Research Achievements  

Defect-free Monolayer MoS2 to Take the Place of Silicon Semiconductors

An important study conducted by an international research team that includes researchers from NTU may have solved the greatest challenge in the material scientists’ quest for the perfect monolayer, an ultra-thin semiconductor material that could lead to such futuristic consumer products as flexible LED displays that become transparent when turned off.

Scientists striving to create the atom-thin monolayer semiconductors confront two frustrating obstacles. First, the perfect materials they seek simply do not appear in the natural world. Second, the stubborn fact is that the thinner the semiconductor materials, the more the defects impact the performance of the electrical and optical components.

Recently, however, these frustrations were overcome with a simple new approach to fixing the flaws in molybdenum disulfide (MoS2);namely, by forging an optoelectronically perfect two-dimensional monolayer by rinsing MoS2 in a bath of the organic superacid—bistriflimide.  This boosted the monolayer material’s photoluminescence quantum yield from less than 1% to an unheard of nearly 100%. The team presented its revolutionary discovery in the November 27 issue of Science.

Three members of the Department of Electrical Engineering participated in the study: Ph.D. student Der-Hsien Lien, one of the study’s three co-lead authors; distinguished professor and former NTU President Si-Chen Lee; and former NTU professor Dr. Jr-Hau He.

In recent years, material scientists have been exploring ways todevelop new two-dimensional monolayer semiconductor materials because such materials possess special optoelectrical and mechanical characteristics that could be integrated into existing semiconductor manufacturing processes.

At an infinitesimal seven-tenths of a nanometer thick, a single layer of MoS2 is thinner than even a strand of human DNA, which is relatively bulky at 2.5 nanometers in diameter. However, despite the advantages offered by MoS2, scientists have been stuck at an impasse primarily because their synthesis techniques result in materials marred by a high density of flaws.The team’s method of creating a defect-free MoS2 that achieves perfect optoelectrical performance has opened the way to exploit the powerful properties of monolayer semiconductors.

These findings will open up enormous possibilities for the practical use of two-dimensional monolayer semiconductors, such as MoS2 in optoelectronic devices and high-performance transistors. In addition to flexible, transparent LED displays, some of the astonishing products we might see stemming from this new technology include super high-efficiency solar cells, ultra-sensitive light detectors, and low power consumption nanoscale transistors. MoS2 also shows great promise for replacing silicon-based components and becoming one of the materials scientists turn to create the next generation of semiconductor components.