Hole transport, description

Finally, we point out that there is a close relation in description of ion electro-diffusion and the phenomenological theory of the electron and hole transport in semiconductors. In order to facilitate the reading we present below a brief ionics-semiconductor vocabulary. ... 

The Urbach edge represents the joint density of states, but is dominated by the slope of the valence band, which has the wider band tail. Expression (3.37) for is therefore also an approximate description of the thermal broadening of the valence band tail. It is worth noting that the slope is quite strongly temperature-dependent above 200 K. This may have a significant impact on the analysis of dispersive hole transport, in which the temperature dependence of the slope is generally ignored. 

Following the general trend of looldng for a molecular description of the properties of matter, self-diffusion in liquids has become a key quantity for interpretation and modeling of transport in liquids [5]. Self-diffusion coefficients can be combined with other data, such as viscosities, electrical conductivities, densities, etc., in order to evaluate and improve solvodynamic models such as the Stokes-Einstein type [6-9]. From temperature-dependent measurements, activation energies can be calculated by the Arrhenius or the Vogel-Tamman-Fulcher equation (VTF), in order to evaluate models that treat the diffusion process similarly to diffusion in the solid state with jump or hole models [1, 2, 7]. 

MIM or SIM [82-84] diodes to the PPV/A1 interface provides a good qualitative understanding of the device operation in terms of Schottky diodes for high impurity densities (typically 2> 1017 cm-3) and rigid band diodes for low impurity densities (typically<1017 cm-3). Figure 15-14a and b schematically show the two models for the different impurity concentrations. However, these models do not allow a quantitative description of the open circuit voltage or the spectral resolved photocurrent spectrum. The transport properties of single-layer polymer diodes with asymmetric metal electrodes are well described by the double-carrier current flow equation (Eq. (15.4)) where the holes show a field dependent mobility and the electrons of the holes show a temperature-dependent trap distribution. 

Values of ft for charge transfer in proteins were determined experimentally in the range 1.0-1.4 A-1 [16]. In comparison, apparent /J values for DNA-mediated hole transfer were found in a wide range from /J < 0.1 up to 1.5 A-1 [11, 12]. For the alternative mechanistic description of DNA-mediated charge-transport phenomena over long distances which typically exhibit a very shallow distance depen-... 

In the former case, the ions migrate among the interstitial defects, which may be relevant only to small ions such as Li+. This leads to a transference number close to 1 for the cation migration. In the other case, the lattice contains both anionic and cationic holes, and the ions migrate from hole to hole [39], The dominant type of defects in a lattice depends, of course, on its chemical structure as well as its formation pattern [40-43], In any event, it is possible that both types of holes exist simultaneously and contribute to conductance. It should be emphasized that this description is relevant to single crystals. Surface films formed on active metals are much more complicated and may be of a mosaic and multilayer structure. Hence, ion transport along the grain boundaries between different phases in the surface films may also contribute to conductance in these systems. 

An accurate description of a single-layer LED should be obtained by using the injection and transport properties of electrons and holes, determined independently from the Schottky energy barrier and single-carrier device measurements, to describe the two carrier LED structure. To test this procedure consider structures fabricated from the conjugated oligomer 2-metooxy-5-(2 -etoylhexyloxy)-... 

The response of a semiconducting material to an applied electric field can be described in terms of the behavior of the conduction and valence electrons that exist within it. In a nondegenerate semiconductor ( 1), these electrons may be considered as a classical ideal gas mixture, of electrons (in the conduction band) and holes (in the valence band). The goal of this paper is to show that the methods of continuum mechanics, as developed by C. Truesdell (2), can provide a useful description of the transport phenomena which are observed. 

Free-volume concepts have a long standing in the literature. It goes back to the times of van der Waals and the ideas of molecular mobility in the description of transport phenomena. Next came the Doohttle ideas and the WLF equation (Section 8.6.1). Simha and Card (88) examined free volume from an equation of state point of view (see Section 4.3.4), arriving at a general equation between Vf and the hole fraction, h,... 

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