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Magnetic semiconductors and ferromagnet/semiconductor hybrid structures are now the most important topics of investigation in the field of new functional semiconductor devices. This chapter aims to provide a comprehensive review on crystal growth and characterization of magnetic semiconductors. Developments in epitaxial growth techniques and doping...
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Mn-doped Ge quantum dots (QDs) were grown on Si (001) substrates by molecular beam epitaxy. At the same time, modulation doping of boron (B) with different concentrations at 10 nm beneath the QD layers is utilized to modulate the concentration of holes in the QDs. For Mn uni-doped and B uni-modulation-doped Ge QD samples, no credible ferromagnetic...
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... This is in order to enhance the performance of electronic devices. To get this new kind of material, a part of the host material's cations is usually substituted by magnetic impurities, which are the transition metals (TM) such as Co, Ni, Fe, and Mn [1][2][3][4][5][6][7][8][9][10][11][12]. ZnSe compound is a wide band gap semiconductor, which represents a large family of alloys that belongs to the II-VI group. ...
Using KKR-CPA method within the spin-polarized density functional theory (DFT) with the local density approximation (LDA), we have performed our calculations on ZnSe compound, doped with chromium atoms, for different concentrations. This is to study the effect of this magnetic impurity on the magnetic properties and Faraday rotation of the studied alloy. We also have investigated the effect of defects, by introducing vacancies in Zn sites. On one hand, we have doped our compound with (0.01; 0.05; 0.1; 0.15; 0.2; 0.25) of chromium atoms; on the other hand, we have introduced (0.01; 0.03; 0.05) of vacancy defects in Zn sites, for each state of chromium doping. We have investigated that there is a magnetism appearing when doping with chromium atoms. In addition, the adding of vacancy defects improves the ferromagnetic state. The density of states (DOS) illustrates the analyzed results. Moreover, the energy of each case has been calculated for both the DLM (disordered local moment) and the ferromagnetic states.
... They still remain the most natural candidates for red, blue, and green lasers and light-emitting diodes (LED), which are widely used for producing the full-color visible optical devices [3,4]. Moreover, CdTe-based DMSs are widely studied in the field of solar cells, besides the wide range of spintronic applications, such as visible infrared lasers and infrared detectors [5][6][7][8][9]. The CdTe is a ferromagnetic material at room temperature, with high thermal equilibrium stability. ...
In this paper, we aimed to study the effect of doping of the compound CdTe with the cobalt impurity (Co), as well as the vacancy defects in Cd sites. On one hand, this leads to the investigation of the magnetic properties and the Faraday rotation effect for the studied alloy, doped with different concentrations of cobalt (0.01, 0.05, 0.1, 0.15, 0.2, 0.25). On the other hand, we have created 0.01 of vacancy defects in Cd sites. Then, we raised the vacancy defect concentration to 0.05, keeping the same concentrations of cobalt. As a result, we have investigated that there is a magnetism appearing with the cobalt doping, while the vacancy defects in Cd sites affect the stability of the magnetic states. In general, it improves the ferromagnetic state that will be well explained in the discussion. Our calculations were performed using the KKR-CPA method within the spin-polarized density functional theory (DFT) with the local density approximation (LDA). The curves of the density of states (DOS) illustrate the results of this study which has been discussed, analyzed, and explained below. In addition, the energy of each case was calculated and given in the tables below for both the DLM (half of the cobalt spins are up while the other half are down) and the ferromagnetic state in order to confirm which one of them is stable.
... This material is also used in solar cells, infrared detectors, and visible and infrared lasers [6,10]. It is considered as one of the most studied DMSs in solar cells, while it is distinguished by its high solubility, especially for Mn atoms (as high as 77%) [7,8]. CdTe alloy is a wide direct band gap belonging to the group of II-VI semiconductors which is a large family of compounds that have suitable physical properties, for developing electronic and opto-electronic devices. ...
In this paper, we aimed to investigate the effect of vanadium doping on the CdTe compound and also the effect of introducing vacancies in Cd sites, as a type of structural defect. For this purpose, we used the Akai-KKR-CPA method within the spin polarized density functional theory (DFT) with local density approximation (LDA). We performed our calculations on doping CdTe with different concentrations of vanadium, which are 0.05, 0.07, 0.09, and 0.11. Then, we added to each one of them 0.03 and 0.05 of vacancies in Cd sites, in order to examine the effect of the defects on the electronic structure and magnetic properties of the alloy CdTe. We also aimed to check if doping and vacancy defects have any effect on the Faraday rotation and the critical temperature of this material. We have also found that all the studied cases show a half-metallic behavior and have a stable ferromagnetic state. In addition, the critical temperature increases with the increasing of vacancies in Cd sites, especially in the case of adding 0.03 of vacancies. This improves well the ferromagnetic state and ensures its stability up to higher temperatures.
... So, the host material of our alloy is CdTe, which is used in a wide range of applications in spintronics and also in optic solar cells, infrared detectors, and magneto-optical devices [3][4][5]. The CdTe compound is characterized by its belonging to the II-IV DMS group, which makes it one of the most studied and used materials in the domain of solar cells, thanks to its high solubility for Mn impurities which is close to an important value (as higher as 77 %) for II-IV DMSs [6,7]. ...
We performed ab initio calculations to investigate the effect of the doping in CdMnTe1−yN
y
and also of the defects in CdMnTe alloy. Moreover, we studied the magnetic properties in the both cases. Our calculations were carried out using the Akai-Korringa-Kohn-Rostoker method combined with coherent potential approximation (KKR-CPA) within the spin-polarized density functional theory (DFT) and local density approximation (LDA). The density of state (DOS) has also been calculated for different dopants and defect concentrations. The compound Cd1−xMnx = 0.38Te is the diluted magnetic semiconductor (DMS) we studied in one of our earlier works (Ait Raiss, A. et al., doi:10. 1016/ j. jmmm. 2015. 02. 077). The p-band of the doping with nitrogen (N) atoms lies in the Fermi level, which is similar to the half-metallic behavior. The stabilized magnetic state in all these concentrations is the disordered local moment (DLM) state. The defect effect depends on their positions, either these defects are in the Cd sites or in telluride (Te) sites. In the both cases, we obtained different stable magnetic states. These states are either ferromagnetic or DLM ones. We also examined the effect of the N doping atoms on the Faraday rotation as a magneto-optical property of CdMnTe.
... It is used in Infra-Red detectors, solar cells, visible and Infra-Red lasers [2,3]. The compound CdTe is one of the most studied DMSs in solar cells, and it is distinguished by its high solubility for Mn atoms (as high as 77%) [4,5]. ...
... Максимальная температура Кюри в Ga 1−x Mn x As T C = 110 K была достигнута для концентрации [Mn] = 5.3% и концентрации свободных дырок p = 3.5 · 10 20 cm −3 , но для дальнейшего увеличения T C необходимо реализовать повышенную концентрацию атомов марганца с одновременно высоким значением p > 5 × 10 20 cm −3 , причем [Mn] > p123 . Известно, что прямое введение Mn в GaAs (например, методом низкотемпературной молекулярнопучковой эпитаксии — LT–MBE) позволяет достичь концентраций 6–9% [4], а специальным многослоевым (или цифровым) способом — до 14% [5,6]. Эти способы основаны на моновалентном Ga 3+ → Mn 2+ замещении и поэтому не могут привести к повышению температуры Кюри. ...
... Due to the existence of a gap for both of the spin channels, the total magnetic moment of per chemical formula is an integer 6m B for both CdCr 2 S 4 and CdCr 2 Se 4 with either of mBJ and GGA. We summarize related data in Table 1 for the energy gaps calculated with both GGA and mBJ and experimental gap values [30] at 0 K. ...
We use a modified Becke–Johnson (mBJ) exchange plus local density approximation correlation functional within the density functional theory (DFT) [semi-local, orbital-independent, producing accurate semiconductor gaps, see Tran and Blaha, Phys. Rev. Lett., 102 (2009) 226401] to investigate the electronic structures of CdCr2S4CdCr2S4 and CdCr2Se4CdCr2Se4 as two ferromagnetic semiconductors. Our results show that mBJ makes the empty Cr d-eg character bands higher by about 1.1 eV for CdCr2S4CdCr2S4 and 0.7 eV for CdCr2Se4CdCr2Se4 for the majority-spin channel with respect to the generalized gradient approximation (GGA). For the minority-spin channel, mBJ raises the Cr d character bands by about 0.8 eV for CdCr2S4CdCr2S4 and CdCr2Se4CdCr2Se4. The mBJ gap is enhanced by about 104% for CdCr2S4CdCr2S4 and 170% for CdCr2Se4CdCr2Se4 compared to GGA results, and is consistent with experiment in both of the cases. Our mBJ dielectric functions and the zero frequency refractive index n(0) for CdCr2S4CdCr2S4 and CdCr2Se4CdCr2Se4 are also consistent with experimental results available. The improved DFT results can be understood in terms of mBJ-enhanced spin exchange splitting and the reduced band width of Cr d character bands.
... Surprisingly, according to first-principles calculations, the quantized anomalous Hall effect can be realized in HgCr 2 Se 4 , and it is predicted to be a Chern semimetal [8]. However, the experimental gap is 0.32 eV [9], so it is important to correctly calculate the gap by means of first-principles calculations and to establish whether pressure can easily induce semiconductor-metal transitions. Because the energy gap is underestimated by the LDA and the generalized gradient approximation (GGA), to make first-principles electronic gaps comparable with experimental results, some further approximations are usually needed. ...
... Since there is a gap for both of the spin channels, the total magnetic moment of per chemical formula is an integer: 6 µ B . We summarize the energy gaps calculated with both GGA and mBJ, and the experimental gap values [9] at 0 K, in table 1. We also summarize the related gaps for CdCr 2 S 4 and CdCr 2 Se 4 in table 1, and the gaps between the mBJ results and experiment also agree well, which proves that mBJ gives an appropriate description for this kind of ferromagnetic semiconductor. ...
... The gaps (eV) for the majority-spin channel (UpGap), the minority-spin channel (DnGap), and spin non-conservation (Gap) calculated with mBJLDA and GGA, and the 0 K experimental (EXP) gaps[9] for HgCr 2 Se 4 , CdCr 2 S 4 and CdCr 2 Se 4 . ...
We investigate the electronic structures of the ferromagnetic semiconductor HgCr(2)Se(4) by using a modified Becke and Johnson exchange potential. The energy gap calculated with the experimental lattice structure is in good agreement with the experimental value. When the pressure reaches 9.0 GPa, HgCr(2)Se(4) becomes a so-called spin gapless semiconductor due to the closure of the spin non-conservation energy gap, and when the pressure increases to 11.4 GPa, the spin conservation energy gap closes, leading to a semiconductor-semimetal transition.
We have investigated theoretically the role of Cr-d states in the electronic and optical properties of the CdCr2X4 (X = S, Se) normal ferromagnetic spinels using the framework of an all-electron full-potential linearized augmented plane wave method. The calculations are performed using Coulomb corrected Perdew–Burke–Ernzerhof (PBE+U) and Tran–Blaha modified-Becke–Johnson (TB-mBJ) approximations with the adding of spin–orbit coupling in both schemes. The lattice parameters have been optimized and are in agreement with the existing experimental values. We found band gap values 1.606 eV and 0.972 eV of CdCr2X4 (X = S, Se), respectively, using the TB-mBJ scheme. Analysis of the site and momentum projected densities shows that the larger splitting of Cr-d states is responsible for the larger band gap by the use of the TB-mBJ scheme. Optical properties along the directions of lattice constants are studied on the basis of band to band transitions. We found the isotropic nature of the optical properties. Reflectivity stays low up to 1.6 eV, consistent with the energy gaps obtained using the TB-mBJ scheme in both the compounds. The refractive index, n(ω), and the extinction coefficient, k(ω), are also studied by the PBE and the TB-mBJ schemes.
n-CdTe/p-CdMnTe/p-GaAs diluted magnetic diode was grown by molecular beam epitaxy technology. The forward- and reverse-bias capacitance–voltage (C–V), conductance–voltage (G–V), series resistance–voltage (R
s–V), impedance–voltage (Z–V), and phase–voltage (θ–V) characteristics of this diode have been analyzed in the frequency range of 5 kHz to 1 MHz at room temperature. Both the density of interface states (N
ss) and series resistance (R
s) are strongly frequency dependent and decrease with increasing frequency. The values of the built-in potential (\( V_{\rm{bi}} \)), the doping concentration (\( N_{\rm{d}} \)), and the barrier height (\( \varphi_{{{\rm{b}}(C - V)}} \)) of the diode were calculated at different frequencies. Our experimental results revealed that both the series resistance and interface state density must be taken into account in studying the impedance spectroscopy on heterojunction diodes to understand their performance for electronic and optoelectronic applications. Diluted magnetic semiconductors are promising materials for future technology.
