Controlled vapour growth and phase engineering of large-area bilayer WSe2 for optoelectronic applications

The engineering of stacking order plays an important role in regulations of electronic and optical properties of layered van der Waals materials.Here,we demonstrate a developed physical vapour deposition approach to grow WSe2 atomic layers with controllable 3R and 2H phases.The 3R WSe2bilayer tends to form at a lower deposition temperature(830℃),and the 2H WSe2bilayer prefers to grow at a higher deposition temperature(930℃).Efficient phase engineering was demonstrated by simply controlling the deposition temperature.Moreover,by photoluminescence,Raman,selected area electron diffraction and so on,it was determined that the AA’-stacking corresponds to the 2H phase,and the AB-stacking corresponds to the 3R phase.So,different layer stacking and interlayer coupling result in differences in the optical and optoelectronic properties of the two phases.The responsivity of 3R bilayer WSe2is ～195 times higher than 2H phase exhibiting dramatically improved photoelectric detection performance by phase engineering(R3R=2.54 A/W vs R2H=0.013 A/W at 780 nm,82.7 mW cm-2).Hence,the findings of this study not only contribute to the controllable synthesis of two-dimensional materials with diverse stacking phases but also hold promise for advancing the design and fabrication of future optoelectronic devices.