The band structure and optical gain of a new IV-group alloy GePb: A first-principles calculation

Abstract

A new Si-based material GePb which has been predicted to possess a direct-bandgap attracts much attention in the field of fabricating Si-based light source recently. To precisely investigate its band structure and lighting efficiency, the first principal calculations combined with DFT + U method and supercell models are employed. For unstrained GePb, the calculated crossover value of Pb concentration changing it from an indirect to a direct bandgap is evaluated to 3.4%, which is much lower than that of GeSn. Meanwhile, its maximum optical gain is much higher than that of GeSn, which means GePb could be a better choice for fabricating Si-based laser. To reduce the direct-bandgap GePb's need for Pb, its band structures and optical gains under the effects of alloying Pb and applying (111)-biaxial strains are calculated. The results indicate that GePb's need for Pb can be further reduced to 2.1% with the aid of 1.13% compressive strain, and the moderate strain strength is more beneficial to improve its optical gain. This means the combination of these two methods could be a better way to tune the band structure and optical gain of GePb. Aiming to the compressively strained GePb grown on (111) Ge buffer, the band structures and optical gains of fully strained GePb are calculated. The calculated crossover value of Pb is 2.7%, and the optical gain of GePb increases as Pb concentration increases. This means growing GePb on (111) Ge buffer not only can reduce its need for Pb, but also can improve its lighting efficiency.