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

Amorphous germanium films 600 to 18 800 A{} 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.