Nitrures d’éléments III sur silicium : une plateforme de photonique intégrée de l’ultraviolet jusqu’au proche infrarouge

III-nitride semiconductors (AlN, GaN, InN and their alloys) have become an integral part of our daily lives as they are used in white, blue, green, and ultraviolet light emitting diodes, as well as laser diodes and power and high frequency electronics. This material is highly versatile due to its tuneable large direct band gap from the ultraviolet to the visible. III-nitrides give access to a very wide range of electronic, optoelectronic, and photonic applications. In photonics, a promising field relies on the III-nitride on silicon platform for next generation photonic integrated circuits due to its large transparency window from the ultraviolet to the near-infrared and the possibility of monolithic integration of active emitters such as quantum wells and quantum dots. In this thesis, we study different photonic devices and their integration into active and passive photonic circuits at wavelengths going from the ultraviolet to the near-infrared. We demonstrate low threshold pulsed optically pumped lasing and the first active microlaser photonic circuits in the blue and ultraviolet spectral ranges. We also propose a scheme for electrical injection in microrings that is compatible with photonic circuits and investigate III-nitrides bonded on SiO₂ as a platform for passive photonic circuits in the near-infrared.Les semi-conducteurs nitrures d’éléments III (AlN, GaN, InN et leurs alliages) sont devenus très importants dans notre vie quotidienne, car ils sont utilisés dans les diodes électroluminescentes blanches, bleues, vertes, et ultraviolettes, ainsi que pour des diodes lasers et l’électronique de puissance et hyperfréquence. Les matériaux nitrures sont fortement polyvalents grâce à leur grande bande interdite directe et accordable de l’ultraviolet jusqu’au visible. Ils donnent accès à une très large gamme d’applications électroniques, optoélectroniques, et photoniques. En photonique, un domaine très prometteur s’appuie sur la plateforme des nitrures d’éléments III sur silicium pour la prochaine génération de circuits photoniques intégrés grâce à sa grande fenêtre de transparence de l’ultraviolet jusqu’au proche infrarouge et la possibilité d’intégration monolithique d’émetteurs actifs comme des puits et boîtes quantiques. Dans cette thèse, nous étudions différents dispositifs photoniques à base de nitrures et leur intégration dans des circuits photoniques actifs et passifs à des longueurs d’onde allant de l’ultraviolet jusqu’au proche infrarouge. Nous démontrons des seuils lasers bas en pompage optique pulsé et les premiers circuits photoniques actifs à microlaser dans les gammes spectrales bleue et ultraviolette. Nous proposons également une approche pour l’injection électrique dans des micro-anneaux qui est compatible avec des circuits photoniques et nous étudions des nitrures d’éléments III collés sur SiO₂ comme plateforme pour des circuits photoniques passifs dans le proche infrarouge

Metasurface of strongly coupled excitons and plasmonic arrays

Metasurfaces allow to manipulate light at the nanoscale with planar lenses and holograms as prominent applications. Integrating metasurfaces with transition metal dichalcogenide monolayers provides additional functionality to ultrathin optics, such as tunable optical properties and enhanced light-matter interaction. Here, we developed a novel fabrication method that allows to directly integrate such a monolayer with a plasmonic lattice without compromising optical quality or coupling strength, by embedding the gold nanodisk array into an encapsulating hBN layer. We demonstrate plasmon-exciton-polaritons in this metasurface with a large Rabi splitting and strongly modified polarization and emission characteristics, as compared to a bare monolayer, achieving narrow-angle, directional, linearly polarized emission

Lattice reconstruction in MoSe2_2-WSe2_2 heterobilayers synthesized by chemical vapor deposition

Vertical van der Waals heterostructures of semiconducting transition metal dichalcogenides realize moir\'e systems with rich correlated electron phases and moir\'e exciton phenomena. For material combinations with small lattice mismatch and twist angles as in MoSe$_2$-WSe$_2$, however, lattice reconstruction eliminates the canonical moir\'e pattern and instead gives rise to arrays of periodically reconstructed nanoscale domains and mesoscopically extended areas of one atomic registry. Here, we elucidate the role of atomic reconstruction in MoSe$_2$-WSe$_2$ heterostructures synthesized by chemical vapor deposition. With complementary imaging down to the atomic scale, simulations, and optical spectroscopy methods we identify the coexistence of moir\'e-type cores and extended moir\'e-free regions in heterostacks with parallel and antiparallel alignment. Our work highlights the potential of chemical vapor deposition for applications requiring laterally extended heterosystems of one atomic registry or exciton-confining heterostack arrays.Comment: 10 pages, 5 figure

Nitride-on-silicon platform for UV-visible photonics with integrated microlaser sources.

International audienceAbstract-Biochemical detection applications and on-chip optical interconnects are examples of the useful applications considered for integrated photonic platforms dedicated to the UV and visible spectral range. This achievement requires the realization of efficient and compact microlaser sources that can be coupled to optical waveguides and are compatible with photonic circuitry. We develop a cost-effective practical approach relying on the controlled growth of thin AlN buffer layers on silicon substrates, followed by the growth of multiple quantum wells (MQW) GaN/AlN (for UV operation), or InGaN/GaN MQWs (for violet and blue operation) with a high radiative efficiency up to T=300K. This unique Nitride-on-Silicon platform could be released into a membrane by the selective under-etching of the silicon substrate.We present a series of microdisk lasers operating at room temperature under pulsed optical excitation over a broad spectral range extending from 275nm to 470nm. All microdisks present a Q factor above 1000 and reach 4000 in the best resonators. We are able to investigate the gain threshold of the different active layers. The microlasers operate under pulsed optical excitation, and the lasing threshold is reduced by a factor 10 from deep-UV GaN/AlN microdisks to the violet InGaN/GaN ones. This work allows us to expect a variety of integrated photonics applications, including for example multi-color integrated laser sources: we demonstrate here the versatility of this nitride-on-silicon platform, and the first realization on this platform of efficient active layers for a tunable lasing action over a 200nm broad UV to visible spectral range. [1,2].Acknowledgements: The authors acknowledge support from the projects GANEX (ANR-11-LABX-0014) and QUANONIC (ANR-13-BS10-0010). GANEX belongs to the public funded 'Investissements d'Avenir' program managed by the French ANR agency. This work was also partly supported by the RENATECH network.REFERENCES1.Sellés et al., APL 109, 231101 (2016)2.Sci. Rep. 6, 21650 (2016

Monolithic integration of ultraviolet microdisk lasers into photonic circuits in a III-nitride-on-silicon platform

International audienceUltraviolet microdisk lasers are integrated monolithi-cally into photonic circuits using a III-nitride on silicon platform with gallium nitride (GaN) as the main waveguiding layer. The photonic circuits consist of a microdisk and a pulley waveguide terminated by out-coupling gratings. We measure quality factors up to 3500 under continuous-wave excitation. Lasing is observed from 374 nm to 399 nm under pulsed excitation, achieving low threshold energies of 0.14 mJ/cm 2 per pulse (threshold peak powers of 35 kW/cm 2). A large peak to background dynamic of around 200 is observed at the out-coupling grating for small gaps of 50 nm between the disk and waveguide. These devices operate at the limit of what can be achieved with GaN in terms of operation wavelength

Demonstration of critical coupling in an active III-nitride microdisk photonic circuit on silicon

International audienceOn-chip microlaser sources in the blue constitute an important building block for complex integrated photonic circuits on silicon. We have developed photonic circuits operating in the blue spectral range based on microdisks and bus waveguides in III-nitride on silicon. We report on the interplay between microdisk-waveguide coupling and its optical properties. We observe critical coupling and phase matching, i.e. the most efficient energy transfer scheme, for very short gap sizes and thin waveguides (g = 45 nm and w = 170 nm) in the spontaneous emission regime. Whispering gallery mode lasing is demonstrated for a wide range of parameters with a strong dependence of the threshold on the loaded quality factor. We show the dependence and high sensitivity of the output signal on the coupling. Lastly, we observe the impact of processing on the tuning of mode resonances due to the very short coupling distances. Such small footprint on-chip integrated microlasers providing maximum energy transfer into a photonic circuit have important potential applications for visible-light communication and lab-on-chip bio-sensors

Analysis of low-threshold optically pumped III-nitride microdisk lasers

International audienceLow-threshold lasing under pulsed optical pumping is demonstrated at room temperature for III-nitride microdisks with InGaN/GaN quantum wells on Si in the blue spectral range. Thresholds in the range of 18 kW/cm 2 have been achieved along with narrow linewidths of 0.07 nm and a large peak to background dynamic of 300. We compare this threshold range with the one that can be calculated using a rate equation model. We show that thresholds in the few kW/cm 2 range constitute the best that can be achieved with III-nitride quantum wells at room temperature. The sensitivity of lasing on the fabrication process is also discussed

Q factor limitation at short wavelength (around 300 nm) in III-nitride-on-silicon photonic crystal cavities

International audienceIII-nitride-on-silicon L3 and H2 photonic crystal cavities with resonances down to 315 nm and quality factors up to 1085 at 337 nm have been demonstrated. The reduction of quality factor (Q) with decreasing wavelength is investigated. Besides the QW absorption below 340 nm a noteworthy contribution is attributed to the residual absorption present in thin AlN layers grown on silicon, as measured by spectroscopic ellipsometry. This residual absorption ultimately limits the Q factor to around 250 at 300 nm when no active layer is present

Blue Microlasers Integrated on a Photonic Platform on Silicon

International audienceThe main interest of group-III-nitride nanophotonic circuits is the integration of active structures and laser sources. A photonic platform of group-III-nitride microdisk lasers integrated on silicon and emitting in the blue spectral range is demonstrated. The active microdisks are side-coupled to suspended bus waveguides, and the coupled emission is guided and outcoupled to free space using grating couplers. A small gap size of less than 100 nm between the disk and the waveguide is required in the blue spectral range for optimal evanescent coupling. To avoid reabsorption of the microdisk emission in the waveguide, the quantum wells are etched away from the waveguide. Under continuous-wave excitation, loaded quality factors greater than 2000 are observed for the whispering gallery modes for devices with small gaps and large waveguide bending angles. Under pulsed excitation conditions, lasing is evidenced for 3 μm diameter microdisks integrated in a full photonic circuit. We thus present a first demonstration of a III-nitride microlaser coupled to a nanophotonic circuit