Gated lateral silicon p-i-n junction photodiodes

Research in silicon photonics has recently seen a significant push to develop complete silicon-based optical components for optical communications. Silicon has shown its potential to overcome the bandwidth limitations of microprocessor interconnect, whereas, the silicon platform has already displayed the benefits of low manufacturing costs and CMOS compatibility. The work on “gated lateral silicon p-i-n junction photodiodes” has demonstrated the silicon potential, to detect optical radiations, compatibility to standard CMOS process flow and tuneable spectral response. The lateral structure of gated p-i-n junction photodiodes contributes to high responsivity to short wavelength radiations in these single and dual gate devices. The final objective of this work was to develop high responsivity, CMOS-compatible silicon photodiodes, where the spectral response can be modulated. The lateral p-i-n junction architecture led to high responsivity values, whereas, the MOS gate structure became the basis for tuneable spectral response. The MOS gate structure, made the devices appear as a transistor to the surrounding circuitry and the gate structure in dual gate devices can be used to modulate the spectral response of the device. Single gate devices showed higher responsivity values and comparatively high blue and ultraviolet (UV) response as compared to conventional photodiodes. Surface depletion region in these devices is utilized by placing a MOS gate structure and by patterning an integrated metal grating to detect polarized light. Single and dual gate devices with two variations were fabricated to characterise the device response. Novel lateral architecture of p-i-n junction photodiodes provides a surface depletion region. It is generally anticipated that photodetectors with surface depletion region might produce higher noise. In these devices the surface depletion region has a lateral continuation of gate dielectric which acts as a passivation layer and thus considerably reduced the noise. Physical device modelling studies were performed to verify the experimentally obtained results, which are provided in the relevant measurement chapters. In these devices the speed of operation is a compromise over the high responsivity, CMOS compatibility and tuneable spectral response

Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies

Photodetectors based on low-dimensional materials and hybrid systems

Premi extraordinari doctorat UPC curs 2015-2016, àmbit de CiènciesIn the last decade, two-dimensional (2D) materials have attracted attention both in the nascent field of flexible nanotechnology as well as in more conventional semiconductor technol-ogies. Within the rapidly expanding portfolio of 2D materials, the group of semiconducting transition metal dichalcogenides (TMDCs) has emerged as an intriguing candidate for various optoelectronic applications. The atomically thin profile, favorable bandgap and outstanding electronic properties of TMDCs are unique features that can be explored and applied in novel photodetecting platforms. This thesis presents highly sensitive two-dimensional phototransistors made of sub-nanometre thick TMDC channels. Firstly, an encapsulation route is developed to address the detrimental and, to date, uncontrollable impact of atmospheric adsorbates, which severely deteriorate detector performance. The passivation scheme improves the transport properties of TMDCs, leading to high photoconductive gain with gate dependent responsivity of 10 -10^4 A/W throughout the visible, and temporal response down to 10 ms, which is suitable for imaging applications. The atomic device thickness yields ultra-low dark current operation and record detectivity of 10^11 - 10^12 Jones for TMDC-based detectors is achieved. The use of monolayer TMDCs, however, has disadvantages like limited spectral absorption due to the bandgap and limited absorption efficiency. In order to increase the absorption and to extend the spectral coverage, TMDC channels are covered with colloidal quantum dots to make hybrid phototransistors. This compelling synergy combines strong and size-tunable light absorption within the QD film, efficient charge separation at the TMDC-QD interface and fast carrier transport through the 2D channel. This results in large gain of 10^6 electrons per absorbed photon and creates the basis for extremely sensitive light sensing. Colloidal quan-tum dots are an ideal sensitizer, because their solution-processing and facile implementation on arbitrary substrates allows for low-cost fabrication of hybrid TMDC-QD devices. Moreover, the custom tailored bandgap of quantum dots provides the photodetector with wide spectral tunability. For photodetection in the spectral window of NIR/SWIR, which is still dominated by expensive and complex epitaxy-based technologies, these hybrid detectors have the potential to favorably compete with commercially available systems. The interface of the TMDC-QD hybrid is of paramount importance for sensitive detector operation. A high density of trap states at the interface is shown to be responsible for inefficient gate-control over channel conductivity, which leads to high dark currents. To maintain the unique electrical field-effect modulation in TMDCs upon deposition of colloidal quantum dots, a passivation route of the interface with semiconducting metal-oxide films is developed. The buffer-layer material is selected such that charge transfer from QDs into the channel is favored. The retained field-effect modulation with a large on/off ratio allows operation of the phototransistor at significantly lower dark currents than non-passivated hybrids. A TMDC-QD phototransistor with an engineered interface that exhibits detectivity of 10^12 - 10^13 Jones and response times of 12 ms and less is reported. In summary, this work showcases prototype photodetectors made of encapsulated 2D TMDCs and TMDC-QD hybrids. Plain TMDC-detectors have potential for application as flexible and semi-transparent detector platforms with high sensitivity in the visible. The hybrid TMDC-QD device increases its spectral selectivity to the NIR/SWIR due to the variable absorption of the sensitizing quantum dots and reaches compelling performance thanks to im-proved light-matter interaction and optimized photocarrier generation.En la última década ha surgido un gran interés por los materiales bidimensionales (2D) tanto para las tecnologías emergentes de dispositivos flexibles, como para las tecnologías de semiconductores tradicionales. Dentro del creciente catálogo de materiales 2D, los semiconductores basados en dicalcogenuros de metales de transición (DCMTs) han surgido como candidatos para aplicaciones optoelectrónicas. Sus características únicas, tales como grosor atómico, banda prohibida y propiedades electrónicas pueden ser examinadas y aplicadas en nuevas plataformas de fotodetección. En esta tesis se presentan nuevos fototransistores bidimensionales ultrasensibles basados en canales de DCMTs subnanométricos. Se presenta una ruta de encapsulación para intentar solucionar el impacto negativo, e incontrolable hasta la fecha, producido por la adsorción de sustancias atmosféricas que degradan el funcionamiento de los detectores. Este proceso mejora el transporte en los DCMTs dando lugar a una gran ganancia fotoconductora, una respuesta, dependiente de la tensión aplicada en el gate, de 10-10^4 A/W en el visible y una respuesta temporal de tan solo 10 ms, todo ello adecuado para aplicaciones de imagen. El grosor atómico de los dispositivos da lugar a corrientes de oscuridad muy bajas y una detectividad de 10^11-10^12 Jones. Sin embargo, el uso de monocapas de DCMTs presenta ciertas desventajas como por ejem-plo una eficiencia en la absorción baja. Con el fin de mejorar la absorción, los canales de DCMTs se han recubierto con puntos cuánticos (QDs) para fabricar fototransistores híbridos. Esta sinergia combina la alta absorción de los QDs, una eficiente separación de cargas en la interfaz DCMT-QD y un rápido transporte de cargas a través del canal 2D. Todo esto resulta en una ganancia de 10^6 electrones por fotón absorbido y crea la base para sensores de luz extremadamente sensibles. Los puntos cuánticos coloidales son sensibizadores ideales ya que su procesado en disolución y su fácil incorporación sobre cualquier sustrato permiten la fabricación de sistemas híbridos DCMT-QD a bajo coste. Además, la posibilidad de modifi-car la banda prohibida, ofrecida por los QDs, proporciona al fotodetector una amplia respuesta espectral. Para fotodetección en la ventana espectral del infrarrojo cercano (NIR/SWIR), estos detectores híbridos presentan el potencial de competir favorablemente con los sistemas comerciales disponibles. La interfaz entre el híbrido DCMT-QD es de la mayor importancia para la sensibilidad del detector. Se ha demostrado que una alta densidad de trampas en la interfaz es la responsable del ineficiente control mediante el gate de la conductividad del canal, dando lugar a corrientes de oscuridad muy altas. Para mantener la excepcional modulación de efecto campo aún después de la deposición de los QDs, se ha desarrollado una ruta de pasivación de la interfaz con óxidos metálicos semiconductores. El material de esta capa amortiguadora (buffer) es seleccionado de tal manera que permita la transferencia de cargas desde los puntos cuánticos hasta el canal DCMT. Esto retiene la modulación de efecto campo con una relación encendido/apagado muy alta, permitiendo el funcionamiento del fototransistor con corrientes de oscuridad significativamente menores que las de los híbridos sin pasivar. Así, se presenta un fototransistor híbrido DCMT-QD, con una interfaz cuidadosamente diseñada, que exhibe una detectividad de 10^12-10^13 Jones. En resumen, este trabajo presenta unos prototipos de fotodetectores basados en DCMT 2D encapsulados y en híbridos DCMT-QD. Los fotodetectores basados en DCMT simples presentan potencial para su aplicación en detectores flexibles y semitransparentes, con gran sensibilidad en el visible. Los híbridos DCMT-QD amplían la selectividad espectral al infrarrojo cercano gracias a la absorción variable ofrecida por los puntos cuánticos y alcanzan un muy interesante rendimiento gracias a una mejor interacción luz-materia.Award-winningPostprint (published version

CMOS SINGLE-PHOTON AVALANCHE DIODES AND MICROMACHINED OPTICAL FILTERS FOR INTEGRATED FLUORESCENCE SENSING

This dissertation presents a body of work that addresses the two most pressing challenges in the field of integrated fluorescence sensing, namely, the design of integrated optical sensors and the fabrication of high-rejection micro-scale optical filters. Two novel enabling technologies were introduced. They are: the perimeter-gated single-photon avalanche diode (PGSPAD), for on-chip photon counting, and the benzotriazole (BTA)-doped thin-film polymer filter, for on-chip ultraviolet light rejection. Experimental results revealed that the PGSPAD front-end, fabricated in a 0.5 μm standard mixed-signal CMOS process, had the capability of counting photons in the MHz regime. In addition, it was found that a perimeter gate, a structural feature used to suppress edge breakdown in the diode, also maximized the signal-to-noise-ratio in the high-count rate regime whereas it maximized sensitivity at low count rates. On the other hand, BTA-doped filters were demonstrated utilizing three commonly used polymers as hosts. The filters were patternable, utilizing the same procedures traditionally used to pattern the undoped polymer hosts, a key advantage for integration into microsystems. Filter performance was analyzed using a set of metrics developed for optoelectronic characterization of integrated fluorescence sensors; high rejection levels (nearing -40 dB) of UV light were observed in films of only 5 μm in thickness. Ultimately, BTA-doped filters were integrated into a portable sensor, and their use was demonstrated in two types of bioassays

Miniaturized Silicon Photodetectors

Silicon (Si) technologies provide an excellent platform for the design of microsystems where photonic and microelectronic functionalities are monolithically integrated on the same substrate. In recent years, a variety of passive and active Si photonic devices have been developed, and among them, photodetectors have attracted particular interest from the scientific community. Si photodiodes are typically designed to operate at visible wavelengths, but, unfortunately, their employment in the infrared (IR) range is limited due to the neglectable Si absorption over 1100 nm, even though the use of germanium (Ge) grown on Si has historically allowed operations to be extended up to 1550 nm. In recent years, significant progress has been achieved both by improving the performance of Si-based photodetectors in the visible range and by extending their operation to infrared wavelengths. Near-infrared (NIR) SiGe photodetectors have been demonstrated to have a “zero change” CMOS process flow, while the investigation of new effects and structures has shown that an all-Si approach could be a viable option to construct devices comparable with Ge technology. In addition, the capability to integrate new emerging 2D and 3D materials with Si, together with the capability of manufacturing devices at the nanometric scale, has led to the development of new device families with unexpected performance. Accordingly, this Special Issue of Micromachines seeks to showcase research papers, short communications, and review articles that show the most recent advances in the field of silicon photodetectors and their respective applications

Enabling Technologies for Next Generation Ultraviolet Astrophysics, Planetary, and Heliophysics Missions

Our study sought to create a new paradigm in UV instrument design, detector technology, and optics that will form the technological foundation for a new generation of ultraviolet missions. This study brought together scientists and technologists representing the broad community of astrophysicists, planetary and heliophysics physicists, and technologists working in the UV. Next generation UV missions require major advances in UV instrument design, optics and detector technology. UV offers one of the few remaining areas of the electromagnetic spectrum where this is possible, by combining improvements in detector quantum efficiency (5-10x), optical coatings and higher-performance wide-field spectrometers (5-10x), and increasing multiplex advantage (100-1000x). At the same time, budgets for future missions are tightly constrained. Attention has begun to turn to small and moderate class missions to provide new observational capabilities on timescales that maintain scientific vitality. Developments in UV technology offer a comparatively unique opportunity to conceive of small (Explorer) and moderate (Probe, Discovery, New Millennium) class missions that offer breakthrough science. Our study began with the science, reviewing the breakthrough science questions that compel the development of new observational capabilities in the next 10-20 years. We invented a framework for highlighting the objectives of UV measurement capabilities: following the history of baryons from the intergalactic medium to stars and planets. In astrophysics, next generation space UV missions will detect and map faint emission and tomographically map absorption from intergalactic medium baryons that delineate the structure of the Universe, map the circum-galactic medium that is the reservoir of galaxy-building gas, map the warm-hot ISM of our Galaxy, explore star-formation within the Local group and beyond, trace gas in proto-planetary disks and extended atmospheres of exoplanets, and record the transient UV universe. Solar system planetary atmospheric physics and chemistry, aurorae, surface composition and magnetospheric environments and interactions will be revealed using UV spectroscopy. UV spectroscopy may even detect life on an exoplanet. Our study concluded that with UV technology developments within reach over the next 5- 10 years, we can conceive moderate-class missions that will answer many of the compelling science questions driving the field. We reviewed the science measurement requirements for these pioneering new areas and corresponding technology requirements. We reviewed and evaluated the emerging technologies, and developed a figure of merit based on potential science impact, state of readiness, required investment, and potential for highly leveraged progress in a 5-10 year horizon. From this we were able to develop a strategy for technology development. Some of this technology development will be subject to funding calls from federal agencies. A subset form a portfolio of highly promising technologies that are ideal for funding from a KISS Development Program. One of our study’s principal conclusions was that UV detector performance drives every aspect of the scientific capability of future missions, and that two highly flexible detector technologies were at the tipping point for major breakthroughs. These are Gen-2 borosilicate Atomic Layer Deposition (ALD) coated microchannel plate detectors with GaN photocathodes, and ALDantireflection (AR) coated, delta-doped photon-counting CCD detectors. Both offer the potential for QE>50% combined with large formats and pixel counts, low background, and sky-limited photon-counting performance over the 100-300 nm band. Ramped AR coatings for spectroscopic detectors could achieve QE’s as high as 80%! A second conclusion was that UV coatings are on the threshold of a major breakthrough. UV coatings permeate every aspect of telescope and instrument design. Efficient, robust, ultra-thin and highly uniform reflective coatings applied with Atomic Layer Deposition (ALD) offer the possibility of high-performance, wide-field, highly-multiplexed UV spectrometers and a broadband reach covering the scientifically critical 100-120 nm range (home of 50% of all atomic and molecular resonance lines). Our study concluded that UV coating advances made possible by ALD is the principle technology advance that will enable a joint UV-optical general astrophysics and exoEarth imaging flagship mission. A third conclusion was that the revolution in micro- and nano-fabrication technology offers a cornucopia of new possibilities for revolutionary UV technology developments in the near future. An immediate example is the application of new microlithography techniques to patterning UV diffraction gratings that are highly efficient and designed to enable wide-field, high-resolution spectroscopy. These techniques could support the development of new detectors that could discriminate optical and UV photons and potentially energy-resolving detection. Relatively modest investments in technology development over the next 5-10 years could provide advances in detectors, coatings, diffractive elements, and filters that would result in an effective increase in science capability of 100-1000! The study brought together a diverse community, led to many new ideas and collaborations, and brought cohesion and common purpose to UV practitioners. This will have a lasting and positive impact on the future of our field

Gated lateral silicon p-i-n junction photodiodes

Research in silicon photonics has recently seen a significant push to develop complete silicon-based optical components for optical communications. Silicon has shown its potential to overcome the bandwidth limitations of microprocessor interconnect, whereas, the silicon platform has already displayed the benefits of low manufacturing costs and CMOS compatibility. The work on “gated lateral silicon p-i-n junction photodiodes” has demonstrated the silicon potential, to detect optical radiations, compatibility to standard CMOS process flow and tuneable spectral response. The lateral structure of gated p-i-n junction photodiodes contributes to high responsivity to short wavelength radiations in these single and dual gate devices. The final objective of this work was to develop high responsivity, CMOS-compatible silicon photodiodes, where the spectral response can be modulated. The lateral p-i-n junction architecture led to high responsivity values, whereas, the MOS gate structure became the basis for tuneable spectral response. The MOS gate structure, made the devices appear as a transistor to the surrounding circuitry and the gate structure in dual gate devices can be used to modulate the spectral response of the device. Single gate devices showed higher responsivity values and comparatively high blue and ultraviolet (UV) response as compared to conventional photodiodes. Surface depletion region in these devices is utilized by placing a MOS gate structure and by patterning an integrated metal grating to detect polarized light. Single and dual gate devices with two variations were fabricated to characterise the device response. Novel lateral architecture of p-i-n junction photodiodes provides a surface depletion region. It is generally anticipated that photodetectors with surface depletion region might produce higher noise. In these devices the surface depletion region has a lateral continuation of gate dielectric which acts as a passivation layer and thus considerably reduced the noise. Physical device modelling studies were performed to verify the experimentally obtained results, which are provided in the relevant measurement chapters. In these devices the speed of operation is a compromise over the high responsivity, CMOS compatibility and tuneable spectral response.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Beyond solid-state lighting: Miniaturization, hybrid integration, and applications og GaN nano- and micro-LEDs

Gallium Nitride (GaN) light-emitting-diode (LED) technology has been the revolution in modern lighting. In the last decade, a huge global market of efficient, long-lasting and ubiquitous white light sources has developed around the inception of the Nobel-price-winning blue GaN LEDs. Today GaN optoelectronics is developing beyond lighting, leading to new and innovative devices, e.g. for micro-displays, being the core technology for future augmented reality and visualization, as well as point light sources for optical excitation in communications, imaging, and sensing. This explosion of applications is driven by two main directions: the ability to produce very small GaN LEDs (microLEDs and nanoLEDs) with high efficiency and across large areas, in combination with the possibility to merge optoelectronic-grade GaN microLEDs with silicon microelectronics in a fully hybrid approach. GaN LED technology today is even spreading into the realm of display technology, which has been occupied by organic LED (OLED) and liquid crystal display (LCD) for decades. In this review, the technological transition towards GaN micro- and nanodevices beyond lighting is discussed including an up-to-date overview on the state of the art

Printable 2d Material Optoelectronics and Photonics

Graphene and structurally similar 2-dimensional (2d) materials such as transition metal dichalcogenides (TMDs) and black phosphorus (BP) hold enormous potential for the next generation optoelectronics and photonics. Pairing 2d materials with printing is an emerging cost-effective large-scale device fabrication strategy. However, the current inks are far from ideal to support reproducible device fabrication. In addition, the instability of BP in ambient limits its applications. In this thesis, I present formulation of 2d material inks for inkjet printing for optoelectronic and photonic applications. To begin with, I produce mono- and few-layer 2d material flakes via ultrasonic assisted liquid phase exfoliation. This allows one-step formulation of a polymer stabilised graphene ink. For TMDs and BP, I design a binary solvent carrier for binder-free ink formulation. I show that these 2d material inks have optimal fluidic properties, drying dynamics and interaction with substrates for spatially uniform, highly controllable and print-to-print consistent large-scale printing on untreated substrates. In particular, the rapid ink drying at low temperatures leads to minimal oxidation of BP during ambient printing; the printed BP with passivation retains a stability over one month. On this basis, the printed graphene is employed as active sensing layer in CMOS integrated humidity sensors and as counter-electrodes in dye-sensitised solar cells, while the printed TMDs and BP are used to develop nonlinear photonic devices (i.e. saturable absorbers for femtosecond pulsed laser generation) and visible to near-infrared photodetectors (e.g. MoS$_2$ and BP/graphene/silicon hybrid photodetectors). Beyond inkjet printing, I present an ink formulation of commercial graphene nanoplatelets for roll-to-roll flexographic press ($\sim$100 m min$^{−1}$ printing speed). This allows hundreds of conductive electronic circuits to be printed in a minute for capacitive touchpads. Though I investigate only graphene, TMDs and BP, the ink formulation strategies can be effortlessly transferred to other 2d materials such as boron nitride, MXenes and mica. In addition to the demonstrated applications, printing of 2d materials can be potentially exploited to fabricate devices such as transistors, light emitters, energy storage conversion, and biosensors. This significantly expands the prospect of printable 2d material optoelectronics and photonics.China Scholarship Council, Cambridge Overseas Trust, and St John’s College