Hexagonal WSe₂ Nanoplates for Large-Scale Continuous Optoelectronic Films

Two-dimensional materials, especially the transition-metal dichalcogenides, have shown their potential application for next-generation electronics and optoelectronics devices. In view of the practical application, large-scaled synthesis of high crystallinity continuous films has attracted much attention. Even though large-scaled films or flakes synthesized on insulating substrates have already been reported, growing continuous films on SiO₂ substrates remains challenging. Also, generally, p-typed triangular WSe₂ nanoplates are used as seeds in the synthesis process. In this work, hexagonal WSe₂ nanoplates are successfully grown on SiO₂ substrates by a NaCl-assistant vapor deposition method. The temperature dependence of the recombination dynamics was studied by a combination of Raman and photoluminescence spectroscopy. Interestingly, as-grown crystals show tunable polarity characteristics by applying back gate voltages. The carrier mobility is calculated to be 0.4 and 0.05 cm²·V^–1·s^–1 in the p and n regimes, respectively. Moreover, WSe₂-based photodetectors generate photocurrent with a fast response time, which together with the photoswitch ratio exceeds 4.8×10² illuminated by a 633 nm laser light. The responsivity and detectivity are 3.64 mA/W and 1.67 × 10⁸ Jones at a bias of 1 V, respectively. Importantly, comparing this with the synthesis process using triangular WSe₂ nanoplates, it is demonstrated that hexagonal ambipolar WSe₂ with promising probability to synthesize large-scaled continuous films with large grains is possible.