The [100] direction strained Ge[formula omitted]Snx nanowires with low Sn contents towards the application of SWIR or MWIR lasers

Abstract

The band structures of Ge1−xSnx nanowires with low Sn contents at the Γ-valley and L-valley under the [100] direction stress are studied via effective-mass theory, and we find that Ge0.95Sn0.05 and Ge0.92Sn0.08 nanowires can be tuned to direct-bandgap semiconductors even for the stress less than 4 GPa. Moreover, as increasing the stress, the calculations of the optical gain manifest that the z direction peak gain can be enhanced sharply regardless of the diameter and Sn content since more electrons are filled at the Γ-valley. The further research shows that the FCA loss of Ge1−xSnx nanowires can almost be neglected, meanwhile remarkable and positive net peak gain along the z direction can be acquired even though electron concentration is as low as the order of 1018 cm−3, which can overcome the non-negligible FCA loss caused by electron concentration of the order of 1019 cm−3 in Ge or strain-free Ge1−xSnx nanowires.