Vapour-liquid-solid-solid growth of two-dimensional non-layered β-Bi₂O₃ crystals with high hole mobility

Currently, p-type two-dimensional (2D) materials lag behind n-type ones in both quantity and performance, hindering their use in advanced p-channel transistors and complementary logic circuits. Non-layered materials, which make up 95% of crystal structures, hold the potential for superior p-type 2D materials but remain challenging to synthesize. Here we show a vapour-liquid-solid-solid growth of atomically thin (<1 nm), high-quality, non-layered 2D β-Bi₂O₃ crystals on a SiO₂/Si substrate. These crystals form via a transformation from layered BiOCl intermediates. We further realize 2D β-Bi₂O₃ transistors with room-temperature hole mobility and an on/off current ratio of 136.6 cm² V^-1 s^-1 and 1.2 × 10⁸, respectively. The p-type nature is due to the strong suborbital hybridization of Bi 6s²6p³ with O 2p⁴ at the crystal's M-point valence band maximum. Our work can be used as a reference that adds more 2D non-layered materials to the 2D toolkit and shows 2D β-Bi₂O₃ to be promising candidate for future electronics.