No description available.

My research regarded the fabrication of InSb and InAsSb large diameter nanowires for infrared applications. / InSb and InAsSb pillars, which are large diameter nanowires (NWs), were investigated as an alternative infrared (IR) detector technology to HgCdTe (MCT) for tunable multispectral IR detection with optical properties manipulated by pillar diameter and pitch. Undoped InSb and InAsSb thin films were grown on undoped Si (100) substrates by molecular beam epitaxy (MBE) with a thin AlSb buffer layer. A top-down etching method was used to fabricate pillars of diameters ranging from 300 nm to 1500 nm for InSb, and 1700 nm to 4000 nm for InAsSb. Pillar arrays were analyzed optically by Fourier transform IR spectroscopy (FTIR). The InSb and InAsSb pillars produced narrow absorption peaks with wavelength ranging from 1.61 μm to 6.86 μm for InSb and 8.1 μm to 16.2 μm for InAsSb. A 100 nm increase in pillar diameter corresponded to a 0.495 μm increase in peak absorption wavelength. InSb thin films were also grown on n-type (As doped, ≤ 0.005 Ω cm) Si (100) substrates to create a p-i-n junction, with an initial 2 μm thick undoped InSb region grown directly on the substrate, and a 0.5 μm thick p-type (Be doped, 2x1019 cm-3) InSb top layer. These films were used to create two devices; an interdigitated contact photoconductor with varying finger geometry, and a photovoltaic device with square top contacts of varying area. I-V characterization demonstrated trends in current with varying finger geometry. Photocurrent measurements were obtained for both the photoconductor and photovoltaic devices under IR and solar illumination. The photocurrent values were orders of magnitude higher for the photoconductive device compared to the photovoltaic device, indicative of potential photoconductive gain. Photocurrent generation in the InSb p-i-n structure introduces the possibility of diameter-dependent photocurrent generation in etched pillar devices. / Thesis / Master of Applied Science (MASc) / Infrared light (IR) falls in the wavelength range of 0.75 μm to 1000 μm, with IR based technology having numerous applications in society. With uses in the sciences, research, medicine, and general everyday technology, common IR ranges for material analysis range from 1.4 to 3 μm in the short-wavelength IR (SWIR), 3-5 μm in the mid-wavelength IR (MWIR), and 8-15 μm in the long-wavelength IR (LWIR). These ranges include IR absorption due to molecular vibrations, and includes wavelengths corresponding to the bandgaps of relevant semiconductor materials for IR detectors. To aid in light absorption in semiconductor materials, nanometer scale cylindrical structures called nanowires or pillars can be used on the detector surface, enhancing light absorption, and allowing for absorption wavelength manipulation by adjusting nanowire diameter. This work focuses on developing IR detectors with wavelength absorption in the 1-16 μm range, dependent on nanowire geometry.

abstract: This work demonstrates novel nBn photodetectors including mid-wave infrared (MWIR) nBn photodetectors based on InAs/InAsSb type-II superlattices (T2SLs) with charge as the output signal, and visible nBn photodetectors based on CdTe with current output. Furthermore, visible/MWIR two-color photodetectors (2CPDs) are fabricated through monolithic integration of the CdTe nBn photodetector and an InSb photodiode. The MWIR nBn photodetectors have a potential well for holes present in the barrier layer. At low voltages of < −0.2 V, which ensure low dark current <10-5 A/cm2 at 77 K, photogenerated holes are collected in this well with a storage lifetime of 40 s. This charge collection process is an in-device signal integration process that reduces the random noise significantly. Since the stored holes can be readout laterally as in charge-coupled devices, it is therefore possible to make charge-output nBn with much lower noise than conventional current-output nBn photodetectors. The visible nBn photodetectors have a CdTe absorber layer and a ZnTe barrier layer with an aligned valence band edge. By using a novel ITO/undoped-CdTe top contact design, it has achieved a high specific detectivity of 3×1013 cm-Hz1/2/W at room temperature. Particularly, this CdTe nBn photodetector grown on InSb substrates enables the monolithic integration of CdTe and InSb photodetectors, and provides a platform to study in-depth device physics of nBn photodetectors at room temperature. Furthermore, the visible/MWIR 2CPD has been developed by the monolithic integration of the CdTe nBn and an InSb photodiode through an n-CdTe/p-InSb tunnel junction. At 77 K, the photoresponse of the 2CPD can be switched between a 1-5.5 μm MWIR band and a 350-780 nm visible band by illuminating the device with an external light source or not, and applying with proper voltages. Under optimum conditions, the 2CPD has achieved a MWIR peak responsivity of 0.75 A/W with a band rejection ratio (BRR) of 52 dB, and a visible peak responsivity of 0.3 A/W with a BRR of 18 dB. This 2CPD has enabled future compact image sensors with high fill-factor and responsivity switchable between visible and MWIR colors. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

Photodetectors are semiconductor devices that can convert optical signals into electrical signals. There is a wide range of photodetector applications such as fiber optics communication, infrared heat camera sensors, as well as in equipment used for medical and military purposes. Nanowires are thin needle-shaped structures made of semiconductor materials, e.g. gallium arsenide (GaAs), indium phosphide (InP) or silicon (Si). Their small size, well-controlled crystal structure and composition as well as the possibility to fabricate them monolithically on silicon make them ideally suited for sensitive photodetectors with low noise. In this project, Fourier Transform Infrared (FTIR) Spectroscopy is used to investigate the optical characteristics of InP nanowire-based PIN photodetectors. The corresponding electrical characteristics are also measured using very sensitive instrumentation. A total of 4 samples consisting of processed nanowires with 80 nm diameter but different density and length have been examined. The experiments were conducted from 78K (-196oC) to room temperature 300K (27oC). The spectrally resolved photocurrent and current-voltage (IV) curves (in darkness &amp; under illumination) for different temperatures have been studied and analyzed. The samples show excellent IV performance with very low leakage currents. The photocurrent scales with the number of nanowires, from which we conclude that most photocurrent is generated in the substrate. Spectrally resolved photocurrent data, recorded at different temperatures, display strong absorption in the near-infrared region with interesting peaks that reveal the underlying optical processes in the substrate and nanowires, respectively. The nature of the absorption peaks is discussed in detail. This study is an important step towards integration of optically efficient III-V nanoscale devices on cheap silicon substrates for applications e.g. on-chip optical communication and solar cells for energy harvesting.

In this study, we prepare the zinc oxide nanotip with aqueous solution on Al doped ZnO/glass substrate. In excess of 6 hours growth, the film-liked layer is obtained in the bottom of ZnO nanotip. In order to study the photoresponse of maximum ZnO nanotip length without film-like layer, we choose 6 hours as the growth time of ZnO nanotip, which the height is almost the same of about 4 £gm. For the fabrication of ZnO nanotip UV photodetector, In-Zn was use as anode and cathode electrodes in digitate type on the top of ZnO nanotip array. The photoresponse which use AZO buffer layer of 300 s is better than others due to the larger surface to volume ratio. We obtain that Ron/off is 10.9, rise time is 280 s, and decay time is 870 s. The thermal annealing at 300 ¢XC in N2, O2, and N2O for 1 hr can improve the photoresponse, because the Zn(OH)2 in the ZnO nanotip gets converted into ZnO. Among annealing ambiences, the annealed ZnO nanotip in N2O show higher performance due to high decomposition of O atoms, which fills in the oxygen vacancy. We obtained that Ron/off is 26.04, rise time is 50 s, and decay time is 70 s at 300 oC in N2O.

Ultra Wide Band (UWB) is a short-pulse electrical signal, which is widely used for short distant wireless communication due to its low path loss, good immunity to multipath propagation, and high data rate. The main target transmission area of UWB is within 10 meters. Using optical fiber as carrier can bust up the communication capacitance in long distance range because of high capacitance, low loss propagation, and TDM and WDM compatible properties of fiber. Thereby, the technique of UWB on fiber has become more and more important. In this work, a novel method using waveguide photodetector (WP) with short termination for interface of optical fiber and wireless is proposed and demonstrated. The structure is simple without employing any complicated frequency mixer, intermediate frequency, or complex systems. This work is divided into two parts: (1) generation of UWB electrical signals and (2) wavelength conversion of UWB through WP. In the former, a WP with short termination is used in the device. The photocurrent excited by short optical pulse is distributive generated through the waveguide, forming two opposite directions of electrical waves. By reflection on the short termination, the reversed phase of one electrical wave is added to another electrical wave through a delay line, forming a monocycle of UWB signal. By appropriate design on the length of waveguide, the band of 2-10GH is demonstrated, fitting the requirement of FCC (Federal Communications Commission). In the second part of this paper is the wavelength conversion of UWB. The active region of WG is multiple quantum wells (M.Q.W.), which is not only served as photo-absorption layer, but also can be used the electroabsorption material. By pumping M.Q.W.s with high optical power, the cross absorption properties can be applied for wavelength conversion. By pumping power of 12dBm, the wavelength-converted UWB signal is successfully demonstrated at range of 1545nm-1570nm. Using this method, the application of UWB on router of fiber optical network is expectable.

Graphene and layered two-dimensional (2D) materials have set a new paradigm in modern solid-state physics and technology. In particular their exceptional optical and electronic properties have shown great promise for novel applications in light detection. However, several challenges remain to fully exploit such properties in commercial devices. Such challenges include the limited linear dynamic range (LDR) of graphene-based photodetectors (PDs), the efficient extraction of photoexcited charges and ultimately the environmental stability of such atomically-thin materials. In order to overcome the aforementioned limits, novel approaches to tune the properties of graphene and semiconducting \ce{HfS2} are explored in this work, using chemical functionalisation and laser-irradiation. Intercalation of graphene with \ce{FeCl3} is shown to lead to a highly tunable material, with unprecedented stability in ambient conditions. This material is used to define photo-active junctions with an unprecedented LDR via laser-irradiation. Intercalation with \ce{FeCl3} is also used to demonstrate the first all-graphene position-sensitive photodetector (PSD) promising for novel sensing applications. Finally, laser-irradiation is employed, to perform controlled oxidation of ultra-thin \ce{HfS2}, which leads to induced strain in the material and a consequent spatially-varying bandgap. Such structure is used to demonstrate, for the first time, efficient extraction of photogenerated carriers trough the so-called ``charge-funnel'' effect, paving the way to the development of ultra-thin straintronic devices.

Le monde des détecteurs infrarouge a été révolutionné, depuis le milieu des années 2000, par l'apparition de nouvelles structures photodétectrices dont les performances surclassent celles des photodiodes. Ces photodétecteurs ont permis le développement d'une nouvelle génération de caméras plus compactes, plus fiables et moins gourmandes en énergie. Cette thèse avait pour objectif l'étude de ces nouvelles structures photodétectrices haute performance à base d'antimoniures pour la détection du moyen infrarouge entre 3-5µm.Les performances d'un photodétecteur dépendent directement de la qualité des matériaux utilisés pour la fabrication de celui-ci. Aussi, le matériau retenu pour faire office de couche d'absorption a donc dans un premier temps été finement caractérisé. Les mesures de durée de vie (DDV) des porteurs minoritaires dans le matériau se sont révélées être les plus pertinentes pour juger de la qualité des échantillons, et il est reporté une mesure de (DDV) à l'état de l'art pour une température de 80K. Le second volet de cette thèse portait sur le dimensionnement d'une structure photodétectrice à l'aide du logiciel de simulations numériques SILVACO. Une structure optimisée a été proposée puis a été fabriquée par épitaxie à jets moléculaires. A partir de celle-ci, des composants ont été réalisés en salle blanche par un procédé technologique standard. Le courant d'obscurité mesuré se situait une décade plus bas que le photocourant typique ce qui s'est avéré très encourageant pour le développement futur d'une filière basée sur ce type de structures. La dernière partie de ce manuscrit propose une piste pour faire varier la longueur d'onde de coupure de la nouvelle structure photodétectrive grâce à l'utilisation d'une couche absorbante à base de superréseaux antimoniures. / Since the middle of the 2000's, new infrared photodetectors have been proposed that demonstrate better performances than photodiodes. This type of new detectors allowed the development of the compactness, reliability and energy consumption of the next generation of infrared cameras. The aim of this thesis is to study these new high performance photodetectors based on antimony semiconductors dedicated to the 3-5µm mid-infrared domain.Photodetectors performance strongly depends on the quality of its absorption material that has been characterized by diffenrent techniques. Lifetime measurements were identified as the most relevant criterion the evaluation of material quality. A state-of-the-art lifetime value has been reported at a temperature of 80K. Then, an optimized design of the photodetector has been determined using the TCAD SILVACO software. The photodetector structure has been grown by molecular beam epitaxy and devices were made by a standard fabrication process in clean room. The measured dark current was a decade lower than the typical photocurrent : this confirmed the potential of this new structure to be used as a high performance mid-infrared photodetector. Finaly, we demonstrate that the cut-off wavelength of the detector can be tuned using antimony-based superlattices.

Doctor en Ingeniería Eléctrica / Los fotomezcladores Verticalmente Iluminados (VI) de Onda Viajera (TW) de Portadores Unipolares (UTC) son fuentes continuas de radiación de THz. Este dispositivo usa la conversión heterodino para generar señales de onda milimétrica. Este dispositivo genera además una corriente distribuida para incrementar su capacidad de manejar mayores cantidades de corriente y además eliminar la limitación de constante RC. Este trabajo se divide en simulaciones electromagnéticas de alta frecuencia y simulaciones de dispositivos semiconductores. Los estudios de dispositivos semiconductores se enfocan en el modelado numérico del fenómeno de transporte de portadres proveyendo una descripción cualitativa y cuantitativa del transporte de portadores en fotodiodos UTC. Como resultado del análisis de semiconductor, resultados de brecha de energía, espacio de carga, densidad electrónica, velocidad del electrón, todos ellos bajos diferentes valores de potencia de iluminación son presentados en esta sección. Una curva de responsividad versus potencia óptica se muestra también. Esta tesis desarrolla además simulaciones electromagnéticas de alta frecuencia para estudiar la propagación de la onda electromagnética a lo largo del dispositivo VI-TW-UTC. Los fotodiodos VI-TW-UTC ultra-rápidos requieren una capa base altamente dopada que hace de conexión conductora entre el fondo de la estructura mesa y los contactos metálicos de la capa base. Tal estructura se denomina mesa vertical p-i-n o de Uni-Portador. La capa base dopada tiene una fuerte influencia en las perdidas de THz. Por lo tanto, simulaciones electromagnéticas de alta frecuencia fueron ejecutadas en HFSS y CST Microwave Studio para estudiar las pérdidas de THz. El dispositivo VI-TW-UTC fue modelado como una línea de transmisión cuasi-coplanar (Q-CPW). Posteriormente, las pérdidas de THz fueron calculadas indirectamente a través de los parámetros de dispersión S21. Las simulaciones muestran un valle de baja pérdida cerca de la conductividad 5×〖10〗^4 Sm-1, en medio de un rango de conductividad de excesiva absorción de THz haciendo este valor la mejor elección para el rango de frecuencia de 0 a 2000 GHz. Adicionalmente, estructuras de Mushroom-CPW y Wall-CPW se desarrollaron y simularon en la presente tesis para comparar sus pérdidas de THz. Un modelo analítico describiendo la potencia entregada a la entrada de antena del fotomezclador se desarrolló. El modelo analítico tiene como variables de entrada la curva de responsividad versus potencia óptica y la absorción de THz. Como resultado, la conductividad de la capa base muy alta es necesaria para alcanzar una potencia de THz razonablemente alta. / Esta tesis de investigación fue financiada por la Comisión Nacional de Investigación Científica y Tecnológica CONICYT

Dans ce manuscrit, je présente mon travail dédié à la réalisation et à la caractérisation des émetteurs et détecteurs de lumière à base de nanofils de nitrures. Je détaille la fabrication des dispositifs utilisant des outils de nanofabrication à l’état de l’art, ainsi que l'étude de leurs propriétés électriques et optiques.Le premier chapitre résume brièvement les propriétés de base des semi-conducteurs nitrures et décrit les méthodes d’élaboration des nanofils. Dans le deuxième chapitre, je présente mon travail sur la fabrication et la caractérisation de LED à nanofil unique InGaN/GaN ayant un contact transparent en graphène pour l’injection des trous. L'électroluminescence des LEDs à nanofils uniques montre l'impact de la forme du contact sur les propriétés d'émission. En particulier, la position du contact détermine l'évolution spectrale avec le courant d'injection. À savoir, pour un contact étendu et un contact localisé sur le plan m, l’émission passe du vert au bleu en fonction du courant d’injection alors que pour un contact localisé sur la jonction entre le plan m et le plan semipolaire l'émission reste verte.Dans le troisième chapitre, je décris la fabrication et la caractérisation des LEDs à nanofils uniques fabriqués à partir d'une matrice de nanofils verticaux avec une morphologie des contacts identique à celle mise en œuvre pour les LEDs à base d’ensemble de nanofils. L'émission montre une évolution similaire à celle observée pour les LEDs à nanofils uniques avec un contact latéral. L’influence de la morphologie des contacts sur l'électroluminescence ouvre la possibilité de contrôler la couleur d'émission de la LED à l'étape de la fabrication. J'ai utilisé un traitement par plasma de fluor afin de réduire la conductivité de la coquille GaN dopé p et d’inhiber l'injection électrique dans la région riche en In du puits quantique. En outre, j'ai analysé l'effet de l’inhomogénéité d'injection. Afin d'améliorer l’homogénéité, j'ai développé un système de contact par le haut permettant d’injecter les électrons directement dans la sous-couche n-GaN. Les LEDs fabriquées selon cette procédure montrent un rendement amélioré avec 65% de nanofils actifs contre 19% pour une procédure standard.Le dernier chapitre est consacré à l'étude des photodétecteurs à nanofils de nitrure. Je décris d'abord la fabrication et la caractérisation d'un photodétecteur de rayonnement ultraviolet basé sur un ensemble de nanofils de GaN avec un contact transparent en graphène. Ensuite, des détecteurs à nanofils uniques InGaN / GaN ont été fabriqués fonctionnant dans la gamme spectrale du visible à ultraviolet. L'influence de la morphologie de contact est également étudiée en comparant deux types de contacts, à savoir un contact métallique localisé et un contact étendu en oxyde d'indium-étain (ITO). Dans la dernière partie, je présente une technique pour la fabrication de photodétecteurs flexibles basée sur des ensembles de nanofils verticaux et je discute leurs performances. / In this manuscript, I present my work dedicated to the realization and characterization of nitride nanowire light emitters and detectors. I detail the device fabrication using state-of-the-art nanofabrication tools as well as the investigation of their electrical and optical properties.First chapter briefly summarizes the nitride semiconductor basic properties and discusses the present status of nanowire elaboration. In the second chapter, I present my work on the fabrication and in-depth characterization of single nanowire InGaN/GaN LEDs with a transparent graphene contact for hole injection. Reference single wire LEDs with metal contacts are also investigated for comparison. The electroluminescence of single nanowire LEDs evidences the impact of the contact layout on the emission properties. In particular, the position of the contact determines the spectral evolution with injection current. Namely, for an extended contact and a contact localized on the m-plane, a transition from the green to blue emission is observed whereas for a localized contact on the m-plane/semipolar plane junction the emission remains green.In the third chapter, I describe the fabrication and characterize single wire LEDs made out of a vertical NW array with the contacting scheme identical to array LEDs. The emission shows a similar evolution as the lateral-contacted single nanowire LEDs. The dependence of the electroluminescence on the contact morphology opens the way to control the LED emission color at the device processing stage. I used fluorine plasma treatment to reduce the conductivity of the p-doped GaN shell for inhibiting the electrical injection in the In-rich region of the quantum well. Furthermore, I analyze the injection inhomogeneity effect. In order to avoid this effect, I developed a top down contacting scheme with electrons injected directly into n-GaN underlayer, which is called “front contacting” process. The “front contacting” LEDs show an enhanced yield of active nanowires from 19% to 65%.The last chapter is dedicated to the study of nitride nanowire photodetectors. I first describe the fabrication and characterization of a GaN ultraviolet (UV) photodetector based on a NW array with a transparent graphene contact. Moreover, single NW InGaN/GaN detectors were fabricated operating in the visible to ultraviolet spectral range. The influence of the contact morphology is also investigated by comparing two types of contacts, namely a partial metal contact and an indium tin oxide (ITO) conformal contact, respectively. In the last part, I present an up-to-date technique for fabricating flexible photodetectors based on vertical NW arrays and I discuss their performances.