Ordering-Induced Direct-to-Indirect Band Gap Transition in Multication Semiconductor Compounds

Using first-principles calculations and symmetry analysis, we show that as cation atoms in a zinc blende-based semiconductor are replaced through atomic mutation (e.g., evolve from ZnSe to CuGaSe2 to Cu2ZnGeSe4), the band gaps of the semiconductors will become more and more indirect because of the band splitting at the zone boundary, and in some cases will even form the segregating states. For example, although ZnSe is a direct band gap semiconductor, quaternary compounds Cu2ZnGeSe4 and Cu2ZnSnSe4 can be indirect band gap semiconductors if they form the primitive mixed CuAu ordered structures. We also find that the stability and the electronic structure of the quaternary polytypes with different atomic ordering are almost negative-linearly correlated. We suggest that these intrinsic properties of the multication semiconductors can have a large influence on the design and device performance of these materials.