856 research outputs found
Spectral absorption coefficients of carbon, nitrogen, and oxygen atoms
Spectral absorption coefficients of carbon, nitrogen, and oxygen atoms tabulated for use in radiant energy transfer calculation
Ti and V layers retard interaction between Al films and polycrystalline Si
Fine-grained polycrystalline Si (poly Si) in contact with Al films recrystallizes at temperatures well below the Si-Al eutectic (577 °C). We show that this interaction can be deferred or suppressed by placing a buffer layer of Ti or V between the Al film and the poly Si. During annealing, Ti or V form TiAl3 or Val3 at the buffer-layerâAl-film interface, but do not react with the poly Si so that the integrity of the poly Si is preserved as long as some unreacted Ti or V remains. The reaction between the Ti or V layer and the Al film is transport limited ([proportional]t^1/2) and characterized by the diffusion constants 1.5Ă10^15 exp(â1.8eV/kT) Ă
^2/sec or 8.4Ă10^12 exp(â1.7eV/kT) Ă
^2/sec, respectively
Ion implantation and low-temperature epitaxial regrowth of GaAs
Channeling and transmission electron microscopy have been used to investigate the parameters that govern the extent of damage in ionâimplanted GaAs and the crystal quality following capless furnace annealing at low temperature (âŒ400â°C). The implantationâinduced disorder showed a strong dependence on the implanted ion mass and on the substrate temperature during implantation. When the implantation produced a fully amorphous surface layer the main parameter governing the regrowth was the amorphous thickness. Formation of microtwins after annealing was observed when the initial amorphous layer was thicker than 400 Ă
. Also, the number of extended residual defects after annealing increased linearly with the initial amorphous thickness and extrapolation of that curve predicts good regrowth of very thin (<400 Ă
) GaAs amorphous layers produced by ion implantation. A model is presented to explain the observed features of the lowâtemperature annealing of GaAs
Pulsed electron beam induced recrystallization and damage in GaAs
Single-pulse electron-beam irradiations of 300-keV 10^(15)Kr+/cm^2 or 300-keV 3Ă10^(12)Se+/cm^2 implanted layers in unencapsulated GaAs are studied as a function of the electron beam fluence. The electron beam pulse had a mean electron energy of ~-20 keV and a time duration of ~-10^(â7) s. Analyses by means of MeV He + channeling and TEM show the existence of narrow fluence window (0.4â0.7 J/cm^2) within which amorphous layers can be sucessfully recrystallized, presumably in the liquid phase regime. Too high a fluence produces extensive deep damage and loss of As
Identification of the dominant diffusing species in silicide formation
Implanted noble gas atoms of Xe have been used as diffusion markers in the growth study of three silicides: Ni2Si, VSi2, and TiSi2. Backscattering of MeV He has been used to determine the displacement of the markers. We found that while Si atoms predominate the diffusion in VSi2 and TiSi2, Ni atoms are the faster moving species in Ni2Si
Strain in epitaxial CoSi2 films on Si (111) and inference for pseudomorphic growth
The perpendicular x-ray strain of epitaxial CoSi2 films grown on Si(111) substrates at ~600 °C was measured at temperatures from 24 up to 650 °C. At 600 °C, the perpendicular x-ray strain is â0.86%, which is about the x-ray strain that a stress-free CoSi2 film on Si(111) would have at that temperature. This result shows that the stress in the epitaxial CoSi2 film is fully relaxed at the growth temperature. Strains in the film below the growth temperature are induced by the difference in the thermal expansion coefficient of CoSi2 and Si, alphafâalphas=0.65Ă10^â5/°C. Within experimental error margins, the strain increases linearly with decreasing temperature at a rate of (1.3±0.1)Ă10^â5/C. The slope of the strain-temperature dependence, obtained by assuming that the density of misfit dislocations formed at the growth temperature remains unchanged, agrees with the measured slope if the unknown Poisson ratio of CoSi2 is assumed to be nuf=1/3. These observations support three rules postulated for epitaxial growth
Epitaxial regrowth of thin amorphous GaAs layers
Channeling and transmission electron microscopy have been used to investigate the parameters that govern the crystal quality following capless funace annealing at low temperature (~ 400 °C) in ion-implanted GaAs. From the results obtained, we concluded that the crystal quality after annealing depends strongly on the thickness of the amorphous layer generated by ion implantation and the number of residual defects increases linearly with the thickness of the implanted layer. Single-crystal regrowth free of defects detectable by megaelectron volt He + channeling was achieved for a very thin amorphous layer (<~ 400 Ă
)
Steady-state thermally annealed GaAs with room-temperature-implanted Si
Semi-insulating Cr-doped single-crystal GaAs samples were implanted at room temperature with 300-keV Si ions in the dose range of (0.17â2.0)Ă1015 cmâ2 and were subsequently steady-state annealed at 900 and 950°C for 30 min in a H2 ambient with a Si3N4 coating. Differential Hall measurements showed that an upper threshold of about 2Ă1018/cm3 exists for the free-electron concentration. The as-implanted atomic-Si profile measured by SIMS follows the theoretical prediction, but is altered during annealing. The Cr distribution also changes, and a band of dislocation loops ~2â3 kĂ
wide is revealed by cross-sectional TEM at a mean depth of Rp~3 kĂ
. Incomplete electrical activation of the Si is shown to be the primary cause for the effect
Gammaâray spectroscopy with singleâcarrier collection in highâresistivity semiconductors
With the standard planeâparallel configuration of semiconductor detectors, good Îłâray spectra can only be obtained when both electrons and holes are completely collected. We show by calculations (and experiments) that with contacts of hemispherical configuration one can obtain Îłâray spectra of adequate resolution and with signal heights of nearly full amplitude even when only one type of carrier is collected. Experiments with CdTe detectors for which the Â”Ï product for electrons is about 10^(3) times that of the holes confirm these calculations. The adoption of hemispherical contacts thus widens the range of highâresistivity semiconductors potentially acceptable for Îłâray detection at room temperature
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