Thermal properties charge carriers

We shall briefly discuss the electrical properties of the metal oxides. Thermal conductivity, electrical conductivity, the Seebeck effect, and the Hall effect are some of the electron transport properties of solids that characterize the nature of the charge carriers. On the basis of electrical properties, the solid materials may be classified into metals, semiconductors, and insulators as shown in Figure 2.1. The range of electronic structures of oxides is very wide and hence they can be classified into two categories, nontransition metal oxides and transition metal oxides. In nontransition metal oxides, the cation valence orbitals are of s or p type, whereas the cation valence orbitals are of d type in transition metal oxides. A useful starting point in describing the structures of the metal oxides is the ionic model.5 Ionic crystals are formed between highly electropositive... 

A key feature of our polyphenylene dendrimers is that they can be planarized and thus reduced in dimensionality by intramolecular dehydrogenation [29,35]. This results in large, fused polycyclic aromatic hydrocarbons (PAHs). PAHs serve as structurally distinct, two-dimensional subunits of graphite and show attractive properties such as high charge carrier mobility, liquid crystallinity, and a high thermal stability, which qualifies these materials as vectorial charge transport layers [81]. 

Electrical conductivity is due to the motion of free charge carriers in the solid. These may be either electrons (in the empty conduction band) or holes (vacancies) in the normally full valence band. In a p type semiconductor, conductivity is mainly via holes, whereas in an n type semiconductor it involves electrons. Mobile electrons are the result of either intrinsic non-stoichiometry or the presence of a dopant in the structure. To promote electrons across the band gap into the conduction band, an energy greater than that of the band gap is needed. Where the band gap is small, thermal excitation is sufficient to achieve this. In the case of most iron oxides with semiconductor properties, electron excitation is achieved by irradiation with visible light of the appropriate wavelength (photoconductivity). 

All TSRs involve the release of trapped charge carriers into either the conduction band or valence band and their subsequent capture by recombination centers and recapture by other traps (retrapping). Their experimental investigation is undertaken with the goal of determining the characteristic properties (parameters) of traps cap-tnre cross sections, thermal escape rates, activation energies, concentration of traps. 

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. 

Classical theories of electrical and thermal conductance assume a huge number of atoms and free electrons. Let s assume a silicon cube with one side dimension of a and with common doping of lO cm. In an n-doped silicon cube with the size of (100 nm) there are 5><10 atoms and 10 free electrons at 300 K, but in the Si cube with the size of (10 nm) there are 5x10 atoms and 1% chance only to find one free electron. Free electrons are necessary for electrical conductance as charge carriers. In order to keep the conductive properties of the semiconductor material one should apply more intensive doping, 10 ° cm. However, such intensive doping decreases resistivity of the material dramatically (from 2x10" Qm to 10 Qm, respectively, for n-type Si, at 300 K). Low number of free electrons should be scattered evenly in whole volume of a material. 

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