bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface characteristics of Inp MOS capacitors
Authors: Pande K. P. , Roberts G. G.
Published: July 2002

A new electrolyte based on a solution of 10 g of ammonium pentoborate in 100 ml of ethylene glycol buffered to a ph of 6.0 has been used to produce a dielectric layer on the surface of InP. The relative permittivity of the anodic oxide is 7.9 and its dielectric breakdown strength is 3×106v/cm. The electrical characteristics of the surface states at the anodic oxide–-type InP interface have been investigated using MOS capacitors. Capacitance–voltage data at 200 kHz indicate that the InP surface is already depleted at zero bias with a flat band voltage of 0.85 V. An inversion-type low frequency (1 Hz) response has been observed for the first time on an InP MOS structure using an anodic oxide. Our analysis of the admittance data yields a U-shaped surface state distribution having a minimum density of 4×1011 cm−2 eV−1 at mid-band gap. Many other fea ures of our results also resemble those previously obtained with InP/organic insulator structures.
Characterization of improved InSb interfaces
Authors: Langan J. D. , Viswanathan C. R.
Published: July 2002

Improved quality surfaces on n-type InSb have been produced using a low-temperature chemical vapor deposition (LTCVD) of SiO2 by pyrolytic decomposition of silane in the presence of oxygen. Preservation of the thin, natural oxide on the InSb surface through a suitable LTCVD process results in a surface state density ≳1010 eV−1 cm−2 and without C–V hysteresis. Confirmation of these results is made by both quasistatic C–V and conductance measurements on MIS structures. Complications introduced by the presence of lateral nonuniformity of the LTCVD oxide and thus in the surface potential, have been accounted for in the observed low density measurements. The presence, chemical identification, and thickness of the natural oxide, both before and after the LTCVD process, has been idependently confirmed by XPS. The apparent oxidation state and resultant electrical properties are identified with changes in LTCVD reactor conditions.
Rectification at n-GaAs–n-Ga0.7Al0.3As heterojunctions grown by liquid phase epitaxy
Authors: Chandra Amitabh , Eastman Lester F.
Published: July 2002

Heterojunctions between n-type GaAs (2×1014cm−3, 1017cm−3) and high purity n-type Ga0.7Al0.3As (∠1×1015cm−3) have been grown by LPE at 700°C, and significant current rectification has been observed across them at room temperature. At low temperatures, the current drops and the degree of rectification increases considerably. The reverse current characteristic shows reasonable semiquantitative agreement with theoretical I–V curves, calculated by using a thermionic emission model. The N–W profile (where N is the concentration and W the depth) measured across the interface indicates qualitatively the presence of a dipolar space–charge region, as expected.
Carrier transport coefficients across GaAs–GaAlAs (100) interfaces
Authors: Osbourn G. C. , Smith D. L.
Published: July 2002

We present calculations of reflection and transmission coefficients for electrons and holes at (100) interfaces for the GaAs–Ga1–xAlxAs system. We consider semi-infinite crystals of the two semiconductors joined at an abrupt or compositionally graded interface. The calculations are performed using the empirical tight binding approximation. The transport coefficients were computed as a function of the components of the incident carrier wavevector normal and parallel to the interface. We have investigated the transport coefficients for incident states near various band minima into different final state channels. The transmission into states with qualitatively similar character to the incident state is found to be much greater than transmission into states of different character. For example, an electron near the X minimum normal to the interface in Ga1–xAlxAs transmits into the X valley of GaAs with much greater probability than it transmits into the Γ minimum of GaAs. We have investigated the dependence of the transport coefficients on alloy composition. The effect of compositional grading of the interface on the transport coefficients has also been investigated.
Tellurium coating of PbTe surfaces
Authors: Bettini M. , Brandt G. , Rotter Sh.
Published: July 2002

In this study PbTe surfaces have been coated with thin elemental tellurium layers, in order to prevent surface oxidation. The coating layers have been prepared either by preferential Pb etching of the PbTe surface or sublimation of Te films onto sputter cleaned surfaces. Surface investigations (XPS and LEED) show that Te layers prepared by etching are porous. Sublimed Te films (∠300 Å thick), however, prevent oxidation and carbon absorption at the Te–PbTe interface for at least several hours of air exposure. The coating quality is attributed to the good crystalline growth of the Te epilayers. Since thin Te films are expected to act as surface passivation, the electrical characteristics of Te–PbTe junctions have been investigated. They show ohmic behavior on p-PbTe and rectification on n-PbTe, indicating band bending in the latter case.
Line profiles in thick electron resist layers and proximity effect correction
Authors: Phang J. C. H. , Ahmed H.
Published: July 2002

A theoretical and experimental investigation of the developed profile shape in thick resist layers is described. The profiles that are exposed by a single line scan at various incident doses and by two adjacent scans with increasing separations between the scans are compared with a threshold solubility model and a development model. Near the neck of the profiles, the predictions of the theoretical models are in good agreement with experiments. In the resist substrate interface regions, the development model is satisfactory but the threshold solubility model is found to be inadequate. A proximity effect correction method is also described in which the edge of the exposed pattern is monitored to obtain accurate pattern fidelity. Experimental results using this method of correction are presented.
Investigations of hydrogen gettering by means of mass spectrometry and microgravimetry
Authors: Röhrig H. D. , Fischmann K. D. , Haubold W.
Published: July 2002

Experiments were conducted on different bulk getter materials (Ti, Zr, Ce) in order to study their potential in a new gas purification concept for high-temperature gas-cooled reactors. Since the removal of hydrogen and tritium represents the main problem, the measurements concentrated on plateau pressures of the metal hydrides, the kinetics of absorption, passivation, and hydrogen isotope effects. The apparatus used for model investigations with H2 and D2 is a UHV device involving two hot metal beds one of which consists of a microbalance system, various total pressure gauges, and a quadrupole mass spectrometer. The absorption rates were found to be linear with pressure, which is consistent with gas kinetic theory. Plateau pressure measurements down to 10−8 mbar confirm extrapolated literature data, while an observed significant isotope effect near ambient temperature may be understood as a specific passivation effect.
Closed loop control of thin film sputter deposition processes using glow discharge mass spectroscopy
Authors: Tisone T. C. , Bolker B. F. T. , Latos T. S.
Published: July 2002

Sputtering in general can be viewed as reactive sputtering due to the presence of virtual leaks in addition to the normally considered controlled gas leaks. A method is needed to reproducibly control critical film properties for practical manufacturing situations, especially in the case where the incorporation of precise amounts of a reactive gas like O2 or N2 are desired in a deposited film. These considerations have led to the development of a closed loop control system which uses glow discharge mass spectroscopy (GDMS) to detect plasma ions and thus act as a transduction element for feedback control to a servo leak valve. An LSI–ll microprocessor provides real time control of the desired process signals. GDMS control is more reproducible than merely controlling gas flow or monitoring gas partial pressure since the former does not account for virtual leaks, and the latter does not always reveal the reactive species present in the plasma. The general theory behind this approach is discussed, along with consideration of the system design and hardware. System control is achieved by using an algorithm based on ratios of ion signals in order to eliminate nonreproducibility caused by variation in the multiplier gain of the GDMS. Representative GDMS spectra and the techniques for determining optimum control signals are presented. In the Ta system, to control small amounts of O2, the Ta+/TaO+ ratio is used; and for control of N2, the Ta+/TaN+ ratio is satisfactory. For Ta films reactively sputtered in either O2 or N2, GDMS control ratios are well correlated with resultant film composition and electrical properties. Comparisons between GDMS control ratios of TaO cermet films and their respective Auger profiles, microprobe measurements, ρ and TCR are shown. Validity of this closed loop control concept is further demonstrated by the fact that three sputtering systems, including one in manufacturing, are now in operation and during a two-year period have provided similarly reproducible films to a ±5% level.
SiO2/InP interface formation: Thermodynamic considerations
Authors: Wager J. F. , Wilmsen C. W.
Published: July 2002

Chemical vapor deposited SiO2 has previously been shown to form a useable insulator for InP MIS devices. In this paper possible reactions between Si, SiO, SiO2, O2, and InP and its oxides are investigated by calculation of the change in enthalpy of the reactions. The calculations indicate that no reaction is expected between SiO2 and InP or its oxides. However, both Si and SiO reduce the oxides of In and P. The reaction between InP and Si appears to be weak but possible. The various methods of depositing SiO2 are also examined in order to predict which of these methods is the least likely to cause reaction between the substrate and the depositing species.
Postdeposition annealing behavior of rf sputtered ZnO films
Authors: Lad R. J. , Funkenbusch P. D. , Aita C. R.
Published: July 2002

The crystallographic orientation of rf reactively sputtered ZnO has been characterized by x-ray diffraction after postdeposition heat treatment. Diffractometer measurements were made on as-deposited films as well as on films which were annealed up to 700°C. The heat treatment accounted for improved crystallite orientation as evidenced by increased alignment of (002) crystal planes parallel to the substrate (c-axis normal orientation), possible crystallite growth, and considerable stress relief. Rocking curve half widths indicate that annealed films have a very small angular deviation from the c-axis normal orientation.
Deposition of epitaxial layers by ion beam methods
Authors: Weissmantel C. , Hecht G. , Hinneberg H.-J.
Published: July 2002

The possibilities and the limitations of ion beam sputter deposition are discussed in connection with results obtained for the growth of epitaxial semiconductor films. It turns out that homo- and hetero-epitaxial films of good structural quality can be deposited at relatively low substrate temperatures and that effective doping offers no difficulties. On the other hand, some radiation damage caused by energetic particles must be taken into account. More recently, ion beam deposition methods could be realized under UHV conditions using about the same diagnostic equipment as in MBE. It can be expected that in preparing special film structures combinations between molecular and ion beam techniques might become attractive, while ion beam methods also will stand on its own in synthesizing unusual film phases.
Electronic structure of the diamond (111) 1×1 surface: Valence-band structure, band bending, and band gap states
Authors: Pate B. B. , Spicer W. E. , Ohta T. , Lindau I.
Published: July 2002

Photoemission, LEED, and AES measurements were made on the mechanically polished (111) surface of a type IIa diamond. No emission from filled states in the fundamental gap was found over the photon energy range 13.3 eV?h/ω?200 eV. This result, coupled with the sharp 1×1 LEED patterns which were obtained and the relative cleanliness (of elements which can be detected by AES) of the diamond (≲1 at.% oxygen, <0.5 at.% Si) suggests hydrogen termination of the lattice. Photoelectric yield measurements demonstrate the photoelectric threshold to be at band gap energy radiation. Investigation of the photoemission electron distribution curves (EDC’s) shows that, while the electron affinity at the surface is always positive, band bending is sufficient to result in an effective negative electron affinity under certain conditions. A variable surface dipole on the atomic scale, possibly due to the adsorption–desorption of a background gas, is reported. A study of the relative cross section of the upper (p-like) versus the lower (s-like) portion of the diamond valence band indicates comparable cross sections at a photon energy h/ω=160 eV.
Characterization of strain at Ga1−xAlxAs–GaAs interfaces using electrolyte electroreflectance
Authors: Pollak F. H. , Woodall J. M.
Published: July 2002

Utilizing electrolyte electroreflectance we have been able to detect the strains at the interface of epitaxial Ga1−xAlxAs(x∠0.9) grown on a GaAs substrate. Use has been made of the fact that the Ga1−xAlxAs is transparent in the wavelength region (1.3–1.9 eV) corresponding to the direct gap (and the spin–orbit split component) of GaAs. The sensitive technique of electrolyte electroreflectance has thus enabled us to ’’see through ’’ the Ga1−xAlxAs and to observe the properties of the GaAs in the interfacial region. Structures of p–p–nGa1−xAlxAs–GaAs–GaAs solar cell material were prepared using three different modifications of the liquid phase epitaxy method. These various growth conditions produced different interfacial strains which have been observed in shifts of the GaAs substrate electroreflectance spectra. Above 2.5 eV we have observed electroreflectance structure corresponding to the Ga1−xAlxAs epitaxial layer. These optical features have yielded information about the properties of the Ga1−xAlxAs material.
Low pressure CVD of III–V compounds
Authors: Duchemin J. P.
Published: July 2002

In this paper it is shown that the low pressure organometallic chemical vapor deposition (LP-MOCVD) technique of growing semiconductors is generally applicable to most of the III–V compounds that are currently of interest. The principles of the technique are described and then specific applications are detailed. It has been found that the LP-MOCVD technique offers the following advantages: reduction of autodoping, virtual elimination of parasitic reactions, and the possibility of growth on large areas of semiconductor substrates.
Effect of residual gases on surface morphology and microstructure of Pb–In–Au films deposited at 95 K
Authors: Huang H. -C. W. , Baker J.M. , Serrano C. M. , Kircher C. J.
Published: July 2002

Fine-grained, 200 nm thick films of Pb–In(12 wt%)–Au(4 wt%) have been obtained by depositing sequential layers of Pb, Au, Pb, and In at 95 K in high vacuum. The use of such films as base electrodes for Josephson tunnel junctions has enabled achievement of an ≊100× improvement in junction stability during repeated thermal cycling between 300 K and 4.2 K. However, the morphology and microstructure of such films were found to be strongly dependent on the level and composition of the residual gas during deposition. This effect was studied in an ultrahigh vacuum system by intentionally introducing H2O, CO2, and CO individually and in mixtures at pressures between 7×10−6 and 3×10−4 Pa. The films were then examined with Scanning Electron Microscopy (SEM) and Transmission Elecron Microscopy (TEM). Whereas the presence of the individual gases caused relatively minor changes in the films, the combination of H2O and CO2 caused holes and hillocks to form at a level that increased strongly with gas exposure. A factor of five increase in exposure produced a five order of magnitude increase in hole density. In order to obtain hole-free Pb–In–Au films with a smooth surface morphology, it was found that the sum of the partial pressures of H2O and CO2 had to be maintained below 1×10−5 Pa during deposition and the amount of exposure between depositions had to be limited to less than 0.02 Pa s. The average grain size of the films, as determined by TEM, was found to decrease weakly with increasing gas exposure.
Antisite defect in GaAs and at the GaAs–AlAs interface
Authors: Lin-Chung P. J. , Reinecke T. L.
Published: July 2002

Calculations are performed of the local densities of states for the As antisite defect and for the ideal Ga vacancy in GaAs, of the changes in their electronic properties near an ideal (100) GaAs–AlAs interface, and of the total interaction energy of these defects with the interface. The calculations were made using a novel recursion approach and are based on tight binding Hamiltonians.
Ohmic contacts to lightly doped n and p indium phosphide surfaces
Authors: Tseng W. , Christou A. , Day H. , Davey J. , Wilkins B.
Published: July 2002

Both n- and p-type Ge films have been grown on InP substrates by vacuum-vapor-deposition. Contact resistivity for n-Ge films on 1.3×1016 cm−3 n-InP was measured to be 10−5 Ω cm2. On the other hand, p-Ge films on lightly doped p-InP resulted in poor ohmic behavior. For contacts to lightly doped p-InP, the AuZn system was used, resulting in a contact resistance of 5×10−3 Ω cm2 for 1.2×1016 cm−3 p-InP. The sintering behavior of this AuZn contact to InP and the doping characteristics of deposited Ge films have been correlated with Auger measurements of similarly heat-treated InP surfaces.
Molecular parameters and lithographic performance of poly(chloromethylstyrene)—a high-performance negative electron resist
Authors: Choong H. S. , Kahn F. J.
Published: July 2002

Poly(chloromethylstyrene) (PCMS) is shown to have a desirable combination of properties, including high sensitivity, high dry-etch resistance, and high resolution. As a consequence, it is a very attractive candidate for high performance (throughput, resolution, process compatibility) electron beam lithography. PCMS lithographic performance is higher than that of any other previously reported, high-sensitivity negative electron resist. Performance results are compared specifically with COP, PGMA, and CMPS, and are correlated with molecular and chemical properties. PCMS synthesis and evaluation results are reported for polymers with molecular weights (?w) between 20 000 and 450 000 and polydispersivities between 1.3 and 2.3. A typical high molecular weight (?w = 381 000) material with polydispersivity of about 1.6 has sensitivity (Dg0.5)<0.5 μC/cm2, contrast ≳1.5, and resolution <1.0 μm (equal lines and spaces). Respective values for a typical low molecular weight (?w = 22 000) material with polydispersivity of about 1.3 are sensitivity <7 μC/cm2, contrast ≳2.0, and resolution <0.5 μm.
An e-beam microfabrication system for nanolithography
Authors: Lee K. L. , Ahmed H.
Published: July 2002

An electron beam lithography system designed for making structures with dimensions in the range 100 to 1000 Å is described. The beam diameter is 10 Å and the maximum beam energy is 100 keV. The system is calibrated for resist exposure by measuring the beam size and current after magnifying it with projector lenses. The beam is deflected electromagnetically under computer control and vector scanning is used during lithography. The system has been used to make fine lines and grids with linewidths in the range 150 to 500 Å. Relatively dense structures with large ratios of resist thickness to linewidth have been demonstrated on both thick and thin electron-transparent, silicon substrates with the system operated at 50 keV. Results have been obtained on both single layer crosslinked resists and double layers of crosslinked resists and PMMA. It is concluded that finer lines and more densely packed structures over larger areas can be obtained on solid substrates using 100 keV beam energy.
Stationary anode x-ray source for the evaluation of conventional resists
Authors: Warlaumont J. M. , Maldonado J. R.
Published: July 2002

We have developed a high-power stationary aluminum anode x-ray exposure system in order to perform experiments and evaluate conventional resist processes, x-ray mask substrates, and alignment techniques applicable to an x-ray lithography system using an electron storage ring source. The source output energy (AlK α fine) falls within the broad energy peak from a properly filtered 700–1000 MeV storage ring spectrum. In this paper we describe the x-ray source and also present results on sensitivity and patternability of conventional resist under x-ray exposure.
Proximity effect correction using a dose compensation curve
Authors: Greeneich J. S.
Published: July 2002

A new concept, the dose compensation curve, is described for use in a proximity effect correction algorithm. The dose compensation curve links dose compensation factors, developed resist images, and calculated values of energy density at pattern boundaries. An experimentally measured dose compensation curve agrees very well with theoretical predictions. This technique has been successfully implemented in a fast promixity-effect correction algorithm which automatically corrects the exposure dose factor in the electron-beam data base for vector scan machines.
Auger spectrum changes and work function of clean and contaminated zirconium
Authors: Danielson L. R.
Published: July 2002

The work function of zirconium metal in the presence of C and O impurities was measured from the changes in the Auger spectra.(AIP)
Molecular beam source for high vapor pressure materials
Authors: Myers T. H. , Schetzina J. F.
Published: July 2002

A molecular beam source for deposition of high vapor pressure materials in MBE systems is described. The source consists of a collimating effusion cell of original design which is heated by a temperature-controlled Radak II oven (Luxel Corporation). Construction details of the source are given along with calibration and performance data.
UV–Ozone Cleaning of GaAs for MBE
Authors: McClintock J. A. , Wilson R. A. , Byer N. E.
Published: July 2002

A simple method of removing carbon contamination from GaAs substrates using exposure to ozone and ultraviolet light is described.
Photoionization and thermal activation of compound semiconductor MOS interfaces and origin of interface states
Authors: Hasegawa Hideki , Sawada Takayuki
Published: July 2002

Dynamic properties of GaAs and InP anodic MOS interfaces are studied, using photocapacitance transient spectroscopy (PCTS) and deep level transient spectroscopy (DLTS) techniques. Measured PCTS spectra possess a gate bias dependent portion corresponding to U-shaped continuous distribution of interface states and a bias-independent portion with a large photoionization rate. The photoionization cross section of a state continuum increases monotonically with photon energy, similarly to Si MOS, but very differently from bulk deep traps. Anomalously reduced DLTS activation energies of interface states are observed for electron emission in GaAs and for hole emission in InP, and they are correlated to a bias-independent portion of PCTS spectra. Measured results are explained by coexistence of an energetically and spatially distributed localized state continuum region and a partially delocalized state region. Surface disorder is proposed to be the origin of such composite interface state structure rather than the surface-vacancy based model.
Band structure of impurity-sheet-doped superlattice alloys
Authors: Hjalmarson Harold P.
Published: July 2002

The band structure and density of states for large superlattices of (100) Ga-site Ge and As-site N impurity sheets in GaAs have been calculated by a semiempirical tight-binding technique. Both of these two-dimensional conduction-band derived bands with a J-point indirect minimum which is deep in energy (∠0.5 eV) relative to the bulk conduction band edge. The calculation, which was performed on a single impurity sheet, demonstrates that, in general, a planar defect localizes or binds one or more states. It is suggested that the large binding energies of these sheets will confine electric-field-accelerated carriers and thus such superlattices will be highly conductive parallel to the impurity sheets.
Properties of a new molybdenum nitrogen phase
Authors: Fuller W. W. , Wolf S. A. , Gubser D. U. , Skelton E. F. , Francavilla T. L.
Published: July 2002

A new Mo–N phase has been prepared by rf reactive sputtering. The structure, as determined by x-ray analyses matches well with the hexagonal Mo2C structure. The films were produced by reactively sputtering Mo in a gaseous N2 atmosphere in an attempt to prepare thin films of the predicted high Tc superconductor MoN in the B1 phase. By further nitriding these Mo2N films with NH3 at 780 °C for 24 h, they appeared more stoichiometric as determined by their superconducting properties. These films are superconducting Tc ≊7 K and have high critical magnetic fields Hc2(0) ≊7.5 T. Varying both the temperature of the substrate between 500 and 900 °C, and the power density did not effect the phase of the Mo–N compound.
Influence of the microstructure on the corrosion behavior of magnetron sputter-quenched amorphous metallic alloys
Authors: Thakoor A. P. , Khanna S. K. , Williams R. M. , Landel R. F.
Published: July 2002

Numerous amorphous metallic alloys exhibit excellent corrosion resistance in acidic and/or basic aqueous solutions, mainly due to the absence of grain boundaries and other structural defects in the homogeneous phase. However, the microstructure and surface texture of the films, and thus their corrosion behavior, strongly depend on the quenching atmosphere, presure, and other deposition parameters. In this paper, we report the microstructure and corrosion behavior of magnetron sputter deposited amorphous metallic films of (Mo60Ru40)82B18 under varying sputtering atmospheres (e.g., Ar, Ar+O2 and Ar+N2 gas mixtures). Their microstructural details and topology have been studied by scanning electron microscopy and correlated with the deposition conditions. For example, films deposited in argon pressure in excess of 5 μm or in the presence of O2 (∼2 μm) in Ar (∼5 μm) exhibit columnar growth patterns, whereas addition of N2 (∼2 μm) in Ar (∼5 μm) seems to trigger crystallization of the deposits. The deposition kinetics can be understood with the help of the growth model proposed by Thornton. The influence of the microstructure and surface texture on the corrosion behavior is also discussed.
Raman scattering in Hg0.8Cd0.2Te
Authors: Amirtharaj P. M. , Tiong Kwong-Kau , Pollak Fred H.
Published: July 2002

We report the first polarization dependent Raman scattering study in Hg0.8Cd0.2Te from the (100) and (111) faces. The Raman spectra were recorded in the back scattering geometry at 77 K using several lines of an Ar+ laser near resonance with the E1 optical gap. The study leads to an unambiguous identification of the HgTe and CdTe-like transverse optical (TO) and longitudinal optical (LO) phonon features. The HgTe-like TO and LO phonons occur at 122±1 cm−1 and 140±1 cm−1 and the CdTe-like LO phonon occurs at 156±1 cm−1; the CdTe-like TO–LO splitting was too small to be observable. The presence of a symmetry forbidden HgTe-like TO phonon from the (100) face indicates the presence of defects or disorder. A defect mode was observed at ∼108 cm−1. In addition, an extremely surface sensitive feature was seen at 132 cm−1 and has been tentatively assigned to a coupled LO phonon–intersubband excitation from the natural occurring surface inversion layer. A strong feature observed at 135 cm−1 may arise from clustering effects.
Application of generalized effective mass theory to some native point defects in Hg1−xCdxTe
Authors: Wang C. L. , Wu S. , Pan D. S.
Published: July 2002

We have studied a few native defects in Hg1−xCdxTe in the effective mass approximation. For the case of mercury vacancy, which is of particular interest, this approach is quantatatively meaningful. The calculated levels for the neutrals and charged vacancies are reported.
HgCdTe heterojunctions
Authors: Bratt Peter R.
Published: July 2002

HgCdTe heterojunctions consisting of a wide band gap n-type Hg1−xCdxTe layer grown epitaxially on a narrow band gap  p-type Hg1−yCdyTe substrate (x>y) were studied. The heterojunction transition region between x and y materials was found to be graded over distances of about 0.4 to 0.8  μm. The position of the  p–n junction depletion layer within the graded transition region was the major factor controlling the heterojunction properties. When the depletion layer was located near the narrow band gap material, normal photodiode behavior was observed. When the depletion layer was at the center of the transition region or near the wide band gap material, a potential barrier was formed which inhibited minority carrier photocurrent originating in the  p-type material from crossing the heterojunction. Qualitative energy band models based on the analysis of HgCdTe heterojunctions recently published by Migliorato and White were constructed to explain the observed results.
Surface and interface recombination in thin film HgCdTe photoconductors
Authors: Graft Ronald D. , Carlson Frederick F. , Dinan John H. , Boyd Phillip R. , Longshore Randolph E.
Published: July 2002

A method is described for the separation of bulk and surface recombination parameters using experimentally measured photoconductive decay curves. Curve fitting procedures using numerical solutions to the time dependent hole continuity equation permit a unique determination of surface recombination velocities and bulk lifetime. The method is applied to thick and thin films of HgCdTe to determine recombination velocities at several technologically important interfaces. Values of recombination velocity ranged from 300 to 20 000 cm/s depending upon material growth method and surface preparation. Experimentally observed deviations from the assumed model are discussed in terms of a spatially dependent bulk lifetime.
Analysis of oxygen isotope interfaces using negative molecular ion SIMS
Authors: Mitchell D. F. , Hussey R. J. , Graham M. J.
Published: July 2002

The extent of oxygen diffusion in oxide scales formed on metals during high-temperature oxidation can be studied by sequential oxidation in 16O2 and 18O2 followed by SIMS profiling. Previously, 16O− and 18O− profiles have been used to examine oxygen penetration, but the analysis is limited in its ability to quantify diffusion, e.g., because of instrumental interface broadening and nonuniformity of both oxide thickness and isotope distribution. A method which, to a large extent, overcomes these and other difficulties is to analyze molecular ion species of the type M 16O2−, M 18O2−, and M 18O 16O−. The strength of this approach in interpreting diffusion is demonstrated by analysis of a 470-Å oxide formed on Cr(100).
Adhesion of evaporated titanium to polyethylene: Effects of ion bombardment pretreatment
Authors: Bodö P. , Sundgren J.-E.
Published: July 2002

Titanium films, 1 μm thick were electron-beam evaporated onto polyethylene (PE) that had been pretreated in situ by 2 keV Ar+ bombardment. A measure of the film adhesion was obtained by measuring the pull strength required to remove the Ti films. A strong dependence of the adhesion on the ion dose was found. The pull strength had a maximum of approximately 20 MPa after a dose of 6×1014 ions/cm2 but decreased for higher ion doses. Without any ion bombardment prior to deposition, the adhesion was very poor with a pull strength of approximately 2 MPa. XPS analysis was used to examine the effect of the ion bombardment on the chemistry of the PE substrate and the Ti/PE interface. Untreated PE samples were contaminated with surface impurities and probably also with low molecular weight hydrocarbons. As the adhesion is maximized, most of the impurities are removed by the ion bombardment. The strong adhesion is suggested to be due to formation of a carbidelike Ti–C interfacial layer, detected by XPS.
A method for the calculation of LEED angular profiles to estimate overlayer spacings and island size distributions
Authors: Saloner D. , Lagally M. G.
Published: July 2002

We present a brief summary of a general approach to calculate, in the kinematic approximation, angular profiles of LEED beams that allows a quantitative evaluation of finite-size effects in overlayers adsorbed with arbitrary unit mesh [including p(1×1)] on arbitrary substrates. The calculation includes realistic atomic scattering factors and electron beam attenuation. The procedure is general in that an evaluation of correlation functions for arbitrary distributions of overlayer atoms is possible. The method can also be used to estimate overlayer z-spacings. A comparison is made with experimental results for GaAs(110) p(1×1)-Sb.
Reactive deposition of low loss Al2O3 optical waveguides by modified dc planar magnetron sputtering
Authors: Este G. , Westwood W. D.
Published: July 2002

A modified planar magnetron system has been used to dc reactively sputter Al2O3 films with optical waveguide losses of 1 dB/cm and refractive indices of 1.65±0.005 at 632.8 nm. The target and substrate are separated by two 176×45 mm graphite grid plates with either 2 or 4 mm diam apertures in a hexagonal array. When the Al target was sputtered in argon and the oxygen flow rate increased, the value f2c at which an Al2O3 layer formed on the target depended upon the configuration of the apertures and the rf power coupled to the substrate holder; for a sputtering power of 1.25 kW, f2c increased from 11 to 13 ml/min when the aperture diameter was reduced from 4 to 2 mm or when the rf power increased from 0 to 50 W, due to increased gettering of oxygen outside the target region. The low optical loss films were obtained by controlling the ‖oxygen flow rate between 40% and 70% of f2c; at low flow rates, the films were absorbing due to oxygen deficiency whereas scattering loss increased near f2c due to particle ejection caused by arcing of the partially oxidized target. Although the deposition rate of Al was reduced by the grids, the Al2O3 deposition rate obtained was approximately three times the value obtained by rf reactive sputtering without grids to obtain the same optical loss. The flux through the grid structures was calculated and agreed with the measured deposition rates; for the 4 mm apertures, the calculated flux was 8.3% of the value without apertures and the experimental value was 10%. The modified magnetron system provides a higher deposition rate method for depositing low optical loss Al2O3 films than is obtained by rf reactive sputtering.
Observation of surface states on gold films by electron tunneling spectroscopy
Authors: Lambe John , Thakoor A. P. , Khanna S. K.
Published: July 2002

We report the observation of intrinsic surface states on gold films at room temperature and 77 K using electron tunneling spectroscopy. Since resolution of such a spectroscopy is of the order of kT, one can examine surface states even at room temperature fairly well. The devices used in these measurements consist of aluminium–aluminium oxide–gold tunnel junctions fabricated by evaporation of Al, in situ oxidation of the Al surface using wet oxygen plasma, followed by evaporation of Au through appropriate masks in an oil free ultrahigh vacuum system. The aluminium is 400 Å thick, the oxide is 10–30 Å thick, and the gold is 400 Å thick. The gold films are highly textured with the 〈111〉 direction perpendicular to the plane of the film. A surface state exists on the 〈111〉 surface of gold at about 0.5 eV below the Fermi level; however, significant surface Stark effect shifts the level downward and shows at ∼0.68 eV below the Fermi level in the tunneling spectrum (d2I/dV2 vs V) of the junction. Our observations of the surface state are in good agreement with observations made using other surface spectroscopic techniques such as electroreflectance and electromodulation spectroscopy. Since the electrons in such a state are confined only to metal surfaces, they form potential basis for a new kind of chemical sensor based on solid state surface spectroscopy.
Comparative study of Nb and TiW barrier layers between Au and a-SiO2
Authors: Liehr M. , Delrue J. P. , Caudano R. , Herbots N. , Vanden Berghe R. A. L. , Vlaeminck R. , Loos H.
Published: July 2002

The performance of Ti0.3W0.7 and Nb thin films as diffusion barriers for Au was investigated by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). The films were sputter deposited in Ar:N2 (70:30 vol%) or pure Ar on amorphous SiO2. They were annealed in air at temperatures ranging from 250 °C up to 750 °C for several hours. In-depth profiles revealed an onset of oxidation of the barriers at 520 °C for Nb and about 600 °C for TiW. Barrier oxidation and extensive diffusion could be correlated. Distinct diffusion behavior as a function of temperature was established between TiW and Nb. A Nb multilayer structure was found to provide the best reliability as the barrier and as the adhesion layer.
SIMS study of ion assisted etching of Si by Cl2
Authors: Vitkavage D. J. , Ameen M. S. , Mayer T. M.
Published: July 2002

The ion assisted chemical etching of Si with Cl2 using 1 kev Ar+ and Ne+ was investigated using secondary ion mass spectrometry (SIMS). The secondary ions detected included Si+, Cl+, SiCl+, SiCl+2, SiCl+3, and Cl−. All these ions except Cl+ were found to increase rapidly with increased Cl2 ambient pressure until a saturation level was reached. The Cl+ signal exhibited behavior characteristic of different bonding environments at low and high surface coverage. The ion-induced removal cross section of Cl measured from the time decay of the SiCl+ signal was found to be ∼250 Å2 for Ar+ and 80 Å2 for Ne+, decrease at low Cl coverage, and increase with increased angle of incidence up to 70 °. The Cl+ intensity relative to Si+ greatly increased at large angles of incidence.
Thermal decomposition of titanium hydride and its application to low pressure hydrogen control
Authors: Hirooka Yoshihiko
Published: July 2002

Thermal decomposition behavior of titanium hydride (TiH2) powder at temperatures between 250 and 330 °C (523 and 603 K) has been studied from both thermodynamic and kinetic viewpoints. Equilibrium hydrogen pressure measured in a closed system was found to vary from the order of 10−3 to 10−2 Torr (10−1 to 1 Pa) and the enthalpy of formation of titanium hydride in the two phase (α+γ) region was evaluated to be 31 kcal/mol (130 kJ/mol). It has been found that steady state decomposition can be realized also in an open (continuously pumped) system as long as the two phases coexist. Hydrogen pressure at the steady state was in the order from 10−4 to 10−3 Torr (10−2 to 10−1 Pa) and the activation energy for the decomposition was determined to be 29 kcal/mol (122 kJ/mol). In addition, it has been demonstrated that hot titanium hydride can simply be applied to low pressure hydrogen control in vacuum systems.
Formation and electrical properties of Hf Si2 grown thermally from evaporated Hf and Si films
Authors: So F. C. T. , Lien C.-D. , Nicolet M-A.
Published: July 2002

2 MeV 4He+ backscattering spectrometry and x-ray diffraction have been used to study Hf Si2 formed by thermal annealing of a Hf Si film on evaporated Si (Sie) at temperatures between 575 and 650 °C. A laterally uniform layer of Hf Si2 forms and its thickness is proportional to the square root of time at a fixed temperature. The activation energy of this reaction is found to be 3.5±0.3 eV. This transport-limited process differs from that observed on single crystal Si, where Hf Si2 forms at temperatures above 700 °C by a process believed to be nucleation controlled. Four-point probe measurements of resistivity and Hall coefficient at room temperature on samples with both Hf Si and Hf Si2 were used to determine that both Hf Si and Hf Si2 are electron conductors. For Hf Si2, the electron concentration is 2.9±0.2×1021 cm−3 and the mobility is 36±4 cm2/Vs, giving a resistivity of 60±3 μΩ cm. Schottky barrier diodes formed either by reacting a Hf film deposited directly on 〈111〉 Si or by reacting a Hf film with Sie in a 〈111〉 Si/Hf/Sie/Hf configuration at temperatures above 600 °C were prepared. The Schottky barrier height of Hf Si2 on n-type 〈111〉 Si as evaluated from forward and reverse I–V characteristics is 0.54±0.01 eV in both cases.
Secondary ion and sputtered neutral formation from oxygen loaded Si(100)
Authors: Sander P. , Kaiser U. , Jede R. , Lipinsky D. , Ganschow O. , Benninghoven A.
Published: July 2002

We have studied the problem of quantification of secondary ion yields from oxygen covered Si(100) using secondary ion mass spectrometry (SIMS), secondary neutral mass spectrometry (SNMS) with electron impact postionization, Auger electron spectroscopy (AES), and photoelectron spectroscopy (XPS). Implantation of oxygen does not lead to detectable amounts of SiO2, whereas exposure to gas phase O2 during Ar+ or O+2 ion bombardment leads to a closed SiO2 layer. The surface chemical state evaluated from the secondary ion fragmentation distributions exhibits only minor changes between the pure implantation and the additional gas-phase adsorption case. It is proposed that the secondary ion emission of the Si–O system is influenced by a ‘‘first-order’’ effect of collision-induced SiO2 formation during the individual sputtering event.
Surface segregation of impurities induced by photon absorption in CdTe and (Hg,Cd)Te
Authors: Tregilgas J. , Gnade B.
Published: July 2002

Noble metal impurities have been observed to segregate toward the surface of p-type CdTe and heavily p-type (Hg,Cd)Te samples during room temperature aging in ambient room light. This behavior has not been observed in n-type CdTe or lightly p-type (Hg,Cd)Te. The photon-induced segregation is believed to involve the redistribution of positively charged impurity interstitials in a field generated by absorbed photons with energies greater than the band gap. A qualitative electromigration model based on the Dember effect and simple ionic conduction, has been used to explain the experimental results.
Investigation of generation processes at the SiO2/HgCdTe interface by gate controlled diodes
Authors: Rosbeck J. P. , Blazejewski E. R.
Published: July 2002

HgCdTe gated photodiodes are studied theoretically and experimentally for surface leakage current mechanism limiting diode performance. Use of a second field plate beyond the perimeter gate has allowed clear identification of leakage components associated with surface state generation, depletion region generation, and field induced tunneling. The fundamental features of the leakage current profiles are derived from MOS theory, and exhibit characteristics similar to the properties of the SiO2/Si interface with some added features peculiar to narrow band gap semiconductors. Both boron implanted and double layer p–n junction devices in the 2 to 5 μm range are examined. Surface potential was found to have a significant effect on diode impedance and breakdown characteristics. Minimum surface state densities derived from diode leakage current versus gate bias curves were in the range of 1011 cm−2 eV−1.
Activation and redistribution of implanted P and B in polycrystalline Si by rapid thermal processing
Authors: Chow R. , Powell R. A.
Published: July 2002

Rapid thermal processing (RTP) allows electrical activation of implanted semiconductors to be carried out at high temperature in times so short (∼10 s) that minimal dopant redistribution occurs. Use of RTP to activate implanted species in single-crystal Si is well documented, but relatively little has been reported for poly-Si. In this paper, we present measurements on 0.4 μm thick poly-Si films implanted with n-type (31P+) or p-type (11B+) dopants. RTP was carried out in vacuo (∼1×10−5 Torr) by exposing samples for 5–30 s to the blackbody radiation of a graphite heater at 1150–1300 °C. Dopant activation and redistribution following RTP was measured by spreading resistance and four-point probe. In poly-Si, unlike similarly implanted and rapidly annealed single-crystal Si, we find considerable redistribution for both dopants. For P, significant dopant loss occurred from the uncapped poly-Si surface; however, a thin (600 Å) SiO2 cap prevented this outdiffusion. For B, on the other hand, uncapped poly-Si surfaces exhibited minimal dopant loss. The time evolution of carrier concentration profiles depended both on implant dose and RTP conditions.
Plasma phase polymerization reactions in the deposition of glow discharge deposited a-Ge:H alloy films
Authors: Ross R. C. , Chao S. S. , Tyler J. E. , Czubatyj W. , Lucovsky G.
Published: July 2002

Films of a-Ge:H deposited from low power rf plasmas of GeH4 and H2-diluted GeH4 at substrate temperatures Ts=100 to 400 °C have been characterized by IR spectrometry to determine the levels of Ge monohydride and polyhydride bonding. Correlation of the changes in hydrogen bonding and deposition rate for these and previously studied a-Ge:H films with the plasma phase deposition parameters (power density and degree of dilution) and the Ts parameter leads to a general model of H incorporation which involves both plasma phase and surface reactions. Plasma reactions can generate either monomeric or polymeric reactive species. These species then undergo thermally activated surface reactions which further determine the degree of hydrogen elimination and subsequent incorporation as monohydride or polyhydride.
Ultrathin gate dielectrics on 150 mm Si wafers via rapid thermal processing
Authors: Nulman J. , Krusius J. P. , Shah N. , Gat A. , Baldwin A.
Published: July 2002

The scalability from 75 to 150 mm silicon wafers of a new oxidation process is discussed. This process is based on rapid thermal processing (RTP) in a controlled oxygen ambient with heating provided by tungsten-halogen lamps, temperature monitored via an optical pyrometer and controlled by a computer. Silicon dioxide films with thicknesses in the range from 45 to 400 Å were obtained at 1150 °C, with a uniformity of 1.5% across the wafers and from wafer to wafer, independent of the wafer size. Electrical characteristics show typical breakdown fields of 15 MV/cm for 100 Å films with a statistical distribution similar to that of furnace oxides. Capacitance–voltage studies show midgap density of states of less than 1×1010 cm−2 eV−1 and ideal flat band voltages.
The anodized Al–InP interface
Authors: Hwang T. , Chang R. R. , Geib K. M. , Wilmsen C. W.
Published: July 2002

High quality MOSFET’s have been reported for InP using an anodized Al film as the gate dielectric. In order to achieve this high quality, the anodization has to be carried out in such a manner so as to also partially oxidize the InP substrate. This paper presents a chemical analysis of this interfacial native oxide. The oxide composition is found to vary with depth and contains primarily InPO4 and P2O5 with some In(OH)3 incorporation. Also, the amount of substrate species diffused into the Al2O3 bulk becomes significant for native oxides over ∼300 Å in thickness.
The impact of process parameters and coating source on the properties of magnetic recording layers
Authors: Röll K.
Published: July 2002

The use of continuous ferromagnetic thin films, instead of conventional particulate media, promises an increase of data storage capacity by more than one order of magnitude. For large scale mass production, specially designed equipment, new sources, and modified deposition processes are required. The magnetic properties of the recording layers can be influenced in various ways. In evaporated CoNi video tapes the coercivity Hc is adjusted by an oblique angle of incidence during evaporation. For sputtered CoNi for rigid disks, an undesired signal modulation can be suppressed by randomizing process parameters. Perpendicular recording requires well oriented columnar crystallites prepared by the magnetron sputtering of CoCr at elevated substrate temperatures. In-line evaporation and sputtering systems enable the sequential deposition of underlayers, magnetic layers and protective layers required for long term reliability of thin film recording media.