有机电致发光器件中载流子的输运和复合发光

以高场作用下载流子对三角势垒的FowlerNordheim隧穿理论为基础,建立了单层有机电致发光器件中载流子输运和复合发光模型,给出了薄膜中电子空穴对的解离和复合概率及电子和空穴的密度分布.计算并讨论了外加电压和注入势垒对器件电流和复合效率的影响. 关键词： 电致发光器件 载流子输运 载流子复合     

Drift mobility and kinetics of transport of excess charge carriers in glassy CdGexAs2

Conclusions We tried to measure transient conductivity response to pulse strongly absorbed excitation (light, accelerated electrons) in sandwich type samples of glassy CdGe _x As₂ compounds. We observed the signal due to transport of free excess carriers. From analysis of experimental results we conclude that in our materials strong trapping effects are present, so the range of excited carriers is very short (10^–4-10^–3 cm) even in the highest electrical fields used (to 10⁴ V. cm^–1). Estimates of upper limit of drift mobility give the values 10^–1- 1 cm² V^–1 sec^–1. We did not succeed in determining the type of carriers which are responsible for the observed effects.     

Photogeneration of charge carriers in amorphous selenium

A model is proposed to explain the outstanding features of the free-carrier photogeneration process in amorphous selenium. The excitation of an electron-hole pair and the subsequent separation or recombination are considered as a function of photon energy, applied electric field and temperature. The results of the model are compared in detail with new experimental data and also with published results from a number of sources.     

Mobility of charge carriers in disordered dielectrics

We compare experimental data on the mobility of holes (the majority charge carriers) in polyepoxy-propylcarbazole, measured using the time-of-flight technique (drift mobility) and the nonsteady-state radiation-induced electrical conductivity method (effective mobility). We show that these two quantities are quite different in the dispersive transport regime; and while the second quantity is a characteristic of the material, the first quantity depends in a complicated fashion on the ratio of the electric field strength to the sample thickness. The untreated data on drift mobility measurements using the time-of-flight technique do not have direct physical meaning and cannot be compared with the conclusions of modern microscopic theories of the mobility of charge carriers in disordered matrices.High-Voltage Scientific-Research Institute at Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 82–88, July, 1994.     

Lifetime of charge carriers in multiwalled nanotubes

The nature of low-energy excitations in multiwalled nanotubes (MWNTs) is investigated by means of two-color time-resolved photoemission. A careful analysis of the ballistic transport, secondary excitations, and band structure effects was employed in order to extract single electron lifetimes from the observed relaxation trend. It is demonstrated that in the vicinity of the Fermi level the energy dependence of e-e scattering times is inversely proportional to approximately the square of the excitation energy. This result provides strong evidence that electron transport in MWNTs exhibits a Fermi-liquid behavior, indicating that long-range e-e interaction along the tube vanishes due to screening.     

Experimental determination of the translational kinetic energy of liquid and solid hydrogen

TOSCA is a novel inelastic spectrometer operating on the pulsed neutron source ISIS (UK). It covers a wide momentum and energy range, even though its kinematic region is close to a line in the (k, E) plane. Its use is mainly intended for vibrational spectroscopy. However, taking advantage of its good resolving power, we have carried out a test experiment aimed to use this instrument to measure the centre of mass kinetic energy of molecular hydrogen. The experiment was successful and we have obtained the translational kinetic energy of liquid and solid para-hydrogen improving the overall accuracy by almost an order of magnitude with respect to previous determinations. The data are compared with the results of a Path Integral Monte-Carlo simulations with almost perfect agreement. We have demonstrated that TOSCA can be used for measuring the translational kinetic energy of small molecular systems, taking advantage of the intrinsic incoherence that is introduced in the scattering process by the intra-molecular transitions. Received 9 June 1999     

Accumulation of the excess of one type of charge carriers and the formation of trions in GaAs/AlGaAs shallow quantum wells

The dynamics of excitons and trions in GaAs/AlGaAs heterostructures with shallow quantum wells is studied in time-resolved photoluminescence experiments carried out with different repetition rates of picosecond pump pulses for the cases of intrawell, above-barrier, and“two-color” excitation. It is established that excess charge carriers of one type accumulated in the quantum wells under above-barrier excitation play a key role in the formation and dynamics of the exciton-trion system and determine its composition and kinetic properties. The lifetime of excess charge carriers in the quantum wells, estimated from the experimental data, exceeds 10 μs.     

Density dependence of mean kinetic energy in liquid and solid hydrogen at 19.3 K

We have measured, using the TOSCA spectrometer at ISIS, the inelastic incoherent neutron scattering spectrum of liquid and solid para-hydrogen along the T = 19.3 K isotherm. From the high-energy region of the spectrum, where the Impulse Approximation for the Centre of Mass motion applies, we have been able to extract the mean translational kinetic energy, which, as expected, turns out rather different from the classical value and density dependent. We find that the density behaviours in the liquid and the solid phase are slightly different. This confirms a similar feature already observed in liquid and solid helium at T = 6.1 K [M. Celli, M. Zoppi, J. Mayers, Phys. Rev. B 58, 242 (1998)]. The spectra from the solid phase have been also analysed in the low-energy region and allowed us to derive the Debye-Waller factor of solid para-hydrogen as a function of density. The comparison with the available experimental data in the literature is rather good and confirms the excellent performances of TOSCA in the spectroscopic analysis of the condensed phases of para-hydrogen.     

Spatially inhomogeneous states of charge carriers in graphene

The interaction of two-dimensional quasiparticles characterized by a linear dispersion E = ±u|p| (graphene) with impurity potentials is studied. It is shown that discrete levels corresponding to localized states are present in a one-dimensional potential well (quantum wire), whereas such states are absent in a two-dimensional well (quantum dot). The cross section for the scattering of electrons (holes) of graphene by an axially symmetric potential well is determined. It is shown that the cross section tends to a constant value in the limit of infinite particle energy. The effective Hamiltonian is derived for a curved quantum wire of graphene.     

Electrodynamic convection of free charge carriers in semiconductors

The possibility is demonstrated of convective motion of free charge carriers in a thin semiconducting layer with a transverse electric field applied to it. The conditions for the development of this kind of electrodynamic convection and the criteria for stability of the convection cells are studied. Fiz. Tverd. Tela (St. Petersburg) 39, 280–283 (February 1997)     

Mobility of charge carriers in porous silicon layers

The (conduction) mobility of majority charge carriers in porous silicon layers of the n and p types is estimated by joint measurements of electrical conductivity and free charge carrier concentration, which is determined from IR absorption spectra. Adsorption of donor and acceptor molecules leading to a change in local electric fields in the structure is used to identify the processes controlling the mobility in porous silicon. It is found that adsorption of acceptor and donor molecules at porous silicon of the p and n types, respectively, leads to a strong increase in electrical conductivity, which is associated with an increase in the concentration of free carrier as well as in their mobility. The increase in the mobility of charge carriers as a result of adsorption indicates the key role of potential barriers at the boundaries of silicon nanocrystals and may be due to a decrease in the barrier height as a result of adsorption.     

Evidence of polaronic charge carriers in oxide superconductors

The analysis of photoemission and femtosecond optical absorption spectroscopy in oxide superconductors supports the view that the charge carriers are polaronic in nature. These carriers are found to exist in the (Ba/Sr)-O planes and are coupled toB _1g vibrations of the apical oxygen.     

Internal waves of free charge carriers in semiconductors

We show that internal waves that are similar to internal gravity waves in the ocean can propagate in semiconductors with a gradient of free charge carrier concentration. Unlike internal gravity waves in the ocean, which are observed at infrasonic frequencies, the waves under consideration are excited in the microwave range, which opens up interesting possibilities for creating new types of electron devices. In the nonlinear rigime such waves assume the form of solitons described by the KdV equation. State Technical University, Ul’yanovsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 370–377, March, 1997.     

The sign of charge carriers in luminescent transitions

A thorough treatment of the luminescent mechanisms in high resistivity semiconductors (up to 10¹² ohm cm), has as yet not been satisfactorily established. This is due to the lack of data as is provided by the Hall effect. An AC-AC Hall apparatus has been assembled to determine the sign of charge carriers, and their densities when involved in luminescent transitions. Results of preliminary measurements on CdS will be presented.We would like to thank J. Hickmott for his assistance in designing and assembling the synchronous detector filter system.     

A universal thermal conductance of charge carriers

Summary A universal thermal conductance of charge carriersK=2π² k _B ² T/(3h) is rigorously derived within a correlation-function formalism. Similar to the case of the universal electrical conductanceG=2e ² /h this result pertains to one-dimensional, ballistic, and degenerate conditions for non-interacting particles.     

New mechanisms of localization of charge carriers in nanosilicon

This paper reports on the results of investigations into the spectral dependences of thermally stimulated luminescence and the temperature dependences of tunneling luminescence in highly oxidized porous silicon samples. Two new mechanisms of localization of charge carriers are considered in terms of the specific features revealed in the spectral dependences of the thermally stimulated luminescence and nonmonotonic temperature dependences of the Becquerel index of tunneling luminescence decay. The proposed mechanisms of charge carrier localization are associated with structure heterogeneities inherent in these objects, namely, superficial SiO_x oxide shells (0<x≤2) enclosing silicon particles and an undulating structure of silicon wires.     

Magnetic charge and hyperfine splitting in hydrogen

The large spatial size of magnetic charges (or dyons) and parity considerations are used to show that in models of the proton based on dyons the hyperfine splitting must be due to the magnetic moment produced by the electric charge. The contributions of the magnetic monopoles cancel, otherwise the proton would have a large electric dipole moment.