bluuebunny/crossref_metadata_2025 huggingface dataset:
Instabilities of (110) III–V compounds grown by molecular beam epitaxy
Authors: Wang W. I.
Published: July 2002

We have grown GaAs and AlGaAs on (110)-oriented GaAs substrates by molecular beam epitaxy (MBE). The epitaxial growth was studied in situ by reflection high energy electron diffraction. Hall measurements, low temperature photoluminescence, and scanning electron microscopy were used to characterize the epitaxial layers. Significant instabilities were found for this orientation under the growth conditions employed. The experimental results are discussed with bonding considerations of the (110) surfaces.
The Schottky barrier height of platinum nickel silicide
Authors: Ellwanger R. C. , Morgan A. E. , Stacy W. T. , Tamminga Y.
Published: July 2002

Films of Pt0.4Ni0.6 of different thicknesses were sputter deposited onto n-type (111)Si and annealed at various temperatures. The structure and composition of the ensuing PtxNi1−xSi films were determined using STEM/EDS, AES, RBS, and electron diffraction. The films were found to consist of several layers of distinct composition. The barrier height (φB) as determined from the diode forward I–V characteristics bore little relationship to the composition of the interfacial silicide layer. Furthermore, when successively thinning a film, φB decreased from 0.737 to 0.694 eV upon removal of the adjacent Pt-rich (x=0.75) layer thereby leaving only the Ni-rich (x=0.1) interfacial layer. These and other data are presented which indicate that the barrier height of platinum nickel silicide is not determined solely by interfacial properties.
Charge control model of inverted GaAs–AlGaAs modulation doped FET’s (IMODFET’s)
Authors: Lee Kwyro , Shur Michael , Drummond Timothy J. , Morkoç Hadis
Published: July 2002

Current–voltage characteristics of an inverted GaAs–AlGaAs modulation doped transistor are calculated using a charge control model. Our calculations show that the electron concentration of the two dimensional electron gas for the inverted structure is comparable to those obtained in normal MODFET’s. The optimum design of an inverted device calls for a doped AlGaAs layer thin enough to be fully depleted. The sheet carrier concentration of the two dimensional electron gas will be only slightly less than the maximum possible. For such devices the predicted transconductances are close to those for normal modulation doped transistors.
Low energy electron diffraction study of (221) and (311) GaAs surfaces
Authors: Stiles K. , Kahn A.
Published: July 2002

The atomic structures of A- and B-polar (221) and (311) GaAs surfaces, prepared by ion sputtering and annealing, are investigated with low energy electron diffraction (LEED). The (221) surfaces are unstable and develop large {110} facets which display the atomic geometry of the (110) GaAs surface. Both A- and B-(311) surfaces are stable to about 600 °C and exhibit (1×1) structures. The LEED patterns have a mirror symmetry which corresponds to the mirror symmetry of the surface about the (011̄) plane. Preliminary single scattering analyses of the LEED intensity profiles of both A and B faces have been performed.
Growth of InP, GaAs, and In0.53Ga0.47As by chemical beam epitaxy
Authors: Tsang W. T.
Published: July 2002

A new epitaxial growth technique, chemical beam epitaxy (CBE), was demonstrated and investigated with the growth of InP and In0.53Ga0.47As GaAs. In this technique, all the sources were gaseous group III and group V alkyls. The In and Ga were derived by the pyrolysis at the heated substrate surface of either trimethylindium (TMIn) or triethylindium (TEIn), and trimethygallium (TMGa) or triethylgallium (TEGa), respectively. The As2 and P2 were obtained by thermal decomposition of triethylphosphine (TEP) and trimethylarsine (TMAs) in contact with heated Ta or Mo at 950–1200°C, respectively. Unlike conventional vapor phase epitaxy, in which the chemicals reached the substrate surface by diffusing through a stagnant carrier gas boundary layer above the substrate, the chemicals in CBE were admitted into a high vacuum growth chamber and impinged directly light of sight onto the heated substrate surface in the form of molecular beams. The beam nature of CBE resulted in very efficient use of the impinging chemicals and allowed the utilization of mechanical shutters. A similar gas handling system to that employed in conventional metalorganic chemical vapor deposition (MOCVD) with precision electronic mass flow controllers was used for controlling the flow rates of the various gases admitted into the growth chamber. Growth rates as high as 3–5 μm/h have been achieved for both InP and GaAs. The InP and GaAs epilayers grown have smooth surfaces and comparable optical quality to bulk substrates. Since TMIn and TEGa emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the In0.53Ga0.47As epilayers grown. Lattice mismatch Δa/a≲4×10−4 was obtained.
Emission characteristics of the ZrO/W thermal field electron source
Authors: Tuggle D. W. , Swanson L. W.
Published: July 2002

The ZrO/W thermal field emitter (TFE) has proven to be a useful high brightness electron source for a variety of microprobe applications. Desirable source characteristics are: 1 to 2 mA/sr angular intensity, 1 to 1.5 eV energy spread for an emitter radius of 0.6 to 1 μm, and <0.5% noise level between 1 Hz and 25 kHz. In this study we examine the effect of the faceted shape1 of the ZrO/W TFE on the angular distribution of the emission and virtual source size. In particular the scwim computer program1 is employed to compare the emission characteristics of faceted and spherical shaped emitters. The computer derived results agree qualitatively with experimental angular emission distributions measured for various emitter radii. It is shown that the high angular intensity obtained from the ZrO/W TFE is due in part to a large angular demagnification caused by the faceted emitter region. Nevertheless, a comparison of the virtual source size of the faceted and the spherical shapes shows only a small source image increase due to faceting. The minimum values of virtual source size at an angular intensity of 1 mA/sr for the spherical and faceted emitters are 8 and 12 nm, respectively.
Recent trends in III–V strained layer research
Authors: Osbourn G. C.
Published: July 2002

Current directions in III–V strained layer superlattice research are briefly reviewed. Areas of recent emphasis include the study of the tailorable light hole mass values, the development of new III–V strained layer materials for infrared detector applications, and work on modulation-doped field effect transistors employing strained quantum wells. Recent theoretical and experimental results as well as unresolved issues in these areas are discussed.
Initial formation of the interface between a polar insulator and a nonpolar semiconductor: CaF2 on Si(111)
Authors: Olmstead Marjorie A. , Uhrberg R. I. G. , Bringans R. D. , Bachrach R. Z.
Published: July 2002

The initial stages of interface formation between CaF2 and Si(111) have been studied with both core-level and angle-resolved valence band photoemission spectroscopy. Both the Si 2p and Ca 3p core levels indicate that a Si–Ca bond is present at the CaF2–Si(111) interface. Annealing of thin CaF2 films at 700–800 °C results in preferential evaporation of F, and the surface undergoes a number of reconstructions until a stable Si(111):Ca 3×1 reconstruction is obtained on which there is calcium, but no fluorine. This surface exhibits a surface state with an upward dispersion of 0.4 eV towards the K̄ point of the 1×1 surface Brillouin zone. Our results show that the CaF2 molecule can be dissociated on the Si(111) surface at typical epitaxial growth temperatures, with the Ca being more strongly adsorbed to the Si than is the F.
Theoretical calculations of semiconductor heterojunction discontinuities
Authors: Van de Walle Chris G. , Martin Richard M.
Published: July 2002

We have performed self-consistent density functional calculations on semiconductor heterojunctions, using ab initio nonlocal pseudopotentials, and have derived valence band discontinuities for many different interfaces between both lattice-matched and strained epitaxial layers. The agreement with reported experimental values is very reasonable. Based on the information obtained from the interface calculations, we have developed a new and simple approach to derive band discontinuities. In this scheme, the lineup of potentials between two materials is determined by the difference in average potentials which are calculated for a ‘‘model solid’’ consisting of neutral, spherical atoms. Band structures for the bulk solid are then aligned according to these average potential positions. This is a valuable ansatz which, for many cases, yields results close to those obtained from full self-consistent interface calculations. We also discuss examples, such as polar interfaces, where this simple ansatz is not sufficient.
TiW nitride thermally stable Schottky contacts to GaAs: Characterization and application to self-aligned gate field-effect transistor fabrication
Authors: Geissberger A. E. , Sadler R. A. , Balzan M. L. , Crites J. W.
Published: July 2002

The thin-film properties and temperature stability of titanium–tungsten nitride (TiWNx) Schottky contacts to GaAs have been investigated as a function of x, the atomic percent of nitrogen in the film. A Ti30W70 composite target was reactively sputtered onto GaAs substrates in nitrogen using argon as the diluent gas. The partial pressure of nitrogen was varied from 0% to 100%. This resulted in x varying from 0 to 27 at. %; however, the films contained a constant Ti–W atomic ratio of 0.18, regardless of x. The film stress and resistivity were well-behaved and reproducible functions of x. Schottky contact characteristics were measured after annealing at several temperatures. After an 810 °C furnace anneal, the ideality factor (n) and barrier height (φB) displayed well-defined, broad extrema as a function of x. Both the best average values of n and φB and their smallest standard deviations occurred for x=10 at. % of nitrogen. Thus the most stable and uniform TiWNx–GaAs Schottky contact was obtained from TiWN10. TiWN10 has been used as the refractory metal in ITT’s self-aligned gate digital GaAs integrated circuit process to obtain gate delays as low as 19 ps at a power-delay product per gate of 19 fJ.
The interface and its role in surface-parallel transport
Authors: Ferry D. K.
Published: July 2002

For many decades, surface scientists have been concerned with the details of the physics and chemistry of microscopic states at surfaces and interfaces. Devices, on the other hand, depend upon the actual transport properties of carriers along the interface, which measure macroscopic properties of the interface by averaging over the entire ensemble of electrons involved in the conduction process. Transport is sensitive to the global properties at the interface, such as interface roughness, defect scatterers, or periodic potentials. Only recently have constrained dimensional systems allowed one to begin to study discrete state properties of the interface.
Tungsten: An alternative to gold for x-ray masks
Authors: Karnezos M. , Ruby R. , Heflinger B. , Nakano H. , Jones R.
Published: July 2002

An x-ray mask fabrication process is presented using tungsten absorber instead of the commonly used gold. The W is dc sputter deposited directly on the boron nitride membrane with low stress, low defect count (<1/cm2) and density 18.3±0.5 g/cm3. Good linewidth control is obtained during the PMMA trilayer resist patterning by applying e-beam proximity corrections and in situ endpoint detection for the resist development. The patterns are reactive ion etched into the W using SF6 gas. Geometries down to 0.25 μm have been transferred into W with vertical walls and excellent adhesion. Preliminary results on mask repair using laser processing of W and focused ion milling are given. The advantages of using W instead of Au are briefly discussed.
Properties of positive resists. II. Dissolution characteristics of irradiated poly(methyl methacrylate) and poly(methyl methacrylate–co-maleic anhydride)
Authors: Parsonage Edward E. , Peppas Nikolaos A. , Lee Ping I.
Published: July 2002

Poly(methyl methacrylate) and poly(methyl methacrylate–co-maleic anhydride) were prepared by free-radical, bulk polymerization using 0.005 mole % benzoyl peroxide as an initiator at 50 °C for 24 h. The resulting transparent cylinders were cut in a lathe into disks of 14-mm diameter and 2.2-mm thickness. Samples were also prepared in the form of thin slabs of 14×2×1 mm3. Subsequently, they were irradiated by γ rays at the level of 2–12 Mrad and their molecular weight distribution was determined by gel permeation chromatography. Changes in their structure before and after irradiation were determined by infrared spectroscopy. Their sensitivity values Gs and solubility characteristics in various solvents were determined. Planar and radial dissolution studies were performed in pure methyl ethyl ketone or ethanol at 26 °C. The positions of the solvent/gel and gel/glassy fronts were followed as functions of time. The results were correlated with the pseudosteady-state solutions of a new mathematical model incorporating the simultaneous effects of swelling and dissolution of the polymers.
X-ray lithography
Authors: Heuberger A.
Published: July 2002

X-ray lithography with wavelengths between 0.2 and 5 nm provides both high-structural resolution as good as 0.1 μm and a wide scope of advantages for the application in circuit production. Examples for this better process performance compared to optical techniques are: lower particle and dust sensitivity, applicability of simple single-layer resist technique, high depth of focus without any influence of substrate material and chip topography, and presumably, the highest throughput of all lithography methods which are able to go into the submicron range. However, the introduction of x-ray lithography into the semiconductor production means a revolutionary change of production technology. This begins with a completely different mask technology which makes, for example, the classical separation of mask substrate fabrication from pattern generation by different manufacturers very problematical and ends with the necessity to introduce x-ray lithography in relatively large production capacity units consisting of a larger number of x-ray steppers. The latter is caused by the fact that a storage ring—even in the smallest version, e.g., COSY (Kompakt Speicherring für Synchrotronstrahlung)—has to supply up to 10 x-ray steppers with light in order to clearly beat the optical techniques with respect to throughput and lower cost level. To prove such statements in pilot production lines, the necessary tools and components for x-ray lithography are already or will be available for the first time on a commercial basis in the very near future. Especially steppers, sources, and resists with satisfying specifications have been announced by a growing number of vendors. The most critical problem at present is the mask technology and the tools for defect elimination. However, with the existing technologies, the requirements for 0.5-μm-design rules will be met very soon on a pilot scale.
Passivation of donors in electron beam lithographically defined nanostructures after methane/hydrogen reactive ion etching
Authors: Cheung R. , Thoms S. , McIntyre I. , Wilkinson C. D. W. , Beaumont S. P.
Published: July 2002

We show that while the methane/hydrogen gas mixture is capable of etching GaAs and AlGaAs controllably and with little residual damange, it leads to the passivation of donors in both semiconductors. The passivation can, however, be annealed out with a short thermal cycle to 300 °C. The effects of passivation are illustrated and characterized by processing uniform epilayers and quantum wires in n+-GaAs and modulation doped AlGaAs/GaAs heterostructures.
SiO2 film stress distribution during thermal oxidation of Si
Authors: Kobeda E. , Irene E. A.
Published: July 2002

A laser reflection technique is used to investigate the relaxation of SiO2 film stress which occurs during the dry thermal oxidation of Si between 700 and 1000 °C. Included is a determination of the stress distribution in the oxide by two independent methods: (1) measurement on oxides of various thicknesses from 100 to 800 Å, and (2) repeated stress measurements on chemically thinned SiO2 films, viz. etch-back analysis toward the interface. Agreement is found between these experiments. These thin film stress measurements are achieved by the use of ultrathin Si substrates (75 μm). Essentially, an increase in film stress with decreasing film thickness is observed. Rapid stress relaxation is observed for all temperatures studied and is attributed to a time-dependent oxide viscosity. The influence of these measured properties on the kinetics of Si oxidation is discussed.
Kinetic aspects of growth front surface morphology and defect formation during molecular-beam epitaxy growth of strained thin films
Authors: Ghaisas S. V. , Madhukar A.
Published: July 2002

The influence of lattice mismatch induced strain on the growth mode, surface morphology, and kinetically controlled introduction of defects at the earliest stages of molecular-beam epitaxical growth of semiconducting compounds is investigated via computer simulations. A variety of combinations of the possible ways in which compressive or tensile in-plane strain may modify the atomistic kinetic rates involved in growth have been considered and their consequences compared with the available experimental information. A few illustrative examples relevant to systems such as InGaAs/GaAs(100), InGa(Al)As/InP(100), and GaAs/Si are presented.
Modulation-doped HgCdTe quantum well structures and superlattices
Authors: Han Jeong W. , Hwang S. , Lansari Y. , Yang Z. , Cook J. W. , Schetzina J. F.
Published: July 2002

Photoassisted molecular-beam epitaxy (MBE) has been employed to successfully prepare p-type and n-type modulation HgCdTe. In this paper, we report details of the MBE growth experiments and describe the structural, optical, and electrical properties that these new quantum well structures and superlattices of HgCdTe possess.
Particulate contamination in silicon grown by molecular-beam epitaxy
Authors: Pindoria G. , Houghton R. F. , Hopkinson M. , Whall T. , Kubiak R. A. A. , Parker E. H. C.
Published: July 2002

A retrospective view of several hundred epilayers provides an insight into the factors relating to molecular-beam epitaxy (MBE). The major source of particulates was found to be associated with the high electron flux in the deposition region of the MBE system, coming from the electron beam evaporator, and with the unstable excess Si deposits in the growth chamber. Reduction of Si accumulation in the deposition zone by containment of the Si flux significantly reduces particulate densities in epilayers. Voltages applied to a tantalum plate, situated adjacent to the growth flux zone, affected particulate densities in the epilayers confirming that a significant percentage of the particulate contamination is derived from charge effects. Other factors affecting the particulate contamination of the epilayer include the stability of the electron beam evaporator, the substrate rotation mechanism, and the method of evacuation of the load lock when transferring the samples into vacuum. Two types of particulate-related features have been identified. The first type thought to be due to microscopic particulates is decorated by crystallographic defects, whereas the second type, which is free of these defects, appears to be related to shadowing of growth by larger particulates. A correlation in the densities of both types of particulate defects in epilayers grown under a variety of experimental conditions suggests a common source.
Photoemission study of the novel Sn/GaAs(110) interface structures
Authors: Tang Ming , Joyce J. J. , Meng Y. , Anderson J. , Lapeyre G. J.
Published: July 2002

Synchrotron radiation photoemission spectroscopy is used to study the electronic structure and growth mechanisms of Sn on cleaved GaAs(110) surfaces. Detailed core-level analysis, along with the substrate intensity attenuation and valence-band information, indicate that Sn forms nondisruptive bilayer patches on cleaved GaAs(110) surface for coverage θ between 0≤θ≤ 1 monolayer (ML). In the 1<θ<2.5 ML coverage range, the bilayer growth atop the substrate is accompanied by the initial growth of Sn-based structures on top of the bilayer. The bilayer and Sn-based structures are semiconducting. The substrate is completely covered at ∼2.5 ML. Continued deposition above 2.5 ML results in Sn clusters. A Sn-induced density of states progressively fill in the region between the valence-band maximum (VBM) and the Fermi level (EF) with Sn deposition. At coverages above 3 ML, Sn derived states show emission at EF. The electronic structure changes during the interface development leads to the continuous band bending towards midgap. The total amount of band bending at 8 ML is about 0.67 eV.
Growth of AlN/GaN layered structures by gas source molecular-beam epitaxy
Authors: Sitar Z. , Paisley M. J. , Yan B. , Ruan J. , Choyke W. J. , Davis R. F.
Published: July 2002

AlN/GaN layered structures with layer periods between 1.5 and 40 nm have been grown on (0001) oriented sapphire and α(6H)-SiC substrates. The growth was performed using a modified gas source molecular-beam epitaxy (MBE) technique. Standard effusion cells were used as sources of Al and Ga, and a small, MBE compatible, electron cyclotron resonance (ECR) plasma source was used to activate nitrogen gas prior to deposition. Chemical analysis of the layers was conducted using Auger spectrometry. X-ray diffractometry, transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM) were employed for the structural and microstructural studies. Coherent interfaces (no relaxation by misfit dislocations) were observed for bilayer periods smaller than 6 nm. By contrast, completely relaxed individual layers of GaN and AlN with respect to each other were present for bilayer periods above 20 nm. Cathodoluminescence showed a shift in the emission peak from 3.42 eV for the sample with individual 10-nm thick GaN wells and AlN barriers to 4.11 eV for the sample having 1-nm thick individual layers.
Growth of boron nitride films by gas molecular-beam epitaxy
Authors: Paisley M. J. , Sitar Z. , Yan Benda , Davis R. F.
Published: July 2002

Boron nitride is a thermally stable and chemically inert material with a wide bandgap. As such, it has potential optoelectronic applications as windows, deep ultraviolet (UV) detectors, or UV light-emitting devices. Since it has a very high surface energy and a lattice parameter which is very similar to diamond, it may also prove to be an excellent substrate material for heteroepitaxial thin film growth of this material. This paper reports the preliminary results of the growth of BN thin films using gas source molecular beam epitaxy. The B source evaporated elemental B produced in a new high temperature effusion cell. The nitrogen source consisted of N ions as well as activated N atoms and molecules obtained from the decomposition of purified N2 by passing it through an electron cyclotron resonance plasma unit designed specifically for molecular-beam epitaxy (MBE) systems. A graded GaN–BN layer deposited on a monocrystalline β-SiC (100) film was used as the substrate for growth of each BN film. Transmission electron microscopy of the latter films showed them to be amorphous; however reflection high-energy electron diffraction (RHEED) patterns obtained during deposition indicated the presence of some microcrystallinity.
Markle–Dyson optics for 0.25 μm lithography and beyond
Authors: Grenville A. , Hsieh R. L. , von Bünau R. , Lee Y-H. , Markle D. A. , Owen G. , Pease R. F. W.
Published: July 2002

Using a modified Dyson design working at 0.7 NA with 248 nm illumination, reflective 1X masks, and conventional single-layer resists, 0.25 μm lithographic resolution has been obtained over a semicircular field 4 mm in diameter. 0.19 μm lines and spaces have been printed using an experimental bilayer resist. To offset the small depth of focus, two precision autofocus schemes have been demonstrated and FLEX has been shown by computer simulation to triple the depth of focus for isolated features. A full size system has been designed with a 20×40 mm2 field sufficiently large for patterning 256 Mbit DRAM chips. This concept can be extended to shorter wavelengths limited only by availability of one refractive material and a suitable light source. Thus optical projection lithography appears feasible for features at least as small as 0.15 μm.
Fabricating binary optics: Process variables critical to optical efficiency
Authors: Stern M. B. , Holz M. , Medeiros S. S. , Knowlden R. E.
Published: July 2002

While conventional photolithographic and reactive ion etching techniques are employed in the manufacture of binary optical elements, the nested character of these diffractive surface relief structures, coupled with submicron linewidths and additive etch depths, puts stringent demands on process tolerances. To quantitatively assess the effects of process variables, we have utilized a mask set that incorporates ten different lenslet designs as single elements and as 10×10 arrays. All lenslets are 200 μm×200 μm with focal lengths ranging from 170 μm to 14 mm at 632.8 nm wavelength. Overlay registration accuracy is evaluated by optical microscopy of vernier-style alignment marks, etch depths are determined by stylus profilometry, and linewidths are measured by optical and scanning electron microscopy. The optical efficiency is evaluated as a function of the focal length and compared to theoretical predictions. The eight-phase-level 𝔉/4 microlenses, measured at 96% of the expected value, exhibit the highest optical efficiency reported to date for such a lens in the visible.
Chemically assisted ion beam etching of InP and InSb using reactive flux of iodine and Ar+ beam
Authors: Bharadwaj L. M. , Bonhomme P. , Faure J. , Balossier G. , Bajpai R. P.
Published: July 2002

Results are presented on chemically assisted ion beam etching of InP and InSb using reactive flux of iodine vapours derived from elemental iodine and A+ ion beam. The effect of iodine partial pressure has been studied on the etch rate at different ion beam current densities. The etch rate increases with increase in iodine partial pressure; but above 6×10−5 Torr, the trend changes depending upon ion current density. The results are discussed in terms of etch mechanism. The scanning electron microscopy and transmission electron microscopy (TEM) results show that use of iodine flux overcomes the differential etching problem associated with inert ion beam etching of In containing compound semiconductors. The high-resolution electron microscopy shows that no crystalline defects are introduced by the use of iodine. The technique has been successfully used for anisotropic etching of 1.5 μm test patterns using Dynachem OFPR-800 postive resist and for preparation of TEM specimen.
Atomic resolution images of metallic materials in oil
Authors: Endo T. , Yamada H. , Sumomogi T. , Kuwahara K. , Morita S.
Published: July 2002

Bulk metallic sample surfaces of Pt, Au, and Mo were etched with HF just before immersing in diffusion pump oil and/or were polished with diamond compounds in the diffusion pump oil. The surfaces were directly observed in the oil using a scanning tunneling microscope (STM), and atomically resolved current images were obtained. It is confirmed that the diffusion pump oil is effective to maintain the fresh surface of metals. The surface flatness is most important for obtaining atomic resolution images for the observation of bulk metals in the oil.
Near-field optics: Microscopy with nanometer-size fields
Authors: Denk Winfried , Pohl Dieter W.
Published: July 2002

The electromagnetic fields that can build up around metallic or dielectric pointed tips are of increasing interest in context with the new scanning probe microscopies (tunneling, near-field optics, Coulomb and van der Waals forces etc.). The paper presents exact solutions of Laplace’s equations for the tip/sample geometry. For suitable media, plasmons are found whose electric fields are highly localized in the gap region. We believe that the field enhancement associated with such tip plasmons is instrumental for inelastic tunneling and light emission during scanning tunneling microscopy.
Relation between reflection high-energy electron diffraction specular beam intensity and the surface atomic structure/surface morphology of GaAs(111)B
Authors: Chen P. , Rajkumar K. C. , Madhukar A.
Published: July 2002

The intensity behavior of the specular beam in reflection high-energy electron diffraction (RHEED) from GaAs(111)B grown by molecular-beam epitaxy (MBE) is investigated for various growth and diffraction conditions. The temporal behavior during the initial growth of a buffer layer is examined at a fixed diffraction condition. Intensity increase is observed during and after the initial stages of buffer layer growth and found to saturate after about 80 monolayer growth. Intensity oscillations are seen starting at different moments of initial growth, the earliest observed after only 14 monolayer growth. These results are used to guide and control GaAs(111)B growths with mirrorlike surface morphology.
Radio frequency or microwave plasma reactors? Factors determining the optimum frequency of operation
Authors: Moisan M. , Barbeau C. , Claude R. , Ferreira C. M. , Margot J. , Paraszczak J. , Sá A. B. , Sauvé G. , Wertheimer M. R.
Published: July 2002

It is now generally accepted that the frequency ω/2π at which a high frequency (hf) discharge is sustained has considerable influence on the properties of the plasma. For example, the electron density obtained for a given hf power density deposited into the plasma is usually higher at microwave than at radio frequencies (rfs). This paper reviews a series of experiments at the Université de Montréal designed to investigate the influence of ω on the power balance between the hf field and the plasma, and the plasma processing of materials. For the two particular etching and deposition processes which are described here, the ‘‘optimum’’ frequency (at which the process is most efficient) appears to be in the range between 50 and 100 MHz. This suggests that converting a plasma process from 13.56 to 2450 MHz does not necessarily lead to the greatest possible process enhancement, and that optimization may require the plasma reactor to be constructed in such a way as to allow the excitation frequency to be changed. To provide insight into these results, the most recent models dealing with the influence of ω on the electron energy distribution are reviewed and extended to calculate parameters that can be compared with our experimental data.
High-efficiency infrared light emitting diodes made in liquid phase epitaxy and molecular beam epitaxy HgCdTe layers
Authors: Bouchut P. , Destefanis G. , Chamonal J. P. , Million A. , Pelliciari B. , Piaguet J.
Published: July 2002

We report in this article, for the first time the performance of light emitting diodes (LEDs) made in HgCdTe (MCT) epilayers on CdZnTe (CZT) lattice-matched substrates grown either by liquid phase epitaxy (LPE) or molecular beam epitaxy (MBE). Diodes are n/p homojunctions made by ion implantation. The MCT composition was chosen in order to get the emission wavelength between 3 and 5 μm. Electroluminescence spectra were recorded between 20 K and 300 K. A comparison of the two materials is made, demonstrating that they exhibit similar performances. Internal quantum efficiencies as high as 25% (λ peak=4.1 μm at 77 K) and 6% (λ peak=3.5 μm at 300 K) were obtained on both LPE and MBE materials and they reach a maximum for a temperature of about 90 K. For a material with λ peak=5.5 μ at 77 K, internal quantum efficiency remains as high as 5%. The external quantum efficiency is considerably increased using backside emission through the CZT substrate and optical coupling with a CZT lens: in such conditions 20% of the emitted light could be extracted from the structure. These results show that MCT can already be used for LEDs in the 3–5 μm region.
Key issues in HgCdTe-based focal plane arrays: An industry perspective
Authors: Tennant William E. , Cockrum C. A. , Gilpin J. B. , Kinch M. A. , Reine M. B. , Ruth R. P.
Published: July 2002

Technological limits, not fundamental issues, are all that keep HgCdTe from completely dominating almost all infrared (IR) applications. The technological limits result from our incomplete understanding of HgCdTe materials science. This article’s snapshot view, from the unique perspective of the major United States HgCdTe IR detector array companies, suggests directions that HgCdTe detector technology should take as we approach the next century. We argue that the Government, industrial users, and industrial producers of HgCdTe must support continuing scientific investigation of this material to parallel the manufacturing of second generation HgCdTe-based systems. Without this manufacturing science base, systems will develop too slowly, cost too much, and fail too often. To assist developing this critically important technology, the article highlights some of the more vexing and as yet unsolved HgCdTe materials science and engineering problems that we see as being important.
Thin silicon nitride films for reduction of linewidth and proximity effects in e-beam lithography
Authors: Dobisz E. A. , Marrian C. R. K. , Shirey L. M. , Ancona M.
Published: July 2002

A thin silicon nitride layer (50–300 nm), deposited on a semiconductor substrate, prior to resist deposition, greatly enhances the resist resolution during electron beam lithography. The resolution enhancement was manifested by smaller feature sizes, for a given dose and full resolution of individual array elements at higher doses than on a bare semiconductor substrate. The effect has been observed in 50–100 nm of both SAL-601 and PMMA spun onto silicon nitride coated Si and GaAs substrates. The samples were patterned with a 50 keV, 15 nm diam probe generated by a JEOL JBX-5DII system. Improved resolution was found on two types of silicon nitride film grown by chemical vapor deposition: one deposited at 800 °C on Si and the other deposited at 200 °C on GaAs. Linewidth reductions in SAL-601 of 40% at low doses and an order of magnitude at high doses were observed on silicon nitride coatings of 50–300 nm thickness. In PMMA, the resolution enhancement was less than in SAL-601, with only a 15% linewidth reduction observed at high doses (≥10 nC/cm). A reduction in proximity effects due to the presence of the nitride layer, is apparent in SAL-601, for array periods of 1 μm and less. Analysis of the results, combined with Monte Carlo simulations and electron microscopy suggests that fast secondary electrons, generated by the substrate are prevented by the silicon nitride layer from exposing the resist.
Improvement of the threshold current of AlGaAs/GaAs single quantum well lasers by substrate tilting
Authors: Tao I. W. , Schwartz C. , Wang W. I.
Published: July 2002

We have grown AlGaAs/GaAs single quantum well lasers by molecular-beam epitaxy on differently misoriented substrates. The threshold current density was observed to be lower on the (511) orientation than the 4° off (100) orientation. We explain this result based on the fact that step-edge densities are different for differently oriented substrates.
Application of a new analytical technique of electron distribution calculations to the profile simulation of a high sensitivity negative electron-beam resist
Authors: Glezos N. , Raptis I. , Tsoukalas D. , Hatzakis M.
Published: July 2002

An analytical model for the exposure of electron-beam sensitive resists is developed. A point beam incident on a multilayer substrate at a right angle is considered. The model uses the diffusion approximation to the Boltzmann transport equation as a starting point for a self-consistent calculation. Results are applied in the case of a new high sensitivity epoxy-based resist, and development patterns are effectively simulated using the analytical method.
Heterodimensional Schottky metal–two-dimensional electron gas interfaces
Authors: Gelmont B. L. , Peatman W. , Shur M.
Published: July 2002

This article presents the results of theoretical and experimental studies of the interface between a two-dimensional electron gas (2DEG) and a Schottky metal. Such an interface is an example of a new class of heterodimensional interfaces which have unusual properties with great potential for practical applications in ultrahigh speed and ultrahigh frequency devices. The unique features of such junctions include a very small effective cross section (equal to the product of the thickness of the 2DEG and the device width) leading to a small capacitance, a large breakdown voltage because of the electric field streamlines spreading in two dimensions near the metal–2DEG interface (and in three dimensions near the metal–1DEG interface) and very large electron mobility (especially at cryogenic temperatures) because of the modulation doping. Our capacitance–voltage (C–V) calculations for a 2D-Schottky junction are in good agreement with our experimental data. We also discuss the properties of other heterodimensional systems, including a one-dimensional electron gas–Schottky metal barrier contact which could be realized using advanced lithographic and etching techniques.
Role of energetic atoms and ions in Ta films grown by different physical vapor deposition methods
Authors: Roy R. A. , Catania P. , Saenger K. L. , Cuomo J. J. , Lossy R. L.
Published: July 2002

Tantalum film deposition is performed using a variety of energetic physical vapor deposition methods. The goal is to isolate the common factors in these processes that contribute to phase selection in the deposited Ta films. The techniques examined include bias-magnetron sputtering, ion-assisted evaporation, pulsed laser deposition, and cathodic arc deposition. The microstructure is primarily examined by x-ray diffraction, while resistivity and temperature coefficient of resistivity were determined using a four-point probe. Methods in which the depositing Ta atoms are energetic produce films with the highest fraction of the low resistivity bcc phase. The results further show that there is an optimum range of energetic ion and/or atom bombardment for stabilization of the low resistivity bcc phase. This is expressed in terms of momentum-per-Ta atom deposited during growth.
Amphoteric doping of Si in InAlAs/InGaAs/InP(311)A heterostructures grown by molecular-beam epitaxy
Authors: Li X. , Wang W. I. , Cho A. Y. , Sivco D. L.
Published: July 2002

High-quality InAlAs/InGaAs/InP modulation-doped field effect transistor (MODFET) structures were grown using silicon as an n-type dopant on the (311)A orientation for the first time by the planar-doping technique in molecular-beam epitaxy. An electron mobility as high as 50 000 cm2/V s with a sheet carrier concentration of 1.9×1012/cm2 at 77 K is achieved. MODFETs with 1.2 μm gate length exhibit an extrinsic transconductance of 400 mS/mm and a maximum drain current of 485 mA/mm. The results are comparable to that of MODFETs grown on (100) InP substrates. Our results point to the new possibility of making p–n multilayer structures with all-silicon doping.
Band offset determination in parabolic and triangular quantum wells of GaAs/AlGaAs and GaInAs/AlInAs
Authors: Kopf R. F. , Herman M. H. , Schnoes M. L. , Colvard C.
Published: July 2002

The band offset parameter Qc≡ΔEc/ΔEg for both GaAs/AlGaAs, and GaInAs/AlInAs (lattice matched to InP) was extracted from electron beam electroreflectance interband transition energies obtained from molecular-beam epitaxially grown parabolically and triangularly shaped quantum wells (QWs). Most of the QWs were grown using continuous analog grading. Additionally, for comparison, two 500 Å GaAs/AlGaAs, superlattice (digitally) graded, parabolic QWs, with bilayer thicknesses of 25 and 12.5 Å, were also evaluated. Qc values obtained were 0.661±0.015 and 0.650±0.005 for GaAs/AlGaAs and GaInAs/AlInAs, respectively. Measurements also revealed that Qc was both temperature and concentration independent.
Interface and relaxation properties of chemical beam epitaxy grown GaP/GaAs structures
Authors: Freundlich A. , Bensaoula A. , Bensaoula A. H. , Rossignol V.
Published: July 2002

In this work, the influence of phosphorus exposure on As-stabilized GaAs(100) surfaces over a temperature range between 500 and 580 °C is studied using a combination of reflection high-energy electron reflection (RHEED) and x-ray diffraction analysis. Through x-ray wave field analysis, it is found that 1 ML of GaP is formed during phosphorus exposure of an As-stabilized (2×4) GaAs surface. Furthermore, relaxation properties of GaP/GaAs(100) (3.8% lattice mismatch), grown by chemical beam epitaxy, are investigated using real-time RHEED oscillation analysis. Although RHEED analysis suggests that the GaP critical thickness, where the onset of relaxation occurs, increases at lower temperatures, x-ray diffraction data indicate a constant critical thickness of 5 ML in the temperature range covered in this study.
Structural and electrical properties of low temperature GaInAs
Authors: Metzger R. A. , Brown A. S. , McCray L. G. , Henige J. A.
Published: July 2002

GaInAs lattice matched to InP was grown by molecular-beam epitaxy over a temperature range of 100–450 °C and characterized by x-ray diffraction, resistivity, and secondary ion mass spectroscopy. X-ray diffraction analysis indicated the incorporation of excess As for samples grown below 250 °C. As-grown GaInAs was n-type, with electrical concentration increasing with decreasing growth temperature, ranging from 5×1014 cm−3 (450 °C) to 1.8×1017 (150 °C). Secondary ion mass spectroscopy indicated that this behavior was not due to the incorporation of background n-type dopants. Be- and Si-doped GaInAs at 5×1018 cm−3 showed full electrical activation for growth temperatures down to 260 °C, with only partial activation for Si and no activation for Be for growth temperatures below 260 °C.
Process control system for improved run-to-run control of molecular-beam epitaxial growth of GaAs/AlxGa1−xAs heterostructures
Authors: Robertson A. , Levkoff J. , Leiberich A. , Anyanwu V. , Moore J. , Lord H. A.
Published: July 2002

A system was developed that significantly improves the accuracy of molecular-beam epitaxial flux calibration and provides ±1.0% run-to-run control of film thickness as demonstrated by double-crystal x-ray diffraction analysis of 980 nm GaAs/AlAs Bragg reflector stacks. The system combines PC-based data acquisition and analysis of reflection high-energy electron diffraction (RHEED) wave forms and beam flux gauge signals with mechanical improvements in RHEED sample preparation and mounting. In developing this system, an extensive series of experiments were performed to determine the sources and magnitudes of error in RHEED flux measurements. Proper flux transient corrections, precisely centered 1 mm×1 mm RHEED slices, and improved signal processing and analysis of RHEED wave forms were found to significantly enhance run-to-run flux control.
Electron trapping in thin oxide on n-InP
Authors: Eftekhari G.
Published: July 2002

Electron trapping in anodized thin oxide on InP was studied using the flatband voltage method. Aluminum and gold were used as the contact metal. Three trap sites for aluminum contact and two trap sites for gold contact were obtained. Rapid thermal annealing (500 °C, 30 s) of oxide before metal evaporation caused reduction in trap density and capture cross section. Similar annealing of oxide after metal evaporation resulted in similar information except a new trap site is generated in the case of gold contact.
Selective dry etching in a high density plasma for 0.5 μm complementary metal–oxide–semiconductor technology
Authors: Givens J. , Geissler S. , Lee J. , Cain O. , Marks J. , Keswick P. , Cunningham C.
Published: July 2002

0.5 μm complementary metal–oxide–semiconductor structures were utilized to investigate the selective nature of a high density plasma reactor. The formation of borderless contacts and local interconnects by the selective etch stop film approach was discussed and shown to be affected by topography, planarization, and nonuniformities. A factorial design of experiments determined the optimum conditions of the selective oxide etch chemistry. The resulting etch chemistry was characterized by measurable quantities such as an oxide etch rate of 1200 nm/min, a patterned (0.5 μm image) etch-rate ratio for oxide:nitride ≳100:1 and 5%-3σ uniformity. And, finally, an integrated in situ oxide etch/resist strip/nitride etch was presented.
Atomic layer epitaxy deposition processes
Authors: Bedair S. M.
Published: July 2002

Atomic layer epitaxy (ALE) is emerging as a promising epitaxial growth technique for thickness control at the atomic level. The article outlines recent progress in ALE of III–V and Si thin films. Also models describing the self-limiting processes will be outlined.
Investigation of optical and electrical properties of ZnO ultrafine particle films prepared by direct current gas discharge activated reactive method
Authors: Zhao Dachun , Pan Xiaoren
Published: July 2002

The electrical and optical properties of ZnO ultrafine particle (UFP) films prepared by a new dc gas discharge activated reactive deposition technique were investigated. IR spectra and work function were used to study the samples. The results show that ln σ vs 1000/T accords with the Arrhenius equation at 227–300 °C, the absorption edge is near 480 nm, IR eigen absorption peaks of ZnO (UFP) films shift to high energy (short wavelength) with decreasing particle size. The work function changes with gas pressure was discussed.
50-nm x-ray lithography using synchrotron radiation
Authors: Chen Y. , Kupka R. K. , Rousseaux F. , Carcenac F. , Decanini D. , Ravet M. F. , Launois H.
Published: July 2002

A technology of proximity x-ray lithography has been developed to replicate patterns of sub-100-nm feature size using synchrotron radiation. Process modeling has been done in advance in order to optimize the mask absorber thickness. It is shown that with tungsten absorber, a 0.3 μm thickness is the most desirable for 50 nm linewidth processing. Masks compatible with a Karl Suss stepper have been fabricated using 50 keV electron-beam lithography and reactive ion etching techniques. As a result, well-defined 50-nm-wide isolated W lines and small gratings of period down to 100 nm have been fabricated. Then they have been replicated under proximity condition using Super ACO synchrotron radiation. We present details of a replication procedure with gap settings down to 5 μm and show how sub-100 nm structures can be 1:1 printed into both poly (methylmethacrylate) (PMMA) and (8.5%) MAA/PMMA resists. Finally, the results are analyzed in terms of a scaling rule to evaluate the resolution limit as a function of proximity gap using a synchrotron source.
25 nm chromium oxide lines by scanning tunneling lithography in air
Authors: Song H. J. , Rack M. J. , Abugharbieh K. , Lee S. Y. , Khan V. , Ferry D. K. , Allee D. R.
Published: July 2002

An ambient scanning tunneling microscope is used to oxidize a thin Cr film to different oxidation states depending on the exposure conditions. These oxidation states have shown very different chemical and physical properties and can be used as positive or negative masks for lithography. Chromium oxide lines down to 25 nm have been formed.