bluuebunny/crossref_metadata_2025 huggingface dataset:
Large refractive index enhancement in PbTe/Pb1−xEuxTe multiquantum-well structures
Authors: Yuan Shu , Krenn H. , Springholz G. , Bauer G. , Kriechbaum M.
Published: July 2002

Optical interband absorption between confined carrier states is studied in PbTe/Pb1−xEuxTe multiple quantum wells (MQWs). The frequency dependence of the refractive index is calculated by the Kramers–Kronig transformation of the absorption coefficient of the MQWs. It is shown that the observed interference fringes in mid-infrared transmission can only be accounted for if the enhancement of the refractive index η(ω) at the interband transition energies which follow from the Kramers–Kronig transformation are taken into account. These changes in η are as large as 19% (at T=77 K) and are thus relevant for the design and fabrication of mid-infrared QW lasers.
Uniform plasma produced by a plane slotted antenna with magnets for electron cyclotron resonance
Authors: Sato N. , Iizuka S. , Nakagawa Y. , Tsukada T.
Published: July 2002

A uniform plasma is produced by a new plane slotted antenna with permanent magnets for the electron cyclotron resonance. The plasma is uniform within a few percent in a diameter of 25–30 cm at a distance of 25–30 cm from the antenna. The plasma density, 1.5×1010 cm−3 with electron temperature of 1.8 eV at a microwave power of 100 W, is almost proportional to the microwave power. A magnetic distribution provided by the magnets is essential for producing such a uniform plasma.
Effect of N doping on the structural properties of ZnSe epitaxial layers grown by molecular beam epitaxy
Authors: Petruzzello J. , Gaines J. , van der Sluis P. , Olego D. , Ponzoni C.
Published: July 2002

The structural properties of ZnSe doped with N, in the concentration range of 1×1018–2×1019 cm−3, were characterized by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy techniques. The relaxation of the lattice mismatch induced compressive strain between ZnSe and GaAs is less for N doped layers for a given ZnSe thickness. The smaller amount of strain relaxation with N doping results in layers that contain residual compressive strain up to thicknesses of at least 1.7 μm. In addition, the misfit dislocation array becomes a regular rectangular grid when N is incorporated in ZnSe layers. The ZnSe lattice constant, as measured by x-ray diffraction, decreases as the N concentration increases. The reduction in lattice constant, however, is greater than can be explained by the shorter Zn-N bond distance of model predictions. We attribute the excess lattice contraction to the generation of point defects accompanying N doping. The Raman spectra display a broadening of the linewidth as the N concentration increases, which supports the notion of point defect creation with N doping.
Strain relaxation and mosaic structure in relaxed SiGe layers
Authors: Mooney P. M. , LeGoues F. K. , Chu J. O. , Nelson S. F.
Published: July 2002

We report high-resolution x-ray diffraction measurements of relaxed Si0.7Ge0.3 layers on (001) Si substrates. Strain was relieved either by a glide-limited mechanism in structures where the composition was changed abruptly or by a nucleation-limited mechanism in structures having a compositionally graded intermediate layer. We find that the broadening of the x-ray peak of the surface alloy layer is similar in both cases, although the threading dislocation densities ranged from 1011 cm−2 to 5×106 cm−2. The effect of the threading dislocations on the x-ray peak widths is masked by the mosaic structure caused by the network of misfit dislocations underneath the layer.
Photodetectors fabricated from rapid-thermal-oxidized porous Si
Authors: Tsai Chaochieh , Li K.-H. , Campbell Joe C. , Tasch Al
Published: July 2002

A metal-semiconductor-metal (MSM) photoconductor and a p-n photodiode have been fabricated from rapid-thermal-oxidized (RTO) porous Si. The MSM photoconductor achieved 2.8×higher responsivity at 350 nm than a UV-enhanced Si photodiode, and the RTO photodiode exhibited an external quantum efficiency of 75% at 740 nm.
Raman study of electron confinement in Si δ-doped GaAs
Authors: Mlayah A. , Carles R. , Bedel E. , Muñoz-Yagüe A.
Published: July 2002

In this letter Raman spectroscopy measurements on Si δ-doped GaAs are reported. The coupling of two-dimensional (2D) intersubband plasmons with the polar phonons is clearly demonstrated. The change undergone by the coupled mode signal as a function of the depth explored by the Raman probe is studied and allows for an original and accurate investigation of electron gas confinement. Indeed, it is shown that a quantitative analysis of depth profiling measurements allows the real-space extent of the quasi-2D electron gas in δ-doped structures to be estimated.
Photoluminescence and electro-optic properties of small (25–35 nm diameter) quantum boxes
Authors: Davis L. , Ko K. K. , Li W.-Q. , Sun H. C. , Lam Y. , Brock T. , Pang S. W. , Bhattacharya P. K. , Rooks M. J.
Published: July 2002

The luminescence and electro-optic properties of buried 25–35 nm quantum boxes have been measured. The quantum boxes were defined by a combination of molecular beam epitaxial growth and regrowth, electron beam lithography, and dry etching. The photoluminescence from 35 nm boxes shows a blue shift of ∼15 meV compared to the bulk luminescence and an enhancement, taking into account the fill factor. An enhanced effective linear electro-optic coefficient, rl, is observed for the quantum boxes.
Effect of Auger recombination and differential gain on the temperature sensitivity of 1.5 μm quantum well lasers
Authors: Zou Y. , Osinski J. S. , Grodzinski P. , Dapkus P. D. , Rideout W. , Sharfin W. F. , Crawford F. D.
Published: July 2002

The temperature sensitivity of both strained and lattice-matched 1.5 μm quantum well lasers has been studied. From a complete experimental investigation of the temperature behavior of carrier lifetime, gain, and internal loss, it is found that Auger recombination is not the dominant factor in affecting the temperature sensitivity of threshold currents in 1.5 μm lasers. Instead, the dominant contribution to the temperature dependence of threshold currents in 1.5 μm lasers is the change in differential gain with temperature—a characteristic not improved by strain.
YBa2Cu3O7 thin film SQUID gradiometer for biomagnetic measurements
Authors: Tavrin Y. , Zhang Y. , Mück M. , Braginski A. I. , Heiden C.
Published: July 2002

Low-noise rf SQUID washers fabricated from YBa2Cu3O7 epitaxial thin films have been used to construct a first-order electronic gradiometer operating at 77 K and suitable for biomagnetic measurements. Mechanical adjustment of the two-SQUID gradiometric setup made it possible to attenuate signals due to far magnetic field sources by three orders of magnitude. A magnetic field resolution of ≤280 fT/Hz1/2 above 2 Hz was attained through the use of large flux focusers. The fine structure of human heart magnetocardiograms was recorded in unshielded space. In a shielded room, magnetoencephalograms were obtained. The system was used to obtain new data on auditory evoked cortical response.
Noncritical second harmonic generation of CO2 laser radiation in mixed chalcopyrite crystal
Authors: Bhar G. C. , Das S. , Chatterjee U. , Datta P. K. , Andreev Yu N.
Published: July 2002

We have generated a tunable second harmonic of CO2 laser radiation noncritically for the first time in a potential mixed chalcopyrite crystal AgGaxIn1−xSe2. Wide angular acceptance and increased conversion as compared to AgGaSe2 have been observed and the tuning characteristics have been explained using the dispersion data of its two end crystals.
Carrier transport and intersubband population inversion in coupled quantum wells
Authors: Yee W. M. , Shore K. A. , Schöll E.
Published: July 2002

We theoretically study the possibility of achieving intersubband population inversion in coupled GaAs quantum wells, taking into account the relevant physical mechanisms of resonant tunneling and intersubband emission-absorption processes. Two coupled quantum well structures having intersubband resonant wavelengths of 10 and 60 μm are considered. We find that, in the case of an operating wavelength of 60 μm, intersubband population inversion is achievable at acceptable injection current densities even for room-temperature operation. However, achievement of intersubband population inversion is significantly more difficult at the shorter wavelength. The temperature and carrier transit time dependence of intersubband population inversion are also calculated.
Damage accumulation during high-dose, O+ implantation in Si
Authors: Holland O. W. , Zhou D. S. , Thomas D. K.
Published: July 2002

High-dose O+ implantation of Si between 450 and 500 keV is investigated to better understand the mechanisms responsible for ion-induced growth of damage, especially in the top Si layer ahead of the region where a buried oxide forms. Two distinct states are identified in this Si layer over an extended range of fluence (≥1018 cm−2): a low-density defect state and a high-density one. These states are observed at all irradiation temperatures, including ambient temperature. The transition between the states is rather abrupt with the onset at a high fluence, which decreases with decreasing temperature. The existence of the low-density state offers a possibility of forming dislocation-free silicon-on-insulator wafers, even for ambient temperature irradiations. A processing method for achieving such wafers is discussed.
Band-gap engineered digital alloy interfaces for lower resistance vertical-cavity surface-emitting lasers
Authors: Peters M. G. , Thibeault B. J. , Young D. B. , Scott J. W. , Peters F. H. , Gossard A. C. , Coldren L. A.
Published: July 2002

We report on a technique of grading the heterobarrier interfaces of a p-type distributed Bragg reflector mirror to reduce the operating voltages of vertical-cavity surface-emitting lasers (VCSELs). We report VCSELs with lower operating voltages (2–3 V) and record continuous-wave room-temperature power-conversion efficiencies (17.3%). We experimentally demonstrate that by using a parabolic grading and modulating the doping correctly, a flat valence band is generated that provides low voltage hole transport. The low resistance mirrors are achieved using low Be doping, digital-alloy grading and 600 °C growth temperatures.
Effect of dc electric field on the effective microwave surface impedance of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 trilayers
Authors: Findikoglu A. T. , Doughty C. , Anlage S. M. , Li Qi , Xi X. X. , Venkatesan T.
Published: July 2002

We have studied the effect of a dc electric field on the effective microwave surface impedance of a thin film YBa2Cu3O7/SrTiO3/YBa2Cu3O7 (YBCO/STO/YBCO) trilayer by a dielectric resonator technique. At large dc electric fields (≳105 V/cm), both the effective surface resistance and reactance of the sample decrease monotonically with increasing dc voltage applied to the to YBCO film, yielding at 25 K and 24.7 GHz ‖δRs/δVdc‖∼0.25 μΩ/V and ‖δXs/δVdc‖∼1.8 μΩ/V, respectively. A two-fluid analysis indicates that the changes in the surface impedance can be explained in terms of field induced changes in the superconducting carrier density of the top YBCO film.
Low-threshold buried-ridge II-VI laser diodes
Authors: Haase M. A. , Baude P. F. , Hagedorn M. S. , Qiu J. , DePuydt J. M. , Cheng H. , Guha S. , Höfler G. E. , Wu B. J.
Published: July 2002

Blue-green (λ=511 nm) separate confinement laser structures based on lattice-matched MgZnSSe-ZnSSe-CdZnSe have been grown by molecular beam epitaxy. Wide stripe gain-guided devices have been fabricated from several such wafers. These devices exhibit room-temperature pulsed threshold current densities as low as 630 A/cm2 and threshold voltages less than 9 V. Using a novel self-aligned process that results in a planar surface, buried-ridge laser diodes have also been fabricated. These devices have demonstrated room-temperature threshold currents as low as 2.5 mA, which is more than a factor of 50 lower than that of any previously reported II-VI laser diode. Room-temperature operation at duty factors up to 50% has been demonstrated. The far-field patterns from these devices indicate single lateral mode operation, suitable for diffraction-limited applications, such as optical data storage.
Frequency and power stabilization of a three longitudinal mode He-Ne laser using secondary beat frequency
Authors: Suh H. S. , Yoon T. H. , Chung M. S. , Choi O. S.
Published: July 2002

A method of frequency and power stabilization for an internal-mirror He-Ne laser using the secondary beat frequency between the three longitudinal modes is presented. Frequency and power fluctuation was ±1 MHz (2 parts in 109) and ±0.10% over 10 000 s, respectively. The square-root Allan variance between the laser stabilized in this study and the iodine stabilized He-Ne laser was 5×10−11 at average time of τ=1 s. Furthermore, we could obtain the output power of 2 mW in a single longitudinal mode.
Room-temperature luminescence from Er-implanted semi-insulating polycrystalline silicon
Authors: Lombardo S. , Campisano S. U. , van den Hoven G. N. , Cacciato A. , Polman A.
Published: July 2002

Semi-insulating polycrystalline silicon films with oxygen concentrations in the range 4–27 at. % were deposited by low-pressure chemical vapor deposition of SiH4 and N2O onto silicon substrates, annealed at 920 °C, and then implanted with 2×1015 500 keV Er ions/cm2. After annealing at temperatures in the range 300–900 °C, the samples show intense room-temperature luminescence around 1.54 μm, characteristic of intra-4f emission from Er3+, upon excitation using an Ar ion laser. The luminescence intensity increases with increasing oxygen concentration in the film. The luminescence is attributed to Er3+ ions in oxygen-rich shells around Si nanograins, excited by a photocarrier-mediated process.
Temperature profile along the cavity axis of high power quantum well lasers during operation
Authors: Dabkowski F. P. , Chin A. K. , Gavrilovic P. , Alie S. , Beyea D. M.
Published: July 2002

Measurements of the temperature distribution along the cavity of 0.5 W AlGaAs quantum well lasers are presented. The spatial distribution of temperature was determined by measuring the spectral shift of electroluminescence emitted through a window in the GaAs substrate metallization. The average temperature of the active layer is 10–15 K higher than the heatsink temperature at 0.5 W output. Facet temperatures can exceed the average active layer temperature by over 100 K. Data are also presented illustrating the temperature profile at different drive currents between threshold and the maximum operating current. A temperature profile of a laser with a damaged front facet is presented, showing a hot region that is twice the size of the defect.
Room temperature study of strong lateral quantization effects in InGaAs/InP quantum wires
Authors: Ils P. , Michel M. , Forchel A. , Gyuro I. , Klenk M. , Zielinski E.
Published: July 2002

We have fabricated In0.53Ga0.47As/InP quantum wires with lateral widths down to 8 nm by high voltage electron beam lithography and deep wet chemical etching. The wires were studied by photoluminescence spectroscopy at room temperature. Down to the smallest wire widths a clear photoluminescence signal is observed. The decrease of the luminescence yield with decreasing wire width indicates that no significant damage has been induced at the sidewalls of the wires during the fabrication process. For wires with widths below about 60 nm a blue shift of the photoluminescence energy is observed, which reaches up to 73 meV for 8 nm wide wires. The experimentally observed width variation of the lateral quantization can be modeled quantitatively by using the measured width of the wires and standard band parameters.
Semiconductor laser cavity dispersion measurement based on interferometric crosscorrelation of amplified spontaneous emission
Authors: Naganuma Kazunori
Published: July 2002

The Fourier transform of the interferometric crosscorrelation of amplified spontaneous emission (ASE) is proposed as a general-purpose method for measuring cavity dispersion. The electric field correlation of the ASE from a cavity shows subfringes displaced from the ordinary interferogram by the cavity round-trip time. The cavity transfer function is derived from the subfringe using the Fourier transform. This method is demonstrated on semiconductor devices. It provides a very quick way to measure round-trip group delay dispersion as well as gain across a device’s whole gain band.
Transient resistive photoresponse of YBa2Cu3O7−δ films using low power 0.8 and 10.6 μm laser radiation
Authors: Lindgren M. , Trifonov V. , Zorin M. , Danerud M. , Winkler D. , Karasik B. S. , Gol’tsman G. N. , Gershenzon E. M.
Published: July 2002

Thin YBa2Cu3O7−δ laser deposited films were patterned into devices consisting of ten parallel 1 μm wide strips. Nonequilibrium picosecond and bolometric photoresponses were studied by the use of 17 ps full width at half-maximum laser pulses and amplitude modulated radiation from an AlGaAs laser up to 10 GHz and from a CO2 laser up to 1 GHz. The time and frequency domain measurements were in agreement. The fast response can be explained by electron heating. The use of low optical power and a sensitive measurement system excluded any nonlinear transient processes and kinetic inductance changes in the superconducting state. At 1 GHz modulation frequency, the responsivity was ∼1.2 V/W both for 0.8 and 10.6 μm wavelengths. The sensitivity of a fast and spectrally broadband infrared detector is discussed.
Electroluminescence from trap-limited current transport in vacuum deposited organic light emitting devices
Authors: Burrows P. E. , Forrest S. R.
Published: July 2002

We investigate the current transport and electroluminescence mechanisms controlling the efficiency of organic heterojunction, green light emitting devices consisting of tris-(8-hydroxyquinoline) aluminum (Alq) and a hole transport layer (HTL). From the dependence of the current-voltage characteristics and luminescence efficiency on layer thickness and HTL composition, we find that current is controlled by trap-limited transport of electrons injected into Alq. Electroluminescence efficiency, on the other hand, is controlled by hole injection from the HTL into Alq. The luminescence is generated by recombination of electrons localized at a high density trap in the Alq, and holes injected from the HTL. These results provide insight into the fundamental processes which control the operating voltage and luminescence efficiency of vacuum deposited organic light emitters.
Two-dimensional model of ion dynamics during plasma source ion implantation
Authors: Sheridan T. E. , Alport M. J.
Published: July 2002

Ion dynamics in the plasma sheath following the application of a negative voltage pulse to a two-dimensional target are modeled using a time-dependent, two-fluid simulation. The target considered is a square bar of infinite length. We find that the sheath focuses ions near to, but not on, the corner of the bar, resulting in an enhancement of the dose received there.
Optical and electrical degradations of GaAs-based laser diodes grown on Si substrates
Authors: Egawa T. , Jimbo T. , Hasegawa Y. , Umeno M.
Published: July 2002

A GaAs-based laser diode grown on a Si-substrate suffers from degradation, which results from the deterioration of electrical and optical characteristics. An initial deterioration of a p-n junction is observed in a reverse current-voltage (I-V) characteristic, and becomes ohmic-like under a higher ambient temperature and a larger forward current. Electroluminescence observation shows that the optical deterioration is caused by the growth of dark spot regions, which act as nonradiative recombination regions. The deterioration of the I-V characteristic is probably due to defect-accelerated impurity diffusion because the growth of GaAs/Si involves a high dislocation density, a large tensile stress and a large amount of Si near the GaAs/Si interface.
Uncooled InSb/In1−xAlxSb mid-infrared emitter
Authors: Ashley T. , Elliott C. T. , Gordon N. T. , Hall R. S. , Johnson A. D. , Pryce G. J.
Published: July 2002

Using heterostructures of InSb/In1−xAlxSb, grown by molecular beam epitaxy, diodes have been fabricated which emit at room temperature with a peak wavelength in the range 5.5–5.8 μm and an internal efficiency of 0.2%.
Finite-element modeling of stress distribution and migration in interconnecting studs of a three-dimensional multilevel device structure
Authors: Shi L. T. , Tu K. N.
Published: July 2002

A finite-element method taking into account plasticity and temperature-dependent properties of materials was used to calculate the stress distribution in interconnecting studs of a three-dimensional multilevel device structure. A good correlation between the calculated locations of stress concentration and the experimentally observed failure sites was obtained. On the basis of this, the failure mechanisms associated with different stress components were inferred. In addition, the calculated locations of stress concentration were found to migrate as temperature changed. The phenomenon was also observed experimentally.
High-resolution spatial light modulators using GaAs/AlGaAs multiple quantum wells
Authors: Bowman S. R. , Rabinovich W. S. , Kyono C. S. , Katzer D. S. , Ikossi-Anastasiou K.
Published: July 2002

We report improved performance in semi-insulating GaAs/AlGaAs quantum well based spatial light modulators grown by molecular beam epitaxy. The optically addressed modulator reported here are of a new design and have significantly higher spatial resolution than previously reported devices. Strong diffraction efficiencies are described for spatial periods as fine as 2.6 μm at framing rate as high as 600 kHz. Two modulators are characterized, one with x=0.1 and the other with x=0.3 for the AlxGa1−xAs quantum barriers of the superlattices.
Electron emission from chemical vapor deposited diamond and dielectric breakdown
Authors: Shovlin Joseph D. , Kordesch Martin E.
Published: July 2002

After coating with a smooth, nonreactive, sputtered gold layer, previously nonemitting chemical vapor deposited diamond films are observed to emit electrons in an applied field of 30–50 kV/cm in an electron emission microscope. The gold overlayer increases the effective field strength applied to the film. The consequent dielectric breakdown of the film provides conductive channels for the observed electron emission.
Generation of 21.5 T by a superconducting magnet system using a Bi2Sr2CaCu2Ox/Ag coil as an insert magnet
Authors: Tomita Naruaki , Arai Mikako , Yanagisawa Eiji , Morimoto Takeshi , Fujii Hiroki , Kitaguchi Hitoshi , Kumakura Hiroaki , Inoue Kiyoshi , Togano Kazumasa , Maeda Hiroshi , Nomura Katsumi
Published: July 2002

We fabricated a Bi2Sr2CaCu2Ox/Ag pancake coil by applying a dip-coating process, which was used as an insert coil of conventional superconducting magnet system. The critical current of the insert coil at saturated superfluid helium temperature (1.8 K) in the bias field of 20.8 T, was 275 A, and the field generated at this current was 0.7 T. As a result, we could achieve the field generation of 21.5 T at the center of the magnet system which was the highest field obtained by the full superconducting state.
Observations on the limits to p-type doping in ZnSe
Authors: Fan Y. , Han J. , He L. , Gunshor R. L. , Brandt M. S. , Walker J. , Johnson N. M. , Nurmikko A. V.
Published: July 2002

In this letter secondary ion mass spectroscopy measurements of nitrogen concentrations in p-type ZnSe and ZnTe, doped using a nitrogen plasma source with molecular beam epitaxy, are correlated with transport data from the temperature-dependent Hall effect measurements. The results suggest that, at least for the growth conditions employed in this study, the nitrogen acceptor solubility is the controlling factor in determining that the acceptor concentration in ZnTe exceeds that in ZnSe by about one order of magnitude despite the similar growth conditions.
High-energy electron-free plasma source
Authors: Yabe Eiji , Takahashi Keiji
Published: July 2002

A capacitively coupled 13.56-MHz radio-frequency (rf) plasma is produced in the presence of a magnetic ring-cusp field. In order to determine an accurate electron energy distribution function (EEDF) and an electron density by means of Langmuir probe in this rf plasma, an asymmetrical double probe was used. The measured EEDF showed the Maxwellian-like distribution from a drift motion in the magnetic ring-cusp field. Furthermore, it is seen that this rf plasma is favorable for excluding high-energy electrons. The electron density for helium (He) is proportional to the rf power, being equal to 2×1010 cm−3 at 400 W.
Relaxation of InGaAs layers grown on (111)B GaAs
Authors: Sacedón A. , Calle F. , Alvarez A. L. , Calleja E. , Muñoz E. , Beanland R. , Goodhew P.
Published: July 2002

The relaxation behavior of InGaAs layers grown by molecular beam epitaxy on (111)B GaAs is investigated and compared with simultaneously grown (100) reference samples. Surface morphology, defect microstructure, and optical quality of the layers during the relaxation process are studied by Nomarski interference contrast, transmission electron microscopy, low-temperature photoluminescence, and Raman spectroscopy. These techniques reveal an inhomogeneous and anisotropic relaxation in (111) samples. In (111) samples, the increase of critical thickness and the slower relaxation dependence on thickness, as compared with the (100) reference samples, is discussed
Thermal stability and electrical properties of hydrogenated amorphous carbon film
Authors: Callegari A. , Buchanan D. A. , Hovel H. , Simonyi E. , Marwick A. , Lustig N. E.
Published: July 2002

The thermal stability of a plasma-deposited amorphous carbon film was enhanced by using acetylene heavily diluted with He. The film preserved its hardness even after annealing at ≂590  °C in Ar/H2, while a film deposited in similar conditions in an acetylene/Ar mixture softened significantly. The I-V characteristics of n- and p-type Si/amorphous carbon heterojunctions showed a 0.2 eV discrepancy. This is attributed to an offset in the conduction band of the amorphous carbon with respect to Si.
Real-time investigations of GaAs surface cleaning with a hydrogen electron cyclotron resonance plasma by optical reflection spectroscopy
Authors: Weegels L. M. , Saitoh T. , Kanbe H.
Published: July 2002

The composition changes during GaAs oxide removal and the subsequent cleaning with a hydrogen electron cyclotron resonance plasma have been investigated with real-time optical reflection spectroscopy. It is found that the oxide is not completely removed at low temperatures, resulting in a thick damaged surface region. At moderate temperatures (300–500 °C) the plasma exposure is characterized by a two-step process: a removal of the native oxide in a few seconds followed by a gentle etch of the GaAs. In the latter step the plasma exposure leads to a surface region with little damage to the crystal.
Counter-oxidation of superficial Si in single-crystalline Si on SiO2 structure
Authors: Takahashi Yasuo , Ishiyama Toshihiko , Tabe Michiharu
Published: July 2002

This work proposes an oxidation mechanism for single-crystalline Si overlying a buried SiO2 layer (SOI wafer). Experimental results show that not only the surface oxide but also the buried oxide layer of the SOI wafer grows during the thermal oxidation process. The oxidation behavior is analyzed with a simple model including oxygen diffusion through the superficial single crystalline Si layer, which agrees well with the experimental data. Furthermore, oxygen penetration through the superficial Si layer is verified by oxidation experiments using isotope oxygen.
Stable secondary electron emission observations from chemical vapor deposited diamond
Authors: Mearini G. T. , Krainsky I. L. , Dayton J. A. , Wang Yaxin , Zorman Christian A. , Angus John C. , Hoffman R. W.
Published: July 2002

High secondary electron emission (SEE) from chemical vapor deposited (CVD) diamond films (σ=14–48) has been reported previously. Effective negative electron affinity of the diamond surface due to hydrogen termination is believed to be responsible for these high yields. Typically the total secondary yield is unstable under continuous electron beam exposure due to desorption of the surface hydrogen but stable when exposed to electrons in a hydrogen environment. Recent observations of SEE from a CVD diamond film on Mo suggest that impurities on the diamond surface may lead to stable high secondary yields under continuous electron beam exposure without the use of hydrogen. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and Raman spectroscopy were used to characterize the diamond surface as well as the bulk.
New method for the study of mirror heating of a semiconductor laser diode and for the determination of thermal diffusivity of the entire structure
Authors: Bertolotti M. , Liakhou G. L. , Li Voti R. , Sibilia C. , Syrbu A. , Wang R. P.
Published: July 2002

A new method based on the photothermal deflection technique is described to determine the mirror temperature of a semiconductor laser diode as a function of intensity of drive current. The device’s effective thermal diffusivity can also be measured. A short theoretical discussion is presented together with experimental measurements performed on three different kinds of laser diodes.
Implantation and transient B diffusion in Si: The source of the interstitials
Authors: Eaglesham D. J. , Stolk P. A. , Gossmann H.-J. , Poate J. M.
Published: July 2002

Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during initial annealing, due to Si interstitials being emitted from the region of the implant damage. The structural source of these interstitials has not previously been identified. Quantitative transmission electron microscopy measurements of extended defects are used to demonstrate that TED is caused by the emission of interstitials from specific defects. The defects are rodlike defects running along 〈110〉 directions, which consist of interstitials precipitating on {311} planes as a single monolayer of hexagonal Si. We correlate the evaporation of {311} defects during annealing at 670 and 815 °C with the length of the diffusion transient, and demonstrate a link between the number of interstitials emitted by the defects, and the flux of interstitials driving TED. Thus not only are {311} defects contributing to the interstitial flux, but the contribution attributable to {311} defect evaporation is sufficient to explain the whole of the observed transient. The {311} defects are the source of the interstitials.
Optimization of growth conditions for strain compensated Ga0.32In0.68As/Ga0.61In0.39As multiple quantum wells
Authors: Smith A. D. , Briggs A. T. R. , Scarrott K. , Zhou Xiao , Bangert U.
Published: July 2002

The results of an investigation into the growth of Ga0.32In0.68As/Ga0.61In0.39As strain compensated multiple quantum well stacks are presented. We show that these structures, which contain alloys that are not prone to compositional clustering, do suffer from thickness modulated growth. A growth strategy has been developed to inhibit this phenomenon and a 50 well, strain compensated stack has been grown with planar and abrupt interfaces.
Gain dynamics of ionic excimer (XeCs)+ emission at 160 nm in Ar/Xe/Cs mixtures
Authors: Kochetov I. V. , Napartovich A. P. , Lo Dennis , Lawless John L.
Published: July 2002

Gain and absorption of the ionic excimer (XeCs)+ emission at 160 nm in Ar/Xe/Cs mixtures were studied by kinetic model calculations. Both the e-beam and the self-sustained discharge excitation schemes were investigated. Model results indicate that when pumped by 20 ns, 1 MeV e-beam, the mixtures exhibit only loss as absorption due to atomic Cs dominates. Under discharge pumping, 99.9% of the atomic Cs is ionized. Positive net gain up to 2%/cm in the ternary discharge plasma is predicted by model calculations.
In situ spectroscopic ellipsometry of porous silicon layers annealed under ultrahigh vacuum
Authors: Larré A. , Halimaoui A. , Glowacki F. , Ferrieu F. , Campidelli Y. , Bensahel D.
Published: July 2002

In situ spectroscopic ellipsometry measurements in the 1.8–2.8 eV spectral range were performed on porous silicon (PS) layers annealed in an ultrahigh vacuum chamber up to 600 °C. It is shown that both the refractive index and the absorption coefficient increase after the thermal anneal and the effect is reversible when samples are returned to atmosphere and HF dipped. These changes in the optical properties of the material can be attributed to an intrinsic strain modification in the PS cellular structure induced by hydrogen desorption upon annealing.
Post-anodization filtered illumination of porous silicon in HF solutions: An effective method to improve luminescence properties
Authors: Koyama Hideki , Nakagawa Takashi , Ozaki Tsuyoshi , Koshida Nobuyoshi
Published: July 2002

A useful method is presented to improve the luminescence efficiency of porous silicon (PS) based on the post-anodization illumination of samples in HF solutions. In the present method the illumination is performed by a white lamp through sharp-cut long-wavelength-pass filters to remove the short wavelength component from the illumination light. The PS samples prepared by this method exhibited the visible photoluminescence (PL) with an efficiency of one order of magnitude higher than those illuminated without filters. The efficiency improvement is attributed to the reduction of the deteriorative surface oxidation of Si crystallites in PS. The filtered illumination technique is also useful to produce a larger PL blue shift and precise control of PL spectra.
Production of uniform large-diameter radio-frequency discharge plasma
Authors: Li Yunlong , Iizuka Satoru , Sato Noriyoshi
Published: July 2002

A new radio-frequency (rf) discharge plasma source at frequency of 13.56 MHz is presented. The rf plasma is produced by a modified magnetron-typed rf discharge using a cylindrical electrode with permanent magnet rings. The electron density of 2.5×1010 cm−3 with an electron temperature of 3.7 eV, uniform within a few percent over 50 cm in diameter, is obtained on both sides at 5–6 cm from the axial center of the rf electrode when the rf power is 600 W under argon pressure of 3.6×10−4 Torr.
Microstructure and photoluminescence of GaN grown on Si(111) by plasma-assisted molecular beam epitaxy
Authors: Ohtani A. , Stevens K. S. , Beresford R.
Published: July 2002

Wurtzite GaN films on AlN buffer layers were grown on Si(111) by plasma-assisted molecular beam epitaxy. High resolution x-ray diffraction and scanning electron microscope studies indicate that the mosaic disorder decreases with increasing film thickness and increasing growth temperature. The grain size increases with the growth temperature. The best (0002) diffraction peak full width at half-maximum is 22 arcmin for a film 1.7 μm thick. Prominent low-temperature exciton luminescence is observed at 3.46 eV. The plasma I-V characteristics are measured with a Langmuir probe near the growth position and analyzed to extract the nitrogen ion density and energy for the growth conditions used.
Room-temperature preparation of the highly crystallized luminescent CaWO4 film by an electrochemical method
Authors: Cho Woo-Seok , Yashima Masatomo , Kakihana Masato , Kudo Akihiko , Sakata Tadayoshi , Yoshimura Masahiro
Published: July 2002

Highly crystallized polycrystalline film of single-phase CaWO4 has been prepared on a tungsten substrate at room temperature in an alkaline solution containing calcium ions by an electrochemical method with the current density of 1 mA/cm2. This film showed blue emission (456 nm wavelength) with excitation light (254 nm wavelength) at room temperature.
Fabrication of magnetic quantum wires by step-flow growth of cobalt on copper surfaces
Authors: de la Figuera J. , Huerta-Garnica M. A. , Prieto J. E. , Ocal C. , Miranda R.
Published: July 2002

One-dimensional-like Co structures 50-Å-wide and 3000-Å-long have been grown by decoration of the monoatomic steps of a Cu(111) surface and visualized with scanning tunneling microscopy. In order to achieve step-flow growth, terrace width, evaporation rate, and substrate temperature have been carefully adjusted. The choice of the (111) terrace orientation and 〈11̄0〉 compact steps ensures a homogeneous width of the Co wires and a lateral confinement of minority-spin electrons.
Electron temperature fluctuation noise in hot-electron superconducting mixers
Authors: Ekström H. , Karasik B.
Published: July 2002

An experimental study is presented of the output noise in hot-electron superconducting NbN bolometer mixers. Fluctuations of the electron temperature have been shown to be the main source of electrical noise. The rolloff frequency of the spectral noise density corresponds well to the inverse electron temperature relaxation time (≊230 ps). Equivalent noise data have been obtained for the device at a physical temperature within superconducting transition region, and at a somewhat lower physical temperature with the device pumped by 350 GHz radiation to reach the same operating point. The single sideband (SSB) mixer noise temperature due to intrinsic noise mechanisms for the NbN device is estimated to 360 K independent of radiation frequency. A larger critical current density may promote a further reduction of the intrinsic conversion loss of the mixer device.
Effects of chlorine addition on the silicon dioxide properties deposited with remote plasma enhanced chemical vapor deposition at low temperatures
Authors: Park Young-Bae , Rhee Shi-Woo
Published: July 2002

The properties of SiO2 films deposited in a remote plasma enhanced chemical vapor deposition (RPECVD) process with chlorine addition into the SiH4–N2O reactants has been studied. With Cl2 addition, the interface trap density (located at ∼Ev+0.3–0.35 eV) was decreased and strained silicon bonds were relaxed. As chlorine partial pressure and deposition temperature were increased, however, porosity and surface roughness of the film were increased due to the formation and desorption of Si–Cl or O–Cl bonds.
Phosphorus ablation process as a hydrogen atom probe in a remote H2 plasma reactor
Authors: Bruno G. , Losurdo M. , Capezzuto P.
Published: July 2002

The ablation process of phosphorus by H atoms has been applied to the measurement of the H atom density in the downstream current of a H2 plasma. The calibration of the etching rate in terms of absolute density of H atoms has been done on the basis of their decay kinetics in the afterglow region. H atom density data have been determined by operating H2 plasmas at different values of gas flow rate, rf power, and pressure.
Analysis of the lumped τ2 effect in relaxation calorimetry
Authors: Shepherd John P.
Published: July 2002

In thermal relaxation calorimetry, the heat capacity can be calculated from the time constant τ1=Cp/Kb of the exponential decay of the cooling curve. If the thermal bond between the sample and sample holder is poor, the cooling curve is described by T−T0=A1 exp(−t/τ1)+A2 exp(−t/τ2). Analysis shows that the heat capacity of the sample plus addenda is Cp=Kb (A1τ1+A2τ2)/(A1+A2). For most cases, a good approximation is given by Cp=Kb (A1τ1/ΔT), which does not require the measurement of A2 or τ2. An expression is presented for calculating the conductance of the thermal bond of the sample to the substrate.
Real-time operating 16-bit microcomputer in experimental physics
Authors: Agusti i Cullell J. , Lecas M. , Brenot J. C. , Houver J. C.
Published: July 2002

A complete system performing data acquisition as well as process control is presented. This apparatus is based on a commercially available microcomputer coupled with a quite simple hardware environment. The high versatility of the device is obtained through a more elaborate software whose main ideas are detailed. Two typical applications in the atomic physics field are described.
Strain-gauge transducer signal conditioning with square-wave ac excitation and thermal error compensation
Authors: Hill Kenneth D.
Published: July 2002

The paper describes a signal conditioning circuit for strain-gauge pressure transducers of the metal wire and metal foil types which provides square-wave ac excitation of the transducer, amplification of the signal, and compensation for both the thermal zero shift and the thermal sensitivity shift of the transducer.
Computer-controlled mass spectral search for reaction products in a thermal desorption experiment
Authors: Liu A. C. , Friend C. M.
Published: July 2002

A method for monitoring a broad mass range (>100 masses) in a single thermal desorption experiment using a conventional quadrupole mass spectrometer and microcomputer is described in this article. This approach is used to eliminate the possibility of overlooking one or more reaction products. Typical results obtained using the experimental scheme described herein are presented for the reaction of cycloheptatriene on W(100)–(5×1)-C, and are compared with thermal desorption data collected using a more conventional configuration. While the mass scanning system provides useful qualitative information regarding desorption products, conventional experiments are still necessary for extracting results of a quantitative nature.
Technique of surface-wave scattering and calibration with simple liquids
Authors: Sano M. , Kawaguchi M. , Chen Y-L. , Skarlupka R. J. , Chang T. , Zografi G. , Yu H.
Published: July 2002

Heterodyne detection of light scattered from capillary waves is used to study the surface properties of the air–liquid interface. A diffraction grating is employed to select a precise ripplon wave vector k and to provide a stable local oscillator field. The optics are designed to form a real image of the grating on the surface, thus allowing the measurements to be reproducible within 5%. The power spectrum detected in frequency domain is well fitted by a Lorentzian profile for the range of ripplon wave vectors 260≤k≤390 cm−1. The shape of the scattered spectra at each wave vector is corrected for the incident beam profile by effecting a convolution of the Lorentzian and Gaussian functional forms. The surface tensions and the kinematic viscosities of water, anisole, and ethanol are deduced from the ripplon dispersion relation corrected to the first order in damping, and found to be within 5% of the literature values. Thus we confirm the validity of approximations made for the instrumental function and the dispersion relation.
Determination of the two-dimensional density distribution in a tokamak plasma using phase-imaging interferometry (invited)
Authors: Doyle E. J. , Howard J. , Peebles W. A. , Luhmann N. C.
Published: July 2002

Conventional interferometer systems used on fusion devices are typically limited to approximately ten channels or views, thus precluding the use of tomographic reconstruction techniques. Instead, a priori assumptions have to be made in order to obtain the electron density distribution. To overcome these problems, interferometer systems have been developed at the University of California, Los Angeles (UCLA), which use imaging techniques to provide many channels per probe beam. Using a two-dimensional, 40-channel, imaging far infrared (FIR) interferometer measurements have been made of the density distribution in the minor cross section of the UCLA Microtor tokamak. The heterodyne interferometer consists of two probe beams expanded so as to completely fill orthogonal views of the plasma cross section. These views are then imaged onto two 20-channel, linear microbolometer detector arrays. Using data from this system, the spatial electron density distribution in a tokamak plasma has been recovered for the first time using tomographic reconstruction techniques.
Precision limits of lock-in amplifiers below unity signal-to-noise ratios
Authors: Gillies G. T. , Allison S. W.
Published: July 2002

An investigation of noise-related performance limits of commercial-grade lock-in amplifiers has been carried out. The dependence of the output measurement error on the input signal-to-noise ratio was established in each case and measurements of noise-related gain variations were made.
Simple, versatile, and compact capacitance dilatometer
Authors: Steinitz M. O. , Genossar J. , Schnepf W. , Tindall D. A.
Published: July 2002

We describe a novel capacitance dilatometer, which is simple to construct, compact in size, and which can be used with samples of any shape, size, conductivity, or dielectric constant.
Inductively insulated Marx generator
Authors: Rhee M. J.
Published: July 2002

We describe a modified Marx generator system in which each capacitor stage is insulated by an inductive cavity instead of by insulating dielectric eliminating most of the insulation volume and circuit inductance which are inevitable in the conventional Marx generator system. This feature permits use of this system as a fast pulsed power system of very high voltage by stacking a very large number of stages. Necessary relations needed for pulsed power applications are derived by a simple circuit analysis. Design parameters of a charged particle beam accelerator are given as an example illustrating the utility of this concept.
Spinning water film power meter for high-power cw lasers
Authors: Seguin H. J. J. , Seguin V. A. , Nath A. K. , Radzion J.
Published: July 2002

The design, construction, and operational characteristics of a new type of power meter for high average power cw lasers is described. This multikilowatt calorimeter unit employs a novel high-velocity spinning water film to provide complete absorption of the incident laser radiation, at either high- or low-power levels, while still retaining good dynamic response and sensitivity. The design is sufficiently simple such that it can be easily fabricated from readily available workshop materials. Utilization of a suitably selected recirculating absorbing dye allows the power meter to be used with a number of different cw lasers.
Determination of the detection efficiency of a channelplate electron multiplier
Authors: Sakurai Toshio , Hashizume T.
Published: July 2002

Making use of a technique of layer-by-layer field evaporation developed in the time-of-flight atom probe, the detection efficiency of a microchannelplate supplied by Galileo Electro Optics is determined. The detection efficiency for single ion impact is 57±8%, close to the fraction of the active channel area of the surface. It increases slightly, but no more than a few percent, even the front surface is positively biased.