Abstract
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.
Highlights
Germanium is an indirect semiconductor and it has a face centered cubic crystal lattice structure of diamond type with a lattice constant of a = 5.657 >
Germanium is a typical semiconductor carrying a specific resistance of 500 cm at room temperature
Germanium-based materials are in use for light emitting devices [1], infrared sensors [2], and solar cells [3]
Summary
The related indirect electron transitions are with higher probability responsible for absorption and emission of light For this case, the width of the energy gap is given by 0.6 ≤ Egi ≤ 0.8 eV. It is possible to transform amorphous deposited films into crystalline structure by annealing the specimens in vacuum at 300∘C [10]. This multiplicity of properties makes such films suitable for broad usage in manufacturing a number of electronic devices such as light detectors, heterojunctions, and sensors for temperature and magnetic field. In the research for cheap substrates for electronic devices, thin films of germanium deposited on glass appear to be an excellent candidate, if one succeeds in obtaining a grain-like structure [11]. The goal of this paper is to study the effect of annealing temperature on structural phase of germanium thin films and there optical properties
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