Transition metal dichalcogenides (TMDs) have attracted considerable interest for exploration of next-generation electronics and optoelectronics in recent years. Fabrication of in-plane lateral heterostructures between TMDs has opened up excellent opportunities for engineering two-dimensional materials. The creation of high quality heterostructures with a facile method is highly desirable but it still remains challenging. In this work, we demonstrate a one-step growth method for the construction of high-quality MoS ₂ –WS ₂ in-plane heterostructures. The synthesis was carried out using ambient pressure chemical vapor deposition (APCVD) with the assistance of sodium chloride (NaCl). It was found that the addition of NaCl played a key role in lowering the growth temperatures, in which the Na-containing precursors could be formed and condensed on the substrates to reduce the energy of the reaction. As a result, the growth regimes of MoS ₂ and WS ₂ are better matched, leading to the formation of in-plane heterostructures in a single step. The heterostructures were proved to be of high quality with a sharp and clear interface. This newly developed strategy with the assistance of NaCl is promising for synthesizing other TMDs and their heterostructures.

We report a spontaneous phase transformation of GaTe, occurring when the bulk is exfoliated to a few layers. The results demonstrate the crucial role of interlayer interactions in the structural stability.

We demonstrate the fabrication of field-effect transistors based on single-layer MoS₂ and a thin layer of BaTiO₃ (BTO) dielectric, isolated from its parent epitaxial template substrate. Thin BTO provides an ultrahigh-κ gate dielectric effectively screening Coulomb scattering centers. These devices show mobilities substantially larger than those obtained with standard SiO₂ dielectrics and comparable with values obtained with hexagonal boron nitride, a dielectric employed for fabrication of high-performance two-dimensional (2D) based devices. Moreover, the ferroelectric character of BTO induces a robust hysteresis of the current vs gate voltage characteristics, attributed to its polarization switching. This hysteresis is strongly suppressed when the device is warmed up above the tetragonal-to-cubic transition temperature of BTO that leads to a ferroelectric-to-paraelectric transition. This hysteretic behavior is attractive for applications in memory storage devices. Our results open the door to the integration of a large family of complex oxides exhibiting strongly correlated physics in 2D-based devices.

In this paper, we demonstrated AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) with AlN gate dielectric grown by plasmaenhanced atomic layer deposition (PEALD). The high-quality interface of AlN/AlGaN/GaN MIS-HEMTs resulted in a very small threshold voltage (Vth) hysteresis and dispersion. Simultaneously, the MIS-HEMTs exhibited a high-peak transconductance of 289 mS/mm and a small Vth shift of 0.8 V, while those for Al ₂ O ₃ /AlGaN/GaN metal-oxide-semiconductor HEMTs were 203 mS/mm and 5.2 V, respectively. Furthermore, analysis indicated that PEALD-grown AlN significantly reduced the interface charges at dielectric/III-N interface (from 1.2 × 10 ¹³ to 8 × 10 ¹² cm ^-2 eV ^-1 for interface traps, and from 1.01 × 10 ¹³ to 3.1 × 10 ¹¹ cm ^-2 for fixed charges) and improved channel transport properties (the full-width at half-maximum of channel transconductance increased from 0.9 to 2.7 V), compared with ALD-grown Al ₂ O ₃ , which could explain the differences of device characteristics.

MoO ₂ is used as a new source material for the growth of large area and high optical quality monolayer MoS ₂ . However, a systematic study of the growth parameters is still missing and large-area growth of discreet single crystals is still challenging. Hereby, we report the shape evolution of monolayer growth of MoS ₂ and develop a methodology to achieve centimeter-scaled discrete MoS ₂ by adopting MoO ₂ as Mo source material in an atmospheric-pressure chemical vapor deposition process. Our results indicate the growth of monolayer MoS ₂ could benefit from the precise control of the introduction time of sulfur and the S/MoO ₂ ratio in experiments. Micro-Raman and photoluminescence spectra confirm the properties of the material. E-beam lithography was utilized to make contact with the as-grown MoS ₂ located at the selective area. The electrical properties of MoS ₂ with different morphologies were compared. In the end, the persistent photoconductivity properties of monolayer MoS ₂ were emphasized and the underlying mechanism was proposed. These studies demonstrate a better understanding of the growth and application of MoS ₂ -based 2D materials.