bluuebunny/crossref_metadata_2025 huggingface dataset:
InAs/AlSb heterostructure field-effect transistors using a Si-doped InAs/AlSb short-period superlattice modulation doping barrier
Authors: Bolognesi C. R. , Dvorak M. W. , Chow D. H.
Published: July 2002

Modulation doping of InAs/AlSb quantum wells generally requires the use of chalcogenide donor impurities because silicon, the usual donor of choice in molecular beam epitaxy, displays an amphoteric behavior in antimonide compounds. In the present article, we demonstrate the use of a Si-doped InAs/AlSb short-period superlattice (with Si co-deposited with the InAs) to modulation dope the current-carrying InAs channel of an InAs/AlSb heterostructure field-effect transistor (HFET). Using this new approach, we have fabricated 1.5 μm gate InAs/AlSb HFETs with a measured extrinsic transconductance of 550 mS/mm at 300 K. The present band gap engineering approach eliminates the requirement for captive chalcogenide donor sources to modulation dope InAs/AlSb quantum wells. Design alternatives to the use of the short-period superlattice are also considered and demonstrated.
Line-of-sight mass spectrometric study of As/Sb exchange on Sb-terminated and Ga-terminated GaSb (001) during molecular beam epitaxy
Authors: Xie Qianghua , Nostrand J. E. Van
Published: July 2002

Rates and total amounts of the arsenic for antimony exchange reaction on the GaSb (001) surface are measured via line-of-sight mass spectrometry during molecular beam epitaxial growth. On the Sb-terminated GaSb (001) surface, an As for Sb exchange is observed to occur at all levels of incident As2 flux studied. By contrast, on the surface with one monolayer of Ga, there exists a critical As2 flux below which the As for Sb exchange is suppressed, and a two-dimensional (2D) surface morphology is maintained. Above the critical As2 flux, the As for Sb exchange is observed to be linear with increasing As2 flux. Substrate temperatures above 470 °C and As2 fluxes greater than 1×10−6 Torr beam flux pressure lead to a drastic increase in As/Sb exchange accompanied by the occurrence of 3D surface morphology. As/Sb exchange at the interfaces of InAs/GaSb type-II superlattices leads to a reduced average lattice constant of the superlattices and degrades interface quality, as determined by x-ray diffraction.
Nanotribology of single crystal ZnO surfaces: Restructuring at high temperature annealing
Authors: Nainaparampil J. J. , Zabinski J. S. , Prasad S. V.
Published: July 2002

Atomic force microscopy is used to study low friction structures formed on single crystal zinc oxide because of annealing. Zinc oxide thin films deposited in this laboratory showed low friction (∼0.2) and long wear life (over one million cycles) in humid air at room temperature. Research into the mechanisms for this low friction behavior, far exceeding the life of typical solid lubricants (e.g., MoS2 and graphite) led to the present work, which focuses on the nanotribology of single crystal ZnO surfaces. Thermal annealing was used to cause surface reconstruction and defect formation. Etch pits were formed on the (101̄0) surface and roughening or reconstruction occurred on the (0001) surface. These pits and roughened areas showed low friction that could be originating from interactions of defects and restructured crystal faces due to adsorbates. Adhesion and relative contact stiffness were not significantly different between friction contrasting regions. The results of lateral force microscope analysis of the different single crystal surfaces are presented here.
Inductively coupled plasma-induced etch damage of GaN p-n junctions
Authors: Shul R. J. , Zhang L. , Baca A. G. , Willison C. G. , Han J. , Pearton S. J. , Ren F.
Published: July 2002

Plasma-induced etch damage can degrade the electrical and optical performance of III–V nitride electronic and photonic devices. We have investigated the etch-induced damage of an inductively coupled plasma (ICP) etch system on the electrical performance of mesa-isolated GaN pn-junction diodes. GaN positive-insulating-negative mesa diodes were formed by Cl2/BCl3/Ar ICP etching under different plasma conditions. The reverse leakage current in the mesa diodes showed a strong relationship to chamber pressure, ion energy, and plasma flux. Plasma induced damage was minimized at moderate flux conditions (⩽500 W), pressures ⩾2 mTorr, and at ion energies below approximately −275 V.
Schottky barrier formation and intermixing of noble metals on GaAs(110)
Authors: Pan S. H. , Mo D. , Petro W. G. , Lindau I. , Spicer W. E.
Published: July 2002

Photoemission measurements are used to study the Schottky barrier formation and the intermixing (with GaAs) of the three metals, Cu, Ag, and Au, deposited at room temperature on GaAs(110) cleaved surfaces. It is tentatively concluded that Fermi level pinning cannot be followed satisfactorily for metal coverages above a monolayer. The work of Palau on Schottky barrier height (I–V and C–V) for Au and Ag deposited on cleaved GaAs(110) in UHV indicate pinning positions surprisingly close to those found for other overlayers in the ‘‘unified defect’’ model. It was found that ‘‘intermixing’’ between noble metals and GaAs decreases in the order of Cu, Au, and Ag. Although island formation probably occurs, it is tentatively concluded that the principle reason for difficulty in using our photoemission measurements to determine Efs for the noble metals is the inclusion of Ga (as well as As) in or on the noble metal overlayer.
Thin film transistors for large area electronics
Authors: Thompson Malcolm J.
Published: July 2002

This paper reviews thin film transistor technology with a detailed emphasis on amorphous silicon (a-Si:H) devices. The fabrication and large area technology issues are described. The materials parameters that affect device performance are dominated by interface effects and the gate dielectric. The problem of characterizing the interfaces is discussed. Applications in liquid crystal displays (LCD) and image sensors are described. It is concluded that there is considerable promise for this rapidly expanding technology.
Dissolution dynamics of soft x-ray exposed novolak resist films
Authors: Peters Darryl W. , West Richard J.
Published: July 2002

Soft x-ray exposed films of WX242 resist were analyzed by ultraviolet (UV) and Fourier transform infrared (FTIR) spectroscopy. To assist in identification of chemical species produced, UV and FTIR spectral data from soft x-ray exposed samples were compared to that from UV exposures performed in air and in a vacuum. A 25% reduction in DNQ concentration was sufficient to result in dissolution rate ratios of ≥10:1. No evidence for ester formation was observed in either the x-ray or UV exposures performed in a dry ambient. Soft x-ray exposure of WX242 in dry helium produced indenecarboxylic acid (ICA) in measurable amounts, but less than that for UV exposure in air or in a vacuum. The dependence of the dissolution rate on ICA concentration (reaction order of 1.5) and the reduced ICA yield are sufficient to explain the reduced development rate for soft x-ray exposed films.
Electron, ion, and photon beam induced reduction of SnO2(110): Power dissipation thresholds
Authors: Erickson J. W.
Published: July 2002

Incident electrons, ions, and photons stimulate the desorption of surface oxygen from the (110) surface of SnO2. In the case of incident electrons, this oxygen desorption provides an extremely sensitive in situ measure of electron beam effects, by means of the surface conductivity properties of the substrate. Energy relaxation processes other than stimulated desorption also follow the initial excitation, and raise the effective local temperature. Subsequent temperature-dependent changes in the surface and subsurface composition and structure provide characteristic material-dependent power dissipation thresholds, which can be detected with great sensitivity. At the (110) surface of the ionic semiconductor SnO2, the thermal threshold or activation energy for ion diffusion is apparently lowered by an electrostatic field, induced by the electron beam in the space-charge region.
Microgap control in x-ray nanolithography
Authors: Moel A. , Schattenburg M. L. , Carter J. M. , Smith Henry I.
Published: July 2002

In order to conduct x-ray nanolithography at linewidths of ∼50 nm, using the CuL line at 1.3 nm, the mask-to-sample gap should be ≲5 μm in order to avoid the detrimental effects of diffraction. Improved process latitude can be provided at such gaps by means of a pi-phase shifting mask. We have experimented with a variety of techniques for achieving uniform microgaps of such dimensions. In order to perform dynamic mask–substrate alignment, while holding such a small, uniform microgap, we have developed a scheme based on sapphire ball bearings, about 200 μm in diameter. The balls are recessed into pits anisotropically etched into the Si substrate or the x-ray mask such that the final microgap is ∼5 μm. Using a piezoelectrically driven x–y stage, designed for aligning x-ray nanolithography masks, we have shown that the mask–substrate gap is unchanged during x and y excursions. Fixing the mask–sample gap greatly simplifies the mask alignment problem by reducing the number of degrees of freedom from 6 to 3. An alignment signal obtained from matching pairs of diffraction gratings on mask and substrate is repeatable and should permit sub-100 nm alignment.
High-energy lithography illumination by Oxford’s synchrotron: A compact superconducting synchrotron x-ray source
Authors: Andrews D. E. , Wilson M. N.
Published: July 2002

Successful results on a development scale have demonstrated the benefits of x-ray lithography for producing fine features with broad process latitude. This paper is concerned with design of an x-ray source appropriate for production scale utilization of this technology. General considerations of throughput required show that, regardless of type, the source must provide several kilowatts of continuous x-ray power. At present, only synchrotrons can achieve this level. Conventional synchrotrons are too large for installation in a wafer fabrication facility, but superconducting synchrotrons can be relatively compact. Oxford Instruments Ltd. are presently building high-energy lithography illumination by Oxford’s synchrotron (HELIOS), a compact superconducting synchrotron, for installation in the IBM Advanced Lithography Facility at East Fishkill, New York. HELIOS will produce over 8 kW of continuous x-ray power with a characteristic critical wavelength of 0.84 nm. The design and performance of HELIOS are described, together with a discussion of the design choices which lead to the key features of HELIOS.
Proximity-effect correction in electron-beam lithography
Authors: Vermeulen P. , Jonckheere R. , Van Den Hove L.
Published: July 2002

A survey is given of the dose correction method we have developed to compensate for the proximity effect. Accurate values for the parameters of the double Gaussian function have been obtained with the doughnut method. A self-consistent correction method has been implemented that is not limited to rectangles, which is successful in correcting polygons by splitting them into trapezoids and computing the interactions between these trapezoids. By applying a clustering technique, the speed of this correction software has been remarkably increased. Furthermore, programs have been developed to perform different fracturing strategies on the input pattern. Also the influence of the various fracturing methods on the quality of the correction can be checked by software. In this way, time consuming experiments can be avoided.
Detection of low-contrast fiducial marks for electron beam direct write
Authors: Garofalo J. G. , Kostelak R. L.
Published: July 2002

Precise registration to substrate fiducial marks is crucial to high density, fine-line device fabrication. Mark detectability is a function of both the mark contrast with respect to its surrounding substrate and also its interior topography. Since the accuracy and speed of detection of any scheme is related to the signal-to-noise ratio (SNR) of the mark image presented to the detection filter, one is compelled to develop higher contrast marks in order to enhance the effective SNR and thereby keep pace with the more stringent registration requirements of today’s processes. Unfortunately, some higher contrast marks, being developed by more advanced processes, are characterized by a rather severe interior topography. Standard edge detectors are hampered by the apparent interior ‘‘edges’’ of such marks. Another complication arises from the pulsed type data acquisition scheme used on the AT&T in-house EBES4 system that demands high bandwidth detection electronics. This prohibits the reduction of the detection noise power spectral density by low-pass filtering operations. While this acquisition architecture has the potential for accurate mark location with little electron beam induced mark degradation or errors due to charging, the detection filter must cope with a relatively strong noise energy content. To register to both low contrast and moderate contrast ‘‘rough terrain’’ marks under these circumstances, a two-stage matched filter has been developed. This variant of the standard matched filter was designed to improve its edge localization characteristics. The approach incorporates computationally intensive signal processing algorithms executed on special purpose hardware. Our detection system consists of a custom digitizer that feeds a VMEbus based array processor. The digitizer is equipped with a large, fast memory buffer so that scan data may be processed as a new scan is being acquired. This parallelism results in detection times commensurate with high throughput. Detection accuracy from chrome marks has been investigated using three detection techniques. Optimum ‘‘‖mean‖+3σ’’ overlay errors of ≤0.06 μm were achieved by utilizing the two-stage filter.
High-resolution technology for silicon-integrated surface acoustic wave devices
Authors: Blok B. M. , Visser J. H. , van der Drift E. , Romijn J. , Venema A.
Published: July 2002

A high-resolution technology for the fabrication of surface acoustic wave (SAW) devices is presented. In particular, to obtain an accurate and reproducible aluminum electrode width and shape, a process compatible with the fabrication of integrated electronic circuitry was developed. It is based on HR e-beam lithography, dry etching of the bilayer mask system in a low pressure O2 plasma, and the patterning of the aluminum in a SiCl4 plasma. SEM photos of electrodes in ZnO–SiO2–Si layered structures with widths down to 200 nm (and a corresponding pitch of 400 nm), together with experimental results on silicon-integrated SAW bandpass filters, demonstrate the feasibility of the fabrication process.
Tape automated bonding inner lead bonding with a laser for high performance applications
Authors: Spletter Phillip J. , Galanakis Claire T. , Luijtjes Neik , MacKay Colin , Jee Yong , Woodard Ollie C.
Published: July 2002

Since 1985, MCC has been developing the use of flashlamp pulsed Nd:YAG (YAG) laser technology to bond tape automated bonding (TAB) leads to I/O pads on integrated circuits (ICs). The I/O pads have 22 micron high gold bumps and the leads are copper plated, in the case described here, with electroless tin. As a result of the work presented here, a methodology has been developed that will result in a high throughput, reliable bonding process that overcomes the limitations of conventional thermocompression (T/C) and thermosonic (T/S) bonding technologies. In addition, because the position of the laser beam is software controlled, the process is very desirable for applications where a broad range of different IC form factors and sizes are to be bonded. Laser bonded devices have been exposed to degrading environments without failure, indicating the long term reliability of the process.
An alignment technique using diffracted moiré signals
Authors: Hara Kenji , Uchida Yoshiyuki , Nomura Tsutomu , Kimura Seiichiro , Sugimoto Dai , Yoshida Akihiro , Miyake Hiroshi , Iida Takahide , Hattori Shuzo
Published: July 2002

The authors have proposed an automatic and precise alignment technique for proximity printing in x-ray lithography, using two pairs of moiré gratings, with moiré signals from each pair being 180° out of phase with each other. A control reproducibility better than 50 nm was obtained with the mask and the wafer alignment system. This technique has also been applied to projection photolithography, as part of a program to mix and match optical projection lithography with proximity x-ray lithography. An alignment accuracy of ±0.12 μm(3σ) was obtained by an actual step and repeat photolithographic system. This paper discusses experimentally determined characteristics of diffracted moiré signals appropriate for automatic alignment. The moiré alignment technique was determined to be suitably precise for mix and match lithography once difficulties with interference between the parallel mask and wafer in the proximity system and chromatic effects in the projection system were overcome.
X-ray lithography two-state alignment system
Authors: Chen G. , Cerrina F. , Wu Z.
Published: July 2002

We present a novel alignment system for x-ray lithography. A linear Fresnel zone plate, defined on the mask, is used to focus a laser beam on a wafer mark (a series of dots). A fast electro-optic modulator is used to make the laser beam hop between two positions at the mark edges. The light diffracted by the periodic mark is measured at each position and a misalignment signal is originated when the mark is not illuminated equally in the two states. A signal that is proportional to the misalignment is generated when the error is within the alignment range (±0.2 μm); outside that range a capture signal is present as long as the beam is on the mark, which would be typically 2–4 μm wide. The method is highly sensitive with resolution in excess of 0.003 μm, has a wide capture range, no moving parts, and is suitable for real-time alignment during exposure. Sensitivity to gap changes is highly reduced, making the system ideal for synchrotron-based x-ray lithography aligners.
Measurement and control of absorber stress in the fabrication of x-ray masks
Authors: Foss Gordon O. , Hughes Gregory P. , Doyle Gary F. , Gorbachenko Nikolay P.
Published: July 2002

One of the primary obstacles to overcome in the development of x-ray masks is the registration error caused by stress in the patterned absorber. Registration error is caused primarily by in-plane distortion of the supporting membrane that results from absorber stress. Our specification for registration is 0.08 μm 3-sigma which translates into an absorber stress of 1.5×108 dyn/sq cm for a ‘‘worst case’’ ASIC structure with approximately 50% absorber pattern density over a 3-cm field. Two major factors in the fabrication of x-ray masks are measurement and control of fabrication processes to maintain absorber stress within the required limits. Measurement of absorber stress is perhaps the most difficult of the tasks. A resonant frequency measurement technique is used to determine the stress in each layer as deposited during blank fabrication. The technique utilizes the fundamental resonant frequency of the air damped membrane and corrects for atmospheric changes which affect the results. This technique has also been used to develop a gold-plating process and to measure stress changes caused by processes after plating. Stress in the patterned absorber is determined by measuring the out-of-plane distortion in a large geometry using a stylus measuring system. The final test is the measurement of registration using MEBES MARKET measurements. Control of process parameters at each fabrication step have been evaluated for impact on final absorber stress. Stress in the sputter deposited layers has been minimized by controlling sputter pressure, power, and substrate temperature to appropriate limits. Absorber stress in the electroplated gold is minimized by controlling bath temperature, and plating current, and by monitoring the plating solution pH, specific gravity, brightener, and conducting salts concentration to ensure plating reproducibility.
Optical column design for large area voltage contrast electron beam testing of multichip packaging substrates
Authors: Goruganthu R. R. , Bahasadri A. , Kumar N. , Woodard O. C.
Published: July 2002

The large field of view involved in voltage contrast electron beam opens and shorts testing of packaging substrates results in unique electron optics requirements. These are long working distance, small beam diameter and high beam currents. Beam energies required for this application range from 3 to 10 keV. An optics system consisting of a Steigerwald electron gun and a magnetic lens with appropriate beam aperturing was designed. The Steigerwald gun has an integral immersion lens which produces a collimated beam with low divergence angle. Virtual crossover size of this source was estimated to be about 0.1 μm. The column was built and tested. The column produced 200 nA into a 10 μm beam spot diameter at a working distance of 20 cm operating at 10 keV. Improved performance of the present design is predicted for a brighter electron source operating at lower temperatures than tungsten filament.
Mechanical distortions of support frames for x-ray lithography masks
Authors: Lenius P. , Engelstad R. , Palmer S. , Brodsky E. , Cerrina F.
Published: July 2002

The stringent requirements for low-distortion x-ray lithography masks make it essential to minimize the mechanical displacements of the supporting structure. Basic axisymmetric models of a mask frame are investigated to determine the out-of-plane deflection (or bow) induced in the support structure by the tension in the membrane. Circular rings with both rectangular and nonrectangular cross sections are evaluated by finite elements. A theoretical analysis verifies the finite element models and also provides analytical expressions for determining the bow as a function of the membrane stress. In-plane distortions created by the effects of gravity on a vertically supported mask blank are also considered. Two- and three-dimensional finite element models are developed for mapping the membrane distortions resulting from the gravitational loads. Results show that in-plane displacements can be minimized by optimizing the type of mount and actual mounting position for the specific mask considered.
Scanning tunneling microscope microlens with magnetic focusing
Authors: Hordon L. S. , Pease R. F. W.
Published: July 2002

We describe a design for a low-energy scanning tunneling microscope microlens with magnetic focusing, to achieve several improvements over conventional lens systems and previously reported microlens systems. First, scaling of the lens dimensions yields corresponding scaling of spherical and chromatic aberration coefficients. Second, magnetic focusing avoids the difficulty inherent in electrostatic microlenses of withstanding large potential differences over short distances, which can lead to dielectric breakdown in insulating elements of the lens, although magnetic focusing has an analogous problem with maximum achievable fields. Third, a low-energy (100–200 eV) electron beam offers a significant advantage in lithography, where proximity effect and scattering within the resist from conventional high-energy (>1 keV) electron beam systems act as serious limitations on pattern fidelity. Calculations indicate that for reasonable values of lens parameters (aperture potential=60–200 V, Bz=1.4–2 T, tip radius=300 Å, aperture diameter=0.25–0.5 μm, and convergence semi-angle=20–100 mrad), aberration coefficients on the order of 40–80 μm and beam diameters down to 150 Å are obtained, with beam current up to several μA.
Tunneling transducers: Quantum limited displacement monitors at the nanometer scale
Authors: Bocko Mark F. , Stephenson Kendall A.
Published: July 2002

Displacement transducers based upon quantum mechanical tunneling of electrons can potentially achieve a sensitivity far superior to conventional transducers. The reason for this is that the dynamical influence of the tunneling transducer on a test mass is insignificant compared to that of traditional capacitive, inductive or piezoelectric transducers. Thus the fluctuating ‘‘back action’’ force from electrical noise in the tunneling transducer is nearly eliminated. The ‘‘back action’’ force becomes dominant as the test mass is miniaturized, thus the tunneling transducer may be especially useful in micro-fabricated sensors. In this paper we present an equivalent circuit model for a tunneling transducer including noise and outline a method for calculating the minimum detectable signal in any given application. We also discuss some practical limits for tunneling-based sensors.
The surface structure of natural membrane of macrophages in water as studied by the scanning tunneling microscope
Authors: Dai J. W. , Jiao Y. K. , Dong Q. , Su Y. X. , Lin K. C. , He J. , Shang G. Y. , Yao J. E.
Published: July 2002

STM may open a new way to probe the molecular structure of the lipids and proteins on the membrane of living cells. In this paper, the surface structure of noncoated membrane of microphages in water was studied by STM. We probed the lipids and proteins on the membrane before and after ConA was combined with the membrane receptors. Results with different patterns were obtained. An experiment with optical microscopic image analysis system has also been done.
Surface structures of stage-1 CuCl2 graphite intercalation compound observed by scanning tunneling microscopy
Authors: Olk C. H. , Heremans J. , Dresselhaus M. S. , Speck J. S. , Nicholls J. T.
Published: July 2002

We report a scanning tunneling microscope (STM) study of a stage-1 graphite intercalation compound (GIC) of approximate stoichiometry C6CuCl2. When the sample bias is positive with respect to the tip, we observe a hexagonal symmetry in which all the atoms of the graphite surface plane are imaged. This is in contrast to the threefold symmetry usually seen in atomic resolution STM images of highly oriented pyrolytic graphite (HOPG), which we also observe on a reference sample of HOPG. The threefold symmetry is attributed to the ABAB stacking of the atomic layers in HOPG. In GICs, this stacking sequence is interrupted by the layer of intercalant, so that for the stage-1 compound all carbon atoms in the plane become equivalent, and sixfold symmetry develops. When the sample is biased negatively with respect to the tip, we observe a strikingly different STM image for the GIC; we believe that the pattern in this case is mainly due to the intercalate layer and the change in the electronic structure of graphite resulting from the presence of the intercalate layer.
Logic-state measurement for passivated integrated circuits using multistroboscopic sampling
Authors: Okubo K. , Anbe T. , Ito A. , Goto Y.
Published: July 2002

To measure the logic state of passivated integrated circuits (ICs) using an e-beam tester, we have devised voltage measurement and logic thresholding techniques to reduce the heavy e-beam dosage required in very long test sequences. These techniques make measurement stable by reducing both the e-beam dosage and measurement time without compromising a reliability. It takes 30 s to measure logic states of a 16 K-step-length test sequence at a probe point. Measurement is estimated as stable up to 200 K steps for passivated ICs, sufficient for the practical failure analysis of complex logic ICs.
Application of scanning tunneling microscope in magnetic storage device manufacturing
Authors: Strecker H. , Persch G.
Published: July 2002

The magnetic storage device technology is still proceeding to higher capacities and faster data access. The performance of such devices depends strongly on the surface finish of the medium, i.e., the disk. However the requirements for the surfaces of the disks are somewhat contradictory. Optimization with respect to low magnetic noise requires smooth surfaces. Smooth surfaces, on the other hand, lead to high stiction forces between the read/write heads and the disks. Therefore the substrates of so-called thin-film disks have to be textured to get a surface with a defined roughness. The depth and wavelength of this roughness are in the submicron range. The features are below the resolution of mechanical and optical stylus instruments. It was shown, that the scanning tunneling microscope allows a detailed characterization of the texturing and can be a tool for controlling the manufacturing process.
Imaging of dimer atoms of Si(100) with the scanning tunneling microscope
Authors: Sugihara Kazuyoshi , Sakai A. , Kato Y. , Akama Y. , Shoda N. , Tokumoto H. , Ono M.
Published: July 2002

Atomic structure of dimers of Si(100) has been investigated with use of scanning tunneling microscope (STM). In contrast to the usual bean-shaped image of the dimer, individual dimer atoms are clearly resolved in the occupied state images. This observation of dimer atoms cannot be explained by current dimer models and implies some effects of tip–surface interactions in STM imaging. Possible amplification mechanisms of STM corrugation by an elastic deformation of the tip or the sample are discussed.
Epitaxial growth and interface parameters of Si layers on GaAs(001) and AlAs(001) substrates
Authors: Bratina G. , Sorba L. , Antonini A. , Vanzetti L. , Franciosi A.
Published: July 2002

Thin Si epitaxial layers (1–14 monolayers) were fabricated by molecular beam epitaxy on GaAs(001) and AlAs(001) substrates also obtained by molecular beam epitaxy on GaAs(001) wafers. In situ studies by monochromatic x-ray photoemission show initial layer-by-layer Si growth on both substrates with only minor Si indiffusion. Reflection high energy electron diffraction analysis shows good epitaxy with some indication of three-dimensional growth at Si coverages higher than 4–8 monolayers. Comparison of our results with recent heterojunction theories suggests that the best predictions for the band offsets are obtained with the model solid approach using deformation potentials to describe the effect of strain. The Si epitaxial layers are found to remain stable upon growth of AlAs or GaAs layers on top of the Si layers.
Surface photovoltage at Cs/GaAs(110): Photoemission experiments and theoretical modeling
Authors: Bauer A. , Prietsch M. , Molodtsov S. , Laubschat C. , Kaindl G.
Published: July 2002

The effects of a surface photovoltage on band bending were investigated with photoemission for interfaces of thin Cs films with p-type GaAs(110) as a function of substrate dopant concentration n and temperature T. Theoretical calculations, which consider recombination by both thermionic emission and tunneling, were found to be in excellent agreement with experimental data. As a result, surface photovoltages are found to contribute only for low dopant concentrations and at low temperatures, with limits depending on the Schottky-barrier height, ΦB : n<1×1018/cm3 and T<280 K for ΦB=0.7 eV, and n<1.5×1018/cm3 and T<390 K for ΦB=1.0 eV. At high coverages (Θ>2.5 ML), the surface photovoltage is strongly reduced due to edge-leakage currents. Finally, general predictions for the occurrence and magnitude of a surface photovoltage will be given, and recent data will be critically reviewed.
Laser-chemical three-dimensional writing for microelectromechanics and application to standard-cell microfluidics
Authors: Bloomstein T. M. , Ehrlich D. J.
Published: July 2002

A high-speed technique has been developed for machining three-dimensional silicon parts using laser-induced chlorine etching reactions. Parts are created directly from solid-modeling computer-aided-design/computer-aided-manufacturing software. Removal rates exceeding 2×104 and ≥105 μm3/s are achieved at 1 and 15 μm x–y resolution, respectively. This is several orders of magnitude faster than electrodischarge machining methods. Submicrometer resolution has been achieved. Laser-induced metallization of resulting structures as well as replication through compression molding have been demonstrated. A class of microfluidic flow-channel devices is under development using a standard-cell software architecture combined with field stitching.
Profiling of ultra-shallow complementary metal–oxide semiconductor junctions using spreading resistance: A comparison to secondary ion mass spectrometry
Authors: Osburn C. M. , Berkowitz H. L. , Heddleson J. M. , Hillard R. J. , Mazur R. G. , Rai-Choudhury P.
Published: July 2002

Spreading resistance profiling (SRP) and secondary ion mass spectrometry (SIMS) were used to characterize ultra-shallow (<100 nm deep) doping profiles. For junctions below 100 nm, the sheet resistances determined from carrier concentrations calculated from spreading resistance data in the traditional manner were considerably greater than values measured by the variable probe spacing technique. A new model which includes the effect of a damaged layer on the beveled surface is presented which accounts for the discrepancy between the measured and calculated sheet resistances. A Poisson analysis (SRP2) of the measured SRP data show that the doping profile and on-bevel carrier concentration profile differ only slightly near the junction for the shallow, heavily doped layers considered in this study.
On the interface structure in InAs/AlSb quantum wells grown by molecular-beam epitaxy
Authors: Bolognesi C. R. , Sela I. , Ibbetson J. , Brar B. , Kroemer H. , English J. H.
Published: July 2002

Three roughness scales relevant to the growth of InAs/AlSb quantum wells have been studied using three techniques yielding complementary information. Reflection high-energy electron diffraction measurements were used to monitor the roughness of growing surfaces. Comparison with the interface roughness extracted from transport measurements suggests the microscopic interface roughness arises because of the bonding crossover from AlSb to InAs. The possibility of strain-induced ordering at the interfaces due to the difference in bond lengths between InSb and AlAs interfacial bonds was investigated. Raman scattering from mechanical interface modes (related to the atomic masses and bonding force constants involved at the interface) was used to gain insight in the microscopic interface configuration.
Improved optical properties of low temperature molecular-beam epitaxially grown AlGaAs by In incorporation
Authors: Tomioka Takeshi , Sasa Shigehiko , Fujii Toshio
Published: July 2002

It was found that the optical properties of AlxGa1−xAs (x: 0.1, 0.3) improved with In incorporation at low substrate temperature by molecular-beam epitaxial growth. The photoluminescence (PL) intensity at 77 K of n-In0.03(Al0.1Ga0.9)0.97As increased as the substrate temperature was decreased from 590 to 480 °C. The PL intensity at 77 K of n-Iny(Al0.1Ga0.9)1−yAs grown at 480 °C increases as the In content, y, is increased from 0 to 0.05. For growth at 480 °C, the PL intensity of n-In0.03(Al0.1Ga0.9)0.97As increased by a factor of 17 and the PL intensity of n-In0.03(Al0.3Ga0.7)0.97As increased by a factor of 4 compared to those without In, respectively. The improved PL intensity of AlxGa1−xAs (x: 0.1, 0.3) is thought to be from a reduction of group III vacancies by In incorporation, resulting in decreased defect-related nonradiative recombination.
Optically detected magnetic resonance of sharp luminescence from Si/Si1−xGex superlattices
Authors: Kennedy T. A. , Glaser E. R. , Godbey D. J. , Thompson P. E. , Chern C. H. , Wang K. L. , Xiao X. , Sturm J. C.
Published: July 2002

The sharp emission from three Si/Si1−xGex superlattices has been analyzed experimentally using optically detected magnetic resonance techniques. Two types of response were observed in samples grown by molecular-beam epitaxy and rapid-thermal chemical vapor deposition. First, two samples exhibited spectra due to carrier heating in the underlying Si at the condition of cyclotron resonance. No spin resonance was observed, consistent with the previous assignment of the photoluminescence to an impurity-bound exciton. Second, one sample showed spin resonance from a weakly coupled electron and hole. Hence, the recombination mechanism is different from other samples. Various mechanisms are discussed.
Fabrication of a lateral p-i-n photodiode in a Si/(Si0.8Ge0.2/Si) superlattice/Si/sapphire structure
Authors: Hanafusa H. , Taguchi E. , Dan T. , Yoneda K.
Published: July 2002

We have fabricated the first silicon on insulator (SOI)-type lateral pin photodiode in a Si0.8Ge0.2/Si superlattice layer grown by molecular-beam epitaxy on a sapphire substrate. The superlattice structure is maintained even after processing at a maximum temperature of 850 °C, and the lateral pin photodiode fabricated in the Si0.8Ge0.2/Si superlattice layer generated about five times as much photocurrent in the 400–1000-nm wavelength range as that in a lateral pin photodiode fabricated in a Si layer of the same film thickness. It is therefore concluded that the lateral pin photodiode in the Si0.8Ge0.2/Si superlattice layer holds tremendous promise as a thin-film photosensor offering high sensitivity throughout the visible spectrum.
Modeling and characteristics of bistable optoelectronic switches and heterojunction field effect transistors in molecular-beam epitaxially grown SiGe/Si
Authors: Kovacic S. J. , Simmons J. G. , Ojha J. J. , Noel J.-P. , Houghton D. C.
Published: July 2002

Recent progress in experimentally realizing, characterizing, and modeling bistable digital optoelectronic switches (DOES) and heterojunction field effect transistors (HFETs) is presented in this communication. Using a computer-based model, the design of the molecular-beam epitaxially grown Si/SiGe heterostructure is shown to affect a number of operational parameters in both the DOES and the HFET. For the DOES, these parameters include the switching voltage Vs and the sensitivity of the device to injected current via a third terminal. For the HFET, the threshold voltage Vth and gate leakage are both shown to be affected by heterostructure design. Experimentally, the sensitivity of Vs to third terminal input which modulates the hole population at the heterointerface is compared to that for a contact made to the active region. In addition, the observation of steplike transitions in the source-drain current–voltage characteristics for a range of gate voltages is reported for HFETs. These transitions are explained as feedback in the transistor structure and are related to the feedback in the DOES. These electrical characteristics form the basis for a new inversion-channel device designated, the bistable field effect transistor.
Laser light scattering detection of InGaAs strained layer relaxation during molecular-beam epitaxial growth
Authors: Celii F. G. , Kao Y. C. , Liu H.-Y. , Files-Sesler L. A. , Beam E. A.
Published: July 2002

The in situ detection of strained layer relaxation in the InGaAs/GaAs system using laser light scattering (LLS) is reported. Samples were prepared by molecular-beam epitaxial deposition of InGaAs at 515 °C, and were characterized ex situ with x-ray diffraction, transmission electron microscopy, and atomic force microscopy. The LLS signal rapidly increased after an onset period which depended on the InGaAs composition. Azimuthal rotation [about the (100) surface normal] was a useful diagnostic for analyzing the contributions to the LLS signal. For InxGa1−xAs films with x<0.25, the LLS signal was strongly peaked toward wafer-plane directions normal to the [011̄] or [011] axes, due to scattering from α or β misfit dislocations, respectively. Nearly isotropic scattering was observed for films with In content above 25%, indicating three-dimensional growth which followed an initial two-dimensional growth period. The results were compared to model predictions of the critical layer thickness. Dynamic effects of the relaxation were observed, in which the LLS signal continued to increase after InGaAs layer growth had terminated. It was also observed that the density ratio of α to β dislocations changed with GaAs cap layer growth. These results demonstrate the utility of LLS for in situ monitoring of layer relaxation and determination of critical thickness.
High performance heterojunction bipolar transistors grown by molecular-beam epitaxy using novel growth method
Authors: Chin Albert , Yang Li-Wu , Martin Paul A. , Nordheden Karen J. , Ballingall Jim M. , Yu T. H. , Chao P. C.
Published: July 2002

A new molecular-beam epitaxial (MBE) growth method is proposed to study the Be diffusion problem in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors (HBTs). The base layer was grown at As-stabilized conditions under minimum V/III beam equivalent pressure of 8 to enhance Be migration and reduce the concentration of nonradiative recombination centers. For a base doping of 4×1019 cm−3 (Be) and emitter dimensions of 2.0 μm×10 μm, the device demonstrates excellent direct-current as well as microwave performance as a power transistor. The unit current gain cut-off frequency fT is 54 GHz and the maximum frequency of oscillation fmax is above 85 GHz. For power transistors with large emitter periphery (120 μm2), 66% power-added-efficiency and 11 dB power gain have been achieved at 4.5 GHz. After the device was continuously stressed at current densities of 2, 4, and 8×104 A/cm2, its current gain, hfe (measured at stressed current density), turn-on voltage Vbe and junction ideality factor n remain almost identical to the original values. This suggests that heavily Be-doped base AlGaAs/GaAs HBT grown by MBE at low V/III flux ratio may be reliable for small signal-type application in microwave and millimeterwave frequencies.
Accurate profiling of ultra-shallow implants with mercury gate metal–oxide–semiconductor capacitance–voltage
Authors: Dudal Roger Le , Hillard R. J. , Heddleson J. M. , Weinzierl S. R. , Rai-Choudhury P. , Mazur R. G.
Published: July 2002

The precise control of ion implants for threshold voltage adjustment requires formation of ultra-shallow electrically active carrier profiles, which begin at the Si–SiO2 interface. Obtaining accurate and precise carrier density profiles near the interface with metal–oxide–semiconductor capactiance–voltage (MOS C–V) requires special data acquisition, numerical analysis, and surface corrections. These methods, when applied to C–V data collected with a unique, highly repeatable mercury (Hg) probe, provide rapid data acquisition and analysis for threshold adjust implant control in a production environment. Pulsed MOS C–V measurements were used to profile implanted layers with peak carrier densities of ∼1017 cm−3, located 15 nm from the Si–SiO2 interface.
Electron-beam induced current determination of shallow junction depth
Authors: Fitzgerald E. A. , Gossmann H.-J. , Unterwald F. C. , Luftman H. S. , Monroe D.
Published: July 2002

Electron-beam induced current (EBIC) was investigated as a possible method of determining shallow junction depth. Molecular-beam epitaxy Si n+/p junctions 200–1800 Å deep were explored with both cross-sectional and plan-view EBIC geometry. Cross-sectional EBIC analysis proves to be accurate and reproducible in determining the center of the depletion region for the deep junctions (1800 Å) when using a conventional scanning electron microscopy (SEM) with a LaB6 filament. Confidence in the location of shallow junctions decreases due to sample drift and the resolution limits of the SEM and EBIC techniques. In the plan-view geometry, in which the EBIC current is recorded as a function of electron beam energy, we can distinguish between shallow junctions with greater precision than deeper junctions. Collection efficiency versus electron-beam energy curves reveal junction depth through shifts in both peak position and height. The collection efficiency versus electron-beam energy curves were modeled assuming the n+ layer is equivalent to a Schottky barrier. The model agrees well with peak shifts, but carrier loss due to the n+ layer must be implemented to sufficiently describe the change in peak height.
Fabrication and characterization of silicon field emission diodes and triodes
Authors: Li Q. , Yuan M. Y. , Kang W. P. , Tang S. H. , Xu J. F. , Zhang D. , Wu J. L.
Published: July 2002

I–V characteristics of silicon field emission diode and triode were investigated. The maximum emission current of 17 μA and the lowest onset voltage of 60 V were obtained by an array of 245 silicon tips. The typical reverse recovery time of the diode was 350 ps. The typical transconductance of the triode was about 10−7 S. The fabrication processes for forming sharp silicon conical tips with a gate hole diameter 1 μm smaller than the corresponding oxide mask is described. The results of a high temperature activation process for improving emission characteristics of the device are presented. The stability and uniformity of the devices affected by the fabrication process and emission environment are also discussed in this paper.
Construction of model supported metal catalysts for scanning tunneling microscopy examinations: Platinum ultrafine particles on silica and on alumina
Authors: Komiyama Masaharu , Kirino Manabu , Kurokawa Hiroyuki
Published: July 2002

Scanning tunneling microscopy (STM) images of Pt ultrafine particles dispersed on silicon oxide and on aluminum oxide surfaces were obtained. The silicon oxide sample employed consists of a thin (ca. 0.6 nm thick) native silica film present on a Si(100) surface. The aluminum oxide sample was prepared by vacuum-depositing aluminum metal on a native-oxide-covered single crystal silicon surface, followed by its air oxidation. Model Pt/SiO2 and Pt/Al2O3 catalysts were prepared by vacuum-depositing Pt metal on those oxide surfaces. The STM observations of these sample surfaces were critically dependent on the tunneling conditions, and the optimum STM observation conditions for those supported metal catalyst systems were identified.
Electronic states of C60 molecules on Si(001)2×1 and Si(111)7×7 surfaces
Authors: Yamaguchi Tsuyoshi
Published: July 2002

Electronic states are calculated by the DV-Xα linear combination of atomic orbitals method for two model clusters, C60Si57H44 of the C60/Si(001) surface, where the C60 molecule resides on the trough between dimer rows and C60Si70H46 of the C60/Si(111) surface, where the C60 molecule resides on the center of the unfaulted half of the unit cell. For both clusters, occupied (unoccupied) orbitals of the C60 molecule near the Fermi level have high charge density around double bonds between two hexagons (around single bonds on pentagons). The charge density of individual orbitals has five or more stripes for the former cluster, and it has a shape like a doughnut or trigonal clover leaves for the latter cluster. These should be compared with the scanning tunneling microscopy images.
Structural analysis of domain boundaries on Si(111)7×7 surfaces by scanning tunneling microscope
Authors: Gu Q. J. , Zhao W. B. , Ma Z. L. , Liu N. , Xue Z. Q. , Pang S. J.
Published: July 2002

The scanning tunneling microscope has been used to study domain boundaries on Si(111)7×7 surfaces. Several kinds of regular defect structures along the domain boundaries on Si(111)7×7 surfaces have been observed with atom resolution. By combining with the dimer-adatom-stacking fault model, their detailed atom structural models are given. It is found that there are three important factors that determine the boundary structure. The most important factor is the strong interaction between dimer and adatom. The next one, in some cases, is the difference between the faulted half and the unfaulted half. Additionally, the metastable (2n+1)×(2n+1) triangle subunit structure such as the 5×5 triangle subunit may play an important role in determining the defect structure along the domain boundary in some cases.