LDA + U Study of Induced Half Metallicity in Cr-Doped GaN

Half-metallic ferromagnetism in the Ga_{1 ? x}Cr _x N compound at different concentrations, x = 25, 12.5 and 6.25 %, have been investigated using density functional theory as implemented in code Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) using LDA + U as exchange-correlation (XC) potential, to find out the possibility of new diluted DMSs. The outcomes reveal that transition metal atom (Cr) doping in GaN induces ferromagnetism. The 3d levels of the TM ion originate a half-metallic gap at the Fermi level in the majority spin channel for all concentrations. Moreover, diluted magnetic semiconductor compounds retain the half-metallic nature at all concentrations, i.e., x = 0.25, 0.125 and 0.0625, with 100 % spin polarization at the Fermi level (E _F). The total magnetic moment of these compounds is due to Cr-3d states, and the existence of a small magnetic moment on Ga and N, non-magnetic atoms, for all doping concentrations is a consequence of p-d hybridization of Cr-d and N-p states. The calculated values of s-d exchange constant N α and p-d exchange constant N βconfirm the ferromagnetic character of the Cr-doped GaN compound.     

Light non-metallic atom (B, N, O and F)-doped graphene: a first-principles study

First-principles calculations are performed to study the geometry, electronic structure and magnetic properties of light non-metallic atom-doped graphene (B, N, O and F). The planar structure and the quasi-linear energy dispersion near the Dirac point remain through doping with B and N atoms, by which p-type doping and n-type doping graphene are respectively induced. A bandgap of about 0.5 eV is generated through O doping, and geometrically the O atom is also in the graphene plane. No magnetic moment is detected in B- , N- and O-doped graphene. For F doping, the F atom bonds with one of the carbon atoms close to the vacancy, with the other two carbon atoms undergoing a Jahn-Teller distortion. A weak polarized magnetic moment of 0.71 μ(B) is detected through F doping.     

Structural Stability, Electronic and Magnetic Properties of Cu Adsorption on Defected Graphene: A First Principles Study

Structural stabilities, electronic structures, and magnetic properties of Cu atom adsorption on pure, B(N)-doped and single-vacancy graphene have been studied using the first-principle method. It was found that the electronic property of graphene can be tuned by B or N doping. B-doped and N-doped graphene turned into a p-type and n-type semiconductor with a band gap of 0.2 eV, respectively. Total energy calculation results demonstrated the most stable site for the Cu atom adsorption on pure, B-doped and N-doped graphene is the top, bridge, and hollow site, respectively. B doping and vacancy both enhance the adsorption capacity for the Cu atom, while N doping weakens the capacity. Furthermore, B and N atoms do not induce magnetism in graphene, while the magnetic moment is induced when Cu is adsorbed on the graphene sheet, which is mainly caused by the unsaturated s-electrons of the Cu atom.     

Mn掺杂锶铁氧体SrFe12O19电子结构及磁性的第一性原理研究

为了揭示掺杂离子对具有磁铅石构型的锶铁氧体材料磁性能的影响, 本研究探讨了锶铁氧体及其锰掺杂体系的稳定构型及其磁结构。研究结果表明, 锶铁氧体为亚铁磁性, 与前期的研究结果相吻合。通过比较GGA和GGA+U计算方法, 发现U值的选取对体系的电子结构和原子磁矩有显著影响。当U值为3.7 eV时, 体系由金属性转变为自旋向上带隙为1.71 eV的半导体。原胞总磁矩为40 μ_B。对于Mn替换掺杂的SrFe_12-xMn_xO₁₉体系, 通过不同占据位能量比较, 当单个Mn原子替换(x=0.5)时, Mn离子优先占据Fe (12k)位置; 而当两个Mn原子替换Fe原子(x=1.0)时, 两个Mn分别占据Fe (12k)和Fe (2a)位置。Mn掺杂对锶铁氧体的结构影响较小, 但对于体系的总磁矩和电子结构有较明显的影响。在Mn含量x=0.5和x=1.0时, 自旋向上带隙值分别降低到0.85和0.59 eV, 原胞的总磁矩为39和38 μ_B。本研究可为实验研究提供理论指导。     

Impurity-Induced Magnetization of Layered Semiconductor LaCuSeO as Predicted from First-Principles Calculations

Using the ab initio FLAPW-GGA method, we systematically examined the effects of various doping types on the magnetic and electronic properties of the layered semiconductor LaCuSeO. Magnetization of LaCuSeO induced by 3d impurities (M=Mn, Fe, and Co) in the Cu sublattice was found as a result of spontaneous spin polarization of M?3d _???? impurity bands. Partially filled M?3d _?? bands lie in the gap of LaCuSeO and are crossed by E _F , whereas M?3d _?? bands are admixed to the top of the valence band resulting in a magnetic half-metallic behavior of these doped systems. The other possible types of doping (i.e., introduction of arsenic atoms into Se sublattice as well as the introduction of N or F atoms into an oxygen sublattice) remain the semiconductor LaCuSeO non-magnetic, but result in the transition into metallic-like state.     

Electronic structure and half-metallic property of Mn-doped β-SiC diluted magnetic semiconductor

Using ab initio ultrasoft pseudopotential plane wave method, the effect of doping concentration of Mn on the magnetic properties of β-SiC (SiC:Mn) was quantitatively investigated. It is found that the SiC:Mn shows stable ferromagnetism, and the total magnetic moment of SiC:Mn depends on the substitution site of Mn in the SiC lattice. Using the density of states calculation, it is shown that SiC:Mn has half-metallic properties for selected doping concentrations of 1.56, 3.13 and 6.25%, irrespective of substitution site. The conduction electron mobility of SiC:Mn_C was expected to be higher than that of SiC:Mn_Si. On the contrary, SiC:Mn_Si has a wider spin band gap compared to SiC:Mn_C. It is predicted that SiC with 12.5% Mn doping represents desirable characteristics for realizing spintronic devices, which include stable ferromagnetism, half-metallic properties, fast electron mobility and a wide spin band gap.     

First-principles calculations on structural,magnetic and electronic properties of oxygen doped BiF3

First-principles calculations based on density function theory within the generalized gradient approximation (GGA) have been carried out to investigate the effects of O doping on the structural, magnetic and electronic properties of BiF₃. Based on the calculated cohesive energies, O impurities prefer substituting F atom at tetrahedral sites (0.25, 0.25, 0.25). And the geometry of BiF₃ changes little due to similar radius of O and F atoms. By analyzing density of states (DOS) of Bi₄OF₁₁ (II)_, it has been found that Bi₄OF₁₁ (II) presents magnetic character and half-metallic state, implying its potential applications in Li-ion batteries. Finally, the character of bond in Bi₄OF₁₁ (II) was discussed by analysis of charge density and bader charge. The result shows that O doping weakens ionic bond in BiF₃.     

Electronic and magnetic properties of nitrogen-doped finite-size and open-ended zigzag carbon nanotubes

Density functional calculations have been used to investigate the effect of the N doping on the electronic and magnetic properties of finite-size and open-ended zigzag carbon nanotubes (CNT). The carbon atoms at the edge site are more easily replaced by N atoms energetically, compared to other sites. The single N atom substitution can reduce the magnetic moment of edge carbon atoms near the doping site and result in the suppression of spin polarization. Such spin suppression is independent of tube diameter and it can be ascribed into perturbation of the π/π^* state localized at the doped edge. At low N-doping concentrations, the finite-length zigzag CNTs can maintain an antiferromagnetic (AFM) ground state, but the conversion from AFM to a nonmagnetic state can occur at high impurity concentrations. More interestingly, the tunable electronic properties from the half-semiconducting to semiconducting state can be realized in these N-doped finite-size and open-ended CNTs if subjected to a variably external electric field along the tube axis.     

Investigation on structural, electronic, and magnetic properties of Mn-doped Ga12N12 clusters

The structural, electronic, and magnetic properties of Ga₁₂N₁₂ cluster doped with monodoped and bidoped Mn atoms have been investigated based on the density functional theory. Substitutional, exohedral, and endohedral configurations are considered. The substitutional doping is found to be most favorable for monodoped clusters, while the bidoped clusters prefer the exohedral isomers. For all the isomer, the magnetic moment is mainly derived from 3d orbitals of Mn atom. The exohedral and endohedral bidoped Ga₁₂N₁₂ clusters all favor antiferromagnetic state.     

Enhancing linearity in I–V characteristics by B/N doping in graphene for communication devices

To explore communication applications, a study towards achieving linearity in the I–V characteristics through increasing concentrations of Boron (B) / Nitrogen (N) doping on pristine graphene sheet is investigated. Individual B/N doping of 6.25, 12.50, 18.75 and 25% has been done in the same sub lattice using Density Functional Theory (DFT) along with Non Equilibrium Greens Function (NEGF) calculations. The modification in the electronic and transport properties of graphene sheet are also investigated. In comparison to the variation of band gap from 0.35 to 1.183 eV and 0.36 to 1.149 eV for B and N respectively, an insignificant variation in effective mass is reported. Apart from linearity, variation in conductance in doped structures is seen. B doping increases conductivity and yields ON current of 610 µA while N doping gives ON current of 310 µA for maximum doping concentrations. In this work, the sustained carrier mobility and high gain linear characteristics of doped graphene obtained will help to utilise a graphene channel for different communication device applications.     

Magnetism in non-transition-metal doped CdS studied by density functional theory

The electronic structure of non-transition-metal element (Be, B, C, N, O and F)-doped CdS is studied based on spin-polarized density function theory within the generalized gradient approximation. Our results show that the substitutional Be, B and C for S in CdS induces spin polarized localized states in the gap or near the valence band and generates local magnetic moments 2.0 μ_B, 3.0 μ_B and 2.0 μ_B with one dopant atom, respectively. Whereas doping with N, O and F in CdS does not induce spin polarization. It is found the magnetic states in these systems are related to the difference between the electronegativities of the dopant and the anion in the host. Long-range ferromagnetic coupling may occur in Be, B and C-doped CdS, which can be explained by the p–d exchange-like p–p coupling interaction involving holes.     

Magnetism and Optical Property of Mn-Doped Monolayer CrSi<Subscript>2</Subscript> by First-Principle Study

We investigate magnetism and optical properties of intrinsic and Mn-doped monolayer CrSi₂ using the first-principle methods based on density functional theory. The results show that both monolayer CrSi₂ sheets are metallic and ferromagnetic (FM) that hold promise in future 2D magnetic devices. In spite the slight reduction of the total magnetic moment of system after Mn doping in monolayer CrSi₂, the formation energies of ferromagnetic CrSi₂ are also reduced. So, Mn doping in monolayer CrSi₂ can have more promising applications in spintronics and magnetic storage. The optical properties of monolayer CrSi₂, including the absorption spectra, reflectivity, refractive index, loss function and dielectric function are also calculated. The intensity of reflectivity in far-infrared ranges is enhanced and real part n of refractive index decreases after Mn doping. The real part n of the refractive index is nearly constant (?1) beyond 13 eV indicating that monolayer CrSi2 is vacuum like and fully transparent.     

Electrical properties/Doping efficiency of doped microcrystalline silicon layers prepared by hot-wire chemical vapor deposition

Microcrystalline silicon (μc-Si) doped films were prepared by hot-wire chemical vapor deposition (HWCVD) to investigate the doping efficiency. The incorporation probability of different dopant atoms into the solid-phase is always increasing with the doping gas concentrations, but very different for the doping gases used: trimethylboron (TMB), boron trifluoride (BF₃) and phosphine (PH₃). At the same doping gas concentration in the process gas the incorporation of phosphorus atoms into the solid μc-Si phase is much larger than that of boron atoms with respect to the dissociation probability of the doping gases. The electron and hole concentrations, estimated from Hall measurements, are directly related to the solid phase concentration of the doping atoms and independent of the type of dopant and the doping gas used. This results in an equal doping efficiency of about 20 % for the incorporated B and P atoms in doped HWCVD μc-Si films. For the dopant atom concentration regime investigated the doping efficiency of B atoms is in good agreement with corresponding PECVD doping efficiencies however, the doping efficiency of P atoms is considerably lower for our n-doped films.     

Controllable,Wide‐Ranging n‐Doping and p‐Doping of Monolayer Group 6 Transition‐Metal Disulfides and Diselenides

Developing processes to controllably dope transition‐metal dichalcogenides (TMDs) is critical for optical and electrical applications. Here, molecular reductants and oxidants are introduced onto monolayer TMDs, specifically MoS₂, WS₂, MoSe₂, and WSe₂. Doping is achieved by exposing the TMD surface to solutions of pentamethylrhodocene dimer as the reductant (n‐dopant) and “Magic Blue,” [N(C₆H₄‐p‐Br)₃]SbCl₆, as the oxidant (p‐dopant). Current–voltage characteristics of field‐effect transistors show that, regardless of their initial transport behavior, all four TMDs can be used in either p‐ or n‐channel devices when appropriately doped. The extent of doping can be controlled by varying the concentration of dopant solutions and treatment time, and, in some cases, both nondegenerate and degenerate regimes are accessible. For all four TMD materials, the photoluminescence intensity; for all four materials the PL intensity is enhanced with p‐doping but reduced with n‐doping. Raman and X‐ray photoelectron spectroscopy (XPS) also provide insight into the underlying physical mechanism by which the molecular dopants react with the monolayer. Estimates of changes of carrier density from electrical, PL, and XPS results are compared. Overall a simple and effective route to tailor the electrical and optical properties of TMDs is demonstrated.     

Effect of Dopant Concentration on Electronic and Magnetic Properties of Transition Metal-Doped ZrO<Subscript>2</Subscript>

Electronic and magnetic properties of the bulk monoclinic phase of pure and doped zirconia (ZrO₂) are calculated. Calculations have been performed using density functional theory based Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. We have considered substitutional doping of transition metals (TM) V, Cr, Mn and Fe in zirconia corresponding to concentrations ranging from 3.125 to 25 %. Our results show that Cr, Mn-, and Fe doped oxides are half-metallic and the half-metallicity remains intact on reducing the dopant concentrations. The total magnetic moment is mainly due to d states of TM atoms and small induced magnetic moment exists on other nonmagnetic atoms as well. Also as the oxygen vacancy influences the performance of oxidebased devices, therefore we model the influence of oxygen vacancy on the magnetic moments in pure and doped zirconia. Our results show that pure oxide system remains nonmagnetic even on the introduction of oxygen vacancy whereas magnetic moment values for TM doped oxide changes. In the presence of oxygen vacancy, the total magnetic moment of V-, Cr-, and Mn doped cell increases whereas it decreases for Fe doping. This shows that oxygen vacancy (V _O) has a strong influence on the magnetic properties of the doped oxides. The results may be useful for further study on TM doped ZrO₂ system.     

Study of Electronic and Magnetic Properties of Zn1−x M x O (M = Mn and Cr) by ab initio Calculations

The electronic structure and ferromagnetic properties of Zn_1?x M _x O (M = Mn and Cr) have been investigated by using the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA). The half-metal behavior is observed for different doping concentrations. The gap energies are deduced for different dilution x values. The magnetic moment of each atom and the total magnetic moment are computed. A special attention is paid to the discussion of the mechanism of ferromagnetism in these components.     

Structural, Electronic and Magnetic Properties of Zinc-Blende Ga1−x TM x N (TM = Cr, Mn, Fe, V)

In this paper, we present a theoretical study of structural, electronic and magnetic properties for zinc-blende Ga_1?x TM _x N(TM = Cr, Fe, Mn, V) using the full-potential augmented plane wave (FP-APW) method with local-spin density approximation (LSDA). We have analysed the dependence of structural parameters values on the composition x in the range of x=0.25, x=0.50. Also, the role of p–d hybridisation is analysed by partial (PDOS) and total density of states (TDOS). The magnetic moment of Ga_1?x TM _x N has been studied by increasing the concentration of TM atom. The TM atom is the most important source of the total magnetic moment in these alloys, while the contributions from Ga and N are minor. In addition our results verify the half-metallic ferromagnetic character of TM doped GaN.     

Ni定位掺杂4H-SiC(001)磁性与光学性质的研究

采用基于密度泛函理论的第一性原理研究了4H-SiC(001)定位掺杂Ni的磁性,结果表明相对于掺杂前表面悬挂键的存在使体系具有弱磁性,Ni定位取代Si位置后得到的体系更加稳定。对比分析了Ni定位取代不同数量的C与Si原子后,得出取代C原子比取代Si原子得到的磁矩大,而且奇数倍的取代较偶数倍取代得到的磁矩大。定位取代一个C与一个Si比单独取代一种原子得到的磁矩大,因此从稳定性与磁性方面考虑C与Si同时取代是最好的掺杂选择。在导电性方面,随着Ni掺杂原子数量增加光电导相应增加。     

On the appearance of induced magnetic moment of β-FeSi2 by doping halogen or oxygen atoms

We have theoretically examined whether magnetic moment of iron atom can be induced or not when highly electronegative elements such as halogen or oxygen atoms are doped. Based on the impurity Anderson model, we evaluated the green function of d electrons. Through the analysis of green function, it is disclosed that a magnetic moment can be induced by impurity potential caused from doping elements, although intrinsic β-FeSi₂ is non-magnetic. In particular, high electronegativity of doping atoms and/or strong Coulomb repulsive interaction between conduction electrons and doped atoms easily induce magnetic moment from non-magnetic state. In the viewpoint of chemical bonding, such an induced magnetic moment appears as a result of decomposition of covalent FeSi bonds by a strong electronegative impurity potential, because the broken bonds create the unpaired 3d electrons.     

Scalable Substitutional Re-Doping and its Impact on the Optical and Electronic Properties of Tungsten Diselenide

Reliable, controlled doping of 2D transition metal dichalcogenides will enable the realization of next-generation electronic, logic-memory, and magnetic devices based on these materials. However, to date, accurate control over dopant concentration and scalability of the process remains a challenge. Here, a systematic study of scalable in situ doping of fully coalesced 2D WSe₂ films with Re atoms via metal–organic chemical vapor deposition is reported. Dopant concentrations are uniformly distributed over the substrate surface, with precisely controlled concentrations down to <0.001% Re achieved by tuning the precursor partial pressure. Moreover, the impact of doping on morphological, chemical, optical, and electronic properties of WSe₂ is elucidated with detailed experimental and theoretical examinations, confirming that the substitutional doping of Re at the W site leads to n-type behavior of WSe₂. Transport characteristics of fabricated back-gated field-effect-transistors are directly correlated to the dopant concentration, with degrading device performances for doping concentrations exceeding 1% of Re. The study demonstrates a viable approach to introducing true dopant-level impurities with high precision, which can be scaled up to batch production for applications beyond digital electronics.