Dans le moyen-infrarouge, les barrettes de lasers à cascade quantique sont d’un grand intérêt pour la réalisation de sources large bande intégrables dans les systèmes de spectroscopie laser. Une excellente finesse spectrale, la présence d’un seul mode spatial et une gamme d’accordabilité large sont ainsi rassemblées sur une seule puce, compacte et intrinsèquement stable. Afin de bénéficier de l’ensemble des longueurs d’onde sur une sortie unique, les défis majeurs résident dans l’association de technologies pour rassembler les différentes sorties en une seule via l’utilisation de circuits photoniques intégrés (CPI). Ce CPI peut être séparé en trois briques élémentaires : une filière de guidage passif, un combineur de longueurs d’onde et un coupleur actif/passif. Pour la mise-en-forme du faisceau, nous reportons la fabrication et la caractérisation de guides d’onde en InP/InGaAs/InP gravés profondément, avec des performances proches de l’état de l’art. Nous fabriquons et caractérisons des multiplexeurs basés sur des réseaux de diffraction intégrés, sur filière InP et SiGe. Un multiplexeur de 60-vers-1 voies couvrant la gamme de 7-8,5 µm est réalisé. Une méthode innovante mettant en œuvre des multiplexeurs inter-digités et fonctionnant sur trois ordres de diffraction est démontrée. Finalement, nous réalisons des barrettes de laser à cascade quantique sur InP et sur silicium. Un coupleur adiabatique est dimensionné, fabriqué et caractérisé pour associer efficacement les guides actifs et passifs. Des intégrations de types hétérogène et hybride sont envisagées, avec la première démonstration d’une source accordable utilisant une barrette de lasers et un multiplexeur InP. / In the mid-infrared, arrays of distributed feedback quantum cascade lasers have been developed as a serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth, single mode operation and wide tunability are then gathered together on a single chip with high compactness and intrinsic stability. In order to benefit from this extended wavelength range in a single output beam, the key challenge resides in the combination of different technologies to merge the output of different sources via the use of mid-IR photonic integrated circuits (PIC). The PIC can be split into three main blocks: the passive waveguide platform, the beam combiner and the active/passive coupler. For beam handling and guiding, we report fabrication and characterization of deeply etched InP/InGaAs/InP waveguides with state of the art performances. We fabricate and characterize multiplexers based on echelle and arrayed waveguide gratings on InP and SiGe platforms. A 60-to-1 spectral multiplexer operating in the 7-to-8.5 µm range is demonstrated. An advanced multiplexing scheme using interleaved and cross-order operations is also exposed. Finally, we realize quantum cascade laser arrays on InP and silicon. We design, fabricate and characterize an adiabatic coupler to efficiently and monolithically integrate active and passive waveguides. Heterogenous and hybrid integration are also considered with the demonstration of a tunable source using laser array and InP-based multiplexer.

The design of a precision current controller for quantum cascade lasers (QCLs) enables QCLs to be used for calibrating instruments in space-borne applications. This current controller design will enable constant wave (CW) or pulsed mode operation of QCL devices as calibration sources in a space environment. Any differences in the temperature between components of the current controller can result in an erroneous current through the QCL. This design will use previously demonstrated techniques from Pacific Northwest National Laboratory (PNNL) to minimize the effects of temperature changes on the desired current levels. A mathematical model is used to calculate what performance levels can be expected, and if the board can operate with a desired precision level of 0.1% of the desired power output of the QCL. This mathematical model shows the capability to control to the desired 0.1% output power stability with a change in the boards temperature of ±10◦C.

京都大学 / 0048 / 新制・論文博士 / 博士(工学) / 乙第12860号 / 論工博第4107号 / 新制||工||1609(附属図書館) / 31540 / (主査)教授 北野 正雄, 教授 川上 養一, 准教授 酒井 道 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Transistor Quantique InAs à Electrons Chauds: Fabrication submicronique et étude à haute fréquenceL'objectif de cette thèse est le développement de la technologie d'un transistor à électrons chauds constitué d'une hétérostructure quantique InAs/AlSb et exploitant un transport électronique résonant ultrarapide, le QHET (Quantum Hot Electron Transistor). Ce travail a permis l'étude approfondie de ses propriétés et performances à haute fréquence. L'étude aborde tous les aspects, de la conception, la croissance épitaxiale, la technologie de fabrication à la caractérisation statique et dynamique. Ce travail de thèse s'est effectué principalement à l'Institut d'Electronique du Sud (IES), sous la direction de Roland Teissier, et pour partie à l'Institut d'Electronique de Microélectronique et Nanotechnologie (IEMN) sous la direction de Mohamed Zaknoune. Nous avons, dans premier temps, mis en œuvre à l'IES une technologie double mésa afin de fabriquer les transistors avec l'émetteur de 10x10µm². La technologie en grande dimension est aisément réalisable et surtout reproductible. Elle nous a permis de travailler sur un grand nombre de structures transistor fabriquées par epitaxie par jets moléculaires (EJM) sur substrats InAs, afin d'en étudier le transport électronique et d'optimiser leur dessin. Le premier résultat marquant a été d'augmenter le gain statique jusqu'à une valeur de 15 grâce à une modification de la structure de l'émetteur qui une injection plus efficace puis l'utilisation d'une base fine de 85Å, qui améliore le temps de transit. Dans un deuxième temps, nous avons travaillé au sein de l'IES sur l'évolution de la technologie vers des dimensions intermédiaires dont la dimension la plus petite est de 1 µm de largeur. Cette technologie nous a donné une amélioration de performance des QHET grâce à la réduction des résistances et des capacités parasites des composants. Nous avons aussi travaillé à l'IEMN pour développer une technologie submicronique qui permet d'atteindre une largeur d'émetteur de 0.3 µm grâce à l'utilisation de la lithographie électronique. Cette technologie de fabrication plus performante nous a permis de mieux comprendre le fonctionnement du QHET. Et d'atteindre une régime de fonctionnement à forte densité de courant jusqu'à près de 1MA/ cm². Enfin, nous avons développé la structure et la technologie qui vont nous permettre d'évaluer la réponse à haute fréquence des QHET. Un point important a été de à disposer de la structure active du transistor sur un substrat isolant qui permette de réduire les éléments parasites durant la mesure en fréquence. Nous avons développé deux solutions : le transfert de substrat et la croissance métamorphique directement sur un substrat GaAs isolant.Les composants fabriqués par transfert de susbtrat présentent des valeurs de fréquence de transition FT de 77GHz et de fréquence d'oscillation FMAX de 88GHz. Les échantillons métamorphiques ont démontré de meilleures performances avec un FT de 170GHz et un FMAX supérieur à 200GHz. Ces résultats constituent les meilleurs dynamiques de transistors à électrons chauds à température ambiante. Ces études ont également fait progresser la compréhension du transport à haute fréquence dans ces composants. Ils permettent de comprendre les limitations actuelles et de proposer des pistes d'amélioration. / This work aims to develop a new high speed transistor in a vertical transport configuration that exploits the favourable transport properties of III-V semiconductor heterostructures based on InAs. This transistor is similar to a heterojunction bipolar transistor (HBT), but has theoretical assets to overcome the fundamental high speed limits of electron transport in HBT. Our approach uses the concept of hot electron transistor in an original InAs/AlSb quantum heterostructure, that we called a quantum hot electron transistor (QHET) or quantum cascade transistor (QCT). This research was almost done in Southern Electronics Institute (IES) under supervision of Dr. Roland Teissier and other work was realized in Micro-Nanotechnology Electronics Institute (IEMN) under supervision of Dr. Mohamed Zaknoune. The QHET is a unipolar vertical transport device made of a InAs/AlSb quantum heterostructure. Its first advantage over npn HBTs is the low base sheet resistance of 250 Ω/□ , accessible with moderate n-type doping levels (typically 1018 cm-3), which is a key parameter for high speed operation. Secondly, electron transport in the short (typically 100nm) bulk InAs collector is mostly ballistic with calculated transit times much shorter than in InP-based devices. We already developed the design and technology of QHET and demonstrated its resonant transports at cryogenic temperature and its improved static operation in smaller device. From these results, we come to develop our QHET structures to achieve high current gain. Using quantum design of thin base, the current gain is about 15. We fabricated QHET with emitter width scaled down to 0.3µm, using a state of the art electron beam lithography process. The junctions are defined using selective chemical etching. The base contact is self-aligned on the emitter contact. We achieved base resistance lower than 50Ω, comparable to state of the art HBTs. The small dimension allowed reaching the high current density regime of up to 1 MA/cm² required for high frequency operation. The static current gain is about 10, but could be increased up to 14 using a new quantum design. The collector breakdown voltage is greater than 1.2 V.Towards high frequency measurement, the substrate must be non-conducting material but InAs substrate is not available. Two technologies were proposed: transferred substrate and metamorphic substrate. For transferred substrate technology, we obtained a response of cutoff frequency of 77 GHz for FT and 88 for FMAX. For metamorphic substrate technology, we performed the growth of the transistor structures on a semi-insulating GaAs substrate. We used a thin GaSb buffer layer for metamorphic growth of the active part of the transistor, with an adequate growth procedure that allows forming mainly 90° misfit dislocations at the interface between the GaAs and GaSb. This technique permits more convenient and reliable processing of the devices, as compared to use of the more standard AlSb thick buffer layer. The frequency response was determined from S-parameters measured with a network analyser up to a frequency of 70 GHz. The measured gains, after de-embedding of the connection parasitic for a device with 0.5x4µm² emitter for JC=350kA/cm² (Ic= 6.0mA, Ib= 0.7mA, Vce=1.3V). The frequency dependence is not conventional on this device, with a resonance in the current gain close to 10 GHz and a slope different from -20 dB/decade for Mason's unilateral gains. Nevertheless, we could extract the cut-off frequencies FT=172 GHz from H21 and FMAX =230 GHz using -20dB/decade extrapolation of maximum stable gain (MSG). The present results confirmed the validity of this novel device concept. In addition, this is the first demonstration of the ability of a hot electron transistor to operate at high frequency at room temperature.

Nous avons développé un récepteur hétérodyne terahertz (THz) compact et ultra-sensible à base de laser à cascade quantique (QCL) comme oscillateur local et de bolomètre à électron chaud (HEB) comme mélangeur. Le récepteur est basé sur un nouveau concept pour le couplage quasi-optique entre l'oscillateur local et le mélangeur ce qui a permis de ne pas utiliser de lame semi-réfléchissante pour la superposition du signal provenant du QCL et du signal à détecter. Le mélangeur utilisé est un HEB en nitrure de niobium avec une antenne planaire formée d’une double hélice log-spiral. Le HEB est monté sur la partie plane d’une lentille convexe en silicium. L’oscillateur local est un QCL que nous avons développé avec un système de contre-réaction répartie du troisième ordre avec une faible dissipation thermique, un faisceau peu divergent et un fonctionnement mono-mode à la fréquence cible de 2.7 THz. Le couplage entre l’oscillateur local et le mélangeur HEB a également été amélioré en couplant le QCL avec une fibre creuse en diélectrique ce qui a permis d’améliorer la directivité du faisceau laser à 55 dBi. Grâce aux précédents résultats, nous avons obtenu un récepteur THz hétérodyne compact qui présente une sensibilité proche de l’état de l’art à 2.7 THz. / We demonstrate an ultra-compact Terahertz (THz) heterodyne detec- tion system based on a quantum cas- cade laser (QCL) as local oscillator and a hot electron bolometer (HEB) for the mixing. It relies on a new opti- cal coupling scheme where the local oscillator signal is coupled through the air side of the planar HEB an- tenna, while the signal to be de- tected is coupled to the HEB through the lens. This technique allows us to suppress the beam splitter usu- ally employed for heterodyne mea- surements. The mixer is a Niobium Nitride HEB with a log-spiral planar antenna on silicon and mounted on the back of a plano-convex silicon lens. We have developed a low power consumption and low beam di- vergence 3rd-order distributed feed- back laser with single mode emis- sion at the target frequency of 2.7 THz to be used as local oscillator for the heterodyne receiver. The cou- pling between the QC laser and the the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity up to 55 dBi. Upon the high beam quality, sufficient output power in a single mode at the tar- geted frequency and low power dissi- pation of our local oscillator, we have build an ultra compact THz hetero- dyne receiver with sensitivity close to the state of the art at 2.7 THz.

<p>Infrared absorption spectra can provide analytically useful information on a large variety of compounds, ranging from small ions to large biological molecules. In fact, all analytes that possess a dipole moment that changes during vibration are infrared-active. The infrared (IR) spectrum can be subdivided into far-, mid- and near- regions. The focus of attention in this thesis is the mid-IR region, in which the fundamental vibrations of most organic compounds are located, thus providing scope for positive structural identification. However, while such near-ubiquitous signals can be very useful for monitoring simple molecules in simple systems, they can be increasingly disadvantageous as the number of analytes and/or the complexity of the sample matrix increases. Thus, hyphenation to a separation system prior to detection is desirable. Paper I appended to this thesis presents (for the first time) the on-line hyphenation between Fourier transform infrared spectroscopy, FTIR, and capillary zone electrophoresis, CZE. CZE is a highly efficient separation technique that separates ionic analytes with respect to their charge-to-size ratio. It is most commonly performed in aqueous buffers in fused silica capillaries. Since these capillaries absorb virtually all infrared light an IR-transparent flow cell had to be developed. In further studies (Paper II) the applicability of CZE is expanded to include neutral analytes by the addition of micelles to the buffer, and micellar electrokinetic chromatography, MEKC, was successfully hyphenated to FTIR for the first time. Paper III describes an application of the on-line CZE-FTIR technique in which non-UV-absorbing analytes in a complex matrix were separated, identified and quantified in one run.</p><p>Measuring aqueous solutions in the mid-IR region is not straightforward since water absorbs intensely in this region, sometimes completely, leaving no transmitted, detectable light. For this reason, quantum cascade lasers are interesting. These lasers represent a new type of mid-IR semiconducting lasers with high output power due to their ingenious design. The laser action lies within one conduction band (intersubband) and can be tailored to emit light in the entire mid-IR region using the same semiconducting material. To investigate their potential to increase the optical path length in aqueous solutions, these lasers were used with an aqueous flow system (Paper IV), and the experience gained in these experiments enabled hyphenation of such lasers to a CZE system (Paper V).</p>

Infrared absorption spectra can provide analytically useful information on a large variety of compounds, ranging from small ions to large biological molecules. In fact, all analytes that possess a dipole moment that changes during vibration are infrared-active. The infrared (IR) spectrum can be subdivided into far-, mid- and near- regions. The focus of attention in this thesis is the mid-IR region, in which the fundamental vibrations of most organic compounds are located, thus providing scope for positive structural identification. However, while such near-ubiquitous signals can be very useful for monitoring simple molecules in simple systems, they can be increasingly disadvantageous as the number of analytes and/or the complexity of the sample matrix increases. Thus, hyphenation to a separation system prior to detection is desirable. Paper I appended to this thesis presents (for the first time) the on-line hyphenation between Fourier transform infrared spectroscopy, FTIR, and capillary zone electrophoresis, CZE. CZE is a highly efficient separation technique that separates ionic analytes with respect to their charge-to-size ratio. It is most commonly performed in aqueous buffers in fused silica capillaries. Since these capillaries absorb virtually all infrared light an IR-transparent flow cell had to be developed. In further studies (Paper II) the applicability of CZE is expanded to include neutral analytes by the addition of micelles to the buffer, and micellar electrokinetic chromatography, MEKC, was successfully hyphenated to FTIR for the first time. Paper III describes an application of the on-line CZE-FTIR technique in which non-UV-absorbing analytes in a complex matrix were separated, identified and quantified in one run. Measuring aqueous solutions in the mid-IR region is not straightforward since water absorbs intensely in this region, sometimes completely, leaving no transmitted, detectable light. For this reason, quantum cascade lasers are interesting. These lasers represent a new type of mid-IR semiconducting lasers with high output power due to their ingenious design. The laser action lies within one conduction band (intersubband) and can be tailored to emit light in the entire mid-IR region using the same semiconducting material. To investigate their potential to increase the optical path length in aqueous solutions, these lasers were used with an aqueous flow system (Paper IV), and the experience gained in these experiments enabled hyphenation of such lasers to a CZE system (Paper V).

Nonlinearities in quantum cascade lasers (QCL¡¯s) have wide applications in wavelength tunability and ultra-short pulse generation. In this thesis, optical nonlinearities in InGaAs/AlInAs-based mid-infrared (MIR) QCL¡¯s with quadruple resonant levels are investigated. Design optimization for the second-harmonic generation (SHG) of the device is presented. Performance characteristics associated with the third-order nonlinearities are also analyzed. The design optimization for SHG efficiency is obtained utilizing techniques from supersymmetric quantum mechanics (SUSYQM) with both material-dependent effective mass and band nonparabolicity. Current flow and power output of the structure are analyzed by self-consistently solving rate equations for the carriers and photons. Nonunity pumping efficiency from one period of the QCL to the next is taken into account by including all relevant electron-electron (e-e) and longitudinal (LO) phonon scattering mechanisms between the injector/collector and active regions. Two-photon absorption processes are analyzed for the resonant cascading triple levels designed for enhancing SHG. Both sequential and simultaneous two-photon absorption processes are included in the rate-equation model. The current output characteristics for both the original and optimized structures are analyzed and compared. Stronger resonant tunneling in the optimized structure is manifested by enhanced negative differential resistance. Current-dependent linear optical output power is derived based on the steady-state photon populations in the active region. The second-harmonic (SH) power is derived from the Maxwell equations with the phase mismatch included. Due to stronger coupling between lasing levels, the optimized structure has both higher linear and nonlinear output powers. Phase mismatch effects are significant for both structures leading to a substantial reduction of the linear-to-nonlinear conversion efficiency. The optimized structure can be fabricated through digitally grading the submonolayer alloys by molecular beam epitaxy (MBE). In addition to the second-order nonlinearity, performance characteristics brought by the third-order nonlinearities are also discussed, which include third-harmonic generation (THG) and intensity dependent (Kerr) refractive index. Linear to third-harmonic (TH) conversion efficiency is evaluated based on the phase-mismatched condition. The enhanced self-mode-locking (SML) effect over a typical three-level laser is predicted, which will stimulate further investigations of pulse duration shortening by structures with multiple harmonic levels.

Ce travail de thèse porte sur le développement d'un spectromètre laser à cascade quantique (QCL) dans le moyen infrarouge pour des applications en spectroscopie et en métrologie des fréquences. Les principaux objectifs ont été tout d'abord de lever la forte contrainte que constitue le faible domaine spectral accessible au laser à CO2 mais également d'accroître la faible puissance laser disponible pour nos expériences de spectroscopie. Ce nouvel instrument intéresse directement les expériences développées au sein du groupe Métrologie Molécules et Tests Fondamentaux : la mise en évidence de non conservation de la parité dans les molécules chirales et la détermination de la constante de Boltzmann par spectroscopie laser. Au cours de ce travail de thèse, nous avons caractérisé le bruit d'intensité, le bruit de fréquence ainsi que la largeur de raie de la source QCL libre. Les résultats obtenus comparés à la littérature montrent une grande qualité spectrale de cette source laser. L'asservissement en phase de la source QCL sur un laser à CO2 ultra-stable a permis de démontrer le transfert des propriétés spectrales du laser à CO2 à la source QCL. Le spectromètre a ensuite été utilisé pour des expériences de spectroscopie en absorption linéaire des molécules NH3 et de la molécule de Méthyltrioxorhénium, molécules d'intérêt pour les projets de mesure de la constante de Boltzmann et de recherche d'un et de la non-conservation de la parité. Le potentiel de ce spectromètre a également été démontré dans des expériences de spectroscopie à très haute résolution, en absorption saturée. / This thesis is devoted to the developpement of a laser spectrometer quantum cascade to frequency metrology and high-resolution spectroscopy. The objective of this work is to developp a new tool for projects in our group : Measuring the Boltzman constant and test of non conservation of parity. Thus the new source was characterized by measuring its spectral density noise, amplitude noise and its emission line width. The phase locking of the QCL on the CO2 laser has achived spectroscopy NH and MTO, molecules of interest for the projects of the group mentioned aboive respectively.

Ce travail de thèse est constitué de l’étude sous champ magnétique de trois systèmes quantiquesd’un grand intérêt pour leurs propriétés électroniques et leurs applications potentielles àla photonique infrarouge et terahertz : deux structures à cascade quantique, l’une détectrice etl’autre émettrice, et le graphène épitaxié sur SiC face carbone. Le détecteur à cascade quantique enGaAs/AlGaAs, fonctionnant vers 15m, a été étudié dans l’obscurité et sous illumination, pour identifierles chemins électroniques intervenant dans le courant noir et en fonctionnement. Le développementd’un modèle de photocourant a permis d’identifier les paramètres-clé régissant le fonctionnementdu détecteur. L’étude, en fonction de la polarisation et de la température, d’un laser à cascadequantique térahertz en InGaAs/GaAsSb doté d’une structure nominalement symétrique montrel’impact de la rugosité d’interface sur les performances du laser. Nous montrons que le système d’hétérostructurede type II InGaAs/GaAsSb est prometteur pour le développement de lasers à cascadequantique térahertz fonctionnant à haute température. Enfin, l’étude magnéto-spectroscopique dugraphène épitaxié a montré, outre les transitions entre niveaux de Landau du graphène monocoucheidéal, une signature supplémentaire que nous avons attribuée au désordre, et plus particulièrementà l’existence de lacunes de carbone. Une modélisation des défauts sous la forme d’un potentiel deltareproduit remarquablement nos résultats expérimentaux, ce qui constitue la première mise en évidenceexpérimentale des effets des défauts localisés sur les propriétés électroniques du graphène.La structure des niveaux de Landau perturbée par le désordre est clairement établie. / This work reports on the study under magnetic field of three interesting quantumsystems, which present remarkable electronic properties and potential applications for infrared andterahertz photonics : two quantum cascade structures, one detector and one emitter, as well asepitaxial graphene layers grown on the carbon face of SiC. The GaAs/AlGaAs quantum cascade detector,designed to work around 15m, was studied both with and without illumination in order toidentify the electronic paths responsible for the dark current and the photocurrent. The developmentof a photocurrent model allowed us to identify the key points controlling the electronic transport.The investigation, as a function of the temperature and bias voltage, of a InGaAs/GaAsSb quantumcascade laser with a nominally symmetric structure shows the influence of interface roughness onthe laser performances. We demonstrate that the InGaAs/GaAsSb type II heterostructure system ispromising for developing terahertz quantum cascade lasers working at high temperature. Finally,magneto-spectroscopy experiments performed on epitaxial graphene display, besides the transitionsbetween Landau levels of monolayer graphene, additional signatures that we attribute to disorder,more specifically to carbon vacancies. Calculations using a delta-like potential for modeling thedefects are in good agreement with the experimental results. This study is the first experimental demonstrationof the influence of localized defects on the graphene electronic properties. The disorderperturbed Landau level structure is clearly established.