Structural Analyses of Phase Stability in Amorphous and Partially Crystallized Ge-Rich GeTe Films Prepared by Atomic Layer Deposition

Abstract

The local bonding structures of GeTe (x = 0.5, 0.6, and 0.7) films prepared through atomic layer deposition (ALD) with Ge(N(Si(CH))) and ((CH)Si)Te precursors were investigated using Ge K-edge X-ray absorption spectroscopy (XAS). The results of the X-ray absorption fine structure analyses show that for all of the compositions, the as-grown films were amorphous with a tetrahedral Ge coordination of a mixture of Ge-Te and Ge-Ge bonds but without any signature of Ge-GeTe decomposition. The compositional evolution in the valence band electronic structures probed through X-ray photoelectron spectroscopy suggests a substantial chemical influence of additional Ge on the nonstoichiometric GeTe. This implies that the ALD process can stabilize Ge-abundant bonding networks like -Te-Ge-Ge-Te- in amorphous GeTe. Meanwhile, the XAS results on the Ge-rich films that had undergone post-deposition annealing at 350 °C show that the parts of the crystalline Ge-rich GeTe became separated into Ge crystallites and rhombohedral GeTe in accordance with the bulk phase diagram, whereas the disordered GeTe domains still remained, consistent with the observations of transmission electron microscopy and Raman spectroscopy. Therefore, amorphousness in GeTe may be essential for the nonsegregated Ge-rich phases and the low growth temperature of the ALD enables the achievement of the structurally metastable phases.

Developing Precursor Chemistry for Atomic Layer Deposition of High-Density, Conformal GeTe Films for Phase-Change Memory

“…The structure of the Te­(SiMe 3 ) 2 precursor is identical to that in the previous works. ,,− The established ALD process, shown in Figure b, consisted of Ge­(guan)­NMe 2 pulse/purge and co-injection of Te­(SiMe 3 ) 2 and NH 3 and purge. The reason for such a peculiar ALD sequence setup was as follows.…”

“…While this is not a sufficiently high performance for the storage-class memory application where a switching cycle of >∼10 8 –10 10 is required, it is still promising for the mass-storage device, such as Intel’s recent Optane for solid-state drive application. More importantly, this work elucidated that fundamental chemical research for the new precursor synthesis and extensive engineering works for optimizing the ALD process can pave the way for implementing the ALD GeTe films for actual device application, which has not been the case in the previous works. ,,,,,− The GeTe ALD process described here has high potential utilities for building crystalline-as-deposited GST materials whose crystallization temperature is below 180 °C for further performance improvement as described in more detail in a separate paper …”

Structural, Optical, and Magnetic Properties of Erbium-Substituted Yttrium Iron Garnets

“…The FT was processed on k 2 -weighted ( k : electron momentum) EXAFS in a range of 2–10 Å –1 using a Hanning window. 41 The FT EXAFS magnitudes show the bonding distributions of Er ions in both samples. The overall FT spectra are very different from each other, suggesting that the local environment of Er in the x = 0.2 sample is fundamentally different from that of Er 2 O 3 .…”

Effect of Electrode Material on the Crystallization of GeTe Grown by Atomic Layer Deposition for Phase Change Random Access Memory

“…The composition of the GeTe film was close to that of Ge 0.6 Te 0.4 , which was confirmed by X-ray fluorescence spectroscopy and TEM-EDS. It was revealed that the as-grown GeTe films were amorphous with a tetrahedral Ge coordination of a uniform mixture of (major) Ge–Te and (minor) Ge–Ge bonds, according to the X-ray absorption fine structure analysis [20].…”

“…In this study, an atomic-layer-deposited GeTe-based PCRAM device was fabricated on TiN and W as BE, and the effect of electrode material on the crystallization of the GeTe phase-changing material was investigated. GeTe or Ge–Sb–Te phase-changing material, fabricated via atomic layer deposition (ALD), shows excellent step coverage even in a very-high-aspect-ratio (20:1) trench structure [17,18,19,20]. In addition, the conformal deposition will guarantee uniformity in electrical properties, including the crystallization process, because the void and adhesion issue can be avoided.…”