Optoelectronics

2D-Materials-based Optoelectronics

The optical response of semiconducting monolayer transition-metal dichalogenides (TMDCs) is dominated by strongly bound excitons that are stable even at room temperature. Recent demonstrations of optical and electrical control over spin-, charge- and valley- degrees of freedom of these exictons, as well as proposed application of monolayer TMDCs in electronics and photonics ignited intense interest in these materials.

We performed first-principles calculations to study the band structure, optical absorption and exciton binding energy of a a series of transition-metal dichalogenides such as MoS2, MoSe2, and WS2, and compared the calculations with photoluminescence and photocurrent spectroscopy. For monolayer MoS2, in particular, we obtain an extremely large binding energy for band-edge excitons, Ebind>570meV. Along with band-edge excitons, we observe excitons associated with a van Hove singularity of rather unique nature. By tuning the band structure through mechanical strain, the optical absorption and photoluminescence of MoS2 can be further tuned and a direct-to-indirect band gap semiconductor can be triggered. Our results suggest applications of these materials as sensitive photodetectors and efficient energy harvesting devices.The work has been performed in collaboration with Dr. Kirill. I. Bolotin's 

group at Vanderbilt University. 

More recently, we have been collaborating with Ian Sellers in the Department of Physics at OU to study III-V quantum wells and GaInAsN.We are able to identify the defect levels to interpret the experimental findings.

See Scientific Report (2014), Nano Letters (2013), J. Phys. Chem. C (2016); Prog. Photovolt. Res. Appl. (2016); ACS Nano (2017); RSC Adv. (2017)