Crystallization of sputtered-deposited and ion implanted amorphous Ge2Sb2Te5 thin films
ABSTRACT X-ray diffraction and transmission electron microscopy have been utilized to measure the ion irradiation-induced modification in amorphous Ge 2 Sb 2 Te 5 thin films. The isothermal crystallization of sputtered-deposited and Sb + ion irradiated amorphous samples has been studied, focusing on the evolution of the microstructure during the initial stage of the transformation. In both samples, the amorphous to crystal transition occurs through the nucleation of face centered cubic (fcc) crystal domains at the film surface. A fast bidimensional growth of the crystalline nuclei in the sputtered-deposited films occurs by the generation of transrotational grains. The lattice parameter decreases as the crystalline fraction increases above 80%, and it approaches the fcc bulk value at the end of the transformation. Ion irradiation produces a densification of the deposited amorphous film ( ∼4% vertical shrinkage measured by atomic force microscopy) and an enhancement of the crystallization rate. Even in the irradiated amorphous, the nucleation occurs at the film surface and proceeds by the growth of the grains through the thickness of the layer although the density of the transrotational grains is strongly reduced with respect to the unirradiated amorphous. A link between the ion beam induced densification and the reduction of transrotational grains is proposed.
- Pergamon Press. 01/1985; 1.
- [Show abstract] [Hide abstract]
ABSTRACT: The crystallization behavior of amorphous Ge <sub> 2 </sub> Sb <sub> 2 </sub> Te <sub>5</sub> thin films were investigated by using differential scanning calorimetry, x-ray diffraction, and optical reflectivity measurements. The analysis of in situ ellipsometry isotherm Ge <sub> 2 </sub> Sb <sub> 2 </sub> Te <sub>5</sub> films based on the Johnson–Mehl–Avrami equation revealed that the crystallization process near 150 °C was a two-step process. In this alloy thin film, the kinetic exponents in the Johnson–Mehl–Avrami equation were about 4.4 for the first stage and 1.1 for the second stage. A kinetic model based on the cascaded crystallization is proposed. The proposed model showed good agreement with the experimental results obtained by transmission electron microscopy and x-ray diffraction. © 1999 American Institute of Physics.Journal of Applied Physics 08/1999; · 2.21 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: 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 (pm) 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). © 2000 American Institute of Physics.Journal of Applied Physics 04/2000; 87(9):4130-4134. · 2.21 Impact Factor