Carrier transport engineering in wide bandgap semiconductors for photonic and memory device applications

Wide bandgap (WBG) semiconductors play a crucial role in the current solid-state lighting technology. The AlGaN compound semiconductor is widely used for ultraviolet (UV) light-emitting diodes (LEDs), however, the efficiency of these LEDs is largely in a single-digit percentage range due to several factors. Until recently, AlInN alloy has been relatively unexplored, though it holds potential for light-emitters operating in the visible and UV regions. In this dissertation, the first axial AlInN core-shell nanowire UV LEDs operating in the UV-A and UV-B regions with an internal quantum efficiency (IQE) of 52% are demonstrated. Moreover, the light extraction efficiency of this UV LED can be further improved by 63% by utilizing appropriate hexagonal photonic crystal structures. The carrier transport characteristics of the LEDs have been carefully engineered to enhance the carrier distributions and reduce the current leakage, leading to a significantly improved IQE of the LEDs. In this regard, the p-type AlGaN electron blocking layer (EBL) has been utilized to suppress electron leakage. Although the EBL can suppress the electron leakage to an extent, it also affects the hole injection due to the generation of positive polarization sheet charges at the hetero interface of EBL and the last quantum barrier (QB). Moreover, the Mg acceptor activation energy of the Al-rich AlGaN EBL layer is elevated, affecting the Mg doping efficiency. To mitigate this problem, in this dissertation, EBL-free UV LED designs are proposed where the epilayers are carefully band-engineered to notably improve the device performance by lowering the electron overflows. The proposed EBL-free strip-in-a-barrier UV LED records the maximum IQE of -61.5% which is -72% higher, and IQE droop is -12.4%, which is -333% less compared to the conventional AlGaN EBL LED structure at 284.5 nm wavelength. Moreover, it is shown that the EBL-free AlGaN deep UV LED structure with linearly graded polarization-controlled QBs instead of conventional QBs in the active region could drastically reduce the electrostatic field in the quantum well (QW) region due to the decreased lattice mismatch between the QW and the QB. The carrier transport in the EBL-free deep UV LEDs is significantly improved, attributed to the increased radiative recombination, quantum efficiency, and output power compared to the conventional EBL LEDs. Overall, the study of EBL-free UV LEDs offers important insights into designing novel, high-performance deep UV LEDs for practical applications. Further, it is demonstrated that novel WBG materials could be perfectly employed for emerging non-volatile memory (resistive random access memory, RRAM) applications. The resistive switching (RS) capability has been observed in Ga2O3 at low power operation. Importantly, for the first time, the multi-bit storage capability of this types of RRAM devices with a reasonably high Roff/Ron ratio is experimentally demonstrated. In addition, integrating a thin SiNx layer in the conventional SiO2 RRAM device could effectively facilitate the formation of a conducting filament. It is reported that the proposed RRAM device exhibits excellent RS characteristics, such as highly uniform current-voltage characteristics with concentrated SET and RESET voltages, excellent stability, and high Roff/Ron (\u3e 103) even at ultra-low current (10 nA) operation. The multi-bit RS behavior has been observed in these RRAM devices, which pave the way for low-power and high-density data storage applications

Resistive Switching and Hysteresis Phenomena at Nanoscale

Resistive switching at the nanoscale is at the heart of the memristor devices technology. These switching devices have emerged as alternative candidates for the existing memory and data storage technologies. Memristors are also considered to be the fourth pillar of classical electronics; extensive research has been carried out for over three decades to understand the physical processes in these devices. Due to their robust characteristics, resistive switching memory devices have been proposed for neuromorphic computation, in-memory computation, and on-chip data storage. In this chapter, the effects of various external stimuli on the characteristics of resistive switching devices are comprehensively reviewed. The emphasis will be given on 2-dimensional (2D) materials, which are exciting systems owing to superior electrical characteristics combined with their high stability at room temperature. These atomically thin 2D materials possess unique electrical, optical and mechanical properties in a broad spectrum, and open the opportunity for developing novel and more efficient electronic devices. Additionally, resistive switching due to light has also grabbed the attention of optoelectronic engineers and scientists for the advancement of optical switches and photo tuned memristors. The variety of material systems used in the fabrication of memristors is comprehensively discussed

Towards Oxide Electronics:a Roadmap

At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics

One-dimensional titanium dioxide nanomaterial based memristive device and its neuromorphic computing applications

Memristor devices as the alternative to the next-generation non-volatile memory devices has been widely studied recently due to its advantages of simple structure, fast switching speed, low power consumption. Among all the different materials that demonstrate the potential of resistive switching behavior, memristor devices based on TiO2 has attracted particular attention considering its richness in switching mechanism associated with wide range of phases. Furthermore, one-dimensional (1D) nanomaterial based memristor devices demonstrate promising potential considering about its advantages of confinement of electron transport in individual nanowires, enabling precision engineering of electrical performance for stable and reliable memristor devices, high integration density potential, etc. In this research, we propose the use of facile hydrothermal methods to synthesize TiO2 nanowires for the fabrication of memristor devices. Three different types of devices were fabricated, i.e., based on TiO2 nanowire networks on Ti foil, TiO2 nanorod arrays grown on fluorine-doped tin oxide (FTO) substrate, and single TiO2 and titanate nanowire directly synthesized from TiO2 nanoparticles. The corresponding devices demonstrated promising resistive switching performance respectively and were further used for multilevel memory storage and more importantly, the emulation of artificial synapses for the application of neuromorphic computing. The corresponding switching mechanisms were explored and it was found that the oxygen vacancies in TiO2 nanowires during the hydrothermal process play an important role in the switching and charge transport mechanism. This work will improve the understanding of engineering the electrical performance of TiO2 based memristive devices and provide insights into the switching mechanism in 1D nanomaterial based memristive devices

The 2016 oxide electronic materials and oxide interfaces roadmap

Lorenz, M. et al.Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due to their nanostructured nature is another facet of the challenge. The research related to the oxide electronic field is at an impressionable stage, and this has motivated us to contribute with a roadmap on ‘oxide electronic materials and oxide interfaces’. This roadmap envisages the potential applications of oxide materials in cutting edge technologies and focuses on the necessary advances required to implement these materials, including both conventional and novel techniques for the synthesis, characterization, processing and fabrication of nanostructured oxides and oxide-based devices. The contents of this roadmap will highlight the functional and correlated properties of oxides in bulk, nano, thin film, multilayer and heterostructure forms, as well as the theoretical considerations behind both present and future applications in many technologically important areas as pointed out by Venkatesan. The contributions in this roadmap span several thematic groups which are represented by the following authors: novel field effect transistors and bipolar devices by Fortunato, Grundmann, Boschker, Rao, and Rogers; energy conversion and saving by Zaban, Weidenkaff, and Murakami; new opportunities of photonics by Fompeyrine, and Zuniga-Perez; multiferroic materials including novel phenomena by Ramesh, Spaldin, Mertig, Lorenz, Srinivasan, and Prellier; and concepts for topological oxide electronics by Kawasaki, Pentcheva, and Gegenwart. Finally, Miletto Granozio presents the European action ‘towards oxide-based electronics’ which develops an oxide electronics roadmap with emphasis on future nonvolatile memories and the required technologies. In summary, we do hope that this oxide roadmap appears as an interesting up-to-date snapshot on one of the most exciting and active areas of solid state physics, materials science, and chemistry, which even after many years of very successful development shows in short intervals novel insights and achievements.This work has been partially supported by the TO-BE COST action MP1308. J F acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (SEV-2015-0496) and MAT2014-56063-C2-1R, and from the Catalan Government (2014 SGR 734). F.M.G. acknowledges support from MIUR through the PRIN 2010 Project ‘OXIDE’.Peer reviewe

Feature Papers in Electronic Materials Section

This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

Characterization of Nanomaterials: Selected Papers from 6th Dresden Nanoanalysis Symposiumc

This Special Issue “Characterization of Nanomaterials” collects nine selected papers presented at the 6th Dresden Nanoanalysis Symposium, held at Fraunhofer Institute for Ceramic Technologies and Systems in Dresden, Germany, on 31 August 2018. Following the specific motto of this annual symposium “Materials challenges—Micro- and nanoscale characterization”, it covered various topics of nanoscale materials characterization along the whole value and innovation chain, from fundamental research up to industrial applications. The scope of this Special Issue is to provide an overview of the current status, recent developments and research activities in the field of nanoscale materials characterization, with a particular emphasis on future scenarios. Primarily, analytical techniques for the characterization of thin films and nanostructures are discussed, including modeling and simulation. We anticipate that this Special Issue will be accessible to a wide audience, as it explores not only methodical aspects of nanoscale materials characterization, but also materials synthesis, fabrication of devices and applications

Annual Report 2009 - Institute of Ion Beam Physics and Materials Research

The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of the Forschungszentrum Dresden-Rossendorf (FZD), and contributes the largest part to its Research Program \"Advanced Materials\", mainly in the fields of semiconductor physics and materials research using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users