Optoelectronics with Complex van der Waals Heterostructures

Two-dimensional (2D) materials have attracted the attention of the scientific community since the discovery of graphene in 2004 (an atomically thin layer of graphite), due to the new and interesting physical phenomena found in this material. Graphene was not just a scientific breakthrough from a physical point of view, but it also opened the door to research on atomically thin materials. Nowadays, many materials with a wide range of properties (metals, semiconductors, insulators, superconductors) have been achieved in a 2D configuration, and still there are more to come. The discovery of 2Ds has been followed by the combination of such materials in the so- called van der Waals heterostructures. The fabrication of designer materials built by pilling up different 2D layers in complex structures sets a new platform for the study of new physical phenomena or the development of high-performance applications like flexible and transparent electronic and optoelectronic devices. For instance, the Hofstadter butterfly appears when graphene is stacked on hexagonal-boron nitride. Furthermore, van der Waals heterostructures provide a new path towards the realization of high performance electronics, photovoltaics, photonics and optoelectronic devices such as field-effect transistors, photodetectors or light- emitting diodes in a new generation of flexible and transparent devices. However, this field is still in its first baby-steps and a wide range of combinations of 2D materials need to be studied in order to achieve ultra-high performance devices. The proposed project OPTOvanderWAALS aims to the fabrication and study of complex van der Waals heterostructures to study inter-layer excitonic phenomena and use these excitonic effects to fabricate ultra-high-performance optoelectronic devices. I propose to add novel intermediate layers between 2D semiconductors to automatically switch on and off photodetectors with an extraordinarily low dark current, which will be translated in an ultra- high-performance. I also propose to employ these intermediate layers in photovoltaic cells as recombination region, allowing the recombination of unbalanced electron-hole pairs and avoiding charge build-up in the cells, resulting in an increased open-circuit voltage and, therefore, higher efficiency than state-of-the-art 2D photovoltaic cells. Besides, all of these heterostructures will be fabricated following a new procedure to align the crystal structure of different layers by second harmonic generation imaging, resulting in an optimized interaction between layers that will ultimately lead to ultra-high-performance devices in a new generation of flexible and transparent optoelectronics.