Change in local atomic and chemical bonding structures of Ge 2Sb 2Te 5 alloys by isothermal heat treatment

Abstract

In this work, we report evaluation of the atomic-scale phase transformation characteristics in one of the most comprehensively utilized phase change materials today, Ge 2Sb 2Te 5 thin film. The phase transformation of Ge 2Sb 2Te 5 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 (B 1/2) in the extended absorption region of 5.3 × 10 5 and 10 × 10 5 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.