Controlled Vapor–Solid Deposition of Millimeter‐Size Single Crystal 2D Bi2O2Se for High‐Performance Phototransistors

Abstract Atomically thin 2D materials have received intense interest both scientifically and technologically. Bismuth oxyselenide (Bi 2 O 2 Se) is a semiconducting 2D material with high electron mobility and good stability, making it promising for high‐performance electronics and optoelectronics. Here, an ambient‐pressure vapor–solid (VS) deposition approach for the growth of millimeter‐size 2D Bi 2 O 2 Se single crystal domains with thicknesses down to one monolayer is reported. The VS‐grown 2D Bi 2 O 2 Se has good crystalline quality, chemical uniformity, and stoichiometry. Field‐effect transistors (FETs) are fabricated using this material and they show a small contact resistivity of 55.2 Ω cm measured by a transfer line method. Upon light irradiation, a phototransistor based on the Bi 2 O 2 Se FETs exhibits a maximum responsivity of 22 100 AW −1 , which is a record among currently reported 2D semiconductors and approximately two orders of magnitude higher than monolayer MoS 2 . The Bi 2 O 2 Se phototransistor shows a gate tunable photodetectivity up to 3.4 × 10 15 Jones and an on/off ratio up to ≈10 9 , both of which are much higher than phototransistors based on other 2D materials reported so far. The results of this study indicate a method to grow large 2D Bi 2 O 2 Se single crystals that have great potential for use in optoelectronic applications.