Bipolar semiconductor in two-dimensional covalent organic frameworks

As a tunable spintronic device, the bipolar magnetic semiconductor (BMS) has been intensively studied in recent years, but the candidate materials are limited in the magnetic system. In this work, we report an alternative strategy to realize it in a nonmagnetic system called bipolar semiconductor (BS). Utilizing doping-induced ferromagnetism, the enantiomorphic flat bands in BS are used to switch the spin carriers, achieving the same function as the BMS. Based on the frontier orbital of the molecular building blocks, a universal approach is proposed to search the BS in two-dimensional (2D) covalent organic frameworks (COFs), which is confirmed by first-principles calculations in the experimentally synthesized fluoride-graphdiyne (F-GDY). Moreover, the spin-polarized channels and giant anomalous Hall effect can also be created in F-GDY through the light irradiation. Our results demonstrate a new spintronic application for 2D COFs without the intrinsic magnetism.