Abstract
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.
Highlights
Sb-rich Sb-Te binary alloy is shown as a kind of high-speed growth-dominated phase change material [1,2] having fast crystallization rate, low archival stability, and high media noise[2,3]
It is evident that an oscillatory component is superimposed on a normal carrier dynamic profile, which is so-called coherent phonon spectroscopy (CPS) [9,10,11,12,13], and reflects the vibration of coherent optical phonons (COPs) excited by femtosecond pump pulses
70 mW, fast Fourier-transformed (FFT) spectra show a peak at 3.90 THz, whereas up to 70 mW and above, a new peak appears at approximately 4.58 THz, which implies the occurrence of laser-induced phase change because different frequency COP modes correspond to different microstructures
Summary
Sb-rich Sb-Te binary alloy is shown as a kind of high-speed growth-dominated phase change material [1,2] having fast crystallization rate, low archival stability, and high media noise[2,3]. It is shown that Bi doping into Sb80Te20 can further reduce crystallization time but lead to a low crystallization temperature or poor archival stability [4]. SbTe-based multilayer phase change films, such as GeTe/ Sb70Te30 [6], Si/Sb80Te20 [7], and Ga30Sb70/Sb80 Te20 [8], In this article, the effect of the periodic number of Si (5 nm)/Sb80Te20 (5nm) multilayer films on laser-induced crystallization has been studied by coherent phonon spectroscopy.
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