Density of charge carriers

Conductivity depends on a number of factors including the number of density of charge carriers (number of electrons, n) and how rapidly they can move in the sample called mobility /a. 

High relative permittivity, so that the number density of charge carriers is given directly by the nominal concentration of the BGE... 

One problem associated with polymer electrolytes arises from the opposing effects of increasing the salt concentration. Higher salt concentrations generally imply a higher density of charge carriers, which increases conductivity. However, through their... 

When one examines the value of n = p, it turns out that the density of charge carriers in an intrinsic semiconductor (Table 6.16) at room temperature is in the range of 10 to 10 cm, compared with about 10 cm in a metal. It is this relatively low concentration of charge carriers in intrinsic semiconductors that is responsible for the most important differences between semiconductor electrodes and metal electrodes. 

Up to this point we have discussed the properties of metals and insulators. Metals have a high conductivity because the electrons are relatively free to move and they can react to an applied potential. Each metal atom contributes one or two electrons so that the density of charge carriers is high. Typically the density of charge carriers is 1029 per m3. Due to their... 

If the temperature dependence of the electronic conductivity of a semiconductor is to be accounted for, it is necessary to analyse how the density of charge carriers and their mobilities each depend upon T (see Eq. (2.25)). In the first place attention will be confined to the density n of electrons in the conduction band and the density p of holes in the valence band. When the intrinsic properties of the crystal are under consideration, rather than effects arising from impurities or, in the case of compounds, from departures from stoichiometry, the corresponding conductivity is referred to as intrinsic conductivity . The approach to the calculation of n and p in this instance is as follows. 

The parameters and represent effective QE and stripon contributions to the density of charge carriers (reflected in the Hall number). Since they both contribute through the current q of the bare QE states, they are expected to have same sign (corresponding to these states). The values of these parameters are assumed to increase with x (for the same reason that Nj does). Since the coupling between QE s and stripons grows with x, and the increase of Nf with... 

Photoelectrochemistry — In principle, any process in which photon absorption is followed by some electrochemical process is termed photo electro chemical, but the term has come to have a rather restricted usage, partly to avoid confusion with photoemission (q.v.). The critical requirements for normal photo electro chemical activity is that the electrode itself should be a semiconductor that the electrolyte should have a concentration substantially exceeding the density of -> charge carriers in the semiconductor and that the semiconductor should be reverse biased with respect to the solution. To follow this in detail, the differences in potential distribution at the metal-electrolyte and semiconductor-electrolyte interfaces need to be understood, and these are shown in Fig. 1, which illustrates the situation for an n-type semiconductor under positive bias. 

Irradiation of the crystal by electrons or neutrons is the simplest way of introducing the defects by controlled means. Optical properties of organic conductors are sensitive to changes in the electron distribution induced by irradiation defects (i.e., their spectra are sensitive to the localization of the carriers, due to random potentials in the environment of the defects). The electronic absorption spectra give information on the density of charge carriers and their localizations as well as on the electronic energy levels. 

Doping introduces carriers into the -rr-electron system. Since every monomer is a potential redox site, conjugated polymers can be doped to a relatively high density of charge carriers. 

Electrical conductivity depends on two separate microscopic parameters of a material the number density of charge carriers present and the mobility of the carriers. 

The band theory of solids explains the three broad classes of electronic conductivity seen in nature in terms of the number density of charge carriers available in classes of solids. 

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