Optical constants of Ni1-xPtx silicides from spectroscopic ellipsometry

We provide a comprehensive analysis of the dielectric function and optical conductivity for nickel platinum silicides with different platinum concentrations (0 to 30 at.{\%} Pt). After determining accurate optical constants of Ni$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$, alloys with the same thickness were deposited directly on Si to study the optical constants of silicides. Ellipsometric measurements were performed over the same photon energy range (0.6 to 6.6 eV). During Ni$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$ deposition on Si, some metal atoms will diffuse into the Si substrate even at room temperature, creating a metal-rich silicide. Annealing the samples at 500$^{\circ}$C for 30 s creates a monosilicide layer with a thickness of about 200 {\AA}. The imaginary part of the resulting dielectric function of monosilicides shows metallic Drude behavior with two additional peaks at 1.5 eV and 4.5 eV due to interband electronic transitions. Our results will be compared to previous measurements and electronic structure calculations on NiSi and PtSi. In our results, absorption peaks broaden with increasing Pt content in the silicides, similar to our earlier results for Ni$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$ metal alloys.