Mechanism of crystallization of oxygen-doped amorphous Ge1Sb2Te4 thin films

Abstract

The aim of this article is to study the mechanism of the amorphous-to-crystalline phase transformation in Ge1Sb2Te4 alloys doped by oxygen (in the range of 4–28 at. %) using the electrical, optical, and x-ray measurements. Experimental results have shown that samples with oxygen in the range of about 4–10 at. % first crystallize into the Ge1Sb2Te4 fcc phase at temperatures in the range 130–145 °C, at higher temperature (around 275 °C) the fcc phase is transformed into the Ge1Sb2Te4 hexagonal phase. In samples with oxygen in the range of 10–15 at. % the crystallization occurs in two stages producing samples where Ge1Sb2Te4 and the Sb2Te3 coexist. Samples with higher oxygen content, in the range of 15–28 at. % the films crystallized into the rhombohedral Sb2Te3 phase due to the formation of amorphous germanium oxide. The experimental results have been interpreted employing the Johnson–Avrami–Mehl–Kolmogorov theory. Using isothermal measurements and the time dependence of the Avrami exponent, three different crystallization mechanisms are proposed for material with different content of oxygen.

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

“…However, transmittance measurements or other techniques [26][27][28][29][30][31][32][33] generally used, such as differential scanning calorimetry, x-ray diffraction, electrical ͑resistance͒ measurements, and reflectance measurements, provide information only on the overall crystallization process, that is actually an interplay of both nucleation and growth processes. In contrast, transmission electron microscopy ͑TEM͒ is capable of providing separate information on nucleation and growth parameters.…”

Structure of oxygen-doped Ge:Sb:Te films

“…In addition, previous results have shown that, in amorphous Ge:Sb:Te:O films, with oxygen concentration lower than 10 at.%, the temperature of crystallization, the crystal grain size and the lattice parameters increased with increasing oxygen concentration in [1,3,5,7]. On the other hand, the temperature of crystallization in Ge:Sb: Te:O films with oxygen content above 10 at.% decreases and the material crystallizes into the rhombohedral Sb 2 Te 3 phase [7].…”

“…In previous reports, three scenarios of how oxygen incorporates into the Ge:Sb:Te structure have been reported [1,3,5,7]. One of them proposes that oxygen is located at the tetrahedral interstitial site of the Ge:Sb:Te structure [3,5,7].…”

“…In previous reports, three scenarios of how oxygen incorporates into the Ge:Sb:Te structure have been reported [1,3,5,7]. One of them proposes that oxygen is located at the tetrahedral interstitial site of the Ge:Sb:Te structure [3,5,7]. The second model proposed that the oxygen forms oxides such as GeO 2 , Sb 2 O 3 or TeO 2 , which condense at grain boundaries [1,7], and the third one proposed that only some of the metallic bonds in the crystalline Ge:Sb:Te were oxidized, which changed the optical properties toward a more dielectric recording layer [3].…”

Oxygen incorporation into GST phase-change memory matrix

“…Thus, several mechanisms have been proposed in respect to oxygen addition. One of them suggested that oxygen incorporation in GST leads to the formation of germanium oxide and phase separation [19]. Other authors claim that formation of stoichiometric GeO 2 phase is not observed, while stoichiometric Sb 2 O 3 phase is formed instead [20].…”