Optical properties of polycrystalline and amorphous Ni1?xPx layers by ellipsometry

Abstract

The optical properties of polycrystalline and amorphous d.c.-electrodeposited Ni1−xPx alloys in the visible spectral range are reported. Spectroscopic ellipsometry measurements of the pseudo-optical constants were performed from 1.65 to 3.1 eV for specimens with atomic fraction of phosphorus of 0.06<x<0.28. It was found that the dielectric functions of asdeposited Ni1−xPx could be expressed in the modified Drude-like form, including separate contributions from the interband transitions. Estimated values of the plasmon energy in the range of 5.3–3.1 eV and scattering time of the order of 10−15 s seem to show quantitative validity. A decrease in plasma frequency by a factor of about 1.4 across the glass-forming range agrees well with the predicted decrease in the s-p density of states at the Fermi level. Transformation of the amorphous Ni0.725P0.275 to the crystalline Ni3P+Ni phase caused by heating results in changed optical functions which exhibit large deviation from the single nearly-free-carrier approach. This would suggest a two-carrier and/or frequency-dependent Drude parameters model as offering a more reasonable description of the optical conductivity of crystalline two-phase Ni-P systems.