Optical constants of amorphous Se

Abstract

The pseudodielectric-function spectra, ε(E)=ε1(E)+iε2(E), of amorphous (a-) selenium (Se) in the 1.2–5.2 eV photon-energy range at room temperature were measured by spectroscopic ellipsometry. The a-Se films investigated were deposited by vacuum evaporation in a base pressure of 2×10−6 Torr on Si(100) substrates at room temperature. The ε2(E) spectrum showed only a broad peak at ∼4 eV. Such a structureless feature is known to be typically observed in amorphous semiconductors. An ex situ atomic-force-microscopy image confirmed a microscopically flat surface (root-mean-square roughness of ∼0.4 nm) with relatively sharp cones in spots. The Bruggeman effective-medium-approximation analysis suggested that the correction for this microroughness is very small (Δε1,2<0.2). The present ε(E) data and previously published data were used for the modeling of the optical constants of a-Se over the 0–15 eV photon-energy range. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of a-Se were also presented.