Structural change upon annealing of amorphous GeSbTe grown on Si(111)

Abstract

The structural change upon annealing of an amorphous GeSbTe (GST) film deposited by molecular beam epitaxy on a Si(111) substrate is studied by means of X-ray diffraction (XRD), X-ray reflectivity (XRR), and atomic force microscopy (AFM). XRD profiles reveal that both metastable cubic and stable hexagonal phases are obtained with a single out-of-plane orientation. XRR study shows a density increase and consequent thickness decrease upon annealing, in accordance with literature. From both, the XRD and the AFM study, it emerges that the crystalline substrate acts as a template for the film, favoring the crystallization of the amorphous GST into the [111] oriented metastable cubic phase, and the latter turns into the [0001] stable hexagonal phase for higher annealing temperature. V

Exploring the subsurface atomic structure of the epitaxially grown phase-change material Ge2Sb2Te5

“…Here, we explore STM and STS on the prototype phasechange material GST-225 [1,11], grown epitaxially by molecular beam epitaxy (MBE) [21][22][23][24][25]. This provides the first STM study on single crystalline phase-change materials.…”

Thermal annealing studies of GeTe-Sb2Te3 alloys with multiple interfaces

“…Further details of the microstructure can be found in a dedicated publication. 14 From the annealing experiment shown in Figure 1 and the study of Bragaglia et al, 8 which systematically combines morphological and structural measurements, it emerges that the preparation of the Si(111) substrate, acting as a template, plays a fundamental role on the crystallization of a-GST. Crystallization is prevalently of heterogeneous nature, starting at the Si/GST interface, with consequent formation of a propagating front.…”

“…This result is in agreement with a recent STEM based study on epitaxial samples, in which it is shown that by properly choosing the substrate and the capping layers, it is possible to promote or prevent the vacancies ordering in the rocksalt structure or the conversion into the trigonal phase. 8 The study of periodicity evolution upon annealing is now discussed. In Figure 4, the average distance between Te-Te layers (d GST ) and the periodicity of the vacancy layers (Λ VL ), in other terms the size of the GST unit building blocks, are plotted as function of T A .…”

“…Homogeneous nucleation in the a-GST film could not be excluded within the investigations of the mentioned study, even if it is reasonably not dominant if compared to heterogeneous one. 8 In order to clearly address this point, a study on the effect of additional interfaces to the Si/GST was performed. Note that this experiment is of relevance whenever a capping of samples is required to use in the temperature dependent spectroscopy 16 and pump-probe experiments.…”

“…[5][6][7] In most of the cases the investigated material is polycrystalline. In 2014 Bragaglia et al 8 demonstrated that both the metastable c-and stable t-GST phases can be obtained by annealing an amorphous film deposited by molecular beam epitaxy (MBE) on a Si(111) substrate. The relevant point is that the obtained film was highly textured.…”