bluuebunny/crossref_metadata_2025 huggingface dataset:
Systematics of interfacial chemical reactions on InP(110)
Authors: Kendelewicz T. , Petro W. G. , Lindau I. , Spicer W. E.
Published: July 2002

The room temperature chemical reactions of noble metals (Ag, Au, Cu), some transitions metals (Ni, Pd), and Al with the InP(110) surface have been studied using surface sensitive core level photoemission spectroscopy and photon beam excited Auger spectroscopy. It is shown that chemical reactions on InP are largely similar to the reactions of these metals with GaAs and Si surfaces. Metals that react with Si to produce phosphides also produce phosphides with similar types of chemical bonding. Silver overlayers give rise to the most abrupt interface with InP as is also the case for the nonreactive Ag–Si system. The kinetic limitations of the room temperature reaction and the types of overlayer growth are also considered.
A method for eliminating hillocks in integrated-circuit metallizations
Authors: Cadien K. C. , Losee D. L.
Published: July 2002

In a novel method for eliminating hillocks in integrated-circuit metallizations, a sandwich layer is grown between the Al film and the underlying SiO2. This layer must have a thermal expansion coefficient between those of SiO2 and Al. The technique is demonstrated with WSi2 as the sandwich layer.
Photo-metal organic vapor phase epitaxy: A low temperature method for the growth of CdxHg1−xTe
Authors: Irvine S. J. C. , Giess J. , Mullin J. B. , Blackmore G. W. , Dosser O. D.
Published: July 2002

A new epitaxial growth technique, photo-metal organic vapor phase epitaxy (photo-MOVPE), is described for the growth of CdxHg1−xTe (CMT). Ultraviolet radiation is used to decompose the metal-organics, diethyl-telluride (Et2Te) and dimethyl-cadmium (Me2Cd) on the substrate surface. Epitaxial HgTe can be grown at relatively low temperatures (200–300 °C) by a surface photosensitization reaction. However, the growth of CMT is only epitaxial if an inert carrier gas (He) is used instead of H2. These results are described in terms of suppression of vapor phase nucleation while allowing surface nucleation to occur. Vapor phase nucleation results in the deposition of fine particles of CMT and can totally disrupt epitaxial growth. The growth rate dependence of CMT on CdTe substrate orientation is considered and compared with HgTe growth rates on the same orientations. These results show that surface kinetics can dominate the growth process, making it insensitive to vapor concentrations. Secondary ion mass spectrometry (SIMS) profiles through a CMT layer, grown at 250 °C, for the major elements, Cd, Hg, and Te, show an abrupt interface between the substrate and layer of less than 400 Å. Carbon impurity profiles through HgTe layers show that using the inert gas, carbon incorporation is no greater than for H2 carrier gas. It is shown that carbon is not a major contaminant in the epitaxial HgTe and CMT layers, but may still be a problem at lower concentrations.
Mechanisms of metallo-organic vapor phase epitaxy and routes to an ultraviolet-assisted process
Authors: Haigh J.
Published: July 2002

Ultraviolet irradiation during deposition has been reported to improve the morphology and increase the growth rate of GaAs epitaxial layers produced by metallo-organic vapor phase epitaxy. In order to optimize and control these effects for technological applications it is necessary to understand the mechanisms of metallo-organic vapor phase epitaxy (MOVPE). This paper reviews the current state of knowledge relevant to the UV intervention in InP growth. Preliminary experiments on the effect of UV in this system suggest that it may be increasing the mobility of the adsorbed reactant species.
Microscopic description of confinement in quantum well and sawtooth semiconductor superlattices
Authors: Jaros M. , Wong K. B. , Gell M. A. , Wolford D. J.
Published: July 2002

We have studied GaAs–GaAlAs superlattices with quantum well and sawtooth structures and InAs–GaSb quantum well superlattices. Our Hamiltonian is H=H0+V where H0 represents, for example, the perfect (bulk) GaAs and V is the difference between the potential of the atoms in the alloy layers and that of the atoms of GaAs in those layers. We expand the wave function of the superlattice system in terms of the eigenfunctions of H0 and solve the Schrodinger equation numerically by direct diagonalization. We use nonlocal relativistic pseudopotentials adjusted to reproduce the bulk band structures. We recover the states lying deep in the confining potential, in accord with the existing experimental and theoretical results. We also find new well localized states which have large amplitudes in the confining layers or at the interfaces. In particular, we report the existence of a series of confined levels of X and L character. We present charge density plots along the full length of the superlattice period in 〈100〉 direction which show that in a number of cases the microscopic picture of confinement differs significantly from the predictions of simpler models. Our tests indicate that the rapidly varying terms in the potential must be explicitly accounted for in quantitative studies of systems whose characteristic dimensions are of order 100 Å or less.
The growth of GaAlAs/GaAs guided wave devices by molecular beam epitaxy
Authors: Andrews D. A. , Scott E. G. , Houghton A. J. N. , Rodgers P. M. , Davies G. J.
Published: July 2002

The inherent potential of molecular beam epitaxy (MBE) has been exploited to grow large area slices of low defect density GaAlAs/GaAs heterostructures to fabricate several semiconductor guided wave devices. Passive rib waveguides had losses of <2 dB cm−1. Phase modulators exhibited a π phase shift for an applied bias of 9 V, internal losses of less than 2.5 dB with a modulation capability to l.2 GHz. Directional couplers fabricated from the same material exhibited a switching voltage of 16 volts and an extinction ratio better than 14 dB. The MBE growth procedure is outlined and the steps critical to the subsequent successful fabrication of guided wave devices are discussed.
Electronic transport properties of tantalum disilicide thin films
Authors: Huang M. T. , Martin T. L. , Malhotra V. , Mahan J. E.
Published: July 2002

Polycrystalline TaSi2 thin films were prepared by furnace reaction of ion beam sputtered tantalum layers with silicon surfaces. X-ray diffraction measurements indicate that the films are single phase hexagonal disilicide. Impurity levels are at or below the detection limits of Auger spectroscopy. The samples exhibit a room temperature intrinsic resistivity of ∼40 μΩ cm and a residual resistivity component as low as 4 μΩ cm. The Hall coefficient is negative, giving an apparent electron concentration of 6.5×1022 cm−3 at room temperature. A representative carrier mobility of 58 cm2/V s at room temperature (obtained from geometrical magnetoresistance measurements) was much larger than the Hall mobility (1.9 cm2/V s), suggesting multicarrier effects. The galvanomagnetic properties can be described by the equations for two degenerate, isotropic bands and be given a physical interpretation similar to that of Mott’s s-d scattering model. However, it is emphasized that the two-band model is likely only a crude approximation for transition metals and their compounds. A two-layer model shows that in certain instances the apparent transport properties of the films are due to the silicon substrate.
An MBE route towards CdTe/InSb superlattices
Authors: Williams G. M. , Whitehouse C. R. , Chew N. G. , Blackmore G. W. , Cullis A. G.
Published: July 2002

As part of a program aimed at the growth of CdTe/InSb superlattices, a systematic study has been made of the MBE growth of heteroepitaxial CdTe layers on (001)InSb using substrate temperatures, Ts, significantly higher than have been previously reported. Using a modified two-step growth technique, high quality layers have been successfully grown at temperatures as high as 310 °C with no evidence of either preferential Cd loss or CdTe/InSb interdiffusion. The new growth technique is described and cross-sectional TEM and SIMS data from the grown layers is presented.
MBE growth of films and superlattices of diluted magnetic semiconductors
Authors: Kolodziejski L. A. , Gunshor R. L. , Datta S. , Bonsett T. C. , Yamanishi M. , Frohne R. , Sakamoto T. , Bylsma R. B. , Becker W. M. , Otsuka N.
Published: July 2002

In this paper we report the growth of Cd1−xMnxTe superlattices (varying x) on GaAs substrates. Transmission electron microscopy of thinned specimens clearly show layers of uniform composition with abrupt interfaces; the lattice mismatch (≂0.6%) between superlattice layers is accomodated by elastic strain rather than misfit dislocation networks. The superlattices consistently show orders of magnitude greater photoluminescence (PL) intensity compared to thin films and bulk samples; in fact, the PL intensity is somewhat larger than that obtained from state of the art (Ga, Al) As double heterostructures under identical conditions of excitation. Removal of the substrate by etching produces a shift in the PL peak as well as a reduction in the spectral width indicating that the presence of the substrate causes inhomogeneous broadening due to nonuniform strains.
A study of silicon MBE on porous silicon substrates
Authors: Beale M. I. J. , Chew N. G. , Cullis A. G. , Gasson D. B. , Hardeman R. W. , Robbins D. J. , Young I. M.
Published: July 2002

The defect structure of Si MBE layers grown on porous silicon substrates depends critically on the technique for cleaning the substrate surface. Cross-sectional TEM studies demonstrate that a combined sputter-clean and thermal cycle markedly reduces the density of microtwins and dislocations in the epitaxial layer when compared with simple thermal cleaning. X-ray diffraction studies show the porous silicon layer to be lattice-matched to the underlying (100) bulk silicon substrate in the plane of the wafer so that misfit dislocations are not expected in the epitaxial layer. However, both the lattice parameter of the porous layer in the direction normal to the wafer and the thermal stability of the porous layer in vacuum, depend upon the resistivity of the starting wafer. The photoluminescence of a 4-μm MBE layer grown on a sputter-cleaned, high resistivity substrate is still dominated by recombination at dislocations.
Self-aligned enhancement mode FET with AlGaAs as gate insulator
Authors: Ogura M. , Matsumoto K. , Wada T. , Yao T. , Hashizume N. , Hayashi Y.
Published: July 2002

A new self-aligned enhancement mode FET is realized with epitaxial n+-GaAs (0.5 μm) as a gate electrode, undoped AlGaAs (500 Å) as a gate insulator, and undoped GaAs as a channel layer, grown consecutively on a LEC-S.I. GaAs by MBE. This semiconductor insulator semiconductor (SIS) FET operates in enhancement mode at 77 K with a typical gate threshold voltage of 38 mV, and transconductance of 170 mS/mm at VDS=1.0 V , VGS=+0.6 V. The electron mobility of 120 000 cm2/V s at 4.2 K is obtained with a bridge-shaped SISFET. The threshold voltage is very uniform with the standard deviation of 13 mV and not sensitive to the process parameters as expected.
Molecular beam epitaxy growth of ZnSe on (100)GaAs by compound source and separate source evaporation: A comparative study
Authors: Park R. M. , Mar H. A. , Salansky N. M.
Published: July 2002

ZnSe layers have been grown by MBE by both compound source and separate source evaporation on (100)GaAs substrates. Photoluminescence measurements on layers grown from a compound source showed the material to contain a high concentration of impurities and defects as indicated by the presence of large DA pair recombination and SA emission peaks in the PL spectra. Layers grown from separate sources were grown at various Zn to Se beam pressure ratios ranging from 1 to 30, and with substrate temperatures ranging from 300 to 400 °C. For layers grown at 900 Å/h with a Zn to Se beam pressure ratio of 1:1 the 4.2 K PL spectra were dominated by a Ga-bound exciton at 2.7982 eV the intensity of which was strongly substrate temperature dependent. It was found that the Ga-bound exciton peak could be suppressed by using higher Zn to Se ratios, and at beam pressure ratios >10 the dominant exciton peak was a free-exciton related peak at 2.800 eV. DA pair recombination was not detectable in layers grown from separate sources. Layers grown from separate sources at a higher growth rate (∼0.4 μm/h) contained additional defects indicated by the presence of an Ix peak (exciton bound to a native defect) and a much smaller unidentified peak at 2.49 eV.
Submicrometer patterning by projected excimer-laser-beam induced chemistry
Authors: Ehrlich D. J. , Tsao J. Y. , Bozler C. O.
Published: July 2002

Projection imaging with the deep-UV (193 nm) and vacuum ultraviolet (VUV) (157 nm) output of an excimer laser has been applied to submicrometer patterning of thin films by injected-defect, surface-chemical, and solid-transformation processing. The methods have been designed to take advantage of the short-wavelength, high-peak-intensity pulsed radiation from these sources. Examples are described of pattern definition by exposure of multilayer organic resists, by maskless etching and doping of solids in reactive vapors, and by solid-state chemical transformations in inorganic Al/O films. Well-resolved 0.4-μm lines and spaces have been achieved. Required doses, between 0.04 and 1 J/cm2, are compatible with single- or multipulse step-and-repeat projection patterning with a small excimer laser.
High brightness laser/plasma source for high throughput submicron x-ray lithography
Authors: Hoffman Alan L. , Albrecht Georg F. , Crawford Edward A.
Published: July 2002

Laser irradiation of solid targets has been demonstrated to produce an extremely intense source of soft x rays. Conversion efficiencies of greater than 10% emission of over 1 keV radiation into 2π sr have been demonstrated with subjoule 1.06 μ laser pulses. This high conversion efficiency is achieved by using subnanosecond pulse lengths, tight focusing, and shaped pulses. A laser capable of producing the requisite high quality laser pulses at 100 Hz repetition rates has been constructed using newly developed slab techniques to maintain good beam quality at high average powers. A windowless target chamber has been designed to mate to x-ray stepper/aligners which are now being built. The present laser will permit average x-ray intensities of 2 mW/cm2 to be realized behind current (boron nitride) x-ray masks with negligible penumbral effects. This is an order of magnitude higher than possible with conventional electron beam impact sources and, with the present or upgraded laser system, should assist the commercialization of x-ray steppers.
Masked ion beam resist exposure using grid support stencil masks
Authors: Randall J. N. , Flanders D. C. , Economou N. P. , Donnelly J. P. , Bromley E. I.
Published: July 2002

Submicrometer resolution ion beam resist exposure using a new type of stencil mask is described. The mask uses a grid support structure in transmission areas to remove restrictions on pattern geometry and improve stability. The image of the grid is eliminated by rocking the incident angle of the ion beam during exposure, or by special processing of the resist. We describe the mask fabrication sequence and show examples of masks that employ a 320 nm period grid structure. Patterns with a minimum feature size of less than one-half micrometer have been replicated using this type of mask with both single and multilayer resists. In addition, experiments are described which used low energy ion beams to test the ultimate resolution of stencil masks without grid support. 40 nm wide lines were printed in PMMA at a mask-to-wafer gap of 25 μm. The applicability of such masks in high resolution proximity printing systems is discussed.
New selective deposition technology by electron-beam induced surface reaction
Authors: Matsui Shinji , Mori Katsumi
Published: July 2002

A new selective deposition technology using electron beam induced surface reaction has been demonstrated. Electron beam induced W and Cr patterns were deposited by using WF6, WCl6, and Cr(C6H6)2 as sources, respectively. W and Cr depositions were confirmed by analysis using Auger electron spectroscopy (AES) and x-ray microanalysis (XMA). It was observed, with W deposition using the WF6 source, that the W pattern was deposited at below ∼50 °C substrate temperature, but that the substrate was etched at above ∼50 °C substrate temperature. The deposition rate increased with decreasing substrate temperature, and the etching rate increased with increasing substrate temperature. The deposited thickness was proportional to electron beam dose. A 0.15-μm-linewidth Cr pattern was deposited at 5×10−7 C/cm (3.3×10−2 C/cm2) dose by using a modified scanning electron microscope (SEM) system. These results indicate that this technology will be applicable to fabricate nanometer-structure devices.
Design, technology, and behavior of a silicon avalanche cathode
Authors: Hoeberechts A. M. E. , van Gorkom G. G. P.
Published: July 2002

The phenomenon of avalanche breakdown in silicon devices is often accompanied by a current into insulating layers leading to serious degradation, on the one hand, or to practical use in nonvolatile memories on the other hand. By injection of hot electrons towards the gate of a metal-oxide semiconductor (MOS) device, the oxide and/or floating gate is charged. The large initial current is rapidly reduced by this space charge. By removing the oxide at the site of injection, in a structure optimized for its purpose, the electron current can be injected into vacuum. Lowering the work function with, e.g., cesium enhances the vacuum current several orders of magnitude to levels where it can be of practical use. This use is demonstrated in a simple (small) TV tube which already operates hundreds of hours without appreciable degradation. Basic principles and design aspects as well as technological aspects are discussed.
The focused ion beam as an integrated circuit restructuring tool
Authors: Melngailis J. , Musil C. R. , Stevens E. H. , Utlaut M. , Kellogg E. M. , Post R. T. , Geis M. W. , Mountain R. W.
Published: July 2002

One of the capabilities of focused ion beam systems is ion milling. The purpose of this work is to explore this capability as a tool for integrated circuit restructuring. Methods for cutting and joining conductors are needed. Two methods for joining conductors are demonstrated. The first consists of spinning nitrocellulose (a self-developing resist) on the circuit, ion exposing an area, say, 7×7 μm, then milling a smaller via with sloping sidewalls through the first metal layer down to the second, e-beam evaporating metal, and then dissolving the nitrocellulose to achieve liftoff. The resistance of these links between two metal levels varied from 1 to 7 Ω. The second, simpler method consists of milling a via with vertical sidewalls down to the lower metal layer, then reducing the milling scan to a smaller area in the center of this via, thereby redepositing the metal from the lower layer on the vertical sidewall. The short circuit thus achieved varied from 0.4 to 1.5 Ω for vias of dimensions 3×3 μm to 1×1 μm, respectively. The time to mill a 1×1 μm via with a 68 keV Ga+ beam, of 220 Pa current is 60 s. In a system optimized for this application, this milling time is expected to be reduced by a factor of at least 100. In addition, cuts have been made in 1-μm-thick Al films covered by 0.65 μm of SiO2. These cuts have resistances in excess of 20 MΩ. This method of circuit restructuring can work at dimensions a factor of 10 smaller than laser zapping and requires no special sites to be fabricated.
Controlled growth of GaAs layers for monolithic hot electron transistors
Authors: Woodcock J. M. , Harris J. J. , Shannon J. M.
Published: July 2002

In a GaAs monolithic hot electron transistor (MHET), a narrow degenerately doped n-type base layer is grown between two bulk unipolar camel diodes, one for the emission of hot electrons and one for collection. The barrier heights of these diodes can be controlled by changing either the doping level or the thickness of the beryllium-doped p-type layer which forms the barrier. Analysis of such barriers using Poisson’s equation shows that the height is a rapidly varying function of thickness, and indicates that in order to fix the barrier to within ±0.05 eV, a thickness control of ∼±3%, and doping control of ±5% is needed. This precision has been achieved in a Varian MBE-360 machine which we have modified to include a rotating 2-in. substrate holder and a RHEED oscillation monitoring system; this has enabled us to grow MHET layers which have yielded devices with high base transport factors and collector efficiencies, resulting in a room temperature current gain of 15.
Studies of SiOx anodic native oxide interfaces on InSb
Authors: Calahorra Z. , Bregman J. , Shapira Yoram
Published: July 2002

We have investigated a method for passivation of InSb by vacuum deposition of SiOx on native oxide layers grown by wet anodization. We show that this multilayer dielectric approach results in improved passivation properties. Results of high resolution Auger spectroscopy reveal important information on the layer structure and composition of this passivation film. Specifically, we report the experimental observation of SiO2 formation at the SiOx anodic oxide interface. The interfacial reaction is limited to a thin layer, about 10 nm thick. The SiOx oxidation proceeds by reduction of the native oxide and formation of elemental In and Sb. The electrical features observed in the C–V curves (such as flat-band voltage, hysteresis, low-frequency-like response in the inversion region, and other deviations from the ideal curves) are explained in view of the oxidation states of In and Sb, observed at the oxide layers and at their interfaces. These correlations were used for characterization of the desired interlayer parameters.
On the stability and structure of 5×5 and 7×7 reconstruction of the (111) surface of Si and Ge
Authors: Takayanagi Kunio , Tanishiro Yasumasa , Kajiyama Kousei
Published: July 2002

Reconstructed surface structure of Si(111)-5×5-Ge and a 7×7 structure of the Ge(111) deposited on the Si(111) surface are confirmed to have atomic structures similar to a dimer adatom stacking-fault (DAS) structure of the Si(111)-7×7 surface. A structure model, dimer-chain model, which describes these DAS structures and a 2×8 structure having a similar atomic arrangement to DAS structure is presented. Stability of the dimer-chain structures with n×n (odd) and 2×m (even) periodicities is discussed using the Keating method. The result suggests structural change due to softening of the surface bonding.
Structural and electrical properties of lattice-matched Ca0.44Sr0.56F2/GaAs structures grown by molecular beam epitaxy
Authors: Tu C. W. , Wang S. J. , Phillips J. M. , Gibson J. M. , Stall R. A. , Wunder R. J.
Published: July 2002

Single-crystalline, lattice-matched (Ca, Sr)F2 films have been grown by molecular beam epitaxy (MBE) on GaAs(100) and (111) As substrates. The ratio of the Rutherford backscattering yields from the fluoride films in the aligned normal direction to a random direction, or χmin, is 0.03 for a (100) sample and 0.05 for a (111) sample, indicating excellent epitaxy. In fact, the χmin of 0.03 for the (100) sample is the best of all reported as-grown fluoride films on the (100) surface of a semiconductor. It is nearly the same as χmin from a bulk single-crystalline fluoride. For the (111) sample, channeling measurements show that the film has the same orientation as the substrate, i.e., type A. Plan-view transmission electron microscopy confirms these results. Electrical measurements show that the film has a resistivity of 3×1014 Ω cm and breakdown fields of 7×105 to 3×106 V/cm. At room temperature I–V and C–V curves show various amounts of hysteresis that is completely eliminated at low temperature, indicating the presence of positive ions.
Secondary ion mass spectrometry studies of Al, Ga, and In unintentional donors in ZnSe epilayers on GaAs
Authors: Smith T. L. , Cheng H. , Mohapatra S. K. , Potts J. E.
Published: July 2002

High sensitivity secondary ion mass spectrometry (SIMS) measurements have been made to determine upper limits on Al, Ga, and In impurity concentrations in a series of unintentionally doped n-type ZnSe films. The films were grown epitaxially on semi-insulating (100) GaAs by molecular-beam epitaxy (MBE), under conditions differing only in zinc-to-selenium beam pressure ratio. In all the samples, the upper limits for Al, Ga, and In were <1×1015, 4×1015, and 5×1014 cm−3, respectively. The total shallow donor concentrations, as determined from Hall measurements on the same samples, were typically more than one order of magnitude larger than the upper bounds on the total concentrations of the three contaminants studied. It is therefore concluded that contamination by Al, Ga, and In is insignificant in contributing to the n-type behavior of the material.
Application of reactive-ion-beam etching to recessed-gate GaAs metal–semiconductor field-effect transistors
Authors: Imai Yuhki , Ohwada Kuniki
Published: July 2002

Dry-recess etching for GaAs metal–semiconductor field-effect transistors (MESFETs) is developed using reactive-ion-beam etching (RIBE) with the etching gas of BCl3. Barrier height and ideality factor of the diode on 200 V bias-voltage RIBE-etched surface are 0.8 and 1.2 V, respectively, after 400 °C annealing. The damage layer caused by RIBE is very thin and there is no evidence of any influence on field-effect transistor (FET) characteristics, using RIBE for recess etching. A 0.4-μm-gate length recessed-gate MESFET is successfully fabricated with transconductance of 140 mS/mm. Uniformities of the threshold voltage, saturation current, and transconductance are improved, compared to those for a wet-chemical recess-etched FET.
Cathodoluminescence atomic scale images of monolayer islands at GaAs/GaAlAs interfaces
Authors: Bimberg D. , Christen J. , Fukunaga T. , Nakashima H. , Mars D. E. , Miller J. N.
Published: July 2002

Direct images of growth islands differing by 2.8 Å [1 monolayer (ML)] height at GaAs/AlGaAs heterointerfaces and of the columnar structure of quantum wells are reported for the first time. The structures are grown by molecular-beam epitaxy (MBE) with interruptions of the growth of ≊2 min at the interfaces. The method used to obtain these images is scanning cathodoluminescence. The dependence of the lateral extension of these islands on growth conditions is investigated. For fixed growth rate rs≊0.5 ML/s the mean island size decreases from 6–7 μm to 2 μm upon an increase of growth temperature from Tg=600 to 660 °C. Apparently the growth process changes from a planar to a three-dimensional one. For low-growth temperature and rate the lateral extension of such islands can be larger than the carrier diffusion length. Under these conditions interisland thermalization of carriers is largely suppressed. Quantitative information on the reduction of roughness of the quantum well interfaces with increasing growth interruption time is obtained from detailed analysis of luminescence line shapes. A full theory of quantum well luminescence line shapes is given. For heterostructures grown at rs=2.8 Å/s, Ts=620 °C, the interface roughness is observed to decrease from σ=0.44 to σ=0.20 Å for an increase of the interruption time from 1 to 100 s.
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u infrared study on the interaction of oxygen plasmas with Si and fluorine plasmas with SiO2 surfaces
Authors: Claassen W. C. M. , Dieleman J.
Published: July 2002

Infrared spectroscopy has been used to study in situ the oxidation of silicon in an oxygen plasma (10 Pa) and the etching of this silicon oxide in a He:F2 (5%) plasma (50 Pa) by monitoring the Si–O stretch vibration. The sensitivity of the present system is 10% of a monolayer of oxide. A wave number shift is observed from 1088 to 1045 wave numbers during the first stage of the oxidation. The oxide-layer thickness is determined from the integrated-band intensity. This thickness increases with the square root of the oxygen plasma exposure time and decreases linearly with etch time in the fluorine plasma (6 nm/min).
Sub-100-nm gate length GaAs metal–semiconductor field-effect transistors and modulation-doped field-effect transistors fabricated by a combination of molecular-beam epitaxy and electron-beam lithography
Authors: Allee D. R. , de la Houssaye P. R. , Schlom D. G. , Harris J. S. , Pease R. F. W.
Published: July 2002

GaAs metal–semiconductor field-effect transistors (MESFET’s) and modulation-doped field-effect transistors (MODFET’s) with recessed gates ≤100 nm long have been fabricated by incorporating a custom ultrahigh-resolution electron-beam lithography tool for gate fabrication with molecular-beam epitaxy grown wafers and a standard high-performance GaAs FET process. To the author’s knowledge, the MODFET’s have the smallest gate lengths reported to date. The electron-beam (e-beam) column was modified to hold 2- and 3-in. wafers within the final lens to maintain low aberration coefficients and facilitate device processing. 70-nm-thick polymethylmethacrylate (PMMA) was used for the gate definition. The gate recess was accomplished with a citric acid etch that did not attack the PMMA. Liftoff of e-beam evaporated TiAlAu completed the gate fabrication. DC IV characteristics were obtained for all the devices. The MODFET’s demonstrated dc transconductances as high as 400 S/m at 300 K. DC transconductances varied between 230 and 250 S/m for the MESFET’s. The MESFET’s have the desirable properties of low source resistance 0.3–0.5 Ω mm and low output conductance 8 S/m. It is shown that the drain–source saturation current for an arbitrary MESFET can be predicted to within±10% by an examination of the gate recess with a high-performance scanning electron microscope.
Controlled etching of silicate glasses by pulsed ultraviolet laser radiation
Authors: Braren B. , Srinivasan R.
Published: July 2002

Fused glass which is used as an insulation layer in the electrical packaging of integrated circuits can be precisely patterned by etching with pulsed, ultraviolet laser radiation. The glass absorbs weakly at both 193 and 248 nm lines of the excimer laser. Etching by 193 nm pulses (∼20 ns FWHM) begins at a threshold fluence of 0.5 J/cm2 and rises to 1200 Å/pulse at ∼2.5 J/cm2. The etch depth increases linearly with the number of pulses and the tolerance achieved is better than 5 μm. The etched holes are well-defined in outline. Etching by 248 nm pulses has a threshold fluence of ∼1.2 J/cm2. The etched pattern is irregular and shows damage due to shattering that is well outside the irradiated area. The etch depth is difficult to control since the surface that is produced is uneven. The maximum etch depth per pulse that was realized was only 150 Å. The etching by 193 nm laser pulses is believed to depend on the creation of color centers which strongly increases the absorption cross section.
Metals on cleaved gallium antimonide: Schottky barriers and interface reactions
Authors: Walters S. A. , Williams R. H.
Published: July 2002

In this paper we present a study of metal interfaces to vacuum and air cleaved (110) GaSb surfaces, formed at room temperature. Estimates of effective Schottky barrier heights of these diodes have been obtained using the current–voltage (I–V) measuring technique and the interfacial interactions were investigated using synchrotron radiation excited soft x-ray photoemission spectroscopy. For all the metals studied (Au, Ag, Al, Cr, Ni, Ga, Sb) nonideal diode characteristics were observed, with ideality factors close to 2 for both the clean and oxidized GaSb surfaces. These ideality factors suggest a large generation-recombination current. The effective barrier heights have been evaluated, using a curve fitting procedure. As previously found for n-type GaAs and InP gallium contacts yield the largest barrier height on GaSb, for the metals studied. In contrast the lowest barrier height observed was obtained for silver. In order to investigate reasons for the nonideal diode behavior the microscopic nature of the interfaces were studied and the results for Ag are described in detail. In contrast to its behavior on GaAs and InP, silver is found to chemically react with both types of GaSb surface, resulting in the selective removal of Sb from the interface. The thermodynamic aspects of these reactions are considered.
Band offsets in tetrahedral semiconductors
Authors: Cardona Manuel , Christensen Niels E.
Published: July 2002

Experimental and theoretical determinations of the valence band offsets at heterojunctions between tetragonal semiconductors are reviewed. The physical mechanisms underlying the offset are illustrated on the basis of midgap level theories, in particular the dielectric midgap energy version (DME). Results obtained with the DME method for several nearly lattice-matched heterojunctions are presented and critically compared with experimental data and the results of other theoretical evaluations.
Thin-film crystallography using reflection high-energy electron diffraction ‘‘rod intensity profiles’’: Ni/Si(111)
Authors: Bennett P. A. , Tong X. , Butler J. R.
Published: July 2002

We introduce a technique of RHEED ‘‘rocking patterns’’ for measuring rod intensity profiles and show that a simple kinematic interpretation may be used to deduce bulk structural parameters for a thin film. This method is used to identify a pseudohexagonal ‘‘1×1’’ epitaxial layer in the Ni/Si(111) system that is a precursor to single phase B-type (twinned) or A-type (untwinned) NiSi2. This material is a highly defective NiSi2 overlayer which we call NiSi2(A/B). The possible influence of the reconstructed Si(111) 7×7 substrate in generating the NiSi2(A/B) structure is described.
Influence of process parameters on the composition and the electrical properties of thin-plasma-nitrided oxides
Authors: Fazan P. C. , Stocker E. , Dutoit M. , Xanthopoulos N. , Vogel A. , Mathieu H. J.
Published: July 2002

We studied the influence of process parameters on the composition and the electrical properties of thin SiO2 films nitrided in a plasma reactor of a novel design. The process parameters investigated include pressure, temperature, reactant gas species and flow rate, plasma frequency and power, and process duration. The structure and morphology of these films were examined by cross-sectional transmission electron microscopy. Their composition was analyzed using Auger electron spectroscopy, secondary ion mass spectroscopy, and etch rate measurements. Metal–oxide–semiconductors capacitors were fabricated and electrically characterized by C–V, time-dependent breakdown, and charge trapping measurements. Our results show that more nitrogen is incorporated in films treated in a NH3 plasma than in a N2 plasma. Yet, the latter films present better electrical properties. Compositional variations between different films are not sufficient by themselves to explain their electrical properties. It appears that the effect of ion bombardment in the plasma plays an important role. By properly optimizing process parameters, the charge to breakdown of nitrided films can be enhanced over that of SiO2. This improvement is ascribed to a lower electron trapping rate.
Planar quantum wells with spatially dependent thicknesses and Al content
Authors: Goodhue W. D. , Zayhowski J. J. , Nichols K. B.
Published: July 2002

We have developed a process using molecular-beam epitaxy for growing GaAs/AlGaAs quantum wells with thicknesses and Al content that vary in a controlled manner on (100)-oriented GaAs substrates. The control is accomplished by manipulating the Ga sticking coefficient through local variations of the substrate temperature. To indicate the range of thickness and Al content variations that can be achieved, we show that exciton peak energies of the quantum wells can be made to vary as much as 200 meV between predetermined locations <2 mm apart on the wafer. The quality of the exciton spectra is good throughout, indicating good quality epitaxial layers throughout. This process allows flexibility in designing the well dimensions and composition in various regions of the wafer and could lead to a variety of important developments in GaAs devices.
Monte Carlo simulations of the growth of diamond-structure semiconductors and surface-reflected electron-beam intensities during molecular-beam epitaxy
Authors: Rockett A.
Published: July 2002

Monte Carlo simulation results are presented for the growth by molecular-beam epitaxy (MBE) of diamond-structure semiconductors on both specular (001) surfaces and surfaces misoriented by up to 2° from (001) toward (110). The simulation includes calculation of the topography and reconstruction of the surface. Based on the resulting surface structures the streak profile and peak intensity of specularly reflected electron beams are calculated using a kinematic scattering approximation. The results confirm models proposed to explain oscillations observed in the intensity of beams of electrons specularly reflected from terraced surfaces parallel to the terrace edges during MBE. Small clusters of atoms are shown to nucleate on the surface of the terraces and gradually become incorporated into the terrace edges as growth proceeds. On specular surfaces, nucleation occurs randomly followed by growth and coalescence of islands. Stable, statistically random, surface structures are shown to develop leading to an increase in the root-mean-squared roughness of the surface with increasing time. These structures result in a gradual damping of oscillations in the specularly reflected electron beam intensities. The damping rate decreases with increasing surface diffusion and decreasing surface roughness. The strongly bound atomic dimers present on (2×1)-reconstructed diamond-lattice (001) surfaces are shown to influence surface diffusion and hence the critical size for nucleation of new surface layers.
Characterization of Al0.25Ga0.75As grown by molecular-beam epitaxy
Authors: Lin M. J. , Larkins E. C. , Pao Y. C. , Liu D. , Yoffe G. , Ma T. K. , Harris J. S.
Published: July 2002

The effects of growth temperature and As4/Ga beam equivalent pressure ratio on molecular-beam epitaxial Al0.25Ga0.75As were studied with deep level transient spectroscopy (DLTS), photoluminescence (PL), secondary ion mass spectrometry (SIMS), Hall effect, capacitance profiling, and Nomarski microscropy. The room temperature photoluminescence efficiency is controlled by a deep trap at Ec−0.79 eV. Careful analysis shows that the trap concentration is independent of the oxygen concentration. The dependence of this trap on growth temperature and V/III ratio suggests that this trap is related to stoichiometric defects caused by arsenic rich growth. A strong correlation between trap concentration and surface roughness supports the idea that this trap forms as a result of nonstoichiometric growth. SIMS measurements show that the incorporation of oxygen, sulfur, and carbon decreases as the growth temperature increases. Finally, the Hall mobility is found to decrease as the growth temperature increases. This drop in mobility may be caused by material inhomogeneity caused by changes in the growth kinetics.
Embedded growth of gallium arsenide in silicon recesses for a coplanar GaAs on Si technology
Authors: Liang J. B. , De Boeck J. , Deneffe K. , Arent D. J. , Van Hoof C. , Vanhellemont J. , Borghs G.
Published: July 2002

A GaAs on Si coplanar technology by molecular-beam epitaxy, that is suitable to combine GaAs and Si circuits on chip is reported. Coplanarity is obtained after the GaAs is grown embedded in masked wells in the Si substrate, which were formed by wet chemical etching with a controlled solution of HF:HNO3. Scanning electron microscope and profiling studies show the extreme flatness and the intentional misorientation of several degrees of the recessed surfaces. A possible process is proposed to realize a coplanar surface by lifting off polycrystalline GaAs with the masking dielectric. The GaAs surface step height remaining after liftoff is <0.6 μm for a 2-μm-thick deposit. Metallization without loss of continuity is performed over the GaAs to Si border with evaporated metal lines, 150 nm thick and 1.25 μm wide, indicating the feasibility of interconnecting side by side integrated devices in both semiconductor materials.
Via hole filling with gold melting by KrF excimer laser irradiation
Authors: Spiess W. , Strack H.
Published: July 2002

One pulse of a KrF excimer laser emitting radiation at a wavelength of 248 nm was used to completely fill via holes in silicon dioxide (diameter: 2 μm, depth: 1 μm) by melting a 600-nm-thick gold layer on a 100-nm-thick Cr adhesion layer. The pulse width was 23 ns full width at half-maximum (FWHM) and the pulse energy was 160 mJ, yielding a laser fluence at sample surface of ∼0.6 J/cm2. The result is a nearly planar structure.
Proximity correction for electron-beam patterning on x-ray mask blanks
Authors: Reimer K. , Pongratz S.
Published: July 2002

A limiting factor in electron-beam (e-beam) lithography is the proximity effect. In the special case of x-ray mask making, Monte Carlo calculations and resist profile simulations show that the proximity effect can be almost entirely eliminated by using 100 keV electrons for the resist exposure. To verify the theoretical results of the simulation, experiments with available electron energies of 20 and 50 keV were conducted, with good agreement. The poor efficiency of 100 keV electrons results in decreasing resist sensitivity. Electrons passing through the membrane hit holder parts behind it. The x-ray radiation generated in this way was able to expose the resist from the backside of the membrane. A diffuse image of the holder parts could be seen in the resist.
Selected area epitaxy in II–VI compounds by laser-induced photo-metalorganic vapor phase epitaxy
Authors: Irvine S. J. C. , Hill H. , Brown G. T. , Barnett S. J. , Hails J. E. , Dosser O. D. , Mullin J. B.
Published: July 2002

Selected area epitaxy of CdTe onto GaAs(100)2°→(110) substrates is reported where a frequency-doubled argon ion laser, output wavelength of 257 nm, is used to photolytically decompose the precursors. Photodissociation of the precursors dimethyl telluride, dimethyl ditelluride, diethyl telluride, and dimethyl cadmium have been investigated for their suitability in terms of their ultraviolet absorption spectra and thermal stability. Diethyl telluride or dimethyl telluride have strong absorptions at 257 nm and have good thermal stabilities yielding high photoenhancement factors. Nucleation of CdTe onto GaAs substrates has revealed the need to remove the native oxide for epitaxial growth. HeNe laser thin-film interference has indicated a 4-min nucleation delay for pyrolytic precursor decomposition. Photopatterned CdTe epitaxy has been demonstrated at 300 °C for a two-dimensional mesa pattern obtained by shadow masking and a bar pattern obtained by projection onto the surface. Deposition due to vapor diffusion of Cd and Te was only evident at high laser intensities. At low intensities feature definition is very good with feature sizes ∼100 μm. These results are explained by surface-rate-limiting kinetics that can be stimulated by the laser radiation. Such a mechanism could be laser-stimulated hydrocarbon desorption.
Lateral tunneling and ballistic transport in two-dimensional electron gas devices defined by nanostructure gates
Authors: Umbach C. P. , Palevski A. , Heiblum M. , Sivan U.
Published: July 2002

Novel, laterally configured, tunneling hot electron transfer amplifier (THETA) devices have been formed using nanostructure metal gates to induce potential barriers separating emitter, base, and collector regions in a two-dimensional electron gas. The gates were formed by a liftoff technique using PMMA resist and a high resolution electron beam writing tool. Lateral electron tunneling has been directly observed, using electron energy spectroscopy, through potential barriers under metal gates as wide as 52 nm. The energy distribution of the hot electrons was only ≂5 meV wide. Certain gate configurations were found to increase the fraction of emitted electrons which reached the collector. Current gain as high as 105 was observed. This is better than the best results previously obtained with vertical THETA devices.
Replicated resist pattern resolution with synchrotron orbital radiation
Authors: Suzuki M. , Kaneko T. , Saitoh Y.
Published: July 2002

For investigating the fundamental characteristics and resolution limit of patterns replicated with synchrotron orbital radiation (SOR), a computer simulation program, synchrotron orbital radiation lithography simulation system (sorsis) has been developed and resulting resist pattern profiles have been analyzed in detail. In sorsis, Fresnel integrals are performed by a new model based on introducing the SOR wavelength distribution, mask contrast, and phase difference into calculations. Positive-type resist replication pattern profiles are calculated to evaluate pattern characteristics and are compared with experimental results. These results derive a resolution limit evaluation method, representing the equation W=ε(Gλp /2)1/2.3 , where W is the minimum linewidth, G the proximity gap, λp the wavelength peak, and ε the parameter mainly determined by resist characteristics and x-ray mask absorber thickness. In this way, optimum conditions for precise pattern replication and accurate pattern profile control can be realized easily.
Optical and electrical characterization of pseudomorphic AlGaAs/InGaAs/GaAs modulation-doped structures processed by rapid thermal annealing
Authors: Dodabalapur A. , Kesan V. P. , Block T. R. , Neikirk D. P. , Streetman B. G.
Published: July 2002

We describe molecular-beam epitaxial growth conditions to obtain high-quality pseudomorphic AlGaAs/InGaAs/GaAs modulation-doped structures. We discuss the effects of rapid thermal annealing on the electrical properties of these structures. A mobility increase is typically obtained after short-time heat treatments. We also report the first study of the effects of thermal processing on the optical properties of modulation-doped structures. Both the linewidth and the energy of the photoluminescence transition due to channel electrons and photoexcited holes are influenced by the changing free-carrier concentration in the channel. Our results also suggest that there is negligible layer mixing in these structures after annealing.
The influence of interfacial roughness on parallel transport at oxide–semiconductor and heterojunction interfaces
Authors: Goodnick S. M. , Lary J. E. , Owen R. , Sri O. , Wilmsen C. W.
Published: July 2002

Carrier scattering due to surface roughness at a nonideal interface may be an important mechanism in reducing carrier mobility and ultimately semiconductor device performance. We have investigated the role of this scattering mechanism in the low and high field transport of carriers parallel to oxide–semiconductor and heterojunction interfaces through analytic solutions and Monte Carlo simulation of the carrier dynamics. Quantitative differences between the scattering rates in the two types of systems arise from image potential contributions due to the presence of the dielectric in the oxide–semiconductor system which increases the scattering rate relative to a homogeneous system. For the InP/SiO2 system, surface scattering limits the surface channel mobility, even at room temperature. However, from detailed Monte Carlo simulation of high field transport in n-type InP inversion layers, we find that roughness scattering plays a relatively small role in reducing the peak and saturated carrier velocities since interface scattering is elastic and decreases with electron temperature. Thus, the short channel behavior in InP metal–oxide semiconductor field effect transistors may be comparatively better than that indicated by long channel results.