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Borate
Published in S. K. Omanwar, R. P. Sonekar, N. S. Bajaj, Borate Phosphors, 2022
When sunlight incidents on a solar cell, the photons activate the electrons in the cell and promote them into conduction band. Those electrons can then be utilized to constitute an electric current. To prepare a solar cell, the semiconductor is doped with either accepter materials (positive charge carriers, p-type) or donor materials (negative charge carriers, n-type). When two differently doped semiconductor layers are combined then p–n junction forms across the boundary of the layers. The PV conversion efficiency of solar cell is a very important factor that governs the performance of a PV device or panels. For any regular single p–n junction solar cell, the characteristic value of energy bandgap of the semiconductor materials from which the solar cell is made plays key role on its conversion efficiency. Currently, solar cells based on crystalline, polycrystalline and amorphous silicon dominates more than 90% of the world production [7]. The use of c-Si enables PV devices to achieve a maximum conversion efficiency of 25% [8]. Figure 8.5 shows normalized spectral response (SR) of a typical c-Si solar cell and solar spectrum available on earth surface i.e. AM1.5 Global. As the c-Si is an indirect bandgap semiconductor there is not a sharp cut-off at the wavelength corresponding to the bandgap (Eg = 1.12 eV) [9].
Semiconductors
Published in Jerry C. Whitaker, Microelectronics, 2018
In the extrinsic or doped semiconductor, impurities are purposely added to modify the electronic characteristics. In the case of silicon, every silicon atom shares its four valence electrons with each of its four nearest neighbors in covalent bonds. If an impurity or dopant atom with a valency of five, such as phosphorus, is substituted for silicon, four of the five valence electrons of the dopant atom will be held in covalent bonds. The extra, or fifth electron will not be in a covalent bond, and is loosely held. At room temperature, almost all of these extra electrons will have broken loose from their parent atoms, and become free electrons. These pentavalent dopants thus donate free electrons to the semiconductor and are called donors. These donated electrons upset the balance between the electron and hole populations, so there are now more electrons than holes. This is now called an N-type semiconductor, in which the electrons are the majority carriers, and holes are the minority carriers. In an N-type semiconductor the free electron concentration is generally many orders of magnitude larger than the hole concentration.
Semiconductor Light Sources and Detectors
Published in Shyamal Bhadra, Ajoy Ghatak, Guided Wave Optics and Photonic Devices, 2017
As its name indicates, a semiconductor is a material whose electrical conductivity lies between those of good conductors and bad conductors. Good conductors, such as metals, typically have conductivity in the range 104–106/(ohm cm) or siemens per centimetre, while insulators have conductivity in the range 10−18–10−12/(ohm cm). Semiconductors that are used in practice have electrical conductivity in the range 10−6–102/(ohm cm). One of the most important properties, which are made use of in realizing semiconductor devices, is that the conductivity of semiconductors can be changed significantly, through orders of magnitude, by doping the material with suitable impurities, or by changing the temperature, or by illuminating the material with light of an appropriate wavelength. The properties of a semiconductor are determined by the band structure of the material. A majority of useful semiconductors are crystalline, and most crystalline semiconductors have a cubic lattice. Typical interatomic spacings are in the range 3–7 Å and the number of atoms per unit volume is ~1022/cm3. When a semiconductor is doped by an impurity element to change its conductivity, the typical concentrations employed are in the range 1010–1019/cm3, which is a very small fraction of the total number of atoms per unit volume.
Optical, surface and magnetic properties of the Ti-doped GaN nanosheets on glass and PET substrates by thermionic vacuum arc (TVA) method
Published in Particulate Science and Technology, 2018
Suat Pat, Şadan Korkmaz, Soner Özen, Volkan Şenay
Ti-doped GaN is used to the transparent conductive material. The optical properties of the Ti-doped GaN related with the surface morphologies of the deposited layers. Optical properties of the doped GaN materials are important because of they have been used in light emitting, laser diodes and spintronics. The band gap of a semiconductor is changed by the doped element type and doping rate. The band gap energy of GaN thin film is about 3.7 eV (Cui et al. 2016). This value is bigger than the band gap energy of bulk GaN. The band gap of bulk GaN is approximately 3.4 eV (Wang et al. 2010; Majid et al. 2015; Pat et al. 2015; Cui et al. 2016). Ti doping affects the band gap of the GaN to lower value (Cui et al. 2016). Ti-doped GaN is also a transparent conductive material (Sato et al. 1994). This material shows ferromagnetic properties (Xiong and Jiang 2007; Min and Jun-Jie 2013; Jimenez, López, and Espitia 2016). Physical properties of the materials can be adjusted to desired values by changing the doping element. The surface properties of the Ti-doped GaN are descent on the optical properties (Rufinus 2007; Xiong, Shi, and Jiang 2007; Wang et al. 2010; Majid et al. 2015; Cui et al. 2016). So far, the physical properties of the Ti-doped GaN must be identified. Doping mechanism is a realized in conventional GaN growth methods such as metal organic vapour deposition, molecular beam epitaxy and etc. (Sato et al. 1994; Rufinus 2007; Xiong, Shi, and Jiang 2007; Wang et al. 2010; Majid et al. 2015; Pat et al. 2015; Cui et al. 2016).
Bismuth-doped g-C3N4/ZIF-8 heterojunction photocatalysts with enhanced photocatalytic performance under visible light illumination
Published in Environmental Technology, 2023
Qian Yang, Wensong Lin, Zhichang Duan, Sen Xu, Junnan Chen, Xin Mai
The above results show that the compound of g-C3N4 and ZIF-8 can reduce the forbidden bandwidth, thereby promoting the transfer of photogenerated charges in the structure [47]. For doping modification, doping with an appropriate amount of metal element can reduce the bandgap width of the doped substance, and further promote the effective transfer of photogenerated charges between substances [38,48]. For CNZ-1.5(Bi)-12, an appropriate amount of bismuth element was introduced into CNZ-1.5, bismuth reduced the bandgap of CNZ-1.5 to achieve the rapid transfer of photogenerated carriers.
Online automatic anomaly detection for photovoltaic systems using thermography imaging and low rank matrix decomposition
Published in Journal of Quality Technology, 2022
Qian Wang, Kamran Paynabar, Massimo Pacella
Nowadays, there is a growing interest in renewable energy and photovoltaic (PV) systems. PV systems are pollution-free, noiseless, modular, and easily installable in several locations. In a PV system, numerous solar cells convert solar energy into current through the photoelectric effect of doped semiconductor material. Simplifying, a solar cell is a diode designed to absorbs photons with energy. This creates a difference of potential in the internal junction zone. The polarization of the junction zone prevents electrons from crossing it, hence producing a voltage between the diode terminals.