Band alignments at strained Ge1−x Sn x /relaxed Ge1−y Sn y heterointerfaces

Type-I, type-II, reverse type-I, and reverse type-II band alignments are found theoretically in strained Ge1−x Sn x (0 ≤ x ≤ 0.3) grown on relaxed Ge1−y Sn y substrates (0 ≤ y ≤ 0.3) using the model-solid theory. The prerequisite bandgaps, and energy difference between the top valence band edge and the average valence band position of GeSn are obtained by the nonlocal empirical pseudopotential method. For the indirect-gap (L valleys) Ge1−x Sn x on relaxed Ge1−y Sn y , the band alignments are type-I and reverse type-I under biaxial compressive strain (x > y) and biaxial tensile strain (x < y), respectively. For the direct-gap (Γ valley) Ge1−x Sn x on relaxed Ge1−y Sn y , the biaxial compressive strain yields type-I and type-II alignment, while the biaxial tensile strain yields reverse type-I and reverse type-II alignments.