bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric Properties of Reactively Sputtered Films of Aluminum Nitride
Authors: Noreika A. J. , Francombe M. H. , Zeitman S. A.
Published: July 2002

Films of AlN, up to 5 μ in thickness, have been grown by diode reactive sputtering under conditions in which the initial residual gas pressure was less than 10−9 Torr. Measurements of resistivity, capacitance, and dielectric loss were made on film sandwich structures in which the electrodes were sputtered films of tantalum and evaporated films of gold and aluminum. In general, the dielectric properties were superior to those reported for ceramic AlN, with film resistivities in the range 1013 Ω-cm and dissipation factors lower than 0.005. Measurements could be made on samples with tantalum electrodes at temperatures up to 500 °C. The results indicate that the capacitance and dissipation factor show smaller changes with temperature for the sputtered films than for bulk material. Some of the consequences of the film structure in relation to dielectric breakdown and piezoelectric properties are discussed.
Interface and Adhesion Studies of Evaporated Se on Oxide Surfaces
Authors: Chiang Yuen-Sheng , Ing Samuel W.
Published: July 2002

Adhesion of evaporated amorphous Se on oxide surfaces has been studied. For selenium evaporated in a relatively poor vacuum of 10−5 Torr onto aluminum substrates coated with a surface oxide layer, the Se deposit could easily be peeled off the substrate. Electron microscope examination of the separated surfaces showed that the separation, in general, occurred at or in the immediate vicinity of the Se-aluminum oxide interface. Complimentary studies were also conducted on Se evaporated onto oxide substrates in an ultra-high vacuum system. Substrates used were single crystals of sapphire and MgO and virteous quartz. Experimental observations indicated that the relative strength of adhesion and the fractured surface features were dependent on and could be correlated with the substrate preheat temperaure in a high vacuum prior to Se evaporation. With a sufficiently high preheat temperature, the interfacial bond strength exceeded that of the cohesive energy of Se and the failure occurred in the Se layer. Studies on the effect of chemisorbed gas species on adhesion showed that water absorption does not degrade the strength of the Se-oxide structure. However, absorption of long chain organic acids and alcohols on the substrate surface resutled in poor adhesion strength, and the failure occurred at the interface region.
Atomic geometry of cleavage surfaces of tetrahedrally coordinated compound semiconductors
Authors: Duke C. B. , Lubinsky A. R. , Lee B. W. , Mark P.
Published: July 2002

Analyses of low-energy electron diffraction intensities are utilized to determine the surface atomic geometries of GaAs(110), ZnO(101̄0), and ZnO(112̄0). The geometry of GaAs(110) is rippled, with the As atoms protruding upwards and the Ga atoms downwards relative to the truncated bulk (zincblende) geometry in a fashion such that no nearest-neighbor bond lengths are altered. The geometries of ZnO(101̄0) and ZnO(112̄0) are nearly those of the truncated bulk (wurtzite) lattice. Small contractions of the upper-layer spacings of both the oxygen (Δd=−0.1 Å) and the zinc (Δd=−0.3 Å) sublattices appear probable, however, for ZnO(101̄0). The qualitatively different nature of the surface reconstruction on GaAs(110) from those which may occur on ZnO(101̄0) is interpreted in terms of the covalent character of the bonding in GaAs as contrasted with a more ionic bonding in ZnO. Both types of surface reconstruction are consistent with a model in which the cation-to-anion charge transfer in the surface layer is less than in the bulk.
Sputtered insulator film contouring over substrate topography
Authors: Kennedy T. N.
Published: July 2002

Coverage of metal line patterns with rf-sputtered SiO2, Si3N4, and Al2O3 has been investigated. The variation of step coverage with the degree of film resputtering has been studied using optical and scanning electron microscopy of both fractured and polished sections. The observed contouring is controlled by the geometry of the substrate topography and the amount of resputtering of the depositing material. Resputtering was controlled during deposition by applying rf bias voltage to the substrate electrode.
Ion-scattering analysis of copper films oxidized in 18O
Authors: Czanderna A. W. , Miller A. C. , Jellinek H. H. G. , Kachi H.
Published: July 2002

Thirty-six copper films, 200 Å thick, were deposited in vacuum onto Pt, Au, and glass substrates and oxidized to CuO0.67 in 16O2 or in 98% pure 18O2. Depth profiles of the copper oxide films were obtained using ion scattering spectrometry. For 90° scattering of 3He ions, the peak separation between 16O and 18O was 0.030 in E/E0, in agreement with the value expected from the binary collision theory. The intensity distribution of the scattered ions from oxygen is Gaussian with σ of 0.0094 E/E0. The 3.2 σ separation of the peaks permitted measurement of different 18–16 O ratios of oxides grown in varying concentrations of 16O2 and 18O2. Within experimental error, the sum of the peak heights of 18O and 16O is equal to that for pure 16CuO0.67. This result, together with a measured Cu/O peak height ratio of 16.4±1.0 for the 36 films suggests isotopic labeling could be used for studying (initial) oxidation mechanisms for copper oxide. As an example, depth profiles of polypropylene coated onto 18CuO0.67 films are presented before and after oxidative degradation of the polymer in 16O2. The profile data are in agreement with a model of reduction of the oxide by the polymer and partial reoxidation of the copper formed by 16O2.
Implantation temperature for III–V compound semiconductors
Authors: Gamo K. , Takai M. , Yagita H. , Takada N. , Masuda K. , Namba S. , Mizobuchi A.
Published: July 2002

Ion implantation in various III–V compound semiconductors (BP, InSb, GaP, and GaAs) has been investigated to reveal the effect of implantation temperature on the general implantation behaviors of III–V compounds. Lattice location of implanted ions and defects were measured by means of He ion-channeling techniques as a function of implantation temperature. For all of the crystals studied, it was found that no amorphous layer was formed above the critical temperature (Tc), and that Tc is linearly corrlated to a melting point of a crystal. High substitutational fraction of implanted ions and low defect density were obtained by an implanatation above Tc.
Pseudopotential calculations for ultrathin layer heterostructures
Authors: Caruthers Ed , Lin-Chung P. J.
Published: July 2002

With molecular-beam epitaxy it is possible to fabricate semiconductor heterostructures of the form (GaAs)m– (Ga1-xAlxAs)n, 1?m, n?10, where m and n are the numbers of atomic layers of each kind of material in the alternating semiconductor regions. Energy bands of several of these structures have been calculated using new pseudopotentials for Ga, Al, and As. Band discontinuities, localized states, charge densities, and interface charge transfer have been found. Densities of states have also been calculated and the results indicate which kinds of experiments should give the best measure of disorder at the semiconducator–semiconductor interfaces in these heterostructures.
Effect of grain boundaries on the performance of polycrystalline tunnel MIS solar cells
Authors: Singh R. , Bhar T. N. , Shewchun J. , Loferski J. J.
Published: July 2002

Tunnel MIS solar cells utilizing polycrystalline semiconductors are an attractive alternative to conventional p–n junction devices for fabricating large-scale solar energy conversion arrays. The main effect of the grain boundaries in polycrystalline semiconductors is to reduce the lifetime of the minority carriers. Experimental work indicates that the potential barrier near the grain boundary has a very limited effect on the barrier height which, in turn, controls open-circuit voltage of the device. The collection efficiency depends upon the grain size of the crystallites, in addition to other device parameters. A simple description of the performance of polycrystalline MIS solar cells will be presented, based on the above mentioned electrical characteristics.
Developments in electron image projection
Authors: Ward R.
Published: July 2002

Unity magnification electron image projection shows considerable promise in lithography of VLSI the developments discussed are an extension to the alignment system to correct magnification, an automatic alignment technique for magnetic bubble circuits and an improved electrostatic chuck.
Improved resolution for DCOPA negative x-ray resist by exposure under a controlled atmosphere of nitrogen and oxygen
Authors: Moran J. M. , Taylor G. N.
Published: July 2002

A previous paper described the formulation of a negative x-ray resist with markedly improved adhesion that was capable of producing 2 μm minimum features in 0.5 μm final resist thickness. This work describes an exposure technique that further improves resolution so that 1 μm minimum features can be resolved in 0.5 μm of x-ray resist. The technique utilizes the fact that resist exposure is strongly influenced by the partial pressure of oxygen in the space separating the mask and the wafer. The interaction of x-ray photons and oxygen partial pressure produces an ideal exposure and developing profile for the resist. The result is greatly improved adhesion and high resolution of the resist feature. This technique may also be applicable to other resist types that are affected by the presence of O2 during exposure. Some experimental results show straighter edges and square corners as well as improved surface quality. Feature size control is ±0.1 μm for a 2 μm feature with a ±10% variation in exposure dose about the 50% exposure setting.
Area/volume configuration influence on porous material outgassing
Authors: Schalla Clarence A.
Published: July 2002

Outgassing data is introduced for some circumjacent cellular materials and stranded elastic cords used for the shock mitigation of experiments in chambers evacuated to 1 mTorr. The influence of area/volume configuration ratios and the effect of humidity sorption on carbonaceous foam outgassing is shown for pumpdown elapsed-time durations to 10 h, and for A/V ratios from 0.4 to 0.8 cm−1. Combined outgassing and virtual leakage data, from test specimens which were loosely wrapped to control carbon foam particle migration and vacuum pump oil contamination, is discussed. Other test specimens investigated, which had A/V ratios from 0.4 to 4.2 cm−1, are polyurethane foam, aluminum–alloy honeycomb, elastic shock absorber (bungee) cord, and distended-surface steel plate. A cascading chart is presented for lucid determination of outgassing rates from these materials. Outgassing coefficients developed from this data for modeling are referenced.
The high-performance beam deflection system of EL3
Authors: Ho C. T. , Michail M. S. , Stickel W. , Woodard O. C.
Published: July 2002

A new concept of beam deflection was developed and implemented to achieve the high throughput and resolution performance of EL3. It combines the advantages of raster and vector writing techniques by dividing the field into overlapping subfields which are addressed by stepped raster magnetic deflection. Within each subfield electric deflection vectorially writes the pattern elements at high speed. The advantages of dual channel deflection and yokes within the projection lens are fully exploited. The repetitive raster deflection pattern permits the use of an automatic calibration system which corrects beam positioning errors of both deflection channels for fields up to 10 mm. Automatic calibration is utilized to assure good pattern overlay between optical and e-beam lithography tools to eliminate dedicated tool restrictions. It establishes subfield matching so that patterns are stitched together properly. In addition, overall field size and linearity are controlled to the accuracy and stability required. This paper discusses key aspects of the entire deflection system design, its components, and highlights compatibility questions and trade-offs between them. Specific problems such as thermal stability, speed/accuracy trade-offs, noise sources, and their solutions are presented. Calibration data are presented to illustrate the accuracy and stability achieved.
Practicing the Novolac deep-UV portable conformable masking technique
Authors: Lin B. J. , Bassous E. , Chao V. W. , Petrillo K. E.
Published: July 2002

Deep-UV portable conformable masking, a double-layer resist patterning technique, combines the advantages of a noncontact submicron printing technique such as refractive projection imaging or scanning electron-beam patterning with those of deep-UV conformable printing. Feasibility studies were reported earlier.1,2 Here, the processes leading to fabrication of 1-μm MOSFET devices by e-beam and step-and-repeat optical projection printing will be presented. These include processing steps to retain or remove the top resist layer, to obtain resist image profiles suitable for liftoff or for reactive ion etching (RIE), to improve adhesion, to treat the interfacial layer between the two resists, to prevent cracking, and to monitor the development of the two resist layers. Electrical testing results on pin hole density are given, followed by uncapped and capped resist images of 1-μm double-poly-Si MOSFET test sites as well as 0.8-μm thick Al lifted-off images.
Light scattering study of electrons confined at Ge/GaAs interfaces
Authors: Merlin R. , Pinczuk A. , Beard W. T. , Wood C. E. E.
Published: July 2002

Resonant inelastic light scattering experiments in Ge/GaAs interfaces show a new spectral band associated with quasi-two-dimensional electron states in a Ge-accumulation layer. A theoretical fit of the position and shape of this structure indicates that it is due to interband transitions between a quasi-two-dimensional band and the continuum.
Electronic structure of GaP–AlP(100) superlattices
Authors: Kim J. Y. , Madhukar A.
Published: July 2002

The band structure of GaP–AlP(100) superlattices with unit-cell thickness up to 32 atomic layers is reported. It is found that for the expected range of band-edge discontinuity, the superlattices exhibit a direct-gap behavior—an interesting result given the indirect nature of GaP and AlP. The wave functions associated with the top of the valence band show behavior characteristic of interface states, whereas the wave functions associated with the bottom of the conduction band are characteristic of two-dimensionally confined states.
Aluminum plasma etch rate limitations
Authors: Purdes A. J.
Published: July 2002

Etch rates of pure Al films were measured using BCl3–Cl2, SiCl4–Cl2, and He–SiCl4–Cl2 gas mixtures in a parallel plate reactor. Reactant loading was avoided by the use of 1-cm2 etch specimens. Experiments were designed to decouple the affects of Cl2 impingement and ion bombardment upon the Al etch rate. Under conditions of constant ion bombardment, the Al etch rate increased linearly with Cl2 partial pressure. Variations in the slope of Al etch rate versus Cl2 partial pressure were attributed to the presence of B or Si etch residues. The concentrations of these residues were controlled by the energies of ions incident upon the etched surfaces.
Microstructure of dielectric thin films formed by e-beam coevaporation
Authors: Farabaugh E. N. , Sanders D. M.
Published: July 2002

X-ray diffraction measurements were made on a series of mixed films in the ZrO2–MgO and ZrO2–SiO2 systems as part of a larger study to investigate the relationship between processing parameters and morphology of dielectric thin films produced by coevaporation. The primary interest was to determine if amorphous coatings produced by coevaporation would have optical properties superior to their polycrystalline counterparts as is the case in the bulk. The first experiments involved determining the importance of both quantity and composition of dopants which could be used to achieve amorphous films. While using x-ray diffraction to evaluate the extent of film crystallinity in doped ZrO2 films, it was observed that first the lattice spacing normal to the film-substrate interface progressively decreased as either MgO or SiO2 were added and that upon reaching 46 and 21 mol%, respectively, the crystallinity disappeared completely. The intent of this work is to present these results and discuss their possible significance.
Surface topography of oxides on InP thermally grown at high temperatures
Authors: McLaren J. J. , Nelson A. , Geib K. , Gann R. , Wilmsen C. W.
Published: July 2002

The surface topography of the thermal oxides on InP are shown to blister for growth temperatures somewhat above 600 °C. It appears that the oxide softens sufficiently to allow the trapped phosphorus at the interface to expand, thus causing the surface bubbles to form. The size of the bubbles varies considerably across a wafer and they tend to increase in size with temperature. At 780 °C one bubble had a radius of ≊100 μ. At T≲650 °C the elemental phosphorus at the interface is the source of the P and the underlying substrate remains smooth. Above this temperature the InP substrate provides the P as shown by the pits in the substrate. There appears to be a relationship between the surface roughening and a change in oxide layer composition.
The impact of surface analysis technology on the development of semiconductor wafer cleaning processes
Authors: Phillips B. F. , Burkman D. C. , Schmidt W. R. , Peterson C. A.
Published: July 2002

The preparation of clean Si and SiO2 substrates for basic semiconductor processing has become a more important technical problem as device geometries are reduced in order to increase the active element densities of VLSI- and VHSIC-integrated circuits. The traditional surface analysis techniques such as Auger spectrometry and ESCA analysis no longer have sufficient sensitivity to detect and quantitate the surface impurity levels. Therefore, a program to apply secondary ion mass spectrometry (SIMS) analysis to the first several nanometers at the surface of wafers undergoing cleaning processing has been undertaken. After determining the SIMS instrumental parameters needed to perform reproducible analyses, wafers cleaned by FSI-A, aqua regia, fuming nitric acid and Piranha plus HF cleaning procedures were analyzed. Each cleaning procedure removed some of the alkali elements (Na, K) but the difference between the best and worst performance gave greater than a factor of 10 variation in surface alkali content. Typical wafer contaminants (Mg, Ca, Cr, Cu, Al, and B) were removed with greatly differing efficiency by the various cleaning processes used. Data on the relative efficiencies of the various cleaning processes and their suitability for different contaminants will be presented. In addition, an example of a contaminated thin-deposited nitride film analysis will be presented.
Electron trapping levels in rf-sputtered Ta2O5 films
Authors: Seki Shunji , Unagami Takashi , Tsujiyama Bunjiro
Published: July 2002

UV-stimulated photocurrent spectroscopy and photocurrent transient methods have been used to determine the effects of deposition parameters on the electron trapping level density and its energy distribution in rf-sputtered Ta2O5 films. Results of this investigation indicate that the electron trapping level density can be greatly reduced by depositing the film at a pressure of 2×10−3 Torr with an rf-magnetron sputtering system. Experimental results also indicate the presence of the distribution for traps peaked at 2.7 eV below the conduction band in Ta2O5 films sputtered at a pressure of 2×10−3 Torr. A first-order kinetic model was used to compute trapping parameters (trap density and photoionization cross section). The results of this analysis indicate that the density of the 2.7 eV level is on the order of 4×1015 cm−3, which is three orders of magnitude lower than that for anodic Ta2O5 films, and that the photoionization cross section (at 2.7 eV) is on the order of 10−20 cm2.
Deep centers in gold-doped HgCdTe
Authors: Merilainen C. A. , Jones C. E.
Published: July 2002

Gold is a fast-diffusing acceptor in HgCdTe. It has been used as a p-type dopant and as a metal contact. This paper reports the presence of deep levels in gold-doped x=0.48 Hg1−xCdxTe. Two types of spectra were observed; each had energy levels between Ev +1/4 Egap and Ev +1/2 Egap. The capture cross sections for these centers have been determined and for most of the levels they involve small hole capture cross sections, 10−17 to 10−21 cm2, and moderate electron capture cross sections, 10−15 to 10−16 cm2. The hole capture cross sections for these centers had large negative activation energies indicative of hole capture at a positive center with a Coulomb repulsive barrier. The corresponding electron capture is then at Coulombically attractive positive centers. The situation described requires that the DLTS activation energies be corrected for the temperature dependence of the hole capture cross sections and for the Poole–Frenkel effect for electron capture. The energy levels and capture cross sections reported make these centers effective minority carrier recombination sites in p-type material. The minority carrier lifetimes measured are very close to those calculated for Shockley–Read recombination at the DLTS characterized centers.
The preparation of materials for optoelectronic applications by molecular beam epitaxy
Authors: Tsang W. T.
Published: July 2002

0.72–0.88 μm (AlGa)As, 1.3–1.65 μm GaInAsP and AlGaInAs, and 1.78 μm GaSb double-heterostructure lasers were prepared by molecular beam epitaxy. For (AlGa)As DH lasers very low 300 K threshold current densities and long operating life (mean time to failure>106 h at 300 K) were achieved. For lasers with lasing wavelength>1μm, MBE is in an early development stage. The unique capabilities of MBE as an epitaxial growth technology and its important contributions to the field of optoelectronics are illustrated by a discussion of a new generation of device structures including quantum well heterostructure, double-barrier double-heterostructure, and graded-index separate-confinement-heterostructure lasers and by graded-band-gap APD and phototransistors, superlattice APD, and modulated barrier photodiodes. These new devices, made possible by MBE, have characteristics unachieved earlier.
The adsorption of PH3 on Si(100) and its effect on the coadsorption of SiH4
Authors: Yu Ming L. , Meyerson B. S.
Published: July 2002

PH3 is found to chemisorb on Si(100) and the saturation coverage is strongly temperature dependent. Apparently the desorption of the hydrogen at temperatures above 400 °C can open up more Si sites for PH3 chemisorption. Both PH3 and phosphorus adsorbed on the Si surface can effectively block the coadsorption of silane molecules. The data is consistent with the observed rapid decrease in Si deposition rate during in situ doping with PH3 in a SiH4 reactor.
Effects of oxygen in ion-beam sputter deposition of titanium oxides
Authors: Demiryont H. , Sites J. R.
Published: July 2002

Oxides of titanium, 200–400 nm thick, were deposited by ion-beam sputtering of a metallic target. The ion beam consisted of an argon–oxygen mixture where the oxygen percentage was varied from 5% to 50%. Ellipsometry and spectrophotometry were used for optical characterization, x-ray photoelectron spectroscopy to examine the atomic bonding patterns. For each wavelength, the refractive index showed a maximum when the oxygen fraction was near 30%. At 633 nm, the maximum was 2.52. Such films were dense, amorphous, stoichiometric TiO2 with a visible optical absorption of a few tenths of a percent. With less oxygen, films were also transparent, but contained increasing amounts of a titanium suboxide. With substantially less oxygen, opaque cermets were formed. When the oxygen percentage was increased above 40%, the refractive index of the films was less than the maximum, the films apparently contained voids, but they were otherwise stoichiometric.
Electrical transport properties of polycrystalline rf sputtered CdS thin films
Authors: Mártil I. , González-Díaz G. , Sánchez-Quesada F.
Published: July 2002

Temperature dependence, in the range 150–450 K, of the resistivity and Hall mobility were studied on polycrystalline sputtered CdS thin films. The room-temperature values of analyzed samples for resistivities and Hall mobilities ranged between 1–108 Ω cm and 2–8 cm2/V s. The results showed a major scattering mechanism controlled by the intergrain barrier height, the carriers being thermally activated. A temperature dependence of the barrier height φB=φ0 (1+αT) has been observed which allows fitting a general expression for Hall mobility of the form μH=11.6 exp(26.8 φ0) exp(−φ0/kT). A theoretical calculation of the μ0 parameter has been performed. The results show good agreement with the experimental data.
Velocity and electronic state distributions of sputtered Fe atoms by laser-induced fluorescence spectroscopy
Authors: Young C. E. , Calaway W. F. , Pellin M. J. , Gruen D. M.
Published: July 2002

Velocity distributions and relative populations in the fine-structure levels of the a 5DJ ground state of Fe atoms, produced by sputtering with 3 keV argon ions, have been investigated by Doppler-shifted laser-induced fluorescence. The laser system employs a single-mode, scanning ring dye laser, amplified by a sequence of three excimer-pumped flowing dye cells. Frequency doubling in a KD*P crystal was used to produce high energy (>0.5 mJ) pulses of narrowband tunable UV output near 300 nm. Laser power influence on effective velocity bandwidth was investigated. Favorable light-collection geometry minimized distortion of the velocity spectra from apparatus-averaging effects. In impurity flux diagnostic applications in fusion devices, substantial spatial averaging may occur. In the latter case, the narrow velocity bandwidth (70 m/s, transform limit) of the present laser system is particularly useful.
Thermal oxidation of GaP
Authors: Kato Y. , Geib K. M. , Gann R. G. , Brusenback P. R. , Wilmsen C.W.
Published: July 2002

The surface topography and interface structure after thermal oxidation of GaP is reported for the temperature range 600 to 1220 °C. An extensive network of interfacial voids was observed in the substrate under the oxide film. The size of the voids was enlarged by a bulging of the oxide, probably as a result of pressure within the voids but also from a difference in the coefficients of expansion which also caused cracks in the oxide film. The voids begin as isolated cavities but coalesce into winding caverns after further oxidation or with increased temperature. The oxide begins to grow a significant thickness of oxide at approximately 650 °C in dry oxygen. In steam the oxidation rate is approximately ten times faster and there are no interfacial voids even after 2 μ of oxide growth.
Multiple bonding on C(111)-2×1 surfaces: Surface structural determination from energy minimization
Authors: Chadi D. J.
Published: July 2002

The (111) surface atomic structure of diamond is found to be strongly influenced by the ability of C to form multiple bonds. Two structures with different types of C–C bonding were examined. They are: (i) the π-bonded-chain model and (ii) a strongly dimerized version of this model. The surface C–C bonds in these structures are similar, approximately, to those in graphite and the C2 molecule, respectively. The two structures are both stable against small distortions and have nearly equal surface energies of 1.05±0.03 eV per surface atom. The atomic coordinates for the two models, determined from tight-binding based energy-minimization calculations, are given. The accuracy of the tight-binding method in predicting equilibrium bond lengths and energies in graphite and the C2 molecule is discussed.
Compositional microcharacterization of electrically active and chemically passivated silicon grain boundaries
Authors: Kazmerski Lawrence L.
Published: July 2002

The mechanisms controlling the electrical passivation of grain boundaries in polycrystalline silicon, using the incorporation of hydrogen in these regions, are investigated. For the first time, direct and correlated microelectrical and microcompositional measurements of the effects of hydrogen on Si grain boundaries are presented. The detection, spatial mapping and quantification of hydrogen within the polycrystalline Si has been accomplished by a specially developed secondary ion mass spectrometry (SIMS) method. In this, selected secondary ion species corresponding to elements of molecules of interest are measured and stored (indexed for intensity, type, and spatial origin) digitally for an incremental volume encompassing the region of interest (i.e., the grain boundary plane). These data are utilized to determine the diffusion coefficients (temperature dependencies, activation energies, and preexponential coefficient terms) of hydrogen in the grain boundaries and the grains as functions of the processing parameters. The effects of the hydrogen passivation process on the performance of solar cells are discussed.
Cathodoluminescence spectroscopy studies of laser-annealed metal–semiconductor interfaces
Authors: Brillson L. J. , Richter H. W. , Slade M. L. , Weinstein B. A. , Shapira Y.
Published: July 2002

We have extended cathodoluminescence spectroscopy (CLS) to the study of new compound and defect formation at metal–semiconductor interfaces. CLS provides evidence for Cu2S and/or impurity band formation after laser annealing Cu on UHV-cleaved CdS. Al deposition on UHV-cleaved CdS followed by laser annealing leads to formation of at least two deep levels distributed at different depths from the initial interface. The energies, densities, and spatial distribution of these levels depend sensitively on the laser intensity and the presence or absence of particular metal overlayers. These results demonstrate the utility of CLS in revealing electronic features of the buried metal–semiconductor interface while still maintaining depth resolution on the order of hundreds of Å or less.
Thermal stability of Al–Si/TiSi2/Si Schottky diodes
Authors: Chen D. C. , Merchant P. , Amano Jun
Published: July 2002

We have examined the thermal stability of Al–Si/TiSi2/Si Schottky diodes both with and without a sputter-deposited W–Ti (10 wt. %) diffusion barrier after furnace annealing up to 550 °C, 30 min. The diodes having the diffusion barrier exhibit stable Schottky barrier heights up to 550 °C, 30 min. In contrast, after 450 °C, 30 min annealing, diodes which do not have a diffusion barrier exhibit Schottky barrier heights typical of Al/n-Si. Metallurgical interactions have been investigated by He backscattering spectroscopy which shows a stable W–Ti/TiSi2 interface up to 550 °C, 30 min annealing in samples having the diffusion barrier. The samples without a diffusion barrier show evidence of Al–Ti interdiffusion after 450 °C, 30 min annealing. Residual gas incorporation in the barrier layers was investigated by Ar ion sputter-depth profiling Auger electron spectroscopy. Sheet resistance measurements and x-ray diffraction analysis were used to investigate intermetallic phase formation. Selective wet etching combined with scanning electron microscopy were used to determine morphological changes at the TiSi2/Si interface as a result of annealing.
Recent developments in quantitative surface analysis by electron spectroscopy
Authors: Powell C. J.
Published: July 2002

An overview is given of recent developments in quantitative surface analysis by x-ray photoelectron spectroscopy and Auger electron spectroscopy. The two major tasks of an analysis are the identification of the surface phases that are present and the determination of the concentrations of particular elements or compounds. Methods for accomplishing both tasks are described together with the pitfalls and problems that remain. Particular attention is given to the following topics: identification of surface phases and reference data for the calibration of instrumental energy scales; reference data on inelastic mean free paths and attenuation lengths; effects of specimen crystallinity; intensity measurements; measurement of the imaging properties of electron energy analyzers; and the intensity-energy response functions of different instruments.
Dry etching of TiSi2
Authors: Cadien K. C. , Sivaram S. , Reintsema C. D.
Published: July 2002

Dry etching studies of titanium disilicide films in CF4+O2 plasmas are reported. Thin films of TiSi2 were rf sputter deposited at room temperature on to bare single crystal silicon, SiO2, and CVD polysilicon substrates. The effect of the oxygen to CF4 ratio in the gas inlet on the composition of the plasma, on the etch rate, and etch anisotropy have been studied. Etch rates and etch profiles in plasma etch and reactive ion etch modes have been compared. Maximum etch rate corresponded to approximately 20% oxygen in both cases and the etch rate in the RIE mode (1600 Å/min) was more than twice the etch rate that could be obtained in the PE mode (690 Å/min). Etch rate increased with increasing pressure in both modes. RIE pressures up to 50 mTorr, and PE pressures up to 250 mTorr were used with rf powers up to 200 W.
Composition and growth mechanism of anodic oxide on Hg(1−x)CdxTe
Authors: Strong R. L. , Anthony J. M. , Gnade B. E. , Keenan J. A. , Norbeck E. , Li L. W. , Helms C. R.
Published: July 2002

The composition of HgCdTe oxides obtained by anodization in a standard KOH/ethylene glycol solution has been determined by Rutherford backscattering spectroscopy for the first time. This technique is advantageous because it is not as surface sensitive as Auger or x-ray photoemission spectroscopy and it provides a nondestructive depth profile of the oxide which can be quantitatively modeled without relying on standards for comparison, as is necessary when using the electron microprobe. The measured composition (61% O, 23% Te, 11.8% Hg, 4.2% Cd for material with x=0.202) is within 0.4% of a stoichiometric mixture of 51.3% HgTeO3, 18.3% CdTeO3, and 30.4% TeO2. While the Hg content in the oxide relative to Te is reduced from the bulk value, it is substantially larger than what is normally reported by other techniques, which found much higher levels of Cd. This composition is consistent with oxide growth occurring primarily by oxygen ions moving into the substrate by a hopping mechanism, while metal ions simultaneously are hopping toward the oxide–solution interface where they can be dissolved into solution. This is the growth mechanism determined by comparing depth profiles after sequential growths in solutions containing KOH and H2O2, the latter solution producing a significant Hg and Cd depletion which can be easily observed by secondary ion mass spectroscopy and Auger electron spectroscopy.
The effect of interdiffusion on the shape of HgTe/CdTe superlattices
Authors: Zanio K. R.
Published: July 2002

The shape and widths of HgTe wells in HgTe/CdTe superlattices are calculated with a growth and interdiffusion model. For a growth temperature of about 200 °C the model shows the HgTe wells to expand up to about an angstrom and CdTe tails to penetrate several angstroms into the HgTe wells. At superlattice growth temperatures, the extent of interdiffusion from model profiles agrees qualitatively with experimental results.
Infrared absorption measurement and analysis of HgTe–CdTe superlattices
Authors: Baukus J. P. , Hunter A. T. , Marsh O. J. , Jones C. E. , Wu G. Y. , Hetzler S. R. , McGill T. C. , Faurie J. P.
Published: July 2002

The near-band-gap optical properties of superlattice are essential in determining the usefulness of these structures for application in infrared systems. In this paper we report on studies of a HgTe–CdTe superlattice. The optical characterization of the superlattice in the infrared was carried out by measuring its photoluminescence, transmission, and photoconductivity spectra. Results of these measurements as functions of temperature are presented, as are the theoretically calculated absorption spectra. We obtained good agreement between different measurement techniques and the theoretical model for the optical absorption and band gap.
The growth of CdTe/GaAs heteroepitaxial films by metal–organic chemical vapor deposition
Authors: Anderson Philip L.
Published: July 2002

A process for the growth of CdTe/GaAs heteroepitaxial films using metal–organic chemical vapor deposition (MOCVD) has been developed. The initial results of the determination of the deposition mechanism are reported. A pilot production demonstration using experimentally determined operating conditions has been completed. This is the first reported pilot production of CdTe/GaAs using 2 in. diam GaAs substrates in a multiple slice, commercially manufactured MOCVD system. The results reported therein demonstrate that MOCVD is a reliable, reproducible, production worthy process for preparation of CdTe/GaAs heterostructures. These results are applicable to a wide variety of CdTe based device technologies including IR detection, fiber optics, solar cells, and others.
Low-temperature photoluminescence study of doped CdTe films grown by photoassisted molecular-beam epitaxy
Authors: Giles N. C. , Bicknell R. N. , Schetzina J. F.
Published: July 2002

N-type and p-type (100) CdTe films have been grown on (100) CdTe substrates by photoassisted molecular-beam epitaxy, using indium and antimony as n-type and p-type dopants, respectively. The characterization of these as-grown, in situ doped films using low-temperature (1.6–4.5 K) photoluminescence and excitation photoluminescence is reported. The introduction of the dopant atoms using this new growth technique produces immediate changes in the photoluminescence spectra. The effects on photoluminescence spectra of carrier concentration and dopant incorporation are studied. Radiative recombination peaks related to the introduced impurity levels and the associated bound excitons are observed.
Determination of the CdTe–HgTe(111) heterojunction valence-band discontinuity by x-ray photoemission spectroscopy
Authors: Grant R. W. , Kraut E. A. , Cheung J. T. , Kowalczyk S. P.
Published: July 2002

X-ray photoemission spectroscopy has recently been used to measure the valence-band discontinuity (ΔEv) for the CdTe–HgTe(111) heterojunction with the result ΔEv=0.35±0.06 eV. A detailed discussion of the uncertainties associated with this measurement is presented.
Subband related structure in the absorption coefficient of HgTe/CdTe superlattices
Authors: Patten E. A. , Kosai K. , Casselman T. N. , Schulman J. N. , Chang Yia-Chung , Staudenmann J.-L.
Published: July 2002

The current interest in HgTe/CdTe superlattices (SL’s) stems in part from their potential usefulness in advanced IR applications. Of particular interest is the photon energy dependence of the optical absorption coefficient α(E) of these superlattices. Structure in α(E) of superlattices is expected because of the relatively narrow energy subbands (compared with bulk semiconductors) resulting from the large SL period (∼100 Å). Determination of this structure will help to reveal the electronic subband structure of the superlattice. We report here the experimental and theoretical extraction of α(E) at 300 K for six HgTe/CdTe superlattices. The experimentally determined αexp(E) were obtained from transmission/reflection data in conjunction with a computer model. The theoretically calculated αcalc(E) was computed using a two-band tight-binding model for the superlattice energy bands in the growth direction and a nonparabolic approximation in the superlattice plane. Subband related structure is observed for all six superlattices with excellent agreement between theory and experiment for three of the superlattices. The level of correlation between αexp(E) and αcalc(E) appears to be an indicator of superlattice quality as defined by results from x-ray and far-infrared spectroscopy studies.
Electrical measurements of molecular-beam epitaxy HgTe–CdTe superlattices and absorption coefficient analysis of molecular-beam epitaxy HgTe
Authors: Goodwin M. W. , Kinch M. A. , Koestner R. J. , Chen M. C. , Seiler D. G. , Justice R. J.
Published: July 2002

Transport properties of molecular-beam epitaxy (MBE) grown HgTe and HgTe–CdTe superlattices on (112) CdTe substrates and the absorption coefficient for MBE HgTe are measured. The Hall and optical data for HgTe agree with a Kane-type band-structure model with parameters appropriate for HgTe. The Hall data for the HgTe–CdTe superlattices indicate that the superlattices are p-type with an n–p transition temperature which can be used to determine the band gap. The Hall data are modeled fairly well using simple band-structure calculations. Measurements of the Shubnikov–de Haas effect indicate that light-hole-like carriers (m*∼0.01 m0) exist in the p-type conduction range of these samples. This is in disagreement with the Hall data which suggest that the predominate carriers in this conduction range are heavy holes (m*∼0.4 m0).
Vacancy formation energies in II–VI semiconductors
Authors: Berding M. A. , Sher A. , Chen A.-B.
Published: July 2002

Cation and anion vacancy formation energies are calculated for HgTe, ZnTe, CdTe, and their dilute alloys. Harrison’s tight-binding theory is extended to a cluster embedded in an extended crystal. Only neutral vacancies have been considered and two final states for the removed atom have been addressed: a free atom in vacuum and an atom on an ideal (111) surface. Corrections caused by rehybridization of the dangling bonds and Coulomb energies resulting from charge redistribution have been included.
A quartz-crystal microbalance apparatus for water sorption by polymers
Authors: Czanderna A. W. , Thomas T. M.
Published: July 2002

A quartz-crystal microbalance (QCM) apparatus has been assembled for studying the water sorbed by polymeric materials from 0.1 to 100 μm thick. The apparatus consists of an UHV system with a turbomolecular pump, valves, low-pressure gauges, a capacitance manometer, a residual gas analyzer, and reservoirs for water vapor and other adsorbate gases. Up to five different polymer coated quartz crystals can be inserted into hangdown tubes using a 20-in.-long, water-cooled, sensor head with appropriate feedthroughs for the electrical connections and thermocouple leads. The QCM controller consists of a power supply, oscillators, frequency meter, and output for obtaining mass change data. The sensitivity of 14 ng/cm2 Hz corresponds to a mass change of about 0.1% for a 100-nm-thick polymer film. Sample temperatures are controlled to better than 0.1 °C by immersing the hangdown tubes in a liquid water bath. The controller is interfaced with computers for data acquisition, storage, manipulation, etc. to output data for sorption isotherms, the rate of sorption and desorption, and comparing the cyclic reproducibility of rate and capacity. Representative sorption data for three polymers are presented.
Spot deposition by focusing in Penning discharge sputtering
Authors: Sugita T. , Nishikawa E. , Ebisawa S.
Published: July 2002

In order to obtain an efficient spot-sized deposition in Penning discharge sputtering, an electrode configuration for focusing of sputtered atoms has been designed and evaluated. In the apparatus designed, a conical beam of sputtered atoms is produced by a combination of a concave cathode, a planar cathode with a ring-shaped slit, and a hollow conical frustum anode between the two cathodes. By adjusting the distance of the electrodes a sharp focus is obtained on a substrate which lies behind the planar cathode. The focusing position can be controlled easily. When a circular disk gold film is deposited on the glass substrate, its diameter became smaller in inverse proportion to the distance between the substrate and planar cathode. With an input power of 4.5 W the deposition rate of the gold film is found to be 1 nm/s. It has been shown that the technique is very suitable for spot-sized film deposition on various substrates and for other applications such as dental-caries-preventing coating on extracted teeth and the coating for fine adjustment of resonant frequency of quartz-crystal wafers.
Influence of thickness and hydrogen concentration on optical and electrical properties of a-Si:H thin films
Authors: Rava P. , Demichelis F. , Kaniadakis G. , Mpawenayo P. , Tagliaferro A. , Tresso E.
Published: July 2002

The present work reports a study of the effects of thickness and hydrogen concentration on the optical and electrical properties of a-Si:H thin films deposited by glow discharge and by rf magnetron sputtering. UV-visible near-infrared transmittance and reflectance, film thickness, hydrogen content, dark conductivity, and photoconductivity were measured. Parameters such as dielectric constant, index of refraction, absorption coefficient, and optical band gap were obtained. The thickness and the hydrogen concentration are found to have an influence on some optical parameters; this behavior is explained in terms of homogeneity of the films.
Junction and ohmic contact formation in compound semiconductors by rapid isothermal processing
Authors: Singh R. , Radpour F. , Chou P. , Nguyen Q. , Joshi S. P. , Ullal H. S. , Matson R. J. , Asher S.
Published: July 2002

The results of a new application of rapid isothermal processing (RIP) for the junction and ohmic contact formation in compound semiconductors are presented in this paper. In this process, for a particular compound semiconductor a compound is selected so that one element acts as a dopant and the other is one element of the compound semiconductor preferably a high vapor pressure element. A thin layer of this compound is deposited by suitable technique on top of the compound semiconductor followed by low-temperature (∼300–500 °C) RIP step. Results of indium phosphide and cadmium telluride are presented representing group III–V and II–VI, respectively. Preliminary results of CuInSe2 are also presented. This method does not require a sealed quartz ampoule, a capping layer, or a background pressure of high vapor pressure element of the compound semiconductor, as is required in diffusion of most compound semiconductors. This process has resulted in abrupt and shallow junctions having excellent diode characteristics.
On dielectric breakdown in oxidized silicon
Authors: Wolters D. R. , Zegers-van Duijnhoven A. T. A.
Published: July 2002

Breakdown in silicon dioxide films on silicon has been studied making use of various measurement techniques and statistical tools. The use of probability scales is advocated in order to distinguish intrinsic breakdown from defect-related breakdown. In such a way defect densities can be determined and the yield of large-area circuitry can be predicted when the breakdown distribution of small capacitors is known. Comparison of field-dependent, time-dependent, and current-induced breakdown showed that intrinsic breakdown occurred at practically equivalent conditions of field and time. At high fields or large currents breakdown occurred within a short period of time, whereas at low fields or small currents this period can be relatively long. The critical parameter was found to be the time integral of the leakage current until breakdown (Qbd). This charge needed for breakdown is constant for similar capacitors. At not too high currents (Qbd) is found to be only a little dependent on stress conditions: field or time. Qbd appears to be even independent of the measurement technique, i.e., field-, or time-, or current-induced breakdown technique. At higher currents or applied fields (Qbd) values tend to decrease, sometimes over orders of magnitude. It follows from our observations that this is due to space-charge effects. Special attention is given to the energy needed for breakdown, which is different from that which is released at the breakdown itself.