Structural transformations of Ge2Sb2Te5 films studied by electrical resistance measurements

Temperature dependent measurements of the electrical resistance have been e mployed to study structural changes in sputtered Ge2Sb2Te5 films. The prono unced changes of film resistance due to structural changes enable a precise determination of transition temperatures and activation energies. Furtherm ore 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 degrees C and finally a hexagonal structur e (p (3) over bar m) around 310 degrees C. Both structural changes are acco mpanied by a major drop of resistance. Applying the Kissinger method [Anal. Chem. 29, 1702 (1957)] the activation energy for crystallization to the ro ck salt structure is determined to be 2.24 +/- 0.11 eV, and for the phase t ransformation 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 transiti on temperature as well as of the corresponding activation energy (2.7 +/- 0 .2 eV). (C) 2000 American Institute of Physics. [S0021-8979(00)06209-5].