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#CUT OFF WAVELENGTH EQUATION MOLYBDENUM FREE#
These are non-stoichiometric compounds with large free carrier densities, which give them high DC conductivities. Silicides and germanides are compounds of metals with silicon and germanium, respectively. Alexandra Boltasseva, in Handbook of Surface Science, 2014 6.6.3.1 Silicides and Germanides A is extracted to be 5.85 and 1.58 dB/µm for the thin and the thick silicides, respectively. The plots exhibit a good linearity, obeying an equation of Loss=− A× L, where the factor A=4.34× α×Γ, where α is the absorption coefficient of NiSi 2 and Γ is the confinement factor. The excess loss (in decibel scale) induced by a 0.56 µm-wide Ni silicide layer placed on the SOI channel waveguide, as shown schematically in the inset of Figure 10.8c, is depicted as a function of its length in Figure 10.8c. The buried SiO 2 and top cladding SiO 2 are 2 and 1.5 µm thick, respectively. The channel SOI waveguides employed in this study have a width of 1 µm, height of 0.2 µm, and length of 5.5 mm, and have an inverted taper at both facets. The Ni:Si ratio of the 16 nm-thick silicide is very close to 1:2, as determined from EDX, confirming that the formed phase is NiSi 2, whereas the 5 nm-thick silicide is too thin for the EDX analysis. The thinner Ni silicide exhibits smoother silicide–Si interface than the thicker ones. The final Ni silicide thicknesses are 16 and 5 nm, as shown in Figure 10.8a and b, respectively. The silicide thickness is controlled by RTA after deposition of 1-nm Ti and 5-nm Ni sequentially on SOI substrates in a sputtering system: in one procedure, RTA at 450☌ for 30 s, followed by selectively etching in Piranha solution at 90☌ for 10 min to remove the unreacted metal in the other procedure, first RTA at 240☌ for 30 s, followed by the selectively etching, and then second RTA at 450☌ for 30 s. Ni silicide for optical absorption is formed by a titanium-intermediated solid-state epitaxy ( Nakatsuka et al., 2005 Zhu et al., 2009a). In our laboratory, ultrathin epitaxial NiSi 2 films are deposited on Si channel waveguides as the absorber.
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This conflict can be solved by using the waveguide configuration because the light is absorbed along the waveguide so that the silicide film on the waveguide can be lengthened unrestrictedly while keeping its thickness sufficiently thin. However, the number of absorbed photons decreases dramatically with decreasing the silicide thickness. The yield can be significantly enhanced, namely a gain, if the silicide film is thin enough so that the photoexcited carriers moving away from the interface can be reflected to the emission barrier by wall or phonon scattering.
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The internal quantum yield is low of the order of 10 −3 as calculated by the Fowler model ( Fowler, 1931). The performance of SBPDs is primarily limited by the low responsivity because only a small fraction of photoexcited carriers in the silicide layer can emit through the silicide/Si interface to be collected as a photocurrent. Moreover, the speed of SBPDs is inherently faster than the conventional PIN PDs. Therefore, the SBPDs are completely compatible with the standard Si-CMOS processing with no new material addition and few processing modifications. For operating at 1.55-μm wavelength, the conventional silicides used in the standard CMOS technology for local interconnection, that is, Ti, Co, and Ni silicides, can be adopted because they have Φ B of 0.5–0.7 eV, thereby the corresponding cut-off wavelength of 1.8–2.4 μm. Silicide SBPDs have been used for many years to detect infrared light, which is based on the photoexcitation of metal charge carriers across the silicide/Si interface and the cut-off wavelength is mainly determined by the Schottky barrier height (Φ B) ( Cabanski and Schulz, 1991). Shiyang Zhu, Guo-Qiang Lo, in Photodetectors, 2016 10.3.1 NiSi 2 film and absorption