Defect Tolerant Monolayer Transition Metal Dichalcogenides

Researchers from Section for Theoretic Atomic-scale Physics at DTU-Physics have found a simple way to understand and predict why the (opto-)electronic properties of some semiconductors appear to be more tolerant to crystal defects than others.

Mohnish Pandey, Filip A. Rasmussen, Korina Kuhar, Thomas Olsen, Karsten W. Jacobsen, and Kristian S. Thygesen

Nano Letters, 2016, 16 (4), pp 2234–2239. DOI: 10.1021/acs.nanolett.5b04513
Publication Date (Web): March 30, 2016

One of the main performance limiting factors of semiconductors for optoelectronics is the presence of defects such as vacancies, impurities or crystal disorder. Such defects can act as local scattering centers which reduce the mobility of charge carriers and enhance recombination of photo-excited electron-hole pairs. The effectiveness of a defect to scatter charge carriers, trap excitons and induce recombination between electrons and holes depends crucially on the way the defect modifies the electronic structure around the band edges; in particular whether or not it introduces localized states inside the band gap (deep gap states).

Semiconductors with lower tendency to form deep gap states are termed as defect tolerant. In their paper, Mohnish et al. present a systematic first-principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nano-scale optoelectronics. They show that upon formation of a chalcogen (S, Se, Te) vacancy, all TMDs with similar orbital character of their valence and conduction bands form deep gap states while the remaining materials do not. The analysis is made quantitative by introducing a simple descriptor that measures the difference in average orbital character of the valence and conduction bands. 

The simple descriptor proposed by the authors, and the underlying conceptual understanding of defect state formation, enables a quantitative measure of the degree of defect tolerance in semiconductors and could become a powerful tool for high-throughput materials discovery.


Mohnish Pandey
DTU Physics
+45 45 25 31 84


Kristian Sommer Thygesen
DTU Physics
+45 45 25 31 88