bluuebunny/crossref_metadata_2025 huggingface dataset:
The formation of the Schottky barrier at the V/Si interface
Authors: Clabes J. G. , Rubloff G. W. , Reihl B. , Purtell R. J. , Ho P. S. , Zartner A. , Himpsel F. J. , Eastman D. E.
Published: July 2002

Synchrotron radiation photoemission measurements have been used to study the behavior of the Schottky barrier height φbn and electronic structure of the V/Si interface for both cleaved Si(111)–(2×1) and sputter-cleaned Si(111)–(7×7) surfaces. Although the Schottky barrier height φbn of the clean surface is influenced by surface reconstruction (and by steps), the barrier becomes pinned at low (∠2 Å) V coverage at a position essentially independent of the initial clean surface structure. Formation of the bulk V metal band structure is not complete until ∠30–40 Å V coverage, indicating coverage-dependent structural effects in the growth of the metal film. These effects also seem to produce secondary influences on φbn , which are manifested as a gradual increase of φbn with higher coverage or mild (∠200 °C) annealing. However, upon higher temperature annealing (?350 °C) the trend reverses, with φbn decreasing to a value (∠0.64 eV) characteristic of the bulk VSi2 contact which is formed at 500–550 °C; this change in the behavior of φbn is directly correlated with the onset of atomic mixing across the interface.
Improvements in GaAs/plasma-deposited silicon nitride interface quality by predeposition GaAs surface treatment and postdeposition annealing
Authors: Clark Marion D. , Anderson C. Lawrence
Published: July 2002

Substantial improvements in the electrical properties of interfaces between n-type GaAs and Si3N4 formed by plasma-enhanced CVD have been obtained by in situ substrate surface treatment with a hydrogen plasma and postdeposition annealing. For samples with surface treatment and deposition performed at 300 °C, annealing at 600° for 30 min in N2 produced a dramatic reduction of capacitance frequency dispersion. Capacitance and conductance data indicate a major reduction of surface state density. Low-frequency C–V on an illuminated sample show evidence of surface inversion. AES composition profiles are presented as evidence that the hydrogen plasma treatment reduces native oxide on the GaAs.
Structural model of III–V compound semiconductor Schottky barriers
Authors: Lee B. W. , Wang D. C. , Ni R. K. , Xu G. , Rowe M.
Published: July 2002

Schottky barriers have been fabricated on n-type GaP(111) crystals to study the structural characteristics of the diodes. The formation of Schottky barriers by evaporating a metal layer onto the III–V compound semiconductor surface generally created an amorphous film interlayer between the metal and the semiconductor. Current–voltage (I–V), capacitance–voltage (C–V) and Auger electron spectroscopy (AES) data were used to characterize the interface amorphous film. A model of a resistor in parallel with a capacitor and then in series with the metal and the semiconductor layers is used to describe the properties of a real Schottky barrier. The thickness of the amorphous film is in the range 50–500 Å, dependent on evaporation details. The dielectric constant and the resistivity of the amorphous film are experimentally estimated, and are found to be frequency dependent. A metal-amorphous film–semiconductor (MAS) configuration is proposed to be the structural model for a real Schottky barrier. The structural model is combined with the defect model to explain the fundamental transition in interface electronic nature between covalent and ionic semiconductors as well as other properties of a real Schottky barrier.
Structural characterization of the interfacial reactions between palladium and gallium arsenide
Authors: Zeng Xian-Fu , Chung D. D. L.
Published: July 2002

X-ray diffraction was performed in situ at temperatures from 25–550 °C to investigate the process of compound formation at the interface between evaporated Pd thin films (∠1000 Å thick) and GaAs single crystals. For heating in 1 atm argon, the interfacial reactions occurred at temperatures above ∠250 °C—isothermal heating at 250 °C resulted in the appearance of PdGa and a small amount of Pd2Ga after 30–40 min; isothermal heating at 350 °C resulted in the appearance of Pd2Ga, PdGa, and PdAs2 after 15–20 min; isothermal heating at 500 °C resulted in the appearance of PdGa alone after ∠5 min. The PdAs2 phase was found to be a surface layer which could be removed mechanically by ultrasonic cleaning or by the use of an adhesive tape. Removal of PdAs2 was indicated by ex situ x-ray diffraction results, which showed the disappearance of the PdAs2 diffraction peaks and the enhancement of the PdGa peaks. For heating in vacuum (10−6 Torr), the interfacial reactions occurred at temperatures above ∠200 °C—the appearance of PdGa and a small amount of Pd2Ga was observed after ∠15 min of heating at 200 °C; PdAs2 was not observed at any temperature.
Influence of substrate temperature on electron mobility in normal and inverted single period modulation doped AlxGa1−xAs/GaAs heterojunctions
Authors: Drummond T. J. , Fischer R. , Miller P. , Morkoç H. , Cho A. Y.
Published: July 2002

Single period modulation doped AlxGa1−xAs/GaAs heterostructures were grown by molecular beam epitaxy using a substrate temperature range of 580–750 °C. Excellent surface morphologies were routinely obtained throughout the entire range of surface temperatures. The highest mobilities obtained for structures with the AlxGa1−xAs/GaAs on top of the GaAs were 9000, 133 000, and 282 000 cm2/V s at 300, 78, and 10 K, respectively. The sheet carrier concentration yielding the best electron mobility was about 8×1011 cm−2. While the mobilities were independent of substrate growth temperature between 600 and 675 °C, some degradation was observed outside this range. Structures with the GaAs on top of the AlxGa1−xAs showed mobilities as high as 35 400 cm2/V s at 10 K when grown near a substrate temperature of 720 °C. Mobility enhancement was not observed in samples grown at temperatures well below 700 °C.
Orientation relationships between thin films of Au, {100} substrates of GaAs, and their reaction products
Authors: Yoshiie T. , Bauer C. L.
Published: July 2002

Specimens have been prepared by deposition of thin films of gold on {100} substrates of gallium arsenide at 280 °C, annealed up to 30 min at 330 °C, and subsequently examined by transmission electron microscopy. During annealing, polycrystalline thin films of gold, measuring approximately 50 nm in thickness, are transformed into thicker monocrystalline square and/or rectangular patches of nearly pure gold, whose edges are aligned along 〈110〉 directions of gallium arsenide, by a process of hole formation in the gold film and subsequent rapid expansion by surface diffusion. Moreover, the nearly pure cubic phases of gold and gallium arsenide are separated by a hexagonal phase of gold–gallium, which assumes orientation relationships {111}Au∥{011̄0}Au–Ga, 〈110〉Au∥〈0001〉Au–Ga and {011̄0}Au–Ga∥{111}GaAs, 〈0001〉Au–Ga ∥〈110〉GaAs with gold and gallium arsenide, respectively. These relationships correspond to the Kurdjumov–Sachs orientation relationship between fcc and bcc structures, if it is assumed that the hexagonal gold–gallium phase can be represented by a modified bcc structure. This phase is believed to form by a process whereby gold reacts with gallium to form the hexagonal phase on {111} planes of both cubic phases and concomitant release of arsenic in the gaseous phase.
Schottky barrier formation at Pd, Pt, and Ni/Si(111) interfaces
Authors: Purtell R. , Hollinger G. , Rubloff G. W. , Ho P. S.
Published: July 2002

Synchrotron radiation photoemission measurements have been used to study Schottky barrier formation and the electronic structure of interfaces of Si with Pt, Pd, and Ni. High resolution photoemission spectroscopy of the Si 2p core levels has been used to monitor changes in band bending (or Schottky barrier height) when the metal is deposited on the Si surface. Barrier height measurements on sputter-cleaned (i.e., ion bombardment and subsequent annealing) and on heat-cleaned (i.e., annealing only) samples show no effect of the ion bombardment on the rate of change in barrier height with coverage. The Schottky barrier height reaches a saturation value within 1 Å metal coverage for Pt and Ni, but it requires ∼4.5 Å for Pd. For the Ni/Si interface, measurements of the valence electronic structure indicate that the Schottky barrier height is unrelated to the existence of a metallic character of the contact.
Measuring intensity distributions in electron beams by scanning Auger micrographing of a-Si:H
Authors: Schade H. , Hockings E. F.
Published: July 2002

Electron irradiation effects in thin films of hydrogenated amorphous silicon a-Si:H have been used to determine intensity distributions in electron beams as small as about 50 μm diameter. Films of a-Si:H undergo electron irradiation damage effects at relatively small energies (above 1 keV), and thus can be utilized as probes to record damage due to electrons of relatively low energy. The exposure of a-Si:H to electrons of a certain energy and dose results in a resistivity increase of the exposed volume. For undoped a-Si:H, this resistivity increase can be sufficient to cause electrical charging under a primary beam used for Auger excitation, which, in turn leads to an energy shift of the observed Auger transition. The magnitude of this energy shift increases with the dose of exposure, and is thus a measure of the intensity of irradiation. The ‘‘read out’’ of the damaged area and intensity ‘‘contours’’ are obtained from a sequence of scanning Auger micrographs taken for certain Auger transitions (the LMM Si transition, for example), at the nominal and at various shifted energies. The a-Si:H target probe retains the electron damage for extended periods of time, and thus the intensity information can be transferred between separate vacuum devices. Examples of various electron beam intensity distributions are given in the form of contours and intensity profiles.
Photoemission studies of the Au–InP(110) interface
Authors: Babalola I. A. , Petro W. G. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

We report new photoemission studies of the Au–InP (110) interface for both n- and p-type samples using synchrotron radiation in the energy range 80 to185 eV. By slowly increasing Au coverages and by studying core level structures and valence band spectra we have been able to differentiate between two coverage intervals. The lower coverage interval (θ<1 ML) is dominated by band bending with no measurable chemical changes and with a total measured Schottky barrier height of 0.6 eV. In the higher coverage interval (1<θ≤37 ML), we observed changes in the In 4d and P 2p core level shapes and a monotonic shift of the Au 4f to lower binding energies with increased Au coverage. Evidence of intermixing of Au with the P and In atoms indicates the formation of a nonabrupt interface. These results are at variance with the view that Au is a nonreactive metal on InP (110).
Erosion of polymer thin films during ion bombardment
Authors: Braun M. , Emmoth B. , Mladenov G. M. , Sätherblom H. E.
Published: July 2002

Thin films of photoresist material (PMMA and AZ 1450J) have been irradiated by H+ and He+ ions in the low MeV energy region. The composition and thickness of the irradiated layers were determined by RBS techniques. It was found that the composition of the PMMA layer is subject to a drastic change in the initial state of the ion bombardment. The erosion rates of the polymer materials were also measured and were found to vary between 100–20 000 atoms/incoming ion. This could not be explained by conventional sputtering theories. It is assumed that these high erosion rates and compositional changes are connected with the electronic losses of the bombarding ions, giving rise to a bond breaking phenomenon of the resist molecules.
Preparation of Pb–Bi film by alloy evaporation II. Microstructure and morphology
Authors: Huang H.-C. W. , Serrano C. M.
Published: July 2002

In a previous paper, techniques were developed to obtain hexagonal-close-packed (27–32 wt.% Bi) Pb–Bi alloy films by evaporating from an alloy source. For the work reported here, Pb–Bi films were prepared under various evaporation rates, substrate temperatures, and residual gas pressures with a goal to obtain smooth and fine-grained films. Contrary to what is generally expected, the grain size, as measured at room temperature after sample warm up, increased by a factor of 3 to 5 when the substrate temperature Ts was lowered from 273 to ∼180 K and below. Evidence to be presented suggests that although fine grains were obtained at low Ts, significant grain growth had occurred when the films were warmed from Ts<200 K to room temperature. Grain sizes of Pb–Bi films prepared at 77 K were reduced when the films were doped with H20 during deposition or seeded with 5–10 nm thick layers of Pb–Bi or O2-doped Pb. But no grain size reduction was observed for films doped with O2 at 77 K or seeded with Au or Pd at 273 K. The dependence of film morphology on composition, deposition rate, and substrate temperature were also investigated. For fine-grained Pb–Bi films prepared as described above, hillocks and/or holes were typically observed.
The molecular and atomic states of oxygen adsorbed on Rh(100): Adsorption
Authors: Fisher Galen B. , Schmieg Steven J.
Published: July 2002

The adsorption of oxygen at 100 K on Rh(100) has been studied with temperature-programmed desorption and photoelectron spectroscopy. Oxygen adsorbs with a sticking probability of about 0.8 up to a near saturation coverage of 1.1×1015 atoms/cm2 or three-fourths of a monolayer coverage on Rh(100). Initial adsorption is dissociative. However, for coverages above half a monolayer a low temperature molecular state, denoted α, which does not exhibit isotopic exchange, desorbs at 150 K. Dissociated oxygen recombines and desorbs in three high temperature or β states. At low coverages oxygen desorbs in a second order state, β3, between 1200 and 1325 K with an activation energy for desorption of 360 kJ/mole (85 kcal/mole). At coverages above half a monolayer, two first order states, β1 and β2, appear at 820 and 920 K, respectively. Their respective heats of desorption are 210 kJ/mole (50 kcal/mole) and 260 kJ/mole (62 kcal/mole). In contrast with previously reported results, no bulk diffusion of adsorbed oxygen atoms into Rh is observed for temperatures up to the onset of oxygen desorption.
Ion-beam deposition of Nb and Ta refractory superconducting films
Authors: Face D. W. , Ruggiero S. T. , Prober D. E.
Published: July 2002

A Kaufman ion-beam source has been used to sputter deposit high quality superconducting Nb (Tc=9.1 K) and Ta (Tc=4.3 K) films. Superconducting and electrical properties were studied as a function of deposition conditions and an optimum set of conditions was found. Nb films always had the bulk bcc crystal structure. The Nb film deposition rates ranged from 1 to 5 Å/s with a Xe or Ar sputtering gas pressure of ∼1 to 4×10−4 Torr and a beam current density of 5–20 mA/cm2. Values of Tc above 8.3 K for Nb films were obtained with the use of Xe rather than Ar gas. In the case of Ta films, the deposition of a thin (≥3 Å) Nb underlayer was required for the nucleation and growth of Ta in the bulk bcc crystal structure. Ta films deposited without a Nb underlayer always had high resistivity, ∼150 μΩ cm, and a tetragonal β-Ta crystal structure. The Nb and Ta targets and Si substrates all remained below 70 °C during deposition and the films were easily patterned by standard photoresist liftoff.
Modifications of intrinsic disorder in amorphous silicon
Authors: Pilione L. J. , Maley N. , Lustig N. , Lannin J. S.
Published: July 2002

Thin films of amorphous silicon prepared by a number of methods including rf diode sputtering, ion-beam sputtering, and CVD have been studied by Raman scattering and optical absorption measurements. Modifications of the structural order have been examined as a function of the deposition method as well as variations in the substrate temperature and bombardment conditions. The results indicate substantial changes in the Raman spectra that arise from changes in the phonon density of states with disorder in the amorphous network. Modification of the network disorder is attributed to changes in the width of the tetrahedral bond angle distribution which can be estimated from the width of the high frequency peak in the depolarized Raman spectra. While variations in the width of the bond angle distribution are small, they result in significant changes in the phonon density of states. The observation of a direct correspondence between the width of the high frequency peak in the Raman spectra and the optical band gap further indicates that near gap electronic states are also highly sensitive to variations in the structural order.
Rotational-shearing interferometric characterization of inertial fusion targets
Authors: Powers T. F. , Miller J. R.
Published: July 2002

Inertial fusion targets have strict requirements on sphericity, surface smoothness, and layer thickness uniformity. Interferometric characterization techniques have been extensively used to measure target quality. An imperfect target, which can be described as a superposition of defect components on a perfect shell, produces an interferogram with the defect and perfect shell components combined. Separation of the defect-produced components in a target interferogram from the concentric fringe pattern produced by a perfect target is often difficult and limits precise interpretation of the target defects. We have utilized the rotational symmetry of a perfect target to improve defect detection sensitivity by using rotational-shearing interferometry. One advantage of this approach is that rotationally symmetric objects are in phase, making only the nonrotationally symmetric defects visible. Another advantage is that shell nonconcentricity can be measured independently of shell thickness. We have developed a simple analytical model which describes the interferometer’s operation and constructed and tested a prototype device for fusion target characterization.
Band gap variation and lattice, surface, and interface ‘‘instabilities’’ in Hg1−xCdxTe and related compounds
Authors: Spicer W. E. , Silberman J. A. , Lindau I. , Chen A.-B. , Sher A. , Wilson J. A.
Published: July 2002

This paper brings into focus the differences between Hg1−xCdxTe (MCT) and ‘‘ordinary’’ semiconductors such as column 4, 3–5, and most 2–6 compounds. The key characteristic of MCT which makes it both different and of practical interest is the variation of band gap with composition (0 to 1.5 eV). This paper shows that this benefit is not without its difficulties. In particular, the same unusual characteristic of the Hg atomic states which leads to the advantageous movement of  band gap with composition weakens the bonding of Hg in the lattice. This bonding weakness exhibits itself in many ways in the characteristics of MCT, both at surfaces and interfaces and in the bulk. Because of this there is a potential instability associated with the surface or interface; however, this instability depends critically on the crystalline perfection of the MCT to depths far below the surface. The reason for this is defects move from the bulk to the surface (or in the opposite direction) with surprising ease—even at room temperature. As will be discussed in this paper, this is another result of the weakness of the Hg bonding in bulk MCT. In this matter of movement of defects from bulk to surface and vice versa, MCT differs greatly from the other 3–5 and elementary semiconductors studied in detail to date. This difference will be discussed in more detail in this paper. The extreme susceptibility of MCT to mechanical damage is also related to the weakness of the Hg bonding. One object of this paper is to make a first attempt at showing how the Hg bonding affects the electronic structure, lattice bonding, and defect structure of MCT. A key phenomenon in the electronic structure is the breakdown of the virtual crystal potential approximation which has worked to a good approximation in all other covalent semiconductors studied to date. This breakdown is selective and involves only those valence states near zone boundaries containing large cation s wave function admixtures. This again reflects the unusual character of the Hg atomic 6 s2 valence state. Thus, a focal point for understanding of the wide range of unusual phenomena in MCT developed in this paper is understanding of the Hg atomic structure and its effect on MCT electronic structure, bonding, defect formation, and related phenomena. This characteristic of Hg is common to elements with high atomic number and similar or related characteristics can be expected from semiconductor compound alloys containing such heavy atoms.
Transverse magnetoresistance and Hall effect in wide-gap, p-type Hg1−xMnxTe
Authors: Anderson J. R. , Johnson W. B. , Stone D. R.
Published: July 2002

A low frequency ac measuring-current technique has been used to investigate the magnetoresistance and Hall effect in Hg1−xMnxTe over a temperature range from 2 to 300 K. The exchange interaction between the Mn++ ions and the band carriers causes the energy bands to be significantly modified in the presence of a magnetic field. As a result magnetic boil-off and magnetic-field-enhanced hopping have been observed in p-type semiconducting samples. These effects produce a large decrease of resistance with increasing magnetic field at low temperatures.
(HgCd)Te–SiO2 interface structure
Authors: Wilson J. A. , Cotton V. A. , Silberman Joel , Laser D. , Spicer W. E. , Morgen P.
Published: July 2002

Low-temperature chemical vapor deposited (CVD) SiO2 has proven to be a very important material for use as a passivation on HgCdTe, principally because it combines a high resistivity and low-temperature application with excellent interface electronic structure. As previously reported, capacitance measurements show no frequency dispersion, and NSS minima below 1×1010 cm−2 eV−1 have been realized.1 We report here on an investigation of the composition and structure of the interface between PHOTOX■ SiO2 and HgCdTe. Wafers of zone melt HgCdTe, with x=0.3 and coated with PHOTOX■ SiO2, were analyzed with simultaneous Auger electron spectroscopy (AES) and Ne ion milling. The surface of the wafer was also studied with AES and surface ellipsometry before the SiO2 was deposited. Ellipsometry indicates the presence of a thin film on the HgCdTe due to the surface treatment, with thicknesses which vary between 10 and 20 Å from wafer to wafer. The AES measurements indicate a Te count rate similar to that in bulk HgCdTe, plus significant oxygen signal, indicating the thin film is predominantly Te-oxide. Sputter-Auger SiO2 on HgCdTe shows an interface region width of ∼50 Å. The dominant signals from this region are Si, O, and Te. The Te line shift indicates that an oxide is not present. We interpret this to indicate that the initial thin Te-oxide layer has been substatially reduced, leaving an interfacial layer of Si, Te, and O betwen the applied SiO2 and HgCdTe. The increase in NSS of interfaces formed on oxide-free HgCdTe indicate this interface layer is beneficial to device passivation.
Fine-grained base electrode process for Pb-alloy Josephson technology
Authors: Bright A. A. , Klepner S. P.
Published: July 2002

A method of producing fine-grained PbInAu thin films reported by Huang and co-workers has been evaluated for use in Josephson technology integrated circuits. Both junction-related and nonjunction characteristics of the base electrode layer were considered. It was found necessary to interchange the order of deposition of two of the layers in the vertical structure and to modify the homogenization step in the base electrode process. The fine grain size of the films was found to be due to the presence of a layer of AuIn2 precipitates which impede grain growth.
Latest developments in the growth of CdxHg1−xTe and CdTe–HgTe superlattices by molecular beam epitaxy
Authors: Faurie J. P. , Million A. , Boch R. , Tissot J. L.
Published: July 2002

We present here a general survey of our activity since 1981. We show that n- or p-type CdxHg1−xTe with low carrier concentration, high mobility and crystal perfection limited by the substrate itself can be grown by molecular beam epitaxy (MBE) between 180 and 210 °C onto CdTe(111) and (100) orientation. We report for the first time the characteristics of a photovoltaic device processed on a p-type CdxHg1−xTe MBE layer which proves that this material can be grown by MBE with a detection device specification. We also give some information concerning 100 periods of 224 Å CdTe–HgTe superlattice previously reported.
Atomic correlations during the first stages of epitaxy
Authors: Pimbley J. M. , Lu T.-M.
Published: July 2002

We have developed a new scheme to evaluate the atomic pair correlation function analytically and exactly for the combined overlayer and substrate system during the first stages of epitaxy. This function describes the morphology of growth on the atomic scale. The overlayer atoms can be a random lattice gas or islands with an arbitrary distribution of sizes. The atomic pair correlation function is particularly useful in calculating the widths and shapes of the intensity diffracted from epitaxially grown films using low energy or high energy electron diffraction (LEED or RHEED). We have carried out several realistic model calculations involving metal–metal and semiconductor–semiconductor epitaxy. The results are compared to the recent molecular beam epitaxy measurements of W/W(110) and Si/Si(111) reported by Henzler and co-workers.
Measurement of boron segregation at the SiO2/Si interface using SIMS
Authors: Morgan A. E. , Chen T-Y. J. , Reed D. A. , Baker J. E.
Published: July 2002

Quantification of SIMS to measure the segregation coefficient of boron at the SiO2/Si interface has been examined. Standard boron implants into SiO2, Si, and SiO2/Si have been used to derive calibration factors for the oxide, substrate, and interface regions, respectively. Differences between these factors can be minimized by ratioing the 11B+ and 30Si+ secondary ion counts and by using glancing incidence O+2 bombardment without oxygen backfill. A segregation coefficient of six is found for boron-doped Si(100) oxidized at 900 °C in 10 atm steam.
Comments on the composition of anodic films on Hg0.8Cd0.2Te
Authors: Seelmann-Eggebert M. , Brandt G. , Richter H. J.
Published: July 2002

The composition of anodic films on Hg0.8Cd0.2Te is reinvestigated and it is argued that the use of ion sputtering (e.g., as a depth profiling technique) significantly perturbs the chemical structure of these films within the probing depths of electron spectroscopy (AES and XPS). Evidence for this argument is given by a detailed study of HgTeO3 which is suggested as the dominant mercury constituent of anodic films on Hg1−xCdxTe. HgTeO3 was grown by a horizontal Bridgman method and obtained in a triclinic modification. Its XPS data were compared with those of electrochemically grown native oxide on HgTe. A very close correspondence between the two sets of XPS data was observed which implies that HgTeO3 is presumably the only major constituent of anodic films on HgTe. After exposure to ion sputtering (1–3 keV Ar ions) HgTeO3 and the anodic oxide on HgTe were found to exhibit a significant mercury depletion and a large accumulation of TeO2 (sputter artifact) in the XPS-probed surface and subsurface region. Taking this effect of the ion bombardment into account we re-examined previous quantitative XPS depth profiles of anodic films on Hg0.8Cd0.2Te and conclude that these films are mainly composed of HgTeO3 and CdTeO3.
Dual electron beam evaporator for the preparation of composition-modulated structures
Authors: Yang H. Q. , Wong H. K. , Zheng J. Q. , Ketterson J. B. , Hilliard J. E.
Published: July 2002

We describe the construction of an UHV evaporator with two electron beam guns and a heated substrate turntable which is used for the preparation of composition-modulated structures (CMS’s). Using a suitably controlled stepping motor, up to 20 different CMS’s can be prepared in the same run. The system has been used to deposit V/Fe CMS’s and preliminary structural measurements indicate the samples are of high quality.
Tribological properties of boron nitride synthesized by ion beam deposition
Authors: Miyoshi Kazuhisa , Buckley Donald H. , Spalvins Talivaldis
Published: July 2002

An investigation was conducted to examine the adhesion and friction behavior of boron nitride films (BN coating, 2 μm thick) on 440-C bearing stainless steel substrates. The thin films containing the boron nitride were synthesized using an ion beam extracted from a borazine (B3N3H6) plasma. Sliding friction experiments were conducted with BN in sliding contact with itself and various transition metals (Ti, Zr, V, Fe, Ni, Pd, Re, and Rh) at a sliding velocity of 3 mm/min with loads to 0.2 N at room temperature and in a vacuum of 30 nPa. The results of the investigation indicate that the surfaces of ion sputter cleaned BN coating film contain a small amount of oxides and carbides, in addition to boron nitride. The coefficients of friction for the BN in contact with metals have been correlated with the relative chemical activity of the metals. The more active the metal, the higher is the coefficient of friction. The adsorption of oxygen on ion sputter cleaned metal and BN increases the shear strength of the metal–BN contact and increases the friction. The friction for BN–BN contact is a function of the shear strength of the contacts. Ion sputter cleaned BN surfaces exhibit relatively strong interfacial adhesion and high friction. The presence of adsorbates such as adventitious carbon contaminants on the BN surfaces reduces the shear strength of the contact area. In contrast, chemically adsorbed oxygen enhances the shear strength of the BN–BN contact and increases the friction.
A computer model for postdeposition annealing of porous thin films
Authors: Müller Karl-Heinz
Published: July 2002

The changes that a porous thin film undergoes during annealing are studied by means of a two-dimensional computer simulation. The model allows a detailed investigation of thermally activated hopping processes, which result in the migration of excess vacancies and smaller voids quenched-in during film formation. To simulate fluctuations in vibrational energy, Boltzmann-ordered statistics are used. For thin gold film the coalescence of vacancies, their merging with preexisting voids, and the deterioration in adhesion due to the potential diffusion of vacancies to the film–substrate interface are predicted.
High pressure pumping speed measurement on sputter ion pumps
Authors: Audi M. , Pierini M.
Published: July 2002

Sputter ion pumps are nowadays available for operating at pressures up to 10−3 Torr. Problems arise when measuring pumping speed in the high pressure range (namely, 10−5–10−3 Torr) where the usual Fisher–Mommsen test dome is inapplicable. As a matter of fact assumptions on which it is based are not verified at such high pressures. In the present work a method is described for measuring pumping speeds in the high pressure range (10−6–10−3 Torr). Examples of application of this method to different pumps are given. Pumping speed plots are compared with the ones obtained with the Fisher–Mommsen test dome. In the 10−6–10−4 Torr range, where these two methods overlap, pumping speeds obtained by both methods are in fairly good agreement. By combining the two methods it is possible to characterize pumping speeds in the whole operating range.
Etch pit studies in CdTe crystals
Authors: Lu Y.-C. , Route R. K. , Elwell D. , Feigelson R. S.
Published: July 2002

Etch pit formation has been studied on (111)A, (111)B, and (100)CdTe surfaces using a nitric acid/potassium bichromate etch with varying Ag+ ion concentrations. The results can best be explained using an adsorption poisoning model originally proposed to explain etch pit formation in InSb, with modifications to take into account the higher ionicity of CdTe. Although the results were fairly reproducible, the etch pit density was consistently lower than that obtained with the Nakagawa etch. Aβ dislocation pits were seen for the first time in CdTe.
The magnetophonon effect: A tool for characterizing Hg1−xCdxTe
Authors: McClure S. W. , Seiler D. G. , Littler C. L. , Goodwin M. W.
Published: July 2002

We have investigated magnetophonon (MP) resonance oscillations in Hg1−xCdxTe at various temperatures for samples with x≂0.22 and x≂0.31 using magnetic field modulation and lock-in amplifier techniques. Analysis of the MP resonant field positions with a three band model allowed the determination of the fundamental energy gap Eg, the band-edge effective mass, and the effective g factor over a temperature range of 40 to 190 K. The x values were found by fitting the observed MP resonant magnetic field positions to calculated positions using the Hansen, Schmidt, and Casselman empirical relationship for Eg(x,T).
Growth and characterization of MBE grown HgTe–CdTe superlattices
Authors: Chow P. P. , Johnson D.
Published: July 2002

We report on the growth and characterization of the HgTe–CdTe superlattices. Their structural and optical characterization results are presented. The optical absorption characteristic of the superlattice and its temperature dependence are found to be different from the alloys.
A GaP decomposition source for producing a dimer phosphorus molecular beam free of gallium and tetramer phosphorus
Authors: Mondry M. J. , Caine E. J. , Kroemer H.
Published: July 2002

The complications arising in the molecular beam epitaxial growth of phosphides are reduced through the use of a diatomic phosphorus beam. We have fabricated a simple low-cost source for producing such a beam, suitable for a research environment.
Dopant depth distributions as a function of growth temperature in In-doped (100)Si grown by molecular beam epitaxy
Authors: Rockett A. , Barnett S. A. , Greene J. E. , Knall J. , Sundgren J.-E.
Published: July 2002

Indium, a deep acceptor in Si, was found, using secondary ion mass spectrometry (SIMS) and in situ Auger electron spectroscopy (AES), to segregate to the surface of (100) Si films grown by molecular beam epitaxy. The films were deposited at a rate of ∼1 μm h−1 with steady state In concentrations in bulk layers ranging from 1×1016 to 6×1017 cm−3. The amount of segregation-induced profile broadening ΔIn in (2×1)-(100) films was found from SIMS analyses to reach a maximum near a growth temperature Ts of 600 °C where ΔIn∼600 nm and to decrease at both higher and lower Ts values. ΔIn was less than the SIMS depth resolution for Ts>760 °C. Calculated In depth profiles, based upon a model which includes both thermodynamic segregation driving forces and kinetic rate limitations, were found to be in good agreement with experimental results. The shape of calculated profiles was determined primarily by a combination of the Ts-dependent In incorporation probability and the steady state ratio of the surface-to-bulk In fractions. Indium surface coverages θIn large enough to be observed by AES were obtained in layers grown under conditions corresponding to strong segregation. The surface structure of films with θIn≳0.1 was found to transform from the original (2×1) reconstruction to (3×4), as observed by in situ electron diffraction, due to the formation of an ordered In overlayer.
The role of hydrogen in the radical polymerization mechanism of hydrocarbons and chlorosilanes in a low pressure microwave plasma
Authors: Avni R. , Carmi U. , Inspektor A. , Rosenthal I.
Published: July 2002

The introduction of propylene (C3H6) or tetrachlorosilane (SiCl4) in concentrations of 3–10 vol.% into a microwave (2.45 GHz) plasma of Ar or mixtures of Ar+H2, at low pressures (1–10 Torr) and flow velocity in the range of 103 cm⋅s−1 results with the formation of solid carbon (pyrocarbon) or silicon, respectively. In the plasma state, both hydrocarbons and chlorosilanes, dissociate and polymerize to CxHy and SixCly forms with x>1 and x>y. It was found that polymerization process in the Ar (without H2) microwave plasma was mainly propagated by an ion–molecule mechanism, while additions of H2 (6–20 vol.%) to the Ar plasma propagates the polymerization mainly by a radical mechanism. The two mechanisms were determined by sampling the microwave plasmas with a quadrupole mass spectrometer (QMS), by indirect measurement of the plasmas free radicals concentration in an electron paramagnetic resonance (EPR) spectrometer and by measuring the deposition rate of pyrocarbon and silicon on substrates floated, grounded or biased to minus 100 V.
An ultrahigh vacuum multipurpose specimen chamber with sample introduction system for i
n s
i
t
u transmission electron microscopy investigations
Authors: Heinemann K. , Poppa H.
Published: July 2002

A commercial electron microscope with flat-plate upper pole piece configuration of the objective lens and top entry specimen introduction was modified to obtain 5×10−10 mbar pressure at the site of the specimen while maintaining the convenience of a specimen airlock system that allows operation in the 10−10 mbar range within 15 min after specimen change. The specimen chamber contains three wire evaporation sources, a specimen heater, and facilities for oxygen or hydrogen plasma treatment to clean as-introduced specimens. Evacuation is achieved by dual differential pumping, with fine entrance and exit apertures for the electron beam. With the microscope operating at 10−6 mbar, the first differential pumping stage features a high-speed cryopump operating at a stainless steel chamber that can be mildly baked and reaches 1×10−8 mbar. The second stage, containing the evaporation sources and a custom ionization gauge within 10 cm from the specimen, is a rigorously uncompromised all-metal UHV system that is bakable to above 200 °C throughout and is pumped with an 80 l ion pump. Design operating pressures and image quality (resolution of metal particles smaller than 1 nm in size) were achieved.
Unbalanced dc magnetrons as sources of high ion fluxes
Authors: Window B. , Savvides N.
Published: July 2002

We report the characteristics of a new design of magnetron sputter source (a UM-gun), based on the principle of an unbalanced magnetic design, and capable of giving ion fluxes at the substrate greater than the flux of depositing atoms. The dependencies of ion flux and self-bias potential at a typical substrate position for certain target materials (copper and silicon), gas pressures (0.25–5 Pa), gas compositions (Ar with O2, N2, and He), and sputtering power levels (up to 2 kW) have been measured for a particular UM-gun. The results show that such guns can be characterized approximately by an ion flux proportional to the discharge current and a constant self-bias potential.
The magnetic field influence on the photovoltaic effect in Mn alloyed semiconductors
Authors: Wong S. , Becla P.
Published: July 2002

Magnetophotoelectric properties of p-n junctions made in ternary HgMnTe and quaternary HgCdMnTe alloys are presented. The resistivity R0A and photovoltaic response were studied as a function of composition and magnetic field. The R0A product was shown to be dependent on the Mn concentration. Magnetophotovoltaic oscillations were used to determine interband transitions and fitted to an exchange-modified Pidgeon and Brown theory.
Magnetotransport measurements of p-type Hg1−xCdxTe based superlattices and heterojunctions
Authors: Woo K. C. , Rafol S. , Faurie J. P.
Published: July 2002

Magnetotransport measurements are made on p-type type III and type I Hg1−xCdxTe –CdTe superlattices and type III HgTe–Hg1−xCdxTe heterojunctions at high magnetic fields and low temperatures. Quantized Hall effects are observed in type III structures. The resistivity has strong magnetic field dependence in type I superlattices. In the HgTe–Hg1−xCdxTe heterojunctions the i=1 quantized Hall plateau is unusually wide. This can be explained by a magnetic field dependence of the hole concentration.
Nucleation and initial growth of In deposited on Si3N4 using low-energy (≤300 eV) accelerated beams in ultrahigh vacuum
Authors: Hasan M.-A. , Barnett S. A. , Sundgren J.-E. , Greene J. E.
Published: July 2002

Transmission electron microscopy has been used to investigate the nucleation and initial stages of growth of In deposited on Si3N4 from accelerated partially ionized beams in ultrahigh vacuum (UHV). The substrates were thin, electron transparent windows and the number density as well as the size and spatial distributions of the islands were determined as a function of ion energy and nominal film thicknesses t between 1.5 and 12 nm. A UHV-compatible ion source provided In beams in which, for these experiments, the ionized fraction was either 0%, 36%, or 42% and the acceleration energy E ranged from 150 to 300 eV. A quartz-crystal microbalance was used to estimate the amount of material lost by sputtering and to determine the net deposition rate. Comparing results obtained at nearly constant values of t, the use of accelerated beams was shown to alter the film nucleation kinetics leading to a progressive shift towards larger average island diameters with increasing E. The rate of secondary nucleation also decreased giving rise to much more uniform island size distributions in films grown from accelerated beams. These results are discussed in terms of ion-irradiation-induced dissociation of small clusters and enhanced adatom surface diffusion.
New oxidation state of tantalum oxide formed by reactive ion-beam cosputtering of Ta and Si
Authors: Morisaki H. , Masaki S. , Watanabe S.
Published: July 2002

Fabrication of composite films of SiO2 and Ta2O5 with various constituent combinations has been attempted on Si substrates by a reactive ion-beam sputter-deposition technique. The films have been studied by Auger electron spectroscopy, infrared absorption spectroscopy, and x-ray diffraction. Infrared absorption spectra of the composite films have shown that the absorption peak corresponding to the Ta–O stretching mode of Ta2O5 (650 cm−1) is strongly suppressed, and instead a new peak appears at 950 cm−1. New peaks have also been noted in x-ray diffraction from the composite films. According to the quantitative analysis of the Auger spectra, there has been no indication of silicide formation in the films. Crystallographic considerations have shown that a plausible oxidation state of the Ta–Si binary system is an oxy-salt composed of Ta cations and silicate anions rather than a simple mixture of SiO2 and Ta2O5 (a complex oxide). The apparent low dielectric constant of tantalum oxides sputter deposited on Si substrates has also been explained by this new oxidation state of the Ta–Si system formed in the initial stage of the sputtering.
Low-energy ion doping of GaAs
Authors: Cavalieri S. , Gaucherel Ph. , Monnom G. , Paparoditis C. , Roustan J. C.
Published: July 2002

In order to overcome several inconveniences associated with the conventional dopants (Si, Be) used in the binary and ternary III–V compounds obtained by molecular-beam epitaxy, we have developed a method of n-type doping with ionized sulfur at low energy levels (100–300 eV) based on the ionization of a H2S stream by electronic collisions. This also has a main advantage over the use of neutral species, of drastically diminishing the amount of sulfur in the vacuum chamber. Detailed results are reported on the doping concentration (up to 3×1018 cm−3) and corresponding electron mobility and degree of compensation, as a function of the ion current intensity, ion energy, substrate temperature Ts, and As/Ga flux ratio. Typically, at Ts=580 °C, measured transport properties are in all respects similar to those reported in layers doped with neutral species. At Ts=630 °C, the sticking coefficient for sulfur is 3 to 4 orders of magnitude higher than in the hitherto reported values. The means of characterization were Hall effect and infrared reflection spectroscopy. Finally, additional experiences and results are reported on the effect of ionized hydrogen on the electronic properties.
Evaporation characteristics of materials from an electron beam gun II
Authors: Graper Edward B.
Published: July 2002

The evaporation characteristics of Al2O3, As, B, Ba, BaCl2, BaF2, Be, BeO, Bi, B4C, Ca, CaF2, Cd, CdS, Co, Dy, Eu, Gd, Ge, In, Ir, KCl, KF, La, LaB6, Li, LiF, Mn, NaCl, NaF, Nd, Pd, Pt, Pr, Rh, Sc, Se, Sb, Sb2O3, Sr, S8, Ti, V, WO3, Yb, Y2O3, Zr, ZrO2 from an electron beam source are described. In addition, similar, previously published measurements of Ag, Al, Al2O3, Au, C, Cr, Fe, Inconel, Mo, Mg, MgF2, Nb, Ni, Pb, Si, SiO, SiO2, Sn, Ta, TiOx, W, and Zn have been expanded. The nonquantitative characteristics, melt type, stability, and tendency to spit, are reported, in addition to the evaporation rate, power, and pressure.
Characterization and removal of ion yield transients in the near surface region of secondary ion mass spectrometry depth profiles
Authors: Bryan S. R. , Linton R. W. , Griffis D. P.
Published: July 2002

A method for removing ion yield transients from the beginning of secondary ion mass spectrometry (SIMS) depth profiles is evaluated. Ion yield transients, which result from the concentration buildup of yield enhancing primary ion species, may be characterized by depth profiling standards which are bulk doped with the element of interest. The transients of B+ and B− in Si were characterized using an O+2 and Cs+ primary ion beam, respectively. The resulting transient correction functions were used to correct depth profiles of 10 and 4 keV B implants in Si.
Surface chemical analysis of polydiacetylene films exposed to electron beam and ultraviolet irradiation
Authors: Colton R. J. , DiLella D. , Mowery R. L. , Snow A. , Wandass J. H. , Marrian C. R. K.
Published: July 2002

We have investigated the properties and exposure chemistry of a soluble polydiacetylene film used as a negative electron beam resist. This paper summarizes a series of investigations of the chemical changes induced by electron beam and UV irradiation of poly[5,8-(bis-1,12-n-butylcarboxy–methylene–urethane) dodecadiyne], P4BCMU, and its monomer. The exposure induced chemical changes have been studied with a number of spectroscopic techniques including Fourier transform infrared spectroscopy for information on the pendant groups of the polydiacetylene backbone, resonance Raman scattering for details of the polymer backbone, and x-ray photoelectron spectroscopy for elemental and bonding information. Detailed spectroscopic studies indicate that the unsaturated carbon–carbon bonds in the polymer backbone are not destroyed by irradiation, but rather the main change occurs in the N–H and C=O (carbonyl) bonds of the urethane group.
Comparison of Au/GaAs Schottky contact properties modified by ion bombardment damage and mechanical polishing
Authors: Wang Y. G. , Ashok S.
Published: July 2002

A comparative study of the influence of crystal damage on the electrical properties of Au/GaAs Schottky barriers has been made with 10-keV Ar ion implantation and mechanical polishing, respectively. It has been found that the same trend in barrier height modification occurs for both cases, viz., a decrease in barrier height for n-GaAs and an increase for p-GaAs. This behavior is qualitatively similar to that in Si under ion bombardment damage and has been attributed to the generation of positively charged defect states in a shallow surface layer. However, in the case of GaAs, considerable carrier compensation effects are also in evidence, giving rise to large values of series resistance and shunt conductance arising from surface leakage. These results have implications in the formation of Ohmic contacts to GaAs and in the adaptation of ion-assisted processes for GaAs surface modification.