First Principles Study Of Two-dimensional Mg₂Si Semiconductors And Their Heterojunction

The study of two-dimensional（2D）materials is the frontier and hotspot in condensed matter physics research,which shows many peculiar and rich properties.The transition of materials from three-dimension（3D）to two-dimension brings groundbreaking changes in the physical and chemical properties.Graphene has become a typical representative of achieving groundbreaking changes through"dimension reduction".2D materials shows a lot of changes in performance beyond expectations compared to 3D materials.2D Mg₂Si-111 is a semiconductor with a reticulated hexagonal structure,which has excellent photoresponse properties.2D Mg₂Si-111 was predicted by using the first-principles calculation method based on density generalized function theory（DFT）.The prediction was conducted using first-principles calculation software such as VASP（Vienna Ab-initio Simulation Package）and MS（Materials Studio）.The structural stability of 2D Mg₂Si-111 was verified through phonon spectrum calculations,molecular dynamics calculations,and mechanics of elastic calculations.Additionally,the effective mass of electrons,electronic structure,and optical properties of 2D Mg₂Si-111 were studied.The results indicate that the 111-crystal face of Mg₂Si is the important crystal face.There are no imaginary frequency in the phonon spectrum of 2D Mg₂Si-111,which confirms the structure of 2D Mg₂Si-111 is stable.The molecular dynamics simulation and elastic mechanics calculations also demonstrate the structure of 2D Mg₂Si-111 is stable.The band gap value of 2D Mg₂Si-111 is 1.17eV,and the band gap value of 1.17 eV of 2D Mg₂Si-111 is suitable for light absorption.2D Mg₂Si-111 present a tunable band gap that transits from the indirect to direct band gap when 2D Mg₂Si-111 is reduced to a single layer.A monolayer of Mg₂Si-111 has a lower electron effective mass than that of the typical 2D materials such as MoS₂.In addition,2D Mg₂Si-111 has excellent absorption properties in the near-infrared light.The different layers of 2D Mg₂Si-111 have different properties,and the properties of 2D Mg₂Si-111 are modulated by the number of the layers.The band gap values of 2D Mg₂Si-111 can be adjusted from 0 eV to 1.17 eV,which is adjusted from single layer of 2D Mg₂Si-111 to four layers of 2D Mg₂Si-111.The band gap value of 2D Mg₂Si-111 achieves a variation from 0.89 eV to 1.1 eV in the presence of Mg vacancy defects.At a Mg vacancy concentration of 5.5 at%,the absorption peak of 2D Mg₂Si-111 is mainly concentrated in the far-ultraviolet light（200-300 nm）,while at a Mg vacancy concentration of 3.12 at%,the absorption peak of 2D Mg₂Si-111 is mainly concentrated in the visible light.The optical properties of multilayer 2D Mg₂Si-111 are excellent,and the three-layers of 2D Mg₂Si-111 has appreciable absorption properties in the short-wave infrared light to near-ultraviolet light.The way to make the 2D Mg₂Si-111 properties changes more finely is through the method of the Mg vacancy defects,and the difference in the number of layers makes the electronic structure and optical properties of 2D Mg₂Si-111 more variable.The electronic structure and optical properties of 2D Mg₂Si-111/graphene and 2D Mg₂Si-111/MoS₂ heterostructures were calculated.The predicted of 2D Mg₂Si-111 is a more efficient and promising semiconductor for optoelectronic applications.This work paves the way for the preparation,design,and application of 2D Mg₂Si-111-based nanoelectronics devices.