Crystallization and ferroelectric properties of Ge4Sb1Te5 films

The aim of this work is to investigate the crystallization processes and the electrical properties of thin Ge4Sb1Te5 films (material for data storage) using 4-probe impedance, optical reflection, XRD, DSC and Piezoresponse Force Microscopy techniques.Experimental results have shown that bulk and thin films of crystalline Ge4Sb1Te5 have ferroelectric properties with a ferroelectric–paraelectric transition temperature Tc about 600 K. This transition is reversible and probably related to the phase transformation from the fcc-Ge4Sb1Te5 to a phase close to the fcc-GeTe. It was found that films have ferroelectric domains with dimension approximately equal to the dimension of grains, when the films were crystallized without electrical field. An external electric field increases the degree of polarization of Ge4Sb1Te5 films which leads to an increase in domain dimensions and in capacitance at Tc of about two orders of magnitude compared to films crystallized without an electrical field.It was found that the applied external electrical field also increases grain dimensions and changes the crystallization kinetics, decreasing the onset of crystallization temperature, the effective activation energy of crystallization and the Avrami exponent. These changes could be related with an increase in atomic diffusion, promoting the growth of crystalline phase.