k.p theory beyond standard 8-band theory parametrization strategies and its applicability in electronic and optoelectronic devices design

International audienc

Dispositifs à îlots de GeSi pour la microphotonique proche infrarouge sur silicium

Ce travail est consacré à l'étude de dispositifs optiques pour le proche infrarouge avec des îlots de GeSi/Si dont la croissance est compatible avec la filière silicium. Le premier chapitre concerne l'étude théorique des états de trous dans les hétérostructures SiGe/Si par la méthode k.p. Il contient une description d'un modèle à 14 bandes qui tient compte exactement de l'influence des deux premières bandes de conduction sur la bande de valence. Nous montrons le raffinement qu'apporte le modèle à 14 bandes par rapport au modèle à 6 bandes usuellement appliqué à ces systèmes. Nous comparons les deux modèles dans le cadre du calcul des états de la bande de valence et des dipôles de transition optique d'un puits quantique de Si0.5Ge0.5 contraint sur silicium. Les différences obtenues entre les deux modèles permettent d'estimer une marge d'erreur à prendre en compte lors de l'utilisation du modèle à 6 bandes pour les hétérostructures SiGe/Si. Le deuxième chapitre présente une expérience de mesure de photocourant sur des structures p-i-n utilisant des îlots GeSi/Si comme matériaux absorbant à des longueurs d'onde supérieures au seuil de transparence du silicium (1.1 [mu]m). Les structures p-i-n sont insérées dans des guides d'onde du type Si0.98Ge0.02/Si et SOI. Nous donnons les réponses spectrales des photodiodes pour les deux types de guide d'onde. Les meilleures réponses externes obtenues à 300 K et à champ appliqué nul sont de 55 mA/W et 0.25 mA/W aux longueurs d'onde de 1.3 [mu]m et 1.55 [mu]m respectivement. Ces mesures de photoréponse sont comparées avec celles de l'absorption interbande des îlots. Le troisième chapitre présente une expérience d'électromodulation à 300 K de l'absorption interbande et intrabande des couches d'îlots en y modulant électriquement le nombre de porteurs. Pour cela nous avons utilisé la structure p-i-n insérée dans un guide d'onde Si0.98Ge0.02/Si. L'étude de la profondeur de modulation de l'absorption intrabande, associée à une transition du type lié-continuum de la couche de mouillage a permis de déterminer un coefficient de recombinaison Auger de 1.6 x 10^-30 cm^6s^-1 pour les îlots. Le dernier chapitre est consacré à l'étude de l'émission des îlots insérés dans des micro-cavités à cristaux photoniques bidimensionnels sur SOI. Nous observons par microphotoluminescence une forte augmentation de la luminescence aux longueurs d'onde 1.3-1.55 [mu]m qui est associée à une surlinéarité de son évolution en fonction de la puissance du pompage optique. Cette forte augmentation est corrélée à une localisation spatiale des porteurs dans les microcavités. Nous présentons des nouvelles perspectives d'intégration des îlots pour la réalisation de microsources pour l'émission verticale et comme sources internes à des composants à cristaux photoniques bidimensionnels en silicium. Mots-clés: calcul k.p, structure électronique, nanostructures GeSi/Si, photodétection, électroabsorption, microphotoluminescence, cristaux photoniques, guides d'onde, microcavités.This work is devoted to the study of near infrared optical devices with GeSi/Si self-assembled islands whose growth is compatible with standard silicon fabrication. The first chapter relates to the theoretical study of the holes states in the SiGe/Si heterostructures with the k.p method. It contains a description of a model with 14 bands which include exactly the influence of the first two conduction bands on the valence band. We show the refinement which the 14 bands model gives compared to the 6 bands model usually applied to these systems. We compare the two models within the framework of the calculation of the valence band states and the dipoles of optical transition from a quantum well of Si0.5Ge0.5 constrained on silicon. The differences obtained between the two models make it possible to consider a margin of error to be taken into account when using the 6 bands model for the SiGe/Si heterostructures. The second chapter presents an experiment of photocurrent on structures using p-i-n diode with GeSi/Si islands like absorbing materials at wavelengths higher than the threshold of transparency of silicon (1.1 [mu]m). The p-i-n structures are inserted in Si0.98Ge0.02/Si or SOI waveguides. We give the spectral response of the photodiodes for the two types of waveguide. The best external response obtained at 300 K and without applied fiel are of 55 mA/W and 0.25 mA/W at the wavelengths of 1.3 [mu]m and 1.55 [mu]m respectively. These measurements of photoresponse are compared with those of the interbanded absorption of the islands. The third chapter presents an experiment of electromodulation at 300 K of the interband and intraband absorption of the islands layers by modulating the carriers density electrically there. For that we used the p-i-n structure inserted in the Si0.98Ge0.02/Si waveguide. The study of the modulation depth of the intraband absorption, associated to a transition from the ground states of the islands to the continuum states of the wetting layer made it possible to determine an Auger recombination coefficient of 1.6 x 10^-30 cm^6s^(-1) for the islands. The final chapter is devoted to the study of the emission of the islands inserted into two-dimensional photonic crystals microcavities on SOI. We observe by microphotoluminescence a strong increase in luminescence to the wavelengths 1.3-1.55 [mu]m which is associated to a sublinearity of its evolution according to the power of optical pumping. This strong increase is correlated with a space localization of the carriers in the microcavities. We present new prospects for integration of the islands for the realization of microsources for the vertical emission and like internal sources at components with two-dimensional photonic silicon crystals. Key words: k.p calculation, electronic structure, GeSi/Si nanostructures, photodetection, electroabsorption, microphotoluminescence, photonic crystals, waveguides, microcavities.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Diamond 2D-photonic crystals for highly sensitive label-free biosensors

International audienceWe demonstrate design and fabrication of 2D diamond photonic crystals (PhC) allowing record bio-sensing sensitivities higher than surface plasmon resonance (SPR) state of the art. Polycrystalline diamond is probed directly from the surface with angular reflectivity measurements. A 2D PhC was designed with a mode frequency hardly varying with the interrogation angle. Optical experiments were performed at different angles and wavelengths to validate the simulations of the band diagram. The measured reflectivity spectrum is in good agreement with the simulated one

k.p theory beyond standard 8-band theory parametrization strategies and its applicability in electronic and optoelectronic devices design

International audienc

1.55µm InP-based electrically-pumped VECSELs: comparison of buried and implanted tunnel junctions as current confinement schemes for the realization of large diameter devices

International audienceWe report on the design, fabrication, and characterization of InP-based 1.55 µm wavelength large diameter (50 µm) electrically-pumped vertical external cavity surface emitting lasers (EP-VECSELs). The hybrid device consists of a half vertical cavity surface emitting laser (1/2-VCSEL) structure assembled with a concave dielectric external mirror. The 1/2- VCSEL is monolithically grown on InP substrate and includes a semiconductor Bragg mirror and a tunnel junction for electrical injection. Buried (BTJ) and ion implanted (ITJ) tunnel junction electrical confinement schemes are compared in terms of their thermal and electrical characteristics. Lower thermal resistance values are measured for BJT, but reduced current crowding effects and uniform current injection are evidenced for ITJ. Using the ITJ technique, we demonstrate Room-Temperature (RT) continuous-wave (CW) single transverse mode laser operation from 50-µm diameter EP-VECSEL devices. We show that the experimental laser optical output versus injected current (L-I) curves are well-reproduced by a simple analytical thermal model, consistent with the thermal resistance measurements performed on the 1/2-VCSEL structure. Our results indicate that thermal heating is the main mechanism limiting the maximum CW output power of 50-µm diameter VECSELs, rather than current injection inhomogeneity

Fabrication and characterization of 1.55 μm single transverse mode large diameter electrically pumped VECSEL

International audienceWe report on the design, fabrication, and characterization of InP-based 1.55 μm wavelength large diameter (50 μm) electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs). The hybrid device consists of a half vertical cavity surface emitting laser (1/2-VCSEL) structure assembled with a concave dielectric external mirror. The 1/2-VCSEL is monolithically grown on InP substrate and includes a semiconductor Bragg mirror and a tunnel junction for electrical injection. Buried (BTJ) and ion implanted (ITJ) tunnel junction electrical confinement schemes are compared in terms of their thermal and electrical characteristics. Lower thermal resistance values are measured for BJT, but reduced current crowding effects and uniform current injection are evidenced for ITJ. Using the ITJ technique, we demonstrate Room-Temperature (RT) continuous-wave (CW) single transverse mode laser operation from 50-μm diameter EP-VECSEL devices. We show that the experimental laser optical output versus injected current (L–I) curves are well-reproduced by a simple analytical thermal model, consistent with the thermal resistance measurements performed on the 1/2-VCSEL structure. Our results indicate that thermal heating is the main mechanism limiting the maximum CW output power of 50-μm diameter VECSELs, rather than current injection inhomogeneity

Laser infrarouge à base de semi-conducteurs de la filière silicium

International audienceNous présentons les récents développements scientifiques et techniques liés aux sources lasers infrarouges en micro-cavités à base d’alliages germanium-étain (GeSn). Ces alliages sont des matériaux semi-conducteurs de la filière silicium compatibles avec les procédés de fabrication bas coût de l’industrie de la micro-électronique. Un des enjeux est d’obtenir un alignement direct de la structure de bande électronique avec ces éléments de la colonne IV

Imaging of Photonic Crystal Localized Modes through Third-Harmonic Generation

International audienceWe demonstrate high-spatial resolution imaging of localized cavity modes through third-harmonic frequency conversion. The experiments are performed with a III-nitrideon-silicon photonic platform. The resonant cavities are formed within suspended two-dimensional photonic crystals and are excited with a continuous-wave excitation around 1550 nm. The III-nitride materials (GaN and AlN) are transparent for both pump and harmonics. The third-harmonic nonlinear process allows one to indirectly observe the fundamental confined cavity mode with spatial profiles equivalent to those usually obtained by local probe microscopy techniques such as scanning near-field optical microscopy. An excellent agreement is obtained between the measured polarization-resolved third harmonic emission patterns and those calculated through the third-order nonlinear polarization. We show that the spatial profiles of the radiated patterns are strongly dependent on defocusing, thus highlighting the strong sensitivity of the imaging