bluuebunny/crossref_metadata_2025 huggingface dataset:
Selectively doped GaAs/N–AlGaAs heterostructures grown by molecular beam epitaxy for high electron mobility transistor IC applications
Authors: Hiyamizu S. , Saito J. , Kondo K. , Yamamoto T. , Ishikawa T. , Sasa S.
Published: July 2002

Extremely high electron mobilities of 2.4×106 cm2/V s (4.2 K) and 2.05×105 cm2/V s (77 K) with a sheet electron concentration of about 5.3×1011 cm−2 were achieved in a selectively doped GaAs/N–AlGaAs heterostructure with a GaAs–AlGaAs heterostructure buffer layer grown by MBE. A new 3-in.-substrate MBE system having a cell-substrate distance of 25 cm was developed, and sufficiently high uniformity (±1% variation in the layer thickness, doping concentration, and AlAs mole fraction of Si-doped AlGaAs over a 56-mm-diam area) as well as high quality of a GaAs/N–AlGaAs heterostructure (electron mobility of 1.96×105 cm2/V s at 77 K) for high electron mobility transistor IC application was achieved with the new MBE system.
Proximity effects and printability of defects in GexSe1−x resist
Authors: Leung Wingyu , Neureuther Andrew R. , Oldham William G.
Published: July 2002

Simulations and experiments are used to explore the impact of lateral diffusion of Ag in projection printing in a GexSe1−x resist system. The lateral transport of Ag makes more Ag available for photodoping in the bright areas than in the dark areas. This lateral diffusion which is responsible for the edge sharpening effect causes nearby features to interact not only in the aerial image but also in the competition for Ag. Proximity effects arising both from this diffusion and from the optical image itself are simulated and compared with experiments. Good agreement between simulation and experiment is found. Under normal use up to dose of 500 mW/cm2, the proximity effects are predominantly those associated with the aerial image, even under low-intensity exposure conditions which maximize lateral diffusion effects. No unusual increase in the tendency for small defects to print was observed either for line features or contact holes. For very high doses proximity effects due to lateral diffusion can be observed.
Measurement of the conduction band discontinuities of InGaAsP/InP heterojunctions using capacitance–voltage analysis
Authors: Forrest S. R. , Schmidt P. H. , Wilson R. B. , Kaplan M. L.
Published: July 2002

The relationship between the conduction band discontinuity (ΔEc) and the band gap difference (ΔEg) of InGaAsP/InP heterojunctions is measured for the first time using capacitance–voltage analysis. It is found that ΔEc=(0.39±0.01)ΔEg over the entire spectrum of compositions of InGaAsP lattice matched to InP. This result is to be contrasted with those obtained for the GaAs/GaAlAs material system, where 60%–70% of the band gap difference between a particular composition of GaAlAs and GaAs appears in the conduction band. The measurements discussed in this work were made using novel organic-on-inorganic contact barrier devices. Due to the high energy barriers between certain organic materials and InGaAsP, high resolution measurements of the carrier concentrations, layer thicknesses, conduction band discontinuities, and other relevant parameters were made possible. Constructing wafer contour maps of the fixed charge density at the heterointerface (σ) using this technique indicated no systematic dependence of ΔEc on σ for σ<5×10 cm−2, as expected.
Silver diffusion in Ag2Se/GeSe2 inorganic resist system
Authors: Polasko K. J. , Tsai C. C. , Cagan M. R. , Pease R. F. W.
Published: July 2002

Over the past several years a class of silver-doped GeSex materials has received attention as a high gamma, negative resist. The columnar structure of the GeSex films is believed to be linked to some of the lithographic properties of the resist. However, the mechanism of Ag incorporation is not well understood. In this paper we report secondary ion mass spectroscopy (SIMS) observations of the Ag migration in GeSe2 films. Furthermore, we have found evidence for a fast Ag diffusion effect in GeSe2. These findings are consistent with a columnar GeSe2 structure. The Ag concentration depth profile in 3000- and 6000-Å-thick films of GeSe2 on substrates consisting of 300 Å of Ta on silicon wafers has been studied by SIMS. An O+2 primary beam was used in the SIMS analysis, with the bombardment energy reduced to 3 keV to minimize possible beam-induced effects and to increase the depth resolution. The Ag2Se/GeSe2 resist was exposed by an unfiltered mercury arc source and received doses ranging from 0 to 2 J/cm2. The unreacted Ag2Se was stripped prior to the SIMS analysis. The Ag incorporation was found to increase rapidly with exposure first, and then saturate about 1 J/cm2. But instead of Ag being uniformly distributed through the GeSe2 films, its concentration peaks both near the top surface and at the substrate interface. The anomalous Ag peak at the substrate interface indicates that Ag diffuses far beyond the penetration depth of the radiation and presumably piles up in front of the Ta diffusion barrier. Moreover, with the same exposure, the anomalous Ag peaks are identical in both the 3000- and 6000-Å-thick films. These results are consistent with the model of Ag diffusion through the columnar structure of GeSe2, an extremely fast path in regions between the columns extending through the film, and a slower diffusion component in the denser regions within the columns.
Current–voltage characteristics of n-AlGaAs/p-GaAs heterojunction diodes
Authors: Chand N. , Fischer R. , Klem J. , Morkoç H.
Published: July 2002

To understand the current injection mechanism in AlGaAs/GaAs heterojunction bipolar transistors (HBT’s), current–voltage characteristics of n-AlGaAs/p-GaAs heterojunctions have been studied for varying doping densities and as a function of temperature. The bulk space-charge recombination current studied in heterojunction diodes identical to emitter–base junction of an HBT has been found to be an order of magnitude smaller than that in GaAs homojunction diodes. It approximately varies as A(T) exp 20V where A(T) is a decreasing function of temperature. The nature of this current is similar to the excess current in tunnel diodes and is considered to be due to multistep tunneling followed by recombination. The tunneling nature of the current is established by the observed electroluminescence and the effect of varying doping densities. It is concluded that the surface currents normally dominate the base current and that they largely depend on the fabrication process and device geometries.
Effect of epitaxial layer design on the microwave performance of high electron mobility transistors
Authors: Palmateer S. C. , Mishra U. K. , Chao P. C. , Smith P. M. , Duh K. H. G. , Hwang J. C. M.
Published: July 2002

The microwave performance of high electron mobility transistors (HEMT’s) depends on the density, mobility, and velocity of the two-dimensional electron gas (2DEG) in the selectively doped heterostructure (SDH). The 2DEG properties, in turn, depend on the thickness and composition of the undoped spacer at the heterojunction. In this work, we found in GaAs/AlGaAs SDH’s that, by varying the thickness of a conventional AlGaAs (x=0.3) spacer from 0 to 190 Å, the 2DEG density decreased monotonically from 1 to 0.4×1012 cm−2 while the 2DEG mobility increased from 0.3 to 2.2×105 cm2/V s at 77 K. When the spacer composition was changed to AlAs, similar 2DEG behaviors were observed in the case of thin spacers. For thick AlAs spacers (60 to 190 Å), the 2DEG density continued to decrease while the 77 K mobility saturated at 1.2×105 cm2/V s. From the dc drain characteristics of HEMT’s with thin (∼30 Å) AlAs and AlGaAs spacers, the 2DEG velocity in the AlAs spacer SDH did not appear to be any higher than that in the AlGaAs spacer SDH. At 18 GHz, the AlAs spacer HEMT exhibited 12.5 dB gain at room temperature, which, although somewhat inferior to the best of our AlGaAs spacer HEMT’s, is comparable to conventional microwave field-effect transistors (FET’s).
The formation of titanium silicide by arsenic ion beam mixing and rapid thermal annealing
Authors: Shukla R. K. , Davies P. W. , Tracy B. M.
Published: July 2002

The reaction of titanium thin films with n+ doped single crystal silicon induced by As+ ion beam irradiation and subsequent rapid thermal annealing has been studied. Arsenic doping in the silicon substrate retards the thermal growth of silicide resulting in an incomplete conversion of the titanium into titanium disilicide during low temperature (∼600 °C) rapid thermal annealing under a nitrogen ambient. High energy As+ion beam irradiation (90–170 keV) prior to the rapid thermal annealing leads to intermixing of the titanium and silicon which, at sufficiently high energy and dosage, results in complete conversion of titanium to a silicide phase. Subsequent rapid thermal annealing of the ion beam irradiated samples induces further uptake of silicon into the silicide phase leading to the formation of the stable C-54 titanium disilicide phase. However, very little additional titanium consumption occurs during the thermal annealing. The silicide formed by the ion beam mixing process shows superior sheet resistance uniformity and has a smoother morphology compared to thermally grown silicide. The uniformity of the silicidation reaction by ion beam mixing also leads to superior n+p junction characteristics.
Structural studies of (511) and (711) GaAs surface
Authors: Young K. , Kahn A.
Published: July 2002

High-index GaAs (511) and (711) surfaces, prepared by sputtering and annealing chemically polished substrates, are studied with low energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectroscopy. The inequivalent A and B surfaces of each orientation are investigated. The four surfaces exhibit an ordered array of steps. The terraces and steps correspond to (100) and (111) planes, respectively. Calculations of the splitting of the LEED spots and of in-phase, out-of-phase diffraction from the terraces are performed to determine the mean terrace width and step height. The appearance of the Ga surface exciton peak in the energy loss spectrum is linked to the local bonding of the top Ga atoms and is used to distinguish the A surface from the B surface.
Boron contamination of i
n s
i
t
u heated silicon surfaces
Authors: Casel A. , Kasper E. , Kibbel H. , Sasse E.
Published: July 2002

Interfacial  p doping due to B contamination is routinely detected in Si molecular-beam epitaxy (MBE) when using standard MBE cleaning schemes. The influence of the wet chemical precleaning as well as of the in situ cleaning is investigated with respect to this effect: whenever chemical precleaning results in a hydrophilic Si surface, interfacial  p-type doping due to B contamination of 1012 cm−2 is detected, whereas for hydrophobic Si surfaces the B contamination is reduced by a factor of about 50. Concerning the in situ cleaning, a reduction of the preheating temperature TH correlates with a decrease of  p-type doping for hydrophilic cleaned samples, though the chemical B contamination is independent of TH, i.e., the in situ preheating induces an electrical activation of the B contamination.
Self-aligned titanium silicide device technology by NH3 plasma assisted thermal annealing
Authors: Li Bing-Zong , Zhou Shi-Fang , Li Jia , Tang Ting-Ao
Published: July 2002

The self-aligned titanium silicide device technology has been studied by using NH3 plasma assisted thermal annealing and ion implant through titanium metal or silicide film. Enhanced surface nitridation of titanium by activated species suppresses lateral silicide growth and oxide contamination. NH3 plasma assisted annealing can be used as an effective method to form TiSi2 and activate implanted dopant. P+N junction and P channel metal–oxide–semiconductor field-effect transistor can be produced by boron implant through Ti metal or its silicide and the NH3 plasma assisted thermal annealing.
Titanium silicide growth by rapid-thermal processing of Ti films deposited on lightly doped and heavily doped silicon substrates
Authors: de Lanerolle N. , Hoffman D. , Ma D.
Published: July 2002

A series of experiments were conducted to obtain a better understanding of the titanium silicide growth on lightly doped and heavily boron and arsenic implanted single-crystal (100) p-type silicon, as well as on lightly doped and heavily phosphorus diffused polycrystalline silicon. Experiments were carried out under argon and nitrogen ambients using a two-step annealing process with a rapid-thermal processor (RTP). The growth kinetics in the RTP are compared for different ambients, times, and temperatures of annealing and various initial titanium thicknesses. Data will be presented which show that the type and amount of doping have a significant impact on the growth kinetics.
Pressure dependence of the growth of polycrystalline silicon by low-pressure chemical-vapor deposition
Authors: Meakin D. , Papadopoulou K. , Friligkos S. , Stoemenos J. , Migliorato P. , Economou N. A.
Published: July 2002

The growth of polycrystalline silicon at temperatures below 640 °C by the pyrolysis of silane at very low pressures (<40 mTorr) was found to be activated with an activation energy depending on the pressure. Two modes of growth were observed: columnar and twinned, below and above 10 mTorr, respectively. The rate of growth for both types is only slightly dependent on the pressure. The columnar growth is associated with an increase of the activation energy, while the change to the twinned structure is associated with a drop in the activation energy to almost zero from where it increases with pressure. The influence of the flow mode is also discussed.
Molecular-beam epitaxy growth of In0.53 (GaxAl1−x)0.47 As quaternary layers for optointegrated devices
Authors: Genova F. , Morello G. , Rigo C.
Published: July 2002

High quality In0.53(GaxAl1−x) 0.47 As lattice-matched to InP was obtained by molecular-beam epitaxy (MBE). Most of the work was performed at x = 0.64 because this composition is suitable for low loss waveguiding at 1.55 μm. Device quality material wa obtained showing defect densities as low as 2⋅103 cm−2 and 4 K photoluminescence full width at half-maximum (FWHM) of 23 meV, which represents the state of the art of this material. Double crystal (DC) x-ray profiles showed a FWHM of 17.5′′ of arc, demonstrating the lattice perfection of the material. From low temperature photoluminesence measurements, we evaluated the optimum temperature range for MBE growth.

Ridge waveguides fabricated from these layers showed low loss waveguiding, as low as 2.2 db/cm, at 1.55 μm. The excellent of the grown materials is also confirmed by the narrowest DC x-ray profile linewidth ever reported for one of the ternary limits InGaAs (x = 1), which showed a FWHM of 12′′ of arc. The materials obtained are thus suitable for high performance waveguide optointegrated devices.
Growth of PbTe/CdTe on GaAs (100)
Authors: Yoshino J. , Munekata H. , Chang L. L.
Published: July 2002

The depositions of PbTe and CdTe on GaAs (100) by molecular-beam epitaxy have been examined by reflection high-energy electron diffraction. While the dominant nucleation orientation is (111) for CdTe, it can be varied from (111) to (100) for PbTe as the substrate temperature is reduced. Also (100) prevails as the PbTe film thickness increases, regardless of the initial nucleation. Epitaxial growth of PbTe and CdTe on each other have also been achieved, leading to multilayer structures of either (100) or (111) orientation. The orientation in this case is governed by that of the initial material laid on GaAs.
Phase separation in Cd1−xZnxTe grown by molecular-beam epitaxy
Authors: Feldman R. D. , Austin R. F. , Fuoss P. H. , Dayem A. H. , Westerwick E. H. , Nakahara S. , Boone T. , Menéndez J. , Pinczuk A. , Valladares J. P. , Brennan S.
Published: July 2002

The ternary system Cd1−xZnxTe has been a leading candidate for use as a lattice matched buffer layer for a variety of Hg-containing II–VI compounds. We have grown films over the entire composition range on GaAs substrates. We find that both ZnTe and CdTe grow well, but that the films degrade substantially for ternary compositions. Synchrotron x-ray scattering shows that ternary films can phase separate, with CdTe, ZnTe, and differing compositions of Cd1−xZnxTe all present within one film. Transmission electron microscope images show features which are similar to those seen in In1−xGaxAs1−yPy which has undergone a partial spinodal decomposition.
Theory of electroabsorption in asymmetric-graded-gap quantum wells
Authors: Sanders G. D. , Bajaj K. K.
Published: July 2002

Electronic and optical properties of asymmetric-graded-gap triangular quantum wells are studied in the presence of a uniform electric field applied parallel to the [001] growth direction. A triangular quantum well consists of finite barriers of AlyGa1−yAs surrounding a well composed of AlxGa1−xAs whose aluminum concentration x increases linearly with position from the left-hand to right-hand side along the growth direction. We study exciton transition energies, binding energies, and oscillator strengths as well as the total absorption coefficient as a function of applied electric field strength using a multiband effective mass theory, which takes valence subband mixing effects into account. All results are compared with the usual case of a square quantum well, where x is constant along the growth direction. In triangular quantum wells, the electron and hole charge densities are confined near the left-most interface and thus exciton binding energies and oscillator strengths are relatively insensitive to the applied electric field. In addition, the magnitude of the downward shift in the fundamental absorption edge is approximately linear in the applied field strength and the total absorption spectrum tends to retain its overall shape. This contrasts with the situation in square quantum wells, where electron and hole charge densities are more easily separated by the applied field (quantum confined Stark effect). In square-quantum wells, exciton binding energies and oscillator strengths are quite sensitive to the electric field, the shift in the fundamental absorption edge is nonlinear, and the total absorption spectrum varies in a complicated manner due to the varying strengths of the various excitonic transitions. For these reasons, asymmetric graded gap quantum wells would seem to offer possibilities for the design of optoelectronic devices which exploit such electroabsorptive effects in quantum wells.
Properties of direct current magnetron reactively sputtered TaN
Authors: Mehrotra Bhola , Stimmell Jim
Published: July 2002

Tantalum nitride has been investigated for use as a diffusion barrier between aluminum alloy interconnect and shallow source-drain junctions in a 1-μ-complementary metal–oxide semiconductor technology. TaN films were reactively sputtered in a batch sputtering system equipped with dc magnetron cathodes, rf substrate bias, and independently controlled Ar and N2 sources. Film properties and their dependence on deposition parameters are discussed, and these properties are compared with those of titanium nitride films deposited using the same technique. Stoichiometric TaN films have resistivities of ∼220 μΩ cm. AlSi/TaN/Si contacts to shallow N+/P and P+/N junctions can withstand 575 °C 30 min heat treatments with no increase in junction leakage. The films can be etched in chlorine plasma chemistries typically used to etch aluminum alloys, and the aluminum etch has selectivity of ∼4:1 to TaN. This selectivity helps to protect inadvertently exposed Si junctions from damage during metal etch.
Reduced reverse bias current in Al–GaAs and In0.75Ga0.25As–GaAs junctions containing an interfacial arsenic layer
Authors: Rossi D. V. , Fossum E. R. , Pettit G. D. , Kirchner P. D. , Woodall J. M.
Published: July 2002

Interfacial As is shown to reduce reverse-bias current in Al–GaAs Schottky barriers. It is suggested that the leakage reduction is associated with the removal of low work function phases at the interface. In addition, current–voltage measurements performed on In0.75Ga0.25As–GaAs heterojunctions indicate a dependence upon the condition of the GaAs prior to deposition of the In0.75Ga0.25As layer.
Stress-induced grain boundary fractures in Al–Si interconnects
Authors: Hinode K. , Owada N. , Nishida T. , Mukai K.
Published: July 2002

This paper presents a study on grain boundary fracture failures found in Al–Si interconnects during aging tests without electric current flow. Failure rate analysis and microscopic observation by transmission electron microscopy and scanning electron microscopy indicate that failures are caused by slitlike voids formed at grain boundaries during the relaxation process in Al–Si conductors stressed by temperature cycling under the volume constraint of passivation films. Conductors are seen to fail in two modes; an open mode at bamboolike grain boundaries and a high-resistance mode at grain boundaries having large silicon precipitates.
The simulation of two-dimensional surface erosion and deposition processes
Authors: Smith R. , Wilde S. J. , Carter G. , Katardjiev I. V. , Nobes M. J.
Published: July 2002

First-order erosion/deposition theory is applied to some examples of pattern delineation and planarization of microelectronic structures. An analogy between erosion/deposition phenomena and the progression of an optical wave front is developed, which explains many of the observable physical processes. Edges can form from an initially smooth profile and initial edges can expand into smooth curves; and it is demonstrated how they can be properly accounted for in a simulation code. Some examples of erosion and the codeposition phenomena are computed.
Exact solution of the proximity effect equation by a splitting method
Authors: Gerber P. Dean
Published: July 2002

In electron beam lithography, the proximity effect equation is used to model the relationship between exposure (energy absorbed by the resist) and dose (energy delivered by the incident beam). The equation states that the exposure equals the convolution of the dose with a double Gaussian energy intensity distribution. The first term of the double Gaussian represents small range forward scattering effects, and the second represents larger range backward scattering effects. In this paper we present a closed form, explicit, solution of the proximity effect equation. The approach splits the equation into two equations: a backward diffusion equation to correct for the forward scattering and a forward diffusion equation to correct for the backward scattering. We give explicit formulas for the solutions of these two equations, which leads to the explicit solution of the proximity effect equation for sufficiently regular exposures. Finally, we apply these results to two specific examples to show that the proximity equation has no solution for ideal line–space arrays and that it has no physically meaningful solution for ‘‘cosine lines’’ if the line spacing becomes too small.
Pattern definition and formation on curved surfaces
Authors: Deininger William D. , Garner Charles E.
Published: July 2002

This paper will discuss techniques used to delineate and form patterns on curved surfaces. Patterns were generated in AZ1350 photoresist using electron-beam writing and xenon–chloride excimer laser writing and ablation. Experiments were conducted on spherically concave surfaces which had a radius of curvature of 0.879 cm. Surface patterns 10 μm in width and varying in length from 40 μm to 0.6 cm were written. These beam-writing techniques show clear superiority over conventional ultraviolet photolithographic techniques for patterning nonflat surfaces. The resulting patterned photoresist can then be used as a mask for use with wet or dry etching techniques to form the desired surface features.
Achromatic holographic lithography in the deep ultraviolet
Authors: Anderson Erik H. , Komatsu Kazuhiko , Smith Henry I.
Published: July 2002

Holographic lithography, in which the interference pattern of two coherent waves is used to expose a resist film, is the preferred technique for producing large-area gratings with low distortion. The spatial period of a pattern produced by holographic lithography is directly proportional to the wavelength of the radiation and inversely proportional to the sine of one-half the angle between the incoming beams. To expose gratings with periods ≊100 nm (50-nm-nominal linewidth) the source wavelength must be ≊200 nm. Since coherent deep-ultraviolet sources are not readily available, we have investigated an achromatic holographic configuration which permits the use of incoherent sources (e.g., CdXe arc lamp) or short-coherence-length (≊10 μm) excimer lasers. The configuration consists of two gratings, one acting as a beamsplitter, the other as a recombiner. The beam from the source is split into plus and minus first-order beams by the beamsplitter grating, and the zero order is subsequently blocked. The plus and minus first-order beams are again diffracted by the recombiner grating onto the substrate. The intensity recorded at the substrate has a spatial period one-half that of the beamsplitter grating. An analysis of this configuration shows that the intensity pattern on the substrate is independent of both the source wavelength and the angle of incidence (i.e., spatial coherence). For the configuration to be truly achromatic with high contrast the two interferometer arms must have equal path lengths within a small ‘‘window.’’ Tests of this configuration with parent gratings of 540 nm period and a Hg arc lamp produce good contrast photoresist patterns at 270 nm period, and tests with an ArF excimer laser and 250-nm-period parent gratings produce 125-nm-period patterns in polymethylmethacrylate (PMMA). This achromatic deep UV setup is similar to a proposed x-ray interferometer and serves as a test bed for solving problems of alignment.
Radiation effects on metal–insulator–semiconductor diode energetic ion detectors
Authors: Hughes R. C.
Published: July 2002

Palladium gated metal–insulator–semiconductor diodes are efficient and sensitive detectors for low-energy hydrogen ions. Environments which contain fluxes of hydrogen ions, like fusion reactors, may also contain fluxes of ionizing radiation. The effect of ionizing radiation in vacuum and various atmospheres on our diodes is reported. In general, irradiation in vacuum produces little permanent damage in our diodes and will not give signals which will be confused with the signals from hydrogen ions. Irradiation in air for some kinds of diodes produces metastable interface states.
A Monte Carlo microtopography model for investigating plasma/reactive ion etch profile evolution
Authors: Cotler Tina J. , Barnes Michael S. , Elta Michael E.
Published: July 2002

A two-dimensional microtopography etch simulation using Monte Carlo methods is presented. This simulation investigates the topography of an arbitrary profile, periodic semiconductor surface after (ion assisted) plasma etching. The dependence of the topography on the etch chemistry, the ion energy, and the physical bombardment mechanism is discussed. For sputter etching, the degree of anisotropy is shown to be related to both the ion directionality and the sputter yield function. The potential for using this simulation to analyze microscopic properties of plasma etching is discussed.
Anomalous regimes for GaAs etching in Cl2–Ar plasmas
Authors: d’Agostino R. , Cramarossa F. , Fracassi F. , Illuzzi F. , Armenise M. N.
Published: July 2002

GaAs etching process has been studied in Ar–Cl2 rf discharges at 200 mTorr as a function of gas composition, substrate temperature, and bias voltage. Actinometric optical emission spectroscopy has been utilized for gas phase diagnostic. Surface analysis has been carried out by x-ray photoelectron spectroscopy and scanning electron microscopy. Anomalies found in the etching regimes have been interpreted as caused by the presence of an inhibiting oxide–chloride film and by the desorption of chlorine adsorbed on the surface by low-energy bombarding ions.
Selective area nucleation for metal chemical vapor deposition using focused ion beams
Authors: Kubena R. L. , Stratton F. P. , Mayer T. M.
Published: July 2002

Localized growth of metal lines on Si wafers has been demonstrated using a focused Ga+ beam to selectively enhance the nucleation site density during a thermal chemical vapor deposition process. Iron and aluminum lines with thicknesses up to 2 μm have been formed using ion line doses between 4×1010 and 4×1012 Ga+/cm. Thus, the sensitivity of this process can be several orders of magnitude greater than ion beam induced polymerization techniques performed at room temperature. Auger analysis indicated that the total impurity concentration deep within the metal lines was roughly 15%. No Ga was detected in the deposited films.
Electronic properties of sulfur adsorbed on cleaved GaAs surfaces
Authors: Koenders L. , Blömacher M. , Mönch W.
Published: July 2002

The interaction of molecular S2 with cleaved GaAs(110) surfaces was followed by using a Kelvin probe and ultraviolet photoemission spectroscopy. The adsorption of sulfur increases the ionization energy of the cleaved surfaces by up to 0.92 eV and causes a Fermi-level pinning at 0.34 eV above the valence-band top for both types of doping. The sign of the change of the ionization energy can be explained by a chemical charge transfer between the adsorbed sulfur and adsorbate-induced gap states, since sulfur is more electronegative than GaAs. The sulfur-related pinning position of the Fermi level is located below the charge-neutrality level of the virtual gap states (ViGS) of the complex GaAs band structure, where the ViGS predominantly possess donor character. This result confirms the predictions from the ViGS model of adsorbate-induced gap states. The energy of the sulfur as well as the oxygen- and chlorine-related surface states, which are of the acceptor type, correlate with the respective atomic electron affinities.
Accuracy of zero-charge and zero-dipole approximations for the determination of valence-band offsets at semiconductor heterojunctions
Authors: Priester C. , Allan G. , Lannoo M.
Published: July 2002

A tight-binding treatment of (100) heterojunctions with common anions is performed. A new zero-dipole approximation is presented together with a first-order correction that explicitly depends upon the static macroscopic dielectric constant. The difference between the zero-charge and zero-dipole approximations is discussed. These two approximations are then compared to a complete self-consistent calculation and shown to provide band offsets within 0.1 eV of the exact value. The corrected zero-dipole treatment gives a much better accuracy of order of 0.02 eV. Agreement with experiment is very good for the three lattice matched systems: AlAs–GaAs, CdTe–HgTe, and AlSb–GaSb.
Strained-layer interfaces between II–VI compound semiconductors
Authors: Van de Walle Chris G. , Shahzad Khalid , Olego Diego J.
Published: July 2002

II–VI multilayer structures are eminently suitable for various optoelectronic devices covering from the infrared to the ultraviolet spectral range. We present a theoretical study of the band lineups at interfaces involving ZnS, ZnSe, ZnTe, CdTe, and HgTe based on the ‘‘model solid’’ theory. We also experimentally investigate the strains and band offsets in ZnSe/ZnSx Se1−x strained-layer superlattices, using Raman and photoluminescence spectroscopy. The conduction-band offset at such interfaces is found to be small. Theoretical predictions for other interfaces include a large type-II offset in ZnSe/ZnTe, and a small average valence-band discontinuity in ZnTe/CdTe.
The bonding of arsenic to the hydrogen-terminated Si(111) surface
Authors: Bringans R. D. , Olmstead Marjorie A.
Published: July 2002

The interaction of arsenic with the hydrogen-terminated Si(111) surface has been studied using photoemission valence band and core level spectroscopy. The results are compared with those obtained previously for the interaction of arsenic with Si(111) and hydrogen with the arsenic-terminated Si(111) surface. We have found that neither As nor H fully passivates the Si(111) surface with respect to the other species. Hydrogen can be removed from both the Si(111):As + H and Si(111):H + As surfaces by annealing, leaving As bonded to the Si(111) surface. A comparison is also made between arsenic-terminated surfaces made with (i) an As4 deposition onto a substrate whose temperature was varied from 800 °C down to 300 °C and (ii) a deposition at 300 °C followed by a 650 °C anneal. It is found that method (i) yields a surface with significantly better surface order.
Clustering mechanism during growth of GaAs on silicon
Authors: Zinke-Allmang M. , Feldman L. C. , Nakahara S.
Published: July 2002

Cluster growth experiments of Ga on As terminated Si(111) are reported and shown to simulate Ga–As coevaporation in the case of low Ga and very low As fluxes. Based on these observations a model for GaAs clustering is proposed which explains qualitatively the absence of postdeposit clustering and can be quantified in order to be compared to recent substrate temperature dependent GaAs cluster size measurements by transmission electron microscopy techniques.
Control of Fermi level pinning and recombination processes at GaAs surfaces by chemical and photochemical treatments
Authors: Hasegawa Hideki , Ishii Hirotatsu , Sawada Takayuki , Saitoh Toshiya , Konishi Seiichi , Liu Yali , Ohno Hideo
Published: July 2002

The effects of photochemical oxidation in water, Na2 S deposition and exposure to NH3 and HCl gas ambients on the Fermi level pinning, and the surface recombination process at GaAs surfaces were studied by measuring the band edge photoluminescence (PL) intensity, x-ray photoelectron spectroscopy spectra, and surface current transport(SCT). Computer simulation of the surface recombination process was also made on the basis of the disorder-induced gap state model. Marked increase of PL intensity was observed after both photochemical oxidation and deposition of Na2 S as previously reported. However, SCT measurements on n-type materials detected increase of surface band bending in the dark. Exposure to NH3 resulted in a slight reduction in the band bending with little change in the PL intensity. Exposure to HCl, on the other hand, resulted in marked reduction of the band bending with marked increase of the PL intensity. The computer simulation shows that the contradictory behavior of the PL intensity and band bending, as observed after photochemical oxidation and Na2 S deposition, is explicable by a shift of the Fermi level pinning position towards the valence band edge due to a fixed negative interface charge which reduces the effective recombination velocity. On the other hand, exposure to HCl reduces the surface-state density and weakens the pinning remarkably.
Optimum design of electrostatic lenses
Authors: Szilagyi M. , Szép J.
Published: July 2002

A method of design for electrostatic lenses with given source parameters, first-order properties, and minimum aberrations is presented. It is based on constrained nonlinear optimization techniques. The variables in these procedures are spline coefficients of the axial potential distribution, or the electrode potentials of a given multielectrode lens. The optimization constraints are the minimum object- and image-side working distances, maximum possible electrode potentials, and maximum allowed electrostatic fields. The parameters of the source and the final beam voltage are fixed. The goal of the design is to find an electrode configuration that would minimize the beam spot size and maximize the current density at the target. Three examples of the method’s application are presented. Keeping the given source parameters and working distances constant, essential improvements of the optical properties of three well-known designs could be achieved by replacing the lenses with those designed by our procedures. In these examples for field ionization sources the current density at the target is increased by more than an order of magnitude.
Amorphous Ta-rich Ta–Cu films as diffusion barriers between Au and GaAs
Authors: Oh Jae E. , Woollam John A. , Pouch John J. , Alterovitz Samuel A. , Ingram David C.
Published: July 2002

The thermal stability of alloy films in the cosputtered amorphous Ta–Cu alloy systems have been found to be correlated with the measured maximum negative temperature coefficients of resistance as a function of alloy composition. From results of resistivity changes, x-ray diffraction, Auger electron spectroscopy, and Rutherford backscattering, reaction temperatures of Ta93Cu7 alloy films with Au overlayers and GaAs substrates were determined to be 600 and 700 °C, respectively. Electrical measurements were performed with Schottky diodes formed on n-type GaAs. Amorphous Ta93 Cu7 /GaAs Schottky diodes were found to be electrically stable up to annealing temperatures of 400 °C. Also rapid thermal annealing was applied to capitalize on its short processing time for possible application to self-aligned gate technology using this material.
Improved GaAs substrate temperature measurement during molecular-beam epitaxial growth
Authors: Wright S. L. , Marks R. F. , Goldberg A. E.
Published: July 2002

We describe an improvement in optical pyrometry of GaAs substrates, by restricting the pyrometer wavelength to a band of 0.91 to 0.97 μm. This allows temperature measurement of nonbonded GaAs wafers during molecular-beam epitaxial growth, without interference from the radiation emitted by the substrate heater. Error-free readings have been obtained for substrate temperatures as low as 440 °C, which is particularly important for the automated growth of alloys such as (In,Ga)As. By detecting a larger substrate surface area and using a calibration curve, the useful measurement range can be extended even lower.
Improvements to and characterization of GaInAs/AlInAs heterointerfaces grown by molecular-beam epitaxy
Authors: Scott E. G. , Davey S. T. , Halliwell M. A. G. , Davies G. J.
Published: July 2002

High-quality GaInAs/AlInAs quantum well samples have been grown by solid source molecular-beam epitaxy. Single quantum well samples have been characterized by photoluminesence spectroscopy and transmission electron microscopy. Emission from a 6.7 Å well was observed at 908.6 nm, which we believe is the shortest wavelength reported for a GaInAs quantum well. The full width at half-maximum of the luminescence lines from a range of well widths are up to a factor of 5 narrower than previously reported for this materials system. From an analysis of the photoluminescence results comments are made on the GaInAs/AlInAs heterointerface quality. Flux stability, defect levels, and flux transients are discussed. A simple set point ramping technique has significantly reduced flux transients caused by shutter operations. Raman spectroscopy and x-ray diffraction techniques have been used to determine the composition of the constituent layers within multiquantum well samples.
Characterization of focused ion beam micromachined features
Authors: Pellerin J. G. , Shedd G. M. , Griffis D. P. , Russell P. E.
Published: July 2002

The use of the liquid metal ion source focused ion beam (FIB) as a microfabrication tool depends, to a large extent, on the understanding of ion beam/substrate interactions. In addition to material removal and redeposition, the alteration of the underlying substrate by the ion beam can affect the performance and characteristics of semiconductor microelectronic and optoelectronic devices, and the physical properties of micromechanical components. Chemical modification to FIB machined substrates has been investigated by energy dispersive x-ray spectroscopy (EDS) and Auger electron spectroscopy (AES). EDS has proven useful for determining the residual implanted ion dose in micromachined features with good correlation to theoretical values. AES has been used to observe the lateral and depth distribution of the implanted ion species in the machined features and surrounding areas.
Characterization of thin boron-doped silicon membranes by double-crystal x-ray topography
Authors: Ma David I. , Qadri Syed B. , Peckerar Martin C. , Twigg Mark E.
Published: July 2002

Heavily boron-doped silicon transparent membranes and x-ray masks were examined using double-crystal x-ray topography. The topographs revealed the strain distribution in two dimensional (2D) pattern. Slip bands and Frank–Read sources were observed. The stress variation across the membrane was confirmed using the Stoney’s stress analysis by laser beam reflecting technique. Surface strain versus bulk strain were also analyzed by choosing (224) and (115) reflecting planes. Deposition of patterns on a bare membrane did not alter the overall strain pattern of the membrane, which was apparently determined by the warpage of the silicon supporting ring. Local deformations associated with gold absorber features were visible and their associated strain fields were measured.
The effect of substrate growth area on misfit and threading dislocation densities in mismatched heterostructures
Authors: Fitzgerald E. A.
Published: July 2002

We show that mismatched epitaxial growth on small growth areas results in metastable, low dislocation density films. By considering methods of dislocation nucleation in mismatched epitaxial films, we can explain the effect of growth area on the kinetics of misfit dislocation nucleation. We demonstrate this reduction of misfit dislocation density by growth on small areas using the InGaAs/GaAs system, and we also demonstrate a reduction in threading dislocation densities in the GeSi/Si system. InGaAs/GaAs interfaces which have a misfit dislocation density greater than 5000 dislocations/cm for large growth areas are grown nearly misfit-dislocation-free on small growth areas. GeSi/Si structures which have a threading dislocation density of approximately 1000 dislocations/cm2 are grown with a 100% threading dislocation density reduction for small growth areas. We discuss the limits of growth on small areas to reduce both interface dislocation densities as well as threading dislocation densities.
Electrical characterization of an epitaxial ZnSe/epitaxial GaAs heterointerface
Authors: Qian Q. D. , Qiu J. , Kobayashi M. , Gunshor R. L. , Melloch M. R. , Cooper J. A.
Published: July 2002

The electrical properties of pseudomorphic epilayer–epilayer ZnSe/GaAs heterointerfaces, grown by molecular-beam epitaxy, have been investigated by capacitance versus voltage (C–V) and current versus voltage measurements. Undoped stoichiometric ZnSe (<1000 Å), exhibiting high resistivity, performs the function of the insulator in these metal–insulator–semiconductor capacitors. The C–V characteristics of the annealed Au/ZnSe/p-GaAs capacitors are nearly ideal, exhibiting an interface state density (2.5×1011 cm−2) which compares favorably with the densities reported at typical (Al,Ga)As interfaces. The occurrence of both hole accumulation (for p-type GaAs) and inversion (for n-type GaAs) at the ZnSe/GaAs heterointerface indicates the presence of a substantial valence-band offset. The lack of accumulation or inversion layers for electrons suggests a relatively small conduction-band discontinuity.
Structural perfection in poorly lattice matched heterostructures
Authors: Miles R. H. , McGill T. C.
Published: July 2002

Continuum elastic theory is applied to the formation of misfit dislocations and point defects in strained layer structures. Explicit calculations of the energies of misfit dislocations in the double- and single-kink geometries yield line tensions below which strained films are stable with respect to defect formation. Our results yield a mismatch-dependent stability limit which, in the double kink case, differs from the Matthews–Blakeslee model by a geometrical factor and by the addition of a stress term associated with climb of the misfit dislocation. While our calculations yield equilibrium stability limits which may not correspond to observed critical thicknesses, the calculated stresses may be applied to descriptions of the kinetics of strain relief in films grown beyond these limits. Last, calculations of strain-related contributions to the free energy of formation of point defects suggest a contribution ‖ΔGstrain‖ ≂0.25 eV for a 5% lattice mismatch. This suggests a means of suppressing or enhancing the formation of vacancies or interstitials in semiconductors favoring these defects.
High-resolution electron beam lithography and evaluation of first-order distributed feedback lasers
Authors: Korn M. , Klingenstein M. , Germann R. , Forchel A. , Nickel H. , Schlapp W. , Lösch R. , Streubel K. , Scholz F.
Published: July 2002

We have fabricated first-order GaAs and InGaAs distributed feedback (DFB) lasers by high-resolution electron beam lithography and dry etching. Basic laser properties as, e.g., the mode structure, the threshold, the temperature drift, the loss at threshold, etc., are evaluated by optical pumping of the structures.
Compositional modulations in GexSi1−x heteroepitaxial layers
Authors: Fraser H. L. , Maher D. M. , Knoell R. V. , Eaglesham D. J. , Humphreys C. J. , Bean J. C.
Published: July 2002

A study is presented of compositional modulations (i.e., so-called banding) in heteroepitaxial strained layers of nominally uniform Ge0.1Si0.9 grown by molecular-beam epitaxy (MBE). The oscillatory nature of the modulations is studied by transmission electron microscopy (TEM) techniques and the results show that the contrast modulations have a periodicity of ∼23 nm when 1-μm-thick epilayers are grown on a rotated substrate. For growth on an unrotated substrate, contrast modulations are still observed but they are less regular. It is further shown that the electron microscope image features are dominated by strain contrast and not structure factor contrast. The presence of strain is consistent with there being a small change in lattice parameter between adjacent bands of material, together with elastic relaxations afforded by the proximity of the thin-film surfaces. It is concluded that these variations in the lattice parameter are due to the compositional modulations. Limits on the magnitude (Δx) of the compositional modulations are assessed from considerations of diffraction contrast theory (giving an upper limit) and elasticity theory (giving a lower limit). The upper and lower limits for the compositional modulations, assuming an average 9 at. % Ge–Si epilayer, are ±1 at. % and ±0.25 at. % Ge, respectively. The origin of these compositional modulations is thought to be associated with equipment instabilities or a metastable miscibility gap.
Growth and transport properties of (Ga,Al)Sb barriers on InAs
Authors: Munekata H. , Smith T. P. , Chang L. L.
Published: July 2002

We have investigated the transport properties of (Ga,Al)Sb–InAs heterostructures grown by molecular-beam epitaxy with the Al composition in the range of 0.3–0.5 where the alloy serves as a potential barrier for electrons in InAs. Field effect capacitors using a thick (Ga,Al)Sb barrier demonstrate the modulation of carrier densities in InAs by the application of an electric field. In the region of thin (Ga,Al)Sb, where tunneling becomes dominant, a novel negative resistance appears in InAs/(Ga,Al)Sb/InAs single-barrier structures due to the specific band alignment of this system. The results have been further elucidated under a magnetic field.