Abstract: To date, tremendous efforts have been made to explore optical and electrical properties on low dimensional nano materials such as quantum dots, nano wires, and two-dimensional materials. Recently, two-dimensional transition metal dichalcogenides (TMDs) have attracted much more interest due to their tightly bound exciton state, tunable band alignment, doping engineering and giant spin-valley coupling. Owing to their atomically thin structures, monolayer TMDs act as semiconductors that can undergo a complete transition from indirect to a direct bandgap, with energy gaps located at the Brillouin zone producing a strong exciton pump efficiency. Therefore, TMDs are optically active layered materials promising for fast on-chip photonic and optoelectronic applications. One of the current challenges in photonics is developing high speed, chip-integrated and high efficiency light sources and photodetectors. For optoelectronic devices, efficient engineering of carrier concentration and an invulnerable method to create a p-n junction within TMDs become our next challenge.
In this seminar, I will present our latest experimental results in atomically thin light emitting diodes and carriers engineering of TMDs by using ferroelectric materials. The monolayer molybdenum ditelluride light-emitting diode (LED) device has been fabricated. By taking advantage of the quantum tunneling effect, the device has achieved a very high external quantum efficiency (EQE) of 9.5% at 83 K, which is the highest external quantum efficiency obtained from LED devices fabricated from monolayer TMDs so far. Regarding of carrier engineering within TMDs, we have demonstrated a ferroelectric domain modulation that can significantly enhance or inhibit photoluminescence. This domain engineering monolayer TMDs results in an in-plane homojunction that could be used as future optoelectronic devices.