Wurtzite-derived polytypes of kesterite and stannite quaternary chalcogenide semiconductors

The I$_2-$II$-$IV$-$VI$_4$ quaternary chalcogenide semiconductors (\textit{e.g.}, Cu$_2$ZnSnS$_4$, Cu$_2$ZnGeSe$_4$) have been studied for more than 40 years, but the nature of their crystal structures has proved contentious. Literature reports exist for the stannite and kesterite structures, which are zincblende-derived structures, and wurtzite-stannite, which is a wurtzite-derived structure. In this talk we report a new wurtzite-derived structure, wurtzite-kesterite (space group $Pc$), which is the ground state for some I$_2-$II$-$IV$-$VI$_4$ compounds, but is easily confused with the wurtzite-stannite structure. We show that there is a clear relationship between the properties of the wurtzite-kesterite and zincblende-derived kesterite structures,, as well as between wurtzite-stannite and stannite. The energy stability of different structures are studied according to the strain and Coulomb energy contributions, showing a dependence on the size and ionicity of the component atoms. Electronic structure of the wurtzite-derived structures will also be discussed.