Experimental observation of type-I energy band alignment in lattice-matched Ge1−x−ySixSny/Ge heterostructures

We experimentally demonstrated the formation of type-I energy band alignment in lattice-matched Ge1−x−ySixSny/Ge(001) heterostructures and clarified the dependence of Si and Sn contents on the energy band structure. By controlling the Si and Sn contents, keeping the Si:Sn ratio of 3.7:1.0, we formed high-quality Ge1−x−ySixSny pseudomorphic epitaxial layers on a Ge substrate with the lattice misfit as small as 0.05%. The energy bandgaps of the Ge1−x−ySixSny layers, measured by spectroscopic ellipsometry, increased to 1.15 eV at Si and Sn contents of 41% and 15%, respectively. X-ray photoelectron spectroscopy indicated that the top of the valence band of Ge1−x−ySixSny was lower than that of Ge. Additionally, the energy band offsets between Ge1−x−ySixSny and Ge at both the conduction and valence band edges were estimated to be larger than 0.1 eV with an Sn content of more than 8%. These results promise that heterostructures of group-IV semiconductors using Si, Ge, and Sn can have type-I energy band alignment without relying on strain and can confine both electrons and holes.