Mixed-dimensional stacked nanocomposite structures for a specific wavelength-selectable ambipolar photoresponse

Mixed-dimensional composite structures using zero-dimensional (0D) quantum dots (QDs) and two-dimensional (2D) transition metal dichalcogenides (TMDs) materials are expected to attract great interest in optoelectronics due to the potential to generate new optical properties. Here, we report on the unique optical characteristics of a devices with mixed dimensional vertically stacked structures based on tungsten diselenide (WSe₂)/CdSeS QDs monolayer/molybdenum disulfide (MoS₂) (2D/0D/2D). Specifically, it exhibits an ambipolar photoresponse characteristic, with a negative photoresponse observed in the 400–600 nm wavelength range and a positive photoresponse appeared at 700 nm wavelength. It resulted in the high negative responsivity of up to 52.22 mA·W⁻¹ under 400 nm, which is 163 times higher than that of the photodetector without CdSeS QDs. We also demonstrated the negative photoresponse, which could be due to increased carrier collision probability and non-radiative recombination. Device modeling and simulation reveal that Auger recombination among the types of non-radiative recombination is the main cause of negative photocurrent generation. Consequently, we discovered ambipolar photoresponse near a specific wavelength corresponding to the energy of quantum dots. Our study revealed interesting phenomenon in the mixed low-dimensional stacked structure and paved the way to exploit it for the development of innovative photodetection materials as well as for optoelectronic applications.