bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ characterization of thin film growth: Boron nitride on silicon
Authors: Fukarek W.
Published: July 2002

Real-time ellipsometry (RTE) in combination with particle flux measurement is applied to ion beam assisted deposition of boron nitride (BN) films. RTE is used as a tool for process diagnostic to improve the deposition stability. A novel technique for the determination of absolute density depth profiles from dynamic growth rate data and film forming particle flux is employed. From real-time cantilever curvature measurement and simultaneously recorded film thickness data instantaneous stress depth profiles are derived with a depth resolution in the nm range. The synergistic effects on the information obtained from RTE, particle flux, and cantilever bending data are demonstrated. The density of turbostratic BN (tBN) is found to increase slightly with film thickness while the compressive stress decreases, indicating an increasing quality and/or size of crystallites in the course of film growth. Refractive index and density depth profiles in cubic BN (cBN) films correspond perfectly to structural information obtained from dark field transmission electron microscope graphs. The established tBN/cBN two-layer model is found to be a crude approximation that has to be replaced by a three-layer model including nucleation, grain growth, and coalescence of cBN. The instantaneous compressive stress in a homogeneous tBN film is found to decrease, while the density increases during growth. The instantaneous compressive stress depth profiles in cBN films are more complex and not easy to understand but reliable information on the structural evolution during growth can be extracted.
100 nm gate hole openings for low voltage driving field emission display applications
Authors: Choi J. O. , Akinwande A. I. , Smith H. I.
Published: July 2002

A laser interference lithography (LIL) process has been developed for 100 nm gate hole openings of a Spindt-tip field emission cathode. A precursor structure of 200-nm-high and 100-nm-wide resist dots is made at every 200 nm square-grid center over a whole surface area of a substrate by using the LIL. The precursor is transferred to uniform arrays of chromium (Cr) gate holes by using a trilayer resist process. For pixellation of emitter tips, oxide via holes are formed through selected areas of the gate metal holes to prepare a real estate which is to be occupied by molybdenum (Mo) tip emitters. Emission current densities of 0.01 and 10 mA/cm2 have been obtained at gate bias voltages of 10 and 20 V, respectively, from the emitters with a packing density of 2.5×109 tips/cm2. These results suggest that cheaper and lower voltage driving electronics can be used for field emission displays by scaling the gate hole openings down to 100 nm. Manufacturing issues related to the trilayer resist process for the gate hole openings, parting layer deposition, and Mo-tip formation are discussed.
Molecular-beam epitaxy growth of InGaAs–InAlAs high electron mobility transistors with enhanced electron densities and measurement of InAlAs surface potential
Authors: Skuras E. , Pennelli G. , Long A. R. , Stanley C. R.
Published: July 2002

The electron densities in the channel of Si δ-doped InGaAs–InAlAs high electron mobility transistors grown on InP by molecular-beam epitaxy have been investigated by 1.4 K Shubnikov–de Haas (S–dH) measurements. Growth procedures have been developed that result in (i) minimized spreading of the Si δ doping, (ii) significantly improved transfer of electrons from the Si donors to the InGaAs channel, (iii) reduced parallel conduction associated with electrons remaining in the vicinity of the Si donors, and (iv) high sheet density-mobility products (nH×μH), important for a low access resistance into the channel. The Fermi energy of the free InAlAs surface has also been estimated by comparing self-consistent calculations of the channel electron density with the S–dH data from samples with progressively thinner InAlAs Schottky layers. The Fermi energy is found to be pinned at ∼0.6 eV below the conduction band edge, in agreement with the value deduced from photoreflectance spectrometry [J. S. Hwang, W. C. Hwang, Z. P. Yang, G. S. Chang, J. I. Chyi, and N. T. Yeh, Appl. Phys. Lett. 75, 2467 (1999)].
Low-energy carbon and nitrogen ion implantation in silicon
Authors: Barbadillo L. , Hernández M. J. , Cervera M. , Rodrı́guez P. , Piqueras J. , Muñoz-Yagüe A.
Published: July 2002

Silicon wafers have been implanted with C+, N+, and C++N+ ions at low energies to form buried insulating layers. Buried silicon nitride layers with Si or SiC small crystalline clusters were segregated after annealing at high temperature, leaving a high-crystalline-quality overlayer on top. In the samples implanted with C+ alone, after annealing, the silicon overlayer exhibits a lattice contraction of about 0.04%. In the N+-implanted samples this contraction is between 0.08% and 0.13%. The C++N+ implantation leads to relaxation of the lattice after annealing, with no reduction of the lattice constant.
Field-assisted metal-induced crystallization of amorphous silicon films
Authors: Khakifirooz Ali , Mohajerzadeh Shamsoddin , Haji Saber
Published: July 2002

The effect of an applied electric field during metal-induced lateral crystallization of a-Si is reported. Lateral growth of 300 μm is observed upon annealing the samples at 400 °C for 30 min while dc voltage of 100 V is applied between Ni silicide pads. The dependence of growth rate on the applied voltage is studied. The trapezoid test structure employed clearly reveals that the growth rate depends on the voltage applied rather than on the electric field intensity. In addition to field-enhanced diffusion of Ni atoms, which has been supposed to be responsible for the high growth rate, the role of the bombardment of Ni atoms by electrons flowing through the a-Si layer is considered.
High-voltage triode flat-panel display using field-emission nanotube-based thin films
Authors: Xu N. S. , Wu Z. S. , Deng S. Z. , Chen Jun
Published: July 2002

An experimental dismountable high-voltage field-emission display has been fabricated. It is used to demonstrate that gated structures may be adapted to the case where flat-film emitters are made of a carbon-nanotube–epoxy composite. Experiments have been carried out to study the field electron emission characteristics of the display unit and to optimize the structural parameters. Our findings indicate that it is very likely for one to produce a near-market prototype high-voltage field-emission display, if a more sophisticated fabrication and assembly technique is adapted.
Improved interface abruptness in pseudomorphic InGaAs/AlGaAs quantum wells with (411)A superflat interfaces grown by molecular beam epitaxy
Authors: Kitada Takahiro , Nii Keisuke , Hiraoka Tetsuya , Shimomura Satoshi , Hiyamizu Satoshi
Published: July 2002

Improved interface abruptness was achieved in pseudomorphic InxGa1−xAs/Al0.34Ga0.66As quantum wells (QWs) (x≃0.2) with extremely flat interfaces over a wafer-size area [(411)A superflat interfaces] grown on (411)A GaAs substrates by decreasing the substrate temperature Ts under a low V/III ratio during molecular beam epitaxy (MBE). Significant redshifts of low-temperature (12 K) photoluminescence (PL) peaks were observed for the (411)A and simultaneously grown (100) QWs with decreasing Ts because of the improved interface abruptness resulting from suppressed surface segregation of In atoms during MBE. Full widths at half maximum (FWHMs) of the PL peaks from the (411)A QWs grown at Ts=450–540 °C under the low V/III [As4/(Ga+In)] pressure ratio of 10 showed almost no dependence on Ts, and were 20%–30% smaller than the best PL FWHMs of the corresponding (100) QWs of this study, indicating that the (411)A InGaAs/AlGaAs superflat interfaces can be successfully formed even for the low Ts of 450 °C.
Phase boundary fluctuations on Si(111)
Authors: Hannon J. B. , Tromp R. M.
Published: July 2002

We have used low-energy electron microscopy to investigate the thermal fluctuation of phase boundaries separating 7×7 and 1×1 regions of the Si(111) surface near the phase transition temperature of 1135 K. We find that the fluctuations are described by a phase boundary stiffness of 180±30 meV/nm. Analysis of the meandering of the phase boundary is used to characterize the elastic repulsion between phase boundaries. Our estimate of the surface stress difference between the phases, 0.06±0.01 eV/Å2, is consistent with the measurement of Twesten and Gibson [R. D. Twesten and J. M. Gibson, Phys. Rev. B 50, 17628 (1994)].
Preferential resputtering phenomenon on the surface of (100)-oriented Ni–Pt films: Effect of substrate bias during sputter deposition
Authors: Shi J. , Zhou R. , Hashimoto M.
Published: July 2002

Effects of substrate bias during sputter deposition on the structure and composition of Ni–Pt/MgO(100) films were investigated. Ni–Pt films deposited at 220 °C are composed of a Ni–Pt substitutional solid solution of face-centered cubic structure. All the films are single crystalline with identical crystallographic orientation with the substrate, regardless of the substrate bias. However, the composition of the films was significantly affected by the substrate bias: Pt content increased with increasing the substrate bias within the investigated range. This phenomenon is explained in terms of the preferential resputtering of Ni by impinging ions and neutrals generated by the substrate bias. Furthermore, the crystallinity of the films was also affected by the substrate bias.
Fabrication of single and coupled quantum dots in single-wall carbon nanotubes
Authors: Suzuki Masaki , Ishibashi Koji , Ida Tetsuya , Tsuya Daiju , Toratani Kenichirou , Aoyagi Yoshinobu
Published: July 2002

We describe our recent experimental results on the fabrication of single and coupled quantum dots in single-wall carbon nanotubes (SWNTs). As well as our standard method to fabricate electrical contacts on individual SWNTs, an attempt to position them at a desired place is described. For the coupled quantum dot formation a SiO2 layer has been deposited on top of SWNTs, and the transport result which suggests their formation is shown.
Dual exposure glass layer suspended structures: A simplified fabrication process for suspended nanostructures on planar substrates
Authors: Tanenbaum D. M. , Olkhovets A. , Sekaric L.
Published: July 2002

We have developed and demonstrated here a simplified flexible fabrication process for glass nanomechanical systems. This process uses a single layer of spin on glass (SOG) material with two negative tone electron beam exposures at two different exposure energies to define the suspended and support structures, respectively. After development the SOG can be converted into glass. The process is additive and can be applied to any flat substrate. We have fabricated a variety of glass nanomechanical oscillators and measured their mechanical resonances using a mechanical piezoelectric driving force and optical interferometric detection. Suspended structures were fabricated with thickness of less than 50 nm and lateral dimensions of less than 100 nm supported anywhere from 150 to 800 nm above the substrate. Resonance frequencies for glass wires with both ends fixed (cross section 110 nm×180 nm) and lengths of 4–9 μm range from 7 to 30 MHz, with quality (Q) factors of over 1000. Annealing the structures in an oxygen ambient roughly doubles both the frequencies and the Q factors.
Step and flash imprint lithography: Defect analysis
Authors: Bailey T. , Smith B. , Choi B. J. , Colburn M. , Meissl M. , Sreenivasan S. V. , Ekerdt J. G. , Willson C. G.
Published: July 2002

Step and flash imprint lithography (SFIL) is a promising, low cost alternative to projection printing. This technique has demonstrated very high resolution and overlay alignment capabilities, but it is a contact printing technique so there is concern about defect generation and propagation. A series of experiments has been carried out with the goal of quantifying the effect of defect propagation. To that end, each unit process in SFIL was studied independently. The number of particles added during handling and transportation and due to SFIL machinery was deemed acceptable, and the added particles should not complicate the inspection of process defects. The concept of a “self-cleaning” process in which the imprint template becomes cleaner by imprinting was revisited. Inspection of an imprint template before and after imprinting revealed that the template actually becomes cleaner with imprinting. Visual inspection of multiple imprints did not reveal any systematic generation or propagation of defects. The inspection area used in this study was limited, however, since the inspection was both manual and visual. Imprinting for this defect study was performed at the University of Texas in a Class 10 cleanroom, and inspection was performed at International SEMATECH.
Incorporation of helium-implant-induced cavities near the active regions of metal–oxide–semiconductor devices: Effects on dc electrical characteristics
Authors: Terry J. , Haworth L. I. , Gundlach A. M. , Stevenson J. T. M. , Vishnyakov V. M. , Donnelly S. E.
Published: July 2002

Cavities, formed by helium implantation and subsequent annealing, have proved to be effective at trapping metal impurities within silicon. This has led to interest in their use as proximity gettering sites. In this investigation, cavity populations were formed by helium implants of energy 40 keV and dose 5×1016 cm−2 followed by annealing at 900 °C. This regime produces cavities with a mean void radius of 20 nm, located between 100 and 350 nm below the silicon surface. The effect of the presence of such cavities near the active areas of 1.2 μm p-type metal–oxide–semiconductor field-effect transistor devices is described. Electrical characterization of wafers, which have been implanted with helium on the front or rear silicon surface, has been carried out to determine whether the inclusion of void populations near the active regions of silicon devices is detrimental. These measurements found no evidence of any detrimental effect on the performance of working devices.
Photoluminescence of GaSb self-assembled quantum dot layers grown by metalorganic chemical vapor deposition
Authors: Motlan  , Goldys E. M. , Dao L V.
Published: July 2002

We report results of photoluminescence (PL) of GaSb self-assembled quantum dots grown by metalorganic chemical vapor deposition on GaAs substrates. We examined the emission from dots with average height of (5±0.3) nm, width of (38±2) nm, and density of 1.3×1010 cm−2. We found the PL emission from quantum dots at 1.08 eV and from the wetting layer at 1.40 eV. The quantum dot peak energy is almost constant in the temperature range of 10–80 K suggesting that the interdot tunneling effects are insignificant. The emission from quantum dots is thermally more stable than the wetting layer emission. The results are in agreement with those commonly reported for molecular beam epitaxy grown samples.
Properties of combined TiN and Pt thin films applied to gas sensing
Authors: Åbom A. Elisabeth , Hultman Lars , Eriksson Mats , Twesten Ray D.
Published: July 2002

TiN was introduced as a part of the sensing layer of gas sensitive metal–insulator–semiconductor (MIS) devices. Three types of metallic gate layer structures deposited by magnetron sputtering were investigated: TiN, a double layer with Pt on top of TiN, and two-phase Pt-TiN films formed by co-sputtering. The homogeneity of the co-sputtered layer was strongly dependent on the substrate temperature during film growth, with segregation of Pt as a result of high temperature deposition. During the deposition conditions in this work, Pt and TiN appear to be immiscible, resulting in growth of films consisting of the two phases. Furthermore, surface oxidation of TiN and enhanced oxidation of TiN at the grain boundaries to Pt in both the as-deposited films after exposure to atmosphere at room temperature and the films subjected to MIS device processing and to gas response analyses at a temperature of 140 °C resulted in a three-phase TiN–TiOx–Pt system. A segregation of Pt to the growth surface was observed during co-sputtering at 900 °C, but not at 400 °C. The gas response to hydrogen, ammonia, propene, and acetaldehyde was measured and it was found that devices containing Pt were sensitive to all test gases. Devices with pure TiN, showed no response to any of the test gases, and the implication of that result, on the gas response mechanisms, particularly for ammonia, is discussed.
Etching method for fabricating ultracompact three-dimensional monolithic microwave integrated circuits
Authors: Sugitani Suehiro , Onodera Kiyomitsu , Aoyama Shinji , Hirano Makoto , Tokumitsu Masami
Published: July 2002

A sophisticated three-dimensional (3D) interconnection structure for ultracompact 3D monolithic microwave integrated circuits (MMICs) has been successfully fabricated by using inductively coupled-plasma etching with a double-layer mask consisting of WSi covered with a Si-containing photoresist. The developed etching method enables us to form via holes to any levels of interconnection simultaneously. The field-effect transistor (FET) parameters change little when the 10-μm-thick polyimide layer is stacked on metal–semiconductor FETs. A unique inductor with a vertical structure is also fabricated by this new etching method. This method will thus result in smaller chip area, higher performance, and greater design flexibility in MMICs.
Surface and interface characterization of GaN/AlGaN high electron mobility transistor structures by x-ray and atomic force microscopy
Authors: Torabi A. , Ericson P. , Yarranton E. J. , Hoke W. E.
Published: July 2002

We report on the characterization of GaN/AlGaN high electron mobility transistor (HEMT) structures grown by molecular beam epitaxy and metal-organic chemical vapor deposition techniques on semi-insulating SiC substrates. We have exploited the surface and interface sensitivity of the grazing incidence x-ray reflectivity (GIXA) technique and combined it with atomic force microscopy (AFM) and x-ray diffraction to obtain an accurate evaluation of the surfaces and channel interfaces for HEMT structures. The presence of smooth interfaces is responsible for the observation of intensity oscillation in GIXA, which is well correlated to step flow observation in AFM images of the surface. While GIXA provides a macroscopic average of the surface and interface roughness, the AFM provides us with a microscopic view of surface roughness. Further, the x-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AlGaN layer. The capacitance–voltage (C–V) technique is used to determine the electrical properties of two-dimensional electron gas depth and hence the AlGaN layer thickness. The C–V results are in good agreement with the x-ray data.
Mass Spectrometry of Background Gases in Glow-Discharge Sputtering of Tantalum Thin Films
Authors: Sosniak J.
Published: July 2002

The composition of the ambient atmosphere during the sputtering of tantalum films in argon glow discharges has been studied by means of a mass spectrometer adapted both for residual analysis of vacua between 10−9−10−5 Torr, and process monitoring at pressures of (10−50)×10−5 Torr. The partial pressures of a number of residuals were found to increase immediately upon initiation of the discharge in both an oil diffusion and a turbomolecular pump system. The total background gas levels during the discharge were in the 1×10−5−5×10−4 Torr range, with the major component being hydrogen, and smaller contributions from water vapor and methane. The pressure increase of these species resulted from ion bombardment decomposition of adsorbed surface layers, and exhibited two maxima. The first is attributed to desorption from the electrodes, and the second to desorption from the bell jar wall.

The spectrometer was used for detailed studies of the gettering of deliberate additions of N2, CH4 and H2 during sputtering in argon. Considerable differences were found in the effect of the glow discharge on those gases, with the gettering of CH4 and H2 exhibiting a complex time dependence. Tantalum films sputtered without deliberate gas additions, were found to be of the beta-tantalum form even when the discharge-generated background was reduced to ∼1×10−6 Torr by long presputtering.
Resistivity and Structure of Cr–SiO Cermet Films
Authors: Glang R. , Holmwood R. A. , Herd S. R.
Published: July 2002

The structure, resistivity, and temperature coefficient of resistance (TCR) of Cr-SiO films with controlled compositions from 0 to 50 at. % SiO have been investigated. Randomly disordered films condense at −196 °C. Higher temperatures introduce varying degrees of order accompanied by disproportionation of SiO and reaction with Cr. This leads to nonhomogeneous structures consisting of amorphous SiO2 and Cr–Si phases according to the binary diagram. Metallic particles of α-Cr and Cr3Si, with either little or no long-range order or at the most partially crystalline, provide conductivity which decreases with increasing SiO2 concentration. The resistance decreases during annealing are proportional to the Cr3Si concentration over a wide composition range. The TCR's of highly disordered films are negative and shift toward positive values upon annealing. Their interpretation requires metallic and thermally activated conduction mechanisms in parallel. The resistivity and TCR changes during annealing are attributed to recrystallization and bridging between islands.
Preparation and Properties of Unsupported Positive Coefficient Thin Thermistor Films
Authors: Mendelsohn L. I. , Orth E. D. , Curran R. E.
Published: July 2002

Thermistor films 5–25 μ in thickness were sputtered onto a pyrolytic graphite substrate from a lanthanum-doped barium–strontium–titanate (Ba0.600Sr0.397La0.003TiO3) cathode. Heating of the film and substrate from 500 ° to 850 °C in air will separate it from the substrate. The free-films can then be supported on a pure barium-titanate setter-plate, and fired subsequently at 1400 °C in argon and cooled in oxygen to achieve a temperature coefficient of resistance of at least +6%/ °C at 25 °C. If flexible graphite tape is used as a substrate, sputtered films up to 25 μ in thickness can be prepared.
Unipotential lens with electron-transparent electrodes
Authors: Wittels N. D.
Published: July 2002

This paper reports results of the first test of a unipotential electron lens whose end electrodes are electron-transparent foils. This lens is unusual among electrostatic unipotential lenses in that it can have negative values for both its focal length and third-order spherical aberration coefficient. Preliminary measurements of these quantities have been made on a foil lens and are compared with theoretical values. Some of the practical limitations in using foils as lens elements are considered, and a potential use for this lens as part of a spherical aberration corrected doublet is discussed.
Helium release from various metals
Authors: Cost J. R. , Hickman R. G.
Published: July 2002

The metals aluminum, iron, nickel, and types 304 and 316 stainless steel have been doped with helium by allowing dissolved tritium to undergo radioactive decay. Helium concentrations below 1 atomic ppm were produced. Using high−sensitivity, mass−spectrometer techniques, helium release has been observed during isochronal and isothermal anneals. At least two release mechanisms are obvious, their respective gas releases occurring at widely separated temperatures.
Optical properties of thin Au−Cr films and their application to solar energy conversion
Authors: Fuschillo N. , Lalevic B. , Slusark W. , Delahoy A.
Published: July 2002

Opaque Au and Au−Cr films were produced by rf triode sputtering onto a glass substrate at 150°C. Cosputtering of Au and Cr films has extended the solubility limits of Cr in Au from 19 at.% Cr to 48 at.% Cr. Electron microscopy showed polycrystallinity in the entire solubility range and electron microprobe analysis confirmed compositional uniformity of films. Reflectance measurements were made in the range 0.3−15 μ. Reflectance data were analyzed by the Kramers−Kronig method to obtain the optical constants n, k, ε1, and ε2. Good agreement is shown with the previous single crystal data on Au−Cr (up to 19 at.% Cr). The reflectance data are used to calculate α/ε ratio which is applied to the solar energy collector surfaces. Reflectance and transmittance data for very thin Au and Au−Cr films (100−400 Å) are used to calculate the figures of merit for the heat mirror type solar−thermal energy collector design.
Potential optical uses of aggregated metal films
Authors: Tokarsky R. W. , Marton J. P.
Published: July 2002

The Maxwell−Garnett effect is analyzed with the view of utilizing the optical phenomena associated with aggregated metal films for practical purposes. The basic equations are summarized and parameters pertinent to controlling the absorption and resonance wavelength are discussed. Examples are shown and potential uses are proposed.
Polycrystalline silicon layers for solar cells
Authors: Chu T. L.
Published: July 2002

Silicon layers on foreign substrates have been used for various device applications during the past fifteen years. The substrate requirements, the deposition techniques, and the characterization of properties of silicon layers are briefly reviewed. Polycrystalline silicon layers deposited on low-cost substrates is a promising material for the fabrication of low-cost solar cells. In this work, the thermal decomposition of silane and appropriate dopants has been used to deposit polycrystalline silicon layers containing a shallow p–n junction on steel, graphite, and metallurgical-grade silicon substrates. When steel was used as a substrate, a borosilicate interlayer was used as a diffusion barrier to eliminate the formation or iron silicides. Silicon deposited on borosilicate/steel substrates exhibited poor microstructure, and the solar cells had low conversion efficiencies. Silicon deposited on graphite substrates showed considerably better microstructure, and conversion efficiencies of up to 1.5% have been obtained. Silicon deposited on metallurgical-grade silicon was found to be epitaxial with respect to the substrate, and conversion efficiencies of up to 2.5% have been obtained.
Abstract: (D, T) neutron radioactive sputtering yields
Authors: Thomas M. T. , Harling O. K. , Brodzinski R. L. , Rancitelli L. A.
Published: July 2002

(D, T) neutrons have sufficient kinetic energy for various nuclear reactions such as (n,α), (n,p), and (n,2n) to occur. A series of experiments have been performed using a 14.8 MeV (d, t) neutron source in which the radioactive daughters ejected from the near surface region of the target material have been collected and measured. The geometry of the experimental arrangement was such that radioactive daughters ejected in the forward direction (neutron current direction) and backward direction were collected. For example, the forward radioactive sputtering ratio for 92mNb produced by the 93Nb(n,2n) reaction from cold-worked niobium foil is (1.06±0.06) 10−7 radioactive atoms/neutron, and the backward sputtering ratio for 92mNb is (7.58±1.09)10−10 atoms/neutron. For annealed gold the forward sputtering ratio for 196Au produced by the 197Au(n, 2n) reaction is (1.05±0.06)10−7 atoms/neutron, and the backward sputtering ratio for 196Au is (2.83±0.09)10−9 atoms/neutron. These sputtering ratios are the slopes of measured yields versus measured fluence curves and are obtained by a linear least-squares fit to the data. The quoted errors are the standard deviations calculated by the linear regression routine. Figure 1 is a bar graph summary of the forward radioactive sputtering ratios obtained for a large variety of metals and also for 316 stainless steel. The graph includes the reaction producing the radioactive recoil and the half-life of the radioactive daughter. It can be seen that the sputtering ratio for all of the materials studied range from the mid-10−8 to mid-10−7 atoms/neutron range. We have not observed any statistical differences in the radioactive sputtering ratios between annealed and cold worked niobium or between annealed and cold worked 316 stainless steel.

In addition, it is possible to determine an effective emission range of the radioactive recoil. Since the metal targets used in the experiments are thicker than heavy-ion ranges in metals, an effective emission range can be defined simply as the product of the ratio of the number of radioactive recoil atoms on the collector to the number of recoil atoms in the target and the thickness of the foil. As an example, the forward effective range of the 92mNb recoil ion in niobium is 410 Å, while the backward effective range is only about 3 Å. For such small ranges, elemental surface and near surface composition such as oxide and carbide layers may produce errors in the results because of uncertainties in the parent atom density. Complete details of this experiment and data analysis are being submitted to Physical Review or the Journal of Applied Physics.
Electronic structure of nonpolar surfaces of II–VI compounds
Authors: Calandra C. , Santoro G.
Published: July 2002

The nature of surface states in cleaved surfaces of II–VI compounds with zincblende structure is studied. The tight-binding method is used to calculate the electronic structure of a layer of twelve (110) planes. The results show various surface bands both in the gap and in empty lenses of the projected bulk band structure. The nature of these states is discussed and a comparison with the available experiments is presented. The results support the model of ionic surface states previously proposed for these surfaces.
Effect of minority-carrier injection on Schottky-barrier heights that approach the semiconductor band gap
Authors: Huang C. H. , Crowell C. R.
Published: July 2002

A guideline for interpretation of capacitive and photothreshold Schottky-barrier energies has been set forth for metal–semiconductor systems which have barrier energies approaching or exceeding the band gap energy. For such systems the measured apparent barrier energies are always less than the true barrier energy if minority-carrier injection controls the incremental field at the interface. For very strong inversion the apparent barrier energy reaches a maximum value independent of the true degree of inversion. However, when the electric field penetration into the metal dominates over the effect of minority-carrier injection, the capacitively measured apparent barrier energies are greater than the true barrier energy and can be greater than the band gap energy without true surface inversion. An approximate universal relationship between the apparent and the true barrier energies has been found for Schottky barriers with a minority-carrier effective density of states Nv greater than 100× the dopant concentration Ns. Then we know the true barrier energy only when the observed capacitive barrier energy is more than one kT from the maximum possible apparent barrier energy predicted by the relationship for a given Nv/Ns. When Nv?100Ns, characterization of C–V data for Schottky barriers requires individual calculations of the detailed relationship between the apparent and the true barrier energies. Existing C–V data for barrier energies close to the band gap energies were interpreted: (1) true barrier energies of the Au–n-GaSb barrier measured by Mead and Spitzer are less than 26 meV greater than 0.61 eV at 298 K and there is no correction for the reported barrier energy, 0.75 eV, at 77 K, (2) bearing in mind all the existing data for Au–p-InAs Schottky barriers we suggest the true barrier energy should be specified as 470±20 meV in the temperature range 4.2 K to 77 K, (3) there appears to be no surface inversion under operating conditions for the Pb–p-PbTe and Sn–p-PbTe Schottky barriers measured at 77 K by Walpole and Nill, despite the fact that the apparent C–V barrier energy for the Sn–p-PBTe barrier exceeds the band gap energy. Finally we have shown that in the presence of strong minority-carrier injection the observed photothreshold barrier energy is greater the greater the applied bias or the higher the dopant concentration, contrary to the tendency expected by the effect of image force alone.
Factors which maximize the efficiency of Cr–p-Si Schottky (MIS) solar cells
Authors: Anderson W. A. , Vernon S. M. , Delahoy A. E. , Kim J. K. , Mathe P.
Published: July 2002

Processing steps used in fabricating silicon Schottky solar cells have been evaluated to optimize energy conversion efficiency. Factors such as wafer resistivity and orientation, etching, oxide growth, heat treatment, depostiion technique, and grid design are included in the study. The proper heat treatment and metal deposition rate are most crucial in achieving a high open-circuit voltage. The process has produced a solar cell with Voc=0.55 V, fill factor of 0.71, and 8.6% AM1 efficiency with a potential improvement to 12.5%.
Sputtering of polycrystalline InP on CdS and other substrates
Authors: Kaminow I. P. , Stulz L. W. , Standley R. D.
Published: July 2002

Rf sputtering at elevated temperatures was employed to grow polycrystalline layers of InP on various substrates including silica, graphite, and crystalline CdS and InP. Grain sizes were generally less than one μm in diameter so that, as now made, these films are probably not suitable for solar cell applications.
Electrical properties of the Si–SiO2 interface and its influence on device performance and stability
Authors: Nicollian E. H.
Published: July 2002

The two electrically active centers at the Si–SiO2 interface which can influence the performance and stability of MOSFET’s and bipolar transistors used in integrated circuits are interface traps and fixed charges. This paper is a brief review of the properties of interface traps and fixed charge, how these electrically active centers affect silicon device characteristics, and the largely empirical methods used to control the densities of these centers. These methods have been so successful that interface traps and fixed charge show no performance and stability problems in many types of integrated circuits.
Microfabrication in LiNbO3 by ion-bombardment-enhanced etching
Authors: Kawabe M. , Kubota M. , Masuda K. , Namba S.
Published: July 2002

Ion-bombardment-enhanced etching is suggested as an useful microfabrication technique for LiNbO3. Diluted HF was found to be a good selective etchant for a layer damaged by Ar+ and N+. This method is compared with another microfabrication method, ion beam etching. The accuracy of the pattern width by this method is better than that ion beam etching and the slope of the grooved wall is very steep. The etched depths of the layer damaged by 60-keV Ar+ at the dose of 3×1015/cm2 and N+ at the dose of 2×1016/cm2 are 70 and 145 nm, respectively. The depth is controllable by changing the ion energy and dose.
Optical and electrical properties of ion-beam-textured Kapton and Teflon
Authors: Mirtich Michael J. , Sovey James S.
Published: July 2002

An electron bombardment argon ion source was used to ion etch polyimide (Kapton) and fluorinated ethylene propylene, FEP (Teflon). Samples of polyimide and FEP were exposed to 0.5–1.0-keV Ar ions at ion current densities of 1.0–1.8 mA/cm2 for various exposure times. Changes in the optical and electrical properties of the samples were used to characterize the exposure. Spectral reflectance and transmitance measurements were made between 0.33 and 2.6 μm using an integrating sphere after each exposure. From these measurements, values of solar absorptance were obtained. Total emittance measurements were also recorded for some samples. Surface resitivity was used to determine changes in the electrical conductivity of the etched samples. A scanning electron microscope was used to record surface structure after exposure. Presented in the paper are spectral optical data, resistivity measurements, calculated absorptance and emittance measurements, along with photomicrographs of the surface for the various exposures to Ar ions.
Control of pattern dimensions in electron lithography
Authors: Sewell H.
Published: July 2002

In electron lithographic processes pattern dimensions are distorted by ’’proximity’’ and ’’size’’ effects due to the action of backscattered electrons. This presents the mask designer with the problem of controlling these dimensions during the mask fabrication process so that the required patterns can be produced on the final substrate. This paper describes the processing of a resolution pattern, minimum geometry 0.5 μm, as it passes through the various stages of mask fabrication to the final stage where it is replicated in an electron image projector. The results show the pattern changes that take place, first at the electron-beam pattern generation stage, second at the mask etching stage, and third at the mask projection stage.
Preferential sputtering in oxides as metals and revealed by x-ray photoelectron spectroscopy
Authors: McIntyre N. S. , Stanchell F. W.
Published: July 2002

The surface film on an oxidized multicomponent alloy usually contains a number of metallic and oxidized phases. During depth-profile analysis, such metal and oxide phases can be differentiated by x-ray photoelectron spectroscopy (XPS), provided the surface oxides are sufficiently stable to withstand ion bombardment without decomposition. A quantitative analysis of the surface composition, however, is not possible without taking account of the effects of preferential sputtering of some phases. We have investigated the effects of 3-keV argon ion bombardment on the composition of oxide-free surfaces of iron–nickel and iron–nickel–chromium alloys. In addition, the effect of ion bombardment on metal–metal oxide surfaces has been studied using composite preparations of metal particles, 10–50 μm diameter, in an oxide matrix. Quantitative XPS measurements of the sputtered alloy surfaces, using photoelectrons of 1.0–2.0 nm mean free path, do not reveal any significant change in the steady-state compositions (i.e., ≳10%) compared with the bulk compositions. In the composite metal–oxide mixtures studied, depletion of the metallic phase is significant in some cases and must be taken into consideration in a quantitative depth profile.
An apparatus for rapid and accurate measurement of pressure and volume
Authors: Fortucci Paul L. , Meyer Vincent D.
Published: July 2002

A method is described for the rapid and accurate measurement of the pressure and volume of gas containing devices and the internal volume of vacuum systems; a ratio of pressure measurements and a reference volume are the only requirements. (AIP)
Piezoelectric quartz crystal microbalance (PQCMB) for sorption studies under dynamic conditions
Authors: Mecea V. , Bucur R. V.
Published: July 2002

Construction of the measuring cell and of the auxiliary electric and electronic equipments of a PQCMB is described. The cell is designed for equilibrium and kinetic studies on the thin solid (metallic) layer/gas interface with inert carrier gas (dynamic conditions). Special attention is given to the temperature constancy: the auxiliary equipment of PQCMB is thermostated to within ±0.5°C, the cell to within ±0.005°C. Under these conditions a short-term stability of the frequency better than ±0.01 Hz is obtained, at a nominal frequency of 5.023 MHz, i.e., better than ±2 ppb; the weighing limit is about 5×10−11 g. The long-term stability attained under the same conditions is about ±0.02 Hz. The conditions for using the PQCMB in UHV-surface studies within 80 and 400 K are briefly discussed.
Tunneling transmission coefficients for electrons through (100) GaAs–Ga1−xAlxAs–GaAs heterostructures
Authors: Osbourn G. C.
Published: July 2002

We present calculations of tunneling transmission coefficients for electrons through (100) GaAs-Ga1−xAlxAs–GaAs heterostructures. The calculations were performed using the empirical tight binding approximation. For sufficiently thick alloy regions, the tunneling probability is an exponential which decays with alloy thickness multiplied by a prefactor which is independent of alloy thickness. We have investigated the dependence of the tunneling prefactors on incident electron wavevector and alloy composition x. For the prefactors, we find a strong dependence on the incident electron wavevector component, normal to the interfaces and the alloy composition x, and a weak dependence on the incident electron wavevector component parallel to the interface for the energy range of interest.
In-line production system for sputter deposition of graded index solar absorbing films
Authors: McKenzie D. R. , Window B. , Harding G. L. , Collins A. R. , Mackey D. W. J.
Published: July 2002

An apparatus for producing a selective solar-absorbing coating on tubes is described. The coating has absorptance α = 0.88±0.02 and room-temperature emittance ε = 0.035±0.005. When applied to a glass substrate, it consists of layers of stainless steel, copper, and a composite metal–carbon layer. The coating is applied by translation of the substrate through two hollow-cathode magnetron sputter-coating chambers. The metal–carbon layer is applied by reactive sputtering in the presence of acetylene and has a graded refractive index. Coatings have been incorporated into evacuated tubular collectors and their properties are discussed.
Oxygen adsorption on the disordered silicon surface
Authors: Ellsworth D. L. , Wilmsen C. W.
Published: July 2002

Silicon surfaces prepared by inert ion bombardment have been studied by ultraviolet photoemission spectroscopy in an attempt to understand the influence of atomic disorder on oxygen adsorption. The variation in UPS probe depth available from two ultraviolet emission lines of helium (HeI and HeII) is utilized as a means of identifying depth dependence of the surface structure. The surface appears to consist of an outer layer containing a high density of dangling bonds and an inner layer with bond distortions in the form of a more continuous random network. This is then related to a structural dependence of oxygen adsorption state, enabling a regional separation of two simultaneously obtained states to be observed. In addition to structure dependence, dose-rate dependence of adsorption is also found for the continuous random network layer.
Reactive ion etching of niobium
Authors: Foxe T. T. , Hunt B. D. , Rogers C. , Kleinsasser A. W. , Buhrman R. A.
Published: July 2002

The reactive gases CBrF3 and CF4 have both been found to be effective in the reactive ion etching of niobium. At relatively high pressures, 100 mTorr, rapid etching with a small degree of undercutting occurs at moderate rf power levels. At lower pressures, higher rf power levels, ≳1 W/ cm2, are required but vertical edge profiles result. The RIE process can be useful in producing electrodes for Josephson circuits and superconducting microbridges.
Anisotropic and selective reactive ion etching of polysilicon using SF6
Authors: Parrens P.
Published: July 2002

Experiments performed in a reactive ion etching system are discussed with the purpose of displaying the influence of reactive gas nature, ion energy, and the nature of the cathode on etching anisotropy and selectivity. Using SF6 etching, isotropy or anisotropy is believed to be related to the enthalpy of product formation reaction. Cathodes consisting of elements that form volatile fluorides lead to perfect anisotropic etching and low selective etching of polysilicon over Si02; whereas cathode material which does not react leads to higher selectivity but undercutting appears with an overetch. The possibility of achieving anisotropic and selective etching of polysilicon over thermal Si02 (etch rate ratio = 10:1) is demonstrated for NMOS technology. Examples of polysilicon gates of submicron (0.6 μ) MOST are given.
Film thickness distribution at oblique evaporation
Authors: Svensson S. P. , Andersson T. G.
Published: July 2002

The film thickness distribution and lateral distribution of the arrival rate of atoms or molecules at a substrate using evaporation sources with nonperpendicular and nonrotating substrates were determined for gold films and compared with two theoretical models—a cosine distribution and a Knudsen effusion model. (AIP)
On the interface connection rules for effective-mass wave functions at an abrupt heterojunction between two semiconductors with different effective mass
Authors: Kroemer Herbert , Zhu Qi-Gao
Published: July 2002

The problem of the connection rules for effective-mass wave functions across an abrupt heterojunction is investigated by expressing the results of a one-dimensional, tight-binding approximation in terms of effective-mass wave functions. It is shown that the widely used conventional connection rules of continuous wave function and slope break down if the effective masses on the two sides are different, except if a certain interface matrix element happens to equal the geometric mean of two analogous bulk matrix elements, a case referred to as χ normal. In this case the conventional connection rules yield correct energy eigenvalues, but the effective-mass wave functions themselves differ from true probability amplitudes by a factor depending on the local effective mass, different on the two sides. Heterojunctions that deviate from χ normality may, to the first order, be described as if a δ-function potential had been added at the interface.
Channeling measurements of lattice disorder at the GaAs–InAs(100) heterojunction
Authors: Williams R. Stanley , Paine B. M. , Schaffer W. J. , Kowalczyk S. P.
Published: July 2002

Rutherford backscattering spectrometry (RBS) combined with channeling techniques has been used to analyze the lattice disorder present in InAs thin films less than 1 μm thick grown on GaAs(100) substrates by molecular beam epitaxy (MBE). The axial channeling yields along [100], [110], and [111] reveal that roughly one quarter of the atoms in the thin films are out of registry with the InAs lattice at the heterojunction interface. The amount of lattice disorder decreases rapidly to undetectable (<1%) amounts at film thicknesses greater than 0.5 μm. The interface disorder arises as a result of the ≳7% lattice mismatch between GaAs and InAs.
High Schottky barriers on and thermally induced processes at the Au– GaAs(110) interface
Authors: Petro W. G. , Babalola I. A. , Skeath P. , Su C. Y. , Hino I. , Lindau I. , Spicer W. E.
Published: July 2002

New photoemission measurements show higher Schottky barrier heights (≳1.3 eV) on atomically clean GaAs(110) surfaces at a Au coverage of about 25 monolayers. It is suggested that this effect is due to the movement of Au into the semiconductor; at room temperature it creates acceptor states near the valence band maximum (VBM) that cause the Fermi level at the surface (Efs ) to move close to the VBM. We found that heating of the GaAs(110) surface (above 100 °C) covered with a small amount of Au (0.2 monolayer) causes Efs to move back to its original position (on the clean surface before Au deposition). The heating process is found to greatly inhibit the formation of large barrier heights due to the removal of defect states from the surface region.
Modification of vapor-deposited WO3 electrochromic films by oxygen backfilling
Authors: Sun Sey-Shing , Holloway Paul H.
Published: July 2002

The effects of oxygen backfilling during WO3 vapor deposition have been studied. Rutherford backscattering and secondary ion mass spectrometry were used to show that the O/W ratio and alkali/W ratio were increased by oxygen backfilling. The durability of the deposited films in H2SO4 was shown to be limited by two mechanisms—a general uniform film dissolution and an interfacial attack resulting in delamination. The amount of degradation was reduced as the O/W ratio increased. the electrochromic coloration speed remained unchanged, the bleaching speed and self-erasure rates were faster, and the maximum optical density was lowered for oxygen-enriched films. The mechanisms by which these modifications were achieved are discussed.