Crystallization behavior of Ge-doped eutectic Sb_70Te_30 films in optical disks

Abstract

We report laser-induced crystallization behavior of binary Sb-Te and ternary Ge-doped eutectic Sb70Te30 thin film samples in a typical quadrilayer stack as used in phase-change optical disk data storage. Several experiments have been conducted on a two-laser static tester in which one laser operating in pulse mode writes crystalline marks on amorphous film or amorphous marks on crystalline film, while the second laser operating at low-power cw mode simultaneously monitors the progress of the crystalline or amorphous mark formation in real time in terms of the reflectivity variation. The results of this study show that the crystallization kinetics of this class of film is strongly growth dominant, which is significantly different from the crystallization kinetics of stochiometric Ge-Sb-Te compositions. In Sb-Te and Ge-doped eutectic Sb70Te30 thin-film samples, the crystallization behavior of the two forms of amorphous states, namely, as-deposited amorphous state and melt-quenched amorphous state, remains approximately same. We have also presented experiments showing the effect of the variation of the Sb/Te ratio and Ge doping on the crystallization behavior of these films.

Local structural change of amorphous Ge–Sb–Te thin film on annealing

“…Namely, they indicate the structural similarity between local structures in amorphous GeSb-Te thin films and the crystallized structure of GeSb-Te. Khulbe et al [21] examined a crystallization kinetics of an amorphous Ge-Sb-Te, which had a composition similar to our Ge 5 Sb 70 Te 25 thin film, by measuring reflectivity variation. As a result, they found that the Ge-Sb-Te system shows a growth-dominated crystallization: once a nucleation center is generated, the Ge-Sb-Te thin film crystallizes very rapidly.…”

Influence of capping layers on the crystallization of doped SbxTe fast-growth phase-change films

“…[11][12][13][14] Among them doped alloys derived from "eutectic" Sb x Te, showing a growth-dominant crystallization behavior, appear the most obvious choice for both high data transfer rate and high-density recording. [15][16][17][18][19][20] These materials are currently used in optical disk formats including DVD+ RW, DVD-RW, Blu-ray disk, 21 and HD-DVD, 22 and are also proposed for the line concept PRAM. 23 A good trade-off between crystallization speed and data retention time is also expected in these materials, as they appear to have a high activation energy for crystallization.…”

The effect of Ge addition on the RESET operation of a phase-change memory (PCM) device using Ge-doped SbTe

“…For comparison of nucleation and growth kinetics among films of differing Ge contents, time-resolved optical characterization [11,16] was carried out. For each film, we prepared a 4-layer stack on a glass, consisting of a Ge-ST film sandwiched between the two ZnSÁ and SiO 2 layers having thicknesses optimized for a proper optical contrast, and a reflection layer of an Al alloy at the top.…”

“…Of these two Sb-rich materials, Ge-ST is of particular interest in that it exists stably as a single d phase over a wide range of composition while displaying crystallization of markedly varying characteristics with Sb:Te ratio and/or Ge content [11,12], and, therefore, it would provide highly tunable PCM performances in terms of speed, retention and operation current. As for varying Sb:Te ratio in Ge-ST, we recently examined the effect to find that the SET speed of a PCM device becomes enhanced with increasing Sb:Te ratio by virtue of increasingly higher growth speed of crystallites and extremely sluggish nucleation rate [13].…”