Long-range crystal-lattice distortion fields of epitaxial Ge-Sb-Te phase-change materials

Abstract

The structural evolution of Ge-Sb-Te-based phase-change material during molecular beam epitaxy growth is investigated. The in situ and ex situ synchrotron-based X-ray scattering results reveal the formation and evolution of defects-induced inhomogeneities during growth. The scattered intensity in the vicinity of various Bragg reflections indicates a specific scattering vector-dependent anisotropy in the diffuse scattering regime. The average local static distortion fields of the defectsinduced inhomogeneities are estimated to be in between 2.5 and 3.0 nm. The defects-induced diffuse scattering anisotropy, observed for the particular Bragg points, arises from the combination of the elastic and crystalline anisotropies that are caused by the large number of vacancies. The experiments show that the large-size defect clusters create inhomogeneitydriven tetragonal fields inserted into the metastable phase of the Ge-Sb-Te host crystal.

Growth of crystalline phase change materials by physical deposition methods

“…In order to overcome this limitation and confirm this observation, the flux rate for MBE grown films should be increased. Finally, grazing incidence XRD has been used to study the in-plane lattice constant of GST grown on GaSb(0 0 1) [52]. Figure 6 shows the in-plane lattice constant of GST as a function of layer thickness.…”

Local structure of epitaxial GeTe and Ge2Sb2Te5 films grown on InAs and Si substrates with (100) and (111) orientations: An x-ray absorption near-edge structure study

“…It was subsequently argued that distortions in the crystalline phase may be sufficiently large to locally break the resonant bonding 13,14 generating covalently bonded local configurations. [15][16][17] Local structure studies of the crystalline phase reported to date are additionally complicated by the fact that the studied films are polycrystalline, with atoms at grain boundaries affecting the average structure and properties of the crystalline phase. It was thus highly desirable to grow epitaxial layers of GeTe and GST, which has been successfully achieved over the past several years.…”

Electrical performance of phase change memory cells with Ge3Sb2Te6 deposited by molecular beam epitaxy

“…More details about the growth of GST by MBE can be found elsewhere. 8,[11][12][13] After the GST deposition, the samples were cooled down to room temperature and transferred to the in-situ magnetron sputtering chamber (base pressure: 5 Â 10 À8 mbar) for capping with W. For the sputtering of the 50 nm thick W contacting layer, an Ar pressure of 4.6 Â 10 À3 mbar, a 155 V DC bias, and RF power of 100 W were used. The resulting growth rate was approximately 8 nm/min.…”