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).

Articles you may be interested inEffects of germanium and nitrogen incorporation on crystallization of N-doped Ge2+xSb2Te5 (x=0,1) thin films for phase-change memory J. Appl. Phys. 113, 044514 (2013); 10.1063/1.4789388Crystallization of sputtered-deposited and ion implanted amorphous Ge 2 Sb 2 Te 5 thin films

Crystallization processes in different Te alloys, employed in phase change materials for optical data storage, have been investigated by in situ mechanical stress measurements. Upon crystallization a considerable stress buildup is observed, which scales with the volume change upon crystallization. Nevertheless the observed stress change only corresponds to approximately 9% of the stress estimated for a purely elastic transformation. Further evidence of stress relief phenomena comes from the temperature dependence of the stress in the crystalline and amorphous states. Ultrathin dielectric layers have a profound influence on the crystallization process as evidenced by simultaneous optical reflectance and mechanical stress measurements. This observation can be explained by heterogeneous nucleation of crystallites at the interface between the dielectric layer and the phase change film.

AgInSbTe films have recently attracted considerable interest as advanced materials for phase change recording. For this application the determination of crystallization kinetics is of crucial importance. In this work the temperature dependence of structural and electrical properties of sputtered AgInSbTe films has been determined. Temperature dependent measurements of the electrical resistance have been employed to study the kinetics of structural changes of these films. Upon annealing a major resistivity drop is observed at around 160 °C which can be attributed to a structural change as corroborated by x-ray diffraction. X-ray diffraction shows an amorphous phase for as-deposited films, while crystalline films with hexagonal structure (a=4283 Å, c=16 995 Å) are obtained upon annealing above 160 °C. By applying Kissinger’s method, an activation energy of 3.03±0.17 eV is obtained for the crystallization. X-ray reflection measurements reveal a density increase of 5.2%±0.2% and a thickness decrease of 5.5%±0.2% upon crystallization.