16 research outputs found
Bi2O2Se nanowires presenting high mobility and strong spin-orbit coupling
Systematic electrical transport characterizations were performed on
high-quality Bi2O2Se nanowires to illustrate its great transport properties and
further application potentials in spintronics. Bi2O2Se nanowires synthesized by
chemical vapor deposition method presented a high field-effect mobility up to
1.34*104 cm2V-1s-1, and exhibited ballistic transport in the low back-gate
voltage (Vg) regime where conductance plateaus were observed. When further
increasing the electron density by increasing Vg, we entered the phase coherent
regime and weak antilocalization (WAL) was observed. The spin relaxation length
extracted from the WAL was found to be gate tunable, ranging from ~100 nm to
~250 nm and reaching a stronger spin-obit coupling (SOC) than the
two-dimensional counterpart (flakes). We attribute the strong SOC and the gate
tunability to the presence of a surface accumulation layer which induces a
strong inversion asymmetry on the surface. Such scenario was supported by the
observation of two Shubnikov-de Haas oscillation frequencies that correspond to
two types of carriers, one on the surface, and the other in the bulk. The
high-quality Bi2O2Se nanowires with a high mobility and a strong SOC can act as
a very prospective material in future spintronics.Comment: 22 pages, 7 figure
Universal conductance fluctuations and phase-coherent transport in a semiconductor BiOSe nanoplate with strong spin-orbit interaction
We report on phase-coherent transport studies of a BiOSe nanoplate
and on observation of universal conductance fluctuations and spin-orbit
interaction induced reduction in fluctuation amplitude in the nanoplate.
Thin-layered BiOSe nanoplates are grown by chemical vapor deposition
(CVD) and transport measurements are made on a Hall-bar device fabricated from
a CVD-grown nanoplate. The measurements show weak antilocalization at low
magnetic fields at low temperatures, as a result of spin-orbit interaction, and
a crossover toward weak localization with increasing temperature. Temperature
dependences of characteristic transport lengths, such as spin relaxation
length, phase coherence length, and mean free path, are extracted from the
low-field measurement data. Universal conductance fluctuations are visible in
the low-temperature magnetoconductance over a large range of magnetic fields
and the phase coherence length extracted from the autocorrelation function is
in consistence with the result obtained from the weak localization analysis.
More importantly, we find a strong reduction in amplitude of the universal
conductance fluctuations and show that the results agree with the analysis
assuming strong spin-orbit interaction in the BiOSe nanoplate.Comment: 11 pages, 4 figures, supplementary material
Strong spin-orbit interaction and magnetotransport in semiconductor BiOSe nanoplates
Semiconductor BiOSe nanolayers of high crystal quality have been
realized via epitaxial growth. These two-dimensional (2D) materials possess
excellent electron transport properties with potential application in
nanoelectronics. It is also strongly expected that the 2D BiOSe
nanolayers could be of an excellent material platform for developing spintronic
and topological quantum devices, if the presence of strong spin-orbit
interaction in the 2D materials can be experimentally demonstrated. Here, we
report on experimental determination of the strength of spin-orbit interaction
in BiOSe nanoplates through magnetotransport measurements. The
nanoplates are epitaxially grown by chemical vapor deposition and the
magnetotransport measurements are performed at low temperatures. The measured
magnetoconductance exhibits a crossover behavior from weak antilocalization to
weak localization at low magnetic fields with increasing temperature or
decreasing back gate voltage. We have analyzed this transition behavior of the
magnetoconductance based on an interference theory which describes the quantum
correction to the magnetoconductance of a 2D system in the presence of
spin-orbit interaction. Dephasing length and spin relaxation length are
extracted from the magnetoconductance measurements. Comparing to other
semiconductor nanostructures, the extracted relatively short spin relaxation
length of ~150 nm indicates the existence of strong spin-orbit interaction in
BiOSe nanolayers.Comment: 14 pages, 4 figures, and 5 pages of Supplementary Material
Controlled Synthesis of High-Mobility Atomically Thin Bismuth Oxyselenide Crystals
Non-neutral layered crystals, another
group of two-dimensional (2D) materials that lack a well-defined van
der Waals (vdWs) gap, are those that form strong chemical bonds in-plane
but display weak out-of-plane electrostatic interactions, exhibiting
intriguing properties for the bulk counterpart. However, investigation
of the properties of their atomically thin counterpart are very rare
presumably due to the absence of efficient ways to achieve large-area
high-quality 2D crystals. Here, high-mobility atomically thin Bi<sub>2</sub>O<sub>2</sub>Se, a typical non-neutral layered crystal without
a standard vdWs gap, was synthesized via a facial chemical vapor deposition
(CVD) method, showing excellent controllability for thickness, domain
size, nucleation site, and crystal-phase evolution. Atomically thin,
large single crystals of Bi<sub>2</sub>O<sub>2</sub>Se with lateral
size up to ∼200 μm and thickness down to a bilayer were
obtained. Moreover, optical and electrical properties of the CVD-grown
2D Bi<sub>2</sub>O<sub>2</sub>Se crystals were investigated, displaying
a size-tunable band gap upon thinning and an ultrahigh Hall mobility
of >20000 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> at 2 K. Our results on the high-mobility 2D Bi<sub>2</sub>O<sub>2</sub>Se semiconductor may activate the synthesis and related fundamental
research of other non-neutral 2D materials
Diverse Atomically Sharp Interfaces and Linear Dichroism of 1T' ReS2-ReSe2 Lateral p-n Heterojunctions
Creating heterojunctions between different 2D transition-metal dichalcogenides (TMDs) would enable on-demand tuning of electronic and optoelectronic properties in this new class of materials. However, the studies to date are mainly focused on hexagonal (2H) structure TMD-based heterojunctions, and little attention is paid on the distorted octahedral (1T') structure TMD-based heterojunctions. This study reports the large-scale synthesis of monolayer 1T' ReS2-ReSe2 lateral heterojunction with domain size up to 100 mu m by using two-step epitaxial growth. Atomic-resolution scanning transmission electron microscopy reveals high crystal quality of the heterojunction with atomically sharp interfaces. Interestingly, three types of epitaxial growth modes accompanying formation of three different interface structures are revealed in the growth of 1T' heterojunction, where the angle between the b-axis of ReS2 and ReSe2 is 0 degrees, 120 degrees, and 180 degrees, respectively. The 0 degrees and 180 degrees interface structures are both found to be more abundant than the 120 degrees interface structure owing to their relative lower formation energy. Electrical transport demonstrates that the as-grown heterostructure forms lateral p-n junction with intrinsic rectification characteristics and exhibits polarization-dependent photodiode properties. This is the first time the linear dichroism is achieved in 2D lateral heterostructure, which is important for the development of new devices with multi-functionality
2D fin field-effect transistors integrated with epitaxial high-k gate oxide
Precise integration of two-dimensional (2D) semiconductors and high-dielectric-constant (k) gate oxides into three-dimensional (3D) vertical-architecture arrays holds promise for developing ultrascaled transistors(1-5), but has proved challenging. Here we report the epitaxial synthesis of vertically aligned arrays of 2D fin-oxide heterostructures, a new class of 3D architecture in which high-mobility 2D semiconductor fin Bi2O2Se and single-crystal high-k gate oxide Bi2SeO5 are epitaxially integrated. These 2D fin-oxide epitaxial heterostructures have atomically flat interfaces and ultrathin fin thickness down to one unit cell (1.2 nm), achieving wafer-scale, site-specific and high-density growth of mono-oriented arrays. The as-fabricated 2D fin field-effect transistors (FinFETs) based on Bi2O2Se/Bi2SeO5 epitaxial heterostructures exhibit high electron mobility (mu) up to 270 cm2 V-1 s(-1), ultralow off-state current (I-OFF) down to about 1 pA mu m(-1), high on/off current ratios (I-ON/I-OFF) up to 10(8) and high on-state current (I-ON) up to 830 mu A mu m(-1) at 400-nm channel length, which meet the low-power specifications projected by the International Roadmap for Devices and Systems (IRDS)(6). The 2D fin-oxide epitaxial heterostructures open up new avenues for the further extension of Moore's law