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·p theory, and the results manifest eight equivalent L-valleys will be split into fourfold degenerate L1-valleys and L2-valleys. With increasing stress, the electron levels at the L1-valleys and L2-valleys can be pushed close to and away from those at the Γ-valley, respectively, which causes the appearance of a rising inflection point in the Γ-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.