bluuebunny/crossref_metadata_2025 huggingface dataset:
Mg doping studies of electron cyclotron resonance molecular beam epitaxy of GaN thin films
Authors: Berishev I. , Kim E. , Fartassi A. , Sayhi M. , Bensaoula A.
Published: July 2002

A modified electron cyclotron resonance plasma source, allowing optically active GaN thin films at growth rates up to 1 μm per h, was utilized in a molecular beam epitaxy environment for Mg doping studies of GaN. The effect of the growth parameters on the Mg incorporation was studied using secondary ion mass spectroscopy and Hall measurements. We found that Mg does not incorporate when GaN is grown under Ga-rich conditions, independently of the Mg flux, in the temperature range of 700–800 °C. Only N-rich growth conditions allow measurable Mg incorporation. This incorporation increases with decreasing Ga cell temperature. Furthermore, under N-rich growth conditions, the Mg content is more sensitive to the lowering of the substrate temperature than to the increase of the Mg cell temperature.
Effect of inert gas additive on Cl2-based inductively coupled plasma etching of NiFe and NiFeCo
Authors: Jung K. B. , Cho H. , Hahn Y. B. , Hays D. C. , Lambers E. S. , Park Y. D. , Feng T. , Childress J. R. , Pearton S. J.
Published: July 2002

NiFe and NiFeCo thin films have been etched in Cl2/He, Cl2/Ar and Cl2/Xe inductively coupled plasmas as a function of pressure, source power, and rf chuck power. The etch rates decrease with increasing pressure, and go through a maximum with both source and chuck power. The results are consistent with a mechanism involving ion-assisted desorption of relatively involatile etch products, and a balance of ion flux, ion energy, and chlorine neutral density is necessary to achieve practical etch rates and smooth surfaces. Under our conditions, Cl2/He provided the best surface morphologies and the least residual chlorine.
Modeling of large cluster synthesis
Authors: Hosseini-Tehrani A. , Urban F. K.
Published: July 2002

The original idea of the ionized cluster beam thin film deposition technique was based upon producing, ionizing and accelerating beams of atoms clusters from vaporized material onto a substrate in a vacuum environment using a supersonic jet source. However, the conditions and nozzles for this cluster synthesis found so far require rather high stagnation pressures (more than 1 atm) which is impractical for many materials with lower vapor pressures than, for example, zinc. Simulation of this process using classical nucleation theory and one-dimensional gas flow equations is described here. This approach is an extension of previous methods used for simulation of condensation of water vapor during supersonic expansion in nozzles and the simulation mechanism of large clusters from vaporized solid materials. Zinc cluster sizes predicted by the model are in qualitative and quantitative agreement with our experimental results. Simulation results are discussed in terms of the best nozzle geometry which will result in larger clusters at a lower stagnation pressure. Novel nozzle designs simulated in this work show that clusters may be formed at lower pressures which would extend the method to a much wider range of materials. Thus development of such new nozzles for use at lower pressure and temperature would significantly impact this method.
Characterization of 100 MHz inductively coupled plasma (ICP) by comparison with 13.56 MHz ICP
Authors: Nakagawa H. , Morishita S. , Noda S. , Okigawa M. , Inoue M. , Sekine M. , Ito K.
Published: July 2002

The effect of the excitation frequency on the dissociative process of the C4F8 gas was investigated by comparing a 100 MHz [very high-frequency (VHF)] inductively coupled plasma (ICP) with a 13.56 MHz [radio frequency (rf)] ICP. The same apparatus except for the wave generator and matching network was used for both ICPs in order to investigate the frequency effect as precisely as possible. The electron density and electron temperature in an Ar plasma were measured by using a Langmuir probe. From the dependence of the radial distribution of the Ne on the ICP source power, it was found that the rf ICP was produced in a cylindrical space under the coil area, while the VHF ICP was generated throughout the reactor. In C4F8/Ar plasma, the CFx (x=1, 2, 3) radical densities near the reactor wall were measured by using appearance mass spectrometry, and the F radical density was measured by using actinometry through the optical emission spectroscopy of Ar (750.4 nm) and F (703.7 nm). The degree of dissociation of the C4F8 in the VHF ICP was higher than that in the rf ICP, but the CF2/F density ratio in the VHF ICP was 3–5 times that in the rf ICP. This result indicates that the dissociation of high-molecule gases, including C4F8, proceeds more easily in the VHF ICP than in rf ICP and that there is much less dissociation of high-order radicals (e.g., CF2+e→CF+F+e) in VHF ICP than there is in rf ICP. Hence, VHF ICP suppresses F radical generation better than rf ICP.
Photoemission spectroscopy analysis of ZnO:Ga films for display applications
Authors: Forsythe E. W. , Gao Yongli , Provost L. G. , Tompa G. S.
Published: July 2002

We report the physical properties of ZnO:Ga-based films prepared by metalorganic chemical vapor deposition (MOCVD) using ultraviolet and x-ray photoemission spectroscopy (UPS and XPS). In addition, the surface characteristics of the films are modified with a series of cleaning and etching steps. The films were produced in an argon-oxygen atmosphere using metalorganic precursors at low pressure in a rotating disk reactor. The XPS results show a gallium oxide rich layer more than 20 Å on the surface of the as-received MOCVD films, with a small fraction of Zn. This oxide layer is removed by a cleaning and plasma treatment, which enhances the conductivity of the ZnO:Ga films. From UPS, the work function is 4.23 eV after an O2 plasma treatment. Finally, we report on the surface morphology of the ZnO:Ga films after the cleaning process. The post-deposition treatment of these MOCVD films is important for the improved conductivity that is vital to display applications.
Novel reflectron time of flight analyzer for surface analysis using secondary ion mass spectroscopy and mass spectroscopy of recoiled ions
Authors: Smentkowski V. S. , Krauss A. R. , Gruen D. M. , Holecek J. C. , Schultz J. A.
Published: July 2002

We have modeled, designed, built, and tested a novel reflectron time-of-flight (TOF) analyzer, which is capable of performing surface analysis using both secondary ion mass spectroscopy (SIMS) and mass spectroscopy of recoiled ions (MSRI). All elements (including H and He) can be identified, with isotopic resolution, using both MSRI and SIMS. For ions of a given mass, the higher energy ions penetrate further into the reflectron before being turned around while the lower energy ions do not penetrate as deeply. By properly adjusting both the experimental geometry and the reflectron voltages, all ions of a given mass arrive at the detector simultaneously—resulting in enhanced mass resolution compared with simple TOF detection. SIM spectra are complicated by molecular fragments in addition to elemental ions. In MSRI only elemental ions are detected. As a result, data analysis in MSRI is less complicated than in SIMS. Being able to use a single analyzer to selectively obtain SIMS or MSRI data provides complementary surface information. MSRI has a number of unique capabilities for surface studies. In situ, real-time surface analysis can be performed during film growth at pressures of ∼2.5 mTorr at the substrate by differentially pumping both the ion source and the reflectron analyzer region. It has been demonstrated that the ratio of the positive to negative ion yield is phase specific; for example, one can clearly distinguish the different forms of carbon (diamond versus graphite versus amorphous carbon) during film growth. MSRI analysis of poorly conducting surfaces is possible.
Influence of the sputtering variables in the ion bombardment during off-axis deposition of YBa2Cu3Ox films
Authors: Acosta M. , Ares O. , Sosa Victor , Acosta C. , Peña J. L.
Published: July 2002

YBa 2 Cu 3 O x thin films were grown on SrTiO3 substrates using an off-axis-sputtering configuration. Using a target with 100 h of sputtering runs, only medium quality films were obtained. However, a fresh target allowed us to obtain, at the same sputtering conditions, high quality films. The different film properties obtained as a function of the target age, gas pressure, and substrate position were discussed in the framework of a previous model of the angular distribution of oxygen ions which bombard and affect the growing film.
Characterization of magnetron-sputtered partially ionized deposition as a function of metal and gas species
Authors: Allain Monica M. C. , Hayden D. B. , Juliano D. R. , Ruzic D. N.
Published: July 2002

Conventional magnetron sputter deposition with a rf inductively coupled plasma (ICP) has demonstrated that ionized metal fluxes can be effectively utilized to fill trenches and vias with high aspect ratios. The ICP is created with a seven turn (1/2 wavelength), water cooled coil located between the magnetron cathode and the substrate. A large fraction of the metal atoms sputtered from the magnetron cathode are ionized by the ICP. These ions are accelerated across the sheath toward the substrate and deposited at normal incidence, by placing a negative bias on the substrate. A gridded energy analyzer configured with a quartz crystal microbalance is located in the center of the substrate plane to determine the ion and neutral deposition rates. While keeping the magnetron power, rf coil, target to substrate distance, pressure and diagnostic location constant, the ionization fraction was measured for two metal targets: Cu and Ti using three different working gases: Kr, Ar and Ne. Variations in target materials and working gases are shown to have an effect on ionization and deposition rates. The ionization rate is a sensitive function of the metal’s ionization potential. The electron energy distribution in the plasma is affected by the sputtered metal and the working gases’ ionization potential.
Mass-resolved ion energy distributions in continuous dual mode microwave/radio frequency plasmas in argon and nitrogen
Authors: Hallil A. , Zabeida O. , Wertheimer M. R. , Martinu L.
Published: July 2002

The control of plasma-surface interactions in terms of synergistic effects of ions, photons, and chemically active species is important for the optimization of plasma enhanced chemical vapor deposition of thin films and for plasma-induced surface modification. In the present work, we use a dual-mode microwave/radio frequency (MW/rf) plasma system, in which we investigate the effect of plasma parameters (gas type and pressure, self-bias voltage, for example) on the energy and flux of ionic species arriving at the specimen surface. We determine the ion energy distribution functions (IEDFs) using a mass spectrometer/energy analyzer, in Ar and N2 discharges, excited at different frequencies. The results for Ar+, N2+, and N+ ions show structured IEDFs at the rf-powered electrode in the single- and dual-frequency modes, while a single peak is observed in the continuous MW plasma. The MW/rf plasma presents substantially higher ion flux and plasma density, and a much thinner sheath than the rf case. Changes in plasma impedance, measured by a rf current–voltage probe, support the results on plasma density and sheath thickness, determined from the IEDFs. The MW/rf discharge impedance displays a resistive behavior in contrast to rf plasma, where the impedance is capacitive.
Real-time optical characterization of heteroepitaxy by organometallic chemical vapor deposition
Authors: Bell K. A. , Ebert M. , Yoo S. D. , Flock K. , Aspnes D. E.
Published: July 2002

Heteroepitaxy of GaP on Si(100) and GaAs(100) is investigated under organometallic chemical vapor deposition conditions using combined spectroscopic ellipsometry (SE) and non-normal-incidence reflectance-difference (-anisotropy) spectroscopy. Real-time monitoring greatly assists in identifying optimum starting surfaces for heteroepitaxy since prolonged exposure to PH3 results in roughening of Si(100) and GaAs(100) surfaces, in agreement with previous work. Real-time SE data of GaP on Si indicate that under our conditions GaP and Si interpenetrate as optically identifiable materials over the first 75 Å, suggesting that either trimethylgallium or a reaction by-product can act as a catalyst for the formation of Si{111} facets.
Etching mechanism of (Ba, Sr)TiO3 films in high density Cl2/BCl3/Ar plasma
Authors: Kim Seung-Bum , Lee Yong-Hyuk , Kim Tae-Hyung , Yeom Geun-Young , Kim Chang-Il
Published: July 2002

(Ba, Sr)TiO 3 (BST) thin films have attracted great interest as new dielectric materials of capacitors for ultralarge-scale integrated dynamic random access memories such as 1 or 4 Gbit. In this study, inductively coupled BCl3/ Cl2/Ar plasmas was used to etch BST. The Cl2/(Cl2+Ar) was fixed at 0.2, and the BST thin films were etched by adding BCl3. The characteristics of the plasmas were estimated using optical emission spectroscopy (OES). The change of Cl, B radical density was measured by OES as a function of BCl3 percentage in Cl2/Ar. The cross section of BST thin films and residue remaining after the etch was investigated by scanning electron microscopy. The chemical reactions between BST and Cl2 and the surface of BST films etched with different BCl3/Cl2/Ar gas mixing ratios were investigated using x-ray photoelectron spectroscopy.
Modulation of atomic interdiffusion at the Si(111)–Au interface
Authors: Franciosi A. , O’Neill D. G. , Weaver J. H.
Published: July 2002

We attained a wide modulation of the Si(111)–Au interface reaction by deposition of controlled amounts of Cr on the semiconductor surface before in situ junction formation. Synchrotron radiation photoemission studies show that Cr deposition gives rise to a Si/Cr reacted interlayer that dramatically affects the subsequent Si–Au interdiffusion. Negligible interdiffusion of Cr and Au atoms was found in all cases so that the Si–Au intermixing depends upon an exchange reaction at the Si/Cr–Au interface in which Si is the only moving species. Large reduction of the interdiffusion occurs sharply above a critical value of Cr deposition (10 monolayers) that corresponds to a fully reacted Si(111)–Cr interface.
Process and film characterization of low pressure tetraethylorthosilicate–borophosphosilicate glass
Authors: Becker F. S. , Pawlik D. , Schäfer H. , Staudigl G.
Published: July 2002

The pyrolytic decomposition of tetraethylorthosilicate (TEOS) has been used to deposit highly doped borophosphosilicate glass (BPSG) films. The experiments were carried out in a modified low pressure chemical vapor deposition furnace in the 620–680 °C range at a deposition pressure of 0.5 Torr. Trimethylborate and phosphine together with oxygen were found to be the best dopant source combination. The deposited layers adhere strongly to the quartzware and low particle counts of typically less than 0.2 per cm2 were measured. The thickness uniformity was below ±6%, the dopant uniformity was ±0.1 wt. % over a wafer. If compared to low pressure SiH4–BPSG films, the TEOS–BPSG shows superior step coverage and much higher chemical stability up to dopant levels of about 5 wt. % B, 5 wt. % P. The etch rate behavior in buffered HF corresponds to the trends reported for SiH4–BPSG. The electrical characterization of thin TEOS–BPSG and TEOS–SiO2 layers yielded an electrical breakdown strength in the 7–8 MV/cm range. The glass flow properties (wet and dry ambient) were investigated and found to be very good in the 800–850 °C region. By using a rapid optical anneal system, the required step tapering could be achieved at time/temperature combinations of 40 s/900 °C or 10 s/1000 °C. Detailed infrared studies showed strong interaction among the different oxide absorption bands of the TEOS–BPSG layers.
Development of highly reliable synchrotron radiation lithography beamline
Authors: Okada K. , Fujii K. , Kawase Y. , Nagano M.
Published: July 2002

The reliable beamline structure for synchrotron radiation lithography has been investigated using the Photon Factory storage ring (2.5 GeV). The recently built beamline aims at attaining system reliability and safety. This beamline, one of three branch lines split from a basic beamline, is a 10−7 Pa ultrahigh-vacuum system with an oscillating mirror. In addition to a 40 ms fast closing valve (FCV) and an acoustic delay line (ADL), installed in the basic beamline, a <15 ms FCV and 40 ms ADL were set up to protect the storage ring from accidental breakdown. The FCV and ADL were placed far upstream of the oscillating mirror, to cope with accidental gas leakage caused by the oscillating mechanism. A vacuum breakdown test demonstrated that the FCV and ADL are greatly effective in vacuum protection. In order to protect operators from x-ray exposure, two auxiliary shutters made of tantalum were placed upstream of the oscillating mirror. The oscillating mirror, driven through bellows by a combination of a direct current servomotor and a cam mechanism, enabled a highly reliable oscillation. A double-structured bellows was adopted to provide against gas leakage. In addition, a silicon carbide plane mirror (40×17×4 cm) was employed because of its high-heat-resistance capability.
Unpinned Schottky barrier formation at metal–GaAs interfaces
Authors: Brillson L. J. , Viturro R. E. , Mailhiot C. , Shaw J. L. , Tache N. , McKinley J. , Margaritondo G. , Woodall J. M. , Kirchner P. D. , Pettit G. D. , Wright S. L.
Published: July 2002

We have used soft x-ray photoemission spectroscopy measurements to demonstrate that metal–GaAs interfaces can exhibit relatively unpinned Fermi level (Ef) movements. For clean GaAs (100) surfaces obtained by molecular-beam epitaxy (MBE) growth and thermal decapping of a protective As overlayer, the metals Au, Al, Cu, and In produce a 0.6–0.7-eV range of Ef stabilization. For a given metal, this stabilization occurs at the same energies for n-type and p-type GaAs. Furthermore, Ef movements are metal-dependent and can evolve over multimonolayer coverages. These results are examined with respect to pronounced differences in semiconductor quality between MBE versus melt-grown GaAs and in the context of previous GaAs Ef measurements. A self-consistent analysis of the junction electrostatics accounts for the functional dependence of barrier height on metal work function. The results highlight the importance of bulk quality as well as interface specific phenomena in controlling the Schottky barrier formation at metal/III–V compound semiconductor interfaces.
Imaging of cracks in semiconductors using scanning tunneling microscopy
Authors: Foecke T. , King R. M. , Dale A. F. , Gerberich W. W.
Published: July 2002

Scanning tunneling microscopy (STM) has developed into a useful tool for atomic-scale characterization of material surfaces. It has a great advantage over other high-resolution techniques in that no extensive sample modification, such as thinning or polishing, is required to obtain atomic resolution images. This is especially useful in the field of fracture, as the vast majority of high-resolution images of fracture processes are made in the transmission electron microscope, where thin-film effects may greatly modify crack tip stresses and dislocation structures. This investigation involved imaging of cracks introduced in single crystals of galena (PbS) by rapid indentation at 77 K. Images were obtained both at the arrested crack tip and along the flanks of the crack in the dynamic growth region. Measurements were made of both crack-tip morphology and upsets observed along the flanks of the crack. The latter is discussed in terms of plasticity upsets associated with dislocation emission from rapidly growing cracks. Effects of STM tip geometry and scan conditions on the resulting image of the cleavage crack, as well as work in progress on other material systems, is discussed.
Critical dimension control of high resolution metal structures by backscattered electrons
Authors: DiFabrizio E. , Luciani L. , Grella L. , Baciocchi M. , Mastrogiacomo L. , Gentili M.
Published: July 2002

In this article a commercial e-beam lithography machine (Leica Cambridge EBMF 10 cs/120) is used in metrological mode for critical dimension control of metal features with size down to 100 nm. The experimental backscattered electrons signal, collected by a channel plate detector, is described by an analytical function which is the convolution of probe beam function, detector transfer function, and specimen absorption transfer function. The further data processing by means of a developed software algorithm, allowed the determination of the significant structure parameters as linewidth and sidewall angle. Metal test structures, as isolated lines and grooves with size down to 100 nm, fabricated on silicon wafers, are successfully inspected and measured by this method. The comparison between computed dimensions and scanning electron microscopy measurements shows a good agreement (within 5%) for structures of different dimensions, varying their aspect ratio and the sidewall angle at their edges. The effect of beam diameter (BD) value on the measurement was also investigated and accurate measurements have been obtained for BD less than the structure dimension. Finally, a repeatability test performed on a sub-200 nm gold feature showed a precision of 6 nm (3σS value) on a sample of one thousand measurements.
Modeling and experimental verification of illumination and diffraction effects on image quality in x-ray lithography
Authors: Hector Scott D. , Schattenburg M. L. , Anderson E. H. , Chu W. , Wong Vincent V. , Smith Henry I.
Published: July 2002

Most analyses of the effects of diffraction and source coherence on image quality in proximity x-ray lithography have used Kirchhoff boundary conditions and scalar diffraction theory. In this article we treat the x-ray absorber as a lossy dielectric and employ the vector form of Maxwell’s equations to calculate image intensity as a function of position for lines, spaces, and gratings, at 100 nm linewidths and below. We show that vector and scalar theories give different results. Simulations are done for two point sources (CuL and an Fe-plasma) so that calculations could be compared with our experimental results. Agreement was excellent for 80 and 50 nm features at relatively large gaps. We define image contrast and show that, contrary to common intuition, it is enhanced (and spurious ringing is suppressed) as penumbral blurring is increased, reaching a maximum when the extent of blurring is somewhat larger than the minimum feature size.
New approach to low temperature deposition of high-quality thin films by electron cyclotron resonance microwave plasmas
Authors: Chau T. T. , Mejia S. R. , Kao K. C.
Published: July 2002

An electron cyclotron resonance microwave plasma processing system consisting of a plasma chamber and a processing chamber as well as a new apparatus called the ‘‘species selector and energy controller (SSEC)’’ are described in detail. Silicon dioxide (SiO2) films fabricated using this system without and with the SSEC are used for various experiments to demonstrate that the SSEC can effectively suppress the damaging effects resulting from the bombardment on the substrates and the on-growing films by energetic particles and photons produced in the plasma during film deposition, as well as effectively reduce the upstream diffusion of the reactant gas from the processing chamber to the plasma chamber, thus suppressing the formation of microdust particles due to the heterogeneous gas phase reaction. The film growth for the films fabricated without the SSEC is due mainly to mass-limited reaction and that with the SSEC is due to surface rate-limited reaction. The electronic properties of the SiO2 films fabricated with the SSEC at temperatures higher than 250 °C approach those of high-quality thermally grown silicon oxides. The effects of the SSEC on the film properties and the film growth mechanism are also discussed.
Interfacial point defects in heavily implanted silicon germanium alloys
Authors: Zvanut M. E. , Carlos W. E. , Twigg M. E. , Stahlbush R. E. , Godbey D. J.
Published: July 2002

Comparing electron paramagnetic resonance (EPR) spectra from samples of two different alloy compositions we develop a structural model for SG1, a Ge dangling bond defect in O implanted SiGe. Analysis of the angular dependence of EPR spectra from measurements of 10% and 40% Ge alloys reveals that in both cases the defect exhibits 〈111〉 symmetry of the Si lattice; however, the defect in the 40% alloy exhibits a larger g⊥ and broader linewidth than the defect in the 10% alloys. From these observations we propose that for both alloy compositions SG1 is a trivalently bonded Ge atom, and we suggest that the center in the 40% Ge alloy involves a greater number of Ge backbonds than the center in 10% Ge samples. That implantation with Ne does not produce SG1 provides evidence to suggest that the defect is located at interfaces between the SiGe alloy and SiO2 precipitates formed by oxygen implantation.
Noncrystalline films with the chemistry, bonding, and properties of diamond
Authors: Collins C. B. , Davanloo F. , Lee T. J. , Park H. , You J. H.
Published: July 2002

The energetic condensation of multiple charged ions of carbon at keV energies produces textured noncrystalline films having many of the properties of diamond. Prepared in vacuum by the laser ablation of graphite at intensities in excess of 1011 W cm−2, a variety of structural morphologies can result that depend upon the kinetic energies and charge states employed. The most promising is an amorphous ceramic called ‘‘amorphic diamond’’ for convenience. It consists of sp3-bonded nodules of carbon in a matrix of other carbons. The high energies of condensation provide both for the chemical bonding of such films to a wide variety of substrates and for low values of residual compressive stress, 0.7–0.8 GPa. On selected films, hardness cannot be measured because of deformations of the diamond indenter, but a lower limit for hardness has been found at 78 GPa. Coatings of 2–5 μm thicknesses have extended lifetimes of materials such as Si, Ti, and ZnS against the erosive wear from high-speed particles and droplets by factors of tens to thousands.
EL-4 column and control
Authors: Petric Paul F. , Gordon Michael S. , Senesi Joseph J. , Haire Donald F.
Published: July 2002

This article describes the electron optical column and some of its electronic controls for the new generation of electron-beam lithography system at IBM, designated EL-4. This new column utilizes variable shaped-beam technology and incorporates dual shaping optics for both triangular and rectangular shapes and triple deflection. The EL-4 system was designed for high-throughput 1/4 μm lithography with an edge resolution of 50 nm (extendable to 1/10 μm groundrules) over a 10 mm×10 mm field. The beam deflection optics uses a dual variable axis immersion lens system to achieve two stages of magnetic deflection and one stage of electric deflection. By design, all three stages of deflection are telecentric to eliminate overlay errors resulting from target plane height variations. A pixel throughput increase from our existing state-of-the-art system, the EL-3, of over an order of magnitude was required for this new system to write the next generation circuit patterns within reasonable times. A unique mechanical design approach for the column, utilizing a double-walled construction, combines the required mechanical rigidity and vacuum environment with exceptional electromagnetic interference shielding.
Effects of reactive ion etching on optical and electro-optical properties of GaInAs/InP based strip-loaded waveguides
Authors: Thirstrup C. , Pang S. W. , Albrektsen O. , Hanberg J.
Published: July 2002

A systematic analysis of how CH4/H2 based reactive ion etching affects the optical and electro-optical properties of GaInAs/InP multiple quantum well pin diode strip-loaded waveguides is reported. The study includes measurements of waveguiding properties, optical losses and electro-optical phase modulation as function of etch depth, radio-frequency (rf) power, pressure, and the CH4 content in the etch process. It is found that the optical losses of the waveguides are most sensitive to the etching conditions, in particular the rf power. As the rf-power density was varied from 0.27 to 1.09 W/cm2, the optical losses increased from 6.8 to 19.6 dB/cm. The waveguiding and electro-optical properties were found to be much less sensitive to the etching parameters. For a 5-μm-wide waveguide, the full width half-maximum of the optical mode is typically 5 μm and the average voltage needed to produce a π phase shift is 4 V corresponding to a modulation response of 15°/V mm.
Time-of-flight measurement of carrier transport and carrier collection in strained Si1−xGex/Si quantum wells
Authors: Fukatsu S. , Fujiwara A. , Muraki K. , Takahashi Y. , Shiraki Y.
Published: July 2002

Carrier transport and collection was investigated in strained Si1−xGex/Si(100) double quantum wells (QWs) separated by a Si barrier. Steady-state photoluminescence (PL) revealed a clear spectral dominance switch of PL between the two QWs as the Si barrier was systematically varied. Time-of-flight luminescence spectroscopy was used to estimate the mean drift velocity of carriers in terms of the luminescence rise time difference between the two QWs. Carrier collection efficiency was found to be dependent on the well width, which was obtained from the luminescence intensity difference.
Roles of a Si insertion layer at GaAs/AlAs heterointerface determined by x-ray photoemission spectroscopy
Authors: Hashimoto Y. , Tanaka G. , Ikoma T.
Published: July 2002

Roles of an ultrathin Si insertion layer in AlAs/Si/GaAs system are studied by using in situ x-ray photoemission spectroscopy. It is found that a main role of the Si layer is not a control of a valence band offset as was proposed by Sorba et al., but an introduction of band bending in an overgrown layer. The proposed band-bending model explains all the experimental observations in the x-ray photoemission spectra; an Al 2p line broadening and the dependence of a peak energy shift on the crystallographic orientation and an overgrown-layer thickness.
Strict thermal nitridation selectivity between Si and Ge used as a chemical probe of the outermost layer of Si1−xGex alloys and Ge/Si(001) or Si/Ge(001) heterostructures
Authors: Aubel D. , Diani M. , Bischoff J. L. , Bolmont D. , Kubler L.
Published: July 2002

The thermal reactivity of NH3 with Si(001), Ge(001), Si1−xGex(001), and thinly Ge-covered Si(001) or Si-covered Ge(001) surfaces has been studied by means of in situ x-ray photoelectron spectroscopy in a temperature domain (T∼600 °C) compatible with the usual growth of Ge-Si based heterostructures. A very marked difference between Si(001) and Ge(001) initial sticking coefficients is found, the latter surface being totally inert against nitridation by NH3 in contrast with the Si(001) surface. This nitridation selectivity provides easy access to information about surface termination in different situations where Si and Ge are potentially mixed, the reactivity depending on whether Si appears at the reactive interface or not. As a test, comparing the nitrogen uptake curves in the early stages of NH3 exposure, for all the studied structures except Si(001), a Ge-like initial sticking coefficient or a non-nitriding behavior is found. This is fairly explained on the basis of the well-known concepts of the Stranski–Krastanov growth mode for the Ge/Si system and by Ge surface segregation for the Si1−xGex and Si/Ge systems. Our result also implies the need of plasma-assisted treatments in order to achieve simultaneous Si and Ge nitridation of SiGe alloys.
Plasma ion implantation technology for broad industrial application
Authors: Deb Dipten , Siambis John , Symons Robert
Published: July 2002

The recently invented Plasma Ion Implantation (PII) process (1987) [J. R. Conrad, U.S. Patent No. 764394 (August 16, 1988)] is currently under intense industrial engineering investigation and development. A critical component of PII for broad industrial utilization is the availability of an efficient modulator system that applies the high voltage pulse to the workpiece. A modulator technology assessment and selection is carried out. The requirements of the PII process favor the selection of a hard-tube modulator. The PII process favors the application of beam switch tube technology such as the Litton L-5012 and L-5097. These Litton tubes have already been selected by LANL and utilized in their pilot engineering demonstration experiment with GM and the University of Wisconsin. The performance, physical operation, and potential enhancements of the Litton beam switch tubes L-5012 and L-5097 will be discussed in connection with the requirements of the emerging plasma ion implantation industrial modulator technology.
Nanostructure fabrication via direct writing with atoms focused in laser fields
Authors: Scholten R. E. , McClelland J. J. , Palm E. C. , Gavrin A. , Celotta R. J.
Published: July 2002

The techniques of atom optics can be applied during the deposition of atoms onto a surface to produce nanostructures. A laser is used to form a standing wave intensity pattern in front of the substrate. An atom beam, which has been collimated by optical means, is focused onto the substrate by dipole forces from the standing wave pattern so as to deposit a series of lines spaced by half the laser wavelength. We describe the fabrication of a Cr nanograting formed using this new technique. The experimental arrangement for deposition and the optical collimation of the atom beam are described. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the resulting nanostructures are presented.
Scanning tunneling microscopy of ordered C60 and C70 layers on Au(111), Cu(111), Ag(110), and Au(110) surfaces
Authors: Gimzewski J. K. , Modesti S. , David T. , Schlittler R. R.
Published: July 2002

We have conducted a study of the growth of C60 and C70 on a variety of reconstructed and unreconstructed noble metal surfaces using a UHV scanning tunneling microscope. For reconstructed Au(110) and Au(111) surfaces we observe changes in the superstructure of the metal upon (sub)monolayer adsorption at the fullerene–metal interface. In all the metals studied, formation of a well-ordered hexagonal C60 overlayer is observed after annealing. (110) and (111) substrates show preferred nucleation and growth at terrace and steps, respectively. Time-lapsed images illustrate mobility of C60 arrays and clusters. The role of tip–C60 interactions is elucidated by sequences of images and the prospects for manipulation is discussed.
Interpretation of atomic force microscopy images: The mica (001) surface with a diamond tip apex
Authors: Tang H. , Joachim C. , Devillers J.
Published: July 2002

Constant-force atomic force microscopy (AFM) images of the muscovite mica surface are calculated and compared to experimental ones. The surface structure is first optimized using a molecular mechanic procedure. Force–distance characteristics are proposed to determine the applied force range where the surface is not deformed. Calculated rigid substrate and tip apex AFM images are interpreted and compared with the experimental ones. A full relaxed calculated scan is presented and compared to rigid calculated scans.
Mini-column silicon field-emitter arrays
Authors: Yadon L. N. , Temple D. , Palmer W. D. , Ball C. A. , McGuire G. E. , Tang Cha-Mei , Swyden Thomas A.
Published: July 2002

We report emission data of silicon field emitter arrays fabricated with the ultimate goal of their integration within a planar lens structure for beam focusing experiments. The field emitters have been fabricated as linear arrays (with 20 μm separation between tips), square arrays (with 12 μm tip-to-tip separation), and single tips. The emitters themselves are formed on columns approximately 0.7 μm in height and 0.4 μm in diameter, and have gate aperture diameters as small as 1.1 μm. Two types of field emitter tips have been fabricated: One has been formed via isotropic etching of silicon in an SF6 plasma, the second using an orientation-dependent silicon wet etching procedure. Both have been sharpened with an oxidation process, and tip radii as small as 4 nm have been obtained. During testing, 14.4 μA of anode current was obtained from a single tip. From a 100 tip array, 3 mA of current was measured at a gate voltage of 85 V. From a 10 000 tip array, 14.5 mA was obtained.
Patterned, photon-driven cryoetching of GaAs and AlGaAs
Authors: Shih M. C. , Freiler M. B. , Scarmozzino R. , Osgood R. M.
Published: July 2002

We present a high-resolution, damage-free etching technique for GaAs and related compound semiconductors which utilizes surface-specific photochemistry at 193 nm to excite a physisorbed layer of Cl2 on a cryogenically cooled (∼140 K) sample. Etch rates as high as 0.25 Å/pulse (corresponding to 0.09 μm/min) have been achieved. Etching is anisotropic, and etched features of 0.2–0.3 μm linewidth have been routinely obtained. The etch rate has been characterized as a function of several ‘‘system’’ parameters including Cl2-partial pressure, substrate-temperature, laser repetition rate and fluence, and the addition of rare gases. A phenomenological model of this cryoetching has been developed which agrees well with the experimental data. The etch damage and contamination have been studied with Auger electron spectroscopy, photoluminescence, and Schottky-barrier measurements. All results indicate that there is minimal if any damage induced by the cryoetching process.
Effect of substrate miscut on the structural properties of InGaAs linear graded buffer layers grown by molecular-beam epitaxy on GaAs
Authors: Eldredge J. W. , Matney K. M. , Goorsky M. S. , Chui H. C. , Harris J. S.
Published: July 2002

We investigated the effect of substrate misorientation on the structural properties of an InGaAs linearly compositionally graded buffer layer and an AlGaAs/InGaAs superlattice grown by molecular-beam epitaxy on both on-axis and 2° miscut (001) GaAs substrates. Triple axis x-ray diffraction and reciprocal space maps were used to determine the relaxation and tilt of the buffer layer and superlattice with respect to each other and to the substrate. A tilt of 0.17° between the buffer layer and substrate was observed from (004) reciprocal space maps of the heterostructure grown on an off-axis substrate, while none was observed for the heterostructure grown on the on-axis substrate. The layer tilt axis for the miscut substrate, which coincided with a 〈110〉 direction, was 32° from the miscut axis. (224) glancing exit reciprocal space maps showed the majority of the buffer layer to be relaxed, with the top portion corresponding to a strained denuded zone free of misfit segments. Intersubband measurements showed no relation between device performance and the 2° miscut substrate, even though the two samples exhibited different superlattice peak widths.
Technology for high-performance n-channel SiGe modulation-doped field-effect transistors
Authors: Kuznetsov V. I. , Veen R. v. , van der Drift E. , Werner K. , Verbruggen A. H. , Radelaar S.
Published: July 2002

A fabrication process for n-channel SiGe modulation-doped field-effect transistors has been developed in which the strain in the heterostructure is completely preserved by taking into account an appropriate temperature range for the formation of ohmic contacts to source drain by implantation. It yields a low specific contact resistance of 7.1×10−5 Ω cm2 to be compared to 5.7×10−2 Ω cm2 for alloyed Au/Sb contacts. With the same thermal upper limit the application of different gate oxides has been studied. All oxides show negligible gate leakage enabling a superior gate voltage swing compared to devices with a Schottky gate. Application of thermal oxide grown at 650 °C yields a superior field-effector transistor performance compared to devices with sputter and plasma-enhanced chemical-vapor deposition deposited oxides due to its lower and negative charge level. Gate recessing of 0.5 μm Schottky gates yields a transconductance increase up to 310 mS/mm.
Role of gas phase reactions in subatmospheric chemical-vapor deposition ozone/TEOS processes for oxide deposition
Authors: Shareef I. A. , Rubloff G. W. , Gill W. N.
Published: July 2002

Deposition rates, wet etch rates, and thickness uniformity experiments were performed using O3/TEOS thermal chemical-vapor deposition. Our results for oxide deposition show optimum process window around 200 Torr for producing films of good quality (uniformity and material properties). This is in excellent agreement with the modeling predictions over a broad range of pressure (100–600 Torr) and temperature (370–470 °C). The model invokes both gas phase and surface reaction mechanisms. The former is needed to produce deposition precursors and leads to an observed increase-maximum-decrease dependence on the deposition pressure; this decrease is associated with a competing (parasitic) role of gas phase reactions. Our experiments identify particle formation at higher pressures which is consistent with the expected dual role of gas phase reaction in generating (1) required deposition precursors and (2) particulates in the gas phase under some conditions.
Solvent effect on the properties of sulfur passivated GaAs
Authors: Bessolov Vasily N. , Konenkova Elena V. , Lebedev Mikhail V.
Published: July 2002

Photoluminescence and x-ray photoelectron spectroscopy have been used to study the solvent effect on surface properties of GaAs passivated in different sulfide solutions. It has been found that sulfur passivation could be made more efficient by decreasing the solution dielectric constant through the use of various alcohols as solvents. Specifically, the band edge photoluminescence intensity is much higher, the total amount of oxides is lower, and sulfur coverage is higher compared with a GaAs surface treated in an aqueous sulfide solution. The role of the solvent in sulfur passivation is discussed.
Monte Carlo study of hot electron and ballistic transport in diamond: Low electric field region
Authors: Cutler P. H. , Huang Z.-H. , Miskovsky N. M. , D’Ambrosio P. , Chung M.
Published: July 2002

A Monte Carlo simulation of electron transport in the conduction band of diamond as a function of field and film thickness has been performed. It predicts that the energy distribution of field emitted electrons ‘‘heats up’’ when the internal electric field is of the order of 1 V/μm and greater. The energy distribution shifts and becomes broader as the width of the sample increases. With increasing field (≥10 V/μm), there is a transition to quasi-ballistic-like behavior. For thinner films (≤0.1 μm), the transport is more clearly ballistic with the peak energy scaling roughly with the field. It is suggested that if a realistic and viable electron injection mechanism into the conduction band of a diamond–metal or diamond–semiconductor interface could be found for those crystal faces of diamond exhibiting negative electron affinity, then a copious cold cathode electron emitter with field tunable energies is feasible.
Fabrication of arrayed glassy carbon field emitters
Authors: Sohda Yasunari , Tanenbaum David M. , Turner Stephen W. , Craighead Harold G.
Published: July 2002

Glassy carbon has desirable properties for electron field emission such as surface inertness, electrical conductivity, and thermal stability. In addition, a uniform thick substrate with a polished surface is easily obtainable. This enables one to apply large scale integrated circuit processing for fabricating arrayed tips. By using oxygen reactive ion etching, cusps over 3.5 μm in height and 2.5 μm in base diameter are fabricated with a tip radius of under 10 nm. The process is assisted by the formation of a layer of etch products which protects the newly forming tip from bending and over etching. The field emission current up to 50 μA from the glassy carbon tips is obtained by applying high voltage to a mesh anode. The current which passed through the mesh anode is collected at another electrode and measured. The Fowler–Nordheim plot suggests the existence of nm scale structure on the tip. This favorable result indicates glassy carbon substrate is a good substrate for field emitter arrays.
On the electrical deactivation of arsenic in silicon
Authors: Myler U. , Simpson P. J. , Lawther D. W. , Rousseau P. M.
Published: July 2002

Previous work on thermally induced arsenic deactivation in highly doped silicon has proven the generation of vacancies and suggests the formation of arsenic-vacancy clusters as the deactivation mechanism. Using positron annihilation spectroscopy in the two-detector coincidence geometry, we are able to show that the thermally generated vacancies are indeed surrounded by arsenic atoms.
Electronic structure and optical behavior of self-assembled InAs quantum dots
Authors: Berryman K. W. , Lyon S. A. , Segev Mordechai
Published: July 2002

Using both electrical and optical techniques, ground state energy levels and excited states of carriers in self-assembled InAs quantum dots are described, and the first observations of mid-infrared photoconductivity in these structures are presented. Electrical measurements including ac conductance and Hall techniques have been used to determine thermal trapping of carriers, and yield strong binding for holes, less binding for electrons, and an exciton energy that is consistent with photoluminescence (PL) measurements. Further PL experiments have probed the effect of changing the InAs dot size, and using embedding material of different composition. Several of these structures also demonstrate strong electron binding. In devices where the InAs dots have been grown in an Al0.3Ga0.7As matrix and surrounded by AlAs barriers, normal incidence photoconductivity has been observed at a range of wavelengths in the mid-infrared and attributed to single carrier transitions out of the dots. This mid-infrared optical response is investigated for several different dot structures and compared to photoluminescence data from the same samples.
Optical determination of shallow carrier profiles using Fourier transform infrared ellipsometry
Authors: Tiwald Thomas E. , Thompson Daniel W. , Woollam John A.
Published: July 2002

Dopant profiles were determined by ex situ Fourier transform infrared variable-angle spectroscopic ellipsometry. The technique exploits carrier absorption in the mid-infrared spectral range and combines the sensitivity of ellipsometry with a simple Drude free carrier absorption model to determine the carrier profile. The noncontact, nondestructive nature of the measurement suggests both ex situ and in situ monitoring and control applications. In this study, the carrier profiles were modeled as graded multilayers that can be constrained to a given functional form (Gaussian, erfc, etc.) when desired. Boron and arsenic implanted silicon wafers that were rapid thermal anneal and furnace annealed were measured and compared to spreading resistance probe data.
Molecular beam epitaxy growth and characterization of DyP/GaAs, DyAs/GaAs, GaAs/DyP/GaAs, and GaAs/DyAs/GaAs heterostructures
Authors: Lee P. P. , Hwu R. J. , Sadwick L. P. , Balasubramaniam H. , Kumar B. R. , Lai T. C. , Chu S. N. G. , Alvis R. , Lareau R. T. , Wood M. C.
Published: July 2002

Details of the structural and electrical properties of epitaxial DyP/GaAs and DyAs/GaAs are reported. DyP is lattice matched to GaAs, with a room temperature mismatch of less than 0.01%. Both DyP and DyAs have been grown by solid source molecular beam epitaxy. High quality DyP and DyAs epilayers, as determined by x-ray diffraction, transmission electron microscopy, and atomic force microscopy analyses, have been obtained for growth temperatures ranging from 500 to 600 °C and growth rates between 0.5 and 0.7 μm/h. DyP epilayers are n type with measured electron concentrations on the order of 3–4×1020 cm−3, room temperature mobilities of 250–300 cm2/V s, and a barrier height of 0.81 eV to n-type GaAs at room temperature. DyAs epilayers are also n type with measured electron concentrations of 1–2×1021 cm−3 and mobilities between 25 and 40 cm2/V s. DyP is stable in air with no apparent oxidation taking place, even after months of ambient exposure to untreated air.