Effect of amorphization on the structural stability and reversibility of Ge ₂Sb ₂Te ₅ and oxygen incorporated Ge ₂Sb ₂Te ₅ films

The structural stability of Ge ₂Sb ₂Te ₅ (GST) and oxygen incorporated Ge ₂Sb ₂Te ₅ (GSTO) films was investigated during crystallization and amorphization processes. Variations in the transition temperature for the amorphized films during recrystallization showed that the amorphized GSTO film loses its enhanced amorphous stability due to oxygen incorporation, while the stability is maintained in the GST film. EXAFS and XANES data suggest that a tetrahedral-like Ge-Te(O) bonding structure is generated, forming crystalline and amorphized GSTO films. Moreover, an ab initio XANES simulation indicates that the tetrahedral-like Ge-Te(O) geometry, which is similar to the atomic configuration of the crystalline structure, exists in the form of ordered domains with medium range ordering in the amorphized film. This effect can lead to large variations in T _c and can inhibit reversible phase change characteristics.