bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface passivation of GaAs
Authors: Lee H. H. , Racicot R. J. , Lee S. H.
Published: July 2002

We have successfully passivated the surface of n-type (100) GaAs on the basis of P2S5/NH4OH treatment of the surface. A fivefold increase in the photoluminescence (PL) intensity results at room temperature when the surface is passivated and the PL intensity remains the same even after ten days’ exposure to room air. Current-voltage characteristic also corroborates the PL measurements and shows that the GaAs surface retains its integrity when passivated with P2S5 and its electronic characteristic remains invariant with time even after exposure to air for one month. The results are indications of the robust stability of the passivated GaAs surface.
Interaction of MeV ions with pre-existing damage in Si: A new ion beam annealing mechanism
Authors: Holland O. W.
Published: July 2002

A new ion beam annealing phenomenon which occurs during room-temperature irradiation of Si is discussed. The interaction of high-energy ions with different damage morphologies is shown to depend on the detailed nature of the damage. This interaction leads to annealing when the damage consists only of simple types of defects, while irradiation of more complex damage morphologies can result in additional damage growth. A model is proposed which qualitatively accounts for the phenomenon.
Negative differential resistance in AlGaSb/InAs single-barrier heterostructures at room temperature
Authors: Beresford R. , Luo L. F. , Wang W. I.
Published: July 2002

We have observed for the first time negative differential resistance at room temperature in a single-barrier tunneling heterostructure. A typical InAs/AlGaSb/InAs structure exhibits a current peak of 2.1×103 A cm−2 at 0.28 V and a peak to valley ratio of 1.6:1. We attribute the observation of room-temperature negative differential resistance to the favorable band alignment in the AlGaSb/InAs material system, which appears promising for device applications of single-barrier tunneling.
Epitaxial superconducting thin films of YBa2Cu3O7−x on KTaO3 single crystals
Authors: Feenstra R. , Boatner L. A. , Budai J. D. , Christen D. K. , Galloway M. D. , Poker D. B.
Published: July 2002

We have grown thin YBa2Cu3O7−x films on single-crystal (001) KTaO3 substrates by means of coevaporation of Y, BaF2, and Cu, followed by an ex situ anneal in wet oxygen. The films are epitaxial in three dimensions, consisting of grains with either the c or the a axis of the YBa2Cu3O7−x unit cell perpendicular to the substrate. Films with a composition close to the 1:2:3 cation ratio exhibit sharp superconducting transitions at 90 K and critical current densities in excess of 0.3 MA/cm2 in zero magnetic field at 77 K. In Cu-rich films, the Y2Ba4Cu8O16–x phase with a Tc of 80 K is formed in grains with the c axis perpendicular to the substrate.
Field-induced segregation effects during secondary-ion mass spectrometry depth profiling of Cu and Na implanted in silicon
Authors: Vriezema C. J. , Janssen K. T. F. , Boudewijn P. R.
Published: July 2002

Segregation effects during secondary-ion mass spectrometry (SIMS) depth profiling of Cu and Na implanted in n- and p-type Si are investigated under different oxygen bombardment conditions. The segregation effects are studied also with SIMS using Cs bombardment. These experiments revealed that Cu and Na segregate under primary beam conditions by which a SiO2 layer forms and positive primary ions are used. In agreement with the thermodynamics of the Si-Cu-O and Si-Na-O systems, the Na segregates at the oxide side of the SiO2/Si interface whereas Cu segregates at the silicon side of the interface. When primary O− ions are used the electric field is inverted and the segregation of Na disappears and is minimized in case of Cu. This dependence on the charge state of the primary ions demonstrates the overriding importance of the field-induced effect of this phenomenon.
Coupling strengths and flux pinning in oxide superconductors
Authors: Lichti R. L. , Chan K. C. B. , Cooke D. W. , Boekema C.
Published: July 2002

Muon spin relaxation measurements have been performed to obtain penetration depth versus temperature for several high-temperature oxide superconductors. Comparison with theoretical results based on the Eliashberg equations indicates that at 1 kOe the (RE)Ba2Cu3O7 materials (data for RE=Gd, Er, and Eu) are in the very strong coupling, extremely dirty limit, while data at 5 kOe for Bi2CaSr2Cu2O8 and Tl2Ca2Ba2Cu3O10 follow the strong coupling, clean limit curve.
Selective nucleation and growth of diamond particles by plasma-assisted chemical vapor deposition
Authors: Ma Jing Sheng , Kawarada Hiroshi , Yonehara Takao , Suzuki Jun-Ichi , Wei Jin , Yokota Yoshihiro , Hiraki Akio
Published: July 2002

Diamond particles have been selectively synthesized on a SiO2 dot-patterned Si substrate using plasma-assisted chemical vapor deposition (plasma CVD). Nucleation densities on both Si and SiO2 have been increased, first by pretreatment using abrasive powders; then, to eliminate the pretreatment effect from almost all of the substrate and to retain the effect only at designed sites, an Ar beam is used to obliquely irradiate the pretreated substrate. After deposition using plasma CVD, diamond particles have selectively formed on one edge of the SiO2 dots according to the pattern and have grown large to adjoin with adjacent particles. Polycrystals with equal grain sizes have been synthesized.
Effect of Si doping in AlAs barrier layers of AlAs-GaAs-AlAs double-barrier resonant tunneling diodes
Authors: Cheng Peng , Harris James S.
Published: July 2002

AlAs-GaAs-AlAs double-barrier resonant tunneling diodes (DBRTDs) with different doping levels in the AlAs layers have been investigated. Two-step spacer layers were used in all samples. Peak-to-valley current ratios (PVCRs) as high as 3.5 (11.3), 3.5 (11.3), and 2.7 (8.2) were observed at 300 K (77 K) for samples with undoped, 1.2×1017 cm−3, and 3×1018 cm−3 doped AlAs barriers, respectively. These results indicate that resonant tunneling is not strongly affected by ionized Si atoms in the AlAs barriers. The excellent PVCRs observed in DBRTDs with two-step spacer layers is not because of low background impurity densities in the active region, but because of a third barrier formed by band bending in the spacer layers.
Photocurrent collection in a Schottky barrier on an amorphous silicon-germanium alloy structure with 1.23 eV optical gap
Authors: Chu V. , Conde J. P. , Shen D. S. , Wagner S.
Published: July 2002

We report the result of voltage-dependent photocurrent collection measurements in Pd Schottky barriers on an undoped a-Si,Ge:H,F multilayer alloy structure with an effective optical gap of 1.23 eV. The hole mobility-lifetime product (μτ)p, extracted from a fit of the voltage dependence of the photocurrent to the Hecht expression, is 7×10−9 cm2 V−1. Our result is an important indication that it is possible to produce the low-gap a-Si,Ge:H,F alloys with the optoelectronic characteristics needed for efficient tandem solar cells.
Determination of tilted superlattice structure by atomic force microscopy
Authors: Chalmers S. A. , Gossard A. C. , Weisenhorn A. L. , Gould S. A. C. , Drake B. , Hansma P. K.
Published: July 2002

We have analyzed the structure of tilted superlattices on atomically stepped surfaces by using atomic force microscopy to detect ridges of GaAs formed by the selective oxidation and removal of intervening AlAs regions. Oxides were removed in a liquid cell of the atomic force microscope while scanning. We have demonstrated plan views which reveal the superlattice length and width uniformity, but the method is also in principle suited for cross-sectional samples.
Characterization of reorientation of a thin layer of ferroelectric liquid-crystal material under an applied field by excitation of optical modes
Authors: Elston S. J. , Sambles J. R.
Published: July 2002

The director configuration in a thin layer of ferroelectric liquid crystal (FLC) under an applied static field is investigated by exciting optic modes in a FLC cell. The reflectivity data obtained may only be fitted to theory by maintaining in the voltage-distorted optical tensor profile a point in the middle of the cell having the same structure as at 0 V. This unambiguously confirms the chevron structure observed in x-ray diffraction and shows that the layering remains largely undistorted to fields of order 3×106 V m−1.
Capture cross section of Si-SiO2 interface states generated during electron injection
Authors: Vuillaume D. , Bouchakour R. , Jourdain M. , Bourgoin J. C.
Published: July 2002

The evolution of the capture cross section of the Si-SiO2 interface states is analyzed when metal-oxide-semiconductor capacitors are stressed by Fowler–Nordheim injection of electrons from the n-type substrate. The capture cross sections of the energy distribution of the states are measured by a trap filling method using deep level transient spectroscopy. We found that the capture cross sections of near-midgap states increase by a factor 10, while they remain unchanged for the states localized near the conduction-band edge. The capture cross sections are temperature dependent and their associated activation energies increase with the stress from 30 to 100 meV. The exponential prefactor in the temperature-dependence law of the capture cross section is increased from 10−16 to 10−14 cm2 , and we suggest that the Fowler–Nordheim degradation induces new interface states of donor type in the upper part of the silicon band gap.
Transmission through a bend in an electron waveguide
Authors: Lent Craig S.
Published: July 2002

The transmission properties of a circular, right-angle bend in a two-dimensional electron waveguide are calculated. Significant reflections from such a bend would have serious consequences for the development of a quantum electron waveguide technology. The results show nearly perfect transmission around the bend, except for energies very close to the threshold for propagation in the channel. This is true even for rather sharp bends. A significant amount of mode mixing is found, however, for bends with a small radius of curvature.
Molecular field-effect transistors using conducting polymer Langmuir–Blodgett films
Authors: Paloheimo J. , Kuivalainen P. , Stubb H. , Vuorimaa E. , Yli-Lahti P.
Published: July 2002

Thin-film field-effect transistors (FETs) have been prepared using poly(3-hexylthiophene)/ arachidic acid and quinquethiophene/arachidic acid Langmuir–Blodgett (LB) films with thicknesses ranging from a monolayer to some ten monolayers. The effect of the number of layers on the mobility and conductivity has been studied. This is to our knowledge the first demonstration of a LB FET utilizing organic semiconductors as the active material.
Interaction between growing amorphous silicon and glass substrate evidenced by in situ infrared ellipsometry
Authors: Blayo N. , Drévillon B.
Published: July 2002

An in situ study of the formation of glass/hydrogenated amorphous silicon (a-Si:H) and glass/a-SiC:H interfaces by infrared (IR) phase modulated ellipsometry (PME) is presented. The high sensitivity of this new expermental technique is emphasized. In particular as compared to UV-visible ellipsometry IRPME allows a direct identification of the chemical species incorporated in a film. The presence of a chemical interaction during the formation of the Corning glass/a-Si:H (or a-SiC:H) interface is directly revealed by the vibration (near 1480 cm−1) of BO groups, coming from the substrate, incorporated into growing a-Si:H (or a-SiC:H). The boron remains incorporated into an interface layer buried at the interface. The mechanisms of this boron incorporation in the amorphous films during the early stage of the growth are discussed. Some possible technological consequences of these behaviors are mentioned.
Atomic-scale roughness of GaAs/AlAs interfaces: A Raman scattering study of asymmetrical short-period superlattices
Authors: Jusserand Bernard , Mollot Francis , Moison Jean-Marie , Le Roux Guy
Published: July 2002

We present Raman spectra obtained from very short period (a few atomic layers) GaAs/AlAs superlattices with asymmetrical unit cells containing two different GaAs wells. This allows us to analyze quantitatively for the first time the atomic-scale component of the interface roughness. We demonstrate that it mainly originates at the GaAs on AlAs interface and strongly decreases with the growth temperature and the underlying AlAs layer thickness.
Photoinduced hole carriers and enhanced resistance to photorefraction in Mg-doped LiNbO3 crystals
Authors: Wang Hong , Wen Jin-ke , Li Jiang , Wang Hua-fu , Jing Jing
Published: July 2002

The sign of photoinduced free carriers of LiNbO3:Mg and LiNbO3:Mg:Fe(0.05 wt. %) with various MgO contents has been determined by the holographic technique. The photorefraction of these crystals has also been studied. The enhanced resistance to photorefraction of LiNbO3:Mg(≳5 mol % MgO) results from the occurrence of photoinduced hole free carriers, whose concentration is nearly equal to the electron concentration.
Identification of H2(ν″) vibrational excitation processes in a hydrogen discharge
Authors: Hiskes J. R.
Published: July 2002

The enhancement of the H2(ν″) vibrational distribution observed in the medium-density hydrogen discharge of Eenshuistra and co-workers is investigated theoretically as a function of different excitation processes. The observed fivefold enhancement of the ν″=5 population with increasing discharge current is reproduced in the model. Principal excitations generating this enhancement are H3+surface recombination and fast-electron excitation. Atom-surface recombination may be a principal contributor near the ν″=1 portion of the spectrum.
Measurement of the two-photon absorption coefficient in a GaAs/AlGaAs quantum well laser
Authors: Le H. Q. , Choi H. K. , Wang C. A.
Published: July 2002

The two-photon absorption (TPA) coefficient has been measured for a single-mode GaAs/AlGaAs quantum well laser at 0.86 μm, near the lasing wavelength of 0.83 μm. Picosecond laser pulses were employed to resolve the ultrafast TPA from long-lived carrier-dependent effects. The TPA coefficient was found to be 31±6 cm GW−1, which corresponds to a value of (5.7±1.2)×10−11 esu for the imaginary part of the third-order nonlinear susceptibility. At wavelengths near the quantum well exciton, no strong resonance enhancement of the two-photon transition was observed, and the coefficient appears to be characteristic of the AlGaAs cladding layers.
Direct determination of electron mobility in photorefractive Bi12SiO20 by a holographic time-of-flight technique
Authors: Partanen J. P. , Jonathan J. M. C. , Hellwarth R. W.
Published: July 2002

The time development of a photorefractive grating created by intersecting 30 ps (532 nm) beams in a well-characterized Bi12SiO20 crystal (in a static field around 1 kV/cm) unambiguously reveals the mobility of photoexcited electrons to be 0.24±0.07 cm2/V s through what is essentially a ‘‘time-of-flight’’ measurement.
Resonant tunneling of electrons from quantized levels in the accumulation layer of double-barrier heterostructures
Authors: Wu J. S. , Chang C. Y. , Lee C. P. , Chang K. H. , Liu D. G. , Liou D. C.
Published: July 2002

We report the first observation of the resonant tunneling features associated with the quantized levels in the accumulation layer of the double-barrier resonant tunneling structure (DBRTS) with undoped electrodes. This quantum effect causes additional kinks in the current-voltage (I-V) characteristic and an increasingly enhanced oscillation behavior in the differential conductance-voltage (G-V) curve. Three discrete quantum levels have been observed based on the room-temperature G-V curve. Our measurements are made without the presence of magnetic field and thus the experimental results are totally different from the magneto-oscillation.
Leakage mechanisms of titanium silicided n+/p junctions fabricated using rapid thermal processing
Authors: Ada-Hanifi M. , Chantre A. , Levy D. , Gonchond J. P. , Delpech Ph. , Nouailhat A.
Published: July 2002

We report a physical analysis of the reverse leakage currents observed in titanium silicided n+/p junctions fabricated using rapid thermal processing. By studying the dependence of currents on temperature, bias voltage, and diode geometry, we have been able to identify the leakage mechanisms. A defect level at Ev+0.30 eV, detected in concentrations ≳1014 cm−3, is shown to be responsible for a low leakage current component, through a generation-recombination mechanism. Silicide asperities protruding through the metallurgical junction are proposed to account for the tunneling nature of a second, high leakage, distribution of currents.
Effects of low-dose Si implantation damage on diffusion of phosphorus and arsenic in Si
Authors: Park Heemyong , Law Mark E.
Published: July 2002

The effects of low-dose Si implantation damage on diffusion of low-concentration P and As in Si wafers are investigated. Dopants are implanted at a low dose and subsequently preannealed to remove any self-damage. An enhanced diffusion of P is observed by directly comparing dopant profiles in damaged and undamaged regions. Monitoring effective diffusivity of P at various annealing temperatures and times reveals that the enhanced diffusion is a transient process with a time constant which is larger at lower temperature. This enhancement is larger and of longer duration the lower the annealing temperature is. In contrast to P, As diffusion in the damaged region does not show any enhancement. This implies that the defects induced by the Si implants have separate mechanisms for interaction with each type of dopant.
Characterization and determination of the band-gap discontinuity of the InxGa1−xAs/GaAs pseudomorphic quantum well
Authors: Zou Y. , Grodzinski P. , Menu E. P. , Jeong W. G. , Dapkus P. D. , Alwan J. J. , Coleman J. J.
Published: July 2002

Single and multiple quantum well samples have been grown by atmospheric pressure metalorganic chemical vapor deposition at In compositions from 9 to 28% and layer thicknesses ranging from 15 to 140 Å, depending upon the composition. Selected samples containing three quantum wells of a given composition but with different thicknesses were characterized by x-ray double-crystal diffractometry, low-temperature photoluminescence, and transmission electron microscopy (TEM). Using a simulation technique based on the dynamical theory of x-ray diffraction in concert with TEM measurements, the In composition in the quantum well as well as the thicknesses can be directly extracted. The peak positions of the photoluminescence are used to determine the strained and unstrained energy gap and the conduction band offsets associated with InxGa1−xAs of a given composition. We have found the discontinuities to be 60% of the difference in the energy gap of GaAs and strained InxGa1−xAs.
Electrically tunable and polarization insensitive Fabry–Perot étalon with a liquid-crystal film
Authors: Patel J. S. , Lee Sin-Doo
Published: July 2002

A polarization insensitive, electrically tunable Fabry–Perot structure is demonstrated. The polarization insensitivity is realized by using a twisted structure of a nematic liquid crystal such that the molecules at one surface are orthogonal to those at the other surface. In the high-field regime, this configuration can be thought of as a structure composed of two orthogonal, birefringent slabs with the electrically controllable thickness. At low voltages the device is polarization sensitive but becomes polarization insensitive at relatively higher voltages. In the polarization insensitive region, the linewidth of the transmission peak is of the order of 0.5 nm and the tuning range is about 15 nm.
Low-temperature electron spin resonance investigations of silicon paramagnetic defects in silicon nitride
Authors: Warren W. L. , Rong F. C. , Poindexter E. H. , Kanicki J. , Gerardi G. J.
Published: July 2002

We have reproduced and extended some recently reported electron spin resonance (ESR) measurements related to the nature of the dominant charge traps in silicon nitride. We detected defect centers at low temperatures using ESR, in both as-deposited and ultraviolet-irradiated silicon nitride powders and films prepared by low-pressure chemical vapor deposition (LPCVD). Only two silicon dangling bond defects were observed in the silicon nitride, one at g=2.003 (⋅Si≡N3), and the other at g=2.005 (⋅Si≡Si3). The signal intensity at g=2.003 is by far the dominant signal in the LPCVD films and powders subjected to UV illumination; the signal at g=2.005 is only about 3% of its intensity. These results support the idea that there is just one dominant silicon paramagnetic center (⋅Si≡N3), which is responsible for charge trapping in silicon nitride.
Anomaly in C
p/C
v: A possible signature of a liquid-glass transition
Authors: Grimsditch M. , Rivier N.
Published: July 2002

Brillouin scattering from two classic glass-forming materials, ZnCl2 and glycerol, reveals a maximum in the ratio (γ) of specific heats Cp and Cv as a function of temperature. We propose that the temperature at which the maximum in γ occurs in our materials may be indicative of a ‘‘liquid-like’’ to ‘‘solid-like’’ transformation. As such it may be a convenient thermodynamic signature of a ‘glass’ transition.
Ceramic layer epitaxy by pulsed laser deposition in an ultrahigh vacuum system
Authors: Koinuma Hideomi , Nagata Hirotoshi , Tsukahara Tadashi , Gonda Satoshi , Yoshimoto Mamoru
Published: July 2002

Ceramic layer epitaxy, defined as the epitaxial growth of ceramic thin films with thicknesses regulated on an atomic scale, was verified by a new method using pulsed laser deposition in ultrahigh vacuum (UHV). The intensity oscillation of reflection high-energy electron diffraction (RHEED) was observed in an ArF excimer laser deposition of CeO2 and SrTiO3 films on Si(111) and SrTiO3(001) substrates, respectively, at 650–750 °C under 5×10−7 Pa. The oscillation periodicities corresponded well to interplane distances of CeO2(111) and SrTiO3(001). This first observation of RHEED oscillation in laser deposition of ceramic films suggests that UHV laser deposition is a promising method for producing atomically regulated ceramic layers inclusive of possible new high Tc superconductors.
Pulse buildup of the germanium far-infrared laser
Authors: Keilmann F. , Shastin V. N. , Till R.
Published: July 2002

We study the dynamics of an electrically pumped p-Ge laser with frequency fixed to 100 cm−1 by a novel selective cavity. The growing laser power increases the pump current long before it reaches a saturating power level, an effect explained by photoionization. We further find that the laser pulse can be delayed or even quenched by injected off-resonance far-infrared radiation. This effect not only gives a gain coefficient of 0.01 cm−1 and a saturation power of 400 W−which confirms the high-power capability of the laser−but furthermore reveals a novel quasihomogeneous broadening of the gain spectrum caused by transit-time effects of rapidly moving holes.
Hot filament enhanced chemical vapor deposition of AlN thin films
Authors: Dupuie Jeffrey L. , Gulari Erdogan
Published: July 2002

Hot filament enhanced chemical vapor deposition of aluminum nitride thin films from trimethylaluminum and ammonia has been investigated for deposition temperatures ranging from 584 to 732 K. The use of a hot filament resulted in an approximate two orders of magnitude increase in the deposition rate compared to a similar, uncatalyzed growth. The film deposition rate and refractive index did not depend on the substrate temperature. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that the films were high purity aluminum nitride, with negligible carbon and oxygen contamination.
Effect of fluorine on the diffusion of through-oxide implanted boron in silicon
Authors: Fan D. , Parks J. M. , Jaccodine R. J.
Published: July 2002

Annealing of boron through-oxide implanted silicon has been known to induce an incubated, oxygen-precipitation enhanced boron diffusion. In this letter, it is shown that annealing the ‘‘through-oxide’’ implants in a NF3-containing N2 ambient effectively reduces the incubated enhanced diffusion. The effect of fluorine is further demonstrated for boron plus fluorine through-oxide implants with pure N2 annealing. Comparing the boron diffusion between boron plus fluorine and boron plus neon implants suggests that fluorine does not have a chemical effect on capturing the point defects that cause the enhanced diffusion. Rather, fluorine is believed to be incorporated in the oxygen precipitates, which alters the point defect generation.
1.55 μm buried heterostructure laser via regrowth of semi-insulating InP:Fe around vertical mesas fabricated by reactive ion etching using methane and hydrogen
Authors: Kjebon O. , Lourdudoss S. , Hammarlund B. , Lindgren S. , Rask M. , Ojala P. , Landgren G. , Broberg B.
Published: July 2002

A GaInAsP/InP Fabry–Perot-type buried-heterostructure quantum well laser operating at 1.55 μm has been realized utilizing iron-doped semi-insulating InP around vertical mesas fabricated by reactive ion etching using methane and hydrogen. A maximum cw output power of 19 mW has been achieved on as-cleaved chips of 300 μm length with a quantum efficiency of 21% per facet. Threshold currents lie between 20 and 25 mA. As low as 2 Ω series resistance has been measured despite an ohmic contact area not exceeding that of the 2-μm-wide mesa. A 3 dB bandwidth of 7.5 GHz at 12 mW output power is obtained from the small-signal frequency modulation measurements.
Ion beam synthesis of buried α-FeSi2 and β-FeSi2 layers
Authors: Radermacher K. , Mantl S. , Dieker Ch. , Lüth H.
Published: July 2002

Using high dose implantation of Fe+ into (111)Si, followed by rapid thermal annealing (RTA) at 1150 °C for 10 s, we fabricated continuous buried layers of the metallic α-FeSi2 phase. Rutherford backscattering experiments indicate that these layers contain a large number of Fe vacancies, up to 18%. By implanting through a SiO2 mask, we produced Schottky diodes with idealty factors of 1.4±0.1 and a Schottky barrier height of ΦB=0.84±0.03 eV on (111) n-Si. In this letter we report for the first time the formation of the semiconducting stoichiometric FeSi2 (β-FeSi2) phase by annealing the buried α-FeSi2 layers below the phase transition temperature of 937 °C; specifically at 750 °C for 20 h.
Ion-irradiation control of photoluminescence from porous silicon
Authors: Barbour J. C. , Dimos D. , Guilinger T. R. , Kelly M. J. , Tsao S. S.
Published: July 2002

Ion irradiation was used to pattern a region of red-light emitting porous silicon by eliminating visible-light photoluminescence (PL). The PL peak wavelength is approximately 735 nm and shows little dependence on the excitation-light wavelength. The ratio of PL intensities for different excitation wavelengths was shown to be proportional to the ratio of the absorption coefficients. Below saturation, the integrated PL intensity increased linearly with excitation-light power density.
Ultrathin silicon nitride films prepared by combining rapid thermal nitridation with low-pressure chemical vapor deposition
Authors: Ando K. , Ishitani A. , Hamano K.
Published: July 2002

Ultrathin silicon nitride films were prepared using rapid thermal nitridation prior to low-pressure chemical vapor deposition (RTN+LPCVD). The low-field leakage current of the 4.5-nm-thick film was found to be significantly reduced to a value of 10−8 A/cm2 at 4 MV/cm. Additionally, the time needed for 50% of the films to show dielectric failures was extended by about 20 times, relative to conventional LPCVD silicon nitride films. These improvements in electrical characteristics may be attributed to the low interface oxygen concentration as determined by secondary-ion mass spectroscopy and x-ray photoelectron spectroscopy. The RTN+LPCVD films are very suitable for use in future dynamic-random-access memories.
Negative persistent photoconductivity in the Al0.6Ga0.4Sb/InAs quantum wells
Authors: Lo Ikai , Mitchel W. C. , Manasreh M. O. , Stutz C. E. , Evans K. R.
Published: July 2002

We have measured the Shubnikov–de Haas (SdH) effect in the Al0.6Ga0.4Sb/InAs quantum wells under the negative persistent photoconductivity (NPPC) conductions. By illuminating the sample at low-temperature, the carrier concentration of the two-dimensional electron gas in the InAs well was reduced from 5.8 to 3.6×1011 cm−2 and the corresponding quantum lifetime increases from 0.16 to 0.21 ps. The electrons which escaped from the InAs well were captured by the ionized deep donors in the Al0.6Ga0.4Sb layers. The effective mass is equal to (0.0317±0.0005)m0. We also propose, based on the SdH data, that the illumination of the sample with the ionized deep donors at low temperature will exhibit the NPPC effect.
Picosecond duration, large amplitude impulse generation using electrical soliton effects
Authors: Case Michael , Carman Eric , Yu Ruai , Rodwell M. J. W. , Kamegawa Masayuki
Published: July 2002

We report two devices which generate picosecond duration electrical impulses using soliton propagation effects. A high repetition-rate device has generated an 8.1 Vp-p (87 mAp-p), 4.5 ps full width at half-maximum (FWHM) impulse train at a 31.5 GHz rate. A high compression ratio device has generated an 11.4 Vp-p (122 mAp-p), 5.1 ps FWHM impulse train at a 9 GHz rate (sinusoidal input), and a 12.1 Vp-p (130 mAp-p), 4.9 ps FWHM impulse train at a 3.22 GHz repetition rate (28 ps FWHM impulse-train input).
Surface donor contribution to electron sheet concentrations in not-intentionally doped InAs-AlSb quantum wells
Authors: Nguyen Chanh , Brar Berinder , Kroemer Herbert , English John H.
Published: July 2002

The electron concentration in not-intentionally doped InAs/AlSb quantum wells is found to depend sensitively on the top AlSb barrier thickness even for barriers as thick as 100 nm. The carrier concentration increases as the thickness of this barrier is decreased. The analysis of the dependence of concentration on top barrier thickness indicates that the Fermi level is pinned at the surface of the sample, 850±50 meV below the conduction band edge of the AlSb top layer. Surface donors are the main contribution to the high carrier concentrations in these not-intentionally doped wells.
Molecular beam epitaxial regrowth on in situ plasma-etched AlAs/AlGaAs heterostructures
Authors: Choquette Kent D. , Hong M. , Freund R. S. , Chu S. N. G. , Mannaerts J. P. , Wetzel R. C. , Leibenguth R. E.
Published: July 2002

Epitaxial regrowth by solid-source molecular beam epitaxy (MBE) on dry etched heterostructures possessing exposed AlAs surfaces is accomplished for the first time using a vacuum integrated processing. Samples composed of multilayers of AlAs and AlGaAs are patterned with a SiO2 mask and are anisotropically etched using a low damage electron cyclotron resonance (ECR) SiCl4 plasma process. Etched samples are transferred in ultrahigh vacuum between the ECR and MBE chambers to avoid atmospheric exposure before regrowth. Microstructural analysis of the overgrown layers by scanning and transmission electron microscopy indicates that epitaxial regrowth on both the etched field and vertical sidewalls is achieved. The regrown material is found to contain microtwin plates, but few dislocations, indicating the good quality of the overgrowth.
Electro-optic sampling and carrier dynamics at zero propagation distance
Authors: Keil U. D. , Dykaar D. R.
Published: July 2002

We demonstrate 200 fs (full width at half maximum) electrical pulse generation and detection using low-temperature grown GaAs and total internal reflection electro-optic sampling. System limited electrical rise times (10%–90%) of 150 fs are measured. Carrier dynamics are investigated for short times in GaAs and InP using this technique and compared with transient reflectivity measurements.
Electron mobility and Si incorporation in InxGa1−xAs layers grown on GaAs by molecular beam epitaxy
Authors: Ekenstedt M. J. , Songpongs P. , Andersson T. G.
Published: July 2002

Layers of InxGa1−xAs with In-mole fraction ranging from 0 to 1 were grown on GaAs by molecular beam epitaxy. The electron mobility was measured by Hall effect as a function of both In concentration and temperature. The mobility was found to depend strongly on the composition. These experimental results were accurately calculated based on scattering from ionized impurities, polar optical phonons, the disordered alloy, and dislocations. In addition, the effect of space charge scattering is discussed. For layers with 0.2≤x≤0.85 the mobility monotonically declined with reduced temperature below 300 K as an effect of increased ionized impurity and space charge scattering. Free-carrier concentration due to Si-doping of InAs layers was also investigated. This was found to vary exponentially from the 1016 to 1019 cm−3 with the inverse Si-source temperature. The highest measured value was 3.3×1019 cm−3 and the carrier concentration saturated above this. For such high values the surface was deteriorated which we attributed to precipitation of silicon.
Wavelength tuning and absorption line shape of quantum well infrared photodetectors
Authors: Choi K. K. , Taysing-Lara M. , Newman P. G. , Chang W. , Iafrate G. J.
Published: July 2002

We have conducted a systematic theoretical and experimental study on wavelength tuning and absorption lineshape of single-bound-state quantum well infrared photodetectors. By computing the oscillator strength using the exact quantum well eigen functions, we show that an intersubband transition is from the ground state to the first resonant state in one extreme when the ground state is totally localized in the well, or to the second miniband in another extreme when the ground state wave function is delocalized. In the intermediate cases, the absorption wavelength is determined by the energy of a final state with which the oscillator strength is maximum. We also calculated the absorption lineshape and show that it depends sensitively on the position of the final state relative to the global band structure of the detector.
Conditions for the formation of defect-induced bound exciton emissions in GaAs grown by molecular beam epitaxy
Authors: Ohnishi Nobukazu , Makita Yunosuke , Asakura Hisao , Iida Tsutomu , Yamada Akimasa , Shibata Hajime , Uekusa Shin-ichiro , Matsumori Tokue
Published: July 2002

Conditions for the formation of defect-induced bound exciton (DIBE) emissions in GaAs were investigated by molecular beam epitaxial method. Growth was made on both A- and B-polarity substrates with (321), (221), and (211) orientations. For A-polarity samples, (321)A and (211)A presented pronounced DIBE emissions. (221)A, however, exhibited no DIBE emission, instead it presented a dominant carbon donor-carbon acceptor pair emission together with a small hump due to carbon donor-related bound exciton emissions. For B-polarity specimens, DIBE was completely vanished in all the three samples. It was theoretically demonstrated that DIBE is formed only when double-handed Ga adatom site is existing.
Anomalous diffusion of nitrogen in SiO2 under ion bombardment
Authors: Banerjee Indrajit , Kuzminov Dimitry
Published: July 2002

Depth profiling was done by secondary ion mass spectrometry (SIMS) on SiO2/Si3N4/SiO2 (ONO) structures to determine if the nitrogen tail seen going into the silicon substrate was real or an artifact of ion bombardment. To determine this without an element of doubt, samples were thinned from the back side to the ONO layer and SIMS depth profiling was carried out on the exposed underside of ONO. It is determined that the layer of ‘‘nitride’’ at the Si/oxide interface is really an artifact of ion bombardment. Profiling from the back side shows there is no nitrogen tail in the silicon substrate and there is also no nitride at the oxide/Si interface. The interfacial nitride layer, and the apparent nitrogen tail extending into the underlying Si, seen from front-side profiling, are due to anomalous nitrogen diffusion during ion bombardment. It is believed that nitrogen-oxygen complexes are formed in the silicon substrate as a result of nitridation, and this adversely affects device performance. Though this may still be true, one needs to be cautious in interpreting SIMS and Auger depth profiles from the front side in order to corroborate the electrical results.
Normal incidence high contrast multiple quantum well light modulator based on polarization rotation
Authors: Shen H. , Wraback M. , Pamulapati J. , Dutta M. , Newman P. G. , Ballato A. , Lu Y.
Published: July 2002

A novel optically addressed normal incidence multiple quantum well light modulator based on polarization rotation has been demonstrated for the first time. This modulator employs the anisotropic excitonic absorption created by a thermally induced in-plane uniaxial strain in a multiple quantum well structure to achieve rotations as large as ±25°. An exceedingly high contrast ratio of 330:1 has been measured in this device.
Stress releasing mechanisms in In0.2Ga0.8As layers grown on misoriented GaAs [001] substrate
Authors: Werner P. , Zakharov N. D. , Chen Y. , Liliental-Weber Z. , Washburn J. , Klem J. F. , Tsao J. Y.
Published: July 2002

The influence of substrate misorientation on the structure and morphology of In0.2Ga0.8As layers grown by molecular beam epitaxy on vicinal, near (001), GaAs substrates was investigated by transmission electron microscopy. The substrates were tilted at angles between 0° and 10° in 〈100〉, 〈110〉, and 〈120〉 directions. In layers which exceeded the critical thickness, networks of 60° dislocations running along the intersections of the four {111} planes with the interface were observed. Growth uniformity and anisotropy of strain relaxation were shown to depend on the type of growth steps introduced by a particular tilting direction.
Hydrogen enhancement of silicon thermal donor formation
Authors: Lamp C. D. , James D. J.
Published: July 2002

Oxygen-related thermal donor formation in Czochralski silicon is characterized by the capacitance-voltage and deep level transient spectroscopy techniques as a function of 450 °C anneal time following hydrogenation. Increases in the formation rate and number of thermal donor (TD) defects found after hydrogenation are reported. This study finds an increase in TD+/++ concentration in the near-surface region at short anneal times, but at longer times an elevated concentration was not observed. No acceleration through the sequence of thermal donor defects was detected. This fails to support the model of hydrogen lowering the barrier to oxygen diffusion and accelerating the TDn→TDn+1 transitions. This study does, however, support a model in which the hydrogen increases the available thermal donor core sites.
Doping-induced selective area photoluminescence in porous silicon
Authors: Steckl A. J. , Xu J. , Mogul H. C. , Mogren S.
Published: July 2002

The incubation time (ti) for the onset of porous Si formation by stain etching in HF:HNO3:H2O was observed to be a strong function of dopant type and concentration. For B-doped p-Si, ti increased significantly with substrate resistivity (ρ), from ∼0.5 min for 0.004 Ω cm to ∼9 min for 50 Ω cm. P-doped n-Si substrates exhibited a ti which decreased with increasing ρ, from ∼10 min for 0.15 Ω cm to ∼8 min for 20 Ω cm. We have utilized the difference in ti between n- and p-type Si to produce selective area photoluminescence (PL) by Ga+ focused ion beam (FIB) implantation doping and B+ broad beam implantation doping of n-type Si. Using 30 kV FIB Ga+ implantation, PL patterns with submicrometer resolution have been obtained for the first time.
Measurement of frequency spectrum of submillimeter-wave gyrotron output using Michelson interferometer
Authors: Idehara T. , Tatsukawa T. , Ogawa I. , Yamagishi Y. , Kanemaki T.
Published: July 2002

Measurements of frequency spectra of millimeter to submillimeter wave range and its application to gyrotron output are described. The results demonstrate that mode competition in the gyrotron between cyclotron fundamental (n=f/fc=1) and its harmonics (n=2,3,4,...) operations occurs in almost all cases, however, auxiliary operations can be suppressed about 30 dB lower than main operation by controlling an electron beam current and applied magnetic field.
Fabrication of high aspect ratio silicon pillars of <10 nm diameter
Authors: Chen Wei , Ahmed Haroon
Published: July 2002

We report the fabrication of high aspect ratio, sub-10 nm size, structures in silicon without involving any wet chemical etching. A 50 nm thick double layer of low and high molecular weight polymethylmethacrylate resist was exposed with an 80 kV electron beam of diameter smaller than 5 nm. After exposure the resist was developed in 3:7 cellusolve: methanol with ultrasonic agitation during development. A 5 nm thick AuPd film was deposited by ionized beam evaporation and a metal pattern was obtained by liftoff. Sub-10 nm AuPd dots were recorded with a scanning electron microscope. The AuPd pattern was then used as a mask on the Si substrate which was etched with reactive ion etching. Silicon nanocolumns with diameters ranging from 5 to 7 nm and an aspect ratio of height to diameter of about 7:1 were obtained.
Growth kinetics of disk-shaped extended defects with constant thickness
Authors: Dunham Scott T.
Published: July 2002

In this work, we derive a simple analytic expression for the growth rate of disk-shaped extended defects which maintain their thickness as they grow. The analysis includes both the interface reaction and solute diffusion as limiting the growth rate. We consider both the surface energy and the matrix strain energy and assume a toroidal capture surface around the periphery of the disk in determining the rate of the interface reaction. We utilize a series of spheres to approximate a torus and thereby are able to derive a simple expression for the solute concentration near the periphery of the disk as a function of solute diffusivity and defect size.
Three SQUID gradiometer
Authors: Koch R. H. , Rozen J. R. , Sun J. Z. , Gallagher W. J.
Published: July 2002

We have invented a three superconducting quantum interference device (SQUID) gradiometer (TSG) that uses three SQUID magnetometers and a novel feedback method to measure magnetic field gradients. One SQUID, designated the reference SQUID, operates normally except that its feedback loop output is directed to all three SQUIDs through identical nonsuperconducting coils around each SQUID. The feedback loops for the remaining two SQUIDs, the sensor SQUIDs, measure the differences between the magnetic field at the reference SQUID location and those at the sensor SQUID locations. The voltage difference between the two sensor SQUID outputs divided by the gradiometer base line, the distance between the sensor SQUIDs, represents the average magnetic field gradient. We have measured gradient sensitivities of 10−12 and 10−10 T/m√Hz for TSGs made from bare low-Tc and high-Tc SQUIDs. An advantage of a TSG is that a sensitive gradiometer, free of hysteresis error, can be made using relatively small substrates.
Experimental evidence for charge-transfer excitation of Yb in InP
Authors: Bohnert G. , Weber J. , Scholz F. , Hangleiter A.
Published: July 2002

Experimental evidence for a charge-transfer excitation of Yb in InP on cubic lattice site YbIn is obtained from time-resolved photoluminescence spectra. The results strongly indicate that the Yb related electronic level EC−30 meV, up to now only considered to be an electron trap, is indeed the Yb3+/Yb2+ acceptor level. We conclude that this level plays the crucial role for effective excitation of the 4f emission of the Yb3+ ion in InP. The thermal quenching in photoluminescence and for the decay time is ascribed to hole emission from the excited Yb3+ ion into the valence band.
Limiting factors for critical current densities in Bi2Sr2Ca2Cu3O10-Ag composite superconducting tapes at elevated temperatures
Authors: Shibutani K. , Li Q. , Sabatini R. L. , Suenaga M. , Motowidlo L. , Haldar P.
Published: July 2002

Detailed measurements of I-V curves at 4.2, 65, and 77 K as a function of applied magnetic field for two Bi(2:2:2:3)/Ag tapes, having critical current densities Jc of ∼1 and ∼2×104 A/cm2 (at 77 K and 0 T), revealed that (1) the primary limiting factor for the transport critical current densities in these tapes is the presence of a large fraction of weak and/or nonsuperconducting grain boundaries; (2) the observed dissipative voltages are due, however, mostly to the motion of the magnetic vortices in the grains; and (3) the E-J curves are well described by an expression, E∼exp[−(J0/J)μ], rather than the commonly used power law, i.e., E∼Jn, where μ, J0, and n are constants.
Activation volume associated with the relaxation of the second order nonlinear optical susceptibility in a guest-host polymer
Authors: Brower Shane C. , Hayden L. Michael
Published: July 2002

The volume associated with the relaxation of the second order nonlinear optical susceptibility in a guest-host polymer was determined by measuring the change in the rate of decay of the second harmonic signal from poled films as a function of hydrostatic pressure. The logarithm of the decay rates determined from Kohlrausch–Williams–Watt fits was found to vary linearly with pressure from 1–2100 atm. Above 2100 atm a saturation effect was observed. An activation volume of 86±2 cm3/mole, nearly equal to the size of one monomer unit, was found.
Laser annealing of SrTiO3 thin films deposited directly on Si substrates at low temperature
Authors: Otani Seigen , Kimura Mami , Sasaki Nobuo
Published: July 2002

SrTiO3 films sputter deposited directly on a Si substrate at 200 °C were annealed at a scanning cw Ar laser beam at a substrate temperature of 200 °C. The laser annealing improved the crystallinity of the SrTiO3 films and minimized the formation of a SiO2 layer between SrTiO3 and Si. These results are confirmed by x-ray diffraction analysis and secondary ion mass spectrometry. The dielectric constant of the SrTiO3 films increased monotonically with laser power up to 1.2 W. The dielectric constant was improved from the as-grown value of 26–118 for a 160-nm-thick SrTiO3 film annealed at a 1.2 W laser power. At 1.0 W laser power, the annealed dielectric constant varied from 55 to 101 with increasing film thickness from 110 to 380 nm. From the film thickness dependence constant, it is shown that the intrinsic dielectric constant for the SrTiO3 films is about 150.
High power microwaves at 9 GHz from an extended length cavity in a coaxial beam geometry
Authors: Davis T. J. , Schächter L. , Nation J. A.
Published: July 2002

Experiment and simulation demonstrate high power microwave generation at 9 GHz using a 9-cm-diam, 400-keV, 7-kA annular electron beam. The beam is propagated in a coaxial drift tube between inner and outer conductors, a configuration which increases the available beam current and reduces the surface fields from existing high power sources. The microwave interaction is provided by an extended length loaded cavity, overcoming the limitations of radiative loss and low quality factor usually imposed by the coaxial geometry. A coupler samples 25 MW of the total 200 MW produced by the beam-cavity interaction. Simulations indicate that the 7% efficiency can be significantly improved by optimizing the interaction length.
Self-consistent simulation of Stark shift of intersubband transition in modulation-doped step quantum wells
Authors: Huang F. Y. , Li J. , Li Lie-Ming , Morkoç H.
Published: July 2002

Self-consistent simulations, including free carrier screening and many body effects, have been carried out for Stark shifts of intersubband transitions in step quantum wells. Unlike carrier screening in single quantum wells, where the charge distribution screens the applied field and reduces the Stark shift, our numerical results show that the asymmetric nature of the step quantum well may yield to an enhancement in the Stark shift. Discrepancies between experimental data and theoretical simulations are also addressed.