Phase change and optical band gap behavior of Ge-Te-Ga thin films prepared by thermal evaporation

摘要

The amorphous Ge _(11.4)Te _(86.4)Ga _(2.2) chalcogenide thin films were prepared by thermal evaporation onto chemically cleaned glass substrates. Properties measurements include X-ray diffraction (XRD), Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), Four-point probe and VIS-NIR transmission spectra. The allowed indirect transition optical band gap and activation energy of samples were calculated according to the classical Tauc equation and Kissinger's equation, respectively. The results show that there is an amorphous-to-crystalline phase transition of Ge _(11.4)Te _(86.4)Ga _(2.2) thin film. The investigated film has high crystallization temperature (～200°C) and activation energy (2.48 eV), indicating the film has good amorphous stability. The sheet resistance of the crystalline state is ～10 Ω/and the amorphous/crystalline resistance ratio is about 10 ~5. Besides, a wide optical band gap (0.653 eV) of Ge _(11.4)Te _(86.4)Ga _(2.2) is obtained, indicating that the material possesses a low threshold current from amorphous-to-crystalline state for phase-change memory application.