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Semiconductor Physics and Devices
Published in Manoj Kumar Majumder, Vijay Rao Kumbhare, Aditya Japa, Brajesh Kumar Kaushik, Introduction to Microelectronics to Nanoelectronics, 2020
Manoj Kumar Majumder, Vijay Rao Kumbhare, Aditya Japa, Brajesh Kumar Kaushik
Before moving further, we should be able to understand the basics of semiconductors. As explained earlier, the conductivity of the semiconductors lies between that of the conductors and the insulators. On their own, silicon and germanium are classed as intrinsic semiconductors that exhibit their purity. However, by controlling the amount of impurities added to this intrinsic semiconductor material, it is possible to control its conductivity. Various impurities called donors or acceptors can be added to this intrinsic material to produce free electrons or holes, respectively. This process of adding donor or acceptor atoms to semiconductor atoms is known as doping. The doped silicon is no longer pure, whereas these donor and acceptor atoms are collectively referred to as “impurities,” and by doping these silicon materials with a sufficient number of impurities, we can turn them into an N-type or P-type semiconductor materials. The most commonly used semiconductor material is silicon. Figure 1.3 shows the structure and lattice of a “normal” pure crystal of silicon. Silicon has four valence electrons in its outermost shell that shares its neighboring silicon atoms to form full orbitals of eight electrons. The structure of the bond between the two silicon atoms is such that each atom shares one electron with its neighbor making the bond highly stable.
Quantum Mechanics and Its Applications
Published in Sergey Edward Lyshevski, Nano- and Micro-Electromechanical Systems, 2018
The semiconductor with the electrical conduction dominated by donors is called the n-type semiconductor (electrons from the donor levels are thermally activated to the conduction band levels). The semiconductor with the electrical conduction dominated by acceptors is called the p-type semiconductor (electrons of the valence band are thermally activated to the transitions from the band to the acceptor levels, leaving holes in the valence band). Free electrons or free holes produced by this mechanism can conduct the electric current. If in semiconducting materials donors coexist with acceptors, then their energy levels compensate each other. If the donor concentration is Nd and the acceptor concentration is Na, the effective concentration of the impurities is |Nd − Na|. Depending on which of the concentrations is larger, the corresponding n- and p-type semiconductors result.
Methods of Investigation and Constructional Materials
Published in Janusz Turowski, Marek Turowski, Engineering Electrodynamics, 2017
Janusz Turowski, Marek Turowski
A significant influence on semiconductor properties are admixtures and impurities (called dopants), even at relatively small contents (for instance, 10−5–10−6% of the total number of atoms). One type of impurity, or dopants, in semiconductors are called acceptors which capture (accept) electrons from the valence band and thereby leave holes. Such acceptor-doped semiconductors have conductivity of type p, due to the positive (+) charge of hole, and are called p-type semiconductors. The other type of impurities are called donors, which deliver (donate) free electrons to the conduction band of a semiconductor. Such a donor-doped semiconductor has conductivity of type n, due to negative (−) charge of the electron, and is called an n-type semiconductor. Such doping-based conductivity need less energy for exciting free carriers (activation energy, on the order of 0.01–0.1eV) and hence occurs at lower temperatures than the intrinsic conductivity (Figure 1.37).
Engineered hard piezoelectric materials of MnO2 doped PZT-PSN ceramics for sensors applications
Published in Journal of Asian Ceramic Societies, 2021
Hong-Tae Kim, Jae-Hoon Ji, Bo Su Kim, Jin Su Baek, Jung-Hyuk Koh
Hard piezoelectric materials can be used in power generators and sensor applications. In general, an acceptor dopant in a ceramic creates oxygen (anion) vacancies in the crystal structure [8] and results in the formation of hard piezoelectric ceramics. These materials usually have a high Curie temperature exceeding 300°C, low piezoelectric charge constants (d33), low dielectric permittivity (εr), low electromechanical coupling coefficients (kp), low electrical resistance, and high mechanical quality factors (Qm) [9]. They are also more difficult to polarize or depolarize. Among these characteristics, a high mechanical quality factor is the most crucial aspect to be considered when these materials are used for industrial applications. These materials are good for sensors and energy harvesting applications [6]. Soft piezoelectric materials can be prepared by using the donor doping process, which can create cations in the metal oxide structure. Adding the donor dopant such as Nb into piezoelectric materials can be make soft-piezoelectric materials [10].
C20 fullerene and its boron- and nitrogen-doped counterparts as an efficient catalyst for CO oxidation
Published in Molecular Physics, 2020
The natural bonding orbital (NBO) analysis shows that the charge on the B and N atoms is 0.74 e and −0.47 e, in BC19 and NC19 clusters, respectively. As a result, the N and B atoms in the BC19 and NC19 clusters are as electron-deficient (Lewis acid) and electron-rich (Lewis base) sites, respectively. Upon N and B-doping the geometry of the C20 cluster is not notably altered. But the diameter of 5-MR containing B or N atoms slightly increased and the C–N and B-N bond lengths are 1.45 and 1.55 Å, respectively, while the average C–C bond length remains unchanged (∼1.44 Å) (see Figure 1a). According to the MEP diagram of BC19 and NC19 clusters (see Figure 2), upon B and N-doping the negative and positive charges induces on B and N atoms, respectively, which leads to the reduce and increase the bond lengths of B-C and N-C in comparison with the same C-C (1.48 Å) bond length in C20 cluster. Moreover, MEP plots indicate that the positive and negative charges mainly localized over the B and N atoms. This refers to the fact that B and C atoms are as potent center upon nucleophilic attack. Further, since the carbon atom has one less and more valence electron than nitrogen and boron atoms, respectively, the NC19 and BC19 clusters exhibit the electron acceptor property around the carbon atom and boron atom, respectively. Moreover, upon N/B doping the energy gap (Eg) between lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) decreases about 0.13 eV, which leads to strong interaction with incoming gas upon adsorption.
Probing the structural, electronic and spectral properties of a NbB20 − cluster
Published in Molecular Physics, 2021
Chenggang Li, Yingqi Cui, Jiaxiu Li, Jiangshui Guo, Lin Cheng, Baozeng Ren, Yuquan Yuan
Atomic charge is one of the simplest and most intuitive descriptions of charge distribution, which has been widely used to gauge how much charge transfer and charge flow occur during physical and chemical processes. To probe into the internal charge transfer, the natural population analysis (NPA) and natural electron configuration (NEC) are calculated for the lowest energy structure of the NbB20− cluster. The calculated results showed that the niobium atom contains a positive charge of 2.262, which means that the electrons transfer from the niobium atom to boron atoms. That is, boron atoms act as an electron acceptor in the NbB20− cluster. The reason for this is that the electronegativity of Nb:1.59 is smaller than that of B:2.04 [42]. In addition, the Nb atom possesses the electronic configuration of 4d5.235s0.17, showing that Nb donates most of its 4s2 electrons to the B20 ligand; however, its partially occupied 4d orbital accepts approximately two electrons (1.23) from the B20 ligand. For the B atoms, the configuration of valence electrons is 2s0.64−−0.722p2.08–−2.44, indicating that B donates most of its 2s2 electrons to the center Nb atom, while its 2p orbital accepts approximately one electron (1.08). In summary, the electrons transfer from B-2s and Nb-5s to B-2p and Nb-4d orbitals, and the studied cluster possesses strong hybridisation among spd orbitals.