bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of strained InGaAs/GaAs quantum wells and index guided injection lasers over nonplanar substrates by molecular beam epitaxy
Authors: Arent D. J. , Galeuchet Y. D. , Nilsson S. , Meier H. P.
Published: July 2002

Strained InGaAs/GaAs quantum wells were grown on nonplanar substrates by molecular beam epitaxy and studied by scanning electron microscopy and low temperature spatially and spectrally resolved cathodoluminescence spectroscopy. For (100) ridges and grooves formed with (311)A sidewalls, almost complete removal of In from the strained quantum wells on the (311)A facet is observed. Corresponding increases of In content in the quantum wells grown on the (100) facets indicate that most if not all of the In is displaced from the (311)A facet via interplanar adatom migration. Ga adatom migration is also observed under our growth conditions such that quantum wells grown nominally near the critical layer thickness on structures less than ≂2.5 μm wide are no longer pseudomorphically strained, as detected by luminescence linewidth analysis. We present the first results of strained InGaAs/GaAs index guided injection lasers grown by single-step molecular beam epitaxy over nonplanar substrates and show that differences greater than 50 meV in the effective band gap of a 70 Å quantum well can be achieved between the gain region and the nonabsorbing waveguide without relaxing the strain. Room temperature threshold currents as low as 6 mA for 4 μm×750 μm uncoated devices lasing continuously at a wavelength of 1.01 μm have been achieved.
Bismuth and antimony adsorption on III–V(110) substrates: Growth, order, and structure
Authors: Ford W. K. , Guo T. , Lantz S. L. , Wan K. , Chang S.-L. , Duke C. B. , Lessor D. L.
Published: July 2002

The adsorption characteristics of bismuth and antimony on III–V(110) substrates have been studied as a function of overlayer coverage and deposition conditions using low energy electron diffraction (LEED). We examine the different roles of chemical bonding and atomic size for determining surface ordering phenomena and epitaxy in these systems. LEED and Auger data were collected for monolayer range film thicknesses prepared on GaAs, InP, GaSb, InAs, and InSb substrates cleaved in situ. Both IV and diffraction spot profiles were measured. Our results indicate that significant differences exist between the structure and surface chemical bonding of antimony and bismuth to III–V materials which were not revealed from previous studies using GaAs alone.
Tightly bound H2O in spin-on-glass
Authors: Tompkins Harland G. , Tracy Clarence
Published: July 2002

The purpose of this work is to measure the amount of H2O which is bound tightly in spin-on-glass (SOG) and the amount of reabsorption as a function of room air exposure time. Both results are needed in determining bake cycles and wait times prior to metal deposition when SOG is used in the dielectric stack of a multilevel metal system. About a tenth of the amount of gas which remains after a 2 h 150 °C bake is still present after a 2 h 350 °C bake. About half the amount of the tightly bound gas which is desorbed will be reabsorbed upon exposure to air in a period of 4 h or less. The time for half of the reabsorption to occur appears to be of the order of 20 to 60 min.
Use of hybrid reflectors to achieve low thresholds in all molecular-beam epitaxy grown vertical cavity surface emitting laser diodes
Authors: Fischer R. J. , Tai K. , Hong M. , Vandenberg J. M. , Ying J. Y. , Mannaerts J. P. , Cho A. Y.
Published: July 2002

Low current threshold surface emitting lasers were demonstrated with all molecular-beam epitaxy grown vertical resonator diodes. Vertical injection was made possible by a novel reflector structure on the p side of the diode, making use of constructive interference between a distributed Bragg reflector and a metal layer for enhanced reflectivity. Continuous wave room temperature emission at a current threshold of 40 mA in a 15 μm device, and pulsed threshold currents as low as 12 mA were achieved for a 10 μm diam device with a 0.5 μm thick active layer. The quality and periodic structural parameters of the distributed Bragg reflectors could be determined from high-resolution x-ray diffraction.
Electronically wired petri dish: A microfabricated interface to the biological neuronal network
Authors: Eggers M. D. , Astolfi D. K. , Liu S. , Zeuli H. E. , Doeleman S. S. , McKay R. , Khuon T. S. , Ehrlich D. J.
Published: July 2002

Presented is the design, fabrication, and evaluation of 72-channel microcircuit electrode arrays (biochips) built to interface neurons and computers. Contributions include a detailed mathematical model of the electrode/electrolyte interface and subsequent electrode design optimization (in terms of maximum signal-to-noise ratio). Electrode impedance measurements were obtained with the electrodes submerged in electrolytic neural solution. Large sample results indicate a 7% discrepancy between theoretical and measured impedances. In addition to the engineering efforts, biological cell culturing techniques were developed to enable the growth of synaptically interconnected, electrically excitable cells on the biochip. Both dissociated invertebrate neurons and clonal mammalian cell systems were employed. Together these contributions enabled microvolt signals to be recorded from individual neurons grown and synaptically interconnected on the biochip surface. Also recorded were neuronal responses to on-chip stimulation. Consequently, the biochip technology presented represents a step towards a long-term, noninvasive, multisite electrical stimulation and recording capability necessary for extracting the mechanisms governing the way living neural networks connect, integrate, and self-organize.
Calibration and characterization of a pulsed soft x-ray source
Authors: Peters Darryl W. , Dardzinski Bernard J. , Kelly Dan R.
Published: July 2002

Typical x-ray flux measurement methods (diodes, thermopiles, sensitized photographic film, photoresist, etc.) yield questionable accuracy and poor precision. A commercially available nylon-based radiochromic film, developed for monitoring dose during radiation processing of food products, was used to calibrate and characterize a high brightness (106–107 W/srad), pulsed, laser plasma, soft x-ray source. The response of this film can be calibrated using NIST radiation standards, has negligible x-ray wavelength and environmental dependence, and is dose-rate insensitive over a large range. The change in optical density (ΔOD) of exposed film is directly proportional to the incident dose. Excellent agreement was observed for film response to both broadband soft x rays (0.6≤λ≤2.2 nm) and 20 keV electrons. An incident dose of 100 mJ/cm2 resulted in a ΔOD of 1.00 with a measurement precision of ±2%, with no evidence of saturation found up to 120 mJ/cm2. The laser plasma source demonstrated flux stability of better than 5% over a five-month period. Dosimetry film was also used to measure illumination uniformity, measure soft x-ray transmission through various materials, and calibrate an on-board miniature x-ray diode for dose integration.
Electron beam irradiation effects for high-T
c superconducting thin films
Authors: Matsui S. , Ichihashi T. , Yoshitake T. , Miura S. , Satoh T. , Mito M.
Published: July 2002

Electron beam (EB) irradiation effects for Y and Bi system thin films are investigated. It is observed through Auger electron spectroscopy (AES) study that as EB exposure increases oxygen Auger intensity for both films decreases due to EB desorption, while at the same time Cu for Y system and Bi for Bi system Auger intensities increase. Moreover, in transmission electron microscopy (TEM) studies, a BiOx like crystal structure is observed on the Bi system surface after EB irradiation. By measuring electron dose dependencies of resistivity versus temperature, it became clear that the crystal structure of a Bi system thin film is destroyed with a lower electron dose, than for Y system thin films. A 0.1 μm thick Bi film irradiated at 0.54 C/cm2 dose indicates nonsuperconducting characteristics.
Millisecond annealing for complementary metal–oxide semiconductor source and drain implants
Authors: Carter J. C. , Evans A. G. R. , Timans P. J. , England J. M. C.
Published: July 2002

Millisecond annealing using a dual electron beam annealer has been performed on 4 in. wafers for the activation of arsenic and boron difluoride source and drain implants as part of a complementary metal–oxide semiconductor process. Gross wafer distortion has been avoided by the use of a high background temperature and a synthesized line scan. Measurements of electrical activation of the implanted dopant indicates no metastable highly active phases, but activation to electrical solubility limits of longer lamp anneals performed at the same temperature. Measurements on transistors fabricated using single scan millisecond annealing show annealing cycle induced interface damage no worse than that seen in isothermal lamp anneals.
Surface grid technique for noncontact e-beam testing of very large scale integrated package substrate
Authors: Lee K. L. , Schaefer C. , Kern D. P.
Published: July 2002

A surface grid assisted charging technique for noncontact e-beam testing of very large scale integrated package substrates has been developed. Successful charging of packages with a variety of combination of conductor/substrate materials (i.e., Au/alumina ceramic, Mo/alumina ceramic, Solder/polyimide, and chromium/polyimide) has been demonstrated using this technique. In this paper, both theoretical and experimental results concerning the role of a surface grid in addressing various testing issues such as package material parameters, charge localization, secondary electron redistribution, local field effect, and the electron detector response characteristic will be discussed.
Tunneling characteristics of silicon covered molybdenum tip apex
Authors: Nishikawa Osamu , Koyama Haruhiko , Tomitori Masahiko , Iwawaki Fumikazu
Published: July 2002

The variation of field emission characteristics of Mo tip apexes by the adsorbed Si atoms was investigated with an instrument combined of an atom probe and a field emission electron spectrometer. The Si/Mo surfaces were also examined using the scanning tunneling microscope/spectrometer. The deposited silicon was found to form microclusters on the Mo substrate and exhibit the semiconductive electronic states which are retained even at the Si–Mo interface where Si and Mo atoms coexist. Heating the Si/Mo surfaces results in the formation of silicides with metallic states. While the work functions of the Si clusters are about 10% larger than the Mo substrate, the silicide work functions are nearly 10% smaller than that of Mo.
Ultrafast time resolution in scanned probe microscopies: Surface photovoltage on Si(111)–(7×7)
Authors: Hamers R. J. , Cahill David G.
Published: July 2002

The speed limitations conventionally encountered in scanning tunneling microscopy, scanning capacitance microscopy, and atomic force microscopy result from the external electronics and are not inherent to the techniques themselves. Ultrafast time resolution can be achieved through the use of correlation methods. We demonstrate the application of time-resolved optical correlation techniques to scanned probe microscopy by probing the relaxation of photo-excited carriers at the Si(111)–(7×7) surface on the nanosecond and picosecond time scales using scanning tunneling and scanning capacitance microscopy measurements of the surface photovoltage. The observed temporal response demonstrates that the voltage arises from photovoltaic effects and does not arise from direct optical rectification in the tunnel junction gap.
Tunneling spectroscopic analysis of optically active wide band-gap semiconductors
Authors: Bonnell D. A. , Rohrer G. S. , French R. H.
Published: July 2002

Tunneling spectroscopy has been used to detect the photoexcitation of charge carriers in the wide band-gap semiconductors, ZnO and cubic SiC. Because the process is energy sensitive, valence-to-conduction band or defect charge transfer transitions may be selectively excited and detected with the scanning tunneling microscope. Two types of transitions were detected which change the tunneling response; for cubic SiC valence-to-conduction band transitions were excited, while for Co2+ and Mn2+ doped ZnO electron charge transfer transitions from the dopants to the conduction bands occur. Preliminary results on the effect of a continuous energy (ultraviolet) light source on the tunneling spectrum of ZnO are presented.
Prism-coupled light emission from a scanning tunneling microscope
Authors: Takeuchi K. , Uehara Y. , Ushioda S. , Morita S.
Published: July 2002

We have investigated the light emission mechanisms from a scanning tunneling microscope in which the sample surface is a thin film of Au (22.5 nm thick) evaporated on a microscope cover glass. This sample was attached to the flat surface of a hemicylindrical coupler prism. The tunneling electrons from a Pt-Ir tip were directed to the Au film from the air side, and the angle dependence of light emission intensity was measured through the coupler prism using a photon counting system. We found a sharp emission peak centered at 43° from the film surface normal. This is the angle at which the fast mode of surface plasmon polaritons (SPP) mostly localized at the Au/air interface can radiate by conserving the wave vector parallel to the interface. Thus we conclude that most of the light on the prism side is emitted by the delocalized fast mode of SPP of the Au/air interface.
Over-passivation of sulfur treated AlGaAs/GaAs heterojunction bipolar transistors
Authors: Shikata S. , Okada H. , Hayashi H.
Published: July 2002

The over-passivations of sulfur treated GaAs were investigated by the photoluminescence measurement and device characteristics of AlGaAs/GaAs heterojunction bipolar transistors. The two chemical vapor deposition systems of the conventional plasma enhanced process and electron cyclotron resonance process were employed. The surface recombination current density calculated from the current gain and the base current noise was reduced to 25% by sulfur treatment and over-passivation process using the electron cyclotron resonance deposition system, whereas over-passivation by the plasma enhanced deposition system gave some damage to the sulfur treated surface.
Surface and interface structure of epitaxial CoSi2 films on Si(111)
Authors: Stalder R. , Onda N. , Sirringhaus H. , von Känel H. , Bulle-Lieuwma C. W. T.
Published: July 2002

The surface and interface structures of molecular beam epitaxially grown CoSi2 films on Si(111) have been studied by scanning tunneling microscopy and by transmission electron microscopy, respectively. All surfaces are found to be inhomogeneous, exhibiting (2×1) and (2×2) reconstructed domains along with unreconstructed areas, depending on their stoichiometry. All of them could be imaged with atomic resolution. The surface step structure and the formation of pinholes have been examined for a wide range of growth conditions. Evidence is presented for micron-scale surface diffusion of Si on CoSi2 at temperatures as low as 800 K. The interface step structure, studied by transmission electron microscopy, has been found to depend critically on the details of the growth procedure.
A quantitative model of point defect diffusivity and recombination in ion beam deposition and combined ion and molecular deposition
Authors: Vancauwenberghe O. , Herbots N. , Hellman O. C.
Published: July 2002

We are investigating the use of low energy ions (<1 keV) in low temperature thin film growth techniques, ion beam deposition (IBD) and combined ion and molecular deposition (CIMD). In IBD, a thin film is directly grown from a low energy ion beam as the only source of material, while in CIMD, low temperature growth of thin films is achieved by depositing materials simultaneously from a low energy ion beam and one or several molecular beams. A simple model of the IBD process has been developed and accounts for atomic collisions and thermal diffusion during thin film growth. Computer simulation of IBD of Si on Si have been conducted as a function of ion energy to support more quantitatively this physical description of IBD. The results show that the IBD growth mechanism is mediated by the fast diffusing interstitials and establish a low energy limit to achieve epitaxial growth by IBD that depends on the point defect diffusivities. The defect generation has to be confined in the subsurface region in order to favor interstitial recombination with the surface, leading to net thin film growth, and vacancy annihilation to prevent amorphization. The effect of point defect diffusivities on the IBD growth process is also investigated. It is found that a model including fast moving interstitials can account for various experimental observations specific to IBD.
Reflection high-energy electron diffraction patterns of CrSi2 films on (111) silicon
Authors: Mahan John E. , Geib Kent M. , Robinson G. Y. , Bai G. , Nicolet M-A.
Published: July 2002

Highly oriented films of the semiconducting transition metal silicide, CrSi2, were grown on (111) silicon substrates, with the matching crystallographic faces being CrSi2(001)/Si(111). Reflection high-energy electron diffraction (RHEED) yielded symmetric patterns of sharp streaks. The expected streak spacings for different incident RHEED beam directions were calculated from the reciprocal net of the CrSi2(001) face and shown to match the observed spacings. The predominant azimuthal orientation of the films was thus determined to be CrSi2〈210〉∥Si〈110〉. This highly desirable heteroepitaxial relationship may be described with a common unit mesh of 51 Å2 and a mismatch of −0.3%. RHEED also revealed the presence of limited film regions of a competing azimuthal orientation, CrSi2〈110〉∥Si〈110〉. A new common unit mesh for this competing orientation is suggested; it possesses an area of 612 Å2 and a mismatch of −1.2%.
High-precision motion and alignment in an ion-beam proximity printing system
Authors: Stumbo D. P. , Damm G. A. , Sen S. , Engler D. W. , Fong F-O. , Wolfe J. C. , Oro James A.
Published: July 2002

We measure the fluorescent alignment generated by ion bombardment of an SiO2 wafer mark scanned behind a corresponding window pattern in a silicon stencil mask. We conclude that an optimized system can align to 50 nm (mean+3σ) in less than 300 ms. Throughput is shown to be limited not by the alignment system, but by thermal loading of the mask during exposure.
Real time control of the molecular-beam epitaxial growth of CdHgTe and CdTe/HgTe superlattices using ellipsometry
Authors: Hartley R. H. , Folkard M. A. , Carr D. , Orders P. J. , Rees D. , Varga I. K. , Kumar V. , Shen G. , Steele T. A. , Buskes H. , Lee J. B.
Published: July 2002

Ellipsometry is a sensitive nondestructive analytical technique well suited to the molecular-beam epitaxy (MBE) growth process. We report its use in real time to control composition, growth rates, interdiffusion, and growth related surface defects of Cd0.2Hg0.8Te epilayers and CdTe/HgTe superlattices grown on CdTe and Cd0.96Zn0.04Te (100) substrates using a Riber 32 R&D MBE machine that has been custom modified by the manufacturer to facilitate the addition of a phase-modulated ellipsometer. Growth rate data from ellipsometry are in good agreement with reflection high-energy electron diffraction intensity oscillation data, double-crystal rocking curve determinations of superlattice periodicity, and infrared transmission measurements of total thickness. The level of Hg incorporation in CdTe (100) layers is measured with ellipsometry and its temperature dependence is established. Growth-front roughening of CdTe during the growth of CdTe/HgTe superlattices and interdiffusion between these layers on postgrowth annealing, are observed in the ellipsometric data. The results are compared with model calculations and a compositional profile of these interface structures is proposed.
Conductivity changes in Ni films on Si(111) following compound formation during annealing
Authors: Schad R. , Jentzsch F. , Henzler M.
Published: July 2002

The sheet conductance of Ni films deposited onto clean Si(111) substrates has been measured during deposition and after stepwise annealing. Hall effect, surface composition, and surface order have also been monitored. The dependence of compound formation on film thickness and temperature has been studied. It is shown that each silicide has a characteristic bulk conductivity and that the influence of surface scattering is small even for very thin films (≳1 nm).
Properties of very low temperature plasma deposited silicon nitride films
Authors: Juang C. , Chang J. H. , Hwang R. Y.
Published: July 2002

Plasma enhanced deposition of silicon nitride films is shown to have less N–H bonds and provide better heat resistance using SiH4–N2 than SiH4–NH3–N2 plasmas at 100 °C. Properties of silicon nitride using SiH4–N2 plasma are studied versus various deposition parameters such as radio frequency power, silane flow ratio, and deposition pressure. The experimental data indicate that the deposition process at 100 °C has a N2-reaction-controlled mechanism.
Membrane fragility: Fact or illusion?
Authors: Trimble L. E. , Celler G. K. , Frackoviak J. , Weber G. R.
Published: July 2002

Membranes are in wide use today as microsensors, vacuum windows, and lithography mask substrates. They are fragile and difficult to protect, however. We show that membrane strength, and thus process yield, are increased by a newly designed ‘‘skirted’’ membrane. This structure strengthens the attachment of membrane to support, reinforcing a region where fractures usually originate. The skirt design was applied to polysilicon membranes on glass supports, used for x-ray lithography mask blanks, and was shown to increase strength three times over polysilicon or silicon-rich nitride membranes on silicon supports, to an average of 1.5 GPa. More significantly, skirted polysilicon membranes exhibit fracture pressure differentials that are six times higher in the same comparison, having tremendous impact on process and application durability.
Diffraction effects and image blurring in x-ray proximity printing
Authors: Dubner A. D. , Wagner A. , Levin J. P. , Mauer J.
Published: July 2002

The influence of diffraction on the shape and size of features printed using x-ray proximity printing is reviewed, and the effect of image blurring on these results is described. Diffraction can alter the shape of a printed feature, and the systematic shape changes observed in resist images can be explained using simple scaling based on Fresnel diffraction. In addition, the linewidth change with exposure dose is independent of feature type and size, and depends only on the square root of the mask to wafer gap. The shape of printed features and the linewidth change with dose can be modified by smearing the aerial image at the wafer plane. This can be achieved by adding beam divergence or by varying the angle of incidence of the x-ray beam onto the mask (wobbling). A technique for incorporating wobble into an exposure system is described, and exposures of contact holes, spaces, lines, and line-space arrays using this technique are presented. For example, 0.35 μm square contact holes normally print diamond shaped at a 40 μm gap. However, the same contact holes are round in resist when 4 mrad of wobble is incorporated into the exposure. The linewidth change for a 10% increase in dose is 24 nm at a 40 μm gap with 5 mrad of wobble. This linewidth change with exposure dose is larger than the 20 nm measured for exposures at a 40 μm gap without wobble. Finally, wobbling during exposure can either increase or decrease the absolute linewidth of a feature in resist at a given exposure dose.
Photolithography at 193 nm
Authors: Rothschild M. , Goodman R. B. , Hartney M. A. , Horn M. W. , Kunz R. R. , Sedlacek J. H. C. , Shaver D. C.
Published: July 2002

Photolithography at 193 nm is a natural continuation of the progression from 436 to 365 to 248 nm in lithography, dictated by the requirement for continually higher resolution. It is anticipated that 193-nm lithography will enable 0.25-μm patterning in volume production with conventional masks, and 0.18-μm resolution with phase-shifting masks. The main issues related to lithography at this new wavelength are being addressed. It has been shown that highly transparent optical materials are available at 193 nm. Also, they are damaged by the laser radiation at a slow enough rate that high-quality projection optics are expected to perform within specifications for ten years of full-time operation. Consequently, a 193-nm step-and-scan system is being constructed, and it has been designed to attain 0.25-μm resolution over a 22 by 35 mm field. A range of 193-nm photoresist schemes has been demonstrated. They include semitransparent single-layer resists, positive-tone surface imaging (silylation), and negative-tone bilayers using ultrathin silicon-based polymers. In most instances we have demonstrated sub-0.25-μm resolution, high photosensitivity, good exposure–defocus latitude, and very low levels of etch residue. In sum, the first successful steps towards a fully engineered 193-nm photolithography have been taken, and no major obstacles are anticipated.
Fabrication and physics of lateral superlattices with 40 nm pitch on high-mobility GaAs GaAlAs heterostructures
Authors: Smith C. G. , Chen W. , Pepper M. , Ahmed H. , Hasko D. , Ritchie D. A. , Frost J. E. F. , Jones G. A. C.
Published: July 2002

We have shown that a lateral superlattice of dots of period 40 nm can be fabricated and have defined a 60 nm period hexagonal lateral surface superlattice of dots over a high-mobility two-dimensional electron gas. With a negative voltage on the gate a honeycomb potential is created around the dots. The pattern is produced with electron beam lithography by stitching together superlattice regions of area (0.5 μm).2 At gate voltages close to zero the Shubnikov–de Haas peaks are split into subbands with corresponding structure in the Hall voltage. Close to pinch-off, periodic peaks in the conductance versus gate voltage are seen whenever one electron is removed from the 0.5 μm square region. The electrons are localized in this area by the error in the stitching of the fields. There is a sharp drop in conductance when the carrier concentration is such that there is one electron per unit cell, which may indicate the electrons are condensing in a lattice commensurate with the applied periodic potential.
Silicon stencil masks for lithography below 0.25 μm by ion-projection exposure
Authors: Mauger P. E. , Shimkunas A. R. , Wolfe J. C. , Sen S. , Löschner H. , Stengl G.
Published: July 2002

Large-area silicon stencil masks for demagnifying ion-projection lithography have been fabricated and characterized. The masks were made by patterning silicon membranes 120 mm in diameter and 2.5 μm in thickness. The membranes, prepared on 150 mm host wafers using a p/n-junction electrochemical etch stop, were designed with low tensile stress (10 MPa) to obtain minimum pattern distortion. Mask blanks were made by field bonding the membrane-containing host wafers to pyrex rings. The blanks were patterned by e-beam lithography over a 60×60-mm field in a conventional novolak resist. The resist patterns were transferred into the silicon membranes in a magnetically enhanced reactive ion etcher using molecular bromine. The intermediate pattern-transfer layer was low-stress chemical vapor deposition silicon dioxide. Mask openings as small as 0.5 μm were achieved. The sidewalls of the openings were smooth and had positive tapers no more than 3° from vertical. The linewidth uniformity across the mask was <±10%, and linewidth bias was small, nearly constant, and uniform across the mask. Mask pattern distortion measurements indicated a pattern-placement deviation of less than 0.2 μm (3σ).
Large radius new etching system using electron beam excited plasma
Authors: Aoyagi Y. , Hara T. , Hamagaki M. , Ryoji M. , Ohnishi K.
Published: July 2002

A new electron beam excited plasma (EBEP) etching system has been developed. This EBEP system can efficiently generate a high density and uniform plasma by introducing a high current low-energy electron beam into an etching gas chamber. The uniformity of the Cl plasma density is within ±2.5% over an 8 in. wafer and the uniformity of the plasma and floating potential across the wafer is within ±2 V. This ultrahigh uniformity of the potentials overcomes the problem of the breakdown of thin gate insulators during etching that originate from the nonuniformity of the potential at the substrate. The selectivity of etching obtained is 40:1 for poly-Si/resist and more than 100:1 for poly-Si/SiO2. The etch rate is 3600 A/min.
Dry etching of III–V semiconductors in CH3I, C2H5I, and C3H7I discharges
Authors: Chakrabarti U. K. , Pearton S. J. , Katz A. , Hobson W. S. , Abernathy C. R.
Published: July 2002

The characteristics of plasma etching of InP, InAs, InSb, GaAs, AlGaAs, GaSb, AlInAs, InGaAs, and AlInP in microwave (2.45 GHz) discharges of methyl-, ethyl-, and propyl-iodide have been examined with respect to etch rates, surface morphology, damage introduction, and etch anisotropy. The etch rates for all of these semiconductors are somewhat faster than for conventional CH4-based discharges under the same conditions of direct-current bias, pressure, and microwave power, but are not as fast as with HI discharges. Polymer deposition on the mask and within the chamber occurs as with CH4-based mixtures, but is minimized at low pressure (≤10 mTorr) and with H2 dilution. The etched surface morphologies are smooth over a wide range of plasma parameters and show roughness only under conditions of significant polymer deposition. Chemical analysis by Auger electron spectroscopy and x-ray photoelectron spectroscopy also shows that the near surface of the etched samples retains its stoichiometry under most conditions. While the etch rates are slower than for HI-based discharges, the halocarbon iodides are significantly less corrosive and much more stable.
Organometallic molecular-beam epitaxy growth and characterization of InxAl1−xAs on InP
Authors: Quinn W. E. , Tamargo M. C. , Brasil M. J. S. P. , Nahory R. E. , Farrell H. H.
Published: July 2002

We report the growth and characterization of InxAl1−xAs/InP heterostructures grown by organometallic molecular-beam epitaxy. X-ray rocking curves with half-widths as low as 53 arc sec and low temperature photoluminescence linewidths of 26 meV were obtained for the InAlAs layers near lattice-matched to InP. The interface quality was investigated by photoluminescence taking advantage of the type II nature of the interface. Interface quality was improved by reducing the length of the growth halt between layers. The important effects of interface chemistry were studied, and in fact, quality was enhanced by introducing binary interfacial layers only 1 ML in thickness.
Modification of the microroughness of molecular-beam epitaxially grown GaAs/AlAs interfaces through changes in the growth temperature
Authors: Katzer D. S. , Gammon D. , Shanabrook B. V.
Published: July 2002

The interfacial properties of a series of GaAs/AlAs quantum wells (QWs) grown by molecular-beam epitaxy is examined using photoluminescence (PL). These high-quality QWs show splittings in the free exciton peaks, which indicate that large scale island structures exist at the interfaces. By changing the growth temperature we are able to shift the absolute energies of the excitons while keeping the same PL linewidths and lineshapes. Since the absolute energies of the excitons depend only on the GaAs and AlAs material parameters, we conclude that we are able to modify the small scale structure of the interfaces within the large scale islands by changing the growth temperature.
Growth and characterization of ZnTe, ZnMnTe epilayers and single quantum wells
Authors: Duddles N. J. , Nicholls J. E. , Gregory T. J. , Hagston W. E. , Lunn B. , Ashenford D. E.
Published: July 2002

We report the growth of epilayers of ZnTe, Zn1−xMnxTe, and single quantum wells of ZnTe/Zn1−xMnxTe on (001) GaSb by molecular-beam epitaxy. The system has been characterized by photoluminescence spectroscopy and x-ray diffraction. Preliminary calculations indicate that the valence band offset is of the order of 30 meV (x=0.177). Experimental evidence is presented to show that magnetic polaron formation occurs within the ZnTe well region even though absent in the Zn1−xMnxTe epilayers. This has led us to considerations of a dynamic nature and in particular the role of the polaron formation time. By comparing these results with Cd1−xMnxTe, we deduce that the lifetimes of excitons in Zn1−xMnxTe are significantly shorter than in Cd1−xMnxTe.
Latent image diffraction from submicron photoresist gratings
Authors: Yoon Euijoon , Green Christian A. , Gottscho Richard A. , Hayes Todd R. , Giapis Konstantinos P.
Published: July 2002

Light scattering from latent images in photoresist is useful for lithographic tool characterization, process monitoring, and process control. In particular, closed-loop control of lithographic processes is critical for high yield, low cost device manufacturing. In this work, we report use of pulsed laser diffraction from photoresist latent images in 0.24 μm pitch distributed feedback laser gratings. Gated detection of pulsed light scattering permits high spatial resolution probing using ultraviolet light without altering the latent image. A correlation between latent image and etched grating diffraction efficiencies is demonstrated and shows the value of ‘‘upstream’’ monitoring.
InGaAs/InP quantum wells on vicinal Si(001): Structural and optical properties
Authors: Grundmann M. , Krost A. , Bimberg D. , Cerva H.
Published: July 2002

The growth of InGaAs/InP quantum wells (QWs) by low-pressure metalorganic chemical vapor deposition on vicinal Si(001) substrate is reported. Despite the fact that the etch pit density is about 2 × 107 cm−2 the low temperature (T=2 K) luminescence efficiency is very high and about the same as for QWs grown at 640 °C on InP substrates. The high efficiency is a result of the large structural perfection of the optically active QW areas. Microtwins (MTs) present a major source of nonradiative recombination in such structures. Transmission electron microscopy cross sections show a reduced growth rate within the MTs. A decrease of the QW width next to the boundaries leads to an increase of the effective band gap of the QW. Thus, local drift fields lead to a depletion of charge carriers close to the defects. The charge carriers in the QW are localized predominantly in defect-free areas and can efficiently recombine there radiatively. At room-temperature charge carriers are thermally activated to or remain in the narrower well regions next to the twin boundaries leading to enhanced nonradiative recombination and a comparatively larger drop of the quantum efficiency.
Growth of AlN on GaAs(110) by reactive molecular beam deposition
Authors: Baier H.-U. , Mönch W.
Published: July 2002

AlN was synthesized by reaction of Al evaporated from a Knudsen cell with ammonia molecules on clean cleaved GaAs(110) surfaces at a growth temperature of 645 K. The chemical and electronic properties of the overlayers and interfaces were investigated by x-ray, soft x-ray, and UV photoelectron spectroscopy (UPS) and by means of low-energy electron energy-loss spectroscopy and the Kelvin method. With increasing AlN deposition the intensities of the Ga- and As-derived surface-state signals in the energy-loss and photoemission spectra, respectively, were found to decrease to the same extent and to have vanished for nominal coverages larger than 3 monolayers (ML). The intensities of the Ga(3d) and As(3d) core-level lines excited with Zr(Mζ) radiation are reduced exponentially as a function of AlN coverage. The slope of this intensity decrease is smaller than the one observed for room temperature deposition. These findings indicate inhomogeneous growth of AlN at 645 K but abrupt interfaces. Photoemission data obtained with n- and p-type doped GaAs(110) indicate a pinning of the Fermi level at 0.51 eV above the top of the valence band for coverages larger than 3 ML. AlN thus induces surface states of donor and acceptor type which are attributed to a continuum of disorder-induced interface states. For nominal coverages larger than 3 ML the AlN valence-band structure dominates the UPS spectra. The valence-band discontinuity amounts to 2 eV.
Electron microscope investigation of surface features of {100} Cd1−yZnyTe grown by metalorganic chemical vapor deposition
Authors: Hamilton W. J. , Johnson S. M. , Ahlgren W. L.
Published: July 2002

Scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction analyses have indicated that there are three types of hillocks on the surfaces of single-crystal, epitaxial {100} Cd1−yZnyTe grown on {100} GaAs: large, polycrystalline, irregularly shaped particulates, loosely bound to the surface; large ‘‘hillocks’’ approaching regular polygonal shape; and small, regular, four-sided pyramids with planar surfaces making very low angles to the layer surface. Both the large particulates and hillocks appear to have their etiology in precipitation from the gas-phase or reactor wall nucleation, with subsequent nucleation of twins in the growing layer in the case of the large, polygonal hillocks. The small, pyramidal hillocks evidently are single crystal material with geometries dependent upon the crystallographic orientation of the original substrate surface.
Effects of mixed-valence mercury and indium on the electrical properties of Hg1−xCdxTe
Authors: Pain G. N.
Published: July 2002

A new intrinsic defect, the mercurous ion (Hg–Hg)2+, is proposed to account for n-type doping of Hg1−xCdxTe by excess mercury. The double cations can be formed through capture of neutral interstitial mercury atoms by mercuric ions. This effectively decouples the mercuric ion from the four tellurium atoms previously coordinated, releasing two electrons for each mercury atom captured. This model can explain the stability of metal-rich MCT and recent reports of intrinsic acceptor–donor pairs correlated within a lattice constant. Formation of mercurous ions could greatly enhance self-diffusion of Hg through a knock-on effect. Thermodynamic calculations support the proposition that self-compensation of indium in MCT can occur through the presence of nearly equal populations of In3+ (donor) and In+ (acceptor), as occurs in the stable phase InTe. For low or metastable doping levels, the solid phase can be considered as a solid solution of InTe, In2Te3, and MCT. Any excess trivalent In is perfectly compensated by introduction of a cation vacancy for every two In3+ ions. On subsequent mercury-rich annealing, only the excess In3+ will be ‘‘activated’’ through filling of cation vacancies, imposing a limit to the maximum n-type doping achievable.
Proximity exposure compensation and resist debris formation in electron beam lithography
Authors: Deshmukh P. R. , Singh M. , Rangra K. J. , Vyas P. D. , Khokle W. S. , Pal B. B.
Published: July 2002

A theoretical and experimental investigation into the formation of resist debris due to proximity exposure compensation (PEC) in electron beam lithography is provided. The two dimensional simulation of resist contours in closely spaced rectangular patterns shows that the unsupported resist fragments (debris) originate at the top of the resist when a PEC scheme based on dose variation method is used to compensate for the proximity exposure effects within and between the patterns. It is found that by taking some precautions during electron exposure and development process, the adverse effects of resist fragments can be eliminated.
Surface and interface ordering on non-(100)-oriented GaAs substrates
Authors: Nötzel R. , Ploog K.
Published: July 2002

We have observed the formation of highly ordered surface structures on (211), (311), and (111) GaAs substrates. During molecular-beam epitaxy, the flat surfaces break up into regular facets that have nanometer-scale dimensions, which can be directly monitored by reflection high-energy electron diffraction (RHEED). The RHEED intensity dynamics reveals a unique growth mechanism on the stepped surfaces during the growth of GaAs/AlAs multilayer structures resulting in the formation of alternating narrow and wide regions of GaAs and AlAs. The observed energy shift of the luminescence is correlated with the height of the specific surface corrugation and with the average GaAs layer thickness. The additional lateral confinement introduced by the interface corrugation manifests itself in an increased exciton continuum energy, an enhanced exciton-phonon interaction, a pronounced optical anisotropy, and an increased integral luminescence intensity. The observed surface structures offer a unified picture to explain previously unclear results obtained from these non-(100)-oriented GaAs surfaces, and they provide a unique method to directly synthesize quantum-wire and quantum-dot structures.
Epitaxial Ga2Se3 layers grown on GaAs(100) using a heterovalent exchange reaction
Authors: Zahn D. R. T. , Krost A. , Kolodziejczyk M. , Richter W.
Published: July 2002

III2VI3 compounds were found to form when III–V semiconductors are exposed at elevated temperatures to an excess of group VI elements by an exchange and diffusion reaction of the group V and VI atoms. This simple approach was applied to produce high quality epitaxial Ga2Se3 layers on GaAs(100). Here the optimization of the growth parameters is described. The layers were grown by annealing GaAs(100) substrates in a H2Se atmosphere. The substrate temperature Ts during growth was varied in the range from 600 to 900 K. In addition, the Se partial pressure was varied over more than two orders of magnitude at a fixed Ts. After growth the samples were investigated by x-ray diffraction, Raman, photoluminescence, and secondary ion mass spectroscopies. A phase transition from the α modification of Ga2Se3 with an unordered distribution of vacancies to β-Ga2Se3 with an ordered arrangement of vacancies is observed at Ts≊780 K. A strong green luminescence band peaked at 2.46 eV is discovered at 77 K.
Two dimensional profiling using secondary ion mass spectrometry
Authors: Dowsett M. G. , Cooke G. A.
Published: July 2002

As device dimensions decrease and packing densities increase, the need for accurate mapping of dopant profiles in at least two dimensions is becoming ever more acute. Such data are required to establish the limitations of very large scale integrated manufacture, and to verify and refine the process simulators which have been devised. However, direct measurements of dopant atom distributions, using analytical techniques such as secondary ion mass spectrometry, are not possible owing to the limited analyte volume available at high spatial resolutions. The technique described here uses a specially fabricated sample which allows material to be collected from a large number of similar volumes, thus improving the sensitivity. The geometry magnifies the lateral spread many times increasing the lateral resolution achieved with a probe of a given diameter. Relatively low energy probes may be used to obtain high depth resolutions. In subsequent processing, sensitivity, depth, and lateral resolution may be mutually traded to optimize the profile for a given application.
GaAs doping by rapid thermal diffusion of a laser-deposited elemental Zn source film: Shallow and laterally graded diffusions
Authors: Licata Thomas J. , Scarmozzino Robert , Garcia Basilio J. , Osgood Richard M. , Schwarz Steven A.
Published: July 2002

We present an excimer-laser-based doping process useful for shallow uniform and laterally graded p-type doping of GaAs substrates. Specifically, low power 248-nm pulses from a KrF excimer laser are used to nonthermally photodeposit thin Zn layers (∼3–300 Å) from a dimethylzinc (DMZn) ambient onto selected GaAs surface regions. Uniform exposure of a sample to the laser pulses produces a source film which is laterally uniform in thickness, whereas variations in exposure time across a sample deposit a source film which is laterally graded in thickness. The surface is subsequently capped, and the Zn source is diffused into the GaAs using rapid thermal annealing. Secondary ion mass spectroscopy and spreading resistance measurements indicate that uniformly thick source depositions result in uniform diffusions with shallow junction depths and high surface concentrations. Alternatively, our measurements show that gradations in the dopant source profile translate into laterally graded doping profiles for appropriately chosen source thicknesses and diffusion parameters.
Micromorphology study of mercuric iodide crystals by atomic force microscopy
Authors: Azoulay M. , George M. A. , Jayatirtha H. N. , Biao Y. , Burger A. , Silberman E. , Nason D.
Published: July 2002

Atomic force microscopy was used to study the surfaces of mercuric iodide crystals at ambient. Various surface conditions were examined, including as-grown (001), (110), and (013) faces, and cleaved, chemically etched, vacuum etched, and aged (001) surfaces. As-grown (001) faces show a terraced structure and are smoother than as-grown (110) faces. Freshly cleaved surfaces exhibit a terraced structure, with riser heights corresponding to multiples of the c-lattice constant. All surfaces become progressively pitted and rougher by vacuum treatment or chemical etching. Defects identified as pits or hillocks with dimensions of the order of 100 nanometers were also observed, and surface roughness values were obtained for quantitative characterization of the various treatments.
Room temperature observation of photocurrent dependence on applied bias in Si1−xGex/Si multiquantum wells
Authors: Chowdhury Andalib A. , Rashed M. Mahbub , Maziar C. M. , Murtaza S. S. , Campbell J. C.
Published: July 2002

We report the observation of the dependence of photocurrent on applied bias in Si1−xGex/Si multiquantum wells at room temperature. The photocurrents were measured on reverse biased p–i–n diodes containing an intrinsic region comprised of Si1−xGex/Si multiquantum wells. These Si1−xGex/Si multiquantum wells were grown by the remote plasma enhanced chemical vapor deposition method. Using the technique employed by Park et al. [J. Vac. Sci. Technol. B 8, 217 (1990)] to analyze similar experimental observations at lower temperature (77 K), we have estimated the absorption edges from the photocurrents and showed a large transition energy shift under electric field. The observed shape of the absorption coefficient as a function of the photon energy differs from that observed previously at lower temperature.
Hydrogen plasma processing of GaAs and AlGaAs
Authors: Choquette Kent D. , Freund R. S. , Hong M. , Luftman H. S. , Chu S. N. G. , Mannaerts J. P. , Wetzel R. C.
Published: July 2002

Hydrogen plasma processing of GaAs and AlGaAs using an electron cyclotron resonance plasma reactor, which is vacuum-linked to a molecular-beam epitaxial (MBE) growth chamber is reported. Native oxide removal and surface cleaning of GaAs is characterized using hydrogen plasma processing, subsequent thermal Cl2 etching, and vacuum annealing. It is shown that surface reconstruction and excellent GaAs/GaAs interfaces can be achieved using these dry vacuum procedures. It is also shown that AlxGa1−xAs native oxides can be removed for 0≤x≤1 using hydrogen plasma processing before MBE overgrowth. The best AlGaAs/AlGaAs interfaces are obtained using low microwave power during hydrogen plasma processing. O and C impurities detected at these interfaces increase with higher Al composition; Si interface impurities tend to increase with higher microwave power. In general, hydrogen plasma processing is judged effective for surface preparation before MBE growth for the complete range of AlGaAs alloys.