Materials aspects in phase change optical recording

On the crystallization of thin films composed of Sb3.6Te with Ge for rewritable data storage

“…These results might be important for the explanation of the observed decrease in ''complete erasure time'' ͑CET͒ with decreasing film thickness for AgInSbTe alloys. 4,6,7 Although the present alloy is composed of Ge-Sb-Te its composition is such that is shows growthdominated crystallization ͑as can be seen in the present results͒ like usually ascribed to AgInSbTe. 4,6 On the other hand Ge 2 Sb 2 Te 5 (Ge 1 Sb 2 Te 4 and Ge 2 Sb 4 Te 7 ), sometimes confusingly shortened to GeSbTe, shows nucleation-dominated crystallization, because growth of the crystallites hardly occurs with typical final sizes of 10-30 nm.…”

“…[1][2][3][4] Amorphous areas embedded in a crystalline surrounding act as bits of information. A relatively high laser power is used to write these amorphous spots via a meltquench process and medium and low laser powers are used for both erasing ͑crystallization͒ and reading, respectively.…”

“…5 Ge 2 Sb 2 Te 5 shows nucleation-dominated crystallization, i.e., it nucleates easily and fast, but it shows only limited growth, with final sizes of the crystallites within a disk of 10-30 nm. 4,6 With the ongoing decrease of the amorphousmark sizes due to a decrease in laser wavelength and an increase in numerical aperture of the focusing lens, phasechange materials showing very fast growth ͑i.e., growthdominated crystallization͒ tend to become more preferable than Ge 2 Sb 2 Te 5 , that is to say at least with respect to attainable data-transfer rates. 6,7 If the bit size decreases, the distance a fast growing crystal has to proceed from the edge of the amorphous mark to its center decreases and consequently the rewriting speed increases.…”

Electron diffraction and high-resolution transmission electron microscopy of the high temperature crystal structures of GexSb2Te3+x (x=1,2,3) phase change material

“…Note that in the activation energy the interfacial energy ␥ goes to the power of 3 whereas the driving force ⌬G V goes to the power of 2. Since it is now well-proven that in phase change optical recording Ge-Sb-Te shows growth-limited ͑i.e., nucleation-driven͒ crystallization as opposed to for instance, Ag-In-Sb-Te that shows nucleation-limited crystallization, 9 it is particularly clear that nuclei form very easily in Ge-Sb-Te. This is fully consistent with the physical picture presented here based on the difference in stable and metastable crystal structures.…”

“…[1][2][3][4][5][6][7][8][9] Amorphous spots in a crystalline surrounding act as bits of information. Both continuous laser light and short laser pulses at various higher power densities can be employed to read, write, and/or erase those local amorphous areas and thus the phase changes in the material are exploited.…”