Change in local atomic and chemical bonding structures of Ge2Sb2Te5 alloys by isothermal heat treatment

In this work, we report evaluation of the atomic-scale phase transformation characteristics in one of the most comprehensively utilized phase change materials today, Ge2Sb2Te5 thin film. The phase transformation of Ge2Sb2Te5 thin film from amorphous to hexagonal structure via fcc structure was confirmed by XRD measurements. The approximate values of optical energy gap are 0.72 and 0.50 eV, with slopes (B1/2) in the extended absorption region of 5.3 × 105 and 10 × 105 cm− 1∙eV− 1 for the amorphous and fcc-crystalline structures, respectively. In addition, X-ray photoelectron spectroscopy analysis revealed strengthening of the Te–Te bond as well as weakening of the Ge–Te bond during the amorphous-to-crystalline transition. This trend was also observed in extended X-ray absorption fine structure analysis where the Ge metallic bond lengths in the amorphous, fcc, and hexagonal structures were 0.262, 0.280, and 0.290 nm.