Periodic Reporting for period 2 - 2Exciting (Developing optoelectronics in two-dimensional semiconductors)
Reporting period: 2023-01-01 to 2024-12-31
Since 2010, the field of 2D materials has experienced a new boost, originating from the works on 2D semiconductors (2DS), atomically thin semiconducting 'cousins' of graphene. They cover a wide range of band gaps in the visible, UV and IR. Their properties encompass large exciton binding energies and exceptionally strong light-matter interaction. They opened the door to new ways of controlling their electrical and optical properties via the valley degree of freedom, strain, or by creating artificial stacks of 2D materials. All these makes 2DS extremely appealing for optoelectronic applications where conventional semiconductors cannot provide the same performance nor added functionality.
The demand for optical-to-electrical and vice versa transducers has grown exponentially as optics is increasingly adopted for energy-efficient data transmission, also on short distances. Displays and light sensors have been successfully integrated in everyday objects. There is a clear roadmap for achieving broader band width, faster, more sensitive, and brighter devices, and also for devices with new functionalities.
2EXCITING combined complementary expertise to investigate fundamental optoelectronic properties of 2DS and to provide new methods to manipulate them for adding functionalities to 2DS-based optoelectronic devices by:
- Bringing together a consortium of 8 leading academic groups that are amongst the key players in the field of 2DS, and 8 companies with diverse skills ranging from knowledge transfer, R&D to soft skills,
- Studying fundamental physics of the light-matter interaction in 2DSs,
- Developing innovative optoelectronic devices such as excitonic switches, strain-actuated optical modulators, or valleytronic switches,
- Developing strategies to artificially tailor the optoelectronic properties of 2DS through electrostatic or chemical doping, strain engineering, and modifying the twisting angle of stacked layers,
- Training 15 ESRs in the state-of-the-technique experimental and theoretical tools in the field of 2DS-based electronic and optoelectronic devices and related materials preparation, nanoscopy, and optical spectroscopy,
- Preparing the ESRs for their professional career in the growing field of 2D materials through the specialized training programme.
The objectives in 2EXCITING to exploit the photophysical and optoelectronic properties of 2DS, and to manipulate their electronic structure by external means were successfully achieved.
The demand for optical-to-electrical and vice versa transducers has grown exponentially as optics is increasingly adopted for energy-efficient data transmission, also on short distances. Displays and light sensors have been successfully integrated in everyday objects. There is a clear roadmap for achieving broader band width, faster, more sensitive, and brighter devices, and also for devices with new functionalities.
2EXCITING combined complementary expertise to investigate fundamental optoelectronic properties of 2DS and to provide new methods to manipulate them for adding functionalities to 2DS-based optoelectronic devices by:
- Bringing together a consortium of 8 leading academic groups that are amongst the key players in the field of 2DS, and 8 companies with diverse skills ranging from knowledge transfer, R&D to soft skills,
- Studying fundamental physics of the light-matter interaction in 2DSs,
- Developing innovative optoelectronic devices such as excitonic switches, strain-actuated optical modulators, or valleytronic switches,
- Developing strategies to artificially tailor the optoelectronic properties of 2DS through electrostatic or chemical doping, strain engineering, and modifying the twisting angle of stacked layers,
- Training 15 ESRs in the state-of-the-technique experimental and theoretical tools in the field of 2DS-based electronic and optoelectronic devices and related materials preparation, nanoscopy, and optical spectroscopy,
- Preparing the ESRs for their professional career in the growing field of 2D materials through the specialized training programme.
The objectives in 2EXCITING to exploit the photophysical and optoelectronic properties of 2DS, and to manipulate their electronic structure by external means were successfully achieved.
We synthesized high-quality hexagonal boron nitride (hBN) and high-k dielectric materials, using solvent-assisted exfoliation methods to create homogeneous two-dimensional semiconductor (2DS) flakes suitable for inkjet printing, as demonstrated with PtSe2 and SnSe. We enhanced characterization techniques like low-temperature spectroscopy using a Raman/photoluminescence microscope, and developed advanced theoretical methods for 2DS optoelectronics, which were incorporated into the AMS software releases.
Our research on MoSe2/MoS2 heterostructures (HS) identified key factors affecting the degree of polarization (DoP) and the lifetime of interlayer excitons (IX). We achieved long-lived valley polarization by stacking 2D perovskites and transition metal dichalcogenides into type-II HS, observing circularly polarized photoluminescence in (BA)2PbI4/WSe.
In device fabrication, WSe2 served as a standard for studying exciton behavior. By interfacing it with various gates and applying external electric fields, we controlled excitations into specific valleys in the conduction band. We developed methods to enhance photon-waveguide interactions, achieving photodetector responsivities as high as 1000 A/W and photoresponse times below 1 ms by adding an hBN layer.
Our studies on exciton transport showed higher mobility in pristine WSe2 compared to MoSe2/hBN/WSe2 HS. We successfully fabricated excitonic devices from lateral MoS2/WS2 HS, confirming tunable photoluminescence emission energies indicative of IX. Dual-gated MoSe2/WSe2 bilayer devices demonstrated enhanced exciton brightness and lifetime.
We also grew various 2D materials via chemical vapor transport and flux growth, including insulators, semiconductors, antiferromagnets, ferroelectrics, and superconductors. External factors were applied to modify 2DS properties, using van der Waals HS for strain modulation. Twisted bilayers formed superlattices controlling electronic structures, akin to graphene or hBN. Localized strain was engineered via atomic force microscopy on MoS2.
To communicate progress, our researchers participated in conferences, workshops, and published findings in peer-reviewed journals, ensuring engagement with the scientific and industrial communities.
Our research on MoSe2/MoS2 heterostructures (HS) identified key factors affecting the degree of polarization (DoP) and the lifetime of interlayer excitons (IX). We achieved long-lived valley polarization by stacking 2D perovskites and transition metal dichalcogenides into type-II HS, observing circularly polarized photoluminescence in (BA)2PbI4/WSe.
In device fabrication, WSe2 served as a standard for studying exciton behavior. By interfacing it with various gates and applying external electric fields, we controlled excitations into specific valleys in the conduction band. We developed methods to enhance photon-waveguide interactions, achieving photodetector responsivities as high as 1000 A/W and photoresponse times below 1 ms by adding an hBN layer.
Our studies on exciton transport showed higher mobility in pristine WSe2 compared to MoSe2/hBN/WSe2 HS. We successfully fabricated excitonic devices from lateral MoS2/WS2 HS, confirming tunable photoluminescence emission energies indicative of IX. Dual-gated MoSe2/WSe2 bilayer devices demonstrated enhanced exciton brightness and lifetime.
We also grew various 2D materials via chemical vapor transport and flux growth, including insulators, semiconductors, antiferromagnets, ferroelectrics, and superconductors. External factors were applied to modify 2DS properties, using van der Waals HS for strain modulation. Twisted bilayers formed superlattices controlling electronic structures, akin to graphene or hBN. Localized strain was engineered via atomic force microscopy on MoS2.
To communicate progress, our researchers participated in conferences, workshops, and published findings in peer-reviewed journals, ensuring engagement with the scientific and industrial communities.
We paved the road for manufacturing new and interesting 2DS beyond the common family of transition or noble metal dichalcogenides. Our exfoliation techniques were advanced and directly linked to inkjet printing. Similarly, we produced a number of complex devices, allowing to couple various 2DS to external factors such as electric fields or very strong laser beams. Methods were readily available to study complex 2DS, such as twisted bilayer materials. We explored fundamental properties of different 2DS. Our ESRs had the opportunity to participate in various experiments, in which the complexity of influence of the external electric and magnetic fields on various HS was studied. It allowed to understand the interplay between the twist degree of freedom and moiré potential. The experimental results were rationalized by theory. HS were demonstrated as ideal platform for excitonic devices, where the transport of these quasi-particles can be controlled by external electric fields. The results were recognized in several high-impact publications. Our ESRs submitted their PhD theses. Their broad and extensive training prepared them to pursue a carrier in research or industry.