Structural and Optical Properties of Germanium Thin Films Prepared by the Vacuum Evaporation Technique

Germanium (Ge) thin films have been deposited onto the glass substrates by the vacuum evaporation technique. The effect of annealing temperature on the structural and optical properties of the germanium thin films was investigated. The structural and optical properties of thin films were characterized by XRD, SEM, and UV-Vis techniques. XRD results showed that the structure of the deposited thin films changed from amorphous phase for the films, which deposited at room temperature, to crystalline phase for the films, which deposited at high temperature. Optimum temperature to obtain a good crystalline structure was 525°C. The SEM image also showed that the crystallization of the thin films is increased with increasing of annealing temperature. Transmittance and reflectance spectral were used to calculate the absorption coefficient. Two absorption edges in two spectral regions were distinguished according to direct and indirect electron transitions. Energy band gap Eg was calculated by using the Tauc relationship for both direct and indirect electron transitions. The average value of Eg was equal to 0.79 eV and 0.61 eV for direct and indirect transitions, respectively