Sulfurization Growth and HCl Etching Processes for Cubic‐Phase SnS Thin Films

Abstract

The synthesis of cubic‐phase SnS thin films using a sulfurization technique, in particular, the relationship between sulfurization conditions and extra phase contamination such as orthorhombic SnS, Sn2S3, or SnS2 is investigated. In case of SnS films sulfurized for 70–90 min, both cubic and orthorhombic SnS‐related diffractions are observed. Sulfurization time longer than 120 min, orthorhombic SnS and SnS2‐related diffractions are observed because the S vapor reacts with the SnS layer and forms a stable extra phase as SnS2. A single phase of cubic SnS is obtained via 18%‐HCl‐solution etching for 90 min without heating. Since the formation energy of cubic SnS is the same as that of orthorhombic SnS, obtaining single‐phase cubic SnS is difficult by optimizing a sulfurization and/or post‐thermal process. Moreover, because the band discontinuity of CdS/cubic SnS speculates a TYPE‐II band diagram, highly efficient SnS solar cells cannot be realized using CdS as an n‐type layer.