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 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 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.

中文翻译：

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[110]方向应力下L谷分裂引起的Ge纳米线光学增益变化

通过有效质量计算了[110]方向应力下Ge纳米线的电子结构k·p理论，结果表明八个等效L-山谷将分裂成四重退化L _{1 -}山谷和L _2-山谷。随着应力的增加，电子能级L _{1 -}山谷和L ₂谷可以分别被推近和远离 γ 谷，这导致 γ 谷填充率出现上升拐点，并在 2.5 GPa 应力左右获得峰值强度。此外，我们证明考虑到自由载流子吸收损耗，小直径更容易获得正的净峰值增益。