bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly strained GaAs/InGaAs/AlAs resonant tunneling diodes with simultaneously high peak current densities and peak-to-valley ratios at room temperature
Authors: Kapre R. M. , Madhukar A. , Guha S.
Published: July 2002

Highly strained In0.33Ga0.67As/AlAs-based resonant tunneling diodes have been fabricated on GaAs(100) substrates without the use of thick strain relieving buffer layers. These structures exhibit a simultaneously high peak current density (Jp) of 125 kA/cm2 and a peak to valley ratio (PVR) of 4.7. A PVR of 5.9 with Jp=73 kA/cm2 is observed on some devices, the highest PVR seen for such devices. The excellent resonant tunneling characteristics of these devices are attributed to accurate device design using a Γ-X-Γ-X-Γ resonant tunneling path and to high quality interfaces obtained through the use of optimized growth conditions.
Hydrogenation effect in an n-channel metal-oxide-semiconductor field-effect transistor
Authors: Lee Choong Hun , Lee Choochon , Chang K. J. , Kim Sung Chul , Jang Jin
Published: July 2002

The effects of hydrogen plasma exposure on the characteristics of an n-channel metal-oxide-semiconductor field-effect transitor are studied. The helium plasma gives almost no changes in maximum transonductance and subthreshold slope whereas the hydrogen plasma degrades maximum transconductance and increases subthreshold slope. These results indicate that the excess interface traps are generated by hydrogenation, which is also confirmed by quasi-static capacitance-voltage analysis.
Biaxial splitting of optical phonon modes in ZnSe-ZnS strained-layer superlattices
Authors: Yamamoto Aishi , Yamada Yoichi , Masumoto Yasuaki
Published: July 2002

Raman scattering studies were performed on ZnSe-ZnS strained-layer superlattices with the incident light parallel as well as perpendicular to the interface plane. We found for the first time that the optical phonon modes split into two types, that is a singlet and a doublet, by the built-in biaxial stress. A new method to characterize the directional stress is demonstrated.
Photochemical laser writing of polymeric optical waveguides
Authors: Beeson K. W. , Horn K. A. , McFarland M. , Yardley J. T.
Published: July 2002

We report a rapid one-step laser writing process for forming optical channel waveguides by photochemically lowering the index of refraction in selected areas of thin, highly photosensitive polymeric flims. We have demonstrated the concept by forming single- and multimode waveguides in films composed of poly(methylmethacrylate) containing (4-N-N-dimethylaminophenyl)-N-phenyl nitrone. The effects of ultraviolet fluence on the refractive index of the films and on channel lightwave confinement were examined. Low loss (1.5 dB/cm) channels were produced with ultraviolet fluences as low as 20 mJ/cm2.
Optical characterization of ZnSe/ZnS strained-layer superlattices grown on CaF2 substrates
Authors: Yokogawa Toshiya , Saitoh Tohru , Narusawa Tadashi
Published: July 2002

Growth of ZnSe/ZnS strained-layer superlattices on CaF2 substrates has been demonstrated for the first time. Optical transmission measurements at 77 K were carried out to investigate the optical property of excitons confined in ZnSe/ZnS multiquantum wells. Two exciton peaks related to the transitions between n=1 electron and heavy hole (Ee–hh) and between n=1 electron and light hole (Ee–lh) were observed in the transmission spectra. The energy seperation between Ee–hh and Ee–1h increases with decreasing the ZnSe layer thickness, which is due to the increase of strain in the ZnSe well layer. From the relationship between ZnSe well layer thickness and peak energy, the quantum size effect in the quantum well was also confirmed.
Flux pinning in Y1−xPrxBa2Cu3O7−δ high T
c superconductors
Authors: Paulius L. M. , Tsai P. K. , Neumeier J. J. , Maple M. B. , Chen K. C. , Mazdiyasni K. S.
Published: July 2002

Magnetic relaxation measurements have been made on two sets of samples of Y1−xPrxBa2Cu3O7−δ high Tc superconductors with 0≤x≤0.10. The samples were prepared as fibers using a sol-gel process and as polycrystalline pellets using a standard solid-state reaction technique. In an applied field of 5 kOe at 30 K, the fluxoid pinning potential U was observed to increase approximately linearly with Pr concentration x at the rate dU/dx≊1 eV. A mechanism for the enhancement of U may be the suppression of the superconducting order parameter in the vicinity of the Pr ions due to magnetic pair breaking.
Optimal parameters for AlGaAs-InGaAs-AlGaAs p-channel field-effect transistors
Authors: Laikhtman B. , Kiehl R. A. , Frank D. J.
Published: July 2002

Using the model of an infinite well we have performed detailed calculations of the hole band structure in a strained quantum well. In-plane effective masses and energy separations were calculated for different thicknesses of the well and In mole fractions below 0.50. Based on the calculations we estimated the optimal thickness of the well and In mole fraction for which the energy separation between the lowest two subbands has a maximum and the InGaAs layer is stable with respect to misfit dislocations. The results provide useful guidelines for the optimization of p-channel field-effect transistors.
Femtosecond dynamics of the nonlinear optical response in polydiethynylsilane
Authors: Wong K. S. , Han S. G. , Vardeny Z. V. , Shinar J. , Pang Y. , Ijadi-Maghsoodi S. , Barton T. J. , Grigoras S. , Parbhoo B.
Published: July 2002

We have measured the femtosecond dynamics of the nonlinear optical response χ(3) in polydiethynylsilane (C4H2SiBu2)x, a novel class of π-conjugated polymers incorporating Si, using degenerate four-wave mixing and photoinduced absorption techniques. In resonance conditions at 620 nm we found χ(3)=3×10−9 esu, which decays in a record time of 135 fs, followed by a slower decay component of 750 fs, without a long tail even at high laser intensities. This material is an excellent candidate for nonlinear optical devices in the sub-THz frequency range.
Photoelectrochemical evidence for saturated optical absorption in electrolytic cuprous oxide
Authors: Schwartz Daniel T. , Muller Rolf H.
Published: July 2002

An illuminated cuprous oxide-covered electrode immersed in alkaline media exhibits a nonlinear dependence of photocurrent on the intensity of 488 nm laser illumination. Results from intensity modulation experiments show that the differential efficiency for converting photons to photocurrent in the p-type cuprous oxide thin film is inversely proportional to the square root of illumination intensity. A charge transfer model that includes intensity dependent optical absorption in the cuprous oxide layer is found to be consistent with the observed photocurrent response. Analysis of the experimental results using the charge transfer model shows that the saturation intensity for cuprous oxide is approximately 100 mW/cm.2 Photoelectrochemical charge transfer is found to be efficient in the potential region where the nonlinear photocurrent response is observed, with nearly all photoinjected minority carriers being consumed by the interfacial charge transfer reaction rather than by recombination.
Experimental determination of the effects of degenerate Fermi statistics on heavily p-doped GaAs
Authors: Harmon E. S. , Melloch M. R. , Lundstrom M. S. , Lovejoy M. L.
Published: July 2002

The effects of degenerate Fermi statistics on electron injection currents for p+-GaAs grown by molecular beam epitaxy are presented. To achieve Be dopant concentrations of greater than 8×1019 cm−3, the substrate temperature during growth was reduced to approximately 450 °C from the usual 600 °C. In this heavily doped material, we measure unexpectedly large electron injection currents which are interpreted in terms of an effective narrowing of the band gap. At extremely heavy doping densities, the Fermi level pushes into the valence band and degenerate Fermi statistics must be taken into account. For doping concentrations greater than 1×1020 cm−3, effects due to degenerate Fermi statistics oppose the band-gap shrinkage effects; consequently, a reduction in the electron injection currents is observed. The result is a substantial reduction in gain for AlGaAs/GaAs heterostructure bipolar transistors when the base is doped above 1020 cm−3.
Coherent tunneling of mixed state hole wave packets in coupled quantum well structures
Authors: Sankaran Vasu , Singh Jasprit
Published: July 2002

The time-dependent Schrödinger equation is solved numerically to study the coherent tunneling of hole wave packets in asymmetric coupled quantum wells. The importance of selection rules and band mixing is evident in the extremely low rates of the wave-packet leakage from heavy-hole state to a resonant light-hole state at zero in-plane wave vector (k∥). But these rates increase dramatically away from k∥=0, when the hole states acquire mixed character, and rapidly become comparable to the heavy-hole to heavy-hole resonant tunneling rates. The effect of inhomogeneous level broadening arising from well size fluctuations in multicoupled quantum well systems is shown to greatly reduce the effective tunneling rates near resonance.
Patterning and characterization of large-area quantum wire arrays
Authors: Ismail K. , Burkhardt M. , Smith Henry I. , Karam N. H. , Sekula-Moise P. A.
Published: July 2002

Large-area arrays of parallel quantum wires of 30–80 nm width are achieved using a combination of x-ray lithography, wet chemical etching, and low-pressure metalorganic vapor phase epitaxy. The quantum wires are characterized using low-temperature photoluminescence and magnetotransport measurements. The quantum confinement is reflected in a clear blue shift in the luminescence peak, and in deviation from the periodicity of the Shubnikov–de Haas oscillations as a function of inverse magnetic field.
Optical control of millimeter wave high T
c superconducting quasi-optical bandpass filters
Authors: Zhang Dawei , Plant D. V. , Fetterman Harold R. , Chou Kevin , Prakash Shiva , Deshpandey C. V. , Bunshah Rointan F.
Published: July 2002

The optical response of YBa2Cu3O7 high Tc superconducting quasi-optical millimeter wave bandpass filters operating at W band (75–110 GHz) has been investigated under various conditions of illumination. Radiation from a cw Ar+ laser (514.5 nm) and a frequency-doubled Nd:YAG laser (532.8 nm, 120 ps) was used to induce a shift in the resonant frequency of the filter. A shifted Lorentzian line shape function model was used to estimate the magnitude of the light-induced changes. Shifts of the filter’s resonance frequency on the order of 0. 1 MHz were induced by the laser effects on the superconductor pair population.
In situ stress measurement of chemical vapor deposited tungsten silicides
Authors: Washidzu Gen , Hara Tohru , Miyamoto Takaaki , Inoue Toshihiro
Published: July 2002

Peeling is a serious problem in chemical vapor deposited (CVD) tungsten silicide (WSix). In situ stress measurement during annealing is performed for sputtered and CVD WSix films at temperatures of 25–900 °C. In monosilane reduced CVD WSix, intrinsic stress increases abruptly at 400 °C and reaches a maximum of 7.8×108 Pa at 450 °C. However, such abrupt stress changes are not found at low temperatures in sputtered and dichlorosilane reduced CVD films. Abrupt stress change appeared in monosilane WSix at 400–450 °C, which is a cause of peeling during annealing, may be due to the grain growth of hexagonal and tetragonal WSi2 grains.
Highly efficient visible and infrared β-BaB2O4 optical parametric oscillator with pump reflection
Authors: Wang Yunping , Xu Zuyan , Deng Daoqun , Zheng Wanhua , Liu Xiang , Wu Baichang , Chen Chuangtian
Published: July 2002

We report the successful operation of a highly efficient visible and near-infrared optical parametric oscillator (OPO) that uses β-BaB2O4 as the nonlinear medium and is pumped at 354.7 nm. An energy conversion efficiency of 41% corresponding to a quantum conversion efficiency as high as 57% has been achieved in a 10-mm-long crystal. Pump depletion is estimated to be 70% or so. This OPO can generate an average output power to 507 mW at 490 nm and can be continuously tuned from 415 to 2411 nm. The reverse frequency conversion process has also been observed in the OPO. The reason for its high efficiency is discussed.
Radiative properties of a highly excited quantum well
Authors: Deveaud B. , Clérot F. , Fujiwara K. , Mitsunaga K.
Published: July 2002

We study by time-resolved luminescence, the radiative recombination from a single quantum well placed inside a graded confinement structure. We are able to produce a cold (T<50 K), high-density (5×1011<N<5×1012 cm−2) plasma. We compare our spectra with usual lineshape fitting procedures and give evidence for the shortcomings of such an analysis. We detail the consequences of the present work for the determination of band-gap renormalization, the conservation of k-selection rule, and the measurement of the radiative recombination rate.
High-temperature neutron diffraction study of the melting behavior of Bi2CaSr2Cu2Ox
Authors: Garbauskas Mary F. , Arendt Ronald H. , Jorgensen James D. , Hitterman Richard L.
Published: July 2002

High-temperature neutron powder diffraction has been used to study the melting, and subsequent reformation, behavior of Bi2CaSr2Cu2Ox (2122), the 80 K transition temperature oxide superconductor. It was found that the (2122) substantially reforms upon return to a temperature just below the peritectic melting point of the material. This finding implies that difficulties encountered in melt processing this material may be due largely to gross segregation of the constituents while the material is partially molten, as opposed to slow formation kinetics for this species.
Avoiding preamorphization damage in MeV heavy ion-implanted silicon
Authors: Schreutelkamp R. J. , Custer J. S. , Liefting J. R. , Saris F. W.
Published: July 2002

Implantation of 1.0 MeV 115In in Si results in secondary-defect formation during subsequent 900 °C annealing if the total number of displaced Si atoms is greater than 1.6×1017/cm2, achieved with a dose near 1.5×1013/cm2. We demonstrate, though, that higher total In doses can be introduced without forming secondary defects by repetitive subthreshold implants each followed by an anneal to remove the implant damage. While a single 6×1013 In/cm2 implant results in a high density of dislocation loops after annealing, instead using four separate 1.5×1013 In/cm2 implants each followed by an anneal leads to the formation of only a few partial dislocations.
1/f noise in Tl2Ba2Ca1Cu2O8 thin films: Influence of crystal structure
Authors: Misra Anupam , Song Yi , Crooker P. P. , Gaines James R. , Cardona Albert H.
Published: July 2002

1/f noise measurements performed on Tl2Ba2Ca1Cu2O8 thin films show that the amplitude of the noise spectral density (Sv/V2) in the normal state may be comparable with that in conventional metals, in contrast with the much larger Sv/V2 observed in other copper oxide materials. In the superconducting transition region the 1/f noise is greatly reduced in some films that are highly aligned along the c axis.
Digital logic with YBa2Cu3O7−x dc SQUIDs
Authors: Schwarzbek S. M. , Davidheiser R. A. , Fischer G. R. , Luine J. A. , Schneier N. J.
Published: July 2002

We report the operation of and, exor, exnor, and inverting gates in a circuit architecture suitable for the set of all Boolean gates. Series arrays of YBa2Cu3O7−x dc superconducting quantum interference devices with integrated coils exhibit sufficient modulation to allow low-speed tests demonstrating gate logic, and lack of oscillation or latching. The best inverter operated (without load) at 36 μV, with 2 nW of gate dissipation.
Dispersive charge injection model for hydrogenated amorphous silicon/amorphous silicon dioxide thin-film transistor instability
Authors: Fortunato G. , Mariucci L. , Reita C.
Published: July 2002

Bias stress measurements at different temperatures and stress voltage have been performed on a-Si:H thin-film transistors, where very thin (18 nm) plasma deposited a-SiO2 was used as gate insulator. The data are explained on the basis of dispersive charge injection into the first 2–3 nm of the gate insulator. According to the proposed model a new functional form for the threshold voltage shift kinetics is deduced and a very good agreement with the experimental data is found.
Effect of growth temperature on photoluminescence of InAs grown by organometallic vapor phase epitaxy
Authors: Fang Z. M. , Ma K. Y. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

Infrared photoluminescence (PL) from InAs epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE) has been studied as a function of the growth temperature (350–600 °C). It is shown that the PL spectra depend strongly on the growth temperature. The integrated PL intensity decreases by about two orders of magnitude as the growth temperature decreases from 500 to 350 °C. In addition, Hall-effect measurements show that the n-type impurity concentration in InAs increases rapidly as the growth temperature decreases. The results of secondary-ion mass spectroscopy show that the dominant impurity is carbon and its concentration varies with the growth temperature in a similar way to the electron concentration. This confirms that carbon is a donor in InAs. The decreasing PL intensity with decreasing growth temperature is attributed to the increasing carbon concentration.
Nonlinear dependencies of Si diffusion in δ-doped GaAs
Authors: Cunningham J. E. , Chiu T. H. , Jan W. , Kuo T. Y.
Published: July 2002

We examine atomic diffusion of Si, when initially δ doped into very pure GaAs layers grown by gas source molecular beam epitaxy. A nonlinear Si diffusion coefficient versus inverse temperature is observed as a two-component Arrhenius dependence in which the activation energies change by 1.5 eV. Furthermore, when Si diffusion is thermally activated with the lower energy kinetics, the corresponding impurity profile grows in width linearly with the anneal time. We explain the above departures of measured Si diffusivity from classical impurity diffusion via a nonequilibrated concentration of vacancies generated at the δ position during the anneal.
Ga delta-doping layers in silicon
Authors: Zagwijn P. M. , Erokhin Y. N. , Slijkerman W. F. J. , van der Veen J. F. , van de Walle G. F. A. , Gravesteijn D. J. , van Gorkum A. A.
Published: July 2002

Delta-doping layers in silicon have been made by deposition of 0.39 monolayer Ga on Si(001). The dopant atoms have been buried in the host crystal using a solid phase epitaxial growth method. The grown structures are characterized in situ by high-resolution Rutherford backscattering spectrometry. A fraction of 30% of the Ga atoms is located at subsitutional sites in a spike less than 1.0 nm wide; the other atoms are at the surface. The surface atoms desorb upon annealing at 985 K, whereas the buried atoms are redistributed only slightly. At temperatures higher than 1100 K the profile degrades completely.
Selective growth of silicon-germanium alloys by atmospheric-pressure chemical vapor deposition at low temperatures
Authors: Agnello P. D. , Sedgwick T. O. , Goorsky M. S. , Ott J. , Kuan T. S. , Scilla G.
Published: July 2002

Dichlorosilane and germane were used to grow silicon-germanium alloys at temperatures as low as 550 °C at atmospheric pressure. The silicon-germanium alloy composition was varied over the range 15%–44%. Films containing high Ge mole fractions were grown at a temperature of 625 °C and below and exhibit smooth surface morphology. Silicon-germanium/silicon multilayers with abrupt heterointerfaces have been achieved. Selective growth of silicon-germanium on oxide patterned silicon wafers was also demonstrated. A significant feature of the selective deposition is the lack of faceting at the oxide sidewall, which has been commonly observed in high-temperature silicon growth.
Kinetics of thermal stress induced void growth in narrow aluminum lines
Authors: Bo/rgesen P. , Lee J. K. , Paszkiet C. A. , Li C.-Y.
Published: July 2002

1-μm-wide Al lines were passivated at 300 °C and annealed at 400 °C. The thermal stress induced growth of individual voids was monitored during room-temperature storage. The growth kinetics of voids are analyzed in terms of a grain boundary diffusion controlled model.
Etched-facet AlGaAs triangular-shaped ring lasers with output coupling
Authors: Behfar-Rad A. , Ballantyne J. M. , Wong S. S.
Published: July 2002

Total and partial reflection are demonstrated at the bends of V-shaped lasers. By varying the angle of incidence to the facet at the bend, the reflectivity at this facet can be changed. Two totally and one partially reflecting V-shaped lasers are combined in a unibodied structure to realize a triangular-shaped ring laser (trilaser). Trilasers are made of three sections which meet at three facets. Two of the facets provide total internal reflection while the third allows partial transmission from which light output is obtained. The Q of the resultant planar cavity is modified by geometry, without the need for facet coating. V-shaped lasers and trilasers are formed by using the chemically assisted ion beam etching technique in an AlGaAs/GaAs-based single quantum well graded-index separate confinement heterostructure material.
Theory of asymmetric dual quantum well lasers
Authors: Shimizu Akira , Ikeda Sotomitsu
Published: July 2002

A basic theory of asymmetric dual quantum well lasers is presented. The lasers consist of two quantum wells of different energy gaps, which are separated by a high and/or thick barrier layer. The barrier layer blocks carrier transport between the wells so that the rate of the transport becomes comparable to the rate of the radiative recombination. It is shown that this leads to novel phenomena of dual-wavelength lasing and wavelength switching with increasing injection current, in agreement with recent experimental results.
Assessment of compositional disorder in AlxGa1−xAs superlattices from the analysis of Raman spectra
Authors: Miglio L. , Molteni C. , Bernasconi M.
Published: July 2002

We present the calculation of the Raman spectra in backscattering configuration for AlxGa1−xAs (001) superlattices and modulated alloys, based on the bond-charge-model dynamics, the average t-matrix approximation for compositional disorder and the bond polarizability model for the Raman tensor. The features of Raman spectra are shown to reflect the Al concentration profile along the growth axis, hence providing a valuable tool for compositional characterization of superlattices.
Analysis of lateral uniformity of ultrashallow junctions in polycrystalline silicon-on-single crystal silicon systems
Authors: Park Keunhyung , Batra Shubneesh , Banerjee Sanjay
Published: July 2002

The lateral uniformity of n+-p junctions formed by indiffusion of As or P from an amorphous or polycrystalline silicon thin-film source into the underlying silicon substrate has been investigated using a concentration-dependent etch and transmission electron microscopy. Grain boundaries act as fast diffusant pipelines and also possibly inject point defects into the substrate, thereby enhancing bulk diffusivities locally in the substrate. Delineated ultrashallow junctions show significant doping lateral inhomogeneities in the substrate for as-deposited amorphous silicon diffusion sources but not for as-deposited polycrystalline silicon diffusion sources because of a larger final grain microstructure after annealing in the former case. However, the doping inhomogeneities are gradually smeared out as impurities diffuse deeper into the substrate.
Optical and electrical properties of InP/InGaAs grown selectively on SiO2-masked InP
Authors: Wang Y. L. , Feygenson A. , Hamm R. A. , Ritter D. , Weiner J. S. , Temkin H. , Panish M. B.
Published: July 2002

Heterostructures of InGaAs/InP have been grown selectively through windows in SiO2-masked InP substrates using metalorganic molecular beam epitaxy. The structures show high cathodoluminescence efficiency for window sizes down to 5 μm. A significant red shift, consistent with compressive lattice strain, and reduced intensity are observed for smaller features. Anomalous growth is observed near the edges of the windows. Selectively grown InGaAs/InP p-n junctions and bipolar transistors exhibit excellent electrical characteristics after removal of 1–2 μm of edge material.
On the formation of the SbGa heteroantisite in metalorganic vapor-phase epitaxial GaAs:Sb
Authors: Yakimova R. , Omling P. , Yang B. H. , Samuelson L. , Fornell J.-O. , Ledebo L.
Published: July 2002

Metalorganic vapor-phase epitaxial growth of GaAs doped with isovalent Sb is reported. By increasing the trimethylantimony concentration during growth the total Sb concentration was varied between 1×1017–1×1019 cm−3. A new deep level defect with an activation energy of the thermal emission rates of Ec−0.54 eV is observed. The defect concentration increases with increasing As partial pressure and with increasing Sb doping. It is also found that the EL2 concentration decreases with increasing Sb doping. The new energy level is suggested to be the 0/+ transition of the SbGa heteroantisite defect. No photocapacitance quenching effect, reflecting a metastable state as seen for EL2(AsGa), is observed for SbGa.
B diffusion in Si predamaged with Si+ near the threshold dose of amorphization
Authors: Kase Masataka , Kikuchi Yoshio , Kimura Mami , Mori Haruhisa , Ogawa Tsutomu
Published: July 2002

We studied B diffusion in Si predamaged with Si+ near the threshold dose of amorphization. In Si preimplanted in the amorphization condition (Si+ 40 keV, 5.0×1014 cm−2), a B-profile kink appears to be induced from retarded diffusion after 800 °C annealing. In the 3.0×1014 cm−2 preimplanted sample, an enhanced diffusion tail appears in addition to the kink. The tail has a diffusivity of 1×10−14 cm2/s. Amorphous islands about 10 nm in diameter were observed in Si predamaged with Si+ 40 keV, 3.3×1014 cm−2 by a cross-sectional transmission electron microscope. We speculate that the kink and tail originate in the vacancy and interstitial-rich region, respectively.
Carrier concentration determination by photoreflectance at E1 in thin film, highly doped GaAs
Authors: Badakhshan Ali , Glosser R. , Lambert S. , Anthony Mark , Sillmon R. S. , Thompson P. E. , Alavi Kambiz
Published: July 2002

Photoreflectance (PR) response at the E1 (2.9 eV) transition of GaAs doped with Si, Zn, and Be was investigated within the range of 1.5×1015 to 2×1019 cm−3. Growth technique was either metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). We find that Γ1, the broadening parameter of the E1 structure increases linearly with the logarithm of the measured carrier concentration over the range of ≊1×1017 to ≊1×1019 cm−3. A slope of 56±5 meV/decade describes all Si:GaAs samples independent of growth technique. For p-GaAs, the slope is 30±3 meV/decade over a comparable range and is independent of doping element as well as growth technique. This linear relation could be employed as a contactless means of determining carrier concentration. The energy position of E1 shows no significant shift in the above range. We believe that the broadening is a result of the doping produced, electric field within the depletion region.
Thermal acceptor formation in nitrogen-doped silicon
Authors: Yang Deren , Lu Jun , Li Liben , Yao Hongnian , Que Duanling
Published: July 2002

The nitrogen-doped Czochralski (CZ) silicon crystals were grown in a nitrogen atmosphere under reduced pressure. The results show that the resistivity of n-type N-doped silicon increases rapidly with annealing time above 700 °C, but that of p-type N-doped CZ silicon decreases rapidly under the same conditions. It is suggested that thermal acceptors (TA) are formed in N-doped silicon. The concentration of thermal acceptor can reach to 1×1014 atom/cm3. The higher the annealing temperature, the longer the time for the maximum thermal acceptor concentration to appear. Nitrogen and oxygen impurities play important roles for generating the thermal acceptor. It is postulated that the thermal acceptor is a kind of Si-O-N complex.
Wide channeling beam x-ray laser
Authors: Strauss M. , Rostoker N.
Published: July 2002

A channeling beam x-ray laser is proposed which is weakly dependent on the channeling length. The scheme is based on applying Bragg reflections to direct the amplified radiation toward a longitudinal cavity direction which is transverse to the beam propagation. This scheme implements a crystal distributed feedback cavity and is restricted to short radiation wavelength of the order of the crystal unit cell dimension.
Evidence for a transitory composition pattern in the early stages of the photochemical deposition of silica films on semiconductors
Authors: Licoppe C. , Meriadec C. , Flicstein J. , Nissim Y. I. , Papadopoulo A. C.
Published: July 2002

We have studied the early stages of the photodeposition of SiO2 on semiconductors from silane–oxygen gaseous mixtures under UV irradiation. For film thicknesses below 100 Å, the films exhibit a specific oxygen-deficient composition which become stoichiometric if deposition lasts longer, producing SiO2 films with a homogeneous composition throughout the whole dielectric layer. It is shown that the transitory early deposition regime is structurally sensitive to the nature of the substrate. Cathodoluminescence is used to show that the surface carrier recombination properties are altered mostly during this singular early stage of photodeposition.
Observation of an overshoot in the capture transient of the DX center in N-Al0.32Ga0.68As
Authors: Wang Zhiguo , Miller T. , Williamson F. , Nathan M. I.
Published: July 2002

We have measured the deep level transient spectroscopy signal height of two DX levels usually observed in n-type doped Al0.32Ga0.68As as a function of the filling pulse width. We report an overshoot in the capture transient of the DX level having a larger capture rate. We solve the rate equations for the capture processes of these two DX levels simultaneously. The capture transients thus obtained fit the experimental capture transients of these two DX levels reasonably well.
Oxide-nitride storage dielectrics on smooth and rough polycrystalline silicon layers
Authors: Fazan P. C. , Ditali A. , Mathews V. , Chan H. C. , Rhodes H. E. , Liu Y. C. , Dennison C. H.
Published: July 2002

We demonstrate that for the same capacitance value, 9.5-nm-thick oxide-nitride storage dielectrics deposited on rough polycrystalline silicon exhibit a lower leakage current and a higher lifetime than 5.9 nm layers on smooth polycrystalline silicon. Leakage current reduction of more than two orders of magnitude and a lifetime increase of more than three orders of magnitude are reported. These improvements are explained by the nitride bulk-limited type of conduction. Our data show that textured storage capacitors have all the properties required for efficient fabrication of 64 megabit dynamic random access memories.
Effects of sputter gas medium on the nanometer-scale surface structures of the Pt/Co multilayers
Authors: Tang S. L. , Carcia P. F. , McGhie A. J. , James E. B.
Published: July 2002

The surface structure of polycrystalline Pt/Co multilayer thin films, sputter-deposited on glass substrates with Ar, Kr, or Xe, was obtained with near-atom resolution by scanning tunneling microscopy. Monatomic steps separating narrow terraces on the Ar-sputtered films and large step-like structures on the order of the Pt/Co bilayer thickness on the Xe-sputtered films were observed. We attributed differences in surface features to bombardment of the growing film surface by reflected neutral inert gas atoms with different energy distributions. We correlated the observed surface structures with magnetic coercivity of these films.
In situ temperature measurement of α-mercuric iodide by reflection spectroscopy
Authors: Nason D. , Burger A.
Published: July 2002

Crystal face temperatures of single crystals of α-HgI2 growing in transparent ampules by physical vapor transport have been measured, in situ, by a novel, noncontact method which may be called reflectance spectroscopy thermometry. The method is based on the temperature dependence of the energy of the free-exciton peak as detected with a low-energy reflected beam. As presently configured, the accuracy is ±1.5 °C for a slowly varying surface temperature. The method has potential for noncontact temperature measurement in some systems for which pyrometry is unsatisfactory.
The preparation of Ni-P ultrafine amorphous alloy particles by chemical reduction
Authors: Shen Jianyi , Hu Zheng , Zhang Lifeng , Li Zhiyu , Chen Yi
Published: July 2002

Ni-P ultrafine amorphous alloy particles have been prepared by reacting nickel chloride and sodium hypophosphite in an aqueous solution. X-ray diffraction revealed the amorphous structure of the particles and transmission electron microscopy showed that the particles are spherical, with an average diameter of about 150 nm. X-ray photoelectron spectroscopy confirmed that all nickel and phosphorus atoms are in the elementary state on the surface of the particles, which implied the alloying state of the particles. The dynamic process of the reaction has been studied. It is found that the reaction ended within 65 min at a pH value of 10 and 351 K when the sodium hypophosphite was exhausted, and the unreacted solid residue Ni(OH)2 should be washed out with ammonia solution to obtain ‘‘pure’’ Ni-P ultrafine amorphous alloy particles.
Selective WSi2 Schottky diodes made by rapid thermal chemical vapor deposition of WCl6
Authors: Trincat F. , Regolini J. L. , Mercier J. , Bensahel D.
Published: July 2002

Selective WSi2/Si Schottky diodes, with an ideality factor of 1.02, are obtained by limited reaction processing chemical vapor deposition at 800 °C, using WCl6 vapor diluted in H2. The deposition temperature is shown to be the most important parameter for defect formation. The diodes were fabricated on patterned and blanket wafers, and no additional thermal treatment is needed to obtain the final diode characteristics.
Fluorescent micropattern formation on polymer surface by laser ablation
Authors: Uchida Tatsuya , Sugimura Hiroyuki , Kemnitz Klaus , Shimo Nobuo , Masuhara Hiroshi
Published: July 2002

248-nm laser ablation of poly(methyl methacrylate) plates and soaking of the ablated plates in aqueous solution of rhodamine B resulted in fluorescent micropattern formation. A positive or negative fluorescent pattern of the dye was obtained by controlling the laser fluence. Incorporation mechanism of the dye into the ablated polymer is discussed.
Approximate expressions for modulation speed and threshold for performance optimization of biaxially compressive strain quantum-well lasers
Authors: Vahala Kerry J. , Zah Chung-en
Published: July 2002

Simple analytical expressions for transparency, threshold, and relaxation oscillation corner frequency are derived for biaxial strain quantum-well lasers. An optimal operating point loss for high speed operation (in the absence of nonlinear gain) is established which varies as the square root of the number of quantum wells. The corresponding relaxation oscillation frequency is found to depend only on fundamental quantities. Its power dependence is ■νR■max■ = ■87 GHz√μm3■mW■ (Powerout/Vmode)1/2] where Vmode is the mode volume.
Velocity measurements in polyetheretherketone-carbon fiber composite using excimer laser generated ultrasound
Authors: Ablett S. J. , Dyer P. E. , Tait B. L. , Barnes J. A.
Published: July 2002

It is demonstrated that KrF laser ablation provides a suitable source for short pulse ultrasound generation in polyetheretherketone (PEEK)-carbon fiber composite. Measurements of plane wave velocities have been made on thin single laminae (∼130 μm thick) and multiple ply laminates of this anisotropic composite. Velocities for propagation at various angles with respect to the fiber axis have been measured and are shown to be in good agreement with theoretical calculations based on mechanical modulii.
High-temperature hole mobility in strained quantum wells
Authors: Laikhtman B.
Published: July 2002

Strained quantum wells are promising candidates on high-speed p-channel field-effect transistors (FET) because of a low effective mass in the split valence band. Here for the first time the high-temperature mobility of holes is studied taking into account realistic wave functions of split light mass subband. The main limit to the mobility at high temperature is put by LO phonons and only this scattering mechanism is considered here. It is shown that deformation coupling with optical phonons is small in quantum wells with a large splitting between the light- and heavy-hole subbands. Analytical expression for the mobility is obtained. Numerical estimates give the upper limit for the mobility as high as a few thousand cm2/V s.
Low dark current p-i-n photodiodes with an anomalous dynamic behavior
Authors: Buchali F. , Behrendt R. , Heymann G.
Published: July 2002

Up to now, InGaAs/InP photodiodes are the main detectors for the long-wavelength region. The dynamic behavior of these devices limits the maximum bitrate of communication systems. We have investigated the dynamic behavior of these heterojunction devices. If the heterojunction lies outside of the space charge region, the heterointerface shows an additional response due to a storage of carriers in the valley of the conduction band. At higher biases the interface lies inside the space charge region and the time response of the interface is negligible and no additional time response was observed.
Realization of a photovoltaic transistor based on a steady-state internal polarization effect in asymmetric semiconductor superlattices
Authors: Liu C. T. , Liu J. M. , Cho A. Y.
Published: July 2002

We have used molecular beam epitaxy to grow at 500 °C a graded InAlGaAs superlattice structure sandwiched by two heavily doped window layers which are directly connected to the gate and source of a discrete field-effect transistor (FET). Upon band-gap illumination, a steady-state photovoltage controllable by the light intensity is generated by the superlattice structure, which then modulates the drain current of the FET to the same amount as does a dc voltage source. The intrinsic response time of the photovoltaic effect is on the order of picoseconds, thus the modulation speed on the drain current is completely limited by the FET.
Coherent high-power arrays of InGaAs/InGaAsP multiquantum-well grating-surface-emitting diode lasers operating at λ=1.5 μm
Authors: Vangieson E. A. , Palfrey S. L. , Enstrom R. E. , Hammer J. M. , Martinelli Ramon U. , Carlson N. W. , Evans G. A. , Andrews J. T. , Appert J. , Stolzenberger R. , Triano A.
Published: July 2002

We have demonstrated high-power linear arrays of InGaAs/InGaAsP grating-surface-emitting lasers operating at a wavelength of 1.5 μm and emitting over 200 mW cw and 400 mW pulsed power. Arrays 1 cm in length exhibit coherent, mutual-injection-coupled laser action; single-wavelength-mode operation with a linewidth of 100 MHz at a power output of 55 mW has been observed.
Wavelength tuning in low threshold current, partially pumped InGaAs/AlGaAs ridge waveguide lasers
Authors: Williams R. L. , Moss D. , Dion M. , Buchanan M. , Dzurko K.
Published: July 2002

We examine the dependence upon unpumped length of the lasing threshold current in partially pumped InGaAs/AlGaAs graded index, separate confinement heterojunction lasers and demonstrate the tunability of our devices using current injection into the previously unpumped section.
Thermal noise current inside a gas of noninteracting charged bosons
Authors: Hickman H. V. , Dekker A. J. , Chen T. M.
Published: July 2002

An application of Bose–Einstein statistics leads to an expression for the mean-square value of the spontaneous fluctuations in current that give rise to thermal noise inside a gas of noninteracting charged bosons. Above the Einstein condensation temperature the boson gas thermal noise current is seen to be identical to the corresponding Fermi–Dirac thermal noise current. Below the Einstein condensation temperature, the magnitude of the boson gas thermal noise current decreases as the number of bosons in excited states decreases.
InGaAs/InP double-heterojunction bipolar transistors with step graded InGaAsP between InGaAs base and InP collector grown by metalorganic chemical vapor deposition
Authors: Ohkubo Michio , Iketani Akira , Ijichi Tetsurou , Kikuta Toshio
Published: July 2002

We have fabricated InGaAs/InP double-heterojunction bipolar transistors (DHBTs) grown by metalorganic chemical vapor deposition (MOCVD). By inserting step graded InGaAsP layers between p+-InGaAs base and n−-InP collector, the current gain of DHBTs with the graded layers was about twice as large as that without the graded layers, and the dependence of collector current on collector/emitter voltage was smaller than that without graded layers. The current gain was measured up to 2300 with 25×25 μm2 emitter area at a collector current density of 1×104 A/cm2.
Cathodoluminescence observation of excitons confined to a two-dimensional electron gas in a selectively doped heterostructure
Authors: Reynolds C. L. , Lengle S. E. , Swaminathan V.
Published: July 2002

A cathodoluminescence emission near 850 nm has been observed in GaAs/AlGaAs selectively doped heterostructures at room temperature which appears related to excitons confined to a two-dimensional electron gas (2DEG). If the structure is grown without Si in the donor layer or if a top confining layer is removed, then this room temperature emission is not observed. At low temperatures (6 K) three peaks are observed at 797, 812, and 817 nm, in which the highest energy peak corresponds to the 850 nm room-temperature emission. Both the low- and high-energy peaks behave similarly with respect to variations in excitation intensity and temperature. A quadratic excitation dependence of the intensity indicates that these emissions are excitonic in origin. Both peaks exhibit quenching above ∼100 K with an activation energy of 0.11 eV, and the peak energies shift to higher energy as the temperature is lowered. While we attribute our 797 nm emission to excitons confined to a 2DEG in the well above the donor layer, the origin of the 817 nm peak is most likely related to excitons confined to the 2DEG in the 3000 Å buffer layer.
Flux creep and pinning potential distribution in zone-melted YBa2Cu3Ox
Authors: Shi Donglu , Goretta K. C. , Salem-Sugui S. , McGinn P. J. , Chen W. H. , Zhu N.
Published: July 2002

Magnetic relaxation data have been taken on zone-melted and sintered YBa2Cu3Ox samples over wide temperature and magnetic field ranges. We have found that magnetic relaxation varies greatly in the samples with different microstructures and crystallographic orientations. Flux-creep rates have been found to be reduced in the zone-melted samples owing to large amounts of intragranular crystal defects such as edge dislocations and stacking faults. An important flux-pinning behavior related to the pinning potential distributions has been observed in the samples. The relationship between microstructural orientation and pinning potential distributions in YBa2Cu3Ox is discussed.
Enhanced preferential sputtering of a hydrogenated barium surface
Authors: Heeren R. M. A. , Ćirić D. , Hopman H. J. , Kleyn A. W.
Published: July 2002

We have observed a substantial decrease in barium sputter yield as a function of exposure time when a barium surface is bombarded with an intense flux of positive hydrogen or deuterium ions, extracted from a plasma. This effect is attributed to an increase of surface hydrogen concentration which results in enhanced preferential sputtering of hydrogen surface atoms. The sputtering process is observed by means of optical emission spectroscopy. Whenever the surface is saturated with hydrogen, the sputtered barium yield is constant in time, and scales with the sputter coefficient, which is dependent on the energy of the incident ions. The relative decrease of the sputtered barium yield is shown to scale with the incident positive ion current density as the saturation concentration depends on this current density.
Comparison of mode suppression and large signal modulation between lattice matched and strained InGaAs/AlGaAs quantum well lasers
Authors: Lam Yeeloy , Loehr John P. , Singh Jasprit
Published: July 2002

Numerical techniques are developed to study the output spectra and to solve the coupled mode rate equations for InxGa1−xAs/Al0.3Ga0.7As quantum well lasers. The optical properties of the laser are calculated from a 4×4 k⋅p band structure which includes the effects of strain. We find that the side modes are severely suppressed in the strained laser. Large signal switching of the laser is also studied and the role of strain is identified in the device response. If the laser is switched from the off state to a state of given photon density in the lasing mode, then the strained system exhibits a faster time response. If, however, the laser is switched from the off state to a state of given total photon density, then the strained system has a slower time response.
Investigation of SiNX:H/Si interface by capacitance method
Authors: Maeda Keiji , Umezu Ikurou , Kawaguchi Akio
Published: July 2002

A new capacitance method was developed to investigate properties of the SiNX:H/c-Si interface. By comparison of the frequency dependence of C-V characteristics of p- and n-type c-Si substrate sample pairs, flatband voltage for an intrinsic substrate sample can be determined. Analyses of two kinds of frequency dependence, i.e., the variation of voltage at flatband capacitance and the variation of capacitance at flatband voltage, disclose different aspects of the interface state density with respect to the energy level in the band gap, response time, and ionized state. Donor states are predominant in the investigated interface.
Optically activated integrated optic Mach–Zehnder interferometer on GaAs
Authors: Cheng Z. Y. , Tsai C. S.
Published: July 2002

An optically activated guided-wave Mach–Zehnder interferometer has been constructed and used to study photoinduced phase modulation in GaAs channel waveguides. A π radian phase shift at the optical wavelength of 1.15 μm has been achieved with modulating pulse energy of 320 pJ at an interaction length of 22 μm. Our experiment also indicates that for infrared (IR) light with photon energy far below the band-gap energy of the semiconductor material, the free carrier-induced refractive index changes are much more significant than the free carrier-induced absorption changes.
Molecular-beam-epitaxy-deposited nonalloyed Al contacts to n-type and p-type InGaAs
Authors: Shen T. C. , Fan Z. F. , Gao G. B. , Morkoç H. , Rockett A.
Published: July 2002

Nonalloyed Al contacts were deposited by molecular beam epitaxy on both n- and p-type In0.53Ga0.47As layers prior to air exposure. These were shown to be ohmic, with specific contact resistances in the range of mid μΩ cm2 by the transmission-line model method. The thermal stability of these contacts was tested by annealing at temperatures between 350 and 450 °C for 30 min and at 300 °C for 500 h. Both experiments showed stable specific contact resistances.
Annealing and profile of interstitial iron in boron-doped silicon
Authors: Gao X. , Mollenkopf H. , Yee S.
Published: July 2002

Deep level transient spectroscopy and double correlation technique were used to examine the annealing and profiles of interstitial iron in boron-doped silicon at a temperature range from 50 to 400 °C. The results show that iron-boron pairs begin to break-up at a temperature as low as 50 °C. After a short time annealing (5 min) at a temperature up to 400 °C, most of the iron from the breaking is converted into interstitial iron. We also find that the distribution of interstitial iron under the silicon surface is not uniform, and it depends on the annealing time and temperature. The interstitial iron near the silicon surface decreases with the increase of the annealing time.