Type-I Ge∕Ge1−x−ySixSny strained-layer heterostructures with a direct Ge bandgap

The electronic properties of $\mathrm{Ge}∕{\mathrm{Ge}}_{1-x-y}{\mathrm{Si}}_x{\mathrm{Sn}}_y$ strained-layer heterostructures are predicted theoretically. It is found that a lattice-matched system with fully strained $\mathrm{Ge}$ layers and relaxed ${\mathrm{Ge}}_{1-x-y}{\mathrm{Si}}_x{\mathrm{Sn}}_y$ alloys can have a direct fundamental bandgap with spatial localization in the $\mathrm{Ge}$ layers (type I). The $\mathrm{Si}$ and $\mathrm{Sn}$ concentrations for which such a direct bandgap obtains are close to those that have already been experimentally demonstrated [M. Bauer, C. Ritter, P. A. Crozier, J. Ren, J. Menendez, G. Wolf, and J. Kouvetakis, Appl. Phys. Lett. 83, 2163 (2003)]. The required level of tensile strain in the $\mathrm{Ge}$ layers is compatible with $\mathrm{Si}–\mathrm{Ge}$ technology. The predicted direct bandgap values are as high as $0.6\mathrm{eV}$ .