Material gain engineering in GeSn/Ge quantum wells integrated with an Si platform.

H. S. Mączko,R. Kudrawiec,M. Gladysiewicz

doi:10.1038/srep34082

Abstract

It is shown that compressively strained Ge1−xSnx/Ge quantum wells (QWs) grown on a Ge substrate with 0.1 ≤ x ≤ 0.2 and width of 8 nm ≤ d ≤ 14 nm are a very promising gain medium for lasers integrated with an Si platform. Such QWs are type-I QWs with a direct bandgap and positive transverse electric mode of material gain, i.e. the modal gain. The electronic band structure near the center of Brillouin zone has been calculated for various Ge1−xSnx/Ge QWs with use of the 8-band kp Hamiltonian. To calculate the material gain for these QWs, occupation of the L valley in Ge barriers has been taken into account. It is clearly shown that this occupation has a lot of influence on the material gain in the QWs with low Sn concentrations (Sn < 15%) and is less important for QWs with larger Sn concentration (Sn > 15%). However, for QWs with Sn > 20% the critical thickness of a GeSn layer deposited on a Ge substrate starts to play an important role. Reduction in the QW width shifts up the ground electron subband in the QW and increases occupation of the L valley in the barriers instead of the Γ valley in the QW region.

Highlights

Group IV semiconductors (Si and Ge) are widely applied in electronic devices but their application in light emitters still is very limited because of their indirect bandgap nature
It is worth noting that this structure differs from the previously considered quantum wells (QWs) containing GeSn alloys (i.e., GeSn/SiGeSn QWs33–39) since QW barriers are unstrained and the strain in the GeSn QW is well defined by the lattice constant of Ge
The first condition is determined by the nature, it is the positive material gain for the GeSn/Ge QW, while the second one is determined by technology, which allows to grow a good quality GeSn material

Summary

Results and Discussion

It has been shown that the Bir-Pikus theory[49] can be applied to description of the strain-related shifts in the conduction and valence bands in this alloy[28,50] This theory has been used by us to calculate the quantum confinement potential for electrons and holes in strained GeSn/Ge QWs. Regarding the application of GeSn/Ge QWs as the gain medium in lasers, the type I bandgap alignment for electrons and heavy holes is required. It has been found that in the range of Sn > 10% the L valley in Ge barriers are located above the first electron subband in Ge1−xSnx/Ge QW and the Δ1 eL energy increases with the increase in Sn concentration, see Fig. 3(b) Such conditions are very favorable for achieving an inversion of carrier population in the QW region and it is very interesting to calculate the material gain for Ge1−xSnx/Ge QWs with the contents of 0.1

Conclusions

EgΓ energy scale is assumed such

Additional Information