bluuebunny/crossref_metadata_2025 huggingface dataset:
Ex situ formation of HgSe electrical contacts to p-ZnSe
Authors: Fijol J. J. , Trexler J. T. , Calhoun L. , Park R. M. , Holloway P. H.
Published: July 2002

A novel method of forming semimetal HgSe electrical contacts to p-type ZnSe through an ex situ growth process has been developed. The ex situ process consisted of deposition of an amorphous Se capping layer on p-ZnSe prior to removal from the molecular beam epitaxy (MBE) growth chamber. This capping layer protected the p-ZnSe from contamination and oxidation upon removal from the MBE growth chamber. This capping layer was reacted with Hg to form HgSe by heating to 150 °C for ∼15 min in Hg vapor. Transmission electron microscopy and x-ray diffraction data showed that the cubic HgSe phase was formed. Auger sputter depth profiling data were consistent with the formation of stoichiometric HgSe. The electrical characteristics of the contacts were studied using temperature dependent I–V measurements which showed that thermionic emission dominated conduction across the interface for low reverse biases (VR<2.5 V). However, thermionic field emission dominated conduction for VR≳2.5 V. The barrier height for thermionic emission and the energy parameter for tunneling were determined to be ∼0.55 and 0.0076 eV, respectively, consistent with an unpinned Fermi level.
Modifications of the three-dimensional transport properties of Si-doped Al0.25Ga0.75As exposed to CH4/H2 reactive ion etching
Authors: Pereira R. G. , Van Hove M. , Van Rossum M.
Published: July 2002

We study the modifications on the three-dimensional transport properties of Si-doped AlGaAs layers exposed to CH4/H2 reactive ion etching (RIE) by using the temperature dependence of Hall measurements. The persistent photoconductivity (PPC) effect is observed for the samples illuminated at low temperature (4.2 K). A strong capture region is observed between 100 and 160 K. Different annealing temperatures (between 300 and 450 °C) are used to study the effect of the passivation of Si donors and DX centers on the PPC. For annealing temperatures lower than 350 °C a new capture region is identified and attributed to the DX3 center. Also, the resistivity and mobility are modified by RIE exposure. The transport characteristics are recovered after thermal annealing at temperatures higher than 400 °C.
Dynamic motion of mask membrane in x-ray stepper
Authors: Uchida Norio , Kikuiri Nobutaka , Nishida Jun
Published: July 2002

This article presents a new analysis method and experimental results for the deflection and vibration of x-ray masks, which are caused by the squeeze effect of the gas film between a mask and a wafer in x-ray steppers. The deflection and vibration occur when a mask-to-wafer gap setting is executed or if the wafer vibrates in the mask direction during stepping motion with a narrow gap. They are not only detrimental to the throughput, but may also damage the mask membrane. Lees’ difference approximation method is applied to a compressible Reynolds’ equation and the equation of motion for the mask membrane. The main results of calculations and experiments, which showed good agreement with each other, are outlined below. (1) When the wafer approaches the mask at a constant velocity, the mask deflection increases in proportion to the velocity, and the mask deflection is larger for a smaller mask tensile stress. (2) When the wafer vibrates in the mask direction, the amplitude of the mask vibration increases with increasing the wafer frequency, and reaches a maximum value at a frequency that depends on the gap size. The maximum amplitude of a tested mask becomes 4 times as large as the wafer amplitude. (3) For a high frequency and narrow gap, the mask vibrates while deflecting convexly in the direction opposite to that of the wafer.
Information storage using conductance change of Langmuir–Blodgett film and atomic force microscope/scanning tunneling microscope
Authors: Yano K. , Kuroda R. , Shimada Y. , Shido S. , Kyogaku M. , Matsuda H. , Takimoto K. , Eguchi K. , Nakagiri T.
Published: July 2002

Bits of 10 nm in diameter are written in polyimide Langmuir–Blodgett (LB) films using the atomic force microscope (AFM) combined with scanning tunneling microscope (STM) for simultaneous operation (AFM/STM). Clear spots are observed in the current image at the points where voltage pulses are applied, while no specific feature such as protrusions or holes is observed in the AFM image. These results show that the bit cannot be attributed to metal deposition onto the sample surface or destruction of the LB film, but to the change in conductance of the LB film. The transition speed is faster than 10 μs, and reproducibility of the bit formation is so high that 103 bits, at least, can be formed without tip degradation. These facts show that the combination of LB film and AFM or STM is useful for storage devices with huge capacity.
Reconstruction of ribosomal subunits and rDNA chromatin imaged by scanning force microscopy
Authors: Fritzsche Wolfgang , Martin Linda , Dobbs Drena , Jondle Daniel , Miller Richard , Vesenka James , Henderson Eric
Published: July 2002

Scanning force microscopy (SFM) reveals surface topography by scanning a sharp tip in close proximity to the sample. Due to tip–sample interaction, artificial broadening of the real surface structure with the tip geometry occurs. One approach for image reconstruction is the use of calibration standards, preferably in the size range of the samples. In the present study, an image reconstruction method based on colloidal gold as a geometric standard was used to reconstruct SFM images of biomolecules. Sample and calibration standard size were in the nanometer range, and the standards were coadsorbed with the specimen. Raw and reconstructed images of the biomolecules were compared, and the reconstruction was characterized by difference images as well as determination of the difference volume. The application of image reconstruction based on colloidal gold as a calibration standard for SFM of biomolecules is discussed.
Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy
Authors: Xu Jun , Overbury S. H. , Wendelken J. F.
Published: July 2002

Laser irradiated Si(100) surfaces were studied with an ultrahigh vacuum scanning tunneling microscopy system. Our observations indicate that only the dimerized outermost atomic layer is removed if the laser fluence is below the melting threshold at photon energy larger than the band gap. The newly exposed layer, surprisingly, did not have a dimerized atomic structure, but rather, resembled that of a bulk-terminated structure. The uncovered layer remained atomically smooth (no vacancies) even after 90% of the outermost layer was removed. A possible explanation of these observations is that atom removal occurs by a preferential breakage of the atomic bonds in defect sites. When the laser fluence was increased to levels above the melting threshold, extensive surface roughening occurs.
Growth of a uniaxial incommensurate C60 lattice on Ge(100)2×1
Authors: Klyachko D. , Chen Dongmin
Published: July 2002

Room temperature adsorption of C60 on a Ge(100)2×1 surface from a few molecules to a full monolayer coverage was studied using scanning tunneling microscopy and low-energy electron diffraction. The distribution of the C60 molecules at the early stage of adsorption indicates that the molecules dissipate their in-plane kinetic energy primarily through collisions with other bound C60 molecules, rather than steps and vacancies of the surface. Upon thermalization, the molecules reside exclusively in troughs between dimer rows of the substrate. Clustering of the molecules takes place from outset of the adsorption, and the molecules in clusters adopt either a four-dimer or a two-dimer binding site. Subsequent adsorption proceeds in an orderly fashion, leading to the growth of two-dimensional islands and finally an overlayer with a uniaxial incommensurate C60 lattice structure. The adsorption of C60 molecules appears to affect the buckling of the substrate dimers.
In situ observation of the tip shape of Co–Ge liquid alloy ion sources in a high-voltage transmission electron microscope
Authors: Driesel W. , Dietzsch Ch. , Hesse E. , Bischoff L. , Teichert J.
Published: July 2002

For in situ observation in a 1 MeV TEM Co–Ge liquid alloy ion sources (LAISs) were mounted to a special specimen holder revealing the formation of the field-stabilized Co–Ge liquid alloy cone, the change in the tip shape as a function of the ion emission current, spatial shifts of the liquid alloy cone, and microdroplet emission from Co–Ge LAISs. This has facilitated the better understanding of the ion and microdroplet emission process from Co–Ge LAISs in a large range of ion current. Below the onset voltage the shape of the tip covered with the liquid Co–Ge alloy is spherical. At the onset voltage the Taylor cone is formed. A jetlike protrusion at the cone vertex may or may not exist. At higher ion emission currents there is a jetlike protrusion at the Taylor cone vertex. The cone half-angle α decreases and the jet length l increases with increasing emission current Ie. Linear dependences of α and l on Ie are found. Emission of microdroplets is observed at the shanks behind the Taylor cone. The radius of microdroplets varied between 0.035 and 10 μm. These microdroplets are emitted in time intervals of about 0.1 s and more.
Morphology of thin Sb layers grown on Si(111)7×7 at room temperature
Authors: Cuberes M. T. , Ascolani H. , Moreno M. , Sacedón J. L.
Published: July 2002

A systematic scanning tunneling microscopy (STM) study of the surface morphology of thin Sb layers deposited at room temperature on the Si(111)7×7 surface has been performed. Deposition of ≊0.25 monolayers (ML) of Sb results in a rough topography that consists mostly of two-dimensional clusters. For greater Sb coverages, Sb forms three-dimensional islands on the Si substrate. For a Sb thickness of ≊20 ML, a transition from an amorphous to a polycrystalline structure of the Sb overlayers is identified from the STM images.
Buried-gate oxide thinning during epitaxial lateral overgrowth for dual-gated metal–oxide–semiconductor field-effect transistors
Authors: Watts Josef S. , Neudeck Gerold W.
Published: July 2002

During epitaxial lateral overgrowth of single-crystal silicon over thermal SiO2, in the low-pressure chemical vapor deposition reactor environment, thinning and even pinholes can occur in the underlying gate oxide of in dual-gated silicon on insulator metal–oxide–semiconductor field-effect transistors (MOSFETs). The epitaxial lateral overgrowth was grown using dichlorosilane (DCS), HCl, and H2 at 970 °C and 40 Torr. Although the etch rate was very small, the thinning was large enough to change the bottom channel threshold voltage (Vt). Oxide thickness measurements, obtained by ellipsometry and by profilometer measurements, indicated an etch rate of about 0.1 nm/min, which was independently confirmed from MOSFET Vt shift measurements. The oxide etch rate decreased with increasing concentration of HCl and was less for oxides grown from heavily arsenic-doped than from lightly doped boron silicon.
Nanoscale selective adsorption of disilane on the Si(111) surface partially terminated by Ga atoms
Authors: Fujita Ken , Kusumi Yukihiro , Ichikawa Masakazu
Published: July 2002

Selective adsorption of disilane, Si2H6, on the Si(111) surface partially terminated by Ga atoms has been investigated by scanning tunneling microscopy in the temperature range from 390 to 480 °C. When the substrate temperature is below 420 °C, disilane is dissociatively adsorbed in Si(111)7×7 regions, whereas it is hardly adsorbed in Si(111)∛×∛-Ga regions due to Ga termination of Si dangling bonds. The migration of precursors dissociated from disilane is not significant on the Si(111)7×7 surface below 420 °C. Consequently, precursors containing Si atoms are not supplied to Ga-terminated regions by the disilane dissociation in the Ga-terminated regions or the surface migration from 7×7 regions. Above 420 °C, precursors dissociated from disilane migrate from Si(111)7×7 regions to Ga-terminated regions, resulting in a two-dimensional island growth of Si in Ga-terminated regions.
Atomic force microscopic observation at initial growth stage of vacuum-deposited thin film of polyvinylidenefluoride
Authors: Seyama Hideo , Maki Kunisuke , Yamazaki Nobuhiro
Published: July 2002

Vinylidenefluoride and tetrafluoroethylene copolymer powder was evaporated to grow a thin film of polyvinylidenefluoride on a Si wafer with the native oxide layer held at 80 °C in a vacuum of 10−5 Torr. Its initial growth process was studied with an atomic force microscope. Some features in the initial film growth stage at 0.2 to 6 nm in its thickness d are: (1) “plateau” and “mountain” islands with the number density in the order of 107 cm−2 grow with the coverage linearly increasing with d; (2) secondary plateau islands grow at d>2 nm; (3) the height was 6, 25, and 1.5 nm for plateau, mountain, and secondary plateau islands, respectively, which was almost independent of d. These are briefly discussed from the viewpoint of the crystallization of bulk polymer and from the thin film growth process.
Deep level transient spectroscopy study of the damage induced in n-type silicon by a gate oxide etching in a CHF3/Ar plasma
Authors: Adegboyega G. , Perez-Quintana I. , Poggi A. , Susi E. , Merli M.
Published: July 2002

Deep level transient spectroscopy was used to detect the presence of deep levels correlated to the defects induced in the Si substrate by a CHF3/Ar dry etch of a 550 Å gate oxide as a function of the rf power. Several energy levels were observed; some of them were due to the processing before the dry etching. Three traps produced by the dry etching, with Arrhenius plot activation energies, respectively, Ena1=350 meV, Ena2=220 meV, and Ena3=100 meV, and capture cross sections around 10−20 cm2 were detected. The correlation with the surface recombination velocity variations and the F and C diffusion in the Si substrate was investigated.
A simple fabrication method for nanometer-scale thin-metal stencils
Authors: Zimmerman Neil M.
Published: July 2002

We describe a simple fabrication method for the production of thin-metal stencils using the overlayer film from lift-off patterning. While such stencils have been fabricated before using other techniques, this method has several advantages. The advantages include the fact that this method requires only the capability to perform standard lithography and thin-film deposition, but does not require any dry etching or other sophisticated capabilities. In addition, by using the negative of the lithographically defined pattern, we show that a small number of trenches of lateral size down to 100 nm, in an otherwise continuous stencil, can be produced using electron-beam lithography with very little beam rastering necessary (i.e., small exposure times). We also argue that any group with access to simple photolithography and thin-film deposition facilities should be able to make these stencils, with openings much smaller than the lithography resolution limit.
Ga focused-ion-beam shallow-implanted quantum wires
Authors: Itoh M. , Saku T. , Hirayama Y. , Tarucha S.
Published: July 2002

Quantum wires were fabricated by shallow implantation of Ga ions from a focused-ion-beam source into a modulation-doped AlxGa1−xAs/GaAs heterostructure. This type of implantation reduces crystal damage and keeps the implanted ions away from the two-dimensional electron gas. An electron mobility as high as 5.04×105 cm2/V s was obtained for 10-μm-long wires with an effective width of 0.152 μm, which is much higher than any previously reported values. The electron ballistic lengths in the wires were determined from measurements of the bend and transfer resistance and agreed well with the calculated elastic mean free paths. The transfer resistance versus magnetic field profiles exhibited electron focusing peaks associated with good specularity at the boundary.
Cyclotron resonance in asymmetric modulation-doped field-effect transistor heterostructures using InxGa1−xAs quantum well and InAs–GaAs superlattice channels
Authors: Cury L. A. , Matinaga F. M. , Freire S. L. S. , Moreira M. V. B. , Beerens J. , Py M. A.
Published: July 2002

Cyclotron resonance and photoluminescence measurements were carried out on two types of modulation-doped field-effect transistor heterostructures whose channels were made of an InAs–GaAs short-period superlattice and of an InxGa1−xAs quantum well, respectively. From cyclotron resonance data a linear dependence of the channel electron effective mass on indium content was obtained for both series of samples. For a given mean value of the indium content in the channel, the effective mass is found to be systematically higher in samples where the channel is based on a short-period superlattice rather than on an alloy-based channel. This can be attributed to larger nonparabolic effects in the former. Calculations of nonparabolicity corrections are in agreement with these results. In our theoretical model, the energy of the electron and heavy hole levels were determined self-consistently.
Material uniformity improvements in a Gen II molecular beam epitaxy system
Authors: Svensson Stefan P. , Towner Frederick J. , Gill David. M.
Published: July 2002

It has been demonstrated how material uniformity can be improved in a Gen II molecular beam epitaxy system by increasing the incidence angle between the Group III cells and the substrate. The theoretical basis for this behavior has been verified experimentally by studying reflectivity maps from wafers grown without continuous azimuthal rotation. The incidence angle is most easily increased by tilting the substrate holder upward in the machine. For single-heater evaporation cells with conventional 60 cc crucibles (7° taper) the practical substrate tilt limit is approximately 13°. At this point the radius within which the center-normalized uniformity is larger than 99% is about 29 mm for cells in the lowest position. Uniformity dramatically worsens beyond 30 mm due to shadowing. By examining the geometry of the growth chamber it was found that this angle is the initial point where the beam cones from the lowest sources no longer cover the entire wafer surface. The shadowing can be reduced by using crucibles with a larger taper. Using a crucible with a 8.5° taper and a substrate tilt angle of 13° we were able to change the uniformity distribution from having a negative to a positive curvature. The maximum deviation from the center value under these conditions was about 0.5%. The switch of sign of the curvature demonstrates that the tilt angle can be further optimized and near perfect uniformity be obtained.
Development-free vapor laser photolithography with 0.4 μm resolution
Authors: Hong Xiaoyin , Lu Jianping , Yang Yongyuan , Dai Liming , Mau Albert W.
Published: July 2002

We investigated an all-dry etching process of the development-free vapor photolithography (DFVP) with a 351 nm XeF excimer laser. After masked exposure, SiO2 on a silicon wafer and under a microlithographically exposed photoaccelerator polymer film can be directly etched by a vapor containing a mixture of HF, water, and N2. Patterns with 0.4 μm resolution were obtained. In this article, effects of the etching temperature and time, exposure energy, and the concentration of 5-nitroacenaphthene in polymer on the resolution, as well as the mechanism of DFVP, are discussed.
Novel high vacuum scanning force microscope using a piezoelectric cantilever and the phase detection method
Authors: Chu Jiaru , Itoh Toshihiro , Lee Chengkuo , Suga Tadatomo , Watanabe Kazutoshi
Published: July 2002

A novel high vacuum scanning force microscope (HV-SFM) using a piezoelectric cantilever and the phase detection method was developed. A self-excited force sensing PZT microcantilever with dimensions of 125×50×3.58 μm is vibrated in vacuum at its resonance frequency by applying an ac voltage to its PZT layer. The piezoelectric microcantilever possesses a spring constant of 16.7 N/m and a vibrational quality factor of 300 in air and 807 in vacuum. As we know, force gradients acting on the vibrating cantilever cause changes in vibration amplitude and phase. The change of the phase of the output piezoelectric current, which corresponds to the phase variation of cantilever vibration, is measured as the controlling signal in this method. The piezoelectric HV-SFM that was constructed has been proved to be stable and easy to handle in vacuum. Its vertical resolution is higher than 1.1 Å. High resolution images of an evaporated Au film can be obtained in vacuum by this new dynamic HV-SFM. Grains of about 5 nm can be seen clearly. The theoretical sensitivity of phase detection with piezoelectric cantilevers is also analyzed and compared with that of amplitude slope detection in this article.
Oxygen implantation induced interdiffusion in AlGaAs/GaAs quantum well structures
Authors: Hughes Padraig J. , Weiss Bernard L. , Tlali Spirit , Jackson Howard E.
Published: July 2002

The effects of low dose (1014 ions/cm2) oxygen implantation on the subband structure of an AlGaAs/GaAs single quantum well is reported here using photoluminescence and photoreflectance spectroscopy. Postimplantation rapid thermal annealing at 900 °C up to 180 s induces compositional interdiffusion resulting in enhanced transition energy shifts and a reduction in the photoluminescence count rate. Comparisons of transition energy shifts show that the electron two to heavy-hole two transition energy is more sensitive than the ground state electron to heavy-hole transition for these annealing conditions.
Distortion aberration in a symmetric magnetic doublet for an electron beam projection system
Authors: Nakasuji Mamoru
Published: July 2002

It is found that large radial and azimuthal distortions are generated if the geometric conditions defined for the symmetric magnetic doublet lens system are not met for the inner and outer radii of the lens casing. These distortions are found by trajectory calculation and by computing third-order aberration coefficients. When the inner radius of the object side lens casing is decreased, then pincushion distortion is generated. When the outer radius of the cylindrical object side lens casing is decreased, barrel distortion is generated. Anisotropic distortion is generally present, changing sign when the inner radius of the casing is decreased significantly. The radial distortion can be compensated by adjusting the inner and outer radii of the lens casing, whereas the azimuthal distortion cannot be compensated by such adjustment. The origin of these distortions can be well understood by studying the magnitude of the maxima and minima of the axial magnetic field and magnetic vector potential. Field curvature, astigmatism, coma radius, coma length, axial chromatic, and spherical aberrations are not influenced by such variations of the inner or outer radii of the lens casing.
In situ scanning force microscopy study of TiN layers in sulphuric acid
Authors: Herranen M. , Nordin M. , Carlsson J.-O.
Published: July 2002

Morphological changes of sputter-deposited TiN films in 0.1 M sulphuric acid have been followed in situ with scanning force microscopy at different potentials. Disappearance of small structures was observed with increasing potential up to 1.2 V. A further increase of potential above 1.5 V resulted in growth of larger grains. Two passivation peaks at about 0.6 and 1.2 V, respectively, were recorded for the TiN films. The passivating layers formed at these two passivation peaks were characterized by x-ray photoelectron spectroscopy. At the lower passivation peak, titanium suboxides or oxynitrides were detected, while TiO2 was formed at potentials above 1.2 V.
Effects of cleaning and postoxidation annealing on thin oxides
Authors: Franco G. , Camalleri C. M. , Raineri V. , Ghidini G. , Clementi C. , Pellizzer F.
Published: July 2002

The aim of this work is to study the influence on the oxide quality of various cleaning procedures performed before growing a thin dielectric in a steam ambient. Different measurement methods were applied showing the improved effectiveness of constant electric field stress versus constant current density stress method to detect a cleaning, which causes particle problems on the wafer. The effect evaluation of a postoxidation treatment on different oxide thickness was also carried out.
Synthesis of electrostatic focusing and deflection systems
Authors: Szilagyi M. , Cho H.
Published: July 2002

In this article, we present synthesis of an ion beam column as a single entity, based on combined focusing and deflection (CFD). We present seven cases as examples of designing CFD systems by synthesis. Four of those are examples resulting from the a priori given multielectrode approach using a multipurpose multipole system with nine or five units. In these cases, the units have short cylindrical rings or disks cut into segments with geometrically octupole symmetry. In one example we are using the cubic spline method. The other two cases are examples obtained by using both methods in the case of a separate group of axially symmetric electrostatic lenses and electrostatic postlens deflectors. By using a sequential optimization technique combined with the gradient method and the Hooke–Jeeve’s method for a multipurpose multipole system with nine units, our calculations show that one can produce a beam spot radius less than 7 nm and current density of 614 A/cm2, scanned over a 2-mm-square field for a field ionization source. We also present comparison of our CFD system with other published data. The results display substantial improvements, especially for a field ionization source with smaller energy spread ΔU=1 eV and higher acceptance half-angle γ0=2.3 mrad. A sensitivity analysis is given, and the optimum working distances of a given CFD system are presented for the minimum beam spot radius.
Lateral tunnel junction produced by electron-beam-induced deposition
Authors: Komuro Masanori , Hiroshima Hiroshi
Published: July 2002

Electron-beam-induced deposition using a WF6 precursor molecule was applied to making metal/insulator/metal tunnel junctions for single-electron transport devices. Single wires 8 nm high and about 13 nm wide were produced on a SiO2 substrate with Au/Cr electrode pads and their conductance showed a rapid increase of about five orders of magnitude as electron-beam (EB) doses increased between 5 and 15 pC shot. To estimate the deposit thickness distribution, spatial thickness distribution in spot exposure was defined and obtained for specified EB doses. From this function, a single-wire resistivity at 230 and 300 K was determined to be 6×10−4 Ω cm at doses exceeding 15 pC/shot. Single-tunnel junctions, where space with a 2.5 nm increment was at the center of single wire, were produced. The electrical characteristics of these single junctions were fitted to a Fowler–Nordheim plot the absolute value of whose gradient gradually increased with increasing space width. The barrier height of this junction was estimated to be 0.17–0.2 eV, lower than that for SiO2/W junctions. This might be caused by the change from the metallic deposit to the insulator for the single wire as a function of the EB dose. This deposition technique enabled us to fabricate a transistor structure where dots were located in space and a side gate electrode was also deposited. The structure showed Coulomb oscillation even at 230 K and Monte Carlo simulation of this device showed reasonable agreement with the experiment, assuming appropriate circuit parameters of gate capacitance and tunnel resistance.
Selected two-dimensional effects in gas immersion laser doping of unpatterned silicon
Authors: Sadra K. , Ji H.-F.
Published: July 2002

We have performed a theoretical investigation of two-dimensional effects in melting and arsenic gas immersion laser doping of unpatterned silicon under patterned excimer-laser exposure. For pattern sizes below a few microns, the melt depths depend on the pattern size, rendering processing of narrow and wide features with the same laser fluence difficult. For wide exposed areas, molten regions are significantly narrower than the exposed widths, particularly for lower fluences. For deep submicron unexposed spaces, the melt may encroach into unexposed areas, potentially melting through them for higher fluences. Raising concerns regarding the processing of unpatterned wafers, these results indicate that structures on patterned wafers should be exploited to control thermal diffusion effects.
Selective infill metalorganic molecular beam epitaxy of InP:Si n+/n− layers for buried collector double heterostructure bipolar transistors
Authors: Schelhase S. , Böttcher J. , Gibis R. , Harde P. , Paraskevopoulos A. , Künzel H.
Published: July 2002

Fabrication of a prototype Ga0.47In0.53As/Al0.48In0.52As/InP double heterojunction bipolar transistor employing an embedded n+/n−-InP:Si subcollector/collector region in an otherwise semi-insulating InP:Fe substrate was studied. The basic layer structure was accomplished by two sequential growth cycles on the basis of device quality Al0.48In0.52As/Ga0.47In0.53As grown by molecular beam epitaxy (MBE) and InP grown by metalorganic molecular beam epitaxy (MOMBE). For the first time the embedded collector was implemented by truly selective infill growth into a substrate groove with vertical sidewalls defined by reactive ion etching (RIF) using MOMBE. Excellent layer morphology in combination with lateral interfaces without growth irregularities at the lateral substrate/collector interface were achieved in the [0-1-1] direction, while some minor facet formation due to slightly enhanced growth rates appeared in the [0-11] direction. The device layer stack was completed by large area Al0.48In0.52As/Ga0.47In0.53As MBE regrowth due to its ability to highly Be dope the GaInAs base when grown at reduced growth temperatures. Functional devices were obtained. Some degradation in the output characteristics could be directly correlated with inhomogeneities in the MBE regrown structure.
Characterization of an n-GaAs layer grown on a GaAs substrate cleaned by an electron cyclotron resonance hydrogen plasma
Authors: Takanashi Yoshifumi , Kondo Naoto
Published: July 2002

Two kinds of n-GaAs layers doped with Si to a level of 1017 cm−3 are grown by molecular beam epitaxy on GaAs substrates: those grown on substrates cleaned using low temperature electron cyclotron resonance (ECR) hydrogen plasma and those grown on substrates cleaned by conventional thermal treatment. Comparisons between the electrical properties of both layers are made by capacitance–voltage (C–V) measurement; optical deep-level transient spectroscopy (ODLTS); Van der Pauw and Hall effect measurements; and secondary ion mass spectroscopy (SIMS). It is found from SIMS analysis that for thermally cleaned wafers, C, O, and Si accumulate in the vicinity of the interface between the epilayer and the substrate, whereas only oxygen accumulates at the same interface in ECR-cleaned wafers. The C–V and Hall measurements reveal that the carrier concentration, n, as well as the electron mobility, μ, decrease in the vicinity of the interface for thermally cleaned wafers. These results can be explained theoretically by using a physical model in which Si donors are compensated by unintentionally doped C acceptors. On the contrary, no degradation of n or μ is observed for ECR-cleaned wafers. In addition, ODLTS measurement reveals the presence of deep hole traps due to the transition metals Fe and Cu, and a continuously distributed interface defect state for thermally cleaned wafers, whereas such defects are not observed for ECR-cleaned wafers.
Scanning tunneling microscopy study of reconstruction of 0.8 monolayers Ga on an Si (001) surface
Authors: Nakada Yoshinobu , Okumura Hajime
Published: July 2002

The surface structure of 0.8 monolayers (ML) Ga on an Si (001) 2×1 surface has been studied with scanning tunneling microscopy (STM). Periodical clusters, aligned in 〈110〉 directions on an Si (001) surface and reflecting the polarity of terraces on that surface, were observed. The clusters of Ga consist of the 8×5 phase. From the line profiles of the clusters in STM images, each cluster of the 8×5 phase has been found to consist of Ga double layers, the top layer of Ga being composed of four Ga atoms. Clusters in contiguous arrays are out of phase in the direction of the arrays. Pairs of two Ga atoms exist in both longitudinal sides at each cluster along the contiguous arrays. These pairs of two Ga atoms at both sides of the valleys between the contiguous arrays are located alternatively. From the above information on positions of Ga atoms, arrangements of Ga atoms of the clusters of the 8×5 phase are presumed. Two cases are considered for the arrangements of the clusters based on the arrangements of Si atoms on the top and second layers of Si (001). It is concluded that the lateral direction of clusters is parallel to the rows of the top and second layers of Si (001).
Enhanced degradation of gate oxide in negative-gas plasma during reactive ion etching
Authors: Arita Kiyoshi , Takihara Hirotaka , Asano Tanemasa
Published: July 2002

The effect of gas species on the degradation of gate oxides due to plasma exposure in reactive ion etching has been investigated. Gases tested were H2, Ar, Xe, and O2. The oxide degradation was evaluated by applying a constant-current stress and measuring the charge-to-breakdown Qbd of metal/oxide/silicon capacitors. It has been found that O2 plasma significantly degrades the reliability of the gate oxide. Characterization of plasmas using a Langmuir probe has shown that O2 gas tends to produce nonuniform plasma because of its electronegative nature, and thus enhances degradation of gate oxide.
Micropattern-gated diamond field emitter array
Authors: Kang W. P. , Wisitsora-at A. , Davidson J. L. , Howell M. , Kerns D. V. , Li Q. , Xu J. F. , Kim C. K.
Published: July 2002

Gated diamond field emitter arrays with ultralow operating voltage and high emission current have been developed. Two types of built-in gated diamond field emitters have been successfully fabricated: (i) a gated structure created by molding and self-align technique, and (ii) a cap-gated structure created by molding and electrostatic bonding. Depending on the diamond tip’s composition and surface treatment, high emission current at very low operating voltage (varying from <10 V to >10 V) can be designed to meet various applications. The built-in gated diamond tips have a stable emission current at a fixed gate voltage. Current fluctuation is found to be about 1.1% for low emission current and less than 10% for higher emission current. Emission stability is considerably more stable than silicon emitters.
Two-dimensional drift-diffusion simulation of superficial strained-Si/Si1−xGex channel metal-oxide-semiconductor field-effect transistors
Authors: Roldán J. B. , Gámiz F. , López-Villanueva J. A. , Cartujo P.
Published: July 2002

The performance of superficial strained Si/Si1−xGex channel metal-oxide-semiconductor field-effect transistors has been described making use of a two-dimensional drift-diffusion simulator including inversion layer quantization and low-field mobility curves obtained by means of a Monte Carlo simulator. We have reproduced experimental results. In addition, the dependencies of the performance enhancement obtained in these devices on the germanium mole fraction and the drain-source and gate-source voltages are described in depth.
Mechanisms and device applications of light emitting phenomena of Si/Si1−xGex/Si quantum wells
Authors: Miyao M. , Nakagawa K. , Kimura Y. , Hirao M.
Published: July 2002

Photoluminescence (PL) intensity from SiGe mixed crystals was investigated as a function of the growth temperature and/or atomic-hydrogen irradiation rate during molecular beam epitaxy (MBE). As a result, a clear one-to-one correspondence between PL intensity and the surface segregation length of Ge was obtained. This indicated that formation of Ge–Ge pairs during MBE is a key factor in determining PL intensity. Theoretical calculations showed that localized Si–Ge bonds cause s-like symmetry in the conduction band bottom and p-like symmetry in the valence band top. However, pairing of Ge–Ge atoms changes the local symmetry of the Si–Ge bonds and destroys the s-like symmetry in the conduction band. Such calculations explain the experimental results. This new knowledge triggered the development of “Ge-segregation-controlled MBE,” which successfully enhanced the PL intensity. Consequently, a preliminary optoelectronic device, operating at 77 K with a light emitting diode and detector on the same wafer, was fabricated.
Electron field emission from diamond grown by a multiple pulsed laser process
Authors: Badzian A. , Weiss B. L. , Roy R. , Badzian T. , Drawl W. , Mistry P. , Turchan M. C.
Published: July 2002

Among wide-band-gap materials, diamond has been tested extensively in many laboratories for its applicability as an electron emission material. The results are encouraging but also point out the necessity of modifying the diamond films with respect to their chemical composition and/or atomic structure. This article reports on electron emission measurements conducted on diamond coatings deposited on WC/Co alloy by a multiple pulsed laser process. The electron emission has been measured in a diode configuration with a diamond surface–anode spacing of 20 and 50 μm in vacuum at P=10−7 Torr. Current densities of 6 mA/cm2 have been calculated at an applied voltage of 3000 V (for 20 μm). We propose an explanation for electron emission.
Electrical characterization of Si1−xGex p-metal–oxide–semiconductor channel by admittance spectroscopy
Authors: Alieu J. , Souifi A. , Bremond G. , Bouillon P. , Skotnicki T.
Published: July 2002

In contradiction with researchers who try to incorporate a maximum of Ge in the channel, we will demonstrate, in spite of a low Ge fraction (15% or 30%) and in spite of the competition between Sicap and Si1−xGex channels, that we obtain a good trade-off between the gain in drain current, the Si/SiGe interface quality (which is responsible for the mobility reduction by scattering on the interface state and responsible for the drain junction leakage current), and process simplicity. In this article, we also discuss the good quality of the Si1−xGex interface obtained using 15% or 30% Ge. We then propose a new method, directly applicable to the transistor, to study the Si/SiGe interface via admittance spectroscopy.
Photoluminescence from pure-Ge/pure-Si neighboring confinement structure
Authors: Usami N. , Miura M. , Sunamura H. , Shiraki Y.
Published: July 2002

Efficient no-phonon (NP) luminescence was observed from a pair of pure-Ge/pure-Si on relaxed Si0.82Ge0.18 which separately confines electrons and holes in neighboring quantum wells. Anomalous broadening of the photoluminescence linewidth from the wetting layer occurred at around critical Ge coverage of Ge island formation, indicating that the microscopic interface roughness becomes significant at the initial stage of the island formation. At around the critical coverage, the enhanced NP feature was clearly observed at 77 K owing to the realization of rigorous confinement potential for exciton localization.
Oxidation of Si1−yCy (0⩽y⩽0.02) strained layers grown on Si(001)
Authors: Pressel K. , Franz M. , Krüger D. , Osten H. J. , Garrido B. , Morante J. R.
Published: July 2002

We have studied wet thermal oxidation between 700 and 1100 °C of strained Si1−yCy (0⩽y⩽0.02) layers grown by molecular beam epitaxy on Si(001) substrates. The oxidation kinetics and the refractive indices of the oxides grown on Si1−yCy were monitored by ellipsometry. They show no significant differences in comparison with oxides grown on silicon. Secondary ion mass spectroscopy and x-ray photoelectron spectroscopy reveal the appearance of carbon in the oxide. To find an appropriate temperature window for oxidation, we investigated the underlying Si1−yCy layers after oxidation by infrared absorption measurements. We observed a decrease of the substitutional carbon concentration for oxidation temperatures higher than 800 °C. Thus, only a small temperature window for the growth of good thermal oxide on Si1−yCy layers is available. Infrared absorption measurements on the oxide vibrational modes reveal a small influence of the carbon concentration on the structural quality of the oxide.
Relaxation of strained, epitaxial Si1−xSnx
Authors: Fyhn M. F. , Chevallier J. , Nylandsted Larsen A.
Published: July 2002

The thermal stability of high quality, strained Si1−xSnx, 2.5%⩽x⩽5%, grown by molecular beam epitaxy on Si 〈001〉 substrates has been investigated by Rutherford backscattering spectrometry and transmission electron microscopy. As a result of annealing at temperatures in the range 400–950 °C for 1 h, both relaxation by precipitation of Sn and generation of misfit dislocations and dislocation loops were found, consistent with the low solubility of Sn in Si and the large lattice mismatch between Si and Si1−xSnx. In the epitaxial, strained Si1−xSnx layers, where the strain is proportional to the Sn concentration, the threshold temperature for generation of precipitates and misfit dislocations was found to decrease with increasing Sn concentration. Above the threshold temperature the influences of the different relaxation channels change considerably with temperature and composition; an orthogonal interfacial misfit dislocation network is seen at temperatures close to threshold while at higher temperatures mainly dislocations in the bulk are found coexisting with large precipitates. The compositional metastability that leads to the precipitation process, reduces the Sn concentration in the matrix, however, neither this depletion of Sn from the matrix of Si1−xSnx nor the relaxation due to misfit dislocations cause a fully relaxation of the Si1−xSnx layers.
Simple technique for measuring grating periods made using e-beam lithography
Authors: Feder K. S. , Tennant D. M.
Published: July 2002

A simple method for measuring the period of e-beam written gratings is described. The technique allows for measurement of grating periods using a light microscope. Grating periods can be determined with a resolution of about 0.1 Å. Twenty near field holographic photoplates have been made using this method with excellent results. The technique is described for use on a JBX 6000FS electron beam lithography system with fine pitch control software, but may be applicable to other systems.
Electrical characteristics of Ta2O5 films on Si prepared by dc magnetron reactive sputtering and annealed rapidly in N2O
Authors: Eftekhari G.
Published: July 2002

The electrical properties of reactive sputtered tantalum oxide annealed rapidly in N2O ambient improves the leakage current, increases dielectric constant and electric field breakdown. These improvements are the result of incorporation of oxygen into the structure of the oxide. This is simpler than the other methods of supplying oxygen into the oxide such as annealing in oxygen plasma.
Formation of an Sb–N compound during nitridation of InSb (001) substrates using atomic nitrogen
Authors: Haworth L. , Lu J. , Hill P. , Westwood D. I. , Macdonald J. E. , Hartmann N. , Schneider A. , Zahn D. R. T.
Published: July 2002

The effect of atomic nitrogen, generated by a radio frequency plasma source, on clean InSb(001) at 275 °C has been studied using x-ray photoelectron spectroscopy (XPS) and resonant Raman scattering (RRS). Chemically shifted XPS features of the Sb 3d region revealed the formation of a reacted Sb species. This reacted Sb was unambiguously identified as mainly Sb–N by comparison with results from as deposited and nitrided, thick elemental Sb layers on InSb. The Sb 3d feature due to this Sb–N species was found to have a chemical shift of 1.65±0.10 eV to higher binding energy compared with the InSb peak, while for the elemental Sb the shift was only 0.45±0.10 eV in the same direction. Although not obvious from the XPS data the RRS spectra of a much longer nitridation at 275 °C showed the presence of crystalline elemental Sb. Annealing studies of elemental Sb and nitrided Sb layers showed the Sb–N species to be significantly less volatile than elemental Sb.
Chemistry of [(t-butyl)GaS]4 on Si(100)-(2×1)
Authors: Pelzel R. I. , Hopcus A. B. , Owen J. H. G. , Nosho B. Z. , Weinberg W. H.
Published: July 2002

We have studied the chemistry of [(t-butyl)GaS]4 on Si(100)-(2×1) in ultrahigh vacuum. The characterization techniques used in this study were Auger electron spectroscopy (AES), temperature programmed desorption (TPD), and low-energy electron diffraction (LEED). Exposing [(t-butyl)GaS]4 to Si(100)-(2×1) at temperatures below 700 K gives evidence of gallium, sulfur, and carbon on the surface, as judged by AES, while exposing at an elevated temperature (>700 K) results in nearly carbon free adsorption. TPD spectra measured after exposure at 200 K show that the hydrocarbon ligands of the [(t-butyl)GaS]4 undergo a β-hydride elimination reaction and desorb predominantly as isobutene. For low exposures, the GaS core of the [(t-butyl)GaS]4 molecule dissociates upon annealing, as judged by the SiS and gallium TPD peaks. TPD experiments conducted after adsorption of more than 20 Å of [(t-butyl)GaS]4 on the Si(100)-(2×1) surface show evidence of Ga2S desorption. For deposition at 700 K, LEED shows that the (2×1) reconstruction remains intact for low and moderate exposures, and a (1×1) pattern develops for higher exposures.
Key technologies of a focused ion beam system for single ion implantation
Authors: Matsukawa T. , Shinada T. , Fukai T. , Ohdomari I.
Published: July 2002

A focused ion beam (FIB) system was remodeled specially to realize single ion implantation (SII) by which we intended to implant an accurate number of ions one by one into ultrafine semiconductor regions. In the SII, single ions are extracted by chopping the ion beam, and one-by-one extraction of ions have become possible by installing an ultrahigh speed amplifier for chopping. In order to achieve accurate detection of each single ion incidence in the SII, detection of SEs emitted upon ion incidence with a high sensitivity and a high signal to noise (S/N) ratio is essential. Signals from the SE detector which synchronize to an instance of chopping are selectively counted to achieve high S/N ratio. Contaminant particles originating from neutralization and scattering of the ion beam are eliminated by sliding the ion source off the beam axis and cutting off the ion beam at the entrance of the FIB’s mass separator.
High-density inductively coupled plasma etching of GaAs/AlGaAs in BCl3/Cl2/Ar: A study using a mixture design experiment
Authors: Agarwala Sambhu , Horst Scott C. , King Oliver , Wilson Rick , Stone Dennis , Dagenais Mario , Chen Y. J.
Published: July 2002

Inductively coupled plasma etching of GaAs/AlGaAs was investigated in BCl3/Cl2/Ar using a mixture design experiment. According to the model extracted from the experiment, the etch rate was linearly proportional to the gas flows, and the process was reactant or diffusion limited. Etch rates from 200 to over 3000 nm/min were obtained. Equirate etch was observed for AlGaAs films with different aluminum content in the entire gas composition range. A quadratic dependence was observed for the etch rates of the resist mask with the gas flows. Etched profiles ranged from positively sloped to vertical to negatively sloped depending on the gas composition. Smooth etched surfaces and mirror quality smooth sidewalls were obtained.
Emission characteristics of TiN-coated silicon field emitter arrays
Authors: Kang Seung-Youl , Lee Jin Ho , Song Yoon-Ho , Kim Yuon Tae , Cho Kyoung Ik , Yoo Hyung Joun
Published: July 2002

We observed the emission characteristics and stability of TiN-coated Si field emitter arrays (FEAs) with a TiW gate structure. The TiN layer on Si tips was formed by a two-step rapid thermal nitridation process in an NH3 ambient by which a Ti layer was thermally converted to a TiN/ TiSi2 bilayer. This process could suppress the formation of TiO2 on the surface and make the TiN layer thicker than a one-step process. By coating Si tips with TiN, the operating voltage of the TiN-coated Si FEAs was reduced by about 20 V compared with non-coated ones. Also, the TiN-coated Si FEAs showed thermally stable electron emission compared with non-coated ones.