Semiconductors electronic conductivity

Besides the experimental data mentioned above, the kinetic dependencies of oxide adsorption of various metals are also of great interest. These dependencies have been evaluated on the basis of the variation of sensitive element (film of zinc oxide) conductivity using tiie sensor method. The deduced dependencies and their experimental verification proved that for small occupation of the film surface by metal atoms the Boltzman statistics can be used to perform calculations concerning conductivity electrons of semiconductors, disregarding the surface charge effect as well as the effect of aggregation of adsorbed atoms in theoretical description of adsorption and ionization of adsorbed metal atoms. Considering the equilibrium vapour method, the study [32] shows that... 

As for the energy transfer to the subsurface layers of zinc oxide from the singlet oxygen molecules, the transfer should lead to an intn ease in the electrical conductivity of semiconductor either due to ejection of electrons into the conduction band h-om shallow traps [67], or due to the injection of electrons into zinc oxide by excited particles [68]. Effects of this kind were observed in the interaction between a ZnO surface and excited pairs of benzophenone [70], and also in adsorption of singlet oxygen on the surface of ZnO monocrystal in electrolyte [69]. 

Investigations carried out on specimens of the same semiconductor, prepared by different methods, have shown that there is a correlation between the catalytic activity of a specimen in relation to the hydrogen-deuterium exchange reaction and its initial electrical conductivity. Electron... 

Semiconductors are materials that contain a relatively small number of current carriers compared to conductors such as metals. Intrinsic semiconductors are materials in which electrons can be excited across a forbidden zone (bandgap) so that there are carriers in both the valence (holes, p-type) and conduction (electrons, ra-type) bands. The crucial difference between a semiconductor and an insulator is the magnitude of the energy separation between the bands, called the bandgap (Eg). In the majority of useful semiconducting materials this is of the order of 1 eV some common semiconductors are listed in Table 1. 

The heat transfer in a solid is due both to lattice vibrations (phonons) and to conduction electrons. Experiments show that in reasonably pure metals, nearly all the heat is carried by the electrons. In impure metals, alloys and semiconductors, however, an appreciable... 

In most metals the electron behaves as a particle having approximately the same mass as the electron in free space. In the Group IV semiconductors, this is usually not the case, and the effective mass of electrons can be substantially different from that of the electron in free space. The electronic structure of Si and Ge utilizes hybrid orbitals for all of the valence electrons and all electron spins are paired within this structure. Electrons may be thermally separated from the electron population in this bond structure, which is given the name the valence band, and become conduction electrons, creating at the same time... 

Consider the semiconductor device below which is hooked up to a battery (direct current). The n-type semiconductor (a) is connected to the negative terminal of a battery, the p-type to the positive terminal. This has the effect of pushing conduction electrons from right to left and positive holes from left to right. 

Note the flow of positive holes in one direction is, in effect, a flow of electrons in the opposite direction. So, the p-n junction should still have the same orientation in (b) as in (a). Now the conduction electrons are pulled to the right and the positive holes to the left. Because there are very few conduction electrons in the p-type semiconductor and very few positive holes in the n-type semiconductor, there are very few carriers of electric charge across the p-n junction. Very little electric current flows. 

There is a fundamental difference between electron-transfer reactions on metals and on semiconductors. On metals the variation of the electrode potential causes a corresponding change in the molar Gibbs energy of the reaction. Due to the comparatively low conductivity of semiconductors, the positions of the band edges at the semiconductor surface do not change with respect to the solution as the potential is varied. However, the relative position of the Fermi level in the semiconductor is changed, and so are the densities of electrons and holes on the metal surface. 

In metals, valence electrons are conduction electrons, so they are free to move along the solid. On the contrary, valence electrons in insulators are located around fixed sites for instance, in an ionic solid they are bound to specific ions. Semiconductors can be regarded as an intermediate case between metals and insulators valence electrons can be of both types, free or bound. 

The electrical conductance of semiconductors is derived from the mobility of charge carriers, holes h+ in the valence band and free electrons e in the... 

---