Nanowire Photoelectrochemistry.

Recent applications of photoelectrochemistry at the semiconductor/liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run

12CaO.7Al2O3 ceramic: A review of the electronic and optoelectronic applications in display devices

The alumina-based compound, 12CaO.7Al2O3, is a ceramic material with a unique cage-like lattice. Such a structure has enabled scientists to extract various new characteristics from this compound, most of which were unknown until quite recently. This compound has the ability to incorporate different anionic species and even electrons to the empty space inside its cages, thereby changing from an insulator into a conductive oxide. The cage walls can also incorporate different rare earth phosphor elements producing an oxide-based phosphor. All these characteristics are obtained without a significant change in the structure of the lattice. It is, therefore, reasonable to expect that this compound will receive attention as a potential material for display applications. This review article presents recent investigations into the application of 12CaO.7Al2O3 ceramic in various display devices, the challenges, opportunities and possible areas of future investigation into the development of this naturally abundant and environmental friendly material in the field of display.LP Displays Ltd, Blackburn, UK for partial funding of the studentship at Queen Mary, University of London. Dr Lesley Hanna of Wolfson Centre for Materials Processing, Brunel University Londo

Role of wide bandgap materials in power electronics for smart grids applications

At present, the energy transition is leading to the replacement of large thermal power plants by distributed renewable generation and the introduction of different assets. Consequently, a massive deployment of power electronics is expected. A particular case will be the devices destined for urban environments and smart grids. Indeed, such applications have some features that make wide bandgap (WBG) materials particularly relevant. This paper analyzes the most important features expected by future smart applications from which the characteristics that their power semiconductors must perform can be deduced. Following, not only the characteristics and theoretical limits of wide bandgap materials already available on the market (SiC and GaN) have been analyzed, but also those currently being researched as promising future alternatives (Ga2O3, AlN, etc.). Finally, wide bandgap materials are compared under the needs determined by the smart applications, determining the best suited to them. We conclude that, although SiC and GaN are currently the only WBG materials available on the semiconductor portfolio, they may be displaced by others such as Ga2O3 in the near futur

Polarity in GaN and ZnO: Theory, measurement, growth, and devices

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade

Wide and ultra-wide bandgap oxides : where paradigm-shift photovoltaics meets transparent power electronics

Oxides represent the largest family of wide bandgap (WBG) semiconductors and also offer a huge potential range of complementary magnetic and electronic properties, such as ferromagnetism, ferroelectricity, antiferroelectricity and high-temperature superconductivity. Here, we review our integration of WBG and ultra WBG semiconductor oxides into different solar cells architectures where they have the role of transparent conductive electrodes and/or barriers bringing unique functionalities into the structure such above bandgap voltages or switchable interfaces. We also give an overview of the state-of-the-art and perspectives for the emerging semiconductor β- GaO, which is widely forecast to herald the next generation of power electronic converters because of the combination of an UWBG with the capacity to conduct electricity. This opens unprecedented possibilities for the monolithic integration in solar cells of both self-powered logic and power electronics functionalities. Therefore, WBG and UWBG oxides have enormous promise to become key enabling technologies for the zero emissions smart integration of the internet of things

Colloidal quantum dot hybrids: an emerging class of materials for ambient lighting

The rapid growth of the global economy and urbanization have resulted in major worldwide issues such as greenhouse gas emission, air pollution and the energy crisis. Artificial ambient light is one of the greatest inventions in human history, but it is also one of the primary energy consumption constituents and a focus of the global grand energy challenge. Therefore, low cost and low energy consumption lighting technology is in high demand. In this review, we will summarise and discuss one of the emerging lighting technologies – white electroluminescence light-emitting diodes enabled by hybrid colloidal quantum dots (WQLEDs), which have attracted intense attention because of promising potential in both flat-panel backlighting and solid-state lighting. WQLEDs have unique high luminescence efficiency, broad colour tunability and solution processability. Over the past few decades, the development of colloidal quantum dot synthesis, material engineering and device architecture has highlighted the tremendous improvements in WQLED formation. As WQLED efficiencies approach those of molecular organic LEDs, we identify the critical scientific and technological challenges and provide an outlook for ongoing strategies to overcome these challenges

Low Noise, High Detectivity Photodetectors based on Organic Materials

Organic photodetectors (OPDs) are potentially useful in many applications because of their light weight, flexibility and good form factors. Despite the high detectivities that have been frequently reported for OPDs recently, the application of these OPDs for weak light detection has been rarely demonstrated. In this thesis, low noise, high gain photodetectors based on organic and ZnO nanoparticles were proposed and demonstrated for highly sensitive UV light detection. The nanocomposite photodetector works in a hybrid mode of photodiode and photoconductor with the transition controlled by the UV light illumination. The nanocomposite detector shows two orders of magnitude higher sensitivity than silicon detectors in the UV range, which is the first time an organic, solution-processed detector has been shown to significantly outperform the inorganic photonic devices. In the fullerene-based photodetector, the dark-current has been successfully reduced by a cross-linked TPD (C-TPD) buffer layer. The high detectivity of 3.6 × 1011 (Jones) at 370 nm and the wide Linear dynamic range (LDR) of 90 dB, along with a response speed faster than 20 kHz, suggests that the fullerene-based organic photodetectors proposed here can open the way for many potential applications. The ZnO nanoparticles have been introduced into the C-TPD buffer layer of the fullerene-based photodetector to increase the photoconductive gain and reduce the noise current. The peak external quantum efficiency (EQE) value of approximately 400% and the peak specific detectivity of 6.5 × 1012 Jones at the wavelength of 390 nm, along with the record high LDR of 120 dB, enable the photodetector to be used in wide range of applications such as imaging, communication, and defense. The extremely high sensitivity of the photodetector also makes it particularly attractive for very weak light detection. Advisor: Jinsong Huan

Investigation of wide bandgap semiconductors for room temperature spintronic, and photovoltaic applications

Suitability of wide bandgap semiconductors for room temperature (RT) spintronic, and photovoltaic applications is investigated. Spin properties of metal-organic chemical vapor deposition (MOCVD) – grown gadolinium-doped gallium nitride (GaGdN) are studied and underlying mechanism is identified. GaGdN exhibits Anomalous Hall Effect at room temperature if it contains oxygen or carbon atoms but shows Ordinary Hall Effect in their absence. The mechanism for spin and ferromagnetism in GaGdN is a combination of intrinsic, metallic conduction, and carrier-hopping mechanisms, and is activated by oxygen or carbon centers at interstitial or similar sites. A carrier-related mechanism in MOCVD-grown GaGdN at room temperature makes it a suitable candidate for spintronic applications. Zinc oxide (ZnO) doped with transition metals such as nickel and manganese and grown by MOCVD is investigated, and bandgap tunability is studied. A bandgap reduction with transition metal doping is seen in ZnO with dilute doping of nickel or manganese. Transition metals could introduce energy states in ZnO that result in a bandgap reduction and could be tuned and controlled by growth conditions and post-growth processing such as annealing, for spintronic and photovoltaic applications”--Abstract, page iii