Structural transformations of $Ge2Sb2Te5$ films studied by electrical resistance measurements

Temperature dependent measurements of the electrical resistance have been employed to study structural changes in sputtered $Ge2Sb2Te5$ films. The pronounced changes of film resistance due to structural changes enable a precise determination of transition temperatures and activation energies. Furthermore the technique is sensitive enough to measure the influence of ultrathin capping layers on the transformation kinetics. With increasing temperature the $Ge2Sb2Te5$ films undergo a structural change from an amorphous to rock salt structure $(Fm3m)$ around 140 °C and finally a hexagonal structure $(p3̄m)$ around 310 °C. Both structural changes are accompanied by a major drop of resistance. Applying the Kissinger method [Anal. Chem. 29, 1702 (1957)] the activation energy for crystallization to the rock salt structure is determined to be $2.24±0.11$ eV, and for the phase transformation to the hexagonal phase to be $3.64±0.19$ eV, respectively. A thin capping layer of $ZnS–SiO2$ leads to an increase of the first transition temperature as well as of the corresponding activation energy $(2.7±0.2$ eV).