Growth of Large Single Crystals of n-Type SnS from Halogen-Added Sn Flux

We report the growth of large Cl-doped and Br-doped SnS single crystals from a molten Sn-based flux. Compared with the small and lamellar undoped SnS crystals, the addition of SnCl2 or SnBr2 halogen sources in the flux substantially enhanced lateral growth along the (100)-plane and vertical growth. The maximum size of the obtained single crystals reached a diameter and thickness of 16 mm and 0.7 mm for the Cl-doped SnS and 24 mm and 1.0 mm for the Br-doped SnS, respectively. The X-ray rocking curves and the X-ray back-reflection Laue patterns indicated a high crystal quality. The obtained crystals were further characterized via electrical measurements, including electrical conductivity and Hall measurements, optical absorption spectroscopy, and X-ray and ultraviolet photoelectron spectroscopies. Both the Cl-doped and Br-doped SnS single crystals exhibited degenerate n-type conductivity with a high electrical conductivity of 11.1 S cm-1 for Cl-doped SnS and 18.9 S cm(-1) for Br-doped SnS along the (100)-plane at 300 K. Furthermore, the photoelectron spectroscopy results also indicated n-type conductivity. The large single crystals of n-type SnS obtained in this work would enable the fabrication of p-n homojunction SnS solar cells via the deposition of p-type SnS thin films.