Charge carrier transport/mobility

Traditionally, charge-carrier transport in pure and doped a-Se is considered within the framework of the multiple-trapping model [17], and the density-of-state distribution in this material was determined from the temperature dependence of the drift mobility and from xerographic residual measurements [18] and posttransient photocurrent analysis. 

The charge transport in amorphous selenium (a-Se) and Se-based alloys has been the subject of much interest and research inasmuch as it produces charge-carrier drift mobility and the trapping time (or lifetime) usually termed as the range of the carriers, which determine the xerographic performance of a photoreceptor. The nature of charge transport in a-Se alloys has been extensively studied by the TOF transient photoconductivity technique (see, for example. Refs. [1-5] and references cited). This technique currently attracts considerable scientific interest when researchers try to perform such experiments on high-resistivity solids, particularly on commercially important amorphous semiconductors such as a-Si and on a variety of other materials... 

Researchers have used various models to explain the charge carrier transport mechanism in organic semiconductors. Two models have been used frequently, (i) the trapping model, which assumes a certain distribution of traps in the energy space and (ii) the field dependent mobility model, which assumes an exponential dependence of mobility on square root of electric field. 

Charge carrier transport in molecular crystals has been extensively studied employing the time of flight (TOF) method. Mobility values are typically in the order of 0.1 to 1 dll V s and weakly temperature dependent if measured near room temperature. At lower temperatures pt (T) often approaches activated behavior. With the advent of extremely clean samples it became clear, however, tliat this is due to trapping. In its absence, pt (T) approaches a power law dependence,... 

In addition to the morphological features of the pentacene layer, the performance of an OTFT is influenced by the microscopic interface environment at the interface between the pentacene layer and a source and drain metallic contact. The electronic parameters of the interface may give rise to an increased contact resistance. Therefore it is important to understand the relationship between the chcrnical/structural characteristics of the OS/metal interface and charge carrier transport in OTFT. For example the difference in mobility between the top-contact and bottom-contact OTFT was associated to the different morphology of the pentacene layer near the metallic contacts [13],... 

The second approach deals with charge transport macroscopically. An amorphous organic semiconductor can be treated as an ensemble of disordered hopping sites through which injected carriers drift xmder the influence of an external applied field. Historically, the Poole-Frenkel (PF) model was one of the first models to explain the electric field dependence of charge carrier drift mobilities [21,22], The field-dependent mobility can be written as... 

Time-of-llight (TOF) electrical conductivity measurements of ion-based materials Ic CP-TATA, 2c CP-TATA, and Sc CP-TATA" indicated ambipo-lar charge-carrier transport behavior with well-balanced values at high mobilities (10 —10 cm s ) for both holes and electrons without special purification... 

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