Enhanced wavelength-selective photoresponsivity with a MoS2 bilayer grown conformally on a patterned sapphire substrate

In the present study, novel MoS2 bilayers with 3D structures were considered for their application as wavelength-sensitive photodetectors. Using e-gun deposition and a CVD process, MoS2 bilayers can be grown conformally on a patterned (cones or pyramids) sapphire substrate without any wrinkles on the 2D film. After the sulfurization process, the MoS2 bilayer is subjected to a local strain in the patterns and its band gap gets enlarged due to the strain. This phenomenon is beneficial for photo-devices to enable the collection of the photocurrent. Measurements revealed a broadband enhancement of the MoS2-based photodetector with a patterned array in terms of both absorption and photocurrent. It is noteworthy that a cone-patterned sapphire substrate (CPSS) is able to generate more photocurrent when illuminated under blue light illumination, whereas the pyramid-patterned sapphire substrate (PPSS) performs best under green and red light illumination. Simulations of the electric field distributions for MoS2 coatings on different substrates, based on 3D models, revealed that the sensitivity of the MoS2-based photodetector can be greatly enhanced by the light-scattering effect.