RESUMEN
The periodic number dependence of the femtosecond laser-induced crystallization threshold of [Si(5nm)/Sb80Te20(5nm)]x nanocomposite multilayer films has been investigated by coherent phonon spectroscopy. Coherent optical phonon spectra show that femtosecond laser-irradiated crystallization threshold of the multilayer films relies obviously on the periodic number of the multilayer films and decreases with the increasing periodic number. The mechanism of the periodic number dependence is also studied. Possible mechanisms of reflectivity and thermal conductivity losses as well as the effect of the glass substrate are ruled out, while the remaining superlattice structure effect is ascribed to be responsible for the periodic number dependence. The sheet resistance of multilayer films versus a lattice temperature is measured and shows a similar periodic number dependence with one of the laser irradiation crystallization power threshold. In addition, the periodic number dependence of the crystallization temperature can be fitted well with an experiential formula obtained by considering coupling exchange interactions between adjacent layers in a superlattice. Those results provide us with the evidence to support our viewpoint. Our results show that the periodic number of multilayer films may become another controllable parameter in the design and parameter optimization of multilayer phase change films.
RESUMEN
Multiple parameters of nanocomposite Si/Sb80Te20 multilayer films are possibly optimized simultaneously to satisfy the development of ideal phase-change memory devices by adjusting chemical composition and physical structure of multilayer films. The crystallization and structure of the films are studied by coherent phonon spectroscopy. Laser irradiation power dependence of coherent optical phonon spectroscopy reveals laser-induced crystallization of the amorphous multilayer film, while coherent acoustic phonon spectroscopy reveals the presence of folded acoustic phonons which suggests a good periodic structure of the multilayer films. Laser irradiation-induced crystallization shows applicable potentials of the multilayer films in optical phase change storage.
RESUMEN
Amorphous germanium telluride (GeTe) thin films were fabricated on SiO2/Si subtracts by RF sputtering at room temperature. The thickness of the as-deposited films is about 200 nm. Indium-doping on GeTe thin films were prepared by solution doping method. The GeTe thin films were dipped into InCl3 solution with 1 mol/L, 0.8 mol/L, 0.5 mol/L and 0.1 mol/L for an hour at 100 degrees C, respectively. Then the thin films were annealed at 200 degrees C for 10 min. The I-T measurements show that the amorphous-crystalline transition temperature of In-GeTe films is lower than that of the undoped thin films. XRD reveals the formation of rock salt structure after annealing at 280 degrees C. XPS indicates that In-Te bond which may correspond to In2Te3 exists in the doped thin film. The results of calculating density of states (DOS) show that the changes of electronic states are mainly located around Fermi energy level with the increasing Indium content. These results indicate that the transition temperature of GeTe films can be effectively tuned by solution process doping indium, which may be useful to decrease set current.