Charge carriers temperature dependence

The properties of plasmas vary strongly with gas composition, pressure and the method and parameters of the plasma generation process. The charge carrier concentration depends on the pressure and the fractional ionization of the plasma, for instance basically on the power density. The mobility of the electrons depends on the electron temperature, which is typically several orders of magnitudes greater than the gas temperature or the temperature of the ionized species in non-thermal low temperature plasmas used for electrochemical purposes. 

If a semiconductor is so pure that impurities contribute negligibly to - charge carrier densities in the conduction and valence bands, it is called an intrinsic semiconductor and the intrinsic charge-carrier density dependence on temperature is given by n (T) oc T exp (-2 r)> where g is the band-gap energy and ks is the - Boltzmann constant. 

The considerable attention paid to other perovskites such as BaTiOj as oxygen sensors is a result of the fact that the conductivity of these materials can be independent of operating temperatures. It has been suggested that the Fermi level lies in the semiconductor gap far above the valence band, and the concentration and mobility of free charge carriers (holes) depend on the operating temperature under different signs. This effect compensates the temperature-induced variations of the conductivity and results in zero temperature coefficient of resistance (Rothschild et al. 2005). It was... 

So, despite the very small diameter of the MWCNT with respeet to the de Broglie wavelengths of the charge carriers, the cylindrical structure of the honeycomb lattice gives rise to a 2D electron gas for both weak localisation and UCF effects. Indeed, both the amplitude and the temperature dependence of the conductance fluctuations were found to be consistent with the universal conductance fluctuations models for mesoscopic 2D systems applied to the particular cylindrical structure of MWCNTs [10]. 

Under high applied electric fields, electrons can surmount a potential barrier even at very low temperatures. This process is based on field-induced tunneling of the charge carriers across potential barrier. The probability for the tunneling depends strongly on the height and the width of the potential barrier. 

In molecular doped polymers the variance of the disorder potential that follows from a plot of In p versus T 2 is typically 0.1 eV, comprising contributions from the interaction of a charge carrier with induced as well as with permanent dipoles [64-66]. In molecules that suffer a major structural relaxation after removal or addition of an electron, the polaron contribution to the activation energy has to be taken into account in addition to the (temperature-dependent) disorder effect. In the weak-field limit it gives rise to an extra Boltzmann factor in the expression for p(T). More generally, Marcus-type rates may have to be invoked for the elementary jump process [67]. 

Conductivity curves (A versus c ) of salts in solvents of low-permittivity commonly show a weakly temperature-dependent minimum around 0.02 molL-1 followed by a strongly temperature-dependent maximum at about 1 mol L 1. According to Fuoss and Kraus [101,102] the increase of conductivity behind the minimum is due to the formation of new charge carriers from the ion pairs. They assume that coulombic forces suffice to form bilateral cationic [C+A-C+] and anionic [A C+A ] triple ions in solvents of low-permittivity ( <15) if the ions have approximately equal radii. 

Figure 3. (a) Representation of the hexagonal discotic mesophase formed by hexadodecyl substituted HBC 33. (b) The temperature dependence of the intracolumnar charge carrier mobilities for 33 and 34. Phase transition tempera-... 

These different modes of transport result in a dissimilar temperature dependence of the charge carrier mobility, and this often provides a convenient means to investigate which transport regime may apply. In this chapter, due attention is therefore given to experimental approaches that allow for an investigation of the transport mechanism, and concomitantly of the underlying electronic structure. 

Monte Carlo simulations [54], analytical effective medium theory [64], and stochastic hopping theory [46] predict a dependence of the charge carrier mobility as a function of temperature and electric field given in (3) ... 

However, one should be cautious about overinterpreting the field and temperature dependence of the mobility obtained from ToF measurements. For instance, in the analyses of the data in [86, 87], ToF signals have been considered that are dispersive. It is well known that data collected under dispersive transport conditions carry a weaker temperature dependence because the charge carriers have not yet reached quasi-equilibrium. This contributes to an apparent Arrhenius-type temperature dependence of p that might erroneously be accounted for by polaron effects. 

Fig. 8 Temperature dependence of the zero field hole mobility in the low carrier density limit in a polyfluorene copolymer. The data are inferred from space-charge-limited current experiments and analyzed in terms of the extended Gaussian disorder model (see Sect. 4.1). From [90] with permission. Copyright (2008) by the American Institute of Physics...

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