**4. Conclusions**

We have evaluated the effect of applied electric field on the intersubband optical transition, dipole moment, AC, and RIC for various GeSn QD size. The transition energy and dipole moment are found to be strongly affected by the electric field-induced confining potential profile changes. Larger size QD are found to be more sensitive to the effects of applied electric field. The intersubband-related AC and RIC can be widely tuned by employing external electric field. This comprehensive study could help future realization of CMOS compatible nonlinear optical devices.

**Author Contributions:** Conceptualization and Formal analysis M.B. and B.I.; Writing-original draft M.B., Investigation M.B. and B.I. Validation B.S. and N.A.M.; Supervision B.I.; Writing-review & editing B.S., N.A.M., B.I.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors would like to thank the Deanship of Scientific Research at King Saud University for funding this work through the Research Group No: RG-1436-014.

**Conflicts of Interest:** The authors declare no conflict of interest.
