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

Abstract

We report on the highly symmetric excitonic emission, manifested Raman active modes, and electrical properties of WSe2 and WS2 nanoflakes subjected to energetic β-particles. Raman spectra have revealed numerous mixed modes and a declining trend of the E12g-to-A1g intensity ratio with radiation dose (0–4.8 kGy). The nanoscale WSe2 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 WS2 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 WSe2 and WS2 nanoflakes, 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 (φb), 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 WSe2 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.