Optical Properties of Pseudomorphic SnXGe1−x Alloys

Abstract

AbstractSnxGe1−x alloys are grown coherent on Ge(001) substrates by conventional molecular beam epitaxy. The lattice mismatch between SnxGe1−x and Ge produces a biaxial compression of the alloy in the plane of the substrate and a uniaxial elongation in the growth direction. The change of Eg resulting from the biaxial compression is modeled with deformation potential theory for coherent SnxGe1−x on Ge(001) and coherent SnxGe1−x on Ge(111). For SnxGe1−x on Ge(001), the decrease in the energy band gap due to strain is small, 16 meV for x = 0.10, and Γ7 and L6 shift uniformly. In the case of SnxGe1−x on Ge(111), Γ7 and L6 do not shift uniformly; a large uniaxial splitting occurs at L6, 200 meV for x = 0.10. Another interesting result of a uniaxial strain along [111] is the absence of a direct to indirect energy band gap transition for x < 0.30. Fourier transform infrared spectroscopy transmission measurements of coherent SnxGe1−x on Ge(001) confirm the strain-induced change in the energy band gap is a small effect.