Rewritable phase-change optical recording in Ge2Sb2Te5 films induced by picosecond laser pulses

Abstract

The phase transformation dynamics induced in Ge2Sb2Te5 films by picosecond laser pulses were studied using real-time reflectivity measurements with subnanosecond resolution. Evidence was found that the thermal diffusivity of the substrate plays a crucial role in determining the ability of the films to crystallize and amorphize. A film/substrate configuration with optimized heat flow conditions for ultrafast phase cycling with picosecond laser pulses was designed and produced. In this system, we achieved reversible phase transformations with large optical contrast (>20%) using single laser pulses with a duration of 30 ps within well-defined fluence windows. The amorphization (writing) process is completed within less than 1 ns, whereas crystallization (erasing) needs approximately 13 ns to be completed.

Mixed‐Mode Electro‐Optical Operation of Ge2Sb2Te5 Nanoscale Crossbar Devices

“…Chalcogenide-based phase-change materials have been the subject of much scientific interest because of their ability to reversibly switch between two solid states, amorphous and crystalline, at high speed [1] and with relatively low power consumption. [2] Transitions between states are achieved via localized heating with energy applied either optically or electrically.…”

“…[4] The crystalline phase is more reflective and up to three orders of magnitude more electrically conductive than the amorphous phase. [1] These differences in the physical properties between phases, in addition to the ability to retain either phase state for a long time at ambient temperatures, [5] have been utilized in technologies such as rewritable optical data storage (DVD-RW, Blu-ray RW) and nonvolatile electronic phase-change memories…”

Dynamics of laser-induced phase switching in GeTe films

“…In order to achieve crystallization with shorter pulses, additional optimization of the heat-flow conditions is required. 15 We have carried out a study of progressive crystallization upon irradiation with 8 ns pulses in samples with the same GeTe composition but with a larger film thickness (50 nm) and a thicker SiO 2 buffer layer (30 nm). In Figs.…”

“…14) and Ge 2 Sb 2 Te 5 (Ref. 15) films by tailoring the thermal conductivity of the substrate to either facilitate or prevent amorphization. Although the pseudobinary GeTe-SbTe alloy (and especially the Ge 2 Sb 2 Te 5 composition) is the best known candidate for PCMs, 16 both of its binary constituents, i.e., GeTe and Sb 2 Te 3 , have also demonstrated potential for phase change recording.…”

Thermal conductivity of GeTe/Sb2Te3 superlattices measured by coherent phonon spectroscopy

“…4 In the last decade, however, most of the literatures have studied nanosecond dynamics of the phase change in GST materials using nanosecond and picosecond laser (or electrical) pulses. 7 Hence, thermal properties of GST materials have been believed to govern the phase change in GST materials when it is promoted by laser heating. There, thermal conductivity (j) is important to engineer the performance of the phase change, 8 such that lower thermal conductivity enables one to realize low power operation of the switching, where, focused laser irradiation causes lattice heating.…”