Co掺杂ZnO薄膜的局域结构和电荷转移特性研究

采用磁束缚电感耦合等离子体溅射沉积法在不同的氧气分压下制备了Zn_0.95Co_0.05O和Zn_0.94Co_0.05Al_0.01O薄膜.利用X射线吸收精细结构技术对薄膜O-K,Co-K和Co-L边进行了局域结构研究,结果表明：Co²⁺取代了四配位晶体场中的Zn²⁺而未改变ZnO的六方纤锌矿结构,高真空条件下制备的薄膜 关键词： Co掺杂ZnO 稀磁半导体 X射线吸收精细结构 共振非弹性X射线散射     

Charge carrier statistics of semiconductors containing defects with negative electronic correlation energy

The free charge carrier concentration as a function of the reciprocal temperature and the doping level [p(1/T)- andp(C)-characteristics] is calculated from the neutrality equation of a semiconductor containing positive or negativeU centers. The typical exponential laws and power laws of thep(1/T)- andp(C)-characteristics are given both for positive and negative correlation energy of the bound charge carrier pairs. Furthermore, the characteristics are evaluated differentially, in order to obtain criteria for the presence of negativeU centers in semiconductors.Work partly performed while on leave at the IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA     

Subband structure and kinetic characteristics of thin films of gapless semiconductors

The subband structure and effective masses values in quantum-sized film of gapless semiconductors are calculated. Isoenergy surfaces corrugation is taken into account. The results are shown to differ strongly from those got in spherical approximation. The complex subband structure results in a number of peculiarities of kinetic characteristics. Formally one-valley monopolar semiconductor film may behave either like a many-valley on like a bipolar semiconductor.     

Charge carrier energy disorder in polar amorphous organic thin films

We report Monte Carlo calculations of the charge carrier energy level disorder in polar amorphous organic solids arising from electrostatic interactions between polarizable molecular charge distributions. In contrast with previous reports in which the discrete molecular polarizibilities are modeled as a dielectric continuum having dielectric constant epsilon, our calculations take account of the molecular-scale polarization inhomogeneity. We find that the previously reported 1/epsilon scaling rule underestimates the charge carrier energy level disorder by more than a factor of 2 for typical values of epsilon. Such an underestimation strongly impacts the analysis of charge carrier transport in polar amorphous organic thin films, due to the strong dependence of the charge carrier mobility on the energy disorder.     

Electronic transport and carrier concentration in conductive ZnO:Ga thin films

Transparent and conductive Ga-doped ZnO (ZnO:Ga) films were post-annealed after sputter deposition, and their structural and electrical properties were investigated. Post-annealing led to an improvement of crystallinity along the [001] direction, but did not change lateral grain size. Therefore, carrier concentration and electron mobility of films were analyzed as a function of crystallinity. The electrical parameters were obtained with both optical reflectance based on the Drude free-electron model and the Hall method, and similar tendencies were observed within the two methods. Even though the lowest resistivity was demonstrated by the film annealed at 550 °C, the optimum values for carrier concentration and mobility were observed in films with different post-annealing temperatures.     

Polar optical phonon scattering limited free carrier absorption in semiconductors with ellipsoidal energy band structure

A formula is derived for the calculation of free carrier absorption in semiconductors with ellipsoidal energy band structure, including the effects of electron screening, when the dominant scattering mechanism is due to polar modes. Computational results are also presented which show that the magnitude of the FCA is significantly affected by the mass anisotropy coefficient.     

Ultrafast processes of photoinduced charge and energy transfer in nanostructural fullerene-metal films

The primary stages of photoinduced processes in tin-doped C₆₀ fullerene films have been studied using a femtosecond pump-probe technique with 150-fs laser excitation pulses (λ = 400 nm) and differential transmission and reflection probing in the 1100–1700 nm range. The relaxation dynamics strongly depends both on the metal-to-fullerene ratio in the film and on the mutual distribution (packing) of components in the nanocomposite material. The observed response signal dynamics is related to features in the charge carrier generation, energy transfer between fullerene molecules, and charge transport between metal and fullerene.     

Magnetic quantization of the energy states in heavily doped semiconductors with nonparabolic energy bands

A formula for carrier concentration, and a relationship between mobility and diffusivity, have been presented for degenerate semiconductors with a nonparabolic energy band structure under the influence of a magnetic field. The relationships are general; they involve no approximation related to the comparative values of energy bandgap and spin orbit coupling. They should therefore, be applicable to both non-degenerate and degenerate semiconductors. They are quite suitable for the investigation of electrical transport in heavily doped semiconductors under the influence of a magnetic field. PACS 72.20.-I; 73.50.-h     

Electronic structure and work function of potassium-doped PTCDA thin films

The electronic properties of thin films of potassium-doped 3,4:9,10-perylenetetracarboxylic dianhydride (PTCDA) have been studied using photoemission spectroscopy. Potassium addition results in a charge transfer to PTCDA molecules as signaled by the evolution of the valence band photoemission data, and the potassium ions mainly interact with the carbonyl end groups of the PTCDA molecules. None of the potassium-doped PTCDA films prepared in our studies is metallic, which is attributed to the effect of electronic correlations. PACS 71.20.Rv; 79.60.-i     

Optical charge transfer absorption in proton injected tungsten oxide thin films analyzed with spectroscopic ellipsometry

Tungsten oxide thin films with protons injected during deposition (H_xWO₃) were prepared using reactive direct-current magnetron sputtering in a mixture of argon, oxygen, and hydrogen gases. The concentration of injected protons, given by the x-values in H_xWO₃, was evaluated by electrochemically ejecting protons from the films. The complex dielectric functions (? = ?₁ + i?₂) of the films were estimated by analyzing the experimental spectra of Ψ and Δ measured with spectroscopic ellipsometry using the model composed of a homogeneous tungsten bronze layer with an additional surface roughness layer. As a result of this analysis, the imaginary part of the dielectric function ?₂, which represents optical absorption, was composed of two Lorentz oscillator terms whose peak positions were about 1.0 eV (L₁) and 1.6 eV (L₂). The two terms with L₁ and L₂ are assumed using the modified site-saturation model to be due to optical charge transition between W⁶⁺ and W⁵⁺ sites, and between W⁶⁺ and W⁴⁺ sites, respectively.     

Electronic structure and dynamics of quantum-well states in thin Yb metal films

Quantum-well states above the Fermi energy in thin Yb(111) metal films deposited on a W(110) single crystal were studied by low-temperature scanning tunneling spectroscopy. These states are laterally highly localized and give rise to sharp peaks in the tunneling spectra. A quantitative analysis of the spectra yields the bulk-band dispersion in the Gamma-L direction as well as quasiparticle lifetimes. The quadratic energy dependence of the lifetimes is in quantitative agreement with Fermi-liquid theory.     

Electronic structure and chemical bonding of amorphous chromium carbide thin films

The microstructure, electronic structure and chemical bonding of chromium carbide thin films with different carbon contents have been investigated with high-resolution transmission electron microscopy, electron energy loss spectroscopy and soft x-ray absorption-emission spectroscopies. Most of the films can be described as amorphous nanocomposites with non-crystalline CrC(x) in an amorphous carbon matrix. At high carbon contents, graphene-like structures are formed in the amorphous carbon matrix. At 47 at.% carbon content, randomly oriented nanocrystallites are formed creating a complex microstructure of three components. The soft x-ray absorption-emission study shows additional peak structures exhibiting non-octahedral coordination and bonding.     

Electronic properties of the space charge layer of the copper phthalocyanine thin films

Photoemission Yield Spectroscopy (PYS) has been used in studies of the electronic properties of the space charge layer of UHV annealed copper phthalocyanine (CuPc) thin films. The work functionφ, ionization energyΦ, absolute band bendingeV _s and surface electron affinityX _s is determined. Moreover, two filled electronic state bands localized in the band gap are observed. Their origin is briefly discussed.     

Electronic structure and dynamics of muonium in semiconductors

In this paper, a selection of recent results on muonium in semiconductors is presented. These are primarily taken from Si and GaAs and encompass the electronic structure of the diamagnetic centers, charge state cycling, spin‐exchange scattering and interconversion between muonium states. These experiments illustrate the power of μSR for investigating the behavior of muonium and, by analogy, the technologically relevant isolated hydrogen centers in semiconductors. This revised version was published online in August 2006 with corrections to the Cover Date.     

Model of diffusion-drift charge carrier transport in layers with a fractal structure

A new theoretical (semiempirical) model of diffusion-drift charge carrier transport in layers with a fractal structure based on a partial differential equation with a fractional time derivative has been proposed. It has been shown by numerical calculations that a decrease in the order of the fractional derivative in the presence of the external electric field leads to broadening and asymmetry of the spatial distributions of charge carriers, which physically corresponds to intensification of scattering processes.     

Photoluminescence and energy transfer processes in rare earth ion doped oxide thin films with substrate heating

Tm-Er codoped amorphous aluminum oxide thin films were prepared by pulsed laser deposition. Broadband photoluminescence in the wavelength region of 1400-1700 nm comprised of two emissions at around 1532 and 1620 nm was observed. PL performance was investigated as a function of the substrate-heating temperature. Possible energy transfer processes involved in the heat treatment were discussed and nonradiative decay rates were evaluated, by comparing the inverse of measured lifetimes with the calculated radiative decay rates. Our results suggest that Tm-Er codoped Al₂O₃ thin film might be potential candidate as broadband light sources and amplifiers.     

Charge carrier photogeneration in thin films of iodoform

The photogeneration of electrons and holes in thin polycrystalline iodoform films has been investigated as a function of the electric field. Equal values of the primary rates of production of electrons and holes support the idea of an intrinsic photogeneration mechanism. The experimental results are fitted by the Onsager model. The fraction of absorbed photons that produce thermalized electron-hole pairs is found to be close to unity, with an initial pair separation of ca. 3 nm.     

Correlation of inner shell binding energies with shifts of charge transfer bands

Inner shell binding energies were determined for the elements in the crystalline compounds A^IIIX^VO₄ where A  B, Al, Ga, Fe and X  P, As with fourfold coordination of A, and in the corresponding dihydrates of Al having a sixfold coordination of Al. The O 1s binding energies for the dihydrates could be resolved into two bands arising from XO₄ -groups and from the water molecules respectively. The O 1s binding energies from the XO₄ groups decrease by about 0.6 eV in going from the anhydrous compounds to their dihydrates whereas the Al 2p binding energies remain constant within the limits of error. These results correlate surprisingly well with shifts of the first charge transfer band of trivalent iron in these compounds. The binding energy differences between phosphates and arsenates are also in good agreement with concurrent shifts of this charge transfer band. The consequences of these results for the concept of optical electronegativities are discussed.     

Electronic structure of phosphate glasses with a complex oxygen sublattice structure

Calculations of the electronic structure of phosphate glasses are performed in the MO LCAO x _α approximation discrete variation method. On the basis of an analysis of theoretical and experimental electronic spectra of the system BeO-P₂O₅ regularities are found in the formation of the valence band of alkaline-earth phosphate glasses with different types of anion sublattice. Data on the electronic structure are used to refine the models of short-range order; in particular, the possibility of oxygen in the threefold coordination state is confirmed. With the features of the spectrum of electronic states taken into account, localization of charge carriers, the nature of the optical transitions, and hole-transport phenomena are discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1366–1372 (August 1997)