bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of process uniformity by using electron cyclotron resonance plasma produced by multiannular antenna
Authors: Yasaka Yasuyoshi , Nakamura Tomokazu
Published: July 2002

A large-diameter uniform electron cyclotron resonance plasma is produced by using multiannular antenna which has a capability of adjusting the radiated powers from two annular slits driven by two microwave sources. The radial profile of the ion saturation current can be varied from hollow to hill-type shape by controlling radial profile of radiated microwave power of the multiannular antenna. In optimum conditions, the plasma has ±2.9% uniformity over 280 mm in diameter with electron density of 6×1010 cm−3. This plasma source is applied to a-Si:H deposition and c-Si etching. It is shown that the radial profile of the deposition rate as well as that of the etching rate can be controlled by changing the radial power radiation profile.
Formation mechanism for ferroelectric domain structures in a LiNbO3 optical superlattice
Authors: Lu Ya-lin , Lu Yan-qing , Cheng Xiang-fei , Luo Gui-peng , Xue Cheng-cheng , Ming Nai-ben
Published: July 2002

Yttrium solute concentration distribution over periodic domains in a LiNbO3 optical superlattice was measured with x-ray energy dispersive spectrum analysis (EDS). A critical concentration gradient mechanism has been proposed in which it is the concentration gradient which determines the configuration of periodic ferroelectric domains. An islandlike domain in periodic domains has been proved to originate from a solute aggregation during crystal growth.
Resonant impurity scattering contribution to the mobility of Pb1−xSnxTe
Authors: Hong Run-Di , Dow John D. , Sankey Otto F. , Allgaier Robert S.
Published: July 2002

An explanation of the anomalously low mobilities of n-type In-doped Pb1−xSnxTe alloys, based on resonant central-cell scattering by antisite In donors, leads to very close agreement with experimental results.
Characterization of FeSix film by codeposition on β-FeSi2 template
Authors: Chen Xiangdong , Wang Lianwei , Shen Qinwo , Ni Rushan , Lin Chenglu
Published: July 2002

We report the characterization of FeSix (x∼3) thin film prepared by simultaneous electron beam evaporation of Fe and Si onto a β-FeSi2 template at 250 °C. The in situ reflective high energy electron diffraction observation and ex situ cross-section transmission electron microscope characterization of the as-deposited film imply that the as-deposited film has the structure similar to that of β-FeSi2. But the spreading resistance measurement shows that the film is metallic. Auger electron spectroscopy suggests that the chemical environment of Fe atoms in the as-deposited FeSix film is different from that in the annealed film (β-FeSi2 film). We explain this paradox by assuming that the as-deposited film has the crystal lattice similar to β-FeSi2 but with ingredient disorder due to the low transport viscosity of Fe and Si atoms at this temperature.
Time-resolved electroluminescence spectroscopy of resonant tunneling in GaAs-AlAs superlattices
Authors: Bertram D. , Klann R. , Grahn H. T. , Klitzing K. v. , Eberl K.
Published: July 2002

The carrier transport through a resonantly coupled GaAs-AlAs superlattice is investigated by time-resolved electroluminescence. Ultrashort current pulses are used to electrically inject electrons and holes into an externally biased superlattice. The time evolution of the emitted light is recorded, which allows us to directly monitor the temporal development of the carrier transport and the associated dynamics of the electric field. At resonance a strong reduction of the initial rise time of the electroluminescence signal is observed.
Metalorganic molecular beam epitaxy of 1.3 μm wavelength tensile-strained InGaAsP multi-quantum-well lasers
Authors: Sugiura Hideo , Itoh Masayuki , Yamamoto Norio , Ogasawara Matsuyuki , Kishi Kennji , Kondo Yasuhiro
Published: July 2002

We have studied metalorganic molecular beam epitaxy growth on strain-compensated multi-quantum-wells (MQWs) in which well layer tensile strain ranges from 0.5 to 1.45%. Double-crystal x-ray and cross-sectional transmission electron microscopy study reveal that each layer in the six-well, 1.3% strained MQWs has well-defined flat interfaces. The photoluminescence intensities of the MQWs are comparable to those of lattice-matched MQWs and remain unchanged after 620 °C annealing. The threshold current density (Jths) of six-well MQW lasers emitting at 1.3 μm wavelength decreases when increasing the tensile strain from 0.5 to 1.3%. The Jth and the threshold current of the 1.3% strained MQW lasers with a 300 μm cavity length are 0.6 kA/cm2 and 9 mA, respectively.
Space charge fields in photorefractive crystals in the presence of direct current and alternating current fields: A new resonance
Authors: Kalinin V. A. , Solymar L.
Published: July 2002

It is shown theoretically that the space charge field generated by two-wave mixing in a photorefractive crystal may have a resonant response when a dc field and a sinusoidal ac field are simultaneously applied. Resonance occurs when the frequency of the ac field is equal to the eigenfrequency of the space charge wave determined by the dc voltage. Analytical expressions are derived for the magnitude of the space charge wave and the optimum ratio of the ac to dc field is determined. The enhancement of the space charge field is shown to be considerably higher than that obtained by a nonresonant method utilizing a sinusoidal ac field alone. Under optimum conditions the maximum space charge field available is equal to mEq/2√2, where m is the modulation of the interference pattern and Eq is the saturation field.
Photoconductivity spectra for boron acceptors in Si1−xGex alloys
Authors: Shi X. H. , Liu P. L. , Chen Z. H. , Shen S. C. , Schilz J.
Published: July 2002

Far infrared photoconductivity spectra of B-doped Si1−xGex grown by Czochralski technique have been investigated in the temperature region from 4.2 to 34 K as well as under high magnetic fields. The photo ionization transition from the ground state of boron acceptor to P3/2 valence band and that related to spin-orbit splitting valence band (P1/2) are observed. The experimental results show that the ionization energy of boron acceptor in Si1−xGex decreases fast and linearly with the increase of Ge concentration for lower Ge composition, and 4% Ge contents make a decrease of 14 meV for the ionization energy of boron in Si0.96Ge0.04. The photoconductivity spectra hardly change with magnetic field up to 11 T.
Stable operation of self-sustained pulsation in 650-nm-band AlGaInP visible lasers with highly doped saturable absorbing layer
Authors: Kidoguchi Isao , Adachi Hideto , Fukuhisa Toshiya , Mannoh Masaya , Takamori Akira
Published: July 2002

Self-sustained pulsating 650-nm-band AlGaInP visible lasers were fabricated by adopting a new structure, which has a highly doped saturable absorbing (HDSA) layer. Since the doping level and the thickness of the HDSA layer could be controlled accurately by using metalorganic vapor phase epitaxy growth technique, a stable operation of self-sustained pulsation up to 60 °C was obtained. The lasers operated over 1350 h under the average output power of 5 mW at 60 °C. The relative intensity noise values were below −136 dB/Hz in the temperature ranging from 20–60 °C and remained unchanged after life test.
Alloy composition dependence of photoexcited carrier dynamics in GaxIn1−xP/InP:Fe (x<0.18)
Authors: Zhao Y.-G. , Jing R. , Zou Y.-H. , Xia Z.-J. , Huang X.-L. , Chen W.-X. , Masut R. A.
Published: July 2002

We have observed the reflection recovery dynamics of photoexcited GaxIn1−xP/InP:Fe (x<0.18), using the pump-probe technique, and found that the delay time of the reflection recovery dynamics increases with increasing gallium composition. To understand the experimental results, we have also performed a simulation study, which is in good agreement with the measured data, and shows that ambipolar diffusion plays a dominant role in determining the photoexcited carrier dynamics.
Current resolution, noise, and inductance measurements on high-T
c dc SQUID galvanometers
Authors: Il’ichev E. , Dörrer L. , Schmidl F. , Zakosarenko V. , Seidel P. , Hildebrandt G.
Published: July 2002

Single layer autonomous high-Tc dc superconducting quantum interference devices (SQUIDs) have been fabricated and tested. The SQUIDs were designed for application as a galvanometer. The current to be measured is injected directly in a microstrip segment of the SQUID loop. Step-edge as well as bicrystal YBCO Josephson junctions were used. We consider two aspects: (i) optimization of the noise properties with respect to current resolution, and (ii) temperature dependence of the period of voltage-flux relation. The SQUID inductance was calculated numerically taking into account the magnetic field penetration depth λ. The temperature dependence of λ(T) was obtained from experimental results and is found to be in good agreement with λ(T)≊λ(0)[1−(T/TC)2]−1/2.
A method for the assessment of oxide charge density and centroid in metal-oxide-semiconductor structures after uniform gate stress
Authors: Kies R. , Egilsson T. , Ghibaudo G. , Pananakakis G.
Published: July 2002

A method for the extraction of the oxide charge density and distribution centroid based on the exploitation of the Fowler plot derivative characteristics is proposed. To this end, the modification of the tunnel transparency due to the presence of charge within the tunneling region is accounted for. Simple analytical formulas which enable the oxide charge density and centroid to be extracted from the maximum Fowler derivative and its electric field position are derived. The comparison with the DiMaria method confirms the overall consistency of the new approach. The impact of negative charge within the oxide on the apparent Fowler barrier height, which can be deduced from the slope of the Fowler plots after uniform gate stress is also analyzed. Finally, it is pointed out that this method permits the oxide trapping properties to be studied even though only one bias polarization can be utilized for the test structure.
Conduction band offsets in CdZnSSe/ZnSSe single quantum wells measured by deep level transient spectroscopy
Authors: Baude P. F. , Haase M. A. , Haugen G. M. , Law K. K. , Miller T. J. , Smekalin K. , Phillips J. , Bhattacharya P.
Published: July 2002

Conduction-band offsets in wide-band-gap CdZnSSe/ZnSSe single quantum well structures have been characterized by deep level transient spectroscopy (DLTS) measurements. 50 Å thick Cd0.3Zn0.7S0.06Se0.94 single quantum wells with ZnS0.06Se0.94 barriers were grown by molecular beam epitaxy on GaAs substrates. A thermal emission energy from the quaternary wells of 179±10 meV was measured. This corresponds to a conduction-band offset energy of ∼251±20 meV.
Surface periodic structures induced by pulsed laser irradiation of fullerite
Authors: Milani P. , Manfredini M.
Published: July 2002

Fullerite surface modifications induced by 1064 and 266 nm pulsed laser irradiation have been studied by scanning electron microscopy. The formation of micropatterns with a well-defined periodicity is reported. The morphology of the periodic nanostructures can be controlled by varying the laser fluence, the angle of incidence, and the wavelength. The different patterns observed for infrared and ultraviolet irradiation suggest that electronic and thermal effects are responsible of the formation of the periodic structures.
Full capacitance matrix of coupled quantum dot arrays: Static and dynamical effects
Authors: Whan C. B. , White J. , Orlando T. P.
Published: July 2002

We numerically calculated the full capacitance matrices for both one-dimensional (1D) and two-dimensional (2D) quantum-dot arrays. We found it is necessary to use the full capacitance matrix in modeling coupled quantum dot arrays due to weaker screening in these systems in comparison with arrays of normal metal tunnel junctions. The static soliton potential distributions in both 1D and 2D arrays are well approximated by the unscreened (1/r) Coulomb potential, instead of the exponential fall-off expected from the often used nearest neighbor approximation. The Coulomb potential approximation also provides a simple expression for the full inverse capacitance matrix of uniform quantum dot arrays. In terms of dynamics, we compare the current-voltage (I-V) characteristics of voltage biased 1D arrays using either the full capacitance matrix or its nearest neighbor approximation. The I-V curves show clear differences and the differences become more pronounced when larger arrays are considered.
B implants in Si1−xGex/Si
Authors: Berry Alok K. , Thompson P. E. , Rao Mulpuri V. , Fatemi M. , Dietrich H. B.
Published: July 2002

Boron ion implantations were performed into 100 nm thick, undoped, strained Si1−xGex alloy films with x values of 0, 0.1, and 0.2 grown on (100) Si. B implants of 1×1013, 1×1014, and 1×1015 cm−2 were done at 20 keV. Implant activation was accomplished by using either 20 s rapid thermal anneals or 10 min furnace anneals, both at temperatures up to 800 °C. The annealed material was characterized by Hall, secondary ion mass spectrometry, and x-ray rocking curve measurements. We observed an increasing B activation with increasing Ge concentration in the alloy. For x=0.2 we obtained 100% B activation for 1×1013 and 1×1014 cm−2 implants annealed at 700 and 800 °C.
Time and spatially resolved photoluminescence measurements of nonstoichiometric GaAs
Authors: Marcinkevičius S. , Krotkus A. , Jasutis V. , Bertulis K. , Tan H. H. , Jagadish C. , Kaminska M.
Published: July 2002

Carrier trapping times in different parts of chemically profiled samples of nonstoichiometric GaAs obtained by molecular beam epitaxy at low substrate temperatures or by As or Ga ion implantation were determined by using temporally resolved photoluminescence measurement. No shortening of the trapping time by the presence of metallic precipitates and other extended defects was evidenced.
Incorporation of Zn during epitaxial growth of Y1Ba2Cu3O7−d films by pulsed laser deposition
Authors: Ogale S. B. , Rajeswari M. , Sharma R. P. , Venkatesan T.
Published: July 2002

Incorporation of Zn during epitaxial growth of Y1Ba2Cu3O7−d films by pulsed laser deposition is examined. The influence of the substrate temperature, oxygen pressure during deposition, and the laser energy density on the physical and superconducting properties of the film is studied using ac susceptibility, x-ray diffraction, scanning electron microscopy and x-ray analysis, atomic force microscopy, and Rutherford backscattering techniques. It is shown that substrate temperature is the single most critical parameter controlling the substitutional incorporation of Zn in the films with desorption of Zn at higher temperatures.
Evolution of silicon surface morphology during H2 annealing in a rapid thermal chemical vapor deposition system
Authors: Wang C. L. , Unnikrishnan S. , Kim B. Y. , Kwong D. L. , Tasch A. F.
Published: July 2002

The surface morphology of Cz Si(100) after H2 bake has been investigated. It is found that at temperatures as low as 950 °C, and bake times as short as 25 s, steps and terraces are formed by the H2 annealing. The evolution of the step and terrace structure can be clearly seen by virtue of temperature differences across the wafer. The steps are two-atomic layer steps at straight edges, whereas one-atomic layer steps occur when the edge line is irregular.
Scanning tunneling microscopy of Si/SiO2 interface roughness and its dependence on growth conditions
Authors: Shekhawat G. S. , Gupta Ram P. , Shekhawat S. S. , Runthala D. P. , Vyas P. D. , Srivastava P. , Venkatesh S. , Mamhoud K. , Garg K. B.
Published: July 2002

The interface between silicon (100) and thermal silicon dioxide grown by wet, dry, and trichloroethylene oxidation has been investigated by scanning tunneling microscopy and scanning tunneling spectroscopy. The scanning tunneling microscopy images of the silicon surface, after removal of oxide, reveal the presence of silicon bumps (protrusions) in samples prepared by wet and dry oxidation while no protrusions are seen at the interface of trichloroethylene oxidized samples. The spectroscopic measurements predict that these are silicon protrusions and are produced by oxide growth conditions. X-ray photon spectroscopy on samples containing protrusions also supports the above prediction. Thus, our study suggests that roughness of the silicon–silicon dioxide interface depends on oxide growth conditions and a relatively smooth interface is obtained by tricholoroethylene oxidation.
Atomic absorption monitor for deposition process control of aluminum at 394 nm using frequency-doubled diode laser
Authors: Wang Weizhi , Fejer M. M. , Hammond R. H. , Beasley M. R. , Ahn C. H. , Bortz M. L. , Day T.
Published: July 2002

A monitor for Al vapor density based on atomic absorption (AA) using a frequency-doubled external-cavity-diode-laser source at 394 nm has been demonstrated in both evaporation and sputtering processes. Closed loop operation was achieved for electron-beam evaporated aluminum in a vacuum chamber using the AA signal for feedback. A series of runs in a dc sputtering chamber at the deposition rate of 900 Å/min illustrates the system reproducibility and the possibility of controlling the sputtering process and measuring the spatial distribution of the sputtered atoms with the AA monitor. Coherent light in the blue-UV region (380–430 nm) using quasi-phase-matched lithium niobate waveguides was demonstrated with efficiencies of 25–150%/W, a range of wavelengths that covers many technologically important elements in physical vapor deposition processes.
Laser direct writing of oxide structures on hydrogen-passivated silicon surfaces
Authors: Müllenborn M. , Birkelund K. , Grey F. , Madsen S.
Published: July 2002

A focused laser beam has been used to induce oxidation of hydrogen-passivated silicon. The scanning laser beam removes the hydrogen passivation locally from the silicon surface, which immediately oxidizes in air. The process has been studied as a function of power density and excitation wavelength on amorphous and crystalline silicon surfaces in order to determine the depassivation mechanism. The minimum linewidth achieved is about 450 nm using writing speeds of up to 100 mm/s. The process is fully compatible with local oxidation of silicon by scanning probe lithography. Wafer-scale patterns can be generated by laser direct oxidation and complemented with nanometer resolution by scanning probe techniques. The combined micro- and nanoscale pattern can be transferred to the silicon in a single etching step by either wet or dry etching techniques.
Structural characterization of Zn-diffused InP layers by x-ray diffraction and standing-waves method
Authors: Bocchi C. , Franzosi P. , Maslov A. V. , Mukhamedzhanov E. Kh. , Audino R. , Gambacorti N.
Published: July 2002

Zn-diffused InP layers have been prepared in a sealed quartz ampoule at 500 °C using a Zn3P2 source. The diffusion time ranged from 7 up to 90 min. As substrates, nearly dislocation-free S-doped InP crystals have been used. The lattice strain produced by diffusion has been carefully investigated by x-ray double crystal diffraction and the standing-waves method recording photoelectrons. The results show that the diffused layers exhibit a lattice contraction probably related to the Zn atoms substituting In. The diffuse/virgin interface has been found to be very sharp and the secondary ion mass spectrometry measurement of the Zn concentration profile has been confirmed. Finally, the maximum strain seems not to depend on the diffusion time, whereas the thickness of the diffused layer increases by increasing the time as expected for a diffusion process.
The junction characteristics of carbonaceous film/n-type silicon (C/n-Si) layer photovoltaic cell
Authors: Yu H. A. , Kaneko T. , Yoshimura S. , Suhng Y. , Sasaki Y. , Otani S.
Published: July 2002

The junction capacitance for a carbonaceous thin-film/n-type silicon layer photovoltaic cell made by chemical vapor deposition of 2,5-dimethyl-p-benzoquinone on a silicon substrate at 500 °C was measured, and an energy band diagram for this junction was sought out. The result confirms that the carbonaceous thin-film/n-type silicon junction is a heterotype junction. Its junction barrier is about 0.54 eV. This junction shows a depletion layer of about 1.1 μm in thickness at zero bias voltage, and most all of which was established in the silicon substrate. A work function of about 5.0 eV for the carbonaceous film was estimated based on the energy-band diagram of this junction.
Carrier-induced change due to doping in refractive index of InP: Measurements at 1.3 and 1.5 μm
Authors: Chusseau Laurent , Martin Patrick , Brasseur Céline , Alibert Claude , Hervé Philippe , Arguel Philippe , Lozes-Dupuy Françoise , Rao E. V. K.
Published: July 2002

Accurate measurements of the InP refractive index as a function of free-carrier doping are reported at 1.3 and 1.5 μm, the two strategic wavelengths for optical communications. A total of 21 samples with different N- and P-doping levels have been measured using a novel and simplified grating-coupling technique. In contrast to the conventional method, this only involves the use of a directly etched diffraction grating on the sample surface, thereby avoiding the necessity of a specific guiding layer. The measured index, in agreement with earlier predictions, decreases by more than 0.05 when the N doping is increased from below 1015 to about 1019 electrons per cubic centimeter. This effect, however, is much less pronounced with P doping than with N doping.
Nonlinear optical studies of single crystal films of N–(4-nitrophenyl)–L–prolinol
Authors: Quintero-Torres R. , Thakur M.
Published: July 2002

Single crystal films of N–(4-nitrophenyl)-L–prolinol have been prepared by modified shear method and the second order optical susceptibility has been measured by second harmonic generation. The small thickness and high nonlinear coefficient of the films allowed second order optical measurements without considering phase matching. The magnitudes of the tensor elements of second order optical susceptibility were determined by detailed polarization selective measurements. The maximum effective value of the nonlinearity, dmaxeff was found to be approximately 18 times the deff of LiNbO3. The value of d21 is equal to 97 (±5) pm/V and d22 is equal to 30 (±5) pm/V at 1064 nm. Our analyses show that both type-I and type-II phase matching should be possible in waveguides of this material.
Radiation hardness of N2O grown oxynitrides assessed using the conductance technique
Authors: Anthony C. J. , Uren M. J. , Nayar V.
Published: July 2002

Oxynitrides on (100) silicon grown in a N2O ambient have been 60Co gamma irradiated. The conductance technique has been used to show that irradiation under bias can produce lateral charge nonuniformities at the Si:SiO2 interface. The ratio of induced fast to slow interface state density was found to be roughly independent of bias and nitridation, suggesting a common origin for these two types of defects.
Impact of surface stoichiometry control during the initial stages of growth on the stacking fault concentration in ZnSe epilayers grown by molecular beam epitaxy
Authors: Jeon M. H. , Calhoun L. C. , Gila B. P. , Ludwig M. H. , Park R. M.
Published: July 2002

We have determined that the surface stoichiometry maintained during the first five monolayers of ZnSe epitaxial growth can have a significant influence on the stacking fault concentration in 2 μm thick epilayers. In particular, we have been able to minimize the stacking fault concentration to a level in the 104 cm−2 range (comparable to the stacking fault concentration in the ZnSe substrates used for epitaxy) by appropriate selection of a delay time (∼30 s for a substrate temperature of 300 °C) employed during an alternate element (Zn and Se) exposure phase of growth. The delay time in question is the time elapsed between closing the Se shutter and opening the Zn shutter. We show that the surface stoichiometry (Zn to Se atomic ratio) can be tailored during the delay phase since Se thermal desorption occurs at the growth temperature in a controlled fashion from an initially Se-terminated surface, and, it is postulated that selection of an optimum delay time corresponding to the attainment of a near-stoichiometric surface results in the growth of low stacking fault concentration material.
Single mode Lamb wave excitation in thin plates by Hertzian contacts
Authors: Degertekin F. Levent , Khuri-Yakub Butrus T.
Published: July 2002

We present novel techniques to selectively excite the lowest order symmetric (So) and antisymmetric (Ao) Lamb wave modes in thin solid plates. Hertzian contacts are formed between the plates and the end of specially designed quartz rods which guide extensional waves generated by PZT-5H transducers bonded at their other end. Mode selectivity is achieved by applying shear and/or longitudinal traction at the edge or the surface of the plates according to the results of a two-dimensional normal mode theory. In aluminum plates, mode selectivity is measured as a function of frequency for different traction forces. With normal forces, Ao mode selectivity of more than 46 dB is obtained for fd<0.4 MHz mm. With antisymmetric shear traction at the edge of the plate, a selectivity exceeding 55 dB is achieved for single mode So operation.
Morphology of strained epitaxial Fe films on Cu(311)
Authors: Fölsch S. , Choi B.-Ch. , Rieder K. H.
Published: July 2002

Heteroepitaxial growth of Fe on the asymmetrical Cu(311) surface leads to (211)-oriented strained bcc films with a highly anisotropic morphology. In the initial stage the evolution of pseudomorphic Fe islands is observed: anisotropic lateral stress induces the formation of a regular array of Fe patches with a periodic separation. With proceeding growth, the overlayer transforms to bcc structure by means of dislocations introduced along the direction of dominant stress. The topography of the resulting bcc film corresponds to a regular faceted structure whose periodicity is determined by the arrangement of pseudomorphic islands formed in the initial stage of growth.
17.1% efficient metal-insulator-semiconductor inversion layer silicon solar cells using truncated pyramids
Authors: Grauvogl Manfred , Aberle Armin G. , Hezel Rudolf
Published: July 2002

Metal-insulator-semiconductor inversion layer (MIS-IL) silicon solar cells are of significant interest for terrestrial solar electricity production due to their simple, energy-saving fabrication process. In this work we present experimental results for an improved MIS-IL silicon solar cell design based on the truncated-pyramid concept. The cells exhibit independently confirmed 1-sun efficiencies above 17%, by a clear margin the highest values ever reported for this promising class of photovoltaic devices.
Stability of hot-wire deposited amorphous-silicon thin-film transistors
Authors: Meiling H. , Schropp R. E. I.
Published: July 2002

For the first time hydrogenated amorphous silicon, a-Si:H, deposited with the hot-wire technique is incorporated in thin-film transistors (TFTs). Amorphous silicon was deposited at a rate of 20 Å/s. TFTs with a switching ratio of 105, a threshold voltage of 16.9 V, and a field-effect mobility μs of 0.001 cm2/V s are obtained. Upon gate voltage stress, virtually no change in any of these TFT parameters is observed. Conventional state-of-the-art TFTs deposited in a 13.56 MHz glow discharge showed a threshold voltage shift of more than +12 V. The interface between the gate dielectric and the hot-wire a-Si:H layer needs further optimization. After gate voltage stress, the TFTs containing hot-wire a-Si:H have superior quality with respect to the threshold voltage.
Dosimetric characteristics of ultraviolet and x-ray-irradiated KBr:Eu2+ thermoluminescence crystals
Authors: Meléndrez R. , Pérez-Salas R. , Aceves R. , Piters T. M. , Barboza-Flores M.
Published: July 2002

Thermoluminescence (TL) characteristics of KBr:Eu2+ (150 ppm) previously exposed to ultraviolet (UV) light (200–300 nm) and x-ray radiation at room temperature have been determined. The TL glow curve of UV-irradiated samples is composed of six peaks located at 337, 384, 402, 435, 475, and 510 K. The TL glow curves of x-irradiated samples show mainly a TL peak around 384 K. The TL intensities of UV-irradiated (402 and 510 K glow peaks) and x-irradiated specimens present a linear dependence as a function of radiation dose as well as fading stability 300 s after irradiation. These results further enhance the possibilities of using europium-doped materials in nonionizing (actinic region) and ionizing radiation detection and dosimetry applications.
Optical properties of Si nanocrystals prepared by magnetron sputtering
Authors: Baru V. G. , Chernushich A. P. , Luzanov V. A. , Stepanov G. V. , Zakharov L. Yu. , O’Donnell K. P. , Bradley I. V. , Melnik N. N.
Published: July 2002

Visible photoluminescence (PL), optical transmission, and Raman scattering spectra of Si nanocrystals embedded in SiO2 matrix have been studied. Films were deposited by rf magnetron sputtering of compound SiO2/Si targets. Films containing silicon in the form of nanocrystals clusters show intense luminescence at room temperature. Films containing only amorphous Si clusters show little or no PL. Annealing in vacuum or in specific atmosphere leads to strong change of the PL spectrum and its intensity. Results are explained by strong influence of the Si/SiO2 interface state on integral PL emission.
Temperature-dependent orientation of diamond films on titanium and structural evolution of interfacial layers
Authors: Cappuccio Giorgio , Sessa Vito , Terranova Maria Letizia
Published: July 2002

X-ray diffraction analytical techniques have been used to investigate the influence of the deposition temperature (650–850 °C) on the composition and microstructure of the transition layers formed at the interface between titanium substrates and diamond thin films. The diamond coatings were produced by hot-filament chemical vapor deposition using a 1% methane/hydrogen mixture. X-ray diffraction analysis, performed both through θ–2θ scans and at grazing incidence, allowed investigation of the crystallographic properties and of the structural evolution of the various phases (TiC, TiH2, α-Ti) generated inside the intermediate reaction layers. The temperature-dependent orientation of diamond crystallites is discussed with reference to the complex structure of these interfacial layers.
Diffusion barrier performance of chemically vapor deposited TiN films prepared using tetrakis-dimethyl-amino titanium in the Cu/TiN/Si structure
Authors: Kim Do-Heyoung , Cho Sung-Lae , Kim Ki-Bum , Kim Jung Ju , Park Jin Won , Kim Jae Jung
Published: July 2002

We investigated diffusion barrier performance of chemical vapor deposition (CVD) TiN films prepared using tetrakis-dimethyl-amino titanium, Ti[N(CH3)2]4, to copper in the Cu/TiN/Si structure. The in situ treatment of the TiN films using N2/H2 plasma was found to significantly improve barrier performance against copper diffusion. The plasma-treated TiN films were stable up to 650 °C but as-deposited TiN films showed an evidence of copper diffusion into silicon even after annealing at 550 °C. The causes of the different effectiveness as a copper diffusion barrier of the two types of the CVD TiN films were discussed.
Application of near-edge x-ray absorption fine structure for the identification of hexagonal and cubic polytypes in epitaxial GaN
Authors: Katsikini M. , Paloura E. C. , Moustakas T. D.
Published: July 2002

Cubic and hexagonal GaN thin films are studied using the angular dependence of the near-edge x-ray absorption fine structure (NEXAFS) spectra recorded at the N–K edge. It is shown that the energy positions of the NEXAFS resonances are characteristic of the cubic and hexagonal structures and, thus, the NEXAFS spectra can be used as a fingerprint of the symmetry of the examined crystal. Deviations from the zinc-blende or wurtzite phases are clearly detectable since they lead to a systematic energy shift in the NEXAFS resonances. Finally, a method is proposed for the quantitative estimation of the percentages of the cubic and wurtzite phases present in a mixed crystal.
Longitudinal optical phonon relaxation in a GaAs/AlGaAs triple barrier tunnel diode at strong perpendicular magnetic fields
Authors: Wirner C. , Awano Y. , Mori T. , Yokoyama N. , Nakagawa T. , Bando H. , Muto S.
Published: July 2002

Longitudinal optical (LO) phonon relaxation is investigated in a GaAs/AlGaAs triple barrier tunnel diode at strong perpendicular magnetic fields. We observe LO-phonon assisted tunneling to the ground state as well as to Landau level states. Maxima in the LO-phonon assisted tunnel peak are found each time the LO-phonon energy matches multiple of the Landau level spacing. Corresponding maxima as well as parity effects are found in the integral tunnel conductance. The results indicate enhancement of LO-phonon assisted inter Landau level transitions with increasing magnetic field.
Fabrication of flexible monocrystalline ZnSe-based foils and membranes
Authors: Haetty J. , Na M. H. , Chang H. C. , Luo H. , Petrou A.
Published: July 2002

We report the successful fabrication of flexible single crystal semiconductor structures. A highly selective etching solution allowed us to obtain large area foils and membranes of good structural integrity, using films of indium and silicone as flexible substrates. Photoluminescence and transmission measurements verified that the optical properties of these structures were preserved.
CCl4-doped semi-insulating InP as a buffer layer in GaInAs/InP high electron mobility transistors
Authors: Hsu C. C. , Yang Y. F. , Ou H. J. , Yang E. S.
Published: July 2002

The application of CCl4-doped semi-insulating InP as a buffer layer in a pseudomorphic Ga0.2In0.8P/Ga0.47In0.53As/InP high electron mobility transistor (HEMT) grown by metalorganic chemical vapor deposition is reported. This Al-free InP-base HEMT with a gate length of 1.3 μm has extrinsic transconductances of 420 and 610 mS/mm at 300 and 77 K, respectively. A cutoff frequency of 15 GHz and a maximum oscillation frequency of 40 GHz are obtained. The results demonstrate the CCl4-doped semi-insulating InP is a promising buffer layer for InP-based HEMT.
Electron paramagnetic resonance characterization of diamond films fabricated with different methane concentrations
Authors: Keeble D. J. , Ramakrishnan B.
Published: July 2002

Electron paramagnetic resonance (EPR) studies were performed on thin diamond films fabricated by hot-filament chemical vapor deposition using methane concentrations varying from 0.25% to 5%. The bulk spin concentration and the peak to peak linewidth for the characteristic g=2.0027(2) EPR spectrum were found to increase for samples grown with increased methane concentration. The results show the spectrum contains component/s due to paramagnetic defects related to nondiamond carbon phases within the films.
Thermal stability of hydrogen in LiAlO2 and LiGaO2
Authors: Wilson R. G. , Chai B. L. H. , Pearton S. J. , Abernathy C. R. , Ren F. , Zavada J. M.
Published: July 2002

Hydrogen as 2H has been incorporated into LiAlO2 and LiGaO2 by both ion implantation and by exposure to a plasma at 250 °C. In the implanted samples, approximately 50% of the hydrogen is lost from the surface during annealing at 500 °C for 20 min, and essentially all is gone by 700 °C. This hydrogen retention is considerably less than for other materials that are being used as substrates for III-nitride epilayer growth, such as SiC and sapphire. The indiffusion of 2H from a plasma is much faster for LiAlO2 with an apparent diffusivity at 250 °C of ∼10−13 cm−2 s−1, approximately two orders of magnitude larger than for LiGaO2. Hydrogen outdiffusion from LiAlO2 or LiGaO2 substrates during III-nitride epitaxy should not be a significant problem; the hydrogen should have left these materials at temperatures less than epitaxial layer growth temperatures.
Effects of low temperature preannealing on ion-implant assisted intermixing of Si1−xGex/Si quantum wells
Authors: Labrie D. , Aers G. C. , Lafontaine H. , Williams R. L. , Charbonneau S. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

Using photoluminescence we have studied the effect of a low temperature ‘‘preanneal’’ stage on the intermixing of 3 nm Si0.7Ge0.3/Si quantum wells, implanted with silicon ions having energies up to 1 MeV and then exposed to rapid thermal annealing at 850 °C for 300 s. We find that an unwanted quantum well band gap increase in unimplanted samples after rapid thermal annealing can be reduced substantially from ∼30 to ∼5 meV due to the removal of grown-in defects by preannealing at 630 °C for 24 h. Preannealed samples that were implanted and rapid thermal annealed showed at least the same band gap increase (up to 70 meV in these samples) observed for nonpreannealed samples. These results are understood in terms of significantly different activation energies for defect diffusion and quantum well intermixing and a nonlinear dependence of the energy shifts on defect concentrations.
Nonlinear optical mapping of silicon carbide polytypes in 6H-SiC epilayers
Authors: Meyer C. , Lüpke G. , Stein von Kamienski E. , Gölz A. , Kurz H.
Published: July 2002

A fast and noninvasive mapping tool based on spatially resolved optical second-harmonic generation is presented for the detection of silicon carbide polytypes in 6H-SiC epilayers. 3C-SiC microcrystallites of different orientations are identified from second-harmonic rotational anisotropy scans. The method reported can be used as an efficient in situ control of SiC growth processes.
Movable-mask reactive ion etch process for thickness control in devices
Authors: Sandstrom R. L. , Pezeshki B. , Agahi F. , Martel R. , Crockett J. G.
Published: July 2002

By moving the substrate relative to a shadow mask in a reactive ion etching system, we are able to precisely tailor the thickness of critical layers. To minimize disturbing the plasma, all the mechanical components are kept below the anode. The system is highly reproducible, and can be programmed to yield arbitrary vertical profiles along one horizontal axis. Using silicon-on-insulator substrates, the resonance wavelength was modified as a function of position with better than 1 nm control in the vertical dimension. This technique should prove useful for optical devices where the thickness of the layers controls the device characteristics.
Line-focus acoustic microscopy measurements of elastic constants for materials with high acoustic velocities
Authors: Tourlog Ailie , Li Wei , Achenbach Jan D.
Published: July 2002

A method to determine elastic constants of high acoustic velocity materials by line-focus acoustic microscopy is presented. To determine elastic constants the distances between the specular reflection peak and the first interference maximum and minimum of the V(z) curve measured by line-focus acoustic microscopy were compared to the corresponding distances obtained from a V(z) measurement model that simulates the experiment. Elastic constants of a single-crystal diamond sample were determined by this method.
Formation of self-aligned CoSi2 on selective epitaxial growth silicon layer on (001)Si inside 0.1–0.6 μm oxide openings prepared by electron beam lithography
Authors: Yew J. Y. , Tseng H. C. , Chen L. J. , Nakamura K. , Chang C. Y.
Published: July 2002

The self-aligned formation of CoSi2 was achieved on the selective epitaxial growth (SEG) silicon layer on (001)Si inside 0.1–0.6 μm oxide openings prepared by electron beam lithography. The uniform, high quality SEG Si layer was grown by ultrahigh vacuum chemical vapor deposition at 560 °C with Si2H6. Self-aligned CoSi2 film without lateral growth of silicide was grown on the SEG Si layer by rapid thermal annealing at 700 °C in N2 ambient. The successful integration of the self-aligned CoSi2 and SEG of Si processes promises to be a viable process technology for the future deep submicron devices.
Effect of trivalent ion composition on the magnetoresistance behavior of LaxNd0.6−xSr0.40MnO3−δ films
Authors: Zhang Wei , Boyd Ian W. , Elliott Martin , Herrenden-Harkerand William
Published: July 2002

The effect of trivalent ion composition (x) on the transport properties and magnetoresistance (MR) behavior of LaxNd0.6−xSr0.40MnO3−δ films (0.15≤x≤0.45) grown on Si(100) substrates by pulsed laser deposition is reported. It is found that the temperature associated with the peak resistivity can be shifted to higher values by varying the trivalent ion composition, in a similar way to that earlier observed in divalent substituted La1−xMxMnO3−δ (M=Ba, Sr, Ca, Pb) films. MR values near room temperature under a magnetic field of 4.7 T increase with lanthanum ion composition, and the largest MR value of around 30% (Δρ/ρH) appeared in films with x=0.45. Our results suggest that these effects are primarily related to an increase of the Curie temperature of the films as a result of lattice expansion by partial substitution of neodymium with lanthanum, which has a larger ionic radius.
High-reliability blue-shifted InGaAsP/InP lasers
Authors: Noël J.-P. , Melville D. , Jones T. , Shepherd F. R. , Miner C. J. , Puetz N. , Fox K. , Poole P. J. , Feng Y. , Koteles E. S. , Charbonneau S. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

InGaAsP/InP quantum well (QW) ridge waveguide lasers emitting nominally at 1310 nm have been ‘‘blue-shifted’’ selectively (as much as 70 nm) on a full 50-mm-diameter wafer after growth. P+ ion implantation at 1 MeV, 200 °C through a variable thickness SiO2 mask was used to induce various degrees of QW intermixing after postimplantation annealing at 700 °C. Irrespective of the amount of intermixing induced (blue shift), all fabricated devices exhibited 20–25 mA lasing threshold current and 0.25–0.30 W/A differential quantum efficiency. Device reliability was equivalent to standard (nonimplanted) lasers when the wavelength shift was 35 nm or less, corresponding to predicted lifetime in excess of 25 years while operating cw at 25 °C. The performance and reliability data clearly indicate that the concentration of residual defects introduced in the active region by the implantation/annealing process is negligibly small. The present results, which are a product of a straightforward fabrication process, suggest the possibility of manufacturing high-reliability, low-cost, monolithically integrated optoelectronic chips containing, for example, selectively tuned lasers, optical amplifiers, modulators, and waveguides.
The effect of scaling microlasers on modal noise
Authors: Thiyagarajan S. M. K. , Levi A. F. J.
Published: July 2002

Modal noise and speckle visibility in Gb/s multimode fiber interconnect systems depends on a complex interplay of carrier dynamics, spontaneous emission factor, gain compression, and device dimensions. These competing factors allow scaled low-power microlasers with optimized design and operating conditions to exhibit modal noise comparable to large incoherent multimode devices.
Vacuum field induced mixing of light and heavy-hole excitons in a semiconductor microcavity
Authors: Goobar E. , Ram R. J. , Ko J. , Björk G. , Oestreich M. , Imamoglu A.
Published: July 2002

Measurements in a semiconductor microcavity reveal the coupling between light- and heavy-hole excitons that is mediated by the electromagnetic vacuum. Three polariton modes constructed from superpositions of heavy-hole excitons, light-hole excitons, and photons are observed. The experimental results are in good agreement with the theory of three-coupled bosonic modes, each coupled to an independent reservoir.
Electrical measurements of iodine doped amorphous diamondlike films grown on silicon substrate
Authors: Allon-Alaluf M. , Croitoru N.
Published: July 2002

By incorporating iodine gas during the films’ deposition, amorphous diamondlike carbon (a:DLC) films were doped and a:I–DLC films were obtained. Optical measurements showed that iodine affects the optical band gap, decrease it from 1.1 to 0.78 eV. Iodine doping decreased the resistivity by four orders of magnitude, from 108 to 104 Ω cm. Iodine doped film was found to have a larger p doping than a:DLC films. The I–V characteristics of devices made of doped and undoped films grown on silicon substrates, were studied. ac measurements of these devices have shown that the p doped a:DLC films behave as semiconductors, and give a rectification with n-type silicon.
Tapping mode atomic force microscopy using electrostatic force modulation
Authors: Hong J. W. , Khim Z. G. , Hou A. S. , Park Sang-il
Published: July 2002

We have developed a simple tapping mode in atomic force microscopy using a capacitive electrostatic force. In this technique, the probe-to-sample distance is modulated by the capacitive force between tip and sample induced by a sinusoidal bias applied to the conductive probe instead of a conventional mechanical vibration. The electrostatic force versus distance curve of the probe indicates that it is necessary to use a rather stiff cantilever to prevent the snapping of the tip into the surface due to the adhesive force at the surface. We have succeeded in obtaining topographic images of a conductive surface as well as a soft polystyrene sample with a low tracking and lateral force through this method.
Effect of sulfur doping on optical anisotropy of CdSiAs2
Authors: Osinsky Andrei , Chernyak Leonid , Temkin Henryk , Wen Yuan-Chung , Parkinson Bruce A.
Published: July 2002

Polarization dependent photoluminescence and photocurrent measurements were carried out on undoped and sulfur doped single crystals of CdSiAs2. For undoped crystal the interband transition A shows a 40 meV blueshift under perpendicular light polarization with respect to the parallel one. This shift is about twice as large for sulfur doped crystal. A pronounced photoabsorption band at 1.53 eV, related to the sulfur donor, is observed in the low temperature photocurrent spectrum. A significant enhancement of the optical anisotropy of donor-acceptor transition is seen in the low temperature photoluminescence spectra of CdSiAs2 doped with sulfur.
Magnetoresistance size effects in a three-dimensional lattice of InSb quantum dots
Authors: Romanov S. G. , Fokin A. V. , Maude D. K. , Portal J. C.
Published: July 2002

The magnetotransport was studied on three-dimensional lattices of weakly coupled InSb quantum dots (QDs) for different regimes of conductivity. Classical negative magnetoresistance was observed both in high- and low-temperature regimes; for the latter it is accompanied by quantum size effect. The correlation with the geometry of the dot lattice and its ordering was found.
Thermally induced charged carrier transfer and intersubband transitions in an asymmetrical coupled quantum well structure
Authors: Lavon Y. , Sa’ar A. , Wang J. , Leburton J.-P. , Julien F. H. , Planel R.
Published: July 2002

We have observed thermally induced charged carrier transfer in an asymmetrical coupled quantum wells structure with energy separation between the first two subbands of the order of the LO phonon energy. In this structure, the population of the second subband is not negligible and intersubband transitions from the second to higher excited subbands can be measured. Due to charged carrier transfer, the built-in dc space charge electric field is changed, giving rise to a blueshift with increasing temperature of the ground to the first excited state intersubband transition. Also, we have found that the measurements of thermally induced intersubband transitions from the second subband provide a direct way to estimate the energy separation between the second subband and the Fermi energy.
In situ real-time study of chemical etching process of Si(100) using light scattering
Authors: Zhao Y.-P. , Wu Y.-J. , Yang H.-N. , Wang G.-C. , Lu T.-M.
Published: July 2002

We report the development of an in situ real-time light scattering technique to study the wet chemical etching process of Si(100). Based on a simple scattering theory, the number of etch pits and other statistical parameters such as correlation length and interface width on a pitted surface are extracted from the scattering profile. The time evolution of the surface morphology can be interpreted by a simple rate equation.