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 WSe2 bilayer tends to form at a lower deposition temperature (830 degrees C), and the 2H WSe2 bilayer prefers to grow at a higher deposition temperature (930 degrees C). 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 WSe2 is similar to 195 times higher than 2H phase exhibiting dramatically improved photoelectric detection performance by phase engineering (R-3R = 2.54 A/W vs R-2H = 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.