立方半导体中双空位态的电子结构(Ⅳ)——GaAs,GaP中双空位态的电子结构

利用文献[1]中的基本方程组和Vogl等人的紧束缚哈密顿量,计算了以GaAs,GaP为代表的极性半导体中理想双空位的A₁,E态的波函数。计算表明,理想双空位态的波函数在靠近As空位或P空位处的三个Ga原子处具有最大几率,波函数的其余部分随着离缺陷距离的增加而缓慢非单调地递减。 关键词：     

An investigation of the Knight shifts in LiMg alloys

The lithium Knight shift has been measured throughout the full range of LiMg alloys and the magnesium Knight shift has been measured for magnesium rich LiMg alloys. Calculations of the Knight shifts have been performed using the coherent potential approximation to find the partially average Green's functions and taking some account of the Bloch character of the electron wavefunctions. The results are in good agreement with the experiment.     

半导体深能级波函数在Bloch空间的分布特征

在Koster-Slater格林函数以及中心原胞缺陷势近似的基础上第一次给出并讨论了Si,GaAs,GaP深能级波函数在Bloch空间的分布特征。并指出,对于一定能带数目的近似晶体模型,计算深能级波函数的收敛性比计算深能级能量的收敛性要快。 关键词：     

Spin–orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals

Spin–orbit coupling of electrons with the crystal lattice plays a crucial role in materials without inversion symmetry, lifting spin degeneracy of the Bloch states and endowing the resulting nondegenerate bands with complex spin textures and topologically nontrivial wavefunctions. We present a detailed symmetry-based analysis of the spin–orbit coupling and the band degeneracies in noncentrosymmetric metals. We systematically derive the semiclassical equations of motion for fermionic quasiparticles near the Fermi surface, taking into account both the spin–orbit coupling and the Zeeman interaction with an applied magnetic field. Some of the lowest-order quantum corrections to the equations of motions can be expressed in terms of a fictitious “magnetic field” in the momentum space, which is related to the Berry curvature of the band wavefunctions. The band degeneracy points or lines serve as sources of a topologically nontrivial Berry curvature. We discuss the observable effects of the wavefunction topology, focusing, in particular, on the modifications to the Lifshitz–Onsager semiclassical quantization condition and the de Haas-van Alphen effect in noncentrosymmetric metals.     

Bloch electrons in a magnetic field

A complete set of basis functions for the expansion of the wavefunction of a Bloch electron in a uniform magnetic field is derived. In the empty lattice limit this set gives the appropriate Landau free-electron wavefunctions, contrary to the Roth functions which in that limit are plane waves.     

Transition metal impurities in silicon: New defect reactions

Recent investigations on transition-metal impurities in silicon emphasizing the effect of the combined diffusion of two transition metals are presented and briefly discussed. The electronic properties and basic thermal kinetics are analysed by DLTS. The conversion of a Pd-related multivalent defect atE _c-0.35 eV andE _c-0.57 eV to the Pd-related defect atE _c –0.22 eV is observed, and a Pd-Fe complex level atE _c –0.32 eV is identified. The annealing characteristics of the multivalent Rh levels atE _c-0.33 eV andE _c-0.57 eV are observed, and used to analyse the influence of prior Rh doping on the Au diffusion. A complex formed by the codiffusion of Au and Cu is observed atE _v+0.32eV andE _v+0.42 eV, and shown to exhibit bistable behavior as does a similarly produced Au-Ni complex observed atE _v + 0.35 eV andE _v+0.48 eV.     

Si中深能级T2对称波函数理论

木文在文献[5,6]所发展的在位缺陷势格林函数方法基础上,进一步讨论Si中短程缺陷势引入的T₂对称深能级波函数性质。第一次给出了Si禁带中部很宽能量范围之内T_2对称波函数的完整数据。波函数在缺陷最近邻四个格点的占据几率P₁有一高达50％以上峰值。该部分相当于四个最近邻格点指向缺陷的杂化轨道准悬键的T₂组合。第0,1,2三个格点壳层波函数占据几率之和约为70％。波函数其余部分较平缓地分布在一相当大空间。波函数的以上特征与禁带中部能量位置关系不灵敏。但在靠近导带E_c和满带E_v的浅能量区,以上P₁峰趋于消失,整个波函数在空间的分布趋于平坦。Si空位在禁带引入一个T₂对称深能级,位于E_v以上0.51eV处。 关键词：     

Vacancy induced changes in the electronic structure of titanium carbide—I. Band structure and density of states

Results of a self-consistent “Augmented Plane Wave” (APW) band-structure calculation are presented for substoichiometric titanium carbide with 25% vacancies on the carbon sublattice sites (TiC_{0 75}) assuming a model structure with ordered vacancies Comparison with an earlier APW study on stoichiometric TiC reveals that the carbon vacancies induce two pronounced peaks in the density of states (DOS), 0.4 eV below and 0.8 eV above the Fermi energy E_γ, thus forming electronic states in a region where the DOS for stoichiometric TiC exhibits a minimum So-called “vacancy states” with an important amount of charge on the vacancy site are found to be derived from Ti 3d states extending into the vacancy muffin tin sphere An angular momentum decomposition with respect to the center of the vacancy muffin tin sphere shows that the s character predominates for the occupied and the p character for the unoccupied “vacancy states” The theoretical findings explain features near E_γ, observed in recently published X-ray emission spectra Furthermore, we find a slight increase of electronic charge in the carbon muffin tin spheres as compared with stoichiometnc TiC.     

Optical anisotropy of orthorhombic InS

The optical anisotropy of InS single crystals in the range of photon energy from 1.8 to 3.5 eV has been studied by absorption, electroreflectance and wavelength-derivative reflectance measurements. These systematic optical measurements for the polarizations, E//a and E//b, have revealed that the transition at the fundamental absorption edge of InS is allowed for E//b, and there exist three distinct doublet transitions having different selection rules in the photon energy region from 2 to 3.5 eV; Bo and B^'₀doublet allowed only for E//b, A₀ and A^'₀ allowed only for E//a, and E₁ and E^'₁ allowed for both polarizations. The observed results are discussed based on the anisotropic nature of two chemical bonds in InS, cation-cation and cation-anion.     

Fundamental optical properties of α-RuCl3

The fundamental optical properties in the paramagnetic phase of α-RuCl₃ are studied at different temperatures in the photon energy interval 0.03 to 10 eV. Infrared reflectivity spectra show a transverse optical frequency at 0.038 eV (32 μm) for an E_u mode (E⊥c, in plane atomic displacements). The absorption spectra in the energy range 0.2 to 1 eV reveal three bands (0.29, 0.51, 0.71 eV) attributed to d-d electronic transitions. Reflectance and thermo-reflectance measurements indicate the onset of the charge-transfer transitions at 1.1 eV and show structure at 1.85, 2.55, 3.05, 4.5 eV. The marked reflectivity peak at 5.2 eV is probably related to p(Cl) → s(Ru) band-to-band transitions.     

CdS/CdTe薄膜太阳电池的深能级瞬态谱和光致发光研究

用深能级瞬态谱和光致发光研究了无背接触层的CdS/CdTe薄膜太阳电池的杂质分布和深能级中心.得到了净掺杂浓度在器件中的分布.确定了两个能级位置分别在E_V+0365 eV和E_V+0282 eV的深中心,它们的浓度分别为167×10¹² cm^-3和386×10¹¹ cm^-2,俘获截面分别为143×10^-14cm²和153×10^-16cm².它们来源于以化学杂质形式存在的Au和（或）Te_Cd^-复合体,或与氩氧气氛下沉积CdTe时的氧原子相关. 关键词： 深能级瞬态谱 光致发光 CdS/CdTe太阳电池     

Quantum chaos

A quantum system which is allowed to interact with its boundary in a self-consistent way is shown to exhibit chaos. We conjecture that in general genuine wave chaos (decaying autocorrelation functions, exponential sensitivity of wavefunctions to initial wavefunction configurations) can be obtained whenever a wavefield is allowed to modify its confining boundaries in a self-consistent way. We suggest to test this conjecture in the acoustic regime.     

Deep level defects in gamma-ray irradiated ge doped with pb or sn

Abstract

Deep level transient spectroscopy has been used to investigate the electrical properties of deep defect states in γ-ray irradiated Ge doped with the isoelectronic elements Pb or Sn. Three deep levels are observed in the irradiated Pb-doped Ge (E_v +0.28 eV, E_c ?0.33 eV, E_c ?0.39 eV) and two deep levels observed in the Sn-doped Ge (E_v + 0.19 eV, E_c ?0.15 eV). For the same γ-ray irradiation doses, Ge crystals grown from graphite crucibles and doped with Pb or Sn shows about two-thirds the total density of deep level defects observed in undoped Ge grown from synthetic quartz crucibles. All of the defect states observed were removed by a 1 hour, 250°C thermal anneal, and all but the E_c ?0.39 eV state in the Pb-doped material were neutralized by exposure to a low pressure atomic hydrogen plasma.     

Electrical and optical properties of electron-irradiated ZnGeP2

Conclusions and summary The following conclusions are drawn from the reported study:The electrophysical properties of ZnGeP₂ crystals and their optical transparency in the range hG are attributable to the presence of a density-dominant (10¹⁷–10¹⁹ cm^–3) deep [E_v+(0.5–0.6) eV] growth defect associated predominantly with Zn vacancy clusters.Irradiation by high-energy electrons induces a shift of the Fermi level in the direction of E_G/2 and increases the resistivity of ZnGeP₂ to values of approximately 10¹² ·cm at 300 K. Irradiation with high-energy electrons is an effective technique for the optical bleaching of p-ZnGeP₂. The reversible modification of the optical absorption spectra of p-ZnGeP₂ in connection with irradiation and subsequent annealing indicates that the absorption step in the vicinity of h 0.6 eV is not attributable to light absorption by germanium inclusions, but to optical transition from the valence band to the growth-defect level E_v+(0.5–0.6) eV.Enhancement of the optical transmissivity of p-ZnGeP₂ in the range hG can be achieved in two wayss 1) as the result of a decrease in the density of centers with the level E_v+0.6 eV by variation of the growth conditions or subsequent annealing; 2) by shifting the Fermi level above the energy position E_v+0.6 eV through the irradiation-induced injection of compensating donor centers.The injection of radiation defects is an effective technique for controlling the electrical and optical parameters of the compound ZnGeP₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 122–130, August, 1986.     

Global predictions of T2 symmetric deep level wavefunctions in semiconductors

Numerical results of T₂ symmetric SP₃ bonded deep level wavefunctions due to short range defect potentials in Si, Ge, GaAs and InP are presented. The general features of defect wavefunctions are insensitive to either the band structure of the host of defect energy level. The total occupation probability of wavefunction located on 0 . 1 . 2 shells around the defect center is about 60–85%. This part of wavefunction may be expressed in several simple symmetric combinations of SP³ hybrid orbitals. The rest part of the wavefunction extends diversely over a wide range of space.     

Electronic structure and optical properties of CdWO4 with oxygen vacancy studied from first principles

The electronic structures, dielectric functions and absorption coefficient of both perfect CdWO₄ crystal (CWO) and the CWO crystal containing oxygen vacancy (CWO: V _O) have been studied using the CASTEP code with the lattice structure optimized. The calculated total density of states (TDOS) of CWO: V _O indicates that the oxygen vacancy would introduce a new electronic state within the band gap compared with that of perfect CWO. The dielectric functions are calculated since the imaginary part of the dielectric function can reduce the optical absorption of a certain crystal, and then the absorption coefficient is calculated. The calculated absorption spectra show that CWO: V _O exhibits two absorption bands in the ultraviolet and visible region, peaking at about 3.0 eV (413 nm) and 3.5 eV (354 nm), respectively, which are in agreement with the experimental results showing that the yellow CWO has two optical absorption bands in this region peaking at around 350 nm and 400 nm respectively. It can be concluded that oxygen vacancy causes these two absorption bands. The calculations also indicate that the optical properties of CWO exhibit anisotropy, and can be explained by the anisotropy of the crystal lattice.     

Synchrotron reflectivity spectra and the optical properties of CuGaS2 crystal

For a CuGaS₂ crystal, the polarized spectra of complete sets of optical functions in the energy range of 0 to 24 eV are obtained for the first time. The calculations are performed using synchrotron reflectivity spectra for E ∥ c and E ⊥ c polarizations in the energy ranges of 0 to 24 eV and of 1 to 5 eV by means of computer programs using the Kramers-Kronig relations. The main features of the spectra of permittivity, characteristic electron loss, and other optical functions are determined. The band maximum energies for the volume and surface plasmons are obtained, and their independence from the type of polarization is found.     

Photoluminescence and capacitance transients in highly Mg-doped GaN

Behaviors of the photoluminescence blue-band and near-bandgap peak and the relevant thermal ionization energies of the shallow and deep Mg-related acceptors have been studied, respectively. The 2.989 eV blue-band is attributed to the deep donor–acceptor-pair transitions involving a deep Mg-related acceptor at E_v+0.427 eV. The blueshift with increasing excitation power is explained by variation in the contribution of close and distant donor–acceptor-pairs to the luminescence. The redshift with increasing temperature results from thermal release of carriers from close donor–acceptor-pairs. The 3.26 eV near-bandgap peak is attributed to the shallow donor–acceptor-pair transitions involving a shallow Mg-related acceptor at E_v+0.223 eV. The relevant thermal ionization energies of the shallow and deep Mg-related acceptors, being about E_v+0.16 and E_v+0.50 eV, are determined from deep-level transient Fourier spectroscopy measurements. Received: 11 July 2001 / Accepted: 9 August 2001 / Published online: 2 May 2002     

Iron-related deep levels in silicon

Deep levels in iron-doped p-Si are investigated by means of capacitance transient spectroscopy. Five Fe-related defects are observed in suitably prepared samples. Rapid quenching produces interstitial Fe_i and FeB, which give rise to levels at E_v + 0.43 eVand 0.10 eV, respectively. Three further levels at E_v + 0.33 eV, E_v + 0.40 eV and E_v + 0.52 eV are caused by slower quenching rates. The concentration of E_v + 0.33 eV in slowly cooled Czochralski-grown Si strongly exceeds the concentration in similarly treated float-zone Si.     

An interpretation of dlts spectra of Al/Si3N4/ultrathin SI/GaAs structures — Effect of quantum well or interface states?

We discuss DLTS andC-V measurements on Al/Si₃N₄/Si(2nm)/n-GaAs (≈ 5×10¹⁷ cm^?3) structures. Three discrete deep traps superimposed on a U-shaped interface-state continuum have been identified, with respective thermal energies:E _c?0.53 eV,E _c?0.64 eV, andE _v+0.69 eV. The second one (0.64 eV) is presented as an electric field sensitive level, its enhanced phonon-assisted emission resulting in a rapid shift of the corresponding DLTS peak to lower temperatures, as the applied (negative) reverse bias voltage increases. An interpretation through emission from the quantum well, introduced by means of the intermediate ultrathin Si layer, has failed.