bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of interfacial contamination on the structure and barrier height of Cr/GaAs Schottky contacts
Authors: Liliental-Weber Z. , Newman N. , Washburn J. , Weber E. R. , Spicer W. E.
Published: July 2002

The structure of as-deposited and annealed Cr/GaAs Schottky contacts was investigated by high resolution and analytical electron microscopy. The Schottky barrier height for contacts prepared by cleavage and in situ metallization in ultrahigh vacuum was stable upon annealing up to 370 °C in N2. In contrast, the contacts prepared on air-exposed substrates show an increase of the barrier height by 80 meV during annealing in the same range of temperatures. Comparing these two types of contacts, distinct differences in the grain size, presence of an oxide layer at the interface, and change in stoichiometry in the substrate beneath the contact were detected.
Laser plasma source of amorphic diamond
Authors: Collins C. B. , Davanloo F. , Juengerman E. M. , Osborn W. R. , Jander D. R.
Published: July 2002

Amorphic diamond films characterized by a high percentage of sp3 bonds have been prepared in an UHV environment with a laser plasma source of carbon ions. Peak power densities in excess of 1011 W/cm2 were found necessary to produce films at growth rates of 0.5 μm/h over areas of 20 cm2 having optical quality sufficient to show bright interference colors.
Current oscillations at high electrical fields in the two-dimensional electron gas in GaAs/AlGaAs heterostructures
Authors: Hendriks P. , Staring A. A. M. , van Welzenis R. G. , Wolter J. H. , Prost W. , Heime K. , Schlapp W. , Weimann G.
Published: July 2002

In the two-dimensional electron gas (2DEG) of GaAs/AlGaAs heterostructures, we observe a new type of oscillation in the current at electric fields above 0.8 kV/cm. These oscillations have two characteristic frequencies, around 200 MHz and 2.5 GHz. We show that these oscillations arise from properties of the 2DEG and depend on both electric field and magnetic fields. They disappear abruptly when magnetic fields above 0.5 T are applied.
AlGaSb avalanche photodiode exhibiting a very low excess noise factor
Authors: Miura S. , Mikawa T. , Kuwatsuka H. , Yasuoka N. , Tanahashi T. , Wada O.
Published: July 2002

An Al0.053Ga0.947Sb avalanche photodiode (APD) has been fabricated and tested. First, measurement of an excess noise factor as well as an ionization rate ratio has been demonstrated. A low excess noise factor of 3.8, which is 1.2 dB lower than the conventional GaInAs APD, has been obtained. From this excess noise factor, the effective value of the hole-to-electron ionization rate ratio (keff) has been determined as high as 5, being in good agreement with the hole-to-electron ionization rate ratio (β/α) given by the multiplication data. This keff value is the highest ever reported for long-wavelength III-V APDs.
High-field mobility of light holes in strained quantum wells
Authors: Hjalmarson Harold P.
Published: July 2002

The small mass of light holes in strained quantum wells leads to high mobility at low fields. However, at high fields, the holes become hot and populate the heavy hole band, thereby greatly reducing their mobility. An analysis shows that the high-field mobility primarily depends on Δ, the strain splitting of the light and heavy holes, and ℏω0, the optical phonon energy. If Δ<ℏω0, the light holes transfer to the heavy hole band at relatively low power and small fields. If Δ≊ℏω0, the low-field mobility is greatly enhanced without producing negative differential mobility at high fields. If Δ>ℏω0, the high mobility persists until the applied power per carrier P exceeds a characteristic power P0 . Above this power, negative differential mobility (a Gunn effect) occurs when the light holes transfer to the heavy hole band. For thin p-doped In0.2 Ga0.8 As/GaAs single-strained quantum wells, Monte Carlo calculations show that P0 ≊5×10−8 W/carrier.
Fast and slow surface electrons in HgCdTe
Authors: Emtage P. R. , Temofonte T. A. , Noreika A. J. , Seiler C. F.
Published: July 2002

Two groups of interface electrons, one of very high mobility (105 cm2 /V s), have been found in p-type Hg1−x Cdx Te of low band gap (x≤0.2) from studies of the Hall effect up to 50 kG. Both groups are associated with the growth interface. The number of electrons in each group changes rapidly with temperature down to 15 K, causing anomalies in the low-field Hall coefficient.
Alloy broadening of the emission barrier of the D
X center in aluminum gallium arsenide
Authors: Subramanian S. , Anand S. , Chakravarty S. , Arora B. M.
Published: July 2002

The effect of alloy fluctuations on the emission barrier of the DX center in aluminum gallium arsenide (AlGaAs) is studied by constant capacitance deep level transient spectroscopy using Si-doped and Sn-doped samples grown by different growth techniques. All the samples showed single broadened peaks which were analyzed by assuming a Gaussian distribution for the emission barrier. The full width at half maximum for the emission barrier spread was found to be the same (∼0.05+0.005 eV) for all the samples and is of the same order as the reported capture barrier spread for Si-doped AlGaAs, which strongly suggests that the binding energy spread of the DX center in AlGaAs is very small.
Passivation of pinned n-GaAs surfaces by a plasma-polymerized thin film
Authors: Rao V. J. , Manorama Vardhireddy , Bhoraskar S. V.
Published: July 2002

The passivating effects of the plasma-polymerized thiophene thin film on the intrinsic properties of n-GaAs surfaces have been investigated by means of scanning electron microscopy–electron beam induced current and capacitance-voltage techniques. Reduction of the surface recombination velocity and the surface barrier at the interface between polymer and GaAs has been reported. These results indicate that the Fermi level is no longer pinned at midgap, but is moved closer to the conduction band. We discuss a possible unpinning mechanism.
Novel self-aligned W/TiN/TiSi2 contact structure for very shallow junctions and interconnections
Authors: Joshi R. V. , Moy D. , Brodsky S. , Charai A. , Krusin-Elbaum L. , Restle P. J. , Nguyen T. N. , Oh C. S.
Published: July 2002

This letter describes a novel structure for very large scale integrated contact and interconnect technology that involves selective deposition of W on self-aligned TiN/TiSi2. The TiN layer serves to protect reaction between WF6 and TiSi2 and underlying Si during W deposition as well as to promote adhesion of W layer and minimize contact resistance. The selective deposition of W on TiN, very difficult with conventional hydrogen reduction process, is accomplished by employing a recently developed silane reduction process. The structure prevents silicon consumption leading to the encroachment commonly found in tungsten deposited directly on silicon in very shallow junctions. It is demonstrated that such a structure results in low contact resistance and junction leakages and is applicable to subhalf-micron devices. Tungsten with low resistivity of 8–9 μΩ cm can be achieved at room temperature with the resulting drop by a factor of 3–4 at liquid-nitrogen temperature making the structure more attractive for low-temperature application.
Thermal stability of tungsten ohmic contacts to the graded-gap InGaAs/GaAs/AlGaAs heterostructure
Authors: Lahav Alex , Ren F. , Kopf R. F.
Published: July 2002

Nonalloyed tungsten ohmic contacts to the Inx Ga1−x As/GaAs/Aly Ga1−y As (x=0.4, y=0.25) graded-gap heterostructure showed excellent surface morphology after annealing of up to 1000 °C for 10 s. The minimum value for the specific contact resistance (1.3×10−6 Ω cm2 ) was obtained following annealing at 600 °C for 10 s. The increase in contact resistivity at higher temperatures was related to the increase in the heterostructure sheet resistance due to layer intermixing and In and Ga outdiffusion. The W/InGaAs graded-gap refractory ohmic contact can be used as a self-aligned emitter in heterojunction bipolar transistors.
General interfacial layer expression for the equilibrium Schottky barrier height and its application to annealed Au-GaAs contacts
Authors: Horváth Zs. J.
Published: July 2002

A general expression based on the interfacial layer model is derived for the equilibrium Schottky barrer height, and it is applied to annealed Au-GaAs contacts. Relations between the experimental barrier height, relative interfacial layer thickness and interface charge values, and the interface state energy distribution spectra are presented. The validity of the interfacial layer model is demonstrated. The obtained barrier height values and the near-ohmic behavior after high-temperature annealing are probably due to ionized donor type interface states in the upper half of the forbidden gap.
Silicide/silicon Schottky barriers under hydrostatic pressure
Authors: Werner Jürgen H.
Published: July 2002

We investigate several silicide/silicon Schottky barrier heights under hydrostatic pressures up to 10 kbar. The barriers of polycrystalline TiSi2, PtSi, and WTi on n-type Si decrease with −1.l3, −1.35, and −1.42 meV/kbar, respectively. The coefficients for A- and B-type NiSi2/Si amount to −0.77 and −0.89 meV/kbar and are too small to support models which ascribe the l40 meV barrier difference of these two types to different interface bond lengths. The pressure coefficients are, on the other hand, within a range of predictions of Cardona and Christensen which are based on pure bulk properties.
Pb-doped Bi-Sr-Ca-Cu-O thin films
Authors: Tanaka Atsushi , Machi Takato , Kamehara Nobuo , Niwa Koichi
Published: July 2002

We prepared Pb-doped Bi-Sr-Ca-Cu-O thin films by rf-magnetron sputtering with multiple targets. A Bi2O3 target compensated for lack of Bi and a PbO target was used to dope Pb into films in sufficient quantity. In thin films, Pb evaporates easily during sintering. We prepared heavily Pb-doped films and they exhibited zero resistance at 94.5 K with sintering as short as 10 min. After 1 h of sintering, more than half of the Pb evaporated and the film showed a sharp transition to its superconducting state. Tce was 106.5 K. Pb doping promotes high Tc phase formation; however, the high Tc phase does not always have to contain Pb.
Fully textured growth of Y1Ba2Cu3O7−δ films by sputtering on LiNbO3 substrates
Authors: Höhler A. , Guggi D. , Neeb H. , Heiden C.
Published: July 2002

We present details about the deposition of thin Y1Ba2Cu3O7−δ films on single-crystal LiNbO3 substrates by planar dc magnetron sputtering. Among other data, results of transition temperature (Tc(R=0) =88 K) and critical current density (jc >2×109 A/m2 at 77 K) plus some details about film-to-substrate orientation which is present in all three crystallographic directions are reported.
Microstructure of heteroepitaxial Si/CoSi2/Si formed by Co implantation into (100) and (111) Si
Authors: Bulle-Lieuwma C. W. T. , van Ommen A. H. , van IJzendoorn L. J.
Published: July 2002

Heteroepitaxial Si/CoSi2/Si structures have been synthesized by high-dose implantation of Co into (100) and (111) Si at an energy of 170 keV and subsequent annealing. In the as-implanted state the implanted Co is found to be present as CoSi2. For a dose of 2×1017 Co/cm2, the Co is present in the form of epitaxial precipitates, which exhibit both the aligned (A-type) CoSi2 and twinned (B-type) orientation. For a higher dose of 3×1017 Co/cm2, a monocrystalline epitaxial CoSi2 layer near the top of the implanted Co distribution is formed during the implantation. The heteroepitaxial structures that are formed in this way are fully aligned. In contrast, when these structures are formed by sequential surface deposition techniques, twinning occurs at every Si/CoSi2 interface. The formation of the aligned orientation of the buried CoSi2 layer can be attributed to the larger stability of aligned precipitates as compared to twin-oriented precipitates.
Critical currents at 77.3 K under magnetic fields up to 27 T for an Y-Ba-Cu-O film prepared by chemical vapor deposition
Authors: Watanabe K. , Yamane H. , Kurosawa H. , Hirai T. , Kobayashi N. , Iwasaki H. , Noto K. , Muto Y.
Published: July 2002

Critical currents of an Y1Ba2Cu3O7–δ film prepared by a chemical vapor deposition technique have been measured resistively. Excellent critical current properties in high fields up to 27 T are obtained at 77.3 K. The value of Jc is 4.1×105, 1.9×105, and 6.5×104 A/cm2 at 2, 10, and 27 T, respectively. The upper critical field defined by zero resistivity is estimated to be 35 and 180 T at 77.3 and 0 K, respectively. A peak effect in the critical current is observed at high fields.
Single target sputtering of superconducting YBa2Cu3O7−δ thin films on Si (100)
Authors: Migliuolo M. , Stamper A. K. , Greve D. W. , Schlesinger T. E.
Published: July 2002

Thin films of YBa2Cu3O7−δ have been grown on (100) silicon substrates by single target rf diode sputtering. Yttria-stabilized zirconia buffer layers were used to minimize substrate-film reactions. Off-stoichiometric targets were used to compensate for differences between film and target stoichiometries. The composition of the superconducting layer is also influenced by post-deposition anneals, with films closer to the desired stoichiometry resulting from the higher temperature anneals. Film thicknesses spanned the 0.5–2.0 μm range and the onset and zero resistance ( ρ<10−7 Ω cm) temperatures were found to be 95 and 70 K, respectively, for 1.8-μm-thick films.
Transition range viscosity of rapidly quenched Bi-Ca-Sr-Cu-O glasses
Authors: Tatsumisago M. , Angell C. A. , Tsuboi S. , Akamatsu Y. , Tohge N. , Minami T.
Published: July 2002

As a precursor of high Tc superconductors, glasses in the system BixCaSrCu2Ow (x=1.5,2.7) have been prepared using twin-roller and metal-plate quenching procedures. Transition range viscosities have been measured on samples as thin as 0.02 mm using the beam-bending method with a technical modification. From the viscosity data, the system Bi-Ca-Sr-Cu-O can be characterized as a ‘‘fragile’’ liquid like the ZrF4-based fluorides. The possibility of drawing fibers of high Tc superconductor precursors is discussed on the basis of the temperature dependence of viscosity.
Submilliampere threshold current pseudomorphic InGaAs/AlGaAs buried-heterostructure quantum well lasers grown by molecular beam epitaxy
Authors: Eng L. E. , Chen T. R. , Sanders S. , Zhuang Y. H. , Zhao B. , Yariv A. , Morkoç H.
Published: July 2002

We report on low threshold current strained InGaAs/AlGaAs single quantum well lasers grown by molecular beam epitaxy. Broad-area threshold current densities of 114 A/cm2 at 990 nm were measured for 1540-μm-long lasers. Threshold currents of 2.4 mA at 950 nm were obtained for an uncoated buried-heterostructure device with a 2-μm-wide stripe and 425-μm-long cavity. With reflective coatings the best device showed 0.9 mA threshold current (L=225 μm). Preliminary modulation measurements show bandwidths up to 5.5 GHz limited by the detector response.
Carrier-lifetime control of photochemical dry etching using elevated impurity concentrations
Authors: Ashby C. I. H. , Myers D. R. , Vawter G. A. , Biefeld R. M.
Published: July 2002

Virtually total suppression of carrier-driven photochemical etching of semi-insulating GaAs, n-GaAs, and n+-GaAs has been achieved by indiffusion of Zn to a surface carrier concentration greater than 1020/cm3. This technique for photochemical reaction suppression can be used as a self-aligned etching technology for semiconductor device fabrication.
Folded-cavity transverse junction stripe surface-emitting laser
Authors: Takamori Takeshi , Coldren Larry A. , Merz James L.
Published: July 2002

A novel surface-emitting laser with a transverse junction stripe (TJS) and a folded-cavity configuration, which has an internal 45° mirror facet to direct the light normal to the surface, has been achieved for the first time. The fabrication of the 45° mirror facet was carried out using a simple angled reactive ion etching technique, and the laser performance yielded a threshold current of 31 mA and an external differential quantum efficiency of 24% per facet, which are comparable to those of conventional TJS lasers.
Ultralong minority-carrier lifetime epitaxial GaAs by photon recycling
Authors: Ahrenkiel R. K. , Dunlavy D. J. , Keyes Brian , Vernon S. M. , Dixon T. M. , Tobin S. P. , Miller K. L. , Hayes R. E.
Published: July 2002

The minority-carrier lifetime has been measured by time-resolved photoluminescence in epitaxial films of GaAs grown by metalorganic chemical vapor deposition. The measured lifetimes in thicker devices are 4 to 6 times the theoretical or radiative lifetime. These long lifetimes are the result of photon recycling or self-generation of the self-absorbed radiation.
Laser patterning and critical current measurements of submicrometer lines of Y-Ba-Cu-O
Authors: Zheng J. P. , Kim H. S. , Ying Q. Y. , Barone R. , Bush P. , Shaw D. T. , Kwok H. S.
Published: July 2002

Superconducting strips of 0.6 μm width were fabricated by direct laser writing on mirror-like Y-Ba-Cu-O thin films on various substrates. These films were grown by laser deposition without post-annealing. Laser ablation etching had no effect on the Tc and Jc until the lines were <1 μm wide. The 0.6-μm-wide strip showed some degradation of Tc. The critical current densities for all patterned lines were measured to be ∼4×106 A/cm2 at 20 ° K.
Optical phonon energies in pseudomorphic alloy strained layers
Authors: Haines M. J. L. S. , Cavenett B. C. , Davey S. T.
Published: July 2002

Using Raman scattering we have measured the longitudinal optic phonon energies of Ga1−xInxAs layers with 0.48≤x≤0.55 grown on InP substrates. In order to interpret these data successfully it was necessary to consider the effect of the strain induced by the lattice mismatch. Existing theory has been extended to consider the case of alloy pseudomorphic layers and is approximated to a linear form. This theory is also applied to Ga1−xInxAs on GaAs and compared with previously published data with 0≤x≤0.2. Close agreement between theory and experimental data is found indicating that the Raman technique, combined with this theory, can be used to measure the alloy composition of pseudomorphic strained layers of diamond or zinc blende structure accurately without the need for detailed experimental calibration. It is suggested that this method could be particularly useful for determining the composition of alloy layers in thin layer pseudomorphic Ga1−xInxAs/InP heterostructures.
High-frequency performance of InGaAs metal-semiconductor-metal photodetectors at 1.55 and 1.3 μm wavelengths
Authors: Soole J. B. D. , Schumacher H. , LeBlanc H. P. , Bhat R. , Koza M. A.
Published: July 2002

The high-speed performance of InGaAs interdigitated metal-semiconductor-metal (M-S-M) photodetectors illuminated with 1.55 and 1.3 μm wavelength radiation is modeled using a two-dimensional transit time calculation. Excellent agreement is found with the experimental pulse response of detectors with interdigital spacings of 2 and 3 μm. We study the dependence of the bandwidth on the device dimensions, and also examine the quantum efficiency. The results should aid the design of InGaAs M-S-M detectors with the optimum combination of bandwidth and efficiency for a given application.
Integrated injection-locked high-power cw diode laser arrays
Authors: Hohimer J. P. , Myers D. R. , Brennan T. M. , Hammons B. E.
Published: July 2002

We report the first integrated injection-locked high-power continuous-wave diode laser array with an on-chip independently controlled master laser. This device emits a near-diffraction-limited (0.5° full width at half maximum) single-lobed far-field emission beam at single-facet powers up to 125 mW. Also, by current tuning the emission wavelength of the master laser, we observe steering of the single-lobed emission over an angular range of 0.50° at a rate of −1.2×10−2 deg/mA. Our work demonstrates the feasibility of incorporating active optical injection and control in the structure of high-power diode laser devices.
Stability of boron- and gallium-induced surface structures on Si(111) during deposition and epitaxial growth of silicon
Authors: Headrick R. L. , Feldman L. C. , Robinson I. K.
Published: July 2002

We have undertaken a new set of experiments to investigate the behavior of adsorbed-impurity induced reconstructions at growth interfaces. We have observed a striking difference in the stability of the B(3)1/2×(3)1/2 and Ga(3)1/2×(3)1/2 two-dimensional structures at the interface between Si(111) and a-Si, and in their segregation behavior during molecular beam epitaxy crystal growth. This leads to a new model of dopant behavior in silicon molecular beam epitaxy.
Observation of intrinsic bistability in resonant tunneling diode modeling
Authors: Mains R. K. , Sun J. P. , Haddad G. I.
Published: July 2002

Intrinsic bistability has been observed experimentally and attributed to the effect on the potential profile from stored charge in the quantum well through Poisson’s equation. This effect leads to two possible current states corresponding to a single voltage within the negative resistance region. In this letter a simulation method is presented which clearly shows bistability in the current-voltage curve of a resonant tunneling diode. This method self-consistently combines a Thomas–Fermi equilibrium model for the electron concentrations outside the double-barrier structure with a quantum calculation for the concentration inside the structure.
Pb1−xSrxS/PbS double-heterostructure lasers prepared by hot-wall expitaxy
Authors: Ishida A. , Muramatsu K. , Takashiba H. , Fujiyasu H.
Published: July 2002

Pb1−xSrxS/PbS double-heterostructure stripe contact lasers were prepared for the first time using a hot-wall expitaxy technique. The laser operated up to 245 K pulsed (2.97 μm) and 174 K cw, which are the highest operating temperatures ever reported for any semiconductor diode lasers operating around 3 μm. In this letter preparation and properties of the Pb1−xSrxS lasers are presented.
Optical spectroscopy and field-enhanced emission of an oxide trap induced by hot-hole injection in a silicon metal-oxide-semiconductor field-effect transistor
Authors: Bourcerie M. , Marchetaux J. C. , Boudou A. , Vuillaume D.
Published: July 2002

The oxide traps created by hot-hole injection in the thin gate oxide of n-type metal-oxide-semiconductor transistor are optically and electrically characterized. Photodepopulation spectroscopy is used to investigate their photodetrapping kinetics. A threshold at 3 eV is found for the photoionization cross section. The effect of the electric field on the emission is analyzed using the Poole–Frenkel model. We show that a localized energy level in the range 2–3 eV below the SiO2 conduction band is associated with trap. It is spatially localized above the drain region of the transistor.
Low-temperature growth of HgTe and HgCdTe using methylallyltelluride
Authors: Ghandhi S. K. , Bhat I. B. , Ehsani H. , Nucciarone D. , Miller G.
Published: July 2002

HgTe and HgCdTe (MCT) layers have been grown by organometallic vapor phase epitaxy at low temperature by using methylallyltelluride (MATe), dimethylcadmium (DMCd), and elemental mercury. Use of MATe enabled the growth of layers in the 250–320 °C temperature range, which is 50 °C lower than the growth temperature when diisopropyltelluride is used as the tellurium alkyl, for the same growth rate. The layers were characterized by optical microscopy, double crystal x-ray diffraction, and Fourier transform infrared spectroscopy. Growth at 320 °C resulted in featureless surfaces for both HgTe and HgCdTe layers. The high quality of HgTe layers grown at 320 °C is demonstrated by the very narrow full width at half maximum of x-ray diffraction (29 arcsec), which is comparable to that of the CdTeZn substrates used in this study. MCT layers grown at 320 °C showed sharp interference fringes even for very thin layers, indicating the presence of a very sharp interface with the substrate.
High-precision band-gap determination of Al0.48In0.52As with optical and structural methods
Authors: Oertel D. , Bimberg D. , Bauer R. K. , Carey K. W.
Published: July 2002

The band gap of Al0.48In0.52As lattice matched to InP is determined with high precision at 1.5 and 300 K as 1.511 and 1.439 eV, respectively. This determination, which resolves a long lasting dispute on the most fundamental material parameter of this semiconductor, is based on a comparative study of temperature-dependent photoluminescence, wavelength-dispersive x-ray analysis, and triple-crystal x-ray diffractometry.
InGaAs/InP superlattice waveguides by elevated temperature argon ion mixing
Authors: Xia W. , Lin S. C. , Pappert S. A. , Hewett C. A. , Fernandes M. , Vu T. T. , Yu P. K. L. , Lau S. S.
Published: July 2002

Optical waveguides fabricated by argon ion mixing in InGaAs/InP superlattice structures grown by low-pressure metalorganic chemical vapor deposition are demonstrated for the first time. Implantation of argon ions at ∼400 °C eliminates the need for a high-temperature post-anneal to induce the compositional disordering. As-grown and argon-implanted samples were studied using x-ray diffraction and optical absorption measurements. Planar buried rib waveguides operating at a 1.5 μm wavelength are fabricated by selective ion implantation.
Homoepitaxial films grown on Si (100) at 150 °C by remote plasma-enhanced chemical vapor deposition
Authors: Breaux L. , Anthony B. , Hsu T. , Banerjee S. , Tasch A.
Published: July 2002

Low-temperature silicon epitaxy is critical for future generation ultralarge scale integrated circuits and silicon-based heterostructures. Remote plasma-enhanced chemical vapor deposition has been applied to achieve silicon homoepitaxy at temperatures as low as 150 °C, which is believed to be the lowest temperature reported to date. Critical to the process are an in situ remote plasma hydrogen cleaning of the substrate surface in an ultrahigh vacuum growth chamber prior to epitaxy, and substitution of thermal energy by remote plasma excitation via argon metastables and energetic electrons to dissociate silane and increase adatom mobility on the surface of the silicon substrate. Excellent crystallinity with very few defects such as dislocations and stacking faults is observed.
Electron transport in an AlSb/InAs/GaSb tunnel emitter hot-electron transistor
Authors: Chiu T. H. , Levi A. F. J.
Published: July 2002

We report preparation of high quality AlSb/InAs/GaSb heterostructures by molecular beam epitaxy. Using this crystal growth technique we have fabricated unipolar AlSb tunnel emitter transistors and used them to explore electron transport as a function of electron injection energy Ei across a 100-Å-thick InAs quantum well base. A low-energy threshold for collector current is observed for Ei>φbc, where φbc is the base/collector potential barrier. A maximum collection efficiency of ∼0.9 is obtained at Ei≂1.5 eV and at larger values of Ei, the collection efficiency decreases due to wave function symmetry and velocity mismatch across the abrupt base/collector heterointerface.
Crucial influence of the twist deformation on degenerate four-wave mixing process in homeotropically aligned nematic liquid crystals
Authors: Chen Shu-Hsia , Kuo Chen-Lung
Published: July 2002

The diffraction efficiency suppression and peak shifting from the Freedericksz threshold voltage are predicted for degenerate four-wave mixing process in a low-frequency ac voltage-biased homeotropically aligned nematic liquid crystal film. The crucial factor is the twist deformation in the induced phase grating. Significant amounts of diffraction efficiency suppression and peak shift are shown both in numerical and experimental results.
Excimer and CO2 laser interactions with foamed polystyrene
Authors: Duley W. W. , Allan G.
Published: July 2002

We report the results of a study of excimer (308 nm) and CO2 laser etching of foamed polystyrenes. The relative role of photochemical and photothermal effects in material removal can be seen by comparing vaporization energies λ obtained under different material removal regimes. The most efficient material removal occurs with 308 nm pulses at a high repetition rate. Under these conditions λ=10–20 J cm−3 corresponding to 0.3–0.6 eV per monomer. This should be compared to 2–5 eV per monomer with photochemical ablation.
Thermal stability of the Cu/Pd/Si metallurgy
Authors: Chang Chin-An
Published: July 2002

The reaction between Cu and Pd/Si is studied using Cu/Pd/Si structures between 200 and 600 °C. The structural analyses show the reaction between Cu and Pd/Si between 200 and 300 °C, with both Pd and Si diffusing into Cu, and Cu accumulating inside the Si region under the Pd2 Si layer formed. An extensive reaction between Cu and Pd2 Si is observed at 400 °C, forming Cu silicides and Cu3 Pd. The instability of the Cu/Pd2 Si metallurgy is comparable to those of Al/Pd2 Si and Cu/PtSi. In this regard, the difference in stability between the Cu/Pd/Si and Cu/Pt/Si structures is much smaller than that between the Al/Pd/Si and Al/Pt/Si ones. For the latter structures, a difference of about 100 °C is observed, with or without common barrier layers, with Al/Pt/Si being the more stable one. The ready formation of both Cu silicides and Cu3 Pd contributes to the instability of the Cu/Pd/Si structure. The Cu silicide reaction is also responsible for the low thermal stability of the Cu/Pt/Si structures.
Superconducting properties of Ba2YCu3O7−x thin films prepared by chemical vapor deposition on SrTiO3 and a metal substrate
Authors: Yamaguchi Taichi , Aoki Shinya , Sadakata Nobuyuki , Kohno Osamu , Osanai Hiroshi
Published: July 2002

Superconducting Ba2 YCu3 O7−x thin films were prepared by chemical vapor deposition using β-diketonate chelates on SrTiO3 single crystalline substrates, metal substrates, and metal substrates with a polycrystalline SrTiO3 buffer. The temperatures of complete superconducting transitions were observed at 89, 81, and 84 K, respectively. Reduced critical current density of the film on a single crystalline substrate in magnetic fields up to 600 mT at 77 K remained one or two orders of magnitude higher than that of powder metallurgical processed specimens. According to x-ray diffraction patterns, the existence of a well-oriented orthorhombic Ba2 YCu3 O7−x structure has been confirmed in all specimens.
Helical resonators containing high T
c ceramic superconductors
Authors: Peterson G. E. , Stawicki R. P. , McN. Alford N.
Published: July 2002

Resonators are the single most important ingredient in microwave and radio frequency circuits. We have produced some helical resonators using a bulk Ba2YCu3O7 high Tc ceramic superconductor. These resonators, which operate at 77 K and cover the frequency range from 0.1 to 2.0 GHz, outperform their all copper counterparts by at least a factor of 5 in unloaded Q.
Observation of the early stages of growth of superconducting thin films by transmission electron microscopy
Authors: Norton M. Grant , Tietz Lisa A. , Summerfelt Scott R. , Carter C. Barry
Published: July 2002

A method for the direct observation of the early stages of growth of superconducting films by transmission electron microscopy (TEM) is reported. The technique uses well-characterized, single-crystal TEM foils as substrates for the deposition process. Ultrathin films of YBa2Cu3O6+x (YBCO) were prepared by pulsed laser deposition from stoichiometric bulk samples directly onto (001) oriented MgO thin-foil substrates. Observation of the film by TEM is possible without any post-deposition specimen preparation. The epitactic nature of the film growth is shown by analysis of the moiré fringe pattern and by selected area diffraction. In addition to an interconnected film, copper oxide particles and stoichiometric ablated clusters were observed.
Optical plasma monitoring of Y-Ba-Cu-O rf sputter target transients
Authors: Klein J. D. , Yen A.
Published: July 2002

The plasma emission spectra resulting from rf sputtering Y-Ba-Cu-O targets were observed as a function of sputter time. Although most lines of the observed spectra are not attributable to target species, peaks associated with each of the cation elements were resolved. The Ba and Cu peaks can be used as tracking indicators of process conditions. For example, switching from an O2/Ar sputter atmosphere to pure Ar enhanced the Ba peak much more than that associated with Cu. The emission spectra from a newly fabricated target exhibited a slow first-order transient response in seeking equilibrium with the rf plasma. The transient response of a previously sputtered target is also first order but has a much shorter time constant.
Novel method of patterning YBaCuO superconducting thin films
Authors: Ma Q. Y. , Yang E. S. , Treyz G. V. , Chang Chin-An
Published: July 2002

A unique method of patterning YBaCuO thin films based on the inhibition of superconductivity by Si-YBaCuO intermixing has been developed. In the experiment, a thin Si film was first evaporated on a MgO substrate and subsequently patterned using laser direct-write etching. Multilayered YBaCuO thin films were then deposited by e-beam evaporation and annealed in a rapid thermal annealing system for 30–90 s at 980 °C. The YBaCuO film deposited on the silicon regions became insulating. Auger depth profiling measurements indicate that Si-YBaCuO intermixing had occurred in these areas. Between the insulating regions, narrow YBaCuO superconducting lines were formed. For both 10-μm-wide, 1-mm-long and 2.5-μm-wide, 80-μm-long lines, the Tc was observed above 76 K. The critical current density of the lines was measured to be 300 A/cm2 at 75 K. This patterning technique may be useful for fabrication of high Tc superconducting interconnects and devices.
Blue Stark shift in modulation strained InGaAs/InP quantum wells
Authors: Gershoni D. , Hamm R. A. , Panish M. B. , Humphrey D. A.
Published: July 2002

We show that by a proper design and modulation of the composition of a ternary InGaAs quantum well one can considerably alter the optical properties of the system. We demonstrate a novel InGaAs/InP strained-layer heterostructure in which a blue Stark shift of the absorption edge of more than 10 meV is achieved. This blue shift, together with a field-enhanced room-temperature excitonic effect, has applications to bistable electro-optic devices.
Silicon temperature measurement by infrared transmission for rapid thermal processing applications
Authors: Sturm J. C. , Schwartz P. V. , Garone P. M.
Published: July 2002

The use of optical transmission at 1.3 and 1.55 μm is reported to measure the temperature of silicon wafers in a rapid thermal processing environment. Physically, as the wafer temperature increases, infrared transmission drops due to band-gap reduction and an increased phonon population. This method has been used to measure wafer temperature with a resolution of several degrees from 400 to 800 °C, and is compatible with the thick quartz walls of the processing chamber. As part of this work, the absorption constant of silicon at 1.3 and 1.55 μm from 400 to 800 °C has also been measured.
Acceptor diffusion across InGaAs/InP heterointerfaces
Authors: Ambrée P. , Hangleiter A. , Pilkuhn M. H. , Wandel K.
Published: July 2002

Results on Zn and Cd diffusion across InGaAs/InP and InP/InGaAs heterointerfaces are reported. Drastic changes in the group III sublattice were obtained near the interface when Zn diffused from an InGaAs top layer across the heterojunction. Diffusion from an InP top layer, as well as Cd diffusion, or simple annealing of the samples had no measurable influence on the stability of the interfaces. The strong interdiffusion of In and Ga host atoms as well as the Zn gettering at the interface is discussed in terms of two diffusion mechanisms, namely, the ‘‘kick-out’’ mechanism and the vacancy mechanism. The activation energy for the Zn-stimulated Ga interdiffusion across the InGaAs/InP heterojunction was estimated to be EA =3.8±0.3 eV.
Demonstration of a grating-surface-emitting diode laser with low-threshold current density
Authors: Carlson N. W. , Evans G. A. , Bour D. P. , Liew S. K.
Published: July 2002

This letter reports the demonstration of grating-surface-emitting (GSE) lasers with threshold current densities as low as 440 A/cm2. When the distributed-Bragg-reflector sections were cleaved from these lasers, the resulting edge-emitting lasers had threshold current densities that were essentially unchanged from that of the GSE laser. However, the operating wavelength of the Fabry–Perot laser was typically 70 Å shorter than that of the surface emitter.
Optimum Si-Si1−xGex structures with strong infrared spectra
Authors: Turton R. J. , Jaros M.
Published: July 2002

We have identified symmetrically strained Si-Si1−xGex superlattices with optimum strength infrared spectra in the range 50–300 meV. The growth structure parameters required for implementing such systems are provided.
Gate-controlled subband structure and dimensionality of the electron system in a wide parabolic quantum well
Authors: Wixforth A. , Sundaram M. , Ensslin K. , English J. H. , Gossard A. C.
Published: July 2002

Remotely doped parabolic quantum wells have been used to produce thick (>2000 Å) layers of high-mobility electron systems. Using a front gate electrode we are able to simultaneously deplete the well and change the actual thickness of this quasi-three-dimensional system. Thus, we can successively depopulate the elecrical subbands in the well, leading to step-like changes in the gate to channel capacitance. This yields direct insight into the subband structure of the electron system and allows its spectroscopy without the need of a magnetic field. The experimental results are compared with those of a self-consistent subband calculation and we obtain a qualitative agreement.
A simple method for elimination of gallium-source related oval defects in molecular beam epitaxy of GaAs
Authors: Chand Naresh
Published: July 2002

By evaporating gallium from an aluminum-treated pBN crucible in a molecular beam epitaxy (MBE) system, ‘‘Ga spitting’’ and formation of Ga cell related oval defects have been eliminated. MBE GaAs layers as thick as 20 μm were totally free from the Ga cell related oval defects. Remaining defects were particulates or oval defects related to surface contamination and their densities were 100 and 500 cm−2 for 5 and 20-μm-thick layers of GaAs. The particulates-related oval defects were, however, hardly seen when 4-μm-thick GaAs was grown on Si substrates. Aluminum wets and reacts with the pBN crucible when heated to 1300 °C. Condensed gallium near the orifice wets the aluminum-treated surface. As a result, Ga droplets and related oval defects do not form. The method also avoids any gallium oxide in the Ga melt and provides a better outgassed pBN crucible. Contamination of the initial GaAs layers with Al was negligibly small with Al content x=0.0016 which reduced in subsequent layers. The results are presented for GaAs layers but the method should be equally applicable for evaporation of indium to prevent In-related oval defects in In-based compounds.
Detailed characterization of HgCdTe/CdTe multiple quantum wells
Authors: Cesar C. L. , Islam M. N. , Feldman R. D. , Austin R. F. , Chemla D. S. , West L. C. , DiGiovanni A. E.
Published: July 2002

We present absorption measurements in HgCdTe/CdTe multiple quantum wells as a function of temperature, polarization, and well size in the 3–4 μm wavelength region. The energy levels are calculated using a model that includes band nonparabolicity. The spectra are fitted to a sum of continuous broadened steps including the two-dimensional Sommerfeld enhancement factor. Polarization measurements confirm the assignment of heavy and light holes. The ratio between heavy and light hole absorption of 2.3/1 agrees well with theory. The fit of the linewidth with temperature shows a homogeneous linewidth of 4.6 meV times the density of longitudinal optical phonons and an inhomogeneous linewidth of 6.4 meV, which is similar to the alloy broadening in the bulk material.
Lateral beam steering in mutual injection coupled Y-branch grating-surface-emitting diode laser arrays
Authors: Hammer J. M. , Evans G. A. , Carlson N. W. , Bour D. P. , Lurie M. , Palfrey S. L. , Amantea R. , Liew S. K. , Carr L. A. , James E. A. , Kirk J. B. , Reichert W. F.
Published: July 2002

We have observed lateral electronic beam steering of light emitted by monolithic, two-dimensional, grating-surface-emitting, mutually injection coupled arrays of diode lasers in the AlGaAs/GaAs system. Positionally staggered Y-branch subarrays are optically connected through pumped waveguides which provide the required phase shift. These observations taken in conjunction with previously reported work on steering such arrays in the longitudinal direction now demonstrate, for the first time, monolithic, two-dimensional-coherent-diode-laser arrays that may be electronically steered in two orthogonal directions.
Electrically inactive grain boundaries in rapid thermal annealed boron-implanted polycrystalline silicon films
Authors: Almaggoussi A. , Sicart J. , Robert J. L. , Chaussemy G. , Laugier A.
Published: July 2002

The effect of heat treatment rapid thermal annealing (RTA) or conventional thermal annealing on the electrical properties of polycrystalline silicon films implanted with boron in the intermediate concentration range is examined. A standard furnace anneal uniformly redistributes the dopant and results in an electrical activity of grain boundaries (GBs). On the contrary, a rapid thermal anneal does not activate GBs. Impurity gettering does not occur at GBs in RTA and implanted boron does not redistribute uniformly within the grains leading to a strong increase of the Hall mobility in small-grained silicon films.
Amorphous silicon edge detectors for application to neural network image sensors
Authors: Sah Wen-Jyh , Lee Si-Chen , Tsai Hsiung-Kuang , Chen Jyh-Hong
Published: July 2002

The initial steps in the biological visual signal processing are the extraction of the edge position and its orientation of an object image. These edge detection capabilities can be simulated by semiconductor edge detectors. In this letter, two types of such detectors, i.e., concentric and directional ones for detecting edge and its orientation, respectively, are successfully fabricated using an amorphous silicon hydrogen alloy. The measured performance of these edge detectors is similar to that of the biological ones. A three-dimensional image array, made by fabricating two-dimensional amorphous silicon edge detectors on top of the single-crystal Si very large-scale integrated circuit is proposed, which can be used as the preprocessor of a smart vision system.
Deposition-induced defect profiles in amorphous hydrogenated silicon
Authors: Hata N. , Wagner S. , Roca i Cabarrocas P. , Favre M.
Published: July 2002

The thickness dependence of the subgap optical absorption in plasma-deposited hydrogenated amorphous silicon is carefully studied by photothermal deflection spectroscopy. The deep-level defect concentration decays from the top surface into the bulk where it approaches the thermal equilibrium defect density. This defect profile is interpreted in terms of the annealing, during growth, of growth-induced surface defects. It is also shown that this defect profile is compatible with the known growth-temperature dependence of the defect density in amorphous silicon.
Low-loss microstrip delay line in Tl2Ba2CaCu2O8
Authors: Bourne L. C. , Hammond R. B. , Robinson McD. , Eddy M. M. , Olson W. L. , James T. W.
Published: July 2002

We have fabricated and tested a 1 ns microstrip delay line using thin films of Tl2Ba2CaCu2O8. We determined the loss in the delay line by weakly coupling at the input and output and measuring the width of the fundamental resonance at 461 MHz. At 15 K, the loss was lower than that calculated for an equivalent cryogenic copper line by a factor of 300. Resonance peaks were observable up to 102.7 K. At 77 K and 3.29 GHz, the observed loss was lower than that calculated for an equivalent Cu line by a factor of 10. Power limiting due to film defects occurred at an effective power level in the line of −43 dBm at 15 K.
Selective dry etching of InGaAs and InP over AlInAs in CH4/H2/SF6
Authors: Pearton S. J. , Hobson W. S.
Published: July 2002

The addition of SF6 to CH4/H2 discharges is shown to produce a significant increase in the selectivity for dry etching of both InGaAs and InP over AlInAs. The selectivity is a strong function of the dc bias on the sample during the reactive ion etching, with equirate removal of InGaAs and AlInAs for biases above 300 V. For lower bias values, the etch stop mechanism is related to the formation of Al-F and In-F species on the AlInAs surface, as evidenced by x-ray photoelectron spectroscopy. The use of SF6 allows independent variation of the ratio of F to the other reactive species, in comparison to the use of fixed ratio gases such as C2H4F2 or CH3F.
Grating-surface-emitting lasers in a ring configuration
Authors: Bossert D. J. , DeFreez R. K. , Ximen H. , Elliott R. A. , Hunt J. M. , Wilson G. A. , Orloff J. , Evans G. A. , Carlson N. W. , Lurie M. , Hammer J. M. , Bour D. P. , Palfrey S. L. , Amantea R.
Published: July 2002

A monolithic grating-surface-emitting ring laser has been fabricated and its spectral properties and far-field radiation pattern studied. The ring laser was configured from two columns of two-dimensional grating-surface-emitting diode laser arrays. The columns were optically linked at each end with total-internal-reflection corner turning mirrors formed by micromachining grooves in the wafer with a focused ion beam. Single longitudinal mode operation with a high degree of spatial coherence between the two columns and a narrowing of the lateral far-field pattern were observed.
p-type conductivity control of ZnSe highly doped with nitrogen by metalorganic molecular beam epitaxy
Authors: Taike A. , Migita M. , Yamamoto H.
Published: July 2002

p-type ZnSe with resistivity low enough for device application has been realized by metalorganic molecular beam epitaxy. This method has enabled growth of p-type ZnSe doped with nitrogen at concentrations as high as 1019 cm−3 by using ammonia as a dopant source. The dependence of photoluminescence and electrical properties on substrate temperature has been investigated. Hall measurements show p-type conductivity with a resistivity of 0.57 Ω cm, a carrier concentration of 5.6×1017  cm−3, and a Hall mobility of 20 cm2/V s.
Effects of stress in TiSi2 gate metal-oxide-silicon structures
Authors: Reuters P. J. , Offenberg M. , Balk P.
Published: July 2002

Metal-oxide-silicon capacitors with TiSi2 gate were studied to determine the relation between gate-induced stress and the electrical characteristics of the system. TiSi2 is found to exert a compressive stress on the oxide film. With increasing silicide thickness, i.e., larger stress, the rate of trapping of injected electrons, which is a measure of the defect (trap) density, was found to increase. Moreover, the rate of generation of Si-SiO2 interface states upon electron injection shows a similar correlation with the stress.
Post-deposition relaxation of electronic defects in hydrogenated amorphous silicon
Authors: Parsons G. N. , Wang C. , Williams M. J. , Lucovsky G.
Published: July 2002

Electronically active defects in hydrogenated amorphous silicon thin films, deposited by the conventional glow discharge process in the temperature range between about 225 and 325 °C with ∼10–15 at. % hydrogen, undergo a thermally activated relaxation during film deposition. We determine the kinetics of this relaxation process in films with similar hydrogen concentrations deposited by reactive magnetron sputtering at a substrate temperature of ∼40 °C, and annealed at temperatures greater than 150 °C. We present a quantitative relationship between the relaxation time, and the deposition and/or annealing conditions required to produce low defect density material.