Periodic Reporting for period 3 - LEON (Compact THz lasers based on graphene quantum dots)
Berichtszeitraum: 2022-09-01 bis 2024-02-29
THz radiation is extremely attractive for fundamental investigations of matter and emerging applications including, for example, security screening, medical imaging and spectroscopy. However, the THz spectral range remains one of the least exploited spectral regions, mainly due to the lack of compact powerful sources. The development of the typical semiconductor-laser scheme emitting at THz frequencies has been seriously hampered by the absence of an appropriate material with a sufficiently small bandgap.
The LEON project addresses this technological and scientific blocking point with new semiconductor-laser schemes for THz emission centered on the integration of graphene-based materials.
Indeed, graphene is potentially an excellent candidate for a THz semiconductor-laser model owing to its ‘zero’ bandgap. However, non-radiative recombination mechanisms, especially Auger recombination, reduce the lifetime of the optical gain to few hundreds of femtoseconds. This phenomenon drastically limits the feasibility of a THz laser. In order to suppress these detrimental non-radiative processes, a new concept is needed. The project proposes to exploit the full discretization of electronic states in graphene quantum dots.
The outcome of this project will overcome this major lack of modern THz technology by developing compact THz amplifiers and powerful lasers operating at room temperature. Furthermore, this project will have an industrial impact by improving the portability and mobility of THz systems and reducing cost. It will strongly contribute to elevate THz technology towards the levels that exist in the electronic and infrared regions. It will also lay the basis through the establishment of advanced know-how of a new physical system for future successive activities and opening new horizons in THz optoelectronics.
This project has three major cornerstones: i) the demonstration of THz amplifiers based on graphene quantum dots, ii) the demonstration of THz lasers based on graphene quantum dots in a microcavity, iii) the exploitation of these THz amplifiers/lasers for security and communication applications.
The LEON project addresses this technological and scientific blocking point with new semiconductor-laser schemes for THz emission centered on the integration of graphene-based materials.
Indeed, graphene is potentially an excellent candidate for a THz semiconductor-laser model owing to its ‘zero’ bandgap. However, non-radiative recombination mechanisms, especially Auger recombination, reduce the lifetime of the optical gain to few hundreds of femtoseconds. This phenomenon drastically limits the feasibility of a THz laser. In order to suppress these detrimental non-radiative processes, a new concept is needed. The project proposes to exploit the full discretization of electronic states in graphene quantum dots.
The outcome of this project will overcome this major lack of modern THz technology by developing compact THz amplifiers and powerful lasers operating at room temperature. Furthermore, this project will have an industrial impact by improving the portability and mobility of THz systems and reducing cost. It will strongly contribute to elevate THz technology towards the levels that exist in the electronic and infrared regions. It will also lay the basis through the establishment of advanced know-how of a new physical system for future successive activities and opening new horizons in THz optoelectronics.
This project has three major cornerstones: i) the demonstration of THz amplifiers based on graphene quantum dots, ii) the demonstration of THz lasers based on graphene quantum dots in a microcavity, iii) the exploitation of these THz amplifiers/lasers for security and communication applications.
During the first reporting period, modeling, fabrication and characterization of graphene quantum dots (GQDs) have been performed. The main piece of equipment funded by the project, a laser system, has been installed in December 2020. Several achievements have been made regarding the WP1 and WP2 of the project.
-WP1: we have modelled the electronic states and the optical properties of GQDs using a tight-binding approach. Interesting features are predicted according to their shape, size, edges and doping. In particular, large absorption resonances relying on intraband transitions in the THz spectral range are predicted for doped graphene quantum dots of typical size 100 nm (task 1.1). This work will be submitted very soon. We have successfully fabricated a single GQD in a single electron transistor configuration and arrays of GQDs (task 1.2). Using transport and photocurrent measurements, we have demonstrated ultrasensitive photoresponse to THz radiation of a hBN-encapsulated GQD in the Coulomb blockade regime at low temperature (170 mK). This work has been published in NanoLetters (2020). We have also measured the THz absorption of an array of GQDs using THz time domain spectroscopy system (task 1.2).
-WP2: We have designed and fabricated original THz waveguides and THz microcavities optimized for their coupling to GQDs (task 2.1). This work has been published in ACS Photonics (2020). We have investigated the influence of pumping conditions on non-equilibrium carrier dynamics in graphene and related materials (task 2.2). This work has been published in Nature Communication (2020). We have started to implement a high-sensitive mid-infrared pump-THz probe experiment based on the new laser system to probe the non-equilibrium carrier dynamics in the GQDs.
-WP1: we have modelled the electronic states and the optical properties of GQDs using a tight-binding approach. Interesting features are predicted according to their shape, size, edges and doping. In particular, large absorption resonances relying on intraband transitions in the THz spectral range are predicted for doped graphene quantum dots of typical size 100 nm (task 1.1). This work will be submitted very soon. We have successfully fabricated a single GQD in a single electron transistor configuration and arrays of GQDs (task 1.2). Using transport and photocurrent measurements, we have demonstrated ultrasensitive photoresponse to THz radiation of a hBN-encapsulated GQD in the Coulomb blockade regime at low temperature (170 mK). This work has been published in NanoLetters (2020). We have also measured the THz absorption of an array of GQDs using THz time domain spectroscopy system (task 1.2).
-WP2: We have designed and fabricated original THz waveguides and THz microcavities optimized for their coupling to GQDs (task 2.1). This work has been published in ACS Photonics (2020). We have investigated the influence of pumping conditions on non-equilibrium carrier dynamics in graphene and related materials (task 2.2). This work has been published in Nature Communication (2020). We have started to implement a high-sensitive mid-infrared pump-THz probe experiment based on the new laser system to probe the non-equilibrium carrier dynamics in the GQDs.
The objectives of this project are far beyond the state-of-the-art. Indeed, despite their appeal for THz lasing, no THz amplifiers and lasers relying on graphene-based materials have been reported yet. The main raison is that the few practical attempts performed to increase the optical gain lifetime have not succeeded as described in the state of the art exploiting discretization of the Landau levels in graphene.
The project relies on three major ambitious but feasible cornerstones from medium to very high risk:
• The demonstration of THz amplifiers based on GQD (medium risk)
• The demonstration of THz lasers based on GQD in microcavity (high risk)
• The integration of these THz devices for homeland security to devise stand-off imaging at distances >10 m and for telecommunications to improve the point-to-point distance to >100 m (high risk)
Thus, each of the aforementioned cornerstones will be a world’s first and will constitute a breakthrough for the realization compact and powerful THz amplifiers and lasers.
Advances in these ambitious research lines will be highlighted by several milestones:
• Suppression of Auger recombination processes in GQD
• Key increase of the optical gain lifetimes at THz frequencies in GQD up to 10 ps, i.e. 2 orders of magnitude monger than in monolayer graphene
• Strong carrier-light interaction in GQD microcavities for THz laser action of a mW level.
The project relies on three major ambitious but feasible cornerstones from medium to very high risk:
• The demonstration of THz amplifiers based on GQD (medium risk)
• The demonstration of THz lasers based on GQD in microcavity (high risk)
• The integration of these THz devices for homeland security to devise stand-off imaging at distances >10 m and for telecommunications to improve the point-to-point distance to >100 m (high risk)
Thus, each of the aforementioned cornerstones will be a world’s first and will constitute a breakthrough for the realization compact and powerful THz amplifiers and lasers.
Advances in these ambitious research lines will be highlighted by several milestones:
• Suppression of Auger recombination processes in GQD
• Key increase of the optical gain lifetimes at THz frequencies in GQD up to 10 ps, i.e. 2 orders of magnitude monger than in monolayer graphene
• Strong carrier-light interaction in GQD microcavities for THz laser action of a mW level.