Surface plasmons for enhanced metal-semiconductor-metal photodetectors

Surface Plasmon Polaritons (SPPs) are quantized charge density oscillations that occur when a photon couples to the free electron gas of the metal at the interface between a metal and a dielectric. The extraordinary properties of SPP allow for sub-diffraction limit waveguiding and localized field enhancement. The emerging field of surface plasmonics has applied SPP coupling to a number of new and interesting applications, such as: Surface Enhanced Raman Spectroscopy (SERS), super lenses, nano-scale optical circuits, optical filters and SPP enhanced photodetectors. In the past decade, there have been several experimental and theoretical research and development activities which reported on the extraordinary optical transmission through subwavelength metallic apertures as well as through periodic metal grating structures. The use of SPP for light absorption enhancement using sub-wavelength metal gratings promises an increased enhancement in light collection efficiency of photovoltaic devices. A subwavelength plasmonic nanostructure grating interacts strongly with the incident light and potentially traps it inside the subsurface region of semiconductor substrates. Among all photodetectors, the Metal-Semiconductor-Metal photodetector (MSM-PD) is the simplest structure. Moreover, due to the lateral geometry of the MSM-PDs, the capacitance of an MSM-PD is much lower than capacitances of p-i-n PDs and Avalanche PDs, making its response time in the range of a few tens of picoseconds for nano-scale spacing between the electrode fingers. These features of simple fabrication and high speed make MSM-PDs attractive and essential devices for high-speed optical interconnects, highsensitivity optical samplers and ultra-wide bandwidth optoelectronic integrated circuits (OEIC) receivers for fibre optic communication systems. However, while MSM-PDs offer faster response than their p-i-n PD and avalanche PD counterparts, their most significant drawbacks are the high reflectivity of the metal fingers and the very-low light transmission through the spacing between the fingers, leading to very low photodetector sensitivity. This thesis proposes, designs and demonstrates the concept of a novel plasmonicbased MSM-PD employing metal nano-gratings and sub-wavelength slits. Various metal nano-gratings are designed on top of the gold fingers of an MSM-PD based on gallium arsenide (GaAs) for an operating wavelength of 830 nm to create SPP-enhanced MSM-PDs. Both the geometry and light absorption near the designed wavelength are theoretically and experimentally investigated. Finite Difference Time Domain (FDTD) simulation is used to simulate and design plasmonic MSM-PDs devices for maximal field enhancement. The simulation results show more than 10 times enhancement for the plasmonic nano-grating MSM-PD compared with the device without the metal nano-gratings, for 100 nm slit difference, due to the improved optical signal propagation through the nano-gratings. A dual beam FIB/ SEM is employed for the fabrication of metal nano-gratings and the sub-wavelength slit of the MSM-PD. Experimentally, we demonstrate the principle of plasmonics-based MSM-PDs and attain a measured photodetector responsivity that is 4 times better than that of conventional single-slit MSM-PDs. We observe reduction in the responsivity as the bias voltage increases and the input light polarization varies. Our experimental results demonstrate the feasibility of developing high-responsivity, low bias-voltage high-speed MSM-PDs. A novel multi-finger plasmonics-based GaAs MSM-PD structure is optimized geometrically using the 2-D FDTD method and developed, leading to more than 7 times enhancement in photocurrent in comparison with the conventional MSM-PD of similar dimensions at a bias voltage as low as 0.3V. This enhancement is attributed to the coupling of SPPs with the incident light through the nano-structured metal fingers. Moreover, the plasmonic-based MSM-PD shows high sensitivity to the incident light polarization states. Combining the polarization sensitivity and the wavelength selective guiding nature of the nano-gratings, the plasmonic MSM-PD can be used to design high-sensitivity polarization diversity receivers, integrating polarization splitters and polarization CMOS imaging sensors. We also propose and demonstrate a plasmonic-based GaAs balanced metalsemiconductor- metal photodetector (B-MSM-PD) structure and we measure a common mode rejection ratio (CMRR) value less than 25 dB at 830nm wavelength. This efficient CMRR value makes our B-MSM-PD structure suitable for ultra-high-speed optical telecommunication systems. In addition, this work paves the way for the monolithic integration of B-MSM-PDs into large scale semiconductor circuits. This thesis demonstrates several new opportunities for resonant plasmonic nanostructures able to enhance the responsivity of the MSM-PD. The presented concepts and insights hold great promise for new applications in integrated optics, photovoltaics, solidstate lighting and imaging below the diffraction limit. In Chapter 10 we conclude this thesis by summarizing and discussing some possible applications and future research directions based on SPP field concentration

Multi-dimensional modeling and simulation of semiconductor nanophotonic devices

Self-consistent modeling and multi-dimensional simulation of semiconductor nanophotonic devices is an important tool in the development of future integrated light sources and quantum devices. Simulations can guide important technological decisions by revealing performance bottlenecks in new device concepts, contribute to their understanding and help to theoretically explore their optimization potential. The efficient implementation of multi-dimensional numerical simulations for computer-aided design tasks requires sophisticated numerical methods and modeling techniques. We review recent advances in device-scale modeling of quantum dot based single-photon sources and laser diodes by self-consistently coupling the optical Maxwell equations with semiclassical carrier transport models using semi-classical and fully quantum mechanical descriptions of the optically active region, respectively. For the simulation of realistic devices with complex, multi-dimensional geometries, we have developed a novel hp-adaptive finite element approach for the optical Maxwell equations, using mixed meshes adapted to the multi-scale properties of the photonic structures. For electrically driven devices, we introduced novel discretization and parameter-embedding techniques to solve the drift-diffusion system for strongly degenerate semiconductors at cryogenic temperature. Our methodical advances are demonstrated on various applications, including vertical-cavity surface-emitting lasers, grating couplers and single-photon sources

Nano-scale TG-FinFET: Simulation and Analysis

Transistor has been designed and fabricated in the same way since its invention more than four decades ago enabling exponential shrinking in the channel length. However, hitting fundamental limits imposed the need for introducing disruptive technology to take over. FinFET - 3-D transistor - has been emerged as the first successor to MOSFET to continue the technology scaling roadmap. In this thesis, scaling of nano-meter FinFET has been investigated on both the device and circuit levels. The studies, primarily, consider FinFET in its tri-gate (TG) structure. On the device level, first, the main TCAD models used in simulating electron transport are benchmarked against the most accurate results on the semi-classical level using Monte Carlo techniques. Different models and modifications are investigated in a trial to extend one of the conventional models to the nano-scale simulations. Second, a numerical study for scaling TG-FinFET according to the most recent International Technology Roadmap of Semiconductors is carried out by means of quantum corrected 3-D Monte Carlo simulations in the ballistic and quasi-ballistic regimes, to assess its ultimate performance and scaling behavior for the next generations. Ballisticity ratio (BR) is extracted and discussed over different channel lengths. The electron velocity along the channel is analyzed showing the physical significance of the off-equilibrium transport with scaling the channel length. On the circuit level, first, the impact of FinFET scaling on basic circuit blocks is investigated based on the PTM models. 256-bit (6T) SRAM is evaluated for channel lengths of 20nm down to 7nm showing the scaling trends of basic performance metrics. In addition, the impact of VT variations on the delay, power, and stability is reported considering die-to-die variations. Second, we move to another peer-technology which is 28nm FD-SOI as a comparative study, keeping the SRAM cell as the test block, more advanced study is carried out considering the cell‘s stability and the evolution from dynamic to static metrics

Miniaturized Transistors

What is the future of CMOS? Sustaining increased transistor densities along the path of Moore's Law has become increasingly challenging with limited power budgets, interconnect bandwidths, and fabrication capabilities. In the last decade alone, transistors have undergone significant design makeovers; from planar transistors of ten years ago, technological advancements have accelerated to today's FinFETs, which hardly resemble their bulky ancestors. FinFETs could potentially take us to the 5-nm node, but what comes after it? From gate-all-around devices to single electron transistors and two-dimensional semiconductors, a torrent of research is being carried out in order to design the next transistor generation, engineer the optimal materials, improve the fabrication technology, and properly model future devices. We invite insight from investigators and scientists in the field to showcase their work in this Special Issue with research papers, short communications, and review articles that focus on trends in micro- and nanotechnology from fundamental research to applications

Development of Hybrid Deterministic-Statistical Models for Irradiation Influenced Microstructural Evolution.

Ion irradiation holds promise as a cost-effective approach to developing structured nano--porous and nano--fiberous semiconductors. Irradiation of certain semiconductors leads to the development of these structures, with exception of the much desired silicon. Hybrid deterministic-statistical models were developed to better understand the dominating mechanisms during structuring. This dissertation focuses on the application of hybrid models to two different radiation damage behavior: (1) precipitate evolution in a binary two-phase system and (2) void nucleation induced nano--porous structuring. Phenomenological equations defining the deterministic behavior were formulated by considering the expected kinetic and phenomenological behavior. The statistical component of the models is based on the Potts Monte Carlo (PMC) method. It has been demonstrated that hybrid models efficiently simulate microstructural evolution, while retaining the correct kinetics and physics. The main achievement was the development of computational methods to simulate radiation induced microstructural evolution and highlight which processes and materials properties could be essential for nano--structuring. Radiation influenced precipitate evolution was modeled by coupling a set of non-linear partial differential equations to the PMC model. The simulations considered the effects of dose rate and interfacial energy. Precipitate growth becomes retarded with increased damage due to diffusion of the radiation defects countering capillarity driven precipitate growth. The effects of grain boundaries (GB) as sinks was studied by simulating precipitate growth in an irradiated bi-crystalline matrix. Qualitative comparison to experimental results suggest that precipitate coverage of the GB is due to kinetic considerations and increased interfacial energy effects. Void nucleation induced nano--porous/fiberous structuring was modeled by coupling rate theory equations, kinetic Monte Carlo swelling algorithm and the PMC model. Point defect (PD) diffusivities were parameterized to study their influence on nano--structuring. The model showed that PD kinetic considerations are able to describe the formation of nano--porous structures. As defects diffuse faster, void nucleation becomes limited due to the fast removal of the defects. It was shown that as the diffusivities' ratio diverges from unity, the microstructures become statistically similar and uniform. Consequently, the computational results suggest that nano--pore structuring require interstitials that are much faster than the slow diffusing vacancies, which accumulate and cluster into voids.PhDNuclear Engineering and Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111424/1/efrainhr_1.pd

The Boston University Photonics Center annual report 2014-2015

This repository item contains an annual report that summarizes activities of the Boston University Photonics Center in the 2014-2015 academic year. The report provides quantitative and descriptive information regarding photonics programs in education, interdisciplinary research, business innovation, and technology development. The Boston University Photonics Center (BUPC) is an interdisciplinary hub for education, research, scholarship, innovation, and technology development associated with practical uses of light.This has been a good year for the Photonics Center. In the following pages, you will see that the center’s faculty received prodigious honors and awards, generated more than 100 notable scholarly publications in the leading journals in our field, and attracted $18.6M in new research grants/contracts. Faculty and staff also expanded their efforts in education and training, and were awarded two new National Science Foundation– sponsored sites for Research Experiences for Undergraduates and for Teachers. As a community, we hosted a compelling series of distinguished invited speakers, and emphasized the theme of Advanced Materials by Design for the 21st Century at our annual symposium. We continued to support the National Photonics Initiative, and are a part of a New York–based consortium that won the competition for a new photonics- themed node in the National Network of Manufacturing Institutes. Highlights of our research achievements for the year include an ambitious new DoD-sponsored grant for Multi-Scale Multi-Disciplinary Modeling of Electronic Materials led by Professor Enrico Bellotti, continued support of our NIH-sponsored Center for Innovation in Point of Care Technologies for the Future of Cancer Care led by Professor Catherine Klapperich, a new award for Personalized Chemotherapy Through Rapid Monitoring with Wearable Optics led by Assistant Professor Darren Roblyer, and a new award from DARPA to conduct research on Calligraphy to Build Tunable Optical Metamaterials led by Professor Dave Bishop. We were also honored to receive an award from the Massachusetts Life Sciences Center to develop a biophotonics laboratory in our Business Innovation Center