Abstract: Publication date: Available online 14 March 2019Source: Semiconductors and SemimetalsAuthor(s): Cheng Guo, Shanhui FanAbstractWe discuss the implementation of several isotropic image filters in the wavevector domain using a single photonic crystal slab device. Such a slab is designed so that the guided resonance near the Γ point exhibits an isotropic band structure. Depending on the light frequency and the choice of transmission or reflection mode, the device realizes isotropic high-pass, low-pass, band-reject, and band-pass filtering in wavevector space. These filter functions are important for various image processing tasks, including edge detection, smoothing, white noise suppression, and suppression or extraction of periodic noises. We numerically demonstrate these filter functionalities by simulations. This work expands the application of nanophotonics-based optical analog computing for image processing.
Abstract: Publication date: Available online 27 February 2019Source: Semiconductors and SemimetalsAuthor(s): Ken Xingze Wang, Yu Guo, Zongfu YuAbstractLight trapping is of paramount importance in efficiency improvement and cost reduction in practical solar cells. We develop a statistical temporal coupled mode theory of light trapping based on a rigorous electromagnetic approach. We show that the upper limit of the angle-integrated light trapping absorption enhancement is proportional to the density of states in any given structure. Our theory reveals that the conventional limit can be substantially surpassed when optical modes exhibit deep-subwavelength-scale field confinement. Numerical simulations are used to illustrate the theory and the design of both two- and three-dimensional photonic crystals for the purpose of light trapping. Our theory is applied to achieve absorption enhancement in ultrathin crystalline silicon solar cells with antireflection and light trapping nanocone gratings. Our work envisions the theoretical possibility and provides the design guidelines of nanophotonic light trapping.
Abstract: Publication date: Available online 25 February 2019Source: Semiconductors and SemimetalsAuthor(s): Alexander Drayton, Isabel Barth, Thomas F. KraussAbstractOptical techniques are used in some of the most highly performing biosensors demonstrated to date. A number of techniques already exist, such as surface plasmon resonance, resonant, and interferometric sensors, many of which have shown very high sensitivity, even without the use of labels. Nevertheless, many of these techniques require expensive instrumentation, while sensing is inherently a low-cost application. Therefore, it is worth exploring alternatives to the existing sensing modalities. Here, we review the use of guided mode resonances in a label-free biosensing context and show that the versatility of the GMR approach offers new functionalities, such as multiparameter sensing and imaging, while simultaneously offering competitive sensing performance. The ability to couple light easily is a particular asset and innovations such as the chirped GMR approach that combines sensing and wavelength-selective readout in the same structure add further interest. Adding phase sensitivity is another aspect that, altogether, make GMR sensors a particularly attractive proposition for low-cost sensors in a wide range of applications.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Dimitris Fitsios, Fabrice RaineriAbstractPhotonic crystal nanolasers on silicon are approaching a point of maturity and seem ready for the leap to the application level. In this chapter, we revisit the basic principles and concepts of photonic crystal nanolasers, starting from the core principles for designing up to the analysis of specific nanolaser solutions. The targets for the development of enhanced future photonic crystal nanolaser solutions are defined. Optically and electrically pumped photonic crystal nanolaser structures are presented and the transition between them is discussed. Finally, the chapter concludes with the presentation of alternative uses of the analyzed technologies for applications such as optical memories.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Shigehisa Arai, Tomohiro AmemiyaAbstractIn this chapter, theoretical and experimental characteristics of lateral current injection (LCI)-type membrane distributed feedback (DFB) and distributed reflector (DR) lasers intended for ultra-low power consumption optical communication systems such as on-chip optical interconnections are presented. First, fundamentals of the membrane laser such as an enhancement of the optical confinement factor of the active region and its effect on threshold current and modulation speed are explained. Then the energy cost analysis of the membrane DR laser is discussed from aspects of an output power and modulation speed. Fabrication and static and dynamic lasing characteristics of membrane DFB and DR lasers bonded on a Si substrate are also explained. A p-i-n membrane photodiode and its integration with the membrane DFB laser are explained.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Brian Corbett, Ruggero Loi, James O’Callaghan, Gunther RoelkensAbstractSilicon-based photonics allows thousands of optical components to be integrated. It provides a path to the development of scalable, low-cost photonic integrated circuits akin to electronics enabling many applications in communications, medical, and sensing. Waveguides, multiplexing, and routing are straightforwardly implemented. While integrated detection and modulation can be implemented for certain wavelength ranges, functional performance across the full optical spectrum requires separately optimized components. In addition, to enable integrated lasers, the key component of a III–V semiconductor gain block is required. Microtransfer printing is emerging as an effective, accurate, and massively parallel technique to address these issues through the heterogeneous integration of optimized photonic materials and devices. We describe some recent developments in this emerging technology as applied to silicon-based photonics.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Johann Peter Reithmaier, Mohamed BenyoucefAbstractA new class of Si-based hybrid materials is envisioned and first important steps in their realization were performed. Direct growth of InAs/GaAs core–shell quantum dots with high optical quality could be obtained without any relaxation buffer layer. By applying a multistep epitaxial process, InAs clusters were successfully embedded in a defect-free planar Si matrix. Detailed transmission electron microcopy studies were performed showing a consistent picture in the formation process of relaxed InAs clusters fully embedded in silicon matrix.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Eric Tournié, Jean-Baptiste Rodriguez, Laurent Cerutti, Roland Teissier, Alexei N. BaranovAbstractWe review the recent achievements in the epitaxial integration of III-Sb-based semiconductor lasers on Si substrates. Much work has been done on substrate preparation and III-Sb on Si nucleation, which allowed demonstrating GaInAsSb/AlGaAsSb quantum-well laser diodes operating in continuous wave above room temperature in the 1.5–2.3 μm range and InAs/AlSb quantum cascade lasers emitting near 11 μm operating up to 400 K. Although work remains to be done, in particular toward crystal defect density reduction, the wide wavelength range at reach with the III-Sb technology opens the way to the development of a large portfolio of mid-IR sensing systems.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Olivia D. Hentz, Jayce J. Cheng, Paul H. Rekemeyer, Nina Andrejevic, Silvija GradečakAbstractIn contrast to the gradual development of mature wafer-scale silicon photovoltaic (PV) technologies, more recent development of nanostructured PV devices has experienced an explosive growth. These materials are solution-processable and as such can be deposited on flexible substrates, in a form of semitransparent devices, and potentially at low cost. In this chapter, we review our present understanding of the basic mechanisms that govern operation of nanowire-based bulk heterojunction PV devices by focusing on current limitations and future opportunities. In particular, colloidal quantum dots (QDs) have been studied as promising candidates for single-junction and tandem solar cell applications due to their direct and tunable band gap in the visible and near-IR spectral regions. However, a mismatch between the optical absorption length and the carrier collection length prevents these devices from achieving optimal photocurrent generation. To enhance charge collection, it is possible to combine (1) hydrothermally grown ZnO nanowire arrays to form an ordered bulk heterojunction and (2) a band alignment engineered PbS QD film that utilizes inorganic and organic ligands to generate cascaded energy-level offsets. Furthermore, the hydrothermal method enables the growth of high-quality ZnO nanowires on graphene electrodes resulting in flexible semitransparent devices.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Jos J.G.M. van der Tol, Yuqing Jiao, Kevin A. WilliamsIMOS (InP membrane on silicon) is a platform-based approach to create indium phosphide (InP) nanophotonic integrated circuits. It uses monolithic integration of all photonic functions in the InP layers to leverage the most efficient optoelectronic processes and to remove optical interfaces between separately grown wafers. Using an optoelectronic material for the photonic components provides a powerful route to nanoscale miniaturization and circuit-level performance enhancements.In this chapter, we review the progress in the passive and active InP building blocks and highlight routes to miniaturization and performance scaling. We address the interfaces between building blocks, which are critical to a powerful platform approach. The platform approach enables customization by designers to create new components and circuits. The process design kit methodology is applied to provide a route to circuit design abstraction.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Francesco Rossella, Giovanni Pennelli, Stefano RoddaroAbstractThe advent of nanotechnology and nanomaterials is opening new perspectives for the achievement of efficient solid-state heat converters. After decades of slow progress, in recent years innovative ideas have been put forward to improve the thermodynamic conversion efficiency and, as a consequence, new thermoelectric nanomaterials have been developed. A key and challenging ingredient for the progress of this research ambit is today the refinement of precise methods for the measurement of the thermoelectric parameters of nanostructures.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Gerard Gadea, Alex Morata, Albert TaranconAbstractSemiconductor nanowires present outstanding properties for implementation of the thermoelectric effect, i.e., the direct conversion of thermal to electrical energy, which can be exploited within thermoelectric generators (TEGs) in order to power electronic devices. In nanowires, thermoelectric transport properties—Seebeck coefficient, electrical and thermal conductivity—are modified with respect to bulk leading to a higher figure of merit ZT, indicative of TEG performance. Determination of these properties in low-dimensional systems is a difficult but necessary task in order to be able to improve and optimize the nanowires toward their intended application. Moreover, in order to be able to exploit nanowire properties, one must come up with fabrication routes that allow massive growth and integration in devices. Besides, one must optimize—apart from nanowire thermoelectric properties—design parameters such as diameter, length, areal density, and electrical and thermal external elements such as heat sinks or connected devices. This chapter presents a comprehensive description of all the relevant topics for the application of nanowires in thermoelectric generation. The first section briefly introduces thermoelectricity in semiconductors and explains the working principle and applications of TEGs and micro-TEGs (μTEGs). Afterward, a survey of the size effects modifying nanowire transport properties as well as design considerations affecting TEGs with small thermoelectric elements is presented. The available methods for the fabrication and integration of nanowires in devices together with the currently employed measurement techniques for the determination of nanowire thermoelectric properties are described in subsequent sections. Finally, an updated review of nanowire-based μTEGs and final conclusions and future outlook of the topic are given.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Valerio Piazza, Lorenzo Mancini, Hung-Ling Chen, Stéphane Collin, Maria TchernychevaAbstractSemiconductor nanowires are key materials for next-generation solar cells and light-emitting diodes (LEDs), which can improve the performance and bring new functionalities. However, the performance of nanowire devices today is still below theoretical predictions. Standard macroscopic characterizations averaged over millions of nanowires do not provide all the information necessary to optimize the device efficiency. Nanoscale analyses of individual nanowire properties are required in order to evaluate the material quality, to assess the wire-to-wire homogeneity and to detect eventual electrical or optical failures. In this chapter, nanoscale characterizations of nanowire LEDs and solar cells are reviewed. Electron beam-induced current microscopy, photo- and cathodoluminescence, and atomic probe tomography are applied to single nanowires and to macroscopic nanowire devices to address the compositional homogeneity, to analyze defects, to estimate the doping, to measure the minority carrier diffusion lengths and to assess the nonradiative recombination.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Samik Mukherjee, Simone Assali, Oussama MoutanabbirAbstractThis chapter presents the recent progress in growth and characterization of group IV nanowires and discusses their relevance for energy conversion applications. In a broader sense, the chapter elaborates on two main approaches to enhance the capabilities of silicon-compatible nanowires and expand their applications. The first approach focuses on phonon-engineering processes in nanowire-based structures and their impact on nanoscale heat transport and thermoelectric applications. A review of the current theoretical and experimental understanding of the interplay between nanowire properties and thermal conductivity is provided and recent progress in characterization of nanowire thermoelectric figure of merit is outlined. Moreover, special emphasis is made on nanowires with tailor-made isotopic composition as a rich playground to elucidate subtle but important phenomena governing heat transport in nanowires. The second approach elaborated in this chapter consists of bandgap engineering in nonequilibrium tin-containing group IV nanowires and quantum-sized structures based on silicon–germanium–tin (SiGeSn) nanowires. This emerging family of semiconductors provides two degrees of freedom to tune the band structure, namely, alloying and strain. The ability to independently manipulate strain and lattice parameter in this emerging class of group IV semiconductors is central to engineer low-dimensional systems and heterostructures in a similar fashion to the more mature III–V semiconductors. The chapter outlines the state of the art in the development of these semiconductors and provides a comprehensive overview of the progress in the growth and characterization of GeSn nanowires and nanowire heterostructures. A critical discussion is included to evaluate their potential use to implement high-performance and/or cost-effective optoelectronic devices with emphasis on light absorption engineering and its implication for nanowire-based photovoltaics.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Amit Solanki, Handon UmAbstractThis chapter provides an overview of fabrication of silicon nanowires by top-down etching methods. The focus will be on wet and dry etching methods to achieve vertically aligned silicon nanowires. We will start by building an understanding of the dry etching process. Then we will delve deeper into the mechanisms, benefits, and drawbacks of these dry etching processes. This is followed by wet etching methods, primarily metal-assisted chemical etching methods. Finally, we will provide a guideline to fabricate vertically aligned Si nanowire arrays with both dry and wet chemical processes.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Tim Ludwig, Christoph Bohr, Albert Queraltó, Robert Frohnhoven, Thomas Fischer, Sanjay MathurAbstractElectrospinning is a promising technique for producing ultrafine fibers of a large variety of one-dimensional materials that can be assembled into nonwoven architectures useful for various smart technologies and lightweight applications such as wearable and flexible electronics, lightweight batteries, and high-surface area substrates for catalysis and sensing. Self-integration of electrospun fibers into webs and yarns not only enhances their functionality but also opens new innovative directions ranging from energy and environment applications to regenerative medicine. This chapter presents a comprehensive account on the processing of single-phase and composite nanofibers and their manifold applications in batteries, supercapacitors, transparent conducting materials, photovoltaics, as well as solar fuels. Using multinozzle approaches in electrospinning, heterojunctions and sophisticated 3D architectures at the nanoscale can be achieved in a single process step by engineering the spinnerets and fiber collectors. Given its modular nature and variability of precursor chemistry, electrospinning enables scaled-up production of micro- and nanofibers at reasonable cost and represents a promising fabrication method for integrating functional nanomaterials into devices. Nanofibrous meshes of carbon, metal, metal oxide, and their mixtures have been obtained in different geometries such as core–shell, Janus-type fibers, and yarns to demonstrate the possibility of net shaping at the nanoscale and possible conversion of interconnected 1D networks into 3D structures. The insufficient strength of nanofiber meshes can be reinforced through infiltration of a secondary phase that also decreases the intrinsic porosity of electrospun mats thereby offering new experimental space to create multimaterial junctions and bulk heterostructures. The chapter also alludes to the future trends and existing challenges of shape control and retention of flexible and fibrous structure after heat treatment that is often mandatory to obtain crystalline materials.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 99Author(s): Michael L. Davenport, Minh A. Tran, Tin Komljenovic, John E. BowersAbstractIntegration of III–V materials with silicon photonics using bonding allows the addition of lasers and optical amplifiers to this platform, which are critical elements in most photonic integrated circuit applications. The bonding approach allows integration of a wide range of materials with silicon and is compatible with high-volume wafer-scale production in sophisticated silicon fabrication facilities. Alternatively, the addition of the superior silicon waveguide to III–V laser devices enables better performance in narrow-linewidth single-wavelength and mode-locked lasers. This chapter will provide an introduction to the technology, the basic elements of the fabrication process for a heterogeneous laser, and then follow with technological demonstrations of these devices.
Abstract: Publication date: 2018Source: Semiconductors and Semimetals, Volume 98Author(s): Yonatan Calahorra, Canlin Ou, Chess Boughey, Sohini Kar-NarayanAbstractPiezoelectric semiconducting nanowires have generated much interest due to the interplay of their mechanical, electrical, and optical properties, which paves the way for potential applications in mechanical energy harvesting as well as sensing. The nature of piezoelectricity in these nanowires is governed by the crystalline phases present, which in turn can be controlled during the nanowire growth process. This chapter provides insight into the manifestation of piezoelectricity in semiconducting nanowires, the effect of growth on their piezoelectric properties, and importantly, how piezoelectricity is characterized at the nanoscale in these materials. Energy-related applications of semiconducting piezoelectric nanowires are described in detail, including their incorporation into nanogenerators for energy harvesting, as well as in piezotronic and photo-piezotronics devices based on the electromechanical and opto-electromechanical interactions taking place in piezoelectric semiconductor-nanowire junction-based devices. Advances in nanofabrication, nanoscale characterization, and device engineering, coupled with a greater understanding and control of piezoelectricity in semiconducting nanowires, will ultimately help unlock the full potential of these fascinating nanomaterials.
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