Chemical environment dependent Stabilities, electronic properties and diffusions behaviors of intrinsic point defects in novel Two-Dimensional MoSi2N4 monolayer

A novel 2D semiconductor, MoSi2N4 monolayer, was very recently successfully fabricated and shown great potential for future broad applications in nanoelectronic devices and catalysis. For the synthesis and application of the material, intrinsic point defects are required to be considered, because they are inevitably formed during the bottom-up synthesis and following substrate transfer process, and also can be intentionally introduced by defect engineering to modulate properties and explore applications of materials. Herein, eight types of intrinsic point defects including two vacancies (N mono- and di-vacancies; VN(m) and VN2(m)), four antisites (SiMo, SiN(t), MoN(m) and MoSi) and two adatoms (Siada and Nada) are found to have highly thermodynamic stabilities in MoSi2N4 monolayer under various chemical environments. Electronic properties calculations suggest the existence of VN(m) and VN2(m) leads to the emergence of the recombination center, reducing the carrier lifetime and thus showing the potential for high-speed switching device applications. SiN(t) and Siada-defected structures show p-type and n-type conducting characters, respectively, which can be explored for possible PN junction applications. Also, the existence of MoSi may induce unusual resistance–temperature dependence behavior, providing some chances to design high-mobility semiconductors. Combined with the migration behavior of point defects (monovacancies and adatoms), the Schottky defect formation mechanism of VN(m) could be reasonably explained. Besides, high migration barriers of monovacancy defects (VN(m), VSi and VMo) demonstrate their higher kinetic stability in monolayer, compared with monovacancies in graphene and silicene. The migration of N adatom is relatively difficult than that of Si adatom, increasing opportunities to detect it in experiments. This work will provide insight into defect engineering of MoSi2N4 monolayer and the MA2Z4 monolayer family for various applications.