3 research outputs found
Oxidation Mechanism of Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> Nanowires with Au Catalyst Tip as a Function of Ge Content
Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> nanowires (NWs) (0.22
≤ <i>x</i> ≤ 0.78) were synthesized using
a vapor–liquid–solid procedure with a Au catalyst. We
measured the intrinsic physical, chemical, and electrical properties
of the oxidized Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> NWs using several techniques, including transmission
electron microscopy, X-ray photoemission spectroscopy, and optical
pump-THz probe spectroscopy. We suggest two distinct oxidation mechanisms
depending on the Ge content in the Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> NWs: (i) when the Ge content
is around 0.22, a Au catalytic effect brings about oxidation in both
the axial and lateral directions; and (ii) when the Ge content is
greater than 0.22, the Au tip is detached from the NW body and does
not act as a catalyst, which is a result of the high degree of Ge-atom
participation in the oxidation process. Additionally, we measured
the photoconductivity decay time distribution for the Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> NWs before and after
oxidation process; the decay time is significantly shortened in oxidized
Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> NWs (0.22 < <i>x</i>), whereas it is maintained for
Si-rich Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> NWs (<i>x</i> ≈ 0.22) as compared to the
as-grown Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub> NWs. It indicates that the number of defect states is generated
with the formation of defective Ge oxide at the oxide-shell-layer/Si<sub>1–<i>x</i></sub>Ge<sub><i>x</i></sub>-core-NW
interface
Structural and Electrical Properties of EOT HfO<sub>2</sub> (<1 nm) Grown on InAs by Atomic Layer Deposition and Its Thermal Stability
We report on changes in the structural,
interfacial, and electrical characteristics of sub-1 nm equivalent
oxide thickness (EOT) HfO<sub>2</sub> grown on InAs by atomic layer
deposition. When the HfO<sub>2</sub> film was deposited on an InAs
substrate at a temperature of 300 °C, the HfO<sub>2</sub> was
in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and
low preexisting interfacial defect states. During post deposition
annealing (PDA) at 600 °C, the HfO<sub>2</sub> was transformed
from an amorphous to a single crystalline orthorhombic phase, which
minimizes the interfacial lattice mismatch below 0.8%. Accordingly,
the HfO<sub>2</sub> dielectric after the PDA had a dielectric constant
of ∼24 because of the permittivity of the well-ordered orthorhombic
HfO<sub>2</sub> structure. Moreover, border traps were reduced by
half than the as-grown sample due to a reduction in bulk defects in
HfO<sub>2</sub> dielectric during the PDA. However, in terms of other
electrical properties, the characteristics of the PDA-treated sample
were degraded compared to the as-grown sample, with EOT values of
1.0 nm and larger interfacial defect states (D<sub>it</sub>) above
1 × 10<sup>14</sup> cm<sup>–2</sup> eV<sup>–1</sup>. X-ray photoelectron spectroscopy data indicated that the diffusion
of In atoms from the InAs substrate into the HfO<sub>2</sub> dielectric
during the PDA at 600 °C resulted in the development of substantial
midgap states
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