OPTICAL EFFECTS OF FREE CARRIERS IN THIN ALPHA-AG2S FILMS

The intrinsic and the free carrier absorption has been investigated in thin α‐Ag2S films as a function of carrier concentration. By producing an excess of silver the electron concentration in α‐Ag2S increases from the intrinsic concentration value ne = np = 1.2 × 1018 cm−3 up to ne = 3.6 × 1019 cm−3 (at 200 °C). Since the silver to sulfur ratio cannot be frozen in, either the chemical potential of silver or that of sulfur must be fixed by external conditions during the measurements. From the spectral dependence of the dielectric constant direct transitions (ΔEdirect = 0.87 eV), the conduction band mass (m*e = 0.24 m0) and the scattering mechanism of the electrons (scattering by charged centres) were determined. It was not possible to deduce the band gap (≈ 0.1 eV from electrical data) from optical measurements. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim