First-Principles Insights on Intrinsic Stability and Electronic Properties of Cu 2 ZnGeS 4 Surface

Cu 2 ZnGeS 4 is a promising semiconductor that has potentially wide applications. Intrinsic stability and electronic properties of the Cu 2 ZnGeS 4 surface are investigated in this work. The surfaces are stabilized by defects that are found to show diverse physics from that of the bulk. Under Cu-rich conditions, the acceptor-like Cu-enriched and Zn-deficient defects dominate both in the bulk and on the surface. However, under Cu-poor conditions, acceptor-like Cu-deficient defects dominate in the bulk, whereas donor-like Cu-deficient and Zn-enriched defects dominate on the surface. Therefore, an n-p type inversion occurs at the area between the bulk and surface. Moreover, among the possible surface con figurations, only the 2Zn Cu ( 112 ) surface does not generate surface states in the band gap. Hence, the Cu-poor condition is proposed if Cu 2 ZnGeS 4 acts as a solar cell material. The results can also be generalized to other quaternary chalcogenides.