decreasing defect density in the InP:Fe epitaxial layers. A reduction of the crystal defect density by one order of magnitude in InP/Si(111) as compared to InP/Si(001) almost suppresses the undesired effects of strong Si incorporation and parasitic conductance channels.
High power gasdynamically cooled carbon monoxide laser
Authors: Bülow H. von , Schellhorn M.
Published: July 2002

A capacitively coupled transverse radio frequency discharge has been successfully applied to excite a gasdynamically cooled supersonic CO laser operating at 105 K in a semiclosed gas cycle. The laser head is characterized by a very compact design and a high discharge power density (160 W/cm3). At a discharge pressure of 390 mbar a maximum laser output of 6 kW is obtained with an efficiency of 12.4%.
Effects of n-type modulation doping of quantum wells on the dynamics of photoluminescence
Authors: Sweetser J. N. , Dunn T. J. , Waxer L. , Walmsley I. A. , Shank S. M. , Wicks G. W.
Published: July 2002

The rise time of band-edge photoluminescence (PL) in n-type modulation-doped quantum-well structures has been studied. The PL turns on less than 1 ps after carriers are photoinjected into the conduction band, or six times more rapidly in the n-doped structures than in comparable undoped structures. This is attributed to the rapid intraband relaxation of holes and the presence of a large ambient electron population due to the doping. We discuss the implications of this result for the direct modulation bandwidth of n-type modulation-doped quantum-well lasers.