Enhanced wavelength-selective photoresponsivity with a MoS ₂ bilayer grown conformally on a patterned sapphire substrate

In the present study, novel MoS ₂ bilayers with 3D structures were considered for their application as wavelength-sensitive photodetectors. Using e-gun deposition and a CVD process, MoS ₂ 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 MoS ₂ 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 MoS ₂ -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 MoS ₂ coatings on different substrates, based on 3D models, revealed that the sensitivity of the MoS ₂ -based photodetector can be greatly enhanced by the light-scattering effect.