China
Africa
Explore chapters and articles related to this topic
Saturation of Free Carrier Concentration in Semiconductors
Published in Kazumi Wada, Stella W. Pang, Defects in Optoelectronic Materials, 2021
The results of the calculations are shown in Figure 3. They were obtained assuming Cent = 1. A good fit to experimental data was obtained adopting the value Ef = 2.4 eV for the Fermi energy located at the intrinsic level, EF = Ei. As is seen in Figure 3 the results of the calculations quite well reflect the overall dependence of the electron concentration on the doping level, Nd. At low Nd the Fermi energy is located well below the conduction band, EF is large and the concentration of VGa small. Under these conditions all donors are electrically active and n = Nd. With increasing doping the Fermi energy shifts upwards towards the conduction band resulting in a lower EF and higher [VGa]. Gallium vacancies compensate the donors and n becomes a sublinear function of Nd. In fact, it can be shown that in a limited concentration range, n is proportional to (Nd)1/3. The 1/3 power reflects the fact that VGa is a triply charged acceptor. Such dependence is expected when electrons can still be described by nondegenerate statistics. At even higher doping levels the Fermi energy enters the conduction band and becomes strongly dependent on electron concentration. This leads to a rapid reduction of EF, an increase of VGa and as a consequence saturation of n.
Electrical Parameter Variations in Bipolar Devices
Published in Pradeep Lall, Michael G. Pecht, Edward B. Hakim, Influence of Tempemture on Microelectronics and System Reliability, 2020
Pradeep Lall, Michael G. Pecht, Edward B. Hakim
If the nth energy level is some maximum value such that all the state below this level are filled, and all the states above this are empty, then the energy of this nth level is termed as the Fermi energy at 0°K. The total number of states per unit volume is Nst=∫Nst(E)dE=13π2(2melecEh2)3/2
Short Review of Atomic and Semiconductor Theory
Published in Vijay B. Pawade, Sanjay J. Dhoble, Phosphors for Energy Saving and Conversion Technology, 2018
Vijay B. Pawade, Sanjay J. Dhoble
In the case of light-emitting materials such as phosphors and scintillators, the doping impurity is known as an activator. When an impurity is doped into the semiconductor crystal structure, it forms allowed and possible energy levels within the semiconductor. Therefore, the energy levels that are formed by the dopant inside the material are close to the energy band levels of the semiconductor. When a donor impurity is doped into a semiconductor, it forms the electron donor level near the CB, whereas acceptor impurities form the acceptor level near the VB. The energy gap between the energy level formed and the nearest energy band level is called the dopant site energy band (EB), and it is relatively small in value (EB for boron in silicon = 0.045 eV, and Si = 1.12 eV). The EB for the doping atom is so small that the atoms are thermally ionized at room temperature, creating free charge carriers in the VB or the CB, respectively. The doping atom may also affect the shifting of energy level with respect to the Fermi energy level.
Phase stability and physical properties of lanthanum dicarbide under pressure
Published in Philosophical Magazine, 2023
Djalel Mebarki, Souad Dilmi, Salima Saib, Nadir Bouarissa, Souad Louhibi-Fasla
To comprehend better the electronic structure, the Fermi surface in the BZ of the body-centered tetragonal LaC2 is sketched in Figure 2(c). There exist two electronic bands which traverse the Fermi energy level. The first Fermi-crossing band has basically quasi-conical-like characteristics, producing hole-like pockets in the vicinity of the zone outline electronic bands which is shown in Figure 2(c). The second Fermi-crossing band is dominated by Sphere-like characteristics, mainly an electron pocket that encircles the Γ point. To evaluate the spin–orbit coupling (SOC) effect on the electronic structures, we have compared the obtained outcomes of the electronic band structure with and without considering this coupling. Our outcomes are plotted in Figure 2(d). It is observed that SOC extracted some of the abasements at the high symmetry points that are present in the non-SOC calculations. The most affected bands are those arising from f states of La atoms. The states close to the Fermi level are barely affected by SOC. This recommended that the SOC has no compelling effect on the superconducting properties in the intermetallic compound LaC2.
Ultrafast Electron–Phonon Coupling at Metal-Dielectric Interface
Published in Heat Transfer Engineering, 2019
Qiaomu Yao, Liang Guo, Vasudevan Iyer, Xianfan Xu
The optical response resulting from the energy transfer process described above can be explained by the band structure of gold. Gold has a typical band structure as a noble metal. The free electrons in the s/p band follow the Fermi–Dirac distribution [6]: where E denotes the energy, Ef is Fermi energy of gold, kB is Boltzmann constant, and T is absolute electron temperature. Due to the variation of electron occupancy with temperature, both the d band and s/p band excitation will affect the absorption of light and cause the change in optical response. Figure 1 shows the electron occupancy of gold and the Fermi–Dirac distribution near the Fermi energy, which can explain the impact of the change of the Fermi–Dirac distribution on the optical reflectance. As the temperature increases, the occupation of electrons with energy above the Fermi energy increases and the occupation of electrons with energy below the Fermi energy decreases. For probe photon energy larger than ITT (as indicated by the dashed arrow in Figure 1), the change in the electron distribution will decrease the photon absorption for electron transitions from the d band to unfilled energy states above the Fermi energy and thus increase the reflection. On the other hand, for probe photon energy less than ITT, the absorption increases and the reflection decreases. These trends were experimentally observed [2], [8].
Adsorption of HCN molecules on Ni, Pd and Pt-doped (7, 0) boron nitride nanotube: a DFT study
Published in Molecular Physics, 2018
Aziz Habibi-Yangjeh, Hadi Basharnavaz
In order to further analyse the structural, electronic and magnetic properties of the pure, doped and HCN-adsorbed (7, 0) BNNTs systems, we calculated the polarised electronic band structures of these systems (see Figure 2). The band structure plots clearly show that the pure (7, 0) BNNTs is a large-gap semiconductor (3.320 eV) and by replacing B atom of (7, 0) BNNTs with Ni, Pd and Pt atoms, band gap energy is remarkably reduced from 3.320 to 0.000 eV. The results of Figure 2 display that transition metal doped BNNTs and HCN-adsorbed transition metal doped BNNTs have metallic properties, because valence bands and conduction bands have crossed each other at the Fermi energy levels, which are in good agreement with the previous reports [52–56,60]. Furthermore, these results showed that the doping and adsorbing essentially introduce new energy states near the Fermi energy levels, resulting in modifications of the electronic structures. Also, Figure 2 shows that the Fermi energy levels shift to the CB energy level with adsorption of HCN molecules and transition metals doping on the pure (7, 0) BNNTs. As seen in this figure, the majority spin (top panel) and minority spin (bottom panel) of the VB and CB energies of the pure, Ni, Pd and Pt-doped (7, 0) BNNTs before and after adsorption of HCN molecules are essentially identical and zero magnetic moment was found for the mentioned systems.