bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the focused output from a selenium soft x-ray laser
Authors: Nilson D. G. , Brown S. B. , Keane C. J. , MacGowan B. J. , Matthews D. L. , Trebes J. E. , Wood O. R. , Silfvast W. T. , Al-Salameh D. Y. , Harvey T. E. , Maloney P. J.
Published: July 2002

The output energy (90 μJ), focal spot diameter (235 μm), and pointing accuracy (±75 μrad) for a 3.7-cm-long Se soft x-ray laser operating at 20.6 and 20.9 nm are reported. Now that this intense soft x-ray source has been well characterized it may find use in such diverse applications as lithography, contact microscopy, holography, and photoionization pumping.
Fabrication of quasi-zero-dimensional submicron dot array and capacitance spectroscopy in a GaAs/AlGaAs heterostructure
Authors: Fang H. , Zeller R. , Stiles P. J.
Published: July 2002

A new and very simple technique has been developed for fabricating two-dimensional periodic submicron structures with feature size down to about 300 Å. The etching mask is made by coating the material surface with a monolayer of closely packed uniform latex particles. We have performed capacitance measurements on GaAs/AlGaAs heterostructure samples with a quasi-zero-dimensional dot array of 3300, 3640, and 3940 Å periodicities. A series of nearly equally spaced peaks in a curve of the derivative of capacitance with respect to gate voltage, which corresponds to the energy levels formed by the lateral electric confining potential, is observed.
Demonstration of large peak-to-valley current ratios in InAs/AlGaSb/InAs single-barrier heterostructures
Authors: Söderström J. R. , Chow D. H. , McGill T. C.
Published: July 2002

We report large peak-to-valley current ratios in InAs/AlxGa1−xSb/InAs single-barrier tunnel structures. The mechanism for single-barrier negative differential resistance (NDR) has been proposed and demonstrated recently. A peak-to-valley current ratio of 3.4 (1.2) at 77 K (295 K), which is substantially larger than what has been previously reported, was observed in a 200-Å-thick Al0.42Ga0.58Sb barrier. A comparison with a calculated current-voltage curve yields good agreement in terms of peak current and the slope of the NDR region. The single-barrier structure is a candidate for high-speed devices because of expected short tunneling times and a wide NDR region.
Transfer matrix approach to the analysis of an arbitrary quantum well structure in an electric field
Authors: Hutchings D. C.
Published: July 2002

A new transfer matrix technique is presented for the exact analysis of quantum well structures in an electric field using the exact Airy function form of the wave function. This method is applied to an asymmetric-coupled quantum well structure and the electronic eigenfunctions are generated.
Submicron trenching of semiconductor nanostructures
Authors: Lee K. Y. , Smith T. P. , Ford C. J. B. , Hansen W. , Knoedler C. M. , Hong J. M. , Kern D. P.
Published: July 2002

We have devised and demonstrated a novel technique for fabricating structures with nanometer scale features in semiconductor heterostructures. The technique is based on definition of nanometer scale patterns by submicron trenches in a GaAs-AlGaAs heterostructure. The depletion of free carriers below the trenches gives rise to very strong electrostatic confinement. This technique avoids the complications associated with the use of negative resist materials and lift-off techniques while minimizing the time required to expose densely packed patterns. Aharonov–Bohm rings fabricated using this technique exhibit interference oscillation larger than any reported previously.
Control of preferential orientation by i
n s
i
t
u plasma supply during growth of polycrystalline silicon films
Authors: Hasegawa S. , Yamamoto S. , Kurata Y.
Published: July 2002

Polycrystalline silicon (poly-Si) films were prepared on a fused quartz substrate at 700 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced CVD (PECVD) using the same fabrication system. Poly-Si films with a strong 〈100〉 and 〈110〉 preferential orientation (P.O.) are obtained by changing the rf power for generating the plasma under the same preparation condition. The surface of the PECVD films with dominant 〈100〉 and 〈110〉 textures is very smooth in contrast with that of LPCVD films. These textures are maintained after thermal oxidation at 1000 °C, and the degree of P.O. and the grain size increase.
Tungsten metal film formed by spin-coating amorphous peroxopolytungstic acid
Authors: Okamoto Hiroshi , Ishikawa Akira
Published: July 2002

A homogeneous, amorphous peroxopolytungstic acid film can be formed easily with the spin-coating method. The film is found to provide a homogeneous tungsten metal film after reduction with hydrogen at ∼400 °C. Although the electric resistivity (∼450 μΩ cm) is higher than that for the bulk (5.65 μΩ cm), this method has an advantage in addition to spin coatability: tungsten metal films with fine patterns can be easily obtained because the starting material is photosensitive.
Absolute pressure dependence of the second ionization level of EL2 in GaAs
Authors: Bliss D. E. , Nolte D. D. , Walukiewicz W. , Haller E. E. , Lagowski J.
Published: July 2002

We report the results of deep level transient spectroscopy experiments with the second ionization level of the double donor defect (EL2) under uniaxial stress in p-type GaAs. We measure the shift in the hole emission rate as a function of stress applied in the [100] and [110] directions. By modeling the valence band with two independently displacing bands and appropriately derived effective masses, we determine the absolute hydrostatic pressure derivative of the defect to be 39±15 meV GPa−1. The shear contribution is negligible. These results are very different from those obtained for the first ionization level, which has a much higher absolute pressure derivative of 90 meV GPa−1.
Rapid thermal oxidation of GeSi strained layers
Authors: Nayak D. , Kamjoo K. , Woo J. C. S. , Park J. S. , Wang K. L.
Published: July 2002

The experimental results of the rapid thermal oxidation in the initial oxidation regime of molecular beam epitaxy grown GeSi strained layers are reported. It is shown that the dry oxidation rate of GeSi is the same as that of Si at different temperatures. After a very short initial time (∼10 s), the oxide thickness appears to be a linear function of time, which suggests that the kinetics of oxide growth during dry oxidation is limited by surface reaction controlled mechanisms. Further, the oxidation rate in the thin oxide regime is not affected by the Ge content up to 20% in the GeSi strained layer for dry oxidation. Using secondary-ion mass spectrometry, it is found that Ge is completely rejected out of the SiO2 layer which is formed during oxidation, and a Ge-rich layer is formed at the SiO2/GeSi interface. A significant amount of Ge is found to diffuse into the underlying GeSi layer during the growth of thin oxide films.
Superconducting YBaCuO thin films on GaAs/AlGaAs
Authors: Rao M. R. , Tarsa E. J. , Samoska L. A. , English J. H. , Gossard A. C. , Kroemer H. , Petroff P. M. , Hu E. L.
Published: July 2002

Superconducting YBaCuO (1-2-3) thin films have been deposited on GaAs by laser ablation, in the presence of an oxygen plasma, at a substrate temperature of 600 °C. The (100) GaAs had a thin (100 Å) Al0.3Ga0.7As cap layer, in order to prevent decomposition of the GaAs. The as-deposited YBaCuO film had a Tc (onset) of 80 K and a Tc (zero) of 20 K. Transmission electron microscopy studies showed the presence of voids in the GaAs, ∼1000 Å in length, and extending 500 Å into the GaAs.
Nonalloyed ohmic contacts on low-temperature molecular beam epitaxial GaAs: Influence of deep donor band
Authors: Yamamoto H. , Fang Z-Q. , Look D. C.
Published: July 2002

The Ohmic nature of the nonalloyed metal contact on molecular beam epitaxial GaAs grown at 200 °C was studied. The specific contact resistances at room temperature and 120 K were 1.5×10−3 and 7.0×10−1 Ω cm2, respectively. These values are anomalously low considering that the conduction-band electron concentration in this material is less than 1011 cm−3 at room temperature. The experimental results indicate that the carrier transport at the metal/semiconductor interface is dominated by a dense (∼3×1019 cm−3) EL2-like deep donor band, rather than the usual conduction band.
Time-of-flight measurement of electron velocity in an In0.52Al0.48As/In0.53Ga0.47As /In0.52Al0.48As double heterostructure
Authors: Shigekawa Naoteru , Furuta Tomofumi , Arai Kunihiro
Published: July 2002

The electron velocity versus electric field (v-E) relationship was measured between 0 and 12 kV/cm at room temperature for a selectively Be-doped In0.52Al0.48As/In0.53Ga0.47As /In0.52Al0.48As double heterostructure. It was found that the observed electron velocity is greater than that previously measured for an AlGaAs/GaAs/AlGaAs double heterostructure over the enitre range of field investigated. This indicates the superiority of In0.53Ga0.47As as a material for high-speed semiconductor devices. The experimental results were also compared with those of the Monte Carlo calculation, and a remarkable discrepancy between the experiment and the calculation was found above the threshold field.
High-resolution ablation of amorphous polymers using CO2 laser irradiation
Authors: Sonnenschein Mark F. , Roland C. Michael
Published: July 2002

Etching of various amorphous polymers by the application of CO2 laser radiation (10.6 μm) is described. By passage of the radiation through a high-resolution mask in contact with the polymer surface, this ablation can produce images having submicron resolution and good edge acuity. The laser intensity required for ablation is compared for various thermoplastic and thermosetting polymers. Below the required level of intensity, no ablation is observed, but the laser irradiation can result in thermal crystallization. The energy necessary to induce ablation with infrared radiation is comparable to that required for UV decomposition.
Wet oxidation of GeSi strained layers by rapid thermal processing
Authors: Nayak D. K. , Kamjoo K. , Park J. S. , Woo J. C. S. , Wang K. L.
Published: July 2002

A cold-wall rapid thermal processor is used for the wet oxidation of the commensurately grown GexSi1−x layers on Si substrates. The rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the increase in the Ge content in GexSi1−x layer. The oxidation rate of GexSi1−x appears to decrease with increasing oxidation time for the time-temperature cycles considered here. Employing high-frequency and quasi-static capacitance-voltage measurements, it is found that a fixed negative oxide charge density in the range of 1011– 1012/cm2 and the interface trap level density (in the mid-gap region) of about 1012/cm2 eV are present. Further, the density of this fixed interface charge at the SiO2/GeSi interface is found to increase with the Ge concentration in the commensurately grown GeSi layers.
Infrared diode laser diagnostics of methane plasmas produced in a deposition reactor
Authors: Davies P. B. , Martineau P. M.
Published: July 2002

Tunable infrared diode laser spectroscopy has been applied to the study of CH4 plasmas generated in a deposition reactor run at 20 kHz. Absolute number densities of CH4, C2H4, and CH3 have been measured as functions of pressure and current. A qualitative explanation of the results is presented.
Hertzian stress contribution to low friction behavior of thin MoS2 coatings
Authors: Singer I. L. , Bolster R. N. , Wegand J. , Fayeulle S. , Stupp B. C.
Published: July 2002

Friction coefficients were measured for bearing materials slid in dry air against sputter-deposited MoS2-coated substrates. Ball versus flat tests were performed over a wide range of initial Hertzian pressures (200–1500 MPa) by varying loads (1–50 N), elastic moduli (70–615 GPa), and ball diameters (1.6–12.7 mm). The friction coefficient μ decreased as load L increased according to μ∝ L(−0.32), in agreement with the Hertzian contact model. Regression analysis of over 600 data points for friction coefficient versus Hertzian pressure (PH), fitted to μ=(S0/PH)+α, gave mean values of the shear strength S0=24.8 MPa±0.5 and α= 0.001±0.001, with S0 in good agreement with values in the literature.
Flux noise from superconducting YBa2Cu3O7−x flux transformers
Authors: Ferrari M. J. , Kingston John J. , Wellstood Frederick C. , Clarke John
Published: July 2002

Using a dc superconducting quantum interference device (SQUID) at 4.2 K, we have measured the magnitude and temperature dependence of the flux noise generated by superconducting flux transformers made from YBa2Cu3O7−x. If the transformer loop is opened, the observed noise decreases by a factor of 10, demonstrating that moving vortices generate noise primarily by altering the screening current, rather than by coupling their magnetic flux directly into the SQUID. Model calculations are given for the various noise contributions, and shown to be reasonable predictions of the observed effects.
Impact ionization of Se-related DX centers in AlGaAs
Authors: Izpura I. , Muñoz E. , García F. , Calleja E. , Powell A. L. , Rockett P. I. , Button C. C. , Roberts J. S.
Published: July 2002

The ionization processes of Se-related DX centers have been studied in AlGaAs Schottky diodes under high reverse bias conditions. A spectroscopy technique that provides directly the free-electron concentration has been used. Besides the well known thermal and optical electron emission processes, a new mechanism, attributed to an impact ionization process of DX centers, is described, and its kinetics is analyzed.
Texturing of epitaxial in situ Y-Ba-Cu-O thin films on crystalline substrates
Authors: Zheng J. P. , Dong S. Y. , Kwok H. S.
Published: July 2002

The degree of texturing of the grains in epitaxial in situ Y-Ba-Cu-O films was studied by x-ray pole-figure measurements. These high Tc and Jc laser deposited films were all aligned with the c axis perpendicular to the substrate surface. It was found that films on SrTiO3(001) and LaAlO3(001) were totally aligned with the YBCO a axis parallel to the 〈100〉 direction on the substrate. For MgO(001), 4% of the grains are aligned in the 〈110〉 direction. For yttria stabilized zirconia (001), the a axes of the YBCO grains were distributed between the 〈100〉 and 〈110〉 directions on the substrate. These observations are consistent with the degree of lattice mismatch in the various crystal orientations.
Native-oxide stripe-geometry AlxGa1−xAs-GaAs quantum well heterostructure lasers
Authors: Dallesasse J. M. , Holonyak N.
Published: July 2002

Data are presented on the room-temperature continuous (cw) operation of native-oxide single-stripe AlxGa1−xAs-GaAs quantum well heterostructure (QWH) lasers. The device quality native oxide is produced by the conversion of high Al composition AlxGa1−xAs (x∼0.8) confining layers via H2O vapor oxidation (400 °C) in a N2 carrier gas. The 10-μm-wide cw 300 K QWH lasers, which are fabricated by simplified processing, have excellent spectral quality and have been operated to powers in excess of 100 mW per facet.
Preferential excitation and enhanced emission of Pb atoms following detonation of lead azide
Authors: Bar I. , Cohen A. , Heflinger D. , Tzuk Y. , Rosenwaks S.
Published: July 2002

Preferential excitation of the 3P°1 state of the lead atom and enhanced emission in the Pb(3P°1Pb(3P°1→1D2) transition at 722.9 nm have been observed following the detonation of lead azide, Pb(N3)2. The detonation is initiated by a short laser pulse and the products are expanded through a supersonic nozzle. It is suggested that the enhanced emission is due to preferential excitation of Pb(3P°1) via energy transfer from electronically excited N2 combined with the effect of self-trapping of the emission from 3P°1 to the 3P0,1,2 states. The implications to short-wavelength chemical lasers are discussed.
Etching polyimide films with continuous-wave ultraviolet lasers
Authors: Srinivasan R.
Published: July 2002

Continuous-wave laser radiation from an argon-ion laser in the wavelength range 300–330 nm or 350–380 nm, when focused to a spot such that the power density is ∼10 kW/cm2, can be used to etch polyimide (DuPont KaptonTM) films with as little thermal damage as from an excimer laser (308 or 351 nm) provided the laser spot is moved over the surface at speeds at which the transit time over its own diameter is in the order of 1–1000 μs. There is an optimum speed at which the cutting action is a maximum for a given power density per unit area. The fluence (in J/cm2) at which etching occurs is comparable to results obtained with excimer laser pulses but the depth of the material that is removed per joule of incident laser is energy is ∼100-fold less. In the present process there is no ablation and no acoustic report accompanies it. Only a fraction of the polyimide that is removed from the surface is seen as debris.
Competition between fundamental and second-harmonic operations in a submillimeter wave gyrotron
Authors: Idehara T. , Tatsukawa T. , Ogawa I. , Mori T. , Tanabe H. , Wada S. , Brand G. F. , Brennan M. H.
Published: July 2002

Competition between electron cyclotron fundamental (f=fc) and second-harmonic (f=2fc) operation in a submillimeter wave gyrotron is described. Even when the magnetic field intensity is adjusted to the optimum value for second-harmonic operation, we can get a pure mode only for small beam currents. As the beam current is increased, excitation of the fundamental appears and eventually suppresses the second harmonic. The observed competition between the fundamental and second harmonic is compared with a computer simulation.
Stability of hydrogenated amorphous silicon deposited at high temperatures with a remote hydrogen plasma
Authors: Johnson N. M. , Nebel C. E. , Santos P. V. , Jackson W. B. , Street R. A. , Stevens K. S. , Walker J.
Published: July 2002

It is demonstrated that the stability of hydrogenated amorphous silicon (a-Si:H) is improved by deposition under the combined conditions of high substrate temperature (e.g., TD=400 °C) and high hydrogen dilution, as are readily achieved in a remote hydrogen plasma reactor. In comparison with optimized films from conventional rf glow discharge deposition (e.g., silane, 230 °C, 2 W), undoped high TD films possess a lower midgap defect density, the dark dc conductivity in n-type (phosphorus-doped) films displays higher equilibration temperatures and longer relaxation times at a given temperature with an activation energy of 1.0 eV, and undoped high TD films have a lower saturated density of light-induced defects. It is proposed that the ability to achieve the improved stability is a consequence of two effects: (1) the use of hydrogen dilution during deposition to maintain the hydrogen concentration in the film near 10 at. % even at 400 °C and (2) the possibility that at high TD’s the hydrogen is more stably incorporated in the random network and/or that the density of weak Si—Si bonds is smaller.
Room-temperature photopumped blue lasing in ZnSe-ZnS0.06Se0.94 double heterostructures
Authors: Sun Gang , Shahzad Khalid , Gaines James M. , Khurgin Jacob B.
Published: July 2002

We present results on room-temperature photopumped lasing action in the blue region (∼4650 Å) of the spectrum for double heterostructures with ZnSe active layers. The confining layers are ZnS0.06Se0.94, providing lattice match to the GaAs substrate. The room-temperature lasing, observed under pulsed excitation, yields threshold pump intensity as low as 58 kW cm−2 for an active layer thickness of 1500 Å.
Electric field effect in high T
c superconducting ultrathin YBa2Cu3O7−x films
Authors: Xi X. X. , Li Q. , Doughty C. , Kwon C. , Bhattacharya S. , Findikoglu A. T. , Venkatesan T.
Published: July 2002

A multilayer high Tc superconducting field-effect transistor-like structure was made from ultrathin YBa2Cu3O7−x films. An epitaxially grown dielectric SrTiO3 insulation layer, which had a forward bias breakdown voltage of about 20 V, allowed an electric field induced change in the channel layer of 1.25×1013 carrier/cm2 per volt of the gate voltage. A significant modulation of the normal state and superconducting properties was observed in samples with YBa2Cu3O7−x channel layers of a few unit cells thick. By applying gate voltage of different polarities, Tc was both suppressed and enhanced by ∼1 K. The resistance was modulated by as much as 20% in the normal state and by over 1500% near the zero resistance temperature.
X-ray reflectivity studies of SiO2/Si(001)
Authors: Rabedeau T. A. , Tidswell I. M. , Pershan P. S. , Bevk J. , Freer B. S.
Published: July 2002

X-ray reflectivity has been utilized in a study of the SiO2/Si interfacial structure for dry oxides grown at room temperature on highly ordered Si(001) surfaces. Scattering near (±110) demonstrates the Si lattice termination of the wafers studied is characterized by a highly ordered array of terraces separated by monoatomic steps. Specular reflectivity data indicate the ‘‘native’’ dry oxide thickness is approximately 5 Å with a 1-Å vacuum interface width. Residual laminar order in the oxide electron density along the oxide/Si interfacial normal decays exponentially from the oxide/Si interface with a ∼2.7-Å decay length.
Activation energy for electromigration in Cu films
Authors: Park C. W. , Vook R. W.
Published: July 2002

Copper is a possible substitute for Al in very large scale integration interconnects because of its higher resistance to electromigration damage (EMD) and its lower electrical resistivity. In the present work, we report on electrical resistance measurements of the activation energy for EMD in Cu films as determined by an isothermal annealing method carried out under high vacuum conditions. Temperature measurement and control were accomplished by means of a Cu thin-film thermistor. The activation energy for EMD of evaporated Cu films was found to be 0.79±0.02 eV.
Determination of epitaxial AlxGa1−xAs composition from x-ray diffraction measurements
Authors: Goorsky M. S. , Kuech T. F. , Tischler M. A. , Potemski R. M.
Published: July 2002

The correlation between the aluminum composition in epitaxial AlxGa1−xAs and double crystal x-ray diffraction measurements was quantitatively determined. The angular separation ΔΘ, between the diffraction peaks from the AlxGa1−xAs layer grown by metalorganic vapor phase epitaxy and the GaAs substrate increased nonlinearly with the Al content, which was independently determined using photoluminescence and electron microprobe measurements. The calibration curve was used to determine AlAs materials parameters. The AlAs lattice constant and Poisson ratio were determined to be 5.6622 Å and 0.275, respectively, assuming that the GaAs parameters are 5.65325 Å and 0.311.
Dopant diffusion during high-temperature oxidation of silicon
Authors: Dunham Scott T. , Jeng Nanseng
Published: July 2002

In order to test models of oxidation enhanced diffusion, we measure phosphorus diffusion in 〈100〉 silicon at high temperature (1150 °C) under both oxidizing and nonoxidizing conditions in ambients containing dry O2 diluted with N2. We find enhanced diffusion even at extremely low rates in contrast to observations in 〈111〉 material. Based on the observations for both 〈100〉 and 〈111〉 material, we evaluate proposed models for interstitial concentration during oxidation.
Quantum interference in ultrashort channel length silicon metal-oxide-semiconductor field-effect transistors
Authors: Hartstein A.
Published: July 2002

Silicon metal-oxide-semiconductor field-effect transistors have been constructed, using a novel edge deposition technique, which have active channel lengths ranging from 7.7 to 124 nm. The electrical conductance of the devices, at temperatures below 4.2 K, shows oscillations which are attributed to quantum mechanical interference due to reflections from the device edges. Model calculations are in good agreement with the experiment.
Liquid phase epitaxy of cubic FeSi2 on (111) Si induced by pulsed laser irradiation
Authors: Grimaldi M. G. , Baeri P. , Spinella C. , Lagomarsino S.
Published: July 2002

Epitaxial βFeSi2 layers thermally grown on (111) Si substrates have been irradiated by 25 ns ruby laser pulses in the energy density range 0.3–0.7 J/cm2. Rutherford backscattering analyses in combination with the channeling effect have shown that the silicide stoichiometry does not change for irradiations up to an energy density of 0.5 J/cm2, while alignment of the irradiated silicide along the [111] substrate normal direction is observed. Transmission electron diffraction in the plan view configuration showed that this silicide phase has a cubic symmetry with a lattice parameter very similar to that of Si. Diffraction patterns taken along different poles of the substrate indicated that the epitaxial phase is 180° rotated about the [111] normal direction like the B type NiSi2 and CoSi2 silicides.
Thermal and photochemical decomposition pathways of AsH3 on GaAs(100): Implication for atomic layer epitaxy
Authors: Zhu X.-Y. , Wolf M. , Huett T. , Nail J. , Banse B. A. , Creighton J. R. , White J. M.
Published: July 2002

We report spectroscopic evidence for the thermal and photochemical decomposition pathways of arsine (AsH3) adsorbed on Ga-rich GaAs(100). Arsine adsorbs molecularly on the Ga-rich GaAs surface at 120 K and dissociates upon either heating to above 200 K or irradiation with 6.4 eV photons. The dissociation of arsine is accompanied by the formation of surface Ga-H species, which is both thermally and photochemically more stable than surface AsHx. This implies that the removal of hydrogen from Ga is the rate-limiting step in the initial stage of As deposition from AsH3 in the thermal or photoassisted atomic-layer epitaxy of GaAs.
Photoelectrochemical conductivity selective etch stops for SiC
Authors: Shor J. S. , Osgood R. M. , Kurtz A. D.
Published: July 2002

Recent advances in SiC technology have demonstrated that the material is a potentially useful semiconductor for high temperature and high frequency applications. However, unlike silicon and GaAs, SiC is chemically inert, thus limiting the amount of etchants that can be effectively used to pattern devices. In fact, no patterning technique has been reported to date for SiC which shows high selectivity between p- and n-type material. In this letter, we will show how an n-type SiC epilayer can be patterned using photoelectrochemical etching, while a p-type substrate underneath acts as an etch stop. This process is useful for the fabrication of electromechanical transducers, mesa structures, and bipolar and CMOS devices in SiC.
Surface-selective x-ray topographic observations of mechanochemical polished silicon surfaces using synchrotron radiation
Authors: Kimura Shigeru , Mizuki Jun’ichiro , Matsui Junji , Ishikawa Tetsuya
Published: July 2002

Surface-selective topographic observations have been performed by extremely asymmetric diffraction, in which the glancing angle of the incident x rays is near the critical angle of total reflection. This was achieved by using the wavelength tunability of synchrotron radiation. Mechanochemical polished surfaces of Si(001) and Si(111) wafers were investigated. Strain images arising from the polished surfaces were obtained by selecting the penetration depth to be several tens of nanometers.
Heteroepitaxial growth of AlAs using dimethylethylamine alane as an Al precursor
Authors: Chen K. M. , Castro T. , Franciosi A. , Gladfelter W. L. , Cohen P. I.
Published: July 2002

Dimethylethylamine alane (DMEAA) has been used to grow AlAs thin films by metalorganic molecular beam epitaxy. In situ reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) measurements indicate that high-quality AlAs films with atomically smooth surfaces can be epitaxially grown on GaAs(100) at relatively low temperatures (less than 550 °C) with no detectable carbon or oxygen content by AES. Strong oscillations in the specular RHEED intensity indicates a layer-by-layer growth mode of AlAs using this new Al precursor. The growth rate, determined from the period of the intensity oscillations, is linearly dependent on the DMEAA partial pressure, but is independent of substrate temperature, at least in the range from 320 to 620 °C. An enhancement of the Al adatom mobility over that obtained using an elemental Al source was observed.
Texturization of polycrystalline silicon films using excimer-laser processing for memory device applications
Authors: Yu C. , Mathews V. K.
Published: July 2002

We report the first systematic investigation of texturizing polycrystalline silicon films utilizing an excimer laser to achieve an increased cell capacitance for high-density memory-device applications. The degree of surface roughness after laser processing was found to be sensitive to polycrystalline silicon deposition temperature and laser fluence. In the laser-fluence range of 0.2 to 0.7 J/cm2, the reflectivity of polycrystalline silicon films varied from ∼10% to 80%. A significant increase in the degree of surface roughness was achieved at optimized conditions. This, in turn, resulted in an increased effective surface area of the polycrystalline silicon film used as the capacitor-storage node. Primary capacitance-voltage measurements indicated a 10% increase in the cell capacitance, and current-voltage characterizations showed no device degradation due to laser processing.
Carrier capture times in 1.5 μm multiple quantum well optical amplifiers
Authors: Weiss S. , Wiesenfeld J. M. , Chemla D. S. , Raybon G. , Sucha G. , Wegener M. , Eisenstein G. , Burrus C. A. , Dentai A. G. , Koren U. , Miller B. I. , Temkin H. , Logan R. A. , Tanbun-Ek T.
Published: July 2002

The carrier capture times in multiple quantum well semiconductor amplifiers of different structures are studied under high plasma density conditions. Fast (<1 ps), slow (≳150 ps), and intermediate time constants (2–7 ps) are identified in InGaAs quantum well structures. The intermediate time constant is attributed to carrier diffusion in the cladding layers and identified as the carrier capture time. Short capture times can be achieved by proper design of the device structure.
Fermi level pinning in low-temperature molecular beam epitaxial GaAs
Authors: Shen H. , Rong F. C. , Lux R. , Pamulapati J. , Taysing-Lara M. , Dutta M. , Poindexter E. H. , Calderon L. , Lu Y.
Published: July 2002

The Fermi level position in low temperature (LT) GaAs has been studied by photoreflectance (PR). By etching the LT-GaAs to a different thickness, we find the Fermi level in the as-grown as well as the annealed LT-GaAs is firmly pinned. The pinning position, however, occurs at different energies: 0.47 eV below the conduction band edge for the as-grown samples and 0.65 eV below the conduction band edge for the annealed samples. The pinning in the as-grown LT-GaAs is believed to be the result of a high degree of charge compensation by deep levels, while the pinning in the annealed LT-GaAs is due to the depletion of carriers by the Schottky barrier at the metallic As precipitates. From the measured Fermi level and ionization ratio of As antisites, the (0/+) donor level of the As antisite in LT-GaAs is, for the first time, determined at Ec−0.57 eV.
Fabrication of free-standing quantum wells
Authors: Williams M. D. , Shunk S. C. , Young M. G. , Docter D. P. , Tennant D. M. , Miller B. I.
Published: July 2002

Standard lithographic techniques have been utilized to fabricate quantum wells which are confined on both sides by vacuum. These ‘‘naked’’ quantum wells are fabricated from spatially and compositionally modulated III-V superlattices in which alternate layers of the structures are sacrificed by selective etching. These structures are patterned such that the quantum wells are suspended between support posts.
Etching of screw dislocations in YBa2Cu3O7 films with a scanning tunneling microscope
Authors: Heyvaert I. , Osquiguil E. , Van Haesendonck C. , Bruynseraede Y.
Published: July 2002

We report on the systematic unrolling of screw dislocations with the scanning tunneling microscope at the surfaces of sputtered, c-axis oriented YBa2Cu3O7 films. The etching is dominated by field induced evaporation and not by mechanical milling of the surface. The process also enables the controlled drawing of nanometer scale grooves on the film surface.
Memory effects of silicon-implanted oxides for electrically erasable programmable read-only memory applications
Authors: Hao Ming-yin , Hwang Hyunsang , Lee Jack C.
Published: July 2002

The memory effects of silicon-implanted oxides are reported in this letter. Due to the trap-like characteristics of the implanted silicon, hysteresis capacitance-voltage loops have been measured after voltage pulse stressing. A positive voltage pulse leads to a positive shift of the capacitance-voltage curve, while a negative voltage stress results in a negative drift. It was found that using these Si-implanted oxides, writing/erasing operations of electrically erasable programmable read-only memories could be realized by applying short voltage pulses (e.g., 100 ns, ±12–16 V). Moreover, excellent retention characteristics were also detected for these memory devices. The implanted silicon alters the conduction mechanism such that the I-V behavior does not follow the Fowler–Nordheim tunneling. The implantation process did not yield noticeable degradation to the oxide quality; and a lifetime over 10 yr can be achieved even with ±16 V stressing.
Comparative influence of bias and nucleation layer thickness on the heteroepitaxial growth of InN on AlN-nucleated (111) silicon and (00.1) sapphire
Authors: Kistenmacher Thomas J. , Bryden Wayne A.
Published: July 2002

The effects of bias and nucleation layer thickness on heteroepitaxy in thin films of InN grown at 400 °C on semiconducting (111) silicon and insulating (00.1) sapphire are shown to be dramatically different. For example, the thickness of an InN film on nucleated (00.1) sapphire is independent of bias, while on nucleated (111) silicon the thickness varies by over a factor of two. Similarly, the excellent epitaxy of the InN films on nucleated (00.1) sapphire is unaffected by bias or AlN layer thickness, while quality epitaxy on nucleated (111) silicon is achieved only in a narrow range of these parameters. Determining the bounds for heteroepitaxial growth on (111) silicon is a crucial first step toward devices incorporating both sources or detectors and processing elements.
Electrical characteristics of directly-bonded GaAs and InP
Authors: Wada Hiroshi , Ogawa Yoh , Kamijoh Takeshi
Published: July 2002

The electrical characteristics of directly bonded GaAs/InP heterointerfaces have been investigated for the first time. The mirror-polished surfaces of GaAs and InP wafers were put face to face and bonded by heat treatment at temperatures ranging from 450 to 700 °C. The wafers were successfully bonded without using any solders at all the temperatures tested. 1.3 μm InP/GaInAsP lasers were fabricated on GaAs substrates using direct bonding at 450 °C, and room-temperature lasing operation has been achieved with the threshold current identical to that of conventional InP lasers.
Ultraviolet and violet light-emitting GaN diodes grown by low-pressure metalorganic chemical vapor deposition
Authors: Goldenberg Barbara , Zook J. David , Ulmer Robert J.
Published: July 2002

Both metal-insulator-semiconductor and p-n junction electroluminescence have been observed in thin-film, metalorganic chemical vapor deposition-grown GaN diodes thermally annealed in N2. UV radiation, peaking near 380 nm, is emitted when electrons are injected from the undoped, n-type material into the Mg-doped, p-type GaN. Violet light, peaking near 430 nm, is obtained by injecting electrons into p-type material from either n-type material or non-ohmic metal contacts. The present results support and extend earlier interpretations of the nature of the recombination centers in GaN.
Experimental verification of a longitudinal beam-envelope model for a space-charge dominated parabolic bunch
Authors: Wang D. X. , Wang J. G. , Kehne D. , Reiser M.
Published: July 2002

The longitudinal drift expansion and compression of a space-charge dominated electron beam with a parabolic line charge profile has been studied experimentally to verify the validity of the longitudinal envelope equation. The experimental configuration and measurement results are reported. Good agreement is found between theoretical predictions from the envelope calculations and experimental results.
Decrease in the intrinsic microwave loss of YBa2Cu3O6.95 by Zn doping
Authors: Zhang Kuan , Bonn D. A. , Liang Ruixing , Baar D. J. , Hardy W. N.
Published: July 2002

Measurements of the microwave surface resistance of single crystals of YBa2(Cu1−xZnx)3O6.95 at 3.8 and 34.8 GHz have been performed with zinc contents of x=0, 0.0015, and 0.0031. The microwave loss in the superconducting state decreases when zinc impurities are added, demonstrating that some defects are required to achieve state-of-the-art surface resistance in this material.
Quality of ZnSe/GaAs epilayers studied by spatial correlation model of Raman scattering
Authors: Wang J. , Yao W. H. , Wang J. B. , Lu H. Q. , Sun H. H. , Wang X. , Pang Z. L.
Published: July 2002

In this letter, the spatial correlation model has been used for interpreting the line shapes of the first-order longitudinal-optical phonon Raman spectra of ZnSe/GaAs epitaxial layers. The good agreement between theoretical line shapes and the experiment measurements was illustrated for the samples grown by the molecular beam epitaxy (MBE), hot wall epitaxy (HWE), and hot wall beam epitaxy (HWBE).
Defect generation sensitivity depth profile in buried SiO2 using Ar plasma exposure
Authors: Stesmans A. , Vanheusden K.
Published: July 2002

The sensitivity to oxygen-vacancy defect (E′) generation of buried SiO2 (BOX) layers in separation by implantation of oxygen (SIMOX) structures is studied by electron spin resonance. The E′ generation tool used is exposure to a dc Ar glow discharge that produces E’s predominantly in a surface layer of ≊100 Å thick, reaching local volume densities at the surface up to 8×1019 cm−3. Reoxidation of the layers is observed to reduce this value close to that of regular dry thermal oxide (≥29 times lower). This glow discharge exposure, alternated with step-by-step etch back, allowed mapping of the defect generation sensitivity depth profile for the entire buried layer, revealing a fairly uniform sensitivity with a strong decline towards the BOX/substrate interface. The results provide evidence that the buried oxide contains excess Si, exceedingly so near the BOX/substrate interface.
Focused ion beam direct deposition of gold
Authors: Nagamachi Shinji , Yamakage Yasuhiro , Maruno Hiromasa , Ueda Masahiro , Sugimoto Seiji , Asari Masatoshi , Ishikawa Junzo
Published: July 2002

Focused ion beam direct deposition has been developed as a new technique for making patterned metal film directly on substrates. The 20 keV Au+ ion beam is focused, deflected, and finally decelerated to 30–200 eV between the objective lens and substrate. The decelerated beam is deposited on the substrate at room temperature. The beam diameter can be tuned between 0.5 and 8 μm and the beam current varies from 40 pA to 10 nA, corresponding to the beam diameter. Current density was about 20 mA/cm2, so that the deposition rate in the beam spot was estimated about 0.02 μm/s. The purity of gold film was measured with Auger electron spectroscopy and contents of carbon and oxygen, undesirable impurities, were below detection limits. The resistivity was constant at 3.7±0.1 μΩ cm for deposition over the ion energy range of 34–194 eV.
Room-temperature lasing action in In0.51Ga0.49P/In0.2Ga0.8As microcylinder laser diodes
Authors: Levi A. F. J. , Slusher R. E. , McCall S. L. , Pearton S. J. , Hobson W. S.
Published: July 2002

We report room-temperature operation of electrically pumped whispering-gallery mode In0.51Ga0.49P/In0.2Ga0.8As microcylinder laser diodes with emission at wavelength λ=1.0 μm and threshold current Ith=5 mA. Because the lasing modes do not overlap the diode’s central region, carrier density is not efficiently pinned by above-threshold stimulated emission.
Visible light emission from a pn junction of porous silicon and microcrystalline silicon carbide
Authors: Futagi Toshiro , Matsumoto Takahiro , Katsuno Masakazu , Ohta Yasumitsu , Mimura Hidenori , Kitamura Koich
Published: July 2002

We have fabricated a new type of light-emitting diode based on a porous silicon and microcrystalline silicon carbide pn junction. The visible light emission from 580 to 820 nm with a peak of 700 nm was observed at forward bias voltages larger than 18 V, and the emission was quite uniform over an area of 1 cm2.
Self-aligned passivation on copper interconnection durability against oxidizing ambient annealing
Authors: Itow Hitoshi , Nakasaki Yasushi , Minamihaba Gaku , Suguro Kyoichi , Okano Haruo
Published: July 2002

A self-aligned niobium (Nb) passivation method has been developed in order to improve the stability of copper (Cu) in an oxidizing ambient. A Cu/Nb/SiO2/(100)Si structure was annealed between 400 and 850 °C for 30 min in a gas mixture of H2 and N2. The underlying Nb diffused to the Cu surface and turned into its nitride at 750 °C. The surface Nb nitride layer acted as a passivation layer against oxidation. The passivated Cu was found to retain its resistivity of 2.0 μΩ cm even after oxidation at 400 °C for 30 min in a dry oxygen ambient.
Determination of the density of states at the Fermi level of hydrogenated amorphous silicon in thin-film transistor structure by space charge limited current measurement
Authors: Soh Hoe Sup , Lee Choochon , Jang Jin , Jung Moon Youn , Yoo Soon Sung
Published: July 2002

We studied the space charge limited current effect in hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs). We demonstrate that the drain current is space charge limited when the source-drain voltage is large and the gate voltage is small. Using this space charge limited current we determined the density of states in the gap of a-Si:H in a-Si:H TFT.
Thin oxynitride film metal-oxide-semiconductor transistors prepared by low-pressure rapid thermal chemical vapor deposition
Authors: McLarty P. K. , Hill W. L. , Xu X.-L. , Misra V. , Wortman J. J. , Harris G. S.
Published: July 2002

Thin silicon oxynitride (Si-O-N) films have been deposited using low-pressure rapid thermal chemical vapor deposition (RTCVD) with silane (SiH4), nitrous oxide (N2O), and ammonia (NH3) as the reactive gases. Metal-oxide-semiconductor transistor transconductance measurements showed decreasing peak gm values but improved high field degradation characteristics. This is consistent with previous work on thermally nitrided oxides and suggests that the films are perhaps under tensile stress. Hot carrier stress at maximum substrate current was performed with the Si-O-N films displaying larger threshold voltage shifts when compared to furnace SiO2 indicating the possible existence of hydrogen related traps.
Dislocation relaxation in InAsyP1−y films deposited onto (001) InP by gas-source molecular beam epitaxy
Authors: Okada T. , Kruzelecky R. V. , Weatherly G. C. , Thompson D. A. , Robinson B. J.
Published: July 2002

The strain relaxation of InAsyP1−y layers grown on (001) InP substrates by gas-source molecular beam epitaxy was examined using transmission electron microscopy (TEM) and cathodoluminescence (CL) imaging. InAsyP1−y films with a thickness of 190 Å were prepared, systematically varying the As content from y=0.30 and 0.77, corresponding to a lattice mismatch between 0.97% and 2.5%. Relaxation was anisotropic, with 60° misfit dislocations lying predominantly along [11̄0], with a much lower density of dislocations along [110]. For y≳0.48, CL and plan-view TEM observations show slip traces which make angles of about ±40° with the [11̄0] direction. These slip traces correspond to pure-screw dislocation segments (gliding on {111}) cross slipping to glide on planes approximately parallel to {011}.
Electron cyclotron resonance chemical vapor deposition of silicon oxynitrides using tris(dimethylamino)silane
Authors: Boudreau Marcel , Boumerzoug Mohamed , Mascher Peter , Jessop Paul E.
Published: July 2002

A new compound, tris(dimethylamino)silane was used as an organosilicon source for the deposition of silicon oxynitride thin films. The depositions were carried out at low substrate temperatures (<150 °C) in an electron cyclotron resonance plasma enhanced chemical vapor deposition reactor. Films with compositions varying from Si3N4 to SiO2 were deposited on silicon substrates by varying the N2/O2 flow ratio to the plasma chamber. In situ ellipsometry measurements of the film optical index were well correlated with film composition. Auger electron spectroscopy showed that only low levels of carbon (<3 at. %) were present, while Fourier transform infrared spectroscopy showed low levels of bonded hydrogen. The deposition rate of high quality Si3N4 was as high as 220 Å/min.
Magnetotunneling spectroscopy in wide In0.53Ga0.47As/In0.52Al0.48As double quantum wells
Authors: Smet Jurgen H. , Fonstad Clifton G. , Hu Qing
Published: July 2002

Magnetoquantum oscillations in the tunnel current of wide In0.53Ga0.47As/In0.52Al0.48As double quantum wells have been exploited to trace the energy levels in the adjacent wells as a function of the applied voltage. The dominant inelastic scattering mechanism was identified as GaAs-like longitudinal-optical-phonon emission. This powerful spectroscopy probe allows an unambiguous identification of the transmission channels responsible for the peaks observed in the current-voltage characteristics and provides a large number of consistency checks. The obtained experimental results can be used to verify the accuracy of self-consistent simulation programs.
Observation of step bunching on vicinal GaAs(100) studied by scanning tunneling microscopy
Authors: Hata K. , Kawazu A. , Okano T. , Ueda T. , Akiyama M.
Published: July 2002

Similar step bunchings which consist of 7–9 single steps were observed by scanning tunneling microscopy on both vicinal GaAs(100) surfaces grown by metalorganic chemical-vapor deposition (MOCVD) and annealed in AsH3 atmosphere. Growth parameters, including deposition rate, layer thickness, V/III ratio, and growth temperature, did not affect the morphology of the step bunching. These results indicate that step bunching is induced during the annealing process and its surface morphology is preserved during MOCVD growth for a wide range of growth parameters.
Room-temperature photoreflectance as an efficient tool for study of the crystalline quality of InAlAs layers grown on InP substrates
Authors: Monéger S. , Tabata A. , Bru C. , Guillot G. , Georgakilas A. , Zekentes K. , Halkias G.
Published: July 2002

Photoreflectance and photoluminescence experiments have been performed on molecular beam epitaxy (MBE) grown InAlAs layers lattice matched to InP substrates in order to evaluate the influence of the growth temperature on the crystalline quality of this material. The study of the photoreflectance broadening parameter at room temperature provides the same indication on crystalline quality as the well-known linewidth broadening of the photoluminescence at cryogenic temperatures. We show that the best material quality is obtained for the MBE growth temperature of 530 °C.
Atomic layer epitaxy of Si on Ge(100) using Si2Cl6 and atomic hydrogen
Authors: Koleske D. D. , Gates S. M.
Published: July 2002

The surface composition is measured during atomic layer epitaxy (ALE) growth of Si on Ge(100) using Si2Cl6 and atomic hydrogen (Hat) at TS=400 °C. During each Si2Cl6 exposure, Si is adsorbed until Cl fully terminates the surface, making the Si deposition step self-limiting. The terminating Cl layer is removed by Hat exposure. At 400 °C, H2 rapidly desorbs from Ge(100) and Si/Ge alloy surfaces, regenerating the surface dangling bonds for the next Si2Cl6 adsorption cycle. A thin alloy is grown epitaxially on the Ge(100) substrate, which displays a linear increase in Si content and a linear decrease in Ge content, measured over 1–20 Si ALE cycles.