Two-dimensional atomic layer semiconductors based on transition metal dichalcogenides have attracted intense interest due to their exceptional optoelectronic properties. Compared to silicon, they have substantial advantages for flexible electronics as they are inherently flexible and their properties are highly tunable. However, they have been very difficult to fabricate with conventional methods because they are atomically thin and fragile. This award investigates laser-assisted chemical processing to fabricate stable, high-performance atomic layer semiconductor devices with ultra-high sensitivity and extraordinary functionalities. It contributes a new technology for the processing, functionalization and patterning of transition metal dichalcogenide-based two-dimensional semiconductor devices. The chemical composition of the two-dimensional semiconductor materials are modified and controlled at the nanoscale by incorporating doping atoms from a selected gas source by means of laser irradiation. This process is stable in ambient air and enables precise tuning of the electronic properties of the material that is necessary for fabricating high performance devices. This coupled materials synthesis, processing and characterization methodology provides significant opportunities for undergraduate and graduate students, including women and minorities, to gain valuable research experiences and training in nanoscience and engineering.
The objective of this project is to utilize laser driven chemical processing for localized functionalization of two-dimensional atomic layer semiconductors in a dual-beam processing system. The process involves a laser beam irradiated at normal incidence to generate vacancies and another synchronized ultraviolet nanosecond laser beam irradiated parallel to the target specimen for dissociation of dopant precursor gas molecules. In this manner, it is possible to decouple and control the mechanisms involved in the doping and alloying processes. Near-field optical processing is implemented to reduce feature resolution and generate highly defined nanoscale patterns. Scalability and integration into functional devices are explored to demonstrate large-scale nanomanufacturing. The first contribution entails stable and spatially controlled writing of p- and n-doped domains in these materials, followed by the deliberate tuning of the semiconductor band gap via laser induced alloying. The second contribution is the direct nanopatterning of the target materials using assembled microlens and nanowire elements integrated into the laser CVD system. The research work is validated by fabricating transistors having sharp nanoscale PN junctions and lateral tandem optoelectronic devices. Finally, this project offers a robust and repeatable platform for discovering entirely new and exciting physics of these exotic materials.
