2 research outputs found
Effect of the Thermal Conductivity on Resistive Switching in GeTe and Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> Nanowires
The thermal conduction characteristics
of GeTe and Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub>(GST) nanowires
were investigated using an optical method to determine the local temperature
by Raman spectroscopy. Since the localization of surface charge in
a single-crystalline nanostructure can enhance charge-phonon scattering,
the thermal conductivity value (κ) of single crystalline GeTe
and GST nanowires was decreased significantly to 1.44 Wm<sup>–1</sup> K<sup>–1</sup> for GeTe and 1.13 Wm<sup>–1</sup> K<sup>–1</sup> for GST, compared to reported values for polycrystalline
structures. The SET-to-RESET state in single-crystalline GeTe and
GST nanowires are characteristic of a memory device. Unlike previous
reports using GeTe and GST nanowires, the SET-to-RESET characteristics
showed a bipolar switching shape and no unipolar switching. In addition,
after multiple cycles of operation, a significant change in morphology
and composition was observed without any structural phase transition,
indicating that atoms migrate toward the cathode or anode, depending
on their electronegativities. This change caused by a field effect
indicates that the structural phase transition does not occur in the
case of GeTe and GST nanowires with a significantly lowered thermal
conductivity and stable crystalline structure. Finally, the formation
of voids and hillocks as the result of the electromigration critically
degrades device reliability
Characterization of Rotational Stacking Layers in Large-Area MoSe<sub>2</sub> Film Grown by Molecular Beam Epitaxy and Interaction with Photon
Transition metal
dichalcogenides (TMDCs) are promising next-generation
materials for optoelectronic devices because, at subnanometer thicknesses,
they have a transparency, flexibility, and band gap in the near-infrared
to visible light range. In this study, we examined continuous, large-area
MoSe<sub>2</sub> film, grown by molecular beam epitaxy on an amorphous
SiO<sub>2</sub>/Si substrate, which facilitated direct device fabrication
without exfoliation. Spectroscopic measurements were implemented to
verify the formation of a homogeneous MoSe<sub>2</sub> film by performing
mapping on the micrometer scale and measurements at multiple positions.
The crystalline structure of the film showed hexagonal (2H) rotationally
stacked layers. The local strain at the grain boundaries was mapped
using a geometric phase analysis, which showed a higher strain for
a 30° twist angle compared to a 13° angle. Furthermore,
the photon–matter interaction for the rotational stacking structures
was investigated as a function of the number of layers using spectroscopic
ellipsometry. The optical band gap for the grown MoSe<sub>2</sub> was
in the near-infrared range, 1.24–1.39 eV. As the film thickness
increased, the band gap energy decreased. The atomically controlled
thin MoSe<sub>2</sub> showed promise for application to nanoelectronics,
photodetectors, light emitting diodes, and valleytronics