Highly symmetric and delayed excitonic emission response and space charge-limited current transport in P-irradiated WSe2 and WS2 nanoflakes

摘要

We report on the highly symmetric excitonic emission, manifested Raman active modes, and electrical properties of WSe_2 and WS_2 nanoflakes subjected to energetic β-particles. Raman spectra have revealed numerous mixed modes and a declining trend of the E_(2g)~1-to-A_(1g) intensity ratio with radiation dose (0-4.8 kGy).The nanoscale WSe_2 exhibits a remarkable luminescence peak, located at ~ 675 nm and characterized by a combinatorial effect of both 2s and 2p excitons, whereas the nanoflakes of WS_2 offered a testimony to charged excitons (trions) in the range ~ 624-630 nm. Moreover, a moderate (from ~ 2.29 to ~ 2.88 ns) and a nearly sevenfold enhancement in the slow life-time decay parameters have been observed for the irradiated WSe_2 and WS_2nanoflakes, respectively. Furthermore, the rectifying nature of the I-V trends suggests formation of metal-semiconductor nanojunctions with transport characteristics described by parameters such as ideality factor (η) and barrier height (Φ_(b)), both of which gave a declining trend with increasing β-dose. As substantiated by transport characteristics and first principle calculations, a semi-metallic behavior of WSe_2 was also realized due to the introduction of excessive chalcogen defects at the highest radiation dose. The results would strengthen our insights prior to their deployment in next-generation nanodevices integrating nano-electronics and nano-photonics at large.