Reviewed by Lexie CornerNov 12 2024
Researchers from Huazhong University of Science and Technology and Hebei University have optimized the nucleation process by regulating the interactions between the epitaxial layer and the substrate. Through careful design of lattice and symmetry matching, they successfully achieved unidirectional nucleus formation, a critical factor in producing uniform crystal structures. The study was published in the journal National Science Review.
(a) Schematic of monolayer Sb2O3 with (111) plane. (b) Schematic illustration of growth modes and molecule behavior during the typical vdW epitaxy process. (c) Illustration of the proposed growth pathway of single-crystal Sb2O3 thin film. (d-g) Corresponding AFM images. Scale bar, 200 nm. Image Credit: ©Science China Press.
This pioneering study on van der Waals (vdW) epitaxy has created new opportunities for producing wafer-scale, single-crystal molecular films, addressing a long-standing challenge in semiconductor technology.
The fabrication of high-quality 2D materials is essential for creating ultrathin materials for next-generation ultra-scaled devices. While vdW epitaxy has been effectively applied to 2D atomic crystals, the weak vdW forces in all three dimensions within molecular crystals pose a challenge in achieving the ordered molecular alignment needed for high-quality thin films. This limitation has hindered the wider use of these materials in advanced devices.
The team also addressed the Schwoebel-Ehrlich barrier, which enabled layer-by-layer growth and controlled coalescence of nuclei. These breakthroughs have facilitated the growth of single-crystal Sb2O3 films with precise thickness control, which is vital for scalable semiconductor applications.
The research team used ultrathin, highly oriented Sb2O3 films as gate dielectrics in MoS2-based field-effect transistors (FETs), leading to devices with improved performance. The enhanced dielectric quality of these Sb2O3 films resulted in an exceptionally low leakage current (~10-14 A) and an ideal van der Waals (vdW) interface with the channel material, both of which contributed to superior switching characteristics.
This configuration enabled the device to achieve a subthreshold swing close to the theoretical limit of 60 mV/dec, signifying highly efficient gate control. This achievement marks a significant breakthrough in controlling molecular alignment in vdW epitaxy, opening the door to the large-scale synthesis of 2D molecular crystals with high crystallinity—a crucial factor for future electronic and optoelectronic devices.
The study not only advances vdW epitaxy technology but also highlights the growing potential of molecular crystals for next-generation device applications, suggesting new directions in the development of high-performance 2D materials.
Journal Reference:
Liu, L., et al. (2024). Van der Waals epitaxial growth of single-crystal molecular film. National Science Review. doi.org/10.1093/nsr/nwae358.