Theory of the strain-symmetrized silicon-based Ge-Si superlattice laser

A unipolar p-i-p silicon-based intersubband laser consisting of a symmetrically strained GeSi superlattice on a relaxed Si_0.5Ge _0.5 buffer layer is modeled and analyzed. The strain-symmetrization removes the limitation on the size of the superlattice. The procedure for calculating the in-plane energy dispersion is extended to a superlattice. Analysis of the in-plane energy dispersion shows that the population inversion is local-in-k-space. For an 11 ML/11 ML superlattice (15.4 Å/15.4 Å), interminiband lasing between HH2 and HH1 is predicted at λ=2.2 μm. From the envelope functions and material properties, the miniband lifetimes and laser gain are calculated. For a current density of 10 kA/cm², a gain of G_L=96/cm is calculated. Alternate structures with larger expected gains are considered. Quantum-parallel, quantum-cascade, and quantum-staircase lasing are examined