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The electrical characteristics of Au/Ni/Ti/ n-SiC contacts have been examined as a function of implant dose (1013-1014 ions/cm2) at 5 KeV and temperature of annealing (750-1000 °C). Measurements of specific contact resistance, ρc, were approximately constant at lower implant doses until increasing at 1 x 1015 ions/cm2 for both C and P ions. Annealing at a temperature of 1000 °C has reduced the value of ρc by an order of magnitude to ∼1 x 10-6 Ω.cm2 at implant doses of 1013-1014 ions/cm2. Auger Electron Spectroscopy (AES) has shown that annealing at 1000 °C resulted in a strong indiffusion of the metallization layers at the interface.
The origin of red supergiant mass loss still remains to be unveiled. Characterising the formation loci and the dust distribution in the first stellar radii above the surface is key to understand the initiation of the mass loss phenomenon. Polarimetric interferometry observations in the near-infrared allowed us to detect an inner dust atmosphere located only 0.5 stellar radius above the photosphere of Betelgeuse. We modelled these observations and compare them with visible polarimetric measurements to discuss the dust distribution properties.
We present a preliminary report on radial–velocity and infrared interferometric observations, with emphasis on the newly resolved nearby sources Gl 609.2 and Gl 804. We briefly discuss their low–mass companions, their luminosities, and their individual masses inferred from the combined solution of their spectroscopic and visual orbits.
A Fourier Transform Spectrometer has been employed to obtain low and medium resolution spectrophotometry in the range 700 to 10000 cm-1. The method is described briefly and typical data are shown. The technique is applied to a study of 15 K giants, and spectra of 4 and 16 cm-1resolution in the range 4000 to 6500 cm-1 are discussed briefly. CN strong stars are found to be CO strong as well. Five K giants are found to have a relative 13C enhancement over probable primordial abundances.
The effect of low energy implantation of P or C ions in 3C-SiC on the properties of Ti/Ni/Au contacts has been examined for doses in the range 1013-1015 ions/cm2. Measurements of specific contact resistance, ρc, were performed using the two-contact circular test structure. The magnitude of ρc for the Ti/Ni/Au contacts on unimplanted SiC was 1.29 x 10−6 Ω.cm2. The value of ρc increased significantly at an implant dose of 1 x 1015 ions/cm2. The dependence of ρc on ion dose has been measured using both C and P implant species.
Silicide formation on strained GexSilx layers by the thermally-induced metal/GexSi1−x reaction results in enhanced relaxation of the underlying strained layer. Silicide formation on an amorphous layer is a potential means of decreasing processing temperatures, increasing reacted-layer/GexSi1−x interface planarity and hence, decreasing strained layer relaxation. For the present report, the thermally-induced Co/Ge.17Si.83 reaction on crystalline and amorphous substrates at temperatures of 500-600°C has been compared. Though the rate of silicide formation increased with amorphous substrates, strained layer relaxation was not inhibited.
Deep level acceptor and donor centers are created in III-V materials by energetic ion bombardments. The controlled introduction of these centers by selective area implantation can be used to provide electrical and optical isolation of neighbouring devices. We will contrast the implant isolation characteristics of GaAs and AlGaAs with materials such as InP and InGaAs, and also with the ternary compounds InGaP and AllnP, for which there has previously been little information. In all of these materials the as implanted resistivity is controlled by hopping conduction processes, with p « e×p (T 0.25). Post-implant annealing can be used to achieve resistivities of > 108 Ωcm in initially highly doped material provided the implant doses are correctly chosen. These defect engineered regions may be made many microns deep by using overlapping multiple-energy keV implants or a single MeV implant. In the latter case a nearly flat damage profile can be achieved over depths typical of HBT, SEED or long-wavelength laser epitaxial thicknesses. Examples of these devices which rely on controlled introduction of deep level defects for their operation will be given.
Epitaxial CoSi2 layers on Si substrates have been amorphized with Co and/or Si ion implantation. The influence of nonstoichiometry on the rate of solid-phase epitaxial growth (SPEG) of amorphized CoSi2 has been investigated with time-resolved reflectivity, Rutherford backscattering spectrometry and Mossbauer spectrometry, the latter with radioactive 57Co probes. A decrease in SPEG rate was apparent with an increase in nonstoichiometry. For a given ion dose, the decrease was greater following Co implantation. The means by which non-stoichiometry is accommodated in a crystalline CoSi2 lattice - either through phase separation or defect formation - has been considered. SPEG rate retardation was also evident in samples implanted with both Si and Co ions with a Si:Co dose ratio of 2:1. Additional mechanisms may thus also contribute to the observed SPEG rate reduction.
We present preliminary results on fitting of SEDs to 142 z < 1 quasars selected in the mid-infrared. Our quasar selection finds objects ranging in extinction from highly obscured, type-2 quasars, through more lightly reddened type-1 quasars and normal type-1s. We find a weak tendency for the objects with the highest far-infrared emission to be obscured quasars, but no bulk systematic offset between the far-infrared properties of dusty and normal quasars as might be expected in the most naive evolutionary schemes. The hosts of the type-2 quasars have stellar masses comparable to those of radio galaxies at similar redshifts. Many of the type-1s, and possibly a one of the type-2s require a very hot dust component in addition to the normal torus emission.
Modern time-domain surveys have demonstrated that finding variable objects is relatively straightforward. The problem now is one of selecting and following up discoveries. With even larger-scale surveys on the horizon, the magnitude of the problem will inevitably increase. One way to prepare for the coming deluge is to have realistic estimates of the numbers of potential detections so that resources can be developed to meet that need. To that end, astronomers at the National Optical Astronomy Observatory (NOAO) have begun a project to characterize the variable sky in terms of type of objects, distribution on the sky and range of variation.
Non-stoichiometric GaAs layers with semi-insulating properties can be produced by low-temperature molecular beam epitaxy or ion implantation. The latter is the subject of the present report wherein the solid-phase epitaxial growth of amorphized, non-stoichiometric GaAs layers has been investigated with time-resolved reflectivity, Rutherford backscattering spectrometry and transmission electron microscopy. GaAs substrates were implanted with Ga and/or As ions and annealed in air at a temperature of 260°C. The recrystallized material was composed of a thin, crystalline layer bordered by a thick, twinned layer. Non-stoichiometry results in a roughening of the amorphous/crystalline interface and the transformation from planar to non-planar regrowth. The onset of the transformation and the rate thereof can increase with an increase in non-stoichiometry. Non-stoichiometry can be achieved on a macroscopic scale via Ga or As implants or on a microscopic scale via Ga and As implants. The influence of the latter is greatest at low doses whilst the former dominates at high doses.
The influence of implantation-induced non-stoichiometry on the electrical activation and depth distribution of Group IV (Ge and Sn) and VI (Se and Te) elements in InP has been investigated with a variety of analytical techniques. Electrical measurements indicate that P co-implantation can increase the electrical activation of the Group IV elements through reductions in amphoteric behaviour and dopant-defect complexes for Ge and Sn, respectively. The relative influence of P co-implantation increases as the dopant ion dose increases. Though others have demonstrated that co-implantation increases the electrical activation of Group II elements, similar observations were not apparent for Group VI elements, the latter attributed to the lack of Group VI element interstitial character.
The effect of 4.2 MeV, low dose Si irradiation before annealing of 1 MeV, high dose O-implanted Si has been studied. Si irradiation results in differences in the defect structure both before and after high temperature annealing. With no Si irradiation, annealing results in polycrystalline Si (polySi) formation and microtwinning at the front SiO2/Si interface. With Si irradiation, the polySi volume fraction is greatly reduced after annealing, twinned Si having grown in its place. Si irradiation has no effect on Si inclusions within the SiO2 layer. The dependence of secondary defect formation on Si dose and implant temperature is presented. In particular, Si irradiation at low implant temperatures (150°C) and moderate doses (5×1016 cm−2) is shown to be most effective in the reduction of the polySi volume fraction at the front SiO2/Si interface.
A novel methodology for altering the amount and/or nature of post-anneal disorder in SIMOX substrates has been investigated. A pre-anneal, secondary Si-ion implant (with an ion range less than that of the primary O-ion implant) is shown to effectively getter Si interstitials to the near-surface region during annealing. As a consequence, post-anneal disorder at the front. Si/SiO2 interface is significantly reduced. Alternatively, a Si-ion implant with an ion range greater than that of the O-ion implant can alter the post-anneal disorder at the back Si/SiO2 interface.
Diamond films were implanted with Au or O ions at multiple energies in order to produce a uniform region of C vacancies. Analysis of the implanted films by Raman spectroscopy has shown that the proportion of non-diamond or amorphous carbon increased with dose (5 × 1013 − 5 × 1015 ions/cm2). For implantation with Au ions, a complete amorphisation near to the surface was evident at a dose of 5 × 1015 ions/cm2. We have examined the ion beam etch (IBE) rate of the films as a function of the implant species and dose. The etching experiments were performed using either Ar or Ar/O2 gases at a bias energy of 500 -1,000 eV. In Ar gas, the process of sputter etching has produced a similar increase in etch rate with dose for both the Au and O implants. In Ar/ O2 gases, the process of ion-enhanced chemical etching produced greater etch rates than obtained in Ar gas with higher rates for the Au than the O implants.
The influence of non-stoichiometry on the solid-phase epitaxial growth of amorphized GaAs has been studied with in-situ Transmission Electron Microscopy (TEM). Ion-implantation has been used to produce microscopic non-stoichiometry via Ga and As implants and macroscopic non-stoichiometry via Ga or As implants. It has been demonstrated that amorphous GaAs recrystallizes into a thin single-crystal layer and a thick heavily twinned layer. Video images of the recrystallization process have been quantified for the first time to study the velocity of the crystalline/amorphous (c/a)-interface as a function of depth and ion species. Regrowth rates of the single crystal and twinned layers as functions of non-stoichiometry have been calculated. The phase transformation is rapid in Ga-rich material. In-situ TEM results are consistent with conventional in-situ Time Resolved Reflectivity, ex-situ Rutherford Backscattering Spectroscopy and Channelling measurements and ex-situ TEM.