Layered Zn-based semiconductors K2Zn3S4 and Rb2Zn3Se4: Crystal growth, structure and potential p-type transparent conductivity

Exploring semiconductors with a large band gap and a small hole effective mass are of great importance for the development of outstanding p-type transparent conducting materials. In this work, we report the single crystal growth of two Zn-based chalcogenides K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 . Single crystal X-ray diffraction revealed that K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 crystallize in P 2/ c and Ibam space group, respectively. Both compounds show layered structure, and the layers are formed by edge-sharing tetragonal [Zn 3 Q 4 ] 2- units and alkali-metal cations are distributed between the layers. To our surprise, compared to the previously reported structure obtained by powder X-ray diffraction, K 2 Zn 3 S 4 crystallized in a new type of structure in which adjacent layers were displaced. Both experiments and theoretical calculations indicate that K 2 Zn 3 S 4 and Rb 2 Zn 3 Se 4 are direct semiconductors with large band gaps, and the experimental values are 3.6 eV for K 2 Zn 3 S 4 and 3.1 eV for Rb 2 Zn 3 Se 4 . Based on first-principles calculations, the hole effective masses of K 2 Zn 3 S 4 are calculated to be as small as 0.425 me, revealing the potential remarkable transparent conductivity in this Zn-based chalcogenide.