The variation of optical gain in Ge nanowires induced by the ΔEeΓ,L and symmetry of hole states under the axial stress

Abstract

The electronic structures of Ge nanowires at the direct Γ-valley and indirect L-valley are calculated under the axial sterss based on the effective-mass theory. The optical gain is also investigated, and strangely, the peak gain along the z direction almost does not change, while the peak gain along the x direction goes up rapidly as the stress increases. For the first time, we clarify the variation of the peak gain in detail via the decrease of a physical quantity ΔEeΓ,L in combination with the change of the symmetry of hole states under stress. Furthermore, the net peak gain of Ge nanowires with different diameters and axial stresses is calculated after considering the free-carrier absorption loss, and the results demonstrate that the positive net peak gain along the x direction can be achieved when the stress is up to 4 GPa.