Controllable growth of multilayered XSe ₂ (X = W and Mo) for nonlinear optical and optoelectronic applications

Abstract The layered transition metal dichalcogenides (TMDs) exhibit the intriguing physical properties and potential application in novel electronic devices. However, controllable growth of multilayer TMDs remains challenging. Herein, large-scale and high-quality multilayer prototype TMDs of W(Mo)Se ₂ were synthesized via chemical vapor deposition. For Raman and photoluminescence measurements, 2H and 3R multilayer WSe ₂ crystals displayed significant layer-dependent peak position and intensity feature. Besides, different from the oscillatory relationship of second harmonic generation (SHG) intensity for odd–even layer numbers in 2H-stacked multilayer WSe ₂ , the SHG intensity of 3R-stacked ones parabolically increased with the thickness due to the absence of inversion symmetry. For device application, photodetectors based on WSe ₂ with increasing thickness exhibited p -type (bilayer), ambipolar (trilayer), and n -type (four layers) semiconductor behaviors, respectively. Furthermore, photodetectors based on the as-synthesized 3R-stacked WSe ₂ flakes displayed an excellent responsivity of 7.8 × 10 ³ mA W ⁻¹ , high specific detectivity ( D _a * ) of 1.7 × 10 ¹⁴ Jones, outstanding external quantum efficiency of 8.6 × 10 ² %, and fast response time ( τ _Rise = 57 ms and τ _Fall = 53 ms) under 532 nm illumination with bias voltage of V _ds = 5 V. Similar results have also been achieved in multilayer MoSe ₂ crystals. All these findings indicate great potential of 3R-stacked TMDs in two-dimensional optoelectronic applications.