Two-dimensional Mg2Si-111: A direct bandgap semiconductor with excellent optical response properties predicted by first-principles calculations

Abstract

A new two-dimensional(2D) direct bandgap semiconductor material, 2D Mg2Si-111, with a reticulated hexagonal structure and excellent photoresponse properties is predicted by using the first-principles calculation method based on density generalized function theory (DFT). 2D Mg2Si-111 has excellent properties that can be tuned with the number of layers and Mg defects. The calculation shows that the semiconductor of 2D Mg2Si-111 is stable at absolute temperature, and the bandgap value increases to a range suitable for light absorption, which is 1.17 eV. The electronic transition in 2D Mg2Si-111 is changed from the indirect transition of three-dimensional(3D) Mg2Si to direct transition, and its high-efficiency application potential in optoelectronic devices is more prominent. The electron effective mass in single-layer Mg2Si-111 ranges from 0.277 mo to 0.357 m0, which is lower than typical 2D materials, and exhibits an unconventional optical response that is not lower than the bulk parent body and has excellent absorption characteristics in the near-infrared region. Meanwhile, consider the effects of layer number modulation and defect regulation on 2D Mg2Si-111. The band gap value of 2D Mg2Si-111 can be modulated with the number of layers, from single layer to four layers, with an adjustable band gap of 0 eV - 1.17 eV that changes with the number of layers. The band gap change caused by Mg vacancy defects is only 0.89 eV - 1.1 eV, lower than the band gap of multilayer modulation, however, defect control can maintain a higher value of the band gap in 2D Mg2Si-111. Therefore, vacancy defects are a more refined means of regulation, and the influence of layer-number modulation on the characteristics of 2D Mg2Si-111 is significant. The light absorption characteristics of three-layer Mg2Si-111 have considerable light absorption responses from short-wave infrared to near-ultraviolet. Therefore, the layer number modulation has obvious changes to 2D Mg2Si-111. Compared with Mg2Si, 2D Mg2Si-111 is predicted to be a more efficient and promising optoelectronic material, and this work paves the way for the preparation, design and application of novel 2D Mg2Si-111 in 2D optoelectronic devices.