Crystallization Study of Ge‐Rich (GeTe)_m(Sb₂Te₃)_n Using Two‐Step Annealing Process

Abstract

A combination of X‐ray diffraction and Raman scattering is employed to investigate (GeTe)m(Sb2Te3)n alloys crystallized by thermal annealing from the amorphous (a‐) phase. The films are deposited by molecular beam epitaxy on Si(111) substrates. First, a series of a‐GeSbTe (GST) films of different composition is deposited and studied by Raman spectroscopy to identify the Ge‐rich features of the alloys. Second, the crystallization properties of Ge10Sb2Te13 are studied upon different annealing conditions. The aim of this work is to develop a procedure to avoid segregation of Ge and GeTe at the GST crystallization onset (Tx). This is here achieved by means of an incubation step at temperature lower than Tx. The crystallization onset Tx increased to 270 °C, which is about 160 °C higher compared to a reference GeTe sample, while the alloy always crystallizes in the stable Ge1Sb2Te4 composition. The increase of Tx is observed for all annealing conditions, regardless the amount of crystalline Ge segregated. For the optimized annealing treatment, the presence of Ge nanocrystals along with crystalline GeSbTe is unveiled by Raman measurements, paving the way for the control of the microstructure and electrical/thermal properties of Ge‐rich alloys.

Interface Formation during the Growth of Phase Change Material Heterostructures Based on Ge-Rich Ge-Sb-Te Alloys

“…In particular, the introduction of a Sb 2 Te 3 (sample A) or GST225 (sample B) underlayer beneath the GGST layer induces a lowering of the crystallization temperature in comparison with GGST single layers. Furthermore, although there are several reports that phase separation can occur upon annealing of GGST single layers, leading to the crystallization of Ge and other GST phases [ 9 , 36 , 37 ], no evidence of Ge segregation could be found in the XRD curves collected on our GGST-based heterostructures at increasing annealing temperature. All these observations suggest that the nature of the first layer and the extent of the interface can affect the crystallization behavior upon annealing.…”

Phase Change Materials and Superlattices for Non‐Volatile Memories

“…Francesco Di Biagio et al studied the crystallization properties of Ge‐rich compounds along the GeTe–Sb 2 Te 3 pseudo‐binary line. For these compounds, e.g.…”