Structure and phonon behavior of crystalline GeTe ultrathin film

Abstract

We report the drastic effect of film thickness on the structure and corresponding phonon behavior of crystalline GeTe ultrathin film. GeTe film with film thickness at ∼5 nm still shows good crystallization behavior and this highly scaled dimension confined almost all the crystallites to have preferred [111] orientation. The large specific interface area in ultrathin film give rise to the increase of tetrahedral coordinated Ge atoms and a rising Raman mode at low frequency is observed. These findings give implications for the thermal and electrical characters of phase change ultrathin films and thus for relevant scaling properties of Phase Change Memory.

Phase-change like process through bond switching in distorted and resonantly bonded crystal

“…The contribution of the B peak to the defective mode or symmetric mode can be investigated by the depolarization factor corresponding to the absolute peak area ratio of B peak between VV and HV states 40 . The obtained depolarization factor of B peak is ~0.4, which corresponds to symmetrical vibration 41 or contains only a very small percentage of symmetry broken one. Thus, the increase in the B peak height under the uniaxial stress is not caused by the structural deformation related to the defective octahedral structure but by the other kind of structural deformation maintaining the local structure.…”

Manipulation of dangling bonds of interfacial states coupled in GeTe-rich GeTe/Sb2Te3 superlattices

“…For example, the intercalation of nano-sized GeTe blocks with varying thickness can allow the topological surface states in superlattices to be manipulated depending on changes of the interactions between two blocks 20 – 22 . In studies of the local structure of GeTe films, the chemical bonds have been shown to gradually change with decreasing film thickness to nano scale 23 , 24 . Thus, an unknown relationship exists between the incompatible bonds (reconfiguration of the 2D and 3D dangling bonds) and interfacial states in superlattices.…”

A Review on Material Selection Benchmarking in GeTe-Based RF Phase-Change Switches for Each Layer

“…Besides the (111) lattice planes with a plane spacing of 3.5 Å, the other exhibits a series of (200) planes with a lattice spacing of 3.0 Å, intersecting with the (111) planes at an angle of 55°. The corresponding fast Fourier transform (FFT) patterns (insets in Figure 2 d) of the GeTe film reveal a face-centered cubic pattern [ 50 ], confirming the rock salt structure of the crystallite. Across all crystallites, the (111) planes align parallel to the film surface, suggesting that the preferential orientation of the crystallites within the C-GeTe film lies in the (111) direction along the film thickness.…”

“…( c ) TEM of GeTe film deposited and annealed at 573 K for 24 h (inset: corresponding FFT) (adapted from [ 49 ]). ( d ) High-resolution TEM images crystalline GeTe film annealed at 673 K (inset: corresponding FFT) (adapted from [ 50 ]). ( e ) Calculated band structures of R-GeTe and C-GeTe, respectively (adapted from [ 51 ]).…”