Charge-carrier concentration

For insulators, Z is very small because p is very high, ie, there is Htde electrical conduction for metals, Z is very small because S is very low. Z peaks for semiconductors at - 10 cm charge carrier concentration, which is about three orders of magnitude less than for free electrons in metals. Thus for electrical power production or heat pump operation the optimum materials are heavily doped semiconductors. 

A conjugated polymer of a high charge carrier concentration (n> 1017 cm-3) arranged between two mclal electrodes, can be understood as a MSM structure [40. ... 

How can such problems be counterbalanced Since a large capacitance of a semiconductor/electrolyte junction will not negatively affect the PMC transient measurement, a large area electrode (nanostructured materials) should be selected to decrease the effective excess charge carrier concentration (excess carriers per surface area) in the interface. PMC transient measurements have been performed at a sensitized nanostructured Ti02 liquidjunction solar cell.40 With a 10-ns laser pulse excitation, only the slow decay processes can be studied. The very fast rise time cannot be resolved, but this should be the aim of picosecond studies. Such experiments are being prepared in our laboratory, but using nanostructured... 

FIGURE 6.7 Optical band gaps as functions of charged carrier concentration in ITO films. 

Figure 4.22 Schematic diagram of a field effect transistor. The silicon-silicon dioxide system exhibits good semiconductor characteristics for use in FETs. The free charge carrier concentration, and hence the conductivity, of silicon can be increased by doping with impurities such as boron. This results in p-type silicon, the p describing the presence of excess positive mobile charges present. Silicon can also be doped with other impurities to form n-type silicon with an excess of negative mobile charges.

Many fast ion conducting glasses contain several salts of the same alkali metal to optimise the conductivity. The expression for the charge carrier concentration in terms of the thermodynamic activities of all the... 

Figure 8. Hydration isotherm for Nation 117 (equivalent weight (EW) of 1100 g/equiv) and the distribution of the dielectric constant and protonic charge carrier concentration across the hydrated hydrophilic channels (pores) for three different water contents (top).

R. Muller, U. Kunecke, A. Thuaire, M. Mermoux, M. Pons and P. Wellmann, Investigation of the charge carrier concentration in highly aluminum doped SiC using Raman scattering, Phys. Status Solidi C, 3, 558-561 (2006). 

Fig. 16 Calculated charge carrier mobility in a Gaussian-type hopping system parametric in the charge carrier concentration and plotted (a) on a In U vs aIkT scale and (b) on a In U vs (alkTf scale. From [100] with permission. Copyright (2007) by the American Institute of Physics...

Fig. 20 Charge carrier mobility in P3HT as a function of the charge carrier concentration. Squares refer to an experiment performed on a field effect transistor while circles refer to experiments done on an electrochemically doped sample. In the latter case the mobility is inferred from the steady state current at a given doping level. Solid and dashed lines have been fitted using the theory of [101]. The fit parameters are the site separation a, the prefactor Vq in the Miller-Abrahams-type hopping rate, the inverse wavefunction decay parameter y and the dielectric constant e. From [101] with permission. Copyright (2005) by the American Institute of Physics...

Coehoom R, Pasveer WF, Bobbert PA, Michels MAJ (2005) Charge-carrier concentration dependence of the hopping mobility in organic materials with Gaussian disorder. Phys Rev B 72 155206... 

Coehoom R (2007) Hopping mobility of charge carriers in disordered organic host-guest systems dependence on the charge-carrier concentration. Phys Rev B 75 155203... 

Eishchuk II, Arkhipov VI, Kadashchuk A, Heremans P, Bassler H (2007) Analytic model of hopping mobility at large charge carrier concentrations in disordered organic semiconductors polarons versus bare charge carriers. Phys Rev B 76 045210... 

Further studies (54) suggested that the Tc was dependent on the carrier concentration. A plot of the transition temperature versus nc, the charge carrier concentration, is presented in Figure 12. 

Figure 12 The critical transition temperature (Tc/K) plotted against charge-carrier concentration (nc) for SrTiOs x, as published in Reference 54.

Calculate conductivity from charge carrier concentration, charge, and mobility. Differentiate between a conductor, insulator, semiconductor, and superconductor. Differentiate between an intrinsic and an extrinsic semiconductor. 

Figure 6.15 Temperature dependence of charge carrier concentration of -type extrinsic germanium with two different As impurity levels. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by lohn Wiley Sons, Inc. This material is used by permission lohn Wiley Sons, Inc.

There have been many attempts to relate bulk electronic properties of semiconductor oxides with their catalytic activity. The electronic theory of catalysis of metal oxides developed by Hauffe (1966), Wolkenstein (1960) and others (Krylov, 1970) is base d on the idea that chemisorption of gases like CO and N2O on semiconductor oxides is associated with electron-transfer, which results in a change in the electron transport properties of the solid oxide. For example, during CO oxidation on ZnO a correlation between change in charge-carrier concentration and reaction rate has been found (Cohn Prater, 1966). 

Illumination of a semiconductor, leading to a change of the charge-carrier concentration in the bands, also affects, according to Eqs. (23) and (24), the electron-hole currents. It is this effect that underlies a specific behavior of semiconductor electrodes under illumination. Obviously, illumination affects most strongly the current of minority carriers, whose relative concentration may vary especially noticeably. 

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