The project has yielded results that constitute new advances in exciton physics in two-dimensional materials, with the first report of electroluminescence of multi-particle exciton complexes in W-based TMDs, the report of complexes not previously observed before and the additional tunability of the emitted light. Our technique extends and complements gate-dependent PL spectroscopy and will enable further investigations of manybody phenomena in two-dimensional materials. From an applied point of view, our devices may find application as wavelength tunable light emitters or furnish new opportunities for quantum light sources, e.g. by quantum-confinement of electrically induced biexcitons.
In the field of photodetection, we have demonstrated a new concept of programmable photodetector based on monolayer WSe2 in a split-gate self-driven photodetector configuration including charge-storing floating gates. Our photodetectors are capable of retaining configured and fully customizable responsivity values over time with remarkable performance and can be easily programed, erased and rewritten by just varying the value of the control gates. These programmable photodetectors could be employed as building blocks in devices such as pixels arrays or image sensors, solving the problem of unbalanced responsivities in individual pixels, as well as in more complex devices such as neural networks.
Furthermore, we have studied the spectral photocurrent of monolayer WSe2 in a p-n junction configuration, where we observe single-photon emission at locations in which high strain is induced in the monolayer. We find that the photocurrent spectra match very well the photoluminescence, with an enhanced response at the same photon energy as the one of the single-photon emitter. Finally, the dependence of the photocurrent intensity with the drain-source voltage suggests that the photocurrent at single-photon emitter locations, at low electric fields, is governed by a Fowler-Nordheim tunneling process. Our results shed light onto the optoelectronic mechanisms for quantum emitters in two-dimensional materials and provide a basis for further studies towards a deeper understanding of the underlying physics.
In addition, we have studied new combinations of materials for the development of infrared photodetectors with higher responsivity than previously reported ones. Although work is still in progress, the proposed heterostructure based on franckeite and graphene seems as a promising candidate for this research field.
Finally, in the field of photovoltaic energy harvesting devices, we have developed a new concept of vertical photovoltaic cell based on WSe2 with double gates that provides tunable doping distribution in the device. The election of materials and thicknesses is based on the enhancement of the light absorption according to an internal reflection model. We have studied the device performance from both experiments and theory, providing a theoretical model of the device functioning. Furthermore, we have observed that dielectric screening limits the functioning of the device, suggesting that the optimization of the device performance undergoes a reduction of the active material thickness and thickening of the insulating layers. These results set a new route to the design of vertical solar cells based on van der Waals heterostructures and the optimization of their performance.
