Air passivation of chalcogen vacancies in two-dimensional semiconductors

TL;DR

This study reveals that oxygen in air can chemisorb at chalcogen vacancies in 2D semiconductors, transforming harmful defects into benign sites and offering a simple method to enhance 2D semiconductor performance.

Contribution

It uncovers the interaction between air and chalcogen vacancies in 2D semiconductors, showing oxygen's role in passivating defects and improving material properties.

Findings

O2 can chemisorb at chalcogen vacancies with a barrier related to cohesive energy.

Chemisorbed O2 converts defect sites from harmful to benign.

Air exposure can be used to passivate defects in 2D semiconductors.

Abstract

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. In this work, we unravel the interaction between air and chalcogen vacancies (VX)-the most typical defects in 2D SCs. We find that, although the interaction is weak for most molecules in air, O2 can be chemisorbed at VX with a barrier that correlates with the SC cohesive energy and can be overcame even at room temperature for certain SCs. Importantly, the chemisorbed O2 changes the VX from commonly-believed harmful carrier-traps to electronically benign sites. This unusual behavior originates from the iso-valence between O2 and X when bonded with metal. Based on these findings, we propose a facile approach to improve the performance of 2D SCs by using air to passivate the defects.