GaAs_(1-x)P_x中3d过渡金属杂质的电子结构

本文推广了Vogl等人的理论方法,将其用于对GaAs_(1-x)P_x中3d过渡金属杂质电子结构的研究。文中就不同的合金成份x,预言了不同3d杂质的受主能级、施主能级、局域电荷和自旋密度。理论预言与实验数据符合,并且揭示了它们的主要化学趋势。文中还就与理论和实验结果变化趋势有关的物理机制进行了讨论。     

流体静压下AlAs合金化的GaAs中Cr~(2+)(3d~4)杂质态的理论研究

本文将一个自旋极化的紧束缚格林函数方法发展到用于流体静压和合金下GaAs:Cr~(2+)(3d~4)杂质态的研究。文中给出了GaAs:Cr~(2+)系统~5E激发态和~5T_2基态受主能级随压力和AlAs合金成份的变化趋势。理论证明了在一定的压力和Al成份下,~5E激发态将从导带底进入带隙,原在通常条件下观察不到的~5E→~5T_2发光就能被观察到。理论预言与实验结果符合得很好。理论还预言:当GaAs与GaP合金的时候,类似的发光过程也能在一定的合金成份下观察到,这一预言有待于实验证实。     

KⅡ离子3p光吸收谱的MQDT分析

利用多通道量子数亏损理论对钾的一价离子的3p光吸收光谱进行了分析,计算并预言了80多个实验上未观察到的能级以及相应能级的朗德g因子,对于实验上未区分的能级做了重新的认定,预言了自电离区的3p5ns(1/2,1/2)n=17-21的能级,讨论了通道之间的干扰情况。     

Si中S~0/Se~0,S~0/Te~0和Se~0/Te~0对的电子结构

利用紧束缚近似下的格林函数方法,讨论了Si中硫属元素混对杂质(即 S~0/Se~0,S~0/Te~0和Se~0/Te~0)基态的电子结构。混对杂质在Si禁带中引入两个A_1能级,其中成键性的A_1能级位置在反键性的A_1能级之上。数值计算得到的混对杂质能级与实验符合得相当好。理论分析表明,在Si中测到的那些未定的比最近邻混对杂质能级更浅的能级 (S~0/Se~0(X_1),S~0/Te~0(X_1),Se~0/Te~0(X_1)…)不是由非最近邻位型的混对杂质引入的。本文还指出了一个极性分子放入Si晶体中,两个不同原子间s波函数的转移方向与通常极性分子相反,并讨论其物理原因。     

Fe XVII离子能级和振子强度的相对论多组态Dirac-Fock计算

本文用相对论多组态的狄拉克-福克(Dirac-Fock)(MCDF)近似方法计算了铁的类氖离子FeXVII的2p~53s,和3p和3d态的所有能级以及3s—3p,3p—3d跃迁的电偶极振子强度f值.理论计算的能级值同实验值的比较表明,使用MCDF方法计算类氖等电子序列的能级会得到与实验值符合得比较好的结果.因无实验数据可作比较,本文得到的振子强度值纯属理论预言值.     

Si中S0/Se0,S0/Te0和Se0/Te0对的电子结构

利用紧束缚近似下的格林函数方法,讨论了Si中硫属元素混对杂质(即S⁰/Se⁰,S⁰/Te⁰和Se⁰/Te⁰)基态的电子结构。混对杂质在Si禁带中引入两个A₁能级,其中成键性的A₁能级位置在反键性的A₁能级之上。数值计算得到的混对杂质能级与实验符合得相当好。理论分析表明,在Si中测到的那些未定的比最近邻混对杂质能级更浅的能级(S⁰/Se⁰(X₁),S⁰/Te⁰(X₁),Se⁰/Te⁰(X₁)…)不是由非最近邻位型的混对杂质引入的。本文还指出了一个极性分子放入Si晶体中,两个不同原子间s波函数的转移方向与通常极性分子相反,并讨论其物理原因。 关键词：     

硅中的过渡元素杂质能级

本文提出了半导体中过渡元素杂质的一个简单模型,用格林函数方法计算了硅中替代和间隙原子产生的杂质能级和波函数。发现两者的性质有很大的差别。替代原子只有当d原子能级V_d低于价带顶时才能产生杂质能级。它的波函数主要是悬键态,当能级靠近导带边时变成正键态。间隙原子只有当V_d高于价带顶时才能产生杂质能级。它的波函数主要是中心原子d态,当能级靠近导带边时变成弱反键态。最后定性地说明了过渡元素杂质能级的化学趋势和一些实验事实。 关键词：     

与闪电过程有关的NII离子能级寿命的理论计算

用相对论多组态DiracFock方法,系统地计算了与闪电过程有关的NII离子2p2,2s2p3,2p3s,2p3p,2p3d组态能级之间的辐射跃迁概率,并由此推算出这些组态的35个能级的寿命.计算中考虑了相对论效应、电子关联、延迟效应等重要贡献.与已有的理论计算比较,目前计算的结果更接近最新实验值.据此,进一步给出了2p3d3F能级寿命新的理论预言值     

(La1-xYx)2/3Ca1/3MnO3(x=0.195)系统中的磁电阻行为

本文实验上探讨了 (La1-xYx)2/3Ca1/3MnO3(x=0.195)窄带系统不同磁场下的磁电阻行为.实验表明,最大磁电阻效应随磁场增加而实质性提高,例如,7T磁场下最大磁电阻效应高达1.8×105%.同时,我们在远远低于半导体-金属转变温度下也观察到明显的磁电阻效应.文中就磁电阻的起因进行了讨论,特别是基于最近提出的自旋-极化子模型,对实验数据进行了定量的比较性分析,结果表明,该模型虽能预言实验的主要特征,但理论预言随磁场增加而明显偏离实验.     

C掺杂锐钛矿相TiO2吸收光谱的第一性原理研究

运用第一性原理,对C掺杂锐钛矿相TiO₂的电子结构进行了研究,从能带结构理论解释了C掺杂TiO₂吸收光谱的一些实验现象.发现在C掺杂后的锐钛矿相TiO₂的禁带宽度增大,并且在带隙中出现了杂质能级,这些杂质能级主要是由C 2p轨道上的电子构成的,它们之间是独立的,正是这些独立的杂质能级使TiO₂掺杂后可以发生可见光响应.价带上的电子可以吸收一定能量的光子跃迁到杂质能级,而杂质能级上的电子也可以吸收一定能量的光子跃迁到导带,所以从理论上可以计算出掺杂后的TiO₂在可见光范围内存在两个吸收边,与实验中所得到的现象相一致. 关键词： C掺杂 2')" href="#">锐钛矿TiO₂ 能带结构 吸收光谱     

流体静压下AlAs合金化的GaAs中Cr2+(3d4)杂质态的理论研究

本文将一个自旋极化的紧束缚格林函数方法发展到用于流体静压和合金下GaAs:Cr²⁺(3d⁴)杂质态的研究。文中给出了GaAs:Cr²⁺系统⁵E激发态和⁵T₂基态受主能级随压力和AlAs合金成份的变化趋势。理论证明了在一定的压力和Al成份下,⁵E激发态将从导带底进入带隙,原在通常条件下观察不到的⁵E→⁵T_关键词：     

Ab initio study of the EFG tensor at Cd impurities in Sc2O3 semiconductor

We present an ab initio study of diluted Cd impurities localized at both cation sites of the semiconductor Sc₂O₃. The electric-field-gradient (EFG) tensor at Cd impurities located at both cationic sites of the host structure was determined from the calculation of the electronic structure of the doped system. Calculations were performed with the full-potential augmented-plane wave plus local orbitals (APW+lo) method within the framework of the density functional theory. We studied the atomic structural relaxations and the perturbation of the electronic charge density induced by the impurities in the host system in a fully self-consistent way. We showed that the Cd impurity introduces an increase of 8% in the nearest oxygen neighbors bond-lengths, changing the EFG sign for probes located at the asymmetric cation site. The APW+lo predictions for the charged state of the Cd impurity were compared with EFG results existent in the literature, coming from time-differential γ–γ perturbed-angular-correlations experiments performed on ¹¹¹Cd-implanted Sc₂O₃ powder samples. From the excellent agreement between theory and experiment, we can strongly suggest that the Cd acceptor impurities are ionized at room temperature. Finally, we showed that simple calculations like those performed within the point-charge model with antishielding factors do not correctly describe the problem of a Cd impurity in Sc₂O₃.     

Transport properties of HTSC + Ba(Pb, Met)O3 composites as functions of the electrical and magnetic characteristics of nonsuperconducting components

Composites simulating a network of weak metallic links and consisting of a classic 1–2–3 HTSC and a BaPbO₃ metal oxide with incorporated Sn, Ni, and Fe impurities have been prepared. Experimental resistivity, magnetic, and Mössbauer studies of the BaPb_0.9Met_0.1O₃ nonsuperconducting components are presented. The transport properties of the HTSC + BaPb_0.9Met_0.1O₃ composites have been investigated. The superconducting properties of the composites are observed to be suppressed, both when the carrier mean free path in nonsuperconducting components with tin impurities decreases, and as a result of an additional interaction of the magnetic moments of (Fe, Ni) impurities with the spins of supercurrent carriers. The experimental temperature dependences of the composite critical current are analyzed in terms of the de Gennes theory for the superconductor-normal metal-superconductor structures.     

Native defects and Pr impurities in orthorhombic CaTiO3 by first-principles calculations

Formation energies of native defects and Pr impurities in orthorhombic CaTiO₃ are explored using the first-principles calculations. The Ca vacancy (V_Ca), Ti vacancy (V_Ti) and Ca antisite (Ca_Ti) are found to be energetically preferable. The Ti antisite (Ti_Ca) and O vacancy (V_O) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO₃, Pr substituting for Ca (Pr_Ca) is likely to form under condition A in which CaTiO₃ is in equilibrium with CaO and O₂. Under condition B (TiO₂, CaTiO₃ and O₂ are in equilibrium), Pr_Ti defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO₃ are coincided with several different defects in Pr-doped CaTiO₃ reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca_1−xV_Ca(x/2)Pr_xTiO₃ is not the best for efficient red photoluminescence, which is realized via the experimental measurements.     

Electronic properties and deep level transient spectroscopy of CdS/CdTe thin film solar cells

It is well known that preparing temperatures and defects are highly related to deep-level impurities. In our studies, the CdTe polycrystalline films have been prepared at various temperatures by close spaced sublimation (CSS). The different preparing temperature effects on CdS/CdTe solar cells and deep-level impurities have been investigated by I--V and C--V measurements and deep level transient spectroscopy (DLTS). By comparison, less dark saturated current density, higher carrier concentration, and better photovoltaic performance are demonstrated in a 580oC sample. Also there is less deep-level impurity recombination, because the lower hole trap concentration is present in this sample. In addition, three deep levels, E_v+0.341 eV(H4), E_v+0.226 eV(H5) and E_C-0.147 eV(E3), are found in the 580oC sample, and the possible source of deep levels is analysed and discussed.     

Exchange mechanism of half-metallic ferromagnetism of TiO2 doped with double impurities: A first-principles ASW study

The electronic structure and ferromagnetic properties of rutile TiO₂ doped with double-impurities Ti_1−2xCr_xMn_xO₂ has been investigated using first-principles calculations within the density-functional theory (DFT) and the local density approximation (LDA), functional for treating the effects of exchange and correlation. They were performed using the scalar-relativistic implementation of the augmented spherical wave (ASW). The advantages of doping TiO₂ with double impurities instead of single impurities are the increase of the total moment of the system and the exhibition of the half-metallic ferromagnetic nature in Cr- and Mn-doped TiO₂ rutile. These behaviors are due to the hybridization of Cr 3d states and nearest-neighboring O 2p states. The spin-spin interaction between magnetic impurities examined by the total energy between parallel and antiparallel aligned states indicated that the Cr and Mn impurities are energetically favorable to be parallel coupled, which mean that the ferromagnetic state is more stable than the ferrimagnetic one. We proposed a bond magnetic polarons (BMP) model, based on localized carriers, to explain the mechanism of ferromagnetism in these systems.     

钪原子的自电离里德伯能级3d4s(1D2)nf2 D3/2,3d4s(1D2)nf2 F5/2和3d4s(1D2)np2 D3/2<

在多通道量子亏损理论框架下,利用相对论多通道理论,分别在冻结实近似和考虑偶极极化下计算钪原子的J^π=(3/2)^-,(5/2)^-的三个收敛于 3d4s(¹D₂)的自电离里德伯系列的能级.对3d4s(¹D₂)np²D_3/2和3d4s(^{1 关键词： 相对论多通道理论 多通道量子亏损理论 电子-电子关联 自电离里德伯系列}     

Coexistence of paramagnetism and ferromagnetism in Fe-TiO2 nanoparticle

Magnetic properties of pure and Fe doped rutile TiO₂ and TiO_2-ε are investigated using the first principle density functional theory. The results show that the considered systems are ferromagnetic. Furthermore, the origin of ferromagnetism is discussed and it is found that the double exchange and super-exchange are the main interactions in these compounds. Based on the calculations, the magnitude of the magnetic moment depends on the concentration of impurities and oxygen vacancies and the largest magnetic moment corresponds to the Fe_xTi_1-xO_2-ε. Moreover, using a model based on the bound magnetic polarons, the coexistence of ferromagnetic and paramagnetic phases can occur in Fe_xTi_1-xO₂ containing different impurity ions such as Fe⁺² and Fe⁺³ with different Curie temperatures. The finding may presents the potential application of the considered system as diluted magnetic semiconductor.     

Energy levels and crystal-field analysis of Tm in YAl3(BO3)4 crystals

The electronic structure of the Tm³⁺ in YAl₃(BO₃)₄ crystals has been investigated by means of low temperature absorption and emission spectroscopy in the 5000-30,000 cm⁻¹ range. The assignment of the lines composing the observed manifolds to transitions between the Stark levels of Tm³⁺ is complicated by the presence of extra features having different origins. The energy levels scheme of the doping ion has been compiled after a careful analysis of the spectra by reproducing the observed transitions by means of theoretical calculations based on a Hamiltonian, including the free ion and the crystal field (CF) terms. The agreement between experimental and calculated energy values was reasonably good, the overall r.m.s. deviation being 16 cm⁻¹. The resulting CF parameters have been tabulated and compared with those reported in literature for other rare earth ions doped in YAB. The analysis of trends observed along the lanthanide series evidences some inconsistencies and the necessity of a systematic investigation of these systems.     

Electric-field gradients at Ta impurities in Sc2O3 semiconductor

In this work we present an ab initio study of Ta-doped Sc₂O₃ semiconductor. Calculations were performed at dilute Ta impurities located at both cationic sites of the host structure, using the Augmented Plane Wave plus Local Orbitals (APW+lo) method. The structural atomic relaxations and the electric-field gradients (EFG) were studied for different charge states of the cell in order to simulate different ionization states of the double-donor Ta impurity. From the results for the EFG tensor at Ta impurity sites and the comparison with experimental results obtained using the Time-Differential γ–γ Perturbed-Angular-Correlations technique we could determined the structural distortions induced by the Ta impurity and the electronic structure of the doped-semiconductor.