Thickness dependence of optical gap and void fraction for sputtered amorphous germanium

Amorphous germanium films 600 to 18 800 Å thick were deposited using rf-diode and dc-magnetron sputtering. Spectroscopic ellipsometry measurements were conducted on these samples over the photon energy range of 1.8–4.5 eV. These measurements were used to determine the void content of the deposited films. Transmission and reflectance measurements from 0.5–2.0 eV were used to determine the optical absorption spectra. Tauc’s plots were constructed and optical gaps extrapolated from these plots. A correlation was found between void-content and optical-gap values.