“Cage-confinement” controlled dimensionality conversion of Bi2O2Se crystals towards high-performance phototransistors

Abstract

2D Bi₂O₂Se is an intriguing building block for next-generation optoelectronic devices owing to its ultrahigh electron mobility and ultrabroadband photodetection capability. However, fully exploiting its advantages in advanced optoelectronic applications remains greatly challenging owing to the lack of in-depth understanding of the morphological evolution of Bi₂O₂Se crystals and efficient methods for enhancing their photoresponse. Herein, we developed a novel “cage-confinement” technique to achieve dimensionality-tunable growth of Bi₂O₂Se crystals in a space-confined CVD system. It can effectively control the key parameter of determining the dimensionality of crystals, referred to as the elastic strain energy of nucleation (ΔG_s), by tuning the active area size of Bi₂O₃ seeds at a suitable flow rate of carrier gas. Furthermore, based on an optimized van der Waals transfer technique of crystals and electrodes, a sheet-shaped phototransistor of Bi₂O₂Se has a high responsivity (R) of ∼74 000 A W⁻¹ and detectivity (D*) of ∼4.0 × 10¹¹ Jones. Meanwhile, a wire-shaped device demonstrates an impressive R value of 300 000 A W⁻¹, D* value of 3.9 × 10¹² Jones and photoconductance gain (G_ph) of 1.2 × 10⁵. These results surpass most reported Bi₂O₂Se-based detectors and pave the way for the applications of 2D layered semiconductors in advanced optoelectronic devices and technologies.