Laser-induced crystallization phenomena in GeTe-based alloys. II. Composition dependence of nucleation and growth

Abstract

The laser-induced crystallization behavior of GeTe-based amorphous alloys has been measured with a novel multipulse laser technique. This enables the composition dependence of the nucleation rate and crystal growth speed to be independently followed. Two types of crystallization are investigated. The first involves single-phase crystallization of quaternary alloys based on Ge39Sb9Te52, in which the composition dependence of nucleation and growth is followed as Se, S, Sn, and Si are included. Both the nucleation rate and crystal-growth speed vary exponentially with the composition, and a correlation is found between crystallization behavior and bond strengths. The second involves multiphase crystallization in the GeSbTe ternary system. It is shown that the observed variations in crystallization behavior primarily arise from the composition dependence of nucleation rather than crystal growth. The implications of this finding for the importance of long range diffusion during crystallization in the GeSbTe system are discussed.

Extended versus Localized Electronic States in Amorphous TlX and CsPbX3 Films (X = Br, Cl) Studied by Optical Absorption Measurements

“…The drastic change in curve 1 is very similar in sharpness to previous results on amorphous CsPbCl 3 [17], and provides an evidence of a well-defined phase transition from amorphous to crystalline states in the quench-deposited CsPbBr 3 film, though structural studies are necessary for a direct support. (It has been reported for a ternary Ge±Sb±Te solid solution, which is a promising material for fast phase-change optical disks [18,19], that an abrupt transmittance change during slow heating of the amorphous film is due to nucleation followed by a fast grain-growth process resulting in a crystalline film [20].) The transition temperature (crystallization temperature, T c ), which we defined here as the onset temperature for the drastic change, was 296 K as compared with 302 K for CsPbCl 3 .…”

Microscopic studies of fast phase transformations in GeSbTe films

“…This fast recrystallization is attributed to one of the two different mechanisms of recrystallization: Either small crystalline nuclei which are incorporated inside the amorphous material can start the recrystallization or it is started from the surrounding rim [ 10]. A differentiation can be made by measuring the recrystallized fraction e after the second pulse as a function of the diameter of the initial, amorphous bit where E is defined as R -R E= -R '" .... .…”

“…This can be explained by the different optical properties of V1.8. 10 both crystalline phases: The recrystallized volume will always consist of the cubic phase, so no difference between the initial and the final phase occurs (e=1). In case b), the initial phase and final phase are different in respect to their crystal structure and also their optical properties (r=0.6).…”

Crystallization of Ge:Sb:Te Thin Films for Phase Change Memory Application

“…In contrast to other Ge:Sb:Te ternary compounds, it does not belong to the GeTe -Sb 2 Te 3 homologous series, although it lies on (or very close to) the GeTe-Sb 2 Te 3 pseudobinary line in the Ge:Sb:Te phase diagram between GeTe and Ge 2 Sb 2 Te 5 . It is suggested (Coombs et al, 1995) that this alloy is a solid solution between GeTe and a compound with a composition close to Ge 4 Sb 1 Te 5 . This material, in contrast to stoichiometric alloys, demonstrates only one amorphous-NaCl-type phase transition, but it has the largest optical (Kato et al, 1999) and electrical (Morales-Sanchez et al, 2005) contrast between the crystalline and amorphous states, compared with other Ge:Sb:Te ternary alloys.…”