Coexistence of Anisotropic Large Magnetoresistance and Ferroelectricity in Two-Dimensional Narrow-Bandgap Bi 2 O 2 Te.

Characteristics like air-stability and high carrier mobility make non-van-der-Waals layered Bi 2 O 2 Se a good prospect for planar integrated nanosystems. However, experimental investigation about its analogue Bi 2 O 2 Te is rather rare due to difficulty in synthesis. Herein, a low-pressure CVD process is proposed that is adjusted to the rigorous growth condition required, with large-scale Bi 2 O 2 Te ultrathin film obtained. Magneto-transport behavior reveals a very large anisotropic nonsaturating low-temperature magnetoresistance (∼1133% under 9 T magnetic field). Despite the contradiction between high conductivity and ferroelectricity in principle (mobile electrons screen electrostatic forces between ions), the high-conductive Bi 2 O 2 Te film here is revealed experimentally as another intrinsic ferroelectric with the polarization switchable by external electric field (predicted in Nano Lett. 2017 , 17, 6309). These results prove that Bi 2 O 2 Te possesses a very narrow bandgap (∼0.15 eV), high conductivity, large magnetoresistance, and room-temperature ferroelectricity, displaying great potential as a high-performance nanoelectronic two-dimensional semiconductor and, in advanced functional devices, working in the mid-infrared region.