Dielectric relaxation in amorphous and crystalline Sb2Te3 thin films

Abstract

Sb 2 Te 3 is an end-point of the GeTe-Sb 2 Te 3 quasibinary tie-line that represents phase-change alloys widely used in optical and non-volatile phase-change memory devices. In the crystalline form it is also a prototypical topological insulator with a layered structure where covalently bonded quintuple layers are held together by weak van der Waals forces. One of the ways to fabricate a crystalline phase is solid-state crystallisation of an amorphous film, whereby the three-dimensional (3D) structure relaxes to the two-dimensional (2D) crystalline phase. The mechanism of the 3D-2D transformation remains unclear. In this work, we performed a study of relaxation processes in thin Sb 2 Te 3 films in both amorphous and crystalline phases. We found that both phases possess two kinds of relaxators (type I and type II), where the type I fragments are identical in the two phases, while the relaxation of type II fragments are shifted to lower temperature in the amorphous phases. The activation energies of the associated relaxation processes and the values of the Havriliak-Negami parameters were determined. The differences between the relaxation processes in the two phases are discussed. The obtained result will contribute to better understanding of the 3D-2D transformation during the crystallisation of van der Waals solids.

Reduction of write current with improved thermal stability in GeSe2 doped Sb2Te3 films for phase change memory applications

“…where J, σ, C p , ρ, k, T, Q are electrical current density, electrical conductivity, specific heat capacity at constant pressure, density, thermal conductivity, temperature, and heat flux, respectively. Parameters used are tabulated in table 2 [18,[62][63][64][65]. These equations were solved iteratively in each mesh.…”

Impact of structural short‐range order and tetrahedral germanium on electronic and dielectric properties in phase‐change materials

“…The central findings of these DFT-D2 studies have been the presence of important topological disorder that consists in miscoordinations and mixed geometries, among which tetrahedral Ge sites which represent the dominant motifs (55% for GST225), consistently with Mössbauer spectroscopy measurements 11 and AXS. 18 Sb sites change from a dominant pyramidal geometry typical of Group V chalcogenides to a defect octahedral one which is reminiscent 36 of the PC crystalline polymorph Sb 2 Te 3 . A similar situation holds for a-GeTe which contains about 65% Ge tetrahedra 25 in the considered structure models (Figure 2).…”