Synthetic control of monolayer, bilayer, and trilayer WSe2 single crystals for high-performance 2D p-type transistors

The two-dimensional (2D) complementary metal–oxide–semiconductor circuits require balanced performance between p-type and n-type devices, but currently, among two-dimensional semiconductor materials, the electrical performance of p-type WSe2 is significantly inferior to that of n-type MoS2. This performance bottleneck is primarily attributed to issues with the growth quality of WSe2, interfacial defects, and the influence of charged impurities, which collectively limit the application of WSe2 in low-power integrated circuits. To address this challenge, we report that the monolayer (1L), bilayer (2L), and trilayer (3L) WSe2 single crystals can be selectively grown on high-κ SiNx/Si substrate by precisely adjusting the carrier gas direction over time in a reverse-flow chemical vapor deposition system. Using this growth method, Raman/photoluminescence spectroscopy, scanning transmission electron microscopy, and selected-area electron diffraction confirm that the as-grown 1–3L WSe2 nanosheets are single-crystalline with excellent quality. By employing Pt metallization process to construct optimized metal–semiconductor contacts, the fabricated mono-to bilayer WSe2 transistors exhibit pronounced p-type characteristics with superior performance. In particular, the 1L WSe2 transistors with a channel length of 2 μm display a record-breaking on-state current of ∼500 μA/μm at room temperature. This controllable synthesis strategy demonstrates potential for advancing WSe2-based p-type electronics in microelectronic applications.