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Resin-Based Composites in Dentistry—A Review
Published in S. M. Sapuan, Y. Nukman, N. A. Abu Osman, R. A. Ilyas, Composites in Biomedical Applications, 2020
Z. Radzi, R. A. Diab, N. A. Yahya, M. A. G. Gonzalez
The Light-Emitting Diode (LED) technology has been proven to be an efficient, cost-effective lighting source. It has been widely used shortly after the blue LEDs became available using indium-gallium-nitride (InGaN) substrates (Rueggeberg, 1999). These devices rely on the forward-biased energy difference (band gap) between two dissimilar semiconductor substrates (n-type conduction band and p-type valence band), to determine the wavelength of emitted light (Rueggeberg, 1999). Electrons are forced to traverse from one side of a semiconductor material (the “N” material, having an excess of electrons) to a substrate having an electron deficiency (the “P” material). When electrons travel through this potential energy “gap”, they emit light with wavelengths depending on the composition of each semiconductor substrate (Nakamura, 2015). The spectral emission from such units could successfully photoactivate CQ-based products.
III-Nitride Semiconductor Single Photon Sources
Published in Wengang (Wayne) Bi, Hao-chung (Henry) Kuo, Pei-Cheng Ku, Bo Shen, Handbook of GaN Semiconductor Materials and Devices, 2017
Pei-Cheng Ku, Chu-Hsiang Teng, Hui Deng
The results are shown in Figure 22.5 for various QD materials. In all materials, the DLP of the QD emission increases with the aspect ratio of the ellipse, which is defined as the ratio of the long axis to the short axis. In QD materials with a split-off band farther apart from the heavy and light holes, characterized by the split-off energy, the DLP is generally lower due to a weaker mixing between the light hole and split-off bands. InGaN exhibits a very small split-off energy compared to other compound semiconductors. Thus, the strong valence band mixing from all three bands leads to a very high DLP in elliptical QDs with a large aspect ratio. Experimentally, this has been confirmed as shown by the data points in Figure 22.5. A DLP as high as 0.99 has been observed in the experiment from elliptical QDs with an aspect ratio approaching 2. Elliptical InGaN/GaN QD nanodisks are, therefore, a potential source for single photon qubits.
III-Nitride Nanowires and Their Laser, LED, and Photovoltaic Applications
Published in Fumitaro Ishikawa, Irina A. Buyanova, Novel Compound Semiconductor Nanowires, 2017
Wei Guo, Pallab Bhattacharya, Junseok Heo
Due to the constantly increasing oil prices, there is an urgent need to develop high-efficiency solar cells to harvest the solar energy as the alternative energy source. In order to reduce the cost of solar cells, it is essential to significantly increase the conversion efficiency of photovoltaic materials and devices. In this context, progress has been made in design, demonstration, and understanding of solar cell devices with improved efficiency. Due to the large band gap, from 0.7 to 3.4 eV, (In)GaN materials have drawn huge interest in the research of high-efficiency solar cells. (In)GaN-based solar cell devices have the potential to absorb full sun spectrum more efficiently beyond the 2.2 eV band gap limit of the solar cells made from the traditional III–V alloys [62, 63]. However, the development has been impeded due to a variety of reasons: (1) large dislocation density in GaN template grown on foreign substrate; (2) difficulty in growing high- quality InGaN with indium contents >50% due to the large lattice mismatch between InN and GaN; and (3) the fact that indium contents tend to segregate into regions with high and low indium content (indium phase separation). Due to the large surface-to- volume ratio, InGaN nanowire material becomes an ideal candidate for photovoltaics applications. In addition, in PV devices, an antireflection coating (ARC) layer for solar cells is essential to reduce the surface reflection loss [64]. This layer usually contains dielectric materials with small effective refractive index to reduce the Fresnel reflection at the air/device interface [65]. Recently, one-dimension nanoscale structures such as nanowire, nanotube, and nanorods have been studied as the potential candidates for wide-angle and broadband antireflective coatings [66–69]. As a result, this is another inherent advantage of employing nanowire materials for photovoltaic applications.
Intrasubband-related linear and nonlinear optical absorption in single, double and triple QW: the compositions, temperature and QW’s number effects
Published in Philosophical Magazine, 2023
Redouane En-nadir, Haddou El-ghazi, Walid Belaid, Mohammed Tihtih, Hassan Abboudi, Ibrahim Maouhoubi, Anouar Jorio, Izeddine Zorkani
During the last decade, group III-N semiconductor alloys including InN, GaN and AlN and their ternary alloys InGaN and AlGaN have been widely studied. They are beneficial materials for optoelectronic engineering and energy harvesting due to their particular optical and electrical properties. Their wide and direct band gap covers almost the entire electromagnetic spectrum from infrared (IR) to ultra-violet (UV) passing through the visible light. These properties make them potential candidates for various applications in the optoelectronic market dominated by conventional semiconductors including silicon (Si) and gallium-arsenide (GaAs) and aluminium-gallium-arsenide (AlGaAs) (e.g. blue and green LEDs, laser diodes, photodetectors, solar cells, all types of switches, etc.) [1–5]. InGaN-based heterostructures are one of the few systems capable of providing band gaps ranging from 0.7 (InN) to 3.4 eV (GaN) [6,7]. The adjustment of the forbidden band could be achieved directly by modifying the In-content in the InGaN alloys. InGaN-based systems can cover almost the entire visible spectrum. Therefore, InGaN alloys could be a perfect candidate for optoelectronic devices that operate under harsh temperature, voltage and pressure conditions [8,9]. Due to a direct band gap, the absorption coefficient of InGaN alloys is very high and reaches 105 cm−1 for a photon energy of 0.5 eV above the absorption edge for all ranges of in-compositions [10]. One of the challenging lockouts of Group III-N materials, especially the InGaN alloy, is that it is difficult to grow a thick layer of this later on GaN due to the high mismatch rate between them. The thick matrix layer of GaN is usually developed to match different materials by dislocation, bending and annihilation. Although the lattice mismatch between GaN and InN is lower (only 10%) compared to InN/sapphire and GaN/sapphire, it is still sufficient to cause stresses at the InGaN/GaN [11]. However, there is a critical thickness for InGaN layers above which stresses are released by forming dislocations. This critical thickness is much lower for InGaN grown on a GaN substrate and it is less than 5 nm for in-compositions greater than 20% [12]. Once the critical thickness is reached, thread dislocations form, damaging the performance of the device. One of the suggested ideas to avoid this problem is to grow thin layers of InGaN (InGaN-quantum wells) on GaN instead of a thick layer. This will certainly influence the performance of the device such as the optical absorption, which is the subject of this study. Quantum wells are a type of low-dimensional system (e.g. quantum dots and quantum wire wells) that allow us to confine carrier charges (electrons and holes) [13].