The optical gain variation of Ge nanowires induced by L-valley splitting under the [110] direction stress

The electronic structures of Ge nanowires under the [110] direction stress are calculated via effective-mass k center dot p theory, and the results manifest eight equivalent L-valleys will be split into fourfold degenerate L- 1-valleys and L- 2-valleys. With increasing stress, the electron levels at the L- 1-valleys and L- 2-valleys can be pushed close to and away from those at the Gamma-valley, respectively, which causes the appearance of a rising inflection point in the Gamma-valley filling ratio and gain peak intensity at around 2.5 GPa stress. Moreover, we prove the positive net peak gain with small diameters is apt to be obtained considering the free-carrier absorption loss.