Air Passivation of Chalcogen Vacancies in Two-Dimensional Semiconductors

Defects play important roles in semiconductors (SCs). Unlike those in bulk SCs, defects in two-dimensional (2D) SCs are exposed to the surrounding environment, which can potentially modify their properties/functions. Air is a common environment, yet its impact on the defects in 2D SCs still remains elusive. Here we study the interaction between air and chalcogen vacancies (V_X), the most typical defects in 2D SCs. Although the interaction is weak for most molecules in air, O₂ can be chemisorbed at V_X with a barrier that correlates with the SC cohesive energy and can be overcome even at room temperature for certain SCs. Importantly, the chemisorbed O₂ changes the V_X from commonly believed harmful carrier-traps to electronically benign sites. This unusual behavior originates from the isovalence between O₂ and X when bonded with metal. Based on these findings, a facile approach is proposed to improve the performance of 2D SCs by using air/O₂ to passivate the defects. The interaction between air and chalcogen vacancies (V_X), the most typical defects in 2D semiconductors (SCs), is calculated. The chemisorbed O₂ changes the V_X from commonly believed harmful carrier-traps to electronically benign sites. This unusual behavior originates from the isovalence between O₂ and X when bonded with metal. A facile approach is proposed from this to improve the performance of 2D SCs by using air/O₂ to passivate the defects.