Making Semiconductor Monolayers Perfectly Bright
Der-Hsien Lien1*
1Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, USA
* Presenter:Der-Hsien Lien,
Once semiconductors are thinned down to the atomic level, strong many-body interactions cause new physics to emerge that deviates from well-known free carrier models. A prominent effect is that carriers turn from “free” to “bound” species even at room temperature, so-called room temperature excitons. Using monolayer semiconductors as the platform (i.e., semiconductors at their ultimate thickness limits), I will show that such thickness-determined excitonic systems are promising for optoelectronic applications due to their near-unity photoluminescence (PL) quantum yields (QYs) [1], a key figure of merit dictating the maximum efficiency achievable in light-emitting diodes, lasers and solar cells. I will discuss the comprehensive recombination mechanisms of excitons in monolayers and showed that the non-radiative recombination pathways can be fully suppressed by electrostatic gating, despite the presence of native defects [2]. This research reveals that room-temperature excitons are robust and bright regardless of monolayer quality, indicating the potential of achieving highly efficient excitonic devices. To deal with the injection inefficiency caused by Schottky contacts, I will show an AC carrier injection architecture, a device concept that is capable of efficiently injecting carriers in various excitonic systems, including monolayer semiconductors, with demonstrations of bright light-emitting devices from infrared to ultraviolet regimes [3].
[1] Science 2015, 350, 1065.
[2] Science 2019, 364, 468–471.
[3] Nature Communications 2018, 9, 1129.

Keywords: Monolayer semiconductor, Exciton photophysics, Excitonics