Effect of Point Defects on Electronic Structure of Monolayer GeS

Abstract

Using density functional theory calculations, atomic and electronic structure of defects in monolayer GeS were investigated by focusing on the effects of vacancies and substitutional atoms. We chose group IV or chalcogen elements as substitutional ones, which substitute for Ge or S in GeS. It was found that the bandgap of GeS with substitutional atoms is close to that of pristine GeS, while the bandgap of GeS with Ge or S vacancies was smaller than that of pristine GeS. In terms of formation energy, monolayer GeS with Ge vacancies is more stable than that with S vacancies, and notably GeS with Ge substituted with Sn is most favorable within the range of chemical potential considered. Defects affect the piezoelectric properties depending on vacancies or substitutional atoms. Especially, GeS with substitutional atoms has almost the same piezoelectric stress coefficients eij as pristine GeS while having lower piezoelectric strain coefficients dij but still much higher than other 2D materials. It is therefore concluded that Sn can effectively heal Ge vacancy in GeS, keeping high piezoelectric strain coefficients.

Electrical Transport Properties Driven by Unique Bonding Configuration in γ-GeSe

“…Owing to the low vaporization temperature of Se, the chemical environment during γ-GeSe synthesis is likely to be Se-rich, which further lowers the formation energy of the Ge vacancies. Figure S7a compares the vacancy formation energies in Ge monochalcogenides from the literatures. − Overall, the formation energy of Ge vacancies was smaller than that of chalcogen vacancies for all monochalcogenides. Moreover, as shown in Figure S7a, the significantly lower formation energy of Ge vacancies is attributed to both γ-GeSe and GeTe, which provides strong evidence that the highly p-doped behavior shared by γ-GeSe and GeTe can be attributed to Ge vacancies.…”