Band and luminescence regulation of SiGeSn ternary alloy: A first-principles investigation

Current experiments show that the ternary alloy SiyGezSnx has larger crystal lattice and bandgap control range than group IV binary alloy, and it is a popular material for the preparation of silicon-based high-efficiency light sources. However, the physical laws of the bandgap and luminescence properties of SiyGezSnx with concentration changes have not been fully elucidated because of high experimental costs and time-consuming research. Therefore, the band structures and optical gains of SiyGezSnx (x∈0–0.35, y∈0–1) were investigated in this study using a first-principles method based on density functional theory combined with special quasi-random structures and Heyd-Scuseria-Ernzerhof hybrid functional correction. The quantitative relationship between the bandgap and concentration change of SiyGezSnx was theoretically clarified. In addition, the optical gain coefficient of the SiyGezSnx with direct bandgap characteristics was studied. Compared with the structure of GeSn with the same Sn concentration, SiGeSn can maintain the direct bandgap when Si is introduced. The results show that the bandgap increases with increasing Si concentration whereas it decreases when more Sn is introduced. Thus, the best way to maintain a direct bandgap is to simultaneously increase the Si and Sn concentrations. To facilitate experimental research, a formula to determine the direct bandgap region of SiyGezSnx was realized. Regarding optical gains, the positive gain regions are consistent with the direct bandgap regions, and the optical gain values are related to fluctuations in electron and hole numbers in the different valleys. For Siy(y=0–0.21)GezSnx(x=0.1–0.31), there are two maximum optical gain regions around Ge0.9Sn0.1 and Si0.17Ge0.56Sn0.27. These results can directly provide theoretical guidance for experimental research, as well as accelerate the research and development of group IV alloy high-efficiency light sources.