Atom-thick semiconductors with tunable bandgaps

Transition metal dichalcogenides, such as molybdenum disulphide, are a new class of semiconductors that structurally resemble graphene and exhibit a large bandgap. This bandgap determines the electrical conductivity of such materials. 

However, the structures and electronic properties of such semiconductors are not well understood, hindering their uses in device fabrication. 

To better understand such semiconductors, a research team from the National University of Singapore and King Abdullah University of Science and Technology, Thuwal, has deposited atom-thick layers of molybdenum disulphide films on a graphite substrate. Using high-resolution scanning tunneling microscopy and spectroscopy, they found that these films exhibit tunable bandgaps that could potentially be used in the manufacture of electronic devices¹. 

The films’ bandgaps decreased with their increasing thicknesses. Single-layer film had higher bandgap than those of bilayer and trilayer films. The single-layer film consisted of different grains with sizes between tens of nanometers to a few hundred nanometers. Each grain was separated from a neighbouring grain by a boundary known as a grain boundary.     

The researchers say that strains formed around the grain boundaries also contributed to decrease in bandgap. 

“This work allows us to evaluate a new class of semiconductor materials whose thickness and grain boundaries can be engineered to spawn flexible electronic and optoelectronic devices with tunable bandgaps,” says lead researcher Andrew T. S. Wee. 

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