Threshold current reduction in spin-polarized lasers: Role of strain and valence-band mixing

We show that valence-band mixing (VBM) plays a dominant role in determining the current threshold I-th of spin-pumped lasers. The degree of VBM is controlled by tuning the strain through the selection of alloy composition and layer structure. In a well-designed InxGa1-x As structure, VBM can lead to a nearly a fourfold decrease in I-th. However, it can also lead to a 25-fold increase for a different composition, in marked contrast to common expectations. In certain cases, larger threshold reductions are achieved for smaller injected spin polarization, a counterintuitive result.