A research team led by Prof. REN Wencai from the Institute of Metal Research, Chinese Academy of Sciences (IMR, CAS), has successfully achieved the wafer-scale epitaxial growth of monolayer MoSi₂N₄ single crystals, a high-performance p-type two-dimensional semiconductor. The findings, published online on July 8 in Nature Materials, mark a significant step toward realizing complementary metal-oxide-semiconductor (CMOS) integrated circuits based on 2D materials.
As electronic devices continue to shrink, conventional semiconductors such as silicon face fundamental physical bottlenecks including short-channel effects. Van der Waals layered 2D semiconductors, with their atomically thin thickness and dangling-bond-free surfaces, offer compelling advantages for sub-5-nanometer technology nodes. While various n-type 2D semiconductors including MoS₂ and WS₂ have been successfully prepared as wafer-scale single crystals, p-type counterparts that combine high mobility and excellent stability remain extremely scarce, and their single-crystal wafer growth has proven even more challenging.
In 2020, this team pioneered the creation of the p-type 2D semiconductor MoSi₂N₄ by introducing silicon into a non-layered molybdenum nitride growth system, establishing the MA₂Z₄ family of van der Waals layered materials (Science 369, 670, 2020). Monolayer MoSi₂N₄ exhibits a bandgap comparable to that of MoS₂, yet surpasses it in theoretical carrier mobility, thermal conductivity, Young's modulus, and fracture strength, with exceptional stability. However, until now, only polycrystalline MoSi₂N₄ films had been experimentally attainable; grain boundaries severely degrade electrical transport performance and compromise film integrity during transfer.
To overcome this challenge, the team developed a chemical vapor deposition approach using Cu(111) single crystals enriched with Mo and Si atoms as the growth substrate. They discovered that the <110> steps on Cu(111) induce the oriented nucleation of monolayer MoSi₂N₄ domains in a single orientation, enabling seamless stitching into a continuous single-crystal film. The resulting monolayer MoSi₂N₄ exhibits outstanding crystalline quality, with an intrinsic carrier mobility reaching 154 cm² V⁻¹ s⁻¹. Field-effect transistor arrays fabricated from this material deliver excellent electrical performance, including an on/off ratio of approximately 3.8 ± 1.4 × 10⁶ and an on-state current density up to 17.96 μA μm⁻¹ at a channel length of 1 μm, along with superior stability compared with monolayer WSe₂-based devices. Moreover, the method proves versatile, enabling the wafer-scale growth of monolayer WSi₂N₄ single crystals as well.
This work not only establishes a highly promising p-type 2D semiconductor platform for future integrated circuits, but also provides a general strategy for the wafer-scale single-crystal growth of other 2D materials, advancing their applications in the field of electronics and information technology.
Growth of monolayer MoSi₂N₄ single-crystal wafers. (Image by IMR)
Structural characterization of monolayer MoSi₂N₄ single crystals. (Image by IMR)
Single-orientation nucleation mechanism of monolayer MoSi₂N₄ induced by surface steps on Cu(111) single crystals. (Image by IMR)
Optical characterization of monolayer MoSi₂N₄ single crystals. (Image by IMR)
Field-effect transistor device arrays and electrical performance based on monolayer MoSi₂N₄ single crystals. (Image by IMR)
