China
Africa
Explore chapters and articles related to this topic
Semiconductors
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
For dopants to be effective they must be ionized at the temperature of operation, and this depends on their activation energy, Ea. At room temperatures Ea should be ≤ kT or ~1/40 eV. For low enough temperatures, excitation from donors and acceptors is the only source of carriers and the conductivity can be considered solely extrinsic. In this regime, the doping of the semiconductor determines whether the semiconductor is n-type or p-type. At increasingly higher temperatures, direct thermal excitation from the valence band to the conduction band begins to dominate the extrinsic density. At some point, there will be essentially equal numbers of electrons and holes and the conductivity can now be considered intrinsic. Impurities that can serve as either acceptors or donors are called amphoteric impurities. Semiconductors that can be doped either p-type or n-type are called ambipolar semiconductors. Those that can only be made n or p type (such as ZnTe) are called unipolar semiconductors.
Renewable Energy
Published in Takashiro Akitsu, Environmental Science, 2018
Photovoltaic effect on p–n junction: Currently common solar cells have a structure in which p-type and n-type semiconductors are bonded. That is, it is a large p–n junction diode (photodiode). The following silicon type and compound type solar cells correspond to this. Light energy is absorbed (photo excitation) to electrons through a process reverse to that of light-emitting diodes, and electrons having energy are directly extracted as electric power by utilizing the properties of semiconductors. In theory, it is calculated that if you increase the junction indefinitely, it will be calculated to be about 86% conversion efficiency, but in reality, it is a problem of loss of light when passing through the upper layer device and current matching between the devices. The record, as of 2012, is obtained with three joined cells. Cells of four junctions and five junctions have also been studied.
Zeolite Transformation Layers in Discriminating Metal Oxide Semiconductor Gas Sensors
Published in Kevin Yallup, Krzysztof Iniewski, Technologies for Smart Sensors and Sensor Fusion, 2017
In metal oxide semiconductor (MOS) gas sensors, the target gas interacts with the surface of the metal oxide film, typically through reaction with surface-adsorbed oxygen ions. The electrons for such ionized oxygen species originate in the conduction band of the semiconductor and, on reaction with analyte gas, may be injected back into the material or further electrons withdrawn depending on the reaction that takes place resulting in a change in charge-carrier concentration of the material. This change in charge-carrier concentration serves to alter the conductivity (or resistivity) of the material. An n-type semiconductor is one where the majority charge carriers are electrons, and upon interaction with a reducing gas, an increase in conductivity occurs. Conversely, an oxidizing gas serves to deplete the sensing layer of charge-carrying electrons, resulting in a decrease in conductivity. A p-type semiconductor is a material that conducts with positive holes being the majority charge carriers; hence, the opposite effects are observed with the material and showing an increase in conductivity in the presence of an oxidizing gas (where the gas has increased the number of positive holes). A resistance increase with a reducing gas is observed, where the negative charge introduced into the material reduces the positive (hole) charge-carrier concentration. A summary of the response is provided in Table 12.1 [3].
Techno-economic analysis of thermoelectrics for waste heat recovery
Published in Energy Sources, Part B: Economics, Planning, and Policy, 2019
Thermoelectric generators are primarily composed of two semiconductor materials, which are both subjected to a thermal gradient. One of the conductors is made from an n-type semiconductor material containing an excess of free electrons, whereas the other is made from a p-type material containing electron holes. At the cold junction of the n-type material, there is a build-up of high electrostatic potential, with a corresponding build-up of low electrostatic potential at the p-type cold junction. If an external circuit is connected between the two cold junctions, then the voltage differential will drive a flow of charge. A schematic indicating the flow of heat and the names of the most critical components is shown in Figure 1 (Snyder and Toberer 2008).
Effect of Sr-doping on electronic and thermal properties of Pr2-xSrxFeCrO6 (0≤x≤1) oxide materials synthesized by using sol-gel technique
Published in Journal of Asian Ceramic Societies, 2023
Lav Kush, Sanjay Srivastava, Sanjay Kumar Vajpai, Serguei V. Savilov
After doping, the increase in thermal conductivity of PSFCO compounds, in comparison to pristine PFCO compounds, can be attributed to the combined effects of lattice vibration and electronic dispersion effects, as illustrated in Figure 5 (f). These effects contribute significantly to the efficient transfer of heat within the PSFCO compounds, resulting in their higher thermal conductivity across a wide temperature range. Interestingly, after doping, the rise in lattice thermal conductivity (κl) with temperature suggests a tuned rate of phonon scattering at higher temperatures, i.e. the rate of phonon scattering can be tuned by adjusting the p-type carrier concentration, which suited well to our explanation of electrical conductivity in Figure 5 (a). In fact, a decrease in the p-type carrier concentration does not directly lead to a decrease in the rate of phonon scattering but the presence of p-type carriers, such as holes, can actually enhance phonon scattering and decrease thermal conductivity in some materials [45]. Therefore, a decrease in p-type carrier concentration would result in reduced scattering of phonons and potentially higher thermal conductivity. This was either due to the structural variations or the presence of impurities in the materials. Surprisingly, the slight increase in κl with temperature was accompanied by a decrease in electrical conductivity. This suggests that p-type carrier concentration decreased due to increased diffuse scattering, indicating that thermal conductivity rises with temperature and eventually reaches a plateau before phonon-phonon scattering takes over at higher temperatures.
Stability of characteristics of neutron and gamma radiated overvoltage diodes
Published in Radiation Effects and Defects in Solids, 2022
Nenad Kartalović, Alija Jusić, Aleksandar Žigić, Teodora Nedić
The radiation defect affects the electrophysical characteristics of the starting semiconductor material, namely the lifetime of minority carriers τ, specific resistance ρ, the concentration of minority carriers n (if the semiconductor material is p-type) and the mobility μ. The lifetime of minority carriers is the most important characteristic of semiconductor materials used to make drain diodes (as well as other semiconductor components). Since the lifetime of minority carriers is determined by the rate of volume recombination at ‘traps’ and local centers, (36), the efficiency of recombination, that is the lifetime of minority carriers depends on the concentration of traps and the probability of minority carriers catching from the recombined center. Radiation defects that are generated in the band gap of the semiconductor, that is the local energy level are efficient recombination centers. Based on these facts, a conclusion can be drawn about the high sensitivity of the parameter τ to the influence of radiation. An empirical experiment that has been confirmed experimentally gives a quantitative characteristic of the change in τ from the integral radiation flux, (37). where is the lifetime of minority carriers after irradiation, is the lifetime of minority carriers before irradiation, is the radiation constant of the life of minority carriers depending on the specific resistance of semiconductor material (before irradiation), radiation spindle and radiation defect generation rate and Φ integral radiation flux.