Electrostatic control of exciton charge. (a) MoSe2 PL (color scale in counts) plotted as a function of back-gate voltage. Near zero doping, we observe mostly neutral and impurity-trapped excitons. With large electron (hole) doping, negatively (positively) charged excitons dominate the spectrum. (b) Illustration of the gate dependent trion and exciton quasi-particles and transitions. (c) trion and exciton peak intensity vs. gate voltage at the dashed arrows in (a).
For the first time, the observation and full tunability of charged and neutral excitons in sub-nanometer, monolayer MoSe2 field effect transistors have been reported in photoluminescence (PL) measurements. The current trend towards device miniaturization has highlighted the importance of novel two-dimensional (2D) materials, with graphene being the most famous example. MoSe2 belongs to a new class of 2D materials whose electronic properties rivals that of graphene. The current work demonstrates that with high quality synthesized samples, monolayer MoSe2 supports neutral and charged excitons with extraordinary long lifetime for photonic applications under ambient conditions, and may revolutionize the semiconductor optoelectronic and photonic device industry. In particular, charged exciton species make it possible to control energy flow via electric field, which may play an essential role in solar energy applications. This research was made possible by a broad collaboration in which BES-MSED supported the MoSe2 synthesis and theoretical explanations.
For more information, please contact Dave Mandrus, mandrusdg@ornl.gov or Brian Sales, salesbc@ornl.gov.
Jason S. Ross, Sanfeng Wu, Hongyi Yu, Nirmal J. Ghimire, Aaron M. Jones, Grant Aivazian, Jiaqiang Yan, David G. Mandrus, Di Xiao, Wang Yao, and Xiaodong Xu, “Electrical control of neutral and charged excitons in a monolayer semiconductor,” Nature Communications 4, 1474 (2013).