Laser irradiation-induced modification of the amorphous phase in GeTe films: the role of intermediate Ge-Te bonding in the crystallization mechanism

Modified amorphous GeTe, formed by the pulsed laser irradiation of as-grown GeTe, was analyzed in terms of variations in the local bonding structure using Raman spectroscopy and X-ray absorption fine structure in tandem with first-principles density functional theory. Amorphized GeTe (acquired from the crystalline phase) was compared with the modified amorphous GeTe to investigate the similarities and discrepancies between these two amorphous phases. Raman spectroscopy showed that these materials have a similar distribution of Ge-centered local structure in both phases, which is mainly composed of an octahedral-like structure. However, extended X-ray absorption fine structure results show the presence of a unique second type of Ge-Te bonding in the amorphized GeTe, which can effectively reduce the energy required for recrystallization. A computational study based on molecular dynamics simulations verified our experimental observations, including the existence of a second type of Ge-Te bonding in the amorphized phase. Moreover we distinguished the structural characteristics underlying the different amorphous phases, such as local atomic configurations and structural symmetries.