Positive holes polarization energy

Electronic point defects, displaced electrons, almost always exist in connection with atomic point defects. A purely electronic defect, the so-called self-trapped electron trapped by induced polarization in a solid, has been suggested by Landau 29) but never found. If an incoming quantum imparts enough energy to an electron of one of the atoms of a solid, the electron will be freed from the atom and can wander through the solid. If it is not to be recaptured by the radiation-produced positive ion, it must be trapped at some other point in the solid, one with an effective positive charge. This will almost always be an atomic defect, specifically a negative ion vacancy or an impurity of suitable electron affinity relative to that of the host solid. When an electron is thus removed from an atom, the vacancy in the electronic structure is termed a positive hole. Such a hole has mobility like that of an electron... 

The polarization energies of positive holes in rare gas crystals have been calculated by Lyons and Sceat (1970). The location of the positive hole in the lattice is assumed to coincide with the position of an atom. The main contributions to the polarization energy are the ion-induced dipole interaction, Eid/ and the interaction between two ion-induced dipoles, P d. With gas phase polarizabilities, the values compiled in Table 3 were obtained. 

Table 3 Polarization Energies of Positive Holes in Solid Rare Gases...

Table 5 Emission Threshold, Gas Phase Ionization Energy, and Polarization Energy of the Positive Hole/Ion...

Fig. 4 Energy landscapes for ground- (solid line) and excited-state (dashed line) hole transfer in DNA. Arrows indicate mean positions of a hole matching the location of two GC sites bridged by a single AT pair. The width of the energy gap was estimated assuming that the contribution to polarization comes from nuclear motion...

As already shown by the spectrum in Fig. 10.8, a cathodic photocurrent was also observed with n-GaP, its potential dependence being shown in Fig. 10.12b. Since the UfY, of n-GaP was found at a rather negative electrode potential, the energy bands are bent upwards at potentials positive of Ufh. Accordingly, the hole injected from the excited dye, cannot move into the bulk of the n-electrode (see insert of Fig. 10.12b) and are transferred back to the reduced dye molecule. The cathodic photocurrent shows a maximum, i.e. it decreases again at high cathodic polarization. This decrease is due to a reduction of the dye in the dark. The sensitization of the n-GaP electrode is, of course, a minority carrier process. The injected holes recombine with the electrons in the bulk and the current is carried by electrons. Many investigations have shown, however, that more reliable results could be obtained with majority carrier systems. 

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