Optical Properties of Cuprous Sulfide

Abstract

Measurements of transmission and reflection over the ranges 400–10 500 cm⁻¹ and 300–4000 cm⁻¹, respectively, in Cu₂S are reported. The bandgap changes from 1.21 eV at 300°K to 1.26 eV at 80°K. The minimum gap is apparently indirect with an effective phonon of frequency ∼280 cm⁻¹ participating. In the region 700–8000 cm⁻¹ the reflection and absorption is characteristic of free carriers. Lattice vibrational bands were observed in the region 400–700 cm⁻¹, arising probably through excitation of the fundamentals and combinations of the zone‐edge frequencies.