The optical gain of Ge nanowires engineered by the [100] direction uniaxial stress perpendicular to the nanowire axis

Abstract We calculate the electronic structures of Ge nanowires at the direct Γ-valley and indirect L-valley under the [100] direction uniaxial stress perpendicular to the nanowire axis using the effective-mass k.p theory, and the results demonstrate the stress along the [100] direction is effective to transform Ge nanowires from the indirect-band-gap to direct-band-gap semiconductor. Moreover, the optical gain and net peak gain under the [100] direction stress are also investigated, and it is interesting that the pure optical gain along the z direction can almost be obtained. Importantly, we find that the photon energy around 0.8 eV corresponding to the gain peak can be realized in Ge nanowires under an appropriate [100] direction stress when the diameter is in the range of 10∼20 nm, which means Ge nanowires can be engineered to be suitable for the telecom wavelength 1550 nm in the field of Si photonics via the [100] direction stress.